Early in 2009, the City of Williston recognized the need for additional infrastructure as the new oil boom had begun and started the process of planning for their wastewater collection and treatment system needs. With a huge amount of uncertainty with regard to potential population growth, the City started the planning and design for an expansion of their existing aerated pond system to get them by for the next five years until they could better understand the growth potential in the region. In the spring of 2011, with the aerated pond project out for bid, flooding conditions were experienced all along the Missouri River system causing the water elevation in Williston to come within a foot of topping the Corps of Engineers levee. Due to structural concerns for the levee, the Corps rescinded its decision of an easement swap with the City that would have allowed the expansion of the aerated ponds. Caught between a rock and a hard place, the City immediately began planning for a new mechanical wastewater treatment facility to meet their long-term needs. With growth happening rapidly and more confidence in the long-term viability of “the boom,” the City embarked on a planning effort that would take the current “pond” design population of 15,000 to an ultimate population of 120,000. The first phase of the new WRRF accommodates a population equivalent to 60,000 with an average design flow of 6 million gallons per day (MGD) and a peak hour flow of 12 MGD. The WRRF site and facilities have been planned for expansion to meet an ultimate 12 MGD average and 24 MGD peak flow.
In August 2013, the design of the WRRF was initiated. Key project components of the first phase of the WRRF include new preliminary treatment building (influent pumping, fine screening, grit removal, septage receiving); biological nutrient removal (BNR) extended aeration activated sludge biological treatment with two three-stage oxidation ditches, two final clarifiers, return activated sludge building, and chemical feed tanks and equipment; tertiary filtration building (cloth media filtration, ultraviolet disinfection, effluent aeration, effluent pumping); sludge digestion building (waste activated sludge storage, gravity belt thickening, polymer feed system, ATAD digestion); dewatering building (polymer feed system, conditioning feed system, screw press dewatering, cake conveyance and storage system); and cake storage facilities. Construction was started in August 2014, and fully operational by July 2017. Due to the great need to get some form of treatment online at an earlier date, AE2S helped phase multiple interim completion milestones to bring one train of the activated sludge system online in September 2015. The phasing provided the City of Williston the flexibility to treat up to 2.0 MGD until the rest of the project was completed and meet effluent limits early during construction.