MIDDLETOWN, Conn. -- The massive cleanup of an oil spill has been under way at the Connecticut Valley Hospital campus in Middletown for about a month and a half.

The cleanup came after the discovery of thousands of gallons of fuel oil missing from an underground storage tank. The bad news, officials said, is the leak sits near an underground stream.

The state, which owns CVH, said the good news is the No. 6 oil that leaked is thicker than molasses. It said it does not believe the oil spread far.

The state said one of three rarely used underground storage tanks at CVH had a leak, and it’s estimated that 3,000 to 6,000 gallons of oil spread into the soil.

Since late October, crews have been working on removing the tanks and oil-soaked dirt.

Officials said there will be a cost to the project, but the right steps are being taken, which is what is needed. They said the cost could be tens of thousands of dollars.

State and town officials said they don’t believe the oil has impacted a public water supply nearby, but a study is being done to confirm that belief.

However, Eyewitness News was sent a photograph last month from one of the sources who tipped the station off to the problem. The photograph shows a stream just downhill from the hospital, and some of the rocks appear to have oil on them. There’s also a sheen in parts of the water.

The same source also took a picture around the same time of the oil-soaked ground where the tanks once sat.

The tank that leaked was 10 years old, and the state said it's warranteed for 30 years.