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4 ' 0 <br /> California Regional Water Quality Control Board ' <br /> l\- Central Valley Region <br /> vSacramento Main Office Gray Davis <br /> inston H.Hickox Governor <br /> Internet Address: htento w Main <br /> O .ca.gov/rwgcb5 <br /> Secretaryfor 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Environmental Phone(916)255-3000•FAX(916)255-3015 <br /> Protection <br /> 9 January 2001 <br /> Ed Koberstein Jay Allen <br /> Nick Nickerson <br /> Unocal DBG/AMG Montgomery Wards Stone Brothers <br /> 8788 Elk Grove Blvd. 1331 South Harbor Blvd. Management Company <br /> Building 3, Suite 15 <br /> Fullerton, CA 92632 1024 W. Robinhood Drive <br /> Elk Grove, CA 956624 Stockton, CA 95207 <br /> REVIEW RESULTS OF CPT INVESTIGATIONAND WORKPLAN <br /> FORMER UNOCAL STATION#5098 AT 5606 PACIFIC AVENUE,AND MONTGOMERY WARDS <br /> AUTO SERVICE AT 5400 PACIFIC AVENUE, STOCKTON,SAN JOAQUIN COUNTY <br /> CLEANUP AND ABATEMENT ORDER (C&A)NO. 5-00-707 <br /> I reviewed the 27 December 2000 Results of CPT Investigation and Work Plan (Workplan), and the <br /> 5 January 2000 Installation of Groundwater Monitoring Wells Memorandum submitted by Environmental <br /> Audit, Incorporated(EAI). I also reviewed the 13 October 2000 Supplemental Investigation Report <br /> Problem Assessment Report and Workplan for well installation and sampling references made in the <br /> Workplan. <br /> EAI completed three cone penetrometer test (CPT)borings to 150 feet below ground surface (bgs)near <br /> San Joaquin Delta College's Robinhood Irrigation Well (RIW) in November 2000, and collected soil and <br /> depth-discrete groundwater samples. Benzene was detected in soil at 86 to 125 feet bgs in CPT-3, and <br /> TPHg and BTEX were identified in groundwater at 60 to 63 feet in CPT-2 and at 88 to 92 feet bgs in <br /> CPT-3. This work was completed to investigate the vertical extent of contamination downgradient of the <br /> former Unocal and Wards sites. <br /> Based on the results of the CPT investigation, EAI proposes to install nine monitoring wells to define the <br /> vertical extent of soil and groundwater contamination at the former Unocal site,the Wards site, and near <br /> the RIW. Three dual-completion, nested wells will be completed at the proposed locations, and screened <br /> at 85 to 90 feet, and 100 to 105 feet. The borings will be continuously cored from 85 to 105 feet to assure <br /> a minimum 5-foot silt or clay layer is present between the two screened intervals, and soil samples will be <br /> collected at five foot intervals and analyzed for TPHg,BTEX, fuel oxygenates, ethylene dibromide, <br /> 1,2-dichloroethane,methanol, and ethanol. The three additional borings will be completed as single- <br /> completion monitoring wells. The results of this added investigation will be used to complete a Final <br /> Remediation Plan. <br /> The proposed work-is necessary to investigate the vertical extent of groundwater contamination, and is <br /> approved with the following comments: <br /> • Monitoring well screen intervals must be installed based on the lithology encountered, and not <br /> arbitrarily set at the proposed intervals. <br /> California Environmental Protection Agency <br /> ea Recycled Paper <br />