Wastewater/ CALCULATOR
Septic solids service interval
Use measured sludge and scum layers to estimate when a chosen service threshold may be reached.
Measure or obtain the depth from the tank bottom to the normal liquid level.
Use a safe measurement made from outside the tank by a qualified person.
Use layer thickness, not the distance from the cover to the top of the layer.
Enter the threshold required by local guidance or the service provider; 33% is only an example.
Prefer the change between two comparable measurements. Do not invent a rate from tank age alone.
Allow time for seasonal access, booking and uncertainty.
Current combined solids depth
26.0 cm
Current share of liquid depth
21.7 %
Chosen service threshold depth
39.6 cm
Depth remaining to threshold
13.6 cm
Estimated time to threshold
20 months
Plan inspection or service within
17 months
Sludge and scum are combined only as a transparent screening indicator. The measured annual growth remains constant and the normal liquid depth is unchanged. Tank geometry, separate sludge and scum criteria, outlet clearance, occupancy changes, hydraulic faults, infiltration, local rules and service-provider requirements are excluded. A zero result means the chosen threshold is already reached or exceeded; it is not permission to delay action.