SITE INFORMATION AND CORRESPONDENCE

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PUBLIC F� EALTH SERVI't' ' ES OµCN SAN JOAQUIN COUNTY r ENVIRONMENTAL HEALTH DIVISION y: Karen Furst, M.D., M.P.H., Health Officer 304 East Weber Avenue, Third Floor • Stockton, CA 95202 \g 2091468-3420 E{ eCd !J DAVID ATWATER OCT 16 i7. VAN DE POL ENTERPRISES P O BOX 1107 STOCKTON CA 95201 Re: California Fuels Station Site Code: 1214 2402 Pacific Avenue Stockton CA 95204 San Joaquin County Public Health Services, Environmental Health Division(PHS/EHD)has completed review of the Advanced GeoEnvironmental's "Quarterly Report-July 1997"dated August 11, 1997, the"Work Pian Addendum - August 1997"dated August 25, 1997 and the site map locating the proposed air sparging well dated October 7, 1997. PHS/EHD has the following comments for your consideration and response. The quarterly report presented the results of soil and groundwater analysis of samples collected during the advancement of B3-137(December 1996)during the installation of monitoring wells, MWS,MW6,MW7,MW8,M1*9 and vapor extraction wells,VWl and VW2 (June 1997)and characterized stockpiled soil for disposal(July 1997). The results of the July 17, 1997 groundwater monitoring event were also included. Significant concentrations of contaminants were evidenced in the soil and groundwater samples which were collected. The lateral groundwater plume appears to extend several hundred feet and has not yet been defined to the south. An additional j monitoring well will be required off site to determine the lateral extent of groundwater contamination. The groundwater sample results from MW9, which was placed south of the site, evidenced benzene contamination of 300 ppb, warranting additional investigation. The soil plume appears defined laterally, although not vertically. Significant soil contamination was detected during the installation of VWI and VW2 which were placed in the area of the former tanks to maximum depth of 35 feet. The maximum depth that was investigated immediately outside of the area of the former tanks evidenced soil contamination at 60 feet below ground surface(bgs)during the drilling of 132 (July 1996). Additional investigation will be required to determine the vertical extent of the contamination and the horizontal extent of the contamination evidenced during the vertical investigation. Soil samples collected at the maximum depth that B4 (December 1996)was investigated,40 feet bgs,evidenced significantly higher contamination than was evidenced at 30 feet bgs, suggesting that the contamination may have migrated with the water when the water table was much lower than it is I currently. The current depth to water was reported at approximately 38 feet bgs while San Joaquin Flood Control District records indicated that groundwater in the area has recently(1979)been as low as approximately 70 feet bgs. The site is thought to have been the location of operating gasoline stations since the I940's with several generations of tanks and piping. The most recently operating tanks were reportedly installed in the 1970's. The work plan addendum proposed the installation of one air sparge well to a depth of approximately 40 feet bgs with the screened interval between 35 and 45 feet bgs. As a part of the vertical investigation which is required, based on the results of the investigation which has been conducted thus far,PHS/EHD staff suggests strongly that when this well is installed, , that additional air sparge(discretely screened)wells be installed which can be used both for remediation and to monitor the j vertical extent of the groundwater contamination. The monitoring wells which have been installed are all screened between 25 and 50 feet bgs to characterize the shallow dissolved groundwater contamination,may not characterize the full extent of the groundwater contamination. F A Division of San Joaquin County Health Care Services '