Do You Need a Perc Test in Massachusetts? (And When a Soil Evaluation Is Required)
If you’re dealing with a septic system in Plymouth County, Bristol County, or Cape Cod, you may hear terms like:
“Perc test”
“Deep hole”
“Soil evaluation”
And naturally, the question comes up:
👉 “Do I need a perc test?”
The answer:
👉 Not always—but in some cases, it’s required, and it can determine whether your system can be repaired or must be replaced.
What Is a Perc Test?
A percolation test (perc test) measures how quickly water drains through soil.
It helps determine:
Whether the soil can support a septic system
What type of system is required
How the system must be designed
👉 It’s a key part of septic system design—not routine inspection.
What Is a Soil Evaluation (“Deep Hole” Test)?
A soil evaluation involves digging a deep observation hole to:
Identify soil types
Determine seasonal high groundwater levels
Evaluate whether the site meets Title 5 requirements
👉 This is often more important than the perc test itself.
When Do You Need a Perc Test in Massachusetts?
You typically need a perc test when:
1. Installing a New Septic System
New construction
Replacing a failed system
2. Designing a Replacement System
If your system fails and needs replacement:
👉 A perc test + soil evaluation are usually required for design approval.
3. Expanding or Upgrading a Property
Adding bedrooms
Increasing flow
When a Soil Evaluation May Be Required (Even Without Immediate Replacement)
This is where things get important—and often misunderstood.
In some cases, a soil evaluation may be triggered during inspection or troubleshooting.
1. Systems Installed Before 1995
Many older systems in:
Bridgewater
Middleboro
Plymouth
Cape Cod
👉 Were installed before modern Title 5 standards.
If:
Records are limited
System design is unclear
Compliance is questionable
👉 A soil evaluation may be required to determine if the system meets current standards.
2. When the System Appears to Be in Groundwater
If an inspector observes signs that the Soil Absorption System (SAS) may be too close to groundwater:
Saturated conditions
Evidence of high water table
System performance issues
👉 A soil evaluation may be needed to confirm:
Actual groundwater elevation
Required separation distances
Why This Matters
Title 5 requires a minimum vertical separation between:
The bottom of the system
Seasonal high groundwater
If that separation is not met:
👉 The system is non-compliant and may fail.
3. When System Performance Is Questionable
If a system:
Shows signs of hydraulic failure
Has inconsistent performance
Doesn’t match expected design
👉 A soil evaluation may be needed to understand site conditions.
Perc Test vs. Inspection — Don’t Confuse Them
This is a common mistake:
👉 A perc test is NOT part of a Title 5 inspection
Inspection = Evaluate existing system
Perc test / soil evaluation = Design or site analysis
Who Performs These Tests?
Soil evaluators (often engineers or certified professionals)
Designers / engineers
Overseen by the local Board of Health
👉 This is separate from the role of a septic inspector.
Why This Matters in Southeastern Massachusetts
This region has:
High groundwater levels
Sandy soils (Cape Cod)
Older systems (pre-Title 5 updates)
Strict environmental regulations
👉 Soil conditions are everything when it comes to septic compliance.
The Biggest Mistake Homeowners Make
👉 Assuming their existing system “must be fine” because it’s been there a long time.
In reality:
Older systems may not meet current standards
Groundwater conditions may have changed
Documentation may be incomplete
The Smart Approach
If you’re:
Buying a home
Selling a home
Dealing with a failing system
👉 Start with a thorough inspection
From there, you can determine:
If the system is compliant
If further evaluation (soil testing) is needed
What your next steps are
Onsite Wastewater Inspections LLC – Helping You Understand the Full Picture
At Onsite Wastewater Inspections LLC, we provide:
Detailed septic inspections
Title 5 evaluations
System troubleshooting
Clear guidance on when further testing (like soil evaluations) may be needed
We do not perform system design or installation.
👉 Our role is to give you accurate, unbiased information so you can make informed decisions.
Serving Southeastern Massachusetts
We serve:
Plymouth County, Bristol County, and Barnstable County (Cape Cod), including:
Bridgewater, Raynham, Middleboro, Berkley, Hanson, Halifax, Pembroke, Hanover, Kingston, Marshfield, Norwell, Plymouth, and Cape Cod.
The Bottom Line
👉 You don’t always need a perc test—but when you do, it’s critical.
And in cases involving:
Older systems (pre-1995)
Groundwater concerns
System failure
👉 A soil evaluation can determine whether your system can stay—or must be replaced.
