Thief samplers are designed to obtain a grab (point) groundwater sample at the depth to which they are lowered. They are activated either by pulling up or using an up and down motion to force water into the sampler (HydraSleeve™) or by a triggering device at the well head (Snap, Discrete Interval, Kemmerer). Other devices that are not covered in this discussion include Point Source Bailer, and Pneumo-Bailer. Each of the thief sampler types is described in greater detail below:

Discrete Interval Sampler

System Components and Operation

The Discrete Interval Sampler offered by Solinst is a stainless steel sampler with Viton® O-rings and Teflon® or polypropylene check balls. Low density polyethylene (LDPE) tubing that is transported on a reel is attached to the sampler and to a high pressure hand pump. The system is pressurized before lowering into the groundwater. The air pressure activates switches that keep the sampler closed. These switches prevent any water from entering before the target depth is reached. Once at the target depth, the air pressure is released allowing the sampler to fill. After filling, the system is pressurized again to prevent any mixing of sampler water with non target groundwater as the sampler is retrieved. Once at the surface, the water is decanted into sample bottles. The equipment requires decontamination between wells. The air line tubing is also available in Teflon® and Teflon® lined polyethylene.

Solinst has a similar device that allows locking the pressure switches once the sampler is at the surface for direct shipment to a laboratory. This type of sampler may be useful when volatile degassing may occur during sample transfer due to differences between the water pressure in the sampler and atmospheric pressure at the surface.

Solinst Discrete Interval Sampler (Source: Parker 2002)

Solinst Discrete Interval Sampler (Source: Parker 2002)

Sampler capacities for sampling 2-inch monitoring wells range from 175 to 1000 mL (Solinst).

Target Analytes

The Discrete Interval Sampler should be effective for most organic and inorganic chemicals of concern. Depending upon the chemicals of concern, the size of the sampler may necessitate resampling the depth interval of the well several times to obtain sufficient water for analysis.

Costs

$600 to $1000 (April 2010) depending upon sampler size and length of tubing (sampling depth).

Advantages

The discrete Interval Sampler:

• Is good for all analytes.
• Does not mix water from different intervals.
• Collect samples from a narrow depth range within a well with no movement of the sampler position during collection.
• Does not require bringing gas (e.g., nitrogen, air) or electricity into the field.

Limitations

• Because of the sampler size, sampling time may be increased in order to retrieve sufficient water for project detection limit requirements.
• The sampler requires decontamination between wells.
• The expense is greater than some other thief samplers.

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HydraSleeve™

System Components and Operation

A HydraSleeve™ installation consists of three basic components:

• A reusable weight,
• The HydraSleeve™ sampler, and
• A suspension tether for lowering, locating, and retrieving the sampler.

The sampler is a flexible, collapsible sample tube or sleeve (usually made of 4-mil polyethylene tubing) closed at the bottom with a self-sealing reed-valve at the top. The weight is attached to the bottom of the sampler or tether line to carry the sampler below the water surface to the intended depth (ITRC 2006).

The typical length of the sampler is 30 inches with a 1.5 inch fill diameter (650 mL). A 36-inch 1.75 inch fill diameter (1000 mL) sampler is also available. Samplers for 4-inch wells have larger volumes. ITRC (2007) reported that lengths greater than 36 inches present handling problems, however, the vendor reports that this problem is now limited to lengths over 60 inches (GeoInsight, 2010) Note that the bottom weight may add six inches to the sampler length (GeoInsight, 2010).

HydraSleeve™ samplers can be deployed singularly or in a stacked array. During deployment and sample collection the sampler (or string) is slowly lowered into the well to minimize disturbance. Upon reaching the target depth, the sampler is tethered to allow for the well to stabilize and for some analytes to come into equilibrium with the sampler. The amount of time the HydraSleeve™ sampler should be left in the well prior to recovery depends on the DQOs for the sample, the analytes being sampled, the well and sampler size, and the sample interval flow characteristics (ITRC 2007).

Full HydraSleeve™ (Courtesy: GeoInsight)

1.5 Inch HydraSleeve™ with Weight (Courtesy: GeoInsight)

To collect a sample, the sampler is pulled up at a rate of one foot per second or greater. It will require ~1 to 1.5 sampler length of screen to completely fill (GeoInsight, 2010). The 36 inch sampler therefore samples a 3-foot aquifer interval above it. The upper bound of this sampling interval should always fall well within the top of the screen. Note: New HydraSleeves (since Jan. 2010) have larger check valves enabling them to fill at a 1:1 to 1:1.5 rate, reduced from the earlier 1:2 rate reported in ITRC ( 2007). The field manual (GeoInsight 2006) suggests two alternative sample retrieving methods to obtain samples over a shorter aquifer interval. The first is to pull the sampler upward at about 1 to 2 feet per second for the length of the sampler and let it drop back to the starting point, repeating the cycle 3 to 5 times. The second method, which reduced the sampling interval to the smallest achievable, is to cycle the HydraSleeve up and down using rapid, short strokes (6-inch cycle at a minimum of 1 cycle per second) 5 to 8 times. Both of these methods are likely to create turbid samples. The manufacturer no longer (October 2010) recommends cycling the sampler up and down. In the summer of 2009 the HydraSleeve SS (Super Sleeve) was introduced. It is specifically designed to maximize sample volume out of short water columns.

The sample from the HydraSleeve™ should be transferred to sample containers immediately to minimize diffusive loss of volatile organic compounds (VOCs) through the walls of the sampler. To transfer a sample from the HydraSleeve™ with the least amount of aeration and agitation, use the short pointed discharge tube included with the sampler (ITRC 2007). Following sample collection, the bag is disposed of, and if they are not dedicated, the tether and steel weight are decontaminated. ITRC (2007) provides the most detailed description of the use of HydraSleeve™ samplers. Note that the company has modified the sampler design (January 2010) and some of the information in ITRC 2007 may be dated. Also note their standard operating procedure manual provides a step by step explanation of the sampler's use.

Target Analytes

HydraSleeve™ is essentially a point source sampler and as such should be suitable for sampling most chemicals of concern. Depending upon the chemicals of concern, the size of the sampler may limit the number of chemical classes that can be analyzed for.

Costs (as of April 2010)
HydraSleeve™ sampler for a 2 inch monitoring well with 635 mL capacity*	$20 each
HydraSleeve™ sampler for 2 inch monitoring well with one liter capacity*	$28 each
Custom sizing*	$30 each

*Does not include bottom weight or line for lowering device into well

Advantages

The HydraSleeve™:

• Requires minimal or no decontamination.
• Is effective for most environmental parameters.
• Reduces sampling time compared to low flow methods.
• Reduces or eliminates generation of purge water.
• Does not require bringing gas (e.g., nitrogen, air) or electricity into the field.
• Requires minimal equipment O&M.
• May be able to determine if there is contaminant stratification under some site hydrogeologic and well hydraulic conditions.

Limitations

• Some circumstances can produce turbid samples.
• Sampling wells with short screen (2 - 5 feet or less ) may be difficult because of the short screen interval. (GeoInsight suggests that this is now 2 1/2 feet because of the new design.)
• The volume of water collected in one sampler may be insufficient for all project-required parameters and their specified detection limits, regardless of screen length.

Demonstration Sites

Additional Resources

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Kemmerer

System Components and Operation

While generally thought of as surface water samplers, Kemmerer samplers can be used for groundwater (USGS 2003). The sampler is a flow-through point source device. It consists of a sample container with stoppers on each end. The sampler is attached to a line and lowered through the water column in an open configuration. This allows water to flow through the sampler. At the desired depth, a messenger is sent down the line, causing the two stoppers to close and capture the water that has entered the sample container at that depth. The stainless steel, polyurethane, or PVC filling tube comes in various sizes and the stoppers are constructed from polyurethane, silicone, or Teflon®.

Teflon® Kemmerer Sampler (Courtesy: Wildlife Supply Company)An all Teflon® 1.2 L sampler is available but its outside diameter (2.2 inches) makes it impractical for 2-inch monitoring wells. The water sample obtained should be exactly representative of the sampler length at the target dept. For groundwater wells, there may be a need to leave the sampler in the well for an equilibration period that, depending upon the analytes, the sampler construction materials, and the site hydrogeology, could range from hours to weeks.

Target Analytes

The Kemmerer is a point grab sampler that should be suitable for most chemicals of concern, when constructed of appropriate materials. The size of the sample chamber may necessitate repeat sampling to obtain sufficient sample for all chemicals of concern.

Advantages

The Kemmerer sampler:

• Is effective for most environmental parameters.
• Does not require bringing gas (e.g., nitrogen, air) or electricity into the field.
• Collect samples from a narrow depth range within a well with no movement of the sampler position during collection.
• May reveal whether there is contaminant stratification, depending upon site hydrogeology and well hydraulics.

Limitations

• The limited capacity of the sample chamber may necessitate repeat sampling to obtain sufficient sample size.
• The equipment requires decontamination.
• The open sampler passes through the water column lying over the sample depth.
• Teflon® seals on stainless steel or PVC sample bodies may not be as tight as silicone, according to the manufacturer.

Costs

$400 to $1,000 depending upon size and materials of construction (Wildlife Supply Company April 2010)

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Snap Sampler

System Components and Operation

The Snap Sampler passive groundwater sampling system includes four basic components:

1. A specially designed bottle that is open at both ends and includes end caps retained on the bottles with an internal Teflon-coated spring. Bottle types include a 40ml glass VOA vial and 2 sizes of HDPE bottle (125mL and 350mL).
2. The sampling body that holds the special bottle and contains a release pin mechanism that holds the bottle in an open position during deployment. Samplers come in two sizes and hold three different bottle types. Samplers are "stacked" in series to combine bottle types and achieve the required number of sample bottles/volume.
3. A sampler triggering line that can be activated manually, pneumatically, or electrically.
4. A well-head docking station on which the trigger line and samplers are supported downhole.

Figure 1. Snap Sampler Components (Source: ProHydro)

Snap Samplers are usually dedicated systems. Individual wells are outfitted with samplers as specified by the user to achieve sample depth requirement and sample volume. Number and type are selected based on the analytical need. Trigger type is determined by depth and user preference. Required equipment is determined by the user prior to deployment and supplied pre-assembled for each individual well by the manufacturer. To deploy the Snap Samplers, the special sampler bottles are loaded into the samplers body (Figure 2).

Figure 2. Loading Snap Sampler (Source: ITRC 2007)Samplers are connected together in series and attached to a single trigger line. Each bottle is set into an open position (at both ends) prior to deployment downhole. Samplers are lowered downhole and supported at the well head on a docking ring (adapted from Parker and Mulherin 2007, ProHydro 2009).

The diameter of the Snap Sampler with bottles installed ranges from 1.65 to 3.1 inches, depending on sampler and bottle type. Samplers equipped with 40-mL and 125-mL bottles will fit into 2-inch or larger monitoring wells; samplers with 350-mL bottles will fit into 4-inch or larger wells. The length of the Snap Sampler "string" (Figure 3) depends on the number of samplers placed in series and which samplers are used. Each 40-mL sampler is 7.8 inches long and each 125-mL and 350-mL sampler is 10.4 inches long (ITRC 2007).

Figure 3. Snap Sampler "String" (Source: ProHydro)

The samplers are deployed in the well with the end caps of the bottle(s) in an open position. After an equilibration period that may be as little as 72 hours (Parker and Mulherin 2007), to as much as 6 months or more (ITRC 2007, ProHydro 2009) the trigger is activated, closing the sample bottle(s). Once retrieved, the sample can remain in the sampler bottle, eliminating exposure of the sample at the well head. For volatile organic compounds (VOCs), the VOA vials can be used in common autosamplers (e.g., Tekmar, Varian, Centurion), eliminating transfer in the laboratory as well. Up to 6 Snap Samplers can be deployed in series on the same trigger line to achieve required sample volume (adapted from Parker and Mulherin 2007, ProHydro 2009).

The recommended minimum deployment period prior to sampling is two weeks where site hydrogeology and flow are not well established. There are hydrogeologic conditions where a shorter deployment is possible, but two weeks would generally ensure a well is restabilized (Vroblesky 2001 as cited in ITRC 2007). The most common deployment approach is to initially set the samplers in their respective wells, return after a suitable equilibration time, trigger and remove the sample bottles for analysis. The sampler bodies are reloaded with new bottles and redeployed downhole until the next sampling round.

Target Analytes

The whole-water samples collected with the Snap Sampler can be tested for any analyte, subject to sample volume requirements (ITRC 2007, Britt et al. 2010).

Third-party demonstration/validations have been conducted for a variety of analyte types. These comparisons have show statistical equivalence to standpipe tests in laboratory settings and side-by-side comparisons to low-flow purging and volume-based purging approaches.

• Volatile organic compounds (Parsons 2005, Parker and Mulherin 2007)
• Semivolatile organic compounds
• Metals (Parker et al. 2008, Parker et al. 2009)
• Perchlorate and explosives (Parker and Mulherin 2007)
• Inorganics (Parsons 2005, Parker et al. 2008, Parker et al. 2009)

Cost

Cost for the dedicated Snap Sampling equipment depends on the number of Snap Samplers required and depth of deployment. Cost per well can range quite widely depending these factors. One-time equipment cost is typically in the range of $250 to $850. Ongoing cost includes replacement bottles during each sampling event.

Costs
Plastic (Dedicated) Snap Samplers (body)	$165 each
Manual Trigger (up to ~50ft)	$30, plus $1.25 per foot for line
Pneumatic Triggering lines (up to ~200ft)	$195 for actuator; $25 plus $0.25/ft for line
Electric Trigging lines (not limited)	$325 for actuator; $85 plus $1.75/ft for line
Well Head Docks	$32 for 2-inch, $42 for 4-inch
40ml glass VOA bottles	$16
125ml or 350ml polyethylene bottles	$16
Manufacturer prices as of October 2010

Advantages

• Generate no wastewater—all water collected is sample that goes to the lab.
• Can collect samples in sealed containers that are not subject to exposure to air at the wellhead or differences in bottle filling technique.
• Collect samples from a narrow depth range within a well with no movement of the sampler position during collection.
• Can sample low yield, short screen, and short water column wells.
• Requires one mobilization per sampling event to collect and replace bottles (after the initial deployment event where the well is equipped with the sampler).

Limitations

• Requires wells 2 inches or larger.
• Sample volume, especially in 2-inch wells, may limit analyte types or longer analyte lists.
• Trigger lines are custom built and samplers are typically dedicated to each well.
• Sample preservation (if required) requires handling preservatives in the field.
• Pneumatic triggers require a 12v air pump and electric triggers require battery pack or plug-in power.

Demonstration Sites

Demonstration/Validation of the Snap Sampler: Cost and Performance Final Report
Parker, L., N. Mulherin, G. Gooch, T. Hall, C. Scott, J. Clausen, W. Major, R. Willey, T. Imbrigiotta, J. Gibs, and D. Gronstal.
ERDC/CRREL TR-11-11, ESTCP Project ER-0630, 65 pp, 2011

Demonstration/Validation of the Snap Sampler Passive Groundwater Sampling Device at the Former McClellan Air Force Base. Final Report (Version 2)
Parker, L., N. Mulherin, T. Hall, C. Scott, K. Gagnon, J. Clausen, W. Major, R. Willey, J. Gibs, T. Imbrigiotta, and D. Gronstal.
ERDC/CRREL TR-11-3, ESTCP Project ER-0630, 131 pp, 2011

Demonstration/Validation of the Snap Sampler Passive Ground Water Sampling Device for Sampling Inorganic Analytes at the Former Pease Air Force Base
Parker, Louise, Nathan Mulherin, Gordon Gooch, William Major, Richard Willey, Thomas Imbrigiotta, Jacob Gibs, and Donald Gronstal
U.S. Army Engineer Research and Development Center (ERDC), Cold Regions Research and Engineering Laboratory (CRREL), Hanover, NH, ERDC/CRREL TR 09-12, 115 pp, 2009

Results Report for the Demonstration of No-Purge Groundwater Sampling Devices at Former McClellan Air Force Base, California
Parsons, 79 pp, 2005

Additional Resources

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