Grading and Excavation Contractor

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	Photo: CMI

Avoiding sediment and erosion problems makes sense and saves money.

At every construction site, big or small, the ground is disturbed. That’s what excavation and grading contractors do, isn’t it? Those activities disturb the soil and we turn it into a shape and evenness that are just right for building. Most of the excavation is planned but there is always an amount of soil that is dislodged unintentionally and unnoticed, just because we have been active. It’s this displaced soil (and it could be moved by the wind and rain onsite, too, apart from boots, blades, tracks, and wheels) that becomes sediment. Along comes the rain. The sediment joins the rush of stormwater runoff. It finds its way to our streams, lakes, and rivers and ends up clogging pipes and systems, killing fish and making the water unsafe for kids to swim in. Soil from construction sites is not the only sediment that is a problem, because items like pesticides, fertilizers, picnic leftovers, cans, plastic, grease, and oil can also join the attack on our water and wastewater systems, but it is one that we can control.

Up in Livingston County, MI, at the drain commissioner’s office, Derek Huff tells us that the number of people who break the county regulations concerning discharges is only about 1% or 2%. He praised the attitude and education of his community and credited those with success rather than the use of any particular product or method. That county is about halfway between Detroit and Lansing, covers some 650 square miles, and has a population around 150,000. “It may be difficult at first for contractors,” notes Huff. “But once they see there is an easy way to do the job and a difficult way, they choose the easy way. The easy way is to comply with regulations because the state can impose serious fines if you don’t. The contractors control the sediment from leaving the site, with silt fences or socks or something like that, and they also report to us how conditions change after a rain event.” How “serious” could a fine be? In another state, in the Northwest, the contractor for a highway construction project (along with the state’s department of transportation) was fined almost $1 million for the sediment discharged into a lake and had to pay about half as much again to the homeowners whose territory was damaged. Protective methods do not cost that much. As with many of our daily tasks, like vehicle or machine maintenance, it’s remembering to do it that matters so much.

There are two related problems at construction sites: sediment and erosion. They are not the same. Sediment is, as it were, bits and pieces that escape to become an army of pollutants in waterways. Erosion occurs when the ground gives way, often due to human activities, and the effects are easily seen. The most obvious form of erosion is the bank of a river or lake that seems to fall away gradually; we’ve all seen that. It can be caused by the water channel itself or by changes on the riverbanks, such as new landscaping or docks and jetties built at the end of private properties. A big difference is that erosion may be permanent while sediment from a construction site is usually as temporary as the construction activity itself. Your program to control sediment at your construction site will last as long as your work is continuing, as long as the site itself is active, and it is this aspect of our business that may be considered your everyday problem, rather than the effects of excavation and building on longer-term erosion.

Photo: Armortec

Some locations and situations call for a combination of techniques.

Photo: NCDWQ

Sediment control can be in the suburbs, too, not just in the country.

Please, Fence Me In
Contrary to the plea of singers like Bing Crosby, Frankie Laine, and Roy Rogers who crooned, “Don’t fence me in,” the areas where sediment can gather and be kidnapped by rain or any stormwater are begging to be fenced in. Consider it protective custody. They are a familiar sight, those black plastic silt fences; they are also the objects of regular controversy and complaint. Too often they look torn, crumpled, or broken down, and they are obviously not doing what they were designed to do. The stakes holding the shields are broken, the plastic is flapping around, and the water has run over everything. According to just about everybody with whom we spoke, the reason for the ugly silt fence sights along highways or on construction sites is simple: They were not properly installed. Some fences have their stakes driven into the ground to an easy depth of 3 or 4 inches and the contractor wonders why a wave of stormwater uproots everything! An interesting point made by several experienced contractors was that there are only three states that require the stakes for silt fence to be steel rather than wood.

“Silt fence is a joke on many construction sites,” observes Tom Carpenter, whose company Carpenter Erosion Control makes the tommy, a tool for installing silt fences quickly and firmly. These fences are often the main sediment control tools in the early phases of construction because they are the most practical when the site work has not been completed. A silt fence will be placed at the perimeter of a site and along any waterways to minimize any loss of sediment from the ongoing work. Most silt fences are placed in trenches. “Excavated soil from the trench is meant to embed the silt fence, but it is often neither adequately backfilled nor properly compacted,” comments Carpenter. “If the posts are installed in the trench before backfilling, the ensuing compaction will not serve the full width of the trench. If the depth of the trench is not uniform, shallow areas may be created, which will wash out more easily than the main fence.” The fault is not always the contractor’s. He may be following specifications (as he should) that are inadequate, untested, and unsupported by scientific data.

Who issues specifications? The rules for sediment and erosion control tend to be strictly local, recognizing that each community has challenges and situations that are specific. It is imperative that a contractor know the local regulations and specifications for his construction site. But be assured that there is usually room for negotiation between owner and contractor about the best local business practices. “BMPs [best management practices] are site specific,” notes Dennis Clute, manager at the Fort Worth office for the NRCS (Natural Resources Conservation Service, a division of the US Department of Agriculture). A stormwater pollution prevention plan (SWPPP) is a fundamental requirement for stormwater permits, and it should identify all potential sources of pollution that may reasonably be expected to affect the quality of stormwater discharges from the site. The plan should describe practices to be used to reduce pollutants in stormwater discharges from the construction site. One point we should emphasize is that stormwater, despite its name, is not necessarily a gushing torrent; it can be little more than a trickle, but it does keep going and going till it finds a stream or river to take it along.

Don’t underestimate the potential helpfulness of public agencies like your local NRCS office. “NRCS provides a draft SWPPP in construction contracts that include BMPs for the specific site being constructed,” advises Clute. “The contractor is allowed to adopt the SWPPP in whole or in part as agreed to by the contracting officer.” NRCS regional offices do not advise contractors directly, but technical assistance is given to state offices and from there it is available through local field offices. Each plan for sediment control is designed to handle the specific needs of a particular construction site.

A Web site that contains much interesting information and case histories that could help or inspire you in your work is that of the Great Lakes Basin (GLB). It has a program for soil erosion and sediment control—including some that have economic incentives for construction sites. The states included in the Basin States are Wisconsin, Pennsylvania, Minnesota, Michigan, Illinois, Indiana, Ohio, and New York. The Web site is www.glc.org.

Installation Alternatives
One vitally important fact about silt fences is that they are meant to contain sheet flows, not concentrated flows. The material of their construction today is usually a geosynthetic and has a minimum tensile strength of 100 pounds, usually specified. If you look for “silt fences geosynthetics” or something like that on the Internet, you’ll find some very good sources. The quality of the fabric for silt fences varies, so discuss this aspect with your supplier. CASQA (California Stormwater Quality Association) has some excellent advice on silt fences. The association offers a best management practice handbook, which is well worth acquiring (for free). “Silt fences are suitable for perimeter control,” says the handbook. “They are placed below areas where sheet flows discharge from the site. Silt fences are generally ineffective in locations where the flow is concentrated and are only applicable for sheet or overland flows.” At a construction site where we do the excavation, dozing, and grading, the water flow is usually sheet or overland (= running across the surface).

A silt fence should be installed on a level contour—not on a slope—and there should not be water ponded at more than 18 inches anywhere along the fence. A recommended maximum length of slope draining to any point along the silt fence is 200 feet. Less than that is better. Inspection and maintenance are as important for a silt fence as they are for any equipment or tool. “It’s a good idea to inspect your silt fence when you expect rain,” comment experienced users. “And don’t forget to remove regularly the sediment you have trapped. A good rule of thumb for this would be to remove sediment if it reaches one-third the height of the fence.”

Photo: Great Lakes Commission

Photo: John Francis

This is not how silt fences are supposed to work.

About 10 years ago, somebody figured there had to be a better way of installing silt fences so that they would do their job correctly. (Isn’t this how many advances in construction techniques develop? Has anybody ever written a book about how many ingenious improvements were started in our Midwest?) A technique called “static slicing” was invented and tried. Three states tested it and liked it: Iowa, Minnesota, and Nebraska. It’s used all over the country now. With static slicing, a custom-shaped blade is inserted into the ground to a depth of at least 10 inches. At the same time, the machine pulls the silt fence fabric into the trench created as the blade goes through the ground. There is no vibration or oscillatory motion with the blade. The blade’s tip disrupts the soil slightly upward, which prevents horizontal compaction and creates the best soil condition for future mechanical compaction. The tire of the tractor or skid-steer loader used to pull the slicing machine can do the compaction; it usually takes three or four passes. The installation is completed by setting and driving the posts and then fixing the fabric to the posts. [If you see this slicing done, the most obvious advantage over a standard trencher is that you don’t end up with spoil on both sides of the trench. Think about it. You need that soil for backfill and it will take considerable (manual?) effort to move half of it to the right place.]

The tommy is the attachment that goes with a tractor or skid-steer loader to cut into the soil, deeply enough for a good foundation for the stakes, and pulls a generous roll of silt fence behind it straight into the ground. It’s quick and it saves labor. “The tommy technology eliminates many labor factors,” advises Tom Carpenter. “Whether you’re using a tractor or a skid-steer loader, slicing through the soil is from two to four times faster than excavating tons of soil. The second greatest time saver is probably eliminating the need to backfill, especially when you’re excavating in saturated soils, sand, or sod.” Using this attachment to cut your silt fence trench means there are no joints to wrap together and no workers fighting the wind, the billowing fabric, and the sagging fence. You can find more in-depth details and comments on this promising technique on the Web site for IECA (the International Erosion Control Association).

There’s another regulation that is gaining popularity. Some communities (New York City is one) have a “no-trackout policy” for vehicles and machines that work on city job sites or even just visit them. You can’t take the debris you collect on wheels and tires out into the street. Construction job sites are ideal places for collecting unwanted deposits, whatever the weather. To solve such problems, a company called Wheelwash has developed the Rhino Multi, a self-contained cleaning system that you use at the job site. “We provide customers with a fast, efficient, and environmentally safe way to contain job-site trackout,” explains Ben Taylor, manager at Kiely Equipment, who represents Wheelwash in five big eastern states. “By controlling the amount of dirt that leaves a job site, we help contractors avoid some hefty penalties,” adds Taylor. One contractor has been using the unit at a site where there are 60 trucks per day moving in and out of the site. The average time needed to clean a truck’s wheels and tires in this environmentally sensible way is about 30 seconds, with more than 90% of the water used recycled.

Stabilizing the Edges
If your site is near water, you, as contractor, may have to provide some form of erosion control, too. Erosion, you remember, is a more permanent problem than sediment and your provision of remedies could be a useful value-added service for your customers. For many years wood was the favorite choice for piles, walls, and docks, for shoring up the banks of streams and rivers. Today we know that the wood must be the right wood, probably treated to resist the effects of water and little bugs like marine borers, and there are regulations about which treated wood you may use and which is not satisfactory.

Photo: Tom Carpenter

This method of laying silt fence is known for speed and strength.

Riprap has been used for settling or stabilizing the banks of rivers, but some communities have found this inconvenient, especially for people (residents or visitors) who like to walk along the banks of those waterways. In southern California, this was the case. “The Port Authority prefers our wall system, due to the controlled location of the wall,” comments Nick Jansson of Soil Retention Systems in Carlsbad, CA. “Since the Port Authority owns public waterfront property, riprap can be dangerous for liability reasons when, for example, a person is walking the dog on the waterfront.” Riprap tends to be haphazard in its final form, whereas pre-engineered systems can be designed and laid to suit specific conditions. Soil Retention offers Enviroflex, an articulating concrete block erosion control mattress designed for many applications where environmentally responsible surroundings are a concern. “Enviroflex allows for vegetation and groundwater recharge,” notes Jansson. “It is reinforced with fibers so it can take some traffic loading. As the main failure mechanism in articulated concrete blocks has been caused by uplift and overturning, we developed Enviroflex with an overlap, making it impossible for the block to overturn or have protruding edges.”

Erosion, then, is a problem that must be stopped with as permanent a schedule as possible. Most examples we have seen concern properties built near water. People love to live near streams, rivers, lakes, and ponds, don’t they? It has been that love that has (perhaps unintentionally) caused many of our nation’s waterway problems. This is not just a rural problem! It’s not just the big house by the lake that can cause constant erosion because many developments called urban have small streams, creeks, or swales running through them.

For new developments, contractors look at more than the finished homes or commercial buildings. In some places there will be a potential for flooding; anything you can do at the time of construction will prove invaluable should the floods arrive. If you are an expert in excavation, dozing, and grading, the installation of erosion control devices should present few problems and a good opportunity for increased business at the construction site. That’s why, when you think about erosion control at the construction site, you may be thinking forward to the future protection of that site rather than just today’s problems.

The most common reason for continuing to use a system or materials when there are better alternatives seems to be “We’ve done that for 20 years and we’ll it do for the next 20.” This applies to some of those contractors who insist that wood is the best material for pilings, even when the wood they use is promptly attacked (and eaten) by underwater bugs like marine borers. For your protection system, wood may be the best material, but it must be the right wood, treated correctly, according to your channels’ specific needs. If you are considering freshwater channels, treated wood may be forbidden. A common perception encountered by manufacturers like Crane Materials International (CMI) is that vinyl could not be as effective as wood … could it? “It could,” explains Joseph Gondek of CMI. “After hurricanes last year, when old walls were ripped out, they were replaced by vinyl. An important consideration is that wood solutions must be built and require all the equipment and people that implies, whereas vinyl can simply be driven in.” CMI vinyl has been used successfully in different locations, with many projects in the Caribbean and Europe, as well as in the US. “Vinyl’s qualities have been proven in canals in New Jersey, runoff channels in Missouri, and streams in Jefferson Parish, Louisiana,” adds Gondek.

“Advances in new construction material involving a vinyl structural sheet pile offer a new application for stream bed grade control structures. The vinyl sheet pile system offers unique properties for a hydraulic structure, including minimizing normal construction impacts and the heavy equipment usually required,” notes Bruce M. Phillips of the American Society of Civil Engineers. “Grade control structures offer the advantage of minimizing the impact to natural stream features through adjustment of the dominant hydraulic forces rather than providing measures to resist those forces.” At Martin Creek in California, almost a mile of stream developed a sinuous path with numerous twists and turns that showed historical streambank migration and lateral erosion. Invert control structures of GeoGuard vinyl sheet piles (from CMI) extend the full width of the channel and are embedded 5 feet beyond the top of channel banks to prevent potential flanking. The structures are located with a maximum net drop of 3 feet to ensure the structure was “low drop.” The erosion process is expected to slowly expose the drop structure further and develop the maximum drop in the streambed elevation at the structure. A unique feature at Martin Creek, which was one reason for selecting vinyl sheet piles, is the flexibility in the installation. There was no need for pile driving equipment. The installation used excavated piles (rather than driven), and after installation, the piles were backfilled with a slurry mix.

Another product that could be appropriate if you are working near waterways and wish to offer the owner protection from erosion is Armorflex. This comes from Armortec, now a division of Contech. Armorflex mats comprise compressed cellular concrete blocks that interlock; the mats are easy to transport and install. The open areas of the mat (about 20%) allow free drainage of groundwater and the development of natural vegetation; the latter is possibly the best permanent victor in the erosion battle. The Armorflex mats arrive at your site ready to install. The recommended base for the mats would be a site-specific geotextile with a subgrade laid by your standard equipment.

Paul Hull writes on construction topics for several international magazines.

GEC - January/February 2007

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