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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Unpaved Roads and Unpaved Parking Lots: Applying and Maintaining Reasonably Available Control Measures (RACM)

NOTE: This content is no longer being updated. The most up to date information can be found in Federal Register Notices and Approved Air Quality Implementation Plans in Region 9.

Where Must RACM be Applied?

  • On any unpaved road or road segment located within the Phoenix nonattainment area with 250 or more vehicle trips a day on average.
  • On any unpaved parking lot > 5,000 square feet. RACM needs to be applied on all surfaces where vehicles enter and park. Unpaved parking lots need to be stabilized on any days when more than 10 vehicles enter and park. For Low Use Lots (lots used no more than 35 days a year, excluding days when 10 or fewer vehicles enter and park), RACM should be applied on any days when over 100 vehicles park on the lot. For more information, see Federal Rule Requirements for Unpaved Parking Lots, Unpaved Roads, and Vacant Lots in Maricopa County.

What are my choices to apply and maintain RACM?


  • A road or parking lot may be paved with asphalt, recycled asphalt, concrete or asphaltic concrete. (However, paving roads is subject to local and state requirements and some form of maintenance may be included.)
  • Once an unpaved road or parking lot is paved, it is no longer subject to the FIP rule. No test methods are needed to verify compliance.  

Chemical/Organic Stabilization

  • There are a number of dust suppressant products offered for sale. Before selecting one, consider the amount of vehicle traffic and type of soil among other factors.
  • Soil stabilizers require re-application, typically between 3 and 6 months. Some products claim longer stabilizing effects, however, their ability to stabilize will likely depend upon traffic characteristics. With some types of stabilizers, re-applications over the course of a year or two will harden into a pseudo-paved or crusted surface which for all practical purposes has the same effect as paving. If there is no loose surface material, the source is in compliance.
  • As the chemically/organically stabilized surface deteriorates over time, you should measure its silt content by conducting the silt content test method in order to ensure compliance with the FIP rule. Use the test method results and manufacturer recommendations to determine when re-applications are necessary.  


  • This control measure is best used for less heavily trafficked unpaved roads and parking lots. Try to avoid using a type of gravel which grinds up easily under heavy loads and will ultimately produce more fine particles. Use "riverbed" or "washed" gravel that is hard and rounded but has enough edges to allow for vehicle traction. Avoid using gravel mixtures that contain fine dirt particles. If possible, apply gravel so that the bottom layer is firmly embedded in the surface. This could greatly reduce maintenance requirements under the FIP rule.
  • Use the silt content test method to determine when reapplication is necessary. Depending on the amount of gravel first applied, the only maintenance required may be re-shuffling the gravel to the regularly trafficked portions (usually evidenced by bare or semi-bare patches) of an unpaved road or unpaved parking lot. By routinely checking the road to ensure that the gravel is uniformly distributed and conducting the silt content test method, you can maintain compliance with the FIP rule.  


  • Remember to keep records of any RACM you apply. If you pave or gravel, keep a record or receipt of the location the RACM is applied, type of material applied, the date(s) of application and the extent of coverage. If you use chemical or organic stabilizer, in addition to the above information, keep a record or receipt with the vendor name, label instructions for approved use, the method used to apply the stabilizer, the concentration and quantity of application, and the date(s) of re-application.

For more information:

Please contact Colleen McKaughan, Associate Director, air Division, U.S. EPA Region 9 at (520) 498-0118, or email her at mckaughan.colleen@epa.gov

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