Atkinson served as a subcontractor on the Connecting Tunnels and Gates Thornton Composite Reservoir project. The tunnels linked the existing underground water system to the Thornton Quarry through connecting tunnels and a gate shaft. The quarry acts as a temporary holding reservoir for wastewater prior to being treated and released into Lake Michigan.

Atkinson completed their scope of work in two phases. Phase One, which was completed in 18 months, consisted of the excavation of a 63-foot-diameter shaft through 14 feet of common overburden, as well as the drill and blast excavation of 335 feet of hard rock. This phase also included drill and blast excavation of a 215-linear-foot, 60-foot-wide by 40-foot-high bifurcation chamber, and 970 linear feet of a 33-foot-diameter horseshoe drift. The excavation was supported using a combination of resin-grouted dowels and rock bolts along with fiber-reinforced shotcrete.

During the second phase of the project, crews performed drill and blast excavation of a 50-foot by 33-foot-diameter tunnel connection and placed 70 feet of 30-foot-diameter reinforced concrete lining. Crews accessed Phase Two through an existing 340-foot-deep, 30-foot-diameter shaft.