Hoover Dam is currently the Reclamation facility least-affected by quagga mussels on the lower Colorado River. However, colonization is occurring -- inspections conducted during the 2007-2008 maintenance season revealed mussel populations in some of the smaller water supply pipes used to cool generators, compressors, transformers and other equipment at the dam. In addition, colonization on some of the dam’s exterior surfaces, such as intake tower walls, has also increased.

The colonization that has occurred to date has not affected the dam’s power generation or water delivery functions, or required any extraordinary maintenance. To reduce the chances that increased and continuous maintenance will be needed to deal with the mussel infestation, Reclamation has developed and is implementing a proactive quagga mussel control plan.

The first priority of this plan is to increase monitoring activities to pinpoint where colonization is occurring and at what rate. Accordingly, Reclamation has:

• installed a substrate system on the intake towers to show how fast colonization is occurring;
• increased underwater inspections of exterior surfaces from semi-annually to monthly; and
• installed bio-boxes on two cooling water lines that have already shown indications of colonization.

The next priority is to, within the next year, purchase and install a strainer and ultra-violet system or a 50-micron Self-Cleaning Filter on the dam’s domestic water supply line, which delivers drinking water to the facility and visitor center. The Self-Cleaning Filter has been installed and is currently being tested at Parker Dam.

These control measures would also be installed on systems that supply cooling water to generator bearings, heat exchangers, air compressors, equipment in elevator machine rooms, office ceiling coolers and other, similar equipment.

Reclamation is also considering several potential long-term control measures that could be implemented at Hoover Dam. These include:

• Using water from the tailbay (the area below the dam where water exits the generators) for the dam’s cooling water supply. The cooling water for the dam’s systems now comes directly from Lake Mead. But the mussel population below the dam is much lower than it is in Lake Mead, above the dam. This system could be designed and built with specific barriers -- small strainers, self-cleaning filters, ultra-violet light systems -- to treat the water before it is delivered to operating equipment inside the powerplant.

• Using coated metals, anti-fouling metal coatings, or foul release coatings to deter or prevent the mussels from attaching to specific surfaces. Reclamation is currently conducting a study of the effectiveness of various types of metal coatings at Lake Havasu, on the upstream side of Parker Dam.

• Testing a freshwater bacterium that contains a toxin known to destroy the digestive system of zebra mussels, a close cousin of the quagga, by giving it something akin to a fatal bleeding ulcer. The bacterium, which does not harm other aquatic life, is being tested at Hoover Dam to determine its effectiveness as a mussel control agent. The test is being coordinated by Reclamation’s Research and Development office in Denver, Colo.