Hydrogeological Desktop Study

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Proposal for Field Investigation:
Assessment of Permits for water Extraction Establishment of Managed Aquifer recover (MAR) System

1. Introduction
2.1. Managed Aquifer Recovery Systems

As reported by the South Australian local government of Charles Sturt (2012), Aquifer Storage and Recovery (ASR) or Managed Aquifer Recharge (MAR) is essentially the deliberate storage of surface water (i.e. in the form of stormwater, treated effluent etc) within aquifers. This process is used where water is pumped into aquifers for future usage. Furthermore, MAR systems avoid the need for expensive above ground water tanks, or reservoirs which are subject to significant water evaporation (Charles Sturt, 2012).

As reported by the Australian Government National Water Commission (AGNWC, 2009) MAR systems can be used for urban and rural irrigation and industrial purposes. Of particular interest is that MAR systems can be used to prevent seawater intrusion or provide environmental benefit.

Further reported by the AGNWC (2009) is that MAR systems are even being trialled for potable use in some Australian cities.

2.2. Study Area

This site investigation has been designed to assess the appropriateness for a Managed Aquifer Recovery (MAR) system within an unconfined aquifer consisting of well-sorted sand. The aquifer is bordered by the ocean to the east, a river to the north, and granite (yielding no flow) to the west and south with a reservoir situated on the western boundary, as shown in Figure 1. The ocean has a constant head of 0m AHD, the river has constant heads ranging from 8 m AHD at the inland boundary to 0 m AHD at the ocean discharge boundary, and the reservoir has a constant head of 40 m AHD. The top of the aquifer is at 50 m AHD and the bottom of the aquifer is at -10 m AHD.

Figure 1 – Plan View of Study Area and location of Monitoring Wells A network of 34 observation wells exists to monitor the groundwater levels of the primary (shallowest) aquifer, along with one deep well has been drilled approximately in the middle of the study area as shown in Figure 1. The lighological logs from the 34 shallow observation wells suggest that the primary aquifer consists of only one material and is homogeneous and isotropic. The lighological log from this well suggests that there are three aquifers existing at this location; two confined aquifers and one unconfined. Each is separated by a tight confining unit, with bedrock at the base of the deepest aquifer.

The hydrogelogical system is known to be in steady state, and is shown in cross section in Figure 2.

Figure 2 –Cross Section view of interpreted Hydrogelogical Scenario, based upon lighological logs 2.3. Previous Studies – Water Balance

A previous study of the Study Area provided a water balance, which will be adopted for the purposes of this study. The water balance yielded values as follows: * Precipitation 1,350 mm/yr;
* Evapotranspiration 2,100 mm/yr;
* External river inflow to the reservoir 30.56 GL/yr;
* 2.978 ML/hr for 8 hours a day, 7 days a week is pumped from the reservoir; * Overland flow 120 mm/yr;
* Inflow to the river 16.58 GL/yr;
* Outflow from the river to the ocean 15.43 GL/yr; and
* 420 kL/hr for 8 hours a day, 7 days a week is pumped from the river * Reservoir leakage to the primary aquifer 10.45 GL/Yr
* Discharge from the primary aquifer to the river 8.89 GL/yr * Discharge from the primary aquifer to the ocean 1.56 GL/Yr This data will be used to assess the appropriateness of the proposed permits in the context of a new water balance assessment. Note that there are a number of proposed measures mentioned in section 4 which will allow improvements upon the current water budget / balance.

2. Water Extraction Permitting and amount of water injected from the MAR

Permits have been requested to establish two industrial plants within the study area, one 2km due east of the...
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