When it comes to choosing a silt fence or wattle to contain sediment and filter water for a construction project, cost is often a priority. Whether they’re made of natural fibers or geotextiles or a combination of both, some are less expensive up front; others cost more, but are more affordable in the long run, often either because of their flexibility, durability, or ease of use.
Four different products were used in the following very different, but successful projects.
Lake Okeechobee
Being chased by alligators is only one of the challenges of installing silt fence in the Florida Everglades, but it’s worth it, says Tom Burst, who bought Twin Oaks Silt Fencing in Winter Park, FL, with his two sisters, Kim Wood and Laura Burst, two years ago.
“We were born here,” he says. “We’ve seen the changes from the effects of the chemicals in the water. The areas where we used to fish have a green carpet now. Native sawgrass and bulrushes are being crowded out by invasives like cattails. But they’re manmade problems, and there are manmade solutions for them.”
The company has installed silt fence for the South Florida Water Management District (SFWMD), which has been purchasing old farmland that was built on drained marshes in the Everglades and restoring it to marshland. Over time, the SFWMD, the state of Florida, and the US Army Corps of Engineers have acquired a large section of land around Lake Okeechobee and farther south to the Everglades. They are concentrating restoration efforts mainly on the south shore, south of Clewiston, the home of US Sugar.
The contractors, Harry Pepper and Associates of West Palm Beach and WR Compass of Tampa, are building levees between the developed land, mostly cattle ranches and sugarcane fields, and the lake to create marshes called stormwater treatment areas (STAs). The nutrient-laden runoff will feed exotic species in the marshes, which will remove the nutrients before they reach the Everglades.
The contractors are also removing canals to allow water from the lake to regain its original flow to the Everglades and out to Florida Bay.
“They’re moving a lot of dirt,” Burst says, and Twin Oaks, the subcontractor, is using the tommy Silt Fence machine from Devon Distributing Corp. in Ankeny, IA, to install silt fence along a 5-mile section of the levee to keep the sediment from the construction from going into the river.
“Silt fence is an effective filter,” he says, “But we also used a wattle. It adds a second level of filtration.”
The Everglades is essentially a shallow, wide, slow-flowing, gentle river, he explains. Lake Okeechobee feeds the Everglades and is an important part of south Florida’s water supply and flood-control systems. It provides habitat for fish, birds, and other wildlife. Its surface area is 730 square miles, but it’s only 9 feet deep on average. Its drainage basin is approximately 2.8 million acres. It receives approximately 600 metric tons of phosphorus alone from runoff per year.
You have to pay attention when you’re working in the Everglades, Burst notes. “The sawgrass can cut you. There are snakes, including some poisonous ones, like water moccasins and rattlesnakes. And we discovered that an 8-foot alligator can jump and clear silt fence. He went one way and we went the other.”
Twin Oaks uses a fence made of high-quality Type III (Florida rating) synthetic woven fabric, which lasts about a year. The wooden stakes take about the same amount of time to biodegrade.
“A lot of engineers have us paint the date it was installed on the fence,” Burst says. “We’ll come through and remove the old one and replace it.” Crews roll up the material and take it to a landfill or to be recycled, leaving the stakes on the ground to biodegrade.
The fence does get damaged occasionally. Twin Oaks doesn’t cause any harm to the creatures in the area, but when construction begins, they all want to leave, Burst says. Wild hogs and alligators (the ones that don’t leap over) do occasionally break through the fence. The company goes back and repairs it by adding new fabric, restapling it to the stakes, reburying the base, and compacting the soil by hand. Occasionally the contractors purchase about 1,000 feet of fabric and stakes and do the repairs themselves; it’s cost effective when it’s a small patch, Burst says.
Twin Oaks used the wattles because they were in the engineer’s specifications, but Burst says they aren’t really necessary with the tommy-installed silt fence. Wattles often are used with traditional silt fence because it’s installed in a trench, which results in loose soil under the fence. Wattles prevent rain from washing out the soil from the trench and undermining the fence’s effectiveness.
But the tommy slices into the soil and a wheel forces the silt fence into the ground, disturbing less than 1 inch of soil at ground level. Burst uses a 6,000-pound pickup truck to drive over the slice and compact it, something that can’t be done with prestaked silt fence and a trencher, he says, and there have been no problems with blowouts. As specifiers become more familiar with the tommy, Burst believes, wattles will be used less with the fence. Using wattles in addition to silt fence can triple the cost, so the money that’s saved could go back into the general intent, protecting the environment.
Work on these STAs started about seven years ago. As with many government projects, there are a lot of politics involved, he says, but work will be continuing for years as money is allocated to help restore one of the world’s most unusual ecosystems.
This project has gone well and the district has been pleased with the results, he says. He expects it to be functioning the way other STAs have that he’s worked on.
“It took three years for the grasses to start coming up and attracting game and wildlife to the one in Palm Beach. Now it has fish and gators-and the best duck-hunting in the country.”
NASA Glenn Research CenterThe NASA Glenn Research Center in Cleveland, OH, manages experiments on space shuttles and conducts them on the International Space Station, but what happens on the ground-literally-is important, too.
The campus covers 350 acres between the Cleveland Hopkins International Airport on one side and a ravine with Rocky River flowing through it on the other. In the summer of 2009, construction began on 7 acres of the campus. The project includes a new main entrance, a new security building, new roadways, and a truck loop as well as the demolition of old roadways and buildings.
“There is a large volume of stockpiles,” says Lindsey Schweizer, who is part of the team that managed the project for Pinnacle Construction Development Group in Willoughby, OH. “We’re trying to keep the soil onsite. We’re hoping to reuse most of it.”
Crews used both SiltShield and a traditional silt fence at the beginning of the project. The traditional one cost much less to purchase, but it needed more maintenance, making SiltShield more economical in the end.
“SiltShield worked much better,” Schweizer says. It stood up well to deer and wind, as well as a significant amount of rainfall.
Pinnacle installed about 2,400 linear feet of SiltShield. The company also used Dandy bags for inlet protection, organic compost silt socks, sediment ponds, and check dams for sediment control.
“SiltShield is relatively simple to install using the correct tools,” Schweizer says. A tool similar to a ground saw slips the fence into the ground without trenching. The drainage holes in the fence act as a guide to make it easy to install at a consistent depth, at or just above grade. Then the soil is compacted and the fiberglass support stakes put in every 6 to 10 feet, depending on the soil and the area where it’s installed.
According to SiltShield, the product also can be used against existing curbing. Where it is already backfilled, the backfill is removed, SiltShield is placed against the rear of the curb 6 inches deep, and then the backfill is replaced and compacted the same way as with traditional silt fence. Where curbing is installed but not yet backfilled, SiltShield can be placed against the rear of the curb and held in place with the company’s Curb Claws.
SiltShield comes in rolls up to 250 feet long. It consists of three layers: a middle one that filters water through drainage holes between two semi-rigid layers that are similar to foam. The smaller holes face downhill.
Although the company recommends against driving vehicles over the fence, it can be done if necessary. Ideally, the stakes will be removed first, and the SiltShield laid flat on the ground. The area to be driven over should then be covered with a mud mat or other solid fabric.
“The product itself is pretty solid,” Schweizer says. “The material bends over. It hasn’t been damaged yet, after one year of use.”
If it is damaged, it can be repaired by overlapping the damaged piece with a section of new material and securing the two together with rivets.
The SiltShield and the stakes are both reusable. “We do a lot of our own dirt work,” she says. “We can reuse the SiltShield. It certainly beats traditional silt fence.”
O’Hare Airport
When airline passengers look out their windows at one of the world’s busiest airports, Chicago’s O’Hare International Airport, chances are they’ll see Burchland-installed silt fence.
The area’s unpredictable weather, from thunderstorms in spring and summer to snow and ice storms in winter, has been causing runway closures since the airport was built, in 1942 and 1943. And because the runways intersected, when one shut down, the runways that intersected it had to shut down, too.
Construction on the O’Hare Modernization Program at the 7,300-acre site began in 2005 and will continue until 2014. This is the largest construction project in the country and should reduce flight delays during bad weather. It will also increase the capacity of the airport from 929,000 aircraft operations in 2004 to approximately 1.6 million when the project is completed.
The main focus is the realignment of the runway system. The project includes the construction of six new, parallel runways, two crosswind runways and runway extensions, and the closure of other intersecting runways. It also includes two new terminal buildings, a new access road, additional parking, a detention basin, improvements to the remaining terminals, and the relocation of part of the Union Pacific railway.
Contractors have moved more than 3.2 million cubic yards of dirt on the north airfield and approximately 12 million cubic yards on the south field.
“The goal is to contain all the soil onsite,” says Dave Anthony, production manager at Countryside Industries Inc., the Illinois landscape contracting and architectural firm that is installing the silt fence. “We looked at a number of silt fence installers a few years ago and chose the Burchland. We thought it was the easiest to use and the most reasonably priced.”
Countryside Industries might be installing the silt fence on an area anywhere from 1 acre to 400 acres in size, depending on whether a building or a runway is being constructed, Anthony says. Crews typically work from the end of March to December, when the ground isn’t frozen.
The Burchland Silt Fence Installer, from Burchland Manufacturing Inc. in Gilman, IA, is less expensive than other installers, and the distributor is local, he adds. It can cut through trash, roots, and virtually any soil type.
“Burchland customer service has been very good, too,” he says. “We’ve had a couple of issues with parts for the Silt Fence Installer breaking, and they’ve been very good about replacing them.”
The installer moves on a roller system and is adjustable. “It can install the fence on the right wheel, the left wheel, or in the middle, so you can get close to the work,” he says. It knifes the fabric into the ground, so the soil stays compacted, and an optional assembly strings out wire reinforcement horizontally or vertically at the same time as the fence. Thousands of feet of fabric can be installed per hour, down to a depth of 20 inches.
“Prior to purchasing the machine, we were using a trencher and prebuilt silt fence,” he says. “With this newer system, we have nearly tripled our production with the same number of people per day-and we still save money on materials and time.”
Although driving over the fence usually will damage it, sometimes the stake will break and the fabric will stretch instead of tearing, he says. In that case, crews can replace the stake and staple the fence back up. When small sections tear, they replace them by hand. For larger ones, they use the installer. When the project is finished, they will remove the fence by tying it to a skid-steer loader and pulling it out.
“We purchased a second Burchland about a year after the first one,” he says. “It’s been very good for us.”
A memorial to the passengers of Flight 93 is taking shape in the field in Pennsylvania where the plane crashed on September 11, 2001. The federal government bought the property, and the National Park Service is developing the memorial in an area with green fields and gently rolling hills thick with hardwood trees.
“There are some projects that are an honor to work on,” says Michael A. Zock, business development manager for Weaver Express LLC of Sugarcreek, OH. “This certainly is one of them.”
Weaver Express’s involvement in the project began when the company got the nod from general contractor Kinsley Construction Co. of York, PA, to install compost filter sock, known as Siltsoxx, from Filtrexx of Grafton, OH, on the site.
“The plan called for SiltSoxx to be used for perimeter erosion control, around earthen stockpiles, and for a sediment trap during construction” says Zock. “Kinsley came to the right place.”
The memorial is spread across a 2,200-acre park in a fairly remote part of central Pennsylvania, miles from Shanksville, the nearest town. It will include an entry portal, the Tower of Voices, the Field of Honor, and the Sacred Ground, as well as ponds and groves of trees. Work began in April 2010 and includes excavation, grading, and moving large amounts of dirt for the construction of the memorial, a new entrance road, and trails.
Topsoil is abundant in the area, and the subsoil is an orange clay. A layer of Marcellus shale, a very hard shale that can be 200 feet thick, lies 3,000 to 7,000 feet below the surface.
“There was a fairly large amount of earthwork to protect,” Zock says. “The weather at the time the site work began, the remoteness of the site, and the rugged terrain were all a bit of a challenge. No worries, though-Weaver Express has specialized installation equipment that gets the job done in the most difficult of situations.”
Compost filter sock (CFS) is very popular in Pennsylvania, he says. One of the reasons is the abundant supply of hardwood compost made from oak, poplar, and cherry. Scrap wood from land-clearing operations, tree trimming, and the lumber industry all can go into the compost used for this erosion and sediment control material.
Another use of the sock is for Marcellus exploration. This shale is full of natural gas, he explains. “All the oil and gas guys use CFS because it just plain works.”
Rod Tyler, president of Filtrexx International LLC, came up with the idea of a long knit mesh sock filled with compost for sediment control. The sock fabric comes in several materials, including cotton and polypropylene, and doesn’t rip in the wind like silt fence, Zock says. Typical installations use either a biodegradable or a photodegradable material. For this project, Weaver used a polypropylene-based sock, which lasts onsite for between one and two years.
All the fabrics have fairly large openings to let sediment-laden water pass into the filtering compost. CFS typically has twice the flow-through rate of silt fence and twice the sediment removal, Zock says.
“The filtering action of the engineered compost mimics nature. It cleanses water the way decaying wood, bark, and leaves would on a forest floor. All we’re doing is replicating that natural action.”
Although sediment was the only pollutant concern on the Shanksville site, additional Filtrexx “filter boosters” can be added to the compost where other pollutants such as heavy metals, phosphates, or hydrocarbons are at risk of moving with stormwater.
Siltsoxx comes in sections that can be continuous for hundreds of feet. During installation, the empty socks are placed on the end of a blower hose, and then composted hardwood is blown in until the sock is packed tight and laid right in place. “Because a 24-inch-diameter sock easily can weigh 80 to 85 pounds per linear foot, they don’t need to be trenched in, just staked in place,” Zock says.
Some suspended solids drop out of the runoff as it temporarily ponds behind the socks. As water seeps through the socks, more sediment is filtered out, and the clean water flows into vegetated areas and ultimately into waterways.
The second use of CFS for this project was for the level spreading filtration berm of a sediment trap, which resulted in less excavation and cleaner dewatering. The three higher sides of the sediment trap were built in the traditional way (earthen berm), but the lowest wall was made of a sock pyramid: three socks on the bottom, two in the middle, and one on top.
“When it rains, the sediment trap fills up,” Zock says. “Then the water filters out through the berm of sock into the vegetated area.”
Compost filter socks also can be used to reduce runoff flow velocities on sloped surfaces.
The cost of the socks is initially higher than for silt fence, Zock says, but when the life span of silt fence and the cost of maintaining it is factored in, the overall cost of the socks is lower. When sediment builds up behind silt fence, it often compromises the fence, and that section needs to be replaced. And once the area is stabilized, the fence has to be removed. Both are time-consuming because the fence is trenched in.
When sediment builds up against CFS, though, Zock says, it’s generally easier to remove and for the sock to survive. Typically a sock will survive three servicings. It’s also easy to replace a section because the sock lies on ground. When the area is stabilized, the sock can be slit open with a utility knife and the compost left in place.
“On a scale of one to 10, I would definitely say this project is a 10,” he says. “We’ve been back several times to check on things and to add a few additional controls. Everything looks good.”
The initial phase of the memorial is scheduled to be dedicated on September 11, 2011. EC
