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G.
Water
Resources
Groundwater
Groundwater is an important source of drinking water for
many of the rural residents in
Ohio
and is no exception in the Darby Watershed.
In
Ohio, more than 40 percent of the population depends on groundwater to meet its
daily water needs. In the Darby
Watershed, most of the population uses groundwater as their source of drinking
water. Groundwater is water that has
infiltrated the earth’s surface and is temporarily stored in the pores of soil
or rock. Larger amounts of
groundwater are typically found in porous geologic formations such as sand,
gravel, or bedrock. Geologic
formations that produce usable amounts of groundwater are referred to as
aquifers. The most productive
aquifers in
Ohio
are typically buried valley aquifers that consist of thin layers of glacially
deposited sand and gravel surrounded by bedrock.
Buried valleys in the Darby Watershed are likely to be remnants of Wisconsonian glacial activities and possibly tributaries to
Teays
River
which cut through parts of
Madison,
Franklin
and Pickaway
Counties
within the Darby Watershed (See
Map 9).
The buried valley follows the present day course of the southern part of
the Little Darby Creek and then follows the
Big
Darby
Creek
south to Circleville. Another area
that contributes a large amount of groundwater is an area in Champaign
County, in the headwaters of the Little Darby Creek (See Map 9). This area is
another buried valley of a tributary to the
Mad
River. The yields in the remainder of the
watershed are largely dependant on the thickness of the glacial deposits and the
presence of the highly porous areas of sand and gravel.
Though sand and gravel deposits are excellent sources of groundwater, many wells
in the Darby Watershed extend to layers of porous Devonian and Silurian age
limestone. The depth to the
limestone or bedrock varies across the watershed.
Domestic wells in the Darby Watershed typically yield between 20 to 30
gallons per minute depending on the type of limestone, number of fractures, and
proximity to streams. At well depths
of greater than 100 feet Silurian age bedrock in most of the watershed can yield
greater than 100 gallons per minute (Angle, Personal Communication, 2003).
Areas within the watershed that have minimal groundwater supplies are those that
lack sand and gravel lenses. In
western
Franklin
County
, well logs reported fewer sand and gravel lenses accounting for the lower
groundwater yields in Map 9
(Angle, Personal Communication, 2003).
Groundwater is not only an important source of drinking water but is a major
source of water to surface water. Groundwater
is only temporarily stored beneath the earth’s surface because it moves from
areas of recharge (places groundwater enters the earth) to areas of discharge
such as surface water. Groundwater
is the essential source of water for streams during prolonged dry spells.
The large amount of groundwater flow in streams in the watershed is
believed to be one reason why the
Darby
Creeks
achieve high levels of water quality. Ohio
EPA documented noticeable groundwater contributions from the Cable Moraine
Complex in
Logan
,
Champaign
, and
Madison
County
to portions of
Upper
Big
Darby
Creek, Little Darby Creek, Clover Run, Hay Run, Pleasant Run, and Spain Creek.
The London Moraine influences groundwater flow to Gay Run, Smith Ditch,
and Springwater Run in eastern Madison and southern
Franklin
counties (See Map 3).
The influence of cool groundwater into these streams has allowed
coldwater species the ability to survive in streams that would not normally
harbor such species. Ohio EPA has
designated a few of these streams as both a
warmwater and
coldwater habitat (See
Section IV, B. Water Quality Data, Aquatic Life Standards).
   
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