If you’re planning to build on undeveloped land, install a septic system, add living space to an existing home, or subdivide a property, you may have been told that your project “depends on perc testing” or that you’ll need to wait for “perc season.” For many property owners, these terms raise more questions than answers.
Understanding what perc testing is, why it’s required, and how perc season affects timing can help you avoid surprises and plan your project more confidently.
At COA Barrett, we help landowners, builders, and developers navigate every phase of site evaluation and preparation. One of the most important early steps in many projects is the percolation test, commonly called a perc test.
What Is Perc Testing?
A perc test measures how quickly water drains through the soil at a proposed septic drain field location. This information helps determine whether the soil can safely absorb and treat wastewater from an onsite septic system.
During a perc test, holes are excavated to specific depths, filled with water, and monitored over time. The rate at which the water drains—known as the soil’s permeability—is recorded and evaluated by the local Health Department.
Why Perc Testing Is Required
Perc testing is a critical step in determining whether a property is suitable for development where an onsite septic system is required. Test results are used by the Health Department to evaluate public health protection and inform septic system design, placement, and long-term functionality.
Perc testing is commonly required for:
- Onsite septic system design and approval
- Subdivision approval and permitting
- Identifying suitable buildable areas on a property
- Proposed additions that increase living space, in order to:
- Establish designated replacement areas for a future failing septic system
- Identify areas needed for potential septic repair or expansion
In certain situations—such as septic system failures—the Health Department may require or authorize perc testing outside of the typical perc season. For public health reasons, Health Departments have flexibility to evaluate sites as needed and determine the appropriate testing approach based on site conditions.
What Is Perc Season—and Who Determines It?
Perc season refers to the designated period of the year when percolation testing is permitted by the local Health Department under typical site evaluation conditions. This timeframe is determined exclusively by the Health Department based on groundwater levels, soil saturation, and environmental conditions that ensure accurate and reliable test results.
In many areas, including our local jurisdiction, perc season typically occurs between March and May. However, this window can vary from year to year depending on weather patterns, groundwater conditions, and Health Department guidance.
Because soil and groundwater conditions change throughout the year, perc season does not follow a fixed calendar. Health Departments monitor environmental conditions and decide when testing may begin and when it must stop to ensure results reflect long-term site conditions.
Key takeaway: While perc season timing varies, understanding the general window and planning early can help reduce delays.
Why Perc Season Matters
Soil conditions change with the seasons. During dry periods, soil may absorb water too quickly, creating test results that don’t accurately represent how the soil performs over time. Perc season ensures testing occurs when soils are more fully saturated and groundwater levels are higher, providing a more realistic assessment of septic system performance.
For property owners, this means that when testing occurs can be just as important as how it’s performed.
How and When Is Perc Testing Scheduled?
While perc season dates are established by the Health Department, perc testing appointments are typically scheduled on a first-come, first-served basis. Once perc season opens, demand is often high, and existing application queues can affect scheduling timelines.
Starting the process early allows time for site evaluation, preparation, and submission of required documentation so your project is ready when testing becomes available.
What Can Affect Perc Testing Timelines?
Several factors can influence when perc testing occurs, including:
- Weather patterns and groundwater conditions
- Health Department application volume
- Health Department existing testing queues
Because these factors vary from year to year, testing timelines can differ even for similar properties.
Who Should Be Thinking About Perc Testing Early?
Perc testing is especially important for:
- Homeowners planning new construction on undeveloped land
- Property owners considering subdivision
- Homeowners proposing additions that increase living space
- Builders and developers working in areas that require onsite septic systems
If your project depends on septic approval, perc testing and perc season should be considered early in the planning process.
How COA Barrett Helps You Navigate Perc Testing and Perc Season
At COA Barrett, we understand that perc testing is both time-sensitive and highly regulated. Our team helps clients prepare early and navigate the process efficiently by providing:
- Early site evaluation and preparation
- Coordination with local Health Departments and specialists
- Guidance through Health Department requirements and procedures
- Surveying and engineering support for permitting and septic system design
By preparing sites in advance and coordinating required documentation, we help position projects to move forward as efficiently as possible once testing becomes available.
Planning Ahead
Perc testing and perc season can feel complex—but understanding the process and planning early can significantly reduce delays. If you’re considering development, an addition, or septic-related improvements and aren’t sure how perc testing may affect your timeline, COA Barrett can help you understand what to expect and how to prepare.
Contact COA Barrett to discuss your site evaluation needs and take the first step toward keeping your project on track.
