ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

calculated effluent fractions facilitate the use of a mass balance model to estimate changes in the selected water quality parameters due to an increase in WQCF discharge. Historic Delta water quality data and historic Manteca effluent data were then used to estimate incremental changes in the Delta under the maximum full build-out WQCF discharge scenario of 27 mgd. Potential incremental increases in the fully mixed river temperature, downstream of the discharge outfall,were extrapolated from the dilution analysis model runs for two one-year periods: October 1991 through September 1992, a critically dry year,and January 2002 through December 2002, a normal dry year(see Section 4.9 and Appendix F for details on modeling approach). The fully mixed downstream dilution of the discharge for the proposed project condition was compared to that simulated for the existing condition to determine potential project-specific temperature increases where the effluent initially becomes fully-mixed with the river(i.e., downstream of thermal plume). Comparison of the simulated dilution/temperature under the proposed project to that modeled for the existing condition facilitated determination of the downstream effect. Summary statistics were used to determine whether the project-specific incremental increase in fully mixed downstream river/Delta water dilution/temperatures would be expected to cause population- or community-level effects on aquatic biota inhabiting the San Joaquin River and Delta system, or result in adverse effects to individual organisms that are listed under the federal and/or State ESA. The scientific basis for making this determination considered: 1. the magnitude and frequency of the incremental change in temperature; 2. the seasonal temperature regime of the San Joaquin River/Delta downstream of the discharge outfall under the existing condition and proposed project conditions; 3. the available scientific literature regarding thermal tolerances of key fish species of primary management concern; 4. the nature of the use of the lower San Joaquin River by fish species of primary management concern; and 5. factors dictating lower San Joaquin River temperatures during the summer and fall months of the year. THRESHOLDS OF SIGNIFICANCE The significance criteria described below were developed for use in assessing potential impacts to fisheries and aquatic resources resulting from Manteca WQCF effluent discharges and constituent loading under the proposed project or its alternatives. Application of these significance criteria to findings determined from modeled output was used to make impact significance determinations. Effects of the proposed project on fish or other aquatic resources were considered significant if the project would: ► cause changes to San Joaquin River and/or Delta water quality, outside the zone of initial mixing, of sufficient magnitude and frequency to adversely affect an aquatic species' long-term population levels in these water bodies; ► degrade the quality of San Joaquin River and/or Delta aquatic habitats used by special-status aquatic species, including habitat(s)designated as critical habitat,to an extent that could cause a reduction in species abundance or long-term population levels(special-status species are defined as those that are currently listed as endangered or threatened under the federal ESA or State CESA and species formally proposed for federal and/or State listing as threatened or endangered); ► cause sufficient degradation in near-field water quality that would substantially delay,block,or otherwise substantially interfere with the success of upstream adult immigration or downstream juvenile emigration of Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.13-19 Fisheries and Aquatic Resources