Wagait Shire in the Northern Territory covers a small area, comprising a single community of approximately 350 residents on the north east coast of the Cox Peninsula, across the harbour from Darwin. As the population is so small, the shire council’s budget is severely restricted, limiting its options for managing waste disposal. The council provides no garbage collection and residents take their own garbage to the local dump, which is unsupervised apart from a low fence restricting dumping to the active part of the cell.
The community has no sewerage or reticulated water supply, but treated water is available from two large tanks which are operated by the NT Power and Water Authority and fed from bores situated a few kilometers away from the community and the dump.
The Wagait Shire landfill site consists of a single trench about 5m wide by about 30m long, as well as areas for collection of glass bottles, plastic containers, and aluminium cans for recycling, an area for dumping green waste, and an area for dumping large items of non putrescible waste, such as cars and building materials. Council workers set fire to the rubbish in the landfill trench several times a week. When the active part of the trench is full up, it is capped and the dumping zone moves along.
There is no lining in the trench to prevent leachate draining into the ground water. No form of leachate collection or gas venting is implemented. In the wet season the trench can fill up with water to within a meter or so of the top.
Smoke from burning rubbish is a serious health hazard for people dumping at the site while it’s burning, as well as being an undesirable source of air pollution. However, as well as reducing volume – and therefore landfill costs – it may have the added benefit of reducing landfill gas and possibly some types of leachate.
The lack of any form of leachate control is a serious concern. The dump is several kilometers from the community bores, but there is a likelihood that leachate will eventually find its way into the aquifer which supplies the community with water.
The absence of any form of gas collection or venting may have implications for rehabilitating the area after the dump is capped, as landfill gas in the root zone is likely to restrict the future growth of trees on the site (Chan et al., 1991; Flower et al., 1981). There also seems likely to be a small risk of explosion in previously capped cells – particularly as there are regular fires on the site.
The hot climate in that part of the Northern Territory would speed up the production of landfill gas – of which, about 30% is likely to be released to the atmosphere through the surface of the landfill (Park & Shin, 2001). This means that gas production from such a small cell would probably be a relatively short term concern.
Leachate collection and treatment can be problematic in the wet tropics, because at the time of year when the quantity of leachate is highest, the quantity of water in the cell would make it difficult to treat (Kawai, et al., 2012). This could possibly be partly overcome by mounding the waste, rather than simply digging a hole to put it in. However, that would make dumping more complicated and require extra management, which in turn would require funding that is probably not available.
Conventional treatment of the leachate would be expensive (Kawai et al., 2012) and out of reach for Wagait Shire Council, but some cheaper methods could be investigated. Anerobic digestion is one possibility – which can be successful in the wet tropics (Kawai, et al., 2012). However, that method is probably still too expensive for this community.
Other possible biological treatments such as aerated lagoons and conventional activated sludge are simple and cost effective (Ahmed et al., 2012) and could be considered here, although they probably require too much management and maintenance for this situation.
The leachate treatment method which would probably be the most likely to succeed in Wagait Shire is some form of wetland purification. This method of treatment is low cost and sustainable (Białowiec et al., 2012), but is able to remove metals, including heavy metals, from the leachate (Yalcuk & Ugurlu., 2009). Leachate treated in this way would still contain some pollutants, but is unlikely to result in high concentrations of heavy metals or salts (Justin & Zupančič., 2009). This approach would not be without its challenges though – in particular, the seasonal variation in rainfall and the need to pump leachate to the surface, which requires power and maintenance. Again, mounding, rather than burying the waste could help remove that requirement.
Białowiec, A., Davies, L., Albuquerque, A., Randerson, P.F. (2012) Nitrogen removal from landfill leachate in constructed wetlands with reed and willow: Redox potential in the root zone. Journal of Environmental Management, Volume 97, 30 April 2012, Pages 22–27.
Flower, F.B., Gilman, E.F., Leone, I.A. (1981) Landfill gas, what it does to trees and how its injurious effects may be prevented. Journal of Arboriculture, 7(2), Pages 43-52. Retrieved from http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=1710&Type=2 on 19/11/12.
Kawai, M., Purwanti, I.F., Nagao, N., Slamet, A., Hermana, J., Toda, T. (2012) Seasonal variation in chemical properties and degradability by anaerobic digestion of landfill leachate at Benowo in Surabaya, Indonesia. Journal of Environmental Management, Volume 110, 15 November 2012, Pages 267–275.
Yalcuk, A., Ugurlu, A. (2009) Comparison of horizontal and vertical constructed wetland systems for landfill leachate treatment. Bioresource Technology, Volume 100, Issue 9, May 2009, Pages 2521–2526.