Fundamentals of Groundwater Hydrogeology - Introduction to Phytoremediation of Contaminated Groundwater - page 111

flows through the open end of the drum inserted into the bed
sediment, groundwater increases the volume of water in the
bag. Conversely, if the drum is located in a groundwater
discharge area, the initial bag of water will decrease in
volume as it recharges the bed sediments. Sampling for
differences in water temperature or chloride concentration
also can be performed to determine the presence of ground-
water discharge (Conant 2004).
The majority of the downgradient part of most surface-
water systems in humid areas tends to be at low topographic
elevations. When the surface-water level is lower than that
of the groundwater in adjacent stream bank or streambed
sediments, groundwater discharge occurs. As can be seen in
Fig. 4.16 , groundwater recharge that occurs over a broad
area and far upgradient tends to discharge in smaller areas,
such as lakes, ponds, wetlands, seeps, springs, or streams.
Even when groundwater discharges to larger bodies of sur-
face water, the location of groundwater discharge typically
is restricted to near the shoreline.

are found in arid areas where infrequent precipitation rapidly
enters dry river channels but then infiltrates into deeper
sediments before substantial open-channel flow develops.
Losing streams also occur in humid areas. For example,
most wetlands or swamps are located in low-lying areas,
which receive both runoff and groundwater discharge, and
are, therefore, considered to be gaining. Some swamps,
however, like the Okeefanokee Swamp in Georgia, are
located on higher ground than surrounding areas and have
a higher surface-water level than the surrounding wetland
areas. Such swamps contain water supplied by precipitation
rather than an inflowing stream, and the water will leak into
shallow aquifers.

4.9 Wells

Because groundwater is not readily observable, any direct
connection to it provides not only a source of water but also
further insight into the subsurface. A well is an excellent
means to achieve both goals; a well truly provides a looking
glass into the subsurface. A well is a hole created into the
earth that intersects saturated sediments or bedrock. A well
is a point of artificially created discharge when pumped,
if not drilled into an artesian system. As groundwater is
removed from a well, the groundwater-level surface in the
well becomes lower than the groundwater surface in
the surrounding aquifer. As a result, groundwater flows to

4.8.1 Wetlands and Swamps

Although groundwater tends to discharge to surface-water
bodies, it is possible for surface-water bodies to recharge
groundwater systems under natural conditions in certain
types of geologic environments. When this occurs, the surface-
water bodies are called losing streams. Losing streams often

Fig. 4.16 Deep groundwater-
flow lines ( arrowheads ) across
the full thickness of an aquifer
can converge near the surface at
focused locations of discharge,
such as shallow surface-water
bodies (Modified from Fetter
1988). The contour interval for
the equipotential lines is in feet,
and is variable. One foot is
equivalent to 0.304 m.