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1 identified approximately 5.4 miles to the southeast (West Yost Associates, 2008). The Facility is located in an industrial area that is supplied by the city municipal system for domestic purposes. There are no known residential or domestic use wells within 2-miles of the Facility. Dissolved- phase petroleum hydrocarbons and MTBE do not extend more than 500 feet from the Facility and the extent is stable. Therefore,groundwater use is not a complete pathway. 5.0 Revised Cleanup Plan The following presents proposed cleanup goals for groundwater at the site, as well as the proposed approach and rationale to achieve these goals. 5.1 Cleanup Goals To develop the cleanup goals for the site, constituents of interest (COI) were compared to risk-based screening levels to identify constituents of potential concern (COPCs) and the Site Conceptual Model (Section 4.0)was reviewed to identify the potentially complete exposure pathways. Identification of COPCs. The Region 2 Water Board has published Environmental Screening Levels (ESLs) for chemicals commonly found in soil and groundwater at sites where releases of hazardous substances have occurred (Region 2 Water Board, 2007; revised May 2008). According to the Region 2 Water Board (2007), the ESLs are considered to be conservative, but provide guidance for determining whether further evaluation and/or remedial action may be needed at a facility that has experienced a release. Site data was screened against the ESLs for groundwater that is not a current of potential drinking water source(Table F-1 b of the ESL guidance document)to identify COPCs. Table 6 lists the COI in groundwater for the Facility and the maximum concentrations of each COI detected above the ESL in the past year. As can be seen in Table 6, there were no detections of TBA, DIPE, TAME, ETBE, ethanol, or methanol that exceeded ESLs; therefore, these constituents are not considered COPCs for the Facility. TPHg, TPHd, benzene, toluene, ethylbenzene, xylenes, and MTBE were present in one or more monitoring wells at concentrations that exceeded the ESLs and are considered the COPCs at the Facility. General Criteria for Low-Threat Case Closure. The Low-Threat Policy was created to streamline closure for sites that pose a minimal threat to human health or the environment (Water Board, 2012). While the policy does not specifically address ASTs, it states that"if a particular site with a different petroleum release scenario exhibits attributes similar to those which this policy addresses, the criteria for closure evaluation of these non-UST site should be similar to those in this policy". The Low-Threat Policy provides criteria to determine whether a site qualifies for consideration under low-threat closure. Facility conditions were compared to the criteria to determine whether site conditions are consistent with the policy; as identified Revised Cleanup Plan Page 16 NuStar Stockton Terminal-Stockton,California November 7,2012 1014-11