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Paleozoic Karst Aquifers in the Mid-Continent
Topics• Overview
• Conceptual model
• Aquifer Properties
• Dynamics
• Water quality
• Karst Geomorphology
• Modeling difficulties
Paleozoic carbonates in mid-continent
Edwards
Floridan
Roswell
Wisconsin arch
Ozark plateau
Finlay archCincinnati archLexington domeNashville dome
Illin
ois
basi
n
Mic
higa
n b
asin
Mis
siss
ippi
em
baym
ent
Biscayne Aquifer (Pleistocene)
Floridan Aquifer (Tertiary)
Edwards Aquifer (Cretaceous)
Permian (Roswell in NM and Blaine in TX)
Mississippian
Silurian
Cambrian-Ordovician (Nashville and Lexington, Ozarks, Arbuckle Mtns in OK)
Paleozoic Karst in the Appalachians
Conceptual Models
Mechanism for cave development
Flow through small fractures,
diffuse flow, similar to
porous media
Conduit development and migration of the water table
Conceptual model for Paleozoic Karst Aquifer, Based on Mammoth Cave Area, KY Topo
divideWatershed divide
Erosion of base level stream causing multiple levels of caves. Based on Mammoth Cave area
Properties
• Intact Limestone: Low K and S
• Karstified LS: High K, Low S
• Epikarst (surface): Low K, High S
Hydraulic diffusivity: T/S
Water level response to rainfallLarge Kb/S = fast response (rise and fall)
Small Sy = large magnitude
Water level in well
and local rainfall, Ozark Plateau
Well in Big Clifty Sandstone
Well in St. Louis LS
Rainfall in Mammoth Cave Area
Water Quality
Depth to saline ground water
Vulnerability of Karst Aquifers to Contamination
1. Sinkholes funnel surface contamination into cave conduits.
2. Rapid transport in caves (km+/day) moves contaminants away from source
3. Thin soils provide minor sorption/retention
4. Turbulent flow transports clay. Increase tubidity and contaminants sorbed to clay
Important Hydro-Geomorphic Features in Karst Aquifers
1. Sinkholes: Recharge, ground stability
2. Estevelles: Recharge and discharge
3. Vertical fractures w/dissolution: Recharge/discharge
4. Epikarst: Storage
5. Solution channels: water pathways; high velocity flow
6. Springs: Focused discharge
Porosity
Sinkholes and Estevelles
Sinkhole collapse related to hydrogeology
Flooding caused by sinkholes
.
Sinkhole risk evaluation. Controlled largely by underlying formation. Mississippian produces most sinkholes
Springs
First-order spring. Discharge > 100 cfs
Discharge from
springs
Percent of days when discharge equaled or exceeded
2 springs in Ordovician rocks
2 springs in Silurian rocks
Discharge Probability Plots
Hydrograph for karst spring
Discharge as function of time
recharge recession recharge recession recharge recession
Vertical fractures and faults
Karst systems and biodiversity
Blind Cave Fish Blind Salamander
Cave Ecosystems
Modeling Flow in Karst Conduits• Porous Aquifer, Darcy:
• Conduit, Manning:
1
;
dx
dh
n
Kv
dx
dhKq
exx
2/13/2
dx
dh
n
Hv r
x
Fundamental difference in
physics of flow
Hr: hydraulic radius=x-section area/wetted perimeter
n = wall roughness
Conduit geometry and wall roughness highly variable—how to determine in the field for an aquifer?
Ozark Plateau Aquifer System
Stratigraphy of the St. Francois and Ozark
Aquifers
caves typically underlie sandstone
Pb-Zn
Geology
Thickness of Springfield Aquifer Thickness of
Ozark Aquifer
Regional potentiometric surface on Ozark Plateau and Western Interior Aquifer System
•
Cross-section on NW side of Ozark Plateau. Fresh water mixes with saline water in laterally equivalent units deeper in basin.
Potentiometric surface in Ozark Plateau in Missouri
330 Mgpd
Lead and zinc mining districts in Ozark Plateau
Biggest producer of Pb,Zn in the world in 1920s
Viburnum Trend Active
Site Mining area
Lead Zinc
Water(µg/L)
Bedsediment(µg/g)
Tissue(µg/g)
Water(µg/L)
Bedsediment(µg/g)
Tissue(µg/g)
Center Creek Tri-State <1 370 0.3 67-270 5,600 770Big River Old Lead Belt <1 2,300 134 8-19 670 514Meramec River Old Lead Belt -- 180 12.2 -- 140 296West Fork ofBlack River
Viburnum Trend <1-11 10-95 0.5-8.3 13-33 12-46 70-110
Strother Creek Viburnum Trend <1-3 20 0.7 33-148 120 150Background -- <1-20 15-28 <0.1-0.6 <1-44 43-140 57-230
Pb and Zn concentrations in water, sediment and tissue