1 - paducah environmental information center

Paducah Site
o ~~~TURATED
D PERCHED AQUIFER
(unconfined)
~ CONFINING LAYER
D CONFINED AQUIFER
Figure 9.4 Typical path for' rainwater accumulation
as groundwater.
quality. Wells positioned to sample groundwater
flowing away from a site are called downgradient
wells, and wells placed to sample groundwater
before it flows under a site are called upgradient
wells. Any contamination of the downgradient
wells not present in the upgradient wells at a site
may be assumed to be a product of that site.
Wells can be drilled to various depths in the
saturated zone and be screened to monitor the
recharge area above the aquifer , different
horizons within the aquifer, or water-bearing
zones below the aquifer. Vertical and horizontal
groundwater flow directions are determined by
horizontal clay layers, the downgradient
direction tends to be more horizontal than
vertical.
Groundwater aquifers are one, of the
primary pathways by which potentially
hazardous substances can spread thrOugh the
environment. Substances placed in the soil may
migrate downward due to gravity or be dissolved
in rainwater, which moves them downward
through the unsaturated zone into the aquifer.
The contaminated water then flows downgradient
toward the discharge point. Monitoring wells
(MWs) are used extensively to assess the effect
of plant operations on nearby groundwater
lnlATlRATED
ZOtE
SATURATED
ZOtE
SAI'I)
PACK
Figure 9.6 Monitoring well'constructlon showing
relationship between screened'zone and water
levelln,wells where limited fiow In the aquifer Is to
the right.
SEDIMENT
GRAINS
the permeability and continuity of geologic
strata in addition to hydtaulic head. To
effectively monitor the movement of
groundwater and any hazardous constituents it
may contain, hydrogeologists at the Paducah
Site have undertaken many detailed studies of
the geology of strata beneath the site.
Figure 9.5 Pore spaces in soli.
9-6
Groundwater