Current through Register Vol. 48, No. 12, March 22, 2024
This Section shall apply to all monitoring wells, except those
wells installed to monitor chemicals leaking from underground storage tanks
which are installed within the excavation made for the installation of the
underground storage tank.
a) Casing.
All monitoring wells shall have casing which meets the requirements of Section
920.90(a),
except where the design specifications require the use of another material.
Threaded joints shall be required where plastic casing is used. Casing must be
clean, free of rust, grease, oil or contaminants and be composed of materials,
including but not limited to steel and plastic, that will not affect the
quality of the water sample. All casing shall be watertight. The casing shall
be centered in the borehole, be free of any obstructions and allow sampling
devices to be lowered into the well.
b) Well Screen. All monitoring well screens
shall be constructed of non-corrosive and non-reactive material. All well
screens shall be permanently joined to the well casing and shall be centered in
the borehole.
c) Filter Packs. All
monitoring wells installed in unconsolidated material shall be constructed with
filter packs. When used, the filter pack shall be the only material in contact
with the well screen.
1) The filter pack
shall consist of sand or gravel. The sand or gravel used for filter packs shall
have an average specific gravity of not less than 2.50. The filter pack
material shall be sized to match the screen slot size and the surrounding
formation to prevent the formation materials from entering the screen. The sand
or gravel shall be free of clay, dust and organic matter. Crushed limestone,
dolomite or any material containing clay or any other material that will
adversely affect the performance of the monitoring well shall not be used as
filter pack.
2) Installation. The
filter pack shall extend a maximum of 6 inches below the bottom of the screen
to 2 feet above the top of the screen. For water table observation wells
constructed in areas where the depth to the water table is less than 5 feet,
the required filter pack height above the top of the well screen may be reduced
to 6 inches to allow for the required amount of annular space sealant to be
placed.
d) Grouting
Requirements. All materials and procedures used in the installation of annular
seals for groundwater monitoring wells shall meet the requirements of this
Section. The annular sealing material above the filter pack shall prevent the
migration of fluids from the surface and between aquifers. Sealing material
shall be chemically compatible with anticipated contaminants.
1) Annular Space Seal. All monitoring wells
shall be installed with an annular space seal. The annular seal shall extend
from the top of the filter pack to the surface.
2) Above Ground Surface Completion. Where the
monitoring well does not terminate flush with the ground surface in accordance
with Section
920.170(d)(3),
the casing shall extend at least 8 inches above the ground surface. The top of
the casing shall be provided with a locking cap. If the monitoring well is
located in a floodplain, the cap shall be watertight. Protective devices, such
as rings of brightly colored posts around the well, shall be installed in areas
where the casing is likely to be struck by farm vehicles or by individuals who
are unaware of the existence of the well.
3) Ground Surface Completion. Monitoring well
casing may terminate at the ground surface provided a flush-mounted well
completion pipe is installed over the casing. The flush-mounted completion pipe
shall consist of a metal casing at least four inches larger in diameter than
the well casing. Monitoring wells terminating at the surface may be allowed
only in areas traveled by vehicles. The flush-mounted well completion pipe
shall have a water tight seal and the annular opening around the well
completion pipe shall be grouted. The well casing shall be sealed with a
watertight locking cap.
e) Drilling Methods and Fluids. The drilling
method shall introduce the least possible amount of foreign material into the
borehole, produce the least possible disturbance to the formation and permit
the proper construction and development of the required diameter well. Water
from a source free of bacterial and chemical contamination shall be used in the
drilling fluid mixture.
f) Disposal
and Decontamination.
1) All drill cuttings and
fluids and surge and wash waters from borehole and monitoring well construction
and development shall be disposed of in a manner which will not result in
contamination of the immediate area or result in a hazard to individuals who
may come in contact with these materials.
2) All monitoring well construction equipment
shall be decontaminated by washing and triple rinsing or high pressure heat
cleaning to prevent cross-contamination of monitoring wells or in accordance
with design specifications, whichever is more stringent.
g) Special Circumstances and Exceptions.
1) The Department may require more
restrictive or alternative well material, assembly or installation if the
contaminant concentrations or geologic setting require alternative
construction.
2) Variances to the
requirements of this subsection may be approved by the Department prior to
installation or abandonment. A variance request shall state the reasons why
compliance with the rule is impractical or impossible. The Department shall
approve a variance when it can be shown that the particular contaminant or
drilling method requires alternative materials or procedures to safeguard
against contamination of the groundwater.
h) Abandonment or Decommissioning of
Monitoring Wells. All abandoned monitoring wells shall be sealed in accordance
with Section
920.120.
i) Reporting. Within 30 days after a
monitoring well has been constructed or abandoned, the owner, designer or
consulting firm shall submit a report of construction or abandonment to the
Department on such forms as are prescribed and furnished by the
Department.