Characterisation of Acid Mine Drainage Using a Combination of Hydrometric, Chemical and Isotopic Analyses, Mary Murphy Mine, Colorado

The legacy of mining continues to affect stream water quality throughout the western United States. Traditional remediation, involving treatment of acid mine drainage from portals, is not feasible for the thousands of abandoned mines in the West as it is difficult and expensive. Thus, the development of new methods to address acid mine drainage is critical. The purpose of this study was two fold; to identify and test new tools to identify sources of metal pollution within a mine and to identify low-cost treatment alternatives through the use of these tools. Research was conducted at the Mary Murphy Mine in Colorado, a multiple-level underground mine which produced gold, silver, copper, lead and zinc from 1870 to 1951. Source waters and flowpaths within the mine were characterised using analysis of hydrogen and oxygen isotopes of water (water isotopes) in combination with solute analysis and hydrometric techniques. Hydrometric measurements showed that while discharge from a central level portal increased by a factor of 10 during snowmelt runoff (from 0.7 to 7.2 Ls^–1), Zn concentrations increased by a factor of 9 (from 3,100 to 28320gL^–1). Water isotopes were used as conservative tracers to represent of baseflow and snowmelt inputs in a hydrologic mixing model analysis. The results showed that less than 7% of peak discharge was from snowmelt. Within the mine, approximately 71% of the high-flow Zn loading was caused by a single internal stream characterised by extremely high Zn concentrations (270600gL^–1) and low pH (3.4). Somewhat surprisingly, hydrologic mixing models using water isotopes showed that new water contributed up to 79% of flow in this high-Zn source during the melt season. Diversion of this high-Zn source within the mine resulted in a decrease in Zn concentrations at the portal by 91% to 2,510gL^–1, which is lower than the base-flow Zn concentration. The results suggest that in some mines remediation efforts can be concentrated on specific areas within the mine itself. Using the characterisation techniques demonstrated in this study, problem areas can be identified and contaminated flows diverted or isolated. The results also suggest that it may be possible to dewater contamination areas, greatly reducing costs of remediation.     

Entitlements, missing markets, and environmental uncertainty: Reply

At one level Dore and Ward seem intent on immunizing received doctrine. They say that I did not prove that rights violated Nozick's principles of justice, and that I did not prove that missing markets were the problem. More telling, they allege I did not prove that my story was better than the particular story favored by Dore and Ward. That is, they argue that : “ … there is an alternative approach, based on the theory of public economics, which is indeed operational.”³ They then use the bulk of their comment to explain and defend this alternative model. They hope to convince the reader that the model of “public economics” survives intact in the face of my alternative model. To the extent that their model allows one to define the problem away, it is not difficult to see why they find it so compelling.More seriously, Dore and Ward fail to make a coherent argument about the concept of rights and duties and the logic of a particular rights structure that happens to prevail. They seem concerned that my article was tampering with some sacred social construct—the status quo rights structure—and that my article threatened the received wisdom of both “public economics” and Paretian-Walrasian bliss. Indeed, theirs seems to be a genuine fear that if economists release their grip on the certitude of received orthodoxy the floodgates will be open to all manner of bumbling regulators seeking to shift rights and wealth positions across generations. My article is apparently threatening because it seems to suggest that the received wisdom may, at times, be misleading.