Salt water takes two routes to aquifer

New research increases concerns about the speed of saltwater intrusion,
though modeled scenarios not so dire.

New research offers a fresh look at the salt water creeping into Georgia's groundwater and at what may happen if current pumping continues unabated.

Salt water is oozing through the previously pure aquifer not only laterally from Hilton Head Island, where a highly documented problem has been monitored for years, but also from the top down, according to Camille Ransom, a geologist with the South Carolina Department of Health and Environmental Control.

Much of the most heavily used area of the aquifer is overlain by marshes, tidal rivers and the ocean. Ransom's data shows the saltwater in those areas is moving downward through the clayey layer that was previously believed to protect the aquifer.

That layer, which geologists call a confining bed, is 71 percent sand.

"While it is a decent confining bed, it should come as no surprise that it is leaking," Ransom said.

Researchers used drill rigs to pull sausage-shaped samples of that confining layer from numerous test spots in and around Savannah. Then they squeezed water out of the samples.

"We've used pore water as a looking glass to look into the confining bed to see if (we) could see saltwater," he said.

Over and over again, it did.

Ransom presented his findings Tuesday to the Technical Advisory Committee of the Sound Science Initiative, a multimillion dollar research effort aimed at finding the causes of saltwater intrusion into the Upper Floridan Aquifer, the source of drinking water for most of coastal Georgia.

he committee also heard the results of computer modeling of the aquifer done by the United States Geological Survey. The models offered a series of "what if" scenarios including how water levels and salt concentration in the aquifer would be affected by a complete stoppage of pumping in Savannah or Hilton Head. Other scenarios mapped out the predicted results of increased water usage as expected by conservative and aggressive 30-year regional growth estimates.

The model showed that decreased pumping could raise water levels in the aquifer. For example, both the model and actual field data showed large increases in water levels when the Durango paper mill in St. Mary's shut down in 2002, decreasing daily water usage in the area by about 35 million gallons.

Surprisingly though, water usage didn't appear to dramatically affect the speed at which the plumes of saltwater near Hilton Head grew.

Even if the water usage stayed at its current restricted level for the 24 coastal Georgia counties, which caps usage at 1997 levels, those plumes would still be growing a century from now, according to John Clarke, a hydrogeologist and assistant director with the USGS.

Some committee members were concerned that Ransom's results, which point toward greater urgency in dealing with saltwater intrusion, were contradicted by these results from the model runs. Even though the current model accounts for some downward motion of saltwater, they called for an incorporation of Ransom's findings directly into the model, which USGS researchers said they could do.

Committee member Harry Jue, chief of Savannah's Water and Sewer Bureau, said Ransom's information increases Savannah's worries about salt water intrusion.

"In the 1990s we were talking about (saltwater intrusion in) hundreds of years, now it's expected in 75-80 years for certain areas offshore near Tybee," he said.

Bob Scanlon, the environmental affairs officer for the city of Savannah, agreed.

talking about, it could have salt water under it before the mortgage is paid off.

Because of these concerns and others about incomplete modeling of saltwater intrusion near Brunswick, the committee postponed giving its seal of approval to the research, which has already undergone scientific peer review. It plans to take up the issue again at its September meeting.

In the meantime, the Georgia Environmental Protection Division is planning public meetings beginning next week to disseminate the research findings. EPD had hoped for the committee's blessing, beforehand, but won't delay the meetings.

"The general public needs to have the opportunity to understand the scenarios produced, the results that have been produced," said EPD Director Carol Couch.