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Brief Explanation of the Rationale for the Finding CEQA requires that all feasible and reasonable mitigation be applied to the project to reduce impacts from hazards and hazardous materials. Implementation of Mitigation Measure 4.5-9 would reduce the vector impacts. Despite this mitigation measure, the project will nonetheless result in some impacts from vectors. All reasonable or feasible mitigation has been identified that will reduce vector impacts for the project to less than significant. However, with the other sources of vectors in the area, as well as some vector increase from this project,the cumulative vector impact is considered significant and unavoidable. Hydrology And Water Quality A. Environmental Effects Of The Project Found To Have No Impact On The Environment,or Have A Less Than Significant Impact On The Environment. The project will not cause sheet flow storm runoff to enter the disposal pits and create groundwater quality impacts. The project will not substantially deplete groundwater supplies from project water demand. B. Environmental Effects Of The Project That Are Potentially Significant, But That Can Be Mitigated To A Less Than Significant Level. Potential Significant Effect Without appropriate mitigation, the project could violate Waste Discharge Requirements or Standards or provide for degradation of water quality. Description of Specific Impact The soils underlying the Project site display, non-permeability characteristics exceeding those normally required, by the RWQCB of disposal facility liners (See Section 4.4 and 4.6.1 of this EIR, and Rule 4570 recently adopted by the RWQCB). All of the proposed waste streams are subject to classification as "inert waste"under Title 23, Section 2524 except for biosolids. The total dissolved solids concentrations, ranging from 3,000 to 9,000 parts per million in first-encountered groundwater under the site, exempts the area groundwater from a municipal supply designation under State Water Board Regulation No. 88-63. The history of past consideration by the RWQCB of waste disposal operations at the Project site, and the status of current consideration thereof by the RWQCB, are pertinent to evaluation of this impact. Historic discharge operations at the facility had been classified as an unclassified waste management unit by the Regional Water Quality Control Board (RWQCB). Discharge operations were authorized under Revised Waste Discharge Requirements (WDR) Order No. 97-078 (RWQCB 1997a). This WDR authorized disposal operations at only Pit `B" and contained provisions to authorize discharge at additional locations upon demonstration that the sites would not pose a threat to water quality and that subsurface conditions throughout the pit bottoms (lithology, hydraulic conductivity of soils, highly mineralized groundwater, etc.) are similar to conditions documented for Pit "E." A Groundwater and Geotechnical Investigation and Site Characterization Report for Pits F and G (Hersh Consulting 1997) was prepared to provide this demonstration to the RWQCB. This report was reviewed and approved by the RWQCB on July 9, 1997 (RWQCB 1997b). The approval to discharge wastes into Pits "F" and"G" Findings of Fact—Section 15091 March 15,2016 H.M.Holloway Landfill Modification Project Final Board of Supervisors 40