ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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► increase levels of any priority pollutant or other regulated water quality parameter in a water body such that the water body would be expected to more frequently exceed state and/or federal numeric or narrative water quality objectives,resulting in adverse effects on one or more beneficial uses; ► cause violation of existing requirements of the City's NPDES permit that serve to avoid significant environmental impacts; ► otherwise substantially degrade water quality. IMPACT ANALYSIS Hydrology IMPACT Hydrology and Water Quality—Effects on Potential On-site and Off-site Flooding Risk from 4.9-1 Increased Stormwater Runoff. The project would result in the generation of minor volumes of additional stormwater;however, adequate stormwater capacity would be available to covey increased stormwater generated by the project, and the project would not increase the potential for on-site or off-site flooding during storm events. This would be a less-than-significant impact. The proposed project involves construction of new facilities designed to increase the wastewater treatment capacity of the existing WQCF and wastewater collection system, effluent outfall, and recycled water distribution system pipelines to serve the city's urban growth areas. The proposed pipelines would be located below ground and would not result in the installation of any impervious surfaces. As such,these facilities would not result in a substantial increase in stormwater runoff in the project area. Minor amounts of additional impervious surfaces (e.g.,buildings, structures)would be constructed to house new facilities at the WQCF site and at the proposed wastewater pumping station sites. The additional runoff caused by the increase in impervious surfaces would lead to a minor increase in localized stormwater runoff compared to existing conditions. Additional stormwater would be directed to the on-site stormwater system at the WQCF and to the neighborhood stormwater systems where proposed wastewater pump stations would be located. These stormwater facilities could adequately accommodate the minor volumes of stormwater generated by proposed facilities. Because adequate capacity is available to convey the minor volumes of stormwater generated by the project,the project would not increase the potential for off-site flooding risks during storm events. Therefore,the project would result in a less-than-significant impact related to flooding risks from increased stormwater runoff. IMPACT Hydrology and Water Quality—Reduction in Groundwater Recharge. The City of Manteca does not 4.9-2 serve as a substantial groundwater recharge area. Therefore,proposed development would result in a less-than-significant groundwater recharge impact. The WQCF site and proposed pipeline alignments do not contain streams or alluvial fan conditions that could function as substantial groundwater recharge areas and construction of minor amounts of impervious surfaces at the WQCF site or wastewater pumping station sites are not expected to affect overall groundwater supplies or recharge rates. Further,undeveloped areas in the proposed project area and agricultural lands located to the west, north, and south of the project area would continue to provide limited amounts of groundwater recharge. The City of Manteca General Plan DEIR concluded that no areas in the Manteca area provide a substantial source of groundwater recharge(City of Manteca 2003a). Therefore,implementation of the project is not anticipated to substantially affect groundwater recharge rates in the area. This would be a less-than-significant groundwater recharge impact. IMPACT Hydrology and Water Quality—Effects of Potential Off-site Flooding Risk from Increased Treated 4.9-3 Effluent Discharge. Project implementation would increase the amount of treated effluent discharged into the San Joaquin River;however, the incremental amount of treated effluent(i.e., up to 17.13 mgd) EDAW DER Hydrology and Water Quality 4.9-32 City of Manteca