Scientists study natural processes affecting Eastern Shore aquifers
“Environmental conditions that lower, recharge, or cause increases in groundwater withdrawals can have negative effects on groundwater resources.”
Oyster reefs within salt marshes off Oyster, Va., on the Eastern Shore emerge at low tide in November 2020. (Sarah Vogelsong/Virginia Mercury)
For years, the Eastern Shore has had trouble sustaining its aquifers, underground water reservoirs used for public consumption, and for agricultural and industrial uses.
Data recently collected by the United States Geological Survey in conjunction with the Department of Environmental Quality found that natural processes are affecting surficial aquifers – water that pools above the aquifers near the surface.
The water in those surficial aquifers is being depleted quicker than the surficial aquifers can be refilled in summer months explained Jason Pope, a hydrologist at the USGS Virginia and West Virginia Water Science Center, during an Eastern Groundwater Management Advisory committee meeting at the Department of Environmental Quality last week.
Other topics broached in the meeting included the level of groundwater withdrawals, increasingly salty groundwater in some areas and data showing private ponds in the Eastern Shore may have more pollutants in them than the older water stored away in the deeper underground aquifers.
Water withdrawal levels hold steady
“Regarding withdrawals of groundwater for the Eastern Shore, there do not appear to be significant increases in withdrawals in recent years,” said Pope. “Withdrawal patterns appear [to] have been fairly steady for the past decade or so, with fluctuations based on changing environmental conditions.”
Those monitoring the levels of the aquifers have historically pointed to heavy use of them, particularly among the poultry industry, as a cause for groundwater depletion. But the data recently collected by USGS found an important factor may be environmental processes such as evapotranspiration, when water evaporates from the ground into the air during different times of the year.
“While our recent analyses have better quantified evapotranspiration as a large component of the water budget, there doesn’t appear to be any notable recent increase in evapotranspiration,” Pope stated by email outside of the meeting. “Rather, there appears to be a seasonal cycle of much higher evapotranspiration in the summer, which would be expected.”
Insufficient data has been collected to say how climate change, which is prompting rising global temperatures and sea levels, is a contributing factor, Pope said. Still, “Environmental conditions that lower, recharge, or cause increases in groundwater withdrawals can have negative effects on groundwater resources,” Pope said.
The data, which will still being gathered through 2024, will guide the Department of Environmental Quality in its permitting decisions for groundwater withdrawal and use by the Eastern Shore’s 45,000 residents, as well as tourists, farmers and industrial users.
“Evaluating saltwater intrusion and replenishment of aquifers are aspects of this purpose,” wrote DEQ Spokesperson Irina Calos in a statement. “The effort by USGS has resulted in a better understanding.”
Digging into the data
DEQ and the USGS have monitored the groundwater withdrawal use for years, but the current model from 2009 doesn’t have new data available; that may skew which natural processes are at play.
The new studies have pulled data collected in 2019 from 202 holes dug into the ground, compared to 49 in 1994, and changed the breakdown of the data from yearly to monthly to better simulate the seasonal variations for pumping and recharging.
“A whole lot of updates to make here,” said Pope.
In 2019, USGA researchers did uncover more data on the “hydrogeologic framework,” or system of underground water channels that travels through the Eastern Shore, to provide a baseline understanding of how groundwater flows through the aquifers.
“All of the water input into the system is from precipitation that flows downward through the system and [is] hopefully recharging the deep rock aquifers as well,” Pope said. “The lower density freshwater keeps it on top of the saltwater. The water’s moving outward to the coast.”
Recent data has also identified surficial aquifers as a source of groundwater; a small fraction of water enters the ground and recharges the deeper buried aquifer system. But, “additional model detail is needed to better represent the role of surficial aquifers,” according to USGS.
Evapotranspiration is harming surficial aquifers
Evapotranspiration is the act of water moving from the ground to the atmosphere via evaporation from the soil surface or transpiration. Transpiration is when plants take up water from the ground and release it as vapor into the air from their leaves.
The different types of plants, soil type and temperature are among the different factors affecting how much water transpires. As temperatures go up, the tiny openings on plants, called stomas, can release more vapor into the air. During a drought, evapotranspiration becomes more significant because of its depletion of remaining water in lakes and streams and soil, according to a USGS paper.
On the Eastern Shore, USGS researchers found that 69% of rainfall is lost through evapotranspiration. About 10% runs off into the coast through the underground channels, leaving about 20% of water that actually infiltrates the aquifer system.
Through the water cycle, that amount of infiltration lessens. “That little raindrop already fought its way into the groundwater; now you put it back out on the surface, 70% of that is gone,” said Matt Kearns, a hydrologist also in the Virginia and West Virginia Water Science Center.
That finding, coupled with new data showing the monthly water withdrawal rates increasing in the summer compared to the winter and the spring, are leading to “negative summer recharges.”
The stickers saying “Salt Life” could be placed on the rear windows of cars on the Eastern Shore, not because of an interest in ocean life, but because of an increase in water salinity that can impact health.
DEQ stopped collecting data on saltwater in 2016 after monitors noticed salinity wasn’t changing, explained Pope. But DEQ has kept monitors in certain locations in Chincoteague and Cape Charles, where salinity trends upward.
A key component of preventing high levels of salt in groundwater is the surficial aquifers balancing out any saltwater intrusion from brackish water, or ocean water that mixes with freshwater. Fresh groundwater is less dense than saltwater, so it sits on top in the aquifer, Pope explained. By the fresh groundwater not entering the aquifer as often, it isn’t able to push out the more salinated water.
“Now that we’re pumping a lot of groundwater out there, and there’s less freshwater pushing [saltwater] out, the saltwater interface is moving inward and upward, so you have the increased risk of saltwater intrusion,” Pope said.
According to a 2019 Virginia Tech paper that states saltwater can intrude into freshwater aquifers in coastal areas, high levels of salt in drinking water can lead to a salty taste, and can corrode plumbing components. An increase of salt in a human’s diet can cause some people to develop high blood pressure, leading to damage to the heart and arteries in other organs.
“Salty groundwater in water supply wells is obviously undesirable, so regular monitoring of chloride (salinity) in wells can provide warnings of increases in groundwater salinity in specific locations,” Pope said.
Private ponds may introduce pollutants
Compounding the water issues, farmers are creating private ponds filled with water from the surficial aquifers, because it can be more easily applied to their crops. These ponds could intersect the groundwater channels beneath the Earth’s surface, preventing further refilling, or recharging, of the reservoirs, Pope said.
That realization came after an increase in data collected from private domestic wells; previously, data from less than 200 wells was recorded in 2008. Scientists are now collecting data from over 1,300 private wells. The withdrawals from the private domestic wells are also in line with the seasonal water pulls, which increase from 7 million gallons in the winter to over 36 million gallons in the summer.
There’s been an increased push by people on the Eastern Shore to use ponds, Pope said. “That’s already being done.”
Additionally, the way the ponds are created could lessen water quality because more surface-level groundwater is susceptible to contamination from human activities like applying fertilizers, compared to the deeper aquifers.
“That water has been in the ground for 15,000 years, which means it doesn’t have any anthropogenic contaminants,” Pope said of aquifer water. “While at the surface, the water may be a little more plentiful,” it may also have more contamination.
The Chesapeake Bay Foundation, which tracks pollution contaminants reaching the Bay to clean it up, said they’re reviewing what USGS presented. Zach Jacobs, legislative specialist with the Virginia Farm Bureau, another member of the committee alongside CBF, said his organization took special note of the increased use of private ponds. Farmers use private ponds to help ensure water availability and are adopting nutrient management plans to ensure water quality, Jacobs added.
Hobey Bauhan, president of the Virginia Poultry Federation, said the chicken industry on the Eastern Shore follows requirements under DEQ’s Virginia Pollution Abatement Regulation to reduce water contamination. In general, the poultry group said the findings from USGS are “expanding analytical tools” and helping to gain “a better scientific understanding to better manage these water resources.”
“We’re supportive of that,” Bauhan said.
This story was updated with the correct name for the United States Geological Survey, the spelling of Bauhan’s name and clarification that 69% of rainfall is lost through evapotranspiration.
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