As floodwaters rise, toxic contaminants released from old landfills pose more of a hazard to nature and to us

Extensive flooding of the River Thames and its tributaries across south-east England in February 2014 was caused by extraordinary weather conditions. Very heavy rain had fallen on ground already saturated by multiple storms since the previous December. Hundreds of residents were evacuated and the flooding damaged thousands of homes and businesses.

One family, whose home was near an old landfill in Chertsey, Surrey, suffered a particularly devastating loss. Their seven-year-old son, Zane Gbangbola, died on the night of the floods. A coroner ruled that the cause of death was carbon monoxide poisoning from the petrol pump used to clear floodwater from their home.

But the family have long contested that when the River Thames burst its banks and flooded a nearby old landfill, toxic hydrogen cyanide gas was released, causing their son’s death.

Flooding does have the potential to stir up long-forgotten sources of pollution – and climate change is exacerbating that. Over the last century, we’ve buried millions of tonnes of our household, industrial and hazardous waste, often in old quarries, or dumped on saltmarshes and floodplains.

In the case of Gbangbola, the concerns related to a number of old, abandoned and worked-out gravel pits in the Thames floodplain that were landfilled with household, industrial and even military wastes during the 1950s and 1960s.

Modern, highly engineered landfills are lined and sealed with strong, impermeable materials like clay to stop liquid wastes or gases escaping into the environment. But these old sites weren’t lined. So, when they flooded in the winter of 2013-2014, pollutants, including hydrogen cyanide, could have leaked into the floodwaters that entered peoples’ homes.

While there is still significant debate about what exactly happened in Chertsey, hydrogen cyanide was allegedly detected in the Gbangbola family home on the night of the floods.

The concerns around Gbangbola relate to a small handful of old dumps, but there are at least 20,000 “historic landfills” across the UK. Historic landfills are defined by the Environment Agency as “sites where there is no environmental permit in force”. They generally predate the 1994 waste management licensing regulations.

They also predate other environmental laws such as the landfill regulations introduced in 2002 that require landfills to be lined to control the release of gases and leachates and protect the surrounding environment. Gases, such as methane, hydrogen sulphide or hydrogen cyanide are produced by the breakdown of food and animal waste. Leachates are liquid pollutant mixtures created by breakdown and chemical reactions between wastes.

These historic landfills can contain heavy metals, persistent organic chemicals such as pesticides, “forever” chemicals or per- and polyfluoroalkyl substances (PFAS), pharmaceuticals, medical waste and plastics.

They probably also contain materials that are now banned or restricted because of their harmful effects on the environment and human health, such as asbestos (fibrous, naturally occurring minerals known to harm human health) and polychlorinated biphenyls (synthetic industrial chemicals which were banned in the 1980s).

Landfilling was considered a long-term solution as waste gradually breaks down to become inert and harmless. But historic landfills were constructed with little understanding of climate change.

Analysis by my research team shows that in England alone, 4,000 historic landfills are in areas where there is greater than 1% annual probability of river flooding or 0.5% or greater annual probability of flooding from the sea. Those locations do not have flood defences.

Thousands more landfills are in areas known as groundwater source protection zones where modern environmental regulations would not permit their construction because of the potential risk of contaminating groundwater and drinking water sources.

Past pollution, future threats

I’ve been studying historic landfills for more than a decade, during which time there has been little movement from government or the landfill sector to address the issue of historic landfills. This is possibly because both the potential scale of the problem and the cost of implementing sustainable solutions are just overwhelming. But the problem of our waste legacy is not going to go away and with climate change will become even more pressing.

More severe and more frequent floods will increase the chance that historic landfills are inundated with water. That will release more toxic chemicals into surface and groundwaters. This is even more problematic in coastal areas where sodium and chloride in seawater can combine with some chemicals to make them more mobile.

Extreme flood and coastal storm events could erode historic landfills releasing solid waste materials such as plastics, old batteries and asbestos into our rivers and seas. Drought could dry and weaken landfill structures making them more vulnerable to failure and potential release of pollutants. While, increasing temperatures can increase the volatility of some chemicals so they can escape more easily as gases or degrade quickly into toxic byproducts.

Our rivers are already heavily polluted from road runoff, sewage, industry and agriculture. Release of pollutants from old landfill sites will make this worse.

We test drinking water to ensure that it is safe to drink. But, additional release of chemicals, particularly forever chemicals that are harmful at very low concentrations and are problematic to remove from landfill leachate may affect our drinking water. This could increase the need to monitor or require expensive upgrades to our drinking water treatment facilities.

When I visit eroding coastal landfills, I recognise discarded objects from the time of my own childhood – a spirograph, 1970s fabric, a sweet wrapper – carefully thrown away, but still here. Our waste legacy will be a burden for future generations for decades, if not centuries. Right now, we need to learn to live with the consequences of climate change, while trying to protect our waterways and human health from the potential harm associated with these old landfills sites.

The task is monumental.

The first step is to understand the scale of the problem and know which of the thousands of historic landfill sites pose the greatest risk to human and environmental health. Then, pollution from the highest-priority landfills can be cleaned up, waste could be removed – perhaps even mined for precious resources – or better protected from flooding and erosion. That all requires political will, huge investment and substantial technological innovation.

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