Forest Lake Alum Treatment

Project Description & Outcomes

The first phase of the Forest Lake Alum Treatment was completed during the week of September 25th to 29th, 2023. The District will monitor project effectiveness in 2024 in order to determine alum dosing requirements for a second alum application in 2025.

The Forest Lake Alum Treatment Project is a milestone project in achieving Forest Lake’s water quality goals. The Comfort Lake-Forest Lake Watershed District has worked with many partners to construct water quality projects for more than a decade. With the critical support of the City of Forest Lake and the Forest Lake Lake Association, these projects have led to a significant decline in phosphorus entering the lake. The watershed district targets phosphorus, because in excess amounts, it causes algae blooms and lowers water quality. Less phosphorus is entering the lake, but a project is needed to address the phosphorus that is already in the water.

The lake is treated with alum which binds to phosphorus and makes it unavailable for algae growth. Alum is a non-toxic water quality treatment that will result in a cleaner and clearer Forest Lake.

The alum treatment took place in September 2023. The Watershed District will monitor the lake after the treatment to measure success and determine if a second application is needed in 2025.

Public Hearing Presentation

Alum Treatment Video

FAQ

Project Status

In-Progress

Project Outcomes

527 lbs/yr phosphorus removal

Financials

Clean Water Fund Grants: $533,600

CLFLWD Grant Match: $133,400

Total Project Budget : $667,000

Lifecycle cost:
$100 per pound of phosphorus removed
(What does this mean?)

Timeline

Fall 2023: Alum application #1

2024: Effectiveness Monitoring

Fall 2025: Potential alum application #2

Project FAQ

What is an alum treatment?

Alum (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 applied to a lake by a specialized service provider, liquid alum forms a white, cotton-ball looking substance called flock. The flock sinks to the bottom of the lake and forms a one-inch thick layer on the bottom. The alum flock attracts and binds phosphorus in the water. 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. The watershed district targets phosphorus, because in excess amounts, it causes algae blooms and lowers water quality.

Why are we conducting an alum treatment on Forest Lake

The CLFLWD has worked with many partners to construct water quality projects for more than a decade. These projects have led to a significant decline in phosphorus entering the lake. While less phosphorus is entering the lake, a project is still needed to address the phosphorus that is already in the water. Alum treatments specifically address the phosphorus that is already in the water and as such are often the final step in a multi-year effort to reduce phosphorus in our lakes. The CLFLWD has performed alum treatments on both Shields Lake and Moody Lake.

Are alum treatments safe for people, pets, and wildlife?

Yes. Alum is a non-toxic water quality treatment that has been used to improve lake water quality for decades. District staff and engineers will be actively monitoring the lake during the application to ensure the proper dosing is being applied and that the pH of the water remains stable.

Read the alum treatment FAQ sheet for answers to more commonly asked questions

Information Sessions

Past Info 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!)

Arts in the Park

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.

Project Description & Outcomes

Project Status

Project Outcomes

Financials

Timeline

Project FAQ

Information Sessions

Project Partners

Project Gallery (photos from Moody & Shields)