Interstate 65 northbound between Fern Valley road and Grade Lane will remain under construction until mid-October.Work crews had planned to replace soft soil with a firm aggregate on the northern half of the project, but the same weak ground was found underneath I-65 farther south. Work has to be extended an additional seven days to give crews time to firm up the ground.Transportation Cabinet spokesperson Andrea Clifford says she's not sure how much this will add to the project's $28.7 million cost."[The cost] is based on the amount of material taken out and material put back in," she says. "There was a certain amount set up in the job for the northern half of the project, and it'll just be dependent upon the amount of material that gets used putting it back in in the southern half."The project's completion date is now October 14th. Current lane closures will remain in effect in the meantime.Crews will resurface the southbound lanes between the Watterson Expressway and Fern Valley Road once the northbound work is completed.