Case Study - Tanking of Drinking Water Reservoir at Matla Coal, Witbank, South Africa, using SWS Slurry

Background

The reservoir is situated at the Matla Coal Mine, near Witbank (approx. 2 hours from Johannesburg), which produces coal to fuel the nearby power stations.

The purpose of the reservoir is to store drinking water for consumption by people working in the mine. Unfortunately, the reservoir had started to leak to such an extent that the water bill at the end of every month did not justify the continued use of the reservoir. As a temporary measure, the reservoir was closed. This meant that drinking water had to be drawn from a second reservoir that was intended to provide water for the mine's cooling system.

Obviously the first reservoir needed to be waterproofed, as the mine was now relying on just one reservoir for all its water. The Safeguard SWS system was chosen because it is simple to apply, is proven in use, and conforms to WRC (UK Water Research Council) standards, demonstrating that it is safe to use in contact with drinking water.

Work Carried Out

The work was carried out by the Witbank branch of Specialist Services.

The inside of the reservoir was cleaned using a high pressure cleaner and scrubbing brushes. The water used for cleaning had to be pumped out using a submersible pump. The sides of the reservoir were then checked for cracks and structural faults. Any defects were made good.

The capacity of the reservoir is 1211.6 cubic metres. This meant that it was too large for the waterproofing to be carried out in one day. The workers were therefore divided into two groups. The first group applied the first coat of SWS slurry with block brushes, using vertical brush strokes. The second group followed 24 hours behind, applying a second coat using horizontal brush strokes.

Due to the large surface area to be covered, the reservoir was divided into marked sections. This helped ensure that a total overlap was achieved between the first and second coats. It also assisted in monitoring and controlling the rate at which the product was applied, ensuring an even thickness of application.

Specific problems encountered during the application of the product were the height of the structure (3.6m) and the lack of any lighting. These were overcome by the use of scaffolding and the installation of temporary lighting.

To ensure that the slurry gained its maximum possible strength, it was kept wet for a 28 day hydration period. During the first week it was hosed down once every day, however, due to the enclosed nature of the reservoir it was later found that twice weekly was adequate to keep the slurry damp enough to keep curing.

The reservoir has now been filled with water and is functioning normally again.