2019-03-05_REVISION - M1977348 (5)

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r March 1,2019 18107649 ' 1 .0 INTRODUCTION On behalf of Holcim (US) Inc., Golder Associates Inc. (Golder) is submitting this request for a technical revision (TR-10)to permit M-1977-348 to for the Boettcher Limestone Quarry located at 3060 West County Road 56, ' Laporte, Colorado 80535. This technical revision demonstrates that groundwater samples at the time of and prior to tritium dating conducted in August 2014 represent ambient concentrations pre-January 31, 1994 groundwater. Therefore, per Regulation 41- Colorado Basic Standards for Groundwater(5 CCR 1002, BSGW), ' Section 41.5 (C) (6): 1)the recent data can be used to assess ambient conditions as of January 30, 1994; and 2) in cases where ambient conditions are greater than the Regulation 41 Table Values Standards, a less restrictive ' standard based on the ambient conditions could be applied. 2.0 BACKGROUND INFORMATION ' 2.1 Site History and CKD Placement The Boettcher Limestone Quarry (the Site) is located in Larimer County near Laporte, Colorado (Figure 1). More specifically, the quarry comprises portions of Township 8 and 9 North, Range 69 West of the 6th Principal Meridian. The original permit for Ideal Basic Industries to operate the Boettcher Quarry(Permit No. M-1977-348) was approved on October 10, 1978 by the Colorado Mined Land Reclamation Board (MLRB)of the Department of Natural Resources. Although the Boettcher Quarry has had several owners during the active lifetime of the quarry, it is currently owned by Holcim (US) Inc., thus Holcim is referred to as the owner/operator in this document. Cement kiln dust (CKD)was generated on Site during operations, which occurred from the early 1900s to 2002. ' Disposal of CKD in mined out portions of the Boettcher Quarry began in 1980. Per the approval of Technical Revision No. 3 (TR-003)to Permit No. M-1977-348 by the Division of Minerals and Geology(DMG) on October 15, 1999 (DRMS 1999), CKD disposal would be limited to area A2. CKD disposal in area A2 began in the fall of ' 1999, and approximately 140,000 cubic yards were placed in the area by August 2002, when the plant closed. Limestone mining operations ceased in August 2002. Reclamation and monitoring activities have been occurring on Site since the plant closure in 2002 (Holnam 2002; Holcim 2004, 2005, 2006, 2007, and 2009). Figure 1 shows ' the approximate location of CKD disposal area A2 in the A-band mining cut. 2.2 Groundwater Monitoring History Seven monitoring wells MWA through MW-7 are present at Site. The location of these wells is presented in Figure 1 and the construction details are summarized in Table 1. Appendix A provides monitoring well construction and lithological logs for monitoring wells MWA, MW-2 and MW-3. No monitoring well construction ' details are available for monitoring well MW-4. Appendix B provides monitoring well construction and lithological logs for monitoring wells MW-5, MW-6 and MW-7. The water quality data for these wells are summarized in Table 2 through Table 8. A timeline of the groundwater sampling history at Site is provided below: ' ■ June 1998: MWA, MW-2, and MW-3 were installed ' ■ April 1999: MW-4 was installed ■ May 1999—September 2000: Bi-monthly sampling of MWA through MW-4 (8 sampling events) conducted by Secor ' ■ September 2010: Initial Golder sampling event of MWA through MW-4 ' ■ 2011- 2012: Quarterly sampling of MWA through MW-4 ' > GOLDER 1