New Developments in Protection Drains
If dirt would just stay put, there’d be no problem. But, as we all know, dirt doesn’t stay put. Once disturbed, the earth’s topsoil tends to wander off and get lost someplace. Wind blows it away, feet and vehicles track it out, and stormwater washes it away.
BY MICHAEL MAZZARELLA & MARY ELIZABETH WILLIAMS-VILLANO
This last method of dispersal is the most troublesome of all. Because when that happens, dirt, or as we call it, sediment, finds the nearest storm drain and makes its getaway. But it doesn’t stop there. From the drain inlet, sediment eventually finds its way to larger bodies of water such as rivers, lakes, streams, and even oceans.
Sediment by itself is a bad enough actor, but then it brings its nasty little gang along, too; chemicals, fertilizers, herbicides, pesticides, petroleum distillates, dog waste, heavy metals and trash.
This bunch does even more environmental harm. Now that the body of water is polluted, it’s not safe for humans or other living things. Nutrients that grow grass and flowers on land are now in the water, causing algae blooms. The algae sucks all the oxygen out and kills the fish.
That’s why inlet protection devices, both temporary and permanent, have been invented, and re-invented, and reinvented again. The happy result is a number of new devices to help us do the job of sediment control.
New temporary devices
Companies that are in the business of disturbing earth are required to take measures to keep sediment onsite and file stormwater pollution prevention plans (SWPPP’s) for every project. Once a project is completed, these temporary devices are removed.
Inlet protection drains are intended to limit, if not completely eliminate, harmful materials from entering into bodies of water where they can do real damage. They perform this by functioning as filters, letting water pass through them and keeping everything else out.
In the effort to keep water clean, the inlet protection drain has been the frontline infantryman. “You should also have controls upstream,” says Rick Schmitt, CEO of Down to Earth Compliance in Aurora, Colorado. “But the inlet drain protection is really your last line of defense.”
Most temporary inlet protection devices either go directly on top of or across storm drain or curbside registers, or just below them. A witch’s hat is an example of a temporary device, essentially a geofabric bag that goes underneath a grate. Other catch basin devices can be either temporary or permanent, depending on the materials used.
“The old way of doing inlet protection is to pull a grate up, cut a square of silt fence, and put the grate back down over it,” said Vince Morris of Ertec Environmental Systems in Alameda, California.
“It’s not a great solution, as silt fence material doesn’t allow water to flow through. It plugs it up and backs up, and you get water in the street. That’s unsafe. But it’s still being used in many places around the country.”
Probably not for much longer. Morris says that municipalities, state DOTs (departments of transportation) and inspectors frown on that practice. Many DOTs across the country are forcing contractors to go to manufactured devices instead.
“Inlet protection used to be two-by-fours and a silt fence, then you’d make a wooden box around the perimeter of the grate to support the silt fence,” said Greg Vreeland, president of Dayton, Ohiobased SedCatch. “The problem is, it just doesn’t hold up to the heavy stuff.”
Of course, temporary drop and curb inlet protection devices are nothing new; we’ve been using them for years. The difference is that newer devices use geotextile fabric or media-filled geotextile tubes to trap and filter sediment, oils and chemicals. Water can flow through. That’s not new either; what is new is some of the forms they’re taking.
Some manufacturers of newer devices have discovered geometry. They’ve gotten away from the old box shape, and are literally going around in circles, exploiting the inherent strength found in the round shape or cylinder.
Vreeland cites a case where a cylindrical drop inlet protector, (essentially a steel frame with geotextile covering the sides, with an open top), was used at a Superfund site in Miamisburg, Ohio. A large volume of high-velocity water was rushing downstream at this site, carrying with it a great deal of rocks and gravel.
During an EPA inspection, it was found that the cylindrical protection device held up extremely well against a large torrent of runoff, rocks, gravel and sediment. The same event would probably have broken a wooden cage with ease. “The circular shape of the steel rod frame makes it difficult to crush,” said Vreeland. “Have you ever tried to push a cylinder with equal pressure from all around? If you push on a circle from all sides, it won’t give.”
Another cylindrical sediment catcher is designed to fit inside the ends of culvert pipes. A cylindrical wire frame forms an open tube, over which geotextile is stretched. The top remains open. These are made in different sizes to fit various pipe widths.
While the circle is a muscular shape, it’s not the only geometric form found in the new face of inlet protection devices.
Another device uses a polygon that’s been known for thousands of years, the pyramid. Geotextile fabric is stretched over a metal pyramidal frame, forming a tent. “The pyramid is one of the strongest shapes known in the world,” said Bryant Montague, designer at Raleigh, North Carolina-based Triangle Stormwater Solutions, Inc.
“It can’t fail. It’s a win for contractors, and it’s a win for municipalities.” The geotextile filter skirt stops sediment and debris, but allows the filtered water to leave the site.
In designing his pyramid device, Montague was motivated by the fact that he also operates a commercial development, grading and utilities business. “I wanted a system that was easy to maintain,” he said. “I didn’t want to worry about the inspector calling me, saying my chicken wire fell down, and my box is full of mud. It has cut down our costs much more than in the past, when all we had was silt fencing. But silt fences fail when you have too much rain.”
What’s new in permanent protection
Inlet protection isn’t just for construction sites, of course. When the need for inlet protection is ongoing, either post-construction or otherwise, you’ll need devices that are designed to work as occupation forces.
Some of the more permanent devices are more complicated. These products go far beyond mere collection and screening.
One class of device, made by several different manufacturers, functions like a small water treatment plant. Called hydrodynamic separators, they’re considered part of “emergent stormwater technology,” even though they’ve been around for a few years. The technology in them, however, is constantly being tweaked and refined.
Zach Crear, marketing director at Bio Clean Environmental Services, Inc., in Oceanside, California, explains how they work. “Stormwater enters the hydrodynamic separator and goes through a couple of stages. The first stage separates out the organic and trash solids; these are held separately from the water that’s now in the system.”
Separation occurs as the stormwater flows through a series of baffles. Sediment settles to the bottom. In the final stage, a “hydrocarbon boom,” essentially a filter sock, absorbs oils and other pollutants in the water.
“These kind of look like marine floats—that’s why they’re called booms,” Crear says. “They float on the surface of the water, and collect the greases and oils that sit on that surface.” Because the boom floats, it’s able to adapt to both low and high stormwater flows.
The main benefit of hydrodynamic separators is that organics aren’t left standing and stewing in the stormwater. Simpler devices filter out organics and trash, but until they’re cleaned out, the contaminating materials sit there, breaking down and producing still more contaminants. If another storm event follows before the device is cleaned, those contaminants will eventually wash into water bodies.
Many of the permanent solutions gaining in popularity have a distinct, eco-green flavor to them, as they incorporate bioretention principles into the way they work.
Bioretention is simply the process or removing contaminants and sedimentation by collecting runoff into a treatment area. This consists of a grass buffer strip, a sand bed, a ponding area, an organic or mulch layer, planting soil and plants.
A bioswale is a popular bioretention system; essentially it’s a shallow, trough-like depression, with gently sloped sides, filled with riprap and vegetation. Compost is sometimes used as well. The longer the runoff water sits in the swale, the more silt and pollutants —such as heavy metals, oils and other potentially harmful chemicals—are absorbed by the vegetation.
Bioswales are often used around parking lots. They’re a great example of symbiosis, as the nutrients in the water actually feed the vegetation.
“They’re very easy to set up, as long as you grade them properly,” says John Kincheloe, owner of Mitered Drains in Windsor, California. “With the right plantings, they’re very effective. The longer the bioswale, the more it’s able to filter out contaminants.”
It’s now possible to create a wetlands-in-a-box that filters and purifies water by mimicking nature’s own process. Like hydrodynamic separators, this system incorporates screening, hydrodynamic separation and absorptive media filtration, but adds a bioretention system.
Another new wrinkle is the use of recycled products in inlet protection devices. Using inlet protection that incorporates recycled material can earn you LEED points, and could be important to your client.
Even the best-designed systems require maintenance, a “gunking out” once in a while to keep them from clogging. In the past, cleaning out a drop inlet meant removing everything keeping it in place, a time-consuming practice. Some of the newer units can simply be pulled straight up; they’re designed to hold everything in place.
Fortunately, the manufacturers of the newer devices have made them easier to maintain than ever before. It makes the act of inspection and cleaning much less labor-intensive, saving time and money. The easier it is to clean out a device, the more likely it is to get cleaned out more often.
One bioswale-building company has developed a cartridge system that allows you to swap out soils and plants after they’ve reached maximum absorption of heavy metals and hydrocarbons.
“Instead of spending three to five days pulling out twenty inches of contaminated soil, our maintenance can be done before lunch,” said Jeff Coffman, founder of Clean Green Technology in Huntington Beach, California. “And the contaminated soil can be diluted down and turned into compost.”
Those of us involved in stormwater compliance have a bright future to look forward to. Manufacturers are rushing to provide us with new methods and devices that are easier than ever to install, inspect and maintain. Every day, the tools we use get more efficient and better for the environment.
It’ll be exciting to see what they come up with next.