For the second time since September 1999, a water hammer shut down a major water supply for San Juan, Puerto Rico.

Repair crews were already working on pipe sections damaged last fall when a violent water hammer struck the $340-million Superaqueduct, which will eventually provide an additional 100 million gallons per day of drinking water to Greater San Juan. This time an electrical variation in the pump station at the city's primary water source, Lake Carraizo reservoir, created a surge in the water line from the pumps to the water filtration plant. The resulting water hammer cracked a cast iron elbow joint near the system's outlet manifold on Jan. 21.

Officials from the Puerto Rico Aqueduct and Sewer Authority say about 75,000 households lost water for two days, and the same number lost water for four days. The lake supplies about 100 mgd of water to San Juan.

The elbow has a diameter of 16 in. on the pump side and widens to 24 in. on the manifold side. The water hammer caused a 180¯ crack in the pipe on the 24-in. side, according to Lucas Diaz, an official with CompaEia de Aguas de Puerto Rico, who spoke at a senate hearing. The local firm is a division of France's Vivendi Group, and has a maintenance and operation contract with PRASA.

The break flooded the pump station, partially submerged the pump motors and flooded the motor control panel. Crews repaired the elbow and replaced damaged motor control panel parts, but operations could not resume until the motors were dried in special ovens, Diaz said. CompaEia also added additional drains to the pump station floor.

The pumps and all the piping from the reservoir inlet to the outlet manifold are scheduled to be replaced under a $3.2-million contract awarded Jan. 4 to El Dorado Technical, San Juan. Six 22.5-mgd pumps will replace five existing 20-mgd pumps and a single 30-mgd pump there now.

The lake was completely dredged in 1999 to remove 5 million cubic meters of silt that had accumulated since the dam was built in 1952. Additional system improvements include a $16.7-million contract to Nielsen Dillingham Construction Co., San Diego, CA, to replace the dam's gates.