Walsh Construction's work included improvements to the odor control and HVAC systems at the Nut Island Headworks. Walsh replaced carbon treatment units, fans, dampers, chemical systems and controls, as well as air handling units, boilers and unit heaters. Crews also installed new ductwork, removed and repaired an underground roof; installed roof hatches; replaced the emergency spillway isolation gates; installed a new egress stairway along with miscellaneous site work.