Work Plan to Locate Level 2 Adit Standard Mine Superfund Site Crested Butte, Colorado June 29, 2017 Contents 1 Introduction ................................................................................................................................... 1 1.1 Purpose ............................................................................................................................... 1 1.2 Site Location and Description ............................................................................................. 1 1.3 2016 Drilling Activities ......................................................................................................... 2 2 SCOPE OF GEOPHYSICAL SURVEYS ...................................................................................... 7 2.1 Work Tasks ......................................................................................................................... 7 2.1.1 Survey Planning ..................................................................................................... 7 2.1.2 Mobilization ............................................................................................................. 8 2.1.3 In-Field Testing ....................................................................................................... 8 2.1.4 Data Collection/Recording ...................................................................................... 8 2.1.5 Demobilization ........................................................................................................ 9 2.1.6 Data Processing and Interpretation. ....................................................................... 9 2.2 Health and Safety.............................................................................................................. 10 2.3 Schedule ........................................................................................................................... 10 3 References.................................................................................................................................. 11 Tables Table 1. Standard Mine Level 2 Drilling Summary............................................................................ 3 Figures Figure 1. Site Location Map ................................................................................................................ 5 Figure 2. Cross Sectional View of the Standard Mine Complex ........................................................ 6 Figure 3. Proposed Seismic Line Locations ..................................................................................... 13 Appendices Appendix A.Refraction Field Form Appendix B.Resume 1 Introduction 1.1 Purpose This work plan includes steps for acquiring data, processing data, and data interpretation to aid in the locating the Level 2 adit. The information collected will be used to select the location(s) for borehole drilling intended to intercept Level 2 adit. 1.2 Site Location and Description The Standard Mine Superfund Site (U.S. Environmental Protection Agency [EPA] site identification #CO0002378230) is located in Gunnison County, Colorado, approximately 5 miles west of the Town of Crested Butte. The Site is an abandoned hard rock mine located in Elk Basin in the Ruby Mining District in the Ruby-Anthracite Range of west central Colorado at an elevation of approximately 10,900 to 11,600 feet above mean sea level. The Site is located within the boundaries of the Gunnison National Forest and includes approximately 10 acres situated on a combination of both U.S. Forest Service (USFS) land and private mining claims. The Site is remote and is accessed by traveling 1.5 miles through the Mount Emmons Mine Company (MEMCO) private property and then 2.7 miles over Forest Development Road 732. Harsh winter weather conditions and the remote location result in difficult Site access during the winter and limit the construction season. A Site location map is shown on Figure 1. The mine area drains into Elk Creek, which forms within the Site boundary and flows southward to Coal Creek, the drinking water source for the Town of Crested Butte. Copley Lake and several natural seeps discharge into Elk Creek downstream of the Site. Coal Creek flows east towards the Town of Crested Butte. The Crested Butte municipal water intake is located on Coal Creek approximately 2 miles downstream of the confluence with Elk Creek. The MEMCO Water Treatment Plant (WTP) discharges into Coal Creek downstream of the Elk Creek/Coal Creek confluence and downstream of Crested Butte’s drinking water intake. The Colorado Department of Public Health and Environment (CDPHE) is the support agency for this Site. Because the Site is partially located on USFS property, EPA and CDPHE are coordinating with the USFS on cleanup activities. USFS is considered a cooperating agency for this project, and is not responsible for funding or implementing the construction work. The Site includes several discrete areas of mining disturbance: Level 1, Level 2, Level 3, Level 4, Level 5, and Level 98. Levels 1, 2, and 3 are interconnected through a series of raises and sublevels. Level 4 consists of two shafts that connect to the Level 3 workings. Levels 5 and 98 are not connected to Levels 1 through 4 or each other. The Colorado Division of Reclamation, Mining, and Safety (CDRMS) investigated and mapped over 1,800 feet of the Level 2, Level 3, and Level 5 underground mine workings in 2006 and 2009. Figure 2 provides a Site Profile. hdrinc.com 1670 Broadway, Suite 3400, Denver, CO 80202-4824 (303) 764-1520(303) 764-1520 1 1.3 2016 Drilling Activities Following the 2015 construction season, the project team developed a plan to install a well into Level 2 adit to intersect the mine pool that was observed in 2009 by CDRMS and is believed to be formed by blockage of Level 2 near the portal (CDRMS, 2009). A well into Level 2 can serve several purposes: • Monitor water levels in Level 2 adit; • Dewater the Level 2 mine pool and monitor the response following dewatering; • Monitor water levels in Level 2 adit during impoundment of MIW in Level 1 through closing the valve on the Level 1 bulkhead; and • Monitor water levels in Level 2 adit during the long-term site operation and maintenance. HDR contracted with Authentic Drilling, Inc., to perform drilling services at the Standard Mine, Crested Butte, Colorado on September 6 through 9, 2016. The services included drilling boreholes in an attempt to intercept the Level 2 adit. Once the adit was intercepted, a well was to be installed to monitor water levels in the adit and be large enough to efficiently pump impounded water in Level 2. The borehole locations were selected based on the following information obtained by HDR field technicians and site managers: • Mine maps developed by Jeff Graves during a 2009 reconnaissance of Level 2. • Onsite discussions with Jeff Graves regarding orientation of Level 2 portal. During RA work in 2012, the portal of Level 2 was excavated from above to top of water but no discernable alignment of the drift could be determined. Mr. Graves indicated the approximate position of the Level 2 portal and the area of excavation. • Historical photographs from the Denver Public Library collection of Level 2 original trestle and ore chute. • Aerial photographs of the Standard Mine site on display at the MEMCO WTP. • Measurements of the strike and dip of the Standard Fault within the Level 3 adit (Station 2+50) indicated it continued downward at a 60° dip angle. This dip angle would place the Level 2 adit approximately 35 feet southeast of the Level 3 centerline (represented by a straight line from Portal 3 to the DOWL survey stake #701). • Attempts were made to locate the original rail alignment of Level 2 at the portal using a metal detector. The alignments indicated by the metal detector have Level 2 running almost directly underneath Level 3. This could not be verified; however, as hand shoveling efforts could not find the buried rail. Heavy equipment excavation was not an option due to the threat of releasing impounded water. Based on this information, it was estimated that the alignment of Level 2 at the desired well location was approximately 30 to 50 feet southeast of the Level 3 portal centerline. HDR geologists were on site to oversee drilling operations, log drill cuttings from borings, and supervise the installation of the well. The drilling operations were not able to locate the Level 2 adit; therefore, the well was not installed during this mobilization. Four borings were drilled using an ATV-mounted CME-750 drill rig capable of performing both Hollow Stem Auger (HSA) drilling and air rotary drilling. Air rotary drilling was the only method hdrinc.com 1670 Broadway, Suite 3400, Denver, CO 80202-4824 (303) 764-1520(303) 764-1520 2 required as there was little overburden encountered at the drilling site that would necessitate HSA drilling. Pilot hole borings were advanced with a 3 7/8-inch diameter tri-cone air rotary drill bit. The four borings were drilled to depths ranging from 83 feet below ground surface (bgs) to 89 feet bgs and were located approximately 30 to 50 feet southeast of the Level 3 portal centerline in an area thought to be directly above (approximately 70 feet vertical) the Level 2 adit. Borings were approximately 6-feet apart. The boring locations summarized in Table 1 as follows: Table 1. Standard Mine Level 2 Drilling Summary Total Drilled Depth Depth to Water Boring ID Lithology (ft bgs) (ft bgs) 1 83 38.65 Wasatch Fm., Metamorphosed