Landfill sites can have severely detrimental effects on surrounding land, and as a result are often under intense scrutiny. Interest in the remediation of contaminated land has never been higher with Brownfield developments for new housing on the up and up 1, resulting from the rise in demand for the development of new housing. Contamination of land can result from many different sources ranging from various industrial processes to the incorrect disposal of waste. In the case of landfill sites, a common reason for contamination of the surrounding area results from the dispersion of landfill leachate2.
A landfill site is defined by the Environment Agency as being “a waste disposal site for the deposit of waste onto or into land including; internal waste disposal sites (when the waste is disposed of at the place of production); a permanent site which is used for the temporary storage of waste but excluding:
- Facilities where waste is unloaded in order to permit its preparation for further transport for recovery, treatment or disposal elsewhere, and
- Storage of waste prior to recovery or treatment for a period less than 3 years as a general rule, or
- Storage of waste prior to disposal for a period less than 1 year.”3<
Once the waste has been buried within the landfill site it begins to decompose. This produces a mixture of noxious liquids, known as leachate, and landfill gases – produced by the interactions of microorganisms with the waste materials under anaerobic conditions – which consist predominantly of methane and carbon dioxide with varying amounts of minor components. Landfill sites are one of the oldest methods of waste disposal and were largely unregulated until the early 1970s4. Consequently, large areas of land across the United Kingdom have become contaminated by various materials from heavy metals to hydrocarbons. This contamination of land surrounding landfill sites is largely due to inadequate designs, relying on the ‘dilute and disperse’ principle (see below).
A common area of interest with landfill sites, and resultant contaminants, is the distribution of heavy metals; 5, 6 these can result from both natural and anthropogenic sources and form a number of compounds within waste products, listed in table 1.
Construction
Prior to the introduction of engineered landfill sites, the majority were selected for naturally occurring depressions in the land surface. These were either void spaces created by resource extraction e.g. disused quarries, or the creation of a hill where this would be most suited within the local topography of the area.3 The land is, wherever possible, reclaimed for a variety of uses from construction to agriculture. However, this is dependent on the condition of the landfill. These un-engineered landfill sites rely on the ‘dilute and disperse’ principle; this allows water to penetrate into the landfill site and react with the waste and leachate, causing the contaminants to become diluted. This contaminant-rich water is then dispersed into the local environment, usually into the surrounding soil and groundwater, by the local hydrogeological flow regime which reduces the concentration of leachate within the landfill site. However, this process is slow. The speed at which this occurs is largely defined by the hydraulic conductivity of the underlying geological units. 8, 9
Modern landfill sites, however, are engineered to ensure that there is minimal to zero damage to the environment. One of the most widely used designs is an engineered double-lined landfill site which uses two impervious plastic liners with re-compacted clay between them adding a third impervious layer. The landfill site is then capped by a further clay layer, a geo-membrane cap and a drainage layer which are subsequently topped by topsoil material for re-landscaping purposes. A collection system is installed prior to filling the landfill in order to extract and dispose of any leachate it produces, as well as a detection system for any possible leaks that may occur. While in operation, the landfill site is separated into cells to fill the site in a logical order and to ensure that wastes of a similar nature are located within the same area of the site, as this will reduce the risk of different refuse types reacting and potentially causing damage to human health. Another potential advantage of engineered landfill sites is the possibility of harnessing methane gas produced from the site for industrial uses. However this requires planning prior to construction of the site.
Estuarine and Coastal Landfill
Estuarine and coastal landfill sites pose different risks and present different problems compared to standard inland landfill sites as there is an increased risk of environmental damage due to the effects of saline intrusion and coastal erosion. The main risk from landfill sites being situated within or near to an estuarine environment is from the potential for leachate from the landfill to locally enrich the sediment in both organic compounds and particular heavy metals due their strong affinity with fine-grained estuarine sediments.10 While the contaminants remain locked within the sediment there is minimal risk of human exposure, however these substances can be re-mobilised into the environment via saline intrusion resulting in ion exchange, coastal erosion which returns the substances into the water column, or via anthropogenic processes which can also return contaminated sediments into the water column. This can have a serious impact on the estuarine environment due to its sensitive nature.11
Landfill company fined
Despite the more advanced construction techniques and monitoring systems that are now utilised, landfill sites are still required to operate within limits set out by permits granted by the Environment Agency. Recently we have seen that these are not always adhered to, with the likes of SITA (a specialist recycling and resource management company) being fined £110,000 for breaching the associated permit of the Albury Landfill site in Surrey. The Albury Landfill is a former sand quarry which was licensed to accept non-hazardous waste since c.1992, and is currently undergoing the final capping phase and restoration. The breach of the permit occurred throughout 2013 and was due to the leachate levels of the landfill being consistently too high, as it exceeded the 3 metre maximum set out by the Environment Agency within the permit. It wasn’t until February 2014 that the site became compliant by extracting the leachate from the site to be treated at another facility.12
It goes to show that, even with so many advancements in technology and understanding over the years, it is still possible for contamination to occur when disposing of our waste material. As it stands the Pollution Prevention and Control Officer from the Environment Agency confirmed that the company are placing their focus on completing the capping layer and restoration of the landfill site, which they believe will help to reduce the volume of leachate being generated.12
References
1. Porsani, J.L., Filho, W.M., Elis, V.R., Shimeles, F., Dourado, J.C., & Moura, H.P. (2004). The use of GPR and VES in delineating a contamination plume in a landfill site: a case study in SE Brazil. Journal of Applied Geophysics, 55: 199-209.
2. Leachate. (No Date) Collins English Dictionary – Complete & Unabridged 10th Edition (online). UK, http://dictionary.reference.com/browse/leachate, Accessed 12th May 2015.
3. Eastleigh Borough Council. (2006) What is a Landfill Site (online). UK, http://www.eastleigh.gov.uk/pdf/Whatisalandfillsite.pdf, accessed 7th April 2015.
4. Department of the Environment (1996) Waste Recyclying, treatment and disposal sites (online). UK, https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/314258/scho0195bjll-e-e.pdf, accessed 12th May 2015.
5. Östman, M., Wahlberg, O., Agren, S., & Martensson, A. (2006). Metal and organic matter contents in a combined household and industrial landfill. Waste Management, 26: 29-40.
6. Kamon, M., Plata, H., Katsumi, T., Oya, Y., Miyazaki, S., & Inui, T. (2007). Heavy metal mobility in incinerator ash coastal landfill. Annuals of Disas. Prev. Res. Inst, Kyoto Univ., No. 50B.
7. Sparks, D.L. (2005) Toxic Metals in the Environment: The Role of Surfaces. Elements, 1: 193-197.
8. Allen, A. (2001). Containment landfills: the myth of sustainability. Engineering Geology, 60(1): 3-19.
9. Optimum hydraulic conductivity for the dilute and disperse process is between 10-7m s-1 and 10-9m s-1, which equates to several years e.g. 1 x 10-7m s-1 = 3.15m/year.
10. Lee, S.V., & Cundy, A.B. (2001). Heavy metal contamination and mixing processes in sediments from the Humber Estuary, Eastern England. Estuarine, Coastal and Shelf Science, 53: 619-636.
11. Krech, S., & McNeill, J.R. (2004). Encyclopedia of World Environmental History: 001. Routledge, London.
12. Environment Agency (2015). SITA fined over £100,000 for breaching permit at Surrey landfill (online). UK, https://www.gov.uk/government/news/sita-fined-over-110000-for-breaching-permit-at-surrey-landfill, accessed 7th April 2015.
