Surface Waters Assessed for Chloride [Minnesota]
Minnesota Pollution Control Agency (MPCA) · 2025 Full Details
Full Details
- Title
- Surface Waters Assessed for Chloride [Minnesota]
- Description
- The MPCA and its partners systematically evaluate waters in each major watershed in Minnesota every 10 years. This process begins with comprehensive lake and stream water quality and biological monitoring. Once completed, the MPCA and its partners assess the monitoring data to determine if the water bodies meet state water quality standards. Protection of “aquatic life” with applicable Class 2 chronic standards means protection of the aquatic community from the direct harmful effects of toxic substances, and protection of human and wildlife consumers of fish or other aquatic organisms. Chloride is a toxic pollutant and has an aquatic life toxicity-based chronic standard. This data set includes a subset of the waterways and waterbodies in Minnesota which have gone through MPCA’s surface water quality assessment process and have been assessed for chloride and information about: <ul><li> the impairment status (in regard to the beneficial use of Class 2 (Aquatic life and recreation)) where the chloride parameter was indicated to be not-supporting, regardless of report cycle (assessment year)</li><li>the parameter judgement code associated with the most recent (to that WID) assessment (for the chloride parameter)</li><li>the chloride “Risk Status” (as defined by the Smart Salting Team), where a WID would be identified as “high-risk” due to having results (used in the most recent assessment) which have a concentration of 120 mg/L or greater of chloride.</li></ul> <b>Background</b> The federal Clean Water Act requires states to designate beneficial uses for all waters and develop water quality standards to protect each use. Beneficial uses identify how people, aquatic communities, and wildlife use water. Water quality standards specify the conditions water must meet to protect those specific uses. Measuring lakes and rivers against water quality standards shows which bodies of water need restoration and protection and dictates limits on pollutant discharges from public and private facilities. In Minnesota, the MPCA is charged under both federal and state law with the responsibility of protecting the Minnesota’s water quality. Surface waters (lakes, wetlands, rivers and streams) provide multiple beneficial uses, and so are assigned multiple designated use classes. Chloride is used for assessing the aquatic life beneficial use (Class 2 – Aquatic life and recreation). This use protects ecosystems, habitats, and aquatic biota including fish, insects, mollusks, crustaceans, plans, microscopic organisms, and all other aquatic-dependent organisms and protects recreational uses such as swimming, fishing, hunting, and boating. Minnesota water quality standards protect lakes and streams by defining how much of a pollutant such as bacteria or nutrients can be in the water and allow it to still provide beneficial uses. A surface water is considered to be ‘impaired’ if the extent of its exceedances of applicable water quality standards are more than the levels spelled out in the MPCA Assessment Guidance Manual. This manual is updated every two years in conjunction with the update of the Impaired Waters List. The manual is available on the MPCA’s public website: https://www.pca.state.mn.us/sites/default/files/wq-iw1-04m.pdf If the waters are not meeting their intended beneficial use, they are placed on the impaired waters list (IWL) for detailed tracking of future improvements. Being placed on this list also helps prioritize writing of restoration plans and/or total maximum daily load (TMDL) studies, which aid in mitigation of the pollutants in the waterbodies to bring them once again into a clean water state to meet their intended use. <b>Monitoring strategy</b> Prior to 2008, the monitoring and assessments of waters within state boundaries was minimal. After receiving clean water funds, many more sites were able to be added to the monitoring program. The large increase of data made it impractical to conduct assessments of the entire state’s water quality data annually. Therefore, a watershed approach was created where watersheds were designated a rotational schedule and data from those watersheds are now collected and assessed only once every 10 years. This allows for extensive monitoring to be conducted on waterbodies across the state, and staff to not be overwhelmed with annual assessments. This approach is now called the watershed approach, or the intensive watershed monitoring approach. The MPCA’s primary monitoring activities are organized around Minnesota’s 80 major watersheds. The watershed monitoring approach involves intensive monitoring for conventional pollutants on a subset of major watersheds every year. The MPCA has implemented a schedule for intensively monitoring each major watershed once every 10 years. These monitoring activities result in the identification of waters that are impaired and need restoration, as well as waters that need continued protection to prevent impairment. Assessments are conducted annually in spring, utilizing the previous 10 years of data. The MPCA assessment guidance manual details the procedures and methods MPCA uses to determine if waters are placed on the impaired waters list. Every two years the watershed and statewide assessment results are packaged together into the Impaired Waters List and Integrated Report and submitted to the EPA. Assessment decisions are publicly available via the EPA’s How’s My Waterway (https://mywaterway.epa.gov/), the Minnesota impaired waters list (https://www.pca.state.mn.us/air-water-land-climate/minnesotas-impaired-waters-list), or via MPCA data request. <b>Water quality assessment</b> Surface waters are assessed to determine if they are of a quality needed to support the aquatic community that would be found in the water body under natural conditions. Assessments for aquatic life utilize both water chemistry data and biological data. Technical experts doing the assessments use the assessment database and consider data quality. A key step in the assessment process is to determine if individual parameters meet or exceed their criteria (numeric or narrative standards) or have insufficient data to make that determination. In addition to this comparison against standards, the assessor also makes a determination of the confidence of the parameter assessment, assigning a low, medium, or high-quality rating. For some parameters, the parameter-level evaluation is equivalent to the final use assessment decision (e.g., E. coli bacteria). For other parameters (e.g., biota), the parameter-level evaluations are then used in conjunction with supporting data, including consideration of dataset quality, to make a final determination if a waterbody is meeting its designated use or is considered impaired. Assessors must determine if the water body is not meeting its beneficial use and is considered as having an impaired condition. Any waters determined to have an impaired condition will then be placed on the impaired waters list. However, this is more complex and requires more data reviews than simply analyzing if individual parameter readings are above or below a numerical standard. For example, there needs to be determination on how many exceedances of the standard from individual samples are required in order to label something as impaired. Also, if any of those exceedances can be considered a result of natural weather or habitat conditions, that exceedance may be ruled out as data usable to make an impaired determination since that exceedance is naturally occurring and not anthropogenic. See the MPCA assessment guidance manual to see a detailed break-down how assessors determine if a parameter is exceeding the standard, as well as how to determine if there are enough measurements of that parameter exceeding the standard to count a waterbody as impaired. All assessments are subject to review by a team of professional water quality experts. Review of the data by professionals is an important part of minimizing erroneous impairment determinations and is required whether statistical tests of data uncertainty are used or not. <b>Chloride assessments</b> The MPCA uses data collected over the most recent 10-year period for all the water quality assessments. This period is long enough to provide reasonable assurance that the data have been collected over a range of weather and flow conditions and that all seasons are adequately represented. From a practical standpoint, the ten-year period means there is a better chance of meeting the minimum data requirements for each parameter. A full ten years of data are not required to make an assessment. Protection of “aquatic life” with applicable Class 2 chronic standards means protection of the aquatic community from the direct harmful effects of toxic substances, and protection of human and wildlife consumers of fish or other aquatic organisms. Chloride is a toxic pollutant and has an aquatic life toxicity-based chronic standard. These numeric standards are applied based on a four-day average concentration for the chronic standard (230 mg/L of chloride). Chloride is assessed at a parameter level but if a waterbody exceeds the standard, the parameter-level evaluation can be equivalent to the final use assessments. The necessary number and type of samples can vary considerably from one situation to another and the determination of adequacy for the purpose of assessment will necessarily involve considerable professional judgment. It should benoted that because impairment can result from only one or two exceedances, a designation of meeting the standard generally requires extensive monitoring during times when exceedances are most likely to occur. <b>Chloride assessment of streams</b> When concentrations are judged to be relatively stable over the four-day period in question, single samples can be sufficient. If more than one sample is taken within a four-day period the values are averaged as a mean, and the four-day average is counted as one value in the assessment. This includes multiple samples in four days at one station or multiple stations along an WID. Because the chronic standards are expressed as four-day averages, care must be taken to ensure that the water quality measurements used in assessments provide an adequate representation of pollutant concentrations over the relevant time period. When concentrations are more variable, multiple samples or time-weighted composite samples are can be used in order to calculate a sufficiently accurate average concentration. Flow-weighted composite samples are taken with the purpose of calculating average concentrations by volume rather than by time. As flow-weighted composite samples can be very difficult to interpret in assessment contexts they are not used. <b>Chloride assessment of lakes and wetlands </b> For lakes, depth of sample must be taken into consideration, as concentrations may change with depth (i.e., chloride often increases with depth). Within the four-day period, samples will typically be averaged as follows: those samples collected at depths of 2 meters or less (including both grab samples and 0 - 2 meter integrated samples), those at maximum depth (defined as the deepest two meters of the water column), and the mid-depth values (taken between 2 meters from the surface and the maximum depth). As with flowing waters, this averaging applies to both samples at a single station or samples collected at multiple stations along the WID. Each depth will be compared against the chronic standard. If any four-day average, regardless of depth, exceeds the chronic standard, it counts as a single exceedance for the water body (e.g., the surface average may meet the standard, while the average at 12 meters may exceed the standard – for that four-day period, a single exceedance will be counted). , These data are intended to be used for planning, informational, and cartographic purposes related to general high-level information about the most recent assessment cycle for chloride in surface waters. These data can be used to aid prioritization efforts and inform both interagency and public inquiries as it relates to chloride in surface waters, in the context of the MPCA’s surface water monitoring and assessment efforts. , The dataset itself represents data from the most recent assessment cycle, however the currentness reference refers to the date on which the dataset was last updated on the Minnesota Geospatial Commons.
- Creator
- Minnesota Pollution Control Agency (MPCA)
- Temporal Coverage
- 2025-01-03
- Rights
- None
- Access Rights
- Public
- Format
- Files
- Language
- English
- Date Added
- January 24, 2025
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Citation
Minnesota Pollution Control Agency (MPCA) (n.d.). Surface Waters Assessed for Chloride [Minnesota]. . https://gisdata.mn.gov/dataset/e082d8bc-195e-40eb-bc9a-f9601b577df8 (dataset) -
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