What Determines If My Property Can Be Permitted For A Septic System?
There are several factors that come into play in evaluating a property for a septic system. The main factor is the soil itself. To evaluate a property, at least two soil borings are done by DHEC staff in the area where the septic system is most likely to be located. The soil in the borings is closely examined before a determination is made on suitability. Let's look at the key soil properties:
- Color: Can tell how high the water table gets at the wettest time of year, regardless of when the boring is done. A field book of soil color chips is used in classifying the various soil colors.
- Texture: The varying amounts of sand-, silt-, and clay-sized particles that comprise the texture (sandy loam, silty clay loam, etc.) can tell how fast water will move through the soil layers, and can influence how well it treats the wastewater. The size of the drainfield is determined in part by the soil texture. For example, the higher the clay content, the more drainfield is needed; the higher the sand content, the less drainfield is needed. There are hand methods in the field used by experienced staff to classify texture.
- Structure: See diagram below for structure examples. The way the soil is held together in structural units determines how water moves through the soil and can affect the treatment efficiency of the soil. Blocky structure provides the best overall water movement and treatment efficiency and granular is second best. Platy and massive structures result in very poor water movement and treatment efficiency. Single-grained structure (which is closer to no structure) allows fast movement of water, but provides little treatment of the wastewater contaminants. Again, hand methods are used to classify structure.
The size of the house, more specifically the number of bedrooms, will determine what size septic tank is needed and what volume of wastewater to base the system design on. The wastewater volume, or hydraulic loading, is based on the estimated water use of two persons per bedroom per day of 120 gallons. Also, the septic tank must provide a two to three day retention time. So the septic system for a three bedroom house would be designed for a hydraulic load of 360 gallons per day and would require a 1000 gallon septic tank.
In addition, the location of surrounding features such as wells (including on neighboring properties), property lines, surface waters, buildings, drainage ditches, and the proposed house foot print, driveway, and outbuildings will determine if there is enough space for a proper septic system. The slope of the lot is also critical in determining if the property is suitabe and if so, how the system must be built.
The soil on the property determines how big the drainfield must be to accept the estimated hydraulic load and to provide good treatment of the wastewater pollutants. Finding enough suitable soil for the septic system takes priority over the location of the house and any outbuildings, and may even restrict the number of bedrooms allowed for the house. If the intended number of occupants is misrepresented in the permitting phase (e.g., underestimating the number of bedrooms on the permit application), the system could eventually become hydraulically overloaded and ultimately fail (see What Causes System Failure). Finally, protecting that soil from damage by being driven over or significantly altered before, during, and after construction, is very important to the overall "health" of the septic system.
