Geoscience Reference
In-Depth Information
Table 7.2. Parameter for the steps of the pilot study; horizontal dashed lines mark a change in the schedule,
steps not shown after a change in schedule remain unchanged.
Pumping
Infiltration
Discharge
Time
rate
rate
rate
FeCl
2
-dosage
Fe-dosage
Fe-dosage
Duration
[m
3
h
−
1
][m
3
h
−
1
]
3
h
−
1
]
[mg L
−
1
]
[d]
Step
[
[mL/cycle]
[g/cycle]
[h]
0-22
1
3.0
1.0
0.5
50
5.9
11.8
-
2
3.0
2.5
0.5
-
-
-
0.5
3
3.0
2.5
0.5
-
-
-
5.0
4
3.0
2.5
0.5
-
-
-
2.0
23-40
1
3.0
1.0
0.5
100
11.8
23.6
-
41-103
1
3.0
1.0
0.5
150
17.7
35.4
-
104-134
1
3.0
1.0
0.5
200
23.6
47.2
-
135-194
1
3.0
1.0
0.5
300
35.4
70.8
-
195-222
1
3.0
1.0
0.5
375
44.3
88.5
-
223-333
1
3.0
1.0
0.5
500
59.0
118.0
-
334-355
1
3.5
1.0
1.0
500
59.0
118.0
-
2
3.5
2.5
1.0
-
-
-
0.5
3
3.5
2.5
1.0
-
-
-
5.0
4
3.5
2.5
1.0
-
-
-
2.0
356-377
1
2.8
1.0
0.3
500
59.0
118.0
-
2
2.8
2.5
0.3
-
-
-
0.5
4
2.8
2.5
0.3
-
-
-
2.0
378-466
1
2.8
1.0
0.3
750
88.5
177.0
-
467-487
1
2.8
1.0
0.3
1000
118.0
236.0
-
488-501
1
-
-
-
-
-
-
-
2
-
-
-
-
-
-
-
3
3.0
2.5
0.5
-
-
-
7.0
4
-
-
-
-
-
-
-
502-533
3
-
-
-
-
-
-
-
4
3.0
2.5
0.5
-
-
-
7.0
534-637
1
2.8
1.0
0.3
1000
118.0
236.0
-
2
2.8
2.5
0.3
-
-
-
0.5
3
2.8
2.5
0.3
-
-
-
5.0
4
2.8
2.5
0.3
-
-
-
2.0
638-705
1
4.1
1.0
0.3
1000
118.0
236.0
-
2
4.1
3.9
0.3
-
-
-
0.5
3
4.1
3.9
0.3
-
-
-
5.0
4
4.1
3.9
0.3
-
-
-
2.0
no fixed duration since reaching the concentration threshold for oxygen lasted a variable amount
of time.
The dosage of FeCl
2
-solution was increased in six stages up to 500 mL/cycle (118 mg Fe L
−
1
).
The discharge water was increased to 1 m
3
h
−
1
after 334 days and reduced for the steps (1), (2) and
(4) after 365 days again. The next changes were the increase of the dosage up to 1000 mL/cycle
(238 mg Fe L
−
1
). Subsequently, a remobilizing experiment was conducted between day 488 and
day 533. Hence, the FeCl
2
dosage was switched off, and water with an increased DO-concentration
was infiltrated into the wells for two weeks after which the oxygen enrichment was switched off
for another four weeks.
In the last phase, it was attempted to decrease the t-As concentration to a technical minimum.
For this, the discharge rate was decreased to 0.3 m
3
h
−
1
(operational minimum of the pilot plant)
and the Fe dosage was increased to 1000 mL/cycle (236 mg Fe L
−
1
, operational maximum of the
pilot plant). After 103 days (day 638 of the experiment) the pumping rate was increased from 3.0
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