2023-10-03_REVISION - M1977344 ‎(31)‎

• Permit No: M1977344
• IBM Index Class Name: Revision
• Doc Date: 10/3/2023
• Doc Name Note: 2.7 Exhibit G - Water Information
• Doc Name: Request For Amendment To Permit
• From: Holcim ‎(US)‎ Inc.
• To: DRMS
• Type & Sequence: AM2
• Email Name: TC1
• Email Name: MAC
• Media Type: D
• Archive: No

Bear Creek Quarry (M-1977-344) Permit Amendment
Holcim US Inc, 3500 Highway 120, Florence, CO 81226
Phone [phone] www.holcim.us 66
Field activities conducted as part of this investigation included installation of five groundwater monitoring
wells, installation of pressure transducers to collect water level data, and the collection of groundwater
samples for laboratory analysis. Additional field activities included the installation of a ramp flume and
stilling well transducer, visual observation and documentation of surface flow locations, and the collection
of surface water samples for laboratory analysis. Groundwater modeling was conducted in support of mine
permitting activities to evaluate potential groundwater impacts from planned mining operations at the
RCQ. The groundwater modeling report is provided under separate cover.
The results of the five quarterly surface and groundwater monitoring events identified several naturally
occurring analytes present at concentrations above regulated water quality standards, including selenium,
uranium, radon, and sulfate. Several groundwater and surface water studies conducted by others also
found elevated concentrations of these analytes within the same lithological units and similar surface
water bodies in Colorado.
Water quality data suggests the source of the surface water within the perennial section of Red Creek is
groundwater based on the similarities of major ion and metal concentrations. Surface water concentrations
of major ions tend to fall within the ranges observed in samples collected from the groundwater wells.
Variations in the water composition of the surface water samples indicate the influence of creek bed
sediments, evaporation, precipitation, and multiple groundwater seeps or springs contribute to the water
quality and flow in Red Creek.
2.7.3.2 Groundwater Modeling
Groundwater flow modeling (Modflow) was performed on Red Creek to estimate the potential rate s of
groundwater entering the RCQ. In addition, the model was used to estimate potential mining impacts to
Red Creek. The technical memo is provided in its entirety as Appendix 4.6. The site conceptual model was
built on available data in the area and information obtained from the existing Holcim mine plan Leapfrog
model. The site-specific Leapfrog geologic model includes the base Codell Sandstone, overlying Fort
Hayes Limestone, and additional overlying sediments. The contact between the Codell and Fort Hayes
dips toward the north across the site. Groundwater occurs primarily within the Codell Sandstone and
within the lower portion of the Fort Hayes limestone in localized areas. Sediments overlying the Fort
Hayes are generally unsaturated.
Based on conservatively high potential impacts to the Codell, it was determined that the rate of
groundwater entering the quarry may increase from Mine Plan Block 0-10 through Mine Plan Block 20-30.
Following Mine Plan Block 20-30 the pit floor elevations are above the interpolated water table and are
therefore dry. The evaluation of mining impacts to Red Creek suggested no significant influence on the
creek.
The model results discussed represent a simplistic assessment for mining influence on groundwater in
RCQ. To improve and extend model predictions beyond Mine Plan Block 20-30, additional groundwater
monitor wells will be installed throughout the site as mining progresses into Year 20-30 block.
2.7.4 Potential Mining Impacts to Water Quality and Quantity
Based on groundwater modeling, mining will not impact water quantity in Red Creek. To be protective of
water quality, Holcim will implement a surface and groundwater monitoring plan.
2.7.4.1 Monitoring Plan
Surface and groundwater monitoring will recommence on a semi-annual basis immediately prior to mine
development. Sampling and monitoring will occur during the second calendar quarter (April thru June) and
fourth calendar quarter (October thru December) each year. Groundwater locations will include Well 1 that
lies north of Red Creek, and Wells 3 and 4 that lie south of Red Creek. Two wells will be monitored south
of Red Creek because the groundwater shows natural variation in water quality as observed during the