A drop of the brown stuff

Compost. It smells, Alan Titchmarsh likes to use it on his begonias, and old people keep huge steaming piles of it in their back gardens. If your knowledge of the brown stuff is more or less limited to the above, then you’ll no doubt be surprised to learn that high-grade compost can also be used as a highly-sustainable and economic topsoil for brownfield sites.

At Ebbw Vale in Wales, about 40km north of Cardiff, 200 acres of a former steelworks are being remediated using topsoil manufactured on site using locally-sourced compost mixed with inert waste taken from the ground. Promoted by the Waste & Resources Action Plan (WRAP) as a viable alternative to dumping waste soil in landfill and importing virgin topsoil, at Ebbw Vale it’s helping cut thousands of lorry trips, while improving the quality of landscaping and simultaneously ticking waste management boxes.

The £89,000 government-funded scheme is one of 24 WRAP trailblazer projects in the UK designed to investigate and demonstrate the financial and environmental benefits of specifying locally-sourced quality compost in brownfield projects.

‘At first we thought importing a two metre-thick crust of clean fill to cover the whole site would be the cheapest thing to do,’ says Christian Cadwallader, project manager for Blaenau Gwent County Borough Council.

‘But then we realised it would take about 100,000 lorry trips to bring it in, which would have cost a bomb and is not the environmentally sustainable thing to do. We took a bold decision by saying no, but we haven’t regretted it.’

Located in a narrow valley, the Ebbw Vale development project will breathe new life into a community once dependent on the steel industry, but now in decline. When complete, in phases up until 2018, the mixed-use development will include a learning campus, local general hospital, a leisure centre, sports pitches, a theatre, offices and around 500 new homes.

WRAP became involved in the project in 2005, after Blaenau Gwent and the Welsh Assembly Government purchased the site from steel manufacturer Corus. ‘Once all the structures on site had been decommissioned and demolished, we were left with the reinforced concrete slabs, plus any potential unknowns in the ground, including contamination,’ says Cadwallader.

Reclamation and remediation works are being carried out in two phases. A 50-acre area earmarked for the hospital was first cleaned over 12 months starting in winter 2005 and then in early 2007 Edmund Nuttall began the current remediation and reclamation phase, which is due for completion this September or October.

Sustainability finds its ultimate expression on this development. All waste generated during remediation is being recycled in one way or another and, apart from steel rebar removed from concrete, nothing will leave the site. As Paul Mathers, landscape and regeneration project manager for WRAP, points out: ‘You couldn’t get a better waste management strategy than this – there is no waste.’

All contaminated material is being environmentally cleaned on site and every ounce of concrete, brick, spoil, slag and other inert matter is being reused in the topsoil.

You couldn’t get a better waste management strategy than this – there is no waste

Paul Mathers, WRAP

Although it sounds very scientific, the compost used here conforms to the PAS 100 standard and is produced from municipal garden waste such as grass cuttings, pruning and leaves. It’s fibrous and rich in nutrients and moisture, making it ideal for growing plants and trees. Local producers are supplying about 60% of the compost requirement at Ebbw Vale. ‘We’d have loved to source it all from Wales, but 0-10mm fine-graded stuff had to come from England,’ says Mathers.

Topsoil is made on site, based on specifications drawn up in the laboratory by a soil scientist, with relative mixture amounts selected based on the plant, tree or shrub being planted. Inert materials are first broken down in a crusher, then crushed again into finer graded material of different sizes. After it has been combined with sewage sludge and the compost, the mixture must be placed within 24 hours – it cannot be stockpiled.

‘Although mixing and placing topsoil aren’t new to earthworks guys like Nuttall, they were at first wary of the precise mixing method needed on this project,’ says Mathers. ‘It was a steep learning curve, but once they had tried it they were fine.’

A major feature of the Ebbw Vale site is a 40-acre wetlands area, which will bisect the entire site and return the valley to its original profile. ‘It has been a tough job,’ says Cadwallader. ‘Over time, the steel industry gradually built itself up the sides of the valley, so buildings previously sat on or inset into the valley have become basement structures that have been built on top of. The legacy is a huge labyrinth of basements, about 140 complexes in all, most of which had to broken up and removed.’ When CM visited the project last month, Nuttall was placing topsoil in two thicknesses along slopes bordering a culvert at the valley bottom.

‘The 2:2/2.5 slopes make it very difficult to place material, but we’ve got a very skilled excavator driver who is trained to create multi-directional rutting in the surface,’ says Cadwallader. ‘A major advantage of composting is that it requires very little maintenance after placement, it compacts well and the coarse inert material in the mixture prevents slippage.’ These benefits could have vast implications for the Highways Agency, says Mathers, who wants to see composting used on the hundreds of thousands of kilometres of embankments and cuttings around the UK.

‘A restrictive factor is the amount of inert colliery spoil available, however,’ says Cadwallader. ‘We’re going to run out. We’ll either have to start importing inert material later in the project, or revert to the traditional method of importing topsoil. We’re using everything we possibly can.’

A total of 15,000 tonnes of compost will have been imported to Ebbw Vale before the end of this month, and although at £15 a tonne it costs more than traditional topsoil, lorry trips to the site have been cut by 50% compared with importing the entire topsoil requirement, and nothing is going to landfill. Mathers says the medium-to-long-term savings are also significant due to the reduced maintenance and improved plant growth. Although the results of the Ebbw Vale trial won’t be available for a couple of years, composting at a contaminated ex-munitions factory site in Chorley, Lancashire, resulted in a 50% reduction in costs compared with traditional methods.

WRAP is hoping that the published results of the Ebbw Vale trailblazer will help educate clients, contractors and landscape architects in the benefits of using compost as topsoil, so that in future it can be written into project specifications as early as possible. ‘At the moment no one seems to know about this way of saving money or that they have got the option of manufacturing it themselves,’ says Mathers.

‘Site waste management plans become mandatory in April and contractors will have to assess their waste horizons at the start of a project. Most will consider what they’re doing with waste bricks and mortar etc, but what about soil? Don’t think of it as waste, think of it as future soils. Don’t throw them away, they are an important resource.’