Transcript Paleozoic Karst Aquifers in the Mid- Continent

Paleozoic Karst Aquifers in the MidContinent
Topics
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Overview
Conceptual model
Aquifer Properties
Dynamics
Water quality
Karst Geomorphology
Modeling difficulties
Floridan
Edwards
Roswell
Paleozoic
carbonates
in midcontinent
Wisconsin arch
Ozark plateau
Finlay arch
Cincinnati arch
Lexington dome
Nashville dome
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
Flow through
small fractures,
diffuse flow,
similar to
porous media
Mechanism for
cave development
Conduit development
and migration of
the water table
Conceptual model for Paleozoic Karst Aquifer,
Topo
Based on Mammoth Cave Area, KY
Watershed
divide
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
Well in Big Clifty Sandstone
Water level in well
and local rainfall, Ozark Plateau
Well in St. Louis LS
Water level response to rainfall
Large Kb/S = fast response (rise and fall)
Small Sy = large magnitude
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.
2.
3.
4.
5.
6.
Sinkholes: Recharge, ground stability
Estevelles: Recharge and discharge
Vertical fractures w/dissolution: Recharge/discharge
Epikarst: Storage
Solution channels: water pathways; high velocity flow
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
First-order
spring.
Discharge >
100 cfs
Springs
2 springs in Ordovician rocks
Discharge
from
springs
Hydrograph for karst spring
2 springs in Silurian
rocks
Discharge as function of time
Percent of days when discharge equaled or exceeded
Discharge Probability Plots
recharge recession recharge recession recharge recession
Vertical fractures and faults
Karst systems and biodiversity
Blind Salamander
Blind Cave Fish
Cave Ecosystems
Modeling Flow in Karst Conduits
• Porous Aquifer, Darcy:
1
dh
K  dh 
qx   K ; vx    
dx
ne  dx 
• Conduit, Manning:
Fundamental
difference in
physics of flow
1/ 2
H  dh 
vx 
 
n  dx 
2/3
r
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
Pb-Zn
caves typically underlie sandstone
Geology
Thickness of Springfield Aquifer
Thickness of
Ozark Aquifer
Regional potentiometric surface on Ozark Plateau and
Western Interior Aquifer System
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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
Viburnum
Trend
Active
Lead and zinc mining districts in Ozark Plateau
Biggest producer of Pb,Zn in the world in 1920s
Pb and Zn concentrations in water, sediment and tissue
Lead
Zinc
Site
Mining area
Center Creek
Big River
Meramec River
West Fork of
Black River
Strother Creek
Background
Tri-State
Old Lead Belt
Old Lead Belt
Bed
Water
Tissue
sediment
(µg/L)
(µg/g)
(µg/g)
<1
370
0.3
<1
2,300
134
-180
12.2
Bed
sediment
(µg/g)
67-270 5,600
8-19
670
-140
Viburnum Trend
<1-11
10-95
0.5-8.3
Viburnum Trend
--
<1-3
<1-20
20
15-28
0.7
33-148 120
<0.1-0.6 <1-44 43-140
Water
(µg/L)
13-33
12-46
Tissue
(µg/g)
770
514
296
70-110
150
57-230