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1 <br /> This alternative may not be effective in the clayey soils found at <br /> Y Y Y <br /> Site #2 The low permeability of the clayey soil makes the extraction <br />' process difficult and time-consuming To make the process more <br /> effective, an increased number of wells would be required, thus <br /> increasing the cost of the alternative Even with the additional wells, <br />' treatment in fine-grained soils at Former Tank Site #2 may not be <br /> sufficient For these reasons, vapor extraction was eliminated as an <br /> alternative for the Former Tank Sites #1 and #2 <br /> No Action <br /> In the no action alternative, no measures would be taken to contain or <br /> treat the hydrocarbons in site soils This passive response would <br />' employ natural biodegradation as the only treatment This alternative <br /> is easily implementable, as no action is required Review of chemical <br />' quality data for ground water samples collected from monitoring wells <br /> located at both tank sites suggest that biodegradation may be occurring, <br /> however, the speed at which biodegradation occurs may be limited <br />' The no action alternative would also be the least expensive alternative <br /> Preferred Alternative <br /> The preferred alternative for Former Tank Sites #1 and #2 soil is no <br /> action The impacted soils do not appear to pose a significant threat to <br /> human health and the environment due to their limited extent The <br /> presence of the overlying building at Former Tank Site #2 further <br /> limits potential human exposure to petroleum hydrocarbons In <br /> addition, the impacted soils do not appear to comprise a major source <br /> of petroleum products to ground water at either site <br /> The reduction of concentration of TPH and BTEX concentrations in <br /> ground water samples collected from monitoring wells located at both <br />' sites is an indication that the majority of the source of hydrocarbons <br /> was removed in 1993 At Former Tank Site #1, concentrations of these <br /> compounds in ground water samples collected from MW-5 have been <br /> decreasing since 1991 Review of historic ground water chemical <br /> quality data for other Site #1 monitoring wells indicate that these <br />' compounds have been only sporadically detected at low concentrations <br /> since 1991 At Former Tank Site #2, TPH and xylenes have been <br /> detected in only one sample collected from monitoring well MW-4A <br /> This well is located immediately downgradient of the impacted soils <br /> This finding suggests that hydrocarbon products are not being readily <br /> transported from the vadose zone to the underlying confined ground <br /> water system For this and the other reasons stated above, the no <br /> 5-3 <br />