Sludge accumulation in the first anaerobic pond at the Alsamra Wastewater Treatment Plant in Jordan has been monitored over a period of years. Homogeneous distribution of sludge over the pond bottom has not been achieved. The maximum amount of sludge has not accumulated near the inlet. This is due to scouring of the settled materials near the pond inlet and outlet by the high jet velocity of the incoming flow. A model has been developed to describe the volume of sludge accumulated (VAS) in the primary anaerobic pond. The model has been derived on the basis of the non-biodegradable materials in the settled sludge. VAS has been described in terms of the mass rates (F) of suspended solids and total BOD5 in the raw wastewater and an accumulated sludge coefficient (KAS).