Frequently Asked Questions (FAQs)

Passive sampling involves acquiring a sample from a discrete location without the active media transport induced by pumping or purge techniques (ITRC 2023).   Passive sampling bypasses the stagnant casing water and acquires a representative groundwater sample from an interval in the saturated screen without purging the well.

Yes! Because you don’t have to purge the well or wait for parameters to stabilize, passive sampling is easier and much more efficient than active sampling methods. Consultants share their experiences with us and consistently refer to cutting their sampling time by 50-80%.

Yes! Numerous third-party field studies and lab-controlled bench studies have been conducted since passive sampling in groundwater began over 25 years ago. The overwhelming evidence is that passive sampling does provide accurate results for groundwater sampling.  See Studies Here.

Cost savings depend on many factors, including number of wells, frequency of sampling, type and amount of purge-water, and the sampling method that passive sampling will replace. A study conducted at McClellan AFB in 2005 showed that the sampling cost was ~$250 less expensive (80%) per well / per event when comparing passive sampling to pumping methods. A 30-year monitoring program with a 20 well network sampled semi-annually, will save $300,000 by converting to passive sampling! See Study Here.

A While passive samplers can be used in any groundwater monitoring project, they provide the most benefits when used on long term monitoring projects with two or more sampling events per year. Due to volume limitations within groundwater wells, the benefits of passive samplers are less practical if you need to sample more volume than is held within the saturated screen portion of the monitoring well.

Over the 25+ years since the USGS introduced passive groundwater sampling, regulators have approved passive sampling on projects at federal, state, and private sites in all USEPA regions including, Superfund, CERCLA, and DoD sites. There are many individual regulators, each with their own background and experience, and some regulators are unfamiliar with passive sampling or hesitant to change sampling methods without more information. EON always recommends approaching your regulator for a discussion about the project benefits of passive sampling, and we can provide technical information, case studies, and SOPs so that nobody feels like they are trying something new!

Passive sampling is extremely easy and requires very little training! EON takes pride in our hands on approach to training new users. We provide free virtual training on all of our passive samplers: including how they work within the monitoring well and the deployment/recovery process for sampling. EON will partner with you to ensure you enter into your first passive sampling event prepared and confident.

There are two main types of passive groundwater samplers that function differently but  have the same general benefits of cost reduction, ease of use, and they do not produce purge water.

• Passive Grab Samplers capture a whole-water sample at an interval in the saturated screen. The water and everything in the water (including PFAS) are recovered without inducing flow in the well that could cause mixing with stagnant well water. The HydraSleeve is the most-used passive grab sampler. 
• Passive Diffusion Samplers use a semi-permeable membrane filled with deionized water that is installed at an interval in the saturated screen. A concentration gradient will exist between the groundwater and the water in the sampler that causes contaminants molecules to diffuse through the membrane until the sampler and the groundwater have equal concentrations, without inducing flow in the well that could cause mixing with stagnant well water. The Passive Diffusion Bag (PDB) sampler for VOCs only and the Dual Membrane Passive Diffusion Bag (DMPDB) sampler for any contaminant, (including PFAS) are the most-used passive diffusion samplers.