The introduction of zebra mussels, Dreissena polymorpha, into North American fresh waters from Europe just over a decade ago and their spread through inland waters have resulted in a major economic impact to raw-water-dependent infrastructures, including power generation facilities. Because of the ability of these tiny mussels to quickly colonize hard substrates in high densities (e.g., tens of thousands per square meter), they have become a major macrofouler within North American freshwater conduits, causing damage and increased operating expenses worth hundreds of millions of dollars (O'Neill 1996, 1997).
Zebra mussels have caused expensive problems, blocking pipes that deliver drinking and process water to cities and factories and cooling water to power plants; attaching in enormous numbers to ship and boat hulls, marine structures and navigational buoys; and covering beaches with sharp-edged mussel shells and rotting mussel flesh. In the United States, congressional researchers estimated the mussel cost the power industry alone $3.1 billion in the 1993-1999 period, with its impact on industries, businesses, and communities over $5 billion (New York Sea Grant 1994a). In Canada, Ontario Hydro has reported zebra mussel impacts of $376,000 annually per generating station (New York Sea Grant 1994b).
The zebra mussel, though small in size, has become the most troublesome freshwater biofouling organism in North America. Once a single mussel is in place, others settle on or around it. The colonization increases until a pipe or an opening is partially or completely blocked. A piece of equipment may become fouled or so encrusted with mussels that it becomes unusable, and costly control measures must be implemented. Even if mussels are killed by a chemical or thermal control technique, the shells and decaying tissues may remain behind causing additional problems. Prevention is the best weapon against initial infestation, for once a water body is infested with a zebra mussel population, there is virtually no eliminating it. For further information on prevention, see the Slowing the Spread of the Zebra Mussel section.
Virtually any submerged area with a moderate flow rate that draws water from an infested water source is vulnerable to colonization. This is especially true of areas that offer protection to small mussels, such as crevices or seams. Intake screens, for example, are common settlement areas and are often coated with clumps or druses of mussels. The presence of dislodged shells in the discharge of a facility's raw well or forbay is a common first indicator of the presence of zebra mussels in the raw water main. Facilities may also experience a noticeable decrease in head pressure. Most facilities have numerous components subject to severe biofouling, including:
The impacts associated with zebra mussel infestation of a facility are: the loss of intake head as mussels line the area and restrict and interfere with laminar flow, the obstruction of valves and other components, problems related to the decay of mussel tissue, the buildup of methane gas, and an increase in the corrosion of colonized areas.
For information on the management of the zebra mussel, see the Management and Control section.
Impacts on Private, Federal, State, and Municipal Facilities