Monitoring guidance presented below will assist Municipal Separate Storm Sewer System (MS4) permittees evaluate and demonstrate compliance with total suspended solid (TSS), total phosphorus (TP), bacteria, and chloride wasteload allocations (WLAs); and evaluate the impairment status of waterbodies and monitor the impact of total maximum daily load (TMDL) implementation strategies.
Contents
Section Overview
The guidance in this section provides specific recommendations related to four (4) monitoring strategies.
- Monitoring receiving waters: lakes
- Monitoring receiving waters: streams
- Monitoring major outfalls
- Monitoring BMPs
Links to each of these pages if provided above and in the left sidebar menu for this section.
The four (4) monitoring strategies were selected based on input from and coordination with the Minnesota Pollution Control Agency (MPCA) and response of MS4 permittees 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 monitoring strategies discussed below, the applicable TMDL(s) and MS4 WLA(s) should be reviewed and compared to recommendations in the table below. 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 quality assurance/quality control (QA/QC) methods for data collection and reporting.
| 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 | |||
Monitoring Survey
In 2018, the MPCA conducted a survey of MS4 permittees related to water quality modeling and water quality monitoring. Half of respondents (26 of 54) actively perform water quality monitoring or are otherwise involved in the collection of water quality monitoring data, with monitoring of receiving waters being the most commonly reported form of water quality monitoring. Responses from permittees were used to inform the selection of monitoring strategies and are summarized below.
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, the MPCA has provided specific data and assessment requirements needed to consider removing a water body from the 303(d) Impaired Waters List. See the requirements for the four (4) pollutants on the lake or stream monitoring pages, but keep in mind that the Guidance Manual is updated every two years, and should be referenced for current impairment assessment and removal parameters. Each section in the Guidance Manual describes the data required to add a water to the 303(d) Impaired waters list (impairment assessment) as well as the data requirements to remove an impaired water from the 303(d) list (impairment removal assessment). The types of impairments that MS4 permittees are currently affected by include:
- aquatic life (this includes river eutrophication and total suspended solids (TSS)),
- toxins for aquatic life (chloride),
- aquatic recreation (E. coli, lake eutrophication).
The water quality standards referred to in the delisting criteria, 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, 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.).
Note: Use links in the sidebar menu or below to view specific guidance related to monitoring of receiving lakes and streams. Additionally, the monitoring case studies 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.
Guidance pages for each of the four (4) monitoring strategies discussed in this section also includes:
- A section Establishing a Monitoring Program provides guidance on when, where, and what to sample, and
- A section or page for Establishing a Monitoring Protocol that provides guidance on how to sample (i.e., sampling SOP).
Related pages
- Recommendations and guidance for utilizing lake monitoring to meet TMDL permit requirements
- Recommendations and guidance for utilizing stream monitoring to meet TMDL permit requirements
- Recommendations and guidance for utilizing major stormwater outfall monitoring to meet TMDL permit requirements
- Recommendations and guidance for utilizing stormwater best management practice monitoring to meet TMDL permit requirements
- Case studies for monitoring to meet TMDL permit requirements