| Sirs [at Coronado National Forest]: I wish to submit this concern relating to the lack of hydrologic isolation of tailings in the Rosemont POO as documented by the Vector and Tetratech documents in the dvd you released on June7, 2008. My comments are below: 2008 Rosemont DVD -- tailings seepage and recharge to aquifers My primary concern is that insufficient attention has been paid to controlling and limiting the movement of impacted waters off the mine site. In particular, leachate from the dry-stack tailings is expected to move down and mingle with the existing groundwater system. Monsoon rains will provide seasonal water inputs to the tailings impoundments. Flood routing deals with a hypothetical 15-inch rainfall event. Shouldn't a permeability barrier exist between the tailings and the underlying wast rock? I am not questioning the desirability of the dry-stack tailing approach, but I would like to see the mines implementation prevent offsite migration of metals such as zinc and other oxidation products such as sulfate. Dry Tailings Facility Design p. 3 Section 3.2 3rd paragraph. Sample of milled tailings from where and milled how? Is this just "mining material" or is it a sample of Rosemont sulphide ore milled using the projected methodology and with the proposed final screen (sieve) sizes? It is not clear how this material is related to the proposed mine and if it is, how representative of the tails that will be produced by the proposed mine. Rosemont Tailings Siting Study (Vector) Figure 11 and text p. 11, 3.4.4 claims that water quality is a top concern (weighted 9). Yet there will be no engineered or designed permeability barrier installed to prevent downward migration of fluids from the tailings into the underlying soils (see photos at end of Tailings Siting Study and section 3.7.2, p. 23) and to underlying groundwater systems. Monsoon rains are expected to occur during the life of the mine. This will provide annual "pulses" of recharge to the tailings. I haven't found any discussion about how recharge to the northern dry-stack tailings will be dealt with. Is horizontal runoff in the waste rock base expected because of equipment compaction of the rocky native soils? Will the mine manage to dewater this area so that waters enriched in metals and sulfate from the tailings are captured in the open pit? If that is the case, what will happen when mining ceases? If not, where will mining impacted recharge go? Does this really meet BADCT standards? _______________________________ John Sonderegger [email protected] |