Why is infiltration testing required ?

The incorporation of sustainable drainage systems (SuDS) into drainage designs is an important criterion to meet the requirements of Local Planning Authorities (LPA), Lead Local Flood Authorities (LLFA), and Drainage Authorities. The National Planning Policy Framework (NPPF) indicates that the primary means of surface water disposal from a site development should be via infiltration. Therefore, it is essential that ground conditions are assessed at every site to ascertain the viability of applying infiltration techniques for the development.

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It is a common requirement of LPAs and LLFAs to provide evidence of infiltration testing, often as a pre-commencement planning condition, so it is essential that tests are undertaken at an early stage in the planning process.

What is involved ?

Trial pits will be required at each test location. The trial pits are generally 1.5m long, 450mm wide and 3m deep. 

Each trial pit is filled with water to a depth 1m below ground level. The trial pit is then allowed to empty and measurements are taken at regular intervals. The tests should be undertaken three times at each pit and the worst result of the three assessments should be used for design purposes.

If all tests can be undertaken on the same day, this is deemed to be in accordance with BRE Digest 365. If all tests cannot be undertaken on the same day, they must be undertaken on three consecutive days in order to be compliant.

How we can assist

We are able to attend site and monitor trial pits, take the required measurement and produce an infiltration report, suitable to submit to LPAs or LLFAs. For most of the tests that we undertake, the client provides a digger, operator and water supply, however where this is not possible, we can source the plant, water supply and provide a digger operator.

Our Fees

Our fees for assisting with infiltration testing are set out below:-

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1 day of an engineer attending site to supervise an infiltration test: £625 + VAT

Half day rates for 1 Engineer:£310 + VAT

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2 days site attendance:£1150 + VAT

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3 days site attendance:£1575 + VAT

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Preparation of an infiltration report

£625 + VAT

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If the provision of a digger, digger operator and water supply is required, a separate fee would be required based on current plant hire costs.

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