2023-08-03_PERMIT FILE - M2023025 ‎(32)‎

• Permit No: M2023025
• IBM Index Class Name: Permit File
• Doc Date: 8/3/2023
• Doc Name Note: Exhibit G - Water Information
• Doc Name: Application
• From: J & T Consulting Inc.
• To: DRMS
• Email Name: RDZ
• Email Name: MAC
• Email Name: AWA
• Media Type: D
• Archive: No

Bernhardt Pit Groundwater Evaluation
May 2023 Page 11 of 31
study on the SPR as part of the South Platte River Decision Support System project(CDM, 2006
and 2013). In 2014, in response to observed evaluated water levels around Gilcrest (4 miles to
the east), and LaSalle, the Colorado Geological Survey (CGS) conducted a study (Barkmann and
Others,2014)focusing on groundwater level trends. Barkmann reported using the SPDSS data as
the basis for their analysis. The most recent geologic mapping was also prepared by the Colorado
Geological Survey (Palkovic and Others, 2018), which we used to better refine the western edge
of the alluvial aquifer.
Surficial Geology
Figure A2 shows the site surficial geology mapped by the CGS(Palkovic and Others,2018). The
alluvium within the model areas consists of alluvial (Qa) sand and gravel (geologic map symbols:
Qa, Qal,Qa2,and Qa3 based on their age (recent to older). The western alluvial aquifer boundary
is in contact with the Fox-Hills sandstone (geologic symbol Klf) at the western edge of the
Bernhardt pit. The floodplain extends approximately four miles east of the proposed pit to near
the Town of Gilcrest where it becomes overlain by wind blow dune sand and loess (fine silt and
sand) deposits (Qe).
Well Depth
Figure A2 also shows the reported well depths from 200 wells within the study area. For this
map to be meaningful, we assume that the depth of the wells is at the base of the alluvial aquifer
(ie. top of bedrock). Assuming this, the alluvium appears to deepen to approximately 60 feet on
the eastern side of the model and be>70 feet by the eastern edge of the study area.
Water Level Contours
We created a water table map (Figure A3)using available data from registered SEO wells (Table
Al)and the Bernhardt monitoring wells(Table A2)using the March 31,2023 measurements. The
water table elevations from SEO wells were determined by subtracting the reported depth to water
when drilled from well site elevations interpreted from US Geological Survey 10m Digital
Elevation Model (DEM) data sets. The white 10 ft elevation contour lines shown on Figure A3
are best drawn approximately 500 feet upgradient from the river elevation based on USGS DEM
data which reflects the slight imprecision of the DEM elevations(Haneberg,2006).
Groundwater flows perpendicular to the water level contours. The water table elevation at the
west end of the model is at approximately 4630 ft (msl) and the water table gradient falls
approximately 25 feet to approximately 4605 ft (msl) on the east end of the model. Most of the
water coming into the model area is from the south and southeast. The contours show that the SPR
is a gaining stream throughout the reach.
Bedrock Elevation Contours
Figure A4 shows the elevation contours of the structural top of bedrock digitized from Robson
and Others (2000) based on the ground surface topography above the floodplain combined with
the elevation of bedrock determined from drilling data. West of the pit,the bedrock rises abruptly
to a large hill known locally as the Wildcat Mound (within 4900 ft contour) which extends over
200 feet above the floodplain. Although the Robson contours match very well with the SEO well
data, we did need to modify the contours slightly to reflect the Bernhardt monitoring wells (Table
McGrane Water Engineering,LLC
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