Water Wells 101

In our trade, when one mentions “PUMP” we naturally think of a well pump. Today’s topic: Water wells.

To define it, a well is simply a deep, skinny hole in the ground from which we pump water.


The illustration shows a typical 6” well such as we see in many yards. A well driller drills about an 8” diameter hole in the ground until he hits bedrock. He continues drilling 2 feet into the bed rock. He then inserts 6” steel or plastic casing into the hole until the casing rests on the bedrock. Once this is done, the driller pumps cement-like slurry (a semi-liquid mixture) called grout into the annular space between the casing and the hole up about 30 feet from the bedrock to hold the casing in place for the next phase. A smaller bit that fits into the casing is used to continue drilling into the bedrock. Once sufficient water is found, the drilling process is over. The driller then pumps more grout into the annular space to the surface. In addition to holding the casing in place, the grout hardens and prevents surface water from getting into the well and contaminating the water. Depending on local codes, the well casing will extend about 18” above grade.

What is “sufficient water” you ask? Well, that’s a deep subject (get it… Sorry, I couldn’t resist). Local health departments dictate sufficient water. The following is taken from the Carroll County Health Department web site:
• Yield Test: Required of all new wells. Domestic wells must be capable of producing at least 1 gallon per minute. Also, at least once a day, the well must be able to produce 500 gallons in a 2-hour period. Well storage and tank storage is taken into consideration for this requirement. A well yield test must be conducted for a minimum of 3 hours. If after 3 hours, the well has consistently yielded 4 gallons per minute or more, the test may be terminated. If a well yields under 4 gallons, it must be yield tested for a minimum of 6 hours.

Here we go: We have a well that produces 1 gpm. That is 120 gallons in 2 hours. If we need 500 gallons in 2 hours to meet Health Department requirements, then we need 380 gallons storage in the well. At 1½ gallons /ft., we would need approximately a 253’ column of water from the bottom of the well to the static water line. If a well yields 10 gpm (a really great yield) then in 2 hours, it will produce 1,200 gallons! This certainly exceeds the 500 gallon requirement.

There is no minimum depth requirement for a well in Carroll County, although there must be at least 20 feet of casing. I’ve seen some wells in the county less than 100’ deep…they are generally older wells.

Now, there are other types of wells beyond the 6” drilled type we see in our area. BUT you’ll have to stay tuned and check back next week to find out what they are! (I love a good cliffhanger ending).

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