Soil Evaluation, Site Assessment and Drainfield Sizing
Because the soil is the treatment plant, evaluating it correctly is the most consequential
technical judgement in onsite wastewater work. Everything downstream - system type, size, cost
and whether the site can be used at all - follows from it.
What the evaluation is looking for
- Texture - the proportions of sand, silt and clay, which largely set how fast the soil
accepts water.
- Structure - how particles are aggregated. Structure can make a fine-textured soil perform
far better than texture alone would predict, and its destruction by compaction or smearing can
ruin a good soil.
- Depth to the seasonal high water table.
- Depth to bedrock or to a restrictive layer - a hardpan, a dense till, a fragipan, a claypan.
- Slope, landscape position and evidence of past disturbance or fill.
Redoximorphi