Soil Types

Soil types in Fairfax County are identified by numbers on a soil map. Each number corresponds to the name of a soil. Fairfax County offers an online description and rating for soil types. The ratings are useful in determining the suitability of development on particular soils in an urban area. To view the soil maps and learn what soil you have on your property, visit the NVSWCD office at 12055 Government Center Parkway, Suite 905, or fill out an online e-mailable form.

Please note that about 40,000 acres of land currently are unmapped. The largest unmapped parcels are in Lee and Mount Vernon Districts. These two districts also contain the most problematic soils. With assistance from NVSWCD and the USDA's Natural Resources Conservation Service, the county is in the process of completing the soil survey and updating the soil maps for ultimate availability on the county's GIS.

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 of 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. Learn more about the soil test.

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.