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Tue April 1, 2014
The geology behind Columbia's water supply
You've probably read the headlines about the drought in California. It got me to thinking about what many of us probably take for granted, our water supply.
So I decided to trace Columbia's water supply to its source. It all begins with Missouri River Relief which is a non-profit organization out of Columbia that helps connect people to the Missouri River through clean-ups and educational events. Educational events like one on a cold February night with the temperature barely above zero earlier this year at the Les Bourgeois Winery and Bistro in Rocheport. Alex Dzurick from Columbia Water and Light was there to give a talk to about a dozen hearty souls about the McBaine aquifer. "44 billion gallons of water stored in that aquifer in McBaine," said Dzurick. That aquifer in McBaine, which is underground by the way, is the source of all the drinking water in Columbia.
That's important to be sure but it was that figure of 44 billion gallons that intrigued me. Dzurick's presentation was full of fun facts about testing the water from the aquifer and all that but it was the geology of it all that got my attention. Dzurick said, "There is an aquifer under most of Missouri. But it's a bedrock aquifer. What McBaine is is an alluvial aquifer." Silt, clay and gravel. But U.S. Geological Survey hydrologist Joe Richards out of Rolla said that's not all. "This aquifer is the equivalent of a giant bucket of sand. The water is interspersed between the sand grains and larger grains down at the bottom of the aquifer. It freely moves within that sediment package." Richards knows aquifers. He was part of a team that did testing in this area for the city of Columbia and the state of Missouri from 1992-2004. I met up with him recently for a tour of the aquifer area. An area in and around McBaine, population 10. Just a handful of miles southwest of Columbia.
So, if you have ever hiked or biked on the Katy Trail in and around McBaine or north toward Rocheport, or visited the big tree, well, you weren't far from the aquifer. Dig down 20 feet or so from the surface and you are in aquifer territory. Aquifer size courtesy of Richards, "It's roughly nine miles long by a mile wide." And 100 feet deep. Columbia's water supply right under the surface of that big flat floodplain otherwise known as the Missouri River bottoms.
Columbia residents use about five billion gallons from the aquifer in an average year. That's about one tenth of what's in there. And the city has a way of getting it out. 15 wells are spread out over a wide area on top of the surface of the aquifer. Pumping out a total of about 30 million gallons a day to the nearby water treatment plant and eventually to you.
And even though there's 44 billion gallons of water down there, not all of it can be pulled out. Dzurick said there is a reason for that. "The stuff that is stuck in there is stuck because of surface tension. So no matter how hard you pull with the well, some of it stays stuck to the sediment that is in the aquifer. Won't come out."
So, the wells are concentrated in an area of the aquifer where it's easier to get water out. And the water also gets a helping hand before it's pumped out. Dzurick said that's because material in the aquifer acts like a natural filter. "So a lot of the minerals in the sediment that would be present in the water, aren't."
And new water is continually coming back into the aquifer via mother nature, mostly by way of precipitation. Dzurick said it's coming in off the miles and miles of bluffs and foothills. "The nice thing about this kind of aquifer is that it's permeable to be re-charged very often, rather quickly."
Re-charged. That means generally the five billion gallons Columbia uses a year gets put back.
So the next time you use some water out of the tap in Columbia, just think alluvial, aquifer and of course, McBaine.