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r : .. S -- DU font Biosystems Page 38 August 10, 1989 Job No.211-71-6 CONCLUSIONS i The subsurface characteristics of the site are summarized below. 1. Soils encountered in the subsurface(i.e_within approximately 70 fect of the existing grade) consist primarily of silty sands and clay. The aquifer consists of interbedded sand with At and silty sand.The base of the uppermost aquifer lig at approximately 77 feet below the 4 existing grade; the oils below the aquifer consist of clay and clayey sand. T 2_ 'The ground-water gradient is slightly mounded beneath the tanks but generally flows towards the southeast with a gradient of approximate:y 0.015 (1.5 font/100 feet). - I 3. Gasoline constituents were encountered in selected soil samples from a41 boreholes except monitoring wells MW-18, MW-19, MW-21 , MW-24 and MW-25. f;te highest concentrations of total petroleum hydrocarbons (as gasoline) and BETX constituents were reported from the boring;drilled!P.the immediate vicinity of the underground fuel tants. Based on field readings using an OVA meter, petroleum hydrocarbons were detected in the soii samples collected from boring B-3 to a maximum depth of 74 feet. 4. Gasoline constituents were detected in water samples collected from all of the monitoring rations of total petroleum hydrocar wells except well MW-20. Minor concentbons and BETX components were identified in monitoring wells MW-15,MW-16,MW-18,MW-19, f MW-21, MW-24, and MW-25 (located along the plume fringe). Several feet of free- floating product has been absewed in monitoring wells MW-8, MW-10, and MW-17 E (located in the north-ccatral portion of the property). 5. Gasoline-contaminated ground-water appears to be migrating off-site as demonstrated by the presence of TPHg and BETX in wells located on neighboring properties. t