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California r ;ional Water Quality Contr-1 Board <br /> Central Valley Region <br /> Katherine Hart,Chair ` �+ <br /> Linda S.Adams 11020 Sun Center Drive#200.Rancho Cordova.California 95670-61 14 Arnold <br /> Secrelarp for Phone(916)464-3291 •FAX(916)464-4645 Schwarzenegger <br /> F_nwronmenlal htip://w,\+,A,.walerboards.ca.gov/centralvallep Governor <br /> Prolecllon <br /> 30 June 2010 nEETV(;;D <br /> Ms. Anne Conner JUL 01 2010 <br /> Pacific Gas and Electric Company ENVIRONMENT HEALTH <br /> 3401 Crow Canyon Road PERMIT/SERVICES <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 EnvironmentalProtection Agency <br /> �a Recicled Poper <br />