The Stormwater Blog 

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


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Designing Stormwater Filtration Systems: Design Red Flags
With stormwater pollutant removal requirements increasing nationwide, the demand for robust filtration has also increased.  Designing and specify...
Categories: Treatment, Filtration
What About Plants?
One could argue that plants are the most essential part of biofiltration systems such as bioretention, high performance biofilters, and rain gardens.&...
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. 
Don’t Bypass Good Design Part 2: Diverting the Flow
In a previous post (Don’t Bypass Good Design Part 1: Offline Vs. Online Diversion Structures), I wrote about bypass structures and argued that they deserved more attention. In this follow-up, we’ll do just that by comparing two different ways to divert flow in a precast manhole. 
Categories: Treatment
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.

Filter Loading: Why Mass Load Capacity Matters in Flow-Through Filters
Given the number of conversations I’ve had in recent months with other stormwater professionals that don’t entirely understand the value of incorporating the sediment mass load capacity of a filtration BMP into the design process, I feel it’s time to revisit the subject.  
Sizing Considerations for Stormwater Filtration Systems
There are several factors to consider when selecting the most appropriate stormwater filtration solution for a specific site.  Several of these factors easily come to mind, such as: state or jurisdiction regulations, hydraulic grade line limitations, footprint constraints, and other site restrictions.  One variable that is often overlooked when reviewing a site is the methodology used to determine the specific quantity of filter cartridges or filter media.  Filter designs fall under one of three methods: flow-based design, volume-based design, or mass-load design.  
Categories: Treatment, Filtration
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. 
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