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Geo-Loqk ASSOGIATES Geologists,Hydrogeologists and Engineers August 21, 2012 JN 2011-0115 ISan JoaquinY p Count Department of Public Works ' 1810 E. Hazelton Avenue Stockton, California 95205 Attention: Mr. W. Michael Carroll SUBMITTAL OF EVALUATION MONITORING PROGRAM REPORT- PHASE II FOR THE EVALUATION MONITORING PROGRAM AT THE CORRAL HOLLOW SANITARY LANDFILL, SAN JOAQUIN COUNTY, CALIFORNIA Geo-Logic Associates is pleased to provide the San Joaquin County Department of Public Works (County) with the attached Evaluation Monitoring Program Report—Phase II for the Evaluation Monitoring Program (EMP) at the Corral Hollow Sanitary Landfill (CHSL). This document fulfills a reporting requirement outlined in an Order to the County from the Central Valley Regional Water Quality Control Board (RWQCB) staff dated July 7, 2011. As described in this report, as well as in our previous submittal of the Well Installation Report and EMP - Phase I Report, three temporary wells were initially installed and L sampled in accordance with the EMP workplan approved by the RWQCB staff. Volatile organic compounds (VOCs) were detected in primary and verification samples collected from each temporary well, suggesting that the three temporary well sites are within the VOC plume that extends to the north of the CHSL. As a result, a second phase of EMP field work was conducted that included construction, sampling, and aquifer testing of three permanent monitoring wells. Although VOCs were detected in samples from each of the three permanent monitoring wells, the concentrations are very low, and the results were sufficient to allow extrapolation of the limits of VOC-impacted groundwater. The data suggest that VOC impacts extend approximately 1000 feet outward from the CHSL. All measured VOC concentrations were below State and Federal Maximum Contaminant Levels. More recent routine groundwater monitoring data suggest that VOC concentrations are decreasing. With the completion of this EMP investigation, an Engineering Feasibility Study (EFS) will be prepared that outlines the County's proposed course of corrective action. It is anticipated that the EFS will be completed by the end of September 2012. The attached report has been developed based on the data described therein. Our firm should be notified if conditions are found that differ from those described in this report, since this may require a re-evaluation of the conclusions and recommendations. If you 11415W. Bernardo Court, Suite 200, San Diego, California 92127 Phone: (858) 451-1136 FAX: (858)451-1087