Frequently Asked Questions on the HydraSleeve No-Purge Groundwater Sampler
HydraSleeve - The Original Low-Purge Sampler
The HydraSleeve No-Purge Sampler by GeoInsight is a cost-effective, energy-efficient, faster and simpler method for collecting groundwater samples. It has a three-step operation technique that makes it more effective than bailers, passive diffusion bags,portable or dedicated pumps.
HydraSleeves are a no-purge grab sampling device that captures the “core” of water from any discrete interval in the screened portion of the well with no change in water level and minimal disturbance to the water column. It only collects a sample from the screen, as it excludes water from any other parts of the well due to its self-sealing check valve at the top of the sampler.
Step 1: Placing the HydraSleeve Sampler– To collect a representative groundwater sample without purging, the HydraSleeve is lowered into place and positioned in the well screen. Water pressure will keep the bag collapsed and check the valve closed, preventing water from entering the sampler. The well is then allowed to return to equilibrium.
Step 2: Sample Collection – To collect a sample, the HydraSleeve must be pulled upward at a rate of one foot per second or faster for the water to flow through the check valve into the sample sleeve. For most applications, the HydraSleeve will fill the length of the sampler. There is no change in the well water level and minimum sample agitation during the collection process.
Step 3: Sample Retrieval – Once the sample sleeve is full and the check valve is closed the sampler can be recovered without entry of extraneous over-lying fluids. The sample can then be discharged into a desired container and sent to the lab for analysis.
No-purge sampling includes any method where no water is removed (i.e., purged) from the well prior to sample collection. The traditional purge method of sampling monitoring wells required 3 to 5 times the volume of standing water in the well screen to be removed and casing the surrounding filter pack prior to collecting a sample of analysis. This is done as it assumes the fluid collected comes from the formation and doesn’t contain stagnant water from the non-perforated portion of the well. The use of traditional sampling devices such as bailers or various pumping systems makes sample collection time-consuming (usually 1 to 2 hours per well) and costly. If the well was contaminated, the water will be required to be containerised and disposed of in an environmentally acceptable manner. Disposal of groundwater that qualifies as a hazardous material can be expensive to dispose of. When multiple wells are sampled, the costs quickly mount. Obviously, the less water that must be removed prior to collecting a sample the better.
No-purge sampling devices such as the HydraSleeve collects water samples under undisturbed natural flow conditions. With the HydraSleeve, there is no drawdown and minimal displacement of the water column as it collects a water samples from only the user-defined interval (typically within the well-screen) without mixing fluids from other intervals. One or more HydraSleeves are placed within the screened interval of the monitoring well and a period of time is allocated for the well to re-equilibrate. To collect a sample, the HydraSleeve is pulled up in a rapid upward motion for the check valve to open. When the sampler is full, the check valve collapses preventing the mixing of non-representative fluid during recovery.
The HydraSleeve no-purge groundwater sampler is for all contaminants. It collects representative samples of groundwater for volatile organic compounds (VOCs), semi-volatile organic compounds (SVOC’s), common metals, trace metals, dissolved gases, total dissolved solids, pesticides, Polychlorinated Biphenyl (PCBs) and more. This proven methodology is suitable for both short- and long-term groundwater sampling programs. It is useful in narrow, constricted, or damaged wells and is also effective for sampling slow recharge wells, monitoring interfaces, and concentration profiling. HydraSleeve samplers can be filtered using Waterra Groundwater Filters.
No purge sampling devices are restricted to collecting the volume of fluid contained within the well screen. For eg: a 2-inch well with a 10-foot-long saturated screen has an absolute maximum of 6.4 litres (1.6 gallons) of water available for no-purge sampling. The HydraSleeve holds a minimum of 600ml -1 litre of sample volume using the standard HS-2 or HS-2-1L HydraSleeve.
To address this issue GeoInsight developed a sampler that will collect the most water available from a 2-inch (5cms) well. The HydraSleeve Super Skinny Sleeve can collect almost double the amount of water from a 2-inch (5cms) well as compared to earlier designs of the HydraSleeve. The Turbo Sleeve can be used to collect sample volume of water up to 4 litres from a 10-foot screen (3 meters)
It all depends on the amount of water displaced when placing the HydraSleeve. Restabilisation depends on the infiltration time of the soil and the geomorphology at the time the sample is collected in the well. Using a HydraSleeve SpeedBag eliminates the need for well equilibration at all. Traditional HydraSleeves and SuperSleeves however will still require well equilibration.
Studies have shown that any sampling device made of plastic is required to equilibrate with the fluid being sampled for a period of time. According to GeoInsight, the suggested time is a 2-week period as it provides a margin of safety, and it is the amount of time needed for all the contaminants to equilibrate in the sample bag.
The primary difference between the Passive Diffusion Bags (PDB) and HydraSleeves (HS) is how the sample enters the device. PDB samplers rely on the diffusion of specific volatile organic contaminants (VOC) across a membrane, usually polyethylene, which is fabricated into a long, thin bag and filled with deionised water. Over a period of time, VOC concentrations adjacent to the PDB will pass through the membrane and equilibrate with the water in the bag.
In contrast, the HydraSleeve physically collects a core of water from within the well screen, with minimal displacement and disturbance of the water column. Once full, the sample is sealed within the sleeve and isolated from overlying, extraneous fluids. These very different collection methods result in a few considerations about the use of the two samplers.
Use of the PDB is limited to contaminants that will diffuse across the selected membrane; the water sample collected by the HydraSleeve can be analysed for all contaminants.
PDB samplers require varying time periods for different contaminants to equilibrate across the membrane. The resulting sample is a time-integrated average. When activated, HydraSleeve provides an instantaneous sample of contaminant concentrations in the well.
Both devices sample from a discrete interval. Normally, the length of the PDB sampler defines its sample interval. By using different activation methods, a single HydraSleeve can be used to collect samples from a range of intervals (from a few feet to over 8 feet), depending on sampling objectives.
Because the HydraSleeve goes into the well empty and flat, it displaces much less water than the PDB, resulting in less disturbance and much faster equilibration of the water column in the well.
There are four varieties of HydraSleeve low-flow samplers available. These are:
Standard HydraSleeves
Universal Super/SkinnySleeves
SpeedBags
W3 HybridSleeve
To determine which sampler is required for your water monitoring needs, here are some factors to consider:
Required sample volume – How much sample volume does the lab require
Well diameter – The larger the internal diameter of the screen the greater the available sample volume
Length of the water column in the well screen - a 40-foot deep (12 meters) well with a 10-foot (3 meters) well screen and a 20-foot (6 meters) column of water in the well means the 10-foot screen defines the amount of water available for sample collection. If the same well has 5 feet of water in the screen, this means there is only 5 feet (1.5 meters) of available fluid for no-purge sampling.
HyraSleeves samplers are designed for single-use (disposable) purpose and not intended for reuse, so there are no decontamination requirements for the sampler itself.
HydraSleeve is the original low-purge sampler. Its simple design allows the total assembly, deployment, collection and discharge conducted in a lesser period of time. To learn more about this revolutionary product used for groundwater sampling, please contact your local Air-Met Scientific representative.
