What is a modern drilled water well & how is the well constructed? What is a bored water well? Definition of & Formula for Determining Water Well Recovery Rate. Definition of Total Water Available from a Water Well over a Given Time Period
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This article describes the properties & construction of drilled wells that use a steel well casing, modern drinking water wells.
We discuss well problem diagnosis, testing, & repair procedures - advice about what to do when things go wrong with the well such as loss of water pressure, not enough water volume, contaminated wells, wells that have smelly water, wells that just run out of water or have a low recovery rate. We describe the parts of a water well and its piping and controls including the pitless adapter.
We explain how a well water recovery rate is measured or calculated. We explain the role of static head of water in a well and how to measure the static head.
Drilled Wells - guide to modern steel casing wells
Here we describe modern steel-casing drilled water wells, including how the well is constructed, sealed against contaminants, and how the well flow rate or water recovery rate is evaluated.
The page top photo is of a modern well casing, in good condition, extended properly above ground.
The small-diameter pipe parallel to the six-inch steel well casing is an electrical conduit - so we
know that for this particular water supply system a submersible water pump is used and it is
installed in the well itself.
The electrical conduit carries electrical power to the water pump
down in the well.
The blue and white plastic rope in the page top photo was probably used to raise and lower
the well piping and pump from within the casing.
In Carson Dunlop's sketch at left we show the typical construction of a drilled water well in cross section.
You can see that the typical well casing diameter is 6" (4" in some areas), that the well depth can be considerable (50 50 ft. to 900 ft. or more), and that the steel well casing does not extend down into the bedrock.
As we show in In Carson Dunlop's sketch at left, there are several types of well casings and more than one type of well casing sealant.
Drilled well casing types: Drilled well casings can also be constructed of plastic pipe, brass pipe, copper pipe, or fiberglass pipe.
Drilled well casing sealant with concrete or gravel and slurry: A concrete slurry or gravel and mud mixed grout is poured around the exterior of the well casing after it has been pushed into the drilled well opening.
This grout is necessary to prevent surface water from leaking into and contaminating the well water. The water that enters this well comes from cracks or fissures in water bearing rock shown at the bottom of the sketch.
Not shown in this sketch are the well details such as submersible well pump, well piping, pitless adapter, and piping between the well and the building it serves. We discuss the pitless adapter and these other parts below.
The photo shown just above is of an older drilled-well casing which has been placed with its casing
cap at ground level - increasing the risk of well contamination from surface runoff.
All we can see is the well cap.
Pitless Adapters for Well Casings
The water pipe leaving this well to carry water to the building will be buried below ground,
and in freezing climates, below the frost line. A special fitting, the "pitless adapter" is
used to seal the passage cut into the round well casing.
a = air - the distance from the ground surface to the top of the water when the well is at rest and is fully "recovered" from recent use
c = clearance distance between the bottom of the well pump (or foot valve) and the very bottom of the drilled well. this distance is required to avoid having the pump pick up mud and debris from the well bottom.
h = static head: the volume of water available to the well pump when the well is at rest and is fully recovered.
Bored Water Wells
A bored water well is a lot like a 'drilled well' and the use of this term is confusing to some.
The differences between a bored well and a drilled well are these:
Unlike a drilled well described above, the bored well is prepared using different equipment which is not capable of boring to as great a depth.
As Carson Dunlop's sketch shows, the bored well is often lined with interlocking sections of concrete piping rather than a continuous steel casing.
A bored well is likely to be found in areas of high water table, and where the water supply is obtained from water bearing soil or sand rather than bedrock.
The usual depth of a bored well is 50' to 100' - not as deep as a drilled water well.
Definition of & Formula for Determining Water Well Recovery Rate
We provide an introduction to well recovery rate just below. Details of "how much water is in the well" are discussed
at WELL FLOW RATE
The well recovery rate is the rate at which water flows into the well opening from surrounding rock (or soil or other water source). The well recovery rate is a complex number comprised of the water flow rate and water flow duration from various rock fissures and openings into the well casing or well opening.
Because water flowing into the well from a particular rock crack or fissure often flows at a varying rate, typically falling to a lower rate or even stopping after time, the total well recovery rate involves a summation equation adding up the individual rock fissure flow rates and considering the length of time that each flow rate can be expected to occur.
The length of time that each flow rate at each fissure may occur varies from just a few minutes to more than 24-hours. Flows that continue at a given rate for 24-hours or more are considered "indefinite" for practical purposes because the usage level (taking water out) at a residential property is typically measured on a 24-hour use cycle.
R = total recovery rate
r = individual rock fissure well flow rate for individual flow rate times (for example rock fissure #1 may involve one or more flow rates depending on how its flow rate varies. We add all of these r's for each rock fissure together to get the total flow from that fissure over 24-hours)
n = the total number of rock fissures feeding the well at all depths of the well opening
R0 = SUM [r1 - rn]
To include the variation in flow rate over time at each rock fissure that feeds a water well, we write an integral equation something like this:
R = [INTEGRAL 0 to X] SUM [r1 - rn] where the interval 0-X represent the varying flow rates over time.
Definition of Total Water Available from a Water Well over a Given Time Period
The total volume of water available from a water well is the sum of the static head plus the recovery rate for the time period, typically 24-hours.
Volume of Water over 24-hours = Static Head (h) + Recovery Rate (R)
Details of "how much water is in the well" are discussed
at WELL FLOW RATE
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