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Section 19. Requirements for Destroying Monitoring Wells and Exploration
Holes.
General requirements for destroying monitoring wells and exploration holes
are contained in Section 23 of the Water Well Standards.
Special considerations for monitoring wells and exploration holes are as follows:
- Monitoring Wells. Monitoring wells shall be destroyed in accordance with
the following requirements and Section 23 of the Water Well Standards,
irrespective of their original date of construction:
- Preliminary Work. A monitoring well shall be investigated before it is
destroyed to determine its condition and details of its construction. The
well shall be sounded immediately before it is destroyed to make sure no
obstructions exist that will interfere with filing and sealing.
The well shall be cleaned before destruction as needed so that all
undesirable materials, including obstructions to filling and sealing, debris,
oil from oil-lubricated pumps, or pollutants and contaminants that could
interfere with well destruction, are removed for disposal.
The enforcing agency shall be notified as soon as possible if pollutants or
contaminants are known or suspected to be present in a well to be destroyed.
Well destruction operations may then proceed only at the approval of the
enforcing agency. The enforcing agency should be contacted to determine
requirements for proper disposal of all materials removed from a well to be
destroyed.
- Sealing Conditions. The following minimum requirements shall be followed
when various conditions are encountered:
- The monitoring well casing, and any other significant voids within the
well, shall, at a minimum, be completely filled with sealing material, if the
following conditions exist:
- The monitoring well is located in an area of known or potential pollution or
contamination, and,
- The well was constructed and maintained in accordance with these standards.
Sealing material may have to be placed under pressure to ensure that the
monitoring well is properly filled and sealed.
- A monitoring well shall be destroyed by removing all material within the
original borehole, including the well casing, filter pack, and annular seal;
and the created hole completely filled with appropriate sealing material, if
the following conditions exist:
- The well is located in an area of known or potential pollution or
contamination, and,
- The well's annular seal, casing, screen, filter pack, or other components
were not constructed or maintained according to these standards so that well
destruction be merely filling the well casing with sealing material, as in
"a" above, would not prevent potential water-quality degradation from the
movement of poor-quality water, pollutants, or contaminants through the
destroyed well structure.
Material to be extracted from the original borehole shall be removed by means
of drilling, including overdrilling, if necessary. The enforcing agency
should be contacted to determine requirements for proper disposal of removed
materials.
Casing, filter pack, and annular seal materials may be left in place during
sealing operations, if the enforcing agency agrees they cannot or should not
be removed. In such a case, appropriate sealing material shall be placed in
the well casing, filter pack, and all other significant voids within the
entire well boring. Casing left in place may require perforation or
puncturing to allow proper placement of sealing materials. Sealing material
may have to be applied under pressure to ensure its proper distribution.
- Monitoring wells shall, at a minimum, be destroyed in accordance with the
requirements of Section 23 of the Water Well Standards if located in an area
free of any known or potential contamination or pollution.
- Exploratory Borings. Exploratory borings shall be completely filled with
appropriate sealing material from bottom to top, if located in areas of known
or suspected contamination or pollution. Borings located outside such areas
shall, at a minimum, be filled with sealing material from ground surface to
the minimum depths specified in Section 23 of the Water Well standards.
Additional sealing material shall be placed below the minimum surface seal
where needed to prevent the interchange if poor-quality water, pollutants, or
contaminants between strata penetrated by the boring.
Appropriate fill or sealing material shall be placed below and between
intervals containing sealing material. Sealing material is often economical
to use as fill material.
The boring shall be inspected immediately prior to filling and sealing
operations. All obstructions and pollutants and contaminants that could
interfere with filling and sealing operations shall be removed prior to
filling and sealing. The enforcing agency shall be notified as soon as
possible if pollutants or contaminants are known or suspected to be in a
boring to be destroyed. Well destruction operations may then proceed only at
the approval of the enforcing agency. The enforcing agency should be
contacted to determine requirements for proper disposal of removed materials.
- Placement of Material. The placement of sealing material for monitoring
wells and exploratory borings is generally described in Section 23 of the Water Well Standards and
Appendix B (Bulletin 74-81). The following additional
requirements shall be observed when placing sealing material for monitoring
well or exploratory boring destruction.
- Placement Method. The well or exploratory boring shall be filled with
appropriate sealing, and fill material where allowed, using a tremie pipe or
equivalent, proceeding upward from the bottom of the well or boring.
Sealing material shall be placed by methods (such as the use of a tremie pipe
or equivalent) that prevent freefall, bridging, and dilution of sealing
materials, and/or prevent separation of aggregate from sealants. Sealing
material may be placed by freefall only where the interval to be sealed is
dry and no more than 30 feet in depth. Fill material shall be placed by
methods that prevent bridging and voids.
- Timing and Placement. Sealing material shall be placed in one continuous
operation (or "pour") from the bottom to the top of the well or boring,
unless conditions in the well or boring dictate that sealing operations be
conducted in a staged manner, and prior approval is obtained from the
enforcing agency.
- Groundwater Flow. Special care shall be used to restrict the flow of
groundwater into a well or boring while placing sealing and fill material, if
subsurface pressure producing the flow is significant.
- Sealing Pressure. Pressure required for the placement of cement-based
sealing materials shall be maintained long enough for cement-based sealing
materials to properly set.
- Verification. It shall be verified that the volume of sealing and fill
material placed during destruction operations equals or exceeds the volume to
be filled and sealed. This is to help determine whether the well or boring
has been properly destroyed and that no jamming or bridging of the fill or
sealing material has occurred.
- Sealing and Fill Materials. Materials used for sealing exploratory
borings and monitoring wells shall have low permeabilities so that the volume
of water and possible pollutants and contaminants passing through them will
be of minimal consequence. Sealing material shall be compatible with the
chemical environment into which it is placed, and shall have mechanical
properties consistent with present and future site uses.
Suitable sealing materials include neat cement, sand-cement, and bentonite,
all of which are described in Section 9 of these standards. Bentonite shall
not be used as a sealing material opposite zones of fractured rock, unless
otherwise approved by the enforcing agency. Drilling mud or drill cuttings
are not acceptable as any part of sealing material for well destruction.
Concrete may be used as a sealing material at the approval of the enforcing
agency.
Fill material, if any, shall meet the requirements of Section 23 of the Water
Well Standards. Fill material shall be free of pollutants and contaminants
and shall not be subject to decomposition or consolidation after placement.
Drilling mud or cuttings are not acceptable as any part of fill material.
- Additional Requirements for Monitoring Wells and Exploratory Borings in
Urban Areas. The following additional requirements shall be met for
destroying wells and exploratory borings in urban areas, unless otherwise
approved by the enforcing agency:
- The upper surface of the sealing material shall end at the depth of 5
feet below ground surface; and,
- If the well casing was not extracted during destruction and sealing
operations, a hole shall be excavated around the well casing to a depth of 5
feet below ground surface after sealing operations have been completed and
the sealing material has adequately set and cured. The exposed well casing
shall then be removed by cutting the casing at the bottom of the excavation.
The excavation shall be backfilled with clean, native soil or other suitable
material.
- Temporary Cover. The well or borehole opening and any associated
excavations shall be covered at the surface to ensure public safety and to
prevent the entry of foreign material, water, pollutants, and contaminants;
whenever work is interrupted by such events as overnight shutdown, poor
weather, and required waiting periods to allow setting of sealing materials
and the performance of tests. The cover shall be held in place or weighted
down in such a manner that it cannot be removed, except by equipment or
tools.
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