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City of Santa Ana -F On -Call Stormwater Project Design Services RFP No.: 20-102 Challen Geotechnical explorations will be performed at a variety of Low infiltration rates depths to check if deeper or shallower infiltration systems could be used Geotechnical exploration will include testing to determine if Geotechnical hazards liquefaction potential is high onsite, and if so, other options will be explored Lack of open space If geotechnical conditions permit, deeper infiltration systems such as d ells can be implemented without a large footprint High sediment loading in Pretreatment to be implemented upstream of infiltration system influent flows to reduce clogging and focus maintenance in pretreatment Open spaces in public Outreach is critical in working with the community and it may be I use areas beneficial to require work during times of lower use Basin and/or Wetlands Basin and wetlands are great opportunities to provide greater capture volumes when there is available open space. If landscape design is incorporated, basins/wetlands can be considered nature -based solution, which makes additional funding opportunities available. It is often more challenging to place open facilities in developed environments, such as the City. They can be incorporated into parks and can be coupled with trails and walking paths to provide the community different recreation opportunities, like the Torrance Stormwater Basins described under our experience. Open basins can be used to support infiltration (additional discussion on benefits above), or more commonly, for treatment when infiltration is not feasible. These types of facilities can enhance the local habitat while providing water quality and community benefits. We understand the City is implementing open bioretention basins at Mabury and Raitt & Myrtle Parks. Table 2 Common Basin/Wetland Challenges and Constraints Challenge/Constraint Strategies Lack of open space Combine above and belowground features to maximize capture available and utilize open surfaces ace available Include an underdrain and/or overflow system to take advantage Infiltration infeasible of treatment benefits before discharging downstream Evaluate opportunities to use the captured runoff for irrigation Create a barrier or lining to provide some treatment and verify Shallow groundwater design can take lateral loading from groundwater or create deep and shallow zones, some of which may have permanent water source Mosquito concerns Verify water movement (infiltration/filtration), use aerators, and/or design shallow/emergent zones to move flows C WE