Multispecies Reactive Tracer Test in an Aquifer with Spatially Variable
Chemical Conditions: An Overview
By James A. Davis, Douglas B. Kent, Jennifer A. Coston, Kathryn M. Hess,
and Jennifer L. Joye
ABSTRACT
A field investigation of multispecies reactive transport was conducted in
a well-characterized, sand and gravel aquifer on Cape Cod, Massachusetts.
Ten thousand liters of ground water with added tracers (Br, Cr(VI), and EDTA
complexed with Pb, Zn, Cu, and Ni) were injected into the aquifer and the
distributions of tracers were monitored for 15 months. Most of the tracers
were transported more than 200 meters; transport was quantified using spatial
moments computed from the results of a series of synoptic samplings. The aquifer
is characterized by different geochemical regimes caused by sewage contamination;
the interactions of the reactive tracers with the aquifer sediments varied
due to the differing chemical conditions. For example, retardation of the
tracers varied with pH and Cr(VI) reduction varied with the concentration
of dissolved oxygen. Transport of the metal-EDTA complexes was affected by
the extent and rates of various metal exchange reactions, especially those
involving Fe(III) dissolution and complexation with EDTA. These reactions
also were influenced by the spatial distribution of Zn contamination in the
aquifer from sewage disposal. The results of the field experiment provide
a well-characterized, chemically complex data set that can be used for future
development and testing of hydrogeochemical transport models of flow coupled
with chemical reactions.