2024-04-08_PERMIT FILE - M2024015

• Permit No: M2024015
• IBM Index Class Name: Permit File
• Doc Date: 4/8/2024
• Doc Name: Application
• From: J & T Consulting, Inc
• To: DRMS
• Email Name: BFB
• Email Name: EL1
• Media Type: D
• Archive: No

SVRC Groundwater Evaluation
January 2024 Page 2 of 58
3. Appendix B that evaluates impacts and mitigation measures of the other pits with and
without the SVRC.
All figures are located after each section. Some important unnumbered figures are located within
the text to facilitate reading. Small numbered tables are located within the text with larger tables
after each section. Figures and tables with prefixes "A" and ''B" are located after the associated
Appendix.
EXECUTIVE SUMMARY
We:
1. Reviewed published technical groundwater literature focusing on the hydrogeology of the
South Platte River(SPR)near Gilcrest;
2. Compiled well data from the State's Well database (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
monitoring well drilling data;
4. Compiled monitoring well water level from monitoring wells drilled around the SVRC and
Section 20 Pit by the applicants (Table A2).
5. Updated the table map (Figure A4a) created by the CGS (Topper et al.. 2014), by
considering more recent measurements around the pits (Figure A4b);
6. Evaluated the hydrogeology of the study area and created a Modflow groundwater model
(Appendix A) that we used to create the "Pre-pit"water table;
7. Evaluated seasonal water level changes at the site;
8. Updated depth to water maps prepared by the CGS (Topper et al., 2014) within the study
area (Figures A5a, b, c, and d);
9. Evaluated changes in groundwater levels compared to the "Pre-pit" water table caused by
the SVRC liner(Pit Scenario 1);
10. Evaluated changes in groundwater levels from other pit scenarios (Appendix B)
including:
Pit Scenario 2 - Section 20 pits;
Pit Scenario 3 - Monarch Pits;
Pit Scenario 4 - Both Section 20 and Monarch Pits; and
Pit Scenario 5 - All Pits (Section 20, Monarch and SVRC).
1 1. Each Pit Scenario includes at least one mitigation run that reduces mounding and
shadowing using dewatering wells and infiltration and exfiltration drains discussed
below.
Model Results Summary
The groundwater model was constructed using reasonable aquifer properties and boundary
conditions (aquifer sides, bottom, thickness and river leakage assumptions). The Pre-pit Run was
calibrated to recent water levels such that Root Mean Square (RMS)error is less than 3 ft(Figure
A10). The modeled elevation contours are very similar to our Pre-pit water table (Figure A4b).
Pit Scenario 1 simulates the effects of installing the SVRC liners. When the SVRC liners are
installed, water level changes in the range of plus or minus (+/-) 1 to 3.5 feet occurs within a half
mile upgradient (mounding) and a half-mile downgradient(shadowing). There are two registered
McGrane Water Engineering,LLC
1669 Apple Valley Rd. • Lyons,CO 80540 • Phone:[phone];email:[e-mail]