EXPERTS in Solid Waste say the term "landfill" can be treated as synonymous to "sanitary landfill" of Municipal Solid Waste (MSW).
The only condition that qualifies it to be so is, only if the latter is designed on the principle of waste containment and is characterised by the presence of a liner and leachate collection system to prevent ground water contamination.
The term "sanitary" landfill has been extensively used in the past to describe MSW disposal units constructed on the basis of "dump and cover" but with no protection against ground water pollution.
It is important to analyse the new development on the ambitious mega project known as Dar es Salaam Metropolitan Development Project which is to take off next year. This project has focused on the building of infrastructure which includes the solid waste management systems in the Dar es Salaam Region.
I was keen to look at this project with a critical eye for the best interest of people living in such dump sites, which we have found to be exposing them to emissions and other pollutions including the nasty smell that comes out of it. In some countries where I was able to visit such as US, Turkey, and Middle East, there is a system in place which handles the Landfilling of Municipal solid waste.
The following types of waste are categorised. The mixed waste will be done for the following types of waste: Comingled waste (mixed waste) not found suitable for waste processing; Pre-processing and post-processing rejects from waste processing sites; Non-hazardous waste not being processed or recycled. Landfilling is usually not be done for the following waste streams in the municipal solid waste: Biowaste/ garden waste; Dry recyclables.
The process of handling garbage in such modern sites involves Landfilling of hazardous waste stream in the municipal waste site. It will be done at a hazardous waste landfill site. Such a site will be identified by the State Government and is likely to be operated by industries of a district/state. For example since the Dar es Salaam city Council has already identified a dump site at Pugu Kinyamwezi which has passed the feasiblity stage and Environmental Impact Assessment tests, the question of looking at the landfill does not arise.
But in places where the councils have to start from scratch, If such a landfill is not available, municipal authorities will dispose the hazardous waste in a special hazardous waste cell in the MSW landfill. Such a cell will be designed as per environment and forests authorities guidelines and in our case, by the Vice-President's Office (Environment) and the National Environment Management Council (NEMC).
In these countries that I have visited the authorities have been able to get rid of the garbage nuisance in a systematic way. For example the use of Landfilling of construction and demolition waste is done in a separate landfill where the waste can be stored and mined for future use in earthwork or road projects. If such a landfill site is not available, the waste will be stored in a special cell at a MSW landfill from where it can be mined for future use.
Construction and demolition waste can be used as a daily cover at MSW landfills; however only minimum thickness of cover should be provided as indicated in the council. For example in Tanzania the standard is between three and six inches. According to some local experts interviewed including Mr Protus Membe who is a Waste Management expert at the Dar es Salaam City Council he said under the waste management modernisation plan there are some sophisticated procedures.
Experts in different countries that I have visited have a consensus that the procedure of handling such waste is as follows: All excess construction waste should be stored in the separate landfill cell. All existing and old landfills will be inspected and boreholes will be drilled for recovery of leachate samples from the base of the landfill, recovery of subsoil samples beneath the base of the landfill for evaluation of permeability and soil properties and recovery of waste samples for waste characterisation.
A minimum of 3 boreholes will be drilled with at least one borehole for each acre of landfill area. The quality of leachate samples will be compared with the ground water quality in existing bore wells 2 km away from the landfill and the Central Pollution Control Board (CPCB) norms for limits of contaminants in leachate.
If the leachate quality and the permeability of the subsoil strata is observed to be satisfactory, the existing landfill can continue to operate with bi-annual monitoring of leachate quality in the drilled boreholes. If the leachate quality is observed to be of poor quality with respect to the local ground water quality or with respect to the CPCB norms, steps will be taken to close the existing landfill site and remedial measures adopted. All future landfilling will be undertaken in properly designed and constructed new landfills.