2014-07-07_REVISION - M2012032 (16)

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Revenue Mine Monitor Well Installation The original monitor well concept was prepared by Buckhorn Geotech, Inc. and designed by Wayne Pandorf, P.E, who has 40 years of experience in geotechnical, hydrogeologic and environmental consulting. The details were dated May 2, 2014 and envisioned that the wells would be double cased with outside diameter of 8 inches and an inner 2 inch diameter sampling portion of the well encased in a minimum 3 inch annular space sand pack. Conceptually, this design offered the highest degree of sample water quality. Monitor well installation began on May 20, 2014 under the full -time observation of Mr. Pandorf with the contractor attempting to advance an approximate 10 inch diameter hole to set the 8 inch outer casing. Because of the large and small waste rock present, the 10 inch bit produced more displacement than cutting which resulted in an approximate 36 inch diameter hole that was only about 8 feet deep after 8 hours of drilling. It was apparent that trying to advance a large hole disturbed too much surrounding material and would be problematic. Therefore, a decision was made to advance as small a borehole as possible with an optimal cutting bit (in laser -like fashion) to minimize disturbance of surrounding rocky material. Since this would result in a reduced /limited sand pack around the well screen, it was decided to wrap the filter screen section with a minimum two layers of geotextile fabric and provide whatever sand pack possible. The resultant plan was as follows: Advance four inch casing with a diamond core shoe and a tri -cone inner drill stem, leave the casing in place, flush cuttings with Sneffels Creek water, lower the 2 inch well screen with geotextile wrap into the casing, add sand and bentonite chips in small vertical increments while pulling the casing at the same increments, and sealing the hole with cement grout. At the first well installed, cement grout was not available so shotcrete was used as the well seal. Overall this method proved cumbersome but produced a "clean, precise" cased 4 inch diameter borehole into which the 2 inch monitor well casing could be installed. All monitor well construction was performed under the full -time observation of either Mr. Pandorf, or Jeramy Harshman, Staff Geologist, both of Buckhorn Geotech, Inc. The depth of the shallow well at each location was set by using the test pit stratigraphy provided by the mine which had indicated a shallow depth to a thin apparent "impermeable" layer of tailings at each well location. At well locations 2A and 3A, there was no drilling fluid return from the borehole so the depth to this tailings layer was done "in- the - blind" using the test pit depth and staying about a half foot above top of layer. At well location 1A, there was drill fluid return and the well borehole was stopped when a color change (orange) of drill fluid occurred. We point out that the term "drill fluid" herein refers to water from Sneffels Creek injected through the drill stem. No drill fluid thickener such as bentonite was used. The deeper wells at each location were to be set at the top of bedrock. This was the case at well locations 1B and 2B. However at location 36, bedrock was not encountered until a depth of 71 feet. This borehole was advanced with casing set to 40 feet and straight drilled with the inner drill stem and bit below that depth. Until a depth of about 40 feet, there had been no drilling fluid return up through the casing out of the borehole. However below that depth, there was complete circulation of drilling fluid from the borehole even though it was only cased to 40 feet. Observation of the solids from the drilling fluid indicated that the soils were predominantly fine - grained. Also from 40 feet to 71 feet, the soil was soft enough that the drill rod was advanced without hydraulic pressure, i.e., it advanced under Revenue Mine TR -04 Appendix 15 Page 4