SNAP SAMPLING IS A "SNAP"

Why is passive, no-purge, sampling with the Snap Sampler such a "Snap?"

Passive sampling relies on natural flow-through in the well and "passive" re-equilibration between the well and aquifer before collecting samples.  No water is pumped from the well, so you don't need pumping equipment or heavy waste containers.  Sampling takes 5-15 minutes per well and you have virtually no preparatory logistics for equipment--you really don't even need a truck.  That's why sampling with the Snap is a Snap.

The Snap Sampler takes "passive" a step further by sealing the sample in situ--eliminating the pour step at the well head.  As a result, Snap Samples are truer to the condition of the sample while it is still in the well.  You don't add artifacts from pouring under variable weather conditions, seasons, or the technique of the field sampler.

Is it OK to sample without purging?

Academic research, EPA, and ASTM guidance indicates flow-through in the well screen is normal and usual*.  In most circumstances truly "stagnant" water is present only in blank well casing above the screen.  The sceen interval inside the well normally contains free flowing formation water.

*ASTM, 2002, Standard Practice for Low-Flow Purging and Sampling and Devices Used fro Ground-Water Quality Investigations, ASTM designation D-6771-02.

*Powell and Puls, 1993, Passive Sampling of Groundwater Monitoring Wells Without Purging:  Multilevel Well Chemistry and Tracer Disappearance. Journal of Contaminant Hydrology 12: 51-77.

*Puls and Barcelona, 1996, Low-Flow (Minimal Drawdown) Ground-Water Sampling Procedures, USEPA Ground Water Issue Paper, EPA/540/S-95/504.

*Robin and Gillham, 1987, Field Evaluation of Well Purging Procedures, Ground Water Monitoring Review, v. 7,  no. 4,  p. 85-93.

The Interstate Technology and Regulatory Council (ITRC) has been providing guidance and information on passive technologies for several years.  The web site ds.ITRCWEB.org contains plentiful information on the efficacy of passive technologies.  Numerous studies show that many passive methods are comparable to purge methods.  So, yes, using the right techniques, you can sample effectively without purging.

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