How much does it cost to perc test a soil sample?

A perc test, sometimes referred to as a “perk test” or percolation test, determines the water absorption rate of your soil—specifically, how much time it takes for the soil to drain. Landowners and homeowners that utilize a septic system should get a perc test before installing or replacing it. The perc test aids in designing the septic system layout and determining where to best place a drain or leach field ¹.

A perc test is sometimes performed on one area with one hole or on different areas of your property with multiple holes. The cost largely depends on the condition and size of the land. The average cost to perform a percolation test is $600 - $800, with the average customer paying $750 for a percolation test with one or two holes measuring more than 2 feet deep.

Perc test costs

Why to perc test a soil?

A percolation test provides important information regarding soil drainage for any property owner. It is necessary before installing a septic tank or drainage system due to local health department permit requirements. A septic tank, unlike local city or town sewer systems, requires a drain or leach field. Good drainage is incredibly important when installing a leach field or drain field and a necessity for the wastewater disposal system. This system removes contaminants that drain out of the septic system. Improper drainage leads to the sewage backing up and contaminating the soil. A perc test determines where the leach field should go based on the drainability of the soil.

Besides septic systems, perc tests are also used for agricultural purposes. Knowing the drain rate of your soil is helpful in determining what type of crops you can grow and where you should grow them. For example, potatoes require dryer, more loamy soil than other vegetables and fruits that require moist soil. Therefore, potatoes require higher drainage ability than some other crops. Fruit trees need soil that drains well since over-saturation removes the oxygen and prevents root growth. However, this type of perc test is not mandated by government agencies.

Cost factors

A number of variables have a direct effect on how much a homeowner can expect to pay for a percolation test. All perc tests for septic systems must abide by strict guidelines for permit processing.

• Size of testing field. When performing a percolation test on your soil, more holes equals better accuracy with test results. In most cases, at least two holes are dug with at least 40 feet of space between each one. Sometimes a hole can be small and dug by hand with a shovel. Other times, larger holes need to be dug with heavy equipment like excavators and backhoes. Professionals might charge a higher amount if they need to make more holes or use heavy equipment.
• Depth and width. The standard depth for most holes will be between 2 and 3 feet, but can reach up to 6 feet deep. The width starts at 6 inches, but can be as wide as 3 feet. The size of each hole impacts the cost because if the depth or width requires the use of a backhoe, the cost may be increased by $200 or more.
• Labor requirements. The number of people required to perform the test changes the cost. More people equals a higher labor price. Smaller properties, where fewer holes are dug, require fewer people than larger properties.
• Soil type. The type of soil will factor into the results of your perc test and where the test should be performed. Sandier soil with gravel absorbs water at a faster rate than clay-based soil or silt. Soil with hard rock is also not great for draining water. If the soil is difficult to excavate for testing purposes, the cost increases due to more labor hours and the need for heavy-duty equipment.

Process

To request a perc test, you’ll need to contact local or county health or environmental agencies. The agency will inform you if a government agent must perform the test or if you can hire an independent engineer. Before a perc test is ordered, an engineer will discuss any site preparation that is needed. A survey is typically done to make a determination of where the perc test holes should be placed. If a land survey is needed, the cost is approximately $575.

To begin a perc test, holes are dug into the soil of the proposed leach or drain field. After the holes are dug, any loosened soil is scraped away from the sides of each dig site. A professional fills the hole with gravel to a depth of about two inches.

It is then required to pre-soak the soil to mimic septic system saturation conditions. At a minimum, 12 inches of water should sit in the hole for at least four hours during the pre-soak phase. Clay soils need to soak for longer than sandier soils. Sandy soils are porous, which means water flows through it faster. In comparison, clay soils are denser with smaller pores, which make water flow through them at a slower rate. A return time is usually scheduled the next day for the technician to complete the perc test.

After pre-soaking, the actual testing procedure commences. To start, the holes are filled with water to cover the gravel with 6 inches of water. The technician may need to wait until the water is measuring exactly 6 inches before recording the depth. Measurements are then taken of the water every 15-30 minutes to determine how low the water is.

The percolation rate is calculated by the amount of water divided by the amount of time taken for the water to dissipate down into the subsoil. As an example, if the level of water dropped 1 inch every 30 minutes, the soil would have a percolation rate of 2 inches per hour.

Report

In most locations, a perc test report is required for the planning of a new or renovated septic system. Once finalized, the report is provided to the local health department, and becomes public record. A perc test report provides standard data such as testing date, location of the test, technician name, and under what conditions the perc test was performed.

A standard perc test report is two pages, with the first page featuring a graph with times of each reading, water depth, percolation rate, and any comments about the testing process from the examiner. The second page will feature a scaled drawing of the site plan. Within the report, it will list whether the site passed or failed the perc test. For the latter, your engineer may provide site recommendations, but that would appear on a different report, not the perc test results.

A good perc rate for a septic system is between 1 and 30 minutes per inch. Between 30 and 60 minutes per inch might require hydraulic analysis for installing a septic system. Anything under 1 minute per inch or over 60 minutes per inch is not an ideal perc rate.

Failed perc test

Soil fails a perc pest if it doesn’t drain the water at all or the water doesn’t drain fast enough. It can also fail if water drains too rapidly. A property with a low water table has a higher chance of passing a perc test than those with a high water table. High water table indicates the presence of water in the soil that doesn’t drain properly. The site may need to go through minor or major modifications to be able to pass another perc test ordered at a later date. If your soil fails a perc test, there are a few options you can try.

• Speak to a local health department representative. Ask for any records of perc tests that may have been done on the property before since they are public record. This helps you determine if the entire property was searched thoroughly for an ideal septic site.
• Dig holes in another area of your property where there are different soils. Soil with a different composition might provide better drainage. It is possible to get a pass result for the property, even if the perc test failed in a different area.
• Excavate deeper. Excavate deeper to get below the frost line if the perc test failed during the winter season. If perc testing is not done immediately after excavating, an insulating material like hay should be placed over the hole.
• Appeal the results. You may be able to appeal the results of the perc test depending on any special considerations set by your jurisdiction. As an example, if a county’s Department of Health rejects the perc test results, appeals can be made to the state Board of Health.
• Install a treatment system with the septic. With a treatment system between the drain field and septic tank, contaminants are filtered out. A sand filter septic treatment system will cost between $7,000 and $10,000.
• Install a larger septic tank. Larger tanks and pumping ² it out periodically to half the tank’s volume can accommodate higher water tables by reducing waste amounts that accumulate in the tank.
• Alternative septic systems. Alternative septic systems may be required in areas with high water tables. Consider getting a different kind of septic system, such as a mound system. A mound system requires a man-made mound as the drain field. The mound is created above the natural soil line and usually made with sand and gravel filler. Mound systems require a designated replacement area in case the system fails. Mound systems are more expensive with costs starting around $15,000 and require more maintenance to operate.

Labor

Sometimes a septic system designer can perform a perc test. However, often it is performed by a local government agent to confer adherence to environmental regulations. The agent can bring in other professionals such as engineers or contractors depending on needs. Independent contractors can be used in some cases, but the health department may require an official be present during the perc test to confirm the legitimacy of the results.

Depending on the soil and testing sites, the testing window is usually between one and four hours. This does not include preparations such as digging and pre-soaking. Prices vary by a municipality in each state, but the average labor cost is around $100 to $150 per hour. As an alternative, a flat fee of $300 or more may be charged by the technician performing the perc test.

Sometimes an engineer is needed to determine the height of the water table, as well as the septic designer to take measurements and help perform the test. Hiring an engineer or septic designer costs between $100 and $150 per hour. Engineers assist with issues like high water tables. Engineers can come up with strategies to de-water the leaching area. They achieve this by planning out placements for gravel-filled trenches and drain pipes. The pipes and trenches move water away from the drain field to make it possible for the property to pass the perc test.

Additional considerations and costs

• Permits. A permit is not required for a perc test, but a perc test is required to obtain a septic system permit.
• DIY. There are test kits that you buy at your local hardware store. Different areas for testing (lawn, garden, vegetable garden, etc.) require different kits. DIY is not appropriate for septic planning since perc test results will be denied by the health department if not done by a certified technician.
• Time of year. Perc tests are done seasonally—usually in the spring and summer. Performing a perc test in the winter will cost more since extra equipment is required.
• Renewal. Each health department has its own rules about how long perc tests are valid. Results of a perc test are generally valid from 2 to 5 years before renewal is needed. At this time, the health department reviews previous perc test results and will make a determination if additional testing is needed. Renewal helps government agencies confirm that the perc test abided by all the current regulations.
• Septic planning. The Health Department dictates rules on how to make a septic system, so you’ll need to comply with those requirements. As an example, some local and state governments don’t allow for garbage disposal units to be hooked into septic systems since the system may not have the ability to handle the excess waste.
• Slope. The soil should always drain water away from the house and not towards it, therefore, the gradient of the land also determines where the perc test should be completed.
• Lab testing. The fastest way to get results is on-site testing. In some instances, however, a lab can test the soil for content. This type of perc testing is more commonly seen in the agricultural industry rather than for septic planning purposes. Depending on how busy the lab is at the time they receive your sample, turnaround for results may range from 7 to 10 days. Rush service is usually available. The average cost of laboratory soil testing is $1,200.

Remodeling Terms Cheat Sheet

² Pumping: A device used to move air, liquid, or gas by mechanical means