sentences:  In 1975 and 1976 the Department of Energy, at the insistence of the Treasury, considerably increased the charges for the use of Plumley.However, this resulted in three of the oil companies removing their product from the cavities leading to a dramatic drop in income.Around 1980 BNOC, who managed Plumley on behalf of the DoE, concluded that approximately £500,000 would need to be spent over a two-year period to keep it operational.