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O Ll Ll ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY s.• _,�� .oG Unit Supervisors 2. ' ? Donna K.Heran,R.E.H.S. Carl Borgman,R.E.H.S. 304 East Weber Avenue, Third Floor Director Mike Huggins,R.E.H.S.,R.D.I. Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. �q• a�P . Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. �t FR OLaurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. ROBERT J COCHRAN (1 �� AUG 1 1 2004 CHEVRON ENVIR MGMT COMPANY AUG 12 2004 PO BOX 6004 SAN RAMON CA 94583-0904 By .................... RE: Chevron Bulk Terminal #1001621- UST Site Code: RO#1471 22888 S. Kasson Rd. Banta, CA. San Joaquin County Environmental Health Department (EHD) has reviewed UST Site Assessment Report dated July 16, 2004 as submitted by Secor International on July 19, 2004 and has the following comments. On May 21,_2003 EHD notified Chevron that corrective action was required to investigate the unauthorized release noted after the "transmix" UST removal on March 5, 2003. On August 28, 2003 EHD approved a work plan to meet the requirements and four soil borings were installed in September 2003. Laboratory analyses for the soil samples collected from the four borings indicated low levels of petroleum were detected in about half of the samples. Ground water samples collected from the two soil borings and two monitoring well installations indicated that elevated concentrations of total petroleum hydrocarbons as diesel and gasoline (TPH-d and TPH-g) as well as BTEX, MtBE, TBA, TAME, and 1,2-DCA, have impacted the area in and around the former'transmix' UST. Monitoring well, MW-68A, was installed in the former UST pit and the water sample from it, "MW-68A-W", showed 4,400 ug/I of TPN-d. Monitoring well MW-67UA was installed 50 feet northeast and down gradient from the UST pit and the ground water sample from it, "MW-67UA-W", showed TPH-d at 4,900'*bg/I. Soil boring USB-2 was installed --160 feet north/northeast of the former UST pit and the ground water grab sample from it indicated 2,100,000 ug/I of TPH-d. The increasing TPH-d concentrations in the ground water samples, as the sampling points get further away from the UST, does not appear to fit the typical pattern of plume migration from an UST. Without additional proof, EHD cannot consider the very high TPH-d in USB-2 as part of the plume emanating from the former UST release. With above ground storage tanks (AST) piping in this area, EHD does not consider this area as part of the UST investigation. The Central Valley Region Water Quality Control Board (CVRWQCB) may require further investigation of this area and Chevron should not include this area in UST work plans.