ASTM D6725/D6725M-16

Standard Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers

SIGNIFICANCE AND USE
5.1 This practice is intended to provide the user with information on the appropriate methods and procedures for installing prepacked screen monitoring wells by direct push methods. The monitoring wells may be used to obtain representative water quality samples for aqueous phase contaminants or other analytes of interest, either organic or inorganic (3, 6-8). The monitoring wells may also be used to obtain information on the potentiometric surface of the local aquifer and properties of the formation such as hydraulic conductivity or transmissivity.  
5.2 Use of direct push methods to install monitoring wells can significantly reduce the amount of potentially hazardous drill cuttings generated during well installation at contaminated sites. This may significantly reduce cost of an environmental site investigation and groundwater monitoring program. Minimizing generation of hazardous waste also reduces the exposure hazards to site workers, local residents, and the environment.  
5.3 Direct push methods for monitoring well installation are limited to use in unconsolidated formations such as alluvial/stream sediments, glacial deposits, and beach type sediments. Direct push methods are generally successful at penetrating clays, silts, sands and some gravel. Deposits such as soils with thick caliche layers, or glacial tills with large cobbles or boulders may be difficult or impossible to penetrate to the desired depth. Direct push methods are not designed for penetration of consolidated bedrock such as limestone, granite or gneiss.
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. Rel...
SCOPE
1.1 This practice is based on recognized methods by which direct push monitoring wells may be designed and installed for the purpose of detecting the presence or absence of a contaminant, and collecting representative groundwater quality data. The design standards and installation procedures herein are applicable to both detection and assessment monitoring programs for facilities.  
1.2 The recommended monitoring well design, as presented in this practice, is based on the assumption that the objective of the program is to obtain representative groundwater information and water quality samples from aquifers. Monitoring wells constructed following this practice should produce relatively turbidity-free samples for granular aquifer materials ranging from gravels to silty sand.  
1.3 Direct push procedures are not applicable for monitoring well installation under all geologic and soil conditions (for example, installation in bedrock). Other rotary drilling procedures are available for penetration of these consolidated materials for well construction purposes (Guide D5092). Additionally, under some geologic conditions it may be appropriate to install monitoring wells without a filter pack (1, 2)2. Guide D6724 may be referred to for additional information on these and other methods for the direct push installation of groundwater monitoring wells.  
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 Practice D6026, unless superseded by this standard.  
1.6 This standard does not purport to address all of the safety co...

General Information

• Status: Published
• Publication Date: 14-Jul-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 D6725-04(2010) - Standard Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers
• Effective Date: 15-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 D5912-20 - Standard Practice for (Analytical Procedure) Determining Hydraulic Conductivity of an Unconfined Aquifer by Overdamped Well Response to Instantaneous Change in Head (Slug)
• Effective Date: 01-Jun-2020
• Refers: ASTM D5881-20 - Standard Practice for (Analytical Procedures) Determining Transmissivity of Confined Nonleaky Aquifers by Critically Damped Well Response to Instantaneous Change in Head (Slug)
• Effective Date: 01-Jun-2020
• Refers: ASTM D5088-20 - Standard Practice for Decontamination of Field Equipment Used at Waste Sites
• Effective Date: 01-May-2020
• Refers: ASTM D5787-20 - Standard Practice for Monitoring Well Protection At or Near Land Surface
• Effective Date: 01-Jan-2020
• 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 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 D4448-01(2019) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Feb-2019
• Refers: ASTM D6542-05(2018)e1 - Standard Practice for Tonnage Calculation of Coal in a Stockpile
• Effective Date: 01-Dec-2018
• Refers: ASTM D5881-18 - Standard Practice for (Analytical Procedure) Determining Transmissivity of Confined Nonleaky Aquifers by Critically Damped Well Response to Instantaneous Change in Head (Slug)
• Effective Date: 01-Dec-2018
• Refers: ASTM D6542-05(2018) - Standard Practice for Tonnage Calculation of Coal in a Stockpile
• Effective Date: 01-Nov-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 D4104-17 - Standard Test Method (Analytical Procedure) for Determining Transmissivity of Nonleaky Confined Aquifers by Overdamped Well Response to Instantaneous Change in Head (Slug Tests)
• Effective Date: 01-Nov-2017
• Refers: ASTM D5786-17 - Standard Practice for (Field Procedure) for Constant Drawdown Tests in Flowing Wells for Determining Hydraulic Properties of Aquifer Systems
• Effective Date: 01-Jan-2017

Overview

ASTM D6725/D6725M-16: Standard Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers details recognized procedures for installing prepacked screen monitoring wells using direct push technology. This standard supports environmental site investigations and groundwater monitoring by enabling reliable construction of wells in unconsolidated materials such as alluvial sediments, glacial deposits, and sands. The adoption of direct push methods minimizes drilling waste and enhances efficiency, while helping to generate representative groundwater quality data, determine contaminant presence, and monitor aquifer properties.

Key Topics

• Direct Push Methods: This standard outlines the use of direct push techniques, including percussion and static weight, to install prepacked screen wells without generating excessive drill cuttings.
• Monitoring Well Applications: Prepacked screen wells installed by these procedures are intended for sampling groundwater quality, gauging water levels, and collecting hydrogeological data (hydraulic conductivity, transmissivity). The practice helps assess the presence of aqueous phase contaminants, both organic and inorganic.
• Site Suitability: Direct push installation methods described are best suited for unconsolidated aquifers-clays, silts, sands, and some gravels. These techniques are not designed for consolidated materials such as bedrock.
• Well Construction Materials: The standard emphasizes the use of compatible well materials (PVC, stainless steel) and clean, appropriately sized filter media to avoid altering sample quality. Seals, grouts, and risers must be selected based on both hydrogeologic compatibility and regulatory requirements.
• Annular Seal and Grout: Proper sealing above the screen interval is critical to prevent surface contamination and preserve groundwater sample integrity.
• Well Protection: Specification for above-ground and flush-mount well protectors ensures wells are safeguarded from physical damage or potential surface infiltration.
• Safety and Compliance: The standard stresses the competence of personnel, adherence to state/local/federal regulations, and the importance of thorough site characterization prior to well placement.

Applications

ASTM D6725/D6725M-16 delivers practical value for various sectors:

• Environmental Site Assessment: Environmental consultants and engineers use this method for efficient monitoring well installation, minimizing site disruption and reducing hazardous waste.
• Groundwater Monitoring Programs: Environmental compliance, remediation projects, and long-term water quality monitoring rely on these procedures to sample and analyze aquifer conditions.
• Contaminant Detection: Direct push installed monitoring wells provide rapid and cost-effective means of confirming the presence and extent of groundwater contamination.
• Hydrogeological Studies: By allowing the measurement of water levels and aquifer properties, this practice supports the development of conceptual site models and informs remediation strategies.
• Regulatory Compliance: Adhering to the standard ensures monitoring well installation meets accepted environmental and public health standards, reducing the risk of regulatory non-conformance.

Related Standards

To provide comprehensive guidance throughout groundwater site investigations, ASTM D6725/D6725M-16 references and complements several related ASTM standards, including:

• ASTM D5092: Practice for Design and Installation of Groundwater Monitoring Wells
• ASTM D6001: Guide for Direct-Push Groundwater Sampling for Environmental Site Characterization
• ASTM D6724: Guide for Installation of Direct Push Groundwater Monitoring Wells
• ASTM D5088: Practice for Decontamination of Field Equipment Used at Waste Sites
• ASTM D5778: Test Method for Electronic Friction Cone and Piezocone Penetration Testing of Soils
• ASTM D6634: Guide for Selection of Purging and Sampling Devices for Groundwater Monitoring Wells

By following ASTM D6725/D6725M-16, organizations can ensure accurate, efficient, and environmentally responsible installation of monitoring wells in unconsolidated aquifers-an essential step in groundwater protection and site remediation.

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: D6725/D6725M − 16
Standard Practice for
Direct Push Installation of Prepacked Screen Monitoring
Wells in Unconsolidated Aquifers
This standard is issued under the fixed designation D6725/D6725M; 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 standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice is based on recognized methods by which
responsibility of the user of this standard to establish appro-
direct push monitoring wells may be designed and installed for
priate safety and health practices and determine the applica-
the purpose of detecting the presence or absence of a
bility of regulatory limitations prior to use.
contaminant,andcollectingrepresentativegroundwaterquality
1.7 This practice offers a set of instructions for performing
data. The design standards and installation procedures herein
one or more specific operations. This document cannot replace
are applicable to both detection and assessment monitoring
education or experience and should be used in conjunction
programs for facilities.
with professional judgement. Not all aspects of this practice
1.2 The recommended monitoring well design, as presented
may be applicable in all circumstances. This ASTM standard is
inthispractice,isbasedontheassumptionthattheobjectiveof
not intended to represent or replace the standard of care by
the program is to obtain representative groundwater informa-
which the adequacy of a given professional service must be
tionandwaterqualitysamplesfromaquifers.Monitoringwells
judged, nor should this document be applied without consid-
constructed following this practice should produce relatively
eration of the project’s many unique aspects. The word
turbidity-free samples for granular aquifer materials ranging
“Standard” in the title of this document means only that the
from gravels to silty sand.
document has been approved through the ASTM consensus
1.3 Direct push procedures are not applicable for monitor-
process.
ing well installation under all geologic and soil conditions (for
example, installation in bedrock). Other rotary drilling proce-
2. Referenced Documents
dures are available for penetration of these consolidated
2.1 ASTM Standards:
materials for well construction purposes (Guide D5092).
D653 Terminology Relating to Soil, Rock, and Contained
Additionally, under some geologic conditions it may be appro-
Fluids
priate to install monitoring wells without a filter pack (1, 2) .
D1586 Test Method for Penetration Test (SPT) and Split-
Guide D6724 may be referred to for additional information on
Barrel Sampling of Soils
these and other methods for the direct push installation of
D3740 Practice for Minimum Requirements for Agencies
groundwater monitoring wells.
Engaged in Testing and/or Inspection of Soil and Rock as
1.4 The values stated in either inch-pound units or SI units
Used in Engineering Design and Construction
presented in brackets are to be regarded separately as standard.
D4043 Guide for Selection of Aquifer Test Method in
The values stated in each system may not be exact equivalents;
Determining Hydraulic Properties by Well Techniques
therefore,eachsystemshallbeusedindependentlyoftheother.
D4044 Test Method for (Field Procedure) for Instantaneous
Combining values from the two systems may result in non-
Change in Head (Slug) Tests for Determining Hydraulic
conformance with the standard.
Properties of Aquifers
D4104 Test Method (Analytical Procedure) for Determining
1.5 All observed and calculated values shall conform to the
Transmissivity of Nonleaky Confined Aquifers by Over-
guidelines for significant digits and rounding established in
damped Well Response to Instantaneous Change in Head
Practice D6026, unless superseded by this standard.
(Slug Tests)
D4448 Guide for Sampling Ground-Water Monitoring Wells
This practice 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 15, 2016. Published August 2016. Originally
approved in 2001. Last previous edition approved in 2010 as D6725–04(2010). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/D6725_D6725M-16. contactASTM Customer Service at [e-mail]. ForAnnual Book ofASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. 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
D6725/D6725M − 16
D4750 Test Method for Determining Subsurface Liquid Contaminant Logging with the Membrane Interface Probe
Levels in a Borehole or Monitoring Well (Observation (MIP)
Well) (Withdrawn 2010) D7929 Guide for Selection of Passive Techniques for Sam-
D5088 Practice for Decontamination of Field Equipment pling Groundwater Monitoring Wells
Used at Waste Sites
3. Terminology
D5092 Practice for Design and Installation of Groundwater
Monitoring Wells
3.1 Definitions—For common definitions of terms in this
D5434 Guide for Field Logging of Subsurface Explorations
standard, refer to Terminology D653.
of Soil and Rock
3.2 Definitions:
D5521 Guide for Development of Groundwater Monitoring
3.2.1 tremie pipe, n—in wells, a small-diameter pipe or tube
Wells in Granular Aquifers
that is used to transport filter pack materials and annular seal
D5785 Test Method for (Analytical Procedure) for Deter-
materials from the ground surface into an annular space.
mining Transmissivity of Confined NonleakyAquifers by
(D5092).
Underdamped Well Response to Instantaneous Change in
Head (Slug Test) 3.3 Definitions of Terms Specific to This Standard:
D5786 Practice for (Field Procedure) for Constant Draw- 3.3.1 dual tube systems, n—a system whereby inner and
down Tests in Flowing Wells for Determining Hydraulic outer tubes are advanced independently or simultaneously into
Properties of Aquifer Systems the subsurface strata.
3.3.1.1 Discussion—The outer casing tube is used for bore-
D5787 Practice for Monitoring Well Protection
D5881 Test Method for (Analytical Procedure) Determining hole stabilization. The inner rod system is used for sampler
recovery and insertion of other devices.
Transmissivity of Confined Nonleaky Aquifers by Criti-
cally Damped Well Response to Instantaneous Change in
3.3.2 prepacked screen—a manufactured well screen that is
Head (Slug)
assembled with a slotted inner casing and an external filter
D5912 Test Method for (Analytical Procedure) Determining
media support. The external filter media support may be
Hydraulic Conductivity of an Unconfined Aquifer by
constructedofastainlesssteelwiremeshscreenorslottedPVC
Overdamped Well Response to Instantaneous Change in
that retains filter media in place against the inner screen. The
Head (Slug) (Withdrawn 2013)
filter media is usually composed of graded silica sand.
D6001 Guide for Direct-Push Groundwater Sampling for
Environmental Site Characterization
4. Summary of Practice
D6026 Practice for Using Significant Digits in Geotechnical
4.1 This practice provides information for installing a pre-
Data
packed screen monitoring well using direct push techniques.
D6067 Practice for Using the Electronic Piezocone Pen-
When constructed following this Standard Practice the direct
etrometer Tests for Environmental Site Characterization
push installed monitoring wells can meet most local regula-
D6151 Practice for Using Hollow-StemAugers for Geotech-
tions and environmental guidelines (2-5) for well construction
nical Exploration and Soil Sampling
(Fig. 1) and protection of the aquifer and groundwater re-
D6282 Guide for Direct Push Soil Sampling for Environ-
sources.
mental Site Characterizations
4.2 Initially the outer casing tube of the dual tube system is
D6285 Guide for Locating Abandoned Wells
advanced to depth using direct push methods. The monitoring
D6286 Guide for Selection of Drilling Methods for Environ-
well is constructed inside the casing with prepacked well
mental Site Characterization
screens and riser pipe. The casing tube is retracted to set the
D6542 Practice for Tonnage Calculation of Coal in a Stock-
well at the desired depth in the formation. Bottom up tremie
pile
installation of the annular seal and grout is conducted through
D6634 Guide for Selection of Purging and Sampling De-
the outer casing as it is retracted. This grouting method is
vices for Groundwater Monitoring Wells
advised to obtain the highest integrity well construction.
D6724 Guide for Installation of Direct Push Groundwater
Commonly available types of above ground or flush mount
Monitoring Wells
well protection are installed to physically protect the well and
D6771 Practice for Low-Flow Purging and Sampling for
prevent tampering (D5787). The small diameter wells may be
Wells and Devices Used for Ground-Water Quality Inves-
developed using bailers, peristalic pumps, bladder pumps or an
tigations (Withdrawn 2011)
inertial check valve system (D6542). The inertial check valve
D6914 Practice for Sonic Drilling for Site Characterization
and tubing system is especially effective when used for
and the Installation of Subsurface Monitoring Devices
development in medium to coarse-grained aquifers. This de-
D7242 Practice for Field Pneumatic Slug (Instantaneous
velopment method simultaneously surges and purges fines
Change in Head) Tests to Determine Hydraulic Properties
from the screen interval. Slug testing of the wells (D7242) can
of Aquifers with Direct Push Groundwater Samplers
be conducted to determine local aquifer properties and verify
D7352 Practice for Direct Push Technology for Volatile
that development has been successful. Low flow (D6771) and
other sampling techniques (D4448, D7929) may be used to
obtainrepresentativewaterqualitysamples.Clearandaccurate
The last approved version of this historical standard is referenced on
www.astm.org. documentation of the well construction is advised.
D6725/D6725M − 16
NOTE 1—This well design is consistent with most regulatory requirements promulgated prior to development of direct push techniques (after Practice
D5092)
FIG. 1 Specifications for Conventional Monitoring Wells Installed with Rotary Drilling Methods.
5. Significance and Use information on the potentiometric surface of the local aquifer
and properties of the formation such as hydraulic conductivity
5.1 This practice is intended to provide the user with
or transmissivity.
information on the appropriate methods and procedures for
installing prepacked screen monitoring wells by direct push
5.2 Use of direct push methods to install monitoring wells
methods. The monitoring wells may be used to obtain repre-
can significantly reduce the amount of potentially hazardous
sentative water quality samples for aqueous phase contami-
drillcuttingsgeneratedduringwellinstallationatcontaminated
nants or other analytes of interest, either organic or inorganic
sites. This may significantly reduce cost of an environmental
(3, 6-8). The monitoring wells may also be used to obtain
D6725/D6725M − 16
site investigation and groundwater monitoring program. Mini- information obtained during the site characterization activities
mizing generation of hazardous waste also reduces the expo- and background research. In general at least one well is placed
sure hazards to site workers, local residents, and the environ- at a depth and location considered to represent undisturbed
ment. background water quality conditions. The length and depth of
the screened interval for the background well(s) should reflect
5.3 Direct push methods for monitoring well installation are
those of the wells installed hydraulically down gradient of the
limited to use in unconsolidated formations such as alluvial/
site. Information obtained during site characterization regard-
stream sediments, glacial deposits, and beach type sediments.
ing local hydrogeology, water level(s), contaminant
Direct push methods are generally successful at penetrating
distribution, and groundwater flow direction should be used to
clays, silts, sands and some gravel. Deposits such as soils with
determine appropriate well placement. If multiple aquifers
thick caliche layers, or glacial tills with large cobbles or
separated by aquitards are present beneath the site monitoring
boulders may be difficult or impossible to penetrate to the
wells with screened intervals at multiple depths may be needed
desired depth. Direct push methods are not designed for
at each location. The purpose for installation should be
penetration of consolidated bedrock such as limestone, granite
considered in selecting the locations of the monitoring wells.
or gneiss.
Purposes may include detection monitoring, long term
NOTE 1—The quality of the result produced by this standard is
monitoring, or data collection to determine the presence,
dependent on the competence of the personnel performing it, and the
extent, and concentrations of potential contaminants. Guidance
suitability of the equipment and facilities used. Agencies that meet the
on selection of well locations, screen lengths and intervals are
criteria of Practice D3740 are generally considered capable of competent
found m several references, some of which are: (1, 3-5, 9-15).
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
7. Monitoring Well Construction Materials
provides a means of evaluating some of those factors.
Practice D3740 was developed for agencies engaged in the laboratory 7.1 General—Thematerialsthatareusedintheconstruction
testing and/or inspection of soils and rock. As such, it is not totally
of a prepacked screen monitoring well should not measurably
applicabletoagenciesperformingthisfieldpractice.However,userofthis
alter the chemistry of the groundwater sample(s) to be col-
practice should recognize that the framework of Practice D3740 is
lected when appropriate sample collection methods are used.
appropriate for evaluating the quality of an agency performing this
Ideally, PVC should not be used when monitoring for neat
practice. Currently there is no known qualifying national authority that
inspects agencies that perform this practice.
organic solvents that are PVC solvents (16). While conven-
tional steel materials (for example, carbon steel or galvanized
6. Site Characterization and Well Placement
steel) are not suitable for use under most groundwater moni-
toringconditionsstainlesssteelhasbeenfoundtoperformwell
6.1 Characterization—Understanding the project goals as
wellasthesubsurfacegeology,hydrogeology,andcontaminant in most corrosive environments, particularly under oxidizing
conditions (11). In most cases Type 304 stainless steel will
distribution at a site is necessary before installation of moni-
toring wells can be completed successfully. Steps in a site perform satisfactorily for many years (17, 18). Under highly
corrosive and reducing conditions Type 316 stainless steel will
characterization program may include investigating site
history, literature search, site reconnaissance, and field inves- perform better than Type 304 stainless steel (11). The pre-
packed screens and well casing used in the well construction
tigation and sampling efforts. The field investigation may
should be delivered from the manufacturer to the field site in a
include completion of borings to collect soil and groundwater
clean state sealed in protective wrapping.Any other equipment
samples and to determine the groundwater flow direction.
used in the well construction process (for example, casing,
Geophysical methods may also be applied to obtain an under-
measuringtapes,grouthoses,otherdownholetools)thatcould
standing of the subsurface geology. Several ASTM standards
impact the resultant water quality should be cleaned and
are available for use in conducting the site characterization and
sampling efforts; these include water sampling Guide D6001, decontaminated following appropriate methods (Practice
D5088) prior to use in the well installation. Additional guid-
soil sampling Guide D6282, cone penetrometer Practice
D6067, slug testing Test Method D4044 and Practice D7242, ance and information on well construction practices can be
obtained from Practice D5092.Always verify compliance with
standard penetration Test Method D1586, and membrane
interface probe (D7352). Other important sources of informa- local regulations by contacting the appropriate regulating
agency or organizations.
tion include local agencies having responsibilities for ground-
waterprotectionandregulation.Alistofgeologicalsurveysare
7.2 Water—In general, little water is used in the construc-
included in Guide D6285. Depending on site conditions, when
tion of direct push installed prepacked screen wells other than
direct push methods are used for site characterization (for
in preparation of annular seal and grout mixtures. However,
example, D6001 and D6282) it may be possible to complete
there are situations that may require addition of water to the
the site characterization and monitoring well installation ac-
well or borehole during installation. One of the most common
tivities in one mobilization. Practice D5092 provides further
situations that may require addition of water is under drilling
details on site characterization necessary for successful instal-
conditions where formation blow-in may occur. Under these
lation of monitoring wells and development of a site concep-
conditions (most often saturated sands) water must be added to
tual model.
the boring to prevent blow-in and assure that the well is
6.2 Well Placement—The well location, depth and length of properly installed at the desired depth. When water is used in
screen interval should be based on project requirements, the well installation and construction process (to prevent
D6725/D6725M − 16
blow-in, or mix grout) water of known quality (generally further details on the selection of screen slot size refer to
potablewater)thatwillnotadverselyaffectthesamplemustbe Practice D5092. The most widely available slot size is 10 slot,
used to ensure that the sample integrity will not be compro-
0.010-in. [0.25 mm] in the prepacked well screens. The slot
mised. The volume of water added to each well must be
sizeusedfortheinternalwellscreenshouldretainatleast90 %
documented.
of the filter media.
7.3.2 External Filter Media Support—The purpose of the
7.3 Prepacked Screen—Therearethreeprimarycomponents
of the prepacked well screen (Fig. 2). These are the internal externalfiltermediasupportistwofold.Theprimarypurposeis
wellscreen,theexternalfiltermediasupport,andthecontained to retain the filter media around the internal well screen as the
filter media (sand pack). Some prepack screens are assembled
screen is being placed in the boring. Additionally the external
withtheinternalPVCscreenasanintegralpartoftheassembly filter media support assures accurate and complete placement
(Fig. 2a). Alternatively, some prepack screens are available as
ofthefilterpackmediainthedesiredscreeninterval.Emplace-
sleeves or jackets (Fig. 2b) that may be installed over factory
ment of the filter media in this fashion eliminates problems
available casing. The components used in construction of the
with formation collapse against bare screen or bridging and
prepacked well screen must not adversely affect the ground-
creation of voids around the bare screen as when gravity
water quality so that representative samples may be acquired.
installation of the filter media is conducted. One of the most
Subsurface conditions, including but not limited to site
common materials used for construction of this screen compo-
geology, geohydrology, groundwater chemistry, and the ana-
nent is a stainless steel wire mesh. Slotted PVC, fluoropoly-
lytes to be monitored must be considered to assure that the
mers or other compatible materials may be used for construc-
prepacked well screens are compatible with the system to be
tion of this screen component when and where appropriate.
monitored.Asump may be attached to the base of the screen to
The external diameter of the prepacked screen ranges from
capture any fines enteringthewell.Thebottomofthescreenor
about 1.4- to 3.0-in. [35 to 75 mm], depending on the inner
sump must be sealed with a plug constructed of compatible
well screen diameter and the inside diameter of the probe rods
material. The prepacked well screen must be of sufficient
used to advance the boring.
strength to withstand the forces and stress of installation and
7.3.3 Filter Media—The filter media or gravel pack most
development without being damaged or otherwise compro-
commonly consists of uniformly graded siliceous particles
mised. Some of the prepacked well screens are packed with
washed and screened to have the appropriate particle size
filter media by the manufacturer. Other prepacked screens are
distribution. Refer to Practice D5092 for details on the selec-
shipped without filter media and are packed in the field with
tion of appropriate grain size distribution for the filter media.
acceptable filter media materials just prior to installation.
One of the most widely used grain size distributions for
7.3.1 Internal Well Screen—The most common material
prepacked screen well filter media is 20-40 grade silica sand.
used for construction of this component is polyvinyl chloride
However, finer grained formations may require finer sand
(PVC). Other materials (for example, stainless steel or fluo-
gradation (see Practice D5092).
ropolymers) may be used where and when appropriate. Rou-
7.3.4 Sump—The sump is usually constructed of a length of
tinely used internal well screen diameters include nominal
0.5-in., 0.75-in., and 1.0-in. [15, 25, 50 mm] PVC. For well casing material ranging from a few inches in length to
optimumperformanceofthewellthescreenslotsizeshouldbe several feet [1 m] in length depending on the well design and
determined relative to the grain size analysis of the stratum to formation characteristics. It is attached to the base of the well
be monitored and the gradation of the filter pack material. For screenandispluggedatthebottom.Thesumpprovidesaspace
NOTE 1—The internal well screen is usually constructed of Schedule 40 or 80 PVC (a) with a factory cut 0.010 in. slots while some are available with
0.25 slots. The external filter media support is usually constructed with stainless steel wire cloth with pore size of approximately 0.011 in. and graded
silica sand or equivalent material is used for the filter media. Some prepacked screens are available as sleeves or jackets (b) that slide over factory
available slotted PVC.
FIG. 2 Typical Prepacked Well Screens.
D6725/D6725M − 16
for fine sediments entering the well to settle without obstruct- 7.6.1 Annular Seal—Regulations may recommend the use
ing a portion of the screen interval and interfering with of sodium bentonite in construction of the annular seal imme-
recharge or sampling activities. The sump also allows for the
diately above the grout barrier. Recent research on sealing
collection of dense nonaqueous phase fluids (DNAPLs) at
methods shows that bentonite seals are not effective above the
locations where they are present.
water table and that a minimum of 20 % solids mix should be
used for grouting (Practice D5092). Different sealants may be
7.4 Casing or Riser—The well casing should be made of
needed when subsurface geology, chemistry of the
clean, new materials that will not alter the quality of the water
groundwater, or high concentrations of contaminants are pres-
samples being collected. Most casing or riser is made of PVC
ent. When present in high concentrations, some organic con-
but other materials (for example, stainless steel,
taminantscancausedesiccationandcrackingofbentoniteseals
fluoropolymers, etc.) may be appropriate in some situations.
resulting in cross contamination of the well and potential
The inside diameter and wall thickness of the casing should
migrationofcontaminantstoapreviouslycleanaquifer.Efforts
match that of the internal well screen of the prepacked well.
should be taken in the site characterization program to deter-
Threaded and flush jointed casing fitted with o-rings of
mine if these conditions may exist at the site. Annular seals
appropriatematerialaregenerallyrecommendedforthecasing.
Glued or solvent welded joints are not recommended as the may be installed by gravity or tremie methods and modular
glues and solvents generally contain hazardous chemicals that seals are available for some prepacked well systems.
can cause contamination of the groundwater to be sampled.
7.6.1.1 Gravity and Tremie Installations—Bentonite chips,
The casing and casing joints must be of sufficient strength to
granules, or pellets may be used to construct the annular seal
withstand the forces of installation and development. Further
when the field conditions and size of the well annulus permit.
information on the selection of appropriate casing materials
Gravityortremieinstallationofthesedrybentonitematerialsis
can be found in Practice D5092 and (1, 10-12, 15, 17-21).
most successful when the top of well screen is at or near the
7.5 Grout Barrier—The grout barrier serves to prevent the water table. Use of a small diameter tremie tube and grout
pump with bentonite slurries may provide the most reliable
annular sealants from entering into the screen interval resulting
in the alteration of the water chemistry, because common method of placing the annular seal (Fig. 4). Bentonite slurries
annular sealants and grouts (for example, bentonite and Port- ranging from 20 to 30 % solids by weight are required. Check
land cement) can have a significant impact on the local the local regulations to verify compliance. A side port tremie
groundwater chemistry a grout barrier is emplaced immedi- tube may be used to reduce the jetting of the slurry into the
ately above the screened interval. The grout barrier may be
grout barrier.
constructed by gravity or tremie installation of fine sand or by
7.6.1.2 Modular Seals—These seals are constructed with
installation of a mechanical or modular barrier.
paper sleeves containing bentonite attached to a segment of
7.5.1 Gravity or Tremie Installation—The grout barrier may
blank casing. This modular seal (Fig. 3) is placed above the
be constructed with silica sand having the same or finer
grout barrier (modular) and prepacked screens to provide an
gradation than the materials used in the filter media. When the
annular seal.
filter media is course-grained use of a finer grained grout
7.6.2 Grout—There are two primary types of grout slurry
barrier is recommended. The grout barrier usually extends 1 to
used in monitoring well construction. These are bentonite
2 ft [1 m] above the top of the screened interval. The granular
grouts and cement grouts. The grout slurries should be mixed
material used for the grout barrier may be poured through the
until smooth to prevent clogging of the tremie tube. Local
annular space in the well for installation or placed through a
regulations for grout compositions and density vary consider-
tremie tube if conditions permit (see 9.4.1).
ably and these regulations should be reviewed to assure
NOTE 2—Slowly add the barrier material to prevent bridging and to
compliance. Additional information on grouting requirements
allow time for the material to settle through the water column.
is provided in Practice D5092 and (22).
7.5.2 Modular Barriers—Some direct push well systems
7.6.2.1 Bentonite Grout—Some bentonite powders contain
offertheoptionofinstallingamodulargroutbarrier(see9.4.1).
additives to accelerate the gelling of the slurry and increase
This modular barrier is assembled with the screen and casing
viscosity. For the smaller diameter direct push installed moni-
and lowered into the well annulus. When the outer casing is
toring wells where a small well annulus may require the use of
retracted this modular barrier expands and creates a seal above
smalldiametertremietubestheseadditivesmaycauseclogging
the prepacked screen. These modular barriers are constructed
of the tremie tube. The use of bentonite powders (200 mesh)
with polyurethane foam covered with a polyethylene sleeve.
without additives is commonly used for grout when small
Thesemodularbarriersarenotrecommendedforusebelowthe
diameter tremie tubes are advised. In general bentonite slurry
water table because of potential for absorption and desorption
densities of 20 to 30 % solids by weight are required by
of some contaminants.
regulation. A 20 % solids by weight bentonite slurry may be
prepared by adding 2.0 lb [0.9 kg] of bentonite powder to 1 gal
7.6 Annular Seal and Grout—Theannularsealandgroutare
[3.8 L] of clean water (D5092). Bentonite grouts are recom-
prepared of materials that will eliminate or at least reduce the
mended for use only in the saturated zone as dessication may
potential for surface or up-hole water (or fluids) from moving
down the well annulus. This is important because these fluids occurintheunsaturatedzonecompromisingtheintegrityofthe
seal (22).Additional information on grout mixtures is provided
could significantly alter the water quality or cause cross
contamination in the zone being monitored. in Practice D5092 and regulations should be consulted.
D6725/D6725M − 16
FIG. 4 Another option for installation of the annular well seal is with a side-port tremie tube and grout pump. This may be the most ef-
fective option when the screen is below the water table.
FIG. 3 Some direct push prepacked well systems use modular grout barriers and modular annular seals attached to the well casing.
The modular foam barrier, used primarily above the water table, expands when the drive casing is retracted. The modular annular seal
with polyethylene barrier is used below the water table. The bentonite in the modular seal is hydrated by the groundwater and expands
to seal the annulus prior to grouting.
7.6.2.2 Cement Grout—Cements containing additives to cement shrinks away from the casing and this problem can be
accelerate the setting process are not recommended for use in alleviated by using a metal riser in that section or non-shrink
cement (D5092).
grouting.These additives may prematurely cause thickening of
the slurry and result in clogging of the tremie tube used for
7.7 Well Protection—There are two primary types of well
bottom up installation.Additionally, these additives may leach
protection commonly used for monitoring wells, these are
from the grout and alter the local water chemistry. In most
above-ground and flush mount well protectors. The above
cases neat cement shouldbeusedforgrouting.Cementgroutis
ground protector is used in locations where vehicular traffic is
typically mixed by adding one 94-lb [50-kg] bag of Type I
notaconcern.Theabovegroundprotectionisalsomorewidely
portland cement to 6 to 7 gal [22-27 L] of clean water, check
approved because of its ability to eliminate or at least reduce
local regulations to verify compliance. When small diameter
the potential for surface runoff to enter the well head and thus
tremie tubes are required it is best to use fresh cement so that
contaminate the local aquifer. Flush mount well protection is
lumps of hardened cement will not clog the tremie tube.
used in areas where vehicular traffic is a concern. Most
Additional information on grout mixtures is provided in agencies require a regulatory variance for use of this well
Practice D5092 and applicable local regulations should be
protection design because of the increase in potential for cross
consulted. Research (22) as shown that in the unsaturated zone contamination of the local aquifer by infiltration from surface
D6725/D6725M − 16
runoffwatersorchemicalspills.Checklocalregulationsbefore subsurface using the static force of the vehicle weight. Large
using flush mount protection and obtain the necessary vari- CPT trucks (Fig. 6) may use anchors or add ballast to the
ance(s)whereneeded.Furtherspecificationsonwellprotection vehicles (tanks of water, or lead blocks) to increase vehicle
are available in Practice D5787. weightanddepthofpenetration.Capabilitiesandlimitationsof
the static weight method are similar to those of the percussion
8. Direct Push Methods
methods.
8.1 General—There are three basic methods for advancing 8.1.3 Sonic or Resonance Drilling Methods—These are
direct push tools into the subsurface. Traditionally, cone generally more powerful drilling methods that combine high
penetration testing (CPT) equipment (D6067) has used the frequency sonic or resonance with rotary action to advance
static weight of the vehicle (15 to 30 tons), sometimes coupled tools into the subsurface (D6914). These methods can gener-
with anchors, to advance tools down hole. Smaller and lighter ally penetrate to greater depths than percussion or static
weight direct push vehicles rely on percussion methods to- methods and have been used to penetrate difficult formations
gether with vehicle weight to advance tools. Another method such as cobble rich glacial till.
for advancing tools or casing into the subsurface is sonic or 8.1.4 Rotary Drilling—Some conventional rotary drilling
resonance drilling (D6914). This method uses high frequency
methods can be combined with direct push methods for
percussion combined with rotary action to advance tools and
sampling and well installation (D6286). Hollow stem augers
casing into the subsurface. A review of the local geologic
(Fig.6)(D6151)aresometimesadvancedtodepthandthenthe
conditions and any available records of previous sampling by
hydraulic hammer generally used for standard penetration
direct push or rotary drilling methods should be conducted
testing (Test Method D1586) may be used to advance tools or
prior to mobilization to determine which direct push method
casing ahead of the augers. Occasionally, the manual cathead-
should be applied for well installation at the site under
and-rope method is used to advance tools or casing ahead of
consideration. If site specific conditions are not amenable to
the augers to facilitate sampling or well installation.
directpushmethodsotherrotarydrillingmethods(D6286)may
8.2 Advantages and Limitations—Direct push methods have
be reviewed for potential use.
some advantages and limitations when compared to rotary
8.1.1 Percussion Methods—Advancement of tools or casing
drilling methods. One of the primary advantages of direct push
into the subsurface with percussion methods can be completed
methods is that essentially no waste cuttings are generated as
with hydraulic, pneumatic and mechanically operated ham-
the tool string or casing is advanced into the subsurface. At
mers. These hammers are used in conjunction with hydraulic
locations where hazardous contaminants may be present this
slides and vehicle weight to advance tools. Typical DP units
significantly reduces the handling, drumming, storage,
maybemountedintrucksorothervehicles(Fig.5)tofacilitate
sampling, testing, transportation, and disposal of contaminated
site access. The percussion procedures are some of the most
cuttings. Elimination of these waste handling and disposal
widely used direct push methods. These methods are generally
activities will not only reduce cost but also reduce potential
capable of penetrating clays, silts, sands, and some gravel as
exposure hazards for site workers, local residents and the
commonly encountered in alluvial and glacial deposits. Moni-
environment. Direct push methods are generally limited to
toring wells are routinely installed at depths of 20 to 50 ft [10
unconsolidated formations composed of clays, silts, sands and
to 15 m] with percussion methods, and may be installed at
some gravel. Conventional rotary drilling methods will be
depths exceeding 200 ft [60 m] in amenable geologic condi-
required for penetration of consolidated bedrock (for example,
tions.Denselypackedglacialdeposits,depositswithcobblesor
limestone,granite,gneiss)andsomeverydenseunconsolidated
boulders, or thick zones of caliche may make penetration with
formations or formations with an abundance of cobbles or
percussion methods difficult or impossible. Some percussion-
boulders.
type direct push units are also equipped with rotary drilling
capabilities. These capabilities make it possible for direct push
9. Monitoring Well Installation
methods to be used where a significant gravel, cobble, or
caliche layer may have previously limited their use. 9.1 General—Severaloftheproceduresdescribedbeloware
8.1.2 Static Weight Methods—Cone penetration (CPT) sys- similar to those used for installation of monitoring wells by
tems are the most commonly used static weight method for rotary drilling techniques and Practice D5092 may be refer-
advancing tools and installing monitoring wells (D6067). enced for additional information or guidance as needed.
Hydraulic rams are used to advance the tool string into the Manufacturer’s standard operating procedures for installing
FIG. 5 Typical percussion type direct push units are often mounted in conventional pick-up trucks or more rugged track vehicles for
access to difficult locations. Some percussion-type units, such as the track unit shown here, are fitted with optional auger heads.
D6725/D6725M − 16
FIG. 6 Hydraulics and SPT hammers on rotary drilling rigs may be used to advance direct push tools under some conditions. CPT
units may weigh from 15 to 30 tons. These vehicles have been used to install monitoring wells by direct push methods at many loca-
tions.
direct push prepacked screen monitoring wells (23-25) may 9.2.1 Advance Casing—Information from the site character-
also provide additional information on installation techniques.
ization is used to determine the appropriate depth and screen
Installation of monitoring wells in an open/uncased borehole is length for each well. The direct push unit is set up over the
not recommended for direct push or rotary drilling procedures.
proposed well location and leveled. Depending on the specific
Installationofamonitoringwellthroughanopenboreholemay
well construction and casing advancement procedures to be
result in slough of potentially contaminated material down the
used either an expendable point, anchor point, or expendable
well bore either prior to or during the well installation
cutting shoe is installed on the lead casing section. If the dual
procedure. This can lead to cross contamination and water
tube casing is to be advanced without sampling either an
quality samples that are biased and inaccurate and ultimately
expendable point or expendable anchor point (Fig. 7) is placed
abandonment and replacement of the incorrectly installed well.
in the lead casing section. If continuous or targeted dual tube
While open hole installation of temporary piezomenters for
soil sampling (see Guide D6282) is to be conducted as the
water level monitoring in uncontaminated formations may be
casing is advanced an expendable cutting shoe (Fig. 8) can be
acceptable this is not an acceptable installation method for
installed on the lead casing section to permit well installation
monitoring wells to be used for water quality sampling.
after sampling is completed. The appropriate drive cap (Fig. 7)
is used to advance the tool string to depth. New sections of
9.2 Installation of Drive Casing—The direct push method
casing are added incrementally as needed to achieve the
(percussion, static, sonic) which is selected based on site
conditions is used to advance the drive casing to the desired desired depth. To prevent the infiltration of potentially con-
taminated formation water as the casing is advanced o-rings or
depth. Use of O-rings or Teflon tape on casing joints is
recommended to eliminate the potential for cross contamina- other acceptable materials (for example, PTFE tape) may be
tion as the tools are advanced to depth. usedtosealeachcasingjoint.Awaterlevelindicatorshouldbe
NOTE 1—Some prepack well systems are available with expendable anchor points with either a thread or click on mechanism to anchor the screens
in position.
FIG. 7 Advanced Direct Push Casing (or probe rod) to Depth with an Expendable Point to Prepare for Installation of a Prepacked
Screen Monitoring Well.
D6725/D6725M − 16
FIG. 8 When an expendable cutting shoe is used during dual tube soil sampling prepacked screens may be installed after sampling is
completed. In saturated noncohesive formation (sands) it may be necessary to add water to the probe rods to prevent blow-in during
sample collection activities.
used to check the bore of the rods prior to installation of the screen section or sections are assembled and riser added as the
prepacked screens to determine if water is present (D4750). If
screen(s)is(are)loweredthroughthecasing(Fig.9).Sufficient
potentially contaminated water is present in the drive rods it PVC riser is added to the assembly so that the final piece of
should be evacuated before continuing with the well installa-
riser extends above the drive casing. If an expendable anchor
tion.
point is used the adapter on the base of the screen is attached
9.2.2 Assembly and Installation of Screen and Riser—The
to the anchor point. If a threaded anchor point is used, the
well screens to be installed may have been prepacked by the
screenattachesdirectlytothepointbythreadingthebaseofthe
manufacturer prior to shipping, or may require addition of the
PVC onto the anchor point.
filter media in the field before installation. Follow the manu-
9.3 Retraction of Drive Casing—To deploy the assembled
facturer’s specifications for adding the filter media to prepack
prepackedwellscreenandrisersthedirectpushcasingmustbe
the screens. If an expendable point or cutting shoe is used in
retracted. A rod retraction system that allows for access to the
the installation then the lower end of the screen or sump will
open ID of the casing is recommended. Such a system will
require a bottom plug (Fig. 8).Athreaded anchor point may be
enable the operator to confirm that the well screen(s) and riser
used and in this situation the base of the screen or sump is
threaded directly onto this point to seal the bottom of the well stay at the required depth as the casing is retracted. The unit
hydraulics are used with the retraction tools to retract the
(Fig. 9). If an expendable anchor point is to be used to anchor
thewellscreen(s)intheformationanadapter(Fig.9)mayhave casing above the top of the screened interval. If the casing is
to be installed in the base of the screen or sump. Then the advanced well below the static water level of the aquifer in a
NOTE1—Asimpleplugmaybeaddedtothebaseofthewellscreensandasumpmaybeused.Aspecialadaptermaybeusedifthescreensareattached
to an expendable anchor point. Some threaded anchor points make it possible to thread the PVC screen directly to the point.
FIG. 9 Lowering Assembled Prepacked Screens Through the Casing as PVC Riser is Added to the Well Assembly.
D6725/D6725M − 16
cohesionless formation it may be necessary to add water (of 9.4.2 Modular Grout Barrier—There are at least two types
known quality) to the annulus of the rods prior to retracting the ofbarriersthatfallinthiscategory.Thefirstisasealcomprised
screen to prevent flow of formation materials between the of a polyurethane foam and the second is a combination of a
screen and casing. If flow-in occurs the prepacked screen can modular bentonite annular seal with a polyethylene sleeve
become lodged inside the casing. If for any reason the barrier (Fig. 3).The foam seal may be thre
...

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: D6725 − 04 (Reapproved 2010) D6725/D6725M − 16
Standard Practice for
Direct Push Installation of Prepacked Screen Monitoring
Wells in Unconsolidated Aquifers
This standard is issued under the fixed designation D6725;D6725/D6725M; 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 practice is based on recognized methods by which direct push monitoring wells may be designed and installed for the
purpose of detecting the presence or absence of a contaminant, and collecting representative groundwater quality data. The design
standards and installation procedures herein are applicable to both detection and assessment monitoring programs for facilities.
1.2 The recommended monitoring well design, as presented in this practice, is based on the assumption that the objective of the
program is to obtain representative groundwater information and water quality samples from aquifers. Monitoring wells
constructed following this practice should produce relatively turbidity-free samples for granular aquifer materials ranging from
gravels to silty sand. Strata having grain sizes smaller than the recommended design for the smallest diameter filter pack materials
should be monitored by alternative monitoring well designs which are not addressed in this practice.
1.3 Direct push procedures are not applicable for monitoring well installation under all geologic and soil conditions (for
example, installation in bedrock). Other rotary drilling procedures are available for penetration of these consolidated materials for
well construction purposes (Guide D5092). Additionally, under some geologic conditions it may be appropriate to install
monitoring wells without a filter pack (EPA(1, 21991).) . Guide D6724 may be referred to for additional information on these and
other methods for the direct push installation of groundwater monitoring wells.
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 in parentheses are for information only.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 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
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 judgement. 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 the
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.
2. Referenced Documents
2.1 ASTM Standards:
D1452D653 Practice for Soil Exploration and Sampling by Auger BoringsTerminology Relating to Soil, Rock, and Contained
Fluids
D1587D1586 Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical PurposesTest Method for
This practice 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 15, 2016. Published September 2010August 2016. Originally approved in 2001. Last previous edition approved in 20042010
as D6725D6725–04(2010).–04. DOI: 10.1520/D6725-04R10.10.1520/D6725_D6725M-16.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
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.
*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
D6725/D6725M − 16
Penetration Test (SPT) and Split-Barrel Sampling of Soils
D2488D3740 Practice for Description and Identification of Soils (Visual-Manual Procedure)Minimum Requirements for
Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
D3694 Practices for Preparation of Sample Containers and for Preservation of Organic Constituents
D4043 Guide for Selection of Aquifer Test Method in Determining Hydraulic Properties by Well Techniques
D4044 Test Method for (Field Procedure) for Instantaneous Change in Head (Slug) Tests for Determining Hydraulic Properties
of Aquifers
D4104 Test Method (Analytical Procedure) for Determining Transmissivity of Nonleaky Confined Aquifers by Overdamped
Well Response to Instantaneous Change in Head (Slug Tests)
D4448 Guide for Sampling Ground-Water Monitoring Wells
D4700D4750 Guide for Soil Sampling from the Vadose ZoneTest 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
D5314D5434 Guide for Soil Gas Monitoring in the Vadose ZoneField Logging of Subsurface Explorations of Soil and Rock
(Withdrawn 2015)
D5521 Guide for Development of Groundwater Monitoring Wells in Granular Aquifers
D5778 Test Method for Electronic Friction Cone and Piezocone Penetration Testing of Soils
D5781 Guide for Use of Dual-Wall Reverse-Circulation Drilling for Geoenvironmental Exploration and the Installation of
Subsurface Water-Quality Monitoring Devices
D5782 Guide for Use of Direct Air-Rotary Drilling for Geoenvironmental Exploration and the Installation of Subsurface
Water-Quality Monitoring Devices
D5783 Guide for Use of Direct Rotary Drilling with Water-Based Drilling Fluid for Geoenvironmental Exploration and the
Installation of Subsurface Water-Quality Monitoring Devices
D5784 Guide for Use of Hollow-Stem Augers for Geoenvironmental Exploration and the Installation of Subsurface
Water-Quality Monitoring Devices
D5785 Test Method for (Analytical Procedure) for Determining Transmissivity of Confined Nonleaky Aquifers by Underdamped
Well Response to Instantaneous Change in Head (Slug Test)
D5786 Practice for (Field Procedure) for Constant Drawdown Tests in Flowing Wells for Determining Hydraulic Properties of
Aquifer Systems
D5787 Practice for Monitoring Well Protection
D5881 Test Method for (Analytical Procedure) Determining Transmissivity of Confined Nonleaky Aquifers by Critically
Damped Well Response to Instantaneous Change in Head (Slug)
D5912 Test Method for (Analytical Procedure) Determining Hydraulic Conductivity of an Unconfined Aquifer by Overdamped
Well Response to Instantaneous Change in Head (Slug) (Withdrawn 2013)
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
D6151 Practice for Using Hollow-Stem Augers for Geotechnical Exploration and Soil Sampling
D6282 Guide for Direct Push Soil Sampling for Environmental Site Characterizations
D6285 Guide for Locating Abandoned Wells
D6286 Guide for Selection of Drilling Methods for Environmental Site Characterization
D6542 Practice for Tonnage Calculation of Coal in a Stockpile
D6634 Guide for Selection of Purging and Sampling Devices for Groundwater Monitoring Wells
D6724 Guide for Installation of Direct Push Groundwater Monitoring Wells
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—Refer For common definitions of terms in this standard, refer to Terminology D653 for definitions of
terminology.
The last approved version of this historical standard is referenced on www.astm.org.
D6725/D6725M − 16
3.2 Definitions:
3.2.1 tremie pipe, n—in wells, a small-diameter pipe or tube that is used to transport filter pack materials and annular seal
materials from the ground surface into an annular space. (D5092).
3.3 Definitions of Terms Specific to This Standard:
3.3.1 dual tube systems, n—a system whereby inner and outer tubes are advanced independently or simultaneously into the
subsurface strata.
3.3.1.1 Discussion—
The outer casing tube is used for borehole stabilization. The inner rod system is used for sampler recovery and insertion of other
devices.
3.3.2 prepacked screen—a manufactured well screen that is assembled with a slotted inner casing and an external filter media
support. The external filter media support may be constructed of a stainless steel wire mesh screen or slotted PVC that retains filter
media in place against the inner screen. The filter media is usually composed of graded silica sand.
3.2.2 tremie pipe or tube—a pipe or tube that is used to transport filter pack materials and/or annular sealant materials from the
ground surface into the borehole annulus or between casings and casings or riser pipe of a monitoring well.
4. Summary of Practice
4.1 This practice provides information for installing a prepacked screen monitoring well using direct push techniques. When
constructed following this Standard Practice the direct push installed monitoring wells can meet most statelocal regulations and
federalenvironmental guidelines (EPA(2-5) 1986, 1991, 1992) for well construction (Fig. 1) and protection of the aquifer and
groundwater resources.
4.2 Initially the outer casing (or probe rod) tube of the dual tube system is advanced to depth using direct push methods. The
monitoring well is constructed inside the casing with prepacked well screens and riser pipe. The casing tube is retracted to set the
well at the desired depth in the formation. Bottom up tremie installation of the annular seal and grout is conducted through the
outer casing as it is retracted. This grouting method is requiredadvised to obtain the highest integrity well construction. Commonly
available types of above ground or flush mount well protection are installed to physically protect the well and prevent tampering.
tampering (D5787). The small diameter wells may be developed using bailers, peristalic pumps, bladder pumps or an inertial check
valve system. system (D6542). The inertial check valve and tubing system is especially effective when used for development in
medium to coarse-grained aquifers. This development method simultaneously surges and purges fines from the screen interval.
Slug testing of the wells (D7242) can be conducted to determine local aquifer properties and verify that development has been
successful. Low flow (D6771) and other sampling techniques (D4448, D7929) may be used to obtain representative water quality
samples. Clear and accurate documentation of the well construction is required.advised.
5. Significance and Use
5.1 This practice is intended to provide the user with information on the appropriate methods and procedures for installing
prepacked screen monitoring wells by direct push methods. The monitoring wells may be used to obtain representative water
quality samples for aqueous phase contaminants or other analytes of interest, either organic or inorganic (Kram(3, 6-8et). al. 2000,
McCall 2000, McCall et al. 1997). The monitoring wells may also be used to obtain information on the potentiometric surface of
the local aquifer and properties of the formation such as hydraulic conductivity or transmissivity.
5.2 Use of direct push methods to install monitoring wells can significantly reduce the amount of potentially hazardous drill
cuttings generated during well installation at contaminated sites. This may significantly reduce cost of an environmental site
investigation and groundwater monitoring program. Minimizing generation of hazardous waste also reduces the exposure hazards
to site workers, local residents, and the environment.
5.3 Direct push methods for monitoring well installation are limited to use in unconsolidated formations such as alluvial/stream
sediments, glacial deposits, and beach type sediments. Direct push methods are generally successful at penetrating clays, silts,
sands and some gravel. Deposits such as soils with thick caliche layers, or glacial tills with large cobbles or boulders may be
difficult or impossible to penetrate to the desired depth. Direct push methods are not designed for penetration of consolidated
bedrock such as limestone, granite or gneiss.
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.
D6725/D6725M − 16
NOTE 1—This well design is consistent with most state regulatory requirements promulgated prior to development of direct push techniques (after
Practice D5092)
FIG. 1 Specifications for Conventional Monitoring Wells Installed with Rotary Drilling Methods.
6. Site Characterization and Well Placement
6.1 Characterization—Understanding the project goals as well as the subsurface geology, hydrogeology, and contaminant
distribution at a site is necessary before installation of monitoring wells can be completed successfully. Steps in a site
characterization program may include investigating site history, literature search, site reconnaissance, and field investigation and
sampling efforts. The field investigation may include completion of borings to collect soil and groundwater samples and to
determine the groundwater flow direction. Geophysical methods may also be applied to obtain an understanding of the subsurface
geology. Several ASTM standards are available for use in conducting the site characterization and sampling efforts; these include
water sampling Guide D6001, soil sampling Guide D6282, cone penetrometer Practice D5088D6067, Standard slug testing Test
Method D5778D4044, Standard Test Method and D4044, Practice D1452D7242, standard penetration Test Method D1586,
Practice D1587, Practice D2488, Practice D3694, Guide D4448, Guide D4700, Method D4750, and Guide and membrane interface
D6725/D6725M − 16
probe (D5314D7352.). Other important sources of information include state and local agencies having responsibilities for
groundwater protection and regulation. A list of state geological surveys are included in Guide D6285. Depending on site
conditions, when direct push methods are used for site characterization (for example, D6001 and D6282) it may be possible to
complete the site characterization and monitoring well installation activities in one mobilization. Practice D5092 provides further
details on site characterization necessary for successful installation of monitoring wells and development of a site conceptual
model.
6.2 Well Placement—The well location, depth and length of screen interval should be based on project requirements,
information obtained during the site characterization activities and background research. In general at least one well is placed at
a depth and location considered to represent undisturbed background water quality conditions. The length and depth of the screened
interval for the background well(s) should reflect those of the wells installed hydraulically down gradient of the site. Information
obtained during site characterization regarding local hydrogeology, water level(s), contaminant distribution, and groundwater flow
direction should be used to determine appropriate well placement. If multiple aquifers separated by aquitards are present beneath
the site monitoring wells with screened intervals at multiple depths may be requiredneeded at each location. The purpose for
installation should be considered in selecting the locations of the monitoring wells. Purposes may include detection monitoring,
long term monitoring, or data collection to determine the presence, extent, and concentrations of potential contaminants. Guidance
on selection of well locations, screen lengths and intervals are found m several references, some of which are: EPA(1, 3-51986,,
9-151991, ).1992, 1998, Nielsen 1991, Fetter 1994, and USGS 1997.
7. Monitoring Well Construction Materials
7.1 General—The materials that are used in the construction of a prepacked screen monitoring well should not measurably alter
the chemistry of the groundwater sample(s) to be collected when appropriate sample collection methods are used. Ideally, PVC
should not be used when monitoring for neat organic solvents that are PVC solvents (Parker(16). 1992). While conventional steel
materials (for example, carbon steel or galvanized steel) are not suitable for use under most groundwater monitoring conditions
stainless steel has been found to perform well in most corrosive environments, particularly under oxidizing conditions (EPA(11).
1991). In most cases Type 304 stainless steel will perform satisfactorily for many years (Driscoll(17, 181986).). Under highly
corrosive and reducing conditions Type 316 stainless steel will perform better than Type 304 stainless steel (EPA(11). 1991). The
prepacked screens and well casing used in the well construction should be delivered from the manufacturer to the field site in a
clean state sealed in protective wrapping. Any other equipment used in the well construction process (e.g. (for example, casing,
measuring tapes, grout hoses, other down hole tools) that could impact the resultant water quality should be cleaned and
decontaminated following appropriate methods (Practice D5088) prior to use in the well installation. Additional guidance and
information on well construction practices can be obtained from Practice D5092, EPA 1986, 1991, 1992, Nielsen 1991, and USGS
1997. . Always verify compliance with state and local regulations by contacting the appropriate regulating agency or
agencies.organizations.
7.2 Water—In general, little water is used in the construction of direct push installed prepacked screen wells other than in
preparation of annular seal and grout mixtures. However, there are situations that may require addition of water to the well or
borehole during installation. One of the most common situations that may require addition of water is under drilling conditions
where formation blow-in may occur. Under these conditions (most often saturated sands) water must be added to the boring to
prevent blow-in and assure that the well is properly installed at the desired depth. When water is used in the well installation and
construction process (to prevent blow-in, or mix grout) water of known quality (generally potable water) that will not adversely
affect the sample must be used to assureensure that the sample integrity will not be compromised. The volume of water added to
each well must be documented.
7.3 Prepacked Screen—There are three primary components of the prepacked well screen (Fig. 2). These are the internal well
screen, the external filter media support, and the contained filter media (sand pack). Some prepack screens are assembled with the
internal PVC screen as an integral part of the assembly (Fig. 2a). Alternatively, some prepack screens are available as sleeves or
jackets (Fig. 2b) that may be installed over factory available casing. The components used in construction of the prepacked well
screen must not adversely affect the groundwater quality so that representative samples may be acquired. Subsurface conditions,
including but not limited to site geology, geohydrology, groundwater chemistry, and the analytes to be monitored must be
considered to assure that the prepacked well screens are compatible with the system to be monitored. A sump may be attached to
the base of the screen to capture any fines entering the well. The bottom of the screen or sump must be sealed with a plug
constructed of compatible material. The prepacked well screen must be of sufficient strength to withstand the forces and stress of
installation and development without being damaged or otherwise compromised. Some of the prepacked well screens are packed
with filter media by the manufacturer. Other prepacked screens are shipped without filter media and are packed in the field with
acceptable filter media materials just prior to installation.
7.3.1 Internal Well Screen—The most common material used for construction of this component is polyvinyl chloride (PVC).
Other materials (for example, stainless steel or fluoropolymers) may be used where and when appropriate. Routinely used internal
well screen diameters include nominal 0.5-inch, 0.75-inch,0.5-in., 0.75-in., and 1.0-in. [15, 25, 50 mm] PVC. For optimum
performance of the well the screen slot size should be determined relative to the grain size analysis of the stratum to be monitored
D6725/D6725M − 16
NOTE 1—The internal well screen is usually constructed of Schedule 40 or 80 PVC (a) with a factory cut 0.010 in. slots while some are available with
0.25 slots. The external filter media support is usually constructed with stainless steel wire cloth with pore size of approximately 0.011 in. and graded
silica sand or equivalent material is used for the filter media. Some prepacked screens are available as sleeves or jackets (b) that slide over factory
available slotted PVC.
FIG. 2 Typical Prepacked Well Screens.
and the gradation of the filter pack material. For further details on the selection of screen slot size refer to Practice D5092. The
most widely available slot size is 0.010-in. 10 slot, 0.010-in. [0.25 mm] in the prepacked well screens. The slot size used for the
internal well screen should retain at least 90 % of the filter media.
7.3.2 External Filter Media Support—The purpose of the external filter media support is two fold. twofold. The primary purpose
is to retain the filter media around the internal well screen as the screen is being placed in the boring. Additionally the external
filter media support assures accurate and complete placement of the filter pack media in the desired screen interval. Emplacement
of the filter media in this fashion eliminates problems with formation collapse against bare screen or bridging and creation of voids
around the bare screen as when gravity installation of the filter media is conducted. One of the most common materials used for
construction of this screen component is a stainless steel wire mesh. Slotted PVC, fluoropolymers or other compatible materials
may be used for construction of this screen component when and where appropriate. The external diameter of the prepacked screen
ranges from about 1.4- to 3.0-in., 3.0-in. [35 to 75 mm], depending on the inner well screen diameter and the inside diameter of
the probe rods used to advance the boring.
7.3.3 Filter Media—The filter media or gravel pack most commonly consists of uniformly graded siliceous particles washed and
screened to have the appropriate particle size distribution. Refer to Practice D5092 for details on the selection of appropriate grain
size distribution for the filter media. One of the most widely used grain size distributions for prepacked screen well filter media
is 20-40 grade silica sand. However, finer grained formations may require finer sand gradation (see Practice D5092).
7.3.4 Sump—The sump is usually constructed of a length of well casing material ranging from a few inches in length to several
feet [1 m] in length depending on the well design and formation characteristics. It is attached to the base of the well screen and
is plugged at the bottom. The sump provides a space for fine sediments entering the well to settle without obstructing a portion
of the screen interval and interfering with recharge or sampling activities. The sump also allows for the collection of dense
nonaqueous phase fluids (DNAPLs) at locations where they are present.
7.4 Casing or Riser—The well casing should be made of clean, new materials that will not alter the quality of the water samples
being collected. Most casing or riser is made of PVC but other materials (for example, stainless steel, fluoropolymers, etc.) may
be appropriate in some situations. The inside diameter and wall thickness of the casing should match that of the internal well screen
of the prepacked well. Threaded and flush jointed casing fitted with o-rings of appropriate material are generally recommended
for the casing. Glued or solvent welded joints are not recommended as the glues and solvents generally contain hazardous
chemicals that can cause contamination of the groundwater to be sampled. The casing and casing joints must be of sufficient
strength to withstand the forces of installation and development. Further information on the selection of appropriate casing
materials can be found in Practice D5092 and (1, 10-12EPA, 151986,, 17-211991 ).and 1992, Nielsen 1991, Ranney and Parker
1997, 1998a, 1998b, and USGS 1997.
7.5 Grout Barrier—The grout barrier serves to prevent the annular sealants from entering into the screen interval resulting in
the alteration of the water chemistry, because common annular sealants and grouts (e.g. (for example, bentonite and Portland
cement) can have a significant impact on the local groundwater chemistry a grout barrier is emplaced immediately above the
screened interval. The grout barrier may be constructed by gravity or tremie installation of fine sand or by installation of a
mechanical or modular barrier.
7.5.1 Gravity or Tremie Installation—The grout barrier may be constructed with silica sand having the same or finer gradation
than the materials used in the filter media. When the filter media is course-grained use of a finer grained grout barrier is
D6725/D6725M − 16
recommended. The grout barrier usually extends one to two feet 1 to 2 ft [1 m] above the top of the screened interval. The granular
material used for the grout barrier may be poured through the annular space in the well for installation (Fig. 9) or placed through
a tremie tube if conditions permit. permit (see 9.4.1).
NOTE 2—Slowly add the barrier material to prevent bridging and to allow time for the material to settle through the water column.
7.5.2 Modular Barriers—Some direct push well systems offer the option of installing a modular grout barrier ((seeFig. 10 9.4.1).
This modular barrier is assembled with the screen and casing and lowered into the well annulus. When the outer casing is retracted
this modular barrier expands and creates a seal above the prepacked screen. These modular barriers are constructed with
polyurethane foam covered with a polyethylene sleeve. These modular barriers are not recommended for use below the water table
because of potential for absorption and desorption of some contaminants.
7.6 Annular Seal and Grout—The annular seal and grout are prepared of materials that will eliminate or at least minimizereduce
the potential for surface or up-hole water (or fluids) from moving down the well annulus. This is important because these fluids
could significantly alter the water quality or cause cross contamination in the zone being monitored.
7.6.1 Annular Seal—State regulations Regulations may recommend the use of sodium bentonite in construction of the annular
seal immediately above the grout barrier. However, different Recent research on sealing methods shows that bentonite seals are
not effective above the water table and that a minimum of 20 % solids mix should be used for grouting (Practice D5092). Different
sealants may be requiredneeded when subsurface geology, chemistry of the groundwater, or high concentrations of contaminants
are present. When present in high concentrations, some organic contaminants can cause desiccation and cracking of bentonite seals
resulting in cross contamination of the well and potential migration of contaminants to a previously clean aquifer. Efforts should
be taken in the site characterization program to determine if these conditions may exist at the site. Annular seals may be installed
by gravity or tremie methods and modular seals are available for some prepacked well systems.
7.6.1.1 Gravity and Tremie Installations—Bentonite chips, granules, or pellets may be used to construct the annular seal when
the field conditions and size of the well annulus permit. Gravity or tremie installation of these dry bentonite materials is most
successful when the top of well screen is at or near the water table. Use of a small diameter tremie tube and grout pump with
bentonite slurries may provide the most reliable method of placing the annular seal (Fig. 114). Bentonite slurries ranging from 20
to 30 % solids by weight may be required by state or local regulations. Check the state and are required. Check the local regulations
to verilyverify compliance. A side port tremie tube may be used to minimizereduce the jetting of the slurry into the grout barrier.
7.6.1.2 Modular Seals—These seals are constructed with paper sleeves containing bentonite attached to a segment of blank
casing. This modular seal (Fig. 103) is placed above the grout barrier (modular) and prepacked screens to provide an annular seal.
7.6.2 Grout—There are two primary types of grout slurry used in monitoring well construction. These are bentonite grouts and
cement grouts. The grout slurries should be mixed until smooth to prevent clogging of the tremie tube. State and local Local
regulations for grout compositions and density vary considerably and these regulations should be reviewed to assure compliance.
Additional information on grouting requirements is provided in Practice D5092 and EPA (221991.).
7.6.2.1 Bentonite Grout—Some bentonite powders contain additives to accelerate the gelling of the slurry and increase viscosity.
For the smaller diameter direct push installed monitoring wells where a small well annulus may require the use of small diameter
tremie tubes these additives may cause clogging of the tremie tube. The use of bentonite powders (200 mesh) without additives
is commonly used for grout when small diameter tremie tubes are required.advised. In general bentonite slurry densities of 20 to
30 % solids by weight are required by regulation. A 20 % solids by weight bentonite slurry may be prepared by adding 2.1 pounds
2.0 lb [0.9 kg] of bentonite powder to one gallon 1 gal [3.8 L] of clean water. water (D5092). Bentonite grouts are recommended
for use only in the saturated zone as dessication may occur in the unsaturated zone compromising the integrity of the seal.seal (22).
Additional information on grout mixtures is provided in Practice D5092 and state regulations should be consulted.
7.6.2.2 Cement Grout—Cements containing additives to accelerate the setting process are not recommended for use in grouting.
These additives may prematurely cause thickening of the slurry and result in clogging of the tremie tube used for bottom up
installation. Additionally, these additives may leach from the grout and alter the local water chemistry. In most cases neat cement
should be used for grouting. Cement grout is typically mixed by adding one 94-pound 94-lb [50-kg] bag of Type I Portlandportland
cement to 6 to 7 gallons gal [22-27 L] of clean water, check state and local regulations to verify compliance. When small diameter
tremie tubes are required it is best to use fresh cement so that lumps of hardened cement will not clog the tremie tube. Additional
information on grout mixtures is provided in Practice D5092 and state applicable local regulations should be consulted. Research
FIG. 35 Typical percussion type direct push units are often mounted in conventional pick-up trucks or more rugged track vehicles for
access to difficult locations. Some percussion-type units, such as the track unit shown here, are fitted with optional auger heads.
D6725/D6725M − 16
FIG. 46 Hydraulics and SPT hammers on rotary drilling rigs may be used to advance direct push tools under some conditions. CPT
units may weigh from 15 to 30 tons. These vehicles have been used to install monitoring wells by direct push methods at many loca-
tions.
NOTE 1—Some prepack well systems are available with expendable anchor points with either a thread or click on mechanism to anchor the screens
in position.
FIG. 57 Advanced Direct Push Casing (or probe rod) to Depth with an Expendable Point to Prepare for Installation of a Prepacked
Screen Monitoring Well.
FIG. 68 When an expendable cutting shoe is used during dual tube soil sampling prepacked screens may be installed after sampling is
completed. In saturated noncohesive formation (sands) it may be necessary to add water to the probe rods to prevent blow-in during
sample collection activities.
(22) as shown that in the unsaturated zone cement shrinks away from the casing and this problem can be alleviated by using a metal
riser in that section or non-shrink cement (D5092).
D6725/D6725M − 16
NOTE 1—A simple plug may be added to the base of the well screens and a sump may be used. A special adapter may be used if the screens are attached
to an expendable anchor point. Some threaded anchor points make it possible to thread the PVC screen directly to the point.
FIG. 79 Lowering Assembled Prepacked Screens Through the Casing as PVC Riser is Added to the Well Assembly.
FIG. 810 Small diameter extension rods equipped with an adapter may be used to free the prepacked screens if they become lodged
inside the casing. Care must be used to prevent damage to the well.
7.7 Well Protection—There are two primary types of well protection commonly used for monitoring wells, these are
above-ground and flush mount well protectors. The above ground protector is used in locations where vehicular traffic is not a
concern. The above ground protection is also more widely approved because of its ability to eliminate or at least minimizereduce
the potential for surface runoff to enter the well head and thus contaminate the local aquifer. Flush mount well protection is used
in areas where vehicular traffic is a concern. Most statesagencies require a regulatory variance for use of this well protection design
because of the increase in potential for cross contamination of the local aquifer by infiltration from surface runoff waters or
chemical spills. Check local and state regulations before using flush mount protection and obtain the necessary variance(s) where
needed. Further specifications on well protection are available in Practice D5787.
8. Direct Push Methods
8.1 General—There are three basic methods for advancing direct push tools into the subsurface. Traditionally, cone penetration
testing (CPT) equipment (D6067) has used the static weight of the vehicle (15 to 30 tons), sometimes coupled with anchors, to
advance tools down hole. Smaller and lighter weight direct push vehicles rely on percussion methods together with vehicle weight
to advance tools. Another method for advancing tools or casing into the subsurface is sonic or resonance drilling. drilling (D6914).
This method uses high frequency percussion combined with rotary action to advance tools and casing into the subsurface. A review
of the local geologic conditions and any available records of previous sampling by direct push or rotary drilling methods should
be conducted prior to mobilization to determine which direct push method should be applied for well installation at the site under
D6725/D6725M − 16
FIG. 911 One method to construct the grout barrier is by pouring medium to fine grained sand through the casing annulus. If any
bridging occurs an extension rod or jetting with water may be used to re-open the well annulus.
FIG. 103 Some direct push prepacked well systems use modular grout barriers and modular annular seals attached to the well casing.
The modular foam barrier, used primarily above the water table, expands when the drive casing is retracted. The modular annular seal
with polyethylene barrier is used below the water table. The bentonite in the modular seal is hydrated by the groundwater and expands
to seal the annulus prior to grouting.
consideration. If site specific conditions are not amenable to direct push methods other rotary drilling methods (D5781D6286,
D5782, D5783, D5784, D5785, D5786) may be reviewed for potential use.
8.1.1 Percussion Methods—Advancement of tools or casing into the subsurface with percussion methods can be completed with
hydraulic, pneumatic and mechanically operated hammers. These hammers are used in conjunction with hydraulic slides and
vehicle weight to advance tools. Typical DP units may be mounted in trucks or other vehicles (Fig. 35) to facilitate site access.
The percussion procedures are some of the most widely used direct push methods. These methods are generally capable of
penetrating clays, silts, sands, and some gravel as commonly encountered in alluvial and glacial deposits. Monitoring wells are
routinely installed at depths of 20 feet to 50 feet ft [10 to 15 m] with percussion methods, and may be installed at depths exceeding
100 feet 200 ft [60 m] in amenable geologic conditions. Densely packed glacial deposits, deposits with cobbles or boulders, or thick
zones of caliche may make penetration with percussion methods difficult or impossible. Some percussion-type direct push units
are also equipped with rotary drilling capabilities. These capabilities make it possible for direct push methods to be used where
a significant gravel, cobble, or caliche layer may have previously limited their use.
8.1.2 Static Weight Methods—Cone penetration (CPT) systems are the most commonly used static weight method for advancing
tools and installing monitoring wells. wells (D6067). Hydraulic rams are used to advance the tool string into the subsurface using
the static force of the vehicle weight. Large CPT trucks (Fig. 46) may use anchors or add ballast to the vehicles (tanks of water,
or lead blocks) to increase vehicle weight and depth of penetration. Capabilities and limitations of the static weight method are
similar to those of the percussion methods.
D6725/D6725M − 16
FIG. 114 Another option for installation of the annular well seal is with a side-port tremie tube and grout pump. This may be the most
effective option when the screen is below the water table.
8.1.3 Sonic or Resonance Drilling Methods—These are generally more powerful drilling methods that combine high frequency
sonic or resonance with rotary action to advance tools into the subsurface. subsurface (D6914). These methods can generally
penetrate to greater depths than percussion or static methods and have been used to penetrate difficult formations such as cobble
rich glacial till.
8.1.4 Rotary Drilling—Some conventional rotary drilling methods can be combined with direct push methods for sampling and
well installation. installation (D6286). Hollow stem augers (Fig. 46) (D6151) are sometimes advanced to depth and then the
hydraulic hammer generally used for standard penetration testing (Test Method D1586) may be used to advance tools or casing
ahead of the augers. Occasionally, the manual cathead-and-rope method is used to advance tools or casing ahead of the augers to
facilitate sampling or well installation.
8.2 Advantages and Limitations—Direct push methods have some advantages and limitations when compared to rotary drilling
methods. One of the primary advantages of direct push methods is that essentially no waste cuttings are generated as the tool string
or casing is advanced into the subsurface. At locations where hazardous contaminants may be present this significantly
minimizesreduces the handling, drumming, storage, sampling, testing, transportation, and disposal of contaminated cuttings.
Elimination of these waste handling and disposal activities will not only reduce cost but also reduce potential exposure hazards
for site workers, local residents and the environment. Direct push methods are generally limited to unconsolidated formations
composed of clays, silts, sands and some gravel. Conventional rotary drilling methods will be required for penetration of
consolidated bedrock (for example, limestone, granite, gneiss) and some very dense unconsolidated formations or formations with
an abundance of cobbles or boulders.
9. Monitoring Well Installation
9.1 General—Several of the procedures described below are similar to those used for installation of monitoring wells by rotary
drilling techniques and Practice D5092 may be referenced for additional information or guidance as needed. Manufacturer’s
standard operating procedures for installing direct push prepacked screen monitoring wells (Geoprobe(23-25) Systems 1998,
1999, GeoInsight 2000) may also provide additional information on installation techniques. Installation of monitoring wells in an
open/uncased borehole is not recommended for direct push or rotary drilling procedures. Installation of a monitoring well through
an open borehole may result in slough of potentially contaminated material down the well bore either prior to or during the well
installation procedure. This can lead to cross contamination and water quality samples that are biased and inaccurate and ultimately
abandonment and replacement of the incorrectly installed well. While open hole installation of temporary piezomenters for water
level monitoring in uncontaminated formations may be acceptable this is not an acceptable installation method for monitoring
wells to be used for water quality sampling.
9.2 Installation of Drive Casing—The direct push method (percussion, static, sonic) which is selected based on site conditions
is used to advance the drive casing to the desired depth. Use of O-rings or Teflon tape on casing joints is recommended to eliminate
the potential for cross contamination as the tools are advanced to depth.
9.2.1 Advance Casing—Information from the site characterization is used to determine the appr
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