LANDFILL STANDARDS IN SOUTH AFRICA
Graded landfill requirements in South Africa - four years of experience


By Professors Geoff Blight and Andy Fourie, Civil Engineering Department, Witwatersrand University, Johannesburg, South Africa

Although South Africa has large mining and industrial sectors, it cannot be regarded as an industrialised or developed country. The average gross national product per capita in 1995 was only $US 1,800 and levels of unemployment stand at about 40% of the economically active sector of the population.

Non-payment for services provided by local councils became a form of protest during the apartheid years and levels of payment have since remained low, despite every effort by the new government to persuade the population that non-payment is no longer patriotic. At the same time, the population growth rate in developing communities (which comprise 80% of the population) continues at an extremely high 2.4% per year. The spending of scarce resources, even on services as vital to community health as waste management, has thus to be prioritised carefully.

The development of rational and affordable standards for the management and disposal of municipal solid waste by landfilling is one way in which expenditure on health-related service provision can be optimised. In terms of South Africa's Environment Conservation Act (Act 73 of 1989), legislative power for the control of pollution caused by waste disposal sites is vested in the Minister of Water Affairs and Forestry. To date, control has been applied by means of a landfill site permit system. As a further measure, a committee was formed by the Department of Water Affairs and Forestry in 1990 to formulate a system of Minimum Requirements, which represent a set of graded standards for the siting, design, operation and closure of landfills. This document was released as a trial document in 1994 and is being implemented on an experimental basis as part of the permitting system to promote compliance with environmental policy and legislation. A new version of the Minimum Requirements, revised on the basis of experience, will be published this year.

The stated objective of the Minimum Requirements is to ensure that the most cost-effective means are used to protect the environment and public health from the adverse impacts of solid waste disposal. The Minimum Requirements contradict regulatory trends in developed countries in several ways:
  • they apply differential requirements for landfilling depending on climatic conditions, landfill size and type of waste;
  • they reject the conventional wisdom that every landfill will inevitably produce leachate;
  • controlled co-disposal of liquid hazardous wastes with general or municipal solid waste is permitted; and
  • they provide for calculated releases of pollutants into the local groundwater system.
Two criteria are considered when evaluating the need for a leachate collection and management system beneath a landfill receiving municipal or general solid waste (G waste). These are a climatic water balance and the size of the landfill. The climatic water balance approach, based on extensive research into water balances for landfills in South Africa, uses published, easily available figures for the weather station closest to the landfill. The potential for a landfill to generate leachate is evaluated by the difference between precipitation or rainfall and evapo-transpiration (E) based on standard A-pan evaporation. This is defined as the climatic water balance

B=R-E

Factors such as the moisture storage capacity (or field capacity of the waste), runoff and capillary moisture movement are ignored, usually resulting in a conservative estimate of leachate generation potential. The approach is based on research carried out over a period of more than 10 years into water balance conditions in South Africa, where the climate is arid to semi-arid over much of its area.

Because of climatic variability, it is accepted that leachate may be generated occasionally. But this is regarded as acceptable, provided historical records show that it is unlikely to occur more frequently than once in five years. If this requirement is met, the landfill is classified as B- and no underliner and leachate collection system is required. Otherwise, in wetter parts of the country, a landfill would be classified as B+. An underling and leachate collection system is required for all but very small B+ landfills.

Cognisance is taken of the likelihood that (other things being equal) small landfills pose a lesser environmental risk than do large landfills, by virtue of the smaller total pollution load of the refuse that is stored within them. The Minimum Requirements document distinguishes between four different landfill size categories (Communal, Small, Medium and Large). It relates the landfill size classification to the maximum predicted rate of refuse deposition for the life of the landfill.

These classifications further influence the requirements for installation of underliners and leachate collection systems at a landfill. Hazardous wastes are classified into low hazard (h) and high hazard (H) wastes. H and h wastes must be disposed of at hazardous waste (H) landfills which are thus classified as H1 or H:H respectively. The requirements for the underliners of H landfills are more demanding than for landfills storing general wastes (G landfills), and those for H:H landfills are, in turn, more severe than for H1 landfills.

It is permissible to co-dispose of liquids with dry solid wastes (either hazardous or general). Non-hazardous liquid wastes can be codisposed with general (G) wastes, but such a landfill would then be classified as B+, regardless of the local climate, and an appropriate underliner and leachate collection system would be required. Hazardous liquids can only be co-disposed at H:h or H:H landfills, depending on the hazard rating, but it is common to dispose of G dry solid wastes at H landfills, in order to control the co-disposal ratio.

Leakage of leachate through underliners into the groundwater is limited by specifying both a recipe design (succession of different specified layers) and a performance (maximum outflow rate) for the underliner of each type of landfill. For example, for class G:B+ landfills (a landfill for general wastes in a B+ climatic zone) the maximum permitted outflow rate is 300mm/y (equivalent to a permeability or hydraulic conductivity of Ix10-6cm/s). For an H:H landfill, the maximum permissible outflow is 30mm/y.

The environmental effects of the escape of this leachate from the landfill liner are mitigated by maintaining a minimum separation of 2m between the underside of the liner and the highest seasonal elevation of the groundwater phreatic surface. This allows for some attenuation of pollutants to occur in the unsaturated separation layer.

In the case of hazardous wastes, the quantity of a particular waste that is permitted to be disposed is limited by an estimate of the likely concentration that the particular pollutant will reach in the groundwater. This 'estimated environmental concentration' or EEC is limited to 0.1 % of the corresponding LD50. LD50, is that dose of a toxic substance that would prove lethal to 50% of the population of a certain organism (e.g. trout in a stream). The estimate of the EEC ignores any attenuation in the waste body and in the unsaturated zone, and is based solely on the estimated outflow rate through the underliner and dilution of the escaping leachate by the groundwater flow.

Implementation results
Implementation of the Minimum Requirements over the past four years has revealed some short-comings, and these are being addressed in the 1998 version, due for release in October. The major technical problems that have cropped up are the following:
  1. If unusually wet general wastes are disposed at a GB- landfill, leachate may be generated. This occurred at a GB-landfill where reject paper pulp was being disposed. The problem was overcome by requiring that the paper pulp be mixed with dry ash (fortunately available at the paper mill) to reduce the overall water content and also to reduce the compressibility of the material.

  2. The difficulties of designing a physically stable landfill on steeply sloping terrain were not sufficiently emphasised, nor were the extremely low interfacial friction angles between geomembranes and geotextiles and between geomembranes and waste. Attention is specifically drawn to these problems in the revised document.

  3. It has been realised that many landfill sites are on the borderline between B- and B+. A landfill may, for example, be marginally classified as B+, yet produce only, say, 15mm of leachate per year. If the Minimum Requirements are applied bureaucratically, an underliner would be required that would limit the outflow to 300mm per year. This is clearly nonsensical, but in one case, this is what is being insisted on.

  4. It has been realised that co-disposal ratios for H landfills require tighter specification and control. In the 1994 version of the Minimum Requirements, co-disposal ratios received scant attention, the documents stating merely that "a volumetric co-disposal ratio of 9 units of solid waste to 1 unit of liquid waste is usually recommended." The 1998 version defines the co-disposal ratio in mass terms and requires a water balance calculation to be made to ensure that the leachate produced does not exceed 200mm per year. Thus higher co-disposal ratios became permissible in dry climatic areas than in wetter areas.
The major non-technical inadequacy of the first version of the Minimum Requirements lay in the section on landfill site selection, where the topic of public participation in the process of site selection and public acceptance of the chosen site was neither emphasised nor treated adequately. The inadequacy of this section was realised when a citizen group objected to the siting of a proposed H:H landfill. After protracted, bitter and costly court proceedings, the citizens forced the proponents of the landfill (which by this time had been prepared and equipped with an underliner to receive H waste) to change the classification from H:H to GB-, thus substantially and adversely affecting the financial viability of the project.

The new section on public participation and approval sets out a detailed procedure for advertising the need and intention to seek and select a new landfill site, identifying "interested and affected parties" holding public consultations and forming an interested and affected parties' committee. The aim of the procedure is to encourage the public to play a major role in the site selection and environmental impact assessment and then, during operation of the landfill, in monitoring its operation.

As a result of the high level of unemployment in South Africa, scavenging of landfills has become prevalent, and in some cases, communities of several hundred people, men, women and children, have became entirely dependent on scavenging for their livelihood. The 1994 version of the Minimum Requirements dismissed the problem (and it certainly is a problem of health and safety for the scavengers) with the words: "Primarily for the purpose of protecting public health and safety, illegal scavenging and squatting should be discouraged at all waste disposal sites." The 1998 version has retained these words but adds "... no reclamation [can] be allowed at hazardous waste disposal sites."

The document also, however, recognises that once scavenging is occurring at a landfill, it is difficult to stop. It suggests identifying leaders among the group of scavengers and the formation of a representative committee with whom to communicate. It also suggests ways in which scavenging can be made more compatible with normal landfilling operations. One suggestion is to operate two cells or working areas simultaneously. Waste can then be offloaded in one area and picked over by the scavengers, while the second cell is being compacted and covered. It is also suggested that scavengers be provided with protective clothing by the license holder of the landfill. In particular, stout boots and industrial gloves should be provided. Highly visible waistcoats and dust masks are also suggested.

In summary, four years of experience with the implementation of the Minimum Requirements have shown the scheme to be acceptable to the waste industry, and generally technically sound. The short-comings that have shown up so far have been addressed, and the 1998 version should further improve the standards and practice of landfilling in South Africa.

Once it has been published in October 1998, the new version of the Minimum Requirements for Waste Disposal by Landfill will be available from:

The Department of Water Affairs and Forestry, Division of Waste Management, Private Bag X 313, Pretoria 0001, South Africa.

Wastes Management September 1998
Pages 48-49