Our customers frequently ask us about sizing soakaway crate systems, and the first step should always be conducting a percolation test. In this guide, we'll walk you through the basics of performing a percolation test, which is essential if you're planning to install a septic tank or a soakaway crate system.
Key Takeaways:
- Percolation tests must be done prior to installation to ensure the soakaway system will effectively disperse rainwater.
- VP values between 15 and 100 are ideal for a soakaway.
- Soakaways are not meant for foul water disposal.
A percolation test is essentially a way to measure how quickly water drains into the soil. Different soil types absorb water at varying rates—sandier soils will drain faster than dense clay. In the UK, clay soil is common and historically used for waterproofing structures. For instance, while watching a documentary on Oak Island, I learned that builders in the 1700s utilized clay to prevent seawater from infiltrating their construction sites.
Therefore, the suitability of your soakaway depends largely on the type of soil present. A percolation test helps determine this.
When Should You Conduct a Percolation Test?
Before installing any soakaway crate system—whether it's our smallest 1m³ kit or a septic tank—you should perform a percolation test after completing a Groundwater Source Protection Zone search and Trial Site Assessment Hole to fully evaluate the water table.
Please note that the procedure varies depending on whether the soakaway will handle foul water or surface water. In this guide, we'll focus on performing a percolation test for foul water. For systems dealing with large volumes of water over short periods, larger pits (typically 1x1 meter wide and 2 meters deep) are usually required.
Considerations for Soil Types:
Identifying the type of soil in your area is crucial when planning a drainage method. Dense soil might hinder water drainage, leading to surface water accumulation. Conversely, overly porous soil can make it difficult to control and manage water effectively, potentially causing issues down the line.
Superior soil types for soakaway installations include:
- Sandy soil
- Chalk-based soil
- Loamy soil
Poorer soil types to avoid:
- Clay soil
- Silty soil
Once the test is completed, understanding the soil type is key to determining the feasibility of your project.
Steps for Performing a Percolation Test:
Now that we understand the "what" and "why," let's cover the "how."
A percolation test involves digging holes in the proposed soakaway area to a certain depth. These holes need to be pre-soaked to saturate the soil, followed by timing how quickly the water level drops as it permeates the surrounding ground. Based on these results, you can calculate the necessary size of the soakaway or drainage field. It's important to avoid conducting the test in extreme weather conditions, as heavy rain, frozen ground, or drought can distort the water table and produce inaccurate results.
Here’s a step-by-step guide:
1. Dig a hole 300mm wide and 300mm deep below the required invert level of the underground pipe. This might mean digging a hole large enough to stand in before excavating the percolation test hole.
2. Pre-soak the hole by filling it to at least 300mm and leaving it for at least 12 hours to allow the water to drain away.
3. Refill the hole to 300mm with fresh water and time how long it takes to drain from 3/4 full (225mm) to 1/4 full (75mm). Divide this time by 150mm to get the average time in seconds it takes for the water to drop 1mm. This is called the “VP.â€
4. Repeat this process several times, with a minimum of three holes, calculating the average time for each.
If the average VP value falls between 15 and 100, the ground is suitable for a soakaway. This ensures the water drains at an appropriate rate, avoiding both overly rapid absorption and complete ineffectiveness.
Calculating the Percolation Test Results:
V = The time in seconds for the water in the test hole to drop by 1mm.
P = Maximum number of people the tank or plant is designed to serve.
For sewage treatment units, Area (A) = V × P × 0.20.
For septic tanks, Area (A) = V × P × 0.25.
These calculations provide the area in square meters required for the soakaway system. Further calculations will be needed to determine the length of piping, based on trench width.
This guide should give you a general idea of what a percolation test is and how to perform one. However, always consult with your local authorities, as regulations vary by location. Other considerations include avoiding installing soakaway systems under driveways, parking areas, buildings, or near trees, dwellings, boundaries, rivers, or streams. Additionally, a minimum of 1.2 meters of soil between the drain and the water table or bedrock is required. Less than this, and the water won't have sufficient soil to drain effectively.
Importantly, soakaway crate systems MUST NOT be used for foul water under any circumstances. They do not comply with building regulations for this purpose and are unsuitable. Soakaway crates are intended only for rain or surface water. If a company tries to sell you this for foul water, report them to trading standards immediately.
We hope this guide has been helpful. For further assistance, feel free to reach out to us. We’ll do our best to guide you in the right direction.
Shop Soakaway Crates:
Explore our selection of soakaway crates and related products to find the perfect solution for your needs.
Shower System Kit,Thermostatic System,Concealed Shower Set,Shower Package
JANGMEN MOON SHOWER SANITARYWARE CO.,LTD , https://www.moonshowerglobal.com