Assessing the environmental impact of geothermal residues

Scale, sludge and drilling mud from three geothermal fields (Bulalo, Philippines; 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 procedures were used to assess the risk posed by the residues: whole rock analysis, X- ray diffraction, radioactivity counting, protocol leach tests, toxicity testing, accelerated weathering test and a preliminary acid mine dramage potential test. There was no evidence of toxicity or genotoxicity present in any of the samples tested. Leaching tests indicated that all of the wastes could be classified as non-hazardous. One sample showed a low-level radio activity but it was still within the occupational dose limit. Three samples tested positive for acidification potential while none of the regulated elements were found in the leachate after three months of weathering test