Abstract
Abstract. 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 multi-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, as well as 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.
Highlights
Heavy metals, including chromium, arsenic, copper, nickel, selenium, technetium, uranium, and zinc, are widespread and hazardous subsurface contaminants in groundwater aquifers (Appelo and Postma, 2004; Tchounwou et al, 2012)
We developed CHROTRAN based on the existing PFLOTRAN code, taking advantage of the reaction sandbox interface to implement complex model features not included in its basic microbial packages while leveraging other aspects of PFLOTRAN, such as its high-performance computing capabilities
For modeling in situ remediation of aqueous groundwater contaminants by injection of aqueous amendment, we recognized the importance of mathematical formulations and numerical codes that can represent multi-dimensional fluid flow and multi-species contaminant transport in heterogeneous aquifers with arbitrary injection regimes
Summary
Heavy metals, including chromium, arsenic, copper, nickel, selenium, technetium, uranium, and zinc, are widespread and hazardous subsurface contaminants in groundwater aquifers (Appelo and Postma, 2004; Tchounwou et al, 2012). For U(VI), field-scale modeling studies have been performed on bio-reduction under anaerobic conditions at the Old Rifle Site in Colorado (Li et al, 2010, 2011; Yabusaki et al, 2011) These conceptions treat the contaminant as the sole electron acceptor, with an externally applied electron donor, and the implied equations have a similar form to those devised by Chiang et al (1991): linear in biomass, Monod in contaminant, and Monod in electron donor. A general three-dimensional bio-reactive transport model (not focused on heavy metals) which models biomass as a separate species, and explicitly models electron donors and acceptors, was presented by Schafer et al (1998). The CHROTRAN 1.0 user manual is presented in Appendix A, which gives instructions on how to install and use the software
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