Conceptual Groundwater Flow Model Research Articles

Sustainability of groundwater in Mali, West Africa

The following paper describes the goals and some preliminary work in the Bani sustainability study, an ongoing project in Mali, West Africa. Rural communities in Mali are increasingly relying on hand-pumps, which tap groundwater resources, as a means of obtaining potable water. The long-term sustainable yield of groundwater resources is not known but can be evaluated in sustainability study. In 2005, a groundwater sustainability study was established along the Bani River of Mali. The Bani study collected groundwater levels that were used in a conceptual groundwater flow model—the Bani model—to develop an understanding of current aquifer conditions and to make limited predictions of sustainability under various future scenarios. The Bani model showed the climatic parameters of recharge (derived from precipitation) and evapotranspiration to influence simulated groundwater levels and groundwater volume available, while increased pumping rates, due to population growth, showed little effect. When considered in the context of the actual Bani sustainability study area, the change in groundwater levels resulting from climatic parameters may have negative implications, especially during several consecutive years of decreased precipitation, such as drought, or if downward trends anticipated for precipitation continue.

Tracing groundwater flow and sources of organic carbon in sandstone aquifers using fluorescence properties of dissolved organic matter (DOM)

Abstract The fluorescence properties of groundwaters from sites in two UK aquifers, the Penrith Sandstone of Cumbria and the Sherwood Sandstone of South Yorkshire, were investigated using excitation–emission matrix (EEM) fluorescence spectroscopy. Both aquifers are regionally important sources of public supply water and are locally impacted by pollution. The Penrith Sandstone site is in a rural setting while the Sherwood Sandstone site is in suburban Doncaster. Fluorescence analysis of samples from discrete sample depths in the Penrith Sandstone shows decreasing fulvic-like intensities with depth and also shows a good correlation with CFC-12, an anthropogenic groundwater tracer. Tryptophan-like fluorescence centres in the depth profile may also provide evidence of rapid routing of relatively recent applications of organic slurry along fractures. Fluorescence analysis of groundwater sampled from multi-level piezometers installed within the Sherwood Sandstone aquifer also shows regions of tryptophan-like and relatively higher fulvic-like signatures. The fluorescence intensity profile in the piezometers shows tryptophan-like peaks at depths in excess of 50 m and mirrors the pattern exhibited by microbial species and CFCs highlighting the deep and rapid penetration of modern recharge due to rapid fracture flow. Fluorescence analysis has allowed the rapid assessment of different types and relative abundances of dissolved organic matter (DOM), and the fingerprinting of different sources of organic C within the groundwater system. The tryptophan:fulvic ratios found in the Penrith Sandstone were found to be between 0.5 and 3.0 and are characteristic of ratios from sheep waste sources. The Sherwood Sandstone has the lowest ratios (0.2–0.4) indicating a different source of DOM, most likely a mixture of terrestrial and microbial sources, although there is little evidence of pollution from leaking urban sewage systems. Results from these two studies suggest that intrinsic fluorescence may be used as a proxy for, or complementary tool to, other groundwater investigation methods in helping provide a conceptual model of groundwater flow and identifying different sources of DOM within the groundwater system.

Pathogen and chemical transport in the karst limestone of the Biscayne aquifer: 1. Revised conceptualization of groundwater flow

The Biscayne aquifer is a highly transmissive karst limestone that serves as the sole source of drinking water to over two million residents in south Florida. The aquifer is characterized by eogenetic karst, where the most transmissive void space can be an interconnected, touching‐vug, biogenically influenced porosity of biogenic origin. Public supply wells in the aquifer are in close proximity to lakes established by surface mining. The mining of the limestone has occurred to the same depths as the production wells, which has raised concerns about pathogen and chemical transport from these surface water bodies. Hydraulic and forced gradient tracer tests were conducted to augment geologic and geophysical studies and to develop a hydrogeologic conceptual model of groundwater flow and chemical transport in the Biscayne aquifer. Geologic and geophysical data indicate multiple, areally extensive subhorizontal preferential flow zones of vuggy limestone separated by rock with a matrix pore system. The hydraulic response from an aquifer test suggests that the Biscayne aquifer behaves as a dual‐porosity medium; however, the results of the tracer test showed rapid transport similar to other types of karst. The tracer test and concurrent temperature logging revealed that only one of the touching‐vug flow zones dominates transport near the production wells. On the basis of the rising limb of the breakthrough curve, the dispersivity is estimated to be less than 3% of the tracer travel distance, which suggests that the fastest flow paths in the formation are likely to yield limited dilution of chemical constituents.

Evaluating the recharge mechanism of the Lower Kuiseb Dune area using mixing cell modeling and residence time data

Summary A mixing cell approach was extended by a method incorporating mean cell residence times derived from 14C to further constrain and validate the modeling results. This extended approach was used to model the groundwater system of the Lower Kuiseb Dune area in Namibia. The Kuiseb river is a 560 km long ephemeral river that crosses the Namib Desert from east to west. Transmission losses from the riverbed during flood events are an important source of groundwater recharge to the underlying aquifer system. The Lower Kuiseb area is located in a hyper arid region with annual precipitation less than 25 mm/yr. Hydrochemical data from 13 wells in the area were used in the mixing cell model (MCM). End members were identified as sources for the groundwater found in the Lower Kuiseb, including inflow from the crystalline basement plateau north of the Kuiseb as well as floodwater from the Kuiseb river. A conceptual groundwater recharge and flow model was developed, and then inverse mixing cell modeling was carried out using hydrochemical tracers. This approach generally allows for several possible solutions. After completing the inverse modeling, a forward mixing cell model was developed by varying the mean residence time of each cell to fit calculated 14C data to the measured 14C data. This new approach joins previously developed methods solely based on conservative mixing or residence time optimization. Based on the results of the model the fraction of floodwater in different sections of the Lower Kuiseb groundwater systems was calculated, ranging from 61% to 98.2%. In addition to floodwater, groundwater inflow from the crystalline basement north of the Kuiseb was shown to contribute to the Lower Kuiseb aquifer, accounting for salinization during periods without flooding.

Coupling mineral analysis with conceptual groundwater flow modelling: The source and fate of iron, aluminium and manganese in a back-barrier island

Mineral and aqueous geochemical data are combined with a conceptual groundwater flow model, to establish the origin and fate of iron, aluminium and manganese in the groundwater system of a small back-barrier island. The flow model domain consists of an unconfined island fresh groundwater lens overlying a semi-confined hypersaline aquifer. The two aquifers are separated by a discontinuous, clay-rich aquitard and both contain diffusion governed variable density flow fields. High concentrations of dissolved iron and manganese are associated with brackish to hypersaline groundwater, although there is no systematic relationship with salinity. Calculation of S 2−/SO 4 2− and Fe 2+/Fe 3+ redox couples and the results of thermodynamic modelling show that redox disequilibrium in the groundwater is widespread. Groundwater samples containing aqueous sulphide and ferric iron complexes are supersaturated with respect to pyrite, goethite and haematite but the prevailing state of redox disequilibrium controls mineral dissolution and precipitation. Aqueous iron in the deeper regions of both aquifers is derived from the dissolution of iron oxide–hydroxides in lateritic palaeosols controlled by seasonal fluctuations in groundwater redox state. Aqueous manganese is potentially derived from the dissolution of ilmenite and amorphous oxide–hydroxides. The oxidation of iron sulphides contributes to the aqueous iron concentration and sulphuric acid production in the shallow groundwater. The solubility of aluminium is also limited by this process, governed by acidity regulation. A significant proportion of aqueous iron is transmitted from the semi-confined to the overlying unconfined aquifer through discontinuities in the aquitard layer. Movement of metals in solution outside the island groundwater system is restricted by the presence of diffusion boundaries within variable density transition zones.

Classification of springs of Jeju Island using cluster analysis of annual fluctuations in discharge variables: investigation of the regional groundwater system

The springs of Jeju Island have been studied since 1999. However, previous studies did not provide a systematic analysis of survey results. Thus, we performed a systematic analysis of the groundwater flow system using cluster analysis of discharge variables, i.e., discharge rate, electrical conductivity (EC), and temperature, at 121 springs. The 121 springs were categorized into nine major groups based on discharge rates and ten groups based on EC. Springs in groups 1, 2, and 3 in discharge cases had peak discharge rates in September, October, and occasionally in November, following the rainy season. Other springs showed complex seasonal variation in discharge rates. Springs in groups 4–1, 4–3, 5–2, 9–1, and 9–2 had peak discharge rates in winter (December–February). The results of classification by EC were directly correlated with the absolute values of and seasonal variation in EC. Based on EC, springs in group 1 had relatively low EC of > 500 μS/cm in general. The highest EC at each spring in group 1 was 110–18,000 μS/cm. Coastal springs generally had higher EC than did springs located inland. The relation between discharge rate and EC was of interest. At some springs, discharge rate and EC were proportional, especially in winter. The proportionality between discharge and EC cannot be explained by the conventional groundwater management model of Jeju Island. To explain this proportionality, we examined the results of previous studies with regard to geological features, well locations, hydraulic head and hydraulic gradient distributions, and vertical reduction in groundwater EC within the zone influenced by saline water. We then proposed a hypothetical regional conceptual model of groundwater flow for Jeju Island. More precise studies are needed to clarify the relationships among responses at surveyed springs, hydraulic features in coastal areas, and the regional conceptual model for groundwater circulation on Jeju Island.

Groundwater resource sustainability in the Nabogo Basin of Ghana

In order to address groundwater resource sustainability, a conceptual groundwater flow model is developed for a hydrographic basin of northern Ghana. A three-dimensional steady-state model is applied to the Nabogo Basin, a sub-catchment of the White Volta River Basin. Mean annual data are used for input parameters. Parameters include rates of precipitation, recharge, surface water discharge, and groundwater extraction (pumpage). The model indicates that current well pumpage rates are significantly less than annual groundwater recharge to the basin. Model results for several scenarios tested (i.e., increased population, access to potable water for all citizens, and/or decreased rainfall) indicate that extraction rates will still be less than groundwater input to the basin.

Analysis of flows from a large Carboniferous Limestone drainage adit, Derbyshire, England

The flow hydrograph of a large mine drainage adit, the Meerbrook Sough, has been analysed to determine the large-scale hydraulic behaviour of the artificially drained Carboniferous Limestone aquifer. A conceptual model has been constructed using available hydrological and hydrogeological data. The analysis shows that the Carboniferous Limestone can behave at a larger scale as a dominantly diffuse flow system in which storage processes are also important. The conceptual model of groundwater flow is supported by numerical modelling. The dominance of a diffuse flow response is attributed to the large-scale dewatering below the base level of drainage, which has disconnected a significant proportion of the natural conduit flow system. The storage process that provides the relatively reliable flow response from the Carboniferous Limestone is discussed with reference to hydrogeological field data and historical and industrial archaeological sources on the mining in Derbyshire.

Groundwater noble gas, age, and temperature signatures in an Alpine watershed: Valuable tools in conceptual model development

Bedrock groundwater in alpine watersheds is poorly understood, mainly because of a scarcity of wells in alpine settings. Groundwater noble gas, age, and temperature data were collected from springs and wells with depths of 3–342 m in Handcart Gulch, an alpine watershed in Colorado. Temperature profiles indicate active groundwater circulation to a maximum depth (aquifer thickness) of about 200 m, or about 150 m below the water table. Dissolved noble gas data show unusually high excess air concentrations (>0.02 cm3 STP/g, ΔNe > 170%) in the bedrock, consistent with unusually large seasonal water table fluctuations (up to 50 m) observed in the upper part of the watershed. Apparent 3H/3He ages are positively correlated with sample depth and excess air concentrations. Integrated samples were collected from artesian bedrock wells near the trunk stream and are assumed to approximate flow‐weighted samples reflecting bedrock aquifer mean residence times. Exponential mean ages for these integrated samples are remarkably consistent along the stream, four of five being from 8 to 11 years. The tracer data in combination with other hydrologic and geologic data support a relatively simple conceptual model of groundwater flow in the watershed in which (1) permeability is primarily a function of depth; (2) water table fluctuations increase with distance from the stream; and (3) recharge, aquifer thickness, and porosity are relatively uniform throughout the watershed in spite of the geological complexity of the Proterozoic crystalline rocks that underlie it.

Utilising seasonal variations in hydrogeochemistry and excitation-emission fluorescence to develop a conceptual groundwater flow model with implications for subsidence hazards: an example from Co. Durham, UK

Groundwaters were sampled from four research boreholes, a private supply well and a natural karst resurgence in southern County Durham, England. Time series data sets of piezometric levels, groundwater major ions, and fluorescence of dissolved organic matter (DOM) were interpreted in the light of new geological mapping to assess the movement of groundwater and its potential for the dissolution of gypsum. Three distinct groundwater facies were identified representing contact with gypsiferous strata, dolomitic limestone and Quaternary Till. Piezometric data indicated time varying transverse flow across the gypsifeorus strata, which was confirmed from gradational mixing of groundwater types and cation ratios. Fluorescence of dissolved DOM identified variations in protein and fulvic-like acid fluorescence. The former was taken to represent surface derived, short-lived material. Spatial and temporal variations in protein fluorescence offered a means to trace groundwater movement along the regional groundwater gradient and indicated rapid lateral movement of groundwater. It was concluded that gypsum dissolution is occurring beneath the town of Darlington, however, the presence of a thick deposit of Quaternary till effectively confines the small head differences of approximately 1 m, across the gypsum strata beneath the town. Further to the south, the lowering of the ground surface results in a greater upwards flow of water across the gypsum and is used to explain the presence of historic collapse sinkholes.

Numerical testing of conceptual models of groundwater flow: a case study using the Dumfries Basin aquifer

Synopsis The current understanding of the groundwater flow regime in the Dumfries Basin aquifer has been developed over a number of years and encapsulated in a conceptual model. A numerical modelling study has been undertaken to test the confidence in this understanding. This study has included three activities: recharge estimation, water balance calculations and steady-state groundwater flow modelling. It has been confirmed that the highest recharge is found in the NW of the basin and that the peat and marine clay deposits limit direct recharge in the east and south. The water balance is dominated by surface water flow, in particular the River Nith brings over 3200 Ml day −1 onto the basin. Conceptualized flow directions were confirmed by the steady-state modelling. The understanding and model validity are severely constrained by a lack of flow data in the lower River Nith and scarcity of water level and aquifer property information. These knowledge gaps could be filled by flow gauging just above the tidal limit of the river and additional drilling and testing.

Testing the interbasin flow hypothesis at Death Valley, California

Interbasin flow is a process by which groundwater moves from one topographic basin to another through an intervening structural or topographic barrier. For decades, interbasin flow has been the prevailing conceptual paradigm for groundwater movement in the arid southwestern United States wherever carbonate rocks are thought to be in continuous contact [e.g., Anderson, 2002]. This conceptual model of groundwater flow is especially relevant in the Death Valley region where water resources are scarce and where the U.S. government has conducted underground nuclear tests and has planned for the storage of spent nuclear fuel at Yucca Mountain, Nevada. Recent studies of large flux springs (∼10,000 L/min) in the Furnace Creek area of Death Valley, California (Figure 1), however, indicate that the concept of interbasin flow may be fundamentally flawed, or at least not as universally applicable as previously thought. Rather, it appears that aquifers supplying Furnace Creek springs were replenished locally during episodes of wet climate more than 9500 yr ago, a contention supported by extensive regional fossil spring deposits [Quade et al., 2003].

Groundwater flow and solute transport in fracture zones: an improved model for a large-scale field experiment at Äspö (Sweden)

157-172 Groundwater flow and solute transport in fracture zones: an improved model for a large-scale field experiment at Äspö (Sweden) Jorge Molinero E.T.S. Ingenieros de Caminos Canales y Puertos, Campus de Elvina Universidadde A Coruña 15192 A Coruña Spain E-mail: molinero@iccp.udc.es Javier Samper E.T.S. Ingenieros de Caminos Canales y Puertos, Campus de Elvina Universidad de A Coruna, 15192 A Coruna, Spain. E-mail: jsc@iccp.udc.es Several countries around the world are considering the final disposal of high-level radioactive waste in deep repositories located in fractured granite formations. Evaluating the long term safety of such repositories requires sound conceptual and numerical models of groundwater flow, solute transport and chemical and radiological processes. These models are being developed from data and knowledge gained from in situ experiments carried out at deep underground laboratories such as that of Äspö, Sweden, constructed in fractured granite. The Redox Zone Experiment is one of such experiments performed at Aspö in order to evaluate the effects of the construction of the access tunnel on the hydrogeological and hydrochemical conditions of a fracture zone intersected by the tunnel. Hydrochemical and isotopic data of this experiment were interpreted by Banwart et al. (Appl. Geochem., 14, 1999, 873) using a mass-balance approach based on a qualitative description of groundwater flow conditions. Such an interpretation, however, is subject to uncertainties related to an oversimplified conceptualization of groundwater flow. Here we present finite element numerical models of groundwater flow and solute transport for this fracture zone. The first model is based on Banwart's conceptual model. It presents noticeable inconsistencies and fails to match simultaneously observed drawdowns and chloride breakthrough curves. To overcome its limitations, a revised flow and transport model is presented which relies directly on available hydrodynamic and transport parameters, is based on the identification of appropriate flow and transport boundary conditions and uses, when needed, solute data extrapolated from nearby fracture zones. A significant quantitative improvement is achieved with the revised model because its results match simultaneously drawdown and chloride data. Other improvements are qualitative and include: ensuring consistency of hydrodynamic and hydrochemical data and avoiding inconsistencies in the hydrodynamic model. These results enable us to conclude that quantitative analyses of hydrochemical data should rely on sound conceptual and numerical flow and transport models which provide an appropriate framework for checking the consistency of hydrodynamic and hydrochemical data. This framework can be subsequently used for coupling groundwater flow, solute transport and chemical processes in the future.

The hydrogeology of the Ballimore region, central New South Wales, Australia: an integrated study

The integrated use of geophysical, geological, hydrogeochemical and hydrogeological data has allowed the development of a plausible conceptual model for groundwater flow in the Ballimore region. A realistic model for this under-explored system could not be derived solely by the use of hydrogeological data. Interpretation of the available datasets indicates that two groundwater systems are active: a regional and a local system. These are separated by a regionally extensive aquiclude. Groundwater flow in the regional groundwater system is controlled by the structural fabric of the Palaeozoic basement rocks. The local groundwater system is restricted to the Permian to Recent sequence of cover rocks. The local groundwater system is subdivided into three cells: the deep, intermediate and shallow cells. Groundwater flow within the deep cell of the local groundwater system is controlled by fracture flow. Groundwaters from this aquifer are under artesian pressure and are effervescent (CO2-gas). The intermediate cell is a leaky aquitard that acts as a mixing zone between the deep and shallow cells. Groundwater flow within the shallow cell is controlled by the influx of surface waters which migrate laterally through permeable beds.

The saturated zone at Yucca Mountain: an overview of the characterization and assessment of the saturated zone as a barrier to potential radionuclide migration

The US Department of Energy is pursuing Yucca Mountain, Nevada, for the development of a geologic repository for the disposal of spent nuclear fuel and high-level radioactive waste, if the repository is able to meet applicable radiation protection standards established by the US Nuclear Regulatory Commission and the US Environmental Protection Agency (EPA). Effective performance of such a repository would rely on a number of natural and engineered barriers to isolate radioactive waste from the accessible environment. Groundwater beneath Yucca Mountain is the primary medium through which most radionuclides might move away from the potential repository. The saturated zone (SZ) system is expected to act as a natural barrier to this possible movement of radionuclides both by delaying their transport and by reducing their concentration before they reach the accessible environment. Information obtained from Yucca Mountain Site Characterization Project activities is used to estimate groundwater flow rates through the site-scale SZ flow and transport model area and to constrain general conceptual models of groundwater flow in the site-scale area. The site-scale conceptual model is a synthesis of what is known about flow and transport processes at the scale required for total system performance assessment of the site. This knowledge builds on and is consistent with knowledge that has accumulated at the regional scale but is more detailed because more data are available at the site-scale level. The mathematical basis of the site-scale model and the associated numerical approaches are designed to assist in quantifying the uncertainty in the permeability of rocks in the geologic framework model and to represent accurately the flow and transport processes included in the site-scale conceptual model. Confidence in the results of the mathematical model was obtained by comparing calculated to observed hydraulic heads, estimated to measured permeabilities, and lateral flow rates calculated by the site-scale model to those calculated by the regional-scale flow model. In addition, it was confirmed that the flow paths leaving the region of the potential repository are consistent with those inferred from gradients of measured head and those independently inferred from water-chemistry data. The general approach of the site-scale SZ flow and transport model analysis is to calculate unit breakthrough curves for radionuclides at the interface between the SZ and the biosphere using the three-dimensional site-scale SZ flow and transport model. Uncertainties are explicitly incorporated into the site-scale SZ flow and transport abstractions through key parameters and conceptual models.

Active and inactive groundwater flow systems: Evidence from a stratified, mountainous terrain

We present a new conceptual model of groundwater flow that describes active and inactive groundwater flow regimes. The model is based on an analysis of interactions between surface water and shallow and deep groundwater in the 240-km-long Wasatch Range and Book Cliffs, Utah, USA. Active zone groundwater flow paths are continuous, responsive to annual recharge and climatic variability, and have groundwater resident times “ages” that become progressively older from recharge to discharge area. Active zone groundwater systems discharge at thousands of springs that issue from the 700+-m-thick, gently dipping, clastic bedrock formations. Springs waters contain appreciable 3 H and anthropogenic 14 C. In contrast, inactive zone groundwater has extremely limited or no communication with annual recharge and has groundwater mean residence times that do not progressively lengthen along the flow path. Groundwater in the inactive zone may be partitioned, occur as discrete bodies, and may occur in hydraulically isolated regions that do not have hydraulic communication with each other. Inactive zone groundwater is encountered in-mines (coal-mines 300–700 m below ground surface) where groundwater discharge rates decline rapidly and the waters have δ 2 H and δ 18 O compositions that are distinguishable from near surface groundwater. In general, deep waters have no 3 H and have mean 14 C residence times of 500 to 20,000 yr (45.9 to 4.9 pmc). Chemical evolution modeling, porosity-permeability core plug analysis, and in-mine hydrographs also indicate hydraulic partitioning.

Modeling density‐driven flow and radionuclide transport at an underground nuclear test: Uncertainty analysis and effect of parameter correlation

The effects of uncertainty associated with input parameters and conceptual groundwater flow and transport models are studied and evaluated for radionuclide transport modeling at the Milrow underground nuclear test site on Amchitka Island, Alaska. Two‐dimensional numerical simulations in conjunction with a multiparameter uncertainty analysis are adapted and used to evaluate the effects of the uncertainties associated with the definition of the modeled processes and the values of the parameters governing these processes. Density‐driven flow caused by the mixing of fresh and salt water in a coastal aquifer and radionuclide mass transport resulting from the nuclear test are the two major processes analyzed. The parametric uncertainty analysis is performed in two stages. In the first modeling stage, one parameter is varied at a time, and the effects of this variability on transport results are evaluated. The analysis indicates that the solution to the flow problem, and thus the transport results, are very sensitive to the values of recharge and hydraulic conductivity. However, fracture porosity does not affect density‐driven flow but dramatically influences the transport results in terms of arrival times of radionuclides from the test cavity to the seafloor. Matrix diffusion is also crucial in affecting arrival times and mass flux values. The second modeling stage utilizes multiple realizations of the flow field generated by considering random combinations of recharge, conductivity, macrodispersivity, and fracture porosity drawn at random from their respective distributions. For each one of these realizations, transport parameters are also drawn at random from their assigned distributions. Different correlation models are considered and compared with scenarios with no parameter correlation. The results indicate that incorporation of correlation between hydraulic conductivity and recharge significantly reduces the uncertainty in both travel time and transverse plume location. This results from the impact of these parameters on the transition zone, which dominates flow velocity variability in this coastal aquifer setting. Correlation between fracture porosity and matrix diffusion has the largest impact on the transport results, with a positive correlation providing the critical scenario of most rapid transport (thus less radioactive decay) and a negative correlation leading to longer travel times with significant decay.

Fracture flow and groundwater compartmentalization in the Rollins Sandstone, Lower Mesaverde Group, Colorado, USA

This paper presents a site-specific conceptual model of groundwater flow in fractured damage zones associated with faulting in a package of sedimentary rocks. The model is based on the results of field and laboratory investigations. Groundwater and methane gas inflows from fault-fracture systems in the West Elk coal mine, Colorado, USA, have occurred with increasing severity. Inflows of 6, 160 and 500 L s−1 discharged almost instantaneously from three separate faults encountered in mine workings about 460 m below ground level. The faults are about 600 m apart. The δ 2H and δ 18O compositions of the fault-related inflow waters and the hydrodynamic responses of each fault inflow indicate that the groundwaters discharge from hydraulically isolated systems. 14C data indicate that the groundwaters are as much as 10,500 years old. Discharge temperatures are geothermal (≈30°C), which could indicate upwelling from depth. However, calculations of geothermal gradients, analysis of solute compositions of groundwater in potential host reservoirs, geothermometer calculations, and results of packer testing indicate that the fractured groundwater reservoir is the Rollins Sandstone (120 m thick) directly beneath the coal seams. The packer test also demonstrates that the methane gas is contained in the coal seams. A geothermal gradient of 70–80°C km−1, related to an underlying intrusion, is probably responsible for the slightly elevated discharge temperatures. Large discharge volumes, as great as 8.2×105 m3 from the 14 South East Headgate fault (14 SEHG), rapid declines in discharge rates, and vertical and horizontal permeability (matrix permeability generally <0.006 Darcy) indicate fracture flow. An in-mine pumping test demonstrates that the 14 SEHG fault has excellent hydraulic communication with fractures 50 m from the fault. Aeromagnetic data indicate that the faults are tectonically related to an igneous body that is several thousand meters below the coal seams. Exploratory drilling has confirmed a fourth fault, and two additional faults are projected, based on the aeromagnetic data. The conceptual model describes a series of parallel, hydraulically separate groundwater systems associated with fault-specific damage zones. The faults are about 600 m apart. Groundwater stored in fractured sandstone is confined above and below by clayey layers.

Predicting ground-water movement in large mine spoil areas in the Appalachian Plateau

Spoil created by surface mining can accumulate large quantities of ground-water, which can create geotechnical or regulatory problems, as well as flood active mine pits. A current study at a large (4.1 km 2), thick, (up to 90 m) spoil body in eastern Kentucky reveals important factors that control the storage and movement of water. Ground-water recharge occurs along the periphery of the spoil body where surface-water drainage is blocked, as well as from infiltration along the spoil–bedrock contact, recharge from adjacent bedrock, and to a minor extent, through macropores at the spoil's surface. Based on an average saturated thickness of 6.4 m for all spoil wells, and assuming an estimated porosity of 20%, approximately 5.2×10 6 m 3 of water is stored within the existing 4.1 km 2 of reclaimed spoil. A conceptual model of ground-water flow, based on data from monitoring wells, dye-tracing data, discharge from springs and ponds, hydraulic gradients, chemical data, field reconnaissance, and aerial photographs indicate that three distinct but interconnected saturated zones have been established: one in the spoil's interior, and others in the valley fills that surround the main spoil body at lower elevations. Ground-water movement is sluggish in the spoil's interior, but moves quickly through the valley fills. The conceptual model shows that a prediction of ground-water occurrence, movement, and quality can be made for active or abandoned spoil areas if all or some of the following data are available: structural contour of the base of the lowest coal seam being mined, pre-mining topography, documentation of mining methods employed throughout the mine, overburden characteristics, and aerial photographs of mine progression.

Constraints Added by the Strontium and Boron Isotopes on the Geochemical Characterization of the Palmottu Hydrosystem (Finland)

The Palmottu U-ore deposit, located in a granitic host rock in southern Finland, provides an excellent location for analogue studies to assess the radionuclide transport from the U-ore deposit along welldefined pathways in the fractured crystalline rock [ 1 ]. In this context, strontium and boron isotope ratios are used to trace the degree of water-rock interaction and mixing processes in groundwaters. Sr and B analyses have been performed on groundwater from the Palmottu hydrosystem and, in particular, on the deep geochemical boreholes R385 and R386 [1]. This study should contribute to the understanding of recent hydrogeological and hydrogeochemical conditions of the site, including the design of a conceptual groundwater flow model.