Indianola Water Resource Recovery Facility Enhances Community Resilience

The City of Indianola, Iowa, is the county seat of Warren County and is located south of the Des Moines metro. The City’s existing Indianola Wastewater Treatment Facility was nearing the end of its life and was not suitable for the additional nutrient removal requirements currently proposed by the Iowa DNR. Failed equipment and numerous processes were near the end of their useful life, and the replacement of the plant with a new Water Resource Recovery Facility was a critical need for the area.

Facility Siting and Funding

A Siting Study evaluated multiple options, including renovating the current site, connecting to the Wastewater Reclamation Authority (WRA) in Des Moines, or building a new facility. Building a new wastewater treatment plant at Indianola’s 360-acre city-owned farm site was determined to be the most economical option.

The new Indianola Water Resource Recovery Facility uses the slope of the hill to facilitate the hydraulic flow of wastewater through the treatment process by gravity. Additionally, the hillside location, an existing tree line, and new landscape berms help shelter the new facility from public view.

Innovative Peak Flow Treatment and Water Reuse

Working closely with the Iowa DNR, HR Green’s wastewater team designed an innovative peak flow treatment system that was approved specifically for the City of Indianola. The peak flow treatment system consists of diverting the high dilute flows that statistically come to the wastewater treatment plant one percent of the time and sending them to a small equalization tank, then a tertiary cloth media filtration process ahead of UV disinfection and effluent sampling followed by final discharge to the outfall sewer.

These one-percent peak flows do not go through the normal secondary treatment system. As a result, the biological secondary treatment system is properly sized, the feed organics during these peak flows are less impacted by peak flow dilution, and the peak flow is partially treated using media filters which are more economical and efficient with dilute wastewater than secondary treatment. The peak flow system as designed resulted in considerable cost savings for a smaller secondary treatment.

The wet weather flows are treated in real-time instead of hampering the operation for the next month or so, and most importantly, the combined plant effluent meets the effluent discharge permit throughout the peak flow treatment event.

The disinfected effluent is of higher quality and lower in nutrients than the Middle River into which it discharges and can also be reused for flush down, washing, or for process service water throughout the facility. Additionally, the treated water is reused for irrigation of the nearby Indianola Country Club by a dedicated force main from the new treatment facilities to the irrigation ponds at the golf course.

Facility Features and Construction

The Indianola WRRF incorporates many other features beyond the treatment of the liquid stream:

• Aerobic digestion solids treatment which produces a biologically stable low odor and low supernatant organic concentration.
• Sustainable land application from the biosolids storage tank to nearby farm ground where biosolids can be applied through an umbilical system and used as fertilizer.
• Administration Building with offices, locker rooms, breakroom, and Emergency Operations Center which can be used for emergency preparedness, emergency management, and disaster management.
• Vehicle storage bays in Administration Building with sectional overhead doors, wash bay, working spaces, and mezzanine storage.
• Process control and data acquisition system connected by a fiber optic loop that will allow staff to efficiently operate the plant and interface with process equipment.

HR Green provided Construction Phase Services for the Indianola WRRF and the construction was completed with extremely low change orders. The overall cost of the project increased by less than 0.1% (compared to an industry average of 4-5%) of the awarded construction cost.

The new Indianola Water Resource Recovery Facility supports the communities’ goals for growth and affordability through the project’s strategic funding, innovative approach, thoughtful design, and conscientious construction process.

“A wastewater treatment facility is an important, technology-driven, environmentally safe, heavily relied upon resource in a community. It is also necessary to foster and support growth. With the City’s local option sales tax supporting this project, we are able to remain an affordable greater Des Moines metro area community to live and develop in.”
– Former Indianola City Manager