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*ft/ Nnow <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> QW; Katherine Hart,Chair (a <br /> Linda S.Adams Arnold <br /> Secreta'yfor 11020 Sun Center Drive#200,Rancho Cordova,California 95670-6114 <br /> Phone(916)464-3291•FAX(916)464-4645 Schwarzenegger <br /> Environmental Protection http://www.waterboards.ca.gov/centralvalley Governor <br /> 30 June 2010 <br /> Ms. Anne Conner <br /> Pacific Gas and Electric Company <br /> 3401 Crow Canyon Road <br /> San Ramon, CA 94583 <br /> SITE INVESTIGATION AND MODELING REPORT, PG&E FRENCH CAMP GENERAL <br /> CONSTRUCTION YARD, FRENCH CAMP, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the 26 May 2010 Site Investigation and Modeling Report(Report) <br /> submitted by Stantec Consulting Corporation (Stantec) on behalf of Pacific Gas & Electric <br /> Company (PG&E) for the general construction yard at 401 East French Camp Road in French <br /> Camp (Site). <br /> PG&E has used the Site since the late 1950s as a general construction yard and purchased <br /> the property in 1991. In June 2005, PG&E performed a Phase I environmental site <br /> assessment, which found that in 1995, PG&E removed one concrete ConVault-style <br /> aboveground tank (AGT). The ConVault tank had replaced older steel AGTs and consisted of <br /> separate vessels for storing diesel and gasoline. The French Camp Fire Department oversaw <br /> the 1995 removal of the ConVault AGT. It is unknown when the steel AGTs were removed. <br /> In March 2010, PG&E drilled three soil borings adjacent to the locations of previous borings <br /> with high petroleum hydrocarbon concentrations in soil. Each boring was advanced to <br /> groundwater, and soil samples were collected and analyzed for petroleum hydrocarbons. The <br /> maximum concentrations of total petroleum hydrocarbons as diesel (TPHd) were detected in <br /> the soil samples collected from 11 feet below ground surface (bgs). Soil concentrations <br /> decreased to below laboratory detection limits in the 28-foot bgs and deeper samples. Depth <br /> to water is about 28 feet bgs. <br /> The Report also includes the results of modeling to evaluate the leaching potential of <br /> petroleum hydrocarbons in Site soil. PG&E used VLEACH to model the vertical migration of <br /> petroleum hydrocarbons in soil to groundwater. PG&E concluded that (1) the maximum <br /> concentrations in groundwater would occur within the first year of release and (2) at 10 years <br /> after release, concentrations would be below water quality objectives (WQOs). Prior to <br /> abandonment in 2008, petroleum hydrocarbons in all Site groundwater monitoring wells were <br /> below WQOs. <br /> PG&E proposes to excavate about 200 tons of contaminated soil to a depth of 11 feet bgs. It <br /> estimates about 1,000 pounds of petroleum hydrocarbons will remain in soil following the <br /> excavation. PG&E estimates that between this excavation and the one conducted in 2007, it <br /> will have removed about 86 percent of the contamination at the Site. <br /> California Environmental Protection Agency <br /> �a Recycled Paper <br />