March-April 2006

Keeping Sediment Onsite

Effective ESC during construction.

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By Dan Rafter

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J.P. Johns faces a challenge early this year. That's when his company's plans will serve as the blueprint for moving an unnamed stream—which, over the years, has steadily eaten a new path into the earth—back to its original position as a tributary to the Reedy River in South Carolina's Greenville County.

PHOTO: WOOLPERT
Flexible growth matrik sprayed onto exposed soil

Moving the stream will require workers following plans created by Johns and his fellow engineers with Greenville-based Woolpert Inc. to dig up large mounds of earth, cut deep into surrounding slopes, and stabilize the repositioned stream's new banks. If a heavy rainfall should hit the site during construction, scheduled to begin early in 2006, sediment and dirt from displaced earth could easily wash into either the stream or the Reedy River, dirtying the water in either.

Johns, though, is confident that his company can meet this challenge. His firm has been planning for the job for months, first beginning work on site plans in the middle of 2005. As of late October, Woolpert engineers had completed about 95% of the project plans, were preparing to request bids on the work, and were confident that they had taken the steps necessary to limit sediment runoff.

"At certain stages of the project the land surrounding the stream will almost be in a completely bare soil state," says Johns, an engineer and project manager with Woolpert. "We're going to be removing vegetation, and we won't have any distance from our work site to the stream. We are going to be working right where the stream is."

To prevent sediment runoff, the engineers at Woolpert are turning to a host of tools. They'll be using the Silt-Saver, a round-framed inlet protection device. They'll rely on A-Jacks, interlocking pieces of concrete that workers will place at the top of the stream's slope. And that's just the beginning. Johns expects his company to also turn to sediment tubes, erosion control blankets, turf reinforcement mats, and a sediment trap with three lines of baffles in it, a device that will act as a replacement for silt fence.

PHOTO: WOOLPERT
Erosion control blankets being installed on a slope on a South Carolina Department of Transportation project.

Using so many products may seem extreme, but the way Johns sees it, providing many layers of sediment control makes good sense.

"We want the water coming into this stream to be as clean as possible," Johns says. "And the county officials want that, too. People are more aware now of controlling sediment runoff than they ever have been."

Contractors, engineers, and developers across the country are steadily growing more comfortable dealing with the Phase II requirements of the National Pollutant Discharge Elimination System (NPDES). Under these regulations, now even professionals working on smaller job sites face heavy fines when large amounts of sediment leave their work sites and infect nearby surface waters.

Fortunately for both private and public planners, engineers, and developers, companies offer an ever-growing number of products designed to help them keep dirt and other sediment from draining into lakes, rivers, or ponds. The options include some old standbys, such as silt fence and hay bales, but also more advanced products, such as straw or coir wattles, settling ponds, and coagulants, that contractors can use to cause sediment particles in water to clump together and, thanks to their heavier weight, settle out.

PHOTO: WOOLPERT
Hydraulically applied products provide fast coverage.

The manufacturers of these products are not naive when it comes to the increased demand they are seeing for their products. They know that the threat of fines is the primary motivator for many of the contractors and developers calling for more efficient ways to stop sediment runoff.

"Going to the next phase of the NPDES regulations really shook some people up," says Rob Stump of Sacramento, CA–based Sacramento Bag Manufacturing Co. "Everyone is aware of the growing regulations in this marketplace. Everyone is out to avoid the fines. They look at a lot of sediment control as a necessary evil. They'd rather pay a little upfront for the products than pay a lot more for the fines and the cleanup later."

Whatever the motive, though, it is clear that increased demand has led to a growing number of options for builders, engineers, and developers looking to keep sediment under control. Here is a look at some of the strategies contractors and developers can now use to keep their sediment from running off their work sites.

Moving Quickly
Max Boone, owner of MB Erosion Control in Memphis, TN, is thrilled that technology is making the task of controlling runoff easier. Boone tackles erosion problems each year on a host of projects, both residential and commercial construction. The less time he has to spend on worrying about dirt running into streams or ponds, the more time he can spend grabbing new work.

This is why Boone is such a fan of the Silt Fence Plow manufactured by Pleasantville, IA–based McCormick Equipment. The plow allows contractors to install silt fence—one of the traditional methods of controlling runoff—at a far faster rate than they could by using a traditional trencher. The machine also disturbs far less earth than a trencher does, making runoff less of a problem.

Boone estimates that the plow allows him and his crews to install 7,000 square feet of silt fence in a workday. If using a trencher, his crews can only install about 2,500 feet a day, Boone says.

"It's a blessing. I am surprised that more people don't use it," he says. "But I have to admit, I'm glad they don't. When we can go in and install it so quickly, it sort of mesmerizes people. They're used to seeing the fence put in the old way."

Boone's plow has come in handy in Pontotoc, MS. In the middle of October, Boone and his crews began erosion control work on a site that will soon host a new Wal-Mart store. The job calls for MB Erosion Control to install 14,000 feet worth of silt fence.

"It's not that unique, really," Boone says. "We've been in business now going on four years. With the plow, especially, this job is like another day in paradise for us." With a trencher, Boone says, it would probably take his crews five or six days to install the 14,000 feet of silt fence. Boone estimated before the project that it would probably take the same workers just two to two-and-a-half days to do the same job.

Boone's company also worked late last year to install 6 miles of silt fence outside a new housing subdivision being built in Collierville, TN. That is a big job, not a routine one. But Boone was far from worried about being able to complete it in a timely fashion. Next Page >

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