Contractors in Colorado will get more work from the late passage of a $567-million bond issue in Jefferson County, the state’s second-largest school district. Measure 5B, which was losing by more than 9,000 votes on election night, crept back to win by only 1,537 votes after late ballots and overseas mail-ins were counted. That margin is just above the threshold that would have triggered a recount. Most of the funds, nearly 60%, will be used to upgrade safety and security systems to protect the district’s 86,000 students. Another 20% of the money will go toward classroom upgrades, major renovations and additions. The district has experienced three mass shootings across its 155 schools, including the killing of 12 students and one teacher at Columbine High School nearly 20 years ago.