Types of wells
Almost half of the United
States depends on ground water for its drinking water supply. If you have a well, it’s
important to understand the different materials that comprise your well system.
The most common water supply for the home that is not served by a public system
is a drilled well. They are
constructed by either percussion or rotary-drilling machines that penetrate about 100-400 feet into the bedrock. Where you
find bedrock at the surface, it is commonly called ledge. To serve as a water supply, a drilled well must intersect bedrock
fractures containing ground water.
The upper part of a well is lined with casing to prevent well walls from collapsing and contaminants
from entering the water supply. The casing is usually metal or plastic pipe, six inches in diameter that extends into the
bedrock to prevent shallow ground water from entering the well. The casing must extend at least 18 feet into the ground, with
at least five feet extending into the bedrock. The casing should also extend a foot or two above the ground’s surface.
A sealant, such as cement grout or bentonite clay, should be poured along the outside of the casing to the top of the well.
The well is capped to prevent surface water from entering the well.
Submersible pumps, located near the bottom of the well,
are commonly used in drilled wells. Wells with a shallow water table may have jet pumps inside the home. Most modern drilled
wells incorporate a pitiless adapter designed to provide a sanitary seal at the point where the discharge water line leaves
the well to enter the home. The device attaches directly to the casing below the frost line and provides a watertight subsurface
connection, protecting the well from contamination.
Dug wells are one of the oldest water supply technologies available. They are created by digging a hole in the ground
with a shovel or backhoe. Dug wells have usually been excavated below the groundwater table until incoming water exceeded
the digger’s bailing rate. The well was then lined (cased) with stones, brick, tile, or other material to keep it from
collapsing. It was covered with a cap of wood, stone, or concrete. Since it is so difficult to dig beneath the ground water
table, dug wells are not very deep. Typically, they are only 10 to 30 feet deep.
Dug wells are used extensively on many low-lying
islands and are often used as a supplement to rainwater harvesting systems. However, because they are so shallow, dug wells
have the highest risk of becoming contaminated. These wells also tend to go dry during a drought when the ground water table
To minimize the likelihood of contamination, a dug well should be cased with a watertight material and a cement
grout or bentonite clay sealant poured along the outside of the casing to the top of the well. It should be covered by a concrete
curb and cap that stands about a foot above the ground. The land surface around the well should be mounded to allow surface
water to run away from the well.
Driven wells are made by driving a tube into the earth to a water table above the bedrock. Also referred to as a
sand point well, the driven well can only be constructed in areas with loose or sandy soil. Lengths of pipe with a well-point
at the end are driven into the ground to reach the water, which flows into the pipe through the screened openings in the well-point.
The driven well is typically 2 inches in diameter and up to 30 feet in depth. Driven wells are commonly used for irrigation.
Similar to dug wells, driven wells are relatively shallow and have high risk of contamination.
Well Clearance Distances
Distances from Well to: |
Note 1 below
|Minimum Horizontal Distance (feet)
from Drinking Water Well to Potential Sources of Pollution ||Supplemental Requirements*
|Property line ||10 ||(*EP)|
||50 || |
|Absorption field ||100 [Old distance was 75] (may
be modified based on local conditions) ||(SUP1)(*EP) |
||100 [Old distance was 75] (may be modified based on local conditions) ||(SUP1) - clearance may be
increased or reduced depending on special circumstances given below |
|Absorption pit ||100
[Old distance was 75] (may be modified based on local conditions) ||(SUP1) |
line ||10 if line has permanent watertight joints || |
sewer line ||50 || |
|Chemically poisoned soil ||25
||(SUP3) - can reduce to 15 ft in special circumstances given below |
||50 || |
|Cisterns ||Properties served by cisterns are not
acceptable for mortgage insurance. However, the HOCs have the authority to consider waivers in areas where cisterns are typical.
||See notes below for link to key document |
|Other requirements ||
||(SUP2) - local health regulations also apply |
& SEPTIC SYSTEM CLEARANCE DISTANCES - TABLE NOTES:
Distances from a drinking water well to the contamination
sources above are in feet unless otherwise stated.
HUD distances to septic drainfield, and similar
components changed from 75' to 100' prior to 10/2009 - thanks to a reader
[anonymous by request].