by Allan C. Nix, PG

Georgia EPD Response and Remediation Program

RRP follows the EPA Region 4 operating procedure for groundwater sampling, EPA Science and Ecosystem Support Division OP Number SESDPROC-301-R3

http://www.epa.gov/region4/sesd/fbqstp/Groundwater-Sampling.pdf

Individual RRP compliance officers may authorize exceptions to the SESD groundwater sampling OP

Other EPD programs may have their own groundwater sampling procedures 2

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Are purging methods utilized prior to groundwater sampling, to draw representative groundwater from the surrounding formation into the well

Are often confused with each other Low-flow/low-stress purging typically involves a multi-volume well

evacuation,whereas,

Low-flow/low-volume purging, often called “low flow” or “low flow (minimal drawdown)” purging, does not require a multi-volume well evacuation

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Has traditionally been the preferred purging method for RRP sites Only passing references to this method in latest GW Sampling OP,

but is often still preferred by RRP compliance officers

Is designed to minimize turbidity prior to sampling (can also keep wells in tight formations from going dry)

Typically involves multi-volume purge, three well volumes minimum, unless well is evacuated to dryness beforehand

Latest version of EPA SESD GW sampling OPs describes the “Traditional Multiple Volume Purge” method Relatively rapid flow rate during purge Acceptable method if turbidity not a problem and if water column

stabilizes (well is not purged to dryness) 5

Low pumping rate The type of pump with the lowest achievable

pumping rate should be chosen If the depth from the top of casing to the top of

the water column is within the limit of suction (generally about 25 to 30 feet), a peristaltic pump is preferred

If the depth to the top of the water column exceeds the limit of suction, a variable-speed electric submersible pump is a good choice

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Tubing intake is submerged to a depth near top of water column This is important; otherwise the stagnant well water

above the intake may not be removed, potentially lowering the sample quality.

Submersible pump will need to be placed a little deeper initially, to a maximum 3 to 5 feet below top of the water column. Raise it if no drawdown occurs, to within 1 foot of top of water column.

If drawdown occurs, reduce pumping rate until water column stabilizes If drawdown still occurs, lower the tubing or pump

until the water column stabilizes or well is evacuated to dryness 7

Periodically measure and record chemical parameters Specific conductance (stabilization at +-5%) pH (stabilization at +-0.1 standard unit) Turbidity (stabilized or <10 NTUs)

Adequate purge is achieved After purge of three well volumes, and Chemical parameter stabilization over three

consecutive measurements

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Other names for this method include low flow, low flow (minimal drawdown), micropurging, and tubing-in-screened interval

Multiple volume purge not necessary

Intended for sites where generated volume of IDW would otherwise be excessive

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Permission to use this method must be obtained from RRP compliance officer Site conditions must be conducive to low flow/low

volume purging K values >10-5 cm/sec

No problems with excessive turbidity

May not be conducive to metals analysis (<10 NTU turbidity may not be achieved)

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Peristaltic pump best for this method, if depth to water is within the limit of suction Variable-speed electric submersible pump a good

choice if depth to water exceeds the limit of suction End of tubing or pump intake is positioned at

midpoint of well screen In theory, water will be drawn directly through

screen from surrounding formation Installation of tubing or pump for a period of time

prior to purging often a good idea to lessen turbidity

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Drawdown is kept to a minimum Continuously monitored <0.1 meter of drawdown is desirable Flow rates are kept low to minimize drawdown,

generally between 0.1 to 0.5 L/min Excessive drawdown places unacceptable stress on

well Intake may be pulling in stagnant water from above

screened interval May create turbidity problems

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Adequate purge is achieved at chemical parameter stabilization over three consecutive measurements (pH, specific conductance, turbidity)

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Low-flow/low-stress pump intake is near the top of the water column

Low-flow/low-volume pump intake is at or near the midpoint of the screened interval

Low-flow/low-stress typically requires a minimum three well volume purge

Low-flow/low-volume requires purging only until groundwater chemical parameters stabilize

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When certifying to RRP risk reduction standards, Teflon tubing must be used Bailers used for sampling must be Teflon

VOC groundwater samples should not be obtained through a peristaltic pump head The “soda straw” sampling method should be used

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When groundwater sampling results are submitted to RRP, each groundwater sample obtained should have one of these to accompany it

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Depth to pump intake Depths to top and bottom of screened interval Depth to bottom of casing Drawdown measurements Height of initial water column in well Sampling Method (peristaltic pump, bailer, etc.) Well diameter Type of tubing (polyethylene, Teflon)

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HydrasleeveTM

PDBs Etc. Permission to use non-traditional methods for

periodic groundwater monitoring will be at the discretion of your RRP compliance officer

Certification to Risk Reductions Standards will require sampling with pumps or bailers

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Passive Diffusion Bags (PDBs) RRP has recently allowed the use of these on a site-

by-site basis for periodic groundwater monitoring Can obtain depth-discrete groundwater samples On a national scale, side-by-side comparisons with

analytical results from traditional sampling methods have been favorable

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EPA Region 4 Groundwater Sampling OPshttp://www.epa.gov/region4/sesd/fbqstp/Groundwater-Sampling.pdf

EPA Region 4 Science and Ecosystem Support Division Field Branches Quality System and Technical Procedureshttp://www.epa.gov/region4/sesd/fbqstp

Georgia Hazardous Site Response Act Guidancehttp://epd.georgia.gov/hazardous-site-response-act-guidance

Georgia Hazardous Site Response Act Notification FAQshttp://epd.georgia.gov/hsra-notification-391-3-19-04-frequently-asked-questions

Georgia EPD Voluntary Remediation Programhttp://epd.georgia.gov/voluntary-remediation

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