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i Geology r The first water bearing zone encountered is in sandy gravel at a depth of more than 200 feet. Groundwater elevations range from approximately 46 to 61 feet MSL. The groundwater is unconfined or partially confined. Groundwater elevations fluctuate less than one foot seasonally. Above the water bearing zone, the soil layers are moderately to well-cemented layers of sandstone and siltstone with claystone and conglomerates. This soil is mostly moderately slow in permeability with sporadic sandy layers that are well drained. Construction Module "I" is an unlined module covering approximately 80 acres. Module 1 includes approximately 34 acres of composite liner. This module was completed in December 2003. The liner system of Module 1 and future modules consists of(from top to bottom): • 2-foot-thick soil operations layer • 8 oz/synthetic nonwoven geotextile separator/filter • Drainage layer: Base: 0.75-foot-thick gravel drainage layer with leachate collection troughs with 4-inch-diameter piping Side slopes: geocomposite drain layer with nonwoven geotextile separator/filter • 60-mil HDPE geomembrane • Geosynthetic clay liner(GCL) on prepared surface • 1-foot thick prepared subgrade (base only). COMPLIANCE HISTORY SUMMARY Prior to March 2000, the landfill was found not to impact groundwater. From March 2000 to October 2001, volatile organic compounds (VOCs) were consistently and repeatedly detected at groundwater monitoring well MW-3. These detections have been ascribed to ponding along a road on refuse immediately adjacent to that monitoring well during the winters of 1995/1996, 1996/1997, and 1997/1998. Impact to groundwater at other wells was not indicated. In the spring of 1998, ponding was corrected by covering with refuse and grading. However, penetration of water into the refuse below the ponding area apparently caused an increase in landfill gas (LFG) production in the years after ponding was corrected, sufficient to impact the groundwater. Correction of the ponding has since allowed the LFG production to dissipate, and groundwater contamination has not been confirmed in MW-3 since October 2002. Contamination has not been confirmed at other groundwater monitoring wells at any time. On November 6, 2002, the County submitted an Evaluation Monitoring Plan which proposed methods to delineate the nature and extent of groundwater impact seen at MW-3. The Plan Foothill Sanitary Landfill 2 Department of Public Works/Solid Waste 2nd Semester Groundwater Monitoring County of San Joaquin—January 31,2007