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 | |||
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.