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90371-R COT-5 <br /> W1V )jward-Clyde Consultants <br /> CONCLUSIONS <br /> In view of the results of the various laboratory analyses and observations <br /> made during excavating and drilling, it appears that the extent of <br /> contamination is limited and that much of the soil contamination has been <br /> removed and treated. The significant decrease in TPH levels (920 to 130 <br /> mg/kg) between samples E-4 and 17-2-1 which are only 12 ft apart suggests <br /> that the soil contamination does not extend much past MW-17. As a possible <br /> worst case, the soil contamination may be assumed to extend approximately <br /> 40 ft in the general downgradient direction from the south end of the <br /> existing tank. The same conclusion may be reached for the groundwater <br /> contamination due to the absence of detectable TPH or BTX in MW-18. Due to <br /> the presence of low levels of hydrocarbons in E-1, it appears that the <br /> contamination has spread out in somewhat of a fan-shaped a pattern which is <br /> indicative of a relatively flat groundwater gradient. Although there are <br /> insufficient data points to calculate the gradient at the spill site, data <br /> from the wells at the back of the facility do indicate a fairly flat local <br /> gradient. <br /> r <br /> The contamination appears to have been present for some time due to the <br /> lack of any known recent or past spills and because it exists across a <br /> 2-foot thick zone indicating it has undergone one, if not several , seasonal <br /> water table fluctuations. The absence of product on the water in the <br /> excavation and in either well suggests that any free product that was i <br /> present has migrated to exhaustion and remains in the soil as residual <br /> contamination. If the contamination (residual or dissolved) has been <br /> present for several years as suspected, and has only migrated a maximum of <br /> 40 ft from he source, it is unlikely that it will migrate significantly <br /> further. <br /> The actual source of the contamination is somewhat unclear at this time. <br /> As mentioned above, it appears to be centered around the fill pipe end of <br /> the existing tank. The tank has undergone a leak test twice which resulted <br /> 6 <br /> i <br />