Identification and prioritisation of groundwater contaminants and sources in South Africa's urban catchment
Report No 1326/1/04
In many regions, economic growth is closely linked to the availability of groundwater. In most urban areas in South Africa, groundwater is less utilized than surface water, but often the bulk of water used in rural communities is groundwater. With increasing scarcity of fresh water resources, urban groundwater may be utilized to a greater extent in future.
Contamination of South Africa's urban aquifers presents a threat to the sustainability of this water resource. Man's activities, use of chemicals and generation of wastes tend to concentrate potential sources of contamination in the urban areas. The threat caused by undesirable substances is recognized in this country, but the understanding of the extent of the problem in South Africa's urban catchments is poor (Sililo et al., 2001). In their WRC project No. 1008 (Sililo et al., 2001) identified several research priorities for understanding the extent of urban groundwater contamination. This project is therefore geared towards filling the gap in the understanding of groundwater contamination in South Africa's urban environments. By doing so, the principal pollutants can be identified and, based on their risk, prioritised. This will facilitate better management of groundwater quality in South Africa by assisting future land use planning and vulnerability studies.
AIMS OF THIS STUDY
The Institute for Groundwater Studies, entered into a research contract with the Water Research Commission for collaborative research with the CSIR Environmentek and the University of the Western Cape's Groundwater Group to investigate groundwater contaminants and sources in South Africa's urban catchments.
The aims of the investigation are to:
APPROACH TO STUDY
The initial stages of the project involved the collection of information that would give a general overview of the status of urban groundwater pollution, mainly from textbooks and published international literature. Information on general sources of groundwater contamination and types of groundwater contaminants in the urban environment are summarised. Various approaches that have been used to classify groundwater contaminants and their sources are discussed.
General information on urban groundwater contamination was related to the South African context using information on local urban areas and summary statistics from Statistics South Africa (South African census data); Chamber of Mines (South African mining statistics); State of the Environment Reports (South African Metro Areas); Municipal websites (South African Metro Areas) and Water Research Commission Reports. These were used to identify potential sources of groundwater contamination in South African urban areas.
Case studies of reported contaminated sites were identified from archives of newspaper articles; conference and workshop proceedings (International Association of Hydrogeologists, Water Institute of Southern Africa, Institute of Waste Management) and project reports and monitoring databases, where available. Case studies from literature were intended to provide a baseline of the current level of groundwater contamination in South Africa's urban areas. The availability of published data and information, however, proved to be a major limitation in quantifying groundwater contamination in South Africa's urban areas.
A questionnaire requesting information concerning contaminant sources, activities likely to cause contamination, main contaminants of concern and contaminated aquifers were sent to Water Affairs officials, municipalities and consultants. Unfortunately the response to these questionnaires was poor. The project team then set up meetings with relevant parties such as DWAF, municipalities, water boards and private consulting companies, who could potentially supply information/data on contamination in various areas across the country. Since it was not possible to cover all urban areas within the scope of this project, detailed information and data were only collected for the major urban centres, namely Johannesburg-Pretoria (Gauteng), Durban (Kwa-Zulu Natal), Cape Town (Western Cape) and Port Elizabeth (Eastern Cape), as being the main areas likely to be affected by pollution.
Contamination incident reports and databases supplied by various organizations involved in potentially polluting activities or the monitoring of these activities could then be used to compile the contaminant inventories.
METHODOLOGIES DEVELOPED FOR THE PRIORITIZATION OF SOURCES AND CONTAMINANTS
A risk based prioritization framework
Rating occurs when contaminant sources are given a quantitative or qualitative measure of the potential hazard they pose to groundwater. Prioritisation methods focus on aspects such as contaminant loading, mobility, persistence and risk. A risk analysis estimates the probability and consequences of a contaminant event and usually considers both the properties of the contamination source and the hydrogeological environment.
Based on the amount of data available a tiered approach is followed when considering risk assessments. The first tier (LEVEL 0) is a rapid assessment of sources and contaminants in which minimal data are required and it produces low confidence results. This assessment should be completed within a few minutes. LEVEL 1 is the second tier which is a rapid assessment of contaminants on a local scale. It is intended to give the assessor a guideline of the risks. The assessment should take a couple of hours to complete. The next tier (LEVEL 2) is an intermediate assessment. The first step in the intermediate assessment is to collect all relevant data. Data requirements include aquifer and contaminant parameters, as well as health information. Most of the general information will be obtained from databases, but it is sometimes necessary to have site-specific data. The confidence attached to this assessment should be medium to high.
Level 0 is based on a rating system while LEVELS 1& 2 are based on complete risk assessments.
A fuzzy logic based approach was followed when conducting the risk assessments. The factors taken into account in the risk assessments are:
A protection zone can be defined as the surface and subsurface area surrounding a borehole or wellfield, supplying water (for example basic human needs), through which contaminants are reasonably likely to move and reach such a borehole or well field. In many cases it is difficult to protect the whole area, therefore various zones are established within the area. These zones have been defined as (Braune, 2000; EPA, 2000 & and Boulding, 1995):
Excel-based data information system
The objective of the Excel-based data information system is to provide a user-friendly, easy-to-update inventory on South Africa's groundwater contaminants in urban catchments. The idea originated from the need to capture, store and make information easily accessible, as well as for future linkage with national GIS-database systems. The Excel database includes the following components:
The inventory of inorganic and organic contaminants includes the type of source (urban settlement, agriculture, mining, non-metallurgical industry, metallurgical and metal products manufacturing), expected contaminants, examples and references.
The inventory of properties of inorganic and organic contaminants includes values of properties for about 2500 contaminants. These properties are mainly relevant to groundwater pollution, for example Henry's constant for volatilization, half-life and the organic carbon partitioning coefficient. CAS numbers are available for each contaminant, as well as links to international web sites where properties can be found, in particular those that are variable depending on environmental conditions and are not filled in the Excel-database.
A simple model developed by Rao et al. (1982) was included in the Excel database as a tool for prioritisation and site-specific ranking of contaminants. The model of Rao et al. (1982) calculates the attenuation and retardation factors of specific contaminants, based on properties of contaminants included in the database (Henry's constant, half-life and organic carbon partitioning coefficient) and user's input of hydrogeological characteristics (groundwater depth and net recharge rate, air-filled soil porosity, volumetric soil water content at field capacity, soil bulk density and organic carbon content in the soil).
The products resulting from this research are:
Using the above-mentioned products, contaminants found in the urban environment can be prioritized on a national, regional and local scale. Therefore a source and contaminant prioritization list was established for:
These prioritization lists are based on a national inventory, together with inventories for each of the above-mentioned cities.
Case studies from literature were intended to provide a baseline of the current level of groundwater contamination in South Africa's urban areas. Data that exists is often localised to a particular industry and in most cases no time series data is available. The availability of published data and information, however, proved to be a major limitation in quantifying groundwater contamination in South Africa's urban areas. One of the problems is that under South African law (National Water Act, Act 36 of 1998), monitoring of potential pollution sources is the responsibility of the polluter. This means that any data relating to the impact of polluting activities also resides with the polluter and they may be reluctant to release it to the public domain. Despite this, a large set of representative case studies has highlighted problems and lessons at different urban activities, with regards to groundwater quality.
The reviews of the transport of contaminants has revealed the importance of proper hydrogeological characterisation, as this largely determines the risk that a pollutant holds. The fuzzy logic approach combines the expert knowledge generated in this project with site-specific considerations so that sources and pollutants can be identified and prioritised in any area, at various scales of implementation. Using a multi-tiered approach facilitates management of sources, according to available information and expertise of the user. Through case studies, both real and generic, the methodologies and tools developed in this project have been tested and refined.
The results of this project therefore include:
In conclusion these documents and the associated software should serve as a good guide to expected contaminants associated with different activities. Methodologies have been created whereby a water manager in any urban area can identify and prioritise the potential groundwater contaminants in the area. The software packages should be very useful tools for persons ranging from municipal water mangers to researchers and hydrogeologists with detailed knowledge of a site.
RECOMMENDATIONS FOR FURTHER RESEARCH
Groundwater monitoring in urban areas needs to be addressed as a matter of priority. Based on the research conducted in this project, several sources and contaminants have been highlighted as potential priorities. Of great concern is the fact that for many of these the currently available datasets show that very little attention has been paid to the constituents in most groundwater monitoring programs. The following contaminants of concern are highlighted:
The National Water Act of 1998, provides the framework within which the Department of Water Affairs and Forestry (DWAF) can manage the protection, use, development, conservation and control of South Africa's water resources. In this context groundwater quality can be managed in an integrated and sustainable manner within the context of the National Water Resource Strategy and thereby to provide an adequate level of protection to groundwater resources and secure the supply of water of acceptable quality. In the Policy and Strategy for Groundwater Quality Management in South Africa (DWAF, 2000) DWAF describes the means and measures available to achieve groundwater quality management.
Implementation of the three strategies (source-directed, resource-directed and remediation) must be integrated to achieve the overall objective of sustainable groundwater utilization. Regulatory instruments provide DWAF with the means to intervene and influence the behaviour of the community targeted for regulation. Intervention is intended to ensure that the policy goals are achieved by inducing the desired behaviour from polluters and potential polluters.
In order to implement the Policy and Strategy, DWAF will launch a series of groundwater quality management programmes. These programmes will have a clearly defined objectives, action plans and time frames. The purpose of each programme will be to develop a component of the strategy and to oversee its implementation into the operational part of the regulatory system.
This investigation took a holistic approach and considered all activities that could influence groundwater quality in an urban environment. The issues highlighted in the recommendations must be considered in the implementation of the Policy and Strategy by DWAF, especially in specific groundwater management plans related to the identified activities and contaminants. Of highest importance is a need to develop policy and guidelines for monitoring of groundwater for organic contaminants. Secondly the development of modeling tools for the prediction of the fate and behaviour of NAPLs and pesticides, under South African aquifer conditions are essential in addressing the above issues.