Environmental impact assessment of the proposed National Oil Corporation of Kenya Truck Loading Facility, Industrial Area, Nairobi, Kenya

Abstract

An environmental impact assessment study was carried out in the area covering the proposed National Oil Corporation of Kenya (NOCK) truck loading facility which is located in Nairobi's industrial area. The main objective of the study was to assess the state of the environment before the development and commissioning of the facility, in order that the design of the facility can objectively take into account the minimisation of the risk of possible negative environmental impacts that may be generated by activities at the facility, and that a baseline of the current environmental state in the area be provided for monitoring such changes in the future. This environmental impact assessment study included: a geological/geophysical survey to establish the geology and structures of the proposed construction site; establishment of baseline levels of groundwater and existence of water wells within the area; determination of current levels of pollution in air, soil and groundwater by chemical analysis of samples collected in the area; qualitative investigation of noise pollution status; assessment of existing factory activities in the vicinity of the site vis a vis their effect on the environment and complementarity of the proposed facility; determination of possible effects of various pollutants on human settlements adjoining the area; and rating the potential health risk to workers within the truck loading facility. Black cotton soils with a thickness of about 70cm overlie relatively thick (51m) phonolites which characterise the geology of the area. There are a number of fractures/cracks traversing the area in a nearly north-south direction. These are believed to be shallow fractures, and it is recommended that pits be dug 3 to 4 m deep to establish the depth of the fractures. Beneath the phonolites (>51m depth) are the Athi tuffs and lake beds where most of the groundwater in the area occurs. This is consistent with water strike levels in boreholes drilled in the Industrial Area. Given the thickness and impermeability of the phonolites and shallow depth of the fractures, contamination of groundwater (>52m depth) by infiltration of pollutants from the surface is most likely insignificant. Groundwater quality in the area does, however, not appear to be suitable for drinking due to its high Fl and Fe content, but is suitable for other domestic and factory use. Heavy metal analysis of the soils reveals that the only metal that could threaten ground water quality in the area is lead, which appears to come from automobile exhaust emissions and atmospheric loading and fall-out of the volatile gasoline additive, lead tetraethyl. This may contaminate the transient (seasonal) groundwater that accumulates in the near surface zone (weathered, fractured phonolite and soil <8m deep) during the rainy seasons, and dries up soon after the rains. Analysis of organic volatiles reveals the presence of hydrocarbons (hexane, benzene and xylenes) which are components of petrol. The source of these hydrocarbons appears to be the Kenya Pipeline Company pumping station to the West and Shell, Caltex and Mobil loading facilities to the East of the proposed site. Although the concentrations are not of serious concern, it is recommended that frequent monitoring be done to check any danger that might be posed to the new facility. The air concentrations of sulphur dioxide, hydrogen chloride, ammonia and nitrogen-dioxide suggest a low acid and base deposition in the area. Nitrogen dioxide levels are, however, close to critical limits. Concentrations of the various air pollutants warrant further monitoring, to check the likely risk on human health within the facility. The nearest human settlements are located at least two kilometres to the North and East of the area, so air pollutants and noise that may emanate from the facility are unlikely to pose a threat to them. The overall finding of the environmental impact assessment study is that the site is suitable for development of a truck loading facility as proposed by National Oil Corporation of Kenya. It is, however, strongly recommended that this baseline study should form the basis for monitoring and evaluation of the environmental conditions as site development proceeds, and when the facility is operational.