Thursday, September 27, 2007

Response to news article by Professional Geologist

Here is the original news article as submitted. It is sometimes edited for grammer, spelling, clarity and to fit a certain space.

Q. I was left wondering about the potential effects of your response in today's paper about whether your neighbor's well could cause yours to run dry. While I understood your response--it would probably be difficult for one person alone to cause his neighbor's well to run dry, it caused me to consider how it might push others into digging wells.
My limited impression is that many, many people in this community think mainly about themselves. To the extent they begin to feel that their precious lawns are threatened, they may well begin thinking about the need for their own well, especially if having their own well does no harm, except to their pocketbook.
Suppose, I wondered, 1,000 people in and around the downtown area of Concord, each decides to dig a well--a bonanza for the local well-diggers of Cabarrus County. What happens to the water supply in Cabarrus County then?

A. Thanks for reading my article. If by water supply you mean the municipal water supply of Kannapolis, Concord, Mt Pleasant, etc, then the 1000 wells you posit would have no effect. At times they would slightly decrease the water supply in the Rocky River which flows to the Pee Dee which flows to the Atlantic Ocean but I doubt it would be enough to worry about. Maybe I should worry but compared to other environmental damage occurring today it is fairly low on the worry scale. This decrease would be due to increased evaporation decreasing the springs and underground water supply to the creek that flows along Branchview. The groundwater "aquifer" that residents of Concord would tap into is basically confined between that creek and Irish Buffalo Creek. The amount of water in that "aquifer" is unknown. I have seen some figures for watersheds in Orange County. There is a large amount of water for a few households, a very small amount for 1000 households. The situation I mentioned last week where neighbors have dried up wells involved over 45 households who irrigate lawns and maintain water gardens, swimming pools and fountains. If 1000 wells were drilled into downtown Concord, there would be winners and losers which brings us back to the well known problem of the commons. If you want to try to get a handle on the local groundwater systems start here. Pay careful attention to figures 3 and 4. All of Cabarrus County has this type of hydrology. Areas with similar hydrology are located from Pennsylvania to Alabama. Parts of North Carolina have different hydrology. I have seen this mapped on the internet but can’t find it at this moment.

Here is a reponse by Andrew Pitner P.G.

Hi David,
You're a real trooper for fielding these kinds of hypothetical questions. Your response is pretty reasonable. Here are a few things that you might want to note:
1) There are already thousands of wells in Cabarrus County that are pumping groundwater for the purposes of drinking water, irrigation, and various commercial/industrial processes. In general, supply wells in the piedmont have sufficient yield to serve the average residential uses. However, the aquifers around here simply don't have the capacity to produce the huge volumes of water that some of NC's coastal plain aquifer systems are able to manage. In addition, there are practical aspects and rules regarding the installation of wells and the amount of existing development in downtown Concord that would limit the number of wells that could be installed in such an area (i.e. buildings, power lines, underground utilities like sewer, etc).
2) You could point out that the municipal supply is largely from surface water impoundments. In general, the bulk (60-70%) of surface water flowing in a stream throughout a year's time in the piedmont is a result of shallow groundwater discharge to the stream (also called baseflow).
The remainder of surface water comes from runoff of precipitation. This all kind of points to the fact that, after glaciers & ice caps, the largest percentage of freshwater on earth is groundwater (
3) Here's another good link to general information about crystalline bedrock aquifer systems in the eastern US from the Ground Water Atlas, which was compiled by the USGS:
A simple way to conceptualize of piedmont aquifer systems is that we've got a big sponge made up of red, clay-rich soils and regolith sitting on top of a fractured bedrock piping system. There's lots of storage for water within the sponge and relatively little storage in the bedrock fractures, but the water is transmitted fastest through the pipes (fractures). Physical aspects of the sponge (permeability of clays) limits how much water will be available to the pipes at any one time.

Due to the geologic setting, groundwater availability can vary significantly across the state. In general, the mountains & piedmont are conceptually similar (sponges sitting on pipes, with less sponge in the mountains). The coastal plain is an entirely different beast with extensive, thick unconsolidated sandy aquifers that can support municipalities. Most coastal towns are served by wells and most western towns utilize surface water for municipal supplies. In addition, there is widespread use of groundwater by rural residential homes, such that there are estimates that about 50% of NC's total population is served by groundwater.

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