SITE INFORMATION AND CORRESPONDENCE

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Anne M. Farr, Ph.D. Steve Sasson March 21, 1995 It is my understanding, that the County requested that additional soil samples be collected, due to the detection levels for BTEX for the soil samples collected from the tank excavations being higher than required by the County. Two borings were drilled in November 1993 to address this concern of the County. One of the borings (B-1) was located at the former location of Waste Oil Tank WO-1. The second boring (B-2) was located in the vicinity of the three other USTs. As summarized in Table 1, TPH , ethylbenzene, and xylenes, were detected in one of the soil samples collected from B-1 at a depth of 8 feet. The boring log for this sample indicates that there were no hydrocarbon odors below a depth of 91/2 feet. The absence of petroleum hydrocarbons below this depth was confirmed by analyzing a sample from boring B-1 at a depth of 15 feet. This soil sample had non-detectable concentrations of TPH and BTEX. Review of Soil Samples Results As specified by the Tri-Regional Guidelines, one soil boring was installed at the former location of the 500-gallon UST. The results from this boring were reviewed relative to the methodology specified in the LUFT Manual. Applying the leaching potential analysis outlined in the LUFT Manual results in a Site rating of 44. Based on this rating' and the concentration of xylenes and TPH' detected in one sample from Boring B-1, the LUFT manual states that a "General Risk Appraisal' needs to be performed. Further, the LUFT Manual states that "the general risk appraisal is more sophisticated than the leaching potential analysis" (LUFT, p.29) and that the appraisal "is based on a technical foundation which conservatively accounts for influences on pollutant migration." (LUFT, p.28) Using the General Risk Appraisal, as recommended by the LUFT Manual, the acceptable cumulative soil contamination levels for protection of groundwater at the Brannon Tire Site are as follows ': 1 ppm Benzene, 100 ppm toluene, 200 ppm xylenes, and 300 ppm ethlybenzene. As summarized in Table 1, of these four compounds, only xylenes and ethylbenzene have been detected. The maximum cumulative soil contamination levels for these two compounds at the Brannon Tire Site are: 2.7 ppm for xylenes and 0.49 ppm for ethylbenzene. These soil concentrations are signifimn_tly less that the acceptable curnudative soil contamination levels specified by the General Risk Appraisal. In fact, the concentrations detected would be acceptable if the distance to highest groundwater was only 5 feet. 1 The numbers specified in Table 2-1 provide "a simplified way to assess the possible threat to ground water from contamination soils. Alternate cleanup levels, based on additional site-specific analysis, would supersede the initial allowable levels." (LUFT, p.20). Z As stated in the LUFT Manual, the concentrations for TPH listed in the Leaching Potential Table were approximated by using the acceptable BTX&E levels divided by their percent composition in gasoline. 3 Based on a mean annual precipitation of 14.4 inches (measured at Stockton Fire Station #4) and a distance to highest groundwater from soil sample of 35-40 ft