SITE INFORMATION AND CORRESPONDENCE_FILE 2

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PUBLIC HEALTH SERVICES .. o` �ogAYtN SAN JOAQUIN COUNTY a ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D. , M. P. H. , Health Officer • d , a 304 East Weber Avenue, Third Floor • Stockton, CA 95202 209/468-3420 RAYMOND FARMER SEP 0 52001 BESS FARMER 3810 14 - MILE DR STOCKTON CA 95219 RE : TOYOTA TOWN SITE CODE : 1151 610 HUNTER ST STOCKTON CA 95202 A 4-hour soil vapor extraction (SVE) feasibilitytest was conducted by ATC Associates, Inc. (ATC) at the above-referenced site on May 17, 2000. On the following day, a 2-hour Air-sparging (AS) feasibility test and a 2-hour combined AS/SVE test were conducted at the site. San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has received AirSpa7 and Vapor Extrauiwz Pilot Test Results and Feasibility Study (the stud)) dated November 2, 2000 prepared by ATG The study reported a radius of influence (ROI) of 30 feet for SVE and 30 feet for AS . Analytical results of the SVE test vapor sample collected at the influent were 13,500 milligrams per cubic meter (mg/m3) of Total petroleum hydrocarbons as gasoline (TPH g) and 25.9 mg/ m3. The results of the vapor samples collected at the effluent of the internal combustion engine (IC) were 54.7 mg/m3 of TPH g and 1.38 mg/m3. ATC interpreted it as a destruction efficiency of approximately 96 percent for benzene and over 99 percent for other petroleum hydrocarbon constituents. Analytical results of the groundwater samples from the northeast monitoring well MW-7 in June 2001 were 11,000 micrograms per liter (µg/1) of TPH g and 1,200, <5.0, 470, and 110 µg/1 of BTEX Analytical results of the groundwater samples collected from the south well MW-6 were 4,700 µg/1 of TPH g, and results of the groundwater samples collected from north well MW- 5 were 490 µg/1 of TPH g. Analytical results of the grab groundwater sample taken from soil boring 10 (SB- 10) in March 1999 located across the property on the east side of San Joaquin Street were 1,010 µg/1 of TPH g. The north, east, and south extent of the contamination in groundwater has not been defined. ATC evaluated three remedial alternatives in the study: natural attenuation with groundwater monitoring, groundwater extraction with soil vapor extraction, and in-situ Air sparging with soil vapor extraction. ATC recommended in-situ AS/SVE for remediation based on cost (estimated to be between $140,000 and $220,000), effectiveness (estimated 1 to 3 years of implementation), and the test results of the study. ATC expressed that a final remediation plan would be prepared and submitted upon concurrence of the recommendation by this office. PIIS/EHD agrees that in-situ AS/SVE appears to be the most cost-effective remedial alternative based on the results reported in the study. However, since the lateral extent of the contamination in groundwater has not been defined, any remedial alternative can be implemented only as interim remediation. A final remedial action plan will be expected after the delineation is complete. A Division of San Joaquin County Health Care Services