New wells to protect aquifer: Additional water needs won't compromise source
By Laura Matthews • Pacific Sunday News • January 10, 2010
Water quality remains one of the top priorities for utility officials as the island inches closer to the military buildup.
Local water officials and the military agree there is enough fresh water underground to support the military's additional needs, estimated at 13 million more gallons per day. The question is where to place new wells on military land to prevent salt water from contaminating fresh water, similar to what happened in Saipan.
Guam's underground water supply is made up of limestone soaked with fresh water, and in some places it sits on top of limestone soaked with salt water. It is not a single aquifer, but is divided into six "sub-basins" separated by walls of volcanic rock.
Simon Sanchez, chairman of the Consolidated Commission on Utilities, said there are about 130 water wells on Guam, and between 30 and 40 additional wells will be added to deal with the water demands of increases to both the military and civilian populations.
The draft Environmental Impact Statement for the military buildup states the military could install as many as 22 wells on the island, on existing military property over the northern aquifer. The military and the local government operate separate water systems, with the ability to share water.
The military intends to drill pilot test wells soon "to verify the production capacity" of the wells, which the draft EIS said could change the proposed locations of the wells.
The location and depth of the new wells is important.
"The trick is to sink the well to the appropriate depth so that you tap into the fresh water and not go beyond that into the seawater," said Gary Denton, director of the University of Guam's Water and Environmental Research Institute of the Western Pacific. "And that is relatively easy to do, depending on the thickness of the lens."
The lens of fresh water is thickest in the middle of the aquifer, he added.
"You want to look for the best parts of the aquifer because that is where you put the wells," Sanchez said. "So we are mapping out where to put the additional wells in order to protect the aquifer's sustainable yield and to avoid saltwater intrusion, which affects taste and quality."
Guam Waterworks Authority spokeswoman Heidi Ballendorf said, depending on the size of the well, the water agency can pump anywhere from 150 gallons per minute to 250 gallons per minute.
Pumping water out of the ground influences the movement of water in surrounding rock, and it is important to space wells far enough apart to prevent those areas from overlapping, according to Brett Railey, supervising engineer for the GWA water system.
Pumping too much fresh water too quickly from the ground can cause salt water to rise upward into the zone of fresh water, he said, and it takes a long time for the system to correct itself.
The ability of a well to produce fresh water is not easy to quantify, he said -- some are consistent producers of fresh water, while others have inconsistent chloride levels -- which is why regular testing is important.
"If you overpump the aquifer, as water leaves the aquifer, ocean water takes its place and you begin to bring salt into the natural aquifer and you don't want to do it," Sanchez said. "That's what happened in Saipan and we don't want that to happen on Guam. Guam has avoided it all this time, because we are nowhere near the full capacity of the aquifer. There is plenty of room left."
There already is a safety net to identify possible saltwater contamination at the island's water wells before it becomes a problem.
Railey said all water wells on Guam are tested quarterly for chloride, and the results are sent to the Guam Environmental Protection Agency, which won't allow salt levels to exceed 250 parts per million.
Depending on the test results, the amount of water being drawn from wells can be scaled back or stopped in order to reduce salt levels, he said.
"The reason we test the wells on a periodic basis is to make sure we don't overpump," Sanchez said, adding that Guam gets a lot of rain, so the aquifer is always being refilled.
The aquifer can produce as much as 80 million gallons of water a day, Sanchez said, and the military buildup would bring the island's total water demand to about 65 million gallons a day.
Guam also needs to implement a comprehensive water management program, said David Bice, Executive Director of the Joint Guam Program Office.
"What I am concerned about for Guam is that there is not a comprehensive water management program to ensure that we -- all of us -- are not overpumping one sector or another of the aquifer," Bice said.
No matter how many wells are evenly spread across the island, if too much water is pulled out of a few wells, it could create the same problems that would come from too few wells, Bice said.
Bice said he once was in charge of a large military base in southern California, which, like Guam, has a limited water supply and a growing population.
The entire area was guided by a water management program that ensured water wells were placed correctly and not overused, he said.
Bice said the military and the Consolidated Commission on Utilities have agreed to collaborate to create a comprehensive water management program here, but he couldn't say when it would be ready.
"We are going to get that going," Bice said.