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Page 9 September 11,2023 Brusca File No. 260-004 Anderson Barngrover Ranch lateral extent of fuel-related VOCs in groundwater are defined by non-detect results to the north, east, and south, and by extrapolation of concentrations to the west. As shown on Plate 7, the extent of the diesel groundwater plume is generally defined to the north, west, and east(by non-detect results and extrapolation). However,the southerly extent of diesel groundwater plume is yet defined. f. Secondary source has been removed to the extent practicable: It has not yet been determined that secondary source removal at the subject property is necessary, and no such work has been completed. Given the proximity of buildings to the area of the former UST, removal/excavation of a substantial amount of secondary source materials (i.e., impacted soils) could be difficult and somewhat impractical. g. Soil or groundwater has been tested for methyl tent-butyl ether (MTBE) and results reported in accordance with Health and Safety Code section 25296.1 S: Soil and groundwater samples from the area of the former diesel UST have been tested for MTBE. None of the tested soil or groundwater samples contained MTBE at concentrations above the laboratory reporting limits, except that the groundwater samples from Borings TH5 and TH 10 contained very low MTBE concentrations(1.2 ug/L and 1.7 ug/L, respectively) that are below the drinking water standard of 5.0 ug/L. h. Nuisance as defined by Water Code section 13050 does not exist at the site: The cited Water Code defines "nuisance" as conditions that are injurious to health, are offensive to the senses, affects the community, or occurs as a result of waste disposal. The subsurface diesel impacts are not considered a"nuisance"per the cited code definition. Media-Specific Criteria 1. Groundwater The referenced State Water Resources Control Board's LTCP presents characteristics for five different groundwater site classes; the characteristics of at least one site class must be met for site closure. Classes 1 through 4 of the LTCP guidelines are based in part on the length of the groundwater plume, which is yet undefined to the south. Additionally, the proximity of the onsite water wells precludes conformance to the criteria of groundwater Classes 1 through 4 of the LTCP. However, it is possible that the site could meet the criteria for Class 5; Class 5 of the groundwater-specific criteria applies to cases where the regulatory agency determines that, based on an analysis of site-specific conditions, the contaminant plume poses a low threat to human health and safety and to the environment. Testing of the main water supply well in March 2023 did not identify contaminants at concentrations above the laboratory reporting limits, and the very low concentration of TPH as diesel detected in the northerly irrigation well in May 2023 is below the referenced ESL value(MCL Priority). As indicated earlier in this report,as a part of UST case closure it would be prudent to resample the main water supply well at the site to confirm that the water supplied by this deep well is unaffected by the shallow diesel release.