consistent field sampling of shallow wells with minimum decontamination

2650 East 40th Avenue • Denver, Colorado 80205 • www.geotechenv.com2650 East 40th Avenue • Denver, Colorado 80205 • www.geotechenv.com

GROUND WATER SAMPLING • WATER LEVEL & PRESSURE • WATER SAMPLE FILTRATION • GROUND WATER REMEDIATION • GEOPHYSICAL MEASUREMENTSGROUND WATER SAMPLING • WATER LEVEL & PRESSURE • WATER SAMPLE FILTRATION • GROUND WATER REMEDIATION • GEOPHYSICAL MEASUREMENTS

CONSISTENT FIELD SAMPLING OF

SHALLOW WELLS WITH MINIMUM

DECONTAMINATION

The Nielsen Environmental Field School, Inc.

2012 North American Environmental Field Conference & Exposition



Agenda

• Introductions

• Low flow sampling

• Equipment examples

• Documentation of low flow samples

• Decontamination





Jeff Popiel

President and CEO

[email protected]

303.320.4764



www.GeotechEnv.com

…a world leader in environmental technology,

manufacturing and product training since 1978.

Geotech Corporate HeadquartersDenver, Colorado USA



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Audience Introductions

• Name

• Company name

• Experience with groundwater sampling



Just the Facts

• “Low Flow” does not refer to the flow-rate of water discharged by a pump at the surface, which can be affected by valves, tubing restrictions or flow regulators.

• “Low Flow” refers to the impact on formation hydraulics of pumping the well. Water level draw down provides a measurable indication of the stress on a given formation imparted by a pumping device operated at a given flow rate.

• Objective: pump in a manner that minimizes stress or disturbance to the groundwater system to the extent practical.



Low Flow Sampling

• All methods have error and bias, which can influence samples

• Method evolved to improve sample accuracy

• Also called; – Consistent field sampling,

– Low-stress purging,

– Low-impact purging, and

– Minimal draw-down purging

• No removal of large volumes of water from the well– Less than one half the well volume

– Vs. 3 to 5 times the well volume



Characteristics of Low Flow Sampling

• Deliver representative sample of water from formation

• Submerged pump

• Movement of water in well is minimized

• Sample at a rate equal to or less than the water entering the well from the surrounding formation



Advantages of Low Flow Sampling

• Improved sample quality

• Reduced disturbance in the well/formation

• Reduced purge water volume (less $)

• Improved detection of contaminant distribution

• Increased well life

• Reduced field labor costs



Low Flow vs. Traditional Sampling

In low flow sampling, a well is purged at a

very low rate to minimize draw-down and

avoid disturbance in the well, as opposed

to the traditional method of purging at a

high rate and removing 3 to 5 times the

well volume.

Low Flow

Minimizes drawdown,turbidity &

purge volume

Increases drawdown,turbidity &

purge volume

Traditional



Advantages of Low Flow

Sampling

• Less well disturbance leads to

lower sample turbidity

• Reduced variability in the sample

results

• Purge volume reduced up to 95%

can reduce purge time and labor

• Reduces problems related to

excessive drawdown and pumped

volumes

• Dedicated equipment for low flow

sampling saves field time and also

eliminates contamination from

other wells and from equipment

handling

• Saves time and cost of disposing of

contaminated purge water

Dedicated bladder pump

samples undisturbed

well

Bailer movement surges and mixes well, increasing turbidity

Low Flow Traditional



• Purge flow rate– Determine a purge flow rate which will

minimize drawdown, commonly lessthan 1 liter per minute

• Purge duration– Passing the purge flow through a

flowblock measures key water quality parameters, allowing observation of the point when the readings become stable.

– Commonly within 10 to 20 minutes, but depends on the well.

– Sample collection can begin at this point.

Low Flow Sampling Decisions



Low-Flow Samples to Expect

• Yes for: Collection of ground water samples for all categories of aqueous phase contaminants and naturally occurring analytes, including VOCs, metals and other organics, pesticides, PCBs, organic compounds, radionuclides, and microbiological constituents.

• Not for:Collection of LNAPLs (light non-aqueous phase liquids) or DNAPLs (dense non-aqueous phase liquids). It is not appropriate for wells that purge dry because these wells typically purge dry before all indicator parameters stabilize.



Low flow sampling requires:

• A sampling device capable of

consistently providing low flow

rates without agitating the water

in the well or altering the sample

quality

• A flow cell to determine

completion of purging

• A water level measurement device

to measure drawdown



Documentation of Low Flow Sample

According to ASTM Guide D 6089

• Equipment calibration

• Equipment decontamination

• Equipment configuration for

sampling

• Pump placement

• Initial static water level

• Initial pump rate

• Drawdown measurements

• Stabilized pumping water level

• Final pump rate

• Water quality and turbidity

measurements, with times

• Final sampling flow rate



Low Flow Components

Pump

Water Level

Reel and

Probe

Bonded

Tubing Reel

Air

Line

Water

Line

Sample

Power Source

(Battery)

Pump

Controller

Flowblock

Water Quality

Instrument

Well



Bladder Pumps

• Flexible bladder inside a rigid housing.

• Water enters the bladder from the bottom.

• Gas pressure is applied to the outside of the bladder.

• Water is squeezed to the surface.

• Air compressor and regulator turn the pressure on and off.

• Sample does not contact the compressed air.

• Check valves prevent backwash from the sample tube and bladder.



Bladder Pumps

• Generate reproducible

analytical results

• Suitable for collecting

samples of almost any

constituent.

• Bladder pumps are

recommended for

purging and sampling.



Flowblocks

• Less than 40mL of void volume with probes installed

• Flow rates of 100 mL/min to 1 gpm (3.8 LPM)

• Sensors in direct line of sample stream

• Block design for field durability

• Tubing quick-connect barbs for easy connections

• Easy cleaning



During low flow sampling, the water level in the well is continuously monitored using

any water-level measurement equipment that does not disturb the water column and

that provides the accuracy required by the sampling program. These devices include:

Pressure transducers

(for continuous measurements)

Electronic water level meters

(for periodic measurements)



Portable Not Recommended

• Lowering a portable device into the well mixes the water column between the upper, more stagnant zone, and the screened zone, adding significantly to the time required to complete purging.

• Portable equipment requires cleaning, handling and set-up steps while dedicated systems do not.



If Portable is Necessary:

Decontamination: Change Bladder1. Remove the intake

assembly by screwing

counter-clockwise.

2. Pull to remove the

outer housing from

the upper cap.

3. Slide the lower

compression ring off.

4. Remove the upper

compression ring and

slide the ring off.

5. Slide new bladder

over the O-ring.

6. Replace the

compression rings,

outer housing and

intake assembly.



Summary

• Low flow sampling is not complicated

• Provides more reliable sample

• Following steps keeps things organized,

functional and clean

• There is equipment that is easy to

decontaminate

consistent field sampling of shallow wells with minimum decontamination

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