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Ms Linda Turkatte March 6, 1992 Page 2 Free-Phase Hydrocarbon Measurements The presence of free-phase hydrocarbons or free-hydrocarbon sheen in the monitoring wells was recorded using procedures described in Enclosure A Free-phase hydrocarbon was detected in monitoring well MW-2 (thickness 0 33-foot), and in monitoring well MW-4 (thickness 0 03 foot) on January 28, 1992 Hydrocarbon sheen was not observed on water samples collected from the other monitoring wells Observations are included in Table 1 A Westinghouse pneumatically-operated product-only pump was operating alternately in monitoring wells MW-2 and MW-7 between January and April 1991 Hydrocarbon recovery pumps have been operating in both wells simultaneously since May 1991 The pumps were modified in January 1992 to recover free-phase hydrocarbons and ground water (total fluids) The total amount of free-phase hydrocarbons recovered since May 1991 is not known because the pumps have been discharging ground water as well as product Ground Water Sampling and Analytical Results Ground water samples were collected from monitoring wells MW-1, MW-3, MW-5, MW-6, MW-7, MW-8, MW-9, and MW-10 on January 28, 1992 Monitoring wells MW-2 and MW-4 were not sampled due to the presence of free-phase hydrocarbons, as described above Monitoring well MW-7 was manifolded for pumping ground water, therefore, the well was not sampled Ground water samples were collected using procedures described in Enclosure A Each ground water sample was submitted for analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), and total petroleum hydrocarbons (TPH) as gasoline, using U S Environmental Protection Agency and California Department of Health Services approved methods The analytical laboratory results for groundwater samples collected on January 28, 1992, are summarized in Table 2 Previous results are also provided in Table 2 for comparison Copies of the certified laboratory reports for the January 1992 sampling event are included in Enclosure B Analytical test results indicate that detectable concentrations of petroleum hydrocarbon constituents were present in each of the ground water samples collected on January 28, 1992, except for MW-6 Concentrations of TPH as gasoline ranged from none detected (less than 0 03 parts per million(ppm)) in MW-6 to 200 ppm in MW-9, and benzene concentrations ranged from none detected (less than 0 0003 ppm) in MW-6 to 25 ppm to MW-9 Concentrations of total petroleum hydrocarbons in ground water samples show an increase from the October sampling event A dissolved benzene isoconcentration map prepared using the January 28, 1992, ground water sampling results is included as Figure 5 Future Work Quarterly sampling of the ground water monitoring wells will continue The next sampling event is scheduled for April 1992 Installation of the ground water extraction and treatment system was completed in January 1992 The 10 system is pumping total fluids from monitoring wells MW-2 and MW-7 and directing the flow through a separation tank Ground water from the separation tank will be directed through two carbon adsorption canisters prior to discharge to the Stockton sanitary sewer Sewer discharge