A thorough inspection of the water system at a facility should be undertaken prior to initiation of a monitoring and sampling program. Facility components susceptible to zebra mussel infestations are identified in subsequent chapters. The initial inspection is intended to determine existing infestation levels and map zebra mussel concentrations throughout the water system.
An underwater inspection by divers may initially be in order; however, dewatering or drylocking (in the case of floating plants) is preferable and can also be accomplished in conjunction with routine maintenance. Both types of inspection allow for the documentation of zebra mussel infestation levels. Professional divers are an important component of underwater inspection. Most commercial diving companies use underwater cameras for documenting conditions and work performance. Remotely operated underwater vehicles equipped with cameras can be used without divers. The larger commercial underwater inspection companies and some engineering companies supply these services.
Inspection of dewatered facilities and structures allows for a complete evaluation of zebra mussel infestations in conjunction with regular structural maintenance. Thorough cleaning and the addition, replacement, or repair of control mechanisms should be completed during dewatering. Recently settled mussels often are not apparent; however, they can be detected in the early stages in crevices or seams of concrete or steel structures when mussels are in the 1- to 4-mm size range.