The applicable water quality standards for the TCMA lakes, wetlands, and streams are included in Minn. R. ch. 7050. The lakes, streams and wetlands listed as impaired for chloride are classified as 2B for protection of cool and warm water sport fish and 3C waters for protection of industrial consumption. Minn. R. 7050.0222 and 7050.0223 define the aquatic life and recreation and industrial consumption use classifications:
The chronic standard for chloride to protect for 2B uses is 230 mg/L. The chronic standard is defined in Minn. R. 7050.0218, subp. 3.l., as “the highest water concentration of a toxicant to which organisms can be exposed indefinitely without causing chronic toxicity.” The 230 mg/L value is based on a 4-day exposure of aquatic organisms to chloride. The maximum standard to protect for 2B uses is 860 mg/L. The maximum standard is defined in Minn. R. 7050.0218, subp. 3.T., as “the highest concentration of a toxicant in water to which organisms can be exposed for a brief time with zero to slight mortality.” The 860 mg/L value is based on a 24-hour exposure of aquatic organisms to chloride. These criteria are adopted from the EPA's recommended water quality criteria for chloride. The industrial consumption chloride standard to protect for 3C uses is 250 mg/L.
The MPCA’s approach to determining whether or not a stream, lake or wetland is impaired by chloride is outlined in the MPCA document Guidance Manual for Assessing the Quality of Minnesota Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List (2014). The MPCA conducted an assessment for chloride in the TCMA waterbodies in 2013. Two or more exceedances of the chronic criterion within a three-year period are considered an impairment. One exceedance of the acute criterion is considered an impairment. This TMDL has been developed with the goal of eliminating these exceedances. The chronic standard of 230 mg/L has been applied as the numeric WQT for the chloride TMDLs for all impaired lakes, wetlands and streams.