ASTM D7242/D7242M-26

5.1 Combining slug test methods with the use of direct push installed groundwater sampling devices provides a time and cost-effective method that was previously not available for evaluating spatial variations of hydraulic conductivity (K) in unconsolidated aquifers. Current research (Ref (4)) has found that small (decimeter/inch) scale variations in hydraulic conductivity may have significant influence on solute transport and therefore design of groundwater remediation systems. Other investigators (Ref (5)) report that spatial variation in K is believed to be the main source of uncertainty in the prediction of contaminant transport in aquifers. They found that increasing the data density for K in model input noticeably reduced the uncertainty of model prediction. Because of increased efficiency and reduced costs, the combination of slug test methods with DP groundwater sampling devices makes it possible to obtain the decimeter scale information required to reduce uncertainty in contaminant transport models and improve remedial action design (Butler and Dietrich 2004 (6), Dietrich et al. 2008 (7), Kober et al. 2009 (8), Quinnan et al. 2010 (9), Liu et al. 2011 (10), Dietz and Dietrich 2012 (11), Suthersan et al. 2015 (12)).

5.2 The data obtained from application of this practice may be modeled with the appropriate analytical method to provide information on the transmissivity and hydraulic conductivity of the screened formation in a timely and cost effective manner.

5.3 The appropriate analytical method selected for analysis of the data will depend on several factors, including, but not limited to, the aquifer type (confined, unconfined, leaky) well construction parameters (partially or fully penetrating), and the type of aquifer response observed during the slug test (overdamped or underdamped). Some of the appropriate methods may include Test Methods D4104/D4104M, D5785/D5785M, D5881, and D5912. A thorough review of many slug test models and analytical methods is provided in Ref (1).

5.4 Pneumatic slug tests may be conducted in conventional 2-in. and 4-in. diameter monitoring wells (Practice D5092/D5092M, (1, 2)) and even larger diameter wells that are screened below the water table. However, the long screens of many of these wells results in an averaging of K, often across several zones with large changes in K. The long screen wells make it difficult to observe the vertical changes in K that often influence or control contaminant migration (Suthersan et al. 2015 (12))

5.5 Slug tests may be conducted in materials of lower hydraulic conductivity than are suitable for pumping tests. Slug tests may be used to obtain estimates of K for aquitards consisting primarily of silts and clays. Special field procedures may be required using shorter screen intervals, smaller casing radius and alternate development methods (1). As lower permeability zones of a formation may behave as barriers to contaminant migration or conversely, as storage zones for back diffusion of contaminants, knowledge of their hydraulic conductivity can be important (Suthersan et al. 2015 (12), Sale et al. 2014 (13)).

5.6 The pneumatic slug test provides some advantages when compared to pumping tests or slug tests conducted by other methods.

5.6.1 Some of the advantages relative to pumping tests include:

5.6.1.1 No water added to or removed from the well. An important consideration when water quality must not be altered for purposes of environmental sampling.

5.6.1.2 Large volumes of water not removed from the well as during a pumping test. An important consideration if the groundwater is contaminated and will require disposal as a regulated waste.

5.6.1.3 Slug tests usually require only a fraction of the time needed to complete a pump test.

5.6.1.4 No large diameter pumping well or down well pump required.

5.6.1.5 Slug tests provide information on K for the formation in the vicinity of the well.

5.6.2 Some advantages relative to slug tests using water or a mechanical slug include:

5.6.2.1 No water added to or removed from the well or DP sampler to conduct the test. Generally, does not change water quality for sampling. Use of vacuum to induce a falling head test could result in loss of volatiles from water in the well column. Additional purging may be required before sampling for volatile contaminants.

Note 1: When a groundwater quality sampling event is to be performed after pressurization for pneumatic slug testing, an inert gas (for example, nitrogen) is recommended to be used to pressurize the well head. Use of an inert gas minimizes alteration of the natural redox and ORP conditions of the formation, groundwater and any redox sensitive species present.

5.6.2.2 Pneumatic initiation of the slug test provides clean, high quality data with minimal noise, especially important in high hydraulic conductivity formations and small diameter wells.

5.6.2.3 In small diameter DP tools, inserting a mechanical slug or adding water may be difficult or even preclude accurate measurement of changing water levels.

5.6.3 Some disadvantages of slug tests as compared to pumping tests include:

5.6.3.1 Slug tests provide information on K for the formation only in the vicinity of the well, not a large-scale average value as obtained from a pumping test.

5.6.3.2 Most slug test analytical methods can provide information only on aquifer transmissivity and hydraulic conductivity. Pumping test analysis can provide additional information on aquifer parameters such as specific storage, etc.

5.6.4 Some disadvantages of the pneumatic slug test relative to slug tests using water or a mechanical slug include:

5.6.4.1 Airtight seals needed on the well casing or drive rods.

5.6.4.2 The screen must remain below the water level throughout the slug test. Wells screened across the water table cannot be slug tested with the pneumatic method.

5.6.4.3 Pressure transducers and electronic acquisition methods usually required for pneumatic slug testing. Not always needed for manual methods.

5.6.4.4 Equilibration of water level after pressure (or vacuum) applied to the wellhead increases time required to complete the slug test, especially important in low-K formations.

5.7 Direct push methods provide some advantages as compared to conventional drilling methods for the installation of wells and temporary groundwater monitoring devices to be used for slug testing. Some of the advantages include:

5.7.1 DP methods minimize generation of soil cuttings reducing waste handling and disposal costs at contaminated sites during the installation of permanent wells (Guide D6724/D6724M, Practice D6725/D6725M) and temporary groundwater sampling devices (Guide D6001/D6001M).

5.7.2 Several types of temporary groundwater sampling devices may be installed by DP methods (Guide D6001/D6001M). These tools may be installed at various depths and various locations for slug testing and groundwater sampling in unconsolidated materials. Most of these tools are extracted for decontamination and multiple re-use, and can minimize the need for permanent well installations.

5.7.3 Short screens may be used to slug test discrete depth intervals to document vertical and lateral variations of K within an aquifer in a cost and time effective manner.

5.7.4 Equipment required to install DP wells and temporary groundwater samplers are often smaller and more mobile than conventional rotary drilling equipment. This can make site access easier and more rapid.

5.7.5 Direct push logging methods (Practices D6067/D6067M, D7352 and D8037/D8037M; McCall et al. 2014 (14)) including electrical conductivity (Geoprobe 1994 (15), Schulmeister et al. 2003 (16), Sellwood et al. 2005 (17), Wilson et al. 2005 (18), McCall et al. 2017 (19)) and soil sampling Guide D6282/D6282M can be used to identify locations and depth intervals for slug testing.

5.7.6 Direct push tests are minimally intrusive.

5.7.7 Direct push tests are generally more rapid and less expensive than other drilling methods.

5.8 Some disadvantages of DP methods as compared to conventional rotary drilling include:

5.8.1 DP methods generally provide a smaller diameter bore hole than traditional rotary drilling. This may limit the size of equipment than can be placed down hole.

5.8.2 Direct push tools are designed to penetrate unconsolidated materials (soils) only. Other rotary drilling methods will be required to penetrate consolidated rock.

5.8.3 Some subsurface conditions may limit the depth of penetration of DP methods and tools. Some examples include thick caliche layers, cobbles or boulders, or very dense materials, such as high-density glacial tills.

Note 2: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors.Practice D3740 was developed for agencies engaged in the testing or inspection of soils and rock, or both. As such, it is not totally applicable to agencies performing this practice. However, users of this practice should recognize that the framework of Practice D3740 is appropriate for evaluating the quality of an agency performing this practice. Currently there is no known qualifying national authority that inspects agencies that perform this practice.

1.1 This standard practice covers the field methods used to conduct an instantaneous change in head (slug) test when pneumatic pressure is used to initiate the change in head pressure within the well or piezometer. This practice focuses on direct push water sampling systems that are designed for pneumatic slug tests at multiple targeted depth intervals and locations. These procedures may be applied to wells or piezometers installed with rotary drilling methods when appropriate.

1.2 This standard practice is used to obtain the required field data for determining hydraulic properties of an aquifer or a specified vertical interval of an aquifer. Field data obtained from application of this practice are modeled with appropriate analytical procedures (Test Methods D4104/D4104M, D5785/D5785M, D5881, and D5912, Ref (1)).

1.3 Target intervals for testing can be identified by performing continuous profile soil samples (Guide D6282/D6282M), or other methods such as CPT (Practice D6067/D6067M), electrical conductivity logging, or HPT logging Practice D8037/D8037M (see 5.7.5).

1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

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 practice offers a set of instructions for performing one or more specific operations. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be applicable in all circumstances. 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 means that the document has been approved through the ASTM consensus process.

1.8 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.