Columbia Gas has fallen behind in one part of its plan to restore gas service to customers in the Merrimack Valley.

The company has been working to ready properties in Lawrence, Andover and North Andover for gas service restoration, which includes replacing damaged appliances and completing safety inspections. Close to 700 customers' properties are ready to have service restored, but about 7,000 customers are still waiting, more than a month after a series of explosions and fires rocked the three towns.

The utility company has broken down those thousands into weekly targets, leading up to a target date of Nov. 19 target for full restoration. These targets accelerate dramatically each week, and while the company was on track two weeks ago, last week it fell behind by about 500 customers.

The goals are set to double in the coming weeks, and the company would not tell WGBH News when or how it would make up this lag. In a statement, the company said it's been focusing on those most vulnerable to the cold, and that some customers will now have to wait longer for restoration.