Monday,
January 9, 2006
6:00 - 7:30 pm
Pellissippi
State Technical Community College
10915 Hardin Valley Road, Knoxville
Lamar Alexander Building
Room 223
JANUARY PRESENTATION
Structural
Controls on Karst Development and Groundwater Flow
Redstone Arsenal, Huntsville, Alabama
Tom Zondlo and Mark
Shoemaker
Shaw
Environmental & Infrastructure, Inc.
Knoxville, Tennessee
Abstract
Redstone
Arsenal (RSA) is a 38,000-acre facility located in Huntsville,
Alabama. At RSA there are 424 identified springs, 1,886 mapped
sinkholes, a highly evolved epikarst, solution cavities in nearly
70% of the bedrock boreholes drilled, and 26 mapped caves. RSA is
situated on the south flank of the Nashville Dome where geologic
structure has always been assumed to consist of gently southward
dipping beds of Mississippian-age carbonate sequences overlying
the Chattanooga Shale. Given the available information, five
distinct hydrogeologic regimes have been identified, and a
generalized network of subsurface conduits inferred based upon a
simple structural/stratigraphic model.
More recently the Army completed nearly 30 miles of reflection
seismic surveys, performed nine dye traces, and drilled
thirty-two deep coreholes at RSA. These results document a
significantly more complex structural picture than was previously
imagined, with considerable block faulting superimposed on the
regional southerly dip. The faulting appears to have played a
significant role in development of the shallow karst flow system;
this is supported by the dye tracing. But the faulting may also
have facilitated other processes which enhanced karst development
at depth.
From the deep drilling, highly transmissive,
solutionally-enlarged features ranging up 0.2 ft thick have been
revealed at depths well below the Tennessee River base level.
These features occur within the lower Tuscumbia limestone and
Fort Payne formations that host naturally-occurring hydrocarbons,
the occurrence of which is most likely related to localized block
faulting. Groundwater samples within these deeper strata document
a Na-SO4 type water chemistry, with a transition to
Na-Cl water at increasing depth approaching the Chattanooga
Shale. Preliminarily, considering pyrite and gypsum infilling
identified in deep cores, H2S and methane gases
detected at depth, and the distinct water chemistries, a
hypogenic origin may explain this deeper karst development.
Consequently, the faulting may be responsible for the
juxtaposition of all of these conditions and the overall karst
network we observe in the subsurface. Possibly in the caves as
well.
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