Housing Association Site, Cornwall

An effervescent (oily) and rusty sheen was noted on water within initial foundation excavations and concern was raised about possible heavy contamination from a former nearby railway siding.

A walkover survey and geological knowledge identified the effervescent and rusty sheen as being of natural origin. Some bacteria (Leptothrix discophora) that live in waterlogged places get their energy from iron and manganese, and, as these harmless bacteria grow and decompose, the iron may appear oily or form red or orange films, fluffs, and coatings. It was also noted that a mining report stated that mines in the area were mainly mined for manganese, i.e. the underlying geology is rich in manganese. Therefore, no remedial measures were required.

This was confirmed by contamination laboratory testing.

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Housing Association Site, Cornwall image

Housing Association Site, Cornwall image