Phoolendra Kumar Mishra

Basin-scale transmissivity and storativity estimation using hydraulic tomography

While tomographic inversion has been successfully applied to laboratory- and field-scale tests, here we address the new issue of scale that arises when extending the method to a basin. Specifically, we apply the hydraulic tomography (HT) concept to jointly interpret four multiwell aquifer tests in a synthetic basin to illustrate the superiority of this approach to a more traditional Theis analysis of the same tests. Transmissivity and storativity are estimated for each element of a regional numerical model using the geostatistically based sequential successive linear estimator (SSLE) inverse solution method. We find that HT inversion is an effective strategy for incorporating data from potentially disparate aquifer tests into a basin-wide aquifer property estimate. The robustness of the SSLE algorithm is investigated by considering the effects of noisy observations, changing the variance of the true aquifer parameters, and supplying incorrect initial and boundary conditions to the inverse model. Ground water flow velocities and total confined storage are used as metrics to compare true and estimated parameter fields; they quantify the effectiveness of HT and SSLE compared to a Theis solution methodology. We discuss alternative software that can be used for implementing tomography inversion.

On Simulation and Analysis of Variable-Rate Pumping Tests

Analytical solutions for constant-rate pumping tests are widely used to infer aquifer properties. In this note, we implement a methodology that approximates the time-varying pumping record as a series of segments with linearly varying pumping rates. We validate our approach using an analytical solution for a sinusoidally varying pumping test. We also apply our methodology to analyze synthetic test data and compare the results with those from a commonly used method where rate variations are represented by a series of constant-rate steps.

Saturated-unsaturated flow in a compressible leaky-unconfined aquifer

An analytical solution is developed for three-dimensional flow towards a partially penetrating largediameter well in an unconfined aquifer bounded below by a leaky aquitard of finite or semi-infinite extent. The analytical solution is derived using Laplace and Hankel transforms, then inverted numerically. Existing solutions for flow in leaky unconfined aquifers neglect the unsaturated zone following an assumption of instantaneous drainage due to Neuman. We extend the theory of leakage in unconfined aquifers by (1) including water flow and storage in the unsaturated zone above the water table, and (2) allowing the finite-diameter pumping well to partially penetrate the aquifer. The investigation of model-predicted results shows that aquitard leakage leads to significant departure from the unconfined solution without leakage. The investigation of dimensionless time-drawdown relationships shows that the aquitard drawdown also depends on unsaturated zone properties and the pumping-well wellbore storage effects.

Advances in hydrogeology

Recent Advances in Statistical and Scaling Analyses of Earth and Environmental Variables Environmental Variables.- A new P-K-S Characteristic-Based Multiple Phase Flow Model for Simulation Compressible Subsurface Flows.- Fluid Pressure Redistribution Events within a Fault: Impact of Material Property Correlation.- Sparsity-Promoting Solution of Subsurface Flow Model Calibration Inverse Problems.- Analytic Modelling of Transient Multi-Layer Flow.- Tortuosity and Archies Law.- Measurement of Streaming Potentials Generated during Laboratory Simulations of Unconfined Aquifer Tests.- Description, Analysis and Interpretation of an Infiltration Experiment in a Semi-Arid Deep Vadose Zone.- Unconfined Aquifer Flow Theory - From Dupuit to Present.- Index.

Unconfined Aquifer Flow Theory: From Dupuit to Present

Analytic and semi-analytic solution are often used by researchers and practitioners to estimate aquifer parameters from unconfined aquifer pumping tests. The nonlinearities associated with unconfined (i.e., water table) aquifer tests make their analysis more complex than confined tests. Although analytical solutions for unconfined flow began in the mid-1800s with Dupuit, Thiem was possibly the first to use them to estimate aquifer parameters from pumping tests in the early 1900s. In the 1950s, Boulton developed the first transient well test solution specialized to unconfined flow. By the 1970s, Neuman had developed solutions considering both primary transient storage mechanisms (confined storage and delayed yield) without nonphysical fitting parameters. In the last decade, research into developing unconfined aquifer test solutions has mostly focused on explicitly coupling the aquifer with the linearized vadose zone. Despite the many advanced solution methods available, there still exists a need for realism to accurately simulate real-world aquifer tests.

Thermal Modeling of High-Level Nuclear Waste Disposal in a Salt Repository

Abstract Salt formations have received recent attention for geologic disposal of heat-generating, high-level nuclear waste (HLW). Existing investigations are summarized and expanded upon using analytical and numerical models to investigate simulated temperatures in the salt after emplacement of HLW. Analytical modeling suggests that temperature variations near canisters will be smooth, indicating that the system can be approximated by a coarsely discretized numerical model. Two multidimensional parameter studies explore canister configuration using characteristics from (a) defense HLW and (b) spent nuclear fuel (SNF) waste. Numerical modeling was conducted for a disposal concept consisting of emplacement of waste canisters on the floor of drifts and covering each with salt backfill. Results indicate that waste forms with U.S. Department of Energy (DOE) waste characteristics can be easily configured to maintain simulated temperatures far below 200·C at spacings as close as 0.3 m (˜1 ft), the minimum feasible spacing that could practically be achieved. For SNF waste packaged into canisters with heat loads of 1500 or 1000 W with canister spacing of 6 m (˜20 ft) and 3 m (˜10 ft), respectively, simulated temperatures can be maintained below 200·C; much higher maximum temperatures would result for designs with higher canister heat loads and smaller spacings. These results indicate that from a thermal loading perspective, in-drift disposal of HLW in salt deposits is feasible for DOE-managed waste as long as the maximum temperature is managed through proper selection of canister heat loads and spacings. The results will aid in the design of potential future field tests to confirm this conclusion.

Computational modeling of subsurface systems

Site characterisation aims to obtain fundamental data needed to describe the subsurface flow pathways and distribution of contaminants. The study describes the application of various geohydrological techniques as complimentary tools to characterise an LNAPL contaminated fractured rock aquifer on the Beaufort West study area in South Africa. Field investigations were designed to define and determine the properties of the fracture preferential flow paths responsible for LNAPL transportation in a typical Karoo fractured rock aquifer system. The research places emphasis on the integration of results to maximise the subsurface geological understanding in particular location of fracture features chiefly responsible for facilitating LNAPL migration and distribution. T.he core and percussion drilling explorations, cross correlated with borehole geophysics, were valuable for geological subsurface investigations in particular locations of bedding fractures, which are often associated with high hydraulic conductive flow zones. Tracer and pump tests were conducted to determine hydraulic and mass transport parameters respectively. Hydraulically conductive bedding plane fracture flow zones were identified by integrating results from the geological core logs, borehole geophysics and aquifer tests. The chemical characterisation of the study area was conducted by means of organic hydrocarbon, inorganic water analyses and volatile organic carbon measurements in the soil during air percussion drilling. Based on the findings, the hydrogeological structure of the formation was conceptualised as a fractured sandstone aquifer, characterised by bedding plane fracture preferential flow paths at contact areas, with shale and mudstone formations. The study findings demonstrate the merit and value in the application of various geohydrological tools to complement one another for optimised site understanding. The findings and recommendations of the case study are not necessarily confined to LNAPL contaminated fractured rock aquifers, but may also be applicable to other types of contaminants in fractured rock aquifer formations.Hydrology-2012 September 10-12, 2012 Hydrol Current Res ISSN: 2157-7587 HYCR, an open access journal A solutions are obtained for two cases, first one for uniform and second for increasing input source by using Laplace transform technique for temporally dependent dispersion along a uniform flow in a horizontal two-dimensional semiinfinite domain. Due to human activities and other responsible sources of pollution, the domain (groundwater) is not solute free. It is combination of exponentially increasing function of position variable and ratio of zero order production and first decay which are inversely proportional to dispersion coefficient. The variable advection–dispersion equation is reduced into constant coefficients by introducing new space and time variables. Results and discussion are given with set of numerical values of various parameters and effects of these parameters are shown in graphs.Seismic reflection method applied to investigate the shallow strata around Ain Al-Faras spring area (AAF), as a part of UNDP Sustainable Human Development for Rehabilitation of the Old City of Gadames, Libya. The old city of Gadames is located in the Western Libya about 600Km southwest of Tripoli at a major cross-roads of trade routes linking sub-Sahara Africa with the Mediterranean. Gadames is an outstanding example of historic human settlement in a desert oasis. Its architecture and social organization are adapted to the arid climate, water supply, and agricultural activities. The aim of the seismic refraction survey was to investigate the possible presence of cavities or any other geologic features that might caused what is believed to be fracture zones in subsurface strata underneath the spring sites