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3164 Gold Camp Drive Delta Rude o //- Cordova,CA 95670 916163 Environmental 9161638 2085 Consultants,Inc FAX 9161638 8385 December 5, 1996 Mr Edward C Ralston Unocal Corporation 2000 Crow Canyon Place Suite 400 San Ramon, California 94583 Subject Additional Hydrogeologic Assessment Results Unocal Service Station No 5886 2701 West March Lane Stockton, California Delta Project No D095-066 Dear Mr Ralston Delta Environmental Consultants, Inc (Delta), has been authorized by Unocal Corporation (Unocal) to conduct additional hydrogeologic assessment activities at Unocal Service Station No 5886, located at 2701 West March Lane, Stockton, California The site is shown in Figure 1 and site features are illustrated in Figure 2 The hydrogeologic assessment is intended to further evaluate the distribution of petroleum hydrocarbon constituents in soil and ground water beneath the site Following the installation of the wells, Delta developed and sampled the three wells to assess and monitor dissolved petroleum hydrocarbon constituents in ground water at the site This letter report describes the assessment work performed in accordance with Delta's work plan dated August 16, 1996, and an addendum to the work plan dated September 3, 1996, as approved by the San Joaquin County Public Health Services A copy of the approved well permit is included in Enclosure A. Scone of Work On September 4, 1996 a representative from Delta was on site to observe Wayne Woodward Drilling, of Rio Vista, California advance four soil borings to depths ranging from 10 feet to 25 feet below surface grade (bsg) Following the drilling, three soil borings were completed as 2-inch diameter monitoring wells (MW-1 through MW-3) Work conducted at the site was performed in accordance I to the field methods and procedures outlined in Enclosure B I Soil samples were collected from each soil boring at five foot vertical intervals The soil samples from each boring were logged using visual and manual methods according to the Unified Soil Classification System Soils encountered included sandy silt underlain by clayey silt to the total depth explored The methods used to drill and sample the soil borings are described in Enclosure B Copies of the soil boring logs containing descriptions of the soils encountered and other drilling information are mcluded in Enclosure C r� Soil samples collected in the field were screened for the presence of petroleum hydrocarbon vapors using a photoionization detector (PID) Soil samples chosen for chemical analyses were selected based on stratigraphic location, soil type, and field screening results Providing a Competitive Edge