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1 <br />' SECTION 4 <br />' <br /> EVALLTATIDN OF REMEDIAL ALTERNATIVES <br />' In this section, an evaluation of remedial alternatives is presented for the <br /> remaining affected soils delineated at Former Tank Site #2 As <br /> summarized above, previous investigations have indicated that TPH- <br /> impacted soils are not present at appreciable volumes at Site #1 soils, and <br /> further soil remediation is not warranted for that site <br /> Ground water remediation is not included in this Plan Ground water <br /> i <br /> extraction events have not appreciably improved ground water quality, <br /> and continued ground water extraction has not proven to be a cost- <br /> effective remediation approach TPH as gasoline and BTEX compounds <br /> continue to be detected in ground water samples collected at the two sites, <br /> but historical trend analysis indicates that TPH and BTEX concentrations <br /> have decreased significantly over time At both sites, the highest <br /> detections are associated with the wells located in the immediate vicinity <br /> of the former tanks Based on more than seven years of monitoring data, <br /> TPH and BTEX detections decrease dramatically in nearby wells, <br /> indicating that 1) the extent of affected ground water is lirruted, and 2) the <br />' TPH plumes do not appear to be migrating As previously noted, <br /> enhanced natural attenuation of hydrocarbons in ground water (via ORC <br />' introduction) has been performed at Sites #1 and #2 since October 1996 <br /> The introduction of ORC appears to have enhanced the level of microbial <br /> activity at each site, as evidenced by the increase in heterotrophic plate <br /> count results and decrease in chemical concentrations Based on the <br /> steadily declining chemical concentrations and limited lateral extent of <br /> ground water impacts, further ground water remediation is not <br />' warranted <br /> The first subsection describes the criteria used to screen the soil <br /> remediation alternatives The following two subsections present a <br /> description of the alternatives screened, including an evaluation of each <br /> alternative based on the screening criteria The final subsection identifies <br />' the preferred alternative <br /> 1 <br /> I <br /> 4-1 <br /> I <br />