The Agency first received reports of oil - and oiled birds - on the estuary on 13 December. Investigating officers were unable, however, to trace the source of the spill until the following morning.
The oil was found to be leaking from a pipeline in Total’s Lindsey Oil Refinery in South Killingholme near Immingham. The 5mm hole had developed in the pipeline, which takes crude oil from a terminal, as a result of localised corrosion. The pipeline dates from 1972.
The oil had been leaking for two days and had entered a pit designed to hold such spills. The pit had overflowed into the South Killingholme drain, which runs for two miles into the South Killingholme Haven area.
"As soon as we were informed of the spill we did all we could to resolve it," said Jean-Pierre Poncin, the refinery’s general manager. "The only environmental impact was to the grass on the sides of the drain."
The leak itself was immediately stopped when it was discovered, Mr Poncin said. It was small enough to be blocked by a finger.
The drain’s sluice gate was immediately closed, and the oil it contained was mopped up using absorbent booms and vacuum tankers. The sides of the drain were dredged and the grass on the banks was cut to remove oil contamination.
The clean-up operation lasted one week and cost Total £300,000. Around 60,000 litres of crude oil were lost in the spill, Total estimates. The vacuum trucks recovered half of it.
Any oil that did get into the estuary is presumed to have dispersed naturally.
In spite of the operation’s success, questions have been raised about the refinery’s inspection programmes. Pipelines at the site are inspected only once every five years, although "visual inspections" occur once a week, according to Mr Poncin.
"We have to improve our inspection programme," he said. "The pipeline was last inspected five years ago, and that regime has been very reliable up until now. We will be reinforcing it." He would not say what this would involve.
The Environment Agency is currently investigating the incident. "We’re taking this seriously," said Phil Huskin, environmental management team manager. "Clearly it could have been a big problem; the estuary is a sensitive area, especially for birds."
When asked how Total would defend any prosecution brought by the Agency, Mr Poncin said: "I couldn’t plead not guilty, it was our oil. But we certainly did the most we could to limit environmental damage."