Holding Something Back: Sediment Containment Measures

From traditional hay bales and various types of silt fencing to inlet protectors to sand-, rock-, or water-filled berms, sediment containment devices are essential at almost any work site where ground cover is disturbed. Stormwater and construction-generated runoff can make off with soil by the cubic yard, clogging storm drains, polluting waterways, and landing permit holders in regulatory hot water. Especially now with Phase II of the Clean Water Act National Pollution Discharge Elimination System (NPDES) Stormwater Program in effect, new devices and old standbys are being put to ever-more-stringent tests of efficiency. We talked to people using various products in the field to see what’s available and how it’s being used.

On any project, of course, sediment containment best management practices (BMPs) are only part of the picture. “You have to have erosion and sediment control,” emphasizes Hossain Kazemi, an environmental specialist supervisor with the San Francisco Regional Water Quality Control Board. Kazemi teaches workshops introducing contractors, municipal employees, inspectors, and others in the field to available erosion and sediment control technologies. “I haven’t seen any sediment control work by itself so far. Just depending on one, even if you design a sediment basin, might not be very efficient if you don’t have good erosion control upstream of the sediment pond. Sediment like silty clay does not settle in an hour or a day; it remains in suspension for a long time. Such fines need substantial settling time and a large pond, which can be cost-prohibitive to build. Erosion control measures minimize detachment of sediment before entering the pond.”

Many of the products described here have multiple uses, and many are designed to be used in combination with erosion control or other sediment control measures in a multilayered defense strategy.

Berms and Dikes: Three-Dimensional Solutions

At the higher-tech end of sediment containment products is an array of three-dimensional barriers: triangular and burrito-shaped, prefilled and fillable on-site, reusable and disposable, and temporary and more-or-less permanent.

Triangular Silt Dikes, manufactured by the Triangular Silt Dike Company Inc. in Midwest City, OK, are temporary, reusable barriers consisting of a triangular urethane foam core covered by permeable, woven geotextile fabric. From 16 to 20 in. wide at the base and usually 8-10 in. high, the Silt Dike is typically used at the toe of a slope to contain sediment from runoff or perpendicular to the flow of water in a drainage ditch.

“It’s bulkier than silt fence. It holds up a whole lot better against runoff when it’s raining. It doesn’t lie down or lay over or wash out,” points out Jay Lemon of Haskell Lemon Construction Company in Oklahoma City, who has used the Triangular Silt Dike for just over a year. Lemon’s company has the contract for two interstate highway projects for the Oklahoma Department of Transportation, which typically specifies silt fencing, hay bales, or the Triangular Silt Dike for sediment containment. U-shaped wire staples anchor the Silt Dike’s apron to the ground, and a portion of the apron, which extends 2-3 ft. on either side of the core, can also be buried. “You bury a piece of fabric so that the water is forced to go through it instead of under it. Put in properly, these things are holding up a whole lot better than our silt fence and hay bales.”

Los Alamos National Laboratory (LANL) in New Mexico also employs the Triangular Silt Dike on its 43-mi.² facility. Steve Veenis, CPESC, a technical staff member with LANL’s Water Quality and Hydrology Group, explains, “We have several ongoing construction projects at any given time during the year, and we also have erosion control in general for keeping the infrastructure up to date.” Nuclear testing, as well as testing of other chemicals and explosives in its 57-year history, gives LANL additional need for sediment containment. “We’ve got some rather unusual problems here in that, in a lot of cases, our sediments and soils are contaminated,” notes Veenis. “Our approach is to try to keep the sediments in place and slow down the migration while we’re planning to do the cleanups. We’ve got so many sites that we really had to get out there and hustle to get the BMPs in place and implement a pretty good inspection and maintenance program to keep up with all the sites while the environmental restoration folks do their job, which is to get out there and characterize it and clean it up if need be.”

Although LANL uses hay bales and silt fencing in addition to the Triangular Silt Dike, Veenis says, “We’ve been trying to minimize the use of hay bales for several reasons. The maintenance is just too time consuming and too expensive. They start biodegrading. Plus we have a big problem with elk eating them.” Because hay bales have to be replaced fairly often depending on rainfall-and elk grazing-the reusable Triangular Silt Dike has proven more cost-effective. “They’re a little more expensive up front, but they pay for themselves after about a year,” says Veenis. “We did a little study to figure that out.”

The configuration of a site often determines which product to use. “There are places where a long, straight line of silt fence actually fits better than the Silt Dike or the hay bales,” states Lemon. “We’re traditionally putting in silt fence parallel to the roadway in long, straight stretches. Then we’re using the Silt Dikes to line the ditches perpendicular to the water flow-quite a few rows of Silt Dike, which will actually stop the silt from flowing down into the streams, creeks, or rivers.” Ease of installation and maintenance is also important. “You don’t need any machinery, so it’s pretty low-cost to install, and the maintenance is just darn near nil if you put it in properly.”

“We’re using them for a variety of terrains: along roadways, parallel to the road, perpendicular to the road, and along the drainage that follows the road,” says Veenis. “We’re using them quite a lot at construction project sites to keep stormwater out of storm drains.” Using additional staples at the junctions between the standard 7-ft.-long dikes helps prevent gapping.

An added benefit for LANL is that the Silt Dike is available in several colors. “When we first started buying them, they pretty much came in black, like silt fence fabric. Now they’ve got green, which is a little more environmentally friendly, and orange, which is really good for construction projects because you want people to see them,” Veenis notes.

Although some barriers arrive preassembled at the site, the Continuous Berm Machine, manufactured by MBW Inc. of Slinger, WI, is a fill-as-you-go proposition. The machine extrudes a made-in-place continuous berm that serves not only to control sediment but also to contain spills and, when stacked, stabilize streambanks and sandbag areas against flooding. A truck or tractor tows the 7.5-ft.-long, 700-plus-lb. Continuous Berm Machine, and a skid-steer loader, backhoe, or similar equipment loads the machine’s hopper with fill material-sand, rock, or native soil. As the machine extrudes a foot-wide, 8- to 12-in.-high filled berm, a person walking behind the machine secures the berm with a staple gun. “Instead of digging trenches, a two- to three-man crew can install a continuous berm on top of the ground at a rate of up to 15 feet per minute for approximately $1.50 a foot or less,” points out Brad DeRosa, an MBW sales representative. Geosynthetic fabrics of various porosities are used depending on whether the goal is to filter or contain water.

Although the retail price of just over $6,700 makes the Continuous Berm Machine an initially expensive option, it could save money in the long run because the berm requires less labor to install and less maintenance than hay bales or silt fencing. The berm is not reusable, however, as are devices like the Triangular Silt Dike. The berm can be removed by slitting open the fabric and mixing the fill into the onsite soil, or for permanent applications it can be seeded and left in place.

Because the berm is extruded to whatever length needed, it avoids the “gap” risk encountered with hay bales-water might spill through at each point where the bales adjoin-and to a lesser extent with any other device installed in sections.

For effective drainage and sediment control, a short section of a sand- or soil-filled berm can be filled with rock at a low-lying point; water flows along the berm to that point and drains easily through the larger rock particles. MBW says the continuous berm has been rated at up to 95% effective for sediment removal.

Aqua-Barrier, manufactured by Aqua-Barrier of Houston, TX, is similar in concept to the continuous, in-place berm but is filled with water rather than sand. The reusable, vinyl-coated polyester tubing is first laid in position and then filled with water. As with the continuous berm, Aqua-Barrier’s filled weight keeps it in place with no trenching or staking and also helps it conform to the terrain. An inner restraint diaphragm stops Aqua-Barrier from rolling once in place. Threaded fittings of rigid PVC installed on the top and bottom of the barrier serve as fill and drain ports. With its standard 50- and 100-ft. lengths and overlapping connections, Aqua-Barrier also avoids the gap problem. Standard heights range from 2 to 7 ft., and the company also manufactures custom sizes to order.

Often used for dewatering construction sites, containing spills, or controlling flooding, Aqua-Barrier can also be effective in channeling water to an appropriate area so that sediment can be filtered out. Preventing sediment contamination in the first place is another way Aqua-Barrier helps handle the problem, reports Arnold Mallard, treasurer and contract administrator for VA Paving Inc. in Cocoa, FL. Mallard has worked for more than 40 years on projects for the Kennedy Space Center, where he put Aqua-Barrier to use during a recent storm-drain repair job. Drainage pipes beneath a four-lane causeway were leaking; to slide new polyethylene pipe liners into the existing storm drains, Mallard needed to block the 90-ft. canals on both sides of the road and pump out the water. Rather than employing the traditional method of constructing dirt dams across the canal in two places and pumping out the water in between, Mallard, who had recently purchased 50- and 25-ft. lengths of Aqua-Barrier, came up with a faster and cleaner solution. “We had to have working room there about 22 feet out from the existing headwall. We took a 50-foot one and put it out in the canal, which had about 5 feet of water, and then we put the two 25s up toward the bank, and another 50 we put on the opposite end just across the end and blocking it so we could pump it down. We did two different sites this way. We didn’t silt-up the canals by putting dirt in and then having to dig it back out.”

The weight of both Aqua-Barrier and MBW’s continuous berm, which typically weighs more than 100 lb./ft.³, depending on the fill, causes them to conform tightly to the underlying terrain. The smaller the particles of the fill material in the berm, the more tightly they can compact and the greater the contact with the ground. The weight of both products also prevents them from easily blowing or washing out of place, so unlike silt fencing and hay bales, they require no trenching, backfilling, or staking. Trenching has raised objections in some areas because the trench itself further disturbs the ground, breaking through the soil crust and increasing erosion potential by allowing water to penetrate more easily to subsoil layers.

Silt Fencing

Still a mainstay of sediment containment, silt fencing comes in a variety of materials, widths, and prices. Its advantages: It’s inexpensive, it’s familiar, and it’s the sediment control device specified on many state and federal projects. Its disadvantages: It can be ineffective if not properly installed, and it requires periodic inspection and maintenance-especially after heavy rainfall-to ensure that the stakes are holding it upright and in place and that the buried lower edge hasn’t washed out of its trench, which would allow water to flow freely underneath the fence.

It also tends to be much maligned by users. “It looks nice until it rains,” one contractor remarks. “Invariably, if you get a big heavy rain, it’s gonna wash out and you’re gonna get to go replace it.”

Kazemi of the San Francisco Regional Water Quality Control Board stands by it as a secondary control measure and as long as it’s properly installed-never on a hill, for example. “If you have a good erosion control, then silt fence is very effective. In the San Francisco Bay area, we require that erosion and sediment control be used as complementary measures, especially during the rainy season.”

Such companies as Mutual Industries North Inc. of Philadelphia, PA, offer polypropylene mesh backing for supported silt fences; some state departments of transportation require wire backing for added strength, while others also accept mesh backing for supported fences. Indian Valley Industries Inc. of Johnson City, NY, offers a variety of preassembled silt fencing that meets specifications for state and federal projects.

Special Applications: All Shapes and Sizes

A number of products are available to trap sediment not from water flowing through a channel or from general runoff but at specific points such as drains and catch basins. Used in combination with barriers or silt fencing, these products provide a second line of defense. “Ninety-five percent of the time silt fence is improperly installed or tipped over. Once the sediment leaves the site, these products are your last chance to catch it before it goes down the drain,” says Dan Cleveland Jr., national product manager for Dandy Products in Columbus, OH.

Three of Dandy’s products, the Beaver Dam, True Dam, and Dandy Bag, are designed to trap silt and sediment at the point of entry to a storm drain. Each is designed and shaped for a different type of inlet. The Beaver Dam, which covers curb and gutter inlets, and the True Dam, designed for median barrier inlets without grates, both conform to the shape of the curb. The Dandy Bag comes in round or square shapes and various sizes and covers flat-grate and mountable curb inlets.

“It’s cheap insurance,” remarks Tom Wynkoop, a project engineer with Kokosing Construction Company Inc. in Fredericktown, OH, speaking of the Dandy Bag. Wynkoop works on many projects for the Ohio Department of Transportation (ODOT). “ODOT standard is erosion control fence, and if that fails, then there’s nothing else there. But if you use the Dandy Bags in addition, this is a fail-safe system.” Dandy’s products fit into tight spaces as well. For pavement side inlets and catch basins, Wynkoop explains, ODOT’s standard calls for silt fencing fabric to be wrapped around four posts placed at the inlet corners. “At a lot of the side inlets you don’t have room to do that, where construction materials are in the way. It gets easily torn up. If you’re widening a road or putting down base, a lot of times you’ll get construction debris inside the inlets. Dandy Bags are a good application for that, all the way up through asphalt paving and all the way up until finish. You bring in the seeding subcontractor, and they’re blowing straw all over the place. It keeps straw and everything else from going down into the drainage system.

“In some areas we don’t have a choice,” he adds. “There’s an old town we’re restoring, and there’s a lot of brick paving. We’re using sand, setting the bricks in sand. There’s no room to build a typical erosion fence. We’re using Dandy Bags. This is really the only way you can protect the drainage system in that area.”

Designed to capture sediment inside catch basins, Siltsack, manufactured by ACF Environmental of Richmond, VA, fits under and is held in place by a drainage grate. Siltsack comes in two permeabilities, accommodating either 40- or 200-gal./min./ft.² flow rates. Siltsack is also available with an oil-absorbent insert-useful for airports, truck maintenance lots, and other places where oil contamination is a potential problem.

Rob Pine, project manager for Modern Continental Construction Company in Cambridge, MA, uses Siltsack to meet NPDES II requirements when dewatering sites. “Each catch basin that’s within the construction site is required to be protected by geotex fabric. That’s an NPDES requirement. We use Siltsacks to meet that requirement.”

The reusable sacks need to be emptied every two to three weeks or after heavy rainfall. Removal flap pockets extend above the grate, and iron rebar-which is run through the pockets-is attached to heavy lifting equipment that lifts the sack, carries it to a dumping area, raises it by its dumping straps, and turns it inside out. Siltsack can be manufactured to fit catch basins of any size or shape.

The Dirtbag, also from ACF Environmental, helps during site dewatering, filtering sediment by attaching to the end of a discharge hose. Kazemi features both products in his workshops. As with other sediment control BMPs, he advises that upstream filtration be used. “It’s very effective for short-term discharge, but it should be done with some added provision.”

Turbidity Curtains: Catching the Problem in Midstream

When runoff occurs close to rivers, streams, lakes, or reservoirs or when construction projects take place on or under water, floating turbidity curtains or silt containment barriers can prevent sediment from being carried downstream. These “floating silt fences” allow water to pass through but retain soil particles and other debris. Depending on the curtain’s permeability, they can also slow the flow of water enough to give sediment time to settle. “Anytime you’re working in the water, the environmental agencies require some type of protection of your work,” notes Modern Continental’s Pine. He has used thousands of feet of Siltdam turbidity barriers, manufactured by Brockton Equipment & Spilldam Inc. of Brockton, MA, on various projects including the Boston Central Artery/Tunnel Project. Known as the “Big Dig,” the project will replace an elevated six-lane artery with an underground highway on the edge of Boston Harbor. Modern Continental is building and installing a tunnel that crosses Fort Point Channel, a narrow extension of Boston Harbor into South Boston. “There’s a significant amount of dredging that must occur inside the Fort Point Channel,” Pine explains. “We’re using the Siltdam to contain any silt from the dredging operation from migrating beyond the construction site and impacting the rest of the channel or the harbor.”

Brockton Equipment customizes the Siltdam in a number of ways. Vinyl-cased polyethylene flotation logs are attached to a skirt of woven polypropylene, and the skirts are available in different permeabilities and lengths. A sealed pocket at the bottom of the skirt holds a galvanized steel chain for ballast. “The floating boom is very durable,” remarks Pine. “The not-so-durable parts are the panels underneath because of the tugboats, tides, and currents and the amount of use they get. They’ve customized them so that we can replace those panels as they become torn and do not have to buy a completely new silt curtain.”

Indian Valley Industries also produces turbidity curtains to specification, depending on water-flow rate, depth of channel, desired filtering properties and, if necessary, tide action. The 50-ft. standard curtains have grommets along the bottom skirt edge so they can be anchored to the channel bottom.

The SiltMaster, a floating turbidity curtain manufactured by Parker Systems Inc. of Chesapeake, VA, comes with various skirt lengths. Similar to the Siltdam, it has a chain ballast at the bottom of the skirt. The skirt is of either a permeable geotextile fabric to allow water but not silt to pass through or, if specified, an impermeable vinyl or urethane-coated fabric.

No matter which products they’re using, many of the contractors we talked to say private companies, state departments of transportation, and local regulatory agencies are looking at erosion control and sediment containment measures in a new light. “I think with the next step of legislation, the enforcement’s getting a little bit more important, and the whole awareness of erosion control-putting it in and putting it in properly and maintaining it-has gone up dramatically in the last year,” comments one contractor. “They’re taking it a lot more seriously.”