Silt fence and other inlet protection strategies

By Tara Beecham

Just as a prizefighter pummels through a one-sided match, controlling sediment can sometimes seem like battling a force of nature. Just one powerful storm system can cause project delays or penalties if sediment is carried offsite. But connecting the right erosion and sediment control methods to the project site can feel like winning the first round.

Not just a matter of keeping a schedule anymore, sediment control is essential for compliance with Phase II of the National Pollutant Discharge Elimination System (NPDES), and avoiding the fines and stop-work orders that can sometimes result from a poorly controlled site.

Financial motivation and pressure to complete the work on deadline under the new restrictions has led contractors to seriously consider their own methods of sediment and inlet control for effectiveness.

Silt fence remains a common fixture on American work sites, nearly as much so as the hardhat. But popularity is rarely without a challenge, and many state department of transportation workers and erosion control specialists have their own preferences when it comes to fence installation, which is so critical to effectiveness, and usage.

Facing Challenges in the Midwest
Providing sediment control on highway construction projects can present a challenge for the Kansas Department of Transportation (KDOT).

“Some of these challenges include controlling erosion during construction to prevent destruction of completed work; meeting local, state, and federal regulations; vegetation establishment; and the long-term maintenance costs associated with improper erosion and sediment control during construction,” says Scott Vogel, chief of the environmental services section of KDOT. “An additional challenge KDOT faces is maintaining erosion and sediment control for the safety of drivers on Kansas roadways, as uncontrolled sediment and erosion can lead to flooding or undercutting of established roadways.”

PHOTO: CARPENTER EROSION CONTROL

PHOTO: CARPENTER EROSION CONTROL

The organization uses erosion control products that have been pre-approved by the Texas Transportation Institute (TTI), explains Greg Morgan, an environmental scientist with KDOT, because all of the TTI-approved products meet KDOT’s standard specifications when used properly.

“The specifications and control measures are used in areas that are in need of specialized erosion and sediment control, which are based upon soil type, slope, hydrology, and in some cases wind erosion potential,” says Vogel. “In general, KDOT specifies straw mulch with a tacking agent overspray to be placed over the seedbed throughout the entire project and ditch checks [hay bales or rock] to be used in ditches to reduce water flow velocity and shear stress on the soil resulting from these velocities.”

During a highway project on US-36, for example, bonded fiber was used to keep soil in place “on temporary slopes that were going to be rebuilt before vegetation had time to be established,” according to Vogel. The cost-effectiveness and the quality of erosion control temporary seeding bring appeals to KDOT, which uses it in all the projects it proposes.

“KDOT has found a combination of erosion and sediment control practices to be the most effective in preventing erosion on construction sites,” notes Vogel. “For example, many projects use hay bale or rock ditch checks to protect ditch channels in combination with turf-reinforcement matting for slope protection.”

The organization holds inspections daily during a project’s construction. According to Vogel, KDOT must approve all of a contractor’s sediment and erosion control practices that will be implemented during construction. Weather can affect inspections as well.

“During the vegetation establishment phase, completed portions of all projects are inspected within 24 hours after a rain event,” says Vogel.

PHOTO: WEYERHAEUSER CO.

PHOTO: DAVE STEINFELD

Even fair weather can have a negative effect on a project’s budget. “You may place a lot of money into sediment control, and due to lack of erosive forces—rain—they may not have been needed,” explains Dean VanDeWiele, a design engineer and specialty squad leader for erosion and sediment control plans at the South Dakota Department of Transportation (SDDOT). “Thus, the money spent is scrutinized.”

In addition to protecting the site from the weather, other highway project challenges have to do with balancing the erosion control steps taken with the project itself.

“One problem is timing and workspace,” notes Phil Dwight, field engineer for SDDOT. “[Another is] trying to get the job done without erosion control devices being in the way but getting the devices in place when needed.”

Dan Neaton, co-owner of Neaton Brothers Environmental Control in Watertown, MN, has used between 10,000 and 15,000 feet of silt fence for sediment control along the boundary of an ongoing project on Highway 12 in Long Lake, MN, during the past two years. It was necessary to grade large areas of the site at one time, and he used Burchland Manufacturing’s silt fence installer to install the fence as his company worked to prevent erosion.

“It’s cost-effective compared to some other ones,” he says. “Once you plow it in, it’s a foot down. As you go over terrain, the [silt fence] material stays exactly in depth. They don’t have to adjust the fabric height. Once you plow it into the ground, you don’t have to worry about pulling it back up or setting it in deeper. You can get onto the next step without worrying about one step being lower, one step being higher.”

The fact that the machine can perform in narrow spaces appealed to Neaton. The pivot on the machine that follows the tractor is sharp, he says, allowing the fabric to remain both straight and even.

“The main feature that sets our plow apart from other silt fence installers is the tight turning radius. Our machine has a narrow frame design with a pivot directly behind the three-point or skid-steer mount,” says Aaron Burchland, owner of Burchland Manufacturing. “This allows the plow frame to pivot 45 degrees from centerline when plowing around a curve. The whole plow follows the tractor or skid-steer like a trailer when going around a curve. No moving parts are required to put the fabric into the ground.” This is important, Burchland notes, because static plowing is faster than digging by hand or trenching. Cost control is important to clients, which, in turn, makes it important to Burchland.

PHOTO: ENVIRONMENTAL SOLUTIONS OF IOWA

PHOTO: FOREST CONCEPTS

“Clients save money with the speed of installation and low labor costs,” he says. “Our machine does not fold the fabric, allowing full use of the 36-inch material. With 12 inches below ground and 24 inches above ground, blowouts are much less likely. Also, static slicing can be compacted much better than the trenching method.”

It was the owner’s open-minded attitude and a good working relationship that also appealed to Neaton, who notes that Burchland sought input from his clients, asking them what they liked and didn’t like about the company’s products.

David Pautz, co-owner of Pautz Construction Services in Prior Lake, MN, has found that it’s very common that preassembled silt fence does not get properly installed by contractors and doesn’t hold sediment. He uses the tommy Silt Fence Machine on several projects because it properly buries the material so the fencing works correctly.

“The soil disrupter disrupts soil upward to prevent horizontal soil compaction and simultaneously condition that same soil for compaction after the installation,” explains Thomas Carpenter, founder, owner, and president of Carpenter Erosion Control in Ankeny, IA. “The moving pivot technology enables efficient, smooth flowing transition into the soil, and installation following all terrains.”

Pautz has used the tommy on a variety of projects, beginning soon after the machine was developed in 1996.

“I was not in the industry, but developed a machine because I wanted to save myself all the work involved with trenching. Since I was not in the industry, I did not know about the specification for silt fence installation, and invented a better mousetrap in the process—other people had tried to build a machine following the specification, but they were bulky and the specification was, and is, very poor,” says Carpenter. “I invested $100,000 of my own money for an independent research project co-sponsored by the EPA with protocol developed by industry leaders to verify the effectiveness of the tommy slicing method, and—because there was no other research on silt fence—also had to research the effectiveness of trenching in order to have something to compare to. From this research, the tommy slicing method was added to the ASTM standards. Many other critical installation elements were identified in the process and incorporated into the ASTM, the main one being the requirement for significant compaction—at least 50% of the in situ soil, for effectiveness of the silt fence.”

In Minnesota, Pautz has noticed an increased enforcement of erosion control methods. He says the EPA has specifications for silt fence installation and that the tommy method he uses meets all of them.

Carpenter shared his thoughts about cost-effectiveness regarding silt fence installation. “The tommy machine has consistently enabled contractors to install 1,000 linear feet per man per day since its conception. The more men on the job, the more feet that can be installed, because the other aspects of posting and attaching are the time restraints, although still considerably faster than prefab and trenching,” he says. “I have had contractors from Kansas talk of 20,000 feet per day with 15 to 20 laborers. And, yes, it seems that labor savings is the benefit for contractors, but in reality it is the large number of feet installed and the related gross profit per foot of fence. For instance, for the same labor, 4,000 feet per day at $1 per foot gross profit versus 2,000-foot trenching is where the productivity pays off.”

When working with large amounts of fencing, a weak section can increase project costs. More than 10,000 feet of silt fence have been installed as part of an ongoing commercial project in the Jordan Creek Mall area in West Des Moines, IA. Nick Cimaglia is a partner in Environmental Solutions of Iowa, based in Grimes, IA; his company worked on all sites around the mall area, though not the mall itself. The company has three silt fence plow machines from Pleasantville, IA–based McCormick Equipment and uses them 12 hours a day, explains Cimaglia

“It’s a lot more durable because of its design. It doesn’t have plastic parts,” says Cimaglia of the McCormick plow, noting that these types of parts could bend or break in the wide variety of terrain where he uses the machine. “Out of the 3 feet of material we plow with, we have a foot below and 2 feet above. Our clients get more for their money with that plow, because it will hold back more. It allows you to use more of the silt fence by design.”

McCormick says his company’s machine can slice the material into the ground as quickly as a person can drive. “The ground actually grabs the material as the machine is moving forward,” he explains. “So the fence is always at the bottom of the slice that cuts through the ground, and it’s always tight in the ground. One of the other main features of ours is it pivots in the rear of the machine, so your turning radius is very short.”

Cimaglia explained that with the Jordan Creek Mall area project, silt fence was installed around the perimeter of the site before the company performed interior controls. The site was revegetated in stages and was inspected frequently.

As silt fence installation machines get the job done better and faster than in the past, and as regulations tighten, sediment control has become increasingly appealing as an employment prospect. John Warren, branch manager of the Kansas City, KS, area for A.S.P. Enterprises, has seen an increasing number of people moving into the erosion control business for opportunities.

“There’s still plenty of work for everybody, maybe even more in the future,” he says. “Most of the people that get into it try to be full service or put down erosion control blankets. The more you can do, the more valuable you are to the contractor.”

A.S.P. is a dealer that sells silt fence installation machines, including those made by Burchland Manufacturing and Carpenter Erosion Control. Warren’s clients are typically developers, landscapers, excavating contractors, and seeding contractors. He explains that increased regulation has had a positive effect on sales of silt fence installation machines.

“What’s happened is that municipalities and the regulators have endorsed mechanical installation as being a little superior to the standard trenching in,” he says, noting that in the past prefabricated silt fence was commonly sold, while now it is rarely used. “They know if it’s put in with a machine it will be done correctly. The EPA came through a few times and fined a few people and warned a few others.”

People now understand the importance of protecting sediment on a site. “I think it’s trickled down to homebuilders now, not just commercial sites,” says Warren. “Certain municipalities favor certain products or methods.”

Preventing a Mississippi Washout
When the state is named for a river, it’s difficult for department of transportation workers to keep stormwater runoff and sediment control from a priority to-do list.

“Some of the more common practices include silt fence, hay bales, and silt basins,” says Bill Wilson, assistant state construction engineer for the Mississippi Department of Transportation (MDOT) in Jackson, MS, noting that lack of adequate rights of way are often a challenge. “Silt basins were used in a side [ditch] to prevent sediment from leaving the right of way. Silt basins were chosen because of the volume of runoff from the exposed area and the potential amount of sediment.”

MDOT doesn’t usually include combinations of sediment control practices in its project designs. “We might use silt fence backed up by hay bales in a location that has a potential for a concentrated flow during a large rainfall event,” says Wilson. “We are beginning to use temporary grassing on unfinished locations if we are experiencing a planned work stoppage or when we approach a rainy season, typically winter.”

Maintaining the sediment control methods ensures their effectiveness. “Our inspection personnel observe the erosion control measures daily as part of their normal inspection responsibilities,” he says.

Protecting Stream Water in the Northwest
During the planning stages of a project at South Medford Interchange in Medford, OR, an interchange that will stretch over I-5, Merle Anderson, an erosion control designer for the Oregon Department of Transportation (ODOT), anticipates some difficulty with erosion control.

PHOTO: ACF ENVIRONMENTAL

“We’re near a very sensitive stream and we’re putting in a supportive silt fence, and wire backing with steel posts, with straw bales behind,” says Anderson. “Basically, it’s in an area where we have a lot of construction equipment. We put dual protection there to protect against the equipment and extra support to make sure we don’t have sediment going into the stream.”

The project will take place in three primary stages. ODOT will establish the erosion control plan for each stage and includes several mobilizations for reseeding.

Michael Lucker, RLA, the erosion control program coordinator in the Geo/Environmental Section of ODOT, explained that often projects begin with the practice of clearing as little vegetation as possible. The contractor reviews the proposed erosion control plan and adapts it to his schedule. Products used for erosion control vary, says Anderson, but will be read through at a county level.

“The contractor is required to have an erosion control/pollution control manager appointed,” he notes. “He and the inspector meet at specific times. It’s in the contract.”

In the erosion and sediment control field, the silt fence’s ability to perform has frustrated contractors and regulation officials, often because it wasn’t properly installed or because it wasn’t effectively maintained. But Carpenter feels there is another important improvement that needs to be implemented within the industry. “The number-one problem with the whole sediment control spectrum,” he says, “is there are no independent comparative scientific studies as to the effectiveness of each sediment control device.”

Alternatives to Silt Fencing
Winter in the Rogue River Natural Forest in southern Oregon is cold, dry, and unforgiving. Dave Steinfeld, a revegetation specialist with the US Forest Service, was faced with a challenge when, this past spring, he worked to promote new growth on some north-facing cutslopes.

PHOTO: PAUTZ CONSTRUCTION SERVICES

“These are Federal Highway Administration projects. It’s a steep north-facing site, and cold,” he explains. “The snow has been off it for a while, and the soil is frozen an inch or two down. It expands and shrinks, and as it does that, it moves the soil downhill. Any germinated seeds are on their way downslope.

“You have to stabilize,” he continues. “A hydromulch seemed to tear apart after the freeze/thaw [effect]. I’ve also put straw on this site. The germination is great under it. Most people tell you they get a little better generation once you put straw over it. I think that’s because you are controlling your microclimate.”

Because of the extreme slope of this particular site, however, Steinfeld chose to use wood straw from Forest Concepts based in Federal Way, WA, because regular straw would not likely be able to remain in place.

“My interest in the wood straw was: Would it stabilize the freeze, the seed bed, and create a microclimate? It stabilizes the creep, and it’s heavy enough and interlocking enough and that’s why I used it. I think it’s more stable than straw. I think this stuff will stay around for two years. I’m strictly looking at establishing native plants. Sometimes they need one year to get established and two years to take off. It has been successful in terms of seed germination under it.”

In the forests just outside Aberdeen, WA, forester Marty Brooks of Weyerhaeuser also had success with Forest Concepts’ wood straw on an excavated road bank in the autumn of 2004. “We did tests with it. It kept the soil from washing away. We put some grass seed down and then we put wood straw down,” he says, noting that it took only a few weeks to determine the wood straw was serving its purpose. “It had some mild gentle slopes and then it steepened off away from the road. I was really intrigued by it, because you have a lot of bare ground. It allows a lot of bare spots for grass to grow through it, yet it still keeps the soil in place. It doesn’t get blown away by the wind, either.”

Normally, Brooks uses regular hay on such projects. The road bank project is monitored periodically. Because it’s along one of the area’s main roads, the site is easy to see. He doesn’t plan to remove the wood straw, and simply will allow the grass to grow through it. “Wood fiber blends right in with the wood,” he notes.

Straw wattles are commonly used for some erosion control projects completed by SDDOT. “We would use a Triangular Silt Dike or GeoRidge as ditch checks during the grading practices, but wattles after the topsoil and seeding are complete,” says VanDeWiele. “The reason is we can let the wattle stay in place and degrade, and we don’t have to pay maintenance forces to remove them like we would have had we installed a silt dike or silt fence.

“Wattles are great due to their ability to make intimate contact with the soil on any contour. However, in major flows, we prefer to go to silt dikes as velocity checks. We rarely use rock unless flows are major; the fear is the errant vehicle hitting the rock check.”

Some erosion control methods are used by SDDOT in combination, according to Dwight, who says erosion control blankets are commonly used with wattles and snake bags with silt fence. For example, on the US-12 expressway in Day County, blankets were used in combination with wattles to protect the area around median inlets, says Dwight.

Fiber mulch or bonded fiber matrix is used by SDDOT on long backslopes, says Mike Carlson, an SDDOT field engineer, who adds that silt fence is also used on culverts and in areas where drainage leaves a project.

Coping with limitations for seeding during June and July and getting the contractor to mobilize on remote locations for highway projects are other sediment control issues SDDOT faces, he notes.

Inlet Protection Methods Go High Tech
Whether it’s wetland mitigation, dredging, shoreline revetments, or remediation, when sediment is disturbed, turbidity barriers can be useful solutions for a particularly complicated problem.

“Massachusetts has regulations that require some sort of erosion control device anytime someone works within 500 feet of a waterway,” explains Timothy Prevost, operations manager of Brockton Equipment/Spilldam Inc. based in Brockton, MA. “Sometimes it’s simply the installation of silt fence and hay bales if space permits. Otherwise, a turbidity curtain is warranted.”

Long gone are the days of lashing canvas to logs to create a vertical barrier for pollutants during construction work or after a spill. Creating the modern high-end turbidity barrier is hard work.

“We typically wrap and heat seal all of our flotation elements in a vinyl fabric. We also go the extra step to segment each float section in its own individual pocket. The vinyl prevents water from entering the float compartments and has the added benefit of acting as an oil containment boom along the waterline, important when you’re dealing with heavy equipment,” says Prevost. “The segmentation prevents the floats from shifting, maintaining a consistent buoyancy across the entire length of the barrier. Without the individual segments, floats have a tendency to shift to one end of the barrier.”

The barriers also use a permeable, geotextile filter fabric skirt, which acts like a sail under the water, he explains. “If you don’t make some sort of allowance for the water to pass by or through the curtains, they will billow toward the surface and be much less effective. In areas where there are hazardous materials present, an impermeable barrier is often the only choice.”

Priced by the linear foot, based on the water depth, turbidity barriers are deployed based on the project, type of sediment that must be contained, and whether the material is hazardous or not, says Prevost. Based on these parameters, the appropriate fabric material, flotation size, and ballasting necessary will be determined. The overall cost can also include the anchors, navigation lights, and installation.

For the specific application of protecting storm drain inlets, several options are available. Since the late 1980s, ACF Environmental in Richmond, VA, has been developing and marketing sediment control products including Siltsack, says the company’s David Kelley, explaining that it was one of the first catch basin filters available for purchase.

“Our approach is to attack problems at the source and use an overall approach to sites. No single product can stabilize an entire site. We provide the full gamut of products from slope stabilization to inlet protection, providing a start-to-finish protection system for stormwater leaving a site,” says Kelley. The company currently carries an extensive variety of products related to construction, stormwater, and erosion control.

Rick Schmitt, operations manager of Denver, CO–based Dtech, notes that a customer recently requested a product called Inlet Pro for use in a Denver-area residential project. “We were just installing these originally. They are required to provide inlet protection at the site. They used them in the past and liked them,” he says. “You need to maintain it, just like any other BMP [best management practice]. It could be used on commercial sites as well in the same way.”

Developed through trial and error during a 10-year period, the Inlet Pro is designed to remain tight against the curb and is harder to move than previous inlet protection devices, explains Greg Priest, president of Priest Construction in Parker, CO. “Ten years ago we were pushed into the field as it was getting started,” he says. “The EPA was taking a solid stand on this stuff. Then all of a sudden there was a demand.”

As regulations are enforced, it’s important to remember many problems can be given a knockout punch while a project is still in its planning stages. Taking a few extra precautions when it comes to installing sediment control products can prevent future project headaches.

Tara Beecham is based in Morgantown, PA.

EC - November/December 2005