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Y. <br /> 1VE/SS ASSOClA7ES ; <br /> n <br /> Gordon Boggs / 10 June 1988 / Page 2 <br /> 2 What is the lateral movement of away hydrocarbons from the excavation? <br /> Y Y <br /> 3) Were-native soil samples collected from the sides of the tank excavation pit at <br /> the soil/water interface? <br /> 4) There is no downgradient monitoring well. <br /> 5) What are the feasible alternative remediation options for the site? <br /> 6) How will-leaving the slab in place affect future site remediation? <br /> Each of these concerns is addressed individually below, and an outline of our preferred <br /> remedial option is presented as Attachment B. <br /> -4 <br /> 1) COMPARISON OF HYDROCARBON CONCENTRATIONS IN SOIL BENEATH <br /> THE SLAB TO CONCENTRATIONS IN SOIL FROM PERIMETER BORINGS AND <br /> THE EXCAVATION SIDE-WALLS <br /> Av detailed in our reportf dated 10 Jung 1987 and 15 Ootober 1987, hydraearbona <br /> were detected in only one out of 17 samples collected from 11 soil borings drilled around <br /> the perimeter of the tank excavation. A sample collected from a depth of 20.7 ft during <br /> drilling of boring B-2, near the southwestern corner of the excavation, analyzed by EPA <br /> Method 8015, gas chromatography with flame ionization detection (GC/FID), contained <br /> 1,200 parts per million total fuel hydrocarbons (TFHC) (Figure 1). <br /> Seven native soil samples, collected from the side-walls of the excavation adjacent to <br /> the slab on 22 January and 15 March 1988, have been also been analyzed by EPA Method <br /> 8015 for TFHC (Figure 1). Analytic results for the five samples collected on 22 January, <br /> Presented with analytic reports and chain-of-custody forms in our report dated 10 <br /> February, show between 65 and 3,700 ppm TFHC in samples from the southwestern corner <br /> of the excavation and Icss than 10 ppm in samples from the eastern wall. Analytic results <br /> and sampling procedures for the remaining two samples collected on March 15, which will- <br /> be presented in our excavation closure report following the next phase of site <br /> remediation, show 420 ppm TFHC in the southwest corner and less than 10 ppm TFHC in <br /> the northoaot oornor. <br />