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� 3 A <br /> T <br /> 4VEISS ASSOCL47ES <br /> Gordon Boggs / !0 June 1988 / Page 4 <br /> As reported in our correspondence dated 30 March 1988, EPA Method 8015 analysis <br /> of four native soil samples, collected beneath the slab, showed an average of 28 ppm <br /> TFHC (Figure 1). <br /> Comparison of the analytic results for the samples collected from the perimeter <br /> borings and the excavation side-wall to the analytic results for the samples collected <br /> below the slab indicates that hydrocarbons are present in significantly higher <br /> concentrations in soil immediately adjacent to the slab than in soil below the slab or in <br /> soil from the perimeter borings. This suggests that the majority of the hydrocarbons from <br /> the leaking fuel tanks migrated laterally and downward away from the edges of the slab <br /> and are contained in soil adjacent to the present,cxcavation. <br /> 2) LATERAL MOVEMENT OF HYDROCARBONS <br /> As discussed above, hydrocarbons appear to be confined to soil immediately adjacent <br /> to the excavation and, other than in the vicinity of the southwestern corner, there is little <br /> indication of lateral migration of hydrocarbons in unsaturated soil. <br /> 3) NATIVE SOIL SAMPLES FROM THE SOIL/WATER INTERFACE <br /> Since ground water occurs at depth of about 17 to 18 feet in the three ground <br /> r water monitoring wells on site and the bottom of the excavation occurs at only 14 feet <br /> below ground surface, the soil samples from the excavation side-walls and from beneath <br /> ng <br /> the slab were unsaturated. Samples collected from <br /> we wells MW-1 and MW2'anddfromgof <br /> l8 3 <br /> borings B-3 and B-7, from 15.8 ft in the_borings <br /> ft in the boring for well '.AW-3, were collected close to tlty soil/water interface. As <br /> detailed in oui 10 June and 13 October 1987 reports, no hydrocarbons were detected in <br /> these samples. <br /> 4) DOWNGRADIENT MO.�-TORING WELL <br /> Three ground water monitoring wells have been installed at the site and sampled for <br /> hydrocarbons. Bc. .-bole stratigraphy, construction characteristics, ground water sampling <br /> procedures and analytic results for the wells are detailed in our report dated 15 October <br /> - ----_ _--- —_---_ ---—- ---1987._According to wsicr <br /> ta recorded on 28 March 1988, well MW-2 lies directly <br />