What is a soil scientist?
Why do I need a septic permit?
What is a “perc” test?
What is an onsite septic system?
Can I design my own septic system?
I’m thinking of buying a house—how can I find out about its septic
  system?
I want to buy some land—how can I find out about the soils and
  whether it will “perk”?
How do I get a soil test for my garden?

What is a soil scientist?

A soil scientist is a person with specialized knowledge of soil morphology (i.e., the arrangement and characteristics of the layers, or horizons, in a soil profile), soil chemistry, soil biology, and/or soil physics. This specialized knowledge has a variety of applications. Soil scientists often work in such agriculture related areas as soil fertility and soil/water relations (as in irrigation, for example) or in environmental science related areas such as land disposal of animal and municipal waste, onsite wastewater (septic systems, for example), mine spoil reclamation, and hazardous waste sites. In North Carolina and other states a professional license is required in order to practice soil science.

Why do I need a septic permit?

If you are planning to build in an area that is not served by public sewer, some form of onsite wastewater treatment and disposal is needed in order to prevent the spread of sewage-related diseases and to prevent pollution of nearby waterways. Often this will be a septic system, which is generally the cheapest way to treat and dispose of wastewater onsite. Other options might include water reuse, which will allow the wastewater to be used for industrial processes or for watering non-direct consumption crops, lawns and gardens, or land application of the waste. “Pump and haul” systems, in which wastewater is collected in a tank where it is picked up and taken away by a honey wagon, are not allowed in North Carolina. NC law requires that all permits regarding wastewater treatment and disposal be approved before construction begins.

Septic system permits in North Carolina are issued by the local health department and have three stages. The first stage is an “improvement permit”, which simply states that the lot has an adequate area of suitable soil to allow a septic system for a given design daily flow. It generally indicates the system type and location of the soil area. Next an “authorization to construct” or “AC” is issued. In the “AC” the location of the house, driveway and other proposed appurtenances such as pools or outbuildings are detailed as well as the layout of the septic system. An “AC” is required before construction can begin. The final stage is an “operating permit” or “OP”. This states that the system has been installed in accordance with the “AC”, and allows use of the septic system. An “OP” is required before a certificate of occupancy is issued by the building and inspections department.

What is a “perc” test?

Properly speaking, “perc” (or, “perk”) test is short for percolation test, in which a hole is dug in the ground and the rate at which water moves out of the hole and into the soil is measured. North Carolina no longer uses “perk” tests to determine the suitability of a soil for septic systems. Instead soil suitability and design parameters such as drainfield size and type are determined by a soil investigation. A soil investigation has several advantages over a “perk” test. The biggest advantage is that it is more reliable and allows a broader range of issues to be considered. For example, if done during a drought, a perk test might come out very differently than if it is done during a wet season—this is particularly true if there is a high water table or expansive clays. However, wet or dry, the appearance (or morphology) of the soil will show if there is a seasonal water table. Wet or dry, expansive clays can be identified by an experienced soil scientist or environmental health specialist.

There are situations where an accurate onsite measurement of the percolation rate, or permeability, of the soil is needed in addition to the soil investigation. In these cases a constant head permeameter can be used to measure permeability at different depths in the soil to aid in design.

What is an onsite septic system?

Onsite wastewater systems are just what they sound like. The wastewater generated on a site—whether it is a house, store, restaurant, institution or an industry—is treated and disposed of onsite rather than being transported to a central wastewater treatment plant. They generally, although not always, use the soils on the site to treat and/or dispose of the wastewater.

Septic systems are one type of onsite wastewater system. In a septic system the wastewater is first sent to a septic tank. The septic tank serves two functions. One, it allows the solid and liquid parts of the waste to be separated. The solids, or septage, have to be pumped out of the septic tank at regular intervals (every 3-5 years) and hauled away. The liquid part is called effluent and is discussed below. Two, the septic tank provides habitat for anaerobic bacteria which provide the first level of treatment of the wastewater. From the septic tank the effluent flows into the drainfield. The drainfield is a series of perforated pipes or chambers laid out on contour. The waste spreads through the pipes and drains slowly into the soil. The soil acts as a filter to clean the effluent. In addition, the soil below the pipes is a perfect medium to allow the growth of aerobic bacteria and other organisms. These organisms eat the waste, providing the final treatment. Once the wastewater has been treated, it continues to pass through the soil and eventually returns to the groundwater. Sometimes onsite wastewater treatment is called “water recycling” because it can help replenish the groundwater. There are a number of variations on the basic septic system described above—for example, a pump may be needed to move the effluent from the septic tank to the drainfield. In some cases pretreatment can be added to the system between the septic tank and the drainfield in order to allow use of soils that would otherwise not be suitable.

Other types of onsite wastewater systems include surface application and water reuse. Surface application of wastewater is generally only used on sites that are not suitable for septic systems and have a lot of available space because the setbacks from houses and property lines are very large. Water reuse is used where septic systems are not an option or where the landowners want to beneficially reuse their wastewater. In water reuse systems the water is treated to a tertiary level, and while it is not of drinking water quality, it is safe to apply to trafficked areas such as lawns, gardens or golf courses. With drought conditions in the Carolinas for the last few years this option has been increasing in popularity.

Can I design my own septic system?

NO! Because of the potential for the spread of disease and pollution of surface and ground water, septic systems must be designed by certified personnel that have been trained in septic system design. In North Carolina this includes environmental health specialists who work for local health departments, soil scientists, system designers and engineers. More complex systems may require both an engineer and a soil scientist.

I’m thinking of buying a house. — How can I find out about its septic system?

If the house you are looking at has an existing septic system the local health department should have a copy of the permit, which will have information about the location of the system and what type of system it is. You can contact the local health department by finding it in the phone book, typically under the county name as “Health Department” or “Environmental Health”. You can also find your local health department on the NCDENR Onsite Water Protection webpage at the following link: http://www.deh.enr.state.nc.us/ehs/images/ehsdir2000.PDF

The realtor or owner of the property you are looking at may also have information about the septic system or a copy of the permit.

I want to buy some land. — How can I find out about the soils and whether it will “perc”?

You can get preliminary information by going to the USDA Web Soil Survey and Soil Data Mart pages (links can be found under the “About Soils section of the “Resources” page of this website). You should be aware that the information available from these sources is very general. The county level soil surveys are done on small scale maps (for example, 1”=2000’) and can have inclusions, or dissimilar soil areas, of up to three acres.

For more detailed, site specific information, it is recommended that you either have a soil investigation done by a licensed soil scientist or apply for a septic system permit, depending on your time frame and the proposed use of the property. Getting this information before you buy a lot or a piece of property can save a lot of money and trouble.

How do I get a soil test for my garden?

The North Carolina Department of Agriculture’s soil lab will test your soil for a nominal fee. Boxes and instructions for collecting a soil sample can be found at your local Cooperative Extension office. To locate your local Cooperative Extension office, look in the phone book under “County Government”, “NC Cooperative Extension Service”. It can also be listed under “North Carolina State Government” as “Cooperative Extension Service”. Detailed instructions for collecting a soil sample can be found under the “About Soils and Agriculture” section of the “Resources” page of this website.