This is a text-only version of the document "Eagle Butte Mine - SW Ext 2 Amendment - Hydrological Impacts -". To see the original version of the document click here.

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Table of Contents
EXECUTIVE SUMMARY .......................................................... -J-

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1. INTRODUCTION ................................................... ~ ........ .. 1.1 Description of the Area .................................................. " 1.1.1 Topography, Geomorphology, and Geology ........................... 1.1.2 Climate, Soils, and Vegetation ..................... . . . . . . . . . . . . . . .. 1.1.3 Hydrology .....................................................

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2. CUMULATIVE IMPACT AREA ......................'........................... -11-

2.1 Surface Water .......................................................... -112.2 Groundwater............................................................ -113. BASELINE HYDROLOGIC CONDITIONS ... .................................... 3.1 Surface Water .......................................................... 3.1.1 Flow System ................................................... 3.1.2 Individual Drainages ............................................. 3.1.2.1 Hay Creek ............................................. 3.1.2.2 Rawhide Creek .......................................... 3.1.2.3 Little Rawhide Creek .................................... , 3.1.2.4 Dry Fork of the Little Powder River ........................ , 3.1.2.5 Little Powder River ..................................... , 3.2 Groundwater .................... ; ...................................... 3.2.1 Flow systems ................................................... 3.2.2 Groundwater Quantity & Quality of Aquifers & Leaky Aquitards ......... 3.2.2.1 Alluvial Aquifer ........................................ 3.2.2.2 Wasatch Aquifer ........................................ 3.2.2.3 Clinker Aquifer ......................................... 3.2.2.4 Coal Aquifer .......................................... 3.2.2.5 Interburden & Underburden Leaky Aquitards ................. 3.2.2.6 Tullock Aquifer ........................................ 3.2.3 Recharge ...................................................... -13-13-13-14-14-16-16-16-17-18-19-20-21-23-23-2S-2S-2S-26-

4. HYDROLOGIC CONCERNS ................................................... 4.1 Surface Water .......................................................... 4.1.1 Water Quantity ................................................ 4.1.2 Water Quality ................................................. 4.2 Groundwater ........................................................... 4.2.1 Groundwater Quantity and Level Changes. . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.2.2 Reclaimed Backfill Aquifer Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.2.3 Groundwater Quality ............................................

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MATERIAL DAMAGE CRITERIA .............................................. -31CHIA Northern PRB. Southwest Extension 2 Amendment,
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RAG Eagle Butte Mine Pennit 428-T4. Change No 13

5.1 Surface Water .......................................................... 5.1.1 Water Quantity ................................................ 5.1.2 Water Quality ................................................. 5.2 Groundwater ........................................................... 5.2.1 Groundwater Quantity and Elevation Changes ........................ 5.2.2 Physical Changes in the Reclaimed Backfill Aquifer ......... ~ .......... 5.2.3 Changes to Groundwater Quality ................................... 6. ANALYSIS OF CUMULATIVE HYDROLOGIC IMPACTS .•••••••••••••••••••••••• 6.1 Surface Water .......................................................... 6.1.1 Water Quantity ................................................ 6.1.2 Water Quality ................................................. 6.2 Groundwater ........................................................... 6.2.1 Cumulative Aquifer-Head Drawdowns .............................. 6.2.1.1 Alluvial Aquifer ......................................... 6.2.1.2 Clinker Aquifer ........................................ 6.2.1.3 Coal Aquifer .......................................... 6.2.1.4 Backfill Aquifer ........................................ 6.2.1.4.1 Hydrologic characteristics ................... , 6.2.1.4.1 Published research . . . . . . . . . . . . . . . . . . . . . . . . .. 6.2.1.4.2 Permit predictions .......................... 6.2.1.4.3 Backfill monitoring water quality .............. 6.2.1.4.4 Conclusions ............................... 6.2.1.5 Wasatch Aquifer ......................................... 6.2.1.6 Interburden and Underburden Leaky Aquitard Units ........... , 6.2.1.7 Tullock Aquifer ........................................
7. MATERIAL DAMAGE POTENTIAL ............................................. 7.1 Surface Water ................ '.' ....................................... , 7.1.1 Water Quantity ............................................... , 7.1.2 Water Quality ................................................ , 7.2 Groundwater........................................................... 7.2.1 Cumulative Aquifer-Head Drawdowns .............................. 7.2.2 Physical Changes in the Backfill Aquifer ............................ , 7.2.3 Changes to Groundwater Quality .................................. ,

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8. MATERIAL DAMAGE STATEMENTS OF FINDINGS ••••••.••••••.•••••••••.••••• 8.1 Surface Water .......... " . ; ............................................ , 8.1.1 Water Quantity ................................................ 8.1.2 Water Quality ................................................. 8.2 Groundwater ........................................................... 8.2.1 Cumulative Aquifer-Head Drawdowns .............................. 8.2.2 Physical Changes in the Reclaimed Backfill Aquifer ................... , 8.2.3 Changes to Groundwater Quality .................................. , 8.3 Determination of Material Damage .........................................

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CHIA Northern PRB,"
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SELECTED REFERENCES ........................................................ -53Abbreviations .......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -60-

CHIA Northern PRB.
Southwest Extension 2 Amendment,

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Tables
Table 1. Northern Powder River Basin Mines in Wyoming with their associated date of permit issuance, permit or temporary filing number, permit area, and projected area to be disturbed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -10Table 2. Summary of surface water classes and uses, Wyoming. ......................... -14Table 3. Selected groundwater class of use standards. ................................. -15................................................................................. -15-

Table 4. National Pollution Discharge Elimination System emuent standards for Wyoming. .. -28Table S. Inmtration rates from tests at Belle Ayr Mine, Wyoming. . ........ ~ . . . . . . . . . . . .. -34Table 6. Predicted time for recovery of draw down at northern mines, Powder River Basin, Wyoming•...................................... ~ . . . . . . . . . . . . . . . . . . . . . . . . .. -36Table 7. BackfUI aquifer properties, Northern Powder River Basin, Wyoming•............. -39Table 8. Summary of the backf'ill water quality predictive techniques and the predictive results used by the northern mines, Powder River Basin, Wyoming. ...................... -42Table 9. Years of monitoring, percent recovery, sample date, total dissolved solids (TDS) concentration and sulfate concentration for backf'ill monitor wells, northern mines, Powder River Basin, Wyoming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -44-

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CHIA Northern PRB. Southwest Extension 2 Amendment, RAG Eagle Butte Mine Pennit 428-T4. ChangeNolJ

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Figures
Figure 1. - Location of Southwest Extension 2 Amendment Area. . . . . . . . . . . . . . . . . . . . . . . . . .. -5Figure 2 - Generalized geologic and hydrologic characteristics of the alluvium, clinker, Wasatch Formation, and Fort Union Formation, Powder River Basin, Wyoming. [Information
modified from BLM, 1994; Glass, 1980; Lewis and Hotchkiss, 1981; Mapel, 1958; Martin et aI., 1988; and Wyoming Water Resources Center, 1997] ........................ ',' ....... -7-

Figure 3. - Generalized surface and groundwater flow directions for the Powder River structural basin and the Powder River, Tongue River, Belle Fourche River and the Cheyenne River Basins, Wyoming. ............................................................ -9Figure 4. - Average annual discharge at U. S. Geological Survey gaging station 06324890 between 1977 and 1985, Wyoming•................................................... -17Figure 5. - Number of coal mine monitoring wells in shallow aquifers in the northern Powder River Basin, Wyoming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -18Figure 6. - Fingerprint diagram of median major ion concentrations, in milliequivalent, for the alluvial, Wasatch, clinker and coal aquifers, northern Powder River Basin mines, Wyoming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -20Figure 7. - Median of major ion concentrations in milligrams per liter for the alluvial, Wasatch, clinker and coal aquifers, northern Powder River Basin mines, Wyoming. . . . . . . . . . .. -22Figure 8. - Coal bed methane discharges over time in the Little Powder River Basin, Wyoming.
[Data from the Wyoming Oil and Gas Commission web site on 6/18/2002.] ............. -24-

Figure 9. - Comparison of predicted five-foot drawdown contours in the coal aquifer due to coal mining and to coal bed methane development, Powder River Basin, Wyoming, (from Meyer, 2000)•....................... " ...................................... -38-

Plates
Plate 1 Plate 2 Cumulative Impact Area, Northern Mines, Powder River Basin, Wyoming BacidUI Areas and Backf"dl Monitor Wells, Coal Mines, Northern Powder River Basin, Wyoming.

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CHlA Northern PRB. Southwest Extension 2 Amendment, RAG Eagle Butte Mine Permit 428-T4 • Change No13

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EXECUTIVE SUMMARY
Eagle Butte Mine proposes to add the Southwest Extension 2 Amendment Area to their currently approved permit area of almost 7,000 acres. The 558 acres in the amendment will increase the size of the RAG Eagle Butte Mine by about 8 percent.

In order to issue a coal mining permit or approve an amendment to an existing coal mining permit, the Surface Mining Control and Reclamation Act of 1977 requires the regulatory authority to assess the probable cumulative impacts to the surface and groundwater systems caused by current and proposed mining activities in a cumulative impact area. In the State of Wyoming, the Wyoming Department of Environmental Quality (WDEQ), Land Quality Division (LQD) is responsible for preparing the Cumulative Hydrologic Impact Assessment (CHIA), based on the evaluations of the probable hydrologic consequences of mining. The Wyoming State Engineer's Office (WSEO) provides assistance on surface and groundwater quantity and the WDEQ, Water Quality Division (wQD) provides assistance on surface and groundwater quality. The assessment must be sufficient to determine whether the mining operation has been designed to prevent material damage to the hydrologic balance.
Several coal mines are present near the Southwest Extension 2 Amendment Area. Buckskin, Rawhide, Eagle Butte, Dry Fork, KFx, Fort Union, and Wyodak Mines all lie adjacent to each other (Plate 1). For this CHIA, the surface water cumulative impact area (CIA) is identified as the Little Powder River watershed drainage basin upstream from U. S. Geological Survey (USGS) gaging station No. 06324890, while the predicted maximum extent of the five-foot drawdown in the coal aquifer associated with mining is identified as the groundwater CIA for evaluating potential impacts to groundwater. Coal bed methane (CBM) is being developed in the Powder River Basin (PRB) proximate to the coal mines in the CIA and is expected to grow substantially during the next decade. Groundwater drawdown caused by CBM de-watering is impacting the same coal aquifer as the coal mines. Impacts of CBM development to the surface and groundwater systems could potentially exceed any impacts caused by the coal mines. This CHIA is strictly an evaluation of the impacts of coal mining. Projected post mining runoff volumes for the base of the CIA at the USGS gaging station No. 06324890 are expected to be comparable to pre-mining runoff volumes. Twenty-two percent of the surface water CIA is projected to be disturbed and reclaimed. No impacts to surface water rights are expected within, or downstream from the CIA. Reclamation activities are expected to minimize sediment loss. Post-mining surface water quality is expected to meet pre-mine water quality class-of-use. The groundwater can be generally characterized by five flow systems - the alluvial aquifer, the Wasatch aquifer, the coal aquifer, the clinker aquifer, and the Tullock aquifer. Aquitards consisting of clay, claystone, and isolated sand and sandstone lenses lie below and between the coal. The Wasatch sediments store water and function regionally as leaky aquitards, but on a local scale may be an aquifer. The alluvial, Wasatch, clinker and coal aquifers are often interrelated. The Tullock aquifer is
CHIA Northern PRB,
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isolated from the overlying units by an extensive thickness of sediment and, on the scale of the CIA, does not interact with the overlying aquifers. Water quality is variable in all the aquifers and is generally suitable for livestock use in the alluvial, Wasatch, clinker and coal and aquifers. A natural systematic change in water quality is observable in the coal aquifer as the water flows to the west. The water quality evolution in the coal aquifer is due to the change from oxidizing to reducing conditions, the presence of sulfate reducing bacteria, and the process of ion exchange. Water quality in the Tullock aquifer is generally suitable as a drinking water source. Water level drawdowns are expected to occur in all aquifers with the coal aquifer being most impacted by coal mining. The water elevation in the coal aquifer will decrease during mining with the greatest decrease of water level being closest to the mine. The maximum worst-case extent of the fivefoot groundwater drawdown contour in the coal aquifer is predicted to occur up from 10 to 13 miles from the mine permit boundaries. Under worst-case analysis, the post-mine potentiometric surface in the coal aquifer is expected to approximate the pre-mining potentiometric surface in several hundred years after mining ceases, with most of the recovery occurring in approximately 50 to 100 years. This recovery analysis does not account for the effects of CBM. Material damage to the coal aquifer and private wells is not expected. Due to differing hydrologic characteristics, the maximum extent of the five-foot groundwater drawdown contours in the Wasatch, interburden, underburden and clinker are expected to occur within approximately one mile from the mine permit boundaries. Impacts to these resources will not be permanent and material damage is not expected. The backfill aquifer will hydra_ulically connect the alluvial, Wasatch, clinker, and coal aquifers and the interburden and underburden aquitards. As a result, recovery of the potentiometric surfaces for these units will partially depend on the re-saturation of the backfill aquifer as well as water released from storage in the aquifers and natural recharge. As the backfill aquifer re-saturates, water levels in adjacent, undisturbed aquifers will also stabilize. Groundwater elevations are estimated to fully recover in these units. Several hundred years are estimated for water level recoveries in the center of the reclaimed backfill with most of the recovery occurring in the other units within 10 to 50 years. Most mine facility water supply wells are completed in the deeper Tullock aquifer which is the lowest member of the Fort Union Formation and is generally suitable for drinking water. The Tullock aquifer is expected to have a cone of depression in the potentiometric surface of about a one mile radius around the water supply wells. There are no cumulative impacts anticipated in the Tullock aquifer. Reclaiming pits with backfill will result in physical changes to the post-mine aquifer. Once the backfill aquifer re-saturates, pre- and post-mine groundwater flow patterns will be similar. Hydraulic conductivity of the backfill aquifer will initially be high during placement, but with time the backfill aquifer will settle and consolidate and the hydraulic conductiyity is predicted to decrease and to approach the hydraulic conductivity of the surrounding undisturbed materials. Long-term physical changes to the aquifers by backfill placement will be insignificant and material damage is not expected. Pre-mining water quality in the alluvial, Wasatch, clinker, coal, aquifers and post-mine groundwater quality in the backfill aquifer is projected to be similar. Pre-mining groundwater quality in those aquifers varied but in most instances was classified as suitable for livestock or lower quality. PostCHIA Northern PRB. Southwest Extension 2 Amendment. RAG Eagle Butte Mine Permit 428-T4. ChangeNo\3

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mining groundwater quality will also vary but will likely be suitable for l~vestock or lower quality. Transient impacts to groundwater quality occur as the backfill aquifer re-saturates, such as an increase in total dissolved solids (IDS) and sulfates, but are predicted to be followed by a steady decrease approaching pre-mining concentrations. Backfill aquifer water quality data in the northern mines in the PRB appears to be following the predicted pattern of increased mineralization· as the backfill re-saturates. Some of the wells have relatively high TOS consisting of sulfate, sodium, calcium, and magnesium ions. These elevated concentrations are predicted to drop as the initial saturated water is . flushed through the system. Based on the published research, predictive tests presented in.the pennit applications, and the backfill water quality data available at this time, the overall quality of the water in the backfill aquifer is expected to meet the livestock water standards after the fIrst flush of the backfill is completed. Monitoring of the water quality in the backfill will continue and this conclusion will be verifIed using the additional data. Permanent adverse impacts to groundwater quality are not predicted, and material damage is not expected. Based on existing available infonnation, the WDEQ has determined that surface coal mining operations within the CIA will have local and short tenn impacts to the environment. However, no permanent adverse impacts to the hydrologic balance are expected and material damage to surface and groundwater quality and quantity is not expected to the CIA as a whole.

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CHIA Northc:m PRB. Southwat Extension 2 Amendment, RAG Eagle Butte Mine Permit 428-T4. CbangeNo13

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