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Received: 11 / 9/99 11 :24AM; 916 227 4349 -> CDAA/SJDA EPU; Page 2 <br /> 'hh'�U-09-1999 10 18 MRCB/CLEAN WATER PRGMS 916 227 4349 P.02/35 <br /> NNW w./ <br /> STATEMENT OF <br /> STEPHEN J. CULLEN, Ph.D., CPSS,REA and WADE F. ALLMON, R.G., C.E.G., <br /> ARCADIS GERAGHTY AND MILLER, INC. <br /> November 3, 1999 <br /> SUBJECT: PETITION OF UNOCAL CORPORATION FOR REVIEW OF DENIAL OF PETROLEUM <br /> UNDERGROUND STORAGE TANK SITE CLOSURE AT 1665 PACIFIC AVENUE, <br /> STOCKTON, CALIFORNIA <br /> We have read the discussion pertaiaiug to the subject matter submitted to the State Water Resources <br /> Control Board(SWRCB)and concur with the summary and conclusions of the SWRCB stag. Our opinion <br /> is based on the results and findings of site characterization field work file reviews,and analyses conducted <br /> by ARCADIS Geraghty and Miller. Inc., on behalf of UNOCAL,between August, 1998 and March, 1999, <br /> regarding the former service station number 2859, located at 1665 Pacific Avenue, Stockton`, California. <br /> Additionally,We have examined and analyzed the historical record of data and events regarding the Site and <br /> offer the following summary of our findings: <br /> PRIMARY SOURCES OF PETROLEUM HYDROCARBONS HAVE BEEN REMOVED <br /> • The primary petroleum hydrocarbon sources (USTs, dispensers, and piping), relating.to the <br /> dispensing of gasoline products at the Site,have been removed. <br /> • The amount of excavated impacted soil removed at the Site is in question. However, previous <br /> consultants report having excavated impacted soil to a depth of approximately 30 feet in the <br /> area of the 1988 lank excavation. <br /> • Approximately 2,745 pounds (over 400 gallons) of TPHg and 12 pounds (1.6 gallons) of <br /> benzene have been removed by an Soil Vapor Extraction(SVE)pilot study at the Site. <br /> BACKGROUND WATER QUALITY IN THE SITE VICINITY IS POOR <br /> • General water quality in the vicinity of the Site is poor and does not meet Califf rnia State <br /> standards(MCLS)ofthe Basin Plan for nitrates and total dissolved solids in drinking vwater. <br /> • The waxer sample in NP-1, $5 to 90 feet below ground surface (bgs), is of clearly different <br /> quality (as indicated by differences in bicarbonate allmluuty. chloride, pH, and total dissolved <br /> solids) than that from water samples collected at shallower depths_ It appears that the water <br /> sampled in NP-1 may represent the influence of an intruding salt water front documented in the <br /> 1997 San Joaquin County Flood Control&Water Conservation Report- <br /> THE PETROLEUM HYDROCARBON PLUME IS OF LIMITED EXTENT <br /> • The Site release has resulted is a dissolved petroleum hydrocarbon groundwater plume of <br /> limited extent. Free-phase petroleum hydrocarbons have not been detected at the Site. Methyl <br /> tertiary bury!ether(MTBE)was confirmed to be at non-detect levels in water samples collected <br /> Poo: <br />