The Stormwater Blog 

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


Treatment


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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 de...
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 disapp...
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 b...
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. 
Hydrodynamic Separation Devices: Online Vs. Offline
The question of whether a hydrodynamic separator should be online vs. offline is something that engineers and stormwater treatment manufacturers deal with on a daily basis.  Online systems allow storm events that are greater than the design storm to be bypassed through the treatment unit, eliminating the need for a separate bypass structure.  This results in fewer structures and a smaller system footprint; which leads to a lower landed cost.  
Rain Gardens Not Permitted?

Current stormwater design guidance typically recommends starting with preservation of the natural landscape and hydrology wherever feasible. But, even with preservation, new stormwater management facilities are likely to be required to capture and clean runoff from pollution generating surfaces. These new stormwater facilities are likely to include imported soil or soil amendments that add permeability and/or optimize soil structure for vegetative growth. For many years, the industry has characterized media in vegetated facilities generically as soil, sand, compost, etc.

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.

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