Laserfiche WebLink
<br />North County Recycling Center & Sanitary Landfill Department of Public Works/Solid Waste <br />First Semiannual 2025 Groundwater Monitoring Report ©2025 COUNTY of San Joaquin. All Rights Reserved <br /> 3 <br />2 COMPLIANCE SUMMARY <br />Data from the groundwater wells at the North County Landfill did not indicate impact until five <br />volatile organic compounds (VOCs) were confirmed at low concentrations in well G-4 in July <br />2002. Due to the close proximity of G-4 to the western property boundary, County staff contacted <br />the neighbor immediately to the west, requesting permission to drill temporary groundwater <br />monitoring wells. This was done in an effort to determine the extent of groundwater impact <br />according to the “step out, step down” approach. That property owner did not grant this request, <br />but allowed County staff to sample the water from their existing well. No contaminants were <br />detected. <br />County staff implemented a phased approach for evaluation monitoring within the landfill <br />property. The first phase was to install and monitor the new groundwater well G-6 and the soil <br />gas wells that were installed in 2003 within Area 4. Under Evaluation Monitoring, groundwater <br />and soil gas were sampled quarterly (the WDRs require semi-annual sampling). The soil gas <br />wells on the landfill property boundary were also used to monitor for off-site migration of landfill <br />gas in accordance with CCR Title 27 Section 20925. <br />Groundwater sampling during the January 2004 monitoring event, indicated that no VOCS were <br />detected at new groundwater well G-6 or well G-4. <br />VOCs above the trace level have not been detected at G-4 since 2007. The well went dry in <br />January 2015. All groundwater wells continued to be free of VOCs since 2008. <br />The results of the first phase of evaluation monitoring allowed the County to delineate the <br />problem sufficiently enough to proceed with engineering feasibility of corrective action options. <br />It was apparent that the cause of the impact at G-4 was landfill gas (LFG), and that sporadic <br />detections at G-4 could occur in the future unless corrective action was taken. After evaluating <br />soil gas extraction as a possible method to prevent further impacts to G-4, the County submitted <br />an addendum to the Engineering Feasibility Study with the associated Amended Report of <br />Waste Discharge (December 21, 2004). This addendum proposed active LFG collection. <br />The LFG system was installed in the autumn of 2006, and has been in full operation since May <br />2007. Eight additional vertical LFG extraction wells were installed in May 2022 in Modules 1 <br />through 4 to control LFG surface emissions and migration. <br />In accordance with the Report of Waste Discharge (January 29, 2010), all groundwater <br />monitoring wells will continue to be sampled semiannually for field and monitoring parameters <br />per the WDRs. Soil gas continues to be sampled semi-annually per the WDRs. This data is <br />included in semi-annual reports for this site. <br />Due to falling groundwater elevations, reliable samples could no longer be collected from <br />groundwater monitoring wells G-2 and G-5. Therefore, these wells were replaced with wells <br />G-2A and G-5A in 2013. Analyses of samples taken from the replacement wells were consistent <br />with the most recent analyses from the wells they replaced. Due to the continued falling <br />groundwater elevation conditions in the Central Valley, monitoring wells G-1A, G-2A, G-3D, G-4, <br />G-5A, G-5B, and G-6 cannot be sampled on a consistent schedule.