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Whetstone <br />ASSOC/c7teS4 Technical Memorandum <br />To: Ken Mushinski, Cotter Corporation (N.S.L.) 4109C <br />From: Susan Wyman, P.E., P.G. (Whetstone), Levi McEwen (Whetstone) <br />Date: July 30, 2015 <br />Subject: Summary Report on the 2015 Schwartzwalder Mine Grouting Program <br />This Memorandum has been prepared to document the installation of a grout curtain at the <br />Schwartzwalder Mine in Jefferson County, Colorado. The grout curtain was installed from June 3 to <br />July 1, 2015, to reduce seepage into alluvium from the underground mine. <br />Hayward Baker, Inc., of Broomfield, Colorado, was contracted by Cotter Corporation (N.S.L.) <br />(Cotter) to seal a zone of the Illinois Fault at the Schwartzwalder Mine to reduce groundwater inflow <br />to Sump 10. Whetstone Associates, Inc. (Whetstone) was contracted by Cotter to provide geologic <br />consulting and oversight of the grouting program. <br />1. GROUT CURTAIN LOCATION <br />The proposed grouting program was summarized in Technical Revision 22 (TR22) to the Mine <br />Reclamation Plan. The original plan called for up to 19 primary holes to be drilled and grouted on a <br />10 -foot spacing and up to 19 secondary holes to be drilled and grouted as needed to complete the <br />grout curtain. <br />At total of 30 hole locations were drilled, tested, and grouted, including 17 primary holes (F 1 — F17) <br />and 13 secondary holes (S 1 — S 13). The initial 14 primary holes (F 1 — F 14) and 13 secondary holes <br />(S 1 — S 13) were staked on May 27, 2015. Additional earthwork was performed prior to the start of <br />the grouting program to provide access for hole F 14. Additional grout holes were added as the <br />grouting program progressed, to in response to pressure test results in holes F13 and F14 at the east <br />end of the array. Two primary hole locations (F15 and F16) were added on June 18, 2015, and a <br />third primary hole location (F 17) was added on June 25. <br />The holes were aligned approximately perpendicular to the Illinios Fault zone and parallel to Ralston <br />Creek Canyon. The collar locations were determined by Whetstone Associates on June 11, 2015 and <br />June 26, 2015 using a transit and stadia rod, based on the benchmark elevation and location of <br />monitoring well MW 18. The location and elevation of MW 18 were professionally surveyed by <br />Accurate Engisury of Westminster, Colorado in November, 2012, and coordinates are available in <br />both State Plane NAD27/NGVD29 and in State Plane NAD83/NVD88. The hole locations are <br />shown in Figure 1 and coordinates are provided in Table 1. <br />4109C.150730 1 <br />