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5.6 POTENTIAL IMPAIRMENT CAUSED BY NCRC&SL The groundwater wells at the NCRC&SL did not indicate impact until three volatile organic compounds (VOCs) were confirmed at well G-4 in July 2002. This prompted the County to install a new groundwater monitoring well (G-6) and soil gas wells, SG-1 through SG-8. Monitoring at G-6 indicates no groundwater impact at that location. With the exception of VOCs in G-4, groundwater wells continue to be free of VOC impacts. VOCs were found at many of the soil gas wells; however, the presence of VOCs in the soil gas does not impair the use of the site. One soil gas well (SG-6) has shown combustible gas consistently above 20%, indicating a possible breach in the landfill liner near that well. Because of the proximity of this well to the interface between Modules 2 and 3, it was speculated that the breach was on the anchor trench berm. An additional soil gas well, SG-8, was installed beyond SG-6 at the property boundary. Combustible gas is not detected in SG-8. The County speculates that the cause of impact at groundwater well G-4 was landfill gas, and that sporadic detections at G-4 were likely to occur unless corrective action was taken. The County proposed to proceed with engineering feasibility evaluation. The RWQCB staff accepted the proposal. The County submitted an Engineering Feasibility Study to the RWQCB on August 12, 2004. In that study, the County found that the most effective and beneficial corrective action to be a system collecting soil gas from beneath the liner and carrying it to a central location for treatment prior to venting, or for venting without treatment. North County RC&SL Page 25 of 48 Public Works/Solid Waste JTD County of San Joaquin—November 30,2004