Maryland groundwater dated to more than 2 million years old

Finding stirs questions on water supply sustainability, geologists say

  • Jeff Raffensperger, hydrologist with the U.S. Geological Survey, co-authored part of a large study of groundwater supply in the coastal plain.
Jeff Raffensperger, hydrologist with the U.S. Geological… (Amy Davis, Baltimore Sun )
July 15, 2012|By Scott Dance, The Baltimore Sun

Most people throw out a jug of milk after a week or so. The oldest bottle of wine, on the other hand, is the most savored.

But what about water?

Some of what comes out of faucets in Annapolis, Leonardtown or Easton, it turns out, is older than the finest vintage — and the practice of dairy farming itself.

Glaciers that melted more than two million years ago deposited layers of sediment around what is now the Chesapeake Bay. Underground rivers run between those layers, tapped by wells and recharged by rainfall over time. The water flowing in them is tens of thousands to more than 2 million years old, according to recently published research, a fact that had been theorized but never proved.

The finding stacks Maryland aquifers up against the few to have been dated so old, including those underneath the Sahara Desert and the Australian outback. And it shows that a resource many take for granted cannot, in fact, be renewed on a human time scale, geologists said.

It also provides fodder for a shelved report urging a long-term plan to steward groundwater resources that are being pumped out far faster than they are being refilled. Even more pumping is expected in rural counties that are some of the state's fastest-growing, but there hasn't been political will to channel tens of millions of dollars needed to better evaluate the problem.

"I think we're going to wake up thirsty one day if we're not smarter," said Del. Galen Clagett, a Frederick County Democrat who sat on a state commission dedicated to groundwater issues.

While in much of the Baltimore area, drinking water is stored in reservoirs created by dammed rivers and streams, for the Coastal Plain to the east and south of the Interstate 95 corridor, aquifers are the primary source of water for more than 1 million people. The massive stores of water come to the surface near the fall line, roughly along the length of I-95, and deepen toward the southeast under the Chesapeake and Eastern Shore.

Layers of clay and sediment separate the aquifers, which vary in depth from as little as 20 feet to more than 1,000 feet underground. Where they meet the surface, what rainfall is absorbed into the ground slowly fills the aquifers. There are about six major systems containing 40 to 60 aquifers in the Coastal Plain, stretching across parts of Southern Maryland and the Eastern Shore.

"These layers were laid down millions of years ago by streams or estuaries," said Jack Eggleston, a geologist with the U.S. Geological Survey who co-wrote the water-dating study. "It's all a very tight package."

Demand for water deepens

Because many of the shallow aquifers have been increasingly tapped for decades, well-drillers have had to go deeper to find sources of water. Geologists have been able to measure how much the pumping has reduced the aquifers' water levels — as much as 6 inches per year in Anne Arundel County and 2 feet per year in St. Mary's County — but, they say, that isn't enough to determine the overall impact of pumping.

Geologists began taking samples from one of the deeper aquifers in recent years for data that will help evaluate that impact.

Known as the Upper Patapsco, the aquifer as of 2005 supplied more than 1 million gallons of water per day to residents and businesses around Arnold, and hundreds of thousands to those around Severna Park, Parole, Leonardtown, Easton and Cambridge. Rainfall recharges the Upper Patapsco along a strip a few miles across at its widest that stretches from Glen Burnie southwestward to Washington.

Geologists extracted a few gallons of water from the Upper Patapsco and measured Chlorine-36 and Helium-4 isotopes to reveal that along the western shore of the Chesapeake, the water was tens of thousands to hundreds of thousands of years old, while deeper, under the Eastern Shore, it was more than 2 million years old.

The information is a valuable piece of the puzzle when it comes to unearthing just what is happening to groundwater, said Jeff Raffensperger, a geologist with U.S. Geological Survey's Maryland office. The ultimate goal is to create a sophisticated model that shows not just how much water is in the aquifers, but how pumping is shifting it around and how quickly (or slowly) it is being recharged. The model could help inform decisions on development based on the estimated impact on groundwater.

"You're trying to, with this data, extrapolate over space and map these aquifers out," said Raffensperger. "The framework we have now, that will be the basis for this model."

Glacial pace for recommendations

The model came out of a 2008 study of what became known as the Wolman commission, a group former Gov. Robert L. Ehrlich Jr. called together after a 1999 drought. It was known by the name of its leader, Johns Hopkins University professor M. Gordon Wolman, and it recommended an $80 million effort to tackle the unknown hazards and unanswered questions surrounding Maryland's aquifer systems. Wolman died in 2010.

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