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r sampling). The soil gas wells on the landfill property boundary were also used to monitor for off-site migration of combustible gas in accordance with CCR Title 27 Section 20925. Monitoring at new groundwater well G-6 indicated no groundwater impact at that location. At G-4, one VOC was detected in the January 2003 monitoring event. Since January 2003, analytical results from G-4 have not indicated any detections above the trace level. All other groundwater wells continued to be free of VOC impact. Note that VOCs were found at many of the soil gas wells but not in the groundwater. Although the groundwater impact appears to have subsided, the results of the first phase of evaluation monitoring allowed the County to delineate the problem sufficiently to proceed with engineering feasibility of corrective action options. It was apparent that the cause of the impact at G-4 was landfill gas (LFG), and that sporadic detections at G-4 could occur in the future unless corrective action was taken. After evaluating soil gas extraction as a possible method to prevent further impacts to G-4, the County submitted an addendum to the Engineering Feasibility Study with associated Amended Report of Waste Discharge(December 21, 2004). This addendum proposed active LFG collection. In accordance with the revised Report of Waste Discharge (May 27, 2005), groundwater wells G-4, G-5, and G-6 will be sampled for VOCs quarterly until corrective action is implemented. All groundwater monitoring wells will continue to be sampled semi-annually for field and monitoring parameters per the WDRs. Soil gas continues to be sampled semi-annually per the WDRs. This data is included in semi-annual reports for this site. MONITORING PROGRAM Waterualit is monitored consistent with WDR Order No. R5-2002-0219. q Y Groundwater The groundwater well network consists of up-gradient well G-1 and down-gradient wells G-313, G-4, G-5, and G-6 (Figure 3). Groundwater samples are analyzed semiannually for the following field and monitoring parameters as specified in WDR Order No. R5-2002-0219: Temperature Nitrate-Nitrogen Electrical Conductivity(EC) Sulfate pH Calcium Turbidity Magnesium Total Dissolved Solids (TDS) Potassium Chloride Sodium Carbonate Volatile Organic Compounds (VOCs) (Short List) Bicarbonate North County RCSL 3 Public Works/Solid Waste 1st Semester 2006 Groundwater Monitoring County of San Joaquin—July 31,2006