Theory of Operation

Integrating samplers (also called kinetic samplers) generally have a sampling frame that contains a receiving phase medium chosen for the chemicals of concern. The sampling frame acts as a barrier between the medium to be sampled and the receiving phase medium. Its materials of construction can be chosen to provide chemical selectivity to the sampler and also to determine its chemical-specific sampling rate. The chemicals of concern reach the receiving phase by diffusion or permeation through the barrier. It is important that there is sufficient receiving phase capacity to ensure that the chemicals of concern are being captured and that equilibrium conditions do not develop (i.e., the desorption or release of chemicals back into the water is negligible).

Sampling rates are used to convert the amount of chemicals found in the receiving phase into a time-averaged concentration. Sampling rates for a given sampler are determined in the laboratory for each chemical of concern. These rates can be affected by environmental factors such as water temperature, water flow rate, and potential biofouling. To compensate for potential deviations from laboratory determined rates, some practitioners spike the receiving phase with performance reference compounds (PRCs) whose offloading kinetics are similar to the uptake kinetics of the chemicals of concern. Analysis of the PRCs that remain at the end of the sampling period allow for the calculation of an offloading rate that can be used to adjust the laboratory determined sampling rate.

By sequestering (concentrating) chemicals over time, integrative samplers can provide evidence of episodic changes in concentrations that grab samples may miss. Also, since they sample a relatively large quantity of water and sequester the chemicals of concern, they have ultra low detection limits. Other advantages include:

• Easy to use.
• Good for many analytes.
• Do not require bringing gas (e.g., nitrogen, air) or electricity into the field.
• No purge water to dispose of.

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Chemcatcher®

System Components and Operation

While Chemcatcher® has been deployed primarily for measuring contaminants in surface water, it has the potential to be deployed in monitoring wells with inside diameters greater than 6.5 cm. The device consists of a 5.5 cm wide and 1.8 cm thick platform for holding the receiving phase and diffusion limiting membrane, a retaining ring to secure the receiving phase and membrane, and a lid for use during transport.

Assembled Chemcatcher® (Courtesy: Professor Richard Greenwood)

Chemcatcher® sampler, retaining ring, and transport lid (Courtesy: Professor Richard Greenwood)

The receiving phases are 47 mm extraction disks (Empore™ disks, 3M Corporation). When metals are the target contaminant, a disk containing a chelating resin in combination with a cellulose acetate membrane is employed. For polar organics, a disk containing a polymeric phase and a polyethersulfone membrane is employed. For non-polar organics, a C₁₈ phase disk (loaded with n-octanol) and a low density polyethylene (LDPE) membrane is used. The disks may require some preparation before deployment (Greenwood 2010).

The device may be deployed in a well by tethering (e.g., polyethylene mesh bag) it to a line of appropriate length and lowering to the desired point in the screened interval or open borehole. Stacking is also possible. Note that a literature search did not find an example of the device being used in a monitoring well and well flow dynamics may not be favorable for its use.

Target Analytes

The Chemcatcher® can be used to sample both polar and non-polar organics as well as metals. The most prominent chemical classes found in the literature are polycyclic aromatic hydrocarbons (PAHs), pesticides, chlorobenzenes, polychlorinated biphenyls (PCBs), organotins, and polybrominated biphenylethers (De La Cal et al. 2008, Allan et al. 2007, Aguilar-Martínez et al. 2009, and El-Shenawy et al. 2010).

Advantages

• Can achieve low detection limits.
• Does not have sample volume issues.
• Receiving phase immobilized in Empore™ disk, and so easy to insert in body prior to deployment, and to remove and handle after deployment.
• Extraction can be carried out in standard vacuum manifold for Empore™ disks.
• Extracts of receiving phase post deployment require little or no clean up before analysis.
• Can sample both polar and non-polar organic chemicals as well as most metals.
• Does not require electricity or other support.
• Sampler body re-usable.

Limitations

• One licensed vendor.
• Sampling rate for target contaminants must be determined.
• Integrator window varies by compound (for accurate concentrations the uptake rate must remain linear).
• Water flux is needed to make environmental adjustments to laboratory determined sampling rates (improve accuracy).
• Does not provide water quality parameters and inorganic (non-metals) data.
• May be subject to biofouling when deployed for extended period of time (Allan 2009).
• Commercially available equipment is not designed for 5 cm monitoring wells.
• Requires two trips; one for deployment, one for retrieval.

Cost

The sampler with membranes to sample metals, polar, and non-polar contaminants cost about $38.00 plus shipping and handling. It is available from Janine Bruemmer University of Portsmouth, United Kingson. The receiving phase disks are available from 3M Corporation in packages of 60 (chelating $796.72; C18 $595.79; and SDB-RPS (polymeric) $732.98.

Demonstration Sites

Application of Chemcatcher Passive Sampler for Monitoring Levels of Mercury in Contaminated River Water (Abstract)
Aguilar-Martínez R, M. Gómez-Gómez, R. Greenwood, G. Mills, B. Vrana, and M. Palacios-Corvillo
Talanta; 77(4), p 1483-9, 2009

Field Performance of the Chemcatcher Passive Sampler for Monitoring Hydrophobic Organic Pollutants in Surface Water (Abstract)
Vrana B, G. Mills, P. Leonards, M. Kotterman, M. Weideborg, J. Hajslová, V. Kocourek, M. Tomaniová, J. Pulkrabová, M. Suchanová, K. Hájková, S. Herve, H. Ahkola, and R. Greenwood
J Environ Monit. 12(4), p 863-72, 2010

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Enviroflux Passive Flux Meter (PFM)

System Components and Operation

The PFM is a self-contained permeable unit (nylon mesh tube) that is inserted into a well or boring such that it intercepts groundwater flow but does not retain it. The interior composition of the meter is a matrix of hydrophobic and hydrophilic permeable sorbents that retain dissolved organic and inorganic contaminants present in fluid intercepted by the unit. The sorbent matrix is also impregnated with known amounts of one or more fluid soluble "resident tracers." These tracers are leached from the sorbent at rates proportional to the fluid flux (ESTCP 2006d). The permeable unit should be the same length as the screened interval.

Small Flux Meter (Courtesy: Enviroflux)

Flux Meter (Source: ESTCP 2006d)

After a specified period of exposure to groundwater flow, the flux meter is removed from the well or boring. Next, the sorbent is carefully extracted to quantify the mass of all contaminants intercepted by the flux meter and the residual masses of all resident tracers.

Movement of Tracer Due to Groundwater Flow (Adapted from ESTCP 2007)The contaminant masses are used to calculate cumulative and time-averaged contaminant mass fluxes, while residual resident tracer masses are used to calculate cumulative or time-average fluid flux. Depth variations of both water and contaminant fluxes can be measured in an aquifer from a single flux meter by vertically segmenting the exposed sorbent packing, and analyzing for resident tracers and contaminants. Thus, at any specific well depth, an extraction from the locally exposed sorbent yields the mass of resident tracer remaining and the mass of contaminant intercepted. Note that multiple tracers with a range of partitioning coefficients are used to determine variability in groundwater flow with depth that could range over orders of magnitude. This data is used to estimate local cumulative water and contaminant fluxes (taken directly from ESTCP 2007). Key design criteria for the PFM are available.

Provided well construction does not cause a change in groundwater gradient and there is no naturally occurring vertical gradient, the measurement of flux at a given screen segment should represent aquifer conditions opposite the screen (Vroblesky 2001).

Target Analytes

Successful demonstrations of the technology focused on tetrachloroethene, trichloroethene, dichloroethene, vinyl chloride, ethylene, methyl tertiary butyl ether, and perchlorate. However, since the sorbent is chosen to match the chemical properties of the contaminants of concern, the method should apply to many other chemicals. Activated charcoal was the sorbent of choice for these demonstrations.

Advantages

• Provides an estimate of both ground water and contaminant fluxes.
• Different sorbents can be used, making it good for most analytes.
• Does not require bringing gas (e.g., nitrogen, air) or electricity into the field.
• No purge water to dispose of.
• With regulatory approval, flux measurements can be used for process control, remedial action performance assessments, and compliance monitoring.

Limitations

• Releases of resident tracers into the groundwater that may require regulatory approval.
• For measurements taken in excess of 60 meters, the current PFM design can be difficult to implement (ESTCP 2007).
• In very heterogeneous aquifers the number of wells and hence PFMs needed to provide adequate flux assessments will increase (ESTCP 2007).
• Only measures contaminants passing through well screen (as opposed to integral pumping tests which draw water from around the wells).
• Must be retrieved before resident tracers are exhausted.
• Sampler may be site or well specific, ideally, one should know enough about the aquifer being sampled to supply the Key Design Criteria when ordering sampler.

Costs

The ESTCP (2007) report estimates a cost of $202 to $404 per linear foot of screened interval. This cost includes materials, mobilization/demobilization, disposal expenses, and analytical services. For specific breakdown see Table.

Demonstration Sites

Field Demonstration and Validation of a New Device for Measuring Water and Solute Fluxes
ESTCP (Environmental Security Technology Certification Program), Cost and Performance Report ER-0114, 47 pp, 2007

Field Demonstration and Validation of a New Device for Measuring Water and Solute Fluxes at CFB Borden
ESTCP (Environmental Security Technology Certification Program), 152 pp, 2006a

Field Demonstration and Validation of a New Device for Measuring Groundwater and Perchlorate Fluxes at IHDIV-NSWC, Indian Head, MD
ESTCP (Environmental Security Technology Certification Program), 138 pp, 2006b

Field Demonstration and Validation of a New Device for Measuring Water and Solute Fluxes NASA LC-34 SITE
ESTCP (Environmental Security Technology Certification Program), 172 pp, 2006c

Field Demonstration and Validation of a New Device for Measuring Water and Solute Fluxes at Naval Base Ventura County (NBVC), Port Hueneme, CA
ESTCP (Environmental Security Technology Certification Program), 112 pp, 2006d

Oxyanion Flux Characterization Using Passive Flux Meters: Development and Field Testing of Surfactant-Modified Granular Activated Carbon
Leea, Jimi, P.S.C. Rao, I. C. Poyera, R. M. Toolea, M.D. Annable, and K. Hatfield
Journal of Contaminant Hydrology 92 (2007) 208-229

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GORE® Module

System Components and Operation

Figure 1. GORE® Module with Shipping Container (Source: W. L. Gore & Associates, Inc.)

Each module is approximately 1/4 inch in diameter and 13 inches in length and consists of a GORE-TEX® membrane tube containing four or more packets of sorbent material in series (Figure 1). The GORE-TEX® is a microporous, chemically-inert expanded polytetrafluoroethylene (ePTFE) material. The gas permeable, hydrophobic nature of the membrane allows vapor migration to the sorbent, but prevents water and sediments from reaching the inner sorbent material. The membrane is designed for diffusion and does not offgas compounds. A typical Sorber packet is about 25 mm in length, 3 mm in diameter, and contains a granular adsorbent material that is selected on the basis of the specific compounds to be detected (ITRC 2006).

For typical groundwater sampling, the GORE Module is tied to a string with weights and lowered to the desired sampling depth (Figure 2). The module is left exposed for 15 minutes to four hours, then retrieved and analyzed at an off-site laboratory (ITRC 2007). For vertical stratification sampling, it can be deployed in a stacked configuration.

Depth to the water table relative to ground surface, depth of the well (well bottom), and screen length and location within the well should be known. The water temperature should be recorded at the sample depth(s). Both the water depth above the module (i.e., from the water table to module location) and the water temperature are used in the concentration calculations.

Figure 2. GORE® Module Deployment (Source: ITRC 2007)

The modules are shipped inside individual sample vials in boxed containers to and from the site. Each vial lid has the same unique serial number (bar code) as the module. No ice or other special handling needs are required for shipping (ITRC 2007).

Provided well construction does not cause a change in groundwater gradient and there is no naturally occurring vertical gradient, the samplers should represent aquifer conditions horizontal to their deployment position (Vroblesky 2001). If only one sampling interval is to be taken, Vroblesky (2001) recommends that the vertical distribution of contaminants be determined in wells having 10-ft-long well screens, and that both the vertical distribution of contaminants and the potential for intra-borehole flow be determined in wells having screens longer than 10 ft. This will help ensure the proper interpretation of the analytical results.

Target Analytes

The adsorbents are analyzed by a modified EPA SW846 8260 method (gas chromatography, mass selective detection; GC/MS) following thermal desorption (TD). Target analytes include volatile and semi-volatile organic compounds(VOCs and SVOCs) and include water-soluble compounds (e.g., tert-butyl alcohol and 1,4-dioxane), and polycyclic aromatic hydrocarbons(PAHs) (ITRC 2007). The vendor states that the laboratory analysis has been accredited to ISO 17025, NELAC, and DoD's ELAP requirements by A2LA for their US EPA 8260M method for relative mass value reporting.

The compounds accumulated by the GORE Module are quantified and reported in units of mass (µg). Concentration reporting requires a conversion of the mass to concentration units using a calibration that incorporates the sampling rate of compounds by the module in water, water temperature, and water pressure (ITRC 2007).

The reference sampling rate, SR_o, is determined experimentally under controlled conditions. The temperature of the ground water affects the partitioning of dissolved compounds from the water to the air and therefore the sampling rate. The weight of water (pressure) above the module can also affect the sampling rate. Thus, the specific sampling rate for each monitoring well, SR_(well), varies slightly based on the water temperature and water level. For example, if the ground water temperature is less than the reference temperature (21°C), the vapor pressure will be less and the sampling rate will be lower. Both calibration terms are computed from the well information collected during the sampling.

Volatiles		Semi-Volatiles	Explosives
methyl t-butyl ether benzene toluene ethylbenzene o-xylene m,p-xylene octane 1,1-dichloroethane 1,2-dichloroethane 1,1,1-trichloroethane 1,1,2-trichloroethane 1,1,1,2-tetrachloroethane 1,1,2,2-tetrachloroethane	1,1-dichloroethene trans-1,2- dichloroethene cis-1,2-dichloroethene trichloroethene tetrachloroethene chloroform carbon tetrachloride chlorobenzene 1,4-dioxane freons fuel oxygenates	1,3,5-trimethylbenzene 1,2,4-trimethylbenzene 1,2-dichlorobenzene 1,3-dichlorobenzene 1,4-dichlorobenzene undecane tridecane pentadecane naphthalene 2-methylnaphthalene	nitrobenzene 2-nitrotoluene 3-nitrotoluene 4-nitrotoluene 1,3-dinitrobenzene 2,4-dinitrotoluene 2,6-dinitrotoluene 1,3,5-trinitrobenzene 2,4,6-trinitrotoluene
Source: ESTCP 2007

Advantages (adapted from ITRC 2007)

• The narrow diameter of the module facilitates deployment in piezometers and wells 1/2 inch in diameter or larger.
• Does not collect a water sample and therefore does not require sample transfer.
• Is single use and therefore requires no decontamination.
• Minimally disturbs the water column at deployment.
• Is applicable for VOC and SVOC compounds, including water-soluble compounds.
• Requires no ice or coolers for sample storage or shipping.
• Has a short exposure time, 15 minutes to 4 hours.
• Has no minimum sample volume limitation.
• Contains duplicates samples.
• Can be deployed for longer time periods to detect low concentrations.
• Can collect a sample in a short water column (as low as 6 inches of water).
• Can be deployed in a series for vertical profiling with intervals as small as six inches.

Limitations

• Currently has a single source supplier and laboratory (ITRC 2007).
• Does not measure field parameters or inorganics (ITRC 2007).
• Is limited by vapor pressure for compound detection (ITRC 2007).
• Requires an algorithm to convert measured mass to concentration (ITRC 2007).

Costs

The GORE® Module pricing includes the sampler, trip blank, deployment supplies, lab analysis, and reporting. Costs are $200 to $300 per sample depending upon the analytes tested (J. Hodny personal communication May 2010).

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Polar Organic Chemical Integrative Sampler (POCIS)

System Components and Operation

The POCIS consists of a solid material (sorbent) contained between two microporous polyethersulfone membranes. The membranes allow water and dissolved chemicals to pass through to the sorbent where the chemicals are trapped. Larger materials, such as sediment and particulate matter, are excluded. The membrane resists biofouling, which can significantly reduce the amount of the chemical sampled. The type of sorbent used can be changed to specifically target certain chemicals or chemical classes (ITRC 2006). The polyethersulfone membranes are not amenable to standard sealing techniques (i.e., heat sealing) and therefore must be secured with a compression ring system to prevent loss of sorbent. The compression rings are typically made from stainless steel or other rigid inert materials. Individual POCIS can be secured on a support rod or on a rack system for insertion in a protective deployment canister (ITRC 2006).

POCIS Samplers (Source: USGS 2004)

Although POCIS samplers have been used extensively to determine contaminant levels in surface waters, the literature search failed to find an example where they had been used for groundwater sampling. The standard commercially available sampler disc is 4 inches in diameter and the protective canister is about 6.3 inches in diameter and about 6 inches in length.

Target Analytes

The POCIS was designed to sequester and concentrate waterborne polar organic chemicals with log K_ow≤3.0 (Alvarez undated). If a quantitative concentration is desired, sampling rates must be developed for chemicals of concern at ambient conditions. Without the sampling rates, analytical results will provide qualitative measures of contaminant water concentrations; relative differences between sites; identification of chemicals (is it there? YES / NO ); and bio-mimic assessment of an organism's exposure to chemicals (Alvarez undated). The table below provides a sampling of the contaminants that the sampler is capable of capturing.

23 pharmaceuticals including Acetaminophen Azithromycin Carbamazepine Dextropropoxyphene Diphenhydramine Erythromycin Propranolol Sulfa drugs (antibiotics) Tetracycline antibiotics Thiabendazole Trimethoprim Illicit drugs Methamphetamine MDMA (Ecstasy) Natural and synthetic hormones 17β-estradiol 17α-ethynylestradiol Estrone Estriol 12 Triazine herbicides including Atrazine Cyanazine Hydroxyatrazine Terbuthylazine

Various polar pesticides including Alachlor Chlorpyrifos Diazinon Dichlorvos Diuron Isoproturon Metolachlor Various household and industrial products and degradation products including Alkyl phenols (nonyl phenol) Benzophenone Caffeine DEET PFOS/PFOA Tonalide Triclosan Fire Retardants Fryol CEF Fryol FR2 Tri(2-butoxyethyl)phosphate

Source: ITRC 2006

Advantages

• Can achieve very low detection limits.
• Does not have sample volume issues.
• Ideally suited for emerging contaminants (e.g., endocrine disruptors).
• Does not require electricity or other support.

Limitations

• One licensed vendor.
• Sampling rate for target contaminants must be determined.
• Water flux is needed to make environmental adjustments to laboratory-determined sampling rates (improve accuracy).
• Does not provide water quality parameters and inorganic data.
• Commercially available equipment is not designed for 2 inch monitoring wells.
• Requires two trips-one for deployment, one for retrieval.

Costs

POCIS Item ID	Sequestering Medium	Price per POCIS
A	Pharmaceuticals	$65.00
B	Pesticides	$65.00

POCIS Processing and Extraction
$75 per POCIS

POCIS Stainless Steel Deployment Devices	Purchase	Rental
POCIS Holder (up to three Aquasense-P)	$50.00	$10.00/mo
Small Canister w/ POCIS Holder	$300.00	$110.00/mo
Large Canister w/ 2 POCIS Holders	$450.00	$145.00/mo

Source: Environmental Sampling Technologies (May 2010)

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Semi-Permeable Membrane Devices

System Components and Operation

SPMD with Stainless Steel Deployment Device (Courtesy: Environmental Sampling Technologies)

The Semi-Permeable Membrane Device (SPMD) consists of a neutral, high molecular weight lipid (> 600 daltons) such as triolein which is encased in a thin-walled (50-100 µm) lay-flat polyethylene membrane tube. The nonporous membrane allows the nonpolar chemicals to pass through to the lipid where the chemicals are concentrated. Larger molecules (> 600 daltons) and materials such as particulate matter and microorganisms are excluded. A standard SPMD is 2.5 cm wide by 91.4 cm long containing 1 mL of triolein. SPMDs of different sizes can be made by maintaining the ≈ 100 cm²/g SPMD ratio (ITRC 2006).

SPMD deployments typically are for one month, however, depending on the study design, deployment times can range from days to months. SPMDs are transported to and from the sampling site in gas-tight metal cans. Following receipt of a field deployed SPMD, the device is stored frozen until processing. Chemical residues in the SPMD are recovered by using an organic solvent dialysis step. SPMDs are submersed in an organic solvent such as hexane and analytes diffuse out into the hexane while lipids remain inside the tubing. Following dialysis, all targeted chemicals are in the hexane and the used SPMD can be discarded. At this point, the sample is ready for further processing (cleanup and/or fractionation), analysis, toxicity screening (ITRC 2006).

Target Analytes

Because they are made from polyethylene, molecules greater than about 10 angstroms are unable to pass through the bag (Huckins et al. 2006).

Priority pollutant PAHs and alkylated PAHs Many heterocyclic aromatics, cyclic hydrocarbons (e.g., decalin and alkylated decalins) and aliphatics Organochlorine pesticides Other pesticides: includes diazinon, endosulfans, pyrethroids, toxaphene, and trifluralin PCB congeners Chlorinated naphthalenes Chlorinated dibenzofurans, including 2,3,7,8-TCDF	Chlorinated dibenzodioxins, including 2,3,7,8-TCDD Polybrominated diphenyl ethers Chlorinated benzenes Chlorinated anisoles and veratroles Alkyl phenols (nonyl phenol) Triclosan Tributyl tin Sulfur Essentially, any compound with log Kow ≥ 3.0
Source: Huckins et al. 2006

Advantages

• Can provide very low detection limits.
• Does not collect a water sample and therefore does not require sample transfer.
• Sample volume is not an issue.
• Excludes sediments, so concentration values of chemicals such as PAHs truly represent the dissolved phase.
• Does not require electricity or other support equipment (e.g., gases).

Limitations

• Depending upon the chemicals of concern and the groundwater flow rate, SPMDs may require long deployment times
• The only commercial U.S. vendor requires that that they do the dialysis step.
• Requires two trips-one for deployment, one for retrieval.
• Sampling rate for target contaminants must be determined.

Costs (as of May 2010)

Stainless steel deployment device (purchase)	$350 each
Stainless steel deployment device (rental)	$75 per month
71-92 cm polyethylene bag with ultra high pure triolein	$60
Dialysis Separation	$115
Gel Permeation Chromatography Separation	$150

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