Arlington County this year will begin a years-long effort to replace its aging underground storm-water system, a feat that will require digging up some streets to reach an extensive network of deteriorating or too-small pipes.

County staff are still working out the logistics of replacing 215 miles of the county’s 360-mile underground pipe network, which is reaching the end of its 50-year life, but plans have already been drawn up for some of the most critical projects.