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Baffles May Allow Effective Multilevel Baffles May Allow Effective Multilevel Sampling in Traditional Monitoring WellsSampling in Traditional Monitoring Wells
Mr. Sandy Britt, PG, CHGProHydro, Inc.
Monica Calabria, CH2M Hill
BATTELLEConference on the
Remediation of Chlorinated and
Recalcitrant Compounds
Monterey, CaliforniaMay 19, 2008
Groundwater Flow
UST
Dissolved Contaminant
Subsurface Contaminant Transport and Monitoring
The The zz dimension is often the most importantdimension is often the most important
Alternatives to learn about the z-dimension:
• Multilevel approach with transects• Waterloo Profiler, CMT, Westbay, nested wells
• Historically, most sites have long screen wells.
What to do about this?
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• By purging wells, we get one sample resultone sample result
• How do you know what the interaction is between inside and outsideinside and outside a well?
• Try multimulti--intervalintervalsampling?
The Black Box
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Does a concentration Does a concentration found inside a well found inside a well correspond tocorrespond to……
• A specific interval?
• A flow weighted average?
Stratification testing can give clues, but not a definitive answer
How does water entering a well really behave?
1:1 Correspondence?
? ?
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Dye source with gravity feed to injection port
Simulated 4-inch well
Upgradient/ influent reservoir
Piezometers
Dye port
Constant head reservoir
Homer’s water supply bucket
Influent supply from constant head reservoir Effluent drain
Effluent reservoir
DTSC Sand Tank Well Model
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P3070009@ 3/07/03 1217atest start 420p on 3/06/03calc. dye density: 0.999986 g/cc-1:00 hrs. since dye emerged seepage velocity: 0.47 ft/day
72 cm vertical
flow
50 cm50 cm
7 cm deep
10 cm wide
flow
flow
flow
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P3070011@ 3/07/03 217atest start 420p on 3/06/03calc. dye density: 0.999986 g/cc
1:00 hrs. since dye emerged seepage velocity: 0.47 ft/day
Dye
Clear water
Clear water
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P3070017@ 3/07/03 817atest start 420p on 3/06/03calc. dye density: 0.999986 g/cc
7:00 hrs. since dye emerged seepage velocity: 0.47 ft/day
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P3070031@ 3/07/03 1017ptest start 420p on 3/06/03calc. dye density: 0.999986 g/cc
21:00 hrs. since dye emerged seepage velocity: 0.34 ft/day
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P3080046 @ 3/08/03 117ptest start 420p on 3/06/03calc. dye density: 0.999986 g/cc
36:00 hrs. since dye emerged seepage velocity: 0.55 ft/day
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P3090070 @ 3/09/03 117ptest start 420p on 3/06/03calc. dye density: 0.999986 g/cc
60:00 hrs. since dye emerged seepage velocity: 0.46 ft/day
12Britt, 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
percent of initial dye concentration
33%
40%
35%
Flow weighted averaging
Mixing/averaging effect
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P21000024 @ 2/10/03 1240atest start 0900 on 2/9/03calc. dye density: 0.999996 g/cc10:06 hrs. since dye emergedseepage velocity: 1.08 ft/day
~1-4 x 10-5
higher density
Density Effects – Passive/ambient
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P21000059 @ 2/10/03 1038ptest start 0900 on 2/9/03calc. dye density: 0.999996 g/cc32:04 hrs. since dye emergedseepage velocity: 0.90 ft/day
~1-4 x 10-5
higher density
Density Effects – heavier
~3%
~70%
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P2210125@ 2/21/03 0325ptest start 1120a on 2/20/03calc. dye density: 0.999935 g/cc16:00 hrs. since dye emerged= seepage velocity: 0.79 ft/day
~1-4 x 10-5
lower density
Density Effects – lighter
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P2230046@ 2/23/03 1134ptest start 1120a on 2/20/03calc. dye density: 0.999935 g/cc 72:09 hrs. since dye emergedseepage velocity: 0.54 ft/day
~1-4 x 10-5
lower density
Density Effects – lighter
~70%
~3%
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For those wells that doshow ambient stratification:
Aquifer must be stratified
But what causes contaminants to maintain stratification?
∇ Entry point∇ Density differential∇ Pressure gradient
!! Contaminants may !! Contaminants may stratify at different stratify at different intervals than they enter !!intervals than they enter !!
Stratification correspondence?
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What about sampling passively--with a zone isolation device?
> DMLS> Passive Flux Meter
PDB or Snap Sampler with bafflePDB or Snap Sampler with baffle
Dick Willey, Dick Goehlert, R1 USEPA; Phil Harte, USGS
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The Snap Sampler is a dedicatedpassive sampling system
• Deploy double-ended bottles in an open position.
• Sample after short or long residence time in the well—1-2 weeks or 3 or 6 months
• Mechanical or electric trigger closes bottles in situ.
• Sample transfer is not requiredat the well head for VOCs-No exposure to air
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How the Snap Sampler works….
Insert
40ml 125ml
Rotate to set Snap Cap
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How the Snap Sampler works…continued
Lower downhole
• Modular samplers allow up to 4 bottles per trigger
• Multiple triggers can be used for multiple sampling depths
Hang on Dock Ring Secure
• Mechanical or electric trigger
Attach Trigger
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Stratification Testing, using Snap SamplersSite in southern California (private site)
55
60
65
70
75
80
200 400 600 800 1000Concentration (ug/L)
Dep
th (f
t)
TPH (gas) MTBE
55
60
65
70
75
80
0 20 40 60 80 100Concentration (ug/L)
Dep
th (f
t)TBA
• 20 ft 4” PVC well, 5 zones, separated w/ bafflessomewhat stratified
Site in Orange County, CAData Courtesy ERI
MW-2 MW-2
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Stratification Testing, using Diffusion BagsSite in New Hampshire (USEPA Superfund site)
48
50
52
54
56
58
60
0 100 200 300 400 500Concentration (ug/L)
Dep
th (f
t)
PCE
20
22
24
26
28
30
5000 10000 15000 20000 25000 30000Concentration (ug/L)
Dep
th (f
t)PCE
PW-25d PW-22
• 10 ft 2” PVC wells, 3-4 zones, separated w/ baffles, with
low-flow pump samples
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Stratification Testing, using Snap Samplers(Private site in NJ) w/ No Baffles
• 4” PVC well
• Overburden silty sand
• Submerged 10 foot screen
• 4 Snap Samplers at 2.5 ft
intervals
• Phenol results in ppm
Results relatively close—
not stratified
Site in northern New JerseyData Courtesy CH2M Hill
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• 4 Snap Samplers at 2.5 ft intervals
• Mixing inhibitor devices
• Phenol results in ppm
Results range over 5 orders of magnitude
very stratifiedvery stratified
Site in northern New JerseyData Courtesy CH2M Hill
Stratification Testing, using Snap Samplers(Private site in NJ) w/ Baffles
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Mixing inhibitors:
• Simple mechanical device
• Attach to Snap Sampler Trigger or PDB tether
• Allows multilevel testing
• No new wells needed
• Existing well can still be used for traditional monitoring
• Won’t work everywhere!