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Eagle Butte Mine – Cumulative Hydrologic Impact Assessment – 2000 @ Coal Diver
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Herschler Building • 122 West 25th Street • Cheyenne, Wyoming 82002
ADMIN/OUTREACH (307) 777-7758 FAX 777-3610 ABANDONED MINES (307) 777-6145 FAX 777-6462 AIR QUALITY (307) 777-7391 FAX 777-5616 INDUSTRIAL SITING (307) 777-7369 FAX 777-6937 LAND QUALITY (307) 777-7756 FAX 777-5864 SOLID & HAl. WASTE (307) 777-.7752 . FAX 777-5973 WATER QUALITY (307) 777-7781 FAX 777-5973
August 23,2000
Mr_ Larry G_ Kline U.S. Office of Surface Mining
1999 Broadway, Suite 3320 Denver, CO 80202-5733
TFN 3 4/159, Eagle Butte Southwest Amendment, Permit 428~T3, Cumulative Hydrologic Impact Assessment (CIDA)
Please find enclosed the final copy of the CHIA for the Eagle Butte Southwest Amendment area to Pennit 428-T3. Should you have any questions regarding the above document, please do not hesitate to call me at (307) 777-7047. Sincerely,
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Georgia A. Cash Program Supervisor Land Quality Division Enclosure cc: Jon Sweet, District III, LQD wlo enclosure Ramona Christensen, LQD wlo enclosure
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Cumulative Hydrologic Impact Assessment for the Rawhide Creek and Little Rawhide Creek Drainage Basins Northeast Wyoming
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Wyoming Department of Environmental Quality Land Quality Division July 2000
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EXECUTIVE SUMMARY. . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . • . • • . . . iii 1. INTRODUCTION............................................................... 1 2. BACKGROUND................................................................ 1 3. CUMULATIVE IMPACT AREA ..•..•....... ~ . . . . . . . . . . . . . . . . • . . . . • . . . . • . . . . . . . .. 1 3.1 Surface Water .............................................................. 2 3.2 Groundwater............................................................... 3 4. REGIONAL CONDITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 4.1 History .................................................................... 4.2 Climate ........................ '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.3 Soils ..................................................................... 4.4 Vegetation· ..................................... '........................... , 4.5 Structure ................................................................. , 4.6 Geology ................................................................... 4.7 Geomorphology............................................................. 4.8 Hydrology ............................... :-.................................
4 4 4 5 5 5 5 7 7
5. LOCAL GEOLOGY AND HYDROGEOLOGY ..................................•... 8
5.1 5.2 5.3 5.4 Streams ................... ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Wasatch Formation .......................................................... 8 Fort Union Formation ......................................................... 8 Clinker and Quaternary Deposits ............................................... 10
6. BASELINE HYDROLOGIC CONDITIONS .....................................•.. 6.1 SurfaceWater ............................................................. 6.2 Groundwater.............................................................. 6.3 Groundwater - Surface Water Interaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
7. HYDROLOGIC CONCERNS ...................................................... 17 7.1 Surface Water .............................................................. 17 7.2 ,Groundwater.............................................................. 19 8. MATERIAL DAMAGE CRITERIA .............................................•. 20 8.1 Surface Water ............................................................. 21 8.2 Groundwater .............................................................. 22 9. ANALYSIS OF CUMULATIVE HYDROLOGIC IMPACTS .........•.••••••••••.••••• 22 9.1 Surface Water .............................................................. 22 9.2 Groundwater .............................................................. 28
Cmnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-TII·AI, Change No.'
10.' MATERIAL DAMAGE POTENTIAL •..•.••.•.••...••••..•.••••••..•••••..••.•..• 31 10.1 Surface Water ............................................................. 31 I, 10.2 Groundwater .............................................................. 32 11. MATERIAL DAMAGE STATEMENTS OF FINDINGS. . . • . . • . • • • • • • • • • . • • . • • • • • • . . •. 11.1 Surface Water ........................................ '..................... 11.2 Groundwater .............................................................. 11.3 Determination of Material Damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12.
~COMMENDATIONS
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13. REFERENCES ............. -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 37 14. FIGURES .................................................................... 39
Figure 3-1 Location Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Figure 4-1 Data for Climate Stations Near Rawhide Creek and Little Rawhide Creek Drainage Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Figure 4-2 Generalized Stratigraphic Section .......................................... Figure 9-1 Approximate Maximum Extent of Cumulative 5 Foot Drawdown Contour in Coal Aquifer ............................................ , . . . . . . .. Plate 1
Area Map ......................................................., .. Pocket
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Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit428-T'1-Al, Change No.'
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RAG owns and operates the Eagle Butte Coal Mine in northeast Wyoming and has proposed to amend 1,198 additional acres southwest of the currently approved pennit area.
In order to issue a coal mining pennit or approve an amendment to an existing coal mining pennit, the Surface Mining Control and Reclamation Act (SMCRA) of 1977 requires the regulatory authority to assess the probable cumulative impacts to the surface and groundwater systems caused by current and proposed mining activities in a cumulative impact area. In the State of Wyoming, the Wyoming Department of Environmental Quality, Land Quality Division is responsible for preparing the cumulative hydrologic impact assessment. The Wyoming State Engineer's Office provides assistance on surface and groundwater quantity and the Wyoming Department of Environmental Quality, Water Quality Division provides assistance on surface and groundwater qua,lity. The assessment must be sufficient to determine whether the mining operation has been designed to prevent material damage to the hydrologic balance.
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Several coal mines are present near the Eagle Butte Coal Mine. Buckskin and Rawhide are present to the north and Dry Fork, KFx, Fort Union, East Gillette, Clovis Point, and Wyodak are present to the south and· southeast. Currently, 4 mines are operating (Eagle Butte, Buckskin, Dry Fork. and Wyodak).and 5 mines are inactive (Rawhide, Fort Union, East Gillette, Clovis Point, and KFx). For this cumulative hydrologic impact assessment, the Rawhide and Little Rawhide Creek drainage basins are identified as the cumulative impact area for evaluating potential impacts to surface water and groundwater. Buckskin, Rawhide and Eagle Butte Mines are located in the Rawhide and Little Rawhide Creek drainage basins. '
Coal bed methane is being developed in the eastern Powder River Basin proximate to the coal mines and is expected to grow substantially during the next decade. Groundwater drawdown caused by coal bed methane development is already impacting the coal mines. Impacts of coal bed methane development to the surface and gr~undwater systems may potentially exceed any impacts caused by the coal mines. However, coal bed methane is outside the jurisdiction of SMCRA. Therefore, this cumulative hydrologic impact assessment is strictly an evaluation of the impacts caused by coal mining. Pre- and postmining runoff volumes in Rawhide and Little Rawhide Creek drainage basins are expected to be similar. Measurable changes in peakflow magnitudes are not expected. Baseflow is expected to recover to near premine levels. There are no anticipated impacts to surface water rights. Reclamation activities are expected to minimize sediment loss. Postmine surface water quality is expected to meet premine water quality class-of-use. The maximum extent of the 5 foot groundwater drawdown contour in the coal aquifer is expected to occur up to approximately 13 miles from the mine permit boundaries. The coal aquifer will be affected by mining; however, the postmine potentiometric surface in the coal aquifer is expected to approximate the premine potentiometric surface several hundred years after mining ceases. Some private wells are presently being affected by coal aquifer drawdown. However, the magnitude of the effects is not yet defined. The maximum extent of the 5 foot groundwater drawdown contours in the overburden, interburden and underburden is expected to occur approximately 1 mile from the mine pennit boundaries. Mining and subsequent backfilling will hydraulically connect the coal aquifer, overburden, interburden and underburden with the spoils aquifer. As a result, recovery of the potentiometric surfaces for these units depends on the . resaturation of the spoils aquifer. As the spoils aquifer resaturates so will the underburden, interburden and
Cwnulative Hydrologic Impact Assessment (ClUA) Eagle Butte Mine, Permit 428-T'f-Al. Change No.' . Page iii
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overburden. Groundwater elevations will recover in these units in several hundred years. The area affected by groundwater drawdown in the overburden is relatively small and few private wells are present. The area affected by groundwater drawdown in the underburden is relatively deep and few private wells are present. Impacts to the overburden and underburden are not pennanent and material damage is not expected.
Minefacility.wa~r s\lpply wells ~e colJlplete4iA.the under~ying Tul~C?<=kaquifer, the lowest member of the Fort Union Formation. The Tullock Member is approximately 600+ feet below the base of the rnk~' pits. The Tullock aquifer is expected to be impacted in an approximately 1 mile radius around the water supply wells. There are no cumulative impacts anticipated in the Tullock aquifer.
Reclaiming pits with spoils will result in physical changes to the postrnine aquifer. Once the spoils aquifer resaturates, pre- and postmine groUndwater flo~ patterns will be similar. Hydraulic conductivity of the spoils aquifer will initially be high, but with time the spoils aquifer will compact and the final hydraulic conductivity will decrease and approach the hydraulic conductivity of the surrounding undisturbed materials. Long term physical changes to the aquifers by spoils placement will be insignificant and material damage is not expected. Pre- and postmine groundwater quality in spoils aquifers will be similar. Premine groundwater quality in all aquifers varied but in most instances was cl~sified as suitable for livestock or lower quality. Postmine groundwater quality will also vary but will likely be suitable for livestock or lower quality. Transient impacts to groundwater quality are expected as the spoils aquifers resaturate, such as an increase in IDS followed by a steady decrease approaching premine concentrations. Impacts to groundwater quality are expected to be minimal and transient, and material damage is not expected. The only potential concern identified is a J)Ortion of the Little Rawhide Creek and East Pr~ Little Rawhide Creek adjacent to the ~e Butte Coal Mine. This reach was a ~~ stream under Dremine conditions and is expected to become a 10s~ stream in the J)OStmine environment which will J)Otential1v affect areas of desiW'ated alluvial valley floor. However, the affected area is relatively small (27 square miles (mi~ disturbed my mining) compared to the area of the Rawhide and Little Rawhide Creek drainage basins above the Downstream Rawhide gaging station near the Eastern boundary of Rawhide Mine (110 mi 2). This amounts to approximately 25 percent of the area of interest being affected my mining. Even with this potential impact, based on·the amount of stream affected and the maximum potential stream loss, there will likely be no measurable change in observed surface water runoff at the Downstream Rawhide gaging station near the eastern boundary of Rawhide Mine. Based on existing available information, the Department has determined that surface coal mining operations at the Eagle Butte, Buckskin, and Rawhide Mines will have local and short term impacts to the environment. However, no permanent adverse impacts to the hydrologic system are expected and material damage to surface and groundwater quality and quantity is not expected to the drainage basin as a whole.
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Cwnulative Hydrologic Impact Assessment (CRIA) Eagle Butte Mine, Permit 428-T'f AI, Change No.'_
In September 1997. Amax Coal West. Inc. (Amax) submitted an IUlPlication for the proposed Southwest Extension amcmdment which would add land to the currentIv IUlProved ~ Butte Coal Mine oermit (permit Number 428-T3) located in northeast Wvo~. The amendment IUlPlication has jtone tbroue several reviews and revisions and is now considered complete. In late 1999. RAG purchased Amax and in early 2000 the Wvo~ Department of Environmental Qua1ity(WDEQ), Land Quality Division (LQD)
approved the transfer of ownership.
In order to issue a coal mining pennit or approve an amendment to an existing coal mining pennit, the
Surface Mining Control and Reclamation Act (SMCRA) of 1977 requires the regulatory authority to assess the probable cumulative impacts to the hydrologic system caused by current and proposed mining activities in a cumulative impact area (SMCRA, Sections 507(b) and 510(b». The State of Wyoming is a primacy state under SMCRA and the WDEQ, LQD is responsible for preparing the cumulative hydrologic impact assessment or "CHIA" (LQD Coal Rules and Regulations Chapter 2, Section 2(b)(xii) and Chapter 19, section 2(a)(i». The Wyoming State Engineer's Office provides assistance on surface and groundwater quantity and the WDEQ, Water Quality Division provides assistance on surface and groundwater qUality. The assessment must be sufficient to determine whether the mining operation has been designed to prevent material damage to the hydrologic balance outside the pennit area (Wyoming Statute § 35-11-406(n)(iii». This document describes the cumulative hydrologic impacts associated with mining in this area and was prepared using the December 1985 Draft GUidelinesfor the Preparation ofCumulative Hydrologic Impact Assessments (CHIA) and the January 1999 Managing Hydrologic Information. both presented by the U.S. Department of the Interior, Office of Surface Mining Reclamation and Enforcement.
All the coal mines in the northern Powder River Basin are open pit surface coal mines. Draglines and truck and shovel operations are utilized to strip overburden and remove the coal. One or several working faces are present at each mine in order to blend the coal quality to meet customer specifications. Mine sites include crushing, storage, loading, administrative and equipment maintenance facilities. Coal is transported off site primarily by rail car with minor amounts of coal transported off site by truck.
3. CUMULATIVE IMPACT AREA
A cumulative impact area (CIA) is the area where existing and proposed mining activities may cause measurable changes to hydrologic parameters, and depends on the characteristics of the surface and groundwater systems. Surface and groundwater impact areas are defined separately because groundwater impact'areas may overlap surface water divides. The final CIA encompasses both the surface and groundwater CIAs. There are 9 mines north of Gillette in the northern Powder River Basin of Wyoming (Figure 3-1 and Plate 1). Presently, 4 mines are operating Wagle Butte, Buckskin, Dry Fork, and Wyodak) and 5 mines are inactive (Rawhide, Fort Union, East Gillette, Clovis Point, and KFx). Allor parts of these mines are located in the Little Powder River drainage basin. The remaining portions of these mines are located in the Belle Fourche River drainage basin to the south. Based on geologic and hydrogeologic controls and available gaging station data, the CIA for this CIDA is 'delineated as the Rawhide and Little Rawhide
Eagle Butte Mine, Permit 428-T'f-Al, Change No.t
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drainage basins and contains the Eagle Butte, Buckskin and Rawhide Mines (Plate 1). This area consists of the portion of the Little Powder River drainage basin, upstream from the Downstream Rawhide stream gage at the Rawhide Mine This gage is located on Rawhide Creek, approximately 1 mile downstream from ;i the confluence of Rawhide and Little Rawhide Creeks. This area is within the larger Little Powder River drainage basin in the northern Powder River Basin which is part of the Missouri River drainage basin. 3.1 Surface Water Conceptually, the surface water CIA extends from a downstream point where all mining impacts can be cumulated, and upstream to either a drainage basin boundary or to a point at which upstream effects can be isolated from mining impacts (e.g., a stream gaging station). For purposes of evaluating surface water impacts, the CIA encompasses the Rawhide Creek and Little Rawhide Creek drainage basins upstream from the Downstream Rawhide gaging station. This gage is located at the Rawhide Mine approximately 1 mile downstream from the confluence of Rawhide and Little Rawhide Creeks.(plate 1). Any impacts to surface water caused by mines outside the Rawhide and Little Raw~de drainage basins will be downstream from the Rawhide and Little Rawhide drainage basins, and will not affect this CIA. USGS gaging station No. 06324890 is sited at a location where it could be used to monitor impacts from all of the mines in the northern Powder River Basin. The capture area is 204 mi 2 with 27 percent of the area impacted by coal mining activities. However, the period of record is short (1975 to 1983) and other physical features make it an undesirable gage for evaluating impacts related to miping in this area. Surface water diversions for irrigation occur between the Downstream Rawhide gage and the USGS gage making it difficult to accurately measure discharge or surface water quality parameters. A significant amount of clinker is also present in this reach of stream. Clinker is very permeable which causes the local surface water system to become a losing stream in the area. Some of the surface water recharges the local groundwater table and some of the water discharges at springs downstream from the mines. It was determined that it would be more accurate to evaluate two separate smaller CIAs in this area rather than one single large CIA. The surface water CIA drainage area upstream from the Downstream Rawhide gage is approximately 110 square miles (mi2). The Eagle Butte Mine is primarily located along Little Rawhide Creek which has a drainage area of approximately 34 mi 2 (permit No. 240-T4, Appendix D-6, Figure 18, 1986). The Buckskin Coal Mine is located on Rawhide Creek, just upstream from its confluence with Little Rawhide Creek. The Rawhide Creek drainage area is 76.4 mi 2 measured from the Downstream Rawhide gage (permit No. 240-T4, Appendix D-6, Figure 18, 1986). The Eagle Butte Mine permit is 5,717 acres with 5,706 acres scheduled to be disturbed during the life of the mine. The proposed Southwest Extension amendment would add 1,198 acres and bring the total permitted area to 6,915 acres with a planned disturbance of 6,904 acres (Eagle Butte Amendment Application. December '1 6, 1999). The Buckskin Mine is 5,446 acres with 3,789 acreS planned for disturbance and the Rawhide Mine is 8,874 acres with 7,295 acreS of planned
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Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-Tij-AI, Change No.'
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The ~ Butte. Buckskin. and Rawhide permit boundaries collectivelv encompass 21.235 acres. The permits boundaries have some overlap which accounts for approximately 1.695 acres. rcducin.ct the total permitted area to 19.540 acres. However. approximately 2.020 acres arc located outside the Rawhide and Little Rawhide Creek drainaste basins leavin$t 17.S20 acres within the CIA. This accounts for a total of 90 percent of the permitted areas of these 3 mines.
Approximately 2.020 acres (10 percent) of the permitted areas is located either downstream from the Downstream Rawhide ~e or in the Dry Fork Little Powder River drainasce basin to the east of the CIA. Of this area.. approximately 1.980 acres are scheduled to be disturbed. Based on the analysis of the CIA area. this area will have an insWllficant imDact and will not be included in the surface water portion of this evaluation. However. this area will be considered when the Little Powder and Dry Fork Little Powder River drainage basins are evaluated in a subsequent CHIA. Approximately 228 acres (1 percent) of the permitted areas is located within closed~. All 228 acres arc scheduled to be disturbed. 1bese areas will not be reclaimed as closed ~es and will contribute to the reclaimed local drainage network. Therefore, this area is considered part of the surf3ce water CIA. 3.2
Groundwater Conceptually, the groundwater CIA consists of: (1) areas impacted by mine indu~ groundwater level drawdown; (2) the extent of any measurable impacts the groundwater drawdown may have on the surface water system; and (3) areas where plumes of degraded groundwater may migrate. For assessing groundwater impacts, the CIA is delineated by the maximum cumulative 5 foot drawdown contour for the Eagle Butte Mine, its proposed southwest extension amendment area, and the other 8 coal mines in the northern Powder River Basin (Figures 3-1 and 9-1). The CIA for groundwater impacts includes the Rawhide Creek and Little Rawhide Creek drainage basins and portions of adjacem drainage basins. Portions of the East Gillette. Clovis Point and Wyodak Mines are located in the Belle Fourche River drainage basin to the south. The predicted groundwater impacts from these mines is being considered in this assessment. The maximum extent of the predicted cumulative 5 foot drawdown contour for the mines in the northern Powder River Basin is estimated using the most recent data from all 9 facilities. Even though the mines are not all currently active, all the predicted maximum extent of the 5 foot drawdown contours are considered in order to conservatively predict the maximum extent of the cumulative 5 foot drawdown contour. Potential impacts to the groundwater system from mine facility water supply wells are considered insignificant and not further evaluated for the following reasons: 1. Potable water at the mines is produced from wells completed 900+ feet below the land surface and 600+ feet below the deepest anticipated mining activities. The wells are typically completed in the Tullock aquifer of the Fort Union Formation. The 600+ feet of strata located below the coal and above the Tullock aquifer consist of low to very low permeability sediments of the lower Tongue River Member (below the mineable coal) and Lebo shale. a confining unit
Cumulative Hydrologic Impact Assessment (CRIA) Eagle Butte Mine, Permit 428-T~-A I, Change No.' Page 3
(Eagle Butte, Mine Hydrology, 1998). In addition, water level declines in sub-coal Fort Union wells generally occur within 1 mile of the pumped wells (USGS, 1988). Mine supply wells are separated by distances of 1 mile or more, therefore, little interference is expected between mine supply wells (BLM, 1994). 2. The City of Gillette has municipal water supply wells located within and around the city limits completed in the Tullock Member of the Paleocene Fort Union Formation and the underlying Cretaceous Lance and Fox Hills Fo~tions. These wells are completed approximately 2,500 feet below the land surface. The City also has a well field in Carlile, WY, located 42 miles northeast of Gillette. These wells are completed approximately 2,500 feet below the land surface in the Madison Formation. The Madison and Fort Union wells are the primary water supply wells for the city and the LancelFox Hills wells are utilized during peak demand in the summer (Schultz, 2000). City of Gillette municipal wells and Gillette area subdivision water supply wells have caused documented water level declines in the sub-coal Fort Union Formation (USGS, 1991). The sub-coal mine water supply wells are located at least 6 miles from Gillette. The nearest municipal or subdivision water supply wells are located greater than 2 miles from the mine water supply wells. The quantity of water pumped from the mine water supply wells is small compared to the municipal wells. As stated in the previous paragraph, water level declines in . sub-coal mine wells generally occur within 1 mile of the pumped wells (USGS, 1988). Therefore, little to no interference is expected between mine water supply wells and the City of Gillette municipal and subdivision water supply wells (BLM, 1994).
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4. REGIONAL CONDITIONS
The cumulative impact area (CIA) lies entirely within the northern portion of the Powder River Structural Basin in northeast Wyoming, hereafter, referred to as the Powder River Basin. 4.1 History The primary historic land uses throughout the basin are open range, ranching, and farming. Largescale, commercial, coal mining began in this area in the 1970s. In 1999,23 coal mines in the Powder River Basin disturbed appro~tely 59,000 acres, of which, approximately 10,100 acres are located in the northern Powder River Basin. Coal bed methane development began in the late 1990's when developers began pumping groundwater from large areas of basinal coal. Coal bed methane development continues to grow today. 4.2 Climate The northern Powder River Basin is semi-arid with cool, dry winters and warm dry summers. Windy conditions exist year-round with prevailing winds from the west to northwest at 8 to 10 mph. Isolated but intense thunderstorms occur during the warmer months and light to moderate snow falls during the colder months. The basin receives approximately 13 to 16 inches of precipitation annually, with most (71 to 77 percent) of the precipitation occurring during the growing season which extends from April through SePtember. The potential evapotranspiration rates exceed precipitation in the basin. The National Weather Service haS several climate monitoring stations in the Gillette area. However,
Cumulative Hydrologic Impact Assessment (CHIA) Page 4
Eagle Butte Mine, Pennit 428-T~AI, Change No.1
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only a few have the necessary data and length of record. The Gillette 9ESE (Station No. 483855), Weston (Station No. 489580) and Echeta 2 NW (Station No. 482881) are the three nearest climate stations (plate 1) and their climate summaries are provided on Figure 4-1 (Western Regional Climate Center, 1999). 4.3 Soils Soils in the basin are primarily residual and vary from 20 to 30 inches thick on gentle slopes and swales to only a few inches on steeper slopes. Sandy soils tend to develop in areas underlain by sandstone and sandy shale. Fine-textured, clayey soils tend to develop in areas underlain by shales or claystones (Martin and others, 1988). Soils at the Eagle Butte Mine vary from 6 to 60 inches thick (Eagle Butte, Section 2.1, 1996). 4.4 Vegetation Native vegetation in the Powder River Basin is a mixture of grasses and shrubs, with local coniferous and deciduous woodland areas. Common vegetation communities include upland, mixed shrub, and big sagebrush grasslands, lowland meadows, rough breaks and wetlands (Martin and others, 1988). 4.5 Structure The Powder River Basin is a large north-northwest to south-southeast trending asymmetric syncline in northeastern Wyoming and southeastern Montana. The basin is approximately 250 miles long by 90 miles wide, and contains as much as 23,000 feet (ft) of sediment (Denson et. aI., 1989). The structural fold axis is located along the western part of the basin with the western limb characterized by steeply dipping bedrock and the eastern limb characterized by gently dipping bedrock (Wyoming Water Resources Center, 1997). The mines and CIA are located on the eastern limb of the Powder River Basin. In the study area, bedrock regionally dips less than 1 degree west-northwest (Eagle Butte, Section 2.5.1, 1996). Local folding and faulting may cause steeper dips in the coal beds (BLM, 1994). 4.6 Geology The following discussion addresses the fonnations which will be affected by mining, as identified in the mine permits. In ascending order, these geologic units are the Paleocene Fort Union Formation, Eocene Wasatch Formation, Quaternary deposits and clinker. Regional geology is presented on Figure 3-1 and Plate 1., A stratigraphic column showing typical lithologies and geophysical log characteristics of these fonnations is presented in Figure 4-2. The following descriptions were modified from Martin and others (1988) and Wyoming Water Resources Center (1997), unless otherwise noted. Fort Union Formation The Paleocene Fort Union Formation is up to 6,200 feet thick and consists of fluvial, deltaic, and lacustrine sediments. The Fort Union Formation is subdivided into three members; in ascending order they are the Tullock Member, Lebo Shale Member, and Tongue River Member. Many laterally persistent coal seams are present in the upper Tongue River Member.
Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-Tl\-Al, Change No.1
Most commercial coal production in the Powder River Basin is from the WyOdak-Anderson coal It seam present in the upper Tongue River Member. The Wyodak-Anderson coal consists ofan upper and lower coal seam with little to no shale parting. In other parts of the basin, these same two coal seams are referred to as the Anderson (upper) and Canyon (lower) seams. In the Gillette area the main coal seams are referred to as the Roland (upper coal seam) and the Smith (lower coal seam), separated by a shale parting of variable thickness. The combined thickness of the coal seams is approximately 100 to 110 feet (USGS, 1991).
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The contact between the Fort Union Formation and the overlying Wasatch Formation has been defined differently in various publications. In general, strata above the WyQdak Coal are more
thinly bedded, contain more shale and limestone, and indicate deposition in more lake-dominated environments (Flores, 1986). Throughout the basin and for this report, the top of the main coal (Roland-Smith, Anderson-Canyon, or Wyodak-Anderson) seam is informally considered the contact between the Fort Union Formation and the overlying Wasatch Fonnation. Wasatch Formation The Upper Paleocene to Lower Eocene Wasatch Fonnation consists mainly of alluvial mudstone' and sandstone. The maximum preserved thickness of the Wasatch Formation is about 3,000 feet along the structural axis of the Powder River Basin (Seeland, 1992) and thins toward the edges of the basin where the upper parts have been removed by erosion (Fogg et. aI., 1991). In Wyoming, the Wasatch Formation is second only to the Fort Union Formation in coal deposits, having as many as eight thick, laterally persistent coal beds (Glass and Jones, 1991). The Felix Coal is located in the Wasatch Formation, Quaternary Deposits Quaternary alluvium, colluvium and terrace deposits are found in the region. Alluvium consists of Unconsolidated silt, sand, and gravel and is present in stream beds and covering the floodplains of the major streams in the Powder River Basin. Colluvium consists of rock fragments and soil and is present at the base of steep slopes. Alluvial fans of varying size and consisting of unconsolidated silt, sand, and gravel are present throughout the region. Terraces contain alluvial and colluvial deposits and indicate a recent history of alternating cycles of erosion and deposition.
Clinker . '- .. ,' -Ciinker is'roekthailiciS-beenbaked or partially meltedin'place by the-natural prehistoric burning""" !$1.~ of underlying coal beds. Clinker covers approximately 500 square miles (mi~ of the Powder II River Basin in northeastern Wyoming (Heffern and Coates, 1996). LQD mine permit appendices indicate clinker is commonly 100 feet thick and locally may be up to 200 feet thick. Clinker is more resistant to erosion than unbaked sediments and, therefore, controls the topography of many land forms in the Powder River Basin. Clinker is highly fractured and penneable, and allows precipitation to infiltrate rapidly which plays an important role in the storage and flow of water in the Powder River Basin. Clinker is able to store large amounts of rainfall and snow melt, protect it from evaporation, and discharge the water to springs, streams, and aquifers (lIeffern et. at., 1996).
Cwnulative Hydrologic bnpact Assessment (CHIA) Eagle Butte Mine, Pennit 428-1"'4 -AI, Change No.l·
The following description was modified from Martin and others (I988) and Wyoming Water
Resources Center (1997), unless otherwise noted. The Powder River Basin landscape is characterized by plains and low, rolling hills, scoria capped hills and uplands dissected by streams. The Little Powder River is perennial with most of its tributaries being ephemeral flowing in response to rainstorms and snow melt. The present landscape of the Powder River Basin can be divided into three general-land types described below (Coates and Naeser, 1984).
Land west of the clinker consists of gently rolling topography with only a few steep hills, where' clinker of the Felix Coal (within the Wasatch Formation) caps isolated buttes. Soils have sufficient permeability resulting in little run off and a loosely knit, poorly integrated drainage network. Wind deflation has created areas of closed drainage now occupied by playas. Land dominated by clinker consists of nearly flat to gently rolling uplands. Clinker is highly fractured and permeable, which quickly absorbs water resulting in little through drainage and minimal surface erosion. Clinker is typically underlain by impermeable clay and shale of the Fort Union Formation, which limits downward migration of groundwater and forces the development of . springS at the base of the clinker where the water table intersects the land surface. Slopes along the edge of clinker-capped escarpments are usually steep. The clinker protects the less resistant Fort Union Formation; however, where erosion has breached the clinker, steep slopes ofless resistant Fort Union Formation develop into clinker capped escarpments.
Land east of the clinker is underlain entirely by the Fort Union Formation. The Fort Union Fonnation has a higher clay content and lower permeability than the Wasatch Formation, resulting in greater surface water runoff. Most of the Fort Union Formation is poorly consolidated and weathers to a landscape of low relief. 4.8 Hydrology Alluvium and clinker both have favorable hydraulic properties. However, due to their limited thickness and aerial extent the alluvium and clinker typically have low well yields. The Wasatch Formation is not considered an aquifer, but tends to provide limited amounts of groundwater to wells from laterally discontinuous sandstone Iayer~. These Wasatch sandstones have sufficient hydraulic properties to serve as aquifers for stock and domestic uses on a local scale, however, the water quality is marginal for human and livestock consumption and some vegetation. Fort Union coal seams appear to be the only major continuous units having the potential to be aquifers, however, within a couple of miles west of the mines the coal becomes too deep to be an economical source of Water on a residential scale . Groundwater in the Wasatch Formation regionally flows to the north-northeast. However, local groundwater flow is poorly defined due to the discontinuous nature of the permeable units in the formation. Shallow groundwater flows towards local drainages such as Rawhide Creek, Little Rawhide Creek and Dry Fork Little Powder River. Groundwater in the Fort Union coal seams regionally flows down dip to the west-northwest with local variations. The coal cutout feature at the Eagle Butte Mine acts as a groundwater dam which causes the local groundwater to flow around the feature or discharge at the surface as a spring (Eagle Butte Hydrology, 1996). Groundwater in the
Cumulative Hydrologic Impact Assessment (CHJA) Eagle Butte Mine, Permit 428-TL{-AI, Change No.' -. Page 7
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coal around the mines flows towards the open pits under an induced conical gradient caused by local dewatering at the mine. .. 5. LOCAL GEOLOGY AND HYDROGEOLOGY Mining at the Eagle Butte, Rawhide, and Buckskin coal mines disturbs the Wasatch Formation, Fort Union Formation, and Quaternary deposits. The following describs the local geologic and hydrogeologic conditions. 5.1 Streams The main streams in the CIA are Rawhide and Little Rawhide Creeks. These streams flow generally to the north and northeast. 5.2 Wasatch Fonnation The upper Eocene Wasatch Formation is considered overburden at the sites and varies iii thickness from zero at the coal outcrop to 300 to 400 feet. The Wasatch Formation consists of interfingering silt shales, clay shales and sandstone. Very soft and poorly consolidated Wasatch sand bodies are present in the area. The Wasatch Formation is locally considered a low yield, perched aquifer due to the thin, discontinuous sandstone beds interbedded with siltstone and claystone. Local hydraulic conductivity values generally range from 0.1 to 30 gpd/ft? Storage coefficients range from 10.2 to 10-4, which indicate both confined and unconfined conditions; however, unconfined conditions predominate. The hydraulic conductivity for the overburden is 1 to 2 orders of magnitude lower than the underlying Anderson-Canyon coal seam. Also, the head elevations in the Anderson-Canyon coal seam rise above the top of the coal indicating confining conditions. Therefore, the Wasatch Formation is a confining unit for the underlying Anderson-Canyon coal seam. Based on premining potentiometric maps, groundwater flows toward three different drainages: Rawhide Creek; Little Rawhide Creek; and Dry Fork Little Powder River (based on GAGMO, 1999). Overburden samples collected from the facilities are analyzed for physical properties and chemical composition. Spoils which are unsuitable due to physical or chemical properties which may adversely affect revegetation or postmining water quality are handled preferentially. Parameters such as nitrates, potential acidity and acid-base potential are identified locally and require preferential handling. Salinity and trace metals do not appear to pose any potential problems (Eagle Butte Geology, 428-T3).
Fort Union Formation Locally, the Fort Union Formation is approximately 3,000 feet thick (BLM, 1994). The Fort Union Formation consists of the Anderson (upper) and Canyon (lower) coal seams, interburden and underburden. The interburden or split between the coal seams ranges from approximately 0 to 40 feet thick, but approaches 200 feet west of the Buckskin Mine. Based on cross-sections presented in the permits, the coal is generally 100 to 110 feet thick with lOcal variations ranging from approximately 80 to 130 feet. There are nomajor faults mapped in the area.
Cumulative Hydrologic Impact Assessment (ClllA) Eagle Butte Mine, Pennit 428-TCi-AI. Change No.1
Tongue River Member The Tongue River Member is locally approximately 1,000 feet thick (BLM, 1994) and consists of predominantly sandstone and siltstone interbedded with shale, and many thick and laterally persistent coal beds. The mineable coal is present at the top of this member. Stratum below the mineable coal is considered underburden. The coal is laterally persistent and has sufficient secondary'permeability to he considered an aquifer. The coal aquifer is confined between the Wasatch Formation above and the lower Tongue River and Lebo Members below (Wyoming Water Resources Center, 1997). Lebo Member The Lebo Member is locally approximately 600 feet thick (BLM, 1994) and consists of predominantly shale and concretionary sandstone with siltstone, and thin coal beds. The Lebo Member is considered a confining unit due to the predominance of shale (Wyoming Water Resources Center, 1997). Tullock Member The Tullock Member is locally approximately 800 feet thick (BLM, 1994) and consists of shale, fine-grained sandstone, siltstone, and thin coal beds. The Tullock Member has sufficient sand and penneability to be considered an aquifer. Most coal mine facility wells are completed in the Tullock Member as are many City of Gillette municipal wells and some Gillette area subdivision water supply wells. These wells may cause some groundwater head losses (Wyoming Water Resources Center, 1997). However, in the area of the mines, there are few wells completed in the Tullock Member and they are located sufficient distances apart, minimizing the potential for interference and cumulative impacts to the aquifer. In addition, due to the presence of the overlying confining strata, the TuJlock aquifer is considered hydrologically isolated from the coal aquifer above. Based on this infonnation, any mine related impacts from facility wells to the Tullock Member are expected to be negligible. Fort Union Formation - General . In the study area, the strata locally dip from less than 1 degree to 3 degrees west-northwest. The coal seams are continuous in the study area except for a major cutout (area where coal was not deposited) at the Eagle Butte Mine in the south half of Section 16 and north half of Section 21. The structure of the coal within a short distance of the cutout is modified by folded, burned, pinched out, or split coal seams. (Eagle'Butte Section 2.5.1, 1996). The cutout trends east-west and is characterized by a large shale-sandstone body which was presumably deposited contemporaneously with the lower coal seam. Deposition of the upper coal continued after the cutout channel was filled, thus the upper seam overlies the cutout channel. Immediately adjacent to this cutout channel, the parting, which elsewhere averages 6 feet thick, may approach 90 feet , thick (Eagle Butte Section 2.5.2, 1996). A structural 'rise is present in the coal as the coal seams approach the cutout. This is likely due to differential compaction of the paleochannel cutout and the coals following deposition. Uplift and erosion exposed the upper coal seam, which then burned, resulting in the clinker present in the coal cutout. Loca1 topography is characterized by rolling hills covered with grass and sagebrush except in the coal cutout area where the rolling hills give way to steep sandstone and scoriacapped hills (Eagle Butte Sections 2.5.1 andi.5.2, 1996) ..
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Cumulative Hydrologic bnpact Assessment (CHIA) Eagle Butte Mine, Permit 428-T't AI, Change No.1
The saturated thickness of the coal increases to the west as the coal seam dips further below the land surface and below the water table. Artesian conditions exist within 2 miles west of the outcrop. Where present, fractures trend northwest-southeast, consistent with other structural features in the Powder River Basin. The primary permeability of coal is very low. It is the secondary (fracture) permeability which controls the flow of groundwater through coal. The mines have performed pump tests on wells completed in the coal. The mines have reported the hydraulic conductivity of the coal to range from 0.015 to 0.I'gpd/ft2 in the unfractured portion of the coal and approximately 10 to 610 gpd/ft2 in fractured portions of the coal with one value as high as 7,450 gpd/ft2. Storage coefficients were approximately 10-4 indicating confined conditions. Based on premining potentiometric maps, groundwater in the coal seams flowed to the north-northwest (Eagle Butte Hydrology, 1996). The coal seams are confined throughout much of the permit area and unconfined to semi-confined near the eastern portions of the permit boundaries where the coal crops out at the surface. The Anderson coal seam is exposed and burned along the eastern portions of the mines resulting in clinker along the eastern portions of the permit boundaries. Interburden between the coal seams consists of claystone and siltstone with minor fine gravels and discontinuous sandstone lenses. The hydraulic conductivity of the interburden at the Buckskin Mine was estimated to range from 0,5 to 23 gpd/ft2 and the storage coefficient is approximately lO-s (Buckskin, Mine Plan and Hydrology, 1999). However, the limited thickness of the interburden and discontinuous nature of the sandstone limits sustained water yields, The interburden is a confining unit for the underlying Canyon coal seam as evidenced by the head differences between the Anderson and Canyon coal seams. Due to the discontinuous nature of the water bearing lenses, a potentiometric map was not constructed for the interburden. Underburden in the study area consists of low permeability shale and claystone with discontinuous lenses of coat" and sandstone. The hydraulic conductivity of the underburden is estimated to range from 0.05 to 4 gpd/ft2 with a storage coefficient of 10-3 to 10"" (Buckskin Hydrology, 1999; Rawhide Hydrology, 1998). The underburden is confined away from (west of) the outcrop with head elevations substantially higher than the top of the underburden. Based on limited premining data, groundwater in the underburden generally flows west. Recent modeling by the Powder River Coal Company for the North AntelopeIRochelle Complex Mine indicates the underburden recharges the overlying coal where the potentiometric surface is under artesian conditioiIs (NNRC Appendix D-6, 1998). Therefore, groundwater in the underburden likely recharges the overlying coal. Due to the discontinuous nature of the water bearing sandstone lenses, a potentiometric map was not constructed for the underburden. 5.4 £linker and Quaternary Deposits Clinker deposits are present east of the mines along the coal crop line and in the vicinity of the coal cutout on the Eagle Butte Mine (Eagle Butte, Section 2.5.7, 1996). Local estimated hydraulic conductivities for clinker range from 102 to 106 gpd/ft2. Based on hydraulic conductivity, clinker would make a good aquifer. However, the aerial extent of clinker deposits are limited and the saturated thickness is typically only a few feet to tens of feet. Therefore, clinker is expected to have high well yields but for only a short duration.
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Quaternary alluvial and colluvial sediments are found in the Rawhide Creek and Little Rawhide Creeks valleys and tributary drainages. These deposits are generally less than 15 feet thick and range from sandy loam to clay loam (Eagle Butte Section 2.5.2, 1996). Based on the silty and clayey sediments present in their channels, the local streams should have very low hydraulic conductivities. There are areas with coarser sediments (sands and gravels) which will have greater hydraulic conductivities, however, these deposits are of limited thickness and aerial extent. Some stream reaches are in direct contact with bedrock or clinker. These areas may have greater volumes of water flowing from the stream (in the case of a losing stream) or to the stream (in the case of a gaining stream).
6. BASELINE HYDROLOGIC CONDITIONS
6.1 Surface Water Surface water baseline monitoring was performed at each of the mines in the CIA. This data was compiled and is presented in the permit for each mine. Monitoring was conducted to document upstream and downstream water quantity and quality at each mine. Eagle Butte Mine monitored baseline conditions on Little Rawhide Creek at station EB-l (upstream, 1974 to 1985) and EB-12 (upstream, 1982 to present) and station EB-2 (downstream) from their mining operations. Rawhide Mine monitored Rawhide' Creek at the Upstream Rawhide and Downstream Rawhide locations. Buckskin Mine monitored Rawhide Creek upstream at station CR-7 and downstream at station CR-5. 6.1.1 Surface Water Quantitv Stream Classification Within the CIA, Rawhide and Little Rawhide Creeks are intermittent. At the Downstream Rawhide gage, Rawhide Creek is an intermittent stream with an average discharge of 3 cubic feet per second (cfs). Spring runoff tends to have the greatest flow with convective thunderstorms providing flows in the late summer and early fall. Flow is not measured from November 1 through March 31 due to freezing conditions (Rawhide, Mine Plan, 1998). Average Annual Runoffand Unit Area Runoff The CIA encompasses 110 mi 2 within the Rawhide and Little Rawhide drainage basins upstream from the Downstream Rawhide gaging station near the eastern boundary of Rawhide Mine. This gaging station has a period of record from 1980 to 1997. Extremes for the period of record range from no-flow to 640 cfs in May, 1985. The average flow for the period is 3 cfs, average annual runoff is 2,121 acre-feet (ac-ft), and the unit area annual runoff is approximately 19 ac-ftlmi 2/year. Gaging station CR-7 at the Buckskin Mine is an upstream gage that encompasses 71.6 mi 2 and averages 365 ac-ft per year. This results in a unit area runoff of approximately 5.1 acftlmj?/year. Gaging station EB-l, mined through and replaced by EB-12 is an upstream gage at the Eagle Butte Mine with a unit area runoff of approximately 10 ac-ftlmi 2/year. By using CR-7 and EB-IIEB-12 to make a prediction for the CIA, the area weighted unit area runoff is approximately 7 ac-ftlmi 2/year, 720 ac-ft annually, and an average flow of 1 cfs. The flows represented by the seven month period is believed to represent the majority of the annual runoff.
Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-TI4-AI, Change No.1 ' Page 11
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Peak Dischante Peak di.scbarJtes for the CIA were estimated by Rawhide. Buckskin, and EaJde Butte Mines usin.ct the Soil Conservation Service (SCS) Triangular Hydrograph Method. The estimated peak disCharges are presented in Table 6-1. Please note that for purposes of detennjni~ lo~-tenn ave~e runoff and peakflow. all of the records for the CIA are short. The vast majority of observed flow measurements at any of the JWtes within the CIA derived from either snowmelt or ~e precipitation events. maki~ it difficult to characterize the system. Lowham (1988) ~ that a minimum of2S years of data is necessary to reasonably establish flow characteristics such as annual runo£( mean daily flow, and unit area runoff.
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Surface water rights within the permit boundaries and surrounding areas are currently limited
to livestock and wildlife watering, industrial, domestic, and irrigation uses (Rawhide Mine, Table D-6-8). As per Wyoming's OSM approved coal program, coal mines are responsible for
replacing any surface water right or supply affected by contamination, diminution, or interruption resulting from surface coal mining (W.S. 35-11-415(b)(xii) and 416(b».
Table 6-1 24 Hour Storm Peak Discharge Estimates* for Various Return Periods Return Period Buckskin Mine Rawhide Creek above Little Rawhide Creek (69
mi 2)
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Rawhide Creek above Red Little Rawhide Creek above 'Rawhide Creek (34 mi2) Fox Draw (113 mi 2) (cfs) 600 2700 4400 5900 6500
(years) 2 10 25 50 100
(cfs) 140 1200 2200 3100 4100
(cfs) 170 1000 1500 2100 2600
*Discharge Estimates are based on the SCS Triangular Hydrograph Method (1972)
6.1.2 Surface Water Quality Eagle Butte Mine Surface water quality at Eagle Butte Mine is characterized as a calcium-sulfate (caSo 4) type. Total dissolved solids (TOS) concentrations average 2,000.milligrams per liter (mg/l) and total suspended solids (TSS) concentrations average approximately 9 rngll at station 007 as reported in Eagle Butte's baseline water quality data (Eagle Butte, Appendix 2.6.1-4, 1984) The majority of trace elements were at or below detection limits. Based on the WDEQ, Water Quality Division (wQD) Chapter VIII quality criteria for groundwater (Table 6-2), premine
Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-T'IAI,Change No.1 "
surface water for Little Rawhide Creek is suitable for livestock watering. Please note that the . WQD has not developed numerical surface water standards for various chemical parameters for each class of use.
Table 6-2 WQD Selected Groundwater Class-of-Use Standards·
Class I, Domestic Concentration Class II, Agriculture Class III, Livestock Concentration Concentration
ammonia (NH3 as NJ arsenic boron cadmium chloride fluoride iron manganese nitrate+nitrite (N03 + N02 as N) [pH selenium sulfate TDS@ 1800F zinc aluminum barium
0.58 0.05 0.75 0.01 250 1.4-2.47 0.3 0.05
0.1 0.75 . 0.01 100 5 0.2
0.2 5 0.05 .2000
6.5-9 0.01 250 500 5
100 6.5-8.5 ' 0.05 3000 5000 25 5
1 1 0.3 0.002
4.5-9 0.02 200 2000 2 5
lead mercury nickel • from WaD Rules and Regulations, Chapter VIII
Rawhide Mine Premine surface water quality samplin,g of Little Rawhide Creek indicate surface water quality is Jtenerallv a calcium-sulfate type (caSo 4 ). TDS concentrations ave~ed 4.600 m.WL and TSS concentrations avera,ged approximately S6 m.Wl on the Upper Little Rawhide Creek as reported in Rawhide's baseline water quality data (Rawhide. ADpendix D-6 Addendum D. 1986). Based on exi.stiIlJt data. and classification by WQD, the surface water in the vicinity of Rawhide Coal Mine is suitable for livestock.
Buckskin Mine Premine water quality sampl.ing and analysis on Rawhide Creek indicate a sodium-sulfate (NaSo4 ) type water. TDS concentrations ave~ed 5200 mWl and TSS concentrations ave~ed approximately 110 mWl at station Rawhide W in Buckskin's baseline water quality data. (Buckskin. Table D6-E-1. 1989). Analysis also shows that the premine water quality is generally suitable for ~k (Buckskin, Table D6-E-3, 1989).
Cumulative Hydrologic Impact Assessment (CHJA) Eagle Butte Mine, Permit 428-T~-AI, Change No.1
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Sediment production on the Little Rawhide and RawhidC Creek ~e areas will be controlled ~ mininst with sediment detention structures and alternative sediment control measures (ASCM's). Based upon the intermittent nature of these ~ areas. the sediment load carried in these streams is believed to be event driven. The use of sediment detention ponds and ASCM's will control sediment throwdlout the affected areas of the CIA. In the J)OStmine environment the overall basin relief and sloJ)C will be reduced. ~c density will be increased.. ~on will be increased, and totai sediment deliVery to stream clumDels will 1ikely be reduced. . 6.2 Groundwater
6.2.1 GroundWater Quantity Alluvium and Clinker Alluvium and clinker are shallow water bearing units in the CIA. The alluvium is generally low permeability fine-grained sediments. However, locally, the alluvium may consist of thicker and coarser sediments with higher permeabilities. Due to the limited thickness, the alluvium provides only limited quantities of water (Rawhide Hydrology, 1998). Also, the saturated thickness of the alluvium varies seasonally. Where alluvium is in direct contact with bedrock or clinker the movement of water is more feasible. In these areas, the streams can be gaining or losing reaches depending on the season. Clinker deposits are highly permeable and groundwater is usually present in unconfined conditions. Confined conditions may occur where overlain by alluvium or colluvium. Depending on local conditions, clinker may be a zone of groundwater recharge to the underlying units, or a zone of groundwater discharge. In general, clinker is considered a significant source of groundwater recharge to the coal aquifer (Rawhide Hydrology, 1998). Overburden The overburden water table generally reflects the surface topography. Sand and sand-rich lenses and interbeds are present in the Wasatch Formation. These sand bodies have sufficient permeability and are the primary water bearing units in the overburden. However, these sands are discontinuous and generally provide sufficient groundwater on a local scale only. Therefore, the Was~tchJ~~ormation.is not ~nsideredaregional aquifer. The overburden is recharged by direct infiltration and leakage from the underlying coal. Locally, the overburden dips gently (1 to 3 degrees) to the west and the thickness and saturated thickness of the overburden both increase to the west under predominantly unconfined conditions (Rawhide Hydrology, 1998; Eagle Butte Hydrology, 1996). Premine groundwater flowed towards Rawhide Creek, Little Rawhide Creek and Dry Fork Little Powder River. Where the sand bodies are present, the groundwater and surface water interact.. The overburden is a confining unit to the underlying coal aquifer in the Fort Union Formation. Coal Aquifer The saturated thickness of the coal increases to the west as the coal seam dips below the water table. Artesian conditions exist within 2 miles from (west of) the outcrop. The coal may be dry or partially saturated in the eastern portions of the CIA. Premine groundwater in the
Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-T4-A I, Change No.J
Anderson-Canyon coal flowed north-northwest in the CIA. However, some eastward flow in the coal toward discharge sites in local creek or river valleys occurs (Buckskin Hydrology, 1998; Eagle Butte Hydrology, 199Q). Interburden at these mines is typically thin «10 feet), but increases in thickness near the western pennit boundaries. The interburden is saturated in most places. The siltstones and claystones inhibit vertical groundwater movement to either of the coal seams. No coal or thin coal deposition areas have been identified at all three mines in the CIA. As described earlier, these areas contain silt- and clay-rich stream and overbank deposits most likely deposited concurrently with the coal. At the Eagle Butte Mine, the no coal area trends east-west across the center of the site in T51N, R72W, Sections 16,21 & 22. The area is approximately 4,000 to 5,000 feet wide (Eagle Butte Geology, 1996). At the Rawhide Mine, the no coal zones trend northeast to southwest in T51N, R72W, Sections 5,7 & 8 and T52N, R72W, Section 33 (Rawhide Hydrology, 1998). At the Buckskin Mine the no coal and thin coal areas are described as approximately 1,000 feet wide and are present at T52N, R72W, Sections 27, 28 & 29. In addition, small north-south striking anticline and syncline structures in the coal strata were described in the Buckskin pennit (Buckskin Hydrology, 1998). Due to differential compaction the coal seams appear to "ramp up" on the no coal or thin coal deposition areas. Also, the no coal and thin coal sediments are less penneable than the adjacent coal seams causing aberrations in local groundwater flow. Underburden Underburden consist of thin discontinuous sandstone lenses interbedded with siltstone and claystone. The underburden has low penneability, however, where sand lenses are present, the underburden is confined and under artesian conditions away from the outcrop. Recent modeling by Powder River Coal Company for the North AntelopeIRochelle Complex Mine (1988) indicates that the underburden locally recharges the coal seam. Similar recharge may occur locally at the mines in the northern Powder River basin. Recharge Recharge to the water bearing strata in the CIA occurs primarily along upland areas where bedrock outcrops are located. Small amounts of recharge also occur along local streams and creeks .. Groundwater recharge is estimated to be as high as 4 inches per year (Rawhide Hydrology, 1998). 6.2.2 Groundwater Quality
, In the CIA, groundwater quality is primarily calcium sulfate (caSo4) type with sodium
bicarbonate (NaHC0 3) type present locally. Total dissolved solids (TDS) levels are generally high throughout the area, but tend to be higher where CaS04 type groundwater is encountered. The caSo4 type water is likely due to the widespread occurrence of gypsum and other sulfate minerals in: the Wasatch and Fort Union Fonnations. Shallow groundwater quality is marginal to poor with respect to recommended water quality standards for human and animal consumption. In addition, the water quality is marginal for agricultural use for sulfate and total dissolved solids recommended standards. The pH for local groundwater in alluvium, clinker, overburden, interburden and underburden is considered,normal, ranging from 6.2 to 8.9. ~e pH for
Cwnulative Hydrologic Impact Assessment (CffiA) Eagle Butte Mine, Pennit 428-T'f-AI, Change No. J
groundwater in coal ranges from 7.4 to 11.8 and was the only water to have a pH outside the range for all other strata. Groundwater quality is discussed in greater detail below for each mine in the CIA. The following summaries are based on infonnation in the hydrology sections of the Eagle Butte, Buckskin, and Rawhide Mine Permits. AJluvium and Clinker - Groundwater in alluvium is consistently a magnesium sulfate (MgS04) type with relatively high concentrations of calcium and high TOS. TOS concentrations were reported in the permits and annual reports for Eagle Butte (489 to 11,543 mgll), Buckskin (7,234 to 10,111 mg/l) and Rawhide (1,284 to 22,900 mgll) Mines. The alluvium is unconfined and the . saturated thickness varies seasonally. In general, TOS concentrations increase with distance from the coal outcrop. High TOS and sulfate concentrations limit the use of alluvial groundwater to irrigation of salt tolerant crops and possibly livestock. Groundwater in the clinker is consistently a calcium sulfate (caSo4) type and is generally suitable for irrigation of salt tolerant crops. TOS concentrations were reported in the permits and annual reports for Buckskin (3,036 to 3,546 mgll) and Rawhide (1,300 to 8,420 mg/l) , Mines. Overburden Overburden groundwater quality varies and is dominated by calcium. magnesium and sodium sulfate «CaMgNa)S04) and is generally suitable for livestock and irrigation of salt tolerant crops. IDS concentrations range from each mine as reported in the permits and annual reports: Eagle Butte (645 to 4,834 mgll); Buckskin (538 to 2,926 mgll); and Rawhide (900 to 9,530 mgll). No seasonal or long term trends have been identified in the overburden groundwater quality. Coal Coal groundwater quality is highly variable from calcium, magnesium and sodium sulfate «CaMgNa)S04) type to sodium bicarbonate (NaHCO) type. Groundwater varied only slightly between the Anderson and Canyon coal seams. TOS concentrations range from each mine as reported in the permits and annual reports: Eagle Butte (763 to 3,016 mgll); Buckskin (469 to 3,348 mgll); and Rawhide (352 to 6,060 mgll). No seasonal or long term trends have been identified in'theeoal groundwater quality; Interburden Interburden in the CIA is relatively thin «10 feet). Therefore. little groundwater quality information is available. The Buckskin Mine reported that based on limited sampling, interburden groundwater quality was of calcium and magnesium sulfate (CaMgS04) type and TOS concentrations range from 746 to 879 mgll. Sub-Coal Limited data is available in the mine permits regarding underburden. The Buckskin Mine reported that underburden and interburdenare similar in lithology and groundwater quality, ) both having calcium and magnesium sulfate (CaMgS0 4 type.
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Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428·T(,f.Al, Change No.1
Good quality groundwater is found below the Lebo Shale Member of the Fort Union Formation in the Tullock Member sand aquifer. This groundwater is located approximately 800 to 1,000
feet deep in the Eagle Butte Mine area. The water meets recommended drinking water standards. TDS concentrations are as high as 284 mgll. All three mines utilize the Tullock Member sand aquifer for potable water. No seasonal or long term trends have been identified in this groundwater. Spoils Limited data is available for the spoils aquifer water quality. This is primarily due to the fact that groundwater recharge to the spoils aquifer has not occurred to the degree where the mines can collect representative samples. Based on the limited sampling that has been performed, only Eagle Butte Mine provided data on spoils aquifer groundwater quality. IDS ' concentrations at the Eagle'Butte Mine range from 3,841 to 5,502 mgll. Based on laboratory , batch leach tests, these concentrations are not unexpected. Initially the IDS concentrations should be relatively high and then decrease to concentrations representative of local undisturbed strata. 6.3 Groundwater - Surface Water Interaction Prior to mining, the coal and overburden aquifers discharged groundwater to stream alluvium as well as directly to reaches of Rawhide Creek, Little Rawhide Creek, Dry, Fork Little Powder River and their tributaries. It is not clear whether these contributions supported baseflow conditions. Within the CIA, reaches of premine Rawhide Creek, Little Rawhide Creek, Dry Fork Little Powder River are intermittent except during drought years. The only perennial reach of stream in the area is due to discharge at Moyer Springs, located east and outside the CIA. No flow conditions are typical during the winter when baseflow is so low that the creeks ice over.
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7. HYDROLOGIC CONCERNS
The objective of this assessment is to determine the probable cumulative hydrologic impacts of the existing and anticipated mine operations within the delineated CIA. Impacts to the quantity and quality of surface and groundwater as well as changes to geomorphology are addressed. The following discussion in this section and the following section identifies the hydrologic concerns that are addressed in this evaluation, specific parameters analyzed, and the locations where the parameters were evaluated. 7.1 Surface Water 7.1.1 Surface Water Quantity During Mining Increase Runoff: Mine pit and ahead-of-mine dewatering may cause a short term increase in surface water quantity. This may temporarily change an ephemeral stream to an intermittent or perennial stream while the channel receives discharge from dewatering operations.
Cumulative Hydrologic bnpact Assessment (CIDA) Eagle Butte Mine, Permit 428-T~Al. Change No."
Decrease Runoff: Stream flow is temporarily diverted around active mining and reclamed .areas until postmine stream channels and topography are established. This temporary diversion changes the contributing drainage area for a stream. In addition, the impounded water may be used on-site for dust control, equipment washdown, and other activities. These activities tend to reduce runoff volumes and peak flows which may impact downstream water rights. Postmine Increase Runoff: Open pit mining operations may change runoff volumes and peakflows in the postrnine environment. Topsoil removed from native landscapes is stockpiled and later placed over mine spoils during reclamation. This disturbed topsoil lacks structure which affects infiltration rates. Ifinfiltration rates are reduced, increased runoff may occur. Changes in vegetation species may affect the amount of precipitation lost through interception and . evapotranspiration. Vegetation takes time to develop root structure. Early in the reclamation phase root structure is typically poorly developed which may· increase runoff. Decrease Runoff: Some Powder River Basin coal mines are thin overburden mines. This means there is insufficient material available to restore the landscape to approximate original contour. This results in a decrease to average slope, an increase to surface water travel time, and an increase in infiltration or decrease in runoff. Differential settling may cause closed depressions. Although these closed depressions are typically small and any decrease to the contributing drainage area would be negligible, postmine impoundments or wetlands intercept runoff. Justification to leave these features in the postmine environment is usually associated with maintaining or enhancing the postmine land use or uses. If a postmine feature does not have a premine counterpart, runoff volumes and peak flows may decrease. 7.l.2 Surface Water Quality During Mining Degrade Quality: Removing topsoil and vegetation exposes overburden which results in a potential increase in sediment production. Stormwater runoff from the disturbed areas at the mine sites may contain increased concentrations of sediments (e.g., coal fines, silt, clay, etc.) or other constituents which may degrade water quality. All surface water runoff from the site is required to pass through a sedimentation pond or alternative sediment control measure and meet specific water quality criteria prior to off-site discharge. Improve Quality: Water produced by pit and ahead-of-mine dewatering is often collected, treated, and released into native stream channels which are within or adjacent to the mine permit boundary. Surface runoff leaving areas affected by mining is treated and released after NPDES effluent standards are met. The treated water tends to be of higher quality than the premine water quality. Postmine ReClaimed postmine landscapes may affect the-sediment yield and load'dfnearby streams . Where reclaimed landscapes have a lower potential for erosion than premine landscapes the
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Cumulative Hydrologic Impact Assessment (ClllA) Eagle Butte Mine, Permit 428-TLI-AI, Change No.1.
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sediment yield and load of surrounding streams may decrease. Conversely, where reclaimed landscapes have a higher potential for erosion than premine landscapes the sediment yield and load of surrounding streams may increase. Surface water runoff from a reclaimed site is required to pass through a sedimentation pond or ASCM prior to off-site discharge. The sediment control structure may be released by the DEQ and reclaimed by the operator when surface water runoff leaving the site meets specific water quality criteria. After the reclaimed spoils aquifer resaturates and the local hydrologic balance is restored the reclaimed spoils aquifer may discharge groundwater to the local stream channels. Based on the available chemical quality data of the groundwater discharging from the spoils aquifer surface water quality may be adversely affected at least in the short term.
If erosion on upland areas or within a reclaimed stream channel exposes mine spoils water quality may be adversely affected.
7.1.3 Geomorphic Changes During Mining All surface water leaving an active permit area must be treated before it is discharged. Streams in the arid and semi-arid west are often characterized by sediment loads. When water leaves a mine-site treatment facility, water quality is usually better than that of the receiving stream. This decreased sediment load may cause changes in the morphology of the receiving channel. Dewatering operations which directly and continuously discharge to a native stream, may also affect channel morphology. Postmine Physical changes created during reclamation may result in geomorphic instability of reclaimed drainage basins. Potential instability may be created through: (1) changes in hillslope profiles; (2) changes in stream channel profiles; (3) removal of bedrock control; and (4) changes in sediment yield and stream channel loads. These changes may also affect areas upstream and downstream from a mine permit area. 7.2 Groundwater
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7.2.1 Groundwater Elevation Changes Activities at coal mines will lower groundwater elevations. Groundwater elevations in private wells located within and adjacent to a permit boundary will be lowered by ahead-of-mine dewatering activities, pit inflow from overburden, and pit sumps dug into the underburden. Lowering groundwater elevations will decrease groundwater available to some private wells.
In many areas of the Powder River Basin, groundwater from coal seams and overburden
contribute to baseflow by discharging to creek alluvium or directly to streams. Lowering groundwater elevations may decrease the amount of groundwater available for baseflow into creeks which may affect downstream water rights. 7.2.2 Reclaimed Spoils Aquifer
Cwnulative Hydrologic Impact Assessment (CRIA) Eagle Butte Mine, Pennit 428-TltAl, Change No.1 Page 19
Moving overburden, removing coal, and backfilling excavations with spoils consisting of mixed overburden and interburden material results in a reconstructed aquifer with different physical properties than the premine aquifer. This spoils aquifer may initially have higher penneability than the prernine overburden and coal strata. Resaturation rates for spoils may be greater than that for prernine strata. However, with time, the spoils will settle and compact and the resaturation rate will decrease. ~poils aquifer ~missivity may be less than that for premine strata. This may alter the groundwater flow regime and may locally alter the location and amount of groundwater discharging to the surface. Rahn (1976) and Van Voast (1976) perfonned studies indicating the horizontal penneability of dragline replaced spoils was greater than prernine coal or overburden horizontal penneability. 7.2.3 Groundwater Ouality Groundwater flowing through a reclaimed spoils aquifer may become more mineralized because more mineral surfaces are exposed for chemical reaction in the spoils than in the undisturbed premine strata. This increase in mineralization may affect pH and cause an increase in total dissolved solids and other constituents in groundwater. Changes to groundwater quality may affect water rights and, if the groundwater discharging as stream baseflow is of poor quality, the use of the downstream surface water may be affected. Van Voast (1976) found that the first groundwater to enter a spoils aquifer dissolves a high percentage of the available salts. However, subsequent groundwater is less mineralized. This subsequent, less mineralized water probably results from the clay content of the spoils causing reduction and cation exchange. Studies in the Powder River Basin indicate that spoils water quality is similar to premine overburden water quality (Van Voast and Hedges, 1975; Davis, et. al., 1978).
8. MATERIAL DAMAGE CRITERIA
The objective of this section is to develop appropriate material damage criteria. Material damage occurs when estimated mining impacts are compared to threshold levels which indicate material damage to the hydrologic balance has occurred. This section will specify appropriate threshold values used to indicate when material damage to the hydrologic balance may occur. The Wyoming Environmental Quality Act requires that no surface mining be approved unless the operation is designed to prevent material damage to the hydrologic balance outside of the permit area and will not materially damage the quantity and quality of water in surface or groundwater systems that supply alluvial valley floors (Article 4, §35-11-406(n)(iii) and §35-11-406(n)(v)(B». To detennine whether a proposed operation has been designed to prevent material damage, the DEQ-LQD defines material damage to the hydrologic balance as a significant long-tenn or pennanent adverse change to the hydrologic regime (LQD Coal Rules and Regulations, Chapter I, Section 2(bd». A significant long-tenn or pennanent adverse change is defined as changes to the surface or groundwater hydrology that are inalterable conditions contrary to the Wyoming State ConStitution, or of statutes administered by the State Engineer, or water quality standards administered by the Water Quality Division (Director of the Wyoming DEQ, Dennis Hemmer, and the Wyoming State Engineer, Gordon Fassett, February 7, 1997 Memorandum).
Cwnulative Hydrologic Impact Assessment (CIllA) Eagle Butte Mine, Permit 428·~·Al, Change NoJ
Except where authorized by pennit, it is prohibited to cause, threaten, or allow discharge of any pollution into waters of the state (W.S. §35-11-301). Pollution is defined as contamination or other alteration of the physical, chemical, or biological properties of any waters of the state which creates a nuisance or renders any waters hamlful, detrimental or injurious to the public health, safety or welfare, to domestic commercial, industrial agricultural, recreational, or other legitimate beneficial uses, or to livestock, wildlife or aquatic life, or which degrades the water for its intended use, or adversely affects the environment (W.S. §35-11103(b)(i». WQ:t;> Rules and Regulations, Chapter I, classifies surface waters of the state and identifies the protection required for these classes . . A groundwater appropriation permit does not include the right of the appropriator to have the water level or artesian pressure maintained at any level or pressure higher than that required for maximum beneficial use of the water in the source of the supply (W.S. §41-3-933). Additionally, the State of Wyoming has agreed to several river compacts that address the allocation of surface water flows out of Wyoming (W.S. §41-12101, -201, -301, -401, -SOl, -601, and -701). 8.1 Surface Water 8.1.1 Physical Changes to Surface Water Cumulative effects on downstream surface water rights and the change to the surface water flow patterns are examined to detennine if sediment loading has increased and surface water availability has decreased to the extent that downstream surface water rights are materially affected. Assessing material damage depends on the proximity of downstream water rights, extent of dewatering, and changes to postmine drainage basins. 8.1.2 Changes to Surface Water Quality Cumulative effects on surface water quality are evaluated using available baseline data and applicable WQD Rules and Regulations. WQD has classified surface waters according to their use or potential use. Material damage is assessed by comparing the available surface water quality baseline data, concentration limits identified for surface water classification, current or potential future use of the water, and predicted postmine water quality. 8.1.3 Geomorphic Changes in the CIA Drainage Basin Reclamation plans identify postmine topography within each mine pennit boundary. Postmine channel design and topography should result in streamflow and sediment loading similar to baseline conditions. Material damage is assessed by reviewing the reclamation plan to determine channel stability and estimate sediment load from the reclaimed surface. 8.2 Groundwater 8.2.1 Aquifer-Head Drawdowns Locally, overburden, interburden and underburden produce limited quantities of groundwater. Typically, the areal extent of drawdown in the overburden, interburden and underburden is limited and mitigative measures are rarely necessary. Maximum drawdowns in the coal seams usually
Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-T~-Al, Change No.1 Page 21
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occur several miles from the mine pennit boundaries. Coal is not present east of these mines, therefore, groundwater drawdown in the coal cannot occur to the east. The material damage assessment depends on the lateral extent of the maximum drawdown, the predicted postmine potentiometric surface in each aquifer, and the effects on nearby groundwater wells. 8.2.2 Physical Changes in the Reclaimed Spoils
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In order to assess how physical changes in spoils will affect resaturation and groundwater flow, it
is generally necessary to review local conditions. Local conditions are usually identified in the potential hydrologic consequences portion of the permit or permit application. Altered flow regimes at adjacent mines may be cumulative. Therefore, hydraulic heads in spoils aquifers should be viewed on a regional scale to detennine if lower heads in the spoils aquifers affect the availability of water to private wells. Material damage is assessed by reviewing the predicted postmine potentiometric surface in each aquifer and the postmine flow regimes.
8.2.3 Changes to Groundwater Quality Groundwater which resatui-ates spoils may become more mineralized than groundwater in undisturbed overburden or underburden. The groundwater in resaturated spoils may impact groundwater quality in adjacent aquifers or affect the quality of stream baseflow. If mining impairs water quality, water uses may be affected and may be so severe as to prohibit the intended use of the water. Cumulative effects of spoils groundwater from the mines in the CIA will be determined and the identification of material damage will be based on the available baseline data. Constituents of concern, in whole or in part, that are used to assess mining impacts on groundwater are presented in Table 6-2. Effects of spoils groundwater on stream flow and stream water quality is discussed in Section 7.1.
9. ANALYSIS OF CUMULATIVE HYDROLOGIC IMPACTS
The Rawhide and Little Rawhide ~e basins. UPstream from the Downstream Rawhide ~ .station near the eastern boundary of Rawhide Mine are identified as the CIA for.this CHIA. .·Rawhide and Little Rawhide Creeks are diverted around mine areas. These diversions are desW1ed to safely pass the flow of this d.ra.ina.Ite area throuldl areas affected bv m.inin.ct. This rerouting of flow will cause a negligible impact to the quantity of surface water flowing through the CIA. 9.1.'1 Physical Changes to Surface Water Surface water runoff is affected by climate, geology, topography, soil characteristics, vegetation, and land use. Mining affeCts geology, topography, soil characteristics and vegetation. Generally, postmine land use will be similar to premine land use. 9.1.1.1 During Mining
Cwnulative Hydrologic Impact Assessment (CHJA) Eagle Butte Mine, Permit 428-Tij-A I, Change No.1 .
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At an active mine, surface water flow paths are disrupted when soil, sediment, and bedrock are removed. Runoff upstream from the mine is nonnally routed around disturbed areas and returned to the stream channel at a downstream location. In cases where the upstream drainage area is small, the runoff may be captured in upslope ponds and left to evaporate or be utilized by livestock and wildlife. Runoff from disturbed lands must pass through a treatment facility. If the treatment facility is a detention pond, the water is either discharged after meeting effluent quality standards or is utilized on-site for dust control, equipment washdown, and other activities. Mining affects streamflow in the following manner: 1. Total runoff volume for a given event should remain approximately the same due to the release of water from treatment ponds after effluent quality standards are met. The quantity of water used by mines from treatment ponds is approximately offset by the quantity of water produced through dewatering operations; and, 2. Peaktlow for a given event is attenuated due to interception and subsequent release by treatment ponds. Due to the above operating procedures, high climatic variability and limited amount of available premine data, the potential for detecting physical changes to surface water due to mining is low. 9.1.1.2 Postmine
Mining affects geology, topography, soil characteristics, and vegetation. Topsoil replaced during reclamation lacks soil structure. Infiltration rates for disturbed topsoil are lower than infiltration rates for undisturbed topsoil. This results in a potential increase in runoff. As root and soil structure develop over time, infiltration rates will increase, resulting in decreased runoff. Hutten and Gifford (1984) perfonned a series of rainfall-simulator tests to compare changes in infiltration rates with time for native and reclaimed soils. The results indicated with time, infiltration rates for reclaimed soils approach those for some native soils (Table 8-1). Schafer and others (1979) concluded there were no differences between infiltration rates in reclaimed and natural soils. The Eagle Butte Mine is considered a thin overburden mine, whereas the Buckskin and Rawhide Mines are considered thick overburden mines. A thin overburden mine has a small overburden to removed coal ratio resulting in insufficient material to reclaim the mined areas. A thick overburden mine has a sufficient overburden to removed coal ratio resulting in sufficient material to reclaim the mined areas. Reconstructed topography at the Eagle Butte Mine will have a decreased average slope and an overall reduction in the elevation of the surface. The lowered reclaimed surface elevation will result in an environment where the postmine water table elevation will be greater than the postmine topographic surface, resulting in a potential marsh-like environment. This postmine water table above the actual ground surface elevation may pose a potential problem for the planned land use in the
Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-T~-Al, Change No. /
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postmineenviromnent. To handle this potential problem the Eagle Butte Mine has designed the postmine topography to drain available water. This plan involves increasing the drainage density allowing for more surficial points for drainage to occur. After the postmine water table recovers, the majority of the main stem of Little Rawhide and Rawhide Creeks will be above the postmine water table except where spring-fed tributaries converge. The Bucksin and Rawhide Mines are thick overburden mines and have sufficient overburden to reclaim to approximate original contour. The postmine water table at the Buckskin and Rawhide Mines is expected to be below the postmine topographic surface.
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Table 8-1 Summary of Rainfall-Simulator Infiltration Tests
Reclaimed Soil InfilI. Rate (inlhr) Plots (number)
Natural Soil InfilI. Rate (inlhr) Plots· (number)
1979 1979 1979 1981 1981 1981 1983 1983 1983 1984
Heavy Medium Light Heavy Medium Light Heavy Medium Light Lumped results
0.6 1.9 2.1 1.8 2:7 2.3 2.6 3.5 3.8 1.66
10 10 10 10 10 10 10 10 10 30
0.7 0.6 0.3 1.4 1.5 1.8 2.8 2.4 2.8 1.52
10 10 10 10 10 30
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Testing completed at the Belle Ayr Mine, Gillette, WY From Hutten and Gifford (1984)
During the initial stages of reclamation, vegetation cover will be inferior to premine vegetation cover. Final cover and vegetation cover for each vegetation community type ~ust be equal to or exceed premine conditions to obtain fina1 bond release. In many mining affected areas, the premine landscape was characterized by a dense cover of large shrubs. There is no requirement concerning shrub size, however, the postmine enviromnent must contain the required density of shrubs. . A postmine landscape may appear dominated by grasses. Nevertheless, during their maximum growth, grasses have the potential to intercept as much precipitation as trees (Dunne and Leopold, 1978). Based on the above, interception losses at the time of final bond release are predicted to be similar to premine interception.losses.
Cumulative Hydrologic Impact Assessment (CHJA) Eagle Butte Mine, Permit 428-~AI, Change No. ,.
Based on the qualitative analysis discussed above~ runoff at the end of the bond release period or shortly thereafter is expected to be equal to or slightly less than premine runoff. Due to the subdued postmine topography, postmine peakflows, are expected to be slightly lower than premine peakflows. The CIA is subject to a precipitation regime that is characterized by local and intense thunderstontlS. This precipitation regime, along with natural climate fluctuation, makes it difficult to validate these conclusions using quantitative techniques. Little Rawhide Creek The alluvial valley floor (AVF) assessment for the Eagle Butte permit area identified approximately 133 acres of alluvial valley floor within the Little Rawhide Creek drainage basin. Sub-irrigation of the valley floor within the Eagle Butte permit area was maintained by contributions from the alluvial aquifer. Sub-irrigation at the Eagle Butte Mine will be restored by replacing the essential hydrologic functions of the AVF (Eagle Butte, Appendix 4.6-2, 1996). . Along Rawhide Creek, through the Buckskin and Rawhide permit areas, an additional 94 acres of A VF exists. Mines are required to re-establish the essential hydrologic function of . AVFs. Without restoring the groundwater regime the. function of the AVFs will be difficult to re-establish. To achieve this the mines all have siMilar plans that require the use of subsurface materials to function as a groundwater storage mechanism, the design of channels to maintain flow without loss to the spoils aquifer, and use the design of the channel itself to conserve water for sub-irrigation.
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Some changes in vegetation type are likely along Rawhide Creek and Little Rawhide Creek channels. Changes in the hydrologic regime will have a limited affect on the designated AVF. Natural flood irrigation will be similar to the premine environment. Sub-irrigation will be limited in extent. These limitations are governed by the amount of runoff that can be stored in Little Rawhide and Rawhide Creeks' alluvium and time it remains stored before it is lost through leakage or evapotranspiration. 9.1.2 Changes to Surface Water Quality 9.1.2.1 During Mining At an active mine, runoff from undisturbed land is normally diverted around the inining operations. These diversions are designed to be erosionally stable and should result in nondetectable changes in sediment load. All runoff from disturbed lands arid process water are treated by some type of facility which range from simple alternate sediment control measures (ASCMs) (e.g., rock check dams) to treatment ponds. To date, surface water quality samples collected and analyzed indicate the quality of water leaving the permit area is equal to or better than the water quality measured during baseline data collection. Thus, to date, mine related impacts have had no measurable effect on surface water quality in the CIA. 9.1.2.2 Postmine
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Cwnulative Hydrologic bnpact Assessment (CHIA) Eagle Butte Mine, Permit 428-Tlf-A I, Change No.,
Postrnine surface water quality is anticipated to be similar to observed baseline data. The CIA encompasses 110 mi 2 of which 34 mi2 is the Little Rawhide Creek drainage area and 76 mi2 is Rawhide Creek drainage area. Eagle Butte Coal Mine The Eagle Butte Coal Mine permit area will encompass 6,915 acres (10.8 mi~ with 6,904 acres (10.8 mil) scheduled to be distiirl>ed by inining actiVities during the life of the mine. A simple analysis using a drainage area ratio indicates that 10 percent of Little Rawhide and Rawhide Creeks' drainage basins will be disturbed by the Eagle Butte Coal Mine. Based on the amount of acreage affected, if the mine did impact water quality in the permit area dilution from the type and size of flow from outside the permit area would mask any differences in water quality. Determining that a change in surface water quality has occurred is made more difficult given the paucity of baseline data available. Rawhide The Rawhide Mine encompasses approximately 8,874 acres (13.9 mi 2) with 7,295 acres (13.4 mi 2) scheduled to be disturbed by mining activities during the life of the mine. Approximately 1,210 acres (l.9 mi2) of the Rawhide permit area is within the Dry Fork Little Powder River drainage basin leaving 6,085 affected acres (9.5 mi~ in the CIA. A drainage area ratio analysis indicates that approximately 9 percent of Little Rawhide and Rawhide Creeks' drainage basins will be affected by mining activity at the Rawhide Mine. Again, the limited acreage suggests that the ability to detect differences in water quality due to mine related activities is low. Buckskin The Buckskin Mine permit area is 5,446 acres (8.5 mi2) with 3,789 acres (5.9 mi2) scheduled to be disturbed by mining activities during the life of the mine. Analysis of the drainage area indicates 5 percent of Little Rawhide and Rawhide Creeks' drainage basins will be affected by mining activity at the Buckskin site. Any impact to the water quality at this site will not be easily detected given baseline infonnation and water control measures within the mine site. At present, none of the mines within the CIA have reclaimed an entire drainage basin area and gaged it to provide quantitative answers to questions concernirig potential water ·quality impacts. Thus, a prediction concerning postrnine water quality must be based on a qualitative analysis. Prior to placing topsoil, all mines have committed to cover unsuitable spoil with a minimum of 4 feet of suitable material. During early stages of reclamation, infiltration rates are lower than those observed in undisturbed native areas, but will approach undisturbed infiltration rates with time (Rahn, 1976). Final bond release requires the postrnine reclaimed final cover and vegetation cover to meet or exceed premine conditions. If postmine vegetation cover and total cover meet the requirements, it is assumed that interception losses and protection of the soil surface will closely resemble premine conditions.
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Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-T'l-AI, Change No.1
Toy (1989) perfonned a study at the Dave Johnston Mine near Glenrock, WY concerning sheetwash erosion of natural and reclaimed slopes. The study concluded that within the accuracy of the techniques used, the difference in sheet erosion at reclaimed and natural slopes was virtually non-detectable. Big Hom Coal Company near Sheridan, Wyoming perfonned a series of plot studies on reclaimed and native lands from 1982 to 1996. Based on these studies, Big Hom Coal (1997) concluded that sediment yield from reclaimed lands is less than that from native lands. Reclaimed,hillslopes at the mines in the CIA tend to have either a concave up profile or a mixture of concave up and concave down profiles, which should result in less sediment transport to stream channels. The average postmine slope for each of the three mines is less than the average premine slope. Also, the number of postmine slopes having a gradient of 2 percent or less is greater than the number of prernine slopes with a gradient of 2 percent or less. Reclaimed stream channels are designed with gradients generally less than or equal to native, undisturbed gradients. Reclaimed channel beds are wider than their premine counterparts which provides greater retardance and lower flow velocities.
In conclusion, prior to placing topsoil, unsuitable cover material will be buried by a
minimum of 4 feet of suitable material, resulting in a low p~tential for migration of constituents of concern. Reclamation designs, regulatory constraints, and observations to date indicate that sediment yield will be less than or equal to premine levels. Therefore, postmine surface water quality is expected to meet or exceed premine surface water quality class-of-use standards. 9.1.3 Geomomhic Changes in the CIA Drainage Basin The Eagle Butte Mine is a thin overburden mine. Buckskin and Rawhide Mines are thick overburden mines. A thin overburden mine has insufficient material available to restore the landscape to approximate original contour, whereas thick overburden mines can restore to approximate original contour. Reclaimed mine landscapes are more subdued than premine landscapes, with Eagle Butte being more subdued than Buckskin and Rawhide due to the volume of overburden available. Compared to the premine landscape, the average reclaimed hillslope gradient will decrease and the percentage of slopes between 0 and 2 percent will increase. Hillslopes will generally be reconstructed with a concave up profile. However, some areas will be reconstructed with a mixture of concave up and concave down profiles. Reconstructed landscapes incorporate geomorphic and engineering principles. Longitudinal profiles of hills lopes are generally concave. In areas where concave profiles are not possible, erosion control measures will be utilized to limit potential stability problems. Channels are constructed with gradients at or less than those measured in the natural environment. Crosssectional geometry is designed using vegetative retardance methodology. Transitions between native and reclaimed drainages have been designed to minimize the angle of confluence. Some adjustments within the reconstructed channels are expected. However, based on the above analysis, reconstructed channels characterized by shallow gradients and wide bottoms should be relatively stable.
Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-T~-A I, Change No.'
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9.2 Groundwater Analysis of the cumulative impacts on groundwater as a result of mining at the Eagle Butte, Buckskin and Rawhide Mines was performed by qualitatively assessing the additive impacts of the mines. Mines usually model groundwater drawdown using the conservative, worst case scenario. Therefore, it is likely that the actual drawdown will not extend as far from the mine permit boundaries as predicted. The groundwater system is expected to fully stabilize in several hundred years. It is difficult to place a number on the predicted time for groundwater recovery since each mine used different predictive tools and modeling techniques and reported different recovery time periods. This issue is discussed in greater detail below. 9.2.1 Cumulative Aquifer-Head Drawdowns Impacts to the local aquifers will occur as groundwater levels are drawn down, temporarily decreasing the quantity of groundwater available. Each mine evaluated or modeled impacts to each affected aquifer based on site specific characteristics such as hydraulic conductivity, mining sequence, local geology, etc. The predicted drawdown from each mine was combined additively to determine the cumulative drawdown. Using the mines' predictions and combining the drawdowos' is more reasonable than trying to simplify the drawdowns by assuming simultaneous mining, similar hydraulic conductivity, simplify geology, and other simplifications. In general, drawdown, in water levels in both the coal and overburden will be greatest adjacent to the pit area and decrease with distance away from the mine. Coal Seams Cumulative effects of mining on the coal seams are presented in Figure 9-1. For purposes of predicting cumulative drawdown, the Anderson and Canyon coal seams are considered to be a single unit. ' The 5 foot cumulative groundwater drawdown contour is predicted to occur up to approximately 13 miles from mine permit boundaries. The maximum extent of the 5 foot drawdown contour was reported in the respective mine plans as follows: Eagle Butte (10 miles west and 7 miles south); Buckskin (10 to 11 miles west); and Rawhide (4 to 5 miles south and west). Where coal is mined, the excavation will be backfilled with spoils creating a spoils aquifer. Each mine modeled groundwater recovery and reported the following predictions in their respective mine plans: Eagle Butte (100% reCovery in 650 years); Buckskin (80% recovery by 300 years and full recovery in 1,500 to 2,000); and Rawhide (50% recovery in 200 to 300 years and 100% recovery in 800 to 1,000 years). , Overburden Cumulative effects of mining on the overburden appear insignificant. Sandstone units are thin, discontinuous and interbedded with claystone and siltstone, all of which limit the extent of groundwater impacts in the overburden. Eagle Butte reported that the 5 foot groundwater drawdown contour in the overburden would be located approximately 2,600 feet from the highwaIl cuts (Eagle Butte Mine Plan, 1998). Mining and subsequent reclamation will cause the overburden to be in direct contact with the spoils aquifer. This will hydraulically connect the units and allow groundwater to flow from
Cwnulative Hydrologic Impact Assessment (CIllA) Eagle Butte Mine, Permit 428-T~AI. Change No.1
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one unit to the other depending on the gradient. As a result, the overburden will lose groundwater to the spoils aquifer while the spoils aquifer resaturates. Once the spoils aquifer resaturates, the overburden can resaturate. Due to this relationship, the overburden is expected to recover to premine water levels in a similar time frame as discussed above in the coal section; although Eagle Butte reported that the overburden will recover in less than 5 years.
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Interburden Cumulative effects of mining on the interburden is insignificant. The sandstone layers are thin, discontinuous and interbedded with claystone and siltstone, thereby limiting the extent of groundwater impacts in the interburden away from the mines. Underburden Underburden consists of discontinuous sandstone layers interbedded with claystone and siltstone. In general, the underburden has a low hydraulic conductivity, lower than the hydraulic conductivity for the coal aquifer. Therefore,' impacts to the underburden are expected to be limited and the aerial extent of the affected area for the underburden is expected to be less than that for the coal aquifer. In the Eagle Butte Mine permit, the 5 foot drawdown contour for- the on-site wells completed in the underburden is predicted to extend approximately 1 mile radially from the wells. However, in the Rawhide Mine permit mine plan, that the 5 foot drawdown contour in the underburden is reported to extend up to approximately 13 miles west from the mine permit boundaries. This prediction conflicts with the Eagle Butte Mine prediction and with intuition. Because the physical properties of the underburden and overburden are similar, drawdown in the underburden should be similar to those predicted and observed to date in the overburden. No predictions were encountered in the Buckskin Mine permit. The mine permits did not specifically define a prediction for time for groundwater to recover in the underburden. Based on the discontinuous stratigraphy and relatively low hydraulic conductivity, the 5 foot drawdown contour is expected to affect an area less than the area affected by the coal aquifer. The WDEQ-LQD feels the Eagle Butte prediction of approximately 1 mile is more appropriate than the Rawhide prediction of 13 miles. Therefore, impacts to the underburden are expected to be local and negligible. The Tullock aquifer is located approximately 600 to 700 feet below the underburden and will not be disturbed by mining. Therefore, the Tullock aquifer is not really considered underburden. The Tullock aquifer is deep enough that mine facility wells will affect the aquifer only locally and within a 1 mile radius (Eagle Butte Mine Plan, 1998). Therefore, no cumulative impacts are expected. Alluvium Impacts to the Rawhide and Little Rawhide Creeks' alluvium are expected to be minimal, Surface flow will begin to recharge the alluvium shortly after reclamation activities are completed. Where the alluvial systems are reconstructed, the alluvium is expected to recover shortly after the surface flow is restored. At the Eagle Butte Mine sand from the Wasatch sand bodies is being used to reconstructed alluvial systems which are expected to have hydrologic properties similar to the premining systems. Clinker
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ClDDulative Hydrologic bnpact Assessment (CHIA) Eagle Butte Mine, Permit 428-T'l-AI. Change No.1
Economic deposits of coal are usually located west of the clinker. Therefore, disturbance of the clinker will be avoided at all of the ntines. In addition, the clinker has very high hydraulic conductivity and, if disturbed, may present a significant water problem to a mine. Therefore, impacts to springs and alluvial water tables will be slight or non-existent. Any impacts that may occur due to mine site dewatering will be limited to the respective mine sites and no offsite impacts are expected. . 9.2.2 Physical Changes in Reclaimed Spoils The spoils aquifer will likely have a hydraulic conductivity greater than the overburden and less than the fractured coal. The spoils aquifer will be a groundwater sink while the spoils aquifer resaturates. Once the groundwater elevations in the spoils, overburden, and coal aquifers reach steady state, groundwater will move through the system in a manner similar to the premine environment. All three mines in the CIA utilize truck and shovel operations. Once groundwater elevations recover, alluvium will receive discharge from the reclaimed spoils groundwater system. Based on available aquifer tests results on spoils wells within the CIA, the hydraulic conductivity of the spoils is similar to but greater than the hydraulic conductivity of the overburden. With time, the spoils will resaturate, settle and compact, and their hydraulic conductivity will decrease and should approach premine values (Eagle Butte Mine Plan, 1998). 9.2.3 Changes to Groundwater Oualitv Studies in the Powder River Basin indicate postmine groundwater quality in spoils aquifers is similar to premine groundwater quality in overburden (Van Yoast and Hedges, 1975; Davis, et. al., 1978). Column leach tests performed on spoils indicate various chemical species will increase up to 3 times the pre-disturbance concentrations. In particular, sodium, magnesium, calcium, sulfate, bicarbonate and TDS all tend to increase. However, after only 2 pore volumes of groundwater pass through the spoils materials, the chemical species decrease. And as more pore water passes through the sediments the chemical species continue to decrease and begin to approach pre-disturbance concentrations (Eagle Butte Mine Plan, 1998). Limited analytical results from spoils aquifer water quality testing is available for the mines in the CIA. Current spoils aquifer wells completed in the CIA have had little time to recover and therefore have litdeto nOgToundWater monitor. Based on data reported in the North AntelopelRochelle Complex Mine (North AntelopeIRochelle Complex Mine Hydrology, 1998), using spoils well SP-I-NA as an example, initial water was dominated by calcium and sulfate with TDS concentrations slightly greater than 4,000 mgll. Over time, groundwater elevations have increased and TDS concentrations have steadily decreased to below 2500 mgll. Trace metal concentrations have remained at or below detection limits for all spoils wells. Based on column leach tests and actua!monitoring data, postmine groundwater TDS concentrations will likely average between 3,000 and 4,700 mgll, which is below the WQD groundwater standard of 5,000 mgll for livestock. Therefore~ once any transient groundwater quality changes have stabilized, postmine groundwater quality should remain similar to premine groundwater quality and suitable for livestock watering.
MATERIAL DAMAGE POTENTIAL
CllDlUlative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-T!.IAI, Change No.1 ( .
The potential for material damage was detennined for each of the above hydrologic concerns. 10.1 Surface Water 10.1.1 Physical Changes to Surface Water The potential for measurable changes in surface water quantity is low. Surface runoff within the CIA is primarily driven by snowmelt and intense rainfall events. Rainfall events which generate runoff tend to be localized and intense. There is insufficient baseline flow data to accurately characterize the native system. Therefore, any change in runoff volume caused by mining will likely be masked by natural variability in precipitation. Within areas affected by mining, topography will be lowered and hillslope gradients will be reduced resulting in a potential reduction in peakflows within Rawhide and Little Rawhide . Creek drainage basins. The impacts from increasing drainage density and lowering topography will result in an increase in surface water flow after the postmine overburden/spoils aquifer is recharged. In addition, if a surface water supply is affected by surface mining, the mines are required to mitigate the impact (W.S. 35-11-415(b)(xii) and 35-11-416(b». 10.1.2 Changes to Surface Water Quality The potential for material damage to surface water quality is low for the following reasons:
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1. Replaced topsoil will cover spoils to a thickness within ±25 percent of premine
conditions. 2. All unsuitable spoils will be covered with a minimum of 4 feet of suitable material prior to replacing topsoil. The thickness may be increased to 8 feet in areas underlying reclaimed drainages. 3. Based on very limited spoils aquifer groundwater quality sampling and analysis, water quality of the partially resaturated spoils aquifer is similar to premine alluvial aquifer water quality. 4. Reconstructed landscapes at all the mines in the CIA are designed to be erosionally stable. In addition, postmine sediment loss is predicted to be lower than premine sediment loss. Thus, postmine surface water quality is expected to be similar to or better than premine surface water quality. 10.1.3 Geomorphic Changes in the Cumulative Impact Area Drainage Basin Mining at the Eagle Butte, Rawhide, and Buckskin Coal Mines will disturb approximately 17,520 acres (27 mi2), or approximately 25 percent (27 of II 0 mi~ of the CIA. Sediment loading rates on streams may be affected by changes to premine drainage basin slopes, hillslope profiles, and vegetation cover. Any impacts due to geomorphic changes are expected to be negligible. Therefore, the potential for material damage due to geomorphic changes is low.
Cwnulative Hydrologic Impact Assessment (CHIA)
Eagle Butte Mine. Permit 428-T~A 1. Change No.1 Page 31
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10.2 . Groundwater 10.2.1 Cumulative Aquifer-Head Drawdowns For potentially affected aquifers, each mine quantitatively detennined the maximum extent of groundwater drawdown. These predicted potentiometric surfaces were evaluated in addition to the cumulative drawdown in these aquifers. The maximum extent of the 5 foot drawdown coritour in the coal aquifer is expected to occur up to approximately 13 miles from the mine permit boundaries. The Anderson and Canyon coal aquifers are not present east of the mines due to erosion. In addition, few wells are completed in the coal seam west of the mines in the CIA because the coal dips to the west which results in increasing depth to coal toward the west. As a result, most wells west of the mines are cOmpleted in overburden. The cumulative drawdown in the overburden is predicted to extend less than 1 mile from the mine permit. boundaries. Therefore, few groundwater wells will be affected by cumulative aquifer head drawdown. If a groundwater supply is affected by surface mining, the mines are required to mitigate the impact (W.S. 35-11-415(b)(xii) and 35-11-416(b».
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Physical Changes in the Reclaimed Spoils Spoils aquifers will be groundwater sinks until they have resaturated. Once the spoils and overburden resaturate, groundwater flow will approximate premine groundwater flow conditions. With time, soil and root structure will develop and ~e infiltration rate into spoils may increase, thereby, decreasing runoff and possibly decreasing surface flow to streams. However, ifpostrnine infiltration into the spoils is greater than premine conditions, the spoils will likely saturate more quickly and groundwater discharge to the creeks will occur earlier than predicted. Aquifer tests performed in the reclaimed spoils has provided information on the hydraulic conductivity of the spoils shortly after reclamation. The hydraulic conductivity of the spoils at Eagle Butte was reported to be greater than but similar to the hydraulic conductivity of the premine overburden. With time, the· spoils will resaturate and compact and the hydraulic conductivity will decrease and become closer to premine conditions.
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Changes to Groundwater Qualitv The predicted postrnine groundwater quality was examined for effects on surrounding aquifer quality and surface water quality. Initially, IDS concentrations may increase. However, with time the IDS concentrations will decrease and approach premine groundwater quality. Even with the changes in IDS and other constituents, groundwater quality in most instances has the same use classification as the premine groundwater. for the affected aquifers, premine groundwater quality was classified as suitable for livestock or lower. In some instances, the alluvial water is lower qualitY. Spoils groundwater quality is similar to alluvial ~ter quality. Studies per:£ormed at other min~ the Powder River Basin
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Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit 428-Tt.f.Al, Change No.t',
similar results. The potential for the mines in the CIA to have a cumulative impact on groundwater quality is low.
pr~uced
MATERIAL DAMAGE STATEMENTS OF FINDINGS
Physical Changes to Surface Water Projected postmine runoff volumes for the base of the CIA at the Downstream Rawhide gaging station are expected to be nearly identical to premine runoff volumes. Baseflow measured at this station may decrease slightly due to alluvial aquifer losses while the spoils aquifer resaturates. Measurable changes in peakflow magnitudes are not expected. There have been . surface water rights identified on Rawhide Creek downstream of the Downstream Rawhide gaging station near the Eastern boundary of the Buckskin Mine. The first water right encountered downstream from the gaging station is located on Rawhide Creek above its confluence with Little Powder River. Due to the small area of the mines compared to the drainage as a whole, no impacts to surface water rights are expected downstream from the CIA.
Changes to Surface Water Quality Postmine surface water quality is expected to be similar to premine water quality. In addition, class-of-use standards are not expected to change. Based on Wyoming DEQ, WQD Chapter 'VIll quality criteria for groundwater, premine surface water quality is suitable for livestock watering. High concentrations of sulfates and IDS prevented the surface water from being suitable for agriculture (irrigation) with the exception of salt tolerant crops.
Geomorphic Changes in CIA Drainage Basins Postmine topography will be more subdued than premine topography. Eagle Butte's postmine topography will be most noticeably subdued. Buckskin and Rawhide will be r~laimed to approximate original contour. Reclaimed hills lopes are generally constructed with concave up profiles or a mixture of concave up and concave down profiles, with micro-relief and a lower average slope than their premine counterparts. Therefore, sediment loss is expected to decrease.
11.2 Groundwater 11.2.1 Cumulative Aquifer-Head Drawdowns Groundwater drawdown was modeled by the mines. The maximum extent of the 5 foot groundwater drawdown contour in the coal aquifer is expected to occur up to approximately 13 miles from the mine permit boundaries. Groundwater in the coal aquifer will recover but will take several hundred years (650 years according to the Eagle Butte Mine) after mining ceases for the postmine potentiometric surface in the coal aquifer to approximate the premine potentiometric surface. Few private wells are completed in the coal aquifer. In addition, the
Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Permit428-T~AI, Change No.1
mines are required to mitigate water rights impacted by surface coal mining. The coal aquifer will be affected by mining, however, with time, the aquifer will recover. As a result, material damage is not expected. Pre- and postmine potentiometric surfaces for the overburden, interburden, and underburden will be similar. The maximum extent of the 5 foot groundwater drawdown contours in the overburden, interburden and underburden is expected to occur approxnnaiely 1 mile fromthe mine permit boundaries. Mining and subsequent backfilling Will hydraulically connect the coal, overburden, interburden and underburden with the spoils aquifer. As a result, recovery of the potentiometric surfaces for these units depends on the resaturation of the spoils aquifer. As the spoils aquifer resaturates so will the coal, underburden, interburden and overburden. The time for groundwater elevations to recover in these units should be similar to the coal aquifer recovery, several hundred years. The area affected by groundwater drawdown in the overburden and interburden is relatively small and few private wells are present. The area affected by groundwater drawdown in the underburden is relatively deep and few private wells present. Impacts to the overburden, interburden and underburden are not permanent and material damage is not expected.
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Coal bed methane development is presently a booming industry in the Powder River Basin proximate to the coal mines. Coal bed methane generation generally ,consists of pumping groundwater from the coal aquifer to lower the potentiometric head, which reduces the confining pressure on the methane in the coal and allows the methane to volatilize and collected at wells. In the process, vast amounts of groundwater are removed from the coal aquifer" structurally down dip from the coal mines. At the time of this report, most coal bed methane development has occurred in the northern and central portions of the Powder River Basin. The nearest coal bed methane development to the mines in this CIA is approximately 1.5 miles west. .Coal bed methane development in the Powder River Basin is expected to grow substantially during the next decade. Groundwater drawdown caused by coal bed methane projects may impact the coal mines in the next severalyears. Impacts to the groundwater system Caused by coal bed methane has the potential to exceed impacts from the surface coal mmes. 11.2.2 Physical Changes in the Reclaimed Spoils Reclaiming pits with spoils results in a reconstructed aquifer with physical properties different than the pre~ne aquifer. The hydraulic conductivity of the spoils aquifer will be transient. The initial hydraulic conductivity will be high during spoils placement and resaturat~on rates for spoils may be greater than that for premine strata. However, with time the spoils aquifer will compact and the final hydraulic conductivity will decrease and approach the hydraulic conductivity of the surrounding undisturbed materials. Until the spoils aquifers resaturate, the spoils will be temporary groundwater sinks. However, the postmine groundwater flow patterns will be approximately equal to premine flow patterns including groundwater discharge to the surface. Physical changes to the aquifers by spoils placement are expected to be insignificant and material damage is not anticipated. 11.2.3 Changes to Groundwater Quality
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Cumulative Hydrologic Impact Assessment (CRIA) Eagle Butte Mine, peririit 428-T~ AI, Change No.1.'
Studies on reclaimed spoils in the Powder River Basin indicate that postmine groundwater quality in spoils aquifers will approximate premine groundwater quality (Van Voast and HedgeS, 1975; Davis, et. al., 1978). Premine groundwater quality in all aquifers varied but in most instances, was suitable for livestock watering or lower quality. Available infonnation indicates postmine groundwater quality will also vary but will likely meet livestock or lower . quality criteria similar to premine groundwater quality. Transient impacts to groundwater quality are expected, such as an initial increase in IDS followed by a steady decrease approaching premine concentrations. Pennanent adverse impacts to groundwater quality are expected to be minimal and material damage is not anticipated. 11.3 Determination of Material Damage Based on existing available infonnation, the Department has detennined that surface coal mining operations at the Eagle Butte, Buckskin, and Rawhide Coal Mines will impact the environment locally and for a limited time .. However, no pennanent adverse impacts to the hydrologic system are and material damage to surface and groundwater quality and quantity is not expected to the 'P'i.u",'!>e basin as a Ie.
7- 3(- 00
e sHemmer irector, Wyoming D Date
Richard Stockdale Interim Wyoming State Engineer .
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Cumulative Hydrologic Impact Assessment (ClUA) Eagle Butte Mine, Permit 42S-T'I·Al, Change No.1·
This section is not included in OSM's 1985 guidelines for preparing a CHIA. However, data gaps and other issues were identified during this evaluation which may affect the next CHIA for this area. It is the Department's goal to build on this report and improve the next CHIA prepared by the LQD for this area, as well as improve future renewal applications and Probable Hydrologic Consequences (pHC) evaluations submitted by the mines. The following list describes the data gaps or other issues identified during this evaluation and the Department's recommendation for addressing the issues: 1. Potential impacts. from coal bed methane development need to be addressed. This cumulative hydrologic impact assessment is strictly an evaluation of the potential impacts from coal mining. No attempt was made to evaluate potential coal bed methane impacts. Coal bed methane development is booming in the Powder River Basin immediately west of the coal mines. Coal bed methane development in the Powder River Basin is expected go grow substantially during the next decade. In some areas, groundwater drawdown caused by coal bed methane development has impacted groundwater elevations at coal mines. In other areas, impacts may occur within the next several years. Impacts of coal bed methane development to the surface and groundwater systems have the potential to exceed impacts from the surface coal mines. 2. LQD should perform a more quantitative evaluation for the next CHIA for this area. This report was written using a more qualitative approach to evaluate potential impacts due to mining on the hydrologic system. This report may be utilized during the next evaluation and may be built on using quantitative techniques to evaluate potential impacts.
Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-T'i AI, Change No.' Page 36
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Big Hom Coal Company, 1997, LQD Pennit No. 213-T4, 1997 Annual Report.
• Bureau of Land Management, 1994. Final, Eagle Buttes Environmental Assessment, Casper District Office. Coates, D.A., and Naeser, C.W., 1984, Map Showing Fission-Track Ages of Clinker in the Rochelle Hills, southern Campbell Count and Weston County, Wyoming; U.S. Geological Survey Miscellaneous Investigations, Map 1-1462.
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Davis, RW., Hasfurther, V., and Rechard, P.A., 1978, Shallow Groundwater Distribution and Movement as Influenced by Surface Coal Mining in the Eastern Powder River Basin, Wyoming; Water Resources Series No. 77, Water Resources Research Institute, University of Wyoming, Laramie, Wyoming. Denson, N.M., Macke, D.L., and Schumann, R.R., 1989, Geologic Map and Distribution of Heavy Minerals in Tertiary Rocks of Reno Junction 30'x60' Quadrangle, Campbell and Weston Counties, Wyoming; U.S. Geological Survey Miscellaneous Investigations Series, Map 1-2025. Dunne, T. and Leopold, L., 1978, Water in Environmental Planning; W.H. Freeman and Company, San Francisco, CA. Flores, .R.M., 1986, Evolution of Thick Coal Deposits in the Powder River Basin, Montana and Wyoming; In Lyons, P.S., and Rice, C.L., editors, Paleoenvironmental and Tectonic Controls Coal-Fonning Basins in the United States, Geological Society of America, Special Paper, no. 21, pp. 79-104. Fogg, J.L., Martin, M.W., and Daddow, P.B., 1991, Geohydrology and Potential Effects of Coal Mining in 12 Coal-Lease Areas, Powder River Structural Basin, Northeastern Wyoming; U.S. Geological Survey Water Resources Investigations, WRI-87-4102. Glass, G.B., and Jones, RW., 1991, Coal Fields and Coal Beds of Wyoming; Wyoming Geological Association Guidebook, 42nd Annual Field Conference, pp. 133-167. Hadley, RF., and Schumm, S.A., 1961, Sediment Sources and Drainage Basin Characteristics in Upper Cheyenne River Basin; In Hydrology of the Upper Cheyenne River Basin, U.S. Geological Survey Water Supply Paper 1531. Heffern, E.L., and Coates, D.A., 1996, Clinker: its Occurrence, Uses, and Effects on Coal Mining in the Powder River Basin; In Proceedings of the 32nd Annual Forum on the Geology of Industrial Minerals, May 1996. Heffern, E.L., and Coates, D.A., Peacock, K.T., Ogle, K.M., and Oakleaf, J.R, 1996, Recharge from Clinker, Powder River Basin, Wyoming and Montana; Geological Society of America, Abstracts with Program, p. 354. Hutten, N.G. and Gifford, G.F., 1984, Survey of Interrill Erosion and Infiltration Rates on Natural and Reclaimed Lands, Gillette, WY; AMAX Coal Company Report.
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Cwnulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-T;JlA I, -Change No.1
Lowham. H.W., 1988, Streamflows in Wyoming; U.S. Geological Survey; Water-Resources Investigations
Report No. 88-4045. Martin, L.1., Naftz, D.L., Lowham, H.W., and Rankl, lG., 1988, Cumulative potential hydrologic impacts of surface coal mining in the eastern Powder River Structural Basin, northeastern Wyoming; U.S. Geological Survey Water-Resources Investigations Report 88-4046. North AntelopelRochelle Complex, 1998, LQD Permit Application No. TFN 3 6/179. Office of Surface Mining Reclamation and Enforcement, 1985, Draft, Guidelines for Preparation of a Cumulative Hydrologic bnpact Assessment (ClllA). Office of Surface Mining Reclamation and Enforcement, 1999, Managing Hydrologic Information, A Resource for Development of Probable Hydrologic Consequences (PHC) and Cumulative Hydrologic bnpact AsSessments (ClllA).
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Rahn, P.H., 1976, Potential ofCoai Strip-mine Spoils as Aquifers in the Powder River Basin; Project Completion Report prepared for the Old West Regional Commission, Proj. No. 10470025.
Schafer, W.M., Dollhopf, D.l, Nielsen, G.A., and Temple K., 1979, Soil Genesis, Hydrologic Properties, Root Characteristics and Microbial Activity of 1 to 50 Year-Old Stripmine Spoils; EPA-600/7-79-100. Schultz, Tara, City of Gillette, verbal communication, May, 2000. Seeland, D., 1992, Depositional Systems of a Synorogenic Continental Deposit-the upper Paleocene and lower Eocene Wasatch Formation of the Powder River Basin, Northeast Wyoming, U.S. Geological Survey Bulletin, no. 1917-H. Toy, T.1., 1989, An Assessment of Surface-Mine Reclamation Based Upon Sheetwash Erosion Rates at the Glenrock Coal Company, Glenrock, Wyoming; Earth Surface Processes and Landforms, Vol. 14., page 289-302. United States Geological Survey, 1998. Water Resources Data Wyoming Water Year 1998, Water Data ReportWY-98-1 and -2. Van Voast, W.A., Hedges, R.B., and McDermott, 1.1., 1976, Hydrologic Aspects of Strip Mining in the Subbituminous Coal Fields of Montana; Fourth Symposium on·Surface Mining and Reclamation, NCAlBCR Coal Conference and Expo Ill, p. 106-172. Van Voast, W.A., and Hedges, R.B., 1975, Hydrogeologic Aspects of Existing and Proposed Strip Coal Mines Near Decker, Southeastern Montana; Montana Bureau of Mines and Geology, Bulletin 97. Wyoming Department of Environmental Quality, Water Quality Division, 1993, Chapter VIll. Wyoming Water Resources Center, 1997, A Pilot Study of Techniques to Assess Surface Water and Groundwater bnpacts Associated with Coal Bed Methane and Surface Coal. Mining, Little Thunder. Creek Drainage, Wyoming; Wyoming Water Resources Center,"University of Wyoming, Laramie,WyonUng.
Cumulative Hydrologic Impact Assessment (CHIA) Eagle Butte Mine, Pennit 428-T41·A 1, Change No. ,
Cumulative Hydrologic Impact Assessm ent (CHIA) Eagle Butte Mine, Permit 428-HM I, Change No.' . Page 39
Rawhide Creek and Little Rawhide Creek Draina e Basin CHIA
Climate Station Stream Gage
Stream Alluvium
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Wasatch Fm Upper Fort Union Fm Tongue River & Lebo Members Lower Fort Union Fm Tullock Member
Figure 3-1 Location Map
Data for Climate Stations Near Rawhide Creek and litt!e Rawhide Creek Drainage Basins
from Westem RAllrnl'1l~1 Climate Center 2000
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