Environmental fluxes of arsenic from lignite mining and power generation in northern Thailand

Abstract.

This study evaluated arsenic environmental fluxes in the Mae Moh lignite basin and Mae Moh lignite-burning power plant complex, Mae Moh valley, north Thailand. The excavated lignite, fly ash, stream sediment and surface water surveys were carried out to determine the arsenic distribution in the mining area. Arsenic-rich overburden waste and fly ash piles are scattered throughout the lignite mining area and these have increased the load of arsenic-rich sediment in the nearby streams. A geochemical and hydrogeochemical sampling of the streams that drained into Mae Moh reservoir was completed. The main objective was to study the receiving stream water quality below the area of mining and power plant waste disposal. Arsenic concentration was highest in residual part of the stream sediments. The highest arsenic concentrations were 515 mg/kg in borehole lignite, 312 mg/kg in fly ash, 5,213 mg/kg in reservoir bottom sediment, 325 µg/l in mine sump water, and 8 µg/l in Mae Moh reservoir water. Monitoring of arsenic concentrations around the mining and power plant area, for 1 year, showed the increase of this element around the high fly ash pond and main drain area.