How to Redevelop Groundwater Monitoring Wells Using the Air Lift Method
[Narrator] Hi, my name is Randy Bayless. I am the Groundwater
Specialist for the Indiana Kentucky Water Science Center of the U.S. Geological Survey
and today, we are going to talk about the air-lift method for well redevelopment.
Over time, groundwater wells may become partially or even fully blocked by accumulation of materials
at the well screen or openings. This blockage is typically the result of sediment, chemical
or biological accumulation of materials which may restrict the connectivity between a well
and an aquifer. If left unresolved, the water data collected from the affected well might
not be representative of the aquifer and the data will be biased or even erroneous.
There are several methods can be used to identify a well that needs to be redeveloped, including
hydrograph inspection, annual total depth of well measurements, regular well integrity
tests (slug tests) and inspection with a borehole camera. This will allow you to identify potential
problems as they arise. Comparing these results with a drillerís log will provide you the
best standard for what the total depth should be.
Safety is a very high priority.
Please read, understand and follow your Centerís Safety Plan and all pertinent equipment manuals
to prevent injuries. It is highly recommended to consult your local
safety coordinator for additional safety concerns. Minimum safety equipment but not limited to:
Steel toe boots Safety glasses or goggles
Ear plugs or muffs Leather gloves
Nitrile gloves
The standard 185 CFM, 125 psi compressor should work at most sites.
Air hoses Electrical (E) and weighted steel tapes
Misc. tools: wrenches, screwdrivers, hammers, etc.
Field computer with field forms Station description
Drillerís well log Deionized water
Inspect the Gage
Read the station description for the driving directions, site specific safety requirements
and to become familiar with the gage and equipment. Read the well log, including the casing/screen
information, the depth of water and previous redevelopment information.
Prior to redeveloping any well, you will want to complete a thorough gage inspection.
First, make consecutive tape downs to water surface using an E-tape until two measurements
agree within 0.02 feet. Record all values and corresponding times
in your field notes. Measure and record the total depth of the
well using a weighted steel tape.
Preparing the Well
Remove all equipment from the well, including the shelter above well casing.
Place the equipment a safe distance from the well to prevent creating a trip hazard.
The water in the well needs to rise and fall several feet to flush the screen.
This causes water to rapidly enter the screen during the rise and then during the fall forces
the water inside the well out the screen, removing clogging material and debris from
the well and well screen, and cleaning the gravel pack surrounding the screen.
Well Screen Cleaning
Lower the air hose several feet below the water surface.
Set the E- tape to stop several feet above the water surface.
Partially open the air supply to start raising the water level and listen and watch for the
alarm on the E-tape to go off. Shut off air supply.
Allow the well to stabilize. If possible make TDs to water surface as the
well stabilizes Repeat the process 2 or more times.
Redeveloping
Remove the E-tape from the well. Lower the air hose down 60 percent of distance
from water surface to well screen for most wells. For deep wells (greater than 300 feet)
less submergence is needed. Start the maximum flow of air.
Within a short period of time the air should force a powerful burst of water and debris
from the well. Shut off air supply and allow the well to
stabilize. Repeat the process until visual observation
indicates that the water is relatively clean. Shut off the air compressor and remove hose.
Final Inspections
Measure and record the final Total Depth of the well using a weighted steel tape.
If all of the debris at the bottom of the well has been removed from the well, the final
total depth measurement should generally be in closer agreement with the original drillerís
log. Re-install gage structures and all equipment.
Make consecutive tape downs to water surface using an E-tape until two measurements agree
within 0.02 feet. Record these measurements in your field notes.
At continuous recording sites and set the recorder to the tape down to water surface
measurement and start the recordings and transmission of data.
Decontaminate all equipment using deionized water.
Caution
Please consult your local groundwater specialist or the Office of Groundwater before attempting
any of this method on your own. The air lift method can change the geochemistry
of the formation surrounding the well or the water quality within the well.
If your well is sampled for water quality, another method should be considered.
Credits
U.S. Geological Survey, U.S. Department of the Interior
Special Thanks to Office of Groundwater, U.S. Geological Survey, Reston, VA
Produced by J. H. Poehler, Hydrologic Technician, U.S. Geological Survey, IN-KY-WSC
Field Assistant: B. C. Long, Hydrologic Technician, U.S. Geological Survey, IN-KY-WSC
Technical Advisors: R. A. Sheets, Acting Assistant Chief of Office
of Groundwater, U.S. Geological Survey, Reston, VA
E. R. Bayless, Groundwater Specialist, U.S. Geological Survey, IN-KY-WSC
J. S. Woods, Supervisor Hydrologist, U.S. Geological Survey, IN-KY-WSC
Post processing and IT Support: J. H. Poehler, Hydrologic Technician, U.S.
Geological Survey, IN-KY-WSC M. N. Gonzales, Information and Technology
Specialist, U.S. Geological Survey, IN-KY-WSC M. Worland, Computer Assistant, U.S. Geological
Survey, IN-KY-WSC
Narrated by: E. R. Bayless, Groundwater Specialist, PhD.,
U.S. Geological Survey, IN-KY-WSC
Resources Cunningham, W.L., and Schalk, C.W., 2011,
Groundwater Technical Procedures of the U.S. Geological Survey, Techniques and Methods
1-A1. Driscoll, F.G., 2nd ed. 1986, Groundwater
and Wells. St. Paul, MN: Johnson Screens. USGS Guide for Social Media, http://communities.usgs.gov/blogs/vis/audiovisual/video-and-film/