Monitoring Well Post-Installation Consideration

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Monitoring Well Post-Installation Consideration

• By
• Pierre-Orly Dupont

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Introduction

• Post-Installation Considerations is important
  for
• Wells and systems integrity.
• Wells Identity.
• Long-term operation.

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Well Post-Installation considerations include

• Monitoring well development.
• Reporting of construction details.
• Maintenance and rehabilitation.
• Abandonment (decommission).

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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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General Considerations

• During installation
• There can be a loss of drilling fluids when
  encountering high permeable materials.
• This loss must be recovered.
• Fine materials from adjacent formation must be
  removed as they can alter the permeability of
  filter-packed monitoring wells.
• Extraneous materials may be dropped into the
  well.
• Cuttings may stick to the borehole wall above
  water table (air-rotary drilling).
• Cuttings from silt or clay can smear the borehole
  wall (hollow stem auger).

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General Considerations

• Goals of monitoring well development
• Remove fine materials (silt, clay, fine sand).
• Remove water lost during drilling.
• Correct damage to the borehole wall.
• Stabilize the filter pack and formation
• Maximize the hydraulic communication between the
  well and the adjacent formation material.

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Installation of a monitoring well should not be
considered complete until it has been properly
developed.
In other words, developing a well involves
procedures used to maximize its yield by
attempting to restore the geologic formation to a
predrilling state.
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Well development activity

• The application of sufficient energy to create
  ground-water flow reversals (surging).
• Pumping to draw water lost to the formation
  during drilling out of the borehole and adjacent
  formation, along with the fines that have been
  brought into the well during surging.

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Monitoring well development should continue until

• Visibly clear water is discharged during the
  active (surging) portion of the development
  process.
• Field-measured quality (e.g., pH, Eh,
  conductivity) of the discharged water stabilizes
  and the turbidity is reduced to less than 10
  Nephelometric Turbidity Units (NTU).
• The total volume of water discharged from the
  well is at least equal to the estimated volume of
  fluid lost to the formation during drilling and
  well installation.
• Therefore, there are methods to accomplish this
  development.

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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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Airlift Surging and Pumping with Compressed Air

• Work for most monitoring wells.
• Should use a dual-line airlift system instead of
  conventional single-line airlift.
• Introduction of oil.
• Change in water chemistry.
• May reduce hydraulic conductivity of formation.
• Difficult to control

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Airlift Surging and Pumping with Compressed Air

• Work for most monitoring wells.
• Should use a dual-line airlift system instead of
  conventional single-line airlift.
• Introduction of oil.
• Change in water chemistry.
• May reduce hydraulic conductivity of formation.
• Difficult to control.
• Must be at least 20-40 of submergence of the
  air discharge line.

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Determine submergence

• pumping submergence
• Length of air line below pumping water level
• Total length of air line
• X
• 100

(195/395) X 100 50
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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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Mechanical Surging

• To force water to flow into and out of a screen
  by operating a plunger up and down in the casing.

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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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Mechanical Surging
using

• For shallow well.
• Surface Centrifugal Pump
• Can be performed only if the depth to water is
  within the practical limit of suction lift.
• Less than 20 feet below ground surface.

• For wide variety of depth.
• Submersible Pump
• Pump must be decontaminated.
• New, unused discharge line from the pump should
  be used.
• No touching ground to avoid contamination.
• Not limited by suction lift.

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Mechanical Surging
with

• Surge Block
• Swab.
• Raising and lowering a surge block heavy enough
  to free-fall through the water.
• Dependent on the length and force of the surging
  strokes.
• For deeper well, should use mechanical
  assistance.
• Involves only surging.

• Bailer
• Useful for wells in low-yield formations.
• Bailer needs to clean.
• Labor-intensive.
• Require more time than other methods.

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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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High-Pressure Water Jetting

• Required equipment is large.
• Not man-portable.
• May be done by water or air.
• Use centrifugal pumps or submersible pumps.
• Help correct damage to the formations porosity
  and permeability.

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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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Well Development
Work for most monitoring well
Variety of depth-to-water conditions
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Surveying

• Locations of monitoring wells may be plotted onto
  maps for developing and interpreting hydrologic
  data.
• Water-level measurements.
• Ground water contour map.
• Elevations (National Geodetic Vertical Datum)
• GPS.
• Well Identification
• Placing a number on protective case.

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Well Post-Installation considerations include

• Monitoring well development.
• Reporting of construction details.
• Maintenance and rehabilitation.
• Abandonment (decommission).

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Reporting of construction details.

• Results of monitoring can be affected by the
  details of the wells construction.
• Presented in full detail as an appendix to a
  report.
• Report include (page 866-817)
• Borehole diameter.
• Length of screen.
• Ground surface elevation.

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Well Post-Installation considerations include

• Monitoring well development.
• Reporting of construction details.
• Maintenance and rehabilitation.
• Abandonment (decommission).

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Monitoring Well Maintenance and Rehabilitation

• Maintenance program (page 870)
• Surface Observations
• Subsurface Observations
• Ground-water sample quality (wait for lab result)
• Rehabilitation program
• Well performance has been reduced.
• Ground-water sample quality has changed.

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Well Post-Installation considerations include

• Monitoring well development.
• Reporting of construction details.
• Maintenance and rehabilitation.
• Abandonment (decommission).

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Monitoring Well and Borehole Decommissioning.
(abandonment)

• One of most important post-construction of a
  ground-water monitoring program.
• 2 main objectives to decommissioning
• Restore the borehole to its original condition.
• Prevent cross-contamination between formation.
• Should be planned and well document just like
  original well.

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Planning for Decommissioning

• 6 key element
• State, federal or local regulations (Table 12.3)

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Planning for Decommissioning

• 6 key element
• State, federal or local regulations (Table 12.3)
• Type of well or borehole to be decommissioning.
• Hydrogeologic environment.
• Chemical environment.
• Disposal of potential contamination.
• Type of equipment and quantity of grouting needed.

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Decommissioning Material

• TYPE I Portland Cement.
• Sodium bentonite.
• Use of granular, chip, or pellet forms of
  bentonite (when little water is present)
• Use a tremie pipe to place those materials

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Procedures for Decommissioning

• Recheck planning of decommissioning.
• Be sure well is free of debris.
• Determine depth of well.
• Fill the length of the screen with fine sand.
• Place decommissioning material.
• Make records and reports.

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FIN

• Any questions?