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Water Tank Addition

Client: City of O’Fallon

Location: O’Fallon, Missouri

The City of O’Fallon owns and operates an MDNR-permitted public water supply that includes a 6-million-gallon-per-day treatment plant, distribution system, and water storage facilities. The City recognized that the water system needed additional finished water storage and retained Donohue to evaluate the best means of providing ground level storage. 

Donohue prepared a preliminary study that evaluated two candidate tank sites and investigated tank volumes and types. The study was completed in less than 60 days and concluded that a 2-million-gallon pre-cast, pre-stressed concrete tank located at the water treatment plant site was the most viable option. This approach had the benefit of giving the operations staff a nearby place to store finished water after production, allowing the City to produce most of the water needed daily during first shift, saving the cost of night-time production.

 The tank design included a passive mixing system within the tank consisting of a series of inlets fitted with “duckbill” type check valves. This mixing system helps ensure that the tank’s contents are well-mixed, resulting in reduced sweating of the tank contents during the summer months. To further enhance the plant’s reliability and to help the plant meet daytime demands, the project added a fourth variable speed high service pump to its high service system. This addition allows operations staff to more closely match plant production with hourly demand fluctuations. 

Donohue completed the final design within three months.