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SUBSURFACE SOIL AND GROUNDWATER ASSESSMENT REPORT CONCLUSIONS FROM SOIL AND GROUNDWATER ASSESSMENTS ' Soil analysis and field observations during the April 7, 2000 UST removal did not indicate a significant mass of residual petroleum hydrocarbons remaining beneath the former tank ESA's subsurface soil and groundwater investigation on July 5,2000 indicated that a very low MTBE concentration (1 Ipg/L) in soil was localized at the north end of the former UST excavation MTBE was not detected in soil samples collected east or west of the excavation perimeter, or from beneath the center of the former UST cavity Groundwater samples collected during the July 5th investigation only detected MTBE at the north (1,300 Ng/L)and south (1 4 pg/L) ends of the former UST However, MTBE was not detected in groundwater collected immediately downgradient from the southern portion of the tank, indicating the groundwater impact is localized Non-detected levels of MTBE in groundwater samples collected east and west of the UST excavation further indicate the restricted extent of impacted groundwater Results of the most recent,January 2001 investigation confirm that the slight impact to shallow groundwater appears localized MTBE was not detected in groundwater collected from concentric sampling locations around the former UST, indicating that MTBE has not migrated laterally or vertically In addition, detected lead concentrations in soil are low,representative of naturally occurring concentrations and do not suggest an impact from a petroleum UST release Given the underlying geology and hydrogeologic conditions discussed in the previous sections, the low MTBE concentrations previously detected at this site are not expected migrate significantly or eventually represent a threat to public water supplies or surface water bodies RECOMMENDATIONS ' Considering the minimal impact of MTBE to the soil and groundwater, it is ESA's opinion that the conditions at site are not significantly impacting soil and groundwater, and therefore recommends no further investigative or remedial action regarding this case This trecommendation is based on the conclusions, as summarized below, that have been developed from the findings of the UST removal in April 2000, and subsurface assessment performed in July 2000 and January 2001 by ESA A completed copy of the Tri-Regional Checklist of Required Data for No Further Action Requests at Underground Tank Sites is provided in Attachment D ' a The occurrence of MTBE in soil is localized at the north end of the former UST excavation and does not represent a significant mass capable of migrating vertically downward through the soil ' • MTBE does not appear to have migrated laterally or vertically beyond the areas of detected soil impact ' a The geology and hydrogeology does not appear conducive to initiating the future migration of MTBE from the former UST excavation ' • Public groundwater sources are located at substantial distances both laterally and vertically from the former UST location and migration of the detected MTBE to those sources is ' remote Additional Groundwater Assessment Repon 15 ESA 1200352 March 26 2001