Proper sizing of hydrodynamic separators (HDS) should start with checking applicable regulations. In many cases, local or state regulations will dictate how to size an HDS system and even provide a list of what products are approved for use.  If there are no regulatory requirements, the engineer must identify which pollutant(s) need to be removed

It’s that time of year again - temperatures have dropped below freezing, and the wintery weather has blown in. Departments of Transportation, state, local and city road crews are being kept on their toes, applying roadway treatments and safe passage for all of us. It is estimated that the US spends approximately $2.3 billion annually to keep highways free of snow and ice, and roughly 20% of transportation department budgets goes toward winter road maintenance.

There are certain hazards with any profession. For a stormwater engineer, mine takes the form of gentle teasing from friends and family as I stoop in parking lots peering down grates into the abyss.What am I looking for? Well, like most stormwater infrastructure, nearly every Contech product is buried. My work is completely hidden underground!

When it comes to using hydrodynamic separator (HDS) treatment devices, it is becoming commonplace to integrate them into storm sewer networks without worrying about the hydraulic impact of the device. After all, the majority of these devices are manholes or vaults with flow-through treatment, which are seemingly uncomplicated when compared to those

With stormwater pollutant removal requirements increasing nationwide, the demand for robust filtration has also increased.  Designing and specifying a properly functioning filter extends beyond specifying the correct product (media or membrane filter) and sizing correctly (flow or volume based).  These additional considerations are classified as

One could argue that plants are the most essential part of biofiltration systems such as bioretention, high performance biofilters, and rain gardens.  However, plant design presents a unique challenge for system designers.  What types of plants should be selected?  Will they work well in the system? Will they be aesthetically pleasing?  Designing a

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

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. Option One: Using a manhole with different elevation outlet pipes With

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

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

Read Part 1: Frustration is a Two-Way Street 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

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.  We tend to think about BMP design in terms of treatment capacity which is

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

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

Plants provide fresh oxygen to breathe and beautiful aesthetics that can take our breath away, but many people don’t think about the role plants can play in stormwater treatment. The principal notion of Low Impact Development (LID) is founded upon mimicking pre-development conditions. Part of mimicking pre-development conditions includes not just

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

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

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

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

There are a vast number of stormwater separators on the market which can make it challenging when selecting the ideal solution for each project.  Hydrodynamic separators and oil/water separators are often used interchangeably in the industry but each system is unique and one may be better suited for the overall treatment goals of the project.   So

Stormwater regulations are calling for an increased level of treatment. This often takes the form of filtration systems. Two types of filtration systems used in stormwater are media filtration and membrane filtration.Media Filtration systems function through physical capture of pollutants, as well as adsorption of pollutants through chemical

The only sure way to eliminate stormwater pollution is to eliminate stormwater runoff. In recognition of this fact, Green Infrastructure (GI) and Low Impact Development (LID) practices have prioritized runoff reduction as a primary regulation for stormwater management.  These practices have proliferated throughout the United States.Surface

Using harvested rainwater is not new, it has been in practice for thousands of years (3000 B.C., and may be even earlier).  But we have something that wasn’t available back then; the ability to disinfect rainwater to make it safe for human contact or ingestion.  Harvested rainwater can be safely used outdoors and indoors if the correct steps are

In my last blog post, What Kind of Trash and Debris is in Stormwater Runoff?, I wrote about the types of trash found in stormwater and the effects trash and debris have on our environment and infrastructure. Continuing with the topic of trash control; if your community is interested in developing a trash control strategy here are six key points

Remember when stormwater filtration was at the forefront of runoff water quality treatment?  Have the variables and performances that led to its successful history been displaced by recent Green Infrastructure (GI) or Low Impact Development (LID) initiatives, or is filtration a viable partner in the GI and LID arena?  Boiling it down, why should we

We all know that stormwater runoff carries trash and debris into our water ways, but have you ever wondered what kind of material this runoff picks up?A Contech Continuous Deflective Separation unit (CDS) was installed on a site in California and the performance of the unit was monitored over a 12 months. During a maintenance event, the trash and

Stormwater infiltration is defined as the process by which water enters the soil and recharges streams, lakes, rivers, and underground aquifers. Stormwater infiltration is a fundamental component of the water cycle and is quickly becoming the centerpiece of stormwater management strategies across the United States.  Stormwater infiltration is an

System hydraulics refers to how water flows through a stormwater filtration system. The following three steps should be part of the hydraulics evaluation process.1. Evaluate the hydraulic grade line (HGL) at the design flow rate. Typically, a backwater calculation from the point of downstream control should be performed to ensure the system can

During the past decade, a number of different media have been used for stormwater filtration and more recently for bioretention.  Media such as sand, peat, and compost have been used successfully.  Uses of perlite, zeolite, carbon, and other "exotic" media have expanded the choices for targeting specific pollutants.   Media are now being used to

Since the Environmental Protection Agency, and in turn state and local regulators, have gone all in on green infrastructure (GI) and low impact development (LID) concepts a seemingly regrettable consequence has emerged.  Topics specific to the broader adoption and implementation of GI have monopolized our collective dialog on stormwater management

Traditional stormwater criteria require both improving the quality and managing the quantity of runoff. One of the best practices is to incorporate pretreatment, detention and treatment into an integrated system. This approach can meet total daily maximum load requirements by providing a high level of pollutant removal and preventing erosion damage

As the need for effective stormwater treatment and volume control grows, so does the number of available stormwater control measures (SCMs) such as filtration systems, hydrodynamic separators, bio-retention  systems, green roofs and pervious pavement. As part of their due diligence, engineers go through an evaluation process to determine if the

The removal of site-specific pollutants can be maximized with the variety of filtration media available. Understanding the hydraulics of the media you choose is a key, albeit misunderstood, factor in determining the effectiveness of the filtration system. Here are five things you should consider.1) Evaluate the specific flow rate (q) through the

An increasing challenge that we see with our customers is balancing water quality with water quantity. Conventional design would be to use an in ground detention pond. But, if this is not an option, whether the owner does not want the aesthetics of a pond, the land needs to be used for parking, or you have a layer of clay soil that makes

During the past few years, a number of different filter media have been used for stormwater filtration. Media such as sand, peat, and compost have been used successfully. Recent uses of perlite, zeolite, carbon, and other “exotic” media have expanded the choices for targeting specific pollutants. Here are some questions you should ask when

 This short video explains how rainwater harvesting is a logical and feasible approach to managing stormwater runoff, citing example usage for a typical commercial office building.Current engineering practice divides management of drinking water, stormwater, and wastewater. A typical commercial office building may average 3.1 million gallons of

This patented technology is employed by the Stormwater Management StormFilter in order to prevent surface blinding, ensure use of all media, and prolong cartridge life. In principal, the system siphons stormwater runoff through its cartridge.First, stormwater enters a StormFilter cartridge, percolates horizontally through the cartridge’s filter

Filtration CharacteristicsMedia Surface AreaFiltration flow rates are typically expressed as a surface area specific operating rate such as gallons per minute per square foot (gpm/ft2) of surface area. Lower specific operating rates translate to better performance and longer maintenance cycles. Specific operating rates higher than 2 gpm/ft2 of

Filtering stormwater is an effective way to remove the most challenging pollutants from urban runoff - including fine solids, soluble heavy metals, and total nutrients. Though the physics of filtration are the same, there are many variables to consider when designing a stormwater filtration system. It’s important when designing a filter treatment

All stormwater BMP’s will require maintenance at some time or time interval. Long-term maintenance costs and maintainability are very important considerations. Here are some other things you should consider when discussing maintenance of your stormwater filtration system.1. Evaluate availability of maintenance contracting. It is the nature of