When you're considering buying land, especially if you plan to build a home or install a septic system, you might come across the term "perc test." This term might sound a little technical if you're not familiar with it, but understanding what it is and why it matters can play a significant role in your decision-making process. In this blog, we’ll break down what perc testing is, how it works, and why it’s so important when buying land.
What Is a Perc Test?
A perc test, short for percolation test, is a procedure used to assess the ability of the soil on a piece of land to absorb and filter water. This test is crucial for determining whether or not a septic system can be installed on the property. In the past, filling a hole with water and timing it was the preferred method for completing a perc test. Nowadays, most perc tests are completed by using the Unified Soil Classification Method. This method involves characterizing the soil profile based on soil type, color, and texture. In both the old and new method, determining the seasonal high water table is paramount for a successful test.
In areas that aren't connected to a municipal sewer system, properties rely on septic systems to handle waste. A septic system uses soil to naturally filter and treat wastewater, so the soil’s absorption rate is a key factor in whether the system will work properly.
Perc Testing: What It Looks For and Why Soil Types Matter
In our area of Alabama, most of the perc tests are conducted between 30-60 inches deep. This depth is essential because it helps to determine the seasonal high water table—the highest level to which groundwater rises during the year. If the water table is too high, it can prevent a septic system from properly draining and filtering wastewater, as the system would be flooded or ineffective.
While measuring the perc rate (the rate at which water is absorbed into the soil) is a significant part of the test, it's not the only factor that matters. Soil type plays a huge role as well. Sandy soils, for example, tend to drain much faster than clay-heavy soils, which can absorb water very slowly. Understanding the soil composition helps determine the exact type of septic system that can be installed—if any. A traditional septic system works best in soil that allows for adequate drainage, but if the soil is too slow to absorb the water, an engineered septic system may be required.
Traditional Septic System vs. Engineered Septic System
A traditional septic system relies on natural soil to filter wastewater. The system consists of a septic tank that holds the waste and a drain field (also called a leach field) where the water is slowly filtered through the soil. For this system to function properly, the soil must have a good percolation rate, meaning it can absorb water at a certain speed, typically between 16 and 60 minutes per inch. Characteristics of a conventional septic system could include a septic tank (1,000 gallon minimum), solid pipe, drain field product, up to 12 inches of cover materials, and an effluent pump. Conventional septic systems can cost between $5,000-$7,000 locally.
However, not all properties pass the perc test required for a traditional septic system. Some lands have heavy clay soils, high water tables, or rocky terrain that prevent proper drainage. Furthermore, a small or subdivided parcel, an ineligible structure type, or too much “design effluent flow” could prevent a traditional septic system from passing the regulations of conventional septic systems.
In these cases, an engineered septic system may still be an option. These systems are designed to handle poor soil conditions by using advanced technologies such as aerobic treatment units, raised drain fields, or sand filtration systems. Although engineered systems can be more costly to install and maintain, they allow you to develop land that otherwise wouldn’t meet the requirements for a traditional septic system. Only a licensed engineer in the state of Alabama can complete an engineered system. Design costs for an engineered system could cost between $1,500 to $3,500, or even higher. Local installation costs for engineered systems have been known to cost over $20,000!
Preliminary Perc Test vs. Full Perc Test
When researching land for purchase, you may come across two types of soil tests: a preliminary perc test and a full perc test. While both serve to assess the soil’s suitability for a septic system, they differ in purpose and depth.
A preliminary perc test is usually a less formal, initial test conducted by a landowner or a professional to get a rough idea of the soil’s drainage capabilities. It involves digging a small hole and collecting data about the soil profile, but it doesn’t provide a permit to install a septic system. The field work should be completed to the current standards of the Alabama Department of Public Health, Onsite Sewage Treatment and Disposal rules in order to properly represent data likely to occur as a result of an official perc test. Generally, a preliminary perc test is accompanied by a certified letter (signed and sealed by a professional engineer, surveyor, soil scientist, or geologist). This letter can offer you the assurance that at the right time, your land will be suitable to obtain a permit. It should be noted that cutting or filling of the natural ground after the preliminary perc test is completed, will change the results. A conventional septic system cannot be placed within fill dirt brought in without the approval of a licensed engineer in the state of Alabama.
A full perc test, on the other hand, is a more detailed, regulated process typically required by local authorities or health departments before approval for septic system installation. It follows specific guidelines and is often necessary for obtaining building permits. While a preliminary test can give you a general idea of the land’s suitability, a full perc test provides the official results needed for compliance and decision-making, ensuring that the land meets all local standards for waste management. In order to obtain a full perc test, there are certain requirements that must be met prior to scheduling your perc test. The exact location, dimensions, and use of the structure must be determined before the field work. The area also must be cleared and free of debris. Furthermore, the location of the soil tests must be maintained from the time the test is completed all the way until the septic system is installed. Your drain field will run right through the perc testing holes. That means that if you move your structure after the test is completed, that the perc test will be null and void, and you will have to obtain a new one. Additionally, if the holes are covered, or lost, the test will be null and void, and you will have to obtain a new one. For these reasons, a preliminary perc test can be a good idea if you are in the early stages of development, but still want the assurance that a permit can be obtained. It is recommended that the property owner contact a professional before installing.
Why This Matters When Buying Land
The information you gathered from a local expert highlights how the seasonal high water table and soil composition play a crucial role in determining whether a property is suitable for septic installation. Even if a property doesn't pass a traditional perc test, it doesn't necessarily mean the land is unusable. With the right engineered septic system, you might still be able to build on the property and meet environmental and health standards.
In summary, perc testing is essential when buying land for building purposes, particularly if you plan to install a septic system. Understanding the soil type and perc rate will help you determine if a traditional septic system is feasible or if you’ll need to look into engineered options. Whether you're working with a traditional system or exploring more advanced solutions, having a clear understanding of the land’s soil and drainage capabilities will ensure that your investment is sound and that your septic system will work properly for years to come.
Who Can Perform a Perc Test for Me?
In the state of Alabama, a licensed engineer, surveyor, soil professional, or geologists can perform a perc test. These individuals have obtained at least a BS degree in their respective area of expertise. Concerning engineers specifically, they have also passed two eight-hour exams and have been credited with a minimum of 4 years of engineering experience. When you order your perc test, the professional will complete the field work and application on your behalf. All you should have to do is sign the application, attach your deed showing ownership of the property, and turn that packet into your local health department. In southeast Alabama, health departments sometimes charge $50-$75 to issue you a permit. Generally, this is the property owner’s responsibility. Remember, keep your perc holes marked, and don’t let them get covered.
Conclusion
Perc testing is a simple but essential part of the land-buying process, especially for properties where you plan to build a home or other structures that require wastewater treatment. Whether you're building a family home, a vacation cabin, or a business, understanding the results of a perc test ensures that your septic system will function properly and meet local environmental standards.
So, before you buy land, make sure to factor in the cost and process of a perc test. It could save you money, time, and headaches in the long run, giving you peace of mind knowing that the land you’re purchasing is suitable for your intended use.
Disclaimer: The information in this blog is based on our area in southeast Alabama. Regulations, requirements, and methods may vary based on your location.
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