Assessing Groundwater Vulnerability to the Activities of Artisanal Refining in Bolo and Environs, Ogu/Bolo Local Government Area of Rivers State; Nigeria

Abstract

Artisanal refining typically involves primitive illegal stills in which crude oil is boiled and the resultant fumes are collected, cooled and condensed in tanks to be used locally for lighting, energy or transport. The distilleries are heated on open fires fed by crude oil that is tipped into pits in the ground. As part of the oil burns away, some seeps into the ground. The waste from the process is stored in open pits thereby increasing the risk of the contamination of the environment and possibly impacting the underground aquifer. It is this concern of crude oil seeping to the groundwater that necessitated the current investigation with the sole objective of assessing the vulnerability of the aquifer to the activities of artisanal refining. Soil, water and crude oil samples from artisanal refining sites were collected according to standard procedures and transferred to the laboratory for analyses to determine their properties. An empirical method was adopted in estimating the permeability. The Kozeny – Carman equation for deriving the coefficient of permeability takes the porosity (η) into account. Using a typical soil porosity η = 0.4, mean particle size = 0.05 and mean viscosity determined from crude samples permeability estimate was calculated to be 3.6 x 10-8cm/s, infiltration was assessed using a simplified version of Darcy’s law. With a typical superficial soil permeability of 3.6 x 10-8 cm/s, depth of ponding of 0.5m, and a wetting front of 0.4m, an estimated infiltration rate of 1.15 x 10-8cm/s can be expected. Given the infiltration rate and the depth to groundwater (water table is between 3m and 8m), we calculated the time for crude oil contaminant plume to intercept the water table simply re-expressing the equation for velocity as distance/time which results in approximately 4.6 years. The character of the water from the area indicates that groundwater is already being impacted given that artisanal refining has been going on in the area since 2002.