Passive Sampling

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Passive Sampling

Snap Sampler


Van Walt is the exclusive distributor of the Snap Sampler in the UK and Ireland. The Snap Sampler is suited for most groundwater monitoring and sampling situations and also especially helpful in difficult conditions such as with low yield wells.

The Snap Sampler seals groundwater samples down well, in bottles that can then be directly analysed in a laboratory. The sample is never exposed to the open air and collection of the sample does not require pumps, controllers, meters and purge water waste containers. It is quick and easy to collect the samples and so can save money on sample collection costs.

The Snap Sampler with 40ml and 125ml bottles fits in 2-inch or larger monitoring wells. With 350ml bottles the sampler will fit in 4-inch or larger monitoring wells.

Snap Sample bottles are loaded into the Snap Samplers, set open, deployed for a period of time — usually all the way between sampling events — are "snapped" shut downhole, retrieved, secured, and sent to a lab without opening them.


  • A non-purge device for passive sampling techniques
  • Simplified sampling process
  • Works on the principle of grabbing a sample rather than diffusion
  • Minimal or no disturbance of the water
  • Collects undisturbed sample
  • Less equipment, manpower and time required to collect samples
  • No waste disposal of purge water
  • Seals sample down well so no outside contamination of sample
  • Tests for any analyte
  • Collects sample from same depth for consistency of results
  • Reduced time to collect each sample
  • Samples up to 2 litres by stacking samplers
  • Improved Health & Safety with no lifting of heavy equipment and less time in potentially hazardous environments
  • Repeatable use of equipment
  • Green technology
  • Easy to use

Specifications: Snap Sampler

Input Power:
Pneumatic System: 12V Air Pump
Trigger Activating Pressure: 10-30 PSI (.69-2 bar) – typical
Pressure Block: Includes fittings and gauge for applying pressure from pump to pneumatic actuator
Snap Sampler Specifications
Maximum Operating Pressure1: 80 PSI (5.5 bar)
Minimum Operating Pressure1: ~10 PSI (~.69 bar)
Maximum Sampling Depth: 2,500 ft. (609 m)
Capacity: Up to 6 Snap Samplers in any combination can be "stacked" with one actuator
Operating Temperature: 0° to 100°C
Input Protection: Pressure Block has 80 PSI (5.5 bar) relief valve
40 ml Snap Sampler: 3 oz. (85 g) – each, empty
125 ml Snap Sampler: 3 oz. (85 g) – each, empty
Pneumatic Actuator: 13 oz. (368 g)
Stainless Steel Weight: 3.1 lb. (1.4 kg) – optional
40 ml Snap Sampler: 8 in.(20 cm)
125 ml Snap Sampler: 10.5 in. (26.7 cm)
Pneumatic Actuator: 11 in. (27.9 cm)
Outer Diameter:
40 ml Snap Sampler: 1.7 in. (4.3 cm)
125 ml Snap Sampler: 1.85 in. (4.7 cm) – with 125 ml bottle
350 ml Snap Sampler: 3.4 in. (8.6 cm) – with 350 ml bottle
Min. Well I.D:
40 ml Snap Sampler: 2 in. (5 cm)
125 ml Snap Sampler: 2 in. (5 cm)
350 ml Snap Sampler: 4 in. (10 cm)
Material: Acetal

Videos, Manuals & Downloads

Snap Sampler Assembly

Manual Trigger Assembly

Manual Trigger Disassembly

Pneumatic Trigger Assembly

Triggering Operation

Removing Bottles

VOA Vial Preparation

POLY Bottle Preparation

Snap Sampler Promo Video

EOS Remediation Webinar - March 12, 2015 Webinar Presented by Sandy Britt


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Environmentally friendly low flow monitoring sampling solutions

Better, cheaper, more accurate and environmentally friendly monitoring solutions

We have bladder or peristaltic pumps and water quality meters to measure stability of parameters such as pH, DO and turbidity – full micro purging solutions available to buy or rent.

No purge sampling devices can save time and money so it's easy to see why they are gaining acceptance. In addition to the cost savings the logistics of no purge samplers are simple and above all it's 'green' technology. Like most new techniques it would appear that there is no "one size fits all" solution as some no purge samplers are good for VOC's and others for inorganics.

The Snap Sampler, now used extensively by companies like Shell, DuPont, Eastman-Kodak and Chevron who have 400 in boreholes in Australia, takes an instant 'snap' sample at a point in time. This sample can be depth specific and importantly is never exposed to the atmosphere. Alternatively Sorbisense collects a time interval profile, absorbing the sample over a period of time.

High Volume Purging

Prior to March 2011, high volume purging and sampling was mandatory for groundwater investigations on behalf of environmental research. After a well is constructed, well development should occur as soon as possible but not sooner than 48 hours after the swelling of the bentonite is completed. Thereafter groundwater sampling may take place after a 14 day wait. The well must then be purged at 3 times the wet well volume which includes the filter sand pack, prior to each sampling. During this process field parameters should be measured. Clearly, high volume purging produces much waste water which must be disposed of correctly and this can be expensive. Additionally, this technique may be risky for low recharge wells as it may draw the water level below the filter section of the well and introduce air to the sample.

Low Volume Purging

Low flow or micro purging is now an accepted method in the United States (Puls and Barcelona 1996) and in the UK following the publication of BS 10175:2011 in March 2011. With this type of sampling, a pump is hung in the well opposite the most contaminated zone in the well screen and adjusted to a very low speed. There is no need to renew (purge) the water in the blind section of the well. By using this method, the volume of the purge water can be reduced, sometimes significantly over the conventional purging method. Water quality indicator parameters are measured (pH, EC, DO and increasingly turbidity: EC and DO are the best stability indicators) until stability is achieved. After 3 successive readings of the water quality indicator parameters have stabilized (recorded after a minimum of one tubing, pump and flow-cell volume) per cycle then sampling can begin. It is customary, but not written in stone that drawdown is kept within 10 and 20cm and this should be regularly checked with a dipmeter. This technique is excellent for slow recovering wells and saves much time and purge water disposal volumes. A dedicated pumping system for each well is recommended. This ensures minimal mixing of the stagnant water above the screen.

Passive or Diffusion Sampling

"No purge devices are now beyond the infancy stage in the United States and have been gaining more acceptance since their first introduction in 2006. No doubt the technique will gain popularity in the EU. The idea is to deploy a device and leave it in a well for a certain period which may vary depending on the instrument used. Diffusion samplers need to reach an osmotic equilibrium with the surrounding water. Diffusion samplers are not a "one size fits all" solution and some are good for VOC's and SVOC's, such as the GORE samplers whereas others might be good for inorganics such as Columbia's RPP samplers. The common factor is that there is minimal disturbance in the water and whereas samplers such as the Hydrasleeve are an attractive low cost solution care must be taken that they do not disturb the sediment within the well which can cause excessive turbidity and perhaps cannot be implemented for sensitive analytes such as Redox, pH and Turbidity. Other systems are coming on the market and some offer a completely different solution for a buffet of compounds. Of great interest is the Snap Sampler from Prohydro which does not work on the principle of diffusion but rather grabs or "snaps" a sample of groundwater. Of all the samplers available at the moment this has the best proven track record of repeatability. Unlike the Hydrasleeve, it does not disturb the well water and therefore is perfectly suitable for all analytes. Where a conservation liquid needs to be used (such as metals) then that facility is catered for.

Passive, diffusion or no purge sampling has three huge benefits: They save time and money (50-80%), the logistics are simple and above all it is "green" technology.

Low Flow or No Flow Sampling Solutions