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San Joaquin County DIRECTOR <br /> Environmental Health Department Donna Heran,REHS <br /> .o Department DIRECTOR <br /> 600 East Main Street Laurie Cotulla, REHS <br /> :{ Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> ' ------- -- — — --- - Carl Borgman,REHS <br /> c., <br /> Website: www.sjgov.org/ehd Mike Huggins,REHS,RDIMargaret Lagorio,REHS <br /> Phone: (209) 468-3420 Robert McClellon,REHS <br /> Fax: (209) 464-0138 Jeff Carruesco,REHS,RDI <br /> Kasey Foley,REHS <br /> EDNA MOORE JAN 1 0 2008 <br /> 3400 WAGNER HEIGHTS ROAD <br /> APT 346 <br /> STOCKTON CA 95209 <br /> RE: Moore Truck Lines Stockton SITE CODE: 1701 <br /> 3400 Newton Road RO: 677 <br /> Stockton, CA 95205 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed Additional <br /> Site Assessment and Aquifer Pump Test Work Plan, dated December 4, 2007, prepared <br /> and submitted by Advanced GeoEnvironmental, Inc. (AGE) on your behalf for the above- <br /> referenced site. The work plan was submitted in response to the EHD letter dated <br /> October 5, 2007, directing additional site investigation southeast of the former <br /> underground storage tank (UST) area to delineate the groundwater plume laterally in this <br /> direction. <br /> In the work plan AGE proposes the installation of three monitoring wells (MW-5 through <br /> MW-7) screened between fifty-five and seventy-five feet below surface grade (bsg); <br /> installation of one monitoring well (MW-8) screened between sixty and eighty feet bsg; <br /> and performance of a forty-eight-hour groundwater extraction pilot test. <br /> EHD approves the installation of monitoring wells MW-5 through MW-8 at the proposed <br /> locations illustrated on Figure 2 of the work plan. However, EHD recommends the four <br /> monitoring wells be screened between approximately fifty or fifty-five feet and seventy <br /> feet bsg instead of the proposed screened intervals stated above. Although soil lithology <br /> for MW-2 indicates silty sand is encountered at seventy to seventy-five feet bsg, results <br /> for cone penetration testing (CPT) boring CPT-01 indicate a high pore pressure interval <br /> occurs between those depths, indicating a potential barrier to vertical migration for <br /> chemicals of concern. This is supported by soil lithology for MW-3. Considering MW-8 <br /> is proposed to be installed in the former UST area, it may be important that this potential <br /> natural barrier not be breached. <br /> EHD believes methyl tertiary-butyl ether (MTBE) concentrations found in soil samples <br /> collected from soil boring B1/MW-1 at twenty, thirty, and forty feet bsg, and soil boring <br /> B2 at thirty feet bsg are migrating downward through the vadose zone and are impacting <br /> groundwater. To date, this secondary source of contamination has not been addressed <br /> and must be considered when evaluating methods for site mitigation. <br />