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Digging Deep: How Soil Evaluations Shape the Blueprint of Your Septic System

Soil Auger

Imagine building a house without checking the foundation—it wouldn’t stand a chance. The same goes for installing a septic system without a proper soil evaluation—it’s the cornerstone of a healthy, efficient, and long-lasting wastewater treatment for your home. Soil isn't just dirt; it's a living, breathing foundation that can vary¬†dramatically from one yard to the next. In this blog we'll uncover the layers of soil evaluation…because when it comes to septic systems, what’s beneath the surface really does matter.

Does designing a septic system require such detailed soil analysis? Let's explore the key factors that influence the design process in greater detail:

Key Factors for Site and Soil Evaluation

In North Carolina, as in many regions, six primary factors must be assessed to determine the feasibility of an on-site septic system.

  1. Slope and Landscape Position: The gradient and position of the land can affect surface runoff and the movement of effluents in the soil. For example, a steep slope can lead to rapid surface runoff, reducing the soil’s ability to absorb and treat wastewater, potentially causing erosion or system overflow. Conversely, flat areas may not allow for adequate surface runoff, leading to water saturation and possible system failure.
  2. Soil Morphological Characteristics: The physical and chemical properties of the soil determine how well it can filter and treat wastewater. Soil morphology, which includes the texture, structure, consistency, porosity, and color of the soil. A couple examples and comparisons may help to understand; soils with high sand content typically have great porosity and permeability which offer nice drainage, they may not however always allow sufficient treatment time, risking groundwater contamination. Clay soils, although slow to permit water passage, can be modified with advanced systems to ensure appropriate treatment.
  3. Soil Wetness: The presence of water within the soil profile can significantly influence the system's functionality, system placement and design. Soil wetness conditions can be caused seasonal high-water tables, seasonally saturated soil, or by lateral movement. Soils that remain wet for long periods may not have enough oxygen, which is necessary for the breakdown of effluents. Designing systems for such environments requires careful consideration to ensure that the effluent does not surface or create unhealthy conditions.
  4. Soil Depth: Adequate soil depth is required to treat wastewater before it reaches groundwater. The depth of the soil above the groundwater table or an impermeable layer (like rock or clay) is critical for the effective treatment of wastewater. Adequate soil depth allows for the complete biological treatment of effluent through filtration and microbial action before it reaches the groundwater. Shallow soils may need alternative or modified system designs, such as raised beds, to ensure proper treatment.
  5. Restrictive Horizons: Restrictive horizons are layers within the soil profile that impede water movement, such as hardpan, clay layers, or bedrock. These layers can prevent the downward movement of effluent, leading to saturation and potential system failure. Identifying these layers during the site evaluation is crucial as they may require modifications in system design or even suggest that a site is unsuitable for traditional septic systems.
  6. Available Space: Sufficient space is necessary to accommodate the septic system without impacting nearby water bodies or properties. Space must be adequate not only for the system itself but also for the repair area or replacement field, if necessary. Additionally, regulations typically require buffer zones between the septic system and property boundaries, water bodies, wells, and other sensitive areas to prevent contamination and ensure system access for maintenance.

The design of an on-site septic system is an intricate process that often goes beyond what most would initially imagine. Now you understand the elements and factors that go into soil evaluations. Keep an eye out for our upcoming blog where we'll unravel the different site classifications resulting from those soil evaluations.