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Page 8 September 11,2023 Brusca File No. 260-004 Anderson Barngrover Ranch LTCP EVALUATION We have updated the LTCP evaluation for the former diesel UST based on additional data obtained from this investigation. The updated evaluation is presented below in the general format as outlined in the referenced policy. LOW-THREAT UNDERGROUND STORAGE TANK CASE CLOSURE CRITERIA General Criteria a. The unauthorized release is located within the service area of a public water system: The subject site is not located within an area where public water is provided. Onsite water is provided by two supply wells; the main water supply well is situated to the south of the farm facility and an irrigation well is situated to the north of the facility. Groundwater data from the recent Boring TH9 indicate that notable diesel impact to shallow groundwater extends southerly to the area of the main water supply well. However, March 2023 sampling and testing of the main water supply well did not reveal petroleum hydrocarbon contaminants at concentrations above the laboratory reporting limits; these results indicate that the deeper water supplied by this well (screened from a depth of 328 feet to 475 feet) is not affected by the shallow release. Nonetheless, in light of the recent data from Boring TH9, in our opinion it would be prudent to resample the main water supply well for analysis for petroleum hydrocarbons and VOCs to confirm the lack of deeper water impact. The water sample collected in May 2023 from the irrigation water well situated to the north of the former UST contained a very low concentration of TPH as diesel which is below the ESL (MCL Priority) value. b. The unauthorized release consists only of petroleum: The former UST at the site was used for storage of diesel. Soil and groundwater analytical data from the area of the former underground tank indicate that the on-site release consists of petroleum hydrocarbons and related VOCs. C. The unauthorized " rimary'; release from the UST has been stopped.• The UST was removed in November 2022; as such, the primary release has been stopped. d. Free product has been removed to the maximum extent practicable: No free product has been identified during the UST removal activities or during the subsequent site investigations. e. A conceptual site model that assesses the nature, extent, and mobility of the release has been developed.• Data obtained during the UST removal work and subsequent investigation generally establish a conceptual site model that characterizes the nature of soil and groundwater impact attributable to the former UST. The data from peripheral borings TH6, TH4, TH9, and TH 10 generally constrain the extent of soil impacts. The