GEOLOGY OF NW ARKANSASCONSIDERATIONS AFFECTING LANDFILLS IN KARST SETTINGS

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GEOLOGY OF NW ARKANSAS--CONSIDERATIONS AFFECTING
LANDFILLS IN KARST SETTINGS

• Van Brahana
• Department of Geosciences
• University of Arkansas
• Fayetteville, AR

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OBJECTIVES

• Overview of karst (hydrogeology)
• Overview of regional geology, stratigraphy, and
  structural geology of NW Arkansas (geology)
• Overview of rock/water and garbage/water
  interaction (geochemistry)
• Overview of solid-waste landfills (engineering)
• Integration and synthesiswhat does the science
  tell us, and how can we educate others so that we
  optimize our decision-making?

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HYDROGEOLOGIC PROBLEMS IN KARST

• Anisotropy
• Heterogeneity
• Rapid recharge
• Little attenuation of contamination
• Possible subsidence
• Sinkhole flooding
• Unpredictability

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Collapse Sinkhole
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Cave Spring
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Stroud Spring
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Overview of Geology

• Carbonate rocks (limestones and dolomites) are a
  predominant rock type here. These rocks are much
  more reactive to ground water, and they form
  karst
• The carbonate rocks are brittle, and they are
  nearly flat-lying. Joints and faults are common
• Ground water moves downgradient
• Ground water follows the path of least resistance
• Bedding planes and fractures are the focus of
  most ground-water flow in karst

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Stratigraphy

• Stratigraphic units mid-Paleozoic in age.
• Weathering of carbonate rocks formed a mantle of
  regolith
• The Boone Formation is a limestone composed of
  varying amounts of chert
• The St. Joe is composed of limestone
• The Chattanooga Shale is the regional confining
  unit, strongly fractured and jointed

(Brown, 2000 and Manger, 1988)
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Occurrence of Springs and Caves in the Western
Portion of the Buffalo National River Karst
System
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Flow pathways are bedding planes and joints
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Distribution of the main body and St. Joe
limestone member of the Boone Formation
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Overview of Rock/Garbage/Water Interaction

• Water reacts with most substances (universal
  solvent)
• Flowing water that moves through rock dissolves
  the rock, increasing permeability and flow
  velocity over the course of time
• Flowing water that moves through garbage reacts
  with the garbage, forming a leachate
• Leachate moves from points of recharge to points
  of discharge (springs and streams)
• If we intercept a leachate along a gw flowpath
  (well), the water quality will be degraded
• Attenuation processes are poorly effective in
  karst

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Overview of Solid Waste Landfills

• Main conceptIsolate the waste from water, and
  isolate any leachate from human and
  environmental/ecological exposure
• Cover the top to stop infiltration
• Put in layers of low permeability liner to keep
  any leachate contained
• Put in layers of reactive clay to capture any
  possible leachate and bind it to the clay
• Put in a drain to capture any ground water that
  seeps to the bottom of the landfill
• Select a geologic condition that does not favor
  ground-water flow

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SAVOY
FIELD RESEARCH FACILITY
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Conceptual Model
Conceptual Model

Box A Regolith Box B Epikarst Box C Main
Conduit System Box D Smaller Conduit
System Box E Cave System Box F Spring
Location of E.coli Storage Areas
Regolith
A
Boone Formation
B
C
D
F
E
St. Joe Formation
Chattanooga Formation
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CONCLUDING COMMENTS

• Seek understanding--overviews
• Consilience
• Work with true community spirit
• Maintain vigilance
• Anticipate problems beforehand
• Avoid known risks
• Common sense should prevail