Appendix A Water Quality Memo - Laserfiche WebLink

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20 Groundwater dewatering may be required during construction of the bridge piles to ensure groundwater levels are below the pile cap elevation (Earth Mechanics, Inc. 2018). Release of dewatered groundwater to surface waters can introduce total dissolved solids and other constituents to surface waters. As specified in Measure WQ-2, if groundwater dewatering becomes necessary during construction, the proposed Project would be required to comply with the requirements of the De Minimus Permit. In compliance with this permit, groundwater would be tested and treated (as necessary) prior to release to surface waters to ensure that discharges do not exceed water quality limits specified in the permit. Therefore, no adverse water quality impacts are anticipated during groundwater dewatering activities. 4.5 Long-Term Impacts During Operation and Maintenance No Build Alternative Under the No Build Alternative, no improvements to Fairview Street between 9th Street and 16th Street would occur and the Fairview Street bridge over Santa Ana River would not be replaced. In addition, under the No Build Alternative, there would be no increase in impervious surface area. Therefore, the No Build Alternative would not result in an increase in stormwater runoff or long-term pollutant loading compared to existing conditions. Furthermore, Treatment BMPs would not be implemented, and stormwater would remain untreated. Build Alternative According to the Draft Water Quality Management Plan (WQMP) (Civil Works Engineers 2019b) prepared for the proposed Project, expected pollutants of concern during operation of the proposed Project include suspended solids/sediment, nutrients, heavy metals, pathogens (bacteria/viruses), pesticides, oil and grease, toxic organic compounds, and trash and debris. The pollutants of concern for the project are metals and oil and grease. The proposed Project would increase impervious area by approximately 8,500 square feet (approximately 0.2 acre), which would increase the volume of runoff during a storm and more effectively transport pollutants to receiving waters. In addition, an increase in impervious surface would increase the total amount of pollutants in the stormwater runoff, which would increase the amount of pollutants discharged to downstream receiving waters. As specified in Measure WQ-3 (see Section 5.0), a final WQMP would be prepared for the proposed Project that would specify the LID, Source Control, Site Design BMPs, and/or Treatment Control BMPs to be incorporated into Project design to reduce the discharge of pollutants of concern to the maximum extent practicable. LID BMPs mimic a project site’s existing hydrology by using design measures that capture, filter, store, evaporate, detain, and infiltrate runoff, rather than allowing runoff to flow directly to piped or impervious storm drains. Source Control BMPs are preventative measures that are implemented to prevent the introduction of pollutants into stormwater. Site Design BMPs are stormwater management strategies that emphasize conservation and use of existing site features to reduce the amount of runoff and pollutant loading generated from a project site. Treatment Control BMPs are structural BMPs designed to treat and reduce pollutants in stormwater runoff prior to release to receiving waters. Currently, proposed BMPs include a vegetated swale adjacent to Fairview Street in the Fairview Triangle rest area. Additional treatment BMPs to treat runoff from the bridge deck may be incorporated into the bridge design at a later date during final design. According to the Draft Water Quality Management Plan (WQMP) (Civil Works Engineers 2019b), proposed non-structural Source Control BMPs include right-of- way landscape management, right-of-way litter control, right-of way catch basin inspection, and street