Sustainability of Human, Plant, and Aquatic Life: A Theoretical Discussion from Recharge to Discharge

Groundwater comprises about 1.7% of the earth’s total water and over 30% of the total freshwater supply. Is there enough groundwater to meet human, plant, and aquatic life needs? In many parts of the world, yes; however, with changing demographics and concordant land use and climate change, the distribution and availability of groundwater may not be sustainable. This chapter considers some of the current and past stressors of groundwater by using case examples from around the world. We explore hydrogeologic settings where anthropogenic activity has impaired or has the potential to impair human, plant, and aquatic life. Stressors include well pumping, mining, climate change, chemical use, water law/regulation, and manipulation of surface water. These examples serve to inform those concerned about sustainable management and offer insight into the links between groundwater, climate, and land use

Riverine‐Based Aquifers and Riparian Exchange: A Conceptual Discussion

This chapter presents a conceptual discussion of the aquifers that typically occur along river channels and the riparian exchange of water as influenced by valley and channel type and management. Definitions of alluvial and bedrock river channel, based on literature, are provided while highlighting their general attributes and exchange options. Conceptual aquifer models occurring along alluvial and bedrock river channels are then described and presented with respect to groundwater‐surface exchanges and solute fate and transport. There is theoretical reasoning to suggest that channel aquifers and concordant riparian zones can be conceptualized and classified based on valley type and the nature of the river channel hosting the aquifer. The information presented in the conceptual models can be used during desktop studies to strategically plan the optimal management for aquifer and riparian protection and restoration activities subject to anthropogenic risk. Riparian zone management is needed more so today, because basin land use in many parts of the world has advanced to the point of creating both water quantity and quality disequilibrium

Groundwater Quality Assessment of Shallow Aquifer Hand Dug Wells in Rural Localities of Ilorin Northcentral Nigeria: Implications for Domestic and Irrigation Uses

Published ArticleThis research determined the quality of shallow hand dug wells for domestic and irrigation uses in the rural localities of Ilorin, Northcentral Nigeria. Twenty (20) water samples were collected from shallow hand dug wells in the study area during wet and dry seasons. The water samples were assessed for physical and chemical qualities. Results indicates that pH of water samples is acidic to alkaline which ranges between 6.7 and 7.6 in dry season and ranges from 6.6 to 7.2 for wet season. The pH values fall within the permissible limits of World Health Organization (WHO) standards and Nigerian Drinking Water Quality Standards (NDWQS). Quality standards of chemical parameters analysed in the water samples falls within the permissible limits. MgHCO3 is considered as the most dominant water type in both seasons. Magnesium occurrence was traced to the disintegration of rock minerals while dominance of bicarbonates in the water contributed mostly by carbon dioxide charged recharge water during precipitation. Irrigation parameters tested includes Soluble Sodium Percentage (SSP), Residual Sodium Bicarbonate (RSBC), Sodium Absorption Ratio (SAR) and Magnesium Adsorption Ratio (MAR) which all indicates that the water samples are also suitable for irrigation

A New Method For Estimating Hydraulic Conductivity In Un-Screened Concrete-Lined Large-Diameter Hand-Dug Wells

ArticleThe use of large-diameter hand-dug wells as main source of rural water supply for drinking, domestic and irrigation uses in many developing countries has offer an opportunity to developed Darcy-based methods for estimating hydraulic conductivity in screened-lined large-diameter hand-dug wells to determine the yield and discharge potential of the wells. However, in many rural areas of sub-Saharan African countries, the use of unscreened concrete lining is most common method of protecting large-diameter hand-dug wells against collapsing and pollution due to the affordability of the method. The use of un-screened concrete lining prevents horizontal water flow to the well and inflow of water in un-screened concrete well occur through well base, therefore, existing Darcy-based method not suitable to estimate hydraulic conductivity for this well design. This study proposed a new method for estimating aquifer hydraulic conductivity for un-screened concrete-lined largediameter hand-dug wells. To demonstrate the viability of the new method, field recovery tests were conducted in twelve (12) un-screened concrete lined large-diameter hand-dug wells to estimate apparent hydraulic conductivity (Ka) of aquifer formation. The twelve (12) un-screened concrete wells were screened for the second round of recovery tests to estimate horizontal hydraulic conductivity K. The results showed that the estimated apparent hydraulic conductivity Ka values were lower than the horizontal hydraulic conductivity K values and this show effect of un-screened concrete-lining. A relationship between Ka and K was established to make a correction factor for estimation of K from Ka by a regression analysis which showed a linear regression of 0.78 with a significant strong relationship of 0.00 between Ka and K using a bivariate Pearson correlation coefficient. The new method will be useful to determine well yield most especially in the rural areas of developing countries where un-screened concrete-lined large-diameter hand-dug wells are being practiced

A groundwater-surface water interaction study of an alluvial channel aquifer

The study describes the application complimentary geohydrologic tools to investigate the geohydrological properties of an alluvial channel aquifer and its interaction with the river surface water resources. Primary field investigations were designed to determine the geologic, hydraulic, hydrogeochemical and solute transport properties of the alluvial channel aquifer as an important component of the groundwater‐surface water (GW‐SW) interaction system. The secondary investigations were then aimed at assessing groundwater discharge and recharge mechanisms of the alluvial channel aquifer at a local scale (< 1000 m). A water balance model was developed for the groundwater‐surface system as a tertiary level of investigation. Geological characterisation results show the spatial variation in the physical properties of unconsolidated aquifer materials between boreholes and at different depth. The drawdown derivative diagnostic analysis shows that the alluvial channel aquifer system response during pumping can be described by the following major groundwater flow characteristics; Typical Theis response; transition period from initial Theis response to radial acting flow (RAF); radial acting flow in the gravel‐sand layer and river single impermeable boundary effects. Detailed studies of the hydrogeochemical processes in the alluvial aquifer system have shown that dissolution of silicate weathering, dolomite and calcite minerals, and ion exchanges are the dominant hydrogeochemical processes that controls groundwater quality. Quantitative and qualitative investigations indicate that the alluvial channel aquifer is being recharged through preferential infiltration recharge as facilitated by cavities and holes created by the burrowing animals and dense tree rooting system. Tracer tests under natural gradient were successfully conducted in an alluvial channel aquifer, thus providing some advice on how to conduct tracer breakthrough tests under natural gradients in a typical alluvial channel aquifer. The findings of the study also highlights the value of developing a water balance model as a preliminary requirement before detailed GW‐SW interaction investigations can be conducted. Based on the theoretical conceptualizations and field evidence it is suggested that studies be conducted to determine if alluvial channel aquifers can be further classified based on the nature of the hosting river channel. The classification would split the alluvial channel aquifer into alluvial cover and fractured‐bedrock, or a combination of the two. The applications of the PhD thesis findings are not only limited to the case study site, but have important implications for GW‐SW interaction studies, groundwater resource development and protection in areas where groundwater occurs in alluvial channel deposits

Site characterisation of LNAPL-contaminated fractured-rock aquifer

English: Site characterisation aims to obtain fundamental data needed to describe the subsurface flow pathways and distribution of contaminants. The study describes the application of various geohydrological techniques as complimentary tools to characterise an LNAPL contaminated fractured - rock aquifer on the Beaufort West study area in South Africa. Field investigations were designed to define and determine the properties of the fracture preferential flow paths responsible for LNAPL transportation in a typical Karoo fractured - rock aquifer system. The research places emphasis on the integration of results to maximise the subsurface geological understanding in particular location of fracture features chiefly responsible for facilitating LNAPL migration and distribution. The core and percussion drilling explorations, cross - correlated with borehole geophysics, were valuable for geological subsurface investigations in particular locations of bedding fractures, which are often associated with high hydraulic conductive flow zones. Tracer and pump tests were conducted to determine hydraulic and mass transport parameters respectively. Hydraulically conductive bedding plane fracture flow zones were identified by integrating results from the geological core logs, borehole geophysics and aquifer tests. The chemical characterisation of the study area was conducted by means of organic hydrocarbon, inorganic water analyses and volatile organic carbon measurements in the soil during air percussion drilling. Based on the findings, the hydrogeological structure of the formation was conceptualised as a fractured sandstone aquifer, characterised by bedding plane fracture preferential flow paths at contact areas, with shale and mudstone formations. The study findings demonstrate the merit and value in the application of various geohydrological tools to complement one another for optimised site understanding. The findings and recommendations of the case study are not necessarily confined to LNAPL contaminated fractured - rock aquifers, but may also be applicable to other types of contaminants in fractured - rock aquifer formations.Afrikaans: Die doel van terrein karakterisering is om fundamentele data te verkry wat benodig word om die ondergrondse vloeirigtings en verspreiding van kontaminasie te beskryf. Die studie beskryf die toepassing van verskeie geohidrologiese tegnieke as komplimenterende middele vir die karakterisering van 'n LNWV (ligte nie-wateroplosbare vloeistowwe) besoedelde fraktuur-klip akwifeer in die Beaufort-Wes studie area in Suid-Afrika. Veldondersoeke is ontwerp om die eienskappe van fraktuur voorkeur vloeirigtings te definieer en bepaal. Hierdie vloeirigtings is verantwoordelik vir LNWV vervoer in 'n tipiese Karoo fraktuur-klip akwifeer stelsel. Die ondersoek plaas klem op die integrasie van resultate om die begrip van ondergrondse geologie te maksimeer, veral in terme van die ligging van frakture wat verantwoordelik is vir LNWV migrase en verspreiding. Die kern- en slagboorgat ondersoeke is gebruik en 'n kruis-vergelykking was gemaak met boorgat geofisika. Dit was waardevol in terme van ondergrondse geologiese ondersoeke, spesifiek met betrekking tot die ligging van stratifikasie frakture, wat dikwels geassossieer word met hoë hidroliese en massavervoer parameters. Hidrolies geleidende stratifikasie vlak fraktuur vloei sones is geidentifiseer deur die integrasie van resultate vanaf die kernaantekeninge, geofisiese en akwifeer toetse. Die chemiese karakterisering van die studieterrein is voltooi deur middel van organiese hidrokoolstof, anorganiese water analiese en deur die meting van vlugtige organiese koolstof in die grond gedurende lug slagboorwerk. Die bevindinge dui aan dat die hidrogeologiese struktuur van die formasie as 'n fraktuur sandsteen akwifeer gekonseptualiseer is. Dit word gekenmerk deur stratifikasie vlak fraktuur voorkeur vloeiroetes in kontakareas, met leiklip en modderklip formasies. Hiermee word die meriete en waarde van die bevindinge gedemonstreer in terme van die toepassing van verskeie geohidrologiese middels vir optimale terrein bepaling. Die bevindinge en aanbevelings van die studie is nie noodwendig beperk tot LNWV besoedelde fraktuur-klip akwifere nie; dit kan ook toepaslik gemaak word op ander tipes kontaminasie in fraktuur-klip akwifeer formasies.Water Research Commission (WRC

Site characterisation of LNAPL-contaminated fractured-rock aquifer

Site characterisation aims to obtain fundamental data needed to describe the subsurface flow pathways and distribution of contaminants. The study describes the application of various geohydrological techniques as complimentary tools to characterise an LNAPL contaminated fractured - rock aquifer on the Beaufort West study area in South Africa. Field investigations were designed to define and determine the properties of the fracture preferential flow paths responsible for LNAPL transportation in a typical Karoo fractured – rock aquifer system. The research places emphasis on the integration of results to maximise the subsurface geological understanding in particular location of fracture features chiefly responsible for facilitating LNAPL migration and distribution. The core and percussion drilling explorations, cross - correlated with borehole geophysics, were valuable for geological subsurface investigations in particular locations of bedding fractures, which are often associated with high hydraulic conductive flow zones. Tracer and pump tests were conducted to determine hydraulic and mass transport parameters respectively. Hydraulically conductive bedding plane fracture flow zones were identified by integrating results from the geological core logs, borehole geophysics and aquifer tests. The chemical characterisation of the study area was conducted by means of organic hydrocarbon, inorganic water analyses and volatile organic carbon measurements in the soil during air percussion drilling. Based on the findings, the hydrogeological structure of the formation was conceptualised as a fractured sandstone aquifer, characterised by bedding plane fracture preferential flow paths at contact areas, with shale and mudstone formations. The study findings demonstrate the merit and value in the application of various geohydrological tools to complement one another for optimised site understanding. The findings and recommendations of the case study are not necessarily confined to LNAPL contaminated fractured - rock aquifers, but may also be applicable to other types of contaminants in fractured - rock aquifer formations.Water Research Commission (WRC

A transboundary aquifer of potential concern in Southern Africa

Abstract Tuli Karoo transboundary aquifer (TBA) is shared between Botswana, South Africa and Zimbabwe in the Southern African Development Community (SADC) region. The TBA provides groundwater resources for various economic activities. Irrespective of the value offered by this TBA, there is very little research that has been conducted to improve understanding of the physical system and potential cross-border impacts that can result from exploitation of the aquifer. In the wake of this limited research, this paper uses theoretical background and conceptual understanding to highlight some of the activities that have the potential to cause conflicts within the TBA. This article presents and discusses the current hydrogeological conceptual understanding of the Tuli Karoo TBA system, social and economic activities and their potential impacts on the TBA. Based on the discussions of various scenarios, it can be argued that the potential for groundwater cross-border flow and impacts exist within the TBA. With the ever-increasing and competing demands for fresh water and unpredictable rainfall patterns in the region, the possibility of future conflicts cannot be ruled out. It is hoped that this study can assist in raising awareness about the need to address aspects of sustainable exploitation and management of the TBA.</jats:p