The City of Bismarck currently operates a conventional water supply intake on the Missouri River for its 30 MGD Water Treatment Facility (WTP). In 1997 the City of Bismarck retained AE2S to update the WTP master plan and pursuant to the recommendations in the plan update, the City hired AE2S to complete an investigation into the viability of using horizontal collector well technology as a reliable water supply alternative. A four phase study was completed to determine if a horizontal collector well was a feasible alternative for the Bismarck WTP raw water intake. At the conclusion of the study, the results showed that a horizontal collector well was a viable solution, and the City obtained the services of AE2S to move forward with the design of the new intake.
AE2S followed a phased approach for design of the HCW system. The project was separated into three components; Phase I consists of the collector caisson and lateral wells, Phase II is the raw water transmission line from the well to the WTP, and Phase III includes the pumping station at the well.
The construction of Phase I began in June 2009 and substantial completion was in October 2010. The 20-foot diameter well extends 92 feet below the surface. Approximately 2,500 linear feet of 12-inch stainless steel horizontal screen was installed. The well has a capacity of 34 MGD and water quality within expected parameters.
Having determined the actual well yield and water quality, the City directed AE2S to complete design on Phase II and Phase III of the project. Phase II will consist of 5,200 linear feet of 36” raw water pipeline and 2,300 linear feet of 24-inch watermain. The transmission line will be constructed using fused high density polyethylene (HDPE) pipe and ductile iron pipe (DIP). The Phase III pumping facility will be situated directly on the well caisson. Pumping will be accomplished using a series of four pumps capable of pumping from 4 million to 34 million gallons per day. Both phases were delayed due to the flooding in 2011 and began in the spring of 2012.
The successful implementation of the horizontal well technology will eliminate variations in the raw water quality and the future need for expanded pretreatment at the Bismarck WTP. In addition, the horizontal collector well will also provide regulatory benefits that may be secured in the form of "riverbank" to provide removal credits for water borne micro-organism such as cryptosporidium.