Pollution of groundwater in the coastal Kwale District, Kenya

Abstract

Groundwater is a “last-resort” source of domestic water supply at the Kenya coast because of the scarcity of surface water sources. NGOS, the Kenya government, and international aid organizations have promoted the drilling of shallow boreholes from which water can be pumped using hand-operated pumps that are easy to maintain and repair. The shallow nature an the location of the borehole in the midst of dense population settlements have made these boreholes susceptible to contamination from septic tanks and pit latrines. Thirteen percent of boreholes studied were contaminated with E. coli, compared to 30% of natural springs and 69% of open wells. Areas underlain by coral limestones show contamination from greater distances (up to 150 m away) compared to areas underlain by sandstones (up to 120 m). Overpumping of the groundwater has also resulted in encroachment of sea water into the coastal aquifers. The 200 ppm CL iso-line appears to be moving increasingly landwards. Sea level rise is expected to compound this problem. There is therefore an urgent need to formulate strategies to protect coastal aquifers from human and sea water contamination.