Shields Lake Stormwater Harvest, Irrigation Reuse, and Alum Treatment Project

Alum (potassium aluminum sulfate) is a nontoxic compound that many people have in their kitchen cupboard. It is used as an additive in pickling and canning, and used by many municipalities for drinking water clarification. When pumped into a lake by a specialized service provider, liquid alum forms a white, cotton-ball looking substance called flock. The flock then sinks to the bottom of the lake and forms a one-inch thick layer on the bottom. The alum flock attracts phosphorus in the water and has numerous binding sites where the phosphorus can attach. Once it has sunk to the lake bottom, it compresses and creates a seal that prevents phosphorus in the sediment from re-circulating. On average, a typical alum treatment is capable of binding 70-90% of the internal phosphorus load in a lake.

Alum treatments are safe, cost effective, and often the final step in a multi-year effort to reduce phosphorus loads to a lake. The CLFLWD has performed alum treatments on both Shields Lake and Moody Lake.