Estimation of the Quantity of Water in the Abandoned Underground Mine of Gold Fields Ghana Limited Tarkwa: A Potential Source to Augment Water Supply to Tarkwa Municipality

The Tarkwa district is an important gold mining area in the Southwestern part of Ghana. The main source of potable water supply to the Tarkwa Nsuaem Municipality is from the Bonsa River treatment plant managed by the Ghana Water Company Limited (GWCL). The River is under threat from serious contamination by illegal mining ("galamsey") activities within its catchment area. Consequently, the amount of water supplied to the Municipality has not kept pace with its growing population due to increasing treatment cost and supply difficulties. The need to find alternative and sustainable sources of potable water supply to augment that from GWCL to the Municipality has become imperative. A large void volume created as a result of the abandoned underground mine operated by Gold Fields Ghana Limited (GFGL), after its closure in 1999 has flooded. This potential water resource is being pumped out daily, and wasted, sometimes spilling-over to low lying areas around the mine when allowed to reach its decant level. This study estimated the quantity of water in the Abontiakoon Vertical Shaft (AVS) which is part of the large underground void using survey production figures and post-closure void filling parameters resulting in 2.8 x 106 m3 and 2.9 x 106 m3 respectively. The rate of recharge to the underground water was also estimated to ascertain the sustainability of the void water should it be considered for use by employing the model of predicting rebound on “void filling” basis and average dewatering rate before closure at 2 535 m3/day and 2 618 m3/day respectively; indicating that recharge to the AVS reservoir is about 6 x 106 gal/day or 30% of current daily water supply deficit in the TNM. The estimated potential volume of mine water in storage in the entire Tarkwa underground void is 32 x106 m3. Two samples of the mine water were taken in November 2011 and February 2015 for quality analysis, in order to have a fair knowledge of the water quality parameters. The quality of the underground water was found to be potentially good, and not likely to cause any health threats, or water quality problems. Depth sampling is recommended to determine the chemical profile of the reservoir. Keywords: Reservoir, Municipality, Bonsa River, Contamination, Tarkwa