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1 July 31, 1992 iffZffMA ARCO Service Station No 2130, Stockton, California ture GROUND-WATER MONITORING Field work was conducted by RESNA and Emcon Associates (Emcon) of Sacramento, California Emcon was contracted by ARCO, Emcon forwarded their field notes and the laboratory reports to RESNA Data obtained from Emcon is presented in the Appendix to this report Sub1ecthve Analysis and Water-Level Measurements A technician from RESNA was onsite on February 24, March 31, May 11, and June 23, 1992, to take water-level measurements and collect ground-water samples from monitoring wells MW-1 through MW-3 for subjective analyses On April 21, 1992, a technician from Emcon measured depths to water and performed subjective analyses of ground water No floating product, product sheen, or obvious product odor was noted in samples from the wells during the site visits (Table 1) The wellhead elevations of the monitoring wells at the site were previously surveyed by Tom Morrow of West Sacramento, California, a licensed land surveyor (California Land Surveyors No 5161) The surveyed elevations and the depth-to-ground-water measurements, summarized in Table 1, were used to evaluate the potentiometric surface beneath the site • The ground-water flow direction on April 21, 1992, was to the southeast with a hydraulic gradient of 0 0020 (Plate 3) Ground-Water Sampling and Analyses On April 21, 1992, Emcon collected ground-water samples from monitoring wells MW-1 through MW-3 for laboratory analyses Ground-water samples from each well were analyzed for total petroleum hydrocarbons as gasoline (TPHg) and benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) using Environmental Protection Agency Methods 5030 and 8020 and standard methods prescribed by the State of California The samples were analyzed at Columbia Analytical Services, Inc in San Jose, California (Hazardous Waste Testing Laboratory Certificate No 1426) Samples from the three wells were also submitted to Sequoia Analytical in Sacramento, California, for analysis of fecal coliform bacteria The samples were also to be analyzed for total coliform bacteria if fecal coliform bacteria were not detected Although fecal coliform bacteria were not detected, the laboratory did not analyze the samples for total coliform bacteria because the sample holding time had expired , The results of analyses are summarized in Table 2 Copies of the laboratory analysis reports are in the Appendix hr 30003- 30003-G 2