Put simply, the interceptors are large tanks situated underground, which collect contaminated water and separate out oils and fuel, to prevent these substances from flowing into watercourses. When it rains, the surface water runs into the tanks and is allowed to settle. The fuels and oils in the water are collected and separated and then the clean water is allowed to flow out.
The harbour is situated on very dense sand and therefore, coffer dams were used to ensure that when the holes were dug, the walls didn't collapse. The tanks are situated well below sea-level and as the sea is not very far away, pumps had to be installed within the coffer dams to keep the water out. Three of the four interceptors have now been installed and the fourth is due to go in at the end of November.
