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J GOLDER <br /> TECHNICAL MEMORANDUM <br /> ' DATE February 19, 2021 Reference No. 20378105-1-TM-0 <br /> TO Amy Eschberger <br /> ' Colorado Division of Reclamation, Mining and Safety <br /> CC Michael Toelle and Travis Bennett (Holcim (US) Inc.) <br /> ' FROM Sara Harkins, Joanna Moreno, Tricia Hall EMAIL sara_harkins@golder.com <br /> HOLCIM BOETTCHER QUARRY MW-8 MONITORING WELL INSTALLATION FIELD REPORT <br /> ' On behalf of Holcim US Inc., Golder Associates Inc. Golder is providing a field summary for the newt installed <br /> ( ) (Golder) P 9 Y Y <br /> ' well associated with the groundwater monitoring network at the Boettcher Limestone Quarry (Site) located at <br /> 3060 West County Road 56, Laporte, Colorado 80535. The new background well MW-8 was installed <br /> side-gradient to the north of the CKD disposal areas and on the east side of the access road (Figure 1). The <br /> side-gradient location was selected instead of a directly upgradient location because a suitable location does not <br /> exist upgradient of the CKD disposal areas that would intercept the same geologic units as the existing Site <br /> monitoring wells. Well MW-8 was installed in accordance with the plan described in Technical Revision #11 <br /> ' (TR-11) of Permit M-1977-348. Activities associated with the drilling, installation, development, surveying, and <br /> permitting of the well occurred between November 11, 2020 and February 4, 2021. <br /> 1 .0 DRILLING ACTIVITIES <br /> ' Drilling Engineers, Inc. was subcontracted to Golder to drill and install MW-8. Drilling began on November 11, <br /> 2020 and the borehole was finished to total depth on November 13, 2020. Based on previous drilling activities at <br /> ' the Site, the target interval for screening MW-8 was approximately five feet above the contact of the Upper <br /> Cretaceous Niobrara Formation and the underlying Codell Sandstone, which is the uppermost, Middle Cretaceous <br /> member of the Carlile Formation. <br /> ' 1 .1 Drilling Methods <br /> Three drilling methods were used to complete the MW-8 borehole: hollow stem auger, air-rotary, and air-coring. <br /> ' Hollow stem auger drilling was used from the surface until 15 feet below ground surface (ft bgs)through two feet <br /> of overburden and 13 feet of bedrock. Air-rotary drilling was employed from 15 ft bgs to 165 ft bgs. Air-coring was <br /> used from 165 ft bgs to 235 ft bgs. The switch to air-coring ensured a higher-quality sample with which to identify <br /> the Niobrara—Codell contact, above which MW-8 was screened. The Niobrara—Codell contact was observed at <br /> 230 ft bgs. <br /> ' No water was added during drilling. Upon identifying the Niobrara —Codell contact, the borehole was reamed <br /> to eight inches in diameter to a depth of 229 ft bgs. The borehole was allowed to collapse from 229 ft bgs to <br /> 235 ft bgs. <br /> 1 <br /> ' Golder Associates Inc. <br /> 7245 W Alaska Drive,Suite 200,Lakewood,Colorado,USA 80226 T:+1 303 980-0540 F:+1 303 985-2080 <br /> ' Golder and the G logo are trademarks of Golder Associates Corporation golder.com <br />