A sludge survey of both the anaerobic and aerobic lagoons was undertaken by Johns Environmental. This revealed that the anaerobic lagoon has lost approximately 40% (9.3ML), and the aerobic lagoon 27% (54ML) of their working volume. The loss is due to a combination of a surface crust (especially in the anaerobic lagoon) and an accumulation of a sludge layer in both ponds.
In the anaerobic lagoon, the crust and sludge layers appear to comprise a combination of paunch solids and oil and grease. This suggests that the primary treatment system is not working properly to capture excess paunch solids. The conclusion of the sludge survey was that the anaerobic pond has a limited remaining lifetime, and if it is not replaced shortly even greater quantities of solids may be carried over into the aerobic pond, further reducing its remaining lifetime. It is recommended that the anaerobic lagoon be replaced as part of Stage 2 of this project.