Recharge systems for protecting and enhancing groundwate

TOPIC 6
Region issues and artificial recharge case studies / Case studies 765
Figure 4 shows the water level responses in the re-injection bore, two nearby dolomite monitor bores and one
shallow calcrete monitor bore during the trial. When the levels are compared to the type curves developed by Pyne
(1995) for air entrainment and suspended solids, there is no evidence of either clogging mechanism. However the
rate of drawup rate in the injection bore was found to increase after two days of operation, with no corresponding
increase in water level in the observation bores to suggest an aquifer boundary influence. This reaction may indicate
the possibility of a low degree of clogging by air, bacterial growth or chemical precipitation during the trial.
690
Rate increase
Rate increase
688
Water Level (mAHD)
686
684
Static water level
682
Static water level
680
0.1 1 10 100 1000 10000 100000
Pumping Time (minutes)
Figure 4. Marandoo BWT trial reinjction site water levels
Reinjection Bore TIB1a
TIB1 (7m)
OW30d (14m)
OW30s (shallow)
Injection bore TIB1 bore has essentially the same construction as TIB1a, and the two were designed to operate in
tandem if required. TIB1 was test-pumped at a rate of 3.0 ML/d in May 2003. The drawdown after 1 hour was
7.2 m. By comparison, the ‘drawup’ in TIB1a after 1 hour of re-injection at a rate of 3.7 ML/d was 5.9 m. This
comparison suggests that in this case the re-injection operation may be slightly more hydraulically efficient than
pumping. The open-hole construction of the re-injection bores undoubtedly influenced the efficiency of the injection
process.
The effectiveness of the injection tube and downhole cone arrangement to manage air entrainment was demonstrated
by the trial. This low-cost arrangement is to be refined during an upcoming multi bore re injection project
also at Marandoo where the re-injection tubes will be sized to the maximum design flow rate, and cones will be
used to manage lower flow rates.
The trial required a full-time (10 hours per day) presence on-site throughout the duration of the 44 days of operation.
A technician was retained to refuel and maintain generators, maintain pumping rates, monitor water levels
and inspect the pipeline pressures and general condition. The only notable infrastructure problems were three
generator/electrical failures, which caused a combined individual pump downtime of 23 hours. In general the infrastructure
operated successfully and enabled collection of a good dataset.
Assessment of aquifer interconnection
The extent of lateral connection across the deep groundwater system can be seen in the cones of depression/
impression overlayed on Figure 1. The cones display net ‘drawup’ in some Marra Mamba monitor bores on the mine
10 – 16 June 2005, Berlin ■ 5th International Symposium ■ AQUIFER RECHARGE ■ ISMAR 2005