Principal Aquifer Research Articles

Strategic groundwater resources in the Tagliamento River basin (northern Italy): hydrogeological investigation integrated with geophysical exploration

The western sector of the Tagliamento River basin (Friuli Venezia-Giulia Region; northern Italy) is characterized by important water resources, both superficial and underground. In particular, in the Quaternary deposits of the plain, up to a depth of 500 m, six artesian aquifer systems exist. A large amount of lithological, geomorphological, and hydrogeological data is presented, allowing for definition of (a) the principal aquifer system of the area to a depth of about 500 m; (b) geometrical characteristics of the aquifers (thickness, lateral extension, etc); (c) the hydraulic parameters (hydraulic conductivity, transmissivity); (d) chemico-physical characteristics of the water; and (e) vulnerability to pollution of the aquifer systems. In a test area, where many boreholes were drilled for fresh water supply, the conceptual hydrogeological model was integrated by a detailed and repeated three-dimensional (3D) resistivity survey using combined electrical resistivity tomography (ERT) and time-domain electromagnetic (TDEM) soundings. ERT investigation was mainly used to get detailed information about geometry and porosity of the overburden and to calibrate the shallowest TDEM information.

Source and transport controls on the movement of nitrate to public supply wells in selected principal aquifers of the United States

In 2003–2005, systematic studies in four contrasting hydrogeologic settings were undertaken to improve understanding of source and transport controls on nitrate movement to public supply wells (PSW) in principal aquifers of the United States. Chemical, isotopic, and age tracer data show that agricultural fertilizers and urban septic leachate were the primary sources of large nitrate concentrations in PSW capture zones at Modesto, California (Central Valley aquifer system) and York, Nebraska (High Plains aquifer). Urban septic leachate and fertilizer (possibly nonfarm) were the primary sources of large nitrate concentrations in PSW capture zones at Woodbury, Connecticut (glacial aquifer system), and Tampa, Florida (Floridan aquifer system), respectively. Nitrate fluxes to the water table were larger in agricultural settings than urban settings, indicating that it would be beneficial to reduce PSW capture zone areas in agricultural regions. Mixing calculations indicate that about 50 to 85% of the nitrate in water from the PSW could be from those modern anthropogenic sources, with the remainder coming from sources in old (>50 years) recharge or sources in young recharge in undisturbed settings such as forests. Excess N2 concentrations and age tracers showed that denitrification at Modesto occurred gradually (first‐order rate constant of 0.02/a) in a thick reaction zone following a ∼30‐year lag time after recharge. Denitrification generally was not an important nitrate sink at Woodbury. At York and Tampa, denitrification occurred rapidly (0.5 to 6/a) in thin reaction zones in fine‐grained sediments that separated the anoxic PSW producing zones from overlying oxic, high‐nitrate ground water. Particle tracking showed that a major pathway by which anthropogenic nitrate reached the York and Tampa PSW was by movement through long well screens crossing multiple hydrogeologic units (York) and by movement through karst features (Tampa), processes which reduced ground water residence times in the denitrifying zones. These results illustrate how PSW vulnerability to nitrate contamination depends on complex variations and interactions between contaminant sources, reaction rates, transit times, mixing, and perturbation of ground water flow in contrasting hydrogeologic settings.

Redox Processes and Water Quality of Selected Principal Aquifer Systems

Reduction/oxidation (redox) conditions in 15 principal aquifer (PA) systems of the United States, and their impact on several water quality issues, were assessed from a large data base collected by the National Water-Quality Assessment Program of the USGS. The logic of these assessments was based on the observed ecological succession of electron acceptors such as dissolved oxygen, nitrate, and sulfate and threshold concentrations of these substrates needed to support active microbial metabolism. Similarly, the utilization of solid-phase electron acceptors such as Mn(IV) and Fe(III) is indicated by the production of dissolved manganese and iron. An internally consistent set of threshold concentration criteria was developed and applied to a large data set of 1692 water samples from the PAs to assess ambient redox conditions. The indicated redox conditions then were related to the occurrence of selected natural (arsenic) and anthropogenic (nitrate and volatile organic compounds) contaminants in ground water. For the natural and anthropogenic contaminants assessed in this study, considering redox conditions as defined by this framework of redox indicator species and threshold concentrations explained many water quality trends observed at a regional scale. An important finding of this study was that samples indicating mixed redox processes provide information on redox heterogeneity that is useful for assessing common water quality issues. Given the interpretive power of the redox framework and given that it is relatively inexpensive and easy to measure the chemical parameters included in the framework, those parameters should be included in routine water quality monitoring programs whenever possible.

Groundwater interaction in the coastal environment: hydrochemical, electrical and seismic approaches

The heterogeneous Plio-Quaternary coastal aquifer of the Mamora Basin is the most significant reservoir of Morocco. It is composed of sandstones, conglomerates, limestones and more or less argillaceous sands. The increase in the requirements for water in this area requires further information on the relations between the geometry of the aquifer and the salinity of the water. A hydrochemical analysis was undertaken and highlighted three zones of high mineralization. A geophysical approach allowed the determination of the principal aquifer levels, the localization of the various types of water (fresh, brackish and salt) and the geometry of the aquifer base. The results obtained by these two approaches provide a better image of the phenomena governing the groundwater flows and their interactions

Development and Implementation of a Bayesian-based Aquifer Vulnerability Assessment in Florida

The Florida Aquifer Vulnerability Assessment (FAVA) was designed to provide a tool for environmental, regulatory, resource management, and planning professionals to facilitate protection of groundwater resources from surface sources of contamination. The FAVA project implements weights-of-evidence (WofE), a data-driven, Bayesian-probabilistic model to generate a series of maps reflecting relative aquifer vulnerability of Florida’s principal aquifer systems. The vulnerability assessment process, from project design to map implementation is described herein in reference to the Floridan aquifer system (FAS). The WofE model calculates weighted relationships between hydrogeologic data layers that influence aquifer vulnerability and ambient groundwater parameters in wells that reflect relative degrees of vulnerability. Statewide model input data layers (evidential themes) include soil hydraulic conductivity, density of karst features, thickness of aquifer confinement, and hydraulic head difference between the FAS and the watertable. Wells with median dissolved nitrogen concentrations exceeding statistically established thresholds serve as training points in the WofE model. The resulting vulnerability map (response theme) reflects classified posterior probabilities based on spatial relationships between the evidential themes and training points. The response theme is subjected to extensive sensitivity and validation testing. Among the model validation techniques is calculation of a response theme based on a different water-quality indicator of relative recharge or vulnerability: dissolved oxygen. Successful implementation of the FAVA maps was facilitated by the overall project design, which included a needs assessment and iterative technical advisory committee input and review. Ongoing programs to protect Florida’s springsheds have led to development of larger-scale WofE-based vulnerability assessments. Additional applications of the maps include land-use planning amendments and prioritization of land purchases to protect groundwater resources.

Afghanistan: An Overview of Ground Water Resources and Challenges

Afghanistan: An Overview of Ground Water Resources and Challenges

Geochemical evidences of landfill leachate in groundwater

To evaluate the environmental risks associated with leachate flowing into groundwater resources, in the present research, a hydrogeological and geochemical monitoring of the two principal aquifer systems developed below the landfill of Sant'Agostino (Ferrara Province, Northern Italy) was performed. Several stratigraphic columns and penetrometric tests have been analysed in order to reconstruct in detail a lithological and hydrogeological model of the underground. The integrated elaboration of the data allowed to obtain information and to make inferences on i) the influence of the landfill on the contamination of the underground resources (high concentration in the same elements, like Cl, Al, Zn, Pb, Cr, Ni); ii) the contribution of the frequency in lithological variability (sand–peat–clay) on the propagation process of the contaminant elements on the aquifer system; iii) the importance of the position of the monitoring network on the identification of the pollution process and the protection of the water resources.

Coupled fluid flow, heat and mass transport, and erosion in the Alberta basin: implications for the origin of the Athabasca oil sands

Regional topography-driven flow systems related to Laramide tectonic rebound were simulated using two-dimensional, coupled fluid-flow, heat transport, and solute transport numerical models to replicate present formation water salinity and temperature distributions and investigate the accumulation of the Athabasca oil sands. Previous modelling of this system was replicated, and it predicted repeated replacement of all basin formation water with freshwater during deposition of the oil sands due to high permeabilities. To match present Alberta basin temperature and salinity distributions, model hydrostratigraphy, permeabilities, and heat fluxes were adjusted. This revised model conducts fluids along the Mannville aquifer, rather than the Upper Devonian aquifer, and replicates present salinity distributions, assuming instantaneous uplift around 60 Ma. Fluid fluxes in principal aquifers decrease by two-orders of magnitude using new permeabilities, resulting in primarily conductive heat transport. Thus, genesis of the Athabasca oil sands cannot be explained by dissolved-phase petroleum transport due to low simulated fluxes. Model simulations representing constant erosion of a higher topographic gradient produce similar flow patterns, but fluid fluxes, temperatures and hydraulic heads uniformly decrease over 58 million years. Increased erosion rates in the last stage of simulations produce sub-hydrostatic pressures near the uplift, which trigger a flow reversal in the basin. Thinning of the capping Cretaceous aquitard and Mannville permeability distribution causes discharge in the vicinity of the Peace River, coincident with Peace River oil sands and solonetzic soil zones. Regional topography-driven flow gradually decays via diminishing fluid fluxes, underpressuring near the disturbed belt, and development of local flow sub-systems driven by small-scale relief.

Participatory groundwater management in Jordan: Development and analysis of options

Groundwater over-exploitation has been on the rise in Jordan. Competing demands have grown in the face of perennial water shortages, a situation which has been exacerbated by drought conditions in the past decade. This paper reports findings of a project in which management options to address over-exploitation were developed for one of Jordan’s principal aquifer systems, the Amman-Zarqa Basin. Options for addressing the situation were developed through a participatory approach that involved government officials and various public and private sector interest groups. Particular efforts were made to involve well irrigators, who are likely to be heavily impacted by the changes required to reduce groundwater pumping to a sustainable level. With information obtained from a rapid appraisal survey as well as from interviews with farmers, community groups, government officials, and technical experts, an extensive set of options was identified for evaluation. Based on integrated hydrogeologic, social, and economic analysis, five complementary management options were recommended for implementation. These included the establishment of an Irrigation Advisory Service, buying out farm wells, placing firm limits on well abstraction and irrigated crop areas, exchanging treated wastewater for groundwater, and measures to increase the efficiency of municipal and industrial water use. Various combinations and levels of these options were grouped in scenarios, representing possible implementation strategies. The scenarios were designed to assist decision makers, well owners and other stakeholders in moving gradually towards a sustainable abstraction regime. Social and economic aspects of each option and scenario were analyzed and presented to stakeholders, together with a summary of legal, institutional and environmental ramifications. Combining scientific analysis with a participatory approach in the Amman Zarqa Basin groundwater management was devised as a prototype to be used in the management of other groundwater basins in Jordan. This participatory management approach would also be useful in other parts of the world that are experiencing similar groundwater over-exploitation problems.

Fluids in sedimentary basins: an introduction

Understanding paleohydrologic systems in terms of basin evolution requires the integration of information derived from the sedimentology, stratigraphy, diagenesis and geology of basin-filling successions. Combination of these is prerequisite for realistic basin analysis and to guide any hydrologic or geochemical modeling. Ancient basins, in particular, represent systems that can record protracted burial histories, thereby constraining the composition of specific fluid events that normally affected vast areas. The papers in this volume are concerned with tracing the fluid history of several sedimentary basins. These papers, which were presented in a special session at the Geological Association of Canada and Mineralogical Association of Canada meeting in Calgary, Alberta, Canada in May 2000, illustrate some of the methods, techniques and approaches required to document significant fluid events in basins and how this information can be used in some cases to evaluate the economic potential of basins. The focus of these studies deals with the interaction between basinal fluids and both chemical and clastic sediments. Both types of sediments can act as principal aquifers or aquitards for fluids in basins because of their changing reactivity and permeability as basins evolve.

Using noble gases to investigate mountain-front recharge

Mountain-front recharge is a major component of recharge to inter-mountain basin-fill aquifers. The two components of mountain-front recharge are (1) subsurface inflow from the mountain block (subsurface inflow), and (2) infiltration from perennial and ephemeral streams near the mountain front (stream seepage). The magnitude of subsurface inflow is of central importance in source protection planning for basin-fill aquifers and in some water rights disputes, yet existing estimates carry large uncertainties. Stable isotope ratios can indicate the magnitude of mountain-front recharge relative to other components, but are generally incapable of distinguishing subsurface inflow from stream seepage. Noble gases provide an effective tool for determining the relative significance of subsurface inflow, specifically. Dissolved noble gas concentrations allow for the determination of recharge temperature, which is correlated with recharge elevation. The nature of this correlation cannot be assumed, however, and must be derived for the study area. The method is applied to the Salt Lake Valley Principal Aquifer in northern Utah to demonstrate its utility. Samples from 16 springs and mine tunnels in the adjacent Wasatch Mountains indicate that recharge temperature decreases with elevation at about the same rate as the mean annual air temperature, but is on average about 2 °C cooler. Samples from 27 valley production wells yield recharge elevations ranging from the valley elevation (about 1500 m) to mid-mountain elevation (about 2500 m). Only six of the wells have recharge elevations less than 1800 m. Recharge elevations consistently greater than 2000 m in the southeastern part of the basin indicate that subsurface inflow constitutes most of the total recharge in this area.

Geology and geochemistry of groundwater within the Taieri Basin, east Otago, New Zealand

The Taieri Basin, in east Otago, New Zealand, is a tectonic depression bounded in part by active faults. The basin is floored and surrounded by Otago Schist that is locally overlain by Cretaceous‐Tertiary sediments and volcanic rocks. Basin fill is predominantly Quaternary gravels, sands, and silts derived from the Otago Schist, and these sediments are at least 150 m thick in places. Aquifers are hosted in the Quaternary sediments, principally gravels and sands. A wedge of estuarine silts and sands (c. 8000–5000 yr BP) extends for 18 km to the downstream outlet of the basin, where it is 25 m thick. Irregularly interfingered fluvial gravels and sands, interbedded with silts, make up the principal aquifers at the upstream end of the basin. This complex fluvial sequence dips beneath the estuarine wedge. The estuarine wedge acts as a confining layer for groundwater in the underlying aquifers, and artesian water bores occur in the lower reaches of the basin. Alluvial fans on the western side of the basin are conduits for recharge from adjacent schist ranges. Alluvial fans on the southeastern side of the basin have their toes truncated by active faults, and recharge from these fans is structurally inhibited. Ca, Mg, and bicarbonate contents of Taieri Basin surface waters and groundwaters indicate chemical interaction with calcite and chlorite of Otago Schist, in basement and/or aquifer sediment clasts. All waters have Na and Cl− contents dominated by rainout of NaCl in marine aerosols. Surface waters have lower Na and Cl− than groundwaters. Numerical modelling of groundwater flow at the upstream end of the basin can reproduce field‐based inferences of flow patterns and together indicate southwestward flow beneath the estuarine wedge confining layer. This is significant because it implies low‐concentration NO3+NO2 contamination of shallow aquifers at the upstream end of the basin will be carried to groundwaters in the southwest.

Methods to determine storativity of infinite confined aquifers from a recovery test.

Starting from the equations of Theis and Cooper-Jacob, two new mathematical methods are proposed for interpreting the residual drawdown data for an infinite confined aquifer. Under Theis' assumptions and using the Cooper-Jacob approximation, the principal aquifer characteristics of transmissivity, pumping storativity, and recovery storativity are expressed without any correction or additional assumption. An actual case is used for illustration and confirms the validity of proposed equations and methods.

MOVEMENT OF LEACHATE FROM BENEATH TURKEY LITTER SITED OVER CHALK IN SOUTHERN ENGLAND

Farm waste stores are widespread in the UK, with many overlying the principal aquifer, the Chalk. The stores pose a threat to groundwater quality through the infiltration of high concentrations of nitrogen species and organic carbon together with pathogenic microbes. Two cored boreholes have been drilled into the unsaturated chalk to depths of 15 and 20 metres, respectively, through a site which has been used to store turkey litter for in excess of 20 years. Porewaters were extracted from the cores and analysed for a range of chemical elements. In addition, chalk core material was also taken for microbial examination. Both boreholes showed very high concentrations of nitrate-N (3000 mg/L), ammonia (5000 mg/L), organic carbon (3000 mg/L), and potassium (10,000 mg/L) in the top 5 metres of the profile. Below this depth concentrations declined dramatically. Highest concentrations were found in the borehole constructed in the middle of the site. The borehole constructed at the edge of the store showed much lower concentrations but did show a peak of nitrate around 10 metres below ground level. The apparent lack of movement beneath the centre of the store suggests the turkey litter is relatively impermeable and most leaching occurs where the covering of litter is thin or when the litter is annually cleared. If the leachate continues to migrate at this apparent rate, it will take more than 100 years to reach the water table.

The environmental hazards of locating wastewater impoundments in karst terrain

A wastewater storage lagoon failed due to the development of a sinkhole at a site in the Lehigh River valley in Allentown, Pennsylvania (PA). The polluted wastewater from the lagoon entered into the underlying aquifer and moved within a narrow pathway controlled by cracks, fissures, and solution channels within the karstified Allentown Formation of the Cambrian Period. The Allentown Formation serves as the principal aquifer for the public water supply of the area. To develop appropriate remedial measures, a thorough understanding of the geologic setting was required. Therefore, a geologic and hydrogeologic characterization of the area was completed, aerial photography and satellite imagery interpretations were performed, stratigraphic core holes were drilled and geophysically logged, and the data correlated to define structural control and movement of ground water and pollutants. A number of wells were drilled and constructed, and water levels were monitored on a continuous basis to correlate with climatic changes and determine the direction of flow. Water samples were collected periodically and analyzed to delineate the vertical and lateral extent of migration of pollutants. Five saturated (water-bearing) zones were identified within the bedrock based on the analysis of cores and interpretation of geophysical logs. Ground water in the lower zones is polluted; the concentration of pollution increases with depth. Monitoring stations were established in the creek, south of the site, to measure flow rate several times during different seasons, and at different reaches, to determine the losing and gaining sections of the creek. Pumping tests were conducted to determine hydraulic characteristics of the aquifer. Based on the hydrogeologic model of the karstified aquifer, flow regime and structural control, a plan of action was defined and initiated to remediate the aquifer. The ground water is being remediated using a pump and treat methodology. The cleanup effort is continuous and the pollutant level is fluctuating with an overall-declining trend. The application of this technology has also created a pressure trough, thereby controlling off the site migration of pollutants.

Hydrogeologic framework of Pico Island, Azores, Portugal

Pico, the youngest island of the Azores archipelago, is composed of basaltic volcanic deposits less than 300,000 years old. The principal aquifer system consists mainly of recent lava flows that are very permeable and whose head is influenced by tidal fluctuations. Groundwater abstraction is almost entirely by drilled wells. The hydraulic gradient is very low, about 10–4, which agrees with observations made on similar volcanic islands. Groundwater also occurs in perched-water bodies, but the spring discharge from them is very low, about 10–3 L/s.

Scheme for development of monitoring networks for springs in Bavaria, Germany

The present groundwater monitoring network in Bavaria consists mostly of wells and only a small number of natural groundwater springs, all of which are analyzed for mainly the common physical and chemical constituents in groundwater. In order to develop a long-term groundwater management plan for all the groundwater resources of Bavaria, the Bavarian State Office for Water Management intends to establish a separate spring-monitoring network throughout the 11 groundwater provinces of the state. As a first step, significant physicochemical parameters that show considerable annual fluctuation (after monitoring 1–3 years) were determined at 21 springs or spring systems to create a basic data set to guide future monitoring. A selection procedure was developed around four parameters: (1) geological units, which includes the principal aquifers; (2) rate of spring discharge; (3) land utilization within a catchment; and (4) approximate size of the subterranean catchment. However, in the initial phase of the study, only the first three parameters were investigated. These parameters established a matrix for evaluating each groundwater region of Bavaria to aid in the selection of additional springs for the proposed monitoring network.

Localized Sulfate‐Reducing Zones in a Coastal Plain Aquifer

AbstractHigh concentrations of dissolved iron in ground water of coastal plain or alluvial aquifers contribute to the biofouling of public supply wells for which treatment and remediation is costly. Many of these aquifers, however, contain zones in which microbial sulfate reduction and the associated precipitation of iron‐sulfide minerals decreases iron mobility. The principal water‐ bearing aquifer (Magothy Aquifer of Cretaceous age) hi Suffolk County, New York, contains localized sulfate‐redudng zones hi and near lignite deposits, which generally are associated with clay lenses. Microbial analyses of core samples amended with [14C]‐acetate indicate that microbial sulfate reduction is the predominant terminal‐electron‐accepting process (TEAP) in poorly permeable, lignite‐rich sediments at shallow depths and near the ground water divide. The sulfate‐reducing zones are characterized by abundant lignite and iron‐sulfide minerals, low concentrations of Fe(III) oxyhydroxides, and by proximity to clay lenses that contain pore water with relatively high concentrations of sulfate and dissolved organic carbon. The low permeability of these zones and, hence, the long residence time of ground water within them, permit the preservation and (or) allow the formation of iron‐sulfide minerals, including pyrite and marcasite. Both sulfate‐reducing bacteria (SRB) and iron‐reducing bacteria (IRB) are present beneath and beyond the shallow sulfate‐reducing zones. A unique Fe(HI)‐reducing organism, MD‐612, was found in core sediments from a depth of 187 m near the southern shore of Long Island. The distribution of poorly permeable, lignite‐rich, sulfate‐reducing zones with decreased iron concentration is varied within the principal aquifer and accounts for the observed distribution of dissolved sulfate, iron, and iron suit Ides in the aquifer. Locating such zones for the placement of production wells would be difficult, however, because these zones are of limited aerial extent.

The Dammam aquifer in Bahrain - Hydrochemical characterization and alternatives for management of groundwater quality

Over-abstraction of the Dammam aquifer, the principal aquifer in Bahrain, by the agricultural and domestic sectors, has led to its salinization by adjacent brackish and saline water bodies. A hydrochemical study identified the locations of the sources of aquifer salinization and delineated their areas of influence. The investigation indicates that the aquifer water quality is significantly modified as groundwater flows from the northwestern parts of Bahrain, where the aquifer receives its water by lateral underflow from eastern Saudi Arabia, to the southern and southeastern parts. Four types of salinization of the aquifer are identified: brackish-water up-flow from the underlying brackish-water zones in north-central, western, and eastern regions; seawater intrusion in the eastern region; intrusion of sabkha water in the southwestern region; and irrigation return flow in a local area in the western region. Four alternatives for the management of groundwater quality that are available to the water authorities in Bahrain are discussed and their priority areas are proposed, based on the type and extent of each salinization source, in addition to groundwater use in that area. The effectiveness of the proposed management options in controlling the degradation of water quality in the Dammam aquifer should be evaluated using simulation modeling.

Watershed Delineation and Ground Water Discharge to a Coastal Embayment

AbstractNonpoint source management strategies for watersheds to eutrophic coastal waters require an adequate characterization of subsurface hydrogeology to understand the sources and fate of ground water and contaminant flow. An investigation was conducted to define the watershed to Waquoit Bay, a shallow eutrophic coastal embayment at the margin of the sand and gravel aquifer of Cape Cod, Massachusetts. This investigation included: (1) the development of a subregional water table map over 56 square kilometers; (2) delineation of a watershed and subwatersheds by plotting reverse ground water flowpaths; (3) a water budget based on a mass balance between recharge rates over riverine watershed segments and measured stream flows; and (4) a series of well points driven beneath the bed of the embayment and a transect of deep geologic borings perpendicular to the shore to characterize submarine ground water and hydrogeologic conditions at depth. The principal aquifer thins from the apex of the watershed, where it is approximately 46 m thick, to approximately 11 m thick as it nears Waquoit Bay. The detailed water table map shows extremely high hydraulic gradients to the rivers and comparably smaller gradients near the bay, indicating the thinning aquifer forces ground water to discharge into the rivers and causes them to function as significant surface drains for the aquifer. A classic sharp salt water interface was found in the upper 11.3 m thick High K unit, while the interface in the lower 34 m thick Low K unit was estimated to extend 700 m from the shoreline beneath the saline water of the bay. Eighty‐nine percent (89%) of the bay water budget is from ground water flow (55% channeled into rivers and 34% direct ground water discharge), while 11% is from atmospheric deposition. The Low K unit is an insignificant source of fresh water to the embayment. The conceptual hydro‐geologic model of the watershed is consistent with the water table configuration and the mass balance water budget and was confirmed by subsurface characterization of the near shore hydrogeology. This type of watershed characterization provides a firm basis for the development of nonpoint source management options for coastal embayments.