Hydrogeochemical Characterization of Groundwater from Fissured Aquifers in the Angovia Mine Operating Permit Area (Central-West Côte d’Ivoire)

The main objective of this study is to determine the hydrogeochemical specificities of the groundwater of the Angovia mine operating permit, located in the Yaouré mountains in the center-west of Côte d’Ivoire. To do so, descriptive and multivariate statistical analysis methods with the SOM (Self Organizing Maps) algorithm were applied to the physicochemical parameters of 17 boreholes using the calcite (ISC) and dolomite (ISD) saturation indices. The results obtained have shown that the groundwater in the Angovia mine operating permit area has an average temperature of 27.52°C (long rainy season) and 27.87&degC (long dry season) and has an average pH of 7.09 ± 0.35 during the main rainy season and 7.32 ± 0.35 during the main dry season. They are mineralized with an average electrical conductivity of 505.98 ± 302.85 μS/cm during the long rainy season and with 450.33 ± 233.74 μS/cm as average during the long dry season. The main phenomena at the origin of groundwater mineralization are water residence time, oxidation-reduction and surface inflow. The study of the relative age of the water shows that the groundwater in the Angovia mine operating permit area is mainly undersaturated with respect to calcite and dolomite. They are therefore very old in the aquifer with a slow circulation speed during the long rainy season and the long dry season.

Assessment of Vulnerability to Groundwater Pollution in the Lobo Watershed at Nibéhibé(Central-West, Côte d’Ivoire)

Drinking water supply to people in rural areas is increasingly oriented towards the search for groundwater. However, these resources, which were once of good quality, are currently threatened by various sources of pollution points and diffuse. The objective of this study is to map the intrinsic vulnerability to groundwater pollution of the Lobo watershed in Nibéhibé. The intrinsic vulnerability mapping method, PaPRIKa adapted or PaPRI which acronym is the protection of aquifers (Pa) based on three criteria: P for protection, R for rock type, I represents infiltration was used. The results show three (3) vulnerability classes, which are moderate, high and very high. This map shows that the high vulnerability class (89%) dominates the study area. This predominance shows that the groundwater of the Lobo watershed is at high risk of pollution.

Development of a Model for Assessing Vulnerability to Pollution of Groundwater in Fissured Aquifers: The Case of the Ehania Watershed (South-Eastern Côte d’Ivoire)

The protection of aquifers is a major concern for the authorities, especially in areas where there are large agro-industrial exploitations. The objective of this study is to define a new method of aquifer protection based on the characteristics of the structures of aquifers. The intrinsic vulnerability mapping method, PaPRI was used. It is a variant of the PaPRIKa method applied in karstic environment which has been adapted for its application in basement environment. This method uses three factors, including aquifer protection (P), using the soil cover, the unsaturated zone and the thickness of the alteration layer, (R) for the rock type and (I) for infiltration which including slope and drainage density. PAPRI is a method based on the weighting of different factors. The results obtained show 4 classes that evolve from low vulnerability classes (5% of the study area) to high and very high vulnerability classes (58%) and average vulnerability classes (37%). The classes of high and very high vulnerability, which indicate the zones that are very exposed to pollution, are more present in the central-northern part of the study area, with a few appearances towards the south. These zones could be related to topography due to the often very high slopes observed in the area. One of the advantages of this new method lies in the characterization of the alterations that strongly influence the migration of pollutants towards the water tables according to their nature and their thickness.

Desorption of Methylene Blue Adsorbed on Activated Carbon from Cocoa Pod Shell

Environmental protection has become a concern for the world. For this reason, the objective of this work is to remove methylene blue adsorbed on activated carbon. The coal used comes from cocoa pod shells. Before pyrolysis, the shells were ground, sieved and impregnated with orthophosphoric acid. Before desorption, the activated carbons were initially saturated with MB. These saturated coals were brought into contact with a sodium chloride (NaCl) solution and then stirred. The evolution of the resorbed MB concentration was monitored by spectrophotometry. The desorption tests showed a remarkable elimination from the first 10 minutes. The desorption kinetics comprises two phases: a rapid kinetics between 0 and 30 minutes and a slow kinetics between 30 and 60 minutes. The desorption of the dye reaches a concentration aqual to 0.84 mg/l at pH = 4 at temperature = 80°C. For modeling, the coefficient of the Langmuir II model is greater than or equal to O.9893. The model of Langmuir III is less than or equal to 0.9373. The Freundlich model coefficient is 0.9842 or less. The desorption is thefore carried out on energy-homogeneous adsorption sites and without any interaction between the adsorbed cations of the dye. Experimental parameters such as pH, temperature and concentration of sodium chloride (NaCl) solution influence the desorption of MB. And the model of Langmuir II describes well the process of desorption of the MB.

Potential Groundwater Pollution Risks by Heavy Metals from Agricultural Soil in Songon Area(Abidjan,Cote d’Ivoire)

The soil samples were collected taking into account the land use in Songon area. The hydraulic conductivity (K) of soils was characterized in-situ when specific yield (Sy), pHw and concentrations of Cooper, Iron, Zinc, Cadmium, Chromium and Lead were measured in the laboratory. Pollution load indices (PLI) were calculated to evaluate the soil contamination levels. The soils were neutral and alkaline (6.7≤ pH ≤ 9.20), permeable (1.9 í 10-5?m·s-1?≤ K ≤ 8.2 í 10-4?m·s-1), with a high specific yield (13.33% ≤ Sy ≤ 33.33%) which can favor the pollutants transfer. The heavy metals (Fe, Cu, Zn, Cd, Cr and Pb) have very high concentrations in soils. The integrated pollution indices (PLI) indicate that almost 70% of Songon soils are moderately contaminated by the investigated heavy metals, with windows presenting high indices of pollution related to the intensive use of fertilizers and pesticides. The establishment of new boreholes in the Songon area should consider these heavy metals, so as to avoid the risk of groundwater pollution due to the physical properties of soils.

Modeling of Quaternary Groundwater Pollution Risk by GIS and Multicriteria Analysis in the Southern Part of Abidjan District(Cote d’Ivoire)

The pollution generated by human activities in the area “Vridi canal-Grand Bassam” puts more at risk the quaternary groundwater that supplies water to a large part of the population of the southern part of Abidjan city. This paper deals with the combined approach of geographic information systems and multicriteria analysis to delineate areas at risk of pollution of groundwater in the study area. The multicriteria analysis also incorporated the statistical and geostatistical techniques for defining the factor ratings and weightings of all the parameters under a GIS environment. The criterion for these factor ratings and weightings was the correlation coefficient of each parameter with the nitrates concentration in groundwater. Two indicators were combined for creating situations of pollution risks according to their importance: the intrinsic vulnerability indicators which combined the depth to groundwater, the net recharge, the slope, the soil media, the unsaturated hydraulic conductivity and extrinsic vulnerability characterized by the land use. The results showed that all to the site presents nitrate pollution risks with 50.7% of moderate risk, and 49.3% of high and very high risks. The areas which present the highest risks of pollution are the densely urbanized communes of Treichville, Marcory, Koumasi, Port-Bouet and Grand-Bassam. The sensitivity analysis indicates that parameters causing high sensitivity on the nitrate pollution risks map are the depth to groundwater and the recharge. The errors committed on the maps establishment are ±0.15%, ±0.40% and ±6% respectively for IV map, EV map and pollution risk map.

Prospects for Minimizing the Potential Environmental Impacts of the Hydro-Agricultural Dam of M’Bahiakro(Cote d’Ivoire)

This study aims at characterizing the physical environment and suggesting solutions for a better management of the hydro-agricultural dam of M’Bahiakro which is being constructed over the N’Zi River and is the first inflatable dam in Cote d’Ivoire. In this survey, data related to hydrology, characteristics of the dam and the irrigated rice production area were obtained with the Water Resources Agency and the National Office of Rice Development of Cote d’Ivoire. Physicochemical parameters of the N’Zi River were collected seasonally at three monitoring stations. Results showed that the N’Zi River is characterized by a high water level period from April to November and a low water level period from November to April. The gap between the low flows and the high flows is important (about 206 m3/s on average). The annual average flow is 40 m3/s with a standard deviation of 32.52 m3/s and a variation coefficient of 0.88. The SAR average value (1.63) and the average conductivity (78.44 μS/cm) showed that waters of the N’Zi River are of high quality to be used for irrigation. Suspended sediment concentrations do not present significant difference along the river. But the seasonal variations are important;they are higher during the rainy seasons (45.8 mg/L on average) than in the dry seasons (17.7 mg/L on average). The annual solid flux of the N’Zi River is 41897 tons, i.e. 15810 m3 of sediments. The annual sediment flux is important and can lead to high depositions in the line-shaped reservoir of the dam and that calls for attention to control the silting up of the reservoir. Great efforts concerning interdisciplinary approaches, as well as extensive and intensive field work are needed in order to better manage the hydro-agricultural dam of M’Bahiakro.

Characterization of the Origin of Pollutants in Groundwater from Biostatistical Tests:The Case of Catchment Ehania,South-Eastern Cote d’Ivoire

The threat of agro-industrial exploitations on the quality of groundwater resources has become a major concern for the world’s population, mainly in agricultural areas. To solve this problem, several methods such as vulnerability to pollutants and statistics methods, have been adopted to protect these groundwaters. In this study, statistical tests were used to determine the likely source of pollutants in the groundwater resources. First, we made a comparative analysis and then analyzed pollutants parameters using Kohonen self-organizing map (SOM) which allows basic on the similarity to help out any correlation between the physic-chemical parameters. To validate these results, a land use map was developed to identify the sources of pollutants in production functions of different activities taking place on the catchment area. The results indicate very high levels of certain pollutants such as NO3-, Cl- and SO42- with generally higher than World Health Organization (WHO) standards values. These high levels observed could be attributed to the generally free nature of aquifers alteration and sedimentary formations in areas of high agro-industrial production. The analysis of the data from SOM method reveals a strong correlation between pollutants (NO3-, SO42-,Cl- ) and conductivity showing the likely origin of these surface pollutants,an origin that is linked to the existence of larges agro-industrials exploitations. These results are reinforced by those of the overlay map of the sampling sites on the land use map, which shows a strong coincidence between high values of pollutants and production areas of the pollutants that are agro-industrial exploitations. These areas of coincidence are observed in the north where found banana’s industrials plantations that are less visible and mostly in the southwest part where is one of the largest oil palm plantations in the world (36,000 hectares).