IMPORTANCE OF IMPROVED GEOLOGY AND GEOCHEMISTRY TO IMPROVING THE ENVIRONMENTAL IMPACT STATEMENT PROCESS

A two-year study has been completed that examined the reliability of water quality predictions at hard rock mine sites in the United States. Water quality predictions for 71 mines were reviewed, and 25 case-study mines were selected for comparison of predicted and actual water quality. Results indicate that water quality predictions are largely unreliable and that the majority of mines (76%) had mining-related exceedences of water quality standards. Adverse water quality impacts were caused by failed mitigation measures and errors in geochemical and hydrologic characterization of mined materials. Mitigation measures failed at 64% of the case study mines. Advances in geochemical characterization are needed to improve mining water quality predictions. Acid-base accounting (ABA) tests are the most commonly used geochemical tests at mine sites, yet the nature of the tests and difficulties in gathering representative samples almost ensure unreliable results. Evaluation of mineralogy, including available weathering surface area for sulfides, silicates, and carbonates, may be a more accurate approach than ABA testing. This will require mineralogic examination that is more detailed and sophisticated than simple bulk powder X-ray diffraction, but costs, turnaround times, and availability of skilled mineralogists currently prevent more widespread use of detailed mineralogy in mined material characterization. If some of these stumbling blocks could be alleviated, detailed mineralogy could be conducted at a level that is commensurate with the level of ore characterization. Needed kinetic testing improvements include measuring the surface area available for reaction, longer test times, and more comprehensive list of analytes. With improvements, results of characterization tests could be applied to ore deposit block models or watershed models to better predict the ability of the wastes or mined materials to generate acid and contaminants.