Bass Lake Alum Treatment Facility

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City Project No. 12031

Project Overview
Bass Lake, located south of Bass Lake Road (Co. Rd. 10) and east of Northwest Blvd. (Co. Rd. 61), is a highly valued water resource providing both recreation and aesthetic benefits to City residents. Bass Lake is listed as an impaired water by the State of Minnesota and has an approved Total Maximum Daily Load (TMDL) for phosphorus. The TMDL report indicates a 480 pound reduction in phosphorus loading to Bass Lake is necessary to meet water quality goals and the City of Plymouth is required to make progress toward meeting the water quality goals in the TMDL.

A feasibility study was completed to provide a conceptual analysis of projects which would assist in making progress toward the water quality goal for Bass Lake. Thirty-nine sites were analyzed for potential improvements, which was reduced to several viable alternatives including a combination of smaller water quality ponds and alum treatment. A larger regional water quality pond was preferred; however, a site for a large regional pond could not be identified without the displacement of occupied properties.

An alum treatment facility would pump water from a lake, pond, or wetland where the water would be dosed with alum to bind with phosphorus and the flocculation produced would be discharged to the sanitary sewer. “Clean” water would be discharged back into the waterbody. Facilities of this type work differently than ponds by removing the dissolved fraction of phosphorus from the waterbody where ponds remove the particulate fraction via sedimentation. Approximately ½ of the phosphorus in our environment is in the dissolved state and ½ in the particulate state. Based on the feasibility study it is estimated that 50-80 pounds of phosphorus could be removed annually, thereby assisting the City in making progress toward TMDL goals. A potential location of the treatment facility is adjacent to the Bass Lake Lift Station and would make use of existing infrastructure and technology to the extent practicable.

Derek Asche, Water Resources Manager
Plymouth City Hall | 3400 Plymouth Blvd. | Plymouth, MN 55447-1485
P 763-509-5526 |