EPA-600/2-84-024
January 1984 • .
A GUIDE TO THE SELECTION OF MATERIALS
FOR MONITORING WELL CONSTRUCTION
AND GROUND-WATER SAMPLING
by
Michael J. Barcelona
James P. Gibb
Robin A. Miller
Illinois State Water Survey
Department of Energy and Natural Resources
Champaign* Illinois 61820
EPA No. CR-809966
Project Officers
/ Marion R. Scalf
Leslie G. McMillion
Robert S. Kerr Environmental Research Laboratory, Ada, Oklahoma
and
Environmental Monitoring Systems Laboratory, Las Vegas, Nevada
U.S. Environmental Protection Agency
REPRODUCED ti
NATIONAL TECHNICAL
INFORMATION SERVICE
US DIPHRTMlNi Of COMMfRCE
SPRIHCFitlC1, VA. 22161
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The information in this document has been funded wholly or in part
by the U.S. Environmental Protection Agency under assistance agreement
No, CR-8Q9966. It has been subject to the Agency's peer and administra-
tive 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.
ii
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FOREWORD
The Environmental Protection Agency was established to coordinate
administration of the major Federal programs designed to protect the
quality of our environment.
An important part of the Agency's effort involves the search for
information about environmental problems, management techniques and new
technologies through which optimum use of the Nation's air, land, and
water resources can be assured and the threat pollution poses to the
welfare of the American people can be minimized.
EPA's Office of Research and Development conducts this search through
a nationwide network of research facilities. As one of these facilities,
the Robert S. Kerr Environmental Research Laboratory is the Agency's center
of expertise for investigation of the soil and subsurface environment. Per-
sonnel at the laboratory are responsible for management of research programs
to: (a) determine the fate, transport and transformation rates of pollutants
in the soil, the unsaturated zone and the saturated zones of the subsurface
environment; (b) define the processes to be used in characterizing the soil
and subsurface environment as a receptor of pollutants; (c) develop techniques
for predicting the effect of pollutants on ground water, soil and indigenous
organisms; and (d) define and demonstrate the applicability and limitations '
of using natural processes, indigenous to the soil and subsurface environment,
for the protection of this resource.
This report contributes to that knowledge which is essential in order
for EPA to establish and enforce pollution control standards which are
reasonable, cost effective, and provide adequate environmental protection
for the American public.
'•The subsurface environment of ground water presents many challenges to
effective monitoring efforts. Physical, microbiological and geochemical
forces interact over variable time frames as ground-water quality character-
istics evolve. Monitoring data'.should be collected with minimum-disturbance
of the subsurface. This goal implies careful attention to the details of
sound drilling, well construction, and sampling methodologies.
The complex nature of ground-water monitoring further demands that cost-
effective choices of materials, target chemical constituents, and procedures
are made prior to implementation of the network design. Attempts to cut
costs for the sake of short-term "savings" can result in substantial added
expense. This may occur when the goals of the monitoring effort are expanded
and information needs require increased analytical detail. There are few
merits to penny-wise, pound-foolish approaches to ground-water monitoring.
Hinton W. Hall
Director
Robert S. Kerr Environmental Research Laboratory
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CONTENTS
Foreword ........................................ ....................................... iii
Figures .............. - ............................ . — ................................. vi
Tables ................................................. ' ................................. vii
Acknowledgements ....... . .......... . ........... ..... ................................. viii
Section 1 . Introduction ............. . .............................................. ... 1
Need for and Importance of Monitoring .................................... 2
Section 2 . Objectives ............................... , .................................. 4
Section 3. Ground-Water Monitoring Requirements ......... . ..................... 5
Resource Conservation and Recovery Act (RCRA) ................ . ....... 5
The Comprehensive Environmental Response, Compensation and Lia-
bility Act (CERCLA) [[[ 5
, State Requirements for Ground-Water Monitoring ........................ 6
Section 4. Background .............................. . ................................. 7
Previous Studies ......................... . .......................... . ........... 7
Monitoring in General ............... . ...................................... 7
Monitoring Well Design and Construction ................................ 8
Ground-Water Sampling [[[ 9
Materials Used in Monitoring Efforts ..................................... 10
Current Research Efforts ............................... , — . ................ 11
Section 5. -Monitoring Wells and Sampling Apparatus ............................. 13
Monitoring Well Components ..................... . . ........................ . 13
Well Location ......... . ...... . ...................................... ......... 14
Well Diameter ............ . .................................................. 14
Well Depth ............ , [[[ 15
Well Design and Construction Materials .................................. 15
Drilling Methods ............................... . ............ . . .............. 17
Well Development .................... ... ........................ . ..... , ..... 20
Sampling Apparatus [[[ 22
Section 6. Sampling Strategy [[[ . ..... 26
Effects of Subsurface Conditions on Ground-Water Quality and
Sampling ........................... .. ........................................... 26
Effects of Hydrologic Conditions on Sampling Strategy ____ ..... .......... 27
Section 7. Evaluation of Materials ....... . .......... . ............................ .... 31'
Overview of Subsurface Conditions .......................................... 31
Chemical Properties of Water and Their Effects on Various
Materials ......... ' ................................ . ........................... 31
Candidate Test Solutions for Materials' Evaluation .......... . ....... . ..... 33
Preliminary Ranking of Well Construction/Sampling Materials ........... 34
Evaluation of Selected Materials ............................................. 37
Teflon® Well Casing .......... . .............................................. 38
Stainless Steel Well Casing ........................... . .............. ........ 38
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Evaluation of Selected Materials (Continued)
Casing Made from Other Ferrous Materials , 44
Pumps Used in Development 45
Grouts, Cements, Muds, and Drilling Fluids <.,.. 46
Drilling aids 46
Seals, grouts and cements 48
Evaluation of Sample Collection Materials 48
Sampling devices 49
Tubing and transfer lines 50
Storage containers , 51
Sources of Error in Monitoring Efforts ., 52
Comparison of analytical method performance with materials'
related error , , 53
Section 8. Cost Considerations 58
Description of an Example Monitoring Effort 59
Well Installation and Sampling Costs , , 59
Analytical Costs -. 61
Project Cost Comparisons for Selected Materials' Combinations for
./ Networks of Varying Analytical Detail 64
Tailoring the Monitoring Well and Sampling Apparatus to the Antici-
pated Analytical Scheme 65
Section 9, Conclusions 66
Section 10, Recommendations 67
General Recommendations 67
Specific Recommendations 67
References 69
LIST OF FIGURES
Figure Page
5-1 Schematic diagrams of typical water supply (a) and monitoring (b) well
installations ' 14
5-2 Schematic diagram of an air driven well development device, —, 21
6-1 Percent of aquifer water versus time for different transmissivities 29
7-1 Sources of error involved in ground-water monitoring programs con-
tributing to total variance 52
8-1 Capital costs for drilling and well construction of four point array 61
VI
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LIST OF TABLES
Table • , , . Page
5-1 Description of Saturated Zone-Sampling Devices for Use in Small-
Diameter Boreholes and Monitoring Wells : 23
7-1 Chemical Composition of Contaminated Ground Water Near Hazardous
Waste Sites • '. 33
7-2 .Solution Composition for a Range of Ground-Water Conditions 34
7-3 Chemical Exposures Grouped in General Solution Categories 35
7-4 Relative' Compatibility of Rigid Well Casing Material 36
7-5* Relative Compatibility of Semi-Rigid or Elastomeric Materials ' 36
-7-6 Representatis'e Classes of Additives in Rigid PVC Materials Used for
1 , Pipe or Well Casing 40
7-7 Chemical "Parameters Covered by NSF Standard; 14 for Finished Prod-.
, ucts* and in Standard,Leach Tests...:' 41
7-8 Components of Drilling Fluids .• 47
7-9 Frequency of Occurrence of Phthalate Esters in Waste water and Ground-
Water Samples '. , • 50
7-10 Analytical Performance Data for Selected Water Quality
Parameters. >, •. 54
7-11 Analytical Performance Data for Selected Inorganic Chemical
Constituents —; ' 55
7-12 Analytical Performance Data for Selected Organic Chemical • j
Constituents v 56
8-1 Cost Estimates for Drilling, Well-Construction, and Sampling (1983
Dollars) : '. ' 60
8-2 Description of Analytes and Costs for Four Analytical Schemes for
Ground-Water Samples 62
8-3 Analytical Cost Detail V , 63
8-4 Comparison of Reanalysis Cost with Cost "Savings" on Materials 63
'8-5 Total Project Costs for Monitoring Programs , .• 64
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ACKNOWLEDGEMENTS
This manual was prepared under cooperative agreement #CR 80996601 from
the U.S. Environmental Protection Agency, Office of Research and Development,
under the direction of project managers Marion R. Scalf of the EPA R. S. Kerr
Environmental Research Laboratory, Ada, Oklahoma, and Leslie G. McMillion of the
EPA Environmental Monitoring and Support Laboratory, Las Vegas, Nevada. ,
The manual was written by Michael J. Barcelona, James P. Gibb, and Robin A.
Miller, all of the Water Survey Division of the Illinois Department of Energy and
Natural Resources.
A review panel consisting of agency personnel, ground-water professionals,
representatives of industry and national standards organizations participated in the
planning and review of the report. The authors wish to recognize the helpful guidance
and comments of the following panel members:
Gordon Bellen
National Sanitation Foundation
Olin Braids
Geraghty & Miller, Inc.
George Dixon
USEPA Office of Solid Waste
William Dunlap
USEPA Robert S. Kerr Environmental Research Laboratory
Robert Wilging and Robert Hinderer
The B.F. Goodrich Company
Particularly valuable inputs were received from many scientists and engineers
active in ground-water work and related fields. Among these contributors the authors
would like to acknowledge the valuable comments, suggestions, and access to unpub-
lished data from:
Robert Brobst City of Arttigo, WI
Fred and James Doane Industrial and Environmental Analysts
Roy Evans USEPA/EMSL-Las Vegas, NV
Thomas Imbriggiotta U.S. Geological Survey
Gregor Junk Iowa State University
George Kish ' U.S. Geological Survey
Jerry Kotas USEPA Office of Drinking Water
Jerry Leenheer U.S. Geological Survey
Paul Mills Meade Compuchem, Inc.
Stan Mruk Plastic Pipe Institute
Michael O'Hearn Illinois State Water Survey
Jack Sosebee Environmental Science and Engineering, Inc.
Jerry Thornhill USEPA/RSKERL-Ada, OK
Bert Trussell J. M. Montgomery, Consulting Engrs.
James Vennie Department of Natural Resources, State of Wisconsin
The support of Pamela Lovett, Pamela Beavers, and a host of other individuals too
numerous to mention is also greatly appreciated.
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SECTION 1
INTRODUCTION
Ground water provides the base flow of all perennial streams and over 90
percent of the world's freshwater resources. Ground water also is a source of one-half
of the United States' drinking water supplies (1). Yet until recently ground water has
received only token scientific attention in terms of its quality and protection. Insufficient
attention has been given to proper monitoring procedures to accurately determine the
quality of ground water, -,
With the beginning of the industrial age, a variety of new_/chemicals were
introduced into the hydrologic cycle by man's indiscriminate use and waste disposal
activities. "Since World War II, the explosive development of the synthetic chemical
industry added thousands of additional chemicals to the environment. Chemical Abstracts
announced in March 1972 that it had registered 2,000,000 unique chemicals since
'January 1965" (2). A large number of these organic and inorganic chemicals enter
both surface water and ground water not only through waste disposal but also as a
result of normal use of these water resources.-
The presence of many trace substances in ground water, even at very low
concentrations, ma}' create short-term or long-term health hazards (3). The inclusion
of approximately 113 organic chemicals on the EPA priority pollutant list indicates the
significance accorded these chemicals by U.S. health officials.
The passage of the Safe Drinking Water Act (PL 93-523) in 1974 finally
recognized ground water as a major source of drinking water and established standards
of ground-water quality protection. Later, passage of the Toxic Substance Control Act
(PL 94-469) and the Resource Conservation and Recovery Act (PL 94-480) further
recognized the significance of ground water resources and the importance of their
protection against the threats increasingly posed by human activities.
Regulatory agencies are charged with regulating the disposal of waste to insure
that the environment is not adversely affected. To accomplish this task, these agencies
must set design and operational standards based on available technology to minimize
potential pollution. Disposal facilities then must comply with these standards and
monitor the effects of their operation on the surrounding environment. The use of
wells or piezometers for collecting water samples and water level data has been and
probably will continue to be the method for monitoring the effects of waste disposal
facilities on ground water.
Considerable research has been conducted to develop analytical laboratory
techniques to detect the low levels of the many constituents named in water quality
standards or legislation related to ground-water protection or waste management
practice. Monitoring well construction, water sample collection, and preservation
techniques have been established by several different laboratories and agencies in an
attempt to insure that water samples delivered to the laboratory are chemically
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representative of the water contained in the ground. However, there is considerable
controversy among laboratories, agency policies, and researchers concerning proper
well construction and sampling techniques and appropriate procedures for preserving
the original chemical character of the samples. If monitoring wells and water samples
are to provide the performance yardstick for disposal facilities' design and operation,
the significance of various monitoring well construction and sampling procedures and
preservation techniques must be determined.
Need for and Importance of Monitoring
Ground-water monitoring is essential to determine the quality of the nation's
ground-water resources and the effectiveness of ground-water pollution control regu-
lations. Only through the collection of accurate data can we ascertain the chemical
nature of our ground-water resources. Ground-water monitoring can be divided into
four types: ambient monitoring, source monitoring, case preparation monitoring, and
research monitoring.
Ambient ground-water quality monitoring establishes an understanding of char-
acteristic regional water quality variations and changes over time. This type of
monitoring is normally accomplished through routine sampling of wells on an areal or
regional basis. The wells sampled are often public water supply, industrial or domestic
wells as opposed to specially constructed monitoring wells. The sample collection
techniques also are often quite different from those for monitoring wells. Therefore,
data obtained from ambient monitoring programs may not be comparable to that
obtained by more rigorous well construction and sampling procedures. However, the
data are invaluable in detecting significant changes in water quality and protecting
public health.
Source monitoring is the type normally conducted at a potential pollution source.
Source monitoring detects and quantifies the migration of pollutants from potential
pollution sources. Most regulatory programs have monitoring guidelines that detail
minimum standards for source monitoring. In an effort to minimize cost to the
regulated community, a two-step approach to source monitoring has been used by most
states.
The first step is a minimum-requirement approach based on the principle of
detecting leakage of pollutants from disposal or storage facilities. It is understood that
data collected from a detective monitoring scheme will not define the extent or
seriousness of a developing problem. Therefore, once the detective monitoring system
has sounded the alarm, most states require a more definitive monitoring program to
provide interpretive information concerning the extent and seriousness of the problem.
The second step is interpretive monitoring which normally requires expanded
information needs and the installation of additional wells. The purpose of interpretive
monitoring is to define the limits and concentrations within the plume of pollutants
moving from the presumed source. The addition of wells areally, and vertically nested
well sets often is required to adequately define plume geometry and concentration
gradients.
Case-preparation or enforcement monitoring is undertaken by the regulatory com-
munity to collect evidence,for prosecution of ground-water pollution cases. This type
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of monitoring usually is developed in response to the language in the appropriate laws
intended to be used in the prosecution of the case. The detailed information resulting
from this type of monitoring generally is more specific with respect to concentrations
and changes in concentrations at the legal points of regulation. Further definition of
plume geometry or concentrations normally is not required for successful litigation.
Research monitoring often results in a level of data collection far beyond that
required for other types of monitoring activities. Added information is required to
help understand-and document the mechanisms controlling solute transport of pollu-
tants. The collection of this type of monitoring data is very rigoro.us and demanding
although limited to specific research goals.
„ " Selection of the types and levels of monitoring to be used in any situation should
be made with care and judgment. The goals of a proposed monitoring program should
be clearly stated and understood before consideration is given to what types of wells
should be constructed, where they should be located, how deep they should be, what
materials-should be used, what chemical constituents should be analyzed, and how
samples should he collected. Successful and cost-effective monitoring at all levels can
be accomplished only after the 'goals or purposes of the monitoring program are
thoroughly understood. . . - '
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SECTION 2
OBJECTIVES
This publication was produced as part of a cooperative agreement between the
Illinois State Water Survey and the U.S. Environmental Protection Agency (EPA CR
809966-01). The objectives of this project are as follows:
1) To assess the state of our knowledge of the potential effects of well construction
and pump and sampling materials on the integrity of ground-water samples, and
.2) To develop a guide that will facilitate the selection of pumps and devices ,
used to collect water samples, and materials used in the construction of monitoring
wells.
To achieve these objectives, the project was divided into two phases. Phase One
entailed a thorough investigation and assessment of the existing literature. Phase Two
involved laboratory and field studies to identify and assess efficient sampling techniques
and materials for ground-water monitoring near waste disposal sites.
This manual represents the culmination of the work in Phase One of the project.
It aspires to fill in the gaps left by previous studies of ground-water monitoring. Subject
.areas unexplored or treated superficially in the past are examined here in detail to
present a more complete exposition of ground-water monitoring. These areas include
the effects of materials on water samples, and the cost of materials vs' the'cost of the
total monitoring project. Cost is addressed from an important, but often overlooked,
perspective: How the initial investment in materials suitable for a particular monitoring
project can pay dividends in terms of lower overall project cost. Use of appropriate
materials can obviate the need for the additional work involved in' designing and
constructing new wells and in repeating sampling and analysis efforts when the use of
inappropriate materials renders monitoring results unrepresentative of in-situ ground-
water quality. -/
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SECTION 3
GROUNDWATER MONITORING REQUIREMENTS
Requirements for ground-water monitoring exist at both the federal and the
state levels. At the federal level, the Resource Conservation and Recovery Act (RCRA)
and the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) provide for monitoring to regulate hazardous wastes from generation to
disposal to cleanup of substances accidentally released into the ground-water environ-
ment.
The Resource Conservation and Recovery Act (RCRA)
Ground-water monitoring at applicable hazardous waste management facilities
is required by regulations issued pursuant to RCRA (Subpart F of 40 CFR Parts 264
and 265). While there are many intricate provisions in these rules, it is important to
stress here that there are three basic monitoring objectives, and that there are two sets
of requirements, one for existing facilities prior to permitting (Part 265) and one for
permitted facilities (Part 264), The basic monitoring objectives are 1) to detect whether
or not a facility is discharging hazardous wastes to the uppermost aquifer; 2) to
determine whether concentrations of specific hazardous waste constituents are within
prescribed limits; and 3) to measure the effectiveness of corrective actions.
Prior to permitting, the rules are standardized. All facilities follow the same
rules and the rules are self-implementing. That is, for existing (interim status) facilities
the parameter selection is pre-set. This means that the federal rules provide no authority
for the regulatory agency to require the use of specific materials or equipment for well
construction or sampling. However, during the permitting process, the regulatory
agency will have the authority to evaluate an applicant's proposals and to make final
specifications concerning well construction and sampling in the facility permit. There-
fore, a major function of this document will'be to provide a resource document to
assist applicants and permit writers in making these important determinations.
The RCRA monitoring regulations (Parts 264 and 265) also require facility
owners or operators to develop sampling and'analysis programs which include moni-
toring parameters, sampling schedules, sampling procedures, sample preservation and
shipping procedures, and analytical procedures.
For disposal facilities, the RCRA monitoring requirements are applicable through-
out the post-closure care,period (Subpart G of 40 CFR Parts 264 and 265).
The Comprehensive Environmental Response, Compensation,
and Liability Act (CERCLA)
While RCRA created one of the largest regulatory programs enacted by the
federal government to protect ground water, it could not address the problem of
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abandoned waste sites or accidental spills of hazardous substances. For this reason,
Congress enacted CERCLA to deal with the cleanup problems created by those
uncontrolled hazardous waste sites where reponsibility cannot be assigned (e.g., aban-
doned sites) and accidents in the handling or transportation of hazardous substances.
The Act provides for the generation of a trust (called Superfund) to finance the
emergency cleanup of accidentally released hazardous substances and to assume the
financial liability of closed permitted sites,
At present, no specific systems of ground-water monitoring are required by
CERCLA. If hazardous contaminants from a waste facility or accidental spill are
suspected or known to be entering the ground water, the choice of monitoring equipment
and methodology to be used to determine the scope of the contamination is left to the
states. Monitoring systems may be patterned after those outlined in RCRA, or states
may develop systems of their own. Like the post-closure monitoring requirements of
RCRA, those of CERCLA are relatively vague and untested. As they are applied in
more cases, more specific recommendations, and perhaps regulations, for ground-water
monitoring may develop.
State Requirements for Ground-Water Monitoring
Individual states may have their own requirements for ground-water monitoring.
While EPA allows states to take authority for imposing monitoring requirements under
RCRA and CERCLA, the actual requirements mandated by the various states may be
more stringent than those of these two acts. For this reason, it is important that those
involved in ground-water monitoring be familiar with the requirements of the state in
which the monitoring is being performed. Such information usually can be obtained
from the state's Environmental Protection Agency.
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SECTION 4
BACKGROUND
Previous Studies
This section presents an overview of work previously published on the subject
of ground-water monitoring. These works cover various aspects of monitoring in
general, well design and construction, well sampling, and materials' considerations for
use in monitoring applications,
Monitoring in General
The need for groundwater monitoring is evidenced in an article by Pettyjohn et
al. (4), which presents an overview of the prevalence and significance of organic
contamination in ground water. He explains where these organic compounds originate
and includes observations on their chemistry, toxicity, mobility, sorption, volatility,
dilution, biodegradation, and abiotic degradation.
A number of authors and"researchers address the federal and state regulations
that mandate monitoring. The National Council of the Paper Industry for Air and
Stream Improvement (NCASI) (5) has prepared a Guide to Groundwater Sampling
that describes the regulations developed under the Resource Conservation and Recovery
Act (RCRA), The Council highlights requirements for system design, sampling and
analysis, and monitoring preparation, evaluation and response. A USEPA publication
(6) provides guidance for owners and operators of hazardous-waste land disposal
facilities in complying with the interim status requirements for ground-water quality
monitoring in Subpart F of 40 CFR 265. Clark and Sabel (7) report on a survey
conducted to learn of states' requirements for monitoring wells, chemical analyses, and
data interpretation.
The importance of defining the purpose of the monitoring program before
designing the monitoring system is addressed by Geraghty and Miller, Inc. (8), They
note that site-specific hydrogeologic data also play a part in system design and describe
elements of a comprehensive hydrogeologic investigation. On monitoring in general,
they address the design and installation of monitoring well networks, including deter-
mining the number and location of wells; selecting well casing and screen materials;
and backfilling, sealing, developing and completing monitoring wells. They also discuss
sampling protocol.
Grisak et al. (9) identify the technical difficulties involved in monitoring ground-
water quality. Past ground-water monitoringf efforts are critiqued by Todd et al. (10).
A manual prepared for the USEPA by Perm et al. (11) presents a comprehensive
discussion of the many' aspects of ground-water monitoring. Written to address
monitoring at solid waste disposal facilities in particular, the manual also covers general
monitoring principles, including network design; monitoring and well technology;
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ground-water contamination by leachates; sample withdrawal, preservation and storage;
and analytical methods.
Fenn et al. (11) discuss the methodology of various monitoring techniques,
including wells screened or opened over a single vertical section of aquifer, piezometers,
weil clusters, single wells with multiple sample points, sampling during drilling, and
pore water extraction from core samples. They list the advantages and disadvantages
of each of these techniques and advise how to implement them. Estimates of the costs
involved for the alternatives are supplied.
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Tinlin (12) sho%vs, by example, site-specific procedures for monitoring various
classes of ground-water pollution sources. He covers brine disposal, plating waste
contamination, landfill leachate, oxidation ponds, and multiple-source nitrate pollution.
Monitoring Well Design and Construction
Lewis (13) stresses the importance of custom-designing ground-water monitoring
systems for specific monitoring objectives which are compatible with local hydrogeologic
and chemical conditions.
Dunlap et al, (14) describe technology for construction of wells capable of providing
representative, uncomaminated samples of ground water. Scalf et al. (1) and Sisk (15)
detail various techniques for constructing monitoring wells, highlighting advantages
and disadvantages of each method listed. Well construction practices are elaborated
upon in a manual developed for EPA by the National Water Well Association (16),
which sets forth standards prepared by NWWA for engineers and government personnel
whose expertise is not in the field of well construction.
Selection of an appropriate well casing and screen for monitoring well applications
is addressed by Fenn et al. (11). Pettyjohn et al. (17) discuss well casings and sampling
equipment made from glass, Teflon®, stainless steel, polypropylene, polyethylene, other
plastics and metals, and rubber, and suggest which materials are best suited to sampling
for organic contaminants. A manual that reviews the proper selection, installation and
utilization of thermoplastic water well casing has been published by the National Water
Well Association and the Plastic Pipe Institute (18).
Seanor and Brannaka (3) discuss the potential effects of well construction, including
well construction materials and drilling, on the results of organic water quality analyses.
The Manual of Ground-Water Quality Sampling Procedures by Scalf et al. (1) describes the
principles of operation and the' advantages and disadvantages of the more common
types of drilling techniques suitable for construction of ground-water monitoring wells,
as does Fenn et al, (11)..
Considerations for the selection of a drilling method are outlined by Minning
(19), who addresses common drilling and sampling procedures for hazardous waste
facilities. He also compares various aspects of different drilling methods, including cost,
effectiveness in various formations, depth capability, cross-contamination potential, and
quality of samples. Luhdorff and Scalmanini (20) present a methodology for rating
several drilling methods based on their ability to achieve typical tasks in a ground-
water quality investigation. They illustrate the application of the rating system to two
ground-water contamination problems in California.
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Ground-Water Sampling
Recommended methods of acquiring water data are presented by the USGS in
a handbook published by its Office of Water Data Coordination (21). Scalf et al. (1)
cover ground-water sampling comprehensively in a manual published by the National
Water Well Association. The manual presents considerations in the selection of sampling
procedures, including objectives of the sampling program, (characteristics and nature
of pollutants, and hydrogeology of the area. It also describes procedures currently
utilized to sample ground water and highlights advantages and disadvantages of each.
Sisk (15) also discusses sample parameter selection and sampling-considerations. He
further describes various types of monitoring wells and presents examples that suggest
appropriate sampling procedures for each.
Gibb et al. (22) provide recommendations on sampling protocol and sample
preparation, preservation, and storage, noting how these sampling steps can affect the
chemical composition of the water samples. Grant (23) also provides information on
sample collection and preservation. He describes grab or discrete sampling and composite
sampling and explains the differences between them. Wood (24) offers guidelines for
collection and field analysis of ground-water samples for selected unstable constituents.
Schmidt (25) addresses sample collection, too, and speaks to the question of optimum
pumping rates and duration prior to sampling, Scalf et al. (1) go farther and discuss
sample records and chain-of-custody procedures. Others that detail the basics of sample
withdrawal, preservation and storage include Carriere and Canter (26) and Fenn et al.
(11).
General guidelines for volume requirements, container preference, preservative
measures, and holding times when sampling for specific parameters are provided in a
useful table by Fenn et al. (11).
Suggestions as to types of sample containers and preservation techniques to use
when analyzing for various parameters can be found in many of the monitoring
publications mentioned throughout this section. Regulatory agencies also may stipulate
specific recommended practices. Several sources that deal with the effects of using
particular containers in the presence of certain contaminants include King et al. (27),
Struempler (28), Laterall et al. (29), and Coyne and Collins (30).
Sampling of purgeable organic compounds performed as part of the National
Organic Monitoring Survey conducted by the USEPA is described by Brass et al. (31).
A study by Dunlap et al. (14) that presents methods for acquiring grab samples of
ground water suitable for total organic analysis, as well as other sampling information,
aims to provide a basic capability for sampling for organic pollutants in shallow
subsurface environments. Goerlitz and Brown (32) recommend preservation techniques
for organic substances in water.
The potential for contamination posed by equipment and instrumentation used
.in ground-water monitoring is described by Seanor and Brannaka (3). They discuss
the use of bailers and various pumps and describe how such sampling equipment can
alter the chemical properties of ground water.
Todd et al. (10) highlight the need to check out the effects of sampling materials
on analytical results for the contaminants of interest. This type of research was performed
by Gibb et al. (22), who studied four types of pumps to determine their effects on
water samples.
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Selection criteria for pumps are offered by Gass et al (33). A number of authors
detail various pumping and water collection devices, including McMillton and Keeley
(34), Buss and Bandt (35), and Tomson et al, (36).
Everett et al. (37) provide detailed cost data for various monitoring methods and
techniques, They also supply a breakdown of capital and operational costs and suggest
sources of information for updating the cost estimates provided. Fenn et al. (11) also
offer cost estimates for various monitoring techniques and well construction methods.
To aid. in the selection of monitoring methods, Tinlin (12) presents hypothetical
illustrative examples for making decisions based, in part, on cost comparisons among
monitoring alternatives. i
Materials Used in Monitoring Efforts
Scalf et al. (1) offer guidelines in the selection of well construction materials when
sampling for specific contaminants in Appendix A of their manual. An EPA report
prepared by Geraghty and Miller, Inc. (8) names materials best suited to monitoring
efforts and notes exceptions to their general recommendations, Pettyjohn et al. (17)
suggest materials of choice when sampling for organic contaminants.
A number of researchers and authors detail the limitations inherent in using
certain well construction materials. Scalf et al. (1) cite the high cost of Teflon®-
constructed wells, and a USGS study by Imbrigiotta and Martin (38) draws attention
to PVC's drawbacks in terms of its lack of physical strength and its susceptibility to
damage. The same study points out that metallic casing materials may be subject to
chemical degradation or dissolution.
Some previous studies provide in-depth analyses of these and other problems
relating to compatibility of well construction and sampling materials with various
contaminants. Miller (39) reports results of a laboratory study that aimed to identify
chemicals that may ieach from well casing material when it is exposed to selected
pollutants and to quantify adsorption of selected pollutants on various well-casing
materials. The leaching of organic and organotin compounds from PVC and CPVC
pipe was documented in a USEPA report by Boettner et al. (40).
Gass et al. (33) describes the various metals used in water well applications,
particularly in well pumps, and the types of corrosion that may afflict them. He also
lists well and pump construction materials in order' of preference based on their
resistance to certain types of corrosion. Seanor and Brannaka (3) point out the potential
sample contamination posed by steel casing, which is exposed to oils and solvents in
its production. Another report by Fenn et al. (11) highlights the advantages of PVC
casing over metals, and the contamination of ground water by the adhesives and
primers associated with synthetic well casings'has been addressed by Sosebee et al. (41).
The Uni-Bell Plastic Pipe Association (42) issued a report that describes the
results of research into the control of residual vinyl chloride monomer (RVCM) in
PVC water pipe. Dressman and McFarren (43) and Sachs and Banzer (44) addressed
this same topic, as did Mantel! and others (45). Berens and Daniels (46) discussed the
prediction of vinyl chloride monomer migration from rigid PVC pipe. Earlier, Daniels
and Proctor (47) reported on the extraction of RVCM from PVC bottles.
10
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Curran and Tomson (48) describe the leaching of low levels of contaminants
from tubing made from various materials. Junk et al, (49) detail organic contamination
contributed to water samples by certain tubing materials. Study results on the adsorption
of specific contaminants on walls of containers made from certain materials are reported
by Massee et al, (50), Shendrikar et al. (51), Robertson (52,53), and Eicholz et al. (54).
Current Research Efforts
Monitoring methodology research presently is being conducted through three
principal EPA programs as well as through a number of U.S. Geological Survey projects,
private consultants, and foreign organizations. The EPA programs addressing sampling
methodology include the Ground Water Research Branch of the Robert S. Kerr
Environmental Research Laboratory in Ada, Oklahoma; the Ground Water Branch of
the Environmental Monitoring and Support Laboratory in Las Vegas, Nevada; and the
Solid and Hazardous Waste Research Section of the Municipal and Environmental
Research Laboratory in Cincinnati, Ohio.
Research at RSKERL-Ada is directed principally at defining the processes which
control the movement of contaminants through the subsurface. Currently, two activities
sponsored by RSKERL specifically address sampling ground water for monitoring
purposes. Through a cooperative agreement with the National Center for Ground
Water Research, the University of Oklahoma is investigating the possible sorption of
specific trace organic pollutants and metals from ground water onto the surface of
monitoring well casing materials and the possible'leaching or release of such substances
from well casing materials into sampled water. Another cooperative agreement with
the Illinois State Water Survey, partially supported by EMSL-Las Vegas, seeks to
evaluate and develop methods for constructing, completing, and sampling ground-
water monitoring wells to obtain representative physical, chemical, and biological
analyses. This manual is a product of that research effort.
Several projects in the RSKERL program have sampling components indirectly
related to ground-water monitoring. These are concerned primarily with collecting
ground water and uncontaminated subsurface material for various research projects.
Cores of subsurface materials are being used to measure physical, chemical, and
microbial characteristics and to relate these to the ability of the subsurface to attenuate
pollutant movement.
Stanford University has an extensive research project designed to evaluate
ground-water contamination risks resulting from hazardous waste disposal. A portion
of this project involves extensive sampling of ground water at field installations by the
University of Waterloo.
EMSL-Las Vegas is active in several research areas directly related to ground-
water monitoring. In addition to co-sponsoring the Illinois effort with RSKERL-Ada,
EMSL-Las Vegas supports research into both drilling and non-drilling techniques for
ground-water monitoring as well as into methods for vadose zone monitoring at
hazardous waste sites. Methods under investigation that require drilling include down-
hole sensors for smal! diameter boreholes, indicator parameters for hazardous constit-
uents, x-ray fluorescence and infrared spectrometry screening for hazardous wastes,
and compound-specific ground-water monitoring using fiber optics technology in
combination with laser fluorescence spectroscopy.
11
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Considerable effort at EMSL-Las Vegas is directed toward monitoring ground-
water quality using non-drilling or remote-sensing techniques, especially at hazardous
waste sites. One project is investigating the feasibility of sampling by cone penetrometer
in lieu of conventional drilled wells. Other projects involve using geophysical methods
such as complex resistivity for tracking Seachates from hazardous waste sites.
Research at MERL-Cincinnati does not specifically address ground-water mon-
itoring. The emphasis there is on providing technical support to RCRA and Superfund
activities of the Agency. Most research is related to remedial action activities at waste
disposal sites and/or the evaluation of the effectiveness of these activities. Ground-,,
water monitoring is necessarily a part of such evaluations, but development of new
monitoring techniques is generally not a part of MERL's research efforts.
12
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SECTION 5
MONITORING WELLS AND SAMPLING APPARATUS
The success of a ground-water monitoring program depends, in part, on the
selection of the proper type of well.
Production or traditional wells often are used to obtain samples in ambient
ground-water monitoring programs. Designed to yield large quantities of turbidity-free
water for potable or irrigation supplies, these wells generally tap the more permeable
portions of an aquifer. Chemical data obtained from these wells depict the quality of
water being delivered to the user community. Because water pumped from these wells
is a composite of water from different horizontal and vertical strata in the aquifer
systems, the presence of relatively narrow or small plumes of polluted water can be
masked by dilution with water obtained from unaffected portions of the aquifer.
Production or traditional wells should not be used for the more detailed source,
case-preparation, and research types of monitoring. Such detailed monitoring efforts
call for wells designed to determine the ground-water quality at a given location and
depth within1 the geologic materials being monitored. All available geologic and
hydrologic information for the site of interest should be reviewed prior to selecting
preliminary locations and depths for monitoring wells. The potential paths of pollutant
movement from the site should be estimated and wells should be placed so that they
can effectively and quickly detect releases. Information gained during the drilling
process should be used to modify the monitoring plan to make it more effective. -
Monitoring Well Components
The principal reason for constructing monitoring wells is to collect ground-water
samples which, upon analysis, enable describing a contaminant plume and tracking
movement of specific chemical or biological constituents. Obviously, the location of
monitoring wells spatially and vertically is important. Of equal importance is the design
and construction of monitoring wells to provide easily obtainable samples that will yield
reliable, meaningful information. In general, monitoring well design and construction
follow production well design and construction techniques. However, emphasis is placed
on the effect these practices may have on the chemistry of the water samples being
collected rather than on maximizing well efficiency.
From this emphasis, it follows that an understanding of the chemistry of the
suspected pollutants and the geologic setting in which the monitoring .wells are
constructed plays a major role in the drilling technique and materials used. There are
several components to be considered in the design of a monitoring well, including
location, diameter, depth, casing, screen, sealing material, and well development. As
these components are discussed in detail, it may 'be helpful to refer to Figure 5-1,
which portrays two typical well installations: one for water supply and the other for
ground-water quality monitoring.
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Pump Discharge
Removable Cap
on Well Protector
J/S^//&S/s&//^
*
Schedule 80 Pipe _L
(4" dia. or greater) /
/
Backfill and/or '
Clay Slurry "*"/•
/
Sand or — *-;•
Gravel Pack ;
Well Screen — :
(length: entire
thickness of
water-bearing
material)
fill,
iJ
1^7 '
- L.
' /•
' <•
'. „,-,-,
^•n:;rri
- :
&//£z$?/£ys/fz>Js/ ^^ " ^^^//xS^v/i'oVi'V^v^ .
- Concrete or CemenK:;. ^ * f < . or^ntl
;_..'•'•••'• ' -' v i .''.- ;
" - e • '• '.' *• ' o .' '/ Schedule 80 —
s .' x ' TILL" ^ ' ' • , • pVC Pipe ^
Static '-'; .-.-•.-• :••-•; <2"dia.) ,
-Water Level '/. 0 '.'*"' o •','-.'.• '
•'-.'.... 'o ';-••.•.«• s' ^
0 •.''••« ' o /
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vV :-.:-.- :-;::-;.'-: •••-••;•:•:: .-:-:. {
;";•"..• ^:---^v.-.V;\:-/-; ^^
... .0 •...•..,..-.•-....••_•;• 1
-..^SAND AND GRAVE L.-.-- — I— t
.*••'! ' (water-bearing) .". • . ' •' p\
'•'••' •'••' '•'•' •'.•••'• '•'-.''^^r'-''-
'•:'•'•'•.• ••'. e. •-•.'•:- v -.''-."• ':>-v-'.
.'''". • .' :. ' • • ' '"•,•'.' •'. ° .''•.' '' ' • o
'•';:. :-':-r^?>>Tr-. ::'..oV.
•
i
/
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* t^
^
/
/
/
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/
: —
•|
'///^VA-///-- .
Static
— Water Level
Cement or
•*- Bentonite
Seal
Sand or
"*" Gravel Pack
X
/C Well Screen
(2" dia.)
a. Water Supply Wei
SHALE BEDROCK b. Monitoring Well Piezometer
Figure 5-1. Schematic diagrams of typical water supply (al and monitoring tbl well installations
Well Location
The location of a monitoring well should be selected on the basis of the purpose
of the program. This purpose may be to verify predictions of contaminant migration;
to detect contaminants in drinking water supplies and thus protect public health; to
activate a contingency plan such as a program for leachate collection; to protect the
operator; or to reassure the public by demonstrating that their water quality is being
monitored. Each of these purposes will require a somewhat specialized array of
monitoring points and a somewhat different sampling program. The monitoring system
must be designed to suit the purpose(s) in mind.
The positioning of a monitoring point in a contaminant flow path for an
"interpretive" monitoring effort must be determined on the basis of reliable preliminary
data. To do this, the contaminant flow path must be clearly defined in three dimensions
during the "detective" phase. Only then can the optimum location for proposed
monitoring wells be effectively determined.
Well Diameter
A domestic water supply well is commonly 4 inches in diameter to accommodate
a submersible pump capable of delivering 5-10 gallons per minute. Municipal and
14
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industrial supply wells have greater diameters to handle larger pumps and to increase
the available screened open area so the well can produce water more efficiently. Like
that of a water supply well, the diameter of a monitoring well is determined by the"
size of the sampling device or pump. This strategy'works well in very permeable
formations, but unlike most water supply wells, monitoring wells are quite often
completed in very marginal water-producing zones. Pumping one or more well volumes'
of water from a monitoring well built in such zones may present a serious problem if
the well has a large diameter. Large quantities of water must be disposed of, and it
may take several hours or even days for enough water to return to the well for
successful collection of a representative sample. With the advent of several commercially
available small-diameter pumps (le'ss than 2 inches outside diameter) capable of lifting
water from several hundred feet, it Is rarely necessary-to construct monitoring wells
larger than 2 inches in diameter. Additionally, the smaller the diameter, the less it will
cost for drilling and construction. A thorough discussion of advantages and disadvantages
of monitoring well diameter has recently been published (55).
Well Depth "
The depth of each monitoring well normally is determined by the geohydrologic
conditions at the site being monitored. Most "detective" monitoring wells are completed
in ' the first relatively permeable water-bearing zone encountered, since potential
pollution sources requiring the installation of monitoring wells are frequently at ground
surface. Locating the monitoring well in the first relatively permeable zone therefore
yields an early warning of the migration of pollutants in most situations. However, care
must be taken to assure the .well is completed at a depth sufficient to allow for seasonal
water table fluctuations. Under confined or semi-confined (leaky) conditions the water
level will rise above the top of the water-bearing zone. In this instance, the well should
be finished in the water-bearing zone and not above it.
f "-
If the water-bearing zone is thick (greater than 10 feet) or contamination is
known or suspected in deeper formations, multiple wells completed at different depths
should be used. For sampling at various depths, some engineers have nested several
wells in a single borehole. This requires drilling a large diameter hole and exercising
special care to ensure that the vertical integrity of the sampling points is maintained.
It is important that monitoring wells be constructed so that they are depth-discrete,
that is, so that they sample from one specific formation or zone without interconnection
to others. To assure that this requirement is met, provisions for placing cement grout
above and, if necessary, below the intake portion of the well, must be made in the
design of the well. ; -
Well Design and Construction Materials
The type of material used for monitoring well casing can have a distinct effect
pn the quality of the water samples collected. Galvanized casing will impart iron,
manganese, zinc and cadmium to many 'waters. Steel casing 'may impart iron and
manganese to the water samples. PVC pipe has been shown to release and adsorb trace
amounts of various organic constituents to water after prolonged exposure.;PVC solvent
cements used' to attach sections of PVC pipe also' have been shown to release'significant
quantities of organic compounds. Teflon® and glass.are among the most inert materials
; . is'
-------
that have been considered for monitoring well construction. Glass, however, is very
difficult.and expensive to use under most field conditions. Stainless steel also has been
found to work satisfactorily. A detailed discussion; of materials is presented in later
portions of the text. ', • I
In many situations,, it may be possible to compromise accuracy or precision for
initial cost. For example, if the contaminants of-interest are already defined and they
do not include substances which might bleed from, sorb or interfere with other
analytical methods, it might be reasonable to use wells cased with a less expensive
material. Wells constructed of less-than-optimum materials might be used for sampling
if identically constructed wells are available in both uncontaminated and contaminated
parts of the aquifer to provide ground-water samples for use as "blanks." Obviously,
such "blanks" may not address adequately problems of adsorption on or leaching from
the casing material induced by contaminants in the ground water. Careful consideration
is required in each individual case, and the analytical laboratory should be fully.aware
of construction materials used. .
Care must be given to the preparation of the casing and welt screen materials
prior to installation. As a minimum, both "should be washed with detergent and rinsed
thoroughly with clean water. Care also: should be .taken to ensure that these and other
sampling materials are protected from contamination by using some type of ground
cover such as plastic sheeting for temporary storage in the work area.
AH wells should allow free entry of water. They also should produce clear, silt-
free water; For drinking water supplies, the reason •• is obvious: sediment in the raw
water can create additional pumping and treatment costs and lead to the general
,unsuitability of the finished water. With monitoring wells, sediment-laden water can
greatly lengthen filtering times and create chemical interferences with the collected
• samples. * :
Commercially manufactured well screens generally work best provided the proper
slot,size is chosen. In formations where fine sand, silt, and clay predominate, sawed qr
torch cut slots will not retain the material, and the well may clog. It may be helpful
to have well screens of several slot-sizes on site so that the correct manufactured screen
can be placed in the hole after the water-bearing materials have been inspected. Gravel-
packing materials compatible with the selected screen size will further help retain fine
materials and also allow freer entry of water into the well by creating a zone of higher
permeability around the well. '
Well screen length is an ^important consideration. When monitoring a potable-
water-supply aquifer, the entire thickness of the water-bearing formation should be
screened. This provides a!n integrated water sample similar to what would be found in
the drinking water supply. A monitoring program to describe contaminant plume
geometry requires sampling discrete intervals of the water-bearing formation. In this
situation, screen lengths of no more than 5 feet (1.5 m) should be used. Thick aquifers
would require completion of several wells at different depth intervals. In some situations,
only the first water-bearing zone encountered will require monitoring. Here the
"aquifer" may be only 6 inches to a few feet (0.2-2 m) thick, and the screen lengtfi
should be limited to I or 2 feet (
-------
such a case, the screen must be long enough to extend above the water level in the
formations so these lighter substances can enter the well.
It is critical that the screened portion of each monitoring well access ground
water from a specific depth interval. Vertical movement of water in the vicinity of the
intake and around the casing must be prevented to obtain samples representative of
that in the formation of interest. Specifically, rainwater can infiltrate backfiil materials
and dilute or contaminate samples collected from the screened portion of the well.
Vertical seepage of leachate or contaminated water from adjacent formations along the
well casing also may produce unrepresentative samples for the depth interval being
sampled. More serious indeed is the creation of a conduit in the annulus of a monitoring
well which could contribute to or hasten the spread of contamination.
Monitoring wells usually are sealed with neat cement grout, dried bentonite, or
bemonite slurry. While a neat cement grout often is recommended, shrinkage and
cracking of the cement upon curing can create an improper seal. The .use of bentonite
traditionally has been considered more effective than neat cement grout. However,
recent studies have shown that some organic compounds migrate through bentonite
layers with little or no attenuation (56). Therefore, expanding cement appears to-offer
the greatest potential for, the effective sealing of wells. There are .several commercial
formulations of this type of cement which generally is more chemical resistant than
clays. The seal should extend from just above the well intake to a level above the
highest known seasonal water level. Backfill cuttings then may be used to fill the annulus
in the unsaturated zone provided that they are free of contamination, and a mounded,
expanded cement collar can be placed around the well casing to divert surface drainage
from the "immediate area of the well casing. This collar should extend well below the
frostline and should be checked periodically for cracks or fissures,
When sealing materials must be placed below the water table (or where water
has risen in the borehole), it is recommended that they be pumped down the annulus
through a tremie pipe and filled from the bottom upward.
Drilling Methods
The selection of a drilling method best suited for a particular installation is based
on the following factors, listed in order of importance:
1) Hydrologic information
a. types of formations
b. depth of drilling
c. depth of desired screen setting below water table
2) Types of pollutants expected
3) Location of drilling site, e.g., dry lands or inside a lagoon
4) Design of monitoring well desired ,
5) Availability of drilling equipment
The principles of operation and the advantages and disadvantages of the more
common types of drilling techniques suitable for constructing ground-water monitoring
wells are discussed by Scalf (1). The following is a brief summary of material presented
in that publication.
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Auger drilling frequently is accomplished by rotating a solid-stem, continuous-
flight auger into the soil. As the augers are "screwed" into the soil, the cuttings are
brought .to the surface on the rotating flights. Auger bits are essentially of two types;
fish tail or drag bits for use in unconsolidated materials, or claw or finger bits for use
in consolidated or cemented soils. Once the desired depth is reached, the augers are
allowed to rotate to clean out the borehole. The augers then are removed from the
borehole and the well screen and casing installed.'This method is best applied when
installing monitoring wells in shallow unconsolidated formations that will maintain an
open borehole long enough to permit emplacement of the well, piezometer, or sampling
device.
Hollow-stem, continuous-flight auger drilling differs from the solid-stem augers
in that the stem is hollow. Upon reaching the desired depth, a small-diameter casing
and screen can be set inside the hollow stem. The augers then are pulled out as the
casing is held in place. If the borehole stands open after withdrawing the augers, an
artificial gravel pack is placed opposite the screened portion of the well. If the material
collapses around the screened portion of the well, those materials are ultimately
removed or altered in grain size by the development procedures employed after well
construction.
Auger drilling rigs generally are mobile, fast, and inexpensive to operate in
unconsolidated formations. Because no drilling fluid is required, contamination problems
are minimized. However, these types of rigs cannot be used in hard-rock drilling. Depth
limitations vary with the equipment and types of soils, but usually are a maximum of
150 feet. Collection of formation samples is not expedited by the use of solid-stem,
continuous-flight augers. However, conventional soil sampling techniques (split spoon
and Shelby tube sampling) can be accomplished effectively during the drilling procedure
through the hollow-stem, continuous-flight augers. Formation sampling has been covered
in detail by Scalf et al. (1).
Straight rotary drilling is accomplished by pumping a drilling mud down the
inside of a rotating drill pipe and allowing it to return to the surface through the
annulus. The drilling mud cools the drill bit, carries the cuttings to the surface, prevents
excess fluid loss into the formation and prevents the formation from caving. The
rotating drill pipe turns the bit, which cuts the formation, allowing the cuttings to be
flushed out. The drilling fluid (or mud) may be clear water, water mixed with bentonite,
or water mixed with various synthetic or natural drilling aids. Rotary rigs generally
are available throughout the United States. They are capable of drilling in all types of
formations to almost any depth desired for monitoring and are fairly reliable in most •
formations. Casing is not required during the drilling and logging of formations.
The use of drilling fluids or muds during construction can bias the results of
samples-collected from wells. The introduction of clear water has a tendency to allow
water to migrate into permeable formations which may be of interest. This water must
be effectively removed before the quality of "native ground water" can be determined.
Drilling rnuds also present a problem during the well development and have the ability
to affect the transport of certain pollutants as water moves toward the well. Organic-
based muds add significant quantities of foreign organic material into the aquifer system
(57,58,59). Studies concerning the effects of these types of muds on the analytical
results of collected samples and the biodegradability of the muds have not been
conclusive.
18
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Air rotary rigs operate in the same manner as the mud rotary rig except that air
is circulated down the drill pipe and returns with the cuttings up the annulus. Some
rotary rigs are equipped to operate with either mud or air. Air rotary rigs are available
throughout much of the United States and are well suited for many drilling applkatons.
Air rotary rigs operate best in'hard rock formations. Formation water is blown
out of the hole along with the cuttings, so it is possible to determine when the first
water-bearing zone is encountered. After filtering of water blown from the hole,
collection and field analyses may provide preliminary information regarding changes
in water quality for some parameters. Formation sampling ranges from excellent in
hard, dry formations to nonexistent when circulation is lost in cavernous limestones
and other formations with cavities.
Casing is required to keep the borehole open when drilling in soft, caving
formations below the water table. When more than one water-bearing zone is encoun-
tered and where the hydrostatic pressures are different, flow between zones will occur
between the time when the drilling is done and the time when the hole can be properly
cased and one zone grouted off. Commonly, no synthetic drilling aids are used in air
rotary drilling. If the air is filtered to capture compressor lubricants, contamination
can be minimized relative to other methods. The use of air rotary drilling in badly
contaminated subsurface situations must be approached carefully to minimize the
exposure of drilling personnel to potentially hazardous materials.
A cable tool rig uses a heavy, solid-steel chisel-type drill bit suspended on a steel
cable which, when raised and dropped, chisels or pounds a hole through the soils and
rock. When drilling through the unsaturated zone, some water must be added to the
hole. Cuttings are suspended in the water and periodically bailed. After enough water
enters the borehole to replace the water removed by bailing, no additional water needs
to be added. When soft, caving formations are encountered, it is necessary to drive
casing as the hole is advanced to prevent collapse of the hole. Often the drilling can
be advanced only a few feet below the bottom of the casing. Because the drill bit is
lowered through the casing, the hole created by the bit is smaller than the casing.
Therefore, the casing (with a sharp, hardened casing shoe on the bottom) must.be
driven into the hole. The shoe, in fact, cuts a slightly larger hole than does the drill
bit. This tight-fitting drive shoe cannot be relied upon to form a seal when overlying
water-bearing zones are encountered.
Formation samples can be excellent when a skilled driller uses a sand-pump bailer.
Information regarding water-bearing zones is readily available during drilling. Relative
permeabilities and some water-quality data also can be obtained from different zones
penetrated if a skilled operator is available. Cable tool rigs can operate satisfactorily in
all formations, but they are best suited for large, caving, gravel-type formations or
formations with large cavities above the water table.
Cable tool drilling is slow compared with rotary drilling. The necessity of driving
the casing along with drilling in unconsolidated formations requires that the casing be
pulled back to expose selected water-bearing zones. This process complicates the well
completion process and often increases cost. Relatively large diameter casing is required
(minimum 4-inch casing) which increases the costs compared with rotary drilled wells
with plastic casing. The use of cable tool rigs for small-diameter (2-inch) wells is not
recommended.
19
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Reverse circulation drilling is accomplished by allowing water or mud to circulate
down the annulus and up the inside of the drill pipe (reverse flow direction from direct
rotary mud drilling). This type of drilling is used for construction of high-capacity
production wells and is not suited for small, water-quality sampling wells. Custom
drilling techniques may be necessary for specialized investigations (60).
Weil Development
Development is a facet of monitoring-well construction that is often overlooked.
During the drilling process, fines are forced into the open borehole, forming a mud
cake that reduces the hydraulic conductivity of the materials opposite the screened
portion of the well. To allow free entry of water into the monitoring well and to
maximize well yields (a particularly important factor for low-yield geologic materials),
this mud cake must be broken down and the fines removed from the well.
Additionally, monitoring wells must be developed to provide water free of
suspended solids for sampling. When sampling for metal ions and other inorganic
constituents, water samples must be filtered and preserved at the well site at the time
of sample collection. Improperly developed monitoring wells will produce samples
containing suspended sediments that will both bias the chemical analysis of the collected
samples and frequently cause clogging of the field filtering mechanisms (61).
The development procedures used for monitoring wells are similar to those used
for production wells. The basic principles include creating alternately high and low
velocities of water flow in the well to break down the mud pack or loosen fines,
followed by pumping to remove the fines from the well and the immediate area outside
the well screen.
Successful development methods for relatively productive wells include the use
of a surge block, bailing, and surging by pumping. A surge block is a plunger device
that fits loosely inside the well casing. It is moved forcibly up and down, causing water
to surge in and out of the well screen. After surging, the well must be pumped to
remove the fines carried into the well screen and casing. The use of surge blocks for
monitoring well development has not been widely attempted. The potential for
damaging a relatively fragile, 2-inch-diameter PVC well with a tight-fitting surge block
has generally overruled the potential benefits that would be gained from this type of
development.
A bailer sufficiently heavy to fall quickly through the water can be raised and
lowered rapidly through the screened portion of the well. This action will create the
same alternating surging action as the surge block. The use of bailers for developing
wells is more common than the use of the surge block.
Another method for developing wells in relatively productive geologic materials
is to surge either with a pump or by air. When using a pump, the well is alternately
pumped and left idle to simulate the surging action desired to loosen the fines and
remove them from the well. However, in most applications, no outward movement of
water from the well is experienced, and bridging of fines moving toward the well limits
the effectiveness of this technique.
When pumping with air, the effectiveness of the procedure depends on the
geometry of the device injecting air into the veil. Figure 5-2 illustrates a simple device
20
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Flattened nozzle with
1/8" opening
3/8" OD stainless or
,copper pipe
Overall dimension
less than 1-'/z"
1/8" diameter hole (both sides)
Figure 5-2. Schematic diagram of an air driven well development device
that diverts air through the well screen to loosen the fines and forces air, water and
fines up the well casing and out of the well. These devices are particularly effective
for developing monitoring wells in relatively productive geologic materials. Air devel-
opment techniques also may cause the exposure of drilling personnel to hazardous
materials when badly contaminated ground water is present. Careful precautions must
be taken to minimize personnel exposure.
Development procedures for monitoring wells in relatively unproductive geologic
materials is somewhat limited. Due to the low hydraulic conductivity of the materials,
surging of water in and out of the well casing is extremely difficult. Also, when the
well is pumped, the entry rate of water is inadequate to effectively remove fines from
the well bore and the gravel pack material outside the well screen.
In this type of geologic setting, clean water can be circulated down the well
casing, out through the screen and 'gravel pack, and up the open borehole prior to
placement of the sealant in the annulus. Relatively high water velocities can be
maintained and the mud cake from the borehole wall can be broken down effectively
and removed. (Because of the low hydraulic conductivity of geologic materials outside
the well, a negligible amount of water will penetrate the formation being monitored.)
Immediately following this procedure, the well sealant should be installed and the well
pumped.
In summary, all monitoring wells should be developed. The additional time and
money spent for this important procedure will expedite sample filtration and result in
samples more representative of water contained in the formation being monitored.
The time saved in filtration alone will more than offset the cost of development.
21
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Sampling Apparatus
Many brands of pumps are available for use in small-diameter (2-inch) wells.
Table 5-1 Jists selected commercially available sampling devices and their principal
features. Devices in Table 5-1 can be divided into five general categories based on
their methods of operation: bailers, suction lift pumps, gas contact samplers, positive
displacement samplers, and syringe samplers.
Bailing is one of the simplest and oldest methods for sampling small-diameter
monitoring wells. Bailers, which can be constructed from a wide variety of materials,
require no power sources and are easy to transport. They are economical and easy to
clean. One of the drawbacks of using a bailer is that it is time-consuming and sometimes
impractical when dealing with large quantities of water. Special care also must be taken
to keep the rope, wire, or chain clean during bailing to prevent the introduction of
contaminants. The transfer of water from the bailer to the sample container may allow
aeration of the sample and outgassing of volatile chemical constituents. Bottom-draw
bailer designs with dual check valves minimize these sources of bias.
Suction lift sampling devices listed in Table 5-1 include peristaltic and Venturi-
type pumps. The peristaltic pumps are relatively portable and can operate over a wide
range of pumping rates. However, their use is limited to situations where water levels
are less than about 20 feet. The suction created by the peristaltic pumping action
changes pressure in the transfer lines and may result in degassing and loss of volatile
organic compounds from the sample.
The Venturi pump operates in the same way as the domestic-size two-pipe jet
pump. Water is pumped at the surface by a centrifugal pump. A portion of the water
is circulated clown a return pipe and through a Venturi section where suction is created,
and water from the well is pulled into the Venturi section and up the discharge pipe.
The pressure drop created at the Venturi section may cause degassing or volatilization
of organic compounds. The circulation of water back into the Venturi section and
priming vessel also makes it difficult to determine when a particular well volume is
being delivered to the surface.
Gas-drive contact pumps normally use nitrogen gas to force water from a
sampling chamber up through a discharge line. The surface-area-to-water ratio is small
to minimize the effects of the gas contact. Data have not yet been obtained.to accurately
determine the effect of gas/water contact,
Positive displacement pumps listed in Table 5-1 include the helical-rotor, piston,
and bladder-type pumps. All three can operate over a wide range of pumping rates.
Though the pumps are relatively portable and easy to operate, they do require power
(electricity or compressed gas) and are somewhat difficult to clean. Available data
suggest that these pumps are more versatile and desirable than other devices for
sampling most chemical constituents.
Syringe-type samplers are used to collect samples for analysis of volatile organic
compounds. After purging the well with another pump, sampling devices are lowered
into the well and positive pressure is maintained to prohibit the entry of water until
the desired depth is reached. Pressure is then released, and the hydrostatic pressure
in the well fills the syringe. The sample is raised to the surface and preserved for
analysis.
22
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Table 5-1, Saturated-Zone Sampling Devices for Use in Small-Diameter Boreholes and Monitoring Wells
Manufacturer
BarCod Systems, Ine,
Cole-Farmer Inst.
Co.
ECO Pump Core,
Galiek Corp.
GeoEngmeer ing.
, Inc.
Industi ial and
IsO Environmental
03 Analysts. Inc.
(IEA!
IEA
Instrument Special-
ties Co. IISCO)
Keck Geophysical
Instruments,
Inc.
Leonard Mold and
Die Works, Inc.
Oil Recovery
Systems, Inc.
Q,E.D, Environmental
Systems, Inc.
Model name/
number
BarCad Sampler
Master Fie*
7570 Portable
Sampling Pump
SAMPLtfier
Bailer 219-4
GEO-MONITOR
Aquarius
Syringe Sampler
Model 2600
Well Sampler
SP-81 Submer-
sible Sampling
Pump
GeoFiller
Small Dia. Well
Pump 1#Q5QO!
Surface Sampler
Well Wrzard®
Monitoring
System (P 100)
Principle of
operation
dedicated; gas
df tve (poshive
displacement)
portable;
peristaltic
{suction}
portable; venturi
portable, grab
(positive dis-
placement}
dedicated; gas
drive (positive
displacement)
portable; bladder
(positive dis-
placement)
portable; grab
(positive dis-
placement!
portable; bladder
(positive dis-
placement!
portable; helical
rotor (positive
displacement)
portable; bladdei
(positive dis-
placement)
portable; grab
(positiVB dis-
placement)
dedicated; bladder
(positive dis-
placement)
Maximum outside
diameter /length
linchcsl
1.5/16
<1,0/NA
-------
Table 5-1. (Concluded}
Manufacturer
Randolph Austin Co.
Robert Bennett Co.
Slope Indicator Co.
ISINCOl
Solinst Canada Ltd.
TJMCO MJg. Co.,
Inc.
TlMCO
Tole Devices Co.
Model name/
number
Model 500
Vari-Flow Pump
Model 180
Model 514124
Pneumatic
Water Sampler
5W Water Sampler
Std. Bailer
Air or Gas
Lift Sampler
Sampling Pump
Principle of
operation
portable; peri-
staltic (suction)
portable; piston
(positive dis-
placement)
portable ; gas
drive {positive
displacement!
portable; grab
(positive dis-
placement!
portable; grab
(positive dis-
placement!
portable, gas
drive (positive
displacement)
portable; bladder
(positive dis-
placement!
Maximum Oiitsido Construction Lift
diameter /length materials range
(Inches) fw/linvs & tubing) ill)
-------
In addition to the effects the pumping mechanism may have on the sample, ihe
materials that contact water in the pump and delivery tubes also should be examined.
Chemical constituents can be sorbed (adsorbed or absorbed)and leached from improperly
selected materials in pumps. Considerations for materials selection is discussed later in
Section 7 of this report.
Dedicated m-silit sampling devices also are available for saturated-zone sampling.
These devices are placed directly into the geologic materials to be sampled and are
pumped by gas-drive contact. The literature does not address the suitability of these
devices for organic sampling.
In-line detection and sampling devices are valuable tools for ground-water
monitoring. During the collection of samples, flow-through cells for monitoring tem-
perature, pH, redox potential, and conductivity should be used. These devices should
be constructed to allow for a constant flow of,water without the accumulation of gases.
The accumulation of gases on the probes can cause erroneous values to be recorded.
Probes should be noncoiitaminating or as inert as possible.
As with well construction and drilling method precautions, all sampling devices
should be carefully cleaned prior to use, A dilute hydrochloric acid rinse followed by-
successive rinses with deionized water, acetone, and distilled water are routinely
recommended. In badly contaminated situations a hot water detergent wash prior to
the above rinsing procedure may be necessary. Hexane rinses prior to the final distilled
water rinse aid the remo%'al of sparingly soluble organic materials prior to sampling
for low-level organic pollutants.
25
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SECTION 6
SAMPLING STRATEGY
The importance of proper sampling of monitoring wells cannot be overem-
phasized. Even when the wells are correctly located, constructed and developed, special
precautions must be taken to ensure that the sample collected is representative of the
ground water at that location. Care also is needed to ensure that the sample is neither
altered nor contaminated by the sampling and handling procedures,
To select proper sampling procedures for monitoring wells, several basic questions
must be reviewed. First, the purpose of the monitoring program and collection of
samples must be reevaluated. Monitoring commonly is undertaken to comply with state
or federal regulations that set forth a list of chemical constituents to be monitored.
They also usually stipulate the concentrations of various chemical constituents that
must be analyzed and reported. Sampling procedures for defining plume geometry
and migration may require different procedures than those for routine regulatory
monitoring. Sampling procedures for research projects may be particularly specialized
and more demanding. In all instances, it is essential to develop a complete list of
chemical parameters to be measured and the sensitivity at which they will be measured.
Secondly, the physical limitations of the well and the well site must be considered. The
diameter of the well, depth to water, length and location of the well screen, and
accessibility of the well site all bear on the practical application of various sampling
procedures.
Prior to discussing the effects of well flushing and pumping mechanisms on
ground-water quality, it would be instructive to review briefly the factors controlling
ground-water quality. An understanding of these factors enables one to better plan
sampling efforts and minimize the effects of reactions that may occur due to sample
handling.
Effects of Subsurface Conditions on Ground-Water Quality and Sampling
The subsurface is a condensed, geologic, and geochemical environment which
also serves as a habitat for microorganisms (62,63). It is difficult to describe the entire
range of subsurface conditions since local effects can drastically alter regional properties
of temperature, pressure, oxidation-reduction potential, mineral solubility, solution
chemistry, and biological activity. The relevance of average conditions must be evaluated
on a case-by-case basis in order to account for the changes in ground-water chemistry
which may occur during sample collection and retrieval. Temperature and pressure
are major physical influences in this regard.
Temperature fluctuations in the upper 10m (33 ft) of the subsurface occur in
response to seasonal air temperature variations. In the United States, average ground-
water temperatures range from 3°C to 25°C (37°F to 77°F) to a depth of 20 m (66
ft) (64). Local effects can be quite marked, however, since increases from 7°C to 16°C
26
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(42°F to 60°F) above background have been observed in contaminated aquifers near
landfills (65), Pressure gradients in the subsurface may be approximated as those due
to the hydrostatic pressure of a column of water equivalent to the depth of interest.
The strength of the pressure gradient may vary, though it is generally about 0,1 atm
• m"' (0,4-0.5 psi ' ft"1). Summarizing average physical conditions in the subsurface, one
can expect that from the screened portion of a shallow monitoring well 10-20 m (33-
66 ft) deep to the surface, temperature and pressure differentials may range from 10-
30°C (45-83°F) and from 2-3 atm, respectively. Regardless of the choice of well
construction methods or materials which contact the sample, the impact of temporal
and spatial physical changes must be minimized to provide the most representative
ground-water sample possible.
Chemical and biological indicators of subsurface conditions vary greatly in
response to small changes in the above-mentioned physical factors. Considerations of
sample handling procedures and the compatibility of materials with the ground-water
system are subtle. In general, the subsurface environment is not in equilibrium with
ambient surface conditions. This is particularly true of the atmospheric gases oxygen
and carbon dioxide, which exert control over the oxidation-reduction potential, pH,
buffer capacity, and chemical speciation of dissolved substances. Several reference works
on aquatic and ground-water chemistry provide background information on the range
of potential conditions to which samples, well casing, and sampling devices may be
subjected (66,67,68,69).
Within an aquifer, there are six major processes which affect subsurface geo-
chemistry. These are: 1) compiex formation; 2) acid-base reactions; 3) oxidation-
reduction processes; 4) precipitation-dissolution reactions; 5) sorptive interactions; and
6) microbiological processes.
All of these processes can be affected by sample collection procedures- Shifts in
solution chemistry caused by rapid changes in temperature, pressure, or gas content
may result in nonrepresentative samples. This is particularly true of the carbonate
buffer system since ground water is normally oversaturated with carbon dioxide (CCX).
The system is sensitive to temperature and pressure changes since gaseous, dissolved, •
and solid chemical constituents participate in equilibrium reactions. For example, the
loss of dissolved CO2 on simultaneous temperature increase and sample depressurization
will cause an increase in the pH. The pH changes in turn affect mineral solubility, the
kinetics of iron and manganese oxidation, and hydrolysis reactions. Products of these
reactions in turn may shift the chemical speciation of nutrients and metals and either
stimulate or inhibit microbial activity.
Many potential changes can take place in a ground-water sample while being
collected or before it is preserved (22,70), The previous discussion described general
subsurface conditions and examples of solution chemical changes in inorganic constit-
uents if samples are improperly collected. The impacts on volatile organic compound
concentrations also can be quite marked. Samples collected from sites exhibiting unusual
chemical properties may respond differently.
Effects of Hydrologic Conditions on Sampling Strategy
Hydrologic factors can exert controlling effects on the collection of representative
samples. The yield potential of a monitoring well will determine the length of time
27
-------
that a well must be pumped at a given rate to produce a sample representative of the
aquifer at that location, The transmissivity of the materials tapped by the well also is
important in determining reasonable sampling frequencies and predicting rates of
ground-water movement. To determine these parameters, well or slug tests should be
conducted on the monitoring wells to be sampled.
Traditional analysis of well test data usually involves the use of equations derived
by Theis (71) and Jacob (72). One of the basic assumptions made in deriving those
equations was that all of the water pumped from a well during a pumping or aquifer
test comes from the aquifer and that none comes from storage within the well. Since
this condition is seldom fulfilled in practice, particularly for the low-yield situations
common!}' encountered for monitoring wells, these equations are somewhat inappro-
priate for describing the behavior of water levels during pumping for most monitoring
wells.
Popadopulos and Cooper (73) presented an equation describing the discharge
from a pumped well which takes into account the volume of water removed from
casing storage.
Drawdown values calculated with the relation developed by Popadopulos and
Cooper differ significantly from those based on the Theis and Jacob equations. During
the early stage of a pumping test a relatively high percentage of discharge comes from
casing storage and smaller drawdowns are observed than would be predicted by Theis
or Jacob methods. In the later stages of the test a negligible quantity of water is
obtained from casing storage and all three drawdown calculation methods produce
equivalent results. If the effects of casing storage are not taken into account, it is
possible to misinterpret the data and assume an erroneous transmissivity value based
on early drawdown data,
Well test data For six monitoring wells studied in Illinois (22) were analyzed
using the equations presented by Popadopulos and Cooper. At all of the sites studied,
the nonpumping water levels were significantly above the top of the aquifers tapped,
suggesting artesian conditions. In this case, a storage coefficient of 0.0001 was used in
the analysis of data. The drawdown values described by the Popadopulos and.Cooper
equation are relatively insensitive to changes in storage coefficient. The storage
coefficient values selected therefore should have little effect on the aquifer properties
determined at most sites.
Using the Popadopulos and Cooper equations, the percent of aquifer water
pumped was calculated for a 2-inch-diameter well at a pumping rate of 500 mL/min
for a range of transmissivities and time (see Figure 6-1). Relationships of this type can
be developed for any given set of hydrologic parameters' to predict the time at which
a high percentage of aquifer water would be obtained.
Conducting slug tests on monitoring wells also provides estimates of aquifer
transmissivity. Analytical methods described by Freeze and Cherry (68) are recom-
mended for the interpretation of slug test data. Once the transmissivity of aquifers has
been determined, the relationships developed by Popadopulos and Cooper can again
be applied to predict the quantity of water coming from the aquifer during various
phases of pumpage.
28
-------
100 -
cc
LLJ
r-
CC
LLJ
u_
5
o
LLJ
O
cc
UJ
o.
Q = 500 mL/mirt
DIAMETER = 5.08cm
25 30
TIME, minutes
Figure 6-1. Percent of aquifer water versus time for different transmtssivities
Based on the studies by Gibb and others (22), the following recommendations
are presented for collection of ground-water samples:
1) A brief 2 or 3 hour pumping test should be conducted on each monitoring
well to be sampled. Analysis of the pump test data and other hydrologic information
should be used to determine the frequency at which samples will be collected and the
rate and period of time each well should be pumped prior to collecting the sample. If
pumping tests cannot be conducted, slug tests may be substituted to provide the needed
hydrologic information.
2) A general rule 'of thumb of pumping four to six well volumes will, in most
cases, produce samples representative of aquifer water. For aquifers with unusually
high transmissivities, pumping for periods long enough to remove the "stagnant" water
column may induce migration of water from parts of the aquifer remote from the
monitoring well. The calculations of percent aquifer water with time provide a more
rational basis on which the length of pumping can be determined. Samples should be
collected in the minimum time required to produce water representative of the aquifer.
3) A controlled sampling experiment [monitoring indicator parameters (pH, T,
fl'1, and Eh) or collecting samples during an extended period of pumping] should be
conducted to accurately determine the chemical quality of aquifer water and to verify
the response of the monitoring well to pumping, as predicted from the pump test data.
This is best accomplished with an in-line closed measurement cell (74). When the values
of the indicator parameters are observed to vary less than ± 10% over three consecutive
storage volumes, the well may be presumed to have been adequately flushed for
representative sampling. Once the chemical character and response of the monitoring
29
-------
systems have been determined, chemical constituents for routine sampling can be
selected.
4) Based on the sensitivity of the selected chemical parameters, a choice of
pumps for routine'sampling can be made.
5) The monitoring wells should be pumped at a constant rate for a period of
time that will result in delivery of at least 95 percent aquifer water. The rate and time
of pumping should be determined on the basis of the transmissivity of the aquifer, the
well diameter, and the results of the sampling experiment.
6} Measurements of pH, Eh, temperature, and specific conductance also should
be made at the time of sample collection. Field determinations of alkalinity together
with a mineral analysis, the foregoing measurements and total dissolved solids permit
mass and charge balance calculations to be made which are valuable analytical quality
control checks,
The steps outlined above are designed for collecting representative samples for
inorganic analysis. The same procedures likely will produce representative samples for
nonvolatile organic analysis. The use of a syringe sampler (75) in conjunction with
pumping or a bottom-draw bailer is desirable for collecting samples for volatile organic
constituents.
Special care must be taken to prevent cross-contamination when carrying sampling
apparatus from one well to another. The sampling devices must be cleaned thoroughly
to ensure that contaminants from one well are not carried to the other. Cleaning
procedures should be tailored to the analytes of interest. The use of detergents, dilute
hydrochloric acid, hexane, and deionized rinse water often is necessary. In addition,
cleaning of sampling devices, all delivery tubes, and tether cables also must be performed
thoroughly. The effects of cross-contamination also can be minimized by sampling the
least contaminated wells first and progressing to the more contaminated ones. Dedicated
sampling devices for each well also may be desirable in certain cases where the potential
for cross contamination is high.
In the case of monitoring wells that will not yield water at a rate adequate to
be effectively flushed, different procedures must be followed, There are divergent
points of view on how flushing should be performed in these situations. The principal
difference in the arguments concerns the degree to which such wells should be evacuated.
One suggested procedure includes the removal of water to the top of the screened
interval to prevent the exposure of the gravel pack or formation to atmospheric
conditions (5). Then the sample is taken at a rate which would not cause rapid
drawdown. On the other hand, the wTells may be pumped dry and allowed to recover.
The samples should be collected as soon as a volume of water sufficient for the intended
analytical scfiteme re-enters the well. Exposure of water entering the well for periods
longer than 2 or 3 hours may render samples unsuitable and unrepresentative of water
contained within the aquifer system. Finally, in these cases, it may be desirable to
collect small volumes of water over a period of time, each time pumping the well dry
and allowing it to recover. At present there is very little reliable data on which to
choose one sampling method over another in "tight" formations.
30
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SECTION 7
EVALUATION OF MATERIALS
The selection of materials used for well construction and sample collection,
handling, and storage is a critical consideration in planning the well-conceived moni-
toring program. The materials of .choice should retain their structural integrity for the
duration of the monitoring program under actual subsurface conditions. They should
neither adsorb nor leach chemical constituents which would bias the collection of
representative samples. The material combinations also must be compatible with each
other-and the goals of the program. For example, in a detective monitoring situation
where the presumed inorganic contaminant source (e.g., brine or pickling liquor) is
held in a surface impoundment, material selection should be inade so as to ensure the
reliability of analytical determinations of chemical constituents of the waste in ground-
water. These parameters may include pH, specific conductance (fi"1), alkalinity, hardness,
total dissolved solids (TDS), chloride, and trace metals. In this hypothetical situation,
the "background" ground water is relatively high in ionic solids, and the goals of a
long-term (e.g., 30-year) monitoring program would be most closely met by a properly
constructed network of non-metallic or corrosion-resistant monitoring wells. .Sampling
gear and sample handling precautions also should be chosen carefully to ensure that
the samples are neither contaminated nor biased by the effects of materials.
Overview of Subsurface Conditions
The structural requirements for well casings to withstand normal subsurface
pressures are met by most common piping materials: steel, polyvinyl chloride, and iron
for depths up to ~30 m. In deeper monitoring situations, the use of corrosion-resistant
metallic casing of large diameter (>10 cm or 4 inches) may be required to provide
necessary structural integrity. Local water well construction practices should serve as
a guide.
Metallic corrosion problems may be encountered under either oxidizing or
reducing conditions and are aggravated by high dissolved-solids content. Other materials
(thermoplastics) may deteriorate under the influence of dissolved chemical substances
or direct contact with wastes. Whether the well construction or sampling materials
retain their integrity or not, there are also potential problems due to microbial
attachment and growth and the sorptive capacity of the exposed materials for the
chemical species of interest. Representative sampling depends on the proper choice of
materials which can retain their integrity over the entire length of a well casing, from
the aerobic, unsaturated surface zone to the unique conditions in the saturated zone.
Chemical Properties of Water and Their Effects on Various Materials
To achieve the goals of a detective monitoring program in a cost-effective manner.
one must carefully design and construct the sampling network after consideration of
31
-------
the compatibility of casing and materials with the subsurface environment. If an initial
detective network is to be used during the interpretive phase, then the materials should
be compatible with probable mixtures of ground water and chemical substances from
the source. Compatibility must be judged from a structural and chemical standpoint.
Structural considerations are treated in detail in a National Water Well Association
manual (18). The main criterion for chemical compatibility should be that the long-
term interaction of the casing or sampling materials with the ground water will not
cause analytical bias in the interpretation of chemical analysis of the water samples.
For example, assume that a long-term detective monitoring network is to be
designed for an acidic metal-plating waste impoundment in a shallow ground-water
system where the background water is low in pH and high in dissolved solids. The
contaminants of interest are Fe, Mn, Zn, Cr, Cd, and Pb. Under these conditions, it
would be imprudent to construct the monitoring wells with black iron or galvanized
steel, since inevitable corrosion of the casings would be expected to contribute several
of the above metals to the water samples. One may argue that flushing the well will
minimize this source of bias or that upgradient and downgradient wells will experience
the same degree of interference from corrosion. This argument may hold in some
cases; however, the degree of interference in specific wells will depend on the actual
conditions at each well site. High background levels of chemical substances contributed
by deteriorating well casing might interfere with the analytical determination of the
parameters of interest, Very difficult interpretation problems may result if a downgra-
dient galvanized well were at the margin of a plume of acidic waste, and casing
corrosion contributed a high "background" of Fe, Mn, Zn, and Cd to water samples
drawn from both upgradient and downgradient wells. f
In a long-term (e.g., 30-year) detective monitoring program, the judicious selection
of casing materials is of utmost importance. The corrosive and leaching properties of
ground water over an extended period at a particular site are nearly impossible to
predict "a priori." Testing the materials of choice with admixtures of ground water
and wastes from a source may be a valuable step prior to the construction of the
monitoring well network. If organic contaminants are of concern, it may be necessary
to investigate the leaching (or adsorption) of specific compounds at the microgram-
per-liter level. In this case, the impact of interfering organic compounds on the
separation and analysis of the compounds of interest (e.g., the priority pollutants) may
be quite serious. For example, the ubiquity of phthalate esters in flexible plastic (non-
polyolefinic) materials and in the environment has caused numerous analytical problems
in the determination of many compound classes in natural-water samples (76,77).
The study of the effects of water or aqueous solutions on materials and vice versa
presents many obstacles to the investigator. For leaching effects alone, there are at least
six critical system variables which must be controlled or considered, including chemical
composition of the solution; temperature; rate of flow; composition of the material, its
age, pretreatment, and surface area exposed. For purposes of material selection for
ground-water monitoring, static or flowing tests with solutions approximating the range
of solution composition expected should be sufficient. Protocols for conducting such
tests are detailed in several publications (78,79). Additional references have been
included in the section which follows along with the performance data available for
selected materials.
32
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Candidate Test Solutions for Materials' Evaluation
The composition of ground water or contaminated ground-water solutions varies
quite markedly, so there can be no universal test solution applicable to the'specific
• requirements of all ground-water monitoring programs. Tap water or carbonate-1-
buffered distilled water may be a suitable starting point if raw water from the site is
unavailable. This is, in effect, what is used in the national certification program of
piping materials for potable-water use conducted by the National Sanitation Foundation
(80). The chemical composition of leachate and- contaminated ground water From -
investigations of sanitary or hazardous waste landfills provides some composition limits
for additional test solutions. Municipal landfill leachate compositions are detailed in a
number of publications (11,81). The use of a standardized acetic acid solution has
.several distinct advantages over a synthesized leachate for testing purposes (81). >
" Leachate and ground water collected from the vicinity of industrial-waste handling
sites are difficult to characterize due to the diversity of sites and wastes involved.
However, there are some .general indications from the recent literature that two
categories of chemical composition predominate. Briefly, from a survey of data from
43 monitoring investigations of hazardous waste sites in the United States, Shuckrow
et al. (82) identified high organic/low inorganic and low organic/high inorganic
.solution compositions as accounting for'nearly 44 percent of the sites where ground-
water samples were collected. High-inorganic samples contained inorganic constituents
at five times the water-quality criteria levels, while low-inorganic samples contained less
than the corresponding regulated levels. Similarly, high-organic samples contained
greater than 400 micrograms " L"1 of individual hazardous organic constituents, while
low-organic samples had less 'than 5 micrograms '• L"1 of such substances.
Profiles of these two loose categories of contaminated ground-water composition
are shown in Table 7-1.
The high-organic group typically exhibited near-neutral pH with TOG and COD
levels five to ten times the background values, TDS values were generally two to three
times background levels. The four organic compound classes noted below account for
5-32 percent of the TOG. Specific compounds identified in these classes at concentrations
exceeding 0.1 mg " L"1 include phenols (pentachlorophenol, phenol, nitrophehol);
Table 7-1. Chemical Composition of Contaminated Ground Water Near Hazardous Waste Sites
High organic/law inorganic ~ Low organic /high inorganic
6-8 ' . 3-6
pH
TOC
COD
TDS
Phenols
Organic Bases •
Aromatic Hydrocarbons
Chlorinated Aliphatic
.Hydrocarbons ' 0,1-150
All values in mg-L . except for pH
denotes insufficient data to1 present a range of values
Source: Reference 82
,, > 10 • •
25-41,000
1,000-2,000 ' .-
0.5-3 . '' Zn
0.8-25 , ' Cd '
0.1-14 Cr.'
'. 1,000-13,000
1-100
1-8
1-200
As
10-10,000
33
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organic bases (aniline, nitroaniline); aromatic hydrocarbons (benzene, toluene, xylene,
'substituted benzenes); and chlorinated aliphatic hydrocarbons (dichloroethane, trich-
loroethane, trichloroethylene, tetrachloroethylene). The presence of these slightly water-
soluble compounds in ground water would be expected to affect sorptive or leaching
characteristics of the subsurface environment, particularly toward thermoplastic or
elastomeric materials. .. "•
On the other hand, the low-organic group showed mineral acidity and low pH
values. It also was associated with TDS levels five to ten times ambient background.
Several metallic'elements (Zn, Cd, Cr) normally.present in trace amounts were observed
at concentration's,exceeding background ground-water levels by factors of 10 to 1,000,
These low pH.'high TDS solutions would be expected to be quite aggressive toward
.metallic casing materials after extended exposure periods.
It is clear that a reasoned strategy for ground-water monitoring must consider
the effects of contaminated water on well construction materials. Unfortunately, there
is very little'published ^information on the performance of specific materials in varied
hydrogeologic situations. The 'monitoring strategy must be tailored to fit unique
situations, and strict guidelines'are currently unavailable.
In the preceding discussion, four categories of subsurface solution conditions
were identified. These categories range from carbonate-buffered water to leachate-
impacted ground water. The categories are outlined in Table 7-2 with the principal
chemical species identified.
The range of chemical exposures represented by these four categories of solution
composition should provide general test cases for •consideration of compatible well
construction materials. ' •'
Table 7-2. Solution Composition for a Range of Ground-Water Conditions
_ So/ids content. Principal soluble
Genera! category pH ' (mg-L"'l species present
Buffered Weak Acid 5 100-200 NaVHCO, -, H*. H, C03
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Table 7-3. Chemical Exposures Grouped in General Solution Categories
weak acid
Ammonium Carbonate
Ammonium Chloride
Calcium Carbonate
Aqueous Carbon Dioxide
Distilled Water
Potassium Bicarbonate
Sodium Acetate
Sodium Benzoate
Sodium Bicarbonate
Sodium Carbonate
Sodium Phosphate
Sodium Suifide
Sulfite Solutions
Weak acid
Acetic Acid
Benzoic Acid
Citric Acid
Glycolic Acid
Fatty Acids
Formic Acid
Gallic Acid
Hydrogen Suifide (aq.
Lactic Acid
Oxalic Acid •
Tannic Acid
Tartaric Acid
Mineral acid/
high dissolved sotids
Acid Mine Waters
Brine Acid
Hydrochloric Acid
Metallic Chlorides
Metallic Sulfates
Mixed Acids
Plating Solutions
Seawater
Sulfuric Acid
Aqueous organic
mixtures
Aniline
Beer
Benzene
Butyl Alcohol
Carbon Tetrachloride
Chlorobenzene
Cresol
Methyl Alcohol
Methylene Chloride
Naphtha
Phenol
Toluene
Trichioroethylene
Wine
Xylene
second-order effects such as adsorption, absorption or leaching were considered.
Compatibility ratings were as follows; (3 points) no significant deterioration, embrittle-
ment, or corrosion in general use; (2 points) the potential exists for deterioration,'etc.,
and this material is recommended only after testing; (1 point) the possibility of
deterioration, etc., clearly exists and is likely after extended use. Rigid materials used
for well casings or sampling gear, as well as semi-rigid or elastomeric materials for
tubing and other apparatus, were treated.in the same fashion. The compatibility of
each material was ranked after the total rating in each category was converted to a
percentage of the maximum possible score. The percent ratings in each category served
to rank the materials in order, and the sum of the ratings for each material in all four
categories provides an overall ranking scheme.
There are limitations in this approach which stem from the lack of detailed
information on testing conditions, the subjective nature or varied sources of judgment
of "significant" deterioration, and the tenuous relationship of exposures to pure
chemicals or dilute aqueous solutions to actual subsurface conditions. However, this
preliminary ranking is a starting point for in-depth consideration of materials perform-
ance under actual site conditions. Generally recommended materials for monitoring
applications are noted'by Pettyjohn et al. (17).
The following rigid well-casing materials were considered: PVC I (unplasticized
polyvinyl chloride), galvanized steel, carbon steel, Lo-Carbon Steel, Stainless Steels 304
and 316, and Teflon®. Flexible (or semi-rigid) materials commonly used for pump
parts, sample transfer, lines, in-line devices or storage vessels were rated, including
flexible PVC (plasticized), polypropylene, polyethylene (conventional), polyethylene
(linear),'polymethylmethacrylate (Lucite or Plexiglas), Viton®, silicone, and neoprene.
Glass was not considered among the rigid materials due to the unavailability of well
screening and hazards associated with its use for casings. Rating results in each category
and overall are shown in Tables 7-4 and 7-5 for the rigid and flexible or semi-rigid
materials, respectively. Sources for the exposure ratings (83-91) are included in the
references.
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Table 7-4, Relative Compatibility of Rigid Well-Casing Material
PVC Galvanized Carbon to-carbon Stain/ess Stainless
I steel steel steel steel 304 steel 316 Tefton®'
Buffered Weak Acid 100 56 51 59 97 100 ' TOO
Weak Acid 98 59 43 47 96 100 100
Mineral Acid/High Solids 100 48 57 60' ,80 82 100
Aqueous/Organic Mixtures 64 69 73 . 73 98 100 100
Percent Overall Rating 91 58 56 59 93 36 100
'Trademark of DuPont
Preliminary Ranking of Rigid Materials
Teflon©
Stainless Steel 316
Stainless Stee! 304 • ,
PVC I
Lo-Carbon Steel
Galvanized Steel
Carbon Steel
Table 7-5, Relative Compatibility of Semi-Rigid or Elastomeric Materials
PB PE
flexible PP conv, linear PMM Vitort®" Silicone Neoprens Teflon®'
Buffered Weak Acid 97 97 100 97 90 92 87 85 100
Weak Acid 92 90 94 96 78 78 75 75 100
Mineral Acid/High Solids 100 100 100 100 95 100 78 82 100
Aqueous/Organic Mixtures 62 71 40 60 49 . 78 49 44 100
Percent Overall Rating 88 90 84 88 78 87 72 72 WO
'Trademark of DuPont
Preliminary Ranking of Semi-Rigid or Elastomeric Materials .
Teflon®
Polypropylene (PP)
PVC flexible/PE linear
Viton®
PE conventional
Plexiglas/Lucite (PMM)
Silicone/Neoprene
Both tables clearly show that superior performance can be expected of the
polymeric materials under acidic or high-dissolved-solids conditions. However, as the
organic content of the solution increases, one must be prepared for either direct attack
on the polymer matrix or more subtle effects due to solvent absorption, adsorption
and/or leaching. The only exception to this observation is Teflon®. Provided that
sound construction practices are followed, Teflon® can be expected to consistently
outperform all other casing and sampling materials. The stainless steels predictably are
the most chemical resistant of the ferrous materials. Stainless steel performance may
be sensitive to the chloride ion, which can cause pitting corrosion, especially over long-
term exposures under acidic conditions. Given the similarity in price, workability, and
performance, the remaining ferrous materials provide little advantage for casing/
36
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screen construction. Indeed, the manufacturers' recommendations frequently were
contradictory (89,90,91), and as a result, the rankings are essentially equivalent.
The semi-rigid or elastomeric materials ranking in Table 7-5 follows the general
chemical resistance expected from manufacturers' recommendations. The "true"
polymeric materials — Teflon®, polypropylene, polyethylene, Viton®, sil'icone, and
neoprene — may have an added advantage over polymer formulations (PVC) for
rigorous applications since they generally contain fewer extenders, stabilizers, or
antioxidants which may cause interferences in analytical determinations. One should
be aware of the fact that many flexible materials contain plasticizers, which are potentially
troublesome contaminants, especially when industrial solvents are encountered in
ground-water systems. The polyolefin materials — polyethylene and polypropylene —
are exceptions to this statement since they generally do not contain plasticizers and
are more resistant to organic solvent attack than the formulated plastics.
The general rankings provided in the above tables should serve as a basis for
preliminary considerations of the suitability of specific materials for ground-water
monitoring applications. In the next section, the available literature on actual materials
performance in water-handling systems is reviewed for both rigid and flexible materials.
This more detailed information is provided in order to permk reasoned considerations
of performance in specific applications.
Evaluation of Selected Materials
Since well casing materials are rigid and nonporous, they present a very low
surface area to water in the well bore relative to that of the adjacent soil or aquifer
particles. There is an extensive body of literature dealing with sorptive interactions of
dissolved chemical species in natural waters with solid surfaces. Most of these studies
describe the adsorption of trace metals or organic compounds (adsorbates) on mineral
particles (adsorbents). Surface area (or particle size) and the organic content of the
solid phase are cited almost universally as important variables in the adsorption process.
Mineral phases such as quartz (92), aluminum (93), hydrous metal oxides (94), and
clays (95), as well as natural sediments (96), have been studied with surface areas
ranging from 5 to over 250 m2 " g'1. These active surfaces have been observed to
adsorb routinely up to several hundred micrograms of adsorbate per square meter
surface area. The applicability of laboratory adsorption experiments to the condensed
media of the subsurface is a matter of some controversy (97,98,99,100). However, a
simple qualitative comparison of well casing versus subsurface solids should suffice to
discount adsorptive interferences from materials selection considerations.
As an example, let us assume that we have constructed a 50-foot (15.3 m)
monitoring well with a 2-inch (~5 cm) diameter. The well is screened in the lower 3
feet (1 m) of a 33-foot (10 m) saturated thickness, and the standing water level is 17
feet (~'5 m) from the land surface. This hypothetical well bore contains approximately
21 liters of water exposed to about 2 m2 of casing/screen surface, roughly a 10:1 ratio
of water to casing surface. If the solids in the saturated zone were coarse sands with a
minimum surface area of 1 m* ' g"1, the casing water volume would have been exposed
to at least 104 irr of solid surface! If we presume that the casing has been in place long
enough to equilibrate with subsurface conditions, we may expect that the surface
37
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activity of the coatings (microbial slimes, organic films, or micro precipitates) on
neighboring particles and the casing material would be roughly equivalent. Thus, the
occurrence of adsorptive bias in our representative water sample, taken after purging
the stored volume, would be likely only if the well casing presented an extremely active
surface uncharacteristic of nonporous materials and if the rates of desorption/adsorption
were very fast relative to the duration of a sampling operation.
Although reports on the rates of adsorption and desorption in aqueous solution
are sparse, most workers have employed at least a 4-hour equilibration period in
laboratory studies. Reported half-times for maximum adsorption of metals and nutrients
are in the range of 0.5-2 hours (27,29,54). These times are much greater than the
time necessary to sample most monitoring wells after the removal of stagnant water
from the well bore. On this basis, the potential bias effects due to adsorptive interactions
with well casings may be discounted. Such effects would be far more critical in sample
transfer and storage procedures prior to separation or analysis. A note of caution
should be added with regard to the absorption of organic solvents by polymeric
materials. Past exposures of casing or tubing surfaces to high aqueous organic mixtures
may cause the migration of organic solvents into the polymer matrix. Normal cleaning
procedures may not be sufficient to remove this potential source of contamination in •
succeeding samples. Also, freshly cleaned materials may represent active surfaces for
sorption or leaching effects,
Teflon® Well Casing
Teflon® represents a nearly ideal well construction material. Inertness to chemical
attack, poor sorptive properties, and low leach potential are clear advantages of rigid-
Teflon® PFA for well screen and casing. However, these advantages are rather expensive
in comparison to other materials. Where situations allow, using Teflon® casing and
screen in the saturated zone with another suitable material as the upper casing may
be a viable, less-expensive alternative (17). The structural properties of Teflon® are
sufficient for the most exacting environments, and this factor gives it a clear advantage
over glass. Teflon® has not been reported to contribute organic or inorganic contam-
inants to aqueous solutions.
Stainless Steel Well Casing
Stainless steel has been the material of choice for casing and screen when subsurface
conditions require a durable corrosion-resistant material. In the preliminary materials
ranking, 316 Stainless showed a slight edge over type 304, The principal compositional
difference between the two types is the inclusion of 2-3 percent molybdenum in type
316 (101). The molybdenum content gives 316 Stainless improved resistance to sulfur-
containing species as well as sulfuric acid solutions. Resistance to oxidizing acids is
somewhat poorer than other chromium-nickel steels; however, reducing conditions are
more frequently encountered in well-casing applications. The 316 Stainless Steels are
less susceptible to the pitting or pin-hole corrosion caused by organic acids or halide
solutions. They are the materials of choice in industries where excessive metal contam-
ination of process streams must be avoided (e.g., pharmaceuticals). Provided that surface
coating residues from manufacture or storage are removed, stainless steel well casing,
screen, and fittings can be expected to function nearly as well as Teflon® in most
38
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monitoring applications. Chromium or nickel contamination may result after long
exposure to very corrosive conditions; however, physical failure of the casing would
probably accompany or precede such an occurrence. Proper well flushing prior to
sampling should be sufficient to minimize problems with these materials (102). Details
'of well-executed monitoring efforts in which stainless steel well'casing and screen have
been used successfully are provided by several recent publications (38,103,104).
PVC Welt Casing
Polyvinyl chloride (PVC-Type 1) thermoplastic well casing is composed of a rigid
unplasticized polymer formulation with many desirable properties for monitoring well
construction. It is a rigid material with very good chemical resistance except to low-
molecular-weight ketones, aldehydes, and chlorinated solvents. The preliminary ranking
in the previous section establishes PVC as a close second to Teflon® and 316 Stainless
Steel with respect to resistance to acid solutions, and it may be expected to outperform
any of the ferrous materials in acidic environments of high ionic strength. There may
be potential problems when PVC is used in contact with aqueous organic mixtures or
under conditions which might encourage leaching of substances from the polymer
matrix. It should be noted that manufacturers do not recommend the use of threaded
schedule 40 PVC casing because of potential mechanical failures. Schedule 80 threaded
PVC well casing is sufficiently durable for most well construction applications.
PVC product formulations and applicable standards
There are few piping materials that have received the scrutiny to which PVC
products have been subjected. Discussions of durability, health effects of leachable
components, and modes of fabrication have gone on since U.S. commercial production
began in the 1940's (105). A number of standard specifications exist covering PVC
well casing (106,107,108,109), which is tested by the National Sanitation Foundation
(NSF) using a protocol equivalent to that for all plastic pipe used in potable water
applications (80). In general, the chemical resistance of polymeric materials is improved
by the incorporation of fewer ingredients in the formulation (88), and unplasticized
PVC bears this out in tests of weatherability (110).
There have been many concerns voiced about the release of vinyl chloride
monomer from PVC products. Process control technologies have significantly reduced
the total residual vinyl chloride monomer (RVCM) levels in the resin and finished
products. In fact, the NSF chemical, taste, and odor testing protocol (67) limits the
levels of RVCM to <10 ppm in NSF-listed products. This level of residual monomer
limits the potential leached concentrations to 1-2 micrograms ' IA From 1977 to
1980, the RVCM failure rate in NSF tests of PVC formulations fell from 9 percent to
less than 1 percent (111). It would be expected that the leachable amounts of vinyl
chloride monomer decrease as the total RVCM levels in products are reduced. This
has been borne out in several laboratory and field studies which demonstrate that vinyl
chloride monomer (VCM) does leach into potable water at the,low ppb level as a result
of prolonged solution exposures. For example, an EPA field study of five potable water
supplies with plastic pipe manufactured between 1964 and 1975 showed VCM levels
between 0.03 and" 1.4 microgram • L'1 (43). The higher levels observed were from
samples taken from more recently constructed installations. Levels of VCM leached
39
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into water from static or flowing tests have been shown to be a function of exposed
surface area and actual levels of RVCM in the product (42,112,113). These laboratory
results on samples that meet NSF Standard 14 specifications (80) show chat leached
VCM levels are in the <1 to 2 microgram • L"1 range. Though these levels are below
those of toxicological concern (111) the potential exists for organic analytical interfer-
ences in monitoring situations where prolonged exposure.to aggressi%re aqueous organic
mixtures may occur.
Rigid PVC materials used for pipe and well casing with NSF-listingare essentially
free of plasticizers. Although plasticizers are unnecessary for rigid pipe applications, a
small number of sources of well casing may include plasticizers which are added along
with the thermal stabilizer component. Plasticizer levels in such pipe samples would
not be expected to exceed 0,01%. These levels are far lower than those in flexible
PVC formulations for tubing or sheet materials which can contain up to 30-50 percent
by weight of plasticizer. Rigid PVC contains several types of other additives at levels
approaching 5 percent by weight, which may ,pose a source of bias or analytical
interferences in ground-water monitoring programs (113). These additives include
pigments, antioxidants, thermal stabilizers, and inorganic fillers (114,115). Some rep-
resentative chemical classes of additives which have been used in rigid PVC manufacture
are contained in Table 7-6. There are clearly many possible combinations of substances
which may be included in PVC formulations. The potential for their release into
aqueous solutions or ground waters may be determined by the individual formulation,
rigor of exposure, manufacturing techniques, and the chemical state of a particular
component in the finished product. Here again, NSF-listed products for well casing
and potable water applications are continually checked and tested. Products that are
found to exceed the maximum contaminant levels set by the National Interim Primary
Dnnking Water Standards in leach tests (Table 7-7) do not qualify to carry the NSF
logo. Their use should be avoided in monitoring well construction since many manu-
facturers include compounding ingredients that are not permitted by the specifications.
Table 7-6, Representative Classes of Additives in Rigid PVC Materials
Used for Pipe or Well Casing
(Concentration in wt, %}
Hear stabilizers (0.2-1,0%) fillers (1-5%)
Dibutyltin diesters of lauric CaC03
and maleic acids diatomaceous earth
Dibutyltin bis (lauryimercaptide) . clays
Dibutyitin-(3-mercaptopropionate Pigments
di-n-octyltin maleate
di-n-octyltin-S,S'-bis tsoctyl ! TiO:
mercaptoacetate carbon black
di-n-octyltin-j3-mercaptopropfanate iron and other metallic oxides
Various other alkyltin compounds Lubricants (1-5%)
Various proprietary antimony compounds
stearic acid
calcium stearate
gtyeerol monostearate
montan wax
polyethylene wax
(Reference 11 51
40
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Table 7-7. Chemical Parameters Covered by 1MSF Standard 14
for Finished Products* and in Standard Leach Tests
Parameter
Antimony (SbS
Arsenic (As)
Barium (BaJ
Cadmium (Cd)
Chromium {CO
Lead (Pb)
Mercury (Hg)
Phenolic substances
Residual vinyl chloride monomer* !RVCM)
Selenium (Se)
Tin (Sn)
t Mot covered under National Interim Primary Drinking Water Regulations,
* Total residua! after eorrplets dissolution of polymer matrix,
Tabulated vaiues are the maximum levels permissible in NSF-l!sied products
after standardized ieach lesrnc :n weakly acidic aqueous solution. [Carbonic
acid solution with "00 rng-L"1 hardness as CaCO|j with 0,5 mg- L"1 chlorine;
pH 5,0 to 0,2; and surface to solution ratio'of 6.5 cm1 -mL~l ]
Source: National Sanitation Foundation
Maximum contaminant level lmg-L~{ i
0.05t
0.05
1.0
0.01
0.05
0,05
0.002
0.05t
10t
0.011
0.05
0.05T
Practical considerations and potential for analytical bias due to use of PVC well casing
The use of NSF-lisied well casings provides us with a minimum standard material
that can be judged for suitability in specific monitoring situations. AD types of well
casings should be cleaned with detergent and rinsed with water prior to well construction
to remove processing lubricants and release agents. This is particularly true of PVC
well casing, which may be coated with natural or synthetic waxes, fatty acids, or fatty
acid esters.
Threaded joints are the preferred means of connecting sections of PVC well
casing. In this way, problems associated with use of solvent primers and cements can
be avoided. Threaded joints on PVC well casing (or pipe) can be provided in three
ways: solvent cementing a molded thread adaptor to the end of the pipe, molded flush-
threaded joints built into each pipe section, and cutting tapered threads on the pipe
with National Pipe Thread sized dies. The latter method is only recommended by the
industry for schedule 80 PVC well casing or pipe. Numerous studies have pointed out
analytical interferences and direct sources of bias caused by the migration of the
components of solvent mixtures into water samples (79,41,116,117). The mixtures
frequently contain two or more of the following solvents: methyl-ethylketone (2-
butanone), methyl-butylkeiones, cyclohexanone, tetrahydrofuran, and dimethylformam-
ide. Some of these substances may not be among the analytes of interest; however,
their presence in a water sample can cause severe problems in the determination of
priority pollutants (41). In the experience of the Illinois State Water Survey, even
minimal solvent-cement application is sufficient to supply consistent levels of cement/
primer components above 100 ppb in actual ground-water samples despite proper well
development and flushing prior to sampling. This problem may persist for months
after well construction even after repeated attempts to develop the wells. Prolonged
exposure to aggressive aqueous mixtures is probably the single most important factor
41
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contributing to leaching problems. This situation is decidedly different from the high-
volume flow-through testing conditions employed for PVC plumbing for potable water
transport applications,- There are various alternative joining procedures for PVC pipe
other than solvent cementing or threaded joints. These include: twist-lock or spline
unions which employ O-ring seals. For these procedures the integrity of the ring
material must also be considered in evaluating appropriate materials for well casings.
Other sources of potential bias from the use of PVC well casing may arise from
the additives present as compounding ingredients, such as those in Table 7-6. These
substances are added to color the pipe, protect it from oxidation or exposure to sunlight
and aid in the maintenance of the integrity of the virgin resin in extrusion or molding.
For example, thermal stabilizers such as the organotin compounds (e.g., dimethyltin-
bis-isooctylthioglycolate) are added to scavenge HC1 released when the resin is heated.
Liberated HC1 would otherwise attack the polymer matrix and degrade the product.
Ideally, minimal amounts of such substances should be added to insure product integrity.
In practice, however, it is difficult to determine ideal additive concentrations and an
excess may be present in most finished products. Therefore, the initial compounding
ingredients, as weil as the products of their reaction with species generated during
processing or use, the ingredients themselves, and the polymer matrix, must be
considered among the species that-may leach or migrate from the finished product.
, At present there are very few data available on the identity and concentrations
of chemical species leachable from PVC pipe under actual subsurface conditions.
Metallic and organometallic compounding ingredients have received the most attention
in the literature due mainly to the ease of spectroscopic metal determinations relative
to that of specific organic compounds. Specific organic compound determinations are
difficult since both the mixtures of original ingredients and their reaction products are
present in a solid matrix which is more or less insoluble (114-118).
Lead and cadmium compounds are not permitted as compounding ingredients
in U.S.-manufactured, NSF-listed PVC well casing, There are a series of papers from
the United Kingdom which demonstrate various aspects of the leaching process for
rigid PVC materials stabilized with lead stearate or tribasic lead_sulfate (78,119,120).
In this comprehensive study, R. F. Packham detailed the equilibration of lead-stabilized
rigid PVC over a range of pretreatment, aging, and leach-solution conditions. His
conclusions include the following points: 1) total Pb content was'not simply related to
the quantity extractable, although surface area was an important variable (he also noted
significant variations along a length of pipe and the consequences of proportionately
longer heat exposure for larger-diameter pipe); 2) the bulk of the extractable Pb
seemed to be present in a surface-rich layer (~30 mg • Pb • m'3), which could be
removed by abrasion, ethanolic-NaOH or oxidizing acids; 3) pre-exposure of rigid PVC
to organic acids, organic mixtures, and trichloroethylene actually increased the amounts
of Pb extracted by the standard bicarbonate solution; 4) even after removal of the
surface layer, additional leachable Pb could be attributed to a slow diffusion process
of the order of 0.2 mg • Pb • week"1 • m's; and 5) there was some indication that lead
stearate stabilizers would support higher leachable lead quantities than inorganic tribasic
lead sulfate. This study significantly supplemented the earlier work of Niklasand Meyer
(121). The results of this work clearly show some of the important variables involved
in the leaching of compounding ingredients from rigid PVC well casing. Pretreatment
42
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and cleaning, aging, and the effects of multiple extractions (static or flowing test
conditions) are factors which should be considered in PVC well-casing applications.
Actual field conditions may either decrease or increase the long-term release of
compounding ingredients (81) through surface area effects, and the chemical species
of interest must be carefully considered,
In more recent work, Boettner et al, (40) studied the release of alkykin species
from PVC pipe stabilized with dialkyltin-bis-isooctylthioglycolate compounds. Their
results clearly showed that levels of leachable organometallics were of the order of 10-
50 ppb on initial exposure to chlorinated, buffered, pH 5 carbonic- acid solution.
Concentrations of leachable tin due to successive exposures gradually decreased in a
biphasic manner for up to 3 weeks. The actual mobile tin species were not identified;
however, there was an indication that they were ionic in nature. The leaching of related
tin compounds from coatings is recognized to be a complex process which may occur
from an active fraction of the exposed area (122) and is certainly affected by the
chemistry of individual species (123). The leaching process is an active area of research
which will prove most helpful in the interpretation of chemical investigations of materials
effects in many environmental applications. Though the tin or antimony compounds
used as stabilizers are rarely of interest for monitoring,, their impact as analytical
interferences and/or sources of bias must be carefully considered,
The bulk of the data available on PVC chemical resistance and leaching strongly
suggests that there are potential pitfalls involved in the use of PVC well casing in
situations where trace chemical species are of interest. At this time, it is clear that PVC
exposed to aqueous organic mixtures has the potential to act as a source of foreign
organic or metallic compounds in excess of what may occur in predominantly inorganic
solutions. Detailed monitoring efforts for organic compounds at the microgram • L'1
level may be significantly biased by the sole use of PVC well casing, particularly during
the initial study period. Thereafter, the slow diffusive release of PVC additives may be
expected to continue for some time. Whether or not these effects significantly bias
monitoring results will depend on specific conditions and the actual formulations used.
Caution is indicated from the available data on these processes. .
The potential for solvent absorption, and the adsorptive uptake or release of
organic compounds and metals by PVC pipe, has been discussed by several authors
(39). However, there are few data documenting this potential under field conditions.
The mechanism for solvent-cementing lies in the absorption of the solvent and partial
dissolution of the PVC matrix to produce a "solvent-weld." Therefore, the exposure
of PVC to low molecular ketone, aldehydes, acids, amides, chlorinated alkenes or
alkanes may cause the actual degradation of the polymer matrix and/or the release of
compounding ingredients which otherwise would remain in the solid. The concept of
discrete adsorption "sites" on PVC which may be expected to equilibrate with stored
water in monitoring wells (124) may be applicable to certain situations, though the
inevitable adsorption of natural organic matter and microbial coatings argue against
any specific adsorptive interaction. If circumstances do not permit the use of a more
appropriate material (e.g., Teflon®, stainless steel) under high-organic or unknown
conditions, then at least several paired wells should be constructed of a non-polymeric
material and PVC. This will allow at least an order-of-magnitude determination of the
potential bias due to PVC well casing.
43
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Further, manufactured casing and screen is preferable to off-the-shelf PVC pipe.
The practice of sawing slots in the pipe (e.g., home-made screens) should be avoided
since this procedure exposes fresh surfaces of the material, increasing the risk of
releasing compounding ingredients or reaction products. Also, it is very difficult to
properly slot casing materials by sawing operations.
i f
Casing Made from Other Ferrous Materials
Ferrous metal well casing and screen materials, with the exception of stainless
steels, include carbon steel, low carbon or copper (0.2%) steels, and various steels with
a galvanized coating. In the preliminary ranking contained in Table 7-4, these materials
ranked consistently poorer than Teflon® and stainless steels. They do, however, show
an advantage over rigid PVC in exposures to aqueous organic mixtures. The carbon
steels were formulated to improve resistance to atmospheric corrosion. To achieve this
increased resistance, it is necessary for the material to undergo alternate wetting and
drying cycles. For non-coated steels buried in soils or in the saturated zone, the
difference between the corrosion resistance of either variety is negligible (125). Both
carbon- and copper-steel well casings may be expected to corrode, and corrosion
products may include oxides of Fe and Mn (and trace constituents), as well as various
metal sulfides. Under oxidizing conditions, the principal products are solid hydrous
oxides of these metals, with a large range of potential particle sizes. The solids may
accumulate in the well screen, at the bottom of the well, or on the casing surface. The
potential also exists for the production of stable colloidal oxide particles that can pass
through conventional membrane filtration media (126), Reducing conditions will
generally provide higher levels of truly dissolved metallic corrosion products in well
storage waters (127,128). Galvanized steels are protected by a zinc coating applied by
hot dipping or electroplating processes, The corrosion resistance of a galvanized steel
is generally improved over conventional steels; however, the products of initial corrosion
will include iron, manganese, and zinc (and trace cadmium) species which may be
among the analytes of interest in a monitoring program.
Corrosion products from conventional or galvanized steels represent a potential
source of adsorptive interferences, The accumulation of the solid products has the
effect of increasing both the activity and the exposed surface area for adsorption,
reaction, and desorption processes. Surface interactions can thereby cause significant
changes in dissolved metal or organic compound concentrations in water samples (102).
Flushing the stored water from the well casing may not be sufficient to minimize this
source of bias because the effects of the disturbance of surface coatings or accumulated
products in the bottom of the well would be difficult, if not impossible, to predict. In
comparison with glass, plastic, and coated steel surfaces, galvanized metal presents a
rather active surface for adsorption of orthophosphate (29). The age of the surface
and the total area of exposure have been found to be important variables in the
adsorption process; however, adsorption is not a linear function of galvanized-metal
surface area.
Field data for conventional and galvanized steels provide additional reasons for
caution in their use for well casings or screens. The water well industry routinely
chooses alternative nonconductive or corrosion-resistant materials in areas where normal
groundwater conditions are known to attack the common steels. In fact, regional or
44
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local practices in the selection of water well construction materials provide valuable
preliminary-guidelines, for routine, monitoring efforts.
The preliminary ranking of ferrous materials in the previous section is well
supported by available monitoring data. Results from studies of the glaciated terrain
of Maine demonstrate that water samples from steel production wells used for monitoring
consistently showed Fe and Mn levels 30-50 times higher than those of samples from
adjacent PVC monitoring wells finished at the same depth (129). In thess data, water
sample composition {DO, T, and TDS)-was remarkably similar, with the exception of
iron and manganese levels. Again, though iron and manganese may not be among the
parameters of interest in a specific situation, the presence of their, metallic oxides or
soluble complexes may interfere with the determination of other metals. This source
of bias may be particularly serious in unfiltered samples which cannot be preserved
properly in the field, , : :
Galvanized steel well casing and screen may seem to be a less costly alternative
to the use of more appropriate materials (e.g., Teflon®, stainless'steel, PVC) in saturated,
high-dissolved-solids environments since it corrodes less rapidly than conventional steels
(130,131). Under reducing conditions at pH values between 5 and 7, the presence of
chloride, carbonate, and nitrate can encourage rapid aggressive attack of the material,
In some cases, CO3= and NO3~ may actually reverse the electrochemical potential
between the zinc oxide coating and the base metal, resulting in accelerated dissolution
of the iron pipe. Sulfur compounds, organic compounds, and dissolved copper concen-
trations also are implicated in the rapid deterioration of galvanized steels under
saturated conditions. Monitoring data from wetland soils and bog environments disclose
that galvanized imaterials are a liability/ in ground-water investigations. Instances of
casing or screen dissolution under these conditions resulting in zinc concentrations
approaching 10 ppm are common (38,132,133). In these cases, water samples "from
PVC and stainless steel monitoring wells showed zinc concentrations 1-2 orders of
magnitude below those observed in samples from adjacent galvanized steel wells despite
'the fact that comparable well flushing techniques were used. This is consistent with
the dissolution and migration of zinc from galvanized monitoring installations, providing
an additional source of bias that- careful flushing does not minimize.
It appears, ttherefore, that in corrosive environments, galvanized steel presents
little or-no advantage over .conventional steels, and more appropriate materials should
be considered. Some degree of compromise may be achieved by casing the upper
unsa'turated zone with steel casing and then using PVC, stainless, or Teflon® casing
and screen in the saturated zone. However, the potential for abrasion during sampling
operations or galvanic corrosion effects'should be evaluated prior to installation.
Pumps Used in Development
The large variety of centrifugal, peristaltic,'impeller, and submersible pump
designs precludes an in-depth, discussion of their potential effects on the results of
ground-water monitoring efforts. According to the situation, one must carefully consider
the compatibility of the materials/ found in high capacity pumps with subsurface
conditions. The methodology of monitoring well development is probably far more
critical in this respect than the pumping mechanism or water-contacting materials. One
45
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of the most serious problems, arises in the use of water of poor or indeterminate quality
for surging or jetting operations. This'water can migrate into the formation of interest
and alter local aquifer properties. Exhaustive pumping of a well after development to
determine hydraulic conductivity from time-vs-drawdown or recovery curves should
be sufficient to minimize this problem.
,, Special precautions may be: called for in severely contaminated areas and where
flammable or toxic materials are present in ground water. In,these, cases, a'plan for
the management of water (as welTas cuttings) extracted during drilling or development
should be designed. All'such operations should be carefully supervised by the'chief
field engineer or scientist. The practice of returning contaminated water to the
formation is strongly discouraged since there is no tested procedure to account for
changes which occur during surface storage or mixing.
Grouts, Cemenfs, Muds, and Drilling Fluids \
, 'Various drilling aids, cements, and sealant formulations are used to achieve two
,main goals: to maintain an open borehole in rotary and cable tool operations in
unconsolidated formations, and to effect a seal between the surface or overlying
formations and the casing/screened intervals so that runoff or other sources'of water
do not enter the well bore. Problems involved in obtaining representative water samples
stem mainly from the persistence of drilling aid components and the long-term integrity
of grouts or cement seals.
Drilling aids ' *
For the most part, water-based drilling fluids are used in freshwater applications
where the total-dissolved-solids content of ground water is below 10,000 mg • L"1. The
fluids are introduced for several purposes, including cooling and lubrication of the bit,
suspension and removal of cuttings, stabilization of the borehole by building up a cake
on the sides of the hole, and minimization of formation "damage due to water loss or
penetration-of solids. Freshwater muds are formulated mainly in three types: 1)
bentonite, attapulgite or clay-based muds with pH adjusted to 9-9.5 with caustic; 2)
polymer-extended clay (organic) muds; and 3) inhibited clay muds which utilize
lignosulfonates or lignin to counteract the effects of contaminants which would otherwise
destabilize the slurry and prevent effective cutting removal. The first two types are
used most frequently in water-well drilling applications (134). Both of these main types
of mud formulations and a spectrum of combined compositions have been used for
the construction of monitoring wells. The basic ingredients in a drilling mud are shown
in Table 7-8, and the main distinction L between bentonite and organic muds is the
addition of natural or synthetic organic polymers to adjust consistency, viscosity, or
surface tension.
For monitoring applications, there are distinct advantages to angering, air-rotary,
or clear-water rotary drilling techniques where conditions permit. The desired approach
is the least possible introduction of foreign materials into the borehole. Compressor
lubricants for air-rotary rigs may rule out this method for trace organic moniloring
work although''filters are available'to minimize such problems. In geologic situations
where water-based drilling fluids are a necessity,,the predominantly inorganic clay muds
are preferable over those containing organic materials, since the ."introduction of
46
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Table 7-8. Components of Well-Drilling Fluids
Functional class Examples
Inert solids calcium and barium sulfates
Inorganic salts ' sodium chloride
Active solids bentonite (~90% Na-monimorillonite clay),
attapulgite, calcium carbonate
Bacterrcides formaldehyde, hypochlorite
Organic polymers partially hydrolyzed polyacrylamide, corn
or bean starch, carboxymethylcellulose,
copolymers of acrylamide end sodium
acrylaie, lignosulfates/lignin
(References 57, 134, 135, 136!
substrates for microbia! activity can seriously impact the integrity of water samples
(57,58). The decomposition of the organic components of drilling muds may be
expected to be a function of their chemical -structure, microbial populations, the
presence of nutrients, and various physical and chemical factors controlling the
distribution of organic substances in the subsurface. Studies to dale have been confined
primarily 10 oil or gas drilling operations in marine or subarctic regions where permafrost
impacts have been investigated (137,138).
Comprehensive freshwater drilling studies of the persistence of organic additives
are sparse; however, Brobst and Buszka (59) have investigated the problem using
chemical oxygen demand (COD) as an indicator of the organic mud. In this study,
monitoring wells were constructed by rotary methods using various clay and organic
muds. Since background COD levels were in the range of 2-10 mg • L' and the drilling
muds of interest were in the range of 1-10,000 mg • L"1, COD was a reliable indicator
of persistent analytical bias. Their results show that, despite careful well development,
and flushing prior to sampling, COD levels from mud-drilled -wells were consistently
3-10 times higher than the background levels measured in adjacent wells. Somewhat
longer persistence was noted for bentonite muds as compared with organic muds, and
the effectiveness of supplements to speed organic decomposition was not uniform. The
effects were found to persist from 20 to 120 days after well completion.
The potential consequences of using drilling aids should be obvious. Although
COD is a surrogate parameter for a number of reduced inorganic and organic chemical
species, levels 3-10 times background can be expected to seriously bias analytical results
in ground-water monitoring programs. Filtration or well flushing prior to sampling
may not be sufficient to reduce mud-related bias. The stable colloidal-sized particles in
some muds will readily form emulsions in organic solvent extraction procedures. The
addition of large amounts of organic substrate for microorganisms into the subsurface
will have the effect of lowering the oxidation-reduction potential, perhaps drastically
shifting both the chemical and biochemical processes in the vicinity of the well bore.
Since organic decomposition processes will depend largely on microbial activity, there
may be significant differences in the dominant pathways, rates, and products from
installation to installation. It is also most unlikely that biocides, enzyme supplements,
or chemical oxidants (hypochlorite) %vill totally ameliorate the situation. An additional
word of caution should be added against the return of mud-contaminated cuttings to
the borehole, since this will only increase the amount of foreign material in the vicinity
of the sampling interval.
47
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Seals, grouts, and cements
Seals, grouts, and cements are the primary safeguards against the migration of
water from the surface and from overlying or adjacent formations into monitoring
wells. Surface seals also must be completed with concern for the security at the well-
head by including, casing sheaths and locking caps. Most seals between the formation
of interest and regions above or below are made by the addition of clay materials or
cement. Bentonite clay can swell from 10-15 times in volume after wetting with
deionized water. Variations in the composition of the contacting solution can severely
reduce the swelling of clay seals. Swelling volumes of 25-50 percent of the maximum
values are not uncommon. The organic content of the solution in contact with the
clay can have a dramatic effect on the integrity of the seal. Organic compounds can
cause significant disruption of normal shrinking, swelling, or dehydration of the clay
lattice during alternate wetting and drying cycles (139). Alcohols, ketones, and other
polar organic solvents have a significant potential for these changes. On the microscopic
level, these phenomena can materially increase the permeability of the clay seal. This
is presently an active area of research which has wide application in well construction,
landfill liners,'and slurry or grout cutoff walls (56,140). Macroscopic changes in the
permeability of clay or cement seals can occur due to solution channeling by aggressive
solvents, compaction or subsidence, and freezing and thawing processes at the surface.
Chemical-resistant and expanding cement formulations effectively minimize these
problems. Faulty seals or grouts can seriously bias the analytical results on water samples
from the formation of interest, particularly if water quality conditions vary or surface
soils are badly contaminated. The impact of leaking seals may go far beyond the realm
of analytical interferences or non-representative samples. A leaky well bore may act as
a conduit to permit rapid contaminant migration, which otherwise would not have
occurred. This is one aspect of a ground-water monitoring program which should not
be left to an unsupervised drilling crew or last-minute substitutions for preferred
materials.
Evaluation of Sample Collection Materials
The choices of sample collection devices, procedures, and all materials which
ultimately contact water samples are probably the most critical considerations in a
ground-water monitoring program. The materials' related problems which may be
encountered in well construction are secondary to those involved in sample handling.
The careful monitoring program planner must evaluate the potential of collection
mechanisms and all materials which contact the samples to introduce interference or
bias into the final analytical result. For example, a collection mechanism that creates
turbulent transfer of the sample and the opportunity for gas exchange (e.g., air-lift
pumping mechanisms) is clearly inappropriate in sampling for volatile organic com-
pounds and pH- or redox-sensitive chemical species. The act of sampling alone would
alter solution composition, introducing bias'into subsequent analytical determinations
as well as matrix effects which may not be totally accounted for by spiked field samples.
Desirable attributes for sample collection materials include:
1) Durability, reliability, and ease of repair
2) A minimum number of moving parts or combinations of materials
48
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3) Capability of being cleaned and sterilized effectively to prevent cross-contam-
ination between sampling points
4) Capacity for being checked for deterioration or malfunctions such as stuck
check valves, clogging, and breakage
5) Verified low potential For introducing contamination, bias, or interferences
into the analytical results
Each of these attributes plays an important role in the overall performance of
monitoring efforts and bears directly on the successful retrieval of respresentative water
samples. The difficulties involved in the evaluation of materials for sample collection
apparatus stern mainly from the variety of combinations of components in pumps (or
other samplers) and the properties of polymeric and elastpmeric materials for tubing
or transfer lines,
Sampling devices
Apart from the actual mechanisms employed by sampling devices, the consid-
eration of materials is of prime .importance in the. choice of a suitable sampler,
Fortunately, most types of devices are constructed in several models which may be
chosen for specific monitoring situations. For example, bailers are presently fabricated
by commercial suppliers in Teflon®, stainless/Teflon®, stainless/PVC 1, and totally
PVC I. These materials satisfy the major critical materials' specifications. Problems
arise in materials selection with samplers employing non-rigid components. Even those
devices which incorporate a single pair of 0-rings may be limited in their application
by the material employed.
The preliminary ranking of materials in Tables 7-4 and 7-5 serves-as a general
guide for materials selection for sampling devices. Teflon® again incorporates most of
the characteristics for an ideal material in sampling applications, However, it is a
difficult material to machine and threaded components are very easily damaged. For
chemical resistance and durability, several materials other than stainless steel may be
expected to perform satisfactorily in low-organic environments. These materials include
polypropylene, linear polyethylene, plasticized PVC, Viton®, and conventional polyeth-
ylene, Viton® is a preferred material for elastomeric parts, since it may be expected
to give improved-chemical resistance over silicone and neoprene.
One may expect that the least desirable material in a given sampler design will
eventually cause monitoring problems. For example, significant differences have been
observed in the organic contamination potential of impeller pumps as a function of
impeller material (3). In this instance, consistently high PCB (polychlorinated biphenyl)
values due to cross-contamination were observed in samples obtained by a plastic
impeller pump relative to those obtained from a device with a stainless steel impeller.
Similarly, solvent cements used in the construction of rigid-PVC bailers can result in
gross analytical errors for volatile organic compounds (41) in samples collected shortly
after bailer fabrication.
Flexible materials in collection devices can be particularly problematic since they
owe their flexibility and resiliency to plasticizers as well as a range of compounding
ingredients no less diverse than those contained in Table 7-6 for polyviny! chloride.
Here, a considerable overlap between materials selection for samplers and tubing or
transfer lines arises. Careful consideration should be given to flexible components of
49
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diaphragm, bladder, or peristaltic pumps based on the discussion in the next section,
The intimate contact of water samples with tubing materials requires that absorption,
adsorption, and leaching potential be carefully considered for specific materials in
monitoring applications. True polymeric materials like the polyolefins may be expected
to cause fewer -problems than formulations or "sandwich" materials.
Tubing and transfer lines
Tubing and transfer lines are available in a variety of polymeric or elastomeric
materials. Certain applications (e.g., peristaltic or bladder pumps) demand a high-
resiliency material, and it may be necessary to sacrifice chemical resistance to achieve
the desired structural performance. The bulk of common tubing materials, with the
exception of Teflon®, contain a .wide range of additives. In addition to the major classes
of additives in Table 7-6, plasticizers, lubricants, antistatic agents, tackifiers, and other
ingredients may be present in flexible synthetic materials (115). In general, true
polymers (e.g., polyolefins like polyethylene and polypropylene) contain far lower
amounts of such ingredients. Formulations change frequently as manufacturers strive
to keep production costs low, so a particular material may show significant variation
from lot to lot. Piasticizers are frequently present at levels between 15 and 50 percent
of the total weight of flexible products. As a result of this fact and widespread plastics
usage, major plasticizers, such as phthalate esters, have been consistently identified in
environmental samples.
There are numerous lab and field studies which detail the contamination of
water samples by contact with plastic tubing. Plasticized PVC is a particularly problematic
material in this respect, showing a high potential for both the absorption/release of
organic compounds (3), and the leaching of compounding ingredients (49,141). By
these mechanisms, PVC tubing may contribute to cross-contamination between sampling
points as well as directly bias the determination of several classes of priority pollutants.
Several studies have reported data that illustrate such interferences, particularly due
to the presence of phthalates (142,143). Table 7-9 shows the frequency occurrence of
phthalate esters in industrial wastewaters (144) and ground-water samples. A comparison
of the frequency levels at similar analytical sensitivities from USEPA monitoring in the
"Superfund" program (145) and those from the New York State study (143) relative
to that in industrial wastewaters is quite revealing. Careful sampling and analytical
quality assurance procedures drastically reduce the overall frequency of detection. This
Table 7-9. Frequency of Occurrence of Phthalate Esters
in Wastewater and Ground-Water Samples
N. Y. state "Superfund"
Industrial public water monitoring
Phthalates wastewaters supply wells samples
bis-(2-ethy!hexyl) phthalate 42% 98% 0%
Dibutyl phthalate 19 • 72 4,8
Diethyl phthalate 8 35 1.9
Butylbenzyl phthalate 8 26 <1
Dioctyt phthalate 6 11 1.1
Number of Samples 2532-2998 56 '1150
Savg. 2617)
Reference , 112 39 ' 113
50
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is supported by the fact that the "Superfund" sites were of concern as potentially
contaminated areas, while the New York State samples were from public water supply
wells. It is quite difficult to determine from the reported data whether analytical bias
entered into these data sets from sampling or analytical procedures. This is an area
which deserves careful attention in an overall ground-water monitoring effort,
Polyethylene and polypropylene are clearly superior plastic materials for sampling
applications in situations where Teflon® is not cost-effective. Teflon® is the tubing
material of choice in monitoring for low-level organic compounds in complex, chemically
aggressive environments. Silicone rubber tubing for moving components of sampling
devices represents a special case where alternate choices of material may not be feasible.
The material is available in several grades which have widely varying compositions and
additives. Metallic contamination from certain laboratory grades of silicone rubber
tubing can be quite serious at the ppb level. Fe and Zn concentrations 2-5 times those
of control samples are not uncommon even after short contact times (146). Medical-
grade silicone rubber tubing is relatively free of unreacted organic initiators (peroxides)
or zinc and is a reasonable alternative to other tubing formulations. Together with the
potential bias introduced by the suction mechanism of peristaltic pumps, the need for
silicone rubber tubing makes it a poor choice of sampler for detailed organic analytical
schemes. The use of other elastomeric materials, such as natural rubber, latex, neoprene.
or chloroprene, is not recommended for transfer lines or surfaces that contact ground-
water samples.
There is little information available on the performance of flexible materials in
ground-water applications. From the available observations, Teflon®, polypropylene,
• and linear polyethylene may be expected to outperform plasticized PVC, since they
have superior chemical resistance over a range of environments and are less likely to
cause contamination or bias problems. Microbial transformations of plastics' additives
introduces another dimension to the problem posed by materials with high concentra-
tions of additives. There are a number of reports on the microbial colonization of
flexible PVC and the degradation of plasticizers from the polymer matrix (147).
The closest evidence to actual field testing of flexible materials comes from the
testing of landfill liners by exposure to municipal leachate (148) or actual waste streams
(149). These observations were obtained on plasticized PVC and 11 other landfill liner
materials. A major conclusion of the work confirms the overall superior performance
of plasticized PVC over most elastomers or chlorinated polyolefinic materials.
Storage containers
The choice of materials for sample storage containers for monitoring programs
has been made by the USEPA after 15-20 years of development by- environmental
scientists all over the world. The choice of container materials is dictated by the group
of analytes of interest and the prescribed preservation techniques. Inorganic constituents
are determined in samples stored in high density linear polyethylene bottles, with the
exception of ammonia, sulfide, or ferrous iron. These species demand oxygen-imperme-
able glass containers and short storage times prior to analysis. Organic chemical
constituents, including priority pollutant classes, TOC, and COD, are required to be
stored in glass bottles with Teflon®-lined screw caps.
Details on specific preservation procedures, sample volumes, and limits on sample
storage times are contained in several reference works (150,151). It is reasonable to
51
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expect that preservation' procedures for organic surrogate parameters such as BOD,
COD, and TOC are minimal steps to preserve samples for specific organic compounds
at-the ppb level.
Sources of Error in Monitoring Efforts
In Figure 7-1, sources of error contributing to the overall variance (square of
the standard deviation from the mean) of ground-water monitoring program data are
schematically depicted. Site selection, sampling, and the analytical problems of meas-
urement, reference samples and data handling are the principal contributing factors.
The overall variance (S2) associated with each factor must be known and minimized in
order to permit reliable comparisons of related data sets, The relative magnitude of
analytical error and errors due to site selection or sampling will determine whether
systematic problems in network design, genuine trends, or significant concentration
differences can be observed in related samples.
Errors may be classed as systematic or random. Simply stated, random errors
enter into overall determinations by handling or human failures and contribute to the
lack of precision in a methodology. Systematic errors are the inherent sources of bias
or inaccuracy in an overall determination which may consistently prevent the reporting
of an accurate result. In ground-water monitoring, the overall determination of a
chemical constituent in a sample from a particular well includes flushing of standing
water to permit collection of a representative sample; sample collection; handling and
storage; and execution of the appropriate analytical, laboratory method.
For example, if a particular chemical constituent can be determined analytically
with a precision of ±20% relative standard deviation, then errors arising from site
selection or sampling must be less than ± 20% to permit reliable evaluation of statistically
significant differences in related samples. If, on the other hand, systematic sampling
SITE
SELECTION
Sg = S VERT. + S HORIZ.
SAMPLING
S2
*!
Ss = S SYSTEMATIC +
S RANDOM + S NAT'L.
MEASUREMENT
METHODS
REFERENCE
SAMPLES
DATA
HANDLING
Thus the overall variance = S2 = S^ + S2 + S^ + S^ + S^
Figure 7-1. Sources of error involved in ground-water monitoring programs contributing to total variance
52
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error (biased accuracy) caused by the introduction or loss of this constituent From a
particular sampling results in worsened overall precision, there is a danger of reporting
a false positive or no trend when, in fact, an unbiased series of samples would show
the opposite to be true. This type of problem may go undetected and has been discussed
by several authors (102,152,153, 154).
To ensure quality and inter-comparability of ground-water monitoring data, one
must seek to eliminate the systematic sources of error (contamination, loss, or intro-
duction of an interfering constituent) and minimize the random errors due to handling
or human intervention. Systematic sampling errors could arise from poor drilling
techniques, the use of persistent drilling fluids, improper well development, poor choice
of well casing, or inappropriate sample handling materials for the hydrochemical
environment. Sample collection mechanisms and techniques also can significantly bias
analytical results.
It is obvious that the choice of materials is a controllable source of systematic
error. Whether or not materials' selection can adversely affect the quality of the analytical
data will depend on the concentration range for the specific chemical constituents of
interest, the magnitude of analyte loss, contamination or interference contributed by
the material, and the performance data for the respective analytical methods.
Comparison of analytical method performance with materials' related errror
In order to best present the background information on various materials which
will aid in making an appropriate selection, we have chosen two degrees of analytical
detail for hypothetical monitoring programs. The simplest program is patterned after
minimum RCRA. compliance involving TOC (total organic carbon), TOX (total organic
halogen), pH, and O'1 (specific'eonductance) determinations. The more detailed approach
will involve a complete priority pollutant scan on the ground-water samples. The
reported precision, accuracy, and routine detection limits for the analytical determi-
nations will be discussed.
A minimal monitoring program may include the determination of selected
indicator variables such as pH or conductance and organic surrogate parameters (TOC
or TOX) to detect changes in the chemical quality of ground water. The introduction
of acidic or basic contaminants in excess of natural buffer capacity would be indicated
by pH changes, and these, as well as other inorganic substances, may cause a change
in ionic composition which would show up in the solution conductivity. Increases in
TOC and TOX may be expected to signal the introduction of organic compounds or
halogenated organics. The significance of changes in these parameters over time is
judged by statistical comparison of results from upgradient and downgradient wells.
One may argue that if both wells were constructed identically, the effects of materials
on the analytical results would be minimal. This may be true when the hydrochemical
environments at each well site are .identical. However, it is precisely when there is a
chemical difference between the subsurface zones as a result of a release that the need
is greatest for reliable signals from high-quality (unbiased) analytical data. Table 7-10
contains performance data on the analytical determinations of TOC, TOX, pH, and
O"1. The table includes precision data for repetitive determinations at various values of
these parameters and corresponding accuracy information. Precision is reported as the
relative standard deviation (r.s.d.) expressed as a percentage of the mean value. Accuracy
53
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Table 7-10. Analytical Performance Data for Selected Water Quality Parameters
Parameter
(method)
TOC
icombusticn-
infraredj
TOX
(C-trap, pyrolysis,
conductivity!
pH
(eiectrometnc)
(conductivity
bridge)
Type of
determination'
Value
107
36,1
0.09mg-C1- •
org
IT'
3,5 (pH units)
7,1 j
8.0
7.7
1 00 (micro Siemens)
808
1640
536
Precision
(relative
standard
deviation)
%
80
7.8!
14.0
17.9
6.0
3.0
2.8
1.6
1.3
7.6
8.2
6.5
1.1
Accuracy
fas bias}
+ 15.27
+1.01
-11 4
-21.9
+7.0 •
-0,29
+1.01
-0.12
-2.02
-3.63
-4.54
Practical
detection
limit
tmg-L~lJ
0.10
0.01
NA
NA
Reference
150
155
156
150
150
150
150
= Interlaboratory Comparison; S = Single Laboratory Results
is reported as bias or the difference of the analytically determined value from the
"true" or assigned value. Accuracy is the critical value to examine for the effect of
systematic errors.' In an actual monitoring program, one would be careful to note a
significant decrease in precision (increased r.s.d.) for repeated determinations on natural
samples, since the "true" or assigned value is not known. The goal, of course, is to
get representative samples.
From Table 7-10 it is clear that the more involved procedures for the surrogate
parameters (TOC and TOX) involve considerably larger relative standard deviations
and more variable values of analytical bias than do the direct instrumental methods
for pH and 0"'. To some extent "this is due to differences in laboratory conditions and
operator consistency, and in the overall efficiencies of the methods for standard
compounds. For high-quality data, sampling or site selection bias should be less than
the values for analytical bias. Therefore, one should weigh the potential for materials'
effects in situations where they may contribute bias approaching that practically
attainable in the analytical method. For example, consider the use of plastic storage
bottles which can contribute 2-3 rng • C • L"1 consistently to TOC samples. At TOC
levels below 10-15 mg • C • L"1, this level of leached material would bias the determination
by more than 20 percent which would exceed the analytical bias. A grossly inaccurate
analytical result would be observed, so this material is clearly inappropriate for the
application. A similar treatment would extend to the other parameters in Table 7-10.
The overall determinations of the surrogate parameters (TOC, TOX) or solution
properties such as pH and conductance are probably not very sensitive to materials'
effects, since they measure classes of compounds or electrolyte properties. Gross errors
in this type of program would probably result from improper construction or sampling
techniques, particularly inadequate well flushing prior to sampling,
54
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In a more detailed analytical data collection effort, the effects of materials may
be much more critical, since low levels of degradation or corrosion products and
leachables could directly bias the determination of specific chemical species at concen-
tration levels well above detection or quantification limits. Sampling bias, apart from
material-related errors, remains a large gap in our understanding of overall inaccuracies
in the data. In this respect, each case must be carefully considered with regard to the
relative magnitudes of contributing errors for the .contaminants of interest.
Tables 7-11 and 7-12 contain analytical method performance data for inorganic
and organic chemical constituents which might be included in a comprehensive
interpretive monitoring program. The performance data on these analytical methods
reflect the optimum condition of good laboratory practice and high-quality reagent
water. Table 7-11 details performance data for inorganic chemical parameters which
provide an indication of water quality and the presence of inorganic contamination.
The precision and accuracy values are expressed as they were in Table 7-10. -The
tabulated values indicate that routine analytical reproducibility is generally better than
20 percent and that the mean may be expected to be within about 10 percent of the
"true" value. Detection limits for the anionic constituents are in the pprn range, while
those for the metallic elements are in the low ppb range. The same overall accuracy
and precision ranges apply to the priority pollutant organic compounds in Table 7-12.
Modern analytical instrumentation enables the precise determination of many metallic
elements and organic compounds on a routine basis. Although accuracy varies somewhat
for compounds such as benzidine and the phthalate esters, a conscientious laboratory
staff can adjust raw analytical results for actual recoveries through the use of suitable
Table 7-11, Analytical Performance Data for Selected Inorganic Chemical Constituents
Precision
(relative Practical
standard Accuracy detection
Parameter Type of deviation} fas bias! limit
{method! determination* , % % (mg-L~'J Reference
CL~ I ' 9.1 2.16 1.0 150
(titrimetry) 31 _Qgi ^g
S 2.9 - -
SO^ I 19,3 -8,26 1.0 150
(turbidimetry) 5.9 -1.70 1.0
Alkalinity • | 15.9 +10.61 - 150
(titrimetry} 4,5 -7.42
N0"3 I 43.7 +8.30 0,1 150
(colorimet'ry) 17.3 +2.82 0.1
Major Cations: Ca, Mg, Na, and K S 4.4 ±2 0.01 150
(AAS)t
Trace Metals; Fe, Mn j '27.8 *3 0.03 150
(AAS)t
Pollutant Metals: Cu, Cd, Pb, Ni, Zn S 4,6 +6 ' 0.01 155,157
(AAS) tt S 5.2 ±7 0.01
*l = interlaborstory Comparison; S - Single Laboratory Results
(AAS)t = Atomic Absorption Spectrometrv-Direci Aspiration/Flame
(AAS)Tt - Aiom'ic Absorption Spectromatry-Graphite Furnace/Flameless
55
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Table 7-12. Analytical Performance Data* for Selected Organic Chemical Constituents
Compounds
Vo tat iles
benzene
chlorobenzene
1,1-dichtoroethane
1,1,2-tnchlorcethane
trichlcroethyiene
tetracMoroethylene
chioroform
ethyl benzene
toluene
o-xylene
Bass-Neutrals
anthracene
banzidine
benzo (A) pyrene
bis (2-ethyihexyl) phthalate
2-chloron3phthalene
chrysene
. 1,2-dich'orobenzene
hexachiorobenzene
nitrobenzene
1,2,4 trichlorobenzene
4-chlorophenyl phenyl ether
Acidics * *
c-chlorophenol
2-nitrophenol
2,4-rjichlorophenol
phenol
pentacHlorophenol
4-nitrophenol
2,4,6-trichlorophenol
Pesticides**
aldrin
4,4' DDT
dieldnn
endrin
heptachlor
chlordane
Precision
frelative
standard
deviation)
12,0
13.1
19.1
12,8
14.0
13.0
17.5
12.5
12.6
7.0
20.0
22.0
22.0
18.0
20.0
33.0
13.5
42.0
21.0
22.0
5.0
22.0
20.0
20.0
19.0
31.0
20,0
26.0
8,0
29.0
2.5
11.0
11.0
5.0
Accuracy
(as bias)
29
-6
5
-5
6
-20
10
-7
-4
-5
-7
-66
11
20
-14
-16
-9
50
38
-26
10
5
5
-39
14
-5
10
-16
-23
"™»J
-6
-41
-20
Practical
detection
limit
10
10
10
10
10
10
10
10
10
10
10
10
10*
10
10
10
10
10
10
10
25
25
25
25
25
25
25
10
10
10
10
10
10
Reference
143,156,157
143,156,167
143,156,157
143,156,157
*The date represent average minimum levels of precision and accuracy obtainable by the referenced laboratories
using 500 series Priority Pollutant Methods, Detection limits are those estimated [eveis routinely achieved by
several laboratories for aqueous standards in each class. These s/alues will vary considerably depending on the
analyst ano whether CC/MS, GC" /MS, or chromatographic methods with selective detectors are used.
**lnterlaboratory values varied over an extremely wide range (greater than one order of magnitude), particularly
for methods 624 and 625.
56
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standards carried through the procedure. The. laboratory staff cannot be expected to
account for sampling'or materials-related errors in the analytical .results. '
For the trace contaminants in Tables 7-11 and'7-12 determined at the 10 ppb
level, one may expect that the corrected analytical.results will be within 20 percent of
the actual value in the absence of bias or unknown interferences. It is the responsibility
of the monitoring program director to inform the lab of any known interferences as
well' as sampling-procedures and materials' contacted which may bias the analysis of
ground-water samples. For example, it has been shown by several 'groups that solvent
cements used in the construction of PVC well casing and bailers contain chemical
constituents which directly interfere with the chromatography of several , priority
pollutants (41,79,' 116). Such' interferences may persist for many months, even after
proper development of solvent-cemented PVC monitoring wells. It may be possible to
assess analytical problems by saving a sample of the PVC primer or solvent cement for
complete analysis. However, the composition of these products has been shown to .vary
significantly from that noted on the label (41).
There are many'Other sampling and materials-related problems which can bias
the analytical data from monitoring programs. Several decades of study on the effects
of such artifacts have resulted in significant improvement hr the quality of chemical
data. This process has taken place in fields as diverse as oceanography..(117,158). and
lunar geochemistry (159), where the effects of "conventional" sampling gear or an
inadvertant fingerprint have led to substantial confusion in the scientific literature.
Ground-water -monitoring programs can benefit from this body of experience, even
though the aims of such efforts are more practical.
57
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SECTION 8
COST CONSIDERATIONS
Once the goals of a ground-water monitoring program have been identified, an
' estimate must be made of the costs that will be incurred in all the various tasks of data.
collection. Preliminary screening of existing data and hydrologic and geophysical
surveys are valuable planning, tools which provide estimates'of the type, extent, and
costs of data collection. Professional consultation can supplement this planning by
identifying potential options for altering network design in, the event of specific
contingencies. As a rule, the degree of detailed information to be collected is roughly
proportional to the cost of the effort to obtain it. Both the minimum quantity and
quality of data, as well as the maximum, must be incorporated into the monitoring
plan. Since there are 'many unknowns involved in ground-water investigations, the
maximum cost/benefit condition may be achieved by designing the initial plan so that
minimum information needs will be met and at least part of the network design will
serve future needs. Careful consideration of data reporting and standards for high-
quality data are available to aid this effort (160).
Water chemistry data collection entails the siting and construction of wells and
sampling points followed by the collection, analysis and evaluation of the analytical
data. The analytes of interest, necessary sensitivity, precision and accuracy at specified
limits of quantitation must be identified in the, planning stages. From this point, the
particulars of materials' selection, sampling protocol development and prospective
interpretive' techniques can be planned 'to insure that high-quality information is
collected in a cost-effective manner.
The preceding chapter dealt with the selection of appropriate material for a
range of ground-water conditions. Also, sources of potential bias or inaccuracy which
can result from the use of inappropriate materials in 'contact with water samples were
identified. The choice of well casing (or sampling device) materials is a key element in
planning a ground-wafer monitoring effort for two reasons. First, all of the water
samples pass through this point. Secondly, once the initial sampling points of a network
are constructed, it will require significant cost and effort to replace them should their
emplacement or interactions with the subsurface render them useless. An additional
caution in material selection is that bias or inaccuracy may be detected too late to
salvage even the minimum information required for program success. All of the other
materials which contact the samples can be independently evaluated for potential bias
and replaced if necessary while the program is in motion. Fortunately, the case for
choosing appropriate well casing materials can be made on a reasonable cost/benefit
basis.
The following discussion details the relative costs of essential elements of general
ground-water monitoring efforts, including well drilling and construction, sampling,
and analysis. Relative costs are presented for four suitable combinations of well
construction materials over a range of analytical complexity. It is presented as an
58
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example of potential planning scenarios for a successful, cost-effective monitoring
program. A very detailed consideration of the costs involved in monitoring efforts has
been developed by Everett et al. (37).
Description of an Example Monitoring Effort
For purposes of discussion, assume that a network of one upgradient and 'three
downgradient, 2-inch, 50-foot wells is to be constructed at a waste disposal site. The
veils are. to be completed at 48-foot depths with 2 feet of screen and approximately
2 feet of casing above ground surface. The screened interval was chosen from the
results of a hydrogeologic and geophysical survey Contract drilling/well construction
services will be used. Sampling is to be done by salaried personnel, and the purchase
of some equipment for sample collection and field determinations will be necessary.
Since very little chemical information is available on the wastes involved, the site, or
conditions, a range of analytical schemes must be considered. The principal questions
in the mind of the monitoring network design staff are: What are the background
chemical conditions present in ground water upgradient from the site? How do we
distinguish background chemistry from chemical species which may be contributed by
the waste? How do we choose well construction materials so that we can obtain
representative samples of ground water if both inorganic and organic contaminants
may be found? The decision is made that the initial network design and installation of
sampling points will be operated for at least 5 years unless the results of the first year's
sampling indicate that additional wells or an expansion of the design is necessary. The
cost-effective choke of well casing materials needs to be made in order to insure the
quality of the analytical information and to build a degree of flexibility into the 5-year
program.
i
Well Installation and Sampling Costs
Consideration of the optimum requirements for reliable techniques and materials
for well construction or sampling presented in the preceding sections limits the spectrum
of drilling techniques and materials' selection. Specific choices among the possible
combinations are likely to be very situation-dependent. Therefore, the cost detail for
key elements of monitoring efforts will be somewhat general.
Three types of well casing/screen are to be considered; threaded rigid PVC
(unplaslicized), 304 stainless steel (SS), and Teflon®. The costs involved in using paired
PVC/SS wells are developed to enable comparison with Teflon®. Pairs of PVC/SS
wells appear to be a reasonable alternative when a range of inorganic and organic
contaminants are of interest under conditions where either PVC or SS may be attacked
or otherwise introduce bias into subsequent analytical determinations. These three
material combinations are recommended for well casing materials selection in planning
a monitoring effort.
Table 8-1 contains a breakdown of approximate well construction and sampling
costs for the first year's operation of a monitoring effort. Drilling costs were estimated
in 1983 dollars for the mobilization and operation of a hollow-stem-auger drill rig and
for the installation of four wells. The costs for well construction materials were
developed for manufactured casings/screens currently available from commercial
59
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Table 8-1. Cost Estimates for Drilling, Well-Construction, and Sampling
(In 1983 dollars)
Drilling
Mobilization (within 150 miles}
Hourly Fee
(4 50-ft wells with 2" casing at 10 ffhf1
plus formation sampling)
Well Construction Materials
Well casings and screen (2 ft)
Fittings, Well Protectors'**
Cement, Sand, Bentonite
PVC
700
640
460
Subtotal S1800
SS
2000
640
460
3100
Subtotal
PVC/SS
7900*
640
460
9000
Sampling***
Quarterly (10 man-days-yf1 ; at SlS.OOO-yr"1 )
Staff
Supplies
Equipment (pH and conductivity meter, electrodes,
samplers and filtration apparatus!
First year costs for drilling, well construction
materials and sampling
PVC
$9850
ss
11,150
Subtotal
PVC/SS
17,050
1st Year
$ 700
3000
$3700
Teflon®
8700
640
460
9800
$ 600
300
3450
$4350
Teflon®
17,850
'includes cost of sxira drilling necessary for PVC/SS pairs
"optional for SS wells
'"'field determinations of pH, conductance, and alkalinity are assumed to be included in sampling operations
suppliers. The added cost involved in drilling pairs of wells for the PVC/SS option
was included in the materials cost for purposes.of comparison. Sampling costs were
developed by including staff, supplies and equipment outlays for the first year. This
procedure lumps together capital, personnel, and operating cost categories for purposes
of comparison. Details of financing arrangements and calculation of the actual cost of
a monitoring program must be made by the individuals involved on a case-specific
basis. It is clear from the data in the table that the first-year well construction and
sampling costs for a PVC well network versus one of stainless steel differ by less than
15 percent. For a program initially aimed at assessing background chemical conditions,
the added cost of installing stainless steel wells may be warranted to provide a degree
of flexibility in future operation should organic contaminants later be encountered.
The paired PVC/SS and Teflon® monitoring arrays are significantly more expensive
to construct and sample but are cost-effective choices in chemically aggressive subsurface
situations.
A graphical comparison of the capital costs for drilling and well construction as
a function of depth is shown in Figure 8-1. The figure projects a linear increase in
costs correlated with the depth of monitoring interests and demonstrates the similarity
in capital costs between the PVC, SS and the PVC/SS or Teflon® options. An important
note here is that considerable cost savings may accrue from casing the upper zones of
the well bore with a less expensive material and using a more appropriate material
below static water levels.
60
-------
CO
co
O
o
0.
<
o
100
200 300
DEPTH, feet
400
Figurg 8-1, Capital costs for drilling and well construction of four point array
Analytical Costs
The minimum degree of analytical detail necessary to adequately meet the needs
of ground-water monitoring programs varies significantly according to program goals.
In regulatory monitoring efforts, the prescribed parameters may be mandated and the
successful performance of the monitoring effort may be little more than an exercise.
There are pitfalls in this minimal approach. For example, natural variations in ground-
water chemistry may not be evident from quarterly determinations of "contaminant-
indicator" parameters (e.g., RCRA analytical parameters, pH, specific conductance,
Total Organic Carbon, and Total Organic .Halogen). If natural variability in the
background electrolyte chemistry is high, it may prove quite difficult to distinguish
natural versus contaminant-release fluctuations. A minimal interpretive analytical scheme
should include indicator parameters as well as a total-dissolved-mineral analysis in order
61
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to provide a basis for future work as well as checks on sample handling and analytical
procedures. This approach also enables close analytical quality control via mass and
charge balances for the evaluation of "representative sample" information, Further,
more detailed interpretive monitoring schemes eventually may be called for at the site
of interest. Well construction techniques and materials should be chosen to permit
expansion of the analytical scheme, as well as monitoring network goals, should the
need arise. After background conditions have been established in the early stages, the
goals can be extended and specific parameters of interest can be added to serve the
more demanding needs of detailed interpretation. Well-conceived network planning,
design, and operation will support the detailed information needs which may be
encountered in the future.
In Table 8-2, four sample analytical, schemes and corresponding derived param-
eters are listed. Average prices have been included from the price quotes of three high-
volume analytical laboratories based on a minimum often samples (including replicate,
field blanks, and field standards) per submission. One can see that as the number of
individual analytes is increased, the cost per sample increases proportionately for
detailed inorganic and organic analysis.
After the degree of analytical detail appropriate for the program has been
chosen, a sampling frequency must be determined. Also, the number of replicate
samples must be decided upon in order to provide the necessary precision for evaluation
procedures. The sample monitoring program has been designed for quarterly sampling
frequency using the four analytical schemes shown in Table 8-2. At least duplicate
** *-
Table 8-2, Description of Analytes and Costs for Four Analytical Schemes for Ground-Water Samples
Dissolved
(field-filtered'
Tots/ snd preserved) Cost per samplet
1. Minimal Detective '
pH.rr1, roc, TOX * ?s.oo
2, Minimal interpretive 175.00
pH.rr1, TOC, TOX = '
Alk, Cl~, NOs", S04= , P04", SiOz *
Na+, K4, Ca++, Mg++, Fe, Mn
3. Inorganic Interpretive ' 410.00
pH, Q'1, TOC, TOX_
Aik, CI", NOs"; S04-,P04=, Si02, B
Ma"1", K+, Ca++, Mg++, Fe, Mn *
Fe(ll), Zn, Cd, Cu, Pb, O, Ni • »
Ag, Hg, As, Sb, Se, Be, Ti *
4. Derailed Interpretive 1400,00
AD of the above (3) PLUS
Volatiles {Method 624) *
Base-Neutrals (Method 625)
Acidics (Method 625)
Pesticides (Method 808) *
tCosts determined in 1983- U.S. dollars from the average of three high-volume
analytical services using EPA approved methodology.
A minimum of ten samples per submission is assumed.
62
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samples of ground water from each well are to be collected, or one may elect to
concentrate more replicates on the upgradient and one particular downgradient well.
Five-year total costs are detailed in Table 8-3 for several combinations of analytical
schemes and sample replication. The number of samples per year includes at least one
field blank and field standards per sampling date at the stated level of replication. The
5-year totals for analytical costs have been calculated at a 5 percent annual increase in
the cost of these services. In comparison with the first-year drilling, well construction
and sampling costs presented in Table 8-1, it is evident that analytical costs (even for
a minima! monitoring effort) make up a large share of total project costs. Of particular
note is the fact that in a detailed interpretive network (3A, 3B, 4A, 4B), the difference
between choosing PVC over stainless steel well casing material (which is less likely to
introduce bias into the analytical data) results in a cost "savings" of $1300. A comparison
of reanalysis costs with apparent savings by the choice of a cheaper material (PVC)
over stainless steel are shown in Table 8-4. One can readily see that the expected
"savings" realized from the use of an inappropriate, cheaper material are actually
penalties.
Ana/yiica/ scheme '
1. Minima! Detective
(4 replicates of each sample)
2. Minimal Interpretive- '
(Duplicates of each sample).
3. A - inorganic Interpretive
(4 replicates in 1st year;
duplicates in years 2-5)
3. B - Inorganic Interpretive
(Duplicates of each sample)
4. A -Detailed Interpretive
(4 replicates in 1st year;
duplicates in years 2-5)
4. B- Detailed Interpretive '
(Duplicates of each sample)
Table 8-3. Analytical Cost Detail*
Samples' yr~l
. 80
48
80/48
48
80/48
48
Cost (Si
1 Year
4,800
8,400
32,800
19,680
112,000
67,200
5 Years"
26,523
46,415
121,864
108,744
416,122
371,322
"Quarterly sampling of 4 wells; unless otherwise specified, 4 replicates plus field blanks and
field standards in duplicate for each analytical workup. Field determinations: pH, ft* and
alkaniinitv included in sampling costs.
""Calculated at a 5% annual increase in cost,
Table 8-4. Comparison of Reanalysis Cost with Cost "Savings" on Materials
Analytical
scheme
1
2
3A
3B
4 A
4B
Single sample
reanalysis cost
JS)
450
1050
2460
1640
8400
5600
Materials t
"ssvings"
(S)
1300
1300
1300
1300
1300
1300
Actual
"savings"
(S)
850
250
-1160
-340
-7100
-4300
TDifference between PVC versus stainless steel well construction materials
63
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Project Cost Comparisons for Selected Materials' Combinations
for Networks of Varying Analytical Detail
The example monitoring network has been developed as a general guide for
planning network design. Though the emphasis has been on well casing materials, the
methodology applies as well to the choice of materials for sampling gear or tubing. To
put the costs of total project implementation and well casing material in perspective,
it is a relatively simple matter to repeat the process for a specific case to complete the
cost/benefit analysis.
In Table 8-5, the approximate total project costs for the sample analytical
schemes and various well casing materials are presented. It is evident that the incremental
increases for more idea! (and costly) materials is far less than the increases incurred in
satisfying more involved analytical needs, On the basis of initial material costs, the
most expensive materials options, paired PVC/SS and Teflon®, make up a small
percentage of total project costs. One must carefully weigh the value of the information
needed versus the "insurance" value of making appropriate choices of materials which
may contact the samples. For long, term five-year project operations, stainless steel
clearly is the material of choice for minimal analytical schemes.
The selection of materials for pumps and tubing are important to both the
reliability and the cost/benefit considerations of ground-water monitoring programs.
They are somewhat less critical than materials for well construction since there are
few significant additional costs (e.g., drilling, mobilization, etc.) that must be included
as well, except in the case of dedicated samplers. The cost comparison can be made
in a similar fashion to that for well drilling and construction.
Table 8-5. Total Project Costs for Monitoring Programs
(S1.0K 1983 dollars rounded to nearest S0.5K)
including the Percentage of Materials Costs
1st Year 5 Years t
Mater/3/s
Analytical Scheme
1, Minimal Detective
% Increase over PVC
2. Minimal Interpretive
% Increase over PVC
3A. inorganic Interpretive
% increase over PVC
3B. inorganic Interpretive
% Increase over PVC
4A. Detailed Interpretive
% Increase over SS
4B. Detailed Interpretive
% Increase over SS
T5 year project costs calculated using yearly totals, including: 1% annual increases per year for maintenance on well installations
and 5% annual increases per year for supplies, sampling staff time and analytical services. IPVC/SS installations require twice
the maintenance effort and therefore exceed aM Teflon©costs after 5 years.)
MR _ Material is not recommended for use with a detailed.organic analytical scheme due to the likelihood of analytical bias
and imprecision,
PVC
14.5
18.0
42.5
30.0
122,0
MR
77.0
NR
SS
16.0
10
19.5
8
44.0
3
31.0
3
123.0
78.0
PVC/SS
22.0
38
25.5
42
50.0
17
37.0
23
129,0
5
84.0
8
Teflon®
22.5
i5
26.0
44
50.5
18
37.5
25
130.0
6
85.0
9
PVC
42.0
62.0
137.5
124.0
431.5
NR
387.0
MR
SS
43.5
4
• 63.0
2
139.0
1
125.0
1
433,0
<1
388.0
<1
PVC/SS
51.5
23
73,0
18
147.0
7
134.0
8
441.0
2
396
2
Teflon©
50.5
20
70.0
13
146.0
6
132,5
7
440.0
2
395.0
2
64'
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Tailoring the Monitoring Well and Sampling Apparatus
to the Anticipated Analytical Scheme
The successful planning of a monitoring program demands the consideration of
several factors: the ultimate goal of the monitoring program; the hydrologic conditions
of the site to be monitored; the sources of pollution and their chemical nature; the
quality of the ground water to be protected; the levels at which selected indicator and
specific monitoring parameters are to be analyzed; and appropriate cost-effective choices
of materials, drilling or sampling techniques.
Given these factors, preliminary decisions can be made concerning the location,
depth, physical features, and materials selection for the monitoring wells. Appropriate
drilling and well development techniques also must be selected. It is important to
maintain flexibility in this preliminary planning stage because the initial monitoring
plan may require revision as new information is collected during well construction.
Preliminary planning must be undertaken after consideration of the complexity of the
analytical scheme.
The objective in siting a monitoring well is to place the screened interval in the
predicted flow path of contaminant migration from the monitored site. Optimum
placement should allow for early detection of contamination to prevent a crisis situation
caused by the undetected migration of pollutants. Well construction materials should
be selected to minimize bias and interference with anticipated pollutants at the specified
levels of analysis. Careful attention should be given to possible expansion of the original
information needs of the monitoring effort.
The selection of sampling apparatus also should be. based on the proposed
analytes of interest and planned (as well as achievable) levels of detection. Sampling
devices should be selected so that neither their component materials nor their pumping
operation will significantly alter solution chemistry.
In the case of detective monitoring, consideration should be given lo the use of
the monitoring wells and sampling apparatus in a more rigorous interpretive monitoring
program. Upgrading wells and sampling devices in the early phases of monitoring may
save considerable time and expense later. Trying to save money by compromising on
materials quality or suitability in detective monitoring may eventually increase program
cost by causing reanalysis or triggering unwarranted interpretive monitoring. The
choice of appropriate robust materials and proven methods can provide significant
long-term benefits to a well-conceived program.
In summary, each monitoring program must be approached on the basis of its
own information needs and conditions. There are no standard monitoring approaches
that prove satisfactory for all sites. The multiple goals of monitoring projects, the
heterogeneity of geologic materials, temporal and spatial variability in chemistry and
hydrology, and the wide variety of chemicals to be monitored provide an unlimited
number of unique conditions that call for different approaches to monitoring. All of
these factors must be examined to determine the impact they may have on the reliability
of the analytical data as well as the long-term costs and benefits involved in obtaining
this information.
65
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SECTION 9
CONCLUSIONS
Ground-water monitoring is an important part of a reasoned resource manage-
ment and protection strategy. Monitoring programs include the modeling, planning,
analysis and interpretation of information on the subsurface environment of ground
water. These programs can be expensive as well as time consuming. However, with
careful planning of field efforts, the yield of high quality information will prove to be
invaluable to our understanding of the dynamics of ground-water systems,
Critical considerations for the design of monitoring networks are the selection
of drilling and sampling techniques in addition to the choice of materials which will
contact groundwater samples. With the knowledge of the principal chemical constituents
of interest, locai hydrogeology, and an appreciation of subsurface geochemistry, appro-
priate selections of materials, drilling, and sampling techniques can be made. Whenever
possible, physical disturbance and the amount of foreign material introduced into the
subsurface should be minimized.
The choices of drilling methods and materials for both well casing and sampling
apparatus are very important decisions to be made in 'every type of ground-water
monitoring program. Details of network construction can introduce significant bias
into monitoring data which frequently may be corrected only by repeating the process
of well siting, installation, completion, and development. This can be quite costly in
time, effort, money, and loss of information. Undue expense is avoidable if planning
decisions are made cautiously with an eye to the future.
Sampling techniques similarly should be tailored to the information needs and
goals of the monitoring efforts. If appropriate network design decisions are made, the
effect of sampling errors can be corrected before major 'decisions on expansion of the
monitoring goals are necessary.
The expanding scientific literature on subsurface phenomena and effective
ground-water monitoring techniques should be read and evaluated on a continuing
basis. This information alone will supplement published guidelines and suggestions for
application to specific monitoring efforts in the future.
66
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SECTION 10
RECOMMENDATIONS
General Recommendations
The Agency should focus its aid and technical assistance to state ground-water
management and protection efforts so as to encourage a degree of uniformity and
consistency in monitoring efforts. A central element of federal policy should include a
mechanism for the retrieval and interpretation of monitoring information which includes
detailed site-specific data,on network design, construction, and operation to minimize
the continued use of unreliable techniques or incompatible materials which result in
useless data collection. Of necessity, this must be conducted to protect source confi-
dentiality in some instances, but this requirement should not prove to be an impediment
to effective technology transfer.
Similarly, the claims of manufacturers or ground-water professionals concerning
the -integrity of materials, the reliability of specific designs or techniques, and the
performance of sampling equipment should be very carefully evaluated on a case by
case basis. The concerted attention of design, technical, and analytical staff should be
trained on each aspect of a ground-water monitoring effort before the implementation
of the network.
Specific Recommendations
Non-contaminating drilling methods are available to provide access holes to the
geologic formation of interest which need not be overly expensive or expose workers
to undue hazard even in badly contaminated situations. Well casings and screens should
be selected with the understanding that analytical requirements demand a* durable,
stable sampling point which can be relied upon to maintain the integrity of the in-situ
ground-water condition. Well casing and screen materials in decreasing order of
preference for most monitoring situations are:
Teflon®, stainless steel, and rigid threaded PVC
Commercially manufactured casing products are recommended over home-made
varieties. The choice of inappropriate, less expensive well casing/screen materials is
rarely cost-effective even in minimal" monitoring efforts with limited analytical detail.
Future contingencies and the cost of reanalysis can convert apparent "savings" into
real costs with a corresponding penalty in lost time, effort, and information. The
convenience of using PVC well casing or screens must be carefully considered in this
regard since the potential for biased analytical data clearly exists in detailed analytical
schemes.
The methods and materials involved in ground-water sampling are equally critical
to the collection of high quality monitoring 'information, Overreliance on simple,
traditional collection mechanisms (e.g., bailing) entails a serious potential for the
67
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continued collection of unreliable, poor data particularly where the analysis of volatile,
pH-sensitive, or reduced chemical constituents is of interest. Integral sampling methods
which minimize turbulence, atmospheric content, gas exchange, and depressurization
are preferable for these applications. Materials which contact water samples during
collection are no less critical than storage vessels. Recommended materials for pump
parts, tubing, and associated apparatus in 'decreasing order of preference are;
Teflon®, stainless steel, polypropylene, polyethylene, linear polyethylene,
Viton®, conventional polyethylene, PVC
Though other materials appear promising from the standpoint of structural
integrity and chemical resistance, there are very few hard data on which to recommend
their use in ground-water monitoring.
Ground-water monitoring is more complex and challenging than the collection
of reliable data-in natural surface waters. The lessons of past monitoring efforts clearly
demonstrate the need for multi-disciplinary inputs to planning ground-water investi-
gations. The input of both chemical professionals and laboratory personnel is essential
to a successful program.
The wise monitoring program director should attempt to consider carefully all
existing information on local well drilling practices, hydrogeology, and the potential
'impact of waste constituents on subsurface geochemistry prior to implementation of a
ground-water monitoring plan. In this way, maximal benefits will accrue from the
considerable outlay of funds, time, and effort involved in subsurface monitoring
activities. The most important result may be-that in the future1 we will be in a far
better position to effectively manage and protect our ground-water supplies.
68
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131. Hubbard, D. J., and C. E. A. Shanahan. 1973. Corrosion of Zinc and Steel in Dilute
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134. McGlothlin, R. E., and H. Krause. 1980. Water Based Drilling Fluids, pp. 30-37. In
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76
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78
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TECHNICAL REPORT DATA
(Please read Jaaructions on (he reverse before completing}
REPORT NO.
EPA-6QQ/2-84-Q24
3, RECIPIENT'S ACCESSlON>NO, _
PBS 4 i U 7 7 9
riTLE AMDSU8T1TLE
"A GUIDE TO THE SELECTION OF MATERIALS FOR MONITORING
WELL CONSTRUCTION AND GROUND-WATER SAMPLING"
5, REPORT DATE
January 1984
6, PERFORMING ORGANIZATION CODE
7 AUTHORiSI
8. PERFORMING ORGANIZATION REPORT NO
Michael J. Barcelona, James P. Glbb, and
Robin A. Miller
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Illinois State Water Survey •
Department of Energy and Natural Resources
Champaign, IL 61820
10. PROGRAM ELEMENT NO,
CBPC1A
11. CONTRACT/GRANT NO-
CR-809966
12. SPONSORING AGENCY NAME AND ADDRESS
Robert S. Kerr Environmental Research Lab.
U.S. Environmental Protection Agency
Post Office Box 1198
Ada, OK 74820
- Ada, OK
13. TYPE OF REPORT AND PERIOD COVERED
Interim (05/82 - 05/83)
14, SPONSORING AGENCY CODE
EPA/600/15
16. SUPPLEMENTARY NOTES
16. ABSTRACT
The project was initiated to supplement and update existing guidance
documents for effective, ground-water monitoring efforts. The areas of
primary concern were the potential sources of errors in chemical analyses
of subsurface samples caused by well construction and sampling materials,
techniques or procedures. A critical review of the literature was conducted
on various aspects of monitoring natural waters, materials' performance
data and unpublished information on the success of various ground-water
monitoring techniques. The results of the literature review were collected
and reviewed by a panel of experts from government agencies, private hydro-
logical consulting firms, the manufacturing industry and national standards
organization. The publication consists of a thorough discussion of ground-
water monitoring strategies, requirements and pitfalls. It concludes,with a
detailed treatment of the costs and benefits of recommended monitoring design
criteria.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS c, COSATI Field/Group
Hydrology
Ground water
Aquifers
Chemistry and analysis of pollutants
Control techniques and equipment
Monitoring well con-
struction
68 D
3, DISTRIBUTION STATEMENT
Release unlimited.
19. SECURITY CLASS (This Report)
Unclassified
20, SECURITY CLASS (This page)
Unclassified
EPA Form 2220-1 (S-73!
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