4.8 GEOLOGY, SOILS, AND PALEONTOLOGICAL RESOURCES … · 4.8 GEOLOGY, SOILS, AND PALEONTOLOGICAL RESOURCES This section addresses geologic, seismic, and soils hazards, including the

4.8 GEOLOGY, SOILS, AND PALEONTOLOGICAL RESOURCES

This section addresses geologic, seismic, and soils hazards, including the potential for construction-related erosion and loss of topsoil. The potential for long-term erosion effects is addressed in Section 4.19, “Water Quality and Groundwater Resources.” This section also provides a description of rock formations where earthmoving activities would occur, a determination of the paleontological sensitivity of those formations, and a discussion of the types of fossils that have been recovered from other recorded localities within the same rock formations.

4.8.1 REGULATORY SETTING

FEDERAL

U.S. Army Corps of Engineers Engineering Manuals and Technical Letters

There are a several engineering manuals (EM) prepared by the U.S. Army Corps of Engineers (USACE) that contain guidelines for design and construction of embankments, levees, and seepage berms. The primarily USACE guidance is contained in EM 1110-2-1913 Design and Construction of Levees (USACE 2000). In addition, engineering technical letters (ETL) 1110-2-569, Design Guidance for Levee Underseepage (USACE 2005) and 1110-2-555, Design Guidance on Levees (USACE 1997), contain guidance that is applicable to the proposed levee design and reconstruction.

Federal Emergency Management Agency

For levees to be certified by the Federal Emergency Management Agency (FEMA) as providing flood protection, evidence also must be provided that adequate design and operation and maintenance systems are in place to provide reasonable assurance that protection exists from a base flood (in the case of the proposed project, the Urban Levee Design Criteria (ULDC). Specific requirements pertaining to amount of freeboard, closure devices, embankment protection from floods, embankment and foundation stability, settlement, interior drainage, operation plans, and maintenance plans are contained in 44 Code of Federal Regulations (CFR) Section 65.10. Applies to project design and levee reconstruction.

Earthquake Hazards Reduction Act

In October 1977, the U.S. Congress passed the Earthquake Hazards Reduction Act to reduce the risks to life and property from future earthquakes in the U.S. through the establishment and maintenance of an effective earthquake hazards reduction program. To accomplish this goal, the act established the National Earthquake Hazards Reduction Program (NEHRP). This program was substantially amended in November 1990 by the National Earthquake Hazards Reduction Program Act (NEHRPA), which refined the description of agency responsibilities, program goals, and objectives.

The mission of NEHRP includes improved understanding, characterization, and prediction of hazards and vulnerabilities; improved building codes and land use practices; risk reduction through post-earthquake investigations and education; development and improvement of design and construction techniques; improved mitigation capacity; and accelerated application of research results. The NEHRPA designates FEMA as the lead agency of the program and assigns several planning, coordinating, and reporting responsibilities. Other NEHRPA

North Sacramento Streams, Sacramento River East Levee, Lower American River, and Related Flood Improvements Project DEIR AECOM Sacramento Area Flood Control Agency 4.8-1 Geology, Soils, and Paleontological Resources

agencies include the National Institute of Standards and Technology, National Science Foundation, and U.S. Geological Survey (USGS). Applies to project design and levee reconstruction.

STATE

Alquist-Priolo Earthquake Fault Zoning Act

The Alquist-Priolo Earthquake Fault Zoning Act (Alquist-Priolo Act) (California Public Resources Code [PRC] Sections 2621–2630) was passed in 1972 to reduce the hazard of surface faulting to structures designed for human occupancy. The main purpose of the law is to prevent the construction of buildings used for human occupancy on the surface trace of active faults. The law addresses only the hazard of surface fault rupture and is not directed toward other earthquake hazards. The Alquist-Priolo Act requires the State Geologist to establish regulatory zones known as Earthquake Fault Zones around the surface traces of active faults and to issue appropriate maps. The maps are distributed to all affected cities, counties, and State agencies for their use in planning efforts. Before a project can be permitted in a designated Alquist-Priolo Earthquake Fault Zone, cities and counties must require a geologic investigation to demonstrate that proposed buildings would not be constructed across active faults. Applies to project design and levee reconstruction.

Seismic Hazards Mapping Act

The Seismic Hazards Mapping Act of 1990 (California PRC Sections 2690–2699.6) addresses earthquake hazards from non-surface fault rupture, including liquefaction and seismically induced landslides. The act established a mapping program for areas that have the potential for liquefaction, landslide, strong ground shaking, or other earthquake and geologic hazards. The act also specifies that the lead agency for a project may withhold development permits until geologic or soils investigations are conducted for specific sites and mitigation measures are incorporated into plans to reduce hazards associated with seismicity and unstable soils. Applies to project design and levee reconstruction.

National Pollutant Discharge Elimination System and Storm Water Pollution Prevention Plans

As discussed in detail in Section 4.12, “Hydrologic and Hydraulic Resources,” the State Water Resources Control Board (SWRCB) and Central Valley Regional Water Quality Control Board (Central Valley RWQCB) have adopted specific National Pollutant Discharge Elimination System (NPDES) permits for a variety of activities that have the potential to discharge wastes (including sediment) to waters of the State. The SWRCB’s Statewide stormwater general permit for construction activity (Order 2009-0009-DWQ) is applicable to all land-disturbing construction activities that would disturb 1 acre or more. Compliance with the NPDES permit requires submittal to the Central Valley RWQCB of notices of intent (NOI) to discharge, and implementation of stormwater pollution prevention plans (SWPPPs) that include best management practices (BMPs) to minimize water quality degradation during construction activities. Applies to earthmoving activities throughout the project study area.

California Building Standards Code

The California Building Standards Commission is responsible for coordinating, managing, adopting, and approving building codes in California. The State of California provides minimum standards for building design through the California Building Standards Code (CBC) (California Code of Regulations [CCR] Title 24). The CBC applies to building design and construction in the State and is based on the Federal Uniform Building Code

AECOM North Sacramento Streams, Sacramento River East Levee, Lower American River, and Related Flood Improvements Project DEIR Geology, Soils, and Paleontological Resources 4.8-2 Sacramento Area Flood Control Agency

used widely throughout the country (generally adopted on a state-by-state or district-by-district basis). The CBC has been modified for California conditions with numerous more detailed or more stringent regulations.

The State earthquake protection law (California Health and Safety Code Section 19100 et seq.) requires that structures be designed to resist stresses produced by lateral forces caused by wind and earthquakes. The CBC requires an evaluation of seismic design that falls into Categories A–F (where F requires the most earthquake-resistant design) for structures designed for a project site. The CBC philosophy focuses on “collapse prevention,” meaning that structures are designed for prevention of collapse for the maximum level of ground shaking that could reasonably be expected to occur at a site.

Chapter 16 of the CBC specifies exactly how each seismic design category is to be determined on a site-specific basis through the site-specific soil characteristics and proximity to potential seismic hazards. Chapter 18 of the CBC regulates the excavation of foundations and retaining walls. This chapter regulates the preparation of a preliminary soil report, engineering geologic report, geotechnical report, and supplemental ground-response report. Chapter 18 also regulates analysis of expansive soils and the determination of the depth to groundwater table. The potential for liquefaction and soil strength loss must be evaluated for site-specific peak ground acceleration magnitudes and source characteristics consistent with the design earthquake ground motions. Peak ground acceleration must be determined from a site-specific study, the contents of which are specified in CBC Chapter 18. Finally, Appendix J of the 2010 CBC regulates grading activities, including drainage and erosion control and construction on unstable soils, such as expansive soils and areas subject to liquefaction. Applies to proposed encroachment removal.

Professional Paleontological Standards

The Society of Vertebrate Paleontology (1995, 1996), a national scientific organization of professional vertebrate paleontologists, has established standard guidelines that outline acceptable professional practices in the conduct of paleontological resource assessments and surveys, monitoring and mitigation, data and fossil recovery, sampling procedures, specimen preparation, analysis, and curation. Most practicing professional paleontologists in the nation adhere to the Society of Vertebrate Paleontology assessment, mitigation, and monitoring requirements, as specifically spelled out in its standard guidelines. Applies to the paleontological sensitivity determination of rock units in the project study area and protection of potential paleontological resources.

REGIONAL AND LOCAL

Sacramento County General Plan

The following policies from the Sacramento County General Plan of 2005-2030 Safety and Conservation Elements regarding geology and paleontological resources apply to the proposed project (Sacramento County 2011:2 and 79).

► Policy SA-1: The County shall require geotechnical reports and impose the appropriate mitigation measures for new development located in seismic and geologically sensitive areas. (Applies to proposed levee reconstruction activities.)

► Policy CO-161: As a condition of approval for discretionary projects, require appropriate mitigation to reduce potential impacts where development could adversely affect paleontological resources. (Applies to project-related earthmoving activities in paleontologically sensitive rock units.)


► Policy CO-162: Projects located within areas known to be sensitive for paleontological resources should be monitored to ensure proper treatment of resources and to ensure crews follow proper reporting, safeguards and procedures. (Applies to project-related earthmoving activities in paleontologically sensitive rock units.)

► Policy CO-163: Require that a certified geologist or paleoresources consultant determine appropriate protection measures when resources are discovered during the course of development and land altering activities. (Applies to project-related earthmoving activities in paleontologically sensitive rock units.)

Sacramento County Grading Ordinance

The County’s Land Grading and Erosion Control Ordinance (County Code, Title 16, Chapter 16.44) was enacted for the purpose of minimizing damage to surrounding properties and public rights-of-way; limiting degradation of the water quality of watercourses; and curbing the disruption of drainage system flow caused by the activities of clearing, grubbing, grading, filing, and excavating land. The ordinance includes administrative procedures, minimum standards of review, and implementation and enforcement procedures for the control of erosion and sedimentation that are directly related to land-grading activities. Applies to land-disturbing activities throughout the project study area.

City of Sacramento 2030 General Plan

The following policies from the City of Sacramento 2030 General Plan Environmental Constraints Element regarding geology and soils apply to the proposed project (City of Sacramento 2009:2-331).

► EC 1.1.1 Review Standards. The City shall regularly review and enforce all seismic and geologic safety standards and require the use of best management practices in site design and building construction methods. (Applies to project design and construction.)

► EC 1.1.2 Geotechnical Investigations. The City shall require geotechnical investigations to determine the potential for ground rupture, ground-shaking, and liquefaction due to seismic events, as well as expansive soils and subsidence problems on sites where these hazards are potentially present. (Applies to project design and construction.)

The following policies from the City of Sacramento 2030 General Plan Historic and Cultural Resources Element regarding paleontological resources apply to the proposed project (City of Sacramento 2009:2-136 and 2-137).

► HCR 2.1.6 Planning: The City shall take historical and cultural resources into consideration in the development of planning studies and documents. (Applies to the protection of paleontological resources in the project study area.)

► HCR 2.1.10 Early Consultation: The City shall minimize potential impacts to historic and cultural resources by consulting with property owners, land developers, and the building industry early in the development review process. (Applies to the protection of paleontological resources in the project study area.)

► HCR 2.1.15 Archaeological Resources. The City shall develop or ensure compliance with protocols that protect or mitigate impacts to archaeological, historic, and cultural resources including prehistoric resources. (Applies to the protection of paleontological resources in the project study area.)


4.8.2 ENVIRONMENTAL SETTING

GEOLOGY

The project study area lies within the Sacramento Valley, which is part of the Great Valley Geomorphic Province. The Great Valley is an asymmetric trough approximately 400 miles long and approximately 50 miles wide that is bounded by the Sierra Nevada Mountains to the east and south, the Coast Ranges to the west, and the Klamath Mountains to the north. The Great Valley is drained by the Sacramento and San Joaquin Rivers, which join and flow out of the Great Valley province through San Francisco Bay. This geomorphic province is characterized by a relatively flat alluvial plain made up of a deep sequence of sediment deposits from Jurassic (approximately 180 million years Before Present [B.P.]) to recent age. The sediments in the Great Valley vary between 3 and 6 miles in thickness and were derived primarily from erosion of the Sierra Nevada to the east, with lesser material from the Coast Ranges to the west.

The Sacramento Valley was a depositional basin throughout most of the late Mesozoic and Cenozoic time. A vast accumulation of sediments was deposited during cyclic transgressions and regressions of a shallow sea that once inundated the valley. Overlying the thick sequence of sedimentary rock units that form the deeply buried bedrock units in the mid-basin areas of the valley are Pleistocene (1.8 million–11,700 years B.P.]) and Holocene (i.e., 11,700 years B.P.–Present Day) alluvial deposits, consisting of reworked fan and stream materials that were deposited by streams before the construction of the existing flood control systems. The youngest geomorphic features in the project study area are low floodplains, which are found primarily along the Sacramento and American Rivers. The natural floodplains of these rivers are very wide in this area because the land is relatively flat. These major drainage ways were originally confined within broad natural levees sloping away from the rivers or streams. The natural levees formed through the deposition of alluvium during periods of flooding. As flood waters lost energy, the coarser materials settled out nearest the rivers and streams, forming the natural levees and sand bars in the vicinity of the river channel. The finer material was carried in suspension farther from the rivers or streams, and settled out in quiet water areas such as swales, abandoned meander channels, and lakes. However, because the streams have meandered and reworked the previously deposited sediments, extreme variations in material types may be found over a limited distance or depth.

Flanking the Holocene alluvial deposits in the project study area are late Pleistocene alluvial fan and terrace deposits of the Modesto and Riverbank Formations (Helley and Harwood 1985). Stream terrace deposits, mapped as the Modesto Formation, are higher in elevation and older than floodplain sediments. Before the construction of the existing levees, these stream terraces were occasionally flooded, but only small amounts of sediment were deposited during flood events. The lower fan terraces of the Riverbank Formation are higher in elevation and older than stream terraces, and were only rarely flooded. In most areas of the project study area, the younger Modesto Formation has been worn away by erosional processes, thus leaving the older Riverbank Formation exposed at the surface.

SEISMICITY

The Sacramento Valley has experienced relatively low seismic activity in the past and does not contain any Alquist-Priolo Earthquake Fault Zones (California Geological Survey [CGS] 2012). Numerous earthquakes of magnitude (M) 5.0 or greater have occurred on regional faults in the Coast Ranges, approximately 38–55 miles west of downtown Sacramento. The nearest known active (Holocene or Historic) fault trace to the project study area is the Dunnigan Hills fault, approximately 25 miles northwest of downtown Sacramento (Jennings 1994).


Regionally active faults are listed in Table 4.8-1. In addition, the approximate distance from the project study area (measured from downtown Sacramento), maximum moment magnitude, and slip rate are identified.

Table 4.8-1. Active Regional Faults

Fault Name Approximate Distance

from Downtown Sacramento (miles)

Regional Location Maximum Moment

Magnitude Slip Rate (mm/yr)

Dunnigan Hills 25 Western Sacramento Valley N/A N/A

Great Valley Fault Zone Segment 3 26 Margin between Sacramento Valley and Coast Range 7.1 1.25

Great Valley Fault Zone Segment 4 26 Margin between Sacramento Valley and Coast Range

6.6 1.25

Great Valley Fault Zone Segment 5 37 Margin between Sacramento Valley and Coast Range

6.7 1.5

Hunting Creek-Berryessa 38 Coast Range 7.1 6.0

Green Valley-Concord 40 Coast Range 6.8 5.0

Greenville Fault Zone (includes Clayton and Marsh Creek sections) 45 Coast Range 7.0 2.0

Mount Diablo Blind Thrust 47 Coast Range 6.7 2.0

West Napa 48 Coast Range 6.7 1.0

Hayward–Rodgers Creek 55 Coast Range 7.26 9.0 Notes: mm/yr = millimeters per year; N/A = not available Sources: Jennings 1994; Working Group on California Earthquake Probabilities2008:Supplemental Worksheets and Appendix A

Potential seismic hazards resulting from a nearby moderate to major earthquake can generally be classified as primary and secondary. The primary effect is fault ground rupture, also called surface faulting. Because there are no active faults mapped in the project study area by the CGS or the USGS, and the area is not located within an Alquist-Priolo Earthquake Fault Zone, fault ground rupture is unlikely. Common secondary seismic hazards include ground shaking, liquefaction, subsidence, and seiches. These hazards are discussed briefly below:

► Ground shaking. Seismic ground shaking refers to ground motion that results from the release of stored energy during an earthquake. The intensity of ground shaking depends on the distance from the earthquake epicenter to the site, the magnitude of the earthquake, site soil conditions, and the characteristic of the source.

► Ground failure/liquefaction. Liquefaction is a process by which water-saturated materials (including soil, sediment, and certain types of volcanic deposits) lose strength and may fail during strong ground shaking, when granular materials are transformed from a solid state into a liquefied state as a result of increased pore-water pressure. Structures on ground that undergoes liquefaction may settle or suffer major structural damage. Liquefaction is most likely to occur in low-lying areas where the substrate consists of poorly consolidated to unconsolidated water-saturated sediments or similar deposits of artificial fill. Liquefaction during an earthquake requires strong shaking continuing for a long period and loose, clean granular materials (particularly sands) that may settle and compact because of the shaking. Evidence of liquefaction may be observed in “sand boils,” which are expulsions of sand and water from below the surface due to increased pore-water pressure below the surface. Areas paralleling the Sacramento River that contain clean sand layers


with low relative densities coinciding with a relatively high water table have generally high liquefaction potential.

► Subsidence and settlement. Subsidence is the gradual settling or sudden sinking of the ground surface resulting from subsurface movement of earth materials. Seismically-induced settlement refers to the compaction of soils and alluvium caused by ground shaking. Fine-grained soils are subject to seismic settlement and differential settlement. Areas underlain by low-density silts and clays associated with fluvial depositional environments are susceptible to seismically induced settlement. These environments include old lakes, sloughs, swamps, and streambeds. The amount of settlement may range from a few inches to several feet. The potential for differential settlement is highest and occurs over the largest areas during high magnitude earthquakes. A potential for differential settlement exists where low-density and unconsolidated material is encountered, such as overbank river deposits (present day and historical) common along the Sacramento River. Subsidence and settlement may also occur from construction of the adjacent levee separate from liquefaction or densification due to both immediate settlements in granular soils and the consolidation of fine grained soils.

► Seismic seiches. A seiche is an earthquake-induced wave within an enclosed or restricted body of water, such as a lake, reservoir, or channel. Seiches can cause a body of water to overtop and damage levees and dams and may lead to inundation of surrounding areas.

PALEONTOLOGICAL RESOURCES

Based on a review of regional geologic mapping prepared by Wagner et al. 1987, earthmoving activities in the project study area (including levee improvements, staging and borrow site activities, encroachment removal, vegetation management, and the Conservation Strategy) would occur in the following geologic formations:

► Levee and Channel Deposits. Holocene-age deposits of active stream channels and their natural levees, as well as adjacent broad alluvial fans.

► Basin Deposits. Holocene-age fine-grained deposits of silt and clay in flood basins between modern watercourses (locally includes marsh deposits).

► Riverbank Formation. This formation is Pleistocene in age; estimates place the age between 130,000 and 450,000 years B.P. (Marchand and Allwardt 1981). In the project vicinity, the Riverbank Formation forms higher alluvial fans and terraces of major rivers and can be divided into upper and lower members. Sediments in the Riverbank Formation consist of weathered reddish gravel, sand, and silt that form alluvial terraces and fans. In the Sacramento Valley, this formation contains more mafic rock fragments than the San Joaquin Valley and thus tends toward stronger soil-profile developments that are more easily distinguishable from the younger Modesto Formation (Helley and Harwood 1985).

Paleontological Resource Assessment Criteria

The potential paleontological importance of the project study area can be assessed by identifying the paleontological importance of rock units that are exposed there. Because topographic maps can easily delineate the distribution of a rock unit, this method is conducive to determining the parts of the project study area that are of higher and lower sensitivity for paleontological resources.


A paleontologically sensitive rock unit is one that is rated high for potential paleontological productivity and is known to have produced unique, scientifically important fossils. The potential paleontological productivity rating of a rock unit exposed in a project area refers to the abundance and densities of fossil specimens, previously recorded fossil sites, or both in exposures of the unit in and near the project area. Exposures of a specific rock unit in the project area are most likely to yield fossil remains representing particular species in quantities or densities similar to those previously recorded from the unit in other locations. Therefore, the paleontological sensitivity determination of a rock unit is based primarily on the types and numbers of fossils that have been previously recorded from that rock unit (i.e., the paleontological productivity).

The following tasks were completed to establish the paleontological sensitivity of each rock unit exposed in or near the project study area:

► The potential paleontological productivity of each rock unit was assessed, based on the density of fossil remains previously documented within the rock unit.

► The potential of a rock unit exposed in the project area to contain a unique paleontological resource was considered.

Paleontological Resources Inventory

To develop a baseline paleontological resource inventory of the project study area and to establish the paleontological sensitivity of each geologic unit present within the project study area, background research was conducted and each geologic formation exposed within the project study area was assigned a paleontological sensitivity based on the number of previously recorded fossil sites from that unit and the scientific importance of the fossil remains recorded. These methods are consistent with Society of Vertebrate Paleontology (SVP) 1995 guidelines for assessing the importance of paleontological resources.

Geologic maps and available published and unpublished geological and paleontological literature covering the bedrock and surficial geology of the project study area were reviewed to determine the exposed and subsurface rock units, to assess the potential paleontological productivity of each rock unit, and to delineate their respective areal distribution in the project study area. The number and location of previously recorded fossil sites from rock units exposed within the project study area and the types of fossil remains each rock unit has produced were evaluated based on published and unpublished geological and paleontological literature.

The literature review was supplemented by a records search from the University of California, Berkeley Museum of Paleontology (UCMP) on October 9, 2014.

Paleontological Resources Assessment by Rock Unit

Levee and Channel Deposits, and Basin Deposits

The Levee and Channel Deposits, as well as the Basin Deposits, are of Holocene age. By definition, to be considered a unique paleontological resource, a fossil must be more than 11,700 years old. Holocene deposits contain only the remains of extant, modern taxa (if any resources are present), which are not considered “unique” paleontological resources. Therefore, these formations are considered to be of low paleontological sensitivity.


Riverbank Formation

The Pleistocene epoch, known as the “great ice age,” began approximately 1.8 million years ago. Based on his survey of vertebrate fauna from the nonmarine late Cenozoic deposits of the San Francisco Bay region, Savage (1951) concluded that two major divisions of Pleistocene-age fossils could be recognized: the Irvingtonian (older Pleistocene fauna) and the Rancholabrean (younger Pleistocene fauna). These two divisions of Quaternary Cenozoic vertebrate fossils are widely recognized today in the field of paleontology. The age of the later Pleistocene, Rancholabrean fauna was based on the presence of bison and of many mammalian species that inhabit the same area today. In addition to bison, larger land mammals identified as part of the Rancholabrean fauna include mammoths, mastodons, camels, horses, and ground sloths. The Irvingtonian fauna is more scarce, and is represented by Borophagus (bone-crushing dogs), hyenas, saber-toothed cats, rabbits, giant marmots, horses, mammoths, and mastodons.

Remains of land mammals have been found at several localities in alluvial deposits referable to the Riverbank Formation. Jefferson (1991a, 1991b) compiled a database of California Late Pleistocene vertebrate fossils from published records, technical reports, unpublished manuscripts, information from colleagues, and inspection of paleontological collections at more than 40 public and private museums. Jefferson lists six different localities in Sacramento, all referable to the Riverbank Formation. For example, the Teichert Gravel Pit on State Route 16 in southeastern Sacramento County yielded specimens of broad-footed mole, Harlan’s ground sloth, rabbit, California ground squirrel, Botta’s pocket gopher, pocket mouse, groove-toothed harvest mouse, woodrat, vole, coyote, dire wolf, mammoth, horse, western camel, deer, antique bison, fish (carps and minnows), frog, snake, Pacific pond turtle, and the family Anatidae (ducks, geese, and swans).

There are at least nine recorded Rancholabrean-age vertebrate fossil sites from the Riverbank Formation in Sacramento County. Most recently, Pleistocene-age mammoth remains were discovered on July 2, 2004, during excavation of a Sacramento Municipal Utility District trench in Elk Grove (Kolber 2004). Mammoth remains recovered from that site consisted of a tusk, ribs, teeth, and portions of a shoulder blade. UCMP locality V-74086, located in south Sacramento at Ehrhardt Avenue, also contained fossilized Rancholabrean-age mammoth remains. The other UCMP sites in Sacramento—localities V-6747, V-6846, V-68141, V-69129, and V-75126—contained remains of Rancholabrean-age bison, camel, coyote, horse, Harlan’s ground sloth, mammoth, woodrat, fish, mole, snake, and gopher. Pleistocene-age fossils were recovered from the Riverbank Formation at the ARCO Arena site (Hilton et al. 2000); those fossils included remains of Harlan’s ground sloth, bison, coyote, horse, camel, squirrel, antelope or deer, and mammoth. Finally, San Diego Society of Natural History locality 0663 (Jefferson 1991a, 1991b) included fossil specimens of Rancholabrean-age horse and camel recovered from sediments in Sacramento.

Several localities near the cities of Davis and Woodland have yielded the remains of Rancholabrean-age rodents, snakes, horses, antelope, Harlan’s ground sloth, mammoth, and saber-toothed cat from sediments referable to the Riverbank Formation (Hay 1927; UCMP 2014). Three sites in Sutter County have yielded Rancholabrean vertebrate fossils recovered from Pleistocene-age sediments (UCMP 2014). UCMP locality V-4043 in the Sutter Buttes yielded remains from a Pleistocene-age horse in sediments referable to the Riverbank Formation.

Fossil specimens from the Riverbank Formation have been reported by Marchand and Allwardt (1981) near the type locality in the city of Riverbank. Fossil specimens from sediments referable to the Riverbank Formation have been reported at numerous other locations throughout the Central Valley (UCMP 2014), including Lathrop, Modesto, Stockton, Tracy (along the Delta-Mendota Canal), Manteca, and Merced.


The results of the UCMP paleontological records search (UCMP 2014) indicated that no fossil remains have been recovered from any of the locations where project-related earthmoving activities would occur. However, the occurrence of Pleistocene vertebrate fossil remains in sediments referable to the Riverbank Formation in Sacramento and throughout the Central Valley indicates that this rock formation is paleontologically sensitive.

NORTH SACRAMENTO STREAMS LEVEE IMPROVEMENTS

Based on review of regional geologic mapping prepared by Wagner et al. 1987, earthmoving activities associated with project-related activities in the North Sacramento Streams Levee Improvements area would take place in Holocene Levee and Channel Deposits, Holocene Basin Deposits, and the Pleistocene-age Riverbank Formation. Encroachment removal, vegetation management, and Conservation Strategy activities would occur in the Pleistocene-age Riverbank Formation along the Natomas East Main Drainage Canal (NEMDC)/Steelhead Creek (north of Arcade Creek), on the south side of Robla Creek, and on the north side of Dry Creek.

Table 4.8-2 summarizes several relevant characteristics of soils where levee improvements would occur. Three out of the five soil types have a moderate to high shrink-swell potential. The water erosion hazard is moderate for all soil types, while three of the soils have a moderately high wind erosion hazard. The Natural Resources Conservation Service (NRCS) has rated two of the soil types as very limited for use in levees.

Table 4.8-2. Soil Types and Descriptions for the North Sacramento Streams Levee Improvements Area

Soil Map Unit Name Shrink-Swell Potential1 Drainage Class Permeability2 Wind3 Erosion

Hazard Water4 Erosion

Hazard NRCS Soil Limitations for

Levees Dierssen sandy loam, drained, 0 to 2 percent slopes

Moderate Somewhat poorly drained

Moderately high 3 Moderate

Very limited: shallow depth to saturated zone,

thin soil layer, dusty

San Joaquin fine sandy loam, 0 to 3 percent slopes

Low Moderately well drained

Moderately high 3 Moderate Somewhat limited: thin

soil layer, dusty

San Joaquin-Urban land complex, 0 to 3 percent slopes

Low Moderately well drained

Moderately high 3 Moderate Somewhat limited: thin

soil layer, dusty

Cosumnes silt loam drained, 0 to 2 percent slopes

High Somewhat poorly drained

Moderately high 6 Moderate Somewhat limited: dusty

Clear Lake clay, hardpan substratum, drained, 0 to 1 percent slopes

High Somewhat poorly drained

Moderately low 4 Moderate


thin soil layer, dusty

Notes: NRCS = Natural Resources Conservation Service 1 Based on percentage of linear extensibility. Shrink-swell potential ratings of “moderate” to “very high” can result in damage to buildings,

roads, and other structures. 2 Based on standard NRCS saturated hydraulic conductivity (Ksat) class limits; Ksat refers to the ease with which pores in a saturated soil

transmit water. 3 The soils assigned to wind erodibility group 1 are the most susceptible to wind erosion, and those assigned to group 8 are the least

susceptible. 4 Based on the erosion factor “Kw whole soil,” which is a measurement of relative soil susceptibility to sheet and rill erosion by water. Source: NRCS 2013


SACRAMENTO RIVER EAST LEVEE IMPROVEMENTS

Based on a review of regional geologic mapping prepared by Wagner et al. 1987, earthmoving activities associated with project-related activities in the Sacramento River East Levee Improvements area would take place in Holocene Levee and Channel Deposits and Holocene Basin Deposits. In addition, a detailed geologic map of the Sacramento River East Levee Improvements area was prepared by Fugro William Lettis & Associates, Inc. (2010:Plate 1). This detailed geologic map generally correlates to the regional scale map but provides a further breakdown of geologic units based on the results of site-specific surveys and subsurface testing. As indicated therein, the Riverbank Formation does not outcrop at the surface in the Sacramento River East Levee Improvements area, but instead occurs at depths of approximately 60–70 feet below mean sea level (Fugro William Lettis & Associates, Inc. 2010:Figure 4). Therefore, only Reaches 12 and 13, where deep cutoff walls are proposed from 65–95 below mean sea level, have any potential of encountering the Riverbank Formation during project-related activities.

Table 4.8-3 summarizes several relevant characteristics of soils where levee improvements would occur. Most of the soil types have a low shrink-swell potential and a moderate wind and water erosion hazard. The soils are generally poorly drained, with a moderately high permeability. The NRCS has rated most of the soil types as very limited for use in levees.

AMERICAN RIVER AND BEACH LAKE LEVEES HIGH-HAZARD LEVEE ENCROACHMENT AND VEGETATION REMOVAL

American River

Earthmoving activities associated with encroachment removal, vegetation management, and the Conservation Strategy along the Lower American River would expose soil to erosive forces. The nature of soil properties such as erosion potential is site-specific, and depends on various factors such as soil composition (e.g., clay soils have a very low erosion potential as compared to soils composed primarily of silt or sand), degree of slope, and the duration and intensity of rainfall associated with storm events. Activities along the Lower American River would occur in a variety of soil types including Columbia sandy loam, Laugenour loam, Rossmoor fine sandy loam, and Urban Land. A review of NRCS (2013) soil survey data indicate that these soils have a low to moderate susceptibility to wind and water erosion.

The potential for project-related earthmoving activities to encounter unique paleontological resources is determined by the type of rock formation. As previously described above, the types of rock formations are site-specific and vary widely depending on the location where project-related activities would occur. Encroachment removal, vegetation management, and Conservation Strategy activities (including the proposed riparian plantings at the Woodlake and Camp Pollock sites) along the Lower American River would occur only in Holocene-age Levee and Channel Deposits.

Beach Lake

Earthmoving activities associated with encroachment removal, vegetation management, and the Conservation Strategy along the Beach Lake Levee would occur in Dierssen clay loam, Egbert clay, and Galt clay. A review of NRCS (2013) soil survey data indicate that these soils have a low to moderate susceptibility to wind and water erosion.


Table 4.8-3. Soil Types and Descriptions for Sacramento River East Levee Improvements Area

Soil Map Unit Name Shrink-Swell Potential1 Drainage Class Permeability2 Wind3 Erosion

Hazard Water4 Erosion

Hazard NRCS Soil Limitations

for Levees Columbia sandy loam, drained, 0 to 2 percent slopes, occasionally flooded

Low Somewhat poorly drained High 3 Moderate Very limited: soil

piping, dusty

Sailboat –Urban land complex, partially drained, 0 to 2 percent slopes

Low Somewhat poorly drained



soil piping, dusty

Valpac loam, partially drained, 0 to 2 percent slopes


Moderately high 6 High Somewhat limited: soil

piping, dusty

Valpac-Urban land complex, partially drained, 0 to 2 percent slopes




soil piping, dusty

Lang-Urban land complex, drained, 0 to 2 percent slopes

Low Moderately well drained High 3 Moderate


soil piping, seepage

Laugenour loam, partially drained, 0 to 2 percent slopes

Low Poorly drained High 5 Moderate Very limited: shallow

depth to saturated zone, soil piping, dusty

Laugenour-Urban land complex, partially drained, 0 to 2 percent slopes

Low Poorly drained High 5 Moderate Very limited: shallow

depth to saturated zone, soil piping, dusty

Urban land NR NR NR NR NR NR

Notes: NRCS = Natural Resources Conservation Service; NR = not rated 1 Based on percentage of linear extensibility. Shrink-swell potential ratings of “moderate” to “very high” can result in damage to buildings,

roads, and other structures. 2 Based on standard NRCS saturated hydraulic conductivity (Ksat) class limits; Ksat refers to the ease with which pores in a saturated soil

transmit water. 3 The soils assigned to wind erodbility group 1 are the most susceptible to wind erosion, and those assigned to group 8 are the least

susceptible. 4 Based on the erosion factor “Kw whole soil,” which is a measurement of relative soil susceptibility to sheet and rill erosion by water. Source: NRCS 2013

Encroachment removal, vegetation management, and Conservation Strategy activities along the Beach Lake Levee and at the Upper Beach Lake riparian planting site would occur only in Holocene-age Basin Deposits.

NATOMAS EAST MAIN DRAINAGE CANAL/STEELHEAD CREEK CORRIDOR MANAGEMENT PLAN

The environmental setting for the NEMDC/Steelhead Creek Corridor Management Plan (CMP) activities related to geology, soils, and paleontological resources would be the same as described above for the North Sacramento Streams Levee Improvements. All of the areas identified for riparian plantings are underlain by Holocene-age rock formations.


4.8.3 ENVIRONMENTAL IMPACTS AND MITIGATION MEASURES

METHODOLOGY

Evaluation of potential geology and soils impacts relied on a review of published geologic literature and maps, and NRCS soil survey data for Sacramento County.

In its standard guidelines for assessment and mitigation of adverse impacts on paleontological resources, the Society of Vertebrate Paleontology (1995) established three categories of sensitivity for paleontological resources: high, low, and undetermined. Areas where fossils have been previously found are considered to have a high sensitivity and a high potential to produce fossils. Areas that are not sedimentary in origin and that have not been known to produce fossils in the past typically are considered to have low sensitivity. Areas that have not had any previous paleontological resource surveys or fossil finds are considered to be of undetermined sensitivity until surveys and mapping are performed to determine their sensitivity. After reconnaissance surveys, observation of exposed cuts, and possibly subsurface testing, a qualified paleontologist can determine whether the area should be categorized as having high or low sensitivity. In keeping with the significance criteria of the Society of Vertebrate Paleontology (1995), all vertebrate fossils are generally categorized as being of potentially significant scientific value.

SIGNIFICANCE CRITERIA

The thresholds for determining the significance of impacts for this analysis are based on the environmental checklist in Appendix G of the State CEQA Guidelines, as amended. The proposed project would have a significant impact on geology and soils if implementation of the proposed project would:

► expose people or structures to potential substantial adverse impacts, including risk of loss, injury, or death through the rupture of a known earthquake fault, strong seismic shaking, seismic-related ground failure, soil liquefaction, or landslides;

► result in substantial soil erosion or the loss of topsoil;

► locate project facilities on a geologic unit or soil that is unstable, or that would become unstable as a result of the proposed action, and potentially result in on-site or off-site landslide, lateral spreading, subsidence, liquefaction, or collapse;

► locate project facilities on expansive soil, creating substantial risks to property;

► have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for the disposal of wastewater; or

► create a substantial flooding risk as a result of a seismic seiche.

In addition to the thresholds listed above, the proposed project would have a significant impact on paleontological resources if implementation of the proposed project would:

► directly or indirectly destroy a unique paleontological resource or site or unique geologic feature.


For the purposes of this analysis, a unique resource or site is one that is considered significant under the following professional paleontological standards. An individual vertebrate fossil specimen may be considered unique or significant if it is identifiable and well preserved, and it meets one of the following criteria:

► a type specimen (i.e., the individual from which a species or subspecies has been described);

► a member of a rare species;

► a species that is part of a diverse assemblage (i.e., a site where more than one fossil has been discovered) wherein other species are also identifiable, and important information regarding life history of individuals can be drawn;

► a skeletal element different from, or a specimen more complete than, those now available for its species; or

► a complete specimen (i.e., all or substantially all of the entire skeleton is present).

The value or importance of different fossil groups varies depending on the age and depositional environment of the rock unit that contains the fossils, their rarity, the extent to which they have already been identified and documented, and the ability to recover similar materials under more controlled conditions (such as for a research project). Marine invertebrates are generally common; the fossil record is well developed and well documented, and they would generally not be considered a unique paleontological resource. Identifiable vertebrate marine and terrestrial fossils are generally considered scientifically important because they are relatively rare.

Issues Not Discussed Further in this EIR

Surface Fault Rupture—Because the project study area is not located within an Alquist-Priolo Earthquake Fault Zone and there are no known active faults within the project study area, fault ground rupture is unlikely, and therefore this issue is not addressed further in this EIR.

Strong Seismic Ground Shaking, Liquefaction, and Unstable Soils—All levee improvements would be designed based on the results of detailed geotechnical engineering studies performed previously (e.g., Kleinfelder West, Inc. 2013) and would be required to comply with standard engineering practices for levee design. The Central Valley Flood Protection Board’s (CVFPB’s) standards are the primary state standards applicable to the proposed levee improvements; these are stated in Title 23, Division 1, Article 8, Sections 111–137 of the California Code of Regulations. The Board’s standards direct that levee design and construction be in accordance with EM 1110-2-1913 Engineering Design and Construction of Levees (USACE 2000), the primary Federal standards applicable to levee improvements. Because the design, construction, and maintenance of levee improvements must comply with the regulatory standards of USACE and CVFPB, it is assumed that the design and construction of all levee modifications would meet or exceed applicable design standards for static and dynamic stability, seismic ground shaking, liquefaction, subsidence, and seepage.

Landslides—Because the project study area is relatively flat, there would be no adverse impacts related to landslides, and this issue is not addressed further in this EIR.

Soil Suitability for Septic Systems—Because the proposed project would not involve the use of wastewater disposal systems of any kind, there would be no impact related to the ability of project study area soils to support the use of septic systems. Therefore, this issue is not addressed further in this EIR.


Seismic Seiches—While a seiche in the project study area could be damaging, the risk of seiches is low given the distance from active faults and the anticipated short duration of any seismic ground shaking in the project study area. Furthermore, levee design and construction must be carried out in accordance with EM 1110-2-1913 Engineering Design and Construction of Levees (USACE 2000), which would include design for seismic seiches. Therefore, this issue is not addressed further in this EIR.

Unique Geologic Feature—A unique geologic feature consists of a major natural element that stands out in the landscape such as a large and scenic river, gorge, waterfall, volcanic cinder cone, lava field, or glacier. The American and Sacramento Rivers are unique geologic features located adjacent to areas where project-related work would be performed. However, project-related activities would not result in damage to or destruction of either of these rivers. Therefore, this issue is not addressed further in this EIR. Potential project-related effects on the scenic qualities associated with these rivers are evaluated in Section 4.2, “Aesthetics,” and potential effects on recreational opportunities associated with these rivers are evaluated in Section 4.16, “Recreation Resources.”

Long-term impacts from soil erosion related to project operation, including the bank erosion repair sites, are addressed in Section 4.19 “Water Quality and Groundwater Resources.”

IMPACT ANALYSIS

IMPACT GEO-1

Potential Temporary, Short-term Construction-Related Erosion. Project-related earthmoving activities could result in substantial soil erosion and loss of topsoil. Therefore, this impact would be potentially significant throughout the project study area.

North Sacramento Streams Levee Improvements

SAFCA proposes to use several borrow sites in Sacramento County. The excavation of soil from borrow sites would entail the preservation and replacement of the topsoil on Borrow Sites 2, and 3, so they could be returned to their preproject condition. Borrow Site 1 has been previously used for other projects and contains existing soil stockpiles that are available for use on the proposed project. Borrow activity that entails land disturbance of 1 acre or more is subject to regulation under the California Surface Mining and Reclamation Act (SMARA), which is administered by the county in which the borrow site is located (see Section 4.14, “Mineral Resources,” for further discussion).

In addition, levee reconstruction, encroachment removal, vegetation management, and Conservation Strategy activities would include substantial construction activity over large areas, and would include excavation, soil removal, trenching, construction of earthen berms, levee crown degradation and reconstruction for cutoff wall installation, grading, and other ground-disturbing activities. These activities would result in the temporary and short-term disturbance of soil and could expose disturbed areas to winter storm events. Rainfall of sufficient intensity could dislodge soil particles from the soil surface. Once particles are dislodged and the storm is large enough to generate runoff, substantial localized erosion could occur. In addition, soil disturbance during the summer months could result in substantial loss of topsoil because of wind erosion. Therefore, these proposed project elements would have a potentially significant impact. Mitigation Measure GEO-1, described below, has been identified to address this impact.


Mitigation Measure GEO-1: Acquire Appropriate Regulatory Permits and Prepare and Implement a Storm Water Pollution Prevention Plan and Associated Best Management Practices.

Prior to the start of earthmoving activities, SAFCA shall obtain coverage under the SWRCB’s NPDES stormwater permit for general construction activity (Order 2009-0009-DWQ), including preparation and submittal of a project-specific SWPPP at the time the NOI to discharge is filed. The SWPPP shall identify and specify:

• the use of an effective combination of robust erosion and sediment control BMPs and construction techniques for use in the project area at the time of construction, that shall reduce the potential for runoff and the release, mobilization, and exposure of pollutants, including legacy sources of mercury from project-related construction sites. These may include but would not be limited to temporary erosion control and soil stabilization measures, sedimentation ponds, inlet protection, perforated riser pipes, check dams, and silt fences;

• the implementation of approved local plans, nonstormwater management controls, permanent post-construction BMPs, and inspection and maintenance responsibilities;

• the pollutants that are likely to be used during construction that could be present in stormwater drainage and nonstormwater discharges, including fuels, lubricants, and other types of materials used for equipment operation;

• the means of waste disposal;

• spill prevention and contingency measures, including measures to prevent or clean up spills of hazardous waste and of hazardous materials used for equipment operation, and emergency procedures for responding to spills;

• personnel training requirements and procedures that shall be used to ensure that workers are aware of permit requirements and proper installation methods for BMPs specified in the SWPPP; and

• the appropriate personnel responsible for supervisory duties related to implementation of the SWPPP.

Where applicable, BMPs identified in the SWPPP shall be in place throughout all site work and construction/demolition activities and shall be used in all subsequent site development activities. BMPs may include, but are not limited to, such measures as those listed below.

• Implementing temporary erosion and sediment control measures in disturbed areas to minimize discharge of sediment into nearby drainage conveyances, in compliance with State and local standards in effect at the time of construction. These measures may include silt fences, staked straw bales or wattles, sediment/silt basins and traps, geofabric, sandbag dikes, and temporary vegetation.

• Establishing permanent vegetative cover to reduce erosion in areas disturbed by construction by slowing runoff velocities, trapping sediment, and enhancing filtration and transpiration.


• Using drainage swales, ditches, and earth dikes to control erosion and runoff by conveying surface runoff down sloping land, intercepting and diverting runoff to a watercourse or channel, preventing sheet flow over sloped surfaces, preventing runoff accumulation at the base of a grade, and avoiding flood damage along roadways and facility infrastructure.

A copy of the approved SWPPP shall be maintained and available at all times on the construction site.

Timing: Submittal of the State Construction General Permit NOI and SWPPP before the start of earthmoving activities, and implementation of BMPs throughout project construction.

Responsibility: Sacramento Area Flood Control Agency.

Significance after Mitigation: Implementation of Mitigation Measure GEO-1 would reduce potentially significant temporary, short-term construction-related erosion impacts to a less-than-significant level by requiring preparation and implementation of a SWPPP with appropriate BMPs such as source control and revegetation to reduce erosion and maintain surface water quality conditions in adjacent receiving waters.

Sacramento River East Levee Improvements

The borrow site for the Sacramento River East Levee Improvements area has been previously used by the Sacramento Regional County Sanitation District for its EchoWater project and contains existing soil stockpiles that are available for use on the proposed Sacramento River East Levee Improvements project. Therefore, is not anticipated that excavation would be necessary to obtain borrow from this location and this proposed project element would have a less-than-significant impact.

Mitigation Measure: No mitigation is required.

Levee reconstruction, encroachment removal, vegetation management, and Conservation Strategy activities in the Sacramento River East Levee Improvements area would include substantial construction activity over large areas. Construction would result in the temporary and short-term disturbance of soil and could expose disturbed areas to winter storm events. Rainfall of sufficient intensity could dislodge soil particles from the soil surface. Once particles are dislodged and the storm is large enough to generate runoff, substantial localized erosion could occur. In addition, soil disturbance during the summer months could result in substantial loss of topsoil because of wind erosion. Therefore, these proposed project elements would have a potentially significant impact. Mitigation Measure GEO-1, described below, has been identified to address this impact.

Mitigation Measure: Implement Mitigation Measure GEO-1 (Acquire Appropriate Regulatory Permits and Prepare and Implement a Storm Water Pollution Prevention Plan and Associated Best Management Practices).





American River and Beach Lake Levees High-Hazard Levee Encroachment and Vegetation Removal

Encroachment removal, vegetation management, and Conservation Strategy activities in the American River and Beach Lake Levees High-Hazard Levee Encroachment and Vegetation Removal area would result in the temporary and short-term disturbance of soil and could expose disturbed areas to winter storm events. Rainfall of sufficient intensity could dislodge soil particles from the soil surface. Once particles are dislodged and the storm is large enough to generate runoff, substantial localized erosion could occur. In addition, soil disturbance during the summer months could result in substantial loss of topsoil because of wind erosion. Therefore, these proposed project elements would have a potentially significant impact. Mitigation Measure GEO-1, described below, has been identified to address this impact.





Natomas East Main Drainage Canal/Steelhead Creek Corridor Management Plan

The NEMDC/Steelhead Creek CMP activities would include construction activity that would result in the temporary and short-term disturbance of soil and could expose disturbed areas to winter storm events. Rainfall of sufficient intensity could dislodge soil particles from the soil surface. Once particles are dislodged and the storm is large enough to generate runoff, substantial localized erosion could occur. In addition, soil disturbance during the summer months could result in substantial loss of topsoil because of wind erosion. Therefore, this proposed project element would have a potentially significant impact. Mitigation Measure GEO-1, described below, has been identified to address this impact.






IMPACT GEO-2

Potential to Directly or Indirectly Destroy a Unique Paleontological Resource or Site. Project-related earthmoving activities would occur in the Riverbank Formation, which is paleontologically sensitive. Therefore, this impact would be potentially significant for the North Sacramento Streams and Sacramento River East Levee Improvements areas. Impacts for the American River and Beach Lake Levees High-Hazard Levee Encroachment and Vegetation Removal area would be less than significant because earthmoving activities would only occur in rock formations of low paleontological sensitivity.

North Sacramento Streams Levee Improvements

As discussed in detail above under the environmental setting, the Levee and Channel Deposits, as well as the Basin Deposits, are of Holocene age. Holocene deposits contain only the remains of extant, modern taxa (if any resources are present), which are not considered “unique” paleontological resources. Therefore, these formations are considered to be of low paleontological sensitivity and earthmoving activities associated with levee reconstruction, encroachment removal, vegetation management, and the Conservation Strategy in these formations would have a less-than-significant impact on unique paleontological resources.


Project-related earthmoving activities would also occur in the Pleistocene-age Riverbank Formation along Arcade Creek, NEMDC/Steelhead Creek north of Arcade Creek, the south side of Robla Creek, and the north side of Dry Creek. Because numerous vertebrate fossils have been recovered from the Riverbank Formation in northern and central California, including at least nine different localities from Sacramento County, this formation is considered to be paleontologically sensitive. Therefore, earthmoving activities associated with levee reconstruction, encroachment removal, vegetation management, and the Conservation Strategy in the Riverbank Formation could result in accidental damage to or destruction of unique paleontological resources, and these proposed project elements would have a potentially significant impact. Mitigation Measure GEO-2, described below, has been identified to address this impact.


Mitigation Measure GEO-2: Conduct Construction Personnel Education, Stop Work if Paleontological Resources are Discovered, Assess the Significance of the Find, and Prepare and Implement a Recovery Plan, as Required.

To minimize the potential for destruction of or damage to potentially unique, scientifically important paleontological resources during project-related earthmoving activities, SAFCA shall require the following measures to be implemented to minimize accidental damage to or destruction of unique paleontological resources:

• Before the start of any earthmoving activities in the North Sacramento Streams Levee Improvements area and Sacramento River East Levee Improvements area, the SAFCA shall retain a qualified paleontologist to train all construction personnel involved with earthmoving activities, including the site superintendent, regarding the possibility of encountering fossils, the appearance and types of fossils likely to be seen during construction, and proper notification procedures should fossils be encountered.

• If paleontological resources are discovered during earthmoving activities, the construction crew shall notify SAFCA and shall immediately cease work in the vicinity of the find. SAFCA shall retain a qualified paleontologist to evaluate the resource and prepare a recovery plan in accordance with Society of Vertebrate Paleontology guidelines (1996). The recovery plan may include, but is not limited to, a field survey, construction monitoring, sampling and data recovery procedures, museum storage coordination for any specimen recovered, and a report of findings. Recommendations in the recovery plan that are determined by the SAFCA to be necessary and feasible shall be implemented before construction activities can resume at the site where the paleontological resources were discovered.

Timing: Before and during construction activities in the North Sacramento Streams Improvements area.


Significance after Mitigation: Implementation of Mitigation Measure GEO-2 would reduce potentially significant impacts related to potential damage or destruction of unique paleontological resources to a less-than-significant level because construction workers would be alerted to the possibility of encountering paleontological resources and, in the event that resources were discovered, work would stop immediately and fossil specimens would be recovered and recorded and would undergo appropriate curation.

Sacramento River East Levee Improvements

Encroachment removal, vegetation management, and Conservation Strategy activities in the Sacramento River East Levee Improvements area would take place in Holocene-age rock formations, which are considered to be of low paleontological sensitivity for the same reasons described above in the North Sacramento Streams Improvements area. Therefore, these proposed project elements would have a less-than-significant impact on unique paleontological resources.



Most of the levee reconstruction activities in the Sacramento River East Levee Improvements area would take place in Holocene-age rock formations, which are considered to be of low paleontological sensitivity for the same reasons described above in the North Sacramento Streams Improvements area. However, based on detailed geologic mapping prepared by Fugro William Lettis & Associates, Inc. (2010:Figure 4 and Plate 1), there is a potential that excavations for deep cutoff walls proposed in Reaches 12 and 13 could encounter the Riverbank Formation at depths of approximately 60–70 feet below mean sea level. Because numerous vertebrate fossils have been recovered from the Riverbank Formation in northern and central California, including at least nine different localities from Sacramento County, this formation is considered to be paleontologically sensitive. Therefore, earthmoving activities in the Riverbank Formation could result in accidental damage to or destruction of unique paleontological resources, and the levee reconstruction activities in Reaches 12–13 could have a potentially significant impact. Mitigation Measure GEO-2, described below, has been identified to address this impact.

Mitigation Measure: Implement Mitigation Measure GEO-2 (Conduct Construction Personnel Education, Stop Work if Paleontological Resources are Discovered, Assess the Significance of the Find, and Prepare and Implement a Recovery Plan, as Required).

Timing: Before and during construction activities in the Sacramento River East Levee Improvements area.


Significance after Mitigation: Implementation of Mitigation Measure GEO-2 would reduce potentially significant impacts related to damage or destruction of unique paleontological resources to a less-than-significant level because construction workers would be alerted to the possibility of encountering paleontological resources and, in the event that resources were discovered, work would stop immediately and fossil specimens would be recovered and recorded and would undergo appropriate curation.

American River and Beach Lake Levees High-Hazard Levee Encroachment and Vegetation Removal

Project-related activities associated with encroachment removal, vegetation management, and the Conservation Strategy in the American River and Beach Lake Levees High-Hazard Levee Encroachment and Vegetation Removal area would take place in Holocene-age rock formations, which are considered to be of low paleontological sensitivity for the same reasons described above in the North Sacramento Streams Improvements area. Therefore, these proposed project elements would have a less-than-significant impact on unique paleontological resources.


Natomas East Main Drainage Canal/Steelhead Creek Corridor Management Plan

Project-related earthmoving activities associated with the NEMDC/Steelhead Creek CMP would occur in the Pleistocene-age Riverbank Formation along Arcade Creek, NEMDC/Steelhead Creek north of Arcade Creek, the south side of Robla Creek, the north side of Dry Creek. Because numerous vertebrate fossils have been recovered from the Riverbank Formation in northern and central California, including at least nine different localities from Sacramento County, this formation is considered to be paleontologically sensitive. Therefore, earthmoving activities associated with the NEMDC/Steelhead Creek CMP in the Riverbank Formation could result in


accidental damage to or destruction of unique paleontological resources, and this proposed project element would have a potentially significant impact. Mitigation Measure GEO-2, described below, has been identified to address this impact.

Mitigation Measure: Implement Mitigation Measure GEO-2 (Conduct Construction Personnel Education, Stop Work if Paleontological Resources are Discovered, Assess the Significance of the Find, and Prepare and Implement a Recovery Plan, as Required).

Timing: Before and during construction activities in the Sacramento River East Levee Improvements area.


Significance after Mitigation: Implementation of Mitigation Measure GEO-2 would reduce potentially significant impacts related to damage or destruction of unique paleontological resources to a less-than-significant level because construction workers would be alerted to the possibility of encountering paleontological resources and, in the event that resources were discovered, work would stop immediately and fossil specimens would be recovered and recorded and would undergo appropriate curation.

RESIDUAL SIGNIFICANT IMPACTS

The potentially significant impacts from short-term construction-related erosion (Impact GEO-1) and potential damage to or destruction of unique paleontological resources (Impact GEO-2) would be reduced to a less-than-significant level following implementation of Mitigation Measures GEO-1 and GEO-2. Therefore, no residual significant impacts would occur.


Documents

4.8 GEOLOGY, SOILS, AND PALEONTOLOGICAL RESOURCES … · 4.8 GEOLOGY, SOILS, AND PALEONTOLOGICAL RESOURCES This section addresses geologic, seismic, and soils hazards, including the