Carnelian-Marine-St. Croix breaks ground on major Clean Water Project with big benefits for Sand Lake

On January 12, the Carnelian-Marine-St. Croix Watershed District broke ground on a major project to improve water quality in Sand Lake in Scandia. The district will be installing an iron-enhanced sand filter in a wetland on the northeast corner of Sand Lake to prevent approximately 80 pounds of phosphorus per year from entering the lake. This project will meet 100% of the pollution reduction goal established by the Minnesota Pollution Control Agency (MPCA) and the Watershed District to ensure a healthy aquatic ecosystem and clean, clear water for people who swim, fish and boat on the lake. A $77,000 Clean Water Partnership grant from the MPCA will pay for approximately half of the $164,599 project, with Carnelian-Marine-St. Croix Watershed District covering the rest of the cost.

CMSCWD manages water resources in northeastern Washington County.
CMSCWD manages water resources in northeastern Washington County.

Work to improve water quality in Sand Lake began in 2008, when the lake was temporarily added to the state’s impaired waters list for failing to meet standards for phosphorus, chlorophyll a (an indicator of algae growth), and water clarity. Two years later, the lake was removed from the list when the MPCA revised their standards for shallow lakes. Nonetheless, the Watershed District and local homeowners wanted to see fewer noxious algal blooms and also to protect Sand Lake from future water quality problems. The district engineering firm, Emmons & Olivier Resources, Inc. (EOR), conducted a diagnostic study and created an implementation plan in 2013, which identified several potential projects that could help keep phosphorus out of Sand Lake. After review, the iron-enhanced sand filter quickly became the obvious choice. This one project will treat 90% of the drainage area to Sand Lake, with the exception of the Hay Lake overflow, and will remove twice as much phosphorus as all the other possible projects combined.

Iron-sand filtration is a relatively new technology that works thanks to a chemical process in which phosphorus molecules in water bind to iron in a sand filter as water passes through. Iron-sand filters are able to pull dissolved phosphorus out of water, making them unique compared with other practices like stormwater ponds and sediment basins that can only catch phosphorus attached to sediment. The project on Sand Lake will be entirely gravity-fed, meaning there will be no pumps or electricity required to move water through the filter. Currently, a ditch system transports water and runoff into Sand Lake from land almost as far north as the Wayne Erickson Memorial Ball Park. The water contains high levels of phosphorus, which feeds algae in the lake during the summer. For the project, the District will be installing a weir structure near the end of the ditch, which will back water up into a nearby wetland. From there, the water will flow downhill through the iron-sand filter for additional treatment. During high-flow events, such as after a large rainstorm, water will continue to flow over the weir and into Sand Lake, so the system will not create a flooding risk. Peterson Companies from Wyoming, MN is doing the excavation and construction work and anticipates the project will be done by the first week of February.

There has been strong public support for the Sand Lake Clean Water project since the beginning, with dozens of area residents attending Watershed District meetings and sharing their local knowledge with the Watershed District and EOR staff. The Lindgren family, who owns the land where the project is being installed, have been supportive as well. The Lindgren’s have owned land along Sand Lake since farm-steading the property more than 100 years ago and Dean Lindgren was one of the founding members of the Marine Watershed Management Organization, serving on the board of directors for more than 20 years. The Sand Lake Clean Water Project is a fitting tribute to a man who worked hard for so many years to protect water resources in Scandia and Marine on St. Croix.

To learn more about the Carnelian-Marine-St. Croix Watershed District, visit