A plummeting frost line has made as many as 20 percent of fire hydrants inoperable, prompting the Haines fire department to consider new response procedures.

Meanwhile, municipal water customers are advised to set aside some jugs of water for possible interruptions of service, and the Haines Borough has told some Skyline Estates residents to leave taps running to avoid freezing in lines that pass through rocky soil at higher elevations.

Prolonged cold and a dearth of insulating snowfall were blamed for conditions not seen here in recent memory.

“We’ve had ones freeze before, but we’ve never had a hydrant break. That’s pretty impressive,” said Scott Bradford, a water and sewer department worker for 22 years.

Freezing around fire hydrants was responsible for breaks in water lines near 1 Mile on March 10 and near the post office Sunday. The post office break interrupted water service downtown for about five hours, as crews worked to isolate the section.

Besides having to excavate frozen soil, Sunday’s fix was complicated by freezing of valves near the broken section. Workers fixing recent breaks have hit frozen ground as deep as five feet.

A midweek warming trend won’t alleviate all concerns, borough officials said. “The frost isn’t going away easily or quickly. Even if the temperature goes up into the forties, it just drives the frost deeper into the ground. People should have some water stored inside their home,” Bradford said.

Fireman Al Badgley said as many as 25 of 125 hydrants around town may not work due to cold. Hydrants in areas with a high water table have always been susceptible to freezing up, but others that “stub out” at dead ends, holding still water, also are freezing.

“The problem this year is very little snow and lots of cold weather for a long time. People’s (private) sewer lines are freezing,” Badgley said.

To work around frozen hydrants, the fire department can send its 4,000-gallon tanker to blazes, Badgley said. “For most house fires, four-thousand gallons is all the water you’d use.”

Other trucks also carry 500 gallons of water, he said. A worst-case scenario would be a large structure fire requiring entry by firefighters. “We wouldn’t have volumes of water potentially to do an interior attack.”

Borough facilities director Brad Maynard said more fire hydrant lines may burst with warmer temperatures. The pressure of frozen earth around frozen lines may be preventing ice inside the pipes from bursting them, Maynard said.

Once the earth warms and that equilibrium is lost, the ice trapped inside may break the pipes, he said.

Early this week, the temperature of water in mains in the Skyline Subdivision was 33 degrees F. The water leaves the treatment plant on FAA Road at 35.9 F.

Science instructor Pam Randles made weekly checks of a “frost tube” in the woods across from the school last year as part of an international research project. The water-filled tube, installed in 2009, extends one meter into the ground.

Water in the tube froze to a maximum depth of 11.5 centimeters at the end of January 2010, she said. At the end of January this year, the frozen water had dropped to 24 centimeters. This week it had frozen to 45.5 centimeters, Randles said.