COMPLIANCE INFO_CASE 2 - Laserfiche WebLink

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M. Scott Mansholt - 3 - 11 March 2008 TAOC Tracy Gravel Pits within the gravel pit excavation and north-central part of the site. Geomatrix theorized this material was distributed across the site as the result of tilling associated with weed control activities. Nine soil samples from targeted locations in close proximity to the former railroad spur, within the gravel pit excavation, were submitted for Title 22 metals analysis. Based on the analysis, several metals results did not exceed their respective reporting limits. Low concentrations of metals detected in other samples were at or slightly above their reporting limits. Geomatrix suggested that the metals reported in soil are consistent with background values and their presence is not likely the result of former site activities associated with the site or the rail spur. Soil samples from 98 test trenches were submitted for TPHd, TPHmo, and PAH analysis. Affected soil results, including TPHd, TPHmo, and/or PAHs at concentrations exceeding the laboratory reporting limits were reported in 53 test trenches at sample depths of 1 to 11-feet. Generally, without exception, corresponding deeper samples beneath affected soil and in trenches where none was observed, the lab results were ND for TPH constituents. According to the Geomatrix report, TPHd was detected at concentrations from 1.2 milligrams per kilogram (mg/kg) to 140,000 mg/kg. TPHmo was reported at 51 to 260,000 mg/kg. (It should be noted that TPHd and TPHmo detections do not indicate that diesel and motor oil are present rather they occur within petroleum hydrocarbon "carbon ranges"evaluated by the analytical laboratory method). According to the report, PAHs were detected in soil samples with elevated TPH concentrations from 39 trenches; carcinogenic PAHs were reported in samples from 31 trenches, and the benzo(a)pyrene toxicity equivalency factor (B(a)P TEF) ranged from 0.004825 mg/kg to 15.92 mg/kg. The residential CHHSLs (California Human Health Screening Levels) for PAH in soil by OEHHA (Office of Environmental Human Health Hazard Assessment) are 0.038 mg/kg and 0.13 mg/kg for residential and commercial scenarios, respectively. The residential Environmental Screening Level (ESL) is also 0.038 mg/kg. The total B(a)P TEFs were above the residential CHHSLs and the ESLs in impacted soil from 29 test trenches. Samples results from 19 other trenches likely exceeded the residential ESLs and CHHSLs due to use of elevated PAH reporting limits. Increased reporting limits, was caused by matrix interference by elevated TPH present. The elevated reporting limits exceeded the minimum residential and commercial screening levels. Consistent with prior investigations, analytical and visual results indicated that there was limited to no vertical migration of petroleum hydrocarbons below visibly affected soil. TPH (including PAHs) concentrations occurred with visually affected soil and underlying "clean" soil was ND for TPH compounds. These observations and findings are consistent with field observations of open trenches where the TPH material noted occurs in distinct layers, somewhat uniform thickness, and depth. Geomatrix indicated that these findings can be correlated to residual tank bottoms/TPH waste material in historical sumps/ponds identified at the site based on historical photographs and records. At some unknown time the sumps/ponds containing the residual petroleum hydrocarbon material were filled/covered with soil.