Despite trumpeting that it was pursuing its groundwater drilling programme “with no regrets” the City of Cape Town has taken a step back to afford greater consideration for environmental impact.
This emerged during a media visit to the Steenbras borehole wellfield on Thursday, during which project manager, David Allpass, responded to questions during a briefing session on the nature and scope of the drilling programme.
Asked by Bolander whether the open letter by a group of concerned scientists questioning the wisdom of the City’s drilling programme, had influenced the decision to suspend drilling operations at two environmentally sensitive sites, Mr Allpass responded: “You could say that.”
The City had applied for and been granted a National Environmental Management Act (NEMA) Section 30A directive, by the Department of Environmental Affairs and Development Planning (DEADP), which empowers the City to proceed with borehole drilling operations in environmentally sensitive areas without first completing an environmental impact assessment and obtaining a DEADP record of decision.
This directive does not however, exempt the City from observing various environmental provisions which might be triggered by these drilling operations.
The scientists, Jasper Slingsby, Nicky Allsop, and professors William Bond, Ed February and Adam West, all leading experts in their respective fields, questioned the immediate surface impacts of drilling operations and the potential impact of long-term aquifer abstraction.
It was in response to this open letter that City of Cape Town deputy mayor, Ian Neilsen, responded with a public statement in which he said: “The City of Cape Town’s groundwater programme, which is based on years of research, follows a ‘no regrets’ approach. This means that we have been doing everything that we can to understand our underground resources. We aim to err on the side of caution so that we do not do anything that could cause permanent damage to this resource.”
The controversial drilling programme has picked up from exploratory drilling that took place at Steenbras in 2009, and since it restarted late last year, five boreholes have been drilled, of which two are suspended and incomplete, two are at target depth, and one, an original exploratory borehole is currently being extended.
Bolander visited the drilling site of this borehole, and found that it was at a depth of over 570m, and according to principal geologist, Dylan Blake of Umvoto, the company contracted to manage the City’s borehole drilling programme, will probably be drilled to 750m before it intersects the target formation, the Peninsula aquifer. “This is a core-drilling operation,” Mr Blake explained. “This process uses a 50mm drill, which allows for the rock strata for the entire depth of the borehole to be extracted in 3m sections for analysis.”
Mr Blake added that once the borehole strikes the Peninsula aquifer, and the water yield is found to be exploitable, the hole will be re-drilled at a diameter suitable for abstraction.
Prior to the drill site visit, Dr Chris Hartnady, research and technical director at Umvoto, gave a detailed briefing about the project, including the history of previous exploratory drilling operations at Steenbras and what was revealed, the geology of the area, including the various aquifer formations, and the rationale for the City’s decision to develop the wellfield.
Bolander also visited one of the “suspended” boreholes in an environmentally sensitive area, and the extent of spillage of sediment as the result of drilling operations, upslope from a nearby water course and the Steenbras Lower Dam, was clearly evident.
The drilling rigs from this and the other “suspended” site have been moved to sites near the Steenbras Lower Dam wall, where drilling operations will commence this week.
During the briefing, it emerged that a formal environmental monitoring group will meet this week to consider measures needed to prevent further environmental impact at the “suspended” sites, and any future drilling sites.
One or more of the group of concerned scientists has been invited to join this group, according to Mr Allpass.
Once all the planned boreholes at Steenbras have been drilled – the final number has not yet been determined – and yields estimated, the infrastructure necessary for sustained abstraction must be installed, which will include pumps and a reticulation network to move the abstracted water into the Steenbras dams, or to a purification works.
Mr Allpass stressed that before that works commence, the City will follow all the required environmental protocols, and acquire all the necessary permissions, as stipulated in the National Environmental Management Act.
Speaking about the extent of abstraction feasible, Mr Blake said: “As a rule of thumb, one third of the potential yield of a borehole is considered a sustainable abstraction rate. The Department of Water and Sanitation (DWS) has granted a licence in three stages. We will proceed cautiously with a staggered approach, abstracting at a given rate over a period of time, while constantly monitoring water levels in the various boreholes, and impacts on surface water and springs.
“We will start by abstracting from one borehole for a period at a set rate, while monitoring aquifer levels in other production diameter boreholes and smaller monitoring boreholes, to determine what abstraction rate is sustainable. We’ll then move to another borehole and repeat this process. Each production borehole will be assessed in the same manner,” said Mr Blake.
The resultant data will be used in a modelling exercise to determine the extent and limits of the aquifer, which in turn, will help to determine a sustainable long term abstraction rate.
“The DWS licence grants rights to abstract 5 million m3 (5 000ML) a year in stage one, 10 million m3 (10 000ML) a year in stage two, and 35 million m3 (35 000ML) a year in stage three,” Mr Blake said. This equates to10, 20 and 70 days water supply at current consumption levels by the City of Cape Town.
Bolander asked Dr Hartnady if he was satisfied that the planned system which will be implanted to monitor abstraction and its impact on aquifer levels once the wellfielde goes into production, will be sufficient to avoid over-abstraction.
“Hermanus uses ground water, and the monitoring system implemented there is robust and effective. Aquifer levels are constantly monitored to avoid over-abstraction, and the system is realtime,” Dr Hartnady said.
“As the level of the aquifer drops below each of a number of alert levels, warnings are sent via mobile phone to various members of the monitoring group, and once the level drops below a particular point, the pumps are automatically shut off. I imagine a similar monitoring and management group will be implemented here.”
Bolander asked Mr Allpass at what cost the project would deliver water.
“Taking into account all costs, exploration, capital and running costs, the price per kilolitre will be about midway between that of surface water, and large scale desalination plant water, “ he said.