TCMA Chloride Management Plan - Appendix A – TCMA Chloride Total Maximum Daily Loads (TMDLs)

Twin Cities Metropolitan Area Chloride Total Maximum Daily Load Study

Project Overview

Purpose

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:

1. Determine the allowable chloride loading to impaired lakes, wetlands and streams in the TCMA;
2. Allocate the allowable loading to the various sources of chloride and establish reasonable and practical expectations for meeting reduction goals; and
3. Provide stakeholders and chloride users with guidance and tools to improve