In addition, local impacts play a very important role when the power plant is sited in a suburban area. The ratio between local and regional impacts for suburban locations can be as high as 10 for the case of the combined cycle block using natural gas at the Ratchaburi site. The local impacts become smaller than the regional ones for power plants in rural areas. The results shown in table 9 provide quantitative evidence supporting the rationale of the normal practice , that dirty fuels should be used in locations with lower populations but cleaner fuels should be used in urban locations. This reduces the total level of impacts.