Laserfiche WebLink
Amelia S. Whiting, Assistant Attorney General <br /> February 23, 1994 <br /> Page 3 <br /> A. Plugging of American Tunnel at the SGC Property Line. <br /> The primary plug is to be located in the American Tunnel just below the SGC <br /> property line, at a point where the rock properties provide the greatest assurance that <br /> maximum sealing effectiveness will be achieved. Conceptual location is shown on Figure <br /> 4. The plug will cut off about 2/3 of the flow of water from the American Tunnel, by blocking <br /> flow into the tunnel from the mine. It is expected to create an effective seal with minimal, <br /> if any, seepage around it. <br /> The American Tunnel plug is to be located in stable, competent rock and will dam <br /> the natural influx of groundwater, currently flowing from the mine into the tunnel. The water <br /> level in the mine workings will rise behind the plug until physical and chemical equilibrium <br /> is reached between water moving toward the mine workings and water moving away from <br /> the flooded mine through naturally occurring fractures and other groundwater pathways. <br /> Due to the physical and chemical properties of the ground water and the surrounding rock, <br /> the quality of the water behind the proposed plug is expected to be at least as good as that <br /> of the water which flows from the portal of the American Tunnel prior to treatment. The <br /> anticipated and intended effect of the installation of the plugs is to return the hydrologic <br /> system to an approximation of pre-mining conditions. <br /> As a result, water which previously would have entered the mine workings and <br /> drained out through the American Tunnel will, over time, seep through the mass of the <br /> mountain and emerge, via natural pathways, at the surface. In our view, such waters would <br /> not constitute point source discharges. Rather, they would represent a return to historic <br /> natural conditions of hydrologic flow. In addition, there would be no discharge of pollutants <br /> or addition of pollutants by human activities. Therefore, C.R.S. 25-8-501 and the statutory <br /> definitions of"discharge of pollutants," "point source," "pollutant," and "pollution" would not <br /> apply, and no NPDES or CDPS permit would be required for surface springs or seeps that <br /> might occur following the plugging of the mine. We request that your office confirm that <br /> conclusion. <br /> B. American Tunnel Below the Property Line. <br /> Historic flows have occurred from the first 3500 feet of the lower portion of the <br /> American Tunnel. The pH of the that water is mildly acidic; the flows derive from fractures <br /> and groundwater infiltration into the tunnel from near surface groundwater, snowmelt, and <br /> runoff in the near surface geologic structures near the portal. There is no mining activity <br /> in that area, and there is therefore no addition of pollutants or discharge of pollutants by <br /> human activity. The only human activity in the area was the driving of the tunnel itself in <br /> the 1920s. Neither SGC nor its predecessors ever mined that area, nor did they build or <br /> enlarge the tunnel. <br /> SGC currently treats the combined flow of water from the mine and from the tunnel <br /> at the portal, under the terms of its CDPS permit. However, once the American Tunnel plug <br /> is set, flow from the portal will consist entirely of water entering the tunnel below the SGC <br /> property line. Would an NPDES or CDPS permit be required for that continuing flow, since <br />