Wahpeton Elevated Storage Structure

Wahpeton, Iowa | Water

Overview

ISG designed a new water tower to increase the City of Wahpeton's water supply capacity during the summer months while simultaneously meeting chlorine contact time (CT) during high demand. Mixing and recirculation was also evaluated/designed to control the formation of disinfection by-products (DBPs) within the increased volume of the new water tower.


Opportunity

Located near popular West Lake Okoboji, the City struggled to provide consistent water service to its community during the summer months, due largely in part to the municipal water tower’s limited holding capacity of 50,000 gallons. Rather than supplementing water use from another community, the City decided to increase its water storage capacity.

Solution

Located by Iowa’s second largest fresh water source, Lake Okoboji, the City of Wahpeton wanted to increase its water storage during the lake community’s peak season. Rather than supplementing its water use from the nearby City of Milford as it had previously done, the City decided to increase its holding capacity of 50,000 gallons through the design and construction of a new 200,000-gallon water tower.

The increase in storage came with other important design considerations. While having greater storage capacity helps maintain supply during peak months, it also creates new challenges throughout days of relatively lower demand, including the tendency for water to sit stagnant in large towers for longer periods of time before use, which creates the potential for DBPs to form. To account for the swings in water storage and usage and avoid water sitting stagnant in the tower for too long, ISG integrated a Tideflex mixing system with a recirculation pump to create active mixing, rather than passive. Because the City utilizes a surface water treatment system, safe drinking water requires significant direction in chlorine contact time (CT). To help make sure the city satisfied these strict CT requirements, the plant was also revised from a direct filtration facility to a conventional filtration facility.


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