Sandow Mark Yidana

Identifying key processes in the hydrochemistry of a basin through the combined use of factor and regression models

An innovative technique of measuring the intensities of major sources of variation in the hydrochemistry of (ground) water in a basin has been developed. This technique, which is based on the combination of R-mode factor and multiple regression analyses, can be used to measure the degrees of influence of the major sources of variation in the hydrochemistry without measuring the concentrations of the entire set of physico-chemical parameters which are often used to characterize water systems. R-mode factor analysis was applied to the data of 13 physico-chemical parameters and 50 samples in order to determine the major sources of variation in the hydrochemistry of some aquifers in the western region of Ghana. In this study, three sources of variation in the hydrochemistry were distinguished: the dissolution of chlorides and sulfates of the major cations, carbonate mineral dissolution, and silicate mineral weathering. Two key parameters were identified with each of the processes and multiple regression models were developed for each process. These models were tested and found to predict these processes quite accurately, and can be applied anywhere within the terrain. This technique can be reliably applied in areas where logistical constraints limit water sampling for whole basin hydrochemical characterization. Q-mode hierarchical cluster analysis (HCA) applied to the data revealed three major groundwater associations distinguished on the basis of the major causes of variation in the hydrochemistry. The three groundwater types represent Na–HCO3, Ca–HCO3, and Na–Cl groundwater types. Silicate stability diagrams suggest that all these groundwater types are mainly stable in the kaolinite and montmorillonite fields suggesting moderately restricted flow conditions.

Groundwater quality in some Voltaian and Birimian aquifers in northern Ghana—application of mulitvariate statistical methods and geographic information systems

Abstract Groundwater is a priceless resource in the economies of the rural populations in northern Ghana. A combination of multivariate statistical and spatial analytical techniques was applied to groundwater data from the Voltaian and Birimian aquifers in parts of northern Ghana. The objective was to classify the groundwater quality control parameters and determine whether the aquifers deliver groundwater of acceptable quality for domestic and commercial irrigation purposes. It was found that groundwater quality is dominated by the weathering of accessory minerals that are predominant in the Obosum and Oti beds of the Middle Voltaian in the north, and incongruent silicate mineral weathering ranks second among the major causes of variation. The two processes account for over 70% of the total variance in the hydrochemistry and interpolation maps generated for these two major factors are discussed. The mineral weathering and dissolution processes are less apparent within the Birimian aquifers. Four spatial groundwater types were distinguished by differences in EC and pH, which are high among the water types within the Obosum and Oti beds, and generally low within the Birimian aquifers. Mineral stability diagrams suggest that montmorillonite is the most stable clay mineral phase in the system, a significant finding in terms of cation exchange processes. This, in turn, has affected the irrigation quality of groundwater from the aquifers in the area. Our findings suggest that the Birimian aquifers are more suitable for irrigation, due to generally low salinities and sodicities, and those associated with the Obosum and Oti beds of the Middle Voltaian are less suitable. Editor D. Koutsoyiannis; Associate editor Y. Guttman Citation Yidana, S.M., Banoeng-Yakubo, B., Aliou, A.-S., and Akabzaa, T., 2012. Groundwater quality in some Voltaian and Birimian aquifers in northern Ghana—application of mulitvariate statistical methods and geographic information systems. Hydrological Sciences Journal, 57 (6), 1168–1183.

Analysis of recharge and groundwater flow in parts of a weathered aquifer system in Northern Ghana

Stable isotope data were used to relate recent meteoric water to groundwater in parts of the Nabogo sub-catchment of the Voltaian Basin. Estimates of the rates of evaporation of recharging groundwater in transit were made on the basis of the stable isotope data. This study finds that groundwater recharge within the weathered zone aquifer system in the study area is of recent meteoric origin. There is, however, evidence of significant evaporation of recharging water in the range of 34–70%, as a result of high temperatures and low relative humidities. This high level of evaporation of rainwater prior to or in the process of recharge is attributed partly to slow infiltration due to significant clay content of the intervening material between the saturated zone and the surface. It suggests limited but variable fortunes in terms of groundwater recharge from precipitation in the area and ties in with previous findings in relation to groundwater recharge estimates. This justified the use of previous estimates of groundwater recharge in other parts of the terrain for the conceptualization of the groundwater flow through a numerical model under steady-state conditions. This study determines that the general groundwater flow is controlled by local flow systems with no obvious preferred direction of flow. Calibrated hydraulic conductivity estimates range between 0.35 and 5.14 m/d. This is consistent with the nature of the material of the aquifer, and will provide the basis for assessing the hydrogeological conditions of the weathered zone.

An integrated approach to environmental risk assessment of cumulatively impacted drainage basin from mining activities in southwestern Ghana

Acid rock/mine drainage and metal leaching constitute major environmental management risks in the mining industry. This paper assesses the environmental risks due to acid rock/mine drainage, and the metal leaching potential of multiple mines of gold and manganese on the Ankobra River Drainage Basin in Southwestern Ghana. The basin is a hub of mining activity in Ghana, hosting several mines. A combination of mineralogical, and static geochemical acid drainage predictive investigation of overburden of varied geological units, complimented with hydrochemical drainage quality analysis was used to assess potential environmental risks posed by acid-generating lithologies and mine spoil. Mineralogical investigations revealed sulphide-bearing lithological units with profound compositional variations due to the incorporation of potentially toxic heavy metals and metalloids, in association with carbonates and silicates. Accounting Base Accounting (ABA) and Net acid generation potential pH (NAGpH) tests delimited two tailing sites as potentially acid generating with NAGpH of 3.5 and 4.8, respectively. Five other samples, representing specific lithological units in the stratigraphic sequence, with net acid neutralization potential ratio (NNPR) less than 5.0, were classified as being potentially acid generating according to the categorization requirement of the US Forestry Service. The rest of the samples exhibited moderate to very strong buffering capabilities. The assessment also evaluated drainage quality of the network of streams and rivers constituting the basin and identified sources of drainage contaminants. Acidic waters emanate from identified acid generating sources, while high metal load regimes were identified with both low pH waters and high pH regimes, coincident with high sulphide and carbonate alteration sites, respectively. The study results show that Zn, Cu, Ni, As, Co, Sb, SO42−, pH, alkalinity and conductivity are essential and adequate parameters in routine environmental risk monitoring programmes of mines in the area. Sites characterized by low pH (<5.5) with high sulphate and metal ions are suggestive of acid mine drainage, while sites with high pH (>7.5), metal ions and sulphate are suggestive of net acid neutralizing.

Evaluation of Groundwater Recharge Estimates in a Partially Metamorphosed Sedimentary Basin in a Tropical Environment: Application of Natural Tracers

This study tests the representativeness of groundwater recharge estimates through the chloride mass balance (CMB) method in a tropical environment. The representativeness of recharge estimates using this methodology is tested using evaporation estimates from isotope data, the general spatial distribution of the potential field, and the topographical variations in the area. This study suggests that annual groundwater recharge rates in the area ranges between 0.9% and 21% of annual precipitation. These estimates are consistent with evaporation rates computed from stable isotope data of groundwater and surface water in the Voltaian Basin. Moreover, estimates of groundwater recharge through numerical model calibration in other parts of the terrain appear to be consistent with the current data in this study. A spatial distribution of groundwater recharge in the area based on the estimated data takes a pattern akin to the spatial pattern of distribution of the hydraulic head, the local topography, and geology of the terrain. This suggests that the estimates at least qualitatively predicts the local recharge and discharge locations in the terrain.

Hydrogeological characterization of a tropical crystalline aquifer system

This research used a numerical groundwater flow model, calibrated under steady-state conditions to develop the groundwater flow system in the West Mamprusi District of Northern Ghana. It was aimed at conceptualizing the flow system to initiate a thorough hydrogeological study of the rocks in the area. Stable isotopes were used to relate groundwater recharge in the area to recent meteoric water that had been evaporated in transit down the surficial material. On this basis, direct vertical groundwater recharge from precipitation was applied in the numerical modeling. This study suggests that the prospects of commercial development of the aquifers are high as the estimated recharge ranges between 3.3% and 29% of the annual precipitation. Estimated horizontal hydraulic conductivity ranges between 3.2 and 48 m/d in the area. The variability in the horizontal hydraulic conductivity has led to the development of four prominent groundwater flowpaths in the area. However, a prominent NE–SW flow has been observed and is in consonance with the reported structural grain of the country. A groundwater flow divide noted in the southern part of the study area has been attributed to the structural heterogeneity rather than topographical complexities as the area is largely flat.

Hydrogeological Conditions of a Crystalline Aquifer: Simulation of Optimal Abstraction Rates under Scenarios of Reduced Recharge

A steady state numerical groundwater flow model has been calibrated to characterize the spatial distribution of a key hydraulic parameter in a crystalline aquifer in southwestern Ghana. This was to provide an initial basis for characterizing the hydrogeology of the terrain with a view to assisting in the large scale development of groundwater resources for various uses. The results suggest that the structural entities that control groundwater occurrence in the area are quite heterogeneous in their nature and orientation, ascribing hydraulic conductivity values in the range of 4.5 m/d to over 70 m/d to the simulated aquifer. Aquifer heterogeneities, coupled possibly with topographical trends, have led to the development of five prominent groundwater flowpaths in the area. Estimated groundwater recharge at calibration ranges between 0.25% and 9.13% of the total annual rainfall and appears to hold significant promise for large-scale groundwater development to support irrigation schemes. However, the model suggests that with reduced recharge by up to 30% of the current rates, the system can only sustain increased groundwater abstraction by up to 150% of the current abstraction rates. Prudent management of the resource will require a much more detailed hydrogeological study that identifies all the aquifers in the basin for the assessment of sustainable basin yield.