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i 15135 Eight Mile Road -6- 1 October 2018 Stockton, San Joaquin County Soil Gas —Soil gas sampling has not been conducted at the Site. RISK EVALUATION In 2014, the Central Valley Water Board recommended that its staff consider the LTCP when evaluating non-UST petroleum releases. The UST unauthorized release case at the Site was closed in 2001 when the current investigation into the AST release began; however, Central Valley Water Board staff has evaluated the applicability of the LTCP for this AST release and found the Site exhibits similar attributes to those which the LTCP addresses. Therefore, it is appropriate to use the criteria in the LTCP to evaluate this Site for closure. The LTCP states that: "While the Policy does not specifically address other petroleum release scenarios such as pipelines or above ground storage tanks, if a site with a different petroleum release scenario exhibits attributes similar to those which the Policy addresses, the criteria for closure evaluation of these non-UST sites should be similar to those in this policy." As shown in Table 4, petroleum constituents remain above Water Quality Objectives (WQOs) in a limited number of Site groundwater monitoring wells. TPHg is present in four shallow groundwater monitoring wells (MW-2 through MW-4 and EW-1)with a corresponding plume length of approximately 150 feet. As part of their No Further Action request, AGE concluded that TPHg will meet WQOs within 16 years. Detections of TPHd are limited to one shallow groundwater monitoring well (MW-2), with a corresponding plume length likely less than 100 feet. AGE concluded that TPHd is expected to achieve WQOs within approximately 4 years at this monitoring location. MTBE and benzene are each detected in one well (MW-2 and MW-3, respectively) above their respective WQOs. Given these limited detections, it is likely that the associated plumes are less than 100 feet in length and will reach their respective WQOs within a reasonable timeframe. TBA is present above WQOs in three shallow groundwater monitoring wells (MW-2, MW-3, and EW-1)with a corresponding plume length likely less than 150 feet. AGE concluded that this constituent is expected to achieve WQOs within approximately 1.6 years. Since May 2015, AGE has not detected petroleum constituents in the groundwater samples collected from deeper groundwater monitoring wells as shown in Table 4. The Site meets all but one characteristic of LTCP Groundwater-Specific Criterion (2). The maximum length of the TPHd, TPHg, benzene, MTBE, and TBA plumes that exceed WQOs are only about 150 feet in length. AGE has not observed free product since 2010 and AGE detected less than 3,000 micrograms per liter(Ng/L) of benzene groundwater during the last sampling event in May 2015, as shown in Table 4. The Site fails condition (c) of LTCP Groundwater-Specific Criterion (2) since an un-named drainage ditch is about 60 feet downgradient from the defined plume boundary and the Little Potato Slough is about 130 feet upgradient of the defined plume boundary. With the exception of one detection in 2008, AGE last detected petroleum in the un-named drainage ditch in March 2004 and the Little Potato Slough is elevated behind a levee with the water surface above grade of the petroleum plume in groundwater; therefore, Central Valley Water Board staff concludes that these surface waterbodies are not threatened by the release from the Site. Additionally, concentrations of petroleum in groundwater are expected to meet respective WQOs within 16 years. Therefore, staff concludes that the Site meets LTCP Groundwater-Specific Criterion (5). The maximum petroleum concentrations detected in shallow soil historically (2002/2003) and more recently (2016) are listed in Table 1. AGE states in their 5 June 2017 Closure Summary Report the