Hydrogeologic Units Research Articles

Geoelectrical Assessment of Groundwater Potential within Zamfara and its Environs, Northwestern Nigeria

Groundwater potential assessment was carried out within Zamfara environs, Northwestern Nigeria using geoelectrical technique with a view of solving the problem of incessant failure of boreholes in the study area. A total of one hundred and eighty-three (183) vertical electrical soundings (VES) were used to identify potential groundwater bearing zones capable of sustaining economic development of the study area. Two hydrogeological units were investigated (basement rock units and sedimentary rock unit), using Omega resistivity meter Model No. 122, to measure and record the resistance of the subsurface by Schlumberger configuration. The data obtained were interpreted quantitatively and qualitatively using the partial curve matching and computer iteration techniques to generate the first order geoelectric parameters. Generally, the VES result from the basement rock units revealed, four geoelectric layers which correspond to lateritic top soil, weathered basement (clay), partially fractured layer/fractured layer and fresh basement. The weathered/fractured layer was identified as the water bearing layer, within the basement rock units of the study area. From geospatial analysis of both weathered thickness/fracture thickness layers, South and Northeastern part tends to be the most prospective area with the best hydrogeologic conditions for borehole siting within the basement rock units. Consequently, three geo-electric layers were delineated from VES result obtained from Gundumi formation, which correspond to sandy clayey top/gravelly sandy top soil, second layer are mostly silty-clay/compacted sandstone/sandy gravel layers, the third layer were majorly saturated sandstone in some instances silty clay. However, the aquiferous layer is saturated sandstone/sandy gravel layer. The Dar Zarrouk result revealed excellent groundwater potential within the Gundumi formation. The values of coefficient anisotropy obtained from Gundumi rock units range from 0.44 to 3.79, which implies moderate saturation of groundwater. This is an indication that the aquifers of the Gundumi formation is more promising and it can be tap for both domestic and agricultural uses.
 Keywords: Vertical electrical sounding; Fractured layer; Saturated Sandstone; Basement rock units; Gundumi formation

Hydrogeological and hydrochemical framework of the distal section of the Salado-Juramento fluvial megafan (Bajos Submeridionales) in South America

The Bajos Submeridionales (BBSS) (Argentina) is a 54,800 km2 hydrological system located at the distal part of the Salado-Juramento Fluvial Megafan (SJRM). Its climate evolves from humid-subtropical in the east to semiarid in the west. Its hydrogeological system is typical of extensive plains, topography locally imposes vertical flows and neotectonic elements define system boundaries and drains. These characteristics and poor data availability represent a major challenge for identifying a hierarchical subsurface flow system and the influence of neotectonics. This work characterizes the hydrogeology of the BBSS and proposes a conceptual model based on integrated systematic information including 453 water level, 145 hydrochemical, and 99 δ18O- δD data. Four hydrogeological units are identified (HU1–HU4), two of which are divided into sub-units based on their sedimentary sequence. The main chemical types are Na-Cl, Na-Cl/SO4, Na-HCO3/Cl, Na-Cl/HCO3, and HCO3-Na. Dominant ions are Na, Cl, and SO4. Measured electrical conductivity reaches values as high as 132,000 μS/cm. Water chemistry modifying processes include halite, gypsum, and carbonate dissolution; ion exchange; inter-HU water mixing; and evapo-concentration. δ18O-δD and EC-δ18O suggest the existence of subsurface flow sectors. In the south, shallow and medium depth groundwater flows respond to the current circulation of the SJRM. Recharge occurs in the sub-Andean Ranges and point discharges, at the western lakes and some lakes of the Golondrina-Calchaquí system. Precipitation recharges shallow flows locally in the north, center, and east. Extreme west HU2 and HU1 receive deep upward thermal flows through structural lineaments. Thus, the Otumpa Hills morpho-structure would be a barrier to shallow HU1 flow, though not to deep regional HU2 and HU4 flows. Regional groundwater flow is from NW to SE and both local and regional flows would discharge in the Paraná River. The new conceptual model developed helps to further understand the groundwater system of a large plain in South America.

Effects of exponentially decaying aquitard hydraulic conductivity on well hydraulics and fractions of groundwater withdrawal in a leaky aquifer system

A hydrogeological unit with a considerable thickness usually demonstrates depth-decaying hydraulic conductivity (K) at the regional scale. In this study, we investigated transient well hydraulics (i.e., aquifer and aquitard drawdown) and groundwater budget (i.e., fractions of groundwater withdrawal including aquifer depletion, aquitard depletion and leakage from the unconfined aquifer) within a leaky aquifer system considering an exponentially decaying K of the aquitard, parameterized with a dimensionless decay coefficient (Ad). Relevant semi-analytical solutions were derived using the Laplace transform and Hankel transform techniques, while drawdown and groundwater budget characteristics and their sensitivities to Ad were theoretically analyzed. Theoretical analysis results suggested that a larger Ad consistently leads to a larger aquifer drawdown, a smaller aquitard drawdown, a larger fraction of aquifer depletion and a smaller fraction of leakage from the unconfined aquifer. Sensitivity analysis results also indicated critical effects of Ad on well hydraulics and groundwater budget. Comparative analysis revealed that none of the three typical mean values of depth-decaying aquitard K can perfectly characterize the well hydraulics and groundwater budget from early to intermediate times. However, the harmonic and geometric mean values can be feasibly used to calculate the final fractions of aquifer depletion and aquitard depletion at late times, respectively. Limitations of the newly developed analytical model have also been discussed. Practical investigations of vertical aquitard heterogeneity and further applications of this new model are recommended.

Assessment of groundwater potential zones and mapping using GIS/RS techniques and analytic hierarchy process: A case study on saline soil area, Nakhon Ratchasima, Thailand

<abstract> <p>The research purpose is to assess and delineate groundwater potential zones (GWPZs) in the saline soil area in the districts of Non-Thai, Non-Sung, Non-Daeng, Khong, and Kham Sakae Saeng, Nakhon Ratchasima province, Thailand, using remote sensing (RS), geographical information system (GIS), and analytical hierarchy process (AHP) techniques. The GWPZs were created by combining multiple influencing factors such as slope, landforms, annual rainfall, soil texture class, drainage density, geology, hydrogeological unit, land use/land cover, groundwater potential, and normalized difference vegetation index of the study area. The AHP technique was used to determine the weights of various thematic layers to identify the groundwater potential zone. The weights of the thematic layers in descending order consisted of hydrogeological unit (17.61%), geology (17.10%), groundwater potential (12.09%), soil texture class (12.09%), drainage density (8.55%), landforms (8.46%), land use/land cover (6.05%), slope (6.01%), annual rainfall (6.01%), and normalized difference vegetation index (6.01%), respectively. The acceptable consistency ratio (CR) is used to evaluate the reliability of AHP techniques, and which coefficient of determination (R<sup>2</sup>) of 0.7131 was used to validate the salinity data of 17 groundwater wells. The overall weightage of the AHP technique assessment was classified into 5 categories of the GWPZs including very high potential, high potential, moderate potential, poor potential, and very poor potential. The mostly groundwater quality distribution represented a moderate potential of about 1,101 km<sup>2</sup> (46.01%) to a poor potential of about 1,114 km<sup>2</sup> (46.57%) from the 2,390 km<sup>2</sup> of the study area located throughout the study area especially Kham Sakae Saeng, Non-Thai, and Non-Sung districts.</p> </abstract>

Natural background levels in groundwater in the Pearl River Delta after the rapid expansion of urbanization: A new pre-selection method

Establishment of natural background levels (NBL) of groundwater in urbanized areas such as the Pearl River Delta (PRD) is challenging. Pre-selection methods are the most common approaches for NBL assessment, but it will overestimate (or underestimate) contaminated groundwater in urbanized areas by using present pre-selection methods with empirical definite values because of complicated human activities. Unlike present pre-selection methods, this study aims to establish a new pre-selection method with the indicative of Cl/Br ratios to identify contaminated groundwaters with convincing evidences. Specifically, this new method consists of indicatives of the oxidation capacity and the Cl/Br ratio combining with contaminated-markers. In addition, factors controlling NBL of Cl and NO3 in groundwater in various hydrogeological units in the PRD were also discussed. Main procedures of this new method: contaminated-markers in various hydrogeological units are extracted by a hierarchical cluster analysis, thereby determining threshold values of Cl/Br ratios and Cl concentration in various hydrogeological units for identifying contaminated groundwater; After that, groundwater chemical datasets was selected by the oxidation capacity, and then tested by Grubbs' test until normal distributions. Groundwater Cl and NO3 concentrations in datasets before and after this new method are dependent and independent of urbanization levels, respectively, indicating that the new method is useful for groundwater NBL assessment in urbanized areas such as the PRD. Both the seawater intrusion and the diffusion of Cl from marine deposits are likely to be responsible for the much higher NBL-Cl in coastal-alluvial and marine aquifers than in other hydrogeological units. Groundwater Cl enrichment resulted from groundwater recharge and evaporation is mainly responsible for the higher NBL-Cl in alluvial-proluvial aquifers than in lacustrine aquifers, fissured aquifers, as well as karst aquifers. More than double times NBL-NO3 in alluvial-proluvial and fissured aquifers than in other hydrogeological units is probably attributed to more oxidizing conditions of their vadose zones and groundwaters.

Transboundary Aquifers between Baja California, Sonora and Chihuahua, Mexico, and California, Arizona and New Mexico, United States: Identification and Categorization

In 2016, research suggested there might be up to 36 transboundary aquifers located along the border between Mexico and the U.S. The main contribution of this study was to put together the available segments already existent in the literature without considering the validity of the criteria used to define the boundaries of those segments. In 2018, updated research reported 33 hydrogeological units (HGUs) crossing the boundaries between Mexico and Texas. This later analysis included the homogenization of geological nomenclatures, standardization of geological and hydrogeological criteria, using a specific methodology to correlate, identify, and delineate each HGU. The purpose of this paper is to use this latter methodology and expand the same analysis to include the transboundary aquifers between Baja California/California, Sonora/Arizona, and Chihuahua/New Mexico. Results of this study indicate that a total of 39 HGUs have been identified in this region which accounts for an approximate shareable land of 135,000 km2 where both countries share half of the area. From the total shareable area, around 40% reports good to moderate aquifer potential and water quality, of which 65% is in the U.S. and 35% on the Mexico side. Border-wide, the total number of HGUs in the border region between Mexico and the United States is 72, covering an approximate area of 315,000 km2 (180,000 km2 on the U.S. side and 135,000 km2 on the Mexico side). The total area that reports good to moderate aquifer potential as well as good to regular water quality ranges between 50 and 55% (of which approximately 60% is in the U.S. and the rest in Mexico).

Appraisal of protectivity and corrosivity of surficial hydrogeological units via geo-sounding measurements.

The surface resistivity method was used to appraise the protectivity of hydrogeological units and corrosivity of the top soil in Obot Akara County, southern Nigeria. A total of 28 vertical electrical sounding (VES) was undertaken in the area using the Schlumberger electrode configuration. The results of the VES data interpretation reveal 3 to 4 geoelectric layers in the study area. The resistivity of the first layer interpreted as the Motley top soil ranges from 34.7 to 929.7 Ωm with a mean value of 381.1 Ωm. The third layer, with a resistivity range of 99.4 to 2716.7 Ωm, constitutes the aquifer unit in most communities in the area, with an average thickness of 58.3m, while the fourth layer penetrated in most communities has a resistivity range of 216.1 to 1475.7 Ωm with a mean value of 657.5 Ωm. The longitudinal conductance and resistivity reflection coefficient of the aquifer protective layers vary from 0.04 to 0.76 mhos and - 0.74 to 0.93, respectively. Analysis of these results shows that 89.3% of the hydrogeological units in the area is weakly/poorly protected, 10.7% has moderate to good protection, while 85.7% of the top soil at the sounding stations is noncorrosive and 14.3% is slightly to moderately corrosive. The implication of these results is that most of the hydrogeological units in the area are likely prone to contamination in particular by some ferrugenized materials from the overlying layers. Also, underground metal storage tanks and galvanized and steel pipes can be buried in the topmost layer in most communities in the area without any risk of failure. Although these findings are very promising especially in groundwater management and exploitation in the area, hydrogeochemical and microbiological analyses of groundwater samples from available boreholes are recommended to corroborate the results.

Populations using public-supply groundwater in the conterminous U.S. 2010; Identifying the wells, hydrogeologic regions, and hydrogeologic mapping units

Most Americans receive their drinking water from publicly supplied sources, a large portion of it from groundwater. Mapping these populations consistently and at a high resolution is important for understanding where the resource is used and needs to be protected. The results show that 269 million people are supplied by public supply, 107 million are supplied by groundwater and 162 million are supplied by surface water. The population using public supply drinking water was mapped in two ways: the census enhanced method (CEM) evenly distributes the population across populated census blocks, and the urban land-use enhanced method (ULUEM) distributes the population only to certain urban land use designations. In addition, a two-dimensional polygon dataset was created for the conterminous U.S. that identifies 177 unique Hydrogeologic Mapping Units (HMUs) with similar hydrogeologic characteristics. The HMUs do not overlap, but they can delineate areas where stacked hydrogeologic regions (HRs) contribute drinking water from below the surface. HRs are waterbearing geologic regions identified as either a principal aquifers (PA) or secondary hydrogeologic regions (SHR). Within each HMU, the wells were used to determine the proportion of each HR that is providing groundwater to the HMU. In 63% of the HMUs, a single HR is providing water to the public supply wells located within it, while the rest of the HMUs show that the wells are tapping up to a maximum of four stacked HRs. In total, groundwater from 108 HRs provide drinking water for public supply, six of which provide more than 50% of the groundwater used for public supply drinking water. The aquifer serving the largest number of equivalent people (>17 million) is the glacial aquifer. The HR providing the greatest number of people per km2 is the Biscayne aquifer in Florida at nearly 453 people per km2.

Preferential groundwater flow directions in a pseudokarst system in Colombia, South America

The correct identification of recharge zones and understanding of groundwater flow through fractured and karstic media are some of the main issues in hydrogeology and are of utmost importance for managing groundwater resources. The Aburra Valley is an excellent example of a promising aquifer system for future water supply in Colombia, with recharge zones and hydrogeological units (HGU) still not well understood. One of those HGUs, the Medellin Dunite, is an ultramafic igneous rock with significant secondary porosity due to the high grade of fracturing and the presence of a pseudokarst system formed by the dissolution of magnesium-rich minerals. In this study, we aimed for the first approximation of this unit's hydrogeologic characteristics by performing a hydro-structural analysis based on a systematic collection of structural data in rock outcrops and secondary information available on karstic landforms. In order to improve the understanding of the relations between the analyzed HGU and the other units in the Aburra Valley, the main objective of our investigation was to calculate the hydraulic weight of discontinuities and determine the associated preferential groundwater flow directions. The results showed that the predominant directions of groundwater flow are WNW and ENE, which imply that lateral flows from the Dunite not only recharge the alluvial aquifers of the Aburra Valley Aquifer System (AVAS) but could also be recharging the San Nicolas Valley Aquifer System (SNVAS), another region with high rates of population growth. However, detailed studies are needed to establish the connections of the Dunite with the Medellin Amphibolite and other hard rocks of the SNVAS. Our findings show the importance of studying the Medellin Dunite and implementing management and protection measures for this aquifer unit.

Geophysical evaluation of geohydrokinetic properties of aquifer units in parts of Enugu state, Nigeria

Abstract Vertical electrical sounding employing Schlumberger electrode configuration was carried out in thirty locations across some parts of Enugu state, to investigate the hydrokinetic properties of hydrogeologic units of the study area. The result shows that resistivity and thickness of aquifer ranges from 27.3 to 59,569.0 Ωm and 23.3 to 242.1 m respectively. Permeability and fractional porosity values range from 4,531.254 to 74,006.76 mD and 0.026 to 0.159. AQI having a mean value of 13.5451 μm range from 6.809 to 52.976 μm. FZI and HFU values range from 37.582 to 1,962.074 μm and 18 to 26 respectively. Contour maps were generated from the results to visualize the variations of the hydrokinetic properties across the study area. From the contour maps, the southern part of the study area was identified to be characterized with high AQI, FZI and HFU with the northwestern part and a small proportion along the southwestern part identified as areas with low AQI, FZI and HFU. HFU along the study area was observed to be fractionated into nine distinct properties (HFU 18, HFU 19, HFU 20, HFU 21, HFU 22, HFU 23, HFU 24, HFU 25, and HFU 26) with HFU 19 and HFU 20 dominating the area. The results from the nine hydraulic flow units based on flow zone indicator cut off values (Log FZI>0.25) show that the reservoir quality is very high.

Insight into watershed hydrodynamics using silica, sulfate, and tritium: Source aquifers and water age in a mountain river

A clear concept of the recharge pathways for surface flow in mountain rivers is important for understanding the effects of climate change on streamflow in mountain block hydrology. In a mountain river in Alberta, Canada, three subsurface end-member sources were identified using silica, sulfate, and the isotopic composition of sulfate: interflow (water that has not undergone significant rock-water interaction), and groundwater derived from two types of hydrogeologic units (carbonate and siliciclastic fractured rock aquifers).A three end-member mixing model was used to determine their relative contributions to river discharge and infer relative groundwater ages using silica dissolution kinetics and tritium.In the three years of sampling, proportional contributions from subsurface end-members varied up to 25% within a given year while mean contributions between years varied as much as 19%. Interflow is the dominant source for the majority of the study period, contributing ~50% of river discharge during spring melt and 40–60% over the rest of the season. Siliciclastic and carbonate aquifer contributions varied interannually and seasonally. Although carbonate rocks comprise the majority of the watershed area, siliciclastic rocks contribute nearly equally to annual streamflow (~30% each), suggesting that siliciclastic aquifers transmit more water.Silica- and tritium-based ages suggest residence times on the order of <5–10 years. The combination of short residence times and significant variability in streamflow provenance suggest streamflow in this river will be rapidly affected by climatic change.

Hydrochemical evolution and assessment of groundwater quality in fluorosis-affected area, Mandla District, central India

Deterioration of groundwater quality is a matter of serious concern today. In Mandla region of central India, fluorosis is common among the local people due to consumption of fluoride-contaminated groundwater. It is, therefore, important to understand the hydrochemical process of contamination and assess the groundwater quality of this region. A total of 173 samples (pre-monsoon and post-monsoon) were collected from borewells and dug wells of different depths for major ions analysis: K+, Na+, Ca2+, Mg2+, Cl−, CO32−, HCO3−, NO3−, SO42−, and F−; along with pH, temperature, TH (as CaCO3), TDS and EC. Broadly, three hydrogeologic units have been identified, viz. Deccan lava flows, infratrappean Lameta and Archean granite and gneiss. In Deccan, two distinct hydrostratigraphic units are Mandla and Dhuma. Mandla is the most prominent and extensive aquifer having hydraulic conductivity 5–15 mday-1 and yield 10–50 m3day−1. Water quality data vis-à-vis well-depth data indicate that Mandla aquifer, lying at a lower elevation than 500 m amsl, is fluoride-contaminated and harmful for human health. Fluoride (41.0% of total samples) and bicarbonate (54.9% of total samples) concentrations in analyzed water are above the global standard for drinking purpose. However, above 500 m msl groundwater is not contaminated with fluoride and is suitable for drinking and irrigation purpose. Fluoride concentration maps depict spatial and seasonal variation. Spatial variation of fluoride in groundwater is due to change in aquifer lithology, varying degree of rock weathering and orientation of structural lineaments. In fluoride concentration map of post-monsoon season, broadening of contour of uncontaminated zone indicates groundwater recharge, which corroborates with water fluctuation map. The fluoride-contaminated water and low-fluoride water are mainly Na–HCO3 and Ca–HCO3 type, respectively. The hydrochemical processes suggest pre-dominance of rock-water interaction; contribution of Na+ and K+ ions in groundwater is due to silicate weathering, whereas Ca2+ and Mg2+ ions are derived due to both silicate and carbonate weathering. Saturation index calculation point towards calcite-dolomite supersaturation and consequent precipitation, along with fluorite dissolution under alkaline condition.

Recharge área maps from precipitation isoscapes. Case study: Aburrá Valley, Colombia

The environmental isotopes are a tool for interpreting the hydrological processes related to underground environments. These are used for the validation of hydrogeological models, in terms of recharge, transit and discharge zones, as well as the identification of groundwater interactions with other water bodies and groundwater residence time in the hydrogeological units. The determination of the recharge processes have usually been validated from knowledge about the stable isotopes present in the water molecule (18O and 2H). At the regional level, this evaluation has been addressed through the construction of isoscapes combined with an understanding of the hydrological characteristics present in the study area and knowledge of conceptual hydrogeological models. The objective of this study is to apply a scheme for the analysis of potential groundwater recharge zones, from 18O and 2H spatial variability in precipitation, baseflow and groundwater, using spatial modelling tools. Based on a preliminary work done for the Antioquia department, a strategic area was chosen in which the results are more forceful and have greater implications in groundwater management: the Aburrá Valley-Colombia.

Assessing the impact of tunnelling on karst groundwater balance by using lumped parameter models

Tunnelling activities may significantly alter the groundwater balance in a karst aquifer, but assessment of this effect remains challenging due to the complex flow geometries and strong hydrogeological heterogeneity. In this study, based on extensive site characterization of an independent hydrogeological unit (HU) in which a deep-buried tunnel is under construction, we present a modified lumped model to evaluate the impact of tunnel construction on the discharge from the aquifer system. The lumped model consists of four interacting flow compartments and the associated water balance equations. A series of simplified models is then developed, by merging or removing some of the flow components that represent different mechanisms and relationships between recharge and discharge. The dominant hydrological processes in the HU are identified by comparing the performance of the models of different structures and by screening analysis of parameter sensitivities. It is found that the tunnel excavation captured a mean portion of 19% discharge from the aquifer system into the tunnel, which is comparable to the result predicted by 3D numerical simulations. This study evidences that as a first and simple approximation, the lumped models provide a useful tool for characterizing the dominant factors that govern the groundwater response and for evaluating the groundwater budget changes induced by anthropogenic activities such as tunnelling and underground mining in karst regions.

Modelling the effect of geo-matrix conduction on the bulk and pore water resistivity in hydrogeological sedimentary beddings

Generally, the electrical method of geophysics is potentially valuable in typifying the subsurface conductivity and its surrounding medium. Sixteen datasets of 1-D electrical resistivity survey was integrated with 8 core samples, which were taken in the neighbourhood of eight of the sixteen VES datasets. The two sets of data were intertwined with geological and hydrogeological datasets to enhance the realization of unique results used in assessing the aquifer geo-matrix and pore water geo-resistivity in four counties in the coastal province of Akwa Ibom State, southern Nigeria. The current electrode separations of 1-D resistivity data were extended up to 300 m to ensure that the prolifically exploited water-bearing units were assessed. The VES data were manually and electronically modeled and each of them showed characteristic four geo-electric layers with KH, HK, KQ, HA and A group of curves. The core samples, which cut across the local Government Areas under survey, included sandy clay (12.5%), fine-grained sand (50.0%), medium-grained sand (12.5%) and coarse sand (25.0%). Bulk resistivities of water-bearing units and other primary geo-electrical indices were measured in all sixteen locations. However, in the eight aquifer core sample locations, water resistivities were measured in situ. The core samples were taken to the laboratory for measurements of fractional porosity and volumetric water content. The measured fractional porosity ranged from 0.189 to 0.267 with an average of 0.232, whilst volumetric water content varied from 0.23 to 0.31 with an average value of 0.268. The transmission coefficients were computed from volumetric water content and other parameters in the work. The values ranged from 0.4135 to 0.5612 with an average value of 0.4945. Fractional porosity was also modeled from field parameters and the results showed a good match with laboratory measurement as the root—mean square error was just 1.3%. Intrinsic specific resistance and conductivity of soil aquifer matrix were found to be $$3.333 \times 10^{3} \;\Omega {\text{m}}$$ and $$3.000 \times 10^{ - 4} \;{\text{Sm}}^{ - 1}$$ respectively. The study has provided useful information about the geo-electrical and geo-pore properties of the prolifically exploited aquifers in the study area. The aquifer parameter contour maps have been delineated and these, together with other parameter relations generated in this study could help in predicting the volumetric conductivity between pore water and the matrix texture of hydrogeological units in the study area and other areas with similar geology.

Application of fuzzy analytic hierarchy process in sandstone aquifer water yield property evaluation

Accurate evaluation of water yield property is the foundation of mine water inrush risk analysis, and is also an important prerequisite for engineering measures selection. There are many factors or parameters that influence the ability of sandstone aquifers to store and transmit water. Furthermore, the degree to which these parameters affect aquifer productivity is variable depending on the spatial distribution of the parameter in question and other hydrogeological parameters that contribute to water yield property When locates in different position of space, or under different hydrogeological condition, influencing degree from the same factor is different. Five hydrogeological parameters were selected and analyzed to rank areas for potential mine inflow risk based on the hydrogeological units to be intersected by the Yongan Coal Mine. The parameters used in the analysis include aquifer thickness, aquifer lithological association, development of fractures, drilling flushing fluid consumption rates and the coefficient of permeability. Firstly, the distribution of each single factor was separately analyzed, parameters were standardized using the standardization range transform method. In this way, dimension and value range difference could be eliminated, and transformation rule of information data could be studied under the same standard scale. The weight of each factor was determined using improved fuzzy analytic hierarchy process (FAHP). Those factors were then overlaid and analyzed according to the multi-source geo-information fusion principal and to the ability of data process and spatial analysis by GIS. Lastly, aquifer water yield property indexes were calculated and zones were identified. The partition result showed that sandstone aquifer water yield property in Yongan Coal Mine was increased from the northeast to the southwest. This finding is consistent with the hydrogeologic understanding of the study area. The distribution of the parameters used to determine aquifer water yield property in this study is relative but will be helpful for engineering design and construction. These analyses are based on data routinely collected as part of the geological exploration data and on published geological reports. The FAHP methodology employed in this study to evaluate sandstone aquifer productivity is considered to be a novel approach to evaluating mine water inrush potential. • Factors were analyzed and standardized by standardization range transform method. • Factors were overlay analyzed by multi-source geo-information fusion and GIS. • Water yield property distribution is relative, and will be helpful to engineering.

Investigating distribution of nitrate concentration using ensemble nonparametric quantile regression

Abstract Nitrate ( NO3−) pollution in groundwater is a major concern due to its negative health effects; therefore, accurately estimating and predicting the NO3− concentration in groundwater is necessary. The NO3− concentration distribution can be used to find less polluted areas, and these identified areas can be candidates for drinking water resources. We considered a total of 14,297 NO3− concentration observations in South Korea. Altitude, slope, land use, hydrogeological unit, and surface soil texture data were also collected to assess the covariates that affect NO3− concentration levels. Sample quantiles display nonlinear patterns based on these covariates. Thus, we propose using an ensemble nonparametric quantile regression approach to determine the NO3− concentration distribution. The proposed approach is a data-driven method that ensembles nonlinear quantile models to capture the complex relationships between quantiles of the response variable and the covariates while controlling the computational complexity, which are advantages over non-ensemble quantile regression methods. The validation study demonstrates that the proposed method exhibits a smaller loss value compared to that of the non-ensemble models considered for comparison. We investigated lower quantile maps of NO3− concentration (5% and 10%), as we are interested in less polluted areas. The proposed model attempts to reach the sample quantile values while a non-ensemble nonlinear model with altitude and slope does not except land use is coniferous at low altitude. We created a proportional map with less polluted areas at the district level using the proposed approach. This provided us with the top five districts (Samcheok City, Geochang County, Yanggu County, Inje County, and Yeongwol County) with the highest proportions of less-polluted areas in South Korea.

Delineation of groundwater quality locations suitable for target end‐use purposes through deep neural network models

Groundwater is the main source of water for beverages, and its quality varies depending on extraction location; this is particularly the case in regions with complex geology, topography, and multiple forms of land use. Thus, it is important to determine a suitable groundwater extraction location based on intended water use and the related water quality standards. In this study, deep neural network (DNN) models and GIS data relating to the groundwater quality were applied to estimate potential maps of Gangwon province, where groundwater is frequently extracted for drinking purpose in South Korea. These maps specify areas wherein the groundwater quality is conducive for being used as mineral water and water for brewing coffee (hereafter referred as 'coffee water'). Sensitivity analysis identified how inputs were sensitive to model estimation, and showed that land-use variables were the most sensitive. The importance of each variable quantified how good or bad its region is for the desired groundwater. The overall features of importance were similar between mineral water and coffee water. However, with differences in hydrogeological units, carbonate rock was a variable of high positive importance for mineral water, while metamorphic rock was its equivalent for coffee water. Our results offer a potential map of desired groundwater quality in the absence of a detailed understanding of the underlying hydrochemical processes governing groundwater quality. Additionally, the development of such a potential mapping model can lead people to determine the appropriate development area of groundwater for their respective purposes. This article is protected by copyright. All rights reserved.

Sources and hydrogeological conditions that cause high iodine concentrations in deep groundwater in the Zhangwei watershed, North China Plain

The sources and primary mechanisms of high iodine concentration in deep groundwater are rarely reported, thereby restricting the development and utilization of the related groundwater resources. To address these issues, 194 deep groundwater samples were collected from the Zhangwei watershed in the North China Plain, China, to analyze their constituents including iodine. Statistics, principal component analysis and hydrological methods were employed to determine the distribution of iodine concentrations and their controlling hydrogeochemical processes. The results show that the iodine concentration ranged from 2 to 446 μg/L and generally increased along the groundwater flow direction. Three zones with high iodine concentration (> 20 μg/L) were delineated as the alluvial–proluvial plain (Zone A, average 70 μg/L), alluvial–lake plain (Zone B, average 83 μg/L) and coastal plain (Zone C, average 199 μg/L), respectively. In Zone A, aquifer minerals weathering probably releases iodate ions into groundwater. The iodate is reduced with nitrate as the electron acceptor of iodine and transported with the precipitation infiltrating through the vadose zone to recharge groundwater, resulting in increasing the groundwater iodine concentration. In Zone B, the iodine concentrations depend on the contents of the organic matter, clay minerals, and iron aluminum oxide in the alluvial–lake sediments, due to that the deeply buried organic matter is rich in iodine which is released into groundwater through the biodegradation of organic matter, In Zone C, the iodine is probably derived from the sediments which were deposited in Quaternary marine transgression events, and its enrichment was controlled by the strong reduction condition of the deep aquifers. In one word, the iodine sources and hydrogeological conditions determined the high iodine concentrations of deep groundwater in the studied watershed. These findings can provide foundation for further insight into the high iodine concentration of deep groundwater in other hydrogeological units of the North China Plain and other similar units over the world, thereby ensuring drinking groundwater safety.

Space-time modelling of groundwater level and salinity

Soil salinization resulting from shallow saline groundwater is a major global environmental issue causing land degradation, especially in semi-arid regions such as Australia. The adverse impact of shallow saline groundwater on soil salinization varies in space and time due to the variation in groundwater levels and salt concentration. Understanding the spatio-temporal variation is therefore vital to develop an effective salinity management strategy. In New South Wales, Australia, a hydrogeological landscape unit approach is generally applied, based on spatial information and expert operators, classifying the landscape in relation to landscape and climate. In this paper, a data science approach (random forest model) is introduced, based on historical groundwater quality and quantity data providing predictions in a 4-dimensional space. As a case study, we demonstrate the spatio-temporal factors impacting standing water levels (SWL) and associated salinity and predict the spatial and temporal variability in the Muttama catchment (1059 km2), in NSW, south eastern Australia. The random forest model explains 77% of the variance in the groundwater salinity (electrical conductivity) and 65% of the SWL. Spatial factors were the most significant variables determining the space-time variation in groundwater salinity and the occurrence of groundwater at the surface. Drilled piezometer depth and elevation are dominant factors controlling SWL, while salinity is mainly determined by underlying geology. The methodology in this study predicts salinity and SWL in the landscape at fine scales, through time, improving options for salinity management.