SITE INFORMATION AND CORRESPONDENCE

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DDJC-Tracy UST NFA Memo -4 - • 24 June 2004 Soil samples collected from beneath the tank during removal in 1988 contained 55,000 mg/Kg TPHD and 286,000 mg/Kg TPHG. It is unclear why gasoline was detected in soil from the tank excavation and the depth of this sample was not recorded. Subsurface investigations were conducted in 1993, 1997, 1998, and 2003. TPHG was not detected in any soil samples. Approximately 58 cubic yards of contaminated soil was removed during the 1997 investigation. Low concentrations of toluene (<0.06 to 0.239 mg/Kg), ethylbenzene (<0.06 to 1.30 mg/Kg),and xylenes(<0.06 to 8.49 mg/Kg)were detected in several soil samples collected during the 1993 investigation,but subsequent investigations did not detect these petroleum hydrocarbons or TPHG. The maximum TPHD concentration of 29,000 mg/Kg was detected in a soil sample collected in 1998. The soil hotspot area was resampled in June 2003 and TPHD was not detected. TPHD was detected at concentrations of 170 and 110,000 gg/L in groundwater grab samples collected in 1998. Groundwater grab samples collected from the hotspot area and several down gradient locations in June 2003 ranged from below detection to 80 µg/L. The remaining mass of TPHD in soil is estimated to be 66 kilograms and the remaining volume of impacted soil is estimated to be 33 cubic yards. Based on June 2003 results, the extent of the TPHD groundwater plume is estimated to be 730 square feet. ** Site 19 UST Site 19 is located adjacent to Building 232 on the northern portion of the Depot. A 500-gallon tank was installed prior to 1956 and was used to store No. 2 fuel oil for a water boiler in Building 232. The tank was abandoned in place in 1957 and removed in 1988. Subsurface investigations were conducted in 1993, 1997, 1998, and 2003 and an estimated 130 cubic yards of soil containing TPHD was removed in 1997. After the soil removal action was completed, the maximum residual concentration of TPHD was 210 mg/Kg. Historical TPHD concentrations of 4,300 and 1,200µg/L were detected in groundwater grab samples collected beneath and approximately 30 feet down gradient of the former UST. These locations were resampled in June 2003 and TPHD was not detected. The remaining mass of TPHD in soil is estimated to be 16 kilograms and the volume of impacted soil is estimated to be 19 cubic yards. Based on June 2003 data the extent of groundwater contamination at this site is considered negligible. ** Site 20 UST Site 20 is located near Building 14 and is the former location of a 500-gallon steel UST. The UST was used to store No. 2 fuel oil for a water boiler in Building 14. The UST was installed in 1956 and abandoned in-place in 1957. The tank was removed in 1988. Subsurface investigations of Site 20 were conducted in 1993, 1995, and 1998. With the exception of one soil sample,the 1993 and 1995 investigations did not encounter elevated concentrations of petroleum **Natural attenuation studies conducted at DDJCGTracy and the documented rapid decline in petroleum hydrocarbons in both soil and groundwater at DDJC-Tracy UST sites indicate residual petroleum hydrocarbon contamination should attenuate naturally.