|
Alluvium (Qa)
Topography
Alluvium underlies floodplains and terraces of all streams.
Hydrology
The alluvium may yield as much as 100 gallons per minute from sands
and gravel along the Green and Pond Rivers. It yields enough water for
a modern domestic supply (more than 500 gallons per day) to wells in
valleys of the Green and Pond Rivers and their larger tributaries, but
practically no water to wells in small valleys, where it is thin and
fine grained. Water is hard or very hard, and may contain objectionable
amounts of iron.
McLeansboro Group (Mattoon, Bond, Patoka and Shelburn Formations),
formerly the Sturgis Formation (Ps)
Topography
This group forms dissected uplands and ridgetops.
Hydrology
This group yields practically no water, except to wells penetrating
sandstone. Water near outcrop areas is hard, but is increasingly soft
downdip. Sodium bicarbonate content increases downdip. Iron may be present
in objectionable amounts.
Carbondale Formation (Pc)
Topography
The Carbondale forms dissected uplands and ridgetops. Resistant sandstone
beds form cliffs.
Hydrology
The Carbondale yields enough water for a modern domestic supply to wells
penetrating sandstone, but practically no water to wells penetrating
shale. Water is hard or very hard in outcrop area, and is increasingly
mineralized downdip.
Tradewater Formation (Pt)
Topography
The Tradewater underlies dissected uplands and ridgetops. Resistant
sandstone beds form cliffs.
Hydrology
The Tradewater generally yields only small quantities of water to wells,
but it may yield enough water for a modern domestic supply to wells
penetrating a sufficient thickness of sandstone. It yields practically
no water from limestone and shale. Water is hard to very hard and low
in dissolved solids near outcrop area, and becomes increasingly mineralized
but softer downdip to the west. Water from the lower part of the formation
generally contains objectionable amounts of iron.
Caseyville Formation (Pca)
Topography
The Caseyville underlies dissected uplands and ridgetops. Resistant
sandstone and conglomerate beds form cliffs.
Hydrology
Yields of 60 gallons per minute have been obtained from thick sandstone beds. The
Caseyville will yield enough water for a modern domestic supply to most
wells penetrating sandstone. At depth, the water becomes salty or may
have a high sodium bicarbonate content. Electric logs indicate that
moderately mineralized water may be obtained locally from this formation
at depths of 1,200 feet.
Mississippian Formations (Chesterian Age) (Mcu)
Topography
These rocks lie in the subsurface below younger rocks across the entire
county.
Hydrology
Water from Mississippian rocks underlying younger rocks contains salt
in objectionable amounts.
Generalized areas of underground mining have been compiled for several
important coal beds as part of the U.S. Geological Survey's National
Coal Assessment Program. Using these data, a map was created showing
mined-out
areas of selected seams in McLean County.
The U.S. Geological Survey's Hydrologic
Atlas Series, published cooperatively with the Kentucky Geological
Survey, provides hydrologic information for the entire state.
Previous--Next--Back
to "Groundwater Resources in Kentucky"
|