AMD is formed when mining activities expose pyrite (iron disulfide minerals) to water and oxygen. Upon exposure to water and oxygen,.pyrite oxidizes to form acidic drainage rich in dissolved metals. The chemical reactions that occur during the formation of AMD can be summarized as this overall reaction:
4 FeS2 + 15 O2 + 14 H2O ---> 4 Fe(OH)3- + 8 H2SO4.
In this reaction, pyrite is oxidized to give ferrous hydroxide (or "yellowboy", that creates the characteristic rust color of AMD contaminated streams) and sulfuric acid. The presence of sulfides also stimulates Thiobacillus, sulfide-consuming bacteria that releases H2SO4 as a by- product, further increasing acidity. AMD water is characterized by low pH (<3.5), high acidity (>500 mg/l as CaCO3), and high concentration of total dissolved metals (>50mg/l) .
Untreated AMD can severely degrade both habitat and water quality of receiving streams. This degradation is manifested by an alteration in the macroinvertebrate community; specifically, there is a reduction in the diversity and total numbers of macroinvertebrates and massive shifts in community structure, favoring pollution tolerant species. In addition to the stress posed by a less abundant food source, fish are also negatively impacted by AMD directly. The primary causes of fish death in acid waters are loss of sodium ions from the blood and loss of oxygen in the tissues. AMD contaminated groundwater can corrode and encrust man-made structures, causing serious problems. For example, AMD can compromise well casings (water supply or oil and gas wells) which can lead to aquifer contamination. In the most severe cases, AMD renders waters unfit for human use and recreation.
The Old Forge borehole is located in Northeast Pennsylvania, a toxic monument to the state's mining history. A mere 100 feet upstream the borehole one can find trout feeding. Below the effluent the Lackawanna River is sterile. No macroinvertibrates, no vegetation, no minnows ... nothing.
When the Old Forge borehole was drilled in 1962, it relieved water building up in the shuttered Anthracite mines in Northeast Pennsylvania. The borehole discharges 65 million gallons of AMD a day making it the single largest point source of pollution in the Chesapeake Bay into which it ultimately drains.
Keystone has tested its system on the water coming from the Old Forge borehole. Keystone's technology is able to reduce the amount of iron and manganese, the principle pollutants, in the water coming from the borehole.