Management of wet-weather flows in wastewater collection systems has remained one of the most intractable problems for utility managers.
Wastewater collection systems are often spread across many square miles of residential, commercial, industrial and rural property with most parts completely obscured from public view.
Traditionally, it has been difficult to acquire live collection system operating data on a regular basis, and this lack of immediacy in the data makes it very challenging to quantitatively predict what the system will do during wet weather. In essence, limited access and lack of live operating data cause the collection system to be a blind spot for most utilities.
Recent policies implemented by the U.S. government have established a mandate for proactive supervision of wastewater capacity, management, operations and maintenance (CMOM). Despite its lack of commensurate funding, the concept has merit: If we can quantify problem overflow areas and repair them, and if we can predict problems before they happen and take steps to prevent overflows in storm situations, we can reduce the risk to public health and improve stream water quality in municipalities.
The results will have a significant positive effect on residents and business owners in areas commonly affected by overflows. In addition, reducing the amount of rainfall-derived infiltration and inflow (RDII) will have a major positive impact on the environment and reduce wastewater treatment costs.
As CMOM becomes a reality, wastewater system owners and operators must identify and prioritize deficiencies in their infrastructure and develop an action plan for rehabilitation of the compromised areas. Municipalities are expected to manage, operate and maintain all parts of the collection system at all times, with an awareness of base and peak flows at every significant point in the overall system. Ultimately, utilities must convey as much sewage as possible to their publicly owned treatment works. Finding ways to do this optimally is of paramount importance to wastewater utilities.
One viable solution, demonstrated effectively by its application in Erie County, N.Y., is a real-time, Web-based, wireless flow-monitoring system and online flow model, which uses a GIS platform as the Web interface. The seamless integration of these three commonly used technologies maximizes the value of each while providing the representatives and dependable information available on wastewater behavior throughout the trunk sewer system.
Solving the CMOM Conundrum
The Erie County Department of Environment and Planning Division of Water Quality Management (DWQM) in Western New York manages all facets of wastewater collection and treatment for seven sewer districts in the eastern and southern suburbs of Buffalo. The DWQM serves close to 300,000 people and includes 1,000 miles of sewers, nearly 100 pumping stations, seven wastewater treatment plants and five overflow retention facilities.
The DWQM has been growing over the past few years and is projected to continue this growth. In order to reduce rates and improve services, smaller communities are merging their sewer systems to become part of the DWQM. There also are areas within the DWQM’s existing system that are experiencing commercial and residential growth, which will induce additional challenges to current efforts to minimize overflows and maximize wastewater conveyance for treatment.
Operations staff members are not familiar with the expanded areas of infrastructure, and as the system evolves, flow patterns will change. To compound the challenges, the DWQM is beginning to receive new operating permits from the state regulatory agency focusing on collection system management.
In a proactive move, Erie County commissioned a demonstration of the real-time system to address these challenges and optimize its collection system management efforts. Working with the engineering firm Conestoga-Rovers & Associates, the DWQM implemented a Web-based system that enables remote, real-time acquisition of collection system operations data; transfer of data to a central server; and extrapolation of data to show operation of the entire trunk sewer system using a hydraulic model. This system was selected to allow simultaneous access by users spread out over a system that spans 30 miles from end to end.
The GIS platform provides a user-friendly means to access all website functions. This enables different types of staff (operators, maintenance personnel, engineers and management) to use this website to access critical information with minimal training. The website user does not need expertise in GIS and flow database software programming or storm water management models (SWMMs) to obtain critical information on the collection system.
Remote data acquisition begins with a series of Telog Ru-33 remote telemetry units (RTUs) connected to flowmeters. The RTUs can run on both battery and solar power, eliminating the need for AC power or field visits to change batteries. The RTUs alert DWQM personnel to emerging problems in the collection system, and they can sound alarms when water level conditions exceed predetermined levels.
The Telog RTUs employ switched packet protocol, which uses the Ethernet capabilities of the existing cellular infrastructure to push data in 15-minute intervals to the Telog Enterprise information management system, which collects and stores the data. From here, the real-time system pulls the collected data into a central database to use for modeling and analysis. The data set is updated every 15 minutes.
Using the data, the DWQM can select specific monitoring facilities to view and overlay sites over one another to see trends and effects of weather and other events. An SWMM-based hydraulic model uses real-time or stored historic data to extrapolate the information at the monitoring points to simulate operation in the entire trunk sewer system.
One of the most powerful tools of the real-time system is initiating a real-time model. At the click of a button, the user can request a model run for the previous 48 hours of flow and precipitation data collected. This allows up-to-the-minute access to sewer system operation, including thematic mapping (color-coded) and model reports, as well as time-series plots and animated sewer profiles of the trunk sewer system.
Benefits of Planning
The benefits of this system are far-reaching. Real-time collection system information allows Erie County to quantify the effects of wet weather on its current weak points and predict pipe surcharges and overflows before these situations occur. Using GIS mapping and running scenarios that range from two-year to 100-year storms, the DWQM can analyze “what-if” scenarios and plan realistically for growth.
The areas with the greatest amount of RDII can be identified and quantified, thus allowing the DWQM to invest in the right sewer rehabilitation projects. The system also will permit the DWQM to develop maintenance plans (e.g., sewer flushing) and wet-weather operating plans, plus cost-effectively implement sewer investigations such as smoke and dye testing or video inspections. Finally, the real-time system will assist the DWQM in furthering its advanced asset management and capital improvement programs.
The results of this expanded modeling capability can be measured in linear feet and, subsequently, in dollars and cents. Erie County can get the most out of rehabilitation efforts and minimize the amount of sewers requiring replacement. This will result in reduced time and capital investments, assist in meeting permit requirements and improve protection of public health and stream water quality.
Author’s note: The author would like to thank Thomas J. Whetham, P.E.; Michael J. Quinn, P.E.; Joseph L. Fiegl, P.E.; and Steven Russell of the DWQM for their contributions.