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City of Santa Ana On -Call Stormwater Project Design Services RFP No.: 20-102 Sewer Diversion Low flow diversions have been used in Southern California over the past several decades to capture dry -weather flows, which have often been associated with high concentrations of pollutants. This allows the wastewater treatment plant to treat runoff before discharging it or using it for non -potable or recycled water, therefore reducing pollutant loads to downstream receiving waters while providing addition conservation/water reliability benefits. These are a great way of addressing dry -weather TMDLs, especially when there are space concerns or infiltration is not feasible. Sewer discharge fees are one thing to consider, as they will continue in perpetuity. Water conservation efforts made in response to recent drought years has resulted in households using less water and creating less wastewater, which has impacted some treatment plants that rely on a specific inflow for the treatment processes to work. Some Sanitation Districts have been open to accepting storm flows in addition to dry -weather flows to help solve these issues. While the discharge fees may make this approach less favorable, it may be an option to consider, especially when infiltration is not feasible and there is limited space for other infrastructure. We have led several similar projects (identified in our experience) and understand the coordination required and electrical components to regulate discharges. We understand a low flow diversion exists in the Newport Bay Watershed on the Santa Ana -Delhi Channel, and there may be additional opportunities within the watershed to assist Diversion' with compliance. Table 4 Common Sewer Diversion Challenges and Constraints Stakeholder coordination early on to understand capacities and Sewer capacity opportunities for upsizing, while alternatively, storage can be provided and used to regulate flows to meet available capacities Fees identified early in the assessment process so that they can Discharge fees be considered as part of operation and maintenance costs before major decisions are made Wastewater treatment plants are not designed to treat high Influent water quality sediment loads; therefore, monitoring may be needed to determine if pretreatment is needed and to what level Flow meters and other equipment can be used to help reduce Sewer overflows risks of overflows, along with coordination with sewer owner/operator Backwash of sewer flows Check valves and pumps may be used to prevent cross into storm drain contamination from occurring and degrading water quality a _111- CWE7