ASTM D7929-20

4.1 General—Passive groundwater sampling has increased use since the polyethylene diffusion bag sampler was first introduced (4.1.1 Because of the large number of passive samplers that have been developed over the years for various types of environmental sampling, it is beyond the scope of this standard to discuss separately each of the methods that could or can be used to sample groundwater. Extensive literature reviews on diffusion- and accumulation-passive samplers can be found in the scientific literature (that is, 4.2 Use—Passive samplers are deployed at a pre-determined depth, or depths, within a well for a minimum or pre-determined period of time. They should remain submerged at the target depth for their entire deployment period. All of the passive technologies described in this document rely on the sampling device being exposed to the groundwater during deployment and the continuous flushing of the open or screened interval of the well by ambient groundwater flow ((4.2.1 As with all types of groundwater sampling methods, the appropriate use of passive methods assumes that the well has been properly located (laterally and vertically), designed, constructed, and was adequately developed (as described in Guide D5521/D5521M) and maintained (as described in Practices D5092/D5092M and D6725/D6725M, or Guide D6724/D6724M). These measures are necessary so that the well is in hydraulic communication with the aquifer.

4.2.2 Each type of passive sampler has its own attributes and limitations, and thus data-quality objectives (DQOs) for the site should be reviewed prior to selecting a device. For wells in low-permeability formations, diffusive flux may become more important than advective flow in maintaining aquifer-quality water in the well.

4.3 Advantages—While passive methods are not expected to replace conventional pumped sampling in all situations, they often offer a faster alternative “tool” for sampling groundwater monitoring wells because purging is eliminated from the pre-sampling procedure. Other advantages include that these samplers can be used in most wells and typically have no depth limitation. These samplers are either disposable or dedicated to a well. This eliminates or reduces the need for decontamination. Passive samplers typically reduce the logistics associated with sampling and are especially useful at sites where it is difficult to bring larger equipment (such as pumps and compressors) to the well location.

1.1 This standard provides guidance and information on passive sampling techniques for collecting groundwater from monitoring wells. Passive groundwater samplers are able to acquire a sample from the screen interval in a well, without the active transport associated with a pump or purge technique (1.2 Methods for sampling monitoring wells include low-flow purging and sampling methods, traditional well-volume purging and sampling methods, post-purge grab sampling methods (for example, using a bailer), passive no-purge sampling methods, and active no-purge sampling methods such as using a bailer to collect a sample without purging the well. This guide focuses on passive no-purge sampling methodologies for collecting groundwater samples. These methodologies include the use of diffusion samplers, accumulation samplers, and passive-grab samplers. This guide provides information on the use, advantages, disadvantages, and limitations of each of these passive sampling technologies.

1.3 ASTM Standard D653 provides standard terminology relevant to soil, rock, and fluids contained in them. ASTM Standard D4448 provides a standard guide to sampling groundwater wells, and ASTM Standards D5903 and D6089 provide guides for planning and documenting a sampling event. Groundwater samples may require preservation (Guide D6517), filtration (Guide D6564/D6564M), and measures to pack and ship samples (Guide D6911). Standard D7069 provides guidance on the quality control and quality assurance of sampling events. ASTM Standard D5092/D5092M provides standard practice for the design and installation of groundwater monitoring wells, ASTM Standard D5521/D5521M provides a standard guide for developing groundwater monitoring wells in granular aquifers, and D6452 provides a standard guide for purging methods used in groundwater quality investigations. Consult ASTM Standard D6724/D6724M for a guide on the installation of direct-push groundwater monitoring wells and ASTM Standard D6725/D6725M for a guide on the installation of direct-push groundwater monitoring wells with pre-pack screens.

1.4 The values stated in SI Units are to be regarded as the standard. Values in inches (such as with well diameters) are given in parentheses, and are provided for information. Use of units other than SI shall not be regarded as nonconforming with this standard.

1.5 This guide provides information on passive groundwater sampling in general and also provides a series of considerations when selecting a passive groundwater sampling method. However, it does not recommend a specific course of action, and not all aspects of this guide may be applicable in all field situations. This document cannot replace education or experience and should be used in conjunction with professional judgment. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word “standard” in the title of this document means only that the document has been approved through the ASTM consensus process.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.