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NGWA 2004 Microbial GWQ Interest Group

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

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  1. 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

  2. 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

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

  4. 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

  5. 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

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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

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