1. NGWA 2004 Microbial GWQ Interest Group
Introduced Coliform Bacteria during Pump Replacement and Well Service: Diagnosis Prevention and Decontamination
2/22/2019
EGIS, Well Video & Geophysical Services:

2. EGIS, Well Video & Geophysical Services: 919-929-8363By
Michael L. Vaught
EGIS
441 Northside Dr
Chapel Hill, NC 27516 or
2/22/2019
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3. Two Wells that Became Coliform Positive after Pump Service
Calvary Baptist Daycare
Piedmont granitic rock aquifer
Salisbury, NC
Orchard at Altapass
Blue ridge gneiss rock aquifer
Altapass, NC (Blue Ridge Parkway)
2/22/2019
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4. EGIS, Well Video & Geophysical Services: 919-929-8363
History of Clean Tests
Calvary Baptist Daycare
Owners memory
Drilled in 1987
Daycare started in 1996
Tested clean until pump pulled
Public Water records
NCDENR Public Water Supply since 1996
Coliform positive = pump service in August, 20003
2/22/2019
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5. EGIS, Well Video & Geophysical Services: 919-929-8363
History of Clean Tests
Orchard at Altapass
Owner/ operators memory
Drilled in 1976
Tested clean until pump pulled
Coliform positive = pump service in October, 20003
Public Water records
Available since Feb 2004
Owners records
2/22/2019
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6. Fractured Rock Aquifers
Partially Cased Open Rock Wells
Unconfined Water Table
Topography and elevation head
Tectonic (Dikes, Faults, Emplacements)
Borehole Stability
Shallow Fractures = Less Filtration Time?
Grout Seal Casing/Conduit
2/22/2019
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7. Downhole Video & Pumping
Observe All Three Stages
Static rest.
Pumping stress.
Recharge.
Characterize well.
Construction (leaky casing?)
Borehole stability (geology)
Biofouling
Water zones
2/22/2019
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13. Salisbury Field Project– Well Data
Calvary Baptist Daycare
21’ of 6.25” galvanized casing- tight
16’ to 170’ Slight biofouling
No shallow exposed water zones
87’ slowly recharging water level
170’ downward walls clean
340’four inch standard submersible pump
415’ significant water producing fracture
455’ drillers well tag “Bottom of the Well”.
(well yield 17 gpm)
2/22/2019
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14. Altapass Field Project– Well Data
Orchard at Altapass
30’ Water level. Walls are clean.
55.5’ Bottom of the 6.25’galv csg. – tight.
74’ Weathered fracture yielding 2 gpm
155’ Major water bearing rock fracture zone
273’ four inch standard submersible pump
304’ “Bottom of the Well” from video.
(well yield about 10 gpm)
2/22/2019
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15. 1st Failed attempt to disinfect
Salisbury
First ever Pump replacement in August
8/14/03 coliform present in regular test
Well Super chlorinated and recirculated
2/22/2019
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16. 2nd Failed attempt to disinfect
Salisbury
8/27/04 coliform present in repeat tests
Well Super chlorinated and recirculated
2/22/2019
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17. 3rd Failed attempt to disinfect
Salisbury
10/06/04 coliform present in repeat tests
Well Super chlorinated and recirculated
11/13/04 coliform present in repeat tests
2/22/2019
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19. Source of Introduced Coliform
Diagnosis by Downhole Video Survey
Construction (Ridgewood – Leaky Csg?).
Shallow water.
Space below the pump.
Grass and debris in the well
Pump service work
Salisbury is playground with wood chips
Altapass surrounded by apple orchard (Oct.)
2/22/2019
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21. Eliminating Introduced Coliform
Salisbury well
Extend pump to within four feet of the bottom
Draw the well down and back flush; cycles
Raise pH to 11 and recirculate overnight
Draw the well down and back flush
Create a 200 ppm chlorine solution in the well
Maintain pH of 6 with the chlorine at 200 ppm
Recirculate solution at least 4 hours
Apply positive head by back flushing
End of second day restore service, chlorinated water
2/22/2019
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22. Eliminating Introduced Coliform
Altapass well
Extend pump to within four feet of the bottom
Draw the well down and recirculate
Pulled the pump assembly onto wooden deck
Add chlorine tablets and gravel
Reinstall pump with sleeve to the bottom
Create a 200 ppm chlorine solution in the well
Maintain pH of 6 with the chlorine at 200 ppm
Recirculate solution overnight
Cyclic Draw down and recirculation
End of second day restore service, chlorinated water
2/22/2019
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23. EGIS, Well Video & Geophysical Services: 919-929-8363
Prevention
Pump service work
Ground cover or reel system
Clean & disinfect drop-pipe and wire
Replace twisted wire
Remove and replace tape
Rubber gloves
Work clean
“… Prevention is Worth a Pound of Cure”
2/22/2019
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26. EGIS, Well Video & Geophysical Services: 919-929-8363
Summary
Avoid repeat chlorinations
Verify Well construction and condition
Flow sleeve for pumps.
Disinfection depends on distribution.
Efficient chlorination (pH & ppm)
Wells remain clean
2/22/2019
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27. EGIS, Well Video & Geophysical Services: 919-929-8363
References
Mansuy, N. (1999) Water Well Rehabilitation: a practical guide to understanding well problems and solutions, Lewis Publishers
Smith, S. A., Borch, M. A., and Noble, L. N. (1993) Evaluation and Restoration of Water Supply Wells, AWWA Research Foundation
Schnieders, J.H. (1999) Chemicals Used In Water Well Rehabilitation, U.S. Filter, Johnson Screens
2/22/2019
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