From a hilly park in Grangetown can be seen panoramic views of Cardiff but little trace of the millions of tonnes of rubbish hidden underneath.
Grangemoor Park was built on top of a giant former landfill off Ferry Road, one of the largest in Britain.
In some ways, restoring the landfill and turning it into a popular park has been a success, with biodiversity increasing and wildlife thriving.
In others, it has not been so successful. Recently it emerged that pollution from the landfill has been leaking into Cardiff Bay and the Ely river for years.
Cardiff council previously said the situation is now under control and the amount of pollution is very small. But the exact source of where the pollution is coming from is unclear, and so efforts to stop it from entering the river and the bay have so far been hampered. Key documents detailing how to stop this from happening were lost, and the methods forgotten.
Originally, the Ely river was bendier than it is now, but was straightened out in 1969. The drained river bed in the former bends was then turned into the landfill, where rubbish was dumped until the 1990s, according to a thesis on landfill monitoring written by a Cardiff University PhD student. When the barrage was built in 1998, the tidal estuary at the end of the Ely and Taff rivers was made into a freshwater lake, now known as Cardiff Bay.
The landfill mostly accepted domestic waste, but also likely took in industrial and commercial waste too. Experts predicted about 4 million cubic metres of waste was dumped there in total. Leachate, which is formed when rainwater becomes contaminated with chemicals from decomposing rubbish, was drained directly into the Taff and Ely rivers from 1970. But this was mostly stopped in 1996, when a system was installed to collect and dispose of the leachate.
Pumping wells were used to collect leachate that had pooled in special drains. The leachate was then taken for treatment and put into the sewer system. Around this time a separate system was installed to collect gases coming from the rotting rubbish, mostly methane, and use it for generating electricity. When the site was closed, it was run by the Cardiff Bay Development Corporation, before then being passed to Cardiff council.
Somewhere along the way key documents about the landfill, and leachate system, were lost. Environmental concerns arose as soon as 2004, with leachate polluting the Ely river through one of the original pipes which hadn’t been closed off. This was later sealed off. However as recently as 2019, environmental inspectors found chemicals in the Bay common in leachate.
In an analysis of nearby groundwater, inspectors found ammonia, chloride, nickel and ammoniacal nitrogen. The testing appeared to confirm the fears of local residents, who since 2017 have been reporting pollution leak into the Bay from an underground pipe near the Watermark building, at the end of Ferry Road.
Now, the council is searching for where exactly the leachate is escaping from the landfill. A spokesman previously said the council was given inaccurate drain maps from the Cardiff Bay Development Corporation. The council is now working with Natural Resources Wales on a landfill management plan and measures to prevent the pollution from continuing to enter the Ely river and Cardiff Bay, including working on Grangemoor Park throughout this winter.