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Ms. Wendy Wyels 0 -2- REQUEST FOR ADDITIONAL TIME, FOOTHILL SANITARY LANDFILL SITE IMPROVEMENT PROJECT (CAO No. R5-2004-0706) Knowledge of the circumstances under which this CAO was issued may be useful in your consideration of this extension request. This CAO was issued as a result of negotiations between the County and Board staff over Findings 5 and 38 of the Waste Discharge Requirements (WDRs) for this site, which were issued in January 2003 (excerpt attached). These findings required closure of the 80 -acre unlined portion of the Foothill Landfill as corrective action against groundwater contamination by landfill gas. Impact to groundwater was indicated by the repeated and consistent detection of trace concentrations at one groundwater monitoring well (MW -3) from March 2000 through October 2001. Two VOCs were detected during that period. However, exploration to find the extent of the contamination completed in June 2003, did not reveal additional contamination, In fact, contamination was no longer found at the originally -contaminated well, and had not been found for 18 months prior to issuing the WDR and is not found now. On evaluating historical data, we discovered that rainwater had been allowed to pond over, and seep into refuse at the toe of the landfill very near well MW -3 for three winters ending in the spring of 1996 (the operator had incorrectly assumed that the toe of the slope marked the edge of refuse). Corrective action was taken in 1998 by placing additional fill to prevent further ponding; however, water had entered the refuse beneath the ponding area. Adding moisture to the refuse caused a temporary increase in landfill gas (LFG) production, which peaked approximately two years after the condition was corrected. After the peak was reached, LFG production apparently faded as the refuse yielded its landfill gas, and the contamination ceased. However, during the peak, LFG production was sufficient to carry VOCs to the nearby groundwater well, located immediately adjacent to the ponding area. Based on this, the County took the position that corrective action against groundwater contamination by LFG had been completed years before the WDRs were issued, and that further corrective action was not necessary if contamination was no longer present. It was on this basis that we negotiated the CAO, which included a landfill gas system and partial closure of the landfill. The closure portion of this project cost the County approximately $1 million. If you have any questions, please contact me at (209) 468-8504. Sincerely, W. MICHAEL CARROLL, PE Senior Civil Engineer WMC:Ij Attachments Todd Del Frate, RWQCB Victor Izzo, RWQCB Robert McClellon, Environmental Health Department LA 63107 N:\1Foothill\SitelmpProj06\WendyWyels-Time Extension.doc