ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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passage zone, and the ability of adult salmon to rapidly avoid and migrate upstream,no substantial adverse impacts to the health or condition of adult salmon or steelhead are anticipated to result from potential short- duration exposure of fish to the higher temperature plume within the channel area. Therefore this impact is considered to be less than significant. Although the temperature modeling shows a technical violation of California Thermal Plan discharge temperature criterion, it is concluded from these analyses that exposure of adult Chinook salmon and steelhead(upstream migrating)to the proposed discharge (27 mgd) for a short period of time is not expected to result in a substantial increase in adult mortality or reduction in reproductive success. IMPACT Fisheries and Aquatic Resources—Thermal Effects on Fish and Benthic Macro!nvertebrates 4.13-2 Exposed to the Plume While Moving Downstream Past the Discharge Outfall.At full build-out, the proposed project would result in a thermal plume of increased temperatures, relative to the ambient temperatures, across portions of the water column, under all conditions, that is larger than the thermal plume that currently exists(and permitted)downstream of the discharge outfall. The project-specific changes to the size and characteristics of this plume would be considerable, as would project-specific effects on the frequency with which specific plume characteristics occur.A zone of passage would remain along the west bank river margin of the water column where river temperatures are unaffected by discharges. When achievable, actively swimming young-of-the-year fishes emigrating from upstream rearing areas would select migration routes past the discharge outfall that avoid elevated temperatures and excessive temperature differentials. The macroinvertebrate communities inhabiting the sediments and drifting through the plume are generally tolerant of the absolute temperature regime and differences created by the proposed project,particularly for the relatively short period of time they would be drifting through the plume. However,passively drifting fish are typically transported past the discharge in the near-shore habitats and along the upper portion of the water column, both of which are noticeably affected by the effluent plume. Based on the findings for passively drifting fish being noticeably affected by the thermal plume, the proposed project would have a potentially significant impact on the populations and communities of fish moving downstream in the lower San Joaquin River and Delta. This assessment of emigrating(i.e., downstream migrating)young-of-the-year fishes addresses the potential effects that the thermal plume may have on: 1) actively-swimming juvenile fish with an ability to avoid the plume; 2)post-emergent fry passively drifting in the current with little to no swimming ability; and 3)benthic macroinvertebrates drifting past the discharge outfall. Fish species with actively swimming emigrants include Chinook salmon, steelhead,white sturgeon, green sturgeon(Wang 1986). Fish species with passively drifting young-of-the-year include post-emergent Chinook salmon fry, Sacramento splittail, striped bass, and hardhead (Wang 1986). Little in the way of fish egg drift is expected in the WQCF outfall area because spawning and hatching typically occur in areas upstream of this location. In this assessment, emphasis was placed on anadromous salmonids (i.e., Chinook salmon and steelhead)because they are among the most temperature sensitive of the fish and are of high management concern. Actively Swimming Young-of-the-Year Fishes As discussed under Impact 4.13-1 above, an approximate 150-foot zone of passage(largely or completely unaffected by the thermal plume) exists along the west river margin in the area where the widest thermal plume occurs(approximately 1,500 feet downstream of the discharge outfall(Appendix F,Figures 20 and 21). As a result of the discharge plume buoyancy,maximum elevated water temperatures occur primarily near the water surface. Emigrating salmonids tend to migrate along the river margins in shallow, slower-moving waters rather than in the higher velocity water near the center of the channel(Bell 1986;Healey 1991;Moyle 2002). In this portion of the water column they use the structure of fallen trees,undercut banks,roots wads, and other near-shore structure to reduce predation pressures and provide shade and food resources. When migrating downstream,the juvenile and Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.13-23 Fisheries and Aquatic Resources