Recommendations and guidance for utilizing monitoring to meet TMDL permit requirements
This page is being developed
Monitoring guidance presented in this technical memorandum has been developed to assist MS4s with (a) evaluating and demonstrating compliance with TSS, TP, bacteria, and chloride wasteload allocations (WLAs), and (b) evaluating the impairment status of waterbodies and monitoring the impact of TMDL implementation strategies. The guidance on this page provides specific recommendations related to four (4) monitoring strategies.
- Monitoring receiving waters: lakes
- Monitoring receiving waters: streams
- Monitoring major outfalls
- Monitoring BMPs
The four (4) monitoring strategies were selected based on input from and coordination with the MPCA and response of MS4s to a voluntary survey conducted by the MPCA. Throughout this document, “MS4s” refers specifically to National Pollutant Discharge Elimination System (NPDES) regulated MS4s (i.e., Phase I and Phase II MS4s required to obtain NPDES permit coverage for their stormwater discharges).
The following table provides a summary of how each of the four (4) monitoring strategies can be used to evaluate WLA compliance and evaluate waterbody impairment status. Before adopting modeling strategies discussed in this memorandum, the applicable TMDL(s) and MS4 WLA(s) should be reviewed and compared to recommendations in Table 1. Additionally, the applicable TMDL(s) should be reviewed to determine (a) if an ongoing water quality monitoring program is or will be implemented and (b) what organization(s) are responsible for water quality monitoring (e.g., individual MS4s, the applicable Watershed District or Watershed Management Organization (WMO), etc.). Note: regardless of whether an ongoing monitoring program has been established, individual MS4s may independently monitor water quality to supplement data collected by other organizations to help track and evaluate impairment status, while employing proper QA/QC methods for data collection and reporting.
MS4 TMDL compliance monitoring strategy summary
Link to this table
| Monitoring strategies | ||||
|---|---|---|---|---|
| MS4 TMDL Compliance Strategy | Monitoring receiving waters - lakes | Monitoring receiving waters - streams | Monitoring outfalls | Monitoring BMPs |
| Monitor improving water quality and delist from 303(d) Impaired Waters List | X | X | ||
| Upstream/downstream monitoring to identify “hot spots” (e.g., locations where intervening flow is causing impairment) | X | |||
| Evaluating compliance with MS4 wasteload allocation (WLA)… | ||||
| WLA in terms of mass reduction (e.g., lbs/year, org/day, etc.) | X | X | ||
| WLA in terms of percent reduction from baseline condition (e.g., 40% reduction) | X | X | ||
| WLA in terms of areal loading reduction (e.g., lbs/acre/year) | X | |||
Contents
Monitoring Survey
In November 2018, the MPCA provided Barr with responses to a MS4 survey related to water quality modeling and water quality monitoring. Half of responding MS4s (26 of 54 MS4s) actively perform water quality monitoring or are otherwise involved in the collection of water quality monitoring data, with monitoring or “receiving waters” being the most commonly reported form of water quality monitoring. Responses from MS4s were used to inform the selection of monitoring strategies and are summarized below.
MS4 responses to MPCA monitoring survey (2018)
Evaluating Impairment Status
A majority of TMDL Implementation Plans include recommendations related to ongoing monitoring of the impaired waterbody. Ongoing monitoring is critical to evaluating the impact of TMDL implementation strategies (e.g., BMP implementation) as they are enacted throughout the watershed. If ongoing monitoring shows that water quality has improved such that the water body is no longer impaired, that water body can be removed (i.e., delisted) from the 303(d) Impaired Waters List. Within the Guidance Manual for Assessing Quality of Minnesota Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List (MPCA, 2018a), the MPCA has provided specific data and assessment requirements needed to consider removing a water body from the 303(d) Impaired Waters List. Requirements for the four (4) pollutants highlighted in the memorandum are included, below.
Note: specific guidance related to monitoring of receiving lakes and streams can be found in Section 4.0. Additionally, the monitoring case studies presented in Section 4.3 and 4.4 provide examples of how TMDL implementation strategies and monitoring were used to delist two impaired waterbodies: Wirth Lake, originally listed for excess nutrient (i.e., TP) impairment, and Nine Mile Creek, originally listed for turbidity (i.e., TSS) impairment.
Total suspended solids (TSS) must have
- At least 20 observations (i.e., water quality samples) (pre- and post-corrective action) in the most recent 10 years, of which at least 10 observations (pre- and post-corrective action) are in the most recent 5 years; or
- At least 20 observations in the most recent 5 years, and evidence of corrective action (i.e., actions taken to improve water quality) in the watershed of sufficient dimension (i.e., sufficient load reduction to impact water quality in the receiving waterbody) to change impairment status. In either case, there must be fewer than 10% of samples exceeding the water quality standard.
Lake eutrophication (TP) must have
- At least 8 paired (i.e., collected at the same time) TP, corrected (i.e., corrected for pheophytin) chlorophyll a (chl-a), and Secchi measurements (June to September) over a minimum of 2 years for the most recent 10 years.
- If TP meets the standard, and either chl-a or Secchi meet the standard, the lake will be removed from the Impaired Waters List.
- If TP exceeds the standard and corrected chl-a AND Secchi meet the standard, and an improving trend in TP is observed or management activities are in place to maintain improved chl-a or Secchi observations, the lake may be delisted.
Delisting based on these criteria will be evaluated by the MPCA on a case-by-case basis, and will require the local entity to provide information that details how the response conditions will be met over time. Stream eutrophication (TP) must have:
- Monitoring of the causative variable (i.e., TP) and the response variable(s) (i.e., chlorophyll-a, BOD5, pH, or diel DO flux) that were used to list the AUID meet the standard within the summer period (June 1 through September 30);
- A minimum of 12 paired samples over a minimum of 2 years of the causative and response variable(s);
- A minimum of 20 pH samples over a minimum of 2 years; and
- A minimum of 2 DO sonde deployments; each with a length of 4 days and occurring in separate years.
E. coli bacteria must have:
- A minimum of 15 observations over a two-year period in the most recent 10 years, with a minimum of 5 observations per month for at least 3 months when the standard is applicable (April – October).
- Impairment is evaluated by calculating the geometric mean of data collected within each month (April – October) since corrective actions were taken in the watershed of sufficient dimension to change impairment status.
- Note: if a sufficient number of observations have been aggregated within a 2-year time period since corrective actions were taken (i.e., 5 observations per month for 3 months, April – October), the most recent 2-year time period may be used to evaluate impairment.
- Note: a “month” can be defined as any non-overlapping 30-day period from April – October (i.e., “month” does not need to be defined by the individual calendar months from April – October).
- To change impairment status, there must be no exceedance of the monthly mean standard (126 organisms per liter) by the geometric mean of data collected within any month period when the standard applies (April – October). Additionally, no more than 10% of samples taken within any month period shall exceed the “maximum” standard (1,260 organisms per liter).
Chloride must have
- At least 5 observations (pre and post-corrective action) for any 3-year interval in the most recent 10 years; or
- At least 5 observations for any 3-year interval in the most recent 5 years, and evidence of corrective action in the watershed of sufficient dimension to change impairment status.
- In either case, no more than one exceedance of the chronic water quality standard in any 3-year interval (note: the chronic standard is a 4-day average concentration).
The water quality standards referred to in the delisting criteria, above, are specific to the pollutant (e.g., TSS), the water body type (e.g., stream), and the water use classification (e.g., Class 2A). The TMDL report for the impaired waterbody is required to outline applicable water quality standards for all water(s) included within the report. Additionally, a complete list of all water quality standards applicable to Minnesota waters can be found in the Minnesota Rule, Chapter 7050 (MINN. R. 7050, 2018). As noted in the Guidance Manual for Assessing Quality of Minnesota Surface Waters for Determination of Impairment: 305(b) Report and 303(d) List (MPCA, 2018a), all delisting decisions are subject to review by the appropriate watershed assessment and professional judgment teams. Because the review team will consider watershed conditions and the representativeness of collected data, watershed improvement information should be summarized and presented to the review team. Special effort should be taken to ensure that collected data are representative of a wide range of watershed conditions (e.g., variability of flow conditions, seasonal variability, etc.).
Monitoring receiving waters
The primary reasons for an MS4 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” section provides guidance on how to sample (i.e., sampling SOP).
Establishing a Monitoring Program
As discussed in Section 1.0, 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 is or will be implemented and (b) what organization(s) are responsible for water quality monitoring (e.g., individual MS4s, the applicable Watershed District or Watershed Management Organization (WMO), etc.). Review of ongoing and planned water quality monitoring programs can help an individual MS4 optimize sampling procedures to supplement ongoing monitoring efforts, and can help individual MS4s 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. As discussed in Section 3.0, 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: lakes
The following subsections outline specific lake monitoring program requirements related to each of the four (4) pollutants discussed in this memorandum: total suspended solids (TSS), total phosphorus (TP), bacteria, and chloride.
Total suspended solids (TSS)
As of 2018 Minnesota Impaired Waters List (MPCA, 2018b) there are no lakes listed as impaired for TSS. For more information regarding establishing a TSS monitoring program for streams, see Section 4.1.2.1.
Eutrophication standard: lakes (TP, chlorophyll-a, and Secchi disk transparency)
Lake eutrophication water quality standards established in the Minnesota Rule, Chapter 7050 (MINN. R. 7050, 2018) require paired observations of TP, chlorophyll-a, and Secchi disk transparency during the summer period (June 1 through September 30) of the monitoring year. From Part 7050.0222, Subp. 2a:
Eutrophication standards for lakes and reservoirs are compared to summer-average data. Exceedance of the total phosphorus and either the chlorophyll-a or Secchi disk transparency standard is required to indicate a polluted condition.
The numeric standards for TP, chlorophyll-a, and Secchi disk transparency vary by use classification (e.g., Class 2B), ecoregion (e.g., North Central Hardwood Forests), and by lake classification (e.g., trout lake, shallow lake, etc.). As discussed in Section 4.1, the applicable water quality standards for the impaired waterbody are outlined in the applicable TMDL report. Based on Minnesota lake eutrophication standards and specific impairment assessment and delisting requirements for lake eutrophication listed in Section 3.0, the following list outlines specific recommendations to develop a lake eutrophication monitoring program. Specific monitoring protocol recommendations are discussed in Section 4.1.2.1.
Lake Eutrophication Monitoring Program Recommendations
- Number of samples per year:
- Minimum: eight (8) paired samples of TP, chlorophyll-a, and Secchi disk over a minimum of a 2 year period within the most recent 10 years.
- Recommended: four (4) or more paired samples of TP, chlorophyll-a, and Secchi disk transparency collected between June 1 and September 30 per year on an ongoing basis to continually monitor and evaluate lake eutrophication. 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 equal intervals throughout the period of June 1 to September 30 (i.e., sampling should capture seasonal changes in water quality).
- Seasonal monitoring requirements:
- Samples must be collected between 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 used to define impairment.
- Sampling protocol (i.e., sample collection guidance):
- See discussion in Section 4.1.2.1.
Bacteria (E. coli)
As of 2018 Minnesota Impaired Waters List (MPCA, 2018b) there are no lakes listed as impaired for Escherichia coli (E. coli). For more information regarding establishing an E. coli monitoring program for streams, see Section 4.1.2.3.
Chloride
Chloride water quality standards within 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 (MPAC, 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 (4) day average concentration. If concentrations in the waterbody are relatively stable, 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 Draft Statewide Chloride Management Plan (MPCA, 2019) and specific protocols related to stream and lake chloride monitoring (see Section 4.2.3.2).
Based on review of chloride standards, statewide guidance documents, and specific impairment assessment and delisting requirements for chloride impairment listed in Section 3.0, the following list outlines specific recommendations for developing a lake chloride monitoring program. Specific monitoring protocol recommendations are discussed in Section 4.1.2.1.
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 (e.g., if daily concentrations vary by more than 30 mg/L), 4-day average sampling is required (i.e., five (5) separate 4-day average chloride concentrations should be used to evaluate chronic impairment).
- Depth monitoring recommendations:
- Recommended: for lakes more than 2 meters deep, samples should be collected at depths along the water column as described below because chloride concentration typically increases with depth. If 4-day averages are used, samples collected at each depth should be grouped and averaged together, rather than averaging all samples collected throughout the water column:
- Shallow: 0-2 meters;
- Deep: deepest 2 meters of the water column; and
- Mid-depth: midway between depths defined as “shallow” and “deep”.
- Recommended: for lakes more than 2 meters deep, samples should be collected at depths along the water column as described below because chloride concentration typically increases with depth. If 4-day averages are used, samples collected at each depth should be grouped and averaged together, rather than averaging all samples collected throughout the water column:
- Seasonal / critical period monitoring recommendations:
- 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:
- Potential critical periods:
- 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:
- January through May for lakes in urban areas and locations near deicing practices.
- April through November for lakes downstream of waste water treatment plant (WWTP) discharge locations.
- April through November for lakes downstream of heavy agriculture, near tile drainage systems, and/or proximal to gravel roadways that receive dust management.
- 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.
- 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 report to determine if a waterbody-specific chloride-conductivity relationship has been established
- Sampling protocol (i.e., sample collection guidance):
- See discussion in Section 4.1.2.1.
Monitoring requirements: streams
The following subsections outline specific stream monitoring program requirements related each of the four (4) pollutants discussed in this memorandum: 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, 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 listed in Section 3.0, the following list outlines specific recommendations related to the development of a stream TSS monitoring program. Specific monitoring protocol recommendations are discussed in Section 4.2.
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:
- Recommended: 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):
- See discussion in Section 4.2.
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 biochemical oxygen demand (BOD5) and diel dissolved oxygen (DO) flux. From Part 7050.0222, Subp. 3b:
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). As discussed in Section 4.1, 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 listed in Section 3.0, the following list outlines specific recommendations related to the development of a stream eutrophication monitoring program. Specific monitoring protocol recommendations are discussed in Section 4.2. 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):
- See discussion in Section 4.2.
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 listed in Section 3.0, the following list outlines specific recommendations related to the development of a stream E. coli monitoring program. Specific monitoring protocol recommendations are discussed in Section 4.2.
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):
- See discussion in Section 4.2.
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 (MPAC, 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 Draft Statewide Chloride Management Plan (MPCA, 2019) and specific protocols related to stream and lake chloride monitoring (see Section 4.2.3.2).
Based on review of chloride standards, statewide guidance documents, and specific impairment assessment and delisting requirements for chloride impairment listed in Section 3.0, the following list outlines specific recommendations for developing a stream chloride monitoring program. Specific monitoring protocol recommendations are discussed in Section 4.2.
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:
- Potential critical periods:
- 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):
- See discussion in Section 4.2.
Establishing a Monitoring Protocol
The MPCA has specific requirements and protocols related to water quality data collection, laboratory processing of water quality samples, data processing of laboratory results, and final submittal of water quality data to the MPCA for review. Specifically, the MPCA uses a data processing system called EQuIS (Environmental Quality Information System) to store and process water quality data collected from over 17,000 sampling location across the state, and requires that data be collected and processed in a manner which is compatible with EQuIS. There are many publically available Quality Assurance Program Plan (QAPP) and monitoring Standard Operation Procedure (SOP) documents which can be used as a framework for developing a monitoring protocol. The following subsections provide an overview of EQuIS requirements and a summary of lake and stream monitoring QAPP and SOP documents.
EQuIS
The MPCA has developed extensive guidance related to establishing EQuIS projects, and developed tools and guidance to assist monitoring and laboratory staff to process data in an EQuIS-compatible format (see links in Table 3). The following steps provide a basic overview of the EQuIS data collection and submittal process: establishing an EQuIS project, processing collected water quality data, and submitting collected data to the MPCA for review. Collecting, processing, and submitting EQuIS data requires contact and coordination with an MPCA EQuIS team member.
- Coordinate with an MPCA EQuIS team member and establish an EQuIS project (i.e., submit the EQuIS Project Establishment Form).
- Submit a location establishment form.
- Collect water quality data and submit to a State-certified laboratory.
- Procedures to collect water quality samples and submit to a certified laboratory, including pre- and post-monitoring protocols, quality assurance and quality control (QAQC), and guidance regarding chain of custody (COC) preparation and documentation are discussed in Section 4.2.2.
- The MPCA EQuIS team member can be contacted regarding State-certified laboratories.
- Submit EQuIS formatted data to the MPCA for review.
- The EQuIS Data Gathering Engine (EDGE) can be used to generate EQuIS formatted data during field data collection.
- The Lab_MN: lab data storage spreadsheet can be used by certified labs to generate EQuIS formatted data of laboratory results.
- If not using EDGE or Lab_MN, data can be manually formatted into the Surface Water Data Template.