ARCHIVED REPORTS_2012_6 - Laserfiche WebLink

Home Browse Search

In the site vicinity, the ground surface generally slopes downward to the southeast toward Corral Hollow Creek, with ground surface elevations ranging from approximately 310 feet above mean sea level (amsl) along the northwestern edge of the site to approximately 240 feet amsl at the southeastern edge of the site. The landfill waste prism forms a roughly rectangular pyramid that rises from the adjacent terrain to a maximum top deck elevation of approximately 352 feet amsl. 3.1.2 Climate The climate for the region surrounding the CHSL is Mediterranean, characterized by mild, wet winters and cool summers. According to the California Department of Resources, California Irrigation Management Information System (CIMIS), during the last 10 years, temperatures range from a minimum average of 45.6 degrees Fahrenheit to a maximum average of 71.6 degrees in the nearby city of Tracy. The area surrounding the CHSL receives an average of about 10 inches of rain per year (CIMIS, 2011), with approximately 70 percent of rainfall occurring between November and April of each year. 3.1.3 Landfill Configuration The CHSL is a closed, unlined Class III landfill. The landfill property is approximately 58 acres, with a refuse footprint that is approximately 44 acres (including recently- discovered refuse outside the closure cap). In 1995 a prescriptive final cover was constructed consisting of a foundation layer, a low-permeability clay layer, and an overlying vegetative soil layer. In 2001, a landfill gas extraction system was installed to mitigate landfill gas migration and control groundwater impacts. The original landfill gas extraction system included 39 gas extraction wells connected by header lines to a flare at the southern end of the site. In 2008, five additional landfill gas extraction wells were added to the system along the northeastern edge of the refuse prism. The County recently submitted a proposal to the RWQCB to extend the closure cover over approximately 1.3 acres of waste outside of the northeastern edge of the main landfill, including portions on adjacent Caltrans property. The proposal includes installing two additional landfill gas extraction wells into refuse on the Caltrans property. 3.2 GEOLOGIC SETTING Past drilling and geologic investigations at the site suggest that the CHSL is underlain by recent alluvium, Quaternary stream terrace deposits, and relatively unconsolidated sedimentary rock of the Plio-Pleistocene age Corcoran Formation. Lithologies within these three units are similar, and include assemblages of clays, silts, sands, and gravels. The Corcoran Clay member of the Corcoran Formation (also referred to as the Tulare Formation in some literature) has been identified in exploratory boreholes drilled around the northern third of the CHSL, and engineers visiting the site during EMP Report—Phase II Geo-Logeic Page ■ 3 Corral Hollow Sanitary Landfill ASSOCIATES August 21,2012