ABSTRACT: Fly and bottom ashes originated from coal burnt in thermal power plants are known to contain several toxicelements, which can leached out and contaminate soils as well as surface and groundwater..Yatağan Thermal Power Plan! ofSx 210 MW power was founded to meet energy need of our country by using low quality lignite reserves of Yatağan- Eskihisar, Tınaz, and Bağyaka basins,. • The plant annually consumes5.4 x l(f tons of coal and annual production capacity is 3.780 x 10 KWh, The plant uses 15000 tons of coaland discharges 5000 tons of fly and bottom ash daily to the disposal site.. The main objective of this study isinvestigation of the effects of these wastes on the groundwater, via water in*ash disposal site and groundwatermonitoring wells.. For these reasons, water samples, leach out from waste disposal site and groundwater monitoring wells in front of disposal site., were analysed large part of the Yatağan Plain is formed by alluvium, which is the principal aquifer in front of waste disposal site.. The alluvium consists of loose, interlay e red clay, silt, sand, and gravel, This aquifer is used for domestic and irrigation,. Three observed wells, which are 20 m depth, were clone for effects of waste .disposal site on groundwater. Also,, some of permeability experiments were applied in these welts. According to experimentalluvium aquifer is very permeable.,Groundwater in the alluvial aquifer in the Yatağan Piain, Muğla- Turkey.,, has been effected by thermalpower plant waste. Waters, in the study area, are rich in SO/" ions. Cadmium (Cd) and lead (Pb) concentrations of groundwater of some well in the alluvial aquifer exceed the Environmental Protection Agency (EPA)standarts.