Passive diffusion bags PDB's

Passive diffusion samplers are used to collect water samples from groundwater aquifers for analysis of specific chemical compounds. The samplers are hung from a cable and placed in monitoring wells at the well screen for periods of at least 14 days, or until equilibrium has taken place between the water in the sampler and surrounding groundwater. They operate by diffusion of contaminants across a polyethylene membrane. No purging or disposal of purge water is necessary, which can dramatically reduce field sampling costs. The passive diffusion samplers act as a filter, so field filtering is not necessary. In fact, passive diffusion bags (PDBs) will block potassium permanganate from samples for sites using it in their remediation processes.

Benefits of Using PDBs:

• Samples volatile organics
• Available in both pre-filled and unfilled versions
• Simple to deploy
• Eliminates the collection and disposal of purged water
• Significantly reduces the cost of sampling
• Ideal for groundwater sampling

Features of PDBs

Pre-filled with laboratory certified analyte-free water. No filling necessary. Our PDBs are pre-filled with polished RO/DI water. Each lot number is tested by low-level EPA Method 8260B, down to 1.0 ppb, to insure the product is contaminant free. A quality assurance certificate is available with each delivery.

Rugged sampler. Our PDBs are made of medical grade, high-strength, low-density polyethylene. Patented tubes have special heat sealed seams that resist abrasion and unique tabs that allow both quick attachment to hanging assemblies and ease in pouring upon retrieval.

Data is valid as volume purge. Over 100,000 of our PDBs have been installed at hundreds of sites in the last 10 years for the collection of volatile organics. Data is considered by most regulators as valid as that obtained from conventional purge sampling.

Simplicity in design and use. Simplicity in design extends to its utility and cost effectiveness in the field. No additional parts are required. Storage space is minimal, handling is easy, deployments and retrievals are fast and pouring into vials is sure and simple.

Stainless steel hanging option. Ready to use, non-corrosive stainless steel hanging assemblies are available. Hardware will be placed at the exact measurements of the well screen so all you need to do is clip the PDBs on and deploy. No stretching, corroding or breaking.

How PDB Samplers Work

PDB samplers are made of low density polyethylene (LDPE), which acts as a semi-permeable membrane. VOCs, excluding certain ketones, ethers and alcohols, diffuse readily through the membrane. An equilibrium is established between the VOCs in the bag and those in the groundwater. The PDB Sampler is filled with analyte-free water and is in the shape of a long cylindrical tube. Upon retrieval, usually 14 days after deployment, bags are opened to fill vials and returned to the laboratory for analysis.

PDB Manufacturing

ALS has been granted a license to manufacture, use and provide the bags by the US Geological Survey (USGS) and The General Electric Company (GE), both co-patent holders on the product (US #5,804,743). The downhole passive water sampler and method of sampling was invented by Don Vroblesky (USGS) and Thomas Hyde (GE).

ALS is a leader in passive diffusion sampler (PDS) technology and has been since March 2000 when it began manufacturing and distributing samplers for Volatile Organic Compounds (VOCs). Wide acceptance of these samplers has spurred ALS to partner with USGS to develop passive diffusion samplers for common LTM inorganic parameters. Both laboratory and field demonstration studies are currently underway to determine feasibility of nylon-screen (NS) and rigid porous polyethylene (RPP).

Available Options

The standard size PDB Sampler is 24" long and 1 ¼" in diameter. It is manufactured from 4 mil-thick, 2" wide, "lay flat", low-density polyethylene. All seams and connections are made by heat-seals only. A standard 24" long pre-filled PDB Sampler holds approximately 220 mL of ASTM Type II certified, laboratory-grade, analyte-free, deionized water. After retrieval, simply cut the top and pour water into 40 mL vials.

Different sizes are available with advance notice. If there is a chance of abrasion or tearing due to the well’s physical condition, we recommend the use of a protective polyethylene mesh cover.

The unfilled PDB sampler must be filled with water prior to deployment; it holds approximately 350 mL. It is fitted at one end with a threaded screw cap for filling and a snap-on spout for pouring water into vials. When ready to sample, just open the snap top and pour.