ARCHIVED REPORTS XR0000632 - Laserfiche WebLink

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Parsons Engineering Science, Inc • Elevated levels of TPH-D and BTEX are limited to the site and have not impacted offsite soils The total volume of soil containing TPH with concentrations in excess of 10 mg/kg is estimated to be approximately 3,700 cubic yards • Since TPH-G was not detected in onsite soil samples, additives to gasoline (methyl tertiary butyl ether, 1,2-dichloroethane, tetraethyl lead) are not considered to be contaminants of concern at this site Groundwater Chemistry • TPH-D and BTEX compounds have been detected in groundwater underlying the site TPH-G has never been detected in any samples collected • TPH-D was not detected in samples collected during 10 of 17 groundwater monitoring events With one exception, reported concentrations in the other samples did not exceed 100 ug/L • compounds have been detected in groundwater samples collected from the BTEX p site, however, the only BTEX compound detected at a concentration in excess of its MCL is benzene (0 7 pg/l, June 1993) No other BTEX compound has been detected in excess of its MCL before or after June 1993 o Analytical results from a groundwater sample collected in well MW-4 indicate that TPH-D and BTEX contamination does not extent beyond the west side of the site • The history of intermittent detection of TPH-D and BTEX in groundwater samples indicates that residual soil contamination is isolated in small pockets and will either attenuate before reaching groundwater or soon after it reaches Groundwater • In view of the lack of beneficial uses of groundwater at the site and distance of the UFST release to Mormon Slough, there is a low potential for impending risk to human health and the environment resulting from groundwater impacted by the former UFST • Since TPH-G was not detected in onsite groundwater, additives to gasoline (methyl tertiary butyl ether, 1,2-dichloroethane, tetraethyl lead) are not considered to be contaminants of concern at this site Recommendations Parsons ES makes the following recommendations • The site should be considered as a candidate for closure by the regulatory agencies PARESSYROI VOLIR IWP1727607 80969127607R03 WW6 13