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aa _ W � � 7 <br /> ``�'S�" L`�' 3"�" y� '-.�x.��'iai' <br /> hydrocarbon fraction (BTEX) had occurred. 'fhe 18 ppb <br /> - toluene concentration is significantly below the 100 ",aximum <br /> Contaminant Level (MCL) for drinking water established by <br /> the State Department of Health Services (DHS). No MCL exists <br /> for TPH-D although nuisance conditions related to taste <br /> and/or odor would have to be considered. The concentration <br /> of fecal coliform in all four wells exceed state water <br /> quality standards indicating poor water quality already <br /> exists beneath the site. <br /> Based on the data collected to date, soil and groundwater <br /> have been impacted by varying concentrations of diesel <br /> hydrocarbons. The limited extent of soil and groundwater <br /> contamination is supported by the non-detectable levels of <br /> diesel hydrocarbons in soil and groundwater samples <br /> collected from well borings MW1 through MW4. The nearest <br /> water resource of beneficial use is the San Joaquin River <br /> located approximately 160 feet south to southwest of the <br /> former diesel tank. Degradation of this resource is nor, <br /> threatened because, 1) , under current groundwater flow <br /> conditions the river lies up gradient of the contamination, <br /> and 2), analysis of a groundwater sample, MW1, collected <br /> between the river and the tank did not detect the presence <br /> T of hydrocarbon constituents. The closest known groundwater <br /> wells (Figure 4) are located a significant distance from the <br /> area of contamination and should not be adversely affected. <br /> Although the original tank pit sample recorded 65000 ppb <br /> TPH-D, the non-detectable levels of BEX and concentration of <br /> xylenes below state drinking water standards indicates the <br /> impact on water quality from the . volatile hydrocarbon <br /> fraction is not significant. It is our opinion that the <br /> documented soil contamination and suspected groundwater <br /> contamination (in the vicinity of Sal) by diesel <br /> 4 = hydrocarbons does not adversely affect the beneficial use of <br /> surface water or groundwater resources under the current <br /> conditions. The presence of fecal coliform in the <br /> r, g%oundwate.r indicates beneficial uses are presently <br /> restricted. <br /> 6.0 Recommendations <br /> Because there is no conclusive evidence that groundwater <br /> F� contamination by diesel hydrocarbons is present above <br /> drinking water standards and not a threat to beneficial uses <br /> E ' of surface or groundwater resources outside the area bounded <br /> by wells MW?, MW3 and MW4, we would propose no active <br /> remediation of diesel contamination be conducted at this <br /> ., site. Natural degradation of the residual hydrocarbon <br /> { contamination recorded in Sal should occur over time. We <br /> tj recommenderiodic monitoring/sam In <br /> P t'�roug _.._...__. .. .. . p. ._....g. of the monito_ring_. <br /> wells MWl h MW4 to provide assurance that, 1 ) <br /> groundwater flow is away from the nearby San Joaquin River <br /> and 2), the suspected groundwater contamination does not <br /> migrate beyond the current monitoring network. <br /> 6 <br />