Journal of Hydrologic Engineering

In situ permeability tests are crucial in hydraulic characterizations of geological formations for the disposal of radioactive nuclear waste. As has been done in most countries where geological disposal of high-level radioactive wastes has been discussed, single-well permeability tests are generally conducted in a preliminary stage of selecting a site where groundwater exists. To determine accurately hydraulic parameters, specifically hydraulic conductivity and specific storage, from single-well permeability tests, it is worth reexamining analytical solutions for modeling test data derived from deep and hydraulically tight (hydraulic conductivity is typically less than ${10}^{-8}\text{m}/\text{s}$ ) formations. In hydraulically tight formations, the radius of influence due to a single-well permeability test is not expected to be large, which should be taken into consideration when using the test results. The present paper revisits three major single-well permeability tests, i.e., the pressure pulse, constant head, and constant flow rate tests, and examines the features of natural formations incorporated into the analytical models, such as hydrogeological boundaries, property alterations around a borehole and anisotropy. The radius of influence in a hydraulically tight formation is examined for the three major single-well permeability tests by a numerical approach.

The safe disposal of radioactive nuclear waste is currently an urgent and challenging issue. Many countries, including the United States, Sweden, Switzerland, Finland, Germany, Canada, Belgium, France, and Japan, have initiated radioactive waste management programs, which now have reached various stages. Experiences and research results obtained in one country may offer valuable references for another, especially for some developing countries where nuclear power is being used and/or is under development. In this paper, we comprehensively overview the history of nuclear energy, the generation of high-level radioactive waste (HLW), and the policies and recent progress made in relation to the management of HLW in Japan.

The retardation effect of radionuclides (RNs) is a key factor to comprehend the performance of the geological disposal system. Since natural rock includes various minerals, the physical and chemical properties are not spatially uniform. However, in general, the performance assessments ignore such heterogeneity. This study focused on the grain size of each mineral in granite, to consider the spatial distribution of retardation coefficients. In a grain size, the retardation coefficient was assumed to be uniform in this study. Through such heterogeneous media, the transport rates of cesium-135 ( $2.1\times {10}^6$ $y$ in half-life) have been numerically examined, using two-dimensional advection-dispersion equations. Here, the sorption data of each mineral in granite were quoted from the past report. The conclusions are summarized as follows: (1) Since the flow test limits the sorption onto biotite (taking the highest sorption-coefficient in the minerals of granite) in the flow paths, the flow test showed less sorption, compared to that expected from the result of batch test for the same material of granite. In other words, because in the batch test the RNs are forcibly sorbed onto a specific mineral, it is possible that the sorption distribution coefficient of granite obtained from batch test is overestimated. (2) When a spatial size of mineral grain boundary is assumed to be a unit size (a few square millimeters), the surface area more than $30\times 30$ unit size at least is needed to obtain the characteristic transport rate for the rock matrix. (3) When the heterogeneity of both sorption efficiency and permeability exists spatially, the assumption of the homogeneity for these distributions yields a conservative result in the breakthrough curve of RNs, compared to the two-dimensional analysis considering the heterogeneity.

The presence of coal tar in the subsurface of former manufactured gas plant sites poses an environmental hazard and a potential threat to public health. Coal tar can release various chemical compounds that are transported into the groundwater. Before any efforts can be made to remove coal tar from contaminated subsurface soils, it is recommended to characterize coal tar properties and composition and to delineate the residual saturation point between mobile and immobile coal tar. This paper presents a new innovative field device, the Res-SAT field tool, and laboratory procedures that can be used to determine the saturation-capillary pressure relationship for a soil-water coal-tar system and the critical pressure for coal tar mobility.

Based on the existing theory such as soil mechanics and fluid mechanics, the transfer mechanism of water vapor inside unsaturated soil is investigated in this paper. A formula that depends on matric suction and temperature is obtained for calculating the saturated water vapor pressure inside the voids of soil. The equation by which the water content changing with time in unsaturated soil resulting from water vapor transfer was also derived. The equation reveals that water vapor transfer is attributed to temperature gradient and water content gradient. The nonuniform distribution of temperature and water content may separately or jointly result in water vapor transfer, which confirms the results demonstrated in experiments. A case history is analyzed using the equation in this paper. The reliability of the equation is verified by analyzing the measured and calculated data. It has to be pointed out that water transfer in unsaturated soil normally occurs simultaneously in both liquid and vapor phases. As a result, it is necessary to conduct a further study on the transfer in mixed phase.

In this paper we describe an approach that is based on fuzzy logic (FL) to solve the groundwater flow equation in the presence of uncertain parameters. An appropriate set of fuzzy rules was developed to represent groundwater flow in saturated and unsaturated systems. These rules were derived from mathematical models based on experience and the physics of the underlying problem. This resulted in a FL-based methodology that is conceptually consistent with the process of incorporating soft/qualitative data during performance assessment efforts, and materialized in the form of a numerical code. The software fuzzy logic flow simulator $\left({\text{FLO}}^2\text{SIM}\right)$ is tested and applied with reasonable success to one-dimensional (1D) unsaturated flow, and 1D and two-dimensional (2D) homogeneous and heterogeneous, saturated flow systems. ${\text{FLO}}^2\text{SIM}$ was also enhanced to provide estimates of the uncertainty associated with the centroid-based defuzzified predictions. Comparisons with a conventional, finite-difference numerical simulator are presented for synthetic problems and a real test case from the Waste Isolation Pilot Plant disposal site in southeastern New Mexico.

A thorough review and geological characterization of the latest geochemical and hydrogeological data of the A_area and M_area at a superfund site was undertaken in order to determine the nature and extent of contamination. An integrated contaminant plume and geologic structure model was developed. The GIS surface topographic map is overlaid on the integrated model. The results of this study provide basic information to identify current or potential problems caused by the contamination and assist in the evaluation and selection of the remedial action. In addition, this study assimilated input data for groundwater flow and contaminant transport modeling and will tremendously reduce the uncertainty of modeling. The geospatial modeling technology was fully used for construction, interactive visualization, and manipulation of three-dimensional models of complex geologic layers where property (chemical concentration) grids populate.

The present work examines the results of factor analysis performed on major ions and total hydrocarbon content (THC) from hydrochemical studies over Benin formation aquifer of the Niger Delta Basin, Nigeria. The dominant cations are $\text{Na}\left(50\%\right)>\text{Mg}\left(27\%\right)>\text{Ca}\left(23\%\right)$ and Cl (96%) as the dominant anion. Five major factors were found to explain the source of the ions and THC in the groundwater. Generally, Factors 1 (EC, ${\text{Ca}}^{2+}$ , ${\text{K}}^{+}$ , ${\text{HCO}}_3^{-}$ , and ${\text{SO}}_4^{2-}$ ) and 4 ( ${\text{Mg}}^{2+}$ , ${\text{Na}}^{+}$ , and CI) are mainly due to ion exchange sea water intrusion and effluent water disposal near oil processing facilities. Factor 2 (Fe and Mn) is attributed to geogenic sources while Factor 3 (temperature, pH, dissolved oxygen, and THC) is due to effluent water disposal, leakages of crude oil pipelines, storage facilities, and indiscriminate disposal of waste. Factor 5 $\left({\text{NO}}_3\right)$ is attributed to the disposal of human and domestic wastes into the environment.