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. KEI-P89-1104 .QR4 February 3 , 1992 Page 9 traces of silt were encountered in MW2 and MW3) . This sandy sequence is inturn underlain by a second relatively thick fine- grained sequence, which consists predominantly of silty clay and clayey silt lenses, and extends to depths below grade of about 53 . 5 to 68 . 5 feet below grade (and varies In thickness from about 13 . 5 to 27 . 5 feet) . This fine-grained sequence is inturn underlain by a second sandy zone consisting predominantly of silty sand and extending to the maximum depths explored in all wells (69 to 75 feet below grade) . Ground water was encountered during drilling in this deeper silty sand zone only in well MW2 . Ground water was encountered approximately 2 . 5 feet above the silty sand zone in wells MW1 and MW3 , and approximately 9 feet above the silty sand zone in MW4 (generally within silt materials) . ANALYTICAL RESULTS Ground water samples were analyzed at Sequoia Analytical Laboratory in Concord, California, and were accompanied by properly executed Chain of Custody documentation. The samples were analyzed for TPH as gasoline using EPA method 5030 in conjunction with modified 8015, and BTX&E using EPA method 8020. In addition, the ground water sample collected from MW1 was analyzed for TPH as diesel using EPA method 3510 in conjunction with modified 8015, TOG using Standard Method 5520B&F, and halogenated volatile organics using EPA method 8010. Analytical results of the ground water samples collected from monitoring wells MW1 through MW4 indicated non-detectable levels of TPH as gasoline and BTX&E for all samples. In MW1, TPH as diesel, TOG and all EPA method 8010 constituents were non-detectable, except for 14 ppb of 1, 2-dichlorobenzene and 2 . 8 ppb of chloro- benzene. Results of the analyses are summarized in Table 2 . Copies of the analytical results and Chain of Custody documentation are attached to this report. DISCUSSION AND RECOMMENDATIONS Based on the analytical results of the ground water samples collected to date, no evidence of free product or sheen in any of the wells to date, and a consistent ground water flow direction at the site, KEI recommends a modification to the existing monitoring and sampling program of the existing monitoring wells. Levels of TPH as gasoline and benzene in the water samples collected from all wells have been non-detectable for at least the past four quarters (one hydrological cycle.) . In addition, TPH as diesel has been non- detectable in well MW1 for the past two quarters. Therefore, KEI recommends reducing the frequency of monitoring of the wells from monthly to quarterly; KEI also recommends reducing the frequency of sampling of the wells from quarterly to semi-annually. Water