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3 All_ Quarterly Monitoring Report, First Quarter 1990 September 17, 1990 AGS 38012-2 Former Unocal Station No. 2859 In lune 1988, we observed the drilling of three soil borings (B-1 through B-3) and installation of three groundwater monitoring wells (MW-1 through MW-3) in the borings (Plate P-2). Soil samples were collected from the borings and groundwater samples were collected from the monitoring wells for laboratory analysis of hydrocarbons. In August 1989, we observed Spectrum Explorati-}n, Inc. of Stockton, California, drill borings B-4 through +" B-6 (Plate P-2). Soil and ground-water samples were collected from the borings and wells for laboratory analyses. Hydrocarbons were detected in sail and groundwater samples collected during both site visits. In response to the detection of hydrocarbons in soil and ground water,Applied Geoiystems began periodic monitoring of the ground water in June 1988. Results of previous monitoring hlt ty5tected in 5 ells W-2anMWt3lowereels have been detected n wells xjW-1, -4 were Band M � . Present uarter! Monitoring Event A geologist visited the site on March 1, 1990,to measure the depth to water and subjectively analyze ground water in monitoring wells MW-1 through MW-5 and to sample the ground water for laboratory analyses. The depth to the groundwater surface was meafrom the top of the well casing to the nearest 0.01 foot with a Solinst water riodendicator. r Y, Depth-to-ground-water data were combined with the elevation of the top of the well casing, previously surveyed by Moldenhauer Engineering Company(a licensed land st!rveyur frc-1 Davis, California) an September 21, 1989, to compile a Potentiometric Map (Plate i?-3). he G&�Con Data used to compile Platt are shown in Tt and the averagebg adient to be 0.0024.le 1. We evaluate6f The:c data arae groundwater flow to be no consistent with the flow direction and gradient previously evaluated. Samples of ground water were taken from the monitoring wells for subjective analysis using the methods described in the attachment to this report. The geologista exinno cd he sa celes for floating product, sheen, and other subjective evidence of by of hydrocarbons was noted. Results of subjective analyses are presented in Table 2. The geologist purged approximately 3 well volumes (30 gallons) of ground water from the five wells using a submersible pump. The wells were allowed to recover to near static water levels. The geologist then collected groundwater samples from each well for laboratory analyses. The methods of ground-water sampling are discussed in an attachment to this beled 17-E see ending te report. The purge water Se star ewater was subsequenily remnsite in properl oedtbylA mourdrumspPetro!uhm results of laboratory analyses. of Fairfield, California, and recycled. -- 2 Applied GOOSYStOMS