ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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IMPACT Fisheries and Aquatic Resources—Potential for Thermal Plume below the Discharge Outfall to 4.13.1 Block or Substantially Delay the Upstream Spawning Migrations of Fishes.A thermal plume currently exists in the San Joaquin River immediately downstream of the Manteca WQCF discharge outfall, but is not believed to block or substantially delay the upstream spawning migrations of fishes due to a relatively large zone of passage that is present during all months of the year, under all conditions.At full build-out(27 mgd capacity), the proposed project would result in increased plume size and changes to certain aspects of the plume's internal characteristics(e.g., temperature contours)and/or the frequency with which specific characteristics would occur, relative to the existing(permitted)condition. However, a viable zone of passage for all migrating fish species would be maintained under worst-case conditions with implementation of the proposed project. Based on these findings, the proposed project would have a less-than-significant impact on the upstream spawning migrations of adult fishes. Upstream migrating temperature sensitive anadromous fish(e.g., Chinook salmon, steelhead)can potentially be blocked or delayed if they encounter sufficiently high fully-mixed river temperatures while migrating to upstream spawning areas(Evans and Johnson 1980; Bell 1986;Boles 1988). If a thermal plume exists, immigrating adult fish could be temporarily blocked or delayed;however,their behavior response would be to avoid the plume and seek a"zone of passage"where river temperatures are more favorable and thus facilitate passage. Thermal Plume Characteristics Under the existing permitted discharge capacity of 9.87 mgd,modeling results show a zone of passage,where the ambient water temperatures are unaffected by the effluent discharge, occurs on the west margin of the San Joaquin River at the Manteca WQCF discharge along the entire length of the plume under all months, flow, and permitted effluent discharge conditions(LWA 2006; see also Appendix F,Figures 20 and 21). The maximum cross-sectional area affected by this plume is approximately 22%at 1,000 ft downstream of the discharge outfall with a maximum increased temperature of approximately 8°F over ambient background river water temperatures. At full build-out(capacity increase to 27 mgd)and under conservative worst-case conditions,' the proposed project would result in an increased thermal plume size and changes in certain aspects of the plume's internal characteristics(e.g.,temperature contours) and/or the frequency with which specific characteristics would occur, relative to the existing(permitted- 9.87 mgd)condition. The width(and cross-sectional area)of the plume was simulated to remain relatively narrow(and small) at the point of discharge, 15%of the cross-section or approximately 45 feet wide,with a maximum increased temperature of approximately 8°F over ambient background river water temperatures. Downstream of the outfall,the plume spreads out laterally and vertically to cover a greater proportion of the river's cross-section. Conversely,the water temperature within the plume decreases as the plume and ambient waters mix(i.e.,become diluted)with increasing distance downstream of the outfall. For example, at approximately 1,500 feet downstream of the discharge outfall,the location of maximum plume cross-sectional area effect,the plume covers 51% (approximately 150 ft)of the channel with a maximum increased temperature of 5°F (see Appendix F,Figures 20 and 21). Consequently,the unaffected passage zone at this cross-section of the river comprises approximately one-half of the river's approximate 300-foot width(or 150 feet)at the widest location of the plume. Due to buoyancy of warmer water temperatures,the plume is slightly wider at the water surface compared to the bottom of the channel. Movement Tendencies of Upstream Spawning Migrations of Fishes Coldwater fish species such as Chinook salmon and steelhead prefer temperatures below those that often exist in the San Joaquin River at the WQCF outfall during the summer months(Cherry et al. 1977)and,therefore, likely 'Appendix F provides graphic characterizations and summary statistics of San Joaquin River temperatures within the initial 2,000 ft downstream of the outfall(i.e.,within the entire length of the plume).The graphic characterization and summary statistics data tables depicts a conservative"worst-case"scenario,based on minimum background flows(i.e.,dry year)in the river during the winter period and a maximum effluent discharge rate of 27 mgd. Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 4.13-21 Fisheries and Aquatic Resources