2018-01-19_REVISION - M2000041

• Permit No: M2000041
• IBM Index Class Name: Revision
• Doc Date: 1/19/2018
• Doc Name Note: Adequacy Review Response #3
• Doc Name: Adequacy Review Response #3
• From: Deere & Ault / Fremont Paving & Redi-Mix, Inc.
• To: DRMS
• Type & Sequence: TR4
• Email Name: ERR
• Media Type: D
• Archive: No

DEERE & AULT
CONSULTANTS, INC.
TECHNICAL MEMORANDUM
TO: File
FROM: Victor G. deWolfe, P.E., P.G.
DATE: January 16, 2018
RE: Pueblo East Pit Groundwater Impact Analysis, Pueblo County, Colorado;
D&A Job No. CG-0212.010.00
INTRODUCTION
This memorandum discusses the groundwater impact analysis for the Pueblo East Pit located
along the Arkansas River near Avondale in Pueblo County, Colorado. The site is located in parts
of Sections 34, 35 and 36 of Township 20 South, Range 63 West; and Sections 1, 2 and 3 of
Township 21 South, Range 63 West(Figure El). The site boundaries include the Arkansas
River to the south and U.S. Highway 50 to the north. The purpose of the groundwater impact
analysis is to provide information related to the potential groundwater mounding due to the
proposed reclamation plan for the mine. These activities include open water storage employing a
slurry wall cutoff and backfilling of another cell with wash fines material. A groundwater model
was constructed to use as a tool for the analysis. The objectives of the groundwater model are to:
1. Approximate the pre-mining groundwater hydrology using available data
2. Simulate the hydraulic effect of the reclamation plan by predicting potential groundwater
mounding upgradient of the property and shadowing downgradient.
3. Simulate the effect of a drain on mounded groundwater upgradient of the property
boundary
To satisfy these objectives, steady state groundwater models were constructed for: 1)pre-mining
conditions, 2)post-reclamation conditions and 3) mitigated slurry wall conditions.
The model domain is set within the alluvial floodplain of the Arkansas River, the primary surface
hydraulic feature in the area. The topography slopes gently from northwest to southeast. The
near surface bedrock is the Cretaceous Pierre Shale. The bedrock outcrops as bluffs along the
southern margin of the river(Figure E-1). Land use in the area consists of mining and
agricultural uses.
This modeling memorandum presents a general conceptual model of the aquifer system followed
by a discussion of the groundwater modeling software; construction of the model; calibration of
the model in terms of target residuals and mass balance; and finally, by a discussion of the
600 S.Airport Road,Building A,Suite 205
Longmont,CO 80503
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