The McKay Bypass Extension project was completed on July 30, 1999. The project included burial of 3,400 feet of 48-inch high-density polyethylene pipe and construction of a concrete diversion structure across the McKay Bypass Ditch. The pipeline allows the City of Broomfield to transport newly acquired water from the South Boulder Diversion Canal, across the northern Rocky Flats Buffer Zone and directly into Great Western Reservoir, east of the Site.

The new McKay Bypass Extension circumvents Walnut Creek, which runs through the Site, and eliminates co-mingling the City of Broomfield's ’s irrigation water with releases from Rocky Flats' stormwater detention ponds. The concrete diversion structure routes Broomfield's water into the pipeline, which runs east across the northeast Buffer zone, under Indiana Street and south to Walnut Creek on the east side of Indiana Street. The project was constructed in conjunction with the City of Broomfield, which completed the boring under Indiana Street and the pipeline to the east of Indiana Street.

The Kaiser-Hill team constructed the on-site portion of the project without a single lost work day or first aid case.