20210903PAC to PIIC Attach 77-3 DC Bulkhead Plan MSHA Submittal.docx

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 andMonitoring Plan
January 2015
Table of Contents
Introduction:1
Mill Fork Mining History1
Document Preparation:2
Water Source:3
Identified Hydrologic Concerns:4Water Chemistry:7Remedial Approaches to Containing Potentially Elevated Iron Water:8
Existing Conditions:9
Bulkhead Stability:10
Construction Location and Impoundment Area:14
Project Timeline:14
Bulkhead Construction Sequence:14Mill Fork Access #2:141st Right:15Construction Details:15
Rilda Canyon Concrete Plugs16
Emergence Response Plan:16
APPENDICES
Appendix AMayo & Associates Deer Creek Mine – Mill Fork Area
Geochemical Evaluation of Groundwater with Elevated Iron
Appendix BGeologic StratigraphicColumn – Surface Exploration Drill HolesEM-187 – Located Near Mill Fork Access #2 Bulkhead Location SiteEM-157 – Located Near 1st Right Bulkhead Location Site
Appendix CARMPS AnalysisofCoalPillars
Appendix DJ-Seal 120 psi Main Line Ventilation Seal Installation Procedure
Appendix EPhotos of the Proposed Bulkhead Locations
FIGURES
Figure 1: Deer Creek Mine Mill Fork Area Active Sumps
Figure 2: Deer Creek Mine Mill Fork Area Sealed Mine Workings Sampling Locations
Figure 3: Deer Creek Mine Area of Water Impoundment
Figure 4: Deer Creek Mine Detailed Seal Location Maps – Plan View and Geologic Cross Section
Figure 5: Deer Creek Mine Rilda Canyon Portals – Concrete Plugs
Figure 6: Deer Creek Mine Bulkhead Monitoring Holes
Figure 7: Deer Creek Mine Proposed Bulkhead Location Plan, Profile and Details
Figure 8: Deer Creek Mine Proposed Bulkhead Location Entry and Pillar Sizes
Figure 9: Deer Creek Mine Isolation of Northern Portion of Mine
Figure 10: Deer Creek Mine Hiawatha Seam Overburden
MAPS
Map 1: Deer Creek Mine Mill Fork Hydrology Map
Map 2: Deer Creek Mine Mill Fork Blind Canyon Seam Workings
TABLES
Table 1: Deer Creek Mine In-Mine Water Sampling Results: Sealed Areas Hiawatha and Blind Canyon
Table 2: Bulkhead Dimensions and Safety Factors
Table 3: Deer Creek Mine Water Sampling Results: Impounded AreaBulkhead Dimensions
Table 4: Impoundment Area Details – Mill Fork Access #2(values are approximated)
Table 5: Impoundment Area Details – 1st Right (values are approximated)
Introduction:
Mine Name: Deer Creek
Location: 8 miles west of Huntington, Emery County Utah
MSHA ID No: 42-00121
In an effort to maintain acceptable compliance quality discharge water from the Deer Creek Mine, Energy West is proposing the construction of nine (9) water impounding bulkheads. 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 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.
Each bulkhead site will be ring grouted with Jennchem 70 pcf polyurethane grout after the J-SEAL foamed cement has fully cured and has met the quality control specifications prescribed by MSHA Approval Number 120M-15.0.Bulkhead installation is a facet of the overall Deer Creek mine closure plan. Mining at the Deer Creek Mine was completed (27th West Outby longwall panel) on January 7, 2015. All equipment will be removed from the mine in a systematic manner from 27th West to outby the bulkhead area. After completion of the bulkheads, no personnel will be traveling inby or working down gradient of the bulkheads. The final phase of the Deer Creek Mine closure plan includes final reclamation of the portal sites in Rilda Canyon.
Mill Fork Mining HistoryPacifiCorp acquired the Mill Fork Lease Area effective April 1, 1999. Between 1999 and 2005, the mine operator, Energy West Mining Company, directed its mine planning obligations to access this newly acquired reserve. After developing a ventilation and portal access near the confluence of the Right and Left forks of Rilda Canyon, Energy West continued development from the existing mine to the west and north towards the Mill Fork Area. Access consisted of driving a set of six entries off the 6th North mains of the Hiawatha Seam to the northwest called the Mill Fork Access. Then development turned directly west through what was called the Mill Fork Access #2 (Map 1).Once mining operations reached adequate reserves for longwall mining, development turned north developing a set of mains called the 7th North Mains. Panels 11ththrough 17th West were developed westward from 7th North and second mining was completed in 2008. Also during this time, operations began developing a set of slopes to access the upper Blind Canyon seam (Map 2). Once the slopes were completed operations developed a set of five entries to the northwest called the 8th North #1 Mains. Exploration operations encountered a 1 foot rock split in the Blind Canyon seam that required revising the Resource Recovery and Protection Plan (R2P2) to remove the uneconomic reserves. Panels 1st through 7th Left were developed within the confines of the rock split and 2nd mining was completed in 2010.At the completion of mining to the extent of the Blind Canyon seam, operations were again concentrated in the Hiawatha seam. Energy West developed the 9th North mains to the northwest while necking off for panels 20th through 23rd West. During exploration drilling operations, geologic mapping, and coal seam sampling, Energy West discovered geologic occurrencessimilar to that of the adjacent Crandall Canyon Mine which revealedboth elevated iron and sulfur concentrations in the Hiawatha Seam coal. The elevated iron concentrations are related to a carbonaceous mudstone in-seam split containing pyritic iron in the lower portion of the Hiawatha Seam. The elevated sulfur is likely in the form of gypsum and is found in the floor and the bottom two feet of the unmined pillars. Sulfur in coal may be in oxidized, reduced, and native forms. Oxidized sulfur includes minerals such as gypsum (CaSO4•nH2O) and anhydrite (CaSO4) which form in evaporative environments and as secondary mineralization. Reduced forms include iron sulfide minerals such as pyrite and marcasite (FeS2). The elevated iron and sulfur concentrations were quantified as the 20th through 23rd West panels were being developed. Also, mine maps obtained from Crandall Canyon allowed Energy West to define this zoneextending to the north of the Mill Fork lease boundary.The final mining in the Mill Fork Area consisted of the development of the 10 North Mains and the 24th through 27thWest panels. Development of the panels encountered the continuation of the carbonaceous mudstone in-seam split containing the pyritic iron, as well as the elevated sulfur concentration in the coal. During panel extraction, these delineated zones, including the zones found in the 20th through 23rdWest panels, were by-passed because of poor coal quality for use in the thermal generation of electricity.Mining at the Deer Creek Mine was completed (27th West Outby longwall panel) on January 7, 2015.
Document Preparation:The following document was prepared under the guidance of the following qualified and licensed professionals:Energy West Mining CompanyMark A. Reynolds, P.E.State of Utah Licensed Professional EngineerLicense Number 5049079-2202Charles A. Semborski, P.G.State of Utah Licensed Professional GeologistLicense Number 5234167-2250Kenneth C. Fleck, P.G.State of Utah Licensed Professional GeologistLicense Number 5224883-2250JennmarCorporation USAAlan A. Campoli, Ph.D., P.E.
State of Utah Licensed Professional Engineer
License Number 8502943-2202
Water Source:Waters entering the groundwater system are mostly from snow melt. The amount of water which enters the groundwater system is highly variable from one site to another. The low surface relief on the top of East Mountain encourages the infiltration of melting snow. Geology controls the movement of groundwater. Because of the low permeability of the consolidated sedimentary rocks in the East Mountain area, groundwater movement is primarily through fractures, through openings between beds, and, in the case of the Flagstaff Limestone, through solution openings.Hydrologic data has been collected from numerous coal exploration drill holes, from within the adjacent mine workings, from surface drainages, and from the springs in the area. The data have identified two separate isolated aquifer systems on the East Mountain property; the first is localized perched water tables in the North Horn and the Price River formations, and the second is a combination of localized perched water tables in the Blackhawk Formation and the Star Point Sandstone which exhibit some limited potential as a regional aquifer. Stratigraphy is the main controlling factor restricting groundwater movement and development of regional and perched aquifer systems within the East Mountain property.Several observations have been made concerning the Blackhawk water-bearing strata. The sandstone, which is semi-permeable and porous, affords an effective route of water transport; while relatively impervious shale in the Blackhawk Formation prevents significant downward movement of the percolating water. Of the water-producing areas, those closest to the active mining face exhibit the greatest flows. As mining advances the area adjacent to the active face continues to be the wettest, and previously mined wet areas experience a decrease in flow. The water source is being dewatered since mined out areas of the mine do not continue to produce water indefinitely. The water source must be either of limited extent, e.g., a perched aquifer, or have a limited recharge capacity.The overall pattern of groundwater flow and surface water-groundwater interactions in the Mill Fork Area and adjacent areas can be described by a fairly simple conceptual model involving both active and inactive groundwater flow regimes. Active zone groundwater flow systems contain abundant tritium, have excellent hydraulic communication with the surface, are dependent on annual recharge events, and are affected by short term climatic variability. Tritium and carbon-14 “age” dating of spring waters demonstrate that most springs issue from active zone groundwater systems and are of modern origin. Groundwater in the active zone generally circulates shallowly and has short flow paths.Inactive zone groundwater systems contain old groundwater, have very limited hydraulic communication with the surface and with other active groundwater flow systems, and are not influenced by either annual recharge events or short term climatic variability as evidenced by the decline in roof drip rates. Groundwater in these systems tends to occur in sandstone channels in the North Horn, Price River, and Blackhawk Formations which are not in direct hydraulic communication with the surface (i.e. greater than about 500 to 1,000 feet from cliff faces). These sandstone channels are vertically and horizontally isolated from each other and when encountered in mine workings are usually drained quickly. The blanket sands of the Star Point Sandstone are also largely in the inactive zone.
Identified Hydrologic Concerns:In the Mill Fork area, all longwall panels trend east and west. On the west side of these panels is the Joes Valley Fault system. The north is restricted by the Crandall Canyon mine workings. A barrier of unmined coal separates the longwall panels from both the Joes Valley Fault and the Crandall Canyon mine workings. The northeastern portion of the Mill Fork Area gently dips toward the Joes Valley Fault.The eastern portion of the Mill Fork Area slopes toward the east.Groundwater from the active mining area and the eastern portions of the tract flow to the east and are collected at the 10th North, 17th West, and 11th West sumps (Figure 1). Groundwaters collected in these sumps have contact with the zones of coal that contain the elevated sulfur concentrations and the discharge water from the sumps has elevated concentrations of total iron (Table 1). Because the eastern portion of the Mill Fork Area slopes dips downward to the east, Energy West projects these waters to discharge from the Rilda Canyon portals if not contained within the mine.
PacifiCorp initiated an underground hydrologic monitoring program in May 2012 to access the potential impacts of groundwater with elevated iron from sealed areas in the Hiawatha seam. Water samples have been collected from two selected sites in the Hiawatha seam and one site from the Blind Canyon seam, (Figure 2). Elevated iron in excess of the State of Utah Department of Environmental Health - Utah Pollutant Discharge Elimination (UPDES) limitation of 1.0 mg/l has been detected from the Hiawatha sampling sites. The values are similar to those recorded during the high-iron situation experienced at the adjacent Crandall Canyon Mine.
Table 1: Deer Creek Mine In-Mine Water Sampling Results: Sealed Areas Hiawatha and Blind Canyon
Water Chemistry:Mayo and Associates LLC was contracted by Energy West to conduct a geochemical investigation of the elevated concentrations of sulfur in the coal and the elevated total iron concentrations found in the discharge from the Mill Fork Area of the mine. Energy West has concerns that with these high mineral concentrations in the mine water from the Mill Fork Area, it would not be able to comply with the effluent limitations of the Utah Pollution Discharge Elimination System (UPDES) for total iron should this water discharge to the surface.The Mayo Report concludes the following:
Zones of elevated sulfur and iron occur in the Hiawatha seam coal in the Mill Fork Area workings.
Several factors suggest that gypsum and MgSO4 dissolution are the primary sources of the elevated concentrations of SO42- in both the Hiawatha 17thWest seals and the Blind Canyon borehole groundwaters. The factors are: 1) the very positive 34S values of all sampled groundwaters, 2) the SO42- concentrations in mine water greatly exceed the concentration available from iron sulfide oxidation, and 3) laboratory leaching experiments demonstrate that almost all of the SO42- is from the dissolution of oxidized sulfate minerals.
Groundwaters discharged from the Hiawatha seam mine workings in the Mill Fork Area contain elevated concentrations of total iron which makes the water rust colored when oxygenated. This elevated total iron is associated with groundwater that has contact with the elevated sulfur zone Hiawatha seam coal.
Based on a 1st order calculation, approximately 958 tons of iron sulfide minerals (pyrite and marcasite)will be potentially available in the elevated sulfur zones to interact with in-mine groundwater at the time of projected mine closure.
Approximately 600 tons of iron would also be available for oxidization from the conveyor belt components if the beltlinesare abandoned in the mine workings.
Chemical interaction with between water containing oxygen and the elevated sulfur zone results in iron sulfide oxidization and is responsible for the formation of rust colored iron hydroxide which is reported as total iron in laboratory analysis.
Assuming that all of the potentially available iron sulfide mineralization will have contact with oxygen rich water it would take about 75 years to exhaust the total supply of iron sulfide. If the beltline iron is included the time to exhaustion would exceed 100 years.When realistic in-mine conditions are considered it is likely that supply of readily available iron sulfide would be exhausted in a few to tens of years under present conditions.
Water quality associated with two future mine closure options have been evaluated:
The first condition, call herein the Open System, envisions groundwater discharging to the surface from the Rilda Canyon Portals via Mill Fork Access workings. This discharge water would be continually oxidized and would contain elevated concentrations of total iron for an indefinite period of time. Total iron concentration in the range of 1-3.5 mg/l would continue for several years. The water will also contain elevated SO42-.
The second condition, called herein the Closed System, envisions no surface groundwater discharge due to the construction of bulkheads in the Mill Fork Access workings. The water impounded in the workings behind the bulkheads would become reducing and willattain elevated and steady state concentrations of total ion and SO42-. For the full description of the water chemistry of the Mill Fork Area, refer to the geochemical evaluation conducted by Mayo and Associates for Energy West Mining in 2014. This document is found in Appendix A
Remedial Approaches to Containing Potentially Elevated Iron Water:
In an effort to maintain acceptable compliance quality discharge water from the Deer Creek Mine, Energy West is proposing the construction of nine (9) water impounding bulkheads. 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 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.
The amount of groundwater that could potentially be impounded by the bulkheads is unknown. Therefore, a worst case scenario is assumed. The elevation of the planned bulkhead location in the Mill Fork Access #2 is 7,977 feet (Map 1 – Mill Fork Hydrology). The mined area behind the bulkheads reaches an elevation of 8,124 feet to the Blind Canyon seam (Map 2 – Mill Fork Area Blind Canyon Seam). In other words, the area behind the bulkheads has a potential head of approximately 147 feet or 63.6 psi (each foot of head equates to 0.433 psi).
Secondary bulkheads proposed for the 1st Right Mains will retain intercepted groundwater produced from the proposed Mill Access #2 bulkheads to the 1st Right area, if any. Elevation of the proposed 1st Right bulkheads is 7,794 ft. The area behind the bulkheads reaches an elevation of 8,025 feet at the top-of-slope (rock slopes from the Blind Canyon [upper seam] to the Upper Hiawatha [lower seam]). Intercepted groundwater from this point will drain to the south toward the Deer Creek portals located in Deer Creek canyon. The potential head is 231 feet or 100.0 psi.
The nine bulkheads will be Jennchem 120 psi Main Line seals (MSHA approval number 120M-15.0) reinforced with keyway notches and polyurethane ring grouting. Appendix D contains the summary of installation procedures for the Jennchem 120 psi Main Line seals.
Existing Conditions:
The pillars on either side of the bulkheads and surrounding the impounded water area were physically inspected on July 15, 2014 by Alan A. Campoli (Jennmar), Utah PE 8502943-2202. No geologic anomalies were found in either the Mill Fork Access #2 and 1st Right Submains bulkhead locations.
The pillars in both locations are stable and with ARMPS stability factors of 2.15 and 8.68 in the Mill Fork Access #2 and 1st Right Submains (ARMPS output is contained in Appendix C and Figure 10 Hiawatha Overburden). As the mine is closing, there will be no changes to the mine geometry. The resistance to water pressure or mine gas explosion induced horizontal displacement of the Upper Hiawatha Seam pillars is underestimated by ARMPS. ARMPS assumes a coal bed compressive strength of 900 psi. NIOSH published coal seam strength data (IC 9446 by Mark and Barton) reports an average Upper Hiawatha unconfined compressive strength of 5,446 psi for 20 tests. Theoretically, coalbed shear strength is 25% of the unconfined compressive strength or over 1,300 psi for the Upper Hiawatha. This is 16 times the shear strength of the J-Seal bulkhead material.
The primary Mill Fork Access #2 bulkheads have no multiple seam or nearby mining considerations, as the nearest 2nd mining is at least 3,148 feet away (Figure 8). The secondary 1st Right Submains are a minimum of 464 feet from 2nd mining in the Upper Hiawatha, providing a solid barrier pillar adjacent to the bulkheads (Figures 3 and 8). The secondary 1st Right Submains are a minimum of 432 feet or 50 times the mining height to the nearest secondary mining in the Blind Canyon Seam (Figures 3 and 8). It is generally assumed that if the interburden thickness is greater than 12 times the mining height minimal and negligible multiple seam mining effects will result. The no multiple seam mining effects assumption is reinforced by the 50 feet thick sandstone member directly above the Upper Hiawatha workings, see core log EM-157 in Appendix B.
Jennchem installation procedures call for a professional engineer to inspect the seal area should convergence in excess of 5% occur. As the mine is closing, there will be no changes to the mine geometry. Thus, the occurrence of mine convergence over 5% is very unlikely.
Bulkhead Stability:
The stability of the bulkhead is estimated by dividing the shear resistance of the bulkhead perimeter by the lateral force applied by the maximum head. The shear resistance is controlled by the 81 psi shear strength of J-Seal. Table 2 assumes the bulkhead thickness will be determined by Jennchem 120 psi Mine Line seal installation procedures (Appendix D).
Table 2 Bulkhead Safety Factors
Bulkhead #
Height , ft
Width, ft
Thickness, ft
Pressure, psi
Shear, psi
Safety Factor
MFA2 #1
7.6
25.0
14
63.6
81
6.1
MFA2 #2
8.4
24.4
15.2
63.6
81
6.2
MFA2 #3
7.5
25.8
13.4
63.6
81
5.9
MFA2 #4
7.5
25.3
13.4
63.6
81
5.9
MFA2 #5
8.9
25.0
15.2
63.6
81
5.9
MFA2 #6
9.3
22.9
16
63.6
81
6.2
1st Right #1
9.1
20.6
15.5
100.0
81
4.0
1st Right #2
8.2
20.6
14.5
100.0
81
4.0
1st Right #3
8.5
22.0
14.7
100.0
81
3.9
The bulkhead safety factors above do not consider the significant increase to lateral resistance provided by the polyurethane ring grouting and 2 foot wide and 2 foot deep floor and rib keyway notches (Figure 7). Each bulkhead site will be ring grouted with Jennchem 70 pcf polyurethane grout after the J-SEAL foamed cement has fully cured and has met the quality control specifications prescribed by MSHA Approval Number 120M-15.0 (Appendix D). This proprietary procedure has recently been approved for bulkhead construction at other locations. Prior to pouring the J-SEAL, a minimum of twenty holes will be drilled into perimeter. A non-conductive hose will be inserted into each hole and secured with hydraulic cement at the borehole collar. The free hose end will be marked to indicate the associated borehole location and run through the fresh air side of the bulkhead form. Jennchem PUR70 polyurethane grout will be pumped into each hose until refusal or consumption of 500 lbs. Historically, the grouting of J-SEAL ventilation seals with this method has consumed a total of 3,000 lbs of polyurethane per seal. Actual consumption will vary with the integrity of the seal perimeter.
J-SEAL’s superior sulfate resistance reduces water quality concerns (see Table 3 for results of water quality for the impounded area). With more than 50% slag cement content, J-SEAL grout exhibits a high sulfate resistance against acidic mine water. Laboratory tests per ASTM C1012 indicate that, J-SEAL grout does not expand/shrink and degrade over 3-year period of exposure to acidic or plain water. In addition, UCS test results show that the submerged samples gained 29% - 43% of strength over the period. It is concluded that submerging J-SEAL grout in plain, mild acidic (pH 6 - 8), or acidic (pH 3) water does not compromise its material strength as a function of time.Submerged J-Seal samples
Table 3: Deer Creek Mine Water Sampling Results: Impounded Area
Construction Location and Impoundment Area:
The bulkheads will beconstructed in two areas of the Deer Creek Mine; 1) Mill Fork Access #2 mains in the six entries between xc-61.5, and 62) 1st Right submains between xc-28.5. Figure3 contains a map of Deer Creek Mine and details the impoundment areas. Figure 4 and 5 contains a detailed map of the proposed installation locations. The installation locations were chosen based on geologic and geotechnical factorsestablishing safe static head pressure limits against the bulkheads. The following Table 4 and 5contains approximated details of the impoundment area.
Table 4: Impoundment Area Details – Mill Fork Access #2(values are approximated)
Dead Storage Volume: Mill Fork Area
impoundment area to bulkheads
1.22 Billion Gallons
23 months to fill
Estimated Inflow Rate
1000 GPM
Estimated Time to Fill
3.9 Years
Table 5: Impoundment Area Details – 1st Right (values are approximated)
Dead Storage Volume: 1st Right Area
impoundment area to bulkheads
114Million Gallons
23 months to fill
Estimated Inflow Rate
<50 GPM
Estimated Time to Fill
4 Years
Project Timeline:
It is anticipated that construction of the bulkheads will commence immediately upon completion of mining of the 27th West Outby panel and withdrawal of mining equipment inby the seal location. It is estimated that construction of all nine bulkheads will not exceed three months. Tentatively, shipping of material shall begin on February 2015. On-site training of contractors shall be during February 2015. Keeping with this schedule, construction of the first bulkhead shall commence on March, 2015. The MSHA Price Field Office will be notified upon completion of the final bulkhead.
Bulkhead Construction Sequence:
Mill Fork Access #2:
The bulkheads shall be constructed in a specific sequence in the Mill Fork Access #2 area in order to keep groundwater from impounding against the structureswhile 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 shall be constructed in entry #6, then entry #5, followed by entry 3, 2 and 4.
1st Right:
Bulkheads in 1st Right will be constructed simultaneously with the construction of the Mill Fork Access #2 bulkheads and mining equipment removal from Mill Fork Access #2, and #1. The bulkheads shall be constructed in a specific sequence in the 1st Right #2 area in order to keep groundwater from impounding against the structure 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 shall be constructed in entry #3, then entry #2.
Construction Details:
Each bulkhead site will be ring grouted with Jennchem 70 pcf polyurethane grout after the J-SEAL foamed cement has fully cured and has met the quality control specifications prescribed by MSHA Approval Number 120M-15.0 (Appendix D). This proprietary procedure has recently been approved for bulkhead construction at other locations. Prior to pouring the J-SEAL, a minimum of twenty holes will be drilled into perimeter (Figure 7). A non-conductive hose will be inserted into each hole and secured with hydraulic cement at the borehole collar. The free hose end will be marked to indicate the associated borehole location and run through the fresh air side of the bulkhead form. Jennchem PUR70 polyurethane grout will be pumped into each hose until refusal or consumption of 500 lbs. Historically, the grouting of J-SEAL ventilation seals with this method has consumed a total of 3,000 lbs of polyurethane per seal. Actual consumption will vary with the integrity of the seal perimeter.
Two rows of Burrell cans will be placed so that the distance from can-to-can does not exceed 36 inches inby and outby each bulkhead. The first row will be placed 5 ft away from the faces of the bulkhead and the second row placed 10 ft away from the faces of the bulkhead.
Construction and installation of the bulkheads will explicitly follow the installation procedures outlined MSHA Approval Number 120M-15.0 (Appendix D), except for items I – Water Drainage System and J - Gas Monitoring System. The intended purpose of these bulkheads is to provide a water tight barrier to segregate potentially iron-contaminated ground waters that could propagate from the Mill Fork Area from better 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. As outlined above, the bulkheads in Mill Fork Access and 1st Right will be constructed simultaneously to the extent possible allowing for the specified curing time. Water drainage and gas monitoring will be precluded upon completion of the bulkheads. As stated previously, after completion of the bulkheads, all equipment and personnel will be evacuated from the mine.
To be compliant with inspection and monitoring criteria of MSHA Approval Number 120M-15.0, specifically the hydrologic pressure and potential gas accumulation inby the bulkhead locations, Energy West installed two monitoring boreholes from the surface to the mine workings just inby each set of bulkheads (Figure 6 and 7). At the primary set of bulkheads (Mill Access #2), 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 monitoring of air and water quality.
In addition to the installation of the bulkheads, Energy West will install a set of seals in 4th North XC-27.5 to further isolate the northern portion of the mine (Figure 9). Seals at 4th North 27.5 will be constructed simultaneously with the construction of the Mill Fork Access #2 and 1st Right bulkheads. Elevation of 4th North XC-27.5 is approximately 8,018’ compared to the 1st Right bulkheads elevation of approximately 7,794’ (difference of 224 feet). In the event water accumulates inby the 1st Right bulkheads (between the 1st Right and Mill Fork Access bulkheads) or if the Mill Fork Access #2 bulkheads fail, the 4th North seals will be built with water drains to allow the water to migrate downdip towards the Deer Creek portals. Installation of the 4th North XC-27.5 seals will comply MSHA Approval Number 120M-15.0.
Rilda Canyon Concrete Plugs
Upon completion of the bulkhead containments (Mill Fork Access #2 and 1st Right) and the seals in 4th North, a set of concrete plugs in will installed at the Rilda Canyon portals (Figure 5). Containment forms will be built at the inby and outby ends of the plugs. A series of holes will be drilled from the surface into the plug forms for pumping of concrete and venting during the filling process.
Emergence Response Plan:
General Overview: Bulkhead installation is a facet of the overall Deer Creek mine closure plan. Mining at the Deer Creek Mine was completed(27th West Outby longwall panel) onJanuary 7, 2015. All equipment will be removed from the mine in a systematic manner from 27th West to outby the bulkhead area. After completion of the bulkheads, no personnel will be traveling inby or working down gradient of the bulkheads except for personnel directly involved with the construction activities related to the bulkheads and the installation of the concrete plugs. The final phase of the Deer Creek Mine closure plan includes final reclamation of the portal sites in Rilda Canyon. Additional safety measures will be incorporated in the reclamation plan of the Rilda Canyon portals to include the installation of the concrete plugs at the portals (Figure 5). Before and during the construction of the bulkheads all mine personnel will be trained on the emergency response plan and bulkhead monitoring.
Monitoring: After completion of the bulkheads, all equipment and personnel will be evacuated from the mine. To monitor head pressure at the primary bulkheads (Mill Fork Access #2), Energy West installed two monitoring holes inby the bulkhead (Figure 6).A pressure transducer and telemetry equipment will be installed to monitor head pressure and the data will be relayed to computer equipment monitored by Energy West. The second hole will serve as a backup and allow for monitoring of air and water quality.
Monitoring Plan: Energy West will monitor head pressure at the primary bulkhead (Mill Fork Access #2), on a daily basis and generate a report on a monthly basis which will be available to review by the governmental agencies.
Leakage: If the primary bulkheads at Mill Fork Access #2 leak, this groundwater will drain to the secondary set installed at 1stRight. Final protection for bulkhead leakage/failure is afforded by the concrete plugs at the Rilda Canyon portals.
Minor Failure: In the event of a minor failure where water is leaking through the primary and secondary bulkheads and ultimately leaking through at the concrete plug, Energy West will install a grout ring at the concrete plugs and nearby surface outcropto minimize leakage.
Warning signs and events that could pose threat of bulkhead failure – The followinglistprovidesobservableeventswhichmayimpactthenormaloperationsof bulkhead(s):
Fluidlevelfluctuations – measured with a pressure transducer installed inby the proposed bulkhead
Seismicactivity – monitored by the University of Utah seismic network
Physical inspections – monitor outcrops down gradient of the proposed bulkheads
Miscellaneous
Althoughmonitoringoftheimpoundedwaterlevelisplanned,itisnotinthiscasea criticalindicatorofpotential problems withbulkheadperformance.Thefactorsofsafety givenclearlyindicatethatthebulkheadswouldbestablestructuresatimpoundedheads muchgreaterthanthosepossibleatthissite. As a facet of mine closure and abandonment, safetyoftheworkforceis notdependentuponfluidlevelfluctuation, electricalinterruptionsand/ormechanical system failures. Rather,thecriticalwarningsigns arepractically limitedtothestratasurrounding thebulkheadstructure. Energy West selected the sites for the bulkheads based on geologic and geotechnical factors (see figures 4 and 5). Floor rock consists of competent sandstone in excess of fifty (50) feet in thickness. Roof lithology consists of a fluvial sandstone unit in entries 4,5 and 6 and mudstone/siltstone strata in entries 1 through 3. No mining has taken place adjacent to the Mill Fork Access #2 mains, thereby, minimizing side abutment pressures.However,seepagearoundthebulkhead isstill possiblethroughtheroof,ribsandfloor.Energy West willmonitor thebulkheads dailyafterhydraulic headisapplied with pressure transducer installed in a borehole located inby the Mill Fork Access #2 bulkheads. Althoughthe bulkhead design includes a grout ring to prevent seepage, it is anticipatedthat some wetness/seepage may occur. A secondary set of bulkheads will be installed down gradient of Mill Fork Access #2 in 1st Right to mitigate potential seepage. In addition to the secondary set of bulkheads, concrete plugs will be installed in the Rilda Canyon portals. Outcrops near the Rilda Canyon portals will be examined for potential seepage. Should wetness/seepage occur, an estimatedflowrateand colorofthedischarge will be recorded.Giventhecharacteristics reportedforthedischarge,Mine Managementwilldecidetheappropriate levelofresponse. AresponsebyMine Management will also be triggeredby rapid fluctuations head levels indicating potentialmovement of the bulkhead or deteriorationofthe surrounding strata thatcouldimpactthestructuralintegrityofthebulkheadand/or a seismiceventofsignificantmagnitude anddurationthatthestructural integrityofthe bulkheadmaybeaffected. Allwetness/seepagewillbereportedtothe governmental agencies within24hoursofdiscovery.
After mine closure and reclamationresponsibilities are met,Mine Managementhasatitsdisposalmonitoring, notification, and mitigation measures that include:Increasedmonitoring ofbulkheads pressure transducer - primary set of bulkheads located at Mill Fork Access #2Monitoring ofbulkheads static water level – 1st Right bulkheadsIncreased monitoring of outcrops a the Rilda Canyon portalsNotificationofminemanagementofficialsNotificationofminepersonnelNotificationofregulatoryagenciesInstallation of grout ring along the outcrops at the Rilda Canyon portals
ShouldconditionswarrantnotificationofMine ManagementorRegulatoryAgencies, the following lists provide contact information.Mine ManagementMine Manager – Rick Poulson, 435-687-6610Chief Engineer – Louie Tonc, 435-687-6637Geology and Exploration Manager – Chuck Semborski, 435-687-4720Geology and Environmental Manager – Ken Fleck, 435-687-4712Regulatory AgenciesMSHA – District 9 – 435-637-3051Utah Division of Oil, Gas and Mining – 801-538-5340Emergency AgenciesEmery County Sheriff – 435-381-2404Emery County Ambulance – 911Castle View General Hospital- 435-637-4800
Prior to hydraulic head being applied to the bulkheads,a training programwill be implemented at the mine. This program will, at a minimum, be included as a part of annual re-training, and also be routinelydiscussed in daily safety talks throughout the year. Training will make the workforce aware of the operation of the bulkheads, including:
Bulkhead locations and anticipated function
Inspection and examination requirements
Procedures to follow in an emergency
Areas of responsibility
Evacuation plans and travel routes
Appendix A
Mayo & Associates
Deer Creek Mine – Mill Fork Area
Geochemical Evaluation of Groundwater with Elevated Iron
AppendixB
Geologic StratigraphicColumn – Surface Exploration Drill Holes
EM-187 – Located Near Mill Fork Access #2 Bulkhead Location Site
EM-157 – Located Near 1st Right Bulkhead Location Site
AppendixC
ARMPS AnalysisofCoalPillars
AppendixD
J-Seal 120 psi Installation Procedures
AppendixE
Photos of the Bulkhead Locations