I don't think this was ever directly stated, rather various experts suggested that there was no design need for the waste pipe that ran out to sea at all and so began speculating on why it was there. then they found evidence of long term collection of cancer records in the NW that weren't conducted elsewhere and added 2 + 2.

Whether they made 4 or 5 I don't think was ever confirmed, but given the cavalier way the UK govt have treated the population as experimental animals on other occasions it wouldn't be remotely surprising.

keep to the Fen Causeway