Upgrades to the jointly owned Davenport/Bettendorf sewage system over the past four years has led to "marked reductions" in untreated and partially treated sewage being dumped into the Mississippi River during flooding and after heavy rainfalls.
According to the annual report to the Iowa Department of Natural Resources (IDNR) filed April 1, the improvements to the sewage treatment plant and sewage collection systems in the two communities have "reduced sewer backups and overflows.
"It appears the cumulative effect of the improvements is making marked reductions in overflows and WPCP (Water Pollution Control Plant) flows during certain events," the report by consulting engineer Veenstra & Kimm, Inc. stated. "Davenport has reported only 29 backups in 2016 versus 123 backups in 2015. Bettendorf has reported zero overflows/pumping in 2017 and over 70 percent reduction in pumping in 2016 versus 2015."
Under the court approved consent order in 2013, the cities agreed to make improvements to stem infiltration of rainwater into their sewer system lines and expand and enhance the sewage treatment plant, located along Concord Street in Davenport. Riverdale and Panorama Park also are joint owners and members of the intergovernmental group that oversees the plant and sewage collection system. Each community pays a percentage of costs for the sewage treatment plant based on the volume of their sewage, while each community is responsible for their own sewage lines.
The consent order estimated the improvements to the sewer collection infrastructure and sewage treatment plant would cost $160 million over a 20-year timeframe.
A $7-million "optimization" project that will boost the secondary treatment capacity of the Davenport treatment plan to 55 million gallons per day, up from the current 40 million gallon processing capacity, is nearly complete, according to the report. The work is projected to be completed by July 1.
By 2023, the consent order also calls for construction of an "equalization" basin sized to handled any flows over the plant's capacity so it can be held for treatment before being released to the river.
City officials argued successfully with the IDNR to delay construction of the equalization basin until steps to reduce stormwater infiltration and sewer interceptor blockages could be addressed. Fixing the leakage of storm water into sewer lines would greatly reduce the size and cost of an equalization basin, they said.
Another requirement of the consent order is for enhanced treatment of bacteria at the sewage plant prior to releasing the effluent into the river. Cedar Rapids currently is the only major city in Iowa to provide the higher level of treatment, which uses an ultra-violet light disinfection system.
When the plant approaches its treatment capacity now, gates are lowered to limit flows along the riverfront interceptor lines, forcing Bettendorf to activate a series of high-volume pumps along its riverfront. Without the pumping, raw sewage could back up into homes and businesses along the riverfront.
The pumps move the untreated sewage from the main sanitary sewer line into a storm water pipe that flows into the river.
When the sewage plant has inflow greater than its capacity – which typically occurs after heavy rains or during flooding – the facility is allowed to complete only "primary treatment" of the sewage before releasing it to the Mississippi River.
Sewage rates in both Bettendorf and Davenport have been steadily increased to pay for the plant upgrades and the repair of leaking sewage lines in both communities, and both communities are projecting future increases will be needed to pay for the remainder of the projects outlined in the agreement.
CLICK HERE to download the full annual report from the cities to the IDNR.