Quantification of in situ biodegradation rate constants and mean hydraulic conductivities using a novel combined isotope methodology
Final Report Abstract
For stable carbon isotopes of the studied BTEX such as o-xylene and toluene, significant isotope shifts are detected indicating active biodegradation under sulphate-reducing conditions, which confirmed previous results that also showed a clear evidence for biodegradation of o-xylene. For the other studied compounds such as benzene, toluene, 1,2,3-trimethylbenzene and naphthalene however no isotope shift for stable carbon isotopes is detected. Unexpectedly, hydrogen isotopes results provided no evidence of biodegradation for all studied organic compounds such as BTEX and naphthalene. Nevertheless, in combining these results with the groundwater residence times, which range between 1 year for the shallow wells (20 m below surface) and 41 years for the deeper wells (40 m below surface), it is feasible to determine effective in situ biodegradation rate constants for at least o-xylene. Conversely, the outcome also evidently demonstrates the major limitations of the novel combined isotope approach for quantifying in situ biodegradation at the field scale, because for the other studied compounds like benzene, toluene, 1,2,3- trimethylbenzene and naphthalene the approach could not be applied. Finally, the tracer-based (3H-3He) groundwater dating (TGD) method demonstrated to be a very powerful and inexpensive method for the estimation of in situ effective hydraulic conductivities, in particular for contaminated aquifers, where pumped water during the hydraulic pumping test has to be expensively treated before reinjection. Thus, we recommend the application of TGD method in non-pristine aquifers and a careful evaluation of the applicability of compound-specific isotope analysis (CSIA) providing often only limited and only compound-specific evidence for active biodegradation.
Publications
- (2014): Quantification of in situ biodegradation rate constants using a novel combined isotope approach. American Geophysical Union, Fall Meeting 2014, B31B-0018
Philipp Blum, Jürgen Sültenfuß, Peter Martus
