ASTM D6001/D6001M-20

5.1 Direct-push groundwater sampling and profiling are economical methods for obtaining discrete interval groundwater quality samples in many soils and unconsolidated formations without the expense of permanent monitoring well installation 5.2 Targeting Aquifer Sample Test Zones for Accurate Sampling—As with any investigation it is important to phase the investigation such that target intervals for groundwater sampling are accurately located. For sites that allow surface push of the sampling device, discrete water sampling is often performed in conjunction with the cone penetration test (Test Method D6067/D6067M) (4-6, 13, 14) or continuous soil sampling (Guide D6282/D6282M) which is often used for stratigraphic mapping of aquifers and to delineate high-permeability zones for sampling. Alternately, resistivity logging, or injection logging (Practice D8037/D8037M) may be used to assess formation permeability and lithology prior to the groundwater sampling or profiling activities to guide selection of sampling intervals 5.2.1 When volatile organic contaminants (VOC) such as trichloroethylene (TCE) or benzene are present in the subsurface, logging with the membrane interface probe (MIP) (Practice D7352) may be performed prior to groundwater sampling. MIP logs identify where significant concentrations of many VOCs are present and may be used to guide selection of groundwater sampling locations, depths and intervals 5.3 Slug tests can be performed with several of the DP groundwater samplers (D7242/D7242M) to determine hydraulic conductivity over discrete intervals. Development of the screened interval should be conducted to assure that formation flow into and out of the device is representative of natural formation conditions. Development with a simple inertial pump to surge and purge the formation is often adequate. Other methods for development (D5521/D5521M) may be advised depending on field conditions and data quality objectives.

5.4 Water sampling chambers may be sealed to maintain in situ pressures and to allow for pressure measurements and permeability testing (Practice D7242/D7242M) (6, 13, 19). Sealing of samples under pressure may reduce the possible volatilization of some organic compounds. Field comparisons may be used to evaluate any systematic errors in sampling equipments and methods. Comparison studies may include the need for pressurizing samples, or the use of vacuum to extract fluids more rapidly from low hydraulic conductivity soils (8.2.3.1(2)).

5.5 DP groundwater profiling tools 5.6 Degradation of water samples during handling and transport can be reduced if discrete water sampling events with sealed screen samplers are combined with real time field analysis of potential contaminants. In limited studies, researchers have found that the combination of discrete sealed screen sampling with onsite field analytical testing provide accurate data of aquifer water quality conditions at the time of testing 5.7 In difficult driving conditions, penetrating to the desired depth to make sure of sealing of the sampler screen may not be possible. If the screen cannot be inserted into the formation with an adequate seal, the water-sampling event would require sealing in accordance with Practice D5092/D5092M to isolate the aquifer. Selection of the appropriate equipment and methods to reach required depth at the site of concern should be made in consultation with experienced operators or manufacturers. If there is no information as to the subsurface conditions, initial explorations consisting of penetration-resistance tests, such as Test Method D6067/D6067M, resistivity profiling, or DP logging with the injection logging system (Practice D8037/D8037M) to perform trials can be performed to select the appropriate testing system.

5.8 Combining multiple-sampling events in a single-sample chamber (profiling) without decontamination (Practice D5088) is generally discouraged. In this application, purging of the screen or sampling chamber should be performed to make sure of isolation of the sampling event. Purging should be performed by removing several volumes of fluid until new chemical properties have been stabilized or elements are flushed with fluid of known chemistry. Purging requirements may depend upon the materials used in the sampler and the sampler design (Guide D6634/D6634M). Rinsate samples may be collected and analyzed to assess concerns with carryover of contaminants from overlying zones that are heavily contaminated. Monitoring water quality parameters (pH, specific conductance, dissolved oxygen, oxidation-reduction potential, etc.) to stability is often used to document when representative water is being purged from a sampling interval (Practice D6771).

5.9 Bottom-up profiling by driving a DP groundwater sampler to the base of the formation and retracting incrementally, while the screen is exposed, for sampling at decreasing depths should be avoided as this may lead to cross contamination and inaccurate contaminant distribution information. Slug tests should not be performed by bottom-up profiling as there is poor or no control on the length of formation being tested under these conditions.

5.10 Screens designed and deployed in dual tube use are generally designed for use inside the dual tubing and overdriving the screen past the casing can damage the sampler screen and subsequent exposed screen samples would be subject to cross contamination. Use equipment according to manufactures instructions.

1.1 This guide covers a review of methods for sampling groundwater at discrete points or in increments by insertion of groundwater sampling devices using Direct Push Methods (D6286/D6286M, see 3.3.2). By directly pushing the sampler, the soil is displaced and helps to form an annular seal above the sampling zone. Direct-push water sampling can be one time, or multiple sampling events. Knowledge of site specific geology and hydrogeologic conditions is necessary to successfully obtain groundwater samples with these devices.

1.2 Direct-push methods of water sampling are used for groundwater quality and geohydrologic studies. Water quality and permeability may vary at different depths below the surface depending on geohydrologic conditions. Incremental sampling or sampling at discrete depths is used to determine the distribution of contaminants and to more completely characterize geohydrologic environments. These explorations are frequently advised in characterization of hazardous and toxic waste sites and for geohydrologic studies.

1.3 This guide covers several types of groundwater samplers; sealed screen samplers, profiling samplers, dual tube sampling systems, and simple exposed screen samplers. In general, sealed screen samplers driven to discrete depth provide the highest quality water samples. Profiling samplers using an exposed screen(s) which are purged between sampling events allow for more rapid sample collection at multiple depths. Simple exposed screen samplers driven to a test zone with no purging prior to sampling may result in more questionable water quality if exposed to upper contaminated zones, and in that case, would be considered screening devices.

1.4 Methods for obtaining groundwater samples for water quality analysis and detection of contaminants are presented. These methods include use of related standards such as; selection of purging and sampling devices (Guide D6452 and D6634/D6634M), sampling methods (Guide D4448 and D6771) and sampling preparation and handling (Guides D5903, D6089, D6517, D6564/D6564M, and D6911).

1.5 When appropriately installed and developed many of these devices may be used to perform pneumatic slug testing (Practice D7242/D7242M) to quantitatively evaluate formation hydraulic conductivity over discrete intervals of unconsolidated formations. These slug tests provide reliable determinations of hydraulic conductivity and can be performed after water quality sampling is completed.

1.6 Direct-push water sampling is limited to unconsolidated formations that can be penetrated with available equipment. In strong soils damage may result during insertion of the sampler from rod bending or assembly buckling. Penetration may be limited, or damage to samplers or rods can occur in certain ground conditions, some of which are discussed in 5.7. Drilling equipment such as sonic drilling (Practice D6914/D6914M) or rotary drilling (Guide D6286/D6286M) can be used to advance holes past formations difficult to penetrate using typical Direct Push equipment. Some soil formations do not yield water in a timely fashion for direct-push sampling. In the case of unyielding formations, direct-push soil sampling can be performed (Guide D6282/D6282M).

1.7 Direct push water sampling with one-time sealed screen samplers can also be performed using cone penetrometer equipment (Guide D6067/D6067M).

1.8 This guide does not address installation of permanent water sampling systems such as those presented in Practice D5092/D5092M. Direct-push monitoring wells for long term monitoring are addressed in Guide D6724/D6724M and Practice D6725/D6725M.

1.9 Units—The values stated in either SI units or inch-pound units [presented in brackets] 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 nonconformance with the standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard.

1.10 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this standard.

1.11 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.

1.12 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide 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 of this document means only that the document has been approved through the ASTM consensus process.

1.13 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.