MS4 permittees and regulatory agencies frequently evaluate program effectiveness through a combination of monitoring, tracking, and reporting. Requirements in MS4 permits are often written to enable iterative improvements as your program grows and learns how to best manage stormwater runoff in your community.
Stormwater monitoring refers to the gathering and analysis of information in order to understand water quality impacts from stormwater runoff and how those impacts change over time. This may include analyzing water sampling data, as well as other pertinent environmental data, but stormwater monitoring also includes the evaluation of programmatic processes and outcomes in order to revise and improve your stormwater program. It should be noted that Phase I MS4 Permits often require the permittee to implement a water quality sampling program to fulfill stormwater monitoring requirements. On the other hand, Phase II monitoring requirements are typically limited to non-sampling exercises such as conducting surveys, tracking progress toward measurable goals, and tracking visual observations in receiving waters.
The more information that your program has about water quality and stormwater runoff impacts, the more empowered your community (and your environmental regulatory agency) is to make well-informed decisions in regard to stormwater management.
Challenges in implementing monitoring programs
It can be challenging for local program managers to detect ambient water quality change due specifically to stormwater and correlate MS4 program actions with quantifiable outcomes. Also, in some instances, new requirements have been added to permits without carefully considering how to evaluate performance and adjust program actions over time. These adjustments sometimes increase the resources needed for monitoring and result in lengthy and intense reporting efforts for permittees with little perceived benefit to the permittee, regulator, or water quality.
It is important to note that not all municipal stormwater programs are required by their MS4 permits to implement formal stormwater monitoring programs. Because monitoring programs can be costly to implement, it might not be feasible for some municipal stormwater programs to exceed the requirements of their permit and use stormwater monitoring as a means to evaluate their success in attaining favorable water quality outcomes. However, all municipal stormwater programs should (and are typically required to) use some sort of objective metric(s) to evaluate program success at least once per year.
Monitoring, tracking, evaluation, and reporting refer to how MS4 programs:
- Track activities
- Evaluate progress and effects
- Pose key questions to answer through monitoring
- Sample stormwater runoff and/or receiving waters
- Analyze results
- Make program changes in response to observations
- Report to permitting authorities
Variations in monitoring approaches
The U.S. EPA developed regulations for MS4s in two phases:
- Phase I requires medium and large MS4s to obtain an NPDES permit coverage for their stormwater discharges.
- Phase II requires small MS4s to do the same.
Both Phase I and Phase II regulations require permittees to assess their stormwater control measures (i.e., BMPs) and perform some level of reporting to regulatory authorities.
Most states are authorized to implement the NPDES program and therefore write MS4 permits. Because states attempt to write permits with clear, specific, and measurable requirements that consider their local conditions, there can be variations in the way different permittees carry out monitoring, tracking, evaluation, and reporting requirements. Differences also exist between Phase I and Phase II MS4 permits. For example, Phase I regulations require permittees to develop a water quality monitoring program; larger MS4s might have requirements that necessitate sophisticated sampling programs with annual expenditures of more than $1M. While the Phase II regulations allow monitoring, they often do not require it. As a result, some MS4 permittees do not have any monitoring programs at all.
The extent to which MS4 permittees are required to implement stormwater monitoring programs has progressed over time. Initially, programs attempted to broadly monitor receiving waters and wet weather and dry weather discharges. This progressed into attempting to measure the effectiveness of specific program elements, post-construction stormwater management and green infrastructure in particular, as a means to better manage stormwater in the long term. More recently, the focus has expanded to include effectiveness monitoring for specific BMPs and water quality-based total maximum daily load (TMDL) requirements. Permittees have taken different approaches to water quality monitoring at varying scales and with different technologies. These are explored in more depth below.
Evaluation Strategies
Other methods can be as useful as monitoring for evaluating the success of your program and making adjustments over time. These include:
- Tracking progress toward measurable goals.
- Tracking pollutants removed from the MS4 or from potentially entering the MS4.
- Tracking visual conditions at receiving waters.
- Conducting surveys to evaluate public awareness and satisfaction with the municipal stormwater program.
Evolution of monitoring programs
There have been many iterations of monitoring approaches and requirements in MS4 permits. These iterations have incorporated lessons learned as permittees developed differing approaches and as regulators and permittees worked to interpret the results. The following table documents some of these changes as exhibited in California Phase I MS4 permits. This table is intended to provide a general point of observation and does not attempt to capture status or changes in all programs nationwide.
Across the country, MS4 programs fall in different places along the continuum of program implementation and monitoring. There remains a need to improve monitoring, tracking, evaluation, and reporting approaches to better determine the effectiveness of program actions and allow for adaptive management. For smaller Phase II communities, it might be most effective to collaborate or build upon existing monitoring efforts with neighboring communities or organizations.
Though terminology varies and reflects differences in program requirements and approaches, general concepts can broadly be viewed as “monitoring, tracking, evaluation, and reporting” and can feed program effectiveness assessment efforts and program implementation adjustments. Stormwater monitoring programs should always be approached by seeking answers to specific questions. For example, does flow in the lower segment of the river, downstream from where stormwater from the industrial park has discharged, contain more or less oil and grease than the upper segment?
The diagram below illustrates a conceptual program framework model for fostering an integrated perspective between water quality monitoring and program implementation activities. This framework can help program managers manage and adjust their programs while enabling permitting authorities to evaluate compliance and adjust permits. To gain a more comprehensive view of a program’s effectiveness, activity tracking information (i.e., non-water quality data) needs to be tied to water quality data obtained through monitoring (e.g., routine monitoring, special studies). Over time, a permittee could use this integrated dataset to track and assess a program’s function and effects and report this information and lessons learned to their permitting authority.
Case Study: Los Angeles County, California
Through its principal permittee and a regional monitoring group, Los Angeles County MS4 permittees conduct monitoring in receiving waters and in-system locations during some storm events. Cause and effect connections are inferred to stormwater program actions taken upstream in the monitored watershed. Permittees use modeling (using effectiveness estimates for existing BMPs and accounting for anticipated load reductions for new BMPs) to estimate the likely overall effect of BMP implementation within the watershed and to assist with BMP targeting. The County also encourages stormwater capture and reuse to reduce runoff and pollutants into waterways.
Case Study: Washington, D.C.
Washington, D.C., has used geographically targeted BMP implementation and monitoring designed to detect “signals” in water quality change based on intensive implementation of green infrastructure BMPs in the targeted area. The efforts include interim measurable milestones so the evaluation timeline is constrained. It should be noted that this program is designed to address both MS4 and CSO LTCP/Consent Decree requirements and has come with significant investment from the community.
Conceptual Program Assessment Framework, Highlighting the Linkage Between Water Quality Monitoring and Evaluation of Implementation Activities to Inform Adjustments to Program Implementation.
Case Study: The Evolution of California’s Phase I Program
| Early Generation Permits (1990s) | Middle Generation Permits (2000s) | Recent Generation Permits (2010s) | |
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Resources
The publications listed below provide more information about stormwater monitoring.