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STANDARDS
Part II. Cathodic Protection Well Construction
Section 7. Sealing the Upper Annular Space.
The space between the cathodic protection well casing and the wall of the
well boring, often referred to as the "annular space," shall be effectively
sealed to prevent it from being a preferential pathway for the movement of
poor-quality water, pollutants, or contaminants. In some cases, secondary
purposes of the annular seal are to stabilize the borehole wall, protect
casing from degradation or corrosion, and ensure the structural integrity of
the casing.
General discussion of sealing requirements and methods is contained in
Section 9 and Section 13 of the Water Well Standards and Appendix B (Bulletin 74-81).
Special requirements for sealing cathodic protection wells are:
- Minimum Depth of Annular Seal.
- Minimum Depth. The annular space shall be filled with appropriate
sealing material from ground surface to a depth of at least 20 feet below
land surface. The annular space shall be sealed to a depth of at least 50
feet below land surface in congested urban areas, or where a cathodic
protection well is within 100 feet of any potential source of pollution or
contamination. Additional annular sealing material shall be installed to
greater depths where adverse conditions exist that increase the risk of
pollution or contamination of groundwater.
- Fill. Any annular space existing between the base of the annular surface
seal and the top of the anode and conductive fill interval shall be filled
with appropriate fill or sealing material. Fill material should consist of
washed granular material such as sand, pea gravel, or sealing material. Fill
material shall not be subject to decomposition or consolidation after
placement and shall be free of pollutants and contaminants. Fill material
shall not contain drill cuttings or drilling mud. Sealing material is often
more practical and economical to use for filling the annular space than
granular material.
- Sealing-Off Strata. Additional annular sealing material shall be placed
below the minimum depth of the annular surface seal, as needed, to prevent
the movement of poor-quality water, pollutants, and contaminants through the
well to zones of good-quality water. Requirements for sealing off zones are
in Section 10, below.
- Sealing Conditions. Requirements for sealing the annular space under
varied conditions are detailed in Section 9, Subsection B of the Water Well
Standards.
- Radial Thickness of Seal. A minimum of 2 inches of sealing material
shall be maintained between all casings and the borehole wall within the
interval to be sealed, except where temporary conductor casing cannot be
removed as noted in Section 9 of the Water Well Standards.
At least 2 inches of sealing material shall be maintained between all casings in a borehole,
within the interval to be sealed unless otherwise approved by the enforcing
agency. Additional space shall be provided, where needed, to allow casings
to be properly centralized and spaced and allow the use of a tremie pipe
during well construction (if required), especially for deeper wells.
- Sealing Material. Sealing material shall consist of neat cement, sand-cement, concrete, or bentonite clay as discussed in Section 9 of the Water
Well Standards. Cement-based sealing material shall be used opposite zones
of fractured rock used. Concrete shall only be used at the approval of the
enforcing agency. Drill cuttings and used drilling mud shall not be used as
any part of sealing material.
- Placement of Seal. Standards for the placement of annular seals are
described in Section 9 of the Water Well Standards and Appendix B (Bulletin 74-81).
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