2014-12-24_REVISION - M2004051 (3)

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1.0 INTRODUCTION This report summarizes construction observations and quality control testing performed during the construction of the Wattenberg Resource, Pond 3 slurry wall. The slurry wall was constructed by Envirocon Inc. ( Envirocon). Upon completion of mining, Pond 3 will be reclaimed as a lined water storage reservoir meeting seepage requirements of the State Engineer. The slurry wall was designed to meet these seepage requirements. A total of approximately 10,045 lineal feet was constructed. The total curtain area of the slurry wall was approximately 328,800 square feet. The construction consisted of trench excavation with bentonite slurry to maintain the trench walls. The trench extended through the site alluvial soils into the underlying bedrock. The trench was backfilled with low permeability material derived from on -site fine grained materials mixed with dry bentonite and excavated material and slurry. Upon completion of mining, the slurry wall will provide the low permeability liner for a below grade water storage reservoir. 1.1 Site Description The Wattenberg Mine is operated by Aggregate Industries (Al) and is located on an alluvial terrace immediately west of the South Platte River approximately % mile northeast of Weld County Road 23 % and approximately 1 mile north of Baseline Road (aka Weld County Road 2), in Weld County, Colorado. Pre - mining topography of the site slopes gently to the northeast. The north part of the mine was previously mined. A stockpile is located southwest of the mined area. The Huett Seep is located immediately east of the Pond 3 slurry wall. The Huett Seep is lined with a geosynthetic clay liner (GCL) and replaces jurisdictional wetlands that previously were present in the mine limits of Pond 3. Overhead Public Service Company of Colorado power lines cross the slurry wall alignment at two locations. Two other power lines are located north of the slurry wall. The screening and wash plant is located on the east side of the river. Z.0 CONSTRUCTIONSUMMARY Prior to construction of the slurry wall, Dirt Doctors constructed a platform of fine grained material along the inside of the slurry wall alignment. The platform consisted of select, fine grained, overburden soils placed in sufficient quantity to provide supplemental fines to the trenched material. Envirocon placed bentonite bags along the platform at calculated distances to result in backfill with at least one percent bentonite based on the dry weight of the backfill. The typical Envirocon slurry wall construction crew consisted of five to six personnel managed by one superintendent. Envirocon delivered two trailers to the site. One was set up at the mine entrance and the other was set up on the north part of the site, south of the previously mined area. This second trailer served as the site QA/QC trailer. - 1 - August 2013 P:\23514\ 133 - 23514 -13003 \Docs\Reports\ Wattenberg_Construction _Report_2013.doc