Multivariate factor analysis (FA) by principal components reduction and varimax rotation techniques were employed to reduce bulk hydrogeochemical data from Iju Community, Southwestern Nigeria into components that explain possible underlying structures existing among the variables. This is with a view to characterizing groundwater chemical facies in relation to underlying hydrogeochemical processes suppossed to be responsible for any variation in water quality. Thirteen water quality variables were investigated at 38 sampling points. The data obtained were standardized to ensure normal distribution and then subjected to factor analysis by principal component extraction method with varimax rotation and Kaiser normalization. The criterion of eigenvalues greater than 1.0 and indications from the scree plot informed the extraction of two components which together explain 83.73 % of the total variance in the dataset. Component 1 with high loadings of TDS, EC, Temperature, Total hardness, Ca, Mg and Cl explains 46.70 % of the total variance. It represents the dissolution-precipitation (exsolution) process involving water-rock and water-soil interactions, which are predominantly silicate mineral weathering processes. Component 2 with high loadings of pH, K, Na, HCO3, Alkalinity and SO4 explains 37.03 % of the total variance, reflecting geological and hydrogeological controls by oxidation and speciation reactions. Water in the area was classified as Na+- K+ - Cl-, Na+ - K+ - Cl- - HCO3- and Na+ - K+ - Cl- -SO42- water types.

Bivariate correlation and regression techniques were employed to evaluate the relationship between pairs of geotechnical variables for residual lateritic soils derived from three genetic crystalline rocks in Ibadan metropolis, southwestern Nigeria. The significance of mean group differences (parent-rock and level of compactive effort) at 5% level of significance was determined using paired t-test analysis. This is with a view to ascertaining the influence of the pedogenic factor of parent rock, percentage fines, and energy of compaction on engineering index properties of the lateritic soils. The clay-size contents had positive correlations with both Optimum Moisture Content (OMC) and plasticity index, and a negative correlation with the Maximum Dry Density (MDD). The MDD and OMC had significant negative and positive correlations respectively with the amount of fines. The amount of fines and Unconfined compressive Strength (UCS) had significant negative and positive correlations respectively with the California Bearing Ratio (CBR). The study shows significant parent-rock group differences in most engineering properties. The banded-gneiss derived soils were found to be better engineering soils than the migmatite-gneiss- and quartzite/quartz-schist-derived soils. The modified American Association of State Highway and Transport Officials (AASHTO) level of compactive effort which produced better compacted soils than the West African level is recommended for the soils.

Integrated multivariate statistical, spatial, and graphical methods were applied to some hydrochemical data in Shagari area, Akure, southwestern Nigeria with a view to elucidating groundwater hydrochemical evolution. Water samples from 23 dug wells were clustered into distinct groups by hierarchical cluster analysis to depict different hydrochemical facies. Factor analysis reduced bulk hydrochemical data to principal components explaining possible dominant processes controlling water chemistry. Three factors which together explain 83.48 % of the total variance in the dataset were retained and interpreted. Factor 1 explains 35.82 % of the total variance and indicates atmospheric controls and silicate mineral weathering processes. Factor 2 explains 35.41 % of the total variance and reflects atmospheric controls and speciation reactions producing inorganic carbon ions in solution. Factor 3 explains 12.24 % of the total variance, indicating silicate mineral weathering processes resulting in elevated pH. Generally, water type tend towards sodium chloride bicarbonate.

DRASTIC model coupled with Geographical information System (GIS) were employed in investigating groundwater pollution potential in parts of Akure-south. This is with a view to developing a vulnerability map as a general guide in strategic planning for sustainable groundwater resources development, and providing urban development planners with tools for preliminary selection of priority areas for land use. Seven hydrogeological parameters associated with the pollution potential of an aquifer were incorporated in the model, viz: Depth to water table, net Recharge, Aquifer media, Soil media, Topography, Impacts of the unsaturated zone, and hydraulic Conductivity. DRASTIC index, the overall grade of vulnerability which expresses the weighted sum overlay of the seven factors was computed. The results obtained indicate that vulnerability index varies between 126 and 154 according to regional environmental characteristics across the study area, with about 40% of the area exhibiting high vulnerability index. The western, central, north-south axis and extreme-eastern parts of the area are in high vulnerability category, thus requiring enhanced density of monitoring points for adequate groundwater quality control. Also, guidelines and limitations must be carefully draw up to control possible groundwater contamination and to protect the groundwater resources for sustainable development. From the vulnerability map produced, urban land use for residential and commercial purposes in highly vulnerabile parts may be outlawed.