Off and on since last fall, the residents on the sloping street in Southeast Washington lived with the smell of gasoline.

Sometimes it was in the toilet bowl, sometimes in the kitchen sink. Carolynette Waddell remembers it was bad in September, so bad the neighbors began talking about it.

Last week, officials said, the longstanding problem was aggravated during a test for a suspected leak in a fuel tank beneath the 7th Police District station. A city worker mistakenly refilled the tank with gasoline instead of a harmless testing fluid. As a result, almost 3,000 gallons of gasoline leaked into the soil, the sewer system and an underground stream.

The spill resulted in a two-day evacuation of 54 families on the 3000 block of 30th Street SE. They were allowed back Friday, although they still do not have gas or hot water.

What is worse is the nagging doubt among residents that the problem is over. Although the city has assured them that their homes are safe, tests still have to be conducted to determine to what extent, if any, the soil beneath the properties has been contaminated.

Based on extensive analysis last week, officials concluded that some of the gasoline went into a stream beneath the station. The contaminated water flowed east and then south.

Some of the gasoline seeped into the sewer system, but officials said that resulted in little damage because it was immediately diluted. None of the gasoline went into the storm drain, which empties into the Potomac River.

Engineers believe the spill was caused by two factors: a structural flaw in the two-year-old fiber glass tank and poor judgment by a Public Works Department employee.

Edward F. McManus, a Public Works Department administrator, said the 10,000-gallon tank was emptied in May because officials began to suspect it had something to do with the gasoline smell.

To test the tank, a company was hired to pump in a harmless liquid and watch to see whether it leaked out. But on June 22, a Public Works employee made a critical mistake by allowing the tank to be filled with gasoline because water would "contaminate it," McManus said.

The leak is in the seam. Apparently the pressure from the full tank forced almost 3,000 gallons out by Tuesday, when McManus realized the error and ordered the tank emptied.

By 3:30 p.m. Wednesday, police ordered Waddell and her children out of their basement apartment. Shortly after, residents in five buildings on the block were told to leave.

The tank is under warranty. If an analysis proves there was a structural flaw, the city may not have to bear the cost of the cleanup, which McManus said could amount to "tens of thousands of dollars."