2002-03-29_REVISION - M1999034 (2)

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L- t~ i RECEIVED Str 1 d 2001 September 18, 2001 Aggregate Industries West Central Division 3605 S. Teller Street Lakewood, Colorado 80235 Attention: Mr. Tom Maul 0 RECEIVED Subject: Consultation Services Slope Stability Analysis Results Arvada Reclamation Pit 104"' Avenue and McKay Road Job No. 32,637 MAR 2 9 2001 Division of Minerals and Geology This letter presents the results of slope stability analysis on materials sampled at the Arvada Reclamation Pit at 104"' Avenue and McKay Road in Thornton, Colorado (Fig. 1). The analysis was conducted to evaluate the stability of the embankment materials and the permeability of the underlying bedrock. The scope was described in our Proposal dated January 23, 2001. Proposed Construction Arvada Reclamation Pit was mined for aggregate. The interior of the resulting excavation, which extends to bedrock, is currently being reconstructed using site overburden soils to create a compacted sloped fill. The reclaiming of the pit is being done by Aggregate Industries. A proposed zoned earth dam will divide the reservoir into two water storage areas. The City of Arvada will acquire the south end of the pit and the City of Thornton will acquire the north end for water storage. The north portion of the proposed storage area has not been mined. The embankments are being constructed by Lawrence Construction and are under the supervision of the Applegate Group. Stationing for the crest perimeter was established by Petter Epp Associates. The circumference of the proposed Arvada storage facility along the crest will be about 6,400 feet. The average depth to the bottom of the pit was approximately 30 feet. A slurry wall was constructed around the perimeter of the gravel pit prior to mining to a depth of approximately 35 feet. The slurry wall was approximately 25 feet back from the top of the slope. Field and Laboratory Investigation Our approach to the analysis was done to determine strength of recompacted soils and permeability and evaluate slope stability based on these test results. Aggregate Industries has indicated that the reservoir may experience a maximum drawdown of 1 foot per day. We obtained nine samples at approximate 500 foot CTL/THOMPSON, INC. CONSULTING ENGINEERS i97t WEST 12TH AVENUE ~ DENVER, COLORADO 80204 ~ (303) 825-0777