Contamination can arise from previous uses, illegal dumping or migration from neighbouring sites.
Your council has a duty to ensure that the land does not pose a significant risk to human health or the wider environment and this is usually done through the planning process.
A phased approach is taken, and often only a phase 1 investigation is necessary. Phases 1 and 2 are usually pre-commencement conditions while phases 3 and 4 are usually pre-occupation conditions.
Phase 1 is a walkover of the site and a desktop risk assessment utilising available historical and factual information. This will highlight if a credible risk exists. Checks will also be done for radon, a naturally-occurring carcinogenic gas.
Phase 2 involves physical sampling and laboratory testing to quantify any identified risk and compare the results to nationally agreed trigger values to assess whether remediation is necessary. Phase 3 is to remediate any harmful contaminants to render them safe, and phase 4 is to produce evidence to show that any potentially harmful contaminants have been dealt with making the site safe for its intended use.
Land contamination presents itself in two main ways. The most common is soil contamination.
Some contamination is obvious. Look for anything that may have been dumped on site, bonfire sites, bare or discoloured patches. Check for healthy plant or weed growth and check around any tanks for spillages. Other contaminants cannot be seen but may reside in the soil from previous uses, things such as heavy metals and pesticides.
The other main contaminant is potentially toxic ground gasses, often produced by putrefiable material included in made-up ground, filling of ponds, or landfill operations. This is relatively expensive to quantify and it is often more cost-effective to incorporate remediation measures into the build instead.
The basis behind remediation is the source – pathway – receptor model. These range from home-grown potatoes taking in contaminants from the soil and then you eating them; through to off site ground gas sources passing through the ground and filtering up into your home.
Removing the contaminant (source) is often impractical or cost prohibitive for a small development. Keeping people (receptor) off the development is defeating the reason to develop, therefore, usually the best and most cost-efficient way of making the site safe is to break the link (pathway) between the contaminant and the users of the site. A good environmental consultancy will endeavour to help you move the project forward, suggest the most appropriate solutions that offer the best value for money and long-term peace of mind.