Flooding Conditions in the Meigs Mine Pool Complex

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Flooding Conditions in the Meigs Mine Pool
Complex
Mary Ann Borch Ohio DNR Division of Mineral
Resources Management October 2008 Information
obtained from CONSOL Energy, Inc., Moody and
Associates, Inc., William Siplivy, P.E., Civil
Environmental Consultants, Inc., personal
communications with SOCCO employees, DMRM
investigations and permits.
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Mine Plan
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Factoids

• Mining for room and pillar began in 1972
• Room pillar and Long wall mining the Clarion
  4a coal seam, a high sulfur coal.
• Permitted in 1984 and 1985
• Mining ceased in 2002,
• Foot print of mine is 23,500 acres (37.6 sq mi)
• If left unpumped, these areas would flood and
  drain into the Raccoon Creek and Leading Creek
  streams.

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Meigs 2 mapOverburden thicknesses range from
100 400 ft.
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Meigs 31 map
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Mine pool information

• Filling since 2002.
• Average fill rate 1.40 feet/month.
• Infiltration rate 0.266 0.284 gpm/acre
• CONSOL established a pool control elevation.
• Meigs 2 560 msl 70 from surface
• Meigs 31 460 msl 150 from surface
• Meigs 2 and 31 maintain different pool
  elevations.

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Mine pool characteristicsFinal pool
elevationMeigs 2 83 floodedMeigs
3155 flooded.
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Cross sections
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Seasonal variation
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Pumping areas at Meigs Mine
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Meigs 2 hydrograph
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Changes in the monthly average rate
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Meigs 31 hydrograph
Pumping begins out of Meigs 2 into Meigs 31.
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Changes in the average monthly rate for Meigs 31
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Water Quality of the Pool

• Pyrite oxidation occurs in the non-flooded
  sections.
• After initial flush, quality improves.
• Alkaline strata (Meigs 31 only) in the roof
  provides neutralization.
• Some short circuiting occurs in the flow path
  result in better water quality
• Sulfate reduction and cation exchange occurs
  along the flow path - resulting in improved
  water quality.
• A long flow path can result in better in-situe
  treatment.
• Stratified water quality from top to bottom.

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Water quality 2004 and 2008
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Future projections for w.q.
Each mine pool volume pumped will have a
corresponding improvement in water quality of
50. Meigs 2 will take approx 52 years for the
iron level to achieve direct discharge standards
lt 3.0 mg/L. Meigs 31 projected to take 40
years to reach lt 3 mg/L Fe. The partially
flooded mine pool and incomplete mixing, would
result in less optimistic predictions, Fe 35
mg/L after 22 years. (CEC 2005)
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Tips to evaluate and avoid unplanned mine pool
problems
What mines are in the entire coal reserve? Added
on mines create more recharge Consider
inter-basin transfer of water
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Determine post-mining head and the potential for
discharge

• Highest topography
• Highest coal seam elevation
• (will often keep rising)
• Note the presence of perched aquifers,
  fractures,
• Pre-mining potentiometric surface,

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Tips continued..

• Dedicated monitoring wells (nested wells) above
  and in the mine pool to determine void filling
  rates and water quality.
• Infiltration rates how fast will the mine fill
  up? If no information, start with 0.5 gpm per
  acre of mine void.
• Create contingency plans in the event of an
  unplanned discharge.
• Obtain pumping record during mining period.