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At Cotterill Environmental, we offer a range of testing services to monitor the ongoing performance of your sewage system as well as identify issues. Our tests can also be used to demonstrate the effluent quality of your system.

Porosity & percolation tests

To determine how suitable the ground conditions are for the installation of a soakaway (drainage field) for properties that unable to connect to a watercourse, we will undertake a percolation test (also known as a porosity test). The test allows us to understand whether the soil conditions will allow water to freely drain or if the water will struggle to permeate because the soil is heavy and clay-based. All septic tanks except for some sewage treatment plant installations require a soakaway so this test is vital to establish suitability.

Sampling & analysis


To understand how well your system is performing, we can undertake selective samples to compare the settled sewage with the final effluent. 

It is vital to ensure your system is producing the required standard of effluent as specified by the Environment Agency. Failure to comply with these standards could result in significant fines and costly legal fees.

Flow measurement analysis


If a sewage system continues to underperform, in spite of regular servicing, we recommend undertaking a flow measurement analysis. By installing temporary equipment to your system, we can measure the total daily flows through it over a set period of time. The results will allow us to recommend the best solution going forward. For example, one cause of issues is an overloaded system. This can happen when the original use of the system is extended beyond what was initially anticipated.

​Contact us today to speak to our sewage specialists!

Why use us?


Top rated customer service

We’ve built up a reputation for being friendly, professional and 100% reliable. You can count on us for excellent service.


We know our stuff

 Our 30 year proven track record of installing wastewater solutions speaks for itself. We're specialists when it comes to the installation, maintenance and repair of sewage systems



Integrity and honesty are core to what we do. We're a family-owned business and are known for being trustworthy and hard working.

            Contact us today for advice 

            0121 461 4861 

Useful information on porosity and percolation tests


Here are some frequently asked questions:

What is a percolation test?

When deciding whether to install a soakaway for your septic tanksewage treatment or soakaway crates system, a percolation test (also known as a porosity test) is required. It is the final test of three mandatory tests and is used to determine if a new or replacement soakaway can be installed. Other tests that are required include a Groundwater Source Protection Zone search and a Trial Site Assessment Hole to assess the water table in your area fully. We can undertake all of these tests for you. The percolation test measures how quickly water drains away from the soil. Different soil types will produce a variety of results. For example, fine sandy soil will drain water away significantly faster than thick clay soil. 

The testing process involves digging a pit to specific dimensions, filling it with water, and then timing how long the water takes to soak into the soil.

What do the results of the percolation test reveal?

The results of the percolation test will determine how large your soakaway will need to be and if you can even install one. The results can also be used to determine the required size of a drainage field.

What areas do we cover?

We cover the whole of the midlands and can also work further afield depending on the drainage project. Areas in the midlands that we cover include: 

Birmingham (West Midlands), Coventry (West Midlands), Hereford (Herefordshire), Lichfield (Staffordshire), Stoke-on-Trent Staffordshire), Wolverhampton (West Midlands), Worcester (Worcestershire), Shrewsbury (Shropshire), Warwick (Warwickshire), Derby (Derbyshire), Leicester(Leicestershire), Oakham (Rutland), Lincoln (Lincolnshire), Nottingham (Nottinghamshire), Buxton(Derbyshire), Glossop (Derbyshire), Cleethorpes (Lincolnshire), Northampton (Northamptonshire) 

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