204 R. W. Buddemeier et a1.
unless the chloride levels rise too high, but is already unsuitable for human
consumption without treatment to reduce the nitrate levels.
Field data collected in northern Stafford County have provided quantitative
information about effects of irrigation, groundwater quality and rates of
deterioration by the accumulation of nitrates and chlorides, and the current
characteristics of the deep and shallow aquifers.
(a)
0
g 2
III
~ 4
:>
Head of Deep Aquifer
rn
~
~
6
\
.,
....J
E
8
~
I
g
"'CI
Head of Permian Zone
! 10
:>
::! 12
~
i 14
l
.
III
Head of Shallow AqUifer
J:
16
0
20
40
60
80
100
Pumping Time (min)
(b)
400
350
300
~
'[250
c:
0
~ 200
l:I
c:
g 150
0
u
100
50
0
a
20
40
60
80
100
Pumping Time (min)
Fig. 4a,b. Results of water quality sampling as a function of pumping time at the Siefkes
intensive study site. a Head in the shallow, deep, and Permian aquifer units. Vertical
hydraulic gradient strongly influences salt transport. b Chloride (originating in the Permian
and deep aquifer units) and nitrate (originating at the land and water table surfaces)
concentrations in irrigation well effluent as a function of pumping time.