2023-01-10_PERMIT FILE - M2023001 ‎(12)‎

• Permit No: M2023001
• IBM Index Class Name: Permit File
• Doc Date: 1/10/2023
• Doc Name Note: Exhibit G - Water Information
• Doc Name: Application
• From: J-2 Contracting Company
• To: DRMS
• Email Name: PSH
• Email Name: JLE
• Media Type: D
• Archive: No

Fair Meadows Pit Groundwater Evaluation
November 19, 2022 Page 6 of 28
Saturated Thickness
We calculated the aquifer saturated thickness as the difference between the water table (Figure
A3) and the top of bedrock (Figure A4). Figure A5 shows how the saturated aquifer thickens
from only 40 feet on the west side of the Fair Meadows pit to over 90 feet on the east side within
the paleochannel.
Well Yield
We plotted reported well yields extracted from the State's well database on Figure A6. All of the
high capacity municipal and irrigation wells that produce over 1000 gpm(blue) are located in the
northern half of the study area where the aquifer is thickest. Well yield is proportional to the
aquifer saturated thickness which is expected to slightly increase up-gradient from the Fair
Meadows (after it is installed) which will slightly benefit well production in the area, but not an
appreciable amount.
Aquifer Transmissivity
Figure A7 shows the contoured aquifer transmissivity (T) which is the product of the aquifer
hydraulic conductivity (a measure of permeability) multiplied by the saturated thickness (Figure
A5). The resulting transmissivity distribution used in the model is consistent with USGS mapped
values of 200,000 to 400,000 gpd/ft)within the paleochannel and across the Fair Meadows pit site.
To obtain the contoured transmissivity values shown in Figure A7, we multiplied the saturated
thickness shown in Figure A5 by the hydraulic conductivity. We assigned a constant hydraulic
conductivity of 600 ft/day in the middle of the paleochannel which created modeled transmissivity
values that closely match the published transmissivity map by the US Geological Survey (Hurr
and Schneider, 1972). We used a lower hydraulic conductivity(K) of 300 ft/day on the north and
south sides of the paleochannel to represent older terrace deposits. This resulted in lower
transmissivity values (<100,000 gpd/ft). The K values we used (300- 600 ft/day) is a reasonable
range for sand and gravel deposits. The range is also consistent with values used by the Colorado
Division of Water Resources (250 to 550 ft/day) for the South Platte Decision Support System
(SPDSS) groundwater model for this area(CDM-Smith, December 6, 2006, Figure 5c).
Modeling
We used the Groundwater Vistas (GV)pre and post processor(version 6.85 Build 11, Rumbaugh,
Environmental Solutions, Inc.) to construct and run a MODFLOW2000 (Harbaugh et al, 2000)
model, and display the results. We exported processed cell-by-cell flow terms from the model
into ArcView GIS software to process prepare report figures.
The model area is 11,000 feet high (north to south) and 15,000 feet wide (west to east) centered
on the Fair Meadows pit. The model consists of 55 rows and 75 columns using 200 foot square
model cells.
McGrane Water Engineering,LLC
1669 Apple Valley Rd. •Lyons,CO 80540 •Phone:[phone]
E-Mail:[e-mail] Web:ttp://www.mcgranewaterengineering.com