BRE 365 SOAKAWAY TESTING
In accordance with Planning Policy Statement 25 (PPS 25) "Development and Flood Risk," which advocates for the incorporation of sustainable drainage systems in all proposed construction work, Jaystones recommends engaging in BRE365 Soakaway Testing whenever possible and practical. This allows for the exploration of the infiltration potential of the ground and the gathering of design information for drainage systems
What is the Difference between Soakaway Testing (BRE365) & Percolation Testing (BS6297) ?
What distinguishes a soakaway test (BRE365) from a percolation test (BS6297) is their respective purposes.
A BRE365 soakaway test is necessary to assess the suitability of a new or substitute soakaway for the discharge of surface water runoff, while a BS6297 percolation test is necessary if a septic tank or sewage treatment plant is being proposed for the treatment of foul water.
What is a BRE365 Infiltration / Soakaway Test?
Before embarking on the design of Sustainable Drainage Systems (SuDS) for any site, it is crucial to determine the natural infiltration rate of the ground. BRE365 soakaway testing is essential for designing effective drainage systems.
At Jaystones our independent geotechnical engineer will conduct thorough BRE365 tests to determine soil infiltration rates, ensuring your drainage design solutions are compliant with current guidelines.
To conduct the test, we excavate a trial pit, fill it with water, and record the water level at specific time intervals to establish the drainage rate. This process is repeated three times in accordance with BRE365 Soakaway Testing. It's important to note that not all soil types are suitable for soakaways and this should be assessed as part of an infiltration assessment investigation.
To perform soakaway testing at any site, Jaystones requires access for a mini-excavator excavator and safe parking within 50m of the proposed soakaway test locations for a 4x4 vehicle and water bower trailer.
Jaystones only use Licensed Water Authority Standpipes to legally and safely obtain clean water.
BRE 365 Soakaway Testing may also be referred to as Infiltration Testing, Percolation Testing, Permeability Testing or Soakage Testing
How is a BRE365 Soakaway Test Carried Out?
A trial pit is excavated to the same depth as anticipated in the full-size soakaway (normally 0.5m to 1.5 m below the invert level of the proposed drain discharging to the soakaway). Overall depths of excavation is typically 1.0 to 2.5 m.
The trial pit will be 0.3m to 1.0m wide & 1.0m to 3.0m long with vertical sides trimmed square.
Depending on the stability of the excavation and other health and safety concerns the trial pit may be infilled with granular material. When granular fill is used, a perforated, vertical observation pipe will be installed in the trial pit so that water levels can be monitored with a dip meter.
A significant volume of water is required to determine the soil infiltration rate and therefore a water bowser is normally required.
The inflow of water needs to be rapid enough that the trial pit can be filled to its maximum effective depth in a short time using a water pump.
The Infiltration / Soakaway trial pit should be filled and allowed drain three times to near empty (at least 75% empty).
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It is normally recommended that the worst result is used for design of the sustainable drainage system.
JAYSTONES have extensive experience in determining soil infiltration rates in accordance with BRE Digest 365 “Soakaway Design” BRE, 2016
Why Have I Been Asked For BRE365 Testing to be Carried Out at Planning Application Stage?
Local Planning Authorities (LPAs) and Lead Local Flood Authorities (LLFAs) often require a BRE365 percolation test during the planning application stage to ensure proper management of surface water runoff for new developments. This test helps to determine if the soil on the site can adequately absorb water through sustainable drainage systems (SuDS), like soakaways, which need to be planned and designed before construction begins.
A typical example of a Planning Condition requiring BRE365 is :
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'Ground investigations and infiltration testing in line with the
requirements of the BRE Digest 365 and undertaken by a competent
contractor so as to assess the feasibility of drainage by ground infiltration.'
Key Reasons for the Test:
1. Ensuring Effective Surface Water Management:
The primary purpose of the BRE365 percolation test is to assess the soil's ability to absorb water. This information is vital for designing SuDS that effectively manage surface water runoff, preventing flooding and waterlogging. Without proper testing, there's a risk that the drainage system might fail, leading to potential environmental and property damage.
2. Planning and Space Requirements:
SuDS often require significant space, and regulations mandate that all infiltration devices must be located at least 5 meters away from buildings. This spatial requirement needs to be considered early in the planning process to ensure that the development layout can accommodate these systems. If the test shows favorable conditions for infiltration but the site lacks the necessary space, adjustments to the site layout may be required to incorporate the needed drainage solutions.
3. Compliance with SuDS Hierarchy:
For larger developments, especially where preliminary geological assessments suggest good potential for infiltration, LPAs and LLFAs will typically require a BRE365 test to confirm that the SuDS hierarchy is being followed. This hierarchy prioritizes sustainable and natural methods of water management over less sustainable alternatives. If the test fails, it helps identify the need for alternative drainage methods, ensuring the development remains compliant with environmental regulations.
4. Suitability of Soil Conditions:
Sites with high clay content or a high water table may not be suitable for soakaways, as these conditions impede proper water infiltration. Conducting a BRE365 percolation test demonstrates to local authorities that the developer has taken the necessary steps to evaluate the site's suitability for SuDS, thereby addressing potential issues before they become problematic.
In summary, the BRE365 percolation test is a critical step in the planning process, ensuring that new developments are equipped with effective and compliant drainage solutions. This pre-emptive measure helps to secure the project's success and sustainability, ultimately benefiting both the developer and the community.