Water pumped from the deep sandstone aquifer in Southeastern Wisconsin usually contains radium. This radionuclide occurs naturally. People drinking water containing a high concentration of radium are at increased risk of developing bone cancer. The maximum allowable concentration of radium in drinking water is 5 picocuries/liter.

A number of treatment techniques can be used to remove radium. A technique Ruekert & Mielke, Inc. (R/M) has found to be economical is the addition of hydrous manganese oxide (HMO) followed by conventional filtration. HMO can be purchased outright or can be produced on site by the reaction of other chemicals. HMO takes the form of a slurry of fine black particles which are kept in suspension by continuous mixing. When added to water containing radium, the radium sticks to the HMO particles. The HMO particles are subsequently removed by a conventional sand and/or anthracite filter.

HMO Filtration Diagram Graphic.jpg

Well 5 located in the Village of Pewaukee was first placed in service in 1997 but taken off line in 2006 because the radium concentration exceeded the allowable limit. In 2015, R/M was hired by the Village to design a treatment system which included HMO addition followed by filtration. A free-standing building was constructed to house the needed equipment. The filter is a 25-foot long by 8-foot in diameter pressure vessel and is designed to handle the well pump discharge rate of 550 gpm. HMO slurry is added upstream of the filter. The media in the filter is 18 inches of sand topped by 12 inches of anthracite.


All filters must be backwashed periodically to remove material accumulated on and in the media. Backwashing is accomplished at Well 5 in Pewaukee by flowing a mixture of air and water backwards through the media. The air and water combination suspends and agitates the media to effectively remove the HMO particles and any other material trapped by the media. The backwash wastewater is discharged to the sanitary sewer.

Other than keeping the chemical tanks full, the HMO/filtration system at Pewaukee requires little maintenance. Backwashing proceeds automatically at the push of a button. An added benefit of this treatment method is the removal of any iron in the water.

Since becoming operational in spring of 2016, all samples collected at Well 5 have been in compliance with the radium standard. The radium concentration in the most recent sample was below the limit of detection.

For assistance with groundwater treatment, contact an expert at R/M today.

About the Author

Daniel R. Butler, P.E.

Daniel R. Butler, P.E. 
Senior Project Manager

Dan has been with Ruekert & Mielke, Inc. (R/M) since 1978. Dan’s expertise in water supply projects is based upon many years of experience involving nearly every community in southeastern Wisconsin. He has worked as a design engineer and a project engineer on a wide variety of water supply projects, including planning studies, well siting studies, well construction, pumping stations, storage facilities, control systems, distribution system modeling and water treatment facilities.

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