17 research outputs found
Stochastic hydrogeology's biggest hurdles analyzed and its big blind spot
This paper considers questions related to the adoption of
stochastic methods in hydrogeology. It looks at factors affecting the
adoption of stochastic methods including environmental regulations, financial
incentives, higher education, and the collective feedback loop involving
these factors. We begin by evaluating two previous paper series appearing in
the stochastic hydrogeology literature, one in 2004 and one in 2016, and
identifying the current thinking on the topic, including the perceived data
needs of stochastic methods, the attitude in regulations and the court system
regarding stochastic methods, education of the workforce, and the
availability of software tools needed for implementing stochastic methods in
practice. Comparing the state of adoption in hydrogeology to petroleum
reservoir engineering allowed us to identify quantitative metrics on which to
base our analysis. For impediments to the adoption of stochastic hydrology,
we identified external factors as well as self-inflicted wounds. What emerges
is a picture much broader than current views. Financial incentives and
regulations play a major role in stalling adoption. Stochastic hydrology's
blind spot is in confusing between uncertainty with risk and ignoring
uncertainty. We show that stochastic hydrogeology comfortably focused on risk
while ignoring uncertainty, to its own detriment and to the detriment of its
potential clients. The imbalance between the treatment on risk on one hand
and uncertainty on the other is shown to be common to multiple disciplines in
hydrology that interface with risk and uncertainty.</p
Estimating pathway-specific contributions to biodegradation in aquifers based on dual isotope analysis: Theoretical analysis and reactive transport simulations
At field sites with varying redox conditions, different redox-specific microbial degradation pathways contribute to total contaminant degradation. The identification of pathway-specific contributions to total contaminant removal is of high practical relevance, yet difficult to achieve with current methods. Current stable-isotope-fractionation-based techniques focus on the identification of dominant biodegradation pathways under constant environmental conditions. We present an approach based on dual stable isotope data to estimate the individual contributions of two redox-specific pathways. We apply this approach to carbon and hydrogen isotope data obtained from reactive transport simulations of an organic contaminant plume in a two-dimensional aquifer cross section to test the applicability of the method. To take aspects typically encountered at field sites into account, additional simulations addressed the effects of transverse mixing, diffusion-induced stable-isotope fractionation, heterogeneities in the flow field, and mixing in sampling wells on isotope-based estimates for aerobic and anaerobic pathway contributions to total contaminant biodegradation. Results confirm the general applicability of the presented estimation method which is most accurate along the plume core and less accurate towards the fringe where flow paths receive contaminant mass and associated isotope signatures from the core by transverse dispersion. The presented method complements the stable-isotope-fractionation-based analysis toolbox. At field sites with varying redox conditions, it provides a means to identify the relative importance of individual, redox-specific degradation pathways
Estimating pathway-specific contributions to biodegradation in aquifers based on dual isotope analysis: Theoretical analysis and reactive transport simulations
At field sites with varying redox conditions, different redox-specific microbial degradation pathways contribute to total contaminant degradation. The identification of pathway-specific contributions to total contaminant removal is of high practical relevance, yet difficult to achieve with current methods. Current stable-isotope-fractionation-based techniques focus on the identification of dominant biodegradation pathways under constant environmental conditions. We present an approach based on dual stable isotope data to estimate the individual contributions of two redox-specific pathways. We apply this approach to carbon and hydrogen isotope data obtained from reactive transport simulations of an organic contaminant plume in a two-dimensional aquifer cross section to test the applicability of the method. To take aspects typically encountered at field sites into account, additional simulations addressed the effects of transverse mixing, diffusion-induced stable-isotope fractionation, heterogeneities in the flow field, and mixing in sampling wells on isotope-based estimates for aerobic and anaerobic pathway contributions to total contaminant biodegradation. Results confirm the general applicability of the presented estimation method which is most accurate along the plume core and less accurate towards the fringe where flow paths receive contaminant mass and associated isotope signatures from the core by transverse dispersion. The presented method complements the stable-isotope-fractionation-based analysis toolbox. At field sites with varying redox conditions, it provides a means to identify the relative importance of individual, redox-specific degradation pathways
Improved regional-scale groundwater representation by the coupling of the mesoscale Hydrologic Model (mHM v5.7) to the groundwater model OpenGeoSys (OGS)
Most large-scale hydrologic models fall short in reproducing
groundwater head dynamics and simulating transport process due to their
oversimplified representation of groundwater flow. In this study, we aim to
extend the applicability of the mesoscale Hydrologic Model (mHM v5.7) to
subsurface hydrology by coupling it with the porous media simulator
OpenGeoSys (OGS). The two models are one-way coupled through model interfaces
GIS2FEM and RIV2FEM, by which the grid-based fluxes of groundwater recharge
and the river–groundwater exchange generated by mHM are converted to
fixed-flux boundary conditions of the groundwater model OGS. Specifically,
the grid-based vertical reservoirs in mHM are completely preserved for the
estimation of land-surface fluxes, while OGS acts as a plug-in to the
original mHM modeling framework for groundwater flow and transport modeling.
The applicability of the coupled model (mHM–OGS v1.0) is evaluated by a case
study in the central European mesoscale river basin – Nägelstedt.
Different time steps, i.e., daily in mHM and monthly in OGS, are used to
account for fast surface flow and slow groundwater flow. Model calibration is
conducted following a two-step procedure using discharge for mHM and
long-term mean of groundwater head measurements for OGS. Based
on the model summary statistics, namely the Nash–Sutcliffe model efficiency
(NSE), the mean absolute error (MAE), and the interquartile range error
(QRE), the coupled model is able to satisfactorily represent the dynamics of
discharge and groundwater heads at several locations across the study basin.
Our exemplary calculations show that the one-way coupled model can take
advantage of the spatially explicit modeling capabilities of surface and
groundwater hydrologic models and provide an adequate representation of the
spatiotemporal behaviors of groundwater storage and heads, thus making it a
valuable tool for addressing water resources and management problems