What Is a Perc Test?
A percolation test is a special soil test 1 that evaluates the soil’s ability to accommodate a septic system to dispose of sewage under the ground. A perc test evaluates both the soil and the site to determine whether a septic system can be installed on the property. The percolation rate refers to the soil absorption rate, or how quickly soil absorbs water. This is important because a septic system installed in a location with poor percolation could lead to significant sewer backup, soil degradation, and structural issues for homes and buildings, in addition to health and safety concerns.
Perc tests are a priority for homeowners or homebuyers looking to build or develop a piece of land. If there isn’t already a municipal sewer system in place and the property is in a semi-rural or rural location, then a perc test is a must-do before any major work can begin. A licensed contractor, excavator, or professional inspector conducts one of these tests by digging or drilling at least one hole, if not several, into the ground and pouring in water. This allows them to observe the rate at which water absorbs or percolates in the soil. Keep in mind the local health department is typically involved in managing these tests to ensure the health of the community. You will need proof of the results before installing a septic system.
How Does a Perc Test Work?
To begin a perc test, holes are dug into the soil of the proposed leach or drain field 2. 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 them faster. In comparison, clay soils are denser with smaller pores, making water flow through them at a slower rate. A return time is usually scheduled the next day for the technician to complete the procedure.
After pre-soaking, the actual testing procedure commences. To start, the holes are filled with water to cover the gravel with six inches of water. The technician may need to wait until the water is measuring exactly six inches before recording the depth. Measurements are then taken of the water every 15 to 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 into the subsoil. For example, if the water level dropped one inch every 30 minutes, the soil would have a percolation rate of two inches per hour.
Average Cost for a Perc Test by Land Size
When performing a percolation test on your soil, land size influences the number of holes needed and the cost you pay. In some situations, more holes equal more accurate test results. However, if you have smaller pieces of land, one hole may suffice. In most cases, though, at least two holes are dug with at least 40 feet of space between each one. More than two holes will be needed if you have land that exceeds two acres.
| Land Size (Acres) | Number Of Holes Needed | Average Cost |
|---|
| ¼ Acre | 1 | $150 - $250 |
| ½ Acre | 1 - 2 | $300 - $500 |
| ¾ Acre | 1 - 2 | $450 - $750 |
| 1 Acre | 2 | $600 - $900 |
| 2 Acres | 2 | $900 - $1,400 |
| 5 Acres | 3 | $1,100 - $2,000 |
Perc Test Cost by Hole Size
The standard depth for most holes will be between two and three feet but can reach up to six 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 a backhoe, the perc test cost may be increased by $200 or more. Here are some of the most common hole sizes and the cost of the perc test if two holes are dug on the property.
| Hole Size (Feet) | Price for Two Holes |
|---|
| 6 in. x 2 ft. | $675 - $800 |
| 1 ft. x 2 ft. | $725 - $875 |
| 2 ft. x 2 ft. | $800 - $950 |
| 2 ft. x 3 ft. | $900 - $1,200 |
| 3 ft. x 3 ft. | $1,100 - $1,450 |
| 3 ft. x 4 ft. | $1,175 - $1,550 |
| 3 ft. x 5 ft. | $1,250 - $1,800 |
| 3 ft. x 6 ft. | $1,400 - $2,000 |
Perc Test Labor Costs
Prices vary by municipality in each state, but the average labor cost for a land perc test is around $100 to $250 per hour. As an alternative, a flat fee of $300 or more may be charged by the technician performing the perc test.
Before it is ordered, an engineer will discuss any site preparation that is needed. A survey is typically done to decide where the holes should be placed. If a land survey is needed, the cost is approximately $600 on average.
Tests are usually performed by government agents, but they can also be done by engineers or independent contractors. They take one to three hours for undeveloped sites and one to two hours for a site that needs a septic system replacement. For complicated, larger sites, it may take up to six hours.
The number of people required to perform the test changes the cost. More people increase the cost of labor. Smaller properties, where fewer holes are dug, require fewer people than larger properties.
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 to undertake the percolation test procedure. If the government agent performs the test, he can bring in other professionals such as engineers or contractors. If the agent does not perform the test, independent contractors can be used, but the health department may require an official to be present during the test to confirm the legitimacy of the results.
Sometimes an engineer or septic system designer can perform a perc test. Engineers can also 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 test.
Why Do You Need a Perc Test?
A percolation test provides important information regarding soil drainage for any property owner. They are required for several purposes, such as septic tank installation, repair, replacement, infiltration basins, agricultural purposes, and flood risk detection.
Septic Tank Installation
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.
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.
Septic System Repair or Replacement
You will also need to have one of these tests done if you plan on repairing or replacing your septic system. Before you start these renovations, a professional needs to check that your soil can drain effectively and that you have a leach field.
Infiltration Basins
Infiltration basins may also need perc tests if you are redoing existing septic systems. An infiltration basin is a low-lying stretch of land that acts as a spot for water or waste runoff. An infiltration basin must drain effectively so that runoff drains into the soil rather than into nearby roadways or waterways, hence the need to perform a perc test.
Agricultural Purposes
Besides septic systems, they are also used for agricultural purposes. Knowing the drain rate of your soil helps determine what type of crops you can grow and where you should grow them. For example, potatoes require drier, more loamy soil than other vegetables and fruits that require moist soil. Therefore, potatoes require higher drainability 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.
Flood Risk Detection
Since a perc test determines the rate at which water absorbs into the soil, it can be valuable for determining the flood risk of the land around your home or property. If you live in an area that may see significant water from weather, it may be valuable to get a perc test and make sure that your yard has a lower flood risk. If you are looking to purchase a property, a poorly draining yard may be something you want to consider before deciding.
Percolation Test Report
In most locations, a perc test report is required to plan a new or renovated septic system, which is included in the price of the test. Once finalized, the report is provided to the local health department and becomes a 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 multiple pages. One page features a graph with times of each reading, water depth, percolation rate, and any comments about the testing process from the examiner. Other pages include a percolation test results table and a scaled drawing of the site plan. The test results table includes columns listing the results of each test. For each test, the table shows the percolation rate, the pre-percolation density, and the post-percolation density. The bottom of the table lists the mean and standard deviation of each test to provide the average results.
At the end of the report, it lists whether the site passed or failed the perc test. Your engineer may provide site recommendations. However, those appear on a different report, not in the results.
How Is Soil Permeability Measured?
Soil permeability is measured in MPI or minutes per inch. If your soil is below 5 MPI, then your soil has one of the highest permeability rates and may be supplemented through alternative systems such as pressure pre-treatment or adding dense soil near the trenches. Soil between 5 and 60 MPI falls in the ideal permeability range for septic systems, as it permits a conventional leach field and does not require alternative solutions. Soil in the 60 to 110 MPI range is slightly less permeable and may require enhanced treatments such as mound systems or pressurized dosing. Soil that is 120 MPI or higher has extremely low permeability and could be improved with specialized wastewater treatment in some cases.
| Permeability Level | Rate in Minutes per Inch (MPI) | Measures Needed for Optimum Permeability |
|---|
| Extremely Low | ≥120 | Specialized wastewater treatment |
| Low | 60 - 110 | Mound systems Pressurized dosing |
| Medium / Ideal | 5 - 60 | Pressure treatment |
| High | <5 | Adding dense soil near trenches |
Which Type of Soil Allows Water to Drain the Quickest?
The soil type factors into your perc test results and where the test should be performed. There are general permeability values for different soils you can expect if you know what kind of soil you have on your property. Most cities and rural towns have different regulations concerning these tests, so keep this in mind when planning for your property. In general, these ranges are used to evaluate soil permeability.
Clean gravel and sand have the most rapid permeability rates, around 1/2 minute per inch. A mix of sand, clay, and gravel is still permeable but not quite as much, around one to three cm/hour. Silt, clay, and stratified clay typically have moderate permeability lower than 1-2 minutes per inch but more than impermeable soil.
| Type of Soil | Permeability |
|---|
| Clay | Extremely low |
| Silty Clay | Low |
| Clay Loam | Medium to low |
| Loam | Medium |
| Sandy Loam | Medium to high |
| Sand | High |
Failed Perc Test
Every city and regional area should have specific perc standards that all properties need to meet as part of the 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. Some properties are more likely to fail a perc test, particularly those built on steep slopes. A property with a low water table has a higher chance of passing it than those with a high water table. A 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 pass another perc test ordered at a later date.
What to Do If Your Land Fails a 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 it than those with a high water table. A 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 pass another perc test ordered at a later date
If your soil fails a perc test, this doesn’t necessarily mean your soil is unusable or unhealthy. You can explore a few options further regarding the quality of your soil and how much it absorbs water. A second opinion can make a big difference to the eventual installation of a septic drain field on your property.
- Speak to a local health department representative. Ask for any records of previous perc tests that may have been done on the property. These documents are public records. 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 the test 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 depending on any special considerations set by your jurisdiction. For example, if a county’s Department of Health rejects the 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 filtered septic treatment system costs between $6,500 and $10,000.
- Install a larger septic tank. Larger tanks and pumping 3 them 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 or grazing fields.
- Check when failed perc tests occurred. Sometimes, a failed test may have something to do with when it occurred. In many locations, the water table is naturally higher or lower in certain parts of the year, usually with the biggest differences in winter and summer. The season can influence how quickly the soil drains. If your failed result came in one season, it might be better to try again in six months.
- Consider municipal water. Perc tests are important for rural properties where a septic system needs to be installed. These are areas where municipal water is not currently available, but that doesn’t mean it won’t be in the future. Consider how long you plan to leave your land undeveloped. If you don’t plan on building for several years and there’s a lot of development in the area, a municipal water and sewer system may be installed, and you won’t need to worry about putting in your own.
Septic System Alternatives Cost
There are several alternatives to traditional septic systems to consider if your property has poor percolation and you have already tried all the measures described above.
You may want to try sewer storage units. These storage tanks can be connected to the home’s plumbing and collect the wastewater until it can be picked up and emptied by the local waste management company.
If you have a small lot, utilizing plastic chamber leach fields is a great option. These chambers are placed in the ground so that wastewater can flow into them. There it is treated and flows back into the ground. Sand filter septic systems purify wastewater by using sand and oxygen in a sealed chamber. The chamber can be placed above or below the ground. They don’t require a leach field, making it a great option for eco-sensitive areas.
Another option is aerobic treatment systems, which use oxygen to purify the effluent before releasing it into the soil. This is a good option for small lots, areas with subpar soil conditions, or soil near bodies of water that may be more sensitive to pollution.
Drip irrigation, or drip distribution, is a method that distributes treated water over a large area of land. It does this by releasing small amounts of water through flexible tubing. Some wetland plants can also help with the filtration work through a constructed wetland system. After your wastewater goes through the initial septic system, it goes to a wetland plot for more purification.
Other solutions include mound systems and pressurized dosing. A mound system requires a man-made mound as the drain field. The mound is created above the natural soil line and is usually made with sand and gravel filler. Mound systems require a designated replacement area in case the system fails. Pressurized dosing is another popular option if your septic tank has failed. It distributes effluent, or liquid waste/sewage, across an area in an even measure by using pressure. This method only focuses on dispersing the effluent, so it can be combined with any other water treatment type.
| Traditional Septic System Alternative | Average Cost (Materials Only) |
|---|
| Storage Units | $300 - $900 |
| Plastic Chamber Leach Fields | $3,500 - $10,000 |
| Drip Irrigation | $4,000 - $10,000 |
| Pressurized Dosing | $5,000 - $7,000 |
| Sand Filters | $6,000 - $10,000 |
| Constructed Wetland Systems | $6,000 - $10,000 |
| Aerobic Treatment Systems | $10,000 - $20,000 |
| Mound Septic System | $10,000 - $20,000 |
How Long Is a Perc Test Good For?
Each health department has its own rules about how long perc tests are valid. Results are generally valid from two to five years before renewal is needed. At that time, the health department reviews previous perc test results and decides if additional testing is needed. Renewal helps government agencies confirm that the perc test abides by all the current regulations.
Perc Test Laws and Regulations
The laws surrounding perc tests and the requirements for conducting them vary widely from place to place. It is essential to contact your county health department to find out the local laws and regulations regarding septic installation and perc tests. Making sure you have all the information from the beginning reduces the chance of running into roadblocks after you get started.
Many counties require a health department employee to witness your perc test. That means that you will need to coordinate with both the soil professionals and the health department to find a time that works for everyone. Most counties also require the perc test to be performed by a licensed soil professional. Your health department may even have a list of approved professionals that they work with regularly.
Your county may have regulations regarding the number of tests that can be performed. Some places run two tests simultaneously in two places on the property, as soil composition and drainage can vary within a short distance. Other regions might require you to request a second test or even appeal the process if you fail your initial perc test.
Some counties require additional tests to be run on the property before approval. They may even require that extra supporting infrastructure be put in place. A common example is a leach field, a system of pipes that conducts waste away from your property. Some of these are required before the initial perc test, so be sure to inquire about the local regulations before you get started.
Unfortunately, perc tests need to be renewed every two to five years. The length of time between tests varies from county to county.
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. A certified technician must perform the perc test or the results will be denied by the health department.
- Septic planning. The Health Department dictates rules on planning and installing a septic system, so you’ll need to comply with those requirements. For example, some local and state governments don’t allow 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 toward it. The gradient of the land also determines where the perc test should be completed.
- Lab testing. The fastest way to get results is with 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 when they receive your sample, the turnaround for results may range from seven to ten days. Rush service is usually available. The average cost of laboratory soil testing is $1,200.
- Additional testing and packages. Perc tests are often included among other tests or services done by soil professionals, such as Septic Permit Packages and Subdivision Soil Reports. While you are looking into the requirements of your county, check to see if perc tests are a part of other services. This can save you time and money by scheduling them at the same time (and may be discounted as a package).
- Land use alternatives. You can do many things on your property that will not require a septic system, including horse stables, grazing fields, farmland, orchards, campgrounds, lumber yards, mining, and drilling.
FAQs
- What is a perc test when buying land?
A perc test is necessary as it helps determine the soil’s absorption rate. The percolation test factors into the design of a septic system for land or homes that are not connected to their local sewer system.
- What is a good perc rate for a septic system?
The preferred perc rate for a septic system is between 1 and 30 minutes per inch. For results between 30 and 60 minutes per inch, a hydraulic analysis may be needed for installing a septic system. Anything under one minute per inch or over 60 minutes per inch is not an ideal perc rate.
- How much does it cost to get a perc test?
The septic perc test cost ranges from $150 to $1,500 or higher depending on the condition and size of the land lot.
- How long does it take to do a perc test?
A perc test takes anywhere from 24 to 48 hours to perform from start to finish. The actual testing phase usually lasts no more than four hours. Prepping the soil takes longer than the test itself.
- How do you get a perc test?
Contact your local regulatory agencies, health department, or building inspectors to request a perc test. The requirements vary significantly based on your location. Each town has its own requirements for who should perform the perc test and when it can be scheduled.
- Can you do a perc test in the winter?
Perc tests are done seasonally, usually in the spring and summer. Performing one of these tests in the winter costs more since extra equipment is required. That is because the contractor, excavator, or inspector must drill through cold, if not frozen, ground. Percolation is naturally lower in the winter or after heavy rainfall when the soil has already absorbed a lot of water.
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