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GROUNDWATER ASSESSMENT REPORT Soil conditions were observed in continuous cores from the ground surface to maximum depths ranging from 20 to 24 feet bgs Boring lobs from this investigation are provided in Appendix B A Native subsurface materials generally consisted of fine-grained clayey sandy silts Backfill materials encountered in the UST excavation consisted of mixtures of pea gravel,compacted silt, clay,and sand The backfill materials were typically less dense than the native materials No physical signs (i e odor,discoloration)of petroleum impact were identified in any of the soil - bonngs during drilling operations Following the completion of each soil boring, a Hydro-punch in-situ groundwater-sampling tool was driven into the groundwater-bearing zone from depths ranging from 20 to 24 feet Groundwater extracted from each soil boring appeared relatively free of sediment and ESA field a geologists did not detect petroleum odors or hydrocarbon sheen on the water samples �= Laboratory analytical results of soil and groundwater samples are summarized in Table 2,below Laboratory analyses detected 11 milligrams per kilogram(mg/kg)of MTBE in the soil sample collected from boring TP4 at 15 feet bgs i Analyses detected 1,300 micrograms per liter(/g/L) and 14 tig/L, of MTBE in the groundwater samples collected from borings TP-4W and TP-5W, respectively Results of the July 200 soil and groundwater assessment indicated that the low MTBE concentrations in soils appeared localized at the north and south ends of the former UST excavation and MTBE concentrations were not found to have had migrated vertically to depths below the groundwater(approximately 15 feet) Analysis of the five groundwater samples further substantiates the conclusion that the impact from residual MTBE was localized and did not suggest a laterally migrating plume of MTBE GROUNDWATER ASSESSMENT, JANUARY 2001 Based upon results of ESA's first assessment in July 2000, SJCEHD requested additional groundwater data to further delineate MTBE concentrations detected in the groundwater near the northern end of the former UST ESA submitted the Additional Groundwater Assessment Workplan to SJCEHD on November 28, 2000 for review Following a strategy meeting with Ms Carol Oz of SJCEHD, Ms Dot Lofstrom of SJCEHD approved the workplan on December 19, 2000 The purpose of the additional assessment was to obtain supplementary groundwater - samples to determine the extent of MTBE in groundwater Secondarily,ESA collected select soil samples in the area of the former UST excavation for analysts of lead, as requested by the SJCEHD - - As-shown in-Figure 5;ESA c.onipleted fourteen-borings on-January-10 and-1-1,-2001-in and-- ---- ` around the former UST location Bormgs TP-9,TP-10, and TP-12 through TP-19 were drilled to 25-feet bgs for the purpose of collect ng representative;groundwater samples A Hydio=punch in-- — �l _ situ groundwater-sampling tool was used to collect groundwater and was typically driven into the groundwater-bearing zone from 21 to 25 feet bgs Groundwater samples from borings TP-9 and Milligrams per kilogram(mg/kg)is roughly equivalent to parts per million(ppm) Micrograms per kilogram (ug/kg)and micrograms per liter(ug/L.)are roughly equivalent to parts per billion(ppb) For purpose of consistency,concentrations will be presented as mg/kg ug/kg,or ug/l Groundwater Assessment Report 8 FSA 1200252 September 2003