Landfill remediation more than just dirt

I am a Caymanian contaminated land environmental scientist who lives in the U.K., and I am extremely distressed by the editorial board’s idea of remediation. I assess former landfills, former gasworks and other brownfield land every single day. My M.Sc. thesis was based on a former landfill that had been remediated, and I studied over 20 years of data from a former landfill that is strikingly similar to the George Town landfill. Assessment and remediation of brownfield land is my bread and butter, and in my opinion, what you have prescribed in your recent editorial feature is not remediation at all. I love my country and I love the stance that the Caymanian Compass has taken on the George Town landfill, but I think that the recent article is a detrimental over-simplification.

Like the George Town landfill, most historical landfills in the U.K. were built with the “dilute and disperse” method. There was no lining and no gas protection measures and the contamination was free to migrate away from the landfill. The idea was that contamination could migrate away and then become less harmful through dilution and degradation. This does not work when considering how much waste we generate and remediation of these types of landfills is very common. I agree, many beautiful parks are former landfills. As stated in the editorial article, Cayman’s problem is not unique and there are many durable and well-tested solutions.

You are very, very right that you don’t remove the waste and stick it somewhere else. Though it is a common remediation strategy, termed “dig and dump,” it is not one that would be practical for the Cayman Islands. But you do need more than just “dirt, maybe a membrane.” I would like to explain what we need to remediate and what I feel is the best remediation option.

There are two main problems with former landfills — landfill gas and leachate. Landfill gas is generally composed of methane and carbon dioxide and is produced through the degradation of waste. Leachate is water which has percolated through landfills and dissolved contamination. Picture it as the nasty water that collects at the bottom of your bin. In order to effectively remediate landfills, you need to put gas control measures in place and reduce the generation of leachate by preventing the ingress of water.

Firstly, we need to stop the leachate from migrating into the North Sound. The easiest way of doing this is via a vertical cut-off wall. In simple terms, we dig a big trench around the landfill and fill it with an impermeable material such as concrete or bentonite (usually with a membrane inside) so that leachate can’t migrate through it. We might install a leachate collection and treatment system if it was deemed practical and cost-effective.

Secondly, we need to stop people who use the site afterwards from coming into contact with contamination from the landfill. We need a membrane and clean fill. The fill would need to have special geotechnical qualities to prevent people from coming into contact with contamination from the landfill. Without this, people could become sick by being exposed to vapours or by ingesting contamination from the soil below. Just adding dirt wouldn’t be enough, we need an effective barrier between the landfill and the people who use the site afterwards. Adding a membrane also reduces the generation of leachate because it prevents rainwater from getting into the waste so a membrane is crucial.

If you don’t control landfill gas, someone could die. I am not exaggerating. Methane can cause explosions and carbon dioxide can cause suffocation. Landfill gas can migrate laterally into nearby buildings and vertically into structures on the landfill. This gas can build up and then explode or suffocate someone. A big driver for landfill legislation in the U.K. was the Loscoe incident, where an explosion caused by landfill gas completely destroyed houses that were built nearby. There are many different ways to control landfill gas but we would probably vent it to the atmosphere. You can sometimes collect it and use it for energy if there is enough methane generation, but again we need to appraise the options.

I am happy that you have tried to clear misconceptions about what remediation is and tried to reduce the misconception that we would need to use the dig and dump method. However you have over-simplified it to the point where people could be injured and the environmental destruction would continue if your suggestion was enacted. The remediation could be relatively straight forward. A vertical cut-off wall, a membrane and gas control measures are all commonplace in the United Kingdom and relatively inexpensive as far as remediation goes. We would need to do a remediation options appraisal and see what is the best for our country but I guarantee it is not a simple level of dirt.

Lauren Dombowsky

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