ARCHIVED REPORTS_2011_19 - Laserfiche WebLink

Home Browse Search

brown to yellow brown dominated by fine to medium-grained sand,with some coarse-grained sand and gravelly layers and a few silt and clay interbeds. Contacts between these three subunits are not distinct and are therefore subject to interpretation. By their nature these sedimentary units interfinger and are discontinuous on an individual basis. The surface soils near the site are mainly comprised of two soil types typical of Victor Formation sediments. The two soils, as mapped by the U.S. Soil Conservation Service, are known as Clear Lake clay (CL) and Jacktone clay (ST). These soils are similar in composition, being formed from alluvium. The Jacktone and Clear Lake clays are equally pervasive at the site with the Clear Lake clay more prevalent in the northern and southern portions of the site and the Jacktone Clay more prevalent through the middle portion. The Jacktone clay (ST) covers the nearly flat terrain 100 to 200 feet from the North and South Creeks. Typically, this soil type is found on 0 to 2 percent slopes forming a moderately deep hardpan of somewhat poorly drained soil made up of generally dark gray clay about 2 inches thick, underlain by light gray clay loam, followed by hardpan of 3 inches. Permeability is low, the available water capacity is moderate,the shrink-swell potential is high,water may be perched on top of the hardpan following heavy rain, runoff is slow, and the water erosion hazard is slight. The typical uses of this soil type are irrigated cropland, orchards, vineyards, and sometimes irrigated pasture and urban development. The Clear Lake clay(CL)soil type is common along the North and South Creeks. The surface layer is dark gray clay about 29 inches thick followed by another 8 inches of dark gray clay,then 5 inches of mixed light brownish gray clay loam, then variegated dark grayish brown, weakly to strongly cemented hardpan to a depth of 60 inches. The permeability of this soil is low, available water capacity is moderate, the shrink-swell potential is high, water erosion hazard is low, and the soil is subject to rare flooding during abnormally high rainfall events. This soil type is typically used for irrigated cropland,orchards,and sometimes irrigated pasture and urban development. Subsurface soil properties have been evaluated in a number of separate soil investigations, including the most recent. The soils encountered during the geotechnical investigations generally consist of interbedded layers of sand, silt, and lean clay. The cohesive materials are generally of very stiff to hard consistency. The cohesionless materials can be characterized as dense to very dense. Because the sediments at the site were deposited as fluvial floodplain and channel deposits, the soil deposits at the site were. found to be heterogeneous and laterally and vertically discontinuous. It is therefore difficult to characterize the subsurface soils into distinct units. 3.5 Seismicity Forward Landfill is located in an area of relatively low seismic activity. No evidence of Holocene- age faulting on the property has been found either through a review of available literature or through site investigations and the site in not within or near any State of California Earthquake Fault Zones(as mandated by the Alquist-Priolo Earthquake Fault Zoning Act passed in 1974 and C:\Documents and Settingsye is&sees\Desktop\Fol d LFGTE-Project Description.doc CORNERSTONE 3-4 LEWIS ENGINEERING E—i...me—i G.m R.LLC