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Section 12. Casing.
The term "casing" in its broadest sense includes all tubular materials that
are permanent features of a well. Screens, collars, risers, liners, and
blank casing in monitoring wells maintain the well bore and provide a passage
for groundwater level measurement and/or sample-collection devices.
Protective casing serves to prevent accidental or intentional damage to a
well. Protective casing normally consists of heavy gauge metallic pipe
placed over the portion of the well casing that extends above ground surface.
Conductor casing usually functions as a temporary means of shoring the walls
of a well boring to allow drilling and the placement of well construction
materials. If used, temporary conductor casing is usually driven into place
during drilling and is withdrawn at the same time filter pack and annular
seal materials are installed around the well casing. Sometimes conductor
casing is left in place and is made a permanent feature of the completed well
structure. Requirements for sealing permanent conductor casing in place are
contained in Section 9.
For the purpose of these standards, the term "casing" applies to screens,
collars, risers, and blank casing, and other specialized products used to
maintain the well bore. General discussion and standards for casing
materials are contained in Section 12 of the Water Well Standards.
Special considerations that apply to monitoring well casing are described below:
- Casing Material.
- Chemical Compatibility. Special considerations shall be given to the
selection of casing materials for monitoring wells installed in environments
that are chemically "hostile". The selected casing shall resist chemical
attack and corrosion.
Special consideration should be given to the selection of casing materials
for wells to be used for sensitive water-quality determinations. Chemical
interaction between casing materials and pollutants, contaminants,
groundwater, filter pack material, and geologic materials could bias ground-
water quality determinations.
- Used Casing. Used casing may be acceptable in certain cases, at the
approval of the enforcing agency.
- Plastic and Steel Casing. Plastic and steel well casing materials are
commonly used for monitoring wells. The principal plastics used for water-
quality monitoring wells are thermoplastics and fluorocarbon resins.
Standards for thermoplastic well casing are in Section 12 of the Water Well
Standards. The principal thermoplastic material used for water quality
monitoring wells is polyvinyl chloride (PVC).
Fluorocarbon casing materials include fluorinated ethylene propylene (FEP)
and polytetrafluoroethylene (PTFE). Fluorocarbon resin casing materials are
generally considered immune to chemical attack. Fluorocarbon casing
materials shall meet the following specifications, including the latest
revisions thereof:
- ASTM D3296, Standard Specification for FEP-Fluorocarbon Tube.
- ASTM D3295, Standard Specifications for PTFE Tubing.
Stainless steel is the most common form of metallic casing in monitoring
wells constructed for sensitive water quality determinations. Stainless
steel casing shall meet the provisions of ASTM A312, Standard Specification
for Seamless and Welded Austenitic Stainless Pipe, and shall meet general
requirements for tubular steel products in Section 12 of the Water Well
Standards.
- Multiple Screens. Monitoring well casing strings shall not have openings
in multiple water-bearing units (multi-level monitoring wells), if poor-
quality water, pollutants, or contaminants in units penetrated by the well
could pass through the openings and move to other units penetrated by the
well and degrade groundwater quality, unless otherwise approved by the
enforcing agency.
- Bottom Plugs. The bottom of a monitoring well casing shall be plugged or
capped to prevent sediment or rock from entering the well.
- Casing Installation. Discussion and standards for the installation of
casing materials are in Section 12 of the Water Well Standards.
Special considerations for monitoring wells are:
- Cleanliness. Casing, couplings, centralizers, and other components of
well casing shall be clean and free of pollutants and contaminants at the
time of installation.
- Joining Plastic Casing. Depending on the type of material and its
fabrication, plastic casing shall be joined (threaded or otherwise coupled)
in a manner that ensures its water tightness. Organic solvent welding
cements or glues should not be used for joining plastic casing if glues or
cement compounds could interfere with water-quality determinations.
- Impact. Casing shall not be subjected to significant impact during
installation that may damage or weaken the casing.
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