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Soils Gone Bad: Acid-sulfate and other problem soils

Soils Gone Bad: Acid-sulfate and other problem soils. What are acid sulfate soils?. Soils formed from the weathering of sulfide-bearing parent materials, which results in extremely low pH (commonly < 3.0) and precipitation of sulfate salts. What are sulfides?.

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Soils Gone Bad: Acid-sulfate and other problem soils

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  1. Soils Gone Bad:Acid-sulfate and other problem soils

  2. What are acid sulfate soils? Soils formed from the weathering of sulfide-bearing parent materials, which results in extremely low pH (commonly < 3.0) and precipitation of sulfate salts.

  3. What are sulfides? Sulfide minerals are combinations of one or more metals (cations) with reduced sulfur (anion). Which sulfides are acid-forming? pyrite FeS2 marcasite FeS2 pyrrhotite Fe(1-x)S In terms of soils, “sulfide” and “pyrite” are commonly used interchangeably.

  4. Massive pyrite crystals in coal

  5. ~ 20 um Pyrite (FeS2) occurs in several different forms. Framboidal pyrite is the worst. In sediment deposits: diameter typically < 50 um.

  6. Major Actors in Pyrite Oxidation • Coal mining (spoils/wastes/water) • Metal mining (spoils/tailings/water) • Sand & gravel mining • Metal smelting (after secondary combustion/volatilization) • Road building & construction • Land drainage in coastal zones

  7. FeS2 + 7/2O2 + H2O  FeSO4 + H2SO4 2FeSO4 + H2SO4 Fe2(SO4)3 + H2O 1/2Fe2(SO4)3 + 2H2O  1/3HFe3(SO4)2(OH)6 + 5/6H2SO4 OR  KFe3(SO4)2(OH)6 (jarosite) NaFe3(SO4)2(OH)6 (natrojarosite) Sum it up all up: FeS2 + 15/4O2 + 7/2H2O  2H2SO4 + Fe(OH)3 1 mole of pyrite produces 2 moles of sulfuric acid

  8. Sulfuricizationoccurs when sulfidic materials are exposed to the atmospheric conditions (i.e. by artificial drainage or excavation). The rapid oxidation of sulfides results in the production of metalliferous acidic drainage and the precipitation of sulfate minerals. This may subsequently result in: • Barren soils • Impaired surface waters • Deterioration of construction materials

  9. Oxidized zone (pre-disturbance) pH = 3.3 – 4.3 Approximated original land surface prior to excavation ~ 3.5 m Dark gray 10YR4/1 Very fine sandy loam Salt crust of hydrated Fe-Al sulfate minerals on exposed cut bank ~ 7.5 m Sulfuric horizon extends approximately 0.3 m into hill. pH = 1.8 - 3.5 Sulfidic sediments: %S ~ 1 Unoxidized zone Dark gray 10YR6/1 silty clay Dark greenish gray 5BG4/1 and 5/1 clay Dark brown 10YR3/3 fine sandy loam ~ 12.0 m Typical soil profile along a cut slope at Stafford Regional Airport

  10. Barren fields of SRAP as they appeared in March, 2002

  11. Erosion of acid sulfate sediments and acidic leachate from an adjacent spoil fill has severely impaired this wetland.

  12. Aerial view of the Beaver Ponds at SRAP SW1 SW5

  13. Shallow groundwater monitoring well. SW6 Drainage from SRAP prior to remediation (April 02)

  14. Iron-staining on concrete culvert at SRAP SW5

  15. Corrosion of metal pipes in drainage basin at SRAP.

  16. Typical young acid-sulfate soil profile Overlying oxidized material is typically a light yellowish brown with pH ~ 3. Underlying reduced material is typically drab blue or gray, with pH > 5.5.

  17. If sulfidic materials can have high pH values, then how do we know how bad they are? Potential peroxide acidity (PPA) and total-S • PPA < 10 Mg CaCO3/1000 Mg material (total-S < 0.2%): can readily be managed. • PPA 10 - 60 Mg CaCO3/1000 Mg material (total-S = 0.2 - 2%): can be remediated with intense management. • PPA > 60 Mg CaCO3/1000 Mg material (total-S > 2%): extremely difficult to remediate.

  18. Sites sampled by Orndorff, 2001

  19. Coastal Plain: the Tabb Formation. Pond at Hampton Roads Center pH = 3.09 Runoff from stockpiled material at Hampton Roads Center. pH = 3.05

  20. Coastal Plain: the Tabb Formation. The Tabb Formation (Sedgefield member) may be considered likely to produce moderately problematic roadside management conditions which could require special reclamation efforts.

  21. Coastal Plain: Tertiary marine sediments. Chesterfield County: Proctor’s Creek was redirected to this excavated channel during road construction.

  22. Coastal Plain: Tertiary marine sediments. Soil pH ~ 3 Interchange of I-295/Rt-360 in Mechanicsville.

  23. Coastal Plain: Tertiary marine sediments. Within 5 years, erosion has removed over 30 cm of sediment... …and the guardrail is severely corroded.

  24. NRCS Flood Structure on Tributary Of Potomac Cr. Waters discharging here in February 2002 were pH 3.5 with 10 ppm Fe, 40 to 50 Al, 150 sulfate, etc.

  25. Fredericksburg Coastal Plain: Tertiary marine sediments. Tertiary marine sediments may be considered highly likely to produce problematic roadside management conditions which require intense reclamation efforts.

  26. Piedmont: Quantico Formation. Roadcut along Mine Road in Stafford County.

  27. Piedmont: Quantico Formation. Iron-staining along curbs and sidewalks through the Hampton Oaks subdivision. Homeowners in this neighborhood apply the equivalent of 2 Mg agricultural lime per hectare per month to maintain soil pH above 5.5.

  28. Piedmont: Quantico Formation. Concrete etching occurs when acid drainage “dissolves” out the cement, deteriorating the concrete.

  29. Fredericksburg Piedmont: Quantico Formation. Exposures of the Quantico Formation may be considered highly likely to produce severely problematic roadside management conditions which require intense reclamation efforts.

  30. Blue Ridge: Ashe Formation. Rt-750, Floyd Co. Acid produced by pyrrhotite. Drainage from this roadcut flows to the culvert on the far right.

  31. Blue Ridge: Ashe Formation. Exposures of phyllitic material from the Ashe Formation may be considered somewhat likely to produce moderate to severely problematic roadside management conditions.

  32. Valley and Ridge: Devonian black shales. pH upstream end of culvert: 6.6 pH downstream end of culvert: 5.3 pH drain into culvert: 2.7 Fe- and Al- precipitates heavily coat the bed of this stream which is biologically dead for at least 0.5 km downstream of the roadcut. Culvert beneath I-64 in Clifton Forge

  33. Inside the culvert at Clifton Forge

  34. Valley and Ridge: Devonian black shales. Exposure of the Marcellus, Millboro, and Chattanooga shales, and the Needmore formation, may be considered somewhat likely to produce severely problematic roadside management conditions.

  35. Appalachian Plateau The majority of this material is relatively low in pyritic-S, and some strata contain carbonate cementing agents which help neutralize acidity.

  36. 1: PPA < 10; S < 0.5%. 3: PPA 10 - 60. 4: PPA - more than 10% of samples > 60. 2: PPA < 10; S > 0.5%. Compiling a state-wide sulfide hazard map for Virginia: the final map. All formations, based on draft version of digital geologic map of Virginia. Not characterized Characterized Sulfides not documented. Sulfides documented. Acid potential unknown.

  37. 1 2 3 4 N Sulfides documented Compiling a state-wide sulfide hazard map for Virginia: the final map. Sulfides undocumented Sulfides undocumented

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