2018-10-16_PERMIT FILE - M2018039 ‎(2)‎

• Permit No: M2018039
• IBM Index Class Name: PERMIT FILE
• Doc Date: 10/16/2018
• Doc Name: Adequacy Review Response
• From: Blue Earth Solutions
• To: DRMS
• Email Name: JLE
• Media Type: D
• Archive: No

HYDROGEOLOGIC EVALUATION FOR THE NORTH WELD COUNTY WATER
DISTRICT
LAMB LAKES SITE
LARIMER COUNTY, COLORADO
1.0 INTRODUCTION
This evaluation provides a hydrogeologic assessment of the alluvial groundwater conditions
across the Lamb Lakes Site (M-2018-039) project area. The evaluation has been prepared for
submittal to the Colorado Division of Reclamation, Mining and Safety in response to adequacy
review comments dated September 11, 2018.
The Lamb Lakes proposed permit area was historically mined for alluvial sand and gravel in
three distinct mine areas and currently consists of three separate groundwater lakes; Lamb A,
Lamb B, and Lamb C (Figure 1). Complete mining and reclamation of the proposed permit area
will consist of lake dewatering, additional excavation, selected slope backfilling, and slurry wall
construction. With final slurry wall construction, the historic mining areas will effectively be
separated from the surrounding alluvial groundwater system, making the pits available for future
below-grade water storage. Adjacent properties are primarily rural and semi-rural residential and
agricultural uses. The Cache la Poudre River runs from northwest to southeast along the eastern
boundary of the site. The Fort Collins Irrigation Canal Ditch diverts water from the Cache la
Poudre River immediately north of the site and the ditch flows along the eastern and southern
edges of the site. The Larimer and Weld Ditch also diverts water from north of the site, but the
ditch diverts east of the river and flows away from the site.
This evaluation will address adequacy review comments related to Exhibit G, Water Information,
of the Minerals Rules and Regulations of the Colorado Mined Land Reclamation Board for the
Extraction of Construction Materials. Specifically, the evaluation provides (1) a hydrologic
impact analysis to demonstrate the radius of influence of the dewatering operation for current
and future mining and reclamation phases, (2) an estimation of the static groundwater elevation
at the site assuming no dewatering, and (3) recommendations to be included in a groundwater
monitoring plan.
2.0 HYDROGEOLOGICAL CHARACTERIZATION
The final mining and reclamation at Lamb Lakes will occur in three phases. Each of the three
lakes will be individually dewatered during separate slurry wall construction periods. Prior to
future lake dewatering and slurry wall construction, piezometers should be installed around the
perimeter of the site to record baseline groundwater elevations. The piezometers should stay in
place and be used to monitor fluctuations in groundwater elevations during and after slurry wall
construction.
2.1 Regional Geologic Setting
The Lamb Lakes Site is located in the Colorado Piedmont Physiographic Province between the
Southern Rocky Mountain Province to the west and the Great Plains Province to the east. The
proposed permit area is located along the Cache la Poudre corridor and floodplain.
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