U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
Small-Scale Chemical Heterogeneities in a Crude-Oil-Contaminated
Aquifer, Bemidji, Minnesota
Isabelle M. Cozzarelli (U.S. Geological Survey, Reston, Va.),
Mary Jo Baedecker (U.S. Geological Survey, Reston, Va.), George Aiken (U.S.
Geological Survey, Boulder, Colo.), and Curtis Phinney (U.S. Geological
Survey, Reston, Va.)
A study of the spatial heterogeneity of biogeochemical reactions was
undertaken in an aquifer affected by a crude-oil spill near Bemidji, Minnesota.
An anoxic plume extended 90 meters downgradient from the crude-oil body
in 1992, and contained elevated concentrations of dissolved organic carbon,
methane, ferrous iron, and manganese. Two 1.5-meter-long continuous cores
were collected from two locations within the anoxic plume to determine small-scale
chemical heterogeneities in the ground water. Chemistry of pore water in
a core collected from near the edge of the crude-oil body indicates that
oxygenated water does not mix with the anoxic plume. The effects of mixing
oxygenated ground water with the anoxic plume is reflected in the chemistry
of pore water in a core collected 25 meters farther downgradient; mixing
resulted in significant small-scale chemical heterogeneity in the concentrations
of organic and inorganic chemical constituents.