2011-09-16_REVISION - M1990057 (9)

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CDRMS question 4. The Applicant has stated a 6 " -8" clay underliner will be placed on the interior slopes and impoundment section. The Division requires clay liners to be constructed with a minimum thickness of 12". Please commit to installing the clay underliner at a minimum thickness of 12". UMC Response UMC concurs with the 12in minimum clay underliner thickness and UMC commits to installing a 12in clay liner of 1 x 10 cm/sec in two lifts, 6in each. CDRMS question 5. Please provide the Division with a Ouality Assurance /Quality Control (OA/OC) Plan for construction of the TSF. Plan should address field compaction testing of the clay underliner; a single compaction test should be performed for every 2,500 cubic yards of placed material. In addition, the OA/QC Plan should address pressure testing and destructive testing of the Polypropylene Geomembrane liner seams. A minimum of two destructive tests should be performed on the liner. UMC Response The Quality Assurance /Quality Control (QA/QC) Plan for the TSF is as follows. Onsite Personnel UMC's mill superintendent or qualified designate will be on site at all times construction activities are being conducted by UMC crews or by contractor crews. UMC has retained an Owner's Engineer, who is a Registered Professional Engineer and a Professional Land Surveyor in the State of Colorado, to monitor the contractors. UMC is contracting clearing and grubbing, topsoil removal and storage, impoundment excavation and embankment construction, clay material segregation and clay liner construction, leak detection and sump construction, impoundment liner installation, and geotextile liner installation. UMC crews will place overliner material on the geotextile liner, construct and place ballast tubes on the impoundment sides, install tailings slurry pipes to the impoundment, and install the decant water pumping station. General Site Preparation • Stake tree clearing/topsoil removal limits for TSF. • Stake grubbing limits for existing tailings storage pad. • Slope stake storage pad for existing tailings. • Oversee tailings storage pad layout and grading. Clearing, Grubbing/Topsoil Removal /Storage • Performed by contractor, monitored by Mill Superintendent and/or Owner's Engineer. • Quantity check between planned and actual material moved. Impoundment Excavation and Embankment Construction • Performed by contractor, monitored by Mill Superintendent and/or Owner's Engineer. • Slope stake exterior and interior embankments. • Red top embankment slopes as being constructed by contractor. • Grade top of sub base on interior slope and bottom of impoundment ( +/- 1 ") on 50' grid. • Monitor compaction lifts, compaction equipment in conjunction with contract soils engineer. M1990 -057 September 16, 2011