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Cease and Desist Order RA,3-XXXX 40 - 6 - San 6 - San Joaquin County Department of Public Works Corral Hollow Sanitary Landfill San Joaquin County 35. Since the additional LFG extraction wells installed in 2008 have become operational, little effect on groundwater impacts have been observed in on site groundwater wells. Ina 24 June 2010 letter, the County stated that the uncovered refuse identified outside the WMU is a likely contributor to groundwater degradation. 36. Inorganics reported in the groundwater monitoring wells also indicate impacts from LFG and possibly leachate. Bicarbonate concentrations reported for VOC impacted wells MW-5, MW-8, MW-10A, and MW-11A range between 290 milligrams/liter (mg/L) to 680 mg/L. Total alkalinity in these wells ranged between 93 mg/L to 560 mg/L. Chloride ranged from 36 mg/L to 110 mg/L. Total Dissolved Solids ranged between 400 mg/L to 860 mg/L. The highest concentrations of these inorganics are being reported from the off site wells MW-10A and MW-11A indicating that a release from the landfill is affecting groundwater beyond the point of compliance. Well MW-10A is located approximately 1,000 feet downgradient (north-northeast) of the landfill. 37. In response to staff's request, the Discharger has conducted an Evaluation Monitoring Program (EMP) and in January 2013 submitted an EMP/EFS report evaluating all soil and groundwater data collected to date. The Engineering Feasibility Study (EFS) postulates that the VOCs found in groundwater are a result of landfill gas, and that by controlling landfill gas, the groundwater will be remediated. 38. The Discharger proposes additional corrective action measures consisting of installation of the landfill cover on 1.6 acres (as required by the WDRs) and installation of seven landfill gas extraction wells and two triple-completion soil gas probes. This work will be completed by 1 September 2013. The Discharger then proposes to monitor the groundwater for a two-year period, and if VOC concentrations in the groundwater are not decreasing, then complete an audit of the landfill gas system. However, because control of landfill gas is crucial in remediating the groundwater, this Order requires that the audit be conducted by the end of 2013. This Order allows the Discharger to monitor groundwater for a two-year period following installation of the cover and audit of the gas system, and requires that additional corrective actions measures be implemented at the end of the two-year period if VOC concentrations in the groundwater have not decreased.