Land contamination phase 1 or phase 2: which you need
A phase 1 desk study decides whether intrusive investigation is needed at all. The trigger is a plausible pollutant linkage, not site history on its own.
A phase 1 contamination report is a desk study and walkover that builds a conceptual site model. A phase 2 is intrusive work, with trial pits or boreholes, samples and laboratory analysis, carried out only where that model identifies a plausible pollutant linkage. You do not choose between them. Phase 1 comes first on every site with a history, and it decides whether phase 2 happens at all. Anyone quoting for both before the desk study is complete is pricing work that may not be needed.
What the desk study produces
A phase 1 assessment to BS 10175 pulls together historical Ordnance Survey mapping, geological and hydrogeological data, regulatory records including landfill and permitted process registers, records of previous uses, and a site walkover. The output that matters is the conceptual site model: a written and usually diagrammatic account of possible contaminant sources, the pathways by which they could reach people or water, and the receptors at the end of those pathways.
The Environment Agency's land contamination risk management guidance frames this as the preliminary risk assessment, the first of a sequence that runs through options appraisal to remediation and verification.
Three findings are possible. No plausible linkage, in which case the report says so and recommends no further work. A plausible linkage, which triggers intrusive investigation. Or insufficient information, which usually means an unresolved question about fill material or a demolished structure, and the honest answer is a targeted phase 2 rather than a guess.
What actually triggers the dig
The trigger is the linkage, not the history alone. A site that was a Victorian orchard has a history and no linkage. A site with a filled pond, made ground of unknown origin and a proposed garden for a new house has all three components: a source, a pathway through soil contact and homegrown produce, and a receptor in the form of future residents.
Residential end use raises the stakes because gardens, children and homegrown vegetables widen the pathway list. A commercial car park on the same ground may need nothing.
| Question | Phase 1 | Phase 2 |
|---|---|---|
| What it is | Desk study, records review and walkover | Intrusive sampling and laboratory analysis |
| Main output | Conceptual site model and risk assessment | Measured concentrations and refined model |
| Triggered by | Site history, previous use, made ground | A plausible pollutant linkage from phase 1 |
| Typical programme | Days to a couple of weeks | Weeks, including laboratory turnaround |
| Site access needed | Walkover only | Rig or excavator access, services clearance |
The distinction is explored further in what triggers the dig on a contamination phase 1 or phase 2.
Sampling strategy and what the laboratory is asked for
A phase 2 is only as good as its sampling strategy, and the strategy comes from the conceptual site model rather than from a standard grid. If the model says the risk is a former fuel tank in the north east corner, the exploratory holes go there. If the model says the whole site is made ground of variable depth, a grid with a rationale for spacing makes sense.
The analytical suite follows the same logic. A standard suite covering metals, polycyclic aromatic hydrocarbons, total petroleum hydrocarbons and asbestos screening answers most residential questions. Ground gas monitoring is a separate exercise with its own duration, usually several visits across a range of atmospheric pressures, and it is the item most often forgotten in a programme.
Ask the consultant to state which UKAS accredited laboratory will be used and which determinands are covered by that accreditation.
The conceptual site model at each stage
The model is not a single document produced once. It starts in phase 1 as a set of hypotheses and it is revised after every piece of new information: after the intrusive work, after gas monitoring, after remediation.
A good report shows the model changing. A weak one repeats the phase 1 model unchanged in the phase 2 report, which tells the local planning authority's contaminated land officer that nobody thought about the results.
Cost and programme, realistically
Neither report has a standard price, because both scale with the site. A phase 1 is driven by the amount of history and the number of records to review. A phase 2 is driven by the number of exploratory holes, the plant needed to reach them, the laboratory suite and whether ground gas monitoring is required.
The programme risk is asymmetric. A desk study can be turned around quickly. Intrusive work needs a rig booking, underground services clearance, sometimes a road closure, and laboratory turnaround of one to two weeks after that. Gas monitoring adds weeks more. On a self-build with a tight mortgage drawdown, that sequence is the reason contamination work should start with the land purchase rather than after permission.
Conditions that build the phases in
Most permissions on land with a contamination history carry a phased condition, and the wording follows a familiar shape: submit a site investigation and risk assessment before commencement, submit a remediation scheme for approval, carry it out, submit a verification report before occupation, and report any unexpected contamination found during works.
Pre-commencement conditions of this kind cannot be imposed without the applicant's written agreement to the terms, so read the draft wording carefully before it is finalised.
The practical trap is the verification report. Discharging that part of the condition requires photographic records, validation sampling of imported soils and delivery tickets for clean cover, all collected during construction. Nobody can recreate them afterwards. Build the record keeping into the site diary from day one.
Remediation and verification
Where remediation is needed, options appraisal comes before design. Excavation and disposal is the simplest route and the most expensive, particularly where the material is classified as hazardous waste. A clean cover system in gardens, a gas membrane under the slab, or in-situ treatment may each be cheaper and are assessed against the same risk criteria.
Verification closes the loop by demonstrating that what was designed was built. Membrane installation photographs, integrity testing records and imported soil certificates form the bulk of it.
An illustrative example: a plot behind a former garage, bought at auction by a self-builder. The phase 1 identifies a fuel tank on a 1962 map and made ground across the rear third. Phase 2 finds hydrocarbons in two of six trial pits at depth. The remediation is a 600 mm clean cover in the garden with a marker layer, and verification is a set of photographs, a soil certificate and a short report. Total programme, from instructing the desk study to discharging the condition, runs across several months. Starting it after permission would have delayed the build by a season.
Who can prepare each report
Both phases must be prepared by suitably qualified and experienced persons. Councils increasingly ask for named competence on the front page, and a contaminated land officer will reject a report where the author cannot demonstrate relevant experience. That expectation is set out in more detail in suitably qualified persons for land contamination reports.
PlanScope can draft the structure and the site history narrative for a contamination submission, and the draft is a starting point for that qualified professional rather than a replacement for the investigation. For specialist technical reports, qualified professional input may be required.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
Browse the report types on PlanScope to see how the contamination documents sit alongside the rest of a small site application pack.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Can I skip phase 1 and go straight to intrusive investigation?
You can, but it wastes money. Without a conceptual site model the sampling strategy has no rationale, so holes go in the wrong places and the analytical suite is either too narrow or too broad. Contaminated land officers expect the phase 2 report to explain how the phase 1 findings determined where each exploratory hole went.
Does every site with a history need a phase 2?
No. Phase 2 follows only where the desk study identifies a plausible pollutant linkage between a source, a pathway and a receptor. Many sites with industrial history nearby have no credible pathway to the proposed end use. The phase 1 report should say plainly that no further work is required where that is the conclusion.
How long does ground gas monitoring take?
It normally needs several monitoring visits spread across a range of atmospheric pressures, because falling pressure draws gas from the ground. That usually means a period of weeks rather than a single visit. It is the item most often left out of programmes, and it commonly sits on the critical path for discharging a pre-commencement condition.
Who is qualified to write these reports?
Both phases must be prepared by suitably qualified and experienced persons, and councils increasingly ask for the author's competence to be stated. Relevant experience in contaminated land risk assessment matters more than a general engineering qualification, and the laboratory used should hold UKAS accreditation for the determinands being tested.
What is a verification report and why does it matter?
It demonstrates that the approved remediation was actually carried out: membrane installation photographs, integrity test records, validation sampling of imported soils and delivery tickets. It is usually required before occupation. The records cannot be recreated after the event, so the site team has to collect them while the work is happening.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.