EARTH-VAS2 model parameters: An answer to complex aquifer vulnerability studies. – E.I. Akaerue and S.O. Onwuka
Factors that enhance groundwater vulnerability also facilitate contaminant migration. In this study the EARTH-VAS2 model is applied to investigate the migration of contaminants in shallow coastal aquifers of the Benin Formation in Calabar area southeastern Nigeria. The EARTH-VAS2 model uses the parameters of Elevation, Aquifer thickness, Regolith, Transmissivity, Hydraulic conductivity, Vadose zone, Aquifer media, Static water level and Specific capacity to investigate contaminant flow and soil vulnerability to pollution. Estimates from pumping test and Dar-Zarrouk model show the aquifer viability and protective capacity of the aquifer zones. The mean values of parameters from zone A are; Longitudinal conductance (0.1μs), Transverse Resistance (245386.5 ohm-m2), Aquifer resistivity (1247.3 ohm-m), Transmissivity (1500m2/day), Hydraulic conductivity (100m/day), Specific capacity (400m3/day) while parametric mean values of Zone B are: Longitudinal conductance (0.1 μs), Transverse Resistance (700 ohm-m2), Aquifer resistivity (100 ohm-m), Transmissivity (352m2/day), Hydraulic conductivity (10 m/day), Specific capacity (40m3/day). The analysis of chemical pollution indictors of N0₃¯ 22.6 – 0.90 (mg/l), EC 301 – 20 (μS/cm), E-coli 5 – 0.01 (mpn/100ml) and Cl¯ 11.73 – 0.10 (mg/l) of groundwater samples were used to validate results within areas prone to contamination. Determination of coefficient (R2) of EARTH-VAS2 parameters point out that Aquifer media, Depth to static water level, Hydraulic conductivity and Transmissivity are the most effective hydrogeological parameters to vulnerability assessment.