Passive Diffusion Bag Research Articles

Polydimethylsiloxane dialysis passive sampler monitoring of chlorinated solvent contaminated sites – A field study

The complexity of the subsurface contaminated by chlorinated solvents such as trichloroethylene (TCE) makes it challenging to gain a complete understanding of contamination distribution and establish a conceptual site model (CSM). High-resolution vertical contaminant concentration profiling across both the unsaturated zone and the saturated aquifer is desirable for mapping the distribution of contamination. A Fick's law-based polydimethylsiloxane (PDMS) dialysis passive sampler was developed and evaluated on a field scale for its potential application. This study tests the passive sampler at two TCE contaminated sites, and the sampling results were compared with the results from different sampling methods based on the relative percent difference. The PDMS dialysis passive sampler obtained more representative soil gas concentrations in the unsaturated zone than a portable monitoring and sampling device, which caused soil gas flow disturbance by soil gas pumping during sample collection. In the saturated aquifer sampling, the results obtained by the PDMS dialysis passive sampler correlated well with those obtained by a commercial polyethylene passive diffusion bag, and exhibited higher sensitivity under low TCE concentration conditions. Furthermore, the PDMS dialysis passive samplers were densely deployed inside each monitoring well at multiple depths, at two sites, to achieve high-resolution monitoring across the unsaturated zone and saturated aquifer. Based on the PDMS dialysis sampler data, a more comprehensive three-dimensional CSM was systematically established.

Lab and field screening of 5 selected passive samplers for the measurement of VOC fluxes in groundwater

The prospects and limitations of direct flux measurement of volatile organic compounds in groundwater with 5 selected passive samplers, currently available or self-constructible, are screened in a series of lab and field experiments. The selection of the 5 samplers for the practical experiments is based on the review of current passive samplers for the measurement of organic contaminants in water (Verreydt et al., 2010). The MESCO sampler and ceramic dosimeter were subjected to a batch lab screening experiment, while the passive flux meter, the sorbi sampler, the passive diffusion bag sampler and the ceramic dosimeter were installed in a monitoring well at a field site. The passive flux meter has proven to be the only passive sampler which effectively determines VOC mass fluxes. The ceramic dosimeter produced time- averaged concentration data comparable to traditional sampling data and can be used for long-term monitoring. The sorbi sampler also produced results which are more or less similar to traditional sampling data, but is not eligible for a long-term practice. The passive diffusion bag sampler has shown to be a reliable equilibrium sampler, but is not suitable for the determination of mass fluxes. The MESCO sampler has the poorest physical robustness and is therefore not suitable for long-term application in a groundwater monitoring well.

Determination of VOCs in groundwater at an industrial contamination site using a homemade low-density polyethylene passive diffusion sampler

A home-made inexpensive passive diffusion bag (PDB) sampler, prepared by filling deionized water in low-density polyethylene (LDPE) tubes, was evaluated for volatile organic compounds (VOC) sampling in groundwater at industrial contamination sites. Impacts of environmentally relevant conditions on the sampling equilibration time and partitioning of VOCs between the sampler and the water sample were investigated. Sample salinity, agitation and temperature can influence the equilibration time, but generally sampling equilibration was obtained in 14 days under real field sampling of VOCs in groundwater. Both laboratory study and field testing in a contaminated site showed that the VOC concentrations in the developed sampler were equal to those in the water samples at equilibrium. Coupled with a purge and trap concentrator-gas chromatograph-mass spectrometer (P&T-GC-MS), the developed PDB sampler provided a low-cost sampling device for routine monitoring of VOCs in groundwater in wells, with LODs in the range of 2.9–10 μg/L. The proposed PDB was applied to determine VOCs in groundwater at an industrial contamination site, and the present results agreed well with those determined using conventional pump-and-sample monitoring. All the studied 13 VOCs were tested in the four wells in the industrial contamination sites, with their concentrations in the range of 12–73660 μg/L. In addition, while benzene and toluene were heavily contaminated up to a maximum concentration of 74000 μg/L and 6000 μg/L, respectively, 1,2,3-trichlorobenzene and bromobenzene had relatively low contamination levels (below 25 μg/L).

Field Investigation of Vapor‐Phase‐Based Groundwater Monitoring

The use of in‐field analysis of vapor‐phase samples to provide real‐time volatile organic compound (VOC) concentrations in groundwater has the potential to streamline monitoring by simplifying the sample collection and analysis process. A field validation program was completed to (1) evaluate methods for collection of vapor samples from monitoring wells and (2) evaluate the accuracy and precision of field‐portable instruments for the analysis of vapor‐phase samples. The field program evaluated three vapor‐phase sample collection methods: (1) headspace samples from two locations within the well, (2) passive vapor diffusion (PVD) samplers placed at the screened interval of the well, and (3) field vapor headspace analysis of groundwater samples. Two types of instruments were tested: a field‐portable gas chromatograph (GC) and a photoionization detector (PID). Field GC analysis of PVD samples showed no bias and good correlation to laboratory analysis of groundwater collected by low‐flow sampling (slope = 0.96, R2 = 0.85) and laboratory analysis of passive water diffusion bag samples from the well screen (slope = 1.03; R2 = 0.96). Field GC analysis of well headspace samples, either from the upper portion of the well or at the water‐vapor interface, resulted in higher variability and much poorer correlation (consistently biased low) relative to laboratory analysis of groundwater samples collected by low‐flow sample or passive diffusion bags (PDBs) (slope = 0.69 to 0.76; R2 = 0.60 to 0.64). These results indicate that field analysis of vapor‐phase samples can be used to obtain accurate measurements of VOC concentrations in groundwater. However, vapor samples collected from the well headspace were not in equilibrium with water collected from the well screen. Instead, PVD samplers placed in the screened interval represent the most promising approach for field‐based measurement of groundwater concentrations using vapor monitoring techniques and will be the focus of further field testing.

Use of Passive-Diffusion Bag Samplers to Profile Low-Level Trichloroethene Concentrations in Ground-Water Extraction Wells

Using passive-diffusion bag (PDB) samplers as a ground-water monitoring technique has become more popular in recent years as various laboratory and field studies have shown acceptable data-quality objectives (DQOs) can be achieved through their use. The PDB sampler is deployed in an aqueous environment (e.g., well or borehole), where passive diffusion through the semi-permeable membrane of the sampler enables the water quality in the sampler, which is typically filled with deionized water, to equilibrate with that in the surrounding aqueous environment (Harter and Talozi, 2004). The type of membrane determines which solutes are able to pass into the sampler medium. Ehlke and others (2004) and Harter and Talozi (2004) discuss sampler membrane types and factors that affect their use. To obtain representative samples with PDB samplers, ground water must be able to flow through the well screen in sufficient volume to permit solute equilibration in the sampler medium during the sampler deployment period. After initial equilibration is achieved, sampler medium and ambient ground water should maintain equilibrium. However, because this constant re-equilibration process is not instantaneous, the sampler medium represents a time-averaged solute concentration of ground water during the preceding days (depending on the rate of equilibration) (Ehlke et al., 2004). The rate at which the medium within the PDB sampler equilibrates with ambient ground water depends on multiple factors, including the type of compound being sampled, ground-water temperature, contaminant distribution, and ground-water flow dynamics (Vroblesky, 2001). Various compounds more easily diffuse into the sampler medium simply because the molecular sizes of the compounds are smaller than the pore size of the PDB-sampler membrane. Vroblesky (2001) presents a list of volatile organic compounds of environmental interest that have shown effective and ineffective equilibration between the PDB-sampler medium and ambient water under laboratory conditions. As presented in Vroblesky (2001), …

Where Do Mistakes Come From?

Where Do Mistakes Come From?

Study of Five Discrete‐Interval‐Type Ground Water Sampling Devices

AbstractFive relatively newly developed discrete‐interval‐type ground water sampling devices—the KABIS, HydraSleeve, Discrete Interval, Pneumo‐Bailer, and USGS passive diffusion bag (PDB) samplers—were tested to determine their ability to recover representative concentrations of a variety of analytes—volatile organics, explosives, pesticides, and metals—from a standpipe and trichloroethylene (TCE) from a deep monitoring well. Samples taken from a well were compared with samples taken using low‐flow sampling.The PDB sampler was the easiest to use, but could only be used to sample volatile organic compounds (VOCs). The HydraSleeve and the KABIS samplers were also easy to use; these devices produced representative concentrations of explosives, pesticides, and metals in the standpipe experiments, but elevated the turbidity in our monitoring well. Although there were statistically significant differences for some VOCs with both devices, these differences were generally very small (< 5%). The one exception was an 18% loss of TCE with the KABIS sampler.The Discrete Interval sampler and the Pneumo‐Bailer are pressurized devices that are designed to only collect a sample when activated. The Pneumo‐Bailer was heavy and awkward to handle, required a nitrogen tank in the field, and involved many steps to operate. The Discrete Interval sampler only required a bicycle pump to pressurize the chamber and was lighter and easier to handle and operate than its counterpart. Both devices generally delivered representative concentrations of all the analytes tested.

Comparison of Temporal Trends in VOCs as Measured with PDB Samplers and Low‐Flow Sampling Methods

AbstractThe effectiveness of passive diffusion bag (pdb) samplers in the measurement of selected volatile organic compounds (VOCs) is dependent on a number of factors. At some sites and wells, pdb sampling methods provide an attractive alternative to other sampling methods. In this discussion, I provide two examples of comparisons of temporal trends in tetrachloroethylene (PCE) concentrations from passive and low‐flow sampling methods. At the example field site, large changes in PCE concentrations occurred over the deployment period(s) of the pdb samplers, yet the concentrations from the pdb samples are similar to the low‐flow samples and the overall trends are the same.

Equilibration times, compound selectivity, and stability of diffusion samplers for collection of ground-water VOC concentrations

Vapor-filled polyethylene diffusion samplers (typically used to locate discharge zones of volatile organic compound contaminated ground water beneath streams and lakes) and water-filled polyethylene diffusion bag samplers (typically used to obtain volatile organic compound concentrations in ground-water at wells) were tested to determine compound selectivity, equilibration times, and sample stability. The aqueous concentrations of several volatile organic compounds obtained from within water-filled diffusion samplers closely matched concentrations in ambient water outside the samplers. An exception was methyl- tert-butyl ether, which was detectable, but not reliably quantifiable using the diffusion samplers. The samplers equilibrated to a variety of volatile organic compounds within 24 h for vapor-filled passive diffusion vial samplers and within 48 h for water-filled passive diffusion bag samplers. Under field conditions, however, a longer equilibration time may be required to account for environmental disturbances caused by sampler deployment. An equilibrium period for both vapor- and water-filled diffusion samplers of approximately 2 weeks probably is adequate for most investigations in sandy formations. Longer times may be required for diffusion-sampler equilibration in poorly permeable sediment. The vapor-filled samplers should be capped and water from the diffusion bag samplers should be transferred to sampling vials immediately upon recovery to avoid volatilization losses of the gasses.