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.