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' Nature and Extent of Contamination <br /> Contaminants of concern at the site of the former tank 81713-2 are TPH as gasoline and <br /> benzene, toluene, ethylbenzene, and xylenes These contaminants were detected in soil samples NCS- <br /> ' 3 and NCS-4, immediately to the east and west of the former UST (Figure 2) As well, lead may <br /> potentially be of concern in soil sample NCS-5, in the area of the product delivery piping trench <br /> ' The reported contaminants may potentially have been released from leaks in pipe fittings and holes <br /> found in the bottom of the UST Lateral and vertical extent of contamination has not been <br /> ' determined Since both tanks 817B-1 and 817B-3 passed the tightness testing, they are not suspected <br /> as the primary sources of contamination <br /> ' 5.0 CONCLUSIONS AND RECOMMENDATIONS <br /> ' Tank 81713-2 removed from NAVCOMMSTA Stockton was observed to have approximately <br /> pp Y <br /> ' 25 dime-sized holes at the time of removal These holes were located along the bottom edge of the <br /> tank and may potentially have been the primary source of soil contamination found in the tank <br /> excavation <br /> Soil samples collected during tank removal indicate that an unauthorized release of gasoline <br /> from the UST resulted in soil contamination Sods beneath and adjacent to the farmer UST location <br /> may also be contaminated Ground water was not encountered during tank removal operations, <br /> ' therefore, impact to the ground water is not known Samples from the stockpiled soil (NCS-lA and <br /> NCS-2A) were not analyzed because a clean closure of the tank pit would not occur <br /> PRC recommends that additional soil and ground-water investigation be conducted to assess <br /> ' the vertical and horizontal extent of contamination in the soil and to determine if the ground water has <br /> been adversely impacted by the unauthorized release The total lead concentration reported for <br /> sample number NCS-5 exceeded 10 times the STLC for lead specified in the California Code of <br /> Regulations, Title 26, 22--66699 PRC recommends a waste extraction test and STLC analysis be <br /> ' performed to determine if the soluble lead concentrations reach or exceed the hazardous waste criteria <br /> of 5 milligrams per liter (mg/L) Soil boring samples and composited hand samples should be <br /> ' collected to assess the chemical and physical characteristics of the soil (both stockpiled and to situ), <br /> and monitoring wells should be installed to assess potential impact to ground water, followed by an <br /> evaluation of possible remedial alternatives <br /> ' TANKRMU NEW <br /> G"-0162urATR1 3114/93 16 <br />