COMPLIANCE INFO_FILE 2 - Laserfiche WebLink

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'I 1 0 0 Nature and Extent of Contamination Contaminants of concern at the site of the former tank 8178-2 are TPH as gasoline and benzene, toluene, ethylbenzene, and xylenes. These contaminants were detected in soil samples NCS - 3 and NCS -4, immediately to the east and west of the former UST (Figure 2). As well, lead may potentially be of concern in soil sample NCS -5, in the area of the product delivery piping trench. The reported contaminants may potentially have been released from leaks in pipe fittings and holes 41 found in the bottom of the UST. Lateral and vertical extent of contamination has not been determined. Since both tanks 81713-1 and 81713-3 passed the tightness testing, they are not suspected as the primary sources of contamination. Tank 81713-2 removed from NCS Stockton was observed to have approximately 25 dime -sized holes at the time of removal. These holes were located along the bottom edge of the tank and may potentially have been the primary source of soil contamination found in the tank excavation. Soil samples collected during tank removal indicate that an unauthorized release of gasoline from the UST resulted in soil contamination. Soils beneath and adjacent to the former UST location may also be contaminated. Ground water was not encountered during tank removal operations; therefore, impact to the ground water is not known. Samples from the stockpiled soil (NCS -IA and NCS -2A) were not analyzed because a clean closure of the tank pit would not occur. ' PRC recommends that additional soil and ground -water investigation be conducted to assess the vertical and horizontal extent of contamination in the soil and to determine if the ground water has been adversely impacted by the unauthorized release. The total lead concentration reported for sample number NCS -5 exceeded 10 times the STLC for lead specified in the California Code of Regulations, Title 26, 22-66699. PRC recommends a waste extraction test and STLC analysis be performed to determine if the soluble lead concentrations reach or exceed the hazardous waste criteria of 5 milligrams per liter (mg/Q. Soil boring samples and composited hand samples should be collected to assess the chemical and physical characteristics of the soil (both stockpiled and in situ), and monitoring wells should be installed to assess potential impact to ground water, followed by an evaluation of possible remedial alternatives. n 1 15