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�J Subsurface Investigation, Well Installation, and Sample Analyses Results Page 15 Cintra Park Phase II Development, S— Tract 2705, Tracy, California July 23, 1998 CTE Job No. 20-0445B 6.0 CONCLUSIONS AND DISCUSSION 4. . Based on the findings of site characterization investigations to date the following conclusions are r - offered: • A release of fuel hydrocarbons (gasoline) occurred from the former USTs onsite. This w release apparently penetrated the soil column to a depth of approximately eight to 10 fbg. • The lateral and vertical extent of hydrocarbon-affected soil onsite has generally been assessed and removed. Hydrocarbon-affected soil remaining onsite appears to be limited in extent. Although four sidewall and bottom soil samples contained TPH-G concentrations, these concentrations were 2.0 mg/kg or Iess. Subsequc�it soil samples from borings/wells installed in March 1998 showed TPH-G,benzene, ethyl benzene, and xylene all below the laboratory reporting limit. Toluene was observed at very low concentrations at selected intervals in .. _ each of the soil borings. Detectable toluene concentrations ranged from 0.007 mg/kg(PMW- 2, 20.5-21.0 and PMW-3, 10.5-11.0) to 0.030 mg/kg (PMW-1, 12.5-13.0). These toluene concentrations are not considered to be high enough to be of concern. Low concentrations in groundwater of TPH-G and BTEX was observed in the April 1998 sampling event but were all below the laboratory detection limit in the May 1998 sampling event and the grab sample collected in March 1998. We attribute this difference to a false positive caused by sampling from the pump in the April 1998 sampling. Free product was not detected at any time during the original excavations or subsequent boring/well installations. I 7.0 RECOMMENDI, TIONS We recommend that the case file for the site be closed. We believe that the soil and groundwater analyses results collected to date show that no significant soil and groundwater contamination is * ' present at the subject site. Although the area immediate) down adient of the excavation has not Y been investigated, we believe the placement of wells at the site is adequate to show that there is no C:ITEEL FILESICINTRA PAMCINTRA743.DOC I' k