What is a Perc test?

What is a Perc test, and why is this type of testing performed? This type of test is used when a septic system is proposed on any land, and it may also be called a perk test.

A percolation test will evaluate the absorption rate of the soil where the septic system will be installed, to ensure that the soil absorption is adequate for the septic system that will be placed on the land and the needed capacity of this system. Some properties have poor soil absorption, and clay or other types of extremely hard soil may not absorb enough water to allow a typical system and drain field to be used.

If you plan on adding a septic system on property then this testing will be required before you can go ahead with the system installation, because if the drain field does not drain properly the result could be a sewer backup and health code violation. A perc test will show whether or not the land is suitable for a typical septic system, and whether the soil will provide an effective filter for the wastewater.

You will be required to have this type of testing done if you're building a new structure and municipal septic services are not an option. In many areas this testing will not be needed, because the homes and other buildings are connected to the local municipal septic system so no additional installation or equipment will be required.

The Importance of a Perc Test

A perc test is one of the most important elements of construction, because the test results will determine what type of septic system you will need to use. A custom engineered septic system may be an option if a traditional system is not acceptable, but these are more expensive to purchase and to maintain in some cases.

When a percolation test is performed there must be someone from the County Health Department, to verify the test results and document the procedure. This step allows the local government an independent verification of the test, so that there is no question the soil has the ability to absorb and filter the wastewater effectively.

The perk test evaluates the soil where the drain field will be placed, to determine whether or not the soil has the ability to absorb and filter the water when it is released into the drain field. Soil which is loose or sandy is far superior for a drain field location, and the test will include having an authorized soil evaluator physically examine the soil.

The traditional perc test can take many hours to complete, and this is not ideal because you will pay for the time that the soil evaluator spends during the testing process. Having this test done is essential, because without the testing results you will not receive approval to install a septic system. This could result in the delay or even the cancellation of your project, and cost you a significant amount of time and money both.

Perc Test Results and What They Can Mean

If you have had a perc test done you obviously want to know the results as soon as possible, but it may take a few days for you to receive them. The soil evaluator who observes the test may be able to tell you if the results failed some of the time, but a successful test result can only come from the appropriate lab after the test data and information is submitted.

If the percolation test results fail then this means you can not install a typical septic system with a drain field on the land, and failure can be caused by a number of reasons. If your property fails this test it means that a typical septic system would not operate properly, and would be susceptible to septic problems, backups, and overflows.

A perk test should be performed very early in the project, and is often one of the very first steps taken before any construction is even started. This is important because if the land fails the test then other options may have to be used instead.

Knowing very early on in your project which septic system type you will be using will prevent any delays or problems later on. Waiting to have the perc test performed could end up costing you a lot of money because of changes and delays caused by the test results, so it is better to know as early as possible whether a drain field is an option.

Steps Involved With a Typical Perc Test Assignment

A perk test assignment will involve a number of different steps, and each is important. The steps involved will include:

  • Client Introduction - The first step in a perc test is an introduction between the land owner and the professional who will be performing the test. These tests are usually performed by a soil scientist, engineer, or land surveyor.

  • The Testing Is Scheduled - This test needs to be scheduled in advance with your local Health Department, because an official from their office will need to be present during the testing to verify that the recorded data and measurements are correct and that the test is performed properly.

  • Pre-Soaking Is Performed - The test holes used for the percolation test must be pre-soaked, and this is usually done overnight. The day before the test the holes are created and then filled with water, and also periodically refilled as the water level drops down.

  • Health Official Arrival - On the scheduled day and time the official from the Health Department will arrive to supervise the testing process. Before the arrival of this official the testing can not begin.

  • Test Pits Are Created - A perk test today includes test pits, which are dug with a backhoe and provide a lot of information for the test. The soil composition and layers are visible, and the high and low water table levels can be determined as well.

  • Visual Soil Inspection Is Performed - The official will perform a visual inspection of the soil using the test pits, and will record their observations on the test form. Sometimes it may become immediately apparent that the soil will not be adequate for a drain field.

  • Test Holes for Perc Test Are Created - Test holes are created in the location where the drain field will be located, and the number of holes used for this test will usually range from three to six. These holes must be a specific distance from the test pits, to ensure that the holes are in soil which has not been disturbed in any way.

  • Fine Sand or Gravel Is Added to the Test Holes - A layer of fine sand or gravel is added to the bottom of each test hole when the perc test starts, and this layer must be two inches deep. This will prevent any scouring and ensure accurate test results.

  • Water Is Poured Into The Test Holes - Water is added to each test hole to a depth of at least six to twelve inches over the sand or gravel layer in the hole, and then the monitoring will begin.

  • Water Level And Absorption Rate Are Measured And Recorded - The water level for each test hole is measured every ten minutes for a minimum of a one hour period, and the last three measurements taken should all be within one eighth of an inch of each other concerning the water drop amount for the test to be concluded and the percolation test to be completed.

  • Test Data Is Sent To The Lab And Analyzed - All of the data gathered during the perc test is sent to the lab at the Health Department, and this is analyzed closely so that the test results and final land conclusions can be determined.

  • Test Results And Final Land Conclusions Are Received - It will take a few days at least for the results of the perk test and the final land conclusion to be received from the Health Department, and if the land passed the testing you will also receive a permit to install the septic system and the project can be started. If the land fails the test then you will need to have an engineer design a custom system which meets approval.

Why Does A Perc Test Require Pre-Soaking?

Pre-soaking is an important part of the perc test, but why is this step performed? It is usually recommended that the test holes are pre-soaked for at least twelve hours, and this step is usually done overnight to make sure the soaking time is adequate.

The purpose of pre-soaking for a perk test is to create a stable test situation which mimics the conditions in an operating drain field. The soaking before the test allows for stable testing conditions which are as realistic as possible, and takes into account the fact that the ground in a drain field will not usually be dry but instead saturated.

There are some soil types which may not require pre-soaking, and this is true if the soil on your land is very loose or sandy. If the test holes empty rapidly even after filling the hole numerous times then pre-soaking may not be required for the percolation test.

Except in certain situations a perc test will require pre-soaking to get valid test results. If this step is not taken then the dry soil may alter the minute per inch reading of the test and throw the results off significantly.

Failing a Perc Test Does Not Mean an End to Your Construction Project

What happens if your land fails the perc test? In this scenario the test result failure is not the end of your construction project usually, it simply means that additional steps and measures must be taken to ensure a septic system that will work with your land and your septic needs.

Failing a percolation test means that a typical septic system and drain field will not work on your land, and that alternate options will need to be used instead. There are a number of alternatives that may be used for a septic system, depending on the specific land being assessed.

If your land has failed the perk test it can be due to several factors and there are alternatives available that will allow you to continue with the project with only a short delay, or none at all when these variables are known before the project is started in the construction phase.

If your land has failed the test then you will need to hire an engineer to develop a custom septic system engineered specifically for your land type and variables. Once the engineer has created the custom plans for the septic system then these plans must be approved by the Health Department.

Failing a Perc Test: What Are Your Alternative Options?

If the perc test results show that your land has failed this crucial test then there are other options available. Alternative septic systems can be found in a wide range and variety of types, and there is at least one that will be ideal for your land and soil characteristics.

Alternative septic system choices when the percolation test is failed can include:

  • Drip irrigation systems

  • Mound septic systems

  • Sand filter systems, both intermittent and recirculating

  • Aerobic treatment systems

  • Disinfection systems, which may use bleach, ultraviolet light, or chlorine to disinfect wastewater

  • The Advantex system

  • Evapotranspiration systems, which can include Evapotranspiration/Absorption systems

  • Glendon biofilter systems

Each of the alternative system types may work well with some land types but not so well with others. The best possible septic system to use can be different with each parcel of land, and you should be aware of all the alternatives and choices possible before you make a final decision on the system you will install.

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