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Extending Bedrock Well Casings
INTRODUCTION
The bacterial quality of the water from a bedrock well (also called
"artesian" or "drilled") is normally very reliable. The principle exception
occurs when the top of a bedrock well is cut off below the ambient ground level,
and thus, subject to flooding. This often results in the leakage of unfiltered
surface water directly into the well. Surface water typically contains total,
fecal, and e-coli bacteria.
The purpose of this document is to provide information relative to raising
the top of a bedrock well casing above the ambient ground level. The top of the
well is commonly called the "wellhead." A buried wellhead is a serious problem
that should be corrected unless you are absolutely sure that the wellhead
will not be flooded, ever!
WELL CONSTRUCTION STANDARD
New Hampshire well construction rule We 602.02(e)(1) requires bedrock well
casings to extend above the ambient ground surface a minimum of eight inches or
more. This requirement has been in effect since 1985. An exception is allowed
only if the projection of the wellhead would create a safety hazard.
Wells constructed before July 2, 1985 are not required to conform to this
rule. However, it is highly recommended that older wells be upgraded to current
New Hampshire standards where possible. In addition, New Hampshire law RSA
482-B:15 states, "all materials and construction practices used in the
construction of a new well or pump installation, or in the maintenance, repair
or replacement of any well or pump installation, shall conform with rules
adopted by the Water Well Board."
PITLESS ADAPTOR DESIGN
The normal design of a modern bedrock well ensures that leakage can not enter
the interior of the well by requiring that the top of the well be above any
possible flood level. This is achieved by using a so called "pitless adaptor."
This configuration places the top of the well above the level of flooding while
allowing the pressurized well water to exit the casing below the ground level in
a way that ensures no leakage of contaminants into the well, and provides
protections of the pressurized water line from freezing.
Value of A Pitless Adaptor
In addition to preventing bacterial contamination, a pitless adaptor also
provides the following additional benefits:
- Easy access for all-weather replacement of a submersible pump. This will
prevent costly delay caused by the difficulty in excavating frozen soil
during the winter.
- Provides an unmistakable indicator of the well’s location relative to
inadvertent placement of a leach field on adjacent properties or damage by
heavy vehicles passing over the well.
Evaluate the Potential for Flooding of the Well Pit
The only justification for a buried wellhead is a safety issue. To determine
if an existing buried wellhead is subject to flooding one can look for staining
caused by flood waters on the inside walls of the well pit. If the staining is
above the top of the bedrock casing, an extension of the casing is absolutely
necessary. It is not reasonable to believe that the top of the buried well can
be made water tight so as to be safe in the event of a flood.
If there is no staining (meaning there is never any water buildup in
the pit), or the maximum level of staining is noticeably below the top of
the well, than extension of the well casing may arguably be deferred for the
moment. If you choose not to extend the casing, the pit should be checked
periodically during spring snow melt and after very heavy rain events to
determine the flood level.
Response to Wellhead Flooding in Hillside Locations
Where a well with a buried wellhead is located on a hillside, it may be
possible to lower the flood risk without raising the wellhead by installing a
"gravity flow" drain. This drain would be installed at the bottom of the pit and
would discharge by gravity to "above ground." Using a sump pump to dewater the
wellhead pit is not recommended due to the eventual failure(s) expected of any
mechanical device and its electrical service.
Response When the Flooding Is Caused by River or Lake
When a well is located in the flood plain of a lake or river, the typical
approach would be to bring in additional fill material to mound up around the
immediate outside of the well, and to
raise the casing using a pitless adaptor configuration. When grading the
backfill around the well, keep the backfill slope shallow on one side so that a
well rig may be easily positioned above the well for future maintenance.
Mobilization of well drilling equipment could be associated with pulling the
pump or deepening the well for more flow.
OPTIONS FOR RAISING THE WELL CASING
Before and after drawings of a well casing extension are shown on page 4.
Well code rules require that when extending the casing, the same casing material
be used as were used in the main lower casing.
Threaded Steel Casing
When the casing is steel the extension can be attached by using either a
threaded or welded connection to the existing casing. If there are threads on
the steel casing, they would be cleaned of rust and a threaded steel coupling of
same size attached. Teflon tape or plumbers’ "sealer" would be used to ensure a
watertight connection.
Where there are no threads on the existing casing, an off-the-shelf
coupling can be machined so as to just fit over the outside diameter of
the existing casing. The cost of this machining is quite reasonable. You can
also purchase these remanufactured slip couplings for particular dimensions.
Please see the details on the graphic of page 4. The bottom half of the coupling
is then welded to the well casing on the inside of the coupling, and the new
steel casing extension can be threaded into the top threaded section of this
coupling. In another option, silicone sealant is applied to the existing casing,
and the new machined coupling is driven down over the existing casing.
PVC Casing
Where casing material is PVC we suggest installation of a protective marker
to the finished area to ensure safety from cars or snowplows. These markers can
be large stone or concrete filled steel pipes set into the soil.
Rubber Sleeve
If the existing casing is PVC, a circular continuous rubber collar that
spans both the existing casing and the new extension is normally used. This
assembly is made water tight by use of stainless steel screw clamps around
both the existing and new casings.
PVC Hard Coupling
PVC coupling and solvent welding chemicals can also be used.
FOR MORE INFORMATION
For more information, please call the Water Well Board at (603)-271-1974. For
a complete list of all water supply fact sheets please request WD-WSEB-15-2. We
would appreciate your comments and suggestions pertaining to this fact sheet.
Drinking water fact sheets are available through the DES web site at: www.des.state.nh.us/wseb then select: fact sheets. Please check the
DES internet site annually for updates to this document. 9/02
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