Researchers at Indiana University Installed Monitoring Wells

The long-term physical and chemical effects of using coal-combustion residues (CCRs), in particular fixated flue gas desulfurisation (FGD) sludge, have been monitored as a major component in the reclamation of a pyritic refuse deposit. This was undertaken to determine the consequences of placing these controversial materials in an unrestricted environment. Researchers at Indiana University installed monitoring wells, neutron probe access tubes, and weirs before and after reclamation. These were used to observe hydrological conditions, and determine how the use of FGD sludge as a recharge barrier was affecting hydrochemical response to ambient weather conditions. Data were collected for six months prior to reclamation, and then for an additional 13 years (more intensively during the first five years). Statistical analyses of water levels in the pyritic refuse deposit indicate a shift from precipitation- to barometric-controlled fluctuations. These findings, along with minimal variability in soil moisture within the CCR cap and transient perching of groundwater above the cap, are evidence that recharge of the refuse aquifer has been minimised. Statistically significant improvements in the quality of groundwater on-site and surface water leaving the site include long-term declines in acidity, arsenic (by an order of magnitude), and iron concentrations within the refuse aquifer. These are attributed to reduced recharge of oxygenated water, which is supported by analysis of calculated mineral saturation indices. Long-term declines in acidity and associated trace metals discharging from the site are attributed to the post-reclamation loss of sulfate salts brought to the surface by capillary forces. This study indicates that strategic use of CCRs in reclamation programmes can produce beneficial effects, including reduced acid drainage. These are beyond those achieved using traditional reclamation approaches, such as the use of mine spoil as capping and fill material. Source: workingwithwater.filtsep.com