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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.

Sandy.Britt@ProHydroInc.com

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!