2017-11-13_GENERAL DOCUMENTS - C1981019

Home Browse Search

The approved backfilling and grading plan for the Colowyo Mine is found in Volume 1 (East and West Pit) and Volume 12 (South Taylor) of the PAP. Maps 19 and 19B show the approved post - mining topography, Maps 29 and 29A show the backfilling and grading schedule, and Maps 41 and 41A show the location of the permanent, post -mining drainage channels. The pre -mining and post -mining cross-sections are shown on Maps 20 and 20B, and the permanent drainage channel profiles are shown on Maps 33 and 33B. Exhibits 2 of the SL -11 application show cross-sections of the SL -11 area, including approved post mining topography alongside the constructed topography. IV. OBSERVATIONS AND FINDINGS The following discussion of observations and findings focuses on the results of backfilling and grading work and drainage reestablishment in East and West Pit for the partial Phase I Bond Release. The evaluation of the bond release application included the bond release inspection, an office review of the permit requirements and regulatory criteria, and review of past inspection reports. The bond release inspection was conducted on July 25, 2017. Several items were reviewed by the Division during the technical evaluation of the bond release application before, during, and after the inspection, including: the post -mining topography and cross-sections of backfilled and graded areas. During the partial Phase I Bond Release inspection, participants walked through most of the bond release request area to allow for visual assessment of compliance with pertinent requirements. Backfilling and Grading For SL -11, observations were made during the bond release inspection with regard to approximate original contour and stability of the reclaimed landscape. To determine compliance with Colowyo's approved approximate original contour (AOC) in the SL -11 areas, elevation data provided in the SL -11 Bond Release application was compared to GPS data collected by the Division. Twenty two points were selected along three transect lines approximately every 300 feet. Two transects with a total of 16 points were taken along the West Pit and one transect with a total of 6 points was taken along the East Pit. Points were placed at selected contour elevations in ArcGIS (to try to cover the majority of the area), and those points were then downloaded into a Panasonic FZ-GI tablet. During the bond release inspection, Zach Trujillo navigated to the points using the data in the Panasonic tablet and a GPS data point was collected at each site with a Trimble R10 GNSS (R10) surveying unit. The static precision of the R10 is 3.5 mm +0.4 ppm RMS and is on a localized geoid. For comparison reasons, a known point was collected at the Colowyo Mine office to determine a correction factor for the elevation collected with the R10. In Colowyo's coordinate system (UTM NAD 27 Colorado State Plane) the elevation is 7,262.91' at the known base station and was Proposed Decision and Findings of Compliance November 13 2017 Partial Phase I Bond Release SL -11 Page 5