Q: Is this "TMG Aquifer" the same as the "Cape Flats Aquifer"
A: No these are completely different groundwater systems which operate independently of each other. The Cape Flats Aquifer is a shallow unconfined sand aquifer, while the TMG Aquifer is a deep, partially confined, fractured rock aquifer.
Q: Why don't you use the water from the Cape Flats Aquifer?
A: The Cape Flats Aquifer is one of the options which the City of Cape Town is considering (See more about the City's Water Resource Planning ) however it was decided that since so little is known about the TMG Aquifer it would be prudent to investigate this potential resource until it was understood to the same degree as the other options- that is why this feasibility study was initiated.
Q: If you remove the water from the Aquifer won't you create sinkholes?
A: The rock in which this aquifer occurs is sandstone which is made up of mostly quartz - the water doesn't dissolve it as can happen with some rock types. The water in this aquifer is flowing in the small cracks between the rock. (See more about how aquifers work. )
Q: Are you mining water? Does the water get replaced?
A: The aquifer does get recharged annually however the exact amounts and how water travels within the aquifer is part of the investigation.
Q: Are you not robbing Peter to pay Paul? Would the water you abstract not emerge in springs or enter rivers and run to the sea?
A: The link between groundwater dependent ecosystems (such as seeps and springs) and the functioning of the aquifer is one of the issues which is being researched in this project. The monitoring programme is aimed at confirming linkages within the system so that potential impacts of abstraction can be predicted.
Q: How old is the water in the TMG Aquifer system?
A: The aquifer has been storing the water for tens of thousands of years. The water at The Baths, near Citrusdal for example, is approximately 2000 years old. The system is like a bucket with a tap constantly dripping water into the bucket- the water is slowly working its way through the system and leaking out over the edges.
Q: Why doesn't the City desalinate rather than using this deep groundwater?
A: Desalination is one of the options which the City of Cape Town is considering (See more about the City's Water Resource Planning) however it was decided that since so little is known about the TMG Aquifer it would be prudent to investigate this potential resource until it was understood to the same degree as the other options- that is why this feasibility study was initiated.
Q: How many borehole sites will there be during the exploratory phase of the Project?
A: There are 28 sites, which have been identified for drilling, but only approximately 10 of these will be drilled during the Exploratory Phase.
Q: When will abstraction take place?
A: During the Exploratory Phase of the project no abstraction, other than some short term pump testing from some of the holes, will occur. If the Pilot Phase is given authorisation, limited abstraction (3 to 5 million m3 per year) would take place at this stage. (See more about the phases of the project. )
Q: Will the exploratory sites be developed as wellfields?
A: This Exploratory Phase of the project is aimed at learning more about the structure and functioning of the Aquifer. The location of the pilot wellfield will be dependent on what is learnt from the exploratory boreholes. It is possible that the pilot wellfield may be located near one of the exploratory boreholes, but this will be the subject of a separate EIA process.
Q: What will the quality of the water be?
A: The quality of water from the TMG is expected to be extremely good.
Q: How will local farmers/users and municipalities benefit from this project?
A: There is no abstraction during the Exploratory Phase and in the Pilot Phase any water abstracted will be channelled into existing City water infrastructure. This project will benefit all sectors and authorities by increasing knowledge of the TMG Aquifer and its potential for acting as a water resource.
Q: Does the term sustainability in the Scoping Report refer to sustainability of the water resource or to the sustainability of the environment?
A: The National Water Act (1998) does not distinguish between surface and groundwater. Guiding principles of an Integrated Water Resources Management (IWRM) strategy include the following:
In other words, a holistic view of the sustainability of the groundwater resource is required by law, and this also includes the sustainability of the ecosystems in the area.
Q: Why should groundwater be monitored in boreholes when surface monitoring of springs and wetlands can be carried out?
A: Rainfall, surface-water and groundwater are all interconnected components of the hydrological (water) cycle. It is not possible to gain a real understanding of the functioning of the system by only measuring selected components. Monitoring of surface-water or springs alone is no substitute or alternative to properly sited and equipped monitoring boreholes.
A comprehensive monitoring programme for groundwater must involve regular measurements of the following:
The TMG Alliance is currently preparing a monitoring protocol that includes the above as well as the ecological monitoring of relevant ecosystems.
The monitoring of groundwater changes at large scales and over long observational periods is by far the most reliable indicator of climate and water cycle changes on the largest scales. Global environmental change (GEC) signals that would remain obscured for decades by the inherent "background noise" of shallow hydrological systems, are much sooner resolved by groundwater monitoring systems.
Q: Should groundwater monitoring take place in the core zone of a Biosphere Reserve?
A: The plants (fynbos), animals, geology and soils (forming the landscapes and providing nutrients to the plants), climate (rainfall and sunshine), hydrology and hydrogeology (rivers and groundwater) all make up the natural environment. The ecosystems in the Kogelberg (and in all other conservation areas) consist of all the living and non-living components interacting and functioning together.
An improved understanding of the natural environment in the Kogelberg Biosphere requires that all of the above components should be studied. Human development and presence is already part of the the buffer and transitional zones of the Biosphere Reserve. As the core zone of the Biosphere Reserve is not an island it is important to understand how activities in the surrounding transitional and buffer zones may impact on it.
In the Provincial Government of the Western Cape's "Manual for the Application of Bioregional Planning" (2003), it is stated that the primary functions of the core areas of Biosphere Reserves include:
Because of its distance from the highest priority exploration sites (T4 at Theewaterskloof and W7 at Wemmershoek), its hydrogeological setting and its ecologically pristine state, monitoring boreholes in the core zone of the Biosphere Reserve would be used as fundamental reference sites that would provide "baseline" information well before any Pilot Wellfield abstraction. Without these boreholes, the far-field monitoring systems of the TMG Aquifer Project will be compromised.
These monitoring boreholes will also be most important to the City of Cape Town, and the South African nation as a whole, as reference sites for the detection of signals of global environmental change in Western Cape mountain environments.
Monitoring boreholes in the Kogelberg Biosphere Reserve will provide an effective early warning system for the Reserve itself. Groundwater is not bound by human defined boundaries and without monitoring and interpretation it will not be possible to take any appropriate action if activities in surrounding areas begin to impact on the groundwater in the core zone. Groundwater monitoring is therefore a risk management tool that can be used to reduce the risk of negative impacts to the groundwater in conservation areas.
Botanical, zoological and climatic monitoring are accepted as routine activities in conservation areas and National Parks. Groundwater monitoring should be accepted as part of holistic environmental monitoring programmes in Biosphere Reserves and other conservation areas.
Q: Will the exploration / monitoring boreholes be used for bulk abstraction?
A: No, the purpose of these boreholes is to gather hydrogeological data only. Selected boreholes may be used for limited pump testing.
Bulk water abstraction for water supply purposes will be technically impossible from any of them. Most exploration boreholes will be drilled with a bit that is impregnated with diamonds in order to be able to extract solid rock borehole core samples. This is called diamond drilling. These boreholes have diameters that are too narrow for the installation of high volume water pumps.
Establishing a pilot wellfield for bulk water abstraction will require an entirely separate EIA process.
Q: What are the impacts of the drilling of exploration and monitoring boreholes?
A: Drill site impacts are local and of short-lived duration. Wherever possible drill sites are to be selected on previously disturbed areas (e.g. old gravel pits, tracks or a road reserve). Drill site impacts will be managed and minimised through the implementation of Environmental Management Programmes (EMPs) that will be prepared by the environmental and ecological task team and monitored by an Environmental Control Officer (ECO).
If a borehole site were to occur within an ecologically sensitive area (e.g. within a Biosphere Reserve or other conservation area), it is planned to develop a site-specific EMP and submit this to DEA&DP for approval prior to implementation. The exact procedure to be followed will be decided by DEA&DP when a Record of Decision is issued for this Scoping Process and/or a subsequent EIA Process.
Drill site impacts could include the construction of access tracks, drilling and refuelling activities and the footprint of the drill site and the associated equipment storage area. These are described in more detail in the Scoping Report.
Once the borehole has been completed and the drill rig moved off site, then the affected area can be rehabilitated. All that should remain at each drilling site is a capped borehole (see Figure 1). In areas where vandalism might be expected, a concrete plinth may be constructed, which can be recessed below ground level and concealed by a manhole cover. These capped boreholes allow for periodic monitoring access in order to collect water samples and measure rest water levels. Solar panels could be installed to provide power to continuous scientific and technical monitoring equipment on selected sites.
Figure 1. Photos showing capped borehole (left) (Source: CSIR, 2003) and concrete plinth with manhole cover (right) (Source: Umvoto Photo Archives, 2002)
Q: What factors were considered in the hydrogeological rating of target areas for the exploratory phase?
A: The area being investigated includes the Table Mountain Group rocks in the Cape Fold Mountains in the areas closest to the dams that are used for providing water (i.e. Voelvlei Dam, Wemmershoek Dam, Theewaterskloof Dam and Steenbras Dam). The study has been separated into different tasks e.g. hydrogeology, ecological and environmental, engineering and infrastructure, drilling etc.
The hydrogeological selection process for Target Site Areas (TSAs) uses hydrogeological criteria only. These were Yield Potential, in respect of (i) permeability, (ii) storage and (iii) recharge consideration, and their Scientific Learning Potential, in respect of (iv) regional aquifer properties, (v) resource-monitoring opportunities and (vi) likely contribution to the larger regional scheme integrity of future groundwater resource development for the City of Cape Town.
The Yield Potential is relevant for monitoring as well as possible abstraction sites because groundwater bearing boreholes are needed to confirm regional groundwater flowpaths and to measure and monitor the hydraulic character of the aquifer.
The 22 final TSAs were placed in three classes:
A - High priority
B - Medium priority
C - Low priority
The exploratory drilling phase is intended to verify the requirements and the predicted hydrogeological characteristics of the TMG Aquifer system, to obtain more monitoring data, and to refine the siting of a potential pilot abstraction wellfield/s - no bulk abstraction of water for water supply purposes will take place during this phase.
After the exploratory phase, if it is decided to proceed with a pilot wellfield, then all other relevant criteria (e.g. ecological and environmental, engineering and infrastructure, social etc.) will be taken into account in the selection process for the pilot wellfield site.
Q: Could the surrounding fynbos be harmed, if a borehole strikes deep artesian water similar to that found in hot water springs and the water shoots out of the ground?
A: Each borehole will be designed to manage and control intersections of water under pressure through the use of appropriate casing, gate valves and pressure metres (see Figure 2).
The temperature in most Table Mountain Group hot water springs varies between 35°C and 45°C. The water at the Goudini and Brandvlei hot springs is classified as "pure" by virtue of its low content of dissolved mineral matter (total less than 100 mg/litre); most of this is silica at 30 to 80 mg/litre. The remainder consists of chlorides, sulphates and bicarbonates of magnesium, calcium, sodium and potassium. The bubble gas consists of carbon dioxide with a little methane.
Any artesian water intersected during the TMG exploration programme will probably have similar characteristics. This type of water will not harm the fynbos.
Figure 2. Photos showing artesian flow of 12 l/s before capping (left) (Umvoto Photo Archives, 2003). Borehole after capping, sealed with gate valve and pressure meter (right) (Umvoto Photo Archives, 2003).
Q: If water is removed from the aquifer during the pilot wellfield stage, will this result in the formation of caverns and ground subsidence?
A: No bulk abstraction of groundwater will take place during the exploratory phase. There will be no ground subsidence problems associated with exploration drilling and boreholes.
Problems associated with the formation of caverns and groundwater subsidence generally only occur in areas underlain by limestone or dolomite. Calcium carbonate is dissolved and removed by water in limestones and dolomites resulting in the formation of caves and a highly irregular weathered surface. If these areas are dewatered (e.g., Carletonville in the 1960s) then sinkholes can develop.
The TMG Aquifer is located in sandstones and quartzites that consist mainly of silica. Water does not dissolve silica under normal conditions. Abstraction of groundwater from the TMG Aquifer will not result in the formation of caverns and / or ground subsidence.
In the case of an aquifer system composed of fractured quartzite such as the TMG, it is unlikely that any compaction resulting from pumping will be measurable at surface. The compressibility of fractured crystalline rock is in the range 10-6 to 10-8 Pa-1, not significantly different from water compressibility.
This concern and the complete technical response will be addressed in more detail in the future EIA Process that is required for a possible future pilot abstraction wellfield.
Q: How has the precautionary principle been applied in this project?
A: This project has to comply with all the National Environment Management Principles as expressed in Chapter 1 of the National Environmental Management Act. A risk-averse and cautious approach has been consistently applied that takes into account the limits of current knowledge about the consequences of decisions and actions.
The environment as defined by NEMA takes into account ecological, social and economic factors.
A rigorous step-by-step approach has been adopted by this project. The TMG Aquifer Feasibility Study and Pilot Project commenced in 2002 and it is probable that the first exploration borehole will only be drilled in 2005.
Each of the reports prepared by the different task teams, (at the end of each project phase), has been subject to review by an independent specialist reviewer.
Site selection for the proposed pilot abstraction wellfield will require integrated input involving all task teams. In addition to hydrogeological aspects, they will be required to consider environmental, ecological, economic, societal, legal, infrastructure and engineering aspects, cumulative impacts, alternatives and the "no go" option. DEA&DP is also required to consider issues and concerns raised through the public participation process. DEA&DP will prepare the Record of Decision.
Q: WIll all springs and seep zones dry up when groundwater pumping starts?
A: Porosity, pore-space compressibility, the mass density of water and water compressibility are all required to calculate the specific storage of the aquifer. Due to the absence of any measured data from the present study area, an extremely conservative range of porosity values was assumed, i.e., 0.1% or 1% for the Table Mountain Group.
In the Preliminary Phase Hydrogeological Report a conservative theoretical calculation for a regionally averaged decline in hydraulic head of 50 m showed that the volume released by aquifer compression remains at most a few percent of the total volume in slow circulation within the deep groundwater flow systems.
This calculation serves to put into quantitative perspective the common public perception that groundwater abstraction from the deep TMG confined aquifer will somehow significantly "drain" or "dry out" the system, with (often unspecified) adverse ecological consequences.
The exploration/monitoring boreholes will provide real measured data from the TMG Aquifer that will improve the confidence levels and reduce uncertainties associated with hydrogeological calculations and models.
Q: What has been happening with the project between May 2005 and February 2006?
A: On 18 May 2005 the Exploratory Phase was given authorisation to proceed by the Department of Environmental Affairs and Development Planning (DEA&DP). All registered interested parties were informed of the decision and their right to appeal during the mandatory appeal period of 30 days. One appeal was lodged against the decision during this time. DEA&DP appointed a Review Case Officer to review the project documentation, the Record of Decision and the appeal. They requested the City of Cape Town to respond to the issues raised in the Appeal and undertook a site visit to inform their review. The findings of this review were provided to the Provincial Minister of Environmental Affairs and Development Planning to inform her decision regarding the appeal. An appeal Record of Decision (RoD) was issued on 22 February 2006. This RoD provides slightly amended conditions of approval but provides authorisation for the exploratory phase to continue. The appeal RoD can be downloaded here.
Q: Are the Table Mountain Group mountains volcanic?
A: The Table Mountain Group (TMG) is a sedimentary geological sequence. The sediments were deposited in a deltaic to shallow marine environment between 500 and 440 million years ago. They are therefore not at all volcanic.
Q: Why are the there hot springs in the study area?
A: The earth has a temperature gradient as one increases in depth the temperature increases. The water which surfaces at hot springs in the study area such as Brandvlei and Goudini has travelled to great depths where it is heated by the rocks. The water then surfaces through fissures relatively quickly retaining some of that heat.
This is the same principle which makes South Africa's deep mines very hot places to work.
Q: Can the utilisation of this aquifer cause geysers or steam to erupt from the mountains?
A: As explained above, the water in so-called "hot water springs" in the study area is warm because of the great depths to which it travels and not due to volcanic activity. It is not physically possible for the water to be heated to the point that it transforms into steam under these conditions. All natural geysers and steam outlets known to man are related to volcanic activity and therefore not relevant in this sedimentary rock system.