  Groundwater contamination by heavy metals is a critical environmental problem
for which in situ remediation is frequently the only viable treatment option.
For such interventions, a three-dimensional reactive transport model of
relevant biogeochemical processes is invaluable. To this end, we developed a
model, CHROTRAN, for in situ treatment, which includes full dynamics for five
species: a heavy metal to be remediated, an electron donor, biomass, a nontoxic
conservative bio-inhibitor, and a biocide. Direct abiotic reduction by
donor-metal interaction as well as donor-driven biomass growth and
bio-reduction are modeled, along with crucial processes such as donor sorption,
bio-fouling and biomass death. Our software implementation handles
heterogeneous flow fields, arbitrarily many chemical species and amendment
injection points, and features full coupling between flow and reactive
transport. We describe installation and usage and present two example
simulations demonstrating its unique capabilities. One simulation suggests an
unorthodox approach to remediation of Cr(VI) contamination.
