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1 <br /> grade It is estimated approximately 300 to 350 cubic yards of residual hydrocarbon <br /> contaminated soil remain Table 2 summarizes soil analyses The estimated areal extent of soil <br />' contamination at depth is exhibited on Figure 3 <br /> 5.2 Groundwater Contamination <br /> First Quarter 1993 groundwater sampling analyses indicated benzene, ethylbenzene, xylenes, <br /> TPHG, and TPHD were present above method detection limits in monitoring well MW1 The <br />' ethylbenzene and xylenes present were below both Primary and Secondary Maximum <br /> Contaminant Levels (MCL), established by the DHS The quantification for diesel (TPHD) <br />' includes all peaks noted, including the gasoline range peaks which overlap the diesel range <br /> Therefore the total contaminant concentration reported in the diesel range may be somewhat <br />' misleading Xylenes were present in monitoring well MW3 at 1 9 µg/P, which is below primary <br /> and secondary MCL concentrations Monitoring wells MW2 and MW4 reported nondetectable <br />' levels for all analytes These results suggest groundwater contamination beneath the site is <br /> limited to the immediate vicinity of the former tank pit The relatively low transmissivity of the <br /> underlying soils is expected to impede movement of dissolved hydrocarbons <br /> 6.0 REMEDIAL ALTERNATIVES <br /> Soil remediation alternatives for the subject site include cap/monitoring, excavation of impacted <br />' soil, and in-situ soil venting/vacuum extraction A summary of each alternative is presented <br /> below <br /> 6.1 Cap and Monitoring <br /> LThe area of documented soil contamination is covered by relatively impermeable surfaces <br /> (asphalt) Because infiltration of moisture to the subsurface is thereby significantly reduced, the <br /> potential for vertical migration (driven by percolation of moisture through the contaminated soil <br /> horizon) is limited Natural degradation of the residual hydrocarbon contamination should occur <br /> over time Periodic monitoring/sampling of well MW1 and MW4 would provide assurance that <br /> groundwater quality is not being adversely affected Due to very shallow groundwater at the <br />' PAR-0593 FNL 4 <br /> 1 <br />