The amount of partially treated sewage dumped into the Mississippi River by Davenport's Sewage Treatment Plant last month totaled more than 136 million gallons.
The so-called "bypassed" sewage received only primary – not secondary – treatment because flows to the plant on Concord Street were beyond its capacity as storm water runoff infiltrated sewer lines after heavy rains.
As the sewage flows backed up in lines to the treatment plant, Bettendorf pumped more than 29 million gallons of sewage and storm water into the river after the heavy rains in late June and early July.
primary treatment of the wastewater involves only removal of solids from the wastewater, bypassing the normal secondary biological treatment of the waste and pumping it into the river.
The bypassing of secondary treatment occurred June 12 through June 20, June 24 and then June 29 and June 30, according to plant reports filed with the Iowa Department of Natural Resources.
In Bettendorf, pumping of the raw sewage mixed with storm water occurred June 14 through June 18 and again from July 7 through July 9.
Davenport, Bettendorf and Riverdale are joint owners of the sewage treatment facility. In 2012, the cities signed a consent order with the Iowa Department of Natural Resources to fix infiltration problems in the sewer lines and expand the treatment capacity of the plant.
The engineering consultant for the three cities submitted plans for expanding the treatment capacity of the plant January 1 of this year, in accordance with the consent order.
The goal of the plant optimization project is to increase "secondary capacity" treatment from 45 million gallons per day to approximately 52 million gallons per day. The optimization project is to be complete by July 1, 2017, under the consent order.
Overall, the sewage treatment system owners are to spend an estimated $160 million over 20 years to upgrade the sewer system.
