Wastewater—Sewage and Stormwater Management in Ashfall

• Sewers/Stormwater Drains
• Wastewater Treatment
• Keeping ash out
• Case Studies

Wastewater (sewage and stormwater) collection systems are vulnerable to damage from volcanic ash. Ash can block catchpits and sumps and drains and cause surface flooding. It can be very difficult to remove from underground drainage. It can also cause severe wear and tear to pump impellers. Ash can enter sewer lines where there is inflow or infiltration through illegal connections, cross connections, gully traps, manhole covers and cracks in sewer pipework. Cities that have combined sewer and stormwater collection systems are particularly vulnerable as ash will readily enter stormwater drains and can then cross over into sewer lines.

If ash enters wastewater treatment plants it can cause serious damage. In particular, mechanical pre-screening equipment (such as rotating or bar screens) is highly vulnerable to costly damage from ash-laden raw sewage. In some cases, the best option may be discharging untreated or partially treated sewage to the environment to protect the treatment plant.