A solid waste is classified as hazardous if it contains sufficient leachable components to contaminate the groundwater and the environment if disposed in a landfill. Scale, sludge and drilling mud from three geothermal fields (Bulalo, Phlippines; Cerro Prieto, Mexico; and Dixie Valley, USA) containing regulated elements at levels above the earthës crustal abundance were studied for their leachability. Cr, As, Cu, Zn and Pb were detected at levels which could impair groundwater quality if leaching occurred. Several procedures were used to assess the likely risk posed by the residues : protocol leaching tests (Canadian LEP and US TCLP), toxicity testing, accelerated weathering test, and a preliminary acid mine drainage potential test. Whole rock analysis, X-ray diffraction, and radioactivity counting were also performed to characterize the samples. Toxi-chromotest and SOSchromotest results were negative for all samples. Leachng tests indcated that all of them could be classified as nonhazardous wastes. Only one of the six showed a low-level radioactivity based on its high Pb-2 10 activity. Initial tests for acidification potential gave positive results for three out of six samples whle none of the regulated elements were found in the leachate after accelerated weathering experiment for three months.

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