The Role of Percolation Testing in UK Land Development

In the United Kingdom, sustainable land use is not just a matter of good practice—it’s a necessity driven by both environmental concerns and legal mandates. Central to this, is the percolation test, a procedure that determines the absorption rate of soil for the installation of septic tank drainage fields, also known as soakaways. Let’s explore the why and how of percolation testing, and its importance in the context of UK environmental regulations.

Understanding Percolation Testing

Percolation testing, often referred to as a ‘soakaway’, assesses how quickly water dissipates into the subsoil of a proposed drainage field. This test is crucial for any property not connected to mains drainage. The results determine if the ground conditions are suitable for a soakaway and influence the design of a septic system that aligns with UK environmental standards.

The Percolation Test Process

The UK’s Building Regulations Part H (Drainage and Waste Disposal), which stipulates guidelines for percolation tests, requires specific conditions to be met:

1. Site Selection and Preconditions:

• Choose a site representative of the area where the drainage field will be installed.

• Ensure the ground is free from standing water, and hasn’t been disturbed recently.

2. Conducting the Test:

• Dig a hole approximately 300mm in length to a depth 300mm below the proposed invert level of the drainage field.

• Fill the hole and monitor how long it takes for water to seep away from 75% full to 25% full.

•Repeat the test 3 times.

3. Interpreting Test Results:

• The ideal percolation rate (Vp) is between 12 and 100 seconds per millimeter.

• Results outside this range may indicate unsuitable soil conditions, necessitating alternative solutions.

Importance in Environmental Planning

Compliance with the Building Regulations ensures that each septic system is designed to minimize the risk of pollution. A well-conducted soakaway can prevent groundwater contamination—a serious concern, as pollutants can enter watercourses and affect the ecosystem and public health.

Regulations and Standards

The Environment Agency in England, Scottish Environment Protection Agency (SEPA), Natural Resources Wales, and the Department for Agriculture, Environment and Rural Affairs in Northern Ireland provide additional regulations and guidance, which must be integrated into percolation testing practices.

Challenges and Considerations

Soil type, seasonal weather patterns, and site accessibility all influence percolation testing. Heavy rain can skew results, as can drought. Tests are generally not conducted in extreme weather conditions to avoid skewed results.

Percolation Testing and Sustainable Development

Accurate testing leads to better-designed drainage fields, which complement the UK’s commitment to sustainable land use. Environmental consultants play a key role in this process, advising on best practices and ensuring compliance with all relevant environmental legislation.


Percolation testing is an indispensable part of environmental planning for land development in the UK. It ensures the longevity and safety of septic systems, protecting both the environment and public health. By adhering to these practices, developers and property owners can ensure they are contributing positively to the environment and staying within the bounds of the law.

Call to Action

For those planning land development in the UK, seeking professional guidance on percolation testing is a step toward sustainable and compliant land use. Contact an environmental consultant to ensure your land’s development is not just viable but environmentally responsible.