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Case File - 3 - 6 July 2012 (amended 25 April 2014) <br /> Former Tosco Bulk Terminal, <br /> 3505 Navy Drive, Stockton, San Joaquin County <br /> SENSITIVE RECEPTORS <br /> No municipal or domestic wells are located within 500 feet of the Site. Several domestic or <br /> irrigation wells are between 0.75 and 1.75 miles upgradient of the Site across the Stockton <br /> Deep Water Channel. There are no water supply wells within two miles downgradient of the <br /> Site. <br /> PUBLIC PARTICIPATION <br /> On 23 October 2012, notifications were sent to the property owners within 200 feet of the <br /> release to provide within 30 days any comments or concerns they may have regarding the <br /> closure of the site. To date, we have not received a response from the property owners. <br /> HUMAN HEALTH RISK ASSESSMENT <br /> In 2011, ConocoPhillips conducted a HHRA to evaluate the risks associated with the remaining <br /> petroleum hydrocarbons in soil and groundwater at the Site. The Site is covered by asphalt and <br /> although historic soil concentrations exceed the ESLs for direct exposure, ConocoPhillips <br /> concludes the asphalt would need to be removed for the pathway to be complete. Based on the <br /> current Site use as a bulk fuel distribution facility, the asphalt will likely remain in place until its <br /> use changes. <br /> Surrounding properties are supplied water by the municipality and the risk of ingestion of <br /> contaminated groundwater, therefore, is low. ConocoPhillips also conducted a Tier 2 risk <br /> assessment for soil vapors to evaluate the potential for vapor intrusion. Table 3 presents the <br /> soil vapor concentrations. ConocoPhillips concluded that there was no vapor intrusion risk to <br /> the residential scenario. In addition, ConocoPhillips estimates that the Site groundwater will <br /> reach water quality objectives (WQOs) within 1 to 14 years. <br /> SUMMARY <br /> In 1987, during replacement of a vapor knock out tank ConocoPhillips noted hydrocarbon sheen <br /> in the excavation. Between 1989 and 2003, ConocoPhillips installed 89 soil borings and <br /> collected soil samples. Soil samples near the ALTs contained concentrations above the ESLs. <br /> ConocoPhillips conducted a Tier 2 risk assessment for soil vapors and concluded there was no <br /> vapor intrusion risk for residential receptors. This area is covered with asphalt and <br /> ConocoPhillips concludes that the soil and vapor intrusion pathways are not complete. <br /> Between 1987 and 2003, ConocoPhillips installed 19 monitoring wells and conducted quarterly <br /> groundwater monitoring. A GWETS operated at the site from 2003 and 2006 and removed <br /> about 25 pounds of petroleum hydrocarbons. ConocoPhillips also operated an oxygen injection <br /> system at the site from 2007 until December 2010. The maximum concentrations of TPHg, <br /> TPHd, and MTBE in March 2012 were 110 pg/L, 790 pg/L, and 11 pg/L, respectively. <br /> ConocoPhillips concludes that the remaining mass of TPHd, TPHg, and MTBE in groundwater <br /> is about 1.57 pounds, 0.12 pound, and 0.05 pound, respectively; and groundwater <br /> concentrations will reach WQOs within 1 to 14 years. <br /> Soil concentrations exceeding the ESL are within the tank farm, which is covered with asphalt <br /> and should remain covered with asphalt so long as the Site is used for bulk fuel distribution. <br /> There are no water supply wells within two miles downgradient of the Site and the Site drinking <br />