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San Joaquin County DIRECTOR <br /> iQ u N Donna Heran, REHS <br /> Environmental Health Department <br /> ,p p ASSISTANT DIRECTOR <br /> 600 East Main Street Laurie Cotulla, REHS <br /> y; Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> - <br /> Carl Borgman, REHS <br /> Mike Huggins, REHS, RDI <br /> Website: www.sjgov.org/ehd Margaret Lagorio, REHS <br /> 4CiFOR \ <br /> Phone: (209) 468-3420 Robert McClellon, REHS <br /> Fax: (209) 464-0138 Jeff Carruesco, REHS, RDI <br /> O C T 0 5 200?sey Foley, REHS <br /> STEPHANIE FURGAL l <br /> CHEVRON ENV MGMT COMPANY CHRISTINE CORONEO <br /> 6001 BOLLINGER CANYON RD SUTTER OFFICE CENTER <br /> ROOM K2240 2001 UNION STREET #300 <br /> SAN RAMON CA 94583 SAN FRANCISCO CA 94123 <br /> RE- Former Chevron Station 9-8227 SITE CODE: 9327 <br /> Sutter Office Center <br /> 242 Sutter Street <br /> Stockton CA 95202 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has reviewed First <br /> Quarter 2007 Monitoring and Supplemental Assessment Report (Report) dated <br /> July 10, 2007 and Second Quarter 2007 Quarterly Progress Report (QMR) dated <br /> August 3, 2007, both submitted on your behalf by Arcadis BBL (Arcadis) and has the <br /> following comments. <br /> The Report documents the January 2007 installation of two groundwater monitoring wells, <br /> MW-6 and MW-6D, to continue the investigation of the lateral and vertical extent of the <br /> impacted groundwater at your site. By correspondence dated August 31, 2006, SJC/EHD <br /> approved the work plan to install these wells with the condition that a soil sample for <br /> laboratory analysis be collected from approximately 80 feet below surface grade (bsg) to <br /> confirm reported contamination in a soil sample collected at 78 feet bsg in boring CPT-1. <br /> However, the deepest soil sample analyzed from the boring for MW-6D was collected at <br /> 63.5 feet bsg. Both this sample and the sample collected at 55 feet bsg had reportable <br /> concentrations of petroleum hydrocarbon contamination. <br /> The site data collected from soil borings, cone penetrometor test (CPT) borings and <br /> groundwater monitoring and sampling events indicate that the contamination at this site is <br /> not defined. As described above, the vertical extent of the soil contamination in the source <br /> area has not been confirmed. Groundwater contamination near the source area was also <br /> explored with boring CPT-1; reported results indicate dissolved contaminant impact extends <br /> to 150 feet bsg. The deepest groundwater monitoring well onsite currently is MW-5, which <br /> was built to total depth of 100 feet bsg near the location of CPT-2. Analytical results from <br /> MW-5 confirm the results reported in the grab groundwater sample collected from CPT-2 at <br /> 97 feet bsg. The highest reported concentrations of contamination in the groundwater at <br /> CPT-2 were from depths of 124 and 150 feet bsg. These results have not been confirmed <br /> with repeatable samples from a monitoring well. <br /> A geophysical survey was included in the completed phase of work, the objective of which <br /> was to locate 550-gallon underground storage tanks (UST) reportedly closed in place at this <br /> site. The results of the survey were apparently inconclusive. <br />