appraisal drilling of geothermal wells in olkaria domes - Orkustofnun

Ogola 300 Report 135. ENVIRONMENTAL RISKS OF THE PROJECT TO NATURAL RESOURCES5.1 Risk to water resourcesDrilling will require fresh water from the lake of up to 1000 m 3 per shallow well and 3000 m 3 for deepwells. The lake has no outlets and has shown a large variation in levels without significant abstractionover the years and is expected to show similar variations in future even in the absence of a powerstation and socioeconomic activities in the area. Drilling mud, additives, cuttings, cement, oil andgrease will be passed through a sump system where drill cuttings and mud particles will settle downand the viscous drilling fluid be recycled back into the system.No significant change will be expected since drilling activities will only last for about one year.During drilling, KenGen will abstract steam from a deep aquifer at an approximate rate of 8 kg/s per3.5 MW. The steam field is not connected to the lake and is not expected to affect the water balanceof the lake. The lake is like a small pan several kilometres above the deep aquifers and hence has nodirect relationship. Studies by Arusei (2001) reveal that groundwater flows from the northern part intothe lake while the resource is located in the outflow zone. However, farming activities springing up inthe north and using borehole water may affect the lake level because the lake is recharged from thenorth. KenGen also plans to have re-injection wells ready once production starts, to recharge theaquifer.In order to limit degradation of the resource, simulation of reservoir performance at differentexploitation capacities has been done. Sustainable management of the reservoir by maintaining anadequate balance between geothermal fluid withdrawal and recharge of disposed fluid will be carriedout once operation begins. Re-injection wells will be drilled after monitoring reservoir flow patternsto avoid cooling of the resource and excessive hydrothermal pressure. There is risk of water pollutionfrom heavy metals like As, B, Hg, Zn, Pb, Cl, Li, etc. from geothermal fluid. Reinjection is, however,the most effective means of controlling the release of heavy metals into the environment.The fisheries’ concern was that water suction would also pull young fry and eggs; KenGen has a wiremesh at the abstraction point to avoid this.KenGen is a member of Lake Naivasha Riparian Association (LNRA) with other stakeholders whoown riparian land. LNRA has a community-based management plan - Lake Naivasha ManagementPlan (LNMP), for sustainable use of the lake. All the requirements of the management plan and otherwater resources will be taken into consideration.5.2 Risk to soil resourcesThe potential for soil erosion in the area is high. Soil erosion may increase during construction anddrilling phases of the project. However, drainage control and soil conservation measures will beprovided. The erosion will not affect the sedimentation yields of Lake Naivasha due to adequatevegetation cover around the area and the drainage direction from the field. The costs of soilprevention measures and reforestation should be included in the total project cost.5.3 Risk to air quality and noiseThe main risks to air quality include emissions of non-condensable gases and dust. If bedrock isencountered during construction of a reserve pit and blasting is required there would be noise from theexplosives and increased dust from the explosion. Dust would also be generated during the drilling ofshot holes for the charges and by traffic movement.