In 2015, the UK Government made a pledge to tackle the housing shortage by delivering one million new homes by the year 2020. The redevelopment of brownfield land is one of many steps being taken to reach this target. Here, Jill Derrick, Foul Water Systems Product Manager at Wavin, details the considerations developers must take when specifying below ground drainage for these sites.

According to the latest figures, between 240,000 and 340,000 more new homes are needed every year to help address the housing shortage and deal with a backlog of almost four million properties. 1 While steps are being taken to meet this, just 220,000 new homes were added to UK stock in 2017/18, a significant deficit.

As such, the Government is facing ever-growing pressure to find solutions that help all those involved in the supply chain deliver new homes. Freeing up disused land for development, thanks to the recent introduction of brownfield land registers, is one of the positive steps that has been taken. However, while this process does have a number of benefits, developers must take extra precautions when working on this land, particularly when it comes to below ground drainage specification.

Making the most of brownfield land

Brownfield land is defined as land that is or has been previously occupied and has the potential to be redeveloped. These sites actually account for a significant proportion of available land in the UK, with research conducted by the Campaign to Protect Rural England (CPRE) recently finding that brownfield sites cover over 28,000 hectares across the country, enough land for a minimum of 1,052,124 homes. 2 Using this land would therefore go a long way to resolving the housing issue.

However, brownfield land doesn’t come without its challenges. Often, but not always, the sites will have been used for industrial or commercial purposes and may be derelict or contaminated. This is one of many reasons why developers must take extra care when selecting products for below ground drainage; any system specified must prevent impurities entering the watercourse or damaging the pipework.

In 2017, it was announced that new brownfield land registers would be introduced to streamline the process of identifying sites that are available for redevelopment, helping to free up land for redevelopment more quickly by local planning authorities and ease the housing crisis.

Brownfield land and below ground drainage

Whether it’s a new block of high-rise apartments or a small collection of two to three-bedroom homes, all new housing developments come with a number of challenges. Developers therefore need a solid understanding of what these challenges are, and an awareness of how they can be addressed, so new homes are delivered safely and effectively.

Site surveys and land assessments are key to identifying and resolving such issues. A site survey will allow developers to determine if the land’s previous use will pose any risk to those who will work, and ultimately live, on the site. Chemicals found could be either be organic or inorganic, and while the presence of both can often vary depending on how the land was used previously, examples that can be present in brownfield sites include:

Inorganics

• Metals (such as arsenic, cadmium, copper, lead and mercury)
• pH (acids and alkalis)
• Asbestos

Organics

• PAH (polycyclic aromatic hydrocarbons, such as anthracene, pyrene, and other complex hydrocarbons formed as a result of burning of organic material)
• TPH (total petroleum hydrocarbons, such as hexane, jet fuels, mineral oils and other hydrocarbons that are found in crude oil)
• BTEX (benzene, toluene, ethylbenzene and xylene, released from vehicle emissions and a variety of industrial processes)
• Phenols

Using plastic drainage

Plastic pipes for drains and sewers are often manufactured from materials that are naturally resistant to inorganic compounds. In fact, plastic pipe solutions have been used in brownfield sites for a number of years.

In rare circumstances, there will be factors that mean plastic solutions may not be suitable. Therefore, it’s important to note that developers should always contact a manufacturer with any questions about product suitability in relation to a particular project or installation.

Guidance on specification

To further support developers in specifying drainage products for brownfield land, the British Plastics Federation (BPF) Pipes Group has published a new guidance document, titled Designing Drains and Sewers for Brownfield Sites. Created in collaboration with leading plastic pipe manufacturers including Wavin, the document features multiple diagrams and flow charts to help drainage designers and housing developers gain greater clarity on which products and materials they can and can’t use, depending on the results of their site surveys.

As well as guidance on identifying the risks that the site’s former use could pose to people living or working on the site, the document also offers advice on how to assess the risks of ingress to the water or wastewater systems. This is known as the Source–Pathway–Receptor model. In this model, ‘Source’ simply means the location of the contamination, and ‘Pathway’ is defined as the route taken by a contaminant to the ‘Receptor’, which is the pipework. The model stipulates that if any one of these elements is missing from a given scenario, then there is no risk of contamination entering the pipework.

Looking ahead

The latest guidance on specifying drainage for brownfield land demonstrates how important it is to share knowledge across the construction industry. Not only does this guidance give developers greater insight into the products available to them, and how they can be used, it also sets a trend that other organisations should look to follow to enhance the delivery of new homes across the UK.