Erosion and Sedimentation: Why Are They a Problem?
The US Environmental Protection Agency lists sediment as the single most common pollutant in rivers, streams, lakes, and reservoirs. With all the potentially harmful chemicals and substances in the world, it seems odd to many people that sediment—dirt, essentially—is singled out as the major culprit. Yet these particles of sand, silt, and clay that are set loose by the process of erosion cause a great deal of damage and cost us a tremendous amount of money each year.
It’s useful to make the distinction between erosion and sedimentation. Erosion is the dislodging of soil particles by rainfall, flowing water, or wind. Sedimentation is the movement of soil—and its accumulation, often in places it shouldn’t be—once it has been dislodged.
Why is sediment considered a pollutant? First, the sheer volume of it can cause problems. When enough sediment accumulates in catch basins and storm drains, it can prevent stormwater runoff from draining freely, causing flooding.
Enough sediment in a river, stream, or lake reduces the capacity of the water body, and this can lead to altered stream flows and, again, flooding. In the worst cases, accumulated sediment can reduce the water’s depth so much that it prevents boat and barge traffic, necessitating dredging of navigation channels.
Sediment can harm aquatic life by smothering the benthic ecosystem, clogging fish gills, and harming the development of fish eggs and larvae. Sediment can also carry with it other pollutants, many of which sorb to the sand and silt particles. Pesticides, hydrocarbons, and other pollutants are often associated with sediment.
Although erosion occurs naturally, EPA estimates that 70% of the erosion taking place in the United States is caused not by natural processes, but rather by human activity—particularly construction activity, such as clearing, grading, excavating, and stockpiling of soil. Eroded soil from these activities is carried away from construction sites by stormwater runoff and ultimately ends up in storm drains, lakes, and rivers. EPA puts the prices tag of sediment pollution in the US at $16 billion a year in environmental damage.
There are many methods to prevent erosion and control sediment. There are also many regulations in place—some at the federal level, some at the state and local levels—to ensure that those engaged in earthmoving and construction activities take steps to control erosion and sedimentation. This paper gives an overview of the federal regulations, including some recent changes and controversial decisions, as well as common erosion and sediment control methods.
The Current Regulations
NPDES Permits for Construction Sites. A program under the federal Clean Water Act called the National Pollutant Discharge Elimination System (NPDES) regulates stormwater discharges from construction-related activities. Before allowing any water to leave the construction site, the site operator must obtain an NPDES permit. The permit is necessary for all construction activities that disturb one acre or more of land. And smaller sites also require a permit if they are part of larger common development plan and if their total area equals an acre or more.
NPDES permits are in most cases administered by the state. A few states—currently, Idaho, Massachusetts, New Mexico, New Hampshire—as well as the District of Columbia and most US territories do not have NPDES permitting authority, so permits in those areas are issued by EPA.
Every five years, EPA issues a Construction General Permit (CGP) that outlines basic requirements construction-site operators must meet. The most recent CGP was issued in 2012. Most states with NPDES permitting authority have their own CGPs, which in some cases include additional requirements beyond those in the federal CGP but which in any case must meet the minimum requirements in the federal version. Those states and territories that do not have NPDES authority generally follow the federal CGP.
You can find EPA’s 2012 CGP, the full title of which is “National Pollutant Discharge Elimination System General Permit for Discharges from Construction Activities,” online at www.water.epa.gov/polwaste/npdes/stormwater/upload/cgp2012_finalpermit.pdf.
Basic requirements under EPA’s CGP, as well as under most state-issued CGPs, include complying with effluent limits where those exist (see the section “The Controversy Over Effluent Limits” below for more discussion) and developing a stormwater pollution prevention plan (SWPPP, pronounced “swip”). Construction-site operators must submit a Notice of Intent (NOI) stating that they have met the eligibility conditions of the permit and that they will comply with permit requirements. Often the NOI can be completed and submitted electronically. EPA’s electronic NOI is available online at http://water.epa.gov/polwaste/npdes/stormwater/upload/cgp2012_appendixj.pdf.
Why is proper permitting and compliance so important? If a site is out of compliance—that is, if sediment-laden water is found to be running off the site—the permitting authority can levy fines, which in some cases run to thousands of dollars for each violation, or can even issue a stop-work order until the problem is fixed. These penalties can be extremely costly, both in dollars and in lost time while construction crews and equipment sit idle.
The owner or operator of a noncompliant site can pay a heavy price in bad public relations, too, if sediment from the site damages local lakes used for fishing and recreation, or if muddy water or airborne dust affects neighboring homes and businesses. In addition to regular site inspections by the permitting authority to make sure all the erosion and sediment control measures are working as they should be, in many places concerned citizens and environmental groups also keep an eye on active construction sites, sometimes bringing problems to the attention of the permitting authority.
The SWPPP. A SWPPP is a detailed document describing the activities a construction-site operator takes to control erosion and sedimentation, prevent discharge of contaminated stormwater, and comply with Clean Water Act requirements. A SWPPP sometimes goes by other names: construction best practices plan; sediment and stormwater plan; erosion, sediment, and pollution plan; construction-site best management practices plan; or something similar. The basic elements of the plan, however, are the same.
A SWPPP template is available online (http://water.epa.gov/polwaste/npdes/stormwater/Stormwater-Pollution-Prevention-Plans-for-Construction-Activities.cfm) to help construction-site operators comply with the minimum requirements of EPA’s 2012 Construction General Permit. In addition to contact information for the site operator and any subcontractors associated with the project, the SWPPP must include the following basic information:
- Site evaluation, assessment, and planning. This section describes the location of the site, the nature of the construction activity, the sequence of the activity and estimated dates, and the types of discharge expected from the site. Site maps and the names of any water bodies that will receive stormwater from the site should be included here as well. If there are any nearby “impaired” waters that are subject to a total maximum daily load (TMDL), this information must also be included.
- Documentation of compliance with other federal requirements. These include endangered species protection, historic preservation, and Safe Drinking Water Act underground injection control requirements.
- Erosion and sediment controls. This section of the SWPPP includes the site operator’s plan for handling a variety of potential erosion-causing activities and ways to prevent sediment from leaving the site. Many of these methods are discussed in more detail in the section of this paper “Best Management Practices to Help You Comply,” but in general, this part of the SWPPP includes perimeter controls, means to prevent sediment track-out (that is, dirt that’s carried offsite on the muddy wheels of vehicles and construction equipment), methods for preventing erosion of stockpiled soil, dust control methods, ways to prevent erosion of steep slopes, methods for dealing with existing infrastructure like storm drain inlets and stormwater channels, and methods (such as planting vegetation) for stabilizing the site.
- Pollution Prevention Standards. This section should identify potential sources of pollution on the site (such as fuels, oils, hydraulic fluid, herbicides, pesticides, and fertilizers); outline spill prevention and response plans; and include other elements such as fueling, maintenance, and washing procedures for vehicles and equipment and storage, handling, and disposal of construction products and waste materials.
- Inspection and corrective action. This section includes the names and qualifications of the people who will conduct site inspections, the frequency of inspections, and the names of the people responsible for taking corrective action if needed.
- Training. This section lists onsite personnel and the dates of their relevant training in erosion and sediment control procedures.
Training and Certification. Some states require specific training relevant to their own CGPs. California, for example, requires SWPPPs to be developed by a Qualified SWPPP Developer (QSD) and sites to be inspected and maintained by a Qualified SWPPP Practitioner (QSP), and training to obtain both of these designations is offered widely within the state. Some other states have similar requirements. If you are working in one of these states you may have to pass an exam to show that you’re familiar with that state’s particular requirements. However, there are a number of national programs that cover basic information on erosion and sediment control practices as well as site inspection practices, and these are recognized nationwide. These are some of the major certifications:
- Certified Professional in Erosion and Sediment Control (CPESC). The CPESC designation provides evidence of qualifications in erosion and sediment control principles and applications. CPESC certification is available to those who have education and demonstrated experience and expertise in computing, analyzing, and evaluating erosion and sediment control principles and methods. Applicants for the CPESC certification must successfully pass a proctored one-day exam covering hydrology, environmental indicators, impacts of urbanization, and federal and state laws and regulations. The exam, along with a full-day review session, is offered at various conferences and events throughout the year. The CPESC program is recognized by EPA and the US Department of Agriculture’s Natural Resources Conservation Service. For more information, an application form, and dates of upcoming review sessions and exams, see www.cpesc.org.
- Certified Professional in Storm Water Quality (CPSWQ). The CPSWQ designation provides evidence of qualifications in stormwater management principles and methods. CPSWQ certification is available to those who have the education and demonstrated experience and expertise in computing, analyzing, and evaluating stormwater quality. Applicants must pass a one-day proctored exam covering these principles. As with the CPESC exam, the CPSWQ exam is offered at various times and locations throughout the year. For more information, an application form, and upcoming dates for the exams and review sessions, see www.cpswq.org.
- Certified Inspector of Sediment and Erosion Control (CISEC). The CISEC designation is available to those who can demonstrate comprehensive knowledge of the principles and practices of sediment and erosion control and their applicability to development of discharge permit documents. Applicants must be able to observe onsite and offsite conditions that impact the quality of stormwater discharges from active construction sites; to inspect installed best management practices and their ongoing maintenance to determine whether they are effective; and to communicate and report on their inspection of active construction sites about whether the sites are in compliance with federal, state, and local discharge permit regulations. Applicants must have inspection skills in one or more types of construction projects: large land development, linear (such as roadway and pipeline), vertical (such as townhomes and single-family residences), or big box (such as commercial buildings). The state of California acknowledges that a CISEC is a “qualified SWPPP practitioner,” able to conduct construction-site sediment and erosion control inspections throughout the state. For more information, an application form, and dates of upcoming CISEC exams and training sessions, see www.cisecinc.org.
- Certified Erosion, Sediment, and Storm Water Inspector (CESSWI). The CESSWI designation is available to those who are qualified in the inspection of erosion, sediment, and stormwater best management practices on sites under NPDES Phase II jurisdiction. Applicants must have the education and demonstrated experience and expertise in site inspections. Full-day proctored exams and review sessions are available at various times and locations throughout the year. For more information, an application form, and upcoming dates of exams and review sessions, see www.cesswi.org.
Best Management Practices to Help You Comply
Among erosion and sediment control practitioners, as well as within the stormwater management industry, the term best management practice or BMP is commonly used to describe all manner of techniques and items that help prevent erosion and contain sediment. All of the BMPs discussed in this section are commonly used on construction sites, and they are also used in other situations as well, such as on landfills, around mining operations, and on industrial sites.
Erosion Control BMPs. Controlling erosion is essentially ensuring that soil particles are not dislodged from the site, or at least that as little soil as possible is set in motion. One of the best ways to prevent erosion on a large construction site is to do the grading work in stages, thus disturbing only one section of ground at a time. It is not always practical to stage the work, however, and there is often a cost savings in doing most of the grading and sit contour work all at once, even if actual construction will not take place on the whole site immediately. In those cases, a number of methods might be used to stabilize the areas that have been disturbed.
- Tackifiers. Tackifiers are “sticky” substances containing guar or polymers that are sprayed onto the soil. They temporarily hold disturbed soil in place, although they might need to be reapplied after a rainstorm. Tackifiers are usually applied with a hydroseeding machine—a large machine with a tank for mixing water, seed, tackifier, fertilizer, mulch, or some combination of these and spraying the mixture over large areas at one time.
- Application of straw or mulch. These substances may be spread over the site and either crimped in place (straw) or mixed with a tackifier.
- Temporary vegetation. For disturbed areas that will remain untouched for several months, vegetation might a more cost-effective solution than tackifier or straw, which have to be reapplied periodically. A quick-growing seed mixture, usually with tackifier and fertilizer in the mix, is applied hydraulically over the site.
- Erosion control blankets. On steep slopes or in areas that will have water running across them, erosion control blankets or turf reinforcement mats may be put in place to prevent soil loss. These products come in rolls and are unrolled and spread on the ground so that the edges slightly overlap; they are fastened down with stakes or staples. Erosion control blankets are usually lighter in weight, less expensive, and less durable—designed to last one or two years, or just until vegetation becomes well established. Blankets usually consist of straw, wood excelsior, or other natural fibers sandwiched between lightweight layers of geosynthetic fabric or netting. Blankets are flexible and coform easily to the contours of the ground. Some are designed to be biodegradable or photodegradable, rarely lasting longer than a single growing season. Some companies manufacture “netless” blankets so that there is no netting that might get caught in a mower or that could entangle wildlife.
- Turf reinforcement mats. Mats are generally heavier, less flexible, more expensive, and longer lasting, often remaining in place for several years. They are made from heavier fibers like coir (coconut fiber) and from long-lasting synthetic materials. TRMs are often used on extremely steep slopes or in areas like streambanks and drainage channels where flowing water would quickly displace a lighter-weight blanket. Although TRMs are more expensive than erosion control blankets, they are less expensive than lining a channel with concrete or riprap. Vegetation can grow through both blankets and TRMs, and some varieties even come with seeds already embedded in them.
Sediment Control BMPs. Devices and techniques to keep sediment from leaving a site include various types of barriers, inlet protection, sediment ponds, and flocculants.
- Silt fence. By far the most common type of barrier used on construction sites is silt fence, which is made of a permeable geosynthetic fabric attached to stakes. The fabric allows water to pass through but filters out silt and sediment. To be effective, the bottom edge of the silt fence must be buried within the ground; this can be done by hand or with various installation machines that create a slit or trench for the fabric. Silt fence must be inspected periodically, especially after a storm, to ensure that it has not fallen over or become displaced. Silt fence and other types of barriers (see below) are usually placed perpendicular to the flow of water, and are often placed on hillsides and at the toe of the slope to slow the velocity of runoff and filter out particulates. Silt fence and other barriers are also placed around the perimeter of a site to contain sediment discharges.
- Berms and wattles. Used as an alternative to silt fence or in addition to it, these barriers are also used to stop sediment from leaving a site. Some are made of bundled straw, while others are made from a synthetic or natural fill material wrapped in a geosynthetic fabric. Some are durable enough to be moved after they are no longer needed and used again on a different site or a different area of the same site. Filter socks are compost-filled fabric tubes that can be left onsite once the job is finished—the fabric is slit open and the compost inside helps in site revegetation.
- Inlet protection devices. Barriers are available in many different configurations to protect existing storm drain inlets. Usually made of geosynthetic fabric or another permeable material that holds back sediment while allowing water to pass through, these devices may fit underneath a grate or in front of a curb inlet. Some are designed with a rigid frame that fits over the inlet and covered with geosynthetic fabric.
- Sediment ponds or basins. Sediment basins can be created onsite to capture and retain all or most of the volume of stormwater runoff. The basin holds the water and slows its velocity so that suspended sediment particles have a chance to settle to the bottom; the cleaner water is then slowly drained from the basin. Sediment basins must be sized so they are large enough to hold sufficient runoff draining from the site.
- Flocculants and active versus passive systems. To encourage faster settling of particles in a sediment basin, a flocculant such as alum or a polyacrylamide- or chitosan-based product may be added. Flocculants promote the aggregation, or clumping, of sediment particles, and the larger particles sink faster. These substances can be used in a passive treatment system, in which water flows through and is exposed to the flocculant, or in an active treatment system, which might involve pumping the water through the system, actively mixing the water with the flocculant, and perhaps routing the water through a sand filter or some other type of filter to remove more particles. Active treatment systems are generally more expensive but can remove more sediment particles and sometimes require less space than passive systems.
The Role of Buffers. EPA’s 2012 Construction General Permit emphasizes the use of natural buffers to protect surface waters. For sites that discharge water to a lake or stream, the CGP requires that a 50-foot-wide undisturbed natural buffer be maintained to help filter sediment and other pollutants If it is not feasible for the site operator to maintain such a buffer space, then other erosion and sediment controls may be used to achieve the sediment load reduction equal to that provided by a 50-foot buffer. Ideally the buffer will include vegetation, which helps to filter out sediment, but if the natural buffer is not vegetated before construction begins, the operator does not need to plant vegetation within the buffer. Appendix G of the CGP contains details of the buffer requirement, and some states in their own CGPs have expanded or modified the buffer requirements.
The Rise of Green Infrastructure. The term green infrastructure (GI) refers to retaining stormwater onsite rather than routing it to a storm sewer system or—in cities with combined storm and sanitary sewers—to a water treatment plant, thus reducing the burden on the public infrastructure. Retaining water onsite reduces not only the volume of runoff that must be dealt with, but also the pollutants, such as sediment, the larger volume of water would carry with it. This philosophy of “treating rain where it falls” has gained great momentum in recent years.
The water retained on a site is captured to be used for irrigation and other purposes, as in rain barrels or cisterns; is disposed of via evapotranspiration; or, most commonly, is infiltrated into the ground. Infiltration BMPs include bioswales, rain gardens, tree planters, permeable pavers, and porous concrete and asphalt. Some of these BMPs are also known collectively as low impact development (LID) techniques. Green infrastructure got a boost in 2007, when the federal Energy Independence and Security Act was released. Section 438 of the act requires federal agencies to reduce runoff from new construction projects and redevelopment sites. Many state and local jurisdictions have since adopted similar guidelines. Private developers whose clients want to earn LEED (Leadership in Energy and Environmental Design) credits for their projects also commonly apply GI techniques.
Green infrastructure BMPs are usually considered to be post-construction stormwater measures. But EPA is increasingly emphasizing the use of GI, and planning for green infrastructure needs to take place during the design and construction phases as well. See the discussion in the section “The Stormwater Rule” below for more on EPA’s encouragement and funding of GI.
What’s Ahead? The Tumultuous Regulatory Environment
The Controversy Over Effluent Limits. The latest Construction General Permit released by EPA in 2012 does not specify a numeric limit for the turbidity of waters discharging from construction sites. Construction-site operators are required to take steps to prevent erosion and sedimentation, as discussed throughout this paper, but they do not necessarily have to test the water and report on the amount of sediment it actually contains. The turbidity of water—the amount of sediment in suspension—is measured in nephelometric turbidity units (NTUs), and in most cases there is no specific NTU requirement.
There is a long and contentious history behind the decision not to have a set numeric limit, and it’s useful to have an idea of the discussions that have taken place, because the question might eventually resurface. In 2000, EPA first developed effluent guidelines for the construction and development (C&D) industry, but it withdrew its proposed guidelines in 2004. Lawsuits followed from environmental organizations and states, which claimed EPA was failing to protect the environment. A court decision ordered EPA to publish its proposed C&D regulations by December 2008 and then to publish a final rule by December 2009.
EPA met the 2008 deadline, issuing proposed guidelines with a limit of just 13 NTUs for some construction sites—those of 30 acres or more in areas with high rainfall energy and clay-like soils. EPA acknowledged that meeting this 13-NTU limit might require active treatment systems on some or all of the covered sites.
There was tremendous objection to this limit, which many in the industry considered to be far too low. Developers, for example, claimed that meeting this limit would be prohibitively expensive and that it would drastically increase the cost of new homes. Even some people within the erosion and sediment control field believed that the limit was too low, because some areas have naturally occurring background turbidity of more than 13 NTUs.
Following a public comment period, which is required for most proposed rulings, EPA revised its guidelines. The revision, published in late 2009, include a numeric turbidity limit of 280 NTUs for sites of 10 acres or more. The rule was supposed to be implemented in phases, beginning with larger sites and gradually including smaller ones. However, in November 2010, EPA stayed the 280-NTU limit, saying that it wanted to revisit how the limit had been calculated. In August 2011, EPA withdrew its proposed rule on the grounds that it needed to gather more data before reaching a final decision.
When EPA issued its new five-year Construction General Permit in February 2012, the CGP did not include a numeric limit as many people had expected it to. It did, however, incorporate many other aspects of the 2009 effluent limitation guidelines—the narrative part of those guidelines, essentially—including those relating to erosion and sediment control provisions like natural buffers, sediment discharge controls, soil stabilization, and guidelines on the use of treatment chemicals to reduce turbidity. At the time the new CGP was issued, EPA stated that even if it established a numeric limit within the next five years, it would not modify the 2012 CGP to include that limit but would instead incorporate the limit into the next iteration of the CGP, which is due in 2017.
The Stormwater Rule. The advent of Phase II of the National Pollutant Discharge Elimination System in 2003 expanded the national stormwater program tremendously, bringing new requirements to smaller cities and construction sites and spawning an entire industry—new BMPs and technologies, new service providers, and new jobs. It led to the creation of hundreds of completely new or greatly enhanced stormwater programs within the newly regulated cities and counties.
For several years, EPA had intended to release an updated stormwater rule. (The agency was required, under a 2010 settlement with the Chesapeake Bay Foundation, to release a new rule.) Even as it postponed issuing the rule several times, EPA representatives gave a fairly good idea of what the new rule was expected to contain. They announced, for example, that it would include retention-based performance standards and that it would emphasize the use of green infrastructure and onsite stormwater management—not only for new developments, but also for redeveloped properties. EPA also indicated, however, that there would be some flexibility in meeting onsite retention requirements, taking into account the climate, soil type, and other factors, as well as different ways to reach water-quality goals if infiltration was not an option, such as credit trading programs or offsite mitigation.
The agency also indicated that redeveloped sites would be held to less-stringent standards, thus encouraging developers to take on infill and redevelopment projects instead of opting always for easier-to-develop greenfield sites.
It was widely expected that in the new rule, EPA would emphasize a watershed-based approach, rather than a jurisdictional approach, to stormwater management—a solution recommended by the National Academy of Sciences in its review of the stormwater program in 2009.
However, after a series of postponements, in March 2014 EPA indicated a change of direction, saying it was no longer pursuing a national rule at all but was taking other actions instead to work toward some of the same goals it had hoped the rule would achieve.
EPA summarized the change: “EPA is updating its stormwater strategy to focus now on pursuing a suite of immediate actions to help support communities in addressing their stormwater challenges and deferring action on rulemaking to reduce stormwater discharges from newly developed and redeveloped sites or other regulatory changes to its stormwater program. EPA will provide incentives, technical assistance, and tools to communities to encourage them to implement strong stormwater programs; leverage existing requirements to strengthen municipal stormwater permits; and continue to promote green infrastructure as an integral part of stormwater management. EPA believes this approach will achieve significant, measurable, and timely results in reducing stormwater pollution and provide significant climate resiliency benefits to communities.”
Based on this statement, it seems as though EPA will be relying on voluntary efforts by local jurisdictions, rather than on the strong enforcement authority a new rule might have provided. However, much of the emphasis is the same. At StormCon 2011, for example, an EPA spokesman said that integrating green infrastructure into project designs would be a major element of the rule, indicating green infrastructure is still an important priority. In fact, the 2015 federal budget request included $5 million plus additional staff to support green infrastructure programs.
What’s Protected? Clarifying the Jurisdiction of the Clean Water Act. In 2014, EPA and the US Army Corps of Engineers jointly released a rule designed to clarify which waters are actually protected under the Clean Water Act. EPA Administrator Gina McCarthy, speaking at a national water-related conference in September 2014, noted that two “confusing” Supreme Court decisions had left nearly 60% of the nation’s streams and wetlands essentially unprotected. (The Supreme Court rulings in question are Solid Waste Agency of Northern Cook County v. US Army Corps of Engineers in 2001 and Rapanos v. United States in 2006.) The new rule does not actually broaden the Clean Water Act’s coverage—the agencies are not trying to “regulate every puddle,” she said—but only makes clearer what the CWA protects.
One result of the Supreme Court’s decisions had been to call into question whether the CWA protects ephemeral streams, or those that flow only seasonally. EPA and the Corps of Engineers contend that streams—both permanent and ephemeral, and of all sizes—are connected and have effects on downstream waters, and that they should therefore fall under the CWA’s jurisdiction. In addition, the agencies says that wetlands within stream floodplains are integrated with streams and rivers and strongly influence downstream waters by affecting flow and trapping pollutants.
About 60% of streams in the US are seasonal, and these streams or the water bodies into which they flow are a drinking water source for about a third of the U.S. population.
As of this writing the public comment on the rule had just closed, and the rule has not yet been approved, but the outcome will ultimately affect many decisions within the erosion and sediment control and the stormwater fields. EPA has a website summarizing the rule at http://www2.epa.gov/uswaters. Public comments that were submitted regarding the rule are accessible from the site.