Addressing Spokane's Wet Weather Challenges with Real-Time Controls

The City of Spokane (City) owns, operates, and maintains the wastewater and stormwater collection systems (collection system) in Spokane. These systems consist of a variety of assets and facilities, and accomplish the important purposes of:
-- Collecting and conveying wastewater from residents and businesses, along with stormwater runoff from areas with combined sewers, to Riverside Park Water Reclamation Facility (RPWRF) for treatment and discharge.
-- Collecting and conveying stormwater runoff from surfaces throughout the City for at least partial treatment and discharge.
Stormwater is discharged to a variety of endpoints, including the Spokane River (as part of the City's municipal separated storm sewer system [MS4]), into the ground (via bioretention and underground injection wells, also known as dry wells), or evaporated. Both the wastewater and stormwater systems have historically been operated with minimal data collection and supervisory or remote control capabilities, primarily because the assets and facilities have generally been achieving their desired performance. However, the City has long recognized the potential for improved performance of the collection system through the implementation of supervisory control and data acquisition (SCADA) for the collection system (referred to as the 'collection system SCADA'). The collection system SCADA will allow for increased monitoring and alarming, improved data management, and the potential application of real-time control (RTC) at combined sewer overflow (CSO) control facilities and interceptor protection tanks (IPTs). These improvements will result in reduced CSOs, reduced risk of sanitary sewer overflows (SSOs), more efficient operations and maintenance (O&M), and an increased understanding of how the system operates. Implementation and operation of the collection system SCADA would also have staffing and cost (capital and O&M) impacts on the City that need to be considered. Now that the City has constructed large and complex CSO control facilities and IPTs throughout the City as part of complying with the City's Waste Discharge Permit for CSOs and the RPWRF, the City has prepared a Collection System SCADA Master Plan (Master Plan), completed in May 2019. The purpose of this Master Plan was to:
-- Identify and evaluate potential opportunities for RTC at CSO control facilities and IPTs that could be implemented in the future, and assess costs and staffing impacts
-- Identify and prioritize monitoring and alarming improvements to the collection system, and assess costs and staffing impacts
-- Identify SCADA network and infrastructure needs to support the implementation and operation of the monitoring, alarming, and RTC improvements identified, and assess costs and staffing impacts

Establish an implementation roadmap for the selected collection system SCADA improvements and assesses the capital, O&M, and organizational impacts of implementing the recommendations As part of the Master Plan, the project team developed a system model of the City's sewer system, and simulated possible RTC scenarios to manage wet weather events. The model results indicated a reduction in CSO volume of between 30 to 40 percent, as shown in Figure 1, depending on the storm and level of RTC implemented. Not only did RTC reduce CSO volumes, but it also allowed for better protection of critical points in the interceptor system that are susceptible to surcharging. In conclusion, this project established a clear and implementable path forward for the City to implement SCADA in their collection system. The SCADA system will provide benefits on many fronts -- CSO reduction through RTC, improved O&M and performance due to real-time data collection, and improved reporting. This presentation will focus on describing the gaps and solutions identified in the Master Plan, with a particular focus on discussing the RTC analysis and results, and presenting the anticipated O&M impacts of making the improvements. This completed project was unique because it focused on using RTC as an adaptive management strategy for completed CSO control facilities. Many other municipalities are now in similar situations, where they have finished building CSO control facilities and are dealing with what to do if the control facilities are not sufficient to meet CSO reduction standards. This project provides an example of retrofitting completed facilities with RTC and monitoring in order to improve performance. Following the completion of this project the City has moved forward with designing and constructing the collection system SCADA, and will be making monitoring improvements at several high-priority pump stations and CSO control facilities.