Soakaway Testing: A Developers Guide
Introduction
National Policy in England requires that all developments must consider how surface water is managed on-site and promote the use of SuDS(Sustainable urban Drainage Systems) where appropriate.
In order to know if SuDS are feasible for your development, you first need to know the infiltration rate. This information must be passed to a drainage engineer to inform the drainage design. Without it, you risk delay, redesign, or rejection at planning.
What Is a Soakaway Test and Why Does It Matter?
A soakaway test (also called a percolation or infiltration test) determines how quickly water drains into the ground. If the soil drains well enough, you can use a soakaway or other infiltration feature to manage surface water on-site to meet planning policy requirements.
The benefit if SuDS are feasible? You avoid costly drainage connections, reduce flood risk, and increase your chance of planning approval.
What Is BRE 365?
BRE Digest 365 is the go-to guidance in the UK for testing infiltration rates. It sets out how to carry out a soakaway test properly, and how to size infiltration systems based on the results. Planners, engineers and Building Control all recognise this method, so following it avoids delays and questions later on.
When Should You Carry Out a Soakaway Test?
As early as possible – ideally before finalising your drainage design or submitting a planning application. It helps:
- Confirm if infiltration is feasible
- Determine how big your soakaway needs to be
- Prevent redesigns or rejections
Doing it early saves money and time.
How a BRE 365 Soakaway Test Works (Without the Jargon)
Here’s how the process looks in practice:
1. Dig a Trial Pit
We excavate a square pit around generally 0.6m wide x 1.0m long and at least 1mdeep (or to proposed soakaway depth). It's done at the planned location of the soakaway to ensure the ground is representative of where water would be draining into following development.
2. Prepare and Fill the Pit
We clear any loose soil and fill the pit with clean water to simulate a storm. The idea is to see how quickly the water drains away into the soil.
3. Measure the Drop
We monitor how fast the water level drops over time. Yes, it’s like watching paint dry, but it’s crucial information to obtain for drainage design.
4. Repeat and Record
The test is done at least three times to get reliable results and to simulate saturated conditions. Calculations are then undertaken to determine the infiltration rate (how quickly the water dropped) based on the time taken for the waterlevel to drop between 75% and 25% of the depth of the water.
5. Report and Advise
We issue a clear summary of the results, including whether infiltration is likely to be viable and what to do next.
Common Mistakes to Avoid
- Not Testing the correct location for example not where the proposed soakaway is going to be on sites with variable geology
- Only testing one location on larger or sloping sites
- Skipping the test entirely and assuming infiltration is possible (or not!)
We make sure the test is done right, in the right conditions, with clear advice.
What Happens If the Test Fails?
If infiltration isn’t suitable, don’t panic. There are other options like attenuation tanks, or discharging to a sewer (with consent). But knowing early lets you plan and cost appropriately.
How Clear Environmental Can Help
We carry out BRE 365 soakaway tests quickly and cost-effectively across the UK.
What you get:
- Fully compliant testing and reporting.
- Fast turnaround for planning applications.
- Straightforward understandable advice.
When a Phase 1 Desk Study identifies potential environmental risks, the next step is a Phase 2 Site Investigation — also called an intrusive investigation. This critical stage gathers real-world data to confirm or rule out contamination, protecting your project from unforeseen costs, planning delays, or environmental liabilities.
In this guide, we break down:
- How Phase 2 builds on Phase 1.
- The different investigation techniques (and when to use each).
- Typical timescales.
- How laboratory testing refines the site’s risk profile.
- What to expect at the end of a Phase 2 investigation.
How Phase 2 Builds on Phase 1
While a Phase 1 is based on desk research and a site walkover, a Phase 2 collects physical evidence through soil, groundwater, and ground gas sampling.
In short:
Phase 1 = Identify Potential Risks.
Phase 2 = Confirm or Dismiss Risks with Hard Data.
The findings from Phase 2 enable:
- Quantitative Risk Assessments (QRA) based on actual contamination levels.
- Decisions about whether remediation is necessary.
- Planning condition discharge if no unacceptable risks are found.
Phase 2 Site Investigation Methods
Different methods are used depending on the site, the anticipated risks, and the required depth of investigation:
- Best For: Shallow contamination, made ground assessment, visual soil profiling, locating foundations.
- Typical Depths: Up to 4 metres.
- Equipment: Mechanical excavator or hand-dug.
- Best For: Shallow contamination, installation of ground gas and groundwater wells, restricted access sites, cost-effective sampling.
- Typical Depths: Generally 5–6 metres, but can extend up to 10 metres depending on ground conditions.
- Equipment: Window sampling rig (tracked or towed).
- Best For: Deeper soils, groundwater sampling, ground gas monitoring, and collecting geotechnical data.
- Typical Depths: Up to 30 metres or more.
- Equipment: Cable percussion drilling rig.
- Best For: Hard ground, bedrock investigations, and installation of deep groundwater wells.
- Typical Depths: Up to 100 metres or more.
- Equipment: Rotary drilling rig (open hole, cored, or augered).
Tip: On smaller development sites, a combination of trial pits and window sampling often provides excellent coverage at a cost-effective price.
Types of Laboratory Testing During Phase 2
After sampling, the materials collected are sent for laboratory analysis to determine contamination levels:
- Soil Testing:
- Heavy metals (e.g., lead, arsenic)
- Hydrocarbons (TPH, PAHs)
- Asbestos in soil
- Emerging contaminants (e.g., PFAS)
- Groundwater Testing:
- Soluble contaminants (e.g., hydrocarbons, BTEX, solvents)
- Metals in solution
- PFAS detection
- Ground Gas Monitoring:
- Methane, carbon dioxide, oxygen concentrations
- Flow rates (for CS classification)
The results are then compared against appropriate assessment criteria (e.g., GACs/SACs) to determine whether remediation is needed.
What Happens After Phase 2 Sampling?
1. Data Analysis and Quantitative Risk Assessment (QRA):
Risk to human health, controlled waters, or property assessed.
2. Conceptual Site Model Update:
Confirmed pollutant linkages mapped and risk-ranked.
3. Decision Point:
No significant risks: Reporting and planning condition discharge.
Significant risks: Recommend remediation (Phase 3).
Phase 1 vs Phase 2 - Quick Comparison Table
FAQs About Phase 2 Site Investigations
What happens if contamination is found in a Phase 2?
If contaminants exceed safe levels, a Remediation Strategy (Phase 3) will be needed to outline how risks will be managed.
Can a Phase 2 rule out the need for remediation?
Yes — many sites require no further action after a properly scoped Phase 2 investigation.
Is ground gas monitoring always required?
Not always. It depends on the site's history, geology, and desk study findings.
Conclusion: Why a Clear Phase 2 Strategy Matters
A well-designed Phase 2 Site Investigation provides confidence, clarity, and control.
It ensures you're fully informed about site risks, avoids unnecessary remediation, and moves your project efficiently through planning.
At Clear Environmental, we tailor Phase 2 investigations to your site — no over-scoping, no hidden costs, just clear advice.
What is a Phase 1 Desk Study (Preliminary Risk Assessment)?
Whether you're planning to develop land, submit a planning application, or purchase a brownfield site, understanding environmental risks early is essential.
A Phase 1 Desk Study — also called a Preliminary Risk Assessment — is the first critical step in managing those risks efficiently, helping avoid costly surprises later in your project.
This guide explains exactly what a Phase 1 involves, why it’s required, and what you can expect from the process.
What is a Phase 1 Desk Study?
A Phase 1 Desk Study is a preliminary environmental assessment that evaluates the potential for land contamination based on historical and current land uses.
It is called a “desk study” because it mainly relies on reviewing existing records and data sources, alongside a site visit.
It does not involve any intrusive ground investigation — that's reserved for Phase 2 if risks are identified.
In simple terms:
A Phase 1 identifies if there’s a potential problem — before you commit to site purchase, design, or construction.
Why is a Phase 1 Desk Study Needed?
A Phase 1 is often required to:
- Support planning applications (especially brownfield or previously developed sites).
- Satisfy lender due diligence for property transactions.
- Manage liability and avoid unexpected abnormal costs.
- Confirm if further investigations (Phase 2) are needed.
Without a Phase 1, local authorities, insurers, and funders may refuse to progress development or financing.
Key Components of a Phase 1 Desk Study
A thorough Phase 1 typically includes:
What Does a Phase 1 Report Contain?
A typical Phase 1 Desk Study Report will include:
- Executive Summary (key findings and recommendations).
- Site location and description.
- Historical land use review (maps and aerial photography).
- Environmental setting (geology, hydrology, groundwater).
- Regulatory database review (permits, enforcement notices, pollution incidents).
- Walkover survey findings (including annotated site photos).
- Preliminary Conceptual Site Model (CSM).
- Risk assessment and clear conclusions.
- Next steps, if further investigation is needed.
At Clear Environmental, our Phase 1 reports are concise, commercially-focused, and designed to satisfy planning authorities and lenders without unnecessary complexity.
How Long Does a Phase 1 Desk Study Take?
Most Phase 1 assessments can be completed within 10 Days.
We also offer fast-track services if you’re working to tight planning or transaction deadlines.
Phase 1 Desk Study vs. Environmental Search: What's the Difference?
Key point: An Environmental Search is not a substitute for a Phase 1 — it’s simply a basic desktop screening.
FAQs About Phase 1 Desk Studies
Q1: When should I commission a Phase 1?
Ideally before site acquisition or at the earliest planning stage, so risks and costs are identified early.
Q2: Will a Phase 1 always recommend a Phase 2?
No — many sites with clean histories and no risk linkages can be signed off at Phase 1.
Q3: Who needs a Phase 1 Desk Study?
Developers, property investors, planners, architects, solicitors, and lenders commonly require Phase 1 studies.
Q4: Will the council accept my Phase 1 report for planning?
Yes — provided it follows UK guidance (such as EA Land Contamination Risk Management (LCRM)) and is prepared by qualified specialists.
Q5: What happens if my Phase 1 shows contamination risks?
We’ll outline the recommended Phase 2 site investigation scope and cost early, so you remain in control.
Why Clear Environmental for Your Phase 1?
A Phase 1 Desk Study isn’t just a box-ticking exercise — it’s your first opportunity to manage risks, reduce abnormal development costs, and protect your investment.
At Clear Environmental, we combine technical expertise with commercial insight to deliver Phase 1 Reports that meet planning, legal, and financial requirements — quickly and clearly.
.jpg)
