WATCH: Journey into the cavern...

Wednesday 17 May 2023

Express was recently given the opportunity to explore the large underground void beneath Snow Hill known as the cavern... Come take a look...

Measuring 38 metres tall, 80 metres long and 17 metres wide, the cavern is used as a storage tank for overflows of sewage and water from the main sewerage system during storms - preventing it from spilling out into St. Aubin’s Bay.

Watch: The journey from the cavern entrance in Snow Hill car park into the main chamber...

"The reason for the cavern is to take flows, predominantly from the town area, when we get wet weather storm events," Duncan Berry, the Head of Liquid Waste Management at IHE, explained.

"When it rains the town system is what we call a combined sewer, so you get clean water and dirty water into one sewer and we try to pump that to Bellozanne for treatment. When we get the rainfall it becomes too much and, before the cavern, that [sewage] would have gone to sea."

He continued: "With the cavern in place, those stormflows flow into the cavern and fill it up. When the flows die down, we empty the cavern out back into the sewer system and it will travel back to Bellozanne for full treatment before discharge into the sea.

"It's protecting the aquatic environment, all of the swimmers, water users and marine life."

Pictured: The cavern is 80 metres long.

The cavern can hold approximately 25,000 cubic metres of sewage overflows and water and is cleaned annually.

Mr Berry said: "If we don't clean it out, it would become unusable - the pumps would get choked.

"It's taken approximately three weeks to clean the cavern, it finished on Friday and it's back into action [today]. So if we do get a storm event it is ready to take that stormflow."