The Stormwater Blog 

Contech Stormwater experts discuss designing stormwater BMP’s, regulations, maintenance issues, and all things stormwater.


Regulations


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Seeing the Forest and the Trees in Stormwater Treatment System Monitoring Data
The International Stormwater Best Management Practices (BMP) Database project website (http://bmpdatabase.org) features a database that includes over 600 BMP performance studies.  This is a tremendous free resource for engineers, scientists, policymakers and others who seek to characterize the pollutant removal and hydrologic performance of various stormwater treatment systems. And, like any database, it is only as reliable as the information that goes into it.  To improve reliability, their website also includes monitoring program design guidance and data input tools that allow a standardized format and content for summary reports.  However, whether looking at an individual test of a single treatment system or a database with hundreds of results, it is important to focus not only what the data tells us, but also what stories we may be missing. 
What Tools Are in Your Stormwater Toolbox?
Over the last 20 years of site-civil design, it has been interesting to see stormwater trends come and go.  Some design methodologies have disappeared, only to return later or in a nearby geography as the “new” approach.  Agency directives can shift based on new leadership or the prevalent regional concerns at the time.  As the construction industry finds less expensive solutions or improved constructability, they can also lead a shift in regional site design.  Things change—and from many angles.
Don’t Bypass Good Design Part 1: Offline Vs. Online Diversion Structures
Months of design, pages of specifications, and tens or even hundreds of thousands of dollars may go into the design of a single bioswale, filtration basin, or other stormwater treatment system. So why do we spend so little time thinking about the flow control devices that make them work? This article is part one of a two-part series on bypass design and focuses on external diversion structures as compared to treatment units with internal bypass capability.
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.

Manufactured Stormwater Treatment Devices (MTDs) Frustrations, Misperceptions, and Concerns.  Part 1: Frustration is a Two-Way Street
Having spent the last sixteen years immersed in the world of stormwater best management practices (BMPs), with particular emphasis on manufactured treatment devices (MTDs), I’ve repeatedly borne witness to the frustrations, misperceptions, and concerns raised by all walks of stormwater professionals relative to MTDs.  
Categories: Regulations
Limited Parking
This month’s blog post comes from Janice Kaspersen, editor of Stormwater magazine.

Did you drive to work this morning? Was a parking space waiting for you when you arrived? Many cities require developers to provide a minimum number of parking spaces for office, retail, and residential buildings; sometimes the number is based on the square footage of the building, sometimes on occupancy. Many calculate the required number of spaces based on peak demand. 

Categories: Regulations
How to Size a Hydrodynamic Separator
Hydrodynamic Separators (HDS) have been used in the stormwater industry for over 20 years.  They are effective at removing TSS, hydrocarbons, and trash and debris from stormwater runoff and are often used for standalone treatment or pretreatment to filtration, detention, infiltration and rainwater harvesting system.  With the varied applications for HDS units comes a multitude of sizing options. 
All Stormwater Particles Are Not The Same Part 2: Particle Shape And Density

EPA selected a removal standard of 80% total suspended solids (TSS) removal as the target pollutant of concern due to high TSS concentrations ubiquitous impact on water quality and degradation to aquatic habitat. Many other pollutants of concern are particle-bound, and TSS is thereby a surrogate for other pollutants. Testing methodologies for stormwater control measures (SCMs) in respects to TSS can vary greatly. There are many sediment characteristics that should be considered when evaluating a SCM for TSS removal performance to ensure apples and apples are being compared among removal efficiencies for SCMs.

All Stormwater Particles Are Not The Same. Part 1: Particle Size And Composition

The EPA selected a removal standard of 80% total suspended solids (TSS) removal as the target pollutant of concern due to high TSS concentrations impact on water quality and degradation to aquatic habitat. Many other pollutants of concern are particle-bound, and TSS is thereby a surrogate for other pollutants. Testing methodologies for stormwater control measures (SCMs) in respects to TSS can vary greatly. In part two, we’ll continue our look at stormwater sediment and discuss particle shape and density and their affect on TSS removal.

Bioretention Part Three: Lessons Being  Learned – Siting Issues and Inlet Design

Not done with siting issues yet, maybe this becomes five parts? One issue on siting and design is the hydraulic grade lines. Recall from your road drainage days the equations that were used to space catch pits and throat openings? The equations allowed for you to estimate gutter efficiency and top width for specified design storms. Well, these equations still apply, and I am thinking maybe even more considerations for very low flows.

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