2021-09-07_REVISION - M1973021 (9)

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Date: September 3, 2021 Mr. Eric Scott, PG., R.G. Colorado Division of Reclamation, Mining and Safety (DRMS) 1313 Sherman St., Room 215 Denver, CO 80203 Re: DRMS Adequacy Review Response: 112 Construction Materials Reclamation Permit Amendment Application Package AM07, Aggregate Industries, Morrison Quarry Dear Mr. Scott: On behalf of Aggregate Industries —WCR Inc. (Aggregate Industries), HDR Engineering, Inc. (HDR) has prepared the response to your Adequacy Review letter to Mr. Andrew Lockman, GEI Consultants dated December 11, 2020. We have provided our responses in two tables attached to this transmittal: • Table 1 addresses DRMS adequacy comments specific to the Application Form and Exhibit A through Exhibit S; and • Table 2 addresses DRMS adequacy comments dated February 18, 2021 specific to Appendix A—Geotechnical Stability Exhibit Your comments identified deficiencies in the original AM07 submission that required Aggregate Industries to undertake a comprehensive evaluation of existing AM05 operating and reclamation requirements, other existing permits and technical revisions, and proposed AM07 requirements to re-evaluate current operations, consider future mining and reclamation goals, and revise the mining and reclamation plans accordingly. These discussions resulted in a substantial change to the contents and focus of AM07. The revised AM07 is included as an attachment to this transmittal, and the substantial changes are summarized below: Water Management During Mining and Reclamation A common theme across DRMS comments focused on the need to address how surface water and potentially exposed groundwater will be managed during mining and reclamation activities in the South Quarry. Aggregate Industries agrees that groundwater is likely to be encountered during South Quarry mining activities at an approximate elevation of 6,500 feet, based on the groundwater monitoring results in two of the South Quarry monitoring wells. Additionally, as has been identified in recent site inspections, stormwater management is needed in the South Quarry to address detained water at the quarry base that does not evaporate or infiltrate within 72 hours. Upon review of AM05 and proposed AM07, Aggregate Industries determined that changes were needed to Exhibit D —Mining Plan, Exhibit E— Reclamation Plan, and Exhibit G —Water Information to discuss water management approaches and, where necessary, identify and prioritize permitting and hydrogeologic investigations critical to ensuring regulatory compliance and supporting continued mining operations.