A plan for controlling erosion and sediment at a construction site is just that: a plan—words and lines on paper. There’s nothing like actually implementing the plan to see just how well it keeps soil onsite. No erosion and sediment plan is perfect, though—that’s the nature of construction. So it might be necessary to adjust the plan, for any number of reasons, as work proceeds. Soil or weather conditions might not match the designer’s perception. The timing and sequence of construction activities may differ from what the designer had in mind. The contractor may see a better, lower-cost way of controlling sediment than the measure shown in the plan.
But seeing an opportunity to improve the plan once work gets underway doesn’t necessarily lead to an actual improvement. In fact, hydrologist Jerry Fifield, CPESC, of HydroDynamics Inc. in Parker, CO, would like to see an improvement to the whole approach to controlling erosion and sediment at construction sites.
“I’m disgusted by colleagues who submit plans that aren’t practical for contractors to follow,” he remarks. “I’m disgusted with contractors who aren’t installing, inspecting, and maintaining erosion and sediment controls called for in site plans. And I’m disgusted with rules and regulations made by people who don’t realize that the requirements might not apply in every case and who are unwilling to bend.”
The solution, Fifield claims, is flexibility. As he sees it, designers must be flexible in specifying erosion and sediment control practices that best fit each individual site. Contractors must be willing to clean up and repair any damages caused by not installing the required practices. Regulators must realize that normal erosion and sediment control measures might not be practical in every situation.
“Everyone involved with erosion and sediment control at construction sites must be willing to change plans as needed when site conditions change,” he says. “An erosion and sediment control plan isn’t absolute. It’s just a conceptional idea on a piece of paper that has to be subject to change, because the actual conditions at the construction site always differ from conditions envisioned when designing that plan in an office.”Here are several ideas and techniques—ranging from a basic mailbox to a simple method for harnessing rain to increase efficiency of sediment basins—to help improve results when planning for erosion and sediment control on paper turns to action on the ground.
For the past 18 years, Warren Faircloth, CPESC, of Hillsborough, NC, has been reviewing, approving, and inspecting erosion and sediment control plans for construction sites in Orange County. He lists some basic principles to follow when implementing erosion and sediment control plans:
- Schedule and sequence timbering, clearing, grading, construction, and stabilization to minimize soil exposure.
- Control runoff to prevent erosion and limit the amount of sediment generated by the project.
- Install drainageways, pipes, and outlets early in construction to handle concentrated or increased runoff volumes.
- Keep sediment onsite to protect water quality and property.
- Understand the limitations and capabilities of sediment control devices.
- Place sediment control devices out of the way of active construction work.
As Faircloth points out, converting good plans into good results requires an effective quality-control program. This includes:
- clear communications between the designer and the contractor;
- a preconstruction conference with enforcement authorities, the project owner/developer, the designer, the contractor, and others involved to review the approved plan and discuss any questions or potential problems;
- regular, competent onsite supervision and inspection of implementation of the approved erosion and sediment control plan;
- proper maintenance and repair of erosion and sediment control measures.
Fifield recommends that the project developer, designer, contractor, and regulatory people meet in the contractor’s trailer at least once every two weeks to discuss any erosion and sediment control problems and to modify plans as necessary to prevent any repeats.
“If we’re serious about controlling erosion and sediment effectively, we have to budget the time and the money for good communications during all phases of construction,” he emphasizes.
Faircloth notes several simple ways to improve communications:
- a mailbox onsite where the inspector can leave reports,
- a fax number where the reports can be sent,
- telephone numbers for pagers and voicemail boxes of key developer and contractor personnel.
The best way to control sediment is to control erosion. Controlling erosion at an active construction site isn’t always possible, however. In fact, disturbed soils can be exposed to wind and water for a significant length of time. Grading can eliminate erosion control measures. Establishing vegetation to protect soil takes time and the right moisture and temperatures. Sometimes efforts to stabilize exposed soil fail as a result of factors beyond anyone’s control. For example, Faircloth notes that in North Carolina torrential rains can strike exposed construction sites at any time throughout the year. Last September, normally one of the driest months of the year in North Carolina, parts of Orange County were deluged with 26 in. of rain – half the yearly average. “Times like this require effective sediment control, not just the minimum effort to meet compliance,” he says.
Sediment basins have proven to be one of the most effective ways to control sediment in concentrated runoff in the rolling topography of Orange Country, observes Faircloth. He likes to place a sediment basin below the disturbed area to control sediment temporarily until the site is successfully stabilized. In this position, the basin doesn’t interfere with construction activities and won’t be damaged by the work. In addition, crews can reach this location to install, maintain, and remove the basin.
A Better Alternative to Curb Inlet Protection
Faircloth normally recommends placing sediment basins at the outlet of the storm drain. When that’s not possible, he favors diverting runoff to the sediment basin rather than installing a device, such as a gravel filter, around curb inlets in an attempt to keep sediment out of storm drains. He faults such curb inlet protection for several reasons:
- It’s ineffective. Inlet control devices can’t filter sediment from the volume and rate of runoff entering the inlet. “Usually designers count on the filtering capabilities of inlet protection devices to keep sediment out of storm drains,” Faircloth points out. “Filtering sediment doesn’t work very well, however. Removing sediment from runoff requires gravity and lots of storage volume. Providing the needed volume for gravity settling at a curb inlet is almost always impractical, given typical space constraints.” He reports that to settle sediment using gravity, typical sediment-basin volume requirements per acre of drainage can total 1,800 ft.3 in North Carolina, 3,600 ft.3 in Virginia, and as much as 7,000 ft.3 in Pennsylvania.
- It can’t be used during several stages of construction, including land-clearing activities or when pipes have been laid but the structures or junction boxes aren’t in place.
- Because water follows the path of least resistance, runoff flows around inlet protection devices at higher elevations to the inlet at the lowest point. In doing so, the runoff overwhelms the lowest inlet protection because the drainage area to the device has been greatly exceeded.
- Inlet protection devices interfere with construction activity and must be removed for grading or for masons to work on the inlet. “Usually the device is not replaced or it’s replaced incorrectly,” Faircloth notes. “Also, if the control at the low point causes water to pond on the subgrade, the soil might be ruined. This requires extra work to excavate the bad soil, add new fill, and compact it.”
- Inlet protection is impractical. “It puts the burden for success and of coming up with a workable plan on the grading contractor instead of where it belongs: on the developer and the designer. No matter how responsible and conscientious, there is little—if anything—a grading contractor can do to make a defective sediment control measure, such as curb inlet protection, work,” he laments.
Linear construction projects, such as highways, pipelines, and power transmission lines, often present more and different types of erosion and sediment control problems than those usually found on more compact sites, such as an apartment complex or a shopping center.
For example, a pipeline can cross many different types of topography, soils, and vegetation – each of which might require different approaches for temporary and permanent erosion and sediment control practices. The choice of practices may also change with the seasons. A natural-gas pipeline project, involving areas in northern and southeastern New Hampshire and stretching over a 14-month period, offers ideas for meeting some of the challenges facing erosion control professionals on linear construction jobs.
Completed last August, the New Hampshire work was part of a larger project that included the neighboring states of Vermont, Massachusetts, and Maine and the Canadian provinces of Quebec and Nova Scotia. In Rockingham County in southern New Hampshire, 32 mi. of 30-in.-diameter pipe crossed 183 wetlands of all types and 41 perennial and 29 intermittent bodies of water. In Coos County in the north, 75 mi. of 24-in. pipeline were built across 430 wetlands and 141 perennial and 130 intermittent water bodies.
One erosion and sediment concern was the amount of land disturbed in such a lengthy project. The construction sequence included clearing, grading, trenching, stringing, bending, welding and lowering pipe, backfilling, and restoration. The front end of the project (clearing and grading) was separated from the back end (restoration) by many miles of disturbed soils and several months of time. Proper maintenance and tight management to make sure temporary and permanent erosion and sediment control practices were installed correctly and on time, however, helped protect stockpiled topsoil and other disturbed areas as much as possible, reports James Spaulding, CPESC, a civil engineer with the state’s Department of Environmental Services.
Three private contractors, experienced in pipeline construction, were employed full time to inspect implementation and maintenance of erosion control measures.
During land clearing, which often involved forests, typical timber-harvesting best management practices (e.g., buffer strips and silt fence) controlled erosion and sediment when properly installed, notes Spaulding.
Erosion and sediment control measures were installed during grading operations when the right of way was prepared for construction activities. Providing room across the 75-ft.-wide right of way for the trench, earth stockpiles and pipe restricted equipment traffic to a one-lane road. This traffic caused severe soil disturbance and rutting. As a result, the road required continuous maintenance of water management structures, such as drainage ditches and water bars. Other erosion and sediment control measures included installation of silt fence in all downslope areas and culverts to convey water underneath the right of way.
Wetlands were crossed using log corduroy (tree trunks laid side by side). Stream crossings were made with mats of large oak timbers bolted together and abutments made of crisscrossed timbers. Proper maintenance of these crossings and approaches was critical in preventing stream sedimentation.
“Going into the project I was concerned about the amount of land being disturbed,” Spaulding recalls. “Where proper management and maintenance of erosion and sediment control practices were implemented, however, we didn’t have many problems except for water in the trenches. We never found a completely satisfactory way to deal with it.”Spaulding emphasizes the importance of correctly implementing the erosion and sediment control plan. The contractor was fined a total of about $200,000 for failing to adequately protect water quality at various times, he reports. One violation involved a 1.5-mi.-long wetland on the side of the hill. The right-of-way area exposed when topsoil was stripped off was used as an equipment road. Because of the very wet conditions, this traffic stirred up a lot of sediment, which ran down the slope to a river. The project was shut down for about a week while the contractor used spoil from the pipeline trench to build a suitable equipment road through the wetland.
In another case, water removed from a trench was discharged into an old channel and flowed directly into a nearby stream.
“In New Hampshire, you can’t go very far without running into a stream or a wetland,” describes Spaulding. “Wetlands on sloping terrain and shallow groundwater tables caused significant challenges with water running across the right of way and the pipeline trench filling with water.”
Trench Water. Trench water was a major source of turbid runoff in the project. Because the terrain was seldom level, groundwater and surface water flowing into the trench would collect and eventually overflow at the lowest point, carrying sediment with it. Often this low point coincided with a stream or wetland. To minimize this problem, dams were installed across the trench. They were either placed close enough to each other to prevent water from overtopping the trench or placed where they could direct trench water to a stabilized, nonsensitive area. Sometimes it was impossible to pump this water to an upland area far enough from a stream or wetland to prevent polluting it with sediment. “Filter bags and settling structures proved only marginally effective,” Spaulding says. “We don’t have an answer to this problem.”
Wetland Crossings. During construction, stripped topsoil was segregated from the trench spoil. After construction, the topsoil was spread over disturbed areas and allowed to revegetate naturally.
Some wetlands were dry enough during construction to support construction equipment. Often, though, they weren’t. Then timber corduroy, timber mats, or geotextile and gravel were installed on the surface to support equipment.
Crossing sloping wetlands with mineral subsoils required a different approach. Here, any disturbance caused water to flow across the right of way and through the construction area. To deal with it, topsoil was stripped from the full width of the wetland. Then soil excavated from the pipeline trench was used to build a construction road atop the exposed wetland subsoil.
In some cases, wetlands were saturated enough to allow preassembled pipe to be floated across the wetland into position. There the floats were removed and the concrete-coated pipes were sunk into place. This limited the amount of equipment crossing the wetland. Other equipment had to be transported around the wetland, however, increasing the contractor’s costs significantly.
One wetland, an old river oxbow, contained several shallow ponds, and at least one was still connected to the main river. Here the contractor used a horizontal directional drill to bore a small tunnel under the wetland, and the preassembled pipe was pulled through it. This crossing created the least environmental impact but was the most expensive. Although it didn’t happen in this case, Spaulding points out that with this method, drilling fluids can break out of the bore and into the wetland through fractures in the soil.
Water-Body Crossings. An open, dry cut was used to cross the majority of water bodies in this project. After diverting the stream around the crossing, the trench was excavated, pipe was installed, and backfilling took place. The stream was stabilized, usually with erosion control blankets or rock, before the flow was returned to the original streambed. Two methods were used to divert the flow. Pumping water across the site after damming the stream proved to be better than using a flume to convey the flow, Spaulding observes. Because of the confined space of the crossing, extra care was required to prevent disturbing the flume while crews were working. Any disturbance of the flume usually resulted in the release of turbid trench water.
“Trench water was a problem on these crossings,” Spaulding says. “Sometimes it was necessary to dewater the trench prior to installing the pipe. If this wasn’t done, backfilling displaced trench water. This water frequently caused turbidity violations on an otherwise clean crossing.”
In a few cases where the stream was too large to divert, it was crossed using an open cut. All construction work was done while the stream continued to flow through the work area.
“The only way to reduce impact of an open cut is to perform the work in a timely manner,” Spaulding states. “Unforeseen circumstances, which delayed work, were common. If possible, other means of crossing a stream should be used.”
Horizontal directional drilling was used to cross all major water bodies in this project. The longest such crossing was about 3,800 ft. “Drilling fluid was released in several cases, but none caused a major impact compared to the impacts of a wet or dry crossing,” says Spaulding.
Strengthening the Hand of Regulatory Agencies
In some areas, the lack of resources—money, time, and expertise—hamper the ability of regulatory agencies to review erosion and sediment control plans and to inspect construction sites for proper implementation and compliance with required rules and regulations. “The smaller the municipality, the less likely they’ll have inspectors with the necessary technical training and experience to do the job properly,” Fifield says.
To solve that problem, he suggests that regulatory agencies hire inspection services from private industry consultants, such as Certified Professionals in Erosion and Sediment Control.“That consultant must be accountable to the regulatory agency,” Fifield says. “It’s no different than an engineer stamping his approval of a drainage plan. This approach would cost more money, but are we serious about controlling sediment and erosion during and after construction activities occur?”
In New Zealand, the Auckland Regional Council for one is serious in its approach to stormwater and sediment management. To keep up with continued growth in land development activities, it has been using outside consultants for the past five years with good success, reports Graeme Ridley. He leads the council’s nine-person stormwater and sediment management team, which also oversees the work of five full-time private consultants. The team is involved with all aspects of the development cycle—planning, bulk earthworks, individual houselot development, and long-term stormwater discharge—and has input from a regulatory, policy, educational, and investigation aspect.
“The consultants contribute to a big part of the regulatory side of our program, including erosion and sediment control plan review, compliance, monitoring, and an inspection program,” Ridley notes. “It works very well.”
These consultants work with developers and their consultants in preparing and approving erosion and sediment control plans. Once these plans are formally approved through a consent process by Ridley’s team, the consultants then monitor compliance and implementation of the plans. If necessary, as a backup, the stormwater and sediment control team follows up with enforcement action.
The consultants used are selected through an interview process in which experience in the stormwater and sediment management field is considered a necessity. Consultants must also have attended the Auckland Regional Council Industry Education Course. This course, which is also available to developers, provides training opportunity in the form of a two-day Plan Preparers (Consultants) Course and a one-day Plan Implementors (Contractors) Course. Both courses focus on the principles and practices of erosion and sediment control. The Plan Implementors Course puts more emphasis on the practices and allows participants to develop an assessment of environmental effects and an erosion and sediment control plan for a development site visited during the course. Participants are required to complete a take-home exercise, which is submitted and marked at a later date with the opportunity to become Auckland Regional Council-registered in erosion and sediment control.
“These courses provide the cornerstone of the education component of the overall program and are likely to become mandatory for people involved in the development industry in the Auckland Region,” Ridley points out. “By having our consultants Auckland Regional Council-registered in erosion and sediment control, we have a degree of comfort that the principles and practices we wish to promote are understood and therefore further endorsed in the field.”
Consultants are hired by the Auckland Regional Council on an annual contract basis, and their work is formally reviewed monthly with a site audit.
Ridley lists benefits of using the consultants.
- No cost to ratepayers. Fees, which developers pay for erosion and sediment control consents (permits) and site monitoring inspections, are used to pay the consultants directly.
- Reduced staff workload. In addition to relieving Ridley’s team of consent processing and compliance monitoring duties, the consultants help conduct many of the educational workshops held for contractors.
- Consistency. The consultants monitor implementation of plans, which they have helped to develop and have approved through the consent. All use a standard inspection procedure and report for each site, which is easily transferred and used internally by the Auckland Regional Council as necessary.
- 24-hour availability. Consultants also respond to complaints related to erosion and sediment around the clock. They report results of their investigation directly to the Erosion and Sediment Control Team, which may act as necessary.
- No impact on budget. If development slows or stops, the Auckland Regional Council isn’t left with staff members who have no work.
A critical part of the Auckland program is centered around a seasonal close-up of all earthworks sites in the region. Winter conditions make it difficult to stabilize sites. That in turn can lead to unacceptable levels of sediment generation and discharge from sites. So only minimal earthwork on development sites is permitted during winter (April 30 to October 1). This creates a very seasonal workload for the program. Ridley reports that the use of consultants allows this seasonal work to be managed easily, since consultant input into the program is reduced over the winter.
“Provided you have the right people, there really aren’t any negatives to this concept,” he remarks. “But you must have consultants who understand our overall program vision and goals. Consultants must be considered an important part of the team and be involved as necessary to make sure this understanding is obtained. We have a good selection process and a rigid audit process to help ensure sound, consistent results.”
Improving Sediment-Trapping Efficiency
Using private consultants to bolster its erosion and sediment control program isn’t the only way in which the Auckland Regional Council is blazing a trail. While the whole program emphasizes erosion control as the first step on any successful project (through a wide range of structural and nonstructural techniques), it is also important for sediment control practices to operate at maximum efficiency, Ridley stresses. The program has recently developed a new technique to help manage the settling of clay particles, a particularly tough challenge in Auckland where high-clay-content soils are typical.
The Auckland Regional Council requires sediment retention ponds on most projects. Research shows these structures are about 70% efficient in keeping sediment—especially the fine clay particles—onsite, notes Ridley. Treating stormwater runoff with floculants has always been considered another option for improving the efficiency of sediment retention ponds in trapping clay particles. These floculants cause the fine soil particles to cling together into larger, heavier particles, which settle out more quickly.
In the past, however, these systems have usually required a source of power, such as electricity, to operate the equipment that dispenses and mixes the floculants. Often, economical power isn’t easily available at the development sites. As a result, the Auckland Regional Council has been involved in developing a simple portable and manual system for adding floculants to sediment retention ponds, which is essentially run by rain.
“It’s one of the most exciting sediment control techniques we’ve seen here in the last decade,” remarks independent consultant Brian Handyside of Erosion Management Ltd. in Devonport.
The system consists of three simple parts: A catch tray—which typically measures about 3.3 x 6.6 ft., depending on such factors as the sediment retention pond size and the catchment size—empties into a reservoir tank. This tank floats inside a larger tank (about the size of the water tank on a toilet) containing a floculant, polyaluminum chloride. As the reservoir tank fills with rainwater, it displaces the floculant, which discharges into the sediment retention pond and treats the sediment-laden runoff. The complete system costs about 1,500 New Zealand dollars ($700 US) to build and can be transferred from site to site in the back of a pickup truck.
Ridley reports sediment-trapping efficiencies of this system to be as high as 98%. While the system greatly improves the expected efficiency of the sediment retention pond, the residual aluminum in the water discharged from the pond might still be a concern. The aluminum doesn’t appear toxic to fish; however, the floculant can lower the pH of receiving waters, which is harmful to fish. Studies are underway to determine if effects of the floculant are acceptable. Other systems are also being tested using a floculant block, polyacrylamides, in a simple weir structure.
Increased efficiency of the sediment retention ponds means requiring more regular maintenance. Sediment removed from stormwater collects as a soupy, viscous material that can be difficult to remove. In an effort to improve sediment removal, several different types of pumps are being tested. Also, Ridley adds, this system requires trained personnel to calibrate, operate, and maintain it.
In field trials last year, the system worked well, he observes. “Depending on the ongoing results of current trials, the council might start promoting these systems during the next earthworks season. While emphasis will always be placed on erosion control systems – keeping sediment at its source – any further improvement in efficiencies of the sediment control techniques we utilize will also provide benefits.
“There is plenty of room to improve this system, but a lot of good things are happening with it.”
