Walsh Construction's work includes improvements to the odor control and HVAC systems at the Nut Island Headworks. Walsh is replacing carbon treatment units, fans, dampers, chemical systems and controls, as well as air handling units, boilers and unit heaters. Crews will also install new ductwork, remove and repair an underground roof; install of roof hatches; replace the emergency spillway isolation gates; install a new egress stairway along with miscellaneous site work.