Our brown and pleasant land

Will Allen of ACO explains why, given the in-depth specification needs that are associated with brownfield remediation, sound awareness of the surface water management criteria that must be met is essential to an effective and successful planning application.

Green belt land has long been the much-prized goal for developers, given its low likelihood of requiring pre-development remedial work, coupled with the ‘up-sell’ advantages of a desirable location. However, in line with the Government’s 2017 White Paper on the housing market, green belt boundaries will now only be amended in exceptional circumstances, once local authorities have examined all other reasonable options for meeting identified housing targets. In short, green belt land will be much more difficult to build on.

However, the same report details Government plans to maximise the contribution of brownfield and surplus public land, to provide an accessible solution to the land availability crisis. While it does represent a viable solution, brownfield land still presents developers with a number of issues, particularly surrounding the cost of remediation.

Fail to plan, plan to fail

Key to the successful redevelopment of any brownfield site is managing the risk of pollution to the surrounding land, both during and post-construction. Water resources are of particular concern, as if sufficient pollution or contamination were to occur, not only would it add significant cost to the remediation process, but it could threaten the suitability of land for redevelopment.

Under the National Planning Policy Framework (NPPF) guidelines, developers must show that all submissions fulfil the planning requirements for the specific intended end-use. This includes the management of surface water run-off during the construction period, to prevent the contamination of surface and groundwater resources, as well as the post-construction removal or isolation of potential sources of contamination to water bodies.

This notion is reinforced by the Environment Agency’s Guiding Principles for Land Contamination 1 (GPLC1), which outline the requirement that successful plans must be able to evidence a disruption between the potential source of contamination (be it construction debris, vehicle brake dust or road salt chlorides), the pathway, surface water and the receptor (either groundwater or a water resource).

From a specification perspective, there is a highly effective way to prevent a potential contaminant entering into a natural watercourse during, and after the development of a brownfield site: that is, using drainage channels with an integrated seal.

Delivering water tightness

One of the biggest risks of secondary (manually) sealed channels is that the integrity of the seal is not assured. A compromised seal will affect the channel’s water tightness, and thus its ability to meet the necessary planning requirements.

According to BS EN 1433/DIN 19580, drainage channels must remain waterproof for 30 minutes ± 30 seconds. However, manual sealing relies on a number of variables, including the contractor, the quality of the sealant and the operating conditions, to deliver an effective seal. Just because a secondary sealed channel may be able to conform to BS EN 1433 on paper, does not necessarily guarantee it will perform in practice if it has not been installed properly.

Junctions between channels, as well as sump pumps and outlets, represent a major risk of egress into the substrate. Poor sealing – or worse still, the use of no sealant whatsoever – could significantly hamper the chance of a developer satisfying the necessary planning criteria. Using a system with an integrated seal dramatically reduces this risk.

Products in practice

There are a number of applications where specifying a fully-sealed system can contribute to an effective remediation of a brownfield site, both during and post-construction.

Given that effective surface water management must be considered from the start of the planning process, specifying a system with an integrated seal for use as a temporary fixture during the construction phase can provide developers with instant control over surface water from the outset of the remediation process.

An integrated seal promotes quick and effective installation times as contractors do not have to manually seal each junction with a secondary seal. This not only helps meet the BS EN 1433 water tightness requirements, but allows further construction work to be undertaken right away, safe in the knowledge it is not likely to pose a contamination risk to the land in question.

Any surface water run-off from the construction site can then be contained within the sealed system, before being collected at predetermined points, and cleaned using specialist rainwater and surface water run-off filtration systems. Crucially, the system can then be removed if necessary, or incorporated into wider post-construction drainage infrastructure.

When repurposing brownfield land, a key post-construction challenge for developers is to demonstrate the long-standing efficacy of the water management system, so that the substrate remains free from any potential contamination.

Heavily-trafficked areas are of particular concern. Surface water run-off in areas such as car parks and high streets can be subjected to a number of potential contaminants, including heavy metals, tyre wear, brake dust, soots and sediments, as well as de-icing products during winter months. It is crucial that surface water which has the potential to come into contact with any contaminants is fully contained within the drainage system as, for example, chlorides present in road salt can lead to the potential weakening of concrete foundations if they are able to egress into the substrate.

Conclusions

Given the land availability crisis facing the UK construction industry, coupled with Government changes to planning documents, developers will soon find themselves in a position where repurposing brownfield land is the only viable option.

Surface water is major contamination risk for the surrounding substrate in brownfield sites, and given the volume of testing and risk assessments that must be undertaken, managing it effectively could determine whether or not a planning submission is successful.

Specification can play a pivotal role in satisfying a number of the water management planning criteria. By incorporating a drainage system with an integrated seal into brownfield specification, developers can take full control of surface water management, and overcome one of the biggest planning permission challenges out there.

Will Allen is marketing manager (Civils + Infrastructure) at ACO Water Management