PAS 100: a refreshing brownfield tonic
Soil quality on brownfield sites can present a significant challenge to developers, but by using PAS 100 compost it is possible to restore soil to the level required to support healthy vegetation. Paul Mathers explains.
One of the main challenges in redeveloping brownfield land is poor quality soil, which as a result of extensive industrial use, can suffer from a lack of nutrients and minerals, making it barren, unproductive and unworkable. When brownfield sites are used for the development of open parkland and nature reserves this is a particularly serious issue because the soil is unlikely to be able to support healthy vegetation or absorb water, leading to water pooling and a greater chance of flooding.
To overcome this it is possible to manufacture new topsoil using a mixture of existing mineral resources - such as sub-soil, quarry fines, shales or steel slag - and organic material such as quality compost.
Environmentally, this is good practice and represents careful resource management because it allows contractors to prioritise the reuse of material over disposal. It can also deliver cost benefits too, such as a reduction in waste disposal costs - including landfill tax - and in the elimination of replacement topsoil.
Soil manufacture presents an enormous opportunity for developers working on brownfield sites. In 2007, it became a key part of the Land Restoration Trust's plan to transform an aging brownfield site at Cronton Colliery in Merseyside into a high-quality country park. Worried about the effects of previous industrial activity on the land, the trust wanted to improve the nutrient and mineral content of the soil to allow for the natural and healthy establishment of vegetation across the site.
To do this, environmental consultancy TEP was commissioned to look at how this could be undertaken using locally produced, high-quality BSI PAS 100 compost as the organic basis for the re-establishment of native vegetation. The main challenge for TEP was identifying the optimum mixture of PAS 100 compost and on-site spoil resources needed to promote healthy and sustained growth, so during May 2007 a proportion of the site was divided into eight different trial areas.
The areas included those that were untouched, those that were top dressed with compost and/or seeded, areas that were cultivated and seeded, and areas that had compost applied before being cultivated and seeded. In each case, the core specification was to incorporate a 30mm layer of quality compost into 120mm of spoil and seed with a native wildflower grass mix.
Even as early as the summer of 2007, the results were plain to see.
Areas where compost had been applied had developed a fresh, green layer of vegetation and demonstrated significantly more vigorous growth than the adjacent areas that had undergone less treatment. Continuing into 2008, the results became more pronounced. With germination having taken place during the previous autumn, the areas where compost had been applied were visibly greener than those without.
Compare and contrast
Areas that had been cultivated as well as having compost applied were even more impressive, and had swiftly developed a healthy coverage of wildflowers. By comparison, areas without compost remained undeveloped and bare even in late 2008. The cost savings were significant.
Had the trust imported and spread natural topsoil to a depth of 150mm it would have cost around £2.25 per square metre. But by importing and spreading PAS 100 compost to a depth of 30mm, the total cost came to £0.28 per square metre, resulting in a total cost saving of 88%.
Crucially, quality compost can also be sourced locally. WRAP's compost suppliers directory is an online resource that allows users to search for their nearest PAS 100 compost supplier by postcode. This not only provides end users with the opportunity to source and use a high-quality material, but it also helps to keep transportation costs to a minimum.
With the Government likely to remain fervent supporters of brownfield regeneration in the UK, finding ways to redevelop derelict land in a cost effective and sustainable manner is increasingly important. Through the use of PAS 100 compost, brownfield developers can make use of a high-quality, safe and reliable material that is practical, easy to source and cost effective. And with more than 2M tonnes of compost being produced each year, using it in schemes such as the trial at Cronton Colliery is a great example of closed loop recycling.