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Califorro Regional Water Quality C@trol Board , Central Valley Region Katherine Hart, Chair 1 1020 Sun Center Drive tl200.Rancho Cordova,California 95670-6114 Matthew Rodriquez Phone(916)464-3291 •FAX(916)464-4645 Edmund G.Brown Jr. Secretur. for http://www.waterboards.ca.gov/centralvalle) Governor Environmental Protection TO: File: Buffalo Tank FROM: Jim Barton 5709 East Fremont Street Engineering Geologist (AKA State Highway 26 East) UST Unit 2 Stockton, San Joaquin Co. DATE: 22 November 2011 SIGNATURE: / SUBJECT: UST CASE CLOSURE, BUFFALO TANK, 5709 EAST FREMONT STREET (AKA STATE HIGHWAY 26 EAST), STOCKTON, SAN JOAQUIN COUNTY, CASE NO. 390791 Site Background: Buffalo Tank (Site) was a former underground storage tank manufacturing facility, which currently operates as a garden nursery, rock, soil, and yard accessory retail facility (Figure 1). In November 1989, one 1,000-gallon and one 2,000-gallon gasoline Underground Storage Tanks (USTs) were removed from the Site. Analytical results of confirmation soil samples collected beneath the southern 1,000-gallon gasoline UST reported maximum petroleum hydrocarbon contaminant concentrations as Toluene, 0.035 mg/kg. Subsequent soil investigations were conducted in March 2003 and April 2005. Maximum confirmation soil sam le results in milligrams per kilo ram m /k are listed in Table 1: Date TPHg TPHd T E X IPB n-PB TMB 124TMB p-IPT Naph 3/03 11,000 NA 3.1 11 600 NA NA NA NA NA NA 4/05 140 3,600 6.2 5.5 81 2.2 5.9 18 45 1.1 7.1 TPHg=Total Petroleum Hydrocarbons as gasoline TPHd=Total Petroleum Hydrocarbons as diesel T=toluene E=ethylbenzene X=xylenes IPB= isopropylbenzene n-PB=n-propylbenzene TMB=trimethylbenzene 124TMB= 1,2,4-trimethylbenzene p-IPT=p-Isopropyltoluene Naph= Naphthalene NA=not analyzed Maximum grab groundwater sample results in micrograms per Liter (ug/L) for April 2005 are listed in Table 2. Date TPHg TPHd T E X IPB n-PB124TMB 135T 180 FP IPB Naph 4/05 3,900 48,000 350 250 1,470 51 100 200 180 17 180 135TMB= 1,3,5-trimethylbenzene Three groundwater monitoring wells were installed in April 2005. Between April 2005 and December 2006, six groundwater monitoring events were conducted. In April 2005, 1 ,2-dicholoroethane (1,2-DCA, 4.9 ug/L) and xylenes (24 ug/L) were detected in groundwater. By August 2005, only 1,2-DCA (2.3 ug/L) was detected in groundwater. No petroleum hydrocarbons were detected above the method detection limits after August 2005. Groundwater monitoring ceased with regulatory approval in December 2006. California Environmental Protection Agency 'a Recycles(Paper