2021-08-02_PERMIT FILE - M2020058 (6)

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Mr. Daniel Cunningham RE.•Baurer Pit M-2020-058 July 27, 2021 are proposed for use to monitor groundwater elevations on and near the Baurer Pit site. A map illustrating the location of the proposed monitoring wells is also attached. Many of the proposed monitoring wells were installed, and have been monitored for over 15 years, as part of the adjacent Wattenberg Lakes Site (M-2004-051). Since the well installations, local groundwater conditions have been continually affected by influences surrounding the Baurer Pit property. As noted in the Baurer Pit 112 Construction Materials Reclamation Permit application, these influences include the South Platte River east of the site and the Brighton Ditch west of the site. Additionally, the existing lake on the western half of the Baurer Pit property and the Stillwater Ski Lake at the eastern edge of the property are previously dewatered mining excavations. Immediately north and south of the Baurer Pit property are additional mining excavations associated with the Wattenberg Lakes Site (1VI-2004-051) and Baseline Resou�ce site (M-1997-058), both of which are now. enclosed within below-grade slurry walls. Even with the local influences affecting groundwater, baseline conditions still exhibit a general southwest to northeast groundwater flow pattern. Although seasonal fluctuations in groundwater elevations are observed at wells upgradient of the Baurer Pit property (Wattenberg MW-7 and Wattenberg MW-8), these fluctuations appear to be muted in wells closer to the slurry walls and/or the South Platte River (Wattenberg MW-4 and Wattenberg MW-6). Although baseline data is not yet available for Baurer Pit MW-1, monitoring for a least 6 months is anticipated prior to Baurer Pit mining and/or slurry wall construction activities. Regardless, it is estimated that groundwater elevations and seasonal fluctuations would be similar to those observed in Wattenberg MW-4 and Wattenberg MW-6. 12. An unforeseen increase or decrease of 2 feet in groundwater elevation at a monitoring well shall be used as a trigger for potential mitigation measures. However, as seen on the attached Baurer Pit Groundwater Monitoring Data chart, recent baseline data often exhibits more than a 2-foot variation in groundwater elevations seasonally. Therefore, monitoring procedures for the Baurer Pit shall include evaluation of the groundwater elevation data following each monitoring event with comparisons to the baseline data of similar seasons. The evaluations shall consider that there are many factors at or near the Baurer Pit property, not including mining and reclamation activities at the Baurer Pit site, that could create a significant groundwater elevation change at any one well. Other potential influences such as natural drought or flooding, changes in local irrigation, or adjacent mining operations shall be considered during data evaluation. 13. Aggregate Industries — WCR, Inc. owns, and has access rights to, the properties where all monitoring wells are located. If properties are sold and/or access agreement deadlines are passed (i.e. the City of Westminster), as long as Aggregate Industries —WCR, Inc. still holds the Baurer Pit 112 Construction Materials Reclamation Permit, property access for monitoring activities will be maintained. Page 3 of 4