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Daniel Arnold, Esq. April 6, 2011 Denver Water Page 9 of 12 location of the corehole contained in Cotter's September 3, 2010 letter to DRMS, describing the excavated corehole pipe (the Cotter letter is included as Attachment B). The corehole is at the southwest corner of the former emergency storage pond. This location is approximately 100 to 150 feet from the J-10 location identified on Figure 13, and coincident with the L -10 location shown on Figure 13. The location of the discharging corehole was also pointed out by Cotter representatives during the November 5, 2010 site tour and the corehole was observed to be near the L-10 location, not the J -10 location. Therefore, it is likely that the discharging corehole is L -10, not J -10, and this would explain why the water chemistry was slightly different than the mine pool because the L -10 corehole is slightly outside of the workings. Furthermore, Figure 13 indicates that there is another corehole at the L-10 location that is directed to the southeast, and appears to be identified as I 12. The significance of the new corehole information is that corehole J -10 was drilled into the workings and collared near the present -day creek. It remains unplugged and could be discharging mine pool water to the alluvium. In addition to J -10, the comment identifies corehole FFC -1 as being unplugged and collared near the Steve Adit. Installation of a well or lysimeter near the Steve Level bench to monitor for possible mine pool seepage is the proposed plan of action to determine if the corehole is impacting the alluvium. Considering the significant water quality impacts to the creek, passive monitoring is not an appropriate course of action and the collared areas of both J -10 and FFC -1 should be investigated and plugged. The second corehole at L -10 (I 12) should be plugged as well. The comment on coreholes also mentions that there is a compilation of information on the unplugged coreholes and the title of Figure 13 implies that unplugged drill holes are identified in the EPP. Our review of the EPP found no information on unplugged drill holes. This information should be made available along with the historical maps of corehole locations for independent review and confirmation. Isolation of the creek from alluvial groundwater is being considered by Cotter. Given the strong hydraulic connection of the two, this is an appropriate corrective measure to protect the water quality in the creek in the near term. The alluvial groundwater will remain impacted by the alluvial fill, waste rock, and mine pool water, and each requires additional characterization and remedial action to protect groundwater quality in the long term. REFERENCES ARCADIS /Malcolm Pirnie. 2011. Technical Memorandum — Draft Review of the Schwartzwalder Mine Environmental Protection Plan. Prepared for Denver Water. January 25. Bernhard, G. et al., 2001. Radiochimica Acta 89: 511 -518. Bernhard, G. et al., 1996. Radiochimica Acta 74: 87 -91.