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water quality monitoring of suburban lake

water quality monitoring of suburban lake
client
Ramsey-Washington Metro Watershed District
location
Minnesota

phosphorus removal improves lake water quality

Barr was hired to diagnose and treat water quality problems at Tanners Lake in Washington County, Minnesota. The lake experienced dense algal blooms and low clarity during the summer months. To identify the source of the problem, we monitored all inflow points to measure the volume of water and quantity of phosphorus entering the lake and then completed watershed and in-lake modeling to determine the sources.

Our modeling indicated that the problems were caused by pollutants in stormwater runoff, and that nearly two-thirds of the watershed phosphorus load was conveyed by a stream entering the lake on its north side. To remove phosphorus before it entered the lake, Barr designed and constructed an inflow alum treatment facility, treatment ponds, an upgrade to an existing pond, and an infiltration basin.

Ongoing monitoring has indicated that the lake’s phosphorus load has been reduced by about half while water clarity doubled. In 2011, it was estimated that about 75 percent of the phosphorus entering the treatment facility had been removed.