Crews found a 4- foot crack in a massive Potomac water main Friday morning, and are struggling to drain a portion of the 96-inch pipe that failed, ushering in water restrictions for nearly 2 million residents in Montgomery and Prince George’s counties.

Workers are trying to drain at least half a million gallons of chlorinated water, but the liquid is seeping into the section that needs to be replaced, according to the Washington Suburban Sanitary Commission, the water agency for the two counties.

However, officials say they are still on track to complete the work  Monday, which would end water restrictions.