Prediction of minesite-drainage chemistry through closure using operational monitoring data

Post-mining drainage chemistry depends strongly on geochemical and hydrolog ic processes that occur during the operational years. Where routine operati onal monitoring data are abundant, the dominant processes can often be eval uated with no additional, special studies. Thus, post-mining drainage chemi stry can be predicted with confidence based on the operational data. This is referred to here as 'empirical drainage-chemistry modelling' (EDCM) . This paper presents examples of EDCM using routine monitoring databases f rom several minesites, each containing thousands of analyses and spanning u p to 30 years of mine operation and closure. Simple statistical interpretat ions in the EDCM can reveal annual cycles and trends that aqueous concentra tions display during operation and into closure. A new compilation of 12 EDCM equations for copper versus pH is presented to illustrate similar trends with pH among the sites. However, this compilati on also shows that average-annual copper concentrations at a particular pH can vary by three orders of magnitude, reflecting site-specific factors. Al so, a new case study comparing actual closure concentrations to those predi cted with EDCM in 1991 demonstrates that predictive accuracy is within a fa ctor of two. (C) 2001 Elsevier Science B.V. All rights reserved.