SITE INFORMATION AND CORRESPONDENCE

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DDJC-Tracy UST NFA Memo - 6 - • 24 June 2004 A TPHD concentration of 21,000 gg/L was detected in 1998 in the groundwater directly beneath the former diesel UST. Groundwater samples collected down gradient from the diesel UST did not contain diesel. The hotspot was resampled in June 2003 and diesel was not detected. The remaining mass of TPHD in soil is approximately 75 kilograms. The estimated volume of affected soil is 140 cubic yards. The extent of the diesel plume is considered negligible. ** Site 32 Site 32 is located on the eastern side of the Depot and adjacent to Building 22. The site was a 600-gallon metal tank that was used to store No. 2 fuel oil for the boiler system in Building 22. The tank was installed in 1956, abandoned in 1967, and removed in 1988. The site was investigated in 1993. Contamination was detected in one of the nine soil samples collected. Concentrations of 2,550 mg/Kg TPHD and 0.161 mg/Kg ethylbenzene were detected at the base of the former tank excavation. Other analytes were not detected. One groundwater grab sample was collected during the 1993 investigation. TPHD was not detected. Toluene,at a concentration of 1.35 gg/L,was the only analyte detected in the groundwater sample. An investigation of the site was initiated in 1998,but was terminated after two borings met refusal on a concrete slab at a depth of 6 feet bgs. No samples were collected. The remaining mass of TPHD in soil is approximately 12 kilograms and the affected volume of soil is estimated to be 13 cubic yards. The 1993 investigation indicates the extent of the groundwater plume beneath Site 32 is negligible. ** Building 201 Sump A two-stage concrete sump was formerly located at the Building 201 Sump site. The sump was reportedly a collection point for waste discharged to floor drains from Building 201,which potentially contained waste oil, antifreeze, and battery acid. The sump was removed in April 1998. Some contaminated soil may have been removed during removal of the sump in 1998,but the soil removal actions are not well documented. Soil samples collected from soil stockpiled during removal of the sump contained 18,000 mg/Kg total recoverable petroleum hydrocarbons (TRPH),200 mg/Kg TPHG, 1,000 mg/Kg, 9,000 mg/Kg total petroleum hydrocarbons as motor oil(TPHMO), 1,400 mg/Kg total xylenes, and 3,000 pg/Kg bis(2-ethylhexyl)phthalate. Metals detected in the stockpile were below residential preliminary remediation goals (DRGs). This site was investigated in 1998 and 2003. In 1998 soil samples were collected beneath and adjacent to the former sump. TPHD,TPHG, and tetrachloroethene (PCE)were detected at concentrations of 22,000 mg/Kg, 86 mg/Kg, and 0.11 mg/Kg,respectively. Bis(2-ethylhexyl)phthalate,TPHMO, and BTEX were not detected during the 1998 investigation of the sump site. The soil hotspot was resampled in June 2003 and petroleum hydrocarbons were not detected. Groundwater samples were collected in 1998 from the former location of the sump 1 and several locations down gradient. TPHD was detected at a concentration of 880 gg/L beneath the former sump and at a **Natural attenuation studies conducted at DDJC-Tracy 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.