CORRESPONDENCE_2007 (1/07 - 6/07)

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PROPOSED INCREASE IN CORRECTIVE ACTION CORRAL HOLLOW SANITARY LANDFILL January 23, 2007 Purpose The purpose of this report is to present proposed actions to increase corrective action at the Corral Hollow Sanitary Landfill. Background General The Corral Hollow Landfill is located at 31130 South Corral Hollow Road, in southern San Joaquin County, approximately 5 miles south of the City of Tracy, at the intersection of Interstate 580 and Corral Hollow Road. This landfill is a closed, unlined Class III landfill. The landfill property includes approximately 58 acres, of which 43 acres was permitted to receive refuse (Figure 1). The remaining area is comprised of access roads, storm water retention ponds, setbacks for environmental monitoring, and firebreaks. The landfill ceased receiving waste in 1991. A final cover was constructed in the fall of 1995 in compliance with Order No. 94-259. The closure cover consists of a 2-to 6-foot foundation layer under a 1-foot minimum low-permeability soil layer,with a 1-foot thick vegetative surface layer. A landfill gas collection system was installed and began operating in December 2001. The access road and drainage ditch along the eastern side of the landfill was installed with closure in 1995. This ditch was composed of galvanized corrugated half-round pipe. Water draining from the northern slope of the landfill was directed to the inlet of this pipe, and carried to the retention pond. Water draining from the eastern slope of the landfill was also intended to drain into the pipe, but the condition of the soil beneath the half-round pipe in 2003 indicated that settlement of the soil adjacent to the pipe prevented the water from flowing over the edge and into the pipe, causing water to flow along but outside of the pipe. The flowing water gradually eroded the soil adjacent to and beneath the pipe, resulting in numerous small puddles beneath the pipe. This condition was corrected in 2003 by the smoothing(to prevent ponding) and regrading of the ditch. Geology and Hydrogeology Surface soils at the site are typically sands and gravels to a depth of about 70 feet, underlain by low permeability silts and clays to 150 feet. Sands and gravels predominate to a depth of approximately 430 feet. Highly impermeable sandy clays are present at 430 feet. Increase in Corrective Action 1 Corral Hollow Sanitary Landfill January 23,2007 San Joaquin County Public Works/Solid Waste