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The Stevens Point Water Department (SPWD) has a long history of supplying water to its residents, and much of that history has been built on wells constructed by Layne Christensen Co. The last two wells added by SPWD were Ranney collector wells . Collector wells are high-yield water wells consisting of a central concrete caisson with horizontal well screens projecting from the base for water collection. Ranney Collector Wells is a div. of Layne Christensen .
With consistent population growth and no new well capacity since 1995, SPWD recently decided to add a second collector well to meet its goal of increased water supply. What it did not anticipate was that an additional collector well would help Stevens Point tap water to be named the “Best of the Best” in the American Water Works Assn. annual water taste test, held in June 2010. After judging regional winners from across North America, Stevens Point tap water was deemed to have the best flavor, taste and odor characteristics.
Hydrogeologists from Ranney worked with the SPWD consulting engineer, Short Elliott Hendrickson Inc. (SEH), to test a potential collector well location and develop estimates of water yield, resulting in a conceptual design for the collector well. The design process utilized drilling rigs from Layne’s Milwaukee office to install monitoring wells and a test well in order to calculate aquifer parameters for the design calculations.
Based on an acceptable yield estimate and well design, Ranney was awarded the contract for construction of the below-grade portion of the well. The construction process consisted of lowering 16-ft.-diameter reinforced concrete central shafts, or caisson sections, into the ground by washing out the soil underneath and letting them sink below the surface. Caisson sections were lowered to a total depth of more than 100 ft.
At the base of the caisson, Ranney installed and developed eight horizontal laterals into the local sand and gravel aquifer. The laterals are 12 in. in diameter, with a total length of more than 1,200 ft and are constructed of stainless steel well screen and packed in gravel to collect groundwater year round.
Once operational, the well began producing at a rate of over 9,000 gal per minute, or almost 13 million gal per day—more than enough to meet the increased supply goal for Stevens Point—and making the well one of the highest-producing wells in the state of Wisconsin. Drawdown for the well was only 12 ft.
Ranney wells use riverbank filtration , as they draw raw water through the sand and gravel aquifer, removing turbidity and most other contaminants, including surface waterborne organisms. It is during the slow infiltration process that many constituents within the source water are removed by natural filtration through aquifer deposits, typically providing more consistent water quality and water temperature and enabling treatment to be simplified and automated in many cases. All of these factors contributed to producing the “best” tap water in the country.
SEH went on to complete aboveground construction by adding a surface pump house for visual impact, and are in process with a new water treatment plant.
Contributing authors include Matt Reed, Ranney Collector Wells, and Brad Fine, marketing specialist for Layne Christenson Co.