ASTM D6724/D6724M-16

Standard Guide for Installation of Direct Push Groundwater Monitoring Wells

SIGNIFICANCE AND USE
5.1 The direct push ground method is a rapid and economical procedure for installing groundwater monitoring wells to obtain representative groundwater samples and location-specific hydrogeologic measurements. Direct push installations may offer an advantage over conventional rotary drilled monitoring wells (Practice D5092) for groundwater explorations in unconsolidated formations because they reduce disturbance to the formation, and eliminate or minimize drill cuttings. At facilities where contaminated soils are present, this can reduce hazard exposure for operators, local personnel, and the environment, and can reduce investigative derived wastes. Additionally, smaller equipment can be used for installation, providing better access to constricted locations.  
5.2 Direct push monitoring wells are typically smaller in diameter than drilled wells, thereby reducing purge water volumes, sampling time, and investigative derived wastes. Practice D5092 monitoring wells are used when larger diameters and/or sample volumes are required, or at depths or in geologic formations to where it is difficult to install direct push wells. Direct push monitoring wells should be viable for monitoring for many years.  
5.3 Prior to construction and installation of a direct push well or any other type of groundwater well the reader should consult appropriate local agencies regarding regulatory requirements for well construction. A regulatory variance may be required for installation of direct push monitoring wells.  
5.4 To date, published comparison studies between drilled monitoring wells and direct push monitoring wells have shown comparability (1-10)4. However, selection of direct push monitoring wells over conventional rotary drilled wells should be based on several criteria, such as site accessibility and penetrability, stratigraphic structure, depth to groundwater, and aquifer transmissivity.  
5.5 Typical penetration depths for installation of groundwater monitoring wells with...
SCOPE
1.1 This guide describes various direct push groundwater monitoring wells and provides guidance on their selection and installation for obtaining representative groundwater samples and monitoring water table elevations. Direct push wells are used extensively for monitoring groundwater quality in unconsolidated formations. This guide also includes discussion of some groundwater sampling devices which can be permanently emplaced as monitoring wells.  
1.2 This guide does not address the single event sampling of groundwater using direct push water samplers as presented in Guide D6001. The methods in this guide are often used with other tests such as direct push soil sampling (Guide D6282) and the cone penetrometer test (Guide D6067). The guide does not address the installation of monitoring wells by rotary drilling or sonic drilling methods such as those presented in Practice D5092. Techniques for obtaining groundwater samples from monitoring wells are covered in Guides D4448, D7929, and Practice D6771. Practice D6725 addresses direct push wells using pre-packed screens.  
1.3 The installation of direct push groundwater monitoring wells is limited to unconsolidated soils and sediments including clays, silts, sands, and some gravels and cobbles. Penetration may be limited, or damage may occur to equipment, in certain subsurface conditions; some of which are discussed in 5.5. Information in this guide is limited to groundwater monitoring in the saturated zone.  
1.4 The values stated in either inch-pound units or SI 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 non-conformance with the standard.  
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Pra...

General Information

• Status: Published
• Publication Date: 30-Jun-2016
• ICS: 13.060.10 - Water of natural resources
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.21 - Groundwater and Vadose Zone Investigations

Relations

• Replaces: ASTM D6724-04(2010) - Standard Guide for Installation of Direct Push Groundwater Monitoring Wells
• Effective Date: 01-Jul-2016
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D6452-18(2023) - Standard Guide for Purging Methods for Wells Used for Ground Water Quality Investigations
• Effective Date: 01-Nov-2023
• Refers: ASTM D5088-20 - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-May-2020
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D6286-19 - Standard Guide for Selection of Drilling and Direct Push Methods for Geotechnical and Environmental Subsurface Site Characterization
• Effective Date: 01-Oct-2019
• Refers: ASTM D4448-01(2019) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Feb-2019
• Refers: ASTM D6452-18 - Standard Guide for Purging Methods for Wells Used for Ground Water Quality Investigations
• Effective Date: 01-Dec-2018
• Refers: ASTM D7352-18 - Standard Practice for Volatile Contaminant Logging Using a Membrane Interface Probe (MIP) in Unconsolidated Formations with Direct Push Methods
• Effective Date: 15-Jul-2018
• Refers: ASTM D5088-15a - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-Aug-2015
• Refers: ASTM D5088-15 - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 15-Jan-2015
• Refers: ASTM D7929-14 - Standard Guide for Selection of Passive Techniques for Sampling Groundwater Monitoring Wells
• Effective Date: 15-Aug-2014
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D4448-01(2013) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Apr-2013
• Refers: ASTM D7352-07(2012) - Standard Practice for Direct Push Technology for Volatile Contaminant Logging with the Membrane Interface Probe (MIP)
• Effective Date: 15-Oct-2012

Overview

ASTM D6724/D6724M-16 provides comprehensive guidance on the installation of direct push groundwater monitoring wells. Issued by ASTM International, this standard outlines recommended procedures for selecting, installing, and maintaining monitoring wells using direct push technology in unconsolidated soils and sediments. Direct push methods offer a rapid and economical alternative to traditional rotary drilling, reducing environmental disturbance, waste generation, and operational hazards. This guide is especially valuable for environmental professionals conducting groundwater quality monitoring, remediation studies, and hydrogeologic investigations.

Key Topics

• Direct Push Methodology: The standard explains how direct push wells are installed by advancing drive rods or casings into the ground without the need for rotary drilling. This process is well-suited to unconsolidated formations such as clays, silts, sands, and some gravels.
• Advantages over Conventional Drilling: Direct push wells minimize disturbance to soil structure and reduce the production of drill cuttings, which is beneficial in environmentally sensitive or contaminated sites. Smaller equipment also provides access to locations inaccessible to larger drilling rigs.
• Well Selection and Design: Guidance is given on selecting suitable well diameters, screen and riser materials, and the need for sand packs or pre-packed screens. Consideration is given to site-specific conditions, regulatory requirements, and monitoring objectives.
• Installation Techniques: The guide categorizes field methods into exposed screen and protected screen techniques, detailing step-by-step procedures and best practices for each. It also covers essential components such as annular seals, grout placement, and completion steps.
• Limitations: The document clarifies that direct push wells are unsuitable for consolidated bedrock, heavily cemented materials, or formations with significant cobbles and boulders. Depth limitations and equipment constraints are addressed.

Applications

Monitoring wells installed via direct push technology, as described in ASTM D6724/D6724M-16, have a wide range of practical applications:

• Environmental Site Assessments: Rapid and minimally invasive groundwater sampling for contaminant detection, plume delineation, and remediation verification.
• Hydrogeologic Investigations: Measuring water table elevations and hydraulic gradients, particularly in unconsolidated sediments where quick deployment is essential.
• Ongoing Compliance Monitoring: Supporting long-term monitoring programs at brownfield redevelopment sites, landfills, industrial facilities, and other locations where groundwater quality must be routinely assessed.
• Sensitive or Restricted Sites: Direct push methods are advantageous where minimizing surface disruption, waste generation, or exposure to contaminated soils is critical, and where access is constrained by infrastructure or property boundaries.
• Supplement to Other Testing Methods: Direct push wells can complement soil sampling, cone penetrometer tests (CPT), and other site characterization tools.

Related Standards

When applying ASTM D6724/D6724M-16, several related ASTM standards may also be relevant:

• ASTM D5092: Guide for the design and installation of groundwater monitoring wells using conventional drilling.
• ASTM D6001: Guide for direct-push groundwater sampling for environmental site characterization.
• ASTM D6282: Guide for direct push soil sampling.
• ASTM D6067: Practice for electronic piezocone penetrometer tests.
• ASTM D6725: Practice for direct push installation of prepacked screen monitoring wells.
• ASTM D4448, D7929, D6771: Various guides and practices for sampling from groundwater monitoring wells.
• ASTM D6026: Practice for significant digits in geotechnical data.

For optimal results and regulatory compliance, it is recommended to review state and local requirements and integrate applicable standards specific to sample collection, well maintenance, and decommissioning.

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By adhering to ASTM D6724/D6724M-16, environmental professionals can ensure effective, safe, and representative installation of groundwater monitoring wells, facilitating high-quality data for water resource management and environmental protection.

Standards Content (Sample)

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.
Designation: D6724/D6724M − 16
Standard Guide for
Installation of Direct Push Groundwater Monitoring Wells
This standard is issued under the fixed designation D6724/D6724M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* 1.6 This guide offers an organized collection of information
oraseriesofoptionsanddoesnotrecommendaspecificcourse
1.1 This guide describes various direct push groundwater
of action. This document cannot replace education or experi-
monitoring wells and provides guidance on their selection and
ence and should be used in conjunction with professional
installation for obtaining representative groundwater samples
judgement. Not all aspects of this guide may be applicable in
and monitoring water table elevations. Direct push wells are
all circumstances. This ASTM standard is not intended to
used extensively for monitoring groundwater quality in uncon-
representorreplacethestandardofcarebywhichtheadequacy
solidated formations. This guide also includes discussion of
of a given professional service must be judged, nor should this
somegroundwatersamplingdeviceswhichcanbepermanently
document be applied without consideration of a project’s many
emplaced as monitoring wells.
unique aspects. The word “Standard” in the title of this
1.2 Thisguidedoesnotaddressthesingleeventsamplingof
document means only that the document has been approved
groundwater using direct push water samplers as presented in
through the ASTM consensus process.
Guide D6001. The methods in this guide are often used with
1.6.1 This guide does not purport to comprehensively ad-
other tests such as direct push soil sampling (Guide D6282)
dress all of the methods and issues associated with monitoring
and the cone penetrometer test (Guide D6067).The guide does
well installation. Users should seek input from qualified
not address the installation of monitoring wells by rotary
professionals for the selection of proper equipment and meth-
drilling or sonic drilling methods such as those presented in
ods that would be the most successful for their site conditions.
Practice D5092. Techniques for obtaining groundwater
Other methods may be available for monitoring well
samples from monitoring wells are covered in Guides D4448,
installation, and qualified professionals should have flexibility
D7929, and Practice D6771. Practice D6725 addresses direct
to exercise judgement concerning alternatives not covered in
push wells using pre-packed screens.
this guide. The practice described in this guide is current at the
time of issue; however, new, alternative, and innovative meth-
1.3 The installation of direct push groundwater monitoring
ods may become available prior to revisions. Therefore, users
wells is limited to unconsolidated soils and sediments includ-
ing clays, silts, sands, and some gravels and cobbles. Penetra- should consult with manufacturers or producers prior to
specifying program requirements.
tion may be limited, or damage may occur to equipment, in
certain subsurface conditions; some of which are discussed in
1.7 This standard does not purport to address all of the
5.5. Information in this guide is limited to groundwater
safety concerns, if any, associated with its use. It is the
monitoring in the saturated zone.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.4 The values stated in either inch-pound units or SI units
bility of regulatory requirements prior to use.
presented in brackets are to be regarded separately as standard.
The values stated in each system may not be exact equivalents;
2. Referenced Documents
therefore,eachsystemshallbeusedindependentlyoftheother.
Combining values from the two systems may result in non- 2.1 ASTM Standards:
conformance with the standard. D653 Terminology Relating to Soil, Rock, and Contained
Fluids
1.5 All observed and calculated values shall conform to the
D3740 Practice for Minimum Requirements for Agencies
guidelines for significant digits and rounding established in
Engaged in Testing and/or Inspection of Soil and Rock as
Practice D6026, unless superseded by this standard.
Used in Engineering Design and Construction
D4448 Guide for Sampling Ground-Water Monitoring Wells
This guide is under the jurisdiction ofASTM CommitteeD18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
Vadose Zone Investigations. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2016. Published July 2016. Originally approved contactASTM Customer Service at [e-mail]. ForAnnual Book ofASTM
in 2001. Last previous editon approved in 2010 as D6724–04(2010). DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6724_D6724M-16. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6724/D6724M − 16
D4750 Test Method for Determining Subsurface Liquid 3. Terminology
Levels in a Borehole or Monitoring Well (Observation
3.1 Definitions—For common definitions of terms in this
Well) (Withdrawn 2010)
standard, refer to Terminology D653.
D5088 Practice for Decontamination of Field Equipment
3.2 Definitions of Terms Specific to This Standard:
Used at Waste Sites
3.2.1 dual tube systems, n—a system whereby inner and
D5092 Practice for Design and Installation of Groundwater
outer tubes are advanced independently or simultaneously into
Monitoring Wells
the subsurface strata.
D5254 Practice for Minimum Set of Data Elements to
3.2.1.1 Discussion—The outer casing tube is used for bore-
Identify a Ground-Water Site
hole stabilization. The inner tube for is used sampler recovery
D5299 Guide for Decommissioning of Groundwater Wells,
and insertion of other devices. In Practice D6282, direct push
Vadose Zone Monitoring Devices, Boreholes, and Other
soil sampling the dual tube system takes soil samples with a
Devices for Environmental Activities
sampler fixed to the inner rods.
D5434 Guide for Field Logging of Subsurface Explorations
of Soil and Rock
4. Summary of Guide
D5474 Guide for Selection of Data Elements for Groundwa-
ter Investigations
4.1 This guide provides information to be used by experi-
D5521 Guide for Development of Groundwater Monitoring
enced groundwater professionals for exploration of the subsur-
Wells in Granular Aquifers
face and ambient groundwater conditions.
D5730 Guide for Site Characterization for Environmental
4.2 This guide outlines a variety of field methods for
Purposes With Emphasis on Soil, Rock, the Vadose Zone
installing direct push groundwater monitoring wells. Installa-
and Groundwater (Withdrawn 2013)
tion methods include: (1) soil probing using combinations of
D5978 Guide for Maintenance and Rehabilitation of
dynamic (percussion or vibratory) driving with, or without,
Groundwater Monitoring Wells
additions of static (constant) force; (2) static force from the
D6001 Guide for Direct-Push Groundwater Sampling for
surface using hydraulic penetrometer or drilling equipment;
Environmental Site Characterization
and (3) incremental drilling combined with direct push meth-
D6026 Practice for Using Significant Digits in Geotechnical
ods. Methods for installation of annular seals and annular
Data
grouts are also discussed as well as abandonment grouting.
D6067 Practice for Using the Electronic Piezocone Pen-
4.3 This guide addresses considerations for selection and
etrometer Tests for Environmental Site Characterization
use of direct push well systems and installation techniques that
D6282 Guide for Direct Push Soil Sampling for Environ-
may be classified into two main categories; exposed screen
mental Site Characterizations
techniques and protected screen techniques. In exposed screen
D6286 Guide for Selection of Drilling Methods for Environ-
techniques, the screened casing may serve as the drive rod, or
mental Site Characterization
may surround a drive rod that is removed following installa-
D6452 Guide for Purging Methods for Wells Used for
tion. In protected screen techniques, the well may be advanced
Groundwater Quality Investigations
along with a protective outer casing, or may be lowered into a
D6564 Guide for Field Filtration of Groundwater Samples
driven casing that is subsequently removed. Alternatively, the
D6634 Guide for Selection of Purging and Sampling De-
screen, riser, and a retractable shield may be driven simulta-
vices for Groundwater Monitoring Wells
neously and all remain in the ground.
D6725 Practice for Direct Push Installation of Prepacked
Screen Monitoring Wells in Unconsolidated Aquifers 4.4 The interval to be tested is determined in advance by
prior exploration, or by soil or water sampling during direct
D6771 Practice for Low-Flow Purging and Sampling for
push driving.Ascreen section, either protected or unprotected,
Wells and Devices Used for Ground-Water Quality Inves-
is connected to riser pipes and either driven on the outside of,
tigations (Withdrawn 2011)
or placed inside of direct push rods. With some monitoring
D6914 Practice for Sonic Drilling for Site Characterization
well designs, it may be necessary to add sand pack and seals to
and the Installation of Subsurface Monitoring Devices
isolate the screened test zone as the rods are retracted. The top
D7242 Practice for Field Pneumatic Slug (Instantaneous
of the installation is usually completed in a manner consistent
Change in Head) Tests to Determine Hydraulic Properties
with regulatory requirements. The well can be developed to
of Aquifers with Direct Push Groundwater Samplers
remove mobile sediments. Water levels can be measured, and
D7352 Practice for Direct Push Technology for Volatile
water samples are taken as required in the sampling plan.
Contaminant Logging with the Membrane Interface Probe
(MIP)
5. Significance and Use
D7929 Guide for Selection of Passive Techniques for Sam-
pling Groundwater Monitoring Wells
5.1 The direct push ground method is a rapid and economi-
cal procedure for installing groundwater monitoring wells to
obtain representative groundwater samples and location-
specifichydrogeologicmeasurements.Directpushinstallations
The last approved version of this historical standard is referenced on
www.astm.org. may offer an advantage over conventional rotary drilled
D6724/D6724M − 16
monitoring wells (Practice D5092) for groundwater explora- 5.7 There have been no conclusive comparisons of effec-
tions in unconsolidated formations because they reduce distur- tiveness of sealing between drilled monitoring wells and direct
bance to the formation, and eliminate or minimize drill push monitoring wells. As with drilled monitoring wells,
cuttings.At facilities where contaminated soils are present, this sealing methods must be carefully applied to be effective.
can reduce hazard exposure for operators, local personnel, and Research on well sealing (11) has shown that bentonite seals
the environment, and can reduce investigative derived wastes. are not effective above the water table and that if used
Additionally, smaller equipment can be used for installation, bentonite grout requires a minimum of 20 % solids.
providing better access to constricted locations.
5.8 Selection of direct push monitoring wells versus con-
5.2 Direct push monitoring wells are typically smaller in ventional rotary drilled monitoring wells should be based on
diameter than drilled wells, thereby reducing purge water many issues. The advantages and disadvantages of the many
volumes, sampling time, and investigative derived wastes. available types of driving equipment and well systems must be
Practice D5092 monitoring wells are used when larger diam- considered with regard to the specific site conditions. Specific
eters and/or sample volumes are required, or at depths or in well systems and components, as well as direct push driving
geologic formations to where it is difficult to install direct push equipment, are described in Section 7.
wells. Direct push monitoring wells should be viable for
5.9 Advantages:
monitoring for many years.
5.9.1 Minimallyintrusiveandlessdisturbanceofthenatural
5.3 Prior to construction and installation of a direct push formation conditions than many conventional drilling tech-
well or any other type of groundwater well the reader should niques.
consult appropriate local agencies regarding regulatory re- 5.9.2 Rapid and economical.
quirementsforwellconstruction.Aregulatoryvariancemaybe 5.9.3 Smaller equipment with easier access to many loca-
required for installation of direct push monitoring wells. tions.
5.9.4 Use of shorter screens can eliminate connections
5.4 To date, published comparison studies between drilled
between multiple aquifers providing better vertical definition
monitoring wells and direct push monitoring wells have shown
4 ofwaterqualitythanlongwellscreens.Shorterscreensarealso
comparability (1-10) . However, selection of direct push moni-
more effective at identifying contaminated zones in heteroge-
toring wells over conventional rotary drilled wells should be
neous formation conditions.
based on several criteria, such as site accessibility and
5.9.5 Generates little or potentially no contaminated drill
penetrability, stratigraphic structure, depth to groundwater, and
cuttings.
aquifer transmissivity.
5.9.6 Less labor intensive than most conventional drilling
5.5 Typical penetration depths for installation of groundwa-
techniques.
ter monitoring wells with direct push equipment depend on
5.10 Disadvantages:
many variables. Some of the variables are the size and type of
5.10.1 Cannot be used to install monitoring devices in
the driving system, diameter of the drive rods and monitoring
consolidated bedrock and deposits containing significant
well, and the resistance of the earth materials being penetrated.
cobbles and boulders.
Some direct push systems are capable of installing groundwa-
5.10.2 Small diameter risers and screens limit the selection
ter monitoring wells to depths in excess of 100 ft [30 m], and
of useable down-hole equipment for purging and sampling.
larger direct push equipment can reach depths of several
5.10.3 Difficulty installing sand pack in small annular space
hundred feet. However, installation depths of 10 to 50 ft [5 to
if gravity installation of sand pack is used.
15 m] are most common. Direct push methods cannot be used
5.10.4 Difficulty installing grout in same annular space
to install monitoring wells in consolidated bedrock (for
unless appropriately designed equipment is used.
example, granite, limestone, gneiss), but are intended for
installation in unconsolidated materials such as clays, silts,
NOTE 1—The quality of the result produced by this standard is
dependent on the competence of the personnel performing it, and the
sands, and some gravels. Additionally, deposits containing
suitability of the equipment and facilities used. Agencies that meet the
significant cobbles and boulders (for example, some glacial
criteria of Practice D3740 are generally considered capable of competent
deposits), or strongly cemented materials (for example, cali-
and objective testing/sampling/inspection/etc. Users of this standard are
che) are likely to hinder or prevent penetration to the desired
cautioned that compliance with Practice D3740 does not in itself assure
monitoring depth. reliable results. Reliable results depend on many factors; Practice D3740
provides a means of evaluating some of those factors.
5.6 For direct push methods to provide accurate groundwa-
Practice D3740 was developed for agencies engaged in the laboratory
ter monitoring results, precautions must be taken to ensure that
testing and/or inspection of soils and rock. As such, it is not totally
cross-contamination by “smearing” or “drag-down” (that is, applicabletoagenciesperformingthisfieldpractice.However,userofthis
practice should recognize that the framework of Practice D3740 is
drivingshallowcontaminationtodeeperlevels)doesnotoccur,
appropriate for evaluating the quality of an agency performing this
and that hydraulic connections between otherwise isolated
practice. Currently there is no known qualifying national authority that
water bearing strata are not created. Similar precautions as
inspects agencies that perform this practice.
those applied during conventional rotary drilling operations
6. Pre-Installation Considerations
(Guide D6286) should be followed.
6.1 Site Characterization—Successful installation of direct
push groundwater monitoring wells must be preceded by
The boldface numbers in parentheses refer to a list of references at the end of
this standard. appropriate site characterization activities. These activities
D6724/D6724M − 16
may include reconnaissance, research, conceptual model can be evaluated by direct push testing on the site prior to well
development, exploratory field investigations, and confirma- installation. Larger diameter monitoring wells may be easy to
tion and re-evaluation of any existing flow models. install on soft or loose ground sites. Smaller diameter moni-
toring wells may facilitate deeper installation on sites that are
6.2 For the installation to be successful, it is imperative that
more resistant to penetration, but also present additional
the target aquifer be located accurately. As with any well
considerations for use as discussed below.
installation, the geologic conditions must be understood and
6.5.1 The availability of appropriate well development and
the stratigraphy must be known. Although direct push wells
sampling equipment for use in small-diameter monitoring
can monitor thinner aquifers, with more precision, they may be
wells may be limited. Many conventional down-hole pumps
ineffective is incorrectly placed. In thicker aquifers, and when
for purging and sampling are too large for use in small-
seeking dense non-aqueous phase liquids, screens may need to
diameter screens and risers. However, simple inertial pumps
be located in the bottom of the water-bearing stratum. Wells
are robust and generally effective for developing smaller DP
placed without determination of nearby geologic conditions
wells installed in coarse grained formations.
can be ineffective and possibly dangerous. Geologic investiga-
6.5.2 Small diameter monitoring wells, because they are
tions should look for perched aquifers and use installation
generally less rigid than larger diameter monitoring wells,
methods which will avoid any cross contamination of the unit.
require special attention during backfilling to maintain vertical
6.3 Environmental site characterization approaches are de-
alignment. This may include the use of centralizers.
scribed in Guide D5730. Proper site characterization for
monitoring well placement is reviewed in Practice D5092 on
7. Direct Push Wells Systems and Components
Monitoring Well Design.
7.1 Drive Rod and Casing—Rod systems can be single rods
6.3.1 Characterization Tools—In geologic settings ame-
or casing tubes or dual tube systems (Practice D6282) specifi-
nable to the use of direct push groundwater monitoring wells,
callydesignedfordirectpushhammers.Insomeinstanceswith
other direct push methods and tools can likely also be used to
single tube system the well itself may serve as the drive rod.
effectively characterize the site. For example, the Cone Pen-
Direct push drive rod is typically constructed of steel in
etrometer Test (CPT) (Guide D6067) is an effective tool for
threaded sections. Lengths of 5 ft [1 m] are common. The
mapping stratigraphy and locating target layers. The Hydraulic
diameter selected will depend on the driving resistance of the
Profiling tool is a method to map formation permeability and
soil and well size considerations. Consult experienced area
may be used to guide well placement. The membrane interface
contractors or qualified manufacturers to select the appropriate
probe (Practice D7352) may be used to identify zones of
diameters for the site. Drive rods used inside of dual tube
volatile organic contamination to guide screen placement.
casings range from 0.5 to 1.25 in. [15 to 30 mm] in diameter.
Other sensors, such as electrical conductivity and optical
Outer drive casings of up to 4.5-in. [10 mm] diameter have
detectors have been placed on CPT and other direct push
been used at relatively soft or loose soil sites allowing
systems. Direct push soil sampling (Guide D6282) and water
installation of 2-in. [50 mm] screen/riser assemblies. The most
sampling (Guide D6001) can be used in advance to locate
common casing sizes are 2 to 3 in. [50 to 75 mm]. Large drive
strata of concern. Direct push characterization experience at a
rods can be advanced with large vibratory drills (Guide
site can guide the user in well design or device selection.
D6286).Threaded sections can be outfitted with o-ring seals or
6.3.2 Sampling During Installation—Many direct push sys-
polytetrafluoroethylene (PFTE) tape to reduce groundwater
tems can take soil or water samples as part of the well
infiltration. Drive casings are equipped with expendable steel
installation process. For example, two-tube systems described
or aluminum drive points that are left in the bottom of the well.
in direct push soil sampling Guide D6282 can be used to
Depending on well design, the bottom of the casing may be
collect soil samples while driving. When the target aquifer is
advanced from a few inches [75 mm] to few feet deeper [1 m]
reached, the well screen system can be installed in the casing.
than the bottom of the desired screen interval to separate the
Sampling data taken prior to well installation can confirm the
expendable point from the well if desired. Alternately, dual
target stratum has been reached.
tube systems may use an inner rod equipped with an attached
6.3.3 Sampling Systems—There is a wide variety of direct
drive point that is removed before well insertion. An expend-
pushgroundwatersamplingsystemswhichcanalsobeusedfor
able cutting shoe is often used with these systems and the shoe
groundwater monitoring. Direct push water sampling Guide
is left in place as the casing is retracted to set the well.
D6001 describes exposed screen versus protected screen sam-
7.2 Well Screen and Riser Pipe—Slotted PVC with flush-
plers. Guide D6282 describes the differences in two-tube and
joint riser pipe is commonly used in the installation of direct
single-rod direct push soil sampling systems.
push monitoring wells. Sizes range from ⁄2 in. to 2 in.
6.4 Access and Clearances—The selection of driving equip-
(Schedules 40 and 80) [15 to 50 mm]. Other riser screen and
ment should consider the accessability of the installation site.
riser materials such as stainless steel, polyethylene, or PTFE
The site should be surveyed for accessibility. Utility clearances
may be used. PVC is preferred due to its low cost and because
may be required. Certain driving methods are incompatible
it is relatively inert. Selection of well material should consider
with nearby hazards (for example, flammables).Also check for
possible material interactions with the contaminant being
overhead utility lines during the site survey.
monitored. While PVC and stainless steel are commonly used
6.5 Well Size Selection—Driving resistance can govern the in most monitoring wells without any problem, there are
selection of an appropriate well diameter. Driving resistance extreme environmental conditions that could lead to failure of
D6724/D6724M − 16
these materials. PVC should not be exposed to neat organic prevent infiltration of surface runoff and to maintain the
solvents (that is, pure products) that are PVC solvents or hydraulic integrity of confining layers. The sealing required
swelling agents or to extremely high concentrations of these depends on the formation, well type, and installation technique
chemicals (approaching a saturated solution) (5, 12-16). Al- (Section8).Severalmethodscanbeusedtoassureasealabove
though there is very little data on the expected life of steel well the screened zone. Most completion methods with cased
casings (17), stainless steel is reported to perform well in most systems use tremie grout placed as the casing is withdrawn.
environments (17-19). Stainless steel should be avoided in The grout can be bentonite or cement similar to that specified
extremely corrosive conditions, which may include water high in Guides D6001, D6282, and Practice D5092. A typical well
in chlorides, low in pH, high in dissolved solids or high in completion diagram is shown on Fig. 1.Agrout barrier of fine
dissolvedoxygen (20-23).Asscreenandriserpipemaycontain to medium sand is used to protect the sand pack or screened
chemical residue from manufacturing, the screen and riser interval from infiltration of grout, which can change the local
should be cleaned prior to installation. Most manufacturers water chemistry. Practice D5092 addresses this subject.
supply pre-cleaned riser pipe. Threaded joints of the riser pipe 7.4.1 Mechanical techniques can also be used to create an
can be sealed with O-rings or by using PTFE tape. effective seal. For example, Fig. 2 depicts a solid metal sleeve
7.2.1 Slotted (PVC) or wire-wrapped (steel) well screen is left in the ground, and Fig. 3 shows modular expandable foam
and bentonite sleeves used above the screened interval. Rubber
normally supplied with slot widths of 0.01 or 0.02 in. [0.25 to
0.50 mm]. The screen can be wrapped with stainless steel wire wiper seal may also be used. Whether this barrier is formed by
the addition of fine to medium sand, by collapse of the
meshof0.006in.[0.15mm]opening.Theselectionofslotsize
depends on the formation grain size distribution and if a sand surrounding formation, or mechanically, the materials em-
ployed must be chosen to be compatible with the local
pack will be needed to reduce turbidity. Practice D5092
provides slot size and sand pack selection criteria. groundwater conditions and contaminants of interest.
7.2.2 A sediment trap may be specified. If the riser is lifted
7.5 Modular Well Systems—The most recent developments
and needs to be pushed back into place, pointed sediment traps
have been towards the use of modular components for placing
are useful.
sand pack and seals. Pre-packed screens can be used with most
drive systems. The screens are stainless steel wire mesh filled
7.3 Sand Pack—The use of sand packs assists in reducing
withsandofdifferentgradations.Fig.1andFig.3showtheuse
turbidity and the amount of well development required to
obtain low turbidity samples. Monitoring wells without sand of these modular sand packs.
packs will likely yield more turbid water, which may impact
7.6 Other Variations—Numerous innovations have been
the results of some chemical analyses. However, a filter can be
developed for groundwater monitoring through direct push
as thin as several grain diameters to be effective. Improving
well systems. For example, multiple screened sections can be
well yield is not the purpose of the sand pack; yield is
completed in one installation, using Continuous Multichannel
controlled by the formation. For monitoring of metals, filtering
Tubing (CMT) and sampling of multiple zones can be per-
of samples (Guide D6564) may be required for samples with
formed by using packers or sampling ports for groundwater
elevated turbidity levels.
extraction (28, 29). This system shown in Fig. 4 and is
7.3.1 Sand Pack Selection and Size Range—Formations of
normally installed in rotary drilling operations, but can be
clean sands and gravels (that is, less than 5 % fines) may not
require a sand pack. For soil containing appreciable fines, use
of a sand pack should be considered. The gradation require-
ment depends on the particle size distribution in the target
aquifer. Refer to Practice D5092 for criteria on sand pack
design.
7.3.2 Pre-packed Screens—Pre-packed screen systems are
intended to ease the installation of sand in direct push cased
monitoring wells by carrying it with the casing. The prepack
sections use hollow stainless steel screen casings to accommo-
date the slotted riser.Ascreen opening of 0.006 in. [0.15 mm]
is typical. Pre-packed screen systems addressed in Practice
D6725 are used in two tube systems and allow for better
control of placement of well screen filter pack and top seal and
allow for placement of fine sand filters needed for fine grained
formations (Practice D5092).
7.4 Seals—In addition to the sand pack, a seal above the
screen is needed. Current local agency regulations and envi-
ronmental guidance documents (7, 10, 24-26) require the
installation of annular seals and grouting of the well annulus to
prevent potential cross contamination along the well bore and
the possibility of surface water or chemical spills from con-
taminating the monitored aquifer(s). Sealing is necessary to FIG. 1 Example of a Completed Direct Push Monitoring Well (27)
D6724/D6724M − 16
require a unique installation procedure. Regardless of the
choice of techniques and systems, a written operating proce-
dure should be developed which allows some flexibility in
response to field conditions. Project sampling plans and stan-
dard operating procedures should be consulted prior to instal-
lation.
8.2 Direct Push Driving Equipment—Direct push Guides
D6001 and D6282 describe typical driving systems. Some
systems are manual (slam bar, hand held electric or pneumatic
hammers), static weight (cone penetrometers), percussion (hy-
draulic hammers, air hammers, electric hammers), and vibra-
tory systems. In some cases, direct push monitoring wells may
be installed in combination with rotary drilling.
8.3 Exposed Screen Techniques—One method of installing
direct push
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6724 − 04 (Reapproved 2010) D6724/D6724M − 16
Standard Guide for
Installation of Direct Push Groundwater Monitoring Wells
This standard is issued under the fixed designation D6724;D6724/D6724M; the number immediately following the designation indicates
the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This guide describes various direct push groundwater monitoring wells and provides guidance on their selection and
installation for obtaining representative groundwater samples and monitoring water table elevations. Direct push wells are used
extensively for monitoring groundwater quality in unconsolidated formations. This guide also includes discussion of some
groundwater sampling devices which can be permanently emplaced as monitoring wells.
1.2 This guide does not address the single event sampling of groundwater using direct push water samplers as presented in
Guide D6001. The methods in this guide are often used with other tests such as direct push soil sampling (Guide D6282) and the
cone penetrometer test (Guide D6067). The present guide does not address the installation of monitoring wells by rotary drilling
or sonic drilling methods such as those presented in Practice D5092. Techniques for obtaining groundwater samples from
monitoring wells are covered in GuideGuides D4448, D7929, and Practice D6771. Practice D6725 addresses direct push wells
using pre-packed screens.
1.3 The installation of direct push groundwater monitoring wells is limited to unconsolidated soils and sediments including
clays, silts, sands, and some gravels and cobbles. Penetration may be limited, or damage may occur to equipment, in certain
subsurface conditions; some of which are discussed in 5.5. Information in this guide is limited to groundwater monitoring in the
saturated zone.
1.4 This guide does not purport to comprehensively address all of the methods and issues associated with monitoring well
installation. Users should seek input from qualified professionals for the selection of proper equipment and methods that would
be the most successful for their site conditions. Other methods may be available for monitoring well installation, and qualified
professionals should have flexibility to exercise judgement concerning alternatives not covered in this guide. The practice
described in this guide is current at the time of issue; however, new, alternative, and innovative methods may become available
prior to revisions. Therefore, users should consult with manufacturers or producers prior to specifying program requirements. The
values stated in either inch-pound units or SI 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 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, unless superseded by this standard.
1.6 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 judgement.
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’sproject’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.
1.6.1 This guide does not purport to comprehensively address all of the methods and issues associated with monitoring well
installation. Users should seek input from qualified professionals for the selection of proper equipment and methods that would
be the most successful for their site conditions. Other methods may be available for monitoring well installation, and qualified
professionals should have flexibility to exercise judgement concerning alternatives not covered in this guide. The practice
described in this guide is current at the time of issue; however, new, alternative, and innovative methods may become available
prior to revisions. Therefore, users should consult with manufacturers or producers prior to specifying program requirements.
This guide is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.21 on Groundwater and Vadose
Zone Investigations.
Current edition approved July 1, 2010July 1, 2016. Published September 2010July 2016. Originally approved in 2001. Last previous editon approved in 20042010 as
D6724D6724–04(2010).–04. DOI: 10.1520/D6724-04R10.10.1520/D6724_D6724M-16.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6724/D6724M − 16
1.7 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 and health practices and determine the applicability of regulatory
requirements prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4448 Guide for Sampling Ground-Water Monitoring Wells
D4750 Test Method for Determining Subsurface Liquid Levels in a Borehole or Monitoring Well (Observation Well)
(Withdrawn 2010)
D5088 Practice for Decontamination of Field Equipment Used at Waste Sites
D5092 Practice for Design and Installation of Groundwater Monitoring Wells
D5254 Practice for Minimum Set of Data Elements to Identify a Ground-Water Site
D5299 Guide for Decommissioning of Groundwater Wells, Vadose Zone Monitoring Devices, Boreholes, and Other Devices for
Environmental Activities
D5434 Guide for Field Logging of Subsurface Explorations of Soil and Rock
D5474 Guide for Selection of Data Elements for Groundwater Investigations
D5521 Guide for Development of Groundwater Monitoring Wells in Granular Aquifers
D5730 Guide for Site Characterization for Environmental Purposes With Emphasis on Soil, Rock, the Vadose Zone and
Groundwater (Withdrawn 2013)
D5978 Guide for Maintenance and Rehabilitation of Groundwater Monitoring Wells
D6001 Guide for Direct-Push Groundwater Sampling for Environmental Site Characterization
D6026 Practice for Using Significant Digits in Geotechnical Data
D6067 Practice for Using the Electronic Piezocone Penetrometer Tests for Environmental Site Characterization
D6282 Guide for Direct Push Soil Sampling for Environmental Site Characterizations
D6286 Guide for Selection of Drilling Methods for Environmental Site Characterization
D6452 Guide for Purging Methods for Wells Used for Groundwater Quality Investigations
D6564 Guide for Field Filtration of Groundwater Samples
D6634 Guide for Selection of Purging and Sampling Devices for Groundwater Monitoring Wells
D6725 Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers
D6771 Practice for Low-Flow Purging and Sampling for Wells and Devices Used for Ground-Water Quality Investigations
(Withdrawn 2011)
D6914 Practice for Sonic Drilling for Site Characterization and the Installation of Subsurface Monitoring Devices
D7242 Practice for Field Pneumatic Slug (Instantaneous Change in Head) Tests to Determine Hydraulic Properties of Aquifers
with Direct Push Groundwater Samplers
D7352 Practice for Direct Push Technology for Volatile Contaminant Logging with the Membrane Interface Probe (MIP)
D7929 Guide for Selection of Passive Techniques for Sampling Groundwater Monitoring Wells
3. Terminology
3.1 Definitions—Terminology used within this standard is in accordance with For common definitions of terms in this standard,
refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 dual tube systems, n—a system whereby inner and outer tubes are advanced independently or simultaneously into the
subsurface strata.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
3.2.1.1 Discussion—
The outer casing tube is used for borehole stabilization. The inner tube for is used sampler recovery and insertion of other devices.
In Practice D6282, direct push soil sampling the dual tube system takes soil samples with a sampler fixed to the inner rods.
D6724/D6724M − 16
4. Summary of Guide
4.1 This guide provides information to be used by experienced groundwater professionals for investigationexploration of the
subsurface and ambient groundwater conditions.
4.2 This guide outlines a variety of field methods for installing direct push groundwater monitoring wells. Installation methods
include: (1) soil probing using combinations of dynamic (percussion or vibratory) driving with, or without, additions of static
(constant) force; (2) static force from the surface using hydraulic penetrometer or drilling equipment; and (3) incremental drilling
combined with direct push methods. Methods for installation of annular seals and annular grouts are also discussed as well as
abandonment grouting.
4.3 This guide addresses considerations for selection and use of direct push well systems and installation techniques that may
be classified into two main categories; exposed screen techniques and protected screen techniques. In exposed screen techniques,
the screened casing may serve as the drive rod, or may surround a drive rod that is removed following installation. In protected
screen techniques, the well may be advanced along with a protective outer casing, or may be lowered into a driven casing that is
subsequently removed. Alternatively, the screen, riser, and a retractable shield may be driven simultaneously and all remain in the
ground.
4.4 The interval to be tested is determined in advance by prior investigation,exploration, or by soil or water sampling during
direct push driving. A screen section, either protected or unprotected, is connected to riser pipes and either driven on the outside
of, or placed inside of direct push rods. With some monitoring well designs, it may be necessary to add sand pack and seals to
isolate the screened test zone as the rods are retracted. The top of the installation is usually completed in a manner consistent with
regulatory requirements. The well can be developed to remove mobile sediments. Water levels can be measured, and water samples
are taken as required in the sampling plan.
5. Significance and Use
5.1 The direct push ground method is a rapid and economical procedure for installing groundwater monitoring wells to obtain
representative groundwater samples and location-specific hydrogeologic measurements. Direct push installations may offer an
advantage over conventional rotary drilled monitoring wells (Practice D5092) for groundwater investigationsexplorations in
unconsolidated formations because they reduce disturbance to the formation, and eliminate or minimize drill cuttings. At facilities
where contaminated soils are present, this can reduce hazard exposure for operators, local personnel, and the environment, and can
reduce investigative derived wastes. Additionally, smaller equipment can be used for installation, providing better access to
constricted locations.
5.2 Direct push monitoring wells generally do not extend to depths attainable by drilling. They are also are typically smaller
in diameter than drilled wells, thereby reducing purge water volumes, sampling time, and investigative derived wastes. Practice
D5092 monitoring wells are used when larger diameters and/or sample volumes are required, or at depths to whichor in geologic
formations to where it is difficult to install direct push wells. Direct push monitoring wells should be viable for monitoring for
many years.
5.3 Prior to construction and installation of a direct push well or any other type of groundwater well the reader should consult
appropriate local and state agencies regarding regulatory requirements for well construction in the state. construction. A regulatory
variance may be required for installation of direct push monitoring wells in some states.wells.
5.4 To date, published comparison studies between drilled monitoring wells and direct push monitoring wells have shown
comparability (11-10, )2, 3, 4, 5). . However, selection of direct push monitoring wells over conventional rotary drilled wells
should be based on several criteria, such as site accessibility and penetrability, stratigraphic structure, depth to groundwater, and
aquifer transmissivity.
5.5 Typical penetration depths for installation of groundwater monitoring wells with direct push equipment depend on many
variables. Some of the variables are the size and type of the driving system, diameter of the drive rods and monitoring well, and
the resistance of the earth materials being penetrated. Some direct push systems are capable of installing groundwater monitoring
wells to depths in excess of 100 feet, ft [30 m], and larger direct push equipment, such as the vibratory sonic type drill (Guide
equipment can reach depths D6286) are capable of reaching much greater depths, sometimes in excess of 400 ft. of several hundred
feet. However, installation depths of 10 to 50 feet ft [5 to 15 m] are most common. Direct push methods cannot be used to install
monitoring wells in consolidated bedrock (for example, granite, limestone, gneiss), but are intended for installation in
unconsolidated materials such as clays, silts, sands, and some gravels. Additionally, deposits containing significant cobbles and
boulders (for example, some glacial deposits), or strongly cemented materials (for example, caliche) are likely to hinder or prevent
penetration to the desired monitoring depth.
5.6 For direct push methods to provide accurate groundwater monitoring results, precautions must be taken to ensure that
cross-contamination by “smearing” or “drag-down” (that is, driving shallow contamination to deeper levels) does not occur, and
The boldface numbers in parentheses refer to a list of references at the end of this standard.
D6724/D6724M − 16
that hydraulic connections between otherwise isolated water bearing strata are not created. Similar precautions as those applied
during conventional rotary drilling operations (Guide D6286) should be followed.
5.7 There have been no conclusive comparisons of effectiveness of sealing between drilled monitoring wells and direct push
monitoring wells. As with drilled monitoring wells, sealing methods must be carefully applied to be effective. Research on well
sealing (11) has shown that bentonite seals are not effective above the water table and that if used bentonite grout requires a
minimum of 20 % solids.
5.8 Selection of direct push monitoring wells versus conventional rotary drilled monitoring wells should be based on many
issues. The advantages and disadvantages of the many available types of driving equipment and well systems must be considered
with regard to the specific site conditions. Specific well systems and components, as well as direct push driving equipment, are
described in Section 7.
5.9 Advantages:
5.9.1 Minimally intrusive and less disturbance of the natural formation conditions than many conventional drilling techniques.
5.9.2 Rapid and economical.
5.9.3 Smaller equipment with easier access to many locations.
5.9.4 Use of shorter screens can eliminate connections between multiple aquifers providing better vertical definition of water
quality than long well screens. Shorter screens are also more effective at identifying contaminated zones in heterogeneous
formation conditions.
5.9.5 Generates little or potentially no contaminated drill cuttings.
5.9.6 Less labor intensive than most conventional drilling techniques.
5.10 Disadvantages:
5.10.1 Cannot be used to install monitoring devices in consolidated bedrock and deposits containing significant cobbles and
boulders.
5.10.2 Small diameter risers and screens limit the selection of useable down-hole equipment for purging and sampling.
5.10.3 Difficulty installing sand pack in small annular space if gravity installation of sand pack is used.
5.10.4 Difficulty installing grout in same annular space unless appropriately designed equipment is used.
NOTE 1—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 facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective
testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable
results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
Practice D3740 was developed for agencies engaged in the laboratory testing and/or inspection of soils and rock. As such, it is not totally applicable
to agencies performing this field practice. However, user 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.
6. Pre-Installation Considerations
6.1 Site Characterization—Successful installation of direct push groundwater monitoring wells must be preceded by appropriate
site characterization activities. These activities may include reconnaissance, research, conceptual model development, exploratory
field investigations, and confirmation and re-evaluation of any existing flow models.
6.2 For the installation to be successful, it is imperative that the target aquifer be located accurately. As with any well
installation, the geologic conditions must be understood and the stratigraphy must be known. Although direct push wells can
monitor thinner aquifers, with more precision, they may be ineffective is incorrectly placed. In thicker aquifers, and when seeking
dense non-aqueous phase liquids, screens may need to be located in the bottom of the water-bearing stratum. Wells placed without
determination of nearby geologic conditions can be ineffective and possibly dangerous. Geologic investigations should look for
perched aquifers and use installation methods which will avoid any crosscontamination cross contamination of the unit.
6.3 Environmental site characterization approaches are described in Guide D5730. Proper site characterization for monitoring
well placement is reviewed in Practice D5092 on Monitoring Well Design.
6.3.1 Characterization Tools—In geologic settings amenable to the use of direct push groundwater monitoring wells, other
direct push methods and tools can likely also be used to effectively characterize the site. For example, the Cone Penetrometer Test
(CPT) (Guide D6067) is an effective tool for mapping stratigraphy and locating target layers. The Hydraulic Profiling tool is a
method to map formation permeability and may be used to guide well placement. The membrane interface probe (Practice D7352)
may be used to identify zones of volatile organic contamination to guide screen placement. Other sensors, such as electrical
conductivity and optical detectors have been placed on CPT and other direct push systems. Direct push soil sampling (Guide
D6282) and water sampling (Guide D6001) can be used in advance to locate strata of concern. Direct push characterization
experience at a site can guide the user in well design or device selection.
6.3.2 Sampling During Installation—Many direct push systems can take soil or water samples as part of the well installation
process. For example, two-tube systems described in direct push soil sampling Guide D6282 can be used to collect soil samples
D6724/D6724M − 16
while driving. When the target aquifer is reached, the well screen system can be installed in the casing. Sampling data taken prior
to well installation can confirm the target stratum has been reached.
6.3.3 Sampling Systems—There is a wide variety of direct push groundwater sampling systems which can also be used for
groundwater monitoring. Direct push water sampling Guide D6001 describes exposed screen versus protected screen samplers.
Guide D6282 describes the differences in two-tube and single-rod direct push soil sampling systems.
6.4 Access and Clearances—The selection of driving equipment should consider the accessability of the installation site. The
site should be surveyed for accessibility. Utility clearances may be required. Certain driving methods are incompatible with nearby
hazards (for example, flammables). Also check for overhead utility lines during the site survey.
6.5 Well Size Selection—Driving resistance can govern the selection of an appropriate well diameter. Driving resistance can be
evaluated by direct push testing on the site prior to well installation. Larger diameter monitoring wells may be easy to install on
soft or loose ground sites. Smaller diameter monitoring wells may facilitate deeper installation on sites that are more resistant to
penetration, but also present additional considerations for use as discussed below.
6.5.1 The availability of appropriate well development and sampling equipment for use in small-diameter monitoring wells may
be limited. Many conventional down-hole pumps for purging and sampling are too large for use in small-diameter screens and
risers. However, simple inertial pumps are robust and generally effective for developing smaller DP wells installed in coarse
grained formations.
6.5.2 Small diameter monitoring wells, because they are generally less rigid than larger diameter monitoring wells, require
special attention during backfilling to maintain vertical alignment. This may include the use of centralizers.
7. Direct Push Wells Systems and Components
7.1 Drive Rod and Casing—Rod systems can be single rods or casing tubes or dual tube systems (Practice D6282) specifically
designed for direct push hammers. In some instances with single tube system the well itself may serve as the drive rod. Otherwise,
it either surrounds the well casing or is contained within it diuring installation, and is then removed. Direct push drive rod is
typically constructed of steel in threaded sections. Lengths of 3.3 ft or 5 ft [1 m] are common. The diameter selected will depend
on the driving resistance of the soil and well size considerations. Consult experienced area contractors or qualified manufacturers
to select the appropriate diameters for the site. Drive rods used inside of dual tube casings range from 0.5 to 1.25 in. [15 to 30
mm] in diameter. Outer drive casings of up to 4.5-in. [10 mm] diameter have been used at relatively soft or loose soil sites allowing
installation of 2-in. [50 mm] screen/riser assemblies. The most common casing sizes are 2 to 3 in. [50 to 75 mm]. Large drive rods
can be advanced with large vibratory drills (Guide D6286). Threaded sections can be outfitted with o-ring seals or PFTE
polytetrafluoroethylene (PFTE) tape to reduce groundwater infiltration. Drive casings are equipped with expendable steel or
aluminum drive points that are left in the bottom of the well. Depending on well design, the bottom of the casing may be advanced
from a few inches [75 mm] to few feet deeper [1 m] than the bottom of the desired screen interval to separate the expendable point
from the well if desired. Alternately, dual tube systems may use an inner rod equipped with an attached drive point that is removed
before well insertion. An expendable cutting shoe is often used with these systems and the shoe is left in place as the casing is
retracted to set the well.
7.2 Well Screen and Riser Pipe—Slotted PVC with flush-joint riser pipe is commonly used in the installation of direct push
monitoring wells. Sizes range from ⁄2 in. to 2 in. (Schedules 40 and 80). 80) [15 to 50 mm]. Other riser screen and riser materials
such as stainless steel, polyethylene, or PTFE may be used. PVC is preferred due to its low cost and because it is relatively inert.
Selection of well material should consider possible material interactions with the contaminant being monitored. While PVC and
Stainlessstainless steel are commonly used in most monitoring wells without any problem, there are extreme environmental
conditions that could lead to failure of these materials. PVC should not be exposed to neat organic solvents (that is, pure products)
that are PVC solvents or swelling agents or to extremely high concentrations of these chemicals (approaching a saturated solution)
(5, 612-16, 7, 8, 9, 10). Although there is very little data on the expected life of steel well casings (1117), stainless steel is reported
to perform well in most environments (1117-19, 12, 13). Stainless steel should be avoided in extremely corrosive conditions, which
may include water high in chlorides, low in pH, high in dissolved solids or high in dissolved oxygen (1420-23, 15, 16, 17). As
screen and riser pipe may contain chemical residue from manufacturing, the screen and riser should be cleaned prior to installation.
Threads Most manufacturers supply pre-cleaned riser pipe. Threaded joints of the riser pipe can be sealed with O-rings or by using
PTFE tape.
7.2.1 Slotted (PVC) or wire-wrapped (steel) well screen is normally supplied with slot widths of 0.01 or 0.02 in. [0.25 to 0.50
mm]. The screen can be wrapped with stainless steel wire mesh of 0.006 in. [0.15 mm] opening. The selection of slot size depends
on the formation grain size distribution and if a sand pack will be needed to reduce turbidity. Practice D5092 provides slot size
and sand pack selection criteria.
7.2.2 A sediment trap may be specified. If the riser is lifted and needs to be pushed back into place, pointed sediment traps are
useful.
7.3 Sand Pack—The use of sand packs assists in reducing turbidity and the amount of well development required to obtain low
turbidity samples. Monitoring wells without sand packs will likely yield more turbid water, which may impact the results of some
chemical analyses. However, a filter can be as thin as several grain diameters to be effective. Improving well yield is not the
D6724/D6724M − 16
purpose of the sand pack; yield is controlled by the formation. For monitoring of metals, filtering of samples (Guide D6564) may
be required for samples with elevated turbidity levels.
7.3.1 Sand Pack Selection and Size Range—Formations of clean sands and gravels (that is, less than 5 % fines) may not require
a sand pack. For soil containing appreciable fines, use of a sand pack should be considered. The gradation requirement depends
on the particle size distribution in the target aquifer. Refer to Practice D5092 for criteria on sand pack design.
7.3.2 Pre-packed Screens—Pre-packed screen systems are intended to ease the installation of sand in direct push cased
monitoring wells by carrying it with the casing. The prepack sections use hollow stainless steel screen casings to accommodate
the slotted riser. A screen opening of 0.006 in. is typical.[0.15 mm] is typical. Pre-packed screen systems addressed in Practice
D6725 are used in two tube systems and allow for better control of placement of well screen filter pack and top seal and allow
for placement of fine sand filters needed for fine grained formations (Practice D5092).
7.4 Seals—In addition to the sand pack, a seal above the screen is needed. Current state local agency regulations and
EPAenvironmental guidance documents (187, 1910, 2024-26) require the installation of annular seals and grouting of the well
annulus to prevent potential cross contamination along the well bore and the possibility of surface water or chemical spills from
contaminating the monitored aquifer(s). Sealing is necessary to prevent infiltration of surface runoff and to maintain the hydraulic
integrity of confining layers. The sealing required depends on the formation, well type, and installation technique (Section 8).
Several methods can be used to assure a seal above the screened zone. Most completion methods with cased systems use tremie
grout placed as the casing is withdrawn. The grout can be bentonite or cement similar to that specified in Guides D6001, D6282,
and Practice D5092. A typical well completion diagram is shown on Fig. 1. A grout barrier of fine to medium sand is used to protect
the sand pack or screened interval from infiltration of grout, which can change the local water chemistry. Practice D5092 addresses
this subject.
7.4.1 Mechanical techniques can also be used to create an effective seal. For example, Fig. 2 depicts a solid metal sleeve left
in the ground, and Fig. 3 shows modular expandable foam and bentonite sleeves used above the screened interval. Rubber wiper
seal may also be used. Whether this barrier is formed by the addition of fine to medium sand, by collapse of the surrounding
formation, or mechanically, the materials employed must be chosen to be compatible with the local groundwater conditions and
contaminants of interest.
7.5 Modular Well Systems—The most recent developments have been towards the use of modular components for placing sand
pack and seals. Pre-packed screens can be used with most drive systems. The screens are stainless steel wire mesh filled with sand
of different gradations. Fig. 1 and Fig. 3 showsshow the use of these modular sand packs.
7.6 Other Variations—Numerous innovations have been developed for groundwater monitoring through direct push well
systems. For example, multiple screened sections can be completed in one installation, using Continuous Multichannel Tubing
(CMT) and sampling of multiple zones can be performed by using packers or sampling ports for groundwater extraction.extraction
(28, 29). This system shown in Fig. 4 and is normally installed in rotary drilling operations, but can be installed in large diameter
direct push casing tubes. The multichannel HDPE tube is equipped with prepack sand packs and bentonite sealing systems to
isolate zones for testing. Another recent development has been the use of an everting flexible sockliner system liners to seal the
borehole and isolate a contaminated zones and water sampling intervalintervals (2230).
FIG. 1 Example of a Completed Direct Push Monitoring Well (2127)
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FIG. 2 Example of a Steel Seal Body Above the Screen
FIG. 3 Direct Push Well with Modular Sealing Components
8. Installation Techniques
8.1 There are several techniques for installing direct push monitoring wells. Techniques can be broadly classifieds into two
categories: exposed screen techniques, and protected screen techniques. Each of the systems described hereafter may require a
unique installation procedure. Regardless of the choice of techniques and systems, a written operating procedure should be
developed which allows some flexibility in response to field conditions. Project sampling plans and standard operating procedures
should be consulted prior to installation.
8.2 Direct Push Driving Equipment—Direct push Guides D6001 and D6282 describe typical driving systems. Some systems are
manual (slam bar, hand held electric or pneumatic hammers), static weight (cone penetrometers), percussion (hydraulic hammers,
air hammers, electric hammers), and vibratory systems. In some cases, direct push monitoring wells may be installed in
combination with rotary drilling.
D6724/D6724M − 16
FIG. 4 Schematic of a CMT Well (Courtesy of Solinist) (28)
8.3 Exposed Screen Techniques—One method of installing direct push wells is to advance a screen and riser of constant diameter
that remain in direct contact with the formation during installation. The riser may be driven either alone or by using a mandrel rod
inside the screen and riser (Fig. 45). Because the well screen is exposed to soil duri
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