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GROUND ZERO ANALYSIS, INC. 1714 Main Street Escalon, California 95320 Telephone: (209) 838-9888 Facsimile: (209) 838-9883 June 11, 1998 Mr. Harlin Knoll San Joaquin County Public Health Services Environmental Health Division 304 East Weber Avenue,Third Floor Stockton, CA 95202 Subject: Workplan for Additional Subsurface Investigation 1140 W. Hammer Lane, Stockton, California Dear Mr. Knoll: This letter report is submitted to present a proposed workplan to conduct additional subsurface investigation at the subject site (Figure 1). Mr. Harlin Knoll and Ms. Margaret Lagorio of San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) requested the additional investigation in correspondence dated March 9, 1998. The general scope of work will consist of drilling and sampling three soil borings in the vicinity of well MW5 to investigate the vertical and lateral extent of residual soil contamination, collecting discrete groundwater samples from the borings to further delineate the extent of dissolved contamination, and preparing a technical report that summarizes the methods and results of the investigation. Scope of Work A soil sample previously collected from a depth of 50 feet below ground surface (bgs) during the drilling of well MW5 contained total petroleum hydrocarbons as gasoline (TPHG) at 580 parts per million (ppm). The proposed borings will be drilled to a depth of approximately 70 feet bgs in the area south of well MW5 to further investigate the extent of subsurface contamination. The locations of proposed borings are shown on Figure 2. Fisch Environmental Exploration Geoservices (C57 #683865) will advance the borings using a truck mounted Geoprobe 5400 direct push rig. Soil samples will be collected for logging and identification at 10- foot depth intervals to a depth of 30 feet bgs and at five-foot intervals from 35 to 70 feet bgs. Samples wi;l be collected using a 1-inch diameter core sampler lined with clear acetate sleeves. The portion of the sample to be analyzed will be immediately capped and preserved in an iced cooler at a temperature of approximately 4° Centigrade. Up to five soil samples per boring will be submitted for analysis of TPHG, and benzene, toluene, ethylbenzene, xylenes (BTEX) using EPA methods 8015m and 8020, respectively, to investigate the extent of residual gasoline contamination in soil at depth. One soil sample per boring will be groundze\knowles.han\r"rts\wpO698.doe