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Geology <br /> iThe first water bearing zone encountered is sandy gravel which is at a depth of more than 200 feet. <br /> Groundwater elevations range from about 46 to 61 feet MSL. The groundwater is unconfined or <br /> ' partially confined. Groundwater elevations fluctuate less than one foot seasonally. <br /> Above the water bearing zone, the soil layers are moderately to well-cemented layers of sandstone <br /> and siltstone with claystone and conglomerates,mostly moderately slow in permeability with <br /> sporadic sandy layers that are well drained. <br /> ' Construction <br /> Module"I" is an unlined module covering approximately 80 acres cover. <br /> Module 1 includes approximately 34 acres of lined landfill base. This module was completed in <br /> December 2003. The liner system of Module 1 and future modules consists of(from top to <br /> ' bottom): <br /> • 2-foot-thick soil operations layer <br /> • 8 oz/synthetic nonwoven geotextile separator/filter <br /> • Drainage layer: <br /> o Base: 0.75-foot-thick gravel drainage layer with leachate collection troughs with <br /> 4-inch-diameter piping <br /> o Side slopes: geocomposite drain layer with nonwoven geotextile separator/filter <br /> • 60-mil HDPE geomembrane <br /> • Geosynthetic clay liner(GCL) on prepared surface <br /> • 1-foot thick prepared subgrade(base only). <br /> ' COMPLIANCE HISTORY SUMMARY <br /> From March 2000 to October 2001,volatile organic compounds (VOCs)were consistently and <br /> repeatedly detected at groundwater monitoring well MW-3. These detections have been ascribed <br /> to ponding along a road during the winters of 1995/1996, 1996/1997, and 1997/1998 on refuse <br /> ' immediately adjacent to that monitoring well. <br /> In the spring of 1998, this situation was corrected by covering with refuse and grading. However, <br /> ' apparent penetration of water into the refuse below the ponding area caused an increase in landfill <br /> gas (LFG)production in the years after the problem was corrected. The increased LFG production <br /> was sufficient to cause groundwater impact. Correction of the ponding has since allowed the LFG <br /> ' production to dissipate, such that VOCs are no longer detected at that well. <br /> Groundwater contamination has not been confirmed in MW-3 since October 2001. Contamination <br /> ' has not been confirmed at other groundwater monitoring wells at any time. <br /> ' Foothill SanitaryLandfill Department of Public Works/Solid <br /> Waste <br /> 2ND Semester/Annual 2003 Groundwater Monitoring 2 <br /> County of San Joaquin-Revised June 29,2004 <br />