ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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IMPACT Hydrology and Water Quality—Effects of Proposed Project Discharges on Dissolved Organic 4.9-21 Carbon (DOC) Concentrations in Receiving Waters.Projected incremental changes in DOC concentrations at far-field monitoring locations would be less than 1 percent during critical water years and less than 3 percent during dry/below normal water years. These changes would not be substantial in relation to existing DOC concentration. Therefore, the project's far-field DOC impacts would be less than significant. The DHS has not recommended a Maximum Contaminant Level (MCL) for DOC. The RWQCB also has not adopted a water quality objective for DOC. For both critical and dry/below normal water year types,the calculated change in DOC at the selected sites is generally less than 0.03 mg/1 with buildout of the WQCF,with the exception of the Stockton Ship Channel Turning Basin where the change is estimated to be 0.08 mg/l during a dry/below normal water year. Median DOC concentrations at far-field monitoring locations range from 3.50 mg/l to 3.94 during critical water years and 2.72 to 3.51 during dry/below normal water years. Projected incremental changes in DOC concentrations at far-field monitoring locations would be less than 1 percent during critical water years and less than 3 percent during dry/below normal water years. These changes would not be substantial in relation to existing DOC concentration. Therefore,the project's far-field DOC impacts would be less than significant. IMPACT Hydrology and Water Quality—Effects of Proposed Project Discharges on Nitrate(as Nitrogen) 4.9-22 Concentrations in Receiving Waters.Modeling results for nitrate as nitrogen corresponding to critical and dry/below normal water years, respectively, demonstrated that, for both water year types the calculated change in nitrate as nitrogen at the selected sites is estimated to be no greater than 0.05 mg/1 with buildout of the WQCF(27 mgd). Median nitrate concentrations at far-field monitoring locations would all be substantially below adopted Basin Plan objectives. Therefore, the project's far-field nitrate impacts would be less than significant. For both critical and dry/below normal water year types,the calculated change in nitrate as nitrogen at the selected sites is generally less than 0.02 mg/1 with buildout of the WQCF (27 mgd),with the exception of the Stockton Ship Channel Turning Basin where the change is estimated to be 0.05 mg/l under dry/below normal water years. Median nitrate concentrations at far-field monitoring locations range from 0.52 mg/1 to 0.91 mg/1 during critical water years and 0.22 mg/1 to 1.64 mg/1 during dry/below normal water years. Median nitrate concentrations at far-field monitoring locations would all be substantially below adopted Basin Plan objectives. Therefore, the project's far-field nitrate impacts would be less than significant. IMPACT Hydrology and Water Quality—Construction and Operation of the Proposed Master Plan Facilities 4.9-23 and Control of Stormwater Runoff. The proposed project would involve updating and implementing a stormwater pollution prevention plan to assure compliance with applicable stormwater discharge permits. These and related actions(e.g., implementation of construction BMPs) that would be taken as part of and/or in response to the proposed project would minimize the impact of construction and operational stormwater quality impacts. Therefore, the project would result in a less-than-significant impact stormwater quality impacts. Impacts to water quality due to stormwater runoff from a facility can generally originate from: (1) construction activities, such as grading and excavation; and(2) contaminant spills that could occur from day-to-day facilities operations. Storm water runoff from the WQCF site flows into the general drainage system. Proposed facilities that would be connected to the general drainage system include equipment, chemical tanks, sanitary, and solids processing overflow drainage. The WQCF operates under a General Industrial Storm Water Discharge Permit(General Permit) adopted by the SWRCB. A condition of the General Permit is the requirement to prepare and keep on site a stormwater pollution prevention plan(SWPPP). The major objectives of the SWPPP are to: (1)identify pollutant sources that may EDAW DER Hydrology and Water Quality 4.9-48 City of Manteca