Conceptual Frameworks for Phytoremediation to Achieve Hydrologic Goals - Introduction to Phytoremediation of Contaminated Groundwater - page 199

Fig. 8.5 Changes in
groundwater levels measured in
monitoring wells MM-03A ( )

○

) in an unplanted
area of the phytoremediation site
and in monitoring well MM-44A
(

and LM-02A (

) in a planted area, 1994-2007,
at the manufactured gas plant site
near Charleston, South Carolina.
Between 1998 and 2003, the
groundwater levels were lowered
due to drought conditions. At the
end of 2007, the groundwater
levels measured in monitoring
wells in the planted area were
lower than the levels measured in
wells in the unplanted area. One
foot is equivalent to 0.304 m.

inflow of water recharged offsite. The removal of water
included the discharge from the shallow aquifer by evapo-
transpiration of native grasses and oak trees and groundwa-
ter flow to the Cooper River (Campbell et al. 1996). Because
groundwater levels in wells in the shallow aquifer were
higher than groundwater levels measured in wells in the
deeper aquifers, some groundwater was removed by vertical
downward flow (Campbell et al. 1996).
Historically, in a monitoring well representative of the
unplanted area, such as MM-03A, and in a monitoring well
that represents the areas planted after 1998, such as MM-
44A (Fig. 8.5 ), groundwater levels were uniformly high
(greater than 5 ft (1.5 m) above mean sea level). However,
precipitation amounts during the summer of 1998 were low,
as this was the beginning of regional drought conditions
across most of the southeastern United States.
After the poplar whips were established during phase one
in late 1998, and up until late 2000 after phase two was
completed, each year was characterized by conditions of
precipitation more than 10 in. (25.7 cm) below normal
amounts. As a result, groundwater levels monitored across
the site decreased uniformly, in both the planted and
unplanted areas (Fig. 8.5 ). Monitoring of water levels in
wells during 2001, however, indicated that although drought
conditions were affecting groundwater levels in both planted
and unplanted areas, the decrease in groundwater level in
wells in the planted area (characterized by trees now greater
than 60 ft (18 m) tall) were greater than groundwater level
changes measured in wells in the unplanted areas (Fig. 8.5 ).
Between March and June 2001, the groundwater level
declined 3.5 ft (1 m) and 2 ft (0.6 m) in wells MZ-55A
(not shown) and MM-44A, respectively, compared to a
decline of 1.5 ft (0.45 m) in background well MM-03A. The
greater groundwater-level change observed in wells in the

planted area appears to be related to the increase in transpira-
tion demands associated with summertime highs in tempera-
ture and photosynthetically active radiation, PAR .Dueto
drought conditions, groundwater would be the most likely
source of water to meet this increase in ET demand. Similar
decreases in groundwater levels have been reported previ-
ously for pristine aquifers (Meyboom 1966) and contaminated
groundwater systems (Eberts et al. 1999).
Groundwater levels in the site monitoring wells were
observed to fluctuate directly with rainfall. Each rainfall
event raised groundwater levels, and storage increased. Dur-
ing the drier winter months, the groundwater level averaged
about 2.2 ft (0.6 m) above MSL. During the wetter summer
months, groundwater levels were raised to about 4.6 ft
(1.4 m) above MSL. However, during the winter months of
2005, unseasonably high rainfall amounts resulted in higher
groundwater levels relative to the same time period during
the 2003 and 2004 monitoring period. The increase in
groundwater levels observed in wells following rainfall
events provides direct evidence that recharge to the shallow
water-table aquifer, and subsequent storage, occurs.
To determine the percentage of rainfall that becomes
recharge, the ratio between the change in groundwater
level and rainfall was determined for rainfall events for
2005. Because infiltrating rainfall fills only the voids in the
aquifer, the change in groundwater level measured was
normalized by aquifer porosity estimated to be between
0.20 and 0.30. The results are presented in Table 8.4 .
The availability of rainfall and groundwater-level data at
the site enabled the volume of recharge to be estimated. For
2005, the annual rainfall is about 40 in. (101 cm). If applied
evenly across the 18,000 ft 2 (1,672 m 2 ) phytoremediation
area, this equates to about 444,000 gal (1.6

10 6 L) of
water input. The volume of rainfall that becomes recharge