Three-dimensional imaging of aquifer and aquitard heterogeneity via transient hydraulic tomography at a highly heterogeneous field site

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.jhydrol.2018.02.024 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Previous studies have shown that geostatistics-based transient hydraulic tomography (THT) is robust for subsurface heterogeneity characterization through the joint inverse modeling of multiple pumping tests. However, the hydraulic conductivity (K) and specific storage (Ss) estimates can be smooth or even erroneous for areas where pumping/observation densities are low. This renders the imaging of interlayer and intralayer heterogeneity of highly contrasting materials including their unit boundaries difficult. In this study, we further test the performance of THT by utilizing existing and newly collected pumping test data of longer durations that showed drawdown responses in both aquifer and aquitard units at a field site underlain by a highly heterogeneous glaciofluvial deposit. The robust performance of the THT is highlighted through the comparison of different degrees of model parameterization including: (1) the effective parameter approach; (2) the geological zonation approach relying on borehole logs; and (3) the geostatistical inversion approach considering different prior information (with/without geological data). Results reveal that the simultaneous analysis of eight pumping tests with the geostatistical inverse model yields the best results in terms of model calibration and validation. We also find that the joint interpretation of long-term drawdown data from aquifer and aquitard units is necessary in mapping their full heterogeneous patterns including intralayer variabilities. Moreover, as geological data are included as prior information in the geostatistics-based THT analysis, the estimated K values increasingly reflect the vertical distribution patterns of permeameter-estimated K in both aquifer and aquitard units. Finally, the comparison of various THT approaches reveals that differences in the estimated K and Ss tomograms result in significantly different transient drawdown predictions at observation ports.Environmental Security and Technology Certification Program (ESTCP) under grant ER201212China Scholarship CouncilDiscovery and Collaborative Research and Development Grants from the Natural Sciences and Engineering Research Council of Canada (NSERC)Ontario Research Foundation (ORF)Canada Foundation for Innovation (CFI

Automatic estimation of aquifer parameters using long-term water supply pumping and injection records

Analyses are presented of long-term hydrographs perturbed by variable pumping/injection events in a confined aquifer at a municipal water-supply well field in the Region of Waterloo, Ontario (Canada). Such records are typically not considered for aquifer test analysis. Here, the water-level variations are fingerprinted to pumping/injection rate changes using the Theis model implemented in the WELLS code coupled with PEST. Analyses of these records yield a set of transmissivity (T) and storativity (S) estimates between each monitoring and production borehole. These individual estimates are found to poorly predict water-level variations at nearby monitoring boreholes not used in the calibration effort. On the other hand, the geometric means of the individual T and S estimates are similar to those obtained from previous pumping tests conducted at the same site and adequately predict water-level variations in other boreholes. The analyses reveal that long-term municipal water-level records are amenable to analyses using a simple analytical solution to estimate aquifer parameters. However, uniform parameters estimated with analytical solutions should be considered as first rough estimates. More accurate hydraulic parameters should be obtained by calibrating a three-dimensional numerical model that rigorously captures the complexities of the site with these data.Grant from the Region of Waterloo to the University of WaterlooDiscovery grant - Natural Sciences & Engineering Research Council of Canada (NSERC

Optimization of the hydrodynamic characteristics of a karst conduit with CFPv2 coupled to OSTRICH

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.jhydrol.2018.10.050 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/In order to better define the characteristics of a karst conduit, an integrated hydrogeological study including numerical modeling using CFPv2 is conducted at a karst aquifer in the Zagros Mountain Region of Iran. The Sarvak limestone aquifer in the Nil Anticline is the main karst aquifer of the study area with major groundwater discharge taking place at Sarkur spring. An annual water balance and a dye tracing test confirmed that the karst system is mainly recharged through rainfall and the Maroon River. Several depressions are observed along the banks of the river with a major one classified as a sinkhole used for dye injection. A groundwater flow model was developed based on the available hydrogeological information. A probable direct conduit flow path with an estimated groundwater flow velocity of 96 m/h is estimated between the injection point and the Sarkur spring. Four scenarios are assumed to simulate the probable conduit flow path using the CFPv2 code. As one of the first attempts in regional groundwater flow modeling of a karst aquifer, CFPv2 is automatically calibrated with field measurements of spring discharge and a dye breakthrough curve through a parameter estimation code OSTRICH to optimize the characteristics of the conduit through the minimization of the weighted sum of square error. Simulated results reveal that a conduit with a diameter of 2.9 m is required to adequately simulate spring discharge and dye tracer migration between the injection and discharge points. Our new approach (linking of CFPv2 and OSTRICH) provides a deeper understanding of groundwater flow and solute transport in karst terrains even when available data are limited and the approach should be applicable to other areas.Shiraz UniversityUniversity of Waterlo

Comparative study of transient hydraulic tomography with varying parameterizations and zonations: Laboratory sandbox investigation

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.jhydrol.2017.09.045 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Transient hydraulic tomography (THT) is a robust method of aquifer characterization to estimate the spatial distributions (or tomograms) of both hydraulic conductivity (K) and specific storage (Ss). However, the highly-parameterized nature of the geostatistical inversion approach renders it computationally intensive for large-scale investigations. In addition, geostatistics-based THT may produce overly smooth tomograms when head data used to constrain the inversion is limited. Therefore, alternative model conceptualizations for THT need to be examined. To investigate this, we simultaneously calibrated different groundwater models with varying parameterizations and zonations using two cases of different pumping and monitoring data densities from a laboratory sandbox. Specifically, one effective parameter model, four geology-based zonation models with varying accuracy and resolution, and five geostatistical models with different prior information are calibrated. Model performance is quantitatively assessed by examining the calibration and validation results. Our study reveals that highly parameterized geostatistical models perform the best among the models compared, while the zonation model with excellent knowledge of stratigraphy also yields comparable results. When few pumping tests with sparse monitoring intervals are available, the incorporation of accurate or simplified geological information into geostatistical models reveals more details in heterogeneity and yields more robust validation results. However, results deteriorate when inaccurate geological information are incorporated. Finally, our study reveals that transient inversions are necessary to obtain reliable K and Ss estimates for making accurate predictions of transient drawdown events.Discovery grant - Natural Sciences & Engineering Research Council of Canada (NSERC)China Scholarship Counci

Theoretical interpretation of a pronounced permeability scale effect in unsaturated fractured tuff

Numerous single‐hole and cross‐hole pneumatic injection tests have been conducted in unsaturated fractured tuff at the Apache Leap Research Site (ALRS) near Superior, Arizona. Single‐hole tests have yielded values of air permeability at various locations throughout the tested rock volume on a nominal scale of ∼1 m. Cross‐hole tests have yielded equivalent air permeabilities (and air‐filled porosities) for a rock volume characterized by a length scale of several tens of meters. Cross‐hole tests have also provided high‐resolution tomographic estimates of how air permeability (and air‐filled porosity), defined over grid blocks having a length scale of 1 m, vary throughout a similar rock volume. The results have revealed a highly pronounced scale effect in permeability (and porosity) at the ALRS. We examine the extent to which the permeability scale effect is amenable to interpretation by a recent stochastic scaling theory, which treats the rock as a truncated random fractal

Single- and cross-hole pneumatic injection tests in unsaturated fractured tuffs at the Apache Leap Research Site near Superior, Arizona

This dissertation documents research results from a series of field experiments and analyses used to test interpretive models for investigating the role of fractures in fluid flow through unsaturated, fractured tuffs. It summarizes the experimental design of single- and cross-hole pneumatic injection tests, including borehole configuration and testing schedules, data collection system, interpretive models developed and tested, data, and conclusions. Single-hole tests were interpreted by Guzman et al. (1996) by means of steady-state analysis to obtain permeability values based solely on late pressure data. This dissertation and Illman et al. (1998) employ pressure and pressure-derivative type-curves to analyze transient data. Air permeabilities determined from transient analyses agree well with those derived from steady-state analyses. Cross-hole pneumatic tests were analyzed by means of a graphical matching procedure using newly-developed pressure and pressure-derivative type-curves. Analyses of pressure data from individual monitoring intervals using these new type-curves, under the assumption that the rock acts as a uniform and isotropic fractured porous continuum, yield results that are comparable with parameters obtained from a numerical inverse procedure described in Illman et al. (1998). The results include information about pneumatic connections between the injection and monitoring intervals, corresponding directional air permeabilities, and air-filled porosities. Together with the results of earlier site investigations, single- and cross-hole test analyses reveal that at the Apache Leap Research Site in central Arizona: (1) the pneumatic pressure behavior of fractured tuff is amenable to analysis by methods that treat the rock as a continuum on scales ranging from meters to tens of meters; (2) this continuum is representative primarily, but not exclusively, of interconnected fractures; (3) its pneumatic properties vary strongly with location, direction and scale, in particular, the mean of pneumatic permeabilities increases, and their variance decreases with scale; (4) this scale effect is most probably due to the presence in the rock of various size fractures that are interconnected on a variety of scales; and (5) given a sufficiently large sample of spatially varying pneumatic rock properties on a given scale of measurement, these properties are amenable to analysis by geostatistical methods, which treat them as correlated random fields defined over a continuum