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SS# 05348, Tracy 2 QM Report: 3rd 1992 In June 1990 an underground waste-oil storage tank was replaced because of suspected leaks. The tank was found to have holes. The pit was overexcavated; however, overexcavation was restricted by the proximity of the pit to the product storage tanks. In July 1991, four monitoring wells were installed and additional soil borings were drilled. Hydrocarbons as gasoline (TPH-G) were identified in soil near the fill spout of the south underground product storage tank. Additional borings were drilled to identify the lateral extent of this contamination. Following well development, groundwater was sampled from the four wells on July 15, 1991 and again on August 15, 1991. Due to the fact that contamination was reported at MW-4 from the July sampling and was not detected from the August sampling, that well alone was again sampled on September 12 , 1991. No TPH-G or BTEX was detected at that time, or from subsequent sampling events. DISCUSSION AND RECOMMENDATIONS On September 21, 1992 the wells were monitored and sampled. The water samples were taken with proper Chain-of-Custody documentation to ChromaLab of San Ramon, California, a state- certified laboratory. Water samples were analyzed for TPH-G and BTEX. Monitoring and sampling procedures are described in the attached Field Notes. The present and past monitoring data are listed in Table 1. ChromaLab reported that TPH-G and BTEX were not detected in the water samples from wells MW-2, at the west boundary of the site, or MW-4, which is at the northwest boundary of the site in a downgradient position from underground storage tanks. Water in MW- 3 , immediately adjacent to the tanks, contained 240 micrograms per liter (ug/1) of TPH-G. Present and past laboratory results are listed in Table 2 . Copies of the current laboratory report and Chain-of-Custody documentation are attached to this report. Water-level measurements indicate that on September 21, 1992 the depth from top of well casing to the water surface averaged approximately 9. 5 feet. The flow direction was towards 7 degrees west of north, with a gradient of 0. 0024 foot per foot. We recommend that the wells continue to be monitored quarterly until they are properly closed.