The rise & rise of Passive Sampling

April 8, 2015

Obtaining representative data is the holy grail of site analysis and modelling. Inaccurate data can lead to incorrect conclusions which could be very costly to land owners, users and developers.

That’s why, particularly in the US, passive sampling is growing in acceptance. Collecting groundwater samples is an expensive exercise and relies upon many factors. For the American Department of Defense, long term monitoring represents a large proportion of their annual research costs. That’s why they have funded research on different monitoring solutions to reduce these costs. One of the methods that has undergone extensive tests is passive sampling.

The results are impressive and contained in their latest guidance notes, December 2014: PASSIVE SAMPLING FOR GROUNDWATER MONITORING: TECHNOLOGY STATUS. The department has found that using a passive sampling technique can significantly reduce the amount of labour needed and the volume of waste generated during a sampling cycle compared to traditional well purging methods. In addition passive sampling strategies also reduce the number of individual sampling events necessary to differentiate between short- (i.e., random) and long-term (i.e., attenuation) variability.

They summarised their key findings on the benefits of passive sampling as:

  • Passive samplers are valid for most analytes, under a wide range of conditions
  • Their limitations are understood and credible guidance is available
  • These devices can greatly reduce monitoring costs, without sacrificing data quality.

The research of the Department of Defense looked at three general types of passive samplers for groundwater:

  • Equilibrium samplers – devices that establish an equilibrium with the groundwater
  • Sorptive samplers – devices that accumulate analytes from groundwater over time
  • Grab samplers – devices that collect water samples at a specific depth and time.

Van Walt’ own information: Not all passive samplers are equal explains the differences between the different types of passive samplers. In this latest report from the USA we were delighted to note that the Snap Sampler, the passive sampler we support, was rated by the Department of Defense as:

  • Excellent for most analytes
  • Linear relationships with slopes = 1.0
  • Estimated cost savings of ~70%.

Overall passive sampling was assessed as providing valid samples for many analytes of concern, under a wide range of conditions and the results obtained indicate: “that these devices can greatly reduce monitoring costs, without sacrificing data quality. In addition, a better understanding of the causes for variability in groundwater monitoring results has led to improvements in sampling strategies. At many sites, monitoring events can be less frequent than the typical quarterly to yearly schedules, while still providing the data needed to quantify long-term trends and ensure environmental protection. These improvements promise to further reduce long-term monitoring costs, and therefore overall management costs”.

To find out more about the Snap Sampler call us on +44 (0)1428 661 660.

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