Freshwater Recharge Research Articles

Composite Geochemical Database for Coalbed Methane Produced Water Quality in the Rocky Mountain Region

Coalbed methane (CBM) or coalbed natural gas (CBNG) is an unconventional natural gas resource with large reserves in the United States (US) and worldwide. Production is limited by challenges in the management of large volumes of produced water. Due to salinity of CBM produced water, it is commonly reinjected into the subsurface for disposal. Utilization of this nontraditional water source is hindered by limited knowledge of water quality. A composite geochemical database was created with 3255 CBM wellhead entries, covering four basins in the Rocky Mountain region, and resulting in information on 64 parameters and constituents. Database water composition is dominated by sodium bicarbonate and sodium chloride type waters with total dissolved solids concentrations of 150 to 39,260 mg/L. Constituents commonly exceeding standards for drinking, livestock, and irrigation water applications were total dissolved solids (TDS), sodium adsorption ratio (SAR), temperature, iron, and fluoride. Chemical trends in the basins are linked to the type of coal deposits, the rank of the coal deposits, and the proximity of the well to fresh water recharge. These water composition trends based on basin geology, hydrogeology, and methane generation pathway are relevant to predicting water quality compositions for beneficial use applications in CBM-producing basins worldwide.

Determination of processes affecting groundwater quality in the coastal aquifer beneath Puri city, India: a multivariate statistical approach

Variability of groundwater quality parameters is linked to various processes such as weathering, organic matter degradation, aerobic respiration, iron reduction, mineral dissolution and precipitation, cation exchange and mixing of salt water with fresh water. Multivariate statistical analyses such as principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to the standardized data set of eleven groundwater quality parameters (i.e. pH, Ca2+, Mg2+, Na+, K+, Fe3+, alkalinity, NO3-, Cl-, SO4(2-), TDS) collected during the post-monsoon and the summer seasons in order to elicit hydrologic and biogeochemical processes affecting water quality in the unconfined aquifer beneath Puri city in eastern India. The application of PCA resulted in four factors explaining 73% variance in post-monsoon and 81% variance in summer. The HCA using Ward's method and squared Euclidean distance measure classified the parameters into four clusters based on their similarities. PCA and HCA allowed interpretation of processes. During both post-monsoon and summer seasons, anthropogenic pollution and organic matter degradation/Fe(III) reduction were found dominant due to contribution from on-site sanitation in septic tanks and soak pits in the city. Cation exchange and mineral precipitation were possible causes for increase in Na+ and decrease in Ca2+ concentration in summer. Fresh water recharge during monsoon and Sea water intrusion in summer are attributed as significant hydrologic processes to variations of the groundwater quality at the study site.

A simulation‐optimization model to control seawater intrusion in coastal aquifers using abstraction/recharge wells

SUMMARYSeawater intrusion is one of the most serious environmental problems in many coastal regions all over the world. Mixing a small quantity of seawater with groundwater makes it unsuitable for use and can result in abandonment of aquifers. Therefore, seawater intrusion should be prevented or at least controlled to protect groundwater resources. This paper presents development and application of a simulation‐optimization model to control seawater intrusion in coastal aquifers using different management scenarios; abstraction of brackish water, recharge of freshwater, and combination of abstraction and recharge. The model is based on the integration of a genetic algorithm optimisation technique and a coupled transient density‐dependent finite element model. The objectives of the management scenarios include determination of the optimal depth, location and abstraction/recharge rates for the wells to minimize the total costs for construction and operation as well as salt concentrations in the aquifer. The developed model is applied to analyze the control of seawater intrusion in a hypothetical confined coastal aquifer. The efficiencies of the three management scenarios are examined and compared. The results show that combination of abstraction and recharge wells is significantly better than using abstraction wells or recharge wells alone as it gives the least cost and least salt concentration in the aquifer. The results from this study would be useful in designing the system of abstraction/recharge wells to control seawater intrusion in coastal aquifers and can be applied in areas where there is a risk of seawater intrusion. Copyright © 2011 John Wiley & Sons, Ltd.

Critical stress scenarios for a coastal aquifer in southeastern Italy

Abstract. Over the last years the sustainable management of coastal water resources has become strategic, especially in southern Salento Peninsula (Apulia), where mal-performing management strategies adopted, together with the vulnerability of the hydrogeological system, have given rise to the deterioration of groundwater quality due to saltwater intrusion. In the study area there is the presence of multilevel shallow aquifer and a deep aquifer that interact by means of faults. The geological system is highly vulnerable to seawater intrusion so there is the need to adopt management strategies to avoid seawater intrusion phenomena. Nevertheless there is a lack of studies that analyze the methodology for the correct exploitation if the water resource in order to avoid further intrusion phenomena. This paper combines a density-driven, flow numerical model (Seawat v.4) with a fault conceptual and hydrologic model to simulate saltwater intrusion phenomenon in the deep as well as in the shallow aquifer of the Salento area. By means of the individuation of an indicator parameter of groundwater quality, it has been possible to simulate different scenarios of exploitation and therefore to define critical stress scenarios for both aquifers. The results show that the deep aquifer is more vulnerable than the shallow one, which means that in the former, in order not to reach conditions of contamination, a lower density of wells is necessary than in the latter. The reduction of well density coupled with the artificial recharge of freshwater into the aquifer may be proposed as a solution strategy to protect the aquifer. Therefore, future developments of the present study will be represented by the simulation of different scenarios of recharging to inhibit the saltwater intrusion front further inland. The proposed methodology and its future developments can represent an empirical tool to provide preliminary guidelines for long-term groundwater management in coastal aquifers.

Coupled modeling of hydrogeochemical and electrical resistivity data for exploring the impact of recharge on subsurface contamination

The application of geophysical methods, in particular, electrical resistivity measurements, may be useful for monitoring subsurface contamination. However, interpreting geophysical data without additional data and without considering the associated hydrogeochemical processes is challenging since the geophysical response is sensitive to not only heterogeneity in rock properties but also to the saturation and chemical composition of pore fluids. We present an inverse modeling framework that incorporates the simulation of hydrogeochemical processes and time‐lapse electrical resistivity data and apply it to various borehole and cross‐borehole data sets collected in 2008 near the S‐3 Ponds at the U.S. Department of Energy's Oak Ridge Integrated Field Research Challenge site, where efforts are underway to better understand freshwater recharge and associated contaminant dilution. Our goal is to show that the coupled hydrogeochemical‐geophysical modeling framework can be used to (1) develop a model that honors all the available data sets, (2) help understand the response of the geophysical data to subsurface properties and processes at the site, and (3) allow for the estimation of petrophysical parameters needed for interpreting the geophysical data. We present a series of cases involving different data sets and increasingly complex models and find that the approach provides useful information about soil properties, recharge‐related transport processes, and the geophysical response. Spatial heterogeneity of the petrophysical model can be described sufficiently with two layers, and its parameters can be estimated concurrently with the hydrogeochemical parameters. For successful application of the approach, the parameters of interest must be sensitive to the available data, and the experimental conditions must be carefully modeled.

Time-lapse resistivity investigation of salinity changes at an ex-promontory land: a case study of Carey Island, Selangor, Malaysia

Time-lapse resistivity measurements and groundwater geochemistry were used to study salinity effect on groundwater aquifer at the ex-promontory-land of Carey Island in Malaysia. Resistivity was measured by ABEM Terrameter SAS4000 and ES10-64 electrode selector. Relationship between earth resistivity and total dissolved solids (TDS) was derived, and with resistivity images, used to identify water types: fresh (ρ ( e ) > 6.5 Ω m), brackish (3 Ω m < ρ ( e ) < 6.5 Ω m), or saline (ρ ( e ) < 3 Ω m). Long-term monitoring of the studied area's groundwater quality via measurements of its time-lapse resistivity showed salinity changes in the island's groundwater aquifers not conforming to seawater-freshwater hydraulic gradient. In some aquifers far from the coast, saline water was dominant, while in some others, freshwater 30 m thick showed groundwater potential. Land transformation is believed to have changed the island's hydrogeology, which receives saltwater pressure all the time, limiting freshwater recharge to the groundwater system. The time-lapse resistivity measurements showed active salinity changes at resistivity-image bottom moving up the image for two seasons' (wet and dry) conditions. The salinity changes are believed to have been caused by incremental tide passing through highly porous material in the active-salinity-change area. The study's results were used to plan a strategy for sustainable groundwater exploration of the island.

Large-scale tracer profiles in a deep claystone formation (Opalinus Clay at Mont Russelin, Switzerland): Implications for solute transport processes and transport properties of the rock

Natural tracers (Cl − and stable water isotopes) in pore water of the Opalinus Clay and adjacent formations were studied in the motorway tunnel at Mont Russelin, Switzerland. The Opalinus Clay occurs in the core of an anticline which is cut by a complex system of thrust faults. Concentration profiles of natural tracers were taken from 17 boreholes along a 363 m long section. Pore waters of drillcore samples were analysed with indirect and direct methods. The Cl − and stable water isotope distribution in the pore water shows a regular and well defined profile, with a conspicuous decrease towards the overlying Dogger limestone aquifer. The highest Cl − values (approximately 23,000 mg/L) are found in the core of the anticline in Liassic claystones underlying the Opalinus Clay. To quantify the large-scale transport properties of the Opalinus Clay formation, a 2D transport model was constructed and used to reproduce the observed concentration profiles. The calculations indicate that the observed tracer distributions are consistent with diffusion as the dominant transport process. Groundwater flow in the overlying Dogger aquifer was initiated about 2–4 Ma ago, which is long after the folding of the Jura Mountains and probably coincides with the exposure of the aquifer to freshwater recharge following continued erosion of the anticline. The calculations suggest that tracer distributions are controlled by 1) the timing of freshwater recharge in the overlying limestone aquifer, 2) the shape of the anticline and 3) the magnitude and the anisotropy ratio of diffusion coefficients.

Quantifying Data Worth Toward Reducing Predictive Uncertainty

The present study demonstrates a methodology for optimization of environmental data acquisition. Based on the premise that the worth of data increases in proportion to its ability to reduce the uncertainty of key model predictions, the methodology can be used to compare the worth of different data types, gathered at different locations within study areas of arbitrary complexity. The method is applied to a hypothetical nonlinear, variable density numerical model of salt and heat transport. The relative utilities of temperature and concentration measurements at different locations within the model domain are assessed in terms of their ability to reduce the uncertainty associated with predictions of movement of the salt water interface in response to a decrease in fresh water recharge. In order to test the sensitivity of the method to nonlinear model behavior, analyses were repeated for multiple realizations of system properties. Rankings of observation worth were similar for all realizations, indicating robust performance of the methodology when employed in conjunction with a highly nonlinear model. The analysis showed that while concentration and temperature measurements can both aid in the prediction of interface movement, concentration measurements, especially when taken in proximity to the interface at locations where the interface is expected to move, are of greater worth than temperature measurements. Nevertheless, it was also demonstrated that pairs of temperature measurements, taken in strategic locations with respect to the interface, can also lead to more precise predictions of interface movement.

Freshwater recharge into a shallow saline groundwater system, Cooper Creek floodplain, Queensland, Australia

Freshwater lenses have been identified as having penetrated the shallow regional saline groundwater beneath the Cooper Creek floodplain near Ballera (south-west Queensland). Piezometers were installed to evaluate the major-element chemistry along a floodplain transect from a major waterhole (Goonbabinna) to a smaller waterhole (Chookoo) associated with a sand dune complex. The floodplain consists of 2-7m of impermeable mud underlain by unconsolidated fluvial sands with a saline watertable. Waterholes have in places scoured into the floodplain. The transect reveals that groundwater recharge takes place through the base of the waterholes at times of flood scour, but not through the floodplain mud. Total dissolved solids rise with distance from the waterhole and independently of the presence of sand dunes. Stable water isotopes (δ2H and δ18O) confirm that recharge is consistent with, and dependant on, monsoonal flooding events. Following floods, the waterholes self-seal and retain water for extended periods, with sulfate-δ34S and δ18O isotopes suggesting bacterial reduction processes within the hyporheic zone, and limited interaction between the surface water and groundwater during no-flow conditions. The area occupied by the freshwater lenses (TDS <5000 mg/L) is locally asymmetrical with respect to the channel flow direction, extending down gradient along distances of ∼300 m.

Assessing environmental flow requirements and trade-offs for the Lower Zambezi River and Delta, Mozambique

The Zambezi Delta is vital to Mozambique's national economy and is a Wetland of International Importance. Large dams in the Zambezi catchment have substantially altered the magnitude, timing, duration, and frequency of flooding events in the delta, resulting in adverse ecological and socio-economic changes. We evaluated conflicts/trade-offs among various water uses and the potential for improving delta conditions through environmental flow releases from Cahora Bassa Dam, using the downstream response to imposed flow transformations (Brown, C.A. and Joubert, A., 2003. Using multicriteria analysis to develop environmental flow scenarios for rivers targeted for water resource development. Water SA, 29 (4), 365–374; King, J.M., Brown, C.A., and Sabet, H., 2003. A scenario-based holistic approach to environmental flow assessments for regulated rivers. Rivers Research and Applications, 19 (5–6), 619–640) model. Five variations in low flows, 18 alternatives for annual floods, and one extreme (1:5 year) flood were considered for a range of uses/concerns, including commercial and small-scale agriculture, estuarine ecology, coastal and freshwater fisheries, livestock, large mammals, waterbirds, vegetation, invasive species, natural resources, water quality, navigation, and groundwater recharge. The study revealed minimal trade-offs among different uses with regard to reinstating environmental flows. The majority of user-representatives perceive reinstatement of the annual flood to be beneficial and the perceived benefits increase with increased magnitude and prolonged duration, provided the timing of the annual flood occurs during the normal wet season. Simulation modelling of the Zambezi system dam operation indicates that these environmental flow releases can be realized within the constraints of firm power commitments and total energy demand. Of the 18 annual flood change levels considered, 7 can be generated with a firm power reliability >95% and hydropower reductions of <2.3%, and 16 require <10% reduction in annual energy production. This work illustrates the potential for environmental flows to overcome conflict in shared water resources and create opportunities for cooperation.

Chemical and isotopic indicators of groundwater evolution in the basal sands of a buried bedrock valley in the midwestern United States: Implications for recharge, rock-water interactions, and mixing

Buried bedrock valley aquifers can be found throughout Canada and the northern United States where glacial deposits have filled in previously exposed bedrock valleys. The Mahomet bedrock valley is an east-west–trending buried valley in central Illinois containing basal Pleistocene sands and gravels making up the Mahomet aquifer and the contemporaneous Sankoty Mahomet aquifer, which are the major sources of freshwater for east-central Illinois. The hydrochemical characteristics of the Mahomet and Sankoty Mahomet aquifers change significantly across the buried bedrock valley. To determine the geochemical processes controlling the chemistry of the water, possible groundwater mixing, and the regions of major recharge, over 80 samples from the Mahomet aquifer, the Sankoty Mahomet aquifer, and shallower aquifers were analyzed for their chemical and isotopic composition, including δ 18 O, δD, δ 13 C, δ 34 S, 14 C, and 3 H. Four geochemical regions were observed across the aquifers. The central and eastern region of the Mahomet aquifer had dilute chemistry and medium 14 C activities, suggesting relatively recent recharge from the surface. The northeastern Mahomet aquifer region had variable sulfate and δ 34 S values, medium chloride concentrations, and low 14 C activity, suggesting mixing with bedrock groundwater along with sulfate reduction. The western Mahomet aquifer region had the highest chloride, dissolved organic carbon, and methane concentrations and showed a continuous decrease in 14 C activity, suggesting seepage from bedrock units, strong reducing conditions, and isolation from surficial recharge. Characteristics of the Sankoty Mahomet aquifer indicated rapid freshwater recharge and mixing with western Mahomet aquifer water. The δD and δ 18 O values indicated little to no Pleistocene water in the Mahomet bedrock valley aquifer system, suggesting an age limit of ca. 11,000 yr B.P. for most of the groundwater. The tritium data indicated modern recharge in some shallower aquifers, but little to none in the Mahomet aquifer and Sankoty Mahomet aquifer, except near a river where stacked sands may have created a hydrologic window to the Mahomet aquifer. It appears that most of the Mahomet aquifer is well protected from surficial contamination. The approach used in this study enabled us to better understand and identify the processes that control the groundwater chemistry within the buried Pliestocene aquifer in central Illinois; processes that may be prevalent in other buried bedrock valley aquifers distributed throughout much of North America.

Long-term persistence of oil from the Exxon Valdez spill in two-layer beaches

Oil spilt from the tanker Exxon Valdez more than 20 years ago still persists in the gravel beaches of Prince William Sound, Alaska. Field data and numerical modelling indicate that some of the oil was trapped in the anoxic environment of the lower layers of the beaches when the water table was low. Oil spilled from the tanker Exxon Valdez in 1989 (refs 1, 2) persists in the subsurface of gravel beaches in Prince William Sound, Alaska. The contamination includes considerable amounts of chemicals that are harmful to the local fauna3. However, remediation of the beaches was stopped in 1992, because it was assumed that the disappearance rate of oil was large enough to ensure a complete removal of oil within a few years. Here we present field data and numerical simulations of a two-layered beach with a small freshwater recharge in the contaminated area, where a high-permeability upper layer is underlain by a low-permeability lower layer. We find that the upper layer temporarily stored the oil, while it slowly and continuously filled the lower layer wherever the water table dropped below the interface of the two layers, as a result of low freshwater recharge from the land. Once the oil entered the lower layer, it became entrapped by capillary forces and persisted there in nearly anoxic conditions that are a result of the tidal hydraulics in the two-layered beaches. We suggest that similar dynamics could operate on tidal gravel beaches around the world, which are particularly common in mid- and high-latitude regions4,5, with implications for locating spilled oil and for its biological remediation.

Evaluation of climate change effects in a coastal aquifer in Morocco using a density-dependent numerical model

A density-dependent numerical groundwater model was applied to study the climate change impact in a shallow aquifer in the Mediterranean coast of Morocco, the Saïdia aquifer. The stresses imposed to the model were derived from the IPCC emission scenarios and included recharge variation and sea level rise. The main effect of the climate change in the Saïdia aquifer will be a decrease in renewable resources, which in the worst-case scenario may decrease to 50–60% of present-day values, due to the decline in recharge and to a reduced inflow from the adjacent Triffa aquifer. The water quality will be affected mostly in the area immediately adjacent to the seashore, where salinity may increase up to 30 g/l. Localised areas may see a decrease in salinity due to the induced freshwater recharge from Oued Moulouya River and diminished inflow from high-salinity springs.

Hydrogeochemical considerations about the origin of groundwater salinization in some coastal plains of Elba Island (Tuscany, Italy)

Several coastal plains of the Elba Island (Marina di Campo, Portoferraio, Schiopparello, Mola, Porto Azzurro and Barbarossa plains) in Tuscany (Italy) were studied to determine the causes of decline in groundwater quality, using major ion chemistry to establish the causes of groundwater salinization. The study demonstrates that salinization of coastal plain alluvial aquifers is not simply linked to seawater intrusion but is also intimately related to inflows from adjacent aquifers. Ionic ratios, correlation graphs and distribution value maps were employed as the means to understand the hydrochemistry of the study areas. The Mg/Cl ratio in particular can be considered a good tracer to distinguish the main salinization processes that control groundwater chemistry. Seawater intrusion only partly determines the chemistry of some groundwaters, which generally belong to a chloride facies where the salinity is derived principally from freshwater-seawater mixing and the participation of cation exchange. Proceeding inland groundwater quality seems to be principally determined by the inflow of Mg, Ca-HCO(3) or Ca, Na-HCO(3) waters formed from the weathering of silicate minerals in adjoining aquifers. Hydrolysis of these minerals is of prime importance in controlling groundwater chemistry in adjacent alluvial plains. The lateral recharge flows introduce water with a different chemical composition and this variable of freshwater recharge changes the hydrochemistry as a result of mixing between two or more waters types. This situation is further complicated when seawater and base exchange reactions participate, due to seawater intrusion.

Variable gas saturation in coalbed methane reservoirs of the Black Warrior Basin: Implications for exploration and production

Gas saturation is highly variable in Carboniferous coalbed methane reservoirs of the Black Warrior Basin (USA), and diverse geologic data derived from more than three decades of exploration and development provides insight into the origin of this variability and the consequences for production performance. Coalbed methane is produced from numerous thin (∼ 0.3 to < 4 m) coal seams that are distributed through 700 to 1200 m of stratigraphic section. Gas content tends to increase with depth, and gas saturation typically ranges from < 10 to > 95%. Importantly, this range of variation is commonly developed among closely spaced seams within the same well. Exploration has to date been successful where coal seams are in the thermogenic gas window. Geochemical evidence indicates that thermogenic gases have been altered by subsurface water movement and may have been augmented with late-stage biogenic gases, particularly in areas affected by fresh-water recharge. Adsorption isotherms of coal samples in the Black Warrior Basin typically have Langmuir volume between 15 and 30 cm3/g and Langmuir pressure between 2 and 6 MPa. Both Langmuir pressure and Langmuir volume correlate significantly with coal rank. In deep, normally pressured coal beds where reservoir pressure is substantially above Langmuir pressure, even a small degree of undersaturation can necessitate prolonged dewatering before a large reservoir volume can reach the critical desorption pressure. Permeability, moreover, decreases exponentially with depth, which can make dewatering coal seams deeper than 800 m difficult. Where reservoir pressure is relatively low, however, isotherm geometry indicates that significantly undersaturated reservoirs can be near the critical desorption pressure. Consequently, areas of underpressure favor high gas production along with minimal water production.

Monitoring the saltwater intrusion by time lapse electrical resistivity tomography: The Chioggia test site (Venice Lagoon, Italy)

Abstract A novel experiment of time lapse electrical resistivity tomography (TL-ERT) aimed at monitoring the dynamics of the saltwater intrusion in the coastland bounding the southern Venice Lagoon is presented. A dedicated apparatus was developed and operated for about 9 months from November 2005. The system acquired ten resistivity tomograms per day, five of which with high resolution by a 97.5 m long and 2.5 m electrode spacing ERT line, and five by a 300 m long and 5 m electrode spacing line down to 50–60 m depth. The stratigraphy of a 50 m deep borehole drilled in the nearby of the ERT-TL alignment outlines the presence of a shallow phreatic aquifer in the shallower 12 m thick unit, followed by a semi-confined aquifer between 18 and 38 m depth and a locally confined aquifer down to the bottom. The shallow aquifer is the most contaminated by the salt intrusion with a minimum value of the formation resistivity equal to 1.0 ohm m corresponding to a salinity of 25–30 gr/l. A seasonal resistivity fluctuation is observed, with the saltwater front that intrudes landward during the autumn–winter season and moves back seaward in spring–summer. The first semi-confined aquifer is characterized by resistivity value of about 5 ohm m, while the confined aquifer is less contaminated showing resistivity values greater than 7.5 ohm m. For both the two confined aquifers the resistivity value rises at the beginning of the summer probably due to the seasonal fresh water recharge supplied regionally from the mainland. The TL-ERT data have been correlated with a number of environmental variables. A relationship is found between the resistivity in the upper 3–4 m of the phreatic aquifer and the rainfalls, and between the water level in the adjacent main channel and the resistivity down to about 10 m depth. With respect to the tidal regime, a daily/weekly correlation with resistivity changes is not evidenced, while a significant negative correlation coefficient exists at monthly to seasonal time scale for depths below 15 m. This experience suggests that TL-ERT is a powerful technique to perform multi-scale contaminant monitoring at different time scales.

Hydrogeochemical Modeling for Natural Analogue Study of CO2 Leakage due to Matsushiro Earthquake Swarm

Abstract For natural analogue study of CO2 leakage, the Matsushiro field in central Japan was selected to investigate hydrogeochemical behavior due to CO2 leakage from a fault zone during the period of the Matsushiro Earthquake Swarm between 1965 and 1967. One of the main objectives of the modeling study is to understand effects of hydrogeological characteristics of shallow aquifers and seal mechanism due to mineral precipitation in a fault zone. Reactive geochemical transport simulations were carried out using TOUGHREACT. Based on the historical data including discharge rate, chemical composition of water and seismic activity, we developed a numerical model to reproduce the geochemical behavior during and after the swarm earthquakes. A two-dimensional model (2000 m×1800 m) for the fault zone using the Multiple Interacting Continua (MINC) method was set up to evaluate geochemical effects during degassing and mixing of brine upwelling along the fault zone. The simulation results can capture the observed trend at the Matsushiro field. Supercritical and gaseous CO2 occur in the deep and the shallow fracture zones, respectively. During the earthquake swarm, CO2 saturated brine moves up along the fracture zone and CO2 degassing occurs in the shallow zone. Subsequently, water pH increases and a small amount of calcite precipitates. Lateral groundwater flow in shallow aquifers, which transports the CO2 away from the fault zone, makes CO2 surface discharge small. At the same time, calcite dissolves after the swarm due to lateral fresh water recharge. The result is consistent with the fact that no calcite observed in the core from the 80 m borehole drilled during the course of this study, indicating that CO2 discharge is likely affected by lateral shallow groundwater flow. Measurements of surface CO2 flux and soil gas δ 13 C indicated that little seepage of CO2 occurs in the area of the fan deposits at present, 40 years after the earthquake swarm. Using the same model, long term leakage simulations (if supercritical CO2 leaked along fault zone from the storage reservoir) were carried out to test whether CO2 surface leakage occurs or not. Two simulations were performed, with CO2 upflow rates of 50,000 and 100,000 kg/year in an area of 25 m×25 m. CO2 surface leakage does not occur in the first case, while CO2 leakage occurs in the second case. CO2 surface leakage is reduced because CO2 dissolves in groundwater flowing laterally in shallow aquifer. These simulations indicate that it is important to understand hydrogeological characteristics of aquifers underlain by reservoir as well as cap rocks.

Multi-disciplinary modeling, in stratigraphy and groundwater stratigraphy of the Jordan River basin

The study area is located along the Dead Sea Rift, the climate is considered arid in its southern margin near the Dead Sea, which is the lowest water reservoir found on the globe (412 m BSL), to semiarid in its northern part. During the last few decades, the water resources became depleted limiting the natural development of the agricultural settlements, which are the most common type of communities in the region. Previous studies suggested that a large amount of freshwater is lost as the result of salinization processes, which occur when fresh groundwater from the mountain aquifers, flow into the saline clastic Neogene aquifer complex. In order to comprehend this complex system, a detailed outlining of the regional hydrogeological system is essential. Since there are no boreholes, which penetrate the aquiferous rock sequences within the Rift, it was necessary to interpolate a large variety of data from several fields of geosciences. The methods applied included geological mapping, geophysical modeling based on interpretation of seismic profiles and geochemical modeling based on chemical and isotopic analysis of runoff, sediments and groundwater. The combined modeling based on results from the different types of analyses implied to several conclusions relevant to the regional water management policy: (1) groundwater becomes saline as it flows from the margins of the Rift to its center. Therefore, it is recommended to exploit it along the foothills of the rift escarpment. (2) Geophysical modeling indicated that the foothills and the Karstic mountain aquifer extend into the subsurface of the valley and can be farther exploited (up to 15 mm3 per annum) by relatively shallow wells. (3) Several mechanisms of groundwater salinization were deciphered: (a) the dense vertical faulting systems act as potential conduits for saline water, which flow-up from deep-seated sources and penetrate into the fresh aquifers. (b) Fresh groundwater in the clastic aquifer complex is rare, furthermore, two evaporates bodies were encountered (Auja and Zaharat el Qurein), also acting as sources for fresh water salinization. (c) Although the quantity of runoff recharge to the Jordan Valley aquifer complex is negligible, the increase in its salt-content (TDS) turns this negligible freshwater recharge to a significant contributor of salts.

The effect of Dead Sea level fluctuations on the discharge of thermal springs

Shalev, E. and Yechieli, Y. The effect of Dead Sea level fluctuations on the dis charge of thermal springs. Isr. J. Earth Sci. 56: 19–27. Thermal springs along the Dead Sea shore have been known to exist long before the great recession of the Dead Sea of the last 40 years. This work studies a possible mechanism that drives the brine discharge along the Dead Sea shore and the effect of the lake level fluctuations on the discharge. The Goldschmidt model suggested for the discharge of the springs at the Sea of Galilee cannot explain the discharge of the springs at the Dead Sea shore. Results from numerical modeling indicate that at steady state conditions the Dead Sea brine sinks through faults, migrates across tilted blocks, and then ascends back to the Dead Sea shore with fresh groundwater. The most signifi cant change in brine discharge is caused by water level changes in the lake. A recession of the Dead Sea causes a significant increase in brine spring discharge. As the Dead Sea level drops it interrupts the steady-state conditions. Since the groundwater was in equilibrium with a higher lake level, it now flows upwards to the lower lake level, reducing the overall hydraulic head. A rise of the Dead Sea level causes a decrease or even disappearance of the thermal spring discharge. An increase in the freshwater recharge in the mountain area causes negligible changes in this brine circulation.

Hydrology and subsurface transport of oil-field brine at the U.S. Geological Survey OSPER site “A”, Osage County, Oklahoma

Spillage and improper disposal of saline produced water from oil wells has caused environmental damage at thousands of sites in the United States. In order to improve understanding of the fate and transport of contaminants at these sites, the U.S. Geological Survey carried out multidisciplinary investigations at two oil production sites near Skiatook Lake, Oklahoma. As a part of this effort, the hydrology and subsurface transport of brine at OSPER site “A”, a tank battery and pit complex that was abandoned in 1973, was investigated. Based on data from 41 new boreholes that were cored and completed with monitoring wells, a large (∼200 m × 200 m × 20 m) plume of saline ground water was mapped. The main dissolved species are Na and Cl, with TDS in the plume ranging as high as 30,000 mg/L. Analysis of the high barometric efficiency of the wells indicated a confined aquifer response. Well-slug tests indicated the hydraulic conductivity is low (0.3–7.0 cm/day). Simplified flow and transport modeling supports the following conceptual model: (1) prior to the produced water releases, recharge was generally low (∼1 cm/a); (2) in ∼60 a of oil production enough saline produced water in pits leaked into the subsurface to create the plume; (3) following abandonment of the site in 1973 and filling of Skiatook Reservoir in the mid-1980s, recharge and lateral flow of water through the plume returned to low values; (4) as a result, spreading of the brine plume caused by mixing with fresh ground water recharge, as well as natural attenuation, are very slow.