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ENSR I AECOM <br /> ENSR <br /> 10461 Old Placerville Road,Suite 170,Sacramento, California,95827-2508 <br /> 7916.362.7100 F916.362.8100 www.ensr.aecom.com <br /> June 20, 2008 �111U11111 JUN 2 3 \l22008 <br /> Mr. James L. Barton ENVIRONMENT HEALTH <br /> Central Valley Water Board PERMIT/SERVICES <br /> 11020 Sun Center Drive, Suite 200 <br /> Rancho Cordova, California 95670 <br /> RE: Performance Monitoring Plan <br /> Cleanup and Abatement Order No.5-00-707 <br /> 5400 and 5606 Pacific Avenue, Stockton, California <br /> Former Montgomery Wards and Former Unocal Station#5098 (Chevron#306620) <br /> ENSR Project—01231-154-R50 <br /> Dear Mr. Barton: <br /> ENSR Corporation (ENSR), on behalf of Chevron Environmental Management Company(EMC), is presenting <br /> to the Central Valley Water Board (CVWB) a Performance Monitoring Plan for the upgraded remediation <br /> system, currently under construction, for both the former Montgomery Ward, LLC (Wards) service station <br /> located at 5400 Pacific Avenue and the former Unocal service station, located at 5606 Pacific Avenue, <br /> Stockton, California, referenced collectively as the Site. <br /> Performance Monitoring Objective <br /> The objective of performance monitoring, and the associated data collection, is to demonstrate the <br /> effectiveness of the upgraded air sparge (AS) and soil vapor extraction (SVE) remediation systems at the <br /> Site. The objective of the remediation systems is to reduce concentrations in selected groundwater <br /> monitoring wells that still have elevated fuel hydrocarbon concentrations: MW-2, MW-3, MW-8D, and MW-11. <br /> In an effort to demonstrate through both abiotic and biological mechanisms that the upgraded AS/SVE <br /> systems are effectively remediating the impacted groundwater, ENSR's performance monitoring plan includes <br /> multiple data gathering and tracking approaches, including the collection of remedial system operational <br /> parameters, groundwater parameters, and Monitored Natural Attenuation (MNA) parameters; and tracking <br /> groundwater concentration trends, performance of compound specific isotope analyses (CSIA), and in-situ <br /> microbial activity indicators. ENSR will use the data obtained from these performance monitoring activities to <br /> evaluate the AS system performance and optimize the operation of the AS/SVE systems. <br /> Scope of Work <br /> Routine operation and maintenance (O&M) events will include the following remedial system operational <br /> parameter data gathering: <br /> AS/SVE System Operational Parameters <br /> o SVE System: vapor flow rates for the total system (measured on the pressure side of the blower), <br /> and individual wells; measurement of volatile organic compounds (VOCs) concentrations by a <br /> photoionization detector(PID)for system influent, system effluent, and individual wells, vacuum <br /> measurements; and system vapor samples for laboratory analysis (on a monthly basis). The system <br /> vapor samples will be analyzed for total petroleum hydrocarbons as gasoline(TPHg); benzene, <br />