2024-11-04_PERMIT FILE - M2024056 ‎(6)‎

• Permit No: M2024056
• IBM Index Class Name: Permit File
• Doc Date: 11/4/2024
• Doc Name: Application
• From: Asphalt Specialties Co., Inc
• To: DRMS
• Email Name: NCG
• Email Name: JLE
• Email Name: EL1
• Media Type: D
• Archive: No

Evans Mining Resource
Groundwater Monitoring Plan
October 2024
Page 1
1.0 INTRODUCTION
Asphalt Specialties Co.,Inc.(ASCI)has prepared this Groundwater Monitoring Plan(GWMP)for
the Evans Mining Resource (Site) located at 17085 County Road 394 in Weld County, Colorado
(Figure 1)in general accordance with the requirements set forth in the Construction Materials Rule
No. 3, Section 3.1.7 and the Division of Reclamation, Mining, and Safety (DRMS) Groundwater
Monitoring: Sampling and Analysis Plan Guidance. Construction Materials and Hard Rock Sites
(July 2024). This GWMP summarizes data available from the baseline groundwater
characterization conducted to-date and details the future monitoring activities that will occur
throughout the operational life of the mine. Note: Baseline characterization data will continue to
be collected until the start of activities which impact groundwater at the Site occur(i.e.,installation
of the slurry wall). The final groundwater characterization data sets used to document the pre-
operational baseline conditions will be submitted as a Technical Revision (TR) to DRMS in a
Baseline Data Summary Report.
1.1 SITE DESCRIPTION
The Site is former agricultural land that is relatively flat with a topographic slope of 0.0028 ft/ft.
Mining activities will occur within the unconfined alluvial aquifer of the South Platte River. As
shown in the mine application Exhibit C maps, a slurry wall will be installed to hydraulically
disconnect the Phase 2 mining operation from groundwater in the surrounding alluvial aquifer. A
second slurry wall will be installed prior to mining Phase 3 through 6 areas. In addition, a French
Drain and infiltration gallery will also be installed to mitigate groundwater mounding to the west
of the Site. The average thickness of the overburden is approximately three (3) feet below ground
surface (ft bgs) before encountering the alluvial deposits of the South Platte River. The deposits
vary from silty sands and gravel in the upper zones to sandy gravels nearer the bedrock. The sand
and gravel deposits slightly vary in thickness but average approximately 36 feet across the Site.
Underlying the sand and gravel deposit is the Denver Formation which is a consolidated bedrock
stratum composed primarily of generally impermeable shale and claystone approximately 550 —
600 feet thick. Surrounding land uses in the area include agriculture, open space, mining, and
commercial/industrial. The total affected area is 159.2 acres. Sand and gravel mining operations
are anticipated to begin in 2025.
Groundwater in the alluvial aquifer at the Site is approximately 5 ft bgs and generally flows to the
northeast towards the South Platte River. Per the Division of Water Resources(DWR) Colorado's
Decision Support System (CDSS) website, the alluvial aquifer has rapid permeability with a
transmissivity of approximately 80,000 gallons per day per foot(gpd/ft) and specific yield of 0.2.
The estimated coefficient of storage is 1.5x10-5 to 3.1x10-5. The Site is not located within a
classified area per Water Quality Control Commission (WQCC)Regulation 42.
2.0 BASELINE GROUNDWATER CHARACTERIZATION
This GWMP summarizes available data collected to-date from March 2022 through October 2024
to characterize baseline groundwater conditions. Data collected includes monthly groundwater
elevations (for groundwater quantity) and quarterly groundwater sampling event results (for