A multiphase flow and multispecies reactive transport model for DNAPL-involved Compound Specific Isotope Analysis
This study presents a multiphase flow and multispecies reactive transport model for the simultaneous simulation of multiphase flow, NAPL dissolution, and reactive transport with isotope fractionation due to degradation, which can be used to interpret of NAPL-involved compound-specific isotope data in complex hydrogeologic systems. The model was verified by comparison to an analytical solution for cases involving multi-species reactive transport and with isotope fractionation for both straight and branching degradation chains. Several illustrative examples are presented to investigate the effect of NAPL spill rates, degradation rate constants, and enrichment factors on the temporal and spatial distribution of the isotope signatures of chlorinated aliphatic hydrocarbons. The results clearly indicate that isotope signatures can be significantly different when considering multiphase flow. A series of simulations indicate that degradation and isotope enrichment compete with dissolution to determine the isotope signatures in the source zone: isotope ratios remain the same as those of the source if dissolution dominates the reaction, while heavy isotopes are enriched in reactants along flow paths when degradation becomes dominant. It is also shown that NAPL composition can change from that of the injected source due to the partitioning of components between the aqueous and NAPL phases even when degradation is not allowed in NAPL phase. Three-dimensional simulations in a heterogeneous sandy aquifer are presented to illustrate the complexities in interpreting the isotopic signatures.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- 1832 HYDROLOGY / Groundwater transport;
- 1847 HYDROLOGY / Modeling;
- 1849 HYDROLOGY / Numerical approximations and analysis