Friday, September 28, 2007

Arguing with a Professional Geologist

Below is an article I wrote for the Cabarrus Neighbors. This was actually written earlier than the previous post. Below that is a reply from a professional geologist followed by my response. Both get fairly technical. So far I haven't heard back from him so I can't determine if he is right or if I am right. I know in general it isn't smart to disagree with people at thier own game but I couldn't resist. Would be glad to hear what you think.

Original article
Q. My neighbor's lawn is still green, so I know he is irrigating. We are both on wells. Can he dry up my well by irrigating, or could we be drawing from different aquifers, since everybody's well is a different depth? Also, my brother down the road went to the biweekly watering schedule, and his lawn turned brown. Since my neighbor's lawn is staying green, doesn't that mean he is watering more than twice a week?
First, you are on the same aquifer, so your neighbor can dry up your well. This has happened at some places in Cabarrus County, although it took more than one person to do it.
Basically, in your area, everybody pumping groundwater from between the major creeks is withdrawing the same water. The depth of the well doesn't change the source of the water.
My suggestion is to monitor your well by measuring the static water level. The static water level changes and has to be measured. Subtract the static water level from the depth of casing. The depth of casing doesn't change and should be on a plate attached to your well. The difference gives you an idea of how much groundwater is available.
Likely there is enough available water that you won't have to worry about talking to your neighbor. If you have only a few feet of water, you need to educate your neighbor about groundwater. Neither of your wives will be happy if you have to start hauling in water.
Your neighbor, however, could be following the biweekly watering schedule, or even a weekly watering schedule, and keeping his lawn green. Your brother's frequent and shallow irrigation regime developed a very shallow root system. This proved impossible to manage on a biweekly watering. A lawn with deeper roots can remain green on biweekly or even weekly watering.
One more thing: Be careful not to contaminate the well when measuring the static water level. I can measure the static water level in a nearby dug well. Beyond that I haven't found any written recommendations.
I think it could also be measured in my drilled well by dropping a nail and cork on a string down the vent pipe after modifying the vent cap so it is removable. I wouldn't use a lead weight.
If I had a laser tape measure on hand, I would try using that first. Without trying it, I just don't know how you can be sure you are hitting the static water level and not the walls. I would also make the measurement at a time when the well has had time to recharge.

Response from Geologist

I appreciate your willingness to take a stab at answering the questions, but I felt compelled to write to clarify a few things about wells and groundwater in the piedmont.
First, the well's static water level when it was drilled should also be listed on the well tag. During times of drought, well owners should expect that the water level will be inches to feet below that level under natural conditions. As you reference, pumping of that well and other nearby wells can also depress the water level. Examples of natural variation in groundwater levels due to current drought conditions can be found at: and you'll notice that crystalline bedrock wells in the western part of the state are typically a foot or two below their 5 year running average.
In this area of the state, most people rely on wells that are drilled into the bedrock. For bedrock wells, the well casing typically extends from just above the land surface to the top of the bedrock (no less than 20 feet by rule and often 40 to 80 feet or more in practice). Much of the groundwater supplied to a bedrock well results from the open borehole below the casing that intersects water bearing fractures in the bedrock. The volume of water available from a well is not dependent upon the casing depth, but really more on the placement of the submersible pump in the open hole interval below the casing. It is common to set submersible pumps 10 to 20 feet above the total depth or bottom of the borehole. Ideally, the well tag and pump tag will provide these numbers to a homeowner. Most of the supply wells that are being drilled these days are deep enough to almost be drought-proof, but common sense dictates that well owners should also be mindful of water conservation in times like this.
As you mention, it is possible to measure the depth to water using a string and a weight, but I'd really recommend that homeowners stick with the estimates provided by the well/pump tags or consult with a certified well driller or a hydrogeologist. If you have any questions, feel free to let me know.

My response
I agree that the tag contains a static water level number. That number should be good for a day. If it is good for more than a day there is no reason to monitor this data on a daily basis like they do on the website you referenced.
The static water level on my property changes a lot more than a foot or two. Since I have been on the property, I have measures a fluctuation of more than 22 feet.
To get a more scientific measurement I worked through the data on the website and this is the first example I come up with. Iredell County, North Carolina
Hydrologic Unit Code 03050101
Latitude 35°31'35", Longitude 80°52'42" NAD83
Land-surface elevation 803.08 feet above sea level NGVD29
The depth of the well is 28 feet below land surface.
The depth of the hole is 28 feet below land surface.
This well is completed in the Piedmont and Blue Ridge crystalline-rock aquifers (N400PDMBRX) national aquifer.
This well is completed in the SAPROLITE (110SPRL) local aquifer. In this example there was a fluctuation of 10 feet within one year. From September 2002 to September 2003.
In my article I said the volume available is the difference between the depth of casing and the static water level. If we have a disagreement this is the crux of our disagreement (or from your point of view, my misunderstanding). I think the amount of water in an underground aquifer is mostly above the bedrock. When I look at examples of bedrocks in mines and in mountain highway cuts, I don’t even see the fractures. My guess is that less than .1% of the total volume of bedrock is water. Once you get above bedrock you start getting 5 to 10% pore space. So the vast majority of underground water here in Cabarrus County is located in this 5 to 10% of the pore space from the bedrock to the static water level. Now the depth of casing in a properly constructed well is the same as bedrock. So it would be fair to substitute depth of casing for bedrock in the previous statement. This means the vast majority of the underground water here in Cabarrus County is contained between the depth of casing and the static water level. My educational goal is that people understand where this water is located and be able to measure and utilize it appropriately.

So far I haven't heard back from this individual. Let me hear what you think.

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.

Thursday, September 20, 2007

New land

Exciting time in the Goforth household. We just purchased 22 acres of land, complete with a creek, spring, old well, and old home site. Yesterday I met with the Forestry Service to discuss management of the forest. It has been clearcut for the most part so I don't need to worry about a timber basis. The well was covered by a piece of tin. First thing I did was cut some cedar from the property and construct a cover over the well so people couldn't fall in. I was surprized by how small the well was particularly toward the bottom. I couldn't have got down in it and whoever dug it couldn't have swung a mattock even if they were a midget. Not sure how they dug it. It was rocked up with quartz rocks all the way to the bottom. I'm sure it was a major effort in its day. My next project is cutting an access road. At first glance a person would say the house is without a doubt beyond repair. A closer look reveals that the first structure was a log cabin built in early 1800's. Then it was remodeled with timber and pegs typical of the late 1800's. The remodeled part has fallen in beyond repair but the log cabin part might be salvageable. I hope to get an expert to give me some advice about that.

Monday, September 17, 2007

Solar Greenhouse

The theme on the Master Gardeners Fair booth this time was Winter Gardening. Part of the display included details on a solar greenhouse for our climate. I have used one for several years. Frequently I grow all my own transplants for my farmers market booth using only solar energy for heat. This year I used a couple of more flats than I produced but still produced the equivalent of 10 or 12 flats.
Details I consider important.
Orientation toward the south. I haven't put a compass on mine but I bet it is within 10 degrees of true south.
Insulation of north wall. I use salvaged card board and plastic.
At least one gallon of water storage for each square foot of glazing. I use 3 50 gallon drums, 1 30 gallon drum and over 200 2 liter drink bottles.
Very little air infiltration. It is particularly helpful not to create a chimney effect with air openings high in the structure.
Here are a few other details.
The glazing angle for our latitude that maximizes February and March temperatures is 45 degrees. Not sure how critical this is. Mine has a rounded conduit shape that goes from 90 to 0 degrees and it works.
On cold nights there are two covering options. One is a single sheet of newspapers laid on the plants. As the temperature drops the newspaper will get wet. This water will release heat when it freezes. I have had it freeze without damaging the plants underneath. The other option is to totally cover the structure with a nonwoven landscape fabric type blanket.
When I put the greenhouse together several years ago, I used all slavaged materials. Eventually, I purchased plastic greenhouse film. I have seen other gardeners use salvaged windows on a similar structure.
My best night this year was on the Easter Freeze when outside temperatures were 19 degrees by 3 am. Inside it was 40 degrees with no supplemental heat. Not sure what the minimum temeperature would have to be to damage plants. I just know my heating bill is less than most greenhouses.