SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

ENVIRONMENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY Unit Supervisors .? Donna K.Heran,R.E.H.S. Carl Bergman,R.E.H.S. ' Director 304 East Weber Avenue, Third F'looC 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. C:a _ program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. FORd Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. SEP 0 5 2002 MARTY HARTZELL REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION 3443 ROUTIER ROAD STE A SACRAMENTO CA 95827-3003 RE: UNOCAL Bulk Plant 8203 W. Eleventh Street Tracy, CA In December 1989 a 5600 gallon underground storage tank (UST) was removed from this site. The UST contained transmission fluid and had previously contained heating oil. There was a cement pad beneath the UST so sidewall samples were taken at about 8 feet below surface grade (bsg). Water did not enter the excavation so a water sample was not collected. There was no detection of contaminants in the soil sample from the west sidewall of the excavation. Total petroleum hydrocarbons as diesel were detected at 17 mg/kg in the soil sample from the east side wall of the excavation. Soil beneath the piping was not sampled because the site had an operating aboveground storage tank system (AST) and the piping from the AST was located in the same area as the piping from the UST. Between October 1990 and March 1992, 10 monitoring wells were installed with screen intervals intersecting first water, which at times is at 6 feet bsg. Screen intervals for the deepest wells (U1, U2, U3) are from 7 to 27 feet bsg. Soil contamination is documented as shallow as 5 feet bsg and as deep as 17.5 feet bsg with the highest concentrations of contamination around 8 feet bsg. In December 1993 operation of the AST ended and in September 1994 all the AST was removed. According to site personnel, a release occurred from the piping between the AST tanks and loading rack sometime during 1976 and was subsequently repaired. In August 1994, 13 exploratory trenches were dug at the site. The greatest soil contamination was found in trenches 8,10 and 11 at about 8 feet bsg. Only 4 grab groundwater samples were collected with the highest concentrations of contamination in samples from trenches 1 and 2 which are in areas associated with the AST.