Thailand’s largest lignite-fired power plant is located at Mae Moh district, Lam Pang province, north of Bangkok. Approximately 15 million tonnes of lignite are needed to run 11 units with a total production capacity of 2,625 megawatts. The plant emits air pollutants through high stacks and discharges wastewater to its surroundings.
In October 1992, due to a high air pressure, SO2 generated by the plant floated above Mae Moh and mixed with air and water to create a highly polluted acid rain which fell over three sub-districts of the Mae Moh district. Analysis showed that rainwater had 50 per cent higher sulphate concentration level as compared with acceptable international standards, and at peak pollution level, more than 2,000 micrograms per cubic metre of SO2 were found in the air. Highly toxic acid rain was recorded from December 1992 until January 1993. Further periodic monitoring of air and water quality in the area also found severe environmental effects.
The pollution incident in October 1992 caused substantial damage to farmers in the area. More than 900 people had difficulty breathing and suffered from sore throats and other related problems. Large and small domestic livestock also suffered, some became sick and others died. In addition, cash crops and trees were destroyed or experienced growth problems. The Electricity Generating Authority of Thailand (EGAT) had to compensate the rural households for their losses and affected people were resettled in safer areas. Mitigation of the effects was urgent and so EGAT had no choice but to reduce production by almost 60 per cent (to 800 megawatts) while further negotiations were underway.
In addition to the climatic conditions, several other conditions contributed to the pollution problems in Mae Moh, such as old machinery and a lack of an environmental impact assessment on the power plant. Several measures have been planned or implemented to solve the problem. Approximately US$ 280 million was approved for investment in pollution control. A limited scale of operation for power units was imposed and it was recommended that high quality coal should be mixed with the low quality coal. To control air pollution, it has been estimated that more than 200,000 tonnes of limestone would be needed per year.
As a result of prompt pollution control measures and frequent checks on air quality in these areas, the air quality in the vicinity of the lignite power plant has been brought under control since late 1993 and early 1994 and is within the local ambient air standard of 300 micrograms per cubic metre.
The case of Mae Moh district indicates the importance of carrying out thorough environmental impact assessments for large investment projects. It shows that sufficient and appropriate management can effectively reduce potential environmental effects. It also shows that adverse environmental effects are costly.

Source: Office of Environmental Protection and Planning (OEPP), Thailand