Spent Lime Treatment System for Wakefield Lake

Wakefield Lake is in the Ramsey-Washington Metro Watershed District (RWMWD) and is impaired for excess phosphorus. Through the Wakefield Lake TMDL process, implementation activities have been identified which include partnerships with the City of Maplewood to install BMPs in the watershed to directly benefit Wakefield Lake. RWMWD has researched, monitored and field tested the use of spent lime for stormwater quality treatment. Spent lime consists of calcium and carbonate and is a byproduct of the drinking water treatment process that has properties that allow it to bind with dissolved phosphorus. When water containing dissolved phosphorus contacts the lime material, calcium from the lime binds with the phosphorus and forms calcium phosphate which is a solid material and does not dissolve in the storm water, thus remaining within the treatment system. Although this is still an emerging concept, three years of monitoring a test spent lime system has shown promising results for the removal of both total and dissolved phosphorus. Total phosphorus removal through the system is approximately 60% and total dissolved phosphorus removal is approximately 70%. With the help of this grant source, RWMWD hopes to install a full scale spent lime filtration system on a City of Maplewood owned lot just upstream of Wakefield Lake at the southwest corner of Frost Avenue and Kennard Street to treat stormwater flow before it reaches the lake. This treatment system will achieve nearly 50% of the needed phosphorus external load reductions to Wakefield Lake as identified in the TMDL. This is great news not only for the very popular Wakefield Lake and the visitors to the adjacent park system but also to its big brother, Lake Phalen, to which Wakefield Lake drains before it heads to the Mississippi River.