Potable Water Aquifers Research Articles

Challenges and Possibilities in the Multi-Parameter Characterization Techniques for Enhanced Monitoring of CO2 in Geological Carbon Sequestration

Scientific investigations and observations show that carbon dioxide is a major contributor to the increasingly damaging effects of global warming. Thus, geological sequestration of carbon dioxide in saline aquifers is already in operations across the globe. However, geological carbon sequestration in an aquifer should be safeguarded from CO 2 leakage into the atmosphere and/or CO 2 migration into potable water aquifers that are also present in the subsurface. To promote safety of living and non-living species that are near and far from the geological sequestration sites, this work presents techniques for monitoring the greenhouse gas stored in geological porous media, using experiments and numerical simulation techniques. The work employed two-phase flow parameters like capillary pressure (P

Protection of transboundary aquifers of Međimurje County (Croatia): status and prospects

Međimurje County abounds in both potable and geothermal water aquifers. Owing to its position in the northernmost part of Croatia, it borders Slovenia and Hungary and shares these resources with them. Transboundary character of shallow alluvial aquifer has been demonstrated, while for deeper geothermal aquifers it can be supposed on the basis of hydrochemical and geological setting, but should be verified by more thorough research. In order to protect the transboundary aquifers, it is necessary to establish a wide cooperation of the three states. Pollution is the greatest threat to the potable water aquifer. Deep geothermal aquifers could be depleted through overpumping in the lack of trilateral consensus. Potable water aquifer receives multiple protective measures, but the geothermal aquifers are not investigated enough and receive no formal protection.

PH, geoelectrical and membrane flux parameters for the monitoring of water-saturated silicate and carbonate porous media contaminated by CO2

Characteristics of potable water aquifer contaminated by CO2 are investigated using well-defined laboratory experiments. The porous media domain was prepared with silica sand and limestone in separate experiments. The investigations used combinations of techniques to measure various parameters in the water-saturated porous media domain on which pressure of CO2 was imposed, under various conditions, which correspond to different geological depths. Measured parameters included the pH, geoelectrical parameters, and the diffusion of the CO2 gas through the water-saturated porous media domain using non-porous silicone rubber sheet. Experimental results revealed the existence of three stages in the profile of pH change with time as CO2 dissolved and diffused in the water-saturated porous media domain, which was composed of silica sand. The first stage was characterised by rapid decline in the pH. This is associated with quick dissolution of CO2 and the formation of carbonic acid together with bicarbonate. The second stage showed short rise in pH value, which was attributed to the reverse reaction, i.e., the formation of aqueous and gaseous CO2 and water from the carbonic acid. The third stage was that of the equilibrium in the forward and the reverse reactions, marked by steady state in pH value, which remained unchanged till the end of the experiment. The bulk electrical conductivity (σb) of the water-saturated porous domain increased in the presence of CO2. This is attributed to the formation of ionic species, especially bicarbonate, as CO2 dissolved in the domain. The rise in σb coincided with the first stage of the change in the pH of the system. In addition, the σb was higher in limestone than silica sand, and it increased with pressure of the domain. But, the bulk dielectric constant (εb) showed no change with the dissolution of the CO2 under different conditions. Furthermore, permeation of CO2 through the silicone rubber indicated the diffusion of the CO2 gas through the water-saturated domain. CO2 flux through the membrane was shown to increase with depth or pressure of the domain. A mathematical expression derived in this work shows the dependence of σb on the pH and the initial value of σb. Predictions of the changes in the σb for different porous domains show the reliability of the mathematical expression developed in this work.

Modelling the hypothetical methane-leakage in a shale-gas project and the impact on groundwater quality

The hypothetical leakage of methane gas caused by fracking a 1,000-m deep Cretaceous claystone horizon at Damme, Germany, is simulated in a TOUGHREACT reactive-transport model with 5,728 elements. A hypothetical leakage zone connects the Cretaceous horizon with a Quaternary potable-water aquifer (q1). Methane gas rises up to the q1 horizon in less than 2 days in all calculated scenarios. The simulations include the major constituents of groundwater as well as the seven most hazardous trace components that are natural constituents of groundwater (As, Cd, Cr, Ni, Pb, Se and U). The general trend is characterised by depletion of the natural hazardous components with decreasing acidity and oxygen fugacity in the relevant pH range (7–9). Nevertheless, the concentrations of elements whose dominant aqueous species are negatively charged in this pH range (Cr and Se) rise against the general trend due to desorption reactions. Slight enhancement effects are produced by the dissolution of contaminant-bearing oxides such as Cr-bearing goethite. In summary, the geological risks of a fracking operation are minor. The technical risks are more important. This is especially the case when rising methane gas gets into contact with fracking fluid that accidentally escapes through faulty well seals.

Semi-analytical Solution for Brine Leakage Through Passive Abandoned Wells Taking Account of Brine Density Differences

Both $$\hbox {CO}_{2}$$ storage and disposal of waste fluid (e.g., co-produced brine) in deep saline aquifers of sedimentary basins create large scale over-pressurization and tend to displace brine upwards if a vertical connection (e.g., an abandoned well) is present. This raises groundwater pollution issues of brine intrusion into shallower potable water aquifers. When saline brine from the deep aquifer is displaced upwards it lifts and replaces the a priori less saline, less dense water initially filling the connection, resulting in a weight increase that counters leakage. This article presents and explains an innovative semi-analytical solution to this problem of leakage between two aquifers connected by a passive well (represented by a porous column and/or an open wellbore) taking account of the effect of the density difference between lifting and lifted brines during both upward and downward flow. It is based on the linearization of brine density profiles against depth and on two improvements made to the approximate evaluation of convolution products introduced in Nordbotten et al. (Water Resour Res 40:W04204, 2004) for calculation of the pressurization induced by transient flows in open aquifers. The comparison with numerical simulations shows good agreement of results. Since the solution uses time discretization but no spatial grid, computation time is reduced by 3–4 orders of magnitude compared to numerical resolution. It does, however, require considering homogeneous aquifers of constant thickness and brine properties.

Measurements of Hydraulic-Fracture-Induced Seismicity in Gas Shales

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 151597, ’Measurements of Hydraulic-Fracture-Induced Seismicity in Gas Shales,’ by N.R. Warpinski, SPE, J. Du, SPE, and U. Zimmer, Pinnacle - A Halliburton Service, prepared for the 2012 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 6-8 February. The original paper was peer reviewed. See SPE Production & Operations August 2012, pages 240-252. Hydraulic fracturing is essential for hydrocarbon extraction from both conventional and unconventional reservoirs. Recently, concern has developed regarding induced seismicity generated in association with multistage fracturing of horizontal wells in shale reservoirs. A review of thousands of fracture treatments that have been monitored microseismically shows that the induced seismicity associated with hydraulic fracturing is very small and not a problem under normal circumstances. Introduction Hydraulic fracturing is important throughout the world. In unconventional reservoirs, such as ultralow-permeability shales, hydraulically fracturing a well is essential to obtain economic levels of production. Contrary to media and general-public perception, hydraulic fracturing is not a new technology, having been applied in the late 1940s. There also is a perception that hydraulic fractures are much larger than ever, but the massive hydraulic fractures performed in the 1970s were of similar size to fracture treatments conducted in horizontal wells today. Also, these early large treatments were performed in shales in the eastern United States (to prove up the resources in the Devonian shales of Appalachia) and in the western tight gas sandstones of the Rocky Mountains. Results from thousands of monitored fractured treatments demonstrate that fractures will not propagate vertically thousands of feet and intersect potable-water sources. In all the shale basins studied, fractures remain several thousand feet below the deepest potable-water aquifer. Recently, however, there has been considerable attention focused on earthquakes associated with hydraulic fracturing. Microseismic monitoring is a valuable technology for assessing the earthquake potential of fracturing operations. The object of this study was the very large suite of microseismic measurements available from the major shale basins of North America. The study showed that earthquakes are not a threat in nor-mal situations. Injection Geomechanics It is well-understood that long-term injection of fluids into the deep subsurface can induce earthquakes. Many cases of minor earthquakes are documented that likely were induced by local injection operations, the most notable of which was the US Army’s injection of chemical waste into a 12,000-ft-deep interval at the Rocky Mountain Arsenal in Colorado in the 1960s. Similarly, geothermal injections are potential sources of induced seismicity, often because optimal geothermal sites are in areas where faults and tectonics are likely to be conducive to Earth movement. Other long-term injection operations, such as solution mining, water disposal, and waterfloods, are potential sources in areas where the geologic conditions are favorable.

Modeling of CO2 Leakage up Through an Abandoned Well from Deep Saline Aquifer to Shallow Fresh Groundwaters

This article presents a numerical modeling application using the code TOUGHREACT of a leakage scenario occurring during a CO2 geological storage performed in the Jurassic Dogger formation in the Paris Basin. This geological formation has been intensively used for geothermal purposes and is now under consideration as a site for the French national program of reducing greenhouse gas emissions and CO2 geological storage. Albian sandstone, situated above the Dogger limestone is a major strategic potable water aquifer; the impacts of leaking CO2 due to potential integrity failure have, therefore, to be investigated. The present case–study illustrates both the capacity and the limitations of numerical tools to address such a critical issue. The physical and chemical processes simulated in this study have been restricted to: (i) supercritical CO2 injection and storage within the Dogger reservoir aquifer, (ii) CO2 upwards migration through the leakage zone represented as a 1D vertical porous medium to simulate the cement–rock formation interface in the abandoned well, and (iii) impacts on the Albian aquifer water quality in terms of chemical composition and the mineral phases representative of the porous rock by estimating fluid–rock interactions in both aquifers. Because of CPU time and memory constraints, approximation and simplification regarding the geometry of the geological structure, the mineralogical assemblages and the injection period (up to 5 years) have been applied to the system, resulting in limited analysis of the estimated impacts. The CO2 migration rate and the quantity of CO2 arriving as free gas and dissolving, firstly in the storage water and secondly in the water of the overlying aquifer, are calculated. CO2 dissolution into the Dogger aquifer induces a pH drop from about 7.3 to 4.9 limited by calcite dissolution buffering. Glauconite present in the Albian aquifer also dissolves, causing an increase of the silicon and aluminum in solution and triggering the precipitation of kaolinite and quartz around the intrusion point. A sensitivity analysis of the leakage rate according to the location of the leaky well and the variability of the petro-physical properties of the reservoir, the leaky well zone and the Albian aquifers is also provided.

Evaluation of Potential Changes in Groundwater Quality in Response to CO2 Leakage from Deep Geologic Storage

Concern has been expressed that carbon dioxide (CO2) leaking from deep geological storage could adversely impact water quality in overlying potable aquifers by mobilizing hazardous trace elements. In this article, we present a systematic evaluation of the possible water quality changes in response to CO2 intrusion into aquifers currently used as sources of potable water in the United States. The evaluation was done in three parts. First, we developed a comprehensive geochemical model of aquifers throughout the United States, evaluating the initial aqueous abundances, distributions, and modes of occurrence of selected hazardous trace elements in a large number of potable groundwater quality analyses from the National Water Information System (NWIS) database. For each analysis, we calculated the saturation indices (SIs) of several minerals containing these trace elements. The minerals were initially selected through literature surveys to establish whether field evidence supported their postulated presence in potable water aquifers. Mineral assemblages meeting the criterion of thermodynamic saturation were assumed to control the aqueous concentrations of the hazardous elements at initial system state as well as at elevated CO2 concentrations caused by the ingress of leaking CO2. In the second step, to determine those hazardous trace elements of greatest concern in the case of CO2 leakage, we conducted thermodynamic calculations to predict the impact of increasing CO2 partial pressures on the solubilities of the identified trace element mineral hosts. Under reducing conditions characteristic of many groundwaters, the trace elements of greatest concern are arsenic (As) and lead (Pb). In the final step, a series of reactive-transport simulations was performed to investigate the chemical evolution of aqueous As and Pb after the intrusion of CO2 from a storage reservoir into a shallow confined groundwater resource. Results from the reactive-transport model suggest that a significant increase of aqueous As and Pb concentrations may occur in response to CO2 intrusion, but that the maximum concentration values remain below or close to specified maximum contaminant levels (MCLs). Adsorption/desorption from mineral surfaces may strongly impact the mobilization of As and Pb.

Identification of thermodynamic controls defining the concentrations of hazardous elements in potable ground waters and the potential impact of increasing carbon dioxide partial pressure

Abstract Concern has been expressed that carbon dioxide leaking from deep storage reservoirs could adversely impact water quality in overlying potable aquifers by mobilizing hazardous elements present in the aquifer rocks to the extent that their concentrations might exceed Maximum Contaminant Levels (MCLs). To evaluate this issue, 38,000 ground water quality analyses from aquifers throughout the United States, each containing one or more analyses for As, Ba, Cd, Hg, Pb, Sb, Se, U or Zn, were retrieved from the Unites States National Water Information System (NWIS). The analyses were used to calculate the saturation indices (SIs) of all identified and thermodynamically characterized minerals containing the listed elements as essential components. These minerals were initially selected through literature surveys to establish whether field evidence supported their postulated presence in potable water aquifers. SI frequency histograms were plotted to evaluate whether these minerals are at saturation in NWIS ground waters (i.e., they show modes at SI 0). Mineral assemblages meeting the criterion of thermodynamic saturation were assumed to control the aqueous concentrations of the hazardous elements at initial system state as well as at elevated CO 2 partial pressure caused by the ingress of leaking CO 2 . The impact on the identified mineral solubilities of increasing CO 2 partial pressures was then predicted over the range from −4 to +1 (i.e., 10 −4 ≤P(CO 2 ) in bar ≤10). Under reducing conditions (characteristic of most ground waters), the most serious problem resulting from intrusion of CO 2 into shallow groundwater may arise through enhanced dissolution of pyrite and solubilization of arsenic. At the highest P(CO 2 ) assumed in our study, Ba, Pb and Zn may also approach or exceed regulatory concentration limits. Of the remaining elements, the MCLs of Cd, and Sb are unlikely to be exceeded, and Hg, Se and U concentrations are unaffected by CO 2 intrusion.

Sources of dissolved solids and water in Wadi Al Bih aquifer, Ras Al Khaimah Emirate, United Arab Emirates

Regional brines that underlie the potable groundwater appear to be responsible for the increase in dissolved solids in the Wadi Al Bih aquifer in the Ras Al Khaimah Emirate, United Arab Emirates. In this karstic carbonate aquifer, groundwater extraction exceeds recharge and the reduced heads can induce transport of underlying brines into the potable water aquifer. Increasing dissolved solids with time threatens the continued use of groundwater for agricultural and domestic uses. The potential of intrusion of seawater, dissolution of minerals, or intrusion of regional brines as a source of these solutes were evaluated based on groundwater samples collected in April and September 1996 from the Wadi Al Bih well field and isotope data from previously collected samples. Hydrogeologic conditions and solute modeling suggest the dominant source of solutes in the Wadi Al Bih aquifer is most likely an underlying regional brine. The pervasive presence of tritium is consistent with recent (since 1960s) recharge in the drainage basin, thus, the solutes and water appear to be from different sources. The chemical and isotopic data are also consistent with enhanced groundwater recharge associated with dams constructed to reduce flooding.

Turf irrigation in hawaii using r‐1 effluent: Microbial and chemical effects

Secondary‐treated, filtered, and chlorinated effluent (R‐l quality) blended with potable water was used for turf grass irrigation at the Hawaii Kai Golf Course on the island of Oahu, Hawaii. Blending was required because of the salinity level in the R‐l effluent. For control, only potable water was used for irrigation. Irrigation amounts varied with time based upon rainfall. Suction lysimeters were installed at 25‐cm and 40‐cm depths to collect soil‐water samples. In addition, water samples from potable water and blended water storage impoundments were collected for analysis. All water samples were analyzed for nitrate, chemical oxygen demand, pH, conductivity, and fecal coliform bacteria density. Grass samples and soil samples were analyzed for fecal bacteria. Results indicated that fertilization of the turf affected the nitrate content of certain suction lysimeter samples. Conductivity of the leachate samples decreased with time, indicating possible dilution with rainwater. The most significant observation was the growth of fecal bacteria in leachate waters and open storage reservoirs. Grass and soil samples also showed the presence of fecal coliform bacteria. This indicates that fecal coliforms should not be used as indicator bacteria in tropical environments, where they are naturally present. For Oahu, using fecal coliforms as indicator bacteria can be a problem if R‐l effluent is used on areas overlying potable water aquifers. Clostridium perfringens, which is present in large numbers in wastewaters, may be a better indicator bacterium since it is not found in large numbers in the natural soil environment.

Stability and Mobility of Metal-Humic Complexes Isolated from Different Soils

The contamination of potable water aquifers by heavy metals is one of the most severe environmental threats. For the transport of heavy metals from various types of contaminated sites into the ground water and also into surface water aquifers, humic substances (HS) are recognized to be of main importance. Dissolved in natural waters humic substances are readily complexed with a variety of metal ions. Therefore, humic substances are of cardinal importance for the migration and, consequently, the pollution of ground waters with heavy metals. Our paper presents the results of a comprehensive comparison of several isolated humic acids of soils of different origin (different geochemical milieu) and their metal complexes. Two polluted sites in Germany, which differ in their geochemical milieu (pH-value) were selected. The aim of our experiments was to describe the properties of terrestrial humic substances depending on their origin and genesis as well as the effects of the transport of humic substance-bound metals into the water-unsaturated soil zone. After determination of heavy metals in the soils by photon activation analysis the activated soil was used as an inherent tracer in batch experiments with the isolated humic acid. After adsorption of the loaded humic acid on an XAD-8 resin column, the partition of metals mobilized by humic acids could be quantified. There are correlations of the formation of metal-humic complexes with the soil pedogenes, with the pH-value as well as with the humic acid concentration.

Groundwater Drought Sensitivity of Southern Manitoba

Groundwater level observations in Manitoba show that a drought affecting soil and surface water does not necessarily correspond to low water levels in aquifers. In fact, the opposite has been observed; groundwater levels have been at maximum high while a drought has been reported and, on the other hand, very low groundwater levels have been observed while summer precipitation has been well above average. Consequently it is necessary to differentiate a drought in the general sense from a groundwater drought. Hence the term groundwater drought should be used where drought in respect to groundwater is meant. Groundwater drought takes place when water level in an aquifer or a part of an aquifer that usually yields adequate supply drops to the base of the aquifer or to a level where wells are practically dry. Most aquifers in Manitoba are groundwater drought proof. In particular, major high yield aquifers developed for municipal and industrial requirements are drought proof. Only a few small areas in Manitoba, where the only potable water aquifers are formed by shallow surface sand with minimal saturated thickness, are groundwater drought sensitive. Drying up of wells should not be confused with groundwater drought; indications are that wells dry up now and did so more frequently in the past for various other reasons and only rarely can a dry well be related to groundwater drought.