January 9, 2006
6:00 - 7:30 pm
State Technical Community College
10915 Hardin Valley Road, Knoxville
Lamar Alexander Building
Controls on Karst Development and Groundwater Flow
Redstone Arsenal, Huntsville, Alabama
Tom Zondlo and Mark
Shaw Environmental & Infrastructure, Inc.
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.
Page updated January 10, 2006