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53o kvz 0033 <br /> California Re6ional `Vater Quality Control Board4. <br /> Central Valley Rection J <br /> ` <br /> Steven T.Butler, Chair Grav avl Davis <br /> Winston H. Hickox <br /> Secren7,7 for Sacramento blain Office Governor <br /> En,ironn:enra[ Internet Address: hup:,/N wrvswrcb.Ca.eov/—nvgcb5 <br /> Protac:ion �? 3443 Routier Road,Suite A,Sacramento.California 96S27-1003 <br /> Phone(916)2n-1000•FA.'{(9l6)256--3016 <br /> , <br /> TO: Gordon L. BoQgs FROM: Marty Hartzell <br /> UST Proa-ram Manager Associate Engineering Geologist <br /> V � tv � f �i <br /> DATE: 17 July 2000 i SIGNATURE: Y / - <br /> SUBJECT: NONCONCURRENCE WITH SAN JOAQUIN COUNTY'S NO FURTHER <br /> ACTION REQUIRED DETERMINATION, REGAL#60-3, 6425 PACIFIC AVENUE <br /> STOCKTON, SAN JOAQU7N COUNTY <br /> I reviewed San Joaquin County's (County) 6 June 2000 Case Closure Summary and the following <br /> docn_ments in response to a No Further Action Required (NFAR) request for the subject site: <br /> • The 18 January 1999 Update Status Report #55, January 1999 Quarterly Groundwater Report <br /> prepared by Western Geo-Engineers (WEGE); <br /> • The 5 February 1999 Request for Closure (Closure) prepared by Blakely Environmental <br /> Investigations (Blakely); <br /> • The 21 March 2000 Gasoline Dispensing System Removal Documentation Sampling Report <br /> prepared by WEGE; and <br /> • The 6 April 2000 Over-excavation of Gasoline Contaminated Soils Associated with the <br /> Dispensing System prepared by WEGE. <br /> My review shows: <br /> 1. The off-site TPHg plume has not been laterally or vertically defined; <br /> 2. The concentrations of TPHg in off-site monitoring well MW-12 are increasing, while TPHg in <br /> on-site wells are decreasing; <br /> 3. The status of a domestic water supply well southeast of the site has not been determined; <br /> 4. The groundwater has not been monitored for all fuel oxygenates and fuel additives; and <br /> 5. The quarterly groundwater monitoring has not been conducted since January 1999. <br /> Background <br /> The Regal#603 service station(Regal) operated until December 1988 when three 10,000-gallon gasoline <br /> underground storage tanks (USTs) were removed and replaced. The new USTs were operated by Exxon <br /> from December 1988 to July 1998. Soil contamination was identified in the tank pits during UST <br /> replacement, and a soil and groundwater investigation was completed. Figure 1 presents a site map from <br /> WEGE's January 1999 quarterly monitoring report. <br /> On-site Investigation <br /> Multiple soil borings were completed on-site, and contaminated soils were identified from 25 feet to a <br /> total depth of 65 feet. At the time of the initial investigation in 1988 and 1989, the depth to water ranged <br /> from 50 to 60 feet. The current depth to water is approximately 33 feet. The highest soil contamination <br /> California Environmental Protection Agency <br />