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.