In the simplest explanation, the user places Snap Sampler bottles into the Snap Samplers, "cocks" the bottles open, deploys the samplers downhole using the trigger cable, and when ready to sample, activates the trigger to seal the water sample in-situ.
The Snap Sampler employs specialty double-opening bottles that collect water in-situ within the well. The Snap Sampler itself provides a mechanical means of holding the Snap bottles open during deployment and a mechanism for triggering the bottles to close only when the user wants to collect the sample.
Snap Sampler bottles have special end caps made of PFA Teflon. The end caps are constructed to attach to a Teflon-coated internal closure spring and to an outer release mechanism. The trigger retracts the release pins, allowing the internal bottle spring to close the end caps. The sampler is retrieved ready for minor preparation and submittal to the lab.
Click here to download our Standard Operating ProcedureSnap SOP(PDF 327K). It is modeled after US EPA's 2002 Groundwater Sampling Guidance for RCRA and Superfund Project Managers. If you like it, please share it!
Click here to download the Snap SOP Appendix A "Snap Sampler Deployment"Instructions in PDF form (428K)
How does the Snap Sampler compare to other sampling methods?
Field testing shows that groundwater sampling with the Snap Sampler is faster and less complicated than pump sampling. No power is needed and no separate devices are needed to determine purge stability, turbidity, or water level fluctuations. Laboratory and field testing of the Snap Sampler show consistent positive results. Blank Snap Sampler bottles are clean and sealed in the same container as an Encoretm soil sampler. Extensive analyte testing by the Army Corps of Engineers and others show the Snap Sampler passes with "flying colors"--with no statistical differences from the control. Additional comparison studies are available on the Data Comparisons page.
The McClellan report by Parsons is one of the more extensive comparisons of passive sampling. While there are some problems with the analysis and broad-brush interpretations, the data sets generated for the Snap Sampler and other methods illustrate graphically how well the method performed.
Visually it is clear which samping methods compared best. The Snap Sampler and Low Flow performed very well in the McClellan study. The Hydrasleeve and several others did not perform as well in the McClellan study. Correlation coefficients below 0.50 are generally poor, and several comparisons with the Hydrasleeve (VOC, hexavalent chromium) had low correlation coeffients compared to purge sampling and other passive methods.
McClellan report Appendix D data shows how different methods compared
The thumbnail to the right can be enlarged to compare a long-term monitoring program using purge-and-pour sampling methods and the Snap Sampler method.
Purge methods incorporate several variables the Snap Sampler method does not. These include: exposure to surface air during pouring to sample bottles, pouring technique, rate of bottle filling, weather, potentially different pump depth settings, duration of pumping, purge volume, changes in stability parameter criteria, equipment used, and other site-specific and event-specific variables.
These factors combined are illustrated in the graphs to the right by increased variation of the "traditional purge" results when compared to the Snap Sampler. The graphs show that concentration trends are disernable much sooner with less variability or "noise" in the sampling data. With data trends discernable sooner, demonstration of remedial effectiveness or monitored natural attentuation (MNA) can be achieved sooner.
Click to get ITRC Protocol Document DSP-5
What about regulatory acceptance?
Like all new technologies, there is a proving stage where individual regulators for individual sites must be consulted and convinced of the merits and benefits of this new technology. Our experience shows regulators are impressed with the consistency and quality of the Snap Sampler data.
The new ITRC Protocol Documnet DSP-5 speeds regulatory approval with its wide distribution and respect of the institution throughout the regulatory community.
Despite inroads passive sampling has made, it is common that individual regulators will approve Snap Sampling on a case-by-case basis. Based on experiences with the diffusion bag and other previously emergent technolgies (including even low-flow purging at one point in time), site owners, consultants, and regulators each can be convinced by data quality and cost savings. These merits are evident in the Snap Sampler technology and they ease transition.
In cases where a direct side-by-side comparison is desired either by the regulator, or by the site owner or consultant, the Snap Sampler consistently performs well. No site has been rejected by regulators during one of these comparison trials.
I've heard passive sampling is a big money saver, how much could I expect to save?
Cost savings using the Snap Sampler is commonly 50%. Some sites even exceed that amount. With no waste to dispose (not even extra sample waste), very little preparatory logistics, and simple operation, sampling 20 wells per day should be expected. Improving productivity by 100% or more is the primary driver for cost savings, along with avoidance of waste handling and disposal.
Another driver for cost-savings is reduction in field sampling variability. Reduction of sampling random error from 30% to 10% can make the difference between seeing a trend and not. Demonstrating remedial effectiveness or natural attenuation in many cases is more important from a cost perspective than the sampling itself. All sources of savings sould be considered when evaluating overall cost of a groundwater sampling program.
Are there limitations of what analytes can be tested with Snap samples?
No. Snap samples are not restricted to certain analytes. The bottles are open to the well environment during deployment, so no special equilibration is needed beyond restabilization of flow in the aquifer/well. All chemicals/parameters in the water column can be sampled with the Snap Sampler.
While no chemical or parameter is excluded from the sample bottles, some analytes require large sample volumes to achieve appropriate detection limits. Sample volume can be a constraint on these analytes or on an extensive analyte list.
What about sample volumes? The sample volume of the Snap Sampler VOA vial is slightly less than 40ml. This is not an issue for EPA method 8260 or other standard lab methods for volatiles. For non-volatile analytes that benefit from larger volumes, such as SVOCs, 1,4-Dioxane, explosives, etc., 125ml and 350ml bottles and samplers are availablethat can increase sample volume for analytes that require more water.
Minimum volume requirements are available HERE where volumes as low as 10 ml can be used for anions and metals, 20 ml for VOCs and 100 ml for SVOCs.
How many Snap Samplers do I need to collect a sample?
In the recommended usage, Snap Samples are collected by deploying the samplers and bottles in advance of sampling. The well re-equilibrates, then you trigger the sampler. Using this method, you need one Snap Sampler for each bottle you plan to collect. The number of samplers you need per sample depends on how much sample volume your laboratory needs. For some analyses such as SVOCs, you may have to combine several bottles to get one analysis.
For simple analysis needs, you may be able to deploy just one Snap Sampler. For longer analyte lists you may have to deploy four or more samplers (and bottles) on one trigger line. There are 40ml glass VOA vials, 125ml and 350 ml plastic bottles available, so combinations of sample bottle sizes usually can accommodate most analyte lists. In 2" wells the maximum sample volume is 750 ml with 6 bottles set in series. In 4" wells, the maximum sample volume is 2L with 6 bottles set in series.
Our best advice is to consult your lab on their requirements.
What's the advantage of no-pour groundwater sampling?
Consistency is vital to assure comparability of data from different sampling events. Variability of sampling conditions from event to event can be significant. Wind, temperature, and sampling personnel can each have an effect on sampling consistency, and are not always controllable. The Snap Sampler VOA vial seals under the groundwater surface right in the monitoring well. When retrieved, the sample is already sealed in the bottle that you ship to the laboratory. Since you never transfer sample from a pump discharge line or a bailer into the sample bottle, there is no exposure of the sample to the ambient conditions at the time of sampling. Differences in pouring technique by different field personnel are not a factor. As a result, consistency of sampling method is considerably improved when samples don't have to be poured.
How hard is it to assemble the Snap Sampler?
It's really not hard at all. Snap Sampler assembly takes just a few seconds. There are four main parts to the sampler, plus screws and the attachment mechanism. The release mechanism (3 of the four parts to the sampler) is held in place with only one screw. Users can become proficient in Snap Sampler assembly with only a few repetitions. Recent improvements include "push-in" trigger cable and single screw connections.
What about decontamination? There are just 4 parts to the sampler, plus screws and connectors. Disassembly is relatively easy with very few moving parts. Cleaning can be accomplished by disassembling, rinsing, and brushing with a bottle brush. No special tools are needed beyond those provided with the sampler and normally used for equipment decontamination. For most applications, the sampler will be redeployed in the well from which it came, limiting the necessity for extensive decontamination before redeployment.
How does the trigger line work? How does it attach at the well head?
The Snap Sampler trigger line is comprised of HDPE tubing with an FEP-coated stainless steel cable. Fluorocarbon (PVDF or PFA Teflon) is also available as tubing material. The tubing attaches to the sampler and a well head docking station shown to the right. Up to 4 trigger lines can be attached at a 4-inch well head. Up to two lines can be attached at a 2-inch well head. The sampler end of the trigger attaches to the release pin mechanism with a press-in ball fitting, similar to a bicycle brake cable. To trigger the sampler, just pull firmly on the trigger cable at the well head. The tubing and sampler stay in place, the cable moves the release pins, the vials close.
What about deep sampling?
The Snap Sampler trigger is now available with a downhole electric trigger. With the electric trigger, you can sample from virtually any depth.
Want to learn more? Under the "Practical Uses" page, you can see additional details about the latest deep well sampling device.
Once you retrieve the bottles, how do you prepare them for the lab?
When Snap Sampler bottles are retrieved, the end caps still have the retainer pin tab. This portion of the cap must be clipped off to allow placement of the septa cap. With the clipper tool provided with Snap Sampler, both caps are easily clipped flush with the top of the cap.
How do you preserve the samples?
To preserve the sample, acid can be added to vial through one of the end caps. Each vial cap has a conical-shaped cavity and a thin membrane for introduction of preservative to the vial. The cavity is sized to accept the proper amount of 1:1 HCl solution to lower the vial pH to <2. To add preservative, one end of the vial should be sealed with a screw septa cap. To the second end, the field or lab technician adds HCl. HCl preservative can be obtained in 1ml ampules or poly bottles from your lab or through a laboratory supply vendor.
Using the sharp piercing tool provided with the samplers, the membrane of the vial cap should be pierced. This allows the HCl preservative to mix with the sample without introducing air to the vial. The cavity should then be topped off with preservative to create a miniscus over the cap cavity. Screw the septa cap onto the vial as usual.
What is the green spring inside the bottle?
The spring inside the Snap Sampler bottles are made of stainless steel with a PFA Teflon-coating. The spring pulls the end caps onto the vial when the Snap Sampler is triggered, and holds the caps in place when the bottle is closed. The green coloring is a primer that allows the PFA to stick to the stainless steel. The PFA itself is clear. The PFA coating is cured at 700 degrees F, so no volatile chemicals remain, and the coating provides an inert barrier between the sample and the stainless steel spring. The spring remains in the sample bottle when submitted to the analytical laboratory. The low-friction PFA Teflon coating on the spring allows autosampler extraction probe to be inserted in the Snap Sampler vials without binding.
Do the laboratories need to do anything they're not used to?
No. For samples that require no dilutions, or where labs have autodilution devices, the Snap Sampler VOA is placed directly in the autosampler just like a normal vial. It doesn't matter which way is up, either end works just as well. For manual dilutions, the analyst can sample with a syringe directly through the septa and cap membrane; or remove the screw the cap and sample through the cap membrane only; or pull the cap off, hook the end of the spring over the lip of the bottle, and sample from the open container.
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