The scheme contains two wellfields, Langebaan Road and Elandsfontyn (Figure 20), already connected to the municipal water supply pipeline. Based on modeling and field observations, boreholes forming part of the extension of the Langebaan wellfield were constructed to be used both for abstraction and injection. The borehole injection method (Figure 23) had already been pilot-tested for this aquifer, because a key part of the aquifer is confined (Tredoux and Engelbrecht, 2009). The Elandsfontyn wellfield is a new wellfield and infiltration tests will be required, as infiltration may be better suited for this area.

Figure 23 – Borehole injection testing at Langebaan Road Aquifer (Weekend Cape Argus – 7.12.08).

Based on data from a regional water level and water quality monitoring program run by the national Department of Water and Sanitation, a model was developed for the area to aid in selecting suitable MAR techniques and locations. It was used as a decision support tool for interacting with stakeholders about the progress of research and potential for implementation. Four scenarios, which involved a mixture of injection and infiltration basins, were presented to stakeholders (Figure 24).

Figure 24 – Scenario for MAR involving infiltration basins, leakage wells to facilitate movement of water from the upper (UAU) to lower (LAU) aquifer units and abstraction wells in the LAU for the Cape West Coast (Jovanovic et al., 2019).

Selection of Sites for Recharge

Research in the area indicated that good hydrogeological data combined with a multidisciplinary science approach to interpret the data, is essential as a forerunner to actual MAR implementation. Earlier injection tests (2008) resulted in downstream boreholes overflowing, thus failing to keep water stored underground as initially expected. By using a two-step approach of combining GIS-based analysis for an overall spatial perspective with modeling of groundwater flow, it was shown that only a relatively small area of the aquifer could benefit from recharging the present wellfield (Zhang et al., 2019).

Major recommendations from the new research phase include the following (Jovanovic et al., 2019):

• monitoring (including water levels and water chemistry) needs to be strengthened around the “clay missing window” area as discussed in Section 5.3 “Aquifer hydraulics”, as this is the natural recharge area for the Langebaan and Elandsfontyn aquifers;
• deep boreholes are needed in the “clay missing window” area to improve understanding of the stratigraphic distribution of the clay layer and the real hydraulic conductivity around this window, and the connectivity between the Langebaan and Elandsfontyn aquifers;
• more detailed analysis of existing available water level records needs to be completed to better understand the hydraulic connectivity between the two aquifers; and,
• monitoring of water levels, water chemistry, clogging potential as well as injection trials to obtain parameters needed for the implementation of MAR.