SITE INFORMATION AND CORRESPONDENCE

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1265-1267 Country Club Blvd. Page 2 Groundwater samples taken from B-2 indicate that 150,000 ug/I (reported as 150 mg/1) of TPH-G and 13,000 ug/I of Benzene are present. Groundwater samples from B-3, approximately 50 feet further down- gradient on the site to the northeast, detected TPH-G at 23,000 ug/I and Benzene at 1,900 ug/I. Without a determination of the size, amount, and extent of the plumes, this site cannot qualify for closure/No Further Action under low risk guidelines. The British Petroleum (BP) site you mentioned is located west of your site and groundwater gradient information since 1990 indicates that your former Shell station was never truly down-gradient from it. In addition, groundwater contamination at the BP site has never been as high as levels recorded on this SHELL site. Since data collection began in 1990, the groundwater at the BP site has never been shallower than 20 feet below the surface. With this in mind, PHS-EHD has concerns over the relatively high levels of soil contamination still in place at 16 feet below the surface and the high levels of relatively fresh (Benzene) groundwater contamination noted from sample B-2. Both low risk (Lawrence Livermore study) and Risk Based Corrective Action (RBCA) guidelines require the site to be fully assessed (lateral and vertical delineated). Under Tier 1, RBCA-ASTM protocols, the user is to identify contaminant source(s), obvious environmental impacts, if any, the presence of potentially impacted humans and environmental resources, and potential significant transport pathways. The investigation that PHS-EHD required in correspondence dated July 25, 1996 was an attempt to guide and assist you in obtaining the minimum information needed that will allow your site to possibly qualify for an evaluation for site closure/No Further Action under guidelines currently established for low risk. This area of Stockton lies on the border between city and un-incorporated areas where private wells still exist. A receptor (potential transport pathways) survey that identifies wells and utility trenches is needed for this site. Wells within 2000 feet of the site may need to be sampled for petroleum constituents if a zero line of groundwater contamination is not determined. In order to verify existing site conditions, PHS-EHD recommends that soil and groundwater data be collected at the extreme west edge of your property to establish if migration from an off-site source is occurring. In addition, soil and groundwater analyses for the other edges of the SHELL site will need to be collected in order to determine the lateral extent of the plumes. The waste oil tank area should be tested for priority metals, (ICAP or AA for Cd, Cr(III &VI), Pb, Zn, and Ni), Oil and Grease (Series 5520 F, and/or C & D), Chlorinated Hydrocarbons (EPA 8010 for soil and 601/624 for water), and EPA 8270 for PCB, PCP, PNA, and Creosote in the soil, and in the groundwater if found in the soil. The work plan originally required by PHS-EHD was due on or before October 28, 1996. In order to allow you more time to prepare your proposal and include the items mentioned above, the revised due date is now December 9, 1996. The completed work plan and boring application with a $89 fee per parcel should be submitted by this date to avoid any formal actions for failure to comply. You may contact Michael Infurna Senior RENS, at(209) 468-3454 should you have any questions. Donna Heran, REHS, Director Environmental Health Division Michael Infurna Jr., :er,7,o RENS Margare Lagorio, REHS LOP/Site Mitigation Unit IV Supervisor MI/ c: CVRWQCB - E. Thayer c: SWRCB - Steve Marquez