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This is a text-only version of the document "Buckskin Mine - Technical Environmental Analysis - 1986". To see the original version of the document click here.

TECHNICAL ENVIRONMENTAL ANALYSIS SHELL OIL - BUCKSKIN MINE TFN 1 4/208 TABLE OF CONTENTS 1. 2. DESCRIPTION OF OPERATION •••••••••••••••••••••••••••••••••••••••••••••• 3 GENERAL DESCRIPTION OF ENVIRONMENT
a. Topography and Geology ...••.•.•..••••.•.•.........•......•.•.... 3-5

b. c.
d.

Hydrology ...........................•........................... 5-9 Climate ........................................................ 9-10

Air Quality ••

.......................... .

•••••••••••••••••••• 10

e.
f.
g.

Soils ............................................................ 10

Vegetation and Land Use .••...••••..•...••.•••.....•.••.•..•..• 11-13
Wildlife ...................................................... 13-19 Cultural Resources ......................................... '... 19-20

ENVIRONMENTAL ASSESSMENT OF MINE PLAN
s. Topsoil Protection •••••.•••.•••••...•••...••.•••••••.••••••••• 20-25

b. c. d. e. f.
g.

Hydrologic Balance - Surface Water •••••••••••••••••••••••••••• 2S-40 Hydrologic Balance - Groundwater •••••••••••••••••••••••••••••• 40-49 Hydrologic Balance - Water Rights ••••••••••••••••••••••••••••• 49-S0 Hydrologic Balance - Permanent Impoundments •••••••••••••••••••••• Sl Hydrologic Balance - Cumulative Hydrologic Impacts •••••••••••• Sl-S7
Blast tng ...................................................... 57-59

h.
1.
j.

Fish and Wildlife Protection •••••••••••••••••••••••••••••••••• S9-63 Backfilling and Grading ••••••••••••••••••••••••••••••••••••••• 63-70 Contemporaneous Reclamation ••••••••••••••••••••••••••••••••••• 70-71
Revegetation .••••.....•••••.........•....•..........•.•.....•• 71-79

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Roads and Transportation •••••••••••••••••••••••••••••••••••••• 79-81 Buildings and Facilities •••••••••••••••••••••••••••••••••••••• 81-83

n.
o.
p.
q.

Prime Farmland •.....••.••••..•••••••••.

....................... . •• 83

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Post-Mining Land Use •.......••.••.•.•••....•.....••••......... 83-87
Air Resources ProtectioJi •••••••••••••••••••••••••••••••••••••• 87-89

Cultural Resources •....•...•.....•....••••..•••••.••••.•..•... 89-91
Bonding Determinations .••...........•.•...•••••..••..•.•....•• 91-93
Alluvial Valley Floors ••••••••••••••••••••••••••••••••••••••• 93-101

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DESCRIPTION OF OPERATION The Buckskin Mine is owned and operated by Shell Oil Company. The operation is a truck and shovel surface mine. The lease contains 84 MT of sub-bituminous coal in-place, of which 43 MT will be recovered by the proposed operation over the 16 year production life. The Buckskin Mine includes federal coal under Federal Coal Lease nW-0325878. The surface estate is in private ownership~ The mine is located about 11 miles northwest of Gillette, Wyoming (Campbell County). Access to the mine is by State Highway 14-16. The operation is located in Sections 31, 32 and 33 of Township 52 North, Range 72 West and Sections 4,5 and 6 of Township 51 North, Range 72 West and consists of 1,467 acres. It is estimated that the mining operation shall affect 959.4 acres over the life of the operation. The Buckskin Mine was granted a permit to mine on March 11, 1980 (Wyoming State Permit No. 500). The mine plan was approved by the Assis~ tant Secretary of Energy and Minerals on July 2, 1980, with stipulations. The mine has been in active operation since that time. GENERAL DESCRIPTION OF ENVIRONMENT (2.a. ) Topography and Geology The Buckskin project lies in the east flank of the Powder River Basin. The topography within the Buckskin Mine Permit area is characteristic of areas of the Wasatch Formation where the coal has not burned and scoria is absent from the geologic column. The area is one of rolling hills or ridges of uneroded Wasatch Formation which is relatively flat. Pinnacles with gradual sides (compared to scoria pinnacles) are found, as are rounded ridges and outcrops with steep faces. These features were caused by the resistance to erosion of the harder or more consolidated sediments. The topography is not as impressive as that of the scoria areas. The topographic features were caused by streams eroding into a nearly flat formation. The streams have a dendritic or modified dendritic pattern. The maximum relief between these streams and the ridge tops is 160 feet in the mine plan area. The surficial geology is delineated on map D-5-3 (Appendix D-5 of the Mine Permit Application). The major geologic units include colluvium, alluvium (including channel deposits and terraces), weathered Wasatch material, unweathered Wasatch materials and clinker (scoria - baked in fused bedrock). The applicant has provided a pre-mining slope map (Map D-5-1 dix D-5). The map was developed by superimposing a 500 foot grid a 1"=400' map. Slope measurements were made from the topographic feet in a downslope direction from the above points. The entire of Appensystem on map, 200 mine plan

- 3 PERMIT 5('(" .... 1

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area had an average slope of 6.6 percent with a maximum slope of 40 percent and a minimum slope of 0 percent. The maximum minimum relief within the area is 160 feet, with a maximum elevation of 4110 feet. The coal to be mined has been designated the Anderson and Canyon seams of the Paleocene Fort Union Formation. Detailed information is provided in Appendix D-5 of the permit application. The Anderson seam is approximately 40 to 50 feet thick, thinning somewhat to the south and to the east. The Canyon seam is about 70 to 80 feet thick, and also thins towards the south and the east. The average quality of the coal (subbituminous) is as follows (Volume IX, page 3):
BTU

Sulfur Pyrite and Marcasite Moisture ASH Volatile Matter Fixed Carbon

8,177 /lb. 0.51% 0.21% 29.80% 6.17% 31.15% 32.88%

The coal is graphically depicted on the geologic cross-sections in Addendum D-5C (Appendix D-5). The cross-section and the Icoal isopach (Exhibit 6) show the coal ranges from 15 to 130 feet thick. One thin coal bed is found in the Wasatch Formation above the Anderson seam. The seam is approximately five feet thick and is found only in the northwest corner of the mine plan area. This seam will be mined where practical (page 8, Appendix D-5). The overall coal recovery of the in-place reserves is 51%. An additional 41 million tons of unmined coal underlies or is isolated by Spring Draw and Rawhide Creek, both of which have been determined to be an "Alluvial Valley Floor". Shell is considering applying for a permit to mine all recoverable coal reserves (page 8, Appendix D-5). From the description of geology contained in the mine plan, the target coal seams to be mined are the Anderson and Canyon seams of the Fort Union Formation. Thicknesses of these two coal seams are 40 to 50 feet for the Anderson seam, and 70 to 80 feet for the Canyon seam. Both seams thin' to the south and east. A gray, sandy or silty claystone parting, two to four feet thick, separates the two seams. Maximum overburden depth to the Anderson seam is 220 feet. Above the Anderson seam is an unidentified coal seam about five feet thick in the northwest corner of the lease. A coal isopach for this seam has not been included in the plan; therefore, the lateral extent and tonnage of coal contained in this seam are unknown. Below the Canyon seam is an unidentified coal seam about five feet thick in the southwest corner of the lease. A coal isopach for this seam

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- 4 PERM!T.

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has not been included in the plan; therefore, the lateral extent and tonnage of coal contained in this seam are unknown. Depth to the next major underlying coal seam cannot be determined from the plan; however, an unidentified seam about 12 feet thick is shown on geologic cross-sections C-D, approximately 160 feet below the Canyon seam. About half of the surface area above the coal sheetwash and quaternary sediments. deposits is quaternary

In-place mineable coal reserves cannot be totally accounted for due to missing isopachs. The applicant identifies 84 million tons of coal from the Anderson and Canyon seams. A 2 to 4 foot gray, sandy or silty claystone parting lies between the Anderson and Canyon coal seams. In the areas where the parting is well defined, its thickness is two to four feet thick. However, the drill logs of Addendum D-5B (Appendix D-5) show that there are some places where there is no parting between the Anderson and Canyon coal seams. There are other places where the interburden is a zone of interbedded coals, sandstones, claystones, and shale. The zone is up to 10 feet thick and some of the coals in the zone are two feet or less. The regional dip of the beds is gently to the west. Some folds were detected by drilling during exploration that trend generally along a north-south axis and are minor anticlines, synclines and monoclines. None of the dips along these structures exceed 10 degrees. No faults were detected from the drill hole information. The Wasatch overburden consists of alternating sandstone, siltstone, claystone, and coal. All of the lithologic units are present in the mine pla~ area and exist in approximately equal amounts. These units change laterally as frequently as vertically with many interfingering changes. Exhibit 7 shows that the overburden thickness varies from 20 to 220 feet. The overburden thickness is also shown on the stratigraphic cross-sections of Addendum D-5C (Appendix D-5).
(2.b.)

Hydrology Surface Water The Shell Buckskin Mine plan area is located within the drainage basin of Rawhide Creek, a northeasterly-flowing tributary of the Little Powder River which drains about 69.1 square miles (U.S.D.I., Final Environmental Statement, Eastern Powder River Coal, 1979). Two other less prominent drainage basins on or near the mine are Little Rawhide Creek and Spring Draw, both tributaries of Rawhide Creek. Rawhide Creek drains into the Little Powder River which drains into the Powder River which drains into the Missouri River.

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PERMIT 500~'1

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In addition to these drainage systems, there are three small internal drainages which terminate in playas. Average valley slopes are about 0.3 percent for Rawhide Creek and 1.2 percent for Spring Draw (U.S.D.I., 1979). Rawhide Creek originates approximately ten miles southwest of the permit area near the rail siding of Oriva. This creek enters the permit boundary and meanders as an intermittent stream (determined through hydro graph separation by Shell Oil Company) in an easterly direction through the southern half of the permit area. Streamflow entering the permit area from this drainage is estimated to average about 0.80 cfs (U.S.D.I., 1979). Spring Draw originates approximately one mile north of the permit area and trends southeasterly across the northern permit boundary to its confluence with Rawhide Creek. This confluence is near the eastern permit boundary. Streamflow entering the permit area from this drainage is estimated to average about 0.045 cfs (U.S.D.I., 1979). Little Rawhide Creek's headwaters are located southwest of the permit boundary and converge with Rawhide Creek at a point approximately one mile downstream from the Buckskin Mine area. Both Little Rawhide Creek and Spring Draw are considered non~perennial streams. Surface runoff flood estimates for the channels of Rawhide Creek and Spring Draw were estimated from precipitation frequericy duration information collected during water years 1976, 1977 and 1978 and estimating rainfall runoff using methods developed by SCS and described in Design of Small Dams (U.S. Bureau of Reclamation, 1973). The table below indicates peak discharges for Rawhide Creek and Spring Draw reSUlting from 24-hour precipitation events of various recurrence intervals. Table I: Peak Discharges (from tables D-6-6 and D-6-10 of Buckskin MRP) Peak Discharge in CFS 2-yr Rawhide Creek: Spring Draw: Water Use Surface water usage for agriculture is confined to periods of spring runoff and precipitation events due to the intermittent and ephemeral nature of the drainage basins. In the past, utilization of this runoff has consisted of flood irrigation of native haylands 160 3-yr 360 21 650 50 10-yr 1300 105 25-yr 2150 220 50-yr 2900 340 100-vr . 3500 460

PERMIT 500.,.1

along Rawhide Creek and Spring Draw as well as providing for livestock and wildlife watering. A total of seven artificial flood irrigation structures in the form of spreader dikes and irrigation ditches are located within the Buckskin Mine plan area. Additional information describing flood irrigation structures and their use and the extent of sub irrigation can be found in the Section 3.s., Alluvial Valley Floor Assessment. Water Quality Samples for baseline surface water quality determination have been collected on a periodic basis, except during no flow periods, since November 1975. The results of the water quality analyses from this sampling period is summarized in Table I. The results indicate that Rawhide Creek water may be characterized as a magnesium-sodium sulfate type which is typical of other streams in the Gillette area. There is no significant change in the relative abundance of the major ions as Rawhide Creek flows through the mine plan area. Spring Draw exhibits water quality that is generally better than Rawhide Creek, but it is still high in TDS and sulfates. Bacteriological analyses indicate that the total coliform numbers, especially fecal coliforms and fecal streptocci, are relatively high. This is typical of surface waters in agricultural regions where runoff from areas grazed by livestock are a source of streamflow. Except for two occasions during which discharges from Rawhide Creek were estimated to be 0.2 cfs and 0.6 cfs, streamflows during the sampling period were insignificant. During these two intervals, chemical analyses revealed that although the TDS of the water increased, the general water quality improved with increased streamflow, as shown in Table 0-6-11 of the MRP. Groundwater In the proximity of the Buckskin Mine area, four lithologic ,units have been identified as aquifers. These aquifers consist of lenticular sandstones and coal beds in the Fort Union and Wasatch Formations; a massive sandstone channel deposit; and Quaternary alluvium deposits. These aquifers, as well as significant lithological influences. are briefly discussed.below. The coal to be mined, the Anderson Canyon seam, is the uppermost unit of the lithologically diverse Fort Union Formation. This formation is approximately 2270 feet thick and, like the Wasatch Formation, Tertiary in age. The Fort Union .consists of lenticular sandstones in a predominately claystone and siltstone sequence with some interbedded coal units. The sandstone members serve as the prinCipal aquifers although the coal beds, when below the water table and sufficiently thick, are also aquifers.

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PERMIT 50.:;.Tl

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The aquifers and lithological characteristics of the Wasatch Formation are very similar to the underlying Fort Union Formation. The Wasatch aquifers consist of coal beds and lenticular sandstone units in a dominant sequence of siltstone and claystone. As in the Fort Union Formation, the vertical permeabilities in the Wasatch stratigraphic section are low. The aquifers are also very low yielding. A unique condition exists at the Buckskin permit area which has an important influence on the areal hydrology. A ~assive sandstone channel is present in the northeast section of the permit area which extends from the surface to the top of the Anderson Canyon coal bed. This sandstone channel is probably the only aquifer to receive direct recharge from precipitation due to the absence of the impermeable claystone and siltstone aquitards which are present within the Fort Union and Wasatch Formations. This sandstone channel will not be affected by the proposed mining activity. Aquifer Characterization The aquifers to be affected by the proposed mining operation are the Anderson Canyon coal (top of Fort Union Formation) and the saturated portion of the overburden (lower part of the Wasatch Formation). Both aquifers appear to be confined throughout the permit area. In some areas, water level data indicate that the two units act as one vertically continuous aquifer. Recharge probably occurs over all of the basin drained by Rawhide Creek. Some small areas of scoria or channel sandstones provide rapid infiltration and a good connection with the aquifers. These areas of high recharge capacity are unidentified on Maps D-6~3 and D-6-4. The lack of water table contour deflections along Spring Draw suggests little interconnection between Spring Draw and the overburden aquifer. The area of springs and seeps along the eastern side of Spring Draw Valley (Maps D-6-1 and D-6-3) are above the permanent water table. Rawhide Creek receives discharge from both the overburden and coal aquifers. Water Quality In general, waters in the overburden are of a calcium sulfate type while waters of the confined Anderson Canyon coal aquifer are of a sodium bicarbonate type. Unconfined aquifers near the coal outcrop also contain waters of a calcium sulfate type. The alluvial groundwater is higher in dissolved solids than the coal or overburden aquifers. Depending upon recharge sources, the alluvium will range from a sodium bicarbonate to a sodium magnesium sulfate type.

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Groundwater Use Most of the water wells within a three mile radius of the Buckskin Mine are owned and operated by the Shell, AMAX or Carter Mining companies for monitoring. Within one-half mile of the Buckskin permit area, there are five known, non-mining related wells. Two of these wells are permitted. Both wells are owned and operated by Gilbert Oedekoven. They have stock and domestic uses. These wells are completed in the overburden and/or Anderson Canyon coal. There are also three non-permitted wells on the Mickey Wagensen property. One well is used for stock and domestic, another for stock and the use and owner of the third well is unknown. Table D-6G-l lists all the water wells inside and within one-half mile of the Buckskin permit area. Table D-6G-2 describes those wells that were inspected in this same area. There are 27 known non-mining related water wells between one-half and three miles from the Buckskin permit area. Fourteen of these wells are used primarily for stock. Eight are domestic wells and the use of the other five is described as miscellaneous. Table D-6G-3 is a list of these wells. Table D-6G-4 describes the wells which were inspected. These four tables can be found in the mining application, Volume III, pages 161-174.
(2. c. )

Climate A meteorological station was established at the Shell - Buckskin mine site in March, 1976 in order to gain specific on-site records. Data from the Gillette, Wyoming weather station which was established in March, 1902 is also presented in the application. The average annual temperature for Gillette is 45 degrees F. The diurnal differences between daytime and nighttime temperatures average about 32 degrees F. in July and 22 degrees F. in January. Tables D-4-1 and D-4-1A in the application present the climatic summary of data from the Gillette weather station for the periods 1931-1960 and 1941-1970 respectively. The Gillette area receives approximately 16 inches of precipitation per year. Less than one-third of this moisture is in the form of snow. This area receives about 57 inches of snow per year. The months of April, May and June (in ascending order) are the three months of greatest precipitation. Short-duration thunderstorms are an important source of runoff to the ephemeral and intermittent streams in the area. In a typical year Gillette receives 25 percent of the year's annual precipitation during 4 daily periods. an Wind speed in the Gillette area is estimated to average about 12 mph on annual basis. The wind is somewhat stronger in winter than in summer,

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r-..,.: PERM!T :'..:, \...- .1'1

Impacts of Proposed Action and Technical Alternative Over the life of the Buckskin Coal Mine, approximately 959 acres will be disturbed. As a result of the mining activity, the soil structure will be destroyed, nutrient cycling interrupted, erosion increased, micro-fauna and flora destroyed and bulk density increased. The applicant proposes to place a uniform depth over the entire site. Overall soil depth, development, and production is expected to decline for a short period. Vegetation production will also be interrupted during the mining operation. The impacts listed above should be temporary and will be reduced as the agricultural management practices proposed by the applicant take effect. Long-term effects, if any,.will be minimal if the practices proposed are followed. Favorable climatic conditions will reduce the time these impacts will have affect after revegetation and vice versa. Therefore, it is difficult to specify a length of time these impacts will have effect. No reasonable alternatives for this site are possible, if the coal is to be recovered.

(3. b.)

A.
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Description of Relevant Factors Surface Water The Shell Buckskin Mine plan area is located within the drainage basin of Rawhide Creek, a northeasterly-flowing tributary of the Little Powder River which drains about 69.1 square miles (U.S.D.I., Final Environmental Statement, Eastern Powder River Coal, 1979). Two other less prominent drainage basins on or near the mine are Little Rawhide Creek and Spring Draw, both tributaries of Rawhide Creek. Rawhide Creek is tributary to the Little Powder River tributary to the Powder River, tributary to the Missouri River. In addition to these drainage systems, there are three small internal drainages within the permit area which terminate in playas. Average valley slopes are about 0.3 percent for Rawhide Creek and 1.2 percent for Spring Draw (U.S.D.I., 1979). Rawhide Creek originates approximately ten miles southwest of the permit area near the rail siding of Oriva. This creek enters the permit boundary and meanders as an intermittent stream (determined through hydrograph separation by Shell Oil Company) in an easterly direction through the southern half of the permit area. Streamflow entering the permit area from this drainage is estimated to average about 0.80 cfs (U.S.D.I., 1979). Spring Draw originates approximately one mile north of the permit area and trends southeasterly across the northern permit boundary to its confluence with Rawhide Creek. This confluence is near the

25 -

PERMIT SOO.T1

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eastern permit boundary. Streamflow entering the permit area from this drainage is estimated to average about 0.045 cfs (U.S.D.I., 1979). Little Rawhide Creek's headwaters are located sout~est of the permit boundary and converge with Rawhide Creek at a point approximately one mile downstream from the Buckskin Mine area. Surface runoff flood estimates for the channels of Rawhide Creek and Spring Draw were estimated from precipitation frequency duration information collected during water years 1976, 1977 and 1978 and estimating rainfall runoff using methods developed by SCS and described in Design of Small Dams (U.S. Bureau of Reclamation, 1973). The table below indicates peak discharges for Rawhide Creek and Spring Draw resulting from 24-hour precipitation events of various recurrence intervals. Table I: Peak Discharges (from tables D-6-6 and D-6-10 of Buckskin MRP) Peak Discharge in CFS 2-yr Rawhide Creek: Spring Draw: Water Use Surface water usage for agriculture is confine'd to periods of spring runoff and precipitation events due to the intermittent and ephemeral nature of the drainage basins. In the past, utilization of this runoff has consisted of flood irrigation of native haylands along Ra~hide Creek and Spring Draw as well as providing for livestock and wildlife watering. A total of seven artificial flood irrigation structures in the form of spreader dikes and irrigation ditches are located within the Buckskin Mine plan area. Additional information describing flo04 irrigation structures and their use and the extent of subirrigation can be found in the Section 3.s., Alluvial Valley Floor Assessment. Water Quality Samples for baseline surface water quality determination have been collected on a periodic basis, except during no flow periods, since November 1975. The results of the water quality analyses from this sampling period is summarized in Table D-6-11, Appendix D-6, Volume III. The results indicate that Rawhide Creek water may be characterized as a magnesium-sodium sulfate type which is typical of 160 3-yr 360 21 5-yr 650 50 10-yr 1300 105 25-yr 2150 220 50-yr 2900 340 100-yr 3500 ' 460

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PERMIT 50('·T1

other streams in the Gillette area. There is no significant change in the relative abundance of the major ions as Rawhide Creek flows through the mine plan area. Spring Draw exhibits water quality that is generally better than Rawhide Creek, but it is still high in TDS and sulfates. Bacteriological analyses indicate that the total coliform numbers, especially fecal coliforms and fecal streptocci, are relatively high. This is typical of surface waters in agricultural regions where runoff from areas grazed by livestock are a source of streamflow. Except for two occasions during which discharges from Rawhide Creek were estimated to be 0.2 cfs and 0.6 cfs, streamflows during the sampling period were insignificant. During these two intervals, chemical analyses revealed that although the TOS of the water increased, the general water quality improved with increased streamflow, as shown in Table D-6-ll of Appendix D-6. B. Evaluation of Compliance Hydrologic Balance - Surface Water Diversions Chapter IV, subsection 2.e. requires that surface water be diverted around the operation to protect the on-going operation, control water pollution and unnecessary erosion, and to protect the water rights of downstream users. Unchannelized Surface Water and Ephemeral Streams Chapter IV, subsection 2.e. and subsection 3.e.(1) and (3)(a), among other things, require that diversions of unchannelized surface water and ephemeral streams be designed to pass the peak runoff from a 10-year flood event or larger, contain side slopes no steeper than 1 1/2 to I, and provide protection against unnecessary erosion~ Permanent diversions should safely pass the 100-year flood event, or larger. Chapter IV, subsection 3.g. and i., among other things, require that drainage from affected lands shall not degrade receiving waters. This should be accomplished through the use of sedimentation ponds and alternative sediment control measures. Diversion and Conve Flow, and Ephemeral Flow and Shallow Groundwater Vol. X, pages 11-1 to 11-5

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Shell has committed to provide collector ditches (Vol. X, pages 11-1 and 11-3; see typical cross-section diagrams attached)to deliver sediment laden water to sediment ponds. They are designed to handle the peak flow from a 10-year, 24-hour precipitation event

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PERMIT 500.Tl

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at velocities not greater than 3.0 FPS. A minimum velocity of 2.0 FPS will be maintained where practical to avoid sediment deposition. Rip-rap drop structures will be installed where slopes are greater than the design maximum. They will be grass-lined with ditch bottoms below topsoil wherever necessary. Shell has also provided for by-pass ditches to divert runoff from undisturbed areas around disturbed areas. Designs are similar to those for collector ditches (Vol. X, pages 11-4 and II-5; see attached diagram). By-pass ditches are designed for the 10-year, 24-hour storm, thereby exceeding the WDEQ/LQD regulation requirement of designing for a two-year, 24-hour event. A permanent diversion is planned along the north boundary of the mine plan area to convey surface runoff from an undisturbed area to the north of the permit boundary (see Exhibit 11 of the Reclamation Plan). This permanent diversion will have a drainage area of approximately 966 acres and is designed to meet the 100 year, 24 hour WDEQ/LQD requirement. The permanent diversion will grade into an existing tributary of Spring Draw. The locations of the ditches and the permanent diversion are shown on the Project Layout Map, Vol. X of the MRP, and on the Mine Plan Map, Exhibit 2, Vol. IX. All temporary diversions will be reclaimed (regraded and revegetated) as indicated in the mine plan (Vol. IX, pages 50 to 51a). Although the plan contains no specific wording relative to ditch reclamation, it is inferred based on the ,reclamation plan map and the statement that .the mine and related facilities will be returned to original contour. Only one permanent diversion, along the north boundary of the permit area, is planned. The natural drainage pattern will be reestablished to conform to pre-mining conditions (Exhibit 9, Reclamation Plan Map, Vol. IX). The channel of the collector and by-pass ditches and permanent diversions will be lined with grass vegetation to safely pass the design velocity of 3 FPS (see Hann and Barfield). Freeboards will be 1.0 foot, exceeding the 0.3 foot requirement. Drop structures will be used to maintain maximum allowable slopes to assure channel stability. . Intermittent and Perennial Streams Chapter IV, subsection 2.f. and 3.e.(2), among other things, require that diversions of intermittent and perennial streams be designed to convey the 10-year flood event, if temporary, or the 100-year event if permanent. The banks and channel of a diverted stream shall be protected where necessary by plants, rock, riprap, etc. to minimize erosion and degradation of water quality. When no longer needed, all temporary stream channel diversions shall be removed, regraded and revegetated.

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PERMIT 500· T1

The applicant does not plan any permanent or temporary diversions of intermittent or perennial streams. The applicant proposes to mine the area in such a way not to directly disturb the two major water courses, Spring Draw and Rawhide Creek. Areal Coverage of Sedimentation Control Structures Chapter IV, subsection 3.g.(1) requires that all surface drainage from affected lands excluding sedimentation ponds, diversion ditches, and road disturbances pass through sedimentation ponds. The use of alternative sediment control measures, in place of sediment ponds, may be used as long as drainage will meet effluent limitations or will not degrade receiving waters. Sediment ponds and collector and by-pass ditches are discussed in the Mine Plan, Addendum I and their location is shoWn on Exhibit 2 of the Mine Plan and Drainage Plan maps of Addendum I of the Mine Plan. Ditches and diversions are discussed in more detail above in the section on Diversions - Unchannelized Surface Water and Ephemeral Streams. Sediment control appeared to be adequate for containing of sediment within the permit area and protecting of the quality of surface waters. Design and Construction of Sedimentation Control Structures Chapter IV, subsection 3.g. and 3.h. specify that sedimentation ponds be designed to safely impound the design event as well as safely passing larger events. Wyoming State Engineer and Wyoming Department of Environmental Quality, Land Quality Division regulations must also be complied with. Appropriate alternative control measures shall be designed, constructed and maintained using the best technology currently available. Twelve impoundments will be constructed during the lifetime of the mine. Ten ponds are to be used for sediment control and two for wastewater and washdown water. Mine pit dewatering will be pumped to Ponds No. I and No.6. Three sedimentation reservoirs will have capacities greater than 20 acre-feet which have special design requirements. Designs, drawings and specifications for all wastewater treatment and sedimentation ponds can be found in Addendum I Volume X. Required permits from MSHA, the Office of the State Engineer, and Water Quality Division are in Appendix J of the Adjudication File-Volume. Emergency spillways for reservoirs less than 20 acre-feet in size and less than 20 feet high are designed to pass runoff from a 25-year, 24-hour precipitation event assuming the reservoir is full to the spillway when the peak flow occurs. For reservoirs larger than 20 acre-feet, emergency spillways are designed for the IOO-year, 24-hour event, when the reservoir is full. Sedimentation

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prPMf T

500.Tl

Pond No. 1 and both wastewater. ponds are .designed with gated (valve) outlet works. All other impoundments will be dewatered by pumping. The ponds are designed for three-year sediment loading and are scheduled to be cleaned out when the accumulated sediment volume reaches 60 percent of the maximum sediment volume. Removal frequency is estimated to be once every two years. Effluent quantity and quality from the sedimentation reservoir (including wastewater ponds) will be monitored. Chemical addition in the form of flocculants will be used only if necessary. Topsoil will be stripped from the reservoir construction sites. Fill material for dams and embankments will be excavated from the reservoir bottoms. Dams and embankments will be brought up in 8 to 12 inch layers, then compacted. / Embankments are designed to allow for five percent settling. Crest widths are 30 feet, sloped inward at a one percent grade. Inside slopes are 2:1 (horizontal:vertical) and outside, slopes will be 3:1. Freeboard allowances have been made accordingly for all sizes of reservoirs. The following table includes reservoir identification. construction date in parenthesis. and a description of water sources:

)

\ ..y

...~~

- 30 -

PERMIT 500.T1

TABLE I RESERVOIR OPERATION Wastewater Res. No. 1 (1980) Coal and oily washdown wastewater Runoff from 20 A. (Total Area) inside R.R. Loop. Combine with sed. res. No. 2 final reclamation phase runoff Washdown wastewater Runoff from building and equipment areas Total Area = 0.94 A. Runoff from building and equipment area Runoff from S.E. overburden stockpile Mine pit water (surface and underground) from north and south pits Total Area = 212.7 A. Runoff from facility area Combined with W.W. Res. No. 1 Total Area = 12.65 A. Runoff from topsoil stockpile on west boundary Total Area = 28.05 A. Runoff from overburden stockpile near north boundary Total Area = 20.38 A. Runoff from topsoil stockpile near east boundary Total Area = 28.0 A. Runoff from topsoil stockpile near north boundary Area to be submitted with design criteria Runoff from lower bench slope near northwest boundary Area to be submitted with design criteria Runoff from overburden stockpile near northwest boundary Area to be submitted with design criteria

Wastewater Res. No. 2 (1980)

Sedimentation Res. No. 1 (1980)

Sedimentation Res. No •. 2 (1980 enlarged 1997) Sedimentation Res. No. 3 (1980)

)

Sedimentation Res. No.4· (1980)

Sedimentation Res. No. 7 (1980)

Sedimentation Res. No. 8 (1981)

Sedimentation Res. No. 9 (1981)

Sedimentation Res. No. 10 (1981)

- 31 -

PERMIT 500·T1

-.~ ...
,

Sedimentation Res. No. 5 (1986)

Runoff from all reclaimed area west of ridge Area to be submitted with design criteria North mine pit dewatering Total Area = 188.24 A.

Sedimentation Res. No. 6 (1985-1986)

-.0 <:

f3~

00'

- 32 -

PERMIT 500.T1

·...

~.) .

All sedimentation ponds are scheduled to be constructed prior to disturbance of the undisturbed area to be drained into the pond. They will be located directly adjacent to the disturbed areas. There are no perennial streams in the disturbed area. A check of the records (Volume III, pages 52-56) confirms that both Rawhide and Spring Creek have records of no flow from mid-summer to early spring. The applicant states that, "All sediment and wastewater ponds were designed to meet applicable DEQ, Land Quality regulations, Office of Surface Mining regulations, DEQ, Water Quality regulations, Mine Safety and Health Administration regulations, and Wyoming State Engineer's Office regulations." The more stringent parts of the applicable regulations were used for the design. The sizes of these ponds have been checked and found to be sufficient for sediment control. The method used to determine sediment storage volume for Sediment Pond No.1, No.2, No.3, No. 4,and No. 7 was to apply to Universal Soil Loss Equation with delivery ratios. A rainfall factor (R) of 50 developed by SCS was used. The unit weight of the predominately fine sandy loam soil with less than 5% organic matter was 100 cfp, giving a soil erodibility factor K of 0.35. Slope-length factors were determined for each contributing area from the mine plan and appropriate SCS curves. The annual sediment load, using appropriate delivery ratios, was determined for each area and summed. The assumptions made are a part of the accepted methodology and appear appropriate. Since Wastewater Reservoir No. 1 receives runoff from the area within the railroad loop, the same procedure was used to determine sediment volume. Eight percent sediment concentration in washdown water was assumed and added to the runoff sediment. For Wastewater Reservoir No. 2 sediment load was assumed to be 20% of the total liquid volume. All sedimentation ponds are designed to detain runoff from a 10-year, 24-hour precipitation event for a minimum of 24 hours. Liquid volumes in the wastewater reservoirs include estimated contributions from facility and equipment washdown. Ground water . inflow t~ the main pits will be pumped to Sedimentation No. 1 and These reservoirs include volume for five days for 6 Reservoirs. ground water inflow, (210 gpm for No. 1 and 95 gpm for No.6) which will result in a minimum five days detention time. Also Sedimentation Reservoir No. 1 and Wastewater Reservoirs No. 1 and 2 will have five-day detention times since they will be receiving coal wastes. Ponds are designed with inlets and outfalls minimize any potential short circuiting. on opposite ends to

- 33 PERMIT 500.Tl

Volume X, Section I, page I-I, states that if standard gravity separation will not provide sufficient partial settling; chemical flocculation will be used to meet applicable effluent limitations. Sediment ponds will be monitored for trap efficiency, sediment volume, discharge quality and quantity as stated in Addendum I. The ponds and spillways are designed to detain the 10-year, 24-hour event without outfall through the emergency spillway. Ponds less than 20 acre-feet will pass a 25-year, 24-hour runoff and ponds greater than 20 acre-feet will pass 100-year, 24-hour events. The All emergency spillways are one foot above the reservoir level. design discharge velocities are less than 3.0 fps. Spillways consist of drop spillways with pipes through the embankment. Page 1-4, Section I-C of Volume X outlines general construction details. Fills will start at the lowest point of the foundation and will be brought up in horizontal layers no greater than 8 to 12 inches in compacted thickness and compacted by rolling. Embankment foundations will be cleared and properly graded. Fili material will be tested during construction and will come from the reservoir bottom and facility area. It will be free of all vegetative matter and frozen soil. Surfaces upon which embankment is placed will be scarified. Sedimentation Reservoir No. 1 has' an appropriate spillway to discharge a 100-year, 24-hour precipitation event. The emergency spillway can safely discharge 46.0 cfs while the 100-year, 24-hour peak flow is 18.90 cfs. The difference is made up by ground water inflow and mine pit water pumping. The embankment is designed with a 2.7 static safety factor for a full pond, greater than the 1.5 requirement. The applicant has received all required approvals from MSHA and has shown that the impoundment will have the required static safety factor. The applicant will monitor pond influence water to determine when the ponds can be removed. (See Monitoring section). The ponds will be drained, graded, and revegetated at such time as they are not longer needed. Diversion ditches will be vegetated as per Section II.B. and II.C., . Volume X. The plan does not specifically address upstream embankment protection measures. The plan does state that downstream embankment slopes will be gentle enough to facilitate establishment of vegetation. Refer to soils and overburden sections for details of existence of these materials. Detention and treatment facilities are adequate to handle any drainage which might contact these materials. The applicant has demonstrated compliance with all applicable regula-

- 34 -

tions concerning sedimentation ponds and impoundments. During quarterly discharge measurements, samples will be taken for water quality analysis. Map D-6-6, Volume III, shows the location of the monitoring sites and the sediment ponds. Following permitting, Shell and the Wyoming Land Quality Division will meet to determine which parameters will be analyzed during and after mining. OSM should also be included in this meeting. Drainage from Acid and Toxic Materials Chapter IV, subsection 3, among other things, requires that drainage from acid and toxic materials either be treated or prevented. Undesirable material must be covered by at least 4 feet of acceptable material and must not be buried or stored in the proximity of a drainage channel or its flood plain. Information regarding the assessment and handling of unsuitable overburden. material can be found in Appendix D-5 and in the Reclamation Plan under Overburden Handling. The overburden is generally of a suitable nature; however, high molybdenum levels were identified in one isolated sample drill hole. The applicant had demonstrated an ability and has conunitted to burying the overburden with a high molybdenum level well below the root zone in a reducing environment. Placing the high molybdenum material below the post-mining static water level, should prevent the molybdenum from moving with the groundwater and degrading the water quality. The applicant has not committed to burying any undesirable materials outside the proximity of any stream channels. This should be considered to minimize the potential for erosion and downcutting exposing any of this previously buried material. Stream Buffer Zones Chapter IV, subsection 3.p.(2) specifies that no land within 100 feet of a perennial or intermittent stream shall be affected unless the administrator specifically authorizes such activities. The area not to be affected shall be designated a buffer zone and be marked as such in the field and on a mine plan map. The State of Wyoming, in a letter dated March 11, 1980, granted the applicant a variance on WDEQ/LQD Rules and Regulations of Chapter IV, subsection 3.p.(2) concerning stream buffer zones. Page 18a, Volume IX of the mine plan and exhibit two describe the applicant's proposed buffer zones. The regulations require a

- 35 -

PERMIT 500.11

!::.') .
,:.~~./

buffer zone of 100 feet. Because of steep slopes bordering the channel in certain locations in the western portion of the mine area, the applicant feels that a buffer zone based primarily on the 100-year, 24-hour flood plain is warranted. Because Rawhide Creek is so deeply incised in the western portion of the permit area the 100 year floodp1~in is contained almost entirely within the stream channel. No mining disturbance will occur within the proposed buffer zone except during the construction of the culvert crossings and bridge for the roads and railroad, and for construction of part of Sedimentation Reservoir No.1. Flow will not be restricted. Any channel segment which will be affected by the placement of fill for bridge or culvert construction will be surveyed for width, depth, length and slope prior to any construction activity. The survey will ensure that the channel stability will be restored upon reclamation. Sedimentation ponds and collector ditches will intercept any surface runoff from affected areas during mining and reclamation to ensure that the water quality will not be degraded. By-pass ditches will route surface runoff from unaffected areas around the disturbed areas to Rawhide Creek. There will be a slight diminishment in the quantity of surface runoff to Rawhide Creek but the effects should be minimal on the flow in the Creek. Based upon the above findings that the 100 year floodplain provides an adequate _buffer zone, a variance from the 100 foot buffer zone should protect the quality and quantity of water in Rawhide Creek. Post-Mining Landform Stability and Drainage Chapter IV, subsection 2.b.and 3.c.(1) and 3.e.(2)(b)(iii) requires the reestablishment of erosionally stable drainage systems and landforms on reclaimed lands. Adequate through-drainage and erosionally stable stream channels and floodplains must be provided. In the case of excess spoil, all spoil not required to achieve the approximate original contour, shall be graded to the lowest practical grade while maintaining the hydrologic balance and providing for long-term stability. The proposed mine plan (Exhibit 2 of the Mine Plan) does not include mining within the 100-year floodplains of either of the two major drainages, Spring Draw and Rawhide Creek. Haul roads and the railroad spur will cross these drainages. These structures will be removed at the conclusion of mining any any affected channel segment will be restored with placement of fill. Hypsometric analysis of the pre-mining and post-mining slope distribution was done (see Topography, Appendix D-5, Volume II). The average pre-mining slope was 6.6% with a maximum slope of 40% and a minimum slope of 0%. The average post-miningslope slope was 5.1% with a maximum slope of 25% and a minimum slope of 0%.

Il . '.',

,.)"
."

. ,,,,:. '~: ......:- ~",

- 36 -

PER MIT 500.~" . I • Tl . :

Eighty-eight percent of the post-mining slopes have a slope of 10 percent or less. The post-mining topography will be generally flatter than pre-mining. This will result in a decrease in runoff velocities. The loss of runoff volume to through drainage should be compensated by the elimination of three Small closed basins. Addendum D-6H in Volume III of the permit application contains the design of the drainage system designated as "Tract Draw" in the northwest corner of the permit area (see Map D-6-14). The main channel of Tract Draw is formed at the confluence of the East Fork and the West Fork. The West Fork is formed at the confluence of two channels designated the North Prong and the South Prong. The Tract Draw drainage system which drains three previously enclosed basins, flows into Rawhide Creek near the western permit boundary. Each channel will be constructed with a v-shaped guide channel within the main channel. The channel and floodplain cross-sections and accompanying calculations show that each drainage is designed to be erosionally stable for a 10-year, 24-hour event and have a floodplain capacity for a 100-year 24-hour event with a minimum of one foot of freeboard. The maximum predicted velocity for a 10-year event is 3.4fps and 5.98 fps for a 100-year event. The maximum mean slope of a channelized section in Tract Draw drainage system is 2.44 percent. The channels will be graded, contoured and vegetated in accordance with the Reclamation Plan. For a description of reestablishment of landforms see section 3.g., Backfilling and Grading. The applicant has demonstrated that the post-mining landform stability can reasonably be expected due to the following factors:
1.

)

The two major drainage's within the permit area - Rawhide and Spring Draw will not be mined through.

Creek

The post-mining slopes will be flatter, i.e., eighty-eight percent of the post-mining slopes have slopes of 10 percent or less. The average slope is 5.1 percent. The construction of stream channels within drainage system will be erosionally stable. A smooth transition between the reclaimed unaffected area exists. the Tract and Draw the

3. 4.

topography

Surface Water Monitoring Chapter IV, subsection 3.i. requires that surface water from affected lands be monitored for water quality and quantity during the course of coal mining and reclamation operations to determine

- 37 -

PERMIT

500 .. Tl

the extent of disturbance to the hydrologic balance. Water quality monitoring results for discharges other than those authorized by the Wyoming Department of Environmental Quality, Water Quality Division shall be reported quarterly. Facilities to monitor stream stage have been installed at four sites (see Map D-6-6). Completion of a continuous water-stage recorder installation on Rawhide Creek near the western lease boundary was accomplished in February 1976. Crest-stage gages and staff gages were installed on Rawhide Creek above Spring Draw and on Spring Draw near the north permit boundary in November, 1975. A staff gage was installed on Spring Draw just above its confluence with Rawhide Creek, also in November, 1975. Several additional crest-stage gages and staff gages were installed in April 1979 at the locations shown on Map D-6-6. During quarterly discharge measurements, samples will be taken for water quality analyses. Prior to the time that a mining permit is issued, analyses will be conducted on each sample for all parameters according to LQD Guideline No.8. Following permitting, representatives of Shell and of the LQD wil"l meet to determine monitoring frequency and which parameters will be analyzed during and after mining.

)
C.

The applicant should commit to quarterly monitoring surface water for both quality and quantity until bond release subsequent to Chapter IV, subsection 3.i. Proposed Departmental Action It is recommended that this part of the proposal until the following deficiencies are corrected. 1. D. The applicant must conduct quarterly water for quality and quantity. not be of approved surface

monitoring

Environmental Consequences During Mining

A network of sediment control structures designed

to control the loss of sediment and minimize the potential for degradation to surface waters is proposed at the Buckskin Mine. The design criteria for the sediment ponds and ditches is the 10 year, 24 hour storm event. ) An event greater than the design storm will produce some sedimentation in Rawhide Creek downstream from the permit area. In all likelihood, there will be less sediment loading to Rawhide Creek during mining due to the sediment control measures for small storm events. This decrease in sediment loading to Rawhide Creek should not have a significant impact on the erosional equilibrium

- 38 -

PERMIT 500.Tl

of the stream, since the Buckskin Mine constitutes less than two percent of the Rawhide Creek drainage area. Because of the sedimentation ponds, there will also be a slight decrease in runoff to Rawhide' Creek and Spring Draw during mining. Sedimentation ponds will act to attenuate the flood peaks rather than permanently capturing runoff. While runoff will be reduced, there will still be an increase in streamflows in Rawhide Creek (approximately 0.07 cfs) due to dewatering of the mine pits. The effects of this increase will be minimized due to several factors. First, the rate of dewatering will decrease with time as the groundwater is released from storage. Second, during the warmer months the water will be used for dust control. Third, some of the pit water discharged to Rawhide Creek will recharge the alluvium/overburden aquifer rather than being carried away as streamflow. The disturbance to Rawhide Creek and Spring Draw will be minimized since neither stream wi~l be mined through. A haul road with culverts and a railroad line will be constructed across Rawhide Creek near the location of sediment pond no. 1. Cross-sections and stream gradient surveys will be taken at the crossing to ensure that the stream channel will be restored. No mining activities other than the road crossings will occur within a 100 foot buffer zone of Rawhide Creek with the exception of the western portion of the permit area. A variance (from WDEQ/LQD letter dated 3-11-80) was granted to the Buckskin Mine to allow the establishment of a buffer zone based upon the 100 year, 24 hour floodplain. Because Rawhide Creek is deeply incised in the western portion of the permit area, the 100 year floodplain is contained almost entirely within the channel. This buffer zone, based upon the 100 year, 24 hour floodplain, is adequate for this portion of Rawhide Creek. Post-Mining The post-mining impacts to the surface water system should be minimal since the surface runoff potential will be similiar to the premining conditions. There are no permanent impoundments proposed at Buckskin Mine. Generally surface runoff on reclaimed mined lands is less due to the greater rate of infiltration. A reduction in average slopes and the greater permeability of reclaimed spoils will increase the infiltration rates and subsequently reduce the surface runoff. At the Buckskin Mine, the major watershed divide will remain intact but three small enclosed basins in the northwest corner of the permit area will drain to Rawhide Creek after reclamation. A permanent diversion (by-pass ditch)along the north boundary will convey runoff from approximately 966 acres of undisturbed area directly to Spring Draw. In compliance with WDEQ/LQD Rules and Regulations the

- 39 -

PERMIT 500.TI

diversion will be designed for the 100 year, 24 hour event. Some of the area previously draining into the playas in the northwest corner of the permit area will be drained by the permanent diversion~ Though the drainage area will increase slightly after reclamation, there should be no increase in surface runoff due to increased infiltration rates.
(3. c. )

Hydrologic Balance - Groundwater A. Description of Relevant Factors Groundwater In the proximity of the Buckskin Mine area, four lithologic units have been identified as aquifers. These aquifers consist of lenticular sandstones and coal beds in the Fort Union and Wasatch Formations; a massive sandstone channel deposit; and Quaternary alluvium deposits. These aquifers, as well as significant lit~agical influences, are briefly discussed below.
J

The coal to be mined, the Anderson Canyon seam, is the uppermost unit of the lithologically diverse Fort Union Formation. This formation is approximately 2270 feet thick and, like the Wasatch Formation, Tertiary in age. The Fort Union consists of lenticular sandstones in a predominately claystone and siltstone sequence with some interbedded coal units. The sandstone members serve as the principal aquifers although the coal beds, when below the water table and sufficiently thick, are also aquifers. The aquifers and lithological characteristics of the Wasatch Formation are very similar to the underlying Fort Union .Formation. The Wasatch aquifers consist of coal beds and lenticular sandstone units in a dominant sequence of siltstone and claystone. As in the Fort Union Formation, the vertical permeabilities in the Wasatch stratigraphic section are low. The aquifers are also very low yielding. A unique condition exists at the Buckskin permit area which has an important influence on the areal hydrology. A massive sandstone channel is present in the northeast section of the permit area which extends from the surface to the top of the Anderson Canyon coal bed. This sandstone channel is probably the only aquifer to receive direct recharge from precipitation due to the absence of the impermeable claystone and siltstone aquitards which are present within the Fort Union and Wasatch Formations. This sandstone channel will not be affected by the proposed mining activity. Aquifer Characterization

- 40 -

PERMIT 500.rl

The aquifers to be affected by the proposed mining operation are the Anderson Canyon coal (top of Fort Union Formation) and the saturated portion of the overburden (lower part of the Wasatch Formation). Both aquifers appear to be confined throughout the permit area. In some areas, water level data indicate that the two units act as one vertically continuous aquifer. Recharge probably occurs over the entire basin drained by Rawhide Creek. Some small areas of scoria or channel sandstones provide rapid infiltration and a good connection with the aquifers. These areas of high recharge capacity are identified on Maps D-6-3 and D-6-4. ,The lack of water table contour deflections along Spring Draw suggests little interconnection between Spring Draw and the overburden aquifer. The area of springs and seeps along the eastern side of Spring Draw Valley (Maps D-6-1 and D-6-3) are above the permanent water table. These seeps are assumed to be fed by perched water in the overburden. Rawhide Creek receives discharge from both the overburden and coal aquifers. Water Quality In general, waters in the overburden are of a calcium sulfate type while waters of the confined Anderson Canyon coal aquifer are of a sodium bicarbonate type. Unconfined aquifers near the coal outcrop also contain waters of a calcium sulfate type. The alluvial groundwater is higher in dissolved solids than the coal or overburden aquifers. Depending upon recharge sources, the alluvium will range from a sodium bicarbonate to a sodium magnesium sulfate type.

)
B.

Evaluation of Compliance Preservation of Non-Affected Groundwaters W.S. 35-11-415(b)(vii) requires the operator to prevent, through the mining and reclamation operations and for a period of five years, the pollution of non-affected groundwaters. The pre-mining potentiometric surfaces for both the overburden and coal indicate that groundwater flows to the permit area from all directions. Rawhide Creek alluvium is a local discharge point for the coal aquifer as well as the saturated portion of the overburden. During mining the flow toward the permit area should increase due to pit dewatering. Predicted pit dewatering peaks at a rate of about 800 gpm in 1987. The predicted steady-state potentiometric surface for the spoils aquifer again shows flow to the permit area from all directions. The transmissivity of the reclaimed spoil will be less than the

- 41 -

PERMIT 500.Tl

transmissivity of the coal aquifer but similar to the pre-mining overburden. Groundwater will continue to flow to the permit area after reclamation and steady-state conditions ar~ achieved. Thus the hydrologic function of the Rawhide Creek alluvium as a discharge point will be preserved and there should be no pollution of non-affected groundwaters. Post-Mining Groundwater Quality Chapter IV, subsection 3.a.(2) and 3.c.(3)(b) and d.; subsection 3.f.; WQD Regulations Chapter VIII, subsection 3.c. and subsection 4; Chapter IV, subsection 3.i., among other things, require that the mining and reclamation operation minimize adverse effects to groundwaters and protect those uses for which it is suitable for. It is recognized that acid-forming or toxic material may have to be isolated from groundwaters to assure non-pollution. Results of baseline groundwater quality are present in Volume III, Addendum D-6C. Addendum D-6J supplies water quality analysis (batch elutriations and column leach) for representative spoil samples •. The physical disturbance of the backfilled overburden material provides a potential for additional exposure of soluble materials to percolating water. It is probable that there will be an increase in total dissolved solids concentrations in the groundwater until any soluble surface materials are diminished and a new equilibrium is reached. The results of the saturated past tests show a worst-case situation where the predicted total dissolved solids levels in the post-mining groundwater could be as high as 4500 mg/l (ppm). The initial recharged pore volume may have total dissolved solids as high as an order of magnitude greater than baseline quality. The pre-mining groundwater quality for the coal and overbur-· de.n aquifers is generally considered to be Class II according to the WDEQ/WQD Rules and Regulations, Chapter VIII. The post-mining groundwater use would be limited to livestock and wildlife watering, i.e., Class III, WDEQ/WQD Rules and Regulations, Chapter VIII, if the worst-case situation developed. With time, the levels of total dissolved solids decrease to baseline quality and equilibrium ·is reestablished. In general, materials which have a potential for contributing to toxic or other harmful contamination, will be given special handling as discussed above in the section "Drainage from Acid and Toxic Materials". The groundwater quality impact should be limited to the permit area. Most recharge to the reclaimed spoils is expected to come from the unmined coal and overburden aquifers adjacent to the permit area. The amount of recharge from the reclaimed surface is expected to be minimal (less than or equal to .15 in/yr.). Recharge was calculated using Stallman's unsteady flow formula

)

- 42 -

PERMIT 500·T1

describing groundwater movement subject to recharge in a homogenous and isotropic aquifer. The water quality of Rawhide Creek should not be affected by the increase in total dissolved solids in the groundwater from the reclaimed spoils since the ground water discharge to Rawhide Creek alluvium constitutes of only about 5-8 percent of the total underflow. Post-Mining Groundwater Recharge and Availability Chapter IV, subsection 3.f. requires that the groundwater recharge capacity of the reclaimed lands be restored to a condition which supports the post-mining land use, minimizes disturbances to the prevailing hydrologic balance, and provides a rate of recharge that approximates that which was present before mining. The mining and related reclamation activities appear to be adequate for assuring restoration of pre-mining recharge capacity. Recharge will be partly through direct infiltration but the major source will be from the coal and overburden aquifers in the surrounding unaffected areas. Overburden will be hauled back around the pit and dumped in two lifts in a controlled manner so that the elevation of the top lift approximates the reclaimed surface shown on the post-mining contour map (Exhibit 9); it will be ripped in preparation for topsoiling. Care will be taken to ensure that the top eight feet of material is silty and sandy material suitable for plant growth (page 39a, Volume IX). This material should be moderately permeable ( 4.0 gpd/ft2) thereby permitting moderate infiltration. It is expected that infiltration will increase. as vegetation is reestablished. This inherent infiltration capacity will be augmented by the flatter post-mining slopes (page 74, Volume IX). The actions will ensure a post-mining infiltration capacity at least equal to the pre-mining. Because the overburden will be broken up, percolation to the water table should be facilitated. The potentiometric surfaces for the coal and the overburden and the . predicted post-mining surface for the spoils are shown on Maps D-6~3, D-6-4 and D-6-7. The groundwater in the permit area generally flows to the southeast or northeast toward Rawhide Creek which then flows west to east across the southern part of the area. Rawhide Creek, an intermittent stream, acts as a sink draining overburden along its reach through the permit area. In its eastern reach, it also receives discharge from the coal aquifers (page 14a, Volume III). Water levels shown in Appendix D-5 and D-l) indicate that the water table also (just barely) intersects the channel of Spring Draw. To preclude or minimize problems of excessively shallow groundwater, a post-mining drainage (performing functions of present Spring

- 43 -

PERMIT SOO.TI

•

""·V'.'·' ......
"'

,:,":

Draw) will be formed to drain excessive post-mining groundwater that might surface in the north pit area (page SIb, c, Reclamation Plan). Groundwater seepage will be confined to approximately on acre where it will be collected in guide channels incised to a depth of about two feet. The collected water will then flow to Rawhide Creek. In areas away from the guide channels the water table will be at least four feet below the surface (pages 51 and 52, Volume IX). Map D-6-7 'shows the estimated steady state post-mining water levels. The potential for saline seeps exist in these guide channels. Over the long-term, the hydrologic balance within and outside the permit area probably will not be adversely disturbed. The postmining groundwater recharge in the disturbed area will most likely equal or possibly exceed the pre-mining recharge rate. Excessive rise in the water table elevation will be prevented by the guide channels along reconstructed Rawhide Creek.
\\

Groundwater Monitoring Chapter IV, subsection 3.i. requires that groundwater quality and quantity be monitored during the course of surface coal mining and reclamation operations to determine the extent of the disturbance to the hydrologic balance. The monitoring program should be adequate to determine infiltration rates, subsurface flows, and storage characteristics of reclaimed lands and adjacent areas. Additionally, monitoring should determine the effects of reclamation on the recharge capacity of the reclaimed lands~ The permit application presents an impressive volume of meaningful monitoring and testing data collected over a several year premining period. This provides good baseline hydrologic and water quality data, which when compared to later data, will indicate changes in groundwater conditions that might be induced by the proposed mining and reclamation operation. During mining, the coal and overburden wells . (Map D-6-12, Pocket Volume III) will be monitored once every three months for water levels (page 22, Volume III). Wells destroyed during mining will be replaced after reclamation. The location of post-mining monitoring wells are shown on Map D-6-9. After replacement, the water levels will be monitored at least semi-annually. Wells P-4-C, P-13, CK-l, and P-12 will be sampled quarterly and analyzed for all components in LQD Guideline No. 8 (until reduced by LQD). These wells are down gradient and should intercept changing water quality conditions that might affect outside areas. The applicant should commit to monitoring on a quarterly basis two additional wells - preferably one in alluvium at the eastern permit

- 44. -

PERMIT 500.'1

boundary and one completed in both the coal and overburden. These wells should also be monitored for both water levels and for water quality. Private wells along the northwest trending fracture zone (owners permitting) will be monitored for water quality and level once a year. This includes wells with permit numbers 21101P, 21102P, 21105P, and 21106P. These wells are about 1 1/2 miles northwest of the permit area on Map D-6-10. A Carter well about 1/2 mile southwest of the permit area (Permit 31197W) is monitoring the southwest trending fracture zone. Alluvial wells (10) noted on Map D-6-12, will be monitored quarterly. Down gradient wells P-12 and P-13-will be used for annual water quality monitoring. Additional downstream monitoring wells will be established if the need is detected in the present wells. To obtain an estimate of infiltration capacities of the area soils, sets of double-ring infiltrometers were installed at the sites shown on Map D-6-S. These sites were chosen to represent the six major soil texture groups on the Buckskin permit area. The proposed groundwater monitoring program appears to be adequate in time, areal extent, and stratigraphic extent, to provide data for any modification of mining activity needed to minimize impacts. This monitoring program includes detection and quantification of changes in groundwater levels, infiltration rates, subsurface flow, storage characteristics and groundwater quality, during and after the period of disturbance. The applicant should commit to determining the post-mining aquifer parameters of storage coefficient and transmissivity of the reclaimed lands and adjacent non-affected lands as reclamation proceeds and data on the reclaimed areas becomes available. Capping, Sealing and Plugging of Drill Holes, Exploration Holes and Wells W.s. 35-11-404(a) .and Chapter XV, Section 3 requires the proper plugging, sealing and capping of all wells, exploration holes and drill holes. The applicant has located and drilled (as shown on Exhibit 12) over 50 exploration and hydrologic monitoring holes within the permit area. All exploration holes have been adequately sealed and plugged, except for those which were drilled prior to Shell's acquisition of the property. These have been backfilled with drill cuttings but no information is available on the sealing of aquifers. Exploration holes have been used to determine coal seams, and overburden chemical and physical properties plus geologic

)

- 45 -

PERMIT 500.T1

cross-sections and conditions. Many of these holes were sampled from drill cuttings, but a number were cored. Monitoring wells are cased, with all stratigraphic units but the monitored aquifer sealed off. Such holes drilled prior to 1979 are protected from tampering or damage by covered and locked sections of corrugated metal pipe. Late 1979 holes have not yet been protected, but the casing projects far enough above ground level to prevent accidental damage. The operator's procedures for casing, sealing, and managing drill holes is adequate. Aquifers encountered in exploration holes will be sealed off with concrete 20 feet above and below the aquifer, while the rest of the hole will be filled with cuttings and plugged to a depth of 10 feet below the collar. All aquifers encountered by monitor holes, except the one being monitored, are sealed off as above. Monitoring wells are temporarily sealed with corrugated steel pipe over the collar. A hinged cover on this pipe is locked in place. Recently drilled holes are not yet so protected, but the casing has been allowed to extend far enough above the hole so that it is easily visible.

)
C.

All holes permanently abandoned are adequately sealed access, further use, and pollution possibilities. Proposed Departmental Action It is recommended that this portion of with the following conditions: 1. the proposal

prevent

approved

the applicant commits to determining the post-mining aquifer parameter's for the reclaimed areas and adjacent non-affected areas as reclamation proceeds and post-mining groundwater monitoring data becomes available; the applicant commits to quarterly monitoring for water levels and groundwater quality in wells P-4-C, P-13, Ct-1, P-12 and two additional wells still to be determined.

Environmental Consequences During mining, the major impact to the groundwater system will be the drawdown of both the overburden and coal aquifers due to the dewatering of the pits. The drawdowns in the coal will be greater because of the confining character of the aquifer. Drawdowns in the coal aquifer will be limited to the east and south of the permit area because of the coal cut which acts as a recharge boundary to the coal (see Map D-6-3, Volume III-A). The presence of the coal cut-out will minimize the cumulative hydrologic impacts of the

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PERMIT 500.Tl

Buckskin Mine with Amax - Eagle Butte and Carter - Rawhide Mines. The Carter Rawhide Mine will not cross the coal cut-out in their mine . plan until after the Buckskin Mine has closed operations (see Plates 2 and 6, Volume XII, Cumulative Hydrological Impacts Report). Map D-6-2C shows that the maximum five-foot drawdown in the coal aquifer extends approximately 2.5 to 3 miles from the permit boundary, primarily in a north, west, south-west direction. The extent of the five-foot drawdown will likely be less since these drawdowns are for a "worst-case" that assumes 0 surface recharge. In some instances, the extent of the five-foot drawdown could extend further due to localized fracturing of the coal; but these drawdowns should not extend significantly beyond the fractured areas. In the overburden aquifer, the drawdown due to pit dewatering is much more limited due to the discontinuous and lenticular character of the lithology. Map D-6-2d shows that the cumulative drawdown in the overburden extends less than one mile from the permit boundary. Because of the low yielding water bearing units, there are only a few wells in the overburden that may potentially be affected by drawdowns. The major impact to the groundwater system will be the removal of the coal and overburden aquifers within the permit area. Because Rawhide Creek will not be mined through, the alluvial aquifer will remain relatively undisturbed. The coal is a major aquifer in the region (T = 1000-3000 gpd/ft). Following the removal of the coal, the pit will be backfilled with overburden spoil material. In place of two confined aquifers (i.e., coal and overburden) there will be one unconfined aquifer (i.e., reclaimed spoil material). The predicted post-mining potentiometric surface will be similar in elevation and configuration to the pte-mining conditions. Estimated recharge rates (0.15 in/yr) and predicted post-mining permeabilities in the spoil aquifer (4.0 gpd/ft2) indicate that it will take a minimum of 75 years for post-mining groundwaters levels to reestablish to equilibrium. Recharge of the spoil ·aquifer will come from several sources. The major source of groundwater recharge to the spoil aquifer will be from the undisturbed coal and overburden aquifers surrounding the permit area. Rawhide Creek serves as a groundwater discharge point for the coal and overburden aquifers, i.e., groundwater flow into the permit area from the south, west, and north. Recharge will also occur through the spoil itself from the land surface. Presently, there is no conclusive data to use in predicting the postmining recharge/discharge rates. To identify the possible range of post-mining water levels, calculations were done using the premining recharge/discharge rate plus or minus 20 percent for the reclaimed area. The maximum range of potentiometric surfaces differed by 1.8 feet •.

- 47 -

P£RMIT 500.Tl

Two other ,sources of recharge to the spoil aquifer include recharge from a massive sandstone channel directly overlying the coal aquifer in places, which outcrops in the north east corner of the permit area and recharge from the coal cut-out to the south and east of the mined areas (see Maps D-6-3, and D-11-3). Neither of these areas will be mined, hence their function as recharge areas to the groundwater system will be preserved. But the importance of the sandstone and coal cut-out areas is minimal because they occur primarily dowri gradient from the spoil aquifer. The affect on the alluvial aquifer along Rawhide Creek by removing the coal and overburden aquifers will be minimal. Groundwater discharge from the coal and overburden aquifer in the permit area accounts for approximately five percent of the groundwater in the alluvium. Most of the alluvium is separated from the underlying coal or overburden by an aquitard composed mostly of alluvial clays, so that discharge to the alluvium occurs only at the coal subcrop (see Map D-11-11A). Once the coal aquifer beneath Rawhide Creek near the subcrop is recharged (approximately 25 years after mining ceases) it will begin discharging to the Rawhide Creek alluvium. Recharge of the alluvium is through streamflow in Rawhide Creek - primarily spring runoff events. Since groundwater contributes such a small portion to underflQw in the Rawhide Creek alluvium it is expected to have little effect on downstream users of water in Rawhide Creek or its alluvium. In general, the post-mining groundwater quality will be similar to the pre-mining water quality-of the saturated overburden. Premining concentration levels of TDS in the overburden aquifer ranged from 180-1400 mg/I. Values for the coal aquifer ranged from 439-1436 mg/l. The predictive capabilities of saturated paste extracts have not yet been determined, but the results of the tests on overburden spoil material at the Buckskin Mine indicate that TDS levels could be an order of magnitude greater for the initial pore volume (approximately 4000 mg/l). Since saturated paste extractions represent a "worst case" situation, the TDS levels may not reach the concentrations of 4000 mg/l. Two of the saturated paste extracts on materials from the south wall had TDS levels of 1300-1600 mg/1 (see Appendix E, Addendum D-6J - "Spoil Permeability and Water Quality Analyses, Appendix D-6, Volume III). In general, the concentration levels of sodium, sulfate and carbonates were also higher than baseline values. Van Voast (1976) in his studies found that the initial pore volume, of the reclaimed aquifer contained the greatest concentration of dissolved solids. By the third ot fourth pore volume, the concentration of dissolved solids has dropped significantly and will continue to decline until equilibriumis established. The groundwater quality outside of the permit area should be unaf-

SO
~'
2:

ia
Q:IIJ

- 48 -

PERMIT 500.T1

fected since groundwater flow is towards the permit area. Rawhide Creek, which flows through the permit area, functions as a discharge point for both the overburden and coal aquifers. It is expected that Rawhide Creek will continue to perform this function. (3.d.) Water Rights A. Description of Relevant Factors Groundwater Use Most of the water wells within a three mile radius of the Buckskin Mine are owned and operated by the Shell, AMAX or Carter Mining companies for monitoring. Within one-half mile of the Buckskin permit area, there are five known, non-mining related wells. Two of these wells are permitted. Both wells are owned and operated by Gilbert Oedekoven. They have stock and domestic uses. These wells are completed in the overburden and/or Anderson Canyon coal. There are also three non-permitted wells on the Mickey Wagensen property. One well is used for stock and domestic, another for stock and the use and owner of the third well is unknown. Table D-6G-l lists all the water wells inside and within one-half mile of the Buckskin permit area. Table D-6G-2 describes those wells that were inspected in this same area. There are 27 known non-mining related water wells between one-half and three miles from the Buckskin permit area. Fourteen of these wells are used primarily for stock. Eight are domestic wells and the use of the other five is described as miscellaneous. Table D-6G-3 is a +ist of these wells. Table D-6G-4 describes the wells which were inspected. These four tables can be found in the mining application, Volume III, pages 161-174. No surface water rights off the permit area will be impacted since neither Spring Draw nor Rawhide Creek are being diverted or mined through. In Table D-6G-6 water right permit No. 11277D and 11278D may potentially be impacted by the mining operations. A diversion dam and ditch along Spring Draw are reported in Table D-6G-6. The applicant should address the potential for impacts to these surface water rights and commit to replacing any surface water rights impacted by Buckskin's mining operation. B. Evaluation of Compliance Replacement of Affected Water Rights W.s. 3S-11-41S(b)(xii) requires that the applicant replace, in accordance with State law, the water supply of any owner of inter-

- 49 -

PERMIT 500.Tl

:)
_,.P/'

est in real property who obtains all or part of his supply of water for domestic, agricultural, industrial, or other legitimate' use from an underground or surface source, where the supply has been adversely affected by surface coal mining operations. The estimation of drawdown produced by the applicant identifies eleven wells which may be impacted by through mine pit dewatering. These wells are listed on page 77a of Volume III. Detailed descriptions of the wells are given on pages 163, 167, 168 and 169. The well locations are shown on Map D-6-10. As written on page 84, Volume III of the mine plan "Shell will replace, according to Wyoming Water law, the water supply of an owner of interest in real property who obtains all or part of his or her supply of water for domestic, agricultural, industrial or other legitimate use from an underground or surface source if the supply is affected by contamination, dimunition, or interruption proximatt!ly resulting from the surface mining activities." C. Proposed Departmental Action This part of the proposal should be stipulation: approved with the following

~)
---_.,

The applicant provides a plan explaining how it will mitigate any adverse impacts to surface water rights no. 11277D and 11278D. D. Environmental Consequences Drawdown in the coal or overburden aquifer is the major impact to water rights at the Buckskin Mine. Drawdown maps for both the overburden and coal aquifer showing the cumulative, drawdowns due to the mining operations of Shell - Buckskin, Amax - Eagle Butte and Carter Rawhide Mines ~ere compiled (Maps D-6-2c and D-6-2d). Most of the groundwater rights are for monitoring wells by mining companies. But 11 groundwater rights were identified as "potentially impacted water rights". Most of these rights should experience a total drawdown of less than 5 feet. But one water right may experience as much as 10 feet of drawdown in the well. Since the cumulative drawdown maps represent a "worst case" situation there may not be significant impacts to groundwater users. Shell has developed a monitoring plan to identify any potential problems early in the process and has committed to replacing the water of any groundwater right that is adversely impacted. More information is impacts to surface Relevant Factors. needed from the applicant concerning the water rights addressed in the Description of

- 50 -

PERMIT 500.Tl

(3.e.) Hydrologic Balance - Permanent Impoundments No permanent impoundments are proposed by the applicant. (3.f.) Hydrologic Balance - Cumulative Hydrologic Impacts

Description of Relevant Factors There are two operating mines adjacent to or in close proximity to the Shell Buckskin Mine. Immediately to the south and east of the Buckskin Mine is the Carter - Rawhide Mine in Sections 3, 4, 5, 6, 9, 10, 11, 12, 13, 14, and 15, T51N, R72W. AMAX - Eagle Butte is adjacent to Carter Rawhide in Sections 16, 21, 22, 23, 26, 27, and 28, T51N, R72W. Both mines are about 2-3 years into their mining operation. Amax - Eagle Butte began their operations in Section 16 and will move south across a coal cut-out running east-west through part of Sections 14, 15, 16, 21, 22 and 23. CarterRawhide began their operations in Sections 12 and 13 in the southeast portion of their permit boundary.Carter - Rawhide will be in the western half of Sections 3 and 10 by 1996 at least a mile and a quarter away from the Buckskin permit boundary. Plates 2 and 6 of the Cumulative Hydrologic Impacts Report (Volume XII) shows the mined areas of Amax - Eagle Butte and Carter Rawhide and their mining limits in 1996 with respect to Buckskin's permit boundary. Plate 6 also shows the coal cut-out trending northeast-southwest across the southeast corner of the Buckskin permit boundary. Both Amax - Eagle Butte and Carter - Rawhide will be mining through Little Rawhide Creek which is a major tributary to Rawhide Creek. Little Rawhide Creek has been declared an alluvial valley floor by the WDEQ/LQD. Little Rawhide Creek flows into Rawhide 'Creek just to the east of the Buckskin Mine and to the north of the Carter - Rawhide permit boundary -- Rawhide Creek.

)

Evaluation of Compliance Cumulative Hydrologic Impacts Chapter XXIII, subsection 2.a.(1), among other things, requires a determination of the short-term and long-term cumulative impacts to the hydrologic regime, including the expected total qualitative and quantitative, direct and indirect effects of all anticipated mining in the general area. The cumulative impact study includes analyses of Buckskin, AMAX Eagle Butte and Carter North Rawhide Mines.

- 51 pe~M'T

500.11

Surface Water The maximum average added discharge due to the dewatering of the pits from all three mining operations (Buckskin, Eagle Butte, and North Rawhide Mines) to Rawhide Creek has been calculated as 2 cfs. All dewatering rates or volumes for the Buckskin, Rawhide and Eagle Butte Mines are based upon estimates or actual data obtained at the mine site. This discharge into Rawhide Creek would be greater during the winter months than during warmer weather when the water is needed for dust control at the mines. .The added discharge to Rawhide Creek from all three mining operations should have minimal or no impact on the flow regime. Given the magnitude of the estimated flood peaks for Rawhide Creek, an additional two cfs in streamflow is within the hydraulic capacity of the channels. Flood peaks in Rawhide Creek should be reduced by capture of surface runoff in sediment ponds, which will also act to attenuate flood peaks. The size of the three mines relative to the size of the entire drainage area for Little Rawhide Creek and Rawhide Creek (106 square miles) is such that flows in Rawhide Creek would be reduced by less than 5 percent due to the attenuation of surface water runoff in the sedimentation ponds. The average annual flow in Rawhide Creek is 2 cfs. The discharge of 2 cfs from pit inflow is a maximum value. Since the time of low flow in Rawhide Creek is during the fall and winter, when discharge from.pit inflows will be higher, it is expected that the reduction in streamflow due to sedimentation ponds will be offset by discharge of pit inflow to Rawhide Creek. Surface Water Quality There are two major impacts to Rawhide Creek due to the three mining operations. The first impact is the reduction in sediment load in the surface runoff to Rawhide Creek. A reduction in sediment delivery could disrupt the equilibria of the fluvial system. Due to the small affected area at the Buckskin Mine relative to the total drainage area, the effect of a reduced sediment load should be negligible. The other major impact to the surface. water quality of Rawhide Creek concerns the increase in total dissolved solids and other water quality parameters such as sulfates and carbonates in the post-mining groundwater discharging to Rawhide Creek. As discussed above in Section 3.c. under "Post-Mining Groundwater Quality", groundwater discharge to the Rawhide Creek alluvium is not expected to have a significant impact since it only constitutes 5-8 percent of the underflow at the Buckskin permit area. It is estimated that the Amax - Eagle Butte, Carter - Rawhide and Shell - Buckskin mines occupy 8 percent of the Rawhide Creek water-

- 52 -

PERMIT 500.Tl

shed (including Little Rawhide Creek watershed). The drainage area of Rawhide Creek below the confluence of Little Rawhide Creek is 106 square miles. In comparing the amount of disturbed area v.s. the amount of undisturbed area in the watershed, it is easy to see that the cumulative impacts of the three mines on surface water quality should be relatively small. The ratio of mined area to the area of the watershed will be relatively small at anyone point in time. The timing of the three mining operations is another important factor to consider in determining the cumulative hydrologic impacts. Both Amax's - Eagle Butte and Shell's - Buckskin mines will have finished mining and reclamation will be almost complete . by the time Carter - Rawhide enters the area immediately adjacent to the two mines. In a sense, this timing of the mining operation will serve to limit the magnitude of the impacts due to mining (mined area v. s. size of total drainage area) but, the' timing will tend to lengthen the time that some portion of the drainage area is disturbed. It would be difficult to quantify the cumulative hydrologic impacts to surface water quality. Since neither Amax - Eagle Butte nor Carter - Rawhide have submitted their reports of the cumulative hydrologic assessment, there is not enough information to make an assessment of all three mines. Until the other two mines submit the information only a general conclusion can be made. The discharge of groundwater from the coal aquifer to Rawhide and Little Rawhide from pit dewatering operations would slightly improve the surface water quality because generally, the groundwater is of better quality than the surface water. With elevated TDS, following mining, the groundwater may have an adverse impact on surface water quality during discharge of the initial pore volume. The magnitude of this impact on the surface water quality depends upon the percentage of streamflow contributed by groundwater. More information on the groundwater contribution to Rawhide Creek is necessary to make a determination on surface water quality. Geomorphology Because Rawhide Creek and Spring Draw will not be mined, the geomorphology of the permit area has riot been analyzed in great detail. Pre-mining and post-mining drainage basin configurations, areas, densities, and stream length are given in Volume III, pages 24-26 and Map D-6-5 of the application. The major change in geomorphology is the removal of the three small internal drainages. The applicant's calculations show that the added area contributing to runoff will be compensated by the increased infiltration capacity. A reduction in overall average slopes in the reclaimed spoils will increase infiltration rates.

- 53 -

PfPMIT 500~Tl

There should be no adverse impacts to the geomorphology of Rawhide Creek outside of the permit area since the post-mining runoff potential will be similar to the pre-mining conditions. The Shell Buckskin mine operation will create relatively minor changes in the topography due to the fact that Rawhide Creek and Spring Draw will not be mined through. Shell - Buckskin's postmining topography approximates the pre-mining contours. Carter Rawhide will coordinate their final regrading and recontouring so that their post-mining topography lines up smoothly with Shell Buckskin's reclaimed topography. Since Amax - Eagle Butte mine is not directly adjacent to the Shell - Bucksin mine there will be no need to coordinate post-mining topographies. Cumulative Impact - Groundwater - Quantity The applicant has predicted very little overlap between the drawdown caused by their operation and the adjacent North Rawhide operation. The hydrogeology of the area is such that the aquifer characteristics of transmissivity and storativity change drastically. A coal cut-out existing between the two operations. The Buckskin operation is scheduled to terminate mining in 1997. North Rawhide will not cross the coal cut-out until 2003. The coal cut-out is more permeable than the surrounding coal and acts as a recharge boundary. Only minimal drawdown should extend beyond this boundary. Map D-6-2A and D-6-2B are the cumulative drawdown in both the coal and overburden aquifers for the Buckskin Mine for the term of permit. Maps D-6-2C and D-6-2D are the maximum cumulative drawdown for both aquifers for the Buckskin mine for the life of the mine (1997). The cumulative drawdown contours are limited in extent to the east of the Buckskin permit boundary - apparently due to the \ presence of the coal cut-out~ During the mining operations, drawdows due to Buckskin's mine will have little effect on the availability of groundwater for domestic-stockwatering wells. Most wells within the cumulative drawdown zone will be subject to drawdowns of less than 5 feet. In those cases where the wells may be subject to more extensive drawdowns, the Buckskin Mine will contact the owners on an annual basis and will take any remedial action that is necessary. Carter - Rawhide's map of drawdowns in the coal and overburden aquifers (Figure 13, Mine Plan, TFN 1 4/215) show quite a bit of overlap to the west - northwest across the coal cut-out. Since Carter - Rawhide will be mining on both sides of the coal cut-out, it is reasonable to expect the extensive drawdown. Again the timing of mining operations will minimize the drawdowns since Buckskin will no longer be dewatering the coal or overburden aquifers.

- 54 -

PERMIT 500.T1

Because the maximum drawdown maps represent the "worst-case", the . drawdowns may in fact be less than predicted. If the "worst-case" occurs some wells to the west - southwest of the Buckskin permit area may suffer drawdowns up to 30 feet. Both Buckskin and Rawhide mines have' committed to replacing any water rights adversely affected in quality or quantity. Cumulative Impact - Groundwater - Quality The groundwater flows to the Buckskin permit area from all directions. The flow to the south is limited by the coal cut-out. Because the groundwater flow is towards the Buckskin Mine permit area (and to Rawhide Creek) the groundwater quality outside of the permit area should not be adversely affected either during mining or during reclamation (see Evaluation of Compliance - Preservation of Non-Affected Groundwaters for discussion on groundwater discharge to Creek). For all three mining operations, Rawhide Creek serves as the regional discharge point for both the coal and overburden aquifers. Groundwater discharge at Amax's - Eagle Butte is primarily to Little Rawhide Creek. At Carter - Rawhide mine the groundwater discharge is to both Little Rawhide Creek and to Rawhide Creek for the coal and the overburden aquifers. Because the regional groundwater flow is towards the permit for all three mines, impacts to the groundwater quality outside the permit area should be minimal. It is difficult to quantify the cumulative hydrologic impacts to the groundwater quality. Until Amax - Eagle Butte and Carter Rawhide submit the results and their analysis of the post-mining groundwater quality, any assessment of the cumulative hydrologic impacts on the regional groundwater quality is based upon very limited and incomplete data. Due to the lack of data only a general qualitative conclusion can be made that assumes a worst case situation. Generally, the lithologic and chemical character of the Fort Union Formation is quite uniform in northeastern Wyoming. Therefore, it was assumed that the overburden and hence the post-mining groundwater quality would be similar for all three mines. Studies at the Buckskin mine showed that an increase in total dissolved solids and sulfates could be expected in the post-mining groundwater quality. The category of use of the post-mining groundwater would be Class III - livestock watering, according to the WDEQ/WQD Rules and Regulations - Chapter VIII.

)

- 55 -

PERMIT 500.Tl

Since Rawhide Creek and Little Rawhide Creek are points of regional groundwater discharge from both the coal and overburden aquifers the major concern of the post-mining groundwater quality is the impact to the surface water quality. Rawhide Creek is considered to be an intermittent stream within the Buckskin permit area. Groundwater discharge from the coal and overburden aquifer accounts for approximately five percent of the groundwater within the alluvium or stream in the.Buckskin permit area. Within the Buckskin permit area surface water accounts for more than 90 percent of the inflow-outflow from the Rawhide Creek alluvial system. In discussions with personnel at Carter-Rawhide mine, baseflow appears to be an important component of stream flow in Rawhide Creek above the Buckskin permit area. Based upon observations over a seven year period of record, at least a minimal flow was recorded 70 percent of the time indicating the relative importance of baseflow. In Little Rawhide Creek, the importance of baseflow to stream flow varied from Amax's - Eagle Butte permit area to Carter's - Rawhide permit. Due to the presence of a sand paleochannel (coal cut-out) in Sections 21 and 16 groundwater from the coal and overburden aquifer discharges to the creek south of the paleochannel. Groundwater discharge is estimated at .42 cfs, accounting for approximately 70 to 80 percent of the recorded stream flow at the north permit boundary. North of the paleochannel there is. little if any groundwater discharging to the creek due to the "daming" effect of the coal cut-out. This stretch of Little Rawhide Creek is considered to be ephemeral. Within the Rawhide permit area there are stretches of Little Rawhide Creek where no flow is present in the channel but groundwater seepage contributes to sub irrigation conditions in the creek bottom. The creek is considered to be ephemeral within the Rawhide permit area. Assuming a worst-case situation where baseflow accounts for a major portion of the streamflow in Little Rawhide and Rawhide Creeks, the surface water quality would most likely not be significantly impacted. In spite of an increase in TOS,and sulfates, the postmining groundwater quality is predicted to be better than the surface water quality. Although the post-mining groundwater quality will be degraded its pre-mining use - livestock watering should be presented. Material Damage to Areas Outside the Permit Area W.S. 35-11-406(n)(iii) requires a finding that the .operation has been designed to prevent material damage to the hydrologic balance outside the permit area.

- 54 -

PERMIT 500.T\

Surface Water There should be minimal or no impact on surface water quantity or quality outside the permit area. The two major drainages, Spring Draw and Rawhide Creek will not be mined. The streamflow through the permit area should increase by no more than 0.7 cfs due to dewatering of the Buckskin Mine. Sedimentation ponds and dust control measures should minimize the time increased flows might occur. The total increase in streamflow due to all 3 mining operations will be no more than 2 cfs, which is well within the channel capacity of Rawhide Creek.

- 55 -

PERMIT 500·Tl

The surface water quality of Rawhide Creek should not be adversely affected since all surface runoff from disturbed areas will be routed through sedimentation ponds so that the water quality meets the NPDES permit requirements. Groundwater discharge to the Rawhide Creek alluvium accounts for 5-8 percent of the underflow and therefore the increased total dissolved solids of the postmining groundwater should have little impact on the surface water quality of Rawhide Creek outside the permit area. It is difficult to quantitively predict the impacts to the surface water quality outside the permit area.for all three mines combined, since Amax and Carter have not submitted data to show the relative importance of groundwater discharge to Little Rawhide Creek or Rawhide Creek. It would be safe to assume that groundwater dis~ charge to Little Rawhide Creek is limited since it is classified an ephemeral stream. But it would be highly speculative to estimate the significance of groundwater to total streamflow in Rawhide Creek without any data. Since surface runoff at both Amax's Eagle Butte and Carter's Rawhide Mine is subject to the same NPDES permit requirements, material damage to the surface water quality of Rawhide Creek, should not occur outside the permit area. Ground Water The pre-mining conditions at the Buckskin Mine show that groundwater flows to the permit area from all directions. Post-mining predictions show the same configuration of the potentiometric surface. Because of the small affected areas, the impact on the coal and overburden aquifers in terms of the groundwater flow system should be minimal outside the permit area. There will be an increase in total dissolved solids of the groundwater in the initial pore volume by as much as an order of magnitude greater than baseline values. This finding is based upon the results of saturated paste extracts of the spoil overburden at the Buckskin mine. Saturated past extracts usually present a "worst-case" situation. Subsequent pore volumes will show a declining concentration of total dissolved solids until the system reaches a new equilibrium. Assuming similar overburden conditions at Amax - Eagle Butte and Carter - Rawhide mines, their post-mining groundwater quality will be similar to the post-mining groundwater quality at the Shell - Buckskin Mine. Because the groundwater flow is toward the permit area for all three mines, the degraded groundwater should' be limited to the permit area with no impacts to the groundwater quality outside the permit area. Based upon the available information, and assuming similar groundwater conditions at all three mines, material damage to groundwater quantity or quality outside the permit area should not occur.

Proposed Departmental Action

- 56 -

PER MIT 500· Tl

~
....

""y
(3.g. ) Blasting A.

The proposed departmental action should be approved. ;

Description of Relevant Factors Blasting will be conducted at the Buckskin Mine in order to fragment both overburden and coal thus facilitating mining. Generally, ANFO will be placed down the hole with primer and detonating cord used to insure initiation. The coal blasting holes will be drilled on a 20 foot square pattern at a depth of either 20 feet or 50 feet depending on the bench height. A powder factor of .2 1bs. of explosives per ton of coal is planned. The 50 foot deep holes will contain 170 1bs. of explosives and the 20 foot holes will contain 70 1bs. of explosives. The overburden will be shot with a powder factor of approximately .40 1bs. of exp10s~ves per cubic yard of overburden on 30 foot centers and 50 foot deep holes with 670 1bs. of explosives per hole. The applicant has committed to the maximum weight of explosives to be detonated in anyone 8ms delay period formula, W = (D/60)2, as outlined in Section 5.b.(5), Chapter VI, Land Quality Regulations. Table 3 gives the pertinent parameters to consider and it was found to be within the limits of the formula. The distances to the nearest dwelling not owned by the applicant are also included as part of this table. The applicant addresses the requirement to publish the blasting schedule as outlined in Section 3, Chapter VI, Land Quality Regulations. F1yrock and airb1ast limitations were briefly discussed on page 29 of the application. Ground vibration should be controlled by the implementation of the W = (D/60)2 formula. The applicant committed to seismograph and airb1ast monitoring, if required.

Evaluation of Compliance The application is essentially in compliance with the regulations controlling airb1ast, ground vibration and f1yrock. The stemming ratios, 2.0 (50 foot holes) and .80 (20 foot holes), for coal blasting are very conservative and should adequately control f1yrock. The stemming ratio for overburden is .83 which is also a very conservative ratio. Table 3 of the application commits the applicant to a maximum weight of explosives per 8ms delay. These calculations were confirmed, but I assumed a hole diameter that most other mines in the Powder River Basin are using (7 7/8 for coal and 9 7/8 for overburden). Therefore, the applicant will be required to submit the hole diameter, see Section C below.

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PERM\T 500-

the Executive Order 11593, the National Historic Preservation Act of 1966, the Advisory Council's "Procedures for the Protection of Historic and Cultural Properties" (36 CFR Part 800), and the Wyoming Environmental Quality Act. OSM, the Wyoming Department of Environmental Quality, and the Wyoming SHPO have reviewed the data recovery plan, as presented in the mine plan, and found that the plan will satisfactorily mitigate the adverse effects to site 48CA89. Therefore, OSM and the Wyoming SHPO have found that a "No Adverse Effect" determination can be made. Documentation of this decision has been sent to the Advisory Council as specified in the PMOA. C. Proposed Departmental Action Approve with the following stipulation: that within 90 days of the approval of the permit to mine, Shell will submit the final report on the mitigation of adverse effects to archeological resources (48CA89) within the Shell Buckskin Mine railroad corridor.
D.

Environmental Impacts and Technical Alternatives During mining operations, some prehistoric sites will be destroyed. Since none of these sites are considered eligible for listing in the National Register of Historic PI_aces, measures will not be proposed to minimize or prevent adverse impacts. One site was located within the proposed railroad corridor right-of-way and will be partially impacted. It (48CA89) has been found to be eligible for the National Register. The company has proposed measures to minimize these impacts through a data recovery program of that portion of the site. However, even during well-developed and implemented mitigation procedures, certain adverse impacts to this cultural resource are unavoidable, and thus there will be environmental impacts even if the mitigation plan is adhered to. Because that portion of the site proposed for mitigation would be destroyed after mitigation is complete, it cannot be reexamined for information as part of later and different research efforts, nor can the data retrieved be reconfirmed. Thus, there is a loss of potential information, and the physical loss of that portion of the site -- both must be considered environmental impacts. Cultural resources which are located adjacent to the mine plan area may be impacted by mining activities as a result of increased population in the general area. There may be increased vandalism and unauthorized collections associated with recreational activities and other pursuits. Based on available technology, there is always a possibility that cultural resources inventories may not have located all sites within the survey boundaries. Therefore, there remains a potential for destroying unknown sites.

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PERMIT 500·Tl

. S'\ .
,

':'~)

Losses could be even greater for sites not currently eligible for the National Register of Historic Places. Such sites may, in the future,. be deemed "significant", even though not presently considered so. Any site which is not avoided or protected through mitigation of the adverse effects W9uld be lost. Cultural resources are a nonrenewable resource, and once lost there is an irretrievable loss of scientific information.
(3. r.)

Bonding Determinations A. Description of Relevant Factors Shell Oil Company's projected costs for reclaiming the acreage disturbed during the first year of permit term totalled $15,133,700 in 1981 dollars. The bond estimate is based on the cost of 70¢ per cubic yard for replacing overburden, $606 per acre to level that overburden and $3,987 per acre for surface reclamation. This figure includes 73¢ per cubic yard for topsoil replacement, which along with the 70¢ per yard for overburden replacement, is somewhat on the low side for mines in this area. On the other hand, the Buckskin has smaller pits and' so haul distances are shorter than for \many other mines. Shell should offer justification for these lower costs by showing how they were derived including the factors used in computation of equipment costs and cycle times.
B.

Evaluation of Compliance Shell Oil Company has submitted an estimate of the reclamation costs along with some supporting calculations. The bond estimate for the first year of the permit term covers 581.5 acres of disturbance. Some information provided with the cost estimate is sufficient to allow back-circulation to be made. Other data is lacking and is requested above. Shell Oil Company has submitted a public liability insurance policy as required by W.S. 35-11-406(a)(xiii) and the Land Quality Division, Rules and Regulations, Chapter XIII, Section 2.(b) and (c). The policy also includes a rider stating the insuror will notify the Administrator of the Land Quality Division within ten (10) days if the Shell Oil ,Company substantially changes, terminates, or fails, to renew the policy.

Proposed Departmental Action

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'.

Approval with the following conditions: Shell should supply detailed information, including calculation sheets, supporting their topsoil and overburden moving costs which, as noted above, are less than the average for other coal mines in the Gillette area.
(3. s.)

Alluvial Valley Floors

Relevant Factors Considered The valleys of Rawhide Creek and Spring Draw flow through the Buckskin permit area. Both valleys have been declared Alluvial Valley Floors (AVF's) by the DEQ (March 11, 1980) and OSM (July 30, 1980). The OSM approval letter with stipulations disagreed with the extent of the unconsolidated streamlaid deposits present in Spring Draw. A joint field inspection was held with OSM, DEQ and Shell personnel. The extent of the streamlaid deposits were reconsidered by the DEQ-LQD which resulted in the most recent AVF declaration of extent which was made on November 14, 1980 (letter to C.R. Reiter from W.C. Ackerman). The extents were determined on the occurrence of unconsolidated stream-laid deposits and agricultural activities. OSM concurred (December 15, 1980) with the November 14, 1980 determination of extent of unconsolidated streamlaid deposits. Shell Oil, in a January 9, 1981 letter to W.C. Ackerman from C.R. Reiter disagreed on the determination of November 14, 1980. The major disagreements expounded on by Shell were as follows: 1. Rawhide Creek a. Although agreement has been reached on the extent of the stream-laid deposits (Surficial Geology Map D-11-1), the extent of the AVF where development potential exists has not been resolved. Shell contends that no potential for future development of flood irrigation activities exists on the disputed area and they should not be included as part of the AVF (Map D-11-6). There is also disagreement as to whether certain cultivated areas found on stream terraces are presently sub irrigated and may have a potential for flood irrigation.

)

Spring Draw a. The major contention is whether the surficial geology (Map D-11-1) has been correctly interpreted. The disagreement is whether the unit df is unconsolidated stream-laid depos-

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PERMI.T 500.Tl

(~). . ..
b.

its or whether it is a colluvial deposit. The significance to farming and developed lands may need to be adjusted depending on the final determination of the extent of the stream-laid deposits.

At. the present time Shell does not propose to mine either of these valleys, however, some surficial disturbance is to take place. Initial significance tests showed that the impact would be insignificant to the farming (ranching) operations. The present extent (November 14, 1981 determination) would be the maximum extent of the AVF, which will be used in the evaluation of the hydrologic functions and material balance ramifications. Shell is presently collecting additional information to clearly define whether the geologic unit df in Spring Draw is fluvial in nature or colluvial in nature. The Rawhide Creek valley contains about 190 acres of unconsolidated stream-laid deposits within the permit area (Map D-II-I). Three terraces have been identified; Qt, Qt2 and Qt3, in addition to the channel/overbank deposits to make up the components identified as the unconsolidated stream-laid deposits (Map D-II-I). The current agricultural practices in the valleys involves haying and grazing (Appendix D-I, Appendix D-II, and Map D-I-I). Approximately 52.8 acres of the stream-laid deposits along Rawhide Creek (page 41) contains flood irrigated and/or sub irrigated agricultural activities. Five spreader dikes deliver irrigation water onto the Rawhide Creek Flood Plain. Spring Draw is different than Rawhide Creek. Flood irrigated/subirrigated agricultural activities, haying and grazing, are presently occurring in Spring Draw. Two water rights were issued for irrigation use of the Spring Draw drainage. Irrigation ditches are present in the valley. Map D-l-l indicates about 39 acres of haying and grazing are occurring in the Spring Draw Valley, with 14 acres being flood or sub irrigated. The sections of the application that were evaluated with regard to the extent of the stream-laid deposits were contained in Volume VIII of the mining application and include the following: 1. 2. . 3. 4. 5. 6. Geologic evaluation - D.5-14. Lithologic logs for alluvial geologic sections - D-Ila p. 189 • Backhoe pit logs - D-llg p. 189. Longitudinal geologic section Rawhide Creek - p. 7. Longitudinal geologic section Spring Draw - p. 8. Geologic cross-section Rawhide Creek (1, 8) - pp. 10, 13. Geologic cross-sections Spring Draw (2, 3) - pp. 11, 12. Summary of stream bed deposits within the Shell Buckskin Mine

)

7. 8.

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PERMIT 50(l. Tl

plan area - Table D-11-1 p. 14. 9. Surficial geology map - D-11-1. 10. Map showing location of stream cross-sections and flood plains - D-1l-5. 11. Map of alluvial and irrigated areas - D-11-6. 12. Map of alluvial deposits adjacent to permit area - D-11-7. The surface water quality ranges from about 2,000 umbos/cm to over 9,000 umhos/cm which makes the water quality marginal to poor for irriga~ion practices (Appendices D-6 and D-11). The waters would be classified as C5-S1 or C4-S1 using U.S.S.L. criteria (Handbook 60). The water has a high to very high salinity hazard but does not appear to have a sodium hazard. The majority of the soils in the valleys would be suitable for irrigation where drainage is adequate. Poorly drained areas are found in the valleys due to a high water table. Salt accumulation is apparent in some areas where the soils are poorly drained (i.e., high water table), Appendix D-7). If water quantities are sufficient to maintain adequate leaching fractions, soil degradation should not occur under proper irrigation management. The potential for flood irrigation was evaluated by the applicant in Appendix D-11 (Volume 8, pages 25 to 32a). Using the criteria outlined by the applicant, those lands which would be identified as having a potential for flood irrigation have been flooded in the past through the use of the spreader systems.
C~

Evaluation of Compliance Determination of AVF The vial map from Rawhide Creek and Spring Draw valleys have been declared alluvalley floors by DEQ and OSM. The extent is defined by the which accompanied by November 14, 1980 letter to C.R. Reiter W.C. Ackerman.

Significance to Farming The applicant does not, at the present, propose to mine either Rawhide Creek or Spring Draw which have been designated alluvial valley floors. The extent of which are defined by the map which accompanied the November 14, 1980 letter to C.R. Reiter from W.C. Ackerman. However, surficial disturbance for access roads, facilities and the railroad loop will occur (most has already occurred). The permit area is comprised of 1,467 acres, 1,277 acres of which is grazed. There are 130 acres of bottomland found on the permit

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PERMIT 500'.Tl

" .r-\ . ':':)
.'----

area with about 62 acres managed as grazing land and 68.4 acres of bottomland, which is associated with Rawhide Creek and Spring Draw (Volume 1, Table D-I-4, page 18) is hayed. Portions of the Wagensen Rawhide Creek Ranch comprises 91 percent of the Buckskin permit area, and all of the area which has tentatively been termed potential alluvial floor by the applicant (Volume 8, page ~7a). The Rawhide Creek Ranch was originally composed of about 9,000 acres; the owner estimates the carrying capacity is approximately 530 AUM's (Animal Unit Month) within the permit area and 5,000 AUM's on the ranch acreage outside the permit area. This represents an annual carrying capacity of 461 AU's (Animal Units). The applicant provides considerable detail concerning production and the carrying capacities for both ranches in the Appendices D-l and D-ll (Volumes 1 and 8). The Wyoming Rules and Regulations (Chapter III Section 2.d.) defines an approach to assess the significance of a given alluvial valley floor to the ranching operation. This technique indicates that a production loss of 3.5 percent or less would be negligible impact to the ranch. The applicant has stated that 17.6 acres of potential alluvial valley floor will be affected through the construction of haul roads, coal handling facilities, Sediment Pond No. 1 and the railroad spur. These disturbances would result in a loss of 0.9 percent of the Rawhide Creek Ranch's total productivity (Volume 8, pages 48 Based on estimates derived from Exhibit 3a and Exhibits and 49). D-l-1 and D-II-6 and additional 13 acres of Alluvial Valley Floor will be disturbed in Spring Draw. Assuming that the entire 13 acres affected in Spring Draw was developed bottomland (hayed bottomland - 3.00 AUM/acre and 0.3 AUM/acre aftermath, Table D-I-4) a total of 42.9 AUM's (3.6 A.U.) of hayed and grazed bottomland would be affected. The applicant had defined that 4.0 A.U. or a 0.9 percent loss of production will occur during the disturbance of Rawhide Creek. A total of 7.6 A.U. (Rawhide Creek plus Spring Draw) will be lost from production during the life of the Buckskin Mine operation. These disturbances would result in a loss of 1.7 percent of the Rawhide Creek Ranch's total productivity (Volume 9, pages 48 and 49 plus the above discussion). According to Guideline No. 9 standards, this is a negligible loss to the ranching operations (Chapter 'III, Section 2.d.). Flood irrigation currently occurs in the Rawhide Creek valley bottom through the use of five spreader dikes (Vol. VIII, page 32). The dikes divert available runoff onto the floodplain of Rawhide Creek in the southeast corner of the mine plan area. The applicant is not explicit regarding the amount of runoff available for irri-

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PERMIT 500 ~ T1

gation (i.e. the amount of water available during the growing season). The acreage of valley bottom that is flood irrigated as opposed to subirrigated is not delineated in the application. The mining application delineates 47 acres in the Rawhide Creek Valley as sub/flood irrigated bottomland hay/grazing. These hay/grazing areas are hayed in most years when water is sufficiently available. Rawhide Creek has an additional four acres on the floodplain that are utilized as sub/flood irrigated· grazing. Spring Draw has 14 acres that are delineated as flood/subirrigated grazing. An additional 17 acres on upper terraces in Spring Draw are currently designated as bottomland hay/grazing; however, Shell did not evaluate whether sub or flood irrigation was occurring on this site. The valleys of Rawhide Creek and Spring Draw contain 200 acres and Water availability 52 acres respectively of streamlaid deposits. is sufficient in both drainages to support the agricultural activities of haying and grazing on parts of the flood irrigated or subirrigated areas. On the other hand, water quality in the alluvium ranges from electrical conductivities of 2380 to 3900 umbos/cm. Salts have also accumulated in the soils ~nthe valley floor (SCS letter, page 170). The soils and water quality information depict a situation that is marginal to poor for irrigation practices. The Rawhide valley currently supports 47 acres of irrigated/subirrigated hayed bottomland, and 19 acres of irrigated/subirrigated grazed bottomland (OSM calculations). Spring Draw supports 14.14 acres of irrigated/subirrigated grazing bottomland and an unknown amount of irrigated/subirrigated hayed bottomland. The current and potential use of the Rawhide Creek and Spring Draw valleys for irrigation/subirrigation agricultural activities justifies designating the valleys as alluvial valley floors. The OSM limit of alluvial valley floor includes 200 acres (OSM calculation) of streamlaid deposits designated for the Rawhide Valley (Maps D-ll-l, D-II-6 and 52 acres of streamlaid deposits in Spring Draw. Essential Hydrologic Functions The essential hydrologic f~nctions of the alluvial valley floor in Rawhide Creek within the Buckskin permit area have been identified in Appendix D-ll, Volume VIII of the application. The applicant completed a study on the alluvial valley floor upon declaration by WDEQ/LQD of the potential for one along Rawhide Creek. Map D-II-6 shows the area covered by stream-laid deposits and irrigated areas that are considered part of the alluvial valley floor. From the study the following essential hydrologic functions were determined to exist. 1. Subirrigation exists along Rawhide Creek but is limited to

)

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PERMIT 500.T!

areas of channel and overbank deposits. The saturated thickness of the alluvium ranges up to 18 feet. The groundwater level either intersects or is within 2 feet of the bed of Rawhide Creek. Soil moisture tubes indicated that subirrigation occurs on the floodplain (fa) but no significant subirrigation was noted on the stream terraces (QTl, Qt2 or Qt3) or slope wash. The only place where seasonal water fluctuations could provide available water for plant growth were limited to approximately 56 acres of channel and overbank deposits along Rawhide Creek. Subirrigation along Spring Draw is confined to approximately 10 acres of alluvial sediments in the bottom of the stream channel itself. It was determined that no subirrigation occurred outside the incised channel of Spring Draw except that associated with some springs and seeps.
2.

Natural flood irrigation on Rawhide Creek was determined to exist for the area inundated by the 2 year flood. The area along Rawhide Creek inundated by the two-year flood covers only 34.1 acres of alluvium close to the creek. The two-year flood which has a 50 percent chance of occurrence in anyone year is the only flood event considered agriculturally useful. . On Spring Draw, the two-year'- 24-hour precipitation event produces no runoff. Acreages inundated by the floods resulting from the two-year and 100-year, 24-hour precipitation event are shown in Table D-11-3 and on Maps D-11-5 and D-11-6.

Lands identified as suitable for potential artificial flood irrigation showed that these areas have been sporadically flooded in the past. The variability in the mean annual flow (range from 0.4 cfs to 2 cfs) prevents further development of areas along Rawhide Creek for' artificial flood irrigation. Since the mean annual flow is not a good indicator of available water supply, the 2 year, 24 hour flood was used to estimate water availability. About 34 acres of the channel and overbank deposits are within the limits of the 2 year, 24 hour flood. There are presently five non-permitted spreader dikes along Rawhide Creek to make use of the rare flood events by causing the flood water to spread over the land surface close to the stream. The dikes make it possible to irrigate those areas designated as floodplain (fa? The dikes are all in the southeast corner of the permit area where the floodplain is relatively wide. None of the dikes makes possible the irrigation of the terraces. There are two water rights for irrigation out of Spring Draw but the current landowner does not maintain them for irriga- .

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PERMIT 500.T1

tion. Most years there is insufficient water in Spring Draw to divert it for irrigation. No mining is proposed to occur in the OSM and WDEQ-LQD designated alluvial valley floors of Rawhide Creek and Spring Draw (Addendum D-5-C cross-sections A-B, C-D, E-F, G-H, and I-J). The effect of the mining operation on surface water for irrigation purposes and groundwater for sub irrigation was assessed to determine if the essential hydrologic functions will be preserved. The drainage divides will not be significantly altered in the plan for the post-mining topography (see Map D-6-l4). Thus, the drainage areas will not change. The total pre-mining relief of the basin will remain the same; however, the headwater slopes will be increased in the vicinity of the final reduced highwall and the slope of the land will be decreased over the remainder of the mined area. It is expected that peakflow will likely decrease from the area due to the generally decreased slope in the disturbed area and the overall volume of runoff will likely be reduced to a slight-moderate degree due to induced infiltration over areas of very low grade. The quality of the surface flow is not expect~d to deteriorate as a result of the mining operation other than what is contributed as dicharge from the post-mining spoil zone. This assumption is based on the premise that revegetation will be successfull and that sedimentation ponds will control erosion prior to revegetation. The changes in post-mining groundwater quality will be discussed below. During mining, surface water flow will be decreased slightly because of seepage, dust suppression and evaporative losses from sedimentation ponds, but most of the runoff will be passed out of the sediment ponds after proper holding times. During periods of high groundwater inflow to the pits, surface discharge from the sedimentation ponds could increase to a slight degree over surface runoff prior to mining. Peakflow for the basin will be reduced during mining because of detention in the settling ponds. During mining partial dewatering of the alluvium of Spring Draw and Rawhide creek will occur in the area between the eastern extent of the aquitard and the area where the aquitard is missing as shown on Map D-ll-l. In the area where the coal is overlain by the aquitard, the coal aquifer is found in a confined condition and is somewhat isolated from the alluvium. Well CT-l completed into the coal under the t3 terrace demonstrates the confined condition. On the other hand, a three-day pump test was conducted using coal monitoring well E-lO-C. This test indicated unconfined conditions. The well is located in the area between the extent of the aquitard an~ the base of the coal outcrop, just above the t2 terrace of Rawhide Creek (Maps D-ll-l and D-6-l). The pump test showed a hydraulic connection between the coal and the alluvium where it was

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PfRMIT SOO.T1

over the coal (Vol. VIII, page 61). Wells that were located beyond the coal outcrop did not show drawdowns during the test. Dewatering of the mine pit will cause a lowering of water levels in the alluvium of the alluvial valley floors. Shell assumes that complete dewatering of the alluvium wiil occur where the coal subcrops to the valley floor. After 90 days, drawdown in the alluvium is predicted to be ten feet at a distance 50 feet from the coal outcrop; at 200 feet from the coal outcrop the drawdown is expected to be approximately one foot (Vol. VIII, page 66). There will be a slight reduction in vegetative production due to a decrease in subirrigation caused by the drawdowns in the alluvium. Evapotranspiration along Rawhide Creek is calculated to be 114.2 ac-ft/yr ,which equates to an average flow of 0.16 cfs. It was assumed that the sub irrigated areas along Rawhide Creek consumed the ideal irrigation requirement for the Gillette area of 1.7 feet (Trelease, et. al~, 1970) and a total of 67.2 acres along Rawhide Creek valley within the mine plan area was estimated to be potentially subirrigated and/or flood irrigated. An estimated average annual inflow of 1.40 cfs from surface water and 0.09 cfs from groundwater is the estimated total input to the alluvial system. Consumptive use within the mine plan area is approximately 0.16 cfs the remainder being outflow 1. 33 cfs (1. 26 cfs as surface water, 0.07 cfs as underflow). The areas that are most conducive to recharge to the coal 'aquifer have been identified by Shell as the area of coal outcrop (see Map D-6-3), and an area northeast of the mine where it appears that the aquitard over the coal is missing, allowing direct recharge to the coal. The area to the northeast will not be mined and much of the coal outcrop is not currently proposed to be mined. The two areas considered to be best suited for recharge will largely be left after mining. Compensating for the decrease in infiltration caused by disturbance of the soil is an expected increase in recharge on the gentle, reclaimed topography. With gradients on the reclamation landscape of 1/2 percent and lower, there is also a potential for water to concentrate in small depressions, contributing to uneven settling of the surface. The end result will be more surface water infiltrating and percolating to the water table. The increased volume of flow expected in the groundwater may result in a higher water table causing Rawhide Creek to flow more regularly. The spoils are not expected to be barriers to groundwater movement and flow patterns should be restored toward Rawhide Creek (Maps D-6-3 and D-6-4). If the hydraulic conductivity of ·the spoil is greater than the coal, flow to the valley floors will still be con~ trolled by the hydraulic conductivity in the remaining coal and overburden that will be left along the valley sides. Because, flow rates are expected to approximate the pre-mining rates, groundwater levels. especially in the undisturbed valleys, should be restored

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PERMIT SOO.TI

'/~ )')
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to near original levels • A plan for monitoring the affects of mining on the alluvial valley floors of Rawhide Creek and Spring Draw is provided for in Appendix D-6, Volume III. Maps D-6-9 amd D-6-12 show the locations of the monitoring sites during mining and upon reclamation the monitoring plan appears to be adequate for monitoring the effects of mining on the alluvial valley floors.

.-'

c.
D.

Proposed Departmental Action The proposed action should be approved. Environmental Impacts of Proposed Departmental Action 'In summary, during mining the essential hydrologic functions of surface water quantity and quality will be maintained for agricultural uses. Groundwater drawdowns during mining will cause a decrease in vegetative production where sub irrigation had previously occurred. After mining, the groundwater quality will be higher in TDS than before mining. The groundwater quality from the spoil aquifer should still be better than the ·groundwater currently in the alluvium (i.e., underflow). Groundwater quality should not significantly affect the function of subirrigation. Groundwater quantities may be increased due to induced recharge caused by ponding on the reclaimed surface. The hydraulic conductivities of the spoil should be equal or higher than pre-mining but flow rates to the valley floor should be controlled by the buffer of coal and overburden that will be left between the mine and the alluvium. It appears that generally, the mining operation, as proposed, will preserve the essential hydrologic functions of the valley floors.

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