Environmental Engineering Reference
In-Depth Information
Groundwater
divide
Distributed recharge
Focused
discharge
Figure 7.9
Groundwater
flow paths and groundwater age
distribution in a cross section of
a hypothetical unconfined aquifer
(Böhlke,
2002
). Flow lines (solid)
and age isochrons (dotted)
were calculated by assuming
homogeneous aquifer properties
and a uniform recharge rate,
R
,
with parameters listed on the
figure (
Z
is aquifer thickness,
φ
is porosity, and
τ
is average
groundwater age).
0
Z
= 20 m
R
= 0.25 m/yr
5
= 0.4
5
10
= 32 yr
15
20
25
30
35
40
45
50
55
10
15
GW age
(years)
vertical exaggeration = 80×
60
65
70
75
20
2000
1500
1000
500
0
Distance from discharge area (m)
0
Figure 7.10
Apparent
groundwater ages derived
from CFC-12 concentrations
in groundwater samples
collected from unconfined
aquifers in the eastern United
States (Böhlke,
2002
). Shading
highlights trends in different
aquifers. Recharge was
calculated by using Equation
(
7.17
) with parameters listed
on right side of the figure (
Z
is
aquifer thickness,
φ
is porosity,
and
R
is average estimated
recharge).
Z
= 5 m
R
= 0.05 m/yr
= 0.50
5
Z
= 11 m
R
= 0.15 m/yr
= 0.40
10
15
Z
= 25 m
R
= 0.25 m/yr
= 0.35
20
Edgewater, MD
Princeton, MD
Locust Grove, MD
Southern NJ
25
Z
= 35 m
R
= 0.45 m/yr
= 0.35
0
10
20
30
40
50
CFC-12 age (yr)
