Phase 2 contamination report: sampling and risk sections
A Phase 2 report tests the pollutant linkages the desk study only suspected. Here is what each section has to show before a contaminated land condition can be discharged.
A Phase 2 contamination report is the intrusive investigation that tests the pollutant linkages your Phase 1 desk study could only suspect. It puts boreholes, trial pits and monitoring wells into the ground, sends soil, water and gas samples to a laboratory, and then compares the results against assessment criteria to say whether a risk to people, controlled waters, buildings or plants is real. On a residential-led major, it is usually the report that decides whether the contaminated land condition can be discharged on programme or becomes a six month delay.
What Phase 2 answers that Phase 1 could not
Phase 1 builds a conceptual site model from historical maps, regulatory records, a site walkover and an environmental database search. It identifies potential sources, pathways and receptors. What it cannot do is confirm that a source exists, how concentrated it is, or whether the pathway is complete.
Phase 2 tests that model. Each hypothesis in the conceptual site model should map to at least one exploratory hole, one sample suite or one round of monitoring. Where the report cannot show that link, the local authority's contaminated land officer will say the investigation was not targeted, and they will be right.
Investigation follows BS 10175 for potentially contaminated sites and BS 5930 for site investigation practice generally. The NPPF places responsibility for securing a safe development on the developer or landowner, and the standard planning condition reflects that, so a weak Phase 2 usually results in more work rather than a discharged condition.
Designing the sampling strategy from the conceptual site model
Sampling density is a judgement, not a formula. On a former works with known process areas you target the tanks, the pits, the fuel lines and the made ground. On a large open site with diffuse fill you use a grid, often a herringbone pattern, to give reasonable coverage without pretending to certainty.
The report needs to explain the choice. A defensible strategy section states the rationale, the number and type of exploratory holes, the depths reached, the rig or method used, and where the strategy departed from the plan because of obstructions or access.
Watch three practical points that cause resubmissions.
- Sampling depth must reach beneath the proposed formation level, not stop at 1 m because that was convenient.
- Garden and soft landscaping areas need coverage, because those are where residential exposure assumptions bite hardest.
- Any groundwater strike should be recorded with the date, the depth and whether it was struck or rested, since that drives the controlled waters assessment.
Laboratory schedules and generic assessment criteria
The laboratory schedule should follow the contaminants of concern named in the conceptual site model, not a generic catalogue chosen by habit. A metals suite, speciated total petroleum hydrocarbons, polycyclic aromatic hydrocarbons, asbestos screening and pH cover many former industrial sites, with volatile organics added where solvents or fuels are suspected.
Results are then screened against generic assessment criteria. The report must state which criteria it used, the land use scenario they assume, the soil organic matter content applied and the source of the values. Residential with plant uptake, residential without plant uptake and commercial scenarios give very different screening values for the same substance, and using the wrong land use is the most common error in a Phase 2 that gets returned.
Where a substance exceeds its screening value, that is not a finding of contamination. It is a trigger for further work, either refined assessment or remediation. Say so plainly in the text, because the phrase "exceeds the screening criterion" is read by non-specialists as a failure.
Ground gas monitoring rounds and characteristic situations
Ground gas is the section most often left incomplete when a report is rushed to meet a planning deadline. Monitoring wells need several visits spread over time, taken during falling atmospheric pressure where possible, because that is when gas emissions from made ground and landfill peak.
CIRIA C665 sets the widely used framework, and BS 8485 covers the design of gas protection measures for buildings. The report should present, for each visit, the atmospheric pressure, the gas concentrations, the flow rate and the calculated gas screening value, then assign a characteristic situation that the building designer can work to.
| Monitoring input | What the report must show | Why it matters |
|---|---|---|
| Number of visits | Dates and spacing across the monitoring period | A single visit cannot characterise a site |
| Atmospheric pressure | Recorded at each visit, with trend | Low pressure drives worst case emissions |
| Flow rate | Measured with an appropriate meter | Gas screening value depends on flow, not concentration alone |
| Well construction | Response zone depth and seal detail | Poor construction gives meaningless numbers |
If your programme cannot accommodate the monitoring rounds before determination, agree a condition wording with the officer that allows monitoring to continue post-decision. Trying to argue a site into a lower characteristic situation on thin data rarely survives review.
Detailed quantitative risk assessment and when it is needed
A detailed quantitative risk assessment refines the generic screening by replacing conservative default assumptions with site specific ones, such as measured soil organic matter, actual building form or realistic exposure frequency. It is worth doing where a marginal exceedance would otherwise force expensive remediation across a large area.
It is not a way of assuming a problem away. The assessment must be transparent about every parameter changed from the default, and it needs to be run by someone who can defend the toxicological basis. Regulators look hard at these, and the Environment Agency takes a close interest wherever controlled waters are a receptor.
Illustrative example: a 3 ha former haulage yard shows lead marginally above the residential screening value in eight of forty samples, all within made ground that will be excavated for the road layout anyway. Refining the assessment with measured organic matter and confirming that the affected material sits under adopted highway removes the need for a site wide cover system. The figures here are illustrative.
Remediation strategy and verification plan sections
Where risk is confirmed, the report moves from assessment to design. The remediation strategy sets objectives for each pollutant linkage, compares options, selects an approach and defines the criteria that will demonstrate success. Cover systems, hotspot removal, in situ treatment and gas protection all need different verification evidence.
The verification plan is written before the works, not after. It says what will be recorded, how many samples will be taken from imported soils, who will sign off each stage and what the verification report will contain. Councils increasingly attach a condition requiring the verification report before occupation, so a vague plan turns into a delay at exactly the wrong moment.
Sequencing matters for the wider evidence base too. Excavation volumes feed the Construction Management Plan and the waste classification feeds the Site Waste Management Plan. Where dewatering or discharge is proposed, an environmental permit may be needed separately from planning.
Why a suitably qualified author is not optional
Land contamination reporting is one of the report types where a competent professional is legally and practically required. The NPPF places the responsibility on the developer, local authorities expect investigation and assessment carried out in accordance with BS 10175 by suitably qualified and experienced persons, and Part IIA of the Environmental Protection Act 1990 sits behind the whole regime.
PlanScope can draft the narrative structure of a contaminated land report and flag where site data is missing with a "TO BE CONFIRMED" marker, and the contaminated land assessment page sets out what the report covers. The interpretation, the criteria selection and the sign off belong to your geoenvironmental consultant. For specialist technical reports, qualified professional input may be required.
If you are scoping the wider technical pack for a major site, our note on what goes in a Flood Risk Assessment and what goes in a Drainage Strategy applies the same discipline to the water evidence, and the full report index shows the rest.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is the difference between a Phase 1 and a Phase 2 contamination report?
Phase 1 is a desk study and walkover that builds a conceptual site model of possible sources, pathways and receptors. Phase 2 is the intrusive stage that tests that model with boreholes, trial pits, laboratory analysis and gas monitoring. Phase 2 confirms whether a suspected pollutant linkage exists and how significant it is.
How many ground gas monitoring visits does a council expect?
Enough visits, spread over a period and including low atmospheric pressure conditions, to characterise the site with confidence. A single round is rarely accepted. CIRIA C665 is the framework most consultants and regulators work to, and the report should present pressure, concentration and flow rate for every visit alongside the resulting gas screening value.
What are generic assessment criteria?
They are published screening values for contaminants in soil, set for a defined land use such as residential with plant uptake or commercial. Results below the value indicate the risk is unlikely to be significant. Exceeding a value is a trigger for refined assessment or remediation rather than proof of harm, and the report must state which criteria and land use it applied.
Can a Phase 2 report be prepared without a specialist?
No. Local planning authorities expect investigation and reporting carried out in accordance with BS 10175 by suitably qualified and experienced persons, and the NPPF places responsibility for a safe development on the developer. Drafting tools can structure the narrative and flag missing data, but the sampling design, interpretation and sign off must come from a geoenvironmental specialist.
When is a detailed quantitative risk assessment worth doing?
When a marginal exceedance against generic criteria would otherwise force costly remediation over a large area, and site specific parameters such as measured soil organic matter would change the answer. It must document every assumption altered from the default. Regulators scrutinise these closely, particularly where controlled waters are the receptor.
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.