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Recommendations and guidance for utilizing stream monitoring to meet TMDL permit requirements

This page contains information specific to stream monitoring programs used to meet TMDL permit requirements of the MS4 General Permit.

The primary reasons for a permittee to perform monitoring of receiving waters are to (a) evaluate the impact of TMDL implementation strategies enacted throughout the watershed, and (b) evaluate impairment status to determine if the impaired waterbody can be removed (i.e., delisted) from the 303(d) Impaired Waters List. The following subsections outline the basics of developing a monitoring program to meet goals established within the Guidance Manual for Assessing Quality of Minnesota Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List (MPCA, 2018a), and developing a monitoring protocol standard operating procedure (SOP). Specifically, the Establishing a Monitoring Program section provides guidance on when, where, and what to sample, while the Establishing a Monitoring Protocol page provides guidance on how to sample (i.e., sampling SOP).

stream monitoring image

Biological monitoring in a stream. Biological impairments are often associated with excess TSS. Photo courtesy of MPCA's Flickr site.

Contents

Establishing a Monitoring Program

Before developing or implementing a lake or stream monitoring program, the applicable TMDL(s) should be reviewed to determine (a) if an ongoing water quality monitoring program exists or will be implemented and (b) what organization(s) are responsible for water quality monitoring (e.g., individual permitteess, the applicable Watershed District or Watershed Management Organization (WMO), etc.). Review of ongoing and planned water quality monitoring programs can help a permittee optimize sampling procedures to supplement ongoing monitoring efforts and help identify potential partnering opportunities with other organizations (e.g., WDs, WMOs, Citizen-Assisted Monitoring Program (CAMP), Soil and Water Conservation Districts (SWCDs), Metropolitan Council, etc.). To encourage statewide water quality monitoring efforts, the MPCA offers Surface Water Assessment Grants (SWAG) to eligible partners, including MS4s. More information on SWAG requirements and grant application can be found on the MPCA’s Surface Water Assessment Grants webpage.

In addition to review of planned or ongoing monitoring programs, the applicable TMDL(s) should be reviewed to determine the specific water quality standard(s) that apply to the impaired waterbody. Water quality standards applicable to the impaired waterbody are specific to the pollutant (e.g., chloride), the water body type (e.g., lake), and the water use classification (e.g., Class 2A).

Monitoring requirements: streams

The following subsections outline specific stream monitoring program requirements related to each of the four (4) pollutants discussed on this page: total suspended solids (TSS), total phosphorus (TP), bacteria, and chloride.

Total suspended solids (TSS)

Based on review of TSS water quality standards within the Minnesota Rule, Chapter 7050 (MINN. R. 7050, 2018), for many use classifications (e.g., Class 2A) and ecoregions (e.g., North River Nutrient Region), TSS standards are structured as follows.

TSS standards for [use classification, e.g., Class 2A] may be exceeded for no more than ten percent of the time. This standard applies April 1 through September 30.

The above standard, which supersedes the previous standard for turbidity, is the most common form of TSS standard within the Minnesota Rules (MINN. R. 7050, 2018), but the TSS standard may vary based on the use classification and ecoregion (e.g., Lower Mississippi River mainstem TSS standards are based on 50 percent exceedance from June 1 through September 30). For this reason, it is critical to review the applicable TMDL(s) to determine what water quality standard(s) apply to the impaired waterbody. Based on the most-common form of TSS standard and specific impairment assessment and delisting requirements for TSS, the following list outlines specific recommendations related to the development of a stream TSS monitoring program. See the page, Establishing a Monitoring Protocol for receiving waters linked below.

TSS Monitoring Program Recommendations

  • Number of samples per year:
    • Minimum: twenty (20) observations in the most recent 10 years, and at least 10 in the last 5 years.
    • Recommended: at least five (5) samples collected per year between April 1 and September 30. Sampling dates should be selected and fixed before the monitoring season to remove sampling bias in selected monitoring dates. Monitoring should, to the extent possible, be collected at intervals throughout the period of April 1 to September 30 (i.e., sampling should capture seasonal changes in water quality).
  • Seasonal monitoring recommendations: Samples must be collected between April 1 and September 30 of the sampling year unless the applicable water quality standard specifies a different period for standard compliance (e.g., TSS standards based on summer average values must be collected between June 1 and September 30 of the monitoring year).
  • Flow monitoring recommendations: because TSS concentrations can vary based on flow rate, monitoring should ideally reflect a variety of flow conditions. For this reason, dry-weather monitoring, post-rainfall sampling, and seasonal sampling should be considered to ensure a variety of flow rates are captured in the TSS monitoring dataset.
  • Sampling location(s): Selected sampling locations should be consistent with sampling locations used to originally define impairment. Sampling locations used to define impairment may be outlined within the applicable TMDL(s). If not, contact MPCA to determine sampling locations used to define impairment.
  • Sampling protocol (i.e., sample collection guidance).

Eutrophication standard: streams (TP, chlorophyll-a, and Secchi disk transparency)

Stream eutrophication water quality standards established in Minnesota Rule, Chapter 7050 (MINN. R. 7050, 2018) require paired observations of TP, chlorophyll-a, five-day biological oxygen demand (BOD5) and diel dissolved oxygen (DO) flux. From Part 7050.0222, Subp. 3b:

impaired stream photo

Intersection of two impaired streams; TSS on the left and phosphorus (eutrophication) on the right. Photo courtesy of MPCA's Flickr site.

Eutrophication standards for rivers, streams, and navigational pools are compared to summer-average data or as specified in subpart 3. Exceedance of the total phosphorus levels and chlorophyll-a (seston), five-day biochemical oxygen demand (BOD5), diel dissolved oxygen flux, or pH levels is required to indicate a polluted condition.

The standard requires paired observations of TP, chlorophyll-a, BOD5, and diel DO flux during the summer period (June 1 through September 30) of the monitoring year. As outlined in Part 7050.0222, Subp. 3, standards for each of the four (4) parameters used to evaluate stream eutrophication vary by use classification (e.g., Class 2B) and ecoregion (e.g., North Central Hardwood Forests). The applicable water quality standards for the impaired waterbody will be outlined in the applicable TMDL report.

Based on Minnesota stream eutrophication standards and specific impairment assessment and delisting requirements for stream eutrophication, the following list outlines specific recommendations related to the development of a stream eutrophication monitoring program. 

Stream Eutrophication Monitoring Program Recommendations

  • Monitored parameters:
    • Minimum: total phosphorus (TP) and the response variable(s) that were originally used to define stream impairment.
    • Recommended: total phosphorus (TP) and all stream eutrophication response variables: chlorophyll-a, BOD5, diel DO flux, and pH.
  • Number of samples:
    • Minimum: twelve (12) paired samples over a minimum of 2 years for TP, chlorophyll-a, and BOD5 twenty (20) samples of pH over a minimum of 2 years, and two (2) four-day DO sonde deployments to evaluate diel DO flux.
    • Recommended: twenty (20) paired samples of TP, chlorophyll-a, and BOD5 per year during the summer period of June 1 through September 30 (i.e., 5 per month), twenty (20) samples of pH over a minimum of 2 years during the summery period, and two (2) four-day DO sonde deployments per year during the summer period.
  • Seasonal monitoring requirements: Samples must be collected during the summer period (June 1 and September 30) of the sampling year.
  • Sampling location(s): Selected sampling locations should be consistent with sampling locations used to originally define impairment. Sampling locations used to define impairment may be outlined within the applicable TMDL(s). If not, contact MPCA to determine sampling location(s) used to define impairment.
  • Sampling protocol (i.e., sample collection guidance)

Bacteria (E. coli)

Based on review of bacteria (E. coli) water quality standards within Minnesota Rule, Chapter 7050 (MINN. R. 7050, 2018), for many use classifications (e.g., Class 2A) and ecoregions (e.g., North River Nutrient Region), E. coli standards are structured as follows.

From Part 7050.0222, Subp. 2 (Class 2A): “Escherichia (E.) coli bacteria shall not exceed 126 organisms per 100 milliliters as a geometric mean of not less than five samples representative of conditions within any calendar month, nor shall more than ten percent of all samples taken during any calendar month individually exceed 1,260 organisms per 100 milliliters. The standard applies only between April 1 and October 31.

The above standard, which supersedes the previous standard for fecal coliform bacteria, is the most common form of E. coli standard in Minnesota Rules (MINN. R. 7050, 2018), but the E. coli standard may vary based on the use classification (e.g., for Class 3C water bodies, the geometric mean standard is 630 organisms per 100 milliliters, rather than 126). For this reason, it is critical to review the applicable TMDL(s) to determine what water quality standard(s) apply to the impaired waterbody.

Based on the most-common form of E. coli standard and specific impairment assessment and delisting requirements for E. coli, the following list outlines specific recommendations related to the development of a stream E. coli monitoring program. 

Bacteria (E. coli) Monitoring Program Recommendations

  • Number of samples per year:
    • Minimum: fifteen (15) samples over a two-year period in the last 10 years, with a minimum of five (5) samples per month for at least 3 months where the standard applies (i.e., April-October).
    • Recommended: five (5) samples per month for the period of April-October (i.e., 35 samples per year), or five (5) samples per month for the critical period of June-September (i.e., 20 samples per year).
  • Seasonal monitoring recommendations: The standard applies for the period of April 1 to October 31.
  • Flow monitoring recommendations: Recommended: because E. coli concentrations can vary based on flow rate, monitoring should ideally reflect a variety of flow conditions. For this reason, dry-weather monitoring, post-rainfall sampling and seasonal sampling should be considered to ensure a variety of flow rates are captured in the bacteria monitoring dataset.
  • Sampling location(s): Selected sampling locations should be consistent with sampling locations used to originally define impairment. Sampling locations used to define impairment may be outlined within the applicable TMDL(s). If not, contact MPCA to determine sampling location used to define impairment.
  • Sampling protocol (i.e., sample collection guidance).

Chloride

Chloride water quality standards within the Minnesota Rule, Chapter 7050 (MINN. R. 7050, 2018) are consistent for all Minnesota waters (i.e., all use classifications). Specifically, Minnesota Rules define a chronic toxicity-based chloride water quality standard of 230 mg/L (i.e., chronic standard), and an acute toxicity standard of 860 mg/L (i.e., maximum standard). Specific data requirements for evaluation of impairment condition for both the chronic and maximum chloride water quality standard established in the Guidance Manual for Assessing the Quality of Minnesota Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List (MPCA, 2014) are outlined, below.

  • Chronic standard (230 mg/L):
    • Exceedances of chronic standards for toxic pollutants are evaluated over a consecutive three year period.
    • Two or more exceedances of the chronic standard in three years is considered an impairment.
    • Chronic water quality standards are defined as a four day (4-day) average concentration. If concentrations in the waterbody are relatively constant, a single sample concentration value may be used to define the 4-day average. When concentrations are more variable, multiple samples or time-weighted composite samples are necessary to calculate an accurate average concentration.
  • Maximum standard (860 mg/L):
    • Exceedances of the maximum standards for toxic pollutants are evaluated over a consecutive three year period.
    • One (1) exceedance of the maximum standard is considered an impairment.

The MPCA has published several Statewide Chloride Resources, including the Statewide Chloride Management Plan (MPCA, 2019) and specific protocols related to stream and lake chloride monitoring.

Based on review of chloride standards, statewide guidance documents, and specific impairment assessment and delisting requirements for chloride impairment, the following list outlines specific recommendations for developing a stream chloride monitoring program. Specific monitoring protocol recommendations are discussed here.

Chloride Monitoring Program Recommendations

  • Number of samples per year:
    • Minimum: five (5) samples over any 3-year interval in the past 10-years.
    • Recommended: five (5) samples per year for a 3-year interval. If chloride concentration show high daily-variability, 4-day average sampling is required (i.e., five (5) separate 4-day average chloride concentrations should be used to evaluate chronic impairment).
  • Location and depth of monitoring: Recommended: samples should be taken mid-stream, mid-depth whenever possible.
  • Monitoring and flow rate: Recommended: because chloride concentrations can vary based on flow rate, monitoring should ideally reflect a variety of flow conditions. For this reason, dry-weather monitoring, post-rainfall sampling, and seasonal sampling should be considered to ensure a variety of flow rates are captured in the chloride monitoring dataset.
  • Seasonal / critical period monitoring requirements:
    • Recommended: chloride concentration can vary significantly throughout the season due to critical chloride loading periods (e.g., winter deicing efforts). For this reason, the TMDL should be reviewed to determine if a critical period was identified (i.e., a seasonal period of most-elevated chloride concentrations). The following list provides examples of periods of elevated chloride concentration related to land use:
      • December through April for streams in urban areas and locations near deicing practices.
      • April through November for streams downstream of waste water treatment plant (WWTP) discharge locations.
      • April through November for streams downstream of heavy agriculture, near tile drainage systems, and/or proximal to gravel roadways that receive dust management.
  • Note: streams dominated by baseflow (i.e., groundwater flow) may show elevated chloride concentrations at periods other than those listed above.
  • Sampling location(s):
    • Selected sampling locations should be consistent with sampling locations used to originally define impairment. Sampling locations used to define impairment may be outlined within the applicable TMDL(s). If not, contact MPCA to determine sampling location(s) used to define impairment.
    • Note: if there are multiple monitoring locations along the reach, all samples collected at a given depth (see definition of “shallow”, “deep”, and “mid-depth”, above) are combined for the 4-day average calculation.
  • Miscellaneous recommendations: **Recommended: conduct paired conductivity (i.e., specific conductance) measurements during chloride monitoring. In some cases, a waterbody-specific chloride-conductivity relationship can be established. In these cases, conductivity can serve as a surrogate for chloride (as monitoring conductance is faster and cheaper than monitoring chloride directly). Review the TMDL to determine if a waterbody-specific chloride-conductivity relationship has been established
  • Sampling protocol (i.e., sample collection guidance).

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