Absorption disposal systems must not be used on land where the following conditions exist:

• Slope instability
• Loose sand
• Clay soils that collapse in contact with water
• Soils with a hydraulic conductivity of less than 0.36 mm/hr,
• Rock and shale
• Slopes greater than 15% (steep grades increase the chance of landslip and water seepage from the subgrade to the lower areas of the site reducing the amount of water infiltration)
• Extensively paved areas such as driveways.

As a guide, sand has a hydraulic conductivity of >180 mm/hr, sandy clay 180–36 mm/hr, medium clay 36–3.6 mm/hr, reactive clay 3.6‑0.036 mm/hr.