Since its inception in 1996, The International Stormwater BMP Database  has been archiving performance, design, and cost data for stormwater treatment best management practices (BMPs) in a publicly accessible database.  At this point, over 600 BMP studies have been added, providing a wealth of information to regulators, engineers, academics, and others seeking to understand and improve the state of the art of stormwater management.  At the end of 2020, a new report was published  that summarizes data made available in the December 2019 release of the database. 

The abstract of the International Stormwater BMP Database 2020 Summary Statistics report states:

“This 2020 analysis not only includes new performance studies, but also new analysis categories for manufactured treatment devices. Data summaries include basic summary statistics for BMP influent and effluent concentrations, graphical summaries of statistics and hypothesis test results for assessing whether the BMP had an effect on influent concentrations for various pollutant-BMP combinations. Additionally, information about typical pollutant sources, dominant pollutant removal mechanisms.”

This new content is excellent!  Previously, the project had grouped manufactured devices together as one category, which made any assessment of group performance highly variable and not very informative.  In the 2016 summary report, it was noted that although there were approximately 100 studies available, manufactured devices were  “no longer provided as a general BMP category for analysis in this report because of the wide range of unit treatment processes present among various manufactured devices.”  Manufactured devices are now grouped into the four categories shown below.

In looking through these data sets, the extensive track record of Contech stormwater treatment system field monitoring shines bright.  For example, the High Rate Biofiltration category is comprised entirely of 6 different Filterra studies, making it possible to use the 2020 summary report to directly compare the performance of Filterra bioretention systems to conventional bioretention.  The results are impressive. Median effluent concentrations for total suspended solids (TSS), total phosphorus, total copper and dissolved copper are significantly lower for Filterra, as indicated by non-overlapping 95th percentile confidence intervals. Phosphorus performance is the most divergent parameter, with conventional bioretention showing a significant increase from influent to effluent, and Filterra showing a significant reduction. Conventional bioretention median total zinc effluent is significantly lower than for Filterra, however both BMPs provide strong significant reductions.

As for high rate media filtration, 15 of the 23 reports in the 2019 database release are for Contech products, including StormFilter, Jellyfish Filter and MFS.  High rate media filters are consistently among the best performing BMPs for TSS, total phosphorus, total nitrogen, total copper, total zinc and total lead.  As a group, high rate media filters are less capable of removing dissolved metals and some nitrogen species than other technologies. 

In the hydrodynamic separator category, 16 of the 30 devices represented are Contech products including CDS and Vortechs systems. As expected, as a category, these systems provided significant TSS removal but had a relatively high mean effluent concentration range. They also provided positive if not always statistically significant removal of total phosphorus and total metals.

There are 19 records for Oil/Grit Separators and Baffle Boxes, which are split about evenly between oil/water separators and baffle boxes.  As a category, these systems provide positive and significant removal of TSS and significant removal of total phosphorus and some total metals. Hydrocarbon removal was not reported on in this summary report. 

Overall, this summary report is an excellent resource that takes a complex body of data and presents it in a very accessible form.  And, for those wanting to take a closer look at individual studies, the entire 2019 database release is available on the International Stormwater BMP Database website for download as an Access database. Details of BMP design, cost, water quality performance and testing protocol can all be queried and analyzed from the original study.

For those engineers designing individual BMPs on land development or retrofit projects, the BMP database summaries are not a substitute for a focused look at the impact of specific design variables on water quality performance.  For example, the design hydraulic loading rate, bed configuration, media gradation and media composition are all critical factors influencing the performance of media filters.  Especially among manufactured treatment systems, there is a wide range of design and sizing approaches available that can result in high performance variability, even for two systems employing the same unit processes. For this reason, performance verification programs like the Washington State Department of Ecology TAPE program  and the New Jersey Department of Environmental Protection Stormwater Manufactured Treatment Device Protocols  and certification program are indispensable.  Both programs require the use of standardized testing protocols, require peer review of test results prior to publication, and issue MTD certifications that include specific design requirements and conditions of use. Performance data from these programs is directly linked to the specific design and sizing criteria of the tested systems and is directly comparable from test to test and technology to technology.

At Contech, we see field monitoring and lab testing following standardized protocols as critical steps in the ongoing process of developing, improving, and documenting performance of our portfolio of stormwater control measures.  As we continue to test our systems in the field, we will continue to add our data to the International Stormwater BMP Database.  We appreciate the visibility to peer reviewed research that the database provides and see it and the 2020 summary report as a great step forward in quantifying the connection between fundamental unit processes and pollutant removal.  

References:

[1] International Stormwater BMP Database. Available online at: https://www.bmpdatabase.org/

[2] The Water Environment Federation. 2020. International Stormwater BMP Database 2020 Summary Statistics. Project 4968. Available online at: https://www.waterrf.org/system/files/resource/2020-11/DRPT-4968_0.pdf

[3] Washington State Department of Ecology. Emerging stormwater treatment technologies (TAPE). Available online at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance-resources/Emerging-stormwater-treatment-technologies

[4] New Jersey Department of Environmental Protection. Stormwater Manufactured Treatment Devices.  Available online at: https://www.nj.gov/dep/stormwater/treatment.html