2011-01-25_REVISION - M1977300 - Laserfiche WebLink

Home Browse Search

Daniel Arnold, Esq. January 25, 2011 Denver Water Page 12 of 21 between the mine pool and alluvium, but rather indicate the opposite is true (i.e., the mine pool and alluvium appear to be connected). Two key indications of the hydraulic connection between the mine pool and alluvial aquifer (and creek) are discussed below. They include open exploration boreholes and the Illinois Fault zone. The EPP discusses the plugging of open exploration boreholes (core holes) performed in May 2000 to limit the hydraulic connection between the mine pool and alluvium. During early exploration of the uranium ore body, boreholes were drilled above the mine and angled down toward the mine from the valley floor. It is reported that 15 boreholes were plugged, but 33 boreholes could not be located and plugged. The EPP does not expand on where these unplugged boreholes may be located or their potential hydraulic connection to the alluvial aquifer. Unplugged boreholes can become conduits for mine pool water to the alluvial aquifer as the mine pool rises above the elevation of the borehole collars. Recent evidence of this connection occurred when a steel pipe was unearthed near the former emergency storage pond, approximately 150 feet north of the Pierce adit (Figure 1). A description of this discovery is contained in a September 3, 2010 letter from Cotter to DRMS and additional information was provided by Cotter representatives during the November 5 site tour. After excavation around the pipe it was found to be inserted into a borehole that was angled approximately 53° down into the mine workings from the valley floor. The pipe was flowing at approximately 20 gpm when it was unearthed and the flow ceased when a flexible pipe was inserted and raised a few feet. When the pipe was below this elevation, the hydrostatic head in the mine pool caused the pipe to flow, and when raised the end of the pipe was above the pool elevation and flow stopped. According to Cotter, the elevation of the end of the steel pipe when it was unearthed was approximately 15 feet below the mine pool; thus, it could have been discharging water for several years. Water from the pipe was sampled by Cotter and uranium was said to be 24 mg /L, while radium was very low. Plotting of the major ion chemistry by Cotter revealed that the water was similar to the mine pool water, and Cotter has acknowledged that the water is sourced by the underground mine pool. Cotter has since placed a pressure packer in the pipe to stop the flow of water. The Illinois Fault passes through the mine workings and trends to the north. The surface trace of the fault is shown on Figure 1 and the fault intersects the creek. The Illinois Fault is referred to as a "fault zone" that is vertically fractured. The fault is reported to be a transmissive zone having a hydraulic conductivity on the order of 0.03 feet /day, or two orders of magnitude greater than the hydraulic conductivity of the unfractured bedrock mass of 0.0003 feet/day. The point of intersection between the fault zone and the creek corresponds to the beginning of a steady increase in specific conductance in the creek that was measured in a November 2008 survey. The survey included specific conductance measurements approximately every 100 feet along the creek, as depicted on Figure 8 -23 of the EPP. Specific conductance values in the creek were consistent upstream of the fault's contact with the creek and steadily increased downstream of the contact. This suggests that high ionic strength water is conveyed by the fault zone to the creek. The