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Stantec <br /> Addendum Work Plan for Human Health Risk Assessment <br /> Former Tosco Bulk Terminal #10013 <br /> February 14, 2011 <br /> transferred ownership to ST Services in October 1998. Valero(currently named as NuStar Energy) <br /> acquired the site in 2005, and is the current site operator. Since 1998, the facility has been used <br /> only for diesel storage. <br /> Historical site operations have resulted in petroleum hydrocarbon impact to the soil and groundwater <br /> beneath the site. Constituents of concern for the site include: total petroleum hydrocarbons as <br /> gasoline (TPH-g) and diesel (TPH-d); benzene, toluene, ethylbenzene, and total xylenes (BTEX); <br /> methyl tertiary butyl ether (MTBE); tert butyl alcohol (TBA) and other oxygenates. The facility <br /> currently includes six aboveground storage tanks (ASTs), two underground storage tanks (USTs) <br /> (UST Nos. 4 and 6), a fuel-loading rack in the central portion of the site, two metal buildings in the <br /> southeastern portion of the site and a small enclosure that formerly contained a groundwater <br /> extraction and treatment system(GWETS)connected to wells MW-8 and MW-14.The GWETS and <br /> associated piping were installed in June and July of 2003. <br /> Groundwater extraction was terminated on July 31, 2006; the rental portions of the GWETS were <br /> dismantled in August 2006. Mobile oxygen injections were started in December 2007 and <br /> performed intermittently through December 2010. The locations of above- and below-grade <br /> structures and equipment at the site are shown in Figure 2. <br /> ADDENDUM SCOPE OF WORK/RESPONSE TO RWQCB COMMENTS <br /> COMMENT 1: "We concur with ConocoPhillips'proposal to prepare an HHRA. However, we do not <br /> concur with ConocoPhillips'assessment that an evaluation of the risk presented by groundwater is <br /> not warranted since there is no current or anticipated potable use. ... potential indoor and outdoor <br /> and outdoor exposure pathways for groundwater that merit evaluation include ingestion, dermal <br /> contact and inhalation of volatiles." <br /> RESPONSE:Although the groundwater beneath the site is not currently used as a drinking water <br /> source, Stantec recognizes the potential for industrial activities to occur in the site vicinity that <br /> according to the Water Quality Control Plan for the Sacramento River and San Joaquin River Basins <br /> allows for the use of groundwater in industrial process and service supply applications. As a result, <br /> Stantec will consider the ingestion, dermal contact, and inhalation of volatiles from groundwater <br /> exposure pathways due to groundwater use, as well as potential exposures to volatiles from <br /> groundwater via soil vapor transport to indoor air, within the proposed HHRA. <br /> COMMENT 2: "The HHRA Work Plan contains no discussion about evaluating data from soil or soil <br /> gas." <br /> RESPONSE: Stantec intends to evaluate soil and soil gas data to assess the migration of volatile <br /> chemicals from soil to indoor air and the risk to construction workers. Due to the lack of soil gas <br /> data generated at the site to date Stantec proposes to collect shallow soil gas samples at two on- <br /> site and one off-site locations to assist in the desired risk evaluations. A detailed description of the <br /> proposed scope of work is summarized below. <br /> 2 <br />