2019-10-01_REVISION - M1986015

• Permit No: M1986015
• IBM Index Class Name: REVISION
• Doc Date: 10/1/2019
• Doc Name: Adequacy Review Response
• From: RPM, Inc.
• To: DRMS
• Email Name: JPL
• Media Type: D
• Archive: No

RPM,Inc.
Patrick Lennberg
August 16.2019
Page 2
History of Mining Activities
Milling in Phase 1 dated back to 1985 under a previous operator.Mining involving active
dewatering operations occurred from late 2001 early 2002 to January 2009. During that
time.the footprint of the dewatering and the mining area expanded.Dewatering operations
continued after mining had stopped until the pinups were shut off in September 2018.The
Phase 1 pit is not lined.
Mining in Phase 2 occurred from late 2008 early 2009 to late 2012. The slurry wall was
installed in January 2009 and the liner test on the slurry wall occurred between January and
April 2010.Because the liner was in place during mining activities.there were no ground
water impacts occurring in the alluvial aquifer outside of the slurry wall resulting from the
Phase 2 mining activities.
Mining in Phase 7 started in December 2012 and extended through February 2015.Phase
7 is not lined.Dewatering in Phase 7 commenced in early 2012.Dewatering activities are
still occurring at Phase 7 although the ruining area has partially been filled in,resulting in
a decrease in the dewatering pumping rate.
Depth to Water Hydrographs
Figures 2 through 4 present hydrographs that include all of the water level measurements
from the monitoring wells.
Figure 2 presents the depth to water data from monitoring wells MW-6,MW-7.MW-70bs.
MW-8.MW-9.MW-10.MW-11 and MW-12.which are generally representative of water
level conditions in the Phase i miring area.The Phase 1 pit is not lured.
Figure 3 presents the depth to water data from monitoring wells MW-1.MW-101.MW-2.
MW-102.MW-3.MW-103.MW-4.MW-4R.MW-5.MW-105.MW-6.MW-70bs.MW-
8. MW-199 and MW-299, which are generally representative of water level conditions
associated with the Phase 2 mining area.Wells MW-1.MW-2.MW-3.MW-5 and MW-
199 are located inside of the slurry wall and are not representative of regional aquifer
conditions. MW-8 is included on both graphs since it is located near both mining areas.
Figure 4 presents the depth to water data from monitoring wells MW-13. MW-130bs.
MW-13R. MW-14. MW-14R and MW-15, which are generally representative of water
level conditions in the Phase 7 mining area.The Phase 7 pit is not lined.
The hydrographs show a period of lacking data in the 2009 to 2010 tinieframe. We
understand that this lapse of data occurred as a result of personnel changes with the operator
and misunderstandings at the time of which wells needed to be monitored.
Trends in Depth to Water Data, Hydrographs
Phase 1 Area
The footprint of mining and dewatering activities increased from 2002 to 2009.and water
levels responded to the expanding dewatering activities. As indicated in Figure 2. water
RPM,Inc.,25049 E.Alder Dr.,Aurora,CO 80016 Phone:[phone] Email:[e-mail]