Crews find devices save time and labor for working with this staple of sediment control.

By Bill Tice

Although it's long been a basic component at countless job sites, silt fence has been frequently criticized over the years as not being a particularly efficient method of silt and sediment control. According to many of the experts who install the product and use it every day, the problem is not the silt fence, but how it is installed. And despite its sometimes less-than-stellar reputation, silt fence is not going to disappear from the radar screen anytime soon, as it is frequently the filtering method of choice of site specifiers and permitting authorities at the city, county, state, and federal levels.

Silt fence is typically defined as a temporary barrier or filter that is manufactured from a fabric. The fence is stretched across an area that could potentially carry silt and sediment from a construction site, or an area that has been disturbed by manmade or natural activity. The product has numerous applications, but it is commonly used on road and highway construction sites, new commercial and residential developments, and golf courses. It is generally manufactured from a woven fabric cloth (also known as a geotextile) and is sometimes backed with a wire or plastic meshing material that adds strength and durability. The product is available with a number of different properties, but most government agencies and developers specify three types of silt fence: A, B, and C.

Type A silt fence is manufactured from a 36-inch-wide fabric and is generally specified on projects that will last more than six months. Type B silt fence is 22 inches wide, but must allow the same flow rate as type A silt fence. Type B is usually limited to smaller projects such as residential home sites where permanent erosion control will be achieved in less than six months. Like type A silt fence, type C is also 36 inches wide, but includes wire reinforcement. Type C silt fence is used where runoff flows or velocities are higher than normal, or where slopes exceed a vertical height of 10 feet. Most silt fence products are available with or without posts attached, allowing installation contractors a number of choices when it comes to silt fence construction methods.

With all of the different types of silt fence available, the product is often touted as "a one product fits all" solution to erosion control problems, and in many cases, the bad rap that silt fence has received in the past can also be attributed to specifiers who are guilty of expecting the product to do too much on a construction site or other runoff site. According to Matt Bryan, the stormwater pollution prevention plan (SWPPP) service manager for Sacramento, CA­based Thunder Mountain Enterprises Inc., if other erosion control methods on a site are used properly, the silt fence will rarely see any action.

"The silt fence is actually one of your last lines of defense against silt and sediment runoff," explains Bryan, whose company specializes in SWPPP design and implementation, along with habitat restoration, containment liners, and wetland mediation for land developers and track builders. "Your silt fence is there for perimeter protection, and if the silt and sediment reaches that point, you are failing somewhere else in your erosion control plan."

In conjunction with silt fence, Thunder Mountain uses a number of other erosion control methods on its sites, including coir and straw blankets, turf reinforcement mats (TRMs), straw wattles, and silt bags and rock bags. In some cases, where there might be a high volume of sediment movement, the company uses a double row of silt fence with rock bags on each side for added strength and protection. But for Bryan, that last line of defense has to be installed properly or it might as well not be there at all.

"We stress proper installation techniques with our crews, including the little things like making sure the fabric is attached properly to the posts, not leaving a gap where two pieces of silt fence meet, and making sure the silt fence is tight. All of our training is on-the-job field training, so we teach new employees by example."

Bryan says the biggest mistake he sees with installation is not going deep enough into the ground with the silt fence, or not trenching the silt fence at all. Typically, the fence must be buried 6 to 12 inches in the ground, and the surrounding area must be re-compacted; otherwise, the water flows under the fence, taking silt and sediment with it.

Silt fence being installed by A.J. Garrett and Associates of Des Moines, IA.

Thunder Mountain purchases most of its silt fence products and supplies from Reed and Graham Inc. in Sacramento, CA, and uses a ride-on Ditch Witch tractor for a majority of its trenching work. Once the trench has been dug, an employee lays the silt fence in by hand, and another employee comes along behind to hammer in the stakes. Finally, a blade on the front of the Ditch Witch is used to push the soil back on one side of the silt fence, while soil on the opposite side is put back in place with a shovel. The soil is then compacted.

"This method works well for us in most scenarios," says Bryan. "We do have to deal with a lot of rock and cobble here in the Sacramento area, so we sometimes have to go with metal stakes as the wood stakes just break, but each job is different."

With manual installation of silt fence being labor-intensive and extremely time-consuming, a number of companies have developed equipment that is designed for the single purpose of installing silt fence. This equipment generally works as an attachment on readily available carrier machines, such as skid-steers or farm tractors.

George Friez, an engineer with Gilman Construction in Butte, MT, found a manufacturer just 80 miles away, in Bozeman, MT, that designed a silt fence installer attachment for skid-steers and front-end loaders. "We had seen the ImpleMax silt fence installer in a magazine, and we had a big job to do for the Montana Department of Transportation [DOT] that required 10 to 12 miles of silt fence installation," notes Friez. "This was a total reconstruction project on State Highway 84, near Bozeman, so there was lots of pipe work, gravel, and paving, which disturbed the existing ground for the entire length of the project. We used straw wattles, straw blankets, and gravel berms in conjunction with hydroseeding for the steep slopes and drill seeding for the flatter ground. The silt fence played a big role in preventing any sediment from leaving the project."

Gilman Construction purchased the ImpleMax SF12c in the spring of 2003, specifically for the Highway 84 project, and used it on a Caterpillar skid-steer. "We knew that we had to do something to get this job completed in a timely and cost-effective manner," says Friez. "We based the purchase of the attachment on the fact that it would pay for itself with the labor savings on just this one job alone, and it has."

The ImpleMax attachment offers an automated process that essentially cuts the ground and inserts the fence material while leaving the surrounding soil undisturbed and firm for staking. It can install up to 100 feet of silt fence per minute (at 12 inches deep), and can also be used to remove silt fencing when the project is completed and natural erosion control methods have taken effect.

Although the Gilman crew found the ImpleMax to be very efficient, Friez says they have not had many other opportunities to use the attachment, as the Montana DOT is one of the few agencies that is moving away from silt fence. "The equipment worked great and saved us a lot of time and money, but here in Montana, the DOT is moving more toward the use of straw wattles and gravel berms, primarily because of the visual effect silt fence has on the landscape and the fact that silt fence needs to stay up for a few months after we leave a project. Then it becomes the responsibility of the state to remove it and dispose of it."

The McCormick silt fence plow, which is manufactured by McCormick Equipment in Pleasantville, IA, is also compatible with farm tractors, and with the use of a skid loader plate can be used with most skid-steer models. Like the ImpleMax, the McCormick plow slices the ground and inserts the silt fence in a single pass, creating less soil disturbance and a tightly installed silt fence.

Greg Banford, of Dirt Works Erosion Control Inc. in Augusta, GA, has been using the McCormick plow for about three years and likes the durability of the product, and the cost savings associated with using the plow.

"The soil we have here in the Central Savannah River Area [CSRA] is clay-based and it can be very hard, so we needed something durable that would have very little downtime," explains Banford, who heads Dirt Works, a general erosion control company that works on hydroseeding projects and installs blankets, mats, and other erosion control products. "The McCormick plow has provided us with that durability, and we have been able to fix any breakages on-site with a minor weld job."

Like Matt Bryan of Thunder Mountain Enterprises in California, Banford stresses that silt fence is a safety measure when used with other best management practices (BMPs), but it still needs to be installed properly.

"Improper placement, improper quantities, improper installation, and the use of improper materials are the biggest mistakes contractors make when installing silt fence," explains Banford. "The plow helps us install the fence properly as it cuts only a 1-inch slice in the ground versus a 4-inch channel that you would get with a standard trenching machine."

For Banford, having the job done correctly is extremely important. "Our company name goes on every piece of silt fence that we install. We started this business doing things properly, and if we can't do it properly because the specifications in the bid are not up to our standards, we won't take on the job."

Having well-trained employees is one of the ways Banford ensures his reputation is kept intact. "We hire long-term employees and we tell them when they start with us that Othis is a career, not just a stop-off point to somewhere else.' We have an extensive training program and all of our employees attend seminars and get certified."

Curt Dalziel of Dalziel Enterprises in Eldridge, IA, has also had success with the McCormick plow. Dalziel was using a trencher but decided to go with the plow because of the slicing technology, which is preferable in the hard ground in his area.

"One of the biggest problems we have here when installing silt fence is scouring, which occurs when the soil is not tight enough around the fence so water gets underneath. With the plow, we can eliminate that problem, which means our silt fence is much more effective."

Dalziel, who has been in the erosion control business for more than 20 years, uses a variety of techniques in conjunction with silt fence, including hydromulching, straw mulch, blankets, native grass seeding, and riprap.

Another popular tool in the marketplace is the tommy Silt Fence Machine, which mechanically installs silt fence under a variety of conditions. The tommy, from Carpenter Erosion Control in Ankeny, IA, also utilizes a slicing method to slice through the soil rather than excavating it. According to the manufacturer, "slicing minimally disrupts the soil upward and slightly displaces the soil, maintaining the soil's profile and creating an optimal condition for future mechanical compaction." At the same time, silt fence is pulled off the roll by a ground-driven vertical wheel, funneled into the apparatus, converted to a vertical position, and inserted into the soil. As the machine moves along, the soil collapses onto the now-inserted silt fence, which secures it in place until a laborer comes along behind the machine and hammers in the stakes.

The One Man Pull allows one person to hold and drive in silt fence stakes.

For the end user, like Tom Lingvai, president and owner of Lingvai Excavating LLC in Bryan, OH, using a machine like the tommy just makes economic sense. Lingvai's company, which employs close to 40 people depending on the season, has been in business for 20 years and does general site development, street reconstruction, subdivision projects, and other types of excavation work.

"Silt fence has become the standard for silt and sediment control in our industry, and generally all of the projects we bid on have a slit fence requirement," explains Lingvai, who pulls the silt fence machine with a basic farm tractor. "Using a task-specific machine can bring the silt fence requirements of our projects in at a third to a half of the cost of using other trench digging equipment or hand installation, and this can have a dramatic effect on our bottom line."

As an example of the cost savings that can be realized, Lingvai points to a school job his company did in Edon, OH, which is close to the Indiana border in the northwest corner of the state. "The Edon job was the first major project we used the tommy machine for, and we had estimated that it would take 60 man-hours to install the 3,300 linear feet of silt fence that was specified. We actually completed the job in just 30 hours, with only five hours of that time used to put the silt fence in the ground. The rest of the time was manual labor to put in the stakes and finish the job."

With the Ohio Environmental Protection Agency requiring silt fence for most of Lingvai's jobs, he thought "there must be a better and faster way of putting up silt fence than the traditional methods." He found the tommy machine six years ago at the Con Expo in Las Vegas, and hasn't looked back since. "Not only can we install the silt fence faster and easier, but we can install it better," adds Lingvai. "After installation, the silt fence can be so tight in the ground that it is difficult to remove it when it comes time to finish the project."

Jay Watson, owner of Twin Oaks Environmental in Winter Park, FL, also uses the tommy Silt Fence Machine, and like his Ohio counterpart, Watson finds the machine is extremely efficient. "We did our first job this morning, which was 800 feet," he says, describing his schedule for the day we caught up with him. "We unloaded the tommy at 8:20 a.m. and put it back on the trailer at 9:00 a.m. Then by 2:00 p.m., we had installed another 2,340 feet of silt fence on another project, and we took an hour for lunch."

Watson, who has only been in business since May 2003 and does mainly subdivision work for new home developments, says he has never used anything else for silt fence installation. He discovered the tommy machine on the Internet, had one shipped to Florida, and has been happy with it ever since.

Even with all of the attachments and installation equipment available, most silt fence installers concede that one of the most labor-intensive aspects of the job is pounding in the posts or stakes. This has to be done after the silt fence has been laid in place, regardless of what equipment has been used.

For Stephen Sweany of Sweany Enterprises in Dallas, GA, a fairly new product from GCS Erosion Control has proven to be helpful in this regard. Sweany purchases most of his erosion control products from GCS, which is also located in Dallas, and has been using the company's One Man Pull for about four years. GCS developed the tool 15 years ago for its own use when installing silt fence but only recently started mass marketing the product. Shawn Whitener of GCS says they realized there was a need for the One Man Pull when the company's crews were installing silt fence and crew members were getting hurt with sledge hammers. The One Man Pull is a belt that hooks around the stake or post, holding it in position while it is being driven into the ground. It also eliminates the man-hours required for the person holding the stake.

"The big benefit is the fact that one person can install the stakes and do it safely," notes Sweany. "We go with a crew of three and one person puts in the fence, one person installs the stakes, and the third person compacts the soil. It works really well for us and we can install up to 3,000 feet of silt fence in a day."

Sweany says he came across the One Man Pull while visiting GCS one day. "They threw one of them to me and said, 'Try this out.' They are very inexpensive, so now we keep one in each of our trucks."

Even with silt fence being a relatively simple product, companies in the industry are constantly trying to improve on what is available in the marketplace, and Silt-Saver Inc. in Conyers, GA, is no exception. Silt-Saver is known in the industry for its inlet protection and filtration devices and is also working with the John Mansville Company to develop and produce belted silt-retention fence. The new product, which is expected to be introduced in late 2004, uses linear belts created from a fiberglass scrim, which are inserted into the spunbond polyester fabric during the manufacturing process. The support system and the filter fabric are created as one piece, eliminating the need for wire reinforcement. The belted system also disperses the load throughout the linear belts, which reduces the pressure points and the subsequent failures that can occur in other types of silt fence materials. The product will also be 42 inches wide, which still allows for 28 inches above the ground and another 14 inches that can form a J-hook in the ditch. By filling the J-hook with dirt during the backfills, blowout can be minimized.

Bill Tice is based in Blaine, WA.

EC - November December 2004