Movement of water below ground

Every watercourse carries both water and sediment.

Most people understand the flow of water underground poorly. The common idea is that water flows in “streams.” When you dig shallow ditches you do observe water flow (if the weather has been sufficiently wet) through crab holes and the like. This is not the major mechanism of movement of water under ground, however.

Imagine a bank of sand along a stream. Water can flow through it moving in the pores between sand grains. These are tiny holes left because the sand grains are irregular in shape. If each was shaped like a brick or a child’s toy block, all the space could be filled in and very little flow permitted. The irregular shapes between sand grains do not completely fill the space, so water is permitted to flow. This is the way water flows down into soil and in some kinds of rock.

Most of the underground water in Central West Virginia (and elsewhere) resides in sandstone (as does the oil and gas). Geologists can measure the porosity of rocks which gives some indication of the space available and the speed liquids can flow through them. Soil is also porous, although not as much as some sandstone. Some rocks are not porous, such as coal and soapstone.

When it rains, water that doesn’t run off seeps down into the soil through pores, some spaces between soil particles, some through earthworm holes, some through spaces caused by plants. It sinks down to some impervious layer, perhaps clay, and there moves laterally (sidewise) through the soil. The process is slow, but it operates through the entire surface. In some places water accumulates due to presence of clay in the soil, and must be drained. Drains must be buried at about 2% grade with no low spots to drain properly. If the work to place drains is not carefully done, the sediment carried by water in drains accumulates in low spots and blocks the drains. Proper design allows for high water in the stream where the outlet is located. The outlet should be far enough above stream level so that there is plenty of time the stream is below the bottom of the outlet. Otherwise the sediment accumulates in the drain. The outlet should be a foot or so above stream level at normal flow. More is better. Anticipate changes in stream level as a result of the processes described in the article “Movement of water above ground.”

An aquifer is a strata of rock which has enough porosity to hold water and allow it to flow into a well bore rapidly enough to be useful. Most aquifers in Central West Virginia are sandstones. To the East there are limestone strata that have enough cracks to allow water to flow in useful amounts.

Water can be pumped readily from the borehole. But the volume of water in the borehole will allow pumping only a brief time. If more than a few gallon is needed, water must be resupplied from the porous rock aquifer. The combination of thickness of the aquifer and porosity determines how rapidly the well will be supplied.

The well may be drilled through a succession of porous and non-porous strata (layers), each aquifer contributing to the production of the well. Aquifers are sometimes held up by some impervious strata, like coal. These are said to be said to be “perched” on the impervious strata. Rarely, drilling through the impervious layer allows the aquifer to drain into an empty porous layer, draining the aquifer.

Some aquifers lie between impervious strata and are replenished from rain percolating down from the soil at some distance from the well at a higher elevation. Drilling into these produces an artesian well. Generally speaking, a well must be in an aquifer thick enough and porous enough to contain a supply of water that will allow the pump to run for several minutes, preferably longer. Often there are several aquifers in an area, in which case the driller should not stop at the first one. The moral of the story is not to stop drilling at the first trickle of water to save yourself money. In some areas, like ours on Jesse Run, go too deep and you get salt water, however. If you have a gas storage field in your area you can expect some of the gas to work its way up through pores toward the surface, away from the pressurized layers to flavor the water. In one of the wells on our farm, gas accumulates above the water, is ignited occasionally by a spark that blows the aluminum well cap off. We know this is the reason, because of the black carbon deposit where the gas-rich mixture explodes.

Aquifers may be thought of as having a lens shape. Not round looking down from above (if you could see through the earth) like a glass lens, nor with a smooth top and bottom, but pinching off in thickness from top to bottom as you move away from the thickest part. When you drill the water well, there is no way to tell where the lens shape of the aquifer is, or how thick it is, in order to best locate the well. The oil and gas people have a way to do this (they only kinda know) looking for their much more valuable target, but such methods are too expensive for water wells. Details of what they do need not concern us here.

The position of the “lens” is unknown and it's shape It can not be found by technology in drilling for small water wells. It bares no relation to surface features with one exception. Very shallow wells may be resupplied by steams in the vicinity. Even when the surface is dry, water continues to follow the unconsolidated material (soil and small gravel) below the surface along streams. If you are a farmer looking to drill a well for a dry time, or a homeowner who doesn’t want to run out of water ever, drilling a well on a hill is a poor choice. The strata tend to drain out in a dry time through the side of the hill into the valley. If you have to drill on a hill, go deep enough to get your water supply below steam level, a few tens of feet.

When you draw water out of the well, the first thing that happens is the water in the bore hole drops. This allows more water from the area of pores around the well to flow toward the hole, refilling it. Then water from further out flows in the newly empty pores, and further out pores resupply those pores. Think about this: When you pump water out of a barrel the water level of the whole barrel goes down, because there is no resistance to the flow of the water. When you pump water out of a hole in a porous strata there is resistance, and so slow flow. The further away from the well the more resistance to flow. Instead of the surface coming down uniformly, like in the barrel, the water nearest the well in the strata comes down most, and further away less. This forms a “cone of depression” in the surface of the water around the well, in the aquifer. If the well is resupplied from above, it is not a good idea to have a shallow well near your septic system, although many people get away with it. The problem is not so much bacteria, but chemicals with molecules nearly as small as water molecules from detergents, cleaners, medicines, etc. that go down the drain. If the water is deep, there is less likelihood of surface water contaminating the resupply.

“Water witching” is an activity that goes back to the time of witches. Although many people “believe” in it, no one has ever been able to prove objectively, that it has any better likelihood of success than pure chance. Drill your well where it is convenient. You are just as likely to hit a lens big enough to meet your needs for a farm or home if you go down until your well is sufficiently deep.

Springs in Central West Virginia (and elsewhere) are most frequently found in the side of a hill or not far from a hill or raised area. They are simply an outlet from an aquifer that can drain, in other words, is above the stream in the valley, and not contained by low porosity rock.. Occasionally they are the result of an artesian aquifer, but not often. If you drill a well in the aquifer above a spring it is likely to reduce the water in the spring.

Fracturing a gas or oil well or blasting by a strip mine or construction job can destroy a well or spring, by making a fracture that lets the aquifer drain below the level of the spring or bottom of the well. If gas or oil well or blasting by a strip mine happens in your neighborhood, it is a good idea to have the production of your well or spring verified in such a way that it can be used in court. In fact it is the law for strip mines to do this. But do it before the work takes place. Afterwards is too late. Consult your friendly lawyer. The company can be expected to fight your claim tooth and nail.