Phase 1 and Phase 2 are the two investigation stages in UK land contamination assessment. The difference is simple: Phase 1 is desk-based and establishes whether there might be a problem; Phase 2 goes into the ground to find out for certain. Here is how they fit together.
Phase 1: the desk study, in brief
A Phase 1 Preliminary Risk Assessment reviews the site's history, geology and surroundings, includes a site walkover, and builds a conceptual site model based on possible source-pathway-receptor linkages. If no credible linkages are found, the process can often stop there. (See our full guide to the Phase 1 PRA.)
What triggers a Phase 2
A Phase 2 intrusive investigation is recommended when the Phase 1 identifies potential pollutant linkages that need to be tested — for example, a history of industrial use, made ground of unknown origin, or a sensitive end use such as housing with gardens over a former works.
What a Phase 2 involves
- Intrusive sampling: trial pits, boreholes and window samples to recover soil, and sometimes groundwater and ground gas.
- Laboratory analysis: testing samples for contaminants relevant to the site's history, such as metals, hydrocarbons and asbestos.
- Quantitative risk assessment: comparing results against assessment criteria appropriate to the end use.
- Ground gas monitoring: where landfill, made ground or organic deposits are present.
Remediation and verification
If the Phase 2 confirms unacceptable risk, a remediation strategy is designed — which can range from cover systems and clean soil capping to gas protection measures or removal of hotspots — followed by a verification report confirming the work was done and the site is suitable for use.
How a thorough Phase 1 keeps Phase 2 proportionate
A carefully evidenced Phase 1 does not just decide whether a Phase 2 is needed — it shapes its scope. By pinning down exactly where potential linkages are and are not, it helps target sampling where it is justified, so the intrusive works stay proportionate to the actual risk rather than defaulting to a blanket investigation.
Read next: Do I need a contaminated land assessment? or see the Phase 1 desk study service.
FAQs
Do I always need a Phase 2?
No. Many sites are cleared at Phase 1. A Phase 2 is only recommended where the desk study identifies potential pollutant linkages that need to be tested in the ground.
How much does a Phase 2 cost compared with a Phase 1?
A Phase 2 is more involved because of fieldwork and laboratory costs, so it is typically several times the cost of a Phase 1 — which is why a sound Phase 1 that scopes it correctly is valuable.
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