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NGWA 2004 Microbial GWQ Interest Group. Introduced Coliform Bacteria during Pump Replacement and Well Service: Diagnosis Prevention and Decontamination. By Michael L. Vaught EGIS 441 Northside Dr Chapel Hill, NC 27516 9199298363 or GWINVEST@JUNO.COM.

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ngwa 2004 microbial gwq interest group

NGWA 2004Microbial GWQ Interest Group

Introduced Coliform Bacteria during Pump Replacement and Well Service: Diagnosis Prevention and Decontamination

EGIS, Well Video & Geophysical Services: 919-929-8363

slide2
By

Michael L. Vaught

EGIS

441 Northside Dr

Chapel Hill, NC 27516

9199298363 or GWINVEST@JUNO.COM

EGIS, Well Video & Geophysical Services: 919-929-8363

two wells that became coliform positive after pump service
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)

EGIS, Well Video & Geophysical Services: 919-929-8363

history of clean tests
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

EGIS, Well Video & Geophysical Services: 919-929-8363

history of clean tests1
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

EGIS, Well Video & Geophysical Services: 919-929-8363

fractured rock aquifers
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

EGIS, Well Video & Geophysical Services: 919-929-8363

downhole video pumping
Downhole Video & Pumping
  • Observe All Three Stages
    • Static rest.
    • Pumping stress.
    • Recharge.
  • Characterize well.
    • Construction (leaky casing?)
    • Borehole stability (geology)
    • Biofouling
    • Water zones

EGIS, Well Video & Geophysical Services: 919-929-8363

salisbury field project well data
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)

EGIS, Well Video & Geophysical Services: 919-929-8363

altapass field project well data
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)

EGIS, Well Video & Geophysical Services: 919-929-8363

1 st failed attempt to disinfect
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

EGIS, Well Video & Geophysical Services: 919-929-8363

2nd failed attempt to disinfect
2nd Failed attempt to disinfect
  • Salisbury
    • 8/27/04 coliform present in repeat tests
    • Well Super chlorinated and recirculated

EGIS, Well Video & Geophysical Services: 919-929-8363

3rd failed attempt to disinfect
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

EGIS, Well Video & Geophysical Services: 919-929-8363

source of introduced coliform
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.)

EGIS, Well Video & Geophysical Services: 919-929-8363

eliminating introduced coliform
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

EGIS, Well Video & Geophysical Services: 919-929-8363

eliminating introduced coliform1
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

EGIS, Well Video & Geophysical Services: 919-929-8363

prevention
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”

EGIS, Well Video & Geophysical Services: 919-929-8363

summary
Summary
  • Avoid repeat chlorinations
  • Verify Well construction and condition
  • Flow sleeve for pumps.
  • Disinfection depends on distribution.
  • Efficient chlorination (pH & ppm)
  • Wells remain clean

EGIS, Well Video & Geophysical Services: 919-929-8363

references
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

EGIS, Well Video & Geophysical Services: 919-929-8363