Project Overview
The decision to build a new treatment facility came after extensive evaluation by city engineers.
The age of the current facility, limited space, flooding issues, and more restrictive limits on wastewater discharges have steered the decision for a new facility. In 2023, the city purchased a 21-acre site adjacent to Oakland Cemetery along Hwy 382 for the new facility.
Wastewater Treatment Facility Options
Iowa DNR Design Standards require a 20-year projection when designing new facilities. It is anticipated that wastewater treatment improvements will not be operational until the year 2029, so the planning period extends to the year 2050. Future population projections are based upon similar communities in growing metropolitan areas in Iowa as well as past growth. Population growth is projected to be approximately 4% annual growth for the planning period.
In the year 2050, the population of Solon is anticipated to be 10,000.
As part of the requirements for increasing a facility’s treatment capacity or discharging to a new location, IDNR/ EPA requires every facility to complete an Antidegradation Alternatives Analysis. The analyses must include less-degrading alternatives, non-degrading alternatives and no discharge alternatives. Upon completing research on six alternatives considered to meet this requirement that were deemed to be practicable, the Carrousel Treatment
Facility with Flow Equalization is recommended by the city engineering firm Veenstra and Kimm, Inc.
Editor’s note: Flow equalization is the process of controlling hydraulic velocity, or flow rate, through a wastewater treatment system. The equalization of flow prevents short term, high volumes of incoming flow, called surges, from forcing solids and organic material out of the treatment process. Flow equalization also controls the flow through each stage of the treatment system, allowing adequate time for the physical, biological and chemical processes to take place (www.norweco.com/wp-content/ uploads/2020/06/Flow_Equalization.pdf)
Recommendation
This alternative utilizes a new treatment facility and new outfall location in Mill Creek. Wastewater would be transported from the existing wastewater facility through a new gravity sewer to the recently purchased Menefee site west of the existing facility. The new facility would include screening, pumping, grit removal, aeration basins, clarifiers, sludge pumping, aerobic digestion, ultraviolet disinfection, and biosolids dewatering and holding.
This facility is most like the existing facility in operation but provides the added benefit of being designed for nutrient removal (removal of total nitrogen and phosphorus from the discharged water) and includes screening and grit removal which is not part of current treatment process.
This alternative allows the City to meet all projected effluent limits for the new outfall location, including new nutrient limits that the City will have to meet as part of Iowa Nutrient Reduction Strategy. In Iowa, facilities with a design capacity of 1.0 MGD (million gallons per day) or greater must comply with annual average limits of 10.0 mg/L total nitrogen and 1.0 mg/L total phosphorus. The City will also comply with limits for CBOD5 (carbonaceous biochemical oxygen demand), TSS, ammonia, E.coli, and chloride.
During periods of high flow, some of the wastewater would be diverted for storage at the existing plant site. After the high flows subside and treatment capacity is available, the stored wastewater will be discharged to the sewer for treatment at the new facility. The main lift station at the existing plant would be routed to existing tanks, and the tanks could be re-purposed for equalization basins. This would require minimal piping and rework at the site but would reduce the load to the stream during peak events.
Cost of a New Wastewater Treatment Facility
The City is planning to finance the improvements using a State Revolving Fund (SRF) loan and cash reserves. Completion of the facility is anticipated in June 2029.
Project Timeline
The timeline below provides a snapshot of the project timeline for the new wastewater treatment facility with completion expected in June 2029.
Public Information Sessions
Two public information sessions are planned for June 2025 to provide the opportunity for residents to learn more about Wastewater Treatment Facility options that have been reviewed and to ask questions about the project options.
Saturday, June 7th from 9 -10 AM at Solon City Hall, 101 N. Iowa Street. Thursday, June 19th at 7PM via Zoom (see link on city website calendar)