SITE INFORMATION AND CORRESPONDENCE

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Wendy L. Cohen -3- 15 March 1993 1. The report states that only two preliminary sampling points (PS/MW-3 and PS/MW- 12) contained detectable petroleum hydrocarbons; from 1988 to 1992, at PS/MW-3, TPHD, TPHG, and BTEX increased in concentration; at PS/MW-12, petroleum hydrocarbons were nondetect in 1988 but were detectable in 1992; and the results at PS/MW-12 may be due to water level fluctuations causing contaminants in the vadose zone to be introduced to the shallow ground water. I concur that the contaminants are likely coming from contaminated ground water moving southeasterly which is the predominant ground water flow direction and also northeasterly as reported by SFPP. Nonetheless, the soil and ground water sample results should be reviewed concurrently to determine if smearing has indeed occurred. 2. The report states that total lead was detected at concentrations ranging from 4 ,ug/l to 1,370 µg/l and occurrences appear to be independent of the distribution of petroleum hydrocarbons. Actually, sampling locations PS/MW-11 and -12 had nondetectable (ND) total lead (<2 µg/1 ) . I concur that the high concentration of total lead at PS/P-17 appears to be unrelated to the petroleum hydrocarbon contamination. However, since two sampling locations were found to be ND, the latter is likely the background concentration for total lead. The STTC terminals have caused some total lead pollution, albeit slight, since all the sampling locations are downgradient of the terminals and all show pollution except those two wells previously mentioned. Field Screening Results 1. The report states that the downgradient edge of the petroleum hydrocarbon plume extends approximately 50-250 feet east of Stork Road. More definition is needed east of PS/MW-3 and -15 and south of Union Pacific (UP). Placement may be a problem for a well east of PS/MW-3 because of the existence of Cogen National . UP may have installed additional monitoring wells in conjunction with the ongoing underground tank investigation. I will contact the San Joaquin. County Public Health Services to get more information on UP activities. 2. The report states that the concentration of TPHG decreased from 50,000 µg/l at PS/CB-25 to ND at PS/CB-17 in a distance of less than 200 feet. The contaminant plume at PS/CB-25 may be flowing easterly instead of southeasterly. This would explain the ND level at PS/CB-17 and also mean that the edge of the plume is somewhere between PS/CB-25 and PS/CB-19 which are approximately 500 feet apart. The distance between PS/CB-25 and PS/CB-17 is about 365 feet and not less than 200 feet as stated in the report. Nonetheless, the drop in TPHG concentration is still significant. Soil Analytical Results The report did not state which are source areas based on the soil sample results.