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If not controlled, the impacts of rain, wind, and snow can leave some costly site-repair bills in their wake. Here are steps you can take to shelter your project profits from these natural perils. By Greg Northcutt |
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Are you dealing in dirty money? You are if muddy rainwater is running off your construction site and into a creek or down a storm drain. The sediment in that water, eroded by the impact of raindrops and overland flows of runoff on disturbed, unprotected soil, can cost you some hard-earned cash - from offsite cleanup expenses to lawsuits and civil fines. Effective erosion and sediment control (ESC) measures, of course, can help stem this loss of money. In some areas, the height of the storm season and resulting erosion threats coincide with peak construction activity. In others, the erosion control challenge isn't so much a prolonged period of inclement weather as it is short-but-intense wind and rainstorms. Elsewhere winter can shut down work for months at a time. In this case, the problem isn't so much the frozen ground as it is the threat of erosion when the snow melts and bare sites begin to thaw out in the spring. Rain with the thaw can make things even worse. Weatherizing an earthmoving project calls for careful planning, based on thorough knowledge of your site. It also calls for solid execution of ESC practices. That's where effective communications pays off. Consider preparations for winter shutdown. The grading or excavating contractor wants to move dirt as long as possible, while the erosion control contractor wants to get on-site to install ESC practices before the ground freezes, relates Tom Carpenter of Carpenter Erosion Control in Ankeny, IA. Carpenter, a Certified Professional in Erosion and Sediment Control (CPESC), points out that the later the grading and excavation work continues in the fall, the fewer your choices for protecting the site over the winter. "You could probably hydromulch a small site at the last minute, even if the ground is frozen. But once frost sets in, you can't crimp in straw or install erosion control blankets to protect a seeded site and you can't put up a silt fence to control sediment. Then you could be out of compliance with your NPDES [National Pollutant Discharge Elimination System] permit or other requirements." The best way to prevent that, he maintains, is good communications. "The erosion control contractor has to make sure the dirt contractor knows that time is running out and that it's critical to allow enough time after the project shuts down to install the appropriate erosion and sediment control practices." Identifying the work zones and developing the phases, sequence, methods, and schedule within each zone, along with an approved ESC plan for each phase, will detail the specific practices and measures for limiting soil losses during construction and any shutdown period. However, simply following the plan might not be enough. Effective erosion and sediment control also requires good communications, notes John Deering with John W. Deering Inc., a land development and construction consulting firm in Bethel, CT. "You have no control over the weather," says Deering, who recalls one earthmoving project where he faced 19 straight days of rain, "so you should pull everyone together as a team to discuss possible erosion and sediment control problems as the project progresses and figure out how to remedy them before they happen. Communication and scheduling are the keys that will bring forward a successful project." When possible, engineer John Gonzalez with Frederick Ward Associates Inc. in Bel Air, MD, likes to work with grading and excavating contractors in designing ESC plans. Such one-on-one communication makes for more efficient, more effective results, he reports. "I can find out how the contractor plans to do the work and can include erosion and sediment control measures that fit in with the planned sequence of construction." If that's not possible, Gonzalez likes to keep an open mind once the project begins. "I may have phased the plan one way, but the contractor sees a less expensive way to achieve the same goal," he says. "Making that revision, however, means getting the project owner and review agencies onboard so they are comfortable with the change." Once again, the key is effective communication. Of course, talking, by itself, won't protect disturbed soil from blowing or washing away. Here are some ideas from the experts on how to do that. Take a Preventative Approach
Just because an ESC plan has been approved doesn't mean it's necessarily a good plan. "I'm convinced that many of my design colleagues are designing plans for themselves and not for the contractors," believes hydrologist Jerry Fifield, CPESC, president of Hydrodynamics Inc. in Parker, CO. "As a result, the contractor gets a set of plans that can't be implemented. What's more, some inspectors require implementing practices on plans, which may not even be necessary. Or they may require using practices in an outdated manual that have been proven incorrect or inferior to current methods. As a result, a conscientious contractor can get very frustrated." That's why he recommends that grading and excavation contractors take the initiative when they see ways to improve an existing ESC plan. "Every contractor I know understands when a particular practice is working and when it's not," Fifield states. "Contractors should be communicating regularly with the project designer or inspector to identify ineffective erosion and sediment control measures. More importantly, contractors should suggest methods that, based on their experience, will work. For example, maybe a silt fence is failing because it wasn't designed for conditions actually occurring on-site. Perhaps a sediment basin, built at the right location above a silt fence, would catch runoff and reduce the amount flowing to the fence so that it doesn't blow out." But what if your suggestions are ignored? "Then," offers Fifield, "document that with a long paper trail to protect [yourself] in case the practice is implemented as originally designed or required and fails later." There's another good reason to take a preventive approach to implementing ESC plans. Failure to revise an approved ESC plan as circumstances change could result in some very costly consequences. Jim Spotts, CPESC, with Southeast Environmental Consultants LLC in Atlanta, GA, cites one example that occurred several years in Georgia in which some fill dirt that was being hauled to a construction site fell onto a nearby road. Rain turned the dirt to mud, clogging a storm drain and allowing water to pond in the road. A car hit this standing water, hydroplaned off the road, and crashed, killing the driver. The contractor was sued in court for not taking appropriate steps to prevent and clean up the dirt spill. The contractor lost the suit and was ordered to pay the plaintiff nearly $2 million. The contractor appealed the award, claiming that all measures called for in the ESC plan had been followed. Once again, the contractor lost. "The court ruled that, even though the erosion and sediment control plan didn't include measures to prevent dirt spills on the road, the contractor was still responsible for the site," recalls Spotts. "The court said that if additional erosion and sediment control practices were needed, then the contractor should have used them." The upshot: "Anticipate possible problems and take preventive action before rains wash things away and create a mess," Spotts advises. "A proactive approach is cheaper than a reactive one." Ed Stein with Tectonic Distributing Inc., a construction products distributor in Edgewood, MD, and president of the International Erosion Control Association, offers this perspective: "Erosion control is a preventive approach because you're trying to eliminate the need for sediment control. When you start controlling sediment, you're reacting to inadequate erosion control practices. The better you control erosion, the less the need to control sediment." Controlling that sediment is one tough challenge. "It's just about impossible to remove all sediment in runoff from a construction site," relates Fifield. "But you can reduce the amount of heavier particles leaving the site substantially by installing the proper practices correctly in the right places. About the only way to keep colloidal clay particles on-site is to control erosion throughout the entire construction process." Minimize Land Disturbance The best way to limit erosion control costs is to limit the amount of land exposed to wind and water forces by earthmoving activities. As Stein points out, many states require that large areas be divided into stages or smaller sections and that one area be graded and stabilized before another is disturbed. State rules in Maryland, he notes, allow contractors to clear no more than 20 ac. at a time, regardless of the total size of the area to be developed. Start at the Top
Tom Williams, CPESC, an associate and senior project manager with the engineering consulting firm Golder Associates Inc. in Lakewood, CO, recommends developing a site from the highest elevation to the lowest whenever possible. That way you can use a sediment pond or other practice to collect sediment from disturbed areas before it can wash onto completed areas or off-site. "That's a top priority for us when working in residential developments," he maintains. "Otherwise, uncontrolled runoff from a large disturbed area following a big storm could wash out bridges, undercut sidewalks or patios, or dump sediment onto lawns around the houses below." Know Where the Water Flows
By controlling the flow of stormwater runoff, you can direct it to protected drainageways and containment areas to limit erosion and offsite transport of sediment, and to minimize downtime. "Proper drainage can improve construction productivity by preventing subgrades from becoming saturated so that earthmoving equipment can keep working without getting stuck," explains Stein. But first you have to know where the water flows. "You can design all you want, but you won't know where the water actually runs or how high the flows are until you actually see them," Williams points out. "So instead of heading home or to the coffee shop when it rains, walk your site so that you can really see the flow paths. Life happens during the storms, not afterward. "Water doesn't always run where you think it will. A slight change in grade could cause water to flow or collect where you didn't expect it. Observing runoff flows from a 1-inch rain and where and how much collects gives you an idea of what to expect from a larger design storm. Then you can assist the design engineer by sharing what you actually know about the site so that, if necessary, the erosion and sediment control plan can be changed to match the reality of the job site." Manage the Runoff The idea of controlling stormwater runoff is to direct overland and concentrated flows away from erosion-prone areas (e.g., fill slopes) or sensitive areas (e.g., wetlands) and to reduce its erosive and sediment-carrying energy by routing it to collection devices, such as sediment basins, that slow the flow. In the case of a rough-cut roadway, for example, that might mean:
"Ideally you want to time grading work so that all water conveyances are vegetated before winter," emphasizes Tim Morris, an environmental scientist with KCI Technologies Inc. in Hunt Valley, MD, who monitors environmental protection practices for the Maryland State Highway Administration. "Unfortunately project schedules don't always permit that. If so, waterways can be stabilized with a natural fiber mat, riprap, or other armor, depending on the amount of flow, to prevent scouring." He notes one option for handling runoff from paved portions of a roadway that's still under construction. "Since this runoff isn't carrying sediment and there's no need to treat it in a sediment pond, it can be dissipated by directing it through a series of check dams or slope drains and discharged onto a stable area." Morris takes a different approach for embankments on his projects if vegetation can't be established prior to winter shutdown: If the slope consists of sandy-textured soils or other highly erodible material, he covers it with topsoil or a finer-grained soil to reduce the likelihood of erosion. That's not necessary for clay slopes, he adds, since they are less likely to erode than topsoil. Then he runs a dozer up and down the slope, perpendicular to the fall line. This compacts the soil, increasing its resistance to erosion. At the same time, the cleats of the dozer tracks create minicheck dams to slow runoff, further reducing the threat of erosion. Finally, he covers the bare slopes with a mulch, such as straw, to protect the soil from the impact of raindrops. More Stormwater Management Techniques
"Controlling the flow of water isn't one or two things you do on a short-term basis but a variety of practices throughout the entire construction process," states Fifield. "It can result in a lot less erosion and much lower sediment cleanup costs over the life of the project. But it requires planning ahead to make sure the erosion and sediment control measures are in place when you need them. For example, spray-on soil binders can reduce erosion, but you need dry weather long enough after application for them to set up and become effective." Williams divides the challenges of controlling water on a construction site into two main areas: low-velocity constant flows, such as those from a neighboring site, and high-velocity flood events. Typically, Williams describes, the first type involves a residential or commercial development that has been disturbed to over-lot grade and install utilities and needs to be protected for several months to a year or longer until construction of homes or buildings is complete. Here, flows might be coming onto the site from an adjacent developed area, or maybe it's runoff from landscape irrigation. Because of the relatively short period involved before the site is developed, Williams favors low-cost, reusable materials for managing flows and protecting disturbed areas in these situations. That could include lining ditches with plastic sheeting or - for short, steep runs - placing 18- or 24-in.-diameter high-density polyethylene pipe, cut in half lengthwise, in the ditches to protect them from erosion. "Slow, continual flows of water can undermine the outlets of culverts and the edges of concrete pads and can erode through asphalt in about six to 12 months," Williams notes. "So we've placed erosion control mats under outlets and concrete pads and used a concrete lining or pan, instead of asphalt, to construct drainageways to sediment ponds." He's also used temporary seedings of nonweed species, such as Canadian bluegrass or perennial rye, to protect slopes in residential areas from slow overland flows. "Crimped-in weed-free straw can stabilize large sheet-flow areas and protect against wind erosion for up to a year in a dry climate like Colorado," Williams points out. "It's relatively inexpensive, and it poses no weed threat when the site is eventually seeded." His first priority when preparing for high-flow storm events is to install drainage ditches that empty into a sediment pond to collect runoff and protect neighboring sites from sediment. In the case of installing temporary practices next to an already-developed site, he likes to overbuild. "It's much easier to dig a drainage ditch 2 feet wider and 2 feet deeper than you'll probably need than it is to go back later and deal with a lawsuit because a sediment pond overflowed and flooded out a neighboring house," Williams remarks. Use the Latest and Best Techniques When it comes to stabilizing slopes and channels and trapping sediment, the effectiveness of a particular material or structure varies, depending on the nature of the problem as well as the product or device itself. Best management practices, or BMPs, include materials and structures, such as mulches, sediment-trapping devices, and storm drain inlet protection. Some of these measures might not necessarily be the best choice for a particular situation. "I'm concerned that some project designers aren't incorporating the latest BMPs in their erosion and sediment control plans," comments Spotts. "Often they're more effective than earlier ones." He's also concerned with improper installation of some BMPs, such as silt fence. "To be effective, a silt fence has to be installed on a contour, not on a straight line across dips and rises in the terrain," he points out. "I've actually walked beneath the bottom of a silt fence, without knocking my hat off, because that's the location called for in the plan." In addition to installing BMPs as soon as possible after grading work is completed, a combination of BMPs might be more effective than a single one in some cases. For example, Spotts notes, filter logs commonly are placed around a curb inlet, about 1 ft. away from the drain. Some contactors add a gravel berm in front of the logs to trap coarser sediment so the log can effectively trap the smaller particles. "We don't have a single BMP for this specific problem, one that will trap sediment and at same time quickly filter water off the road," he adds. Be Prepared While it's often difficult to predict exactly when a storm will hit or the snow will melt, it's bound to happen sooner or later. That's why it pays to have all ESC practices in place and functioning properly in advance. Good maintenance of devices and structures is a key part of this preparation. Plugged culverts and torn silt fences, for example, aren't effective. Sometimes a short interval between storms can hamper maintenance work by not allowing time for a site to dry enough to support equipment needed to make repairs or to adequately clean out sediment control structures to restore its design capacity. "That's why we build sediment ponds small enough that an excavator can reach in from the edge to clean them," says Williams. "Otherwise it might be too wet to use a front-end loader or a dozer." A winter shutdown poses a special challenge for inspecting and maintaining ESC devices. "A contractor is reluctant to come back and fix a problem over the winter since it means remobilizing equipment," observes Morris. So he recommends keeping some machinery on hand and having someone monitor the condition and performance throughout the winter and make any necessary repairs. Besides improving erosion and sediment control, this approach can also improve relationships with regulatory agencies, he adds. "It looks pretty bad if an inspector finds a problem and the contractor says it will take two weeks before it can be fixed." Greg Northcutt is a frequent contributor to Grading & Excavation Contractor.
GEC - September/October 2003
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