With the Homevale Wastewater Treatment Works in the Northern Cape operating at above its design capacity of 30 Mℓ/d, coupled with substantial growth within the catchment area of the works, the Sol Plaatje Municipality identified the urgent need to increase the treatment capacity of the works. Chantelle Mattheus interviews Aurecon Associate Les O’Connell on the progress of the project.
“The project entailed refurbishing an existing 30 Mℓ/d wastewater treatment works (WWTW), extending its capacity to 48 Mℓ/d and diverting purified effluent by pumping it through a 700 mm pipeline to a high point from where it could either gravitate to the Vaal River or be utilised by farmers,” explains O’Connell.
Aurecon was responsible for the planning, design and construction supervision of the project, with numerous other contractors involved in additional aspects of the project, including Marange Construction, Empa Construction, Eigenbau, Botjheng Water, Entsha Henra Construction, HSH Construction, Metsi Projects, IWAC Joint Venture and Tau Pele-Selenane Joint Venture.
The broad thrust of the programme was to refurbish the WWTW in order to stabilise the effluent quality and thereafter, simultaneously extend it to accommodate additional inflows and to implement a scheme to divert effluent from Kamfers Dam to a balancing tank.
“The project lays the basis for sustainable development in Kimberley while at the same time addressing environmental issues related to a large flamingo population that inhabits Kamfers Dam,” says O’Connell, adding that the transfer of purified effluent will also provide economic opportunities for agricultural use to farmers in the vicinity of the transfer pipeline.
“The project also has regional significance in that the transfer of effluent and the associated lowering of the level of the pan will ensure the security of a main railway lines which is critical for the export of manganese from the Northern Cape.”
Additionally, from the sustainable employment viewpoint, a number ofcommunity liaison officers were recruited through the ward councillors in the area and local people were employed, with contractors only using permanently employed personnel to carry out work for which specific skills, that were unavailable locally, were required, notes O’Connell.
a) WWTW refurbishment
This aspect of the project was carried out in three phases under five contracts, of which Phase 1 was the emergency intervention to address the most pressing requirements when the project commenced in June 2009.It involved clearing blocked pipes in the works, replacing a collapsedoutfall sewer and creating a buffer pond to increase retention time before the effluent reach the pan.
Phase 2 referred to the refurbishment of the existing works in order to ensure that the works were in proper working order. Part of this second phase included the provision of an additional Secondary Settling Tank (SST) to add to the existing three SSTs. The purpose of this SSST was to provide operational flexibility with the added benefit of a slight increase in the WWTW’s capacity to 33 Ml/day. During the refurbishment of one of the existing SSTs, the floor of the SST failed and the whole structure had to be replaced.
The Municipal Infrastructure Grant (MIG) funding, as well as R7.2 million from Department of Water Affairs (DWA) was made available for the refurbishment of the works. To date, R67.4 million has been expended on the refurbishment, and it is estimated that once the balance of the retention payments is made, the total expenditure will be R67.9 million.
b) WWTW extension
The extension of the WWTW comprised an additional 15 Mℓ/d treatment lane, which consists of an inlet works, a biological reactor, two SSTs, two detention and one buffer pond, two lane sludge recycling pump stations, an aerobic sludge digester, a thickening sludge pump station, sludge drying beds, as well as a number of ancillary structures, stormwater drainage and roads.
In order for this to be achieved, a new inlet splitter was required to divide the effluent between the old works and the extension. The extension is being implemented through civil, mechanical and electrical contracts.
MIG funding was also obtained for the extension of the works, with the approved funding comprising R153 million MIG funds and R22 million to be sourced from the municipality funds. Additionally, in July last year a further R15 million was made available by the DWA under the Regional Bulk Infrastructure Grant (RBIG) for the utilisation on the Homevale WWTW project. The spending to date, which has been limited to expenditure on acquiring mechanical and electrical components and to professional fees, is approximately R25.25 million.
c) Diversion of effluent from Kamfers Dam
This project comprises a technical/construction portion, as well as a developmental portion; however, the technical/construction portion is currently the most important in addressing what has been termed; crisis levels; at the Kamfers Dam.
The technical construction portion is to be completed in two main phases comprising five separate contracts. The developmental aspects relate to a further two phases, which will be implemented subsequent to the completion of the technical aspects and involve making water available to commercial farmers for irrigation and establishing emerging farmers on a portion of municipal land utilising purified effluent to irrigate crops – although the latter phase has as yet not progressed beyond the conceptual stage.
A recent update on the level of the pan notes that, with the rainfall experienced in 2012, the Johannesburg line no longer appears to be in danger and the level of the pan is steadily dropping to the point where the submergence of the Hotazel line has decreased from 900 mm in September 2011 to a current 400 mm as of the end of 2012.
The Development Bank of Southern Africa (DBSA) is funding an amount of R18 million towards the diversion of effluent, while the R74 million balance is to be funded by Transnet, given that at this stage it is most seriously affected by the rising levels in the dam, with the Hotazel trajectory having to be closed and the main line to Johannesburg under threat since 2011.
According to O’Connell, to date the project in its entirety is progressing well, with the Homevale WWTW having already been refurbished and the contract for the extension on track, to be completed in May 2014. The Effluent Diversion scheme is also nearing completion and, when Water&Sanitation Africa spoke to O’Connell in February, the scheme was on track to be fully operational by the end of March this year.
The biggest challenge on-site to date, according to O’Connell, has been the soil conditionswhic comprised very deep clays subject to ground water infiltration. “This has posed a challenge in terms of the stability of structures,” says O’Connell.
Care has therefore been taken in the design of the interface between the clay,the foundation of structures and under-floor drainage. In addition, pressure relief valves have been included in all the structures that are susceptible to floating, notes O’Connell.
O’Connell adds that an interesting technique utilised on-site is the founding of water retaining structures without layer works in order to minimise the possibility of groundwater accumulating from the surrounding clays. “This is a creative method of handling the prevailing soil conditions.”
“Working on an operational plant has required careful coordination with the municipal staff at the WWTW and a close working relationship between site staff and municipal staff. Much of the success of these interactions can be attributed to the continuous support of Mr Boy Dhluwayo who is the Executive Director: Infrastructure and Services at the Sol Plaatje Municipality”
According to O’Connell, the capacity requirements were informed by various planning documents including the Integrated Development Programme, Spatial Development Framework and by interrogating the institutional knowledge of the planning and technical staff within the municipality.
“It is anticipated that the extension of the capacity of the WWTW will be sufficient to sustain the city until 2020.” However, he concludes that the project does allow room for expansion.