Groundwater Flow Regime Research Articles

Contaminant transport in heterogeneous porous media: a case study. 1. Site characterisation and deterministic modelling

The aim of this study is to illustrate the contribution that geostatistical techniques can make to risk assessment for buried waste repositories. For a hypothetical repository site in Bedfordshire, UK, multiple realisations of the hydraulic properties of the principal aquifers are constructed. For each realisation a numerical model describing the groundwater flow regime at the site is used to predict a possible pattern of migration based on the available hydrogeological data. A statistical analysis of the results is carried out to provide quantitative measures of the uncertainty in the patterns of migration deriving from a lack of knowledge of the media properties. In the first part of this two-part paper, the formulation of the conceptual and numerical models describing the regional groundwater flow regime is presented. A detailed assessment of the site has been undertaken to determine the principal hydrogeological formations within which contaminant migration would occur and the principal controls governing regional groundwater flow and contaminant transport. From the resulting conceptual model a quasi-three-dimensional groundwater flow and transport model has been developed. Part 2 of the paper describes the simulation experiments carried out using this model and the analysis of the results.

Contamination of groundwater in the Te Aroha area by heavy metals from an abandoned mine : Liping Pang, Journal of Hydrology (New Zealand), 33(1), 1995, pp 17–34

Groundwater contamination from the copper/lead Tui mine was investigated by modelling the groundwater flow regime, monitoring groundwater quality, and studying the retention of heavy metal contaminants by the lithologic units of the receiving environments. Metal (Cu, Pb, Zn, Cd, Fe, Mn) concentrations in the groundwater define a leachate plume extending approximately 1 km downgradient of the tailings pond. The contaminated groundwater discharges to surface mountain streams which in turn recharge and contaminate groundwater in downgradient alluvial fans. The contamination front of iron was close to the tailings source because of its high retardation by the andesite aquifer, while the contamination front of cadmium was the furthest from the source indicating that it is the least retarded of the heavy metals. The volume and timing of contaminant desorption from the tailings for each of the heavy metals indicates the tailings will be a pollution source for hundreds to thousands of years. A number of measures to prevent contamination, including minimising groundwater contact with the tailings, are suggested

Effects of climate on numbers of northern prairie wetlands

The amount of water held in individual wetland basins depends not only on local climate patterns but also on groundwater flow regime, soil permeability, and basin size. Most wetland basins in the northern prairies hold water in some years and are dry in others. To assess the potential effect of climate change on the number of wetland basins holding water in a given year, one must first determine how much of the variability in number of wet basins is accounted for by climatic variables. I used multiple linear regression to examine the relationship between climate variables and percentage of wet basins throughout the Prairie Pothole Region of Canada and the United States. The region was divided into three areas: parkland, Canadian grassland, and United States grassland (i.e., North Dakota and South Dakota). The models - which included variables for spring and fall temperature, yearly precipitation, the previous year's count of wet basins, and for grassland areas, the previous fall precipitation - accounted for 63 to 65% of the variation in the number of wet basins. I then explored the sensitivities of the models to changes in temperature and precipitation, as might be associated with increased greenhouse gas concentrations. Parkland wetlands are shown to be much more vulnerable to increased temperatures than are wetlands in either Canadian or United States grasslands. Sensitivity to increased precipitation did not vary geographically. These results have implications for waterfowl and other wildlife populations that depend on availability of wetlands in the parklands for breeding or during periods of drought in the southern grasslands.

Developing A National Groundwater-Monitoring Network In Korea

Since the 1960's, the groundwater resources of Korea have been developed without a proper regulatory system for monitoring and preservation, resulting in significant source depletion, land subsidence, water contamination, and sea-water intrusion. With the activation of the “Groundwater Law” in June 1994, the government initiated a project to develop a groundwater-monitoring network to describe general groundwater quality, to define its long-term changes, and to identify major factors affecting changes in groundwater quality and yield. In selecting monitoring locations nationwide, criteria considered are 1) spatial distribution, 2) aquifer characteristics of hydrogeologic units, 3) local groundwater flow regime, 4) linkage with surface hydrology observations, 5) site accessibility, and 6) financial situations. A total of 310 sites in 78 small hydrologic basins were selected to compose the monitoring network. Installation of monitoring wells is scheduled to start in 1995 for 15 sites; the remainder are scheduled to be completed by 2001. At each site, a nest of monitoring wells was designed; shallow and deep groundwater will be monitored for water temperature, pH, EC, DO and TDS every month. Water-level fluctuations will also be measured by automatic recorders equipped with pressure transducers. As a next step, the government plans to develop a groundwater-database management system, which could be linked with surface hydrologic data.

Hydrological and Chemical Management in the Rehabilitation of an Aquifer

The management of coastal aquifer groundwater must take into account natural hydrological, biological and chemical parameters, as well as the development of anthropogenic stresses. Such stresses may result from:1. degradation of groundwater quality due to introduction into the aquifer of pollutants from diffuse sources (e.g. seawater intrusion, agricultural activity, etc.) and/or point sources (landfills, sanitary devices, industry, etc.);2. hydrological deficits which may cause an undesirable groundwater flow regime and groundwater recirculation problems;3. interrelated chemical-hydrogeological processes.Water, contaminated to various degrees, migrates through rocks having heterogeneous properties. Thus, distinct bodies of water appear in the aquifer space.A characteristic situation is demonstrated in the Hadera region of the Israeli Coastal aquifer. Efficient quality control requires the application of surface and underground management programmes. The objective is an improvement in the aquifer water budget and a reduction in the input of harmful chemical and biological pollutants.

Chemical evolution of groundwater in Triassic gypsum-bearing carbonate aquifers (Las Alpujarras, southern Spain)

A hydrochemical study employing modelling techniques, was carried out using samples taken at 65 points (springs and wells) in Triassic carbonate aquifers (Lújar-Gádor Unit, Alpujárride Complex, Betic Cordillera). These aquifers are made up of limestones and dolomites with some gypsum scattered or interbedded. Though the area is semi-arid, recharge is relatively high because of their mountainous nature. The carbonate rocks contain dense microfissuration; the groundwater flow regime is predominantly diffuse. The karstic forms are in general poorly developed. Two main hydrochemical processes have been identified in these aquifers. One is incongruent dissolution of dolomite that determines the chemical composition of the less mineralised water. The other is dedolomitisation (dolomite dissolution together with calcite precipitation caused by dissolution of gypsum), which becomes predominant when the flow encounters interbedded gypsum. This reaction is also frequently associated with low temperature thermalism, and can play a part in more intense local karstification (cavities, sinkholes, high transmisivity in wells) observed in the sectors of these aquifers where gypsum is more abundant. A reaction path model has been used to simulate the geochemical processes through a hypothetical aquifer (with similar lithology to the Alpujárride carbonate aquifers). Successive stages of evolution through the carbonate sequence, represented by different saturation states with respect to calcite, dolomite gypsum and CO 2, have been modelled and then compared with the field data.

Development of a groundwater-management model using the dbase facility

Software, using the command language of the dBASE data-management system, was developed for managing the groundwater resources of an area. The software may be used for a preliminary estimate of the inflow and outflow components of the groundwater-flow regime of a study area and the resulting net change in storage. The potential for further development of the groundwater resources in the study area also may be assessed from these estimates. The software is applicable especially where insufficient data are available for use in a sophisticated numerical groundwaterflow model

Hydrogeophysical Concepts in Aquifer Test Analysis

Aquifer test data analysis is an art leading to reliable hydraulic parameter identifications rather than a mechanical curve fitting. Most often aquifer test data processing is achieved by matching the data with suitable type curve without detailed interpretations of deviations from this curve. In fact, relevant interpretations might yield valuable qualitative and quantitative features about the subsurface geological composition of the aquifer domain at least in the well vicinity. The view taken in this paper is to obtain additional information from various data segments by considering two or more successive measurements. Such a detailed investigation of aquifer test data is referred to herein as the “hydrogeophysical” approach since it yields important clues about the geological set up as well as the groundwater flow regime in the well vicinity. Main features of hydrogeophysical investigation are given based on author's experience. It is hoped that additional points will be supplemented in future applications by other groundwater hydrologists. The application of hydrogeophysical concepts are exemplified for some field data available in the groundwater literature.

Relationship between regional changes of soil physical properties and volcanic stratigraphy on the southern slope of Batur volcano in the island of Bali, Indonesia

The present paper shows the relationship between the regional changes of soil physical properties and the volcanic stratigraphy on the southern slope of Batur volcano in the island of Bali, Indonesia, from the hydrogeological point of view based on the data obtained from field observations and laboratory experiments. The Bali soils data showed marked differences in regional distribution and their characteristics are closely correlated to the distribution of the volcanic stratigraphy derived from the Batur volcanic activities with the eruption about 23,700 years ago. On the basis of these data, the hydrogeological situation of the slope are presented schematically and groundwater flow regimes on the slope, such as recharge and discharge areas, are also classified according to the hydrogeological information. These classifications of groundwater flow regimes are useful to consider the occurrence of hydrological phenomena such as springs and paddy field distributions observed on the slope.

Saline groundwater in Israel: its bearing on the water crisis in the country

One of the major causes for the deterioration of water quality bearing heavily on the water crisis in Israel is the ongoing contamination of its water resources by saline water bodies. The present paper reviews the geochemical processes forming saline water, lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country's various aquifers. Deterioration of groundwater in Israel is caused by numerous natural processes such as encroachment of sea water, migration of connate, highly pressurized brines penetrating into fresh groundwater, by subsurface dissolution of soluble salts originating in surrounding country rocks and by water-rock interaction. In addition to sea water, two saline water bodies were identified as the main factors causing salinization of fresh groundwater: (a) Ca-chloride brines encountered in the Jordan-Dead Sea Rift Valley, in various parts of the Negev and of the Coastal Plain, and (b) Na-chloride saline water identified in the subsurface of the Negev and in the southern part of the Coastal Plain. Intensive exploitation of groundwater in Israel has disturbed the natural equilibrium which prevailed between fresh and saline water. The newly established groundwater flow regimes have facilitated the migration of saline water bodies, their participation in the active hydrological cycle and the progressive contamination of fresh groundwater. These processes which were not anticipated by planners and water resources managers emphasize that large-scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines.

Carbon-14 behaviour in a cement-dominated environment: Implications for spent candu resin waste disposal

Cement based waste forms and concrete engineered barriers are expected to play a key role in providing 14 C waste containment and control 14 C migration for time periods commensurate with its hazardous life of about 50,000 years. The main thrust of this study was, therefore, to evaluate the performance of cement based waste forms with regard to 14 C containment. Of particular importance are the geochemical processes controlling 14 C solubility and release under anticipated cement dominated low and intermediate level waste repository conditions. Immobilization of carbonate-form exchange resin in grout involves transfer of sorbed 14 CO 3 2− ions, through exchange for hydroxyl ions from the grout slurry, followed by localized precipitation of solid calcium carbonate at the cement/resin interface in the grout matrix. Thus almost a total stoichiometric transfer of labile carbonate, originally present on the spent resin, to a solid carbonate phase takes place upon immobilization of carbonate-form resin in a cementitious matrix. Carbon-14 release behaviour can be attributed to the dissolution characteristics and solubility of calcite present in the cement based waste form. The groundwater flow regime can exert a pronounced effect both on the near-field chemistry and the leaching behaviour of 14 C. For a cement dominated repository, at relatively low-flow or stagnant groundwater conditions, the alkaline near-field chemical environment inhibits the release of 14 C from the cemented waste form. Under high flow conditions, the near-field environment is characterized by relatively neutral pH conditions which promote calcite dissolution, thus resulting in 14 C release from the waste form. These findings point to the importance of selecting a suitable site for 14 C waste disposal with a flow regime so that local equilibrium prevails and 14 C release becomes solubility-limited and coupled to generation and maintenance of alkaline conditions for a long period of time.

Fracture detection and groundwater flow characterization using He and Rn in soil gases, Manitoba, Canada

Surveys of the distribution and migration of He and Rn were carried out in the well-characterized granitic terrane of the AECL Underground Research Laboratory (URL), Manitoba as part of a joint AECL Research, United Kingdom Department of the Environment, and United States Department of Energy research initiative. The investigations were designed to determine whether concentrations of He and Rn in soil gases could be used to identify locations of groundwater recharge and discharge from bedrock fractures. The results obtained indicate that subsurface transport of He and possibly Rn in this setting appears to be controlled largely by the groundwater flow system in the bedrock. Release of dissolved gases near the ground surface causes soil gas anomalies, which reflect discharge from the deeper flow system. In the recharge area of the deep groundwater flow system at the URL site, He abundances are close to the atmospheric level, but the discharge area of the deep flow system is characterized by significant He anomalies (up to 0.5 ppm above atmosphere levels). For Rn, the recharge area has broadly distributed high concentrations, probably caused by local Rn production in U-rich overburden, while the discharge area has only localized concentrations of Rn, which are not at the same location as the He anomalies. The general nature of the groundwater flow regime in both areas is reflected in the presence and distribution of the soil gas anomalies. In addition, major fractures in bedrock, which act as preferential groundwater flow paths, have been located from soil gas anomalies, even when obscured by overburden of variable thickness and character. The distribution of He in soil gas appears to be most representative of groundwater recharge and discharge conditions in the granitic rock, while Rn may be useful for locating specific channels where more rapid groundwater discharge is occurring from deep fracture zones.

Groundwater flow regime within the Gambier Embayment of the Otway Basin, Australia: evidence from hydraulics and hydrochemistry

A conceptual groundwater flow model for the Cainozoic sequence of the Gambier Embayment of the Otway Basin, South Australia, is developed using hydraulic head distribution, environmental isotopes and hydrochemical data. Local flow cells occur within the upper sequence of the Gambier unconfined aquifer and are recognised by local relief of the water table and as rapid lateral variations in chloride, 14C, δ 2H and δ 18O concentrations, indicating that regional flow is not dominant in the upper portion of the unconfined aquifer. These localised systems are topographically controlled and have developed in response to undulating stranded coastal dune ridges of the Bridgewater Formation. Recharge areas correspond to dune highs while discharge is focused towards the lower lying interdunal regions. Total dissolved solids concentrations are controlled by evapotranspiration processes during recharge and ion ratios are modified by water rock interactions within the groundwater system. Groundwaters are more dilute in the southern section of the basin where the surplus of precipitation over evapotranspiration in the winter months is greater than that in the northern section of the basin. A regional flow system with interaquifer mixing has developed within the confined Dilwyn aquifer system. Recharge to the Dilwyn aquifer has been identified downgradient from the basin margin via downward leakage from an intermediate flow system within the Gambier unconfined aquifer to the deeper regional flow system of the confined Dilwyn aquifer. Interaquifer mixing appears to be geologically controlled; in the south by the elevated Gambier axis and in the north by the Kanawinka Fault. Downgradient of the zero head difference line, lateral flow appears to be the dominant transport mechanism within the Dilwyn aquifer as indicated by constant chloride concentrations, monotonic decrease in radiocarbon concentration and more negative δ 2 and δ 18 O composition.

The application of a coupled water-balance-salinity model to evaluate the sensitivity of a lake dominated by groundwater to climatic variability

A dynamic hydrologic model, specifically designed to assess lake-groundwater systems, has been used to provide insight into the effects of climatic variability on Wabamun Lake and its watershed, in Alberta, Canada. This lake is typical of many lakes in the prairies of Canada or western plains of the United States in that groundwater exhibits a dominant role in the hydrologic balance of the lake. Sensitivity analyses indicate that small changes in temperature (1–2°C rise) or precipitation (5–10% decline) throughout the watershed, may significantly impact upon the quality of the lake water and the availability of groundwater resources. Specifically, a long-term temperature rise that increases evaporation, or a decrease in precipitation, will reduce the amount of water available to recharge the groundwater-flow regime. Groundwater storage in the watershed will further decline due to continued discharge to the lake. The effect of climatic variability on the quantity of water in Wabamun Lake (as reflected by its surface elevation) is relatively small. However, the salinity of the lake will increase dramatically, due to: (1) the loss of surface runod and direct precipitation, which act to dilute the salinity; (2) increased evaporation, which concentrates the salts left in the lake water; (3) reduced surface discharge from the lake as its surface elevation falls below the elevation of the outlet, which removes dissolved mass from the lake.

Evaluation of groundwater flow regime at a landfill with liner system

Abstract The High Acres landfill is a 166‐acre (67‐ha) sanitary waste disposal site located southeast of Rochester, New York. The site consists of an existing 92‐acre (37‐ha) unlined landfill and a proposed 74‐acre (30‐ha) landfill expansion. To contain the leachate that may be produced at the new site, the construction of a liner system is proposed. According to regulations, the base of the landfill liner system is required to be above the seasonal high water‐table at the site. A multilayer aquifer model was used, therefore, (1) to simulate the mechanism by which groundwater moves through the High Acres site; and (2) to evaluate the average and seasonal high water‐table conditions at the site with and without the liner system. Based on these simulations, critical design aspects of the landfill liner system and its effect on the local groundwater flow regime is evaluated throughout the entire site.

Influence of Flow Regime on Life History, Production, and Genetic Structure of Baetis tricaudatus (Ephemeroptera) and Hesperoperla pacifica (Plecoptera)

Life histories, annual production, and genetic structure for two insect species were examined for two adjacent streams that differ in flow regime. Birch Creek had a mesic groundwater (seasonally constant) flow regime; Little Lost River had a snowmelt (seasonally cyclic) flow regime. Baetis tricaudatus was multivoltine, whereas Hesperoperla pacifica had a life cycle longer than one year. The life histories of B. tricaudatus were similar between streams, but mean biomass was greater in Birch Creek. Gene frequencies of B. tricaudatus also were similar between streams, Nei's genetic distance being only 0.011. Expected heterozygosities and population polymorphisms were higher in the Little Lost River. In contrast, the life histories of H. pacifica were different between streams, emergence being later in the Little Lost River. This difference could be explained by temperature. However, the genetic structure of H. pacifica showed the same pattern as B. tricaudatus with more polymorphisms and higher heterozygosities occurring in the Little Lost River. Nei's genetic distance between the H. pacifica populations was 0.054. These data support the idea that populations exhibit greater genetic variability in more variable environments than populations in relatively more constant environments.

Geochemistry of vanadium in an epigenetic, sandstone-hosted vanadium-uranium deposit, Henry Basin, Utah

The epigenetic Tony M vanadium-uranium orebody in south-central Utah is hosted in fluvial sandstones of the Morrison Formation (Upper Jurassic). Although the deposit is mined for uranium, vanadium has a higher average abundance in the ore. Thus, the geochemistry of vanadium in the orebody was studied to characterize ore-forming processes within the inferred ground-water flow regime. Measurements of the relative amounts of V (super +3) and V (super +4) in ore minerals show that V (super +3) is more abundant. Thermodynamic calculations show that vanadium was more likely transported to the site of mineralization as V (super +4) . The ore formed as V (super +4) was reduced by hydrogen sulfide, followed by hydrolysis and precipitation of V (super +3) in oxide minerals (e.g., montroseitc or paramontroseite) or chlorite. Uranium was transported as uranyl ion (U (super +6) ), or some complex thereof, and reduced by hydrogen sulfide, forming coffinite. Detrital organic matter in the rocks served as the carbon source for sulfate-reducing bacteria. It was this bacteriogenic H 2 S that reduced the metals in the mineralization process.Possible sources for the V and U in this deposit have been identified previously. Vanadium most likely was derived from the dissolution of iron-titanium oxides, which liberated Fe as well as V. A zone of titanium-rich remnants is observed updip and up the hydrologic gradient from the deposit (M. Goldhaber and R. L. Reynolds, unpub. data). Uranium probably was derived from the overlying Brushy Basin Member of the Morrison Formation (Northrop, 1982). A preliminary age date for the deposit of 115 Ma (K. Ludwig, 1986, pers. commun.) indicates that the ore formed after deposition of the Brushy Basin Member.Previous studies have shown that the ore formed at the density-stratified interface between a basinal brine and dilute meteoric water. The mineralization processes described above occurred within the mixing zone between these two fluids. Stable isotope analyses of ore-stage dolomite show a progressively heavier carbon and oxygen isotope signature with increasing depth through an ore horizon, consistent with the two-solution interface model.

Regional hydrogeology of the Silurian and Ordovician sedimentary rock underlying Niagara Falls, Ontario, Canada

Due to concern over the potential for widespread groundwater contamination in the sedimentary rock underlying the Niagara Falls area, this study was done to investigate the hydrogeology of the Silurian and Ordovician stratigraphy underlying the Upper Niagara River and the Eastern Niagara Peninsula. Seven boreholes (up to 150 m deep) were drilled, instrumented with multiple packer casing, tested for permeability, sampled for inorganic and organic solutes and monitored for hydraulic head to provide data for a conceptual model of regional groundwater flow. Results show that there are at least three distinct groundwater flow regimes in the bedrock. The uppermost regime consists of fracture zones in the Guelph and Lockport Formations, within which hydraulic conductivity, hydraulic head measurements and geochemical analyses indicate active groundwater circulation primarily discharging towards the Niagara Gorge and Escarpment. Underlying the Lockport Formation are an overpressured (high hydraulic head) regime in the Clinton-Upper Cataract-Lower Queenston Formation and an underpressured (low hydraulic head) regime in the Lower Cataract-Upper Queenston Formation. In both regimes, geochemical analyses and permeability measurements indicate very old and saline groundwater which probably has undergone minimal migration since pre-Pleistocene time. The implication based on the study so far, is that potential groundwater contamination below the bottom of the Lockport Formation is probably not significant in the Niagara Falls area except adjacent to the Niagara Gorge where vertical permeability in the lower flow regimes may be enhanced.

Flow regime associated with partially penetrating large-diameter wells in hard rocks

In case of a large-diameter well which penetrates an aquifer only partially, significant vertical flows may set in as a result of withdrawal from the well provided, of course, the vertical permeability below the well bottom is appreciable. A finite difference model of groundwater flow regime associated with a partially penetrating well in a hard rock terrain has been presented. Use of this model in the estimation of hydrogeological parameters in such a situation has been illustrated by a field example. The analysis of pump test data shows that parameter estimation will be in error if the vertical flows are neglected. The same model has also been used for prognosing the efficacy of a borewell in a large-diameter partially penetrating well to increase the yield.

Regional hydrogeology of agricultural drainage wells in Iowa

In Iowa, agricultural drainage wells (ADW9s) represent the largest deliberate transfer of degraded water into major aquifers. An estimated 700 ADW9s remove tile and surface waters from level farmland and inject it into underlying aquifers. Of 174 field-identified ADW9s, 165 were grouped into 3 clusters in north-central Iowa (17 in Floyd County, 44 in Wright County, and 104 in Humbolt-Pocahontas Counties). Geologically, most of the identified ADW9s penetrate the Des Moines glacial lobe and discharge into carbonate aquifers. These aquifers are in the intermediate ground-water flow regime, with recharge mainly from the overlying landscape and discharge mainly to rivers. A graphic flow net model indicates a progressive increase in recharge down gradient, providing increased dilution for contaminants. Modeling suggests that tile-line drainages have averaged about 10-12 ppm nitrate-N during the past decade, mostly derived from fertilizer applications. ADW effluents measured during Spring 1983 ranged between 10 and 20 ppm nitrate-N. Plumes associated with ADW9s would contain nitrate-N in concentrations approaching 20 ppm near the source, decreasing down gradient to 2-6 ppm with ground-water mixing. Joint and bedding-plane openings in the carbonate aquifer formations were measured in quarries, and the effective porosities were about 1%. If it is assumed that diffuse flow approximates isotropic and homogeneous conditions, ground-water flow velocities range from 500 to 26,000 ft/yr. Residence times for ground water in the carbonate aquifers range from a few months to a few decades, depending on the ground-water velocity and the length of individual flow paths.