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How to Conduct a Soakaway Test: A Simple Guide

A soakaway test is a crucial procedure used to assess the drainage capabilities of soil, particularly for projects involving the installation of soakaways, septic systems, or other drainage solutions. This test helps determine how quickly water can drain away from a site, which is essential for effective water management and avoiding waterlogging. This article will guide you through the steps of conducting a soakaway test in an easy-to-understand manner, ensuring you have the knowledge to perform it correctly and effectively.

What is a Soakaway Test?

A soakaway test, also known as a percolation test or infiltration test, measures the rate at which water soaks into the ground. It helps determine the soil’s permeability, which is essential for designing drainage systems. Properly conducted, a soakaway test can prevent flooding and waterlogging by ensuring that the drainage system is appropriate for the soil conditions.

Why Conduct a Soakaway Test?

Understanding the drainage capacity of your soil is vital for several reasons:

  1. Prevent Flooding: Poor drainage can lead to water accumulation, causing flooding.
  2. Avoid Waterlogging: Excess water can damage plants and affect soil health.
  3. Compliance: Many local authorities require soakaway tests for planning permissions and building regulations.
  4. Effective Drainage Design: Helps in designing appropriate soakaway systems, septic tanks, and other drainage solutions.

Preparing for the Soakaway Test

Before starting the test, gather the necessary materials:

  • Spade or digger
  • Measuring tape
  • Stopwatch or timer
  • Water supply (e.g., hose or water tank)
  • Pen and paper for recording results

Step-by-Step Guide to Conducting a Soakaway Test

Step 1: Select the Test Location

Choose a site representative of the area where the soakaway will be installed. Ensure it is at least 5 meters away from buildings and boundaries to avoid affecting foundations.

Step 2: Dig the Test Hole

Dig a hole 300mm wide and 300mm deep. The sides should be vertical, and the bottom should be level. This size ensures the test results are accurate for a typical soakaway system.

Step 3: Saturate the Soil

Fill the hole with water and let it drain completely. This step pre-saturates the soil, simulating real-life conditions where the ground is already wet. It may take several hours for the water to drain completely.

Step 4: Refill the Hole with Water

After the initial drainage, refill the hole with water to a depth of 300mm. Use the measuring tape to ensure accuracy.

Step 5: Measure the Time

Start the timer immediately after refilling the hole. Measure the time it takes for the water level to drop from 75% full (225mm) to 25% full (75mm). This measurement helps calculate the percolation rate.

Step 6: Record the Results

Repeat the test three times to ensure consistency. Record the time taken for each test and calculate the average percolation rate.

Interpreting the Results

To interpret the results, use the following formula:

Percolation Rate=Time (seconds)Drop in water level (mm)\text{Percolation Rate} = \frac{\text{Time (seconds)}}{\text{Drop in water level (mm)}}

Convert the time to seconds and divide it by the drop in water level (225mm – 75mm = 150mm). This will give you the percolation rate in seconds per millimeter.

Understanding Percolation Rates

  • Less than 15 seconds/mm: Excellent drainage.
  • 15 to 30 seconds/mm: Good drainage.
  • 30 to 90 seconds/mm: Moderate drainage.
  • 90 to 300 seconds/mm: Poor drainage.
  • More than 300 seconds/mm: Very poor drainage, indicating a need for an alternative drainage solution.

What to Do with the Results

Based on the percolation rate, you can design an appropriate drainage system. For instance:

  • Excellent to Good Drainage: Standard soakaway system.
  • Moderate Drainage: Larger or deeper soakaway to increase capacity.
  • Poor Drainage: Consider alternative solutions like a drainage field or engineered systems.
  • Very Poor Drainage: Consult a professional for advanced drainage solutions.

Common Mistakes to Avoid

  • Incorrect Hole Size: Ensure the hole is 300mm wide and 300mm deep for accurate results.
  • Inconsistent Measurements: Perform the test three times and average the results.
  • Ignoring Soil Saturation: Always pre-saturate the soil to simulate real conditions.
  • Misinterpreting Results: Follow the guidelines for percolation rates to design the correct drainage system.

Tips for Accurate Soakaway Tests

  • Use Clean Water: Avoid using water with sediments that could affect the drainage rate.
  • Monitor Weather Conditions: Conduct the test during dry weather to avoid skewed results from recent rain.
  • Proper Timing: Perform the test in daylight for better visibility and accurate measurements.
  • Detailed Records: Keep a detailed log of the test times and conditions for reference.


Conducting a soakaway test is a straightforward process that provides valuable insights into the soil’s drainage capacity. By following this guide, you can ensure that your soakaway system is designed to function effectively, preventing waterlogging and flooding issues. If you need professional assistance or further advice, don’t hesitate to contact experts.

For a Quote Contact VIV Construct Group

If you’re planning a project and need a professional soakaway test or expert advice on drainage solutions, contact VIV Construct Group for a comprehensive quote and expert services. We offer reliable and efficient services tailored to your specific needs.


Learn how to conduct a soakaway test easily with our simple guide. Ensure effective drainage with clear steps.