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t California ^ m.gional Water Quality CVrol Board - ` ,, <br /> Central Valley Region ; °� <br /> w <br /> Kathrine Hart, Chair "`��°� <br /> Linda S.Adams Edmund G.Brown Jr. <br /> Acting Secretary for 11020 Sun Center Drive#200, Rancho Cordova, California 95670-6114 Governor <br /> Environmental Phone(916)464-3291• FAX(916)464-4645 <br /> Protection http://www.waterboards.ca.gov/centralvalley <br /> RECEIVE® <br /> Ms. Shelby Lathrop <br /> JAN 2 0 ZQ.1� January 2011 <br /> ConocoPhillips Company <br /> ENVIRONMENTAL HEALTH <br /> 76 Broadway <br /> PERMIT/SERVICES <br /> Sacramento, CA 95818 <br /> WORK PLAN FOR HUMAN HEALTH RISK ASSESSMENT, FORMER TOSCO BULK <br /> TERMINAL #10013, 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 22 December 2010 Work Plan for Human Health Risk Assessment <br /> (HHRA Work Plan) submitted on behalf of the ConocoPhillips Company (ConocoPhillips) by <br /> Stantec Consulting Corporation (Stantec) for the former Tosco bulk fuel terminal at 3505 Navy <br /> Drive in Stockton (Site). ConocoPhillips conducts groundwater monitoring at the Site pursuant <br /> to Monitoring and Reporting Program No. R5-2004-0824. NuStar Energy (NuStar) currently <br /> owns and operates the terminal. <br /> The HHRA Work Plan was submitted pursuant to ConocoPhillips' proposal to discontinue <br /> oxygen injections at the end of the fourth quarter of 2010 and perform risk-based modeling to <br /> determine appropriate site-specific remedial objectives/cleanup goals. During August and <br /> September 2010 meetings and September 2010 conference calls, landowners affected by the <br /> discharge indicated concurrence with the Central Valley Water Board staff's strategy to evaluate <br /> risk-based closure of the Site. <br /> ConocoPhillips proposes that the HHRA determine potential risks to human health and the <br /> environment caused by pollutants emanating from the Site. Also, as requested by Central <br /> Valley Water Board staff, the HHRA Work Plan also presents a statistical methodology to <br /> calculate baseline and compliance concentrations for tertiary butyl alcohol (TBA). The HHRA <br /> Work Plan proposes to estimate the potential human health and ecological risk from exposure <br /> to chemicals of concern (COCs) and derive risk-based cleanup levels that are protective of <br /> commercial/industrial site use as well as potential future residential use. <br /> The HHRA Work Plan proposes to conduct the HHRA in a tiered approach where maximum <br /> concentrations of the detected analytes are compared to screening levels to determine whether <br /> further evaluation is warranted in Tier 1. A site conceptual model (SCM) will be prepared to <br /> examine exposure pathways. Nustar anticipates that the SCM may show that since there are no <br /> current or anticipated potable uses of groundwater at the Site and it does not discharge to an <br /> aquatic environment, further quantitative evaluation as an exposure pathway may not be <br /> warranted. When a screening level is exceeded in the Tier 1 HHRA and a potentially complete <br /> exposure pathway exists, a Tier 2 HHRA will be conducted using simple fate and transport <br /> models with site-specific or empirical data, exposure factors, and toxicity values. <br /> California Environmental Protection Agency <br /> (Ci'Recycled Paper <br />