Jeff Herndon, co-owner of Herndon Inc. in Lugoff, SC, knows that hilly terrain can mean that a relatively high volume of sediment collects in sedimentation barriers in a short time, necessitating short intervals between removals of sediment buildup. Maintaining intact barriers is one thing; having to clean up after a blown silt fence quite another.
Herndon’s company routinely installs Silt-Saver Belted Silt Retention Fence (BSRF) in the medians on highways to protect hydroseeding that is done after the highways are resurfaced and the median elevations are raised to match the road grades. “In upstate South Carolina, it’s not mountainous, but it’s hilly up there, so there are a lot of grade elevation differences,” Herndon says. “Because of that and the volumes of water coming off of the asphalt, the department of transportation goes with the BSRF.”
Erosion control contractors such as Herndon have myriad choices in sediment barrier systems and silt fence installation tools; BSRF is just one example. More and more choices are becoming available to handle the specific attributes of a given job site.
Herndon points out that the state DOT has increasingly specified BSRF due to its superior structural integrity. Its fabric is a spunbond polyester material with a fiberglass scrim or net sandwiched in between the layers, which is designed to integrate the layers. Meshing the support system with the fabric is intended to eliminate the common problem of fabric separation from the supporting wire. The fabric mounts on wooden posts with a bonding strip, eliminating the need for wire or steel posts. According to the manufacturer, with wooden posts spaced at 4-foot intervals and 28 inches of BSRF above the surface, the system withstands the weight of silt and water and provides high sediment filtration.
In 2006, the University of Georgia Department of Biological and Agricultural Engineering compared BSRF and a traditional Type C silt fence to determine if BSRF could be used as a sediment barrier in Georgia. Testing according to ASTM standards indicated that the effluent and sediment removal efficiency of BSRF is more effective at retaining the sediment behind the fence. Additionally, both the suspended solids content and the turbidity of the effluent was lower with the BSRF fence material than with the Type C fence material for three different soils. Finally, grab tests of tensile load using ASTM standard methods indicated high tensile strength consistent with the manufacturer’s own test results. The university concluded that BSRF can be used as an alternative to silt fence and can withstand extreme loads and overtopping without structural failure.
“To me, it’s easier to install, easier to clean up,” Herndon says of the BSRF. “Silt fence can build up too much stuff, and all of a sudden it breaks and you’ve got sediment in the catch basin.” He adds that the South Carolina DOT has increasingly opted for BSRF over silt fence for protecting catch basins.
Silt Fence With Longevity
Silt fence is not going the way of the dinosaurs anytime soon. Ted Pickens, manager of environmental services for Emerald Site Services in Frankfort, IL, does not view any one tool in his erosion control arsenal as a universal solution. According to Pickens, erosion control is a process, and the company approaches each site as a unique microecosystem, taking into account water flow patterns and what may have happened during development to change flow patterns.
So when Emerald began using a Burchland Silt Fence Installer in 2007, Pickens viewed the tool as a means to providing one solution among many. Still, he says, Emerald uses the installer for 90% of its silt fence installations.
The installer is designed to “knife” the fabric into the ground without a fold and without wheels or moving parts, allowing for the entire width of the fabric to be utilized. According to the manufacturer, silt fence installed with this method is stronger due to increased ground tension and also helps prevent washouts under the fabric. Thousands of feet of fabric can be installed per hour at any chosen depth down to 20 inches.
“The key to silt fence is how well it is anchored into the ground, particularly when you have the erosion forces from stormwater slamming into it,” Pickens points out. “How you position it, depending on the contours of the landscape, can make a huge difference in how it performs. This allows us to more effectively get the silt fence to a depth that we want. Once we’ve slipped the silt fence in, we compact it with the tire tread of the machine that we’re using. What we’ve found is that we can’t get the fence out after putting it in.”
Pickens contends that the severe economic downturn of the past several years has affected silt fence installation on residential construction job sites. “When the construction boom was going on, you put silt fence in and usually within six months you were out of there,” he says. “Now, that silt fence may have to last as long as three years, because it’s a much slower development process. A lot of people don’t understand that there are many different types of silt fence you can put in and a lot of techniques that you can use. All of those things combine to determine whether you get good longevity from your silt fence.”
Longevity requires an understanding of the function that silt fence should serve as well as the right equipment, Pickens adds. “Whoever the client is that you’re doing the silt fence for, the number of times that you have to come back and maintain that is money out of their pocket. With silt fence, most people won’t admit it, but a lot them think that you boundary the entire development in silt fence like putting up a little bathtub or a wading pool and keep the water in; that’s not it at all. Any water coming onto the site is going to follow an actual flow pattern that may be abridged by grading, but that water is going somewhere. It’s not going to stay there but migrate down into the natural watersheds.
“We really believe that we direct the water with the silt fence-we don’t stop it,” Pickens continues. “We’re moving it to where it can best and at the lowest cost be managed so that it takes no sediment or pollutants off the site. So, basically, as it goes on clean, it goes off clean. It’s all about directing the water.”
Following the theory of directing water rather than containing it does not mean that the structural integrity of silt fence is any less important. Pickens recalls using a trencher, placing the silt fence into the trench by hand, filling up the trench, and stepping on it to keep the fence in place. That works in some situations, Pickens contends, but not in all situations-especially if pre-staking is used. By using the Silt Fence Installer, Emerald can gain structural integrity in a custom fashion when the terrain dictates. “We can decide in some cases if we’re going to have more force coming,” he says. “We may be able to adjust the spacing on the stakes.” The US Department of Agriculture Natural Resources Conservation Service’s Illinois Urban Manual calls for 5-foot centers for silt fence, but sometimes Emerald reduces the spacing in areas where water flows are higher. By maintaining vegetative growth around the fence, the Silt Fence Installer helps to aid the structural integrity of the fence, Pickens adds.
The installer often proves its worth when ComEd, the electricity provider in the Chicago area, relocates power poles to accommodate road widening or reconfiguration by an owner such as the Illinois Department of Transportation (IDOT), according to Pickens. A ditch is usually excavated to collect stormwater, and Emerald installs silt fence to protect the ditch. “We’ve found that by using the installer, we can quickly pull runs, and sometimes that silt fence will have to stay for over a year.” Often, adjustments must be made to the locations of the poles, and IDOT often integrates the silt fence that Emerald has erected into its own silt fences. Pickens notes that he sees the adjacent fences blowing out. “We call them “˜air fences’ because they no longer have integrity in the ground and everything is just sliding underneath them,” he says.
Pickens recalls one project in particular that demonstrated the efficiency of the installer. Pulte Homes acquired a portion of the land that previously had been the site of the Naval Air Station Glenview, and Emerald installed about 1,000 feet of silt fence as Pulte began to build homes there. The installation took only about an hour. The work went “as fast as I’m able to pull the tractor,” he says, “about 15 minutes, maybe half an hour to pull that thousand feet, and then whatever time it takes the tractor to go down to do one side and then come back on the other side to compact it.” He estimates that a trencher moves at less than 1 mile per hour-less than half the speed of the installer. That means it probably takes at least 50% more time to dig a trench than to use the installer. Additionally, Pickens says, Emerald would have to unroll the stakes and then push the soil against the stakes and fence, which takes more time. “I read the reports about how the silt fence installers were working, that they were seeing about a 50% efficiency improvement, and I would say it has lived up to that,” Pickens says.
Roots present challenges in using the installer, but Emerald has adjusted, according to Pickens. Bushy shrubs and hedgerows, which are often found in and around farm fields, can cause problems when the installer gets caught in their roots. Pickens says that the presence of this vegetation can affect how close to it a silt fence is installed. In addition, pulling up prairie grass can break up the soil and make compaction more difficult after the fence is installed. In these situations, a trencher might actually be a better alternative, Pickens contends.
“There are times when I know I have to hand-dig around a tree or I have to use a small trencher that we have just to get it through the soil,” he says. “But I have found that for 90% of what I’m doing, I can use the Silt Fence Installer with a plow.”
Staying Efficient and Competitive
According to Brycen Buum, manager/estimator at All Cowboy Erosion Control in Fort Lupton, CO, the company purchased a silt fence installation machine to be competitive. All Cowboy does custom seeding and straw mulch installation and often protects its vegetation with silt fence. About three years ago, the company purchased a tommy Silt Fence Machine from Devon Distributing of Ankeny, IA, in order to keep doing its vegetation work as continuously as possible, Buum says. “Obviously, if they shut down a project due to bad BMP [best management practice] installation, then we’re not seeding and we’re not working,” he notes. “And when we’re not working, we’re not making any money.”
The manufacturer points out that trenching requires heavy backfilling, mechanical compacting, and level filling after compaction, and smiles and J-hooks must be employed to pond water. Trenching also requires extra crewmembers, work stoppages in wet weather or rocky soil conditions, slow and costly dirt removal, and backfill and compaction. A trencher cannot turn to install J-hooks and smiles, which are required by many stormwater pollution prevention plans and specifications, or maneuver around obstacles.
All Cowboy’s machine slices through the soil, conditions it for future compaction, and inserts silt fence fabric 8 to 12 inches deep. It can turn to avoid obstacles and creates smiles to contain runoff. It can handle most obstacles, reportedly even 8-inch-thick cobble and concrete waste, by pushing it to one side. A grade-five shear bolt prevents damage to the machine in case it gets caught on a hard object. As Buum can attest, the machine has worked reliably in different types of soils such as saturated soils, rocky soils, and hard-baked compacted clay, as well as in high winds and on steep slopes. “The type of project that we find ourselves really using that tool on is where the ground is a little bit harder and rockier, because you can’t dig it,” says Buum. “Also, if you know without a doubt that there’s going to be a high concentrated flow, it’ll excel way beyond any other method. If you know you’ve got a high concentration of water and extreme winds, you can’t dig it in and have that silt fence survive.”
One particularly productive recent project was near Devil’s Lake, ND, where All Cowboy installed 60,000 feet of silt fence in only four days. A pipeline was installed to relieve chronic flooding caused by a gradual rise in the level of Devil’s Lake, and the silt fence was installed to prevent sedimentation in a buffer area between the pipeline and Highway 20, a major thoroughfare to Minot and Williston, ND, as well as Fargo, via Highway 29. Some farmland was also threatened by the flooding. “It’s a chronic, year-round issue; everybody says that the flooding is coming from the groundwater and it’s always seeping up,” Buum says. All Cowboy is expecting to revisit the site in spring 2012 to remove the silt fence and seed the area.
Buum recalls that All Cowboy installed an average of 15,000 to 20,000 feet of silt fence per day. “Pulling it with that machine, it was nothing for us to pull four and a half miles of silt fence in a day,” he says. “According to our speedometer, we were pulling silt fence at 4, 4½ miles an hour.”
In fact, he notes, All Cowboy would have benefited if 10,000-foot rolls of silt fence had been available. He says that the 3,000-foot rolls were being pulled so fast that the process often had to be stopped for reloading, halting the momentum.
Protecting Shale Gas Exploration Areas
Ecologically sensitive rural areas such as much of the land sitting on the Marcellus shale gas play, which lies underneath most of Pennsylvania and parts of other states in the northeast, may be better suited to passive treatment systems instead of silt fence in some situations. According to Brad Baker, branch manager at Hanes Geo Components in Mercer, PA, a distributor of erosion control solutions, a product like Filtrexx International’s SiltSoxx compost filter sock does not require disruption of the soil. This is a benefit in many rural areas where natural gas exploration occurs.
The product is a mesh tube filled with recycled organics from local recycling operations like yardwaste compost facilities or mulch facilities. It has been adopted into most state regulatory handbooks as well as many federal agencies. EPA, USDA-NRCS, AASHTO, USACE, and many other agencies have specifications recognizing the use of compost filter socks as an effective new BMP.
Current regulations are pushing for products to perform better and result in cleaner water being discharged from job sites. The Filtrexx-targeted pollutant-removal lineup, called the treatment train, includes sediment control, bacteria removal, heavy metal removal, nutrient removal, and hydrocarbon removal. According to the company, peer-reviewed test data shows near 100% removal rates of daily doses of hydrocarbons for 30 straight days.
“If you take, for example, the Marcellus shale gas area, you’ve got a lot of sites that are out in the middle of nowhere with a lot of trees; you can put that sock down without doing any trenching,” says Baker, whose branch supplies 8-, 12-, and 18-inch palletized product and assembles 24- and 32-inch product onsite when necessary. “Some of these sites can be 5 to 10 acres, so you’re moving a lot of earth around, especially in western Pennsylvania, which is mountainous. You do have the tendency for a lot of runoff. Where the SiltSoxx come in handy is putting them around the perimeter of the sites so they help catch any sediment that runs off of the hills.
“You can basically lay the sock down, stake it, and be done with it,” Baker continues. “The reason the Pennsylvania Department of Environmental Protection likes it, from what I understand, is that sometimes you drive down the road and see silt fence that’s been there for 10 years and the contractor doesn’t come back to take it down. The filter socks they can just leave there and go back and cut it, leave the mulch and compost, and let it break down on its own.”
Baker points out that Hanes Geo Components also sells silt fence, and he does not view the SiltSoxx as an apples-to-apples replacement for silt fence. He stresses that the SiltSoxx is a filtration product, and a carefully engineered one at that. For example, he says, the mesh possesses great structural integrity. “They hold up well-the cheaper products don’t,” he notes. “The last thing that these gas guys want to have to deal with-they’ve got enough going on-is erosion control. They want a product that works. If they don’t do something to prevent erosion, there will be fines, so they definitely want to use something that stands up to it.”
Durable and Easier, Less Expensive Installation
Peyton Womble, owner of Womble Erosion Control in Hendersonville, TN, says his company often uses Erosion Eels from ACF Environmental on residential construction sites because of the product’s durability. “Normally we’ll put silt fence up and somebody has a truck; the silt fence gets run over and torn out, and we have to come back and fix it,” he says. “We don’t have to come back and fix the Erosion Eel.”
The product is a low-impact erosion and sediment control device that provides suspended particle capture and flow control. It is made of a woven polypropylene geotextile exterior and washed shredded rubber internal fill. The Eel has a nominal 9.5-inch diameter and is manufactured in lengths of 10 and 4,5 feet. In addition to replacing silt fence, it is designed to be used in the place of rock check dams, temporary diversion berms, and inlet drain protection without the need for trenching. As a result, it can be deployed on both soft surfaces such as soil and grass or hard surfaces such as concrete, asphalt, and bedrock.
Testing at the San Diego State University Soil Erosion Research Laboratory revealed that the Eel is resilient under extreme rainfall intensities and slope conditions and retained as much as 89% solids from a 33% barren slope under rainfall conditions at or exceeding a 1,000-year storm event.
“We use it a lot for check dams above a stream,” Womble says. “If we hit rock, we still have to get some kind of protection up, and we’ll use this instead of silt fence. If we’re tearing out a parking lot or asphalt pavement and we’ve got to have erosion protection for asphalt, it’s better than trying to hammer something through the asphalt.”
Womble recalls that his company first used the product on a Pulte Homes subdivision back in 2007. “They’re liable to have 15 or 20 houses going up at any one time,” he says. “We started using them there as an alternative to silt fence because we wanted to keep the fence up and keep everyone from destroying it. We’re able to pick the Eels up after the house is built and take them to another lot and use them again. They’re more expensive on the front end compared to silt fence, but in the end they’re a lot cheaper.”
One aspect of the product gives it an advantage over silt fence and reduces downtime for contractors, according to Womble: “They really filter the water, where silt fence will make the water pond. Therefore, the soil dries faster and you get back on the site faster.”
He notes, “It’s a pretty straightforward installation. You can install it in about half or a quarter of the time it takes to put in silt fence. You can have two guys install the Erosion Eels, whereas it takes two or three guys and a machine for silt fence. You don’t have to have a machine to put the Eels in. When you install silt fence, you are running a truck, a trailer, a [skid-steer loader], a trencher, and three workers. When you put the Erosion Eel in, you’re running a truck, a trailer, and two workers-you’re basically eliminating a $50,000 piece of equipment.”
Maintenance is not much of a problem, he adds. “We have to back and straighten them up when people move them for whatever reason. When we use them for check dams, we’re able to keep the silt cleaned out in front of them. We’re pretty much able to pressure-wash them and take them to another job.”
Sandbagging Productivity
Mindful of the cost and logistics involved in sandbagging, one manufacturer has sought to significantly speed up the production process. Barrier Systems LLC has developed the SandMaster, an attachment for skid-steer loaders, backhoes and loaders, and excavators. The company is planning to introduce additional models that will be compatible with larger equipment for greater production capabilities.
The attachment is designed with holes to fit bags. Once the bags are loaded, the machine is driven into a pile of sand or fine fill material, filling the bags using hydraulic power. Drawstrings are tensioned and closed around tension rings. Once the operator reaches the dropoff point, the bags are released. According to the manufacturer, it is possible for two workers to process 4,000 bags in an eight-hour period. Additionally, any material that will fit into the apertures can be used in the event that sand is unavailable, reducing transportation costs.
