The TCMA includes Anoka, Hennepin, Ramsey, Washington, Carver, Scott, and Dakota counties, 186 cities and townships and a population of approximately 3,000,000 people. It covers approximately 3,000 square miles with about one-third in urbanized areas. The area is fortunate to be home to nearly 1,000 lakes, creeks, and rivers. These water resources hold high value to the community and visitors to the area.
The TCMA receives approximately 54 inches of snow each year on average. The thousands of miles of streets and highways in the TCMA, along with parking lots and sidewalks, must be maintained to provide safe conditions throughout the winter. Winter maintenance of these surfaces currently relies heavily on the use of salt, primarily sodium chloride (NaCl), to prevent ice build-up and remove ice where it has formed. The chemical properties of sodium chloride make it effective at melting ice, but these properties also result in the chloride dissolving in water and persisting in the environment. The dissolved chloride moves with the melted snow and ice, largely during spring warm-ups, and ends up in the nearby lakes, streams, wetlands and groundwater. Residential water softener use is also a significant source of chloride. In areas with high hardness in their water supply, residential water softeners which use salt are common. The chloride from water softeners makes its way to the environment either through discharge to a septic system or by delivery to a municipal WWTP. Chloride is not removed from wastewater using conventional treatment methods.
At levels exceeding the WQS, chloride is toxic to aquatic life. Water samples from lakes, streams, wetlands, and groundwater show an increasing trend in chloride levels in urban areas across the state. Available monitoring data indicates 39 waterbodies in the TCMA currently exceed chloride levels protective of the aquatic community. This trend calls for immediate attention to the issue, the development of a plan to restore waters already impaired, and protection of waters at risk of further degradation.
The goal of this TMDL study is to:
This TCMA Chloride Special Assessment conducted by the MPCA from 2013-2014 includes 39 waterbodies listed as impaired for chloride in the TCMA. Previously, two streams that had been listed as impaired by chloride had TMDLs developed and approved by the United States Environmental Protection Agency (EPA) (Nine Mile Creek and Shingle Creek). The lakes, streams, and wetlands included on the MPCA’s 303(d) list of impaired waters for chloride are shown in the 2014 Twin Cities Metro Chloride Assessment image and listed in the Lakes and wetlands impaired by chloride in the TCMA and Streams impaired by chloride in the TCMA table. High Risk waters are also shown in the 2014 Twin Cities Metro Chloride Assessment image; however, this TMDL has been developed to address only the impaired waters. See the TCMA Chloride Management Plan for protection strategies.
Lakes and wetlands impaired by chloride in the TCMA
Link to this table
|Waterbody Name||Waterbody Description||Year Added to List||Basin||Lake or Wetland AUID (County + Lake)||TMDL Target Start||TMDL Target Completion|
|Kasota Pond North||Wetland||2014||UMiss||62-0280-00||2009||2015|
|Kasota Pond West||Wetland||2014||UMiss||62-0281-00||2009||2015|
|Loring (South Bay)||Lake||2014||UMiss||27-0655-02||2009||2015|
|Wirth||Lake||Proposed 2016 -||UMiss||27-0037-00||2009||2015|
- Recent local water quality data indicates multiple exceedances of the standard. A formal assessment and listing process will be conducted when the data are received. The 2014 list is currently draft and has not yet been approved by EPA.
Streams impaired by chloride in the TCMA
Link to this table
|Waterbody Name||Waterbody Description||Year Added to List||Basin||River AUID||TMDL Target Start||TMDL Target Completion|
|Bass Creek||Unnamed wetland (27-0096-00) to Eagle Cr||2002||UMiss||07010206-784||2009||2015|
|Bassett Creek||Medicine Lk to Mississippi R||2010||UMiss||07010206-538||2009||2015|
|Battle Creek||Battle Creek Lk to Pigs Eye Lk||2008||UMiss||07010206-592||2009||2015|
|Elm Creek||Headwaters (Lk Medina 27-0146-00) to Mississippi R||2014||UMiss||07010206-508||2009||2015|
|Judicial Ditch 2||Headwaters to Sunrise R||2012||StC||07030005-525||2009||2015|
|Minnehaha Creek||Lk Minnetonka to Mississippi R||2008||UMiss||07010206-539||2009||2015|
|Ninemile Creek||Headwaters to Minnesota R||2004||MnR||07020012-518||-||-|
|Raven Stream||E Br Raven Str to Sand Cr||2010||MnR||07020012-716||2009||2015|
|Raven Stream, East Branch||Headwaters (Lk Pepin 40-0028-00) to Raven Str||2010||MnR||07020012-543||2009||2015|
|Rush Creek, South Fork||Unnamed lk (27-0439-00) to Rush Cr||2014||UMiss||07010206-732||2009||2015|
|Sand Creek||Porter Cr to Minnesota R||2014||MnR||07020012-513||2009||2015|
|Sand Creek||T112 R23W S23, south line to Raven Str||2010||MnR||07020012-662||2009||2015|
|Shingle Creek||Headwaters (Eagle Cr /Bass Cr) to Mississippi R||1998||UMiss||07010206-506||- -||- -|
|Unnamed creek||Headwaters to Medicine Lk||2014||UMiss||07010206-526||2009||2015|
|Unnamed creek||Unnamed ditch to wetland||2014||UMiss||07010206-718||2009||015|
|Unnamed creek||Unnamed lk (62-0205-00) to Little Lk Johanna||2014||UMiss||07010206-909||2009||2015|
- TMDL plan approved 2010 – EPA TMDL ID #40253 - - TMDL plan approved 2007 – EPA TMDL ID #32032
The MPCA’s projected schedule for the TMDL completions, as indicated on the 303(d) impaired waters list and the 2014 Twin Cities Metro Chloride Assessment image and listed in the Lakes and wetlands impaired by chloride in the TCMA and Streams impaired by chloride in the TCMA table above, implicitly reflects Minnesota’s priority ranking of this TMDL. Ranking criteria for scheduling TMDL projects include, but are not limited to: impairment impacts on public health and aquatic life; public value of the impaired water resource; likelihood of completing the TMDL in an expedient manner, including a strong base of existing data and restorability of the waterbody; technical capability and willingness locally to assist with the TMDL; and appropriate sequencing of TMDLs within a watershed or basin.