Subsurface fate and transport of cyanide species at a manufactured-gas plant site

Cyanide is present at manufactured-gas plant (MGP) sites in oxide-box resid uals, which were often managed on-site as fill during active operations. Cy anide can leach from these materials, causing groundwater contamination;. S peciation, fate, and transport of cyanide in a sand-gravel aquifer underlyi ng an MGP sire in the upper Midwest region of the United States were studie d through characterization, monitoring, and modeling of a plume of cyanide- contaminated groundwater emanating from the site. Results indicate that cya nide in the groundwater is primarily in the form of iron-cyanide complexes (>98%), that these complexes are stable under the conditions of the aquifer , and that they are transported as nonreactive solutes in the sand-gravel a quifer material. Weak-acid-dissociable cyanide, which represents a minute f raction of total cyanide in the site groundwater, may undergo chemical-biol ogical degradation in the sand-gravel aquifer. It seems that dilution may b e the only natural attenuation mechanism for iron-cyanide complexes in sand -gravel aquifers at MGP sites.