TRAVELS WITH CHARLIE: IN SEARCH OF AMERICA'S MOST ACID WATER (Invited Presentation)

I received my first enquiry for a USGS post-doc from a UCBerkeley PhD candidate ca. 1986 and thus began a strong friendship and productive scientific collaboration that has lasted to this day. Dr. Alpers was exactly the right person to join me on a study of the Iron Mountain Mines (IMM) superfund site, including negative pH, and enormous quantities of efflorescent salts never seen before. I gave him 12-year-old samples of portal effluent collected during my thesis work which had oxidized and precipitated jarosite and he characterized the solids, interpreted the water chemistry in terms of a solubility product constant, and published an impressive paper. The USEPA needed to know the interconnectivity of water flow paths in the underground workings at IMM because the parties with site liability were convinced that if the main portal drainage were plugged, another lower mine portal drainage would stop draining. Dr. Alpers was able to show using inverse modeling and mixing that the lower portal effluent chemistry was not from the upper portal water. Flow connections between upper and lower workings were minimal to non-existent. During that study, interesting non-correlated trends between copper and zinc concentrations in the seasonal discharge data appeared. Dr. Alpers looked at the change in Cu/Zn ratios during dissolution and precipitation of melanterite in the laboratory and discovered that these metal ratios could be explained in terms of melanterite forming during dry seasons and dissolving during wet seasons. Melanterite, a ferrous sulfate hydrate, accommodates substantial amounts of Cu and Zn, but partitioning to solution is different whether dissolving or precipitating. The highlight of our contribution to the IMM litigation came when I presented a simple graph prepared by Dr. Alpers to a group of the state and federal government representatives and the industry partners showing that if the main portal at IMM were to be plugged there would be 600,000 cu. meters of a mine pool with pH of 1 or less, sitting above the water table, with grams per liter of dissolved metals from soluble salt dissolution, in a rock with negligible neutralization capacity. This conclusion convinced the EPA that mine plugging at IMM was not an option and plugging at some other mine locations with similar geological properties has been shown to have deleterious consequences for exactly these reasons.