Stormwater runoff from typical developed and developing South African urban developments: definitely not for swimming

Abstract

Public water in South Africa is protected from pollution from urban areas and industries through various forms of wastewater treatment and enforced by legislation and standards. However, hardly any standard or guideline exists for an acceptable quality for urban run-off such as stormwater. The microbiological quality of urban run-off from various large urban developments in the Free State Province, South Africa, has been investigated to establish the extent of faecal pollution. Sanitation of a low socio-economic urban residential development was generally limited, comprising mainly pit and bucket latrines. Sanitation of the other developments was typical of the larger more developed South African urban situation. It comprised well developed residential structures with full water-borne sewerage, fully serviced central business districts, developing residential areas with both waterborne sewerage and additional areas of informal settlement with limited facilities. Faecal coliforms (FC) and enterococci (FE) were used as generalised indicator organisms of faecal pollution together with sorbitol-fermenting bifidobacteria (SFB) and Streptococcus bovis (SB). Somatic (SC) and male specific coliphages (MSC) were used as indicators of organic and sewage pollution of the receiving water in the target areas. Samples were collected from perennial flow during the dry season and from stormwater run-off after thundershowers. Stormwater run-off from the large settlement with limited facilities as well as from the residential development with additional informal settlement reached FC counts of <6 logs/100mL, equivalent to many sewage effluents. Stormwater run-off from well developed urban structures reached FC of <4 logs/100mL, which exceeded safety margins in guidelines for recreational water quality. The results show that run-off from developing urban settlements, as well as developed urban structures, constitute a major source of pollution for a river catchment which is downstream used as a source of water for human consumption and recreation. The level of pollution dictates that stabilisation of urban surface run-off should be regarded as an equal priority to the enforced stabilisation of other wastewaters generated by human activities.