Creation of a Geohazard Monitoring Baseline for the Menengai Geothermal Field

Abstract

Appraisal drilling for geothermal resources in the Menengai Geothermal Field is on-going with eight geothermal wells already drilled. In the course of drilling, different materials like cement, bentonite, soda ash etc. are used in the drilling process and cementing jobs. This may result in large amounts of pollutants being discharged into shallow and deep acquifers and reservoirs that feed the water boreholes. The quality of water issuing from the boreholes in this surrounding is very important given that they are the main source of water for Nakuru Town. Monitoring of any changes in the chemistry of water and/or gases in boreholes located in the regions surrounding the Menengai Geothermal Field has been put in place. In this monitoring exercise an attempt has been made to assess the possibility of pollution of the ground water during the drilling exercise thus creating a baseline for any future changes that might be encountered. Geochemical sampling for monitoring purposes in this area started in April 2011, just before completion of the first geothermal exploration well. In this paper, the chemical results of the sampled boreholes have been presented and discussed. The results show that over the 8 months of geochemical monitoring, there hasn’t been a noticeable change in the physical and chemical parameters of the borehole waters in the area. The results hence form the baseline data for monitoring future changes accompanying the exploitation of the geothermal field.