ARCHIVED REPORTS_2012 - Laserfiche WebLink

Home Browse Search

Construction Module "I"is an unlined module covering approximately 80 acres. Module 1 is provided with composite liner conforming to RCRA Subtitle D and CCR Title 27 as follows (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). Module 1 was constructed in two phases. The first phase of approximately 34 acres was completed in 2003. The second phase of approximately six acres was completed in 2006. A portion of the liner installed in the second phase was placed over refuse of Module "I"at the request of RWQCB staff. 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 detected at a single groundwater monitoring well, MW-3. These detections have been ascribed to ponding on refuse along a road immediately adjacent to that monitoring well five years earlier, 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 in this area was corrected by covering the refuse and grading the area to drain. 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 allowed the LFG production to dissipate, and groundwater contamination was not confirmed in MW-3 for a long time period. In February 2002, approximately four years after correcting the surface ponding, water samples from MW-3 indicated that impact to groundwater had ceased. Except for"false positive"detections due to laboratory contamination, impact to groundwater has not been indicated at this well since that time. Contamination has not been confirmed at other groundwater monitoring wells at any time. On November 6, 2002,nine months after the last detection of VOCs at MW-3,the County submitted an Evaluation Monitoring Plan at the requirement of RWQCB staff. This Plan proposed methods to delineate the nature and extent of groundwater impact previously seen at MW-3, as required. The Plan included drilling and sampling from temporary borings, and a step-out step-down approach if groundwater contamination was detected at those borings. On January 30, 2003, eleven months after the last detection of VOCs at MW-3,the California Regional Water Quality Control Board, Central Valley Region (CVRWQCB) issued WDRs. These WDRs required Foothill Sanitary Landfill 4 Department of Public Works/Solid Waste 1 n Semester 2012 Groundwater Monitoring County of San Joaquin—July 17,2012