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�_ = Golder <br />Associates <br />Date: February 17, 2015 <br />To: Eric Scott <br />From: Sara Harkins and Randy March <br />cc: Joel Bolduc, Holcim (US) Inc. <br />RE: BOETTCHER LIMESTONE QUARRY <br />TECHNICAL MEMORANDUM <br />Project No.: 1400159 <br />Company: Colorado Division of <br />Reclamation, Mining and Safety <br />Email: sharkins @golder.com <br />M 141-7-7-3 ,49 <br />Cement kiln dust (CKD) was generated on the Boettcher Quarry site (the Site) during operations, which <br />occurred from the early 1900s to 2002. Disposal of CKD in mined out portions of the Boettcher Quarry <br />began in 1980. Per the approval of Technical Revision No. 3 (TR -003) to Permit No. M -77 -348 by the <br />Division of Minerals and Geology (DMG) on October 15, 1999 (DMG 1999), CKD disposal would be <br />limited to area A2. CKD disposal in area A2 began in the fall of 1999, and approximately 140,000 cubic <br />yards were placed in the area by August 2002, when the plant closed. Limestone mining operations <br />ceased in August 2002. Reclamation and monitoring activities have been occurring on the Site since the <br />plant closure in 2002 (Holnam 2002; Holcim 2004, 2005, 2006, 2007, and 2009). Figure 1 shows the <br />approximate location of CKD disposal area A2 in the A -band mining cut and the nearby dry CKD fill area. <br />The dry CKD fill area is included for reference; however, this area was backfilled prior to approval of <br />TR -003. <br />The Colorado Division of Reclamation, Mining and Safety (DRMS) noted consistent benchmark <br />exceedances of barium in groundwater concentrations at monitoring wells MW -3 and MW -4, consistent <br />benchmark exceedances of total dissolved solids (TDS) at MW -4, and minor benchmark exceedances of <br />boron at MW -3. To address the DRMS questions and concerns about these constituent exceedances, we <br />have evaluated available data and obtained new data to determine if the observed concentrations of <br />barium and TDS are from CKD leachate or are naturally occurring. As described below, this evaluation is <br />based on observed groundwater chemistries, chemical analysis of the CKD and native materials, and the <br />hydrogeologic and hydraulic conditions. <br />1.0 GROUNDWATER CHEMISTRIES <br />Presently, quarterly groundwater monitoring is conducted for the seven Site wells. Time series graphs <br />though 2014 are presented in Attachment A. Groundwater beneath the Site can be classified into three <br />distinct groups. These groups are distinguished based on water chemistry, monitoring well screened <br />intervals, and aquifer lithology. The characteristics of each group are discussed below. <br />is \14\ 1400159\ 0100 \0122 \tm- boeftchedimestonequarry fni- 17febl5 \1400159 tm- boettchedimestonequarry fnl- 17feb15.docx <br />Golder Associates Inc. <br />44 Union Boulevard, Suite 300 On- <br />'m Lakewood, CO 80228 USA <br />Tel: (303) 980 -0540 Fax: (303) 985 -2080 www.golder.com <br />Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America <br />Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation <br />