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concentration of a parameter at a Delta location of interest due to an increase in WQCF effluent flow rate from the <br /> permitted 9.87 mgd to the proposed 27 mgd. The Delta monitoring locations for which far-field water quality <br /> impacts were modeled are shown in Exhibit 4.9-1. <br /> The fraction or percentage of WQCF effluent present at various locations within the Sacramento—San Joaquin <br /> Delta(Delta)was modeled to provide an indication of the far-field impacts of the proposed project on Delta water <br /> quality. Six locations within the Delta(see Exhibit 4.9-2)were chosen as far-field sites for the evaluation of water <br /> quality impacts due to increased WQCF discharge. Sites were selected to provide pre- and postproject water <br /> quality estimates at several drinking water export locations and the Stockton Deep Water Ship Channel(DWSC). <br /> Because of the limited availability of water quality data sets at the various Delta locations of interest covering the <br /> same time periods, only electrical conductivity(EC),nitrate, dissolved organic carbon(DOC), and dissolved <br /> oxygen(DO)were selected for far-field analysis. EC is a useful water quality parameter because it serves as a <br /> surrogate for salts,while nitrate and DOC are constituents of concern for the treatment of drinking water. To <br /> estimate far-field EC,nitrate,and DOC concentrations,the Delta hydrologic model is used to calculate the percent <br /> contribution of WQCF effluent at the various Delta locations. Dissolved oxygen is treated separately from the <br /> other constituents in the current analysis because the physical transfer of oxygen from the atmosphere and <br /> biological consumption of oxygen during respiration greatly affect the concentration DO can not be considered <br /> conservative, and the area of greatest concern for this parameter is the DWSC. The calculated effluent fractions <br /> facilitate the use of a mass balance model to estimate changes in the selected water quality parameters due to an <br /> increase in WQCF discharge. Historic Delta water quality data and historic Manteca effluent data were then used <br /> to estimate water quality in the Delta under two WQCF discharge scenarios: 17.5 mgd and 27 mgd. <br /> The analysis and results for each constituent specified in Table 4.9-11 for near-field and far-field analysis are <br /> summarized on individual fact sheets in an antidegradation analysis report(LWA 2007)which is included as <br /> Appendix C to this DEIR. <br /> THRESHOLDS OF SIGNIFICANCE <br /> For purposes of this analysis,the following applicable thresholds of significance have been used to determine <br /> whether implementing the proposed project would result in a significant impact. These thresholds of significance <br /> are based on the State CEQA Guidelines. The proposed project would result in significant hydrology and water <br /> quality impacts if it would: <br /> ► substantially deplete groundwater supplies or interfere substantially with groundwater recharge such that there <br /> would be a net deficit in aquifer volume or a substantial lowering of the local groundwater table level; <br /> ► expose people or structures to a significant risk of loss, injury, or death involving flooding,including flooding <br /> as a result of the failure of a levee or dam. <br /> ► violate any water quality standards or waste discharge requirements, including violating NPDES waste <br /> discharge or stormwater runoff requirements, state or federal antidegradation policies, enforceable water <br /> quality standards contained in the Central Valley RWQCB Basin Plan or statewide water quality control <br /> plans, or federal rulemakings to establish water quality standards in California; <br /> ► substantially alter the existing drainage pattern of the site or area, including through the alteration of the <br /> course of a stream or river, in a manner which would result in substantial erosion or siltation on-or off-site or <br /> substantially increase the rate or amount of surface runoff in a manner which would result in flooding on- or <br /> off-site; <br /> ► create or contribute runoff water that would exceed the capacity of existing or planned stormwater drainage <br /> systems or provide substantial additional sources of polluted runoff, <br /> EDAW DER <br /> Hydrology and Water Quality 4.9-30 City of Manteca <br />