New techniques and new regulations make a new game of soil stabilization.
The state of Georgia has been a study in contrasts. First there was a prolonged drought. Last year, the state received storms so severe they caused record flooding.
It’s quite a challenge for anyone trying to put together a soil stabilization project under such varying conditions. But those are exactly the conditions that Georgia Transmission Corp. in Tucker, GA, encountered during a project that included the construction of a switching station as part of a larger transmission and substation overhaul. The project is part of the largest upgrade of the state’s power grid in 30 years to accommodate the state’s mushrooming energy demands in response to a growing population.
As part of the project, Georgia Transmission installed a GreenArmor ditch system for the substation, located near metropolitan Atlanta, in February 2009.
The project’s successful design started when Rick Lipcsei, civil project manager for environmental and land services for Georgia Transmission, and a few of his colleagues got together at the International Erosion Control Association conference in Reno, NV, in 2009.
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| Photo: Rick Lipcsei |
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| Photo: McCormick Equipment |
“This project was designed as a riprap-lined flume, and we got to thinking this was a real good candidate for a GreenArmor system,” says Lipcsei. “I did a small ditch with GreenArmor about a year and a half ago, but not to the extent of this.”
GreenArmor had been Lipcsei’s first choice.
“We didn’t like riprap,” he says. “’I’ve had bad experience with riprap-lined channels eroding, so we decided this was a very good place to try the GreenArmor.”
The system, from Profile Products, combines turf reinforcement capabilities of open matrix such as found in the Enkamat turf reinforcement mat manufactured by Colbond with the hydraulically applied Flexterra Flexible Growth Medium for bonding soil and seeds. Another appealing aspect to the approach for Lipcsei was the ability to design the solution using Profile Soil Solutions Software (PS3), an automated, Web-based design and selection tool for erosion control engineering.
The software integrates hydraulically applied erosion materials, rolled erosion control products, sediment retention fiber rolls, and prescriptive agronomic formulations and addresses five critical design considerations: soils, species selection, erosion and sediment control materials selection, installation, and inspection and maintenance. Those factors, plus site-based information, work together to create an engineered solution—in this case, a solution that cost $10,000 less than riprap.
“When we got on the Internet, we had a look at that software, and sitting up in a hotel room we were able to design the project while we were at the IECA convention,” says Lipcsei. “We called up our engineers in Atlanta and got the slope lengths and the cross section of the ditch. We talked with Profile and Pennington about it, and they helped us go through the design. A couple weeks after we got back, we went ahead and installed that in lieu of the riprap swale.”
Lipcsei notes that the site where the GreenArmor was installed was found to be “marginal,” and a 40-foot-tall reinforced earth wall had been erected next to it. “Our GreenArmor system is at the toe of it,” he says, adding that the ditch lies beneath a 33-inch concrete pipe that comes out of a detention pond and drains down a 20% slope about 175 feet long. Installation took no more than a week. Representatives from Profile Products and Pennington Seed were at the site, and several engineers from Georgia Transmission also were there for a demonstration project. The job was executed with the assistance of engineer Randy Wise of Strategic Land Services in Suwanee, GA. The biggest challenge of the project was keeping the grass growing, notes Lipcsei. Because of drought conditions, water trucks were frequently sent to the site to keep it watered to get the grass to germinate. The seed germinated well throughout the summer and early fall following the installation, Lipcsei notes. “The ultimate test came in September of 2009 during the great flood of Atlanta,” he adds. “The site was almost at ground zero of a rainfall event well in excess of the 100-year rainfall and possibly as high as a 500-year event.” Lipcsei was concerned about the system being at the toe of the 40-foot retaining wall. “But it survived the storm event while road and bridges in the area were washed away,” he says.
Mount Washington
With its steep slopes and panoramic view of Pittsburgh, PA, Mount Washington offers one of the most beautiful vistas in the United States. The site attracts many tourists, who can take in from this high perch a wide view of downtown Pittsburgh, including the Three Rivers Stadium.
A few years ago, however, invasive plants were taking over the steep slope.
To help solve the problem, Civil Engineering Consultants contacted Weaver Express, an environmental and erosion control company with offices in Pennsylvania and Ohio that works with performance-based and compost-based solutions.
After the vegetation had been cut back, what remained was a very steep slope that needed to be stabilized and vegetated, says Kevin Weaver, vice president of Weaver Express.
The slope itself ranged from 1:1 to in some places approaching 0.5:1, Weaver adds. Working on the project required using rappelling gear.
Weaver says he always approaches steep slopes with concern. “You need to know what is up the slope from that point,” he says. “If you have concentrated flow that’s at any point discharging onto the slope, that’s something you need to be aware of and either create diversion ditches to rechannel it, or use slope pipes or something similar.”
Otherwise, a compost blanket provides stability even before germination and vegetation takes place, he says.
“The compost absorbs so much water, it’s like a sponge,” he says. “If you get a rain event of a couple inches, a lot of that is just soaked up into the compost.”
At some points, Weaver Express employees used Filtrexx International’s LockDown Netting, a single-net erosion control blanket stapled to the slope before the slope protection is applied to work with it to form an interlocking structure.
The company also installed a Filtrexx slope protection and erosion control blanket. The product is typically used to stabilize bare, disturbed, or erodable soils for both temporary and permanent slope erosion control and vegetation establishment. Pneumatic blower trucks are used to apply slope protection to a depth of 1.5 to 2 inches, or 200 to 270 cubic yards per acre.
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Photo: Rick Lipcsei
At a substation in Georgia, vegetation begins to appear along a channel lined with GreenArmor. |
Weaver Express employees used seed mixes to obtain late germination. “We had done this in a December and actually had germination and some growth in January already,” notes Weaver.
Clay County
When addressing soil stabilization needs for a bridge replacement project on County Road 11 in Clay County, MN, county officials first considered the usual approaches.
“We looked a riprap as the first option, because that’s what we’ve been doing for years and what pretty much everyone else does unless you’re going to do catch basins,” says Nathan Gannon, assistant county engineer. “We looked at catch basins with storm sewer. We could have done a heavier-duty blanket, but we didn’t think that would hold up; we were afraid that it would blow out.”
The county eventually chose ScourStop, a transition mat used as a biotechnical replacement for hard armor. The product is a mechanically anchored 4-foot by 4-foot by 0.5-inch semi-grid polymer with voids that allow for vegetative growth.
The product is typically used over highly erosive areas such as stormwater pipe outfalls, curb outfalls, overflow structures, and shorelines and is said to provide protection against higher shear stresses and velocities than vegetation or rock riprap, and to be comparable in performance to articulated concrete blocks.
In Clay County, the Buffalo River flowed under the bridge, and county officials sought a method to slow down the water and prevent it from washing out the ends of the bridge,
“Rather than putting in catch basins and riprap that we would not be able to drive over the top of with maintenance equipment to do repairs underneath the bridge, we were looking for something we could drive over—and that would not be as expensive as the cost of doing catch basins and subsurface drainage,” Gannon says.
ScourStop, part of Leggett & Platt's Landmark Earth Solutions product line and distributed in Minnesota by Brock White, was laid out on all four corners of the bridge.
“Two of the sides of the bridge were a little bit shorter,” Gannon notes. “We took it from the surfacing all the way down to the ditch.
“On the other two corners, we ran it down a slope for about 20 feet, and we had a skip in there where we just used sod. We used another BMP in the middle, and toward the bottom, we picked it back up with ScourStop.”
The installation was completed last summer and is now doing very well, Gannon notes.
The county doesn’t pave its roads the same year it grades them, says Gannon, citing funding among other reasons.
Yet, he says, “the areas where the ScourStop was worked well before the pavement was put on. We haven’t had a surface on there, which means generally there’s a higher chance of erosion. The gravel material is more highly erosive. It’s actually held that in place fairly well, and the grass has grown very well.”
Gannon says there was a bit of a learning curve in installing the ScourStop, which for the county was done by Sherbrooke Turf.
“The key thing to know is to make sure you prep the site really well,” he says. “We were trying to make about a two-inch or so swale so that the water would be contained inside the ScourStop and not run out on the outside edge.
“It’s a tough thing to do with a skid steer on the slope,” he adds. “There’s a bit of hand work involved in shaping the soil prior to placement. Tightening the straps was a learning curve in how far down to sink them. It’s all dependent on soil types.”
Clay County soil is heavy clay and silts. “I would imagine it would go very different in a sandy soil as compared to our clay material,” says Gannon. “It’s like anything else—the first time you do it, it’s something new. Other than that, it really wasn’t that difficult to install.”
It took less than two days to install the ScourStop at the four corners. Additionally, it was less expensive than the cost of a storm sewer, Gannon says.
Access was another issue of importance for Clay County officials, he adds.
“The right of way in that area is fairly tight,” he says. “Driving over the top of rip-rap is fairly impossible unless you remove a segment of it. If you want quick access, this is definitely the way to go.”
County officials have since specified ScourStop for another project.
Reusable Products
Joseph Vaglica is one of the principles at Gateway Engineering & Surveying in Shelby Township, MI, and also teaches classes in erosion control and soil sciences at Wayne State University in Michigan. At Gateway, he is involved in the design stage of projects; the company also performs some contract work.
A year ago, Vaglica was contacted by Stephen Mini, the chief operating officer of SiltShield in Sterling Heights, MI, to see a sample of an erosion control measure Mini patented. The product is also called SiltShield.
SiltShield consists of a three-layer composition that is trenched into the ground similarly to traditional silt fence. The outer layers provide support, and the inner layer contains filter media that allows water to flow through while holding back sediment. The self-supporting sediment fence is reusable and recyclable.
To that point, Gateway Engineering & Surveying had used silt fencing only around residential lots. There had always been a problem, however, with workers driving over the fencing during construction and maintenance, compromising its sediment control capabilities and subjecting site owners to potential fines.
“I always thought there was a better way to do this,” Vaglica notes.
When he first saw SiltShield, he says, he found it to be a “very smart alternative to fencing.” He also was surprised to learn that it cost about the same. “We paid about $2 a foot for the silt fencing, and his price was approximately $2 a foot as well,” Vaglica says. Vaglica also notes that the SiltShield looks and acts like a “memory foam” system, with plastic stakes that stand back up again after being run over with a vehicle.
“It stands back up again versus the traditional fencing where, if you run over it, you rip it off the stakes and you’re going to break the stakes because they’re made out of wood. Then you’re going to have to be replacing stakes or adding some silt fence to the site,” he says.
Vaglica tried SiltShield on a three-story building project on which he was working in an urban setting. Two sides of the property are adjacent to major roads, one side is next to a parking lot, and the fourth side adjoins vacant property.
“Erosion was a very important issue,” Vaglica says. “We didn’t want sediment to go to the road; when you work in these urban settings, every little mistake you make you’ll notice right away on the road. If you have a big rain event, you’re going to have mud going into the road.”
An additional challenge was that there had been no staging area, because the building occupied about 75% of the property, Vaglica notes. He figured it would be a good test site for the SiltShield.
Over the course of a year, Vaglica noticed people tended to walk around the SiltShield, because it was a solid foam, as opposed to a silt fence, which they tended to step on or over.
“Contractors would drive over it, and you’re always going to get that—they have to deliver something and they drive over it without any regard for the erosion control,” he says. “This one didn’t have any damage at all. It would go back up because of the memory that the foam has.”
The learning curve for installing SiltShield is similar to other erosion control methods, says Vaglica.
“You’ve got to do a trench, and then you put it in the trench,” he says. “The nice thing about this is they custom make it. If you have an entrance to your site, they put a different section there, so it’s like a gate that can be opened and closed. It’s similar to fabrics except it’s a solid foam. It has some openings, which are filled with a cloth that allows the water—but not the sediments—to come through.”
Vaglica has been pleased with the results of using SiltShield. “We are one of those companies that don’t look at the bottom line from a bidding standpoint—we look at the maintenance of something,” he says. “My superintendent told me there had been very little maintenance with the SiltShield. There were some instances where we had to fix parts of it, but it wasn’t a daily thing like we were doing with the fencing.”
Vaglica, who teaches green construction methods, asked Mini if he could make a product from 100% reusable material.
“He went back to his design board with his partners and he brought me a new product this year, which is 100% recyclable material,” says Vaglica. “This may be the solution to a lot of problems that we have in obtaining green points, because part of the criteria is you need to have erosion control. I wonder if this product could also get innovation points.”
Vaglica likes SiltShield not only because it’s recyclable and durable, but also because it is manufactured in Michigan, which is helping the state’s struggling economy.
He notes that restoration efforts are currently underway for the Great Lakes and points out a connection. “People need to understand we can’t destroy the Great Lakes. We’ve done so much damage that it might be already irreversible,” he says. “That’s why it’s very important not only that erosion gets controlled and sedimentation gets controlled, but that [the requirements] get implemented and policed by the local agencies.
“As an environmentalist, I’ve seen firsthand through studies and research that if you’re not doing proper sedimentation and erosion control, eventually somebody’s going to pay for it down the line.”
Vaglica says he’s strongly advocated to local counties to enforce erosion and sediment control requirements.
“You’re always going to get the developers who don’t want to do it,” he says, adding that many who do install control methods are not always committed to maintaining them.
“Why even put it in in the first place?” Vaglica points out.
Installation Methods
The machines used install sediment control BMPs can be as important to a project’s success as the product being applied.
Jeff Pezzetti, president of Environmental Solutions of Iowa in Des Moines, IA, frequently installs silt fence for his customers. “We put silt fence on just about every construction site here in the Des Moines area,” says Pezzetti. “Anything that has to do with grading at the very minimum gets a perimeter silt fence to help keep all of the silt within the job site.”
Pezzetti has been using the Silt Fence Plow from McCormick Equipment for 10 years. “We’ve done it every way, from back in the day when you used to have to install it by hand to trenching. We used to use a trencher, then backfill it and try to compact it.”
He finds that using the Silt Fence Plow is a smoother process. “It’s the easiest for being able to compact the fence, versus trenching it where you have to actually open up the ground and then you have to try to backfill it and compact it,” he says. “The plow literally plows a slot and installs the fabric, and you just close the slot back up with the tractor by compacting it.”
The learning curve for using the Silt Fence Plow was short and simple, Pezzetti notes.
“It’s a lot safer, too, versus the trenching method,” he says.
Pezzetti’s company has realized a time saver by using the Silt Fence Plow rather than a trencher, he says. “It cuts the time over trenching over about half, if not more,” he says. “We’ve saved ourselves a lot of money. It’s basically doubled our production.”
He also says that the fence, once installed, is sturdier. “The fabric is almost impossible to pull out of the ground,” he says. “You couldn’t do it by hand. It takes a machine.”
That’s an advantage in an industry that sees silt fencing continuously compromised by construction equipment running over it or undermined by the pressure of the silt and water the fence is supposed to hold back.
“That was an issue with the trenching method,” Pezzetti says. “They would blow out all of the time. It takes a lot more to blow out a fence that’s been plowed.”
New Regulations
Across the country, erosion and sediment control specialists are gearing up to comply with the EPA’s “Effluent Guidelines for Discharges from the Construction and Development Industry,” published in December.
For the first time, the guidelines set a numeric limit of 280 nephelometric turbidity units (NTU) for sites of 10 acres or more for discharges such as stormwater runoff. The rule’s 18-month phase-in period began in December, starting with sites disturbing 20 or more acres. Within four years, sites disturbing 10 acres or more will need to comply.
Current rules in most places require only visual inspection to monitor construction-site discharges, although some state permits are more stringent than current EPA rules and have incorporated numeric limits into their permits.
Sites covered under the new rule will be required to take water samples throughout the day, with the average of all measurements not allowed to exceed 280 NTU. An individual sample above that level is permitted as long as the daily average remains below 280. The limitation doesn’t apply on days when a storm larger than the local two-year, 24-hour storm occurs.
The new guidelines also require sites that are not subject to the numeric limit to incorporate best management practices for erosion and sediment control, as is the case now under most permits.
Steve Parisi, CPESC and president of Turfmasters in Moscow Mills, MO, is, like many others in the industry trying to bring himself up to speed on the implications of the new rule.
“It’s going to really change the way construction activities take place,” he says. “You’re going to have to discharge water from your site pretty darn clean. It’s going to be huge. Companies are still supposed to comply with the Clean Water Act, and now it’s going to get a lot tougher. They’re going to have to use things like flocculants and water treatment systems to discharge water fairly clean.”
Vaglica says he’s met with metropolitan park officials in his region because they have to meet the guidelines.
“We’re having a hard time with it,” he says. “It’s going to take a while for us to get used to those stricter guidelines. I see potential for a lot of innovation, and we’re doing some studies on it to see if we can come up with better filtration solutions. There are a lot of companies that are going to have to come up with new products.”
Weaver believes the EPA’s new rule will separate the effective BMPs from the ineffective ones. “A lot of them aren’t going to be effective under those new requirements,” he predicts. “Some of them are just bandages, and they’re just not really going to meet that new performance level that’s required. I think it’s definitely taking us to the next step, where we’re looking at the outcome, rather than cosmetic BMPs that may or may not be working.”
Pezzetti points out that no regulation will be effective without proper enforcement. “Right now, it has to get handled at the local level, and it’s only going to be effective if the local authorities decide it’s worth it,” he says. “By federal mandate, they’re supposed to enforce it, but it boils down to whether they enforce it or not. People don’t want to pay for it unless they know someone’s going to ask them about it. That’s the key to it all.”