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hydrocarbons present above laboratory detection limits was from monitor well W-3 with 0 55 parts <br /> per billion (ppb) of xylenes (November, 1992) and monitor well W-6 with 0 06 ppb toluene <br /> (December, 1993) These concentrations are well below the maximum contaminant levels of 1750 <br /> ppb xylenes and 1000 ppb toluene in A Compilation of Water Quality Goals published by the <br /> CRWQCB-Central Valley Region Analytical results of historical groundwater analyses are <br /> presented in Table 5 Petroleum hydrocarbon constituents have not been detected above the <br /> detection limits for the past seven consecutive sampling events <br /> 50 RATIONAL FOR CLOSURE <br /> Based on the above discussion of soil sampling and historical ground water morutonng, SECOR <br /> believes the following justification summary provides sufficient basis to consider this site for <br /> regulatory closure <br /> • Results generated from the confirmation geoprobe borings and previous <br /> environmental investigations have adequately characterized the extent and magnitude <br /> of soil impacted with petroleum hydrocarbons at the site <br /> • No benzene was reported above the laboratory detection limits in any of the soil <br /> samples analyzed from the confirmation geoprobe borings <br /> • A naturally occurring clay layer near the top of the shallow water table together with <br /> a paved ground surface at the site significantly reduces the likelihood of any vertical <br /> migration of remaining petroleum hydrocarbons in the soil <br /> • The results of a bacteria enumeration study indicate that the subsurface soils at the <br /> site are able to support a significant population of hydrocarbon utilizing bacteria <br /> I This suggests that hydrocarbon impacted soil at the site will be degraded by natural <br /> processes <br />' To date, no petroleum hydrocarbon constituents above State or Federal action levels <br /> have been detected in water samples collected from the groundwater monitor wells <br /> at the site <br /> IBased on the preceding justification, it is the opinion of SECOR and Time Oil Company that the <br /> hydrocarbon impacted soil identified during previous environmental investigations at the site does <br /> not pose a significant threat to public health or the beneficial use of groundwater <br /> I <br /> I434INV RPT SECOR <br /> J0710-002 01 4 October 1996 <br /> I <br />