Shields Lake Stormwater Harvest, Irrigation Reuse, and Alum Treatment Project
Project Description & Outcomes
Phase 1 of this project entailed harvesting water runoff from 294 acres, west-southwest of Shields Lake, for irrigation reuse by Forest Hills Golf Course. This process naturally filters out the phosphorus from the water before it enters the lake. Phase 2 of the project entailed a whole-lake alum treatment to Shields Lake which addressed the high levels of phosphorus already present in the lake.
The entire project has brought Shields Lake to a clear water state, and reduced phosphorus loads to Forest Lake by over 500 pounds per year. Additionally, the irrigation reuse system has reduced the need for groundwater pumping by up to 26 million gallons per year!
The Watershed District received a grant for this project in the amount of $824,000 from the Clean Water Fund (CWF), and it would not be possible without our partners at Forest Hills Golf Club.
Project Status
Complete
Project Outcomes
1,000 lbs/yr phosphorus reduction to Shields Lake
500 lbs/yr phosphorus reduction to Forest Lake
26,000,000 gallons/yr groundwater usage reduction
Financials
Clean Water Fund Grant: $824,000
CLFLWD Grant Match: $206,000
Total Project Budget : $1,030,000
Lifecycle cost:
$57 per pound of phosphorus removed
Timeline
2018-2019: Stormwater harvest irrigation reuse
Fall 2019: Whole-lake alum treatment part 1
Fall 2020: Whole-lake alum treatment part 2
Project Partners
Project FAQ
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.
This project was identified as part of the Shields Lake Diagnostic Study.
Information Sessions
Saturday, August 26th | Information Session
Saturday, July 15th | Information Session
Thursday, June 29th | Information Session
Saturday, June 24th | Information Session
Tuesday, June 20th | Forest Lake City Council Meeting
Wednesday, May 17th | Forest Lake Lake Association Annual Meeting
Thursday, May 11th | Project Public Hearing (Watch the recording on YouTube!)
Unable to attend an info session? District staff will be at Forest Lake’s Arts in the Park every Tuesday this summer to answer questions and lead family-friendly water quality activities. Look for the District booth on the north side of the park near the boat launch.
