Water Well Going Dry...Re-drill or Rehab? 2014 Clean & Safe Drinking Water Workshop, Gander, NL. Gil Violette, M.Sc.E., P.Eng.

Transcription

1 Water Well Going Dry...Re-drill or Rehab? 2014 Clean & Safe Drinking Water Workshop, Gander, NL Gil Violette, M.Sc.E., P.Eng., AMEC

2 Near-Well Aquifer Conditions Wilmot Park Wellfield Fredericton, NB 1

3 Water Well Going Dry...Re-Drill or Rehab? Near-well aquifer conditions Outline Well Performance Issues Decision, Decision: What should be done? Cost of re-drilling? Cost of Treatment?...Re-drill or Rehab? 2

4 Near-Well Aquifer Conditions Well Components Several mechanical and electrical components Ongoing maintenance required Well screen and beyond also require maintenance Flow of water entering the well should be as easy as possible 3

5 Near-Well Aquifer Conditions Corrosion / Biofouling Pump Column nodules 4

6 Near-Well Aquifer Conditions Encrustation / Clogging growth in well 5

7 Near-Well Aquifer Conditions Biofouling Aquifer Formation Sand and gravel Bedrock fracture 6

8 Near-Well Aquifer Conditions Aquifer/Screen Plugging/Clogging Images adapted from Droycon Bioconcepts 7

9 Near-Well Aquifer Conditions Aquifer/Screen Plugging/Clogging Images adapted from Droycon Bioconcepts 8

10 Near-Well Aquifer Conditions Aquifer/Screen Plugging/Clogging Filamentous Biofilm Iron Bacteria Moss-like cover on well screen Photos from Groundwater Science, City of Fredericton 9

11 Near-Well Conditions Biofouling : Most common type of bacteria - Iron Bacteria (IRB) - Sulphate Reducing Bacteria (SRB) - Heterotrophic Aerobic Bacteria (HAB) - Slime Forming Bacteria (SLYM) 10

12 Near-Well Aquifer Conditions Aquifer/Screen Plugging/Clogging 11

13 Well Performance Issues Key Well Performance Indicators Factors leading to loss of performance: Discharge (Q) Drawdown (s) Specific Capacity (SC=Q/s) Well Efficiency Geochemistry, microbiology Require historical measurements Q s 12

14 Well Performance Issues Changes in Q and s City of Fredericton 13

15 Well Performance Issues Q equal, s increased City of Fredericton 14

16 Well Performance Issues Well Efficiency: Multi-Step Pumping Test Walton s C Factor (min 2 /m 5 ) for Well Efficiency < 0.5 Properly Designed 0.5 to 1 Mild Deterioration 1 to 4 Severely Clogged > 4 Difficult / Impossible to Restore 15

17 Well Performance Issues Changes in the aquifer - Sedimentation: - Fine Particles silt and sand (Clogging) - Encrustation: - Chemical Deposits such as Calcite, Gypsum (Corrosion) - Biofouling: - Growth of Naturally Occurring Bacteria (Plugging) 16

18 Well Performance Issues Recognizing the signs - Drawdown has increased by 50%? Action - Pumping rate decrease > 50%? Action - Specific Capacity decrease > 25 to 50%? Action - Walton s Well Efficiency (C) > 0.5 Action - Screen area plugged > 50% Action - Nearby wells shown signs of biofouling? Action 17

19 Re-drill...or rehab, or do nothing? Do-nothing approach: - Something is still happening - Production issues with well, decrease discharge - Drawdown issues, changes in pump placement - Rising power costs due to higher head to pump (>s) - Issues get worse, cost to rehab increases - Could lead to permanent loss of well 18

20 Re-drill Well Drilling: 19

21 Re-drill...rehab? Regain Q Re-drill - Pro/Cons: Pros Small well, costs are low Re-use infrastructure Issues are gone Small well, costs are low Re-drill at same site Re-drill at new site Cons Problems can return Large well, costly redo Lengthy timeline Large well, costly redo New distribution infrastructure 20

22 Re-drill...or rehab? Rehab: many methods available - Methods depend on: -Type of problem - type of well - type of aquifer - Each situation can bring on customized solution - Method can range from inserting Javex down the well to a two week aggressive chemical injection / well re-development approach 21

23 Re-drill...or rehab? Rehab - Pro/Cons: Pros Regain Q very quickly Low costs Short well shut-down Re-use infrastructure Can extend life of well indefinitely Cons Preventative program Frequency of treatment unknown Can damage well 22

24 Rehab Hydraulic-Chemical Aquifer Regeneration Specific Capacity (m 3 /h/m) (SC=Q/s) new Hydraulic Chemical Dr. C. Treskatis, Water World Volume 36, Issue 6, December

25 Rehab Hydraulic-Chemical Aquifer Regeneration 700 City of Fredericton Pumping Well Specific Capacity (m 3 /d/m) January 1, 2012 April 10, 2012 July 19, 2012 October 27, 2012 February 4, 2013 Year City of Fredericton 24

26 Rehab Hydraulic Aquifer Regeneration Wire Brush / Swab City of Fredericton 25

27 Rehab Chemical Aquifer Regeneration City of Fredericton 26

28 Re-drill or Rehab... Aquifer Well Screen Photos from City of Fredericton 27

29 Re-drill or Rehab... Good connection with aquifer Photo from City of Fredericton 28

30 Re-drill...or rehab? in Conclusion - Water well performance declines with age of well - Determine cause of loss of Q or increased s, including: - hydraulic tests - biological tests - downhole camera visuals - maintain historic data - Evaluate DO-NOTHING, RE-DRILL OR REHAB approaches - If choosing rehab route, TAKE ACTION, the longer the issues persist, the more costly rehab becomes - Water wells are major investment for municipalities, best to have them perform for the longest period possible 29

31 Re-drill...or rehab? Questions? 30