Manufactured Stormwater Treatment Devices (MTDs) Frustrations, Misperceptions, and Concerns. Part 2: Crossing the MTD Divide

The initial wave of manufactured treatment devices (MTDs) were generally simpler than options available today.  With few exceptions, early MTDs were comprised predominantly of swirl/vortex and other types of gravity separators that targeted solids and floating pollutants.  State and local stormwater programs were in their infancy and were predominantly focused on reducing suspended solids loads.  Our knowledge of particle size distributions and other common pollutants carried by stormwater paled in comparison to what we know today.  MTD testing protocols were non-existent leaving early MTD providers to devise their own and make their case for acceptance.  Regulators recognizing the need for underground solutions, especially in urban areas, implemented crude MTD performance criteria typically rooted in demonstrating removal of coarse solids in the laboratory.

This approach would be fine if coarse solids constituted the bulk of our stormwater pollutant problem, but advances in the science revealed a much more complex suite of pollutants including very fine particulate not readily captured by separators.  These revelations pushed the industry toward increasingly complex regulations and performance expectations for stormwater best management practices.  This also planted the seeds for the misperception that MTDs don’t work based on the limitations of early separators.  The reality is, those separators do work.  They are great at removing coarse particulate, trash, and other floating pollutants.  When we start assessing them for removal of very fine particulate, nutrients and metals then no, they don’t perform very well.  Most builders don’t have much success cutting wood with a hammer, so we shouldn’t expect favorable results when applying stormwater “tools” to tasks they are not intended. 

Today, MTD options have expanded considerably to include advanced screening, filtration, and biofiltration solutions that are capable of achieving high levels of pollutant load reduction.  Advanced MTD solutions can effectively target very fine particulate, both particulate and dissolved nutrients and metals, bacteria, oils and grease, and more.  However, to achieve high levels of performance, they need to be sized properly, and performance assumptions should be backed by robust monitoring data collected in accordance with a recognized protocol.  That’s where the regulatory community is needed to establish sound policy that ensures MTDs are capable of effectively removing the pollutants of concern, are sized to handle the local water quality event, and have been successfully monitored in accordance with a recognized protocol.  For their part, MTD providers should encourage reliance on robust performance data in making approval decisions and avoid misleading claims and literature that perpetuates confusion and frustration among stakeholders. 

Regulatory programs lacking the resources to vet MTDs thoroughly should build on the work that’s already been done by others.  The New Jersey Department of Environmental Protection’s (NJDEP) MTD certification program remains the gold standard for evaluating solids removal in the laboratory.  Meanwhile, the TAPE Protocol administered by the Washington Department of Ecology is producing robust field data that is utilized throughout North America.  Together these programs are expected to serve as the foundation of a national program being shepherded by the Water Environment Federation (WEF) in partnership with a diverse stakeholder group.  The Interstate Technology and Regulatory Council (ITRC) is also actively working on guidance for the regulatory community to aid in making sound decisions relative to MTDs and other BMPs.  Ultimately, there is a growing body of performance data on MTDs, but we need to make sure we are applying them to appropriate applications, not granting carte blanche approvals to MTDs that have not been thoroughly evaluated and ensure there is sound policy in place to govern MTD sizing. 

Fostering a collaborative relationship between MTD providers, regulators, and the research/academic community has considerable upside potential.  We should strive to work together to continually expand our BMP toolbox to protect receiving waters regardless of the constraints presented by a given site.  Ensuring there is a well-defined path for acceptance of new innovative technologies encourages ongoing investment in stormwater research while simultaneously creating jobs.  I think most stormwater professionals are likely to agree that we stand the best chance of protecting receiving waters at the lowest cost through collaboration and innovation.  Let’s all raise the bar to ensure the next generation of stormwater solutions is the most effect yet, and we have the policy in place to properly deploy them.