SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Ms. Shelby Lathrop - 2 - 30 July 2010 Former Tosco Bulk Terminal No. 1 uU13 the site-specific risk-based cleanup goals for groundwater that will be determined through proposed risk modeling. Our comments are presented below. 1. Conceptually, Central Valley Water Board staff believes the plan presented in the RAP Addendum merits consideration. However, the Site is owned by Nustar, not ConocoPhillips, and the pollutant plume flows to the west and south of the Site onto property owned by the Port of Stockton. The Port of Stockton and NuStar are copied this letter, and their opinions will be solicited to determine if they are amenable to the cleanup strategy proposed by ConocoPhillips and incorporating revisions by Water Board staff. 2. The main COC at this site is TBA. The vertical extent of the TBA plume is defined by the concentrations in 70-foot well, MW-19C. The lateral extent is defined to the north, east, and south by MW-4, MW-3, and MW-20, respectively. The TBA plume is not defined to the west. The asymptotic concentrations of TSA and other COCs suggest that the groundwater cleanup may have reached the limits of technical feasibility. The Fourth Edition of the Water Quality Control Plan for the Sacramento River and San Joaquin River Basins (Basin Plan) on page IV-19.00, Section 9g addresses groundwater cleanup levels. This section states that cleanup levels shall be based on (1) background concentrations, (2) applicable water quality objectives (WQOs), (3) concentrations that do not pose a significant risk to human health or the environment and (4) the technologic and economic feasibility of attaining background concentrations and of attaining concentrations lower than defined by (2) and (3). Therefore, in accordance with the Basin Plan and with the concurrence of the landowners, Central Valley Water Board staff is willing to concur with ConocoPhillips' proposal to conduct risk based modeling to determine the appropriate site specific cleanup levels, as long as the CDCs are sufficiently stable after the termination of oxygen injections at the end of 2010. 3. The Basin Plan designates all groundwater in the region as a potentially suitable resource for municipal/domestic (MUN), agricultural (AGR), and industrial supply (IND/PRO) beneficial uses (BU). State Water Board Resolution No. 88-63 includes exceptions to the MUN BU designation, including (1) groundwater that contains TDS in excess of 3,000 mg/L, (2) aquifers that yield less than 200 gallons per day, and (3) groundwater that cannot reasonably be treated for domestic use by best economically achievable treatment practices. However, these exceptions may only be implemented through a Basin Plan amendment to de-designate the MUN BU from a particular groundwater basin. 4. It is not clear how COC or the so-called "drinking water quality constituent" data obtained from MW-10 and MW-6 would be applicable to the proposed cleanup strategy. Our review of Geotracker shows that groundwater monitoring data for these wells dating back to the early 1990s has consistently been non-detect (ND) for CDCs, including TBA. If these data were representative of Site conditions, then a risk assessment would not be necessary. In addition, the parameters listed on Page 2 of the RAP Addendum are not applicable for determining the MUN BU of an aquifer. Therefore, monitoring for these drinking water quality constituents in these two or any other Site wells is unnecessary. The highest concentrations of COCs are present in MW-2, MW-11, MW-16, MW1713, MW18C, MW-20 and MW-21 B. During the first quarter of 2010, TBA concentrations in these