Soakaway FAQ'S
What is a septic tank soakaway?

• Technically: Septic tank soakaways were traditionally pits filled with rubble where wastewater from the septic tank would drain.

• Important Note: Due to environmental regulations, traditional soakaways are no longer allowed for septic tank effluent in the UK.

• Current Practice: The modern equivalent is a drainage field. This consists of a network of perforated pipes laid in trenches filled with gravel. The treated wastewater gradually percolates through the soil in the drainage field.

How does a septic tank drainage field work?

1. Pre-Treatment: Wastewater from your home enters the septic tank, where solids settle to the bottom and bacteria start breaking down the waste.

2. Drainage Field: The partially treated liquid (effluent) flows out of the septic tank and into the drainage field.

3. Distribution: The perforated pipes in the drainage field distribute the effluent evenly across a wider area of soil.

4. Filtration & Treatment: The soil acts as a natural filter. Aerobic bacteria in the soil complete the treatment process, breaking down remaining pollutants.

5. Absorption: The treated water is gradually absorbed back into the groundwater.

What is a rainwater soakaway?

• Purpose: A rainwater soakaway is an underground structure that manages excess rainwater runoff from roofs, driveways, and other hard surfaces.

• Design: It's typically a pit filled with rubble or modern soakaway crates.

How does a rainwater soakaway work?

1. Collection: Rainwater from your roof gutters and other surfaces is directed into the soakaway via pipes.

2. Storage: The soakaway temporarily stores the collected rainwater.

3. Infiltration: The water slowly percolates through the rubble or crates and into the surrounding soil.

4. Groundwater Recharge: The soakaway helps to replenish groundwater supplies and reduce strain on drainage systems.

Key Points:

• Regulations: Building regulations govern the design and installation of both drainage fields and rainwater soakaways in the UK. Always seek professional advice and ensure compliance.

• Soil Suitability: Soakaways are most effective in well-draining soils. Clay soils may not be suitable.

• Maintenance: Septic tank drainage fields need regular maintenance to ensure they function properly. Rainwater soakaways generally require less upkeep.

What is the lifespan of a septic tank soakaway?

• The lifespan of a septic tank soakaway is difficult to pinpoint exactly, but with good maintenance and suitable conditions, they can typically last between 12 and 20 years, and sometimes even up to 30.

• The most significant factor affecting lifespan is regular septic tank maintenance. Emptying your septic tank frequently prevents sludge and solids from overflowing and clogging the soakaway.

What is the lifespan of a rainwater soakaway?

• Rainwater soakaways generally have a much longer lifespan than septic tank soakaways. If installed correctly and well-maintained, they can last for decades or even the lifetime of a house (100+ years).

• Note: It's crucial to get the necessary permits from your local environmental agency before installing a rainwater soakaway.

What are the best soil conditions for a septic tank soakaway?

Septic tank soakaways work best in:

• Moderately Permeable Soils: Soils like sandy loam, which allow water to percolate at a moderate rate. This allows time for bacteria to break down effluent before it reaches groundwater.

• Good Drainage: The soil around the soakaway needs to drain well to prevent waterlogging.

What are the best soil conditions for a rainwater soakaway?

Rainwater soakaways thrive in:

• Highly Permeable Soils: Coarse soils like sand and gravel let water drain quickly, preventing standing water issues.

• Good Drainage: The site needs to drain away excess water effectively.

Important Considerations:

• Soil Testing: Before installing either type of soakaway, a percolation test is essential to determine the soil's drainage and suitability.

• Maintenance: Regular maintenance is crucial for both septic tank and rainwater soakaways to extend their lifespan and prevent issues.

Common Problems Affecting Septic Tank Soakaways:

• Saturation and Blockage: The soakaway is designed to allow treated wastewater to percolate into the ground. Over time, the soil can get saturated and the pores become clogged by solids, preventing it from draining effectively. This can lead to backups and unpleasant odors.

• Tree Root Damage: Roots from nearby trees and shrubs love the moisture and nutrients near soakaways. They can invade and damage the soakaway structure or pipes, causing leaks and blockages.

• Ground Movement and Soil Compaction: Natural ground shifts or heavy vehicles driving over the area can crack or collapse the soakaway. Compacted soil also impedes drainage.

• Poor Design and Installation: A soakaway that's too small for the household or installed in unsuitable soil is prone to fail much earlier.

Common Problems Affecting Rainwater Soakaways:

• Saturation and Blockage: Like septic tank soakaways, rainwater systems can become saturated. Leaves, silt, and other debris can wash in and clog the soakaway.

• Ground Movement and Subsidence: Soil shifts or excessive weight can cause the soakaway to crack or collapse, compromising its function.

• Ponding: If the soakaway can't handle the water flow, you'll end up with ponding water on your property, which can be a breeding ground for mosquitoes and other issues.

Lifespan of Soakaways in the UK

• Septic Tank Soakaway Lifespan:  The typical lifespan of a septic tank soakaway is around  10-15 years, but this can be significantly shortened by problems mentioned above, poor maintenance of the tank, or changes in ground conditions.

• Rainwater Soakaway Lifespan: Rainwater soakaways generally last a bit longer than septic tank soakaways, with lifespans up to 20 years or more with good maintenance and proper installation.

• Regular maintenance to clear potential blockages and inspections to catch potential issues early are key to extending the life of soakaways.

• Avoid flushing inappropriate substances (grease, sanitary items, chemicals) and excessive amounts of waste down your septic system. These contribute significantly to soakaway failure.

• Address any suspected issues quickly. The longer you leave a soakaway problem, the more likely it will cause damage and become costly to repair or completely replace.

Understanding Soakaways

• Purpose: Soakaways are underground structures that allow treated wastewater (from a septic tank) or rainwater to gradually disperse into the soil. They're essential for properties not connected to the mains sewer system.

• Design Factors: Design considers soil type, percolation rates (how quickly water drains), household size (for septic tank systems), and rainfall intensity in your area.

Septic Tank Soakaway

Design:

• Percolation Test: Determines soil suitability and the required size of your soakaway.

• Trench or Pit: Trenches are common. Multiple trenches may be needed for larger systems. Pits are used in less permeable soil.

• Distribution Chamber: Often required to evenly distribute the outflow from the septic tank into the soakaway.

• Sizing: Based on the percolation test and the number of people using the system.

Construction

1. Excavation: Dig trenches or pit to design specifications.

2. Lining: Lay a layer of permeable geotextile membrane to prevent soil clogging the soakaway.

3. Fill: Add a layer of clean gravel or crushed stone.

4. Pipes: Lay perforated pipes on the gravel to distribute the wastewater.

5. More Fill: Cover the pipes with more gravel.

6. Membrane: Top with another layer of geotextile membrane.

7. Backfill: Cover with soil.

Rainwater Soakaway

Design:

• Percolation Test: Also important for rainwater soakaways.

• Crate Systems vs. Trenches: Modular plastic crates can be used instead of gravel-filled trenches, especially with limited space.

• Sizing: Determined by the roof area it collects water from, rainfall intensity, and percolation rates.

Construction

1. Excavation: Size based on whether using crates or a traditional trench design.

2. Geotextile: Line the soakaway area with geotextile membrane.

3. Crates or Fill: Either install modular soakaway crates or fill the space with clean gravel.

4. Connection: Connect the downpipe from your gutters or rainwater collection system.

5. Membrane and Backfill: Wrap crates in geotextile membrane if used, then cover everything with soil.

Important Considerations for Both Types

• Regulations: Adhere to building regulations and Environment Agency guidelines.

• Location: Must be a safe distance from buildings, watercourses, wells, and property boundaries.

• Maintenance: Septic tank soakaways may occasionally need emptying depending on usage.

Additional Notes

• Seek professional advice for sizing and installation, especially for complex situations.

• Incorrect design or construction can cause environmental problems or even system failures.

Absolutely! Here's a breakdown of the General Binding Rules (GBRs) for septic tank soakaways and rainwater soakaways in the UK.

General Binding Rules for Septic Tank Soakaways

The GBRs for septic tank soakaways are aimed at minimizing the risk of pollution from small sewage discharges:

• Discharge Limits:

  • A maximum of 2 cubic meters (2000 liters) of treated effluent per day can be discharged into the ground. This is approximately equivalent to the wastewater output from a 13-person household.

• Wastewater Type: Only domestic sewage is allowed (from toilets, showers, sinks, etc.). Industrial or other potentially harmful waste is not permitted.

• Pollution Prevention: You must make sure the discharge does not cause pollution of groundwater or surface water.

• Approved Treatment System: Your septic tank must meet the relevant British Standard in force at the time of installation (BS EN 12566-1 for septic tanks installed after 2014, or BS 6297:2007 for drainage fields installed after 2006).

• Groundwater Source Protection Zones (SPZ): Discharges are not allowed within a groundwater Source Protection Zone 1.

• Distance Requirements: Your soakaway should ideally be located at least:

  • 10 meters from any watercourse (stream, ditch, etc.)

  • 15 meters from a well used to supply water

  • 50 meters from any borehole or spring used to supply water

Important Notes:

• If you cannot comply with the General Binding Rules, you must apply for a permit from the Environment Agency.

• Existing septic tanks installed before the current regulations may need upgrades to remain compliant.

General Binding Rules for Rainwater Soakaways

Rainwater soakaways generally have less stringent regulations compared to those for septic tanks. The key principles are:

• Clean Rainwater Only: Ensure that only water collected from roofs and paved areas is being directed into the soakaway. Avoid contaminated water from areas like car washing stations etc.

• Pollution Prevention: The soakaway should be designed and situated to prevent the risk of groundwater pollution.

• Suitability: The ground conditions must be suitable for a soakaway. If your soil has poor drainage, alternatives like connecting to the surface water sewer may be necessary (you may need permission for this).

Additional Considerations

• Location: It's best practice to locate your soakaway at least 5 meters away from buildings and boundaries.

• Planning Permission: You may need planning permission to install a soakaway. It's best to check with your local council for specific requirements.

Where to Find More Information

• GOV.UK: The official sources for the GBRs can be found on the GOV.UK website:

  • General binding rules: small sewage discharge to the ground: https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-the-ground

  • General binding rules: small sewage discharge to a surface water: https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-a-surface-water

• Environment Agency: Provides detailed guidance and resources for wastewater management. https://www.gov.uk/government/organisations/environment-agency