DRAFT REMEDIAL INVESTIGATION REPORTstatic.azdeq.gov/wqarf/havasu_holly_draftri.pdf · 2020-02-07 · ) located in Lake Havasu City (the City), Arizona.The Site is generally bounded

DRAFT REMEDIAL INVESTIGATION REPORT

LAKE HAVASU AVENUE AND HOLLY AVENUE

WATER QUALITY ASSURANCE REVOLVING FUND SITE

LAKE HAVASU CITY, ARIZONA

Prepared by

11811 N. Tatum Boulevard, Suite P-186 Phoenix, Arizona 85028

Telephone: (602) 513-5812 www.geosyntec.com

And

Arizona Department of Environmental Quality 1110 West Washington Street

Phoenix, Arizona 85007

January 31, 2020

http://www.geosyntec.com/

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report ii January 2020

EXECUTIVE SUMMARY

This report summarizes the findings of remedial investigation (RI) activities conducted by the Arizona Department of Environmental Quality (ADEQ) at the Lake Havasu Avenue and Holly Avenue Water Quality Assurance Revolving Fund (WQARF) site (the Site; Figures 1 and 2) located in Lake Havasu City (the City), Arizona. The Site is generally bounded to the north by Center Avenue, to the south by Holly Avenue, to the east by San Juan Drive, and to the west by London Bridge Avenue. The Site is in an urban setting that includes a mixture of commercial businesses, light industrial businesses, warehouses, and residential neighborhoods (Figure 2).

Dating back to 1983, the former McCulloch facility at 900 Lake Havasu Avenue and the former Kiowa Ponds (Figure 2) have been the subject of numerous investigations focusing on both soil and groundwater contamination. The former McCulloch facility was situated on approximately 30 acres of commercial property located approximately one mile east of Lake Havasu. From 1972 to 1998, the McCulloch facility manufactured small gasoline-powered equipment. Manufacturing activities included machining, die casting, metal finishing, and chrome plating. Chemicals used at the facility included metals (chromium), acids and bases, cyanide compounds, oxidizers, adhesives, phenolic surfactants, and a variety of solvents.

The results of the Site investigations completed to date indicate that soil, soil-vapor, and groundwater have been impacted at the Site. The contaminants of concern (COCs) identified at the Site are the chlorinated volatile organic compounds (VOCs) tetrachloroethene (PCE), trichloroethene (TCE), and their degradation products, nitrate, benzene, and chromium. 1,2-dichloroethane (1,2-DCA) and 1,1- dichloroethene (1,1-DCE) have also been detected over AWQS periodically at the Site. In 2001 and 2002, a soil-vapor extraction and air sparge system was operated at the Site to remediate hydrocarbon-related soil and groundwater impacts as part of a leaking underground storage tank (LUST) case remediation (LUST Case File #2606.01, Facility ID #0-003088). The LUST case was closed in July 2012.

Various limited early remedial actions have been implemented at the former McCulloch Facility, including excavation and in-situ treatment of vadose zone soil with calcium polysulfide in an attempt to address vadose zone impacts of hexavalent chromium (Cr[VI]) beneath the former plating shop. However, data collected under this RI indicate that COCs are still present in the vadose zone in this area at concentrations that exceed regulatory standards. As groundwater level has risen beneath the Site, these vadose zone impacts have resulted in ongoing groundwater impacts.

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report iii January 2020

The analytical results from Site soil samples indicate that total chromium and Cr(VI) are present in the vadose zone at concentrations exceeding the Arizona Soil Remediation Levels (SRLs) and/or the Groundwater Protection Level (GPL). Additionally, VOCs (primarily PCE and TCE), have been detected in soil-vapor at concentrations that exceed the United States Environmental Protection Agency (USEPA) Regional Screening Level (RSL) for commercial worker ambient air, assuming a conservative 0.03 slab attenuation factor.

COCs in the source area have migrated vertically through interbedded vadose zone sand, gravelly sand, silty sand, and minor layers of fine-grained materials. The COCs have encountered groundwater below the Site and are migrating in a westerly flow direction.

Groundwater elevations at the Site have ranged from approximately 454 feet above mean sea level (ft amsl) to approximately 465 ft amsl. The direction of groundwater flow within the Site is to the west with a hydraulic gradient of approximately 0.004 feet per foot in 2019. Groundwater elevations are rising at the Site compared to historical data.

Historical investigations and ongoing groundwater monitoring have delineated both the lateral and vertical extent of the groundwater COC impacts.

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report iv January 2020

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY .............................................................................................. ii

TABLE OF CONTENTS ................................................................................................ iv

LIST OF FIGURES ........................................................................................................ vii

LIST OF TABLES .......................................................................................................... vii

LIST OF APPENDICES................................................................................................ viii

LIST OF ACRONYMS AND ABBREVIATIONS ...................................................... viii

1. INTRODUCTION ................................................................................................ 1

1.1. Remedial Investigation Objectives .............................................................. 1 1.2. Former Facility Operations .......................................................................... 2

2. PHYSICAL SETTING ......................................................................................... 4

2.1. Topography .................................................................................................. 4 2.2. Climate ......................................................................................................... 4 2.3. Surface Water .............................................................................................. 5 2.4. Geology ........................................................................................................ 5

2.4.1. Regional Geology ............................................................................ 5 2.4.2. Site Geology .................................................................................... 5

2.5. Hydrogeology .............................................................................................. 6 2.6. Ecology ........................................................................................................ 7

3. HISTORICAL INVESTIGATIONS .................................................................... 8

3.1. 1975 to 1995 – Former McCulloch Facility Wastewater Effluent Results.......................................................................................................... 8

3.2. 1983 – Former McCulloch Facility Sludge Sump Investigations and Soil Removal ......................................................................................... 8

3.3. 1990 – Former McCulloch Facility Chrome Plating Area Soil Removal ....................................................................................................... 9

3.4. 1991 – Former McCulloch Facility Preliminary Assessment and Facility Inspection ....................................................................................... 9

3.5. 1992 – Former McCulloch Facility Sub-Basement Soil Investigation ................................................................................................ 9

3.6. 1992 – Former McCulloch Facility Underground Storage Tank Removal ..................................................................................................... 10

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report v January 2020

3.7. 1993 – Former McCulloch Facility Leaking UST Characterization and Soil Removal ....................................................................................... 10

3.8. 1994 – Former McCulloch Facility Leaking UST Phase II Report ........... 10 3.9. 1995 – Former McCulloch Facility Additional Plating Shop Area

Investigation; Kiowa Pond Sludge Sampling ............................................ 11 3.10. 1996 to 1997 –Well Installations and Groundwater Investigation ............ 12 3.11. 1998 – Sludge Removal from Kiowa Ponds; Former McCulloch

Facility Soil-Gas Survey, and Additional Monitoring Well Installations ................................................................................................ 13

3.12. 1999 – Former McCulloch Facility Leaking UST Corrective Action Plan; Soil and Soil-Gas Survey.................................................................. 13

3.13. 2000 – Kiowa Ponds Soil Investigation; Former McCulloch Facility Additional Well Installation ......................................................... 14

3.14. 2001 – Kiowa Pond APP Closure and Well Installation; Former McCulloch Facility Area Remedial Action and Pilot Test Evaluation .................................................................................................. 14

3.15. 2001 to 2002 – Former McCulloch Facility Leaking UST AS/SVE system ........................................................................................................ 16

3.16. 2002 - Former McCulloch Facility Pilot Test............................................ 16 3.17. 2003 - Former McCulloch Facility Phase II Pilot Test .............................. 17 3.18. 2004 – Groundwater Sampling and Chromium Extent Investigation ....... 19 3.19. 2004 to 2007 – Kiowa Ponds APP Closure; Former McCulloch

Facility Monitoring Well Installation ........................................................ 20 3.20. 2008 – Groundwater Monitoring; City Memorandum .............................. 21 3.21. 2012 – Former McCulloch Facility Leaking UST Case Closure .............. 21 3.22. 2014 – ADEQ Groundwater Monitoring; Former McCulloch

Facility Request for In-Situ Soils Closure ................................................. 22 3.23. 2015 – ADEQ Preliminary Investigation .................................................. 22 3.24. 2017 – City of Lake Havasu Production Well Sampling .......................... 23

4. REMEDIAL INVESTIGATIONS...................................................................... 24

4.1. Soil Investigations ..................................................................................... 24 4.1.1. Former McCulloch Facility Soil Investigation Results ................. 24 4.1.2. Former Kiowa Ponds Soil Investigation Results ........................... 25

4.2. Soil-Vapor Investigation ............................................................................ 25 4.2.1. Former McCulloch Facility Soil-Vapor Sampling ........................ 25 4.2.2. Former Kiowa Ponds Soil-Vapor Sampling .................................. 26

4.3. Groundwater Investigations ....................................................................... 26 4.3.1. April 2018 Groundwater Sampling ................................................ 26 4.3.2. Monitor Well Installations ............................................................. 27

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report vi January 2020

4.3.3. 2018 Groundwater Monitoring ...................................................... 28 4.3.4. 2019 Groundwater Monitoring ...................................................... 29

5. EXTENT OF CONTAMINATION .................................................................... 32

5.1. Soil ............................................................................................................. 32 5.2. Groundwater .............................................................................................. 32

6. RISK EVALUATION ........................................................................................ 34

6.1. Human Health Conceptual Site Exposure Model ...................................... 34 6.2. Applicable Regulatory Standards and Screening Criteria Used in

the Human Health Screening Risk Evaluation .......................................... 35 6.2.1. Soil Remediation Standards ........................................................... 35 6.2.2. Soil-Vapor Screening Levels ......................................................... 35 6.2.3. Groundwater Standards .................................................................. 35

6.3. Human Health Conceptual Site Exposure Model ...................................... 36 6.3.1. Vapor Pathway ............................................................................... 36 6.3.2. Soil Pathway .................................................................................. 36 6.3.3. Groundwater Pathway .................................................................... 37 6.3.4. Surface Water Pathway .................................................................. 37

6.4. Potential Receptors .................................................................................... 37 6.5. Ecological Conceptual Site Exposure Model ............................................ 38

7. CURRENT AND FUTURE LAND AND WATER USE .................................. 39

7.1. Land Use .................................................................................................... 39 7.1.1. Current Land Use ........................................................................... 39 7.1.2. Future Land Use ............................................................................. 39

7.2. Groundwater Use ....................................................................................... 40 7.2.1. Current Water Use ......................................................................... 40 7.2.2. Future Water Use ........................................................................... 41

8. DATA GAPS ...................................................................................................... 42

9. REFERENCES ................................................................................................... 43

10. LIMITATIONS ................................................................................................... 50

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report vii January 2020

LIST OF FIGURES

Figure 1: Site Location Figure 2: WQARF Site Plan Figure 3: Historical McCulloch Facility Layout Figure 4a: Groundwater Elevation Contour Map 2014 Event Figure 4b: Groundwater Elevation Contour Map April 2019 Event Figure 4c: Groundwater Elevation Contour Map October 2019 Event Figure 5: Total Chromium and Hexavalent Chromium Soil Impacts Figure 6a: Soil Vapor Impacts PCE Figure 6b: Soil Vapor Impacts TCE Figure 7a: Groundwater Isoconcentration Map PCE April 2019 Figure 7b: Groundwater Isoconcentration Map PCE Oct-Nov 2019 Figure 8a: Groundwater Isoconcentration Map TCE April 2019 Figure 8b: Groundwater Isoconcentration Map TCE Oct-Nov 2019 Figure 9a: Groundwater Isoconcentration Map Nitrate April 2019 Figure 9b: Groundwater Isoconcentration Map Nitrate Oct-Nov 2019 Figure 10a: Groundwater Isoconcentration Map Total Chromium April 2019 Figure 10b: Groundwater Isoconcentration Map Total Chromium Oct-Nov 2019 Figure 11a: Geologic Cross Section A-A’ Total Chromium Figure 11b: Geologic Cross Section B-B’ Total Chromium Figure 12a: Geologic Cross Section A-A’ Hexavalent Chromium Figure 12b: Geologic Cross Section B-B’ Hexavalent Chromium Figure 13a: Geologic Cross Section A-A’ TCE Figure 13b: Geologic Cross Section B-B’ TCE Figure 14a: Geologic Cross Section A-A’ Nitrate Figure 14b: Geologic Cross Section B-B’ Nitrate Figure 15: Conceptual Site Model Figure 16: Exposure Pathway Model Figure 17: Sensitive Receptors Map Figure 18: 𝛿𝛿15N and 𝛿𝛿18O Stable Isotope Analytical Results Figure 19: Hexavalent Chromium Extent in Soils

LIST OF TABLES

Table 1: Well Construction Table 2: Groundwater Elevations Table 3A: Historical Soil Metals Results Table 3B: Historical Soil Nitrate Results Table 3C: Historical Soil VOCs Results – Former Kiowa Ponds

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report viii January 2020

LIST OF TABLES CONTINUED

Table 4A: Historical Groundwater Metals Results Table 4B: Historical Groundwater Nitrate Results Table 4C: Historical Groundwater VOCs Results Table 5A: Remedial Investigation Soil Metals and Nitrate Results Table 5B: Former Kiowa Ponds 2018 Site Characterization Soil Metals Results Table 6A: Remedial Investigation Soil Vapor VOCs Results Table 6B: Former Kiowa Ponds 2018 Site Characterization Soil Vapor VOCs Results Table 7A: Remedial Investigation Groundwater Hydropunch Nitrate Results Table 7B: Remedial Investigation Groundwater Hydropunch General Chemistry

Results Table 7C: Remedial Investigation Groundwater Hydropunch Cr and CrVI Results Table 7D: Remedial Investigation Groundwater Hydropunch Metals Results Table 7E: Remedial Investigation Groundwater Hydropunch VOCs Results Table 7F: Remedial Investigation Groundwater Monitoring Metals Results Table 7H: Remedial Investigation Groundwater Monitoring Nitrate Results Table 7I: Remedial Investigation Groundwater Monitoring VOCs Results Table 8: Remedial Investigation Groundwater Isotope Analysis Results Table 9: Comparison of Passive Sampling Verses Purge Methodology Sampling Table 10: ADEQ-Collected Samples Compared to Split Samples

LIST OF APPENDICES

Appendix A: Boring Logs Appendix B: Historical Maps Appendix C.1: Laboratory Analytical Reports – Soil Appendix C.2: Laboratory Analytical Reports – Soil-Vapor Appendix C.3: Laboratory Analytical Reports – Groundwater Appendix C.4: Microbial Analysis Results Appendix D: Well Survey Report Appendix E: Draft Land and Water Use Report

LIST OF ACRONYMS AND ABBREVIATIONS

µg/L micrograms per liter µg/m3 micrograms per cubic meter A.A.C. Arizona Administrative Code ADEQ Arizona Department of Environmental Quality ADHS Arizona Department of Health Services

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report ix January 2020

LIST OF ACRONYMS AND ABBREVIATIONS CONTINUED

ADWR Arizona Department of Water Resources amsl above mean sea level APP Aquifer Protection Permit A.R.S. Arizona Revised Statutes AS air sparge AWQS Aquifer Water Quality Standard bgs below ground surface BTEX benzene, toluene, ethylbenzene, and xylenes CAP Corrective Action Plan COC contaminant of concern CPS calcium polysulfide CSM conceptual site model 1,2-DCA 1,2-dichloroethane 1,1-DCE 1,1-dichloroethene ft feet Geosyntec Geosyntec Consultants, Inc. GPL Groundwater Protection Level Cr(VI) hexavalent chromium LUST leaking underground storage tank mg/kg milligrams per kilogram mg/L milligrams per liter PCE tetrachloroethene PI preliminary investigation PVC polyvinyl chloride RCRA Resource Conservation and Recovery Act RI remedial investigation RSL Regional Screening Level Shop Vac Shop Vac Corporation SRL soil remediation level SVE soil-vapor extraction TCE trichloroethene TCA trichloroethane USEPA United States Environmental Protection Agency USFWS United States Fish and Wildlife Service UST underground storage tank VOCs volatile organic compounds VRP Voluntary Remediation Program WQARF Water Quality Assurance Revolving Fund

Lake Havasu Ave and Holly Ave WQARF Site Draft Remedial Investigation Report 1 January 2020

1. INTRODUCTION

Geosyntec Consultants, Inc. (Geosyntec) has prepared this Draft Remedial Investigation (RI) Report for the Lake Havasu Avenue and Holly Avenue Water Quality Assurance Revolving Fund (WQARF) Site (the Site) located in Lake Havasu City (the City), Arizona (Figures 1 and 2). Geosyntec was contracted by Arizona Department of Environmental Quality (ADEQ) to prepare this report under an Arizona Superfund Response Action Contract.

The current boundary of the Site is defined by the known limits of the combined plumes for Site-related contaminants of concern (COCs). Site-related COCs include the chlorinated volatile organic compounds (VOCs) tetrachloroethene (PCE), trichloroethene (TCE), and their degradation products, as well as benzene, nitrate and chromium. 1,2-dichloroethane (1,2-DCA) and 1,1- dichloroethene (1,1-DCE) have also been detected over Aquifer Water Quality Standards (AWQS) periodically at the Site. The combined COC plume is bounded to the north by Centers Avenue, to the south by Holly Avenue, to the east by San Juan Drive, and to the west by London Bridge Avenue. The plume boundaries are depicted on the Site Plan (Figure 2).

The former McCulloch facility at 900 Lake Havasu Avenue and the former Kiowa Ponds, located approximately 600 feet (ft) to the west (Figure 2), have been the subject of numerous investigations dating back to 1983, focusing on soil, soil-vapor, and groundwater contamination. The preliminary investigation (PI) stage of the WQARF investigation was initiated in 2015. The Site was placed on the WQARF Registry on 4 December 2017 with an Eligibility and Evaluation Score of 50 out of 120 (ADEQ, 2018). In February 2018, ADEQ sent out notices in accordance with Arizona Revised Statute (A.R.S.) §49-287.03 initiating the RI for the Site.

The RI activities completed by Geosyntec include: drilling and sampling of five transect borings along Arizona State Route 95 (SR-95); installation of seven groundwater monitor wells (Table 1); groundwater sampling; and additional characterization of soil and soil-vapor impacts at the Site. This report describes the results of RI activities conducted by Geosyntec from April 2018 through November 2019. Historical information presented herein is a summary of investigative data made available to Geosyntec that was collected by previous consultants.

1.1. Remedial Investigation Objectives

This RI Report is prepared in accordance with A.R.S. §49-287.03 and Arizona Administrative Code (A.A.C.) R18-16-406. This RI summarizes field investigations in


accordance with A.A.C. R18-16-406(C). Additionally, a Site-specific risk evaluation was conducted pursuant to A.A.C. R18-16-406(E).

1.2. Former Facility Operations

The Site is in an urban setting that includes a mixture of commercial and light industrial businesses, warehouses, and residential neighborhoods. In approximately 1960, a facility at 900 Lake Havasu Avenue was built and operated by Vernco Corporation as a manufacturing facility for the assembly of sewing machine motors and gyrocopters. In 1972 the McCulloch Corporation purchased the property, which eventually included manufacturing of small gasoline-powered equipment (Ecology and Environmental, Inc., 1991). Three buildings formerly housed the manufacturing operations that included die casting, machining, metal finishing, plating, and limited product testing. Known chemicals that were used at the facility included metals (chromium), acids and bases, cyanide compounds, oxidizers, adhesives, phenolic surfactants, and a variety of solvents (Ecology and Environmental, Inc., 1991). The historical layout of the McCulloch facility is presented on Figure 3.

According to a Resource Conservation and Recovery Act (RCRA) Preliminary Assessment (Ecology and Environment, Inc., 1991), the facility’s processes and waste management included aluminum and manganese dye casting, machining chrome and copper plating, dry powder painting, heat treating, assembly, and returned product conditioning. Waste streams included chromium, 1,1,1-trichloroethane (TCA), waste paint filters and bags, waste paint, polyvinyl chloride (PVC) liners, methyl ethyl ketone, cyanide, trichlorotrifluoroethane (Freon 113), baghouse dust, wastewater and waste oil. Chromium waste from plating activities was treated in two sludge ponds prior to 1984. After 1984, chromium waste was filter-pressed to form cake. Cake was stored in roll-off bins and shipped off-site, whereas the water extracted in the process was treated and discharged to the Kiowa Ponds. Waste TCA, paint, rags, filters, PVC liners, and methyl ethyl ketone were stored in 55-gallon drums and shipped off-site for disposal.

The City constructed two infiltration ponds (the former Kiowa Ponds) to the west of the former McCulloch facility (Ecology and Environment, Inc., 1991 and 2000). The ponds were a two-cell, unlined percolation and evaporation lagoon system for wastewater disposal exclusively from the former McCulloch’s manufacturing activities. According to the Waste Storage and Handling Closure Plan (IT Envrioscience, 1983) completed on behalf of the McCulloch facility, industrial sewage was treated on-site through a three-stage clarifier, and the resulting industrial wastewater was discharged at the Kiowa Ponds. Pond A was constructed in 1971 to dispose of pre-treated industrial wastes, while a secondary wastewater Pond B was later constructed in 1978. Approximately 230,000


gallons of wastewater a day were reportedly discharged to the ponds (Ecology and Environment, Inc., 1991). An oil/water separator was installed in 1991 and received processed coolants, oils, metals, sludge, and other constituents (Ecology and Environment, Inc., 1991). According to the Kiowa Ponds Brownfield Target Site Assessment Report (Ecology and Environment, Inc., 2000), while in operation, the Kiowa Ponds received various treated waste streams from the Site, including:

• Overflow from a cooling water cistern;

• Effluent from the die cast clarifier;

• Discharge from floor drains of the machining and die cast floors;

• Effluent from the oil/water separator;

• Waste phosphoric acid cleaner bath;

• Effluent from the industrial waste treatment system in the plating basement;

• Overflow from the chrome plating sludge beds; and

• Chrome sludge press filter water processed in the industrial plating waste treatment system.

If the ponds reached capacity, treated effluent from the Site overflowed via a discharge pipe from the Kiowa ponds into the Kiowa Wash located directly north of the Kiowa Ponds. In 1995, the former McCulloch facility was connected to the City sewer system and the ponds ceased receiving effluent from the former McCulloch facility (Ecology and Environment, Inc., 2000).

Three underground storage tanks (USTs) were also present at the Site: two 10,000-gallon fiberglass tanks that stored fuel and one 1,000-gallon tank used for waste oil (Ecology and Environment, Inc., 1991).

According to the Preliminary Assessment (Ecology and Environmental, Inc., 1991), in 1973 the McCulloch Corporation was purchased by Black and Decker Manufacturing Company, and then was sold to a group of investors in 1983. In 1990, McCulloch was sold again to Shop Vac Corporation (Shop Vac). The present owner of the property is Palo Verde Investments, L.L.C. (Palo Verde), who purchased the property in 2002 from the McCulloch Liquidating Trust through the McCulloch Corporation bankruptcy initiated in 1999 (Ninyo & Moore, 2014a). Currently, Palo Verde leases the property for offices and temporary warehousing of consumer products, excluding the former plating shop area, which is vacant.


2. PHYSICAL SETTING

The following subsections provide the physical setting of the Site, including topography, climate, and surface water.

2.1. Topography

The Site is situated within Arizona’s Basin and Range physiographic province (United States Geological Survey, 1996), which is comprised of broad alluvial basins dissected by northwest-southeast trending block-faulted highlands. These basins are filled with Holocene age alluvial sediments that are primarily derived from the weathering of these adjacent highlands, and consist primarily of fine-grained, well-sorted sediments, but also include coarse to gravelly channel, terrace, and alluvial fan deposits at depth (Rascona, 2005).

The City is located along Lake Havasu, a reservoir formed by Parker Dam on the Colorado River. The area is highly undulating with hills and major/minor washes. Most of the area is sparsely vegetated by typical native desert plants. Major drainage ways extend from the mountains to the east and traverse the City, depositing runoff water into the Colorado River to the west. Small drainage channels and off-road vehicular disturbances dissect portions of the shoreline with flats covered by desert and sparse vegetation. Freshwater marshes and aquatic habitats occur within a narrow (i.e., 10 to 25 ft) stretch of exposed beach in the winter months, when the water level of Lake Havasu decreases by approximately three to five feet (The City, 2016).

Ground surface elevations of monitor wells at the Site range from approximately 629 ft above mean sea level (amsl) in the east portion of the Site at MW-7 to approximately 479 ft amsl to the west at LHH-05 (Figure 2). Well measuring point elevations are included in Table 1.

2.2. Climate

The Site is located within the semiarid climate of the Sonoran Desert. The region experiences hot summers and mild winters. The average high temperature in July, typically the hottest month, is 98.5 degrees Fahrenheit. The average low temperature in December, typically the coolest month, is 54.5 degrees Fahrenheit. Annual precipitation is low, averaging 2.9 inches (Arizona Water, 2019).


2.3. Surface Water

The nearest man-made surface water body is Lake Havasu, approximately one mile to the west of the former McCulloch facility. The closest natural surface water body to the Site is the Colorado River, which feeds into Lake Havasu from the north. The Kiowa Wash, an intermittent wash located directly north and adjacent to the former McCulloch facility and former Kiowa Ponds, drains into Lake Havasu to the west.

2.4. Geology

The following subsections describe the geological setting of the Site.

2.4.1. Regional Geology

The City is located in the Chemehuevi Valley, in the Basin and Range Physiographic Province, and is bounded on the east by the Mojave Mountains and on the west by the Colorado River and Lake Havasu. The Mojave Mountains are mostly composed of Middle Miocene to Oligocene volcanic and sedimentary rocks, Early Proterozoic metamorphic rocks, and Early Proterozoic granitic rocks (Arizona Geologic Survey, 2019). The valley is characterized by quaternary surficial deposits consisting of alluvial fans. Dry washes originating in the Mojave Mountains and trending southwest to the Colorado River cut across these quaternary deposits, resulting in a series of river terraces cut into the alluvial deposits present on the valley slopes. The alluvial deposits consist of interbedded stream and basin-fill sediments comprised of sand, silt, gravel, and cobbles. Surficial soil in the area consists primarily of the Carrizo family very gravelly loamy sand and Coolidge-Denure complex, according to the National Resources Conservation Service (United States Department of Agriculture, 2018).

2.4.2. Site Geology

The Site is underlain by relatively thin deposits of unconsolidated recent alluvium and older basin-fill deposits of sand, gravel, cobbles, and soil, with minor clay and local caliche horizons. Beneath the alluvium and basin-fill deposits is the older, more consolidated Bouse Formation, which is encountered at approximately 300 to 1,110 ft amsl in the Chemehuevi Valley (Pearthee and House, 2014) and compromised chiefly of fine-grained marine and brackish water limestones, along with siltstones and claystones.

Numerous dry washes, including the Kiowa Wash located immediately north of the McCulloch property, cut through the river terraces to the Lake Havasu. The layers of gravels and cobbles, interspersed with discontinuous lenses of fine-grained sedimentary sand and silt, tend to dip to the west.


Lithological logs of continuous-core borings from the Site show very heterogeneous material, typical of subsurface soils observed in alluvial fans. Geosyntec’s digitized boring logs for borings and wells SB-01 through SB-26, B-01 through B-05, Transect-B-1 through B-5, LHC-13, and LHH-01 through LHH-07 (Figure 2) are presented in Appendix A. In general, the subsurface is comprised of mostly interbedded sand, gravelly sand, silty sand, and clayey sand, with minor layers of fine-grained materials, such as silt and clay.

The lithology at the western portion Site has been assessed by the City to a total depth of approximately 517 ft below ground surface (bgs) in production well LHC-13. According to the City’s production well boring logs, interbedded sands and conglomerates with traces of fines were encountered up to a depth of 303 ft bgs. Below 303 ft bgs, bedrock was encountered consisting of an undescribed “rock” between 303 and 337 ft bgs, “fractured rock” from 337 and 372 ft bgs, and “granite” below 372 ft bgs.

2.5. Hydrogeology

The Lake Havasu - Chemehuevi Valley area is designated by the Arizona Department of Water Resources (ADWR) to be within the Lake Havasu Basin of the Upper Colorado River Planning Area.

Lake Havasu is a large reservoir formed on the Colorado River by Parker Dam. Groundwater occurs in the interbedded gravel and sand basin-fill sediments underlying the Site. According to ADWR, most of the wells in the basin penetrate the upper 100-200 ft of the basin-fill, where groundwater is hydraulically connected to the Colorado River. According to ADWR, regional groundwater in the Lake Havasu Basin flows from north to south (ADWR, 2019).

City production wells (LHC-10, LHC-11, LHC-12, and LHC-13) are located approximately 0.7 miles west of the former McCulloch facility (Figure 2), in what is referred to by the City as the north wellfield. Since 2004, production from these wells has discontinued, replaced by City wells located approximately 2.5 miles south of the Site. The City production wells located west of the Site are occasionally operated to maintain pump performance. Shifting water production to the southern wells, and discontinuing pumping from the north wellfield, has contributed to an overall increase in groundwater elevations (Table 2) at the Site.

Based on the April 2019 depth-to-water measurements, groundwater elevations at the Site ranged from approximately 454 ft amsl in LHH-05 (in the western portion of the Site) to approximately 465 ft amsl in LHH-06 (in the central-eastern portion of the Site; Figure3).


Groundwater elevations from 2014 and 2019 are shown in Table 2 and on Figures 4a through 4c. Based on groundwater data collected at KPMW-1, groundwater elevations in April 2019 are approximately 3.5 ft higher than groundwater elevations measured during March 2014 and approximately 25 ft higher than groundwater elevations measured prior to the City ceasing primary use of the down gradient production wells in 2004. During 2019, the general direction of groundwater flow is southwest with a hydraulic gradient of approximately 0.004 ft per foot.

2.6. Ecology

The Site is located in an urban setting that provides low-quality habitat for native terrestrial or aquatic biota. Given the presence of roads and extensive man-made structures, it is likely that the natural vegetation, soils, and hydrology have been altered by filling, grading, and improvement activities in the past. There is a low potential for native terrestrial or aquatic biota to occur within the Site. According to Google Maps, the closest large, natural open spaces are the undeveloped land to the west of Lake Havasu or the Mojave Mountain Range to the north and east of the City. Native aquatic species may also occur in Lake Havasu.

Based on information provided through the United States Fish and Wildlife Service online Information, Planning and Conservation System and by the Ecological Services Program, there are seven federally listed endangered species with the potential to occur on lands within Mohave County, including:

• California Least Tern (Sterna antillarum browni);

• Southwestern Willow Flycatcher (Empidonax traillii extimus);

• Yellow-billed Cuckoo (Coccyzus americanus);

• Yuma Clapper Rail (Rallus longirostris yumanensis);

• Northern Mexican Gartersnake (Thamnophis eques megalops);

• Bonytail Chub (Gila elegans); and

• Razorback Sucker (Xyrauchen texanus) (USFWS, 2019).

The Site and immediate vicinity do not contain suitable habitat for these species since the area is mostly developed as residential and industrial space. However, these species may be present along Lake Havasu, where a more likely habitat is present.


3. HISTORICAL INVESTIGATIONS

This section presents a summary of documentation and investigations associated with the Site prior to this RI Report. A summary of available historical data is presented on Tables 3 and 4.

3.1. 1975 to 1995 – Former McCulloch Facility Wastewater Effluent Results

According to the Kiowa Ponds Brownfield Targeted Site Assessment Report (Ecology and Environment, Inc., 2000), completed on behalf of the United States Environmental Protection Agency (USEPA), data provided by the City indicates that wastewater samples collected from the former McCulloch facility plant from 1975 to 1995 had concentrations of chromium (0.422 milligrams per liter [mg/L]), nitrate (279 mg/L), fluoride (95 mg/L), and TCE (2.0 mg/L) that exceeded their respective AWQS of 0.1 mg/L for chromium, 10 mg/L for nitrate, 4.0 mg/L for fluoride, and 0.005 mg/L for TCE. 1,1,1-TCA (0.0036 mg/L) and chloroform (3.0 mg/L) were also detected but in concentrations less than their respective AWQS. Lead, styrene, toluene, cyanide, phenols, and 1-ethoxyethanol acetate were also detected in the waste stream and effluent discharge to the Kiowa Ponds, however the concentrations were not reported (Ecology and Environment, Inc., 2000).

3.2. 1983 – Former McCulloch Facility Sludge Sump Investigations and Soil Removal

Two below-ground sludge sumps were removed by Western Technologies, Inc. Approximately 1,473,000 pounds of hazardous waste were excavated and disposed of at the BKK Corporation landfill in West Covina, California. Based on review of waste manifests of excavated soil disposed from the Site (Western Technologies, Inc., 1984), concentrations of lead, total chromium, hexavalent chromium (Cr(VI)), barium, nickel, and cyanide were detected in the excavated soil below regularly limits, however the excavated soil was disposed of as listed hazardous waste based on waste category F006 (Electroplating Waste).

A report for a certificate of partial closure was submitted to the Arizona Department of Health Services (ADHS) by Western Technologies, Inc. on behalf of McCulloch Corporation indicating that contaminated soil was excavated from the two former below-ground sludge sumps. The sump walls were a porous concrete with a pea gravel base that allowed the sump to drain. Detectable concentrations of lead, chromium, barium, nickel, and cyanide were detected in the soils beneath the sump. The area was closed by ADHS in 1984 (Western Technologies, Inc., 1984).


3.3. 1990 – Former McCulloch Facility Chrome Plating Area Soil Removal

Approximately 20,000 pounds of soil contaminated with chromic acid was excavated from under the floor of the plating operation (Ecology and Environment, Inc., 1991). The chromium concentrations and the disposal location of this soil were not reported by Ecology and Environment, Inc. The soil removal was conducted by McCulloch Corporation after the discovery of a leaking floor drain. The associated Confirmation Sampling Program Report prepared by a consultant for McCulloch Corporation also identified an area of oil-impacted soil in the northwest corner of the property (Ecology and Environment, Inc., 1991).

3.4. 1991 – Former McCulloch Facility Preliminary Assessment and Facility Inspection

Ecology and Environment, Inc. conducted a RCRA Preliminary Assessment at the Site (Ecology and Environment, Inc., 1991) on behalf of the USEPA. The report details the general facility’s former processes and waste management practices. According to the Comprehensive Environmental Response, Compensation, and Liability Act Hazard Ranking System, this report indicates that the Site had a moderate waste quantity, a high potential for a release to groundwater, a potential to release to surface water and air, and a low potential for soil exposure. Therefore, the USEPA recommended the Site be deferred to another authority under RCRA (Ecology and Environment, Inc., 1991).

A crack in the concrete containment floor in the plating shop was also discovered in 1991 during a routine inspection (SA&B, 1996a).

3.5. 1992 – Former McCulloch Facility Sub-Basement Soil Investigation

STC Environmental, Inc. on behalf of the McCulloch Corporation advanced 15 boreholes near construction joints, cracks in concrete, eroded concrete, and near sumps in the basement on Site. Soil samples were collected from near surface to approximately 43 inches below grade. Laboratory analyses indicated that a maximum total chromium concentration of 40,700 milligrams per kilogram (mg/kg) was detected (in BH 5-1) at the surface in the scrubber slab area. This was above the 4,500 mg/kg total chromium cleanup standard of the time. Additionally, barium, total cyanide, lead, and zinc were reported above their laboratory reporting limits but below state action levels and hazardous waste criteria (STC Environmental, Inc., 1992; ADEQ, 2000; URS, 2015).


3.6. 1992 – Former McCulloch Facility Underground Storage Tank Removal

Two 10,000-gallon unleaded gasoline USTs were removed from the Site in December 1992 by USTank Management on behalf of the McCulloch Corporation (USTank Management, 1992; Figure 3). The USTs were identified as Tank #1 and Tank #2. According to USTank Management, Tank #2 exhibited evidence of a release, likely from a turbine pump connection at the tank. Hand auger samples were collected from the bottom of the excavations, two to three feet below the bottom of the tanks. One of four soil samples was observed to have dark staining and moderate gasoline odors. Laboratory analysis of this sample, collected at 12 ft bgs (USTank Management, 1992), indicated a concentration of 160 mg/kg of total petroleum hydrocarbons (exceeding the applicable 1992 ADEQ Suggested Soil Cleanup Level at the time of 100 mg/kg). In addition, 0.460 mg/kg of toluene, 0.210 mg/kg of ethylbenzene, and 7.1 mg/kg of total xylenes were also reported. A photoionization detector (PID) reading from this sample indicated 608 parts per million by volume (ppmv) total VOCs as isobutylene (ISO). USTank Management concluded that Tank #2 failed the regulatory closure criteria for a UST and recommended that impacted soil be removed at least six-feet below the bottom of the tank, and that additional work was warranted for delineation of vertical and lateral extent of contamination.

3.7. 1993 – Former McCulloch Facility Leaking UST Characterization and Soil Removal

In January 1993, USTank Management completed a site characterization report of a gasoline release at the former UST Tank #2 (USTank Management, 1993). Based on this report, approximately 25 cubic yards of soil were removed from the UST excavation, extending the excavation bottom to approximately 21 feet bgs (8 feet below UST bottom). PID measurements from two excavation bottom samples indicated approximately 300 to 400 ppmv total VOCs as ISO. USTank Management concluded, based on professional experience, that PID measurements above 300 ppmv would result in VOC concentrations above the ADEQ action levels, and therefore did not submit any soil samples to a laboratory. The excavation was backfilled with fill materials.

3.8. 1994 – Former McCulloch Facility Leaking UST Phase II Report

Envirotec Solutions (Envirotec) completed an Environmental Property Evaluation and Remedial Program Phase II report on behalf of the McCulloch Corporation (Envirotec, 1994). The purpose of the study was to present a general review of past and current land uses; evaluate the potential for site soil and/or groundwater contamination resulting from the past use of USTs; provide findings related to contaminations resulting from the UST;


and provide recommendations for additional environmental investigation. Envirotec advanced thirteen soil borings. Based on PID measurements and laboratory results, Envirotec determined that contamination extended beyond 160 ft bgs (see “D&M 1999a, Corrective Action Plan, McCulloch Corporation Facility, 900 Lake Havasu North Lake Havasu City, Arizona” in Appendix B for conceptual figure). Laboratory results for soil samples indicated TPH at a concentration of 1,500 mg/kg in soil boring G at 160 ft bgs, consistent with notes from the lithological log for boring G that described a “smell of contamination” at 160 to 161 ft bgs. Laboratory results for a soil sample collected at 162 to 163 ft bgs indicated 13,000 µg/kg benzene, 5,000 µg/kg ethylbenzene, 32,000 µg/kg toluene, 860,000 µg/kg total xylenes, and 5,000 µg/kg methyl tert-butyl ether (MTBE). The reported benzene and total xylenes concentrations are above the current Arizona non-residential Soil Remediation Level (SRL) of 1,400 µg/kg and 420,000 µg/kg, respectively. As a result of this investigation, Envirotec recommended installation of a soil vapor extraction system for remediation of the Tank #2 area, and three downgradient groundwater monitoring wells.

3.9. 1995 – Former McCulloch Facility Additional Plating Shop Area Investigation; Kiowa Pond Sludge Sampling

In response to a Consent Order issued by ADEQ in 1995, SA&B on behalf of the McCulloch Corporation performed assessment of the extent of chromium contamination in soils beneath the plating shop. Activities included drilling 16 soil borings and installing four groundwater monitor wells (MW-1, MW-2, MW-3, and MW-5; Figure 2). Chromium was detected in soil samples at vertical depths of up to 165 ft bgs, the approximate depth to groundwater at the time. Two sets of samples were collected during September and October 1995 and were analyzed for selected metals, including chromium and VOCs. Chromium was detected above method detection limits only in wells MW-1 and MW-3 at concentrations of 0.005 mg/L and at 0.016 mg/L, respectively.

Cr(VI) was analyzed only in samples collected during the October sampling event. Cr(VI) was detected above method detection limits only in well MW-3 at a concentration of 0.05 mg/L. TCE was detected at MW-1, at a concentration of 5.6 micrograms per liter (µg/L), exceeding the AWQS. TCE was not detected in any other wells. PCE was detected at MW-1, at a concentration of 1.1 µg/L, below the AWQS. PCE was not detected in any other well. 1,1-Dichloroethene (1,1-DCE) was detected at MW-1 and MW-2, at the concentration of 5.0 µg/L and 1.3 µg/L, respectively, below the AWQS. 1,1-DCE was not detected in any other well.

Discharge to the Kiowa Ponds also ceased in 1995, after which the sludge from the ponds was sampled by the City in 1996 and 1997 and analyzed for TCLP metals, VOCs, and


semi-VOCs (Ecology and Environment, Inc., 2000). Results were reported to be below the maximum concentrations for the toxicity characteristics listed under 40 CFR §261.25 Table 1. These samples were not reported to have been analyzed for total metals, therefore cannot be screened against SRLs and/or Groundwater Protection Levels (GPLs).

3.10. 1996 to 1997 –Well Installations and Groundwater Investigation

In 1996 a Work Plan prepared by SA&B (SA&B, 1996b) on behalf of the McCulloch Corporation presented the planned installations of monitor wells MW-6 through MW-8, and installation of one angled boring (SB-14A) below the plating shop area. This work plan states that monitor well MW-5 had been previously installed specifically to investigate potential groundwater gasoline impacts from leaking USTs, and that elevated concentrations of benzene, ethylbenzene, toluene and xylenes (BTEX) constituents were reported in groundwater samples. SA&B summarized the implementation of this work in a report (SA&B, 1996c). After installation of the proposed monitor wells and angled borings (See “Historical Soil Boring Locations from STC and SA&B at the Former McCulloch Facility” in Appendix B), groundwater samples were collected during three events, in January, April and September 1996. Multiple COCs were detected above the AWQS, including TCE (29 µg/L), benzene (24,000 µg/L), and chromium (0.22 mg/L). In addition, soil boring SB-14A was advanced at a 54 degree angle below the plating shop area, targeting the 155 to 165 feet deep soil horizon. The boring was advanced to a total of 210 linear feet. Hexavalent chromium concentrations exceeded the current non-residential SRL of 65 mg/kg in 12 out of 18 samples collected, with the highest detected concentration of 540 mg/kg collected at a depth of 84.9 ft bgs when factoring in the angle of the boring. A groundwater sample collected at the bottom of the boring resulted in a hexavalent chromium concentration of 360 mg/L, exceeding the AWQS for chromium of 0.1 mg/L.

Characterization of a gasoline UST was conducted by SA&B during March 1997 (Dames & Moore [D&M], 1999a). This included sampling of four soil borings to define the lateral extent of hydrocarbon contamination in soil. According to D&M’s summary of the work, BTEX and total petroleum hydrocarbons were detected in borehole SB-17 (located just downgradient, and to the west of the former UST) at concentrations exceeding the applicable SRLs at the time of the investigation.

According to SA&B (SA&B, 1997), monitor wells MW-9, MW-10, and MW-11 were installed in April 1997 pursuant to the UST investigation (Figure 2). Also in April and May 1997, additional groundwater monitor wells MW-12 and MW-13 were installed to further characterize chlorinated solvents and potential Cr(VI) groundwater impacts (SA&B, 1997). During the reported monitoring period, spanning from January 1996


through August 1997, SA&B reported multiple COC exceedances of AWQS, including PCE up to 14.0 µg/L in MW-7, TCE up to 90 µg/L in MW-13, and chromium up to 0.648 mg/L in MW-13.

3.11. 1998 – Sludge Removal from Kiowa Ponds; Former McCulloch Facility Soil-Gas Survey, and Additional Monitoring Well Installations

Approximately 4,600 cubic yards of sludge were removed from the Kiowa Ponds by a contractor operating on behalf of the City. A sampling plan was produced by a consultant for the City; However, no sampling occurred on behalf of the City at the Kiowa Ponds following publication of this plan (Ecology and Environment, Inc., 2000).

SA&B (W.L. Gore & Associates, Inc., 1998) on behalf of McCulloch Corporation conducted a passive soil-vapor survey to evaluate detected mass levels present in vapor phase of select VOCs (TCE, PCE, 1,1,1-TCA, and Freon-113). The report indicated that distinct soil gas plumes were evident for these compounds, with elevated levels of chlorinated compounds and Freon 113 in areas within and adjacent to the Machine Shop, and near MW-6 (Figure 3). 1,1-TCA was also detected near MW-7.

According to ADWR records, additional groundwater monitor wells MW-15, 16, 17 and 19 were installed by SA&B (Figure 2). These wells were installed to further characterize groundwater contamination. Information on the installation or status of monitor well MW-14 was not found.

3.12. 1999 – Former McCulloch Facility Leaking UST Corrective Action Plan; Soil and Soil-Gas Survey

On behalf of Shop Vac, a Corrective Action Plan (CAP) was submitted to ADEQ by D&M to address hydrocarbon impacted soil and groundwater associated with the LUST case (D&M, 1999a). In the CAP report, D&M presented an interpretation of historical data, including a cross section depicting the extent of the plume (Appendix B), a feasibility analysis of multiple potential remediation approaches for the gasoline release resulting from the UST, a remedial alternative analysis, and a selected remedial alternative. The selected alternative for the remediation of the gasoline release was installation of source are soil vapor extraction (SVE) and air sparging (AS) system. The ADEQ UST Section approved the CAP in late 1999 (ADEQ, 2000).

D&M on behalf of Shop Vac conducted a soil-vapor survey and soil sampling “to further evaluate the nature and extent of accidental leakage and/or spillage of certain VOCs to soil underlying the facility” (D&M, 1999b). According to the report, soil-vapor results confirmed that PCE, TCE, 1,1-TCA, and Freon 113 contamination was present beneath


the Warehouse and Assembly Building (Figure 3). Additionally, PCE concentrations detected in soil samples collected from beneath the northeast corner of the warehouse and assembly building exceeded the minimum GPL of 1.3 mg/kg, at a concentration of 37.0 mg/kg in sample location SS-ST-7 at 15 ft, located near the northeast corner of the Warehouse and Assembly Building.

3.13. 2000 – Kiowa Ponds Soil Investigation; Former McCulloch Facility Additional Well Installation

In 2000, a soil investigation was conducted at the Kiowa Ponds by Ecology and Environmental, Inc. on behalf of USEPA to analyze for metals, VOCs and semi-volatile organic compounds (SVOCs) (Ecology and Environment, Inc., 2000). No VOCs or SVOCs were detected above method reporting limits. Results of the investigation indicate metal concentrations below the SRLs; however, three soil sample locations (LHH A 5 0, LH-A-6-0, and LH-A-10-0) collected from the surface of Pond A exceeded the minimum GPL for chromium at concentrations of 736 mg/kg, 805 mg/kg, and 1,260 mg/kg, respectively. All other metals were not detected above the SRLs and minimum GPLs. Six surface soil samples from Pond A were also analyzed for TCLP metals, and an alternative GPL for chromium of 383,082 mg/kg was calculated from these results. The ponds were partially backfilled with clean soil.

During the investigation of the Kiowa Ponds, six samples were collected in the Kiowa Wash, three down-wash from the outfall from Pond A and three down-wash from the outfall prom Pond B (Ecology and Environment, Inc., 2000). The samples were analyzed for metals and SVOCs. No SVOC was detected above reporting limits. Chromium was detected at a maximum of 33.5 mg/kg.

According to ADWR records, an additional groundwater monitor well MW-20 was installed by D&M to further characterize groundwater contamination (Figure 2).

3.14. 2001 – Kiowa Pond APP Closure and Well Installation; Former McCulloch Facility Area Remedial Action and Pilot Test Evaluation

In 2001, a Final Aquifer Protection Permit (APP) was issued for closure of the Kiowa Ponds (Ecology and Environment, Inc., 2000; ADEQ, 2001a). The APP required post-closure groundwater monitoring to demonstrate that AWQSs have not been exceeded. Compliance wells KPMW-1, KPMW-2 and KPMW-3 were installed in response to ADEQ’s request for three years of post-closure quarterly monitoring (ADEQ, 2001a and Figure 2).


The ADEQ Remedial Investigation Hydrology Unit provided a document review summary and remedial options for chromium remediation in soil and groundwater in the area near the former McCulloch facility to the ADEQ Hazardous Waste Section (ADEQ, 2001b). The five general remedial approaches presented were: isolation; immobilization; toxicity reduction; physical separation; and extraction. A remedial option was not recommended at the time due to data gaps: incomplete delineation of impacts from chromium and other potential contaminants (including cyanide) and soil physical and chemical properties, including mineralogy, organic content, pH, and redox; determination of other potential sources (i.e. sludge beds) of chromium. These were requested to be investigated further prior to preparation of a corrective action (ADEQ, 2001a).

URS on behalf of Shop Vac installed MW-21 and collected soil and groundwater samples during drilling. Chromium had notably stained the soil core from 200 to 207 ft bgs and field screenings showed chromium impacts were greatest from approximately 230 to 240 ft bgs (URS, 2001b). An aquifer test was conducted by URS. Monitor well MW-21 was used as the pumping well and MW-15 and MW-6 were used as observation wells. The aquifer test resulted in time-drawdown transmissivity values ranging from 1,500 to 2,095 gallons per day per foot (gpd/ft) in MW-21, and 1,500 to 8,100 gpd/ft in observation wells. The estimated values for storativity ranged from 0.00005 to 0.0004. Aquifer parameters estimated using a distance-drawdown curve resulted in a transmissivity value of 1,100 gpd/ft and storativity of 1.6 x 10-2. According to URS, results reflected the heterogeneity of the alluvial fan sediments, with coarser grained sediments providing preferential pathways for groundwater flow and contaminant transport. URS determined that results also indicate that vertical hydraulic conductivity is substantially lower than horizontal hydraulic conductivity. Groundwater samples were collected from dedicated sampling ports at the wellheads (URS, 2001c), with results exceeding their corresponding AWQSs for chromium (ranging between 240 to 290 mg/L), nitrate (ranging between 180 to 220 mg/L), and TCE (ranging between 22 to 24 µg/L).

On behalf of Shop Vac, URS prepared a geochemical fixation bench scale study and pilot test work plan to evaluate natural attenuation versus in situ chemical fixation with calcium polysulfide (CPS) to remediate impacted soil and groundwater via reduction of Cr(VI) to trivalent chromium. Well MW-15 was proposed for the injections, and MW-1, MW-6, MW-8, MW-19, and MW-21 were proposed with MW-15 to monitor conditions before and after the pilot test (URS, 2001a). URS also evaluated geochemical conditions, including total and dissolved metals, major cations and anions, total dissolved and suspended solids, nitrates, pH, temperature, conductivity, dissolved oxygen, oxidation-reduction potential, alkalinity, cation exchange capacity, and total organic carbon in soil and/or groundwater. Some data suggest that the original chromium plume was characterized by high total dissolved solids and nitrate and was a more calcium-


bicarbonate type of water. Additional general chemistry analysis was recommended to characterize the plume and identify important groundwater indicators (URS, 2001d).

3.15. 2001 to 2002 – Former McCulloch Facility Leaking UST AS/SVE system

In response to the CAP to address VOC and total petroleum hydrocarbon impacts associated with the UST release (ADEQ, 2000), a combined AS/SVE remediation system was installed at the Site. The system consisted of nested wells including five AS wells screened between 180 and 185 ft bgs, and ten vapor extraction wells installed at various depths. Startup of the SVE system was initiated in April 2001 and in October 2001, operation of the combined AS/SVE system began. In July 2002, the system was shut down for rebound monitoring. As of late 2002, the system was offline, but the equipment was maintained.

The last reported sample results were summarized in a Transition to Monitored Natural Attenuation memorandum (URS, 2002d). According to URS, the AS/SVE system had reached asymptotic levels. Groundwater results presented by URS (URS, 2002d) indicate that at the time of the system shutdown MW-05 (located just downgradient of the UST source area) exceeded the AWQS for benzine of 5 µg/L at a concentration of 500 µg/L. All other monitor wells were below AWQS for benzene; however, URS estimated that the average benzene concentration remaining in place across the original boundary of the benzene plume would be approximately 151 µg/L. Justification for termination of the AS system was based on a 90 percent mass removal based on initial estimates in the CAP, and implementation of a monitored natural attenuation program consisting of quarterly groundwater sampling of select wells.

URS estimated approximately 24,267 pounds of total volatile fuel hydrocarbons (approximately 60% of the 41,000 pounds estimated in the CAP) were removed during the SVE operation period from April 2001 to August 2002 (URS, 2002d). According to URS, during this period influent total volatile fuel hydrocarbon concentrations dropped from 9,800 ppm volume (ppmv) to 290 ppmv. After rebound, URS measured benzene concentrations in nine out of ten SVE wells below 100 ppbv, except for SVE-2B which measured 940 ppmv of benzene. Based on these results, and an estimated 60% mass removal, URS recommended cessation of the SVE system and transition to a monitored natural attenuation program consisting of quarterly soil gas sampling of the vadose zone.

3.16. 2002 - Former McCulloch Facility Pilot Test

URS prepared a work plan on behalf of Shop Vac (URS, 2002a) and then performed the geochemical fixation pilot test using well MW-15 and five observation wells. According to URS, results of the test demonstrate that site conditions were favorable for in situ


geochemical fixation with CPS to reduce Cr(VI) without detrimental impact to human health or the environmental (URS, 2002b; URS, 2015). URS also performed a vadose zone pilot test, which reportedly demonstrates the effectiveness of surface infiltration of CPS through a trench system to simulate the natural pathways taken by historical releases of chromium. According to URS, this data provides a better basis for estimating the time for impact to groundwater via surface infiltration (estimated to be 40 to 80 days) as well as the fraction of total chromium in the subsurface in the hexavalent state (estimated to be approximately 50%) (URS, 2002c).

In December 2002, URS prepared a draft work plan for remediation of chromium-impacted media (URS, 2002e). The scope consisted of installing monitor wells, demolishing and disposing of impacted concrete, applying the reducing agent, and monitoring. An alternative GPL was calculated by URS according to ADEQ guidance (ADEQ, 1996) using site-specific data previously obtained during the vadose zone remedy pilot test (URS, 2002c). According to URS, the alternative GPL calculation indicates that a soil concentration of 1,494 mg/kg total chromium would be protective of groundwater. However, chromium concentrations in the groundwater after 2002 continued to persist above AWQS (Table 4a).

3.17. 2003 - Former McCulloch Facility Phase II Pilot Test

In 2003, URS on behalf of Shop Vac performed a Phase II chromium mitigation, consisting of applying CPS solution into shallow trenches (URS, 2015). The scope of work also included the installation of two groundwater monitor wells, MW-23 and MW-24 (URS, 2003b and Figure 2).

Soil samples were collected in the soil column during installation of MW-23, which was installed as an angled boring to reach depths below the former plating area. Chromium was detected in all soil samples from near surface to approximately 145 ft, and that concentrations ranged between 16 mg/kg and 430 mg/kg (below the minimum GPL). Groundwater samples were collected from both MW-23 and MW-24 using a Simulprobe-type sampler to vertically profile groundwater. Because of field conditions, the sampler could not be advanced the minimum of 12 inches below the formation due to cobbly soil conditions. Chromium exceeded the AWQS in MW-23 at 196 ft (0.81 mg/L), 212 ft (1.3 mg/L), 222 ft (2.7 mg/L), and 234 ft (0.19 mg/L), respectively. Chromium exceeded the AWQS at MW-24, installed downgradient from the former plating area at 185 ft (23 mg/L), 195 ft (1.7 mg/L), and 222 ft (19 mg/L), respectively.

The chromium mitigation included the removal of impacted concrete and soil and the installation of a surface infiltration system with CPS. Concrete was removed from seven


trenches to expose impacted soil. Approximately 37.73 tons of hazardous concrete were disposed off-site. Approximately 10.62 tons of hazardous soil generated from MW-23 drill cuttings was also disposed off-site. After concrete removal, the exposed soil was mechanically tilled down to approximately 12 inches to soften the soil, the tilled soil was placed along the sidewalls of the trenches to create earthen berms within the trench network, and infiltration of the CPS mixture commenced. CPS at concentration of 29% was delivered without dilution through conveyance piping at each infiltration trench, chased by clean potable water to maintain hydraulic head. According to URS, this method would result in a “concentrated front by pushing CPS through the soil”. URS used 9,455 gallons of CPS and approximately 46,760 gallons of clean potable water during the 12-day application period.

As part of the pilot test, six lysimeters were installed approximately 8 to 14 feet below the source mitigation area. According to URS, lysimeters were utilized to collect pore water samples of leachable quantity of soil chromium contaminant from the vadose zone within the source mitigation area. Samples indicated a decrease in eight out of nine lysimeter. Chromium concentrations at the beginning of the pilot test ranged from 630 mg/L to 4,100 mg/L. Chromium concentrations at day 416 ranged from 0.048 mg/L to 30 mg/L, except for one lysimeter which had an increase in concentration from 3,600 to 4,300 mg/L, above the minimum GPL for chromium (URS, 2015). According to URS, monitoring of oxidation reduction potential (ORP) and pH in monitor wells MW-23 and MW-24 indicated that CPS injection resulted in conversion of oxidizing to reducing conditions in MW-23, however, due to the limited volume of CPS, URS stipulated that the reducing capacity of the injection did not result in a significant drop in groundwater chromium concentration in the source area (URS, 2015).

URS developed a conceptual site model (CSM), including groundwater flow and chemical transport models, to evaluate changes in movement, predict migration of the plume, and determine placement of a proposed in situ reactive barrier and chemical injection points (URS, 2003a). URS also developed a regional groundwater flow model, which predicted changes in flow patterns with the City’s north production wellfield pumping turned off. Under the new pumping conditions, the hydraulic gradient and velocity were expected to decrease with proximity to the lake. Pumping of the City wells located south of the Site was expected to have a negligible influence on groundwater flow (URS, 2003c). The URS model predicted that with the City north wellfield off and the pumpage transferred to the City wells located south of the Site (See Figure 8 of Appendix E), the change in groundwater flow direction would likely be from northwest to southwest by approximately 30 degrees. URS also predicted that hydraulic gradient and groundwater velocity would decrease with proximity to the lake as a result of the north wellfield being shut off.


3.18. 2004 – Groundwater Sampling and Chromium Extent Investigation

In January 2004, URS on behalf of Shop Vac conducted a quarterly groundwater monitor event using the existing well network (MW-1 through MW-24, KPMW-1 through KPMW-3, and LHC-10 through LHC-18 (URS, 2004b). In January 2004, TCE exceeded the AWQS of 5 µg/L in MW-1, MW-6, MW-8, MW-11, MW-13, MW-15, and MW-21 at concentrations up to 64 µg/L. PCE exceeded the AWQS of 5 µg/L in MW-20 and KPMW-1 at concentrations up to 10 µg/L. Other chlorinated compounds, including 1,1-DCE and 1,2-DCA were also detected above AWQS. Total chromium exceeded the AWQS 0.1 mg/L in MW-1, MW-6, MW-8, MW-10, MW-13, MW-17, MW-21, MW-22 through MW-24 at concentrations up to 28 mg/L. VOCs and chromium were not detected exceeding the AWQSs in City production wells LHC-10 through LHC-18. Historical groundwater concentrations are available in Tables 4A – 4C.

In January 2004, URS also conducted a regional investigation of chromium in groundwater on behalf of Shop Vac (URS, 2004a). The report evaluated total chromium and Cr(VI) concentrations in samples collected during quarterly monitor events completed between 1999 and 2003. The samples were collected from City production wells in the north well field located west of the Site. URS concluded that statistical correlation of these constituents indicates that chromium in these wells is likely to be in the Cr(VI) form. Review of the data indicates that concentrations generally ranged between 0.01 and 0.037 mg/L, below the AWQS of 0.1 mg/L; however, two total chromium exceedances above the AWQS were detected in LHC-3 (0.12 mg/L in March 2000) and LHC-14 (0.11 mg/L in October 2002), and one Cr(VI) detection also exceeded the chromium AWQS in LHC-14 at a concentration of 0.11 mg/L on October 2002. URS also collected samples from off-site wells, including two active wells in the City south well field, three active and one inactive Arizona American Water Company (AAWC, currently known as EPCOR Water USA, Inc.) production wells located approximately one mile north of the Site, and three inactive City wells located south and east of the Site. According to URS, total dissolved chromium was detected in seven out nine wells sampled at concentrations ranging between 0.013 mg/L and 0.038 mg/L, below the AWQS. Cr(VI) was detected at six out of eight sampled locations (one well was not sampled for C(VI) analysis), resulting in concentrations ranging between 0.011 mg/L and 0.033 mg/L. URS concluded that total chromium and Cr(VI) occurs as a groundwater constituent as a result of natural geochemical processes; therefore, concentration in the LHC north wellfield were reportedly assumed to be within the range of naturally occurring Cr(VI). Additionally, Cr(VI) was detected in wells beyond the influence of the Site at concentrations reported to suggest background concentrations (URS, 2004a). Analysis of these data show that the percentage of chromium in hexavalent form is on


average higher in the north wellfield (102%) than the average of the percentage chromium in hexavalent form in the other wells in the area (86%).

In May 2004, URS prepared a draft work plan for a groundwater investigation and CPS treatability testing. The scope consisted of installation of up to four groundwater investigation wells (I-1, I-2, I-3 and I-4), additional potential wells (I-5, I-6, and I-7) to better define the vertical extent of contamination and possibly serve as future treatability test wells, aquifer testing of new wells, and CPS injection in treatability test wells (URS, 2004c). Records of injections through groundwater wells and aquifer testing were not found. Installation of the proposed wells (I-1 through I-6) was conducted between 2004 and 2006 as described below.

3.19. 2004 to 2007 – Kiowa Ponds APP Closure; Former McCulloch Facility Monitoring Well Installation

In October 2005, the Kiowa Ponds met the clean closure criteria under APP and were issued closure by ADEQ (ADEQ, 2005). The closure investigation and related activities are described in a report and an ADEQ APP memorandum (The City, 2005; ADEQ, 2005).

URS on behalf of Shop Vac installed six nested groundwater monitor wells (I-1 through I-6) to assess impacts to groundwater downgradient of the Site (URS, 2005; URS, 2007a; URS, 2007b; URS, 2007c and Figure 2). Groundwater vertical profile samples were collected to characterize the vertical distribution of chromium in groundwater. At I-1, laboratory samples resulted in dissolved chromium concentrations exceeding the AWQS of 0.1 mg/L at concentrations ranging from 0.43 mg/L to 40 mg/L. The highest chromium concentrations in I-1 were detected in the interval between 199 and 277 ft bgs. Total dissolved chromium was detected below the AWQS at I-2 up to a depth of 186 ft bgs, ranging in concentrations between 0.008 mg/L and 0.01 mg/L. Sample results from I-2 collected below 186 ft bgs were below the reporting limit to a total depth of 297 ft bgs. Total dissolved chromium vertical profile samples results from I-3 and I-4 were all either below the reporting limit or below the AWQS. In I-5, total dissolved chromium exceeded the AWQS in 11 out of 17 laboratory samples ranging in concentrations from 0.27 mg/L to 8.0 mg/L. The highest detections in I-5 were in the interval between 230 and 260 ft bgs. Total dissolved chromium concentrations in I-6 ranged between 0.026 mg/L and 0.034 mg/L. The highest detections in I-6 were in the interval between 136 and 165 ft bgs. Historical groundwater concentrations are available in Tables 4A – 4C.


3.20. 2008 – Groundwater Monitoring; City Memorandum

On Behalf of McCulloch/Shop Vac, quarterly monitoring was first conducted by SA&B through May 1998 and then continued at a reduced frequency that was approximately monthly through October 1998. URS Corporation (formerly Dames & Moore) reestablished the quarterly sampling program in May 1999 (URS, 2009). URS continued quarterly groundwater monitoring through at least 2008. Monitoring included 13 “off-site” monitor wells (i.e. wells not within the former McCulloch property), 14 “on-site” monitor wells (i.e. wells within the former McCulloch facility), and five City production wells. The results from the latest monitoring event, completed by URS in October 2008 indicate that TCE detections exceeded the AWQS of 5 µg/L in eight sampled wells, up to a maximum concentration of 28 µg/L in MW-13. PCE exceeded the AWQS 5 µg/L at MW-1 (6.5 µg/L) and MW-20 (20 µg/L). Chlorinated solvents breakdown compounds (1,1-DCE and 1,2-DCA) were also detected exceeding the AWQS of 7.0 mg/L and 5.0 mg/L, respectively. Nitrate exceeded the AWQS of 10 mg/L in MW-8 (92 mg/L), MW-13 (1,000 mg/L), and MW-21 (100 mg/L). Total dissolved chromium exceeded the AWQS of 0.1 mg/L in 12 sampled wells, with the maximum of concentration of 110 mg/L detected in MW-1. Plume maps from the URS 2008 sampling report are presented in Appendix B.

The City prepared a memorandum for ADEQ stating that the extent of impacts and the potential risk to human health were not defined. The City claimed that Shop Vac became responsible for environmental cleanup of the facility, by virtue of the bankruptcy of the former McCulloh Corporation owned by Shop Vac. According to the City, Shop Vac would not proceed with additional investigations or remediation without assistance from Black & Decker (The City, 2008).

3.21. 2012 – Former McCulloch Facility Leaking UST Case Closure

In July 2012, following investigative and remedial actions, ADEQ issued a LUST case (Case #2606.01) closure letter for hydrocarbons in soil and groundwater at the Site (ADEQ, 2012). ADEQ determined that soil contaminant concentrations met the applicable SRLs. ADEQ also determined that although COCs in groundwater exceeded the AWQS for 1,2-DCA (12 µg/L in MW-22 in October 2007), and benzene (6.9 µg/L in MW-11 in January 2006), site-specific conditions met the closure criteria under A.A.C. R18-12-263.04.


3.22. 2014 – ADEQ Groundwater Monitoring; Former McCulloch Facility Request for In-Situ Soils Closure

In February 2014, Tetra Tech on behalf of ADEQ prepared a field sampling work plan. The scope consisted of groundwater level monitoring (which had not been completed since approximately 2008), well condition evaluation, groundwater sampling, and purge water treatment (Tetra Tech, 2014a). In March/April 2014, Tetra Tech conducted groundwater monitoring using the existing well network (Tetra Tech, 2014b). Although monitoring had not been conducted in at least six years, sample results from numerous wells continued to exceed the AWQSs, including TCE up to 31 µg/L in MW-1, PCE up to 60 µg/L in MW-20, nitrate up to 14 mg/L at MW-12, and dissolved chromium up to 16 mg/L in I-4 (Appendix B).

In July 2014, Shop Vac submitted documents to ADEQ’s Hazardous Waste Section pertaining to in situ closure of impacted soils in the vicinity of the former plating shop (Gallagher & Kennedy, 2014). The submittal included the Draft Engineering Control Plan and the Risk Assessment completed by Ninyo & Moore (Ninyo & Moore [N&M], 2014b and 2014c).

In July 2014, N&M on behalf of Shop Vac conducted a risk assessment of Cr(VI) in soil at the former plating shop area. N&M evaluated risks to human health and the environment both with controls and without controls. The proposed remedy to mitigate risk is presented in an engineering control plan (operations and maintenance manual). N&M had proposed an institutional control (Declaration of Environmental Use Restriction [DEUR]; ADEQ, 2014) and an engineering control (an impermeable liner and concrete constructed over the footprint of the former plating shop) as final mitigation measures. An evaluation of the N&M’s risk assessment found that it did not consider risk to health and the environment associated with the groundwater within the source area or down-gradient groundwater impacts, and risks associated with vapor intrusion of VOCs (Geosyntec, 2015).

3.23. 2015 – ADEQ Preliminary Investigation

On behalf of ADEQ, Montgomery & Associates Water Resource Consultants (M&A) conducted a PI at the Site (M&A, 2015). Pursuant to R18-16-201(D), this PI was based on existing information and no additional data collection was found to be necessary to complete the PI.


3.24. 2017 – City of Lake Havasu Production Well Sampling

CH2M Hill Engineers, Inc. (CH2M) on behalf of the City collected five groundwater samples from LHC-11 (Figure 2). Groundwater samples were collected shortly after startup and after 4, 7, 10, and 12 well purge volumes. Analytical results were interpreted to suggest that chromium concentrations decrease with turbidity/amount of sediment. In contrast, the concentrations of dissolved chromium remained relatively constant in the samples collected throughout the purge, except for the first sample. At the beginning of the test, the sample collected shortly after startup measured chromium and dissolved chromium concentrations at 2.9 mg/L and 0.13 mg/L, respectively, both exceeding the AWQS. In subsequent samples, chromium and dissolved concentrations decreased, however chromium concentration still exceeded the AWQS at 0.36 mg/L in the 4-volume purge sample, while dissolved chromium was below the AWQS at 0.027 mg/L. For all other samples collected at 7, 10 and 12 purge volumes, both chromium and dissolved chromium concentrations were below the AWQS (CH2M, 2017).


4. REMEDIAL INVESTIGATIONS

In February 2018, ADEQ provided notices per A.R.S. § 49-287.03 initiating the RI at the former McCulloch Facility (ADEQ, 2018). Simultaneously, Jacobs Engineering Group, Inc. (Jacobs) on behalf of the City, completed a site investigation of the former Kiowa Ponds (Jacobs, 2018a & 2018b). A summary of both investigations is presented in the following subsections.

4.1. Soil Investigations

4.1.1. Former McCulloch Facility Soil Investigation Results

In April 2018, Geosyntec advanced 26 shallow boreholes (SB-01 through SB-26) and five deep angled boreholes (B-01 through B-05; Figure 5) in the vicinity of the former Plating Area at the former McCulloch facility. The total depths of the shallow boreholes ranged from 2 ft bgs to 25 ft bgs. The deep angled boreholes ranged from 170 to 200 linear feet. Soil samples were collected from ground surface to total depth of the borings, with samples collected on approximately 5-foot intervals.

Select soil samples were analyzed for total chromium, Cr(VI), total cyanide, and nitrate as nitrogen. Geotechnical samples were also collected from boring B-03 at 127, 163, and 210 ft bgs; these samples were tested for grain size distribution, permeability, and undisturbed moisture density.

The highest detected total chromium concentration in soil was 6,200 mg/kg from SB-21 at 3 ft bgs. Total chromium exceeded the minimum GPL of 590 mg/kg at eight sampled depths, including all shallow samples at SB-05, SB-19, SB-21, and SB-25, and samples at 125 ft and 130 ft in B-04. The highest Cr(VI) concentration is soil was 1,200 mg/kg in B-04 at 130 ft bgs. The SRL for Cr(VI) was exceeded at all sampled depths, except the 3-ft samples at SB-19, SB-21, and SB-25, and the 5-ft sample in B-05 (Figure 5).

Nitrate was sampled at SB-01, SB-02, SB-03, and SB-04. Although there is no established SRL for nitrate, all nitrate detections were below the minimum GPL of 293 mg/kg, with a highest detected concentration of 17 mg/kg in SB-1 at the surface sample.

A summary of detected chromium and nitrate concentrations in soil is provided in Table 5A. The laboratory analytical reports and the geotechnical laboratory test results are included in Appendix C.1.

VOCs in soil were analyzed via soil-vapor sampling, pursuant to R18-7-203 C (Section 4.2).


4.1.2. Former Kiowa Ponds Soil Investigation Results

Through ADEQ’s Voluntary Remediation Program (VRP), Jacobs on behalf of the City conducted a site characterization of the former Kiowa Ponds (Jacobs, 2018a) that included soil and soil-vapor samples from 15 locations at various depths (5 locations at Pond A and 10 locations at Pond B) (Figure 2). Jacobs estimates that fill material covering the former Kiowa Ponds ranges from 8 to 14 ft in thickness. Soil samples were collected below the fill/native soil interphase up to 40 ft bgs, and soil-vapor samples were collected at depths ranging between 15 to 40 ft bgs. Sample analytical results indicate that total chromium was not detected in exceedance of the residential SRL or minimum GPL. Cr(VI) was not detected in soil. Nitrate was detected at one sample location at a concentration of 2,840 mg/kg. However, in an addendum report, Jacobs submitted revised laboratory reports with a revised nitrate detection from 2,840 mg/kg to 172 mg/kg, based on an initial erroneous calculation performed by the laboratory. There is no SRL for nitrates in soil. The VRP program granted a No Further Action determination for soils at the Kiowa Ponds on August 30, 2019.

A summary of detected chromium and nitrate concentrations in soil from the Former Kiowa Ponds is provided in Table 5B.

4.2. Soil-Vapor Investigation

4.2.1. Former McCulloch Facility Soil-Vapor Sampling

In April 2018, Geosyntec installed temporary multi-depth soil-vapor probes in boreholes SB-01 through SB-17 and SB-25 and collected soil-vapor samples via a SimulProbe-type sampler in B-03 (Figures 6a and 6b). Soil-vapor samples depths ranged from 3 to 153 ft bgs.

Soil-vapor samples were analyzed for VOCs. Thirty-two analytes were detected in the soil-vapor samples, as shown in Table 6A, along with the corresponding derived screening levels. The derived screening levels for non-residential properties are based on the EPA composite worker air Regional Screening Levels (RSLs; USEPA, 2018) and an attenuation factor of 0.03. Eight VOCs were detected in soil vapor exceeded the derived screening levels, including 1,1-DCA at 1,800 micrograms per meter cube (µg/m3) (screening level 257 µg/m3), 1,3-Butadine at 200 µg/m3 (screening level 14µg/m3), benzene at 56 µg/m3 (screening level 53 µg/m3), bromodichloromethane at 56 µg/m3 (screening level 11 µg/m3), chloroform at 34 µg/m3 (screening level 18 µg/m3), freon113 at 37,000,000 µg/m3 (screening level 733,333 µg/m3), PCE at 130,000 µg/m3 (screening level 1,567 µg/m3), and TCE at 11,000 µg/m3 (screening level 100 µg/m3).


A summary of detected analytes is provided in Table 6A. The laboratory analytical reports are included in Appendix C.2. Indoor air investigations have not been conducted at the Site.

4.2.2. Former Kiowa Ponds Soil-Vapor Sampling

Jacobs on behalf of the City installed temporary soil-vapor probes at 15 locations within the former Kiowa Ponds (Jacobs, 2018a). According to Jacobs, soil-vapor probes were installed at two to three depths in each boring below the fill and native soil boundary, ranging from 15 to 40 ft bgs. Samples were analyzed for VOCs, and results were converted to equivalent soil concentrations in accordance with the ADEQ Soil Vapor Sampling Guidance (ADEQ, 2017). According to Jacobs, VOCs were not detected above the reporting limit, except for acetone. Equivalent soil concentrations for acetone did not exceed the residential SRL or minimum GPL. A summary of detected soil vapor concentrations is provided in Table 6B.

4.3. Groundwater Investigations

The following subsections summarize groundwater characterization activities conducted at the Site under the WQARF program. Groundwater sample results collected during drilling using Hydropunch-type push-ahead sampling are summarized in Tables 7A through 7C. Groundwater results collected as part monitoring activities are summarized in Tables 7D through 7F.

4.3.1. April 2018 Groundwater Sampling

Groundwater samples were collected during Site drilling activities conducted at soil borings B-01, B-02, B-03, B-04, and B-05 completed during April and May 2019 (Figure 5). Three groundwater samples were collected from each boring using Hydropunch-type push-ahead sampling. Samples were collected from approximate depths ranging from 146.5 to 200 ft bgs. A summary of the laboratory results is presented in Table 7A through 7E.

COCs exceeded the AWQS at maximum concentrations of 42 µg/L for PCE, 8.6 µg/L for TCE, 280 mg/L for nitrate, and 210 mg/L for total chromium. Although there is no AWQS for Cr(VI), the maximum concentration of 49 mg/L for Cr(VI) exceeded the total chromium AWQS. Benzene was detected at a maximum concentration of 4.6 µg/L, below the AWQS. The Cr(VI) analysis (USEPA Method SM3500) is used to quantify only the soluble fraction of chromium within a sample. Therefore, the analysis is assumed to provide an estimate of total chromium that is biased low versus filtered or unfiltered groundwater samples analyzed for total chromium (USEPA Method 200.7). As such, it


is also assumed that Cr(VI) sample analytical results exceeding the total chromium AWQS would also have exceeded the AWQS had the sample been analyzed via the total chromium analytical method.

4.3.2. Monitor Well Installations

The following subsections describe groundwater monitor well installations conducted under the RI.

4.3.2.1. Monitor Well LHH-01 Installation

In April and May 2018, Geosyntec advanced one borehole (LHH-01; Figure 2) to a depth of approximately 243 ft bgs and completed as a 4-inch diameter groundwater monitor well. Groundwater was encountered at approximately 65 ft bgs and a groundwater sample was collected. Additional samples were collected at approximately 10-foot intervals beginning at 115 ft bgs, up to a depth of 235 ft bgs. Groundwater samples were collected during drilling using Hydropunch-type samplers. Total chromium concentrations ranged from 0.0014 mg/L at 205 ft bgs to 4.6 mg/L at 65 ft bgs. It is likely that the high detections of total chromium during this well installation was due to chromium associated with sediments. No other COCs were reported above AWQS.

The laboratory analytical reports and a data validation memorandum are included in Appendix C.3. The boring log and well construction log are presented in Appendix A.

4.3.2.2. Monitor Wells LHH-02 through LHH-05 Installations

From October to December 2018, Geosyntec advanced four boreholes (LHH-02 through LHH-05; Figure 2) to depths ranging from 270 to 347 ft bgs. The borings were completed as groundwater monitor wells to further delineate the vertical and downgradient lateral extents of the contaminant plumes. Groundwater was first encountered at depths ranging from 29 to 105 ft bgs. Groundwater samples were collected at approximately 20-foot intervals throughout the saturated zone using bailers lowered through a Hydropunch-type sampler.

Nitrate, benzene, and total chromium exceeded the AWQS up to a maximum concentration of 100 mg/L, 34 µg/L, and 22 mg/L, respectively. TCE was detected above the laboratory reporting limit at a maximum concentration of 2.4 µg/L, but it did not exceed the AWQS. Although Cr(VI) does not have an established AWQS, Cr(VI) was not detected exceeding the AWQS for chromium.


The laboratory analytical reports and a data validation memorandum are included in Appendix B.3. The boring logs are presented in Appendix A.

4.3.2.3. Transect Borings Transect-B-1 through Transect-B-5 and Installation of Monitor Wells LHH-06 and LHH-07

In August 2018, Geosyntec advanced five boreholes (Transect-B-1 through Transect-B-5; Figures 6-10) in a transect line perpendicular to the groundwater contaminant plume along the western edge of State Route 95, downgradient of the former McCulloch facility area and upgradient of the former Kiowa Ponds. The transect borings were advanced to further delineate the lateral and vertical extent of the dissolved plume. The total depths of the boreholes ranged from 191 to 245 ft bgs. Groundwater was encountered at approximately 125 ft bgs in each of the borings. Groundwater samples were collected at approximately 20-foot intervals across the saturated zone using bailers lowered through a Hydropunch-type sampler.

Along with analysis for COCs, anions, total and dissolved metals, mercury, and general chemistry parameters (phosphate, alkalinity, bicarbonate/carbonate alkalinity, and dissolved organic carbon) were analyzed in groundwater samples collected from Transect-B-3 in order to further assess groundwater characteristics.

PCE, TCE, benzene, nitrate, and total chromium were detected with maximum reported concentrations of 4.6 µg/L, 17 µg/L, 130 µg/L, 200 mg/L, and 26 mg/L, respectively. All of these except PCE were over their respective AWQS. Additionally, Cr(VI), which does not have an established AWQS, had a maximum reported concentration of 27 mg/L, exceeding the AWQS for chromium.

A summary of detected analytes and the results of the general chemistry analyses of Hydropunch samples is provided in Table 7A through 7E. The laboratory analytical reports and a data validation memorandum are included in Appendix C.3.

Based on the groundwater sample analytical results, boring B-02 was converted into monitor well LHH-06 and B-03 was converted into monitor well LHH-07. The boring log and well construction log are presented in Appendix A.

4.3.3. 2018 Groundwater Monitoring

During August and September 2018, groundwater samples were collected from monitor wells LHH-01, KPMW-1, KPMW-2, and KPMW-3 and production wells LHC-10 through LHC-15. Groundwater samples were not collected from LHC-3 and LHC-18 due to inoperable or removed submersible production pumps and inability to deploy sampling


devices through a well sample port. Groundwater samples were also not collected from monitor wells I-1 through I-6 and MW-1 through MW-24 due to a lack of access to these wells. Vertical profile samples were collected from wells KPMW-1, -2, and -3 at multiple depths using Hydrasleeve-type samplers, whereas LHC-10 and -15 were vertically profiled using low-flow purge sampling techniques, and then subsequently sampled using three well-volume purge sampling techniques. Sampled depths and results of COCs and detections are provided in Table 7F through 7I.

PCE, nitrate, and chromium exceed the AWQS at maximum concentrations of 5.2 µg/L, 26 mg/L, and 9.1 mg/L respectively. TCE was detected above the laboratory reporting limit, but below the AWQS at a maximum concentration of 3.7 µg/L. Cr(VI) was also detected above the laboratory reporting limit, at a maximum concentration of 12 mg/L, exceeding the chromium AWQS of 0.1 mg/L.

Groundwater results from City production wells LHC-10 through LHC-15 indicate that total chromium, Cr(VI), and nitrate were either not detected, or below the applicable AWQS.

4.3.4. 2019 Groundwater Monitoring

In April 2019, Geosyntec conducted groundwater monitoring at wells KPMW-1, and LHH-01 through LHH-07. During this event, these wells were also surveyed by an Arizona licensed surveyor. A survey report is provided in Appendix D. Samples were analyzed for VOCs, nitrate, total chromium, and Cr(VI). These wells were vertically profiled using Hydrasleeve-type samplers at multiple depths (Table 7F through 7I). Groundwater samples were not collected from monitor wells KPMW-2, KPMW-3, I-1 through I-6 and MW-1 through MW-24 due to a lack of access to these wells.

PCE, TCE, 1,2-DCA, nitrate, and total chromium exceed the AWQS at a maximum concentration of 11 µg/L, 17 µg/L, 14 µg/L, 51 mg/L, and 28 mg/L, respectively. Cr(VI) was detected above the laboratory reporting limit at a maximum concentration of 24 mg/L, also exceeding the AWQS for chromium. PCE, TCE, nitrate, and total chromium results are shown on Figures 7a through 10a.

Groundwater results obtained from KPMW-1, and LHH-01 through LHH-07 as part of this investigation, along with groundwater results from LHC wells collected in 2018 (Section 4.3.3), and the results obtained from wells on the former McCulloch facility during previous investigations (Tetra Tech, 2014b) were utilized to develop cross-sections showing the extent of the total chromium, TCE, and nitrate plumes in groundwater (Figures 11a/b through 14a/b).


Groundwater samples were sent for stable isotope analysis at the University of California Davis Stable Isotope Facility to determine the oxygen and nitrogen isotopic composition of the nitrate concentrations present within the Site groundwater. Specifically, 𝛿𝛿15N and 𝛿𝛿18O was determined for the nitrate present within groundwater samples collected from KMPW-1, LHH-01, LHH-02, LHH-03, LHH-04, LHH-05, LHH-06 and LHH-07. The 𝛿𝛿15N and 𝛿𝛿18O values (Table 8, and Figure 18) from the samples were then compared to values expected from synthetic fertilizers, including nitric acid and nitrate from domestic sewage. The 𝛿𝛿15N values obtained through the stable isotope study suggest that the nitrate observed at Site has its origin in domestic sewage and was not likely associated with manufactured fertilizer, the industrial use of nitric acid or synthetically produced reagent salts (G. Michalskiab, M. Kolanowskib, & K. M. Rihaa, 2015). However, elevated 𝛿𝛿18O values may indicate also a synthetic fertilizer source (C. Kendall, 1998).

In October and November 2019, Geosyntec conducted groundwater monitoring of 41 groundwater monitor wells at the Site, including the wells on the former McCulloch facility and the “I” wells. All groundwater monitor wells were surveyed by an Arizona licensed surveyor except KPMW wells and LHH wells, which were previously surveyed in the March 2019 event. A survey report is provided in Appendix D.

Samples were collected via HydraSleeves within the screened interval at depths indicated in Tables 7F through 7I. Following sample collection from the HydraSleeves, additional groundwater samples were collected from MW-20, I-3A, I-3B, I-4A, and I-4B using low-flow sampling techniques. These samples were collected using a low-flow bladder pump with dedicated polyethylene tubing and bladders were used for each well. Each well was purged at a rate of approximately 100 to 200 milliliters per minute (mL/min) until field water quality parameters stabilized, after which a sample was collected. Split samples were collected in wells I-3A, I-3B, I-4A, I-4B, I-5A, I-5B, MW-20, and MW-24 by Synergy Environmental on behalf of Shop Vac. The ADEQ samples were analyzed for VOCs, nitrate, nitrite, ammonia, total chromium, Cr(VI), arsenic, manganese, and iron. Select samples were also analyzed for selenium, total organic carbon, and 1,4-dioxane. Additionally, three samples submitted for microbial analysis via Next Generation Sequencing and six samples were analyzed for microbial DNA.

The VOCs detected that exceeded AWQS were PCE, TCE, 1,2-DCA, and 1,1-DCE at a maximum concentration 14 µg/L, 23 µg/L, 15 µg/L, and 9 µg/L, respectively. Nitrate exceeded AWQS with a maximum concentration of 210 mg/L. Nitrite also exceeded AWQS in at a maximum concentration of 3.4 mg/L. Total chromium exceeded AWQS with a maximum concentration of 31 mg/L. Selenium also exceeded its AWQS in one location at a concentration of 65 µg/L (Tables 7F through 7I). PCE, TCE, nitrate, and total chromium results are shown on Figures 7b through 10b).


As the results of the nitrate isotope analysis in the LHH wells indicated a sewage and/or synthetic fertilizer source for the Site nitrates, ammonia and nitrite analysis were added to this sampling event to determine the possible area of origin, as these compounds tend be quickly converted to nitrogen in groundwater, making their presence an indicator of possible sources. Ammonia was detected in MW-11, MW-15, MW-21, and I-6B. Nitrite was detected in MW-1, MW-2, MW-5 (over AWQS), MW-19, I-4B (over AWQS), I5A, I5B, and KPMW-2.

Analysis of the results of the passive sampling (HydraSleeves) and the purge methodology indicates that the nitrate and chromium results were in general highly comparable between the two methodologies (Table 9); Well I-4B had higher variability than the other wells, but the results were still within the same order of magnitude. In general, VOCs were detected at higher levels in the passive methodology samples than in the purge methodology samples.

A comparison of split samples indicates that ADEQ-collected samples and split samples were within the same order of magnitude, with the exception of Cr(IV) results in I-5A (Table 10).

None of the samples submitted for Gene-Trac® Dhc yielded positive results for genes associated with Dehalococcoides (Dhc) microorganism. Of all the samples analyzed using Gene-Trac®-Geo, only the sample collected from LHH-02 yielded detectable concentrations of genes associated with the presence of Geobacter related microorganisms. All samples submitted for Gene-Trac® nirK except the sample collected from MW-21 contained low concentrations of genes associated with nirK (nitrate-degrading) associated microorganisms. From the samples submitted for DNA analysis, the groundwater sample collected from MW-13 exhibited the highest microbial diversity with 728 operational taxonomic units (OTUs). The sample from LHH-02 had 419 OTUs. The sample from MW-21 had the lowest observed diversity at 216 OTUs (Appendix C.4).

The laboratory analytical reports and a data validation memorandum for the 2019 samples events are included in Appendix C.3.


5. EXTENT OF CONTAMINATION

5.1. Soil

Cr(IV) extent exceeding SRLs were detected in soils in the area near the former plating shop at the former McCulloch facility (Figure 3). Evaluation of 1992 and 1996 data (N&M, 2014b) shows that chromium was present from the soil surface to groundwater (Figure 19). Soil borings drilled for the RI located in the same area in 2018 confirmed that the magnitude of the chromium detected was comparable to Cr(IV), and both constituents remained present in soils in this area (Figures 5 and 19).

PCE, TCE, and other VOCs were detected in soil-gas samples collected in the vicinity of the former plating shop and the former Main Plant Warehouse and Assembly areas at the former McCulloch facility (Table 6a; Figures 6a and 6b). PCE and TCE were detected above screening levels to a depth of 115 feet bgs. While multiple VOCs were detected above the screening levels (see Section 4.1.2), none of the compounds were detected above SRLs or GPLs. Soil-gas samples collected near to the former Kiowa Ponds area did not indicate any PCE or TCE contamination in this area (Table 6b).

5.2. Groundwater

The chromium extent in groundwater in 2019 was determined to extend approximately 3,000 feet, from approximately MW-20 in the east to beyond LHH-02 in the west (Figures 10a and b), in a plume approximately 600 feet wide. The plume dives as it moves downgradient from east to west; in the east is extends from the top of the water table to approximately 150 feet below the water table. In the vicinity of MW-8/KMP-1, the plume only is detectable in the lower part of the screen of these wells (Table 7F), indicating that the top of the plume dives to approximately 30 to 50 feet below the top of the water table. In the area of the former Kiowa Ponds, the chromium plume was not detected in the screen of KMP-3, but was present in I-3A and LHH-02, indicating the plume extended from greater than 50 feet below the water table to approximately 200 feet below the water table (Table 7F). From this the chromium plume was determined to be approximately 150 feet in depth.

Historically chromium was also detected in the LHC productions wells over AWQS (Table 4a). It is unknown if there is an extent of chromium contamination detached from the main plume of the Site in the vicinity of the LHC wells.

The VOC plumes appear to be contained within the chromium plume area. The TCE plume extends from the area near the former plating shop to approximately 1,900 feet


west, to LHH-02 (Figures 8a and b, Figure 13a). The depth of the TCE plume approximates that of the chromium plume, diving as it moves east to west.

The PCE plume is limited to the area near the former plating shop and the former Main Plant Warehouse and Assembly areas (from MW-20 and B-01 – B-05 data, Tables 7E and 7I), extending approximately 100 feet to the west. The depth of this plume appears to be limited to the top of the water table in the area of the Main Plant Warehouse at approximately 145 ft bgs to approximately 200 ft bgs. This is determined from data collected from monitoring well screen depths, including the PCE detections in plating shop area borings, and the 4.6 µg/L of PCE detected in transect boring B-1 at approximately 175 ft bgs.

1,2-DCA, above AWQS, was limited to the area around the LHH-07 and I3-B wells (Table 7I). 1,1-DCE was only detected above AWQS in MW-9 (Table 7I). Benzene was not detected above AWQS in the 2019 sampling events (Table 7I).

The extent of nitrate in the aquifer is influenced by background nitrate concentrations in the area groundwater. Upgradient wells varied from 11 mg/L to 29 mg/L in the fall 2019 sampling event. Levels over these background numbers (ranging from 48 – 210 mg/L) extended approximately 1,300 feet from MW-1 to LHH-02. This plume also dives as it moves east to west as indicated by the results in the I-3, I-4, and I-5 wells (Table 7H, Figures 9a and b, Figure 14).


6. RISK EVALUATION

A risk evaluation was conducted pursuant to R18-16-406(E). The risk evaluation includes identifying the potential migration pathways and receptors within the area of the Site. The potential risk is identified based on the concentration of the hazard present and the potential completion of the pathway.

6.1. Human Health Conceptual Site Exposure Model

This risk evaluation is focused on the potential risk from the identified COCs, which include chromium, PCE/TCE and other breakdown byproducts, and nitrate. Based on the assessment work completed, the COCs at the Site likely traveled through the vadose zone to groundwater and migrated with groundwater to the west and northwest (Figure 14).

Potential exposures to contaminants can occur through a complete exposure or migration pathway. An exposure or migration pathway is the route by which the potential hazard (detected constituent) migrates from the source (soil, soil-vapor, surface water, or groundwater) to a receptor. Pathways can include:

• Inhalation of impacted vapors;

• Dermal contact with impacted soil, groundwater, or surface water; or

• Ingestion of impacted soil, groundwater, or surface water.

An exposure pathway is complete when all four of the following components are present:

1) A source and mechanism of chemical release;

2) A retention or transport medium (pathway);

3) An exposure point (i.e., a setting where potential human or ecological receptor contact with the chemical-affected medium or media occurs); and

4) A route of exposure at the exposure point (e.g., ingestion, dermal, inhalation).

This section discusses the transport mechanisms of the detected constituents and the potential for exposure pathways to be complete. Figure 15 presents the exposure pathway model


6.2. Applicable Regulatory Standards and Screening Criteria Used in the Human Health Screening Risk Evaluation

The following section describes the current applicable regulatory standards and screening criteria used in the risk evaluation for constituents detected in Site soil, soil-vapor (as it relates to potential indoor air exposures), and groundwater.

6.2.1. Soil Remediation Standards

The soil remediation standards are based on commercial/industrial land use consistent with the land use within the remedial investigation area. In addition, GPLs (soil cleanup levels protective of groundwater quality) were used in the evaluation. Non-residential SRLs are listed in Appendix A of A.A.C. Title 18 Chapter 7.

GPLs used to evaluate soil conditions in the state of Arizona for the specific Site constituents are as follows:

• A minimum GPL published by ADEQ (ADEQ, 1996) was used for total chromium. A minimum GPL has not been established for Cr(VI); and,

• A minimum GPL published by ADEQ (ADEQ, 2010) was used for nitrate.

6.2.2. Soil-Vapor Screening Levels

Indoor air investigations have not been conducted at the Site to date. However, constituents have been detected in Site soil-vapor. In accordance with USEPA guidance (USEPA, 2015), the applicable USEPA Region 9 indoor air RSLs were used for the derivation of soil-vapor screening levels. The USEPA indoor air RSLs for composite worker air adjusted by an attenuation factor of 0.03 were used to evaluate soil-vapor data.

6.2.3. Groundwater Standards

AWQS are State of Arizona maximum levels for constituents that apply to groundwater in aquifers designated for drinking water use pursuant to A.A.C., R18-11-405. An AWQS has not been established for Cr(VI); therefore, these results are compared against the total chromium AWQS. These AWQS meet the National Primary Drinking Water Regulations Maximum Contaminant Levels. While groundwater is not currently used for potable


water within the Site, all aquifers in Arizona are considered drinking water aquifers and therefore AWQS apply.

6.3. Human Health Conceptual Site Exposure Model

6.3.1. Vapor Pathway

Transport of vapor-phase constituents present in soil-vapor to indoor air could result in exposure to human health risk via inhalation. The transport mechanism for a soil-vapor pathway is volatilization and vapor intrusion, and the secondary impacted media are indoor and outdoor air, as indicated in Figure 15. The inhalation exposure route that could affect certain exposed receptors is considered a potentially complete exposure pathway.

Volatile organic chemicals can also migrate from groundwater through the subsurface into indoor air through diffusion and advection. The indoor air inhalation exposure route presents a potentially complete pathway from VOCs (PCE, TCE and other breakdown byproducts) off-gassing from groundwater both on- and off-site. However, due to the depth of the groundwater (50 to 125 ft bgs), the relatively low concentrations of VOCs in groundwater, and limited extent of the VOC plumes away from the potential source area, this pathway may not be significant. Other COCs, including chromium and nitrate are not considered a risk for vapor pathways because they are not volatile compounds.

6.3.2. Soil Pathway

Various soil sampling activities have been conducted during Site investigations. Based on the April and May 2018 soil investigation activities conducted at the Site, reported total and Cr (VI) concentrations above screening levels occur at various shallow and deep depths below barriers (i.e., concrete slabs, paved or asphalted surfaces) so they are inaccessible to direct contact by humans unless there is an excavation beneath the barrier. Nitrate was detected during the April and May 2018 soil investigation, although there are no current applicable soil screening values for non-residential scenarios, nitrate soil results were below the applicable GPL. The land use for these properties is industrial/commercial. For a continued future industrial/commercial scenario, the soil direct contact pathway would remain incomplete. If these properties are redeveloped this exposure pathway would require re-evaluation by additional sampling to determine if chromium in soil exceeds screening levels.

The transport mechanisms for a soil pathway include excavation and fugitive dust. For excavation, the secondary impacted media is trench spoils. Dermal and incidental ingestion exposure route (to affect construction workers in contact with trench spoils)


presents a future potentially complete exposure pathway. Fugitive dust generation is also possible under the outlined scenario.

6.3.3. Groundwater Pathway

Direct ingestion is the possible exposure route for potable use chromium- and nitrate-impacted groundwater. Possible exposure routes for VOC-impacted groundwater used for potable water include direct ingestion, inhalation, or dermal contact. Residential inhalation exposures to VOCs could occur from volatilization from water during activities such as showering, bathing, or washing. The Site is serviced by the public water supply. Currently the City utilizes water obtained from an horizontal collector well (HCW) located on Pittsburg Island, approximately 2.5 miles south of the Site. According to the City, the production wells located west of the Site in the north wellfield are used for backup potable supply and only operated occasionally for pump maintenance. According to responses provided by the City to the ADEQ during the land and water use study (Appendix E), two additional production wells are being considered either near or within the north wellfield to provide a 100% redundant backup potable water source to the primary source (HCW) during planned shutdown and maintenance of the HCW. Potable use of groundwater is therefore not currently a complete pathway. If production wells in the north wellfield are utilized in the future for water supply, as discussed in Section 6.4, this exposure pathway would require re-evaluation.

6.3.4. Surface Water Pathway

Dermal contact, direct ingestion of water, and consumption of fish are potential pathways for impacted surface water and recreational receptors. Lake Havasu is a reservoir created on the Colorado River by Parker Dam, and groundwater of the Lake Havasu basin-fill is hydraulically connected to the Colorado River (ADWR 2019). There are no known points of natural discharge of groundwater to surface water within one mile of the Site, and the Site COCs are not known to have reached the lake. Therefore, this pathway is currently considered incomplete. If in the future Site COCs exceeding the AWQSs are detected close to the lake, this pathway would require re-evaluation.

6.4. Potential Receptors

The Site boundary (Figure 2) includes an area encompassing residential and commercial/industrial settings. Land use is limited to commercial/industrial uses in the areas where the results of the RI indicate that concentrations of impacts to soil and soil-vapor exceed standards and screening levels; therefore, a commercial/industrial use scenario is assumed for this risk evaluation.


Commercial/industrial workers include adults working at the businesses within potential source area. Construction workers include adults who are performing construction work for a substantial period (e.g., months to years), resulting in sub-chronic exposures for only that period equal to the duration of the project.

Several categories of sensitive receptors (residential units, medical facilities, schools, and places of worship) are located within a half-mile radius of the estimated plume boundaries. A list of these in the vicinity of the Site was prepared from reviewing Google Earth and Google Map data (accessed online in June 2019) and is presented in Figure 16. Figure 15 presents the human health CSM for the Site.

6.5. Ecological Conceptual Site Exposure Model

As defined in A.A.C., an ecological receptor is “a specific ecological community, population, or individual organism, protected by federal or state laws and regulations, or a local population that provides an important natural or economic resource, function, and value” (A.A.C., Title 18, Ch. 7, 201). Areas and land use within the Site boundary (Figure 2) do not contain green or native space, and do not contain suitable habitat for the federally listed species in Section 2.6. Due to the urban character of the Site, there are no known ecological receptors, including sensitive species or habitats, within the Site boundary (Ninyo & Moore, 2014a).

Lake Havasu, a recreational body of water, is located approximately one mile west and hydraulically downgradient of the former McCulloch facility. Due to its distance from the current known plume boundary a transport mechanism from groundwater to lake water and lake organisms is not likely. Therefore, a complete and significant surface water exposure pathway is not present.

The Kiowa Wash, which runs through the Site, is an intermittent wash that carries surface water to Lake Havasu. Historically, overflow from the Kiowa Ponds was allowed to outflow into the Kiowa Wash (Ecology and Environment, Inc., 2000); however, there is no available record of how much, if any, water was allowed to outflow to the wash. Six surface soil samples were collected from the Kiowa Wash down-wash of the former Kiowa Pond outfalls. No VOCs or SVOCs were detected above method reporting limits. Total chromium was detected at a maximum of 33.5 mg/kg (Ecology and Environment, Inc., 2000). There is no SRL for total chromium. To-date, the Kiowa Wash has not been characterized for the potential presence of hexavalent chromium or nitrates.


7. CURRENT AND FUTURE LAND AND WATER USE

Pursuant to A.A.C. R18-16-406 (A)(3) and (D), the scope of this RI includes a Land and Water Use Study (LWUS). The land and water uses are described in detail in a report presented in Appendix E.

The LWUS includes a collection of information regarding current and reasonably foreseeable uses of land and/or waters of the state that have been or could be impacted by the release of Site COCs, and projected time-frames for future changes in those uses. Reasonably foreseeable future land uses are those that are likely to occur at the WQARF Site. Reasonably foreseeable future water uses are those that are likely to occur within 100 years unless a longer period is shown to be reasonable based on site-specific circumstances.

As part of the LWUS, questionnaires were mailed out to and answers received back from the current property owner of the former McCulloch property and the City. The most likely and relevant uses to the Site based on questionnaire responses and other readily available information are summarized below.

7.1. Land Use

7.1.1. Current Land Use

The City is located within Mohave County. According to the City’s 2015 Water Conservation Plan (The City, 2015), the major land uses within the City are residential, commercial/industrial, recreation/resort, and undeveloped. The residential element is dispersed throughout the City, while the commercial and industrial element is concentrated along Highway 95, Lake Havasu Avenue, and North Kiowa Boulevard, and McCulloch Boulevard. Recreational properties and resorts are concentrated along the Lake Havasu shorelines.

7.1.2. Future Land Use

The zoning for the Site was conceived as part of a master-planned community in 1963 with a recreational and residential emphasis, and the focus of the original master plan remain central to future development.

According to the City (The City, 2015), substantial land absorption via development completion of areas planned for commerce, industry, and residences, with the largest anticipated growth in the form of subdivision development on Arizona State Trust Land. There is also planned open space, designated low density rural residential (The City,


2010; The City, 2015). The City has indicated to ADEQ that funding was approved in 2000 for redevelopment of the former Kiowa Ponds, but there are no current redevelopment plans. Although development has not occurred to date, it is likely that the former Kiowa Ponds will be redeveloped in the foreseeable future.

Currently there are no zoning or developments planned within the area of the Site. The current property owner of the potential source area has indicated to ADEQ that they intend to extend the current lease agreement for the existing businesses on the property into the future.

7.2. Groundwater Use

The City completed Water Conservation Plans in 2010 (The City, 2010) and 2015 (The City, 2015). The plan includes: a City-wide water audit to better understand the root discrepancies between diversion meters and billed consumption through user end meters; proposed rate structure changes; public education and outreach programs; continuation of existing conservation programs; a proposed free water audit program; continuation and tracking of city ordinances for new developments; audits and inspections of current distribution systems; implementation of the 2010 water shortage response plan; and wastewater reclamation and recycling. Current and future groundwater uses within the Site include the following:

• The City owns six production wells in the north wellfield located west of the Site (LHC-10 through LHC-15). These wells are currently not active, and they are only operated during maintenance exercises. According to LHC, future plans for these wells is unknown; and,

• The City anticipates the design and construction of up to two new production wells located in the general vicinity of the existing production wells in the north wellfield. The wells are necessary to provide for a 100% redundant backup water source so that the City’s primary source (the HCW), can be taken out of service for scheduled maintenance.

7.2.1. Current Water Use

The City owns and operates a functional water distribution system including wells, treatment plants, booster stations, transmission and distribution lines, and storage facilities. The water is used primarily for single residential, followed by residential and non-residential irrigation, then multi-family and other commercial, then other classes.

According to the City (The City, 2015), the principal water source for the City is contracted, 4th priority Colorado River water entitlements. The City also uses treated


wastewater for landscape and turf irrigation, lowering the City’s Colorado River allocation requests. The City has reserved water supplies in the form of storage credits firmed with the Arizona Water Banking Authority and the Central Arizona Water Conservation District. The City also diverts water from various Colorado River water diversion points, including: a 25 million gallon per day (MGD) horizontal collector well located on London Bridge Beach and Pittsburg Island; and nine production groundwater wells located in two well fields (7 wells in the north side of the City along London Bridge Road; and 2 wells on Pittsburg Island). The nine production wells are conventional groundwater wells that penetrate the Colorado River Aquifer.

7.2.2. Future Water Use

According to the City (The City, 2015), projections indicate that the City should have enough water for increasing demand under normal water supply conditions and keeping per capita consumption at respectable levels. However, the population projections end at 2050 with a population well under the estimated build-out population of 96,000 stated in the City’s 2015 General Plan. These future needs will be revised as needed by the City to reflect changes in the community that would affect the water consumption rate.


8. DATA GAPS

The following is a list of potential data gaps that are necessary to fully characterize the Site prior to developing a remedial strategy:

• Currently the monitoring well network is insufficient to detect contamination

moving west of the City wells towards Lake Havasu. A sentinel well in this location would be beneficial for long-term monitoring at the Site;

• No indoor air samples have been collected in areas with detected concentrations of VOCs in soil vapor exceeding the EPA RSLs. It is recommended that indoor air samples be collected in buildings where workers are present.

• The Kiowa Wash has not been analyzed for Cr(VI) and nitrate. Data collected from for the USEPA (Ecology and Environment, Inc. 2000) found chromium concentrations up to 33.5 mg/kg. While it is unlikely for any contamination that may have historically entered the wash to remain, sampling of the sediment from the wash could help determine if this needs to be examined as a pathway for the Site.

• The exact location of the apparent contribution of nitrates to groundwater from the Site is unknown. Nitrogen compound results suggest that a source area is located at or near the northern end of the former McCulloch facility property. Additional characterization may be needed to fully characterize the nitrate source; for example collecting additional isotope samples in the MW and I wells, locating sewer lines/former septic systems, etc.


9. REFERENCES

Arizona Department of Environmental Quality (ADEQ), 1996, A Screening Method to Determine Soil Concentrations Protective of Groundwater Quality, presented by the Leachability Working Group of the Cleanup Standards/Policy Task Force, September.

ADEQ, 2000, Memorandum: Summary of the File Review, Identified Data Deficiencies, and Recommendations for the McCulloch Facility, Lake Havasu City, Arizona, 29 February.

ADEQ, 2001a, Memorandum: Final Aquifer Protection Permit (APP) No. 101415 for Closure of the Kiowa Ponds, 14 November.

ADEQ, 2001b, Summary of General Chemistry and Potential Remedies for Soil and Groundwater Contaminated with Chromium, David H. Haag, R.G. Remedial Investigations Hydrology Unit, August 23.

ADEQ, 2005, State of Arizona Aquifer Permit Program Memorandum: Kiowa Ponds, 27 October.

ADEQ, 2010, Methodology for Calculating Groundwater Protection Levels (GPs) for Nitrate, Nitrite, Total Nitrogen, and other “Salts” for Clean Closure at Non-Recharge Sites, 4 November.

ADEQ, 2012, Memorandum: LUST Case Closure Approval, Former McCulloch Facility, 18 July.

ADEQ, 2014, Declaration of Environmental Use Restriction for Property with Engineering Control and Non-Residential Restriction, Former McCulloch Facility, 25 July.

ADEQ, 2017, Soil Vapor Sampling Guidance, April 21.

ADEQ, 2018. Public Notice: Notice of Hazardous Substance Listing and Availability Water Quality Assurance Revolving Fund Remedial Investigation and Feasibility Study, 20 February.

Arizona Geologic Survey, 2019, The Geologic Map of Arizona. http://data.azgs.az.gov/geologic-map-of-arizona/


Arizona Department of Water Resources (ADWR), 2019, Hydrology of the Lake Havasu Basin. http://www.azwater.gov/AzDWR/StatewidePlanning/WaterAtlas/UpperColoradoRiver/Hydrology/LakeHavasu.htm

Arizona Water, 2019. Section 4.5: Lake Havasu Basin Draft: http://www.azwater.gov/azdwr/StatewidePlanning/WaterAtlas/documents/Lake_Havasu_draft_web.pdf (Accessed 15 January 2019).

CH2M Hill Engineers, Inc. (CH2M), 2017, Technical Memorandum: North Well Field Well 11 January 19, 2017 Sampling Results, 27 February.

Dames & Moore (D&M) 1999a, Corrective Action Plan, McCulloch Corporation Facility, 900 Lake Havasu Avenue, North Lake Havasu City, Arizona, ADEQ LUST No. 2606.01, Facility ID No. 0-003088, June 28.

D&M, 1999b. Final Soil Gas Survey Report, McCulloch Facility, 19 October.

Ecology and Environment, Inc., 1991, Environmental Priorities Initiative Preliminary Assessment, 6 September.

Ecology and Environment, Inc., 2000, Kiowa Ponds, Lake Havasu City, Arizona – Brownfield Targeted Site Assessment Report, May.

Envirotec Solutions, 1994, Environmental Property Evaluation and Remedial Program Phase II, , McCulloch Corporation, 900 Lake Havasu Avenue, Lake Havasu City, Arizona 86403, April 25.

Gallagher & Kennedy, 2014, Memorandum: Former McCulloch Facility, 900 Lake Havasu Avenue North, Lake Havasu City, AZ 86403, Documents Related to Soil Closure Pursuant to A.R.S. 49-158, 25 July.

Geosyntec Consultants, Inc. (Geosyntec), 2015, Final Vadose Zone Early Response Action Focused Feasibility Study, State Route 95 and Kiowa Boulevard Site, November.

Geosyntec, 2018, Workplan for Remedial Investigation Activities, Lake Havasu Avenue and Holly Avenue WQARF Site, Lake Havasu City, Arizona, April 5.

IT Enviroscience, 1983, Waste Storage and Handling Facility, Closure Plan, McColloch Division of Black and Decker, 900 Lake Havasu Avenue, Lake Havasu City, Arizona, 1983


Jacobs, 2018a, Site Characterization Report, Former Kiowa Ponds, Lake Havasu City, Arizona, July.

Jacobs, 2018b, Supplemental to Site Characterization Report, Former Kiowa Ponds, Lake Havasu City, Arizona, September 17.

Kendall, C., 1998, Isotope Tracers in Catchment Hydrlogy.

Lake Havasu City (The City), 2005, Lake Havasu City Kiowa Ponds Final Closure Report, 15 February.

The City, 2008, Office of the City Attorney Memorandum: Former McCulloch Facility, 18 March.

The City, 2010, Water Conservation Plan, Lake Havasu City, Arizona, 30 November.

The City, 2015, Water Conservation Plan, Lake Havasu City, Arizona, 20 November.

The City, 2016, 2016 General Plan, Lake Havasu City, Arizona, 8 November.

G. Michalskiab, M. Kolanowskib, & K. M. Rihaa, 2015, Oxygen and Nitrogen Isotopic Composition on Nitrate in Commercial Fertilizers, Nitric Acid and Reagen Salts, Isotopes in Environmental and Health Studies, July.

Montgomery & Associates Water Resource Consultants (M&A), 2015, Technical Memorandum Draft: Preliminary Investigation for McCulloch Site, Lake Havasu City, Arizona, 16 January.

Naval Facilities Engineering Command, 2014, In Situ Biogeochemical Transformation Processes for Treating Contaminated Groundwater, September.

Ninyo & Moore Geotechnical and Environmental Sciences Consultants (N&M), 2014a, Risk Assessment Former McCulloch Facility Plating Shop Area, 25 July.

N&M, 2014b, Engineering Control Plan Former McCulloch Facility Plating Shop Area, 25 July.

N&M, 2014c, Risk Assessment, Former McCulloch Facility Plating Shop Area, 900 Lake Havasu Avenue North, Lake Havasu City, Arizona, July.


Parsons Infrastructure & Technology Group, Inc., 2008, Technical Protocol for Enhanced Anaerobic Bioremediation Using Permeable Mulch Biowalls and Bioreactors, May.

Pearthee and House, 2014, Paleogeomorphology and Evaluation of the early Colorado River Inferred from Relationship in Mojave and Cottonwood valleys, Arizona, California, and Nevada.

Rascona, 2005, Maps showing groundwater conditions in the Phoenix Active Management Area, Maricopa, Pinal and Yavapai Counties, Arizona, Nov. 2002-Feb 2003, Arizona Department of Water Resources.

SA&B Environmental & Chemical Consultants (SA&B), 1996a, Soil and Groundwater Sampling Results, McCulloch Corporation, 19 January.

SA&B, 1996b, Phase II Final Site Characterization Work Plan, McCulloch Corporation – Lake Havasu City Plant, 8 May.

SA&B, 1996c, Soil and Groundwater Sampling Results Phase II, McCulloch Corporation, 20 November.

SA&B, 1997, Site Characterization Report, McCulloch Corporation, 24 October.

Sarria, Mayra, John Michael Gonzales, Daniel Gerrity, Jacimaria Batista, 2018, Biological Reduction of Nitrate and Perchlorate in Soil Microcosms: An Electron Donor Comparison of Glycerol, Emulsified Oil, and Mulch Extract, 5 December.

STC Environmental, Inc., 1992, Subsurface/Analytical Investigation Report, McCulloch Corporation, 29-31 May.

Tetra Tech, 2014a, Field Sampling Work Plan for the Former McCulloch Site, 21 February.

Tetra Tech, 2014b, Summary Report for March/April 2014 Groundwater Monitoring and Sampling Event, Former McCulloch Site, 30 June.

United States Department of Agriculture, 2018, USDA Natural Resources Conservation Service (NRCS) Web Soil Survey. https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx (Last updated 12 September 2018; Accessed 15 January 2019).

https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorStored=Gonzales%2C+John+Michael

https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorStored=Gerrity%2C+Daniel

https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorStored=Batista%2C+Jacimaria


URS Corporation (URS), 2001a, Geochemical Fixation Pilot Test Draft Work Plan, Former McCulloch Site, 27 August.

URS, 2001b, Final Report, Aquifer Test Well MW-21 Installation and Results of Hydropunch Sampling, McCulloch Facility, 27 September.

URS, 2001c, MW-21 Aquifer Test Final Report, McCulloch Facility, 10 October.

URS, 2001d, Evaluation of Geochemical Conditions, Former McCulloch Site, 5 November.

URS, 2002a, Draft Work Plan Vadose Zone Geochemical Fixation, Former McCulloch Site, June.

URS, 2002b, Draft Geochemical Fixation Pilot Test Report, Former McCulloch Facility, 28 August.

URS, 2002c, Draft Report Vadose Zone Geochemical Fixation Pilot Test, Former McCulloch Facility, September.

URS, 2002d, Transition to Monitored Natural Attenuation, Former McCulloch Facility, 25 November.

URS, 2002e, Draft Work Plan Source Mitigation Phase II Chromium Remediation, Former McCulloch Site, 6 December.

URS, 2003a, Draft Report Preliminary Site Conceptual Model, Former McCulloch Facility, 14 April.

URS, 2003b, Monitor Wells MW-23 and MW-24 Installation Report, Former McCulloch Facility, 15 August.

URS, 2003c, Draft Report Regional Groundwater Flow Model for the Lake Havasu Basin, Mohave County, Arizona, 16 December.

URS, 2004a, Revised Regional Investigation of Chromium in Groundwater Phase II Chromium Remediation, 14 January.

URS, 2004b, First Quarter 2004 Groundwater Monitoring Report, Former McCulloch Facility, 26 March.


URS, 2004c, Groundwater Investigation and Treatability Testing Work Plan, Former McCulloch Facility, 14 May.

URS, 2005, Memorandum: Investigation Well I-2 Data, Former McCulloch Facility, 31 January.

URS, 2007a, Installation Report Investigation Wells I-1 and I-2, Former McCulloch Facility, 21 February.

URS, 2007b, Installation Report Investigation Wells I-3 and I-4, Former McCulloch Facility, 6 April.

URS, 2007c, Installation Report Investigation Wells I-5 and I-6, Former McCulloch Facility, 15 June.

URS, 2008, First Half 2008 Groundwater Monitoring Report, Former McCulloch Facility, 2 September.

URS, 2009, Second Half 2008 Groundwater Monitoring Report, Former McCulloch Facility, 6 February.

URS, 2015, Final Source Mitigation Report Phase II Chromium Remediation: February – March 2003, Former McCulloch Facility, 10 July.

USTank Management, 1992, Permanent Closure of 2 USTs Environmental Site Characterization, McCulloch Corporation, 900 Lake Havasu Avenue, Lake Havasu City, Arizona 86403. January 7.

USTank Management, 1993, Environmental Site Characterization, McCulloch Corporation, 900 Lake Havasu Avenue, Lake Havasu City, Arizona 86403. December 16.

USEPA, 2018, Regional Screening Level (RSL) Summary Table (TR=1E-06, HQ=1), November. www.epa.gov/risk/regional-screening-levels-rsls-generic-tables.

United States Fish and Wildlife Service (USFWS), 2019, Information, Planning and Conservation (IPaC) System Information for Planning and Consultation Resource List: https://ecos.fws.gov/ipac/location/3C7AIPFOS5E3HJ7DDLTGJEYV5Q/resources (Accessed 11 March).


United States Geological Survey, 1996, Groundwater Atlas of the United States: Arizona, Colorado, New Mexico, Utah. http://pubs.usgs.gov/ha/ha730/ch_c/index.html (Accessed December 2018).

W.L. Gore & Associates, Inc., 1998, Gore-Sober® Screening Survey Final Report, McCulloch Plant, Lake Havasu, Arizona, 20 August.

Western Technologies, Inc. 1984, Certificate of Partial Closure, McCulloch Corporation, Lake Havasu City, Arizona, February.


10. LIMITATIONS

This Remedial Investigation was performed according to A.R.S. 49-287.03 and A.A.C. R18-16-406, and does not represent an exhaustive investigation of all potential environmental impacts at the Site. The findings of this report, to the best of our knowledge, are valid as of the date the work was performed. However, changes in the conditions of a site can occur with the passage of time, whether due to natural processes or the works of man on the Site or neighboring areas. In addition, changes in applicable or appropriate regulations and standards may occur, whether they result from legislation, from the broadening of knowledge, or from other reasons. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside our control. The work was performed using the degree of care and skill ordinarily exercised under similar circumstances by environmental consultants practicing in this or similar localities. No other warranty or guarantee, expressed or implied, is made as to the findings, opinions, conclusions, and recommendations included in this report.

FIGURES

TABLES

APPENDIX A Boring Logs

APPENDIX B Historical Maps

APPENDIX C.1 Laboratory Analytical Reports – Soil

APPENDIX C.2 Laboratory Analytical Reports – Soil-Vapor

APPENDIX C.3 Laboratory Analytical Reports –

Groundwater

APPENDIX C.4 Microbial Analysis Reports

APPENDIX D Well Survey Report

APPENDIX E Draft Land and Water Use Report