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Rural Roads

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Unpaved rural roads are a source of pollution. Erosion of unpaved roadways occurs when soil particles are loosened and carried away from the roadway base, ditch, or road bank by water, wind, traffic, or other transport means. Exposed soils, high runoff velocities and volumes, sandy or silty soil types, and poor compaction increase the potential for erosion. 

Loosened soil particles are carried from the road bed and into the roadway drainage system. Particles most often settle out where they diminish the carrying capacity of the ditch, and in turn cause roadway flooding, which subsequently leads to more roadway erosion. Most of the eroded soil, however, ultimately ends up in streams and rivers where it diminishes channel capacity, causing more frequent and severe flooding; destroys aquatic and riparian habitat; and has other adverse effects on water quality and water-related activities.

More information from EPA
Recommended Practices Manual: A Guideline for Maintenance and Service of Unpaved Roads

More information from federal agencies
Federal Highway Administration State Road Coordinators Exit EPA
USDA Forest Service: Road Management website

More information from the states Exit EPA
Alabama: Forest Roads and Construction of Associated Water Diversion Devices

More information from other organizations
National Association of County Engineers Exit EPA


Particulate Matter Pollution From Unpaved Roads

The type of equipment used by agricultural producers in rural areas causes particulate matter pollution from unpaved roads to be a concern. The document Compilation of Air Pollutant Emissions Factors (AP-42) has been published by EPA since 1972. Supplements to AP-42 have been routinely published to add new emission source categories and to update existing emission factors. AP-42 is periodically updated by EPA to respond to new emission factor needs of EPA, state, and local air pollution control programs and industry.

Chapter 13: Miscellaneous Sources contains emission factor information on those source categories that differ substantially from, and hence cannot be grouped with, the other "stationary" sources discussed in the publication. Most of these miscellaneous emitters, both natural and manmade, are truly area sources, with their pollutant-generating process(es) dispersed over large land areas. Another characteristic of these sources is the inapplicability, in most cases, of conventional control methods such as wet/dry equipment, fuel switching, process changes, etc. Instead, control of these emissions, where possible at all, may involve such techniques as paving with asphalt or concrete or stabilization of dirt roads. Finally, miscellaneous sources generally emit pollutants intermittently, compared to most stationary point sources.

Section 13.2.2 Unpaved Roads
When a vehicle travels an unpaved road, the force of the wheels on the road surface causes pulverization of surface material. Particles are lifted and dropped from the rolling wheels, and the road surface is exposed to strong air currents in turbulent shear with the surface. The turbulent wake behind the vehicle continues to act on the road surface after the vehicle has passed. The quantity of dust emissions from a given segment of unpaved road varies linearly with the volume of traffic.

More information from EPA
National Center for Environmental Assessment: Particulate Matter Risk Assessment

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Coarse Particulate Matter (PM-10)

The type of equipment used by agricultural producers in rural areas causes coarse particulate matter to be a concern. Particulate matter (PM) is the general term used for a mixture of solid particles and liquid droplets found in the air. Some particles are large or dark enough to be seen as soot or smoke. Others are so small they can be detected only with an electron microscope. These particles, which come in a wide range of sizes ("fine" particles are less than 2.5 micrometers in diameter and coarser-size particles are larger than 2.5 micrometers), originate from many different stationary and mobile sources as well as from natural sources. Fine particles (PM-2.5) result from fuel combustion from motor vehicles, power generation, and industrial facilities, as well as from residential fireplaces and wood stoves. Coarse particles (PM-10) are generally emitted from sources, such as vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations, as well as windblown dust.

Inhalable PM includes both fine and coarse particles. These particles can accumulate in the respiratory system and are associated with numerous health effects. Exposure to coarse particles is primarily associated with the aggravation of respiratory conditions, such as asthma. In addition to health problems, PM is the major cause of reduced visibility in many parts of the United States. Airborne particles also can cause damage to paints and building materials.

More information from EPA
National Trends in Particulate Matter Levels
Information on Particulate Matter

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Maintenance and Service of Unpaved Roads

The U.S. Fish and Wildlife Service and the U. S. Environmental Protection Agency have helped fund a manual of standard procedures that describes and illustrates cost-effective techniques and practices that can be used to enhance stability and maintenance of unpaved roadways while reducing sedimentation and improving the quality of surface waters.  The manual was developed in Alabama for Choctawhatchee, Pea, and Yellow Rivers Watershed Management Authority counties in south Alabama and northwest Florida, but agricultural operators in other areas should also find it useful.

More information from EPA
Recommended Practices Manual: A Guideline for Maintenance and Service of Unpaved Roads

More information from the states Exit EPA
Alabama: Forest Roads and Construction of Associated Water Diversion Devices

More information from other organizations Exit EPA
US Forest Service and National Association of County Engineers Partnership Agreement
National Association of County Engineers Ten Essentials of a Good Road

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Unpaved Roads in Forests

Roads are considered to be the major source of erosion from forested lands, contributing up to 90 percent of the total sediment production from forestry operations. Erosion potential from roads is accelerated by increasing slope gradients on cut-and-fill slopes, intercepting subsurface water flow, and concentrating overland flow on the road surface and in channels. 

Roads with steep gradients, deep cut-and-fill sections, poor drainage, erodible soils, and road-stream crossings contribute to most of this sediment load, with road-stream crossings being the most frequent sources of erosion and sediment. Soil loss tends to be greatest during and immediately after road construction because of the unstabilized road prism and disturbance by passage of heavy trucks and equipment. 

Good road location and design can greatly reduce the transport of sediment to water bodies. Whenever possible, road systems should be designed to minimize road length, road width, and the number of places where water bodies are crossed. Roads should also follow the natural contours of the land and be located away from steep gradients, landslide-prone areas, and areas with poor drainage. Proper road maintenance and closure of unneeded roads can help reduce nonpoint source impacts from erosion over the long term.

The primary pollution outputs during road construction and use may include soil erosion and air emissions from road construction equipment and machinery used for harvesting. 

The following are a few pollution prevention practices that can be used for road construction and use.  More pollution prevention techniques can be found in Profile of the Agricultural Crop Production Industry.

Related publications from the Ag Center
Rural Roads
Forestry
Agriculture Industry Profiles (Sector Notebooks)

More information from EPA
Guidance Specifying Management Measures for Sources of Nonpoint Pollution in Coastal Waters: Ch. 3 -- Management Measures for Forestry
Recommended Practices Manual: A Guideline for Maintenance and Service of Unpaved Roads

More information from USDA
USDA Forest Service: Road Management Web site

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Federal Plan for Particulate Matter in Phoenix

EPA has developed a federal implementation plan (FIP) to control dust from unpaved roads, unpaved parking lots, and vacant lots in the Phoenix area (Maricopa County, Arizona).  The FIP supplements current local regulations and requires the owners and operators of certain unpaved parking lots, unpaved roads, and disturbed vacant lots to control dust. Ways to control dust from these sources include:

The federal plan for particulate matter in Phoenix (FIP) was issued on July 17, 1998, in response to a court order and requires (1) owners or operators of certain unpaved parking lots, unpaved roads, and disturbed vacant lots to control dust, and (2) the development of approaches to control dust from agricultural fields. EPA is not requiring the control of dust from every unpaved road. In fact, unpaved roads do not need to be stabilized unless vehicles drive on them 250 times a day or more. This equals about 3 cars every 5 minutes over a 7-hour period or 2 cars every 5 minutes over a 10 1/2-hour workday.

More information from EPA
Federal Plan for Particulate Matter in Phoenix
The FIP Dust Rule -- What It Is Intended To Do
What's All The Fuss About DUST?
Federal Rule Compliance Assistance for Owners/Operators

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