City of Norwalk issued the following announcement on Sept. 2.
"The WRA has an ongoing project for lining a large diameter interceptor sewer which runs along the Raccoon River near downtown Des Moines. This sewer is more than 50 years old and is in poor condition. In order for the WRA’s contractor to perform their work all the flow needs to be diverted so the lining can take place. The most cost effective and logical way to do this is to use the existing Southwest Diversion facility Pump Station and Norwalk Detention Basin. The diverted flow is pumped from the vicinity of 63rd & Railroad in Des Moines south through a force main to the Norwalk Detention Basin. The force main has air relief pipes which discharge built up pressure in the interceptor pipe and discharges to the atmosphere which is why some residents are noticing odors from the air relief structures. The goose-neck pipes have either had bags placed over them temporarily or will have charcoal filters put on them to help reduce the odors.
The flow from the force main is stored or passes through the Norwalk basin and flows into the North River interceptor sewer to the Southern Tier Pump Station located south of the Highway 5 by-pass. The flow is then pumped to the WRA wastewater treatment facility. The WRA in the past has diverted flow for projects and during normal high flow events. These past events did not present odor issues because the wastewater during these events was diluted with stormwater. During the current diversion the flow has been more concentrated because of the drought and low groundwater conditions around the Metro.
The WRA is currently working with our consultant engineer to develop a plan for chemical odor control. The current plan is to feed a chemical into the system at three locations initially. The first location will be at the SW Diversion pump station. The second at the Norwalk Basin primary diversion structure, and the third at the Southern Tier pump station. We are hoping this system will reduce the odors we have been experiencing in the area.
The current project is a couple months away from completion so the WRA is moving as fast as possible to install the chemical dosing system. The WRA will have future lining projects that will require flow diversion as well. The next phase is scheduled to be constructed in the next couple years. Hopefully by that time the odor control system will be able to reduce the odor to a more manageable level."
Original source can be found here.
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