ENV-11-28 Polyethylene Diffusion Bag - Groundwater Sampling Without Purging

Description:

Polyethylene Diffusion Bag (PDB) samplers offer a new option to collecting groundwater samples with less expense and reduced wastes. PDB samplers are low-density polyethylene bags containing deionized water which are used to interface and collect volatile organic (VOC) water samples from groundwater wells by diffusion instead of mechanical removal. The PDB is placed below the groundwater level within a well screen at a specific depth and left in-place under natural flow conditions. After sufficient residence-time, which is dependent on the analytical constituent(s), the PDBs are removed and contents discharged directly into the analysis vials for standard VOC analysis. Although this technology was first developed in the late 1990s, following field trials and extensive use by the US Air Force and on USEPA superfund sites, it has recently received wide acceptance within the regulatory world especially by the USEPA and the Texas Commission on Environmental Quality (TCEQ). Advantages that have been found over the more traditional purge and sample methods include: The ability to isolate specific flow-zones within the aquifer to determine actual contaminate flow due to the procedures non-transport methodology; A greater accuracy in determining the concentrations of VOCs in the groundwater as compared to the purge and sample “snap-shot”; and Significant cost savings since the procedure eliminates the need for labor-intensive purging, purge-water management and disposal. This paper will explain the advantages and disadvantages of utilizing the PDB method as well as discuss an example facility demonstration to show equivalency with other sampling methods for the purpose of regulatory selection.