As Davenport and Bettendorf complete the third year of a court-ordered sewer system improvement program, dumping of raw sewage into the Mississippi River remains an issue during summer months after heavy rains.
However, there are signs the effort to seal leaky sewer lines and fix blockages in riverfront interceptors is reducing the volume of raw and partially treated sewage that is pumped into the river.
Over three days in July and August, Bettendorf dumped nearly 1 million gallons of untreated sewage into the river. In Davenport, the sewage treatment plant there operated in "blending" mode, pumping nearly 21 million gallons of partially treated sewage into the river in July and nearly 153 million gallons in August.
Blending involves mixing partially treated sewage with fully treated sewage before discharge into the river in order to handle the large inflows to the treatment plant after heavy rains.
While significant, the volume of sewage still going into the river untreated or partially treated appears to be falling in recent years.
In 2010, Bettendorf dumped more than 33 million gallons of wastewater into the river in seven separate instances after heavy rains, while Davenport's treatment plant discharged a total of nearly 548 million gallons of partially treated sewage in the river over 74 days.
The two cities, along with Riverdale and Panorama Park, are joint owners of the sewage treatment plant along Concord Street in Davenport. Under a court-approved agreement in 2013 with the Iowa Department of Natural Resources (IDNR), the cities agreed to make improvements to stem infiltration of rainwater into sewer system lines and expand and enhance the sewage treatment plant.
The court order estimated the improvements to the sewer collection infrastructure and sewage treatment plant would cost $160 million over a 20-year timeframe.
Three years and millions of dollars into the upgrade, the Davenport treatment facility still reaches over-capacity after heavy rains or high water on the Mississippi River. The plant has a daily treatment capacity of 40 million gallons. When it reaches over-capacity, the plant lowers gates to limit flows, 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 stormwater pipe that is connected to a large "Government Interceptor Sewer" running along the Bettendorf and Davenport riverfront.
The Government Interceptor was built in the early 1930's by the U.S. Army Corps of Engineers to direct stormwater and sewage around Lock & Dam 15. The twin 10-foot diameter concrete interceptors drained sewage and stormwater from a 6-mile area upstream of Lock & Dam 15 to the downstream side of the dam where the stormwater and sewage was release into the Mississippi River.
After completion of the Davenport Sewage Treatment Plant in 1938, the long process of separating pipes carrying sewage from underground pipes handling stormwater runoff began.
Only in recent years has the total separation of sewer and stormwater lines been completed by Bettendorf and Davenport. However, the persistent problems has been leakage of stormwater and floodwater into sewer lines, leading to inflows after heavy rains which exceed the capacity of the treatment plant.
One problem identified early by city officials was the clogged condition of the original Government Interceptor line near Lock & Dam 15. Years of sediment had severely reduced the flow of stormwater (and sewage bypassed from Bettendorf after heavy rains) along the section of the interceptor between Lindsay Park and the dam.
The cities lobbied government officials in Washington and the Corps obtained $2 million for cleaning out of the Government Interceptor. That work was completed last year and did manage to restore the line to "functionality," according to a Corps spokesman.
Meanwhile, Bettendorf and Davenport have hired contractors to identify and fix leaky sewer lines throughout both cities.
The Davenport treatment plant also is halfway through a $7-million "optimization" project that will boost the secondary treatment capacity to 55 million gallons per day, up from the current 40 million gallon processing capacity.
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 prior to steps to reduce stormwater infiltration, saying fixing leakage of stormwater into sewer lines would greatly reduce the size and cost of an equalization basin.
Another requirement of the consent order is for enhanced treatment of bacteria at the plant prior to releasing the effluent to 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.
