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

McGrane Water Engineering, LLC
1669 Apple Valley Rd.•Lyons.CO 80540•Phone:[phone] E
E-Mail:dennis ct mcgranewaterxom
McGrane Water Engineering
May 31, 2023
Mr. JC York
J&T Consulting, Inc.
305 Denver Avenue, Suite D Via email at:1cyork(a�_j-tconsultin,,.com
Ft. Lupton, CO 80621
RE: Bernhardt Pit—Groundwater Evaluation
Dear Mr. York:
The proposed Bernhardt gravel pit mine is located approximately 1 mile southeast of Milliken,
Colorado in Section 24, Township 4 North, Range 67 West (6th PM). The site is located on the
west bank of the South Platte River(SPR)which flows north at this location. Figure 1 shows the
proposed pit boundary, groundwater model boundary and study area boundary that covers
approximately 13 square miles. The model area is approximately 7 square miles. The study area
includes approximately 224 permitted water wells per the State's well database (CDWR, 2023).
Figures la, lb, Ic, and ld include the well permits we used to help characterize the aquifer and
identify wells that may be impacted.
As part of the mine permit application process, the mine consultant, J&T Consulting, Inc. (J&T)
requested that McGrane Water Engineers,LLC.(MWE)determine the potential impacts of a slurry
wall around the proposed Bernhardt pit. Impacts typically include a rise in the water table
("mounding") on the up-gradient side of the slurry wall and a decline in the water table
("shadowing") on the down gradient side. Water level increases to within 10 feet of the surface
on the up-gradient side of the pit could also cause flooding of low lying structures such as home
basements. A decline in water levels on the down gradient side could reduce the aquifer saturated
thickness and well yields if the decline is more than approximately 10 percent of the saturated
aquifer thickness.
GROUNDWATER INVESTIGATION
To evaluate the groundwater level changes in response to the slurry wall installation,we:
1. Conducted a literature search of existing published groundwater literature in the vicinity
Milliken and Gilcrest, Colorado;
2. Compiled well data from the State's Well database (CDWR, 2023) including: well name,
permit number, location, well depth, depth to water, and pumping rate (Table Al);
3. Updated maps prepared by the US Geological survey depicting the water table and alluvial
aquifer bottom surfaces (aka bedrock structural elevation map) using more recent drilling
data;
4. Compiled monitoring well data in Table A2 from monitoring wells drilled by Cesare, Inc
during April 2023.
5. Created a MODFLOW groundwater model to evaluate changes in groundwater levels
resulting from a slurry wall installed around the pit; and