REGIONAL CONTEXT

The Brugspruit Water Pollution Control Works is located on the Brugspruit, a tributary of the Klipspruit, draining to the upper Olifants River. The local area was extensively mined for coal in the early part of the 1900's. Several thousands hectares of shallow undermined land are present in the area. The shallow undermining has had a devastating effect on the environment and specifically on the water environment. Acid mine drainage seeping and flowing from the old underground workings impacts directly on the tributaries, Klipspruit and further downstream on Loskop Dam.

The water quality in the Klipspruit has been unfit for any of the recognised users including potable and irrigation use. No significant aquatic life has survived the poor water quality conditions. This impact is felt far downstream.

The Department developed a water quality management plan for the Klipspruit catchment in 1992. The management plan proposed a combination of more stringent pollution control at source, construction of water pollution control works and possibly future re-mining and rehabilitation of the old mine workings.

The Department of Water Affairs and Forestry thus assumed the responsibility on behalf of the State to remediate and install water pollution control works to minimise the impact on the local river system.

DESCRIPTION OF THE WATER POLLUTION CONTROL WORKS

The water pollution control works erected by the Department involves an extensive acid mine drainage collection and treatment system.
The collection system includes a northern and southern collector which run along the Brugspruit, a tributary of the Klipspruit, to intercept and collect acid mine drainage before it enters the Brugspruit. Six collection points were constructed along the collectors and they are located at old seep zones, mine adits and decant points. The acid mine drainage flows under gravity to the treatment plant. The total length of the collector pipe system is 7,8km.

The treatment plant involves a modern lime dosing facility, which neutralises the water and removed the bulk of the toxic metals, specifically iron, manganese and aluminium. The treatment process includes flow balancing, pumping, lime dosing, aeration and final clarification.

The acid mine drainage flow is quite variable and shows a distinct seasonal pattern. The incoming flow is balanced inlined ponds. The acid mine drainage is then pumped to a conditioning / aeration basin, where lime is added for neutralisation. The removal of metals requires some oxygenation of the water. The metals precipitate to form a sludge, which is separated from the clear treated effluent in the clarifiers. Clarifiers underflow sludge is recycled on a continuous basis, back to the conditioning/ aeration basin.

The final effluent is stabilised with soda ash before discharge to the adjacent Brugspruit. The collection system and treatment plant have a combined mine water treatment capacity of 10 000 m3/day. Allowance was also made for the future treatment of acid mine drainage collected from the adjacent Blesbokspruit valley.

The treatment plant sludge generated in the treatment process is discharged into specially constructed sludge lagoons.

SLUDGE LAGOONS

The sludge generated in the treatment process was initially classified and required a H:h disposal facility, because of the expected high concentrations of heavy metals, (Specifically Zn; Mn; Al (3) and Cu).

Because of the larger size of the new sludge lagoons and the low concentrations of heavy metals the waste sludge was reclassified / delisted to a lower hazard rating and now requires a GB+ site with a leachate management facility.

The design for the new sludge lagoons are however similar to that of the existing lagoons. It involves a membrane lined pond system to prevent seepage and potential contamination of the ground water and enable the department to monitor the quantity and quality of the leachate and leakage accurately.

Lagoon volume = 50 000 m3; depth = 5 m and area of liner = 15 000 m2 / dam