Monitoring Recommendations

Addressing the issue of chloride impacts on the environment in the TCMA is a long-term endeavor and it may take some time before water quality improvements are seen due to historical loadings, groundwater inputs, variable residence times, and other complicating factors. Therefore, continued monitoring of the TCMA lakes, wetlands, and streams for chloride is critical as well as the need to document changes in winter maintenance activities, wastewater source discharges, and water softener usage. Continued water quality monitoring, along with improved understanding of the sources of chloride, will allow adaptive management to take place and inform future steps needed to restore and protect the TCMA waters. The CMP is intended to be revisited within five years and revised based on improved understanding.

The MPCA has worked with the Monitoring Sub-Group to develop monitoring guidelines for lakes, streams, wetlands and storm sewers. Monitoring guidance documents are available on the MPCA Chloride Project website at: Metropolitan Area Chloride Project. The key components of continued monitoring to support the implementation of the CMP include:

  • Collect samples during the critical periods for elevated chloride concentrations: January through May for lakes; and December through April for streams. However, always put safety first when assessing conditions for collection of samples through the ice.
  • Analysis of chloride should also be included in typical summer season sampling. Analysis for chloride is relatively inexpensive and should be included if the effort is being made to collect samples for analysis of other parameters, such as phosphorus.
  • In lakes with potential for stratification, collect a bottom sample and surface sample.
  • Maintain consistency in sampling. Chloride concentrations may vary from year-to-year depending on the winter conditions. Assessment of long-term trends to determine if lakes and streams are improving or degrading will have greater confidence with consistent yearly datasets.
  • Collect a "matching" conductivity reading with each sample taken for chloride analysis.
  • Expand the sampling program to additional lakes, streams and wetlands as resources allow. Many waterbodies in the TCMA have not been sampled sufficiently to make a reliable assessment of potential impairment by chloride.

There are a number of organizations across the TCMA that monitor water quality or partner with others to conduct monitoring. In addition the MPCA, Metropolitan Council and the United States Geological Survey (USGS) also collect data throughout the TCMA. Incorporating the recommendations below into existing local water monitoring programs will provide valuable data to assist with tracking progress and meeting water quality goals. Monitoring should take place at the existing sites for consistency and comparison purposes. However, since monitoring activities are lead at the local level it will be dependent on available resources and local priorities. We encourage local monitoring data be shared with MPCA by routinely submitting data to the MPCA’s water quality database, EQuIS. The monitoring that MPCA conducts across the state follows the 10-year monitoring strategy as described in Minnesota’s Water Quality Monitoring Strategy report.

High Risk Monitoring Recommendations

The MPCA has developed specific guidance for monitoring of TCMA waters not currently impaired but showing a “high risk” of impairment. The chronic standard of 230 mg/L for chloride concentration applies as a 4-day time average. In practice, impairment is often judged from monthly sampling results when these show a clear pattern of prolonged concentrations exceeding the standard. Weekly or twice-weekly sampling would provide the basis for a clear determination of impairment or non-impairment. Long-term sampling at such high frequencies, however, is unreasonably expensive in most cases. Therefore, the MPCA suggests the following guidance for additional monitoring of “high risk” waters:

  1. Identify dates or periods of past chloride concentrations that were either:
    1. Exceedances (exceeded the chronic chloride standard), and
    2. "high" occurrences, defining "high" as less than but within 10% of the chronic standard (thus >207 mg/L)
  2. Select a 4-week period centered on each such date or period, and for each:
    1. Sample for chloride weekly, always on the same day of the week
    2. Sample at the same depth or depths as in past sampling
  3. If an electrical conductivity meter is available, take and record a "matching" conductivity reading with each lab sample taken:
    1. "matching" = from the same primary sample that provides the lab subsample, if the primary sample is a sufficiently larger volume than the laboratory bottle used; or otherwise
    2. "matching" = same location and depth as the lab sample
  4. Possible expanded effort:
    1. Monitor twice weekly rather than once, always on the same days of the week (e.g., Monday and Thursday) including, as resources permit:
      1. Chloride sample and conductivity measurement if possible
      2. Chloride sample only if lacking conductivity meter
      3. Conductivity measurement only on the increased frequency if laboratory costs limit sampling but a meter is available

To clarify, sampling for chloride at least weekly during the selected 4-week period(s) is a necessary minimum effort for ensuring the value of this additional monitoring; conductivity measurements alone will not suffice at present. This could change in the future if a reliable and accurate relationship between chloride and conductivity is developed for an individual waterbody or for an area including the waterbody.

Impaired Monitoring Recommendations (tracking progress)

In order to assess “high risk” waters and waters without data, the MPCA recommends monitoring waters already identified as impaired for chloride less frequently. It is recommended that efforts focus on collecting samples during critical periods. For instance, if the impairment is a result of winter maintenance activities, chloride sampling should be conducted during January through May for lakes and wetlands, and December through April for streams. If the impairment is caused by effluent with high chloride concentrations from the WWTPs, monitoring during low-flow periods in the streams should be targeted. If long-term monitoring data has already been collected, less frequent monitoring during critical conditions (monthly or twice monthly) is recommended. If monitoring efforts are limited by costs, and a site-specific chloride-conductivity relationship has been established, the MPCA recommends collecting conductivity measurements during the critical period to track progress.

General Monitoring Recommendations for Waters without Data

At a minimum, collect monthly chloride and conductivity data for waters without data during the critical period. If possible, expand the effort to weekly sampling during the critical period, and include chloride in typical summer season sampling efforts. For lakes with a potential for stratification, collect a bottom and a surface chloride sample. If it is determined that these waters meet the “high risk” criteria, the MPCA recommends following the monitoring guidelines for “high risk” waters.

This page was last edited on 23 November 2022, at 15:57.