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r <br /> California twegional Water Quality Controva3oard <br /> Central Valley Region <br /> Katherine Hart,Chair <br /> Linda S.Adams Arnold <br /> 11020 Sun Center Drive#200,Rancho Cordova,California 956'70114 <br /> Secretary for Phone(916)464-329) •FAX(916)464-4645 SchwarneneWr <br /> Environmental Protection htrp!//www.waterhoards.ca.gov/centralvalIey Governor <br /> To: Antonia K-J. Vorster, P.E. FROM: Kristi Shelton, P.E. <br /> Site and Groundwater Cleanup Water Resources Control Engineer <br /> Program Manager Aboveground Tanks Cleanup Unit <br /> SIGNATURE: <br /> Wendy Cohen, P.E. <br /> Chief, <br /> Aboveground Tanks Unit <br /> DATE: 30 July 2010 SIGNATURE: vvy��w Ud�I��V <br /> SUBJECT: RATIONALE FOR CONSIDERING NO FURTHER ACTION REQUIRED FOR <br /> CHEVRON CORRAL HOLLOW AND GRANT LINE ROADS, TRACY, SAN <br /> JOAQUIN COUNTY <br /> Rationale: The remaining concentrations of petroleum hydrocarbons in groundwater in samples <br /> from the five Site monitoring wells are either stable or below laboratory detection limits. Although <br /> there is not a declining trend in two wells, the remaining concentrations underlie Grant Line Road, <br /> and it is highly unlikely that a water supply well would be installed in this location. <br /> Issues: Chevron has conducted groundwater monitoring at the Site since 1991. Groundwater flow <br /> is to the east, and depth to water is about eight feet below ground surface (bgs). Chevron has <br /> historically detected total petroleum hydrocarbons as gasoline (TPHg), TPH as diesel (TPHd), and <br /> benzene above the water quality objectives (WQOs). During the second quarter 2010 sampling <br /> event, the highest concentrations of TPHg, TPHd, and benzene were 1,600 micrograms per liter <br /> (pg/L), 2,500 pg/L, and 2 pg/L, respectively. Wells MW-6 and MW-12 have consistently had <br /> detections of petroleum hydrocarbons above the WQOs. Naphthalene was tested in the monitoring <br /> wells since 2000 and found primarily in MW-6. The last sample in May 2010 contained 73 pg/L. This <br /> is below the USEPA IRIS reference dose of 140 fig/L and the USEPA health advisory of 100 pg/L, <br /> but exceeds the California Department of Health Services Notification Level of 17 Ng/L. <br /> Chevron submitted a closure request in 2009, and Central Valley Water Board staff responded that <br /> we could not consider unrestricted closure until Chevron shows the groundwater concentrations <br /> will reach WQOs within a reasonable timeframe and soil concentrations are below gross <br /> contamination levels. In July 2010, the City of Tracy requested that Chevron destroy the remaining <br /> monitoring wells to facilitate a street widening project. The current well locations would be in the <br /> middle of Grant Line Road or within a new sidewalk along the road. Thus, Chevron is scheduled <br /> to destroy the wells during August 2010. Board staff agreed to re-evaluate the Site prior to <br /> requiring Chevron to install replacement monitoring wells. <br /> Setting: Chevron operates an underground refined fuel pipeline at the Site that runs underneath <br /> Grant Line Road_ The Site is at the intersection of Corral Hollow and Grant Line Roads and is <br /> surrounded by mixed residential and commercial development. In 1987, about 870 gallons of <br /> refined fuel were released when the pipeline was ruptured during installation of dewatering wells <br /> California Environmental Protection Agency <br /> C4 Recycled Paper <br />