Source Treatment of Acid Rock Drainage at a Backfilled Coal Mine

A biological source treatment (BST) technique using remote sensing and biogeochemistry has been developed to address acid rock drainage (ARD) at its source.  The BST technique utilizes down-hole injections of microbial inoculum and substrate amendments to establish a biofilm on the surface of metal sulfides (ARD source material).  The treatment results in an elevated groundwater pH (from acidic to circum-neutral levels) and prevents further oxidation of ARD source material.  The first 2.5 years of an ongoing field study of the BST technique at a reclaimed coal mine in central Tennessee (USA) have produced successful results.  For instance, the water chemistry in a monitoring well down-gradient from injection wells has improved substantially as follows: the pH increased 1.8 units from 5.7 to 7.5, the dissolved (0.45 µm-filtered) iron concentration decreased by 91% from 93 to 8 mg/L, the conductivity decreased from 1,279 to 500 µS/cm, and sulfate decreased from 724 to 210 mg/L.  Electromagnetic induction surveys were conducted to identify ARD source material and monitor BST performance by measuring changes in subsurface resistivity throughout the site.  These surveys revealed a treatment zone created between injection wells where the conductivity of contaminated groundwater was lower within the treatment zone (10-18 mS/m) than in adjacent untreated zones (20-30 mS/m), thus, suggesting this technique could be used to treat ARD sources directly or to intercept and neutralize sub-surface ARD.