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California "egional Water Quality Coll Board N <br /> Central Valley Region ° <br /> Katherine Hart, Chair <br /> 11020 Sun Center Drive,#200.Rancho Cordova,California 95670-6114 <br /> Matthew-Rodriquez (916)464-3Edmund G.Brown Jr. <br /> Secretaryfor http://v<mW.wa r a v c a Governor <br /> Environmental Protection <br /> SEP 14 2011 <br /> 13 September 2011 ENVIRONMEN AL HEALTH <br /> PERMIT/SERVICES <br /> Ms. Shelby Lathrop <br /> ConocoPhillips Company <br /> 76 Broadway <br /> Sacramento, CA 95818 <br /> HUMAN HEALTH RISK ASSESSMENT, FORMER TOSCO BULK TERMINAL #10013, <br /> 3505 NAVY DRIVE, STOCKTON, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board — Central Valley Region (Central Valley Water <br /> Board) staff reviewed the following documents: <br /> • 29 July 2011 Second Quarter 2011 Site Status Summary Report (QMR) <br /> • 9 August 2011 Human Health Risk Assessment (HHRA) <br /> ATC Associates submitted the reports on behalf of ConocoPhillips for the former Tosco bulk <br /> fuel terminal at 3505 Navy Drive in Stockton (Site). ConocoPhillips conducts groundwater <br /> monitoring at the Site in accordance with Monitoring and Reporting Program (MRP) <br /> No. R5-2004-0824. In 2005, Valero (currently named as NuStar Energy) purchased the Site <br /> and is the current Site operator. Since 1998, the Site has been used solely to store diesel <br /> fuel. <br /> On 11 May 2011, ConocoPhillips conducted the second quarter 2011 monitoring event and <br /> the results are summarized in the QMR. Depth to water ranged from about two feet below <br /> ground surface (bgs) to about 13 feet bgs and flow was to the southwest. Total petroleum <br /> hydrocarbons as diesel (TPHd) was detected in all monitoring wells sampled at a maximum <br /> concentration of 360 micrograms per liter (Ng/L). TPH as gasoline (TPHg), benzene, toluene, <br /> ethylbenzene, xylenes (collectively BTEX), and methyl tert butyl ether (MTBE) were not <br /> detected above the water quality objectives (WQOs) in any of the monitoring wells. <br /> In July 2011, ConocoPhillips drilled three soil borings and installed temporary soil gas <br /> sampling points to evaluate the potential for vapor intrusion. ConocoPhillips collected soil gas <br /> samples at two locations. Soil gas sample SG-2 contained benzene at 40 micrograms per <br /> meter cubic meter (pig/m), which exceeds the California Human Health Screening Level <br /> (CHHSL) of 36 pg/m . All other contaminants from both soil gas sample locations were below <br /> either the CHHSLs or the California Regional Water Quality Control Board — San Francisco <br /> Bay Region Environmental Screening Levels (ESLs). <br /> The HHRA includes an evaluation of the potential exposure pathways and the potential risks <br /> to human health and the environment. The Site is covered by asphalt and although historic <br /> soil concentrations exceed the ESLs for direct exposure, ConocoPhillips concludes the asphalt <br /> California Environmental Protection Agency <br /> cli Recycled Paper <br />