ASSESSING THE ENVIRONMENTAL-IMPACT OF GEOTHERMAL RESIDUES

Scale, sludge and drilling mud from three geothermal fields (Bulalo, P hilippines; Cerro Prieto, Mexico; and Dixie Valley, USA) containing As , Cu, Cr, Zn and Pb at levels above the earth's crustal abundance were studied for their environmental impact. Several techniques and proced ures were used to assess the risk posed by the residues: whole rock an alysis, Xray diffraction, radioactivity counting, protocol leach tests , toxicity testing, accelerated weathering test and a preliminary acid mine drainage potential test. There was no evidence of toxicity or ge notoxicity present in any of the samples tested. Leaching tests indica ted that all of the wastes could be classified as non-hazardous. One s ample showed a low-level radioactivity but it was still within the occ upational dose limit. Three samples tested positive for acidification potential while none of the regulated elements were found in the leach ate after three months of weathering test.