Concrete Susceptibility to Corrosive Soil in Montrose County, Colorado (detail)

Corrosive Soils

Chemical corrosion by certain (corrosive) soils is a geologic hazard that affects buried metals and concrete in direct contact with soil or bedrock. Metals are chemically attacked by chloride solutions while high sulfate levels are harmful to concrete. In western Colorado, the Mancos Shale is considered corrosive to both metals and concrete because of its clay content, saline nature, and pyrite content. Through complex oxidation geochemistry in the presence of calcium carbonate, the Mancos Shale forms abundant secondary sulfate minerals (gypsum) in near-surface weathered zones.