Acid Sulfate Soils

What are acid sulfate soils?

Acid sulfate soils form when sulfide-bearing materials are excavated from below the Earth’s surface and are exposed to the atmosphere. The sulfides (primarily pyrite) oxidize to produce sulfuric acid, iron oxides/hydroxides, and sulfate precipitates. The resulting soil is typically highly acidic (pH less than 3.0), and is often associates with acidic, metal-laden surface runoff.

If you  think you have acid sulfate soils and would like more information, please contact us with any questions, and we can provide guidance on reclamation of your site. You can call us at (540) 231-7175 or email Dr. Lee Daniels at wdaniels@vt.edu.

 
Acid Sulfate Staining of Walkway

Grey reduced sulfidic materials are commonly encountered during active construction in the Fredericksburg/Stafford area of Virginia. These materials will usually acidify over time to pH less than 3.5 unless large amounts of lime are added and incorporated.

What problems are associated with acid sulfate soils?

In construction sites such as road corridors, industrial parks, airports, and housing developments, the exposure of sulfidic materials can present a number of technical, environmental, and social problems:
  • Acids degrade metal and concrete building materials.
  • Weathering of fill material and precipitation of sulfates compromise structural stability.
  • Highly acidic soils cannot support roadside vegetation resulting in increased erosion and acid runoff.
  • Highly acidic and metal-laden runoff impairs surface water quality and aquatic life.
  • Visible pollution and adverse conditions for aquatic life limit recreational use of impacted surface waters.

Acid sulfate materials also produce acidic soil and runoff conditions that can damage concrete, metal, block walls and cause serious local water quality problems.

Which geologic formations in Virginia are associated with acid sulfate soils?

Acid sulfate soils occur at several sites in different geologic and geomorphic settings across the state, including:
  • Coastal Plain: Tertiary marine sediments and the Tabb formation
  • Piedmont: Phyllite and slate of the Quantico Formation
  • Blue Ridge: Alum phyllite
  • Valley and Ridge: Devonian black shale including the Marcellus, Millboro, and Chattanooga shale and Needmore Formation
  • Appalachian Plateau: Coal seams and shale including the Wise, Kanawha, Norton, New River, Lee and Pocahontas Formations