WEBSTER CITY — An important topic of discussion at last week’s Webster City council budget work session was the city’s new wastewater treatment plant and, specifically, how to pay for it.
The proposed new plant, designed by the city’s consultant — Bolton & Menk of Ames — is estimated to cost $78,426,000.
Interim City Manager John Harrenstein, who has been reviewing the plans and cost estimates, told the council during that meeting last week that he believed “prudent alternatives” to the proposed design exist and could result in important cost savings. He suggested city staff review these potential savings and report back to the council before the plant’s final design is approved sometime this summer.
A secondary review of Bolton & Menk’s design and cost, published last summer by Snyder & Associates of Ankeny, who the city retains as general civil engineering consultants, contains hints as to where these cost savings might come from. It concluded as much as $6.6 million might be saved if certain design modifications are adopted. More savings might be available if the city chooses to make further upgrades to the current wastewater plant, or to build the new plant in phases.
The plant’s operating system will be some variation of activated sludge technology, the most widely used method of treating wastewater in the world. Plants of this type have been in use for more than 100 years.
Two particular variations of activated sludge seem to be the finalists for Webster City’s plant: the University of Cape Town — UCT — process, and the Sequencing Batch Reactor — SBR — process.
Of the two, the SBR plant should cost less to build.
The Snyder & Associates report listed 10 Iowa cities using SBR technology for either municipal or industrial wastewater treatment: Marshalltown, North Liberty, Mount Pleasant, Clear Lake, Washington, Atlantic, Oelwein, Eldridge, Clarinda and Oakland.
The Snyder report continued: “It is certain several cost savings ideas may be available, but not all may be practical for one reason or another. The treatment system recommended in the facility plan is certainly capable of meeting current DNR (Department of Natural Resources) requirements.
“Changes to the plan to reduce cost will require difficult decisions. Those decisions could include modifications, ranging from constructing all or part of the proposed improvements on the existing WWTP site (author’s note: On East Ohio Street near the leaf and brush dump site); modifying the city’s growth projections, which would change the anticipated flows and loads; considering another type of treatment process; and/or changing the approach to biosolids management.”
Decisions affecting large capital projects like this are said to have “50-year consequences.” Indeed, the present wastewater treatment plant, built in 1939, expanded and upgraded five times since, has been in service 85 years. In periods of wet weather, the plant has operated beyond its rated capacity, a situation that could, in the future, lead to a major spill of wastewater into the Boone River and a key reason for replacing it.
Two key determinants in the plant’s ultimate size and capability are population growth and demand for wastewater service by present-day and future industries.
When population projections were prepared for the city in 2016, there was a strong possibility the Prestage pork processing plant would be built near Webster City. Taking this into consideration, the population growth model used projected the city’s population would reach 11,609 by 2040, an annual growth rate of 2.4%
History has shown that reality is dramatically different.
Prestage selected a site south of Eagle Grove. Webster City’s actual population in 2015 was 7,825. At present growth rates, the city will have only 7,869 residents in 2040, a growth rate of 0.56% per year.
In theory, this means a smaller, less costly plant is now a viable option.
Another opportunity for reducing the facility’s initial cost is to build it in phases with options for expansion due to unexpected population growth or industrial demand.
A key feature of the Bolton & Menk $78 million plan is two 18-inch “force mains,” (pipelines with powerful pumps to move waste water from the present plant site to the proposed new plant site in the industrial park).
Snyder concluded building one force main now, with provisions for a second later — if required — would save a substantial sum. It cited successful phased construction of a wastewater plant in Coralville, one of Iowa’s fastest-growing cities, as an approach Webster City should consider.
The plant design and size ultimately selected must meet the DNR’s guidelines for phosphorus and nitrogen removal.
Work by Iowa State University, the DNR, and the Iowa Department of Agriculture in 2012 established these standards, today known as the Iowa Nutrient Reduction Strategy. It’s Iowa’s contribution to reducing growth of the “dead zone” in the Gulf of Mexico caused by runoff of phosphorus and nitrogen (the nutrients) from farm fields, lawns, and sewage and wastewater treatment plants in states bordering the Mississippi River
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