01743 298100
enquiries@geosmartinfo.co.uk
GeoSmart Information
  • Home
  • Reports
    • Contaminated Land Reports
    • Flood Risk Assessments
    • Sustainable Drainage Reports
    • Detailed Drainage Design
  • Data & Services
    • Groundwater Flood Risk Map
    • SuDS Infiltration Map
    • BGS Geology Datasets
    • User Guides
    • GWFlood
    • GWSewerFlood
    • Flood Risk Portfolio
  • Risk
    • FloodSmart Analytics
    • Case Studies
    • News
  • Knowledge Hub
    • Contaminated Land
    • Flood Risk Assessment
    • Sustainable Drainage Systems
    • Groundwater Flood Risk
    • CPD
    • Videos
    • News
    • Events
    • Blog
    • Library
    • Case Studies
    • Latest GeoSmart e-Newsletters
  • About
    • Our Customers
    • Our Team
    • Our Partnerships
    • Testimonials
    • Careers
    • Our Responsibility
    • A Sustainable Future
    • FAQs
  • Contact

What is Infiltration Testing?

Posted on January 13th 2020 in Blog, Property, SuDS

In line with the drainage hierarchy, Sustainable Urban Drainage Systems (SuDS) should first consider the discharge of surface water runoff from impermeable areas to ground. This is also known as infiltration testing or percolation to ground. GeoSmart’s SuDSmart Plus report is a desktop based assessment of the Site conditions, which can provide a preliminary opinion on whether infiltration to ground is likely to be feasible at the Site.

Many developers and architects include a soakaway as part of the surface water drainage system, however, if infiltration to ground is recommended in the GeoSmart SuDSmart Plus report, it is recommended to undertake infiltration testing. This needs to be done before plans are finalised as the results could significantly impact the size and/or design of the drainage system. If infiltration to ground is not considered feasible within the SuDSmart Plus report, then infiltration testing is unlikely to be requested by the council; unless they wish for it to be proved infiltration is not feasible on Site.

The calculated soil infiltration rate is used to determine the feasibility of soakaway drainage, the design storage volume and the number of infiltration SuDS features required.

There are many types of soils across the country which absorb (infiltrate) water at different rates depending on their permeability and porosity. The speed at which water enters the soil is known as an infiltration rate and a test can be done to obtain this rate.

Infiltration testing should be undertaken in the area where focused infiltration features such as soakaways are proposed.

It is important to remember that other seasonal factors such as groundwater levels and soil moisture content may affect infiltration testing results. Infiltration testing should be assumed under a worst case basis.

Most planning conditions recommend that infiltration testing should be undertaken in accordance with BRE Digest 365. There are several key stages when undertaking an infiltration test:

  • A soakage trial pit to the same depth as the anticipated SuDS feature.
  • The soakage trial pit should be 1 m to 3 m long and 0.3 m to 1 m wide. It should have vertical sides trimmed square and, if necessary, for stability, should be filled with granular material. When granular fill is used, a full-height, perforated, vertical observation tube should be positioned in the soakage trial pit so that water levels can be monitored with a dip tape.
  • It should be possible to construct a suitably-dimensioned pit with a backhoe loader or mini-excavator. For safety reasons do not enter the soakage trial pit.
  • A lot of water will be used to determine the soil infiltration rate so a water bowser may be needed. The inflow should be rapid so that the soakage trial pit can be filled to its maximum effective storage depth in a short time. Take care that the inflow does not cause the walls of the soakage trial pit to collapse.
  • Fill the soakage trial pit and allow it to drain three times to near empty. Each time record the water level and time from filling, at intervals sufficiently close to clearly define water level versus time. The filling of the soakage trial pit should be on the same or consecutive days.
  • Calculate the soil infiltration rate from the time taken for the water level to fall from 75% to 25% effective storage depth in the soakage trial pit.

An example of a good infiltration rate, which would sufficiently discharge water to ground and where focused infiltration features would be suitable would be x 10 -4 or -5.

A poor infiltration rate would be x 10 -6. This may still support infiltration to ground via focused infiltration, if this was the only discharge method feasible, but would need to be larger in size to accommodate for a slower emptying time.

An example of an infiltration rate where discharge to ground would not be feasible would be x 10 -7. In this case, other discharge options with the drainage hierarchy would have to be explored.

If you wish to discuss infiltration testing or other drainage related matters on your Site, please get in contact with us. Reach us by calling 01743 581 415, or send an email to enquiries@geosmartinfo.co.uk

Posted by Lily

Tags: drainage, infiltration testing, SuDS

Share this Post
« Previous Post
Next Post »

Contact Us

  • Please choose the product(s) you would like further information on.
  • If possible please give as much information about your site / property as you can and attach a site plan if available. This will enable us to provide you with the best assistance.
  • (If available)
  • Please upload your file in PDF format. (Max 4MB)
    Drop files here or
    Accepted file types: pdf, Max. file size: 4 MB.
    • Hidden
    • Hidden

    See what our customers have to say...

    "During the conveyancing process for my current house purchase, I was extremely concerned to find the general search results revealed the house was at 'moderate risk of groundwater flooding'. I was unable to get any further information from anyone until I contacted GeoSmart. The staff I spoke to were friendly, helpful, efficient and extremely knowledgeable. The information provided was very site specific and focused. The staff member who talked me through the information and maps provided was very knowledgeable, answered all my questions and allowed me plenty of time to discuss issues. Thanks to GeoSmart for their great service."
    Linda Barton
    "We were impressed by the speedy, well-informed service and personal contact that we received. The report was thorough and comprehensive. We will certainly use GeoSmart's services in the future"
    Gregory Gray
    Gregory Gray Associates
    "I would like to say that dealing with GeoSmart was a seamless experience from beginning to end - thank you for that"
    Martin Lloyd
    Martin Lloyd Associates
    "Everyone involved from initial approach to receipt of report was knowledgeable, efficient and focused"
    Robert McCall
    OeMO Ltd
    "Great service! Extremely fast and the report was very detailed and well received by the planners. Many thanks GeoSmart, we will definitely use your services again"
    Nigel Slack
    Michael Eyres Partnership LLP
    "The service was great, fast and efficient. Everyone we talked to was very helpful and the details were well received by the planners"
    Ben Thorns
    Solid Digital Marketing Ltd
    "The service for a Phase 1 Contaminated Land Study was excellent, fast and efficient! GeoSmart were willing to assist despite the extremely tight timescale to work with. We will definitely consider using your services again"
    Craig Roberts
    Hunter Page
    "Efficient and friendly service, GeoSmart provided a clear and concise report within the timescales advised. Great service and I would have no problem recommending"
    Geraint Harris
    Vitec Consult
    "We are very pleased with the service provided by GeoSmart. Their reports have been used to assist with numerous planning applications and have always been delivered to budget and on-time, much to our clients’ appreciation. We look forward to working with GeoSmart on future projects"
    Alan Gunne-Jones
    Planning & Development Associates
    "The service provided was efficient and friendly. From the first phone call to GeoSmart they provided a clear, professional approach to my request within the timescales advised. Great service and I would have no problem recommending"
    John Childs
    Private Developer
    Find out more about how we can support you today!
    Get in touch
    Subscribe to our newsletter
    © 2022 GeoSmart Information Ltd.

    Suite 9-11, 1st Floor,
    Old Bank Buildings,
    Bellstone, Shrewsbury,
    SY1 1HU

    Company No. 5475394

    Contact Us
    Call 01743 298100
    Email enquiries@geosmartinfo.co.uk
    Legal Links
    • Privacy Policy
    • CDM Regulations
    • Terms & Conditions
    Website by Ascendancy