20210903PAC to PIIC Attach 77-3 Addendum 2.pdf

PACIFICORP
ENERGY WEST MINING COMPANY
DEER CREEK MINE MSHA ID NO. 42-00121

Mill Fork Access #2 Mains
Rilda Canyon Portals 1st Right Submains
Proposed Bulkheads – Installation and Monitoring Plan

Addendum #2

Review of Submittal for Mill Fork Access#2 Mains and Rilda Canyon Portals 1st Right Submains
Proposed Bulkhead Plan, Energy West Mining Company, Deer Creek, MSHA I.D. No. 42-
00121, Huntington, Emery County, Utah

Summary of Phone Conversation with Steve Sawyer of MSHA concerning Mine Emergency
Operations Review of Energy West Bulkhead Submittal
March 9, 2015

Addendum Submittal March 12, 2015
Phone Conference Call: March 9, 2015
Attendees: Energy West Mining Company
Louie Tonc
Mark Reynolds

MSHA Pittsburgh Safety and Health
Technology Center Mine Emergency Operations
Steve Sawyer

During a conversation with Steve Sawyer, MSHA Mine Emergency Operations, several issues
regarding Energy West proposed bulkhead installation plan were raised:
• MSHA does not consider any structure inby a new set of seals or bulkheads as a
functioning structure.
o As outlined in the proposal, Six (6) primary bulkheads are proposed for the Mill
Fork Access #2 mains, and three (3) secondary bulkheads are proposed for the
1st Right mains inby the Rilda Canyon Right Fork portals. Primary bulkheads
located in Mill Fork Access #2 will provide a potential water tight barrier to
segregate potentially iron-contaminated ground waters that could propagate from
the Mill Fork Area from higher quality compliant groundwater elsewhere in the
mine. It is essential to keep these contaminated waters from entering the
permanent water discharge system planned for the Deer Creek portals or from
seeping out the Rilda Canyon Right Fork portals. If discharged, these waters will
likely have a negative effect on the stream as well as the North Emery Water
Users Special Services District (NEWUSSD) spring collection system, both in
Rilda Canyon.
o If Energy West is required to breach/open valves of the inby seals (Mill Fork
Access #2 bulkheads) prior to constructing the secondary, the benefit of the
primary seals are negated. In fact, as outlined in the plan, construction and
installation of the bulkheads will explicitly follow the installation procedures
outlined in MSHA Approval Number 120M-15.0 (Appendix D), except for item I
– Water Drainage System. Energy West proposes not to install water drainage
systems through the bulkheads as an effort to minimize potential leakage of the
bulkheads.
o Energy West recognizes the fact that during the curing time, installation of the
grout ring of the Mill Fork bulkheads and the construction of the secondary set of
bulkheads at 1st Right, it is possible water could be impounded by the primary
bulkheads at Mill Fork Access #2. Based on measured inflow rates of the Mill
Fork Area, Energy West predicts it would take 3.9 years to achieve the maximum
impoundment inby the Mill Fork bulkheads. Based on the construction sequence
of the bulkhead the potential impoundment will be negligible:
 The Mill Fork bulkheads shall be constructed in a specific sequence in the
Mill Fork Access #2 area in order to keep groundwater from impounding
against the structures while under construction. Inby mine dewatering
systems will be left intact during the initial construction allowing
sufficient time to build the remaining seals without impounding water.
The first bulkhead will be built in entry #1. The next bulkhead will be
constructed in entry #6, then entry #5, followed by entry 3, 2 and 4.
 The secondary set of bulkheads constructed in 1st Right will be
constructed simultaneously with the primary set located in Mill Fork.
o To alleviate MSHA’s concern of potential water impoundment inby the primary
bulkheads prior to completing the secondary set at 1st Right, Energy West will
commit to the following:
 Measure the potential impounded water utilizing the boreholes located
inby the Mill Fork bulkheads;
• Energy West developed two vertical drill holes for the intended
purpose of monitoring inby the Mill Fork bulkheads. A pressure
transducer and telemetry equipment will be installed in one of the
boreholes prior to the completion of the bulkheads to monitor
environmental data that will be relayed to computer equipment
monitored by Energy West. The second hole will serve as a
backup and allow for calibration of the pressure transducer. The
pressure transducer will be positioned within two feet of the base
of the lowest bulkhead.
 Energy West commits to the following:
• If the pressure at the Mill Fork Access #2 bulkheads exceeds 2
feet of head pressure ,< less than 1 psi, (equates to a one
hundred twenty fold safety factor of the approved 120M-15.0
seal), Energy West will immediately halt construction
activities on the 1st Right bulkhead, and immediately
commence portal sealing (concrete plugs).
Additional concern identified during the phone conference:
• Leakage of the bulkheads.
o Energy West is aware of potential for the bulkheads to leak. The proposed
plan includes the installation of Jennchem 120 psi Main Line seals
(MSHA approval number 120M-15.0) reinforced with keyway notches
and polyurethane ring grouting. In addition to the grouted ring specified
in the approval 120M-15.0, Energy West will install an additional grout
ring at the inby edge of each bulkhead, see Figure 12. The secondary set
of bulkheads located at 1st Right will provide an additional measure to
prevent leakage at the Rilda Canyon portals. The concrete plugs at the
Rilda Canyon portals provide a tertiary protection to prevent potential
leakage.
o After all phases of bulkhead construction and installation of the concrete
plugs, Energy West will continue to monitor pressure at each bulkhead
location. Monitoring will allow Energy West to assess:
 Head pressure build-up
 Water quality of the impounded areas.
 Provide time for Energy West to assess water quality treatment
options
o If leakage occurs at the Rilda Canyon Portals, Energy West will treat the
effluent to comply with all State and Federal regulations.
o Energy West is not requesting MSHA to concur that the bulkheads will be
a water tight barrier; simply that, Energy West will be allowed to construct
the bulkheads to minimize potential hydrologic impacts.