THE VIRGINIAN-PILOT
Copyright (c) 1996, Landmark Communications, Inc.
DATE: Monday, July 22, 1996 TAG: 9607220050
SECTION: LOCAL PAGE: B1 EDITION: FINAL
SOURCE: BY KAREN JOLLY DAVIS
STAFF WRITER
LENGTH: 120 lines
The experiment itself is elegantly simple. Ali Nowroozi, director of the geological sciences program at Old Dominion University, sticks four iron rods into the soil. He hooks them to a generator and volt meter, pulses 2,200 watts through the groundwater and measures how it conducts electricity.
Nowroozi's experiment suggests that there is a problem in Northampton County: Salt water is being drawn up into the Eastern Shore's drinking water, particularly around Cape Charles.
Other scientists, like Donna Richardson with the U.S. Geological Survey, have also predicted salt water intrusion in the Cape Charles area.
``That gives me confidence that the technique is maybe right,'' Nowroozi said.
Nowroozi's findings are important because the Eastern Shore's only drinking water comes from underground aquifers. Any talk of development, especially around Cape Charles, hinges on how much fresh water is available.
Salt water intrusion can happen wherever people pump water near the shoreline. Virginia Beach is a good example.
Tom Leahy, Lake Gaston Project manager, said the electrical sounding method was used to study the aquifers under Virginia Beach in the 1980s.
``It's an intelligent way to plot a salt water interface, particularly if you don't have a lot of money,'' said Leahy. ``You get a lot of data for your dollar.''
Groundwater under Virginia Beach is brackish below 200 feet - with some places saltier than seawater.
After testing 25 sites in his pilot project on the Eastern Shore, Nowroozi found that the depth of good water quality varied. On the average, said the study, potable water can be found in Northampton down to 332 feet. In the central area of the county, good water can be found as deep as 492 feet.
But a test site in Dalbys showed that salty water had risen to within 115 feet of the surface.
The Shore's upper aquifers are like a giant freshwater sponge ``floating'' in a sea of salt water. On either side are the Chesapeake Bay and Atlantic, and there is salty water in the deeper aquifers, as well.
Pumping fresh water from the upper aquifers can cause a pressure change that draws salty water toward the pump site. On the Eastern Shore, salt water can encroach from either shoreline or come up from underneath, which is called upconing.
That's what is happening in the Cape Charles area, said Nowroozi. Pumping by the town and businesses like Bayshore Concrete has caused an upconing of salty water.
Nowroozi's experiment can't tell whether Northampton's intrusion problem is getting worse.
``This is the point. Nobody has done it before,'' he said. The experiment would have to be repeated every few years to see if the numbers change.
In the short term, the salt water intrusion problem is irreversible, said Nowroozi. All that locals can do, he said, is not make it worse by more heavy pumping.
In Cape Charles, the salt water interface tested at 153 feet below ground level. In nearby Cherrystone, Nowroozi found salty water at 148 feet. And near the Machipongo Creek salt marsh, water quality deteriorated 66 feet below the surface.
The salt water-freshwater interface is an imaginary line at which drinkable and undrinkable water meet. In reality, the interface is a broad band where fresh water gradually becomes salty.
To map the salt water-freshwater interface Nowroozi used a method called ``Schlumberger resistivity soundings.'' This technique measures the difference in electrical resistance between fresh water and water in which substances like salt - or chemical contaminants - have been dissolved.
Scientists have also used it to map pollution leaking from landfills.
To take a sounding, Nowroozi and his students stuck four 2-foot iron rods into the earth. The outer two rods, called the current electrodes, were connected to a generator that pumped 2,200 watts of 16-amp electricity into the groundwater. A meter connected to the inner rods, called potential electrodes, measured differences in voltage.
Nowroozi repeated this procedure 16 times at each of the 25 test sites around Northampton. Each time, he changed the space between the electrodes. The distance between the current electrodes varied from about 3 to 1,312 feet. The distance between the potential electrodes varied from 7 inches to 98 feet.
When all the information was collected, he fed it into a computer and developed a picture of Northampton's underground water resources.
``The data as you find it is very reliable,'' said Nowroozi.
But, he said, the same information can be interpreted in different ways, and different geological formations can produce the same data. Interpreting the raw numbers so that they make sense, geologically, is the challenge, he said.
But the only other way to test the freshwater-salt water interface is by drilling a lot of wells and sampling the water.
``Obviously that would require a lot of work and a lot of cost,'' Nowroozi said.
The Northampton study was only a pilot project. It took a year, and was funded by $10,000 from the Virginia Water Resources Research Center at Virginia Tech, and $8,000 from the Eastern Shore Institute. So far, its findings have not been presented to local officials.
Nowroozi hopes to do soundings at 50 sites in Accomack County. And he recommends three times as many soundings, particularly in problem spots, before drawing carved-in-stone conclusions.
Of course, he needs funding for the studies.
Meanwhile, Nowroozi hesitates to say what he thinks policy-makers on the Eastern Shore should do about their water resources.
``I would be on the side of conserving the water,'' Nowroozi said. ILLUSTRATION: [Color Photo]
Researcher Ali Nowroozi focuses on Northampton County.
SALT WATER INTRUSION
Because groundwater is the Eastern Shore's only source of drinking
water, any influx of salt is alarming. Pumping too much groundwater
can draw salt water into natural underground storage areas called
aquifers. Salt water intrusion can happen wherever people pump water
near the shoreline, including Hampton Roads. All the deep wells in
Chesapeake are salty, and the groundwater under Virginia Beach is
brackish below 200 feet - with some places saltier than seawater.
But Hampton Roads has rivers, reservoirs and maybe a pipeline to
Lake Gaston to supply its drinking water. The Eastern Shore has no
such options.
LOCATING SALTWATER INTRUSION
GRAPHIC
JOHN EARLE
The Virginian-Pilot
SOURCE: Old Dominion University by CNB