Consistent Field Sampling Of Shallow Wells With Minimum Decontamination

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

The Nielsen Environmental Field School, Inc.
2012 North American Environmental Field Conference & Exposition

CONSISTENT FIELD SAMPLING OF
SHALLOW WELLS WITH MINIMUM
DECONTAMINATION
2650 East 40th Avenue • Denver, Colorado 80205 • www.geotechenv.com


Agenda
• Introductions
• Low flow sampling
• Equipment examples
• Documentation of low flow samples
• Decontamination



Jeff Popiel
President and CEO

JeffP@GeotechEnv.com
303.320.4764



Geotech Corporate Headquarters
Denver, Colorado USA

…a world leader in environmental technology,
manufacturing and product training since 1978.
www.GeotechEnv.com


an environmental industry
products leader since 1978

partners with federal, state,
local and international
government agencies

over 20,000 private sector
clients worldwide

distribution in 72 countries

provides products and product
training to colleges, universities
and technical schools around the globe



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
Low Flow Traditional
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.

Minimizes Increases
drawdown, drawdown,
turbidity & turbidity &
purge volume purge volume



Advantages of Low Flow
Sampling Low Flow Traditional
• 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 Dedicated Bailer movement
other wells and from equipment bladder pump surges and
handling samples mixes well,
• Saves time and cost of disposing of undisturbed increasing
contaminated purge water
well turbidity



Low Flow Sampling Decisions
• Purge flow rate
– Determine a purge flow rate which will
minimize drawdown, commonly less
than 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 Samples to Expect
• Yes for: • Not for:
Collection of ground water Collection of LNAPLs (light
samples for all categories of non-aqueous phase liquids)
aqueous phase or DNAPLs (dense non-
contaminants and naturally aqueous phase liquids). It is
occurring analytes, not appropriate for wells
including VOCs, metals and that purge dry because
other organics, pesticides, these wells typically purge
PCBs, organic compounds, dry before all indicator
radionuclides, and parameters stabilize.
microbiological
constituents.



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 • Drawdown measurements
• Equipment decontamination • Stabilized pumping water level
• Equipment configuration for • Final pump rate
sampling • Water quality and turbidity
• Pump placement measurements, with times
• Initial static water level • Final sampling flow rate
• Initial pump rate



Bonded Water Quality
Sample
Tubing Reel Instrument
Low Flow Components
Air
Line
Water Level
Reel and
Probe
Water
Flowblock
Line

Power Source
(Battery)
Pump
Controller
Pump 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 Electronic water level meters
(for continuous measurements) (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 Bladder
1. Remove the intake 4. Remove the upper
assembly by screwing compression ring and
counter-clockwise. slide the ring off.

2. Pull to remove the 5. Slide new bladder
outer housing from over the O-ring.
the upper cap.

3. Slide the lower 6. Replace the
compression ring off. 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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