UCSD and Fehr Graham design flexible sanitary flow solutions to meet future population demands — By Matthew Johnson, P.E., S.E.
Champaign, Ill., has experienced a dramatic increase in population density and housing in “Campustown” — the area in and around the University of Illinois at Urbana-Champaign (UIUC). The changes resulted in much greater sanitary flows in sewer mains than when the sewers were originally planned and installed between 1898 and 1946. As a result, there was a concern about increased overflow of sanitary sewage onto public streets and parks. It became critical for the Urbana & Champaign Sanitary District (UCSD) to implement a flexible solution for the campus interceptors into the future.
Flexible and innovative solutions
Make way for the Second Street Pump Station and Force Main project, a creative solution that allowed for two major wastewater treatment plants and connected tributary sewer infrastructure to be adaptable during dry and wet weather. This was accomplished using innovative instrumentation and programming, unique flow control configurations, and a diesel dry-prime pump system. This allowed the UCSD to choose either the level to maintain in the sanitary sewers during moderate wet weather events; or how much flow to receive at either of the two plants during heavy wet weather events.
Benefits from this solution were reduced nutrient discharges from the UCSD’s treatment plants, facilitation of effluent reuse, decommissioning of an energy inefficient pump station, and public park and streetscape improvements.
Flexibility was key to the Second Street Pump Station and Force Main project because the surrounding housing developments were privately owned and three different interceptors would be impacted. The solution, conceived by UCSD, was analyzed and designed by Fehr Graham, a Midwest engineering and environmental firm. UCSD contracted the firm to provide all civil and environmental engineering services during the project, including study and planning, preliminary and final design, construction administration, and resident project representation.
Construction of the Second Street Pump Station and Force Main took place from 2014 to 2016. A new 5 million-gallon-a-day (mgd) pump station was installed to redirect downtown flow to an existing pump station in south Champaign, where it is now pumped to UCSD’s Southwest Wastewater Treatment Plant (SWP), which has unused capacity to handle the new flows.
The new pump station was installed between three major interceptors located only a city block apart. Diversion structures, instrumentation, and controls at the pump station allow UCSD to selectively adjust the flow level in the interceptors during moderate flow periods. Flow removed from the interceptors is pumped to the South First Street Pump Station, which then pumps to the SWP. Flow remaining in the interceptors continues to the Northeast Wastewater Treatment Plant.
By selectively removing flow from upstream sewers, the existing downstream interceptors running through Campustown are able to serve almost any mix of new high-rise developments today and well into the future, while optimizing the amount of water treated by UCSD’s treatment plants.
During high flow periods, UCSD can switch to a flow-based control method, selecting which of the two plants should receive more or less flow, and optimize the operation of the two plants. This should maximize the amount of wastewater kept in the sewer system without overflows and maximize the level of treatment before excess flow facilities start at either plant.
During normal flow periods, UCSD may choose to maximize nutrient removal by sending more flow through the AO bio-P removal process at the SWP. There also may be a need to reduce flow at one plant to address tanks being offline due to maintenance.
During drought conditions, UCSD may choose to supplement flow at SWP, which may be providing as much as 6 mgd of plant effluent to a fertilizer plant for reuse. Without the supplemental flow, the SWP does not treat 6 mgd, so the fertilizer plant would likely be forced to tax the local aquifer.
Due to the flows from the Second Street Pump Station, the existing South First Street Pump Station would require an approximate 8 mgd capacity. The remote location of this facility made it cost-prohibitive to provide two independent sources of power to the larger electric pumps. Fehr Graham’s design included a 475-hp self-priming, diesel-powered pump to transfer 8 mgd to the SWP. According to the manufacturer, the diesel pump is the largest installed in this application in the Midwest.
It was found to be most economical to simplify the controls and completely replace the electric pumps’ capacity with the large diesel pump. If the electric pumps are not able to keep up, they are shut down while the diesel pump runs. After the diesel pump reduces the level of the wet well, the electric pumps reengage in a specific sequence to avoid utility overcurrent and increased power factor, attempting to keep the level of the wet well down. If successful, the electric pumps continue to run, maintaining normal levels. If not, the diesel pump reengages and re-starts the sequence.
Several challenges were overcome during detailed design. The routing of the 20-inch force main passes through a utility-congested right-of-way on the west edge of the busy UIUC campus. As a result, the contractor:
- used horizontal directional drilling methods for installation of the force main in the most congested corridors;
- installed the line under two, 10-foot-deep steam tunnels; and
- completed open-trench construction in the more wide-open areas.
Coordination with several utility owners was required for the desired route without causing unnecessary pressure loss or adding air release and vacuum relief valves and associated vaults. Two air release/vacuum relief valve vaults were required to be installed above ground in front of popular campus buildings. The vaults required architectural embellishments and advanced odor control to meet UIUC requirements. The odor-control devices contain a bypass to avoid a vacuum-induced implosion of the force main during a power outage while flowing at full capacity.
Direct and secondary benefits
Several direct and secondary benefits to the community were realized from the project.
Increased nutrient removal — UCSD’s SWP was the first AO Process installed in Illinois to remove phosphorous biologically in 2005. Diverting an estimated 1.5 mgd to SWP means UCSD discharges 12,000 fewer pounds of phosphorous and 45,000 fewer pounds of nitrogen per year.
Increased energy efficiency — The force main from Second Street Pump Station was terminated prior to reaching South First Street Pump Station and a new gravity interceptor sewer was installed to complete the connection between the two stations. A gravity sewer connection was made to an existing pump station, thereby decommissioning it.
Research Park utilities — The gravity interceptor sewer allows the university’s Research Park to use it as the main sewer for an expansion eastward. The Research Park helps new and expanding companies launch ideas based on the university’s research. Keeping fees low helps incubate fledgling companies in their early years.
Social improvements — The Second Street Pump Station building is located adjacent to Scott Park, the site of a multi-million-dollar improvement led by the City of Champaign and Champaign Park District. Recognizing the sensitivity to a large sanitary pump station adjacent to this improvement, Fehr Graham worked closely with the city and park district to coordinate architectural concepts, landscaping, and designs for the building to integrate seamlessly with the surroundings.
Health and safety — The overflow of sanitary sewage onto public streets and parks is a threat to public health and safety and to the environment. The chance of these problems becoming more frequent as the area developed was a primary goal for the project.
Beneficial effluent reuse — With the increased flows to the SWP, UCSD could enter into an agreement to provide 6 mgd of effluent to a new fertilizer manufacturer from the SWP. This “on-demand” effluent can serve the manufacturer’s cooling tower needs for a low-phosphorous, low-chloride, softened water in an area of Illinois without many alternative industrial water supply options. Using UCSD’s effluent allows the company to avoid tapping the Mahomet aquifer for this 6 mgd of flow.
UCSD and Fehr Graham faced a significant amount of complexity throughout the entire life cycle of the project, from initial planning and analysis through construction and completion:
Adjacency to public parks and campus — All improvements considered and incorporated aesthetic improvements, including the Second Street Pump Station building. In addition, all improvements were coordinated with multiple existing utility stakeholders.
Sequencing and coordination with several projects — Numerous ongoing campus construction projects required regular coordination meetings and a tight schedule sequencing to meet the various needs of the multiple projects.
Lack of utility power — The South First Street Pump Station could not be economically served by the electric utility. The largest capacity diesel pump of its type in the Midwest was applied to economically solve this problem.
Control of multiple interceptor sewers and plants — A method was designed to adaptively manage the existing interceptor sewer and treatment plant infrastructure to effectively address inherently unpredictable flows and future development. This provided the excess capacity needed for unplanned population density throughout Campustown, allowing development to grow in whichever sewer basin is best able to meet the demands of the market.
UCSD’s primary goal was to significantly decrease the chance of sanitary sewer overflows in Campustown despite the ongoing surge in population density. UCSD and Fehr Graham provided an innovative and cost-effective solution that will meet the population demands today and well into the future.
Matthew Johnson, P.E., S.E., is branch manager in the Champaign, Ill. office of Fehr Graham (www.fehr-graham.com).