By DAVID GREEN
Think of it as a sponge, says Lauren Bechtol of Bryan, a member of the Michindoh Sole Source Aquifer Group.
Underground water resources are often thought to be a river of slowly flowing liquid, but that’s not accurate. And if you look at a map depicting the outline of an aquifer, the idea of a subsurface lake might arise.
Ditch that concept, too, Bechtol says.
“The easiest way to think of an aquifer is to picture a wet sponge made up of layers of gravel and sand and pockets of sand. All of this is contained within a bowl, shown by the outline of the map.”
Within the sponge are sections that do not soak up water, such as layers and lenses of clay and silt. Over the top is the water resistant layer of soil and rocks visible at the surface.
There is movement within the aquifer, Bechtol said, but not like a river. Instead, water flows down sloping areas underground. Dig down deep enough and you’ll encounter bedrock—the underlying rock that would be exposed if all soil were removed. Bedrock isn’t a smooth surface. There are rises and falls that lead to movement of water in aquifers.
Movement also occurs when water is pumped. A well creates a “cone of depression” and water is drawn in to fill the void.
The Michindoh Aquifer encompasses portions of seven counties in three states—hence the name Mich-Ind-Oh—including the communities of Morenci and Hudson on the north and Hicksville on the south. It serves the drinking water needs of about 20 communities.
“As aquifers go, the Michindoh is rather small,” Bechtol said, “however, it is one of the most productive in Ohio.”
Glaciers advanced as far south as what is now Kentucky, but geological conditions varied from region to region as the ice melted.
“Here, an abundance of gravels and sands were sorted by melt water onto the bedrock and were then covered by finer silt and clays,” Bechtol explained.
Sand and gravel is scattered in multiple layers and patterns, and most of the layers are interconnected. This is what creates an aquifer.
The structure of the underlying bedrock, the presence of water resistant clays and silts, and the existence of the sand and gravel beds together define the border of the aquifer.
Well driller Jim Watson of Bryan, Ohio, explains that sand is about 25 percent porous. An acre of sand four feet deep would hold about 350,000 gallons of water. A square mile would hold 200 million gallons.
Most water-bearing areas of the aquifer are thicker than four feet, he noted, and the water contained in Michindoh is incomprehensible.
Communities within the aquifer area withdraw an estimated 5 million gallons daily.
Recharge zones replenish the original glacial water. Rainwater finds its way down into the aquifer and rivers also serve as recharging agents.
Due to the importance of water to the thousands of people living in the Michindoh area, a group of Williams County residents met in 2004 with the common interest of protecting the aquifer.
In 2005, the Michindoh Sole Source Aquifer Group received non-profit status and began efforts to obtain sole source aquifer status through the U.S. EPA.
A sole source aquifer (SSA) is one that provides at least 50 percent of a region’s water supply, with no affordable alternative source available.
But with a thick layer of protective clay in most areas, is Michindoh vulnerable to contamination?
Mary Ann Thomas of the U.S. Geological Service presented information Thursday at the Michindoh SSA annual meeting that suggested it is.
Thomas discussed findings from the National Water Quality Assessment and focussed on the Lake Erie drainage area, including Michindoh.
Although contaminants were generally found in low concentrations—other parts of the Midwest with sandy soil are much worse off, she said—the study showed that water sources are vulnerable.
For example, low concentrations of 11 pesticides were detected in 41 percent of monitor wells in agricultural areas and in six percent of residential wells studied.
The monitor wells varied in depth from nine to 34 feet and the residential from 31 to 158. One detection was found in a residential well at a depth of 130 feet.
“There is a connection between the surface and deeper water,” Thomas said, but vulnerability varies widely.
“The findings are relevant to your group,” she said, “because when people say the groundwater is protected by clay, you can say ‘No, it’s not.’ It’s a mixed story.”
Watson said the average depth of wells in the area is 118 feet. Some areas have 100 feet of clay atop the water source, others are much more vulnerable with only 20 feet.
Even those sources lying under a hundred feet of clay could develop problems, Watson said, because of interconnected areas of sand and gravel.
Thomas agreed that sand pockets are present in the clay.
Todd Feenstra of Tritium, Inc., a hydrogeologic consulting firm hired by Bryan Municipal Utilities to petition the EPA for SSA designation, said that foresight is important.
“The time to start worrying about it is not when we have a problem, because we can’t fix it,” he said, noting the huge costs of cleanup efforts. “The time to start worrying about it is now.”
Feenstra emphasized that SSA designation from the EPA should not be viewed as opposition to new development.
“We’re not trying to discourage growth in the area,” he said. “We just want to position it wisely. Everything can coexist if it’s done wisely.”
Thomas said the U.S. Geological Service will return to the Lake Erie basin in August for a followup study to see if water quality has changed since 1998 when samples were first taken.
Michindoh SSA members will look at those results with interest, but in the meantime, they’ll continue working toward SSA designation, and raising awareness of the importance of clean water.
Advantages of Sole Source Aquifer designation
• EPA review: Development projects assisted by federal funding would be reviewed and might receive specific recommendations for pollution prevention requirements. Designation does not provide oversight of projects funded by state, county or local entities.
• Education: Designation would lead to a heightened awareness of best management practices.
• Awareness: Awareness of water needs leads to better planning. Certain projects would be located away from sensitive areas of the aquifer, particularly recharge areas.
• Economic Development: Industries with a high need for water in the manufacturing process might prefer to locate in an area where an active water management program exists.
Waste disposal sites, landfills and abandoned dumps; leaks and spills from underground tanks; industrial sources; storm and sewer lines; agricultural chemicals and livestock manure.
Abandoned wells are perhaps the biggest problem, according to well driller Jim Watson.
Without proper sealing of the well, a direct conduit to the aquifer exists through the protective clay layer.– Jan. 17, 2007