2016-12-09_REVISION - M1980244

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 12/9/2016
• Doc Name: Adequacy Review Response #2
• From: CC&V
• To: DRMS
• Type & Sequence: AM11
• Email Name: TC1
• Email Name: AME
• Email Name: ERR
• Media Type: D
• Archive: No

Request#2: 3.4.2 Water Table (continued)
...In the description, please include an explanation of how the groundwater monitoring wells
located in Grassy Valley(GVMW-8A, GVMW-8B, GVMW-23A2, and GVMW-23B3) are adequate
for identifying potential sources of groundwater contamination in Grassy Valley.
Response:
Groundwater monitoring well pairs GVMW-8A-[200-250]4, GVMW-8B-[20-50] and
GVMW-23A-[40-100], and GVMW-23B-[10-40]5 are adequate for monitoring the impact of any
potential source of groundwater contamination in Grassy Valley for the following reasons:
1. GVMW-22. The GVMW-22 well pair is located immediately downgradient of the point
where Grassy Valley crosses the western edge of the diatremal rock, as shown in Plate
276 attached. This is the only location in the Cripple Creek mining district where
groundwater currently emerges from the moderate-permeability diatremal bedrock and
flows over the low permeability Precambrian bedrock in alluvium and as surface flow'. This
location is immediately downgradient of the first permanent flow in Grassy Valley. The
GVMW-22 well pair samples water quality in the valley alluvium/colluvium
(GVMW-23B-[10-40]8) and separately in the shallow Precambrian bedrock
(GVMW-23A-[40-100]9). Any water exiting any mine facility in Grassy Valley as seepage
and leaving the diatreme through Grassy Valley must pass through these monitor wells,
rendering them the appropriate locations for compliance monitoring of facility installations
in Grassy Valley. Any surface water leaving the facility is also monitored for flow and
quality at approximately the same location at the GV-04 surface water monitoring flume,
creating a total monitoring and compliance point set for the portions of the project that fall
within Grassy Valley.
2. GVMW-8. The GVMW-8 well set (OSABH-14-[19-29], GVMW-8B-[20-50], and GVMW-8A-
[200-250]) is located upstream (west) of the GVMW-23 pair, at approximately the
stagnation point for groundwater flow towards the overflow point in Grassy Valley to the
east, and groundwater flow towards Carlton Tunnel to the southwest. The GVMW-8 well
set samples water quality in the colluvium (OSABH-14-[19-29]10), volcanic diatremal rock
immediately below the colluvium in the base of Grassy Valley (GVMW-8B-[20-50]), and
separately in the deeper diatremal bedrock (GVMW-8A-[200-250]). The wells are located
adjacent to GV-03, which monitors surface water quality and flow. Surface water and
2 It is assumed that the well being referred to by DRMS is GVMW-23A, not GVWM-22A as stated in the original letter.
This well is beside Grassy Valley,whereas GVMW-22A is located 213 feet higher on the hillside 1,380 feet to the
north,as shown on Plate 27.The question has been responded to with that assumption.The confusion may have
arisen from interchange of the wells that occurred in some prior ABC documents.
3 It is assumed that the well being referred to by DRMS is GVMW-23B,not GVWM-22B as stated in the original letter,
for the same reasons as stated in Footnote 2 above.
4 The open interval of conventionally-completed monitoring wells are indicated in square braces [...]throughout this
response.
5 Logs of all monitor wells referenced here are provided in Attachment 2 to this response.
6 Plates in this response are numbered sequentially after the Plates in the Hydrogeochemistry Report(Cresson Project
Amendment 11 Hydrogeochemistry Evaluation,Adrian Brown Consultants, December 15,2015.)
The one known possible exception is groundwater collected from beneath the VLF liner in Arequa Gulch.This small
flow is returned to the CC&V water management system for use in the operation. It is sourced from perched
groundwater from the original Arequa Gulch,and was never contributory to the bedrock groundwater system.
8 GVMW-23B-[10-40] is completed in
9 Borehole GVMW-22A was originally drilled to a depth of 220 feet below ground surface.The well was completed in
the highest-yield section of Precambrian rock encountered in the borehole,from depths 50 to 75 feet below ground
surface,with the top of the Precambrian Rock at 42.5 feet bgs.The hole was backfilled from 220 feet to 75 feet with
hydrated bentonite chips prior to completion of the monitoring well.
10 OSABH-14-[19-29] is in general dry,indicating that the colluvium is normally drained in this location. It may be
capable of providing a water quality sampled during high infiltration periods,but these conditions have not been
experienced to date at sample time.
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