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Geo -Logic ti ASSOCIATES Geologists, Hydrogeologists and Engineers February 1, 2012 JN 2011-0115 San Joaquin County Department of Public Works 1810 E. Hazelton Avenue Stockton, California 95205 Attention: Mr. W. Michael Carroll SUBMITTAL OF EVALUATION MONITORING PROGRAM REPORT- PHASE I 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 I 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, three temporary wells were installed and 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 ithe north of the CHSL. The types and concentrations of VOCs are similar to those detected in routine samples collected from on-site wells MW -5 and MW -8. The findings from the first phase of the EMP field work suggest that VOCs migrate in a northeasterly direction from the northwestern corner of the landfill. In order to more accurately determine the extent of the plume and fulfill that requirement of the EMP workplan, three additional well locations are proposed. The "step -out" wells will be located where VOC concentrations are estimated to be at non-detectable levels based on extrapolation of the isoconcentration contours for total VOCs, as presented in the report. These three "step -out" wells will be drilled, logged, and sampled in accordance with the methods outlined in the approved EMP workplan. The next phase of EMP drilling field work will likely commence at the end of February, after well construction and property access permits are received. Once well construction is completed, a revised Well Completion Report will be prepared and submitted to the RWQCB. Afterward, the findings and conclusions from the EMP investigation will be compiled and presented to the RWQCB, followed by an Engineering Feasibility Study outlining the County's proposed course of corrective action. 11415W. Bernardo Court, Suite 200, San Diego, California 92127 Phone: (858) 451-1136 FAX: (858) 451-1087