ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Corrosion is the gradual degradation of materials through electrochemical processes resulting from the interaction between chemical properties of the soil(e.g.,pH,resistivity, and sulfate and chloride concentrations)and metal, concrete, or stone. Based on a review of available geotechnical reports,no soil testing to evaluate the potential for corrosion has been conducted at the WQCF site and along proposed wastewater collection system,recycled water distribution system, and effluent outfall pipeline alignments. In addition, it does not appear that any laboratory testing by a corrosion engineer has been completed, so no definitive conclusion can be reached regarding the soil corrosion potential in the project area. However,the City's engineering design process for the project would ensure the identification of corrosive soils and the implementation of project designs that would minimize damage to buried concrete slabs, foundations, and buried metal pipes. During the project design process, subsurface soil conditions would be characterized and a design-level geotechnical investigation conducted. Multiple soil borings would be staggered throughout the project site or along a pipeline route to capture any change in local soil conditions. Each soil boring would be logged by a geotechnical engineer and soil samples would be submitted for subsequent laboratory analysis of specific engineering properties and corrosivity. This process would reveal the presence or absence of problem soils, and would result in the development of specific engineering recommendations. For pipeline projects,recommendations would be made in the areas of trench design,backfill material, and pipeline selection. Methods to address corrosive soils include the use of cathodic protection, pipeline coatings or wrappings,use of non-metallic pipeline materials, and/or sacrificial anodes to eliminate long- term maintenance concerns. Because the City's engineering design process for the project would ensure the identification of corrosive soils and the implementation of project designs that would minimize damage to buried concrete slabs, foundations, or buried metal pipes, ,this impact would be less than significant. IMPACT Geology,Soils,and Seismicity—Potential Removal of Mineral Resources.Because sand resources in 4.7-6 the project area would not be suitable for aggregate mining, the proposed project would result in less-than- significant impacts to mineral resources. The project area is located on land classified by the California Department of Mines and Geology as MRZ-3, an area where the significance of mineral deposits cannot be evaluated from existing data. Results from geotechnical explorations in 1997(Kleinfelder) at the WQCF site indicated the presence of interbedded sand. Sand has been extracted from two mining sites in the project vicinity in the past, and sand and gravel mined in San Joaquin County is used for construction. Although geotechnical reports prepared for project related elements did identify areas of clean sand,these occurred as a series of discontinuous, shallow lenses at various depths. In addition, Section 8 of the Manteca General Plan 2023 Draft Environmental Impact Report did not include any impacts associated with mineral resources (City of Manteca 2003a). Therefore, sand resources located in the project area including areas in the vicinity of the proposed wastewater collection system, effluent outfall, and recycled water distribution system pipeline alignments would not be suitable for economically viable mining activities. Because sand at the WQCF site occurs as a series of discontinuous shallow lenses, and no mineral resources impacts were documented in the general plan EIR prepared by the City of Manteca,this impact is considered less-than-significant. 4.7.3 MITIGATION MEASURES No mitigation measures are necessary for the following less-than-significant impacts: 4.7-1: Risks to People and Structures Caused by Strong Seismic Ground Shaking. 4.7-5: Risk of Structural Damage Caused by Corrosive Soils. 4.7-6: Potential Removal of Mineral Resources. EDAW Manteca WQCF and Collection System Master Plans EIR Geology, Soils,and Seismicity 4.7-20 City of Manteca