Silt Fence Installation
On construction sites, more attention is being paid to getting it done right.
By Carol Brzozowski
When it comes to sediment control, silt fence still remains the most common method used on construction and other sites in the United States. Made of geosynthetic fabric, the fencing is staked into the ground at intervals, with the lower edge trenched into the ground in an effort to stop muddy water from flowing underneath it. Soil particles are retained by the fabric while water passes through.
Photo: Iowa DOT
Photo: Iowa DOT
Photo: Iowa DOT
|In rural areas, Iowa DOT trusts silt fence to accomplish up to 99% of temporary silt retention, sometimes combining it with a sediment basin.
But one of the problems that plague silt fencing is improper installation and maintenance. The bottom may dislodge from the trench or heavy equipment may run over it, and no one reinstalls it before the next weather event.
On one hand, while the actual costs of sediment and erosion control are increasing in line with other construction-related products, the efficiency of the products is bringing a better return on the investment, experts say.
Ole Skaar is an agronomist and a roadside development specialist for the Iowa Department of Transportation (DOT). His responsibilities include writing and developing specifications for erosion and sediment pollution control. Skaar says the cost of sediment and erosion control is increasing mainly because of the diversity of methods being used. “We are trying to be more innovative, and in doing that, some of the newer products we are using—such as the turf reinforcement mat and the synthetic ditch check—are costing a little bit more than the old standard,” he says. Some products and techniques save time and labor, as well; among the products his DOT uses is the tommy Silt Fence Machine from Carpenter Erosion Control, which makes installation faster and more efficient than hand installation.
Dan Neaton, along with his brother Chris, co-owns Neaton Brothers Erosion Control in Watertown, MN. The company does all types of erosion control for the commercial sector, including silt fence installation, seeding, mulching, hydroseeding, and slope stabilization. His company uses Burchland Manufacturing products.
“There are more products available to ease the installation, make it quicker and more cost-effective,” Neaton says. “When I first started, we had to build our own silt fence plow because there was not one available to buy. Now they are building them cost-effectively.”
Bob Adair is the president of Construction EcoServices in Houston, TX. Construction EcoServices provides stormwater pollution prevention on a turnkey basis for commercial construction projects, including the filings and notifications, writing stormwater pollution prevention plans, best management practice implementation, installation of sediment and erosion control measures, and weekly inspections. The company uses products from ACF Environmental.
As the knowledge base about products increases, it helps reduce costs, Adair says. “We all get smarter about what we are doing. You gain some benefits of that knowledge over a period of time, which maybe offsets the cost.”
Neaton believes the reason for the ongoing popularity of silt fence is its relative cost to other products. “It’s bang for the buck—you can’t beat silt fence,” he says. “They’ve been trying to push wattles in our area, but I don’t have a great feeling of comfort if I use that as a perimeter control and after I leave the site, it gets a 2-inch rainfall when I’m on the way down the road.
“They can be used as a product for permanent establishment, as divider breaks and such, but they also are expensive and are installed by hand. If you figure the cost per foot and what you are getting out of it, silt fence is by far the most cost-effective way to go.”
Those who install and maintain silt fencing say the percentage of a typical job’s budget devoted to erosion and sediment control is rather small—just a fraction of the total cost. For example, Skaar says erosion control costs on DOT projects comprise from 2.8% to 9% of the total cost of grading projects and from 0.5% to 2.5% of the total cost of paving projects. The costs include all temporary measures, including silt fence, he adds.
“The percentage is less on paving projects, because most of the measures were put into place during the grading project, and only what is disturbed during the paving is addressed,” says Skaar.
The percentage cost of sediment and erosion control in comparison with the rest of a construction project is, however, increasing due to one key factor: As more states get general stormwater permits, particularly in areas where stormwater quality wasn’t receiving much attention before, those constructing new projects are spending the money to put ESC measures in place.
In the majority of cases, those doing sediment and erosion control are paid unit prices, rather than a percentage of the cost of the job. For an Iowa DOT project, erosion and sediment control costs are programmed into the design. “We have a contract booklet with average bid prices for a fiscal year and [it includes] the bid price for a silt fence, stabilizing, silt basins, and silt dikes. They’ll estimate what will be required for that project so it can be programmed into the monies we put out to do the project,” says Skaar.
Chris Maj owns Maj’s Services in Brighton, MI. His company provides erosion control silt fencing and barrier fencing. Maj Services charges by the linear foot and pre-pays for supplies. Maj uses products from Rhino Seed & Landscape.
He says it’s difficult to fix a cost for what his company does as a percentage of total project cost, “because you may get one rainstorm and need to do minimal repair, or you may get 10 storms in a month. Therefore, companies are starting to see they need to be more flexible with their allowance for erosion control.”
Neaton’s company is paid a unit price for silt fence and a price per inlet for inlet protection. Maintenance fees also are involved.
Because silt fence has been a familiar product for years, it has a faster learning curve, say those who use it. But while silt fence installation may be relatively easy, there is still much to learn to perfect its installation, Neaton points out.
“Installing a silt fence takes as much knowledge of how to do a good job as just looking at the site and figuring out what you need to do to be prepared,” he says. “Say you get a 4-inch rain—what is this spot going to handle? Should I be suggesting to the contractor that maybe instead of a standard silt fence, I should use a monofilament with a steel back instead?”
The learning curve for installing and maintaining silt fence is a process that, while not “rocket science,” takes time to learn to do well, says Sean Simonpietri, vice president of construction for ACF Environmental in Richmond, VA. His company provides sediment and erosion control, mostly for the commercial sector.
“You’ve got to dig a trench,” he says. “I’ve seen silt fence contractors who didn’t dig a trench. It doesn’t do any good if you don’t put it in a trench; water rolls right under it. If you understand the concept of what it’s supposed to do, it’s easy to figure out how to do it. Practice makes permanent; it doesn’t really make perfect. If you practice the wrong way you’re not getting anywhere.” Simonpietri notes that although silt fence is his company’s most common form of sediment control, it is supplemented by other means of ESC as well.
Photo: Burchland Manufacturing
|Many products are available to ease and expedite silt fence installation.
Maj is on every job site, ensuring employees are installing and maintaining silt fence correctly. Additionally, he and his employees maintain certifications. Maj and his employees attend classes throughout the year to keep up with new techniques and study what has and has not been proven effective. “We understand if we do not do our job effectively, we may cause great harm and expense to the company,” says Julie Bridges, a Maj’s Services employee.
Even methods other than silt fence are not that difficult to learn and install and are less labor-intensive, says Skaar.
When it comes to learning curves on new products, Construction EcoServices puts its employees through extension training and provides ongoing education. Adair speaks regularly with the field installation employees, who are exposed to training about the industry and about the company’s objectives in construction and post-construction activity.
“Our guys have the benefit of education—not just about what they are doing, but the bigger picture—and because we use a machine to install our silt fence, there’s a sense that it’s easier to do it right,” he says. “They have a perception from the beginning that they are focused on doing it the right way, the best way.”
Maintenance is a big issue with silt fence, Adair points out. “If you look at it logically, you’re digging a hole around the perimeter of the property, putting fabric in the bottom of it, and you’re going to put all that loose dirt on top and expect it not to wash out when it rains?”
Adair says his company has no significant maintenance issues with its fence—except that vehicles occasionally run over it, requiring repairs or reinstallation.
Several devices on the market help install silt fence more effectively. Skaar says he is examining the use of machine application for silt fence “because there is less room for error.
“The trenching method will work if it is done right, but we don’t always get the compaction of the back field that we should,” he says. “Any of the methods that are not properly done will fail. There is less chance that the Silt Fence Machine application will fail, because there’s less compaction you have to do, and you can generally install more silt fence in less time.”
He says in the long run, the initial cost of machinery is offset by the efficiencies it offers. “It takes less manpower to do it and you can do more in one day, so I would assume you would recoup the cost of your Silt Fence Machine in a year and also have a more satisfactory product.”
Adair also uses the tommy Silt Fence Machine for installation, saying its speed and lack of needed maintenance offset its initial costs.
Maj’s company uses trenchers for installation unless it is an area that will sink or endanger employees; in that case, installation is done by hand. “Everything must be trenched or installed to the correct depth or it just won’t work,” he notes.
ACF uses trenchers, a hammer, and a staple gun to install silt fence, Simonpietri says. “This is our livelihood; we have several crews out every day installing silt fence,” he says. “If we did it by hand, we’d be broke.”
There are new devices entering the market, some of them designed to be placed around storm drain inlets in an effort to prevent dirt from moving to streams and lakes through the storm drain system.
Skaar points out that for several years, nothing other than silt fence was used for sediment control. “We’ve been trying to keep up with as many new and effective methods of controlling the silt from leaving the highway right of way, and the costs have gone up to reflect newer methods that cost a little bit more.” Additionally, the Iowa DOT has instructed its field personnel to use, when in doubt, some type of structure, whether it be a silt fence or some other method, “but let’s try to control it as early as possible so we can keep the silt on our project,” says Skaar.
Maj says he’s tried newer sediment control and inlet devices on the market. “We know these new devices truly work,” he says, but the problem is getting clients to understand their expense.
“They believe it is not cost-effective,” Maj says. “As the importance of erosion controls spreads, we hope they will realize the importance of what we do as they do with the roofer or masonry trades.”
Adair’s company also has tried some of the newer sediment control products on the market, such as inlet devices. “Inlet protection barriers—outside of the hydraulically applied products—are probably the most exciting new products to happen over the last couple of years,” he says. “We manage in excess of 200 commercial construction projects and go through a lot of these things, so we are particular about what we use.”
Sediment and erosion control specialists have mixed feelings about using a combination of practices. In addition to silt fence, such practices may include hay bales, straw wattles, and check dams to slow water flow, and sediment retention ponds to allow soil particles to settle out of runoff before it’s routed offsite.
Maj’s Services combines silt fence with other practices. “Adding straw blankets or check dams, for example, can impact the rate at which a new site recovers,” Maj says.
Iowa DOT utilizes a combination of sediment control methods, depending on the situation. “In most rural areas, silt fence will probably accomplish 99% of what we need for temporary silt retention,” Skaar says. “We also use sediment basins to impound water and drop silt out before it gets to a crossroad pipe, or, if a large channel may be leaving our road site, we may have a sediment basin prior to that area so we can trap as much silt as possible so it doesn’t get off the project.”
While Neaton’s company does not use methods in combination, some municipalities for whom he’s worked want hay bales staked in front of silt fence nonetheless. “You usually don’t need to do that,” he says. “There are good enough materials out there and if you do a good enough job of installation, [one method] can do a good job by itself.”
Maintenance also is a key factor, he points out. “If it’s checked after every rainfall and taken care of, there’s really not much of a need for a combination,” he says. “A combination can be a hindrance.”
He notes that when using a single method, there is less to clean up when the project is finished. “Usually, if you are using hay bales, the twine’s rotted out and it’s junk. It also takes up area in front of the silt fence which you should be using for the sediment itself.” In addition, because every silt fence has to be maintained and the easiest or most economical way is often to use a backhoe to clean out the accumulated sediment, putting hay bales in front of the fence makes cleaning it out a challenge, he says. If hay bales have been in place for some time and one tries to move them to clean the fence, they’re likely to break from sitting on moist ground, he adds.
Neaton believes that when municipalities insist on hay bales in front of silt fence, it’s because someone on a previous project installed a silt fence in an improper manner and it failed, and the municipalities require the hay bales to avoid similar problems.
“When, really, the best approach is to get a good contractor and if the contractor does not do it properly, make them come back and do it right,” Neaton says.
Some permitting authorities have an approved list of devices and practices contractors are allowed to use, though not all of these lists include newer items on the market.
Adair says the Houston area regulatory authorities follow Texas’s general stormwater permit for the most part; it does not specify particular best management practices but does specify results.
“That’s clearly the best way to go, because it allows for innovation and creativity as opposed to those marketplaces where we go occasionally that specify that only certain things can be used,” Adair says. “Typically, those are the most backward areas in which we work,” he adds. “Let’s face it: Regulatory agencies don’t have a chance to review their specifications every year like they ought to, so it tends to be up to 10 years using old, ineffective products that don’t work very well, and, ironically, those are typically the ones that consider themselves the most experienced.”
Maj, however, has faced limitations by permitting authorities. “Some counties are strict, and we respect that,” he says. “Others are still behind the times on just how important the material we use is.”
Neaton says many times he must follow the specifications of a job when choosing sediment control methods. But his company—which last year was named Contractor of the Year by the State of Minnesota—has taken on more of an advisory role in these matters. “If I come up with a suggestion I think might do a better job for them, most people will let us go with that suggestion,” Neaton says. “I’ve done this for seven years in the field, and I know what works and what doesn’t.”
He says the main factor he considers when examining a site and recommending solutions to clients is whether the client wants sediment control or erosion control. “It’s two different things,” he says. “If you are just doing sediment control, then silt fence is obviously a sediment control. But many times they want long-term control, such as a pond. They want to use silt fence on that pond, and my opinion is it does not belong there at all.”
Another factor he considers is what the client wants to accomplish and how much water flow is expected. Neaton also likes to envision what may happen in the future when doing a layout for a silt fence installation.
Whether grading or earthmoving work is done in its entirety for a whole development, or in sections—influencing how much ground disturbance is done at once—depends on the project. In Maj’s experience, grading and earthmoving is usually done on a large scale to provide room for supplies to be brought in and for members of different trades to do their jobs on the site.
But Neaton has noticed that while in the past, everything was “torn up” at once, Minnesota’s new general stormwater permit for construction activity encourages disturbing as little ground as possible at one time. “When the area is finished, we can come in and stabilize it so they can keep moving on,” he says.
It’s the same case in Iowa, where Skaar notes that on an average DOT project, work is done in sections according to stormwater permits. Seeding must be done in areas of inactivity within 21 days. Silt fence is installed in perimeter locations before any equipment is moved on a job. As a highway is constructed, the state installs additional perimeter silt fence or silt fence ditch checks in channels to slow water down and capture sediments before they run off the project site.
Project requirements dictate whether grading and earthmoving work will be done in stages or all at once, says Simonpietri, adding that it’s usually spelled out in the pre-bid or bid process. He notes that massive excavation tends to be done in commercial developments, whereas in residential projects, developers will work on a few dozen homes in phases and ACF will install the fencing around each phase. Then, before workers start clearing for the next phase, the company will surround the new area with silt fence.
Skaar says it is cost-effective to revegetate portions of a site before the work is completed. “It’s a primary concern for us to get a vegetative cover on the area that is at a finished grade,” he says.
Once paving is completed on a project, permanent erosion control measures follow. “During the paving phase, any additional paving or disturbance adjacent to the shoulders and in the medians will all be stabilized, and then I will field-exam it when the paving project is finished,” he says. “We will do a separate erosion control project to fix any erosion problems that may have occurred during the paving process and establish permanent vegetation.”
Simonpietri says many areas in Virginia also require that portions of the site be revegetated before all work is completed. “If you are going to leave soil undisturbed for more than 30 days, you are required to put temporary seed on it, even if you are going to go back in and change it later,” he says.
Maj says it’s not necessarily cost-effective to revegetate portions of a site before all work is completed—“Not unless it is around a pond or other water source where it will not get torn up immediately,” he says. “We try different solutions. If we can make sure the area is worth vegetating because no one will be working around it for quite some time, seeding might really be worth it.”
In most regions, site inspections are increasing, and inspectors are taking a closer look at how silt fence is installed and maintained.
Skaar says sediment control methods are supposed to be inspected before contractors’ invoices are paid. “Our inspectors will look at all silt fences installed, all synthetic ditch checks, silt basins—they’ll inspect everything prior to making out a pay voucher for it.”
Neaton notes site inspections have greatly increased in his area in the past year. “The inspectors used to come around whenever it rained, but now they’ve switched to [inspecting] when they are starting a project; the construction company has to get a silt fence inspection before they will let them move dirt,” he says.
That has helped out greatly in terms of the quality of work, Neaton adds. “It puts everybody on the same playing field. I think it is a good idea, because they are going to look at the site and do a silt fence inspection and make sure it is installed properly, and then everything can go from there.”
He says it also helps that in his region, inspections are handled by the local watershed authorities, “which helps us too, because they know their area and what’s going on.”
When it comes to inspections, Maj has seen the gamut, from large sites that are inspected weekly and within 24 hours of a large weather event to counties that lack enough qualified inspectors to maintain or shut down sites causing major damage to the environment, so situations in which fencing that is not taut or trenched properly go unnoticed.
“Some fencing does absolutely nothing,” he says. “We hope the future will bring trained inspectors and that counties will make their erosion specialists be certified.”
Journalist Carol Brzozowski writes on erosion control and technology.