5.8.10 Taft-Legion Lake Regional Volume and Load Reduction

Project

Taft-Legion Lake Regional Volume and Load Reduction

Description

The City of Richfield proposed the collaborative implementation of an improvement project  that, when completed, will provide treatment for urban stormwater runoff discharging into Taft Lake and Legion Lake, subsequently improving the quality of water discharged from the City of Richfield’s boundaries to Lake Nokomis and ultimately Minnehaha Creek.

 

Project plans include several different elements working in combination to achieve water-quality and volume-management improvements. Elements under consideration include:

 

Irrigation:    Stormwater runoff will be withdrawn from stormwater basins and applied via irrigation to adjacent park land at Legion and/or Taft Lakes.

 

Infiltration:  The infiltration system will operate concurrent with the proposed irrigation system.  Depending on seasonal rainfall variation, if additional water is available to be withdrawn from the enhanced basins/ponds, water will be directed to underground infiltration systems in park land surrounding Taft Lake and Legion Lake.

 

Flocculation Enhanced Stormwater Pond:  An existing road around the north end of Taft Lake will be removed to facilitate the construction of a stormwater pond with a flocculation system that will remove dissolved pollutants from storm sewer runoff that’s delivered to the system.

 

Flocculation of Water from Taft Lake:  In addition to treating runoff delivered to a constructed stormwater pond on the north side of Taft Lake the flocculation system will have the capacity to treat water withdrawn from adjacent stormwater ponds and/or the hypolimnion of Taft Lake, removing dissolved pollutant loads, before it’s discharged back into Taft Lake.

 

Natively Planted Lakeshore Buffers:  Native lakeshore buffers will be established in select areas surrounding Legion Lake.

 

Pre-Treatment of Runoff to Legion Lake:  A series of sedimentation ponds and/or enhanced grit-removal chambers will be installed to remove sediment and phosphorus loads prior to being discharged into Legion Lake.

 

Stakeholder engagement and educational efforts: Efforts to develop a comprehensive outreach, education and stakeholder engagement plan will be integrated into the design of each element of the project, and communications tools will be used to support citizens’ understanding of the purpose and function of the project. 

Need

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Implementation of this project will address several goals of the 2007 MCWD Comprehensive Water Resource Management Plan and enable the City of Richfield to meet its various obligations to reduce annual stormwater volumes and pollutant loads.

 

MCWD goals addressed include: 

 

MCWD Goal 1: Abstraction/Filtration.  Promote abstraction and filtration of surface water where feasible for the purposes of improving water quality and increasing groundwater recharge throughout the watershed.

 

MCWD Goal 2: Ecological Integrity.  Promote activities that maintain, support and enhance floral, faunal quantity and ecological integrity of upland and aquatic resources throughout the watershed.

 

MCWD Goal 3.  Water Quality.  Preserve, maintain and improve aesthetic, physical, chemical and biological composition of surface waters and groundwater within the District

 

MCWD Goal 5.  Water Quantity.  Maintain or reduce existing flows from drainage within the watershed to decrease the negative effects of stormwater runoff and bounce from existing and proposed development as well as provide low flow augmentation to surface waters.

 

MCWD Goal 6.  Shorelines and Streambanks.  Preserve the natural appearance of shoreline areas.

 

MCWD Goal 9.  Education and Communications.  Enhance public participation and knowledge regarding District activities and provide informational and educational material to municipalities, community groups, businesses, schools, developers, contractors and individuals.

 

Implementation of the various project elements also is expected to address the impairment of Lake Nokomis by excessive nutrients, as described in the Total Maximum Daily Load study for the lake.  The study determined that annual phosphorus loading to the lake from stormwater runoff generated by the City of Richfield and the Metropolitan Airports Commission must be reduced by 16 pounds.

Outcome

This project is designed and intended to provide both volume and phosphorus load reductions as shown in the table below:

 

Project Element 

Water Volume Reduction (ac-ft/yr) 

P Load Reduction (lbs/yr) 

Water Reuse Irrigation System (Legion Lake)

10-40

12-50

Stormwater Infiltration (Legion/Taft Lake) and Ponding (Taft)

120-240

125-240

Mechanical Grit Chambers (Legion)

-

0-24

Native Lakeshore Buffer (Legion)

minor

2-8

Flocculation System (Taft)

-

40-160

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Estimated

Cost

 

 

Project Element 

 Estimated Capital Cost  

Water Reuse Irrigation System (Legion Lake)

 $                                        300,000

Stormwater Reuse Infiltration (Legion/Taft Lake) and Ponding (Taft)

 $                                    1,140,000

Proprietary Grit Chambers (Legion)

 $                                        300,000

Native Lakeshore Buffer (Legion)

 $                                          60,000

Flocculation System (Taft)

 $                                        900,000

TOTAL CAPITAL COST 

 $                                    2,700,000

Annual Operation, Maintenance and Monitoring

 $                                        150,000

TOTAL O&M Cost (20 year life) 

 $                                    3,000,000

 

To avoid or minimize a levy increase, if the project is ordered, consideration will be given to funding the $2,700,000 necessary for construction through a combination of upfront city financing of capital costs and a reduced, recurring annual District ad valorem levy over 20 years.  Other alternative frameworks and sources of funding, such as grants, also will be considered.

 

$2,700,000

 

 

 

Schedule

Implementation between 2012 - 2013