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URS <br /> Mr.Ray Von Flue <br /> San Joaquin County Environmental Health Department <br /> January 23, 2003 <br /> Page 4 <br /> SUMMARY OF FINDINGS <br /> • Before over-excavation of the UST complex, TPHg was reported in one of the <br /> twelve samples collected (PB-10-N) at a concentration of 120 mg/kg. Benzene and <br /> xylenes were also reported in this sample. MtBE, analyzed by EPA Method 8260B, <br /> was reported in nine of the twelve samples at concentrations ranging from 0.0051 <br /> mg/kg(PB-4-N)to 0.98 mg/kg(PB-1-N); <br /> • Approximately 45 tons of soil from beneath the northeast corner of the former UST <br /> complex were over-excavated to an approximate depth of 18 feet bgs; <br /> • Over-excavation was discontinued prior to removal of all of the impacted soil <br /> because it was determined that further excavation could potentially weaken the <br /> sidewalk located to the east of the tank pit; <br /> • After over-excavation of the UST complex, two of the five soil samples collected <br /> reported TPHg at concentrations of 400 mg/kg(PB-M), and 160 mg/kg(SW-E); and <br /> • One or more groundwater samples collected from onsite monitoring wells contained <br /> detectable concentrations of TPHg,BTEX,MtBE,and 1,2-DCA. <br /> CONCLUSIONS <br /> Based on the analytical data collected during the above-described field work, detectable levels of <br /> petroleum hydrocarbons remain in soil near the northwest corner of the UST complex. Petroleum <br /> hydrocarbons were detected in the groundwater samples collected from the three on-site monitoring <br /> wells. In the letter from SJCEHD dated December 27, 2002, it was requested that quarterly <br /> groundwater monitoring of the three site wells be resumed (Attachment A). The next quarterly <br /> sampling event for this site is scheduled for March 2003. <br /> This report presents our understanding of existing conditions at the subject site. The conclusions <br /> contained herein are based on the analytical results and professional judgment in accordance with <br /> current standards of professional practice; no other warranty is expressed or implied. URS assumes no <br /> responsibility for data reported or supplied by other consultants or contractors. <br /> KA\15 BP ARCO\00760\UST Removal\UST removal 2nd report.doc <br />