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POST-CLOSURE LAND USE PLAN Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
Prepared For:
Related Santa Clara, LLC
333 South Grand Avenue, Suite 3550
Los Angeles, California 90071
Prepared By:
Langan Treadwell Rollo
555 Montgomery Street, Suite 1300
San Francisco, California 94111
DJ Hodson, PE
Principal
Jeffrey F. Ludlow, PG
Principal
September 2015
Langan Project No. 770611601
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
770611601
Page i
TABLE OF CONTENTS
1.0 INTRODUCTION AND BACKGROUND ......................................................................... 1 1.2 Site Description.................................................................................................. 2 1.3 Site Background ................................................................................................. 3 1.4 Project Description ............................................................................................ 4 1.5 Previous Investigations ..................................................................................... 5
1.5.1 Solid Waste Assessment Test ............................................................... 5 1.5.2 Ongoing Semi-Annual Monitoring ........................................................ 5 1.5.3 Recent Soil, Groundwater, and Landfill Gas Investigations ................ 6 1.5.4 Human Health Risk Assessment ........................................................... 7
1.6 Feasibility Study of Groundwater Alternatives ............................................. 10
2.0 GEOLOGY AND HYDROGEOLOGICAL INFORMATION ............................................. 14 2.1 Subsurface Conditions .................................................................................... 15 2.2 Hydrological Information ................................................................................ 19
3.0 SOIL AND WASTE MANAGEMENT ............................................................................ 22 3.1 Waste Management During Construction ..................................................... 22 3.2 Nuisance Control Measures ............................................................................ 24
3.2.1 Dust, Litter, and Vectors ...................................................................... 24 3.2.2 Traffic Control ....................................................................................... 25
3.3 Health and Safety Program ............................................................................. 25
4.0 SITE DEMOLITION AND PREPARATION .................................................................... 26
5.0 CONCEPTUAL FOUNDATION ..................................................................................... 27 5.1 Structures ......................................................................................................... 27 5.2 Site Settlement Evaluation ............................................................................. 27 5.3 Seismic Hazards Analysis ................................................................................ 29
5.3.1 Liquefaction .......................................................................................... 29 5.3.2 Seismic Densification ........................................................................... 30 5.3.3 Lateral Spreading ................................................................................. 30 5.3.4 Surface Faulting ................................................................................... 30 5.3.5 Tsunami ................................................................................................ 30
5.4 Proposed Foundation Options ........................................................................ 31 5.4.1 Spread Footings on DDCs .................................................................... 31 5.4.2 Auger Cast In Place Piles ..................................................................... 32 5.4.3 Load Tests and Construction Issues ................................................... 33
6.0 FINAL COVER ............................................................................................................... 34 6.1 Final Cover Design ........................................................................................... 34
6.1.1 General Earthwork Recommendations ............................................... 35 6.1.2 Foundation Layer ................................................................................. 35 6.1.3 Low Permeability Layer ....................................................................... 36 6.1.4 Fill above Low Permeability Layer ...................................................... 37 6.1.5 Utility Trenches .................................................................................... 38
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
770611601
Page ii
TABLE OF CONTENTS
(Continued)
6.2 Existing Topography ....................................................................................... 38 6.3 Preliminary Grading ......................................................................................... 40 6.4 Preliminary Stormwater Management .......................................................... 41
7.0 IRRIGATION AND LANDSCAPING .............................................................................. 44
8.0 UTILITIES ..................................................................................................................... 44
9.0 ENHANCED LANDFILL GAS COLLECTION AND REMEDIATION SYSTEM ............... 46 9.1 Existing LFG Collection System ...................................................................... 46 9.2 Proposed LFG Collection System ................................................................... 47
9.2.1 Proposed LFG Collection Wells ........................................................... 48 9.2.2 Potential Off-Site LFG Migration Monitoring and Mitigation ........... 51 9.2.3 Proposed LFG Collection System Manifold ........................................ 52 9.2.4 Process Equipment............................................................................... 53 9.2.5 Settlement Considerations .................................................................. 54 9.2.6 Other LFG Collection System Design Considerations ....................... 55
9.3 Proposed LFG Collection System Remedial Benefits .................................... 56 9.4 Conceptual Field Implementation Plan .......................................................... 57 9.5 LFG Collection System Monitoring Plan ........................................................ 61
10.0 LANDFILL GAS CONTROL ........................................................................................... 62 10.1 Vapor Barrier Membrane ................................................................................. 62
10.1.1 Platform Structure Area ....................................................................... 62 10.1.2 Non-Platform Structure Area .............................................................. 63
10.2 Passive Vapor Collection and Venting System .............................................. 63 10.2.1 Platform Structure Area ....................................................................... 63 10.2.2 Areas Outside the Platform Structure ................................................ 64
10.3 Exterior Grade Beam Inlet Vents .................................................................... 64 10.4 Contingency Active Blower System ............................................................... 64 10.5 Automatic Methane Sensor Network ............................................................ 66 10.6 Construction Quality Assurance Manual ........................................................ 67
11.0 LEACHATE COLLECTION AND REMOVAL SYSTEM ................................................. 68 11.1 Existing LCR System ....................................................................................... 68 11.2 Proposed LCR System ..................................................................................... 68 11.3 Considerations for LCR System at the Site .................................................... 72 11.4 Conceptual Field Implementation Plan .......................................................... 72 11.5 LCR System Monitoring Plan .......................................................................... 73
12.0 GROUNDWATER AND SURFACE WATER MONITORING ......................................... 74
13.0 EMERGENCY RESPONSE ............................................................................................ 74 13.1 High Methane at Buildings .............................................................................. 74 13.2 Other Emergency Situation............................................................................. 76
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
770611601
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TABLE OF CONTENTS
(Continued)
14.0 OPERATION AND MAINTENANCE PLAN ................................................................... 77 14.1 Final Cover Inspection and Maintenance ....................................................... 77 14.2 Drainage Features Inspection and Maintenance ........................................... 79 14.3 LFG System Inspection and Maintenance ...................................................... 79 14.4 LFGMS Inspection and Maintenance .............................................................. 79 14.5 LCR System Inspection and Maintenance ...................................................... 80 14.6 Groundwater Monitoring System Inspection and Maintenance .................. 80 14.7 Reporting .......................................................................................................... 80 14.8 Planned or Emergency Subsurface Activities ................................................ 81
15.0 SATISFACTION OF POST-CLOSURE LAND USE REQUIREMENTS .......................... 81
16.0 REFERENCES ............................................................................................................... 83
TABLES
FIGURES
APPENDICES
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
770611601
Page iv
LIST OF TABLES
Table 1 Current Development Program
Table 2 Summary of Thickness of Cover Soil, Low Permeability Layer, and
Refuse
Table 3 Summary of Depth to Groundwater
Table 4 Compliance Requirements – Methane Action Levels
Table 5 Compliance Requirements – Final Landfill Cover Maintenance
LIST OF FIGURES
Figure 1 Site Location Map
Figure 2 Site Map
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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Page v
LIST OF APPENDICES
Appendix A Existing Systems
Existing Landfill Gas Collection System
• 8190-P, Santa Clara Landfill, Landfill Gas Recovery System, Real
Environmental Products, 28 April 2011
• Figures 1 through 6, Plans and Details, Santa Clara Landfills, Landfill Gas
Recovery System, Emcon Associates, April 1985
Existing Leachate Recovery System
• Drawings 1 through 4, Parcel 1 Northwest All Purpose Landfill Company,
Inc., Emcon Associates, 30 May 1990
• Drawings 1 through 6, Parcel 3/6 All Purpose Landfill Company, Inc.,
Emcon Associates, 30 May 1990
Existing Groundwater Monitoring Network
• Figure 2, Piezometric Surface Contour Map, February 24, 2014, Golder
Associates, 3 June 2014
Appendix B Phasing Concept Map (Elkus Manfredi Architects, 16 July 2014)
Appendix C Preliminary Architectural Drawings (Pending Preparation)
Building Plans
Exterior Elevations
Building Sections
Appendix D Preliminary Design Drawings
Figure GI1.01, Title Sheet
Figures VT2.01-VT2.04, Topographic Map
Figures CC2.01-CC2.04, Site Constraints Map
Figures CD2.01-CD2.04, Demolition Plan
Figures CS2.01-CS2.04, Site Plan
Figures CG2.01-CG2.04, Preliminary Grading Plan
Figures CG3.01-CG3.05, Grading Profiles Figure BF1.01, Conceptual
Foundation Plan
Figures CSS2.01-CSS2.04, Preliminary Sanitary Sewer Plan
Figures CSD2.01-CSD2.04, Preliminary Storm Drain Plan
Figures SDW2.01-SDW2.04, Preliminary Water Plan
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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Figures CE2.01-CE2.04, Soil Erosion and Sediment Control Plan
Figures CT2.01-CT2.04, Preliminary Stormwater Management Plan
Figure BF5.01, Conceptual Foundation Sections
Figure BF5.02, Conceptual Foundation Details
Figures CU5.01-CU5.07, Utility Details
Figure CE5.01, Soil Erosion and Sediment Control Details
Appendix E Previous Environmental Investigation Results (figures and tables from Draft Site
Investigation and Environmental Risk Assessment Report, City Place Santa
Clara, Langan Treadwell Rollo, 23 December 2014)
Figure 3, Site Plan with Groundwater Sample Locations
Figure 4, Site Plan with Soil Sample Locations
Figure 5, Site Plan with Landfill Gas Sample Locations
Figure 6a, Benzene in Landfill Gas (Collected from LFG Extraction Wells)
Figure 6b, Benzene in Landfill Gas (Collected from Temporary Probes)
Figure 6c, Benzene Exceedances in Landfill Gas
Figure 7a, Ethylbenzene in Landfill Gas (Collected from LFG Extraction
Wells)
Figure 7b, Ethylbenzene in Landfill Gas (Collected from Temporary
Probes)
Figure 7c, Ethylbenzene Exceedances in Landfill Gas
Figure 8a, Vinyl Chloride in Landfill Gas (Collected from LFG Extraction
Wells)
Figure 8b, Vinyl Chloride in Landfill Gas (Collected from Temporary
Probes)
Figure 8c, Vinyl Chloride Exceedances in Landfill Gas
Figure 9, Conceptual Site Model
Figure 10, Illustrated Conceptual Site Model
Table 1, Historical Groundwater Analytical Results
Table 2, Soil Analytical Results – VOCs
Table 3, Soil Analytical Results – Other Non Metals
Table 4, Soil Analytical Results – Metals
Table 5, Grab Groundwater Analytical Results
Table 6, Landfill Gas Analytical Results
Table 7, Summary of Thickness of Cover Soil, Clay Cap, and Refuse and
Depth to Groundwater
Table 8 , Groundskeeper Hazard and Risk Summary
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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Table 9 , Calculations of Blood Lead Concentrations (PbBs) and
Preliminary Remediation Goal (PRG), Groundskeeper Table 10, Construction Worker Hazard and Risk Summary Table 11, Calculations of Blood Lead Concentrations (PbBs) and
Preliminary Remediation Goal (PRG)
Table 12, J&E Soil Gas Model Summary by Parcel
Table 13, J&E Site-Wide Groundwater Model Summary
Appendix F Existing Permits
Waste Discharge Requirements R2-2002-0008, California Regional Water
Quality Control Board, 23 January 2002
Permit to Operate, Bay Area Air Quality Management District, 23 October
2014
Appendix G Boring Logs and Cross Sections
Boring Logs
Figure 1, Site Plan depicting Cross Sections
Figure 2, Idealized Subsurface Profile A-A’
Figure 3, Idealized Subsurface Profile B-B’
Appendix H Waste Management Plan
Appendix I Odor Management Plan
Appendix J Conceptual Foundation Plan and Details and Draft Landfill Cover Investigation
Report
Figure BF1.01, Conceptual Foundation Plan
Figure BF5.01, Conceptual Foundation Sections
Figure BF5.02, Conceptual Foundation Details
Figure 1, Building Edge with Wall
Figure 2, Building Edge with Lightweight Concrete Wall
Figures 7 and 8 from Draft Preliminary Geotechnical Investigation, City
Place Santa Clara, Langan Treadwell Rollo, 22 August 2014.
Draft Landfill Cover Investigation report, Langan Treadwell Rollo,
19 December 2014
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City Place Santa Clara
5500 Lafayette Street
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September 2015
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Appendix K Proposed Landfill Gas Collection and Remediation System Concept Plans
(figures from Draft Technical Memorandum, Enhanced Landfill Gas Collection
and Remediation System Reconstruction Concept Plans, City Place Santa Clara,
30 January 2015)
Figure 9, Proposed Conceptual Landfill Gas Collection System Well and
Manifold Layout
Figure 9A, Proposed Conceptual Landfill Gas Collection System Well and
Manifold Layout, Parcel 1
Figure 9B, Proposed Conceptual Landfill Gas Collection System Well and
Manifold Layout, Parcel 2
Figure 9C, Proposed Conceptual Landfill Gas Collection System Well and
Manifold Layout, Parcel 3/6
Figure 9D, Proposed Conceptual Landfill Gas Collection System Well and
Manifold Layout, Parcel 4
Figure 9E, Proposed Conceptual Landfill Gas Collection System Well and
Manifold Layout, Proposed Contingent Horizontal Wells – Parcel 4
Figure 10A, Proposed Landfill Gas Collection System Conceptual Details
Figure 10B , Proposed Landfill Gas Collection System Conceptual Details
Figure 11, Proposed Conceptual All Parcels Manifold Schematic
Figure 12, Proposed Condensate Collection System Layout
Figure 13, Existing Process Equipment and Proposed Modifications
Figure 14, Interim Measures for Grading and Development – Phase 1
Figure 15, Interim Measures for Excavation at Parcel 3/6
Figure 16, Existing Landfill Gas Collection System Isolation and
Abandonment Phase-Out Plan
Figure 17, Conceptual Schematic of Potential Void Space Under
Structural Slab
Appendix L Conceptual Landfill Gas Mitigation System Design Drawings (figures from Draft
Gas Building Mitigation System Basis of Design and Conceptual Plans, City Place
Santa Clara, 23 December 2014)
Figure MT 1.01, Landfill Gas Building Mitigation System Project Plan
Figure MT 1.02, Phase 1-2 Development Area Conceptual Landfill Gas
Building Mitigation Plan
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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Figure MT 1.03, Phase 3 Development Area Conceptual Landfill Gas
Building Mitigation Plan
Figure MT 1.04, Phase 4 Development Area Conceptual Landfill Gas
Building Mitigation Plan
Figure MT 1.05, Phase 5 Development Area Conceptual Landfill Gas
Building Mitigation Plan
Figure MT 1.06, Phase 6 Development Area Conceptual Landfill Gas
Building Mitigation Plan
Figure MT 1.07, Phase 7 Development Area Conceptual Landfill Gas
Building Mitigation Plan
Figure MT 2.01, Conceptual Landfill Gas Building Mitigation Plan Details
Figure MT 2.02, Conceptual Landfill Gas Building Mitigation Plan Details
Figure MT 3.01, Conceptual Methane Gas Building Monitoring System
Appendix M Leachate Collection and Removal System Concept Plan (figure from Draft
Technical Memorandum, Leachate Collection and Removal System Concept
Plans, City Place Santa Clara, 6 February 2015)
Figure 9, Layout of Existing/Proposed Leachate Recovery System
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
770611601
Page 1
POST-CLOSURE LAND USE PLAN
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
1.0 INTRODUCTION AND BACKGROUND
The City of Santa Clara ( the ‚City‛), as owner and operator of the former Santa Clara All-
Purpose Landfill (Landfill), presents this Post-Closure Land Use Plan (the ‚Plan‛) for the
redevelopment and repurposing of the Landfill. The City proposes to lease City-owned
property, which includes the former Landfill, to Related Santa Clara, LLC (Related) for purposes
of developing City Place Santa Clara (Project), a new multi-building mixed-use development.
The Project will include demolishing existing above-ground improvements and constructing
new buildings and site improvements. Some of the in-ground landfill gas extraction system
(LFG system), leachate collection and removal systems (LCR systems), and landfill cover will be
abandoned, modified and enhanced. The final design and construction of the Project will be
reviewed by the Santa Clara County Department of Environmental Health Local Enforcement
Agency (LEA), the California Department of Resources, Recycling, and Recovery (CalRecycle),
the San Francisco Bay Regional Water Quality Control Board (RWQCB), the Bay Area Air Quality
Management District (BAAQMD), and the City of Santa Clara Planning Department.
Structural improvements developed on landfills must comply with specific construction
standards set forth in California Code of Regulations (CCR), Title 27, §21190. The Plan is being
developed in general accordance with these requirements. The final Plan will be presented for
regulatory agency approval and will provide the basis for preparing a Revised Corrective Action
Plan and Revised Post-Closure Maintenance Plan based on Design and Construction
Documents for the development.
The Plan is organized as follows:
Section 1.0 – Introduction and Background
Section 2.0 – Geology and Hydrogeological Information
Section 3.0 – Waste Management
Section 4.0 – Site Demolition and Preparation
Section 5.0 – Conceptual Foundation
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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Section 6.0 – Final Cover
Section 7.0 – Irrigation and Landscaping
Section 8.0 – Utilities
Section 9.0 – Enhanced Landfill Gas Collection and Remediation System
Section 10.0 – Landfill Gas Control
Section 11.0 – Leachate Collection and Removal System
Section 12.0 – Groundwater and Surface Monitoring
Section 13.0 – Emergency Response
Section 14.0 – Operation and Maintenance
Section 15.0 – Satisfaction of Post-Closure Land Use Requirements
Section 16.0 – References
1.2 Site Description
The overall project site (the ‚Site‛) totals 240 acres and includes four areas designated as
Landfill Parcels 1/1NW, 2, 3/6 and 4 (see Figures 1 and 2) and an area south of and outside the
landfill designated as Parcel 5. Landfill Parcel (‚Parcel‛) designations at the Site are based on
available historical documents, including the Solid Waste Assessment Tests (SWATs) prepared
for the Site (Kenneth D. Schmidt and Associates [KSA], 1988 and Emcon Associates [Emcon],
1988).
The Site boundaries include Lafayette Street, Great America Parkway, Stars and Stripes Drive,
Centennial Boulevard, Tasman Drive the Guadalupe River, and the San Tomas Aquino Creek.
The Site, owned by the City, is currently occupied by the Santa Clara Golf and Tennis Club on
Parcels 2, 3/6, and 4, the Santa Clara Police Action League BMX course on Parcel 1/1N/W, a
City of Santa Clara firehouse on Parcel 4 and paved parking lots on Parcel 5. Associated
addresses include 5451 Lafayette Street, 5500 Lafayette Street, and 5155 Stars and Stripes
Drive. The surrounding land uses generally include commercial and industrial uses to the north
(including the Gateway Development to the northwest and a stormwater retention basin to the
northeast), residential communities to the east, general commercial uses to the south
(including buildings associated with the golf course, a football stadium, and a large commercial
park), and commercial uses to the west (remaining portions of the Gateway Development,
other commercial parks, and the Santa Clara Convention Center).
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5500 Lafayette Street
Santa Clara, California
September 2015
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1.3 Site Background
Portions of the Site (approximately 136 acres) were reported in regulatory documents to be
used for landfill operations between 1934 and 1993 (RWQCB, 2002); however, review of
historical aerial photographs and topographic maps show that landfill operations began only in
the late 1960s, taking place on Parcel 4 from sometime in the 1960s through at least 1977, on
Parcel 2 between approximately 1977 and 1984, on Parcel 1 between approximately 1982 and
1986, and on Parcel 3/6 between approximately 1986 and 1991. Landfill operations resumed
on the Parcel 1NW area (the northwest corner of Parcel 1) in 1991 and continued until the last
refuse was accepted in 1993 (Golder Associates [Golder], 2014b). The Site has been used as
the current golf course and BMX facility since about 1993. The south eastern portion of the
Site is occupied by the City of Santa Clara Fire Station; however, this facility is not underlain by
refuse.
Refuse accepted at Parcels 1/1NW and 2 reportedly included rubbish and residential,
commercial, and industrial garbage and refuse (KSA, 1988). Refuse accepted at Parcel 3/6
reportedly included non-hazardous solid waste. Parcel 4 was reportedly used initially as an
open burning dump and later accepted only dry material, construction debris, yard refuse, and
non-garbage items. Recent investigations at the Site have encountered mixed refuse items
including wood, paper, plastic, ceramics, glass, metals, and cloth in the refuse units. The total
mass of refuse placed is estimated to be 5.5 million tons (Air Science Technologies, Inc., 2012).
The Landfill is no longer active and the Final Closure and Post Closure Maintenance Plan for all
parcels (Emcon, 1992) was approved by the California Integrated Waste Management Board
(CIWMB) in December 1992 and amended multiple times, most recently in December 2013
(Golder, 2013). The CIWMB approved the Landfill Closure Certification Report for the Site in
November 1994.
All parcels include a LFG system consisting of 75 active vertical landfill gas (LFG) extraction
wells connected by horizontal laterals to a landfill gas-to-energy flare system operated by
Ameresco (Golder, 2014a), a private company under contract with the City of Santa Clara.
Parcel 1NW and Parcel 3/6 were developed with a LCR system consisting of a central sump,
laterals, risers and pumps. Additionally, a groundwater monitoring well system and a LFG
monitoring probe network are present at the Site (Golder, 2014b). The City is currently
responsible for all monitoring and reporting programs related to the LFG system, LCR system,
and groundwater well network per applicable regulations (see Appendix A for existing system
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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Page 4
and monitoring well network). Further information on these existing systems is provided in
Sections 9.1, 11.1, and 12.0, respectively.
1.4 Project Description
Related proposes to fully redevelop the Site. Parcel 4 is planned for redevelopment as mixed-
use including retail/entertainment, hotel and office and residential. Residential apartment units
would be constructed above a podium garage structure or above at least one floor of retail
space. The planned future uses for the remaining Parcels included office, rental, and hotel.
Enclosed basement construction will be prohibited.
The Site is zoned ‚B‛ in the City of Santa Clara 2010-2035 General Plan, which is the Public,
Quasi-Public and Public Park or Recreation Zoning District and a portion of Parcel 5 is zoned
‚CP‛ Commercial Park. The City is currently preparing an Environmental Impact Report
reviewing a proposal to approve an amendment to the General Plan and Zoning Ordinance to
change the zoning to a new designation to be called ‚Urban Center/Entertainment District.‛ At
the same time, the City will consider a proposal to approve a Master Community Plan for the
Site. The Project (Related, March 2014) includes up to 9,164,400 gross square feet (gsf) with
associated parking and Site improvements. The current breakdown by Parcel is as follows:
Table 1
Current Development Program
Parcel Parcel Area
(acres)
Potential Development Area
(gsf)
1/1NW 49.6 1,200,000
2 60.9 2,160,000
3/6 34.9 720,000
4 86.6 4,259,400
5 8.0 825,000
The proposed development will occur in phases (see Phasing Strategy in Appendix B) with the
development on Parcel 4 and 5 likely proceeding in the first four phases. The conceptual Site
layout is depicted in the conceptual architectural renderings included in Appendix C (pending
preparation) and the preliminary design drawings included in Appendix D. Since it is outside of
the landfill property, development plans at Parcel 5 are not subject to PCLUP requirements.
Post-Closure Land Use Plan
Former Santa Clara All-Purpose Landfill
City Place Santa Clara
5500 Lafayette Street
Santa Clara, California
September 2015
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1.5 Previous Investigations
Previous investigations at the Site include the Solid Waste Assessment Test (SWAT) Reports
prepared prior to the Landfill closure (KSA, 1988 and Emcon, 1988), semi-annual monitoring
conducted by several consultants on behalf of the City from 1985 to the present, and recent
soil, groundwater, and LFG investigations by Langan Treadwell Rollo (Langan, 2014e). Figures
and tables summarizing the results of the recent soil, groundwater, and LFG investigations are
included in Appendix E.
1.5.1 Solid Waste Assessment Test
In June 1987, the City received correspondence from the RWQCB that a SWAT for the Site
was required. The Water Part of the SWAT was prepared for the Site in 1988 (KSA, 1988).
Based on the findings of the Water Part of the SWAT, elevated concentrations of volatile
organic compounds (VOCs) were encountered in groundwater beneath portions of Parcel 4 and
Parcel 3/6.
The Air Quality SWAT was prepared for the Site in 1988 (Emcon, 1988). At the time of the Air
Quality SWAT, LFG at the Site was generally comprised of methane, carbon dioxide and some
VOCs, including benzene, methylene chloride, tetrachloroethene (PCE), trichloroethene (TCE),
vinyl chloride, and 1,1,1-trichloroethane (1,1,1-TCA).
1.5.2 Ongoing Semi-Annual Monitoring
As part of the Waste Discharge Requirements (WDRs) issued by the RWQCB to the City for
the Site, Golder (on behalf of the City) continues to monitor groundwater, leachate, and surface
water at the Site and near vicinity; the WDRs for the Site are included in Appendix F. Based on
the most recent data (Golder, 2014b), the primary VOCs in groundwater include 1,1-
dichloroethene (1,1-DCE), cis-1,2-DCE, trans-1,2-DCE, TCE, and vinyl chloride. Several other
VOCs, including carbon disulfide, methyl tert butyl ether (MTBE), and chloroform, have been
detected at trace levels intermittently during continued groundwater monitoring at the Site.
Groundwater monitoring results confirm the presence of elevated VOC concentrations in a
limited area at the northeastern portion of Parcel 4 and southeastern portion of Parcel 3/6 (see
Figure 3 in Appendix E). The distribution of the VOCs has not changed significantly since the
1988 SWAT (more than 25 years).
As part of the BAAQMD requirements for the Site, Golder regularly conducts surface emissions
testing for methane; monitors LFG at extraction wellheads for methane, carbon dioxide, and
Post-Closure Land Use Plan
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5500 Lafayette Street
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September 2015
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oxygen; and analyzes LFG at the flare for several compounds, including selected VOCs,
methane, and hydrogen sulfide. The BAAQMD permit to operate (PTO) for the Site is included
in Appendix F. Based on the most recent data (Golder, 2014a), typical constituents of LFG such
as hydrogen sulfide, methane, and several VOCs, including benzene, chlorobenzene,
chloroethane, 1,1-dichloroethane (1,1-DCA), ethanol, ethylbenzene, hexane, 2-butanone (MEK),
4-methyl-2-pentanone (MIBK), toluene, vinyl chloride, and xylenes continue to be detected in
LFG at the flare. Additionally, methane is regularly detected at the extraction wellheads during
the wellhead performance monitoring. Surface emissions testing along designated walking
routes throughout the Site did not detect methane above the 500 parts per million by volume
(ppmv) screening level during the 2013 screening events (Golder, 2014a). Furthermore, based
on monitoring by Golder, surface emission monitoring has never detected methane above
500 ppmv.
1.5.3 Recent Soil, Groundwater, and Landfill Gas Investigations
The summary of existing environmental conditions as described above is based on information
obtained from the SWATs prepared for the Site (KSA, 1988 and Emcon, 1988) and ongoing air,
groundwater, and LFG monitoring by Golder (Golder, 2014a and 2014b). As part of its
consideration of certain environmental aspects of the Project, the RWQCB in 2013 requested a
comprehensive soil, groundwater, and LFG investigation at the Site. The scope was developed
in coordination and with concurrence from the RWQCB (Langan, 2014a, 2014b, and 2014d;
RWQCB, 2014a, 2014b, and 2014c). As a result, several soil, groundwater, and LFG
investigations were conducted at the Site between April 2014 and October 2014. The
investigations included:
Drilling 38 soil borings to depths between 5 and 200 feet below grade for the collection
of soil within the cap layer (hereafter referred to as cap samples, for brevity), soil within
the refuse unit (hereafter referred to as refuse samples, for brevity), native soil, and
groundwater samples throughout the Site (see Figures 3 and 4 in Appendix E);
Collecting LFG samples from 32 selected existing landfill extraction wells throughout
the Site while the LFG system was in operation (see Figures 6a, 7a, and 8a in Appendix
E); and
Installing 14 temporary LFG probes for the collection of LFG samples throughout the
Site (see Figures 6b, 7b, and 8b in Appendix E).
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September 2015
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The laboratory analytical results from the conducted investigations generally indicated:
The cap is comprised of a low permeability layer and cover soil above the refuse;
In groundwater samples, concentrations of total petroleum hydrocarbons in the gasoline
range (TPHg), diesel range (TPHd), and motor oil range (TPHmo), and several VOCs,
including benzene, tert butyl alcohol (TBA), cis-1,2-DCE, naphthalene, TCE, and vinyl
chloride are above groundwater Environmental Screening Levels (ESLs) in Parcels 3/6
and 4 of the Site;
In LFG samples, concentrations of several VOCs, including benzene, ethylbenzene,
PCE, and vinyl chloride, are at or above residential and/or commercial/industrial ESLs at
the Site; and
Methane and hydrogen sulfide were also detected in LFG at significant concentrations.
1.5.4 Human Health Risk Assessment
Based on the laboratory analytical results obtained from the investigations conducted by
Langan, a human health risk assessment was prepared (Langan, 2014e). The technical
approach for the risk assessment consisted of the following basic steps: data analysis and
identification of contaminants of potential concern (COPCs), exposure assessment, toxicity
assessment, and risk characterization, which included an assessment of the uncertainty
associated with each stage of the risk assessment process. The risk assessment used
reasonable maximum exposure point soil and LFG concentrations of COPCs to derive
exposures and risks to potentially exposed human populations for all complete or potentially
complete exposure pathways. The risk assessment found that a complete or potentially
complete pathway for direct groundwater exposure to potential receptors did not exist at the
Site. Incomplete pathways are not relevant to human health risks and were therefore excluded
from the risk assessment.
The potential receptor populations and potential exposure pathways identified during the
evaluation included:
Groundskeepers – Potential exposure pathways include incidental ingestion of soil,
dermal exposure to soil, and inhalation of ambient vapor and fugitive dust.
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Construction Workers - Proper personal protective equipment (PPE) would preclude
exposure of construction workers; however, an evaluation based on potential
construction worker exposures to soil was nonetheless conducted.
Future Residents – Potential exposure pathways include exposure to volatile vapors
from subsurface media that infiltrate the hypothetical buildings into the interior space
through cracks in the slab foundation.
Indoor Commercial Workers – Potential exposure pathways include exposure to volatile
vapors from subsurface media that infiltrate the hypothetical buildings into the interior
space through cracks in the slab foundation.
Shoppers and Other Visitors – Potential exposure pathways include exposure to volatile
vapors from subsurface media that infiltrate the hypothetical buildings into the interior
space through cracks in the slab foundation. Though shoppers and other visitors may
be present on-site on a variable basis, variable or intermittent exposure scenarios were
not quantitatively evaluated because the evaluation of the indoor commercial worker
scenario is protective of these receptors.
The results of the human health risk assessment indicate that:
Under baseline conditions and without active soil vapor/LFG controls, no unacceptable
cancer and non-cancer risks are posed to the groundskeepers, indoor commercial
workers, and construction workers;
Under baseline conditions and without active soil vapor/LFG controls, inhalation of
volatile COPCs from groundwater for the commercial worker scenario results in
incremental human health risks (1E-06 to 6E-07) that were well within the government-
accepted human risk management range risks (i.e. 1E-06 to 1E-04) for such workers.
The hazard index (HI) was below the threshold level of 1, and TCE concentrations in
indoor air are below the short term action level for residential exposure.
For future residents, inhalation of volatile constituents in the interior space of a future
apartment complex without a sub-slab vapor intrusion mitigation including a vapor
barrier also results in carcinogenic risk (5E-06) within the government-accepted risk
management range, but the carcinogenic risks were higher than those for the
commercial workers. The HI for the apartment resident scenario was below the target
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HI of 1, indicating that adverse non-cancer effects are not anticipated. Modeled TCE
concentrations in indoor air are below the short term action level for residential
exposure.
Though the risk assessment indicates that no active soil gas/LFG remediation is required to
mitigate unacceptable risks to the groundskeeper, indoor commercial worker, or construction
worker in any of the parcels, active measures would be advisable to reduce the human health
risks for apartment residents in Parcel 4. To be consistent in providing protection in all parcels
and to add further protective measures for all receptors, Langan recommended the following
remediation and mitigation measures for all parcels in the proposed development to reduce
potential health risks to construction workers and future Site occupants (including
groundskeepers, indoor commercial workers, and residents):
Replacement and enhancement of the existing LFG system at the Site to provide a
more robust remediation system to actively extract LFG from the Site to the existing
gas-to-energy plant for beneficial reuse and reverse the flux of LFG away from building
underslab areas and towards the LFG extraction wells. Construction of a landfill gas
mitigation system (LFGMS) will also address methane and hydrogen sulfide in LFG by
actively removing the LFG from the refuse beneath the development and thermally
destroying the LFG. While odor is not a human health risk issue, it poses the possibility
of unacceptable impacts to human receptors;
Construction of building control systems for LFG (i.e., LFGMS), which will further
mitigate the potential for vapor intrusion by providing a preferential horizontal pathway
to mitigate LFG that may otherwise accumulate at sub-slab areas, in addition to a vapor
barrier membrane (VBM) that would further limit the intrusion of LFG into building
interiors.
Limiting residential construction land uses to areas located above open-air podium level
garages or above at least one level of enclosed retail space; and
Implementation of institutional controls (i.e., deed restrictions) at the Site, restricting the
use of on-site groundwater (i.e., prohibiting the use of on-site groundwater for potable
purposes).
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1.6 Feasibility Study of Groundwater Alternatives
The RWQCB, in a letter dated 23 February 2015, requested preparation of a feasibility study
(FS) of groundwater remediation alternatives to address VOCs in groundwater. The RWQCB
specifically requested that the FS focus on the potential risks from intrusion of groundwater
contaminants from within the VOC Plume into indoor spaces within the future development.
Langan submitted the Feasibility Study of Groundwater Remedial Alternatives (Langan, 2015d),
and the RWQCB concurred with the FS in a letter dated 23 July 2015.
The FS included preparation of a groundwater conceptual site model to describe the history,
source, fate, and potential transport of VOCs within the VOC Plume and to support the
establishment of remedial goals for the VOC Plume. The FS noted that the VOC Plume has
been limited to the northeastern portion of Parcel 4 and southwestern portion of Parcel 3/6
since groundwater data collection began in 1988 and that the extent of the plume has been
stable for at least the past 27 years (Langan, 2015d). As described in the FS, the primary source
of VOCs in the VOC Plume is likely groundwater contact with the refuse beneath the Parcel 4
area. Within Parcel 4, the groundwater table elevation is between approximately 5 and 15 feet
above the bottom of the refuse layer resulting in groundwater contact with refuse. The FS
noted geochemical conditions (low dissolved oxygen and low nitrate concentrations) are
conducive to naturally-occurring anaerobic biodegradation via the reductive dechlorination
pathway. Elevated chemical oxidant demand (COD), which appears to be a result of contact
between refuse and groundwater, appears to provide a long-term source of degradable organic
carbon in the groundwater sufficient to sustain reductive dechlorination. VOC constituents and
concentration trends within the VOC Plume are indicative of an active reductive dechlorination
pathway, including the presence of TCE and daughter products of TCE, including cis-1,2-DCE
and vinyl chloride (Langan, 2015d).
The FS proposed the establishment of groundwater remediation goals based on human health
risk from potential intrusion of VOCs from groundwater into future indoor spaces within Parcel
4 and Parcel 3/6 above the VOC Plume. Risk-based goals, rather than drinking water standards
(i.e., Maximum Contaminant Levels or MCLs) were determined to be appropriate because the
groundwater at the Site is not a potential source of drinking water based on elevated total
dissolved solids (TDS) concentrations exceeding the TDS criterion established in California that
defines a potential source of drinking water (TDS greater than 3,000 milligrams per liter).
Additionally, the Site location near the Bay-margin would likely induce saltwater intrusion from
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the Bay and further increase groundwater salinity (i.e., TDS) if pumping of groundwater for
water supply were to occur. The Johnson and Ettinger (J&E) infinite source groundwater
advanced (GW-ADV) model (Version 3.1, February 2004) was used to evaluate human health
risks associated with groundwater potential vapor intrusion of VOCs from groundwater to
potential residential receptors. The model was used to estimate risk-based groundwater
concentrations based on a residential cancer risk of 1E-06 or systemic risk corresponding to a
hazard quotient (HQ) of 1.
Based on the human health risk assessment, as described in Section 1.5, TCE and vinyl
chloride were the two compounds considered in the risk evaluation. The GW-ADV model
assumed a depth to groundwater based on the median depth to water measured at wells
within Parcel 4 (25.25 feet). The model assumed a landfill cover/cap thickness based on the
current median cover/cap thickness observed in borings within Parcel 4 (9 feet). The model
assumed the subsurface material beneath the landfill cover/cap and the top of the groundwater
table is refuse. Based on site-specific boring log and test pit reports, the GW-ADV model
assumed the following soil types in the risk model:
Refuse Layer = Silty Clay Loam (SICL)
Landfill Cover/Cap = Silty Clay (SIC)
These soils represent reasonably conservative estimates of the total effective rate of diffusion
of VOCs vapors through the vadose zone. The GW-ADV model applied the same building
parameter inputs as presented for the baseline human health risk assessment presented in the
Draft SI/ERA and described in Section 1.5. The default RWQCB exposure parameters for
residential exposures were applied in the GW-ADV model, as presented in the Draft SI/ERA.
Toxicity factors used were consistent with the ESLs for each compound, as presented in the
Draft SI/ERA (Langan, 2014e).
In addition to modeling diffusion of vapors through the vadose zone, the GW-ADV model used
to establish groundwater remediation objectives considered two additional site-specific factors.
First, the GW-ADV model considered the mitigation effect of the proposed vapor barrier
membrane (VBM), which is a component of the LFGMS described in Section 1.5. The VBM
was modeled as a 60-mil (0.15 cm) layer using chemical permeability data provided by CETCO,
the manufacturer of Liquid Boot. Second, the GW-ADV model result was calibrated based on
actual soil gas concentrations (i.e. concentrations present within the landfill gas) present above
the VOC groundwater plume. The FS describes an evaluation of concentrations of TCE and
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vinyl chloride in groundwater samples collected from groundwater wells within the footprint of
the VOC Plume and comparison of the concentrations with soil gas concentrations from soil
gas probes within the footprint of the VOC Plume. Langan predicted soil gas concentrations
based on equilibrium partitioning (Henry’s Law) between soil gas and groundwater, using 2014
concentrations of TCE and vinyl chloride in groundwater and soil gas.
Based on the methodology described above, the GW-ADV model was performed for TCE and
vinyl chloride under residential exposure conditions. The result was a calculation of TCE and
vinyl chloride concentrations in groundwater corresponding to the more restrictive of either a
1E-06 cancer risk or HQ of 1 for residential land use. The modeled target values included the
following:
TCE: 59,600 micrograms per liter (g/L)
Vinyl Chloride: 442g/L
The FS noted that the modeled target values were significantly higher than actual
concentrations on TCE and vinyl chloride in the VOC Plume. For TCE, the risk-based target
concentration was several orders of magnitude greater than actual concentrations found in
groundwater and was well above a concentration that can be reasonably expected to exist
within the VOC Plume. For this reason, the FS did not establish a remedial goal for TCE. For
vinyl chloride, the FS established the risk-based target concentration as the remedial goal. The
FS established the following remedial goals for the VOC Plume:
1. Maintain or reduce vinyl chloride concentration in groundwater at or below 442 µg/L;
and
2. Demonstrate long-term stability or decreasing trend in TCE and vinyl chloride
concentrations at wells G-10, G-18, and G-19.
A range of remedial technologies was considered in the FS for reduction of groundwater vinyl
chloride concentrations within Parcel 3/6 and Parcel 4, consistent with the remedial goals.
Technologies that were screened included: No Action, Monitored Natural Attenuation (MNA),
Chemical Oxidation, Bioaugmentation, Bioaugmentation with Electron Donor, Zero Valent Iron
(ZVI) with Electron Donor, Air Sparging with Soil Vapor Extraction, and Vacuum Enhanced
Pumping. These remedial technologies were evaluated based on the following criteria:
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technical effectiveness, implementability, remedial time frame and relative cost range. These
criteria were ranked as ‘low’, ‘medium’, and ‘high’, as presented in the FS. As part of this
evaluation, a 600 foot long, 60 foot wide treatment area was assumed with a target depth of 15
feet in the saturated zone. The treatment area consisted of areas with elevated or increasing
vinyl chloride concentrations and included the area between monitoring wells G-19 and G-18.
As a result of the alternative screening, the FS eliminated the following alternatives from
further consideration: No Action, Chemical Oxidation, and Air Sparging with Soil Vapor
Extraction. The FS included a detailed evaluation of the remaining remediation technologies:
MNA
Bioaugmentation
Bioaugmentation with Electron Donor
ZVI with Electron Donor
Vacuum Enhanced Pumping
The FS noted that all five of the evaluated remediation technologies were expected to meet the
established remedial goals and could be implemented in a way that was not expected to
interfere with planned development. Based on the remedial alternative evaluation presented in
the FS, MNA was selected to be the preferred remedial alternative for implementation of VOC
Plume remediation. The FS noted several factors that supported the selection of MNA,
including:
1. MNA is already meeting groundwater remedial goals and is expected to continue to meet
these remedial goals in the future;
2. The size of the VOC Plume is stable and has been stable for 27 years;
3. Reductive dechlorination is occurring in the groundwater;
4. Groundwater field and laboratory analytical geochemical parameters conducive to reductive
dechlorination were detected within the VOC Plume;
5. Refuse appears to act as a source of electron donor and thus can continue to sustain
reductive dechlorination of the groundwater VOC plume;
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6. The Proposed LFG System, described in Section 1.5, would result in continued decreases in
VOC concentrations in soil gas within the refuse and will therefore help to mitigate
groundwater VOC impacts; and
7. Aspects of site development will serve to reduce infiltration rates into the landfill, further
reducing leachate production from current low levels. Although leachate is not considered
to be the primary source of VOCs in the VOC Plume, the above items would reduce
potential impacts of leachate on the groundwater.
The FS established the approach for implementation of the MNA alternative, including
monitoring to be performed quarterly for the first two years once the on-site construction has
started, then semiannually for next three years, and annually thereafter. Monitoring parameters
established in the FS included field groundwater monitoring parameters, VOC concentrations,
dissolved gases including concentration, ethene and ethane, geochemical data, total organic
carbon (TOC), and Dehalococcoides (DHC) cell density.
The FS included an iterative contingency approach to be taken to further evaluate, and if
necessary, take action should any increasing VOC concentrations occur during implementation
of the MNA alternative. The steps included review of sampling methodology, confirmation
groundwater monitoring, review of the groundwater conceptual site model, review of the risk
model, and an evaluation of whether MNA remains the appropriate remedial measure for the
VOC Plume. As described in the FS, should MNA not remain the appropriate remedial
alternative, consideration would be given to: 1) an active remediation alternative evaluated in
the FS, and/or 2) adjustment/optimization of existing mitigation systems or selection of
additional mitigation measures.
2.0 GEOLOGY AND HYDROGEOLOGICAL INFORMATION
This section presents a description of the Site geology and hydrogeology based on the results
of multiple phases of investigations and periodic monitoring completed by Langan and others.
Furthermore, the existing soil cover over the refuse was evaluated for suitability to continue to
serve as the final landfill cover per applicable environmental regulations.
Current California Code of Regulations Title 27 regulations require a "prescriptive" cover design,
one that is established by regulation and intended for use in the closure of landfills regulated
under Title 27. The prescriptive cover, as outlined in Title 27, §21090(a)(1-3), contains:
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A foundation layer of not less than 2 feet of appropriate materials. However, Title 27
Section 21090 allows for a lesser thickness, if the ultimate land use will not affect the
structural integrity of the final soil cover. The foundation layer materials may be soil,
contaminated soil, incinerator ash, or other waste materials, provided that such
materials have appropriate engineering properties to be used for a foundation layer.
Low permeability layer not less than 1 foot thick and of hydraulic conductivity not more
than 1E-6 centimeters per second (cm/sec).
Erosion resistant layer (cover soil) not less than 1 foot thick capable of sustaining
vegetation and resistant to wind, raindrop impact, or runoff or mechanically resistant.
The landfill cover, refuse and subsurface conditions beneath the landfill are discussed in the
following subsections.
2.1 Subsurface Conditions
The Site is underlain by varying thicknesses (3 to 35 feet) of cover soil, an artificial fill which
consists of mixed sand, gravel, clay and silt layers (Langan, 2014c and 2014e). Within the cover
soil, a clay soil layer with varying amounts of sand and gravel content was encountered in most
of the borings and test pits. This material, which varies in thickness up to 7 feet throughout the
Site, consists of dark brown stiff clay and was likely used as the low permeability layer of the
previously constructed final cover. The bottom of the low permeability layer generally marks the
top of the refuse layer, which consists of mixed refuse items, including wood, paper, plastic,
ceramics, glass, metals, and cloth in a matrix of soil. The lower one foot of the clay layer (where
it is at least two feet thick) and upper one foot of the refuse layer was likely the foundation
layer during original final cover construction. As discussed above, Title 27 allows for foundation
layer materials to be soil, contaminated soil, incinerator ash, or other waste materials, provided
that such materials have appropriate engineering properties to be used for a foundation layer.
The upper few feet of the refuse unit is generally mixed in with significant soil and likely was
stable and non-yielding to allow for compaction of the clay material above the refuse.
Our estimate of the depth and thickness, based on Langan investigations, of the soil cover, low
permeability and foundation layers are presented in Table 2. In some locations, Borings B-16,
B-23, B-37, B-38 and B-39, the low permeability layer was not observed in the borings; it may
be that the layer is present but not sampled. Additionally, other areas such as near test pit TP-
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1, sufficient cover soil over the low permeability layer was not observed. The presence or lack
of the low permeability layer and cover soil layer in these locations will be further evaluated as
part of a future final geotechnical investigation. Additionally, in areas where proposed utilities
or roadway excavations need to extend below the existing low permeability layer, the landfill
cover including low permeability layer will be designed and repaired to accommodate these
construction details and provide a continuous landfill cover across the Site.
Table 2
Summary of Thickness of Cover Soil, Low Permeability Layer, and Refuse
Boring
No.
Parcel
Number
Approx
thickness
of cover
soil (feet)
Approx
thickness of
low
permeability
layer (feet)
Approx
thickness of
foundation
layer (feet)
Approx
thickness
of refuse
(feet)
Comments
1 2 2 1 2 30
2A 1 4.5 1 2 59.5
4 4 4 1.5 2 31.5 Top of refuse layer
likely used as
foundation layer
5 4 3 1 2 10.5
6 4 10 1 2 19 Top of refuse layer
likely used as
foundation layer
7 4 5.5 1 2 24
8 3 29 1 5 >10
9 3 7 1 2 >1
10 3 18 1 2 >5
11 3 18 1 2 >4
12 3 27 1 2 >6
13 3 34 1 2 >5 Top of refuse layer
likely used as
foundation layer
14 3 7.5 1 2 >0.5
15 3 28 1 2 >5
16 4 4.5 0 2 >30.5 Low Permeability
Layer not
observed
17 4 4 1 2 >24
18 4 4 1 2 >20
19 4 3 1 2 >23 Top of refuse layer
likely used as
foundation layer
20 4 4 1 2 >29
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Boring
No.
Parcel
Number
Approx
thickness
of cover
soil (feet)
Approx
thickness of
low
permeability
layer (feet)
Approx
thickness of
foundation
layer (feet)
Approx
thickness
of refuse
(feet)
Comments
21 4 5 1 2 >33 Top of refuse layer
likely used as
foundation layer
22 4 5 1 2 >28
23 4 4 0 2 >32.5 Low Permeability
Layer not
observed over
refuse and top of
refuse layer likely
used as foundation
layer
24 4 12 1 2 >1
25 4 3 1 2 >2 Top of refuse layer
likely used as
foundation layer
26 4 3 1 2 >1 Top of refuse layer
likely used as
foundation layer
27 1 15 1 2 >6
28 1 6.5 1 2 >4.5
29 1 7.5 1 2 >5.5
30 1 13 1 2 >5
31 1 15 1 2 >6
32 1 2.5 1 2 >8.5
33 2 3.5 1 2 >4 Top of refuse layer
likely used as
foundation layer
34 2 5 1 2 >3
35 2 5 1.5 2 >2.5 Top of refuse layer
likely used as
foundation layer
36 2 6 1 2 >2
37 2 10 0.5 2 >4 0.5 foot thick Low
Permeability Layer
observed over
refuse and top of
refuse layer likely
used as foundation
layer
38 2 6 0 2 >4 Low Permeability
Layer not
observed over
refuse
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Boring
No.
Parcel
Number
Approx
thickness
of cover
soil (feet)
Approx
thickness of
low
permeability
layer (feet)
Approx
thickness of
foundation
layer (feet)
Approx
thickness
of refuse
(feet)
Comments
39 2 7 0.5 2 >2.5 0.5 foot thick Low
Permeability Layer
observed over
refuse and top of
refuse layer likely
used as foundation
layer
Beneath the soil cover unit discussed above is the refuse unit, which varies between
approximately 10 and 60 feet thick. The refuse is underlain by alluvial deposits consisting
predominately of clay and sandy clay layers with occasional interbedded layers of sand and silt.
These sand layers extend over much of the Site; however, they are laterally and vertically
discontinuous which is typical for alluvial deposits. The boring logs and cross sections illustrate
the discontinuous nature of the sand lenses. The soil stratigraphy beneath the refuse will be
further evaluated as part of future geotechnical investigations. Boring logs and idealized
subsurface cross-sections based on our investigations and others are provided in Appendix G.
Groundwater has been observed between approximately 18.5 and 52 feet bgs at the Site
during drilling, corresponding to between elevation (el.) -10 and el. 7 (North American Datum of
1983 [NAD83]/ North American Vertical Datum 1988 [NAVD 88]). Approximate depths to
groundwater and elevations are as follows:
Table 3
Summary of Depth to Groundwater
Parcel Approximate Depth to
Groundwater (feet)1
Approximate Groundwater
Elevation (feet)2
Parcel 1/1NW 52 0
Parcel 2 40 -8
Parcel 3/6 50 to 65 (estimated) 0 (estimated)
Parcel 4 18.5 to 32 -10 to 7
Approximate depth to groundwater recorded during drilling and may not represent stabilized levels.
All elevations reference NAD83/NAVD88.
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Groundwater elevations recorded in our investigations (Langan, 2014c and 2014e) are generally
consistent with the historically measured groundwater elevations. Groundwater monitoring
conducted by Golder Associates in February 2014 measured the groundwater level at the Site
between about el. -4 to el. 43 (Golder, 2014b). The direction of groundwater flow is to the north-
northeast. A groundwater elevation contour map for the Site, based on 24 February 2014
groundwater monitoring data by Golder, is provided in Appendix A, on Figure 2 - Piezometric
Surface Contour Map.
Based on the available groundwater data from previous monitoring at the Site, the groundwater
elevations are generally in or within 10 feet of the bottom portion of the refuse unit. This
suggests that a distinct leachate layer within the refuse unit does not likely exist at a higher
elevation than the regional groundwater elevation. Furthermore, given the apparent lack of
hydraulic head between leachate and groundwater, it is unlikely that contaminants in the first-
encountered groundwater level will migrate vertically to impact underlying aquifers. The
geologic cross sections in Appendix G illustrate similar groundwater elevations from wells
monitored by Golder from July 2013 as those measured in soil borings drilled in the waste
units, which supports an apparent lack of hydraulic head between leachate and groundwater
beneath the Site.
2.2 Hydrological Information
The Site is tributary to the San Tomas Aquino Creek and the Guadalupe River. A brief
description of each waterway and its watershed, as provided by the Santa Clara Valley Urban
Runoff Pollution Protection Program (SCVURPPP), is as follows:
San Tomas Aquino Creek - The San Tomas Aquino Creek watershed covers an area of
approximately 45 square miles. The Creek originates in the forested foothills of the
Santa Cruz Mountains flowing in a northern direction through the cities of Campbell and
Santa Clara, into the Guadalupe Slough, and finally into the Lower South San Francisco
Bay. The major tributaries to San Tomas Aquino Creek include Saratoga, Wildcat, Smith
and Vasona Creeks. Most of the San Tomas Aquino watershed is developed as high-
density residential neighborhoods, with additional areas developed for commercial and
industrial uses. The majority of the San Tomas Aquino Creek channel has been
Golder report references elevation in feet mean sea level (MSL), assumed to be National Geodetic
Vertical Datum of 1929 (NGVD29). Elevations provided herein reference NAD83/NAVD 88.
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modified and lined with concrete (from the Smith Creek confluence in the upper
reaches downstream to Highway 101).
Guadalupe River - The Guadalupe River watershed covers an area of approximately 171
square miles. The headwaters drain from the eastern Santa Cruz Mountains near the
summit of Loma Prieta in heavily forested unincorporated county land with pockets of
low-density residential developments. The Guadalupe River actually begins on the valley
floor at the confluence of Alamitos Creek and Guadalupe Creek, just downstream of
Coleman Road in San Jose. From here it flows north, approximately 14 miles until it
flows into the Lower South San Francisco Bay via Alviso Slough. The upper watershed
is characterized by heavily forested areas with pockets of scattered residential areas.
Residential density gradually increases to high density on the valley floor. Commercial
development is focused along major surface streets. Industrial developments are
located closer to the Bay, primarily downstream of the El Camino Real crossing. Six
major reservoirs exist in the watershed: Calero Reservoir on Calero Creek, Guadalupe
Reservoir on Guadalupe Creek, Almaden Reservoir on Alamitos Creek, Vasona
Reservoir, Lexington Reservoir, and Lake Elsman on Los Gatos Creek.
The climate of the City of Santa Clara is characterized as dry-summer subtropical (often referred
to as Mediterranean), with cool wet winters and relatively warmer dry summers. The mean
annual precipitation in the vicinity of Santa Clara is approximately 15 inches (95 percent [%] of
which falls between October and April) per the 2007 Santa Clara County Drainage Manual
(SCCDM). This value is typical of Santa Clara County east of the coastal range, however, the
Site can experience a wide range of annual precipitation.
Due to the nature of the existing topography and drainage infrastructure, the four parcels along
with the tributary off-site areas have been divided into four distinct sub-watersheds referenced
herein as the San Tomas, East Basin, Eastside Channel and Basin Direct. Note that the East
Basin, Eastside Channel and Basin Direct are tributary to the Guadalupe River via the Eastside
Retention Basin and Pump Station.
San Tomas – The San Tomas sub-watershed includes the areas from Parcel 4 that drain
directly to the San Tomas Aquino Creek via existing outfalls. The Golf Course Pump
Station also conveys runoff to the Creek from areas of Parcel 4 and off-site areas from
Stars and Stripes Drive.
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East Basin – The East Basin sub-watershed includes areas from Parcels 1/NW, 2, 3/6
and 4 along with the off-site areas that drain to the west ditch/channel and ultimately to
the Eastside Retention Basin.
Eastside Channel – The East Side Channel sub-watershed includes areas from Parcels 1
and 2 along with the off-site areas that drain to the Eastside Retention Basin via the
existing Eastside Drainage Channel.
Basin Direct – The Basin Direct sub-watershed includes areas that surface flow directly
to the Eastside Retention Basin.
Within these sub-watersheds, the existing drainage characteristics for each of the Parcels are
as follows:
Parcel 1/1NW – The 49.6 acre Parcel 1/1NW includes open space, a BMX facility, a LFG
recovery facility, access roads, the Eastside Retention Basin, and City operated pump
stations for sanitary sewer and stormwater. The existing surface cover consists of
shrub land, gravel, pavement and open water. The surface water hydrology includes
overland flow and piped conveyance with surface runoff tributary to the Eastside
Retention Basin/Guadalupe River.
Parcel 2 – The 60.9 acre Parcel 2 includes golf course open space, golf cart paths and
access roads. The existing surface cover consists of golf course features (grass, sand
traps, paved golf cart paths), shrub land, gravel and pavement. The surface water
hydrology includes overland flow and piped conveyance systems with surface runoff
tributary to the Eastside Retention Basin/Guadalupe River.
Parcel 3/6 – The 34.9 acre Parcel 3/6 includes golf course open space, golf cart paths
and access roads. Additional fill was placed over the landfill cover creating an elevated
ridge within the center of the site. The existing surface cover consists of golf course
features (grass, sand traps, paved golf cart paths), shrub land, gravel and pavement.
The surface water hydrology includes overland flow and piped conveyance systems
with surface runoff tributary to the Eastside Retention Basin/Guadalupe River. There is
an open depressed area along the toe of the southern slope of the landfill that collects
surface water runoff from both Parcel 3/6 and Parcel 4. This area is utilized as a utility
corridor for the City’s recycled water and sanitary sewer systems.
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Parcel 4 – The 86.6 acre Parcel 4 includes golf course open space, golf cart paths, the
golf course driving range, several buildings, access roads, parking lots and a
maintenance area. The existing surface cover consists of golf course features (grass,
sand traps, paved golf cart paths), shrub land, open water ponds, gravel, paved areas
and building structures. The northern portion of the site drains to the open depressed
area along the toe of the northern slope of the landfill on Parcel 3/6 and the piped
conveyance system within the adjacent property to the north, the eastern portion of the
site drains to a ditch along the adjacent railroad right-of-way (located adjacent to
Lafayette Street), the western portion of the site drains directly to the San Tomas Creek
gravity outfalls and the southern portion of the site drains to the piped conveyance
system in Stars and Stripes Drive. In addition, there is a lined open water pond located
within Parcel 4.
Parcel 5 – The 8.0 acre Parcel 5 includes parking lots and some open space areas. The
existing surface cover consists of pavement and vegetated landscape. The site drains to
on-site catch basins that are connected to the existing storm drainage system in Stars
and Stripes Drive. This storm drain system is tributary to the Golf Course Club House
Pump Station.
3.0 SOIL AND WASTE MANAGEMENT
Site development will require excavating, grading, and conditioning (i.e., soil improvement) of
native material, cover material, and, to a very limited extent, landfill debris within the refuse
unit. The quantity of waste to be handled will be the minimum necessary to construct the
infrastructure, buildings, site improvements, etc. and achieve final grades to support the
Project. A final waste management plan will be developed for the Project to outline proper soil
and landfill debris handling procedures and health and safety requirements (Appendix H). This
waste management plan will help minimize worker and public exposure to toxic materials
during construction. An overview of waste management during construction, nuisance control
measures, and health and safety considerations, are included in the Sections below.
3.1 Waste Management During Construction
Waste management during construction will include waste segregation and characterization,
dust monitoring and control, air monitoring, equipment decontamination, storm water pollution
control, and implementation of a health and safety program. Construction activities that may
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require waste management include grading, excavation for utilities, and possibly pile
installation. An environmental technician who is a Certified Hazardous Waste Worker (per 29
CFR 1910.120) will monitor construction activities to facilitate and document compliance with
the specified waste management procedures, identify potentially contaminated soil and landfill
debris, oversee soil and landfill debris segregation, monitor dust and vapor conditions, and
sample soil for characterization as necessary for off-site landfill disposal profiling (see Appendix
H). Waste handling will be performed in accordance with a Site-specific Health and Safety Plan
(HASP), to be prepared by a certified industrial hygienist (CIH) that represents the general
contractor. General health and safety requirements are discussed in Section 3.3.
The total estimated quantity of waste (including cover soil and, to a very limited extent, the low
permeability layer and refuse) to be excavated will be established as part of final design of the
Project. Based on the preliminary design, the estimated quantity of refuse, as part of the
overall waste generation for the Project, is approximately 100,000 CY. To construct the
trenches for portions of the gravity utilities, excavations are expected to extend into the waste
unit; piping that extends beneath the cap will be water/gas tight to limit leakage into the landfill
refuse and LFG entering into the piping. The design intent is to leave the low permeability layer
and refuse in place to the greatest extent possible and to only disturb it in locations requiring a
deeper excavation, such as main utility trenches.
The cover soil, low permeability layer and refuse will need to be handled and disposed of
properly. Excavated refuse will be monitored for the presence of hazardous or other
unacceptable materials. Refuse will most likely be excavated using conventional earth-moving
equipment such as loaders, backhoes, excavators, or bulldozers. Refuse will be loaded into
trucks and hauled to a staging area to be located on-site for profiling and eventual on-site or off-
site disposal. If any excavated refuse is re-disposed on-site, the disposal of such refuse will
conform to Title 27 requirements and additional applicable regulatory requirements. These
materials will be separated and cordoned off to prevent unauthorized access. A licensed
contractor will be hired to handle the material, including containerization, if necessary, and
transport to an appropriately permitted disposal facility.
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3.2 Nuisance Control Measures
3.2.1 Dust, Litter, and Vectors
Excavating refuse has the potential to create nuisances, such as dust, litter, vectors (as defined
by CCR, Title 27, §20164), and odors. These nuisances could impact adjacent properties. In
addition, toxic materials may be encountered during excavation, which have the potential to
result in worker exposure. LFG could be released or collect in excavations, creating potentially
harmful or explosive conditions. The following project elements address potential nuisances,
hazardous materials, and LFG:
Excavation of refuse will be performed in accordance with a Health and Safety Program
designed to minimize impacts from dust, odor, and other nuisances, and assure the
refuse is handled in a safe and environmentally responsible manner. A site-specific
HASP, to be completed by a CIH on behalf of the general contractor, will address
procedures for monitoring LFG and handling hazardous materials.
During refuse excavation and relocation, the worksite will be monitored for dust, odor,
or other nuisances in accordance with general landfill construction practices and the
HASP. Dust will be controlled by application of a water spray. The amount of water
applied will be the minimum amount required to control dust without creating run-off.
At the end of the working day, exposed refuse will be covered with soil or an alternative
material, such as a geosynthetic blanket, (i.e., interim cover). Covering the refuse at the
end of the working day will control odors, litter, and other potential nuisances. Areas at
final grade will have final cover placed over them.
Odors, should they occur, will be controlled by application of a deodorant, masking
agent, neutralizing agent, or lime, and an interim landfill cover at the end of each
working day. An odor management plan is included in Appendix I.
A "Project Contact" will be designated who will be responsible for responding to local
complaints about dust, odors, or other nuisances associated with the refuse excavation
and re-grading operations. The telephone number of the Project Contact will be posted
at the construction Site and included in the information distributed as part of the
project's outreach program. The Project Contact will determine the source of project-
related nuisances and will coordinate reasonable measures to alleviate the nuisance.
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As discussed in Section 1.4, the Landfill has potential for LFG generation. During
excavation activities, excavation areas will be monitored using a hand-held instrument
calibrated to measure combustible gases (including methane), oxygen, hydrogen sulfide,
and VOCs. Smoking and open flames will be prohibited in excavation areas. Workers
will not be allowed to enter excavated areas, where LFG may accumulate, without prior
monitoring for LFG. If LFG is present, workers will be required to wear appropriate
safety equipment, including respirators if necessary.
3.2.2 Traffic Control
To minimize traffic disruptions during the work, traffic flow into, on, and out of the Site shall be
managed by the general contractor and controlled to minimize the following:
Interference and safety problems with traffic on adjacent public streets or roads,
On-site safety hazards, and
Interference with Site operations.
3.3 Health and Safety Program
During construction of the proposed development, there may be the potential for workers at
the Site, nearby residents, and/or pedestrians, to be exposed to on-site soil or contaminants.
The routes of potential exposure to the Site contaminants (TPH, VOC, and/or metals) could be
through three pathways: (1) dermal (skin) contact with the soil, (2) inhalation of ambient vapor
and fugitive dust, and (3) incidental ingestion of the soil. The highest potential for human
exposure to the contaminants in the soil will be during waste handling operations. Because on-
site materials may contain contaminants in excess of the regulatory guidelines, proper health
and safety procedures, and warning requirements will be implemented during construction.
The potential health risk to on-site construction workers and the public will be minimized by
developing a comprehensive Health and Safety Program. The general contractor shall be
responsible for health and safety conditions related to the work to be performed. Contractor
employees, subcontractor employees, and others who enter the Site must adhere to the
provisions of the contractor Health and Safety Program. All applicable federal, state, and local
regulations and codes relating to health and safety shall be adhered to by the contractor
employees, subcontractor employees, and others who enter the Site.
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The Health and Safety Program will include development of a HASP, including an Air Monitoring
Plan and a Dust Management Plan. These plans will be prepared by a CIH that represents the
general contractor. The general contractor will be responsible for establishing and maintaining
proper health and safety procedures to minimize worker and public exposure to Site
contaminants during construction. The HASP will describe the health and safety training
requirements (i.e., training in accordance with Section 1910.120 of 29 Code of Federal
Regulations [HAZWOPER training]), specific personal hygiene requirements, and monitoring
equipment that will be used during construction. These requirements will protect and verify
the health and safety of the construction workers and the general public; as such, the HASP
will include provisions for Site security and signage. The HASP will also include an emergency
notification list.
A Site Health and Safety Officer (HSO), employed by the general contractor, will be on-site
during construction activities that may require waste management (grading, soil segregation,
soil compaction, excavation for utilities, soil improvement, foundation installation, paving, and
landscaping) to facilitate and document that all health and safety measures are maintained. The
HSO will have authority to direct and stop (if necessary) all construction activities in accordance
with the HASP.
4.0 SITE DEMOLITION AND PREPARATION
Site demolition and preparation will include removal of all existing structures, foundations,
slabs, pavements, and underground utilities within the footprint of the planned development
(see Appendix D for the preliminary design drawings). Existing pavement and foundations will
be removed to expose underlying aggregate base. Underground utilities will be removed to the
service connections and properly capped or plugged. Where existing, inactive, utilities will not
interfere with the planned construction they may be abandoned in-place. All existing utilities
abandoned in place will be filled with lean concrete or cement grout to the limits of the project.
Voids resulting from demolition activities and subgrade preparation above the low permeability
layer will be properly backfilled. All demolition waste materials that cannot be reused or
recycled on-site will be removed from the Site following demolition.
It is anticipated that some components of the existing LFG and LCR systems will be impacted
and that interim measures will be necessary to promote continued effectiveness during
construction (see Appendix A for existing system locations). Additional information on the
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proposed abandonment and replacement of these systems are included in Sections 9.0 and
11.0, respectively. Existing groundwater monitoring wells and LFG monitoring probes shall be
protected during the Site demolition activities (see Appendix A for well locations).
5.0 CONCEPTUAL FOUNDATION
5.1 Structures
A majority of City Center (Phase 1 and Phase 2) portion of the Project within Parcel 4, inclusive
of all buildings, parking garages, plazas and streets, will be a continuous structural slab that is
structurally supported on a deep foundation or ground improvement system that extends
through the cover soil and refuse. For the remainder of the development, the buildings and
parking structures will be supported on a similar deep foundation or ground improvement
system, and the streets, plazas and open space/landscaped areas will be supported on grade.
The structural system for the buildings will include an interstitial space between the first floor
slab and the structural slab. The grading of the streets and plaza areas will be coordinated with
the first floor elevations of the retail, office and parking structures. Residential will be located
above podium parking or first floor retail, thus will not be located on the first floor. Typical
conceptual sections depicting the likely configuration of the foundation system for the various
building types are included in Appendix J.
5.2 Site Settlement Evaluation
As indicated, the Site is underlain by a significant thickness of compressible refuse that will
continue to settle at highly variable rates. Preliminary settlement estimates were estimated
using a model developed by Gibson and Lo (Edil et al., 1990 and Gibson, 1961), which includes
parameters for primary and secondary compression in refuse. The refuse generally consists of
silty clay soil/municipal solid waste, combined with construction debris with high percentages
of wood. Primary compression generally includes the bending, crushing, and reorientation of
landfill material and the movement of finer grained materials into large voids. Settlement
associated with primary compression typically occurs between 1 and 5 years after the initial
application of the load. Secondary compression is associated with landfill settlements that
occur gradually over time. Secondary compression is generally attributable to the physical-
chemical change of the landfill materials, such as corrosion and oxidation, and the biochemical
decomposition of the organic landfill material through anaerobic fermentation and decay. The
majority of secondary compression is typically completed within 50 years after the initial
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application of the load (Sharma and Lewis, 1994). These landfills were closed approximately 20
to 40 years ago; so much of the primary and secondary compression is complete. However,
due to the increased loading from the proposed development, Langan anticipates some future
primary and secondary compression will occur. A detailed settlement analysis will be
performed as part of a final geotechnical investigation for each parcel. Langan preliminarily
estimated refuse settlements for Parcels 1/1NW and 3/6 assuming refuse thicknesses ranging
from 40 to 60 feet. For Parcels 2 and 4, Langan assumed refuse thicknesses ranging from 10
to 40 feet. For all parcels, Langan also estimated refuse settlements which will result from the
addition of 1 foot and 5 feet of new fill. The results of our settlement evaluation are depicted in
Figures 7 and 8 of our Preliminary Geotechnical Investigation Report (Langan, 2014c), which are
included in Appendix J. Because of the heterogeneity of the refuse, it is difficult to accurately
predict the amount of settlement over a given period of time. These estimates will be used as
a guide and may vary significantly. A detailed settlement analysis will be performed as part of a
final geotechnical investigation for each parcel.
On the basis of the currently available data Langan estimate up to about 2 feet of settlement
may occur in Parcels 2 and 4 over the next 30 years. Larger settlements may occur at Parcels
1 and 3/6 due to the thicker and generally younger waste, but will depend on the grading. Piles,
hinged slabs, and settlement vaults would need to be designed to accommodate the estimated
settlement.
Because piles (for lateral capacity) and underground utilities will be designed to accommodate a
set amount of settlement plus a factor of safety, ground surface settlement will be monitored
periodically as part of an overall Site Operation, Monitoring and Maintenance (OM&M) Plan
during the life of the development, and per Title 27 requirements, so mitigation measures can
be implemented if the actual settlement is larger than predicted. Settlement mitigation
measures may include adding fill to restore the lateral capacity of the foundation, and functional
site access. Pumping a light weight material such as Cell-Crete beneath the buildings could be
an alternative to placing fill. Lightweight Cell-Crete can have a unit weight of about 40 to 70
pcf, which is less than typical soil materials and therefore result in less additional settlement
associated with the additional load. Furthermore, Cell-Crete is flowable and self-leveling and
could easily be pumped beneath the building to fill voids and replace the lateral support.
Periodic adjustments to perimeter hinged slabs and other settlement mitigation elements will
also be necessary.
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5.3 Seismic Hazards Analysis
During a major earthquake, strong to violent ground shaking is expected to occur at the project
Site (Langan, 2014c). Strong ground shaking during an earthquake can result in ground failure
such as that associated with soil liquefaction,4 lateral spreading,5 cyclic densification,6
landsliding, or can cause a tsunami. Each of these conditions has been preliminarily evaluated
based on our literature review, field investigation, and analysis, and are discussed below.
5.3.1 Liquefaction
The Site is located within a zone designated with the potential for liquefaction, as identified by
the California Geologic Survey (formerly the California Division of Mines and Geology) in a map
titled, State of California Seismic Hazard Zones, Milpitas Quadrangle, Official Map prepared by
the California Geologic Survey, dated 19 October 2004. Specifically, the map shows the Site is
in an area ‚where historic occurrence of liquefaction, or local geological, geotechnical and
groundwater conditions indicate a potential for permanent ground displacements such that
mitigation as defined in Public Resources Code Section 2693 (c) would be required.‛
We performed our liquefaction analysis in accordance with the State of California Special
Publication 117A, Guidelines for Evaluation and Mitigation of Seismic Hazards in California and
following the procedures presented in the 1996 NCEER and the 1998 NCEER/NSF workshops
on the Evaluation of Liquefaction Resistance of Soils (Youd and Idriss, 2001). The NCEER
methods are updates of the simplified procedures developed by Seed et al. (1971).
To estimate volumetric strain and associated liquefaction-induced settlement, Langan used the
procedure developed by Tokimatsu and Seed (1987).
Saturated layers of loose to medium dense sand with varying amounts of clay and silt and non-
plastic silt were encountered within and just below the refuse unit in one boring (B-4; see
Appendix G). Our analysis indicates these layers could potentially liquefy and result in
4 Liquefaction is a transformation of soil from a solid to a liquefied state during which saturated soil
temporarily loses strength resulting from the buildup of excess pore water pressure, especially
during earthquake-induced cyclic loading. Soil susceptible to liquefaction includes loose to medium
dense sand and gravel, low-plasticity silt, and some low-plasticity clay deposits. 5 Lateral spreading is a phenomenon in which surficial soil displaces along a shear zone that has
formed within an underlying liquefied layer. Upon reaching mobilization, the surficial blocks are
transported downslope or in the direction of a free face by earthquake and gravitational forces. 6 Cyclic densification is a phenomenon in which non-saturated, cohesionless soil is densified by
earthquake vibrations, causing ground-surface settlement.
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seismically induced settlement on the order of 4-inches. However, potentially liquefiable soil
was not encountered in the other borings. Therefore, Langan conclude the potential for soil
liquefaction is likely during a major earthquake. However, it appears that the potential for
liquefaction will be limited to isolated areas and should not be a widespread concern.
5.3.2 Seismic Densification
Seismic densification of non-saturated, cohesionless soil following a major earthquake was
analyzed using the procedure outlined by Tokimatsu and Seed (1987), titled ‚Simplified
Procedure for the Evaluation of Settlements in Clean Sand‛. The borings indicate the sand
deposits above the design groundwater level are generally sufficiently dense and/or clayey such
that seismic densification is unlikely except in the vicinity of boring B-4. We estimate
settlements associated with seismic densification at boring B-4 could be on the order of 1 to 1-
½ inches.
5.3.3 Lateral Spreading
As discussed in Section 5.3.1, the potential for liquefaction appears to be isolated. Because
there does not appear to be a continuous potentially liquefiable layer near the slope faces of the
former Landfill, Langan conclude the potential for lateral spreading is low.
5.3.4 Surface Faulting
We evaluated the risk of surface faulting at the Site associated with active or potentially active
fault traces. Historically, ground surface displacements closely follow the traces of geologically
young faults. Based on our study, Langan conclude the site is not within an Earthquake Fault
Zone, as defined by the Alquist-Priolo Earthquake Fault Zoning Act, and no known active or
potentially active faults exist on the Site. In a seismically active area, the remote possibility
exists for future faulting in areas where no faults previously existed; however, Langan conclude
the risk of surface faulting and consequent secondary ground failure is low.
5.3.5 Tsunami
Recent published maps (California Emergency Agency, 2009) indicate the site is not within the
tsunami inundation zone; therefore, Langan conclude the potential risk of inundation from
tsunami to be low for the site.
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5.4 Proposed Foundation Options
We anticipate the Site will undergo significant settlement caused by the decomposition,
consolidation, and compression of the landfill material due to the weight of landfill refuse,
existing cover soil, and new fill and/or structural loads associated with the proposed
development. These processes will result in differential settlement of the ground surface and
the site improvements. To reduce the potential for settlement of proposed buildings, utility
corridors and surface improvements, Langan anticipate the proposed structures can be
supported on spread footings (isolated or continuous) bearing on drill displacement columns
(DDCs) or on deep foundations consisting of drilled auger cast in place (ACIP) piles. These
foundation options will be designed to address the potential for landfill disturbance and
preserve the integrity of the landfill components and the structures built as part of the proposed
development in a manner that is protective of public health and safety and the environment.
These foundation options are discussed in detail in our Preliminary Geotechnical Investigation
Report and summarized in the following subsections.
5.4.1 Spread Footings on DDCs
In areas with relatively thin refuse (40 feet thick or less) and where relatively lightweight
structures are planned, the proposed buildings and surface improvements can be supported on
shallow foundations bearing DDCs. The DDCs will transfer building loads to stronger native soil
below the landfill refuse. This approach would allow for the use of shallow spread footings at
building column locations rather than deep pile foundations.
DDCs are constructed by using a displacement auger to drill a shaft cased to the desired depth.
The soil, refuse, and leachate, if present, would be displaced laterally (up to about 18-inches
depending on the auger diameter) but not vertically. Controlled low strength material (CLSM),
grout or concrete is injected continuously under pressure as the augers are slowly withdrawn,
replacing the soil or refuse displaced by the drilling operation. The CLSM, grout or concrete is
injected from the tip of the auger before the auger is raised to prevent voids from forming.
DDCs vary from 18 to 36 inches in diameter; the selected diameter is based on building loads
and the number of columns per bearing location. For preliminary planning purposes, Langan
conclude DDCs would need to extend through the entire refuse thickness and approximately 5
to 10 feet into the underlying native soil. Some medium stiff clay was encountered at these
depths. Because DDCs displace the soil laterally, it may help increase the strength of any
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medium stiff clay. The embedment length into native soil will be evaluated as part of a final
geotechnical report and pile load test program.
DDCs are designed and installed by specialty design build contractors. The vertical and lateral
capacities of the DDCs, including the effects of downdrag and settlement on the capacities and
the amount of reinforcing steel necessary to resist lateral loads and resulting bending
moments, will be developed by the design build contractor and reviewed by the geotechnical
engineer of record.
A section view of a typical DDC that would support a shallow foundation is provided in
Appendix J. Because the CLSM grout is injected under pressure during installation of the
DDCs, Langan anticipate the interface between the DDC and the adjacent soil and refuse layers
will be effectively sealed. In addition, the DDCs should not need to extend significantly
beneath the refuse and into the underlying clay unit. For these reasons, Langan conclude that
the potential for introducing leachate or shallow groundwater into underlying aquifers should be
very low both during and after construction. In addition, installation of DDCs should produce
minimal soil and refuse cuttings because the soil and refuse would be displaced laterally during
drilling. Furthermore, because the DDC is installed with an auger that displaces soil laterally,
contamination transport to deeper layers at the tip of the pile while advancing the auger is also
not likely to occur.
5.4.2 Auger Cast In Place Piles
Non-displacement or displacement Auger Cast in Place (ACIP) pile may be used to support the
proposed buildings in areas where the refuse thickness is greater than 40 feet or the building
loads are relatively large. ACIP piles are proprietary piles and are installed by drilling to the
required depth with a hollow-stem, continuous-flight auger. When the auger reaches the
required depth, cement grout or concrete is injected through the bottom port of the hollow
stem auger. Grout or concrete is injected continuously under pressure as the augers, still
rotating in a forward direction, are slowly withdrawn, replacing the soil removed by the drilling
operation. While the grout is still fluid, a steel reinforcing cage is inserted into the shaft. ACIP
piles can range in diameter; however, 16- and 24-inch-diameter ACIP piles are typical. We
preliminarily estimate that ACIP piles would extend at least 50 feet or more into the native soil
below the refuse.
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Displacement ACIP piles are similar in type and installation method to the non-displacement
ACIP piles except that they have a reverse tread on the auger which results in lateral
displacement and densification of the surrounding soil. Drilling of displacement ACIP piles
results in the generation of fewer spoils than that of non-displacement ACIP piles, thus
reducing the need for managing refuse cuttings.
Similar to the DDCs previously discussed, because the grout or concrete for the ACIP pile is
injected under pressure, Langan anticipate the grout would penetrate into the voids in the
refuse and soil surrounding the pile, thereby effectively sealing the interface between the pile
and the adjacent soil and refuse and reducing the potential for introducing leachate or
groundwater into underlying aquifers both during and after construction. This process helps
eliminate the potential for a preferential seepage path along the pile/soil contact. After the grout
is injected, reinforcing steel can be lowered into the pile. A section view of a typical ACIP piles
is provided in Appendix J.
5.4.3 Load Tests and Construction Issues
We are currently developing a pile load test and indicator program to evaluate the vertical
and/or lateral load deformation characteristics for both DDCs and ACIP piles, including potential
issues with installation within the landfill waste. The number of piles, type of load test (tension
and/or compression), strain gauges and locations are currently being developed in conjunction
with the design building contractors. The intent of the load test program is to evaluate the
capacities of both proposed foundation types and provide data that can be used to efficiently
design the deep foundation system for the proposed structures.
Because obstructions may be encountered in the refuse that may prevent the DDCs or ACIP
piles from getting through the refuse, it may be necessary to predrill through the refuse. If an
obstruction is encountered at a shallow depth, it may be possible to remove the obstruction.
However, if it is not practical to remove the obstruction then the pile will need to be relocated.
The structural engineer will design and specify an allowance for relocation of DDCs or ACIP
piles. The potential for buried obstructions will also be evaluated as part of a load test and
indicator program.
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6.0 FINAL COVER
6.1 Final Cover Design
Current California Code of Regulations Title 27 regulations require a "prescriptive" cover design,
one that is established by regulation and intended for use in the closure of all landfills. The
prescriptive cover, as outlined in Title 27, §21090(a)(1-3), shall contain:
A foundation layer of not less than 2 feet of appropriate materials. However, Title 27
Section 21090 allows for a lesser thickness, if the ultimate land use will not affect the
structural integrity of the final soil cover. The foundation layer materials may be soil,
contaminated soil, incinerator ash, or other waste materials, provided that such
materials have appropriate engineering properties to be used for a foundation layer.
Low permeability layer not less than 1 foot thick and of hydraulic conductivity not more
than 1E-6 centimeters per second (cm/sec).
Erosion resistant layer not less than 1 foot thick capable of sustaining vegetation and
resistant to wind, raindrop impact, or runoff or mechanically resistant.
Langan prepared a Draft Landfill Cover Investigation report, dated 13 February 2015 (Langan,
2015c). This report describes background information and the results of several phases of
investigation to evaluate the existing landfill cover for use as the final cover. A full copy of this
draft report is included in Appendix J. The existing data indicates that Parcels 1/1NW, 2 and 3/6
currently have a suitable soil cover which includes the three prescribed layers (foundation, low
permeability and erosion) (Langan, 2014c). Based on the results of the borings and test pits
performed in Parcel 4 the existing clay cover consists predominately of clay with a permeability
of 1x10-6 cm/sec or less. The clay cover varies in thickness from approximately 1 foot to 5.5
feet. Areas where the low permeability soil layer were not observed, i.e. around borings B-16,
B-23, B-37, B-38 and B-39, will be further evaluated as part of a final geotechnical investigation
and final cover design. Assuming the refuse acts as the foundation layer, as it contains a mix of
soil and refuse causing it to be firm and non-yielding, the upper 12 inches of the soil above the
refuse meets the criteria for the low permeability layer. Most of Parcel 4 has sufficient cover
over the low permeability layer. However, there is insufficient cover soil (i.e. the erosion
resistant layer) at some locations, which does not meet the current regulations. This condition
will be further evaluated as part of a final geotechnical investigation and final cover design.
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The subgrade elevation for the development is planned to be about 4 feet above the clay cover.
The earthwork activities will include cutting and filling with both on-site and off-site material to
achieve the subgrade. Over the subgrade, the final cover will include buildings, structural slabs,
paved streets, plazas and landscaped open areas. In areas where the cover will be disturbed,
the cover soil layer will include a concrete structural slab or aggregate base, which are both
suitable as an erosion resistant layer. The final thickness of the cover soil layer will be
evaluated based on final grades, but will be included consistently throughout the Project in
accordance with the final cover requirements.
Penetrations made in the low permeability layer will need to be repaired. In street areas where
a utility corridor extends beneath the low permeability layer it may be necessary to lower and
replace the low permeability layer as described in Sections 6.1.2 and 6.1.5.
The ground surface is expected to settle significantly during and after development; however,
adjacent to pile caps soil may ‚hang up‛ because of adhesion between the soil and the pile.
This may cause differential settlement over a short distance where cracks in the low
permeability layer could develop. Along the perimeter of the structurally supported areas of the
site, the structural slab will minimize water migration into the waste, while a perimeter hinge
slab of pavement will provide a barrier to minimize surface water migration into the waste.
Where a perimeter hinge slab or adjacent pavement will not exist along the perimeter, an
additional barrier or drainage layer will be installed to minimize potential for surface water
migration into the waste.
The following subsections present recommendations for earthwork.
6.1.1 General Earthwork Recommendations
The fill material for the foundation layer and low permeability layer should meet the
requirements of Title 27, §21090(a). General fill and backfill requirements should specify that
material be compacted in lifts of 8 inches or less using mechanical equipment. All materials to
be used as fill, including on-site soil, should be free of organic material (including wood), contain
no rocks, lumps, or rubble larger than 6 inches in greatest dimension.
6.1.2 Foundation Layer
If the low permeability layer is lowered, it is likely the bottom of the excavation would be within
the refuse layer. The foundation layer should form a stable layer on which to place the low
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permeability layer and should be non-yielding. The refuse may be used as the foundation layer
provided the bottom of the excavation is firm and non-yielding. If the refuse layer is used as
the foundation layer, Langan recommend that it be compacted with a smooth drum roller to
provide a firm and non-yielding surface without specified compaction criteria.
If the refuse is pumping and yielding under the weight of the compaction equipment, it may be
necessary to overexcavate the refuse and replace it with more stable granular material such as
baserock and geotextile reinforcement. Typically the foundation layer is at least 2 feet thick;
however, Title 27, §21090 allows for a lesser thickness, if the ultimate land use will not affect
the structural integrity of the final soil cover. In areas where the low permeability layer is
lowered, the overburden pressure will be reduced, which will reduce the expected total and
differentially settlements. This should help maintain the structural integrity of the soil cover.
Therefore, Langan recommend that the thickness of the foundation layer using granular
material necessary to provide a firm and non-yielding subgrade be evaluated in the field during
construction. Our experience indicates that two feet of granular fill above a geotextile or
geogrid will bridge above the refuse and provide a stable foundation layer. If possible, Langan
recommend the thickness be reduced from two feet to minimize the amount of refuse that
would need to be moved; the amount by which the granular fill can be reduced and still provide
a stable subgrade to compact the soil cover will be evaluated in the field on a case by case
basis.
If granular material is used to construct a foundation layer, the exposed refuse subgrade should
be rolled with a smooth drum roller. A geotextile such as Mirafi 500x or geogrid such as Tensar
1200 BX can then be placed on top of the refuse. The foundation layer should then be
constructed by placing granular material in lifts not exceeding 8 inches in final thickness and
compacted to at least 90% relative compaction7.
6.1.3 Low Permeability Layer
If the low permeability layer is removed in areas where utility corridors may need to be
lowered, it will need to be replaced. The on-site clay above the refuse meets the permeability
requirements where tested and would minimize infiltration of water into the refuse unit. If
imported soil is to be used for the new low permeability layer it will be cohesive and tested
7 Relative compaction refers to the in-place dry density of soil expressed as a percentage of the
maximum dry density of the same material, as determined by the ASTM D1557 laboratory
compaction procedure.
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prior to being approved for use. Samples will need to be submitted to a laboratory, remolded to
simulate field conditions and compacted in the laboratory to at least 90% relative compaction
and tested to check the minimum hydraulic conductivity can be achieved.
The new low permeability layer should be at least 12 inches thick (final compacted thickness),
moisture conditioned to about 2% to 6% over optimum moisture content and compacted to at
least 90% relative compaction. The low permeability should have an in-place permeability of 1E-
6 cm/sec or less and a plasticity index of at least 10 or greater. To avoid cracking and
desiccation of the low permeability, it should be kept moist and covered within 1 to 2 days after
being placed. Where the new low permeability layer ties into the existing low permeability
layer, it should horizontally overlap the existing low permeability layer by at least 2 feet.
Where a new low permeability layer is installed in-situ permeability tests should be performed
to check the permeability. One test per 2,500 cubic yards of low permeability layer placed or a
minimum of two tests per new section should be performed. If the tests fail then the layer
should need to be either reworked or replaced.
6.1.4 Fill above Low Permeability Layer
All areas to receive improvements should be stripped of vegetation and organic topsoil. The
surface exposed by excavation/stripping should be scarified to a depth of at least 6 inches,
moisture-conditioned to near optimum moisture content, and compacted to at least 90%
relative compaction. The exposed ground surface should be kept moist during subgrade
preparation.
All fill (excluding landscaping soil) above the low permeability layer, should be placed in
horizontal layers not exceeding 8 inches in loose thickness, moisture-conditioned to near the
optimum moisture content, and compacted to at least 90% relative compaction. The upper 6
inches of the soil subgrade in pavement areas should be compacted to at least 95% relative
compaction. Fill deeper than 5 feet should also be compacted to at least 95% relative
compaction. Fill above the low permeability layer should have a low expansion potential
(defined by a liquid limit of less than 40 and a plasticity index lower than 12). During
construction the on-site and proposed import material should be checked for suitability for use
as fill.
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6.1.5 Utility Trenches
Backfill for utility trenches should comply with the general requirements for fill. The pipe should
be embedded in granular fill and compacted to 95% relative compaction. The granular fill should
extend at least 6 inches above the pipe. To avoid damaging pipes, a light vibratory plate should
be used to compact the granular fill around the pipe. An impermeable plug consisting of clay or
lean concrete will be placed periodically along utility trenches to limit LFG migration along the
trench.
Where the utility trench excavation penetrates into the low permeability layer, the low
permeability layer will have to be replaced. The bottom and sides of the trench should be lined
with a geomembrane, such as 40 mil High Density Polyethylene (HDPE), to the bottom of the
existing low permeability layer (in the trench). The membrane should be keyed into the low
permeability layer and protected (via a protective fabric) within the trench prior to backfill. The
low permeability layer that was excavated within the trench should be replaced at the same
elevation as before with at least a 12 inch thick layer of clay and be compacted to the
recommendations presented herein.
6.2 Existing Topography
The existing topography of the Site was provided by the City of Santa Clara in an AutoCAD file
of an aerial photogrammetric survey performed on November 15, 2013. All elevations noted
herein are in the NAVD 88. The existing topography is shown on the preliminary design
drawings in Appendix D.
Parcel 1/1NW – The existing elevations around the perimeter of Parcel 1/1NW vary
between elevation (el.) 5 and el. 8. The elevation high points are within the central
portion of the parcel at about el. 60 and at the northwest corner at about el. 70. The
grades fall from the high points to the edge of the refuse mound to about el. 40 to the
east and northeast and to about el. 55 to the west and south. From the top of edge of
the Landfill the side slopes down to the perimeter elevations vary from 3H:1V to 5H:1V.
Based on City records and previous investigations performed to date, it is anticipated
that the top of the refuse layer varies between el. 47 and el. 37. The surface grades
vary between 5 feet and 15 feet higher than the refuse.
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There is an existing driveway access to Lafayette Street in the southwest corner of the
Parcel at about el. 8. The paved driveway slopes up into the Parcel at about an 8%
grade to provide access to the existing BMX facility and for golf course maintenance.
There is also a City drainage conveyance ditch along the entire eastern edge of the
Parcel at el. 0 and a levee for the Guadalupe River with the top of berm at el. 25.
Parcel 2 – The existing elevations around the perimeter of Parcel 2 vary between el. 5
and el. 8. The elevation high point is within the north central portion of the Parcel at
about el. 52. The grades fall from the high point to the edge of the refuse mound to
about el. 35 to the east, el. 25 to the south and el. 20 to the west. From the top of edge
of the Landfill the side slopes down to the perimeter elevations vary from 2H:1V to
3H:1V. Based on City records and previous investigations performed to date, it is
anticipated that the top of the refuse layer varies between el. 19 and el. 40. The surface
grades vary between 7 feet and 10 feet higher than the refuse.
There is an existing golf cart bridge over Lafayette Street from Parcel 4 that connects to
Parcel 2 at about el. 25. The bridge span reaches high point of about el. 39. There is
also a City drainage conveyance ditch along the entire eastern edge of the Parcel at el. 0
and a levee for the Guadalupe River with the top of berm at el. 25.
Parcel 3/6 – The existing elevations around the perimeter of Parcel 3/6 vary between el.
9 and el. 11. The elevation high point is within the central portion of the parcel at about
el. 82. The grades fall from the high point to the edge of the refuse mound to between
el. 53 to el. 56 around the majority of the edge and el. 68 in the southwest corner.
From the top of edge of the Landfill the side slopes down to the perimeter elevations
are at about 3H:1V. Based on City records and previous investigations performed to
date, it is anticipated that the top of the refuse layer varies between el. 31 and el. 54.
The surface grades vary between 10 feet and 35 feet higher than the refuse.
There is an existing paved golf cart access path in the southeast corner from Parcel 4
that slopes up to Parcel 3/6 from el. 12 to el. 54 at about a 10% slope. There is also an
access location in the northeast corner of the Parcel from the adjacent property to the
north from el. 10 to el. 30. The Union Pacific railroad tracks are located along the entire
eastern edge of Parcel 3/6 at about el. 9.
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Parcel 4 – The existing elevations around the perimeter of Parcel 4 vary between el. 10
and el. 20. The elevation high points are located throughout the Parcel up to about el.
34. The grades around the edge of the refuse mound are el. 20. There is an area within
the Parcel where no refuse exists and existing grades drop to as low as el. 7 (within a
portion of the existing driving range and lined pond). Based on City records and
previous investigations performed to date, it is anticipated that the top of the refuse
layer varies between el. 18 and el. 27. The surface grades vary between 3 feet and 7
feet higher than the refuse.
The elevation of Great America Parkway along the approximate 340 foot frontage is
between el. 15 and el. 22. Stars and Stripes drive along the majority of the southern
boundary of the Parcel is between el. 13 and el. 19. The Union Pacific railroad tracks are
located along the entire eastern edge of Parcel 4 at about el. 10 to el. 13.
6.3 Preliminary Grading
The goals for the proposed grading include:
Minimizing disturbance of existing refuse;
Phasing of earthwork to efficiently replace, relocate, operate and maintain the landfill
collection systems;
Satisfying and maintaining Americans with Disabilities Act (ADA) slope and access
guidelines recommendations for buildings, site and access to public areas;
Strategically designing site to accommodate future settlement of Landfill; and
Site aesthetics.
The preliminary site design maintains the first floor elevation (for the Parcel 4 structural slab and
other buildings and parking garage structures) a minimum of 10 feet above the anticipated
refuse elevations. Mass earthwork will include grading each parcel to a subgrade level about 5
feet above the top of refuse. This will allow for the protection of the existing low permeability
layer during earthwork, provide a working pad for the installation of the LFG collection system
and deep foundations, maintenance of the leachate recovery system risers, and provide vertical
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clearance above the refuse to minimize refuse disturbance during earthwork, pile cap, utility
corridor, and building slab construction.
The final design for the on-grade streets, plazas and open space/landscape areas will be
designed with a combination of hinged slabs, adjustable footings and other ‚situation specific‛
elements such as lightweight fill. Because of the heterogeneity of the refuse, it is difficult to
accurately predict the amount and location of settlement over a given period of time. As such,
a critical aspect of the site design will be to determine where the settlement will manifest. The
final site and grading plans will be designed for the ultimate grade after site settlement.
Building entrances, plazas, and access pathways will be designed to maintain compliance with
the requirements of the California Building Code, California Disabled Accessibility Guidebook
(CALDAG) and ADA Standards. Within the transition areas (from structural support to at-grade
support), the hinged slabs, adjustable footings, and other measures to address the settlement
will be aesthetically designed. The settlement vaults for the storm drain, sanitary sewer and
water utilities are conceptually shown on the preliminary design drawings. There final locations
will be based on a final design. A robust periodic monitoring and maintenance program will be
implemented to maintain compliance and site aesthetics within the transitions and incorporated
into the overall Project Operations, Monitoring and Maintenance (OM&M) plan.
6.4 Preliminary Stormwater Management
The development is subject to federal, state, county and local municipality regulations. The
regulations provide requirements for stormwater system design, stormwater quality and base
flood elevation. The amended Clean Water Act of 1987 required stormwater discharges to be
in compliance with a National Pollution Discharge Elimination System (NPDES) Permit. In
California this permit is issued through the Regional Water Quality Control Board for the San
Francisco Bay Region RWQCB. The San Francisco Bay Board adopted Municipal Regional
Stormwater NPDES Permit Order R2-2009-0074 NPDES Permit No. CAS612008 (Adopted 10-
14-2009 and amended by Order No. R2-2011-0083 on 11-28-2011), aka the Bay Area Municipal
Regional Stormwater Permit (MRP).
In Santa Clara County, the cities of Campbell, Cupertino, Los Altos, Milpitas, Monte Sereno,
Mountain View, Palo Alto, San Jose, Santa Clara, Saratoga, and Sunnyvale, the towns of Los
Altos Hills and Los Gatos, the Santa Clara Valley Water District, and the County of Santa Clara
(Co-permittees) have joined together to form the Santa Clara Valley Urban Runoff Pollution
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Prevention Program (SCVURPPP). These entities share a common permit to discharge
stormwater to South San Francisco Bay with a mission to assist in the protection of beneficial
uses of receiving waters by preventing pollutants generated from activities in urban service
areas from entering runoff to the maximum extent practicable.
The SCVURPPP Permit Provision C.3 contains requirements for controlling the potential
impacts of land development on stormwater quality and flow. In 2006, the C.3 requirements
became effective for projects that create or replace 10,000 square feet or more of impervious
surface. To meet the C.3 requirements, projects must include appropriate site design
measures, pollutant source controls and treatment control measures. Projects that produce
increases in runoff peak flows, volumes and durations that may cause erosion in downstream
receiving water must also include hydromodification control measures. The SRVURPPP
prepared a C.3 Stormwater Handbook dated April 2012 to assist projects in designing
appropriate post-construction stormwater controls to meet local jurisdictional requirements and
the requirements of the MRP. The Project will include stormwater treatment measures as
preliminarily shown on the design drawings in Appendix D. Hydromodification control
measures are not required as the Site is outside of the mapped hydromodification zones.
The Santa Clara Valley Water District (SCVWD) has jurisdiction over the San Tomas Aquino
Creek and Guadalupe River, their existing levees and the conveyance of stormwater to these
waterways. Since the existing levees adjacent to the Site are certified by the Federal
Emergency Management Agency (FEMA), impacts to or proposed modifications of the levee
will require SCVWD review and approval, and may require a submission to FEMA for levee re-
certification. Furthermore, the SCVWD requires that no increase to the 100 yr. peak flood
elevation within these waterways is permissible without levee recertification.
The Project will disturb one or more acres of soil and is required to obtain coverage under the
General Permit for Discharges of Stormwater Associated with Construction Activity
(Construction General Permit, 2009-0009-DWQ). Construction activity subject to this permit
includes clearing, grading and disturbances to the ground (e.g., stockpiling or excavation). The
Construction General Permit requires the development and implementation of a Stormwater
Pollution Prevention Plan (SWPPP). The SWPPP will contain a site map(s) which shows the
construction site perimeter, existing and proposed buildings, lots, roadways, stormwater
collection and discharge points, general topography (both before and after construction) and
drainage patterns across the project. The SWPPP will list Best Management Practices (BMPs)
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that will be used to protect stormwater runoff and the placement of those BMPs. In addition,
the SWPPP will contain a visual monitoring program; a chemical monitoring program for ‚non-
visible‛ pollutants to be implemented if there is a failure of BMPs; and a sediment monitoring
plan. Erosion control measures will be installed prior to site activities that disturb soil and
maintained throughout the Project. Storm water controls will be based on practices described
in the "Blueprint for a Clean Bay, Best Management Practices for the Construction Industry,‛
provided as part of the Santa Clara Valley Nonpoint Source Pollution Control Program. Storm
water controls comprise the on-site sediment and erosion controls to limit soil and sediment
discharges to off-site drainage channels and storm drains (discharging to the San Tomas
Aquinos Creek and Guadalupe River). These controls may include the placement of straw bale
barriers across runoff channels on the Site, straw bale barriers around storm drains and
catchment basins (once constructed), and covering soil stockpiles with secured tarps or plastic
sheeting. The preliminary erosion and sediment control plans are provided in Appendix D.
The stormwater runoff from Parcel 4 and Parcel 5 will discharge to the San Tomas Aquino
Creek via new stormwater outfalls. The invert of the outfalls will be set above the bottom of
the Creek, at a final elevation to be coordinated with the SCVWD to place the invert above
sediment levels within the Creek. The existing Golf Course Pump Station will remain, or
depending on the Parcel 5 development be reconfigured or abandoned.
The stormwater runoff from Parcels 1, 2 and 3 will discharge to the Eastside Retention Basin
and be pumped to the Guadalupe River via the existing Eastside Pump Station. From Parcels 1
and 2 there will be several new outfalls from the Site to the existing Eastside Drainage
Channel. From Parcel 3, the existing drainage infrastructure located north of the Parcel and
west of the railroad will be utilized. The preliminary evaluation identified that a portion of the
existing off-site system may need to be upsized to accommodate Parcel 3. However, these
upgrades may not be required if enough of the stormwater on Parcel 3 is collected and re-used.
The goal for the final stormwater management design will be to treat the stormwater runoff to
protect water quality through the incorporation of on-site sustainable low-impact development
(LID) stormwater measures. Infiltration is not a feasible strategy for the management of the
stormwater and is not recommended. As such, all stormwater treatment measure over the
landfill will be lined with an impermeable liner and include a perforated underdrain connected to
the storm drainage system. During final design the extent and type of the stormwater
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management measures (such as stormwater treatment, harvesting and re-use) to be
implemented within the Project will be determined.
7.0 IRRIGATION AND LANDSCAPING
Proposed irrigation and landscaping at the development will meet the requirements of CCR
Title 27, §21090(a)(3)(A).
Only shallow rooted vegetation will be utilized in landscaped areas that overlie landfill refuse.
The landscape areas adjacent to the proposed buildings, the rooting depths will be designed to
extend to within 1 foot above the low permeability layer. This will be accomplished through
identifying the depth of the refuse, plant selection and the use of impermeable liners and
perforated underdrains connected to the storm drainage system. Where this is not feasible,
trees must be contained within lined planter boxes.
The use of water-intensive landscaping around the perimeter of the buildings will be avoided to
reduce the amount of water introduced to the landfill. In addition, irrigation of landscaping
around the building will be limited to drip or bubbler-type systems. The Project will be served
by the City’s reclaimed water main and a new reclaimed water network will be incorporated
into the design of the development so that the irrigation needs can be met by this system.
8.0 UTILITIES
The installation of new utilities will be required for the proposed development. The preliminary
design drawings are provided in Appendix D. Existing on-site utilities are limited and will be
replaced and expanded. Utilities installed above the refuse will be designed and maintained in
general accordance with CCR Title 27 §21190. Utilities will be constructed to mitigate the
effects of differential settlement and the utility connections will be designed with flexible
connections and settlement vaults. Utilities to be installed include:
Storm Drainage – The existing storm drain system includes existing river outfalls and a
City owned and operated drainage system inclusive of pump stations, retention basins,
open drainage channels, underground conveyance piping and appurtenant drainage
structures. The storm drainage system for the Project will include an underground
gravity network of pipes, catch basin, manholes, water quality LID treatment measures
and other appurtenances. The building drainage will be via internal systems piped
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directly to the storm drains. The final system will be designed to convey the 10 yr.
event peak flows within the underground piped conveyance system and safely convey
the 100 yr. event peak flows from the Site via a combination of the piped system and
surface conveyance.
Sanitary Sewer – The existing sanitary sewers are located in Lafayette Street and
between Parcels 3/6 and 4. The new sanitary sewers for the Project will connect to the
existing infrastructure at new manholes. The on-site sewer for each parcel will be
designed as a redundant system in accordance with the City of Santa Clara
requirements.
Water – The existing City owned and operated water main system is located in
Lafayette Street, Great America Parkway and Stars and Stripes Drive. The new water
service will be connected to the existing water main distribution system and will be
constructed of steel and HDPE Pipe in accordance with the City of Santa Clara and its
Water District’s requirements.
Gas – The existing Pacific Gas and Electric (PG&E) gas system is located Lafayette
Street, Great America Parkway and Stars and Stripes Drive. The new gas service for
the Project will be extended from the existing service in Lafayette Street.
Electrical and Telecommunication Services – Electrical and telecommunications services
lines are to be installed in a joint trench in and around each parcel. The systems will
connect to the existing system that will be extended to the Site from nearby service
locations.
Most of the on-site utility systems will be located above the refuse unit, and it is anticipated
that a small portion of the utility corridors will disrupt the refuse unit at multiple locations. At
these locations, trenches will be constructed as described in Section 6.1.5.
Where utility trenches enter the building pads and at periodic intervals, an impermeable plug
consisting of bentonite clay will be installed. Furthermore, where trenches cross planter areas
and pass below asphalt or concrete pavements, a similar plug will be placed at the edge of the
pavement. The plugs will extend from the bottom of the trench to the subgrade elevation. The
purpose of these recommendations is to reduce the potential for water to become trapped in
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trenches beneath the building or pavements and limit the migration of methane within utility
trenches.
Due to the potential for methane accumulation in the subsurface some of the underground
utility manholes and vaults will be labeled ‚Confined Space – Hazardous Area, Contact Building
Maintenance Supervisor Prior to Entry, Entry by Authorized Personnel Only‛ to promote the
safety of maintenance personnel. Following completion of the proposed development, periodic
methane gas monitoring will be conducted inside underground utilities in general accordance
with §20933 of Article 6, of Subchapter 4 of CCR Title 27.
A settlement study for gravity flowing utilities will be performed during final design to address
the anticipated settlement. Preliminary design options include steeper pipe slopes, additional
manholes, interim settlement vaults, and inclusion of the monitoring of gravity flowing utilities
in the Project’s OM&M plan.
9.0 ENHANCED LANDFILL GAS COLLECTION AND REMEDIATION SYSTEM
9.1 Existing LFG Collection System
The layout of the existing LFG collection wells and headers and the subsurface details on each
of the Site parcels are included in Appendix A. A total of 88 LFG extraction wells are identified
on the LFG well layout drawings (Real Environmental Products, 2011). As reported in the most
recent LFG collection system monitoring report (Golder, 2014a), the LFG collection system
currently consists of 75 functional LFG extraction wells connected to respective lines,
subheaders, and the main header. The remaining 13 LFG extraction wells (wells E3, C4, A4, H1,
J1, K3, K5, L1, L3, L4, M3, M4, and N3) have been decommissioned because of low methane
levels and high oxygen levels detection (likely due to the damaged well casing below the
ground surface) or due to the presence of excessive water in the well casing. Reportedly, the
decommissioned wells were abandoned by disconnecting them from the gas header system,
the well head vault was removed, the well casing was cut off to about 3 feet below grade, and
the void was filled with soil and bentonite, following procedures in the Post-Closure
Maintenance Plan for the Site (Golder, 2015).
The main header that extends through each parcel is connected to the inlet of a 25 Horsepower
(HP) centrifugal blower/air compressor housed in a fenced area on Parcel 1. Main isolation
valves for repair, shut-down, and vacuum adjustment are installed at each junction of the main
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header and respective subheaders/lines. In addition to the LFG collection wells, multiple
condensate traps are present in each parcel at low points to gravity drain the collected
condensate back into the refuse away from the LFG collection wells through recirculating P-
traps (see Appendix A).
9.2 Proposed LFG Collection System
Replacement and enhancement of the existing LFG collection system is proposed as part of
development at the Site (Langan, 2015a). The proposed LFG collection system is designed to
be consistent with the following state and local regulations:
CCR Title 27, Chapter 3, Subchapter 5, Article 2, §21090 – §21200 – Closure and post-
closure maintenance standards for disposal sites and landfills.
CCR Title 27, Chapter 3, Subchapter 5, Article 2, §21190 – Post-closure land use.
CCR Title 27, Chapter 3, Subchapter 4, Article 6, §20917 – §20937 – Gas monitoring and
control at active and closed disposal sites.
BAAQMD Regulation Rule 8-34.
The proposed plans for LFG collection include installation of vertical LFG extraction wells,
horizontal LFG extraction wells (contingent wells), condensate knock-out pots, and below-grade
horizontal conveyance piping, and manifold connecting the LFG collection wells and condensate
knock-out pots to the process equipment. Considering that detailed Site development plans and
foundation concepts are not yet developed, the proposed concept plans for the LFG collection
system would be modified as the development planning for the parcels progresses. The
concept plans for the proposed LFG collection system are primarily based on concept sections
provided for Parcel 4 (see Appendix K). The well layout and cross sectional details of the
proposed LFG collection system are provided in Appendix K.
These proposed LFG collection and remediation system concept plans presented herein are
based on evaluation of the existing LFG collection well layout, reported radius of influence
(ROI), monitoring reports, and our preliminary pneumatic MDFITTM modeling software results
(Appendix K). MDFITTM is a two-dimensional (2D) analytical model which simulates the air flow
rate in an unsaturated zone and determines the correlation between applied vacuum and air
flow at test well and resultant vacuum, air flow rate, and pore volume exchanges at varying
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distances from the test well. In addition, the conceptual plans were also based on
considerations including but not limited to the estimated LFG and condensate generation rates,
potential refuse settlement, potential seismic activity hazards, potential fire hazard, corrosive
impacts of LFG and design life (durability) of the future LFG collection system. A
comprehensive evaluation of these factors will be performed during the Design Document
Phase.
Although our preliminary modeling results agree with the current system vacuum, air flow
rates, and ROI, a pilot test will be performed during Design Document Phase for the
development to verify the design ROI, air flow rates, and vacuum for the proposed LFG
collection wells at each parcel, considering the critical nature of the system design parameters.
Further, it is anticipated that the number and spacing of pile foundations and columns
particularly beneath the Parcel 4 platform structure could alter the flow of LFG to the vertical
LFG collection wells and may affect their effective ROI. To evaluate this issue, pilot test results
and pile foundation plans would be incorporated into a three-dimensional (3D) pneumatic model
(i.e., AIR-3DTM) to predict the influence of these features on the proposed layout of the vertical
LFG collection wells. Therefore, the results of the proposed pilot test, 3D pneumatic modeling,
the final building locations, and corresponding pile foundation and displacement column
locations for each phase of development will be the basis for determining the final locations of
the proposed LFG collection wells.
The major components of the proposed LFG collection system are described below.
9.2.1 Proposed LFG Collection Wells
The proposed LFG collection system will consist of a total of 86 vertical collection wells spread
over the Site. The proposed LFG collection wells on each parcel are estimated to have an
approximately 200 feet ROI, to be verified based on the results of a proposed field pilot test
and 3D pneumatic modeling. The proposed LFG collection wells would be placed approximately
300 feet on center to provide adequate ROI overlap and would be placed outside of the building
footprints, preferably in roadways, landscaped areas, exterior parking lots, or sidewalks. No LFG
collection wells and condensate knock-out pots will be installed within the proposed building
footprints. Overall, four types of LFG collection wells (Type 1 through Type 4) would be
installed:
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Vertical LFG Collection Well Type 1 – Vertical LFG wells located outside the structural
platform would be constructed of Schedule (SCH) 80 polyvinyl chloride (PVC) (or
equivalent) casing and screen or perforated pipe materials. These wells would be
completed at the finished grade with a precast vault with lockable watertight lid to
provide direct wellhead access for operational adjustments, monitoring, and
maintenance. These wells would be telescoping type with slip joints connecting the
well casings with the screens to allow flexibility and expansion of the well screen
vertically downward. The flexibility of vertical expansion of well screens will prevent
potential damage to the well due to refuse settlement. Wellhead connections to the
system below-grade horizontal conveyance piping will be made using a flexible hose
(i.e., Kanaflex™ or LANDTEC™ or equivalent) with adequate slack to prevent potential
damage to the wellhead or conveyance piping due to refuse settlement.
Vertical LFG Collection Well Type 2 – The vertical LFG wells located within the structural
platform in the roadways, landscaped areas, or exterior parking lots would be anchored
(via dowels) and supported by the structural platform slab to prevent potential
settlement of the well due to refuse settlement. These wells would be telescoping type
with slip joints connecting the well casings with the screens to allow flexibility and
expansion of the well screen vertically downward. The flexibility of vertical expansion of
well screens will prevent potential damage to the well due to refuse settlement. These
wells would be constructed of SCH 80 PVC material (or equivalent). These wells would
be completed at the finished grade with a precast vault with lockable watertight lid to
provide direct wellhead access for operational adjustments, monitoring and
maintenance. Wellhead connections to the system below grade horizontal conveyance
piping will be made using a flexible hose (i.e., Kanaflex™ or LANDTEC™ or equivalent)
with adequate slack to prevent potential damage to the wellhead due to refuse
settlement.
Vertical LFG Collection Well Type 3 – Similar to Well Type 1 and Type 2, the vertical LFG
wells located within the structural platform on the sidewalk would be constructed of
SCH 80 PVC material (or equivalent). These wells would be completed below the
sidewalk finished grade and underneath the structural platform slab to eliminate the
potential for LFG leaks into the buildings interstitial space from the well. A precast vault
with lockable watertight lid for direct wellhead access to these wells would be
constructed adjacent to the sidewalk and outside the extent of the building interstitial
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space. These wells would also be telescoping type with slip joints connecting the well
casings with the screens to allow flexibility and expansion of the well screen vertically
downward. The well riser connection to the vault will be made using below-grade
horizontal conveyance piping anchored to the structural slab with pipe hangers. Manifold
connections will be made using a flexible hose (i.e., Kanaflex™ or LANDTEC™ or
equivalent) with adequate slack to prevent potential damage to the wellhead or
conveyance piping due to the refuse settlement. The preliminary configuration and
construction details of the vertical LFG extraction well Type 3 as presented herein are
conceptual only and will be finalized during the Design Document Phase.
Horizontal LFG Collection Well Type 4 (Contingent) – The need for these contingent
horizontal LFG collection wells will be determined during the Design Document Phase
based on the 3D pneumatic modeling results, final building layout plans, and the final
configuration and layout of the proposed piles. If horizontal LFG collection wells located
inside and outside the structural platform are required, they would also be constructed
of SCH 80 PVC (or HDPE) casing and screen or perforated pipe material. The horizontal
wells would be installed in the upper portion of the waste unit and would be connected
to the vertical well system manifold. Overall, three types of contingent horizontal LFG
collection wells may be installed:
Contingent Horizontal LFG Well Type 1 - Wells in the vicinity of areas with proposed
piles. These wells will be installed if the 3D pneumatic modeling results indicate
influence of cement column piles on the LFG flow into the vertical LFG collection
wells, or on their respective ROI and vacuum propagation.
Contingent Horizontal LFG Well Type 2 - Wells underneath the pads of buildings or
underneath the parking garages with larger footprint (e.g., proposed parking garage
in the western portion of Parcel 4) where vertical LFG wells cannot be installed.
These wells will be installed if the 3D pneumatic modeling results indicate that the
LFG in such areas with larger building footprints cannot be adequately mitigated by
the exterior vertical LFG collection wells.
Contingent Horizontal LFG Well Type 3 - Wells in exterior areas (i.e., roadways,
parking lots, landscaped areas, etc.) outside the structural platform (e.g., western
portion of Parcel 4) with no structural slabs/buildings, building LFG protection
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systems or VBM). These wells may be installed to increase the efficiency of LFG
capture at exterior locations and to eliminate the potential for landfill fire and/or
odors.
The proposed number, location, and type of the above described LFG collection wells are
preliminary and are subject to change during the Design Document phase based on the results
of the proposed pilot testing, subsequent 3D pneumatic modeling, the final building locations,
and corresponding pile foundation and displacement column locations. The proposed well
locations and well types have been designed to address site-specific complexities and
constraints (i.e., non-refuse areas and proposed roadways, sidewalks, and buildings). The
proposed vertical LFG collection wells have been preliminarily positioned to avoid interference
with the planned site development constraints (i.e., wells are to be located only within the
proposed roadways and/or outside of the proposed building footprints) and to minimize the
volume of air extracted from non-refuse areas while still providing sufficient coverage within
the refuse areas. The proposed LFG collection system design also includes contingent
elements such as contingent horizontal LFG collection well Types 1, 2 and 3, as well as a
relatively denser network of perimeter vertical LFG collection wells, need of which, will be
confirmed based on the results of the proposed pilot testing and 3D pneumatic modeling
activities.
9.2.2 Potential Off-Site LFG Migration Monitoring and Mitigation
All existing perimeter LFG probes (approximately 44) will be preserved to the extent possible
and will be used to monitor the potential off-site migration of LFG. The integrity and
functionality of these existing perimeter LFG probes will be evaluated as required during the
Design Document Phase. Installation of approximately 30 additional perimeter LFG probes is
proposed (Figure 9, Appendix K). The proposed additional LFG probes will be located at the
perimeter of all parcels outside the refuse limit and within the site property boundary. The
proposed additional LFG probes will be spaced approximately 1,000 feet from each other and
will be constructed of multi-nested well screens (two to three well screens in one borehole)
depending on the nearby refuse thickness. The proposed location and number of the additional
perimeter LFG probes are preliminary and will be evaluated and finalized during the Design
Document Phase, consistent with CCR Title 27, Chapter 3, Subchapter 4, Article 6, §20921,
20923, 20925, 20931, 20932, 20934, 20937, and 20939 requirements. While the location of
these proposed additional LFG probes will be confined geographically by the existing site
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property boundary, the select point locations will take into consideration the location of nearby
LFG collection wells (i.e., the perimeter LFG probes will be located at or outside the LFG
collection ROI to the extent possible).
In addition, a dense network of LFG collection wells along the landfill perimeter is proposed to
mitigate the potential off-site LFG migration. The effective ROI and spacing of the perimeter
LFG collection wells will be determined based on the proposed pilot testing and 3D pneumatic
modeling results. The proposed conceptual LFG collection well network, as depicted on Figures
9 through 9E (Appendix K), currently does not factor in the denser network of LFG collection
wells along the landfill perimeter. Therefore, the proposed number of new LFG collection wells
(86) is likely subject to increase during the Design Document phase based on the proposed
pilot testing and 3D pneumatic modeling results.
In case elevated methane concentrations are measured at the perimeter wells during Site
development activities or during the future use of the developed property, response steps will
be taken to mitigate the off-site LFG migration to ensure compliance with the regulatory
requirements. The response plan may include optimizing and increasing the flow rate/vacuum
at the perimeter LFG collection wells to more effectively capture LFG before it reaches the
landfill perimeter.
9.2.3 Proposed LFG Collection System Manifold
The LFG collection system below-grade horizontal conveyance piping and manifold will consist
of branch lines (laterals), subheader lines, and main header conveyance pipelines. Each LFG
collection well will first be connected to a branch line, then to a subheader line, and finally to a
main header line. The main header from each parcel will be independently connected to the
existing LFG process equipment. Main header lines will be located in the roadways or
landscaped areas with or without the structural slab support. All branch lines, with the
exception of the LFG collection wells located on the edge of the side walk (LFG extraction well
Type 3), will be sloped towards their respective subheader lines to prevent condensate
accumulation within the piping network. Branch lines associated with LFG collection wells
located on the edge of the side walk (LFG extraction well Type 3) will be sloped towards their
respective collection wells. Similarly, each subheader line will be sloped towards the main
header line. Condensate knockout pots will be located at low points along the branch lines,
subheader lines, and main header lines approximately every 300 to 400 feet of pipe run within
structural platform areas and approximately 1,000 feet of pipe run outside the structural
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platform areas. Condensate knockout pots will also be installed where the proposed piping
makes a right angle turn or any other local low spot within the piping network.
All piping within the structural platform will be placed within the proposed 2 foot crushed stone
fill material of the proposed building methane vapor protection system. To overcome depth
restrictions and still facilitate drainage of condensate via gravity (i.e., sloped piping) in the
knockout pots within the structural platform, all piping will have a slope of approximately 0.5%,
condensate knockout pots will be installed approximately every 300 to 400 feet of pipe run, and
all piping diameters will be approximately 20 to 30%larger than normally required.
All piping in the area outside the structural platform will have a minimum of 1 to 2% slope to
facilitate collection of condensate via gravity into the knockout pots, spaced approximately
1,000 feet of pipe run. All knockout pots will be equipped with a submersible pump and an
associated water level sensor to initiate the transfer of the condensate. Condensate will be
transferred to a holding tank, which is to be installed within the existing process equipment
enclosure on Parcel 1, and further discharged into a sanitary sewer system, pending sewer
discharge permit approval. The layout of condensate knockout pots, collection subheader lines
and the collected condensate holding tank are provided in Appendix K. The proposed number
and location of the condensate knockout pots are preliminary and are subject to change during
the Design Document phase.
9.2.4 Process Equipment
The existing process equipment will continue to be used for future collection of LFG with some
modifications/additions for collection, potential treatment, and disposal of condensate. It is also
proposed that the existing flare be serviced for future use or the process equipment be
upgraded with a new flare. Currently, the flare is used as a standby unit only when the existing
microturbines that are used to generate electricity from captured methane gas are down for
maintenance. The existing process equipment is currently housed outside the old equipment
enclosure (i.e., shed) in a fenced area in Parcel 1. An emergency electrical power backup
generator will be provided to run the entire LFG collection system process equipment (i.e.,
blowers, compressors, motors, flare, and microturbines, etc.) in case of electrical power
interruption due to unforeseen conditions.
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9.2.5 Settlement Considerations
To minimize the effect of differential landfill refuse settlement on the proposed LFG collection
wells and manifold system, high burial pressure and vacuum rated flexible hoses (i.e.,
Kanaflex™ or LANDTEC™ or equivalent) will be used at right angle connection manifold joints
(i.e., branch line to subheader line connections, and subheader line to main header line
connections). The flex hose will be made of flexible material, reinforced with non-corrosive
stainless steel wire helix (or equivalent), capable of withstanding relatively high temperatures.
The flexible hose will have a 3 inch soft scuff at each end of the hose and will be connected to
the branch lines, subheader lines, and main header lines with power lock clamps that will be
tighten to the manufacturer’s recommended torque. In addition, for a more secure connection,
a collar will be welded or glued to the pipe to form a ridge. The collar will be positioned prior to
the installation of the power lock clamps to provide additional support and prevent the flexible
hose connection from slipping. The flexible hose will remain flexible at least at 20% extension.
Other equivalent methods of flexible hose connections will be considered during the Design
Document phase.
The proposed LFG extraction wells will be constructed of a SCH 80 PVC material (or equivalent)
telescoping casing and slip coupling assembly to permit the increase in well casing length due
to potential landfill refuse settlement. Estimations of refuse settlement will be derived and
applied to determine the required increase in length of the telescoping casing. Based on landfill
gas field monitoring log reports previously prepared by Golder, the average temperature of the
landfill gas ranges from 66oF of 104oF and currently does not exceed 120oF. The maximum
operating temperature for SCH 80 PVC is 140oF, which is in far excess of the existing normal
LFG system operating conditions of 90oF to 120oF. It is proposed that the LFG collection wells
will be constructed of SCH 80 PVC (or equivalent); however, if during the proposed pilot testing
activities the LFG temperatures are observed to be in excesses of 140oF, the cause of the
elevated temperatures will be investigated, and the LFG extraction well design will consider the
use of HDPE (or equivalent) material with relatively higher temperature rating. To minimize the
effect of potential refuse settlement, HDPE, which is flexible and absorbs differential
settlement better than SCH 80 PVC, will be used for the majority of main header, subheader,
and branch line construction.
The potential settlement of refuse over time, following the construction of the structural
platform/ slabs, has the potential to create a void space beneath the slab. Figure 17 (Appendix
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K) presents a conceptual schematic of the potential void space under structural platform/slabs
that may be developed due to the potential settlement of refuse over time. The influence of the
potential void space on the performance of the LFG wells is anticipated to be minimal because
the vertical and contingent horizontal LFG extraction wells are designed to be screened
approximately 5 feet and 2.5 feet below the top of refuse, respectively, to hinder the effect of
potential short-circuiting from the void space. The LFG extraction telescoping vertical well
casings are designed to expand vertically downward as the refuse settles, thereby maintaining
the 5 feet interval between the well screen and the top of refuse. The confining clay cap and fill
material above the refuse, the vertical telescoping LFG extraction wells, the contingent
horizontal LFG extraction wells, and all associated piping are also anticipated to settle with the
refuse, thereby maintaining the integrity and functionality of the methane mitigation system.
The development of void spaces under structural platform/slabs may pose a risk of ambient air
intrusion into the LFG extraction well screens. Therefore, the LFG extraction wells are designed
to operate in a balanced way using the wellhead controls and gate valves to prevent ambient air
intrusion from the potential void spaces into the LFG system. The influence of the potential
void space beneath the structural platform/slabs on the LFG system capture zones (ROI) and
performance will be further evaluated using 3D pneumatic modeling during the Design
Document phase.
9.2.6 Other LFG Collection System Design Considerations
In order to ensure protection of human health, public safety, and the environment, potential
seismic hazard, fire hazard, and corrosive impacts will be considered and evaluated during the
Design Document Phase:
Seismic Hazard Considerations – The Site is located within an area where strong to
violent ground shaking could occur, which can potentially cause damage to the
proposed LFG collection system due to potential liquefaction settlement and seismic
densification during an earthquake. A seismic hazard analysis will be conducted during
the Design Document Phase to evaluate seismic effects on the proposed LFG collection
system. Based on the results of the seismic study, the components of the LFG
collection system will be designed to accommodate the anticipated seismically induced
settlements. In addition, a post-construction seismic monitoring and inspection plan will
be developed and implemented as part of the routine OM&M of the system.
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Fire Hazard Considerations – Surface and sub-surface fires can occur during
construction activities at the landfill Site. The primary threat of landfill fires results from
careless on-site smoking, welding or other hot work, improper equipment maintenance,
and improper LFG control system operations. As part of the Design Document Phase, a
fire safety measures and emergency response plan would be developed for general
construction activities, as well as for the construction activities related to the LFG
collection system.
Corrosive Impact Considerations – Decomposition of waste in landfills generates
corrosive gasses (i.e. sulfur-based gas such as hydrogen sulfide) which can be
microbially converted to sulfuric acid (H2SO4), thus producing low pH environments..
Both LFG and fluids can cause corrosion of landfill infrastructure (LFG collection system)
and building infrastructure (slabs and piles). To minimize the impact of corrosion on LFG
collection system, critical units and parts would be fabricated from corrosion resistant
materials, including HDPE, PVC, corrosion-resistant stainless steel, and other materials
with corrosion resistant coatings.
9.3 Proposed LFG Collection System Remedial Benefits
The proposed LFG collection and remediation approach has been developed to improve the
effectiveness of the existing LFG collection system through enhanced subsurface gas flow
characteristics (due to increased borehole and LFG extraction well diameters), increased
capture zone (due to the proposed structural platform/slabs that will act as a low permeability
upper confining layer over the landfill refuse), and better moisture control of the refuse. The
proposed Site development and the LFG remediation efforts are anticipated to reduce the
amount of LFG and leachate generated from the landfill refuse, which in turn will improve the
Site groundwater quality. Key elements of the Site development and the proposed LFG
collection system that will result in remedial benefits include the proposed structural
platform/slabs, building horizontal LFG protection system and VBM, storm water management
system, collection and removal of condensate water, and increased capture zone (ROI) of the
LFG collection well network.
The addition of the proposed structural platforms/slabs and VBM, stormwater
management system, and removal of condensate water will reduce the moisture
content of the refuse over time. Decrease in the refuse moisture content will hinder the
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microbial activity and anaerobic degradation rates of the refuse. This will subsequently
reduce the amount of LFG and leachate generated from the landfill refuse which in turn
will improve the Site groundwater quality.
The increased number of the proposed LFG collection wells as compared to the existing
number of wells will result in an increased capture and removal rate of the LFG.
The addition of the proposed structural platform/slabs and VBM will also act as a low
permeability upper confining layer over the landfill refuse and is anticipated to further
increase the LFG system capture zones (ROI). The proposed pilot testing data and 3D
pneumatic modeling will be used to verify that the proposed increased number of LFG
collection wells and installation of the structural slab (i.e., upper confining layer) will
result in an improved LFG capture and removal rate of the new system.
The improved capture and removal rate of the LFG, including VOCs, resulting from the
operation of the new system will facilitate the mass transfer of VOCs from adsorbed
and dissolved phases to the vapor phase due to concentration gradients that in turn will
result in VOC source remediation.
Continued decreases in the LFG flow rates are expected in the future due to the ongoing
natural refuse degradation processes. The proposed LFG collection and remediation system’s
operation and the expected reduction in refuse moisture content due to the Site development
strategy (i.e., construction of structural platforms/slabs and VBM, stormwater management
system, and removal of condensate water, etc.) are anticipated to further reduce the
subsurface concentrations of LFG in the future.
9.4 Conceptual Field Implementation Plan
The LFG control and monitoring program will continue pursuant to CCR Title 27 §20921 through
§20939, and BAAQMD Regulation 8 Rule 34, but interim measures may be necessary to
facilitate continued effectiveness during construction and reinstallation. The field
implementation for the LFG collection system installation would be primarily dependent on
compliance with BAAQMD Regulations, health and safety issues, and coordination with the
other on-site work. These issues will be addressed as follows:
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Compliance with BAAQMD Regulations - The implementation of proposed LFG
collection system would require compliance with BAAQMD Regulation 8-34. To comply
with the BAAQMD regulations 8-34-117.4, 8-34-117.5, and 8-34-113.2, the LFG
collection system shut down of individual wells would be limited by isolating and
abandoning a group of select LFG collection wells (up to five wells at a time) and
associated lateral manifold in accordance with the BAAQMD. A petition for variance to
allow temporary shutdown and/or abandonment of more than five wells at a time may
be made to the regulatory agencies during the Design Document Phase to allow for a
more expedited Site redevelopment schedule while ensuring protection of public health
and safety and the environment. The remaining LFG collection system would remain
fully operational to continue to mitigate LFG. A temporary above-ground manifold would
be installed and connected to the existing wells and the vacuum source for isolation and
abandonment of existing wells.
Health and Safety Requirements:
Health and safety measures will be needed for construction activities related to
abandonment and replacement of the LFG collection system. Specific HASPs will
be developed as part of the design phase. Health and safety measures will include,
but would not be limited to: weather monitoring stations, air monitoring for
methane, hydrogen sulfide, carbon monoxide, and VOCs, setting action levels for
each monitoring parameter, and specifications for PPE. Procedures to be followed
in case of emergency would also be identified. Temporary industrial fans will also be
used to supply dilution air for active work zones and to limit an increase in methane
levels in ambient air within the construction work zones. Methane monitoring will be
performed to limit the ambient methane concentration to less than 5% of LEL. If
methane concentrations reach 5% of LEL, aggressive venting measures would be
implemented. If the ambient methane concentrations reach 20% of LEL, then the
work area would be evacuated, until the methane concentration decreases below
20% of LEL.
Surface monitoring of methane emissions will be performed routinely. To comply
with the BAAQMD regulation 8-34-303, at no point on the landfill surface will the
methane concentration exceed 500 ppmv, expressed as methane above
background, other than non-repeatable, momentary readings. In case an increase in
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the surface emissions of methane is noted, the temporarily shut down wells will be
immediately connected to the existing process equipment using above-ground semi-
permanent piping and subsequently reactivated for LFG collection.
The health and safety measures related to the construction activities of the LFG
collection system will include use of interim measures for subsurface methane
collection in areas where existing LFG collection system will be shut down or
abandoned. The interim measures will include installation of the proposed full scale
permanent LFG extraction wells in the active work zone to provide continuous
methane extraction in the subsurface, because the existing LFG extraction wells
within the zone would be abandoned during the construction work. As an interim
measure, the proposed LFG extraction well heads would be modified for a
temporary connection to above-ground hoses (further connected to the process
equipment) to make the wells functional.
Coordination with the On-site Construction Work – The installation, mechanical and
electrical connections, startup, and testing of the proposed LFG collection system will
be coordinated with the Site development activities.
The field implementation plan will be executed by the following steps:
Modification at the Existing Process Equipment – A proposed LFG collection system
header manifold to connect to proposed main headers from each parcel will be installed
at the process equipment prior to construction activities.
Excavation at Parcel 3/6 – During excavation, the existing wells on Parcel 3/6 will be first
isolated using a proposed above-ground semi-permanent manifold connected to the
existing process equipment. Prior to the excavation, up to five wells in the excavation
area on Parcel 3/6 will be shutdown at a time (consistent with the BAAQMD regulation
8-34-117.4). During excavation activities, well risers of the shutdown wells will be cut
every 5 feet until proposed final grade is reached and then finished to the required grade
and will be connected to the above-ground semi-permanent piping and process
equipment. At the end of the excavation work, proposed above-grade semi-permanent
piping and manifold will be converted to the below-ground permanent piping and
manifold and the shut-off LFG collection wells will then be reactivated.
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Parcel Development - The following steps will be repeated in each parcel as the parcel
development begins and progresses:
Isolation of Existing LFG Collection Wells: Prior to construction in a parcel, all
existing LFG collection wells in that parcel will be isolated to ensure that
abandonment of the wells does not shut off the LFG equipment connection to the
rest of the LFG collection wells that are operational. Isolation will be limited to one
parcel at a given time and would require temporary system shutoff, installation of
proposed temporary above-ground manifold in each parcel, reconnection of groups
of existing wells to the temporary manifold, and turning on the process equipment.
Interim Measures for Grading and Development: Before the existing LFG collection
wells in an active work area are abandoned, proposed permanent LFG wells will be
installed. The wells will be temporarily connected to the existing LFG process
equipment using temporary above-ground hoses and manifold.
Abandonment of Existing LFG Collection Wells: Abandonment of existing LFG
collection wells will be limited to five wells at a time, consistent with BAAQMD
regulation 8-34-117.4. A petition for variance to allow temporary shutdown and/or
abandonment of more than five wells at a time may be made to the regulatory
agencies during the Design Document Phase. Well layout and manifold connections
that will be used for abandonment and the proposed preliminary sequence of well
abandonment are presented in Appendix K.
Installation of Proposed Condensate Knockout Pots and Piping: The proposed
condensate knockout pots and piping would be installed after grading, piles, and pile
caps installation as per the proposed layouts shown in Appendix K. The installation
of condensate knockout pots and piping will be coordinated with the installation of
the slab, as needed.
Permanent Connection to Existing Process Equipment: The proposed LFG and
condensate collection wells will be finished to the proposed grade. The LFG wells
and condensate knockout pots will be reconnected to the process equipment and
activated using hoses and manifold.
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Installation of proposed LFG collection system will be continued in all the parcels by repeating
the aforementioned steps. Once portions of the new LFG collection system have been
reconnected to the process equipment, system inspection, shakedown, and startup will be
performed. The proposed field implementation details are provided in Appendix K. Details of
the new LFG collection system, shakedown, and startup will be prepared during design phase
for review and authorization by the regulatory agencies prior to implementation.
9.5 LFG Collection System Monitoring Plan
As required by BAAQMB Regulation 8, Rule 34, CCR Title 27, and Synthetic Minor Operating
Permit (SMOP) condition 2935, Part 14:
Monthly monitoring of LFG collection well heads and LFG monitoring wells for vacuum,
temperature, and concentrations of methane, oxygen, carbon dioxide, nitrogen, and
VOCs.
Monthly monitoring of LFG collection system process equipment for vacuum, air flow
velocity, and methane (% Volume and % LEL).
Monthly monitoring of collection and control devices.
Quarterly component leak testing.
Quarterly hydrogen sulfide monitoring at system inlet.
Quarterly LFG migration monitoring.
Quarterly methane surface emission monitoring.
Continuous monitoring of flare temperature and gas flow at the flare and the
microturbines.
Annual flare and microturbines performance test, which will include monitoring for
sulfur, non-methane organic compounds, methane, oxides of nitrogen, carbon
monoxide, and VOCs.
Results of the above will be compiled and included in an annual report. System and individual
wellhead operation and downtime will also be recorded in the report.
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10.0 LANDFILL GAS CONTROL
Potential risk to inhabitants of the proposed development may be present related to intrusion of
LFG into the proposed new structures. As such, a LFGMS will be installed in general
accordance with CCR Title 27 §20937. The purpose of the LFGMS is to mitigate the potential
building occupants’ exposure to harmful compounds from the subsurface.
The LFGMS will consist of a VBM, combined with a horizontal vapor collection and venting
system installed below the VBM so that any soil vapors can migrate, and vent, to the
atmosphere, outside the building. The horizontal vapor collection system will be primarily
passively-driven, but will include a contingency active extraction component that may
supplement the passive system based on automated methane monitoring. Below-grade utility
conduits entering the building will be sealed to mitigate LFG from migrating along the conduits
from outside the building and into the sub-slab space beneath the building. These features are
described in greater detail in the following sections. The LFGMS design drawings are
presented in Appendix L.
10.1 Vapor Barrier Membrane
10.1.1 Platform Structure Area
A platform structure that is supported by pile foundations will be constructed for a majority of
the Parcel 4 development. Above the platform structure will be an interstitial space of
approximately 5 feet. Above the interstitial space will be the building first floor slab,
landscaping, or pavement, depending on the location. A minimum of 12 inches of crushed rock
will be placed on top of the structural slab within the interstitial space. A VBM will be installed
on top of the 12 inches of crushed rock. Depending of the type of VBM used, a carrier fabric
may be placed just beneath the VBM and/or the VBM may be covered by a protection course
layer (e.g. fabric), so that the VBM is not damaged during the subsequent construction of the
interstitial space. VBM will also be placed to seal the interstitial space at the perimeter of each
building. Vertical penetrations through the VBM are not expected because utilities are
expected to be placed within the interstitial space above the VBM. However, utilities crossing
the perimeter of the building footprints will penetrate the VBM and proper sealing of these
VBM penetrations are essential to maintaining the integrity of the VBM.
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10.1.2 Non-Platform Structure Area
A VBM will also be installed as described in Section 10.1.1 at specified locations throughout the
remainder of the development. Within parking structures outside of the platform structure
area, the VBM design is essentially the same as described above, except there will be no
interstitial space between the VBM and overlying parking surface. Re-evaluation of the need for
a VBM beneath parking structures may be considered based on the design of these structures.
For example, open-air parking structures may require VBM only installed beneath a portion of
the garage with enclosed areas on the first floor, based on an evaluation of fresh air exchange
within the open-air portions of the garage. Within other structures outside of the platform
structure area, the VBM design is essentially the same as described above for the platform
structure.
While penetrations of the VBM are not expected beneath buildings (because utilities are
expected to be placed within the interstitial space), slab penetrations may be necessary within
the parking structures. Proper sealing of slab penetrations is essential to maintaining the
integrity of the VBM.
10.2 Passive Vapor Collection and Venting System
10.2.1 Platform Structure Area
A passive, horizontal collection and venting system will be installed within the crushed rock
layer beneath the VBM, described in Section 10.1.1, throughout the entire footprint of the
platform structure. This system will collect potential LFG passing through the structural slab
and into the interstitial space, and vent those gases to atmosphere at the roof-level of buildings.
The system will include an interconnected network of 4-inch perforated SCH 40 PVC piping
embedded in the upper half of a 12-inch ‚blanket‛ of crushed rock. The piping network will be
connected to vertical riser pipes, constructed of cast iron or ductile iron pipe, which will trend
vertically to above the roof level, where they will each be capped with a wind turbine that will
generate a vacuum on the piping network to enhance collection and venting of the vapors. The
precise location of the collection and venting system is dependent on the foundation design
and below-grade utility line locations, and will require close coordination with other members of
the design team.
In general, sub-slab vapor collection piping will be spaced no further than 50 feet apart, and one
riser will be installed per 10,000 square feet of the building footprint. Each vertical riser will
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include a test port above the roof or near the bottom of the riser to allow for LFGMS
performance monitoring, if required. The exact location of the test port will be specified during
the Design Document phase based in part on accessibility to the riser pipes and monitoring
requirements. The collection piping spacing and riser frequency stated above should be
considered conceptual, with final determination at the discretion of the design engineer at the
time of design. This portion of the LFGMS is intended to operate entirely passively, with air
movement induced mainly by convection (‚chimney effect‛).
10.2.2 Areas Outside the Platform Structure
A passive, horizontal collection and venting system will be installed with the crushed rock layer
beneath the VBM under buildings and parking structures throughout the remainder of the
development. For those building and parking structures outside the platform structure, sub-
slab vapor collection piping will be spaced no further than 50 feet apart, and one riser will be
installed per 10,000 square feet of the building footprint. The collection piping spacing and riser
frequency stated above should be considered conceptual, with final determination at the
discretion of the design engineer at the time of design. Each vertical riser will include a test
port above the roof to allow for LFGMS performance monitoring, if required.
10.3 Exterior Grade Beam Inlet Vents
The purpose of the exterior grade beam inlet vents is to facilitate convective airflow up the
vertical riser pipe of the collection and venting system, by allowing fresh air to enter the vapor
collection layer beneath the VBM. The vent is constructed of solid PVC or cast iron pipe, and is
placed through the formwork prior to pouring the concrete. The use of check-valves or back-
flow preventers on the inlet vents to mitigate the possible release of landfill gas will be
evaluated during the Design Document phase based in part on the design of the interstitial
space and/or building slabs below which the LFGMS will be installed. The precise location of
the exterior grade beam vents, and the details of how they will be incorporated into the exterior
walls, or surrounding landscaping, will require close coordination with other members of the
design team, particularly the structural engineer and architect. The frequency of inlet vents will
be determined during final design.
10.4 Contingency Active Blower System
Due to potentially high concentrations of methane and VOCs in LFG, a contingency active
extraction system will be installed to supplement the passive collection system. Like the
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passive collection system, the active, blower-assisted collection system will be installed within
the 12-inch thick crushed rock layer above the entire platform slab and above the structural
slabs beneath buildings and parking structures throughout the remainder of the Site. The
purpose of this system is to force subsurface methane gas and vapors to the atmosphere
through the blowers located at roof level. The active system will function if methane levels are
detected at specified concentrations in the methane sensors as described in Section 10.5. The
blower will also be scheduled for routine (monthly) operation to prevent moisture buildup.
The contingency active collection network consists of solid and perforated PVC pipe that
provide a flow pathway for the collected vapors towards a cast iron pipe vertical riser which
transmits the gases collected from inside the gravel layer to the atmosphere above the roof
level. The perforated collection pipes will be sleeved with a geotextile fabric to prevent
accumulation of fines within the piping system. The riser pipe leads to a blower above the
building roofline. While activated, methane and vapors are collected mechanically.
The required blower vacuum ratings, which are presented on the design drawings in
Appendix L, were calculated considering the following vacuum parameters:
Calculated building-specific pressure losses through the piping network due to friction,
which is dependent on flow rate.
Maintaining a minimum of 10 inches of water of vacuum to pull vapors up to the blower
at roof level.
It is assumed the underlying LFG Collection System will not produce a vacuum within
the LFGMS venting layer, due to the presence of the structural slab between the two
systems.
Contingency blower collection piping will be placed in between the passive collection and vent
piping or at a spacing of 50 feet. The blower flow ratings are designed to flush one pore volume
of air through the 12-inch crushed rock layer every 40 minutes under occupied buildings, and
every 90 minutes under parking structures. The lower flushing rate under parking structures is
because these structures are considered a lower risk for vapor intrusion, due to the lower
duration of human occupancy and garage-space ventilation requirements. These frequencies of
pore volume flushing should be considered conceptual, with final determination at the
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discretion of the design engineer at the time of design. Large flow rate requirements greater
than 400 standard cubic feet per minute (scfm) should be accommodated by multiple blowers.
A backup power source will be provided to power the contingency active blower system in the
event of an outage or failure of the primary building power system.
10.5 Automatic Methane Sensor Network
A continuously operating, automatic methane sensor network will be installed within the
interstitial space of the platform slab and in the first floor of buildings throughout the Site. A
minimum of one methane sensor will be placed within enclosed spaces and the frequency of
sensors is presented on the drawings in Appendix L. Final sensor design locations will be based
in part on the room and HVAC configurations and area coverage. In addition, one methane
sensor will also be placed at the top and/or bottom (depending on Design Document details) of
each stairwell, elevator shaft or other vertical open area that originates at ground level. The
locations and frequencies of the methane sensors in the building are illustrated in the design
drawings (Appendix L). A backup power source will be provided to power methane sensors and
alarms in the event of an outage or failure of the primary building power system.
The methane sensor network shall include low level and fault alarms. An audible horn alarm
will sound during high alarm activation. The automatic methane sensor network will trigger the
following emergency alarms:
The low alarm activation will occur at 10% of the LEL of methane gas. The alarm
signal(s) will be sent to the rooftop controller to activate operation of the contingency
active blower system.
Fault alarm activation will occur at loss of sensor signal, loss of controller power, and/or
loss of sample draw on sensors using remote sampling technology. Upon fault alarm, a
signal will be sent to the building engineer to inspect/repair the system.
High alarm activation will occur at 25% of the LEL of methane gas and signals will be
sent to the fire alarm control panel (FACP). The FACP will activate building horn/strobes
at the Facility Engineering Office, and send an alarm to a 24-hour monitoring company
indicating a ‚25% LEL methane gas alarm.‛
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The methane trigger levels for the alarms described above should be considered conceptual,
with final determination at the discretion of the design engineer at the time of design. Methane
sensors located within the interstitial space may alarm at higher methane levels than for
methane sensors located in interior spaces.
Low alarm activation will result in the activation of the contingency active blower system,
which will mechanically clear methane gas that may have accumulated within the collection
layer of the LFGMS. The gases will be vented directly to the atmosphere above roof level. It is
assumed that the Santa Clara County Fire Department (SCCFD) will be present to observe the
start-up functions of the automatic methane monitoring system.
Automatic monitoring will not be installed for other constituents in landfill gas. Methane will
serve as an indicator compound for other non-methane organic compounds (NMOCs), such as
VOCs. For purposes of the automatic monitoring system and for that reason the NMOC need
not be separately automatically monitored. Manual VOC monitoring may be considered in the
event that elevated methane concentrations indicate that the LFGMS may not be operating
effectively. Manual VOC monitoring may also be considered in the event that VOC
concentrations exceed the risk-based concentrations goals established in the Feasibility Study
of Groundwater Remediation Alternatives (Langan, 2015d).
10.6 Construction Quality Assurance Manual
A Construction Quality Assurance (CQA) Manual for the LFGMS will be prepared prior to
installation as part of the Design Documents. The CQA Manual will outline measures required
for quality assurance testing of LFGMS components and for protection of the VBM during
installation and during subsequent activities performed prior to covering of the VBM. The CQA
Manual will address the following:
The frequency of construction administration performed by the design engineer to
observe and document that installation is being performed in accordance with the
design and specifications;
Coupon testing of the VBM during installation to verify the design membrane thickness;
Smoke testing of the VBM during installation to verify continuity of the VBM;
Placement of a protection course fabric onto the VBM for protection of the VBM;
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Measures for protection of the surface of the VBM during subsequent construction
activities and placement of utilities within the interstitial space.
11.0 LEACHATE COLLECTION AND REMOVAL SYSTEM
11.1 Existing LCR System
The existing LCR system is present only in Parcel 1NW and Parcel 3/6. The leachate recovery
systems in the two parcels are independent. The LCR system in each of these two parcels
consists of a network of parallel leachate collection drains set at the bottom of the refuse and
leachate collection sumps for leachate drainage. Parcel 3/6 also has a perimeter leachate
collection drain. The collection drains are perforated pipes set either in a trench or set above
subgrade. Both types of collection drains are covered with gravel or drain rock. The trenched
collection drains are covered with a drainage layer and the collection drains set above the
subgrade are set within the drainage layer. The leachate can be collected from the sumps using
leachate risers: LR-6, LR-7, LR-8, and LR-9 on Parcel 1NW, and LR-1, LR-3, and LR-4 on Parcel
3/6. In addition to these risers, six piezometers are spread over Parcels 1, 2, and 4. These
piezometers have very slow recharge rate and cannot be used to effectively recover leachate.
Currently, the leachate/groundwater is recovered only from LR-1 using an automated pump.
Approximately 150,000 gallons of leachate were collected from LR-1 in 2013 and discharged
directly into the sanitary sewer. Notable amounts of leachate have been historically recovered
from LR-3 and LR-4 on Parcel 3/6. Leachate has not been recovered from the risers at Parcel
1NW since 1998. The layout of the existing LCR drains, sumps, wells or risers, and additional
subsurface details are provided in Appendix A.
11.2 Proposed LCR System
The proposed plan for LCR system includes preserving and maintaining the operation of riser
LR-1 and LR-4 in Parcel 3/6. Similar to the existing LCR riser LR-1, a submersible LCR pump
and associated float switches (i.e., pressure transducers) will be installed at the bottom of LR-4
for automated leachate recovery. If during construction, LR-1 and/or LR-4 are damaged, repairs
and modification will be performed as needed. Similar to the existing LR-1 LCR system, the
leachate recovered from the future operational leachate risers (LR-1 and LR-4) will be
discharged to a sanitary sewer (pending permit approval).
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Existing groundwater wells will be monitored according to the monitoring program that will be
developed consistent with the RWQCB monitoring requirements. The support and anchoring of
LR-1 and LR-4, to prevent potential settlement would be developed once the Site plans and
foundation plans for Parcel 3/6 are finalized.
For Parcel 1NW, the existing system will not be preserved since leachate has not been
collected from the system since 1998 and groundwater quality beneath and adjacent to Parcel
1NW has not been significantly impacted.
The proposed LCR concept plan is based on the following evaluation and considerations:
Current leachate recovery rates;
Leachate and groundwater elevation comparison;
Groundwater and leachate chemistry data;
LCR system settlement analysis;
Potential impact of deep foundations on existing LCR system;
Anticipated leachate production rates;
Seismic hazards;
Corrosion impacts; and
State and local regulations.
Current Leachate Recovery Rates - Review of the January 2014 and July 2014 water quality
monitoring reports indicates that leachate is currently recovered only from one leachate riser,
LR-1 using an automated LCR system, while LCR from other leachate risers has been sporadic.
Last noted in 1998, leachate was recovered from LR-4 and in the January 2015 Site visit by
Langan, leachate was observed to be present in LR-4 and LR-1.
Leachate and Groundwater Elevation Comparison - Based on our preliminary review of the
leachate and surrounding groundwater elevation data (Appendix M), no notable difference
between the leachate and surrounding groundwater elevations is observed. Groundwater
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monitoring conducted by Golder Associates (February 2014) measured the groundwater table
at the Site between about Elevation -4 feet to 4 feet. Based on the available groundwater data
from previous reports, the groundwater table elevations are generally in or within 10 feet of the
bottom portion of the waste unit. This suggests that a distinct leachate layer within the waste
unit does not likely exist at a higher elevation than the regional groundwater elevation.
Groundwater and Leachate Chemistry Data - The groundwater and leachate chemistry data
comparison presented in Appendix M indicates that the chemistry of leachate extracted from
LR-1 is distinct and less impacted than the groundwater where the VOC plume has been
identified near Parcel 3/6 and Parcel 4. Furthermore, based on the February – March 2014
groundwater data collected at monitoring wells G-4R, G-5, H-7 and G-21, which are farther
downgradient of LR-1 (Parcel 3/6) and downgradient of Parcel 1NW, these wells show no
exceedances above ESLs for metals or VOCs. Thus, it is likely that leachate does not have a
significant impact on the groundwater at the Site.
Leachate Recovery System Settlement Analysis - The measured 1997 and 2003 elevations
of the leachate risers on Parcel 1NW and Parcel 3/6 were compared to estimate potential
settlement of the leachate risers (Appendix M). As expected, the leachate risers, which are
located in the landfill berm did not indicate significant settlement at the top or bottom of the
casing elevations.
In addition, preliminary settlement calculations were performed by Langan for Parcel 3/6 to
estimate the possible settlement in the underlying clay/native soil that could have resulted over
time due to the load of overlying refuse, soil cover, and soil stockpile. The results of the
settlement calculations are provided in Appendix M. A settlement of approximately 10 inches
was estimated in the center of the Parcel 3/6, while a settlement of approximately 3 inches
was estimated at the edges of the Parcel 3/6. Based on these settlement estimates, a
comparison evaluation was performed between the design (pre-construction) elevations of the
bottom of LCR risers and elevations after estimated settlement (Appendix M). The evaluation
shows that even after the estimated settlement at the center of Parcel 3/6, the relative
positions of the sump to riser connection and the bottom of risers LR-1, 3 and 4 would have not
been changed significantly, although the slope of the pipe laterals connecting the risers with
the sump might have been reduced. Given that the construction material used for the LCR
risers and pipe laterals at Parcel 3/6 was SCH 40 PVC (which is relatively more brittle and less
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flexible than HDPE), the deflection of pipe laterals might have caused damage to pipe, pipe
joints, or some of the riser connecting joints with pipe laterals.
Potential Impact of Deep Foundations on Existing LCR System - Construction of deep
foundations (e.g., advancing piles into the native soil underlying the refuse) may damage
potions of the existing LCR drains set at the bottom of refuse and associated sumps for
leachate drainage. Given that the leachate layer within the waste is consistent with the regional
groundwater elevation (i.e. leachate is not mounded within the waste) and the possibility that
the LCR pipe laterals at Parcel 3/6 might have already been damaged from the past differential
settlement of the subsurface soils, the existing LCR system may be collecting groundwater
along with leachate. It is anticipated that the potential future damage of the existing LCR
subsurface infrastructure (LCR drains and sumps) due to deep foundations construction
activities will not impact the effectiveness and performance of the LCR system. Therefore, a
significant effort for preserving, repairing, or rebuilding the LCR subsurface infrastructure is not
needed, rather, efforts to preserve the existing operable components of the LCR system in
Parcel 3/6 (leachate risers LR-1 and LR-4) are proposed.
Potential impacts of deep foundations on the proposed LCR system effectiveness and
performance will be further evaluated during the Design Document Phase.
Anticipated Leachate Production Rates - Leachate production in the developed parcels is
anticipated to be substantially reduced due to the proposed post-construction stormwater
management in combination with the proposed above ground impervious surface construction
(i.e., structural building pads, asphalt roadways, buildings, etc.), which would limit infiltration of
water into the refuse. In addition, the reduction in irrigation along with the proposed automated
condensate recovery and removal system for the new LFG collection system would also
reduce the amount of water infiltration into the refuse and consequently will reduce the amount
of leachate produced.
The proposed LCR system, presented in Appendix M, will meet the following state and local
regulations:
CCR Title 27, Chapter 3, Subchapter 5, Article 2, §21160 – Landfill gas control and
leachate contact.
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CCR Title 27, Chapter 3, Subchapter 2, Article 2, §20200(d) – Management of liquids at
landfills and waste piles.
CCR Title 27, Chapter 3, Subchapter 2, Article 4, §20340– Leachate collection and
removal systems.
RWQCB Waste Discharge Requirements (WDRs), as revised for the proposed
development.
11.3 Considerations for LCR System at the Site
The potential seismic hazards and potential corrosion impacts to the future LCR system will be
considered and evaluated during the Design Document Phase:
Seismic Hazards – A seismic hazard analysis will be conducted during the Design
Document Phase to evaluate potential seismic impacts on the LCR system. Based on
the results of the seismic analysis, the components of the LCR system (i.e., LR-1, LR-4
and associated manifold) will be modified to accommodate the anticipated seismically
induced settlements to the extent practical.
Corrosion Impacts – Both LFG and fluids can potentially cause corrosion of landfill
infrastructure (LFG collection and LCR system) and building infrastructure (slabs and
piles). To minimize the impact of corrosion on the new LCR system components (i.e.,
LR-1, LR-4 and associated submersible LCR pumps and manifold), critical units and
parts would be fabricated from corrosion resistant materials, including HDPE, PVC,
corrosion-resistant stainless steel, and other materials with corrosion resistant coatings.
11.4 Conceptual Field Implementation Plan
The preservation of the existing LCR risers LR-1 and LR-4 would be coordinated with the on-
site construction work. Health and safety measures would be needed for general construction
activities, including those related to the existing LCR system.
Health and Safety Measures - Specific health and safety plans would be developed as
part of the design phase. These health and safety measures would include, but would
not be limited to: weather monitoring stations, air monitoring for methane, hydrogen
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sulfide, carbon monoxide, and VOCs, setting action levels for each monitoring
parameter, and specifications for PPE.
Coordination with on-site Construction Work - The installation, mechanical and electrical
connections, startup, and testing of the proposed LCR system will be coordinated with
the Site development activities.
During excavation of soil stockpile materials overlying Parcel 3/6, the LCR risers LR-1
and LR-4 in Parcel 3/6 would be identified, flagged, cut and capped (secured) as the
excavation progresses and would be finished to the proposed grade at the end of the
excavation.
During the construction phase of Parcel development, the existing LCR risers LR-1 and
LR-4 in Parcel 3/6 would be protected and preserved during construction by flagging the
well heads location, extending the risers, and installing a bollard around each riser.
The preserved LCR risers LR-1 and LR-4 would be completed at the proposed finished
grade. A new submersible LCR pump and associated float switches (i.e., pressure
transducers) will be installed at the bottom of LR-4 for automated LCR. The existing
submersible LCR pump at LR-1 and associated controls will be tested and serviced, as
needed. The LCR risers LR-1 and LR-4 would be routed to the proposed double
contained leachate storage tank that is to be housed in the central process equipment
enclosure on Parcel 1NW from where it will be conveyed ultimately to a single manhole
location sanitary sewer by a transfer pump and associated piping.
11.5 LCR System Monitoring Plan
The LCR system will be checked as scheduled or required for potential damages from seismic
activities, corrosion, etc. The leachate will be extracted and discharged to the sanitary sewer
(pending permit approval).
The LCR system monitoring will be continued as per the monitoring plan issued by the RWQCB
in WDRs Order No. R2-2002-0008 for the Site (Adopted 23 January 2002), which will be revised
to consider the proposed development and modifications to the landfill systems. Leachate
extracted from LCR risers LR-1 and LR-4 will be sampled on a semi-annual basis and analyzed
for VOCs; select metals (i.e., arsenic, chromium, copper, iron, lead, nickel, and zinc); and the
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routine water quality parameters (i.e., chloride, nitrate plus nitrite as nitrogen, pH, electric
conductivity, unionized ammonia as nitrogen, and chemical oxygen demand). Prior to the
sampling activities, the field parameters temperature, electric conductivity, pH, dissolved
oxygen, turbidity, and oxidation reduction potential will be collected. Results of the sampling
will be compiled and included in a semi-annual report submitted to the RWQCB along with
documentation of the volume of leachate removed and method of disposal.
12.0 GROUNDWATER AND SURFACE WATER MONITORING
As required by the WDRs for the Site, groundwater and surface waters at and adjacent to the
Site will be monitored on a semi-annual basis:
Groundwater elevations will be measured from the 22 groundwater monitoring wells
and piezometers associated with the Site.
Groundwater from the 22 groundwater monitoring wells and piezometers associated
with the Site will be sampled and analyzed for VOCs; the metals arsenic, chromium,
copper, iron, lead, nickel, and zinc; and the routine water quality parameters chloride,
nitrate plus nitrate as nitrogen, pH, electric conductivity, unionized ammonia as nitrogen,
and chemical oxygen demand.
Surface waters from four selected surface water sampling locations along San Tomas
Creek and the eastern perimeter drainage ditch will also be analyzed for the above listed
parameters.
Prior to the sampling activities, the field parameters temperature, electric conductivity,
pH, dissolved oxygen, turbidity, and oxidation reduction potential will also be collected.
Results of the sampling will be compiled and included in a semi-annual report.
13.0 EMERGENCY RESPONSE
13.1 High Methane at Buildings
The automatic methane monitoring system within the first floor of the buildings is set with
these levels of alarm as described below:
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The low alarm activation shall occur at 10% of the LEL of methane gas. The alarm
signal(s) will be sent to the rooftop controller to activate operation of the contingency
active blower system.
Fault alarm activation shall occur at loss of sensor signal, loss of controller power, and/or
loss of sample draw on sensors using remote sampling technology. Upon fault alarm, a
signal will be sent to the Building Engineer to inspect/repair the system.
High alarm activation shall occur at 25% of the LEL of methane gas and signals will be
sent to the FACP, which will activate building horn/strobes at the Facility Engineering
Office, and send an alarm to a 24-hour monitoring company indicating a ‚25% LEL
methane gas alarm.‛
Table 4
Compliance Requirements - Methane Action Levels
Compliance Requirement
Percentage of Methane in
Air
LEL 5%
High Alarm Level - 25% LEL 1.25%
Low Alarm Level - 10% LEL 0.5%
In the event of an emergency, such that methane sensors indicate concentrations of methane
in excess of the high alarm level of 25% of the LEL specified in Table 4, the Building
Engineering Manager shall coordinate with the Santa Clara Fire Department approximate
actions and steps necessary to protect public health and safety and the environment. The
Building Engineering Manager will immediately notify the LEA by telephone or electronic
means.
Within one week following a LFG sensor alarm, the Building Manager will:
Verify validity of the alarm by reviewing sensor readings and possible interferences.
Record a description of and submit a letter to the LEA that describes:
The levels of methane and trace gas detected;
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A brief description of the nature and extent of the problem based on information
currently available;
The steps the operator has taken to protect public health and safety and the
environment; and
A brief description of further corrective actions that the operator or others need to
take to adequately protect public health and safety and the environment.
During an evacuation, the building will not be reoccupied until it has been confirmed and
approved by the Santa Clara Fire Department that: (1) concentrations of methane meet the
applicable compliance requirements; and that (2) the LFGMS system is operating in a manner
that ensures adequate control of methane/vapor intrusion.
13.2 Other Emergency Situation
Emergency services (i.e. 911) should be contacted in the event of an emergency such as a fire
or earthquake. During an evacuation, the buildings will not be reoccupied until it has been
confirmed and approved by the Santa Clara Fire Department that: (1) concentrations of
methane meet the applicable compliance requirements; and that (2) the LFGMS systems are
operating in a manner that ensures adequate control of methane/vapor intrusion.
After the risk of immediate danger has subsided:
Site-wide systems such as the landfill cover, LFG system, LFGMS, LCR system, and
groundwater monitoring work shall be inspected for damage and evaluated for
necessary repair; and
A designated Responsible Party will immediately notify the LEA by telephone or
electronic means.
After the damages, if any, have been assessed, the designated Responsible Party will record a
description of and submit a letter to the LEA that describes:
A brief description of the nature and extent of the problem based on information
currently available;
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The steps the operator has taken to protect public health and safety and the
environment; and
A brief description of further corrective actions that the operator or others need to take
to adequately protect public health and safety and the environment.
14.0 OPERATION AND MAINTENANCE PLAN
Ongoing Site maintenance is required following the construction of the proposed development
to maintain Site features (pavement, foundation, and landscaping) which compose the landfill
cap, drainage and storm water management features, LFG system, the LFGMS, and the LCR
system.
14.1 Final Cover Inspection and Maintenance
Post-construction maintenance activities to maintain Site features (pavement, foundation,
landscaping) which compose the landfill cap, will include inspection of landfill cover integrity
and landfill cover repairs as needed. Indications of a loss of integrity include, but are not limited
to: signs of erosion such as channels or rutting, presence of animal burrows, and cracking or
fissuring of pavement or foundations. A list of inspection items and frequency is provided in
Table 5.
Table 5
Compliance Requirements - Final Landfill Cover Maintenance
Inspection Item Frequency of Inspection
Landfill Cover Integrity
Signs of erosion such as channels or rutting
Perform quarterly Site
inspections; monthly
inspections during the wet-
weather season; subsequent to
an emergency event;
subsequent to any intrusive
work and/or repairs.
Presence of animal burrows
Presence of cracking or fissuring of pavement or
foundations that could cause a landfill gas odor release
Irregular condition of vegetation (irregular color or growth
deficiency)
Signs of settlement (depressions, ponded water)
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Drainage Features
Evidence of degradation of drainage features Perform quarterly Site
inspections; monthly
inspections during the wet-
weather season; subsequent to
an emergency event;
subsequent to any repairs..
Evidence of ponding or backup
Irregular condition of storm water (irregular color, odor,
clarity or turbidity, floating solids, settled solids,
suspended solids, foam, oil sheen, and other indications of
stormwater pollution)
Repairs necessary to restore the integrity of the final cover will be executed by the Site
personnel or an independent contractor as described below. Erosion damage which breaches
the cover layer will be repaired with suitable clean soil material. Temporary berms, ditches, and
straw mulch will be used to prevent further erosion damage to repaired areas until Site
conditions permit re-establishment of final cover and subsequent revegetation, as applicable.
Minor erosion and cracks will be repaired with bentonite. Minor erosion and cracks will be
widened, if necessary, to facilitate placing bentonite. The bentonite will be compacted using a
hand tamper or other appropriate equipment. Significant erosion, cracks, or areas with exposed
refuse will be repaired using clean, appropriate soil material which will be placed and
compacted to meet original final cover soil specifications. Repaired areas will be reseeded to
establish vegetation, as applicable. In paved areas, surfaces will be properly sealed.
In landscaped areas, the condition of vegetation will be monitored quarterly and monthly during
wet-weather season by the Site personnel or an independent contractor. Inspections will
identify areas of irregular color or growth deficiency. During future inspections, the spread of
these conditions will be noted. If an area greater than 500 square feet is noted to provide less
than 80% vegetative cover, the area will be hand seeded and fertilized to reestablish plant
growth.
Excessive LFG migration through the final cover could result in loss of vegetation. If noticeable
reoccurring vegetative loss is observed, a LFG detector will be utilized to determine the extent
of potential LFG migration. Screening with a LFG detector should be conducted on a wind-free
day. If necessary, repairs to the LFG system will be performed (see Section 14.3).
Areas that have ponded water or have settled will be filled to reestablish the proper grade.
These areas will be filled with clean soil, free of deleterious material. After filling and regrading,
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the areas will be reseeded. Should a slope failure occur, the area will be closed off to prevent
damage to equipment or harm to individuals. The Site's engineering consultant will be notified
to assess the failure and recommend appropriate corrective action. Specific corrective action
will be dependent on the extent, nature, and location of the failure. A record of final cover
maintenance activities will be kept by Site personnel or an independent contractor. The record
will include the date, location, and extent and nature of the maintenance activity. Regulatory
agencies will be notified if required by the Site's permits and approvals. The Site personnel or
an independent contractor will perform Site inspections.
14.2 Drainage Features Inspection and Maintenance
The Site will be inspected quarterly and monthly during the wet-weather season by the Site
personnel or an independent contractor for evidence of ponding or degradation of the Site's
drainage control system. Ponding on the lower portions of the Site will be remedied by either
backfilling the area to provide positive drainage, or providing an acceptable downstream slope
to an appropriate discharge point. The property perimeter will be inspected for failure. If
necessary, temporary repairs will be made until permanent repairs can be scheduled. Repairs
to drainage facilities will be completed by the Site personnel or a licensed general contractor.
14.3 LFG System Inspection and Maintenance
An examination of accessible portions of LFG system piping for potential system failures such
as leaks or breaks will be conducted on a monthly basis. Detection of a system failure which
would reduce system efficiency and/or effectiveness will be addressed within 24 hours of
detection. Preventative maintenance will be performed at manufacturer recommended
intervals. A LFG system operation and maintenance (O&M) manual will be prepared following
construction of the system and completion of record drawings. The LFG system O&M manual
will include a schedule of maintenance checks of accessible LFG system components (i.e.,
wellhead vaults, wellhead instrumentation and controls, condensate knockout pots, knockout
pot submersible pumps, process equipment, etc.).
14.4 LFGMS Inspection and Maintenance
Ongoing operation and maintenance of the LFGMS is required. The LFGMS must be
maintained by trained personnel who are familiar with the system’s operations. The system
components will be repaired or replaced for operational reliability as needed during routine
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maintenance periods. If building improvement plans (e.g., tenant improvements) impact
LFGMS components, portions of the LFGMS will be properly repaired. For such work, proper
safety measures will be implemented (including gas and vapor monitoring and control). Agency
Notification and reporting to the applicable agencies (i.e. LEA and RWQCB) is required. A
LFGMS O&M manual will be prepared following construction of the LFGMS and completion of
record drawings. The LFGMS O&M manual will include a schedule of maintenance checks of
above-ground LFGMS components, including testing and calibration of the methane sensor
network. The LFGMS O&M manual will also include provisions for protection of the VBM
during future utility maintenance work.
14.5 LCR System Inspection and Maintenance
Ongoing operation and maintenance of the LCR system is required. Inspections of the system
will be conducted by the Site personnel or an independent contractor whenever leachate is
sampled. A LCR system O&M manual will be prepared following construction of the LCR
system and completion of record drawings. The LCR system O&M manual will include a
schedule of maintenance checks of all above-ground and accessible LCR system components
(i.e., LCR risers LR-1 and LR-4, and associated submersible pumps and float switches, etc.).
14.6 Groundwater Monitoring System Inspection and Maintenance
Groundwater monitoring wells will be inspected for signs of failure or deterioration during each
sampling event. If damage is discovered, the well will be replaced or repaired as determined
by a California-registered geologist or certified engineering geologist. Possible repairs include
redevelopment, chemical treatment, partial casing replacement, resealing the annulus, or
pumping and testing. If a well is replaced, the existing, damaged well will be appropriately
decommissioned according to the California Well Standards guidelines for well destruction.
New wells will also be installed in accordance with California Well Standards guidelines.
14.7 Reporting
Results of monthly inspections, quarterly inspections, and a summary of maintenance
performed to the systems discussed in Sections 14.1 through 14.6 will be compiled and
included in quarterly monitoring reports.
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14.8 Planned or Emergency Subsurface Activities
Waste management is required for future, planned or emergency, subsurface activities.
Because the entire Site is anticipated to be capped, exposure pathways to Site tenants and the
public from material that may remain in the subsurface will have been mitigated. Responsible
parties will be required to inspect and maintain the integrity of the cap and provide notification
of activities that disturb the cap and measures performed to mitigate the disturbance. Post-
construction activities which could threaten the integrity of the cap include construction of new
buildings, installation of underground utilities or tanks, excavation below the cap, and
emergency activities, such as repair of broken underground utilities. Post-construction waste
management for subsurface activities may include restoration of the cap, dust and vapor
monitoring and control, and agency notification and reporting.
15.0 SATISFACTION OF POST-CLOSURE LAND USE REQUIREMENTS
The information set forth in this PCLUP above satisfies each of the specific requirements of 27
CCR 21190, and supports the agency findings required by that Section. As such, the proposed
post-closure land uses shall be designed and maintained to:
Protect public health and safety and prevent damage to structures, roads, utilities, and
gas monitoring and control systems (see Section 1.5.4 – Human Health Risk
Assessment and Section 3.3 – Health and Safety Program);
Prevent public contact with waste, LFG and leachate (see Section 6.0 – Final Cover,
Section 10.0 Landfill Gas Control, and Section 11.0 – Leachate Collection and Removal
System
Prevent LFG explosions (see Section 9.0 - Enhanced Landfill Gas Collection and
Remediation System); and
Maintain the integrity of the final cover, drainage and erosion control systems, and gas
monitoring and control systems (see Section 14.0 – Operation and Maintenance Plan).
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Construction of structural improvements at the Landfill will meet the following conditions:
Automatic methane gas sensors, designed to trigger an audible alarm when methane
concentrations are detected, will be installed in all buildings (see Section 10.0 - Landfill
Gas Control);
Enclosed basement construction will be prohibited (see Section 1.4 – Project
Description);
Buildings will be constructed to mitigate the effects of gas accumulation, which may
include an active gas collection or passive vent systems (see Section 10.0 - Landfill Gas
Control);
Buildings and utilities will be constructed to mitigate the effects of differential
settlement. All utility connections will be designed with flexible connections and utility
collars (see Section 5.0 – Conceptual Foundation and Section 8.0 – Utilities);
Utilities will not be installed in or below any low permeability layer of final cover (see
Section 5.0 – Conceptual Foundation and Section 8.0 – Utilities);
Pilings will not be installed in or through any bottom liner unless approved by the
RWQCB, or if pilings are installed in or through the low permeability layer of final cover,
then the low permeability layer will be replaced or repaired (see Section 5.0 –
Conceptual Foundation); and
Periodic methane gas monitoring will be conducted inside all buildings and underground
utilities (see Section 10.5 - Automatic Methane Sensor Network).
The City of Santa Clara is the lead agency preparing a Draft Environmental Impact Report (EIR)
on the Project in accordance with the California Environmental Quality Act (CEQA). A Notice of
Preparation for this EIR was published on July 30, 2014. The City is expected to complete the
Final EIR in late 2015. After the final EIR is certified, the LEA and RWQCB will consider
approval of this PCLUP in reliance on the CEQA analysis in the Final EIR.
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16.0 REFERENCES
Air Science Technologies, Inc., 2012. 2012 Source Test Report. Source Test of a Landfill Gas
Flare and Landfill Gas Characterization. Santa Clara All Purpose Landfill, Santa Clara, California.
Facility Number A3464. 20 July.
California Emergency Agency. 2009. Tsunami Inundation Map for Emergency Planning, State of
California, County of Santa Clara, Milpitas Quadrangle.
Edil, T.B., et al., 1990. Settlement of Municipal Refuse, Geotechnics of Waste Fills – Theory
and Practice, ASTM STP 1070, Philadelphia.
Emcon Associates (Emcon), 1988. Air Quality Solid Waste Assessment Test Report, City of
Santa Clara Landfill, Santa Clara County, California. December
Emcon, 1992. Final Closure and Postclosure Maintenance Plan, City of Santa Clara, All Purpose
Sanitary Landfill, Revision 2. 2 December.
Gibson, R.E., and Lo, K.Y., 1961. A Theory of Soils Exhibiting Secondary Compression, Acta
Polytechnica Scandinavica.
Golder Associates (Golder), 2013. Postclosure Maintenance Plan Update, City of Santa Clara,
All Purpose Landfill, SWIS No. 43-AO-0001, Waste Discharge Requirements Order, No. R2-
2002-0008. 23 August.
Golder, 2014a. BAAQMD Annual 8-34 Report, City of Santa Clara All Purpose Landfill, July 1,
2013 through June 30, 2014. 24 July.
Golder, 2014b. City of Santa Clara All Purpose Landfill, First Semiannual 2014 Self-Monitoring
Program Report. July.
Golder, 2015. Telephone communication with Steve Nguyen. 24 March.
Kenneth D. Schmidt and Associates (KSA), 1988. Results of the Water Part of the Solid Waste
Assessment Test at the City of Santa Clara Landfill. 29 June.
Langan, 2014a. Draft Work Plan for Landfill Gas Characterization, Related Santa, Santa Clara,
California. 13 February.
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Langan, 2014b. Work Plan, Geotechnical Field Investigation, Santa Clara All-Purpose Landfill,
Santa Clara, California. 5 March.
Langan, 2014c. Preliminary Geotechnical Investigation, City Place Santa Clara, Santa Clara,
California. 22 August.
Langan, 201d. Work Plan for Targeted Site Characterization, Santa Clara All Purpose Landfill,
Santa Clara, California. 26 September.
Langan, 2014e. Draft Site Investigation and Environmental Risk Assessment, City Place Santa
Clara, Santa Clara, California. 23 December.
Langan, 2015a. Draft Technical Memorandum, Enhanced Landfill Gas Collection and
Remediation System Reconstruction Concept Plans, City Place Santa Clara. 30 January.
Langan, 2015b. Draft Technical Memorandum, Leachate Collection and Removal System
Concept Plans, City Place Santa Clara. 6 February.
Langan, 2015c. Landfill Cover Investigation, City Place Santa Clara, Santa Clara, California. 13
February.
Langan, 2015d. Feasibility Study of Groundwater Remediation Alternatives, City Place Santa
Clara/Santa Clara All Purpose Landfill Site, Santa Clara, California. 21 July.
Real Environmental Products, 2011. Santa Clara Landfill, Landfill Gas Recovery System. Santa
Clara, California. 28 April.
Related, in conjunction with Elkus Manfredi Architects and RTKL, 2014. Conceptual Land Use
Plans and Programs. March.
Regional Water Quality Control Board San Francisco Bay Region (RWQCB), 2002. Order No.
R2-2002-0008 Updated Waste Discharge Requirements and Rescission of Order No. 94-050
for: City Of Santa Clara Santa Clara All Purpose Landfill Santa Clara, Santa Clara County. 23
January.
RWQCB, 2013. Cover Memo, User’s Guide: Derivation and Application of Environmental
Screening Levels, and Lookup Tables. December.
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RWQCB, 2014a. Response Letter to the Draft Work Plan for Landfill Gas Characterization for
City of Santa Clara - All Purpose Landfill. 21 March.
RWQCB, 2014b. Concurrence Letter for the Work Plan for the Geotechnical Field Investigation
Work Plan, City of Santa Clara - All Purpose Landfill. 10 July.
RWQCB, 2014c. Concurrence Letter for the Work Plan for Targeted Site Characterization for
City of Santa Clara - All Purpose Landfill. 1 October.
Sharma, H.D., and Lewis, S.P., 1994. Waste Containment Systems, Waste Stabilization, and
Landfills, Design and Evaluation. John Wiley & Sons, Inc.
Tokimatsu and Seed, 1987. Simplified Procedure for the Evaluation of Settlements in Clean
Sand.
FIGURES
APPENDIX A
EXISTING SYSTEMS
APPENDIX B
PHASING CONCEPT MAP (ELKUS MANFREDI ARCHITECTS
16 JULY 2014)
APPENDIX C
PRELIMINARY ARCHITECTURAL DRAWINGS
(PENDING PREPARATION)
APPENDIX D
PRELIMINARY DESIGN DRAWINGS
APPENDIX E
PREVIOUS ENVIRONMENTAL INVESTIGATION RESULTS (FIGURES
AND TABLES FROM DRAFT SITE INVESTIGATION AND
ENVIRONMENTAL RISK ASSESSMENT REPORT, CITY PLACE SANTA
CLARA, LANGAN TREADWELL ROLLO, 23 DECEMBER 2014)
APPENDIX F
EXISTING PERMITS
APPENDIX G
BORING LOGS AND CROSS SECTIONS
APPENDIX H
WASTE MANAGEMENT PLAN
APPENDIX I
ODOR MANAGEMENT PLAN
APPENDIX J
CONCEPTUAL FOUNDATION PLAN AND DETAILS AND DRAFT
LANDFILL COVER INVESTIGATION REPORT
APPENDIX K
PROPOSED LANDFILL GAS COLLECTION AND REMEDIATION
SYSTEM CONCEPT PLANS (FIGURES FROM DRAFT TECHNICAL
MEMORANDUM, ENHANCED LANDFILL GAS COLLECTION AND
REMEDIATION SYSTEM RECONSTRUCTION CONCEPT PLANS, CITY
PLACE SANTA CLARA, 30 JANUARY 2015)
APPENDIX L
CONCEPTUAL LANDFILL GAS MITIGATION SYSTEM DESIGN
APPENDIX M
LEACHATE COLLECTION AND REMOVAL SYSTEM CONCEPT PLAN
(FIGURE FROM DRAFT TECHNICAL MEMORANDUM, LEACHATE
COLLECTION AND REMOVAL SYSTEM CONCEPT PLANS, CITY PLACE
SANTA CLARA, 6 FEBRUARY 2015)
City PlaceSanta ClaraCity Place
Santa Clara
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CITY PLACE SANTA CLARASanta Cla ra , Ca lifornia
Da te 12/23/2014 Project No. 770611601 Fig ure 1
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Notes:1. Aerial imagery provided by National Agriculture Imagery Program (NAIP); Santa Clara County, 2012.2. Map displayed in California State Plane Coordinate System, Zone III, North American Datum of 1983 (NAD83), US Survey Feet.
Project Drawing Title
SANTA CLARA CALIFORNIA
SITE MAP
Project No.
Date
Scale
Drawn By
Submission Date
Figure770611601
1/19/2015
CSS
1"=700'
4030 Moorpark Avenue, Suite 210San Jose, CA 95117-1849
T: 408.551.6700 F: 408.551.0344 www.langan.com
CITY PLACESANTA CLARA
SANTA CLARA
2Langan Engineering & Environmental Services, Inc.Langan Engineering, Environmental, Surveying and
Landscape Architecture, D.P.C.Langan International LLC
Collectively known as Langan
LegendApproximate Boundary of Refuse FillProject Site1' Contour Interval
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