Soils Information


The Northern Virginia Soil and Water Conservation District provides soils information to the public and to Fairfax County agencies and helps maintain the Fairfax County soil survey.

Soils Information

Soil types in Fairfax County are identified by alpha-numeric symbols on the soil survey map. In the symbol, the number represents the soil type and the letter represents the landscape slope class. For example, a common soil type in Fairfax County is 39B. In this alpha-numeric code, 39 identifies the soil type as Glenelg silt loam; B indicates slopes of 2-7 percent.

The 2011 Official County Soils Map, which is based on the 2008 soil survey, is available through the digital map viewer. The previous soil survey, published in 1990, is also available on the digital map viewer for informational purposes. Fairfax County offers descriptions and ratings for soil types in both maps. These descriptions and ratings are useful in determining the suitability of various types of activities on particular soils. All official permit applications must rely on maps and ratings from the 2011 map.

Data from the 2008 soil survey is also incorporated in the national Web Soil Survey and Soil Data Mart operated by the USDA-NRCS. The 1990 Soil Map Guide is also available online. If you need assistance obtaining soils information or interpreting the soil maps, descriptions or ratings, please call the conservation district at 703-324-1460, TTY 711 or submit an online soils information request.

Problem Soils

Marine clay is a type of soil found in Fairfax County that contains clays that swell upon wetting and shrink upon drying. Potential problems associated with these soils include land slippage and slope instability, shrinking and swelling of clays, poor foundation support, and poor drainage. In Fairfax County, marine clays occur in widespread areas east of Interstate 95. Read more about the problems associated with marine clay.

Soil Fertility

If you are interested in testing the fertility of the soil in your lawn or garden, you can send a soil sample to Virginia Tech where it will be analyzed for a small fee. Soil test sample boxes and instructions should be available at all branches of the Fairfax County Public Library as well as at Fairfax County Cooperative Extension and the Northern Virginia Soil and Water Conservation District offices. Learn more about the soil test.

Fairfax County Soil Survey

Using a soil auger to take a core sample. A soil survey is a collection of maps, tables and written text that can be used for land use planning. Its maps depict the distribution of soils across the landscape. The tables and written text contain soil descriptions and predictions of soil behavior for selected land uses. The survey also highlights limitations and hazards inherent in the soil, improvements needed to overcome the limitations and the impact of selected land uses on the environment.

The survey is useful in identifying drainage issues, erosion potential, foundation support and many other characteristics. It can be used to evaluate the potential of the soil and the management needed for maximum food and fiber production. Conservationists, teachers, students, homeowners, developers and specialists in recreation, wildlife management, waste disposal, and pollution control can use the survey to understand, protect and enhance the environment.

Fairfax County's original soil survey, published in 1963, was never completed. Approximately 40,000 acres, predominantly in the southeastern part of the county, remained unmapped. An updated soil survey for Fairfax County was completed in 2008. It contains new soil types, ratings and descriptions. The update is a cooperative effort of the U.S. Department of Agriculture's Natural Resources Conservation Service (USDA-NRCS), Fairfax County Board of Supervisors, and Northern Virginia Soil and Water Conservation District.

Soil Education

The Soil Biology Primer, published by the Soil and Water Conservation Society, is an introduction to the living components of soil and how they contribute to agricultural productivity, and air and water quality. The online primer includes units describing the soil food web and its relationship to soil health, and units about bacteria, fungi, protozoa, nematodes, arthropods, and earthworms.

The Urban Soil Primer, published by the USDA's Natural Resources Conservation Service, is an introduction to urban soils for homeowners and renters, local planning boards, property managers, students, and educators. It provides information important in planning and managing land resources in a manner that helps to prevent or mitigate problems associated with sedimentation, contamination, runoff, and structural failure.

Understanding Soils Risks and Hazards, also published by the USDA's Natural Resources Conservation Service, has several chapters relevant to the Northern Virginia area.

  • Acid sulfate soils
  • Compaction
  • Contamination by metals
  • Corrosion
  • Erosion
  • Expanding soils and shrink-swell potential
  • Landslides
  • Radon

S.K. Worm is the official annelid, or worm, of the U.S. Department of Agriculture's Natural Resources Conservation Service. S.K. Worm answers kids' basic questions about soil.


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