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PUBLIC HEALTH SERVICES SAN JOAQUIN COUNTY ? �- ENVIRONMENTAL HEALTH DIVISION Karen Furst, M.D., M.P.H., Health Officer �. P 304 East Weber Avenue, Third Floor • Stockton, CA 95202 249/468-3420 FILE COPY DARIN L ROUSE MARKETING DEPT / EXXON COMPANY USA JUL 2 S 1999 PO BOX 4032 CONCORD CA 94524-4032 RE: EXXON RAS 17-0137 SITE CODE: 1962 1605 S. El Dorado St. Stockton,CA., 95206 Per your request, San Joaquin County Public Health Services, Environmental Health Division (PHS- EHD) has recently re-evaluated the October 1998 "Work Plan for Confirmation Soil Borings in Support of a Request for Case Closure" previously submitted by EA Engineering, Science, and Technology and offers the following comments. The proposal calls for four(4) Geoprobe push points to be placed at areas where previous subsurface soil investigations have indicated that petroleum constituents were detected at elevated concentrations. Of particular concern to PHS-EID is the absence of a confirmation soil boring at location "TK2N" where Total Petroleum Hydrocarbons as Gasoline (TPH-G) were detected at 5,000 mg/kg from 16 feet below ground surface (`bgs). In order to better evaluate the effectiveness of the remedial effort, soil data from this point and depth (TK2N-16) will need to be obtained PHS-EHD recommends that a slant push-point be placed in this area at a slight slant (10-15 degrees off vertical) from north to south. By targeting the soil at 16' bgs and maintaining the shallow angle downward, sod samples could be collected at the depths listed in the proposal (16', 25', 35', and 45' bgs) and still remain very close to under the north end of the previous underground storage tank (UST) location. It is hoped that this shallow angle would also provide data that would support potential conclusions for vertical delineation in this area. It is the understanding of PHS-EHD that the proposed push-point at the extreme southwest corner of the property is to provide groundwater quality data in this quadrant since no monitoring well is located there. PHS-EHD recommends that one or two soil samples be collected and analyzed from this location to verify the condition of the soil,in addition to the groundwater sample collection proposed. If methanol or ethanol was ever a constituent of EXXON gasoline, then these constituents are to be tested for in the soil and groundwater also. The EPA Method for the testing of the oxygenates should be updated to include 8260B and the detection limits should be in the range of 5.0 ug/l for water samples and no more than 10 mg/kg for the soil samples. A Division or San Joa,4uin County Health Care Services