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CIVIL RES URCES, LLC ENGINEERS & PLANNERS May 21, 2024 Colorado Division of Reclamation and Mining Safety Mr. Rob Zuber 1313 Sherman Street, Room 215 Denver, CO 80203 RE: Technical Revision 1 Adequacy Review 2 — Monarch DENM Mine (Permit M-2022-009), Weld County, Colorado Dear Mr. Zuber: The following letter presents Monarch Mountain Minerals and Aggregates, LLC's (MMMA) responses to the Division's second adequacy review letter for Technical Revision 1 (TR-01) dated May 13, 2024 and the discussion with MMMA and the Division on May 15, 2024. The Division's adequacy comments are presented below in italics and MMMA's responses are in bold. 1. Please confirm that only one duplicate sample is to be collected quarterly, and the analytical results of the duplicate sample are to be reported along with the other quarterly results. • Confirmed,this language has been added to Section 5.1 of the plan. 2. In item 9 MMMA states, "Five quarters of baseline quality monitoring is consistent with recently permitted sites in the area such as Ragsdale Reservoirs (M-2020-007) and the Windsor East(M-2022-042) and exceeds the requirements of slightly older permits. Any stormwater discharges will be made under an NPDES discharge permit from CDPHE and the Site will operate under a Stormwater Management Plan. The plant will be designed with stormwater BMPs to reduce the risk of impacts to water quality from surface discharge and will have a spill prevention, control and countermeasure (SPCC)plan in effect to address any potential spills. While MMMA agrees that five (5) quarters of baseline sampling will be beneficial in creating a record of current groundwater conditions, they contend that there is not a "reasonable potential" for the Site to adversely affect the groundwater quality of the area. As such, we believe that the current sampling schedule of five(5) quarters and at release of the reclamation permit is consistent with other sites and will adequately characterize pre and post-mining water quality. For these reasons, MMMA does not agree to continuing quarterly sampling after the five(5) quarters of baseline sampling.' Groundwater levels are to be collected monthly at the Site. The application was approved in July 2022 but was not issued until June 2023. During that time monthly measurements were not completed in October 2022 and February 2023. Additional monthly measurements were not completed in July and August 2023. Please provide an updated Table 1 with groundwater level measurements though March 2024 and update the associated graphs as needed. The Windsor East permit, similar to Monarch, has performed baseline groundwater quality monitoring to the extent possible prior to exposing groundwater. It is noted Windsor East has committed to monitoring groundwater quality beyond the baseline period. There are other permits (one approved and two currently in review) in the area of the Monarch site: the Section 20 Gravel Mine to the east, the Sweet Valley Pit to the south, and the Bernhardt Sand and Gravel to the west. All of these permits will have to collect quarterly groundwater quality samples to establish baseline conditions and continue monitoring throughout the life of mine and not just at the completion of reclamation. Pursuant to Rule 3.1.6(1) disturbances to the prevailing hydrologic balance of the affected land and of the surrounding area and to the quantity or 8308 COLORADO BLVD• SUITE 200• FIRESTONE, CO 80504 • PHONE: 303.833.1416