ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Passively Drifting Young-of-the-Year Fishes Young-of-the-year fishes that passively drift in the water column and young fishes that are weak swimmers include post-emergent Chinook salmon fry, striped bass, Sacramento splittail,hardhead, and delta smelt(Wang 1986). Following hatching,these fish are transported downstream by river currents to rearing habitats in the Delta. Chinook salmon that emigrate as post-emergent fry typically remain in near-shore habitats (Healey 1991;Moyle 2002). Larvae of striped bass, delta smelt, Sacramento splittail, and hardhead are typically transported in the near- surface portions of open waters and along near-shore habitats. Consequently,the early life stages of these fishes could drift into and through the thermal plume without the ability to escape and would be exposed to the higher temperatures for a relatively long period of time(potentially>30 minutes depending on river water velocities and location within the plume). This sudden exposure(minimal acclimation)to the higher temperature plume for a relatively long period of time(drifting through the entire length of the approximate 2,000-foot plume)could result in adverse thermal effects to the health and/or condition of these young-of-the-year fishes.Mortality may not necessarily result from direct thermal effects,but may be related to disease,predation, and other indirect effects resulting from exposure. Drifting Macroinvertebrates As discussed in the setting,the common macroinvertebrate taxa present in the lower San Joaquin River and Delta are species that are tolerant of relatively high temperatures(ranges from 827 to 877). Although the thermal plume along the east margin of the river may change the macorinvertebrate community composition and/or species-specific relative abundances compared to the existing permitted condition, it would not be expected to result in substantial population-level adverse effects. The increased area where community composition and relative abundances may be altered by the enlarged plume is expected to be negligible relative to all available macroinvertebrate habitat of the lower San Joaquin River and Delta(i.e.,many thousands of acres). Summary of Impacts Fish that swim into the thermal plume would encounter a thermal gradient and would likely select a preferred migration path based on temperatures encountered as they continue to move downstream. However,because the plume is relatively wide (maximum of approximately 150 feet)and is situated along the margin of the river, fish may not be able to immediately swim to cooler waters in the zone of passage (along the west margin). At the upstream head of the plume, exposure to the elevated temperatures would be sudden with little time to acclimate to the change. Additionally,passively drifting young-of-the-year fishes could drift into and through the thermal plume without the ability to escape and would be exposed to the higher temperatures for longer periods of time (potentially>30 minutes depending on river water velocities). The sudden exposure to the high temperature plume for relatively long periods of time could result in adverse thermal effects to the health and/or condition of these young-of-the-year fishes. Ultimately,population-level effects could result from potential mortality in fish caused by acute(short-term) exposure to elevated water temperatures when moving past the discharge outfall. Therefore,this impact is potentially significant. IMPACT Fisheries and Aquatic Resources—Population-or Community-level Effects to Fish or 4.13-3 Macroinvertebrates from the Incremental Increase in Downstream Water Temperatures(Fully Mixed Condition). The proposed project would result in small incremental increases in the fully mixed San Joaquin River/Delta water temperatures downstream of the discharge outfall. Under all conditions above critical water year flow rates, the proposed project at full build-out condition would result in a fully mixed regime downstream of the discharge that is near equivalent to that under the existing permitted condition(<1 effluent contribution). These effluent contributions would result in negligible incremental increases in downstream water temperatures. Based on these findings, the proposed project would have a less-than- significant impact to fully mixed lower San Joaquin River/Delta water temperatures. Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.13-25 Fisheries and Aquatic Resources