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URS Mr. Ray Von Flue San Joaquin County Environmental Health Department October 28,2002 Page 3 oxygenates (TBA, MtBE, DIPE, TAME, ETBE, EDB, and 1,2-DCA) by EPA Method 8260B. Stockpile samples were also analyzed for total lead by EPA method 6010B. The results of soil samples collected from the limits of the over-excavation are summarized in Table 1. TPHg was reported in soil sample PB-M at a concentration of 400 mg/kg. Ethylbenzene and xylenes were reported in this sample at concentration of 1.2 mg/kg and 3.0 mg/kg, respectively. The sample collected from the east sidewall of the over-excavation at 18 feet bgs reported TPHg at 160 mg/kg and MtBE at 1.4 mg/kg. After these samples were collected, soil removal was discontinued because it was determined by URS and the SJCEHD inspector that further excavation of impacted soil could potentially weaken the sidewalk located to the east of the tank pit. ' Stockpiled Soil Removal ' The soil and pea gravel generated during UST removal was stockpiled on site. Samples of this material (SP1-1 to SPI-4, and SP1-5 to SP1-8) indicated that it was not impacted with petroleum hydrocarbons, BTEX, fuel oxygenates, or lead (Table 2). Therefore, the excavated material was used to backfill the tank pit. Approximately 45 tons of soil generated by over-excavation activities were sampled on August 23, 2002. Analytical results of the composite sample from the over-excavated soil (SP-1-4) shown on ' Table 2 indicated that TPHg was present at 2.0 mg/kg. Due to the presence of TPHg in this sample,the over-excavated material was hauled off site by Dillard Environmental and disposed of at Forward Landfill in Manteca, California. Stockpiled soil analytical data are presented in Table 2. Laboratory analytical reports and chain-of-custody documentation are presented as Attachment B. The soil disposal manifests are presented as Attachment D. Groundwater Sampling On October 3, 2002, the three existing groundwater monitoring wells MWA, MW-2, and MW-3 were purged and sampled by Blaine Tech Services, Inc. The groundwater samples were analyzed for TPHg by EPA Method 8015, BTEX by EPA Method 8021, and fuel oxygenates by EPA Method 8260B. Groundwater sampling and analysis procedures are presented in Appendix B. Groundwater sampling forms, laboratory analytical reports, and chain-of-custody documentation are presented as Attachment ' C. Depth to water in the monitoring wells was approximately 61 feet bgs. Groundwater sampling field sheets are included in Attachment E. Analytical results of the groundwater samples are presented in Table 3. Figure 4 presents a summary of groundwater analytical data. TPHg was reported in MW-2 at 410 micrograms per liter (µg/L) and in MW-3 at 140 gg/L. Benzene was reported in MW-2 at 3.2 µg/L. MtBE was reported at 0.91 pg/L in ' MWA and at 3.7 µg/L in MW-2. The fuel oxygenate 1,2-DCA was reported in all three wells sampled with a maximum concentration of 26µg/L reported in MW-2. SUMMARY OF FINDINGS 9 Before over-excavation of the UST complex, TPHg was reported in one of the twelve samples collected (PB-10-N) at a concentration of 120 mg/kg. Benzene and xylenes were also reported in this sample. MtBE, analyzed by EPA Method 8260B, KA J5 BP ARCO\00760\UST RemovaAUST removal report.doc