How to Perform a Soil Percolation Test Before Choosing a Drainage Solution

Introduction: Why Soil Percolation Matters

Water always follows the path of least resistance. But if your soil can’t absorb water quickly enough, that path ends at the surface—leading to ponding, runoff, and flooding.

That’s why HydroBlox recommends a percolation (perc) test before any installation. This simple soil test helps determine:

• How well water drains into the soil
  
  
• What size system you need
  
  
• Whether to use stormwater boxes, daylight pipes, or gravel assists
  
  

When You Should Do a Percolation Test

• New home construction or landscaping
  
  
• Foundation waterproofing
  
  
• Stormwater compliance planning
  
  
• Installing HydroBlox in areas with clay or compacted fill
  
  

Step-by-Step: How to Perform a Percolation Test

Step 1: Dig the Test Hole

• Dig a hole 18–24 inches deep and 12 inches wide
  
  
• If testing a large site, dig multiple holes spaced out evenly
  
  

Step 2: Saturate the Soil

• Fill the hole completely with water
  
  
• Let it drain fully (this preps the soil)
  
  

Step 3: Refill the Hole

• After the first drain, refill to 1 inch below the top of the hole
  
  

Step 4: Measure the Starting Water Level

• Use a measuring stick and note the distance from the water to the ground level
  
  
• Record the time
  
  

Step 5: Measure Every 30 Minutes

• At 30-minute intervals, measure how far the water has dropped
  
  
• Do this at least 4 times
  
  

Step 6: Calculate the Percolation Rate

• Find how many inches the water dropped per hour
  
  
• Average your 4 readings
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Percolation Rate Guidelines

What If the Soil Fails?

If your percolation rate is too slow:

• Use double planks in your system
  
  
• Daylight to a slope or pipe discharge
  
  
• Add HydroBlox stormwater boxes to retain and slowly release water
  
  

Never install any subsurface system into 100% compacted clay without daylight or retention planning.

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Real Example: Suburban Clay Soil

A homeowner near Atlanta had standing water in their yard. The perc test showed <0.1 in/hr. The contractor used:

• Two rows of HydroBlox planks
  
  
• Stormwater boxes at each downspout
  
  
• Daylight discharge to a back slope
  
  

Result: Yard dried out within 48 hours after 2” rain.

Internal Linking Opportunities

• Download our percolation test worksheet
  
  
• Explore how HydroBlox handles low-permeability soils
  
  
• See our stormwater boxes for slow-drain sites
  
  

Schedule a drainage system consultation