What should be used to size the system in cases where unsuitable fill is removed?

Sizing the system when unsuitable fill is removed involves assessing the percolation rate or loading rate of the underlying soil. Understanding the percolation rate is crucial because it determines how quickly water can pass through the soil, which directly influences the effectiveness of the absorption system.

By using the underlying soil's percolation rate or loading rate, designers can ensure that the system is appropriately sized to handle the effluent produced, preventing issues like over-saturation or failure of the system. This focus on the rate at which the underlying soil can absorb water helps in creating a system that functions efficiently and mitigates potential environmental impacts.

Other options do not provide the necessary basis for sizing the system in relation to the removal of unsuitable fill. For example, while a soil texture report provides important information about soil types, it does not offer the specific percolation rates needed for sizing. Similarly, site dimension regulations may address spatial requirements but do not consider the functional performance of the soil itself. Soil morphology analysis focuses on the physical characteristics of the soil profile, which may not correlate directly with its hydraulic performance critical for system sizing.