Induced alkaline recharge zones to mitigate acidic seeps

Abstract

A small hydrologically isolated mine in West Virginia was used to test the concept of modifying acid seeps through the deliberate recharge of the groundwater regime of the mine backfill by trenches whose locations and chemistry were controlled. Over a two year period, four acid seeps of the abandoned mine were monitored for background chemistry and seasonal fluctuations. 16 large diameter holes (using a 30 foot backhoe) were dug through the overburden to pavement to obtain samples of the backfill and identify recharge areas and pockets of acidic water. These data were used to locate 15 trenches which averaged 10 feet wide, 3 feet deep, 75 to 725 feet long. These were hand-packed with sodium carbonate briquettes (0.5 pounds/ft/sup 2/) and covered with two feet of limestone reject. This combination will form highly alkaline short-term wetting fronts by the briquettes and be sustained alkaline for long-term by the limestone solutioning. Since the summer of 1983, the four seeps at the toe of the mine have been continually monitored and analyzed. Interestingly, the seeps which previously were colored red, became crystal clear with attendant high levels of Na, reflecting ferrous iron which limits the acid potential of the system. The diminutionmore » in sulfate, and the developed clarity of the seeps, suggest that the alkaline trench technique is capable of affecting changes on the pyrite reaction levels.« less