Reservoir Modeling to Develop AWT Nitrate Standard

A continuous simulation reservoir model was used to develop streamflow‐related effluent standards for nitrate‐N discharges into a water supply impoundment. The nitrogen removal standard for advanced wastewater treatment (AWT) plant represents relaxation of year‐round 1.0 mg/L total N effluent standard intended for lake eutrophication management. During years with average or above‐average streamflow conditions, AWT discharges must reach 40 mgd $(151.6\times {10}^{6}L/\mathrm{day})$ before even limited AWT nitrogen removal operations may be necessary to meet the reservoir's 5 mg/L nitrate‐N standard. During years with relatively low streamflows, the 5 mg/L nitrate‐N standard can be met with limited or no AWT nitrogen removal operations by a 10 mgd $(37.9\times {10}^{6}L/\mathrm{day})$ discharge while extensive nitrogen removal operations during most or all of the low flow period are typically required for discharges in excess of 20 mgd $(75.8\times {10}^{6}L/\mathrm{day})\text{.}$ Streamflow‐related effluent standard and AWT operating rule curves permit annual operation and maintenance cost‐savings of approximately one to two million dollars, depending upon AWT discharge and streamflows, and deferral of nitrogen removal unit expansion for 10–15 years.