ARCHIVED REPORTS_XR0007643 - Laserfiche WebLink

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C A M B R I A i SITE BACKGROUND The subject site is located at 3725 Tracy Boulevard near Highway 205 in a mixed commercial and residential area of Tracy, California (Figure 1) The subject site is an operating Shell- branded service station with a station layout that includes four underground gasoline storage tanks (USTs) six dispenser islands, a car wash, and a station building(Figure 2) Previous Investigations: During October 1985, J H Klemfelder & Associates drilled four soil borings in the vicinity of the USTs Petroleum hydrocarbons were detected with a trace gas analyzer in soil samples collected from 10 feet below grade (fbg) from three of the four soil borings The source of the hydrocarbons was not identified During November 1985 all three USTs were removed and replaced with three 10,000 gallon double-walled fiberglass tanks in the same location Canonie Engineers, Inc collected soil samples from beneath the USTs and water samples from the bottom of the excavation Laboratory analysts of these samples indicated total petroleum hydrocarbons (TPH) were present in soil at concentrations up to 40 parts per nullion (ppm) and in groundwater at concentrations up to 0 7 ppm The source of these hydrocarbons was not identified During August and September 1989 Delta Environmental Consultants, Inc (Delta) drilled and sampled 12 soil borings and converted three of the borings to monitoring wells (MW-1, MW-2, and MW-3) TPH was detected in soil samples from three of the 12 borings at concentrations up to 140 ppm and benzene was detected in only one boring at a concentration of 0 01 ppm TPH and benzene were not detected in groundwater samples collected from the three monitoring wells These findings are documented in Delta's November 22, 1989 Pretank Closure Assessment Report During May 1990, three 10,000 gallon USTs were removed from the site Delta performed soil sampling activities associated with the UST removal Delta directed overexcavatton activities in the vicinity of the eastern fuel dispensers removing soil containing greater than 10 ppm TPH or BTEX (benzene, toluene, ethylbenzene, and xylenes) These activities are documented in Delta's November 28, 1990 Preliminary Report and Tank Closure Report During July 1990 wells MW-1, MW-2, and MW-3 were damaged during site remodeling activities and were subsequently properly destroyed These wells were replaced in August 1990 by wells MW-1A,MW-2A, and MW-3A i 0813 2