Groundwater Flow Rates Research Articles

Cut-off walls alter nitrogen loads and fluxes in small islands

The measure of constructing cut-off walls in coastal islands has been tested effective to upgrade the freshwater lenses (FWL). Meanwhile, cut-off walls can also affect the FWL quality by changing the loads and fluxes of nitrogen (N). Previous research has been focused on the effects of cut-off walls on the N fluxes in groundwater (like, e.g., nearshore denitrification), assuming a constant N source while changes of the N loads and fluxes associated to the N source in shallow soils have only rarely been considered. In this study, we numerically simulated seawater intrusion and transport of land-sourced nitrate on a 2D, vertically oriented island equipped with a cut-off wall. A simplified framework was used to simulate the N fate in the shallow soil. We selected different aquifer permeability and the depth of cut-off wall. The cut-off wall effect on the N loads and fluxes in soil and groundwater, and on the nitrate concentration within the FWL, was quantitatively assessed. The results show that cut-off walls can considerably reduce the soil N load in high permeability islands (> 10−11.5 m2), because of the increased potential crop uptake due to the increased groundwater level and higher soil moisture. The opposite effect was observed in low permeability islands (< 10−11.5 m2) due to the smaller N leaching fluxes from soil to groundwater under the reduced groundwater flow rate. For the high and low permeability islands the leaching flux can generally be reduced by up to 63 %; for the intermediate permeability islands (10-11.5 m2 ≤ k ≤ 10-11 m2), however, the leaching is increased by up to 38 %. Highly depending on how the leaching changes, cut-off walls can reduce the groundwater N load and the nitrate concentration of FWLs, and thus improve the FWL quality in many cases except for the intermediate permeability islands. Therefore, special caution and investigation are required for constructing cut-off walls on islands with intermediate permeability. As a first attempt to assess the influence of cut-off walls on N loads and fluxes considering the N source dynamics, our study is important for the management of FWL quality and coastal environments.

Mechanisms and characteristics of sand seepage deformation under groundwater level fluctuation scenarios

Seepage deformation in sand results from complex water-soil interactions, which are the primary reasons of sand surface collapse, as well as instability and deformation in dam foundations, building foundations, and slopes. Frequent fluctuations in groundwater levels cause changes in the direction, velocity, and pore water pressure of groundwater within the sand. Further research is essential to fully understand the characteristics and mechanisms of sand seepage deformation under varying groundwater conditions. In this study, natural undisturbed sand samples were collected. Laboratory seepage deformation tests were conducted to simulate continuous rises and falls in groundwater levels, exploring the response characteristics of internal erosion and hydraulic behavior of the sand under varying groundwater flow rates and directions. The results show that: As groundwater flow rate increases, the sand undergoes multiple episodes of seepage deformation, which includes the processes of structural stability, seepage deformation, and seepage failure. Initially, the hydraulic gradient for seepage deformation is small, and the particles carried by seepage are small. With a further increase in groundwater flow velocity, the hydraulic gradient rises, larger sand particles are migrated by seepage, and seepage failure may eventually occur. When the karst groundwater level is lower than the elevation of the sand bottom (H2 < z2) and the sand bottom is in a negative pressure state, the hydraulic gradient of seepage deformation is usually smaller than that observed in the other two states of positive pressure. In these cases, pore water pressure exerts an upward buoyant force, while in the negative pressure state, the pore water pressure transforms into downward suction. This downward suction aligns with the direction of gravitational forces and downward seepage force acting on the sand, making seepage deformation of the sand more likely. Sands with greater unevenness, finer particle, and lower density are more prone to seepage deformation but failure at different hydraulic gradients.

Ensuring the Safety of an Extraction Well from an Upgradient Point Source of Pollution in a Computationally Constrained Setting

Shallow groundwater is an important resource, especially in low- and middle-income countries; however, shallow groundwater is particularly vulnerable to point sources of pollution such as latrines or unlined waste disposal ponds. The objective of this paper is to derive a quantitative criterion for siting an extraction well and an upgradient point source of pollution to ensure that they are hydraulically disconnected, i.e., that no water flows from the point source to the well. To achieve this objective, we modeled the flow of shallow groundwater considering uniform regional flow, a single point source of pollution, and a single extraction well. For any set of flow rates and upgradient point source distance, we sought the minimum “off-center distance” ymin (i.e., the distance in the direction perpendicular to regional flow) that ensures the well and the point source are hydraulically disconnected. For constituencies with access to computing resources and coding expertise, we used a computer-based method for determining ymin that is exact to within the accuracy of a root-finding algorithm; this approach is recommended when computer access is available. For constituencies lacking these resources, we determined a simple, closed-form, approximate solution for ymin that has an average error of less than 3% for the conditions we tested. For a subset of scenarios in which the point source is sufficiently far upgradient of the well (n = 77), the root mean square relative error of the approximate solution is only 0.52%. We found that ymin depends on a length parameter (Qw + Qps)/QR, where Qw is the extraction rate of the well, Qps is the injection rate of the point source, and QR is the regional groundwater flow rate per unit of perpendicular length. Either the exact solution or the closed-form approximation can help to site wells near point sources of pollution, or to site point sources near wells, in a manner that protects the health of the well user. The approximate solution is valuable because many constituencies that rely on shallow wells for water supply and latrines for sanitation also lack access to the computer resources necessary to apply the exact solution.

Hydrogeological assessment and aquifer potential of a coastal area, South Nigeria: insights from VES surveys and spatial analysis

ABSTRACT This study provides a comprehensive analysis of aquifer properties using vertical electrical sounding (VES) surveys conducted in Eket, Nigeria, to address the challenges of groundwater management in coastal areas. The VES method was employed for hydrogeo-electrical analysis and to investigate the hydrogeological dynamics of the region. The results reveal varying subsurface layers with distinct resistivity values. Spatial distribution analysis indicates densely settled areas exhibit lower resistivities, while sparsely settled regions show higher resistivities. The spatial location labeled EK2 features the largest aquifer, measuring 246.70 m, predominantly located in the central research area. Aquifer depths range from 87.10 to 250.20 m, with variations in thickness highlighting geographical heterogeneity and its impact on groundwater transport. These spatial differences in groundwater characteristics are crucial for understanding groundwater movement, storage, and extraction potential. The study underscores significant variability in porosity, reflecting differences in the aquifers’ water storage capacity and susceptibility to contamination. These findings have important implications for groundwater flow rates and extraction feasibility. The research provides essential data for hydrogeological investigations and groundwater resource management, emphasizing the intricate relationship among geological formations, aquifer properties, human activities, and the potential risks of contamination in variable porosity zones.

Hydrological response of the largest inland tectonic basin in Japan

The Itoigawa-Shizuoka tectonic line formed the largest inland tectonic basin in Japan. Taking advantage of the characteristics of the large tectonic basin, this study aims to clarify the hydrological response related to groundwater recharge and discharge in this area from field measurements such as monthly spring discharge measurements in the spring belt, infiltration measurements of irrigation recharge in rice paddy fields and analysis of stable isotopic ratios of oxygen and hydrogen. Volumetric water flow measurements in the tectonic basin demonstrate that the hydrological response function (HRF) is expressed as a linear equation. Despite the complex topography and geology of the mountain catchment and artificial recharge within the basin, this HRF is maintained, except for forced artificial irrigation in August when the natural water supply is significantly reduced, and except in March and April when snowmelt flows into the river. This study clarifies that monthly fluctuations in total groundwater flow within a basin can be estimated by applying HRF to monitoring data of total surface flow at the farthest downstream. The field measurements demonstrate that the rainfall in the mountain catchment area and artificial irrigation recharge in the basin greatly influence the fluctuation of groundwater flow rate, especially on the fluctuation of the spring water in the spring belt. Field data inferred that the frequent depletion of the springs in the inland tectonic basin, where all groundwater emerges at the most downstream, depends on the rapid decline in annual rainfall in mountain catchment areas. These observations suggest that the total groundwater resource in this region was affected not only by reduced irrigation recharge due to the historical paddy acreage reduction program implemented in Japan from 1971 to 2018, and by excessive groundwater extraction, but also by rapid decline in annual rainfall in mountain catchments that occurs non-periodically.

Application of the Tracer Test in a Hydrogeological Survey for a Pumped Storage Power Station

In areas with complex hydrogeological conditions, the tracer test method is often used as an effective means in hydrogeological surveys. According to the results of tracer tests, hydrogeological parameters, including hydraulic gradient and permeability coefficient, fracture network leakage passages and their scale, and groundwater flow rate and direction can be quantitatively determined. This paper takes the upper reservoir of Yongxin Pumped Storage Power Station in Jiangxi Province as the research object, and focuses on the complex hydrogeological conditions of the upper reservoir. Three sets of tracer tests and multiple sets of single-hole flow rate and direction tests were conducted on the left and right banks of the reservoir and near surface gullies. The results showed that ZKS18 received tracers in all three tests, which indicates a close hydraulic connection between ZKS18 and the left bank, right bank, and surface gullies within the reservoir. Based on the single or multiple peak values of the tracer, it was determined that there are 1–6 leakage passages in the fractured rocks, with leakage passage sizes of 0.1–0.4 mm. According to the single-hole flow rate and flow direction tests, a self-developed instrument was used to determine the groundwater flow rate and flow direction at different depths in the test holes, which yielded results that were basically consistent with the results of the three-hole method. These results provide a basis for the use of tracer tests in hydrogeological surveys for water conservancy and hydropower engineering, and anti-seepage design of upper reservoirs.

HYDRODYNAMIC MODEL OF SOLOTVYN ROCK SALT DEPOSIT

Rock salt development brings risks of harmful impact on water resources, in particular the Tysa River, posing a threat of cross-border spread of saline pollution on the border between Ukraine and Romania (Solotvyn rock salt deposit, Transcarpathia, western Ukraine). The impact of technogenic load (underground mining of rock salt) within the deposit led to deformation of the structure and nature of water exchange, intensification of suffusion and karst processes, ground surface deformations, catastrophic inflows of groundwater into mines, and, as a result, to the cessation of development of this deposit in 2010. However, the suspension of salt mining did not stop the development of the above-mentioned hazardous geological processes caused by both natural and man-made factors. In order to justify measures for prevention pollution of the Tysa River basin, a hydrogeological model of the Solotvyna rock salt deposit and surrounding areas was created, which allowed to predict the direction and flow rate of fresh and saline groundwater. The model was developed using new data on the geological structure and hydrogeological conditions of the study area (groundwater monitoring data). The modernised hydrodynamic model includes five layers (main aquifers and confining layers). As a result of modelling, maps of the velocity vectors and head contours for two aquifers (Quaternary and Tortonian) were obtained. Based on the results of solving a number of inverse problems, the functional correspondence of the model to natural and anthropogenic conditions was proved. According to the preliminary calculations of the actual groundwater filtration velocity and the path lines of the inert pollutant spreading, it was found that the time of its migration from the salt contour to the Tysa River is approximately 2–3 years. The developed groundwater flow model will be used to substantiate the network of hydrological and hydrogeological observation points in order to optimise the monitoring of water pollution processes.

A model of temporal and spatial river network evolution with climatic inputs

Predicting the temporal and spatial evolution of the river network is part of the Earth's critical zone investigations, which has become an important endeavor. However, modeling integration of the river network and critical zone over millions of years is rare. We address the problem of how to predict integrated river length development as a function of time within a framework of addressing the critical zone depth as a function of time. In case of groundwater-river interaction, we find a non-linear spatio-temporal scaling relationship between time, t, and total river length L, given by t≈Lp with power p being near 1.2. The basis of our model is the presumption that groundwater flow paths are relevant to river integration. As river integration may proceed over disconnected basins with irregular relief, the relevant optimal subsurface flow paths are proposed to be defined within a 3D network, with optimal path exponent 1.43. Because the 2D model of the river length has already been shown to relate to a power of the Euclidean distance across a drainage basin with the predicted universal optimal path exponent from percolation theory, Dopt = 1.21, the optimal groundwater paths should relate to the surface river length with an exponent equaling the ratio 1.43/1.21 = 1.18. To define a predictive relationship for the river length, we need to use specific length and time scales. We assume that the fundamental specific length scale is a characteristic particle size (which is commonly used to define the pore scale flow network), and the fundamental time scale is the ratio of the particle size to the regional groundwater flow rate. In this paper, we consider cases of predicting spatio-temporal scaling of drainage organization in the southwestern USA–the Amargosa, Mojave, Gila (and its tributaries) and the Rio Grande, and Pecos Rivers. For the Mojave and Gila Rivers, theoretical results for time scales of river integration since ca. 10 Ma are quite predictive, though the predicted time scales exceed observation for the Rio Grande and Pecos.

Coupling flow and electric fields to simulate migration and remediation of uranium in groundwater remediated by electroosmosis and a permeable reactive bio-barrier

Combined remediation technologies are increasingly being considered to uranium contaminated groundwater, such as the joint utilize of permeable reactive bio-barrier (Bio-PRB) and electrokinetic remediation (EKR). While the assessment of uranium plume evolution in the combined remediation system (CRS) have often been impeded by insufficient understanding of multi-physical field superposition. Therefore, advanced knowledge in multi-physical field coupling in groundwater flow will be crucial to the practical application of these techniques. A two-dimensional multi-physical field coupling model was constructed for predicting the uranium degradation in CRS. The study demonstrates that the coupling model is able to predict the uranium plume evolution and rapidly evaluate the performance of CRS components. The results show that field electric direction and flow field strength are the key factors that affect the retardation and remediation performance of CRS. The reverse electric field direction significantly affected the contact reaction time of uranium in the system. The uranium residence time in the reverse electric field was 3.8 d, which was significantly greater than the original electric field (2.0 d). Depending on the voltage, the reverse electric field direction was 16%–36% more efficient than the original direction. The strength of the flow field was about two orders of magnitude higher than that of the electric field, so the groundwater flow rate dominated remediation efficiency. Reducing the flow rate by 1/2 could improve the performance of the system by approximately 66%. In addition, the coupling model can be utilized to design standard CRS for real site of uranium contaminated groundwater. To meet the optimal performance, the direction of the electric field should be set opposite to the flow field. This work has successfully used a coupling model to predict uranium contaminant-plume evolution in CRS and estimate the performance of each component.

Estimation of terrestrial heat flow in hydrothermally active areas based on long-term bedrock temperature observations: a case study of northwestern Yunnan, China

Terrestrial heat flow plays an important role in the study of plate tectonics, geothermal resource exploration and earthquake genesis. The measurement of terrestrial heat flow usually utilizes deep boreholes, which is expensive and inconvenient for high altitudes or mountainous terrain. In hydrothermally active areas, the temperature distribution is disturbed by heat convection, resulting in difficulty in obtaining conductive heat flow. In fact, heat can be used as a tracer to quantify groundwater flow. This article presents a method for calculating terrestrial heat flow suitable for hydrothermally active areas, which can correct the influence of groundwater flow to obtain the conductive heat flow reflecting the deep thermal background. The method uses temperature-time series at multiple depths of the shallow crust to calculate the groundwater flow rate. The convective heat flux component is then removed based on information on groundwater movement, and the conductive heat flow can be acquired. The feasibility of the method is verified by a theoretical model. This method has been applied to estimate terrestrial heat flows in northwestern Yunnan, China, which is a hydrothermally active area. The heat flow obtained through our method range from 54.5 to 130.3 mW/m2, with an average of 94.5 mW/m2, consistent with the high-quality measured heat flow values in the boreholes. This study provides new perspectives for acquiring terrestrial heat flow in areas that are affected by fluid activities.

A new discrete model to better consider tracer distribution along boreholes during the Finite Volume Point Dilution Method

The Finite Volume Point Dilution Method (FVPDM) is a single-well tracer experiment which has been successfully used in many hydrogeological contexts to quantify groundwater fluxes. During continuous injection of tracer into a well, the tracer concentration evolution measured within the tested well directly depends on the groundwater flow crossing the well screens. Up to now, the FVPDM mathematical formulation used to simulate the tracer concentration evolution measured in the tested well assumed perfect homogenization of the tracer along the tested interval, which is a reasonable assumption in many cases. However, when FVPDM are performed in long-screened boreholes or in very permeable aquifer materials, the recirculation flow rate imposed to ensure mixing is suspected to be too low to perfectly homogenize the tracer. In order to assess the effect of non-perfect mixing on FVPDM results, we introduce here a new discrete model that explicitly considers the recirculation flow rate. The mathematical developments are validated using field measurements, and a sensitivity analysis is proposed to assess the effect of the mixing flow rate on tracer concentration homogenization within the well. Results confirm that, when the recirculation flow rate applied is not high enough compared to the groundwater flow rate, the tracer distribution is not uniform in the tested interval. In this case, the use of the classical analytical solution, commonly used to interpret the concentration evolution leads to highly overestimated groundwater fluxes. The discrete model introduced here can be used instead to properly estimate groundwater fluxes and assess the tracer distribution within the tested interval. The discrete model offers the possibility of interpreting field measurements conducted under non-perfect mixing conditions and increases the range of fluxes that can be investigated through FVPDM.

Groundwater modeling of the Silala basin and impacts of channelization

AbstractA key issue in the legal case before the International Court of Justice between Bolivia and Chile concerned artificial channels in the headwater wetlands of the Silala River in Bolivia, and their impact on the river and groundwater flow rates across the international border into Chile. In pleadings before the Court, Bolivia had claimed up to 40% changes in river flow, whereas Chile had maintained that these were much smaller. This paper reviews construction of a numerical groundwater model to quantify this impact, based on the hydrogeological conceptual model presented earlier in this volume. The groundwater model domain covers the Silala River topographical catchment, plus three adjacent closed (endorheic) topographical catchments to the northeast, which together form the groundwater catchment of the Silala River. The geometry was based on a 3D geological model, constructed based on knowledge gained from several geological mapping investigations. Surface water flows were simulated within a margin of error less than the range of uncertainty associated with the flow measurements. The resulting calibrated groundwater model was used to simulate scenarios corresponding to (a) the removal of channels in the Bolivian wetlands and (b) backfilling of the channels and a small increase in ground elevation (postulated by Bolivia due to long term peat accumulation). The results of these scenarios indicate that the measures would result in a small reduction to the surface water flow over the border to Chile; for Scenario A less than 1% change in surface flows, and for Scenario B less than 3%.This article is categorized under: Human Water &gt; Rights to Water Science of Water &gt; Hydrological Processes Human Water &gt; Water Governance

Exact simulation of the groundwater flow in anisotropic confined aquifer near time-varying streams by comprehensive new analytical solutions

This paper presents some new analytical solutions to an accurate prediction of the behavior of the groundwater flow in aquifers in response to changes in surface water. The new analytical solutions are obtained using integral transforms. An anisotropic rectangular confined aquifer bounded with four time-varying streams is undertaken. The effects of anisotropy on groundwater head and flow rate near time-varying streams are investigated. Depending on the change rates of the streams level, an anisotropic aquifer may render either lower or higher hydraulic head than an isotropic aquifer. In addition, an anisotropic aquifer has provided less water exchange at the interfaces than an isotropic one. The sensitivity of the hydraulic head to change rate of the streams level in both isotropic and anisotropic aquifers is evaluated. It is shown that the aquifer response is more sensitive to change rate of the streams parallel to y-direction and less sensitive to change rate of the streams parallel to x-direction in an anisotropic aquifer and vice versa in an isotropic aquifer. The results of the present new analytical solutions are compared with numerical model of MODFLOW. The results obtained from the presented solutions showed good agreement with the results of MODFLOW. The results show that the presented new analytical solutions are accurate, robust and efficient. Therefore, the results indicate that the presented new analytical solutions are very effective in the simulation of the groundwater flow in river–aquifer systems. Furthermore, one of the advantages of the new analytical solutions is to investigate the sensitivity analysis of aquifer parameters, which has been carried out in this paper. Also, some other new analytical solutions for steady-state conditions and sudden fall in streams level are provided as well. Feasibility of the proposed new analytical solutions is presented via calculating and simulating the hydraulics of groundwater flow in river–aquifer systems by means of integral transforms.

Numerical investigation of slurry property effect on grouting and blocking of flowing water in rock fractures

AbstractIn order to investigate the slurry flow behavior, our newly proposed numerical method is applied to simulate the fracture grouting with flowing water condition. First, by numerical validation and experiment comparison, the advantages of this method in computation efficiency and accuracy are shown. Second, the initial velocity of water and slurry properties at different levels are selected as the influencing factors, the water reduction effect, grouting pressure, and slurry deposition behavior in different cases are investigated, and the variation characteristics of flow field and slurry outflow are analyzed. The simulation results show that within the range of slurry properties and flow velocity given in this paper, cement slurry cannot seal the water inflow. Instead, quick setting slurry with different material ratios can effectively seal the fracture. The sealing efficiency is more sensitive to the initial flow rate than the slurry property. When the groundwater flow rate is low, the effect of slurry proportion on sealing can be ignored. Meanwhile, slurry properties have more influence on the final grouting pressure. There is an obvious surge in grouting pressure after sealing, which can be used as a criterion for fracture sealing.

Assessing the effectiveness of nanoscale zero-valent iron particles produced by green tea for Cr(VI)-contaminated groundwater remediation

Nanoscale zero-valent iron particles (NZVI) produced by using green tea (GT) extract as a reductant can remove Cr(VI) from water effectively, which can be utilized in groundwater remediation. In order to define the reaction mechanism and removal effect in the aquifer, in this study, GT-NZVI particles were prepared and measured by some characterization methods to define their surface performance, and then batch and one-dimensional experiments were carried out to reveal the reaction properties of GT-NZVI and Cr(VI) in groundwater. The results showed that the prepared GT-NZVI particles were regular spherical with a diameter of 10–20 nm, which could disperse in water stably. The main component of GT-NZVI was α-Fe with superficial polyphenols as a stabilizer. GT-NZVI suspension had good ability to reduce the Cr(VI) to Cr(III) in water. When the concentration of GT-NZVI was 1 g/L, the removal efficiency of Cr(VI) with an initial concentration of 100 mg/L reached 92.8% in 1 h reaction. In column tests, GT-NZVI passed through the natural sand column successfully with an average outflow percentage of 71.2%. The simulated in-situ reaction zone (IRZ) with GT-NZVI was used to remediate Cr(VI) contaminated groundwater. The outflow concentration of Cr(VI) kept in 0.14–0.32 mg/L corresponding to the outflow rate below 0.32% within 15 days, and the removal efficiency of Cr(VI) by IRZ with GT-NZVI decreased with the increase of aquifer medium particle size, groundwater flow rate and ionic strength. Most of Cr(III) as reduzate was adsorbed or immobilized on the surface or in the lattice of GT-NZVI, which indicated effective immobilization for chromium.

222Radon reduction in small-scale water supply systems using low-technology reduction methods in the Republic of Korea: A field research and mass balance model approach

In rural areas, low-technology radon reduction methods are essential for safe access to clean groundwater. This study monitored the radon reduction rates in small-scale groundwater-based water supply systems in the Republic of Korea and also presented a mass balance equation using physical environmental conditions from three radon reduction methods. The mass balance results showed that the radon reduction rate would be affected by the groundwater flow rate (m3/day), capacity of the drainage facility (m3), surface area of air-water interface (m2), air-water ratio (dimensionless), and ventilation system. The radon reduction order was as follows: simultaneously powered and non-powered aeration method (free-fall (60.0 %) > aeration (19.6 %) > decay (0.9 %) > diffusion (0.2 %)), low-technology non-powered aeration (free-fall (60.0 %) > decay (3.4 %) > diffusion (0.9 %)), and only storage (free-fall (35.5 %) > decay (4.4 %) > diffusion (1.1 %)). Overall, non-powered aeration using the maximum free-fall effect has the potential for use as a low-technology reduction method and natural decay during water storage is the most important factor underlying seasonal variations in the reduction effect.

Estimation of Groundwater Flow Rate by an Actively Heated Fiber Optics Based Thermal Response Test in a Grouted Borehole

AbstractThe thermal response test (TRT) in an aquifer establishes a relationship between the groundwater flow rate and the recorded temperature response curve of temporal ground heating. A major challenge for achieving a mature hydrogeological field test is to minimize borehole effects by smart practical solutions of in situ heating and temperature sensing. When borehole effects are substantial, concepts are needed to separate their contribution to the recorded signal. This is especially the case when heating and sensing devices are installed in grouted boreholes as permanent testing stations. Interpretation of a recorded response curve thus means solving a transient heat transfer problem with radial conduction through composite media. Here, a series of numerical models are set up to study the effect of the grout and the jacket of an actively heated fiber‐optic cable on the simulated thermal response measured along a heated borehole. The findings are utilized to further develop existing groundwater flow rate estimation procedures based on the moving infinite line source model. The developed approach is demonstrated in a case study in a borehole near a bank collapse site that penetrates different aquifer layers. Accordingly, significant local groundwater flow rates (9 × 10−7–5 × 10−6 m·s−1) are found that vary with depth. The values derived by the TRT interpretation closely match the expected rates (2 × 10−6–7 × 10−6 m·s−1), which supports the good applicability of the estimation procedure in the field.

Understanding Shallow Basaltic Aquifer System Near West Coast of Maharashtra, India

Two-Dimensional (2D) Electrical Resistivity Tomography (ERT) and geophysical logging and injected tritium tracer studies with hydrogeological tests were carried out at selected location in an area of 5 km2 near the coastal region of Tarapur, Thane district, Maharashtra. The area is in basaltic terrain, overlain by thin cap of alluvium formation and receives an annual rainfall of about 2000 mm. An integrated investigation method was adopted to delineate the subsurface lithological variations, understand the existing aquifer system up to 25 m depth, evaluate aquifer properties, recharge potential and also to monitor the groundwater flow characteristics. The investigation results showed a variable thickness of weathered zone of 1-3 m, existence of two basalt flows, low vertical natural recharge, high transmissivity, high hydraulic conductivity and high groundwater flow rates. The results also depicted that a combination of hydrogeological tests along with resistivity and tracer investigation is an effective tool in mapping and characterizing the shallow potential groundwater aquifer zone in Deccan traps. The integrated study carried out in the coastal area provided detailed subsurface information useful for planning specific water conservation strategies for sustainable groundwater supply. Keywords: Deccan Traps, ERT, Tritium Tracer, Recharge, Groundwater Flow

Temporal and Spatial Evolution Law of the Freezing Temperature Field of Water-Rich Sandy Soil under Groundwater Seepage: A Case Study

We aimed to assess the temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil in underground freezing engineering, taking the newly built west ventilating shaft freezing engineering in the Yuandian No. 2 Mine of Huaibei Coalfield as the engineering background. The influence of groundwater seepage on the freezing temperature field was qualitatively analyzed using field measured data. Based on the mixture medium theory, a hydrothermal coupling numerical calculation model of the freezing temperature field was established. The temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil was obtained via the analysis of field measured data and numerical calculation results. It was found that the proportion of water that froze into ice in the soil mass within the freezing pipe circle is more than that outside of the freezing pipe circle; thus, the phase change in the soil mass within the freezing pipe circle is highly obvious. Groundwater seepage has an “erosion” effect on the upstream and side frozen walls and a “cooling superposition” effect on the downstream frozen wall. Under the effect of groundwater seepage of 2.81 m/d, the average temperature of the effective frozen wall during excavation is below −15 °C, while the thickness is above 5 m for the selected sandy layer at the site, meeting the construction and design requirements. When the groundwater flow rate increases from 0 to 10 m/d, the closure time of the frozen wall increases from 27 to 49 days, an 81.48% increase; the upstream thickness of the effective frozen wall decreases from 5.635 to 4.65 m, which represents a 17.48% decrease, while the downstream thickness increases from 5.664 to 7.393 m, an increase of 30.60%. The numerical calculation model in this paper can be used to predict the development law of the freezing temperature field of the water-rich sandy layers in the Yuandian No. 2 mine and to adjust the on-site cooling plan in real time according to the construction progress. This study provides some theoretical basis and reference for the construction and designs of the freezing temperature fields of water-rich sandy soil layers.

Natural glass alteration under a hyperalkaline condition for about 4000years.

Silicate glasses are durable materials in our daily life, but corrosion rate accelerates under alkaline aqueous environment. Such situation has raised concerns, for example, in nuclear waste disposal where vitrified wastes encounter to alkaline leachate from surrounding concrete materials. Here we report volcanic glass example surviving with a hyperalkaline groundwater (pH > 11) and high flow rate for about 4000 years. The tiny glass fragments were extracted from the volcanic ash layer sandwiched between ultramafic sediments using microanalytical techniques. Sharp elemental distributions at the glass surface, where amorphous-like smectite precursors and crystalline smectites coexist, suggest the corrosion by an interface-coupled dissolution–precipitation mechanism rather than inter-diffusion. The corrosion rate was maintained at, the minimum, 2.5 orders of magnitude less than the rate observed for fresh glass, even in the presence of Fe and Mg that might have consumed Si through the silicate precipitation.