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Erosion, Sediment and Runoff Control for Roads and Highways
United States
Environmental Protection
Agency
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Office of Water
(4503F)
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EPA-841-F-95-008d
December 1995
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The Coastal Zone Management Act of 1972
established a program for states to voluntarily develop comprehensive
programs to protect and manage coastal water resources. There are now
29 coastal states and territories with federally approved coastal
management programs.
The Coastal Zone Act Reauthorization Amendments (CZARA) of 1990
specifically charged coastal states and territories with upgrading
their runoff pollution control programs to protect coastal waters. The
Environmental Protection Agency (EPA) and the National Oceanic and
Atmospheric Administration (NOAA) jointly oversee the development and
implementation of these Coastal Nonpoint Pollution Control
Programs, or CNPCPs.
EPA published Guidance Specifying Management Measures for Sources
of Nonpoint Pollution in Coastal Waters to be used by states to
implement management measures - economically achievable measures that
reflect the greatest degree of runoff pollution control - to control
the addition of runoff pollutants to coastal waters.
The Guidance also includes best management practices,
technologies, processes, siting criteria, and operating methods for
roads, highways, and bridges that states can use to implement the
management measures. States can use alternative management measures if
they provide the same or a greater degree of pollutant control as the
management measures in the Guidance. States will begin
implementing their CNPCPs in 1996 and achieve full implementation by
2004.
CZARA applies to site development and land disturbing activities in
the coastal management area of each State with an approved coastal
management program. Certain road, highway and bridge related
activities are excluded from this program due to coverage under the
National Pollutant Discharge Elimination System (NPDES) permitting
program. These activities include construction activities where 5 or
more acres (2.02 ha) are disturbed, and activities within
municipalities with municipal separate storm sewer systems that have
populations of 100,000 or more.
Why Runoff Control is Needed
Runoff controls are essential to preventing polluted runoff from roads,
highways, and bridges from reaching surface waters. Erosion during and
after construction of roads, highways, and bridges can contribute large
amounts of sediment and silt to runoff waters, which can deteriorate
water quality and lead to fish kills and other ecological problems.
Heavy metals, oils, other toxic substances, and debris from
construction traffic and spillage can be absorbed by soil at
construction sites and carried with runoff water to lakes, rivers, and
bays. Runoff control measures can be installed at the time of road,
highway, and bridge construction to reduce runoff pollution both
during and after construction. Such measures can effectively limit the
entry of pollutants into surface waters and ground waters and protect
their quality, fish habitats, and public health.
Pesticides and fertilizers used along roadway rights-of-way and
adjoining land can pollute surface waters and ground water when they
filter into the soil or are blown by wind from the area where they are
applied. Table 1 shows typical pollutants in runoff waters that can be
traced to the operation of roads and highways.
Principles of Runoff Control for Roads, Highways, and Bridges
Preventing runoff pollution from road, highway, and bridge construction
in coastal areas requires planning, education, inspection, and
maintenance. An erosion and sediment control (ESC) plan that incorporates
the most appropriate and cost-effective best management practices (BMPs)
is essential to effective pollution control. Affected highway personnel
must be educated about the requirements of the ESC plan. Inspection and
enforcement authority are necessary to ensure awareness of and compliance
with the adopted practices. Finally, BMPs require regular maintenance to
ensure that they perform optimally. The following principles apply to an
effective erosion and runoff control program.
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Develop a comprehensive erosion and sediment control (ESC) plan
prior to earth-moving activities. Write ESC requirements into
plans, specifications, and cost estimates for highway and bridge
projects.
Four key factors affect the potential for soil erosion from a
site: soil characteristics, vegetative cover, topography, and
climate. Take all of these factors into consideration to develop
an ESC plan that will minimize soil loss, limit the area exposed
to construction, maximize the vegetative cover, use natural
topographic features to the best advantage, and include BMPs
suitable to the regional climate.
The Federal Highway Administration Local Transportation
Assistance Program, the Association of American State Highway
and Transportation Officials, and many state highway departments
can provide ESC guidelines.
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Apply ESC practices to prevent excessive onsite damage. Use
ESC BMPs to control the flow of runoff water and thereby prevent or
lessen soil erosion. Limiting land disturbance and preserving
natural vegetation are excellent ESC practices.
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Apply perimeter control practices to protect the disturbed area
from offsite runoff and to prevent sedimentation damage to areas
below the construction site. A sediment and runoff barrier
surrounding the disturbed area prevents construction site runoff
from moving offsite and fouling surface waters downstream.
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Keep runoff velocities low and retain runoff on the site.
The erosive power of runoff increases dramatically as distance and
slope increase. BMPs can be used to effectively control runoff
velocity and detain it to remove 80 to 90 percent of the sediment
from runoff.
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Stabilize disturbed areas immediately after final grade has been
attained. Any exposed soil is subject to erosion from rainfall,
wind, and vehicles. BMPs to stabilize soil should be applied as
quickly as possible after the land is disturbed. Temporary
stabilization practices include seeding, mulching, and erosion
control blankets or mats.
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Develop a schedule and implement a comprehensive inspection and
maintenance program. This principle is vital to the success of
erosion control. BMPs must receive regular inspection and
maintenance to ensure that they are operating effectively and
optimally, both during and after construction.
Best Management Practices
CZARA defines management measures as economically achievable measures to
control the addition of pollutants to our coastal waters. Management
measures are achieved by the application of one or more BMPs. The BMPs
described below are especially useful for erosion and runoff control for
roads, highways, and bridges.
Best management practices can be organized by the function they
perform. General maintenance BMPs (listed below) are usually
vegetative practices used to contain polluted runoff from the
operation of highways or from erosion and sedimentation generated at
small construction sites. A variety of practices are used at
construction sites to control both erosion and polluted runoff. These
are identified as Construction Site BMPs. Practices developed as
permanent erosion and sediment control devices are both structural and
nonstructural. Several of these BMPs are listed below as long-term or
Permanent Control BMPs.
Construction Site BMPs
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Straw bale barriers should be bound, entrenched, and
securely anchored to prevent deterioration. A row of straw bales
slows runoff flow and creates a pond behind the barrier where
sediment can settle out. Straw bale barriers are most effective for
filtering low to moderate storm flows, where structural strength is
not required.
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Filter fabrics are engineering fabrics designed to retain
sediment particles larger than a certain size and allow water to
pass through. Filter fabrics can be used in silt fences (see below)
or erosion control mats. Erosion control mats protect soil and seed
from erosion and can be designed to allow vegetation to grow
through the material.
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Silt fences are vertical fences of filter fabric that are
stretched across and attached to support poles. The fabric retains
sediment on the construction site and allows relatively
sediment-free water to pass through. Silt fences are placed to
protect streams and surrounding property from sediment-laden
runoff.
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Sediment basins are ponds created by excavation or the
construction of a dam or barrier. Sediment basins primarily serve
to retain or detain runoff to allow excessive sediment to settle
out during construction. Sediment basins can be converted into
permanent detention ponds or wetlands after construction.
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Stabilized entrances reduce the amount of sediment carried
off a construction site by vehicles when pressure-washed on-site.
These entrances are designed to include stabilized pads of
aggregate underlain with a filter fabric. Stabilized construction
site entrances should be located at any point in the construction
zone where vehicles enter and leave. Wheels and undercarriages of
vehicles should be washed before leaving the site.
Operation and Maintenance
Inspection and maintenance of erosion and sediment control BMPs after
construction has been completed is important to ensure that the BMPs are
operating properly and effectively. Some key operation and maintenance
procedures include:
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Prepare and adhere to a schedule of regular maintenance for
temporary erosion and runoff control BMPs. Two critical
maintenance operations that must be performed regularly are
cleaning out accumulated sediment and replacing worn-out or
deteriorated materials, such as silt fence fabrics, so that the
effectiveness of the controls is maintained. Maintenance can
include dredging and reshaping sediment basins and revegetating the
slopes of grassed swales.
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Remove temporary BMPs from construction areas when they are no
longer needed and replace them, where appropriate, with permanent
BMPs.
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Schedule and periodically inspect and maintain permanent erosion
and runoff controls. This should include a periodic visual
inspection of permanent BMPs during runoff conditions to ensure
that the controls are operating properly. Clean, repair, and
replace permanent erosion and runoff control BMPs when necessary.
General Maintenance BMPs
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Seeding with grass and fertilizing to promote strong growth
provide long-term stabilization of exposed surfaces. Disturbed
areas can be seeded and fertilized during construction and after it
is completed. Sufficient watering and refertilizing 30 to 40 days
after the seeds germinate help establish dense growth.
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Seeding with grass and overlaying with mulch or mats is done
to stabilize cleared or freshly seeded areas. Types of mulches
include organic materials, straw, wood chips, bark or other wood
fibers, or decomposed granite and gravel. Mats are made of natural
or synthetic material and are used to temporarily or permanently
stabilize soil.
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Wildflower cover has been successfully used by many state
and county highway departments to provide attractive vegetation
along roadways and erosion control. Careful consideration must be
given to visibility, access, soil condition, climate, and
maintenance when choosing sites for wildflower cover.
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Sodding with established grass blankets on prepared soil
provides a quick vegetative cover to lessen erosion. Proper
watering and fertilizing are important to ensure the vitality of
newly placed sod.
Permanent Control BMPs
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Grassed swales are shallow, channeled grassed depressions
through which runoff is conveyed. The grass in swales slows the
flow of runoff water, which allows sediment to settle out and water
to infiltrate into the soil. Grassed swales can remove small
amounts of pollutants such as nutrients and heavy metals. Check
dams (see below) can be added to grassed swales to further reduce
flow velocity and promote infiltration and pollutant removal.
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Filter strips are wide strips of vegetation located to
intercept overland sheet flows of runoff. They can remove organic
material, sediment, and heavy metals from runoff. Filter strips can
consist of any type of dense vegetation from woods to grass but
they cannot effectively treat high-velocity flows. They are
therefore best suited to low-density developments.
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Terracing breaks a long slope into many flat surfaces where
vegetation can become established. Small furrows are often placed
at the edge of each terraced step to prevent runoff from eroding
the edge. Terracing reduces runoff velocity and increases
infiltration.
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Check dams are small temporary dams made of rock, logs,
brush, limbs, or another durable material, placed across a swale or
drainage ditch. By reducing the velocity of storm flows, sediment
in runoff can settle out and erosion in the swale or ditch is
reduced.
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Detention ponds or basins temporarily store runoff from a
site and release it at a controlled rate to minimize downstream
flooding. Pollutant removal effectiveness is quite good for
well-designed basins. Effectiveness is greatest for suspended
sediments (80 percent or more removal) and related pollutants such
as heavy metals.
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Infiltration trenches are shallow, three to eight feet deep
(.91 to 2.44 m), excavated trenches that are backfilled with stone
to create underground reservoirs. Runoff is diverted into the
trenches, from which it percolates into the subsoil. Properly
designed infiltration trenches effectively remove sediment from
runoff and can remove some other runoff pollutants.
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Infiltration basins are relatively large, open depressions
produced by either natural site topography or excavation. When
runoff enters an infiltration basin, the water percolates through
the bottom or the sides and the sediment is trapped in the basin.
The soil where an infiltration basin is built must be permeable
enough to provide adequate infiltration. Some pollutants other than
sediment are also removed in infiltration basins.
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Constructed wetlands are areas inundated by water for a
sufficient time to support vegetation adaped for life in saturated
soil conditions. Wetlands effectively filter sediment, nutrients,
and some heavy metals from runoff waters.
Table 1. Typical pollutants found in runoff from roads and
highways.
Sources of Pollution in Highway Runoff
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Pollutant
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Source
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Sedimentation
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Particulates
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Pavement wear, vehicles, the atmosphere and maintenance
activities
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Nutrients
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Nitrogen & phosphorus
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Atmosphere and fertilizer application
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Heavy Metals
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Lead
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Leaded gasoline from auto exhausts and tire wear
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Zinc
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Tire wear, motor oil and grease
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Iron
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Auto body rust, steel highway structures such as bridges and
guardrails, and moving engine parts
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Copper
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Metal plating, bearing and brushing wear, moving engine
parts, brake lining wear, fungicides & insecticides
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Cadmium
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Tire wear and insecticide application
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Chromium
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Metal plating, moving engine parts and brake lining wear
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Nickel
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Diesel fuel and gasoline, lubricating oil, metal plating,
bushing wear, brake lining wear and asphalt paving
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Manganese
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Moving engine parts
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Cyanide
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Anti-caking compounds used to keep deicing salt granular
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Sodium, calcium & chloride
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Deicing salts
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Sulphates
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Roadway beds, fuel and deicing salts
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Hydrocarbons
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Petroleum
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Spills, leaks, antifreeze and hydraulic fluids and asphalt
surface leachate
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Adapted from Guidance Specifying Management Measures for
Sources of Nonpoint Pollution in Coastal Waters
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