Davenport's wastewater treatment plant dumped 317 million gallons of partially treated sewage into the Mississippi River in late June and early July after heavy rains and river flooding overwhelmed the treatment capacity of the plant along Concord Street.
Flood water and storm water runoff infiltrated sewer lines after the heavy rains and the plant began "bypassing" secondary treatment of the sewage, dumping an average of 10 million gallons of sewage per day into the river after only primary treatment of the wastewater. Primary treatment only involves removal of solids from the wastewater, essentially bypassing the normal secondary biological treatment of the waste.
The sewage "bypassed" by the Davenport plant was in addition to the 129 million gallons of sewage Bettendorf pumped into the river during the same period.
Davenport and Bettendorf jointly own and operate the sewage treatment plant and when flows to the plant exceed its capacity, gates along the main riverfront interceptor line are closed. At that point, sewage backs up in the sewer line into Bettendorf and the city turns on pumps that dump the backed up sewage into storm water pipes that drain into the Mississippi River.
Because of the long-standing capacity problems caused by infiltration of storm water into sewer lines, the communities in 2012 signed a "consent order" with the Iowa Department of Natural Resources (IDNR) which requires the cities to begin reducing storm water runoff into sewer lines and addressing the capacity issues at the treatment plant.
Under terms of the legal agreement, the treatment plant owners are to make an estimated $160-million in sewer system improvements over the next 20 years.
By July 1 of last year, the cities were to "install and maintain such permanent sanitary sewer metering devices as are necessary to evaluate flow conditions within the sanitary sewer system and determine the wastewater storage and treatment capacity needs of the cities."
By the first of next year, the consent order calls for the cities to submit construction permit applications to the IDNR for "the wastewater treatment plant optimization project." The goal of that optimization project is to increase the capacity of the sewage treatment plant's "secondary capacity" 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.
In its most recent sewage bypass in July, the plant reported a maximum flow of 72.3 million gallons on July 11. On that day, the plant was able to fully treat approximately 45 million gallons, dumping nearly 27 million gallons of sewage into the river without secondary treatment.
CLICK HERE to download a copy of the Davenport Sewage Treatment Plant report for July showing the sewage bypassed from secondary treatment.
