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u I S <br /> PUBLIC HEALTH SERV C <br /> SAN JOAQUIN COUNTY 2' y <br /> Q: .a <br /> ENVIRONMENTAL HEALTH DIVISION ` <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br /> 209/468-3420 <br /> SAIYED ALI MAY 0 8 2001 <br /> CALTRANS DISTRICT 10 <br /> P O BOX 2048 <br /> STOCKTON CA 95201 <br /> RE: Stockton Maintenance Station SITE CODE: . 1018 <br /> 1604 B Street <br /> Stockton CA 95205 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) <br /> has reviewed the "Site Investigation/Air Sparging Vapor Extraction Test Work Plan" <br /> (work plan) dated April 19, 2001 that was prepared by Professional Service Industries, <br /> Inc. (PSI) on behalf of the above referenced site and has the following comments. <br /> The work plan proposes to install one dual cased air sparge/soil vapor extraction <br /> (AS/SVE) well and one geoprobe direct push soil boring. The stated purpose of the <br /> geoprobe boring is to assess the vertical extent of the groundwater contamination near <br /> the source area at this site, the former underground storage tank pit. In conversation <br /> with PSI, PHS/EHD was informed that this boring will be advanced by Precision <br /> Sampling, Inc., using a direct push rig with the capability of advancing to depths to 140 <br /> feet below surface grade (bsg). The work plan states that discrete groundwater samples <br /> will be collected during the advancement of this boring at intervals of 10 feet, beginning <br /> at the water table and extending until two samples have concentrations below 1.0 <br /> micrograms per liter(µg/1) of benzene. A mobile laboratory will be on site to perform the <br /> analyses. The groundwater samples will be analyzed for total petroleum hydrocarbons <br /> as gasoline (TPHg) and TPH as diesel by United States Environmental Protection <br /> Agency (EPA) Method 8015, and volatile organic compounds including benzene, <br /> toluene, ethylbenzene, xylenes, methyl tertiary butyl ether, ethylene dibromide, 1,2- <br /> dichloroethane and oxygenates by EPA Method 8260. Please note that PHS/EHD <br /> considers the vertical extent of contamination to be defined when two consecutive <br /> samples are non-detect for all constituents analyzed. Current depth to water at this site <br /> is approximately 48 feet bsg. Current monitoring well sampling data shows <br /> contamination in wells screened to 78 feet bsg. <br /> The dual cased AS/SVE well is proposed to be constructed to a total depth of <br /> approximately 60 feet bsg for the installation of one 1-inch diameter AS well and one 2- <br /> inch diameter SVE well. The AS well will be screened from approximately 57 to 60 feet <br /> bsg, with a sand pack extending to 56 feet bsg. The work plan states that bentonite <br /> chips will be used for a transition seal. Please note that installation of bentonite chips <br /> through groundwater must be done by tremmie pipe, and the seal should be a minimum <br /> of 2 feet thick. An annular seal of neat cement grout will be installed, also by tremmie <br /> pipe, from the top of the transition seal to 25 feet bsg. The vapor extraction well will be <br /> installed to this depth, with a screen interval from 10 to 25 feet bsg. <br /> A Division of San Joaquin County Health Care Services <br />