I’ve written a few articles in the past about septic systems. There’s some basic information in these articles, but I’ll review that again here in an effort to have a complete write-up on the topic. As a disclosure, I am trying to provide a guideline for my future customers and readers. However, it’s important to always follow up with the current regulations and restrictions in place at the local Public Health Department.
What is a Septic System?
It would be unrealistic for all areas to have access to infrastructure that would pump sewage and wastewater to a treatment facility. While municipal sewer connections are available throughout area, they are mostly restricted to areas within, or near city limits. Because an alternative method of disposal is needed, septic systems are the go-to method in the area. Essentially, these systems are self-contained wastewater treatment systems. Conventional systems consist of a septic tank followed by a drain field. Both liquids and solids flow into the tank where solids decomposed and liquids are discharged into a series of perforated pipes buried in a field (called a leach field) which slowly releases the effluent back into the soil.
It’s important to know that septic system requirements are not dictated locally. They are done so at the State level, with guidance from the DEQ. In order to install a septic system, or even to obtain a building permit, you must first obtain a permit from your local Health Department. In order to do that, the Health Department must understand the soil composition and water table for the proposed location of your septic system. This information is gathered by performing a site analysis.
A site analysis is performed by having a 10-foot deep hole dug in the approximate location of the proposed septic system. It is preferred that this hole is dug during the Spring when the water tables are at their highest point. Once the hole is in place, a Health Department official can make note of the soil composition and the depth of the water table. A general guideline for the allowance of a “Basic Subsurface Disposal System” is as follows:
A standard septic system can usually be installed if the separation from bottom of the leach field to the top water level is:
Sand: more than 6 feet of separation
Silt: more than 4 feet of separation
Clay: more than 3 feet of separation
It’s also important to note that the health department would prefer to perform these analyses during times of high water. However, if you are obtaining a permit in the fall months when the water table is low, it is possible that they can review nearby information and cross reference other site analysis that have been performed in the immediate area to approve a septic permit during these times. It is possible that the department could require the installation of a simple groundwater monitoring device such as a piezometer tube, or a tube with perforations that measures the level of the water during high-water months to determine the type of system required. Presumably, the department could issue play temporary permit to begin construction to determine the type of system required at a later date.
Standard Septic Systems
As you might have guessed, a basic septic system is usually the most cost-effective form of wastewater disposal. The vast majority of septic systems installed are this type. Throughout most of the region, the water table separation is ample enough to not require any sort of alternative system. There are a few circumstances and areas where the water table is high enough that an alternative system is required. These areas include low-lying areas near wetlands, areas along creeks and riverbanks, and so forth.
Alternative Septic Systems
In the event it is determined during your site analysis that a standard septic system is not suitable do to the soil composition, height of the water table, or both, a variety of alternative systems can be used, so long as they are approved by the state. There are both proprietary, and non-proprietary systems that are approved.
Proprietary Septic Systems
A proprietary septic system is basically a name brand system. At the time of this writing, it is my understanding that there are two proprietary septic systems that are approved with the State. These companies include Presby Environmental and Infiltrator Water Technologies. Both of these companies utilize proprietary materials and methods to enhance the capabilities of a standard system. In years past, other proprietary companies have been approved in the State for septic systems. Some of these required specific maintenance and or maintenance agreements. It is important to be wary of these systems. In the event they no longer service your area, it may be difficult to keep your system in compliance. It is my understanding that Presby nor Infiltrator Water Technologies’ ATL require a specific maintenance plan. It is also my understanding that both of these systems can be used as long as the water level separation (discussed in the site analysis section) is at least 12 inches. Another notable benefit is that neither of these systems require an electrical connection or the use of expensive pumps.
Other Alternative Septic Systems
There are other methods of wastewater disposal that can be used when needed. The state of Idaho has a technical guidance manual that is updated quarterly which includes all of the approved types of septic systems for wastewater disposal. There are more than two dozen types of approved methods, but below are a few of the more common types Alternative Septic Systems.
- Gravelless or Chamber Systems: a conventional septic system usually has gravel embedded around the perforated pipes to promote drainage. Gravelless Systems can you use plastic Chambers or pipe wrapped with media that can help distribute liquid into the soil. These systems can also be used in conjunction with Raised Mound systems in areas with high groundwater.
- Raised Mound Systems: Mound Systems are commonly referenced in our area when needed due to high water levels, and can be used to increase the distance between the drain field and the water level by building up the soil over the leach field and pumping the wastewater up, and into the raised area.
- Drip Distribution Systems: Drip Distribution Systems pump the liquids into the drain field in timed intervals as required by the soil type.
- Aerobic Treatment Units: ATUs introduce aeration into treatment tanks which increases natural bacterial activity helping decompose waste.
Other systems include tanks with sand filtration, tanks that promote evaporation as opposed to liquids being reabsorbed into the soil, and tanks that contain plants and other natural elements that help treat the wastewater.
As a final consideration when looking at your site plan, project, or even the purchase of land, it’s important to know that bodies of water can have an impact on the allowance of a septic system within a certain distance.
Septic Drain Field separation requirements (standard drainfield)
- Permanent or intermittent surface water (ie creek, river, etc) = 100 to 300 feet depending on soil type
- Temporary surface water (ie. irrigation canal) = 50-75 feet depending on soil type
Septic Tank separation requirements
- Permanent or intermittent surface water (ie creek, river, etc) = 50 feet.
- Temporary surface water (ie. irrigation canal) = 25 feet depending on soil type
There are also other separation requirements such as separation from your well, and separation from your property line.
State Resources and Manuals
State of Idaho DEQ Technical Guidance Manual
Useful TGM Notes:
- Section 3: Standard Subsurface Disposal System Design
- Section 4: Alternative Systems. This section is quite long, and describes each system in full. You could compile a list of approved systems from the table of contents. Each type of system is listed under the heading 4.#.
- Section 4.1.3: There is a table of compatible alternative systems in this section that I find very useful.
- Section 5.14: Proprietary Wastewater Treatment Products. Presby is contained in this list, but the Infiltrator ATL is not yet listed. I’ve attached the letter of approval for the ATL and another new proprietary system (Eljen GSF). Also attached are manuals for Presby and Infiltrator ATL.