What is a Perc Test and Why You Need One in Maryland?

What is a Perc Test — and Why You Need One in Maryland?

For Homeowners in Carroll, Howard, Frederick, Baltimore & Montgomery Counties

If you’re planning to build a home, add an addition, or install a new septic system on a property not connected to public sewer, it’s critical to understand what a percolation test (often simply called a “perc test”) is — and why it’s required in Maryland, particularly in counties like Carroll County, Maryland, Howard County, Maryland, Frederick County, Maryland, Baltimore County, Maryland and Montgomery County, Maryland. At Colson’s Septic Services, we’ve helped countless property owners locally navigate this process — and this blog will walk you through the what, why, and how of perc testing.

What Is a Perc Test?

A percolation test (or “perc test” is a soil-drainage evaluation used to determine how quickly water moves through the soil in the area where a septic system’s drain field (also called the leach field) would be installed.

Here’s how it generally works:

• Hole(s) are dug in the proposed drain-field area to the depth required by local regulation.
• The soil may be pre-saturated to simulate worst-case (wet season) conditions.
• The hole is filled with water, and the rate at which the water level drops is measured. That rate (often expressed as minutes per inch) is your “percolation rate.”
• The results are compared to regulatory thresholds in your county to decide whether a conventional septic system can be used, or whether an alternative system is needed.

In short, the perc test gives a snapshot of whether your soil can absorb wastewater at a safe, effective rate.

Why Do You Need One in Maryland?

There are several important reasons why this test is required — and why it matters.

1. Regulatory Compliance
   In Maryland, counties require a successful perc test (and/or full soil-site evaluation) before issuing a permit for a new on-site sewage disposal (septic) system when the property is not on public sewer. For example:

• The Frederick County Health Department states that soil evaluations and percolation tests “are used to determine how quickly the soil absorbs liquid waste … and the type of system needed.”
• The Montgomery County Department of Permitting Services states that properties not eligible for public sewer must complete satisfactory water table tests and percolation/sand-mound testing to establish a sewage disposal area.
  Without a satisfactory test, you may be unable to proceed with a building permit or septic permit.

2. Environmental & Health Protection
   A septic system that is poorly matched to soil conditions can lead to effluent backup, pooling, or contamination of groundwater or nearby surface waters. A proper perc test helps ensure that wastewater will be treated and dispersed safely — protecting your health, your neighborhood, and the local environment.
3. Cost Avoidance
   Imagine buying land or starting construction only to find out the soil cannot support a conventional septic system. The cost of alternative systems (mound systems, sand filters, aerobic treatment units) can be significant. A perc test helps you identify potential issues early in the process — saving time, money and stress.

How Does This Process Work for Homeowners in These Maryland Counties?

At Colson’s Septic Services, when you’re in Carroll, Howard, Frederick, Baltimore or Montgomery Counties, here’s an outline of the typical workflow:

1. Preliminary Site Review
   We examine your property: topography, vegetation, existing wells or septic systems, proximity to water bodies or wetlands, slope, soil type. This helps us determine likely zones for drain-field test holes.
2. Scheduling the Perc Test
   We dig the test holes in the proposed drain-field area (or multiple areas for larger lots / alternative systems). We follow the county-specific procedure for depth and spacing. According to our site, we’ve performed such services in these five counties for decades.
3. Pre-soak and Testing
   Some counties require pre-saturation (wet-season testing), especially where groundwater levels are high. For example, Montgomery County states that if the soils are restrictive, percolation tests must be done during the “wet season.”
4. Results & Reporting
   Once the holes are tested and percolation rates measured, the firm prepares a report: percolation rates, soil conditions, type of system possible, and recommendations if the rate is too slow/fast. At Colson’s, we analyze and explain the results, including next steps if your soil “fails” or is marginal.
5. Next Steps Depending on Outcome
   • If results are satisfactory, you can design and install a conventional septic system.
   • If not satisfactory: you may need an alternative system (mound, sand filter, aerobic treatment), a different location on the lot, or in some cases, public sewer may be required. Colson’s mentions these options.

Key Considerations & Local Tips for Carroll, Howard, Frederick, Baltimore & Montgomery Counties

• Test timing matters: In counties like Montgomery, percolation tests in certain soils must be done in the wet season because that gives a more conservative (safer) assessment.
• Know your soil types: Maryland soils vary significantly. Soils with heavy clay, shallow bedrock, or high groundwater are more challenging for septic systems.
• Multiple test holes may be required: Some jurisdictions require more than one test hole to ensure a reliable result.
• Plan for replacement area: Many health departments require enough space for two drain fields (one active, one backup) in the event of future failure.
• Work with experienced professionals: A company familiar with local health codes, soil conditions and county permit requirements (like Colson’s) reduces risk of delays or surprise costs.
• If you’re buying land: Ask for existing perc test data and septic suitability reports. A prior “perced” lot may still need new testing depending on when and how it was done and whether regulations changed.
• Failing the test isn’t the end: You may still build/design, but with alternative systems. Budget accordingly.

Final Word

If your property in Carroll, Howard, Frederick, Baltimore or Montgomery County is not hooked up to public sewer and you’re planning any kind of construction or building addition, a perc test is not just a procedural step — it’s a foundational part of your site’s viability. A successful perc test protects your investment, ensures regulatory compliance, safeguards your health and the environment, and gives you the data to design a septic system that works long-term.

At Colson’s Septic Services, we’ve been performing perc tests and full septic system services in these counties for over 30 years. We understand the soil conditions, local permitting processes and practical steps required to move forward. If you’re at the stage of investigating land or planning for a septic system, give us a call. Accurate testing up front means no surprises down the road.

Call us today at 443-536-9382 or visit our website to schedule your perc test or learn more about our full suite of septic services in Carroll, Howard, Frederick, Baltimore & Montgomery Counties. Your property, system and peace of mind are worth it.