Understanding groundwater protection

In redeveloping urban areas, there is a need to provide adequate foundations for new buildings and structures, while at the same time preserving, as far as possible, sub-surface archaeological remains and to preserve groundwater resources.

Groundwater Protection

Piling and penetrative ground improvement methods are commonly used on “brownfield sites”, where previous development has resulted in a thickness of loose or compressible soils and “made” ground, which may be contaminated. These methods typically penetrate to greater depths than standard foundations. Consequently, they are likely to increase the risk of contamination being transported by creating new pathways.

To avoid unacceptable risks to groundwater in accordance with NPPF policy 174(e), the Environment Agency recommends that piling on contaminated sites underlain by aquifers is avoided where possible and that non-invasive methods, such as rafts, should be used instead. Where there is no alternative to piling, a method should be selected that minimises the risks of groundwater pollution or gas migration.

Where deep piling and penetrative ground improvement methods are proposed in developments located in SPZ 1, there is also a risk of turbidity to the potable water supply.

Therefore, for sites in vulnerable locations, mitigation measures and/or environmental monitoring will need required. A piling risk assessment and appropriate mitigation measures should be submitted with the planning applications with consideration of the following guidance:

Piling into contaminated sites¹ (National Archives)

This should include:

• Stage 1/ Preliminary Risk Assessment for Land Quality where the Conceptual Site model also includes the number, maximum depth, and diameter of the proposed piles.
• Pollution scenarios that may occur using these techniques
• Potential mitigation measures, e.g., Contingency and action plans that may be appropriate
• Proposals for any monitoring
• Particular problems and uncertainties associated with the methods chosen.

Piling in layered ground: risks to archaeology

This report will help assess the risks to groundwater and archaeological records from piling in contaminated and layered ground. 

Research and analysis: Piling in layered ground²

NB. Water Companies may have relevant guidance and separate requirements in each of their areas. E.g. Thames Water: Guidance on piling, heavy loads, excavations, tunnelling and dewatering³.

An Environmental Permit may be required in certain circumstances if there is potential discharge of hazardous substances to groundwater.

1. http://webarchive.nationalarchives.gov.uk/20140328084622/http://cdn.environment-agency.gov.uk/scho0202bisw-e-e.pdf
2. https://www.gov.uk/government/publications/piling-in-layered-ground-risks-to-groundwater-and-archaeology
3. https://www.thameswater.co.uk/media-library/home/developers/larger-scale-developments/planning/working-near-our-pipes/guidance-on-piling-heavy-loads-excavations-tunnelling-and-dewatering.pdf