Shenandoah Wastewater Treatment Facitlity
The Need for Improvements
The City of Shenandoah is in the process of planning improvements to its wastewater treatment facility to address issues related to the facility’s age and ability to comply with changing regulations.
• The wastewater treatment facility (WWTF) was originally constructed in 1963 and its trickling filter treatment process is nearing the end of its useful life.
• The existing facility does not have redundancy in its major treatment process components, making maintenance operations difficult and the facility vulnerable to breakdowns.
• The volume of water coming from the community’s sewer system overloads the facility and exceeds the design capacity.
• The city received a new National Pollutant Discharge Elimination System (NPDES) permit that requires treatment of ammonianitrogen, E. coli, and dissolved oxygen to levels which cannot be met by the existing WWTF. In addition, new requirements of total nitrogen and total phosphorus are on the horizon.
What is NPDES?
As part of the Clean Water Act of 1972, the National Pollutant Discharge Elimination System (NPDES) regulates direct discharge of wastewater to surface waters. All facilities discharging pollutants into waters of the U.S. and the state are required to obtain an NPDES operation permit. These permits limit the amount of pollutants a wastewater treatment plant can discharge and are renewed in 5-year cycles.
The city received its new permit in March 2016. However, the City of Shenandoah applied for Disadvantaged Community status through the Iowa Department of Natural Resources and was granted an extension due to the extensive improvements needed on the wastewater treatment facility
Following a study of the existing wastewater treatment facility and evaluation of potential alternatives that would meet the new NPDES permit levels, it was determined an activated sludge treatment facility would provide the best value and functionality for Shenandoah’s wastewater treatment facility.
• Replacing the current trickling filter treatment facility with a complete new activated sludge treatment process will help the city meet new NPDES permit levels and provide future growth opportunities.
• Additional proposed improvements include upgraded screening equipment, grit removal, pumps, blowers, disinfection equipment, a new discharge sewer to the East Nishnabotna River, a wet weather equalization pond, and a perimeter flood risk reduction berm.
Improvements are currently in the preliminary design stage, with construction scheduled from the summer of 2023 to summer of 2025.
What is an Activated Sludge Treatment Facility?
Trickling filter facilities treat wastewater by spraying the wastewater over plastic sheets or rocks stacked within a concrete holding tank. Bacteria, or “bugs,” grow on the plastic or rocks and consume the organic materials contained within the wastewater. Activated sludge treatment facilities grow bacteria within a large volume of water contained within multiple concrete holding tanks.
Wastewater from the community flows into these tanks and is combined with pumped air. Bacteria then uses the air to consume the organic material within the wastewater. Each of the tanks can be adjusted for the amount of air that is pumped into it and how long the wastewater stays within each tank to create the right environment to treat for different pollutants providing the flexibility to meet the new NPDES permit.
The improvements are estimated to cost $19.7 million and will be funded through grants and low-interest loans.
• The City of Shenandoah received a $2 million grant from the US Department of Agriculture – Rural Development (USDA-RA) Water & Waste Disposal program and a $17.7 million low-interest loan.
• Historically low interest rates at 1.25% over 40 years provides an additional $3.5 million in buying power to the City.
• Constructing all improvements at one time provides the least impact to net user rates over the next 20 years. User rates will be gradually increased over the next 1-5 years to offset the cost of the project.