EPA160014-891034
                                             March 1991
Handbook of Suggested Practices for the Design and
   Installation  of Ground-Water  Monitoring Wells
                             by:

           Linda Aller, Truman W. Bennett and Glen Hackett
                     Bennett & Williams, Inc.
                     Columbus, Ohio 43231
                        Rebecca J. Petty
                Ohio Department of Natural Resources
                     Division of Groundwater
                     Columbus, Ohio 43215
                  Jay H. Lehr and Helen Sedoris
                 National Water Well Association
                       Dublin, Ohio 43017
                       David M. Nielsen
                     Blasland, Bouck and Lee
                     Westerville, Ohio 43081
              Jane E. Denne (also the Project Officer)
               Advanced Monitoring Systems Division
            Environmental Monitoring Systems Laboratory
                  Las Vegas, Nevada 89193-3478
       Environmental Monitoring Systems Laboratory
             Office of Research  and  Development
           U.S. Environmental Protection Agency
               Las Vegas, Nevada 89193-3478
                                                Printed on Recycled Paper

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                                Notice
    The information in this document has been funded wholly or in part by the
United States Environmental Protection Agency under Cooperative Agreement
Number CR-8 12350-01 to the National Water Well Association. It has been
subjected to the Agency's peer and administrative review, and it has been approved
for publication as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.

    This document has been prepared in cooperation with EMSL-LV, Office of
Research and Development. It is intended to be used as a general reference and will
not supersede program-specific guidance (e.g., the RCRA Ground-Water Monitoring
Technical Enforcement Guidance Document).

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                               Abstract
    The Handbook of Suggested Practices for the Design and Installation of
Ground-Water Monitoring Wells is intended to assist personnel involved with the
design, construction, and installation of ground-water monitoring wells. This
document does not focus on specific regulatory requirements, but instead presents
state-of-the-art technology that may be applied in diverse hydrogeologic situations.
The "Handbook addresses field-oriented practices to solve monitoring well
construction problems rather than  conceptual or idealized practices.  The informa-
tion in this  "Handbook" is presented in both matrix and text form. The matrices use
a relative numerical rating scheme to guide the user toward appropriate drilling
technologies for particular monitoring situations. The text provides the narrative
overview of the  criteria that influence ground-water monitoring well design  and
construction in various hydrogeologic settings.

    The "Handbook" addresses topics ranging from initial planning for a monitoring
well to abandonment.  Factors influencing monitoring well design and installation
include: purpose, location,  site hydrogeology, contaminant characteristics,  an-
thropogenic activities, and testing equipment that  the  well must accommodate.
Decontamination procedures should be planned and executed with care. Detailed
Recordkeeping from the time of well installation through sampling to abandonment
is very important. Numerous drilling and formation  sampling techniques are
available, and many factors must be considered in selecting an appropriate method.
Materials for well casing, screen,  filter pack, and annular sealants also should be
selected and installed carefully. Well completion  and development procedures
should allow collection of representative ground-water  samples and  levels. Main-
tenance of monitoring wells is an important network management consideration.
Well abandonment procedures should include consideration of the monitoring well
construction, hydrogeology, and contamination at the site. The  "Handbook" serves
as a general reference  for the numerous factors involved in monitoring well design,
construction, and installation.

    This report was submitted in  fulfillment of Cooperative Agreement Number
CR-812350-01 by the National Water Well Association under sponsorship of the
Environmental Monitoring Systems Laboratory, Las Vegas, Nevada. This report
covers a period from June 1985 to May  1989, and work was completed as of June
1989.
                                I  I I

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                                                        Contents
Notice	-.1)
Abstract	iji
Figures	V1U
Tables	x
Acknowledgments	X1

Section
         1. Introduction	»	"•»	»•	—	 1
             Objectives and scope	-1
             Purpose and importance of proper ground-water monitoring well installation	„..*...,......,„., 1
             Organization of the document.....	7
             References	.,..„...	.7
         2. Factors influencing ground-water monitoring well design and installation	.........9
             Geologic and hydrogeologic conditions	9
                  Hydrogeologic regions of the United States	—.9
                  Site-specific geologic and hydrogeologic conditions	18
             Facility characteristics................	..18
                  TypeoffaciEty.....	-	19
                  Waste characteristics	20
             Other anthropogenic influences	...23
             Equipment that the well must accommodate...........................	,.	23
                  Borehole geophysical tools and downhole cameras	.....24
                  Water-level measuring devices	.26
                  Ground-water sampling devices	26
                  Aquifer testing procedures	....26
             References	,	.	....27
         3. Monitoring well planning considerations	29
             Recordkeeping	29
             Decontamination „	,.	,	........29
                  Decontamination area	,.....,..,..».	....30
                  Types of equipment	32
                  Frequency of equipment decontamination	......32
                  Cleaning solutions and/or wash water	32
                  Containment of residual contaminants and cleaning solutions and/or wash water	33
                  Effectiveness of decontamination procedures	34
                  Personnel decontamination	•	34
             References	•	-	.................34
         4. Description and selection of drilling methods	35
             Introduction	»«	—«	.....35
             Drilling methods for monitoring well installation	.,.„...,.„»„....„	35
                  Hand augers	35
                  Driven wells	.	35
                  Jet percussion	36
                  Solid-flight augers	37
                  Hollow-stem augers	38
                  Direct mud rotary	40
                  Air rotary drilling	42
                  Air rotary with casing driver	44
                  Dual-wall reverse-circulation	44
                  Cable tool drilling	47

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         Other drilling methods	.	49
    Drilling fluids	49
         Influence of drilling fluids on monitoring well construction	,	,...49
         Drilling fluid characteristics	50
         Mud-based applications	51
         Air-based applications	52
    Soil sampling and rock coring methods	„..,..„..„.„„„	53
         Split-spoon samplers	.........54
         Thin-wall samplers	.	55
         Specialized soil samplers	.....	56
         Core barrels,.	57
    Selection of drilling methods for monitoring well installation	58
         Matrix purpose	,..,..„.......,..,......,.,....	58
         Matrix description and development	58
         How to use the matrices	.61
         How to interpret a matrix number	61
    Criteria for evaluating drilling methods	„,.„.,.,.„..„..	....,...,...,.	,61
         Versatility of the drilling equipment and technology with respect to the hydrogeologic
            conditions at the site	»,.„„„..„.„...»,.......	63
         Reliability of formation (soil/rock/water) samples collected during drilling....	.....64
         Relative drilling costs	67
         Availability of equipment	,	.67
         Relative time required for well installation and development	67
         Ability of drilling technology to preserve natural conditions	...68
         Ability of the specified drilling technology to permit the installation of the proposed
            casing diameter at the design depth	68
         Ease of well completion and development.......	69
    Drilling specifications and contracts	,	69
    References,	.....71
5. Design components of monitoring wells	73
    Introduction ,.„.„........	,	73
    Well casing	73
         Purpose of the casing  .......,..,.„..„...,	............73
         General casing material characteristics	,	73
         Types of casing materials	„.	75
         Coupling procedures for joining casing	83
         Well casing diameter	85
         Casing cleaning requirements	86
         Casing cost	,	86
    Monitoring well intakes	86
         Naturally-developed wells	.„..„„«,.	87
         Artificially filter-packed wells	,.88
    Well intake design	93
    Annular seals	...96
         Purpose of the annular seal	96
         Materials used for annular seals	.97
         Methods for evaluating annular seal integrity	101
    Surface completion and protective measures	 101
         Surface seals	..........101
         Above-ground completions	„.,„„...,	„	101
         Hush-tp-ground surface completions	,	.......................	 102
    References	,	 102
6. Completion of monitoring wells	105
    Introduction	,	 105
    Well completion techniques	105
         Well intake installation	,	105
         Filler pack installation	,	106
         Annular seal installation	,	,	107
    Types of well completions	 109
         Single riser/limited-interval  wells	109
         Single riser/flow-through wells		109
         Nested wells	....„»„...	,..,.,»„„.„..	.......110

                                                    vi

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        Multiple-level monitoring wells	Ill
    General suggestions for well completions	112
    References	112
7.  Monitoring well development	115
    Introduction/philosophy	115
    Factors affecting monitoring well development	115
        Type of geologic material	115
        Design and completion of the well	116
        Type of drilling technology	116
    Well development	117
    Methods of well development	117
        Bailing	120
        Surge block	121
        Pumping/overpumping/backwashing	121
    References	123
8.  Monitoring well network management considerations	125
    Well documentation	125
    Well maintenance and rehabilitation	125
        Documenting monitoring well performance	125
        Factors contributing to well maintenance needs	127
        Downhole maintenance	128
        Exterior well maintenance	128
        Comparative costs of maintenance	130
    Well abandonment	130
        Introduction	130
        Well abandonment considerations	130
        Well abandonment procedures	131
        Grouting procedures for plugging	132
    Clean-up, documentation  and notification	133
    References	133
Master References	134
Appendices
    A. Drilling and constructing  monitoring wells with hollow-stem augers	141
    B. Matrices for selecting appropriate drilling equipment	165
    C. Abandonment of test holes, partially completed wells, and completed wells
         (American Waterworks Association, 1984)	207
Glossary	209
                                             VII

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                                                       Figures
Number                                                                                            Page
   1     Ground-water regions of the United States	,	.„.„,...........,......„,.„..,., 10
  2a    Location of the Western Mountain Ranges region	,	10
  2b    Topographic and geologic features in the southern Rocky Mountains part of the Western
           Mountain Ranges region	10
  3a    Location of Ihe Alluvial Basins region	...............11
  3b    Common ground-water flow systems in the Alluvial Basins region	„	.,..,...	 11
  4a    Location of the Columbia Lava Plateau region	 11
  4b    Topographic and geologic features of the Columbia Lava Plateau region.,.,...,..	 11
  5a    Location of the Colorado Plateau and Wyoming Basin region	12
  5b    Topographic and geologic features of the Colorado Plateau and Wyoming Basin region	„	12
  6a    Location of the High Plains region	12
  6b    Topographic and geologic features of the High Plains region	...,„......„..„...,....,.„..„	12
  7a    Location of the Nonglaciated Central region	13
  7b    Topographic and geologic features of the Nonglaciated Central region	,	13
  7c    Topographic and geologic features along the western boundary of the Nonglaciated
           Central region	„,„„...,...,.„.„.„.„	13
  8a    Location of the Glaciated Central region	......	14
  8b    Topographic and geologic features of the Glaciated Central region	14
  9a    Location of the Piedmont and Blue Ridge region	,	14
  9b    Topographic and geologic features of the Piedmont and Blue Ridge region	14
 lOa    Location of the Northeast and Superior Uplands region	„	 15
 lOb    Topographic and geologic features of the Northeast and Superior Uplands region	 15
 1 la    Location of the Atlantic and Gulf Coastal Plain  region	..„...,„,..,.	15
 lib    Topographic and geologic features of the Gulf Coastal Plain	15
 12a    Location of the Southeast Coastal Plain region	16
 I2b    Topographic and geologic features of the Southeast Coastal Plain	,	16
 13a    Location of the Alluvial Valleys ground-water region	,	..,„...»..,.... 17
 13b    Topographic and geologic features of a section of Ihe alluvial valley of the
           Mississippi River	„.,„„„..	,	17
  14    Topographic and geologic features of an  Hawaiian island	17
  15    Topographic and geologic features of parts of Alaska	17
  16    Migration of a high density, miscible contaminant in  the subsurface	....21
  17    Migration of a low density, soluble contaminant in the subsurface	.21
  18    Migration of a low density, immiscible contaminant in the subsurface ,„.„„.,	.........22
  19    Migration of a dense, non-aqueous phase liquid (DNAPL) in the  subsurface	22
  20    Sample boring log format	....................31
  21     Format for an "as-built"  monitoring  well diagram	32
  22    Typical layout showing decontamination areas at a hazardous materials site	33
  23     Diagram of a hand auger	.....35
  24     Diagram of a wellpoint	36
  25     Diagram of jet-percussion drilling	..37
  26     Diagram of a solid-flight auger	...,„,„.„,„„.„..„	37
  27     Typical components of a hollow-stem auger	„	..39
  28     Diagram of a screened auger	....40
  29     Diagram of a direct rotary circulation system	42
  30     Diagram of a roller cone bit	43
  31     Diagram of a down-ihe-hole  hammer.,..	................44
  32     Range of applicability for various rotary drilling methods	.........................45
  33     Diagram of a drill-lhrough casing driver	.,.,.	46
  34     Diagram of dual-wall reverse-circulation rotary method	46
                                                         viii

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35     Diagram of a cable tool drilling system.,	4S
36     Diagrams of two types of bailers	..,.„.„.,.„,..,..,.„. 51
37     Practical drilling fluid densities ..,..„.„..,	«	>	52
38     Viscosity-building characteristics of drilling clays	.....52
39     Schematic of the behavior of clay particles when mixed into water	,	,,...53
40     Diagram of a split-spoon sampler	•	•	.—55
41     Diagram of a thin-wall sampler	........56
42     Two types of special soil samplers	»•	*•	»	57
43     Internal sleeve wireline piston sampler	58
44     Modified wireline piston sampler............	...60
45     Clam-shell fitted auger head	•	•	-	•	—	60
46     Types of sample retainers			•	......60
47     Diagram of a continuous sampling tube system	61
48     Diagram of two types of core barrels	•	62
49     Format for a matrix on drilling method selection	.63
50     Forces exerted on a monitoring well casing and screen during installation	74
51     Static compression results of Teflon® screen	-	•	«-77
52     Types of joints typically used between casing lengths	84
53     Effect of casing wall thickness on casing inside and outside diameter	87
54     Envelope of coarse-grained material created around a naturally developed well	88
55     Plot of grain size versus cumulative percentage of sample retained on sieve	.......89
56     Determining effective size of formation materials	,	.,	—90
57     Determining uniformity coefficient of formation materials	91
58     Envelope of coarse-grained material emplaced around  an artificially filter-packed well	.........91
59     Artificial filter pack design criteria	.............	92
60     Selecting well intake slot size based on filter pack grain size	93
61     Types of well intakes...	••.«••••	97
62     Cross-sections of continuous-wrap wire-wound screen	97
63     Potential pathways for fluid movement in the casing-borehole annulus	............98
64     Segregation of artificial filter pack materials caused  by gravity emplacement	, 106
65     Tremie-pipe emplacement of artificial  filter pack materials	.„..,...„....,..	 106
66     Reverse-circulation emplacement of artificial filler pack materials	.........107
67     Emplacement of artificial filter pack material by backwashing	,	107
68     Tremie-pipe emplacement of annular seal material (either bentonite or neat cement slurry)	108
69     Diagram of a single-riser/flow-through well	-	•	109
70     Typical nested well designs	..„....„„..„...,	110
71     Field-fabricated PVC multilevel sampler.	 1H
72     Multilevel capsule sampling device installation	,	 112
73     Multiple zone inflatable packer sampling installation	112
74     Diagrams of typical bailers used in monitoring well  development	 122
75     Diagram of a typical surge block...	•	123
76     Diagram of a specialized monitoring well surge block	124
                                                     IX

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                                                       Tables
Number                                                                                           Page
   1     Summary of federal programs and activities related to the protection of
           ground-water quality ,...,	.....„.„	„.„...,	2
   2     Federal ground-water monitoring provisions and objectives	,	.......,.,.„,.,»	3
   3     Use and limitations of borehole geophysical tools	24
   4     Descriptive information to be recorded for each monitoring well	.....„..„„,	30
   5     List of selected cleaning solutions used for equipment decontamination ......		..34
   6     Applications and limitations of hand augers	„	38
   7     Applications and limitations of driven wells	..38
   8     Applications and limitations of jet-percussion drilling	,„	,	38
   9     Applications and limitations of solid-flight augers	,	39
  10     Applications and limitations of hollow-stem augers	,.41
  11     Applications and limitations of direct mud rotary drilling	41
  12     Applications and limitations of air rotary drilling	,	44
  13     Applications and limitations of air rotary with casing driver drilling	47
  14     Applications and limitations of dual-wall reverse-circulation rotary drilling	47
  15     Applications and limitations of cable tool drilling	49
  16     Principal properties of water-based drilling fluids	...............50
  17     Approximate Marsh Funnel viscosities required for drilling in typical types of
           unconsolidated materials	51
  18     Drilling fluid options when drilling with air	,	,„....,.,	....................52
  19     Characteristics of common formation-sampling methods	,54
  20     Standard penetration test correlation chart	„..,..„	55
  21     Index to matrices  1 through 40	59
  22     Suggested areas to be addressed in monitoring well bidding specifications	69
  23     Suggested items for unit cost in contractor pricing schedule	70
  24     Trade names, manufacturers, and  countries of origin for various fluoropolymer materials	....76
  25     Typical physical properties of various fluoropolymer materials	76
  26     Hydraulic collapse and burst pressure and unit weight of stainless steel well casing	78
  27     Typical physical properties of thermoplastic well casing materials at 73.4°F	81
  28     Hydraulic collapse pressure and unit weight of PVC well casing	....81
  29     Hydraulic collapse pressure and unit weight of ABS well casing	,	81
  30     Representative classes of additives in rigid PVC materials used for pipe or well casing	83
  31     Chemical parameters covered by NSF Standard 14	83
  32     Volume of water in casing or borehole	,	86
  33     Correlation chart of screen openings and sieve sizes	.....95
  34     Typical slotted casing slot widths	,„..,..„.,„.,»...,....	96
  35     Intake areas  (square inches per lineal foot of screen) for
           continuous wire-wound well intake..	96
  36     Summary of development methods for monitoring wells	118
  37     Comprehensive monitoring well documentation	 126
  38     Additional monitoring well documentation,	 126
  39     As-built construction diagram information	126
  40     Field boring log information	,....„	,. 127
  41     Regional well maintenance problems	,...,..„„.,....„....	129
  42     Chemicals used for well maintenance	129
  43     Well abandonment data	133

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                          Acknowledgments
    This document presents a discussion of the design and installation of ground-
water monitoring wells without specific regulatory recommendations. The infor-
mation contained within the document is the product of many experiences, both
published and unpublished to date. Assisting in the direction of the project and in
the review of various stages of the document was an able and knowledgeable
advisory committee. Although each of the individuals contributed positively, this
document is a product of the authors and may not be entirey endorsed by each of
the committee members. To the following narmed persons, grateful acknowledgment
of their  contribution is made:

        Roger Anzzolin, U.S. EPA, Office of Drinking Water
         George Dixon, formerly with U.S. EPA, Office of Solid Waste
         Tyler Gass, Blasland & Bouck Engineers, P.C.
         lames Gibb, Geraghty & Miller, Inc.
         Todd Giddings, Todd Giddings & Associates
         Kenneth Jennings, U.S. EPA, Office of Waste Programs Enforcement
         Thomas Johnson, Levine-Fricke, Inc.
         Ken McGill, formerly with U.S. EPA, Region 3
         John Mann, formerly with U.S. EPA, Region 4
         Roy Murphy, U.S. Pollution Control, Inc.
         Marion R. Scalf, U.S. EPA, Robert S. Kerr Environmental Research
           Laboratory
         Dick Young, U.S. EPA, Region 7
         John Zannos, U.S. EPA, Region 1

    The basic conceptual foundation  for this report was  supported in  its infant
stages by Leslie G. McMillion, U.S. EPA, retired. A special note of acknowledg-
ment and gratitude is extended to him for his inspiration  and support in starting this
document.

    In addition to the committee members, many individuals assisted in adding
practical and regional perspectives to the document by participating in regional
group interviews on many aspects of monitoring well design and installation.
Thanks are  also extended to the following individuals  for the donation of their time
and invaluable input

         John Baker, Anderson Geotechnical Consultants, Inc., California
         Dala Bowlin, Jim Winneck, Inc., Oklahoma
         John Braden, Braden Pump and Well Service, Mississippi
         Harry Brown, Brown Drilling Company, Inc., Michigan
         Kathryn Davies, U.S. EPA, Region 3
         Hank Davis, Mobile Drilling, California
         Tim De La Grange, De La Grange and Sons, California
         Lauren Evans, Arizona Department of Health  Services, Arizona
         Jerry Frick, Walkerville Weil Drilling and Supply Co., Michigan
         Tyler Gass, Blasland & Bouck Engineers, P.C., New York
         Jim Hendry, National Water Well Association, Ohio
         Tom Holdrege, Anderson Geotechnical Consultants, Inc., California
         Joseph Keely, Oregon Graduate Center, Oregon
         Larry Krall, Layne Environmental Services, Arizona
         Bruce Kroecker, Layne Environmental Services, Kansas
         David Lang, U.S. EPA, Region 1

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        Bill Long, Jim Winneck, Inc., Oklahoma
        Carl Mason, C.M.  Consulting, Pennsylvania
        Bill McKinnel, West Corp., Wyoming
        Bruce Niermeyer, Interstate Soil Sampling,  Inc., California
        Harry Ridgell, Jr.,  Coast Water Well Service, Inc., Mississippi
        Charles 0. Riggs, Central Mine Equipment  Co., Missouri
        Scott Sharp, Layne Environmental Services, Arizona
        Bill Snyder, William Stothoff Company, Inc., New Jersey
        Steve Story, Layne Environmental Services, California
        Fred Strauss, Layne Environmental Services, California
        Dave  Sullivan, D.P. Sullivan& Daughters Drilling Finn, Inc.. Massachusetts
        Bud Thorton, Associated Well Drillers, Inc., Idaho
        Taylor Virdell, Virdell Drilling, Texas
        Dick Willey, U.S. EPA, Region 1
        Douglas Yeskis, U.S. EPA, Region 5
        John Zannos, U.S.  EPA, Region 1

    In addition, gratitude is expressed to those individuals who participated in reviewing the
document:

        Joe Abe, U.S. EPA, Office of Solid Waste
        Doug Bedinger, Environmental Research Center, UNLV
        Regina Bochicchio, Desert Research Institute, UNLV
        Jane Denne, U.S. EPA, EMSL - Las Vegas
        Joe DLugosz, U.S. EPA, EMSL - Las Vegas
        Phil Durgm, U.S. EPA, EMSL - Las Vegas
        Larry  Eccles, U.S.  EPA, EMSL - Las Vegas
        Steven Gardner, U.S. EPA, EMSL - Las Vegas
        Jack Keeley, U.S. EPA, retired
        Eric Koglm, U.S. EPA, EMSL - Las Vegas
        Lowell Leach, U.S. EPA, Robert S. Kerr Environmental Research
          Laboratory, Ada
        Wayne Pettyjohn, Oklahoma State University
        Mario Salazar, U.S. EPA, Office of Drinking Water
        Kenneth Scarborough, U.S. EPA, EMSL - Las Vegas
        Peter Siebach, U.S. EPA,  Office of Solid Waste
        Kendrick Taylor, Desert Research Institute, University of  Nevada System.
          Reno
        John Worlund, U.S. EPA, EMSL - Las Vegas
        Kendrick  Taylor also provided information contained  in the borehole geophysical
tool section of the  document.
                                  XII

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                                                    Section 1
                                                 Introduction
Objectives and Scope
    The Handbook of Suggested Practices for the Design and
Installation of Ground-Water Monitoring Wells has been pre-
pared as an aid to owners and operators of facilities as well as
others concerned with proper installation of ground-water
monitoring wells.  This document is also designed to assist state
and federal authorities in evaluating all aspects of monitoring
well design and installation in varying hydrogeologic settings.
Information contained within this publication does not address
specific regulatory requirements, which must be followed, but
rather presents state-of-the-art technology that can be used in
differing  situations.

    This document is intended to be both informative and
descriptive in nature. The objectives are to  provide a concise
description of the components of monitoring well design and
installation and to detail the applicability of various drilling
techniques in diverse hydrogeologic  regimes. The information
is presented in both  text and matrix form. Through a relative
numerical rating  scheme, the matrix  guides the user toward
appropriate drilling  technology  for particular monitoring situ-
ations.

    Impetus for  the development of the Handbook of Sug-
gested Practices for the Design and Installation of Ground-
 WaterMonitoring  Wells was provided by the  passage of a series
of federal laws which addressed the need to protect ground-
water quality. Table 1 lists the laws enacted by Congress and
summarizes the applicable ground-water activities associated
with each law. Of the sixteen  statutes listed in Table  1, ten
statutes have regulatory programs  which establish ground-
water monitoring requirements for specific sources of con-
tamination. Table 2  summarizes the  objectives and monitoring
provisions of the  federal acts. While  the principal objectives of
the laws are to obtain background water-quality data and to
evaluate whether or not ground water is being contaminated, the
monitoring provisions contained within the  laws vary signifi-
cantly. Acts may mandate that ground-water monitoring
regulations be adopted, or they may address the need for the
establishment of  guidelines to protect ground water. Further,
 some statutes specify the adoption of rules that must be
implemented uniformly throughout the United States,  while
others authorize adoption of minimum standards that may be
made more stringent by state or local regulations.

    With such diverse statutes mandating ground-water
monitoring requirements, it is not surprising that the regula-
tions promulgated under the authority of the statutes also vary
in scope and specificity. In general, most regulations further
define the objectives of the statute and clarify the performance
standards  to achieve the  stated  objectives.
    More specific ground-water monitoring recommendations
can be found in the numerous guidance documents and direc-
tives issued by agencies responsible for implementation of the
regulations. Examples of guidance documents include the Of-
fice of Waste Programs Enforcement Technical Enforcement
Guidance Document (TEGD) (United States Environmental
Protection Agency, 1986), the Office of Solid Waste Documents
SW-846 (Wehran Engineering Corporation, 1977) and SW-
611 (United States Environmental Protection Agency,  1987).
The purpose of this "Handbook is to be a general (non-
program-specific) reference to provide the user with a practical
decision-making  guide for designing and installing monitoring
wells,  and it will not supersede program-specific guidance.

Purpose and Importance of Proper Ground-Water
Monitoring Well Installation
    The primary objective of a monitoring well is to provide an
access point for  measuring ground-water levels and to permit
the procurement  of ground-water samples that accurately rep-
resent in-situ ground-water conditions at the specific point of
sampling.  To achieve this objective, it is necessary to fulfill the
following  criteria:

     1)  construct the well with minimum disturbance to
        the  formation;
    2)  construct the well of materials that are compatible
        with the anticipated geochemical and chemical
        environment
    3)  properly complete the well in the desired zone;
    4)  adequately seal the  well with materials that will
        not interfere with the collection of representative
        water-quality samples; and
    5)   sufficiently develop the well to remove any
        additives associated with drilling and provide
        unobstructed flow through the well.

    In addition to appropriate construction details, the moni-
toring  well must be designed in concert with the overall goals
of the monitoring program. Key factors that must be considered
include:

     1) intended purpose of the well;
    2)  placement of the well to achieve  accurate water
        levels and/or representative water-quality samples
    3) adequate  well  diameter to  accommodate
        appropriate tools for well development, aquifer
        testing  equipment  and water-quality sampling
        devices; and
    4)  surface protection to assure no alteration of the
         structure or impairment of the data collected from
        the well.
                                                          1

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 Table 1. Summary of Federal  Programs  and Activities Related to the  Protection of Ground-Water Quality (after Office of Technology  Assessment, 1984)
Investiaationa/d ejection
Ground-water
Ambient monitoring Waler
Statutes Inventories ground-water related supply
of source' monitoring to sources' monitoring
Atomic Energy Act 	
Clean Water Act X
Coastal Zone
Management Act 	
Comprehensive Environmental
Response, Compensation
and Liability Act 	 X
Federal Insecticide, Fungicide
and Rodenticide Act
Federal Land Policy end
Management Act (and
associated mining laws) . . .
Hazardous Liquid Pipeline
Safety Act X
Hazardous Materials
Transportation Act 	 X
National Environmental
Policy Act 	
Reclamation Act 	
Resource Conservation end
Recovery Act 	 X
Safe Drinking Water Act 	 X
Surface Mining Control and
Redemption Act 	
Toxic Substances Control Act
Uranium Mill Tailings
Radiation Control Act
Water Research and
Development Act 	
X
X X
X
X
X
X
X X
X
X
X
£nn£r
Federally
funded
remedial
actions
X
X
X
X
X
X
lion Prevention
Regulatory Regulate Standards for
requirements chemical new/existing Aquifer
for sources' production sources' protection Standards Other"
X XX
X XX
X
X
X X
X
X
X
X
X X
X XX
X
X X
X X
X
'Programs and activities under this heading relate directly to specific sources of groundwater contamination.
'This category includes activities such as research and development and grants to the states to develop ground-water related programs.

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Table 2. (Continued)

Statutory  authority
                         Monitoring provisions"
Monitoring objectives
Reclamation Act

Resource Conservation and
   Recovery Act
   -Subtitle C
No explicit requirements established; however, monitoring maybe conducted, as
  necessary, as part of water supply development projects.
Ground-water monitoring is specified in Federal regulations for all hazardous
  waste land disposal facilities (e.g., landfills, surface impoundments, waste piles,
  and land treatment units).
Facilities in existence on the effective date of statutory or regulatory amendments
  under the act that would make the facility subject to the requirements to have a
  RCRA permit must meet interim Status monitoring requirements until a final per-
  mit is issued. These requirements specify the installation of at feast one upgra-
  dient well and three downgradient wells. Samples must be taken quarterly during
  the first year and analyzed for the National Drinking Water Regulations, water
  quality parameters (chloride, iron, manganese, phenols, sodium and sulfate), and
  indicator parameters (pH, specific conductance, TOC and TOX). In subsequent
  years, each well is sampled and analyzed annually for the six background water-
  quality parameters and semi-annually for the four indicator parameters,
If contaminant leakage has been detected during detection monitoring, the owner or
  operator of an interim status facility must undertake assessment monitoring. The
  owner or operator must determine the vertical and horizontal concentration pro-
  files of all the hazardous waste constituents in the plume(s) escaping from waste
  management units.
Ground-water monitoring requirements can be waived by an owner/operator if a
  written determination indicating that there is low potential for waste migration via
  the uppermost aquifer to water supply wells or surface water is made and certified
  by a  qualified geologist or engineer. Ground-water monitoring requirements for a
  surface impoundment may be waived if(1)  it is used to neutralize wastes which
  are hazardous solely because they exhibit  the corrosivity characteristic under
  Section 261.22 or are fisted in Subpart D of Part 261  and (2) contains no other
  hazardous waste. The  owner or operator must demonstrate that there is no poten-
  tial for migration of the hazardous wastes from the impoundment. The demonstra-
  tion must be in writing and must be certified by a qualified professional.
The monitoring requirement for a fully permitted facility are comprised of a three-
  part program:
                                                -Detection Monitoring - implemented when a permit is issued and there is
                                                 no indication of leakage from a facility. Parameters are speeded in the
                                                 permit. Samples must be taken and analyzed at feast semi-annually for
                                                 active life of regulated unit and the post-closure care period. If there is a
                                                 statistically significant increase in parameters specified in permit, owner
                                                 or operator must notify Regional Administrator and sample ground water
                                                 in all monitoring wells for Appendix IX constituents.
                                                -Compliance Monitoring - Implemented when ground-water
                                                contamination  is detected. Monitoring is conducted to determine whether
                                                                                                                                 To obtain background water-quality data and
                                                                                                                                 evaluate whether ground water is being
                                                                                                                                 contaminated.
                                                                                                                                 To obtain background water-quality data or
                                                                                                                                 evaluate whether ground water is being
                                                                                                                                 contaminated (detection  monitoring), to
                                                                                                                                 determine whether groundwater quality
                                                                                                                                 standards are being met (compliance
                                                                                                                                 monitoring), and to evaluate the effectiveness
                                                                                                                                 of corrective action measures.
(Continued)

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Table 2. (Continued)

Statutory authority
                    Monitoring provisions'
    Monitoring objectives
Resource Conservation and
  Recovery Act (cont.)
  -Subtitle C (cont.)
  or not regulated units are in compliance with the ground-water protection
  standard specified in facility permit. Samples must be taken and analyzed
  at least quarterly for parameters specified in the permit. Samples must
  also be analyzed for a specific list of constituents (Appendix IX to
  Part 284).
  -Corrective Action Monitoring - Implemented if compliance monitoring
   indicates that specified concentration levels for specified parameters are
   being exceeded and corrective measures are required. Monitoring must
   continue until specified concentration  levels are met. Parameters and
   monitoring frequency not specified.
  -Exemptions are provided  from these regulations for owner or operator
   exempted  under Section 284.1, or if Regional Administrator finds unit is
   engineered structure; does not receive or contain liquid waste or waste
   containing free liquids; is designed and operated to exclude liquids
   precipitation, and other run-on and run-off; has both inner end outer
   containment  layers; has a leak detection system built into each
   containment  layer; owner  or operator will provide continuing operation
   and maintenance of leak detection systems; and to a reasonable degree of
   certainty will  not allow  hazardous constituents to migrate beyond the
   outer containment layer prior to end of post-closure care period.
-Subtitle D
The 1984 Hazardous and Solid Waste Amendments require EPA to revise criteria
  for solid waste management facilities that may receive household hazardous
  waste or small quantity generator hazardous waste. At a minimum, the
  revisions must require ground-water monitoring, establish location criteria and
  provide for corrective action.
On August 30, 1988, EPA published proposed  rules requiring ground-water
  monitoring at all new and existing municipal solid waste landfills.
-Subtitle I
Ground-water monitoring is one of the release detection options available for
  owners and operators of petroleum underground storage tanks. It is also an
  option at existing hazardous substance underground storage tanks until
  December 22,  1998. At the end of this period, owners and operators must upgrade
  or replace this  release detection method with secondary containment and intersti-
  tial monitoring unless a variance is obtained.
Safe Drinking Water Act
-Part C-Underground
 Injection Control Program
Ground-water monitoring requirements may be specified in a facility permit for
  injection wells used for in-situ or solution mining of minerals (Class III wells)
  where injection is into a formation containing less than 1 0,000 mg/1 TDS.
Parameters and monitoring frequency not specified except in areas subject to
  subsidence or collapse where monitoring is required on a quarterly basis.
Ground-water monitoring may also be specified in a permit for wells which inject
  beneath the deepest underground source of drinking water (Class I wells).
  Parameters and monitoring frequency not specified in Federal regulations.
To evaluate whether ground water is being
contaminated.
(Continued)

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Table 2. (Continued)

Statutory authority
             Monitoring provisions*
      Monitoring objectives
Surface Mining Control  and
  Reclamation Act
Toxic Substance Control Act
  -Section 6
Ground-water monitoring is specified in Federal regulations for surface and
  underground coal mining operations to determine the impacts on the
  hydrologic balance of the mining and adjacent areas. A ground-water
  monitoring plan must be developed for each mining operation (including
  reclamation). At a  minimum, parameters must include total dissolved solids or
  specific conductance, pH, total iron, and total manganese. Samples must be
  taken and analyzed on a quarterly basis.
Monitoring of a particular water-bearing stratum may be waived by the regulatory
  authority if it can be demonstrated that it is not a stratum which serves as an
  aquifer that significantly ensures the  hydrologic  balance of the cumulative
  impact area.

Ground-water monitoring specified in Federal regulations requires monitoring
  prior to commencement of disposal operations for RGBs. Only three wells  are
  required if underlying earth materials are homogeneous, impermeable and
  uniformly sloping in one direction. Parameters include (at a minimum) PCBs,
  pH, specific conductance, and chlorinated organics. Monitoring frequency  not
  specified.
No requirements are established for active life or after closure.
To obtain  background water-quality date and
evaluate whether ground water is  being
contaminated.
To obtain background water-quality data

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    If proper monitoring well design and construction tech-
niques are not employed during monitoring well installation,
the data collected from the well may not be reliable. For
example, Sosebee et al. (1983) determined that the solvent used
to weld lengths of polyvinyl chloride (PVC) casing together can
leach significant amounts of tetrahydrofuran, methylethyl ke-
tone, methylbutyl ketone, and other synthetic organic chemi-
cals into water that comes in contact with the solvent-welded
casing joint. This could result in  false determinations of the
presence of certain chemical constituents in water samples
taken from PVC wells in which the joints were solvent welded.

    Monitoring well installation procedures can also have a
significant impact  on the integrity of ground-water  samples.
For example, Brobst and Buszka (1986) found that organic
drilling fluids and bentonite drilling muds used in mud rotary
drilling can have an effect on the chemical oxygen demand of
ground water adjacent to the wellbore in a rotary-drilled well.
This, in turn, can affect the quality of a water sample taken from
such a well, resulting in the  acquisition of non-representative
ground-water samples.

    Vertical seepage of leachate  along well casing can also
produce  non-representative samples. Monitoring wells are
frequently sealed with neat cement grout, bentonite, or a ce-
ment-bentonite mixture.  The correct choice of a grout and the
proper emplacement method to ensure a seal  are critical to
assure ground-water  sample integrity and prevent cross con-
tamination of aquifers. Wehrmann (1983) noted  that while a
neat cement grout is often recommended, shrinkage  and cracking
of the cement upon curing can create an improper seal. Kurt and
Johnson (1982) have presented the  case that the smooth surface
of thermoplastic casing provides a potential path for vertical
leakage between the casing and the grout material. The impli-
cations of the impact of adhesion,  including chemical bonding,
versus swell pressure have not been documented in the litera-
ture. However, it is known that vertical leakage  between the
casing and the grout  material may occur because of swelling
and shrinkage during the curing of the grout.

    This brief synopsis of potential problems associated with
improper monitoring well design and installation illustrates that
there are a number of design elements that must be addressed in
proper monitoring well construction.  This manual attempts to
discuss the basic elements that lead  to the construction of a
viable monitoring well. Where appropriate, potential problems
or pitfalls are discussed.

Organization  of the Document
    This document contains 8 major sections and  3 supporting
appendices. A complete list of references can be found imme-
diately following Section 8, Section 1, "Introduction," provides
an explanation of the  impetus for this "Handbook" and includes
a brief discussion of the regulatory  framework for ground-water
monitoring regulations. Section 2, "Factors Influencing Ground-
Water Monitoring Well Design and Installation," discusses the
importance of sizing  a monitoring  well in accordance with the
intended purpose of the well. Section 2 also describes the
importance of monitoring well location and the  influence of
hydrogeology,  contaminant characteristics  and  anthropogenic
influences on monitoring  well design.  Section 3,  "Monitoring
Well Planning Considerations," explains the importance of
keeping detailed records during the entire existence of the
monitoring well from installation through sampling to aban-
donment.  A discussion of the necessity of decontamination
procedures for drilling equipment used during monitoring well
installation is also included in this section. Section 4, "Descrip-
tion and Selection of Drilling Methods," includes a brief dis-
cussion of drilling and sampling methods used during monitor-
ing well construction and the advantages and disadvantages of
each technique. The focus of this section is a set of matrices
(included in Appendix B) that indicate favorable drilling
techniques for  monitoring wells with certain specifications
drilled in  selected hydrogeologic settings. Section  5, "Design
Components of Monitoring Wells," describes the materials and
installation techniques  for casing, well intakes, and filter packs.
A discussion of grout  mixtures  and emplacement techniques is
also presented. Section 6, "Completion of Monitoring  Wells,"
provides a description  of well completion techniques and types
of well completions designed to maximize collection of repre-
sentative ground-water samples. Section 7, "Monitoring Well
Development,"  discusses the importance of proper develop-
ment and  describes techniques Used  in monitoring  wells. Sec-
tion 8,  "Monitoring Well Network  Management Considerations,"
discusses the importance of maintenance and proper well
abandonment coupled  with the  necessity for Recordkeeping.

    Also included within the document are a glossary and three
supporting Appendices. The glossary contains pertinent ground-
water monitoring terms. Appendix A contains a detailed dis-
cussion of installing  monitoring wells with a hollow-stem
auger. Appendix B includes a set  of matrices designed to assist
in the  selection of drilling technologies. Appendix C is a
reproduction of a standard for well abandonment.

References
Brobst,R.D. and P.M. Buszka, 1986. The effect of three drilling
    fluids on ground-water sample chemistry; Ground Water
    Monitoring Review, vol. 6, no.  1, pp. 62-70.
Kurt, Carl E. and R.C.  Johnson, Jr., 1982. Permeability of grout
     seals surrounding thermoplastic well casing; Ground
    Water, vol. 20, no. 4, pp.  415419.
Office of Technology Assessment, 1984. Protecting the
    nation's ground water from contamination,  vols. I and II;
    United States Congress, Washington, D.C., 503 pp.
Sosebee, J.B.,  P.C. Geiszler, D.L. Winegardner and C.R
    Fisher, 1983. Contamination of ground-water samples
    with PVC adhesives and PVC primer from monitor
    wells; Proceedings of the ASTM Second Symposium on
    Hazardous and Industrial Solid Waste Testing,  ASTMSTP
    805,  R.A. Conway and W.P. Gulledge, eds., American
     Society for  Testing and Materials,  Philadelphia,
    Pennsylvania, pp. 38-50.
United States Environmental Protection Agency, 1986. RCRA
    ground-water monitoring technical  enforcement guidance
    document; Office  of Waste Programs Enforcement, Office
    of Solid Waste and Emergency Response, OSWER-9950.1,
    United States Environmental Protection Agency, 317 pp.
United  States Environmental  Protection Agency,  1987. Test
    methods for evaluating solid waste, physical/chemical
    methods (SW-846); Office  of Solid Waste and Emergency
    Response, Government Printing Office, Washington, D. C.,
    519pp.
                                                         7

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Wehran Engineering Corporation, 1977. Procedures manual   Wehrmann, H. Allen, 1983. Monitoring well design and
    for ground-water monitoring at solid waste disposal facilities       construction; Ground Water Age, vol. 17, no. 8, pp. 35-38.
    (SW-61  1); National Technical Information Service,
    Springfield, Virginia, 269 pp.

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                                                    Section 2
                                  Factors Influencing  Ground-Water
                              Monitoring  Well Design and Installation
Geologic and Hydrogeologic Conditions
    The geologic and hydrogeologic conditions at a site affect
the occurrence and movement of ground water and contaminant
transport in the subsurface. Concomitantly, these two factors
significantly influence the design and  construction techniques
used to install a monitoring well. The following discussion of
the geologic and hydrogeologic conditions pertinent to the
design and construction of monitoring wells is divided into two
parts. The first part addresses regional geologic and hydrogeo-
logic conditions that impact ground-water occurrence, and
hence the types of water-bearing materials that are likely to be
monitored. Non-exploitable aquifers in some cases, must also
be monitored. The second part of this discussion focuses more
on site-specific geologic and hydrogeologic conditions that can
affect the design of a monitoring well and selection of an
appropriate method for drilling and constructing the well.

Hydrogeologic Regions of the United States
    Heath (1984) has developed a classification system that
divides the United States into ground-water regions based on
ground-water occurrence and availability. Because the presence
of ground water in the subsurface is closely related to geologic
conditions, areas with similar rock composition and structure
tend to form similar  ground-water regions.  The classification
system developed by Heath (1984) uses the type and interre-
lationship of the aquifers in an area as the major division for
regional designation.  Additional factors including:  1) primary
versus secondary  porosity, 2) mineral composition of the aquifer,
3) hydraulic characteristics of the aquifer, and 4) the effects of
recharge and/or discharge areas were used to further define
each region. Figure 1 illustrates the division of the United States
into  15 ground-water regions. For the purposes of this discus-
sion, however, Puerto Rico and the Virgin Islands will be
excluded. Because the primary focus of this discussion is
limited to the hydrogeologic conditions pertinent to monitoring
well construction, the reader is referred to Heath (1984) for
additional information on each ground-water region.

Western Mountain Ranges —
    The  Western Mountain Ranges are comprised of tall,
massive mountains separated by narrow, steep-sided valleys. In
many areas, the  mountains have  been subjected to  alpine
glaciation. Major lowland areas occur between the mountain
ranges in the southern part of this region. With geologic origins
related to major erogenic and tectonic events, most of the
mountain ranges are  comprised of metamorphic and igneous
rocks flanked by consolidated sedimentary rocks of Paleozoic
to Cenozoic age. Other mountain ranges such as the Cascades
and the San Juan mountains are composed primarily of basaltic
lava.
    Bare bedrock exposures or a thin layer of weathered
material cover the slopes and summits of the mountains. The
weathered layer tends to thicken toward the base of the moun-
tains and in the alluvial valleys. Figures 2a and 2b illustrate the
location and main geologic and hydrogeologic features of this
region. Despite high precipitation rates in the region,  ground-
water resources are primarily limited to the storage capacity of
the fractures in the crystalline rocks that serve as an aquifer for
this area. The lowlands between the mountain ranges contain
thick deposits of fine to coarse-grained alluvium eroded from
the adjacent mountains. These deposits serve  as aquifers that
are capable of supplying moderate to large yields to wells. The
alluvial aquifers are often in direct hydraulic connection with
the underlying bedrock.

Alluvial Basins  —
    The Alluvial Basins region is comprised of thick alluvial
deposits in structural lows alternating with igneous and meta-
morphic mountain ranges. This region covers two distinctive
areas: 1) the Basin and Range area of the southwest and 2) the
Puget Sound/Willamette Valley Area of the Pacific Northwest
(Figure  3a).

    The Basin and Range area consists of basins filled with
thick  deposits of unconsolidated alluvial material eroded  from
the adjacent  mountains and deposited as coalescing alluvial
fans.  The alluvial materials in the fans are typically  coarsest
near the mountains and become progressively finer toward the
center of the basin. These basins typically form closed-basin
systems where no surface or subsurface flow leaves the region.
However,  water may move through the permeable deposits and
actually move between basins in a complex hydrogeologic
relationship as illustrated in Figure 3b. Most ground water in
this region is obtained from the permeable sand and gravel
deposits that are  interbedded with finer-grained layers  of
saturated silts and clays.

    The alluvial deposits of the Puget Sound were deposited by
sediment-laden meltwater from  successive glaciation. Thick
layers of permeable sands and gravels that are interbedded with
discontinuous clay layers provide the majority of the water
resources for this area. The Willamette Valley consists  of
interbedded sands, silts and clays deposited by  the Willamette
River and  related streams. High precipitation rates in the region
provide the major source of recharge to these aquifers.

    The mountains bordering these alluvial basins consist of
igneous and metamorphic rocks ranging from Precambrian to
Tertiary in age. The limited water resources in the mountains
are derived from water stored in fractures in the bedrock.

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              2. Alluvial Basin
1. Western
  Mountain Ranges
          4. Colorado Plateau
          and Wyoming Basin
                                                     15. Puerto Rico
                                                          and
                                                      Virgin Islands
                                                                                         800
                                                                                                    a. Northeast and
                                                                                                    Superior Uplands
                       1, Western
                       Mountain Ranges
                        9. Northeast and
                        Superior Uplands
                                                                               6. Nonglaciated
                                                                               Central Region
                       \  7. Glaciated
                          Central Region
                            6. Nonqlaaated
                            Centra Region
                                                                             11. Southeast
                                                                             Coastal Plain
                                                                                                                7. Glaciated
                                                                                                                   Central
                                                                                                                   Region
                                                                                                            6. Nonglaciated
                                                                                                            Central Region
                                                             8. Piedmont and
                                                               Blue Ridge
 Figure 1. Ground-water regions of the United States (Heath, 1984).
Figure 2a. Location of the Western Mountain Ranges region
           (Heath, 1984).
                                                        (b)


                           Figure 2b. Topographic and geologic features In the southern
                                     Rocky Mountains part of the Western Mountain
                                     Ranges region (Heath, 1984).
                                                               10

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Figure 3a. Location of the Alluvial Basins region (Heath, 1984).
 ^•^:^:r^'^:?vx
 ,ife >j™c^' '< •; n™ Ph«,y • A/:V/• • -^v..
                      ;. i Dry Playa •
                                   PhrealophytesA • :^-
        :
                           (b)
Figure 3b. Common ground-water flow systems In the Alluvial
          Basins region (Heath, 1984).
                         (a)

Figure 4a.  Location of the Columbia Lava Plateau region
          (Heath, 1984).
                                                                                                   Older Mountains
                                                                                                     Explanation
                                                                                                  Present Soil Zone
                                                                                                       \ Interflow
                                                                                             Lava *rrrar-VZone
                                                                                                    iiltj and CJay
                                                                                                   Cooling Fractures
                           (b)
Figure 4b. Topographic and geologic features of the Columbia
          Lava Plateau region (Health, 1984).
Columbia Lava Plateau  —
    The Columbia Lava Plateau consists of a sequence of lava
flows ranging in total thickness from less than 150 feet adjacent
to mountain ranges to over 3,000 feet in south-central Washing-
ton and northern Idaho (Figure 4a).  The lava is composed of
basalt that erupted from extensive fissures and produced large
sheet-like flows. The lava beds comprise the principal water-
bearing unit in the region.

    Ground water in basalt flows through the permeable zones
that occur at the contacts between the lava flow layers (Figure
4b). The permeable zones result from the cooling of the crust on
the molten lava as it continues to flow thus producing a zone of
fragments and gas bubbles near the top of the lava sheet.
Cooling of the lava sheet itself also produces vertical fracturing
within the basalt. These interflow zones, created by the cooling
crust, form a complex  series of relatively horizontal aquifers
separated by denser layers of basalt that are often hydraulically
interconnected by the intersecting fractures and faults within
the  lava sheets.
    The region can be divided into two separate hydrogeologic
flow regimes. The Columbia River Group, in the western part
of this region, consists of relatively thick basalt flows that have
been  offset by normal faults. Primary water movement is
through shallow interflow zones. The aquifers are typically
poorly hydraulically  interconnected because the flow is con-
trolled by the faults which form barrier-controlled reservoirs.

    The remainder of the region, occupied by the Snake River
Plain, consists of a series of thin lava flows with well-developed
interflow zones and extensive fracturing.  These interflow
zones exhibit high hydraulic conductivities and are hydrauli-
cally interconnected by cooling fractures. The  large differences
in hydraulic conductivity  between the interflow zones and the
denser basalt often result  insignificant differences in hydraulic
head between aquifers. Consequently, there is the potential for
the movement of water between aquifers through uncased or
improperly cased wells.

    Recharge to the  aquifer is from precipitation and infiltra-
tion from streams that flow onto the plateau from adjacent
                                                         11

-------
mountains. Irrigation of crops in this region provides additional
recharge to the aquifer through the interflow zones when the
source of water is not from the aquifer.

Colorado Plateau  and  Wyoming Basin —
    The Colorado Plateau and Wyoming Basin region is char-
acterized by abroad  structural plateau underlain by horizontal
to gently dipping beds of consolidated  sedimentary rock. In
some areas, the structure of the plateau has been modified by
faulting and folding that resulted in basin and  dome features.
The region contains  small, isolated mountain ranges as well as
extinct volcanoes and lava fields (Figures 5a and 5b).

    The sedimentary rocks in this region consist of Paleozoic-
to Cenozoic-age  sandstones,  limestones  and shales. Evaporitic
rocks such as gypsum and halite also occur in some areas. The
sandstones serve as the principal source of ground water. Water
within the sandstone is contained within pore spaces and in
fractures and bedding planes. Minor deposits of unconsolidated
alluvium occur in major river valleys and contribute small to
moderate yields of ground water.

    Recharge to the aquifers is from precipitation and from
infiltration from streams that cross the outcrop areas. The gentle
                                                  dip of the beds causes unconfined conditions in outcrop areas
                                                  and confined conditions downdip. Aquifers in the region fre-
                                                  quently contain mineralized water at depth.  Aquifers typically
                                                  discharge to springs and seeps along canyon walls.

                                                  High  Plains —
                                                       The High Plains region represents a remnant of an alluvial
                                                  plain deposited by streams and rivers that flowed eastward from
                                                  the  Rocky  Mountains during the Tertiary  period. Extensive
                                                  erosion has subsequently removed a large portion of the plain,
                                                  including most areas adjacent to the mountains.

                                                       The High Plains region is underlain primarily by the
                                                  Ogallala formation, a thick deposit of semi-consolidated allu-
                                                  vial materials consisting of poorly-sorted sands, gravels, silts
                                                  and clays (Figures 6a and 6b).  The Ogallala formation is the
                                                  major  aquifer and is overlain locally by  younger alluvial mate-
                                                  rial that is often  saturated and forms a part of the aquifer. In
                                                  places where the Ogallala is absent, these younger  alluvial
                                                  deposits, that are comprised of unconsolidated sand, gravel, silt
                                                  and clay, are used as the major aquifer. Extensive  areas of
                                                  surficial sand dunes are also present.  In some areas, older
                                                  underlying  consolidated deposits that include the  fine-grained
                                                  sandstones of the Arikaree Group and Brule formation are
                          (a)

 Figure 5a.  Location of the Colorado Plateau and Wyoming
           Basin reqion (Heath, 1984).
                                                   Figur* 6a. Location of the High Plain* region (Heath, 1984).
      Cliff
 Fault Scan
     Extinct Volcanoesc_-__Ridges    Dome
                                                                      Plane River
                               Explanation
                       7—.Fresh r™,,
                       CUwatcr GjSandstone
                       r-iSalty  ^Limestone

                       QShale ^
                  (b)
                                                                                                   xplanation
                                                                                               GUSand  S
                                                                                               Gravel  Sandstone
                                                                                         (b)
Figure 5b. Topographic and geologic features of the Colorado     Figure 6b. Topographic and geologic features of the High Plains
Plateau and Wyoming Basin region (Heath, 1984).
                                                                        region (Heath, 1984).
                                                           1-2

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hydraulically connected to the Ogallala. Where these deposits
are absent, the Ogallala is underlain by other sedimentary rocks
that often contain unusable, highly mineralized water.

    Recharge to the aquifer from precipitation varies across the
area.  The presence of caliche, a low permeability  calcium
carbonate layer at or near the land surface, limits the amount of
precipitation that infiltrates to the aquifer, thereby increasing
the amount of water lost to evaporranspiration. In the sand
dunes area, however,  the permeability of the surface materials
allows increased recharge to the aquifer.

    Extensive development of the aquifer for agricultural irri-
gation has led to long-term  declines in water levels. Where
ground-water withdrawal rates have exceeded available re-
charge to the aquifer, ground-water mining has occurred. The
depletion of water from storage in the High Plains region has
resulted in a decrease in the saturated thickness of the aquifer in
areas  of intensive irrigation.

Nongladated Central Region  —
    The Nonglaciated Central region covers a geologically
complex area extending from  the Appalachian Mountains to the
Rocky Mountains. Most of the region is underlain by consoli-
dated sedimentary rocks, including sandstones, shales, car-
bonates and conglomerates that range from Paleozoic to Ter-
tiary in age (Figures 7 a, 7b and 7c). These rocks are typically
horizontal to  gently dipping with the exception of a few areas,
notably the Valley and Ridge  section; the Wichita and Arbuckle
mountains in Oklahoma, the Ouachita Mountains in Oklahoma
and Arkansas;  and the Triassic basins in Virginia and North
Carolina. The Triassic  basins contain interbedded shales,
sandstones and conglomerates that have been faulted and
invaded by igneous rocks.

    Chemical and mechanical weathering of the bedrock has
formal a layer of regolith that varies in thickness and compo-
sition depending on the composition and structure of the under-
lying parent rock and the effects of climate and topography. The
sandstones and limestones constitute the major aquifers in the
area. Water occurs primarily in bedding planes and fractures in
the bedrock. Many of the limestones contain solution  channels
that increase  the permeability. Limestones in this region often
form  extensive cave systems that directly affect patterns of
ground-water flow.

    Recharge in the region occurs primarily from precipitation
in outcrop areas and varies widely. Small to moderate well
yields are common; higher yields may be available in karstic
areas. Well yields often depend on the size and number of
fractures intersected by the well, the recharge to the area and the
storage  capacity and permeability of the bedrock and/or rego-
lith. In many parts of this region, mineralized water  occurs at
depths greater than 300 feet.

Glaciated Central Region —
    The geology of the Glaciated Central region is character-
ized by relatively horizontal  sedimentary recks of Paleozoic to
Tertiary age consisting of sandstones, shales and carbonates.
The bedrock is overlain by varying thicknesses of poorly-sorted
glacial till that is interbedded with: 1) well-sorted sands and
gravels deposited from meltwater streams, 2) clays  and silts
Figure 7a. Location of the Nonglaciated Central region
          (Heath,  1984).
  Regolith
                                     I   I Fresh Water
                                     OO Salty Water
                            (b)
Figure 7b. Topographic and geologic features of the
          Nonglaciated Central region (Heath, 1984).
                            i—, Fresh
                            1—I Water
Explanation
    t •••! Sandstone
    E~3 Shale
        Metamorphic
                            (c)

Figure 7c. Topographic and geologic features along the western
          boundary of the Nonglaciated Central region (Heath,
          1984).
                                                           13

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  from glacial lake beds and 3) wind-blown silt or loess deposits
  (Figures 8a and 8b).

      In  the eastern part of the region, the glacial deposits are
  typically thin on the uplands and thicken locally in valleys.
  Toward the central and western parts of the region, glacial
  deposits are thicker and often mask the location of preglacial
  river valleys. These thick deposits in the preglacial river valleys
  often contain permeable sands and gravels that form major
  aquifers with significant well  yields. Overlying  till deposits
  often act as confining layers for the underlying sand and gravel
  aquifers.

      The underlying bedrock in this region also commonly
  serves as an aquifer. Water occurs primarily along bedding
  planes and in fractures. Frequently the glacial deposits and the
  bedrock are hydraulically interconnected. The glacial deposits
  often provide recharge to the bedrock aquifers and serve as a
  source of water for shallow  wells. Movement of poor-quality
  water from the bedrock into the glacial deposits may cause local
  ground-water quality problems.  Recharge to the glacial deposits
  is provided by precipitation and by infiltration from streams.
                              Recharge rates primarily vary with precipitation rates, evapo-
                              transpiration rates, permeability of the glacial materials and
                              topography.

                                  Ground-water supplies are abundant in this area well
                              yields are moderate to high. Smaller yields are expected in areas
                              where the glacial deposits are fine-grained or where the un-
                              derlying bedrock has an insufficient amount of fractures or
                              solutioning. Because of the widespread occurrence of carbon-
                              ate rocks, ground water in these areas frequently exhibits high
                              hardness.

                              Piedmont and Blue Ridge —
                                  The Piedmont lies between the coastal plain and the Appa-
                              lachian Mountains. The region is  characterized by a series of
                              low, rounded hills that gradually increase in height toward the
                              west and culminate in the parallel ranges of the Appalachian
                              Mountains in the north and the Blue Ridge Mountains in the
                              south. The bedrock of the region consists of Precambrian to
                              Mesozoic-age igneous, metamorphosed-igneous and sedi-
                              mentary rocks (Figures 9a and 9b).
                            (a)
  Figure 8a. Location of the Glaciated Cantral region (Heath,
           1984).
                                                        (a)
                              Figure 9a. Location of the Piedmont and Blue Ridge region
                                        (Heath, 1984).
          Moraine,.
                                      *"Sind and 0 ravel <^
Loess
igg|^^
•-^...*to,-_^
                                                           BedrockOutcrops
                  , r-   ._ „,      Best Wel1 Sites
                  i Fresh Water   |ndicated with X's
              r~l Saity Water
(b)
                                                                                   (b)
  Figure 8b. Topographic and geologic features of the Glaciated     Figure 9b. Topographic and geologic features of the Piedmont
           Central region (Heath, 1984).                                 and Blue Ridge region (Heath, 1984).
                                                        14

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    Active chemical and physical weathering of the bedrock
has formed  a clay-rich,  unconsolidated deposit that overlies
bedrock. This deposit, called saprolite or regolith is typically
thinner on ridges and thickens on slopes and in valleys. Larger
streams in many valleys have deposited  significant thicknesses
of well-sorted alluvial materials that often overlie the saprolite.

    The regolith serves two purposes in  the  ground-water
system: 1) the regolith yields small to moderate quantities of
water to shallow wells and 2) the  regolith serves as a storage
reservoir to  slowly recharge the bedrock aquifer. The storage
capacity in the bedrock  is limited because the ground water
occurs along fractures and in joints.  Water-supply wells are
often completed in both the regolith and in  the bedrock.

    Well yields in this region are  extremely variable; bedrock
wells that intersect fractures and/or have sufficient recharge
from the overlying regolith are the most productive. A higher
density of fractures typically occurs along valleys and in draws
bordering  ridges.

Northeast  and Superior Uplands —
    The Northeast and Superior Uplands cover two geographic
areas: 1) the Northeast includes the Adirondack Mountains and
most of New England, and 2) the Superior Uplands include
most of northern Minnesota and  Wisconsin. Both areas are
underlain by Precambrian to Paleozoic-age  igneous and meta-
morphic rocks that have been intruded by younger igneous
rocks and have been extensively folded and faulted (Figures
 lOaandlOb).
    The bedrock is overlain by unconsolidated glacial deposits
that vary  in thickness. These  glacial deposits include poorly-
sorted glacial tills,  glacial lake  clays, and well-sorted sands and
gravels  laid down by mekwater streams. The glacial sands and
gravels  serve as important aquifers and are capable of produc-
ing moderate to large yields. Ground water in the bedrock is
typically found in fractures or joints  and the rock has a low
storage  capacity. The glacial deposits provide recharge by  slow
seepage to the underlying bedrock. Wells  are often completed
in both  bedrock and the glacial deposits to provide maximum
yields. Recharge to the glacial deposits occurs primarily  from
precipitation.

Atlantic  and  Gulf Coastal Plain —
    The Atlantic and Gulf Coastal Plain region extends south-
ward from Cape Cod to the Rio Grande River in Texas. The
region is underlain by Jurassic  to Recent-age semi-consolidated
to unconsolidated  deposits of sand, silt and clay laid down by
streams draining the adjacent upland areas. These deposits are
very  thin toward  the inner edge  of the  region and thicken
southward and eastward. The thickest deposits occur in a down-
warped  zone termed the Mississippi Embayment. All deposits
either dip  toward the coast or toward the axis of the embayment;
therefore, the older formations outcrop along the inner part of
the region and the youngest outcrop along the gulf coastal  area.
Coarser-grained material is more abundant updip, and clay and
silt layers tend to thicken downdip (Figures 1 la and 1 Ib).
Limestone and shell beds also occur in some areas and serve as
productive and important aquifers.
Figure 10a. Location of the Northeast and Superior Uplands
           region (Heath, 1984).
 Figure 1 la. Location of the Atlantic and Gulf Coastal Plain
           region (Heath, 1984).
                                                            IZHFresh Water  SBSalty Water

                                                                                        (b)
Figure 10b. Topographic and geologic features of the Northeast    Figure 1 Ib.  Topographic and geologic features of the Gulf
           and Superior Uplands region (Heath,  1984).                       Coastal Plain (Heath, 1984).

                                                           15

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    Recharge to the aquifer occurs in outcrop areas from
precipitation and from infiltration along  streams and rivers.  In
some areas an increase downdip in the percentage of clay in the
deposits limits recharge and affects ground-water flow paths.
Ground-water withdrawals in these  areas sometimes exceed
recharge to the aquifer and result in declining water levels and
land subsidence.

Southeast Coastal Plain —
    The Southeast Coastal Plain includes all  of Florida and the
southern parts of Alabama and Georgia. The surficial deposits
in this area are comprised of unconsolidated Pleistocene-age
sand, gravel, silt  and shell beds. The semi-consolidated lime-
stone beds of the  Biscayne aquifer outcrop in southern Florida.
Throughout much of the region, surficial deposits are underlain
by the Hawthorn  formation, a Miocene-age clay and silt layer.
The Hawthorn formation often serves as a confining layer. The
Hawthorn formation overlies a thick sequence of semi-consoli-
dated to consolidated limestones and dolomites known as the
Floridan aquifer (Figures  12a and 12b).

    The Floridan aquifer is one of the most productive aquifers
in the United States and is the principal ground-water resource
for the entire region. In the  northern part of the region, the
Floridan is unconfined. Most recharge to the  aquifer  occurs
from direct infiltration of precipitation in this area. In  central
and southern Florida, the aquifer is  semi-confined  by the
Hawthorn formation and recharge from the  surface is limited.
Natural discharge from the Floridan occurs from springs and
streams and from seepage through confining beds. Many  springs
with high discharge rates can be found where the Floridan
outcrops.

     In southern Florida, water in the Floridan is typically
saline. In this area, water supplies are developed in the shal-
lower Biscayne aquifer.  The Biscayne is unconfined and is
recharged directly by precipitation and by infiltration from
streams and  impoundments.

     The surficial sands and gravels also serve as aquifers in
many parts of the region, particularly where the Floridan is
saline. These aquifers supply  small to moderate yields to wells
and are recharged by infiltration of precipitation.
Alluvial  Valleys —
     The Alluvial Valleys region encompasses the thick sand
and gravel deposits laid down by streams and rivers. Figure 13a
illustrates  the extent and location of these major alluvial valleys.
Alluvial valleys typically contain extensive deposits of sands
and gravels that are often interbedded with overbank deposits
of silts and clays. The origin of many of the alluvial aquifers is
related to  Pleistocene continental and alpine glaciation. Sedi-
ment-laden meltwater from the glaciers deposited extensive
sands and gravels in many stream  valleys. These permeable
sands and gravels are capable of yielding moderate to large
water supplies to wells. These aquifers are typically confined to
the boundaries of the flood plain and to adjacent terraces
(Figure 13b).

     In many of the alluvial valleys, ground-water systems and
surface water systems are hydraulically interconnected.  Re-
charge to  the aquifer occurs from streams and from precipita-
tion. Withdrawals of ground water near a stream may cause a
reversal of hydraulic gradients; ground water previously flow-
ing from  the aquifer and discharging to the stream may now
receive recharge from the stream by induced infiltration.

Hawaiian Islands —
     The Hawaiian Islands  were formed by volcanic eruptions
of lava. These shield volcanoes rise from the ocean floor and
form the eight major Hawaiian islands. Erosion of the volcanoes
has carved distinctive valleys and has created an adjacent
narrow coastal plain.

     The  islands are formed from hundreds of separate lava
flows composed primarily of basalt. The lavas that were extruded
beneath the sea are relatively  impermeable. Lavas that were
extruded  above sea level contain permeable interflow zones,
lava tubes and cracks and joints formed while the lava  cooled.
Lava flows in the valleys are often covered by a thin layer of
alluvium  eroded from the basalt.

     The mode of deposition of the basalt largely controls the
occurrence and flow of ground water on the islands. The
ground-water system consists of three major parts: 1) dike-
impounded water, 2) basal ground water, and 3) perched
                                                                                                      Discharge
                                                                                     -Recharge Area	1— Area-*
 Figure 12a. Location of the Southeaat Coastal Plain Region.
                            (b)
 Figure 12b.  Topographic and geologic features of the Southeast
            Coastal Plain (Heath, 1984).
                                                           16

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  Figure 13a. Location of the Alluvial Valley a ground-water region
             (Heath, 1984).

  (fresh) water (Figure 14). Dike-impounded water is found in the
 joints developed along the vertical fissures through which the
  lava erupted. Basal ground water is found in the permeable
  zones of the horizontal lava  flows extending from the eruption
  centers and is partially hydraulically interconnected to the dike-
  impounded water. The perched (fresh) water system is found in
  permeable lava or alluvial deposits above thick impermeable
  lava flows or basal ground water.

      Recharge to these aquifers occurs through the infiltration
  of precipitation. Because the volcanic  soils are highly perme-
  able,  approximately thirty percent of the precipitation infil-
  trates and recharges the  aquifer.

       The basal ground-water system is the principal source of
  water to the islands. The basal system occurs as a fresh-water
  lens floating on the denser sea water. Basal and dike-im-
  pounded ground water is  often withdrawn from horizontal
                                                                                              Mississippi River  -rerrace

                                                                                 --f:~ — -Flood PiairH"';-
                                                                                                            Explanation
                                                                                                             Gravel
                                                                                                             Sand
                                                                                                             Silt and Clay
                                                                                                          B Limestone
                                                                                           (b)
                 Figure 13b. Topographic and geologic features of a section of
                            the alluvial valley of the Mississippi River
                            (Heath,  1984).

                 tunnels and vertical  and inclined wells constructed into the lava
                 flows.

                 Alaska —
                     Alaska can be divided into four physiographic divisions
                 from south to north:  1) the Pacific Mountain  System,  2) the
                 Intermontane Plateaus, 3) the Rocky Mountain System and 4)
                 the Arctic Coastal Plain. The mountain ranges are comprised of
                 Precambrian to Mesozoic-age igneous and metamorphic rocks.
                 These are overlain by younger sedimentary and volcanic rocks.
                 Much of the region is overlain by unconsolidated deposits of
                 gravel, sand, silt clay and glacial till (Figure  15).

                     Climate directly  affects the hydrology of Alaska. Much of
                 the water at the surface and in the subsurface is frozen through-
                 out much of the year, forming a zone of permafrost or perenni-
                 ally frozen ground.  Permafrost occurs throughout the state
                                     Volcano.
         .*
Basal  Tunnel
     -~'--
  Spring
 Lava Flows
                 Dikes
                  Dike Spring
I   I Fresh Water
l~~l Sally Water
                                                                    Gravel
                                                                    Glacial Till
I—I Water
r"l Permafrost
   Figure 14. Topographic and geologic features of an Hawaiian
              Island (Heath, 1984).
                  Figure 15. Topographic and geologic features of parts of Alaska
                             (Heath, 1984).
                                                               17

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except along the southern and southeastern coasts. The depth of
permafrost varies, but is typically deeper in the northern areas
and becomes shallower toward the south.

    In zones of continuous permafrost,  ground water occurs
beneath the permafrost and in isolated zones beneath deeper
lakes and alluvial channels. In zones of discontinuous perma-
frost,  ground water occurs below the permafrost and in sand and
gravel deposits in major alluvial valleys. In the  areas where
permafrost is absent, ground water occurs both in the bedrock
and in the overlying unconsolidated deposits.

    Recharge to the aquifers is limited due to permafrost. Even
in non-permafrost areas, shallow groundwater is usually frozen
when spring runoff occurs. Most recharge  to the aquifers occurs
from  stream infiltration as the streams flow across the alluvial
deposits when permafrost is absent.

Site-Specific Geologic and Hydrogeologic
Conditions
    The geologic and hydrogeologic conditions at a specific
site influence the selection of an appropriate well design and
drilling method. Prior to the installation  of monitoring wells,
exploratory borings and related subsurface tests must usually be
made to define the geology  beneath the site and to assess
ground-water flow paths and velocity. Formation  samples and
other data collected from this work are  needed to define the
hydraulic  characteristics of the underlying materials. The logs
of these borings are used to correlate stratigraphic units across
the site. An understanding of the stratigraphy, including the
horizontal continuity  and vertical thickness of formations be-
neath the site, is necessary to identify zones of highly permeable
materials or features such as bedding  planes, fractures or
solution channels. These  zones will affect the  direction of
ground-water flow and/or  contaminant transport beneath the
site. Because the occurrence and movement of groundwater in
the subsurface are closely related to the geology, the geologic
conditions at the site influence the location, design and methods
used to install monitoring wells.

    The required depth of a monitoring well is determined by
the depth  to one or more water-bearing formations that need to
be monitored. Where two or more saturated zones occur beneath
a site and the intent of the monitoring program is to monitor
water quality in the lower zone, the monitoring well may require
surface  casing to "seal-off the upper water-bearing formation
prior  to drilling deeper.

    The formations at the site, whether consolidated or uncon-
solidated, also  influence the type of well completion. In un-
consolidated deposits, screened intakes are typically designed.
The well may have either a naturally developed or artificially-
emplaced filter pack,  depending on the grain-size distribution
of the water-bearing materials. Artificial filter packs and
screened intakes are also often required in poorly-consolidated
formations to minimize potential caving of the borehole and/or
to reduce turbidity in water samples collected from the completed
well.  In some consolidated formations, the well may be com-
pleted as a cased borehole with no screen intake or filter pack.
Where conduit-born fines are a problem in consolidated for-
mations, an artificial filter pack and a screen intake may be
required.
     Drilling methods must be chosen based at least in part on
geologic considerations. Hard, consolidated formations  restrict
or eliminate certain drilling methods. For example, in karstic
formations, cavernous openings create significant problems in
maintaining circulation and in protecting drilling equipment.
Unconsolidated deposits can also present severe limitations for
various drilling methods.  Some drilling techniques cannot be
used where large boulders are present. Conversely, cohesive
geologic deposits and the resultant stability of the borehole may
expand drilling options.  Variations in equipment, drilling
techniques and installation procedures may  be necessary to
overcome specific limitations when using particular drilling
methods.

     Consideration of the hydrogeology at the site is also
important when selecting a drilling method. The depth to which
the well must be drilled to monitor a selected water-bearing
zone may exceed the practical depths of a particular drilling
technique.  In addition, certain saturated geologic materials,
under high  hydrostatic pressures, may either 1) impose increased
frictional resistance (i.e.  expanding clays) which limits the
practical depths reached by some drilling methods or 2)  create
unstable borehole conditions (i.e. heaving sands) that may
preclude the use of some drilling methods for installation of the
monitoring well.

     For a complete discussion of well drilling methods and a
matrix for selecting a drilling method based on the general
hydrogeologic  conditions and well design requirements, the
reader is referred to  Section 4, "Description  and Selection of
Drilling  Methods."

 Facility  Characteristics
     Frequently the purpose of a monitoring,  program is to
evaluate whether or not ground water is being contaminated
from a waste  disposal practice or a commercial operation
associated with the handling  and storage of hazardous materi-
als.  In these instances, the  design and construction of the
monitoring wells must take  into  account the type of facility
being monitored and  the fate  and transport in the subsurface of
the waste materials or commercial products.

     Recognition of the type of facility being monitored is
necessary to determine whether the facility is regulated under
existing federal and/or stage statutes and administrative rules
(see Section 1). Some regulated facilities must comply with
specific ground-water monitoring  requirements,  and program-
specific guidance documents may describe the design and
construction of the monitoring wells. The type of facility or
operation may also determine the types of materials and poten-
tial contaminants which  have been handled onsite, past or
present, and whether or not those  contaminants were  stored or
disposed of on  or below the ground surface. The design  of the
facility may also include  a system  for waste or product con-
tainment that impacts potential release of contaminants, both
onsite and offsite, and may require  separate monitoring.

     The physical  and chemical characteristics of the contami-
nants, including volatility, volubility in water and specific
density,  influence the movement of the contaminant in the
subsurface. Additional factors that affect contaminant fate and
transport include: oxidation, sorption and biodegradation.
                                                           18

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Monitoring wells must be located and designed with these
environmental factors and contaminant characteristics in mind.
Construction materials for the well should be selected based on
their ability to withstand attack by contaminants that are antici-
pated at the  site.

    The following two-part discussion focuses on facility
characteristics that impact the design and construction of
monitoring wells.  The first part presents the more prominent
types of waste disposal facilities or commercial operations for
which ground-water monitoring wells are designed. The second
part focuses on those physical and chemical characteristics of
contaminants that significantly influence the transport of the
contaminant in the subsurface.

Type of Facility
Landfills —
    A landfill is  a facility or waste unit where solid waste is
typically disposed of by spreading, compacting and covering
the waste. The landfill design, construction  and operation
details vary depending on the physical conditions at the site and
the type and amount of solid waste to be disposed. Wastes are
usually emplaced and covered in one of three settings: 1) on and
above the natural ground surface where surface topography is
flat or gently rolling, 2) in valleys, ravines or other land
depressions, or 3) in trenches excavated into the subsurface.
The design of the landfill determines the boundaries of the fill
area and the lowest elevation at which the  solid waste is
disposed. The physical  dimensions of the landfill are important
criteria for locating and designing the depth of monitoring  wells
used to monitor the quality of ground water in  the first water-
bearing zone beneath the bottom of the landfill.

    The wastes that are disposed of in landfills are generally
classified as either hazardous or non-hazardous.  Wastes that are
characterized as  hazardous are regulated in Title 40 of the
United States Code of Federal Regulations (CFR) Part 261. The
distinction between a landfill receiving  hazardous, waste versus
non-hazardous waste is important from a regulatory standpoint
when developing a ground-water monitoring program. Land-
fills receiving wastes classified as hazardous are subject to
minimum federal regulations for the design and operation of the
landfill (40 CFR, Parts 264 and 265, Subpart N and Part 268)
and for ground-water protection and monitoring  (40 CFR,  Parts
264 and 265, Subpart F). These regulations  are mandated under
the Resource Conservation and Recovery Act (RCRA) and
subsequent amendments to RCRA. Individual states may be
authorized by the United  States Environmental Protection
Agency to enforce the minimum federal regulations and may
adopt separate state regulations more stringent than the federal
standards.

    Landfills receiving non-hazardous wastes are also regulated
under RCRA; however, these facilities are  addressed under
different federal guidelines or recommendations for the design
and operation of sanitary landfills and for ground-water pro-
tection measures (40 CFR, Part 241, Subpart B). Properly
designed landfills should include a bottom  liner of compacted,
low permeability soil and/or synthetic liner to minimize the
percolation of leachate from the landfill into the subsurface. A
leachate collection system should also be installed beneath the
landfill to control leachate migration and permit the collection
of leachate for final treatment and disposal. Hazardous waste
landfills are subject to minimum, federal technological guide-
lines for "composite  double liner systems" (including com-
pacted low permeability soils and two flexible synthetic mem-
branes) that incorporate both primary and secondary leachate
collection systems. Many older or abandoned landfillls containing
both hazardous and/or non-hazardous wastes are unlined and
have been unregulated throughout the operational life of the
facility.

     Ground-water monitoring programs at hazardous waste
land disposal facilities are also subject to federal requirements,
including performance criteria. The regulations require that a
sufficient number of wells be constructed at appropriate loca-
tions and depths to provide ground-water samples from the
uppermost aquifer. The purpose of ground-water monitoring is
to determine the impact of the hazardous waste facility on
ground water in the uppermost aquifer. This is done by compar-
ing representative  samples of background water quality to
samples taken from the downgradient margins of the waste
management area. The ground- water monitoring wells must be
properly cased, completed with an artificial filter pack, where
necessary,  and grouted  so  that  representative ground-water
samples can recollected (40CFR,  Sections 264.97 and 265.91).
Guidance for the design and construction of these monitoring
wells is provided in the RCRA  Ground Water Monitoring
Technical  Enforcement Guidance  Document (TEGD). Owners
and  operators should be prepared to provide evidence  that
ground-water monitoring measures taken at concerned facili-
ties are adequate.

     A potential monitoring problem at all landfills, particularly
older facilities, is the accurate location of the boundaries of the
landfill. If the boundaries of the fill area are unknown, monitor-
ing wells may not be accurately placed to properly define
subsurface conditions with respect to the actual location of the
disposal site. Accidental drilling into the landfill causes safety
and health concerns. All personnel involved in the drilling of
monitoring wells at hazardous waste treatment, storage  and
disposal facilities, or in  the direct supervision  of such drilling,
should have received  initial training in working in hazardous
environments in accordance  with the regulations of the Occu-
pational Safety and Health Administration (29 CFR, Section
1910.120).

Surface Impoundments —
     Surface impoundments are used for the storage,  treatment
and/or disposal of both hazardous and non-hazardous liquid
wastes. Impoundments or lagoons  can be constructed either in
natural depressions or excavations or created by surface  diking.
The  impoundments typically are used to settle suspended
solids. Liquid wastes within the impoundment are usually
treated chemically to cause precipitation or coagulation of
wastes. Surface impoundments may  be either "discharging" or
"non-discharging." Discharging impoundments are  designed to
intentionally permit the supernatant fluid to overflow into
receiving streams for  final treatment and  disposal. Non-dis-
charging impoundments can either intentionally or uninten-
tionally lose liquids through seepage into the subsurface or
through evaporation.

    The  size of a surface impoundment can range from a
fraction of an  acre to thousands of acres in surface area. The
                                                          19

-------
depths of these impoundments reportedly range from 2 feet to
more than 30 feet below the ground surface (Office of Technol-
ogy Assessment, 1984). The specific design and operation
requirements  for surface impoundments that contain hazardous
materials are regulated under RCRA (40 CFR, Parts 264 and
265, Subpart  K). To prevent waste infiltration, hazardous waste
impoundments are subject to minimum federal technological
guidelines for a "compacted  soil double liner  system" (includ-
ing compacted, low permeability soil and a single flexible
synthetic liner). A leachate collection system is also required to
contain any leachate that does infiltrate into the subsurface.

    Hazardous waste impoundments are subject to the  same
minimum  federal ground-water protection and monitoring
regulations discussed above for hazardous  waste  landfills.
Water levels in monitoring wells located too close to im-
poundments often reflect the effects of mounding on the water
table  and lead to inaccurate  interpretation of the water-level
data (Beck, 1983). The design depth of the monitoring wells
also depends on the depth of the bottom of the surface im-
poundment below ground level and the depth of the first water-
bearing zone underlying the bottom of the impoundment.

 Waste and  Material Piles —
    Large quantities of both wastes  and materials may be
stockpiled for storage.  Stockpiled material may include poten-
tially  hazardous material such as highway deicing salts, copper,
iron, uranium and titanium ore, coal, gypsum and phosphate
rock. Hazardous waste piles can also  be generated by other
industrial operations and vary in composition. Waste  piles
typically include two types of mining wastes: 1) spoil piles and
2) tailings.  Spoil piles are the overburden or waste rock removed
during either surface or underground mining operations.  Tail-
ings are the  solid wastes generated from the cleaning and
extraction of ores. Both types of mining waste include waste
rock that can contain potential contaminants such as uranium,
copper,  iron, sulfur and phosphate. Waste piles containing
hazardous wastes  are regulated under RCRA and are  subject to
minimum  federal design and  operational requirements (40
CFR,  Parts 264 and 265, SubpartL) and ground-water protection
requirements  (40 CFR, Part 264, Subpart F), particularly where
the waste piles are unprotected from precipitation and surface
drainage. In many instances, waste and material piles remain
uncovered  and exposed to the  atmosphere. Precipitation per-
colating through the material can dissolve and  leach potentially
hazardous constituents into the subsurface. For example, ground-
water quality  problems have  occurred due to the dissolution of
unprotected stockpiles of highway deicing salt. Cyanide leaching
to extract gold  from mine tailings is potentially dangerous and
a widespread problem in some areas. Surface runoff from
stockpiles  can also be a source of potential ground-water
contamination. Ground-water monitoring efforts in waste and
material pile areas need to be designed to detect  or assess
ground-water contamination occurring on site and to  determine
that surface runoff has not contaminated adjacent areas.

Land  Treatment —
    Land treatment involves the application of waste liquids
and sludges onto the  ground  surface for biological  or chemical
degradation of the waste or for the beneficial use of nutrients
contained in  the waste. Land treatment operations commonly
involve spray irrigation or land spreading of sludges on agricul-
tural, forested or reclaimed land. Municipal wastewater or
sludge application to agricultural land is the most common form
of land treatment. Industrial waste sludge includes effluent
treatment waste, stack scrubber residue, fly ash, bottom ash and
slag (Office of Technology Assessment, 1984). Control mea-
sures must be instituted to prevent surface runoff, wind erosion
and excessive percolation into the ground water during site
operation. The rate and duration of sludge application depends
on the waste, soil type and the level of anticipated degradation.

     Wastes applied to the ground surface at a land treatment
facility may be hazardous or non-hazardous. Hazardous waste
land treatment facilities are regulated under RCRA and are
subject to minimum federal design and operational requirements
(40 CFR, Parts 264  and 265, Subpart M) and applicable reground-
water protection and monitoring requirements (40 CFR, Parts
264 and 265, Subpart F).

Underground Storage Tanks  —
     Underground storage tanks are used to store hazardous and
nonhazardous waste, industrial products and raw materials.  The
primary industrial use for tanks is the storage  of fuel oils. It is
estimated that half of all steel tanks  in use store petroleum
products. Both steel and fiberglass tanks are also used to store
other products including solvents, acids and technical grade
chemicals.

     Recent amendments to RCRA now specify design, main-
tenance and operation requirements for tanks containing haz-
ardous waste  and  commercial petroleum products  (40 CFR,
Parts 264 and 265, Subpart J). These regulations include re-
quirements for a double liner system and/or cathodic protection
of steel tanks, leak detection and inventory control.

Radioactive  Waste  Disposal  Sites  —
     Radioactive wastes are produced during the development
and  generation  of nuclear fuel and other radioactive materials.
Waste products include: 1) spent fuel from nuclear  power plant
operations, 2) high-level radioactive waste from initial process-
ing of reactor fuels, 3) transuranic waste from fuel processing,
4) low-level wastes from power plants, weapons  production,
research and commercial activities and 5) medical waste (Of-
fice of Technology Assessment, 1984).

     The radioactive waste disposal method depends on the
radiation levels and  the  waste characteristics. Low-level ra-
dioactive wastes are usually disposed of in shallow burial sites.
High-level radioactive wastes are stored in specially constructed
facilities and may be reprocessed. Spent reactor fuels  maybe
stored on site or transferred to disposal facilities.

     All radioactive waste disposal facilities are regulated by
the Nuclear Regulatory  Commission. Ground-water monitor-
ing requirements for specific facilities coupled with the design
configuration of the facility directly affect the location and
installation of monitoring wells.

Waste  Characteristics
     The physical and chemical characteristics of the waste(s)
present at a site should be carefully evaluated  and considered
together with site hydrogeology when  designing a monitoring
program. The mechanisms that govern the fate and  transport of
contaminants in the subsurface affect the occurrence and con-
                                                          20

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figuration of a contaminant plume. By considering these effects
a monitoring program can be designed to monitor or detect
subsurface  contamination. The monitoring well locations, the
depth of the screened intervals, the method of well installation
and the appropriate construction materials must all be compat-
ible with the specific waste and hydrogeological characteristics
of the site.

    Two physical properties that affect transport and fate of a
compound in the subsurface are the relative volubility and
density of  the contaminant. Based on  these  properties, con-
taminants can be classified into categories that subsequently
influence monitoring well design:  1) compounds that are pri-
marily miscible/soluble in groundwater and 2) compounds that
are relatively immiscible/insoluble in ground water. These
categories  can be further  subdivided  based on the relative
density of the compound.

Primarily  Miscible/Soluble  Contaminants —
    This category of contaminants exhibits a relatively high
volubility in water and typically is mobile in the subsurface.
Soluble contaminants can exhibit  densities greater  than, less
than or equal to  water. In general, where the density of the
contaminant closely approximates that  of water, the contami-
nant moves  in the  same direction and with the same velocity  as
ground water.

    The primary processes that affect  dissolved contaminant
transport in porous media include advection and dispersion
(Freeze and Cherry,  1979; Anderson, 1984; Mackay et al.,
 1985).  Advection is the process by which solutes  are trans-
ported by the  motion of  ground water flowing in response  to
hydraulic gradient, where the gradient reflects the magnitude  of
the driving force. Dispersion refers to the dispersal of con-
taminants  as they move with the ground water. Dispersion
occurs by mechanical mixing and molecular diffusion. Seasonal
changes in gradient may affect lateral movement of a contaminant
more than dispersion. Interactions that cccur between the
contaminant and the porous media include retardation, sorption
(Freeze and Cherry, 1979; Cherry et al., 1984;  Mabey and Mill,
 1984; Mackay et  al., 1985) and biodegradation (McCarty et al.,
 1981; McCarty et al.,  1984; Wilson et al., 1985). These
mechanisms can affect the rate of movement of a contaminant
plume or alter the chemistry within the plume.

    The effects of contaminant density  must also reconsidered
in waste characterization  (Bear, 1972). Figure  16  illustrates the
migration of a high density, miscible contaminant in the sub-
surface. As shown, the contaminant sinks  vertically through the
aquifer and accumulates on top of the lower permeability
boundary. The contaminant then moves in response  to gravity
and follows the topography of the lower permeability bound-
ary, possibly  in opposition to  the direction of  regional ground-
water flow. Because the  contaminant is also soluble, the con-
taminant will concomitantly move in response to  the processes
of advection and dispersion. Therefore, two or more zones  of
different concentration may be present within the plume: 1) a
dense pool of contaminant at the bottom of the aquifer and 2) a
dissolved fraction that moves with the ground water. Because
the dense, pooled portion of the plume is also soluble, the
contaminants will continue  to dissolve and migrate in response
o ground-water flow  conditions. Ground-water monitoring
wells installed in the aquifer may more  easily detect the dis-
solved portion of the plume unless a specific monitoring pro-
gram is devised for the dense phase of the plume. A knowledge
of subsurface topography, determined from a top-of-bedrock
map or overburden thickness maps and confined by surface
geophysics and/or borings assist in accurately locating and
monitoring the denser portion of the plume.

    Figure 17  illustrates the migration of a low density, soluble
contaminant. The contaminant initially accumulates at the top
of the water table. Dissolution and dispersion of the contami-
nant occurs as the accumulated  contaminant migrates with the
ground water.  Continued dissolution of the contaminant causes
eventual dissipation  of the plume. Monitoring for contaminants
with these characteristics is frequently most effective in the
shallow portion of the aquifer.

    Contaminants with a density similar to  water migrate in
response to advection and dispersion. Contaminants in this
category include inorganic constituents such as trace metals and
nonmetals. Because  of the similarity of contaminant movement
to the  ground-water movement, certain nonmetals, such as
chloride,  are commonly  used as tracers to estimate the bound-
Figure 16. Migration of a high density, miscible contaminant in
          the subsurface.
 Figure 17. Migration of a low density, soluble contaminant in
          the subsurface.
                                                          21

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aries of contaminant plumes. The dissolved portion of certain
organic contaminant plumes can also have a density similar to
water  and migrate with the ground water. Monitoring and
detection schemes for plumes  of these contaminants must be
based on the calculated effects  of advection,  dispersion, chemi-
cal attenuation and subsurface  hydrogeology.

Relatively Immiscible/Insoluble Contaminants —
    In both the  saturated and  unsaturated zones, immiscible
compounds  exist as either free liquids or as dissolved constituents
depending  on the relative volubility of the  contaminant. The
migration of dissolved constituents in the  aqueous phase is
primarily governed by the processes of advection-dispersion
and biological/chemical attenuation (Schwamenbach and Giger,
1985). The distribution of free  liquids is complexly interrelated
to capillary pressure, density (gravitational forces) and viscosity
(shear forces) (Kovski, 1984;  Villaume, 1985).  The relative
density of the contaminant affects the occurrence and movement
of the  contaminant in the subsurface and must be considered
when locating monitoring wells and when determining the
interval(s) to be  screened in the aquifer.

    Figure 18 illustrates the migration of a low density, immis-
cible contaminant.  The contaminant moves downward through
the vadose zone  and accumulates at the top  of the water table
and/or  within the capillary fringe. A residual  amount of fluid is
retained in the vadose zone in response to surfical and interstitial
forces (Kovski, 1984; Yaniga and Warburton, 1984). The
contaminant plume accumulates on the water table and typi-
cally elongates parallel to the  direction of ground-water flow
(Gillham  et al, 1983). The movement and accumulation of
immiscible hydrocarbons  in the subsurface has  been discussed
by Blake and Hall (1984 ), Kovski (1984), Yaniga and Warburton
(1984), and Hinchee and Reisinger (1985). Depending on the
physical properties  of the contaminant, a volatile gas phase may
accumulate in the unsaturated  zone.

    Monitoring wells designed to detector assess low density
immiscible contaminants should be screened in the upper part
of the  aquifer. In many instances the  screen should span the
vadose zone and the upper portion of the aquifer to allow the
floating contaminant to enter the well. Many immiscible con-
taminants depress the water table in the well and create an
apparent free liquid thickness that is greater than the thickness
of the floating contaminant within the aquifer. Where volatiles
accumulate in the vadose zone, an explosion hazard may exist.
Various mapping and detection techniques including soil-gas
sampling and geophysical techniques can be utilized in plan-
ning the monitoring well locations  to intercept the plume and
reduce the risk of an explosion (Noel et al., 1983; Andres and
Canace, 1984; Marrin and Thompson, 1984; Saunders and,
Germeroth,  1985; Lithland et al., 1985).

    High density immiscible fluids are  called dense non-
aqueous phase liquids (DNAPLs). DNAPLs include most ha-
logenated hydrocarbons and other aliphatic compounds because
the density of most organic compounds  is significantly  greater
than water. A density difference of one percent or greater has
been shown to cause  migration of contaminants in the subsurface
(Mackay et al., 1985).

    Figure  19 illustrates the movement of DNAPLs in the
subsurface. Movement of DNAPLs in the unsaturated zone is
primarily governed by capillary  forces and density (Villaume,
1985). The contaminant sinks through the aquifer and pools at
the bottom of the aquifer on top of the lower permeability
boundary (Schwille,  1981). The pool of contaminant migrates
in response to the topography of the lower permeability bound-
ary independent of regional ground-water flow. Residual ma-
terial is retained in the pore space of the unsaturated and
saturated  zones. This residual typically  occurs as discrete
fingers of globules. The formation and movement of the glob-
ules in the subsurface  depends on the extant pore-size distribution
and capillary forces (Schwille, 1981;  Villaume, 1985). As
much as five percent by volume of a compound maybe retained
in the aquifer after plume migration.

    Both residual contaminant and the contaminant plume may
continue to contribute dissolved constituents to the ground
water for  an extended period of time. Thus, small spills of
persistent compounds have the  ability to extensively contami-
                           Low Density
                           Immiscible Liquid
                                 Small Dissolved Plume
      777  7   7777   7   7   7  7   7
                                                                                          Small Dissolved Plume

                                                                                           Dense, Immiscible Liquid
Figure 18. Migration of a low density, immiscible contaminant in   Figure 19. Migration of a dense, non-aqueous phase liquid
          the subsurface.                                              (DNAPL) in the subsurface.
                                                         22

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nate ground water. A vapor plume from the contaminant source
may also form and migrate in the vadose zone. These plumes
can often be detected through soil-gas sampling techniques.

    Field investigation sat hazardous waste sites have supported
the phenomena of sinking DNAPLs as demonstrated by Schwille
(1981) in physical model experiments (Guswa,  1984; Reinhard
et al,  1984; Villaume, 1985). Monitoring for these DNAPLs
poses  special  problems.  The actual contaminant plume may
migrate independently of regional ground-water flow and may
be very difficult to locate. Analysis of maps of aquifer thickness
and  bedrock  topography will  aid  in determining potential
migration pathways. The dissolved constituents will migrate
according to the ground-water flow regime. Vapor plumes can
be detected by using soil-gas sampling techniques.

    Villaume  (1985) indicates that monitoring well  installation
through DNAPL-contaminated zones should proceed with
caution to  avoid cross contamination. Where the borehole is
open during drilling or where the annulus is not properly sealed,
DNAPLs may  migrate down the  hole or annulus and  cause cross
contamination.

Other Anthropogenic Influences
    The hydrogeology of a site and the characteristics of the
facility are primary factors that should be assessed when
choosing specifications for a monitoring well program. How-
ever, a variety  of factors that relate to the activities of man also
should be  assessed to determine any potential impacts to  the
monitoring program. These factors can affect ground-water
gradients and flow direction and  might have had past impacts on
ground-water quality that will affect a current monitoring
program.

    To minimize  the possibility  of unknown  anthropogenic
influences, any initial investigation  should include a detailed
review of the  site history. This review should encompass a
study of an y land use prior to the current or proposed activity at
the site. Additionally, a design and operational  history  for any
existing operation also should  be compiled that includes  the
location of all site activities and the type(s) of waste accepted
during the operation of the disposal facility.  For example,
information about tank age, volume of product delivered and
sold, location  of the tank and similar information is needed to
assess  a gasoline-dispensing cooperation. Another example is
where  a presently regulated disposal facility is located on  the
site of a previously unregulated landfill or a turn-of-the-century
industrial facility. Prior waste disposal practices may already
have caused ground-water contamination. Knowledge of the
past site practices  might lead the investigator to the  conclusion
that contaminants are held in the vadose zone and could be
periodical] y released to the ground-water during recharge events
(Pettyjohn, 1976 and 1982). Cyclic fluctuations in ground-
water quality are sometimes difficult to  evaluate because natu-
rally-occurring constituents in the vadose zone can also cause
similar fluctuations.  Additional sources of data to  assess site
history include: 1) historical photographs,  2) air photos, 3)
zoning plats,  4) interviews with local citizens and 5) local
newspapers.

    A complete site assessment must frequently include an
investigation outside the legal boundary of the property, An
 evaluation of past and present land use practices in the area to
 be monitored can  alert the investigator to potential contamination
 problems not related to the activity to be monitored. For
 example, non-point sources such as agricultural practices  may
 affect natural background water quality. Adjacent industrial  or
 commercial facilities may also influence background water
 quality  or may serve as a source of contamination.

     Pumping or injection wells near an area to be monitored
 can affect ground- water flow direction  and velocity and/or can
 influence  ground-water quality. The  presence of a well  or
 collection of wells with resultant cones of depression  or
 impression might reverse anticipated ground-water flow direc-
 tions or alter the rate  of migration of contaminant plumes. The
 influence of a pumping well(s) should be determined before
 completing final design of the monitoring program. Collection
 of water-level measurements and evaluation of pump test data
 and velocity plots can be used to determine the possible hydrau-
 lic effects of the other wells in the monitoring program (Keely
 and  Tsang, 1983). A more detailed discussion  of monitoring
 strategies that are useful near well fields can be found in Keely
 (1986). Potential water-quality effects from injection wells
 near the site must also be evaluated.

     Other  activities that can alter ground-water velocity  and/or
 direction include  infiltration  galleries and ground-water re-
 charge facilities.  Mounding of the water table  beneath these
 areas will  locally affect ground-water gradients. Where the
 quality  of  the recharge water differs from  background water
 quality, the ground-water quality in the  area may also be
 affected.

     Storm sewers, surface runoff catchments, sanitary sewers,
 buried underground cables, underground pipelines or other
 subsurface disturbances may  affect ground-water flow paths
 and  ground-water quality. Preferential  flow paths can be  cre-
 ated when  subsurface trenches or excavations are refilled  with
 unconsolidated backfill and  bedding materials. These more
 permeable materials provide conduits that can influence  or
 control the flow of contaminants in the subsurface and can also
 serve as a vapor migration pathway. Storm and sanitary sewer
 lines and other buried pipelines may be a source of contamina-
 tion  if leakage occurs. The precise location of buried pipelines
 and cables  should be determined to avoid inadvertently drilling
 into  or through the lines. For example, drilling into natural gas
 pipelines poses an immediate health and safety risk to anyone
 near the drilling site. Drilling into pipelines for sanitary or storm
 sewers  poses less of a safety risk, but may exacerbate the
 contamination problem. In summary, a review of all site activi-
 ties and subsurface structures serves to contribute valuable
 information to the monitoring program.

Equipment that the Well Must Accommodate
    The purpose of a monitoring well is to provide access  to a
 specific zone from which water-level measurements and/or
 ground-water quality samples, representative  of the extant
 water quality in the  monitored zone, can be obtained.  These
 conditions  and the size of equipment necessary to obtain the
 desired  measurements or collect the desired samples will de-
 termine the diameter of the well that must be drilled.  For
 example, if the transmissivity of the monitored zone is to be
                                                          23

-------
evaluated, then the well diameter must accommodate a pump or
other device capable of providing the necessary water demand
to make the transmissivity determination. Similarly, if repre-
sentative ground-water quality samples are to be collected from
the well, then an appropriate well diameter must be selected that
accommodates the needed sampling equipment. Equipment
and procedures that influence the choice of a well diameter
include:  1) borehole geophysical tools and downhole cameras,
2) water-level measuring devices, 3) ground-water sampling
devices and 4) aquifer testing procedures.

Borehole Geophysical Tools  and Downhole
Cameras
Use and Limitations of Borehole Geophysical Tools —
     Borehole geophysical methods are often used in monitor-
ing wells to obtain hydrogeologic information. Under  appropriate
conditions, porosity, hydraulic conductivity, pore fluid electrical
conductivity and general stratigraphic logs can be obtained.
Unfortunately, borehole  geophysical methods are  frequently
limited by  the materials and the drilling and completion meth-
ods used to construct the well. If it is anticipated that borehole
geophysical methods will be conducted in a well, it is neces-
sary to consider the limitations that are imposed by the various
methods and materials that are  used to construct the well.

     Virtually all borehole methods that are likely to  be used in
shallow ground-water investigations can be conducted in a 2-
inch diameter well. Four  things that commonly restrict the use
of borehole methods are well  fluid, casing type, perforation
type and gravel pack.  Each one  of these imposes limitations on
the geophysical methods that can be conducted in the well. A
summary of the limitations is  presented in Table 3, and the
limitations are discussed below.

     Some  geophysical methods require that a fluid  be present
in the well. Sonic tools will not  operate in an air-filled borehole
because the acoustic source and  receivers are not coupled to  the
formation.  Television systems  can operate in  air or fluid, but
only if the fluid is not murky.  Radiometric methods, such as
natural gamma, gamma density or neutron moisture logs can
operate in air or fluid-filled wells. However, the calibration of
these tools is different between air and fluid-filled wells.

     Standard Resistivity tools that measure the electrical con-
ductivity of the formation will not operate in air-filled bore-
holes because of the lack of an electrical connection between
the electrodes and the connation. Some individuals have modified
Resistivity tools to operate in air-filled boreholes by altering the
electrode design to insure that the electrode  is always in contact
with the formation. If the well fluid electrical conductivity y is
two orders of magnitude  or more greater  than the formation
electrical conductivity (electrical conductivity is  the reciprocal
of electrical Resistivity), then the lateral  and normal electrical
Resistivity tools cannot be  used because the well fluid  distorts
the electric field  to such a degree that it cannot be corrected.
This situation can  occur in low porosity formations. The induction
log, which measures formation electrical conductivity  by
electromagnetic coupling, does not require fluid in the well to
operate and is usually not affected by the well fluid.

    The casing material also influences which methods can be
used. No measurement of the electrical properties of the for-
mation can be made if the well is cased  with metal. Quantitative
Resistivity measurements can only be made in open boreholes;
limited qualitative measurements can  be made  in perforated
PVC or perforated teflon wells. The formation electrical con-
ductivity can be measured  qualitatively with induction  logs in
wells cased with PVC or teflon. Sonic  methods have not been
demonstrated to be useful in cased wells, although this is an area
that is currently being researched. The  calibration of radiomet-
ric  logs is affected by the  thickness and material used in the
casing. This is particularly true when neutron moisture methods
are used in PVC casing because the method is unable to
distinguish hydrogen in the  PVC from hydrogen in the pore
fluid.

    The type of perforations influence which methods can be
used. Qualitative Resistivity measurements can be made  in non-
metallic wells that are uniformly perforated, but not in wells that
Table 3. Use and Limitations of Borehole Geophysical Tools (K. Taylor, Desert Research Institute, Reno, Nevada, Personal
        Communication, 1988)
Borehole Method
Sonic
Resistivity
Induction
Natural Gamma
Gamma Density
Neutron
Caliper
TV
Borehole Fluid
Fluid Resistivity
Vertical Flow
Horizontal Flow

Air
4
4
1
2
2
2
.- 1
1
4

4
4

Fluid
Water
1
1
1
2
2
2
1
2
1

1
1

Casino Material Perforations Radius of
Investigations
Open Metal Plastic Screen No Screen (cm) Comments
1
1
1
2
2
2
1
1
1

1
1

4444
4334
4111
2211
2 2 1
2 2 1
1
1
1

1
1
1
1
1

1 4
3 4

5-50
5-400
100-400
5-30
5-15
5-15
0
0
0

0
2-6cm






Big effect with PVC

Clear fluid only



Strongly influenced
by screen
  Works, this well property does not adversely affect the log
  Works, but calibration affected
  Works qualitatively
  Doesn't work
                                                           24

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are not perforated because there is no path for the current
between the electrodes and the formation. Vertical flow in the
well is controlled by the location of perforated intervals. Hence,
the location of perforations will dictate what intervals can be
investigated. Horizontal flow through the well is controlled by
the radial distribution of perforations. Attempts to measure the
horizontal flow must have perforations that are continuous
around the well.

     In cased holes, the material in and the size of the annulus
between the casing and the undisturbed formation will influ-
ence geophysical measurements.  This occurs because all bore-
hole geophysical measurements are a weighted average of the
property being investigated over a cylinder portion of the
formation adjacent to  the borehole. The  radius of this cylinder
is referred to as the  radius of investigation. The radius of
investigation is a function of the geophysical method, tool
design, and, to a lesser degree, the formation and annular
material. Table 3  lists  typical radii of investigation for common
borehole geophysical methods. Because it  is generally the
formation, not the material in the disturbed zone, that is of
interest, it is important to ensure that the radius of investigation
is larger than the disturbed zone.

     The radius of investigation for the sonic tool is on the order
of a few wavelengths of the sonic pulse. Hence, it is less for high
frequency tools (greater than 30 kHz) than for low frequency
tools (less than 20 kHz). The radius of investigation of Resistiv-
ity tools is controlled by the  type of array  that is used. Resistivity
tools with multiple radii of investigation can commonly be used
to correct for the  effects of  a disturbed annulus. The Radiomet-
ric logs have a very limited radius of investigation and usually
require a driven casing or open borehole to be accurate. The
spacing between the source and the detector influences the
radius of investigation. Some tools use two spacings to correct
for disturbed zones less than approximately 4  inches in radius.
Horizontal flow through the borehole is strongly affected by the
hydraulic conductivity of the material in the disturbed zone.
Hydraulic testing of discrete intervals with straddle packers is
adversely affected if the annular  material adjacent to the pack-
ers has a hydraulic conductivity significantly greater than the
formation.

     When using  tools that  have a radioactive source (gamma
density or neutron moisture), state regulations vary. Most states
severely restrict the use of these tools in water wells. At a
minimum, it is usually required that the measurements be made
in cased wells. This complicates  the use  of these  tools because
the casing  influences the calibration and creates a disturbed
zone. Another common restriction is that  the well not be
perforated in an aquifer with potable  water. This  further limits
the use of these methods to areas that are already contaminated.

General Applications —
    Natural gamma and self potential (SP) logs are commonly
used to detect lithologic boundaries and  to identify  formations
containing clays and shales (Keys, 1968; Keys and MacCary,
1971; Voytek, 1982; Mickam et al, 1984; Taylor et al, 1985).
Both natural  gamma and SP logging tools can be  accommo-
dated by 2-inch diameter or larger wells and are frequently
available in combination with other logging tools  as a portable
unit  that may be easily transported to sites with restricted
access.
     Formation Porosity and density may be determined through
the use of neutron, sonic and gamma-gamma logs (Keys, 1968;
Keys and MacCary, 1971; Sengcr, 1985). The use of the neutron
tool is generally accepted as an indicator of moisture content
(Keys,  1968). Wilson (1980) and Everett et al. (1984) have
pointed out limitations in using the neutron  tool  inside plastic
casing, in the presence of certain contaminants and in certain
geologic settings. Tool detector sizes are limited to 2-inch
diameter wells or greater and are available as portable units for
remote field access.

     Various types of caliper logs are used to maintain a con-
tinuous record of well or borehole diameter that can be used to
detect broken casings, the location of fractures, solution devel-
opment, washed-out horizons and hydrated clays (Keys and
MacCary, 1971; Mickam et al., 1984; DeLuca and Buckley,
 1985).  Diameters are "sensed" through the use of multiple
feeler arms or bow springs. Calipers  are available for borehole
or well diameters ranging from 1.65 inches to 30 inches.

     Other borehole logging tools may be used  to derive in-
formation about the character of water in  the borehole and the
formation. Induction tools are used to  measure pore fluid
conductivity (Taylor et al.,  1985). Selected  Resistivity tools with
different formation penetration depths are used to detect
variations in pore fluids (Keys, 1968; Keys  and MacCary, 197 1;
Kwader, 1985; Lindsey, 1985). Temperature logs have recently
been applied to the detection of anomalous fluid flow (Urban
and Diment, 1985). Induction, Resistivity  and temperature log-
ging tools have been designed to fit 2-inch diameter or larger
monitoring wells.

    Flowmeters are used to monitor fluid rates in cased or
uncased holes. This tool provides  direct ground-water flow
measurement profiling. Flowmeters can also  be used to detect
thief zones, lost circulation zones and the location of holes in
casing. Flowmeters measure flow using  low inertia impellers or
through changes in thermal conductance as liquids pass through
the  tool (Kerfoot,  1982).  Many professionals remain
unconvinced, however, as to the effectiveness of Flowmeters.
Impeller Flowmeters  are available as small  as 1.65 inches in
diameter conductance Flowmeters are typically 1.75 inches in
diameter.

     Some uncertainty exists  in the  application of almost all
borehole  equipment including  geophysical logs. The correct
interpretation of all such data often depends  on  precise knowledge
of geologic and hydrogeologic conditions that are frequently
not available. Therefore the interpretation  of these data are
invariably  subjective.

    Downhole television cameras can be used to gather in-situ
information on boreholes and monitoring  wells (Huber, 1982;
Morahan and Doorier, 1984). Television  logging maybe used
to check monitoring well integrity (i.e., casing and screen
damage), to inspect installation and construction procedures
and to accurately characterize subsurface fractures  and geologic
strata. Borehole television cameras have recently become
available for wells as small as 2 inches in diameter. Cameras are
available that provide multi-angle viewing, black/white or
color images and recorded depth data during imaging.

    Many of the logging tools discussed in this section are
available as  either combination probes or  single probes. These
                                                          25

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tools have been designed so that they can be run from truck
mounted winches and loggers or from portable units that can be
transported  by backpack to sites where vehicular access is
restricted. In addition, a variety of portable data loggers are
available to  record logging data gathered onsite.

Water-Level Measuring Devices
    The basic  water-level measuring device  is a steel tape
typically coated with ordinary carpenter's chalk. This  is the
simplest water-level measuring device and is  considered by
many to be  the most accurate device at moderate  depths. In
addition to a standard steel tape, the five main types of water-
level measuring devices are: 1) float-type,  2) pressure transduc-
ers, 3) acoustic probes, 4) electric sensors and 5)  air lines.  Float-
type devices rest on the water surface  and may provide a
continuous record of water levels on drum  pen recorders or data
loggers. Float  sizes range from  1.6 inches to 6.0 inches in
diameter, but are only recommended for  wells greater than 4
inches in diameter due to loss of sensitivity in smaller diameter
boreholes. Pressure  transducers are suspended in the well on a
cable and  measure height of water above the transducer center.
Transducers  are available in diameters as small  as 0.75 inches.
Acoustic well probes use the reflective  properties of sound
waves to calculate the distance from the probe at the wellhead
to the water surface. Acoustic probes are designed for well
diameters as small as 4 inches and are limited to water depths
greater than 25 feet (Ritchey, 1986). Electric sensors are sus-
pended on the end of a marked cable. When the  sensor encoun-
ters conductive  fluid, the circuit is completed and an audible or
visual signal is displayed at the surface. Air lines are installed
at a known depth beneath the water and by measuring the
pressure of air necessary to discharge water from the tube, the
height of the water column above the discharge  point can be
determined.

    Steel tapes coated with a substance that changes color
when wetted are also used as water-level measuring devices
(Garber and Koopman, 1968). Tapes are  available as small as
0.75 inches  in width.  Specially coated tape with physical and
chemical resistance  has recently been developed that is 0.375
inches in width and contains electrical conductance probes at
the end  of the tape to sense water levels  (Sanders, 1984).

Ground-Water  Sampling Devices
    A wide variety of ground-water sampling devices are
available to  meet the requirements of a ground-water monitori-
ng program.  A  discussion of the advantages and disadvantages
of sampling  devices  is provided by Barcelona et al. (1983) and
(1985a), Nielsen and Yeates (1985) and Bryden et al. (1986).

    Bailers  are the simplest of the sampling devices commonly
used for ground-water sampling. They can be constructed from
a variety of materials including polytetrafluorethylene (PTFE),
polyvinyl  chloride (PVC) and stainless steel. Diameters  of 0.5
inches or larger are common. Because bailers are lowered by
hand or winch,  the maximum sampling depth is limited by the
strength of the winch and the time required for bailing.

    Grab  samplers such as Kemmerer samplers  can  be used to
collect samples  from discrete sampling depths. These samplers
can be constructed from a variety of materials and can be
manufactured to fit in wells with 0.5-inch diameter or larger.

    Syringe samplers allow for depth discrete sampling at
unlimited depths while reducing effects on sample  integrity
(Nielsen and Yeates, 1985). Syringe samplers have been con-
structed from stainless steel, PTFE and polyethylene/glass with
various modifications (Gillham, 1982). These  samplers maybe
utilized in wells with a casing diameter 1.5 inches or larger.

    Suction lift or vacuum pumps include both centrifugal and
peristaltic pumps. These types of pumps are limited to sampling
depths of less than 25  feet. However, they can be utilized in
wells  of 0, S-inch diameter or larger.

    Gas drive samplers can be used in wells with a casing
diameter of 0.75  inches or larger. These samplers operate on the
principal of applied gas pressure to open/close check valves and
deliver samples to the surface (Robin et al., 1982; Norman,
 1986). Sampling depth is limited by the internal working
strength of the tubing used in sampler construction,

    Positive displacement bladder pumps can be constructed
of various inert materials for wells with a diameter of 1.5 inches
or larger. The use of pressurized bladders ensures that the
sample does not contact the driving gas. Most bladder pumps
are capable  of lifting samples from 300 to 400 feet, although
models capable of 1000  feet of lift have been recently advertised.

    Both gear-drive and  helical rotor submersible pumps have
been  developed for wells with a casing diameter of at least 2
inches. These pumps are capable of lifts of up to at least 150 feet.
Submersible gas-driven piston pumps have been developed that
operate on compressed air or bottled gas  without contact of the
sample with the air. These pumps are available for 1.5 and 2-
inch diameter monitoring wells and have pumping lifts from 0
to 1000 feet. All of these types of pumps can' be constructed
from  various inert materials and may provide continuous,  but
variable flow rates to minimize degassing of the sample.

Aquifer Testing Procedures
    The diameter, location, depth, and screened interval of a
monitoring well should be chosen based on the need  for and the
type of aquifer testing procedures that will be performed on the
well.  Observation wells generally do not have to be designed
with  the same diameter criteria in mind. The type of aquifer
testing procedure should be based on the hydraulic character-
istics  of the aquifer such as transmissivity, storage coefficient,
homogeneity and areal extent.

    Pumping tests are typically performed in wells with a high
transmissivity and in wells with a diameter large  enough to
accommodate the pumping equipment.  Conversely,  slug  in-
jection or recovery tests, that add or remove smaller amounts of
water, are typically performed in formations with  low trans-
missivity and in  smaller diameter wells. Packer tests can be
conducted in wells as small as 2 inches in diameter, but the
optimum well diameter for packer testing is 4  inches. Bailer
tests  to evaluate  aquifer characteristics  can be performed in
wells of all  diameters. Tracer tests are also used to evaluate
aquifer characteristics and can be performed regardless of well
diameter.
                                                          26

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                                                          27

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Mabey, W.R. and T. Mill, 1984. Chemical transformation in
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    315.
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                                                    Section 3
                              Monitoring Well  Planning Considerations
Recordkeeping
    The development of an accurate recordkeeping process to
document the construction, installation, sampling and mainte-
nance phases of a monitoring well network plays an integral
part in determining the overall success of the program. An
accurate account of all phases is necessary to  ensure that the
goals  of the monitoring  program (i.e. accurate  characterization
of the  subsurface hydrogeology and representative water-qual-
ity samples, etc.) are met. It is from these records  that information
will be used to resolve any future monitoring problems that will
be encountered.

    Recordkeeping begins with the drilling of the monitoring
well. Complete documentation of the drilling and/or sampling
process should be accurately recorded in a field notebook and
transferred to a boring log. Notations about weather, drilling
equipment, personnel on the site, sampling techniques, sub-
surface geology and hydrogeology should be recorded. Litho-
logic descriptions should be based on visual examination of the
cuttings  and samples and confined with laboratory analyses
where  appropriate.  The  Unified Soil Classification System is
one universally accepted method of soil  description. In the
Unified  Soil Classification System, soils are designated  by
particle size and moisture content. A description of the system
can be found in a publication by the United States Department
of Interior (1974). Identification and classification of rock
should include  typical rock name, notations  on pertinent  li-
thology, structural features and physical alterations. Although
there is no universally accepted system for describing rock, one
system is described by Williamson (1984). A list of information
that should be recorded in the field notebook  is contained in
Table 4.  Information in the field notebook is transferred to the
boring log for clarity of presentation. Figure 20 illustrates the
format for a sample boring log. Both the boring log and the field
notes become part of the permanent file for the well.

    In addition to the boring log, an "as-built" construction
diagram should be drawn for each well. This differs from a
"typical monitoring  well" diagram contained within the design
specifications because the  "as-built" diagram contains specific
construction information about the materials and depths  of the
well components. An "as-built" diagram eliminates confusion
if the monitoring well was  not built exactly as conceived in the
design specifications. In  addition, the drawing provides an "at-
a-glance" picture of how the well is constructed (similar to the
function  of a boring log). The "as-built" diagram should contain
information about the elevation, depth and materials used in
well construction. Figure 21 illustrates the format for an "as-
built" diagram of a  monitoring well.
    Finally, records should be kept for each well illustrating
not only the construction details for the well, but also a complete
history of actions related to the well. These include:  1) dates and
notations of physical observations about the well, 2) notations
about suspected problems with the well,  3) water-level mea-
surements, 4) dates of sample collection (including type of
sampler,  notations about sample collection and results  of labo-
ratory analyses), 5) dates and procedures  of well maintenance
and 6) date, method and materials used for abandonment. This
record becomes part of a permanent file that is maintained for
each well.

Decontamination
    Decontamination of drilling and  formation-sampling
equipment  is a quality-control measure that is often required
during drilling and installation  of ground-water  monitoring
wells. Decontamination is the process of neutralizing, washing
and rinsing equipment that comes in  contact with formation
material or  ground water that is known or is suspected of being
contaminated. Contaminated material that adheres to  the sur-
face of drilling and formation sampling equipment may be
transferred  via the equipment: 1) from  one borehole to another
and/or 2) vertically within an individual borehole from a
contaminated to an uncontaminated  zone. The purpose for
cleaning  equipment is to prevent this "cross-contamination"
between boreholes or between vertical zones within a borehole.
Although decontamination is typically used where  contaminat-
ion exists,  decontamination measures are also employed in
uncontaminated areas as a quality control measure.

    Planning a decontamination program for drilling and for-
mation sampling equipment requires consideration of:

    1)   the location where the decontamination procedures
         will be conducted, if different from the actual
         drilling  site;
    2)   the  types of equipment that will require
         decontamination;
    3)   the frequency that specific equipment will require
         decontamination;
    4)   the cleaning technique and type of cleaning
         solutions  and/or  wash  water  needed  for
         decontamimtion;
    5)   the  method for  containing the  residual
         contaminants and cleaning solutions and/or wash
         water from the decontamination process, where
         necessary; and
    6)   the use of a  quality control measure, such as
         equipment blanks or wipe testing, to determine
                                                          29

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Table 4. Descriptive Information to be Recorded for each Monitoring Well

General information
        Well Completion information
Boring  number
Date/time to start and finish well
Location of well  (include sketch of location)
Elevation of ground surface
Weather conditions during drilling
Name of driller, geologist and other personnel on site

Drilling information
Type of drilling equipment
Type and design of drill bit
Any drilling fluid used
Diameter of drill  bit
Diameter of hole
Penetration rate during drilling (fee/minute, minutes/foot, feet/hour, etc.)
Depth to water encountered during drilling
Depth to standing water
Soil/rock classification and description
Total well depth
Remarks on miscellaneous drilling conditions, including:
  a) loss or gain of fluid
  b) occurrence of boulders
  c) cavities or voids
  d) borehole conditions
  e) changes  in color of formation samples or fluid
  f) odors while drilling

Sampling information
Types of sampler(s) used
Diameter and  length of sampler(s)
Number of each sample
Start and finish depth of each sample
Split spoon sampling:
  a) size and  weight of drive hammer
  b) number of  blows required for penetration of 6 inches
  c) free fall distance used to drive sampler
Thin-walled sampling:
  a) relative ease or difficulty of  pushing sample OR
  b) pounds per square inch (psi) necessary to push sample
Rock cores:
  a) core barrel  drill bit design
  b) penetration rate (fee/minute, minutes/foot, fee/hour, etc.)
Percent of sample recovered
        Elevation of top of casing (+ .01 foot)
        Casing:
          a) material
          b) diameter
          c) total length of casing
          d) depth below ground surface
          e) how sections joined
          f) end cap (yes or no)
        Screen:
          a) material
          b) diameter
          c) slot size and length
          d) depth to top and bottom of screen
        Filter pack:
          a) type/size
          b) volume emplaced (calculated and actual)
          c) depth to top of filter pack
          d) source and roundness
          e) method of emplacement
        Grout and/or sealant:
          a) composition
          b) method of emplacement
          c) volume emplaced (where applicable)
                (calculated and actual)
          d) depth of grouted interval (top and bottom)
        Backfill  material:
          a) depth of backfilled interval (top and bottom)
          b) type of material
        Surface seal detail:
          a) type of seal
          b) depth of seal (must be below frost depth)
        Well protector:
          a) type
          b) locking device
          c) vents (yes or no)
        Well development:
          a) method
          b) date/time;  start/stop
          c) volume and source water (if used)
         the  effectiveness  of the  decontamination
         procedure, if appropriate.

     The degree to which each of these items are considered
when developing a decontamination program varies with the
level of contamination anticipated at the site. Where the site is
"clean," decontamination efforts  may simply consist of rinsing
drilling and formation sampling equipment with water between
samples and/or boreholes. As the level of anticipated or actual
contamination increases, so should the decontamination effort.
A document by the United States Environmental Protection
Agency (1987) discusses decontamination at CERCLA sites.

     One important factor when designing a decontamination
program is the type of contaminant. The greater the toxicity
or the more life-threatening the  contaminant, the more exten-
sive and thorough the decontamination program must be. The
following discussion focuses on measures to be employed at
sites where contamination is known or suspected or decon-
tamination is desired as a quality control measure. Less formally
defined decontamination efforts  may be employed at any site.

Decontamination Area
     An appropriate decontamination area at a site is selected
based on the ability to: 1) control access to the decontamination
area, 2) control or contain residual material removed from the
surfaces of the drilling and formation sampling equipment and
3) store clean equipment to prevent recontamination before use.
In addition, the decontamination area should be located in close
proximity to the  drilling area to minimize further site con-
tamination.  The importance of these considerations during the
selection process for a decontamination area will be influenced
by the type of contaminants  involved and the extent of con-
tamination at the  site. For example, the decontamination area
for drilling  and  formation sampling  equipment may be located
near the drilling rig when: 1)  the ground surface is regarded as
noncontaminated, 2) the known or suspected  subsurface con-
taminants are non-hazardous and 3) the drilling method permits
good control over the containment of cuttings from the  borehole.
However, the decontamination area should be located an ad-
equate distance away  from the rig to avoid contamination of
clean equipment by airborne lubricating oil or hydraulic fluids
from the drilling rig. Once drilling and sampling  equipment is
cleaned, the equipment should not be placed directly  on the
ground surface even though the area is generally regarded as
noncontaminated. Clean equipment should  be  placed, at a
minimum, on top of plastic ground  sheeting, and the sheeting
                                                             30

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                                                            BORING NO.
                                                                    SH _ 3
                                                                                           OF.
PROJECT  AML Manufacturing
LOCATION   Sussex County
CASING !,D.
CONTRACTOR.
                             BORING LOG
                            	   DATE START
                                                                 Aug. 3D, 1987    FINISH Aug. 31.19S7
4.25"
           CORE SIZE.
GROUND ELEV.
   NX    	
                       337,0f
                                                             TOTAL DEPTH (FT),
                                              Air Rotary w/Casinq Hammer
  Sorowls & Sons
               LOGGED BY
                                                       S. Smith
SCALE
IN
FEET
J
.
5' "^
10' -
ir -
i
20' .

Overbur
Rock
LITHOLOGIC SAMPLE
SYMBOL T^
AND NO.
m
'^x>33'^^0: i
-------
          Well Number 7H
          Start 8/13/87 B:QD am  -1-flfl pm
          Finish 8/14/87 10 am -12:00 p.m.
          Drillin Method Hollow Stem Auoer
           -3.0
  Steel (schedule 40) Protective
  Casing with Hinged Cap
.-Vented  Cap    „„  .   .   .  „.,„„
 • -	!-	Master Lock #632
  urain
 XT Concrete Pad (min. 4" thick on
 / undisturbed or compacted soil)
JT* _.   Fi««tinn 856.03 feet
'IT I  ^^"Uy !
    Frost Sleeve  gancf
                          Concrete Seal
                          Sand
                          	Granular Bentonite Seal
                           2% Bentonite-Cement Seal

                          2" PVC Casing (Schedule 40,
                          Flush Joint, Threaded
                         Granular Bentonite Seal
                          Silica Fine-Grained Sand
                          (Mortar Sand)
                          2" PVC Well Screen with
                          0.010 Inch Slot Open
                          Filter Pack (Clean Medium to
                          Coarse Silica Sand)

                          - 2" PVC Casing
           28.0'
                10.25"
Figure 21. Forms! lor an "aa-bullt" monitoring well diagram.

should be discarded after each borehole is drilled Clean equip-
ment may also be stored off the ground on storage or equipment
racks until used for drilling or formation sampling. Heavy
equipment, such as the drilling rig, water truck or  any  other
support vehicle, should be cleaned in the decontamination area
prior to demobilizing from the site.

    The presence of hazardous materials at a drilling site
dictates that a more controlled access area be established for
equipment decontamination to prevent cross-contamination
and to provide worker safety. Figure 22 shows a general layout
of a contaminant reduction zone where systematic decontami-
nation procedures are employed as personnel and equipment
move from the  hazardous material exclusion zone to a clean,
non-hazardous support zone.

Types of Equipment
    Decontamination  of drilling  and formation  sampling
equipment involves cleaning tools used in the borehole. This
equipment includes drill bits, auger sections, drill-string tools,
drill rods, split-barrel or thin-wall tube samplers, bailers, tremie
pipes, clamps, hand tools and steel cable. Equipment with a
porous surface, such as natural rope, cloth hoses and wooden
blocks or handles, cannot be thoroughly decontaminated and
should be disposed of properly after completion of the borehole.
The specific drilling and formation sampling equipment that
needs to be cleaned should be listed in the equipment decon-
tamination program.

     A decontamination program for equipment should  also
include cleaning heavy equipment including the drill rig and
support trucks. Advanced planning is necessary to ensure that
the decontamination area is adequately sized to accommodate
large vehicles, and  that any contaminants removed from the
vehicles are properly controlled and contained within the de-
contamination area. This should include the "tracking  zone"
created by vehicles as they move into and out of the area.

Frequency of Equipment Decontamination
     A decontamination program for equipment should detail
the frequency that drilling and formation sampling equipment
is  to be cleaned.  For example, drilling equipment should be
decontaminated between boreholes. This frequency of cleaning
is  designed to prevent cross-contamination from one borehole
to the next. However, drilling equipment may require more
frequent cleaning to prevent cross-contamination between
vertical zones within a  single borehole. Where drilling equip-
ment is used to drill through a shallow contaminated zone and
to  install surface casing to seal-off the contaminated zone, the
drilling tools should be decontaminated prior to drilling deeper.
Where possible, fieldwork should be initiated by drilling  in that
portion of the site where the least contamination is suspected.

     Formation sampling equipment  should be decontaminated
between each sampling event. If a sampling device  is not
adequately  cleaned  between successive  sampling depths, or
between boreholes,  contaminants may  be introduced into the
successive sample(s) via the formation sampling device.

Cleaning Solutions and/or Wash Water
     Decontamination of equipment can be accomplished using
a variety of techniques and fluids. The most common and
generally preferred methods of equipment decontamination
involve either a clean potable water wash, steam cleaning or
water/wash steam cleaning combination. Water washing may
be accomplished using either low or high pressure. If a low
pressure wash is used, it may be necessary to dislodge residual
material from the equipment with a brush to ensure complete
decontamination.  Steam cleaning is accomplished using por-
table, high-pressure steam cleaners equipped with pressure
hose and fittings.

     Sometimes solutions other than water or steam are used for
equipment decontamination. Table 5 lists some of the chemi-
cals and  solution  strengths that have been used in equipment
decontamination programs. One commonly used cleaning so-
lution is  a non-phosphate detergent. Detergents are preferred
over other cleaning solutions because the detergent alone does
not pose  a handling or  disposal problem. In general, when a
cleaning solution for equipment decontamination is  necessary,
a non-phosphate detergent should be used unless it is demon-
strated that the environmental contaminant in question cannot
be removed from the surface of the equipment by detergents.

    Acids or solvents should be used as cleaning solutions only
under exceptional  circumstances because these cleaners  are, in
                                                         32

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                                  —I
                   Heavy Equipment
                   Decontamination
                        Area
            —X	X-  -X-fgJ-X-^-X-   -X	X	
             -o—o—
                           Auxiliary
                           Access
                         Control Path
                                                                    Exit Path
            X—  X-EJJ-X-  X	X	X
                                                Contamination
                                               Reduction Zone
                                   -   -o—o—o—o—
                                                                    g c
                                                                    « I 
-------
Table 5. List of Selected Cleaning Solutions Used

Chemical                  Solution
                    for Equipment Decontamination (Moberly, 1985)

                         Uses/Remarks
 Clean Potable Water

 Low-Sudsing Detergents
 (Alconox)
 Sodium  Carbonate
 (Washing Soda)
 Sodium  Bicarbonate
 (Baking  Soda)
 Trisodium Phosphate
 (TSP Oakite)
None

Follow Manufacturer's
Directions
4#/10 Gal Water

4#/10  Gal Water

2#/10  Gal Water

4#/10  Gal Water
 Calcium Hydrochloride (HTH) 8#/10 Gal Water
 Hydrochloric. Acid           1  Pt/10 Gal Water
 Citric, Tartaric, Oxalic Acids 4#/10 Gal Water
 (or their respective salts)
 Organic Solvents  (Acetone,  Concentrated
 Methanol,  Methylene Chloride)
Used under high pressure or steam to remove heavy mud, etc., or to
rinse other solutions
General all-purpose cleaner

Effective for neutralizing organic acids, heavy metals,  metal
processing wastes
Used to neutralize either base or neutral acid contaminants

Similar to sodium carbonate

Useful for solvents & organic compounds (such as Toluene,
Chloroform, Trichloroethylene), PBB's and PCB's
Disinfectant, bleaching & oxidizing agent used for pesticides,
fungicides, chlorinated phenols, dioxins, cyanides, ammonia & other
non-acidic inorganic wastes
Used for inorganic bases, alkali and caustic wastes
Used to clean heavy metal contamination

Used to clean equipment contaminated with organics or well casing to
remove surface oils, etc
 reinforced, curbed, concrete pad which is sloped toward one
 comer where a sump pit is installed (Moberly, 1985). Where a
 concrete pad is impractical, planking can be used to construct
 a solid flooring that is then covered by a nonporous surface and
 sloped toward a collection facility. Catchment of contaminants
 and cleaning fluids from the decontamination of lighter-weight
 drilling equipment and hand tools can be accomplished by
 using  small trenches lined with plastic sheeting or in wash tubs
 or stick cans. The contaminated cleaning fluids can be stored
 temporarily in metal or plastic cans  or drums until removed
 from the site for proper disposal.
                                   safety plan for field personnel should be of foremost concern
                                   when drilling in known or suspected contaminated areas.  Spe-
                                   cific health and safety procedures necessary at the site depend
                                   on the toxicity and  physical and chemical properties of known
                                   or suspected contaminants. Where hazardous materials are
                                   involved or suspected, a site safety program should be devel-
                                   oped by a qualified professional in accordance with the Occu-
                                   pational Safety and Health Administration requirements in 29
                                   CFR 1910.120. Field personnel at hazardous sites should re-
                                   ceive medical screening  and basic health and safety training, as
                                   well as specific  on-site  training.
 Effectiveness of Decontamination Procedures      References
     A decontamination program for drilling and formation
sampling equipment may need to include quality-control proce-
 dures  for measuring the effectiveness of the cleaning methods.
 Quality-control measures typically  include either equipment
 blank  collection or wipe testing. Equipment blanks are samples
 of the final rinse water that are collected after cleaning the
 equipment. Equipment blanks  should recollected in appropriate
 sampling containers, properly preserved, stored and transported
 to a laboratory for analyses of contaminants known or suspected
 at the  site. Wipe testing is performed by wiping a cloth or paper
 patch over the surface of the equipment after cleaning. The test
 patch is placed in a sealed container and sent to a laboratory for
 analysis. Laboratory results from either equipment blanks or
 wipe tests provide "after-the-fact" information that may be used
 to evaluate whether or not the cleaning methods were effective
 in removing the contaminants of concern at the site.

 Personnel Decontamination
     A decontamination program for drilling and sampling
 equipment is typically  developed in conjunction with health
 and  safety plans for  field personnel working at the site. Although
 a discussion of site safety plans and personnel protective
 measures are beyond the scope of this manual, the health and
                                   Electric Power Research Institute, 1985. Ground water manual
                                        for the electric utility industry: groundwater investigations
                                        and mitigation techniques, volume 3; Research Reports
                                        Center, Palo Alto, California, 360 pp.
                                   Moberly, Richard L.,  1985. Equipment decontamination;
                                        Ground Water Age, vol. 19, no.  8, pp. 36-39.
                                   United States Department of Interior,  1974. Earth manual, a
                                        water resources technical publication;  Bureau  of
                                        Reclamation, United  States Government Printing Office,
                                        Washington, D.C.,810pp.
                                   United  States   Environmental Protection Agency,  1984.
                                        Standard  operating safety  guides;  United  States
                                        Environmental Protection Agency Office of Emergency
                                        Response, United States Government Printing Office,
                                        Washington, B.C., 166 pp.
                                   United  States Environmental Protection Agency, 1987. A
                                        compendium of Superfund field operations methods;
                                        United  States  Environmental  Protection  Agency
                                        Publication No. 540/P-87/001, 644 pp.
                                   Williamson, D.A., 1984. Unified classification system; Bulletin
                                        of Engineering Geologists, vol. 21, no.  3, The Association
                                        of Engineering Geologists, Lawrence, Kansas, pp. 345-
                                        354.
                                                           34

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                                                    Section 4
                           Description and Selection of Drilling Methods
Introduction
    Monitoring wells can be, and have been, installed by nearly
every conceivable type of drilling and completion technique.
However, every drilling technology has a special range of
conditions where the technique is most effective in dealing with
the inherent hydrogeologic conditions and in fulfilling the
purpose of the monitoring well. For example,  constructing
wells by driving wellpoint or by jetting provides low-cost
water-level information but severely limits the ability to collect
detailed stratigraphic information.

    The following section contains a description of common
methods of  monitoring well construction  and includes a dis-
cussion of the applications and limitations of each technique. A
matrix that  helps the user determine the most appropriate
technology  for monitoring well installation in a variety of
hydrogeologic settings with specific design objectives is also
included in  this section.

Drilling Methods for Monitoring Well Installation

Hand Augers
    Hand augers may be used  to install shallow monitoring
wells (0 to  15 feet in depth) with casing diameters of 2 inches
or less. A typical hand auger, as shown in Figure 23, cuts a hole
that ranges from 3 to 9 inches in diameter. The auger is
advanced by turning into the soil until the auger is filled. The
auger is then removed and the sample is dumped from the auger.
Motorized units for one- or two-operators are available.

    Generally, the  borehole cannot be advanced below the
water table because  the borehole collapses. It is often  possible
to stabilize the borehole below the water table by  adding water,
with or without drilling mud additives. The auger may then be
advanced a few feet into a shallow aquifer and a well intake and
casing installed. Another option to overcome borehole  collapse
below the water table is to  drive a wellpoint  into the  augered
hole and thereby advance the wellpoint below the water table.
The wellpoint can then be used to measure water levels and to
provide access for water-quality samples.

    Better formation samples may sometimes be obtained by
reducing the hole size one or more times while augering to the
desired depth. Because the head  of the auger is removable, the
borehole diameter can be reduced by using smaller diameter
auger heads. Shaft extensions are usually added in 3-or 4-foot
increments. As the borehole size decreases, the amount of
energy required to turn the auger is also reduced. Where
necessary,  short sections of  lightweight casing can be installed
to prevent upper material from caving into the borehole.
Figure 23. Diagram of a hand auger.

    A more complete list of the applications and limitations of
hand augers is found in Table 6.

Driven Wells
    Driven wells consist of a wellpoint (screen) that is attached
to the bottom of a casing (Figure 24). Wellpoints and casing are
usually  1.25 to 2 inches in diameter and are made of steel to
withstand the driving process. The connection between the
wellpoint and  the casing is made either by welding or using
                                                         35

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                                   - Drive cap

                                   -Coupling
                                S~- Casing
                                    • Coupling
                                     •Screen
                                     Wellpoint
Figure 24. Diagram of a wellpoint.
drive couplings. Drive couplings are specially designed to
withstand the force of the blows used to drive the casing;
however, if the casing is overdriven it will usually fail at a
coupling. When constructing a well, a drive cap is placed on top
of the uppermost section of casing, and the screen and casing are
driven into the ground. New sections of drive casing are  usually
attached in 4 or 5-foot  sections as the well is driven deeper.
Crude stratigraphic information can be obtained by recording
the number of blows per foot of penetration as the wellpoint is
driven.

    Wellpoints can either be driven by hand or with heavy
drive heads mounted on a tripod, stiff-leg derrick or  similar
hoisting device. When driven by hand, a weighted drive sleeve
such as is used to install fenceposts is typically used. Depths up
 to 30 feet can be achieved by hand in sands or sand and gravel
 with thin clay seams; greater depths of 50 feet or more are
 possible with hammers up to 1,000 pounds in weight. Driving
 through dense silts and clays and/or bouldery silts and clays is
 often extremely difficult or impossible. In the coarser materials,
 penetration is frequently terminated by  boulders. Additionally,
 if the wellpoint is not structurally strong it may  be destroyed by
 driving in  dense soils or by encountering boulders. When
 driving the wellpoint through silts  and/or clays the screen
 openings in the wellpoint may become, plugged. The screen
 may be very difficult to clean or to reopen during development,
 particularly if the screen is placed in  a low permeability zone.

     To lessen penetration difficulties and screen clogging
 problems, driven wells may be  installed using a technique
 similar to that used in  cable tool drilling. A 4-inch casing (with
 only a drive shoe and no wellpoint) may be driven to the targeted
 monitoring depth. As the casing is driven, the inside of the
 casing is cleaned using a bailing technique.  With the casing still
 in the borehole, a wellpoint attached to an inner string  of casing
 is lowered into the borehole and the outer casing is removed. As
 the casing is removed, the well must be properly sealed and
 grouted. A second option can also be used to complete the well.
 With the casing still in the borehole, a wellpoint with a packer
 at the top can be lowered to the bottom of the casing. The casing
 is then pulled back  to expose the screen. The original casing
 remains in the borehole to complete  the well.  Either of these
 completion  techniques permit the  installation of thermoplastic
 or fluoropolymer in addition to steel as the screen material.

     A more complete listing of the applications and limitations
 of driven wells is found in Table 7.

 Jet Percussion
     In the jet-percussion drilling method, a wedge-shaped drill
 bit is attached to the lower end of the  drill pipe (Figure 25).
 Water is pumped down the drill pipe under pressure and
 discharges through ports on each side of the drill bit. The bit is
 alternately raised and dropped to  loosen unconsolidated mate-
 rials or to break up rock at the bottom of the borehole. Concomi-
 tantly, the drill pipe is rotated by hand,  at the surface, to cut a
 round and straight hole. The drilling fluid flows  over the bit and
 up the annular space between the drill  pipe and the  borehole
 wall. The drilling fluid lubricates the bit, carries cuttings to the
 surface and deposits the cuttings in a settling pit. The fluid is
 then recirculated down the drill pipe.

     In unconsolidated material the casing is  advanced by a
 drive-block as  the borehole is deepened. If the casing is posi-
 tioned near the bottom of the borehole, good samples can be
 obtained as the cuttings are circulated to the surface and
 stratigraphic variations can be identified. Where the borehole is
 stable, the well can  be drilled without simultaneously driving
 the casing.

     After the casing has been advanced  to the desired  monitor-
 ing depth, a well intake can be installed by lowering through
 the casing. The casing is then pulled back to expose the well
 intake. Casing diameters of 4 inches or less can be installed by
jet percussion. Depths of wells are typically less than  150 feet,
 although much greater depths have been attained. This method
 is most effective in  drilling unconsolidated sands.
                                                           36

-------
                    —Jetting pipe

                      _ Cuttings washed up
                       annular space
                            . Drilling fluid discharged
                             through port in bit
Figure 25.  Diagram of jet-percussion drilling (after Speedstar
           Division of Koehring Company, 1983).
     A more complete listing of applications and limitations of
jet-percussion drilling is found in Table 8.

Solid-Flight  Augers
     Solid-flight augers (i.e. solid-stem,  solid-core or continu-
ous flight augers) are typically used in multiple sections to
provide continuous flighting. The  first, or lowermost, flight is
provided with a cutter head that is approximately 2 inches larger
in diameter  than the flighting of the augers (Figure 26).  As the
cutting head is advanced into the earth, the cuttings are  rotated
upward to the surface by moving along the continuous flighting.

     The augers are rotated by a rotary drive  head at the  surface
and forced downward by a hydraulic  pulldown or feed device.
The individual flights are typically  5 feet in length and are
connected by a variety of pin, box and keylock combinations
and devices. Where used for monitoring well installation,
available auger diameters typically range from 6 to 14 inches in
outside diameter. Many of the drilling rigs used for monitoring
well installation in stable unconsolidated material can reach
depths of approximately 70 feet with 14-inch augers and
approximately 150 feet with 6-inch augers.

     In stable soils, cuttings can sometimes be collected at the
surface as the material is rotated up the auger flights.  The
sample being rotated to the surface is  often bypassed, however,
                                                                           Auger
                                                                           connection
                                                                                       c
                                                                            Flighting •
                                                                        Cutter head
  Figure 26. Diagram of a solid-flight auger (after Central Mine
            Equipment Company, 1987).

by being pushed into the borehole wall of the shallower forma-
tions. The sample often falls back into the borehole along the
annular opening and may not reach the surface until thoroughly
mixed with other materials. There is commonly no return  of
samples to the surface after the first saturated zone has been
encountered.

     Samples may also be collected by carefully rotating the
augers to the desired depth, stopping auger rotation and remov-
ing the  augers from the borehole. In a relatively  stable  forma-
tion, samples will be retained on the auger flights  as the augers
are removed from the borehole. The inner material is typically
more representative of the formation at the drilled depths and
may be exposed by scraping the outer material away from the
sample on the augers. Because the borehole often eaves after the
saturated zone is reached, samples collected below the water
table are less reliable. The borehole must be redrilled every time
the augers  are removed, and the formation  not yet drilled may
be disturbed as the borehole above collapses. This is particu-
larly true in heaving formations.
                                                           37

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Table 6. Applications and Limitations of Hand Augers

App Heat Ion i
Limitation*
  Shallow soils investigations
  Soil samples
  Water-bearing zone identification
  Piezometer, lysimeter and small diameter monitoring well
  installation
  Labor intensive, therefore applicable when labor is inexpensive
  No casing material restrictions
  Limited to very shallow depths
  Unable to penetrate extremely dense or rocky
  soil
  Borehole stability difficult to maintain
  Labor intensive
Table 7. Application and Limitations of Driven Wells

Applications
         Limitation
.Water-level monitoring in shallow formations
.  Water samples can be collected

.  Dewatering

.  Water supply

*  Low cost encourages multiple sampling points
         .Depth limited to approximately 50 feet (except in sandy
           material)

         .Small diameter casing

         .No soil samples

         * Steel casing interferes with some chemical analysis

         .Lack of stratigraphic detail creates uncertainty regarding
           screened zones and/or cross contamination

         .Cannot penetrate dense and/or some dry materials

         .No annular space for completion procedures
Table 8. Application and Limitation of Jet-Percussion Drilling

Appiications
         Limitation
.Allows water-level  measurement
.Sample collection in form of cuttings to surface
.  Primary use in unconsolidated formations, but may be used in
  some softer consolidated rock
.Best application is cinch borehole with 2-inch casing and
  screen installed, sealed and grouted
         .Drilling mud maybe needed to return cuttings to surface
         . Diameter limited to 4 inches
         .Installation slow in dense, boundery day/till or similar
          formations
         .Disturbance of the formation possible if borehole not
          cased immedately
     Because the core of augers is solid steel, the only way to
collect "undisturbed" split-spoon or thin-wall samples is to
remove the entire string of augers from the borehole, insert the
sampler on the end of the drill rod, and put the entire string back
into the borehole. This sampling process becomes very tedious
and expensive as the borehole gets  deeper because the complete
string of augers must be removed and reinserted each time a
sample is taken.  Sampling subsequent to auger removal is only
possible if the walls of the borehole are sufficiently stable to
prevent collapse during sampling.  Boreholes are generally not
stable after even a moderately thin saturated zone has been
penetrated. This means that it is visually not possible to obtain
either split-spoon or thin-wall samples after the shallowest
water table is encountered.

     The casing and well intake are also difficult to install after
a saturated zone has been penetrated. In this situation,  it is
sometimes possible to auger to the top of a saturated zone,
remove the solid augers and then install a monitoring well by
either driving, jetting or bailing a well intake into position.

     A  more complete listing of the applications and limitations
of solid-flight augers is found in Table 9.
  Hollow-Stem  Augers
       Similar to solid-flight augers, hollow-stem auger drilling
  is accomplished using a series of interconnected auger flights
  with a cutting head at the lowermost end. As the augers are
  rotated and pressed downward, the cuttings are rotated up the
  continuous flighting.

      Unlike the solid-flight augers the center core  of the auger
  is open in the hollow-stem flights (Figure 27). Thus, as the
  augers are rotated and pressed into the ground, the augers act as
  casing and stabilize the borehole. Small-diameter drill rods and
  samplers can then be passed through the hollow center of the
  augers for sampling. The casing  and well intake also can be
  installed without borehole collapse.

       To collect the samples through hollow-stem augers, the
  augers are first rotated and pressed to the desired sampling
  depth. The inside of the hollow stem is cleaned out, if neces-
  sary. The material inside the auger can be removed by a spoon
  sampler with a retainer basket jetting and/or drilling with a bit
  attached to smaller-diameter drill rods. If the jetting action is
  carried to the bottom of the augers, the material immediately
  below the  augers will be disturbed. Next, either a split-spoon
                                                             38

-------
               Drive cap
             Center Plug
  Pilot assembly
  components  ,
                \
                 Pilot Bit
 Rod to cap
 adapter

Auger connector
                                          Hollow siem
                                          auger section
                                         Center rod
   Auger
   connector
   Auger head
  Replaceable
  carbide insert
  auger tooth
Figure 27. Typical components of a hollow-stem auger (after
          Central Mine Equipment Company, 1987).
(ASTM, 1586) or thin-wall (ASTM, 1587) sampler is placed on
the lower end of the drill rods and lowered to the bottom of the
borehole. The split-spoon sampler can then be driven to collect
a disturbed sample or the thin-wall sampler can be pressed  to
collect an "undisturbed sample from the strata immediately
below the cutting head of the auger. Samples can either be taken
continuously or at selected intervals.  If sampling is continuous,
the augers are rotated down to the bottom of the previously-
sampled strata and cleaned out if necessary. The sampler is then
reinserted  through the auger and advanced into the undisturbed
sediments ahead of the auger.
    With the augers acting as casing and with access to the
bottom of the borehole through the hollow stem, it is possible
to drill below the top of the saturated zone. When the saturated
zone is penetrated, finely-ground material and water may mix
to forma mud that coats the borehole wall. This  "mud plaster"
may seal water-bearing zones and minimize inter-zonal cross
connection, This sealing is uncontrolled and unpredictable
because it depends on: 1) the quality of the silt/clay seal, 2) the
differential hydrostatic pressure between the zones and 3) the
transmissivity of the zones. Therefore, where possible cross
contamination is a concern, the seal developed during augering
cannot be relied upon to prevent cross contamination. One other
potential source of cross contamination is through leakage into
or out of the augers at the flighting joints. This leakage can be
minimized by installing o-ring  seals at the joints connecting the
flights.

    While drilling with hollow-stem augers with the center  of
the stem open, formation material can rise  into the hollow stem
as the auger is advanced. This material must be cleaned out of
the auger before  formation samples are collected. To prevent
intrusion of material while drilling, hollow-stem auger bore-
holes can be drilled with a center plug that is installed on the
bottom of the drill  rods and inserted during drilling. A small
drag bit may also be added to prevent intrusion into the hollow
stem. An additional  discussion on drilling with hollow-stem
augers can be found in Appendix A, entitled, "Drilling and
Constructing Monitoring  Wells with Hollow-Stem Augers."
Samples are collected by removing the drill rods and the
attached center plug and  inserting the sampler through the
hollow stem. Samples can then be taken ahead of the augers.

    When drilling into an aquifer that is under even low to
moderate confining  pressure, the sand and gravel of the aquifer
frequently "heave" upward into the hollow stem. This heaving
occurs because the pressure in the aquifer is  greater than the
atmospheric pressure in the borehole.  If a center plug is used
during drilling, heave frequently occurs as the rods are pulled
back and the bottom of the borehole is opened. This problem is
exacerbated by the surging  action created as the center plug and
drill rods are removed.

    When heaving  occurs, the  bottom portion of the hollow
stem fills with sediment, and the  auger must be  cleaned out
before formation  samples can be collected.  However, the act of
cleaning out the auger can result in further heaving, thus
compounding the problem. Furthermore, as the sand and gravel
heave upward into the hollow stem, the materials immediately
below the auger are no longer naturally compacted or stratified.
The sediments moving into the hollow stem are segregated by
the upward-flowing  water.  It is obvious that once  heaving has
Table 9. Applications and Limitations of Solid-Flight Augera

Applications	
                           Limitation
• Shallow soils investigations
• Soil samples
• Vadose zone monitoring wells (iysimeters)

• Monitoring wells in saturated, stable soils

• identification of depth to bedrock
• Fast and mobile
                             Unacceptable soil samples unless spilt-spoon or thin-wall
                             samples are taken
                             Soil sample data limited to areas and depths where stable
                             soils are predominant

                             Unable to install monitoring wells in most unconsolidated
                             aquifers because of borehole caving upon auger removal
                             Depth capability decreases as diameter of auger increases
                             Monitoring well diameter limited by auger diameter
                                                           39

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occurred, it is not possible to obtain a sample at that depth that
is either representative or undisturbed.

    Four common strategies that are used to alleviate heaving
problems include:

     1) adding water into the hollow stem in an attempt to
        maintain sufficient positive head inside the augers
        to offset the hydrostatic pressure of the formation;
    2)  adding  drilling mud additives (weight and
        viscosity control) to the water inside the hollow
        stem to  improve the ability of the fluid to counteract
        the hydrostatic pressure of the formation;
    3)  either screening the lower auger  section or
        screening the lowermost portion of the drill rods
        both above and below the center plug, in such a
        manner that water is allowed to enter the auger.
        This arrangement equalizes the  hydraulic  pressure,
        but prevents the formation materials from entering
        the augers; and
    4) drilling with a pilot bit, knock-out plug or winged
        clam to physically prevent the formation from
        entering the hollow stem.

    The most common field procedure is to add  water to the
hollow stem. However, this method is frequently  unsuccessful
because it is difficult to maintain enough water in the auger to
equalize the formation pressure as the drill rods are raised
during the sampling process.  Adding drilling mud may lessen
the heaving problem, but volume replacement of mud displace-
ment by removal  of drilling rods must be fast enough to
maintain a  positive  head on the formation. Additionally, drill-
ing mud additives may not be desirable where  questions  about
water-quality sampling from the monitoring well will arise. A
third option, screening the lowermost auger flight, serves two
purposes: 1) the  formation pressure can equalize with minimal
formation disturbance and 2)  water-quality samples and small-
scale pumping  tests can be  performed on individual zones
within the aquifer or on separate aquifers as the formations are
encountered. Wire-wound screened augers were developed
particularly for  this purpose and are commercially available
(Figure 28). By using a pilot bit, knock-out plug or winged
clam, heaving is physically prevented until these devices are
removed for sampling. In essence, the hollow stem functions as
a solid stem auger.  However, once these devices are dislodged
during sampling, problems with heaving may  still need to be
overcome by using an alternative strategy.

     Hollow-stem augers are typically  limited to drilling in
unconsolidated materials. However, if the cutting head of the
auger is equipped with carbide-tipped cutting teeth, it is often
possible to drill into the top of weathered bedrock a  short
distance. The augers can, then be used as temporary  surface
casing to shutoff water flow that commonly occurs at the soil/
rock interface. The seal  by the augers may not be complete;
therefore, this practice is not recommended where cross con-
tamination is a concern. The rock beneath the casing can then
be drilled with a small-diameter roller bit or can be cored.

    The most widely-available hollow-stem augers are  6.25-
inch outside diameter auger flights  with 3.25-inch  inside diam-
eter hollow stems.  The equipment most frequently available to
                             • Continuous slot
                              screen
                                 - Auger flighting
                                Auger head
Figure 28. Diagram of a screened auger.


power the augers can reach depths of 150 to 175 feet in clayey/
silty/sandy soils. Much greater depths have been attained, but
greater depths cannot  be predictably reached in most settings.
A 12-inch outside diameter auger with a 6-inch inside diameter
hollow stem is becoming increasingly  available, but the depth
limit for this size auger is usually 50 to 75  feet. Because of the
availability and relative ease of formation sample collection,
hollow-stem augering techniques are used for the installation of
the overwhelming majority of monitoring  wells in the United
States.

    A more complete listing of the advantages and disadvan-
tages of hollow-stem augers  is found in  Table 10. A more
comprehensive evaluation of this technology is presented in
Appendix  A.

Direct Mud Rotary
    In direct mud rotary drilling,  the drilling fluid is pumped
down the drill rods and through a bit that is attached at the lower
end of the drill rods. The fluid circulates back to the surface by
moving up the annular space between the drill rods and the wall
                                                          40

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Table 10. Applications and Limitations of Hollow-Stem Augers

Applications
         Limitations
• All types of soil investigations
• Permits good soil sampling with split-spoon or thin-wall
 samplers
• Water quality sampling
* Monitoring well installation in all unconsolidated formations
• Can serve as temporary casing for coring rock
• Can be used in stable formations to set surface casing
 (example: drill 12-inch borehole; remove auger; sets-inch
 casing; drill 7 1/4-inch borehole with 3 1/4-inch ID augers to rock;
 core rock with 3-inch tools; install 1-inch piezometer; pull augers)
         >  Difficulty in preserving sample integrity in heaving formations
         •  Formation invasion by water or drilling mud if used to control
           heaving
         •  Possible cross contamination of aquifers where annular
           space not positively controlled by water or drilling mud or
           surface casing
         •  Limited diameter of augers limits casing size
         •  Smearing of clays may seal off aquifer to be monitored
of the borehole. At the surface, the fluid discharges through a
pipe or ditch and enters into a segregated or baffled sedimen-
tation tank, pond or pit. The settling pit overflows into a suction
pit where a pump recirculates the fluid back through the drill
rods (Figure 29).

    During drilling, the drill stem is rotated at the surface by
either top head or rotary table drive. Down pressure  is attained
either by pull-down devices  or drill  collars. Pull-down devices
transfer rig weight to the bit; drill collars add weight directly to
the drill stem. When chill collars mused, the rig holds  back the
excess weight to control the weight on the bit. Most rigs that are
used to install monitoring wells use the pull-down technique
because the wells are relatively shallow.

    Properly mixed drilling fluid serves several functions in
mud rotary drilling. The mud: 1) cools and lubricates the bit, 2)
stabilizes the borehole wall, 3) prevents the inflow of formation
fluids and  4) minimizes cross contamination between  aquifers.
To perform these functions, the drilling fluid tends to  infiltrate
permeable zones and tends to interact chemically with  the
formation fluids. This is why the mud must be  removed during
the development process. This chemical interaction can inter-
fere with the specific function of a monitoring well and prevent
collection of a sample that is representative of the in-situ
ground-water quality.

     Samples can be obtained directly from the  stream of
circulated fluid by placing a sample-collecting device such as
a shale shaker  in the discharge flow before the settling pit.
However, the quality  of the samples obtained  from the circu-
lated fluid is generally not satisfactory to characterize  the
formations for  the design of monitoring wells. Split-spoon,
thin-wall or wireline samples can and should be collected when
drilling with the direct rotary method.
Table 11. Applications  and Limitations of Direct  Mud Rotary Drilling
      Both split-spoon and thin-wall samples can be obtained in
  unconsolidated material by  using a bit with an opening through
  which sampling tools can be inserted. Drilling fluid circulation
  must be broken to collect samples. The rotary drill stem acts as
  casing as the sample tools are inserted through the drill stem and
  bit and a sample is collected.

      Direct  rotary drilling is also an effective means of drilling
  and/or coring consolidated  reek. Where overburden is present,
  an oversized borehole is drilled into rock  and surface casing is
  installed and grouted in place. After the grout sets, drilling
  proceeds using a roller cone bit (Figure  30). Samples can be
  taken either from the circulated fluid or by a core barrel that is
  inserted into the borehole.

      For the rig sizes that are most commonly used for moni-
  toring well installation, the maximum diameter borehole is
  typically 12 inches. Unconsolidated deposits are sometimes
  drilled with drag or fishtail-type bits, and consolidated forma-
  tions such as sandstone and shale  are drilled with tricone bits.
  Where surface casing is installed, nominal 8-inch casing is
  typically used, and a 7  5/8 or 7 7/8-inch borehole is  continued
  below the casing. In unconsolidated formations, these diam-
  eters permit a maximum 4-inch diameter monitoring well to be
  installed, filter-packed and sealed in the open borehole. In
  consolidated formations, a 4 5/8-inch outside diameter casing
  can be used in a 75/8-inch borehole because there are relatively
  few borehole wall stability  problems in consolidated rock. This
  smaller annular space is usually sufficient to permit tremie
  placement of filter pack, bentonite seal and  grout.

      A more complete  listing of applications and limitations of
  direct mud  rotary drilling is found in Table  11.
Application
                                                              Limitations
.Rapid drilling of clay, silt and reasonably compacted sand and
 gravel
. Allows split-spoon and thin-wall sampling in unconsolidated
 materials
.Allows core sampling in consolidated rock

. Drilling rigs widely available
.Abundant and fexible range of tool sizes and depth capabilities
.Very sophisticated drilling and mud programs available
.Geophysical borehole logs
.Difficult to remove drilling mud and wall cake from outer
  perimeter of filter pack during development
.Bentonite or other drilling fluid additives may influence quality
  of ground-water  samples
.Circulated (ditch) samples poor for monitoring well screen
  selection
.Split-spoon and thin-wall samplers are expensive and of
  questionable cost effectiveness at depths  greater than 150 feet
.Wireline coring techniques for sampling both unconsolidated
  and  consolidated formations often not available locally
.Difficult to identity aquifers
. Drilling fluid invasion of permeable zones may compromise
  validity of subsequent monitoring well samples
                                                             41

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                                                    Pump
                                                    suction
   Borehole wall -\  |   \  /~ Cuttings circulated to surface
                          through annular space
                          Tricone bit
 Figure 29. Diagram of a direct rotary circulation system
           (National Water Well Association of Australia, 1984).

 Air Rotary Drilling
     Air rotary drilling is very similar to direct mud rotary with
 the  exception that the circulation medium is air instead of water
or drilling mud. Air is compressed and circulated down through
 the drill  rods and up the open hole. The rotary drill bit is attached
 to the lower end of the drill pipe, and the drill bit is advanced as
 in direct mud rotary drilling. As the bit cuts into the formation,
 cuttings are  immediately removed from the bottom of the
 borehole and transported to the surface by the air that is
 circulating down through the drill pipe and up the annular space.
 The circulating air also cools the bit. When there is no  water
 entering the  borehole from the formation, penetration and
 sampling may be enhanced by  adding small quantities of water
 and/or foaming surfactant. Foam very effectively removes the
 cuttings  and lubricates and cools the bit. However,  the drilling
 foam is  not chemically inert and may react with the formation
 water. Even if the foam is removed during the development
 process, the representativeness of the ground-water quality
 sample may be questioned.

     As  the air discharges cuttings at the surface, formation
 samples  can be collected. When the penetrated formation is dry,
 samples  are typically very fine-grained. This "dust" is represen-
 tative of the formation penetrated, but is difficult to evaluate in
 terms of the physical properties and  characteristics of the
formation. However, when small quantities of water arc en-
countered during drilling or when water and surfactant are
added to the borehole to assist in the drilling process, the size of
the fragments that are discharged at the surface is much larger.
These larger fragments provide excellent quality samples that
are easier to interpret. Because the borehole is cleaned continu-
ously and all of the cuttings are discharged, there is minimal
opportunist y for recirculation and there is minimal contaminat-
ion of the cuttings by previously-drilled zones. Air discharged
from a compressor commonly contains hydrocarbon-related
contaminants. For this reason,  it is necessary to install filters on
the discharge of the compressor.

     When drilling through relatively dry formations, thick
water-bearing zones can easily be observed as drilling pro-
ceeds. However, thin water-bearing zones often are  not iden-
tifiable because either the pressure of the air in the borehole
exceeds the hydraulic pressure of the water-bearing zone or the
combination and quantity of dust and air discharged is sufficient
to remove the small amount of moisture  indicative of the thin
water-bearing zone. Where thin zones are anticipated, the
samples must be carefully evaluated and drilling sometimes
must be slowed to  reduce absorption of the water by the dust. It
may be desirable to frequently stop drilling to allow ground
water to enter the open borehole. This technique applies only to
the first water-bearing zones  encountered, because shallower
zones may contribute water to the open borehole. To prevent
shallow zones from producing water or to prevent cross con-
tamination, the shallower zones must be  cased off. Identifica-
tion of both  thin and thick water-bearing zones is extremely
important because  this  information assists  greatly in the place-
ment of well intakes and/or in the selection of isolated zones for
packer tests.

     In hard, abrasive, consolidated rock, a down-the-hole ham-
mer can be substituted for a roller cone bit to achieve better
penetration (Figure 31). With the  down-the-hole  drill, the
compressed air that is used to cool the bit is also used to actuate
and  operate the down-the-hole hammer. Typical compressed
air requirements range from 100 pounds per square inch to as
much as 350  pounds per square inch for the latest generation of
down-the-hole hammers. When  a down-the-hole hammer is
used, oil is required in the air stream to lubricate the hammer-
actuating device.  For this reason, down-the-hole hammers
must be used with  caution when constructing monitoring wells.
Figure 32 shows the range of materials in which roller cone bits
and  down-the-hole pneumatic hammers operate most effi-
ciently.

     Air rotary drilling is typically limited  to drilling in consoli-
dated rock because of borehole instability problems. In air
rotary drilling, no  casing or drilling fluid is added to support
the borehole walls, and the borehole is held open by stability of
the rock and/or the air pressure used during drilling. In uncon-
solidated materials, there is the tendency for the borehole to
collapse during drilling. Therefore,  air rotary drilling in un-
consolidated formations is unreliable and poses a risk for
equipment. Where sufficient thicknesses  of unconsolidated
deposits overlie a consolidated formation that will be drilled by
air rotary techniques, surface casing through the unconsoli-
dated material is installed by  an alternative technique. Drilling
can then be accomplished using air with either a roller-cone bit
or down-the-hole hammer.
                                                           42

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Figure 30. Diagram of a roller cone bit.
    Monitoring wells drilled by air rotary methods are typi-
tally installed as open-hole completions. Because the borehole
is uncased, the potential exists for cross connection between
water-bearing zones within the borehole. Futher, the recirculated
air effectively cleans cuttings from the borehole walls so that
the borehole is usually not coated with a wall cake such as
occurs with mud rotary drilling or with augering techniques.
This cleaner borehole wall increases the potential for cross
connection, but increases the effectiveness of well completion
and development Additionally, the air introduced during drilling
may strip volatile organics from the samples  taken during
drilling and from the ground water  in the  vicinity of th
borehole. With time, the effects of airstripping  will diminish
and disappear, but the time necessary for this recovery will vary
  with the hydrogeologic conditions. The importance of these
  factors needs to be evaluated before choosing the air rotary
  drilling  technique.

      The diameter of the roller-cone or tricone bit used in air
  rotary drilling is limited  to approximately 12 inches, although
  larger bits are available. For the down-the-hole hammer, the
  practical limitation is  8-inch nominal diameter.  There is no
  significant depth limitation for monitoring well construction
  with the air rotary technique, with the possible exception of
  compressor capacity limits in deep holes with high water tables
and back Pressure.
      A more complete list of applications  and limitations of air
  rotary drilling is found in Table 12.
                                                           43

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      Cuttings discharge
      through pipe
Air to actuate
hammer and
remove cuttings
                       t
                       r\
                                       • Hammer
   • Button bit
Figure 31. Diagram of a down-the-hole hammer (after Layne.
          Western Company, Inc., 1983).
Air Rotary With  Casing Driver
    This method is an adaptation of air rotary drilling that uses
a casing-driving technique in concert with air (or mud) rotary
drilling. The addition of the casing driver makes it possible to
use air rotary drilling techniques in unconsolidated formations.
The casing driver is installed in the mast of a top head drive air
rotary drilling rig. The casing can then be driven as the  drill bit
is advanced (Figure 33).
    The normal drilling procedure is to extend the drill bit 6 to
 12 inches ahead of the casing. The distance that the drill bit can
be extended beyond the casing is primarily a function of the
stability of the borehole wall. It is also possible to drive the
casing ahead of the bit. This procedure can be performed in
unconsolidated formations where caving and an oversize
borehole are of concern.  Once the casing has been driven
approximately one foot into the formation, the drill bit is used
to clean the material from inside the casing.  This technique also
minimizes air or mud contact with the strata.

    Where drilling through unconsolidated material and into
consolidated bedrock, the  unconsolidated formation is drilled
with a drill bit as the casing is simultaneously advanced. When
the casing has been driven into the top of the bedrock, drilling
can proceed by the standard air rotary technique.  The air rotary
with casing driver combination is particularly efficient where
drilling  through the  sand-gravel-silt-boulder-type  materials
that commonly  occur in glaciated regions.  The sandy  and/or
gravelly, unstable zones are supported by the casing while the
boulder and till  zones are rapidly penetrated by  the rotary bit.
Because the upper zones within the formation are  cased-off as
the borehole is advanced, the potential for inter-aquifer cross-
contamination is minimized. The protective  casing  also permits
the collection of reliable formation samples because the entire
formation is cased except for the interval that is presently being
cut. An additional advantage of the drill-through casing driver
is that the same equipment can be used to drive the casing
upward to expose the well intake after the casing and well intake
have been installed in the borehole.

    Water-bearing zones can be readily identified and water
yields can be estimated as drilling progresses. However, as  with
the direct air rotary method, zones that have low hydrostatic
pressure may be inhibited from entering the borehole by the air
pressure exerted by the drilling process. Additionally, the dust
created as the formation is pulverized can serve to seal off these
zones and then these water-bearing zones may be overlooked.
For these reasons, it is necessary to drill slowly and carefully
and even occasionally to  stop drilling where water-bearing
zones are indicated or anticipated.

    A more complete list of applications and limitations of the
air rotary with casing driver method is found in Table 13.

Dual-Wall Reverse-Circulation
    In dual-wall reverse-circulation rotary drilling, the circu-
lating fluid is pumped down between the outer casing and the
inner drill pipe,  out through the drill bit and up the inside of the
drill pipe (Figure 34).
Table 12. Applications and Imitations of Air Rotary Drilling
   Rapid drilling of semi-consolidated and consolidated  rock
   Good quality/reliable formation samples (particularly if small
   quantities of water and surfactant are used)
   Equipment generally available
   Allows easy and quick identification of lithologic changes
   Allows identification of most water-bearing zones
   Allows estimation of yields in strong water-producing zones with
   short 'down time"
                                    Surface casing frequently required to protect top of hole
                                    Drilling restricted to semi-consolidated and consolidated
                                    formations
                                    Samples reliable but occur as small particles that are
                                    difficult to interpret
                                    Drying effect of air may mask lower yield water
                                    producing zones
                                    Air stream requires contaminant filtration
                                    Air may modify chemical or biological conditions. Recovery
                                    time is uncertain.
                                                            44

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Well Drilling Selection Guide
Type of Formation
Geologic Origin fc_
Examples fr
Hardness »

Drilling Methods
Diameter
Depth
Igneous and Metamorphic
Granite Quartzite
Basall Gneiss Schist
Very hard to hard
1 ft
Downhole
hammer
Carbide
insert bit

*


• — Carbide tooth bi

Small (4-8in)
Shallow (50-aoOft)
Sedimentarv
Limestone Sandstone Shale
Hard to soft



4
(
Ro
ts 	 *
n
V

•
v \
m
ary c
ary


I
rill


Clay Sand Gravel
Unconsolidated
*.
>



Small to medium (6-1 2in)
Shallow to deep (50-1, 000ft)
Figure 32. Range of applicability for various rotary drilling methods (Ingersoll-Rand, 1976).
     The circuiationfluid used in the dual-wall reverse circula-
 tion method can be either water or air. Air is the suggested
 medium for the installation of monitoring wells, and, as such,
 it is used in the development of the ratings in Appendix B. The
 inner pipe or drill pipe rotates the bit, and the outer pipe acts as
 casing. Similar to the air rotary with casing driver method, the
 outer pipe: 1) stabilizes the borehole, 2) minimizes cross
 contamination of cuttings and 3) minimizes interaquifer cross
 contamination within the borehole.

     The dual-wall reverse-circulation rotary method is one of
 the better  techniques available for obtaining representative and
 continuous formation samples while drilling. If the drill bit is of
 the roller-cone type, the formation that is being cut is located
 only a few inches ahead of the double-wall pipe. The formation
 cuttings observed at the surface represent no more than one foot
 of the formation at any point in time. The samples circulated to
 the surface are thus representative of a very short section of the
 formation. When drilling with air, a very representative sample
 of a thin zone can be obtained from the formation  material and/
 or the formation water. Water samples can only be obtained
 where the formation has sufficient hydrostatic pressure to
 overcome the air pressure and dust dehydration/sealing effects.
(Refer to the section on air rotary with casing driver for a more
 complete  discussion.)

     Unconsolidated formations can be penetrated quite readily
 with the dual-wall reverse-circulation method. Formations that
 contain boulders or coarse gravelly materials that are otherwise
 very difficult to drill can be relatively easily penetrated with this
 technique. This increased efficiency is due to the ability of the
 method to maximize the energy at the bottom of the borehole
 while the dual-wall system eliminates problems with lost cir-
 culation and/or borehole stability.

     When drilling in hard rock a down-the-hole hammer can be
 used to replace the tri-cone bit. When the down-the-hole hammer
 is employed, air actuates the hammer by: 1) moving down
 through the hammer,  2) moving back up the outside of the
 hammer and 3) recentering the center drill pipe in a cross-over
                                                            45

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                                                                                   Continuous sample discharge
                                           Air supply
                                          Top-head drive
                                           Mast
                                          Casing driver
                                Discharge for cuttings
                              • Casing


                              • Drill pipe
                                Drive shoe
                                Drill bit
Figure 33. Diagram of a drill-through casing driver (Aardvark
          Corporation, 1977),

channel just above the hammer. When drilling with the ham-
mer, the full length of the hammer is exposed below the
protective outer casing (approximately 4 to 5 feet). Thus the
uncased portion of the borehole is somewhat longer than when
drilling with a tri-cone bit This longer uncased interval results
in formation samples that are potentially representative of a
thicker section of the formation. Otherwise, the sampling and
representative quality of the cuttings are very similar to that of
a formation drilled with a tri-cone bit. This method was devel-
oped for  and has been used extensively by minerals exploration
companies and has only recently been used for the installation
of monitoring wells, Depths in excess  of  1000 feet can be
achieved in many formations.

     When drilling with air, oil or other impurities in the air can
be introduced into the formation. Therefore, when drilling with
                                                                     Top-head
                                                                     drive
                                                                                                   Outer pipe

                                                                                                Inner  pipe
                                                             Figure 34. Diagram of dual-wall reverse-otrcuiation rotary
                                                                       method (Driscoll, 1986).
air and a roller-cone bit, an in-line falter must be used to remove
oil or other impurities from the airstream. However, when using
a down-the-hole hammer, oil is required in  the  airstream to
lubricate the hammer. If oil or other air-introduced contami-
nants are of concern, the use of  a down-the-hole hammer may
not be advised.

    When the borehole has been advanced to  the desired
monitoring depth, the monitoring well can be installed by
either 1) inserting a small diameter casing  and well intake
through an open-mouth bit (Driscoll, 1986) or 2) removing the
outer casing prior to the installation of the monitoring well and
installing the monitoring well  in the open borehole.  When
installing a casing through the bit, the maximum diameter
casing that can be installed is approximately 4 inches. This is
controlled by the 10-inch maximum borehole size that is readily
available with existing drill pipe and the maximum diameter
opening in the bit. When installing a casing in the open bore-
hole, the borehole must be very stable to permit the  open-hole
completion.
                                                           46

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Table 13. Application* and Limitation* of Afr Rotary with Casing Driver Drilling
Application*
                                                                      Limitations
  Rapid drilling of unconsolidated sands, silts and days
  Drilling in alluvial material (including boulder formations)
  Casing supports borehole thereby maintaining borehole integrity
  and minimizing inter-aquifer cross contamination
  Eliminates circulation problems common with direct mud rotary
  method
  Good formation samples
  Minimal formation damage as casing pulled back (smearing of
  clays and sits can be anticipated)
        • Thin, low pressure waterbearing zones easily overlooked il
         drilling not stopped at appropriate places to observe whether
         or not water levels are recovering
        * Samples pulverized as in ail rotary drilling
        »Air may modify chemical or biological conditions. Recovery
         time is uncertain
    A more complete list of applications and limitations of the
dual-wall reverse-circulation technique is  found in Table 14.

Cable Tool Drilling
    Cable tool drilling is the oldest of all the available modem
drilling technologies. Prior to the development of direct mud
rotary, it was the standard technology used for almost all  forms
of drilling.

    In cable tool drilling, the drill bit is attached to the  lower
portion of the weighted  drill stem  that, in turn, is  attached by
means of a rope socket  to the rope or cable (Figure 35). The
cable and drill stem are suspended from the mast of the drill rig
through a pulley. The cable runs through another pulley that is
attached to an eccentric "walking or spudding beam. " The
walking beam is actuated by the engine of the drilling rig. As the
walking beam moves up  and down, the bit is alternately raised
and dropped. This "spudding action" can successfully penetrate
all types of geological formations.

    When drilling in hard rock formations, the bit pounds  a
hole into the  rock by grinding cuttings from the formation. The
cuttings are periodically excavated from  the borehole by re-
moving the drill bit and inserting a bailer (Figure 36). The bailer
is a bucket made from sections of thin-wall pipe with a valve on
the bottom that is actuated by the weight of the bailer. The bailer
is run into the borehole  on a separate line. The bailer will not
function unless there is sufficient water in the borehole to  slurry
the mixture of cuttings in water. If enough water is present the
bailer picks up the  cuttings  through the valve on the bottom of
the bailer and is hoisted to the surface. The cuttings are dis-
charged from either the top or bottom of the bailer, and a sample
of the cuttings can be collected. If the cuttings are not removed
from the borehole, the  bit is constantly  redrilling the  same
material,  and the drilling effort becomes very inefficient.

    When drilling unconsolidated deposits comprised prima-
rily of silt and clay, the drilling action  is very similar to that
described in the previous paragraph. Water must be  added  to the
borehole if the formations encountered during drilling do not
produce a sufficient quantity of water to slurry the mud and silt.
If the borehole is not stable, casing must be driven as the bit
advances to maintain the wall of the borehole.

    When drilling unconsolidated deposits comprised prim-
arily of water-bearing sands and gravels, an alternate and more
effective drilling technique is  available for cable tool opera-
tions. In the "drive and bail" technique, casing is driven into the
sand and gravel approximately 3 to 5  feet and the bailer is used
to bail  the cuttings from within the casing. These  cuttings
provide excellent formation samples  because the casing serves,
in effect, as a large thin-wall sampler. Although the sample is
"disturbed," the  sample is representative because the bailer has
the capability of picking up all sizes of particles within the
formation.

    When drilling by the drive  and bail technique,  "heaving" of
material from the bottom of the casing upward may present a
problem. When heaving  occurs, samples are not representative
of the material penetrated by the  casing.  Instead,  samples
represent a  mixture of materials  from the zone  immediately
beneath the drill pipe. Heaving  occurs when the hydrostatic
pressure on the outside of the casing exceeds the pressure on the
inside of the casing. The heaving is exacerbated by the  action of
the drill stem that is  suspended in the borehole as the pipe is
driven and by the action of the bailer that is used to  take the
samples. If the bailer is lifted  or "spudded rapidly, suction is
developed that can pull the material from beneath the casing up
into the casing. This problem is particularly prevalent when the
drill advances from a dense material into relatively unconsoli-
dated sand and gravel under greater hydrostatic pressure.

    Several techniques have been developed to offset the
problem of heaving. These techniques include:

     1)  maintaining the casing  full of water as it is driven
         and as the well is bailed. The column of water in
         the casing creates a higher hydrostatic head within
         the casing than is present in the formation;
    2)  maintaining a "plug" inside the casing as  the
         samples are  taken with the bailer.  This  plug is
         created by collecting samples with the  bailer
Table 14. Applications and Limitations of Dual-Wall Reverse-Circulation Rotary Drilling

Applications                                                           Limitations
  Very rapid drilling through both unconsolidated and
  consolidated formations
  Allows continuous sampling in all types of formations
  Very good representative samples can be obtained with minimal
  risk of contamination of sample and/or water-bearing zone
  In stable formations, wells with diameters as large as 6 inches
  can be installed in open hole completions
         Limited borehole size that limits diameter of monitoring wells
         In unstable formations, well diameters are limited to
         approximately 4 inches
         Equipment availability more common in the southwest
         Air may modify chemical or biological conditions; recovery
         time is uncertain
         Unable to install filter pack unless completed open hole
                                                            47

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                      Crown
                      sheave
                     Shock -
                     absorber
                        Casing and sand
                        line sheaves
                                                Spudding beam

                                                     Heel sheave

                                                      Pitman
                    Tool
                    guide
 Drilling
 cable

Swivel
socket

  Drill
  stem
                   Operating
                   levers
                   Drill bit
Figure 35. Diagram of a cable tool drilling system (Buckeye Drill Company/Bucyrus-Erie Company, 1982).
                                                                  •Truck mounting
                                                                  bracket
        between 1 and 3 feet above the bottom of the
        casing. The plug maintained in the bottom of the
        "borehole" offsets heaving when the pressure
        differential is low;
    3)  overdriving the casing through the zone that has
        the tendency to heave; and
    4)  adding drilling mud to the borehole until the
        weight of the mud and slurried material in the
        casing exceed the hydrostatic pressure  of the
                                                  heaving zone. This fourth option is the least
                                                  desirable because  it adds drilling mud  to the
                                                  borehole.

                                              If it is necessary to maintain a slurry in the casing in order
                                          to control heaving problems, it is still possible to collect both
                                          disturbed and undisturbed samples from beneath the casing by
                                          inserting smaller-diameter drill rods and samplers inside the
                                          casing at selected intervals.
                                                          48

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     Cable tool drilling has become less prevalent in the last 25
years because the rate of formation penetration is slower than
with either rotary techniques in hard consolidated rock or
augering techniques in unconsolidated formations. Because
cable  tool drilling is much slower, it is generally more expen-
sive. Cable  tool drilling is still important in monitoring well
applications because of the versatility of the method. Cable tool
rigs can be used to drill both the hardest and the softest
formations. Cable tool rigs can drill boreholes with a diameter
suitable to fulfill the needs of a monitoring well or monitoring
well network. There is no significant depth limitation for the
installation of monitoring wells.

     When comparing cable tool to other drilling technologies,
cable tool drilling may be the desired method. In a carefully
drilled cable tool borehole, thin individual zones and changes
in formations are  often more easily identified than with alter-
native technologies. For example,  smearing along  sidewalls in
unconsolidated formations is generally  less severe and is thin-
ner than with hollow-stem augering. Therefore, the prospect of
a successful  completion in a thin water-bearing zone  is gener-
ally  enhanced.

     A more complete listing of advantages and disadvantages
of cable tool drilling is found in Table 15.

Other  Drilling Methods
     There are two other drilling techniques that are commonly
available to  install monitoring wells: 1) bucket auger and 2)
reverse circulation rotary. Bucket augers are primarily used for
large-diameter borings associated with foundations and build-
ing structures. Reverse-circulation rotary is used primarily  for
the installation of large-diameter deep water wells.

     While either of these technologies can be used for the
installation of monitoring wells, the  diameters of the boreholes
and the size of the required equipment normally preclude them
from practical monitoring well application. Unless  an  extraor-
dinarily large diameter monitoring well is being installed, the
size  of the zone disturbed by the large diameter hole excavated
by either of these techniques severely compromises the data
acquisition process that is related to  the sampling of the moni-
toring wells. While either of these techniques have possible
application to monitoring well installation, they are not consid-
ered to be valid for regular application.

Drilling Fluids
    Prior to the development of rotary drilling, water  and
natural clay were added to the borehole during cable tool
drilling to: 1) cool and lubricate the bit, 2) slurry the cuttings for
bailing and 3) generally assist in the drilling process. With the
development of rotary drilling, the use of drilling fluid became
increasingly important. In rotary drilling, the drilling fluid 1)
cools and lubricates the bit,  2) removes the cuttings and 3)
simultaneously stabilizes the hole. Drilling fluid thus makes it
possible to drill to much greater depths much more rapidly.  As
fluid rotary drilling programs became increasingly sophisti-
cated, it became possible either to temporarily suspend cuttings
in the mud column when the mud pump was not operating,  or,
under appropriate circumstances, to  cause the cuttings to drop
out in the mud pit when the cuttings reached the surface. These
improvements served not only to enhance the efficiency of the
drilling operation, but also to improve the reliability of the
geologic information provided by the cuttings.

     Today, the fluid system used in mud rotary drilling is  no
longer  restricted to the use of water and locally-occurring
natural  clays. Systems are now available that employ a wide
variety  of chemical/oil/water-base and water-base fluids with a
wide range of physical characteristics created by additives. The
predominant additives include sodium bentonite  and barium
sulfates, but a variety of other chemicals are also used. This
drilling fluid technology was initially developed to fulfill the
deep-drilling requirements of the  petroleum industry and is not
generally applied to monitoring well installations.

Influence of Drilling Fluids on Monitoring Well
Construction
     Monitoring well construction is typically limited to the use
of simple water-based drilling fluids. This  limitation is imposed
by the necessity not to influence the ground-water quality in the
area of  the well. Even when water-based fluids are used, many
problems are still created or exacerbated by the use of drilling
fluids. These problems  include:  1) fluid infiltration/flushing of
the intended monitoring zone, 2) well development difficulties
(particularly where an artificial filter pack has been installed)
and 3)  chemical, biological and physical  reactivity of the
drilling  fluid with the indigenous fluids in. the ground.

     As  drilling fluid is circulated  in the borehole  during drilling
operations, a certain amount of the drilling  fluid escapes into the
formations being penetrated. The  escape, or infiltration into the
formation, is particularly pronounced in more permeable zones.
Because these more permeable zones are  typically of primary
interest  in the monitoring effort, the most "damage" is inflicted
on the zones of greatest concern. If the chemistry of the water
in the formation is such that it reacts with the infiltrate, then
subsequent samples taken from this zone will not accurately
reflect the conditions that are intended to be monitored. At-
tempts to remove drilling fluids from the formation are made
during the well development process. Water is typically re-
moved in sufficient quantities to try to recover all the infiltrate
that may have penetrated into the formation. When a sufficient
quantity of water has been removed during development, the
effects of flushing are arbitrarily  considered  to be minimized.
Table 15. Applications and Limitations of Cable Tool Drilling

Applications
       Limitations
  Drilling in all types of geologic formations
  Almost any depth and diameter range
  Ease of monitoring well installation
  Ease and practicality of well development
  Excellent samples of coarse-grained materials
         Drilling relatively slow
         Heaving of unconsolidated materials must be controlled
         Equipment availability more common in central, north een
         and northeast sections of the United States
                                                            49

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     Most monitoring wells are typically 2 to 4 inches in
 diameter. They are frequently surrounded by  a filter pack to
 stabilize the formation and to permit the procurement of good
 ground-water samples. Because of the small well diameter, it is
 very difficult, and often  not possible, to fully develop the
 drilling mud from the interface between the outside  of the filter
 pack and the inside of the natural formation. Failure to fully
 remove  this mudcake can interfere with the quality of the
 samples being obtained for a substantial period of  time.

     In practice,  when ground-water sampling is undertaken,
 samples are usually collected and analyzed in the field for
 certain key parameters,  including specific conductance, tem-
 perature and pH. Water is discharged from the well and repeated
 measurements are taken until the quality of the water being
 sampled has stabilized. When this "equilibrium" has been
 achieved and/or a certain number of casing volumes of water
 have been removed, the  samples  collected are  commonly
 considered to be representative of the indigenous quality of the
 ground water.  It is assumed that the drilling fluid filtrate no
 longer impacts the results of the sample quality.  This is not
 necessarily the case. If, for example, the chemical  reactions that
 took place between the  drilling fluid and formation water(s)
 resulted in the precipitation of some constituents, then the
 indigenous water moving toward the well can redissolve some
 of the previously-precipitated constituents and give a false
 result to the sample.  Theoretically,  at some point in time this
 dissolution will be completed and the samples will become
 valid. However, there is currently  no reliable method in practice
 that postulates the time frame required before reliable quality is
 attainable.

     Biologic activity induced by the introduction of the drilling
 fluid may have a similar reaction. In particular,  the use  of
 organic drilling fluids, such as polymeric additives, has the
 potential for enhancing biologic  activity. Polymeric additives
 include the natural organic colloids developed from the guar
 plant that are used for viscosity control during drilling. Biologic
 activity related to the decomposition of these compounds can
 cause along-term variation in the quality of the water sampled
 from the well.

     The use of sodium montmorillonite (bentonite) can also
 have a deleterious long-term impact on water quality. If the
 sodium-rich montmorillonite is not fully removed from the well
 during development, constituents  contained in the ground wa-
 ter being monitored will come in contact with the montmorillo-
 nite. When this  happens, the tendency is for both organic
 molecules with polar characteristics and inorganic  cations to be
 attracted  to positions within the sodium montmorillonite  struc-
 ture.  This substitution results in the release of excess sodium
 ions and the retention of both selected organic molecules and
 cations. Organic molecules  and cations that might otherwise be
 indicative of contamination can be removed from the sample
 and  possibly be re-dissolved at an undefined rate into  subse-
 quent samples.

Drilling Fluid Characteristics
     The principal properties of water-based drilling fluids are
 shown in Table 16. Selected properties are discussed in this
 section. Monitoring well  construction typically  starts by  using
only the simplest  drilling fluid- -water; however, water  should
only be used when necessary. Any  water added  as a drilling
 fluid to a monitoring well should be the best quality of water that
 is available. The chemical and bacteriological quality of this
 water must be determined by laboratoy  analyses in order to
 identify potential interference with substances being monit-
 ored. As this "clean" water is circulated in the borehole, the
 water picks up clay and silt that form a natural drilling mud.
 During this process, both the weight and viscosity of the drilling
 fluid increase. The degree of change in these properties depends
 on the nature  of the geologic formations being penetrated. It is
 possible to attain a maximum weight of approximately 11
 pounds per gallon when drilling in natural clays. The same
 maximum weight can also be achieved by artificially adding
 natural clays or bentonite to make a heavier drilling mud where
 the formation  does not natural] y have these  minerals.

     Where additional weight is needed to maintain stability of
 the borehole, heavier additives are required. The most common
 material used  for drilling mud weight control is barite (barium
 sulfate). Barite has an average specific gravity of approximately
 4.25; the specific gravity of typical clay additives  approximates
 2.65. Figure 37 shows the range of drilling fluid densities that
 can be obtained by using a variety of different drilling additives.

     When the weight of the drilling fluid  substantially exceeds
 the natural hydrostatic pressure exerted by the formation being
 drilled, there  is an excessive amount of water loss from the
 drilling fluid into the formation penetrated. This maximizes the
 filtrate invasion and consequently maximizes the  adverse im-
 pact of filtrate  invasion on the reliability  of water-quality
 samples collected from the monitoring well.

     Another important property of a drilling  fluid is viscosity.
 Viscosity is the resistance offered by the drilling fluid to flow.
 In combination with the velocity of the circulated fluid, viscosity
 controls the ability of the fluid to remove cuttings from the
 borehole.  In monitoring wells where water is  the primary
 drilling fluid, the viscosity is the result of the interaction of
 water with the particulate matter that is drilled. Viscosity is also
 affected by the interaction of water with the clays that are
 sometimes  added during the drilling process.  Sodium montmo-
 rillonite (sodium bentonite) is the constituent  most often added
 to increase viscosity.

    Viscosity has no relationship to density. In the field,
 viscosity is measured by  the time required for a known quantity
 of fluid to  flow through an orifice of special dimensions. The
 instrument  used for this measurement is called a Marsh Funnel.
 The relative viscosity  of the drilling mud is described as the
 Marsh Funnel viscosity, in seconds. Table 17 presents the
 approximate Marsh Funnel viscosities required for drilling in
 typical unconsolidated materials.  These  typical values are based
 on the assumption that the circulating  mud pump provides an
 adequate uphole velocity  to clean the cuttings from the borehole
 at these viscosities.  For comparison, the Marsh Funnel viscos-
 ity of clear water at 70"F is 26 seconds.
Table 16. Principal Properties of Water-Based Drillng Fluids
        (Driscoll, 1986)
Density (weight)
Viscosity
yield point
Gel  strength
Fluid-ioss-controi effectiveness
Lubricity (lubrication capacity)
                                                           50

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^>
                                    A
                                   IV
                                    y
                                                 valve
       (a)
                                       (b)
Figure 36. Diagrams of two types of bailers:
          a) dart valve and b) flat bottom.
Table 17. Approximate Marsh Funnel Viscosities Required for
         Drilling in Typical Types of Unconsolidated Materials
         (Driscoll, 1986)
                      Appropriate Marsh Funnel
Material Drilled            Viscosity (seconds)
Fine sand
Medium sand
Coarse sand
Gravel
Coarse gravel
                         35-45
                         45-55
                         55-65
                         65-75
                         75-85
    Clays are frequently a mixture of illite,  chlorite, kaolinite
and mixed-layer clays. These minerals all have a relatively low
capability to expand when saturated. The reason that sodium
montmorillonite is so effective in increasing viscosity is be-
cause of its  crystalline layered structure; its bonding character-
istics; and the ease of hydration of the sodium cation. Figure 38
demonstrates the variation in the  viscosity building character-
istics of a variety of clays.  Wyoming bentonite (a natural
sodium-rich montmorillonite) is shown at the extreme left.
     The impact of the mix water on sodium bentonite is
indicated by Figure 39. This figure shows the viscosity varia-
tion that results from using soft water versus hard water in
drilling mud preparation. Sodium montmorillonite is most
commonly used as the viscosity-building  clay. However, in
hard water the calcium and magnesium ions replace the  sodium
cation in the montmorillonite structure. As a consequence, a
much lower viscosity is obtained for a given quantity of solids
added. As previously discussed, this sodium cation replacement
is similar to the activity that occurs  in the subsurface when
bentonitic materials are left in the proximity of the well. These
materials have the capacity to prevent ions from reaching the
borehole and to release them slowly back into the ground water
at an indeterminate  rate.  This process  can have a profound
influence on the quality of the ground-water samples collected
from the monitoring  well.

     The loss of fluid from the borehole into permeable zones
during drilling occurs because the hydrostatic pressure in the
borehole exceeds that of  the formation being penetrated. As
fluid moves from the borehole into the  lower pressure zones,
fine particulate matter that has been  incorporated during the
drilling operation, plus any clay additives that have been added
to the drilling fluid, are deposited in the pore space of the zone
being infiltrated. When this happens,  a "filter cake" is formed
on the borehole wall. Where a good quality bentonitic drilling
mud additive is being used, this filter cake can be  highly
impermeable and quite tough. These  characteristics minimize
filtrate invasion into the  formation,  but make it difficult to
develop these clays out of the zone penetrated.

     Yield point and  gel strength are two additional properties
that are considered in evaluating the characteristics of drilling
mud. Yield point is a measure of the amount of pressure, after
a shutdown, that must be exerted by the  pump upon restarting,
in order to cause the  drilling fluid to start to flow. Gel strength
is a measure of capability of the drilling fluid to maintain
suspension of particulate matter in the mud column when the
pump is shut down. There is  a close relationship between
viscosity, yield point and  gel strength. In monitoring well
installation these properties are rarely controlled because the
control of these properties requires the  addition of additives that
can impact the quality of the water produced by the completed
well. They are important, however, in  evaluating the reliability
of samples taken from the mud stream. Where drilling fluid
quality is uncontrolled, ditch samples  are generally unreliable.

Mud-Based Applications
     It is desirable to install monitoring wells with the cleanest,
clearest drilling water that is available. In monitoring well
applications, the properties related to  mud weight and  the
properties that relate  to flow characteristics are only  controlled
under exceptional conditions. This  control is usually exercised
only on relatively deep boreholes or boreholes with moderately
large diameters.

    When drilling using either cable  tool  or hollow-stem
augering techniques, it is sometimes necessary to add water to
the borehole in order to  effectively continue drilling. The
addition of water maybe required to: 1)  stabilize the borehole,
2) improve the cutting action of the bit or 3) enable the driller
to remove the cuttings from the borehole. With drive-and-bail
and hollow-stem auger techniques, it maybe necessary  to add
                                                          51

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                                                   Weight of drilling fluid.lb/gal
                                                          10
                                                                                      15
I      Air


      Mist
           Stiff foam

                 Wat foam
                          Water
         Maximum practical density using polymers
                Polymeric drilling fluid saturated with NaCI
                 Maximum practical density using bentonite
                     Polymeric drilling fluid saturated with CaCi
                                   Weighted bentonite drilling fluid using barite
     0                        600                        1,200

                                                  Weight of drilling fluid,kg/nf

Figure 37. Practical drilling fluid densities (Drlscoll, 1986).
                                                                                     1,800
                                                                                                                2,400
water to the borehole to minimize heaving of the formation
upward into the casing or hollow stem. When the zone imme-
diately  below the augers or the casing heaves,  the samples
collected from this zone are considered disturbed and are not
representative of the natural undisturbed formation.

    When drilling  fluid is added during either cable tool
drilling or hollow-stem augering, the effectiveness of the water
is enhanced by the addition of bentonite to the drilling fluid. The
bentonite is added to the borehole for formation stabilization.
When either clean water or clean water plus additives are added
to the borehole, the problems of flushing, potential contamina-
tion and water-quality modification are the same as when using
fluid rotary drilling. For these reasons,  it is  suggested that
addition of drilling fluid additives and/or even clean water be
avoided when using cable tool or hollow-stem augers if at all
possible. If it is anticipated that the addition of fluids will be
necessary to drill with either cable tool or hollow-stem augers,
it is suggested that alternative drilling techniques be considered.

Air-Based Applications
    In addition to water-based drilling fluids, air-based drilling
fluids are also used. There are a variety of air-based systems as
indicated in Table 18. When using air-based drilling fluids, the
same restrictions apply as  when using water-based  drilling

Table 18. Drilling Fluid Option* when Drilling with Air (after
         Drlscoll. 1986)     	
• Air Alone
• Air Mist
  »Air plus a small amount of water/perhaps a small amount of
    surfactant
• Air Foam
  • Stable foam - air plus surfactant
  • Stiff foam - air, surfactant plus polymer or bentonite
• Aerated mud/water base - drilling fluid plus air
fluids.  When a monitoring well is drilled using additives other
than dry air, flushing, potential contamination and water-
quality modification are all of concern. Even with the use of dry
air, there is the possibility that modification of  the chemical
environment surrounding the borehole may occur due to changes
in the oxidation/reduction potential induced by aeration.  This
may cause stripping of volatile organics from formation samples
and ground water in the vicinity of the borehole. With time, this
effect will diminish and disappear, but the time necessary for
this to occur varies with  the hydrogeologic conditions.
     83.7
                67.5
   Weight, I
71.2   75.0  78.7  82,5 86.2 90.0
      8.5
                 9.0
   Weight, Ib/gai
9.5    10.0  10.5  11.0  11.5 120
         100
              1C   15   20  25.   30   35  40   455Q
                   Percent solids by weight
      200175  5040  3025  201816 14  12   10   8  8
          Yield (16-centipoise drilling fluid), barrels per ton

Figure 38. Viscosity-building characteristics of drilling clays
           (after Petroleum Extension Service, 1960).
                                                            52

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                                                        Bentoniie
                      Complete
                        mixing
                                                                       Incomplete
                                                                         mixing
                                                                                            u
           Higher viscosity per Ib of clay solids
                                                            Lower viscosity par Ib of clay solids
                                                                           Jj
                                                                                         li
    _/  >o     v
     a
#
        Deflocculated
   • Low gel strength
   • Lowest rate of filtration
   • Firm filter cake
                  Flocculated
             • Progressive gel strength
             • High rate of filtration
             • Soft filter cake
   Deflocculated
• Low gel strength
• Low rate of filtration
• Firm filter  cake
     Flocculated
• Sudden, non-progressive
  gel   strength
• Highest rate of filtration
• Soft filter cake
Figure 39. Schematic of the behavior of clay particles when mixed into water (Driscoll, 1986).
    Where dry air is being used, a filter must be placed in the
discharge line to remove lubricating oil. Because a down-the-
hole hammer cannot be used without the presence of oil in the
air stream, this particular variety of dry-air drilling cannot be
used without the danger of contaminating the formation with
lubricating oil.

    Monitoring  wells can be installed in hard rock formations
using air as the  circulation medium and employing roller-cone
bits. Air can also be used successfully in unconsolidated format-
ions when applied in conjunction with a casing hammer or a
dual-wall casing technique. For effective drilling, the air supply
must be sufficient to lift the cuttings from the bottom  of the
borehole, up through the annular space  and to the discharge
point at the surface. An uphole velocity of 5000 to 7000 feet per
minute is desirable for deep  boreholes drilled at high penetra-
tion rates.

Soil  Sampling and Rock Coring Methods
    It is axiomatic that  "any sample is better than no sample;
and no sample  is ever  good enough." Thus, if there are no
samples except  those collected from the discharge of a direct
                                            rotary fluid drilled hole or those scraped from the cutting head
                                            or lead auger of a solid core auger, then these samples will be
                                            collected and analyzed to the best of the ability of the person
                                            supervising the operation. In general, however, it can be stated
                                            that in a monitoring well  installation program these types of
                                            samples  are not sufficient.

                                                 When evaluating the efficiency of a sampling program, the
                                            objectives must be kept in mind.  Where formation boundaries
                                            must be identified in order to establish screened intervals,
                                            continuous samples  are important. If identification of isolated
                                            zones with thin interfingers of sand and gravel in a clay matrix
                                            is important for the monitoring program, then the samples must
                                            allow identification of discrete zones within the interval being
                                            penetrated. If laboratory tests will be performed on the samples,
                                            then the  samples must be of sufficient quality and  quantity for
                                            laboratory testing. Specific laboratory tests require that samples
                                            be undisturbed; other tests permit the use of disturbed samples.
                                            The sample program must take these requirements into account.

                                                 Table 19 demonstrates the characteristics of the sampling
                                            methods available for the drilling techniques that are most
                                                             53

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Table 19. Characteristices of Common Formation-Sampling Methods
Type of
Formation
Sample Collection
Method
Sample
Quality
Potential for
Continuous
Sample
Collection
Samples
Suitable
for Lab
Teats
Discrete
Zones
identifiable
Increasing
Reliability
Unconsolidated
Consolidated
Solid core auger           Poor          No
Ditch (direct rotary)         Poor          Yes
Air rotary with casing driver  Fair           Yes
Dual-wall reverse circulation
rotary                    Good          Yes
Piston samplers            Good          No
Split spoon and thin-wail
samplers                 Good          Yes
Special samplers
(Dennison, Vicksburg)       Good          Yes
Cores                    Good          Yes

Ditch (direct rotary)         Poor          Yes
Surface (dry air)            Poor          Yes
Surface  (water/foam)        Fair           Yes
Cores (wireline or
conventional)              Good          Yes
No
No
No

No
Yes

Yes

Yes
Yes

No
No
No

Yes
No
No
Yes

Yes
Yes

Yes

Yes
Yes

No
Yes
Yes

Yes
frequently employed in the installation of monitoring wells.
The table is arranged such that the general overall reliability of
the samples increases downward in the table for both unconsoli-
dated and consolidated materials.  The least favorable type of
sampling is the scraping of samples from the outside of the
flights of solid-flight augers. This sampling method: 1) permits
only discontinuous sampling, 2) does not allow identification of
discrete zones, 3) provides no  sample suitable for laboratory
testing and 4) generally provides unreliable  sample quality. It
can also  be seen from Table 19 that split-spoon and thin-wall
sampling techniques are the minimum techniques required to
obtain: 1) good sample quality, 2) continuous sampling, 3)
samples suitable for laboratory testing and 4) samples that
allow the identification of discrete zones.

    Split-spoon sampling has become the  standard for obtain-
ing samples in unconsolidated materials by which other tech-
niques are compared. Split-spoon  samples are  "driven" to
collect disturbed  samples; thin-wall  samples are "pressed" to
collect undisturbed samples.  Undisturbed samples cannot be
taken using driving, rotational  or vibratory techniques in un-
consolidated materials. Split-spoon and  thin-wall sampling
techniques are the primary techniques that are used to obtain
data for monitoring well installation.

    Sample description is as important as  sample collection. It
is often difficult to collect good formation samples of non-
cohesive  materials because the fine, non-cohesive  particles are
frequently lost during the sampling process.  The person using
and describing such sampling data must make an on-site,
sample-by-sample determination of sample  reliability if the
data are to be used in a meaningful manner.  Another sampling
bias is that particulate material with an effective diameter
greater than one-third of the inside diameter of the sampler
frequently cannot be collected. It is not unusual  for a single
large gravel or small cobble to be caught at the bottom of the
sampler and no sample at all recovered from a sampler run. It
is also possible in a sequence of alternating saturated clay/silt
                                         and sand to "plug" the sampler with the clay/silt materials and
                                         to drive through the sands without any indication of sand. It is
                                         also common for the sample to be compacted so that if a 2-foot
                                         sampler is driven completely into the sediments, only 1.5 feet
                                         or less may actually be recovered.

                                             It must be stressed that regardless of the sampling equip-
                                         ment  used, the final results frequently depend on the subjective
                                         judgment of the person describing the samples. Therefore, in
                                         order to  properly screen and develop a well in a potentially
                                         contaminated zone, it is often necessary to employ auxiliary
                                         techniques and  substantial experience.

                                         Split-Spoon  Samplers
                                             Split-spoon sampling techniques were developed to meet
                                         the requirements of foundation engineering.  The common
                                         practice in foundation evaluation is  to collect 18-inch samples
                                         at 5-foot internals as the borehole is advanced. The split-spoon
                                         sampler is attached to the end of the drill rods and lowered  to the
                                         bottom of the borehole where it rests on top of fresh undisturbed
                                         formation. In order to obtain valid samples, the bottom of the
                                         borehole must be clean and the formation to be sampled must
                                         be fresh and undisturbed. It is, therefore, easy to see why:  1) the
                                         difficulties of a heaving formation must be overcome prior to
                                         sampling and 2) a good sampling program can only be con-
                                         ducted in a stabilized borehole.

                                             A split-spoon sampler, as shown in Figure 40, is of standard
                                         dimensions and is driven by a 140-pound weight dropped
                                         through a 30-inch interval. The procedure for collecting split-
                                         spoon samples and the standard dimensions for samplers are
                                         described in ASTM D1586 (American Society for Testing and
                                         Materials, 1984). The number of blows required to drive the
                                         split-spoon sampler provides an indication of the compaction/
                                         density of the soils being sampled. Because only  18-inch
                                         intervals are sampled out of every  5 feet penetrated, drilling
                                         characteristics (i.e.  rate of penetration,  vibrations,  stability,
                                         etc.) of the formation being penetrated are also used to infer
                                                          54

-------
     Head assembly
      Split barrel
       Spacer
                                                Liner
          Shoe
Figure 40.  Diagram of a split-spoon sampler (Mobile Drilling
          Company, 1982).
characteristics of unsampled material. "Continuous" samples
can also be taken with the split-spoon method by augering or
drilling to the bottom of the previously-sampled interval and
continuously repeating the operation. In order to obtain more
accurate "N" values, a better approach is to attempt to collect
 two samples every five feet. This minimizes collection of
 samples in the disturbed zone in front of the bit. Continuous
 sampling is more time consuming, but is often the best way to
 obtain good  stratigraphic data  in unconsolidated sediments.

     Table 20 shows the  penetration characteristics of a variety
 of unconsolidated materials. The  samples collected by split-
 spoon sampler are considered  to be "disturbed" samples. They
 are, therefore, unsuitable for running certain laboratory tests,
 such as  permeability.

 Table 20. Standard Penetration Test Correlation Chart (After
          Acker, 1974)
                                                            Soil Type
                    Designation
                                            Bfows/Foot*

Sand
and
silt


Clay



Medium
Dense
, Very Dense
Very Soft
soft
Medium
Stiff
{ Hard
0-10
11-30
31-50
>50
<2
3-5
6-15
1-25
>25
 • Assumes: a) 2-inch outside diameter by 1 3/8 Inch inside diameter
             sampler
           b) 140-pound hammer falling through 30 inches
 Thin-Wall Samplers
     Work performed by Hvorslev (1949) and others have
 shown that if relatively undisturbed samples are to be  obtained,
 it is imperative that the thickness of the wall of the sampling
 tube be less than 2.5 percent of the total outside diameter of the
 sampling tube. In addition, the ratio of the total area of the
 sampler outside diameter to the wall thickness area (area ratio)
 should be as  small as possible. An area ratio of approximately
 10 percent is the maximum acceptable ratio for thin-wall
 samplers; hence, the  designation "thin-wall" samplers. Because
 the split-spoon sampler must be  driven to collect samples, the
 wall thickness of the sampler must be structurally sufficient to
 withstand the driving forces. Therefore, the wall thickness of a
 split spoon sampler is too great for the collection of undisturbed
 samples.

     The standard practice for collecting thin-wall samples,
 commonly referred to as  Shelby tube samples, requires placing
 the thin-wall  sampling tube at the end of the sampling drill rods.
 The sampler and rods are lowered to the bottom of the borehole
just as is done with the split-spoon sampler. Instead of driving
 the sampler into the ground, the weight of the drill rig  is placed
 on the sampler and it is pressed into place. This sampling
 procedure is  described in detail in ASTM D1587 (American
 Society for Testing and Materials, 1983). A typical thin-wall
 sampler is shown in Figure41.

    The requirement that the area ratio be as small as possible
 resents  a serious limitation  on obtaining undisturbed samples
 in compact sediments. A  thin-wall sampler may not have
 sufficient structural  strength to  penetrate these materials.  A
 standard 2-inch inside diameter thin-wall sampler will fre-
 quently collapse without satisfactorily collecting a sample in
 soils with "N" values of 30 or greater. "N" values are a standard
method of comparing relative density as derived from blow
counts and are explained in  ASTM D1586 (American Society
for Testing and Materials, 1984).
                                                          55

-------
                     -^-~ -       Cap screw
                                       • Head assembly
                                    • Cap screw
                                           'Tube
Figure 41. Diagram of a thin-wall sampler (Acker Drill Company,
          inc., 1985).
Specialized Soil  Samplers
    Many  special-function samplers have been developed to
deal with special conditions. These include: 1)  structurally
strong thin-wall samplers that collect "undisturbed" samples, 2)
large-diameter samplers that  collect coarse sand and  gravel for
gradation analyses and 3) piston samplers that collect  samples
in heaving sands. Two good examples of the reinforced-type
design are the Vicksburg  sampler and the  Dennison sampler, as
shown in Figures 42a and 42b. Both samplers were developed
by the United States Army Corps of Engineers and are so named
for the districts in which they were first developed and used.
The Vicksburg sampler is a 5.05-inch inside diameter by 5.25-
inch outside diameter sampler that qualifies as a thin-wall
sampler but is structurally much stronger than a Shelby tube.
The Dennison sampler is a double-tube core design with a thin
inner tube that qualifies as a thin-wall sampler. The outer  tube
permits penetration in extremely stiff deposits or highly ce-
mented unconsolidated materials while the inner tube collects
a thin-wall sample.

    Examples of piston samplers are the internal sleeve piston
sampler developed by Zapico et al. (1987) and the  wireline
piston sampler described by Leach et al. (1988) (Figures 43 and
44). Both samplers have been designed to be used with a hinged
"clam-shell" device on the cutting head of a hollow-stem auger
(Figure 45). The clam shell has been used in an attempt to:  1)
improve upon a non-retrievable knock-out plug technique,  2)
simplify sample retrieval and 3) increase the reliability of the
sampling procedure in heaving sand situations.  The Zapico et
al. (1987) device requires the use of water or drilling mud for
hydrostatic control while the Leach et al. (1988)  device permits
the collection of the sample  without the introduction of any
external fluid. The  limitation of using this technique is  that  only
one sample per borehole can be collected because the clam  shell
device will not  close after the sampler is inserted through the
opening. This means that although sample reliability is good,
the cost per sample is high.

    In both split-spoon and thin-wall sampling, it is common
for a portion of the sample  to be lost during the sampling
process. One of the items to be noted in the sample description
is the percent recovery, or the number of inches that are actually
recovered of the total length that was driven or pressed. To  help
retain fine sand and gravel and to prevent the sample from being
lost back into the borehole as the sample is removed, a "basket"
or a  "retainer" is placed inside the split-spoon sampler.  Figure
46 shows the configuration of four commercially-available
types of sample  retainers. A check valve is also usually installed
above the sampler to relieve hydrostatic pressing during sample
collection and to prevent backflow and consequent  washing
during withdrawal of the sampler.

    Except for loss of sample during collection, it is possible  to
collect continuous samples with  conventional  split-spoon  or
thin-wall techniques. These involve: 1) collecting a sample,  2)
removing the sampler from the borehole, 3) drilling the sampled
interval, 4) reinserting the sampler and 5) repeating the process.
This effort is time consuming and relatively expensive, and it
becomes increasingly expensive in lost time to remove and
reinsert the sampler and rods as the depths exceed 100 feet.

    To overcome this repeated effort, continuous samplers
have been developed. One such system is shown in Figure 47.
A continuous sample is taken by attaching a 5-foot long thin-
wall tube in advance  of the cutting head of the hollow-stem
auger. The tube  is held in place by a specially designed latching
mechanism that permits the sample to be retracted by wire line
when full and replaced with a new tube. A ball-bearing fitting
in the latching mechanism permits the auger flights to be rotated
without rotation of the sampling tube. Therefore, the sampling
tube is forced downward into the ground as the augers are
rotated.
                                                           56

-------
                    M   1/2
                               -5.05"
                               —  5.25'
                                                   Drill rod
                                                   Air hose
                                               "N"  rod coupling
                                                 Plug



                                                Sampler head

                                                   Clamp

                                                   Wrench holes
                                                   Adapter

                                                  -Allen set
                                                   screws
                                                  -Rubber gasket
                                                 -Sampling tube
                                                                                      • Outer head
                                                                                      • Outer tube
                                                                                      . Bearing
                        • Inner head


                        - Cotter pm

                         • Check valve


                         • Inner tube
                          Liner
                                                                                     — Sawtooth bit
                                                                                      - Basket retainer
                                    •5"
                                     (a)
                (b)
Figure 42. Two types of special soil samplers: a) Vicksburg sampler (Krynine and Judd, 1957) and b) Dennison sampler (Acker Drill
          Company,  Inc.,   1985).
Core Barrels
    When installing monitoring wells in consolidated forma-
tions the reliability and overall  sample quality of the drilled
samples from either direct fluid  rotary or air, water and foam
systems  is very similar to  that of the samples  obtained in
unconsolidated formations. Where reliable samples are needed
to fully characterize the monitored zone, it is suggested that
cores be  taken. Coring can be conducted by either wireline or
conventional methods. Both single and double-tube core bar-
rels are available as illustrated in Figures 48a and 48b.
    In coring, the carbide or diamond-tipped bit is attached to
the lower end of the core barrel. As the bit cuts deeper, the
formation sample moves up the inside of the core tube. In the
single-wall tube, drilling  fluid circulates downward around the
core that has been cut, flows between the core and the core
barrel and exits through the bit. The drilling fluid then circulates
up the annular space and is discharged at the land surface.
Because the drilling fluid is directly in contact with  the core,
poorly-cemented or soft material is frequently eroded and the
core may be partially or totally  destroyed. This problem exists
where formations are friable, erodable, soluble or highly  frnc-
                                                           57

-------
     Upper drive
     head with left
     threaded pm
       Piston cable •
   Hardened drive
   shoe   ,
1
1
A
fl
'ffi%<,
""*



t=tt
X-*-
^-^
/
/
/
                                       - Inner core barrel
                                        (dedicated)
                                      - Outer core barrel
Piston with rubber
washers & brass
spacers
 Figure 43. internal sleeve wireline piston sampler (Zapico et al.,
           1987).
tured. In these formations very little or no core may be recov-
 ered.

     In these circumstances a double-wall core barrel may be
 necessary. In a double-wall core barrel, the drilling fluid is
 circulated between the two walls of the core barrel and does not
 directly contact the core that has been cut. As drilling fluid
 circulates between the two walls of the core barrel, the core
 moves up into the inner tube, where  it  is protected. As  a result,
 better cores of poorly-consolidated forrnationscan be recovered.
 Good recovery can be obtained even  in unconsolidated clays
 and silts using a double-wall coring technique.

 Selection of Drilling Methods for Monitoring Well
 Installation

 Matrix Purpose
     The most appropriate drilling technology for use at  a
 specific site can only be determined by evaluating both the
 hydrogeologic setting and the objectives of the monitoring
 program. To assist  the user in choosing an appropriate drilling
technology, a set of matrices has been developed that lists the
most commonly used drilling techniques for monitoring well
installation and delineates the principal criteria for evaluating
those drilling methods. A matrix has been developed for a
unique set of hydrogeologic conditions and well design require-
ments  that limit the applicability of the  drilling techniques.
Each applicable drilling method that can be used in the de-
scribed hydrogeologic setting and with the stated specific
design requirements has been evaluated on  a scale of 1 to 10
with respect to the criteria listed in the matrix. A total number
for each drilling method was computed by adding the scores for
the various criteria. The totals  represent  a relative indication of
the desirability of the drilling methods for the specified condi-
tions.

Matrix Description and Development
    A set of 40 matrices has been developed to depict the most
prevalent  general hydrogeologic  conditions and well design
requirements for monitoring wells. The  complete set of matri-
ces are included as Appendix B. The matrices were developed
from a combination of five factors including:

     1)  unconsolidated  or  consolidated  geologic
        formations  encountered  during drilling,
    2)  saturated or unsaturated conditions encountered
        during  drilling,
    3)  whether or not invasion of the monitored zone by
        drilling fluid is  permitted,
    4)  depth range of the monitoring well 0 to 15 feet,
         15 to 150 feet or greater than 150 feet and
    5)  casing diameter  of the monitoring well: less  than
        2 inches, 2 to 4 inches or 4 to 8 inches.

    Table 21 indicates the number of  the matrix that corre-
sponds to the combination of factors used to develop the
numbers on each matrix.

    Each  matrix provides a relative  evaluation of the  applica-
bility of selected drilling  methods commonly used to  construct
monitoring wells. The drilling  methods evaluated in the matrix
include:

    1)  hand auger,
    2)  driving,
    3)  jet percussion,
    4)  solid flight auger,
    5)  hollow stem auger,
    6)  mud rotary,
    7)  air rotary,
    8)  air rotary with casing driver,
    9)  dual-wall rotary and
    10) cable tool.

    A complete description of these drilling techniques and
their applicability to monitoring well installations can be found
in the  beginning of this chapter under the heading  entitled
"Drilling Methods for Monitoring Well  Installation.*'

    The drilling techniques have been evaluated with respect to
a set of criteria that also influences the choice of a drilling
method. These additional criteria include:

     1) versatility  of the drilling method,
    2) sample reliability,
                                                            58

-------
Table 21. Index to Matrices 1 through 40
                   Matrix Number
1
ta
1
o
tfi

§
"O
I
S
•5
vs
                                                          I
E
1
                                                                    .2
                                                                              f
                                                                                   u.
                              
-------
                                                                Brass bushings
                                                 Teflon wiper disc
                                                                                                         Swivel
                                                                                      Neoprene seals
Figure 44. Modified wireline piston sampler (Leach et al., 1988).
                                                 •Auger-head
                                                  Bit
                                                                      (a) Basket
                                                                     (c) Adapter ring
(b) Spring
                                                                                                             (d) Flap valve
Figure 45. Clam-shell fitted auger head (Leach et al., 1988).         Figure 46. Types of sample retainers (Mobile Drilling Company,
                                                                            1982).
                                                               60

-------
     Auger drill
     rig
  Auger column
   Barrel sampler
                                            Non-rotating
                                            sampling rod
                                               Auger head
Figure 47. Diagram of a continuous sampling tube system (after
          Central Mine Equipment Company, 1987).
     3) relative drilling cost,
     4) availability of drilling equipment,
     5) relative time required for well installation and
         development,
     6) ability of drilling technology  to preserve natural
         conditions,
     7) ability to install design diameter of well  and
     8) relative ease of well completion and  development.

     A complete discussion of the importance of these factors
can be found in this section under the heading entitled "Criteria
For  Evaluating Drilling Methods."

     Each matrix has three main parts (Figure 49). The top
section of the page contains a brief description that delineates
which unique combination of general hydrogeologic condi-
tions and well  design requirements apply to evaluations  made
in that matrix. The middle of the page contains a chart that lists
the ten drilling methods on the vertical axis and the  eight criteria
for evaluating the drilling methods on the horizontal axis. This
chart includes relative judgments, in the form  of numbers,  about
the  applicability of each drilling method. The bottom of the
page contains explanatory notes that further qualify the general
hydrogeologic  conditions and well design requirements that
have influence on the development of the numerical scheme  in
the  chart.
     The numbers in the charts are generated by looking at each
 of the criteria for evaluating drilling methods and evaluating
 each drilling method on that one criteria with respect to the
 conditions dictated by the prescribed five general hydrogeologic
 conditions and well design requirements. The most  applicable
 drilling method is assigned a value of 10 and the other drilling
 methods are then evaluated accordingly. The process always
 includes assigning the number 10 to a drilling method. Once
 each of the criteria is evaluated, the numbers for each drilling
 method are summed and placed in the total column on the right.
 Where a drilling method is not applicable, the symbol, "NA,"
 for not applicable, is placed in the row for that drilling method.

 How To Use the Matrices
     The matrices are provided as an aid to the user when
 selecting the  appropriate drilling technique under selected
 conditions. The user should begin by referring to Table 2 and
 choosing the number of the matrix that most closely parallels
 the hydrogeologic conditions at the site  and that has the same
 anticipated well depth and casing diameter requirements. The
 user should then refer to that matrix in Appendix B, read the
 explanatory notes and refer to the relative values in the "total"
 column of the matrix. Explanatory text for both the drilling
 methods and the criteria for evaluating drilling methods should
 be reviewed to understand the assumptions and technical  con-
 siderations included in the relative numbers.

 How To Interpret a Matrix Number
     The numbers contained in the "total" column of the chart
 represent a relative indication of the desirability of each drilling
 method for the prescribed conditions of the matrix. Higher total
 numbers indicate more appropriate drilling methods for the
 specified assumptions. When numbers are relatively close in
 value, drilling methods may be almost equally  as favorable.
 Where numbers range more widely in value, the matrix serves
 as a relative guide for delineating a favorable drilling method.
 The numbers cannot be compared between matrices; numerical
 results are meaningful only when compared on the same chart.
 The purpose of the numerical rating is to provide the user with
 a relative measure of the applicability of drilling methods in
 specific  situations.

     Once the user consults the matrix for a preliminary evalu-
 ation, it is necessary to reevaluate the numbers in terms of the
 factors that locally impact the ultimate choice of a drilling
 method: equipment availability and relative drilling  cost.  A
 drilling method might be indicated as the  most favorable
 technique according to the matrix totals, but the equipment may
 not be available or the cost factor may be prohibitive. In these
 situations, an alternative drilling method will need to be chosen
 or the design criteria modified.  The drilling costs have been
 evaluated in the matrix based on relative national costs. Recog-
nizing that relative costs may vary, the user of the matrix should
 look carefully at the relative cost column to determine if the
relative costs are applicable for the  specific geographic location
of interest. Adjustments should be made if costs differ signifi-
cantly.

 Criteria for Evaluating Drilling Methods
    In determining the most appropriate drilling technology  to
use at a specific site the following  criteria must be considered.
                                                          61

-------
                          (a)
                                                                                             Core barrel
                                                                                             head outer
                                                                                             Ball
                                                                                             bearings
                                                                                                        Hanger
                                                                                           kv Inner
                                                                                              tube head assembly
                                                                                            Bearing
                                                                                            retainer
                                                                                               -Pin & nut
                                                                  inner tube.*
                                   \/
Reaming
shell
                                      Core lifter
                                                                  Core lifter •
                                       •Blank bit
                                                                                             • Outer tube
                                                                                             '"Reaming shell
                                                      -Blank bit

                                                      - Lifter case
                                                                                   (b)
Figure 48. Diagram of two type a of core barrels:
           a) single tube and b) double-tube (Mobile Drilling Company, 1982).
                                                               62

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                                                MATRIX NUMBER 1
                          General Hydrogeologic Conditions & Well Design Requirements
      Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 2 inches or less; total
      well depth O to 15 feet.
V Z W
^L ^ I
\ 3"
\ a*
\ §!

\ —O
\ Is
\ o
DRILLING \
METHODS \
Hand Ayger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


•g
i
I

1
«
fB
I
1
1
I
3

10

8
NA
7

7
9






2
_ra
"S.

-------
monitoring program by drilling fluid invasion into the moni-
tored zone.

    The interaction between the geologic formations, hydro-
logic conditions and the equipment to be used is best illustrated
by example. After reviewing the discussion of drilling methods
in the  beginning of this section,  it should be obvious that
hollow-stem augers can be used effectively in unconsolidated
materials, but are not applicable to the installation of monitor-
ing wells in solid rock  such as granite. It may be less obvious
that drilling through the saturated, unstable overburden overly-
ing solid rock, such as granite, maybe very difficult with the air
rotary  technique; however, the air rotary technique would be
very effective in drilling the granite. The overburden, con-
versely, can be very effectively dealt with by hollow-stem
augers.

    If the monitoring objectives  in this illustration include
pumping at relatively high rates, then a 4-inch or larger casing
may be required. The installation of the casing mandates the use
of a large inside diameter hollow-stem auger unless the
overburden is sufficiently  stable to permit open-hole  casing
installation. If either the casing diameter is too large or the depth
is too great, then hollow-stem augers are not appropriate and an
alternative drilling technique (e.g. mud rotary, cable tool, drill
through casing hammer, etc.) must be evaluated. Thus, judg-
ment has to be made for each site whether or not the  preferred
drilling technology can deal with the extant hydrogeologic
conditions and the objectives of the monitoring program.

Reliability  of Formation (Soil/Rock/Water)
Samples Collected During Drilling
    The purpose of a monitoring well is to  provide access to a
specific zone for which water level (pressure head) measure-
ments  are made, and from which water samples can be  obtained.
These  water samples must accurately represent the quality of
the water in the  ground in the monitored zone. To this end, it is
essential to acquire accurate, representative information about
the formations penetrated during drilling and specifically about
the intended monitored zone. Sample reliability depends par-
tially  on the type of samples that can be  taken when using
various drilling techniques. The type of samples attainable and
the relative  reliability of the samples are summarized in Table
 19 and discussed below in terms of drilling methods. An
additional discussion of sampling techniques is found in  the
section entitled  "Soil  Sampling and Rock Coring Methods."

Hand Auger —
    Soil samples that are taken by  hand auger are disturbed by
the augering process and are usually collected directly from  the
cutting edge of the auger. Deeper  samples  may be non-repre-
sentative if sloughing of shallow materials  occurs. Drilling by
hand  auger is usually  terminated when the saturated zone is
encountered. It is possible to continue drilling below the satu-
rated zone in some situations by adding water and/or drilling
mud.  However, when water and/or drilling mud are added,
reliable samples cannot usually be obtained. An additional
discussion of hand augering can be  found in the section entitled
'Drilling Methods for  Monitoring  Well Installation."

Driven Wells —
    No samples can be taken during the construction of a driven
well,  although some interpretation of stratigraphic variation
can be made from the driving record. Water-quality samples
can be obtained in any horizon by pumping from that depth of
penetration. An additional discussion of driven wells can be
found in the section entitled  "Drilling Methods for Monitoring
Well  Installation."

Jet Percussion  —
    Neither valid soil samples nor valid water samples can be
obtained during the construction of wells by this method. Only
gross lithology can be observed in the material that is washed
to the surface during the jetting procedure. An additional
discussion of jet percussion drilling can be found in the section
entitled "Drilling  Methods for Monitoring Well Installation."

Solid Flight  Augers —
    Soil samples  collected from solid, continuous flight augers
are rotated up  the auger flights to the surface during drilling or
scraped from the  auger flights upon extraction. The disturbed
samples from either of these sources provide samples of moderate
quality down  to the first  occurrence of water, and  generally
unreliable samples below  that level.

    More valid samples can be obtained where the borehole is
stable enough  to remain open. In this situation, the auger flights
can be removed from the borehole and samples can then be
taken by either split-spoon (ASTM D1586) orthm-wall (ASTM
D1587) sampling  techniques. It is generally not possible to use
these techniques  in saturated  formations with the  augers re-
moved because the borehole  frequently collapses or the bottom
of the borehole "heaves" sand or silt upward into the open
borehole. The heaving occurs as a consequence of differential
hydrostatic pressure and is exacerbated by the removal of the
augers. When caving or heaving occurs, it is very difficult to
obtain reliable samples.  An additional discussion on solid-
flight augers  can be found in the section entitled "Drilling
Methods for Monitoring Well Installation."

Hollow-Stem Augers —
    Where samples are collected from depths of less than 150
feet,  the hollow-stem  auger technique is the method most
frequently used to obtain  samples from unconsolidated forma-
tions. Samples may be taken through the hollow-stem center of
the augers by split-spoon (ASTM D1586), thin-wall (ASTM
D1587) or wireline piston sampling methods  (refer to Figures 40
through 44). The  maximum  outside diameter of the sampler is
limited by  the inside diameter of the hollow stem. If 3.25-inch
inside diameter augers are being used, then a maximum 3-inch
outside diameter  sampler  can be used and must still retain the
requisite structural strength  and meet the requirement to opti-
mize (minimize) the area ratio. An additional discussion on soil
sampling can  be found in the  section entitled "Soil  Sampling
and Rock Coring Methods."

    The rotation of the augers causes  the cuttings to move
upward and debris to  be ground and "smeared" along the
borehole in the thin annular zone between the borehole wall and
the auger flights. This smearing has both positive and negative
connotations.  Because the movement of debris is upward, the
cuttings from the deeper zones may seal off shallower zones.
This minimizes cross-connection of fluids from shallow to deep
zones, but increases the possibility of deep to shallow contami-
nation. Shallow zones that may have been  penetrated in the
upper portion  of the borehole are also difficult to develop once
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smearing occurs. With the shallow zones sealed off by cutting
debris and with the auger flights serving as temporary  casing,
it  is often possible to obtain valid formation samples of discrete
saturated zones as they are initially penetrated.

    Water samples are difficult to  obtain in the saturated zone
during drilling due to formation instability. A special type of
lead auger flight has been designed to overcome the problem of
collecting water samples concurrent with drilling and to make
it possible to sample and/or pump test individual zones as the
augers are advanced. This specially reinforced screened auger
serves as the lead,  or lowermost auger and is placed just above
the cutting head (Figure 28). This screened  section can be used
to temporarily stabilize the borehole while a  small  diameter
pump or other sampling device is installed within the hollow
stem. Appropriate testing can then be performed. The advan-
tage of this technique is low-cost immediate data and water
sample  acquisition during drilling.  The major disadvantages
are: 1) doubt about cross-connection  of zones and ultimate data
validity and 2) the risk of losing both the equipment and the
borehole if extremely difficult drilling conditions are encoun-
tered since there is some structural  weakness in  the  screened
section.  An additional discussion of hollow-stem augers can be
found in the  section entitled "Drilling Methods for Monitoring
Well  Installation."

Direct Mud Rotary Drilling —
    A variety of sampling technologies  can be  used in concert
with mud rotary drilling techniques. These include: 1) grab or
ditch samples from circulated cuttings, 2) split-spoon and thin-
walled samples in unconsolidated materials and 3) single and
double-tube conventional core barrels in consolidated mater-
ials. Indirect rotary drilling, the functions of the drilling fluid are
to: 1) lubricate and cool the bit, 2) remove fragmentary particles
as they are loosened and 3) stabilize  the borehole. The cuttings
are typically circulated up the borehole, through a pipe or ditch,
into a temporary settling tank or pit. The drilling fluid is then
circulated back down the drill pipe (Figure 29).

    Samples taken from the ditch or  settling pond  (mud pit) are
therefore a composite of: 1) materials cut a few minutes earlier
(time lag varies with depth, borehole size, drill pipe and pump
rate), 2) any unstable materials that have washed or fallen into
the borehole from a shallower zone and 3) any re-circulated
materials that failed to settle out during earlier circulation.
These materials are mixed with  the drilling fluid  and any
additives used during the drilling process. The interpretation of
these samples requires experience and even then the interpre-
tation is questionable. Ditch samples  are frequently collected in
the petroleum industry, but have little  practical  value in  the
effective installation of monitoring  wells. Thin,  stratified zones
that require specific monitoring are difficult to identify  from
ditch  samples.

    Both split-spoon (ASTM D1586) and  thin-wall samples
(ASTM  D1587) can be obtained while using direct rotary
drilling methods in unconsolidated materials.  At  shallow depths,
samples are  taken through the drill bit in exactly the same
manner as previous] y described for hollow-stem augers. Corre-
sponding size limitations and  sampling problems prevail.

    As depths increase below about 150 feet, the time con-
sumed in taking split-spoon and thin-wall samples becomes
excessive and wireline sampling devices are used to collect and
retrieve samples. Samples can be taken either continuously or
intermittently. In unconsolidated materials, wireline samplers
can collect only disturbed samples and even then there arc
recovery problems and limitations for both fine and  coarse-
-grained materials. In consolidate rock the best  samples can be
obtained by coring.

    A significant advantage of drilling with a good  drilling
mud program is that typically the open borehole can be stabi-
lized by the drilling mud for a sufficient period of time to
remove the drilling tools and run a complete suite of geophysi-
cal logs in the open hole. This information is used in  concert
with other data (i.e., the drilling time log, the sample log, fluid
loss or gain information and drilling characteristics) to  provide
definitive evaluation of formation boundaries and to select
screen installation intervals.

    When attempting to define the in-situ properties of uncon-
solidated materials,  drilling by the mud rotary method offers
another advantage. Because  the drilling mud maintains the
stability of the borehole, samples taken by split-spoon  or thin-
wall methods ahead of the drill bit tend to be much more
representative of indigenous formation conditions than those
samples taken, for example, during hollow-stem auger drilling.
In auger  drilling it is sometimes very difficult to obtain a
sample from below the cutting head that has not been affected
by the formation heaving upward into the open borehole.

    If the drilling fluid is clear water with no drilling additives,
then it maybe difficult to maintain borehole stability because
little mudcake accumulates on the wall of the borehole. In this
case, the loss or gain of water  while drilling is an indication of
the location of permeable zones.

    Because drilling fluid is used to drill the borehole and
because  this fluid infiltrates  into the penetrated  formations,
limited water-quality information can be obtained while drill-
ing. Drilling mud seals both  high and low-pressure zones if
properly used. However, this sealing action  minimizes
interaquifer cross-contamination while drilling. Before  any
zone provides representative samples, all drilling mud  and fil-
trate should be removed from the formation(s) of interest by
well development.

    The most common additives to drilling mud are barite
(barium sulfate) for weight control and sodium montmorillo-
nite (bentonite) for viscosity and water loss control. Both can
alter indigenous water quality.

    Bentonite  is extremely surface active and forms clay/
organic complexes with a wide range of organic materials. The
water used to mix the drilling mud is potentially interactive both
with the drilling mud and with the water in the formation. At the
very least, the drilling fluid dilutes the formation water that is
present prior to the drilling activity. For these reasons it is very
difficult,  if not impossible, to be confident  that sufficient
development has been performed on a direct rotary-drilled
monitoring well, and that  the water  quality in a particular
sample is truly representative of the water quality in place prior
to the construction of the well.

    Where very low concentrations of a variety of contami-
nants are being evaluated and where the potential reactions are
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undefined, it is not recommended that drilling fluid be used
during monitoring  well installation.  This same concept applies
to boreholes drilled by cable tool and/or augering techniques
where drilling fluid is necessary for borehole stability. Where
drilling mud is used, monitoring well development is  continued
until such time as a series of samples provides statistical
evidence that no further changes are occurring in key param-
eters. When this occurs, the resultant quality is considered to be
representative (Barcelona,  et al, 1985a).  An additional discus-
sion of drilling fluids can be found  in the section entitled
"Drilling Fluids."

     Water-level measurements of different zones penetrated
cannot be determined while drilling  with direct rotary methods.
Accurate water levels can only be determined by installing,
screening and developing monitoring wells in the specific
zones of interest. An additional discussion on direct mud rotary
drilling can be found in the section entitled  "Drilling Methods
for Monitoring Well  Installation."

Air  Rotary —
     Direct air rotary is restricted in application to consolidated
rock. Where the bedrock is overlain by unconsolidated materi-
als,  a borehole can be drilled and sampled by alternative
methods  including: 1) roller-cone bit with water-based fluid, 2)
air with a casing driver, 3) cable tool or 4) augering. Formation
samples are taken  by the  appropriate methods  discussed in the
related sections of this discussion. Once  surface  casing  is
installed  and sealed into bedrock, the underlying bedrock can be
successfully drilled using air rotary methods.

     When using air rotary drilling in semi-consolidated and
consolidated materials, air is circulated down the drill pipe and
through the bit.  The  air picks up the cuttings  and moves the
cuttings up through the annular space between the drill pipe and
the wall  of the borehole. If the formations drilled are dry, the
samples reach the surface in the form of dust. By injecting water
or a mixture of water and surfactant (foam):  1) dust is con-
trolled, 2) regrinding  of samples is minimized  and 3) the sizes
of individual particles are increased  sufficiently to provide
good formation  samples.  Because the injected water/foam  is
constantly in motion and  supported by the air, there is only a
slight possibility  of water loss or formation contamination
during drilling.

     After water is encountered in the  borehole, further injec-
tion of water from the surface can often be eliminated or
minimized and good rock fragments can be obtained that are
representative of the formations penetrated.  Samples obtained
in this manner are  not affected by  the problems of recirculation,
lag time and drilling fluid contamination that plague sample
evaluation when drilling mud is used. Air may cause changes in
the chemical and biological activity in the area adjacent to the
borehole. Examples of quality changes include oxidation and/
or stripping of volatile organic chemicals. The time required for
these changes to be reversed varies with the hydrogeologic and
geochemical conditions. Because the rock boreholes are gen-
erally  stable and penetration rates are high, there is minimal
contamination from  previously-drilled upper  zones.  Water-
quality samples and water levels can be  easily obtained from the
first saturated zone penetrated, but this zone must be cased if
subsequent zones  are to be individually evaluated.
    For monitoring well installation, the injected air must be
filtered prior to injection to prevent contamination of the
borehole by oil exhausted by the air compressor. Because a
down-the-hole hammer requires lubricating  oil for operation, it
has more limitations for monitoring well installation. An addi-
tional discussion on air rotary drilling can be found in the
section entitled "Drilling Methods for Monitoring Well Instal-
lation."

Air Rotary with Casing Driver —
    Unconsolidated formations can be drilled and sampled by
combining air rotary  drilling with a casing driver method. In
this procedure the drill bit is usually extended approximately
one foot below the bottom of the open casing, and the casing is
maintained in this position as the drill bit is advanced (Figure
33). The casing is either large enough to permit retraction of the
bit, in which instance the casing must be  driven through the
undergauge hole cut by the bit; or an underreamer is used, and
the casing moves relatively easily down  into the  oversized
borehole.  Generally, the undergauge procedure is favored  for
sampling unconsolidated formations, and  the underreamer is
favored for semi-consolidated  formations. Either technique
allows good samples to be obtained from the freshly-cut for-
mation and circulated up the cased borehole. If chemical quality
of the formation sample is important, particularly with regard to
volatile organics or materials that can be rapidly oxidized, then
air drilling may not be appropriate. When the casing is advanced
coincident with the deepening of the borehole, the  sample
collection procedures and the sample quality are very  similar to
those prevailing with the use of direct air rotary. An additional
discussion on air rotary with casing driver can be found in  the
section entitled "Drilling Methods for Monitoring Well Instal-
lation."

Dual-Wall Reverse  Circulation Rotary —
    In dual-wall reverse  circulation rotary drilling, either
water or air can be used as the circulation medium. The outer
wall of the dual-wall system serves to case the borehole. Water
(or air) is circulated down between the two casing walls, picks
up the cuttings  at the bottom of the borehole, transports  the
cuttings up the center of the inner casing and deposits  them at
the surface. Because the borehole is cased,  the samples col-
lected at the surface are very reliable  and representative of  the
formations penetrated. Sample collection using dual-wall ro-
tary has the following advantages: 1) third stratigraphic zones
often can be identified; 2) contamination of the borehole  by
drilling fluid is minimized; 3) interaquifer cross-contamination
is minimized; 4) individual zones that are hydraulically distinct
can be identified with specific water levels, and discrete
samples often can be  collected if sufficient  time is allowed  for
recovery; 5) in low hydraulic pressure formations, air pressure
within the borehole may prevent the formation water from
entering the borehole and  6)  sampling at  the surface can be
continuous. Split-spoon samples  can also be collected through
the bit. One disadvantage  is that because  the outer casing is
removable and not sealed by grout, hydraulic leakage can occur
along the outside of the unsealed casing.

    Water or foam can be  injected to increase the penetration
rate and improve sample quality. An additional discussion of
dual-wall reverse circulation rotary drilling can be found in the
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section entitled "Drilling Methods for Monitoring Well Instal-
lation."

Cable Tool —
    When drilling in saturated, unconsolidated sand and gravel,
good quality disturbed samples can be obtained by the cable
tool "drive and bail" technique. In this technique, casing is
driven approximately 2 to 5 feet into the formation being
sampled, The sample is then removed from the casing by a
bailer. For best sample quality, a flat-bottom bailer is used to
clean the borehole (Figure 36). The entire sample is then
collected at the surface, quartered or otherwise appropriately
split and made available for gradation analyses. When drilling
in unsaturated material, water must be added to the borehole
during drilling and  sampling.

    The drive and bail technique is often the best method for
sampling well-graded or extremely coarse-grained deposits
because  both coarse and fine-grained fractions  are collected
during sampling. Large-diameter casing can be driven and large
bailers can be used. The most common size range  for casing is
from 6 inches to  16 inches although larger sizes are available.
For the drive and bail technique to be effective, excessive
heaving of the formation upward into the casing during cleanout
must be prevented. This can usually be controlled by:  1)
overdriving the casing, thereby maintaining a "plug" of the next
sample in the casing  at all times, 2) careful operation of the
bailer and 3) adding water to the borehole to maintain positive
hydraulic head within the borehole.

    During drive and bail-type drilling, split-spoon (ASTM
D1586) and thin-wall (ASTM D1587) samples can be collected
after cleaning out the casing with the bailer.  Samples are
collected ahead of the casing  by inserting conventional sam-
pling tools inside the  casing. This technique permits sampling
of fine-grained,  unconsolidated formations.

    The  quality of cable tool samples from consolidated forma-
tions varies with drilling conditions. When the bedrock is
saturated, good broken chips of the formation can be obtained
by bailing at frequent intervals. If the chips remain in the
borehole too long or if sufficient lubrication is lacking, the
samples  are re-ground to powder.

    When drilling by cable tool techniques  and using a good
casing program, it is  usually possible to identify  and  isolate
individual water-bearing units as they are drilled. This provides
the opportunity to obtain good water-level  and waterquality
data. An additional discussion on cable tool drilling can be
found in the section entitled "Drilling Methods for Monitoring
Well  Installation."

Relative Drilling  Costs
    Drilling and completion costs vary for individual methods
with each set of  general conditions and well design require-
ments. For example, the cost of drilling and sampling with the
hollow-stem auger method may be much higher  for a dense,
bouldery  till than it is for a similar depth in saturated, medium-
soft lake clays. The cost of installing nominal 2-inch diameter
casing and screen within hollow-stem augers varies with depth
and borehole stability.

    The  relative  drilling cost ratings shown on each matrix
apply to the broad range of conditions included within each set
of general conditions and well casing requirements. The rela-
tive ratings reflect the total cost of drilling, sampling, casing,
screening, filter-packing, grouting, developing and surface
protecting the monitoring well. Equivalent costs of mobiliza-
tion and access are assumed. Relative ratings are based on
consideration of the average costs when compared to the other
methods of drilling throughout the continental United States.
Local cost variations can be significantly influenced by  equip-
ment availability and can cause variation in these relative
ratings. Where local costs vary from the ratings  shown, an
adjustment should be made to the specific matrix so that the
actual costs are more accurately reflected.

Availability of Equipment
    The ratings shown in the  matrices for equipment availabil-
ity  are based on the general availability of the drilling equip-
ment  throughout the United States. The availability of specific
equipment on a local basis may necessitate the revision of the
rating in the matrix to make the rating more representative.

    The type of equipment most generally available for
monitoring well installation is  the direct mud rotary drilling rig.
Direct mud rotary techniques are  applicable to water supply
wells, gas and oil exploration and development and soil testing.
As  a result, this equipment is widely available throughout the
country.

    Solid-flight and hollow-stem augering equipment is also
generally available throughout all regions where  unconsoli-
dated  materials predominate. The portability of augering  equip-
ment  and the prevalent use of augers in shallow foundation
investigations have increased auger availability to almost all
areas.

    Air rotary drilling has primary application in consolidated
rock. Availability of equipment is greatest in those consolidated
rock areas where there are mining exploration, water-supply
production activities or quarrying applications. The  availability
of this equipment is greatest in: 1) the western mountainous
sea, 2) the northeast and  3) the nothwest parts of the country.

    Casing drivers used  in combination with direct air rotary
drilling are somewhat sparsely, but uniformly distributed
throughout all regions. Versatility in screen installation,  casing
pulling and application in unconsolidated materials have broad-
ened the use of air rotary with casing driver techniques.

    Dual-wall rotary drilling is becoming increasingly popular
because the technique can be used in a wide range of both
consolidated  and unconsolidated formations. Availability is
generally restricted to the west-central  and southwestern parts
of the country.

    Cable tool equipment availability  is limited in many  por-
tions  of the south, southeast, southwest,  and northwest. It
is generally available  in the north-central and northeastern
portions of the country.

Relative Time Required for Well Installation and
Development
    The time required for drilling the well, installing the  casing
and screen and developing the well can be a significant factor
when choosing a drillng  method. For  example, if a relatively
deep hole drilled with cable tool techniques takes several days,
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weeks or longer, there maybe significant scheduling disadvan-
tages. If longer-tarn supervision is required, then this addi-
tional cost factor must also be taken into account. The excess
cost of supervison is not included in the matrix evaluation.
Similarly, if a direct mud rotary technique is employed to make
a fast installation and an additional three weeks of development
is required before a valid sample can be obtained, the advantages
of the rapid installation need to be re-evaluated.

Ability of Drilling Technology to Preserve Natural
Conditions
     Assuming that the purpose of a monitoring well is to
provide access to a specific zone for which water-level (pres-
sure head) measurements are to be made, and from which water
samples can be obtained to accurately represent the quality of
the water in place in the zone  being monitored, then it is
obviously important that the  drilling methodology employed
must minimize the disturbance  of indigenous conditions or
offer a good possibility that indigenous  conditions can be
restored. To achieve these goals, the drilling methodology
should  result in minimal  opportunity for physical and/or chemi-
cal interactions that might cause substantial or unpredictable
changes in the quality of the water being sampled. The follow-
ing discussions present some of the problems and potential
problems related to the disturbance of the natural conditions as
a consequence of monitoring well drilling and installation:

     1) When using drilling mud in the borehole, filtrate
        from the drilling fluid invades  the adjacent
        formations.  This filtrate mixes with the natural
        formation fluids and  provides the opportunity for
        chemical reaction between the mud filtrate  and
        the formation fluid. If chemical reactions occur,
        "false" water-quality readings may result. The
        mixing effect is minimized by good development;
        potential  chemical reactions are more difficult to
        deal with in a reasonably predictable manner.  For
        example, if a high pH filtrate invades a low pH
        formation and metals are present in either fluid,
        precipitation of the metals can be  anticipated in
        the vicinity of the borehole. The metals may
        subsequently be re-dissolved at an unknown rate,
        if chemical conditions are not constant. Thus, the
        drilling  fluid  filtrate  invasion  can result in
        alternately low and  high readings of metals at
        different intervals of time.
    2) When a monitoring well is drilled with augers,
        fine silts and clays commonly smear along the
        borehole wall  and frequently seal the  annular
        space between the augers and the borehole wall.
        This sealing action can then minimize the cross-
        connection of discrete zones. However, the fine-
        grained particulate matter that is smeared into the
        zone of interest also reduces the flow from that
        zone,  introduces the  possibility of cross-
        contamination from  another zone and presents
        the opportunity  for the clays that are smeared into
        the zone to sorb contaminants and consequently
        generate  non-representative  water-quality results.
        In mud rotary drilling, a  mudcake is deposited on
        the borehole wall. This bentonitic mudcake serves
        to stabilize the borehole  and also has the  capacity
         to sorb both organic and inorganic constituents.

     3) During any drilling process physical disruption of
         the  formation  occurs and  grain-to-grain
         relationships change. Regardless of whether or
         not the well  is completed with a natural or artificial
         filter pack, the flow paths to the well are altered;
         tortuosity is changed; Reynolds numbers are
         modified with flow path and velocity variations;
         and  equilibrium (if, in fact, the indigenous water
         is at equilibrium) is shifted. If the formation is
         permitted to collapse, as may occur in sand and
         gravel materials, the removal of the collapsed
         material exacerbates the problem.

         With the changes that occur in the physical setting,
         it is very difficult to be confident that the water
         samples subsequently  collected from  the
         monitoring well truly reflect  conditions in the
         ground beyond the  influence of the disturbed
         zone around  the well.  The changes are  of particular
         concern when  analyzing for  very  low
         concentrations of contamination.

     It becomes apparent that  a drilling technique that has the
least possible disruptive influence on the zone(s) being moni-
tored is preferable in  any given setting. The matrices  presented
indicate the relative impact of the various drilling methodolo-
gies for the designated circumstances.

Ability of  the Specified Drilling Technology to
Permit the Installation  of the Proposed Casing
Diameter at the  Design Depth
     The design diameter for the casing and well intakes(s) to be
used in any monitoring well depends on the proposed use of the
monitoring well (i.e. water-level measurement, high-volume
sampling, low-volume  sampling, etc.). When installing artifi-
cial  filter packs and bentonite  seals, a minimum  annular space
4 inches greater in diameter than the maximum outside diam-
eter of the casing and screen is generally needed. A 2-inch
outside  diameter monitoring well would then require a mini-
mum 6-inch: 1) outside diameter borehole,  2) auger inside
diameter or 3) casing inside diameter for reliable well installa-
tion. This need for  a 4-inch annular space places a severe
limitation on the use of several current] y-employed drilling
technologies.

     For example, hollow-stem augers have been widely used to
install 2 3/8-inch outside diameter monitoring wells. A signifi-
cant portion of this work has been performed within 3 1/4-inch
inside diameter hollow-stem augers. At shallow depths, espe-
cially less than fifteen feet, it  has been possible to install well
intake and casing, filter pack,  bentonite seal and surface grout
within the small working space. However,  at greater depths, it
is very doubtful if many of these components are truly  emplaced
as specified.  There simply is not sufficient annular clearance to
work effective] y. For a more complete discussion on filter pack
and  screen emplacement in hollow-stem augers, refer to Ap-
pendix A.

     When drilling with direct  air rotary with a casing hammer,
the maximum  commonly-used casing size  is  8 inches in diameter.
The outside diameter of the monitoring well casing should

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therefore be 4 inches or less to maintain adequate working
space. Because pipe  sizes are  classified by nominal diameters,
the actual working space will be somewhat less than the stated
annular diameter unless the actual pipe O.D. is used in calcula-
tions.

    When drilling through unstable formations with dual-wall
reverse circulation methods, the monitoring well casing must
be installed through the bit. The hole in the bit barely permits the
insertion of a nominal 2-inch diameter casing. This method
does not allow the installation of an artificial filter pack because
there is no clearance between the bit and 2-inch casing.

    The ratings presented in each matrix evaluate the relative
ability of the various methodologies to permit the installation of
the design casing diameters in the indicated hydrogeologic
conditions.

Ease of Well  Completion and  Development
    Well completion and development difficulty varies with:
1) well depth, 2)  borehole diameter, 3) casing and well intake
diameter, 4) well intake length,  5)  casing and well intake
materials, 6) drilling technique, 7) mud program, 8) hydrostatic
pressure of the aquifer, 9) aquifer transmissivity, 10) other
hydrogeologic conditions and 11) geologic conditions that
affect the borehole. The relative  ease of dealing with these
variables by the selected drilling equipment is shown in each
matrix for the indicated conditions.  For example, where a
relatively thin, low-yield aquifer has been drilled with hollow-
stem augers, the  muddy clay/silt  mixture from the borehole
tends to seal the  zone where the well intake is to be set. The
development of this zone is very difficult. If a filter pack has
been installed, development becomes almost impossible. If
direct mud rotary is used to drill this same low transmissivity
zone, and the mudcake from the drilling fluid remains between
the filter pack and the borehole wall, very difficult development
can be expected. If the  borehole  is drilled with clear water,
development might be easier.

    For any given scenario a very subtle modification of
procedure may make the difference between success and fail-
ure. The ratings  shown  in the matrices are based on general
considerations. Their relative values expressed in the table  vary
in specific circumstances. Most importantly, however, is that
an experienced observer be able to make on-site observations
and to modify the procedures as the work progresses.

Drilling Specifications and Contracts
    The cost of installing a monitoring well depends on several
factors including 1) site accessibility, 2) labor and material
costs, 3) well design, 4) well use, 5) well development, 6) well
yield  and 7) local geologic conditions (Everett 1980).  Because
these factors are variable, it is important to secure a well
contract that addresses these items in a concise and clear format.
Proper formatting helps ensure that the well will reconstructed
as specified in the contract and for the agreed price. In simple
terms, a well-written contract is a quality control check on well
construction.

    Monitoring well contracts are typically  written  in three
major sections  including: 1) general conditions, 2) special
conditions  and 3) technical specifications.  General conditions
address items dated to the  overall project performance includ-
ing: scheduling,  materials, equipment, labor, permits,  rights  of
various parties,  tests and inspections, safety, payments, con-
tracts, bonds and insurance (Driscoll, 1986).  Special conditions
detail project-specific and site-specific items including: 1) a
general description of the purpose and scope of the work, 2)
work schedule, 3) insurance and bond requirements,  4) perti-
nent subsurface information, 5) description of necessary per-
mits,  6) information on legal easements, 7) property boundaries
and utility location and 8) a description of tests to be performed
and materials to be used  during the project (United States
Environmental Protection Agency, 1975). If general and spe-
cial conditions  appear to conflict, special conditions of the
contract prevail  (Driscoll, 1986).  Technical specifications con-
tain  detailed descriptions  of dimensions, materials, drilling
methods and completion methods.

    Most contracts are awarded as part of a bidding process.
The bidding process may be either competitive or non-competi-
tive. In a competitive bidding  process, contractors are asked to
submit cost estimates based on a set of specifications for drilling
the monitoring wells. The specifications are developed prior to
the request for cost proposal by either the client or  a consultant
to the client. Suggested areas that should specifically be ad-
dressed in the specifications are listed in Table 22.
Table 22. Suggested Areas lo b* Addressed In Monitoring Well Bidding Specifications
Scope of Work
Site Hydrogeoiogy
    • existing reports
    * well logs
    • depth of wells
Schedule of Work Dates
Well Drilling Installation
    • materials
    • drilling method(s)
    • annular seal installation
    • development
    • protective equipment
    • disposal of cuttings
Record-Keeping and Requirements
Sampling Requirements and Procedures
Site Access
    •road construction
    •tree clearing
    •drainage
    •leveling
       Decontamination of Equipment
            • procedures
            • materials
            * disposal of cuttings and liquids
       Site Safety
            • equipment
            • training
       Conditions
            • permits
            • certificates
            • utility location
            * site dean up
            • procedures tor drilling difficulties
            • non-functioning welts
            • government forms required
            • client's right to vary quantities or delete items
       Payment Procedures
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     After cost estimates are obtained, a contractor is selected
based on qualifications  and pricing. Although some contracts
are awarded by choosing the lowest bidder, this practice is not
suggested unless the qualifications of the contractor indicate
that a quality job can be performed. It is  good policy to meet
with the selected bidder prior to signing the contract and clarify
every technical point and related unit cost. This understanding,
duly noted by minutes  of the meeting, can eliminate costly
errors  and misunderstandings. An inspection of the contractor's
equipment that will be used on the job should also be made.

     Qualifications of contractors are often evaluated during  a
prequalification process. A contractor prequalifies by submit-
ting information about previous job experience that is related to
the scope of work. The prequalification process allows the
client  to accept bids only  from contractors that demonstrate
specific qualifications to perform the job. This process helps to
ensure that the monitoring wells will be installed by competent
contractors. When subcontractors for drilling or supplies are to
be employed, the list of subcontractors should also be approved
prior to the contract award.

     Another way to avoid misunderstandings during the bid-
ding process is to hold a bidders meeting. In a bidders meeting,
the potential contractors  meet in a group forum with the  client
to discuss the overall scope of the proposed work and to discuss
specifications for monitoring well installation. Any questions
about  the specifications  or problems with  performance  accord-
ing to the specifications  can be discussed and resolved  prior to
proposal submission.  All information must be provided
equally  to all prospective bidders.

     In non-competitive bidding, cost estimates are provided by
only one contractor. Because the procedure may be less formal,
the contractor may play a more active role in developing the
monitoring well specifications and presenting a cost estimate.
However, a less formal process may also mean that written
specifications for monitoring well  installation may never be
developed. This situation should be avoided to help ensure that
the monitoring wells are constructed properly.

     Cost proposals can be submitted in a variety of formats
including 1) fixed price, 2) unit price and 3) cost plus. Fixed-
price contracts list the manpower, materials and additional
costs needed to perform the work and specify a fixed price that
will be paid upon completion of the work. Unit price contracts
are similar, but establish a freed price for each unit of work that
is performed.  Cost-plus contracts list speific costs associated
with performing the work and include a percentage of those
costs as an additional amount that will be paid to perform job.
A percentage listed  in a cost-plus contract is typically viewed as
the profit percentage being proposed by the contractor. In fixed-
price and unit-price proposals, the profit percentage is included
as part of the itemized pricing structure.

     To ensure  that the monitoring well is constructed accord-
ing to the intent  of the specifications, the contract should be very
specific and list all necessary items and procedures so that
nothing is left to interpretation or imagination. This clarity can
best be obtained by listing individual pay items instead of
combining items into unspecified quantities in lump sum  pric-
ing. Suggested items that should specifically be addressed in the
contract on a unit price basis are listed in Table 23.

     The bidder should also be required to supply information
on:  1) estimated time required  for job completion, 2) date
available to start work, 3) type and method of drilling equip-
ment to be used and 4) insurance coverage. A pay item system
may also reduce the need for change during the drilling process
by further clarifying the procedures to be used (Wayne Westberg,
M-W Drilling, Inc., personal communication, 1986). A change
order is a written agreement from the purchaser to the contractor
authorizing additions, deletions or revisions  in the scope of
work, or an adjustment in the contract price or effective period
of the contract (United States Environmental Protection Agency,
 1975). The contract should  specify what payment provisions
'Table 23. Suggested Items for Unit Cost In Contractor Pricing Schedule

 Item
                                                                      Pricing Basis
 •Mobilization
 •Site preparation
 •Drilling to specified depth
 •Sampling
 •Material supply
     surface casing
     well casing
     end caps
     screen
     filter material
     bentonite seal(s)     '
     grout
     casing protector
 •Support equipment
     water truck and water
     bulldozer
 •Decontamination
 •Standby
 •Field expenses
 •Material installation
 •Well development
 •Demobilization
 •Drilling cost adjustment for variations in depths
       lump sum
       lump sum
       per lineal foot or per hour
       each

       per lineal foot
       per lineal foot
       each
       per lineal foot
       per lineal foot or per bag
       per lineal foot
       per lineal foot or per beg
       each

       lump sum
       per hour
       lump sum
       per hour
       per man day or lump sum
       per hour or lump sum
       per hour or lump sum
       lump sum
       ± per foot
                                                            70

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will be made if the monitoring well cannot be completed as
specified. The contract should also define who bears the costs
and what the basis for payment will be when drilling difficulties
are encountered that were not anticipated in the pricing sched-
ule.

    After the contract is signed and work is scheduled to begin,
a predrilling meeting between the supervising geologist and the
driller  should be held to discuss operational  details.  This meet-
ing reduces the  opportunity for misunderstanding of the speci-
fications and improves project relationships.

References
Aardvark Corporation,  1977. Product literature; Puyallup,
    Washington, 2 pp.
Acker  Drill Company, Inc.,  1985. Soil  sampling tools catalog;
    Scranton, Pennsylvania, 17 pp.
Acker, W.L., 1974. Basic procedures for soil sampling and core
    drilling; Acker Drill   Company,  Inc.,  Scranton,
    Pennsylvania, 246 pp.
American Society for Testing and Materials,  1983. Standard
    practice for thin-wall tube  sampling of  soils: D1587; 1986
    Annual Book  of American Society for Testing and Materials
    Standards, Philadelphia, Pennsylvania, pp. 305-307.
American Society for Testing and Materials,  1984. Standard
    method for penetration test and split barrel sampling of
    soils: D1586; 1986 Annual Book of American Society for
    Testing  and  Materials Standards,  Philadelphia,
    Pennsylvania, pp. 298-303.
Barcelona, M.J., J.P. Gibb, J.A.  Helfrich and E.E. Garske,
     1985a. Practical guide for ground-water sampling Illinois
    State Water Survey, SWS Contract Report 374, Champaign,
    Illinois, 93 pp.
Buckeye Drill Company/Bucyrus Erie  Company,  1982.
    Buckeye drill operators manual; Zanesville, Ohio, 9 pp.
Central Mine Equipment Company, 1987,  Catalog of product
    literature St.  Louis, Missouri, 12 pp.
Driscoll, Fletcher G.,  1986. Ground water and wells; Johnson
    Division, St. Paul, Minnesota, 1089 pp.
Everett,  Lome  G.,  1980, Ground-water monitoring; General
    Electric Company technology marketing  operation,
     Schenectady, New York, 440 pp.
Hvorslev, M.J.,  1949. Subsurface  exploration and sampling of
    soils for civil engineering purposes; United States Army
    Corps of Engineers, Waterways Experiment Station,
    Vicksburg, Mississippi, 465 pp.
Ingersoll-Rand, 1976. The water well drilling equipment
    selection  guide; Ingersoll-Rand, Washington, New Jersey,
    12pp.
Krynine, Dimitri P.  and William R. Judd,  1957. Principles of
    engineering geology  and geotechnics;  McGraw-Hill, New
    York, New York, 730 pp.
Layne-Western Company,  Inc.,  1983. Water, geological and
    mineral exploration utilizing dual-wall reverse circulation;
    Product literature, Mission, Kansas, 8 pp.
Leach, Lowell E., Frank P. Beck, John T. Wilson and Don H.
    Kampbell,  1988. Aseptic subsurface sampling techniques
    for hollow-stem auger  drilling; Proceedings of the Second
    National Outdoor Action  Conference  on  Aquifer
    Restoration, Ground-Water Monitoring and Geophysical
    Methods, vol. 1; National Water Well Association, Dublin,
    Ohio, pp. 31-51.
Mobile  Drilling Company,  1982. Auger tools and accessories;
    Catalog 182, Indianapolis, Indiana, 26 pp.
National Water Well Association of Australia, 1984. Drillers
    training and reference manual; National Water Well
    Association of Australia, St. Ives, South Wales, 267 pp.
Petroleum Extension Service, 1980. Principles of Drilling Fluid
    Control; Petroleum Extension Service, University of Texas,
    Austin, Texas, 215 pp.
Speedstar Division of Koehring Company, 1983. Well drilling
    manual; National Water Well Association, Dublin, Ohio,
    72pp.
United States Environmental Protection Agency, 1975. Manual
    of water well construction practices; United States
    Environmental protection  Agent y, Office of Water
    supply EPA-570/9-75-001, 156 pp.
Zapico, Michael M., Samuel Vales and John A. Cherry, 1987.
    A wireline piston core barrel for sampling cohesionless
    sand and gravel below the water table; Ground Water
    Monitoring Review, vol. 7, no. 3, pp.  74-82.
                                                         71

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                                                     Section 5
                               Design Components of Monitoring  Wells
Introduction
    It is not possible to describe a "typical" ground-water
monitoring well because each monitoring well must be tailored
to suit the hydrogeologic setting, the type of contaminants to be
monitored, the overall purpose of the monitoring program  and
other  site-specific variables. However, it is possible to describe
the individual design components of monitoring wells. These
design components may be assembled in various configura-
tions to produce individual  monitoring well installations suited
to site-specific conditions. Figure  21 illustrates the monitoring
well design components that are described in this chapter.

Well Casing

Purpose of the Casing
    Casing is installed in a ground-water monitoring well to
provide access from the surface of the ground to some point in
the subsurface. The casing, associated seals  and grout prevent
borehole  collapse and interzonal hydraulic communication.
Access to the monitored zone is  through the casing and into
either the open borehole or the screened intake. The casing thus
permits piezometric head measurements and ground-water
quality  sampling.

General Casing  Material Characteristics
    Well casing can be made of any rigid tubular material.
Historically, the selection of a well casing material (predomi-
nantly for water supply wells) focused on structural strength,
durability  in long-term exposure to natural ground-water envi-
ronments  and ease of handling. Different materials have dem-
onstrated versatility in well casing applications, In the late
1970s, questions about the potential impact that casing materi-
als may have on the  chemical  integrity  or "representativeness"
of a ground-water sample being analyzed in parts per million or
parts per billion were raised. Today the  selection of appropriate
materials  for monitoring well casing must  take into account
several site-specific factors including 1) geologic environ-
ment, 2) natural geochemical environment, 3) anticipated well
depth, 4) types and concentrations of suspected contaminants
and 5) design life of the monitoring well. In addition, logistical
factors must also be considered including:  1) well drilling or
installation methods,  2) ease in handling, 3)  cost and 4) avail-
ability.

    The most frequently  evaluated characteristics  that directly
influence the performance of casing materials in ground-water
monitoring applications are 1) strength and 2) chemical resis-
tance/interference. These  characteristics are discussed in more
detail below.
Strength-Related  Characteristics  —
    Monitoring well casing must be strong enough to resist the
forces exerted on it by the  surrounding geologic materials  and
the forces imposed on it during installation (Figure 50). The
casing must also exhibit structural integrity for the expected
duration of the monitoring program under natural  and man-
induced subsurface conditions. When casing  strength is evalu-
ated, three separate yet related parameters are determined:
 1) tensile strength, 2) compressive strength and 3) collapse
strength.

    The tensile strength of  a material is defined as the greatest
longitudinal stress the substance can bear without pulling the
material span. Tensile strength of the installed casing varies
with composition, manufacturing technique, joint type and
casing dimensions.  For a  monitoring well installation,  the
selected casing material must have a tensile strength  capable of
supporting the weight of the casing string when  suspended from
the surface in an air-filled borehole. The tensile strength  of the
casing joints is equally as important as the tensile strength of the
casing. Because the joint is generally the weakest  point in a
casing string, the joint strength will determine the maximum
axial load that can be placed  on the casing. By dividing the
tensile strength by the linear weight of casing, the maximum
theoretical depth to which a dry sting of casing can be sus-
pended in a borehole can be calculated. When  the casing is in
a borehole partially filled with water, the buoyant force of the
water increases the length of casing that can be  suspended. The
additional length of casing  that can be suspended depends on
the specific gravity of the casing material.

    The compressive strength of a material is defined as the
greatest compressive stress that a substance can bear  without
deformation. Unsupported casing has a much lower compres-
sive strength  than  installed casing that has  been properly
grouted and/or backfilled because vertical forces are greatly
diminished by  soil friction.  This friction component means that
the casing material properties are more significant to compres-
sive strength  than is wall thickness. Casing failure due to
compressive strength limitation is  generally  not an  important
factor in a properly installed monitoring well.

    Equally important with  tensile strength is  the final strength-
related property considered in casing selection ~ collapse
strength. Collapse strength is defined as the  capability of a
casing to resist collapse by  any and all external loads to which
it is subjected both during and  after installation. The  resistance
of casing to collapse is determined primarily  by outside diam-
eter and wall thickness. Casing  collapse strength is proportional
to the cube of the wall thickness. Therefore, a small increase in
                                                           73

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                              Borehole
                           Casing Joint
                      Compressive Forces
                                                                   Casing
   Tensile (Pull-apart) Forces
   Critical at Casing Joints
                                                                 Collapse Forces
                                                                . (Critical at Greater Depths)
                                                                 Well Intake (Screen)
Figure 50. Forces exerted on m monitoring well casing and screen during Installation.
wall thickness provides a substantial increase in collapse strength.
Collapse strength is also influenced by other physical properties
of the casing material including stiffness and yield strength.

     A casing is most susceptible to collapse during installation
before placement of the filter pack or annular seal materials
around the casing. Although it may collapse during develop-
ment once a casing is properly installed and therefore sup-
ported, collapse is otherwise seldom a point of concern (Na-
tional Water Well Association and Plastic Pipe Institute, 1981).
External loadings  on casing that may contribute to collapse
include:

     1) net external hydrostatic pressure produced when
         the static water level outside of the casing is
         higher than the water level on the inside;
     2) unsymmetrical  loads resulting from uneven
         placement of backfill and/or filterpack materials;
     3)   uneven collapse of unstable formations;
     4)   sudden release of backfill materials that have
         temporariy bridged in the annulus;
     5)   weight of cement grout slurry and impact of heat
         of hydration of grout on the outside of a partially
         water-filled  casing,
     6)   extreme drawdown inside the casing caused by
         over pumping;
     7)   forces associated  with well development that
         produce large differential pressures on the casing;
         and
     8)   forces associated with improper installation
         procedures where unusual force  is used to
         counteract a borehole that is not straight or to
         overcome buoyant forces.

     Of these stresses, only external hydrostatic pressure can be
predicted and calculated with accuracy; others can be avoided
                                                           74

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by common  sense and good practice. To provide sufficient
margin  against possible collapse by all normally-anticipated
external loadings, a casing should be selected such that resis-
tance to collapse is more  than required to withstand external
hydrostatic pressure alone.  Generally, a safety factor of at least
two  is recommended (National  Water Well Association and
Plastic Pipe Institute, 1981). According to Purdin (1980), steps
to minimize the possibility of collapse include:

     1)  drilling a  straight, clean borehole;
    2)  uniformly distributing the filter-pack materials at
        a slow, even rate;
    3)  avoiding the use of quick-setting (high
        temperature) cements  for thermoplastic casing
        installation;
    4)  adding sand or bentonite to a cement to lower the
        heat of hydration; and
     5)  controlling negative pressures  inside the well
        during development.

Chemical Resistance Characteristics —
     Materials used for well casing in monitoring wells must be
durable enough to withstand galvanic electrochemical corro-
sion and chemical degradation.  Metallic  casing materials are
most subject to corrosion; thermoplastic  casing materials are
most subject to chemical degradation. The  extent to which these
processes occur depends on water quality  within the formation
and changing chemical conditions such as fluctuations between
oxidizing and reducing states. Casing material must therefore
be chosen with a knowledge of the existing or anticipated
ground-water chemistry.  When anticipated water quality  is
unknown, it is prudent to  use conservative materials to avoid
chemical or potential water quality problems. If ground-water
chemistry affects  the structural integrity of the casing, the
products of casing deterioration  may also adversely affect the
chemistry of water samples taken from the wells.

Chemical Interference  Characteristics —
     Materials used for monitoring well  casing must not exhibit
a tendency to either sorb (take out of solution by either
adsorption or absorption)  or leach chemical constituents from
or into  the water that is sampled from the well. If a casing
material sorbs selected constituents from the ground water,
those constituents will either not be present in any water-quality
sample  (a "false negative") or the level of constituents will be
reduced. Additionally, if ground-water chemistry  changes over
time, the chemical constituents that were  previously sorbed
onto the casing may begin to desorb and/or leach into the ground
water. In either situation, the water-quality samples are not
representative.

     In the presence  of aggressive aqueous solutions,  chemical
constituents can be leached from casing materials. If this
occurs,  chemical constituents that are not indicative of forma-
tion  water quality may bedetected in samples collected from the
well. This "false positive"  might  be considered to be an indica-
tion  of  possible contamination when the constituents do not
relate to ground-water contamination per se, but rather to water
sample  contamination contributed by the well casing  material.
The  selection of a casing material must therefore consider
potential interactions between  the casing material and the
natural  and  the man-induced geochemical environment. It  is
important to avoid "false positive" and especially "false nega-
tive" sample results.

Types of Casing Materials
    Casing materials widely available for use in ground-water
monitoring wells can be divided into three categories:

     1)  fluoropolymer  materials,  including  poly-
        tetrafluoroethylene(PTFE),  tetra.fluoroethylene
        (TFE), fluorinated ethylene propylene  (FEP),
        perfluoroalkoxy (PFA) and polyvinylidene
        fluoride (PVDF);
    2) metallic materials, including carbon steel, low-
        carbon steel, galvanized steel and stainless steel
        (304 and 316); and
    3) thermoplastic materials, including polyvinyl
        chloride (PVC) and acrylonitrilebutadene  styrene


    In addition to the three categories that  are widely used,
fiberglass-reinforced  materials  including  fiberglass-reinforced
epoxy (FRE) and fiberglass-reinforced plastic (FRP) have been
used for monitoring applications. Because these materials have
not yet been used in general application across the country, very
little data are  available on characteristics and performances.
Therefore, fiberglass-reinforced  materials are not considered
further herein.

    Each material  possesses  strength-related characteristics
and  chemical  resistance/chemical interference characteristics
that  influence its use in site-specific hydrogeologic and con-
taminant-related  monitoring situations. These characteristics
for each of the three categories of materials are discussed below.

Fluoropolymer materials —
    Fluoropolymers are man-made materials consisting of
different formulations  of monomers (organic molecules) that
can be molded by powder metallurgy techniques or extruded
while heated. Fluoropolymer are technically included among
the thermoplastics, but possess a unique set of properties that
distinguish them from other  thermoplastics. Fluoropolymer
are nearly totally resistant to chemical and biological attack,
oxidation, weathering and ultraviolet radiation; have a broad
useful temperature range (up to 550°F); have a high dielectric
constant: exhibit a low coefficient of friction; have anti-stick
properties; and  possess a greater coefficient of thermal expan-
sion than most other plastics and metals.

     There exist a variety  of fluoropolymer materials that are
marketed under a number of different trademarks. Descriptions
and basic physical properties of some of the mom popular
fluoropolymer with appropriate trademarks are discussed
below.

    Polytetrafluorethylene  (PTFE)) was discovered by E.I.
DuPont de Nemours in 1938 and was available only to the
United States  government until the end of World War II.
According to Hamilton (1985), four principal physical proper-
ties are

     1)  extreme temperature range ~ from -400°F to
        +500"F  in constant service;
    2)  outstanding electrical and thermal insulation;
                                                          75

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    3)  lowestcoefficientoffrictionofanysolidmaterial;
        and
    4)  almost completely chemically inert, except for
        some reaction with halogenated compounds at
        elevated temperatures and pressures.

    In addition, PTFE is flexible without the addition of
plasticizers and is  fairly easily machined, molded or extruded.
PTFE is  by  far  the most widely-used and produced
fluoropolymer. Trade names, manufacturers and countries of
origin of PTFE and other fluoropolymer materials are listed in
Table 24. Typical  physical properties  of the various
fluoropolymer materials are described in Table 25.

    Fluorinated ethylene propylene (FEP) was also developed
by E.I. DuPont de Nemours and is perhaps the second most
widely used  fluoropolymer. It duplicates  nearly all  of the
physical properties of PTFE except the upper temperature
range, which is 100°F  lower. Production of FEP-finished
products is generally faster because FEP is melt-processible,
but raw materials costs are higher.
                                                              Perfluoroalkoxy (PFA) combines the best properties of
                                                          PTFE and FEP, but the former costs substantially more than
                                                          either of the other fluoropolymers. Polyvinylidene fluoride
                                                          (PVDF) is tougher and has a higher abrasion resistance than
                                                          other fluoropolymers and is resistant  to radioactive environ-
                                                          ments. PVDF has a lower upper temperature limit than either
                                                          PTFE or PFA.

                                                              Care should be exercised  in the  use of trade names to
                                                          identify fluoropolymers. Some manufacturers use one trade
                                                          name to refer to several of their own different materials. For
                                                          example, DuPont refers to several of its fluoropolymer resins as
                                                          Teflon® although the products referred to have different physi-
                                                          cal properties and different fabricating techniques. These ma-
                                                          terials may not always be interchangeable in service.

                                                              For construction of  ground-water monitoring  wells,
                                                          fluoropolymers possess several advantages over other thermo-
                                                          plastics and  metallic materials. For example, fluoropolymers
                                                          are almost completely inert to chemical attack, even by ex-
                                                          tremely aggressive acids (i.e., hydrofluoric, nitric, sulfuric and
Table 24. Trade Names, Manufacturers, and Countries of Origin for Various Fluoropolymer Materials
Chemical Formulation
                                Trade Name
                                                         Manufacturer
                                                                                 Country of Origin
PTFE (or TFE)- Polytetrafluoroethylene






FEP- Fluorinated ethylene propylene

PFA- Perfluoroalkoxy

PVDF- Polyvinyiidene fluoride
CTFE- Chlorotrifiuoroethylene

Teflon
Halon
Fluon
Hostaflon
Polyflon
Algoflon
Soriflon
Neoflon
Teflon
Neoflon
Teflon
Kynar
Kel-F
Diaflon
DuPont
Allied
Icl
Hoechs
Daikin
Montedison
Ugine Kuhlman
Daikin
DuPont
Daikin
DuPont
Pennwalt
3M
Daikin
USA, Holland, Japan
USA
UK, USA
W. Germany
Japan
Italy
France
Japan
USA, Japan,
Japan
USA, Japan,
USA
USA
Japan







Holland

Holland



 Table 25. Typical Physical

Properties
                        Properties of Various Fluoropolymer Materials (After Norton Performance Plastics, 1985)

                         Units         ASTM Method TFE           FEP              PFA          E-CTFE
                                                                                                        CTFE
Tensile strength @73°F
Elongation @73°F
Modulus@ 73°F
Tensile
Flexural
Elasticity in tension
Flexural strength@73°F
Izod impact strength
(1/2 X1/2-in. notched bar)
@+75°F

@-65°F
,
Tensile impact strength
@+73°F
@-65°F
Compressive stress <§> 73°F
Specific gravity
psi
%

psi
psi

psi


ft. Ibs./in.
of notch
ft. Ibs./in.
of notch

ft.lbs./sq. in.
ft. Ibs./sq. in.
psi

D638-D651
D638

D638
D790
D747
D790


D256




D1822

D695
D792
2500-6000
150-600

45,000-115,000
70,000-110,000
58,000
Does not break


3,0

2.3


320
105
1700
2.14-2.24
2700-3100
250-330


95,000
250,000
Does not break


No break

2.9


1020
365

2,12-2.17
4000-4300
300-350


95,000-100
-
7000
200

240,000
,000240,000

Does not break 7000


No break







2.12-2.17


No break







1.68
4500-6000
80-250

206,000
238,000
1.5-3.0x1 0s
8500


5.0






4600-7400
2.10-2,13
Coefficient of friction
static & kinetic against
polished steel
Coefficient of linear
thermal-expansion
                                     D696
0.05-0.08

6,6X10"6
                                                                0.06-0,09

                                                                6.6X10'6
0.05-0.06

6.7X10"
0.15-0,65

1 4X10"6
0.2-0,3

2.64X105
                                                        76

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hydrochloric) and organic solvents. In addition, sorption of
chemical constituents from solutions and leaching of materials
from the fluoropolymer chemical structure has been believed
to be minimal or non-existent. Although studies are  still ongo-
ing, Reynolds and Gillham (1  985) indicate that extruded tubing
of at least one fluoropolymer (PTFE) is prone to absorption of
selected organic compounds, specifically 1,1,1 -trichloroethane,
1,1,2,2  -tetrachloroethane,    hexachloroethane    and
tetrachloroethane; a fifth organic compound studied, bromoform,
was not sorbed by PTFE. An observation of particular note
made by Reynolds and Gillham was that tetrachloroethane was
strongly and rapidly sorbed by the PTFE tubing such that
significant reductions in concentration occurred within minutes
of exposure to a solution containing the  aforementioned or-
ganic compounds. These results indicate that PTFE may not be
as inert as previously thought. Barcelona  and Helfrich (1988)
provide a review of laboratory and field studies of well casing
material  effects.

    Although numerous such wells have been successfully
installed, there may be  some  potential drawbacks to using
fluoropolymer as monitoring well casing materials. For ex-
ample, PTFE is approximately 10 times more expensive than
PVC. In addition, fluoropolymer materials  are more difficult to
handle than most other well casing materials. Fluoropolymer
materials are heavier and less rigid than other thermoplastics
and slippery when wet because  of a low coefficient of friction.
Dablow et al. (1988) discuss installation of fluoropolymer wells
and address some of the potential difficulties. As they point out,
several strength-related properties of fluoropolymer (PTFE in
particular) must be taken  into consideration during the well
design process, including:  1) pull-out resistance of  flush-joint
threaded couplings (tensile strength);  2) compressive strength
of the intake section; and 3) flexibility of  the casing string.

    The tensile strength of fluoropolymer casing joints is the
limiting factor affecting the length of casing that can be sup-
ported safely in a dry borehole. According to Dablow et al.
(1988), experimental work conducted by DuPont indicates that
PTFE threaded joints will resist a pull-out load of approxi-
mately 900 pounds. With a safety factor of two, 2-inch schedule
40PTFE well casing with a weight of approximately  1.2pounds
per foot should be able to be installed to  a depth of approxi-
mately  375 feet. Barcelona et al. (1985a) suggest that the
recommended hang length not exceed 320 feet. In either case,
this is less than one tenth the tensile strength of an equivalent-
sized thermoplastic (i.e., PVC)  well casing material. Addition-
ally, because  the specific gravity of PTFE% is much higher than
that of thermoplastics (about 2.2), the buoyant force of water is
not great. However, the buoyant force is sufficient to increase
the maximum string length by approximately 10 percent for that
portion  of the casing material in contact with water.

    Compressive strength of fluoropolymer well casings and
particularly intakes is also a recognized problem area. A low
compressive stress when compared to other thermoplastics may
lead to failure of the fluoropolymer casing at the threaded joints
where the casing is weakest and the stress is greatest.  According
to Dablow et al. (1988), the "ductile" behavior of  PTFE has
resulted in the partial closing of intake openings with a conse-
quent reduction in well efficiency in deep fluoropolymer wells.
Dablow et al. (1988) suggest that this problem can be  minimized
by designing  a larger slot size than is otherwise indicated by the
sieve analyses. In compressive strength tests conducted by
DuPont to determine the amount of deformation in PTFE well
intakes that occurs under varying compressive stresses, a linear
relationship was demonstrated between applied stress and the
amount of intake  deformation. This relationship is graphically
presented in FigureSl.  From this graph, the anticipated intake
opening deformation can be determined and included in intake
design by calculating the load and adding anticipated intake
opening deformation to  the intake opening size determined by
sieve analysis.
 w    0   100  200  300  400  500  600  700  600  900 1000
                     Compassion Load - Lbs.
                              Note: Short Term Test -10 Minutes

Figure 51. Static compression results of Teflon* sceen (Dablow
          et al., 1988).
          'Dupont's registered trademark for Its fluorocarbon
           resin

    According to Dablow et al. (1988), a recommended con-
struction procedure to minimize compressive stress  problems is
to keep the casing string suspended in the borehole so that the
casing is in tension and to backfill the annulus around the  casing
while it remains  suspended. This procedure reduces  compres-
sive stress by supplying support on the outer wall of the casing.
This can only be accomplished successfully  in relatively shal-
low wells in which the long-term tensile strength of the
fluoropolymer casing is sufficient to withstand tensile stresses
imposed on the casing by suspending it in the borehole.  Addi-
tionally, continuous suspension of casing in the borehole is not
possible  with  hollow-stem auger  installations.

    The third area of concern in fluoropolymer well casing
installation is the extreme flexibility of the casing string.
Although easy solutions exist to avoid problems,  the flexibility
otherwise could cause the casing to become bowed  and non-
plumb when loaded,  and the resulting deformation  could cause
difficulties  in obtaining samples or accurate water  levels from
these wells. Dablow et al. (1988) suggest three means of
avoiding flexibility problems: 1) suspending the casing  string
in the borehole during backfilling (as discussed above); 2) using
casing centralizers; or 3) inserting a rigid PVC or steel pipe
temporarily inside the fluoropolymer casing during  backfilling.

Metallic Materials —

    Metallic well casing and screen materials available for use
in monitoring wells include carbon steel, low   carbon steel,
                                                           77

-------
galvanized steel and stainless steel. Well casings made of any
of these metallic materials are generally stronger, more rigid
and  less  temperature  sensitive  than  thermoplastics,
fluoropolymer or fiberglass-reinforced epoxy casing materials.
Table 26  describes dimensions, hydraulic collapse pressure,
burst pressure and unit weight of stainless steel casing. The
strength and rigidity capabilities of metallic casing materials
are sufficient to meet  virtually any subsurface condition en-
countered in a ground-water monitoring situation. However,
metallic materials are  subject  to corrosion during long-term
exposure to certain subsurface geochemical environments.

    Corrosion of metallic well casings  and well intakes can
both limit the useful life of the monitoring well installation and
result in ground-water sample  analytical bias. It is important,
therefore, to select both casing and screen that are fabricated of
corrosion-resistant materials.

    Corrosion is defined as the weakening or destruction of a
material by chemical  action. Several well-defined forms of
corrosive attack on metallic materials have been observed and
defined. In all forms,  corrosion proceeds by electrochemical
action, and water in contact with the metal is an essential factor.
According  to Driscoll (1986), the forms of corrosion typical in
environments in which well casing and  well intake materials
are installed  include:

     1)  general oxidation  or "rusting" of the metallic
        surface, resulting in  uniform destruction of the
        surface with occasional perforation in some areas;
    2)  selective corrosion (dezincification) or loss of
        one element of an alloy, leaving a structurally
        weakened material;
    3)  hi-metallic corrosion,  caused  by  the creation of a
        galvanic cell at or near the juncture of two different
        metals;
    4) pitting corrosion, or highly localized corrosion by
        pitting or perforation, with little loss of metal
        outside of these areas; and
    5) stress corrosion, or corrosion induced in areas
        where the metal is highly stressed.

    To determine the potential for corrosion of metallic
materials, the natural geochemical conditions must first be
determined. The following list of indicators can help recognize
Portentially  corrosive  conditions  (modified  from Driscoll, 1986):

     1)  low pH ~ if ground water pH  is less than 7.0,
        water is acidic and corrosive conditions exist;
    2)  high dissolved oxygen content ~ if dissolved
        oxygen  content exceeds 2 milligrams per liter,
        corrosive water is indicated;
    3)  presence of hydrogen sulflde (H^S) ~ presence of
        HjS in quantities as low as 1 milligram per liter
        can  cause severe corrosion;
    4)  total dissolved solids (TDS) - if TDS is greater
        than  1000  milligrams per liter, the electrical
        conductivity of the water is great enough to cause
        serious electrolytic corrosion;
    5)  carbon dioxide (CO) -- corrosion is likely if the
        COj content of the water exceeds 50 milligrams
        per liter; and
    6)  chloride ion (Cl) content -- if Cl content exceeds
        500  milligramsperliter, corrosion  can be expected.

Combinations of any  of these corrosive conditions generally
increase the corrosive effect, However, no  data presently exist
on the expected life of steel well casing  materials exposed to
natural subsurface geochemical conditions.

    Carbon  steels were produced primarily to  provide  in-
creased resistance to  atmospheric corrosion.. Achieving this
Table 26. Hydraulic Collapse and Burst Pressure and Unit Weight of Stainless Steal Well Casing (Dave Kill, Johnson Division, St.
         Paul, Minnesota, Personal Communication, 1965)
Norn.
Size
Inches
2



2112


3


3 1/2


4


5


6


Schedule
Number
5
10
40
80
5
10
40
5
10
40
5
10
40
5
10
40
5
10
40
5
10
40
Outside
Diameter,
Inches
2.375
2.375
2.375
2.375
2.875
2.875
2.875
3.600
3.500
3.6QO
4.000
4.000
4.000
4.500
4.500
4.500
5.563
5.663
5.563
6.625
6.625
6.625
Wall
Thickness
Inches
0.065
0.109
0.154
0.218
0.083
0,120
0.203
0.063
0.120
0.216
0.063
0.120
0.226
0.063
0.120
0.237
0.109
0.134
0,258
0.109
0.134
0.280
Internal
Inside Cross-Sectional
Diameter Area
Inches Sq. In.
2.245
2.157
2.067
1.939
2.709
2.635
2.469
3.334
3.260
3.068
3.834
3.760
3.548
4.334
4.260
4.026
5.345
5.295
5.047
6.407
6.357
6.065
3.958
3.654
3.356
2.953
5.761
5.450
4.785
8.726
8.343
7.369
11.54
11.10
9.667
14.75
14.25
12.72
22.43
22,01
20.00
32.22
31.72
28.89
Internal Pressure
psi
Test. Bursting
820
1.375
1.945
2.500
865
1.250
2.118
710
1.030
1.851
620
900
1.695
555
800
1.560
587
722
1.391
484
606
1.268
4.105
6.664
9.726
13.766
4.330
6.260
10.591
3.557
5.142
9.257
3.112
4.500
8.475
2.766
4.000
7.900
2.949
3.613
6.957
2.467
3.033
6.340
External
Pressure
psi
Collapsing
896
2.196
3.526
5.419
1.001
1$05
3.931
639
1.375
3.307
431
1.081
2.941
316
845
2.672
350
665
2.231
129
394
1.942
Weight
Pounds
per Foot
1.619
2.663
3.087
5.069
2.498
3.564
5.347
3.057
4.372
7.647
3.505
5.019
9.194
3.952
5.666
10.891
6.409
7.642
14.764
7.656
9.376
19.152
                                                           78

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increased resistance requires that the material be subjected to
alternately  wet and dry conditions. In most monitoring wells,
water fluctuations are not sufficient in either duration or occur-
rence to provide the conditions that minimize corrosion.
Therefore, corrosion is a frequent problem. The difference
between the corrosion resistance of carbon and low-carbon
steels is negligible under conditions in which the materials are
buried in soils or in the saturated zone; thus both materials may
be expected to corrode approximately equally.  Corrosion prod-
ucts include iron and manganese and trace metal oxides  as well
as various metal sulfides (Barcelona et al, 1983). Under oxi-
dizing conditions,  the principal products are solid hydrous
metal oxides;  under reducing conditions, high levels of dis-
solved metallic corrosion products can be expected (Barcelona
et rd., 1983). While the electroplating process of galvanizing
improves the  corrosion resistance of either carbon or low-
carbon steel, in many subsurface environments the improvement
is only slight and short-term.  The products of corrosion of
galvanized  steel include iron, manganese, zinc and trace cad-
mium species  (Barcelona et al.,  1983).

     The presence  of corrosion products  represents  a high
potential for the alteration of ground-water sample chemical
quality. The surfaces on which  corrosion occurs also present
potential sites for a variety of chemical reactions and adsorp-
tion. These  surface interactions can cause significant changes in
dissolved  metal or organic compounds in ground water
samples (Marsh and Lloyd, 1980). According to Barcelona et
al. (1983), even flushing the stored water from the well casing
prior to sampling may not be sufficient to minimize this source
of sample bias cause the effects of the disturbance of surface
coatings or  accumulated corrosion products in the bottom of the
well are difficult, if not impossible, to predict. On the basis of
these observations, the use of carbon steel, low-carbon steel and
galvanized  steel in monitoring well construction is not consid-
ered prudent in most natural geochemical environments.

     Conversely, stainless steel performs  well inmost corrosive
environments,  particularly under oxidizing conditions. In fact,
stainless steel requires exposure to oxygen in order to attain its
highest corrosion resistance  oxygen combines with part of the
stainless steel alloy to form  an invisible protective film on the
surface of the metal. As long as the film remains intact, the
corrosion resistance of stainless  steel is very high.  Recent work
by Barcelona and Helfrich (1986; 1988) and Barcelona et al.
(1988) suggest that biological activity may alter geochemistry
near stainless steel wells. Iron bacteria may induce degradation
of the well  casing and screen.

     Several different types  of stainless steel alloys arc avail-
able. The most common alloys used for well casing and screen
are Type 304 and Type 316.  Type 304 stainless steel  is perhaps
the most practical ;rom a corrosion resistance and cost stand-
point. It is composed of slightly more than 18 percent chromium
and more than 8 percent nickel, with about 72 percent iron and
not more than 0.08 percent carbon (Driscoll, 1986).  The chro-
mium and  nickel give  the 304 alloy excellent resistance to
corrosion; the  low carbon content improves weldability. Type
316  stainless steel is compositionally  similar to Type 304 with
one exception - a 2 to 3 percent molybdenum content and a
higher nickel content that replaces the equivalent percentage of
iron. This compositional difference provides Type 316 stain-
less steel with an improved resistance to sulfur-containing
                                                           79
species as well as sulfuric acid solutions (Barcelona et  al.,
 1983). This means that Type  316 performs better under reduc-
ing conditions than Type 304. According to Barcelona et al.
(1983), Type 316 stainless steel is less susceptible to pitting or
pinhole corrosion caused by organic acids or halide solutions.
However, Barcelona et al. (1983) also point out that for either
formulation of stainless steel, long-term exposure  to very
corrosive conditions may result in corrosion and the subsequent
chromium or nickel contamination of samples.

Thermoplastic Materials —
    Thermoplastics are man-made materials that are composed
of different formulations of large  organic molecules. These
formulations soften by heating and harden upon cooling  and
therefore can easily be molded or extruded into a wide variety
of useful shapes including well casings, fittings and accesso-
ries.

    The most common types of thermoplastic well casing are
polyvinyl chloride (PVC) and acrylonitrile butadiene styrene
(ABS). Casing made of these materials is generally weaker,  less
rigid and more temperature-sensitive than  metallic  casing  ma-
terials. However, casing made of either types of  plastic  can
usually be  selected where the strength, rigidity  and temperature
resistance are  generally  sufficient to withstand stresses during
casing  handling, installation and earth loading (National Water
Well Association and Plastic Pipe  Institute, 1981). Thermo-
plastics also: 1) offer complete resistance to galvanic  and
electrochemical corrosion; 2) are light  weight for  ease of
installation and reduced shipping costs;  3) have high abrasion
resistance; 4) have high strength-to-weight ratios; 5) are  du-
rable in natural ground-water environments; 6) require  low
maintenance; 7) are flexible and workable for ease of cutting
and joining and 8) are relatively low in cost.

    Long-term exposures of some formulations of thermoplas-
tics to the ultraviolet rays of direct sunlight and/or to low
temperatures will cause brittleness and gradual loss of impact
strength that may be significant. The extent of this degradation
depends on the type of plastic, the extent  of exposure and the
susceptibility  of the casing to mechanical damage (National
Water Well Association and Plastic Pipe Institute,  198 1). Many
thermoplastic formulations now include protection against
degradation by sunlight,  but brittleness of casing, particularly
during casing installation remains a problem. Above-ground
portions of thermoplastic well casings should be suitably pro-
tected from breakage. Potential chemical problems  are dis-
cussed in the following  sections.

    Polyvinyl chloride (PVC)-PVC plastics are produced by
combining PVC resin with various  types of stabilizers, lubri-
cants, pigments, fillers,  plasticizers and processing aids.  The
amounts of these additives can be varied to produce different
PVC plastics with properties tailored to specific applications.
PVC used for well casing is composed of a rigid unplasticized
polymer formulation (PVC Type 1) that is strong and generally
has good chemical resistance. However, several publications
(e.g., Barcelona et al., 1983; Barcelona and Helfrich, 1988;  and
Nass, 1976) raised questions of chemical resistance to low
molecular weight ketones, aldehydes and  chlorinated  solvents
which may limit durability of  the casing.

    PVC materials are classified according to ASTM standard
specification D-1785 that  covers rigid PVC  compounds  (Ameri-

-------
can Society for Testing and Materials, 1986).  This standard
categorizes rigid PVC by numbered cells designating value
ranges for certain pertinent  properties and characteristics in-
cluding impact strength, tensile strength, rigidity (modulus of
elasricity) temperature  resistance (deflection temperature) and
chemical resistance. ASTM  standard specification F-480 cov-
ers thermoplastic water well casing pipe and couplings made in
standard dimension ratios. This standard specifies  that PVC
well casing can be made from only  a limited number of cell
classification  materials, predominantly PVC 12454-B, but also
including PVC 12454-C and PVC 14333-C and D (American
Society for Testing and Materials, 198 1). Minimum physical
property values for  these materials are given in Table 27.
Hydraulic collapse pressure and unit weight for a range of PVC
well casing diameters is given in Table 28.

    Acrylonitrile butadiene styrene (ABS)--ABS plastics  are
produced  from three different monomers: 1) acrylonitrile, 2)
butadiene and 3) styrene. The ratio of the components and the
way in which they are combined can be varied to produce
plastics with  a wide range of properties. Acrylonitrile contrib-
utes rigidity,  impact  strength, hardness, chemical resistance
and heat resistance; butadiene contributes impact strength;
styrene contributes rigidity,  gloss and ease of manufacturing
(National  Water Well  Association arid Plastic Pipe Institute,
1918  1). ABS  used for well casing is a ngid, strong unplasticized
polymer formulation that has good heat resistance and impact
strength.

    Two  ABS material types are used for well casings:  1) a
higher strength, high  rigidity, moderate impact resistance ABS
and 2) a lower strength and rigidity, high impact  strength ABS,
These two materials  are identified as cell class 434 and 533,
respectively by ASTM standard specification F-480 (Ameri-
can Society for Testing and Materials, 198 1). Minimum physi-
cal property values for  ABS well casing are given in Table  27.
The high temperature resistance and the ability of ABS to retain
other properties better at high temperatures is an advantage in
wells in which grouting causes a high heat of hydration.
Hydraulic collapse pressure for a range of ABS well casing
diameters is given in Table 29.

    General  strength/chemical resistance and/or interference
characteristics-The tensile strength of thermoplastics is rela-
tively low in comparison to  metallic materials, but the devel-
oped string loading is not a limiting factor because the thermo-
plastic well casing is lighter weight than metallic materials.
Table 27 shows the physical properties of thermoplastic well
casing materials. The tensile  strength, which in part determines
the length of casing string that can be suspended in the borehole
is relatively large. According to calculations by the National
Water Well Association and Plastic Pipe Institute (198  1),
permissible casing  string lengths even in unsaturated  boreholes
exceed the typical borehole depths  of monitoring wells. In
boreholes  where the casing is partially immersed, casing string
length is even less of a problem because the thermoplastics  are
low in density and therefore  relatively buoyant.

    With  respect to  chemical resistance, thermoplastic well
casing materials are non-conductors and therefore do not cor-
rode either electrochemically or galvanically  like metallic
materials.  In addition, thermoplastics are resistant to biological
attack and to chemical attack  by soil, water and other naturally-
occurring substances present in the subsurface (National Water
Well Association and Plastic Pipe Institute, 1981). However,
thermoplastics are  susceptible to chemical attack by high con-
centrations of certain organic solvents, and long term exposure
to lower levels has  as yet undocumented effects. This physical
degradation of a plastic by an organic solvent is called solva-
tion.  Solvent cementing of thermoplastic well casings is based
on solvation.  Solvation occurs in the presence of very high
concentrations  of specific organic solvents.  If these solvents,
which include tetrahydrofuran (THF), methyl ethyl ketone
(MEK), methyl isobutyl ketone (MIBK) and cyclohexanone,
are present in high  enough  concentrations, the solvents can be
expected to chemically degrade thermoplastic well casing.
However, the  extent of this degradation  is not known. In
general, the  chemical attack on the thermoplastic polymer
matrix is enhanced  as the organic content of the solution with
which it is in contact increases.

     Barcelona et al. (1983) and the Science  Advisory Board of
the U.S. EPA list the groups of chemical compounds that may
cause degradation of the thermoplastic  polymer matrix  and/or
the release of  compounding ingredients that  otherwise will
remain in the solid material. These chemical compounds in-
clude 1) low molecular weight ketones, 2)  aldehydes, 3)
amines  and 4) chlorinated alkenes and alkanes. Recent reports
of creosotes and petroleum  distillates causing disintegration of
PVC casing support Barcelona's findings. There is currently a
lack of information regarding critical concentrations of these
chemical compounds at which deterioration of the thermoplas-
tic material is significant enough to affect either the structural
integrity of the material or the ground-water sample chemical
quality.

     Among the potential sources of chemical  interference in
thermoplastic well  casing materials are the basic monomers
from which the casing is made and a variety of additives that
may be used  in the  manufacture of the casing including plasti-
cizers, stabilizers, fillers, pigments and lubricants. The propen-
sity  of  currenty available information on potential contamina-
tion of water that comes in contact with rigid thermoplastic
materials relates specifically to PVC; no information is cur-
rently available on ABS or on other similar thermoplastics.
Therefore, the remainder of this discussion relates  to potential
chemical interference effects from PVC well casing materials.

     Extensive research has been conducted in the laboratory
and in the field, specifically on water supply  piping, to evaluate
vinyl chloride monomer migration from new  and old PVC pipe,
The data support the conclusion that when  PVC is in contact
with water, the level of trace vinyl chloride migration from PVC
pipe is extremely low compared to residual vinyl chloride
monomer (RVCM) in PVC pipe. Since 1976, when the National
Sanitation Foundation established an RVCM monitoring  and
control program for PVC pipe used in potable  water supplies
and well casing, process control of RVCM levels in PVC pipe
has improved markedly. According to Barcelona et al. (1983),
the maximum allowable  level of RVCM in NSF-certified PVC
products (less than or equal to 10 ppm RVCM)  limits potential
leached concentrations of vinyl chloride monomer to 1 to 2
micrograms per liter. Leachable amounts  of vinyl chloride
monomer should decrease as RVCM levels in products continue
to be reduced. Although the potential for analytical interference
exists even at the low micrograms per-liter level at which vinyl

-------
Table 27. Typical Physical Properties of Thermoplastic Well Casing Materials at 73.4° (National Water Well Association and Plastic
         Pipe institute, 1981)
Property
Specific Gravity
Tensile Strength, Ibs. /in.8
Tensile Modulus of Elasticity, Ibs/m.2
Compressive Strength, Ibs/m.2
Impact Strength, Izod, ft. -Ib/inch notch
Cell Class,
per D-1788
ASTM Test Method 434 533
D-792
D-638
D-638
D-695
D-256
1.05
6,000"
350,000
7.200
4.0*
1.04
5,000*
250,000
4,500
6.0*
PVC
Cell Class,
per 0-1784
12454-B & C 14333-C & D
1,40
7,000*
400,000*
9,000
0.65
1.35
6,000*
320,000*
8,000
5.0
Deflection Temperature Under Load

  (264 psi), "F                       D-648

Coefficent of Linear Expansion,
   in./in, - °F                         D-696
190"


5.5 X106
190"


8.0X106
168*


3.0 X10-*
14tY


5.0 X10S
.These are minimum values set by the corresponding ASTM Cell Class designation. All others represent typical values.
Table 28. Hydraulic Collapse Pressure and Unit Weight of PVC Well Casing (National Water Well Association and Plastic Pipe
         institute,  1981)
Outside Diameter
(inches) SCH*
Nom. Actual
2

2112

3

3112

4

41/2

5

6

2.375

2.875

3.500

4.000

4.500

4.950

5.663

6.625

SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40


SCH 80
SCH 40
SCH 80
SCH 40
Wail
Thickness
Min. (in.)
0.218
0.154
0.276
0.203
0.300
0.216
0.316
0.226
0.337
0.237
0.248
0.190
0.375
0.258
0.432
0.280
D R
10.9
15.4
10.4
14.2
11.7
16.2
12,6
17.7
13.3
19.0
20.0
26.0
14.5
21.6
15.3
23.7
Weight in Air
(lbs/100 feet)
PVC 12454 PVC14333
94
69
144
109
193
143
235
172
282
203
235
182
391
276
538
356
91
66
139
105
186
136
227
176
272
196
226
176
377
266
519
345
Weight in Water
(lbs/100 feet)
PVC 12454 PVC 14333
27
20
41
31
55
41
67
49
80
58
67
52
112
79
164
102
24
17
36
27
48
36
59
43
70
51
56
46
98
69
134
89
Hydraulic Collapse
Pressure (psi)
PVC 12454 PVC 14333
947
307
1110
400
750
262
589
197
494
158
134
59
350
105
314
78
756
246
885
320
600
210
471
156
395
126
107
47
260
84
171
62
 .Schedule
Table 29. Hydraulic Collapae Pressure and Unit Weight of ABS Well Casing (National Water Well Association and Plastic Pipe
          Institute, 1981)
Outside Diameter
(inches) SCH*
Nom. Actual
2

21/2

3

3112

4

5

6

2.375

2.875

3.500

4.000

4.500

5.563

6.250

SCH 80
SCH 40
"SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40
SCH 80
SCH 40
Wall
Thickness
Min. (in.)
0.218
0.154
0.276
0.203
0.300
0.216
0.318
0.226
0.337
0.237
0.375
0.258
0.432
0.280
DR**
10.9
15.4
10.4
14.2
11.7
16.2
12.6
17.7
13.3
19.0
14.6
21.6
15.3
23.7
Weight in Air
(lbs/100 feet)
ABS 434 ABS 533
71
52
108
82
145
107
176
129
211
152
294
207
404
268
70
51
107
81
144
106
175
128
209
151
291
205
400
266
Weight in Water
(lbs/100 feet)
ABS 434 ABS 533
3.4
2.5
5.1
3.9
6.9
5,1
8.4
6.1
10.0
7.2
14.0
9.8
19.2
12.8
2.7
2.0
4.1
3.1
5.5
4.1
6.7
4.9
8.0
5.8
11.2
7.9
15.4
10.2
Hydraulic Collapse
Pressure (psi)
ABS 434 ABS 533
829
269
968
350
656
229
515
173
432
138
306
92
275
69
592
192
691
250
466
164
368
124
308
98
218
66
196
49

-------
chloride monomer may be found in a solution in contact with
PVC, the significance of this interference is  not currently
known.

    With few exceptions, plasticizers are not added to PVC
formulations used for well casing because the casing must be
a rigid material. Even if plasticizers were added, levels would
not be expected to exceed 0.01  percent (Barcelona et al, 1983).
By contrast, flexible PVC tubing may contain from 30 to 50
percent plasticizers by weight. The presence of these high levels
of plasticizers in flexible PVC tubing has been documented to
produce  significant chemical  interference effects  by  several
researchers (Barcelona et al.,  1985b; Barcelona, 1984; Barcelona
et al., 1983;  Junket al., 1974). However, at the levels present in
rigid well casing, plasticizers were not reported to pose a
chemical interference problem.

    Rigid PVC may contain other additives, primarily stabiliz-
ers, at levels approaching 5 percent by weight. Some represen-
tative chemical classes of additives that have been used in the
manufacture of rigid PVC well casing are listed in Table 30.
Boettner et al. (1981) determined through a laboratory study
that several of the PVC heat  stabilizing  compounds, notably
dimethyltin and dibutyltin species, could  potentially leach out
of rigid PVC at very low (low to sub micrograms per liter)
levels. These levels decreased dramatically over time. Factors
that influenced the leaching  process in this study included
solution pH, temperature and  ionic composition; and exposed
surface area and surface porosity of the pipe  material. It is
currently unclear what impact,  if any, the leaching of low levels
of organotin compounds may  have on analytical interference.

     In addition to setting  a  limit on RVCM, the National
Sanitation Foundation has set  specifications for  certain  chemi-
cal constituents in PVC formulations. The purpose of these
specifications as outlined in NSF Standard 14 (National Sani-
tation Foundation, 1988) is to control the amount of chemical
additives in both PVC well casing and pipe used for potable
water supply.  The maximum contaminant levels permitted in  a
standardized leach test on NSF-approved PVC products are
given in Table31.  Most of these levels correspond to those set
by the Safe Drinking Water  Act for chemical constituents
covered by the National Interim Primary Drinking Water Stan-
dards. Only PVC products that  carry either the "NSF we" (well
casing) or "NSF pw" (potable  water) designation have met the
specifications set forth in Standard 14. Other non-NSF listed
products may include in their formulation chemical additives
not addressed by the  specifications or may carry levels of the
listed chemical parameters higher than permitted by the speci-
fications. In all cases, the material used should be demonstrated
to be compatible  with the specific applications. For exam pie,
even though neither lead nor cadmium have been permitted as
compounding  ingredients in United States-manufactured NSF-
listed PVC well casing since 1970, PVC  manufactured in other
countries may be stabilized with lead or cadmium compounds
that have been demonstrated to leach from the PVC (Barcelona
etal, 1983).

    In other laboratory studies of leaching of PVC well casing
material  chemical  components  into water, Curran and Tomson
(1983) and Parker and Jenkins (1986) determined that little or
no leaching occurred. In the former study, it was found when
testing several different samples (brands) of rigid PVC  well
casing that trace organics either were not leached or were
leached only at the sub-micrograms per liter level. In the latter
study, which was conducted using ground water in contact with
two different brands of PVC, it was concluded that no chemical
constituents were  leached at sufficient concentrations to inter-
fere with reversed-phase analysis for low  micrograms per  liter
levels of 2,4,6 trinitrotoluene (TNT), hexahydro-1,3,5 trinitro-
1,3,5-tnazme  (RDX), octahydro-1,3,5,7 -tetramtro-1,3,5,7-
tetrazocine (HMX) or 2,4 dinitrotoluene (DNT) in solution.  The
study by Curran and Tom son (1983) confirmed previous field
work at Rice University (Tom son et al., 1979) that suggested
that PVC well casings did not leach significant amounts (i.e. at
the sub-micrograms  per liter level)  of trace organics  into
sampled ground water.

    Another potential  area for concern  with respect to chemical
interference effects is the possibility that  some chemical con-
stituents could be sorbed by PVC well casing materials. Miller
(1982) conducted a laboratory study to determine whether
several plastics, including rigid PVC well casing, exhibited any
tendency to sorb potential contaminants from solution. Under
the conditions of his test, Miller found that PVC moderately
sorbed tetrachloroethylene and strongly sorbed lead, but did not
sorb trichlorofluoromethane,  trichloroethylene, bromoform,
1,1,1-trichloroethane, 1,1,2-trichloroethane  or chromium. In this
experiment, sorption was measured weekly for six weeks and
compared to a control; maximum sorption of tetrachloroethylene
occurred at two weeks. While Miller (1982) attributed these
losses  of tetrachloroethylene and lead strictly to sorption, the
anomalous behavior of tetrachloroethylene compared to  that
for other organics of similar structure (i.e., trichloroethlyene) is
not explained. In a follow-up study to determine whether or not
the tetrachloroethylene could be desorbed and recovered, only
a small amount of tetrachloroethylene was desorbed. Thus,
whether or not strong sorption or  some other mechanism (i.e.,
enhanced biodegradation in the presence of PVC) accounts for
the difference is not clear (Parker and Jenkins, 1986). In the
laboratory study by Parker and Jenkins (1986), it was found that
significant losses  of TNT and HMX from solution occurred in
the presence of PVC well casing. A follow-up study to deter-
mine the mechanism for the losses attributed the losses to
increased microbial degradation rather than to  sorption. These
results raise questions regarding whether or not losses found in
other laboratory or even field studies that did not consider
biodegradation as a loss mechanism could be attributed to
biodegradation rather  than to sorption.

    In another laboratory study, Reynolds and  Gillham (1985)
found  that sorption of selected organics (specifically 1,1,1-
trichloroethane,  1,1,2,2-tetrachloroethane, bromoform, hexa-
chloroethane  and tetrachloroethylene) onto PVC and other
polymeric well casing  materials could be a significant source of
bias to ground-water samples collected from water standing  in
the well. PVC was found to slowly sorb four of the  five
compounds studied (all except 1,1,1-trichloroethane), such that
sorption bias would likely not be significant for the sorbed
compounds if well development (purging the well of stagnant
water) and sampling were to take place in the same day.

    It is clear that with few exceptions the work that has been
done to determine chemical interference  effects of PVC  well
casing (whether by leaching from or sorbing to  PVC  of chemi-
cal constituents) has been conducted under laboratory condi-
                                                           82

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tions. Furthermore, in most of the laboratory work the PVC has
been exposed to a solution (usually distilled, deionized, or
"organic-free" water) over periods of time ranging from several
days to several months. Thus the PVC had a period of time in
which to exhibit sorption or leaching effects. While this may be
comparable to a field situation in which ground water was
exposed to the PVC well casing as  it may be between sampling
rounds, few studies consider the fact that prior to sampling, the
well casing is usually purged of stagnant water residing in the
casing between sampling rounds.  Thus, the water that would
have been affected by the sorption or leaching effects of PVC
would ideally have been removed and replaced with aquifer-
quality  water that is eventually obtained as "representative" of
existing ground-water conditions.  Because the  sample is gen-
erally taken immediately after purging of stagnant water, the
sampled water will have  had a minimum of time with which to
come in contact with casing materials and consequently be
affected by sorption or leaching effects. Because of this,
Barcelona et al. (1983) suggest that the potential sample bias
due to sorptive interactions with well casing materials maybe
discounted. They point out that these effects are far more critical
in sample transfer  and  storage procedures employed prior to
sample separation or analysis. Nevertheless, other researchers
 do not agree that purging avoids casing effects especially for
 wells that recover slowly and thereby allow ample time for
 surface reactions to occur.

 Composite Alternative Materials —
      In certain conditions it maybe advantageous to design a
 well using more than one material for well components. For
 example, where stainless steel or fluoropolymer materials are
 preferred in a specific chemical environment, considerable cost
 savings may be realized by using PVC in non-critical portions
 of the well. These savings may be considerable especially in
 deep wells where only the lower portion of the well has a critical
 chemical environment and tens of feet of lower-cost PVC may
 be used in the upper portion of the well. In composite well
 designs  the use of dissimilar metallic components should be
 avoided  unless an electrically isolating design is incorporated
 (United  States Environmental Protection Agency, 1986).

 Coupling Procedures for Joining Casing
      Only a limited number of methods are available for joining
 lengths  of casing  or casing and screen together. The joining
 method depends on the type of casing and type of casing joint.
 Figure 52 illustrates some common  types of joints used for
Table 30. Representative Classes of Additives In Rigid PVC Materials Used for Pipe or Well Casing (Barcelona et al., 1983)

                                    (Concentration in wt. %)
Heat stabilizers (0.2-1.0%)
Dibutyltin diesters of lauric and maleic acids
Dibutyltin bis (laurylmercaptide)
Dibutyltin-B mercaptopropionate
di-n-octyltin maleate
di-n-octyltin-S,S'-bis isoctyl mercaptoacetate
di-n-octyltin-B mercaptopropionate
Various other alkyltin compounds
Various proprietary antimony compounds
 Filler* (1-5%)
 CaCO,
 diatomaoeous earth
 clays
 pigments
 T,02
 carbon black
 iron and other metallic oxides

 Lubricants (1-5%)
 stearic acid
 calcium stearate
 glycerol monostearate
 montan wax
 polyethylene wax
Table 31. Chemical Parameters Covered by NSF Standard 14 (National Sanitation Foundation, 1938)
Parameter
Antimony (Sb)
Arsenic (As)
Barium(Ba)
Cadmium (Cd)
Chromium (Cr)
Lead(Pb)
Mercury (Hg)
Phenolic substances
Residual vinyl chloride monomer (RVCM)
Selenium (Se)     *
Total dissolved solids
Tin (Sn)
Total trlhalomethanes (TTHM)
Taste and Odor Evaluations
Characteristic
Odor

Taste
Maximum Permissible Level mg/L (ppm)
             0.050
             0.050'
             1.0"
             0.010'
             0.050'
             0.020'
             0.0020'
             0.050
             2.0
             0.010'
             70.0
             O.OSO
             0.10
             Permissible Level
             Cold application 40
             Hot application 50
             Satisfactory	
 1 Established in tie U.S. EPA National Primary Drinking Water Regulations.
 *ln the finished product ppm (mg&g).
                                                           83

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                                                                           Couplin
a. Flush-joint Casing             b- Threaded, Flush-joint Casing
  (Joined by Solvent Welding)       (Joined by Threading Casing
                                Together)
                                                                                 Plain Square-end Casing
                                                                                 (Joined by Solvent Welding
                                                                                 with Couplings)
             d. Threaded Casing
               (Joined by Threaded Couplings)
                              e. Bell-end Casing
                                 (Joined by Solvent Welding)
f. Plain Square-end Casing
  (Joined by Heat Welding)
Figure 52. Types of joints typically used  between casing  lengths.
assembling lengths of casing. Flush-joint, threaded flush-joint,
plain square-end and bell-fend casing joints are typical of joints
available for plastic casing; threaded flush-joint, bell-end and
plain square end casing joints are typical of joints available for
metallic casing.

Fluoropolymer Casing Joining —
     Because fluoropolymers are inert to  chemical attack or
solvation even by pure solvents, solvent welding cannot be used
with fluoropolymers. Similar to thermoplastic casing joining in
techniques, threaded joints  wrapped with  fluoropolymer tape
are preferred.
                                              Metallic Casing Joining —
                                                  There are generally two options available for joining
                                              metallic well casings: 1) welding via application of heat or 2)
                                              threaded joints. Both methods produce a casing string with a
                                              relatively smooth inner and outer diameter. With welding, it is
                                              generally possible to produce joints that are as strong or
                                              stronger than the casing, thereby enhancing the tensile strength
                                              of the casing string. The disadvantages of welding include: 1)
                                              greater, assembly time, 2) difficulty  in properly welding casing
                                            the verthcal position,  3)  enhancement or corrosion  potential
                                              in the vicinity of the weld and 4) the danger of ignition of
                                                            84

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Table 2. Federal Ground-Water Monitoring Provisions and Objectives (after Office of Technology Assessment, 1984)
Statutory authority
                   Monitoring  provisions"
                   Monitoring objectives
Atomic Energy Act
Clean Water Act
  -Sections 201 and 405

  -Section 208
Coastal Zone Management Act
Comprehensive Environmental
  Response, Compensation,
  and Liability Act

Federal Insecticide, Fungicide
  and Rodenticide Act-
  Section 3
Federal Land Policy and
  Management Act (and
  associated mining laws)
Hazardous Liquid Pipeline
  Safety Act

Hazardous Materials
  Transportation Act

National Environmental
  Policy Act
Ground-water monitoring is specified in Federal regulations for low-level radioactive
  waste disposal sites. The facility license must specify the monitoring requirements
  for the source. The monitoring program must include:
  - Pre-operational monitoring program conducted over a 12-month period. Parameters
   not specified.
  - Monitoring during construction and operation to provide early warning of releases of
   radionuclides from the site. Parameters and sampling frequencies not specified.
  - Post-operational monitoring program to provide early warning of releases of
   radionuclides from the site. Parameters and sampling frequencies not specified.
   System design is based on operating history, closure, and stabilization of the site.
Ground-water monitoring related to the development of geologic repositories will be
  conducted. Measurements will include the rate and location of water inflow into
  subsurface areas and changes in ground-water conditions.

Ground-water monitoring may be conducted by DOE, as necessary, es part of
  remedial action  programs at storage and disposal  facilities for radioactive
  substances.

Ground-water monitoring requirements are established on a case-by-case basis
  for the land application of wastewater and sludge from sewage treatment plants.
No explicit requirements are established; however, ground-water monitoring studies
  are being conducted by SCS under the Rural Clean Water Program to evaluate
  the impacts of agricultural practices and to design and determine the effectiveness
  of Best Management Practices.
The  statute does not authorize development of regulations for sources. Thus,  any
  ground-water  monitoring conducted  would be the  result of requirement established
  by  a State plan (e.g., monitoring with respect to salt-water intrusion) authorized
  and funded by CZMA.
Ground-water monitoring may be conducted by EPA (or a State) as necessary to
  respond to releases of any  hazardous substance, contaminant, or pollutant
  (as defined by CERCLA).

No monitoring requirements established for pesticide users. However, monitoring
  may be conducted by EPA  in instances where certain pesticides are  contaminating
  ground water?
Ground-water monitoring is specified in  Federal regulations for  geothermal
  recovery operations on Federal lands for a period of at least one year prior to
  production. Parameters and monitoring frequency are not specified.
Explicit  ground-water monitoring requirements  for mineral operations on Federal
  lands  are not  established in Federal Regulations. Monitoring maybe required
  (as permit condition) by BLM.
Although the statute authorizes development of regulations for certain pipelines
  for public safety purposes,  the regulatory requirement focus on design and
  operation and do not provide for ground-water monitoring.
Although the statute authorizes development of regulations for transportation for
  public safety purposes, the regulatory requirement focus on design and
  operation and do not provide for ground-water monitoring.
The statute does not authorize development of regulations for sources.
To obtain background water quality data
and to evaluate whether ground water
 is being contaminated.
                                                                                                                                 To confirm geotechnical and design parameters
                                                                                                                                 and to ensure that the design  of the
                                                                                                                                 geologic repository accommodates actual field
                                                                                                                                 conditions.
To evaluate whether ground water is being
 contaminated.
To characterize a contamination problem and to
select and evaluate the effectiveness of corrective
measures,
To characterize a contamination problem (e g., to
assess the impacts of the situation, to identify or
verify the source(s),  and to select and evaluate the
effectiveness of corrective measures).
To characterize a contamination problem,
To obtain background water-quality data.
(Continued)

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 Table 32. Volume of Water in Casing or Borehole (Driscoll, 1986)
 Diameter Gallons Cubic Feet
 of Casing per foot   per Foot
  or Hole   of Depth   of Depth
    (In)
  Liters  Cubic Meters
per Meter per Meter
of Depth    of Depth
1
1 1/2
2
21/2
3
31/2
4
41/2
5
51/2
6
7
8
9
10
11
12
14
16
18
20
22
24
26
28
30
32
34
36
0.041
0.092
0.163
0.255
0.387
0.500
0.653
0.826
1.020
1.234
1.469
2.000
2.611
3.305
4.080
4.937
5.875
8.000
10.44
13.22
16.32
19.75
23.50
27.58
32.00
36.72
41.78
47.16
52.88
0,0055
0.0123
0.0218
0.0341
0.0491
0.0668
0.0873
0.1104
0.1364
0.1650
0.1963
0.2673
0.3491
0.4418
0.5454
0.6600
0.7854
1.069
1.396
1.767
2.182
2.640
3.142
3.667
4.276
4.809
5.585
6.305
7.069
0.509
1.142
2.024
3.167
4.558
6.209
8.110
10.26
12.67
15.33
18.24
24.84
32.43
41.04
50.67
61.31
72.96
99.35
128.65
164.18
202.68
245.28
291.85
342.52
397.47
456.02
518.87
585.68
656.72
0,509 X 10*
1.142x10*
2.024 x 10*
3.167 x 10*
4J58 x 10*
6,209x10*
8.110x 10"*
10.26x10*
12,67 x1Q*
15.33 x 10*
18.24 x 10*
24,84 x1CH>
32,43x10*
41,04x 10*
50.67 x 10*
61.31 x 10*
72.96 x 10*
99.35 x 10*
1 29,65 X10*
164.18x10*
202.68 x 10*
245,28x10*
291.85x10*
342.52 x 10*
397.41 x 10*
456.02x10*
518.87x10*
585.68 x 10*
656.72 x 10*
 1 Gallon = .785 Liters
 1 Meter = 3.281 Feet
 1 Gallon Water Weighs 8.33 Ibs. = 3.785 Kilograms
 1 Liter Water Weighs 1 Kilogram = 2.205 Ibs.
 1 Gallon per foot of depth = 12.419 liters per foot of depth
 1 Gallon per meter of depth = 12.419 x 10* cubic meters
  per meter of depth
 cost. For an additional discussion of casing diameter, refer to
 the sections entitled "Equipment that the Well Must Accommo-
 date" and "Description and Selection of Drilling Methods."

Casing  Cleaning Requirements
     During  the production of any casing  material,  chemical
 substances are used to assist in the extrusion, molding, machin-
 ing and/or stabilization of the casing material. For example, oils
 and solvents  aee used in many phases of steel casing production.
 In the manufacturing of PVC well casing, a wax layer can
 develop on the inner  wall of the casing additionally, protective
 coatings of natural or synthetic waxes, fatty acids or fatty acid
 esters may be added to enhance the durability of the casing
 (Barcelona et al, 1983). These substances are potential sources
 of chemical  interference and therefore must be removed prior
 to installation of the casing in the borehole.  If trace amounts of
 these materials still adhere to the casing after  installation, the
 chemical integrity  of samples taken from the monitoring well
 can be affected.

     Careful  pre-installation cleaning of casing materials  must
 reconducted  to avoid potential  chemical interference problems
 from the  presence of substances such as cutting oils,  cleaning
 solvents,  lubricants, threading compounds, waxes and/or other
 chemical residues. For PVC, Curran and Tomson (1983) sug-
 gest washing the casing with a strong detergent solution and
 then rinsing with water before installation. Barcelona et al.
 (1983) and Barcelona (1984) suggest this same procedure for
 all casing materials. To accomplish the  removal of some cutting
 oils, lubricants or  solvents, it may be necessary to steam-clean
 casing materials or employ  a high-pressure hot water wash.
 Casing materials must also be protected from contamination
 while they are on-site awaiting installation in the borehole. This
 can be accomplished by providing a clean storage area  away
 from any potential contaminant sources (air, wafer or soil) or by
 using  plastic sheeting spread on the ground for temporary
 storage adjacent to the work  area. An additional discussion on
 decontamination of equipment can be  found in the section
 entitled, "Decontamination.  "

 Casing Cost
     As Scalf et al. (1981) point out, the  dilemma  for the field
 investigator often is the relationship between cost and accuracy.
 The relative cost of PVC is approximately one tenth the cost  of
 fluoropolymer materials. Cost is  always a consideration for any
 ground-water monitoring project and becomes increasingly
 important as the number  and/or depth of the wells increases.
 However, if the particular components of interest in a monitoring
 program are also components of the casing, then the results that
 are potentially attributable to the casing will be suspect.  If the
 contaminants to be determined are already defined  and they do
 not include chemical constituents that could potentially  leach
 from or sorb onto PVC well casing (as defined by laboratory
 studies), it may be possible to use PVC as a less expensive
 alternative to other materials.

Monitoring  Well Intakes
    Proper design of a hydraulically efficient monitoring well
 in unconsolidated geologic materials  and in  certain types  of
poorly-consolidated geologic materials  requires  that a well
 intake  be placed opposite the zone to be monitored. The  intake
 should be surrounded by materials that are  coarser have a
uniform grain size; and have a higher permeability  than natural
formation material. This allows ground water to flow freely into
the well from the adjacent formation material while minimizing
or eliminating the entrance of fine-grained materials (clay, silt,
 fine sand) into the well. When the well is properly designed and
developed, the well can provide  ground-water  samples that are
free of suspended solids. Sediment-free water reduces the
potential for interference in sample analyses and eliminates or
reduces the need for field sample filtration.

    These purposes can be accomplished  by designing the well
in such a way that either the natural coarse-grained formation
materials or artificially introduced coarse-grained materials, in
conjunction with appropriately sized intake (well semen) open-
ings, retain the fine materials outside the well while  permitting
water to enter (United States Environmental Protection Agency.
 1975).  Thus, there are two types of wells and well intake designs
for wells installed in unconsolidated or  poorly-consolidated
geologic materials naturally developed wells and wells with an
artificially introduced filter pack. In both types of wells, the
objective of a filter pack is to increase the  effective diameter of
the well and to surround the well intake  with  an envelope of
relatively coarse material of greater permeability  than the
natural  formation materiaL

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                     Schedule 5
                   (Stainless Steel)
 Schedule 10
(Stainless Steel)
    Schedule 40
(Stainless Steel, PVC,
   Fluorooplymer}
   Schedule 60
(PVC, Fluoropolymer)

Wall Thickness (Inches)
Nominal 2
Nominal 3
Nominal 4
Nominal 5
Nominal 6
Inside Diameter
Nominal 2
Nominal 3
Nominal 4
Nominal 5
Nominal 6

Sch 5
0.066
0.063
0.083
0.109
0.109
Sch 5
2.245
3.334
4.334
5.345
6.407

Sch 10
0.109
0.120
0.120
0.134
0.134
Sch 10
2.157
3.260
4.260
5.285
6.357

Sch 40
0.164
0.216
0.237
0.258
0.280
Sch 40
2.067
3.068
4.026
5.047
6.065

Sch 80
0.218
0.300
0.337
0.375
0.432
Sch 80
1.939
2.900
3.826
4.813
5.761
Outside Diameter
(Standard)
2.375
3.500
4,500
5.563
6.625






Figure 53. Effect of casing wall thickness on casing Inside and outside diameter.
    In the construction of a monitoring well it is imperative that
the natural stratigraphic setting be distorted as little as possible.
This requires that the development of void space be minimized
in unconsolidated formations. As a consequence, boreholes that
are over-sized with regard to the casing and well intake diam-
eter generally should be filter-packed. For example, where 2-
inch diameter screens are installed in hollow-stem auger bore-
holes an artificial filter pack is generally recommended.  This
prevents the collapse of the borehole around the screen with the
subsequent creation of void space and the loss of stratification
of the formation.  Collapse also frequently results  in the failure
of well seals emplaced on top of the  collapsed zone, although
well development prior to seal installation may help to minimize
this potential problem.

Naturally-Developed  Wells
    In  a naturally-developed well,  formation materials are
allowed to collapse around the well  intake after it has  been
installed in  the borehole. The high-permeability envelope of
coarse materials is developed adjacent to the well intake in situ
by removing the  fine-grained materials from natural formation
materials during the well development process.

    As described in Driscoll  (1986), the envelope of coarse-
grained, graded material created around a well intake  during the
development process can be visualized as a series of cylindrical
zones. In the zone  adjacent to the well screen, development
removes particles smaller than the screen openings leaving
only the coarser material in place.  Slightly farther away, some
medium-sized grains remain mixed with  coarse materials.
                  Beyond that zone, the material gradually grades back to the
                  original character of the water-bearing formation. By creating
                  this succession of graded zones around the screen, development
                  stabilizes the formation  so that no further movement of fine-
                  grained materials will take place and the well will yield sedi-
                  ment-free water at maximum capacity (Figure 54).

                      The decision on whether or not a well can be naturally
                  developed is generally based on geologic conditions, specifi-
                  cally  the grain-size distribution of natural formation materials
                  in the monitored  zone. Wells can generally be naturally devel-
                  oped  where formation materials are relatively coarse-grained
                  and permeable. Grain-size distribution is determined by  con-
                  ducting a  sieve analysis of a  sample or samples taken from the
                  intended screened interval. For this reason, the importance of
                  obtaining accurate formation samples cannot be overempha-
                  sized.

                      After the sample(s)  of formation material is sieved, a plot
                  of grain size versus cumulative percentage of sample retained
                  on each sieve is made (Figure 55). Well intake opening sizes are
                  then selected, based on this grain size distribution and specifically
                  on the effective size and uniform it y coefficient of the formation
                  materials.  The effective size is equivalent to the sieve size that
                  retains 90 percent (or passes 10 percent) of the formation
                  material (Figure  56); the uniformity coefficient is the ratio of
                  the sieve size that will retain  40 percent (or pass 60 percent) of
                  the formation material to the effective size (Figure 57). A
                  naturally-developed well can be considered if the effective
                  grain  size  of the formation material is greater than 0.01 inch and
                  the uniformity coefficient is  appropriate.
                                                            87

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                                                        Zone of
                                                        Coarsest
                                                        Natural
                                                        Material
    Zone of
    Medium-sized
    Granular
    Material
                                                      Original
                                                      Material of
                                                      Water-
                                                      bearing
                                                      Formation
        • • v^^u j^ w • ** •  -j™**^^
Figure 54. Envelope of coarse-grained material crested around a naturally developed well,
    In monitoring well applications, naturally-developed wells
can be used where the maximum borehole diameter closely
approximates the outside diameter of the well intake. By
maintaining a minimum space between the well casing and the
borehole face,  the disturbance of natural stratigraphic condi-
tions  is minimized. If these conditions are not observed, the
radius of disturbance reduce-s the probability y that ambient flow
conditions can  be restored.

Artificially  Filter-Packed Wells
    When the natural formation materials  surrounding the well
intake are deliberately replaced by coarser, graded material
introduced from the surface,  the well is artificial y filter packed.
The term "grovel pack" is also frequently used to describe the
artificial material added to the borehole to act as a filter.
Because the term "gravel" is classically used to describe large-
diameter  granular material and because nearly  all  coarse mate-
rial emplaced  artificially  in wells is an engineered blend of
coarse to medium  sand-sized material, the-use of the terms
"sand pack" or "filter pack" is preferred in this document.
Gravel-sized particles are  rarely used as filter pack material
because gravel does not generally serve  the intended function
of a filter pack in a monitoring well.

    The artificial introduction of coarse, graded material into
the annular space between a centrally-positioned well intake
and the borehole serves a variety of purposes. Similar to
naturally-developed filter pack, the primary purpose of an
artificial filter pack is to work in conjunction with the well
intake to filter out fine materials from the formation adjacent to
the well.  In addition, the  artificial filter pack stabilizes  the
borehole  and minimizes settlement of materials above the well
intake. The introduction of material coarser than the natural
formation materials also results in an increase in the effective

-------

o
100
90
80
70
60
50
40
30
20
10
\
	 ^









^
\
\
\










\
\










\










^



















=s>_































           Slot Opening and Grain Size, Thousandths of an Inch
Figure 55. Plot of grain size versus cumulative percentage of
          sample retained  on slew.

diameter of the well  and in an accompanying increase in the
amount of water that flows toward and into the well (Figure 58).

     There are several geologic situations where the use of an
artificial filter pack material is recommended:

     1)   when the natural formation is uniformly  fine-
         grained  (i.e.,  fine  sand  through  clay-sized
         particles);
     2)   when a long screened interval is required rind/or
         the intake spans highly stratified geologic  materials
         of widely varying grain sizes;
     3)   when the formation in which the  intake will be
         placed is a poorly cemented (friable) sandstone;
     4)   when the formation is a fractured or solution-
         channeled rock in which  particulate matter is
         carried through fractures or solution openings;
     5)   when the formation is shales or coals that will act
         as a constant supply of turbidity to any ground-
         water samples; and
     6)   when the diameter of the borehole is significantly
         greater than the diameter of the screen.

     The use of an artificial filter pack in a fine-grained geologic
material allows the intake opening (slot) size to be considerably
larger than if the intake were placed in the formation material
without the filter pack. This is particularly true where silts and
clays predominate  in the zone of interest and where fine
opening sizes in well  intakes to hold  out formation materials are
either impractical or not commercially available. The  larger
intake opening size afforded by artificial filter pack emplace-
ment thus allows for the  collection of adequate volumes of
sediment-free samples and results in both decreased head  loss
and increased well efficiency.
    Filter packs are particularly well-suited for use in exten-
sively  stratified formations where thin layers of fine-grained
materials alternate with coarser materials. In such a geologic
environment, it is often difficult to precisely determine the
position and thickness of each individual stratum and to choose
the correct position and opening size  for a well  intake. Complet-
ing the well with an artificial filter  pack, sized and graded to suit
the freest layer of a stratified sequence, resolves the latter
problem and increases the possibility that the well will produce
water free of suspended  sediment.

    Quantitative criteria exist with which decisions can be
made concerning whether  a natural or an artificial  filter pack
should be used in a well (Campbell  and Lehr, 1973; United
States  Environmental Protection Agency,  1975; Willis, 1981;
Driscoll, 1986). Generally the use of an artificial filter pack is
recommended where the  effective grain size of the natural
formation materials is  smaller than  0.010 inch and the unifor-
mity coefficient is less than 3.0.  California Department of
Health Services (1986) takes  a different approach and suggests
that an artificial filter pack be employed if a sieve analysis of
formation materials indicates  that  a  slot size of 0.020 inches or
less is required to retain 50 percent of the natural material.

    Economic considerations may also affect decisions con-
cerning the appropriateness  of an  artificial filter pack. Costs
associated with filter-packed wells are generally higher than
those associated with naturally  developed wells, primarily
because specially graded and washed sand must be purchased
and transported to the site. Additionally, larger boreholes are
necessary for  artificially filter-packed wells  (e.g., suggested
minimum 6-inch diameter borehole  for a 2-inch inside diameter
well or 8-inch borehole for a 4-inch well).

     An alternate design  for the artificial filter  pack  is provided
by the "pre-packed" well intake. There are two basic designs
that are commercially  available: 1) single-wall prepack and 2)
double-wall prepack. The  single-wall prepack is fabricated by
bonding well-sorted siliceous grains onto a perforated pipe
base. Epoxy-based bonds have been the most  commonly used,
although other types of bonding materials  have also been
employed. The double-wall  prepack consists of an unbonded
granular layer of well-sorted silica grains between two perfo-
rated casings. The advantage of the double-wall system is that
it is extremely strong  and should not have chemical  questions
from bonding  agent used in  single  wall.

     The advantages of prepack well intakes are: 1) ease of
installation in either a  stable borehole or within boreholes
protected by auger flights or casing (by the pullback method)
and 2) the ability if properly  sized to provide filtrat.ion of even
the finest formations,  thereby effectively  minimizing turbidity
in otherwise "difficult if not impossible to develop formations."
The disadvantages of this type of well intake are 1) the bonding
material for the single-wall design may create chemical inter-
ference; 2) wells with prepack screens are difficult to redevelop
if plugging occurs; and 3) commercial availability of this design
has been extremely variable through time.  The single-wall
epoxy-based well intake is presently available only on an
 import bases the double-wall well  intake  is currently available
from at least one domestic manufacturer.
                                                            89

-------
           100,


           90


           80


            7C


            6C
        I   5°

        I
        g>   4C
                                              U. S. Standard Sieve Numbers
                                       i        16            12
        o
      30
            20
            10

  The Effective Size of This Sand is
  0,018-inch
1100


 30



 80


 70


 60


 50


 40



 30



 20


 10


 0
                            2(     30     40     >0     60

                                   Slot Opening and Grain Size, in Thousandths of an Inch
Figure 56. Determining effective size of formation materials.

Filter Pack Design —
    Artificial filter pack design factors for monitoring wells
include:  1) filter pack grain size; 2) intake opening (slot) size
and length; 3) filter pack length, 4) filter pack thickness and 5)
filter pack material type. When an artificial filter pack is
dictated by sieve analysis or by geologic conditions, the filter
pack grain sizes and well intake  opening sizes are generally
designed as a single  unit,

    The selection of filter pack grain size and well intake
opening size is a function of the formation. The filter pack is
designed first because it is the interface with the aquifer. The
first step in designing the filter pack is to obtain samples of the
formation intended to be monitored and perform sieve  analyses
on the  samples. The filter pack material size is then selected on
the basis of the finest formation materials present.

    Although design techniques vary, all use the filter pack
ratio to establish size differential between  the formation mate-
rials and filter pack materials. Generally this ratio refers to
either the average (50 percent retained) grain size of the forma-
tion material or the 70 percent retained size of the formation
material. For example, Walker (1974) and Barcelona et al.
(1985a) recommend using a uniform filter pack grain size that
is 3 to 5 times the 50 persent retained size of the formation
materials. Driscoll (1986) recommends a more conservative
approach by suggesting  that for fine-grained formations, the 50
percent retained size of the finest formation sample be multi-
plied by a factor of 2 to exclude the entrance of fine silts, sands
and clays into the monitoring well. The United States Environ-
mental Protection Agency (1975) recommends that filter  pack
grain size be selected by multiplying the 70 percent retained
grain size of the formation materials by a factor between 4 and
6. A factor of 4 is used if the formation is fine and uniform; a
factor of 6 is used if the formation is coarser and non-uniform.
In both cases, the uniformity coefficient  of the filter pack
materials should not exceed 2.5 and the gradation of the filter
material should form a smooth and gradual  size distribution
                                                            90

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                                           U.S. Standard Sieve Numbers
         too
    &
    1
    o

    I

    1
    JS
     o
           8C
          70
          60
5C
4C
           3C
           2C
           1C
                           \
                                                    The Uniformity CoefficierrtfofllHriis
                                                    Sand Is:
                                                    0.026-Inch
                                                    0.010-Inch
                                                                        . = 2.6
100


 90


 80


 70


 60



 50


 40


 30


 20


 10


  0
                    10      20      30     40      50      60     70     80     90     100

                                    Slot Opening and Grain Size, in Thousandths of an Inch
                                                                                 110
                                                                                        120
                                                                                               130
Figure 57. Determining uniformity coefficient of formation matarials.
Formation Materia
Filter Pack
Material
* • ' *' *
* ** • . *
* .'. • *•




















* " • * '
4 - *
. L
• ; i •*
                                                     Borehole
Figure 58. Envelope of coarse-grained material emplaced
          around an artificially flter-packed well.
                                                    when plotted (Figure 59). The actual filter pack used should fall
                                                    within the area defined by these two curves.  According to
                                                    Williams  (1981), in uniform formation materials, either ap-
                                                    proach to filter pack material sizing  will provide  similar results;
                                                    however  in coarse, poorly sorted formation  materials, the
                                                    average grain size method may be misleading  and should be
                                                    used with discretion.

                                                        Two types of artificial filter packs are possible for use in
                                                    production wells: 1) the uniform, well-sorted grain size filter
                                                    pack and  2) the graded grain-size  filter pack.  Uniform filter
                                                    packs are  generally preferred to graded packs for monitoring
                                                    wells. Graded packs are more susceptible to the invasion of
                                                    formation  materials at the formation-filter pack  interface.  This
                                                    invasion results in a partial filling of voids between grains and
                                                    a concomitant reduction in permeability. Graded packs are also
                                                    difficult to install in the limited annular space  available without
                                                    segregation of the filter pack material. With a uniform filter
                                                    pack, the fine formation materials can travel between the grains
                                                    of the pack and be pulled into the well during development.
                                                    When this occurs, the formation permeability  is increased and
                                                    the high permeability of the filter pack is also retained.
                                                            91

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               100
                90
                80
                70
            a
            "5   60
            cr
                    IOC
                                        U.S. Standard Sieve Numbers
                                        16	
O-
§
•a
JS
i
o
                50
               40
                30
                20
                10
         Formation
         Gradate
                                         Filter Pack Ratio = 4
                                          iniformitv Coefficient = 2.1
                                        Uniformity Coefficient = 2.5
                                        Filter Pack Ratio = 4 to 6
                                        D70 « 0.014 Inch
                                                                                         Filter Pack Ratio = 6
                                                                                       Uniformity Coefficient
                                                                                           =  2.1
                                                                                                               100
                                                                                                              90
                                                                                                              90
                                                                                                              70
60
                                                                                                              50
                                                                                                              40
                                                                                                              30
                                                                                                              20
                                                                                                              to
                         10     20     30    40    50    60    70    80    90    100

                                        Slot Opening and Grain Size, in Thousandths of an Inch
                                                                                             110   120  130
Figure 59. Artificial filter pack design criteria.
     The size of well intake openings can only be selected after
the filter pack grain size is specified. The opening (slot) size is
generally chosen on the basis of its ability to hold back between
85 percent and 100 percent of  the filter pack materials (United
States Environmental Protection Agency, 1975) (Figure 60).

Filter Pack Dimensions —
     The filter pack should generally extend from the bottom of
the well intake to approximately 2 to 5 feet above the top of the
well intake provided the interval above the well intake does not
result in cross-connection with an overlying zone. If cross-
connection is a potential problem, then the design may need to
be adjusted. The filter  pack placed  above the intake allows for
settlement of the filter pack material that occurs during well
development and allows a sufficient "buffer" between the well
intake and the annular seal above.

     The filter pack must be at least thick enough to surround the
well intake completely but thin enough to minimize resistance
                                                  caused by the filter pack to the flow of water into the well during
                                                  development. To accommodate the  filter pack, the well intake
                                                  should be centered in the borehole and the annulus should be
                                                  large enough and approximately symmetrical  to preclude
                                                  bridging and irregular placement of filter pack  material. A
                                                  thicker filter pack neither increases the yield of the well nor
                                                  reduces the amount of fine material in the water flowing to the
                                                  well (Ahrens, 1957). Most references in the literature (Walker,
                                                  1974;  United States Environmental Protection Agency, 1975;
                                                  Williams, 198  1; Driscoll,  1986)  suggest that a filter pack
                                                  thickness of between 3 and 8 inches is optimum for production
                                                  wells.  A thin filter pack is preferable from the well-develop-
                                                  ment perspective, because it is difficult to develop a well  with
                                                  a thick filter pack. Conversely, it is difficult to reliably construct
                                                  a well with a filter pack that is less than 2 inches thick.
                                                  Monitoring well filter pack thicknesses  are commonly  sug-
                                                  gested to be at least 2 to 4  inches. Methods to calculate the
                                                  volume of filter pack necessary are contained in Appendix  A in
                                                  the section entitled "Installation  of the Filter Pack."
                                                            92

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                                               U.S. Standard Sieve Numbers
                    1007050  40  30  20         16          12:
               100
                                                                                   D?0 Formation = 0.014
                                                                                   Dj0 Fiiter Pack - 0.071
                                                                                   Filter Pack Ratio = 5
                                                                                   Uniformity Coefficient of
                                                                                    Filter Pack.-1.3
                                                                                   Recommended Scrsen
                                                                                    Slot Opening » - 060 in.
                                                                                    (60 SlotJ
                                              1100


                                                90


                                                80


                                                70


                                                60


                                                BO


                                                40


                                                30


                                                20


                                                10


                                                 0
                                20    30     40    50     60    70     80    90     100   110   120

                                   Slot Opening and Grain Size, in Thousandths of an Inch
                                           130
Figure 60. Selecting well intake slot size based on filter pack grain size.
Filter Pack Materials —
    The materials comprising the filter pack in a monitoring
well should be chemically inert to alleviate the potential for
alteration of ground-water sample  chemical  quality. Barcelona
et al.  (1985b) suggest that the filter pack materials should be
composed primarily of clean quartz sand or glass beads. The
individual grains of the filter pack materials should be well-
rounded and consist of less than 5 percent non-siliceous mate-
rial (Driscoll, 1986). For natural materials, well rounded quartz
is preferred because quartz is noneactive in nearly all ground-
water conditions and is generally available. A filter pack
comprised of other types of crushed stone should not be used
because of potential chemical alteration of ground water and
problems from non-rounded material. If crushed limestone is
used, the alterations may  be particularly signifcant and pH
modifications can be expected. Shale and carbonaceous mate-
rial should also be avoided.

Well Intake Design
    Monitoring well intake design factors include 1) intake
opening (slot) size, 2) intake length, 3) intake type and 4)
corrosion and  chemical  degradation resistance. Proper sizing of
monitoring well intake  openings is one of the most important
aspects of monitoring well  design.  There has been  in the pasta
tendency among some monitoring well designers to install a
"standard" or common slot size (e.g., 0.010 inch slots) in every
well, with no  site-specific  design considerations.  As Williams
(1981) points out, this can lead to difficulties with well devel-
opment, poor well performance or, in some severe cases, well
failure.

Well Intake  Opening Sizes —
    For artificially filter packed wells, the well intake opening
sizes  are selected as previously  discussed and illustrated in
Figure 60. For naturally packed wells, well intake opening sizes
are generally selected based on the following criteria that were
developed primarily for production wells:

    1)  where the uniformity coefficient of the formation
        material is greater than 6 and the material above
        the intended screened interval is non-caving, the
        slot size should be that which retains no less than
        30 percent of formation material;
    2)  where the uniformity coefficient of the formation
        material is greater than 6 and the material above
        the intended screened interval is readily-caving,
        the slot size should be that which retains no less
        than  50 percent of formation material;
    3)  where the uniformity coefficient of the formation
                                                           93

-------
        material is less than 3 and the material above the
        intended screened interval is non-caving, the slot
        size should be that which retains no less than 40
        percent of formation material
    4)  where the uniformity coefficient of the formation
        material is less than 3 and the material above the
        intended screened interval is readily-caving, the
        slot size should be that which retains no less than
        60 percent of formation material; and
    5)  where an interval to be monitored has layered
        formation material  of differing  sizes  and
        gradations, and where the 50 percent grain size of
        the coarsest layer is less than 4 times the 50
        percent size of the finest layer, the slot size should
        be selected on the basis of the finest layer.
        Otherwise, separate screened sections should be
        sized for each zone.

    Because these criteria were developed for production wells,
those factors that enhance yield are overemphasized.  The
objective of a monitoring well is frequently to obtain a water
quality sample that is  representative  of the in-situ ground-water
quality. Hence it  is imperative to minimize disturbance or
distortion of flow  lines from the aquifer into the well. To
achieve this objective, construction activities that result in
caving, void space or modification of the stratigraphy in the
vicinity of the wellbore must be avoided or minimized, Proce-
dures for attaining this objective have been discussed in this
chapter in  the  section entitled "Naturally-Developed Wells"
and in Section 4 in the part entitled "Ability of Drilling Tech-
nology to Preserve Natural Conditions."

    The slot size determined from  a sieve analysis is seldom
that of commercially  available screen slot sizes (Table 33), so
the nearest  smaller standard slot size is generally used. In most
monitoring wells, because optimum yield from the well is not
as critical to achieve  as it is in production wells and because
extensive development is more difficult to accomplish in small-
diameter monitoring wells, screens are usually designed to have
smaller openings than indicated by the above-stated design
criteria so that less formation material will be pulled into the
well during the development.

Well Intake Length Selection —
    The selection of the length of a monitoring well intake
depends on the purpose of the well. Most monitoring wells
function as both ground-water sampling points  and piezometers
for a discrete interval. To accomplish  these objectives,  well
intakes are typically 2 to 10 feet in length, and only rarely equal
or exceed 20 feet in length. Shorter intakes provide more spe-
cific  information  about vertically-distributed  water quality,
hydraulic head and  flow in the monitored formation. However,
if the objective of the  well' is to monitor for the gross presence
of contaminants in an aquifer, a much longer screen can be
selected to monitor a greater thickness of the aquifer.  This type
of well can provide an integrated water sample and an inte-
grated hydraulic head measurement as well as access for
vertical profiling.

    There  are also situations where the "flow-through"-type
well  is preferable. In a flow-through installation, a small-
diameter semen of 2 inches diameter or less, is installed to  fully
penetrate an aquifer, or to at least penetrate a significant portion
of the aquifer. The diameter of the screen is small so that
minimal distortion of the flow field in the aquifer is created.
Borehole geochemical profiling is used to evaluate  vertical
variations in contaminant flow; spot sampling can be used to
provide zone characterization with minimal vertical mixing. By
slowly lowering a geochemical probe into the borehole, mea-
surements of parameters such as pH, Eh,  conductivity, dis-
solved oxygen and temperate can be taken at close intervals
(e.g. 1-foot, 2-foot  or 5-foot intervals). These measurements
can be recorded successively from the top of the saturated zone
to the bottom of the  screened interval with very slight disturbance
to the zone being measured. Measurements are taken as the
probe is lowered because vertical mixing in the borehole can be
expected to occur as the probe is withdrawn.

    Once sufficient time has passed after sampling for indig-
enous conditions to be reestablished, a grab sampler can be
lowered to the uppermost zone of interest and a water quality
sample obtained. By slowly  and carefully sampling successively
deeper zones,  a series of relatively undisturbed water quality
samples  can recollected for laboratory analysis. The  laboratory
results can subsequently  be compared with the data obtained
from the geochemical probe. The method of geochemical
evaluation  is particularly  valuable  for evaluating three-dimen-
sional flow in a stratified but relatively homogeneous aquifer
such as fluvial sands and gravels.

Well Intake  Type —
    The hydraulic efficiency of a well intake depends primarily
on the amount of open area available per unit length of intake.
While hydraulic efficiency is of secondary concern in monitoring
wells, increased open area in monitoring well intakes also
permits easy flow of water from the  formation into the well and
allows for effective well development. The amount of open area
in a well intake is controlled by the type of well intake and
opening  size.

    Many different types  of intakes are available for use in
production wells; several of these are also suitable  for use in
monitoring wells.  Commercially-manufactured well intakes
are recommended for use in monitoring wells because stricter
quality control measures are followed by commercial manufac-
turers. Hand-slotted or drilled casings should not be  used as
monitoring well intakes because there is poor control over the
intake opening size, lack of  open area and potential leaching
and/orchemical problems  at the fresh surfaces exposed by hand
sawing or drilling.  Similarly, casing that has been perforated
either by the application of a casing knife or a perforating gun
after the casing is installed  in the borehole is not recommended
because  intake openings cannot be closely spaced, the percent-
age of open area is low, the  opening  sizes are highly variable and
opening sizes  small enough to control fine materials are diffi-
cult or impossible to produce. Additionally,  perforation tends to
hasten corrosion attack  on metal casing because the jagged
edges  and rough surfaces of the  perforations are susceptible to
selective  corrosion.

    Many commercially-manufactured well intakes  have been
used  in monitoring wells including: 1) the louvered (shutter-
type) intake, 2) the bridge-slot intake, 3) the machine-slotted
well  casing and 4) the  continuous-slot wire-wound intake
(Figure  61). The latter two types of intakes are used most
                                                           94

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Table 33. Correlation Chart of Screen Openings and Sieve Sizes (Driscoll, 1986)
Geologic
Material
Grain-size
Range
Johnson
slot
No.
Gauze
No.

Sieve
No.
Tyler
Size of Openings
Inches mm
Sieve
No.
Openings
Inches
   clay
     &
    silt
   fine
   sand
  medium
   sand
  coarse
   sand
   very
  coarse
   sand
   very
   fine
  gravel
   fine
  gravel
 6
 7
 8
 10

 12
 14
 16

 20
 23

 25
 28
 31
 33
 35
 39

 47
 56
 62
 66
 79

 93
 94
111
125
132

157
187
223
250
263
312
375

438
500
90
80
70
60

50
                           40
                            30
                            20
400
325
270
250
200

170
150
115
100
80
65
60

48
42
35

32
28
           24

           20

           16

           14
           12

           10
           9

           8

           7

           6

           5
           4
          31/2

           3
          21/2
          0.371

          0.441
          0.525
0,0015
0.0017
0.0021
0.0024
0.0029

0.0035
0.0041
0.0049
0.0058
00069
00082
0.0097

0,0116
0.0138
0.0164
0.0180
0.0195
0.0232

00250
0.0276
0.0310
0.0328
0.035
0,039

0.046
0.055
0.062
0.065
0.078

0.093
0.094
0.110
0.125
0.131

0.156
0.185
0.221
0.250
0.263
0.312
0.371

0.441
0.525
0.038
0043
0.053
0.081
0.074

0.088
0.104
0.124
0.147
0,175
0.208
0.246

0.295
0.351
0.417
0.457
0.495
0589

0.635
0.701
0,788
0.833
0,889
0.991

1.168
1.397
1.590
1.651
1.981

2.362
2.390
2.794
3.180
3.327

3962
4.699
5.613
6.350
6.880
7.925
9.423

11.20
13.33
400
325
270
230
200

170
140
120
100
80
70
60

50
45
40

35
30
                                       25

                                       20

                                       18

                                       16
                                       14

                                       12
                                       10

                                       8

                                       7

                                       6

                                       5
                                       4
                                      31/2
                                       114

                                      5/16
                                       3/8

                                      7/16
                                       1/2
   00015
   0.0017
   0.0021
   0.0024
   0.0029

   0.0035
   0.0041
   0.0049
   0.0059
   0.0070
   0.0063
   0.0098

   0.0117
   0.0138
0.0165(1/64)
   0.0180
   0.0197
   0.0232

   0.0250
   0.0280
0.0310(1/32)
   0.0331
   0.0350
   0.0394

   0.0469
   0,0555
 0.062(1/16)
   0.0861
   0.0787

   0.0931
 0.094(3/32)
   0.111
 0.125(1/8)
   0.132

   0.157
 0.187(3/16)
   0.223
 0.250(1/4)
   0.283
 0.31  2(5/1 6)
 0.375(3/8)

 0.438(7/16)
 0.500(1/2)
extensively because they are the only types available with 2-
inch inside diameters,

     'The  lowered, (shutter-type) screen has openings that are
manufactured in solid-wall metal tubing by stamping outward
with a punch against dies  that limit the size of the openings
(Helweg et al,  1984). The number and sizes of openings that
can be made depends on the series of die sets used by individual
manufacturers. Because a complete range of die  sets is imprac-
tical, the opening sizes  of  commercially-available screens are
somewhat limited. Additionally, because of the large blank
spaces that must be left between adjacent openings, the percent-
age of open area on louvered intakes is limited.  Louvered well
intakes  are primarily used  in artificially-packed wells because
the shape  of the louvered openings is such that the shutter-type
                                               intakes are more difficult to develop in naturally-packed wells.
                                               This type of intake, however, provides greater collapse strength
                                               than most other intakes.

                                                   Bridge-slot screen is manufactured on a press from flat
                                               sheets or plates of metallic material that are rolled into cylinders
                                               and seam-welded after being perforated. The slot opening is
                                               usually vertical with two parallel openings longitudinally  aligned
                                               to the well axis. Five-foot sections of bridge-slot screen that can
                                               be welded into longer screen sections if desired  are commonly
                                               available. The advantages of bridge-slot screen include:  a
                                               reasonably high intake opening area, minimal frictional head
                                               losses and low cost. One important disadvantage is low collapse
                                               strength that is caused by the presence of a large number of
                                               vertically-oriented slots. The use of this type of intake is limited
                                                             95

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in monitoring well application because it is only produced in
diameters 6 inches and larger.

    Slotted well intakes are fabricated from standard well
casing by cutting horizontal (circumferential) or vertical (axial)
slots of predetermined widths at regular intervals with machin-
ing tools. Slotted well casing can be manufactured from any
casing material although these intakes are most commonly
made from thermoplastic, fluoropolymer and fiberglass-rein-
forced epoxy materials. This type of intake is available in
diameters ranging from 3/4 inch to 16 inches (National Water
Well  Association and Plastic Pipe Institute, 198 1). Table 34
lists the most common slot widths of slotted well casing.

Table 34. Typical Slotted Casing Slot Widths (National Water
         Well Association and Plastic Pipe  Institute, 1981)
0.006
0.007
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0.025
0.030
0.035
0.040
0.050
0.060
0.070
0.060
0.100
    The continuous slot wire-wound intake is manufactured by
winding cold-drawn wire, approximately  triangular in cross
section, spirally around a circular array of longitudinally  ar-
ranged rods (Figure 62). At each point where the wire crosses
the rods, the two members are securely joined by welding,
creating a one-piece rigid unit (Driscoll, 1986) Continuous-slot
intakes can be fabricated of 1) any metal that can be resistance-
welded, including bronze, silicon red brass, stainless steel (104
and 316), galvanized and low-carbon steel and 2) any thermo-
plastic that can be sonic-welded, including polyvinyl chloride
(PVC) and Acrylonitrile butadiene styrene  (ABS).

    The slot openings of continuous-slot intakes  are produced
by spacing the successive turns of the wire as desired. This
configuration provides significantly greater open area per given
length and diameter than is available with any other intake type.
For example, for 2-inch inside diameter well intake, the open
area ranges from approximately 4 percent for the smallest slot
size (0.006 inch) to more than 26 percent for the largest slot size
(0.050 inch) (Table 35).  Continuous-slot intakes also provide a
wider range of available  slot sizes than any  other type of intake
and have slot sizes that are accurate to within +0.003 inch
(Ahrens, 1970). The slot openings are designated by numbers
that correspond to the width of the opening in thousandths of
an inch. A number 10 slot, for example, refers to an opening of
0.010 inch.

    The continuous-slot intake also is more effective in pre-
venting formation materials from becoming  clogged in the
openings.  The triangular-shaped wire is wound  so that the slot
openings between adjacent wires are V-shaped, with sharp
outer edges the slots are narrowest at the outer  face and widen
inwardly. This makes the intakes non-clogging because par-
ticles slightly  smaller than the openings can pass freely into the
well without wedging in the opening.

 Well Intake Material Properties —
    The intake is the part of the monitoring well that is most
susceptible  to corrosion  and/or chemical degradation and pro-
vides the highest potential for sorption or leaching phenomena
to occur. Intakes have a larger surface area  of exposed material
than casing, are placed in a position designed to be  in contact
with potential contaminants (the saturated zone) and are placed
in an environment where reactive materials are constantly  being
renewed by flowing water. To  avoid corrosion, chemical deg-
radation, sorption and leaching problems,  the  materials from
which intakes are  made are selected using  the same  guidelines
as for casing materials.

Annular Seals

Purpose of the Annular  Seal
    Any annular space that is produced as the result of the
installation of well casing in a  borehole provides a channel for
vertical movement of water and/or contaminants unless the
space is sealed. In any  casing/borehole system, there are several
potential pathways for water and contaminants (Figure 63).
One pathway is through the sealing material. If the material is
not properly formulated and installed or if it cracks or deterio-
Table 35. Intake Areas (Square Inches per Lineal Foot of Screen) for Continuous Wire-Wound Well Intake (After Johnson Screens,
         Inc., 1988)
Screen         6 Slot   8 Slot   10 Slot 12 Slot 15 Slot 20 Slot 25  Slot    30 slot  35 slot 40  slot      50 slot
Size (In.)      (0.006")  (0.008")  (0.010")  (0.012")    (0.015'")  (0.020") (0.025")  (0.030") (0.036") (0.040")     (0.050")
1114 PS*
2 PS
1 1/2 PS
2 PS
3 PS
4 PS
4 Spec**
4112 PS
5 PS
6 PS
8 PS
3.0
3.0
3.4
4.3
5.4
7.0
7.4
7.1
8.1
8.1
13.4
3.4
3.4
4.5
5.5
7.1
9.0
9.7
9.4
10.6
10.6
17.6
4.8
4.8
5.5
6.8
8.8
11.3
11.9
11.7
13.1
13.2
21.7
6.0
6.0
6.5
8.1
10.4
13.5
14.2
13.8
15.5
15.6
25.7
7.0
7.0
8.1
10.0
12.8
16.5
17.2
17.0
19.1
19.2
31.5
8.9
8.9
10.2
12.8
16.5
21.2
22.2
21.9
24,7
25.0
40,6
10.8
10.8
12.3
15.4
20.0
25.8
27,1
26.8
30.0
30.5
49.3
12.5
12.5
14.2
17.9
23.2
30.0
31.3
31.0
34.9
35.8
57.4
14,1
14.1
16.2
20.3
26.5
33.9
35.5
35.2
39.7
40.7
65.0
15.6
15.6
17.9
22.4
29.3
37.7
39,7
39.4
44.2
45.4
72.3
18.4
18.4
20.1
26.3
34.7
44.5
46.8
46.5
52.4
54.3
85.6
The maximum transmitting capacity of screens can be derived from these figures. To determine GPM per ft of screen, multiply the intake area
in square inches by 0.31. It must be remembered that this is the maximum capacity of the screen under ideal conditions with an entrance
velocity of 0.1 foot per second.
* PS means  pip size.
** Spec means  special.
                                                           96

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               Bridge Slot Screen
Shutter-type Screen
Slotted  Casing
  Continuous Slot
Wire-wound Screen
Figure 61. Types of well intakes.
t>
t>
D>
                    N
  Vertical Cross-section
                                    Horizontal  Cross-section
Figure 62. Cross-sections of continuous-wrap wire-wound
           screen
rates after emplacement, the permeability in the vertical direc-
tion can be  significant. These pathways can occur because of
any of several reason&including: 1) temperature changes of the
casing and sealing material (principally neat cement) during the
curing or setting of the  sealing material, 2) swelling  and
shrinkage of the sealing material while curing or setting or 3)
poor bonding between the  sealing material and the casing (Kurt
and Johnson, 1982).  Another pathway may result if sealing
materials bridge in the annular space.  All of these pathways can
be  anticipated and usually avoided  with proper annular  seal
formulation and placement methods.

    The annular seal in a monitoring well is placed above the
filter pack in the annulus between the borehole  and  the well
                      casing. The seal serves several purposes: 1) to provide protec-
                      tion against infiltration of surface water and potential contami-
                      nants from the ground surface down the casing/borehole annu-
                      lus, 2) to seal off discrete sampling zones, both hydraulically
                      and chemically and 3) to prohibit vertical migration of water.
                      Such vertical movement can cause what is referred to as "cross
                      contamination." Cross contamination can influence the repre-
                      sentativeness of ground-water samples and can cause an
                      anomalous hydraulic response of the monitored zone, resulting
                      in distorted data. The annular seal increases the life of the casing
                      by protecting it against exterior corrosion or chemical degrada-
                      tion. A satisfactory annular seal results in complete filling of the
                      annular space and envelopes the entire length of the well casing
                      to ensure that no vertical migration can occur within the
                      borehole. Methods to calculate the volume of sealant necessary
                      to  fill the annular space  are contained in Appendix A in the
                      section entitled "Installation of the Filter Pack." Volume calcu-
                      lations are the  same as those performed to calculate filter pack
                      volume.

                      Materials Used for Annular Seals
                          According to Moehrl (1964), the material used for an
                      annular  seal must:

                          1) be capable of emplacement from the surface
                          2) hydrate or develop sufficient set strength within a
                              reasonably  short  time;
                          3) provide a positive seal between the casing  and  the
                              adjacent formations;
                          4) be chemically inert to formations or fluids with
                              which it may come in contact;
                                                           97

-------
                            a) Between Casing and
                               Seal Material
b) Through Seal Material
c) By Bridging
Figure 63. Potential pathways for fluid movement in the casing-borehole annulus.
    5)  be  permanent, stable and resist  chemical or
        physical deterioration; and
    6)  be sufficiently impermeable to fluids to ensure
        that the vertical permeability of the casing/
        borehole system be lower than that of surrounding
        formations.

    The annular seal may be comprised of several different
types of permanent, stable, low-permeability materials includ-
ing pelletized, granular or powdered bentonite, neat cement
grout and combinations of both. The most effective seals are
obtained by using expanding materials that will not shrink away
from either  the  casing or the  borehole wall after curing or
setting. Bentonite, expanding neat cement or mixtures of neat
cement and bentonite are among the most effective materials
for this purpose (Barcelona et al, 1983; 1985a). If the casing/
borehole annulus is backfilled with any other material (e.g.,
recompaeted, uncontaminated  drill cuttings; sand or borrow
material), a low permeability seal cannot be ensured and the
borehole may then act as a conduit for vertical migration. This
is particularly a problem when  drill cuttings are used as a seal
because recompaeted drill cuttings usually have a higher per-
meability than the natural formation materials from which they
are derived,

Bentonite —
    Bentonite is a hydrous aluminum silicate comprised prin-
cipally of the clay mineral  montmorillonile. Bentonite pos-
sesses the ability to expand significantly when hydrated; the
expansion is caused by the incorporation of water molecules
into the clay lattice. Hydrated bentonite in water typically
expands 10 to 15 times the volume of dry bentonite. Bentonite
forms an extremely dense clay mass with an in-place perme-
ability  typically  in the range of Ixlfr7 to lx!0-* cm/sec when
      hydrated. Bentonite expands sufficiently to provide a very tight
      seal between the casing and the adjacent formation material,
      thus making it a desirable sealant for the casing/borehole
      annulus in monitoring wells.

          Bentonite used for the purpose of sealing the annulus of
      monitoring wells is generally one of two types:  1) sodium
      bentonite or 2) calcium bentonite. Sodium bentonite is the most
      widely used because  of its greater expandability and availabil-
      ity, Calcium bentonite may be preferable in high-calcium
      environments because shrinkage resulting from long-term cal-
      cium-for-sodium  ion exchange is minimized.  Bentonite is
      available in several forms  including pellets, granules and
      powder. Pellets  are uniformly shaped and sized by compression
      of sodium montmorillonite powder. Granules are  irregularly
      shaped and sized particles of sodium montmorillonite. Both
      pellets and granules expand at a relatively  fast  rate when
      exposed to fresh water. The powdered  form of bentonite is the
      form produced by the processing plant after mining. While both
      pelletized and granular bentonite maybe emplaced in dry form,
      powdered bentonite is generally made into a  slurry to  allow
      emplacement.

         Bentonite slurry  is generally prepared by mixing dry ben-
      tonite powder into fresh water in a ratio of approximately 15
      pounds of bentonite to 7 gallons of water to yield 1 cubic foot
      of bentonite slurry.  The bentonite and water are mixed by
      moderate agitation, either manually in a large tank or  with a
      paddle mixer. The use of high-shear mixing equipment in-
      creases the viscosity development of the slurry and can  reduce
      the ultimate working time by as much as 20  percent.  Thick
      bentonite slurries may swell  quickly into non-pumpable  gel
      masses that cannot be emplaced. Pre-mix and/or polymer
      (organic and inorganic) additives delay the  wetting  of the
      bentonite and prevent premature hydration. Where additives
                                                         98

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are used, the additives should be evaluated for potential effects
on extant ground-water quality. Once the slurry is mixed, it
should remain workable for between one-half and two hours.
During this time, a positive displacement mud or grout pump
(typically a centrifugal, diaphragm, piston or moyno-type pump)
is used to emplace the seal at the desired depth.

    Bentonite has a high cation exchange capacity. This high
cation exchange capacity allows  the bentonite to exchange
cations that are part of the chemical structure of the bentonite
(principally Na, Al, Fe and Mn) with cations that exist in the
aqueous solution (e.g., ground water) that hydrates the bento-
nite. The bentonite may take up or release cations from or into
aqueous  solution depending on 1) the chemistry of both the
bentonite and the solution and 2) the pH and redox potential of
the aqueous solution. In addition to having a high cation
exchange capacity, bentonite generally sets up with a moder-
ately high pH between 8.5 and 10.5. Thus, bentonite may  have
an impact on the quality of ground water with which it comes
in contact, In particular, pH and metallic ion content may  be
affected. If a bentonite seal is placed too close to  the top of the
well intake, water-quality samples that are not representative of
the aquifer may be collected. The suggested practice is to place
at least 1 foot of very fine-grained sand on top of the filter pack
and to place the bentonite sealing material 2 to 3 feet above the
top of the well intake, where possible.

    The effective use of bentonite  pellets as a sealing material
depends on  efficient hydration following emplacement. Hydra-
tion requires the presence of water of both sufficient quantity
and quality within the  geologic materials penetrated by the
borehole. Generally, efficient hydration will occur only in the
saturated zone. Bentonitic materials by themselves are gener-
ally not appropriate for use in the vadose zone because suffi-
cient moisture is not available to effect hydration of the bento-
nite. Certain water-quality conditions inhibit the swelling  of
bentonite. For example, bentonite  mixed with water that has
either a total dissolved solids content greater than 500 parts per
million or a high chloride content may not swell to occupy the
anticipated volume and therefore may not provide an effective
seal, The degree of inhibition depends on the level of chlorides
or total dissolved solids in the water. Recent studies conducted
to determine the effects of some organic solvents and other
chemicals (i.e., xylene,  acetone, acetic acid,  aniline, ethylene
glycol, methanol and heptane)  on hydrated clays including
bentonite have demonstrated that  bentonite and other clays may
lose their effectiveness as low-permeability barrier materials  in
the presence of concentrated solutions of selected chemical
substances (Anderson et al, 1982; Brown et al,  1983). These
studies have shown that the hydraulic  conductivity of clays
subjected to high concentrations of organic  acids, basic and
neutral polar organic compounds and neutral non-polar or-
ganic compounds may increase by several orders  of magnitude
due to dessication and dehydration of the clay material.  This
dessication and dehydration can provide conduits for vertical
migration within boreholes in which bentonite is used as sealing
material. Villaume (1985) points  to possible attack on and loss
of integrity of bentonite  seals due to dehydration and shrinkage
of the clay by hydrocarbons in the free product phase. Thus,
where these chemical conditions exist in the subsurface, bento-
nite may not perform as an effective seal and another material
may be necessary.
    In summary, factors that should be  considered in evaluat-
ing the use of bentonite as a sealant include:

     1)   position of the static water level in a given borehole
         (including  seasonal  and other water-level
         fluctuations);
    2)   ambient water quality (particularly with respect
         to total dissolved solids conti'nt and chloride
         content); and
    3)   types and potential concentrations  of contaminants
         expected to be encountered in the  subsurface.

Cement —
    Neat cement is a mixture of Portland cement (ASTM C-
150) and water in the proportion of 5 to 6 gallons of clean water
per bag (94 pounds or 1 cubic foot) of cement. Five general
types of Portland cement are produced: Type I, for general use;
Type II,  for moderate sulfate resistance or moderate heat of
hydration; Type III, for high early strength; Type IV, for low
heat of hydration; and Type V, for high sulfate resistance
(Moehrl,  1964). Of the five types of cement, Type I is the most
widely used in ground-water related work.

    Portland  cement mixed with  water in the above-cited
proportions creates slurry that weighs approximately 14 to 15
pounds per gallon. A typical 14 pounds per gallon neat cement
slurry has a mixed volume of approximately 1.5 cubic feet per
sack and  a set  volume of approximately  1.2 cubic feet volumet-
ric shrinkage is approximately 17 percent and the porosity  of the
set cement approximates 54 percent (Moehrl, 1964), The set-
ting time for such a cement mixture ranges  from  48 to 72  hours
depending primarily  on water content.  A variety of additives
may be mixed with the cement slurry to change the properties
of the cement. The more common additives and associated
effects on the  cement include:

    1)  bentonite (2 percent to 6 percent).  Bentonite
        improves the workability y of the cement slurry,
        reduces the shy weight and density, reduces
         shrinkage as the cement sets and produces  a
        lower unit cost sealing material. Bentonite also
        reduces the set strength of the seal, but this is
        rarely a problem because the seal is seldom subject
        to high stress (Ahrens, 1970);
    2)  calcium chloride (1 percent  to 3  percent). Calcium
        chloride accelerates  the setting  time and creates  a
        higher early  strength;  these  attributes are
        particularly useful  in cold climates. Calcium
        chloride also aids in reducing the amount of slurry
        that enters into zones of coarse material;
    3)  gypsum (3 percent to (percent). Gypsum produces
        a quick-setting, very hard cement that expands
        upon setting. However, the high cost of gypsum
        as an additive limits the use to special operations;
    4)  aluminum powder (less than 1 percent). Aluminum
        produces a strong, quick-setting cement that
        expands on setting and therefore provides a tighter
        seal (Ahrens,  1970);
    5)  fly ash (10 percent to 20 percenfj.Fly ash increases
        sulfate resistance and earl y compressive strength;
    6)  hydroxylated carboxylic  acid.  Hydroxylated
        carboxylic acid retards setting time and improves
                                                           99

-------
                                           MATRIX NUMBER 38
                     General Hydrogeologic Conditions & Well Design Requirements
Consolidated; invasion of formation by drilling fluid permitted; casing diameter 4 to 8 inches.
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grouting is done by filling the annulus from the bottom upward
and 2) that as the grout cures, it gains strength and provides
support to the casing.

    Several methods can  be used to  minimize the heat of
hydration. Adding setting-time retardants. such as bentoniteor
diatomaceous earth, to the grout  mix tends to reduce peak
temperatures. Other approaches include: adding inert materials
such as silica sand to the groui; circulating cool water inside the
casing during grout curing; and increasing the water-cement
ratio of the grout mix (Kurt, 1983). However, increasing the
water-cement ratio of the grout mix results in increased shrink-
age and decreased strength upon setting and more potential to
move beyond where expected or intended before setting.

    Neat cement annular seals are subject lo channeling be-
tween the casing and the seal because of temperature changes
during the curing process; swelling and shrinkage of the grout
while the mixture cures;  and poor bonding between the grout
and the casing surface (Kurt and Johnson, 1982). One method
of ensuring a low-permeability grout seal in a monitoring well
is to minimize the shrinkage of the grout as it cures. Minimizing
shrinkage, lowering permeability and increasing the strength of
cured grout can be accomplished by minimizing water/cement
ratios {Kurt and Johnson,  1982). Typical vertical permeabilities
for  casing/grout systems were found by  Kurt and Johnson
(1982) to range from 20 to 100 x lCrs centimeters per second.
These permeabi 1 ities are higher than those determined for neat
cement grout only. This implies that the presence of casing is a
factor that increases the permeability of the system.

Methods for Evaluating Annular Seal Integrity
    There are presently no fooproof field tests that can be
performed  to determine if a  proper  annular  seal has been
achieved. Of the most commonly used field tests for checking
seals in production wells, only one appears to provide basic
information on the integrity of an annular seal in a monitoring
well—geophysical logging. The accuracy of geophysical log-
ging techniques is often questioned because they are indirect
sensing techniques. The  log most commonly used to cheek a
seal composed of neat cement grout is the cement bond (acous-
tic, sonic) log.  A cement bond log  generally indicates bonded
and non-cemented zones but  cannot detect the presence of
vertical channels within the cement nor  small voids in the
contact area with the casing. Cement bond logs are available for
wells with inside diameters of 2 inches or larger.

    Where thermoplastic or fluorocarbon casing is installed,
there is no sound or sonic wave return recorded along the casing
as is  the case with metallic pipe. As a  consequence,  the
information derived is even more difficult to interpret. Further,
there are no good methods available to evaluate the effective-
ness of bentonite seals. This is an area  in need  of further
research.

Surface Completion and Protective Measures
    Two types of surface completions are common for pound-
water monitoring wells: 1) above-ground completion and 2)
flush-to-pound surfacecompletion. An above-ground comple-
tion is preferred whenever practical, but  a flush-to-ground
surface may be required at some sites. The primary purposes of
either type of completion are to prevent surface runoff from
entering and infiltrating down the annulus of the well and to
protect the well from accidental damage or vandalism.

Surface Seals
    Whichever type of completion is selected for a well, there
should always be a surface seal of neat cement or concrete
surrounding the well  casing and filling the annular space
between the casing and the borehole at the  surface. The surface
seal may bean extension of the annular seal installed above the
filter pack or it may be a separate seal emplaced on top of the
annular seal. Because the annular space near the land surface is
large and the surface material adjacent to the  borehole is
disturbed by drilling activity, the surface seal will generally
extend to at least 3 feet away from the well casing at the surface;
the seal will  usually taper down to the size of the borehole within
a few feet of the surface. In climates with  alternating freezing
and thawing conditions, the cement surface must extend below
the frost depth to prevent potential well damage caused by frost
heaving. A suggested design for dealing with heaving condi-
tions is shown in Figure 21, If cement is mounded around the
well to help prevent surface runoff from pending and entering
around the casing, the mound  should be limited in size and slope
so that access to the well is not: impaird and to avoid frost
heave damage. In some states, well installation regulations
were initially developed for water supply wells.  These  stan-
dards are sometimes now applied to monitoring wells, and these
may require that the cement surface seal extend to depths of 10
feet or greater to ensure sanitary protection of the well.

Above-Ground Completions
    In an above-ground completion,  a protective casing is
generally installed around the well casing by placing the protec-
tive casing into the cement surface seal  while it is still wet and
uncured.  The protective casing discourages unauthorized  entry
into the well, prevents damage by contact with vehicles and
protects PVC casing from degradation  caused by direct expo-
sure to sunlight. This protective casing  should be cleaned
thoroughly prior to installation to ensure that it is free of any
chemicals or coatings. The protective casing should have a
large enough inside diameter to allow easy access to the well
casing and to allow easy removal of the casing cap. The
protective  casing should be fitted with  a  locking cap and
installed so that there is at least 1 to 2 inches clearance between
the top of the in-place  inner well casing cap and the bottom of
the protective casing locking cap when in  the locked position.
The protective casing should be positioned  and maintained in a
plumb position. The protective casing should be anchored
below  frost  depth into the cement surface seal and extend at
least 18 inches above the surface of the ground.

    Like the inner well casing, the outer protective casing
should be vented near the top to prevent the accumulation and
entrapment of potentially explosive gases  and to allow water
levels in the well to respond naturally to barometric pressure
changes.  Additiomlly, the outer protective  casing should have
a drain hole installed just above the top of the cement level in
the space between the protective casing and the well casing
(Figure 21). This  drain allows trapped water to drain away from
the casing. This drain is particularly critical  in freezing climates
where freezing of water trapped between the inner well casing
and the outer protective casing can cause  the inner casing to
buckle  or fail.
                                                        101

-------
    A case-hardened steel lock is generally installed on the
locking casing cap to provide well security. However, corrosion
and jamming of the locking mechanism frequently occurs as the
lock is exposed to the elements. Lubricating the locks or the
corroded locking mechanisms is not recommended because
lubricants such as graphite, petroleum-based sprays, silicone
and others may provide the potential for sample chemical
alteration. Rather, the use of some type of protective measure to
shield the lock from the elements such as a plastic covering may
prove a better alternative.

    In high-traffic areas such as parking lots, or in areas where
heavy equipment maybe working, additional protection such as
the installation of three or more "bumperguards" are suggested.
Bumperguards are brightly-painted posts of wood, steel or
some  other durable material set in cement and located within 3
or 4 feet from the well.

Flush-to-Ground Surface Completions
    In a  flush-to-ground surface completion, a protectivestruc-
ture such as a utility vault or meter box is installed around well
casing that has been cut off below grade. The protective
structure  is typically set into the cement surface seal before it
has cured. This type of completion is generally used in high-
traffic areas such as streets, parking lots and service stations
where an above-ground completion would severely disrupt
traffic patterns or in areas where it is required by municipal
easements or similar restraints. Because of the potential for
surface runoff to enter the below-grade protective structure and/
or well, this type of completion must be carefully designed and
installed. For example, the bond between the cement surface
seal and the protective structure as well as the seal between the
protective structure and removable cover must be  watertight.
Use of art expanding cement that bonds tightly to the protective
structure is suggested. Installation of a flexible o-ring or gasket
at the point where the cover fits over the protective  structure
usually suffices to seal the protective structure. In areas where
significant amounts of runoff occur, additional safeguards to
manage drainage may be necessary to discourage entry of
surface runoff.

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Barcelona, Michael J., John A, Helfrich and Edward E. Garske,
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    PP-
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Curran, Carol M. and Mason B. Tomson, 1983. Leaching of
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Dablow,  John  S. Ill, Grayson Walker  and Daniel  Persico,
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    Division, St Paul, Minnesota, 1089 pp.
Dunbar, D., H. Tuchfeld, R. Siegel and R. Sterbentz,  1985.
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    construction, sampling and analysis in the environs of a
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                                                        102

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Gross, S., 1970. Modem plastics encyclopedia; McGraw-Hill
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Hamilton, Hugh, 1985. Selection of materials in testing and
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Helweg, Otto J., Verne H. Scott and Joseph C. Scalmanini,
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Kurt,  C.E., 1983. Cement-based seals for thermoplastic water
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Kurt, Carl E. and  R.C. Johnson, Jr., 1982. Permeability of grout
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Marsh, J.M. and  J.W. Lloyd, 1990, Details  of hydrochemical
    variations in  flowing wells;  Ground Water, vol. 18, no. 4,
    pp. 366-373.
Miller, Gary D.,  1982. Uptake and release of lead, chromium
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Moehrl, Kenneth  E., 1964. Well grouting and well protection;
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Molz, F.J. and C.E. Kurt, 1979. Grout-induced temperature rise
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    269.
Morrison, R.D., 1984. Ground-water monitoring technology,
    procedures,  equipment  and  applications;  Timco
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National Sanitation Foundation,  1988. National Sanitation
    Foundation Standard 14, Ann Arbor, Michigan, 65 pp.
National  Water Well Association and Plastic Pipe Institute,
    1981. Manual on  the selection  and installation of
    thermoplastic water well casing; National Water Well
    Association,  Worthington, Ohio, 64 pp.
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    no. 3, pp. 92-98.
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    wells; Water Well Journal, vol. 34, no. 4. pp. 90-91.
Ramsey, Robert J., James M. Montgomery and George E.
    Maddox, 1982. Monitoring ground-water contamination
    in Spokane County, Washington; proceedings of the Second
    National Symposium on Aquifer-Restoration and  Ground-
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    Worthington, Ohio, pp.  198-204.
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    halogenated organic compounds by polymer materials
    commonly used in ground water monitors; Proceedings of
    the  Second  Canadian/American Conference  on
    Hydrogeology,  National Water Well Association, Dublin,
    Ohio, pp. 125-132.
Scalf, M.R., J.F. McNabb, W.J. Dunlap, R.L. Cosby and J.
    Fryberger, 1981. Manual of ground-water quality sampling
    procedures,    National Water  Well  Association,
    Worthington, Ohio, 93 pp.
Sosebee,J.B.,P.C.  Gciszler, D.L. Winegardner and C.R. Fisher,
    1983. Contamination  of ground-water samples  with PVC
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                                                        103

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                                                    Section  6
                                    Completion  of Monitoring Wells
Introduction
    Once a borehole has been completed to the desired moni-
toring depth, the monitoring well must be properly installed.
Although monitoring wells can be completed in a variety of
configurations, successful completion of any monitoring well
must  incorporate the following objectives:

     1)   the  well completion  must  permit  specific
         stratigraphic zones to be sampled with complete
         confidence  that  the  sample  obtained  is
         representative of the in-situ water quality;
    2)   the  well completion must permit contaminants
         with differing physical properties to be sampled.
         For example, if the contaminant is denser or
         lighter than water and therefore sinks or floats
         accordingly,  the well completion must allow
         collection  of a representative ground-water
         sample;
     3)   the  well must be constructed to prevent cross
         contamination between different zones. Cross
         contamination can occur if a) the intake and/or
         filter pack spans more than one hydraulic unit,
         b) hydraulic communication between zones occurs
         along the borehole/grout interface, the casing/
         grout interface, or through voids in the seal, c)
         fractures intersect the wellbore, or d) if loosely
         compacted  soils are adjacent to the borehole;
     4)   the  well completion should  minimize any
         disturbance created during the drilling process.
         For example, if the  well was  drilled by hollow-
         stem augers,  the completion  techniques should
         eliminate the void space created by  the withdrawal
         of the augers; and
     5)   the well completion method  should be cost
         effective; sample integrity, of course, is of critical
         importance.

     To  achieve these  objectives, the well  intake, filter pack,
 and annular seal must be installed using appropriate techniques.
 The following discussion addresses these techniques.

 Well Completion Techniques
 Well Intake Installation
     In cohesive unconsolidated material or consolidated for-
 mations, well intakes are installed as an integral part of the
 casing sting by lowering the entire unit into the open borehole
 and placing  the well intake opposite the interval to be moni-
 tored. Centralizing devices are typically used to center the
 casing and intake in the borehole to allow uniform installation
 of the filter pack material around the  well intake. I f the borehole
has been drilled by a technique that creates borehole damage, it
is necessary to develop the borehole wall. When the formation
is sufficiently stable, this development should be undertaken
prior to setting the well intake. After the filter pack has been
installed,  it is very difficult to clean fractures or to remove
mudcake deposits that have been formed on the  borehole wall.
If the borehole was drilled with the mud rotary technique, the
borehole should be conditioned and the wallcake removed from
the borehole wall with clean water prior to the installation of the
well intake, if possible. An additional discussion on well
development is  found in Section 7, entitled "Monitoring Well
Development."

    In non-cohesive, unconsolidated materials when the bore-
hole is drilled by a drill-through casing advancement method,
such as a casing  hammer or  a cable tool technique, the well
intake should be centered inside the casing at the end of the riser
pipe and held firmly in place as the casing is pulled back. When
the well intake is being completed as a natural pack, the  outside
diameter of the well intake should be between  1 and 2 inches
smaller than the  outside  diameter of the casing that is being
retracted. If an artificial filter pack is installed, the outside
diameter  of the well intake should be at least 3 to 5  inches
smaller than the  outside  diameter of the casing that is being
retracted. During artificial filter pack installation, the filter
pack material must be maintained above the lower-most level
of the casing as the casing is removed. This means that the filter
pack is being emplaced  continually during the time that the
casing is being pulled back and the well intake is being exposed.
This procedure minimizes the development of  excessive void
space adjacent to the  well intake as  the casing is pulled back.

     When the casing is installed through the hollow stem of a
hollow-stem auger, an artificial filter pack generally should be
emplaced because of the disparity between the outside diameter
of the auger flights and the usual 2-inch or 4-inch outside
diameter of the casing and well intake that are being installed
within the auger flights.  If the augers are withdrawn and the
formation allowed to collapse around the well intake without
installing  an artificial filter pack to stabilize the borehole wall,
the materials that are adjacent to the well intake maybe loose
and poorly compacted. Excessive void space adjacent to the
well intake can provide an avenue for cross contamination or
migration of contaminants. This void or loosely-compacted
zone may also interfere with the placement of proper seals.

     Loosely-compacted material is difficult to  adequately de-
velop from within a small diameter borehole. The surging
methods  that are available generally cannot  recompact the
materials adjacent to the well intake to prevent bentonite or
cement grout from migrating downward into the screened zone.
                                                           105

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 Additionally, where collapse is permitted, the collapsed zone
 around the well intake is highly disturbed and is no longer
 stratified similar to the stratification of the natural formation.
 As a consequence, there will be mixing of horizontal zones,  and
 the possibility exists that chemical changes can be induced by
 the changes in the physical environment.

     Where wells are installed in unconsolidated material by the
 dual-wall reverse-circulation method, the well casing  and well
 intake are installed through the bit. The only option for comple-
 tion with this construction method is to allow the materials to
 collapse around the screen. In this instance, a greater sustained
 effort is  suggested in well-development  procedures than is
 normally required.

 Filter Pack Installation
     Several methods of emplacing artificial filter packs in the
 annular space of a monitoring well are available, including:
 1) gravity (free fall), 2) tremie  pipe, 3) reverse circulation,  and
 4) backwashing. The last  two methods involve the addition of
 clean water to the filter pack material during emplacement. This
 addition of fluid can cause chemical alteration of the environ-
 ment adjacent to the well and pose long-term questions about
 the representativeness of water samples collected from the well.
 As with  other phases of monitoring well  construction, fluids
 (clean) should only be added when no other practicable method
 exists for proper filter pack emplacement. An additional discus-
 sion on choosing filter pack material size can be found in the
 section entitled "Artificially Filter-Packed Wells."

     Placement of filter packs by gravity or free fall can be
 successfully accomplished only in relatively shallow wells
 where  the probability of  bridging or segregation of the filter
 pack material is minimized. Bridging causes unfilled voids in
 the filter pack and may prevent the filter pack material from
 reaching the intended depth. Segregation of filter pack material
 can result in a well that consistently produces sediment-laden
 water samples. Segregation is  a problem particularly in wells
 with a  shallow static water level. In this situation, the filter pack
 material falls through the column of water at different rates. The
 greater drag exerted on smaller particles due to their greater
surface area-to-weight ratio causes finer grains to fall at a
 slower rate  than coarser  grains. Thus, coarser materials will
 comprise the lower portion of the filter  pack and finer materials
 will constitute the upper part (figure 64). Segregation may not
 be a problem when emplacing truly uniform filter packs  where
 the uniformity coefficient is less than 2.5, but placement by free
 fall is not recommended in any  other situation (Driscoll, 1986).

     With the tremie pipe  emplacement method, the filter pack
 material is introduced through  a rigid tube or pipe via gravity
 directly into the interval adjacent to the well intake (Figure 65).
 Initially, the end of the pipe is  positioned at the bottom of the
 well intake/borehole annulus.  The filter pack material is then
 poured down the tremie pipe and the tremie is raised periodi-
 cally to allow the filter pack material to fill the annular space
 around the well intake. The minimum diameter of a tube used
 for a tremie pipe is generally 1 1/2 inches; larger-diameter pipes
 are advisable for filter  pack materials that are coarse-grained or
 characterized by uniform it y coefficients that exceed 2.5 (Cali-
 fornia Department of Health Services,  1986). When installing
 a  filter pack with a uniformity coefficient greater than 2.5 in
 wells deeper than 250 feet, a variation of the standard tremie
                                          Fine portion
                                          of filter pack
                                         Coarse portion
                                         of filter pack
                                            Well intake
Figure 64. Segregation of artificial filter pack materials caused
          by gravity emplacement.
                                          Sand
       Casing
   Well intake
                                   «\— Tremie  pipe
                                     -  Borehole wall
                                       • Filter pack material
Figure 65. Tremie-pipe emplacement of artificial filter pack
          materials.
                                                             106

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method that employs a pump to pressure feed the materials into
the annulus is suggested by the California Department of Health
Services  (1986).

    In the reverse circulation method, a filter pack material and
water mixture is  fed into the annulus around the well intake.
Return flow of water passes into the well intake and is then
pumped to the surface through the riser pipe/casing (Figure 66).
The filter pack material should be introduced into the annulus
at moderate rate to allow for an even distribution of material
around the well intake. Care must be exercised when pulling the
outer casing so that the riser pipe is not also pulled.

    Backwashing filter pack material into place  is accom-
plished by allowing filter pack material with a uniformity
coefficient of 2.5  or less to fall freely through the annulus while
concurrently pumping clean fresh water down the  casing,
through the well  intake and back up the annulus (Figure 67).
Backwashing is a particularly effective method of filter-pack
emplacement in cohesive, non-caving geologic  materials.  This
method also minimizes the formation of voids that tend to occur
in tremie pipe emplacement of the filter pack.

Annular Seal Installation
    The two principal materials used for annular seals are
bentonite and neat cement. Often a combination of the two
materials is used.  Because the integrity of ground-water  samples
depends on good seals, the proper emplacement of these seals
                                Funner
                          Filter pack
                          material     |£
                          and water   T~
                             Pump
    6" Casing
    (Casing pulled back during"
    filter pack installation)
                Riser pipe


              Centralizsr —
                   Filter pack
                    Well intake

                          Water
   Fine-grained
   materials and
   water
Filter pack
material
     Fine-grained
     materials and
     water
                                              Well intake
 Figure 66. Reverse-circulation emplacement of artificial filter
          pack materials.
Figure 67. Emplacement of artificial filter pack material by
          backwashing.

is paramount. An additional discussion on annular seals can be
found in the section entitled "Annular  Seals.  "

Bentonite —
    Bentonite may be emplaced as an  annular seal in either of
two different forms 1) as a dry solid or 2) as a slurry. Typically
only pelletized or granular bentonite is emplaced dry; powdered
bentonite is usually mixed with water  at the  surface to form a
slurry and then is added to the casing/borehole annulus. Addi-
tional discussion on properties of bentonite can be found in
Chapter 5 in the section entitled "Materials Used For Annular
Seals."

    Dry granular bentonite or bentonite pelletsmay be emplaced
by the gravity (free fall) method by pouring from the  ground
surface. This procedure should only be used in relatively
shallow monitoring wells that are less than 30 feet deep with an
annular space of 3  inches or greater. When the gravity  method
is used, the bentonite should be tamped with a tamping rod after
it has been emplaced to ensure that no bridging of the pellets or
granules has occurred. Where  significant thicknesses of bento-
nite are added, tamping should be done  at selected intervals
during the emplacement process. In deeper wells, particularly
where  static water  levels are shallow, emplacing dry bentonite
                                                            107

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via the gravity method introduces both a very high potential for
bridging and the likelihood that sloughing material from the
borehole wall will be included in the seal. If bridging occurs, the
bentonite may never reach the desired depth in the well; if
sloughing occurs,  "windows" of high  permeability may de-
velop as the sloughed  material is incorporated into the seal.
Either situation results in an ineffective annular seal that may
allow subsequent  contamination  of the well.

    In wells deeper than 30 feet, granular or pelletized bento-
nite can be conveyed from the surface directly to the intended
depth in the annulus by a tremie  pipe.  Pelletized bentonite is
sometimes difficult to work with in small-diameter tremie
pipes; a minimum of 1  1/2-inch inside diameter pipe should be
used with 1/4-inch diameter pellets to minimize bridging and
subsequent clogging of the bentonite inside the tremie pipe.
Larger-diameter tremie  pipes should  be  used with larger-diam-
eter pellets. Where a seal of either pelletized or granular
bentonite must be placed at considerable depth beneath the
water surface, the tremie pipe can  be  kept dry  on the inside by
keeping it under gas pressure (Riggs and Hatheway, 1986). A
dry tremie pipe has a much lower potential for bridging in the
tremie because the material does not have to fall through a
partially water-filled pipe to reach the desired depth.

    Bentonite slurry can bean effective well seal only if proper
mixing, pumping, and emplacement  methods are  used. Bento-
nite powder is generally mixed with water in a batch mixer and
the slurry is pumped under positive pressure through a tremie
pipe down the annular space using  some variety of positive
displacement pump (i.e., centrifugal, piston, diaphragm, or
moyno-type pump). All hoses, tubes,  pipes, water swivels, and
other passageways through which the slurry must pass should
have a minimum inside diameter of 1/2 inch. A larger diameter
(e.g., 1-inch) tremie pipe is preferred.  The tremie pipe should be
placed just above the falter pack  or at the level where non-
cohesive material has collapsed into the borehole (Figure 68).
The tremie pipe should be left  at this position during the
emplacement procedure so that the slurry fills the annulus
                                                 Slurry
                                  Annular seal material
                                   Fitterpack
Figure 68. Tremie-pipe emplacement of annular seal material
          (either bentonite or neat cement slurry).
upward from the bottom. This allows the slurry to displace
ground water and any loose-formation materials in the annular
space. The tremie pipe can be raised as the slurry level rises as
long as the discharge of the pipe remains submerged at least a
foot beneath the top of the slurry. The tremie pipe can be
removed after the slurry has been emplaced to the intended level
in the annulus. The slurry should never be emplaced by free fall
down the annulus. Free fall permits the slurry to segregate thus
preventing the formation of an effective annular seal.

    Bentonite emplaced as a slurry will already have  been
hydrated to some degree prior to emplacement, but the ability
to form a tight seal depends on additional  hydration and
saturation after emplacement. Unless the slurry is placed  adja-
cent to saturated geologic materials, sufficient moisture may
not be available to maintain the hydrated state of the  bentonite.
If the slurry begins to dry out, the seal may dessicate, crack, and
destroy the integrity  of the seal. Therefore, bentonite seals  are
not recommended in the vadose zone.

    Curing or hydration of the bentonite seal material occurs
for 24 to 72 hours after emplacement. During this time, the
slurry becomes more rigid and eventually develops strength.
Well development should not be attempted until  the bentonite
has completely hydrated. Because of the potential for sample
chemical alteration posed by the moderately high pH and high
cation exchange  capacity of bentonite, a bentonite seal should
be placed approximately 2 to 5 feet above the top of the well
intake and separated from the filter pack by a 1-foot thick  layer
of fine silica sand.

Neat Cement —
    As with a bentonite slurry, a neat cement grout must be
properly mixed, pumped, and emplaced to ensure that the
annular seal will be effective. According to the United States
Environmental Protection Agency (1975), neat cement should
only be emplaced in the annulus by free fall when 1)  there is
adequate clearance (i.e., at least 3 inches) between the casing
and the borehole, 2) the annulus is dry, and 3) the bottom of the
annular space to  be filled is clearly visible from the surface and
not more than 30 feet deep. However,  to minimize segregation
of cement even in unsaturated annular  spaces, free fall of more
than 15 feet should not be attempted in monitoring wells. If a
neat cement slurry is  allowed to free fall through standing water
in the annulus, the mixture tends to be  diluted or bridge after it
reaches the level of  standing water and before it reaches the
intended  depth of emplacement. The slurry also may incorpo-
rate material that is sloughed from the borehole wall into the
seal. If the sloughed material has a high permeability y, the
resultant seal can be breached through the inclusion of the
sloughed  material.

    In most situations, neat cement grout should be  emplaced
by a tremie pipe. The annular space must be large enough that
a tremie pipe with a minimum inside diameter of 1 1/2 inches
can be inserted into the  annulus to within a few inches of the
bottom of the space to  be sealed.  Grout may then  either be
pumped through the  tremie pipe or emplaced by gravity  flow
through the tremie pipe into the annular space. The use of a
tremie pipe permits the grout to displace ground water and  force
loose formation materials ahead of the  grout. This positive
displacement minimizes the potential for contamination and/or
                                                          108

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dilution of the slurry and the bridging of the mixture with upper
formation material.

    In pressure grouting, the cement discharges at the bottom
of the annular space and flows upward around the inner casing
until the  annular space is completely filled.  A side discharge
tremie may be used to lessen the possibility that grout might be
forced into the filterpack. Depending on pressure requirements,
the tremie pipe may be moved upward as the slurry is emplaced
or it may be left at the bottom of the annulus until the grouting
is completed. If the tremie pipe is not retracted while grouting,
the tremie pipe should be removed immediately afterward to
avoid the  possibility y of the  grout setting around the pipe. If this
occurs, the pipe may  be difficult to remove and/or a channel
may develop in the grout as the pipe is removed.

    In gravity emplacement, the tremie is lowered to the
bottom of the annular  space and filled with cement. The tremie
pipe is slowly retracted, and the weight of the  column forces the
cement into the  annular space. In both gravity emplacement and
pressure grouting, the discharge end of the tremie pipe should
remain submerged at  least one foot below the surface of the
grout at all times during emplacement, and the pipe should be
kept full of grout without air space. To avoid the formation of
cold joints,  the grout should be emplaced in one continuous
pour before initial setting of the cement or before the mixture
loses fluidity. Curing time required for a typical Type I Portland
cement to reach maximum strength is a minimum of 40 hours.

    Moehrl (1%4) recommends checking the buoyancy force
on the  casing during cementing with grout. Archimedes prin-
ciple states that a body wholly or partially immersed in a fluid
is buoyed up by a force equal to the weight of the fluid displaced
by the body. Failure to recognize this fact may result in
unnoticed upward displacement of the casing during cement-
ing. This is particularly true of lighter thermoplastic well
casings. Formulas for computing  buoyancy are provided by
Moehrl (1964).

Types of Well  Completions
    The ultimate configuration of a monitoring well is chosen
to fulfill specific objectives as stated at the  beginning of this
section. Monitoring wells can be  completed either as single
wells screened  in either short or long  intervals, single wells
screened in multiple zones or multiple wells completed at
different intervals in one borehole. The decision as to which
type of monitoring well configuration to install in a specific
location is based on cost coupled with technical  considerations
and practicality of installation.

    In shallow  installations, it generally is more economical to
complete the monitoring wells as  individual units that are in
close proximity to  each other and avoid the complexity of
multiple-zone completions in a single borehole. In deeper
installations where the cost of drilling is high relative to the cost
of the materials in the  well and where cost savings can be
realized in improved sampling procedures, it may be better to
install  a more sophisticated multilevel sampling device. The
cost of these completions are highly variable  depending on the
specific requirements of the job. Cost comparisons should be
made on a site-by-site basis. Individual well completions will
almost always be more economical at depths of less than 80
feet. A discussion of the types of monitoring well  completions
is presented below.
Single-Riser/Limited-Interval Wells
     The majority of monitoring wells that arc installed at the
present time are individual monitoring wells screened in a
specific zone. Well intakes are usually moderate in length,
ranging from 3 to 10 feet. These wells are individually installed
in a single borehole with a vertical riser extending from the well
intake to the surface. Because the screened interval is short,
these are the easiest wells to install and develop. A typical
example of this design is shown in Figure 21.

     The intent of a well with this design is to isolate a specific
zone from which water-quality samples and/or water levels are
to be obtained. If the well intake crosses more than one zone of
permeability, the water sample that is collected will represent
the quality of the more permeable zone. If a pump is installed
just above the well intake and the well is discharged at a high
rate, the majority of the sample that is obtained will come from
the upper portion of the well intake. If the pump is lowered to
the mid-section of the well intake and pumped at a low rate, the
bulk of the sample will come from the area that is  immediately
adjacent to the zone of the pump intake. At high pumping rates
in both isotropic and stratified formations,  flow lines converge
toward the pump so that the sample that  is obtained is most
representative of the ground water moving along the  shortest
flow lines. If the well is not properly sealed above the well
intake, leakage  may  occur from upper zones into the well
intake.

Single-Riser/Flow-Through Wells
     Flow-through wells consist of a long well intake that either
fully or nearly fully penetrates the aquifer. The well intake is
connected to an individual riser that extends to the surface.
Wells of this type are typically small in diameter and are
designed to permit water in the aquifer to flow through the well
in such a manner as to make the well "transparent" in the
ground-water flow field. An illustration of this type of well is
shown in Figure 69.

     This type of well produces water samples that area com-
posite of the water quality intercepted when the well is surged,
                                   Surface protector

                                  Casing or risar
  Water table
      Ground
      water
      flow
      direction
Well
intake
                                . Bottom cap
       Unconsolidated
       aquifer

                 Bottom
                 of aquifer
 Figure 69. Diagram of a single-riser/flow-through well.
                                                          109

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bailed or pumped heavily. For example, if three or more well
volumes are evacuated prior to sampling, the sample obtained
will be a composite sample representative of the more perme-
able zones  penetrated by the well intake; it will not be possible
to define the zone(s) of contribution. However, if the well is
allowed to maintain a flow-through equilibrium condition and
if a sampler is lowered carefully to the selected sampling  depth,
a minimally  disturbed water sample can be obtained by either
taking a grab sample or by pumping at a very low rate. This
sample will be substantially representative of the zone  in the
immediate vicinity of where the sample was taken.  If the
sampler is  successively  lowered to greater depths and the water
within the well intake is not agitated, a series of discrete samples
can be obtained that will provide a reasonably accurate profile
of the quality of the water that is available in different vertical
zones. Furthermore, if the flow-through condition is allowed to
stabilize after any prior disturbance and a downhole chemical-
profiling instrument is lowered into the well, closely-spaced
measurements of parameters such as Eh, pH, dissolved oxygen,
conductivity and temperature can be made in the borehole. This
provides a geochemical profile of conditions in the aquifer. In
specific settings, wells of this design  can provide water-quality
information that is at least as  reliable as either the information
obtained by multiple-zone samplers in a single well or by
information from multiple nested wells. In either application,
the described flow-through well design is lower in cost.

Nested Wells
    Nested wells consist of either a series of 1) single-riser/
limited-interval wells that are closely spaced so as to provide
data from different vertical zones in close proximity to each
other or 2) multiple single-riser/limited-interval wells that are
constructed in a single borehole. Illustrations of these designs
are shown in Figures 70a and 70b. Wells of these designs are
used to provide samples from different zones of an aquifer(s) in
the same manner as individual wells.

    Multiple wells are  constructed in a single borehole by
drilling a 10-inch or larger diameter borehole, then  setting one,
two, or three 2-inch single-riser/limited-interval wells within
the single borehole.  The deepest well intake is installed first, the
filter pack emplaced, and the seal added above the filter pack.
The filter pack  provides stabilization of the deepest zone. After
the seal is installed above the deepest zone, the next succeeding
(upward) well  intake is  installed and the individual riser ex-
tended to the surface. This next well intake is  filter-packed and
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                                                         Surface seal
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                                                   Screened interval -

                       (a)
                   (b)
Figure 70.  Typical nested well designs: a) series of single riser/limited interval wells in separate boreholes and b) multiple single
           riser/limited interval wells In a single borehole (after Johnson, 1983).
                                                            110

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 a second seal is placed above the filter pack that is emplaced
 around the second well intake. If there is a long vertical interval
 between successive well intakes, neat cement grout is emplaced
 above the lower seal. Where vertical separation permits, a  1-
 foot layer of fine silica sand should be emplaced between the
 filter packs and sealants.  This  sand  helps prevent sealant infil-
 tration into the filter pack and loss of filter pack into the sealant.
 This procedure is repeated at all desired monitoring intervals.
 Because each riser extends to the surface and is separate from
 the other risers, a good seal must be attained around each riser
 as it penetrates through successive bentonite seals. A  substan-
 tial problem with this type of construction is leakage along the
 risers  as well as along the borehole  wall.

     The  primary difficulty with multiple completions in a
 single borehole is that it is difficult to be certain that the seal
 placed between the  screened zones  does not provide a conduit
 that results  in interconnection between previously non-con-
 nected zones within the borehole. Of particular concern  is
 leakage along the borehole wall and along risers where overly-
 ing seals  are penetrated. It is often difficult to get an effective
 seal between the seal (e.g., bentonite or cement grout)  and the
 material of the risers.

 Multiple-Level  Monitoring Wells
     In addition to well nests that sample at multiple levels in a
 single location, a variety of single-hole, multilevel sampling
 devices are available. These sampling devices range from the
simple field-fabricated, PVC multilevel sampler shown, in
Figure 71 to the buried capsule devices that are installed in a
single borehole, as shown in Figure 72. The completion of these
wells is similar to the completion of nested wells in  a single
borehole. Some of these samplers have individual tubing con-
nections that extend to the  surface. Samples are  collected from
the tubing. With some forms of instrumentation, water levels
can also be obtained. There are,  additionally, more sophisti-
cated sampling devices available, such as shown in Figure  73.
These consist of multiple-zone inflatable packers that can be
installed in a relatively  small borehole. They permit the sam-
pling  of formation fluids at many  intervals from within  a single
borehole. Disadvantages of these  devices arc:  1) it is difficult,
if not impossible, to repair the device if clogging occurs, 2) it is
difficult to prevent and/or evaluate sealant and packer  leakage
and 3) these installations are more expensive than single-level
monitoring wells.

    Simple vacuum-lift multiple port devices can be  used in
shallow wells where samples can be obtained from the indi-
vidual tubing that extends to the surface. With increasing depth,
greater sophistication is required and a variety of  gas-lift
sampling devices are available commercially. Still more  so-
phisticated sampling devices are available for very deep instal-
lations.  These devices require durable, inflatable packer sys-
tems and downhole tools to open and close individual  ports to
obtain formation pressure readings and take fluid samples.
These can be used in wells that are several thousand feet deep.
                            Ground
                          Water table
                                           End cap

                                           Male & female
                                        / couplings
                                        '   Surface
                                              PVC pipe
                                      	Coupling
                                           Sampling points
                                           End cap
                                      (a)
                       PVC pipe
                                                                                  — Screen
    One-hole
    rubber
    stopper
                                                                       (b)
Figure 71,  Field-fabricated PVC multilevel sampler: a) field installation and b) cross section of sampling point (Pickens et al., 1981).
                                                            Ill

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        Protective
        casing
         Screened
         interval
                                  Sampling
                                  tube
                                                                                      Backfill
                            Packet
                                                                                    Pumping port coupling
                                                                                    Measurement port coupling
                            End cap
Figure 72. Multilevel capsule sampling device installation
          (Johnson, 1983).

General Suggestions for Well Completions
     I)  Use  formation samples,  sample penetration  logs,
        drilling logs, geophysical logs, video logs and  all
        other pertinent information that can be obtained
        relating to the  well installation to make decisions
        on well completion. Make every attempt to define
        the stratigraphy before attempting to install well
        intakes.
    2)  Be  aware of the control that stratigraphy exerts
        over flow-line configuration when the sampling
        pump is and is not operating. In an isotropic
        aquifer, the sample is representative of the quality
        of formation water in the immediate vicinity of
        the pump. In a fractured system or a stratified
        aquifer, flow can be highly directional and
        confined.
    3)  Install the well intake in the exact zone opposite
        the desired monitoring depth. If the well is designed
        to intercept "floaters," the well intake must extend
        high enough to provide for fluctuations in the
        seasonal water table. If the well is  designed to
        monitor "sinkers" the topography of the bottom-
        most confining layer  must be sufficiently defined
        such that a well intake can  be installed at the
        topographical points where  the sinkers can  be
        intercepted. If there is a non-aqueous phase present,
        the well intake must intersect the  appropriate
        pathways. Vertical variations in hydraulic
        conductivity must be recognized as well  as
        horizontal variations. In consolidated rock,
        fracture zones through which migration can occur
        must be intercepted. At all times, the three-
  Figure 73. Multiple zone inflatable packer sampling installation
           (Rehtlane and Patton, 1982).

          dimensional aspect of contaminant migration must
          be taken into consideration.
      4)   Aquifer  disruption must be minimized during the
          completion process. Void space should not be
          unnecessarily created when pulling back casing
          or augers. Non-cohesive material collapse around
          the well  intake should be minimized except where
          natural filter pack is used.
      5)   The depth and diameter limitations imposed by
          the type of equipment and materials used in
          monitoring well construction must be  considered
          as an integral part of well completion. The filter
          pack must be uniformly emplaced; bentonite and
          cement grout must be emplaced by positive
          methods so that the zones that are supposed to be
          isolated  are truly isolated by positive seals. The
          design and installation of a monitoring well are
          impacted by the constraints of cost, but the errors
          resulting  from a well that is improperly  constructed
          are much more expensive than a well that is
          properly constructed. The extra time and cost of
          constructing a well properly, and being as sure as
          possible that  the information being obtained is
          reliable, is well worth the extra cost of careful
          installation.

 References
  California  Department of Health Services, 1986.  The
      California  site mitigation decision tree manual;  California
      Department  of Health Services, Sacramento,  California,
      375 pp.
  Driscoll, Fletcher G., 1986. Ground water and wells; Johnson
      Division, St. Paul, Minnesota, 1089 pp.
112

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Johnson, Thomas L., 1983. A comparison of well nests versus
    single-well completions; Ground Water Monitoring
    Review, vol. 3, no. 1, pp. 76-78.
Moehrl, Kenneth E., 1964. Well grouting and well protection;
    Journal of the American Water Works Association, vol. 56,
    no. 4, pp.  423-431.
Pickens, J.F., J.A. Cherry, R.M. Coupland, G.E. Gnsak, W.F.
    Merritt and B.A. Risto, 1981. A multilevel device for
    ground-water sampling; Ground Water Monitoring
    Review, vol. 1, no. 1, pp. 48-51.
Rehtlane, Erik A. and Franklin D. Patton, 1982. Multiple port
    piezometers vs. standpipe piezometers: an economic
    comparison;  Proceedings of the  Second National
    Symposium on Aquifer Restoration and Ground-Water
    Monitoring, National Water  Well  Association,
    Worthington, Ohio, pp. 287-295.
Riggs, Charles 0. and Allen W. Hatheway, 1988. Groundwater
    monitoring field practice - an overview; Ground-Water
    Contamination Field Methods, Collins and Johnson editors,
    ASTM  Publication  Code Number 04-963000-38,
    Philadelphia, Pennsylvania, pp. 121-136.
United States Environmental Protection Agency, 1975.
    Manual of water well construction practices; United States
    Environmental Protection Agency, Office of Water Supply,
    EPA-570/9-75-001,156pp.
                                                      113

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                                                    Section 7
                                      Monitoring Well  Development
Introduction/Philosophy
    The objective of monitoring well development is fre-
quently misconstrued to  be merely a process that enhances the
flow of ground water from the formation into the well and that
minimizes the amount of sediment in the water samples col-
lected from the well.  These are the proper objectives for the
development of a production well but they do not fulfill the
requirements for a monitoring well. A monitoring well should
be a "transparent", window into the aquifer from which samples
can be collected that are truly representative of the quality of
water that is moving through the formation. This objective is
difficult to attain and  is unattainable in some instances. How-
ever, the  objective should not be abandoned because of the
difficulty.

     The interpretation of any ground-water sample collected
from a monitoring well should reflect the degree of success that
has been reached in the development of the well and the
collection  of the sample.  This objective is frequently overlooked
in the literature and in much of the work that has been done in
the field.  Further research is required before the reliability of
samples taken from a  monitoring well can" be  effectively sub-
stantiated. The United States Environmental Protection Agency
(1986) in the Technical Enforcement Guidance Document
(TEGD) states that, "a  recommended acceptance/rejection
value of five nephelometric turbidity units (NTU) is based on
the need to minimize biochemical activity  and possible interfer-
ence with ground-water sample quality."  The TEGD also out-
lines a procedure for  determining the source of turbidity and
usability  of the sample and well. There are instances where
minimizing turbidity and/or biochemical activity will result in
a sample  that is  not representative of water that is moving
through the ground. If the ground water moving through the
formation is, in fact, turbid, or if there is free product moving
through the formation, then some criteria may cause a well to be
constructed such that the actual contaminant that the well was
installed to monitor will be filtered out of the water. Therefore,
it is imperative that the  design, construction and development
of a monitoring well be consistent with the objective of obtain-
ing a sample that is representative of conditions in the ground.
An evaluation of the degree of success in attaining this objective
should always be included and considered in conjunction with
the laboratory and analytical work that is the final result of the
ground-water sample-collection process.

     If the ultimate objective of a monitoring well is to provide
a representative sample of water as it exists in the formation,
then the immediate objective and challenge of the development
program is to restore  the area adjacent to the well to its
indigenous condition by correcting damage done to the forma-
tion during the drilling process. This damage may occur in
many forms: 1) if a vibratory method such as driving casing is
used during the drilling process, damage may be caused by
compaction of the  sediment in place; 2) if a compacted sand and
gravel is drilled by a hollow-stem auger and then allowed to
collapse around the monitoring well intake, damage may be the
resultant loss of density of the natural formation; 3) if a drilling
fluid of any type is added during the drilling process, damage
may occur by the  infiltration of filtrate into the formation; and
4) if mud rotary, casing driving or augering techniques are used
during drilling, damage may be caused by the formation of a
mudcake or similar deposit that is caused by the drilling
process. Other formatation damage may be related to specific
installations. Some of this damage cannot be overcome satis-
factorily by the current capability  to design and develop a
monitoring  well. One important factor is the  loss of stratifica-
tion in the monitored zone.  Most natural formations are strati-
fied; the most common stratigraphic orientation is horizontal.
The rate of water movement through different  stratigraphic
horizons varies, sorption rates may  differ as stratigraphy changes;
and chemical interaction between contaminants and the forma-
tion materials and ground water can vary between different
horizons. During the development process, those zones with the
highest permeability will be most affected by the development
of the well.  Where a well intake crosses stratigraphic bound-
aries of varying permeability, the water that moves into and out
of the well intake will be moving almost exclusively into and
out of the high permeability zones.

Factors Affecting Monitoring Well Development
    There are three primary factors that influence the develop-
ment of a monitoring well: 1) the type of geologic material, 2)
the design and completion of the well and 3) the type of drilling
technology  employed  it? the well  construction. From these
factors it is also possible to estimate the level  of effort required
during development so that the monitoring well will perform
satisfactorily.

Type of Geologic Material
    The primary  geologic consideration is whether or not the
monitoring  well intake will be installed in consolidated rock or
unconsolidated material.  If the intake is installed in consoli-
dated rock or cohesive unconsolidated material, the assumption
can often be made that the borehole is stable and was stable
during the construction  of the monitoring well. In a stable
borehole, it is generally easier to:  1) install the well intake(s) at
the prescribed setting(s),  2) uniformly distribute and maintain
the proper height of a filter pack (if one was installed) above the
well intake(s), 3) place the bentonite seal(s) in  the intended
                                                           115

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   location and 4) emplace a secure surface seal. However, if the
well intake is opposite unconsolidated material, the borehole
may not be or may not have been stable during well installation.
Depending on the degree of borehole instability during the well
completion process the well intake, filter pack, bentonite seal
and/or surface seal may not have been installed as designed. As
a consequence, there is generally a greater degree of difficulty
expected in the development of wells  that are installed in
unconsolidated   formations.

     The permeability of the formation also influences the ease
of development. Where permeability is  greater, water moves
more easily into and out of the formation and development is
accomplished more quickly. In unconsolidated formations, the
ease or difficulty of development is  less predictable because
there is considerable variation in the  grain size, sorting, and
stratification of many  deposits. Zones that are developed and
water samples that are collected will be more representative of
the permeable portions of a stratified aquifer and may not be
very representative of the less permeable zones.

Design  and Completion of the Well
     A monitoring well can be installed relatively easily at a site
where the total depth of the well will be 25 feet; the static water
level is approximately 15 feet; and the monitored interval is a
clean, well-sorted sand and gravel with a permeability that
approximates 1 x  10' centimeters per  second. However,  a
monitoring well  is much more difficult to  install at a site where
the depth  of the well will be 80 feet; the well will be completed
in an aquifer beneath an aquitard; the water table in the shallow
aquifer is approximately 20 feet deep; the piezometric surface
of the semi-confined aquifer is approximately 10 feet deep; and
the monitored interval  in the deeper zone is composed of fine-
-grained sand with silt. Construction of the monitoring well in
this scenario will be difficult by any technique. No matter what
construction method is  used, a considerable amount of time will
be required for well completion and problems can be anticipated
during setting of the well intake,  placement of the filter pack,
placement of the bentonite seal or placement of the grout.
Difficulties may also be experienced during the development
process.

     Another difficult monitoring well installation is where the
well intake is placed opposite extremely fine-grained materials.
For example, extremely fine-grained materials often occur as  a
series of interbedded  fine sands and clays such as might be
deposited in a sequence of lake deposits. A well intake set in the
middle of these  saturated deposits must be completed with an
artificial filter pack. However, because  the deposits are un-
stable,  it is difficult to  achieve a good distribution of the filter-
pack material around the well intake  during installation. Fur-
thermore, even if the filter pack installation is successful, it is
not possible to design a sufficiently fine-grained filter pack that
will prevent the intrusion of the clays that are intimately
associated with the productive fine-grained sand. As a conse-
quence, every time the well is agitated during the sampling
process, the clays are mobilized and become part or all  of the
turbidity  that compromises the  value of the  ground-water
samples. There currently is no design or development proce-
dures that  are able to fully overcome this problem. The only way
to  minimize the intrusion of the  clays is to install an extremely
 fine-grained porous filter. This falter has very limited utility
 because it rapidly becomes clogged by the clays that are being
 removed. After a short operational period, insufficient quanti-
 ties of samples are obtained and the filter can no longer be used.

     Where an artificial filter pack is installed, the filter pack
 must be as thin as possible if the development procedures are to
 be effective in removing fine participate material from the
 interface between the filter pack and the natural formation.
 Conversely, the filter pack must be thick  enough to  ensure that
 during the process of construction, it is possible to attain good
 distribution of the filter pack material around the screen. It is
 generally  considered that the minimum thickness of filter pack
 material that can be constructed effectively is 2 inches. Two
 inches is a desirable thickness in situations where there is
 adequate control to ensure good filter pack distribution. If there
 are doubts about the distribution, then the filter pack must be
 thickened to assure that there is adequate filtration and borehole
 support.

     In natural filter pack installations where  the natural forma-
 tion is allowed to collapse around the well intake, the function
 of development is twofold: 1) to  remove the fine-particulate
 materials that have been emplaced adjacent  to the well intake
 and 2) to restore the natural flow regime in the aquifer so that
 water may enter the well unimpeded.

     It is easier to  develop monitoring wells that are larger in
 diameter than it is to develop small-diameter wells. For ex-
 ample, mechanical surging or bailing techniques that are effective
 in large-diameter wells are much less effective when used in
 wells that are less than 2  inches in diameter because equipment
 to develop smaller-diameter wells has  limited availability.
 Further,  in small-diameter wells when the depths become
 excessive, it is  difficult to maintain straightness and alignment
 of the borehole because of the drilling techniques that are
 commonly used. It may become imperative in this situation to
 use centralizers on the casing and well intake that are being
 installed within these boreholes or to use other methods to
 center the casing or ensure straight holes.

 Type of Drilling Technology
    The drilling process influences not only development
 procedures but also the intensity with which these procedures
 must be  applied. Typical problems associated with special
 drilling technologies that must be anticipated  and  overcome are
 as follows: 1)  when drilling an air rotary borehole in rock
 formations, fine particulate  matter typically builds up on the
borehole walls and plugs fissures, pore  spaces, bedding planes
 and other permeable zones. This particulate matter must be
removed and openings restored by the development process; 2)
 if casing has been driven or if augers have been used, the
 interface between the natural formation and the casing or the
 auger flights are "smeared" with  fine-particulate matter that
must subsequently  be removed in the development process;  3)
 if a mud rotary technique is used,  a mudcake builds upon the
borehole wall that must be  removed during the  development
process;  and 4) if there have been any additives, as may be
necessary in mud rotary, cable tool or augering procedures, then
the development process must attempt to remove all of the
fluids that have infiltrated into the natural formation.
                                                           116

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Well Development
    Very little research has been performed that specifically
addresses movement of fluid, with or without contaminants
present, through a stratified aquifer into monitoring wells.
Ground-water flow theory is based on the primary assumptions
of homogeneity and isotropism of the formation. In production
wells, these assumptions are acceptable because the aquifer is
stressed over a sufficient area for variations to be "averaged."
Most discussions of monitoring-well flow characteristics are
based on the  acceptance of these assumptions. However, these
are not always valid assumptions for attaining the objectives of
monitoring wells.

    Where it is  intended to intercept a contaminant in a re-
stricted zone of  a three-dimensional flow field,  a monitoring
well must be installed and developed with a much greater
precision than is normal for production wells.  The relative
movement of fluid in specific zones becomes  significantly
more important than  the gross yield. Both installation and
development must be  performed with a "spot precision" that
preserves in  situ conditions and permits the collection of a
representative sample.

    The  methods that are available for the development of
monitoring wells have been  inherited from production  well
development practices. These methods include: 1) surging  with
a surge Mock, 2) bailing, 3) pumping, overpumping and
backwashing through the pump, 4) airlift pumping and 5) air
surging and jetting.  A number of authors have written about
these available methods of development for  monitoring wells.
A summary of these articles is contained in Table 36.

    Based on a review of the literature and on a wide range of
actual field practices, a few generalizations about development
of monitoring wells can be made

     1)  using air for well development can result in
        chemical alteration of the ground water both as a
        result of chemical reaction with the air  and as a
        result of impurities introduced through the air
         stream;
    2)  adding  water to the borehole for stabilization,
         surging, backwashing, flushing or any other
        purpose has an unpredictable effect on ground-
        water quality and at the very least causes dilution.
        Even if the water added to the borehole was
        originally pumped from the same formation,
        chemical alteration of the ground water in the
        formation can occur if the water is reinfected.
        Once water has been pumped to the surface,
        aeration can alter the original water quality;
    3)  developing the formation at the interface between
        the outer perimeter of an artificial filter pack and
        the inner perimeter of the borehole is extremely
        difficult. Any mudcake or natural clay deposited
        at this  interface is very difficult to remove;
        incomplete removal can have unquantifiable short-
        and long-range impacts on the quality of the
         sampled ground water;
    4)  developing a well is relatively easy when the well
        intake is placed in a clean homogeneous aquifer of
        relatively high permeability. It is very difficult to
        develop a representative well in an aquifer that is
         stratified, slowly permeable and fine-grained,
         particularly  where there  is substantial variation
         between the various stratified zones;
     5)   developing  a larger-diameter monitoring well is
         easier than  developing a smaller-diameter well.
         This is particularly true if the development is
         accomplished by overpumping or backwashing
         through the pump because suitable pumping
         capacity is  not commonly available for small-
         diameter wells  with deep static water levels.
         However,  a  smaller-diameter well is more
         "transparent" in the aquifer flow field and is
         therefore more  likely to yield a representative
         sample,
     6)   collecting non-turbid sample may not be possible
         because there are monitoring wells that cannot be
         sufficiently developed by any available technique.
         This may be the consequence of the existence of
         turbid water in the  formation or the inability to
         design and construct a well that will yield water in
         satisfactory quantity without exceeding acceptable
         flow velocities in the natural formation;
     7)   applying  many  of the monitoring  well-
         development techniques in small-diameter (2-
         inch) wells and using the  design and construction
         techniques discussed in the literature are easiest
         in shallow  monitoring  situations with good
         hydraulic conductivity. These techniques may be
         impractical when  applied to deeper or more
         difficult  monitoring  situations.
     8)   Adding clean water of known quality for flushing
         and/or jetting should be done only when no better
         options are available. A record must be kept of the
         quantities of water lost to the formation during the
         flushing/jetting operation and every  attempt must
         be made to reestablish background levels in a
         manner similar to that described in Barcelona et
         al. (1985a) and/or the United States Environmental
         Protection Agency (1986); and
     9)   dealing objectively with the conditions and
         problems that exist for every installation is
         essential. The problems encountered at each site
         should be addressed and clearly presented in the
         final report.  Chemical analyses must be included
         in the  final report so that anyone evaluating these
         analyses is able  to understand  the limitations of
         the work.

Methods of Well Development
     Monitoring well  development is an attempt to remove fine
particulate matter, commonly clay and silt, from the geologic
formation near the  well intake. If particulate matter is not
removed, as water moves through  the formation into the well,
the water sampled will be turbid, and the viability of the water
quality analyses will  be impaired.  When pumping during well
development, the movement of water is unidirectional toward
the well.  Therefore, there is a tendency for the particles moving
toward the well to "bridge" together or form blockages that
restrict subsequent particulate movement.  These  blockages
may prevent the complete development of the well capacity.
This effect potentially impacts the quality of the water dis-
charged.  Development techniques should remove such bridges
                                                         117

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Table 36. Summary of Development Methods for Monitoring" Wells
Reference
gass (1966)








United States
Environmental
Protection
Agency (1966)
Overpumping
Works best in
clean coarse
formations and
some consolidated
rock; problems of
water disposal and
bridging


Effective develop-
ment requires flow
reversal or surges
to avoid bridges
Backwashing
Breaks up
bridging, low
cost & simple;
preferentially
develops




Indirectly indicates
method applicable;
formation water
should be used
Surge Block* Bailer
Can be effective;
size made for£2"-
well; preferential
development where
screen >5'; surge
inside screen



Applicable; forma- Applicable
tion water should
be used; in low-
yield formation,
Jetting
Consolidated
and uncon-
solidated
application;
opens fractures,
develops discrete
zones; disadvantage
is external water
needed




Airlift Pumping
Replaces air surg
ing; filter air







Air should not
be used


Air Surging
Perhaps most
widely used;
can entrain
air in form-
ation so as to
reduce per-
meability, affect
water qualify;
avoid if possible,
Air should not
be used


Barcelona et
al. ** (1963)
Staff et al.
(1901)
National
Council of the
Paper  Industry
for Air and
Stream Im-
provement
(1961)
Productive  wells;
surging by alternat-
ting pumping and
allowing to equili-
brate; hard to create
must be
sufficient entrance
velocities; often
use with airlift
Applicable
drawback of flow in
one direction;
smaller wells hard
to pump if water
level below suction
                        Suitable;  periodic
                        removal of fines
outside  water
source can be
used if  analyzed
to evaluate impact

Productive walk;
use care to avoid
casing and screen
damage
Suitable; common
with cable to of;
not easily used
on other rigs
Applicable; caution
against collapse of
intake or plugging
screen with clay
Productive walk;
more common than
surge blocks but
not as  effective
Suitable; use
sufficiently
heavy bailer;
advantage of
removing fines;
may be  custom
made for small
diameters
                                                                                                                                          Suitable
Effectiveness
depends on
geometry of
device; air
filtered; crew
may be
exposed to
contaminated
water; per-
turbed Eh in
sand and
gravel not
persistent for
more than a
few weeks

Suitable;
avoid injecting
air into intake;
chemical
interference;
air pipe never
inside screen
                        Methods introducing foreign  materials should  be
                        avoided (i.e., compressed air or water jets)

-------
       Table 36. (Continued)
Reference
Everett (1960)
Keely and
Boateng
(1987 a and b)













Overpumping Beckwashing
Development opera-
tion must cause
flow reversal to
avoid bridging; can
alternate pump oft
and on'
Probably most Vigorous surging
desirable when action may not be
surged; second desirable due to
series of disturbance of
evacuation/ gravel pack
recovery cycles is
recommended after
resting the well for
24 hours; settlement
and loosening of
fines ocurs after
the first
development
attempt; not as
vigorous as
backwashing
Surge Block* Bailer
Suitable; periodic
bailing to remove
fines
Method quite
effective in
loosening fines but
may be inadvisable
in that filter pack
and fluids may be
displaced to degree
that damages value
as a filtering media







Jetting Airlift Pumping Air Surging
High velocity jets of
water generally
most effective; dis-
cret zones of
development

Popular but Air can become
less desirable; entrained behind
method dif- screen and
ferent from permeability
water wells;
water displaced
by short down-
ward bursts of
high-pressure injection;
important not to jet
air or water across
screen because fines
driven into screen
cause irreversible
blockage; may subsatantiafly
displace native fluids
reduce













tfl
* Schalla and Landick (1986) report on special 2- valved block
" For low hydraulic conductivity w«Iis, flush water up armulus prior to sealing; afterwards pump

-------
and encourage the movement of participate into the well.
These participate can then be removed from the well by bailer
or pump and, in most cases, the water produced will subsequently
be clear and non-turbid.

     One of the major considerations in monitoring well devel-
opment is the expense. In hard-to-develop formations, it is not
unusual for the development process to take several days before
an acceptable water quality can be attained. Because develop-
ment procedures usually involve a drilling rig, crew, support
staff and a supervising geologist, the total cost of the crew in the
field often ranges in cost from $100 to  $200 per hour. Thus, the
cost of development can be the most expensive portion of the
installation  of a monitoring-well network. When this hourly
cost is compared to an often imperceptible rate of progress,
there is a tendency to prematurely say either, "that is good
enough" or "it can't be done. "

     In most instances, monitoring wells installed in consoli-
dated formations can be developed without great difficulty.
Monitoring  wells also can usually be developed rapidly and
without great difficulty in sand and gravel deposits. However,
many installations are made in thin, silty and/or clayey zones.
It is not uncommon for these zones to be difficult to develop
sufficiently  for adequate samples to be coil.xted.

     Where the borehole is sufficiently stable, due to installa-
tion in sound rock or stable unconsolidated materials, and
where the addition of fluids during completion  and develop-
ment is permissible, it is a good practice to precondition the
borehole by flushing  with clean water prior to filter pack
installation. When water is added to the well, the  quality of the
water must be analyzed so that comparisons can be made with
subsequent water-quality  data.  Flushing of monitoring wells is
appropriate for wells drilled by any method and aids in the
removal of mud cake  (mud rotary) and other finely-ground
debris (air rotary, cable tool, auger) from the borehole wall. This
process opens clogged fractures and cleans thin stratigraphic
zones that might otherwise be non-productive. Flushing can be
accomplished by isolating individual open zones in the borehole
or by exposing the entire zone. If the entire zone is exposed,
cross connection of all zones can occur.

     Where it is not permissible to add  fluids during completion
and development, and the borehole is  stable, mechanically
scraping or scratching the borehole wall with a scraper or wire
brush, can assist in removing particulate from  the borehole
wall. Dislodged particulate can be pumped or bailed from the
borehole prior to filter pack, casing and well intake installation.

     Where the addition of fluid is permissible, the use of high-
-pressure jetting can be considered for screened intake develop-
ment in special applications. If jetting is used, the process
should usually be performed in such  a manner that loosened
particulate are removed (e.g., bailing, pumping, flushing)
either simultaneously or alternately with the jetting. The disad-
vantages of using jetting even in "ideal conditions" are fourfold:
1) the water used in jetting is agitated, pumped, pressurized and
discharged into the formation; 2) the fine (e.g., 10-slot, 20-slot)
slotted screens of most monitoring well  intakes do not permit
effective jetting, and development of the material  outside the
screen may  be negligible or possibly  detrimental; 3) there is
minimal development of the interface between the filter pack
and the wall of the borehole (Table 36) and 4) water that is
injected  forcibly replaces natural formation fluids.  These are
serious limitations on the usefulness of jetting as a development
procedure.

    Air  development forcibly introduces air into contact with
formation fluids, initiating the potential for uncontrolled
chemical reactions. When air  is introduced into permeable
formations, there is a serious  potential for air entrainment
within the formation. Air entrainment not only presents poten-
tial quality problems, but also can interfere with flow into the
monitoring well. These factors  limit the use of air surging for
development of monitoring wells.

    After due consideration of the available procedures for
well development, it becomes evident that the four most suit-
able methods for monitoring well development are:  1) bailing,
2) surge  block surging, 3) pumping/overpumping/backwashing
and 4) combinations of these three methods.

Bailing
    In relatively clean, permeable formations where water
flows freely into the borehole, bailing is an effective develop-
ment technique. The bailer is allowed to fall freely through the
borehole  until  it strikes the surface of the water. The  contact of
the bailer produces a strong outward surge of water that is
forced from the borehole through the well intake and into the
formation. This tends to breakup bridging that has developed
within the formation. As the bailer fills and is rapidly  with-
drawn, the drawdown created in the borehole  causes the par-
ticulate matter outside the well intake to flow through the well
intake and  into the well.  Subsequent bailing removes  the
particulate matter from the well. To enhance  the removal of
sand and other particulate matter from the well, the bailer can
be agitated by rapid short strokes near the bottom of the well.
This agitation makes it possible  to bail the particulate from the
well by  suspending or slurrying the particulate matter. Bailing
should be continued until the water is free from suspended
particulate matter.  If the well is rapidly and repeatedly bailed
and the formation is not sufficiently conductive, the borehole
will be dewatered. When this  occurs, the borehole must be
allowed to refill before bailing is resumed. Care must be taken
that the rapid removal of the bailer does not cause the  external
pressure  on the well casing to exceed the strength of the casing
and/or well intake thereby causing collapse of the casing and/
or well intake.

    Bailing can be conducted by hand on shallow wells,
although  it is difficult to continue actively bailing for more than
about an  hour. Most drill rigs are  equipped with an extra  line that
can be used for the bailing operation. The most effective
operation is where the bail line permits a free fall in the
downward mode and a  relatively quick  retrieval in the upward
mode. This combination maximizes the surging action of the
bailer. The  hydraulic-powered lines on many rigs used in
monitoring-well installation operate too slowly for effective
surging.  Bailing is an  effective development  tool  because it
provides the same effects as both pumping and surging with a
surge block. The most effective equipment for bailing opera-
tions is generally available on cable tool rigs.
                                                           120

-------
    There area variety of dart valve, flat bottom and sand pump
bailers availa ble for the development of larger-diameter wells.
These bailers are typically fabricated from steel and are oper-
ated by using  a specially designated line on the rig. For most
monitoring-well  applications, small-diameter  PVC  or
fluoropolymer bailers arc readily available.  When commercial
bailers are not available, bailers can be fabricated from readily
available materials. Bailers of appropriate diameter, length,
material and weight should be used to avoid potential breakage
of the well casing or screen. Figures 74a and 74b show a
schematic  representation of typical commercially  available
small-diameter  bailers.

Surge Block
    Surge blocks, such as are shown in Figures 75 and 76, can
be used effectively to destroy bridging and to create the agita-
tion that is necessary to develop a well. A surge block is used
alternately with either a bailer or pump so that material that has
been agitated and loosened by the surging action is removed.
The cycle  of surging-pumpingftailing is repeated until satisfac-
tory development has  been attained.

    During the development process, the surge block can be
operated either as an integral part of the  drill rods or on a
wireline. In either event, the surge block assembly must be of
sufficient weight to free-fall through the water in the borehole
and create a vigorous outward surge. The equipment that lifts
or extracts  the surge block after the downward plunge must be
strong enough to pull the surge block upward relatively
rapidly. The surge block by  design permits some of the fluid to
bypass on the  downward stroke, either around  the perimeter of
the surge block or through  bypass valves.

    The surge block is lowered to the top of the well intake and
then operated in a pumping action with a typical  stroke of
approximately 3 feet. The surging is usually  initiated at the top
of the well intake and gradually  is worked downward through
the screened interval, 'he surge block is removed at regular
intervals and the fine material that has been loosened is re-
moved by  bailing and/or pumping. Surging begins at the top of
the well intake so that sand or silt loosened by the initial surging
action cannot cascade down on top of the surge block and
prevent removal of the surge block from the well. Surging is
initially gentle, and the energy of the action is gradually
increased  during the development process. The vigor of the
surging action is controlled by the speed, length and stroke of
the fall and speed of retraction of the surge block. B y controlling
these rates, the surging activity can range from  very rigorous to
very gentle.

    Surging within the well intake can result in serious difficul-
ties. Vigorous surging in a well that is designed such that
excessive sand can be  produced,  can result in sand-locking the
surge block. This should not occur in a properly designed
monitoring well, nor should it occur if the  surge block of
appropriate diameter is properly  used. As in the case of bailer
surging, if excessive force  is used, it is possible to cause the
collapse of the well intake and/or the casing.

    An alternative to surging within the well intake is to
perform the surging within the casing above the well intake.
This has the advantage of minimizing the risk of sand locking.
However, it also reduces the effectiveness of the surging action.
In permeable material, the procedure of surging above the well
intake is effective only for well intakes with lengths of 5 feet or
less.

    If the well is properly designed, and if 1) the surge block
is initially operated with short, gentle strokes above the well
intake, 2) sand is removed periodically by alternating sand
removal with  surging, 3) the energy of surging is gradually
increased at each depth of surging until no more sand is
produced from surging at that depth, and 4) the depth of surging
is incrementally increased from top to bottom of the well intake,
then surging can be conducted effectively and safely.

    Where there is sufficient annular space available within the
casing, which is seldom the case with monitoring wells, it is
effective to install a low-capacity pump above the surge  block.
By discharging from the  well concurrent with surging, a
gradient is maintained toward the well. This set-up assists in
developing the adjacent aquifer by maintaining the movement
of particulate material toward the well.

    Surging is usually most effective when performed by cable
tool-type machines. The hydraulic hoisting equipment that is
normally available on most other types of drilling equipment
does not operate with sufficient speed to provide high-energy
surging. Where properly used,  the surge block in combination
with bailing or pumping may be the most effective form of
mechanical  development.

Pumping/Overpumpin/Backwashing
    The easiest, least-expensive and most commonly em-
ployed technique of monitoring-well development is some
form of pumping. By installing a pump in the well and starting
the pump, ground-water flow is induced toward the well. Fine-
particulate material that moves into the well is discharged by the
pump. In overpumping, the  pump is  operated at a capacity that
substantially exceeds the ability  of the  formation to deliver
water. This flow velocity into the well usually exceeds the flow
velocity that will subsequently  be  induced during the sampling
process. This increased velocity causes rapid and effective
migration of particulate toward the pumping well and en-
hances the development process. Proper design is needed to
avoid well collapse, especially in deep wells. Both pumping and
overpumping are easily used in the development of a well.

    Where there is no backflow-prevention valve installed, the
pump can be alternately started and  stopped. This starting and
stopping allows the column of water that is initially picked up
by the pump  to be alternately dropped and raised up in a surging
action. Each time the water  column falls back into the well, an
outward surge of water flows into the formation. This surge
tends to loosen the bridging of the fine particles so that the
upward motion of the column of water can move the particles
into and out of the well. In this manner, the well can be pumped,
overpumped and back-flushed alternately until such time  as
satisfactory development has been attained.

    While the preceding procedures can  effectively develop  a
well, and have been used for many years in the development of
production wells, pumping equipment suitable to perform these
operations may not be available that will fit into some small-
diameter monitoring wells.  To be effective as a development
tool, pumps  must have a pumping capability that ranges from
                                                          121

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                                               Standard
                                               Sailer of
                                               Teflon®
                                           Standard
                                    Bailer  of
                                           Pvc
                         (a)
                                                           Bottom
                                                           Emptying
                                                           Device
Top for Variable
Capacity Point Source
Sailer of PVC
                                                                                              Retaining
                                                                                              Pin

                                                                                               Ball
                                                                                               Check
                                                                                              Sample
                                                                                         Chamber
                                                                                              1 Foot
                                                                                              Midsection
                                                                                              May Be Added
                                                                                              Here
     _  Retaining
          Pin
                                                                                        -  Sell  Check
                                                                                (b)
Diagrams of typical bailers used in monitoring well development: a) standard type and b) "point source" bailer
(Timco Manufacturing Company, inc., 1982).
                                                  122

-------
                                         Pressure-relief
                                         Hole
Figure 75. Diagram of a typical surge block (Driscoll, 1986).
very low to very high or be capable of being controlled by
valving. The sampling pumps that are presently designed to fit
into small-diameter boreholes  commonly do not provide the
upper range of capacities that often are needed for this type of
development. For shallow wells with water levels  less than 25
feet deep, a suction-lift centrifugal pump can be used for
development in the manner prescribed. The maximum practical
suction lift attainable by this method is approximately 25  feet.
In practice, bailing or bailing  and surging is combined  with
pumping for the  most-efficient well development. The bailing
or surging procedures are used to loosen bridges and move
material  toward  the well. A low-capacity sampling pump or
bailer is then used to remove turbid water from the well until the
quality is satisfactory. This procedure is actually less  than
completely satisfactory, but is the best-available technology
with the  equipment that is currently available.

    Air lifting, without exposing the formations being devel-
oped directly to  air, can be accomplished by properly imple-
mented pumping. To do this,  the double pipe method of air
lifting is  preferred. The bottom  of the airlift should be lowered
to within no more than 10 feet of the top of the well intake, and
in no  event should the air lift be used within the well intake. If
the  air lift is used to surge the well, by alternating the air on and
off, there will be mixing of aerated water with the water in the
well. Therefore,  if the well is to be pumped by air lifting, the
action should be one of continuous, regulated discharge.  This
can be effectively accomplished only in relatively permeable
aquifers.

    Where monitoring well installations are to be made in
formations that have low hydraulic conductivity, none of the
preceding well-development methods will be found to be
completely satisfactory. Barcelona et al.  (1985a) recommend a
procedure that is applicable in this situation: "In this type of
geologic setting, clean water should be circulated down the well
casing, out through the well intake and gravel pack, and up the
open borehole prior to placement of the grout or seal in the
annulus. Relatively  high water velocities can be maintained,
and the mudcake from the borehole wall will be broken down
effectively and  removed. Flow  rates should be controlled to
prevent floating  the gravel pack out of the borehole. Because of
the relatively  low hydraulic conductivity  of geologic materials
outside the well, a negligible amount of water will penetrate the
formation being monitored. However, immediately following
the procedure, the well sealant should be installed and the well
pumped to remove as much of the water used in the develop-
ment process  as possible."

    All of the techniques described in this section are designed
to remove the effects of drilling from the monitored zone and,
insofar as possible, to restore the formations penetrated to
indigenous conditions. To this end, proposed development
techniques, where possible, avoid the use of introduced fluids,
including air, into the monitored zone during the development
process. This not only minimizes adverse impacts on the quality
of water samples, but also restricts development options that
would otherwise be available.

References
Barcelona, MJ., J.P. Gibb, J.A. Helfnch and E.E. Garske,
     1985a. Practical guide for ground-water sampling; Illinois
     State Water Survey, SWS Contract Report 374, Champaign,
    Illinois, 93  pp.
Barcelona, M.J., J.P. Gibb and R. Miller, 1983. A guide to the
     selection of materials for monitoring well construction and
    ground-water sampling; Illinois State Water Survey, SWS
    Contract Report 327,  Champaign, Illinois, 78 pp.
Driscoll, Fletcher G., 1986. Ground water and wells; Johnson
    Division, St. Paul, Minnesota,  1089 pp.
Everett, Lome  G.,  1980.  Ground-water monitoring; General
    Electric Company technology marketing operation,
     Schenectady, New York, 440 pp.
Gass, Tyler E., 1986. Monitoring well development; Water
    Well Journal, vol. 40, no. 1, pp. 52-55.
Keely, Joseph F. and Kwasi Boateng, 1987a. Monitoring well
     installation, purging and sampling techniques  part 1:
    conceptualization Ground Water, vol. 25, no.  3, pp. 300-
     313.
Keely, Joseph F. and Kwasi Boateng, 1987b. Monitoring well
    installation, purging, and sampling techniques part 2: case
    histories; Ground Water, vol. 25, no. 4, pp. 427-439.
National Council of the Paper Industry for Air and Stream
    Improvement 1981. Ground-water quality monitoring well
    construction  and placement;  Stream Improvement
    Technical Bulletin Number 342, New York, New York,
    39pp.
Scalf,  M.R.,  J.F.  McNabb, WJ. Dunlap, R.L. Cosby and J.
    Fryberger, 1981. Manual of ground-water sampling
                                                          123

-------
     procedures; National Water Well Association, 93 pp.
 Schall, Ronald and Robert W. Landick, 1986. A new valved
     and air-vented surge plunger for developing small-diameter
     monitor wells; Ground Water Monitoring Review, vol. 6,
     no. 2, pp. 77-80.
 Timco Manufacturing Company, Inc., 1982. Geotechnical
     Products;  product literature, Prairie Du Sac, Wisconsin, 24
     pp.
United States Environmental protection Agency, 1986.
    RCRA ground-water monitoring technical enforcement
    guidance  document;  Office  of  Waste  Programs
    Enforcement, Office of Solid Waste and Emergency
    Response," OSWER-9950.1, United States Environmental
    Protection Agency, 317 pp.
                          Water Ports {0.25" O.D,)
                                                      fft- Polypropylene Tube (0,375' O.D.)

                                                     W- Stainless Steel Cable (0.063* O.D.
                                                           Ferrule
                                                             Stainless Stael Hex Nut (0.63")

                                                                * Viton Discs (0.05" Thick. 2.1 O.D. &
                                                                  0.68 I.D.)
                                                                  SCH 80 PVC Pipe (1.90" O.D.)
                                                                  Top Fitting
                                                               NPT Threading
                                                               Stainless Steel Coupling
                                                               (1.325' O.D.)
                                                              Stainless Steel Pipe
                                                              (1.067* O.D. i
                                                                  SCH 80 PVC Pipe (1,90" O.D.)
                                                                  Bottom Fitting
                                                            Stainless Steel Hex Nut (0,63")
                                                           Slainlass St*d Tube (0.375" O.D.)

                                                           Swage Block
Figure 76. Diagram of a specialized monitoring well surge block (Schalla and Landick, 1966).
                                                         124

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                                                   Section  8
                    Monitoring Well Network Management Considerations
Well Documentation
    Records are an integral part of any monitoring system.
Comprehensive records should be kept that document data
collection at a  specific site.  These data include boring records,
geophysical data, aquifer analysis data, ground-water sampling
results and  abandonment documentation. Armed with as much
data as possible for the site, an effective management strategy
for the monitoring well network can be instituted.

    Excellent records of monitoring wells must be kept  for any
management strategy to be  effective.  Documentation of moni-
toring well construction and testing  must frequently  be pro-
vided as part  of a regulatory program. Many states require
drillers to file a well log to document well installation and
location. Currently, some states have adopted or are adopting
regulations  with unique reporting requirements specifically for
monitoring wells. At the state and federal level, guidance
documents  have been developed that address reporting require-
ments. Tables 37,  38  and 39 illustrate some of the items that
various states  have implemented to  address monitoring well
Recordkeeping. Table 40 shows the recommendations of the
United States  Environmental  Protection  Agency  (1986). An
additional discussion on field documentation can be found in
the section entitled "Recordkeeping.  "

    The most critical factor in evaluating or reviewing data
from  a monitoring well is location. If a monitoring well cannot
be physically located in the field and/or on a map  in relationship
to other wells, only limited interpretation of the data is possible.
All monitoring wells should be properly located and referenced
to a datum. The degree of accuracy for vertical and horizontal
control for monitoring well location should be established and
held constant for all monitoring wells. In many cases, a licensed
surveyor should be contracted to perform the  survey of the
wells. With few exceptions, vertical elevations should be refer-
enced to mean sea level and be accurate to 0.01 foot (Brownlee,
 1985). Because elevations  are surveyed during various stages
of well/boring installation, careful records must be kept as to
where the elevation  is established. For example, if ground
 elevation is determined during the drilling process, no perma-
nent elevation point usually can be established because the
 ground is disturbed during the drilling process. A temporary pin
 can be established close to the well location for use in later more
 accurate measurements,  but the completed  well must be
resurveyed to  maintain the  desired accuracy of elevation. Each
 completed well should have a standard surveyed reference
 point. Because the top of the casing is not always level,
 frequently the highest point on the  casing is used. Brownlee
 (1985) suggests that the standard reference point should be
 consistent such that the north (or other) side of  all monitoring
 wells is the referenced point. Regardless of what point is
chosen, the surveyor should be advised before the survey is
conducted and the reference point clearly marked at each well.
If paint is used to mark the casing, the paint must not be allowed
on the inside of the casing. If spray paint is used, the aerosols can
coat the  inside of the casing and may  cause spurious water-
quality results in subsequent samples.  An alternative way to
mark the casing  is to notch the casing so that a permanent
reference point is designated. The United States Environmental
Protection Agency (1986) recommends that reference marks be
placed on both the casing and grout apron.

     Well locations should clearly be marked in the field. Each
well  should have a unique number that is clearly visible  on the
well  or protective casing. To ensure good documentation, the
well number may be descriptive of the method used to install the
well. For example, a well designated as  C-l  could represent the
first cored hole, or HS-3 could be a hollow-stem auger hole.  If
multilevel  sampling tubes are being used, each tube should be
clearly marked with the appropriate depth interval.

     Well locations should be clearly marked  on  a map.  The
map  should also include roads, buildings, other wells, property
boundaries and other reference points.  In general, maps illus-
 trating comparable items should be the  same scale. In addition
 to the unique monitoring well number, general well designa-
 tions may be desirable  to include on the  map.  The Wisconsin
 Department of Natural Resources (1985) suggests that PIEZ
 (piezometer), OW (observation well), PVT  (private well),
 LYS (lysimeter) and OTHER be used to clarify  the function of
 the wells.

     Files should be kept on each monitoring well so that any
 suspected problems with the monitoring well can be evaluated
 based on previous well performance. The accuracy and com-
 pleteness of the records  will influence the ability  of the reviewer
 to make decisions based on historical data.

 Well Maintenance and Rehabilitation
      The purpose of maintaining a monitoring well is to  extend
 the life of the well and to provide representative levels and
 samples of the ground water surrounding the well. Maintenance
 includes proper documentation of factors that can be used as
 benchmarks for comparison of data at a later point.  A scheduled
 maintenance program should be developed before sample qual-
 ity is questioned. This  section is designed to assist the  user in
 setting up a comprehensive maintenance  schedule for a moni-
 toring system.

 Documenting Monitoring Well Performance
      A monitoring well network should be periodically  evalu-
 ated to  determine that the wells are functioning properly.  Once
 complete construction  and "as-built" information is on  file for
125

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Table 37. Comprehensive Monitoring Wet) Documentation (After Wisconsin Department of Natural Resources, 1965}
Well Design:
• Length, schedule and diameter of casing
«Joint type (threaded, flush or solvent welded)
• Length, schedule and diameter of screen
• Percentage of open area in screen
« Slot size of screen
• Distance the filter pack extends above the screen
« Elevations of the top of well casing, bottom and top of protective
  casing, ground surface, bottom of borehole, bottom of well
  screen, and top and bottom of seal(s)
• Well location by coordinates or grid systems (example township
  and range)
* Well location on plan sheet showing the coordinate system, scale,
  a north arrow and a key

Materials:
• Casing and screen
• Filter pack (including grain size analysis)
• Seal and physical form
• Slurry or grout mix  (percent cement, percent bentonite powder,
  percent water)

Installation:
« Drilling method
* Drilling fluid (if applicable)
• Source of water (if applicable) and analysis of water
» Time period between the addition of backfill and construction of
  well protection
Development:
• Date, time, elevation of water level prior to and after development
* Method used for development
• Time spent developing a well
* Volume of water removed
• Volume of water added (if applicable), source of water added
  chemical analyses of water added
* Clarity of water before and after development
* Amount of sediment present at the bottom of the wet!
» pH, specific conductance and temperature readings

Soils Information;
• Soil sample test results
• Driller's observation or photocopied drillers log

MUcfltlaneou*:
• Water levels and dates
• Weil yield
* Any changes made in well construction, casing elevation, etc.
Table 38. Additional Monitoring Well Documentation (After Nebraska Department of Environmental Control, 1984)
  Well identification number
  Formation samples (depth and method of collection)
  Water samples (depth, method of collection, and results)
  Filter pack (depth, thickness, grain size analysis, placement method, supplier)
  Date of all work
  Name, address of consultant, drilling company and stratigraphic Jog preparer(s)
  Description and results of pump or stabilization test if performed
  Methods used to decontaminate drilling equipment and well construction malaria!
Table 39. As. Built Construction Diagram information (After Connecticut Environmental Protection Agency,  1983)


     • Top of ground surface
     * Protective grouting and grading at ground surface
     • Well casing length and depth
     « Screen length and depth
     * Location and extent of gravel pack
     • Location and extent of bentonite seal
     • Water table
     * Earth materials stratigraphy throughout boring
     * For rock wells, show details of bedrock seal
     * For rock wells, indicate depths of water-bearing fractures, faults or fissures and approximate yield
each well, the well should be periodically re-evaluated to check
for potential problems. The following checks can be used as a
"first  alert" for potential  problems:

     1)   The depth of the well should be recorded every
         time a water sample is collected or a water-level
         reading taken. These depths should be reviewed
         at least  annually to document whether or not the
         well is filling with sediment;
  2) If turbid samples are  collected from a well,
      redevelopment of the  existing well should be
      considered or a new well should be installed if
      necessary (Barcelona et al,  1985a);
  3) Hydraulic conductivity tests should be performed
      every 5 years or when significant sediment has
      accumulated;
  4) Slug or pump tests should be performed every 5
      years. Redevelopment is necessary if the tests
                                                             126

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Table 40. Field Boring Log Information (United States Environmental Protection Agency, 1988)
General:
• Project name
• Date started and finished*
• Geologist's name*
• Driller's name*
* Sheet number

Information Columns:
.Depth"
.Sample location/number*
. Blow counts and advance rate

Narrative Description:
« Geologic observations:
* soil/rock type*
• color and stain*
• gross petrology"
* friability
• moisture content*
« degree of weathering*
* presence of carbonate*

• Drilling Observations:
• loss of circulation
• advance rates*
• rig chatter
• water levels*
• amount of air used, air pressure
« drilling difficulties*

. Other Remarks:
. equipment failures
.possible  contamination"
.deviations from drilling plan"
. weather
                         • Hole location; map and elevation*
                         • Rig type
                         • Bit size/auger size*
                         ' Petroloflic lithologic classification scheme
                          used (Wentwortri unified soil classification system)
                        • Percent sample recovery*
                        > Narrative description*
                        • Depth to saturation*
.fractures*
.solution cavities*
.bedding*
. discontinuities* - e.g., foliation
.water-bearing zones*
.formational strike and dip"
. fossils
. changes in drilling method or equipment*
.readings from detective equipment, if any*
.amount of water yield or loss during drilling
 at different depths*
.dapositional  structures*
.organic content*
.odor*
.suspected contaminant*
> amounts and types of any liquids used*
• running sands*
• caving/hole stability*
'Indicates items that the owner/operator should record at a minimum.

         show that  the  performance of the well  is
         deteriorating;
    5)   Piezometric surface maps should be plotted and
         reviewed at least annually; and
    6)   High and low water-level data for each well
         should be examined at least every 2 years to
         assure that well locations (horizontally and
         vertically) remain  acceptable. If the water level
         falls below the top of the well intake, the quality
         of the water samples collected can be altered.

    Where serious problems are  indicated with a well(s),
geophysical  logs may be helpful in diagnosing maintenance
needs. Caliper logs provide  information on diameter that may
be used to evaluate physical changes in the borehole or casing.
Gamma logs  can be used to evaluate lithologic changes and can
be applied to ascertain whether or not well intakes are properly
placed. Spontaneous potential logs can locate  zones of low
permeability  where siltation may  originate.  Resistivity logs
identify permeable and/or porous zones to identify formation
boundaries. Television and photographic surveys can pinpoint
casing problems and well intake failure and/or blockage. When
used  in combination, geophysical logs may save time and
money in identifying problem areas. An additional discussion
of the applicability and limitations of geophysical logging tools
can be found in  the  section entitled "Borehole Geophysical
Tools and Downhole Cameras."
                         Factors  Contributing to Well  Maintenance  Needs
                             The maintenance requirements of a well are influenced by
                         the design of the well and the characteristics of the monitored
                         zones.  Water quality, transmissivity, permeability, storage  ca-
                         pacity, boundary conditions, stratification, sorting and  fractur-
                         ing all can influence the need for and method(s) of well
                         maintenance. Table 41  lists major aquifer types by ground-
                         water regions and indicates the most prevalent problems with
                         operation  of the wells in this type of rock or unconsolidated
                         deposit. Problems with monitoring wells are typically caused
                         by poor well design, improper installation, incomplete develop-
                         ment, borehole instability and chemical, physical and/or bio-
                         logical incrustation. A brief description of the major factors
                         leading to well maintenance are discussed below.

                         Design  —
                             A well is improperly designed if hydrogeologic conditions,
                         water quality or well intake design are not compatible with  the
                         purpose and use of the monitoring well. For example, if water
                         is withdrawn during the sampling process and the well screen is
                         plugged, the hydrostatic pressure on the outside of the casing
                         may be great enough to cause collapse of the well intake if  the
                         strength of the material was not sufficient for the application.
                         This is particularly true if the well intake material was chemi-
                         cally incompatible with the ground water and was weakened
                         due to chemical reactions. Another example is where the
                         operational life  of  the monitoring well exceeds the design life.
                                                            127

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If a well was installed for short-term water level measurements
and the well ultimately is used for long-term sample collection,
problems with material comparability may occur. Additionally,
if the well intake openings are improperly sized and/or if the
filter pack is incorrectly designed or installed, siltation and
turbid water samples can result.

Installation  —
    If productive zones are not accurately identified during the
well drilling process, well intakes can be improperly located or
zones can be improperly sealed. Incorrect installation proce-
dures and/or difficulties may also cause dislocation of well
intakes  and/or seals.  Improperly connected or corroded  casing
can separate at joints or collapse and cause interaquifer con-
tamination. Improperly mixed grout can form inadequate seals.
If casing centralizers  are not used, grout distribution may be
inadequate. If the casing is corroded or the bentonite seal not
properly placed, grout may contaminate the water samples.
Drilling mud filtrate may not have been completely removed
during the development process. The surface seal could have
been deteriorated or could have been constructed improperly,
and surface water may infiltrate  along the casing/borehole
annulus. The intake filter pack must be properly installed.

Development  —
    Drilling mud, natural fines or chemicals used during drill-
ing must be removed during the development process. If these
constituents are not removed, water-sample quality may be
compromised.  Chemicals can also  cause  screen corrosion,
shale hydration or plugging of the well intake. In general, the
use of chemicals is not recommended and any water  added
during the development process must be thoroughly tested.

Borehole stability —
    Unstable boreholes contribute to  casing failure, grout fail-
ure or screen failure. Borehole instability can be caused by
factors such as improper well intake placement,  excessive
entrance velocity or shale hydration.

Incrustation   —
    There are four types of incrustation that reduce well pro-
duction: 1) chemical, 2) physical, 3) biological or 4) a combi-
nation of the other three processes. Chemical  incrustation may
be caused by carbonates, oxides, hydroxides or sulfate deposi-
tions on or within the intake. Physical plugging of the wells is
caused by sediments plugging the  intake and surrounding
formation. Biological incrustation is caused by  bacteria growing
in the formation adjacent to the well intake or within the well.
The bacterial growth rate depends on the quantities of nutrients
available. The  velocity at which the nutrients travel partially
controls nutrient availability. Examples of common bacteria
found in reducing conditions in wells include sulphur-splitting
and hydrocarbon-forming bacteria iron-fixing bacteria occur
in oxidizing conditions. Some biological contamination may
originate from  the ground surface  and be introduced into the
borehole during drilling. Nutrients for the organisms may  also
be provided by some drilling fluids, additives or detergents.

    Incrustation problems are most commonly caused by a
combination of chemical-physical, physical-biological  or a
combination of chemical-physical-biological incrustations.
  Particulate moving through the well intake may be cemented
  by chemical/biological masses.

  Downhole  Maintenance
      Many wells accumulate sediment at the bottom. Sand and
  silt may penetrate the screen if the well is improperly developed
  or screen openings improperly sized. Rocks dropped by rock
  and bong technologists (Stewart, 1970), insects or waterlogged
  twigs can also enter the well through casing from the surface.
  Sediment can also be formed by precipitates caused by constitu-
  ents within the water reacting with oxygen at the water surface
  (National Council of the Paper Industry for Air and Stream
  Improvement 1982).

      If sediment build-up occurs, the sediment should be re-
  moved. A sediment layer at the bottom of the well encourages
  bacterial activity that can influence sample quality. In wells that
  are less than 25 feet deep, sediment can be removed by a
  centrifugal pump, and an intake hose can be used to "vacuum"
  the bottom of a well. In wells  deeper than 25 feet, a hose with
  afoot valve can be used as a vacuum device to remove sediment.
  In some situations, bailers can also be used to remove sediment.
  Sediment should be removed  before purging and sampling to
  eliminate sample turbidity and associated questions about sample
  validity.

      More traditional  maintenance/rehabilitation  techniques
  used to restore yields of water supply wells include chemical
  and mechanical methods  that are often combined for optimum
  effectiveness. Three categories of chemicals are used in tradi-
  tional well rehabilitation: 1) acids, 2) biocides and 3) surfac-
  tant. The main objectives of chemical treatment are: 1)  to
  dissolve the incrustants deposited on the well  intake or in the
  surrounding formation,  2) to kill the bacteria in the  well  or
  surrounding formation and 3) to disperse clay and fine materials
  to allow removal. Table 42 lists typical chemicals and applica-
  tions in the water supply  industry. Chemicals have very limited
  application in the rehabilitation of monitoring wells because the
  chemicals cause severe changes in the environment of the wells.
  These changes may last for a long time or may be permanent.
  Before redevelopment with chemicals is considered, the nega-
  tive aspects of chemical alteration in an existing well with a long
  period of record must be evaluated against negative aspects of
  replacing the old well with a new well that may have new
  problems and no history.  If chemical rehabilitation is at-
  tempted, parameters such as Eh, pH, temperature and conduc-
  tivity should be measured. These  measurements can serve  as
  values for comparison of water quality before and after well
  maintenance.

      Mechanical rehabilitation includes:  overpumping, surg-
  ing, jetting and air  development. These processes are the same
  as those  used  in well development and are described in greater
  detail in the section entitled "Methods of Well Development."
  Development with air is not recommended because the intro-
  duction of air  can change the chemical environment in the well.
  Any type of rehabilitation for incrustation can be supplemented
  by use of a wire brush or mechanical scraper with bailing  or
  pumping to remove the loose particles from the well.

  Exterior Well  Maintenance
      Maintenance must also be performed on the exposed parts
  of the well. Any  well casing; well cap, protective  casing,

128

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Table 41. Regional Well Maintenance Problems (Gass et al.,  1980)


Ground Water Regions
Most Prevalent
Aquifer Types
                                             • Most Prevalent Well  Problems
1, Western Mountain Ranges



2. Alluvial Basins


3. Columbia Lava Plateau


4. Colorado Plateau,
  Wyoming Basin


5. High Plains




6. Unglaciated Central Region




7, Glaciated Central Region


8.  Unglaciated Appalachians




9.  Glaciated Appalachians


10. Atlantic and Gulf Coast Plain
Alluvial
Sandstone
Limestone

Alluvial
Basaltic lavas
Alluvial

interbedded sandstone
and shale
Alluvial

interbedded sandstone,
limestone, shale

Alluvial
Sandstone

Limestone

Alluvial
Sandstone

Metamorphic
Limestone

Alluvial

Alluvial
Consolidated  sedimentary

Alluvial  and semiconsolidated
Consolidated  sedimentary
                                             Silt,  clay, sand intrusion,  iron; scale deposition; biological fouling.
                                             Fissure plugging; casing failure; sand production.
                                             Fissure plugging  by clay and silt; mineralization of fissures.

                                             Clay, silt, sand intrusion; scale deposition;  iron; biological fouling;
                                             limited recharge;  casing failure.

                                             Fissure and vesicle plugging by clay and silt; some scale deposition.
                                             Clay, silt, sand intrusion; iron; manganese; biological fouling.

                                             Low initial yields; plugging of aquifer during construction by
                                             drilling muds and fines (clay and silt) natural to formations; fissure
                                             plugging; limited recharge; casing failure.

                                             Clay, silt, sand intrusion; scale deposition;  iron; biological fouling;
                                             limited recharge.
                                             Low initial yield; plugging of voids and fissures; poor development
                                             and  construction; limited recharge.

                                             Clay, silt, sand intrusion; scale deposition;  iron; biological fouling.
                                             Fissure plugging  by clay and silt; casing failure; corrosion: salt water
                                             intrusion; sand production.
                                             Fissure plugging  by clay, silt, carbonate scale; saltwater intrusion.

                                             Clay, silt, sand intrusion; scale deposition;  iron; biological fouling.
                                             Fissure plugging; sand intrusion; casing failure.

                                             Low initial yield; fissure plugging by silt and  day; mineraliztion of fissures.
                                             Predominantly cavernous production: fissure plugging by day and silt;
                                             mineralization of  fissures.
                                             Clay, silt, fine sand intrusion; iron; scale; biological fouling.

                                             Clay, silt, sand intrusion; scale deposition;  biological fouling;  iron.
                                             Fissure plugging; mineralization; low to medium initial yield.

                                             Clay, silt, sand intrusion; mineralization of  screens; biological  fouling.
                                             Mechanical and chemical fissure plugging;  biological fouling; incrustation
                                             of well intake structure.
.Excluding pumps and declining water table.
Table  42.  Chemicals  Used  for Well Maintenance (Gass et cl.,  1980)

                      Chemical  Name      Formula                Application
                                                                        Concentration
Acids and biocides




inhibitors




Hydrochloric acid
Sulfamic acid
Hydroxyacetic acid

Chlorine
Diethyithiourea
DOW A-73
Hydrated ferric sulfate
Aldec 97
Polyrad 110A
HCI
NH,SO,H
C.HA

CI2
(C2H5)NCSN (C2H6)

Fe2(S04).,. 2-3H20


Carbonate scale, oxides, hydroxides
Carbonate scale, oxides, hydroxides
Biocide, chelating agent, weak scale
removal agent
Biocide, sterilization, very weak acid
Metal protection
Metal protection
For stainless steel
With sulfamic acid
Metal protection
15%; 2-3 times zone volume
15%; 2-3 times zone


50-500 ppm
0.2%
0.01%
1%
2%
.375%
volume








Chelating agents
Wetting agents
Surfactant
Citric acid
Phosphoric acid
Rochelle salt
Hydroxyacetic acid

Plutonic F-68

Plutonic L-62


DOW F-33
           C6H,O7                  Keeps metal ions in solution
           H3PO.                   Keeps metal ions in solution
           NaOOC (CHOH)2 COOK Keeps metal ions in solution
           C2H40.,                  Keeps metal ions in solution

                                   Renders a surface non-repellent to a
                                   wetting liquid
                                   Renders a surface non-repellent to a
                                   wetting liquid
                      Sodium Tripolyphosphate
                      Sodium Hexametaphosphate
                                   Lowers surface tension of water thereby
                                   increasing its cleaning power
                                                                   129

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sampling tubing, bumper guard and/or surface seal should be
periodically inspected to ensure that monitoring well sample
quality will not be adversely affected.  Suggested  routine in-
spection and maintenance options  should be  considered:

     1)  Exposed well casing should be inspected. Well
        casing should be of good structural integrity and
        free of any cracks or corrosion;
    2)  The well cap should be removed to inspect for
        spider webs, molds, fungi  or other evidence of
        problems that may affect the representativeness
        of water samples. If no organisms and/or associated
        evidence are found, the upper portion  of the
        casing should be cleaned with a long-handled
        brush or other similar tool.  The cleaning should
        be scheduled after sample collection, and the well
        should be completely purged after cleaning
        (National Council of the Paper Industry for Air
        and Stream  Improvement, 1982);
    3)  When metal casing is used as protective  casing
        and a threaded cap is used, the casing should be
        inspected for corrosion  along the threads.
        Corrosion can be reduced by lightly lubricating or
        applying teflon tape to the threads to prevent
        seizing. Corrosion of the casing can be reduced by
        painting. If lubricants and/or paint are used, the
        lubricants and/or paint  should be prevented from
        entering the well;
    4)  Where multilevel sampling tubes are used, the
        tubes  should rechecked for blockages and labeling
        so that samples are collected from the intended
        zones;
    5)  Where exterior bumper guards  are used, the
        bumperguards should be inspected for mechanical
        soundness and periodically  painted to retain
        visibility; and
    6)  Surface seals should be inspected for settling and
        cracking. When settling occurs, surface water can
        collect around the casing.  If cracking occurs or if
        there is an improper seal, the water may migrate
        into the well. Well seal integrity  can best be
        evaluated after a heavy rain or by adding water
        around the outside of the casing. If the seal is
        damaged, the seal should be replaced.

Comparative Costs  of Maintenance
    Evaluating the cost of rehabilitating a well versus abandon-
ing and redrilling the well is an important consideration. Factors
that should be evaluated are the construction quality of the
well, the accuracy of the well-intake placement and the preci-
sion of the documentation of the well. Capital costs of a new
well should also be considered. The actual "cost" of rehabilita-
tion is hard to  calculate. Different rehabilitation programs may
be similar in technique and price but may produce very different
results. In some situations, different treatment techniques may
be necessary to effectively treat adjacent  wells. Sometimes
techniques that once  improved a well may  only have a short-
term benefit or may no longer be effective. However, the cost
of not maintaining or rehabilitating a monitoring well maybe
very high.  The  money spent through the years  on man-hours for
sample  collection and laboratory sample analyses may be
wasted by  the collection of unrepresentative data. Proper main-
tenance and rehabilitation in the long run is a good investment.
If rehabilitation is not successful, abandonment of the well
should be considered.

Well Abandonment

Introduction
    Unplugged or improperly plugged abandoned wells pose a
serious threat to ground water. These wells serve as a pathway
for surface pollutants to infiltrate into the subsurface and
present an  opportunity for various qualities of water to mix.
Currently, many sites are being monitored for low concentra-
tions of contaminants. As detection limits are lowered, it
becomes more important to have confidence in the monitoring
system. An improperly installed or maintained monitoring
network can produce anomalous sample results. Proper aban-
donment is  crucial to the dependability of the remaining or new
installations.

    The objectives of an abandonment procedure are to: 1)
eliminate physical hazards; 2) prevent ground-water  contami-
nation, 3) conserve aquifer yield and hydrostatic head and 4)
prevent intermixing of subsurface water (United States Envi-
ronmental Protection Agency, 1975; American Water Works
Association, 1984). The purpose of sealing an abandoned  well
is to prevent any further disturbance to the pre-existing
hydrogeologic conditions that exist within  the subsurface.  The
plug should prevent vertical movement within the borehole and
confine the water to the original zone of occurrence.

    Many  states have regulations specifying the approved
procedures  for abandonment of water supply wells. Some states
require prior notification of abandonment actions  and extensive
documentation of the actual  abandonment procedures. How-
ever, few states have  specific requirements for abandonment of
monitoring  wells.

Well Abandonment Considerations
    Selection of the appropriate method for abandonment is
based on the information that has been compiled for each well.
Factors that  are considered include 1) casing material, 2)
casing condition, 3) diameter of the casing, 4) quality of the
original seal, 5) depth of the well, 6) well plumbness, 7)
hydrogeologic setting and 8) the level of contamination and the
zone or zones where contamination occurs.  The type of casing
and associated tensile strength limit the pressure that can be
applied when pulling the casing or acting as a guide when
overdrilling. For example, PVC casing may break off below
grade during pulling.  The condition of any  type of casing  also
may prohibit pulling.  The diameter of the casing  may  limit the
technique that is selected. For example, hollow-stem augers
may not be effective for overdrilling large-diameter wells
because of the high torque  required to turn large-diameter
augers. The quality of the original annular seal may also be a
determining factor. For example, if a poor seal was constructed,
then pulling the casing may  be accomplished  with minimum
effort. The  depth of the well  may limit the technique applied.
The plumbness of a well may influence technique by making
overdrilling or casing pulling  more difficult. The hydrogeology
of the site  may also influence the technique selected.  For
example, hollow-stem augers may be used for overdrilling in
unconsolidated deposits but not in rock formations.  The avail-
ability of a rig type and site conditions may also be determining
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factors. The level of contamination and zone in which contami-
nation occurs may modify the choice of technique. If no cross-
contamination can occur between various zones and contami-
nation cannot enter from the surface, grouting the well from
bottom to top without removing the casing maybe sufficient.

Well Abandonment Procedures
    Well abandonment procedures involve filling the well with
grout. The well may be filled completely or seals placed in
appropriate zones and the well only partially filled with grout.
Completely filling the well minimizes the possibility of bore-
hole collapse and shifting of seals. The material used to fill the
well can be either carefully selected natural material with a
permeability that approximates the permeability of the natural
formation or a grout mixture with a lower permeability. If more
than one zone is present in the well, then either intermediate
seals must be used with natural materials or the well  must be
grouted.  Monitoring wells are most commonly abandoned by
completely filling the well with a grout mixture.

    Wells  can be abandoned either by removing the casing or
by leaving all or  part of the casing in place and cutting the casing
off below ground level. Because the primary purpose of well
abandonment is  to eliminate vertical fluid migration along the
borehole, the preferred method of abandonment involves cas-
ing removal.  If the casing is removed and the  borehole is
unstable, grout must be  simultaneously emplaced as  the casing
is removed in order to prevent borehole collapse and an inad-
equate seal. When the casing is removed, the borehole can be
sealed completely and them is less concern about channeling in
the annular space or inadequate casing/grout seals. However, if
the casing is left in place, the casing should be perforated and
completely  pressure-grouted  to reduce' the possibility of annu-
lar channeling.  Perforating  small-diameter casings in situ is
difficult, if not impossible.

    Many  different materials can be used to fill the borehole.
Bentonite, other clays, sand, gravel, concrete and neat cement
all may  have  application in certain abandonment situations.
Appendix C contains recommendations for well abandonment
that are provided by the American Water Works Association
(1984). These  guidelines address the  use  of different materials
for falling the  borehole indifferent situations.  Regardless of the
type of material  or combination of materials used  for monitor-
ing well  abandonment, the sealant must be free of contaminants
and must minimize chemical alteration of the natural  ground-
water quality.  For example, neat cement should not be used in
areas where the  pH of the ground water is acidic. The ground
water will attack the cement  and reduce the effectiveness of the
seal; the  neat cement also raises the pH and alters ground-water
chemistry.

Procedures for Removing Casing —
    If the well was not originally grouted, the casing maybe
pulled by hydraulic jacks or by "bumping" the casing with a rig.
A vibration hammer also may be used to speed up the  task.
Casing cutters can be used to separate the drive shoe from the
bottom of the casing  (Driscoll, 1986).  If the well intake was
installed by telescoping, the intake may be removed by
sandlocking (United States Environmental Protection Agency,
1975).
    A properly sized pulling pipe must, be used to successfully
implement the sandlocking technique. Burlap strips, 2 to 4
inches wide, and approximately 3 feet long are tied to the
pulling pipe. The pipe is lowered into the borehole to penetrate
approximately 2/3 of the length of the well intake. The upper
portion of the well intake above the burlap is slowly filled with
clean angular sand by washing the sand into the well, The
pulling pipe is then slowly lifted to create a  locking effect.
Constant pressure is applied and increased until the well intake
begins to move. In some instances, jarring the pipe may assist
in well intake removal, but in some cases this action may result
in loss of the sand lock. As the well intake is extracted from the
well, the sand packing and pipe are removed. Many contractors
have developed variations of this sandlocking technique for
specific situations. For example, slots can be cut in the pulling
pipe at the level adjacent to the top of the well intake to  allow
excess sand to exit through the pulling  pipe. These  slots prevent
the well intake from being overfilled and sandlocking the entire
drill sting. Slots can also be cut in the pipe just above the burlap
so that sand can be backwashes or bailed from the inside pipe
if the connection should need to be broken. Right and left-hand
couplings located between the drill pipe and pulling pipe may
be installed to disconnect the drill string if it becomes locked.
Well intakes that are  2 to 6 inches in diameter can be  removed
by latch-type tools. For example, an elliptical plate cut in half
with a hinge may  be used. The plate folds as it is placed in the
well and unfolds when lifted. If the well  intake has a sump, the
tool can be locked under the sump; if there is no  sump, the tool
can be locked under the well intake (Driscoll, 1986).

    Another technique that may be used in conjunction with
sandlocking involves filling  the borehole with a clay-based
drilling fluid through the pulling pipe while pulling the well
intake and casing from the  bottom.  The fluid prevents the
borehole from collapsing. The level of the fluid is observed to
determine if the borehole is collapsing. Fluid rises if collapse is
occurring. If fluid is falling, it is an indication that fluid is
infiltrating into the surrounding formation. In this technique,
the borehole is grouted from the bottom to the surface.

    Overdrilling  can  also be used to remove casing from the
borehole. In overdrilling, a large-diameter hollow-stem  auger
is used to drill around the casing. A large-diameter auger is used
because a larger auger is less likely to veer off the during during
drilling. The hollow stem should beat least 2 inches larger than
the casing that is being removed. For example,  a 3  1/4-inch
inside-diameter auger should not be used to overdrill a 2-inch
diameter casing. The augers are used to drill to the  full depth of
the previous boring. If possible, the casing should  be pulled in
a "long" string, or in long increments. If the casing sticks or
breaks, jetting should be used to force water down the casing
and out the well intake. If this technique fails, the augers can be
removed one section at a time and the casing can be cut off in
the same incremental lengths. After  all casing has been re-
moved, the hollow-stem augers are reinserted and rotated to the
bottom of the borehole. All the debris from the auger interior
should be cleaned out, the augers extracted and the borehole
filled with grout by using a tremie pipe (Wisconsin Department
of Natural Resources, 1985).  The technique of overdrilling is
not limited to hollow-stem augers. Overdrilling  can  also be
accomplished  by  direct rotary techniques using air,  foam or
mud.
                                                           131

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    Limiting factors in overdrilling are the diameter of the well
and the hydrogeology of the surrounding formation. When
overdrilling, an attempt should be made to remove all annular
sealant so a good seal can be obtained between the borehole wall
and the grout. The plumbness of the original installation is a! so
very important if the well was not installed plumb, then
overdrilling may be difficult.

    A variation of overdrilling was used by Perrazo et al.
(1984) to remove  4-inch PVC casing from monitoring wells.
First, the well was  filled with a thick bentonite slurry to prevent
the PVC cuttings from settling in the borehole. The auger was
regularly filled with slurry to keep the casing full and to form a
mudcake on the wall. This mudcake served as  a temporary seal
until a permanent seal was  installed. A hollow-stem auger was
used with a 5 to 10-foot section of NW rod welded onto the lead
auger for use as a guide in drilling out the PVC casing. The auger
was rotated, and the casing  was cut and spiraled to the surface.
A 2-inch diameter roller bit was threaded onto a drill rod and
advanced to ensure the bottom area would be sealed to the
original depth. The grout mixture was pumped down the drill
stem and out the roller bit,  displacing the bentonite slurry and
water to the surface. In wells where there  was not sufficient
pressure to displace the bentonite slurry and  standing water, the
roller bit and drill stem were removed, a pressure  cap was
threaded onto the top auger flight and grout was  pumped
through the cap until increasing pressure forced the grout to
displace the bentonite slurry and water.  The augers were then
removed and the grout was alternately "topped off as each
flight was removed.

    Another technique involves jetting casing out of the well
with water. If the casing sticks or breaks off, a small-diameter
fish tail-type bit is connected to an A-rod to drill out the
thermoplastic casing. The drilling fluid flushes the cuttings to
the surface. After the borehole is cleaned, a tremie pipe is used
to emplace grout from the bottom to the surface (Wisconsin
Department of Natural Resources, 1985).

Procedures for  Abandonment  Without
Casing Removal  —
    If the casing is in poor condition, the interval adjacent to the
water-bearing zones can be ripped or perforated  with  casing
rippers, and then  the casing is filled and pressure grouted
(United  States Environmental Protection Agency, 1975; Driscoll,
1986). A concern when using this method is the accurate
placement and effectiveness of the cuts (Perazzo et al.,  1984).
Casing may begun-perforated by using a device that fires steel
projectiles through the casing and into  the formation.  A jet-
perforating device may be used that is similar to the gun-
perforator except that a pre-shaped charge of high explosives is
used to bum holes through the casing (Ingersoll-Rand,  1985).
The top portion of the casing is then pulled so that a watertight
plug in the upper 15 to 20 feet can be attained. This step may be
omitted where the annular space was originally carefully grouted
(Driscoll,  1986).

Using Plugs —
    Three types of bridge plugs can be used to  isolate hydraulic
zones. These include: 1) permanent bridge seals, 2) intermedi-
ate seals and 3) seals at the uppermost aquifer. The permanent
bridge seal is the most deeply located seal that is used to form
a "bridge" upon which fill material can be placed. Permanent
bridge seals prevent cross-contamination between lower and
upper water-bearing zones. Permanent seals are comprised of
cement. Temporary bridges of neoprene plastic or other elas-
tomers can provide support for a permanent bridge during
installation (United States Environmental protection Agency,
 1975).

     Intermediate seals are located between water-bearing zones
to prevent intermixing  of different-quality water. Intermediate
seals are comprised of cement, sand/cement or concrete mixes
and are placed adjacent to impermeable zones. The remaining
permeable zones are filled with clean disinfected sand, gravel
or other material  (United States Environmental Protection
Agency, 1975).

     The seal at the uppermost aquifer is located directly above
the uppermost productive zone.  The purpose is to seal out
surface water. An uppermost aquifer seal is typically comprised
of cement, sand/cement or concrete.  In artesian conditions, this
seal prevents water from flowing to the surface or to shallower
formations (United States Environmental Protection Agency,
 1975). This plugging technique is generally used to isolate
usable  and non-usable zones and has been used extensively in
the oil and gas industry.

     If artesian conditions are encountered,  several techniques
can be  used to abandon the well. To effectively plug an artesian
well, flow must be stopped and the water level lowered during
seal emplacement. The  water level  can be lowered by: 1)
drawing down the well by pumping nearby  wells, 2) placing
fluids of high specific gravity in the borehole  or 3) elevating the
casing high enough to stop the flow (Driscoll, 1986). If the rate
of flow is high, neat cement or sand/cement grout can be piped
under pressure, or a packer can be located at  the bottom of the
confining  formation above the production zone (United States
Environmental Protection Agency, 1975). Fast-setting cement
can sometimes be used in sealing artesian wells (Herndon and
Smith,  1984).

Grouting Procedures for Plugging
     All materials used for grouting should be clean and stable;
water used should be free from oil and other contaminants
(Driscoll, 1986). Grout should be applied in one continuous
grouting procedure from bottom to top to prevent  segregation,
dilution and bridging of the sealant. The end of the tremie pipe
should  always remain immersed in the slurry  of grout through-
out the emplacement procedure. Recommendations for grout
proportions and emplacement procedures are discussed in the
section entitled  "Annular  Seals."

     Many states permit or recommend a cement/bentonite
mixture.  The bentonite possesses swelling characteristics that
make it an excellent plugging material (Van Eck, 1978). The
grout mixture used should be compatible with soil and water
chemistry. For example, a salt-saturated cement should be used
for cementing in a salt-saturated  area. The  cement/bentonite
mixture should not extend through the vadose zone to the land
surface or be used in areas of low soil moisture because cracking
and channeling due to dessication can allow surface  water to
infiltrate along the casing (Driscoll, 1986). To ensure that the
borehole was properly grouted, records should be kept of the
                                                          132

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calculated volume of the borehole and the volume of grout that
was used; any discrepancy should be explained.

    A concrete cap should be placed on the top of a cement/
bentonite plug. The concrete cap should be marked with apiece
of metal or iron pipe and then covered by soil. The metal allows
for easy location of the well in the future by a metal detector or
magnetometer.

Clean-up, Documentation and  Notification
    After abandonment is accomplished, proper site clean-up
should be performed. For example, any pits should be back-
filled and the area should be left clean (Fairchild and Canter,
1984). Proper and accurate documentation of all procedures
and materials used should be recorded. If regulations require
that abandonment of wells be reported, information should be
provided on the required forms and in compliance with the state
regulations. Table 43 shows information that is typically recorded
on a well abandonment form. The location of abandoned wells
should be plotted on a map and referenced to section lines,  lot
lines, nearby roads and buildings as well as any outstanding
geological features (Aller, 1984).

Table 43. Welll Abandonment Data (After Wisconsin
         Department of Natural Resources, 1985)

  Name of property owner
  Address of  owner/property
  Well location (street, section number, township and range)
  Type of well installation method and date (drilled, driven,
  bored, dug), purpose of well (OW, PIEZ, LYS)
  Depth of well
  Diameter of well
  Depth of casing
  Depth to rock
  Depth to water
  Formation type
  Material overlying rock (clay, sand, gravel, etc.)
  Materials and quantities used to fill well in specific zones,
  detailing in which formations and method used
  Casing removed or left in place
  Firm completing work
  Signature of person doing work
  Address of firm

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                                                         133

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                                                        134

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                                                  Appendix A
                        Drilling and Constructing Monitoring Wells With
                                            Hollow-Stem Augers
                            [This report was produced as a part of this cooperative agreement
                                    and was published by Hackett (1987 and 1988).]
Introduction
    Since the 1950's, hollow-stem augers have been used
extensively by engineers and exploration drillers  as a practical
method of drilling a borehole for soil investigations and other
Geotechnical  work.  The widespread use and availability of
hollow-stem augers for Geotechnical investigations has re-
sulted in the adaptation of this method to drilling and installing
ground-water monitoring wells. To date, hollow-stem augers
represent the most widely used drilling method among  ground-
water professionals involved in constructing monitoring wells
(McCray, 1986). Riggs and Hatheway (1988)  estimate that
more than 90 percent of all monitoring wells installed in
unconsolidated materials in North America are constructed  by
using hollow-stem augers.

    The drilling procedures used when constructing monitor-
ing wells with hollow-stem augers, however, are neither stan-
dardized nor thoroughly documented in the published litera-
ture. Lack of standardization is partially due to variable
hydrogeologic conditions which  significantly influence hol-
low-stem auger  drilling techniques and monitoring well con-
struction practices. Many of these construction practices evolved
in response to site-specific  drilling problems which are unique
to hollow-stem  augers.

     This report presents an objective discussion of hollow-
 stem  auger drilling and monitoring well construction practices.
 The drilling equipment will be reviewed, and the advantages
 and limitations of the method for drilling and installing moni-
 toring wells will be presented.

Auger Equipment
     The equipment used for hollow-stem auger drilling in-
 cludes  either a mechanically or hydraulically powered drill rig
 which  simultaneously rotates and axially advances a hollow-
 stem auger column. Auger drills are typically  mounted on a
 self-contained vehicle that permits  rapid mobilization of the
 auger drill from borehole to borehole. Trucks  are frequently
 used as the transport vehicle; however, auger drills may also be
 mounted on all-terrain vehicles, crawler tractors or tracked
 carriers (Mobile'Drilling Company, 1983).  These drilling rigs
 often have multi-purpose auger-core-rotary drills which have
 been designed for Geotechnical work. Multi purpose rigs may
 have:  1) adequate power to rotate, advance and retract hollow-
 stem augers; 2) adequate drilling fluid pumping and tool  hoisting
 capability for rotary drilling; and 3) adequate rotary velocity,
 spindle stability and spindle feed control for core drilling
 (Riggs, 1986).

     The continuously open axial stem of the hollow-stem auger
 column enables the borehole to be drilled while the auger
column simultaneously serves as a temporary casing to prevent
possible  collapse of the borehole wall. Figure 1 shows the
typical components of a hollow-stem auger column. The lead
end of the auger column is fitted with an auger head (i.e., cutter
head) that contains replaceable teeth or blades which breakup
formation materials during drilling. The cuttings are carried
upward by the flights which are welded onto the hollow stem.
A pilot assembly, which is commonly comprised of a solid
center plug and pilot bit (i.e., center head), is inserted within the
hollow center of the auger head (Figure  1).  The purpose of the
center plug is to prevent formation materials from entering  the
              Drive Cap
         Rod to Cap
         Adapter

       • Auger Connector
                                           Hollow Stem
                                           Auger Section
                                         Center Rod
            Center Plug
 Pilot Assembly
 Components
                Pilot Bit
 L    .,— Auger Connector

^T
[T   ^	Auger Head
\\^^	Replaceable
r\5      Carbide Insert
          Auger Tooth
 Figure 1. Typical components of a hollow-stem auger column
          (after Central Mine Equipment Company, 1987).
                                                          141

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hollow stem of the lead auger, and the pilot bit assists in
advancing the auger column during drilling, A center rod,
which is attached to the pilot assembly, passes through the
hollow axis of the auger column. Once the borehole is advanced
to a desired depth for either sampling the formation or installing
the monitoring well, the center rod is used to remove the pilot
assembly. After a sample of the formation has been collected,
the center rod is used to reinsert the pilot assembly into the
auger head prior to continued drilling. The top of the center rod
is attached to a drive cap (Figure 1). The  drive cap is used to
connect the auger column to the spindle of the drill rig. This
"double adapter" drive cap ensures that the center rod and pilot
assembly  rotate along with the auger column.

    The auger column is comprised of a series  of individual
hollow auger sections which are typically 5 feet in length.
These individual  5-foot auger sections are joined together by
either slip-fit keyed box and pin connections, slip-fit box  and
pin connections or threaded connections (Figure 2).  The major-
ity of hollow-stem augers have keyed, box and pin connections
for transfer of drilling torque through the coupling and for easy
coupling and uncoupling of the auger sections (Riggs, 1987).
Box and pin connection of the connections use an auger bolt to
prevent the individual auger sections from slipping  apart when
the auger  column is axially retracted from a borehole (Figures
2a and  2b). Where  contaminants area concern at the drilling
site, an o-ring may be used on the pin end of the  connection to
minimize the possible inflow of contaminants through the joint.
Joints with o-rings will leak as  the o-rings become worn and it
is difficult to assess the degree of wear at each joint in the auger
column when drilling. Augers with watertight threaded connec-
tions are available; however, these threaded connections
commonly are used with commercial lubricants which may
contain hydrocarbon or metallic based  compounds. When
threaded hollow-stem augers are used for the installation of
water-quality  monitoring wells, the  manufacturer recommends
that no lubricants be used on the threads (H.E. Davis, Vice
President Mobile  Drilling Pacific Division, personal communi-
cation,  1987). When lubricants are  used  on the hollow-stem
auger threads, a nonreactive lubricant, such as  a  fluorinated
based grease, may be used to avoid introducing potential
contaminants that may affect the ground-water samples col-
lected from the completed well.

    The dimensions of hollow-stem auger sections and the
corresponding auger head used with each lead auger section are
not standardized between the various auger manufacturers. A
typical range of hollow-stem auger sizes with slip-fit, box  and
pin connections is shown in Table 1, and the range of hollow-
stem  auger sizes with threaded connections is shown in Table
2. Hollow-stem auger diameters are typically referenced by the
inside versus the outside (i.e., flighting)  diameter. All refer-
ences made to the diameter of the hollow-stem auger in  this
report will refer to the inside diameter, unless stated otherwise.
Tables 1 and 2 also  list the cutting diameter of the auger heads
which are mounted  on the lead augers. Common diameters of
hollow-stem augers used for monitoring well  construction
range from 3 1/4 to 8 1/4 inches for slip-fit, box and pin
connected augers and 3 3/8 to 6 inches for threaded augers.

    The hollow axis of the auger column facilitates the  collec-
tion of samples of unconsolidated formations, particularly in
unsaturated cohesive materials. Two types  of standard sam-
  Key Way
                                               Auger Bolt
                   • O-Ring

a. Keyed, Box and Pin Connection
                                                Auger Bolt
                        Pin End
b. Box and Pin Connection
c. Threaded Connection
Figure 2.  Three common methods for connecting hollow-stem
         auger sections.
                                                          142

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Table 1. Typical Hollow-Stem Auger Sizes with Slip-Fit, Box and Pin Connections (from Central Mine Equipment Company, 1987)
   Hollow-Stem
 Inside Diameter (In.)
Flighting Diameter
      (in.)'
    Auger Head
Cutting Diameter (in.)
       2114
       2314
       3114
       33/4
       4114
       6114
       8114
      55/8
      6118
      65/8
      7118
      7518
      95/8
      11 5/8
       61/4
       6314
       7114
       7314
       81/4
       10114
       12112
.NOTE: Auger flighting diameters should be considered minimum manufacturing dimensions.
Table 2. Hollow-Stem Auger Size with Threaded Connections (from Mobile Drilling Company, 1982)
   Hollow-Stem
Inside Diameter (in.)
    Flighting Diameter
          (in.)"
        Auger Head
    Cutting Diameter (In.)
       21/2
       3318
        4
          6114
          8114
          81/2
           11
             8
             9
             11
           13114
" NOTE: Auger flighting diameters should be considered minimum manufacturing dimensions.
piers which are used with hollow-stem augers are split barrel
and thin-walled tube samplers.

    Split-barrel samplers are typically driven 18 to 24 inches
beyond the auger head into the formation by a hammer drop
system. The split-barrel sampler is used to collect a represen-
tative sample of the formation and to measure the resistance of
the formation to penetration by the sampler. The samples are
used for field identification of formation characteristics and
may also be used for laboratory  testing. Thin-walled tube
samplers may be advanced a variable length  beyond the auger
head either by pushing or driving the sampler into the format-
ion. These samplers are designed to recover relatively un-
disturbed samples of the formation which are commonly used
for laboratory testing. Standard  practices for using split-barrel
samplers and thin-wall tube samplers are established under
ASTM Standards Dl586-84 and Dl587-83, respectively. The
ability  of hollow-stem augers to accommodate these samplers,
and thus to permit the collection of undisturbed samples of the
formation, is often cited as a major advantage  of the hollow-
stem auger method of drilling  (Minning, 1982; Richter and
Collecting, 1983; Gass,  1984).

     In addition to these standard samplers, continuous sam-
pling tube systems are commercially available which permit the
collection of unconsolidated formation samples  as the auger
column is rotated and axially advanced (Mobile Drilling Com-
pany, 1983; Central Mine Equipment Company, 1987). Con-
tinuous sampling tube systems typically use a 5-foot barrel
sampler which is inserted through the auger head. The barrel
sampler replaces the  traditional pilot assembly during  drilling;
however, the sampler does not rotate with the augers. The open
end of the sampler extends a short but  adjustable distance
beyond the auger head, and this arrangement allows sampling
to occur simultaneously with the advancement of the auger
column. After the auger column has advanced a distance up to
5 feet, the loaded sampler is retracted from the auger column.
The loaded sampler  is either immediately emptied and rein-
serted through the auger head or exchanged for another empty
                          sampler. Multi-purpose drill rigs that are capable of core
                          drilling can also use core barrels for coring either unconsoli-
                          dated material or rock.

                          Borehole Drilling
                              There are  several aspects of advancing a borehole with
                          hollow-stem augers that are  important considerations for ground-
                          water monitoring. For clarity and continuity, the topic of
                          drilling a borehole with hollow-stem augers will be presented
                          under three subheadings: 1) general drilling  considerations; 2)
                          drilling with hollow-stem augers in the unsaturated and satu-
                          rated zones; and 3) potential vertical movement of contami-
                          nants within the borehole.

                          General Drilling Considerations
                              When drilling with hollow-stem augers, the borehole is
                          drilled by simultaneously rotating and axially advancing the
                          auger column  into unconsolidated materials or soft, poorly
                          consolidated formations. The cutting teeth on the auger head
                          break up the formation materials,  and the rotating auger flights
                          convey the cuttings upward to the surface. In unconsolidated
                          materials, hollow-stem auger drilling can be relatively fast, and
                          several hundred feet of borehole advancement per day is
                          possible (Keely and Boateng, 1987a). Drilling may be much
                          slower, however, in dense unconsoldiated materials and in
                          coarse materials comprised primarily of cobbles. A  major
                          limitation of the drilling method is that the augers cannot be
                          used to drill through consolidated rock. In unconsolidated
                          deposits with boulders, the  boulders may also cause  refusal of
                          the auger column. According to Keely and Boateng (1978a),
                          this problem may  be overcome in sediments with cobbles by
                          removing the pilot assembly from the auger head and replacing
                          the assembly with a small tri-cone bit. It is then possible to drill
                          through the larger cobbles by limited rotary  drilling, without the
                          use of drilling fluids.

                              The depths to which a borehole may be advanced with a
                          hollow-stem auger depend on the site hydrogeology  (i.e., den-
                                                          143

-------
sity of the materials penetrated and depth to water) and on the
available power at the spindle of the drill rig. Riggs and
Hatheway (1988) state that, as a  general rule, the typical maxi-
mum drilling depth, in feet, with 3  1/4-inch to 4 1/4-inch
diameter hollow-stem augers, is equivalent to the available
horsepower at the drill spindle,  multiplied by a factor of 1.5.
This general rule on  maximum  drilling depths  may be influ-
enced by the types of formations being drilled. Hollow-stem
augers have been used to advance boreholes to  depths greater
than 300 feet; however, more  common depths of borehole
advancement are 75 to 150 feet  (Riggs and Hatheway, 1988).
The United  States Environmental Protection Agency (1986)
generally recognizes  150 feet as the maximum drilling depth
capability of hollow-stem augers in unconsolidated materials.

    One significant advantage of using hollow-stem augers for
ground-water monitoring applications is that the drilling method
generally does not require the circulation of drilling fluid in the
borehole (Scalf et al, 1981; Richter and Colletme, 1983). By
eliminating or minimizing the use of  drilling fluids, hollow-
stem auger drilling may alleviate concerns regarding the poten-
tial impact that these  fluids may have on the quality of ground-
water samples collected from a completed monitoring  well.
Without the use of drilling fluids, the drill cuttings  may also be
more easily controlled. This is particularly important where the
cuttings are contaminated and  must be  contained for protection
of the drilling crew and for disposal.  In addition, subsurface
contaminants encountered during the drilling process are not
continuously circulated throughout the borehole via a drilling
fluid.

    The potential for formation  damage from the augers (i.e.,
the reduction of the  hydraulic conductivity of the materials
adjacent to the borehole) varies with the type  of materials  being
drilled.  In homogeous sands  and gravels, hollow-stem  auger
drilling may cause minimal damage to the formation. Where
finer-grained deposits occur,  however, smearing  of  silts and
clays along the borehole wall is common. Keely and  Boateng
(1987a) indicate that interstratified clays and  silts can be
smeared into coarser  sand and gravel deposits and can thereby
alter the contribution of ground-water flow from various  strata
to the completed monitoring well. Smearing of silts and clays
along the borehole wall may also be aggravated by certain
drilling practices that are designed to ream the  borehole to
prevent binding of the auger column (Keely  and Boateng,
 1987a). These reaming techniques, which may be used after
each few feet of borehole advancement, include either rotating
the auger column in a stationary position or rotating the  auger
column while the column is alternately retracted and advanced
over a short distance in the borehole.

    The diameter of the borehole drilled by hollow-stem au-
gers is influenced by the outside  diameter of the auger  head and
auger flighting, the type of formation material being drilled and
the rotation of the augers. As shown in Tables  1 and 2, the
cutting diameter of the  auger head is  slightly larger  than the
corresponding  outside diameter of the flighting on the hollow-
stem auger. The cutting diameter of the auger head will there-
fore initially determine the diameter of the borehole. However,
as the cuttings are conveyed up  the flights during drilling, the
diameter of the borehole may also be influenced by the packing
of the cuttings on the borehole  wall. Cuttings from  cohesive
formation materials with silts and clays may easily  compact
 along the borehole wall, whereas noncohesive sands and
 gravels may not. Where cuttings are readily compacted on the
 sidewalls, the borehole  diameter may reflect the outside diam-
 eter of the auger flights as opposed to the cutting diameter of the
 auger head. In noncohesive materials, the borehole diameter
 may be enlarged due to caving of the side walls. In addition,
 reaming techniques used to  prevent binding of the auger column
 in the borehole often  serve to enlarge  the diameter of the
 borehole beyond the outside diameter of  the the auger flights.
 The  diameter of the borehole may also be influenced by the
 eccentric rotation of the augers which do not always rotate
 about a vertical axis. As a  result of these  factors, the borehole
 diameter may be variable over the length of the borehole.

 Drilling  with  Hollow-Stem   Augers   in  the
 Unsaturated  and Saturated Zones
      The drilling practices used to advance a borehole with
 hollow-stem augers in saturated materials and unsaturated
 materials are usually the same when drilling in finer-grained
 deposits or compacted sands and gravels. However, certain
 lossely compacted saturated sands, known as  "heaving sands"
 or "sandblows," may pose a particular drilling difficulty
 (Minning,  1982; Perry and Hart, 1985;  Keely and Boateng,
 1987a). Heaving sands can necessitate changes in basic drilling
 equipment and changes in drilling practices. The following
 discussion focuses first on the drilling procedures used to
 advance a borehole through the unsaturated zone. These
 procedures  are then contrasted  with the drilling techniques used
 to advance the auger column into saturated heaving sands.

 Unsaturated Zones  —
      When drilling in the unsaturated zone, the hollow-stem
 auger column is typically comprised of the components shown
 in Figure  1. A pilot assembly,  center rod and drive cap
 commonly are used, and the borehole is advanced without the
 use of a drilling fluid. When the borehole  has been advanced to
 a desired sampling depth,  the drive cap  is detached from the
 auger column, and the center rod and pilot assembly are
 removed from the hollow axis  of the auger column (Figures 3 a
 and  3b). A split barrel sampler or thin-walled tube sampler,
 attached to a sampling rod, is  then lowered through the axis of
 the hollow-stem column. The  sampler is  advanced beyond the
 auger head either by driving or pressing the  sampler  into the
 formation materials (Figure 3c). The loaded sampler and sam-
 pling rod are removed from the  auger column,  and the pilot
 assembly and center rod are reinserted prior to continued
 drilling. When formation samples are  required at frequent
 intervals during borehole advancement, the sequential removal
 and  reinsertion of the pilot  assembly and center rod can be time
 consuming. In order to minimize the time required to collect
 undisturbed formation samples, continuous sampling tube sys-
 tems can be used to replace  the traditional pilot assembly.
 Continuous samplers enable the collection of formation  samples
 simultaneously with the advancement of the borehole (Figure
 4). Driscoll (1986) states that the pilot assembly and center rod
 may be omitted when drilling through some  dense formation
 materials because these cohesive materials usually form only a
 limited  2 to 4-inch thick blockage of material inside the hollow
 center of the auger head. Drilling with an open auger head in
 the unsaturated zone, however, is not a common practice and is
 not recommended where detailed  samples of the formation are
 required.
144

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L "!K ,Cv **.'o AJ* .O ' V1, • e*'^-* -..5-r "~Vft- • s
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 Jy Column ^
                                                                  £& Column ?
                                                                  p^»-\.      j-
                                                                     ..,?
                                                                      '-
                                                                   Split Barref;
                                                                    or Thin
                                                                   ,Walled Tube
                                                                   ^Sampler .•£
                                        Open Axis ol
                                         Auger
                                         Column with
                                         Pilot
                                         Assembly
                                        kand Center j
                                             Removed

                                                                                        Wf^il^fS
                                                                                        •b'o.V^T.-.O.'o - i-V'-^J^VS-^-o • :?'a  "
                                                                   '•'Sampling'
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                                                                   i
                                                                      -'
                                                                                            §^€»«I
                                                              ^>^§
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n:oyb;t.?.- OioSvoSSUn'
                                                                                                                 iO
                                                                                            00^0.:^:v•A^o>.i•\>.o:•.Vo•or
Figure 3. Sequential steps showing borehole advancement with pilot assembly and collection of a formation sample
         (after Riggs, 1983).
Heaving Sands —
     The drilling techniques used to advance the auger column
within heaving sands may vary greatly from those techniques
used when drilling in unsaturated materials.  The problem may
occur when the borehole is advanced to a desired depth without
the use of drilling fluids for the purpose of either sampling the
formation or installing a monitoring well.  As the pilot assembly
is retracted, the hydrostatic pressure within the saturated sand
forces water and loose sediments to rise inside the hollow center
of the auger column (Figure 5). Keely and Boateng (1987a)
report that these  sediments can rise several  tens of feet inside
the lower auger sections.  The resulting "plug" of sediment
inside the hollow auger column can interfere with the collec-
tion of formation samples,  the installation  of the monitoring
well or even additional drilling.

     The difficulties with heaving sands may be overcome by
maintaining a positive pressure head within the auger column.
 A positive pressure  head can be created by adding a sufficient
 amount of clean  water or other drilling fluid inside the hollow
 stem. Clean water (i.e., water which does not contain analytes
                                                             of concern to a monitoring program) is usually preferred as the
                                                             drilling fluid in order to minimize potential interference with
                                                             samples collected from the completed well. The head of clean
                                                             water inside the auger column must exceed the hydrostatic
                                                             pressure within the sand formation to limit the rise of loose
                                                             sediments inside the  hollow-stem. Where the saturated sand
                                                             formation is unconfined, the water level inside the auger col-
                                                             umn is maintained above the elevation of the water table. Where
                                                             the saturated sand formation is confined, the water level inside
                                                             the auger column is maintained above the potentiometric sur-
                                                             face  of the formation. If the potentiometric surface of the
                                                             formation rises above the ground elevation, however, the heav-
                                                             ing sand problem may be very  difficult to counteract and may
                                                             represent a limitation to the use of the drilling method.

                                                                  There are several drilling  techniques used to maintain a
                                                             positive pressure head of clean  water within the auger column.
                                                             One technique involves injecting clean water through the auger
                                                             column during drilling. This method  usually entails removal of
                                                             the pilot assembly, center rod and drive cap. A special coupling
                                                             or adapter is used to connect the auger column to the spindle of
                                                            145

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Auger Drilling
Auger Column
Barrel Sampler
                                        — Non-rotating
                                           Sampling Rod
                                              Auger Head
Figure 4. Diagram of continuous sampling tube system (after
         Central Mine Equipment Company, 1987).

the drilling rig.  Clean water is then injected either through the
hollow-center coupling or through the open spindle of the drill
rig as the auger  column is advanced (Figure 6). Large diameter,
side-feed water swivels are also available and can be installed
between the drive cap and the hex shank which connects the
auger column to the  spindle of the drill rig. Clean water is
injected through the  water swivel and into the auger column as
the augers are advanced.

    Another drilling technique used to overcome heaving
sands is to first advance the auger column by using a
"nonretrievable" knock-out plate.  The knock-out plate is  wedged
inside the auger head and replaces the traditional pilot assembly
and center rod (Figure 7a). A major disadvantage of this
drilling technique is that the knock-out plate cannot be  alter-
nately removed  and reinserted from the auger column to permit
the collection of formation samples as the auger column is
advanced. Once the auger column is advanced to a desired
depth, the column is filled to a sufficient height with clean
water. A ramrod commonly is used to strike and remove the
knock-out plate from the auger head (Figure 7b). The head of
clean water in the auger column must exceed the hydrostatic
pressure in the sand  formation to prevent loose sediments from
rising inside the auger column once the knock-out plate is
removed. The nonretrievable knock-out plate should be con-
structed of inert materials when drilling a borehole  for the
installation of a water-quality monitoring well. This  will  mini-
  mize concerns over the permanent presence of the knock-out
  plate in the bottom of the borehole and the potential effect the
  plate may  have  on ground-water samples collected from the
  completed  well.

      Reverse flight augers represent another unique center plug
  design which  has had measured success in overcoming prob-
  lems with heaving sands (C. Harris, John Mathes and Associ-
  ates, personal communication, 1987). The flighting on the
  center plug and center rod rotates in an opposite direction from
  the flighting on the auger column (Figure 8). As the auger
  column advances through the heaving sands, the sand deposits
  arc pushed outward from the auger head by the reverse flighting
  on the center  plug. A sufficient head of clean water is main-
  tained inside the auger column to counteract further the hy-
  drostatic pressure in the heaving sand formation. Once  drilling
  is completed,  the reverse flight center plug is slowly retracted
  from the auger  column so that movement of sand into the
  hollow stem is not induced.

      Although the use of clean water  as drilling fluid is
  recognized by the United States Environmental Protection
  Agency  as a proper  drilling technique  to avoid heaving sand
  problems (United States Environmental protection Agency,
  1986), the use of any drilling fluid maybe undesirable or pro-
  hibited at some ground-water monitoring sites. In these in-
  stances, the problem  may be overcome by using commercial or
  fabricated devices that allow formation water to enter the auger
  column, but exclude formation sands. Perry and Hart (1985)
  detail the fabrication of two separate devices that allow only
  formation water  to enter the hollow-stem  augers when  drilling
  in heaving sands. Neither one of these two devices permit the
  collection of formation samples as the auger column is ad-
  vanced through the heaving sands. The  first device consists of
  a slotted coupling attached  to a knock-out plate (Figure 9). As
  the auger column advances below the  water table, formation
  water enters the auger column through the slotted coupling
  (Figure lOa). When the auger column is advanced to the
  desired depth,  a ramrod is used to dislodge the knock-out plate
  with slotted coupling from  the auger head (Figure lOb). Perry
  and Hart (1985) report that the slotted coupling generally is
  successful  in counteracting  heaving sand  problems. However,
  where clays  and silts are  encountered during drilling,  the
  openings in the slotted coupling may clog and restrict format-
  ion water from entering the auger column. To overcome this
  plugging problem, Perry and Hart (1985) fabricated a second
  device to be used when the slotted coupling became plugged.
  The second device is  actually a screened well swab (Figure 11).
  The swab is connected to a ramrod and is lowered through the
  auger column once  the column is advanced to the desired
  depth. The ramrod is used to strike and remove the knock-out
  plate from the  auger head (Figure 12). The screened well swab
  filters the sand and allows only formation water to enter the
  auger column (Perry and Hart, 1985). Once the water level rises
  inside the auger  column to  a height that offsets the hydrostatic
  pressure in the formation,  the  screened well swab is  slowly
  removed so that  movement  of sand into the hollow stem is not
  induced.

      Commercial devices that permit only formation water to
  enter the auger column during drilling are also available. These
  devices include a variety of patented designs, including
  nonwatertight  flexible center plugs. These devices replace the

146

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                                                      :•:;•  Pilot Assembly
                                                      ;':•'•... Being Retracted
                 Pilot
                Assembly
                      a. Borehole Advanced into Saturated
                         Sand with Auger Column
                         Containing Pilot Assembly

Figure 5. Diagram showing  heaving sand with hollow-stem auger drilling.
         b. Movement of Loose Sands inlo the
            Hollow Center of Auger as the Pilot
            Assembly is Removed
traditional pilot assembly in the auger head.  Some flexible
center plugs are seated, inside the auger head  by means of a
specially  manufactured groove in the hollow stem. These
flexible center plugs allow split-barrel samplers and thin-
walled tube samplers to pass through the center plug so that
samples of the water bearing sands can recollected (Figure 13).
The flexible center plug, however, cannot be retracted from the
auger head and therefore severely restricts the ability to install
a monitoring well through the auger column. The monitoring
well intake and casing can be inserted through the flexible
center plug, but the plug eliminates the installation of filter pack
and annular sealant (i.e., bentonite pellets) by free fall through
the working space between the well casing and auger column.

Potential Vertical Movement of Contaminants
Within the  Borehole
    The potential for contaminants to move vertically within
the borehole during drilling is an important consideration when
selecting a drilling method for ground-water monitoring. Ver-
tical mixing of contaminants from different levels within a
single borehole may be a problem with several different drilling
methods, including hollow-stem augers. As the auger column
advances through deposits which contain  solid, liquid or gas-
phase contaminants, there may be a potential for these con-
taminants to move either up or down within the borehole.
Where vertical movement of contaminants occurs within the
borehole, the cross contamination may be a significant source
of sampling bias (Gillham et al, 1983).

    Vertical movement of contaminants within the borehole
may occur when contaminants from an overlying stratum are
carried downward as residual material on the augers. The
potential for small amounts of contaminated material to adhere
to the auger head and lead auger is greatest in cohesive clayey
deposits (Gillham et al., 1983). Contaminants may also adhere
to split-barrel samplers and thin-walled tube samplers. If these
sampling devices  are not adequately cleaned between usage at
successive sampling depths, contaminants from an overlying
stratum may be introduced in a lower stratum via the sampling
device.  Where reaming techniques have enlarged  the borehole
beyond the outside diameter of the auger flights, contaminants
                                                          147

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Auger
Drill Rig
                        Water Swivel
                                Clean Water
                           Spindle Adapter Assembly Used for
                           Injecting Fluids Inside Auger Column
Figure 6.  Injecting clean water through open drill spindle to
         counteract heaving sand (after Central Mine
         Equipment Company, 1987).

from  an overlying stratum may slough, fall down the annular
space and come in contact with a lower stratum (Keely and
Boateng, 1987a). Even small amounts of contaminants that
move downward in the  borehole,  particularly to the depth at
which the intake of the monitoring well  is to be located, may
cause anomalous sampling results  when analyzing samples for
contaminants at very low concentrations. According to Gillharm
et al. (1983),  this potential for sampling bias is greatest at
monitoring  sites where shallow geological formations contain
absorbed or immiscible-phase contaminants.

    Contaminants may  also move upward within a borehole
during hollow-stem auger drilling. As  the auger column is
advanced through a stratum containing contaminants, the con-
taminants may be carried upward along with the cuttings.
Contaminated material from a lower stratum may therefore be
brought into contact with an uncontaminated overlying stratum
(Keely and  Boateng, 1987a). Cohesive materials within the
contaminated cuttings may 'smear and pack the contaminants on
the sidewalk Where contaminants are displaced and smeared
on the sidewall at the  intended monitoring depth, these contamin-
ants may serve as  a persistent  source of sampling bias.

    Vertical movement of dissolved-phase contaminants within
a borehole may also occur where two or more saturated zones
with different heads are penetrated  by the auger column.  When
the water level in a contaminated, overlying saturated zone is
higher than the potentiometric  surface of an underlying
uncontaminated zone, downward leakage of contaminated water
within the borehole may occur. This downward movement of
water may occur even if the augers are continually rotated in an
attempt to maintain the  upward movement of cuttings (Gillham
et al., 1983). Conversely, the upward leakage of contaminants
in the borehole may occur where the potentiomernc surface of
an underlying contaminated zone is higher than the water level
in an overlying saturated zone.

    The vertical movement of contaminants within the bore-
hole drilled with hollow-stem augers  is not well documented in
the  published literature. Lack of documentation is partially  due
to the difficulty of diagnosing the problem in the field. The
determination that an aquifer was contaminated prior to dril-
ling, during drilling or after installation of the monitoring well
may not easily be made. Keel y and Boateng (1987b), however,
recount a case history in which  apparent vertical movement of
contaminants in  the borehole occurred either during  hollow-stem
auger drilling antd/or after installation of the monitoring well.
This case study  involves a site at which a heavily  contaminated,
unconfined clayey silt aquifer, containing hard-chrome  plating
wastes, is underlain by  a permeable, confined sand and gravel
aquifer. Water  samples collected from monitoring wells  de-
veloped in the lower aquifer showed anomalous concentrations
for  chromium. Although vertical ground-water gradientsat  the
site were generally downward, the areal distribution and con-
centrations of chromium in the lower aquifer were not indica-
tive of long-term leakage through the aquitard. Based on their
investigation of the site, Keely and Boateng (1987b) conclude
that the localized pattern of chromium values in the lower
aquifer resulted from either vertical movement of contaminants
in the borehole or vertical  movement of contaminants through
faulty seals along the casing of the monitoring wells. The
authors hypothesize that the vertical movement of the contamin-
ants in the borehole may  have occurred when  contaminated
solids from the upper aquifer fell down the annular space during
hollow-stem auger drilling.

     The potential for cross contamination during drilling may
be reduced if contamination is  known or suspected at a site.
Where a shallow contaminated zone must be penetrated to
monitor ground-water quality at greater depths,  a large-diam-
eter surface casing may be used to seal off the upper contami-
nated zone before deeper  drilling is attempted.  Conventional
hollow-stem auger drilling  alone, however, may not always be
adequate for installation of a larger diameter surface casing.
Depending on the hydrogeological conditions at the site, a
"hybrid" drilling method may be necessary in which conven-
tional hollow-stem auger  drilling is combined with a casing
driving technique that advances the surface  casing as  the
borehole  is advanced. Driving techniques used to advance  and
install surface  casing  may include conventional cable tool
drilling, rotary drilling with casing hammer or a drop hammer
system on an auger drill rig.

    Conventional hollow-stem  auger drilling may be used to
set  protective surface  casing where the shallow geological
formations are comprised  of cohesive materials. In this situa-
tion, a large-diameter borehole maybe advanced by the auger
column to a depth below  the known contamination (Figure
14a). The auger column is then fully retracted from the borehole
at sites where the borehole will remain open due to the cohesive-
ness of the formation (Figure 14 b).  A large-diameter surface
                                                          148

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                                                          Clean Wale/*Level
                                                          Within Auger Column"
                       a, Borehole Advanced into Saturated
                         Sand with Auger Column Containing
                         Nonretrievable Knock-Out Plate
         b. Clean Water. Added to Auger
            Column Along with Removal of
            Knock-Out Plate by Ramrod
Figure 7. Use of a nonretrievable knock-out plate and auger column filled with clean water to avoid a heaving sand problem.
casing is then set and grouted into place. After grouting the
large-diameter surface casing into place a hollow-stem auger
column of smaller outside diamteter is used to advance the
borehole to the desired depth for installation of the monitoring
well (Figure 14c). Typical dimensions for augers used in this
scenario might be an 8 1/4-inch diameter hollow-stem auger
with an auger head cutting diameter of 12 1/2 inches to
advance the borehole below the contaminated zone.  A nominal
10-inch diameter surface casing would commonly be installed
within the 12 1/2-inch diameter borehole. Four-and-one-
quarter-inch diameter augers with an eight-and-one-quarter-
inch auger head cutting diameter might then be used to continue
drilling after the  surface casing is set.

    When the shallow geological formations are  comprised of
noncohesive materials and the borehole will not stand open, a
hybrid drilling technique can be used in which the surface
casing is advanced simultaneously with the auger column.
According to Keely and Boateng  (1987a), this alternate drilling
technique is used to advance the auger column a few feet at a
time and then to drive the surface casing to the new borehole
depth. The auger column is telescoped inside the surface casing
  as the casing is driven outside the augers (Figure 15). Five-foot
  lengths of casing typically are used with this technique, and the
  casing is driven either by using the same conventional 140-
  pound drop hammer that is used to advance split-barrel samplers
  or a heavier 300-pound drop hammer. The sequential steps of
  augering and casing advancement continue until the surface
  casing extends below the depth of known contamination. Once
  the surface casing  is set, a smaller diameter hollow-stem auger
  column can be used to advance the borehole to the desired depth
  for monitoring well  installation.

  Monitoring Well Installation
      Monitoring wells may  be constructed for water-quality
  sampling, water-level measurement or both. The intended
  purpose of the well influences the design components of a
  monitoring well. The following discussion will focus on tech-
  niques used to install water-quality monitoring wells  which
  consist of a well casing and intake, filter pack and annular seal.

      The methods  used to construct water-quality monitoring
  wells with hollow-stem augers depend primarily on site
  hydrogeology. In particular,  the cohesiveness of the formation
149

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                 Auger Column—
                 Filled with Clean
                 Water as
                 Borehole is
                 Advanced
                Reverse Flight
                Auger and
                Center Rod
                                                      Water Level

                                                    	4	
                                               7
Saturated Sand
Formation
                                                                                         f
                                                                                            - Reverse Flight
                                                                                             Auger and
                                                                                             Center Rod
                                                                                             Slowly Retracted
                                                                                             from Auger
                                                                                             : Column
                                                                                           -'Auger Column
                                                                                            Filled with Clean
                                                                                            Water as Reverse
                                                                                            Flight Auger is
                                                                                            Retracted
                               a. Reverse Flight Auger Pushes
                                 Cuttings Outwardly While Head
                                 of Clean Water is Maintained
                                 Inside Auger Column
            b. Reverse Flight Auger Slowly
               Being Retracted from Auger
               Column
Figure 8. Use of a reverse flight auger to avoid a heaving sand problem (after Central Mine Equipment Company, 1987).
                              Nipple
                                Lock Nut
                                           • Knock-Out Plate
                                • Slotted Coupling
                                Plug
Figure 9. Diagram of a slotted coupling
         (after Perry and Hart, 1985).
        materials penetrated  by  the auger column may  influence the
        well construction practices used. If the formation materials are
        cohesive enough so that the borehole remains open, the entire
        auger column may be retracted from the borehole prior to the
        installation of the monitoring well casing and intake, filter pack
        and annular seal. However,  even in cohesive formation mate-
        rials, drillers may refrain from the practice of fully  retracting the
        auger column from a completed borehole  to avoid unexpected
        caving of the borehole. The string of well casing and attached
        intake may be centered in the open borehole by  using casing
        centralizers. The filter pack and annular  sealant can then be
        emplaced through the working annular space between the
        borehole and well casing.

            When the auger column penetrates noncohesive materials
        and the borehole will not remain open, the auger column is used
        as a temporary  casing during well construction to prevent the
                                                            150

-------
                                                                                           Ramrod
                   Knock-Out Plate '•%&&£
                   with Slotted
                                                                                              Auger Column
                                                                                              Filled with
                                                                                              Formation Watei
Column as
Borehole is
Advanced
                                                         '"""Ramrod
                                a. Borehole Advanced into
                                   Saturated Sand with Auger
                                   Column Containing Nonretrievable
                                   Knock-Out Plate with
                                   Slotted Coupling
                                                     b. Knock-Out Plate with Slotted
                                                       Coupling Removed from Auger
                                                       Head by Ramrod
Figure 10. Use of a nonretrievable knock-out plate with a slotted coupling to avoid a heaving sand problem
          (after  Perry and Hart,  1985).
                              Supporting Pipe
   Pipe Flange
                                  -t- Brass Screen
                                             Pipe Flange
                             Inside Diameter of
                             Hollow-Stem Auger
                      C  - — Ball Valve
             Nipple
Figure 11. Diagram of a screened well swab
          (after Perry and Hart,  1985).
                                         possible collapse of the borehole wall. When the auger column
                                         is used as a temporary casing during well construction, the
                                         hollow axis of the auger column facilitates the installation of the
                                         monitoring well casing and intake, filter pack and annular
                                         sealant. However, the practices that are used to emplace these
                                         well construction materials through the working space inside
                                         the hollow-stem augers are not standardized among contrac-
                                         tors. Lack of standardization has resulted in concerns about the
                                         proper emplacement of the filter pack and annular seal in the
                                         monitoring  well.  To address these concerns, the topic of
                                         monitoring  well construction through hollow-stem augers is
                                         presented in three separate discussions 1) well casing diameter
                                         versus inside diameter of the  hollow-stem  auger 2) installation
                                         of the filter pack; and 3) installation of the annular seal.

                                         Well Casing Diameter Versus Inside Diameter of
                                         the Hollow-Stem Auger
                                              Once the borehole has been advanced  to the desired depth
                                         for installation of the monitoring well, the pilot assembly and
                                         center rod (if used) are removed, and the depth of the borehole
                                         is measured. A measuring rod or weighted measuring tape is
                                         lowered through the hollow axis of the auger column. This
                                         depth measurement is compared to the total length of the auger
                                        151

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                                                                                 Ramrod with
                                                                                 Screened Welt
                                                                                 Swati Attached
                                                                             Waier Level
                                                                         Water Level
                                                                         Rising Inside
                                                                         Auger Column
                                                                         After Removal of
                                                                         Knock-Out Plate
                                Screened Weil
                                Swab, Attached io
                                Ramrod, Used to
                                Filler Out Sand and
                                Permit Formation
                                Water to Enter
                                Auger Column
                       Knock-out Plate
                       with Clogged
                       Slotted Coupling
                        Removed from
                       Auger Heed by
                        Ramrod
Figure 12. Use of a screened well swab to avoid a heaving and problem (after Perry end Hart, 1985).
column in the borehole to determine whether loose sediments
have risen inside the hollow stem. Provided that the hollow
stem is clear of sediment, a sting of well casing with attached
intake  is lowered inside the auger column. Threaded, flush-joint
casing and intake are commonly used to provide a  string of
casing with a uniform outside and  inside diameter.

    Although the well casing and  intake may be centered
inside the  auger column, many contractors place the well casing
and intake toward one side of the  inner hollow-stem wall
(Figure 17). The eccentric placement of the casing and intake
within  the hollow-stem auger is designed to create a maximum
amount of working space (shown by the distance "A" in Figure
17) between the outer wall of the casing and the inner wall of
the auger.  This working space is used to convey and emplace the
filter pack and the annular sealant  through the auger column.
Table 3 lists the maximum working space (A) that is available
between various diameters of threaded, flush-joint casing and
hollow-stem augers, if the casing is set toward one side of the
inner hollow-stem wall.

    The selection of an appropriate  sized hollow-stem auger
for drilling and monitoring-well construction should take  into
account the nominal diameter of the well casing to be installed
and the working space needed to properly convey and emplace
the filter pack and annular sealant.  The smallest hollow-stem
augers typically used for installing 2-inch nominal diameter
casing are 3 1/4-inch diameter augers; the smallest hollow-stem
augers typically used for installing 4-inch nominal diameter
casing are 6  1/4-inch diameter  augers (Riggs and Hatheway,
1988). Table 3 shows, however, that the maximum working
space available between a 2-inch nominal diameter casing and
a 3 1/4-inch diameter hollow-stem auger is less than 1 inch (i.e.,
0.875 inch). This small working space can make the proper
emplacement  of the filter pack and annular seal very difficult,
if not impossible. Too small a working space can either restrict
the use of equipment (i.e., tremie pipe) that maybe necessary
for the placement of the filter pack and annular seal or inhibit
the ability to properly measure the actual emplacement of these
materials in the borehole. A small working space can also
increase the possibility  of bridging  problems when attempting
to convey the filter pack and  annular sealant between the
hollow-stem auger  and  well casing.  Bridging occurs when the
filter pack or annular seal material spans or arches across the
                                                          152

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Table 3. Maximum Working Space Available Between Various Diameters of Threaded, Flush-Joint Casing and Hollow-Stem Augers
Nominal
Diameter
of Casing
(in.)
2
3
4
5
6
OuUide
Diameter
of Casing
*(in.)
2.375
3.500
4.500
5.563
6.625
Working Space "A" (see Figure 17) for
Various Inside Diameter Hollow-Stem
Augers ** (in.)
31/4 33/4 41/4 61/4
0.875 1.375 1.875 3.875
	 0.250 0.750 2.750
	 	 	 1.750
	 	 	 0.687
81/4
5.815
4.750
3.750
2.687
1.625
   Based on ASTM Standards D-1785 and F-480
 ' inside diameters of hoiiow-stem augers taken from Table 1.
                                                                                         Flexible Center "?:|
                                                                                         Plug Permitting  "-:
                                                                                         Collection of
                                                                                         Water-Bearing
                                                                                         Sands, but
                                                                                         Preventing
                                                                                         Heaving Sands
                                                                                         from Entering   j
                                                                                         Hollow Stem   M
                     Saturated Sand
 Figure 13. Flexible center plug in an auger head used to overcome heaving sands and permit sampling of formation materials
           (after Diedrich Drilling Equipment, 1986).

                                                              153

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                                  Shallow
                                Contaminant
                                   Zone
                           "^  Large-Diameter
                           —  Auger Used to -
                           -x" Advance
                            _ Borehole in    ~
                           _ -. Cohesive    	
                            — ' Materials
                           ~_ Open Borehole •
                                                        <   Shallow
                                                         Contaminant
                                                            Zone
   _ "Protective
      Surface
 _    Set Below
_T~_  Contaminant
      Zone
 a. Large- Diameter Borehole   —
I  Advanced Below Known Depth
-  of Contamination          •
                                          • Auger Column Retracted from-
                                           Borehole Which Remains Open
                                           Qy8 to 0ohesiwa Materials  • —
                                                                                             Grouted Annular
                                                                                        ±_ .  Space
                                      Small-Diameterl.	
                                      Auger Used to — •  —
                                      Advance     ~H~.'J
                                      Borehole to a I—  ". "
                                      Deeper Depth _-—_ __
                                      for Installation of— , .
                                      Monitoring Well • • —
                                                                           c. Surface Casing Installed Below
                                                                              Known Depth of Contamination
                                                                              with Drilling Continued Using
                                                                              Smaller Diameter Auger

 Figure 14. Sequence showing the installation of protective surface casing through a shallow contaminated zone in a cohesive
space between the inner diameter of the auger and the outer
diameter of the casing. The bridge of filter pack or annular seal
material forms  a barrier which blocks  the downward movement
of additional material through the working space. As a result,
gaps or large unfilled voids may occur around the well intake or
well casing due to the nonuniform placement of the filter pack
or annular  seal. Bridged material can lock the casing due to the
nonuniform placement of the filter pack or annular seal. Bridged
material can lock the casing and auger together  and result in the
well casing being retracted from the  borehole along with the
augers.   Most  contractors prefer to use 4 1/4-inch diameter
augers to install 2-inch nominal diameter casing, and 8 1/4-inch
diameter augers to  install 4-inch nominal diameter  casing to
create an adequate working space  that facilitates the proper
emplacement of the  filter pack and annular seal  (C. Harris, John
Mathes and Associates, personal communication, 1987).  Ac-
cording to United States Environmental Protection Agency
(1986), the inner diameter of the auger should be 3 to 5 inches
greater than the outer diameter of the well casing for effective
placement  of the filter pack and annular sealant. Based on the
United Sates Environmental  Protection Agency guideline for
effective working  space,  6  1/4-inch diameter hollow-stem
augers would be the recommended  minimum size  auger for
installing a 2-inch nominal diameter casing. In addition, the
                                                     maximum diameter of a well which could be installed through
                                                     the hollow axis of the larger diameter augers, which are com-
                                                     monly available at this time, would be limited to 4 inches or less.

                                                     Installation of the Filter Pack
                                                         After the well casing and intake are inserted through the
                                                     hollow axis of the auger column, the next phase of monitoring
                                                     well construction commonly involves the installation of a filter
                                                     pack. The filter pack is a specially  sized and graded, rounded,
                                                     clean silica sand which is emplaced in the annular space
                                                     between the well intake and borehole wall (Figure 16).

                                                         The primary purpose of the filter pack is to filter out finer-
                                                     sized particles from the  formation materials adjacent to the well
                                                     intake.  The filter pack  also stabilizes the formation materials
                                                     and thereby minimizes  settlement of materials above the well
                                                     intake.  The appropriate  grain size for the filter pack is usually
                                                     selected based on a sieve analysis of the formation material
                                                     adjacent to the well intake. The filter pack is usually a uniform,
                                                     well-sorted coarse to medium sand (i.e., 5.0 mm to 0.40 mm).
                                                     However, graded filter packs may be used in a monitoring well
                                                     which has an intake installed in a fine-grained formation. The
                                                     graded  filter pack may filter and stabilize silt and clay-sized
                                                     Formation  particles more effectively. The completion of a
                                                           154

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                                                                                            Drop Hammer
                                                                                            used to Drive
                                                                                            Casing
                                                                                                -'
                                        i-^i&Borehale   vtow:
                                                 Driven Flosfi
                                                 with Borehole
                                                 Wall in Non-
                                                 Cohesive
                                                 Materials   '•

                       . Auger Column Advances
                        Borehole Slightly Beyond
                        Casing
      b. Driving the Casing to the
        New Borehole Depth
Figure 15. Sequence showing the installation of protective surface casing through a shallow contaminated zone in a noncohesive
          formation (after Keely and Boateng, 1987a).
monitoring well with a properly sized, graded and emplaced
filter pack minimizes the extent to which the monitoring well
will produce water samples with suspended sediments.

    The filter pack typically extends from the bottom of the
well intake to a point above the top of the intake (Figure 16).
The filter pack is extended above the top of the well intake to
allow for any settlement of the filter pack that may occur during
well development and to provide an adequate  distance between
the well intake and the annular seal. As a general rule, the length
of the filter pack is  10 percent greater than the length of the
intake to compensate for settlement. United States Environ-
mental Protection Agency (1986) recommends  that the filter
pack extend from the bottom of the well intake to a maximum
height of 2 feet above the top of the intake, with the maximum
height specified to ensure  discrete sample  horizons.

     The thickness of the filter pack between the well intake and
borehole wall  generally will not be uniform because the well
casing and intake usually are not centered in the hollow axis of
the auger column. The filter pack, however, should be at least
thick enough to completely surround the well intake. Tables 1
and 2 show that the cutting diameter of the auger head ranges
from 4 to 7 1/4 inches larger than the inside diameter of the
hollow-stem auger. When  the well casing and intake are posi-
tioned toward one side of the inner hollow-stem wall (Figure
 17), the  annular space between the well intake and borehole
wall may be as small as 2 to 3  5/8 inches. This annular space
may still be  adequate to preclude bridging and irregular em-
placement of the filter  pack however, there is marginal
tolerance for borehole sloughing or installation error. The
proper installation of a falter pack with hollow-stem augers can
be difficult if there is an inadequate working space between the
casing and the auger column through which the filter pack is
conveyed (Minning, 1982; Richter and Collentine, 1983; Gass,
 1984; schmidt 1986 Keely and Boateng, 1987b).
                                                           155

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Locking Casing Cap	
        Vent Hole	
  Protective  Casing—^-

    Qround Surface
                                  Inner Casing Cap
  — Lock
Draintole
                                         Surface Seal
      Filter Pack
Completion Depth -
                               r  "J        Water Table
                               r.t
                                          Borehole
                                           Well  Intake
                                           Plug
Figure 16. Typical design components of a ground-water
          monitoring well.

    The volume of filter pack required to fill the annular space
between the well intake and borehole wall should be predeter-
mined prior to the emplacement of the filter pack. In order to
determine the volume of filter pack needed, three design criteria
should be known. These three criteria include 1) the design
length of the fiter pack; 2) the diameter of the borehole; and 3)
the outside diameter of the well intake and casing. This infor-
mation is used to calculate both  the volume of the borehole and
the volume of the well intake  and casing over the intended
length of the filter pack. Once both volumes are calculated,  the
volume of the well intake and casing is subtracted from the
volume of the borehole to determine the volume of filter pack
needed to fill the annular space between the well intake and
borehole  wall. For example, Figure 18 illustrates a 2-inch
nominal diameter well casing and intake inserted through  the
hollow axis of a 4 1/4-inch diameter hollow-stem auger. Based
on the cutting diameter of the auger head, the diameter of the
borehole is  shown as 8 1/4 inches and the length of the well
intake is 10 feet. The design length of the filter pack is 12 feet
to ensure that the filter  pack extends 2 feet above the top of  the
intake. The volume of the borehole over the 12 foot design
length of the filter pack will be 4.36 cubic feet. Using 2.375
inches as the outside diameter of the well intake and casing,  the
volume of the intake and casing over the 12-foot design length
of the filter pack will be 0.38 cubic feet. By subtracting 0.38
cubic feet from 4.36 cubic feet, the volume of filter pack needed
to fill the annular space is determined to be 3.98 or  approxi-
mately 4 cubic feet.

    Once the theoretical volume of filter pack is calculated, this
volume is divided by  the design length of the filter pack to
determine the amount of the material which should be needed
to fill the  annulus for each lineal foot that the auger column is
retracted.  Referring again to the example illustrated in Figure
 18,4 cubic feet divided by  12 feet would equal approximately
 one-third cubic foot per foot. Therefore, for each foot that the
 auger column is retracted, one-third cubic  foot of filter pack
 should be needed to fill the annular space between the well
 intake and borehole wall.

      The methods which are used to convey the filter pack
 through the working space in the auger column and to emplace
 this material in the annular space between the well intake and
 borehole wall depend on:  1) the cohesiveness  of the formation
 materials; 2) the height of a standing water column in the
 working  space between the casing and augers;  and 3) the grain-
 size and uniformity coefficient of the filter  pack.

      In cohesive formation materials in which the borehole
 stands open, the filter pack commonly is emplaced by axially
 retracting the auger column from the borehole in short incre-
 ments and pouring the filter pack down the working space
 between the casing and auger column. Prior to filter pack em-
 placement,  a measuring rod or weighted measuring tape is
 lowered to the bottom of the borehole through the working
 space between the well casing and auger column (Figure 19a)
 so that the total depth of the borehole can be measured and
 recorded. The auger column is initially  retracted 1 or 2 feet
 from the borehole (Figure  19b). A measured portion of the
 precalculated volume of the filter pack is slowly poured down
 the working space between the well casing and auger column
 (Figure  19c). The filter pack is typically  poured at a point
 diametrically opposite from the measuring rod or weighted
 measuring tape. As the filter pack is being poured, the measur-
 ing device  is alternately raised and lowered to "feel" and
 measure the actual placement of the filter pack. If a weighted
 measuring tape is used as the measuring device, the tape is kept
 in constant motion to minimize  potential binding and loss of
 the weighted tape as the filter pack is being poured. Continuous
 measurements of the depth to the top of the emplaced filter
 pack are usually made as the filter pack is slowly poured down
 the working space in order to avoid allowing the emplaced filter
 pack to rise  up between the well intake/casing  and the inside of
 the hollow-stem auger.  If the filter pack is permitted to rise up
 between the casing and auger, the filter pack may lock the
 casing and auger together and result in the casing being re-
 tracted from the borehole along with the augers. Once the filter
 pack is emplaced to the bottom of the auger  column, the augers
 are retracted another 1 to 2 feet and a second measured portion
 of the filter pack is added. These steps are repeated until the
 required length of filter pack is emplaced. By knowing the
 theoretical amount  of filter pack needed to fill the annular space
 between the well intake and borehole wall for each increment
 in which the auger column is retracted, the emplacement of the
 filter pack may be  closely monitored.  Calculations of the "filter
 pack needed" versus "filter pack used" should be made and
 recorded for each increment that the auger column is retracted.
 Any discrepancies should be explained.

      Placement of filter pack by free fall through the working
 space between well casing and auger column can present the
 potential for bridging or segregation of the filter pack material.
 As  described earlier, bridging can result in unfilled voids within
 the filter pack or in the failure of the filter pack materials to be
 properly  conveyed  through the working space between the well
 casing and auger column. Bridging problems, however, may be
 minimized by:  1) an adequately sized working space between
 the well casing and auger column; 2) slowly  adding the filter

156

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                                                              Threaded, Flush-
                                                              Joint Casing
                                                              and Intake
                  Maximum
                  Working Space
                      Hollow-Stern
                      Auger
                                     Inside Diameter of
                                    Hollow-Stem Auger
                                     -A-IL-
                                      Outside D»ameter
                                          of Casing
                                                                        b. Cross-Sectional View

Figure 17. Plan and cross-sectional views showing the maximum working apace (A) between the well casing and the hollow-Stern
          auger.
pack in small amounts; and 3) carefully raising and lowering
the measuring rod or weighted measuring tape while the filter
pack is being added.

     Segregation of graded  filter pack material during free fall
through the working space  between the well casing and auger
column may still occur, especially where the static water level
between the casing and augers is shallow.  As the sand-sized
particles fall through the standing column of water, a greater
drag is exerted on the smaller sand-sized particles due to the
higher surface area-to-weight ratio. As  a result, coarser par-
ticles fall more  quickly through  the column of water and reach
the annular space between  the well intake and borehole wall
first. The coarser parrticles  may therefore comprise the bottom
portion of the filter pack, and the smaller-sized particles may
comprise the upper portion of each segment of filter pack
emplaced. Driscoll  (1986)  states that segregation may not be
a significant problem when  emplacing uniform grain size, well-
sorted filter packs with a uniformity coefficient of 2.5 or less.
However, graded filter packs are more susceptible to  segrega-
tion problems,  and this could result in  the  well consistently
producing water samples with suspended sediment.

     Potential bridging problems or segregation of graded filter
packs may  be minimized by using a tremie pipe to convey and
 emplace the filter pack.  The use of a tremie pipe may be
 particularly important where the static water level between the
 well casing and auger column is shallow. Schmidt (1986) has
 suggested that at depths greater than 50 feet, a tremie pipe
 should be used to convey and emplace filter pack through
 hollow-stem augers. A tremie pipe is a hollow, thin-walled,
 rigid tube or pipe which is commonly fabricated by connecting
 individual lengths of threaded, flush-joint pipe. The tremie pipe
 should have a sufficient diameter to allow passage of the filter
 pack through the pipe. The inside diameter of a tremie pipe used
 for filter pack  emplacement is typically 1  1/2 inches  or greater
 to minimize potential bridging problems inside the tremie.

      Emplacement  of the filter pack begins  by lowering a
 measuring rod or  weighted measuring tape to the bottom of the
 borehole, as previously described in the free  fall method of
 filter pack emplacement.  The auger column commonly is
 retracted 1 to 2 feet, and the  tremie pipe is lowered to the bottom
 of the borehole through the working space between the well
 casing and auger column (Figure 20a). A measured portion of
 the precalculated  volume of filter  pack is slowly poured down
 the tremie and the tremie  is slowly raised as the filter pack
 discharges from the bottom of the pipe, tilling the annular
 space between the well intake and borehole wall (Figure  20b).
 Once the filter pack is emplaced to the bottom of the auger

157

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2-Inch Nominal Diameter -
Well Casing and Intake
   4 1/4+inch Diameter
   Hollow-Stem  Auger
              Design Length
              of Filter Pack
                 12 Feet
   T
 Length of
Well Intake
 10 Feet
                                                 1
                               Borehole
                          '     Diameter     "
                              8 1/4 inches

Figure 18. Illustration for the sample calculation of a filter pack
          as described in the text.
column, the augers are retracted another 1 to 2 feet and a second
measured portion of the filter pack is added through the tremie
pipe. This alternating sequence of auger column retraction
followed by addtional filter pack emplacement is continued
until the required length of filter pack is installed. Similar to the
free fall method of filter pack emplacement, careful measure-
ments usually are taken and recorded for each increment of
filter pack which is  added and emplaced.

    During filter pack emplacement, whether by  free fall or
tremie methods, the auger column may be refracted from the
borehole in one of two ways (C. Harris, John Mathes and
Associates, personal communication, 1987).  One method of
retracting the augers  is to use the drive cap to connect the auger
column to the drill head. The drill head then pulls back the auger
column from the borehole. This technique, however,  com-
monly requires the measuring rod, weighted measuring tape or
tremie pipe (if used) to be removed from the working  space
between the wall casing and auger column each time the auger
column is retracted. A second method of retracting the augers
is to hook a winch line onto the outside of the open top of the
auger column. The winch line is then used to pull the augers
back. The use of a winch line to pull the auger column from the
borehole enables the measuring rod, weighted measuring tape
or tremie pipe to remain in the working space between the well
casing and auger column as the augers are retracted. This latter
auger retraction technique may provide greater continuity be-
tween measurements taken during each increment of filter
pack emplacement. Retracting the  auger column with the
winch line can also permit the option of adding filter pack
while the auger column is simultaneously withdrawn from the
borehole. Bridging problems, which lock the well casing and
augers together and cause the casing to pull out of the borehole
along with the augers, may also be more readily detected when
the auger column is retracted by using a winch line.  The use of
a winch line, however, may pull the auger column off center. If
the auger column is pulled off center, them maybe an increased
potential for the casing to become wedged within the augers.

    When the formation materials adjacent to the well intake
are noncohesive and the borehole  will not remain open as the
auger column is retracted, the method for installing the filter
pack may require the use of clean water (C. Harris, John Mathes
and Associates, personal communication, 1987). Similar to the
other methods of filter pack emplacement, a measuring rod or
weighted measuring tape is first lowered to the bottom of the
borehole through the working space between the well casing
and auger column. Clean water is then added to the working
space between the casing and augers to maintain a positive
pressure head in the auger column. As the auger column is
slowly retracted using a winch line, a measured portion of the
precalculated volume of filter pack is poured down the working
space between the well casing and auger column. The head of
clean water in the working space between the casing and augers
usually holds the borehole open while the filter pack material is
emplaced in the annular space between the well intake and
borehole wall. This procedure of  slowly retracting the auger
column  with a winch line while filter pack material is  poured
through  a positive pressure head of clean water in the working
space continues until the required length of filter pack is
installed. Once again, measurements of the emplaced filter
pack usually are taken and recorded along with calculations of
"filter pack needed' versus "filter pack used."

    If the formation materials adjacent to the well intake are
noncohesive and comprised of coarse-grained sediments, an
artificial filter pack may not have  to be installed. The  natural
coarse-grained sediments from the formation may  instead be
allowed  to collapse around the well intake (with appropriately
sized openings) as the auger column is refracted from the
borehole. This procedure initially involves retracting the auger
column 1 to 2 feet. A measuring rod or weighted measuring tape
is then lowered through the working space between the auger
column and  casing  to verify the collapse of formation material
around the well intake and to measure the depth to the top  of
"caved" materials.   Once the formation materials collapse
around the well intake and fill the  borehole beneath the auger
column, the augers are retracted another 1 to 2 feet. This
alternating sequence of refracting the auger column and  verify-
ing the collapse of formation materials by measuring the depth
to the top of the caved materials  continues until the coarse-
                                                          158

-------
    Weighted
   Measuring Tape
Well Casing

 -C1
    Hollow-Stem
    Auger
                                                                             Weighted
                                                                             Measuring Tape
                                        Well Casing
                                       	 /"""
                   Plan View
      Weighted
      Measuring Tape
              Cross-Sectional view
            a. Placement of Weighted
              Measuring Tape
               Weighted
               Measuring Tape
                     C ^^
            Hottow-Siem
            Auger           -^^^, Fj,ter Pack
                            Plan View  PtMmg
Auger Column
Retracted      Weighted-"'
1 to 2 Feet     Measuring Tape
from Borehole
                     b. Auger Column  Retracted
                                                                                                           Filler Rack
                      Cross -Sectional View
                  c. Filter Pack Free-Fails Through
                    Working Space Between Casing
                     and Auger
Figure 19. Free fall method of filter pack emplacement with a hollow-stem auger.
grained sediments extend to a desired height above the top of the
well intake.  The finer-grained fraction of the collapsed forma-
tion materials is later removed from the area adjacent to the well
intake during well development.

Installation of the Annular Seal
    Once the well intake, well casing and filter pack are
installed through the hollow axis of the auger column, the final
phase  of monitoring well construction  typically involves the
installation of an annular seal. The annular seal is constructed
by emplacing a stable, low permeability  material in the annular
space between the well casing and borehole wall (Figure  16).
The sealant  is commonly bentonite, expanding neat cement or
a cement-bentonite mixture. The annular seal typically extends
from the top of the filter pack to the bottom of the surface seal.
The annular seal provides: 1) protection against the movement
of surface water or near-surface contaminants down the casing-
borehole  annulus; 2) isolation of discrete sampling zones; and
3) prevention of the vertical movement of water in the casing-
borehole annulus and the cross-contamination of strata. An
effective  annular seal requires that the casing-borehole annulus
be completely filled with a sealant and that the physical integ-
rity of the seal be maintained throughout the life of the monitor-
ing well. The  sealant should ideally be  chemically nonreactive
to minimize any potential impact the sealant may have on the
                                 quality of ground-water samples collected from the  completed
                                 monitoring well.

                                     Although bentonite and cement are  the two most widely
                                 used annular sealants for monitoring wells, these materials have
                                 the potential for affecting the quality of ground-water samples.
                                 Bentonite has a high cation exchange capacity and may have an
                                 appreciable impact on the chemistry of the collected ground-
                                 water samples, particularly when the bentonite seal  is in close
                                 proximity to the well intake (Gibb,  1987). Hydrated cement is
                                 highly alkaline and may cause persistent, elevated pH values in
                                 ground-water samples  when the cement seal is  near or adjacent
                                 to the well intake (Dunbar et al,  1985). Raising the pH of the
                                 ground water may further alter the  volubility  and presence of
                                 other constituents in the ground-water samples.

                                     An adequate  distance between the well intake and the
                                 annular sealant is  typically provided when the filter pack is
                                 extended 2 feet above the top of the well intake.  Bentonite
                                 pellets are commonly  emplaced on top of the filter pack in the
                                 saturated zone (United  States  Environmental Protection
                                 Agency,  1986). Water in the saturated zone hydrates  and
                                 expands the bentonite pellets thereby forming a seal in the
                                 casing-borehole annulus above the filter pack. The use of
                                 bentonite pellets direct] y on top of the filter pack generally is
                                 preferred because the pellet-form of bentonite may minimize
                                                           159

-------
                   Weighted
                   Measuring Tape
                           C	
                                  Plan—View
                     Weighted  	
                     Measuring Tape

                           C	
                 Auger Column *«
                 Retracted
                 1 to 2 Feet    j*
                 from Borehole jfif
                    Well Casing
                    - -  C1
                    Tremie Pipe


                       Tremie Pipe
                    	Positioned to
                       Bottom of
                       Borehole
                    - — C'
Weighted
Measuring Tape
                                                                                    ^r
                        Tremie Pipe
                      Slowly  Raised  as
                     Filter Pack  is
                        Poured
mm
                             Cross -Sectional View
                         a. Weighted Measurng Tape and
                           Tremie Ptpe in Retracted
                           Auger Column
Filter Pack
Material Poured
Down Tremie
                                                                   Filter Pack
                                            b. Filter Pack Poured Through Bottom-
                                               Discharge Tremie Pipe
 Figure 20. Tremie method of filter pack emplacement with a hollow-stem auger.
the threat of the bentonite infiltrating the filter pack. United
States Environmental Protection Agency (1986) recommends
that there be a minimum 2-foot, height of bentonite pellets in
the casing-borehole annulus above the filter pack. The bento-
nite pellets, however, should not extend above t.hc saturated
zone.

     Bentonite pellets are emplaced  through  the hollow-stem
augers by free fall of the pellets through the working space
between  the well casing and auger column. Prior to emplacing
the bentonite pellets, the theoretical volume of bentonite pellets
needed to fill the annular space between the well casing and
borehole wall over the intended length of the seal is determined
(see section on Installation of the Filter Pack for a discussion on
how to calculate the  theoretical volume of material needed). A
measuring rod or weighted measuring tape is lowered to the top
of the  filter pack through the working  space between the casing
and augers.  A depth measurement is taken and recorded. The
auger column is then retracted 1 or 2 feet from the borehole and
a measured portion of the precalculated volume of bentonite
pellets is slowly poured down the  working space between the
well casing and auger column. In some instances, the bentonite
pellets may  be individually dropped,  rather than poured, down
this working space. The bentonite  pellets free fall through the
                                     working space between the casing and augers and fill the
                                     annular space between the well casing and borehole wall
                                     immediately above the filter pack. As the bentonite pellets are
                                     being added, the measuring rod or weighted measuring tape  is
                                     slowly raised and lowered to lightly  tamp the pellets in place
                                     and to measure the depth  of emplacement of the bentonite
                                     pellets. Once the bentonite pellets are emplaced to the bottom
                                     of the auger column, the augers are again retracted 1  or 2 feet
                                     from the borehole and more bentonite pellets are added. This
                                     procedure continues until the bentonite  pellets  are installed to
                                     the required height above the filter pack. Actual depth measure-
                                     ments of the emplaced pellets are recorded and compared with
                                     the calculations for the volume of "bentonite pellets  needed"
                                     versus  "bentonite pellets used."

                                         The free fall of bentonite pellets through the working space
                                     between the well casing  and auger  column provides the op-
                                     portunity for bridging problems to occur. Bridging problems
                                     are likely to occur particularly when the static water level in the
                                     working space is shallow and the well is relatively deep. As
                                     bentonite pellets fall through a column of standing water, the
                                     bentonite on the outer surface of the pellet starts to hydrate and
                                     the pellet surface expands and becomes sticky. Individual
                                     bentonite pellets may begin sticking to the inside wall of the
                                                           160

-------
auger column or to the outer surface of the well casing after
having fallen only a few feet through a column of water between
the casing and augers. Bentonite pellets may also stick together
and bridge the working space between the casing and augers.
As a result, the pellets may  not reach the intended depth for
proper annular seal emplacement. The bentonite pellets will
continue to expand as the bentonite fully hydrates. An expand-
ing bridge of bentonite pellets in the working space may
eventually lock the well casing and auger column together
causing the casing to pull back out of the borehole as the auger
column is retracted.

     Careful installation techniques can  minimize the bridging
of bentonite pellets in the working space between the casing and
augers.   These techniques include:  1)  adequately  sizing the
working space between the well casing and auger column; 2)
slowly adding individual bentonite pellets through the working
space; and 3) frequently raising and lowering the measuring
device to breakup potential bridges of pellets.  Driscoll  (1986)
reports that freezing the bentonite pellets or cooling the pellets
with liquid nitrogen to form  an icy outer coating may enable
the bentonite  pellets to free  fall a greater depth through standing
water before hydration of  the pellets begins. The frozen
bentonite pellets should,  however, be added individually in the
working  space between the casing  and  augers to avoid  clump-
ing of the frozen pellets as they contact the standing water in the
working  space.

     The potential problem of bentonite pellets bridging the
working  space between the well casing and auger column may
be  avoided by using instead a bentonite slurry, neat cement
grout or cement-bentonite mixture pumped directly into the
annular space between the well casing and borehole wall in the
saturated zone. In the unsaturated zone, neat cement grout or a
cement-bentonite mixture  commonly is used  as the  annular
sealant. In either instance, the slurry  is pumped under positive
pressure through a tremie pipe which is first lowered through
the working space between the well casing and auger column.
However, tremie emplacement of a bentonite slurry or cement-
based grout directly on top of the filter pack is not recommended
because these slurry mixtures may easily infiltrate into the
filter pack. Ramsey et al, (1982) recommend that a 1 to 2-foot
thick fine sand layer be placed on top of the filter pack prior to
emplacement  of the bentonite  slurry or cement grout. The fine-
sand layer minimizes the potential for the grout slurry  to
infiltrate into the filter pack.  If bentonite pellets are initially
emplaced on top of the filter pack, prior to the addition of a
bentonite slurry or cement-based  grout the pellets serve the
same purpose as the fine sand  and minimize the potential for the
infiltration of the grout slurry  into the filter pack. When bento-
nite pellets are used, a suitable hydration period, as recom-
mended by the manufacturer, should be allowed prior to the
placement of the grout slurry. Failure  to allow the bentonite
pellets to fully hydrate and seal the annular space above the
filter pack may result in the  grout slurry infiltrating into the filter
pack.

    A  side-discharge tremie  pipe, rather than a bottom-dis-
charge  tremie pipe, should be  used to emplace bentonite slurry
or cement-based grouts above the filter pack. Aside-discharge
tremie may be fabricated by  plugging the bottom end of the pipe
and drilling 2 or 3 holes  in the  lower 1 -foot section of the tremie.
The pumped slurry will discharge laterally from  the tremie and
 dissipate any fluid-pumping energy against the borehole wall
 and well casing. This eliminates discharging the pumped slurry
 directly  downward toward the filter pack and minimizes the
 potential for the sealant to infiltrate into the filter pack.

      Prior to emplacing  a bentonite slurry or cement-based
 grout via the tremie method, the theoretical volume of slurry
 needed to fill the annular space between the well casing and
 borehole wall over the intended length of the annular seal is
 determined (see section on Installation of the Filter Pack for a
 discussion on how to calculate the theoretical volume of mate-
 rial needed). An additional volume of annular sealant should
 be prepared and readily available at the drill site to use if a
 discrepancy  occurs  between the volume of "annular  sealant
 needed" versus "annular sealant used."  The installation of the
 annular sealant should be completed in  one continuous opera-
 tion which permits the emplacement of the entire annular seal.

     The procedure for emplacing a bentonite slurry or cement-
 based grout with a tremie  pipe begins by lowering a measuring
 rod or weighted measuring tape through the working space
 between the well casing and auger  column. A measurement of
 the depth to the top of the fine sand layer or bentonite pellet seal
 above the filter pack is taken and recorded. The auger column
 is commonly retracted 2 1/2 to 5 feet, and a side-discharge
 tremie pipe, with a minimum 1 -inch inside diameter, is lowered
 through the working space between the casing and augers.  The
 bottom of the tremie is positioned above the fine sand layer or
 bentonite pellet seal. A measured portion of the precalculated
 volume of bentonite slurry or cement-based grout is pumped
 through the tremie. The grout slurry discharges from the side
 of the pipe, filling the annular space between the well casing and
 borehole wall.  As the grout slurry is  pumped through the
 tremie, the measuring rod or weighted measuring tape is slowly
 raised and lowered to  detect and measure the depth of slurry
 emplacement. Once the slurry is emplaced to the bottom of the
 auger column, the augers are retracted by using a winch line, the
 measuring rod or tape and tremie pipe may remain inside the
 working  space between the casing and augers as the augers are
 pulled back from the borehole. Retracting the auger column
 with the  winch line may also permit the  option of pumping the
 grout slurry through the tremie while the auger column is
 simultaneously  withdrawn from the borehole. A quick-dis-
 connect fitting can be used to attach the grout hose to the top of
 the tremie pipe.  This fitting allows  the grout hose to be easily
 detached from the tremie as individual 5-foot auger sections are
 disconnected from the top of the auger column. By successively
 retracting the auger column and pumping the bentonite slurry or
 cement-based grout  into the annular space between the well
 casing and borehole wall, the annular sealant is emplaced from
 the bottom of the annular space  to the top.  The tremie pipe can
 be moved upward as the slurry is emplaced, or it can be left in
 place at the bottom of the annulus until the annular  seal is
 emplaced to the required height. Measurements of the  depths
 of the emplaced annular seal are taken and recorded. Calcula-
 tions of  the theoretical volume of "annular sealant needed"
 versus "annular sealant used" should also be recorded, and any
 discrepancies should be explained.

Summary
     Hollow-stem augers,  like all drilling methods, have  ad-
vantages and limitations for drilling and constructing monitor-
                                                           161

-------
ing wells. Advantages of using hollow-stem auger drilling
equipment include:  1) the mobility of the  drilling rig; 2) the
versatility of multi-purpose rigs for auger drilling, rotary drill-
ing and core drilling; 3) the ability to  emplace well casing and
intake, filter pack and annular seal material through the hollow-
stem auger, and 4) the utility of the hollow-stem auger for
collecting representative or relatively undisturbed samples of
the formation. Other advantages  associated with hollow-stem
augers relate to the drilling procedure and include: 1) relatively
fast advancement of the borehole in unconsolidated deposits; 2)
minimal formation damage in sands and gravels; 3) minimal, if
any, use of drilling fluids in the borehole and 4) good control
or containment of cuttings exiting from the borehole. Limitat-
ions of the drilling procedure include: 1) the inability to drill
through hard rock or deposits with boulders; 2) smearing of the
silts and clays along the borehole wall; 3) a variable maximum
drilling depth capability, which is typically less than 150 feet
for most rigs; and 4) a variable borehole diameter.

     The drilling techniques used to advance a borehole with
hollow-stem augers may vary when drilling in the unsaturated
versus the saturated zone. In the unsaturated zone, drilling
fluids are rarely, if ever, used. However, in a saturated zone in
which heaving sands occur, changes in equipment and drilling
techniques are required to provide a positive pressure head of
water within the auger column. This may require the addition
of clean water or other drilling fluid inside the augers. If a
positive pressure head of water cannot be maintained inside the
auger column when drilling in heaving sands, the heaving sands
may represent a limitation to the use of hollow-stem augers for
the installation of a monitoring well.

     The vertical movement of contaminants in the borehole
may be a concern when drilling with hollow-stem augers.
When monitoring the quality of ground water below a known
contaminated zone, hollow-stem auger drilling may not be
advisable unless protective surface casing can be installed.
Depending on the site hydrogeology, conventional hollow-
stem auger drilling techniques alone may not be  adequate for
the installation of the protective surface casing. A hybrid
drilling method may be needed which combines conventional
'hollow-stem auger drilling  with a casing driving technique that
advances the borehole and surface casing simultaneously.

     The procedure used to construct monitoring wells with
hollow-stem augers may  vary  significantly depending on the
hydrogeologic conditions at the drill site. In cohesive materials
where the borehole stands open, the auger column may be fully
retracted from the  borehole prior to the  installation of the
monitoring well. In noncohesive materials  in which the bore-
hole will not remain open, the monitoring well is generally
constructed through the hollow axis of the  auger column.

     The procedures used to construct monitoring wells inside
the hollow-stem augers may also vary depending on specific
site conditions and the experience of the driller. The proper
emplacement of the filter pack and annular seal can be difficult
or impossible, if an inadequate working  space is available
between the well casing and hollow-stem auger. An adequate
working space can  be made available by using an appropri-
ately-sized diameter hollow-stem auger for the installation of
the required-size well casing and intake. The maximum diam-
eter of a monitoring well constructed  through the hollow-stem
 auger of the larger diameter augers now commonly available
 will typically  be limited to 4 inches or less. Assurance that the
 filter pack and annular seal are properly emplaced is typically
 limited to careful measurements taken and recorded during
 construction of the monitoring well.

 References
 Central Mine and Equipment Company, 1987. Catalog of
     product literature; St. Louis, Missouri, 12 pp.
 Diedrich Drilling Equipment, 1986. Catalog of product
     literature; LaPorte, Indiana, 106 pp.
 Driscoll, Fletcher G., 1986. Groundwater and Wells; Johnson
     Division, St. Paul, Minnesota, 1089 pp.
 Dunbar, Dave, Hal Tuchfield, Randy Siegel and Rebecca
     Sterbentz,  1985. Ground water  quality anomalies
     encountered during well construction, sampling and
     analysis in the environs of a hazardous waste management
     facility; Ground Water Monitoring Review, vol. 5, No. 3,
     pp. 70-74.
 Gass, Tyler  E., 1984. Methodology for monitoring wells;
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 Gibb, James P., 1987. How drilling fluids and grouting
     materials affect the integrity of ground water samples from
     monitoring wells, opinion I;  Ground  Water Monitoring
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 Gillham, R.W., M.L. Robin, J.F. Barker and J.A. Cherry,
      1983. Groundwater monitoring and sample bias; API
     Publication 4367, Environmental Affairs Department,
     American Petroleum Institute, Washington D.C., 206 pp.
 Hackett, Glen, 1987. Drilling and constructing monitoring
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     considerations; Ground Water  Monitoring Review, vol. 7,
     no. 4, pp. 51-62.
 Hackett, Glen, 1988. Drilling and constructing monitoring
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     installation; Ground Water Monitoring Review, vol. 8, no.
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 Keely, Joseph F. and Kwasi Boateng, 1987a.  Monitoring well
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     313.
 Keely, Joseph F. and Kwasi Boateng, 1987b.  Monitoring well
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 Mcray, Kevin B., 1986. Results of survey of monitoring well
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 Minning, Robert C.,  1982. Monitoring well design and
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 Mobile Drilling Co., 1982. Auger tools and  accessories product
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 Mobile  Drilling Company, 1983. Mobile drill product catalog;
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 Perry, Charles A. and Robert J. Hart, 1985. Installation of
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 Ramsey, Robert J.. James M, Montgomery and  George E.
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162

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    Second National Symposium on Aquifer Restoration and
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Richter, Henry R. and Michael G. Collentme, 1983. Will my
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Riggs,  Charles 0., 1983. Soil Sampling in the vadose zone;
    Proceedings  of the NWWA/U.S. EPA Conference on
    Characterization  and  Monitoring  of the Vadose
    (Unsaturated) Zone, Las Vegas, Nevada, pp. 611-622.
Riggs,  Charles O.,  1986. Exploration for deep foundation
    analyses; Proceedings of the International Conference on
    Deep Foundations, Beijing, China, volume II, China
    Building Industry Press, Beijing, China, pp. 146-161.
Riggs,  Charles O.,  1987. Drilling methods and installation
    technology for RCRA monitoring wells; RCRA Ground
    Water Monitoring Enforcement Use of the TEGD and
    COG, RCRA Enforcement  Division, Office of Waste
    Programs  Enforcement, united  States Environmental
    Protection Agency, pp. 13-39.
Riggs, Charles O., and Allen W. Hatheway 1988. Ground-
    water monitoring field practice - an overview; Ground-
    Water Contamination Field Methods, Collins and Johnston
    editors, ASTM Publication Code Number 04-963000-38,
    Philadelphia, Pennsylvania, pp. 121-136.
Scalf, M.R., J.F. McNabb, W.J. Dunlap, R.L. Cosby and J.
    Fryberger, 1981. Manual of ground-water sampling
    procedures; National Water Well Association, 93 pp.
Schmidt, Kenneth D., 1986. Monitoring well drilling and
    sampling in alluvial basins in arid lands; Proceedings of the
    Conference on Southwestern Ground Water Issues, Tempe,
    Arizona, National Water Well Association, Dublin, Ohio,
    pp. 443-455.
United States Environmental Protection Agency, 1986. RCRA
    Ground-water  monitoring technical enforcement guidance
    document Office of  Waste Programs Enforcement, Office
    of Solid Waste and Emergency Response, OSWER-
    99501.1,  United States Environmental Protection Agency,
    317pp.
                                                       163

-------
                                                 Appendix  B
                   Matrices for Selecting Appropriate Drilling Equipment
    The most appropriate drilling technology for use at a
specific site can only be determined by evaluating both the
hydrogeologic setting and the objectives of the monitoring
program. The matrices presented here were developed to assist
the user in choosing an appropriate drilling technology. These
matrices address the most prevalent hydrogeologic settings
where monitoring wells are installed and encompass the drilling
technologies most often applied. The matrices have been devel-
oped to  act as guidelines; however, because they are subjective,
the user is  invited to make site-specific modifications. Prior to
using these matrices, the prospective user should review the
portion in Section 4 entitled "Selection of Drilling Methods for
Monitoring Well Installation."

    Several general assumptions were used during develop-
ment of the matrices. These are detailed below:

    1) Solid-flight auger and hollow-stem auger drilling
        techniques are limited to a practical drilling depth
        of 150 feet in most areas based on the equipment
        generally  available;
    2) Formation  samples collected:
        a)  during drilling with air rotary, air rotary with
            casing hammer and dual-wall air rotary tech-
            niques are  assumed to be from surface dis-
            charge of the circulated sample;
        b)  during drilling with solid-flight augers, hol-
            low-stem augers, mud rotary or cable tool
            techniques  are assumed to be taken by stan-
            dard split-spoon (ASTM Dl 586) or thin-
            wall (ASTM D1587) sampling techniques to
            a depth of 150 feet at 5-foot intervals;
        c)  below 150  feet,  during mud rotary drilling
            are assumed to be circulated samples taken
            from the drilling mud at the surface dis-
            charge; and
        d)  below 150 feet, during cable-tool drilling are
            assumed to be taken by bailer.
        If differing sampling methodologies are employed,
        the ratings for reliability of samples, cost and time
        need to be re-evaluated. (Wireline or piston
        sampling methods are available for  use with
        several drilling techniques;  however, these
        methods were not included in the development of
        the matrices);
    3)  Except for wells installed using driving and jetting
        techniques, the borehole is considered to be no
        less  than 4 inches larger in diameter than the
        nominal diameter of the casing and screen used to
        complete the well (e.g., a minimum  6-inch
        borehole is necessay for completion of a 2-inch
        diameter  cased well);
    4)  Artificial filter pack installation is assumed in all
        completions  except for  wells installed using
        driving and jetting techniques;
    5)  The  development  of ratings in the  matrices is
        based on the largest expressed casing diameter in
        each range listed in the "General Hydrogeologic
        Conditions & Well Design Requirements"
        statement;
    6)  For  purposes of the "General Hydrogeologic
        Conditions & Well Design Requirements air is
        not considered as a drilling fluid; and
    7)  In the development of the  dual-wall rotary
        technique ratings in the matrices, air  is  consider-
        to be the circulation medium.

    Each  applicable drilling method that can be  used in the
described  hydrogeologic setting and with the stated specific
design requirements has been evaluated on a  scale of 1 to 10
with respect to the criteria listed in the matrix. A total number
for each drilling method was computed by adding the scores for
the various criteria. The totals represent a relative indication of
the desirability of drilling methods for the specified conditions.
                                                         165

-------
                        INDEX TO MATRICES 1 THROUGH 40
      Iff.1
       C MM! mS mt
Matrix
Number
      1
      2
      3
      4
      5
      6
      7
      a
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     S>.
     S3
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
I
"a
•a
=5
E
a

                                                       u.
Q.
o
in
 I
in
*•"
JE
I
8
T~
A
.c
8-
Q
                                                                         ™
                                                                         o
                                                                         V

                                                                               O
                        19
                        5
                                                                                     o
                                         166

-------
                                             MATRIX NUMBER 1
                     General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; saturated; invasion of formation by drilling fluid  permitted:  casing diameter 2 inches or less; total
well depth O to 15 feet.
V Z W
\ K^
\ 3 is
\ > "^
\ w 2

\ °^
\ ^ 5E
^v ~~
\ ^" 11-
\ uf O
\ —
\ cc
\
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


13
c.
1

e
c
D

~O
>•
«^
ro
to
<5
1
1
9
3

10

8
NA
7

7
9






>.
i^
!o
a
•5
CC
0)
Q.
E
CO
5
1
1
4

10

10
NA
5

6
10






o
O
0)
c
'Jz
•IE
Q
01
-^
DC
9
10
8
7

9

8
NA
6

6
5

C
e
'5
O"
LU
O)
C
Q

'o

~
£

'S
>
10
10
10
9

9

10
NA
4

1
7

^,
"5
S|
***" J~l
T3 0
«) ,s£
^ OJ
11
o: -a
c
r- ffl
-— c
1- O
5 IS
'+z ^
^ s
II
5
5
5
10

10

7
NA
6

6
4

0
o "
1.2
-cB
0 C
03 O
1-0
D) —

|^ 3

§1

>
-^ QJ
S 1
< Q.
9
5
1
4

8

4
NA
9


10

b~
2
1
us
b
C

in
O
S;
(C
To
-^
O
*^ —
.£• o
I?
< 0
6
1
1
5

10

10
NA
10


10

g
'o.
E
o
O

1-
^ c
0 ^
01 ^
" a

> ^
.= Q
CC ro
4
4
1
2

9

5
NA
10

9
10














TOTAL
49
37
29
44

75

62
NA
57

56
65
EXPLANATORY  NOTES:

1. Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2. Borehole stability problems are potentially severe.
3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
4. The shallow depth of up to 15 feet, and small completed well diameter of 2 inches or less allows maximum flexibility in equipment.
                                                       167

-------
                                             MATRIX NUMBER 2

                      General Hydrogeologic Conditions & Well Design Requirements

 Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 2 inchesor less; total
 well depth 15 to 150 feet.
\ z w
\ 1*
\ 3 ^""
\ «J
\ > *
\ =1
\ ° ~
\ -
;§
.5
To
cr
.5!
Q.
E
$
NA
I
I
3

9

10
NA
5

8
10





v
o
D)

~
O
I

13
0)
QC
NA
4
5
2

8

10
NA
7

7
5

c
0)
E
Q.
'5
O)
i=
D

^
.ti
£

'5
>
NA
10
10
9

9

10
NA
4

i
7

=
$ ^
>_ 0)
o §
If
y
EC TJ

.E c
1- O
.I?

ro S

F^ C
O ™
OJ O
Po
_c S

s <°
O z

* ?
•^ s>
11
< Q,
NA
5
1
4

8

4
NA
8

9
10

£
0)
E

0
c
g>
OJ
Q
«5

c
Q
JK =

I?
< O
NA
1
1
8

8

10
NA
10

10
10

c
g
cu
Q.

O
o
J: -
"5 g

J§-
•5
> ^

EC (0
NA
7
1
1

9

4
'NA
9

8
10













TOTAL
NA
30
23
37

67

67
NA
60

63
66
EXPLANATORY NOTES:

1,  Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe.
3.  The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
4.  As the depth increases from 15 to 150 feet, the limit of hollow-stem auger equipment is approached. The actual limit varies with
   geologic conditions, specific equipment capability and borehole size (both outside diameter and inside diameter) requirements.
   Hollow-stem auger techniques are favored for shallower depths, with mud rotary being favored as the depth increases.
5.  Where dual-wall air techniques are used, completion is through the bit.
                                                        168

-------
                                            MATRIX NUMBER 3
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 2 inches or less; total
well depth greater than 150 feet.
Z S2
2S
*W 1™" MB*
\ ii
\ i|
\ 2 ^
\. rf* 0-
\ S o
\ o
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



E
.c
33
Dl
C
"H
n
Versatility of 1
NA
NA
NA
NA

NA

10
NA
8

10
9





£>
^
o
ra
"5
tL
"5.

?i
o E
_ Q.
^ O
©
fo
tr -D
0} ^
I I II II
> 1 12
jj ! 1 I!
NA
NA
NA
NA

NA

10
NA
5

8
5
NA
NA
NA
NA

NA

10
NA
4

1
7
NA
NA
NA
NA

NA

9
NA
7

10
4

o

OS M
O C
11
C ?
Is
w«
e 2
~ P
Ability of Dr
Preserve Na
NA
NA
NA
NA

NA

5
NA
10

10
9

ffi
^
CD
b
c
Dl
1
LJ
15
to
Ability to In:
of Well
NA
NA
NA
NA

NA

10
NA
10

10
10
c
a
"5
a
o
O
15
5-
?s

H? Q_
Relative Ea:
and Develo
NA
NA
NA
NA

NA

6
NA
1 0

10
10








TOTAL
NA
NA
NA
NA

NA

61
NA
60

69
62
  EXPLANATORY NOTES:
  1. Unconsolidated formations, predominantly saturated, with saturation exertin9 si9"ificant influence °" the choice of drilli"g
    technology.
  2. Borehole stability problems are potentially severe.
  3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction
  4. Where dual-wall air techniques are used, completion is through the bit.
  5. Depths greater than 150 feet limit technique choices.
                                                         169

-------
                                             MATRIX NUMBER 4

                     General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 2 to 4 inches; total
well depth O to 15 feet.
\ p°

\ 3k
\ > a
\ i^

\ Si
\ K u_
\ t°

\ *
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


E
£
1
O)
c
Q
"o
^
•^
0)
NA
1
2
1

8

7
NA
8

10
10





,~
5
^1

DC

NA
10
10
9

9

10
NA
4

1
7


£ o.
"S °
II
CE T3
as £
.ic
1- 0
ll
Efi ^H
"0 **>
EC £
NA
5
5
10

10

7
NA
6

6
4
0

O) CO
O C
11
1?
a) o
1- O
c 2
— D
§1

II
^o ®
< ot
NA
5
2
4

8

4
NA
9

10
9
 *
1?
EC co
NA
4
1
2

8

5
NA
10

8
10










TOTAL
NA
37
30
41

68

60
NA
58

56
65
EXPLANATORY NOTES:

1.  Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2. Borehole stability problems are potentially severe.
3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
4. Four-inch casing diameter limits technique choices even though depths are shallow (15 feet or less). Large diameter (I. D.)
   hollow-stem augers required. Solid flight augers require open-hole completion in potentially unstable materials.
                                                       170

-------
                                             MATRIX  NUMBER 5

                     General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 2 to 4 inches; total
well depth 15 to 150 feet.
\ 2g
\ ^ H*
\ ~*2
\ =1
\|S
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


o
aJ
0
c
Versatility of Drillii
NA
1
1
3

5

10
NA
8

10
9




Sample Reliability
NA
1
1
3

10

10
NA
5

8
10



»
o
Relative Drilling C
NA
2
3
2

8

10
NA
5

8
6
|
£
"5
s
<3>
Availability of Dril
NA
10
10
9

9

10
NA
4

1
7
* ».
5 t:
° E
if
3 &
Relative Time Re<
Installation and D
NA
1
3
7

9

10
NA
9

8
6
0
nl 
-------
                                             MATRIX NUMBER 6
                      General Hydrogeologic Conditions & Well Design Requirements
 Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 2 to 4 inches; total
 well depth greater than 150 feet.
\ z w
\ OQ
\ c o
\ 1!

\ cr —
\ ,
K=
ro
e
0)
NA
NA
NA
NA

NA

10
NA
7

10
9






i
.2
0)
cr
o>
a
ra
CO
NA
NA
NA
NA

NA

4
NA
8

10
8





§
0
o>
'=
a
.1

n
cr
NA
NA
NA
NA

NA

10
NA
5

6
3

4_
§
O.
'5
UJ
I
6
"5
.£•
i
CO
1
NA
NA
NA
NA

NA

10
NA
4

1
7


—
fl
£ E
*D o
•- ^
l!
c ™
Is
lis

ra 2
0) «
tr £
NA
NA
NA
NA

NA

10
NA
7

6
4


o
O) CO
0 C
0.2
.C "U
OJ O
t-O
?2
._ _j
'^ (Q
DZ
"5 S
^" 0)
= «
3 £
< a.
NA
NA
NA
NA

NA

6
NA
9

10
9

k-
£
03
re
Q
c
'«
Q
13
w
_c
•• _
^"(P
I?
< 0
NA
NA
NA
NA

NA

10
NA
10

7
10

f^
o
a!
ex
o
O

•Q ^
S a

-------
                                             MATRIX NUMBER 7

                      General Hydrogeologic Conditions & Well Design Requirements

 Unconsolidated; saturated; invasion of formation  by drilling fluid permitted; casing diameter 4 to 8 inches; total
 well depth O to 15 feet.
\ ZQ
\ P°
\ ^*~
\ "^ 
C
6
"o
to
tfl
>
NA
NA
NA
NA

NA

10
NA
8

NA
8






Reliability
!
tQ

NA
NA
NA
NA

NA

10
NA
8

NA
10






Drilling Cost
I
w

-------
                                            MATRIX  NUMBER 8
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; saturated; invasion of formation by drilling fluid permitted; casing diameter 4 to 8 inches; total
well depth 15 to 150 feet.
\ z m
\ l§
\ "^ UJ

\ 
NA
NA
NA
NA

NA

10
NA
NA

NA
7

=
3» H
k. 65
Q f~
it
Is
2. B
g^Q
C-O
Is
ill
> JO
'"S S
"5 ffl
or £
NA
NA
NA
NA

NA

10
NA
NA

NA
4

o
ui 
'w
Q)
Q
u>
Q
Si

lo
NA
NA
NA
NA

NA

10
NA
NA

NA
10

|
£
Q.

o
O
IE
•5|
OT CX
ffl o
s J
^ -^
^§
NA
NA
NA
NA

NA

3
NA
NA

NA
10










TOTAL
NA
NA
NA
NA

NA

67
, NA
NA

NA
67
EXPLANATORY NOTES:
1. Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
  technology.
2. Borehole stability problems are potentially severe.
3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
4. Casing diameter 4 to 8 inches requires up to 12-inch borehole and eliminates all techniques except mud rotary and cable tool.
                                                      174

-------
                                           MATRIX NUMBER 9
                     General Hydrogeologic Conditions & Well Design Requirements
unconsoldated; saturated; invasion of formation by drilling fluid permitted; casing diameter 4 to 8 inches; total
well depth greater than 150 feet.
zw
oo
\ p°

\ 3 h
\ 3%

\ *
\ od
\ "-E
\ 3°
\ ^°
\ *




"O
o

«
2
c
™
D
"5
>> I










S
'£
S
"55
C
•I
V 1 II 6
DRILLING \ | 1 |
MiTHOOS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


NA
NA
NA
NA

NA

10
NA
NA

NA
10

"'
NA
NA
NA
NA

NA

6
NA
NA

NA
10









i
o
en
c
0
I
15
«
cc

NA
NA
NA
NA

NA

10
NA
NA

NA
4


c
0)
E
Q.
'5
O"
LU
O>
c
Q
"o
£
2
=
>

NA
NA
NA
NA

NA


llr
"S
5 c
^ fe
o 1
Q.
T3 o
si
is
ffi "O
s§
P§
IS
« 3
a £

NA
NA
NA
NA

NA

10 I 10
NA NA
NA NA

NA
7

NA
2

o
*"
C& *ft
O c


£ "5
8 o
H- O
0>~S
^ Cfl
*— 3
,— *'
Q|
^i
™ s>
xi S
< a.

NA
NA
NA
NA

NA

5
NA
NA

NA
10

Si
ID
E
ra
i5

c
f
o
rz
S
O
$•?
' = 3
< "o

NA
NA
NA
NA

NA

9
NA
NA

NA
10


.-
^t i
a>
o.
E
o
O
1,
0 g
sl
co O
UJ 1
•i: Q
— T3
C i

NA
NA
NA
NA

NA

6
NA
NA

NA
10














TOTAL

NA
NA
NA
NA

NA

66
NA
NA

NA
63

  EXPLANATORY NOTES:
  1. Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
    technology.
  2. Borehole stability problems are potentially severe.
  3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
  4. Casing diameter 4 to 8 inches requires up to 12-inch borehole and eliminates all techniques except mud rotary and cable tool.
                                                        175

-------
                                             MATRIX NUMBER 10
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; saturated; invasion of formation by drilling fluid not permitted; casing diameter 2 inches or less;
total well depth  O to 15 feet.
\
\ p§

\ < 5
\ "z
\ |1
\g
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


o

13
c»
c
O
0
•=
.
£
33
15
CC
111
a.
E
NA
1
NA
1

10

NA
NA
7

8
10




4-
0
O
O)
O
0
J2
32
OC
NA
10
NA
7

9

NA
NA
5

5
5

c
Q>
a.
'5
Q*
til
Oi
_c
o
B
s
"5
NA
10
NA
10

10

NA
NA
4

1
7


I*
i_ «
o e
If
•q >
la
cr -o
<» £
.i™
K O
II
M 2
Hi <2
a: £
NA
6
NA
6

10

NA
NA
6

6
2

S
>,
03 f>
o c
•§.5
5?
o c
ffS
»1
^ 3
'C R3
QZ
"5 ®
i-i
II
< Q.
NA
6
NA
1

9

NA
NA
10

10
9

£
OJ
«s
O
c
ai
0
O
2
Q

II
< 0
NA
1
NA
1

8

NA
NA
10

10
10

c
p
QJ
Q.
E
o
o
Ease 01 V\/e(
etopment
11
5-0
* c
CC re
NA
4
NA
1

9

NA
NA
10

9
10







TOTAL
NA
37
NA
27

75

NA
NA
59

56
60
EXPLANATORY NOTES:
1,  Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe, so open-hole completion (i.e., solid-flight auger) may not be possible.
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  Jetting and mud rotary methods would require the addition of fluid.
6.  When using cable-tool drilling in saturated formations, it is  assumed that no drilling fluid needs to be added in permeable materials
   and that small volumes of drilling fluid are permissible in  less permeable materials.
                                                        176

-------
                                            MATRIX NUMBER 11
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; saturated; invasion of formation by drilling fluid  not permitted; casing diameter 2 inches or less;
total well depth 15 to 150 feet.
Z W
\ QQ
\co
frm —
_J ^^
J3 31
\ s*3
\ jQ |
\^ ^» EC
\ 2 ?
\ ^^ *J?
\ t
\ oc
V
DRILLING \
METHODS \
Hartd Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary wilh
Casing Hammer
Dual Wall Rotary
Cable Tool





J>
o
jC
5
o>
c
"El
Q
B

,^
I
NA
1
NA
NA

8

NA
NA
8

to
10








Jt

£

&
DC
•([,1
"5.
id
tn
NA
1
NA
NA

10

NA
NA
5

8
10








8
O)
c

Q
0)
DC
NA
4
NA
NA

10

NA
NA
8

8
6



c
V
6
Q.
"3
CT
UJ
I
O
"o

.§"
~
'S
>
NA
10
NA
NA

10

NA
NA
5

1
8


—
l|

o E
«f
i- a?
"3-5
fo
CL "C
I ™
,* c
H 0
>"s
ll
NA
1
NA
NA

8

NA
NA
10

8
2


o
D) to
o e
o .S
.c 5
CJ C
tu O
HO
.S t~
•S 3

"o ^
£
I s
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NA
5
NA
NA

8

NA
NA
9

9
to


»-,
j&
1
TO
S
c
o>
'S
a
"c3

c
o
*"* _-.
11
NA
1
NA
NA

8

NA
NA
10

10
10


c
o
i
Q.
E
3
"5
B S
S&
ra Q
UJ .P.
$ 03
-S?
S c
0- TO
NA
7
NA
NA

7

NA
NA
10

10
10














TOTA^L
NA
30
NA
NA

69

NA
NA
65

64
66
' —
EXPLANATORY NOTES:
1. Unconsolidated formations,  predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2. Borehole stability problems are potentially severe.
3. The anticipated use of the monitoring well prohibits the use of drillinq fluid and additives in construction.
4. As depth increases the relative advantage of hollow-stem augering decreases.
5. Jetting and mud rotary methods would require the addition of fluid.
6. When using cable-tool drilling in saturated formations, it is assumed that no drilling fluid needs to be added in permeable materials
   and that small volumes of drilling fluid are permissible in less permeable materials.
                                                        177

-------
                                             MATRIX NUMBER 12
                      General Hydrogeologic Conditions & Well Design Requirements
 Unconsolidated; saturated; invasion of formation by drilling fluid not permitted: casing diameter 2 inches or less;
 total well depth greater than 150 feet.
\ z w
\ °s
\ <°
\. ^i U
\ "" z

\ ^5 J
\°
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



|
"Z

O)
^c
O
"o
2-
CO
CO

«5
a>
CC
NA
NA
NA
NA

NA

NA
NA
10

9
7


c:
a
'5
CT
Ul
OJ
^c
6
"o
^.
'£
CO
1
<
NA
NA
NA
NA

NA

NA
NA
7

4
10


4>
?!
£ E
*f
i_ d)
u
tr -o
0) C
.ic
1- 0
<" 5
> 3
to S
ai «
EC £
NA
NA
NA
NA

NA

NA
NA
10

10
6


o
lls
0.2
fl
(J C
^-8
1"
QC ro
NA
NA
NA
NA

NA

NA
NA
10

9
10








TOTAL
NA
NA
NA
NA

NA

NA
NA
69

72
66
EXPLANATORY NOTES:
-   Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe.
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  Jetting and mud rotary methods would require the addition of fluid,
6.  When using cable-tool drilling in saturated formations, it is assumed that no drilling fluid needs to be added in permeable materials
   and that small volumes of drilling fluid are permissible in less permeable materials.
                                                       178

-------
                                             MATRIX NUMBER 13
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; saturated; invasion of formation by drilling fluid not permitted; casing diameter 2 to 4 inches;
total well depth O to 15 feet.
\ 1s
\ < 3-
\ 3|
\ 2io

\ od
\ -Q
\ ^
\g
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Walt Rotary
Cable Tool


TJ
o
c.
i

01
c
Q
'o
(d
V)
0>
NA
1
NA
1

10

NA
NA
9

9
10





2-
1
JB
1
CO
NA
1
NA
1

10

NA
NA
8

8
10





8
O>
c
6
i:
CD
0)


O
"o
.$•
2
JO
'5
NA
10
NA
10

10

NA
NA
4

1
7

* -
$ ?
>. 0)
•o o
S! ID
•p. g
DC T3
4> c
I *
If
J =
II
NA
5
NA
5

10

NA
NA
6

5
4
o

o.2
-1

o>-=
c c
II
•^1
< ol
NA
1
NA
1

8

NA
NA
10

10
9
V-
3
TV
O
1

S
1
t/t
o
i-l
s?
< 0
NA
1
NA
1

7

NA
NA
10

8
10
c
g

"5.
o
O

is
o g
iSf
01 >
1°
il
NA
4
NA
9

7

NA
NA
10

8
10









TOTAL
NA
33
NA
28

72

NA
NA
62

54
66
EXPLANATORY NOTES:
1,  Unconsolidated formations,  predominantly saturated,  with saturation  exerting  significant  influence on  the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe.
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  Increasing diameter is influencing choice of equipment.
5.  Jetting and mud rotary methods would require the addition of fluid.
6.  When using cable-tool drilling in saturated formations, it is assumed that no drilling fluid needs to be added in permeable materials
   and that span volumes of drilling fluid are permissible  in less permeable materials.
                                                        179

-------
                                              MATRIX  NUMBER 14
                      General Hydrogeologic Conditions & Well Design Requirements
 Unconsolidated;  saturated; invasion of formation by drilling fluid not permitted; casing diameter 2 to 4 inches;
 total well depth 15 to 150 feet.
\ z w
\ 09
\ w O
\ 5 x
\ 1*
\ *i
\ 1*
\ Is
\1
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rolary
Cable Tool




•o
o
£
Q)
O)
C
Q
Versatility of
NA
1
NA
1

5

NA
NA
9

9
10






s
IT

?!
£l
•o §•
H
Is
IE -D
Hi C
Relative Timi
Installation a
NA
1
NA
3

10

NA
NA
9

9
5


0

>>
O) «
*i
if
» o
HO
g-g
= 3
s|
•5 i
£•£
=: 10
a »
< 0.
NA
5
NA
4

8

NA
NA
10

10
9


CD

<0
b
C
w
e
IS
1
o
i|
s*
< 0
NA
1
NA
2

6

NA
NA
10

6
10


o

2
a
o
O
IS
11
!&
W5
¥ »
|S
JS c
a: as
NA
4
NA
2

6

NA
NA
10

6
10







TOTAL
NA
25
NA
24

64

NA
NA
67

57
68
EXPLANATORY NOTES:
L  Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe, so open-hole completion (i.e., solid-flight auger) may not be possible.
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  Depth range is 15 to 150 feet.
6.  Increasing diameter and depth favor cable tool and air rotary with casing hammer techniques.
6.  When using cable-tool drilling in saturated formations, it is assumed that no drilling fluid needs to be added in permeable materials
   and that small volumes of drilling fluid are permissible in less permeable materials.
                                                        180

-------
                                             MATRIX  NUMBER 15
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; saturated; invasion of formation by drilling fluid not permitted; casing diameter 2 to 4 inches;
total well depth greater than 150 feet.
\ Z »
\ -o

\ 3w
\ I*
\ < **
\ f*u.
\ t°
\ tt
\°
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


TJ
O
f
at
c
|
"5
1

O
S
1
O
II
< 0
NA
NA
NA
NA

NA

NA
NA
10

B
10

c
,2
"S3
a.
o
O
"5
S^
°E
0! C
tfi "•
ffl O
tu -5
S Q
a -o
t£ a
NA
NA
NA
NA

NA

NA
NA
10

a
10






TOTAL
NA
NA
NA
NA

NA

NA
NA
74

70
67
EXPLANATORY  NOTES:

L  Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe.
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction
4.  Increasing diameter and depth favor cable tool and air rotary with casing hammer techniques.
6.  Jetting and mud rotary methods would require the addition of fluid.
6.  When using cable-tool drilling in saturated formations, it is assumed that no drilling  fluid needs to be added in permeable materials
   and that small volumes of drilling fluid are permissible in less permeable materials.
                                                        181

-------
                                              MATRIX NUMBER 16
                      General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; saturated; invasion of formation by drilling fluid not permitted; casing diameter 4 to 8 inches;
total well depth O to 15 feet.
\ z w
\ ^0

\ M
\ "i
\ tt3
\ jl
\5
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



|
f
O)
_c
O
"5
£

to
NA
NA
NA
4

NA

NA
NA
8

NA
10




;>•
Reliabilil
o>
Q.
I
NA
NA
NA
5

NA

NA
NA
8

NA
10




3
I
0
S
1
a>
tr
NA
NA
NA
10

NA

NA
NA
8

NA
6


o>
Q.
'3
cr
LJJ
O>
C
0
"5
!5
5
'ti
3
NA
NA
NA
10

NA

NA
NA
8

NA
8


o>
5 c
£|
M
0> >-'
a: -o
0) ^
II
II
S S
0) <2
oc £
NA
NA
NA
8

NA

NA
NA
8

NA
10


0
en m
0 S
11
.C TJ
K o
II
§1
"5 $
3! S
25 £
NA
NA
NA
1

NA

NA
NA
8

NA
10


is
Q?
.S
0
c
Ol
"in
75
a>
.i|
lo
NA
NA
NA
4

NA

NA
NA
8

NA
10


|
"5.
3
I-
li
S o
i|
cr n
NA
NA
NA
4

NA

NA
NA
8

NA
10







TOTAL
NA
NA
NA
46

NA

NA
NA
' 6 4

NA
74
EXPLANATORY NOTES:

1,  Unconsolidated formations, predominantly saturated, with saturation exerting significant influence on the choice of drilling
   technology.
2.  Borehole stability problems are potentially severe, so open-hole completion (i.e., solid-flight auger) may not be possible.
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  Maximum casing diameter exceeds practical equipment capability except for cable tool, air rotary with casing hammer and
   possibly solid-flight augers.
6.  Jetting and mud rotary methods would require the addition of fluid.
6.  When using cable-tool drilling in saturated formations, it is assumed that no drilling fluid needs to be added in permeable materials
   and that small volumes of drilling fluid are permissible in less permeable materials,
                                                         182

-------
                                             MATRIX NUMBER 17

                      General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; saturated; invasion of formation by drilling fluid  not permitted; casing diameter 4 to 8 inches;
total well depth 15 to 150 feet.
V Z «
\ -o
\ 1

\ 2^
\ -< oc
\ S Q
\ OC
\ w o
\ t
\ oc
\°
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


E
IE
c
•^
0

*o
^
^
I
NA
NA
NA
NA

NA

NA
NA
NA

NA
10




>,
:=
3
.2
£
tr
Q)
"5.
I
NA
NA
NA
NA

NA

NA
NA
NA

NA
10



«_
8
O)
c
—
"C


>
s
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

1
a.
3
tr
Ul
D)
c

a

"o
>-
•^
'r>
n
1
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

	
!i
||
|Q

0) C
C ^
.- c
o
^ CO
11
oc £
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

0
is
ll
HO
C. ^
= 3
'>— • CtJ
oz


1 £
< D-
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

a>
(0
O
§.
5)
I
;s
S
CO
JC
o
** _
l§
< 0
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

c
g
"a
0
1-
"o ^
m E
 O
LU "QJ

> ®
DC 
-------
                                            MATRIX NUMBER 18

                     General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; saturated; invasion of formation by drilling fluid not permitted; casing diameter 4 to 8 inches;
total well depth greater than 150 feet.
\ z w
\ p°
\ tf ^
\ 3 H~
\ j IU
\ > a
\ ^ Z
\ O ~^
\ u-
\ i°
\ 1°
\o
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



T3
o
£j
i
o>
c

o
"o
ra
0>
NA
NA
NA
NA

NA

NA
NA
NA

NA
10







>*
!o
.2
0)
QC
4)
Q.
1
NA
NA
NA
NA

NA

NA
NA
NA

NA
10






8
O
O)
Q
1
ra
0)
IT
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

c:
Q)
E
Q.
s
O)
c
•^
o
.$•
•i
«
>
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

	
-0)
> c

•S 1
5 S
S" Q

d £
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

0
*•*
oJ tn
o c
11
H O
*^
.ES
li
"o §
< i
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

o>
^5

a
b
c
O)
0)
Q

c
Q

<0
NA
NA
NA
NA

NA

NA
NA
NA

NA
10

c
g

a>
a
|
"ai
5 **
IE

-------
                                            MATRIX NUMBER 19
                     General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; unsaturated; invasion of formation by drilling fluid permitted: casing diameter 2 inches or less;
total well depth 1O to 15 feet.
\ z w
\ s

\ s
\ "^ u.
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



Versatility of Drilling Method
4
7
3
8

10

8
5
9

9
6



Sample Reliability
5
1
1
10

10

10
5
8

9
10



Relative Drilling Cost
9
10
8
10

10

7
8
6

6
3

c
01
Availability of Drilling Equipm
10
10
8
9

9

10
8
4

1
7

—
0)
Relative Time Required for W
Installation and Development
6
6
5
10

10

8
8
3

3
2

o

Ability of Drilling Technology
Preserve Natural Conditions
9
5
1
8

10

4
7
9

9
9

<5
"m
Ability to Install Design Diami
of Well
6
1
1
10

10

10
8
10

10
10
c
o

Relative Ease of Well Comple
and Development
6
4
5
5

10

5
4
1 0

10
7



TOTAL
54
44
32
70

79

62
53
59

57
54
EXPLANATORY NOTES:

1. Unconsolidated formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
  zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2. Borehole stability problems vary from slight (e.g., dense, silt/clay) to severe (e.g., coarse gravel and boulders).
3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
                                                       185

-------
                                             MATRIX NUMBER 20
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated;  unsaturated; invasion of formation by drilling fluid permitted; casing diameter 2 inches or less;
total well depth 15 to 150 feet.
\ ZQ
\ -o
\ <£
\ li

\ "* z
\ 2^
\o
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
• Casing Hammer
Dual Wall Rotary
Cable Tool



E
H
1
c
a
"o
2-
(0

NA
1
1
8

9

10
7
10

10
9






£
5
.3
"35
tr
o
a.
I
NA
1
1
10

10

10
5
8

9
10






I
O)
c
O
I
15
cc
NA
7
4
10

10

10
8
6

6
3

c

._
§•
"o>
1
lability of Di
'5
>
NA
10
10
9

9

10
8
4

1
7

_
> *-
>. a>
£ E
-1
« w
QC -D
I!
K g
ra 2
"5 <2
cr £
NA
6
5
10

10

8
8
7

6
2

o
>,
o"c
o.g
||
t-0
c*S
= 3
11
< a
NA
5
1
8

10

4
7
9

9
9

£
aS
fc
(0
a
c
g>
'vi
a>
D
2
a>
c
0
< 0
NA
1
1
9

9

10
9
10

10
10

c
g
^5
"5.


"5
$r
o|
si
(0 O
UJ -&
•p
i$ c
OC ra
NA
4
1
5

9

5
4
10

10
7








TOTAL
NA
35
24
69

76

67
56
64

61
57
EXPLANATORY NOTES:
1.  Unconsolidated formations, predominantly unsaturated, with monitoring conducted in  individual, relatively  isolated,  saturated
   zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2.  Borehole stability problems vary from slight (e.g., dense, silt/clay) to servere (e.g., coarse gravel and boulders).
3.  The anticipated use of the monitoring well permits the  use of drilling fluid and additives in construction.
4.  Solid-flight and hollow-stem augers are favored to the  limit of their depth capability
                                                       186

-------
                                             MATRIX NUMBER 21
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated;  unsaturated; invasion of formation by drilling fluid permitted; casing diameter 2 inches or less;
total well depth greater than 150 feet.
\*~ ZOTI
00
c ^5
^i U
^ 2
2l
ES
UJ A
|__ ^5
E
O
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



|

1
en
c
6
'o
11
w
£
NA
NA
NA
NA

NA

10
5
9

10
9





Fteliability

a
E
Ease of Well Co
elopment
Is
S-o
CC §
NA
NA
NA
NA

NA

5
4
10

9
7








TOTAL
NA
NA
NA
NA

NA

61
55
65

64
54
 EXPLANATORY NOTES:
 1.  Unconsolidated formations, predominantly unsaturated, with monitoring conducted  in individual,  relatively isolated, saturated
    zones. Drilling  is through primarily unsaturated  material, but completion is in a saturated zone.
 2.  Borehole stability problems vary from slight (e.g., dense, silt/clay) to servere (e.g., coarse gravel and boulders).
 3.  The anticipated use of the monitoring well permits the use of drilling fluid and additives in  construction.
 4.  Dual-wall air completion is through the bit.
 5.  Air rotary with  casing  hammer and dual-wall air methods  become relatively more advantageous under these conditions.
                                                         187

-------
                                      MATRIX NUMBER 22

                  General Hydrogeologic Conditions& Well Design Requirements

Unconsolidated; unsaturated; invasion of formation by drilling fluid permitted; casing diameter 2 to 4 inches; total
well depth O to 15 feet.
Z 0
\ c o
\ < X
\ li

\ wz
\ J

\ **" rr
\ ES
\°
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



•g
£
2
O)
c

Versatility of Dri
NA
1
1
8

10

8
5
9

9
8








>•
Sample Reliabili
NA
1
1
10

10

10
5
8

9
10






175
o
O
Relative Drilling
NA
10
4
10

10

7
8
5

6
3

CI
0)
1
5
cr
m
c

^
Availability of D
NA
10
10
9

9

10
8
4

1
7


"5>
.- 0)
o E
"§5
•= >
3 3>
-=
Ability of Drillin
Preserve Nature
NA
5
1
8

10

4
7
9

9
9

oj

co
D
c.
g>
'jo
0)
O
Ability to Install
of Well
NA
1
1
10 '

10

10
8
10

8
10

c
Q

"o.
Q
O
~-

> c
Relative Ease of
and Developme
NA
4
1
5

10

5
4
10

10
8









TOTAL
NA
37
24
70

79

62
53
60

57
60
                                                188

-------
                                             MATRIX NUMBER 23
                      General Hydrogeologic Conditions & Well Design Requirements
 Unconsolidated; unsaturated; invasion of formation by drilling  fluid permitted; casing diameter 2 to 4 inches; total
 well depth 15 to 150 feet.
\ 1°
\ =t
\ < s
\ m°
\ u 5t
\ C- ^»
\ *
\°
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary witfi
Casing Hammer
Dual Wall Rotary
Cable Toot

E
XL
1
en
Q
"o
i
1
>
NA
1
1
3

7

10
S
W

10
9




3
CO
S
Q.
CO
U)
NA
1
1
10

10

10
5
8

9
10



8
o
=
o
0)
"s
K
NA
1
1
10

10

10
8
6

6
4
-
a
'5
ty
Ul
I
O
"o
'£
to
"

NA
10
10
9

9

10
8
4

1
7

?!
o 6
if
ii
??
Is
1- 0
>s
fl
tr£
NA
2
3
8

10

9
8
B

B
7
o
>.
O) «
2 c

II
^5
O)-=
c S
= 3
§1
o^l
1 1
 s
f'
a: a
NA
4
1
5

8

5
4
10

9
10







TGT/U-
NA
25
19
59

72

68
51
65

62
66
EXPLANATORY NOTES:
1. Unconsolidated formations, predominantly unsaturated, with monitoring conducted in  individual, relatively  isolated,  saturated
   zones. Drilling is through primarily unsaturated material, but completion is  in a saturated zone.
2. Borehole stability problems vary from slight (e.g., dense, silt/clay) to servere (e.g., coarse gravel and boulders).
3. The anticipated use of the monitoring well permits the  use of drilling fluid  and  additives in construction.
4. Solid flight augers require open  hole completion, which may or may not be feasible.
                                                        189

-------
                                             MATRIX NUMBER 24
                      General Hydrogeologic Conditions & Well Design Requirements
 Unconsolidated; unsaturated; invasion of formation by drilling fluid permitted; casing  diameter 2 to 4 inches; total
well depth greater than 150 feet,
V. Z CO
\ 2°

\ =t
\ < 5
\ ui«
\ ^ 3
\ *£
\ ^
\ o
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



•o
.c
OJ
c
Q
'o
•—
ra
E
o>
NA
NA
NA
NA

NA

9
5
9

10
9






Reliability
CD
Q.
to
W
NA
NA
NA
NA

NA

1
3
9

10
5





_
1
D)
C
Q
.1
i
NA
NA
NA
NA

NA

10
10
6

6
4

^-
c
Q
g
LU
O)
Q
"5
!S
'S
>
NA
NA
NA
NA

NA

10
8
4

1
7


—
1 |
o I
If
|o
 S
.ic
HO
ID '^
ra S
o> «
tr S
NA
NA
NA
NA

NA

9
10
8

10
3


o
&«
•§.i
j-6
o c
o> o
HO
?«
S 3
i ™
Qz
O 5;
^ 0)
:= w
JD w
< Q-
NA
NA
NA
NA

NA

4
8
9

10
8

fc-
£
to
Q
c
o
8
o
"fa
_c
o

<'o
NA
NA
NA
NA

NA

10
10
10

10
10

_
.2
a
a
E
o
O
Ease of Wei
elopment
® m
5?
CC a
NA
NA
NA
NA

NA

5
4
10

8
10








TOTAL
NA
NA
NA
NA

NA

58
58
65

65
56
EXPLANATORY NOTES:
1. Unconsolidated formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
  zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2. Borehole stability problems vary from slight (e.g., dense, silt/clay) to severe (e.g., coarse gravel and boulders).
3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
4. Air rotary method requires generally very difficult open-hole completion. The borehole may, however, be stabilized with fluid after
  drilling is complete.
                                                        190

-------
                                            MATRIX NUMBER 25

                     General Hydrogeologic Condtions & Well Design Requirements

Unconsolidated; unsaturated; invasion of formation by drilling fluid permitted; casing diameter 4 to 8 inches; total
well depth 0 to 15 feet.
\ z w
\ 2°

\ ifc
\ < *
\ s ^
\ z
\ O "^
\ ii "•'
\ *s
\ •*• ii
\ t°
\ DC
V O
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



v
£
u)
2
O)
c

o

"o
•=
(0
!2
0)
NA
NA
NA
4

7

10
5
8

NA
8








>s
£
CO
"5
tr
01
Q.
I
NA
NA
NA
8

10

10
5
7

NA
10






v*
o
O
en
c
—^
Q
0)
~
2
NA
NA
NA
10

10

7
9
6

NA
3

_^
c
Q.
3
D-
LU
O>
.C
T^
Q
'o

S
Q
1
NA
NA
NA
9

9

10
8
4

NA
7


	
!i
,9 E
"D o
fl? -rr
'5-S
oQ
CC -a
r- fO
F§
>!i

io 2
3J <2
a: £
NA
NA
NA
10

9

8
8
8

NA
4


o
O) C»
"o .5
-C T3
o cr
t- o

c" 2
'c to
DZ
" s
-t" (1)
1 £
< a
NA
NA
NA
8

8

5
4
10

NA
10


0)
CO
Q
c
O)
'(A
0)
Q
75
to
O

& 75
1!
< 0
NA
NA
NA
7

7

10
5
10

NA
10


Q
ts
a.
o
O

75
7r
o c
8> o.
(Q O
LU a
$ ^
~ Q
-2-D
en m
NA
NA
NA
4

4

3
4
10

NA
9














TOTAL
NA
NA
NA
60

64

63
48
63

NA
61
 EXPLANATORY NOTES:

 1. Unconsolidated formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
   zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
 2. Borehole stability problems vary from slight (e.g., dense, silt/clay) to severe (e.g., coarse gravel and boulders).
 3. The anticipated use of the monitoring well permits the use of drilling fluid and additives in construction.
 4. Diameter requirements limit the equipment that can be utilized.
 5. Solid-flight augers require very difficult open-hole completion. Hollow-stem auger technique requires open-hole completion
   for casing sizes greater than 4 inches.
                                                        191

-------
                                            MATRIX NUMBER 26
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated unsaturated: invasion of formation by drilling fluid permitted; casing diameter 4 to 8 inches; total
well depth 15 to 150 feet.
\ 2 «
\ ^1
\ $ *"*
\^ . til
\ < 35

\ M4
\ o3
\ y^ ggj
\ 

c

Q
"o
,1?
PO
e
*
NA
NA
NA
NA

NA

10
NA
NA

NA
8








jjK
i
a
"5i
cr
0
a
en
Cfl
NA
NA
NA
NA

NA

10
NA
NA

NA
10







§
O
O)
_c
ss
O
1

"ffi
JT
NA
NA
NA
NA

NA

10
NA
NA

NA
6

1
e
Q.
3

UJ
01
S
is
Q
'S
JD
«
"5
>
NA
NA
NA
NA

NA

10
NA
NA

NA
7

&
51
»- as
«S £

a> —
|I
Jo
cr -o
,1 *
OS 'S
*J "m
B9 JS
el
NA
NA
NA
NA

NA

10
NA
NA

NA
5

o
X
0> 
-------
                                            MATRIX NUMBER 27

                     General Hydrogeologic Conditions & Well Design Requirements

Unconsolidated; unsaturated; invasion of formation by drilling fluid permitted; casing diameter 4 to 8 inches; total
well depth greater than 150 feet.
\ §8
\ *~ i
\ ^ ^"
\ < 5
\ *fc


>l f£ jj™
\ 2^
\ <"
\ * 11.
CHILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual WaH Rotary
Cable Tool


•g
Q
C.
15


Ol
c
^
Versatility ol 0
NA
NA
NA
NA

NA

10
NA
NA

NA
8








>.
™
Sample Reliab
NA
NA
NA
NA

NA








jiS
O
O)
_c
O
1
1
CC
NA
NA
NA
NA

NA

8 10
NA NA
NA|| NA

NA
10

NA
6
c
£
Q.
'5
CT
UJ
>«

o>

=

* —
S
O £
"*" Q.
•o o
3* —
C 
3 >
Jo
Q CET3
Availability of
NA
NA
NA
NA

NA

10
NA
NA

NA
7
Relative Time
Installation an
NA
NA
NA
NA

NA

10
NA
NA

NA
4
o
>,
jsP ^
"5-2
c" *D


.® .Q
01 IS
c 2
Ability of Drill
Preserve Natu
NA
NA
NA
NA

NA

6
NA
NA

NA
10
»
E
ED
Q
C
cn

w
O
15
to
c
o
11
< 0
NA
NA
NA
NA

NA

8
NA
NA

NA
10
.2
»
CL
O
(^

5
l~










o *
Relative Ease
and Developr
NA
NA
NA
NA

NA

4
NA
NA

NA
10
TOTAL
NA
NA
NA
NA

NA

66
NA
NA

NA
65
  EXPLANATORY NOTES:
  ...      ... ,  . ,    ,.        .   .   ,.       ,   ,  .    ...     ,  .       .   ,  .  .  .  , . .   . relatively isolated, saturated
  1.  Unconsolidated formations,  predominantly  unsaturated, with  monitoring  conducted  in individual,
     zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
  2.  Borehole stability problems vary from slight (e.g., dense, silt/clay) to servere (e.g., coarse gravel and boulders).
  3.  The anticipated use of the monitoring well  permits the use of drilling fluid and additives in construction.
  4.  Diameter of borehole, and depth, eliminates  most options.
                                                          193

-------
                                              MATRIX NUMBER 28
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; unsaturated; invasion of formation by drilling fluid not permitted, casing diameter 2 inches or
less; total well depth O to 15 feet.
z w
\ p°
\ 3t
\ 2s

\ fl

\CJ
DRILLING \
METHODS
\
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


•o
o
£
21
O)
O
"5
;=
<3
'

4
7
NA
8

8

NA
5
9

10
NA











5
1
NA
10

10

NA
5
8

9
NA





1
Q
>

B
0)
CC

9
10
NA
10

10

NA
8
6

6
NA

c
|
'5
CT
UJ
O)
C
Q
5
ra
1


10
10
NA
9

9

NA
8
4

1
NA

=
5 c
o I
•D 0
m —
E 0>
Is
CC -o
p
h- O
ffl ^
-— «
13 S
as o
cc -E

5
6
NA
10

10

NA
8
3

8
NA

o
?S
%•£
IS
^8
||
ll
0|
^. 1^
^ QJ
:= (/)
5 £
 >
•* o
^ -o
ac i

6
4
NA
5

10

NA
4
10

10
NA









TOTAL

54
44
NA
70

75

NA
5 3
59

84
NA
EXPLANATORY NOTES:
1.  Unconsolidated formations, predominantly unsaturated,  with monitoring conducted  in individual,  relatively  isolated,  saturated
   zones. Drilling is through primarily unsaturated material,  but completion is  in a saturated zone.
2.  Borehole stability problems vary from slight (e.g. dense,  silt/clay) to severe (e.g. coarse gravel and boulders).
3.  The anticipated use of the monitoring well prohibits the  use of drilling fluid and additives in  construction.
4.  Jetting, mud rotary and cable tool methods  would require the addition of fluid.
5.  Air rotary with casing hammer requires driving 6-inch or greater diameter  casing and  completion  by  pullback
6.  Air rotary, hand auger and solid-flight auger completion  possible  only if unsupported borehole is stable.
                                                         194

-------
                                            MATRIX NUMBER 29
                     General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; unsaturated; invasion of formation by drilling fluid not permitted; casing diameter 2 inches or
less; total well depth 15 to 150 feet.
\ z w
\ 2°

\ =t
\ ^S
\ IT 2

\ "" £
\ Si Q
\ ff U.

\ C
\°
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



-o
£
5
D)
C

Q

"o
~
CO

_c
iS
0
Q>
.Z
s
DC
NA
7
NA
10

10

NA
8
6

6
NA

**
c
CD
Q.
§•
O)
=
S

"5
.^
3
«
I
NA
10
NA
10

10

NA
B
4

1
NA


=:
0>
?!
£|
|f

OC 13
m C
E *"
P|
Q) '•*-*
.5 =
ra  c
0) O
H O

;= 3
"C "(5
QZ
o 9J
^ 0)
11
NA
5
NA
B

10

NA
7
9

9
NA

i_
QJ
(0
5
c
O)
'8
o
15
"55
-
o
^* Q)
s 5
< 0
NA
1
NA
9

9

NA
9
10

10
NA

c
0
0)
Q.
O
O
"S
- S
c
(0 O-
m o
UUa
4) >
•^Q
1?
cc a
NA
4
NA
5

10

NA
4
10

10
NA













TOTAL
NA
35
NA
70

79

NA
56
63

64
NA
EXPLANATORY  NOTES:
1. Unconsolidated formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
   zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2. Borehole stability problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders).
3. The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4. Jetting, mud rotary and cable tool methods would require the addition of fluid.
5. Air rotary with casing hammer requires driving 6-inch or greater diameter casing and completion by pullback.
6. Air rotary and solid-flight auger completion possible only if unsupported borehole is stable.
                                                        195

-------
                                             MATRIX NUMBER 30
                      General Hydrogeologic Conditions & Well Design Requirements
 Unconsolidated; unsaturated; invasion of formation by drilling fluid not permitted; casing diameter 2 inches or
 less; total well depth greater than 150 feet.
\ 1§
\ *"" ?
\ 3*~
\ «c z
\ 5 °
\^ z
\ o 3
\ < **•
V ^J
\ wft
\ E
DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


•o
o
£1
"3
o>
.E
Q

"o
=
SO
v>
>
NA
NA
NA
NA

NA

NA
7
10

10
NA






>,
'£
10
EC
£
(8
C/3
NA
NA
NA
NA

NA

NA
7
9

10
NA





t»
o
O
O)
C
n
6
0>
I
NA
NA
NA
NA

NA

NA
10
8

B
NA
«•>
c
D.
'3
a
m
c

a
"5
.is
s
(d
s
NA
NA
NA
NA

NA

NA
10
8

4
NA

gj
i
Q C
it

il
W •""
£E tj
? (5
•§ C
t- 5
1 1
11
NA
NA
NA
NA

NA

NA
10
9

9
NA
o
~*
OS W
ll
"o C
* o
t-O
.fi
^E S
2^
i-l
:= &«
Sfi
NA
NA
NA
NA

NA

NA
7
9

10
NA
fe
V
1
5
c
o>
'to
Q
1

C
o
5-1
i?
< 0
NA
NA
NA
NA

NA

NA
10
10

10
NA
c
*2
"o.
O
o
"si
5 *-
°1
OS On
ffl D
UJ "Sj
||

NA
NA
NA
NA

NA

NA
4
10

8
NA











TOTAL
NA
NA
NA
NA

NA

NA
65
73

69
NA
EXPLANATORY NOTES:
1.  Unconsolidated formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
   zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2.  Borehole stability problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders).
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  The depth requirement and the decision not to utilize drilling fluid limit equipment options.
6.  Jetting, mud rotary, and cable tool methods would require the addition of fluid.
6.  Air rotary with casing hammer requires driving 6-inch or greater diameter casing and completion by pullback.
7.  Air rotary completion possible only if unsupported borehole is stable.
                                                        196

-------
                                             MATRIX NUMBER 31
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; unsaturated; invasion of formation by drilling fluid not permitted: casing diameter 2 to 4 inches;
total well depth O to 15 feet.
z w
\ — O
\ li
\ 0
\o
DRILLING
METHODS ^
Hand Auger

Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool


|
IS
o>
c
^
Versatility of D
NA

1
NA
8

10

NA
5
9

9
NA



t
Sample Reliab
NA

1
NA
10

10

N/
5
£

c
N/



8
O
O>
Relative Drillin
1
MA

10
NA
10

1C

N/
I
(

I
N

1
Q.
'5
CT
UJ
o>
_c
6
Availability of
NA

10
NA
10

10

NA
8
4

1
NA

=
a>
?I
o E
If
is
C -o
Relative Time
Installation an
NA

5
NA
10

10

NA
8
6

6
NA

0
O) «
«i
J=6
£,3
i1!
Ability of Drill
Preserve Nati
NA

5
NA
8

10

NA
7
9

9
NA

oj
CO
D
c
.a>
CA
a>
O
"<5
Ability to Inst
of Well
NA
1
1
NA
7

9

NA
8
10

9
NA
c
o
«
a.
o
O
1^
o|
Relative Ease
and Developr
NA
4

NA
5

8

NA
"4
10

10
NA




TOTAL
NA
37

NA
68

77

NA
53
62

59
NA
^^^^^^M
   EXPLANATORY  NOTES:
   ...      .. . .  .  ,    ..        .    .   ..       .   .  .  with monitoring conducted in  individual, relatively isolated, saturated
   1,  Unconsolidated  formations,  predominantly unsaturated, M      |etionais in a saturated zone
     zones. Drilling is through primarily unsaturated material,
   2. Borehole stability problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders).
   3. The anticipated  use of the monitoring well prohibits the use of drilling fluid  and additives in construction.
   4. Jetting, mud rotary and cable tool methods would require the  addition of fluid.
   5. Air rotary with casing hammer requires driving  8-inch or greater casing and completion by pullback.
   6. Air rotary and solid-flight auger completion possible only  if unsupported borehole is stable.
                                                            197

-------
                                             MATRIX NUMBER 33
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; unsaturated; invasion of formation by drilling fluid  not permitted; casing diameter 2 to 4 inches;
total well depth greater than 150 feet,
NOQ
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DRILLING \
METHODS \
Hand Auger
Driving
Jetling
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Too)



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NA
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NA

NA

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NA






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NA
NA
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c
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NA
NA
NA
NA

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NA

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2. £
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2 'o
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CE T3
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NA
NA
NA
NA

NA

NA
10
8

10
NA

o
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5 ^5
ai o
HO
c 2
S 3

ft Z
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NA
NA
NA
NA

NA

NA
5
10

10
NA

Q)
a>
E
ra
b
c
01
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en
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< 0
NA
NA
NA
NA

NA

NA
10
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NA
c
o
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E
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5 ~
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tn Q~
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LU •$
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NA
NA
NA
NA

NA

NA
5 .
10

10
NA














TOTAL
NA
NA
NA
NA

NA

NA
60
68

70
NA
EXPLANATORY NOTES:

1. Unconsolidated formations,  predominantly  unsaturated, with  monitoring  conducted  in individual,  relatively isolated, saturated
   zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2. Borehole stability problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders).
3. The anticipated use of the monitoring well  prohibits the use of drilling  fluid and additives in construction.
4. No drilling fluid, increasing depth and diameter requirements  eliminate many options.
5. Air rotary with casing hammer requires driving 8-inch or greater casing and completion by pullback.
                                                        199

-------
                                             MATRIX NUMBER 34
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated;  unsaturated;  invasion of formation by drilling fluid not permitted;  casing diameter 4 to 8 inches;
total well depth O to 15 feet.
z w
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DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool




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NA
NA
NA
NA

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NA
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NA

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NA
NA
NA
NA

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NA
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6
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NA

V.
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NA
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NA
NA
NA
NA

NA

NA
5
10

NA
NA














TOTAL
NA
NA
NA
NA

NA

NA
58
71

NA
NA
 EXPLANATORY  NOTES:
 1. Unconsolidated  formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
   zones, Drilling is through primarily unsaturated material, but completion is in a saturated zone.
 2. Borehole stability problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders).
 3. The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
 4. Diameter and no drilling fluid minimizes options
 5. Jetting, mud rotary and cable tool methods would require the addition of fluid.
 6. Air rotary with casing hammer requires driving 12-inch or greater diameter casing and completion by pullback.
 7. Air rotary completion possible only if unsupported borehole is stable.
                                                         200

-------
                                              MATRIX NUMBER 35
                      General Hydrogeologic Conditions & Well  Design Requirements
Unconsolidated; unsaturated; invasion of formation by drilling fluid not permitted; casing diameter 4 to 8 inches;
total well depth 15 to 150 feet.
\ z«
\ oo
\ *=§
\ 3*-
\ < s
\ ^ /«5
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NA
NA
NA
NA

NA

NA
10
NA

NA
NA







>,
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NA
NA
NA
NA

NA

NA
10
NA

NA
NA






R
O
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f
*£
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t
Relative
NA
NA
NA
NA

NA

NA
10
NA

NA
NA

c
to
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6
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NA
NA
NA
NA

NA

NA
10
NA

NA
NA

S) <-
5 c
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"Tj Q
^ "m
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OC T3
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NA
NA
NA
NA

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NA
10
NA

NA
NA

1
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15
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NA
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NA
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10
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e
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o
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15

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S I
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1!
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NA
NA
NA
NA

NA

NA
10
NA'

NA
NA











TOT*
NA
NA
NA
NA

NA

NA
80
NA

NA
NA
 EXPLANATORY NOTES:
 1,  Unconsolidated formations, predominantly  unsaturated,  with monitoring  conducted  in individual, relatively isolated, saturated
    zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
 2.  Borehole stability  problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders).
 3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
 4.  No drilling fluid, depth and diameter requirements have eliminated options.
 5.  Oversize drillpipe and/or auxiliary air probably required.
 6.  Jetting, mud rotary and cable tool methods would require the addition of fluid.
 7.  Air rotary completion possible only if unsupported borehole  is stable.
 8.  Air rotary with casing hammer unlikely to penetrate to specified depths with  12-inch diameter outer casing that is required for 8-inch
    diameter casing and screen completion.
 9  If borehole is unstable, for 8-inch diameter casing there is no currently available method that can be used to fulfill the requirements
    as stated above. Therefore, fluid would be necessary to install the well and invasion-permitting matrices will apply.
                                                          201

-------
                                              MATRIX NUMBER 36
                      General Hydrogeologic Conditions & Well Design Requirements
Unconsolidated; unsaturated; invasion of formation by drilling fluid not  permitted; casing  diameter 4 to 8 inches;
total well depth greater than 150 feet.
\ go
\ *&
\ < s
\ Sz
\ *3
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NA
NA
NA
NA

NA

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10
NA

NA
NA



_
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NA
NA
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NA

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10
NA

NA
NA
"c
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15
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1
NA
NA
NA
NA

NA

NA
10
NA

NA
NA
 J§

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NA
NA
NA
NA

NA

NA
10
NA

NA
NA
D
ag
1:1
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1-0
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•E D


,*_
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Is
NA
NA
NA
NA

NA

NA
10
NA

NA
NA
5
|
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c
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s
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c
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NA
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10
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c
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"o ^

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Ed a
LU -^
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EH £13
NA
NA
NA
NA

NA

NA
10
NA

NA
NA












TOTAL
NA
NA
NA
NA

NA

NA
80
NA

NA
NA
EXPLANATORY  NOTES:
L  Unconsolidated formations, predominantly unsaturated, with monitoring conducted in individual, relatively isolated, saturated
   zones. Drilling is through primarily unsaturated material, but completion is in a saturated zone.
2.  Borehole stability problems vary from slight (e.g. dense, silt/clay) to severe (e.g. coarse gravel and boulders),
3.  The anticipated use of the monitoring well prohibits the use of drilling fluid and additives in construction.
4.  No drilling fluid, depth and diameter requirements have eliminated options.
6.  Oversize drillpipe and/or auxiliary air probably required.
6.  Jetting, mud rotary and cable tool methods would require the addition of fluid.
7.  Air rotary completion possible only if unsupported  borehole is stable.
8.  Air rotary with casing hammer unlikely to penetrate to specified depths with 12-inch diameter outer casing that is required for
   8-inch diameter casing and screen completion.
9.  If borehole is unstable, for 8-inch diameter casing there is no method that can be used to fulfill the requirements as stated above.
   Therefore, fluid would be necessary to install the well  and invasion-permitting matrices will  apply.
                                                         202

-------
                                           MATRIX NUMBER 37
                     General  Hydrogeologic Conditions& Well Design Requirement
Consolidated; invasion of formation by drilling fluid permitted; casing diameter 4 inches or less.
     Air Rotary with
      Casing Hammer
     Dual Wall Rotary

     Cable Tool
  EXPLANATORY NOTES:
  1.  Consolidated formations, all types
  2.  The anticipated  use of the monitoring well permits the use of drilling fluid and additives in construction
  3.  Boreholes are expected to be sufficiently stable to permit open-hole completion.
  4.  Core sampling will improve the relative value of the mud rotary method.
  5.  Where dual-wall air is available it becomes an equally preferred method with air rotary.
                                                         203

-------
         workability without compromising set strength;
         and
     7) diatomaceous earth. Diatomaceous earth reduces
         slurry density, increases water demand and
         thickening time and reduces  set strength.

     Water used to mix neat cement should be clean,  freshwater
 free of oil or other organic material  and the total  dissolved
 mineral content should be less than 2000 parts per million. A
 high sulfate content is particularly undesirable (Campbell and
 Lehr, 1975). If too much water is used, the grout will be
 weakened and excessive shrinkage will occur upon setting. If
 this occurs, the annul us will not be completely tilled after the
 grouting operation. The voids in the annulus may not be seen
 from the surface but may still be present along the length of the
 casing (Kurt, 1983).

     Mixing of neat cement grout can be accomplished manu-
 ally or with a mechanical mixer. Mixing must be continuous so
 that the slurry can be emplaced without interruption. The grout
 should be mixed to a relatively stiff consistency and immedi-
 ately pumped into the annulus. The types of pumps suggested
 for use with grout include reciprocating (piston) pumps, dia-
 phragm pumps, centifugal pumps or moyno-typepumps.  These
 pumps are all commonly used by well drilling contractors.

     Neat cement, because of its chemical nature (calcium
 carbonate, alumina,  silica, magnesia, ferric oxide and  sulfur
 trioxide), is a highly alkaline substance with a pH that typically
 ranges from 10 to 12. This high pH presents the potential for
 alteration of the pH of water with which it comes in contact.
 This alteration of pH in the ground water can subsequently
 affect the representativeness of any water-quality samples
 collected from the well. Because the mixture is emplaced as a
 slurry, the coarse materials  that comprise the filter pack  around
 the intake portion of a monitoring well maybe infiltrated by the
 cement if the cement is placed directly on top of the filter pack,
 This is particularly true of thinner slurries that are mixed with
 more than 6 gallons of water per sack of cement. The cement
 infiltration problem also can be aggravated if well development
 is attempted prior to the time at which the cement has reached
final set.

     These problems can have a severe and persistent effect on
 the performance of the monitoring well in terms of yield and
 sample integrity. If thin grout is placed on top of the filter pack
 and infiltrates, the cement material can plug the filter pack and/
 or the well intake upon setting. The presence of the high-pH
 cement within the filter pack can cause anomalous pH readings
 in subsequent water samples taken from the well. Dunbar et al.
 (1985) reported that wells  completed  in low-permeability geo-
 logic  materials with  cement placed on top of the filter pack
 consistently produced samples with a pH greater than 9 for two
 and one-half years despite repeated attempts at well develop-
 ment. For these reasons, neat cement should not be emplaced
 directly on top of the filter pack of a monitoring well. Ramsey
 and Maddox (1982) have suggested that a 1 to 2-foot thick very
 fine-grained sand layer be placed atop the filter pack material
 prior to emplacement of the neat cement grout to eliminate the
 grout  infiltration potential. A 2- to  5-foot thick bentonite seal
 will accomplish the same purpose, but requires additional time
 to allow the bentonite to hydrate prior to cement placement.
 Either or both of these procedures  serve to minimize well
performance impairment and chemical interference effects
caused by the proximity of neat cement to the well intake.

    Another potential problem with the use of neat cement as
an annular sealing material centers around the heat generated by
the cement as it sets.  When water is mixed with any type of
Portland cement, a series  of spontaneous chemical hydration
reactions occur. If allowed to continue to  completion, these
reactions transform the cement slurry into a rigid solid material.
As  the hydration reactions progress and the cement cures, heat
is given off as a by-product this heat is known as the heat of
hydration (Troxell et al., 1968). The rate of dissipation of the
heat of hydration is a function of curing temperature, time,
cement chemical composition and the presence of chemical
additives (Lerch and Ford,  1948). General] y, the heat of hydra-
tion is of little concern. However, if large volumes of cement are
used  or if the heat is  not readily  dissipated (as it is not in a
borehole because of the insulating properties of geologic ma-
terials), relatively large temperature rises may result (Verbeck
and Foster, 1950).  The high heats can cause the structural
integrity of some types of well casing, notably thermoplastic
casing,  to be compromised.  Thermoplastics characteristically
lose strength and stiffness as the temperature of the casing
increases. Because collapse pressure resistance of a casing is
proportional to the material stiffness, if casing temperatures are
raised sufficiently this can result in failure of the casing (Johnson
etal, 1980).

    Molz and Kurt (1 979) and Johnson et al. (1980) studied the
heat of hydration problem and concluded:

     1)   peak casing  temperatures increase as the grout
         thickness increases. Temperature rises for casings
         surrounded by 1.5 inches to 4-inches of Type I
         neat  cement  ranged from  16°F   to 45°F;
         temperature rises for casings  surrounded by  12
         inches of grout (i.e. where washouts or caving or
         collapse of formation materials into the borehole
         might occur) can be in excess of 170 °F. In the
         former case, plastic pipe retains a large fraction of
         collapse strength, but in the latter  case, some
         types of plastic pipe lose a large fraction of the
         collapse strength (Gross, 1970);
    2)   the ratio of the grout-soil interface surface area to
         the volume of grout significantly influences peak
         casing  temperatures.   Additionally,  peak
         temperature rise for any casing size is nonlinear
         with  respect to grout thickness. Lower peak
         temperatures can thus be expected for smaller-
         diameter casings; and
    3)   peak temperatures are normally reached  8 to 10
         hours after water is added to the cement, and
         casing temperatures remain near their peak for
         several hours before slowly returning to the
         original temperature.

    The use of setting time accelerators, such as calcium chlo-
ride,  gypsum or aluminum powder can increase the heat of
hydration and cause  casings to overheat while the grout is
curing.  This temperature increase  poses an  increased potential
for casing failure. Both Molz and Kurt (1979) and Johnson et al.
(1980) attribute uncommon premature collapses of neat cement
grouted thermoplastic-cased wells to two factors: 1) that most
                                                           100

-------
                                          MATRIX NUMBER 39

                    General Hydrogeologic Conditions & Well Design Requirements

Consolidated; invasion of formation by drilling fluid not permitted; casing diameter 4 inches or less.

z 
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\ £
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DRILLING \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool



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8
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6
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1
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NA I NA






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NA
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10
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7
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NA
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NA
NA
NA
NA

NA

NA
10
NA

10
NA














TOTAL
NA
NA
NA
NA

NA

NA
74
NA

68
NA

  EXPLANATORY  NOTES:
                                    we,, does not per.it «he Use o, drH,,na ,,„,- and a^Uves ,n construction.
  3  Boreholes are expected to be sufficiently stable to permit open hole completion,
  4. Smud roTary fnd cab.e tool methods are potentiai.y ™ve, thereby reducing options to «r dnH.ng methods.
  5, Air rotary may require extra air and/or special drill pipe.
                                                       205

-------
                                           MATRIX NUMBER 40
                     General Hydrogeologic Conditions & Well Design Requirements
Consolidated; invasion of formation by drilling fluid not permitted; casing diameter 4 to 8 inches.
\ 1s
\ =1
\ «t S
\ ill o

v EC "•"
\ 2 ri
\ S§
X ^" IL
\ 1— ®
\ E
\°
DRILUNG \
METHODS \
Hand Auger
Driving
Jetting
Solid Flight
Auger
Hollow Stem
Auger
Mud Rotary
Air Rotary
Air Rotary with
Casing Hammer
Dual Wall Rotary
Cable Tool

|
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NA
NA
NA
NA

NA

NA
10
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NA
NA
NA
NA

NA

NA
10
NA

NA
NA





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"E
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6
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NA
NA
NA
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10
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NA
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o
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JE'-o
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d> o
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NA
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10
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NA
S3
%
a
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ta
CD
O
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"
-------
                                                 Appendix C
                                       (Supplement to Chapter 8)
     Abandonment of Test Holes, Partially Completed Wells and Completed Wells
                            (American Water Works Association,  1984)
 Section  1.1 —General
    The recommendations contained in this appendix pertain
to wells and test holes in consolidated and unconsolidated
formations.  Each sealing job should be considered  as an
individual problem, and methods and materials should be
determined only after carefully  considering the objectives
outlined in the standard.

Section 1.2 —  Wells in  Unconsolidated Formations
    Normally, abandoned wells extending only into consoli-
dated formations near the surface and containing water under
water-table conditions can be adequately sealed by filling with
concrete, grout, neat cement, clay, or clay and sand. In the event
that the water-bearing formation consists of coarse gravel and
producing wells are located nearby, care must be taken to select
sealing materials that will not affect the producing wells.
Concrete may be  used if the producing wells can be shut down
for a sufficient time  to allow the concrete to set. Clean,  disin-
fected sand or gravel may also be used as fill material opposite
the waterbearing formation. The remainder of the well, espe-
cially the upper portion, should be filled with clay, concrete,
grout,  or neat cement to exclude surface water. The  latter
method, using clay as the upper sealing material, is especially
applicable to large diameter abandoned wells.

    In gravel-packed, gravel-envelope, or other wells in which
coarse material has been added  around the inner casing to
within 20 to 30 ft (6.1  to 9.1 m) of the  surface, sealing outside
the casing is very important. Sometimes this scaling may
require removal of the gravel or perforation of the casing.

Section 1.3 —  Wells in  Creviced Formations
    Abandoned wells that penetrate limestone or other creviced
or channelized rock formations lying immediately below the
surface deposits should preferably be filled with concrete,
grout, or neat cement to ensure permanence  of the seal. The use
of clay or sand in such wells is not desirable because fine-
-grained fill material may be displaced by the flow of water
through crevices or channels. Alternate layers of coarse stone
and concrete may be used for fill material through the water-
producing horizon if limited vertical movement of water  in the
formation will not affect the quality or quantity of water in
producing wells. Only concrete, neat cement, or grout should be
used in this type of well. The portion of the well between a point
10 to 20 ft (3.0 to 6.1  m) below and a point 10 to 20 ft (3.0  to 6.1
m) above should be sealed and a plug of sealing material formed
above the creviced formation. Clay or sand maybe used to fill
the upper part of the well to within 20 ft (6.1 m) of ground level.
The upper 20 ft (6.1 m) should be sealed with concrete or
cement grout.
Section 1.4 — Wells in Noncreviced Rock Formations
    Abandoned wells encountering non-creviced  sandstone or
other water-bearing consolidated formations below the surface
deposits may be satisfactorily sealed by filling the entire depth
with clay, provided there is no movement of water in the well.
Clean  sand, disinfected if other producing wells nearby,
may also be used through the sandstone up  to a point 10 to 20
ft (3.0 to 6.1 m) below the bottom of the casing. The upper
portion of this type of well should be filled with concrete, neat
cenent, grout or clay to provide an effective seal against
entrance of surface water. If there is an appreciable amount of
upward flow, pressure cementing or mudding may be advis-
able.

Section 1.5 —Multiple Aquifer Wells
    Some  special problems may develop  in sealing wells
extending into more than one aquifer. These wells should be
filled and sealed in such a way that exchange of water from one
aquifer to another is prevented.  If no  appreciable movement of
water is encountered, filling with concrete,  neat cement, grout,
or alternate layers of these materials and sand will prove
satisfactory. When velocities are high, the  procedures outlined
in.  Sec. 1.6 are recommended. If alternate concrete plugs or
bridges are used, they should be placed in known nonproducing
horizons or, if locations of the nonproducing horizons are not
known, at frequent intervals. Sometimes when the  casing is not
grouted or the formation is noncaving, it may be necessary to
break, slit, or perforate the  casing to fill any  annular space on the
outside.

Section 1.6 — Wells with Artesian Flow
    The sealing of abandoned wells that have a movement
between aquifers or to the surface requires special attention.
Frequently the movements of water maybe sufficient to make
sealing by gravity placement of concrete,  cement grout, neat
cement, clay or sand impractical. In, such wells, large stone
aggregate (not more than one third of the diameter of the hole),
lead wool, steel  shavings, a well packer, or  a wood or cast-lead
plug or bridge will be needed to restrict the flow and thereby
permit the  gravity placement of sealing material above the
formation producing the flow. If preshaped  or precast plugs are
used, they  should be several times longer than the diameter of
the well, to prevent tilting.

    Since it is very important in wells of this type to prevent
circulation between formations, or loss of water to the surfaces
or to the annular space outside  the casing,  it is recommended
that pressure cementing, using the minimum  quantity of water
that will permit handling, be used. The use of pressure mudding
instead of this process is sometimes permissible.
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    In wells in which the hydrostatic head producing flow to
the surface is low, the movement of water maybe arrested by
extending the well casing to an elevation above the artesian-
pressure surface.  Previously described sealing methods suit-
able to the geologic conditions can then be used.

Section 1.7 — Sealing Materials
    A number of materials that can be used for sealing wells
satisfactorily, including concrete, cement grout, neat cement,
clay, sand, or combinations of these materials, are mentioned
in this appendix. Each material has certain characteristics and
distinctive properties; therefore, one material may  be especially
suited for doing a particular job.  The selection of the material
must be based on the construction of the well, the nature of the
formations penetrated,  the material  and equipment available,
the location of the well with respect to possible sources of
contamination, and the cost of doing the work.

    Concrete is generally used for filling the upper part of the
well or water-bearing formations,  for plugging short sections of
casings, or for filling large-diameter wells. Its use is cheaper
than neat cement or grout, and it makes  a stronger plug or seal.
However, concrete will not penetrate seams, crevices,  or in-
terstices. Furthermore, if not properly placed, the aggregate is
likely to separate from the cement.

    Cement grout or neat cement and water are far superior for
sealing small  openings, for penetrating any annular  space
outside of casings, and for falling voids in the  surrounding
formation. When applied under pressure, they  are strongly
favored for sealing wells under artesian pressure or those
encountering more than one aquifer. Neat cement is generally
preferred to grout because it does not separate.

     Clay, as a heavy mud-laden or special clay fluid applied
under pressure, has most of the advantages of cement grout. Its
use is preferred by some competent authorities particularly for
sealing artesian wells. Others feel that it may, under some
conditions, eventually be carried away into the surrounding
formations.

     Clay in a relatively dry state, clay  and sand, or sand alone
may be used advantageously  as sealing materials, particularly
under water-table conditions where diameters are  large, depths
are great, formations are caving, and there is no need for
achieving penetration of openings in casings, liners, or  for-
mations, or for obtaining a watertight  seal at any given spot.

     Frequently combinations of these materials are necessary.
The  more expensive materials are used when strength, penetra-
tion, or watertightness are needed. The  less expensive materials
are used for the  remainder of the well. Cement grout or neat
cement is now being mixed with bentonite clays and various
aggregates.  Superior results and lower cost are claimed for such
mixtures.

Reference
American Water Works Association,  1984. Appendix I:
     Abandonment of test holes, partially completed wells  and
     completed wells; American Water Works  Association
     Standard for Water Wells, American Water Works
     Association, Denver, Colorado, pp. 45-47.
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                                                   Glossary
Abandonment
    The complete sealing of a well or borehole with grout or
other  impermeable materials  to  restore  the original
hydrogeologic conditions and/or to prevent contamination of
the aquifer.

Absorption
    The penetration or apparent  disappearance of molecules or
ions of one or more substances into the interior of a solid or
liquid.  For example, in hydrated bentonite, the planar water that
is held between the  mica-like layers is  the result of absorption
(Ingersoll-Rand, 1985).

Accelerator
    Substances used to hasten the setting or curing of cement
such as calcium chloride, gypsum and aluminum powder.

Acrylonitrile Butadiene Styrene (ABS)
    A thermoplastic material produced by varying ratios of
three different monomers to produce well casing with good heat
resistance and impact strength.

Adapter
    A device used  to connect two different sizes or types of
threads, also known as sub, connector or coupling (Ingersoll-
Rand,  1985).

Adsorption
    The process by  which atoms, ions or molecules are held to
the surface of a material through ion-exchange processes.

Advection
    The process by which solutes are  transported with and at
the same rate as moving ground water.

Air Rotary Drilling
    A drilling technique whereby compressed air is circulated
down the drill rods and up the open hole. The air simultaneously
cools the bit and removes the cuttings from the  borehole.

Air Rotary with  Casing Driver
    A drilling technique that uses conventional air rotary
drilling while simultaneously driving casing. The casing driver
is installed in the mast of a top-head drive air rotary drilling rig.

Aliphatic Hydrocarbons
    A  class of organic compounds characterized by straight or
branched chain arrangement of the constituent  carbon atoms
joined by single covalent bonds with all other bonds to hydro-
gen atoms.
Alkalinity
    The ability of the salts contained in the ground water to
neutralize acids. Materials that exhibit a pH of 7 or greater are
alkaline. High-pH materials used in well construction may have
the potential to alter ambient water quality.

Aluminum Powder
    An additive to cement that produces a stronger, quick-
setting cement that expands upon curing.

Anisotropic
    Having some physical property that varies with direction
(Driscoll,  1986).

Annular Sealant
    Material used to provide a positive seal between the bore-
hole and the casing of the well. Annular sealants should be
impermeable and resistant to chemical or physical deteriora-
tion.

Annular Space or Annulus
    The space between the borehole wall and the  well casing,
or the space between a casing pipe and a liner pipe.

Aquifer
    A geologic formation, group  of formations,  or part of a
formation that can yield water to a well or spring.

Aquifer Test
    A test involving  the withdrawal of measured  quantities of
water from or addition of water to a well  and the measurement
of resulting changes in head in the aquifer both during and after
the period of discharge or addition (Driscoll, 1986).

Aquitard
    A geologic formation, or group of formations,  or part of a
formation of low permeability that is typically  'saturated but
yields very limited quantities of water to wells.

Aromatic Hydrocarbons
    A class of unsaturated cyclic organic compounds contain-
ing one or more ring structures or cyclic groups with very stable
bonds  through the substitution of a hydrogen atom for  an
element or compound.

Artesian Well
    A well deriving water from a confined aquifer in which the
water level stands above  the ground surface; synonymous with
flowing artesian well (Driscoll, 1986).
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 Artificial Filter Pack
     See Grovel Pack.

 Attenuation
     The reduction or removal of constituents in the ground
 water by the sum of all physical, chemical and biological events
 acting upon the ground water.

 Auger Flights
     Winding metal strips welded to the auger sections that
 carry cuttings to the surface during drilling.

 Backwash (Well  Development)
     The surging effect or reversal of water flow in a well that
 removes fine-grained material from the formation surrounding
 the borehole and helps prevent bridging (Driscoll,  1986).

 Backwashing
     A method of filter pack emplacement whereby  the filter
 pack material is allowed to fall freely through the annulus while
 clean fresh water is simultaneously pumped  down the casing.

 Bailer
     A long, narrow bucket-like device with  an open top and a
 check valve at the bottom that is used to remove water and/or
 cuttings from the borehole.

 Bailing (Well Development)
     A technique whereby a bailer is raised and lowered in the
 borehole to create a strong outward and inward movement of
 water from the borehole to prevent bridging and to remove fine
 materials.

 Barium Sulfate
     A natural  additive used to increase the density of drilling
 fluids.

 Bentonite
     A hydrous aluminum silicate available in powder,
 granular or pellet form and used to provide a tight seal between
the well casing  and borehole. Bentonite is also added to drilling
 fluid to impart specific characteristics to the  fluid.

 Biodegradation
     The breakdown of chemical constituents through the bio-
 logical processes of naturally occuring organisms.

 Bit
     The cutting tool attached to the bottom of the drill stem. Bit
 design varies for drilling in various types of formations and
 includes roller, cone and drag-type bits.

 Bit, Auger
     Used for soft formations with auger drill (Ingersoll-Rand,
 1985).

 Borehole
     A hole drilled or bored into the earth, usually for explor-
 atory or economic purposes,  such as a water well or oil well
 (united States Environmental Protection Agency, 1986).
Borehole Geophysics
    Techniques that use a sensing device that is lowered into a
borehole for the purpose  of characterizing geologic formations
and their associated fluids. The  results can be interpreted to
determine lithology, geometry Resistivity, bulk density,pcmsity,
permeability, and moisture content and to define the source,
movement, and physical/chemical characteristics of ground
water (United States Environmental Protection Agency, 1986).

Bridge  Seal
    An artificial plug set to seal off specific zones in the
abandonment of a well.

Bridge-Slot Intake
    A well intake that is manufactured on a press from flat
sheets that are perforated, rolled and seam welded where the
slots are vertical and occur as parallel openings  longitudinally
aligned to the well axis.

Bridging
    The development of gaps or obstructions  in either grout or
filter pack materials during  emplacement. Bridging of particles
in a naturally developed or artificial gravel pack can also occur
during  development.

Cable Tool Drilling
    A drilling technique whereby a drill bit attached to the
bottom of a weighted drill stem is raised  and  dropped to crush
and grind formation materials.

Calcium Chloride
    A soluble calcium  salt added to cement slurries to acceler-
ate the setting time, create higher early strength and to  minimize
movement of the cement into zones of coarse material.

Calcium Hydroxide
    A primary constituent of wet cement.

Caliper Logging
    A logging technique used to determine the diameter of a
borehole or the internal diameter of casing through the use of a
probe with one to four spring expanding prongs. Caliper log-
ging  indicates variations in the diameter of the vertical profile.

Capillary Fringe
    The pores in this zone are saturated but the pressure heads
are less than atmospheric.

Casing
    An impervious durable pipe placed in a well to prevent the
borehole walls from caving and to seal off surface drainage or
undesirable water, gas, or other fluids and prevent  their en-
trance into the  well. Surface or temporary  casing  means a
temporary casing placed in soft, sandy  or caving surface forma-
tion to prevent the borehole from caving during  drilling. Pro-
tective casing means a short casing installed around the well
casing. Liner pipe means a well casing installed without driving
within the casing or open borehole.
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Casing, Flush-Coupled
    Flush-coupled casing is joined with a coupling with the
same outside diameter as the casing, but with two female
threads. The inside diameterof the coupling  is  approximately  3/
16 inch smaller than that of the casing. Flush-coupled casing
has thinner walls than flush-joint casing (Ingersoll-Rand, 1985).

Casing, Flush-Joint
    Flush-joint casing has a male thread at one end and a female
thread at the other. No coupling is used (Ingersoll-Rand, 1985).

Casing Driver
    A device fitted to the top-head drive of a rotary rig that is
used to advance casing into the subsurface.

Cation Exchange Capacity (CEC)
    The measure of the availability of cations that can be
displaced from sites  on surfaces or layers and which can be
exchanged for other  cations. For geologic materials, CEC  is
expressed as the  number of milliequivalents of cations that can
be exchanged in a sample with a dry mass  of 100 grams.

Cement
    A mixture of calcium  aluminates and silicates made by
combining lime and clay while heating and which is emplaced
in the annular space to form a seal between the  casing and the
borehole.

Cement Bond Log
    A logging device that uses acoustical signals to determine
the integrity of the cement bond to the casing.

Cement, Quick-Setting
    Cement of special composition and freeness of grind that
sets much quicker than ordinary cement. This cement is used for
deviating holes and plugging cavities (Ingersoll-Rand,  1985).

Cementing
    The emplacement of a cement slurry by  various  methods so
that it fills the space between the casing and the borehole  wall
to a prdetermined height above the bottom of  the well.  This
secures the casing in place and excludes water and other fluids
from the borehole.

Center Plug
    A plug within the pilot assembly of a  hollow-stem auger
that is used to prevent formation materials from entering the
stem of the lead auger during drilling.

Center Rod
    A rod attached to the pilot assembly that facilitates removal
from the lead end of the hollow-stem auger.

Centralizer
    Spring-loaded guides that are used to center the casing in
the borehole to  ensure effective placement  of filter pack or
grout.

Check Valve
    Ball and spring valves on core barrels, rods and bailers that
are used to control water flow in one direction only.
Circulate
    To cycle drilling fluid through the drill pipe and borehole
while drilling operations are temporarily suspended to condi-
tion the drilling fluid and the borehole before hoisting the drill
pipe and to obtain cuttings from the bottom of the well before
drilling proceeds (Ingersoll-Rand, 1985).

Circulation
    The movement of drilling fluid from the suction pit through
the pump, drill pipe, bit and annular space in the borehole and
back again to the suction pit. The time involved is usually
referred to as circulation time (Ingersoll-Rand, 1985).

Circulation, Loss of
    The loss of drilling fluid into the formation through  crev-
ices or by infiltration into a porous media.

Clay
    A plastic, soft, variously colored earth, commonly  a hy-
drous silicate of alumina, formed by the decomposition of
feldspar and  other  aluminum  silicates (Ingersoll-Rand, 1985).

Collapse Strength
    The capability of a casing or well intake to resist collapse
by any or  all external loads to which it  is subjected during and
after installation.

Compressive Strength
    The  greatest compressive stress that a substance can bear
without deformation.

Conductivity
    A measure of the quantity of electricity transferred across
unit area per unit potential gradient per unit time. It is the
reciprocal  of Resistivity.

Cone of Depression
    A depression in the ground-water table or potentiometric
surface that has the shape of an inverted cone and develops
around a well from which water is being withdrawn. It defines
the area of influence of a well (Driscoll 1986).

Cone of Impression
    A conical mound on the water table that develops in
response to well injection whose shape  is identical to the cone
of depression formed during pumping of the aquifer.

Confined Aquifer
    An aquifer which is bounded above and  below by  low-
permeability  formations.

Confined Bed
    The relatively  impermeable formation  immediately  over-
lying  or underlying  a confined aquifer.

Contaminant
    Any physical, chemical, biological or radiological sub-
stance or matter in water that has an adverse impact.

Contamination
    Contamination is the introduction into ground water of any
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chemical material, organic material, live organism or radioac-
tive material that will adversely affect the quality of the ground
water.

Continuous Sampling Tube System
    Thin-wall sampling tube attached in advance of the cutting
head of the hollow-stem auger that allows undisturbed samples
to be taken continuously while the augers are rotated.

Continuous Slot  Wire-Wound Intake
    A well intake that is made by winding and welding trian-
gular-shaped, cold-rolled wire around a cylindrical array of
rods. The spacing of each successive turn of wire determines the
slot size of the intake.

Core
    A continuous columnar sample of the lithologic units
extracted from a borehole. Such a sample preserves strati-
graphic contacts and structural features (United States Envi-
ronmental Protection Agency,  1986).

Core Barrel
    A reaming shell and length of tubing used during air or mud
rotary drilling to collect formation samples in both consolidated
and unconsolidated formations. Core barrels may be single or
double walled and of a swivel or rigid type.

Core Lifter
    A tapered split ring inside the bit and surrounding the core.
On lifting the rods, the taper causes the ring to contract in
diameter, seizing and holding the core (Ingersoll-Rand, 1985).

Corrosion
    The adverse chemical alteration that reverts elemental
metals back to more stable mineral compounds and  that affects
the physical and chemical properties of the metal.

Cost-Pius  Contract
    Drilling contracts that list specific costs associated with
performing the work and include a percentage of those costs as
an additional amount that will be paid to perform a job.

Coupling
    A connector for drill rods, pipe or casing with identical
threads, male and/or female, at each end (Ingersoll-Rand,
1985).

Cross Contamination
    The movement of contaminants between aquifers or water-
bearing zones through an unsealed or improperly sealed bore-
hole.

Cutter  Head
    The auger head located at the lead edge of the auger column
that breaks up formation materials during drilling.

Cuttings
    Formation particles obtained from a borehole  during the
drilling  process.
Decontamination
    A variety of processes used to clean equipment that has
contacted formation material or ground water that is known to
be or suspected of being contaminated.

Dennison   Sampler
    A specialized sampler of a double-tube core design with a
thin inner tube that permits penetration in extremely stiff or
highly cemented unconsolidated deposits while collecting a
thin-wall sample.

Density
    The weight of a substance per unit volume.

Development
    The act of repairing damage to the formation caused during
drilling procedures and increasing the porosity and permeabil-
ity of the materials surrounding the intake portion of the well
(Driscoll, 1986).

Diatomaceous Earth
    A cement additive composed of siliceous  skeletons of
diatoms used to reduce slurry density, increase water demand
and thickening time while reducing set strength.

Differential  Pressure
    The difference in pressure between the hydrostatic head of
the drilling fluid-filled or empty borehole  and the formation
pressure at any given depth (Ingersoll-Rand,  1985).

Direct Mud  Rotary
    A drilling technique whereby a drilling  fluid is pumped
down the drill rod, through the bit and circulates back to  the
surface by moving up the annular space between the drill rods
and the borehole.

Dispersion
    A process of contaminant transport that occurs by me-
chanical mixing and molecular diffusion.

Dissociation
    The splitting up of a compound or element into two or more
simple molecules, atoms or ions. Applied usually to the effect
of the action of heat or solvents upon dissolved substances. The
reaction is reversible and not as permanent as decomposition;
that is, when the solvent is removed, the ions recombine
(Ingersoll-Rand, 1985).

DNAPLS
    Acronym  for dense, nonaqueous-phase liquids.

Down gradient
    In the direction of decreasing hydrostatic head (United
States Environmental Protection Agency, 1986).

Downgradient Well
    A well that has been installed hydraulically downgradient
of the site and  is capable of detecting the migration of contami-
nants  from a regulated unit. Regulations require the installation
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contaminant migration (United States Environmental Protec-
tion Agency, 1986).

Down-the-Hole Hammer
    A pneumatic drill operated at the bottom of the drill pipe by
air pressure provided from the surface.

Drawdown
    The extent of lowering of the water surface in a well and
water-bearing zone resulting from the discharge of water from
the well.

Drill Collar
    A length of heavy, thick-walled pipe used to stabilize the
lower drill string, to minimize bending caused by the weight of
the drill pipe and to add weight to the bit.

Drill Pipe
    Special pipe used to transmit rotation from the rotating
mechanism to the bit. The pipe also transmits weight to the bit
and conveys air or fluid which  removes cuttings from the
borehole and cools the bit (Driscoll, 1986).

Drill Rod
    Hollow flush-join ted or coupled rods that are rotated in the
borehole that are connected at the bottom to the drill bit and on
the top 10 the rotating or driving mechanism of a drilling rig.

Drill String
    The string of pipe that extends from the bit to the driving
mechanism that serves to carry the mud down the borehole and
to rotate  the bit.

Drilling Fluid
     A water or air-based fluid used in the well drilling opera-
tion to remove cuttings from the borehole, to clean and cool the
bit, to reduce friction between the drill string and the sides of the
borehole and to seal the borehole  (Driscoll, 1986),

Drive Block
     A heavy weight  used  to drive pipe or casing through
unconsolidated material.

Drive Couplings
     Heavy-duty couplings used to join sections of heavy-wall
casing that are specifically designed to withstand the forces
during driving casing.

Drive Head
     A component fastened to the top of pipe or casing to lake
 the blow of the drive block (Ingersoll-Rand,  1985).

 Drive Shoe    *
     A forged steel collar with a cutting edge fastened onto the
bottom of the casing to shear off irregularities in the hole as the
 casing advances. It is designed to withstand drive pressures  to
protect the lower edge of the casing as it is driven (United S lates
 Environmental Protection Agency, 1986).

 Driven Well
     A well that is driven to the desired depth, either by hand  or
 machine; may employ a wellpoint, or alternative equipment.
Drop Hammer
    A weighted device used to drive samplers during drilling
and sampling.

Dual-Wall Reverse Circulation
    A dri Jling technique whereby the circulating fluid is pumped
down between the outer casing and the inner drill pipe, through
the drill bit and up the inside of the drill pipe,

Effective Grain Size (Effective Diameter)
    The particle grain size of a sample where 90 percent
represents coarser-size grains and 10 percent represents firter-
sii-e grains, i.e., the coarsest diameter in the finest 10 percent of
the sediment.

Electric Logging
    Logging techniques used in fluid-filled boreholes to obtain
information concerning the porosity, permeability and fluid
content of the formations drilled based on thedielectic properties
of the aquifer materials.

Established Grade
    The permanent point of contact of me ground or artificial
surface with the casing or curbing of the well.

Established Ground Surface
    The permanent elevation of the surface at the site of the
well upon completion.

Filter Cake (Mudcake)
    The suspended solids that are deposited on the borehole
wall during the process of drilling.

Filter Cake Thickness (Mudcake)
    A measurement, in 32nd of an inch, of the solids deposited
on filter paper during the standard 30-minute API filter test, or
measurement of the solids deposited on filter paper for a 71/2-
minute duration (Ingersoll-Rand, 1985).

Filter Pack
     Sand, gravel or glass beads that are uniform, clean and
well-rounded that are placed in the annulus of the well between
the borehole wall and the well intake to prevent formation
material from entering through the well intake and to stabilize
the adjacent formation.

Filter Pack Ratio
     A ratio used to express size differential between the forma-
tion materials and the filler pack that typically refers to either
the average grain size (DJO) or the 70-percent (DTO) retained size
of the formation material.

Filtrate Invasion
     The movement of drilling fluid into the adjacent formation
that occurs when the weight of the drilling fluid substantially
exceeds the natural hydrostatic pressure of the formation.

 Fixed-Price Contracts
     Drilling contracts that list the manpower, materials and
additional costs needed to perform the work specified as a fixed
 cost payable upon completion.
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Floaters
    Light-phase organic liquids in ground water capable of
forming an immiscible layer that can float on the water table
(United States Environmental Protection Agency, 1986).

Float  Shoe
    A drillable valve attached to the bottom of the casing.

Flocculation
    The agglomeration of finely divided suspended solids into
larger, usually  gelatinous particles through electrical charge
alignment of particles.

Flow Meter
    A tool used to monitor fluid flow rates in cased or uncased
boreholes using low-inertia impellers  or through changes in
thermal conductance as liquids pass through the tool.

Flow-Through Well
    The installation of a  small-diameter well intake that pen-
etrates all or a  significant portion of the aquifer.  The well is
designed to minimize distortion of the flow field in the aquifer.

Fluid Loss
    Measure of the relative amount of fluid lost (filtrate)
through permeable formations  or membranes when the  drilling
fluid is subjected to a pressure differential (Ingersoll-Rand,
1985).

Fluoropolymers
    Man-made materials consisting of different formulations
of monomers molded by powder metallurgy techniques that
exhibit anti-stick properties and resistance to chemical and
biological attack.

Flush-Coupled  Casing
    See Casing, Flush-coupled.

Flush-Joint Casing
    See Casing, Flush-joint.

F]y Ash
    An additive to cement that increases sulfate resistance and
early compressive strength.

Formation
    A mappable unit  of  consolidated material or unconsoli-
dated material characterized by a  degree of lithologic homo-
geneity.

Formation Damage
    Damage to the formation resulting from drilling activities
(e.g., the invasion of drilling fluids or formation of mudcake)
that alter the hydraulic properties of formation materials.

Formation Fluid
    The natural fluids present in the formation or  aquifer.

Formation Stabilizer (Filter Pack)
    A sand or gravel placed in the  annulus of the well between
the borehole and the well  intake to provide temporary or long-
term support for the borehole (Driscoll, 1986).

Gel Strength
    A measure of the capability of the drilling fluid to maintain
suspension of particulate matter in the mud column when the
pump is off.

Grain Size
    The general dimensions of the particles in a sediment or
rock, or of the grains of a particular mineral that make up a
sediment or rock. It is common for these dimensions to be
referred to with broad terms, such as  fine, medium, and coarse.
A widely used grain size classification is the Udden-Wentworth
grade scale (United States Environmental Protection Agency, 1986.


Gravel  Pack (Artificial Filter Pack);  see also Filter
Pack
     A term used to describe gravel or other permeable filter
material placed in the annular  space around a well intake to
prevent the movement of finer material into the well  casing, to
stabilize the formation and to increase the ability of the well to
yield  water.

Ground Water
    Any water below the surface of the earth, usually referring
to the zone of saturation.

Grout
    A fluid mixture of neat cement and water with various
additives or bentonite of a consistency that can be forced
through a pipe and emplaced in the  annular space between the
borehole and the casing to form an impermeable seal.

Grouting
    The operation by which grout is placed between the casing
and the wall of the borehole to secure the casing in place and to
exclude water and other fluids from moving into and through
the  borehole.

Gypsum
    An additive to cement slurries that produces a quick-
setting, hard cement that expands upon curing.

Halogenated Hydrocarbons
    An organic  compound containing one or more halogens
(e.g., fluorine, chlorine, bromine, and iodine) (United States
Environmental Protection Agency, 1986).

Hand Auger
    Any of a variety of hand-operated devices for drilling
shallow holes into the ground.

Head LOSS
    That part of potential energy that is lost because of friction
as water flows through a porous medium.

Heat of Hydration
    Exothermic or heat-producing reaction that occurs during
the curing of cement.
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Perched Ground Water
    Ground water in a saturated zone that is separated from the
main body of ground water by a less permeable unsaturated
zone or formation.

Percolate
    The act of water seeping or filtering through materials
without a definite channel,

Permeability
    A measure of the relative ease with which a porous medium
can transmit a liquid under a potential gradient (United States
Environmental Protection Agency,  1975).

Piezometers
    Generally a small-diameter, non-pumping well used to
measure the elevation of the water table or potentiometric
surface (United  States Environmental Protection Agency,
1986).

Pilot Assembly
    The assembly placed at the lead end  of the auger consisting
of a solid center plug and a pilot bit.

Plugs, Casing
    Plug made  of drillable material to correspond to the inside
diameter of the casing. Plugs are pumped to bottom of casing to
force all cement outside of casing (Ingersoll-Rand, 1985).

Plugging
    The complete filling of a  borehole or well with an imper-
meable material which prevents flow into  and through the
borehole or well.

Plume
    An elongated and mobile  column or band of a contaminant
moving through the subsurface.

Polumeric Additives
    The natural organic colloids developed from the guar plant
that are used for viscosity control during drilling.

Polyvinyl Chloride (PVC)
    Thermoplastics produced by combining PVC resin  with
various types of stabilizers, lubricants, pigments, fillers and
processing aids, often formulated  to produce rigid well casing.

Porosity
    The percentage of void spaces or openings in a consoli-
dated or unconsolidated material.

Portland Cement
    Cement specified as Type  I or Type  11 under ASTM C-150
standards.

Potentiometric Data
    Ground-water surface elevations obtained at wells and
piezometers that penetrate a water-bearing formation.

Potentiometric Surface
    An imaginary surface representing the total head of ground
 water in a confined aquifer that is defined by the level to which
 water will rise in a well (Driscoll,  1986).

 Precipitate
     Material that will  separate  out of solution or slurry  as a
 solid under  changing chemical and or physical conditions.

 Pressure Sealing
     A process by which a grout is confined within the borehole
 or casing by the use of retaining plugs or packers and by which
 sufficient pressure is applied to drive  the grout slurry into and
 within the annular space or zone to be grouted.

 Protective Casing
     A string of casing  set in the borehole to stabilize a section
 of the formation and/or to prevent leakage into and out of the
 formation and to allow drilling to continue to a greater depth.

 Protectors, Thread
     A steel box and pin used to plug each end of a drill pipe
 when it is pulled from the borehole to  prevent foreign matter or
 abrasives from collecting on the greasy threads and to protect
 threads from corrosion or damage while transporting or in
 storage (Ingersoll-Rand,  1985).

 Puddled Clay
     Puddling clay is a mixture of bentonite, other expansive
 clays, tine-grained material and water,  in a ratio of not less  than
 7 pounds of bentonite or expansive clay per gallon of water. It
 must be composed of not less than 50 percent expansive  clay
 with the maximium size of the remaining portion not exceeding
 that of coarse sand.

 Pulling Casing
     To remove the casing from a well.

 Pumping/Overpumpinf/Backwashing
     A well development technique that alternately starts and
 stops a pump to raise and drop the  column of water in the
 borehole in a surging action.

 Pump Test
     A test used to determine aquifer  characteristics performed
 by  pumping a well for a period of time and  observing the change
 in hydraulic head that occurs in adjacent wells. A pump test may
 be  used to determine degree of hydraulic interconnection between
 different water-bearing units, as well as the recharge rate of a
 well (United States Environmental Protection  Agency, 1986).

 Pumping Water Level
     The elevation of the surface of the water  in a well or the
 water pressure at the top of a flowing artesian well after a period
 of pumping or flow at  a specified rate.

 Radioactive Logging
      A logging process  whereby  a radioactive source is  lowered
 down a borehole to determine formation characteristics. Ra-
 dioactive logging devices typically used for ground-water
 investigations include gamma and neutron logging  probes.

 Radius of Influence (Cone of Depression)
      The radial distance  from the center of a well under pumping
217

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Heaving Sand
    Saturated sands encountered during drilling where the
hydrostatic pressure of the formation is greater than the bore-
hole pressure causing the sands to move up into the borehole.

High-Yield Drilling Clay
    A classification  given to  a group  of commercial drilling
clay preparations having a yield of 35 to 50 bbl/ton and
intermediate between bentonite  and low-yield clays. High-
yield drilling clays are usually prepared by peptizing low-yield
calcium montmorillonite clays or, in a few cases, by blending
some bentonite with the peptized low-yield clay  (Ingersoll-
Rand, 1985).

Hollow-Stem Auger Drilling
    A drilling technique  in which hollow, interconnected flight
augers, with a cutting head, are pressed  downward as the auger
is rotated.

Homogeneous
    Exhibiting a uniform or similar nature.

Hydraulic Conductivity
    A coefficient of proportionality that describes the rate at
which a fluid can move  through a permeable medium. It is a
function of both the media and of the fluid flowing through it
(United States Environmental Protection Agency, 1986).

Hydraulic Gradient
    The change in static head per unit of distance in a given
direction. If not specified, the direction  generally is  understood
to be that of the maximum rate of decrease in head.

Hydrostatic Head
    The pressure exerted by a column of fluid, usually ex-
pressed in pounds per square inch (psi). To determine the
hydrostatic head at a given depth in psi, multiply the depth in
feet by the density in pounds per gallon by  0.052  (Ingersoll-
Rand, 1985).

Immiscible
    Constituents that are not significantly soluble in water.

Incrustation (Encrustation)
    The process by which a crust or coating is formed on the
well intake  and/or casing, typically through chemical or bio-
logical reactions.

Induction  Tool
    A geophysical  logging tool  used to measure pore fluid
conductivity.

Inhibitor (Mud)
    Substances generally regarded as  drilling mud contami-
nants, such as salt and calcium sulfate, are  called inhibitors
when purposely added to mud so that the  filtrate from the
drilling fluid will prevent or retard the hydration of formation
clays  and shales (Ingersoll-Rand, 1985).

Isotropic
    A medium whose properties are the same in all directions.
Jet Percussion
    A drilling process that uses a wedge-shaped drill bit that
discharges water under pressure while being raised and lowered
to loosen or break up material in the borehole.

Kelly
    Hollow steel bar that is in the main section of drill string to
which power is directly transmitted from the rotary table to
rotate the drill pipe and bit (Driscoll, 1986).

Ketones
    Class of organic  compounds where the carbonyl group is
bonded to two alkyl groups (United States Environmental
Protection Agency, 1986).

Knock-Out Plate
    A nonretrievable plate wedged within the auger head that
replaces the traditional pilot assembly and center rod that is
used to prevent formation materials from entering the hollow
auger stem.

Logging, Radioactive
    The logging  process whereby a neutron source is lowered
down the borehole, followed by a recorder, to determine mois-
ture content and to identify water-bearing zones.

Lost Circulation
    The result of drilling fluid escaping from the borehole into
the formation by way of crevices or porous media (Driscoll,
1986).

Louvered Intake
    A well intake with openings that are manufactured in solid-
wall metal tubing by stamping outward with a  punch against
dies that control the size of the openings.

Low-Solids Muds
    A designation given to any type of mud where  high-
performing additives have been partially or wholly substituted
for commercial or natural clays (Ingersoll-Rand, 1985).

Low-Yield Well
    A relative term referring to a well that cannot recover in
sufficient time after well evacuation to permit the immediate
collection of water samples (United States Environmental
Protection Agency, 1986).

Machine-Slotted Intake
    Well intakes  fabricated from standard casing  where slots of
a predetermined width are cut into the casing at regular intervals
using machining  tools.

Male and Female Threads
    Now called  pin and box threads, as  in the oil industry
(Ingersoll-Rand,  1985).

Marsh Funnel
    A device used to  measure drilling fluid viscosity where the
time required for a known volume of drilling fluid to drain
through an orifice is measured and calibrated against a time for
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conditions to the point where there is no lowering of the water
table or potentiometric surface (Driscoll, 1986).

Reamer
    A bit-like tool, generally run directly above the bit, used to
enlarge and maintain a straight borehole (After Ingersoll-Rand,
1985).

Reaming
    A drilling operation used to enlarge a borehole.

Rehabilitation
    The restoration of a well to its most efficient condition
using  a variety of chemical and mechanical techniques that  are
often combined for optimum effectiveness.

Resistivity
    The electrical resistance offered to the passage of a current,
expressed  in ohm-meters; the reciprocal of conductivity. Fresh-
water muds are usually characterized by high Resistivity; salt-
water muds, by low Resistivity (Ingersoll-Rand, 1985).

Reverse  Circulation
    A method of filter pack emplacement where the filter pack
material is fed into the annulus around the well intake concur-
rently with a return flow of water. The water is pumped to the
surface through the casing.

    In dual-wall reverse circulation rotary drilling, the circul-
ating fluid is pumped down between the outer casing and inner
drill pipe, and then up and out through the drill bit to the
surface.

Rig
    The machinery used in the construction or repair of wells
and boreholes.

Rotary Table Drive
    Hydraulic or mechanical drive on a rotary rig used to rotate
the drill stem and bit.

RVCM
    Residual vinyl  chloride monomer.

Samples
    Materials obtained from the borehole during the drilling
and/or formation sampling process that provide geological
information. May also refer to water from completed well used
for hydrogeochemical analysis.

Saturated Zone (Phreatic  Zone)
    The subsurface zone in which all pore spaces are filled with
water.

Scheduling
    Standardization of casing  diameters and wall thicknesses
where wall thickness increases as the scheduling number  in-
creases.

Screen
    See Well Intake.
Seal
    The impermeable material, such as cement grout, bento-
nite or pudded clay, placed in the annular space between the
borehole wall and the permanent casing to prevent the downhole
movement of surface water or the vertical mixing of water-
bearing  zones.

Segregation
    The differential settling of filter pack or other materials that
occurs in the annular space surrounding the intake during
placement by gravity (free fall).

Set Casing
    To  install steel pipe or casing in a borehole.

Shale Shaker
    Vibratory screen connected in line to the circulation sys-
tem of a mud rotary rig through which the drilling fluid passes
and where suspended material is separated and samples are
collected.

Shelby Tube
    Device used in conjunction with a drilling rig to obtain an
undisturbed core sample of unconsolidated strata (United States
Environmental Protection Agency, 1986).

Sieve Analysis
    Determination of the particle-size distribution of soil,
sediment or rock by measuring the percentage  of the particles
that will pass through standard sieves of various sizes (Driscoll,
1986).

Single-Riser/Limited-Interval Well
    An individual monitoring well installed with a  limited-
length well intake that is used to monitor a specific zone of a
formation.

Sinkers
    Dense-phase organic liquids that coalesce in an immiscible
layer  at the bottom of the  saturated zone (United States Envi-
ronmental Protection Agency, 1986).

Slip-Fit Box and Pin Connections
    A type  of coupling used to join two hollow-stem auger
sections.

Slotted Couplings
    A device attached to the knock-out plate at the base of the
lead auger that allows water to pass into the center of the auger
during drilling while preventing the entrance  of sediment or
sand into the hollow stem.

Slotted Well Casing
    Well intakes that are fabricated by cutting slots of prede-
termined width at regular intervals by machining tools.

Slug  Test
    A single well test to determine the in-situ  hydraulic con-
ductivity of typically low-permeability formations by the in-
stantaneous addition or removal of a known quantity (slug) of
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 water into or from a well, and the subsequent measurement of
the resulting well recovery (United States Environmental
Protection Agency, 1986).

Slurry
    A thin mixture of liquid, especially water, and any of
several finely divided substances such as cement or clay par-
ticles (Driscoll, 1986).

Smectite
    A commonly used name for clay minerals that exhibit high
swelling properties and a high cation exchange capacity.

Sodium Bentonite
     A type of clay added to drilling fluids to increase viscosity.

Solids Concentration or Content
     The total amount of solids in a drilling  fluid as determined
by distillation that includes both the  dissolved and  the suspended
or undissolved solids. The suspended solids content maybe  a
combination of high and low specific gravity solids and native
or commercial solids. Examples of dissolved solids are the
soluble salts of sodium,  calcium and magnesium. Suspended
solids make up the mudcake dissolved solids remain in the
filtrate. The total suspended and dissolved solids contents are
commonly expressed as percent by weight (Ingersoll-Rand,
 1985).

 Solid-Flight Auger
     A solid-stem auger with a cutting head and continuous
flighting that is rotated by a rotary drive head at the surface and
forced downward by a hydraulic pulldown or feed device.

 Solvation
     The degradation of plastic well casing in the presence of
 very high  concentrations of specific organic solvents.

 Solvent Cementing
     A method of joining two  sections of casing  where solvent
 is applied to penetrate and soften the casing pieces and fuses the
 casing together as the solvent cement cures.

 Sorption
     The combined effect of adsorption and/or absorption.

 Specific  Capacity
     The rate of discharge of water from a well per unit of
 drawdown of the water level,  commonly expressed in gpm/ft or
 mVday/m, and that varies with the duration of discharge
 (Driscoll,  1986).

 Specific Yield
     The ratio of the volume of water that a given mass of
 saturated rock or soil will yield by  gravity  to the volume of the
 mass expressed as a percentage  (Driscoll, 1986).

 Split-Spoon  Sampler
      A hollow, tubular sampling  device driven by a 140-pound
 weight below the drill stem to retrieve sample of the formation,

 Spudding Beam
      See Walking Beam.
Standard Dimension Ratio
    A ratio expressed as the outside diameter of casing divided
by the wall thickness.

Static Water Level
    The distance measured from the established ground sur-
face to the water surface in a well neither being pumped nor
under the influence of pumping nor flowing under artesian
pressure.

Surface Seal
    The seal at the surface of the ground that prevents the
intrusion of surficial contaminants into the well or borehole.

Surfactant
     A substance capable of reducing the surface tension of a
liquid in which  it is dissolved. Used in air-based drilling fluids
to produce foam, and during well development to disaggregate
clays (Driscoll, 1986).

Surge Block
     A plunger-like tool consisting of leather or rubber discs
sandwiched between steel or wooden discs that maybe solid or
valved that is used in well development.

Surging
     A well development technique where the surge block is
alternately lifted and dropped within the borehole above or
adjacent to the screen to create a strong inward and outward
movement of water through the well intake.

 Swivel, Water
     A hose coupling that forms a connection between the slush
pumps and the drill string and permits rotation of the drill string
 (Ingersoll-Rand,  1985).

 Teflon
     Trade name for fluoropolymer material.

 Telescoping
     A method  of fitting or placing one casing inside another or
 of introducing screen through a casing diameter larger than the
 diameter of the screen (United States Environment Protection
 Agency,  1975).

 Temperature Survey
      An operation to determine temperatures at various depths
 in the wellbore, typically used to ensure the proper cementing
 of the casing or to find the location of inflow of water into the
 borehole (Ingersoll-Rand, 1985).

 Tensile  Strength
      The greatest longitudinal stress a substance can bear with-
 out pulling the material apart.

 Test Hole
      A hole designed to obtain  information on ground-water
 quality and/or  geological and hydrological  conditions (United
 States Environmental Protection Agency, 1975).
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Thermoplastic Materials
    Man-made materials often used for well casing that are
composed of different formulations of large organic molecules
that are softened by heating and hardened by cooling and can be
easily molded and extruded.

Thin-Wall Samplers
    A hollow tubular sampling device that is pressed into the
formation below the drill stem to retrieve an undisturbed
sample.

Top-Head Drive
    A drive for the drill stem where the bottom sub of the
hydraulic drive motor is connected directly to the drill rod.

Total Dissolved  Solids (TDS)
    A term that expresses the quantity of dissolved material in
a sample of water.

Transmissivity
    The rate at which water is transmitted through a unit width
of an aquifer under a unit hydraulic  gradient. Transmissivity
values are given in gallons per day through a vertical section of
an aquifer one foot wide and  extending the full saturated height
of an aquifer under hydraulic gradient of 1 in the English
Engineering  System;  in the International System,  transmissiv-
ity is given in cubic meters per day through a vertical section in
an aquifer one meter wide and extending the full saturated
height of the aquifer under a hydraulic gradient of 1 (Driscoll,
1986).

Tremie   Method
    Method whereby filter pack is  emplaced or bentonite/
cement slurries are pumped uniformly  into the annular space of
the borehole through the use of a tremie pipe.

Tremie Pipe
    A device, usually a small-diameter pipe, that carries grout-
ing materials to the bottom of the borehole and that allows
pressure  grouting from the bottom up without introduction of
appreciable air pockets (United States Environmental Protec-
tion Agency, 1975).

Turbidity
    Solids and organic matter suspended in water.

Unconfined Aquifer
    An aquifer not bounded above by a bed of distinctly lower
permeability than that of the aquifer and containing ground
water below a water table under pressure approximately equal
to that of the atmosphere.

Unconsolidated Formation
    Unconsolidated formations are naturally-occurring earth
formations that have not been lithified; they may include
alluvium, soil, gravel, clay and overburden,  etc.

Underreamer
    A bit-like tool with expanding and retracting cutters for
enlarging a drill hole below the casing (Ingersoll-Rand, 1985).
Unified Soil Classification System
    A standardized classification system for the description of
soils that is based on particle size and moisture content.

Uniformity Coefficient
    A measure of the grading uniformity of sediment defined
as the 40-percent retained size divided by 90-percent retained
size.

Unit-Price Contracts
    Drilling contracts that establish a fixed price for materials
and manpower for each unit of work performed.

Upgradient Well
    One or more wells that are placed hydraulically upgradient
of the  site and are capable of yielding ground-water samples
that are representative of regional conditions and are not affected
by the  regulated facility  (United States Environmental Protection
Agency, 1986).

Vadose Zone (Unsaturated Zone)
    A subsurface zone above the water table in which the
interstices of a porous medium are  only partially  filled with
water (United States Environmental Protection Agency, 1986).

Vicksburg Sampler
    A strong thin-walled sampler for  use in stiff  and highly
cemented Unconsolidated deposits.

Viscosity
    The resistance offered by the drilling fluid to flow.

Volatile Organics
    Liquid or solid organic compounds with a tendency to pass
into the vapor state (United States Environmental Protection
Agency, 1986).

Walking Beam (Spudding Beam)
    The beam of a cable tool rig that pivots at one end while the
other end connected to the  drill line is moved up and down,
imparting the "spudding" action of the rig.

Water Swivel
    See Swivel, Water.

Water Table
    The upper surface in an unconfined ground water body at
which the pressure is  atmospheric (United States Environmental
Protection Agency, 1975).

Weight
    Reference to the density of a drilling fluid. This is normally
expressed in either Ib/gal, Ib/cu ft, or psi hydrostatic pressure
per 1000 ft of depth.

Well
    Any test hole or other excavation that is drilled, cored,
bored, washed, fractured,  driven, dug, jetted or otherwise
constructed when intended  use of such excavation is for the
location, monitoring, dewatering, observation, diversion, arti-
ficial recharge, or acquisition of ground  water or for conducting
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pumping equipment or aquifer tests. May also refer to casing
and intake.

Well Cap
    An approved, removable apparatus or device used to cover
a well.

Well Cluster
    Two or more wells completed (screened) to different
depths in a single borehole or in a series of boreholes in close
proximity to each other.  From these wells, water samples that
are representative of different horizons within one or more
aquifers  can be collected (United States Environmental Pro-
tection Agency, 1986).

Well Construction
    Water well construction means all acts necessary to obtain
ground water from wells.

Well Contractor
     Any person, firm or corporation engaged in the business of
constructing, altering, testing, developing or repairing a well or
borehole.

Well Development
     Techniques used to repair damage to the borehole from the
drilling process so that natural hydraulic  conditions are re-
stored; yields are enhanced and fine materials are removed.

Well Evacuation
     Process of removing stagnant water from a well prior to
sampling (United States Environmental Protection Agency,
 1986).

Well Intake ( Well Screen)
     A screening device used to keep materials other than water
from entering the well and to  stabilize the surrounding forma-
tion.

Well Log
     A record that includes information on well construction
details, descriptions of geologic formations  and well testing or
development techniques used in well construction.

Well Point
     A sturdy, reinforced well Screen or intake that can be
installed by driving into the ground.
Well Seal
    An arrangement or device used to cover a well or  to
establish or maintain a junction between the casing or curbing
of a well and the piping or equipment installed therein to prevent
contaminated water or other material from entering the well at
the  land surface.

Well Vent
    An outlet at or near the upper end of the well casing to allow
equalization of air pressure in the well.

Yield
    The quantity of water per unit of time that may flow or be
pumped from a well under specified conditions.

Yield Point
    A measure of the amount of pressure, after the shutdown
of drilling fluid circulation, that must be exerted by the pump
upon restating of the drilling fluid circulation to start flow.

Zone of Aeration
    The zone above the water table and capillary fringe in
which the interstices are partly filled with air.

Zone of Saturation
    The zone below the water table in which all of the inter-
stices are filled with ground water.

References
Bates, Robert L. and Julia A. Jackson, eds, 1987.  Glossary of
    geology; American Geological  Institute, Alexandria,
    Virginia, 788 pp.
Driscoll, Fletcher, G. 1986. Ground water and wells; Johnson
    Division, St. Paul, Minnesota, 1089 pp.
Ingersoll-Rand,  1985.  Drilling terminology; Ingersoll-Rand
    Rotary Drill Division, Garland, Texas, 120 pp.
United States Environmental Protection Agency, 1975. Manual
    of water well construction practices; United States
    Environmental Protection Agency, office of Water
     Supply EPA-570/9-75-001,156 pp.
United States Environmental Protection Agency, 1986. RCRA
    ground-water monitoring technical enforcement  guidance
    document;  Office of Waste Programs Enforcement,
     Office of Solid  Waste and Emergency  Response,
    Washington, D.C., OSWER-9950.1, 317 pp.
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