SITE INFORMATION AND CORRESPONDENCE FILE 1

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PUBLIC HLALTH SERVICES ,aP SAN JOAQUIN COUNTY ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer IF IF. . 304 East Weber Avenue, Third Floor • Stockton, CA 95202 ` " OR 209/468-3420 ROGER LISTON - �JUN 112001 DARPETRO INC USA SERVICE STATION 3450 EL CAMINO CERES CA 95307 RE: DARPETRO, INC Site Code: 1060 749 E CHARTER STOCKTON, CA 95206 San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has reviewed "Quarterly Report February 2001 ", "Quarterly Report April 2001 ", and a letter dated May 25, 2001 , prepared by California Geophysical Group, Inc. for the above referenced site. In addition, PHS/EHD has reviewed several letters from you stating that contamination from the. ARCO station (K& S Grocery) at 701 E. Charter Way, Stockton, is "leaking and entering" your site and that you are remediating "ARCO's - gasoline problem". Also you expressed in your letters that the BP station (Morita Bros.) at 814 E. Charter Way, Stockton, spread contamination to the Pep Boys site. PHS/EHD staff recently discussed your site and the site at 701 E. Charter Way, Stockton, with Central Valley Regional Water Quality Control Board (CVRWQCB) staff. The site at 814 E. Charter Way is continuing to investigate their contamination. The contaminant levels at that site are not high. The site has monitoring wells screened in various depths to investigate the vertical extent of contamination as well as the lateral extent and the information to date does not indicate that the contamination at that site has migrated towards the Pep Boys site. The site at 701 E. Charter Way is investigating the contamination at their site. The direction of groundwater flow at that site has been toward the south during the six monitoring events conducted since December 1998. The direction of groundwater flow at your site and at 814 E. Charter Way has been primarily toward the east or northeast. In April 1992 the direction of groundwater flow for your site was to the southeast. In February 2001 three CPT borings. were advanced to investigate the extent of the contamination at 701 E. Charter Way. One of the CPT borings was advanced on the south side of Charter Way and contamination was evidenced, supporting a southern groundwater flow direction. Additional CPT borings and additional monitoring well clusters with different screened intervals have been proposed to investigate the contamination at that site. PHS/EBD and CVRWQCB request that you work with the responsible party and consultant for 701 E. Charter Way. The monitoring wells at the two sites should be surveyed to a common point and monitoring events should be conducted at the same time to better evaluate the direction of groundwater flow and contaminant migration. Based on the data submitted to date it does not appear that you are remediating "ARCO 's gasoline problem". There were high levels of contamination in the soil and groundwater at your site when monitoring well BMl was installed in January 1990 and there were high levels of contamination in the soil when vapor wells VW 1 through V W4 were installed in February and March of 1996. When monitoring wells BM4 through BM6 were installed in March and April of 1992 soil contamination was documented to a depth of 50 feet below surface. If contamination was entering your site from 701 E. Charter Way concentrations of dissolved hydrocarbons would tend to decrease in monitoring well (BM)-9 while concentrations in BM-7 and BM-4 would increase. According to the previously referenced reports, this is not the case. Contaminant concentration levels of BTEX and TPH as gasoline have decreased significantly in all monitoring wells except BMl which may be affected by the air sparging. It appears that vapors are continuing to be extracted and that vapor extraction is remediating the contamination at your site so the vapor extraction system should continue to operate. A Division of San Joaquin County Health Care Services