A Primer on Well-Scale Processes
                 Well-Scale
          and uses for the Snap Sampler

               Ambie...
Subsurface Contaminant Transport and Monitoring
     Site-Scale Process
                                         Dissolved...
Well-Scale Processes-            Part 1
     Ambient
Ambient Flow-Through in
 Monitoring Wells:

• “Stagnant” wells?
• Is ...
Well-Scale Processes-                     Part 2
     Pumped
                                          Pumping
Flow to the...
Part 3
Snap Sampler relies on
     Natural Well Processes

Flow to the well/within the well

• Mixing processes
• Stabiliz...
Part 1



“Horizontal Laminar Flow”
A conventional assumption—but
 does it occur in wells?
How does that assumption affect...
In many cases, all we get is
 one sample result



Internal monitoring well
 processes largely remain a
 black box.


    ...
Dye source with gravity feed to      Piezometers
   injection port


Upgradient/                                          ...
72 cm
                    7 cm deep
         vertical

                    10 cm wide
                                    ...
Clear water

              P3070011@ 3/07/03 217a
              test start 420p on 3/06/03
      Dye     calc. dye density...
P3070017@ 3/07/03 817a
test start 420p on 3/06/03
calc. dye density: 0.999986 g/cc
7:00 hrs. since dye emerged
seepage vel...
P3070031@ 3/07/03 1017p
test start 420p on 3/06/03
calc. dye density: 0.999986 g/cc
21:00 hrs. since dye emerged
seepage v...
P3080046 @ 3/08/03 117p
test start 420p on 3/06/03
calc. dye density: 0.999986 g/cc
36:00 hrs. since dye emerged
seepage v...
P3090070 @ 3/09/03 117p
test start 420p on 3/06/03
calc. dye density: 0.999986 g/cc
60:00 hrs. since dye emerged
seepage v...
percent of
                                                                   initial dye
                                ...
Studies with the
Polyethylene Diffusion Bag (PDB)
   Sampler:
~80% of wells show little or no
  stratification
Causes:
1. ...
For those wells that do
 show ambient
 stratification:
Aquifer must be stratified
But what causes
 contaminants to maintai...
P21000024 @ 2/10/03 1240a
                             test start 0900 on 2/9/03
                             calc. dye de...
P21000060 @ 2/10/03 0640a
                             test start 0900 on 2/9/03
                             calc. dye de...
P21000059 @ 2/10/03 1038p
                             test start 0900 on 2/9/03
                             calc. dye de...
~1-4 x 10-5 lower density




                            P2210125@ 2/21/03 0325p
                            test start 1...
~1-4 x 10-5 lower density




                            P2220081@ 2/22/03 0734p
                            test start 1...
~1-4 x 10-5 lower density




                        P2230046@ 2/23/03 1134p
                        test start 1120a on ...
Common   Possible   Possible   Rare, if ever
Got Heterogeneity?

Heterogeneous Sand Tank Well Model at NFESC
Velocity = x

Dye introduced in high K zone
                                              Velocity = ~8x
Bulk velocity is ...
No “Horizontal Laminar Flow”
Concept not replicated in the
 physical model study




  Flow-weighted averaging
  effect ma...
Contaminant Stratification
Reflects aquifer stratification
May not show direct 1:1
 correspondence



Multilevel data usef...
Part 2
                               Pumping




Active Sampling Methods
Water chemistry changes as a
 well is pumped
Why...
Grout




                                                     Varljen, et al., 2006,
                                    ...
Pumping

Stability parameters
 monitored
Proxy for contaminant


Stability could occur…
     early in pumping
     or la...
Well Purging is Designed to Collect
         Representative Samples
             But how effective is it?

Gibs and Imbrig...
a'   b'
                                                              0.5 -0.5
               1.0
                        ...
Questions to Answer

What other factors impact purge stability?


      and how do you KNOW that reflects a
            “r...
Density Effects During Purging




                     Dye trace
      Injected dye

                       P2260032@ 2/2...
Density Effects During Purging




  Note dye slugs
  move               P2260048@ 2/26/03 0344p
  horizontally       test...
Density Effects During Purging


                    “light” dye moves
                        up despite
                ...
Density Effects During Purging




                     P2260082@ 2/26/03 0453p
                     test start 0312p on 2...
Density Effects During Purging




                     P2260096@ 2/26/03 0522p
                     test start 0312p on 2...
Rhodamine Fluorescence
                              Rhodamine WT Fluorescence Results
           Light dye entering cente...
Reducing Purge Rate Prior to Sampling:

          Good practice to limit VOC losses?
        …or trading one problem for a...
Reducing flow rate as acceptable practice.
Historically….USEPA, September 1985, Practical Guide for
  Ground-Water Samplin...
Changing Flow Rate




   No flow       250 ml/min        1000 ml/min
No drawdown   0.10 ft drawdown   0.50 ft drawdown
Changing Flow Rate
                                             Start Pumping with Tracer
                                ...
Changing Flow Rate
 Reduce flow rate, reduce drawdown




                                 3:00 minutes     5:00 minutes  ...
Changing Flow Rate
                                       Large tracer
                                    concentration d...
Pumping


Lots of action occurs in
 the “Black Box”


Averaging of inflow
 occurs in the pump
 tubing, not in the well


 ...
•   Cal/EPA Department of Toxic Substances Control

 •   U.S. Air Force; U.S. Navy

 •   Dr. James Martin-Hayden, Universi...
In-well mixing inhibitors:
               isolating inflow zones

                                                    Snap...
Upcoming SlideShare
Loading in …5
×

R1 Epa Well Dynamics

1,005 views

Published on

This presentation was given to Region 1 EPA. It illustrates flow, transport and mixing that can occur in monitoring wells in ambient conditions and during pumping.

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,005
On SlideShare
0
From Embeds
0
Number of Embeds
14
Actions
Shares
0
Downloads
24
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

R1 Epa Well Dynamics

  1. 1. A Primer on Well-Scale Processes Well-Scale and uses for the Snap Sampler Ambient Flow-Through Flow-Through Flow-Weighted Averaging vs. Stratification Flow-Weighted Pump-Induced Flow Dynamics Pump-Induced SANFORD L. BRITT, PG, CHG Principal Hydrogeologist ProHydro, Inc. CAL/EPA Fairport, New York (585) 385-0023 Sandy.Britt@ProHydroInc.com DTSC
  2. 2. Subsurface Contaminant Transport and Monitoring Site-Scale Process Dissolved phase transport in NAPL (Free Product) Flow ground water In the Unsaturated zone Impact of NAPL at the water table Density important in NAPL phase Volatilization of NAPL into soil gas Density less important in dissolved phase (at least in Dissolution into groundwater the aquifer) Monitoring Well WHAT Vapor ABOUT UST Residual THIS Free Product SCALE? Free Product Dissolved Contaminant Groundwater Flow
  3. 3. Well-Scale Processes- Part 1 Ambient Ambient Flow-Through in Monitoring Wells: • “Stagnant” wells? • Is there really “Horizontal Laminar Flow?” • Flow-weighted averaging? Homogeneous vs. Stratified: • Contaminant inflow position • Density effects • Flow-weighted averaging Vertical Gradient Flow: • When does it occur? • How does it affect sampling?
  4. 4. Well-Scale Processes- Part 2 Pumped Pumping Flow to the well/within the well • Hydraulically controlled • Infinite permeability inside the well Purging • Well Volume • Low Flow Parameter Stabilization • Proxy for contaminant • 1:1 match? • Flow-weighted averaging? Anecdotes • Changing purge rate • Density effects
  5. 5. Part 3 Snap Sampler relies on Natural Well Processes Flow to the well/within the well • Mixing processes • Stabilization Flow-weighted averaging • Stratification testing • High correlations with traditional methods In Situ Sealing • No Surface Pouring • No VOC loss • No Oxygen
  6. 6. Part 1 “Horizontal Laminar Flow” A conventional assumption—but does it occur in wells? How does that assumption affect decision making? ? What does happen to stratified contaminants between sampling events? ? Maintain vertical position? Reposition? Mix and Average?
  7. 7. In many cases, all we get is one sample result Internal monitoring well processes largely remain a black box. ? How do you test internal monitoring well dynamics? Build a physical model
  8. 8. Dye source with gravity feed to Piezometers injection port Upgradient/ Effluent influent reservoir reservoir Constant head reservoir Dye port Homer’s Influent water supply supply from bucket constant head Simulated 4-inch well Effluent drain reservoir
  9. 9. 72 cm 7 cm deep vertical 10 cm wide flow flow P3070009@ 3/07/03 1217a test start 420p on 3/06/03 calc. dye density: 0.999986 g/cc -1:00 hrs. since dye emerged seepage velocity: 0.47 ft/day flow flow 50 cm 50 cm
  10. 10. Clear water P3070011@ 3/07/03 217a test start 420p on 3/06/03 Dye calc. dye density: 0.999986 g/cc 1:00 hrs. since dye emerged seepage velocity: 0.47 ft/day Clear water
  11. 11. P3070017@ 3/07/03 817a test start 420p on 3/06/03 calc. dye density: 0.999986 g/cc 7:00 hrs. since dye emerged seepage velocity: 0.47 ft/day
  12. 12. P3070031@ 3/07/03 1017p test start 420p on 3/06/03 calc. dye density: 0.999986 g/cc 21:00 hrs. since dye emerged seepage velocity: 0.34 ft/day
  13. 13. P3080046 @ 3/08/03 117p test start 420p on 3/06/03 calc. dye density: 0.999986 g/cc 36:00 hrs. since dye emerged seepage velocity: 0.55 ft/day
  14. 14. P3090070 @ 3/09/03 117p test start 420p on 3/06/03 calc. dye density: 0.999986 g/cc 60:00 hrs. since dye emerged seepage velocity: 0.46 ft/day
  15. 15. percent of initial dye concentration 33% 40% 35% Flow weighted averaging Britt, SL, 2005, Testing the In-Well Horizontal Laminar Flow Assumption with a Sand Tank Well Model. Ground Water Monitoring and Remediation 25, no. 3 p.73-81
  16. 16. Studies with the Polyethylene Diffusion Bag (PDB) Sampler: ~80% of wells show little or no stratification Causes: 1. Contaminants not stratified in the aquifer 2. Flow Weighted Averaging in the well 3. Vertical Flow
  17. 17. For those wells that do show ambient stratification: Aquifer must be stratified But what causes contaminants to maintain stratification?  Entry point  Density differential  Pressure gradient !! Contaminants may stratify at different intervals than they enter !!
  18. 18. P21000024 @ 2/10/03 1240a test start 0900 on 2/9/03 calc. dye density: 0.999996 g/cc 10:06 hrs. since dye emerged seepage velocity: 1.08 ft/day ~1-4 x 10-5 higher density
  19. 19. P21000060 @ 2/10/03 0640a test start 0900 on 2/9/03 calc. dye density: 0.999996 g/cc 16:06 hrs. since dye emerged seepage velocity: 1.08 ft/day ~1-4 x 10-5 higher density
  20. 20. P21000059 @ 2/10/03 1038p test start 0900 on 2/9/03 calc. dye density: 0.999996 g/cc 32:04 hrs. since dye emerged seepage velocity: 0.90 ft/day ~1-4 x 10-5 higher density
  21. 21. ~1-4 x 10-5 lower density P2210125@ 2/21/03 0325p test start 1120a on 2/20/03 calc. dye density: 0.999935 g/cc 16:00 hrs. since dye emerged= seepage velocity: 0.79 ft/day
  22. 22. ~1-4 x 10-5 lower density P2220081@ 2/22/03 0734p test start 1120a on 2/20/03 calc. dye density: 0.999935 g/cc 44:09 hrs. since dye emerged seepage velocity: 0.74 ft/day
  23. 23. ~1-4 x 10-5 lower density P2230046@ 2/23/03 1134p test start 1120a on 2/20/03 calc. dye density: 0.999935 g/cc 72:09 hrs. since dye emerged seepage velocity: 0.54 ft/day
  24. 24. Common Possible Possible Rare, if ever
  25. 25. Got Heterogeneity? Heterogeneous Sand Tank Well Model at NFESC
  26. 26. Velocity = x Dye introduced in high K zone Velocity = ~8x Bulk velocity is 0.5 ft/day • High K unit ~1.6 ft/day • Low K unit ~0.2 ft/day  High K unit contributes ~2/3 of the well’s inflow volume { Dye enters well only here Dye migrates vertically in both directions 6h 9h 12h 15h 18h
  27. 27. No “Horizontal Laminar Flow” Concept not replicated in the physical model study Flow-weighted averaging effect may be prevalent under ambient conditions
  28. 28. Contaminant Stratification Reflects aquifer stratification May not show direct 1:1 correspondence Multilevel data useful for interpretation Useful for selection of single sampling interval
  29. 29. Part 2 Pumping Active Sampling Methods Water chemistry changes as a well is pumped Why does chemistry change?  “Stagnant” water? Or  A varying mix of water entering the pump?
  30. 30. Grout Varljen, et al., 2006, Numerical Sand Pack Simulations to Assess the Monitoring Zone Actual Monitoring Zone Achieved during Low-Flow Purging Pump Intake Screen Zone and Sampling, GWMR, 26: p. 44-52 End Cap Hydraulics controls flow But purge time controls what water comes from the pump
  31. 31. Pumping Stability parameters monitored Proxy for contaminant Stability could occur…  early in pumping  or late Depends on:  Pre-purge well stratification  Stratification in the aquifer  Inflow characteristics  Shadow effects in the aquifer  Density effects  How you measure
  32. 32. Well Purging is Designed to Collect Representative Samples But how effective is it? Gibs and Imbrigiotta (1990) showed 3 well volume purging resulted in purge stability parameter stabilization 84% of the time, and VOC contaminant stabilization only 55% of the time. Groundwater, v. 28, p. 68-78 Martin-Hayden (2000) indicated contaminant stratification in the aquifer outside the well may result in relatively large purge volumes to achieve a flow-weighted average—5 well volumes may be needed to achieve 95% of the flow- weighed average. Groundwater, v.38, p. 12-19
  33. 33. a' b' 0.5 -0.5 1.0 -0.5 0.5 1.0 -1.0 -1.0 1.0 1.5 -1.5 C’p = Cp/Cm 0.8 -1.5 1.5 Martin-Hayden, 2000, Pum Sample Concentration p at B o ttom of Screen 2.0 -2.0 Response to Laminar Thorough Mixing -2.0 2.0 Wellbore Flow: f Screen 0.6 at Top o Implications to Ground Pump Water Data Variability, Ground Water 38: p. 12-19. 0.4 0 1 2 3 4 5 Nwv What controls when a FWA is achieved? • Stratified or Unstratified Contaminant • Inflow Location • Pump position relative to stratification Zero volume purge and late-time purge often closest to FWA
  34. 34. Questions to Answer What other factors impact purge stability? and how do you KNOW that reflects a “representative” sample? More Experiments… • Density effects on purge capture • Flow rate changes
  35. 35. Density Effects During Purging Dye trace Injected dye P2260032@ 2/26/03 0312p test start 0312p on 2/26/03 Dye density 0.999935 g/cc Time elapsed pumping 0:00 flow rate = 150 ml/min Cumulative flow = 0 0 WV Discharge from bottom
  36. 36. Density Effects During Purging Note dye slugs move P2260048@ 2/26/03 0344p horizontally test start 0312p on 2/26/03 Dye density 0.999935 g/cc Time elapsed pumping 0:32 flow rate = 150 ml/min Cumulative flow = 4.8L 1 WV
  37. 37. Density Effects During Purging “light” dye moves up despite pumping from the bottom P2260067@ 2/26/03 0423p test start 0312p on 2/26/03 Dye density 0.999935 g/cc Time elapsed pumping 1:11 flow rate = 150 ml/min Cumulative flow = 10.65L 2WV
  38. 38. Density Effects During Purging P2260082@ 2/26/03 0453p test start 0312p on 2/26/03 Dye density 0.999935 g/cc Time elapsed pumping 1:41 flow rate = 150 ml/min Cumulative flow = 15.15L 3WV
  39. 39. Density Effects During Purging P2260096@ 2/26/03 0522p test start 0312p on 2/26/03 Dye density 0.999935 g/cc Time elapsed pumping 2:10 flow rate = 150 ml/min Cumulative flow = 19.50 4WV
  40. 40. Rhodamine Fluorescence Rhodamine WT Fluorescence Results Light dye entering center, pump from middle 3-21-03, light dye in middle port, pump from bottom 100% 90% 80% 70% 60% Dye Pump Result 50% Top of Well Result Bottom of Well Result 40% Flow Weighted Average (est.) 30% 20% 10% 0% 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 W ell V olumes
  41. 41. Reducing Purge Rate Prior to Sampling: Good practice to limit VOC losses? …or trading one problem for another? • Historic understanding that filling bottles at a high rate may cause VOC loss during sampling • Recognition of the advantages of low-flow purging • In-well flow dynamics during purging and sampling hard to examine
  42. 42. Reducing flow rate as acceptable practice. Historically….USEPA, September 1985, Practical Guide for Ground-Water Sampling, EPA 600/2-85/104 Rate should be kept to a minimum. Reduce sampler purge rate to desired 100 ml/minute during sampling Recently… USEPA, May 2002, Ground-Water Sampling Guidelines for Superfund and RCRA Project Managers, EPA 542-S-02-001 “…samples will be collected by lowering the flow rate to a rate that minimizes aeration of the sample while filling the bottles (approximately 300 ml/min).” ASTM, March 2002, Standard Practice for Low Flow Purging and Sampling For wells and devices used for ground-water quality investigations, D 6771-02  “…pumping rate may remain at the established purging rate or it may be adjusted downward…”
  43. 43. Changing Flow Rate No flow 250 ml/min 1000 ml/min No drawdown 0.10 ft drawdown 0.50 ft drawdown
  44. 44. Changing Flow Rate Start Pumping with Tracer Stable water level, stable concentration Drawdown 30 seconds 4:00 minutes 7:00 minutes 13:00 minutes 20:00 minutes 9:00 minutes stable pump rate down For suspense….
  45. 45. Changing Flow Rate Reduce flow rate, reduce drawdown 3:00 minutes 5:00 minutes 7:00 minutes 9:00 minutes 30 seconds 2:00 minutes pump rate down pump rate down pump rate down pump rate down pump rate down pump rate down Casing drawdown recovery is faster than upper zone inflow rate… Resulting in…. …Displacing tracer slug away from pump intake
  46. 46. Changing Flow Rate Large tracer concentration drop Reduce pump rate concentration re-equilibrates Concentration in 5-7 minutes stable in 9-13 (after you’re done sampling) minutes Temporarily overweight water entering below the pump intake
  47. 47. Pumping Lots of action occurs in the “Black Box” Averaging of inflow occurs in the pump tubing, not in the well Purge parameters need close watch Utmost care is required to maintain consistency- disruption is easy
  48. 48. • Cal/EPA Department of Toxic Substances Control • U.S. Air Force; U.S. Navy • Dr. James Martin-Hayden, University of Toledo • Interstate Technology and Regulatory Council (ITRC) Diffusion Sampler Workgroup CAL/EPA DTSC
  49. 49. In-well mixing inhibitors: isolating inflow zones Snap Sampler Purge (open well) 0.004 MW-17 Phenol Snap Sampler (open well) 1200 6.53 1000 C o n c e n tra ti o n m g /L 800 118 Purge 600 Snap, open well 710 Snap w/ isolators 400 200 333 0 ? -0 4 -0 5 -0 6 4 5 6 -0 4 -0 5 -0 6 3 4 5 6 r- 0 r- 0 r- 0 t- 0 t- 0 t- 0 t- 0 327 J ul J ul J ul J an J an J an Ap Ap Ap Oc Oc Oc Oc Date ? 293 Snap Sampler ? 346 (w/ baffles)

×