United States
Enyimmw itil Profoctxxi
^ancy
CERI-87-7
Research and Development
&ERA Ground-Water
Monitoring
Seminar Series
Technical Papers
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6ff\ (ouo
Table of Contents
Mi
I. Critical Elements in Site Characterizations 1-1
Regional and Facility Profiles 1-3
Hydrogeologic Considerations 1-19
Contaminant Behavior Variability 1-43
References 1-71
II. Monitoring System Design 2-1
Introduction 2-1
Indirect Methods for Characterizing Subsurface Migration . . 2-2
Direct Methods for Characterizing Subsurface Migration . . . 2-29
Monitoring System Design 2-46
Problems in Monitoring System Design 2-70
III. Monitoring System Installation 3-1
Contents 3-1
Introduction 3-2
Drilling Methods 3-3
Controlling Factors in Selecting a Drilling Method 3-15
Well Construction Materials 3-19
Well Development 3-27
List of Additional Reading Materials 3-29
IV. Sampling Strategies 4-1
Introduction 4-1
Negotiated Technology, Not Science 4-1
Examples from the Practice 4-4
References 4-8
V. Sample Analysis and Data Reduction 5-1
Sample Analysis and Quality Assurance 5-1
iS}
llliiiii iS LfRARV REGI°N 10 MATERIALS
RXO
0007C
74
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Table of Contents
(Continued)
Page
Appendix A:
Table: Monitoring Well Design Rating System A-l
Table: Drilling Method Rating System A-2
Selection of Drilling Method, Well Design and Sampling
Equipment for Wells to Monitor Organic Contamination . . . A-3
Small- vs. Large-Diameter Monitoring Wells A-10
An Evaluation of Nested Monitoring Well Systems A-14
Custom Designing of Monitoring Wells for Specific
Pollutants and Hydrogeologic Conditions A-32
Method to Avoid Ground-Water Mixing Between Two Aquifers
During Drilling and Well Completion Procedures A-39
Will My Monitoring Wells Survive Down There? Design and
Installation Techniques for Hazardous Waste Studies. . . . A-46
A Technique for Renovating Clogged Monitor Wells A-53
Appendix B:
An Example Prescriptive Groundwater Sampling Protocol
(No Immisciles) B-l
Appendix C:
Excerpt of the RCRA Ground-Water Monitoring Technical
Enforcement Guidance Document (1986) C-l
Appendix D:
Excerpt of the RCRA Ground-Water Monitoring Compliance
Order Guidance (1985) D-l
(J
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CRITICAL ELEMENTS IN
SITE CHARACTERIZATION
G.L. McKown
G.W. Dawson
C.J. English
ICF Technology, Inc.
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CRITICAL ELEMENTS IN SITE CHARACTERIZATION
To design and implement a ground-water protection program that assures
adequate protection of public health, welfare, and the environment, a great
deal of information should be known about the site, the facility located on
the site, and the setting of the site within physiographic and demographic
boundaries. The process by which information having a bearing on monitoring
system performance at a facility is collected, analyzed, and assimilated into
requirements for system design is termed site characterization. Elements of
site characterization include:
• Knowledge of how contamination arises, both from the facility and
from other sources within the region,
• Knowledge of how contamination moves, both locally and within the
region, and how the various transport systems interact, and
c Knowledge of how contamination impacts ground-water quality, as a
special subset of total impacts on health, welfare and the environ-
ment .
The universe of site characterization, then, includes modules describing:
• Sources of contamination,
• Pathways for transport, and
• Impacts and effects.
Detailed knowledge of these three elements, both on a local scale and on a
regional scale, would indicate that the universe is sufficiently well under-
stood that an adequate ground-water protection strategy can be devised.
The complexity of the(site characterization problem can be obtained by
referring to Exhibit 1, which denotes the variety of interactions affecting a
particular site study. Obviously, this document cannot address all of the
possible interactions between local and regional sources, transport pathways,
and potential adverse effects. In fact, the degree of detail necessary in
performing various elements of site characterization will depend on the parti-
cular objectives being pursued. For example, greater depths of knowledge
about the facility, the site, and the setting generally will be required in an
assessment monitoring case than for detection monitoring purposes. .More de-
tailed studies also will be required for:
• Complex facilities, involving multiple and varied waste management
units, waste streams, and constituents, and
• Complex settings, involving complex physiography or sensitive en-
vironments .
Rather than attempting a comprehensive discussion of site characterization,
the material presented below discusses elements of the site characterization
process that are considered critical to most ground-water protection problems.
1-1
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Exhibit 1
Universe of Site Characterization
REGIONAL SOURCES
LOCAL
SURFACE I
WATER
H
AIR
I
ro
ENVIRONMENT
SOIL
¦H-rft
H
GROUND WATER
HUMANS
PLANTS
ANIMALS
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1. REGIONAL AND LOCAL FACILITY PROFILES
A. REGIONAL CONDITIONS
A knowledge of the regional context of a facility is important for two
reasons:
4 Background levels of contaminants have an effect on the level of
ground-water protection necessary,
~ Changes in background levels must be known if observed changes in
monitored parameters are to be interpreted correctly.
Thus, it is necessary to understand major sources of contamination within the
region and the properties of the region that affect transport of contaminants.
(1) Regional Sources
Any description of a facility setting should begin with a discussion
of sources of both general and specific contaminants within the region. Gen-
eral contamination should be addressed because comprehensive analysis is nec-
essary in assessment monitoring and because of potential chemical interactions
with specific contaminants sought in detection monitoring. Thus, regional
profiles of contaminants other than those observed at a particular site should
be developed. For example, the presence of hydrocarbons from petroleum re-
fineries in the region surrounding a facility could have a significant effect
on the transport properties of organic waste constituents (see discussion of
facilitated transport below).
In addition to an inventory of industrial facilities and contaminants
found in a region, the following data should be developed:
• Maps of the site, in relation to other potential sources of
relevant contaminants,
Known or suspected contamination sources in the area other
than industrial facilities (waste handling and disposal facili
ties, CERCLA sites, etc.),
Regional contamination contour and ground-water maps according
to aquifer classification,
Natural sources of contamination, such as ore bodies and geo-
logic formations.
Location and contamination maps within a region should be prepared to
the same scale as geohydrologic maps. In areas where large amounts of data on
contamination are available, the variability over time of contaminant levels
should be analyzed. These analyses could have a significant impact on inter-
pretations of observed variability in parameters monitored at a specific
facility.
1-3
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(2) Regional Conditions
Knowledge of regional geohydrology is necessary for understanding how
ground-water systems originate (recharge), dynamically interact (flow), and
terminate (discharge). The regional flow will dictate the direction and vel-
ocity of contaminant transport in the background and in potential impact areas
of contamination from the site. In addition, the regional scale is essential
in determining recharge and discharge phenomena, which^play large roles in
ground-water contaminant concentrations. Also, details of the regional flow
system are necessary to properly evaluate the effects of other regional
sources on the ground water. For example, details of recharge, discharge, and
flow within the region would be required to assess the situation depicted in
Exhibit 2. Only by developing a thorough understanding of the regional system
(recharge, flux, water table, flow direction, flow velocity, source releases
and discharge) could one properly integrate local site observations into an
adequate ground-water protection strategy.
Regional considerations are particularly critical in cases where
natural or man-made flow-diverting structures have a large influence on
ground-water flow. Consider the case, shown in Exhibit 3, where a permeable
paleochannel diverts contamination arising from regional sources and prevents
their detection in the background wells for the site. The regional contamina-
tion plume, however, would be detected in the downgradient monitoring wells at
the site. Note that neither the flow direction at the site nor the general
regional flow pattern would predict this effect; detection of contamination in
the site monitoring wells would indict the site unless details of the diver-
sions in regional flow were known. Next, consider the same case except that
an artificial flow diversion mechanism (pumping well) has been added (Exhibit
4). The induced "regional" and site flow directions would indicate that the
original background and downgradient monitoring wells are now improperly lo-
cated. In this case, proper interpretation of contaminant profiles has been
increased in complexity.
An example of a complex flow diversion system that has been observed
is depicted in Exhibit 5. Large-diameter irrigation wells effectively divert
ground-water flow and contaminant migration during the period from May to
October, whereas the natural flow system controls migration during the winter
and spring. These effects, together with the highly permeable nature of the
aquifer, resulted in several effects:
• Greater diffusion of the contaminant plume,
• An effective lowering of plume velocity and contaminant con-
centrations ,
• Contaminant levels that were highly seasonally dependent,
• Need for dynamic (non-steady state) models, and
• Need for an exceedingly complex interception scheme for cor-
rective action.
1-4
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I
en
Exhibit 2
Influence of Regional Sources and Flow-I
RECHARGE
AREA
REGIONAL
SOURCES
BACKGROUND
WELL
LOCAL
SITE
MONITORING
WELL
V> A» idmi.l iThm^rrl*MU"fn"nrtiiii /i ¦iinykiwhr.'f.-w
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Exhibit 3
Influences of Regional Sources and Flow-ll
I
GENERAL
REGIONAL
FLOW
DIRECTION
PERMEABLE
PALEOCHANNEL
REGIONAL SOURCES
BACKGROUND
WELLS
GENERAL
SITE
FLOW
DIRECTION
SITE MONITORING
WELLS
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Exhibit 4
Influences of Regional Sources and Flow-
I
INDUCED
FLOW
DIRECTION
REGIONAL SOURCES
"72"'
PUMPING
WELL
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Exhibit 5
Influence of Irrigation Weils in Nebraska
(Simplified)
PLUME
WINTER
FLOW
DIRECTION
\
N
SUMMER
FLOW
DIRECTION
SOURCE
IRRIGATION WELLS
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The actual problem was considerably more complex than depicted because of the
presence of several hundred irrigation wells within the region of interest,
each of which was pumped intermittently.
(3) Summary
Regional sources and flow systems must be considered in developing
ground-water protection strategies at a site. There are a number of points
that are critical to consider:
• Sources and flow regimes should be described at least within
the drainage basin encompassing the site. Often, adjacent
drainage basins also must be addressed in developing an under-
standing of flow.
• Natural systems requiring considerable detail for proper
understanding include:
High-permeability formations and deposits (fracturing,
faulting, solution channels, paleochannels),
Variable interconnections of multiple aquifers,
Perched zones, and
Lakes and rivers (discharge vs. recharge),
• Manmade flow diversion can be created by numerous activities,
including:
Water supply and irrigation systems,
Dams and dikes,
Lakes and impoundments,
Injection wells, and
Corrective actions such as slurry walls and pumping wells.
• Regional chemistry should address parameters other than
specific indicator species at a site.
B. Local Facility Profiles
A great deal of information regarding the facility located at a site will
be necessary to develop ground-water protection strategies. Much of the in-
formation should be readily available from facility records, process descrip-
tions, and general geotechnical studies at a site. However, it is likely that
considerable data collection and analysis will be required especially for the
permitting process. Some of the critical needs for adequate site characteri-
zation purposes are described below.
(1) Waste Characterization
Both the chemical and physical properties of a waste greatly in-
fluence the magnitude of potential releases, transport, and ultimate adverse
1-9
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effects of contaminants. The general characteristics needed to describe ul-
timate effects, and other important parameters for.an assessment include:
• The total composition of wastes (not just indicator constitu-
ents) ,
• Form and phases (liquid, solid, slurry, solution, etc.), in-
cluding ancillary data such as percent solids, percent water
and/or other liquids, and mixed-solvent concentration ranges,
• Chemical composition of each phase, including normal and upset
concentration ranges,
• Percent organic carbon, if organic constituents are potential
contaminants,
• Density and viscosity, including the presence of phases or
stratigraphic variations,
• Quantities and generation/disposal rates within each waste
management unit (WMU) at a facility, and
• For treatment systems, the composition, quantity, and flow
rate of influent, effluent, and in-process materials should be
known.
(2) Facility Characteristics
Facility characteristics include those physical systems at a site
which might influence the release and transport of contaminants. Waste hand-
ling, treatment, storage, and disposal systems must be described in enough
detail that such influences can be quantified. Aspects which are critical to
the ultimate ground-water protection strategy include:
• Engineering design of each facility and a description of com-
plete facility operation,
• Geotechnical considerations such as soil type, structure, and
recharge potential,
• Degree of containment within each WMU; calculation of failure
modes, failure rates, and release estimates during the life of
the facility,
• Siting of WMU's at a facility: topographic influences, drain-
age control, secondary containment, etc.,
• Influence with and relationship between other facilities and
operations at a site,
1-10
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• Influence of past facility and site activities and operations;
history of past waste treatment, storage, and disposal opera
tions, including quantities, rates, compositions, previous cor-
rective actions, process changes, etc., and
• An analysis of current and future corrective actions required
at the site.
In many cases, a fairly complete history of activities at a site may
need to be developed. For example, at one facility the historical input load-
ing of wastes to impoundments was a critical part of analyzing observed
ground-water contamination. It was known that wastes had been disposed in
several impoundments at the site over the past 40 years, although quantities
had not been recorded. To provide input into a contaminant transport model
used to analyze current contamination, future effects, and the benefits of
various corrective actions, a detailed history of the disposal activities was
developed, as follows:
• Current production rates of wastes were determined, according
to the processes used at the site,
• Past annual production rates of wastes were estimated by com-
paring current'and past annual product outputs, taking into
consideration known changes in processes and waste handling
methods,
• The history of active impoundments at the site was recon-
structed from aerial photographs; allocations of wastes to
simultaneously-active impoundments were made on the basis of
size and other factors such as accessibility and magnitude of
activity evident in the photographs, and
• The annual input loading to each of several impoundments was
derived and used in the subsequent modeling effort.
The complexity of facility design and operation analyses will depend
on the type, number, and location of other activities at the site. For
example, a permit application is being developed for a new landfill at a site
where corrective actions are underway at adjacent older landfills. Site char-
acterization performed prior to establishing design requirements for the new
landfill included:
• Evaluation of failure rates of the older landfills as a func-
tion of design,
• Estimates of failure rates for the proposed facility, as a
function of design alternatives,
• Influence of current (pre-corrective action) and future
(post-corrective action) ground-water contamination on the oper-
ation of a detection monitoring system,
1-11
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• Assessment of total risk, and added risk from a new landfill,
afforded by the site, and
• Influence of alternative corrective actions at the older land-
fills, in the event the current action fails, on design and
monitoring requirements.
In summary, a complete description and detailed engineering analysis
including the combined effect of multiple operations will be necessary for
each facility. The complexity of the problem and, therefore, the amount'of
needed detective work, will be increased several-fold if the site has a his-
tory of operations that could affect the current or future situation.
C. Use of Conceptual Models in Site Characterization
Models, being "cartoons of reality," are depictions of a problem which are
simple enough that the problem is tractable, yet contain enough detail that
all important aspects are included. A conceptual model of a facility is a
visual or verbal representation that summarizes essential site characteristics
without unnecessarily burdening the beholder with details. The complexity
needed in a conceptual model depends both on the complexity of the system
being modeled and on the aspects of the problem that must be understood. For
example, the conceptual model, "Atoms are miniature billiard balls," may be
perfectly adequate for understanding simple gaseous diffusion, but it would
not be sufficient for interpreting UV-visible spectra. In the latter case, a
somewhat more complex model, "Atoms are miniature solar systems," may be suf-
ficient. Neither conceptual model, however, would be an appropriate represen-
tation of, say, semiconductor operation or DNA molecular reproduction.
Conceptual models of a site should be developed at each stage of site
characterization. An initial conceptual model of the site should be formed in
response to the question: "What might I expect to find at this site?" As the
description of facility, waste, and other site characteristics unfolds, the
model can be "tested" against the observations and conclusions, which will
show either a good fit with the model or discrepancies that require further
exploration and/or more complex models. Once a site has been well-character-
ized, the conceptual model should at least qualitatively represent observa-
tions and expectations.
Shown in Exhibit 6 is a preliminary conceptual model of a site. Ob-
viously, not every rock, sand grain, water molecule, and waste constituent is
shown, but the rudimentary characteristics of ground-water flow, geologic
fabric, and contaminant transport are represented. This model was used to
develop an initial monitoring system concept. The bases for the model were:
.• Inferred regional flow from topography and limited regional
measurements,
0 General geologic descriptions in the vicinity,
• Expected contaminant migration through glacial till and in the
aquifer, and
1-12
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Exhibit 6
Simple Conceptual Model
llllllilMMMMM—a—B——¦BBH—¦
AQUIFER 1
PLUME
: AQUITARD
<<( rr
AQUIFER 2
SOB
-------
• Typical transmissive properties of regional geologic forma-
tions .
Following initial site characterization efforts, a more complex conceptual
model was both necessary and possible, as shown in Exhibit 7. This concept
provided a summary of observed phenomena and served as a guide for subsequent
investigations.
D. Mathematical Models
In many cases, the complexity of a site cannot be adequately represented
by visual or verbal conceptualizations. In many cases where a more quantita-
tive analysis is required, mathematical treatments are necessary. Although
simple cases of flow and contaminant transport can be solved analytically,
mathematical models and approximate solutions are needed to address most prac-
tical situations. For detailed descriptions of flow and contaminant movement,
it is essentially impossible to "keep in mind" all of the minutae that in-
fluence the results, without the aid of computer models. Although hydrolo-
gists generally do a good job of digesting facts and understanding gross fea-
tures of a hydrologic system, they rend to integrate linearly and (often)
irreversibly and irreproducibly. Consequently, results often contain large,
hidden uncertainties, which can lead to erroneous conclusions and corrective
action strategy development.
On the other hand, sophisticated mathematical models tend to demand large
quantities of site characterization data. If sites are quite complex, the
mathematical constructs and data input requirements can be exceedingly com-
plex. For example, a hydrologist's conceptual model of a complex site is
shown in Exhibit 8, and the finite-element grid (for one of three layers) that
was required in the mathematical model of the site is shown in Exhibit 9.
Obviously, a great deal of effort was required to properly characterize this
site.
E. Data Needs and Data Uncertainties
Characterization of a site, especially one of moderate-to-high complexity,
tends to be a phased process in which the following approach is carried
through several iterations:
• Develop a conceptual model of the site,
• Conduct field investigations to confirm or refute the model, and
• Discover discrepancies between model and data, forcing considera-
tion of more complex conceptualizations.
Only rarely and for very simple sites are all expectations fulfilled by a
single round of studies. In general, a single investigation, the results of
which completely support a conceptualization, is suspect as the basis for
designing a ground-water protection strategy. At a minimum, a discussion of
uncertainties and discrepancies in the data should be performed. Any devia-
tion between observations and expectations based on the conceptual model or
1-14
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r-*
&
e*"cePwa
CO^°
2
-------
Exhibit 8
Conceptual Model of a Complex Site
TRENCH AREA
LASER RANGE WATER TANK
SEWAGE TEST TRACK
POWER TREATMENT
SUBSTATION
METAL PLATING
FACILITY
IWTP
MAIN DIVERSION
CHANNEL
LAYER 1
RESIDUUM
WILCOX AGE
ALLUVIUM
MAIN DIVERSION
CHANNEL
LAYER 2
GRANULAR
POROUS MEDIA
CATFISH
POND
LAYER 4
IMPERMEABLE
UNWEATHERED
BEDROCK
LAYER 3
WEATHERED
DOLOMITE
BEDROCK
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Exhibit 9
Finite Element Model Grid
1-17
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the mathematical model should be listed and explained fully. Weaknesses in
the conceptualization or the mathematical treatment should be discussed.
In addition to a qualitative analysis based on expected source and flow
behavior, one of the best techniques for analyzing a set of site characteris-
tic data is by multivariate statistical analysis. For example, the techniques
of kriging provide an estimate of the spatial variation in data, and an esti-
mate of how uncertainties vary over space, without introducing biases or
theories of the observer into the analysis. A kriging analysis evaluates the
amount of information present in the data itself. For example, consider the
case of plotting poteniiomctric contours from water level measurements. Any
hydrologist can draw such maps by connecting points, estimating how the data
would vary between observations, and generally producing an accurate repre-
sentation of the hydrologic regime. However, a great deal of subjectivity
goes into even the simplest of contour plotting.
Two features of the problem contribute to the uncertainty, largely in an
unknown manner:
• Reliance on the hydrologist's conceptualization, which is a quali-
tative feature that varies with the particular observer, and
• Reliance on understanding all essential aspects of the hydrologic
situation. One assumes there are no "hidden" features that make the
potentiometric surface behave in an unusual manner.
Presumably, an estimate of the uncertainties could be obtained by having a
large number of hydrologists independently plot the contour maps, and then
analyze the differences among the results. However, this type of analysis is
seldom feasible.
Kriging is an analytical method that eliminates these two problem areas by
considering the variability in the data set alone. Variability in data is
considered to arise from two effects: differences owing to the manner in which
the physical system varies over space (systematic variability), and differ-
ences owing to improper representations and measurements (random variabil-
ity) . The relationship between each data point and its neighbors is con-
sidered in terms of these two elements, and the set of variations is described
mathematically and analyzed statistically. In addition to producing "best"
plots of the data, the method also provides maps of uncertainties in the
data. Examples of kriging analysis outputs are shown in Exhibit 10.
Any differences between contour maps produced by kriging and the hydro-
geologist generally will be due to measurement errors or misconceptualization
(or improperly applied statistics; hydrogeologists are not always wrong!).
There is a real value in hydrologists and statisticians working together to
resolve discrepancies and arrive at an understanding of site characteristics.
Exhibit 11 depicts a potentiometric surface produced by a hydrologist which
summarizes the results of a year-long site study. Exhibit 12 shows the re-
sults of kriging the data. In this case, the kriging analysis indicated the
presence of an unknown and unusual formation that governed ground-water flow
in the lower left portion of the figure, a situation which was confirmed sub-
sequently. This formation severely impacted the three-dimensional model of
1-18
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the site characteristics and the establishment of a corrective action at this
location.
A kriging analysis can provide several benefits to processing and inter-
pretation of site characterization data. It can:
• Identify the need for additional field measurements,
• Establish the validity of existing data,
• Produce "best fit" contour plots, digitized data surfaces, and
uncertainty maps, and
• Allow selection of additional measurements to reduce uncertainties
to the greatest extent.
F. Methods For Collecting Needed Data
Once data needs have been established, appropriate methods for collection
of the necessary information should be identified. Exhibits 13 through 19 are
typical types of data that may be needed, some of the most important uses of
the data, and typical means by which these data are acquired. Not all of
these data may be necessary in any given instance, but much of the information
is critical to developing an adequate ground-water protection strategy. The
next section discusses some of the more relevant information relating to
hydrogeologic settings and ground-water impacts.
2. HYDROGEOLOGIC SETTINGS, SUBSURFACE HYDRAULICS, AND
GROUND-WATER QUALITY IMPACTS
The process of characterizing a site sufficiently to resolve the placement
and/or performance of a monitoring well is a complex, time-dependent study
requiring application of numerous laws of physics, chemistry, and hydro-
dynamics. For exact treatment, many of the phenomena require application of
second-order differential equations relating mass, energy or momentum, space,
and time. One result of this complexity is that all but the simplest systems
cannot be solved analytically. Therefore, approximations and simplifications
are needed for all practical problems.
Fortunately, simplifications of the problem exist. However, under the
combined effect of all the interactive processes, the problem may remain quite
complex. A simplified view of the three basic processes is provided in Ex-
hibit 20, which shows the context of the three essential time-dependent steps
of contaminant release, transport through the unsaturated zone, and transport
within the saturated zone. This Section focuses on critical aspects of flow
and transport phenomena as they impact on ground-water quality and monitoring
system design.
A. BASIC PRINCIPLES OF DARCIAN FLOW
Essential differences exist between flow of water in a surface stream and
in an aquifer. Whereas stream flow is a turbulent process, ground water flows
in essentially a laminar fashion. That is, flow is described by essentially
1-19
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Exhibit 10
Kriging Outputs
POTENTIAL SURFACE
ERROR
60
12
87Q,
SITE
>850
SITE
12,
'880
14
840,
18
840
880
20
-------
Exhibit 11
Hand-Drawn Potentiometric Surface
194
196
198
197*
196"
'19
194
192
188
18S
184
300
METERS
FEET
900
1-21
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Exhibit 12
Kriged Potentiometric Surface
V
METERS
300
FEET
900
1-22
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EXHIBIT 13
WASTE AND FACILITY INFORMATION
Information Needed
Waste Characteristics:
Type
r orm
Quantities
Chemical and
Physical Properties
Concentrations
Facility Characteristics:
Type of Waste/
Chemical Containment
Integrity of Waste/
Chemical Containment
Drainage Control
Engineered
Structures
Site Security
Known Discharge
Points (Outfalls,
Stack?.)
Purpose or Rationale Collection Method
Determine physical/
chemical/toxicological
properties
Determine physical/
chemical properties
Determine magnitude of
potential releases
Determine environmental
mobility, persistence,
and effects
Site history, waste
manifests, sampling
Site history, sampling
Site inspection
Handbooks, laboratory
analysis
Determine quantities and Site history, sampling
concentrations potentially
released to environmental
pathways
Determine potential re-
lease modes, magnitude of
potential releases
Determine probability of
release
Determine probability of
release to surface
water
Site inspection,
remote sensing
Site inspection, non
destructive testing
Site inspection
Provide possible conduits Site inspection
for release to environ-
ment
Determine potential for Site inspection
release by direct contact
Provide points for acci- Site inspection
dental or intentional
discharge
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EXHIBIT 1.4
GEOLOGIC INFORMATION
Information Needed
Purpose or Rationale
Collection Methods
Structural Features:
Folds, Faults
Joints, Fractures,
Interconnected Voids,
Solution Channels
Delineate barriers or ,
ground-water flow controls
and recharge/discharge
areas
Predict major boundaries,
avenues of ground-water
flow
Existing geologic maps,
field mapping, surface
and subsurface geophys-
ical techniques,
drilling, coring, and
sampling boreholes
Stratigraphic Characteristics:
Thickness, Aerial Ex- Determine geometry of
tent, and Correlation aquifers and confining
of Units layers, aquifer recharge
and discharge
Mineral Composition,
Gram-Size Distribu-
tion, In-Situ Density,
and Moisture Content
Determine ground-water
quality, movement, occur
rence, productivity, and
extent (horizontal and
vertical) of aquifers
and confining units
Existing geologic maps,
field mapping, surface
and subsurface geophys-
ical techniques,
drilling, coring, and
sampling boreholes
Laboratory analysis of
field samples obtained
from boreholes, and
existing literature
1-24
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EXHIBIT 15
HYDROLOGIC INFORMATION
Information Needed
Purpose or Rationale
Collection Methods
Ground-water Occurrence:
Aquifer Boundaries
and Locations
Aquifer Ability to
Transmit Water
Define, flow limits and
potential recharge/dis-
charge areas, degree of
confinement
Delineate the potential
quantities and rate of
contaminant transport and
feasibility of remedial
actions
Stratigraphy and struc-
ture data from well
logs, water level mea-
surements in monitor
wells and piezometers
Pumping and injection
tests of monitoring
wells
Ground water Movement:
Direction of Flow
Rate of Flow
Identify pathways of
contaminant migration
Determine maximum poten-
tial migration rate and
dispersion of contaminants
Water level measure-
ments in monitoring
wells
Hydraulic gradient,
permeability, and
effective porosity
from water level con-
tours, pump test re-
sults, and laboratory
analyses
Ground-water Recharge/Discharge:
Location of Recharge/
Discharge Areas
Rate
Delineate areas of water
inflow and outflow in the
ground water system which
is important to contami-
nant movement
Calculate unit volume
of water moving through
aquifer(s)
Compare water levels in
monitoring wells,
piezometers, lakes and
streams
Water balance calcula-
tions aided by geology
and soil data
Ground-water Quality:
pH, Total Dissolved
Solids, Dissolved Or-
ganics, Salinity,
Specific Contaminant
concentrations
Determines if aquifer is a Analysis of groundwater
potential or actual drink- samples from monitoring
ing water source, may help wells
define contaminant plume(s)
1-25
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EXHIBIT 16
SURFACE WATER INFORMATION
Information Needed
Purpose or Rationale
Collection Methods
Drainage Patterns:
Over]and Flow, Topo-
graphy, Channel Flow
Pattern, Tributary
Relationships
Determine if overland or
channel flow can result
in on-site or off-site
flow, and if patterns
form contaminant pathways
Topographic maps,
aerial photographs, and
site visits
Surface Water Bodies:
Flow, Stream Widths
and Depths, Channel
Elevations, Flooding
Tendencies
Determine volume and
velocity, transport
times, dilution potential,
and potential spread of
contamination
Public agency data
catalogs, maps and
handbook for background
data, perform field
studies for site-
specific areas
Structures
Determine if manmade
structures affect contam-
nant transport
Public agency maps and
records
Surface Water/Ground-
water Relationships
Establish areas of 'losing
and "gaining" surface
waters to predict contami-
nants pathways and deter-
mine remedial action
Public agency reports
and surveys
Surface Water Quality:
pH, Temperature, Total
Suspended Solids, Sus-
pended Sediment, Dis-
solved Organics,
Nutrients, Salinity,
Tubidity, Specific
Contaminant Concentra-
tions
Provide a baseline and in-
formation on the capacity
of the waterway to carry
contaminants
Public agency (pri-
marily Federal) data
storage systems, and
handbooks
1-26
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EXHIBIT' 17
GEOCHEMICAL ANDSOILS INFORMATION
Information Needed
Soil Characteristics:
Purpose or Rationale
Collection Methods
Type, Holding Capacity, Estimate the effect of the Reports and maps by
Temperature, Chemical
and Sorpt:ve Proper-
ties, Biological
Activity, Engineering
Propert ies
properties on infiltration
and retardation of leach-
ates and the release of
gaseous contaminants
Federal and county
agencies, primarily
the Soil Conservation
Service (SCS)
Unsaturated Zone Characteristics:
Permeability, Varia-
bility, Porosity,
Moisture Content,
Chemical Character-
istics, and Extent of
Contamination
Estimate of leachate
transport which is sensi-
tive to the physical and
chemical properties of the
host media
Existing literature,
primarily SCS, bore-
hole logs, geophysi-
cal surveys
Soil Chemistry Characteristics:
Solubility, Ion
Speciation, Adsorption
Coefficients, Leach-
ability, Exchange
Capacity, Mineral
Content, Partition
Coefficients
Predict contaminant
movement through soils,
and availability of con-
taminants to biological
systems
Chemical'analysis, col-
umn experiments, leach-
ing tests
1-27
-------
EXHIBIT 18
ATMOSPHERIC INFORMATION
Information Needed
Local Climate Trends:
Precipitation
Temperature
Wind Speed and
Direction
Cloud Cover and
Solar Radiation
Presence of Inversion
Layers
Weather Extremes:
Storms
Floods
Winds
Hazardous Air Pollutants
Release Characteristics
of Air Pollutants:
Direction and Speed
of Plume Movement
Rate, Amount, and
Temperature of
Release
Nature of
Contaminant
Relative Densities
Purpose or Rationale Collection Methods
Define important pathways
for transport by defining
recharge, Aeolian erosion,
and evaporation potential
Weather patterns will
affect hydrology
-National Climate Center
(NCC) of National
Oceanic Atmospheric
Administration, local
weather bureaus
•Evaluate potential for
and consequences of
weather extremes
NCC, State Emergency
Planning Offices
Concentrations of hazard-
ous pollutants indicate
potential pathways of
transport and form a base-
line for monitoring
Local Air-Monitoring
station, EPA reports,
and data bases
Characterize the plume
movement and the popu-
lation it will affect
Release facility,
weather services, and
direct measurement
1-28
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EXHIBIT 19
ENVIRONMENTAL AND HEALTH INFORMATION
Purpose or Rationale
Determine presence of
plants and animals that
may be consumed by man;
Determine presence of
endangered species
Information Needed
Fauna and Flora
Critical Habitats
Land-Use Character-
istics
Water-Use Character-
istics
Water-Wells
Human Density
Determine if there are
areas on or near the site
that must be protected
Determine if terrestrial
environment could result
in human utilization of
land; e.g., presence of
game animals, agricultural
land
Determine if aquatic en-
vironment on or near site
could result in human
utilization of water; e.g.
presence of game fish,
recreational waters
Collection Methods
Public records of area
plants and animals
Survey of plants and
animals on or near site
Public records of site
environment
Survey of site
Ara maps and survey
of site
Area maps and survey
of site
Public records and
site survey
Maps and site
survey, EPA data bases,
census data
Health impacts
Human health risks
1-29
-------
Exhibit 20
Flow and Transport Characteristics
INFILTRATION
FLOW
TRANSPORT
DISCHARGE
-------
straight lines Cat. least over short distances). The basic empirical relation
describing flow is Darcy's law, which may be written in terms of flux (V) as:
V = K Ah/AX
where: K = hydraulic conductivity
h = hydraulic head
X = distance of flow path.
Thus, Ah/AX = hydraulic gradient.
Also, K = k d g
U
where: k = permeability,
d = density,
y = viscosity, and
g = acceleration due to gravity.
Finally, the flow velocity v /is given by:
v = V/n
where: n = porosity = volume of voids/total volume.
Almost all flow problems car: be solved using one or more variations of
Darcy's law, if the various factors can be measured or predicted. Some prac-
tical aspects of the most important terms are as follows:
Hydraulic conductivity. K, is the proportionality constant relat-
ing hydraulic gradient to flux. It is a measure of the ease with
which fluids will pass through a formation and, thus, is dependent
both on the fluid and the formation properties. Permeability, k, on
the other hand, is a property only of the formation. Transmissivity,
for a confined aquifer, is the hydraulic conductivity times the aqui-
fer thickness. Exhibit 21 shows how hydraulic conductivity may vary
for flow of water through various formations.
Porosity, n, as the ratio of pore volume to total volume, is
actually the bulk porosity of the formation. However, not all
pores in a formation are involved in the transport of water. The
effective porosity represents the fraction through which water can
pass; i.e., it is the "drainable" porosity. Materials may have a
high bulk porosity but very low effective porosity and permeability
if the pores are not connected. Fractured formations may have low
porosity but high permeability.
The principal driving force behind ground-water flow is the hy-
draulic gradient, or the difference in hydraulic head per unit dis-
tance. Head is the force exerted on a water molecule by gravity and
other more complex factors. The hydraulic gradient is a vector
quantity and affects both the magnitude and direction of ground-water
f ] ow.
1-31
-------
EXHIBIT 21
Aquifer Hydraulic Conductivity Variations
GO
ro
Generic
Classification
Fractured crystalline
silicates
Fractured-solutioned
carbonates
Porous consolidated
carbonates
Porous consolidated
silicates
Porous unconsolidated
silicates
Fractured consolidated
silicates-shale
Data Range
in Orders
of Magnitude
3.0
4.0
4.6
3.0
5.9
4.0
Mean
Value, cm/s
1.53 x 10 3
6.42 x 10
-2
1.16 x 10 -2
1.79 x 10 3
5.55x10
-2
2.4 x 10 3
-------
• The flux, V, is the quantity of water flowing through a formation
per unit cross-sectional area. Flux differs from the flow velocity,
v, because the formation is not totally porous.
° The potentiometric surface is a map of the hydraulic head in a
confined aquifer. The water table is the elevation where fluid
pressure equals atmospheric pressure, in the uppermost aquifer.
Analysis of flow using these concepts assumes that flow is completely
horizontal. It is preferable to analyze flow using equipotential
surfaces (and lines, for cross-sections). Flowlines are perpendicu-
lar to equipotential surfaces. The resulting diagrams are called
flow nets. Flow-net analysis requires that the hydraulic head be
mapped or estimated throughout the subsurface volume of interest.
B. MEASUREMENT OF HYDROLOGIC PARAMETERS
Even the simplest of ground-water systems requires either measurement or
estimation of hydraulic gradient, hydraulic conductivity or permeability, and
porosity. Of these parameters, only porosity varies over a narrow enough
range to be estimated reasonably accurately; estimates from literature values
likely will not vary more than 50 percent from actual values. About the only
precise method for measuring porosity is by use of tracers in iri situ mea-
surements. However, measurements of reasonable accuracy can be made in the
laboratory.
The hydraulic conductivity can vary over about 12 orders of magnitude and
typically can vary over 2 to A orders of magnitude at any given site. In
fact, the hydraulic conductivity will vary greatly depending on the exact
location and the manner in which it is determined. Generally, K is determined
by well testing, either by slug tests or, more accurately, by pump tests.
Models and equations exist for relating the actual field measurements (draw-
down, water level rise and fall) to conductivity or permeability. However,
considerable uncertainties may exist even under the best of circumstances, for
the following reasons:
• Data analysis methods are based on theoretical conditions which may
not prevail at the point of measurement (improper selection of ana-
lytical methodology),
8 Derived conductivities are valid only within the vicinity of the
measurements and may vary widely across a site (sampling error too
large), or
• Derived hydraulic conductivities may depend on the method of drill-
ing and installing wells (uncertainties in the actual property being
measured).
As an example. Exhibit 22 shows the range of transmissivities obtained
from well tests at the same site. It is noted that the reported values vary
by about four orders of magnitude, and there is a statistical difference be-
tween the two methods of well installation. Other observations from this
experience include:
1-33
-------
Exhibit 22
Transmissivity Distribution for Rotary Wash and
Air Drilled Wells
a>
ra
>
10
8
s
c
& 6
ac
- 4
£
E
3
z
Mode (Wash)
\
P
ft
raw
;*X*X
m
Mean (Wash)
\
to JL
Rotary Wash
~ Air Rotary
Mode (Air)
1.
te.
m
II
22E
/
Mean (Air)
P
I,
«*:
i
JZL
10
10
10
10"
10
Transmissivity (m2/day)
-------
• Wei] tests in large-diameter wells generally provide more con-
sistent data,
• Longer-duration tests generally provide more representative data,
• Wells drilled by air rotary methods provide better data than those
drilled by mud rotary techniques, and
• Pump testing is preferable to slug testing because a greater por-
tion of the subsurface is tested, and the measurements are more con-
trollable.
Hydraulic gradients are obtained by mapping hydraulic head (water levels
in monitoring wells) across an area or region. The gradient, or the slope of
these surfaces, is a valid concept only if the measurements are time equiva-
lent and stratigraphically equivalent.
C. HYDROGEOLOGIC SETTINGS; FACTORS AFFECTING GROUND-WATER
OCCURRENCE AND FLOW
A hvarogGologic setting is a composite description of major geologic and
hydrologic factors which affect and control the occurrence and movement of
ground water. In simple terms, a hydrogeologic setting is a mappable unit
with common hydrogeologic characteristics. The setting provides a reasonable
ini- tial conceptual model of a region.
A number of physical characteristics affect the movement of water into,
through, and from an area. The major controlling features, for which data
must be available in order to analyze ground-water problems, are:
• Geologic structure, or the occurrence of formations and strata
which can either hold and transmit water, or which can act as aqui-
tards, is a key controlling factor. Grain size and fracturing affect
the porosity, slope can affect the hydraulic gradient, and mineral
content can affect ground-water quality.
• Recharge is the input of water to an aquifer. The primary source
of ground water is precipitation which infiltrates through the sur-
face of the ground and percolates to the water table. Net recharge
indicates the amount of water per unit area of land which penetrates
the ground surface and reaches the water table. This recharge water
is thus available to transport a contaminant vertically to the water
table and horizontally within the aquifer. In addition, the quantity
of water available for dispersion and dilution in the vadose zone and
in the saturated zone is controlled by this parameter. Recharge
generally occurs more readily in areas with unconfined aquifers than
in areas with confined aquifers. A secondary source of recharge is
the infiltration of water from surface streams.
• Discharge from an aquifer can occur to other aquifers or to the
surface in springs, seeps, or streams. The location of discharge
points and estimates of the discharge rate are important to an analy-
sis of flow problems.
1-35
-------
• The topography, or thp. slope of the land at a site, is useful in
estimating ground-water flow. Gradient and direction of ground-water
flow can often be inferred for the water table aquifer from the gen-
eral slope of the land. Typically, steeper slopes signify higher
ground-water velocity. Topography also influences soil development
and, hence, affects contaminant attenuation and is a key controlling
factor in determining runoff versus recharge.
• Depth to ground water is the depth to the water surface in an
unconfined aquifer or to the top of the aquifer where the aquifer is
confined. The water surface is the point where all the pore spaces
are filled with water. As shown in Exhibit 23, the depth to water
determines the depth of material through which a contaminant must
travel before reaching the aquifer.
D. NATURAL FACTORS AFFECTING WATER QUALITY
In addition to other human activities in a region, a variety of naturally-
occurring phenomena can affect the quality of ground water at a site. Those
factors which are especially important in establishment of ground-water moni-
toring programs are:
• Dissolved Inorganic Constituents. Principal constituents include
bicarbonate, silicates, chloride, sulfate, sodium, magnesium and
calcium ions, and carbon dioxide, but hundreds of potential contami-
nant species are possible. These materials may be leached from geo-
logic formations or introduced by infiltration of water from the •
surface. Key parameters describing the dissolved species (in addi-
tion to specific analyses) are the total hardness, total alkalinity,
and total dissolved oxygen. In addition to including many regulated
contaminant species, dissolved inorganic materials affect the pH,
redox potential, and ionic strength of ground water, all key param-
eters in evaluating contaminant transport.
• Dissolved Gases. The most important dissolved gases are oxygen,
carbon dioxide, methane, and hydrogen sulfide. These gases are indi-
cators of geochemical conditions (e.g., redox potential) in the
ground water.
• Dissolved Minerals. Ground water in the vicinity of ore bodies
can leach significant quantities of iron, arsenic, lead and other
contaminant species. These contaminants are generally setting-
specific .
• Dissolved Organics. Organic materials, principally fulvic and
humic acids and other products of bacterial action and decay (includ-
ing hydrocarbons), may be found in trace to significant quantities in
ground water. These species may play a key role in complexing and
solubilizing inorganic constituents. At a minimum, the total organic
carbon content of the ground water should be specified.
1-36
-------
Exhibit 23
Depth to Water in a Confined and
Unconfined Aquifer
TO
uifer
UNOONrlNtu Auuirtrt i--&\ *?¦:£¦¦?¦$
Hir'Pi- -v-v'^ov»C*:«.v»'¦;«•''*"• >•;:..-'•'~r v> i-ii¦•• <:•-} ¦ • '¦¦¦ ^ri'-V-j"''^'v,>''.-¦•v* * >r.'-¦;: •¦:,» * - \"-'« >>' - m^v,y
CONFINING LAYER
-------
Natural factors can affect the chemical nature of ground water as a medium
for dissolution and transport of contaminants, as well as the utility of the
water for consumption, recreational and agricultural purposes. For example,
streams and shallow ground water in some regions of Colorado are highly acidic
(pH = A), making it unfit for consumption and a good leaching medium (better
than the Toxicity Characteristic Leaching Procedure) for hazardous constitu-
ents from minerals. Similarly, ground water may be high in alkali (southwest
U.S.), organic matter and sulfur (Louisiana), iron and sulfur (Ohio Valley),
or various carbonates (Blue Ridge region).
E. GROUND-WATER FLOW SYSTEMS IN VARIOUS HYDROGEOLOGIC
SETTINGS
Various classification schemes have been developed to describe the occur-
rence and availability of ground water. Among the most useful of these are
geographic systems encompassing hydrogeologic settings, such as the classical
regional system shown in Exhibit 24. Example descriptions of flow regimes in
some of these regions are described below.
Region 3. Columbia Lava Plateau (Exhibit 25)
This region occupies northeastern California, eastern Washington,
southern Idaho, and northern Nevada. This area is underlain by a thick se-
quence of lava flows interbedded with unconsolidated deposits and is overlain
by thin soils.
Depth to the ground water generally ranges from 5 feet to 100 feet
with an average around 50 feet. The large sequence of lava flows is the prin-
cipal water-bearing unit. Movement of ground water occurs primarily through
the interflow zones. Hydraulic conductivity commonly ranges from 200 to 3,000
m/day. The recharge rate ranges from 5 to 300 mm/yr (0.2 to 10 in/yr) with
recharge occurring through losing streams and discharge occurring through
springs and seepage. Topography of the plateau ranges from 2 percent to 18
percent with an average of 5 percent.
Region 6. Nonglaciated Central Region (Exhibit 26)
The geographical area of this region extends from the Appalachian
Mountains in the east to the Rocky Mountains in the west. The topography is
complex, ranging from valleys and ridges to the Great Plains. The surface is
mostly underlain by thin regolith over fractured sedimentary rocks. Ground
water is obtained primarily from fractures in the bedrock. Depth to the
ground water ranges from 5 feet to 100 feet with an average of approximately
30 feet. Hydraulic conductivity commonly ranges from 3 to 300 m/day. The
recharge rate ranges from 5 to 500 mm/yr (0.2 to 20 in/yr) with recharge
occurring upland between streams and discharge occurring through springs and
into other aquifers. The topography of this region ranges from 0 to 12 per-
cent with an average of approximately 6 percent.
Region 8. Piedmont Blue Ridge Region (Exhibit 27)
This region extends from Alabama in the south to Pennsylvania in the
north. The Piedmont part of the region consists of low hills and ridges,
1-38
-------
Exhibit 24
Principal Groundwater Regions in the U.S.
MP
-------
-p*
o
Wfcl I
wt LL
WaS»*OuT
WEIL
•V . V • 9
. ,o • • • • • \ \
K' - / ' ' » .
WELL
t/i'i
# f T . r * _S
*vh*; :-: :V;; vvv -:^; h.;'
£ 'Jlx *- J*'"V
V ; f ~! SAHO ft. GRaj/EL
2S0gravel a coeBi t
&ILVV GRAVEL
B3^3&ILlV SANO«-6ft*V£L
(V^3CLAY ft SlU
IBASAIT |
MtltHb
Hydrogeologic Cross-Section A-A*
-------
EXHIBIT 26
Major aquifers in the continental United States
CS]
V^aicrcourici m *hich
groundwater can be replenished b> perennial streams
\'0 *;.0.V Lnconsohddted and
. •vcmiconsondaied aquiiersimosth sand and gravel)
Consolidated-rock aquifers
imostU limestone -»jnd-stone or \olcanic rock5>
Sol kno*n to be underlain bv
aquifer thai uill generalU vield as much as SO gpm 10 wells
1-41
-------
Exhibit 27
Typical Piedmont Flow System
FLOW MODEL
LAYER
GROUND SURFACE
CONCEPTUAL
MODEL
.LAYER
LAYER
B
¦(J ¦ O .
- a 0 * n ° 0C>
_ Oo 0 0 .¦ a V- cu 0 ,0
0 ^ -S- 1 ~ 1 - 0
^ r a * _ _ . _ . r> 0
S ALLUVIAL AND RESIDUAL
0.
SAND AND GRAVEL
•O-.o *
. V • 0 o O
o o ci.: o ° ' 0 ¦ O
* o o 0 c > °
o. . ° ' o
c^>- w .l-' _ 0'
"S Q> O '¦ '
-------
whereas the Blue Ridge part of the region is mountainous. The area is under-
lain by thick regolith over fractured crystalline and metamorphosed sedimen-
tary rocks. The depth to the ground water is variable, ranging from 5 to
100 feet. Ground water is obtained from the regolith and fractured bedrock.
Yields to wells are generally small with hydraulic conductivity ranging from
.001 to 1 m/day (.003 to 3 ft/day). Recharge occurs in areas above stream
flood plains and rates range from 30 to 300 mm/yr (1 to 10 in/yr). Discharge
occurs as seepage springs.
Region 12. The Hawaiian Islands (Exhibit 28)
The. Hawaiian Islands are underlain by lava flows segmented in part by
dikes, mterbedded with ash deposits, and partly overlain by alluvium. Basal
ground water floats as a lens-shaped body on underlying seawater and it is the
principal source of ground water on the islands. Ground water also can be
perched in dike-bounded compartments. Depth to the ground water is quite
deep, around 800 feet. The ground water system is recharged by precipitation
with the recharge rate ranging from 30 to 1000 mm/yr (1 to 40 in/yr).
Hydraulic conductivity is high, ranging from 200 to 3,000 m/day (500 to 10,000
ft/day).
3. CONTAMINANT PROPERTIES AFFECTING TRANSPORT
As discussed previously, a key aspect of the site characterization process
is understanding and predicting'the movement of contaminants' in ground water.
The previous sections have focused on determining how, where, and how fast
ground water moves. These factors are vital because ground water provides the
transport medium for the contaminants. There are a number of other proper-
ties, however, which must be considered because of their impact on contaminant
movement. These properties are independent of the properties which affect
ground water movement and include chemical properties of the aquifer media as
well as chemical and physical properties of the contaminants themselves. This
section will identify those properties, discuss why these properties are im-
portant, and explain how data on these properties can be obtained.
A. Physical Properties
Physical properties of interest include density, solubility, viscosity,
and surface tension. The importance of each of these properties and illustra-
tive examples are discussed below.
Density
Density is an important property because it determines whether a contami-
nant will float or sink. Such a determination is important in conceptual
model development for addressing the question, "Where do I look for contami-
nants?". Just as with surface water, contaminants which are less dense than
water will float on the surface of the water, requiring that the surface of
the water be monitored. Those contaminants which are more dense will sink,
requiring that the bottom of the water column be monitored.
Consideration of density effects in developing a monitoring program is
illustrated in the following example. Suppose that a hydrologic characteri-
zation has determined that a site is located in an active discharge zone and
1-43
-------
EXHIBIT 28
Fresh Water Perch
On Ash Bed
Caprock
LAVA
FLOWS
y Dike
/Confined
Fresh Water ^
;fresh<^
/, BASAL WATER
«siTVO.H
SALT WATER
UNCRODED STATE
ERODEO STATE
A AMtnoft w«u producing tall watvr
B w«U proOwC «0>tr
C ArtM.Oft «fll pro0uC»ft9 fr*th wO»tf
D Shunning tunftflt
£ D»*t *or»9
F 0»M tu**#l
0 P^fChM «Ot*r funntl
GROUND-WATER OCCURRENCE AND DEVELOPMENT
IN A TYPICAL VOLCANIC ISLAND.
1-44
-------
that there is a net upward movement of water, as shown in Exhibit 29-A. If it
is assumed that contaminants will move as the water moves, one would expect
that contaminants introduced at the surface would remain near the ground-water
surface and be transported toward the discharge point. It would reasonably be
expected that monitoring would only have to occur at the ground-water surface
in order to detect any migration of contaminants from the site. If, however,
the contaminants are more dense than water (e.g., chlorinated solvents), they
will tend to migrate downward in spite of the upward ground water gradient, as
shown in Exhibit 29-B. ]n such cases, monitoring at the surface of the
ground water might be necessary to detect release of contaminants from the
facility while monitoring at the bottom of the aquifer would be necessary to
assess the extent of the contamination problem. The converse of the above
example is also true, with contaminants less dense than water (e.g., light
hydrocarbons) remaining on the surface of the water regardless of a net down-
ward movement of ground water.
While density effects are most pronounced with contaminants that do not
mix well with water (i.e., contaminants that either float or sink), these
effects can also occur with mixtures or solutions of contaminants and water.
The latter most commonly occurs with highly soluble ionic wastes (i.e., salts)
which can dissolve in water to such an extent that the resultant solution is
more dense than the ground water and will sink. As the dense plume sinks,
however, it undergoes mixing with ground water which serves to reduce the
density of the plume and reduces the density effects.
As an example of the above, consider the conditions in Exhibit 29 with a
dense inorganic plume. As the plume leaves the site, density effects cause it
to be drawn downward against the ground-water flow. As it sinks, it is sub-
ject to some lateral movement from the horizontal component of the ground-
water velocity. In addition, by flowing counter to the ground water, the
plume is subject to mixing with the uncontaminated ground water. As mixing
occurs, the density of the plume is reduced to the extent that it cannot over-
come the upward flow and begins to rise. This situation is illustrated in
Exhibit 30. As shown in this exhibit, it is possible for the plume to miss
both shallow and deep monitoring wells.
Data on the density of contaminants are generally obtained from published
sources but are easily determined in the laboratory. Laboratory determination
might be appropriate if the waste consists of a mixture of chemicals since
published data generally give only the densities of individual contaminants.
In determining the density of waste mixtures, it is important to consider
whether the mixture will separate after release to water. (Separation can be
determined by simple testing in the laboratory.) If separation occurs, it
will be necessary to determine the density of each component of the waste.
Solubility
Solubility is an important property to consider during site characteriza-
tion. In terms of developing or testing a conceptual model, solubility
effects are related to the question "How much contaminant should I look
for?". That is, solubility determines how much of the contaminant can be
transported by the water. In addition, solubility concerns can also affect
1-45
-------
Exhibit 29
Contaminant Movement in Discharge Area
A. CONTAMINANTS MOVE
WITH WATER
V
i
-p.
cn
£ 1 1 1 1 1 1 1 1 1 1
1 . 1
1 1 1 1 ! 1 1 1 1
T" 1
i i i
1 1 1 1 1 1 1 1 1 1 B
I
i.i.i.i.i.i, i . i. i! i
1
I.I.I,
I I 1 1.1,1.1.1,1.1
B. WITH DENSE
CONTAMINANT
V
1 ¦ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1
I.I.
1 . ¦
1 B
i 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I'll 1 1 1
1 1 1
1 1
. 1 .
1 1 §
-------
Exhibit 30
Movement of Dense Soluble Contaminant Plume
in Discharge Area
KWSPv 1
B
V=1 :lc.' f; vj ^.1 Xf-' ; j &y* S" J- 'fc
N%g|fS88
-------
the answer to the question "Where do I look for the contaminant?". If the
mass of contaminant introduced to the water is greater than the amount that
can be dissolved by the water, the difference must go somewhere and must be
accounted for by the monitoring program.
The effects of solubility are illustrated in the following examples.
Suppose a contaminant having a solubility of 100 mg/L is leaking from a facil-
ity at a rate of 1 kg/day. The ground-water flow is such that 1,000 L/day
flow beneath the site and mix with the contaminant before reaching the site
boundary and monitoring wells, as shown in Exhibit 31. Dividing the contami-
nant flux by the ground-water flux yields an average expected contaminant
concentration at the monitoring well of 1,000 mg/L, or 10 times the solubility
limit. Because the solubility cannot be exceeded, the other 900 mg/L or 0.9
kg/day will form a second phase, separate from the water. Several things can
happen to this second phase. If the contaminant is denser than water, it may
sink and miss the monitoring well. If the contaminant is approximately the
same density as water, the second phase may be carried along with the water
but at a different velocity because of differences in viscosity.
Solubility effects must also be considered in assessing the monitoring
data. In the above example, an analyst might look at the monitoring results
and plume size and conclude that 0.1 kg/day of contaminant are being released
from the site. Corrective actions based solely on these data would not
address 90 percent of the released contaminant.
Consideration of solubility effects is particularly important when dealing
with inorganic (i.e., metallic) contaminants. Phase separation with inorganic
contaminants usually involves precipitation of the contaminants onto soil or
aquifer media. That is, if the solubility limit is exceeded., the contaminant
will transfer to the solid phase rather than remain with the liquid. In the
above example, the 0.9 kg/day excess of contaminant would accumulate on the
aquifer material beneath the site. In performing assessment monitoring,
therefore, it would be important to sample the soil and aquifer media beneath
the site.
Consideration of geochemical interactions is an important aspect of deter-
mining contaminant solubility. When introduced to ground water, contaminants,
especially inorganic contaminants, can undergo a number of simultaneous chemi-
cal reactions until an equilibrium concentration is reached. These reactions
include dissolution/precipitation, oxidation/reduction, complexation, ion
exchange, and adsorption. The net result of all these reactions is that the
contaminant remains in solution in any of a number of possible forms and
amounts. This solubility is dependent on the amount of contaminant present,
the pH, oxidation/reduction potential (Eh), and temperature of the ground
water, and the concentration of other ionic species in the ground water.
Exhibit 32 presents an example of the solubility of various chromium species
under specific oxidizing conditions. Exhibit 33 shows the solubility of var-
ious chromium species under specific reducing conditions. A comparison of
Exhibits 32 and 33 shows tremendous differences in overall solubility and in
the identity of the species which are most soluble.
1-48
-------
Exhibit 31
Mixing of Release and Flux to Produce
Downgradient Concentration
1 kg/day*;
1000 f/day
_ 1 kg/day _
=1000 mg/f
1000 f/day
1 ' ' 1 1 1
-------
I
c_n
O
Exhibit 32
Solubility of Various Chromium Species Under
Reducing Conditions
Cr(OH)
-------
Exhibit 33
Solubility of Various Chromium Species Under
Oxidizing Conditions
OO-HPO42"
Cr(OH)°
OO3H2PO;
-------
The effects of geochemical reactions on site monitoring can be illustrated
by considering the following example. A leaking storage impoundment contains
acidic chrome plating wastes. Because of the acidic and oxidizing nature of
the wastes, chromium is present in high concentrations in the hexavalent
form. As the p]ating waste migrates downward through the soil column it re-
mains in the hexavalent form because of the oxidizing conditions found in the
soil. The chromium concentration is reduced somewhat, however, because of
reactions with soil minerals. Upon entering ground water, the wastes encoun-
ter reducing conditions and the hexavalent chromium is reduced to trivalent
chromium, which is much less soluble. After undergoing further reactions with
the minerals in the aquifer media and the chemicals in the ground water, the
amount of soluble chromium remaining is below the analytical detection limit.
Under those conditions, the presence or absence of chromium in ground water
could not be used to determine whether or not the impoundment was leaking.
The solubility of organic contaminants is usually obtained from published
values, but can be determined in the laboratory with relative ease. Special
care must be given when determining the solubility of organic mixtures. With
mixtures, the organic chemical may dissolve in each other as well as in the
water, giving results much different than the water solubility alone. The
solubility of such mixtures should be determined by laboratory measurement.
Determination of the solubility of inorganic contaminants is more complex,
particularly with those contaminants undergoing numerous geochemical inter-
actions. Published solubility data can generally be used with simple, salts
which are highly soluble and not very reactive (e.g., sodium sulfate). For
other contaminants, the geochemistry must be evaluated under site specific
conditions. As expected, evaluation of the numerous geochemical reactions
which can occur can be exceedingly complex, particularly when there are a
number of contaminants present. Such evaluations are best made with the use
of geochemical computer models. Exhibit 34 shows the output of one such
model. This exhibit represents one of a series of simulations performed to
evaluate the fate of inorganic contaminants in landfill leachate upon reaching
ground water. These simulations were performed for specific ground-water con-
ditions of pH, Eh, temperature, and ionic composition. The horizontal axis
represents the concentration of copper in the leachate as it enters the ground
water. The vertical axis represents the final copper concentration after the
contaminant has reached equilibrium. In the example shown in Exhibit 34, an
initial contaminant concentration of 25 mg/1 will be reduced to 12 mg/1 by
geochemical reactions. In addition, the contaminant concentration can never
exceed 19 mg/1 under these conditions regardless of how much contaminant is
introduced to the aquifer.
Viscosity
Viscosity can be an important consideration for those contaminants which
are immiscible with water and form separate phases. In these cases, the vis-
cosity of the contaminant will determine how rapidly the contaminant is trans-
ported through the aquifer media. Such considerations are important for de-
signing monitoring programs, evaluating monitoring data, and designing correc-
tive actions. For example, consider a release of an immiscible contaminant
from a site. Assessment monitoring will be needed to determine the impacts of
1-52
-------
Exhibit 34
Reduction of Copper Concentrations from
Unsaturated Zone to Saturated Zone
20.33
17.16
13.98
10.80
0.0E 00 25.4 50.8 76.2 101.6 127
UNSATURATED ZONE COPPER INPUT CONCENTRATION (mg/L)
-------
chat release. The determination of impacts will require an evaluation of the
time required for the contaminant to reach possible receptors. The hydrologic
characterization will define the ground-water velocity, but if the contaminant
has a different viscosity than water, it will move at a different velocity and
affect the travel time estimates.
As discussed earlier, the permeability of the aquifer material is a mea-
sure of how easily fluid can pass through the medium. Permeability is an
intrinsic property of the medium and is independent of the fluid passing
through. Because water is typically the fluid passing through the medium,
permeability is often replaced by a related term, hydraulic conductivity.
Unlike permeability, hydraulic conductivity is applicable only to fluids hav-
ing the viscosity of water. In order to determine the rate of flow of fluids
other than water, therefore, the viscosity of the fluid must be known.
Viscosity values have been published for many contaminants. Viscosity
also can be measured in the laboratory with relative ease. Laboratory mea-
surement should probably be performed with mixtures of chemicals since the
viscosity of the mixture is likely to be different than the viscosity of any
of the components.
Surface Tension
Surface tension is an important property for evaluating the migration of
contaminants that are immiscible with and less dense than water. The surface
tension of a contaminant determines the degree to which a chemical will spread
and how strongly the contaminant will be drawn into the unsaturated soils by
capillary forces. The greater the surface tension of the contaminant, the
less it will spread on the surface of the water. Such considerations would be
important in evaluating the impacts of contaminant releases and in designing
assessment monitoring programs. For example, it is important to know how
widely a plume will spread when designing a monitoring program to evaluate the
movement of that plume. With respect to the effect of capillary forces, the
greater the surface tension, the higher a contaminant will be drawn up into
the unsaturated zone by capillary forces. Consideration of this factor would
be important in determining the relative distribution of a spilled contaminant
between the unsaturated and the saturated zones.
B. Chemical Properties
Several chemical properties of the contaminants are important because they
affect fate and transport processes in ground water. The most important of
these processes are adsorption and degradation. These processes, the chemical
properties which affect them, and data sources for these properties are dis-
cussed below. Illustrative examples are also provided.
Adsorption
Adsorption refers to the process whereby contaminants are transferred from
solution to the surface of a solid. In ground-water transport, adsorption
determines the relative distribution of contaminants between the ground-water
1-54
-------
and the soil and affects the contaminant transport velocity. With respect to
monitoring, adsorption must be considered to address the question "Where do I
look for contamination?"
In environmental studies, the Freundlich sorption model is frequently used
to describe adsorption:
C = K *C n
s D w
where C = the concentration in the solid
s
C = the concentration in the water
w
Kp = the sorption coefficient
n = a constant (sometimes written 1/n).
For organic compounds, n is usually between 0.7 and 1.1. If n is unknown (the
usual case), n is assumed to be unity, and the model becomes linear (C =
The sorption coefficient may vary with the size, structure, and
charge of the contaminant; the temperature, pH, oxidation potential, and com-
position (particularly dissolved organic matter and salts) of the ground
water; and the pll, particle size distribution, surface area, and composition
(.particularly clay and organic matter) of the soil or aquifer media.
Organic compounds of low solubiity and some inorganics sorb primarily onto
(or react primaily with) organic matter in the soil or aquifer material. Thus,
a sorption coefficient, corrected for the organic carbon content of the
solid, appears to be relatively independent of properties of the solid.
K = K /f
- oc D oc
where K = sorption coefficient on organic carbon in soil
f = fraction organic carbon in solid,
oc
The concept of K is usually valid for f greater than 0.01. Because
r oc oc
K is independent of the soil properties, it can be estimated from contami-
nant properties including solubility and octanol/water partition coefficient,
K .
ow
Sorption coefficients have not been published for most contaminants.
Laboratory determinations can be made using batch or column procedures to
determine values for specific contaminants on specific media. The time
and expense involved with these determinations generally limit their applic-
ability. As an alternative, several methods are available to estimate
values from chemical properties of the contaminant. With organic contaminants
chemical properties are generally used to estimate K because this constant
oc
is dependent only on chemical properties and not on soil properties. Values
for K can generally be estimated from the solubility of the contaminant,
S, or from its octanol/water partition coefficient, K Different correla-
ow
1-55
-------
tions exist depending on the particular class of contaminants being con-
sidered. These correlations are available in the literature. Two correla-
tions that are commonly used include:
log K = -0.55 log S + 3.64
° oc
where S is the solubility in mg/1 and
log K = 0.937 log K - 0.006
oc ow
Determination of values for inorganic contaminants is much more diffi-
cult. As discussed earlier, the use of geochemical models is generally nec-
essary because of the numerous reactions that can occur.
Related to the sorption coefficient is the retardation factor, R, which is
defined as the ratio of the velocity of water to the velocity of the contami-
nant. The retardation factor is calculated from the sorption coefficient, the
bulk density of the aquifer material, and the effective porosity of the aqui-
fer material by:
R = ] + B*Kd
n
e
where B = the bulk density of the aquifer material (kg/L);
= the sorption coefficient, and
n^ = the effective porosity of the aquifer.
The contaminant transport velocity is determined by dividing the ground-water
velocity (calculated as described earlier) by the retardation factor.
The importance and use of adsorption data is illustrated by the following
examples.
Contaminants have been discovered to be migrating from a facility.
Assessment monitoring has been performed to carefully delineate the extent of
the plume, as shown in Exhibit 35. The contaminant concentration isopleths
were multiplied by the volume of the plume to determine the total mass of
contaminant present in the plume. This calculation yields a result of 1,000
kg. Disposal records available for the facility indicate that 10,000 kg of
this contaminant were disposed. Comparison of these two quantities leads to
the conclusion that the majority of the contaminant is still present in the
facility, and corrective actions are designed accordingly.
The above analysis ignores the distribution of contaminant mass on the
aquifer material. Suppose the contaminant has a of 1.25 L/kg and the
aquifer material has a bulk density of 1.6 kg/L and an effective porosity of
0.25. Calculations performed using these values show that there will be 9
times more contaminant mass associated with the solid phase than with the
liquid phase. In this example, therefore, there will be an additional 9,000
kg of contaminant adsorbed on the aquifer material. Comparison of this total
with the disposal records then shows that the entire mass of contaminants has
left the facility.
1-56
-------
Exhibit 35
Delineation of Contaminant Plume to Calculate
Contaminant Mass
¦B
KB
PLAN VIEW
FLOW DIRECTION
CONTAMINANT
CONTOURS
FACILITY
BOUNDARY
1 ug/f
10 ug/f
TOO ug/f
DI88OLVED MASS
1,000 kg
SORBED MASS
9,000 kg
MONITORING
WELL
ELEVATION VIEW
100 ug/f )10
1 ug/P
-------
As another example, consider a facility where detection monitoring has
revealed elevated conductivity, indicating possible migration of contaminants
from the facility. Assessment monitoring is being planned to determine if
specific contaminants have left the facility. Hydrogeologic data are used to
calculate a ground-water travel time of 6 months from the boundary of the Was
Management Unit to the monitoring well. The contaminant sorption coefficient
and aquifer characteristics are used to calculate a retardation factor of 30.
The resulting contaminant travel time is 15 yr. Because the facility has not
been in operation that long, it is impossible for the contaminant to have
reached the monitoring well. This situation is illustrated in Exhibit 36.
When a number of contaminants are present it is important to consider the
retardation factor of each contaminant when evaluating monitoring programs and
assessing corrective actions. For example, consider a site where wastes con-
taining three major constituents are disposed of. These constituents have
sorption coefficients in the aquifer material at the site of 3, 10, and 30.
There is a sudden release of waste from the site introducing all three
contaminants into the ground-water. In order to evaluate possible corrective
actions, it is necessary to evaluate the migration of these contaminants off-
site to downgradient residential wells. Initially, the contaminant plume at
the site would contain all 3 contaminants, as shown in Exhibit 37-A. With
time, however, the contaminants would begin to separate because of different
retardation factors, similar to the effect of a chromatographic column. After
several years, the plumes might be expected to appear as shown in Exhibit 37-B.
Degradation
Once released from a site, contaminants may undergo several possible
degradation reactions. These reactions may result in the formation of more or
less toxic, stable, or transportable chemicals with consequent aggravation or
alleviation of the hazard. Or, alternatively, some components may not react
at all but will persist in the environment. The disappearance or transforma-
tion of contaminants in ground water must be considered when designing or
implementing a monitoring program. Specifically, these considerations address
the question "Which contaminants do I look for?".
Numerous reactions are possible for the several thousand chemicals that
may be present in hazardous wastes. These reactions can be divided into two
major categories: those that are caused by interactions among the different
chemicals comprising the waste and those that occur because of interactions
between the chemical and the environment. This discussion will focus on the
second category -- typical reactions controlled by environmental conditions.
The types of reactions to be discussed are biodegradation, oxidation/
reduction, and hydrolysis.
Biologically mediated reactions are possibly the most important processes
for transforming organic hazardous materials in the unsaturated and saturated
zones. Biodegradation can be important for inorganic materials as well.
Biodegradation may involve conversion to other components which are more or
less toxic and persistent, and biodegradation does not necessarily eliminate
hazards from the environment. For example, trichloroethylene can be trans-
formed biologically to vinyl chloride, which is considered to be more toxic
1-58
-------
Exhibit 36
Relative Migration of Plumes of Mobile and
Attenuated Contaminants
cn
PLUME OF ATTENUATED
CONTAMINANT, KD =5
PLUME OF MOBILE
CONTAMINANT. K0 =0
-------
Exhibit 37
Multiple Contaminant Plumes
A. ORIGINAL PLUME
FLOW DIRECTION
CONTAMINANTS A, B. C
B. DEVELOPED PLUMES FOR CONTAMINANTS
WITH DIFFERING SORPTION COEFFICIENTS
FLOW DIRECTION
CONTAMINANT C
Kd =30
CONTAMINANT
Kd =10
CONTAMINANT A
KD = 3
-------
than the parent compound. For some organic compounds, complete degradation or
mineralization to CO^ and H^O may occur. In this case, biodegradation
eliminates the hazardous contaminant once the reaction sequence is complete.
Biodegradation reactions include oxidation/reduction, hydrolysis, dehalogena-
tion, alkylation, acylation, dimerization, and nitration. Frequently, it is
difficult to determine whether these reactions are purely chemical, purely
biological, or a combination of the two processes.
Microbial reactions are highly compound-specific since they are usually
based on enzymatic reactions. However, certain rules of thumb have been de-
vised for estimating the relative rates of biodegradation for different chemi-
cal classes, structures, or properties. In general, branched, short chain,
and saturated compounds are less readily degraded as are water-insoluble com-
pounds since these tend to be less readily available to organisms. Alcohols,
aldehydes, acids, esters, amides, and amino acids are more susceptible to
biodegradation than the corresponding alkanes, olefins, ketones, dicarboxylic
acids, nitriles, amines, and chloroalkanes. These statements are general, of
course, and reaction rates are dependent on specific conditions and biological
species available, i.e., in one habitat a chemical may persist whereas in
another it may degrade quickly. Chemical groups which are poorly degradable
include amine, methoxy, sulfonate, nitro, nitroso, ether, halogens, and
meta-substituted benzene rings.
Microbial populations and metabolic rates (and, consequently, biodegrada-
tion rates) are affected by a number of environmental variables. These in-
clude :
• Temperature -- rates increase with increasing temperature within
the tolerance limits of a given organism,
• pH -- many but not all bacteria favor slightly alkaline conditions
whereas fungi tend to prefer slightly acidic conditions,
• Moisture -- necessary for survival of most organisms, also a factor
in temperature, pH, and Eh control, hydrolysis and oxidation reac-
tions, transport of compounds,
• Eh -- presence or absence of 0^ will determine whether aerobic or
anaerobic processes are involved in biodegradation,
• Salt concentration -- may suppress activity unless species is salt
tolerant,
• Availability of nutrients -- necessary for growth,
• Availability of the compound to be degraded -- may be affected by
sorption due to organic matter or clays or by complexation with or-
ganic matter,
• Presence of inhibitors -- e.g., metals or other components that are
toxic to the microorganism, and
• Presence of another carbon (.and energy; source for cometabolism.
1-61
-------
The rate of biodegradation depends on the structure and concentration of
the compound, metabolic capacity or cell concentration of the microbial com-
munity, and environmental conditions. The rate is very difficult to quantify
because it is often difficult to determine which species are actually involved
in degradation of a particular compound, to determine the number of bacteria
involved, and to separate the effects of biotransformation from chemical
transformation. In addition, the rate can be time dependent. There is
usually an initial lag period (hours to weeks) from the introduction of a
chemical to the initiation of biodegradation because the organisms need time
to produce the required enzymes or to grow until there are sufficient cells to
produce significant degradation. Once the lag period is past, degradation
occurs rapidly as the microbial population increases. One case in which this
does not hold is cometabolism a process that occurs when microorganisms trans-
form a compound without using it as a nutrient source. In cometabolism, there
is no population increase and transformation rates are slow. The chemistry of
biotransformation in the environment is not well known. Laboratory studies
using microbial cultures typically indicate trends or possibilities but,
because of their relative lack of complexity (usually including lack of
diversity of microorganisms), lab studies may not be very useful for predic-
tion of actual field transformations.
In addition to biological reactions, contaminants may be subject to degra-
dation or transformation by chemical oxidation/reduction reactions in the
environment. The working definition of oxidation or reduction depends on
whether inorganic or organic molecules are being discussed. For inorganic
molecules, oxidation is defined either as a loss of electrons or an increase
in oxidation number; reduction is a gain of electrons or a decrease in oxida-
tion number. For organic molecules, oxidation is defined as the conversion of
a functional group in a molpcule from one category to a higher one (see
Exhibit 38) and usually involves a gain of oxygen and/or a loss of hydrogen.'
Reduction is just the opposite, Reduction and oxidation are paired reactions
-- i.e., any oxidation of one compound must also involve a reduction of an-
other compound. Oxidation/reduction (redox) reactions may have significant
effects on the properties of hazardous contaminants. For organic components,
the reaction may change the functional groups present in the molecule; for
inorganic components, the reaction may change the oxidation state of the
metal. For example, trivalent chromium, which generally complexes with other
ions, precipitates and is then adsorbed, can be oxidized to hexavalent
chromium, which is soluble in water, is not readily adsorbed on sediments, and
is quite toxic.
Redox reactions depend on the presence of oxidizing or reducing species in
the environment. The thermodynamic redox potentials can be used to predict
which reactions are possible. The reaction rates depend on the concentration
of the reactive species and the concentration of the chemical. In oxidation
reactions, typical reactive species are free radicals (RO^, RO, HO), ozone,
and singlet oxygen (i.e., oxygen in an excited state in which its electrons
have absorbed energy).
The classes of organic compounds that tend to be susceptible to oxidation
include phenols, aromatic amines, electron-rich olefins, and alkyl sulfides.
Oxidation of the following organic compound classes is not an important mech-
anism: saturated alipyhatic hydrocarbons, haloalkanes, alcohols, esters, and
ketones.
1-62
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EXHIBIT 38
"Oxidation States" of Functionai Groups
Increasing Oxidation State
R-H
i i
-c=c-
C = C- RCOH CO 2
R-OH
1 1
-c-c-
OH OH
1
o=o
1
R-CI
r2cci2
- CCI3 cci 4
r-nh2
r-n-r
i
H
R - N = N+ R - N02
-------
Hydrolysis of orgariics involves the reaction of water with an organic
molecule, RX, in which the OH group substitutes for the X group causing forma-
tion of an R-OH bond: RX + II^O "* ROH + H+ + X . For inorganic com-
pounds, hydrolysis is more formally defined as the reaction between water and
3+
the ion of a weak acid or a weak base. (For example, Fe + 3^0
Fe(0H)„ + 3H+.)
j
Hydrolysis is a very important mechanism for transformation of some or-
gariics in ground water. Derivatives of carboxylic acids such as esters,
amides, and carbamates are susceptible to hydrolysis, as are nitriles, alkyl
halides, epoxides, amines, and phosphoric acid esters. Other organic groups
are resistant to hydrolysis; these include aliphatic saturated and unsaturated
hydrocarbons, aromatic hydrocarbons, carboxylic acids, alcohol and glycols,
aldehydes, aromatic amines, ethers, halogenated aromatics, ketones, aromatic
nitro compounds, and phenols. Hydrolysis reactions usually involve the forma-
tion of smaller, more polar compounds. These reaction products will probably
have a tendency to be less volatile and more soluble than the reactants and
will have associated changes in mobility in environmental media.
Hydrolysis also is very important for inorganic salts since it can lead to
the formation of acidic, basic, or neutral solutions which can influence a
wide variety of reactions. Simple solutions of soluble sulfides or carbonates
will be basic; simple solutions of CI , NCL , or SO, salts of the
3 4
common heavy metals (Fe, Pb, Cd) will be acidic.
Kaiui of hydrolysis reactions for different organic compound classes are
available in the literature as hydrolysis half-lives (the time it takes for
half of a given quantity of material to hydrolyze). Hydrolysis half-lives may
range from about 1 second for certain alkyl halides to 2 years for other alkyl
halides, to 10 years for some phosphoric acid esters.
Rates and mechanisms of hydrolysis reactions may be affected by several
factors: pH, temperature, presence of other organic compounds or trace
metals, and sorption. Increased temperature causes an increase in the hy-
drolysis rate. A useful rule of thumb is that a 10° change in temperature
causes the rate constant to increase 2.5 times at typical temperatures. The
presence of other organic compounds or trace metals may result in catalysis of
some hydrolytic reactions. For example, humic and fulvic acids may catalyze
some hydrolysis reactions in soils, possibly due to the presence of phenolic
or amine groups. Hydrolysis reaction rates in soils have been observed to be
considerably faster in a few cases than rates in solution. In other cases,
sorption may protect chemicals from hydrolysis.
A number of examples are available to illustrate the effects and impor-
tance of degradation reactions. One increasingly common example involves the
organic compounds trichloroethylene (TCE) and perchloroethylene (PCE), both of
which are common hazardous wastes. These two compounds can undergo a series
of biologically mediated dehalogenation reactions leading to the formation of
vinyl chloride, as shown in Exhibit 39. Such transformations can have an
impact on the collection and interpretation of monitoring data. At a large
industrial complex, TCE sludges had been disposed of in a series of trenches
which had leaked into the ground water. An intensive assessment monitoring
program was initiated to determine the extent of the resultant contamination.
1-64
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Exhibit 39
Degradation Reaction of Trichloroethylene
1. 1 DCE
TCE
DAYS
Cis 1. 2 DCE
DAYS
TRANS 1, 2 DCE
VINYL CHLORIDE
-------
Wells installed at and immediately downgradient of the trenches showed high
levels of TCE. Wells installed at some distance downgradient showed dramati-
cally reduced levels of TCE, suggesting that the contamination was being
attenuated by the soils at the site. Further evaluation of the monitoring
data, however, revealed significant levels of 1,2-dichloroethylene (1,2 DCE)
in the downgradient wells. There was some question as to the origin of this
contaminant, since it had never been used at the site and there was no record
that it had ever been disposed of in the trenches. In fact, the monitoring
wells near the trenches showed very low levels of 1,2 DCE. The relative dis-
tribution of the two chemicals in ground water was as shown in Exhibit 40.
The interpretation of the monitoring data was aided by obtaining data on
the degradation mechanisms of TCE and PCE. These data, including half-lives,
were used to construct a family of curves showing the relative amount of each
of the contaminants with time. These curves are shown in Exhibit 41. The
relative half-life data shown in Exhibit 41 and ground water travel time data
obtained from site investigations were used to determine that the trenches
were indeed the source of the 1,2 DCE. That, is, the travel time from the
trenches to. the center of mass of the 1,2 DCE plume compared well with the
time to degrade TCE to produce the peak concentration of 1,2 DCE. These re-
sults indicated that the contamination from the trenches was more widespread
than indicated by the TCE data.
The above example illustrates the importance of identifying possible
degradation mechanisms for the contaminants which are to be monitored. The
importance of understanding these mechanisms was illustrated at a different
site at the same complex. While this site also had received TCE and was leak-
ing, downgradient wells did not show the presence of 1,2 DCE. Further in-
vestigation into the mechanisms of TCE degradation suggested that the process
depended on the availability of an alternate source of organic carbon and
energy. The first disposal area was located upgradient of a trash landfill,
which was suspected of leaching organic-rich leachate into the ground water
and creating conditions favorable for microbial growth. No such facility
existed next to the second disposal site and there were no organics present in
the ground water other than the TCE. It was postulated that the degradation
of TCE to 1,2 DCE was not occurring at the second disposal site because of the
absence of an alternate organic substrate.
The occurrence of the 1,2 DCE as a product of the biological degradation
of TCE was further investigated using additional site monitoring data. Ex-
hibit 41 shows that the biological degradation of TCE results in both the
trans and cis isomers of 1,2 DCE, but favors formation of the cis isomer.
Higher yield of the cis isomer is evidence of a biologically mediated reaction
since a purely chemical reaction would favor the trans isomer. Further analy-
sis of ground-water samples using a method which could differentiate between
the two isomers revealed that the cis isomer was indeed the dominant form.
Consideration of degradation mechanisms is also important in determining
the impacts of contaminant releases. At a facility similar to the one above,
the compound 1,1,1-trichloroethane (TCA) had been used as a degreasing solvent
and had been disposed of in on-site trenches, which subsequently leaked into
1-66
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Exhibit 40
Contaminant Plumes Showing Movement of
Degradation Products
TCE PLUME
FACILITY
DCE PLUME
t—»
-------
Exhibit 41
TCE Decay Profiles
1.0
0.9
0.8
TCE
0.7
Z
o
t-
<
QC
I-
Z
CIS-1, 2-DCE
0.6
0.5
UJ
o
o 0.4
O
VINYL CHLORIDE
0.3
0.2
1, 1-DCE
TRANS-1, 2-DCE
0.1
0.0
0.0
3.0
1.0
2.0
4.0
5.0
TIME (YEARS)
-------
the'-'ground ;w'ater .;SSA,,*ma'jor^a,dv'ariWa^e,,,afi'*TCX''''ovefc:'TCE is that it is far less
toxic arid: is considered much safer. While specific ground-water standards
have not been formally established, the priority pollutant criteria published
by EPA are 2.7 ug/L for TCE (at a 10 ^ cancer risk) and 18,400 ug/L for
TCA. (TCA is not a carcinogen.) At this particular site, TCA had migrated to
off-site residential wells at levels on the order of 100 ug/L, below taste and
odor thresholds and well below the priority pollutant criterion. Because of
the relatively low levels found in these wells, the TCA contamination was not
felt to be a health hazard. Further investigation', however, revealed the
presence of 1,l-dichloroethy]ene (1,1 DCE) in these domestic wells at levels
on the order of 10 ug/L, which is much higher than the EPA priority pollutant
criterion for dichlorethylenes of 0.033 ug/L (at a 10 ^ cancer risk). Fur-
ther investigation revealed data suggesting that 1,1 DCE was a degradation
product of TCA. On the basis of this information, the TCA contamination was
indeed posing a threat to public health and corrective actions were instituted.
The combined effects of contaminant degradation and unique geohydrologic
conditions were illustrated in a site characterization study. At this site,
TCE wastes had escaped from an impoundment into the ground water. Assessment
monitoring at the site revealed a plume of TCE contamination downgradient from
the impoundment, as shown in Exhibit 42. It was believed that the TCE-
contaminated ground wgter was discharging to the creek and that the creek was
the downgradient boundary of the ground-water contamination. No TCE contami-
nation was found downgradient of the creek. Monitoring data collected further
downgradient did. however, reveal an additional contaminant plume, at greater
depth, and consisting almost entirely of vinyl chloride (VC). An investiga-
tion was conducted to determine whether the downgradient VC plume was related
to the facility since this would affect the extent of corrective actions re-
quired .
The geohydrologic portion of the investigation revealed the presence of a
low permeability zone beneath the creek, preventing discharge to the cre'ek and
forcing the ground water to flow downward. The contaminant travel time .from
the facility to the center of mass of the VC plume compared well with the.:time
required to degrade TCE to VC. The conclusion of the investigation was .tfrat
the downgradient VC contamination was related to the facility and corrective
actions were designed accordingly.
The above example also illustrated the importance of considering contami-
nant degradation when selecting analytical methods. Several of the analytical
methods for determining TCE will not detect vinyl chloride. Use of these
methods would not have revealed the additional downgradient contamination
arising from the impoundment and requiring corrective action. Additionally,
the unusual geohydrologic characteristics of the downgradient region would not
have been discovered had the investigators not considered the effects of con-
taminant behavior.
1-69
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Exhibit 42
Multiple Contaminants Plumes Showing
Degradation Products
LOW PERMEABILITY
DEPOSITS
OBSERVED
TCE
CONTAMINATION
OBSERVED VC
CONTAMINATION
-------
4.0 REFERENCES
Cole, C.R., F.W. Bond, S.M. Brown and G.W. Dawson, 1984. Demonstration
Application of Groundwater Modeling Technology for Evaluation of Remedial
Action Alternatives. U.S. Environmental Protection Agency Contract No.
68-03-3116.
Cole, C.R., F.W. Bond, S.M. Brown and G.W. Dawson, 1983. "The Use of
Groundwater Modeling for Evaluation of Remedial Action Alternatives."
Land Disposal of Hazardous Wastes - Proceedings of the Eight Annual
Research Symposium. EPA-60019-83-002.
Dawson. G.W., 1983. "Risk Management and the Landfill for Hazardous Waste
Disposal." Journal of Hazardous Materials, Vol. 8, No. 1.
Dawson, G.W, and C.J. English, 1984. "innovative Approaches to Remedial
Action for Solvent Leaks From Underground Tanks" in Proceedings of the
HAZMAT Southwest Conference, Houston, TX.
Dawson, G.W. and C.J. English, 1986. "A Comparative Evaluation of Methods for
Determining Alternative Concentration Limits" in Proceedings of the
Superfund '86 Conference, Washington, D.C.
Dawson, G.W. and B.W. Mercer, 1986. Hazardous Waste Management. Wiley -
Interscience Co., New York, NY.
Devary, J.L. and R. Schalla, 1983. "improved Methods of Flow System
Characterization" in Proceedings of Management of Uncontrolled Hazardous
WastP Site^ National Conference, Washington, D.C.
Devary, J.L. and W.V. Harper, 1985. "A Hybrid Approach to Uncertainty in Far
Field Groundwater Flow" in Proceedings of Symposium on Groundwater Flow
and Transport Modeling: A Critical Evaluation of the State-of-Art,
Albuquerque, NM.
McKown, G.L., J.L. Devary, and R. Schalla, 1985. "Applied Uncertainty Analysis
at Hazardous Waste Sites" in Proceedings of the HAZMAT 85 Conference, San
Diego, CA.
McKown, G.L., R. Schalla, and C.J. English, 1984. "Effects of Uncertainties
of Data Collection on Risk Assessment" in Proceedings of the 5th
National Conference on Management of Uncontrolled Hazardous Waste Sites,
Washington, D.C.
Schalla, R. McKown, G.L. Meuser, J.M. Parkhurst, R.G., Smith, C.M. Bond,
F.W., and C.J. English, 1984. Source Identification, Contaminant
Transport Simulation, and Remedial Action Analysis, Anniston Army Depot,
Anniston, AL. Contractor Report No. DRXTH-AS-CR-83265, U.S. Army Toxic
and Hazardous Materials Agency, Aberdeen Proving Ground, MD.
U.S. EPA, 1985. Guidance on Remedial Investigations under CERCLA; Chapter 7,
Site Characterization. EPA Report No. 540/G-85/002, Cincinnati, OH.
1-71
-------
GROUNDWATER MONITORING
SYSTEM DESIGN
Charles T. Kufs, C.P.G.S.
Raymond A. Scheinfeld
Roy F. Weston, Inc.
WESTON WAY
WEST CHESTER, PENNSYLVANIA
INTRODUCTION
Designing systems for monitoring groundwater and contaminant
movement is complicated by countless quantitative variables and
qualitative considerations. Because of these complications, the
design o£ monitoring systems sometimes appears to be more of an
art than a science. The objective of this paper is to discuss
some of the data sources for, and key factors in, monitoring
system design. Section 1 provides an overview of indirect
data-gathering methods, including background information,
aerial photographs, environmental surveys, geophysics, and
soil-gas surveys. Section 2 provides an overview of direct
data-gathering methods, including soil and rock sampling,
hydrologic measurements, and aquifer testing. Section 3
discusses some of the considerations in combining indirect and
direct data to design a monitoring system. Finally, Section 4
discusses approaches to preventing and correcting selected
problems with monitoring systems.
0639B
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SECTION 1
INDIRECT METHODS
Indirect methods provide generalized information about, or
specific data that can be correlated to, groundwater movement
and subsurface contaminant migration on and near a site.
Indirect methods fall into five general categories:
• Background records and literature.
• Aerial photography.
• Environmental surveys.
• Geophysical techniques.
• Soil-gas analysis.
These methods are generally inexpensive and efficient approaches
to obtaining information about a site. For this reason, it is
prudent to use applicable indirect methods early in the course
of a site investigation.
1.1 BACKGROUND RECORDS AND LITERATURE SEARCH
Many areas of the country have, at some time, been the focus of
some type of geologic or environmental investigation. It is
advantageous to determine what these previous studies have
revealed about the conditions existing on the site, such as
site use history or underlying geologic conditions. Many
sources of background information exist, and there are various
ways of accessing them. Libraries, both public and private;
regional and local planning commissions; universities,
especially those with geology and/or geography departments; and
Federal, state, and local agencies with an orientation toward
environmental protection, soil, or geologic science, are but a
few of the hundreds of available sources of literature. Table
1-1 lists some of the Federal sources of maps and reports.
Bibliographies obtained from pertinent reports can be used to
guide the investigator to other sources of data. Informal
interviews with people knowledgeable about a particular site
may be a valuable adjunct to any literature search, but they
should always be treated with some skepticism.
0639B
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Table 1-1
Sources of Maps, Reports, and Related Background Information
(After Repa and Kufs, 1985)
Topic Source*
Climate
NCC
, NOAA
Clinometric (Slope)
GS,
SCS
Floodplains
CE,
GS, SCS
Geodetic Control
CE,
GS
Geo logic
GS
Geophysical
GS,
NOAA
Groundwater
GS
Land Use
GS,
SCS
River Basin/Watershed Surveys
BR,
GS, SCS, TVA
Soi Is
SCS
Topography
GS
Water Resources
GS
*Many of these types of maps and reports are also available
from state and local government agencies and universities:
BR: U.S. Bureau of Reclamation
P.O. Box 25007
Denver, Colorado 80225
CE: U.S. Army Engineer District
Corps of Engineers, Chicago
219 South Dearborn Street
Chicago, Illinois 60604
U.S. Army Engineer District
Corps of Engineers, Nashville
P.O. Box 1070
Nashville, Tennessee 37202
U.S. Army Engineer District
Corps of Engineers, Omaha
6014 U.S. Post Office and Courthouse Building
Omaha, Nebraska 68102
U.S. Army Engineer District
Corps of Engineers, Vicksburg
P.O. Box 60
Vicksburg, Mississippi 39180
0639B
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Table 1-1
(continued)
GS: Eastern National Cartographic Information Center
U.S. Geological Survey
Reston, Virginia 22092
Mid-Continent National Cartographic Information
Center
U.S. Geological Survey
1400 Independence Road
Rolla, Missouri 65401
Rocky Mountain National Cartographic Information
Center
U.S. Geological Survey
Federal Center, Building 25
Denver, Colorado 80225
Western National Cartographic Information Center
U.S. Geological Survey
345 Middlefield Road
Menlo Park, California 94025
NCC: U.S. National Climatic Center
Federal Building
Asheville, North Carolina 28801
NOAA: U.S. National Oceanographic and Atmospheric
Administration
Office of Public Affairs
14th Street, NW
Washington, DC
SCS: U.S. Soil Conservation Service
Information Division
P.O. Box 2890
Washington, DC 20013
TVA: Tennessee Valley Authority
Mapping Services Branch
111 Haney Building
Chattanooga, Tennessee 37401
0639B
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1.2 AERIAL PHOTOGRAPHS
Aerial photographs and images are valuable, albeit often
neglected, sources of information for designing groundwater
monitoring systems. The primary uses of aerial photographs
include providing information about:
• Historical development of site.
• Indications of waste or leachate.
• Geologic, topographic, and hydrologic features.
Table 1-2 summarizes the uses of four types of aerial images.
Additional information concerning available aerial images is
summarized in the Map Data Catalog, published by the U.S.
Geological Survey.
Interpreting the chronology of a site's development is
generally not a difficult procedure, provided the appropriate
aerial photos are available. Identifying indications of waste
or leachate and interpreting the significance of geologic,
topographic, and hydrologic features, however, do require more
exper ience.
Indicators of waste or leachate can be spatial (e.g., physical
changes such as gaps in vegetation or snow cover) or spectral
(e.g., color or tonal changes in water or vegetation). In
general, spatial indicators are more consistent and useful than
spectral indicators (Sangrey and Philipson, 1979), but spectral
indicators may be more sensitive to subtle changes in site
conditions.
Interpretation of geologic, topographic and hydrologic
conditions at a site can be quite involved. For example, Table
1-3 summarizes some of the key features of various rock types
as observed in aerial photos. Because of the time and skill
required to evaluate hydrogeologic features, advanced
photointerpretation studies are seldom undertaken unless no
other sources of background information exist, the site is very
large (i.e., hundreds of acres), or the site is underlain by
fractured or cavernous bedrock. In the case of fractured
bedrock or Karst Terrane, fracture trace analyses are often
conducted so that predominant fracture or solution orientations
can be identified. Mean orientations can be calculated using
procedures described in Mardia (1972).
0639B
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Table 1-2
Availability and Usefulness of the Four Most
Commonly Used Types of Aerial Images
Type o f
Image
Relative
Availability
Potential
Usefulness
Technical
Considerations
Oblique photos
Perpendicular
photos
Highly variable
but generally poor.
Excellent for black
and white; poor for
color.
Evaluation of site
history and physical
features.
Evaluation of site
history, physical
features and geo-
morphology; some-
times useful for
detection of contam-
ination effects.
Size and distance
distortion caused by
oblique angle.
Sometimes difficult
to distinguish
features; photos
must be at an appro-
priate scale.
Stereoscopic
photos
Infrared
images
Fairly good.
Fairly poor.
Same as for per-
pendicular photos.
Detection of con-
tamination effects,
Generally allow less
ambiguous interpre-
tation than per-
pendicular photos.
Require some
experience to
interpret.
0639B
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Table 1-3
Key Features of Various Lithologies as Observed in Aerial Photographs
(after NWWA, 1986)
Rock Type
Landforms
Drainage Drainage Photo Special
Pattern Density Vegetation Tone Keys
Humid Climates
Shales Low relief Dendritic, Medium
(fine-grained valleys, parallel to fine
elastics)
smooth and
rounded
Heavy
Medium
to dark
Limestones
(carbonates)
Intermediate
to low
relief,
rounded
Internal,
dendritic,
trellis
Medium
to fine
Heavy to
medium
Light
to
medium
Sink -
holes
Sandstones
(coarse-
grained
elastics)
High relief,
mass ive,
rounded
Dendritic,
trellis
Coarse
Heavy
Light
to
medium
Intrusive
igneous
rocks
Rounded,
outc rops,
subdued
topography
Dendritic,
angular,
radial
Medium
to fine
Medium to
dense
Light,
uniform
Uni form
tone
and
topog-
raphy
Extrusive
igneous
rocks
Subdued
and
undulating
topography
Dendritic Medium
Medium to
dense
Dark
Dark
tone,
dense
vege-
tation
0639B
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Table 1-3
(continued)
Drainage Drainage Photo Special
Rock Type Landforms Pattern Density Vegetation Tone Keys
Arid Climate
Shales
( fine-grained
elastics)
Low relief
slopes and
valleys,
angular
dissection
Dendritic,
parallel
Medium
to fine
Barren
Medi um
to dark
Badlands
Limestones
(carbonates)
High relief. Dendritic, Coarse
angular trellis, to
angular medium
Sparse
Light Ridges
Sandstones High relief. Dendritic,
(coarse- bold cliffs, angular,
grained massive, trellis
elastics) angular
Coarse Sparse
Light
Cliffs
Intrusive
igneous
rocks
Massive
outcrops,
bald domes
Dendritic,
angular,
annular,
radial
Coarse
to
medium
Sparse
Light
uni form
Fracture
pattern,
light
tone
lack of
banding
Extrus ive
igneous
rocks
Inclined Dendritic, Coarse
flows, flat parallel to
topped medium
plateaus,
cliffs
Sparse
Dark
Flow
pattern,
surface
texture,
columnar
jointing
0639B
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The most time-consuming aspect of site evaluations using aerial
photographs involves obtaining photographs of appropriate dates
and scales. There are many governmental and private sources of
aerial photographs. The most commonly used Federal Government
sources are listed in Table 1-4. In general, aerial photographs
obtained from governmental sources are relatively inexpensive
(less than $50) but have long delivery times (4 to 10 weeks).
Aerial photographs obtained from private sources can be
obtained very quickly (2 days to 2 weeks) but are relatively
expensive ($20 to $200). Typically, both governmental and
private photographs must be used to evaluate a site thoroughly.
1.3 ENVIRONMENTAL SURVEYS
The first on-site activity in developing a groundwater monitor-
ing system is to conduct a general reconnaissance of the site.
As part of this reconnaissance, environmental surveys that are
essential to the design of the monitoring system are
identified. Environmental surveys that are particularly
relevant to designing monitoring systems are:
• Existing-well surveys.
• Geologic/hydrologic/soi1 surveys.
• Biological surveys.
1.3.1 Existinq-Well Surveys
Often it is necessary or advisable to incorporate existing
wells into a monitoring system. When this is the case, the
construction of the well and the subsurface stratigraphy are
documented adequately so that water quality data can be
interpreted without ambiguity. When construction details are
not documented adequately, there are several field tests that
can be conducted to evaluate the usability of the well. Some of
these tests are summarized in Table 1-5.
1.3.2 Geoloqic/Hydroloqic/SoiIs Survey
Because a site's geology and soil conditions are closely
interrelated to site hydrology, it is important to perform a
survey of the geologic/hydrologic/soi1 conditions found on and
near a site before designing a monitor well system. Several
stages are necessary to complete such an investigation
successfully.
The geologist should have reviewed the available literature on
the hydrogeology of the site area prior to conducting the site
investigation. Such a review provides a preliminary under-
standing of the distribution of soils, sediments and rock,
general surface water drainage, and groundwater flow, which
will serve to guide the site investigation.
0639B
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Table 1-4
Federal Government Sources of Aerial Photographs and Images
National Archives and Records Service
Cartographic Branch
8 Pennsylvania Avenue, NW
Washington, DC 20408
(for photographs taken prior to 1942)
EROS Data Center
U.S. Geological Survey
Sioux Falls, South Dakota 57198
Agricultural Stabilization and Conservation Service
U.S. Department of Agriculture
205 Parley's Way
Salt Lake City, Utah 84109
Soil Conservation Service
U.S. Department of Agriculture
Cartographic Section
6505 Delcrest Road
Hyattsville, Maryland 20782
Environmental Monitoring Systems Laboratory (EMSL)
P.O. Box 15027
Las Vegas, Nevada 89114
Environmental Photographic Interpretation Center (EPIC)
P.O. Box'1587
Vint Hill Farm Station
Warrenton, Virginia 22186
National Enforcement Investigation Center (NEIC)
Building 53, Box 25227
Denver, Colorado , 80225
/
0639B
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Table 1-5
Field Tests for Evaluating Existing Monitoring Wells
Test Description Results
Surface Qualitative determination of
Integrity how easily the well moves
within the borehole and how
the well is secured.
Evaluate security
provisions and integrity
of surface grout seal.
Sounding
Measurement of well depth.
Plumbness Logged using an inclinometer
and Align-, or tested using plumb bobs
ment and cylindrical dummies.
Evaluate siltation
and accuracy of log.
Evaluate straightness
of the well and its
deviations from
vertical.
Geophysical Cement-bond (sonic) logs
Logs (grout of energy in sound pulses
seals) as they travel through
casing, grout, and voids;
density (gamma-gamma)
logs measure natural
radioactive emissions from
clays; neutron logs measure
neutron attenuation from a
source to identify
rock, grout, water, and
voids.
Evaluate gaps in grout
seals.
Geophysical Temperature logs measure
Logs temperature changes in
(casing groundwater; flow meter
leaks) logs measure movement of
water within the well;
acoustic emission logs
measure noise levels;
caliper logs measure
well diameters; and
television logs provide
visual displays of the
interior of the well.
Evaluate leaks and
other imperfections
in well casings,
joints, and screens.
0639B
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Table 1-5
(continued)
Test Description Results
Step- Measurements of changes in
Drawdown water levels while pumping
Pump Tests and during recovery.
Evaluate well
efficiency.
7. Packer Tests Measurements of water
injection rates over
small well intervals.
Evaluate locations and
size of casing leaks.
8. Hydraulic Measurements of changes in
Connection depth to water in clustered
Tests wells as one of the wells in
the cluster is pumped.
Evaluate inadequate well
seals.
2-12
053QB
-------
The next step necessary to detail the geology beneath a site is
the collection of direct information identifying the lithology
and standard characteristics of the subsurface. Indirect
methods of geologic investigation, such as geophysical studies,
may be used to augment the evidence gathered by direct field
methods but should not be used as a substitute for them.
Direct field methods usually include walking through the site,
mapping visible outcrops on a topographic map, identifying the
observed lithology, and measuring the geometric attitude and
orientation of beds at each location. Other direct methods can
include sampling shallow soil for geomechanica1 or geochemical
analysis. A classification of the surface soils found on-site
according to the U.S. Department of Agriculture, Soil
Conservation Service, or other recognized standard is
necessary. Any soil samples collected during an exploratory
survey and later during well drilling should be logged
according to the same classification.
0639B
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1.4 GEOPHYSICAL SURVEYS
1.4.1 Methods
1.4.1.1 Metal Detection
Many types of metal detectors are commercially available, but
all have a similar mechanism of operation. Two coils, a
transmitting coil and a receiving coil, set up an electrical
field that will be distorted by any metallic object that enters
the field. This distortion is detected by a sensing circuit
which can activate an audible or visible indicator.
Metal detectors will detect any kind of metallic substance,
including both ferrous and nonferrous metals. They have a
fairly short range depending on the size of the metallic
object. Quart-sized buried objects can be detected to a depth
of approximately 3 feet. Large metal objects such as 55-gallon
drums or large piles of buried metal can be detected at a depth
of as much as 10 to 20 feet. An experienced operator can
usually make a reasonable estimate of the depth and size of a
target, but because many variable factors exist, detailed
calibration of this method is not possible.
Some of the factors influencing the operation of a metal
detector include some natural soil conditions, surface metallic
debris, pipes, fences, vehicles, and buildings.
1.4.1.2 Magnetomet ry
Magnetometers measure the strength of the earth's magnetic
field and anomalies created by buried ferromagnetic objects.
Where detectable, a deeply buried ferromagnetic object will
typically produce a positive anomaly south of its location and
a negative anomaly north of its location (in North America).
Shallowly buried objects produce positive anomalies where they
are buried. Key factors in a magnetometer's ability to detect
buried ferrous metal include the mass, depth, shape, and
orientation of the object.
Three types of magnetometers are used to explore sites for
buried ferrous metal - total field magnetometers, vertical
field magnetometers and gradiometers. Total field magnetometers
(e.g., proton precession, cesium) measure the strength of the
geomagnetic field in both vertical and horizontal planes.
Vertical field magnetometers (e.g., fluxgates) measure only the
vertical component of the magnetic field. Gradiometers combine
two total-field or vertical-field magnetometers so that differ-
ences in the vertical field over a small distance are measured
while the strength of the horizontal field is held constant.
All three types of magnetometers have been used to map buried
drums and other iron deposits. Gradiometers are the least
sensitive to cultural interferences (e.g., fences, rail lines)
although the other two types are usually adequate and are more
commonly used.
2-14
0639B
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1.4.1.3 Electromagnetic Conductivity (EM)
EM methods measure the electromagnetic conductivity of
subsurface materials. EM conductivity devices typically have
two wire coils and a control box. A magnetic current is created
by passing an alternating current through one of the wire
loops. When this loop is in close proximity to an earth
material, a current is induced. The current strength is
dependent upon the conductivity of the material being tested.
This induced current is picked up by the other wire coil, the
receiver. By measuring the difference in voltage between coils
and knowing their spacing, the conductivity of the earth
material can be calculated. This measurement is repeated over a
number of points on a grid to allow the determination of
subsurface conditions.
The ability of earth material to conduct electrical currents
primarily depends on the amount, ionic concentration, and
distribution of water found in the pore spaces surrounding the
materials being tested. Minerals found in the. sand and silt
fractions of a rock, or soil are generally poor conductors of
electricity. Dry clays are also poor conductors but become
better conductors when wet. The effect of organic matter on
conductivity measurements has not been determined.
There are two types of EM survey techniques:
• Profiling - When lateral changes in conductivity along
a set depth from the surface are measured.
• Sounding - Where vertical changes in conductivity are
measured.
The type of survey performed is based on the spacing and
orientation of the transmitter and receiver coils around each
grid node. Because EM equipment generally comes with fixed
electrode spacing, it is most often used for profiling.
Commonly available coil separations are 3 feet (e.g., Geonics
EM-38); 12 feet (e.g., Geonics EM-31); and 32, 66, and 131 feet
(e.g., Geonics EM-34), which allow profiling to a depth of 200
feet under ideal conditions. Sounding surveys are generally
performed with resistivity equipment although sophisticated EM
devices (e.g., Geonics EM-37, EM-42) are available for depth
sounding.
0639B
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In order to map contaminant plumes, a contrast in conductivity
must exist between the contaminant plume and local geohydro-
logic background values. Leachates with high total dissolved
solids usually have high conductivity, but an uncontaminated
saturated clay lens may exhibit the same response. In mapping
depth to water table and groundwater flow direction, the great
change in conductivity between saturated and unsaturated
materials is usually sufficient to allow the water table to be
mapped (Repa and Kufs, 1985).
Limitations of EM conductivity include (Pease and James, 1981):
Ability to detect nonconductive pollutants is limited.
Ability to detect plumes is limited if there is not a
sharp contrast between the plume and natural
groundwater.
Lateral variations in stratigraphy complicate inter-
pretation .
Shallow conductive objects may result in anomalous
readings.
1.4.1.4 Resistivity
Resistivity surveys involve applying an electrical current into
the subsurface and measuring the voltage passing between a set
of electrodes. By comparing the values for current and voltage,
the apparent resistivity of earth materials between electrodes
can be calculated. Since the resistivity of soils and rocks is
predominantly controlled by porosity, permeability, amount of
water, and concentrations of dissolved solids in the water, the
method provides a tool to evaluate depths to water tables and
extent of contaminant plumes.
Resistivity equipment can be used for "sounding" or
"profiling." In profiling, the electrodes are moved over the
site in an evenly spaced grid pattern. If site conditions are
homogeneous, apparent resistivity values should remain nearly
consistent. Any changes can be interpreted as being caused by
subsurface heterogeneity (clay lenses in sands, etc.) or
contaminated groundwater. In sounding, the spacing of the
electrodes is increased with the center of the array remaining
in a constant location. The two most commonly used electrode
configurations are the Wenner array and the Schlumberger array.
Each Wenner array electrode is separated by a constant distance
called the "A" spacing. In the Schlumberger array, the voltage
electrode spacing is constant while the current electrode
spacing varies.
0639B
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The Schlumberger array is generally preferable to the Wenner
array unless ground conditions are simple (Johnson and Johnson,
1986). Changes in apparent resistivity after each electrode
spacing change are usually interpreted as the presence of
various layers. Three to four different layers can commonly be
resolved with this technique.
While not as mobile as EM methods, resistivity methods allow
any depth of measurement (up to the limits of the equipment) to
be explored. However, there are limits to its use, including:
• Limited ability to detect nonconductive pollutants.
• Rocks, trees, buildings, etc., may restrict grid
patterns.
® Surface conditions, such as concrete roads, parking
lots, etc., may prevent electrode insertion.
• Power cables and lines can cause interference.
1.4.1.5 Seismic
Seismic reflection and refraction methods are both used to help
determine stratigraphic and lithologic conditions. Seismic
reflection, however, is primarily used to determine deep
stratigraphic relationships (500 feet to 40,000 feet) below the
surface. Since monitor wells are rarely drilled below a depth
of 300 feet, seismic reflection is rarely used in site
investigation work. Seismic refraction can be used to help
define natural geohydrologic conditions, including thickness
and depth of soil and rock layers and depth to bedrock or water
table.
The seismic refraction method measures the time it takes a
compressiona1 wave to travel through a specific medium (i.e.,
soil or rock) over a known distance (i.e., the distance between
geophones. The energy source in seismic refraction work can be
explosive charges or heavy blows on a metal plate. These waves
travel downward through the earth and are refracted back to the
surface from the interfaces between different layers. One of
the waves travels parallel to the ground surface and its time
of arrival to the geophone array is recorded. Deeper moving
waves will arrive at the geophones at a later time. Solutions
to the seismic time-travel equations (defining the corresponding
subsurface stratigraphy and lithology) are usually done on a
computer. Depths to 300 feet can be probed using refraction
techniques.
0639B
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Determining the depth to bedrock, the depth to groundwater in
alluvium, and the location of faults are the major uses of
seismic refraction methods in groundwater studies. This method
is especially applicable in locating buried valley aquifers,
and in some cases, lateral lithologic changes in aquifers can
be mapped. Monitoring well depths, well screen intervals, and
suitable well locations can be determined from this type of
data .
Since the seismic method measures small ground vibrations, it
is susceptible to vibration noise from a variety of natural and
cultural sources. Active industrial facilities are, conse-
quently, poor sites for seismic surveys. In addition, it is a
relatively slow method to perform in the field. It is best
utilized when working at depths beyond the range of other
geophysical methods.
1.4.1.6 Ground-Penetrating Radar (GPR)
GPR systems generate short-duration impulses of electromagnetic
energy that penetrate through and reflect off earth layers
having different dielectric properties. The reflections are
recorded as continuous cross sections along a traverse. GPR is
very effective for delineating shallow site stratigraphy and
may, under certain conditions, be able to detect the surface of
the water table. GPR has also been used in several geologic
environments to map low-density, nonaqueous phase hydrocarbons
(Stanfill and McMillan, 1985). Penetration depths over 100 feet
have been attained under ideal conditions although 10 to 30
feet of penetration is more common. The presence of
fine-grained materials and electrically conductive groundwater
can attenuate GPR signals, thus reducing penetration at some
sites to a few feet. GPR systems also require that the survey
grid be clear of trees, brush, tall grass, or other objects
that may hinder towing the transmitter module.
1.4.1.7 Borehole Geophysical Devices
A variety of devices have been designed to yield data by taking
measurements within the confines of a well. These borehole
logging tools include:
o Temperature probes,
e Specific conductance probes,
e Downhole television camera.
® Caliper plogging tools.
® Resistivity logging tools,
e Gamma logging tools.
« Neutron logging tools.
® Downhole fluorometers.
0639B
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Other types of downhole devices have been developed for use in
the petroleum exploration field but are not generally used in
environmental work.
Temperature probes contain a thermistor and can determine the
water temperature in a well to ±0.1°C. This type of probe can
be employed in a well in fractured rock to identify areas of
fracture flow. In shallow systems, water temperature
differences may exist in different fractures that intersect a
well. The temperature probe may help locate these fractures.
Probes can fit into a 1-inch well.
Specific conductance probes measure the conductance of water, a
parameter that is an indication of ionic substances dissolved
in water. While specific conductance measurements are commonly
taken on water samples with a hand-held probe, downhole
specific conductance measurements can be used to trace flows in
both unconsolidated and fractured rock aquifers. The presence
of a salt introduced into a nearby well can sometimes be
detected in the pumping well during a tracer test. Time-travel
and directional data can be determined from such a test. Probes
can be used in a 1-inch diameter well.
Downhole fluorometers are devices that can detect the presence
of fluorescent compounds by using an internal ultraviolet light
source and filtered fluorescent detector. These devices can be
used in a manner similar to the specific conductance probes for
flow tracing. In a test like this, a fluorescent dye is used
instead of a salt. Models exist that can be used in a 4-inch
well.
Downhole television cameras allow the direct examination of a
well or borehole for determining whether there are well
construction problems, locating fractures, or determining
fracture densities. Downhole TV can be used in a 2-inch well.
Caliper, resistivity, gamma, and
Table 1-6. Excellent reviews of
borehole logging tools are found
MacCary (1971).
neutron logs are described in
these and other traditional
in Kelley (1969) and Keys and
1.4.2 Factors in the Selection of Geophysical Techniques
The geophysical techniques described in the previous subsec-
tions each measure a distinct property of earth or fill
materials. Typically.- these measurements are not highly
correlated. As a consequence, it is usually advantageous to
utilize several different geophysical survey methods in
evaluating a site. Table 1-7 summarizes some of the factors to
consider in selecting complementary geophysical methods.
0639B
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Table 1-6
Traditional Borehole Logging Devices
Devi ce
Principle of Operation
Use
Limitations
ro
I
Caliper Measures variations in
the diameter of a bore-
hole. Softer rock, such
as shale, will create a
slightly larger diameter
hole than sand.
Measures the natural
electrical resistance of
formations and
fluids. Responds to
changes in conductivity.
Measures natural gamma
ray emissions in rocks
surrounding boreholes.
Shales and igneous rocks
are high gamma emitters.
Sand: and silts are mod-
erate emitters. Carbon-
ates are low emitters.
Neutron Measures the reaction of
rocks and fluids to
to neutron bombardment.
Responds to clay content
or shaliness and pore
water in tested rocks.
Resi stivi ty
(E'l ertri c
Logs)
Gamma
Detects lithologic
differences, used in
wet or dry or open or
cased wel1s.
Not conclusive information
when taken alone; must be
used with other loggers.
Can detect zones of
conductive contaminants
or porosity differences.
Used in fluid-filled open
holes.
Cannot be used in cased or
dry wells. Affected by
dri11i ng mud.
Can detect lithological Affected by borehole
differences in an open or diameter. Cannot usually
cased borehole; can be . detect thin (less than
used in dry or wet holes 2-feet thick) beds,
or holes with drilling
mud.
Used to determine both
lithologic differences
and porosity; can be used muds,
in fluid-filled or dry
holes, open or cased.
Affected by borehole
diameter and by drilling
0639B
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Table 1-7
Factors in the Selection of Complementary Geophysical Methods
Primary Secondary Technical
Application Methods Methods Considerations
Detection of
buried metallic
waste
Detection of
buried non-
metallic waste
Evaluation of
subsurface
geology
Metal detection,
magnetometry
GPR, EM
GPR, Seismic
GPR, EM,
Resistivity
Resistivity
EM and GPR respond to nonmetallic
deposits, making interpretation
ambiguous; resistivity often too
inefficient for this application.
GPR attenuated by clay-rich soil;
resistivity often too inefficient
for this application.
Resistivity, GPR is attenuated by clays; seismic
EM
methods require wave-velocity
contrasts; EM is typically not
sensitive enough to depth
variations.
Detection of
water table
GPR
Detection of
leachate
plumes
EM,
Resistivity
EM,
Resistivity,
Seismic
GPR
GPR works best in uniform deposits;
EM and resistivity require conduc-
tive groundwaters; seismic will
work only in uniform unconsolidated
deposits.
EM and resistivity require conduc-
tive deposits; some organic deposits
can be mapped as EM lows.
2-21
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A critical factor in the selection of a geophysical technique
is the suitability of the technique to the site's hydrogeology.
Research on the effectiveness of metal detection, electro-
magnetic conductivity, and ground-penetrating radar under
different site conditions has indicated that the effectiveness
of these techniques is reduced when the conductivity of the
soil/pore fluid exceeds 20 micromhos/meter (Lord and Koerner,
1986). Table 1-8 summarizes the results of this research.
Johnson and Johnson (1986) point out that many geophysical
surveys of hazardous waste sites have been unsuccessful or
misleading. The problems most frequently encountered with these
studies include:
-• Incorrect geophysical method used -- Caused by
insufficient understanding of site conditions,
objectives of survey, or geophysical technology.
e Inadequate Data Quality -- Caused by high ambient
noise, ' poor field procedures, improper use of
equipment, faulty equipment, inexperienced operators,
or adverse site conditions.,
• Inadequate Data .Quantity -- Caused by insufficient
•understanding of survey objectives, site conditions,
or the technology used.
* Faulty Data :Interpretation -- Caused by insufficient
understanding of site conditions and geophysical
interpretation methods.
Johnson and Johnson cite experienced personnel as the key to
successful geophysical surveys.
1.4.3 Evaluation of Geophysica1 Data
Geophysical data can be evaluated in three ways: graphically,
using method-specific techniques, and by statistical modeling.
Graphical interpretation involves evaluating strip charts or
computer-generated cross sections (GPR, seismic); plotting the
geophysical measurements on a site map (maanetometry, metal
detection, EM); and visually checking for patterns, corres-
pondence to site features, and correlations to other geo-
physical measurements. Often, geophysical anomalies can be
accentuated by preparing first-derivative (i.e., measurement
slope) maps. Most of the geophysical data collected at
hazardous waste sites is interpreted graphically because it is
simple and usually effective.
0639B
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Table 1-8
Relative Effectiveness of Four Geophysical Methods for
Detecting Buried Steel Objectives (After Koerner and Lord, 1986)
Electro-
Ground
magnetic
Pene-
Pore Space
Percent
Magneto-
Metal
Conduc-
trating
Water
Saturation
Media
metry
Detection
tivity
Radar
Fresh
0-20
Granular
soil
Excellent
Excellent
Excellent
Excellent
Fresh
50-100
Cohesive
soil
Poor
Excellent
Poor
Excellent
F resh
100
Water
Excellent
Excellent
Excellent
Exce1lent
Brackish
10-50
Granular
soil
Excellent
Excellent
Fair
Excellent
Brackish
100
Water
Excellent
Poor
No good
No good
Saline
50-100
Granular
soil
No good
No good
Poor
Saline
100
Water
Excellent
No good
No good
No good
0639B
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Method-specific techniques involve the use of computer programs
to filter out spurious signals (GPR, seismic) or theoretical
models to determine depth, size, or orientation of a geophys-
ical anomaly (magnetometry, EM, resistivity). Method-specific
techniques are not- used often because they require advanced
training to evaluate, and the additional information they might
provide can usually be obtained more effectively by drilling or
test pitting.
Statistical modeling involves mathematically filtering and
comparing different .types of geophysical measurements (magne-
tometry, metal detection, . EM) to derive more meaningful
interpretations of diverse anomalies. For example, Kufs et al.
(1986) used statistical modeling to process complex geophysical
data from a former open dump. Statistical modeling of geophysi-
cal data is a recent development that will probably not be used
often because of the advanced training required and the
adequacy of graphical methods.
1.4.4 Cost of Geophysical Surveys
The cost of conducting a geophysical survey will depend on a
number of factors, including type of survey, presence of an
existing survey grid, size and topography of the site, and
surface conditions. The surface of a site (i.e., presence of
trees, brush, tall grasses, snow cover) is particularly
important for GPR and can have a great impact on cost. Table
1-9 lists typical costs for the geophysical techniques most
commonly used at hazardous waste sites.
1.5 SOIL GAS SURVEYS
Soil gas surveys are quickly growing in popularity as a method
of determining the existence and extent of volatile con-
taminants in soil and groundwater. Gases and vapors released or
generated from volatile liquids diffuse through pore spaces
toward zones of lower concentrations. The concentrations of
these vapors are influenced by a number of factors such as:
• Volatility of contaminant
• Proximity to source and t
• Porosity and permeability
• Distribution of pressure
• Meteorological conditions
ime since release.
of earth materials,
gradients within pore spaces.
0639B
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Costs for
Table 1-9
Selected Geophysical
Surveys
Survey
Typica1
Cost Range/Day!
Field
Capaci ty/Day
Source'
Magnetometer or
Metal Detection
$1, 9 3 5-$3,890
50-150 stations
A
Conductivity --
continuous
prof i1ing"(EM-31)
$1,950-$4,000
3,000-8,000 linear
feet
A
Conductivity --
discrete
profiling (EM-34)
$1, 9 7 0-$3,9 60
$1,800-$4,800
50-150 stations
100-160 stations
A
B
Conductivity --
sounding (EM-37)
$2,400-$3,750
8-10 stations
B
Resistivity
$2,090-$4,655
$1,500-$6,000
10-15 stations
6-12 stations
A
B
GPR
$2,585-$6,100
$1, 5 00-$6,000
5,000-10,000
linear feet
(manual survey)
5-10 linear miles
(t ruck-mounted
survey)
A
B
Seismic Refraction
$1,750-$4,200
10-12 12-geophone
stations
B
Seismic Refraction
$1,840-$6,750
8-15 12-geophone
stations
B
Microgravity
$ 800-$3,750
40-50 stations
B
'Travel costs ana establishment of site grid are not included;
includes establishment, of base station, periodic calibration,
and preparation of report.
'Sources: A = 3opp
(personal communication); B = Benson
(1986)
0639B
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Contaminants such as gasoline contain volatile hydrocarbons
that vaporize rapidly, whereas diesel fuel and other distil-
lates are composed of low volatility hydrocarbons that do not
vaporize as quickly. Meteorological factors such as precipita-
tion, barometric pressure changes, wind, and evaporation will
also have an effect on vapor migration. Krauss et al. (1986)
describe a case in which ambient temperature and soil moisture
had significant impacts on the measurement of TCE vapors in
soil. However, little is known about the relative importance of
these influences except that they vary widely according to
site-specific conditions and are difficult to assess
(Scheinfeld et al, 1986).
The results of diffusion studies of hydrocarbon vapors include
Bisque (1984) and Levine (1985). In these studies, trace
volatiles from gasoline and diesel fuel samples, introduced at
depth in undisturbed soil media, were collected at the surface
to determine upward migration rates. In all cases trace
quantities were detectable at the surface within hours from a
depth of 10 feet (Scheinfeld et al, 1986).
The depth from which soil gas can be detected is variable. In
sandy or gravely material, a survey can detect a contaminant
buried as much as 100 feet deep. In clay or silt materials, the
maximum detectable depth is much less.
Soil gas surveys involve a gas or vapor collection method and
an analytical method. The results of a survey could, depending
on the method used, give quantitative, semiqua1itative, or
qualitative results.
Gas collection approaches include:
• Surface readings - Measurements made at or just above
the soil surface by portable instruments. These
measurements are routinely made at hazardous waste
sites yet are seldom made in the controlled and
systematic manner.
® Temporary probes - Small diameter tubes driven into
the ground and sampled, usually with a portable
instrument. These tubes are typically removed
immediately after sampling and are decontaminated and
reused. Temporary probes are probably the most
commonly used method of gas collection in soil-gas
surveys at. waste disposal sites.
0639S
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• Semipermanent probes - Small diameter tubes driven or
augered into the ground and sealed with a cement or
clay grout. These probes can be used for time-series
sampling for a period of as much as several months and
are usually sampled with a portable instrument.
Because they can be_ resampled, semipermanent probes
can provide more quantitative results than can
temporary probes or surface readings.
• Sorptive collectors - A special type of temporary
probe that uses a sorbant (activated charcoal) in a
glass tube that is temporarily buried at a location.
After a specified time period, the collector is
exhumed and the sorbant analyzed in a laboratory.
• Vapor wells - Permanently installed small diameter
tubes. These probes are designed for long-term
monitoring of a location such as around an underground
storage tank.
Analytical approaches used for soil gas surveys fall into three
types:
• On-site qualitative instruments - Include such devices
as photoionization or flame ionization detectors.
These generally give a yes-or-no response during • a
survey for contaminants.
® On-site semiqualitative or qualitative instruments -
Include devices such as portable or mobile gas
chromatographs or combination mass spectrometers/gas
chromatographs. These devices usually give semiquali-
tative results during a soil gas survey but, if used
carefully, can produce qualitative results.
• Laboratory-based instruments - Include the full range
of available analytical laboratory equipment such as
GC or GC/MS. Samples of soil gas collected in the
field are brought back to the laboratory for analysis.
This method is the most quantitative of the analytical
techniques.
The use of soil gas surveys to determine the presence or
quantity of contaminants located on or near a site is a very
useful technique due to its flexibility and versatility.
Because the data can be collected and reduced on-site, a
flexible field program in which decisions are made to maximize
data coverage while pinpointing source areas was possible. This
technique is particularly useful because it can quickly screen
a site and locate possible source areas.
0639B
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Some of the limitations of soil gas surveys include:
• Limitations on the detection capabilities of on-site
analytical instrumentation (usually not below 1 ppm).
• False positive readings due to naturally occurring
organic compounds (such as swamp gas).
• Barometric pressure , fluctuation that may purge
existing vapour probes of contaminant vapors, giving
false negative readings.
• A lack of understanding of factors that influence the
movement of soil gas and the effects of different soil
gas sampling and analysis methods.
0639B
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SECTION 2
DIRECT METHODS
A number of direct methods are available for the
characterization of subsurface migration of contaminants. These
methods can be broadly grouped into three categories:
® Soil and rock sampling.
® Hydrologic measurements.
® Aquifer testing.
Each of these categories is examined in detail in the following
subsections.
2.1 SOIL AND ROCK SAMPLING
There are five techniques commonly utilized for the sampling of
soil and rock at a site. These are:
• Grab sampling.
o Split-spoon sampling.
• Shelby tube sampling.
® Soil-core sampling.
• Rock-core sampling.
The advantages and disadvantages of these techniques are sum-
marized in Table 2-1.
2.2 HYDROLOGIC MEASUREMENT
Hydrologic data required as part of a groundwater monitoring
program include measurements of depth to groundwater, the
nature of water in the unsaturated (vadose) zone, and the
interaction of groundwater and surface water.
2.2.1 Depth to Groundwater
There are a variety of methods for measuring depth to ground-
water that are acceptable under different site conditions.
Table 2-2 summarizes the accuracy, ease of use, and cost of six
types of devices.
0639B
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Table 2-1
Methods of Soil and Rock Sampling
Sampli ng
Techm que
Principle of Operation
Advantage
Di sadvantage
Grab Sampling
Spli t-Spoon
Sampli ng
IVJ
i
Shelby Tube
Sampl i ng
Sampling is performed by
removing a soil or rock
sample by hand, usually
with a small trowel,
shovel, or hand auger.
While samples are usually
removed at or just below
the surface, Grab samples
can be collected from
test pits dug wi th a
backhoe to depths of 15
feet or more below grade.
Surface samples - quick,
inexpensive, visually
confirmable for contami-
nants; usually a one-per-
son operation with simple
equipment; large sample
available. Backhoe
Samples - Visually con-
firmable; moderately ex-
pensive; good strati-
graphic exposure; large
sample available.
A 1.5-2.0-foot-long (2-in Can sample as deep as
diameter) hollow split 200+ feet. Can use spoon
tube is advanced by soils penetration rate for
pounding it into the
ground with a large
d ri11-ri g-operated
"hammer." Auger drilling
is required to advance
the hole to the next
level to be sampled.
A 2.0-foot-1ong, 3-inch-
diameter thin-walled
hollow tube is hydraulic-
cally pressed into the
layer to be sampled.
calculating beaming
strength. Can penetrate
moderately hard surface.
Sampling minimizes
disturbance to
strati graphi c relation-
ships. Laboratory con-
ducted hydraulic tests
can be performed on sam-
ple. Larger sample avail-
able than from split
spoon.
Limitations on depth of
sampling; some surfaces are
difficult to penetrate. May
require extra people;
large equipment may present
decontamination problems;
test pits may require
shoring if below 3
to 4 feet. May require
"clean fill" to fill
excavati on.
Expensive and moderately
time consuming; pounding
distorts stratigraphic
relationships; only small
sample available; efficient
decontamination of multiple
split spoons may present
problems.
More expensive than
spoon sampling. Low
covery in hard or
granular soils.
spl i t
re-
0639B
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Table 2-1
(continued)
Sampli ng
Techni que
Principle of Operation
Advantage
Disadvantage
Soil-Core
Sampli ng
(Vi bracori ng)
Rock-Core
Sampli ng
Sampler is a 40-foot- Yields long, continuous
long, 3-inch-diameter relatively undisturbed
aluminum tube advanced soil cores; easy to
by mechanical vibrations, perform; relatively
i nexpens i ve.
Requires saturated or
nearly saturated soil.
Cannot penetrate gravel or
cobbled layer.
Rock-core sample is Only way to obtain whole, Very expensive, slow
obtained by using diamond subsurface, consolidated operation. At depth may
or carbide-tipped, hollow rock sample. Can see lose correct orientation
drill bit advanced by a existing fabric and of core,
rotary drill rig. texture of r.ock sample.
Depths to 1,500 feet are
possible.
0639B
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Table 2-2
Devices for Measuring Depth to Water
Device
Typical
Accuracy
(feet)
Relative
Ease
of Use
Approximate
Purchase
Cost
Recording
Capabi1i ties
Tape/Popper
0.1
Easy
$ 15
No
Tape/Ma rker
0.05
Easy
20
No
Elect r ica1
0.05
Easy
200
No
Mechanica1
0.1
Difficult
1,000
Yes
Sonic
1.0
Moderate
500
Yes
Pressure
Transducer
0.03
Moderate
1,500
Yes
0639B
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2.2.1 Vadose Zone Monitoring
Many techniques are available for collecting vadose zone
information. These techniques can be divided into five
different categories:
• Soil moisture potential.
® Soil moisture content.
• Soil salinity.
• Temperature.
• Soil pore water sampling.
Soil moisture potential is defined as the energy status of a
soil water system, including both osmotic and matrix forces.
These include such measurable forces as surface water tension,
osmotic forces associated with dissolved ion components,
molecular cohesion and adhesive forces to soil grams, and
electrical forces. Since soil moisture potential is inversely
proportional to the amount of water found in a soil, measuring
the soil moisture potential will give indirect data about soil
moisture content. Measurements of soil moisture potential are
usually made with various types of tensiometers or thermocouple
psychrometers.
Soil moisture content is defined as the weight of the water to
the weight of solid particles in a soil mass. Soil moisture
content data are critical to allow the correct method of soil
pore water sampling to be employed. Soil moisture content can
be measured in a variety of ways, including: laboratory drying
methods; electromagnetic methods; capacitance sensors; electro-
thermal methods; and nuclear methods such as neutron flux,
gamma ray attenuation, and nuclear magnetic resonance. The
laboratory drying technique is most commonly used.
The soluble salt concentration, or soil salinity, can be a
valuable pollution indication. To measure this parameter,
laboratory and field techniques usually rely on the
relationship between electrical conductivity/resistance and
ionic strength of the salt. Laboratory techniques involve an
extraction method and resultant conductivity measurements.
Field methods employ different types of sensors that can be
temporarily or permanently emplaced or noncontact
electromagnetic conductivity techniques (EM). EM techniques
will allow a rapid survey of a large area with qualitative or
semiquantitative data collection while the laboratory and
sensor-based techniques will be more quantitative but more
labor intensive.
0639B
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Soil temperature is a basic soil property that can be measured
in a variety of ways. Most soils show rapid and strong gradient
changes with increasing depth along a soil profile. Accurate
soil temperature data can be used to help predict geochemical
reaction kinetics and may be used to determine soil
permeability differences.
Techniques used for soil pore water sampling have generated a
great deal of interest among environmental geologists. In areas
with a shallow water table, in situ soil pore water sampling to
determine the existence of pollution problems is usually not
conducted, but many parts of the country have deep water tables
(100's of feet below grade). It is in these areas that soil
pore water sampling is often used with varying degrees of
success.
Soil water pore samples are obtained either by laboratory
extraction methods from grab samples or with in situ samplers.
Laboratory extraction techniques can include displacement,
compaction, centrifugation, or suction methods.
In situ techniques are generally based on a vacuum-induced
suction method that causes the soil pore water to flow into a
collection vessel and is then analyzed in a laboratory setting.
Sampling devices developed for this purpose include vacuum
plates and tubes, vacuum pressure lysimeters, -membrane filter
samples, and absorbent material based devices. Each of these
types of sampling devices comes in a variety of configurations.
Each type of device has its advantages and disadvantages,
including installation techniques, operating characteristics,
maintenance, and operating lifetime. Morrison (1980) describes
many of the commonly used devices for this program. The EPA
draft document, Unsaturated Zone Monitoring Techniques (1986),
is an excellent reference for these methods. Continued interest
in vadose zone monitoring will undoubtedly help to spawn new
methods of monitoring this important zone for pollution
problems.
2.3 AQUIFER TESTING
Individuals who design and construct wells must have a thorough
understanding of well hydraulics. Most of the real-life con-
ditions found in well hydraulics are quite complicated; there-
fore, it has been difficult to develop the complex mathematical
solutions necessary to solve all of the geologic and hydrologic
uncertainties that are present in an aquifer. Given this com-
plexity, only the most fundamental hydraulic theories can be
applied successfully in everyday well design and construction.
0639B
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Remarkably, these basic methods regularly yield accurate
results in most cases without laborious calculations. This
subsection briefly examines the various aquifer tests and their
mathematical solutions. For additional information on the
subject, see Driscoll (1986), Freeze and Cherry (1979), Lohman
(1979) Bear ,(1972, 1979), and Walton (1970).
2.3.1 Types of Tests
2.3.1.1 Laboratory Tests
These tests are most commonly performed on a small, undisturbed
sample of the rock or sediment in question. The sample is
obtained from a Shelby tube sampler, and laboratory measure-
ments are made on the sample. Because of the way in which the
test is performed, the results are generally reported for
vertical permeability only. Since only a small area is tested,
heterogeneity in the aquifer cannot be considered except with
the use of an extensive sampling program. Additionally, data on
horizontal permeability are more important than vertical
permeability when investigating pollutant migration.
2.3.1.2 Slug Tests
Slug tests offer a quick and inexpensive field method of
obtaining in situ permeability values. These generally give a
good approximation of horizontal permeability values for the
localized zone surrounding a well with hydraulic conductivities
less than or equal to 10"2 cm/sec.
The following general sequence of events is necessary to
conduct a slug test:
• The static groundwater level is determined.
® A slug is injected into or withdrawn from the
groundwater. Note that the analysis assumes an
instantaneous change in volume with this event
recorded at elapsed time equal to zero.
o Groundwater levels (depths) are measured and recorded
with corresponding elapsed times. A number of
measurements are required over time to adequately
represent the test. Typically, a high density of
measurements is necessary during the early stages of
the test with the number of measurements decreasing
over time.
0639B
2-35
-------
• Measurements continue until the groundwater level
approaches equilibrium.
The time required for a slug test to provide sufficient data is
related to the volume of the slug, the hydraulic conductivity
of the subsurface strata being tested, and the construction of
the well. These factors must be such that several incremental
changes in groundwater level can be practically measured during
the test interval.
2.3.1.3 Constant-Rate Pump Tests
The major purpose of pumping tests is to provide data from
which the principal factors of aquifer performance
transmissivity and storage coefficient -- can be calculated.
Pump tests will allow the hydrologist to predict:
• The rate of groundwater migration.
• The effect of new withdrawals on existing wells.
• The drawdowns in a well at future times and different
di scha rges.
• The radius of the cone of influence for individual or
multiple wells.
A pump test consists of pumping a well at a certain rate and
recording the drawdown in the pumping well and in nearby
observation wells at 1 specific times. There are two primary
types of aquifer tests: constant-rate tests and step-drawdown
tests. In the const ant-rate test, the well is pumped for a
significant length of time at one rate, whereas in a step-draw-
down test the well is pumped at successively greater discharges
for relatively short periods. The results obtained from properly
performed pump tests are one of the most important tools in
groundwater investigations.
Measurements required for pump tests include the static water
levels just before the test is started, time since the pump was
started, pumping rate, pumping levels or dynamic water levels
at various intervals during the pumping period, time of any
change in discharge rate, and time the pump stopped.
Measurements of water levels after the pump is stopped
(recovery) are extremely valuable in verifying the aquifer
coefficients calculated during the pumping phase of the test.
In areas where nearby wells being pumped may have an effect on
the well to be tested, data should be collected for a day or
two before the start of the test to determine water table
fluctuation patterns. Pump tests are usually run for a minimum
period of 12 hours. Many pump tests are conducted for a period
of up to 96 hours. High labor costs and disposal of a large
quantity of contaminated water are two major problems that must
be considered during the pump test design.
2-36
0639B
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2.3.1.4 Step-Drawdown Pump Tests
Conventional well hydraulics theory is based on the assumption
that laminar flow conditions exist in the aquifer during
pumping. If the flow is laminar, drawdown is directly
proportional to the pumping rate. Turbulent flow occurs in some
wells, however, when they are pumped at a sufficiently high
rate. Under turbulent conditions, the linear relationship
between drawdown and pumping rate no longer holds, and part of
the drawdown is generally related to the pumping rate raised to
some power greater than 1.
When turbulent flow occurs, the specific capacity will decline,
often dramatically, as the discharge rate is increased. When
this happens, it is useful to have a means of computing the
turbulent and laminar drawdown components in order to make
proper judgments concerning the optimum pumping rate and
pump-setting depth.
The step-drawdown test was developed to examine the performance
of wells having turbulent flow (Jacob, 1946b). In a step-draw-
down test, the well is pumped at several successively higher
pumping rates and the drawdown for each rate, or step, is
recorded. The entire test is usually conducted during one day,
and calculations are simplified if all the pumping times are
the same for each discharge rate. Usually five to eight pumping
steps are used, each lasting 1 to 2 hours. The data from a step
test can be used to determine the relative proportion of
laminar and turbulent flow occurring at any pumping rate. It
can also be used to determine the discharge rate at which a
full-scale pump test should be conducted. The step-drawdown
test is usually conducted at least 24 hours before the pump
test is to be started. This allows the well time to recover
fully.
2.3.1.5 Packer Tests
It may occasionally be necessary to determine aquifer
characteristics for discrete zones either in open boreholes or
in a screened well. In these cases, pressure permeability tests
can be run using one or two packers to isolate various screened
zones or lengths of drill hole in stable rock. While hole
diameters usually do not exceed 3-1/2 inches, larger holes can
also be tested if suitable equipment is available. The tests
may be run in vertical, angled, or horizontal holes and
analyzed if the head and zone relationships can be determined.
Pressure tests are often the only practical tests to use when
it is necessary to determine permeability of stream beds or
lake beds below water.
0639B
2-37
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Compression packers, inflatable packers, leather cups, and
similar types of packers have been used for pressure testing.
Inflatable packers are usually more economical because they
reduce testing time and ensure a tighter seal, particularly in
rough-walled or out-of-round holes. The packers are inflated
through tubes extending to a cylinder of air or nitrogen at the
surface. If a pressure-sensing instrument is included, pressure
in the test section is sensed by the instrument and is
transmitted to the surface by an electrical circuit where it
either is read from a register at the surface or is recorded on
a chart. This double packer arrangement permits successive
tests at different depths in a completed hole without having to
remove the packer between each test. The pressure sensor can
also be adapted where a single packer is used.
2.3.1.6 Tracer Tests
In principle, the tracer method of studying groundwater
movement corresponds to placing a float in a river and timing
its travel between two points. Although the velocity of a float
is readily determinable, the relationship between its movement
and the mean water velocity is not fixed. A tracer, injected as
a slug into a groundwater body, depicts the movement of
groundwater with accuracy, but it is subject to diffusion,
dispersion, dilution, and adsorption. Therefore, the tracer
must be carefully selected.
The ideal tracer:
• Is detectable at low concentration.
• Is absent, or nearly absent, from the water of the
aqui fer.
• Must not react within the aquifer to form a
precipitate.
• Must not be absorbed or adsorbed.
• Has a low toxicity.
• Is cheap and readily available.
There is no substance that meets these requirements for every
aquifer, although reasonably satisfactory tracers may be found
for particular sets of circumstances. Tracers may be classified
by method of detection: color, chemical determination,
electrical conductivity, nuclear radiation, mass spectrography,
and flame spectrophotometry.
0639B
2-38
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Organic dyes, the most common of which is sodium fluorescein,
may be detected in very low concentrations. Fluorescein,
however, is readily adsorbed by the clay fractions of the
geological matrix. The chloride ion in sodium or calcium
chloride also has been used successfully as a tracer.
Radioactive substances provide convenient and very sensitive
tracers since they can be measured by their nuclear radiations
at mass concentrations as low as 10~17. They are, however,
affected by base-exchange and adsorption phenomena. Certain
radioisotopes, tritium in particular, can be used as tracers
without danger of contaminating the aquifer or of being
absorbed.
In some groundwater systems, such as those in Karst Terrane,
tracer tests may be the only way to determine direction and
travel time. For a more detailed discussion of tracer test
procedures, see Davis et al (1985), Smart and Laidlaw (1977)
and Jones (1984).
2.3.2 Aquifer Test Data Analysis
Aquifer characteristics exert primary control over well
performance in terms of yield versus drawdown. Accordingly,
determination of the effects of well geometry on the flow and
head distribution in aquifers and on the yield and drawdown of
wells has been the goal of most research on well hydraulics.
Mathematical analyses have been made on the basis of steady
state flows according to Darcy's law, and Dupuit's assumption
of horizontal radial flow and mixed radii of influence, as well
as unsteady state conditions in ideal aquifers which are
isotropic, homogeneous, of uniform thickness, and infinite
areal extent. The conclusions are generally adequate for
estimating the performance of wells in confined aquifers, as
well as in unconfined aquifers where the drawdown is a small
percentage of the aquifer thickness and the discharging well is
fully penetrating. Corrections for partial penetration of the
discharging well, large drawdowns in unconfined aquifers, and
anisotropy have been derived, but adequate data for application
of the corrections are often not readily available. Much
research has also been done on analogs and other models of
various types, but too often the geometry of the test apparatus
has not duplicated field conditions.
0639B
2-39
-------
Analyses of results of systematic observations of water level
changes and of other test data yield values of aquifer
characteristics. The extent and reliability of these analyses
are dependent on features of the test including duration of
test, number of observation wells, and method of analysis. Two
general types of analyses are available for determination of
aquifer characteristics: (1) steady state or equilibrium
methods which yield values of transmissivity and hydraulic
conductivity, and (2) transient or nonequilibrium methods which
also yield storativity and boundary conditions. The principal
difference between the two methods is that the transient method
permits analysis of groundwater conditions which change with
time and involve storage, whereas the steady state method does
not.
Test analyses also require an understanding and appreciation of
the hydrologic and geologic setting of the aquifer. Conditions
that should be known include: location, character, and
distance of nearby bodies of surface water; depth, thickness,
and stratigraphic conditions of the aquifer; and construction
details of the test well and of observation wells, if used.
The following subsections describe commonly used analytical
models for aquifer pump test data analysis. Also included is a
summary of analytical models used to solve for slug testing.
For further information on any of these analytical solutions,
see the listed papers and Freeze and Cherry (1979), Fetter
(1980), and Driscoll (1986).
2.3.2.1 Analytical Techniques for Slug Test Data
Four analytical techniques used in the analysis of slug test
data are discussed below. These techniques constitute empirical
relationships that are used to solve for the hydraulic
conductivity in an aquifer immediate to the test well. Both
confined and unconfined aquifer conditions are addressed with
two different approaches to solve for conductivity for each
condition. The applicability of each analytical technique is
contingent upon collected data meeting specified validity
criteria as described below.
• Ferris-Knowles Method
In general, this method is applied to wells completed
in confined aquifers with hydraulic conductivities
less than 0.05 cm/sec. The analysis of the data
involves an arithmetic plot of residual drawdown
versus the reciprocal of time. Validity of the
analysis is determined by fitting a straight line
through the plot of the data points, in which the line
intersects the origin (0,0). The equation used to
solve for hydraulic conductivity, K, using this method
is as follows:
2-40
0639B
-------
q(1/t)
K =
4 tt H (t) L
Where:
q = Volume Discharged (Slug Volume)
H(t) = Residual Drawdown at Time = t
t = Time
L = Screen Length
The values of 1/t and H(t) are obtained from a
straight line fit through the plot of slug test data.
Hvorslev Method
The research associated with this method was
originally performed in near-surface saturated soils.
As a result, this method is applied to wells completed
in unconfined aquifers. Analysis of this method
involves a semilogarithmic plot of the residual
drawdown divided by the instantaneous drawdown versus
time. Validity of the analysis. is ascertained by
fitting a straight line through the plot of the data
points so that the line intercepts the coordinate 1,0.
Basic equations are applied for different
configurations of soil. In general, permeability is
proportional to a "shape factor" and inversely
proportional to a "time lag." The shape factor is
determined from the test well characteristics and
dimensions, while the time lag is determined from the
semilogarithmic plot. The equation used to solve for
hydraulic conductivity, K, using this method is as
follows:
r2ln(L/Rw)
K =
2LT„
Where:
r = Well Casing Radius
L = Screen Length
Rw = Borehole Radius
T0 = Time Lag When Residual Drawdown/Instantaneous
Drawdown = 10"°• a 3 4 3
0639B
2-41
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Bouwer-Rice Method
The solution for hydraulic conductivity using this
method is more involved than the other methods,
resulting from empirical derivations. This method is
applied to either partially or completely penetrating
wells in unconfined aquifers. Analysis involves a
semi logarithmic plot of residual drawdown versus time.
A straight line is fitted to the early-time data for
use in calculating conductivity. The equation used to
solve for hydraulic conductivity, K, using this method
is as follows:
rzln(Re/Rw) H0
K = In
2L(t) H(t)
Where:
r = Well Radius
Re = Effective Radius
Rw = Borehole Radius
L = Screen Length
t = Time at Residual Drawdown Measurement
H0 = Instantaneous Drawdown at Time, t = 0
H(t) = Residual Drawdown at Time = t
The term [In (Re/Rw)] is determined with one of
two empirical relationships. These relationships use
one or two empirical coefficients derived from curves
based on the value of Le/Rw.
Cooper-Bredehoeft-Papadopulos Method
This method applies to wells completed in confined
aquifers with hydraulic conductivities less than 0.05
cm/sec. The analysis of the data involves a semilo-
garithmic plot of residual drawdown divided by the
initial residual drawdown versus time. The plot is
then matched to a set of type curves. Resulting match
points are substituted into an equation as time values
for derivation of hydraulic conductivity. The equation
used to solve for hydraulic conductivity, K, using
this method is as follows:
0639B
2-42
-------
K =
tL
Where:
r = Well Casing Radius
t = Time Corresponding to a Metch Point on a Type Curve
L = Screen Length
2.3.2.2 Analytical Techniques for Pump Test Data
Table 2-3 summarizes several of the more commonly used
techniques for analyzing pump test data. Details of these
sources can be found in Kruseman and DeRidder (1976).
0639B
2-43
-------
Table 2-3
Analytical Models for Aquifer Test Data Analysis
(after Kruseman and DeRidder, 1976)
Aquifer Type
Type of
Solution
Method Name*
Type
Comments
Confined
Semiconf ined
Unconf ined
Confined
Steady state Thiem (1906)
DeGlee (1930)
Hantush-Jacob
(1955)
Theim-Dupuit
(1906)
Unsteady state Theis (1935)
Chow (1952)
Jacob (1946)
Theis Recovery
(1935)
Calculation
Curve fitting
Straight line
Calculation
Curve matching
Nanograph
Straight line
Straight line
Semiconfined Unsteady state Walton (1962) Curve matching
Hantush I, II
(1956)
Hantush III
(1956)
Inflection
point
Curve matching
Unconfined
with delayed
yield
Unsteady state Bolton (1963) Curve matching
0639B
2-44
-------
Table 2-3
(continued)
Aquifer Type
Type of
Solution
Method Name*
Type
Comments
Any
Any
Confined
Confined
Conf ined
Any
Unsteady state Stallman
(Ferris et al
1962)
Hantush Image
(1959)
Unsteady state Hantush (1966)
Hantush (1964)
Unsteady state Hantush (1962)
Papadopulos &
Copper (1967)
Unsteady state Aron & Scott
(1965)
Sternberg
(1967, 1968)
Cooper Jacob
(1946)
Curve matching Aquifer crossed by
fully penetrating
recharge or
discharge boundary
Straight line 1 recharge boundary
only
Calculation Anisotropic aquifer
Curve matching Variable thickness
Curve matching Partial penetration
or straight
line
Curve fitting Casing storage
Straight line Variable discharge
Straight line Rate-decreasing
discharge
Step-pumping
~Descriptions of method and reference are available in Kruseman and
DeRidder, 1976.
0639B
2-45
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SECTION 3
MONITORING SYSTEM DESIGN
Designing systems for monitoring groundwater contamination is
as much an art as a science because of the numerous . factors
that should be considered. As a consequence, there may be many
technically acceptable system designs for a given set of site
conditions, and practically speaking, no one perfect system.
Specifying a groundwater monitoring system requires addressing
a variety of elements, as illustrated in Figure 3-1. The focus
of this paper is system design, which involves planning the
number and locations of wells in the system, as well as the
depth (i.e., screen setting) and configuration (Figure 3-2) of
each well. Table 3-1 summarizes some of the technical con-
siderations and sources of data for specifying well numbers,
locations, and depths. Table 3-2 summarizes the advantages and
disadvantages of the five well configurations shown in Figure
3-2 .
Figures 3-3 and 3-4 illustrate some of the factors that should
be considered in selecting well locations, depths, and
configurations. In Figure 3-3, the site is underlain by strata
of substantially different hydraulic conductivities. In this
situation, the depth and location of each well must be closely
coordinated if each hydrogeologic unit is to be monitored
adequately. In Figure 3-4, the site is located on a drainage
divide and is underlain by sands and clays. In this situation,
shallow monitor wells should be placed around the perimeter of
the site boundaries on the assumption that groundwater will
flow in all directions from the site. Provisions would also
have to be made to identify an appropriate off-site location
for one or more "background" wells. Furthermore, it would be
prudent to also monitor deeper sand zones given that very few
geologic units are truly impermeable. In both of these cases,
information from geophysical surveys and soil boring samples
would be needed to support the design of the monitoring systems.
Figures 3-5 through 3-12 illustrate how a groundwater
monitoring system can evolve as additional studies are under-
taken on a site. Figure 3-5 is a map view of a hypothetical
site located between a forest and a lake. An environmental
survey of the site recorded the presence of areas of dead
vegetation, a contaminated spring, and contaminated lake
sediments (Figure 3-5) . Based on this survey and a review of
the geology of the area that indicated bedrock sequences of
sandstones and shales, a monitoring system was designed to
assess groundwater quality. Each of the five wells in the
monitoring system, shown in Figure 3-6, were screened in silty
2-4 6
0639B
-------
Objectives
Assess Groundwater Quality; Delineate Horizontal
and Vertical Rate And Extent of Contamination;
Evaluate Effectiveness of Corrective Actions;
Monitor Long-Term Groundwater Quality
System Design
Numbers, Locations,
Depths, and Configurations
of Wells
Program Design
Sample Analysis Parameters
and Frequency; Field
and Laboratory QA/QC
Well Design
Well Materials
Screen Type and Setting;
Security and Identification Measures
Implementation Procedures
Well Installation, Sampling;
Laboratory Analysis, and
Data Evaluation Procedures
Figure 3-1 Elements of Groundwater Monitoring
-------
Table 3-1
Technical Considerations and Data Sources for Monitoring System Design
System
Des ign
Parameter
Technical Considerations
Primary Data Sources
Well Locations
• Background information review
Objectives of monitoring system,
waste types and locations, con-
taminant geochemistry, access,
and clearance
Stressed vegetation, fracture traces • Aerial photographs
Contamination of surface waters,
springs, or existing wells
EM, GPR and other geophysical
anomalies
Soil-gas anomalies
Soil or rock samples, hydrologic
measurements
• Environmental surveys
• Geophysical surveys
• Soil-gas survey
• Direct field surveys
Well Depths
Objectives of monitoring system,
waste types and locations, con-
taminant geochemistry
Elevations of surface waters,
springs, and water in existing
wel Is
Stratigraphic information from
GPR, seismic, or resistivity
surveys
Soil or rock samples, hydrologic
measurements
• Background information review
• Environmental surveys
• Geophysical surveys
• Direct field surveys
Well Configura-
tions
Objectives of monitoring system,
waste types and locations, con-
taminant geochemistry
Stratigraphic information from
GPR, seismic, or resistivity
surveys
Soil or rock samples, hydrologic
measurements
• Background information review
• Geophysical surveys
• Direct field surveys
0639B
2-48
-------
Multiple
Single Fully Sampling Single Multiple
Zone Screened Point Borehole Borehole
Well Well Well Well Nest Well Nest
Grout
* Seal
777^ 7; A. \<—TTKX
Source: Repa and Kufs, 1985
Figure 3-2 W@B6 Configurations Used
for Groundwater Monitoring
-------
Table 3-2
Advantages and Disadvantages of Monitoring Well Configurations Shown in Figure 3-2
Well
Configurations Advantages Disadvantages
Single Zone
Well
Relatively simple to install by a
variety of methods
Can provide discrete samples from
a precise interval thus aiding data
interpretation
Easy to prevent interaquifer
contamination if designed and
installed properly
Vertical distributions of
contaminants or hydraulic
gradients cannot be
determined
Many wells are needed to
delineate a plume increasing
costs and the time required
to install and sample the
svs tem
Fully Screened
Well
Relatively simple to install by
a variety of methods
Can provide composite samples of
large intervals thus reducing the
number of samples
Produces relatively higher yields
and thus is useful for pump testing
Results are biased if highly
contaminated waters are
diluted by less contaminated
waters during sampling
Vertical distributions of
contaminants or hydraulic
gradients cannot be
determined
Vertical migration of
contaminants may occur over
the screened interval
spreading contaminants to
clean zones
Impossible to prevent inter-
aquifer mixing if screened
over more than one aquifer
Multiple
Sampling Point
Well
Can provide information on the
vertical distribution of con-
taminants and hydraulic gradients
Installation is relatively simple
although construction takes longer
than for wells with a single screen
Can be used to obtain composite
samples
Fewer wells are needed in a
monitoring system thus reducing
costs
Preventing interaquifer
contamination is difficult
if not impossible
Sampling is complicated, time
consuming, and requires
specialized equipment
Cost per well is relatively
high
0639B
2-50
-------
Table 3-2
(continued)
Well
Configurations Advantages Disadvantages
Single- • Provides information on the vertical •
Borehole distribution of contaminants and
Well Nest hydraulic gradients •
• Sampling is not difficult but may
require specialized equipment
depending on well diameters
Multiple- • Provides information on hydraulic
Borehole gradients and the vertical
Well Nest distribution of contaminants
• Simple to install by a variety
of methods
• Preventing aquifer cross contami-
nation is not difficult
• Sampling is simple and usually
does not require specialized
equipment
2-51
0639B
Requires suitable installa-
tion methods
Improper construction can
reduce effectiveness and
allow vertical movement of
of contaminants
Installation is time
consuming
Cost per nest is relatively
high although cost per well
is relatively low
Installation is time con-
suming but not difficult
Cost per nest is relatively
high
-------
to
I
Ul
M
Water
Table
Flow
Silty Sand
Clayey Silt
Gravel
Clay
Impermeable
Bedrock
Source. Repa and Kufs, 1985
Figure 3-3 Example of a Situation in Which
Geologic Units of Different Hydraulic
Conductivities Can Influence the
Design of a Monitoring System
-------
Low Permeability
Clay
, Sandy Zones
in Clay
Sand
Flow
Source: Repa and Kufs, 1985
Figure 3-4 Example of a Situation in Which
Different Groundwater Flow Directions
and Geologic Heterogeneities Can
Influence the Monitoring System Design
-------
Outcrop of
Fractured
Shale
? ^ r
•)r o'
_£i
{?
. y - W r
^ ^ (y & 5
Mature
Waste
"¦¦'¦'¦¦ Disposal
Ci4a
Leachate Seep
and Contaminated
Lake Sediment
Legend
hOOl Areas of Dead Vegetation
After: Repa and Kufs, 1985
Figure 3-5 Result of an Environmental
Survey at a Hypothetical Site
-------
^ V(,^rrr
/A ^ >
—r*-
rs
o
r -^ ¦ fv
c- o ^
f-
Shale
Outcrop
r °
f"1
c
& «*>
^ C
f*
f^> ^
yt
A o
^c V
• -nf* £
f? ^e>
«b ^(i •¦
£\_ {?
Waste
, Disposal1
Site
All Wells Screened in
Silty Sand Above
Fractured Shale Bedrock
Atter: Repa and Kufs, 1985
Figure 3-6 Monitoring System for
Assessing Groundwater Quality
-------
t\J
I
Ln
CTl
Shale
Outcrop
Lake
Waste
Disposal
Site
After: Repa and Kufs, 1985
Figure 3-7 Result of a Fracture-Trace Analysis
-------
w^vrfW^'ta^
-------
Shale
Outcrop
c
Lake
waste
isposal
Site >¦
Legend
# 5 Existing Monitor Wells
O 18 Proposed Borings
After: Repa and Kufs, 1985
Figure 3-9 Result of a Soil-Gas Survey
-------
Shale
Outcrop
Lake
Waste
Disposal
Site
A
o ^
v.
Legend
# 5 Existing Overburden Monitor Wells
O 18 Completed Soil Borings
~ 10 Proposed Overburden Monitor Wells
¦ 4 Proposed Bedrock Monitor Wells
After: Repa and Kufs, 1985
Figure 3-10 Monitoring System
for Assessing Extent of Contamination
-------
Sandstone
Shale
Sand-
stone
iandstone
Overburden-
Leachate
Plume
Lake::
¦ Waste
Disposal
Site
Contaminated
Seep
Bedrock
Leachate
Plumes
Source: Repa and Kufs, 1985
Figure 3-11 Example of the Effects of Site Geology
on Leachate Plume Movement (Map view)
-------
to
I
o
^.\vt 1/
~ . __Water Table V,. - -j
FtowmZLT" It
Seep
Overland Flow
Overburden
Lake
Sand-
stone
Shale
Shale
Sandstone
Sandstone
Source: Repa and Kufs, 1985
Figure 3-12 Example of the Effects of Site Geology
on Leachate Plume Movement
(Cross Sectional View)
-------
sands which overlie shale bedrock. Contamination in the four
downgradient wells prompted the site operator to conduct
additional studies, including a fracture-trace evaluation
(Figure 3-7), a GPR survey (shown in cross section in Figure
3-8), a soil-gas survey (Figure 3-9), and a soil-boring program
(Figure 3-9). These studies revealed the presence of a
sandstone unit underlying the site and the potential for both
bedrock and overburden contamination. Based on these studies,
the monitoring system was expanded to assess the directions,
extents, and rates of contaminate migration, as shown in Figure
3-10.
Actual site conditions are illustrated in Figures 3-11 (map
view) and 3-12 (cross sections). By comparing Figures 3-5
through 3-10 with Figures 3-11 and 3-12, it is easy to
understand how even a carefully designed monitoring system
could fail to detect a zone of contamination, in this case in
the sandstone unit under the lake.
The failures of the hypothetical system described above and
many actual systems are frequently the result of presumptions
that are made about the extent of contamination based on the
pattern of contamination observed in wells. Figures . 3-13
through 3-19 illustrate this point further. Figure 3-13 is a
hypothetical site located near a small lake and the confluence
of two small rivers. Some of the domestic and industrial wells
in the vicinity of the site are contaminated while others are
not. Figures 3-14 through 3-19 are cross sections of the site
illustrating a variety of hydrogeologic and geochemical
conditions that could cause similar contamination patterns.
Figures 3-14 and 3-15 illustrate simple geologic settings in
which the contamination pattern is caused by differences in
well depths or improper well construction. In Figure 3-14, the
uncontaminated wells are shallow while in Figure 3-15 they are
deep. Figure 3-16 illustrates a somewhat more complex geologic
situation in which the uncontaminated wells are set within a
perched water table. Figure 3-17 shows how complex rock
structures can account for the contamination pattern. In Figure
3-17, all the wells are screened at the bottom of sandstone
units above shales, and there is a second source of con-
tamination. In Figure 3-18, all the wells are installed in
unconsolidated materials above fractured and faulted bedrock.
Finally, Figure 3-19 illustrates how two sources of nonaqueous
phase liquids (NAPL's), one high density and the other low
density, can account for the observed contamination.
0639B
2-62
-------
to
I
Artificial
Lake
LEGEND
OUncontaminated Private Wells
# Contaminated Private Wells
B Contaminated Industrial Well
Source. Repa and Kufs, 1985
Figure 3-13 Result of Sampling Existing Wells
at a Hypothetical Site
-------
Artificial
Lake
Water
Table
River
After: Repa and Kufs, 1985
Figure 3-14 Example of a Situation in Which
Well Construction and Depth Influence
the Pattern of Contamination
-------
Artificial
Lake
Water
Table"
River
After: Repa and Kufs, 1985
Figure 3-15 Example of a Situation in Which
WeBS Depth InfBuences
the Pattern of Contamination
-------
to
I
(Ti
(Ti
Artificial
Lake
Spring
fv dler
Table —
•I
After: Repa and Kufs, 1985
Figure 3-16 Example of a Situation in Which
Different Water-Bearing Zones
influence the Pattern of Contamination
-------
Artificial
Lake
Water
River
After: Repa and Kufs, 1985
Figure 3-17 Example of a Situation in Which
Rock Structure and Well Depth
Influence the Pattern of Contamination
-------
Artificial
Water
Table
River
After: Repa and Kufs, 1985
Figure 3-18 Example of a Situation in Which
Rock Faults and Fractures Influence
the Pattern of Contamination
-------
Artificial
Lake
Water
Table"
River
After: Repa and Kufs, 1985
Figure 3-19 Example of a Situation in Which
Contaminant Solubility and Density
Influence the Pattern of Contamination
-------
SECTION 4
PROBLEMS IN MONITORING SYSTEM DESIGN
Because there are so many variables to consider in planning and
implementing a monitoring system, it is understandable that
most systems do not function as designed. Typical problems
found in groundwater monitoring systems can be categorized as:
planning problems, implementation problems, site-condition
problems, and "special" problems.
Planning problems are commonly the result of using incorrect
background information or failing to consider one of the many
factors in system design. Examples of planning problems include:
Wells not positioned appropriately - Usually the
result of an inadequate understanding of the
hydrogeology of the site and the contaminant's
geochemistry or a failure to consider how the system
will be used to collect data for the intended purpose.
o Screen lengths not correctly selected - Usually for
the same reasons as well positions.
• Periodic flow changes not addressed - Usually the
result of a failure to consider interactions between
surface water and groundwater.
Even the most carefully designed monitoring system can fail to
achieve its objectives under certain conditions. Two types of
problems that can occur even in well-planned systems are
associated with the installation of the system and with
unanticipated conditions.
Problems that can occur as a result of implementing the system
include:
» Screen setting not correct
poor judgment in the field
that cannot be monitored
phase liquids (NAPL's)
contaminants for which it
optimal screen settinas.
- Usually the result of
or fractionated leachate
easily. Dense nonaqueous
are good examples of
is difficult to select
« Well silts up after installation -
of a broken screen or joint,
selection of screen and sandpack
material, or inadequate development.
Usually the result
an inappropriate
for the aquifer
0639B
2-70
-------
• Gravel pack clogged - May be the result of a poorly-
specified gravel pack or the presence of NAPL' s or
bacteria that can fill void areas, thus inhibiting
f low.
• Well seal leaks - Usually the result of improper
installation but may be caused by degradation of the
seal by contaminants or aggressive groundwater.
Other implementation problems include inappropriate choice of
drilling technique, poor selection of well materials,
inadequate decontamination, inadequate documentation of well
installation, inadequate development, lack of well top
identification and security, and poor sampling and analysis
techniques.
Problems that can occur as a result of unanticipated site
conditions include:
• Well does not produce - Usually the result of trying
to monitor low-yield zones but may also be caused by
inadequate development or poor screen/sandpack design.
• Water table fluctuates greatly - Can involve
short-term fluctuation such as those caused by tides
or seasonal trends in precipitation and
evapotranspiration or long-term fluctuations such as
those associated with aquifer depletion.
• Pumping wells disrupt flow patterns - Usually
involves high-capacity supply wells screened in the
same zone as the monitoring system and having a large
zone of influence or wells screened in adjacent zones
that induce recharge from the zone being monitored.
• Undocumented waste sources confound results - Usually
attributable to inconspicuous waste sources such as
buried tanks, sewers, or pipelines, especially when
associated with commercial establishments such as gas
stations, dry cleaners, beauty salons, photofinishers,
and analytical laboratories.
Figure 4-1 illustrates a situation in which the proximity of
two sources of contamination could lead to uninterpretable
results from a monitoring system. It would also be difficult in
this situation to determine "background" water quality condi-
tions given that the upgradient groundwater of the site is
contaminated. Confounded results from a monitoring system may
also be attributed to degradation of contaminants downgradient
of the primary contaminant source.
0639B
2-71
-------
rvj
I
-j
1SJ
Recharge
Area
Waste Site
Water
Table
Water Table Mound Beneath Waste Sites
Discharge
Area
Waste
Site
Permeable
Alluvium
Stream
Shale
Aquitard
Source. Repa and Kufs, 1985
Figyre 4-1 Example of a Sityatiosi in Which Multiple
Wast© Soyrees ©an influence monitoring
System Results
-------
The last category of problems with monitoring systems includes
those problems caused by "special" site conditions or
contaminant properties. Site conditions that complicate
monitoring system design include the presence of irregularly
shaped water-bearing zones and zones of high secondary
permeability (i.e., units with fractures or solution cavities).
Irregularly shaped aquifers include perched zones, shoestring
glacial or fluvial aquifers, interfingered layers, and
structurally altered zones (i.e., rock units that have been
folded, faulted, or intruded). Fractured units could include
almost any rock type, as well as unconsolidated deposits having
a high clay content. Solution cavities are most commonly found
in carbonate rocks (e.g., limestones and dolomites) although
other types may also be dissolved. Figure 4-2 illustrates some
of the difficulties of trying to monitor zones of secondary
permeabi1i ty.
Contaminants can also cause problems with monitoring systems
because of the transformations and other interactions they
undergo in the environment (e.g., sorption, biodegradation,
chemical reactions) and because of the way their solubility and
density can influence flow. NAPL's can - be especially
troublesome to monitor. Low-density NAPL's will float on top of
the water table and depress it somewhat requiring that wells be
screened above and below the top of the seasonal high water
table. The top of the screen must also be set far enough above
the top of the seasonal high water table so that the well will
intercept the full thickness of floating NAPL. Furthermore,
because of the different properties of water and* low-density
NAPL's, special equipment is required to determine their depth
and thickness. High-density NAPL's will tend not to migrate in
the direction of groundwater flow, but rather to sink in an
aquifer and follow the topography of a relatively impermeable
unit. Figure 4-3 illustrates this concept.
A summary of some of the more common problems with monitoring
systems and approaches to prevent or correct the problems is
presented in Table 4-1.
0639B
2-73
-------
Nj
I
*0)^ /a\Aaa
Permeable Sandstone
r(unje:-
Bedding Plane
J Leakage
Weil Cemented
Sandstone
Limestone
£rmeable Sandstone
Shales
Semi-Permeable
Siltstone
0/cfe
""Pemieab/e
Fault
Zone
Shales
Permeable
Sandstone
F'9U
r©4«2
Repa and Kufs
In Wh¦
-------
Water Table
Flow
Sand
Plume
Flow
Clay
Source: Repa and Kufs, 1985
Figure 4-3 Example of a Situation in Which
High-Density NAPLs Could Emigrate Against
the Direction of Groundwater Flow
-------
Table 4-1
Selected Problems in Monitoring System Design
Description of Problems Approach to Prevention Approach to Correction
1. Wells not positioned for
triangulating ground-
water flow directions.
PLANNING PROBLEMS
Use basic hydrogeologic
assumptions to estimate
flow directions. Use GPR
to evaluate validity of
assumptions.
2. Wells not positioned
for evaluating extent
of contamination.
3. Screen length or
settings not correctly
selected.
4. Periodic flow changes
not addressed.
Estimate the distance the
plume may have migrated
from the site based on
site history and hydro-
geology and contaminant
geochemistry (See Repa
and Kufs, 1985).
Use aerial image or EM
and soil gas surveys to
check estimation.
Use background geologic
and geochemical infor-
mational to anticipate
contaminant flow. Compare
information to on-site
soil samples collected
from boreholes.
Use basic hydrogeologic
assumptions and back-
ground data to anticipate
possible flow changes.
Install additional wells or
find existing wells screened
in the same water-bearing
zone.
Install additional wells or
find existing wells screened
in the same water-bearing
zone.
Install additional wells or
find existing wells screened
in the same water-bearing
zone.
Install additional wells or
find existing wells screened
in the same water-bearinc
zone.
0639B
2-76
-------
Table 4-1
(continued)
Description of Problems Approach to Prevention Approach to Correction
IMPLEMENTATION PROBLEMS
1. Well seals leak.
Design seals to be com-
patible with anticipated
use of well and site
hydrogeology and geochem-
istry. Monitor installa-
tion of seals closely by
repetitive measurements of
depth to seal.
Abandon leaking wells to
prevent interaquifer leakage
and replace well.
Well silts up after
installation or sand
pack clogs.
Select screen opening size Redevelop well or replace,
and sand pack gradation to
be compatible with geologic
materials to be screened.
Well construction not
documented.
Require contractors to Use downhole TV and geo-
produce as-built diagrams physical logs to approximate
of each well installed. well construction details.
SITE CONDITION PROBLEMS
Water table fluctuates
too far above or below
screened portion of
well.
Estimate water table
fluctuations from
historical precipitation
recorded and regional
water levels in lakes and
existing wells.
Schedule sampling to
correspond with appropriate
water level or replace well.
2. Pumping wells period-
ically disrupt flow
patterns.
Identify presence and
schedule of any high-
capacity wells and
estimate their zones of
influence. Position
monitor wells to assess
the effects of inter-
mittent pumping.
Collect water level data at
regular intervals over time
and attempt to model site.
Add additional wells as
needed.
0639B
2-77
-------
Table 4-1
(continued)
Description of Problems Approach to Prevention Approach to Correction
3. Undocumented waste
sources confound
results.
Identify presence of
potential contaminant
sources and position
wells appropriately.
Develop chemical profiles
for each well to try to
correlate contaminant geo-
chemistry. Add additional
wells if necessary.
1. Presence of irregularly
shaped aquifers.
SPECIAL PROBLEMS
Use background geologic
information; GPR, seismic,
and resistivity surveys;
and soil borings to
evaluate aquifer geomet-
rically. Install monitor
wells in phases to
optimize effectiveness.
Conduct geophysical surveys
and install additional
wells as necessary.
2. Contaminant migration
follows complex fracture
patterns.
Evaluate possible fracture
patterns using background
geologic literature,
aerial photographs,
measurements of outcrops,
oriented cores, downhole
flowmeters, packer tests,
and appropriate borehole
geophysical techniques
(Thomas and McGlew, 1986).
Install wells in phases
to optimize effectiveness.
Conduct additional surveys,
such as packer tests and
tracer studies, and install
wells as necessary.
3. Aquifer-contaminant
interactions confound
results.
Identify contaminants of
concern and potential
environmental transfor-
mations. Conduct labora-
tory tests if appropriate
Use statistical models or
other advanced techniques
to evaluate data inter-
relationships. Install
additional wells as needed.
0639B
2-78
-------
Table 4-1
(continued)
Description of Problems Approach to Prevention Approach to Correction
4. Nonaqueous phase liquids Low-density NAPL's: use Conduct additional surveys
(NAPL's) do not follow soil borings, soil-gas such as packer tests and
expected patterns. surveys, and geophysical trace studies and install
techniques for mapping wells as necessary,
water tables to approxi-
mate contaminant movement
patterns. High-density
NAPL's: use GPR, seismic,
and resistance surveys
and soil borings to
evaluate stratigraphy
relative to movement
patterns.
0639B
2-79
-------
SECTION 5
REFERENCES
Bear, J. Dynamics of Fluids in Porous Media, American Elsevier,
NY, NY. 1972.
Bear, J. Hydraulics of Groundwater 2nd ed. McGraw Hill, Inc.,
NY, NY. 1979.
Benson, R.C. Geophysical Techniques for Sensing Buried Wastes
and Waste Migration: An Update. Seminar Presented at the 7th
National Conference on the Management of Uncontrolled Hazardous
Waste Sites. December 1-3, 1986. Washington, DC. 1986.
Bisque, R.E. Migration Rates of Volatiles from Buried Hydro-
carbon Sources in: Petroleum Hydrocarbons and Organic Chemicals
in Groundwater Prevention, Detection and Restoration, NWWA/API,
pp.267-271. 1984.
Davis, S.N., D.J. Campbell, H.W. Bentley and T.J. Flynn, 1985.
Groundwater Tracers. National Well Water Association, Worthing-
ton, OH.
Driscoll, F.G. Groundwater and Wells 2nd ed. Johnson Division,
St. Paul, MN. 1986.
Fetter, C.W. Applied Hydrogeology. Charles E. Merrill Publish-
ing Co., Columbus, OH. 1980.
Freeze; R.A. and J.A. Cherry. Groundwater. Prentice-Hall, Inc.
Englewood Cliffs, NJ. 604 pp. 1979.
Jacob, C.E. Radial Flow in a Leaky Artesian Aquifer. Trans.
American Geophysical Union, V. 27, no. 2, pp. 198-205. 1946.
Johnson, W.J. and D.W. Johnson. Pitfalls of Geophysics in
Characterizing Underground Hazardous Waste. pp. 227-232 in
Proceedings of the 7th National Conference on Management of
Uncontrolled Hazardous Waste Sites. Hazardous Materials Control
Research Institute (HMCRI), Silver Spring, MD. 1986.
Kelley, D.R. A Summary of Major Geophysical Logging Methods,
Pennsylvania Geological Survey M. R. Report 61. 1969.
Keys, W.S. and L.M. MacCary. Applications of Borehole Geophysics
to Water Resources Investigations. U.S. Geological Survey
Techniques of Water Resources Investigation. Book 2, Chapter
E-l. U.S.G.S. Reston, VA.
0639B
2-80
-------
Krauss, E.V., J.G. Oster, and K.O. Thomsen. Processes Affecting
the Interpretation of Trichloroethylene Data from Soil Gas
Analysis, pp.138-142 in Proceedings of the 7th National Confer-
ence on Management of Uncontrolled Hazardous Waste Sites. HMCRI,
Silver Spring, MD. 1986.
Kruseman, G.P. and N.A. DeRidder. Analysis and Evaluation of
Pumping Test Data. International Institute for Land Reclamation
and Improvement. Wageningen, Netherlands. 1976.
Kufs, C.T., D.J. Messinger and S. DelRe. Statistical Modeling
of Geophyscal Data. pp. 110-114 in Proceedings of the 7th
National Conference on the Management of Uncontrolled Hazardous
Waste Sites. HMCRI, Silver Spring, MD. 1986.
Levine, J.D. Capabilities of Soil Sentry Underground Tank Leak
Detection System Under Field Conditions. Report for Genelco,
Inc., Levine and Fricke, Inc. Consulting Engineers and
Hydrologists, Walnut Knoll, CA 1985.
Lohman, S.W. Ground Water Hydraulics. U.S. Geological Survey
Professional Paper 708. Washington, D.C. 1979.
Lord, A.E. and R.M. Koerner. Nondestructive Testing Location of
Containers Buried in Soil. pp. 161-169 in Proceedings of the
12th Annual Research Symposium on Land Disposal, Remedial
Action, Incineration and Treatment of Hazardous Waste. U.S.
EPA, ORD, HWERL, Cincinnati, OH. 1986.
Mardia, K.V. Statistics of Orientation Data. Academic Press,
Inc., London. 1972.
Morrison, R.D. Ground Water Monitoring Technology: Procedures,
Equipment and Applications. Timco Mfg., Inc. Prairie DuSac,
WI. 1980.
National Water Well Association. Remote Sensing: Applications
to Hydrogeology. NWWA Short Course. October 1-3, 1986. Spring-
field, MA. 1986.
Repa, E. and C. Kufs. Leachate Plume Management. EPA/540/2-
85/004. U.S. EPA, ORD, HWERL, Cincinnati, OH. 1985.
Sangrey, D.A. and W.R. Philipson. Detecting Landfill Leachate
Contamination Using Remote Sensors. EPA/600/4-79/060. U.S. EPA,
ORD, EMSL. Las Vegas, NV. 1979.
Scheinfeld, R.A., J.B. Robertson and T.B. Schwendeman. Under-
ground Storage Tank Monitoring: Observation Well Systems.
Groundwater Monitoring Review, V. 6, no. 4, pp. 49-55. 1986.
0639B
2-81
-------
Smart, P.L. and I.M.S. Laidlaw. An evaluation of Some
Flourescent Dyes for Water Tracing. Water Resources Research,
V. 13, no. 1, pp. 15-33. 1977.
Stanfill, D.F. and K.S. McMillan. Radar-Mapping of Gasoline and
Other Hydrocarbons in the Ground, pp. 269-274 in Proceedings of
the 6th National Conference on the Manageement of Uncontrolled
Hazardous Waste Sites. HMCRI, Silver Spring, MD. 1985.
U.S. Environmental Protection Agency. Unsaturated Zone Moni-
toring Techniques (DRAFT). 1986.
U.S. Department of the Interior. Ground Water Manual. U.S. DOI,
Water and Power Resources Service, Water Resources Technical
Publication. 1981.
Walton, W.C. Groundwater Resource Evaluation. McGraw-Hill Book
Co, NY, NY. 1970.
0639B
2-82
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MONITORJNG SYSTEM
DESIGN AND CONSTRUCTION
PEI Associates, Inc.
1233 20th Street, N.W.
Suite 401
Washington, O.C. 20036
January 1987
-------
CONTENTS
1.0 Introduction. 3-2
2.0 Drilling Methods 3-3
Cable Tool Drilling 3-3
Solid-Stem Countinous-Flight Auger Drilling 3-6
Hollow-Stem Continous-Flight Auger Drilling.......3-6
Water Rotary Drilling 3-9
Mud Rotary Drilling 3-11
Air Rotary Drilling 3-11
Reverse Circulation Rotary Drilling 3-13
3.0 Controlling Factors in Selecting a Drilling Method 3-15
4.0 Well Construction Materials 3-19
Drilling Fluids 3-19
Casing Installation 3-19
Screens 3-25
Grouting 3-25
5.0 Well Development 3-27
References 3-28
List of Additional Reading Materials 3-29
3-1
-------
1.0 INTRODUCTION
Monitoring systems are installed to obtain direct information on the
physical and chemical characteristics of the ground-water environment. The
monitoring well permits determination of hydrologic properties (e.g.,
nydraulic conductivity and transmissivity), water levels from which flow nets
and hydraulic gradients are calculated, and water quality. Well design may
significiantly affect the quality of the data produced by the well. The well
should therefore be designed to maximize the quality of the data produced.
Well design is affected by many integral factors, any of which may
dominate the ultimate monitoring well consuctruction specifications. These
Tactors include monitoring plan objectives (i.e., which specific types of data
will be collected), regulatory criteria (i.e., regulatory guidance or
philosophy on preferred design), geologic environment, containment
characteristics, and drilling method. The successful well design integrates
all of the above factors to maximize the utility and quality of data obtained
from the monitoring well.
Well design and installation involves several physical components
including the drilling equipment, well case, well screen (or open hole),
filter packs, annulus sealers (plugs and grouts), well development, and
above-grade appurtenances. This paper presents an overview of the components
of the well system emphasizing interrelationships with other well components
and advantages and disadvantages of each.
3-2
-------
2.0 DRILLING METHODS
The choice of drilling method is dependent upon the hydrogeology of the
site, intended use of the well, depth of the zone to be monitored, and other
site-specific factors.
In this section, the mechanics of several drilling methods are discussed.
Section 3 details the controlling factors to consider when selecting a
drilling method, Section 4 describes well construction materials, and Section
5 discusses well development techniques.
urilling methods discussed below include:
o Cable Tool
o Solid-Stem Continuous Flight Auger
o Hoi low-Stem Auger
o Water Rotary
o Mud Rotary
o Air Rotary
o Reverse Circulation Rotary Techniques
Cable Tool Drilling
Cable tool drilling machines operate by repeatedly lifting and dropping a
heavy string of drilling tools suspended at the end of a cable. The tools
consist of five components: a drill bit, a drill stem, drilling jars, a
swivel socket, and a cable as shown in Figures 1 and 2. In consolidated rock,
the drill, bit breaks the rock into small fragments; in unconsolidated rock,
the bit primarily loosens the material. The reciprocating action of the tools
mixes the crushed and loosened particles with water (added or naturally
occurring) to form a slurry at the bottom of the borehole. The slurried
cuttings are bailed from the well periodically prior to advancement of the
Dorehole.
The drill stem adds additional length and weight to the bit to maintain a
straight borehole during drilling. Drilling jars consist of a pair of linked,
neat-treated steel bars, whose primary function is to free the bit when it
Decomes stuck. The swivel socket connects the string of tools to the cable,
and the socket's weight supplies upward energy to the drilling jars when the
oit becomes stuck.
The drill line is a wire cable that carries and rotates the drilling
tools. It twists the tool joint on each upstroke to prevent it from
unscrewing.
Cable tool drilling rates are affected by the resistance of the rock, the
weight of the drill tools, the diameter of the bit, the length of the stroke,
the number of strokes per minute, and the thickness and depth of accumulated
cuttings in the borehole. As depth increases, more time is needed to remove
the drilling tools, bail out the slurry, and reinsert the tools.
3-3
-------
socket
Drill line
—Tool joint
Drilling jars
Wrench
square
Drill
stem
Woter
course
a
&
Wrench
square
Tool joint
Drill bit
Figure 1. Cable Tool Drilling Components (Johnson Division, UOP, 1975)
3-4
-------
¦Top Sheave
Moving Sheave
Stationary Sheave
Engine
Crank gear
Drill Stem
Casing
Casing Shoe
Drill Bit
Cable Tool Operation
-------
Advantages in using the cable tool method include:
o Drill rigs are relatively inexpensive
o Drill rigs are simple in design and require little
sophisticated maintenance
o Borehole is stabilized during entire drilling operation
o Collection of excellent undisturbed formation samples is
possi ble
o This method is amendable to most geologic conditions
Disadvantages of the cable tool method include:
o Relatively slow penetration rates result in relatively high
costs
o The use of water during drilling may dilute formation water
Solid-Stem Continuous-Flight Auger
bolid-stem augers consist of auger flights welded to a solid core as
shown in Figure 3. Drilling is performed by rotating the augers, which convey
material to the surface. The solid-stem auger uses either a single flight
(one section) or continuous flights (several sections). Augers with one
flight can have diameters as large as 54 inches, but average diameters range
from 6 to 24 inches. Special hardened teeth or cutters are attached when
drilling through hard ground, cobbles, or soft rock. Single flight augers are
not effective in loose ground or below the water table. However,
single-flight augers are sometimes used to bore a large diameter hole to the
water table, and after casing is set, the well is completed using another
dri11ing method.
Solid-stem continuous-flight augers are used to advance holes in stable
formations. The auger sections are turned by means of a rotary drive head
mounted on a hydraulic-feed mechanism. Auger lengths are usually 5 feet,
and the usual well depth is 40 to 120 feet.
Advantages of using the solid-stem auger include:
o Operating cost is low
o Drilling rigs are highly mobile
Disadvantages include:
o Sample recovery is poor
o Use is limited to unconsolidated materials
o Depth is usually limited to 150 feet
o Borehole tends to cave in
Hollow-Stem Continuous-Flight Auger
ihis method is commonly used when drilling in unconsolidated material.
Figure 4 shows a hollow-stem auger. Flights are welded onto larger diameter
pipe with a cutter head mounted at the bottom. Unlike the solid-stem auger,
a drill stem can be passed through the center of the hollow-stem auger. A
plug with an attached bit may be inserted into the cutter head to prevent soil
from entering the inside of the auger. The bit aids in advancing the hole. A
drill rod and plug, which rotate with the flights, connect through the auger
to the top-head drive unit by small diameter rods. The most common outside
3-6
-------
Figure 3. Solid-Stem Continuous
-------
3 DftlVV
KETfi
BULLOOO
CUTTlfl U* I
HIAO BOOT ! S
AOD BOLT
nr»lACCA«lf
ioc* bolt
BUIHINO
THBtAOEO
LOCK BOCT
Hfl|HAN«
OfllVI CAP
HOD TO-CAP
AOAPTIB
J ORIVfi
KKTD
ClNTfft MOO
HAROfACCD
Flight
eocti
ftEPULCFAaiC
LOCK SOLT
•U5HINO
THRCAOeO
LOCK BOLT
•otrro*
CONICAL
CAA0IOB
tNSCHT
bulldog
BITS
TUNGSTEN
CARBIDE
PILOT BIT
blaoe ttpe
cuttch HtAO
CUTTm
CAffBlOC
•LADE
CJCOUfUNGS INORtn
Figure 4. Hollow-Stem Auger (Johnson Division^ UOP, 1986)
3-8
-------
diameters are 6 1/4 to 22 inches (inside diameter of 2 1/2 to 13 inches).
Auger lengths average approximately 5 feet. Holes as deep as 300 feet have
been drilled with hollow-stem augers with outside diameters of 6 1/4-inches.
More commonly, the hollow-stem auger can drill to about 120 feet in stable
formations with a 6 1/4-inch outside diameter and to about 40 feet with a
120-inch diameter.
Advantages of using the hollow-stem auger include:
o Relatively low operating cost
o No drilling fluids are introduced into the borehole; no
Dossibility of diluting formation water
o Formation waters can be sampled during drilling by using a
screened auger or by advancing a well point ahead of the augers
o it is more effective than solid-stem augers because
hollow-stems can be used as temporary casing to prevent the
borehole from caving
o Drilling is fast and efficient
o Undisturbed samples can be easily obtained
Disadvantages of using the hollow stem auger include:
o It normally cannot drill deeper than 150 feet
o It can be used only in unconsolidated sediments
Water Rotary
in water rotary drilling, water is introduced into the borehole through
the drill pipe and circulates back up the borehole to remove drill cuttings as
shown in Figure 5. Roller-type rock bits consisting of two, three, or four
cones with teeth are mounted on a bit body by means of roller or bail
bearings. The bit is rotated by the drill rod, and the teeth on the bit
strike the formation to break it into smaller pieces. Great care must be
taken to ensure that water used in the drilling process does not contain
contaminants.
Advantages of water rotary drilling include:
o It can drill in both consolidated and unconsolidated formations
o It can drill to any depth
o Drilling is relatively fast
Disadvantages of water rotary drilling include:
o Water-bearing zones are difficult to recognize because of the
addition of water to the system
o Caving of the borehole is a problem in poorly consolidated
sediments
o Water circulation is difficult to maintain in highly fractured
material
o Drilling fluid may affect quality of water in formations
3-9
-------
Sheave
Crown block
Mast
Swive
Kelly
Hoisting drum
Mud pump
Power unit
Controls
Rotary table
Hose
Ground surface
Drilling "fluid
Return ditch
Settling pit
Drill string
Uncased hole
Direction of
drilling fluid
flow
Figure 5.
Components of Rotary Drilling Operation (Geraghty & Miller; Booz,
Allen, and Hamilton, 1982)
3-10
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Mud Rotary
The mud rotary drilling method operates the same way as water rotary
drilling except that various types of muds are circulated instead of air or
water. The use of mud helps to stabilize the borehole. Figure 6 shows a mud
rotary drilling operation.
Muds used include bentonite, barium sulfate, and organic polymers. Care
must be taken to ensure that the muds do not affect ground-water chemistry,
borehole samples, or well operations. For example, bentonite muds often
tighten the formation around the annulus making it difficult to assess aquifer
characteristics.
Advantages of using the mud rotary method include:
o It can drill in both consolidated and unconsolidated material
o It can drill to any depth
o Drilling is fast
o Mud stabilizes the borehole
Disadvantages of the mud rotary method include:
o Undisturbed samples are difficult to obtain
o Bentonite fluids can interfere with well operations
o Organic fluids can sometimes affect monitoring parameters
o Water bearing zones are difficult to locate
Air Rotary Method
in air rotary drilling, air is forced down the drill pipe and back up the
borehole to remove the drill cuttings. Compressed air is directed into the
drill pipe and through the bit as it rotates. The air strikes the rock as it
is cut and blows it away from the bottom of the bit. The velocity of the air
is great enough to carry the cuttings to the surface.
Advantages of using the air rotary method include:
o Drilling does not affect the quality of ground water from
monitoring wells in hard rock formations
o Can drill in both consolidated and unconsolidated material
o Can dri11 to any depth
o Because formation water is blown out of the borehole, it is
easy to determine where water-bearing zones exist
o Drilling is fast
Disadvantages of this method include:
o It is relatively more expensive than other drilling method
o Casing or additives may be required to keep borehole open in
soft formations below the water table
o Undisturbed samples are somewhat difficult to obtain
o It may not be economical for small jobs
o Drilling rig is not very mobile
3-11
-------
-Swivel
Hose
KeUey
Piston Pump
Rotary Table
mmm
•••
* ,* »
• ••
' * I*
l :
.—~--V- Drilling Mud and Cuttings.
. *» »11" ^
• ••••• ' \
Figure 6. Mud Rotary Drilling
3-12
-------
Reverse Circulation Rotary Drilling
The drilling methods described for air, water, and mud rotary drilling
are generally effective in removing drill cuttings from the borehole. If
cuttings are not removed, drilling cannot continue. The reverse circulation
technique is designed to remove drill cuttings more efficiently than other
dri11ing methods.
Drilling is accomplished by using gravity to run drilling fluid down the
annulus around the drill pipe as shown in Figure 7. The fluid picks up
cuttings and is pumped back up through holes in the drill bit. The fluid and
cuttings move upward inside the drill-string assembly and are pumped to a
settling pit. The drilling fluid usually consists of a muddy water rather
than bentonite or mud.
The equipment consists of a rotary table, and two engines: one to run
the rotary table and one to run the pump. A drill rod is used and may range
in diameter from 3 to 8 inches with lengths ranging from 10 to 30 feet.
Several types of bits are used, depending upon the type of material drilled.
All bits have open bottoms to allow cuttings to enter.
Advantages of using the reverse-circulation technique include:
o It is favorable for drilling in sand, silt, or clay
o It is favorable for drilling in areas where the static water level
depth is 10 feet or more
Disadvantages of this method include:
o It is less effective in hard rock formations
o It requires a large water supply
o Rigs can be expensive
3-13
-------
Swivti
Lorgt diomtur suction host
High copocity, tow
htad pump or j«t
Pump ducharg»
Ktlly
with
largt
bort
S*ffl#d land and cuftmgs in pif
Larg« diamtrtr drill pip*
FI * Pi tf 011 bit wl»h lorg# diamtttr opinmq
' PrincipTes of Reverse Circulation (Johnson Divison, UOP, 1975)
3-14
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3.0 CONTROLLING FACTORS IN SELECTING A DRILLING METHOD
Several factors should be considered before a drilling method is
selected. The chief factors to consider are:
o Geologic formation to be drilled
o Depth of the well to be drilled
o Size of well
Because the objective of a ground-water monitoring well is to obtain
representative ground-water data that will yield reliable information, an
accurate description of the site geology should be obtained. This should
include a definition of the geology beneath the site and identification of
ground-water flow paths and rates. Table 1 lists drilling methods for various
geologic conditions.
In addition to considering h.ydrogeologic conditions at the site, it is
important that the intended well use be considered, since this will, to some
extent, dictate well diameter and well depth. The diameter of a monitoring
well is predicated on the size of the sampling device or pump to be used. The
smaller the diameter, the less the cost for drilling and construction. Large
diameter wells are necessary with a well depth of over 200 feet, or if the
well will be used to recover contaminated water for remedial purposes.
Certain drilling methods are most effective when drilling to certain depths.
Table 2 presents well drilling methods and their most effective diameters and
depths.
The cable tool method is used to drill in a variety of hydrogeologic
conditions. It is usually the preferred method when drilling in cavernous
rock or other highly permeable material. Although boulder beds and glacial
material are both difficult to drill through by any method, the cable tool
usually does best since boulders or cobbles can be cracked or chipped by hard
plows of the bit. An advantage of the cable tool method is that it can drill
wells to a depth of 400 feet, and it has no borehole diameter restrictions.
The hollow-stem auger method is most often used when drilling in
unconsolidated sediments. Using this method, wells can be constructed in
rirm, non-caving environments. When the borehole will not stand open by
itself, the hollow-stem auger can be used as a temporary casing. Because no
drilling fluids are involved, there is minimal disturbance to the aquifer.
The hollow-stem auger is less effective in saturated material and below the
water table. The maximum drilling depth is approximately 100 feet, and the
borehole diameter range is limited to 9 to 12 inches. If vertical leakage of
water through the borehole is a concern, the hollow-stem auger method should
not be used.
Use of the solid-stem auger is limited to fine-grained unconsolidated
materials that will maintain an open borehole or in consolidated sediments,
its use below the potentiometric surface is limited, and maximum drilling
depth is about 200 feet.
3-15
-------
TABLE 1
DRILLING METHODS FOR
VARIOUS TYPES OF GEOLOGIC SETTINGS
Dri11inq Methods
Hollow-Stem Solid-Stem
Air Water/Mud Cable Continous Continuous
Geologic Environment Rotary Rotary Tool Auger Auger*
Glaciated or unconsolidated «
materials less than 150 feet
deep
Glaciated or unconsolidated o
materials more than 150 feet
deep
Consolidated rock formations ®
less than 500 feet deep
(minimal or no fractured
formations)
Consolidated rock formations •
less than 500 feet deep
(highly fractured formations)
Consolidated rock formations 9
more than 500 feet deep
(minimal formations)
Consolidated rock formations ®
more than 500 feet deep
(highly fractured formations)
• 49 9
• 9
« «
9 9
e 9
9 9
* Above potentiometric surface.
NOTE:
Although several methods are suggested as appropriate for similar conditions, one
method may be more suitable than the others.
(From Draft RCRA Ground-Water Monitoring Technical Enforcement Guidance Document,
U.S. EPA.)
3-16
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TABLE 2
DRILLING METHOD VS WELL DEPTH AND WELL DIAMETER
Hollow- Solid-
Cable Stem btem Air Mud
Tool Auger Auger Rotary Rotary
Depth Restrictions
up to 400'
+ 100'
+ 200'
none none
Hole Diameter
unlimited
9-12"
18-20"
none none
3-17
-------
Rotary drilling can generally be used to drill holes in all types of
geologic conditions, but it is best suited for drilling in hard rock
formations. In soft r.ock formations, casing is driven to keep the formations
from caving. The use of drilling fluids provide a much more stable borehole
than the auger method. When contamination from drilling fluids is a concern,
air rotary drilling can be used without affecting ground-water quality. The
air rotary method should not be used when drilling in areas where the upper
soil horizons are contaminated because the sloughing off of sidewalls can
contaminate the well. Also, care should be taken when using the air rotary
technique in a highly contaminated environment. Contaminated solids and water
blown out of the hole are difficult to contain at the surface. The rotary
drilling method is capable of drilling to any depth, with any size diameter.
3-18
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4.0 WELL CONSTRUCTION MATERIALS
in this section, the following specific components of well completion are
discussed:
o Drilling fluids
o Casing
o Grouting
o Screens
Drilling Fluids
As discussed in Section 2.0, drilling fluids are essential in the rotary
drilling method. Drilling fluids include air, water, or specially-prepared
mixtures of materials. Drilling fluids perform several functions:
o They remove drill cuttings from the borehole
o They support the borehole and prevent it from caving
o They seal the borehole to prevent fluid loss
o They cool, lubricate, and clean the bit
Grilling fluids used to construct ground-water monitoring wells are either
water-based or air-based. Table 3 outlines some of the more common drilling
fluids used today. Water-based drilling fluids consist of a liquid phase,
colloidal phase, and cuttings from the drilling process. Air-based fluids
usually consist of a dry air phase and a water phase to which a surfactant is
added to produce a foam.
The type of drilling fluid used depends on the porosity of the material
being drilled. When drilling in unconsolidated material, a water-based
drilling fluid system with clay or polymeric additives are typically used.
In wel1-consolidated or semi-consolidated materials, air is generally used.
A great variety of additives are available to modify the chemical and
physical properties of air and water so that drilling can be performed more
satisfactorily. Table 4 lists some of the more common commercial additives
and their uses.
Casing Installation
A well is cased to prevent collapse of the borehole wall and to prevent
surface drainage or polluted water from contaminating the well. Casing
typically extends at least 1 foot above the ground.
A variety of materials have been used to construct casing including
virgin f1uorocarbons, resins, stainless steel, cast iron, galvanized steel,
polyvinyl chloride (PVC), polyethylene, epoxy biphenyl, and polypropylene.
Many of these materials can affect ground-water quality. For example, steel
casing deteriorates in corrosive environments, and PVC deteriorates in the
presence of ketones, esters, and aromatic hydrocarbons as discussed in Table
5. Therefore, selection of a casing material should be made with
consideration to geochemistry, well depth, and chemical parameters to be
monitored for, among others.
3-19
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FABLE 3
MAJOR TYPES OF DRILLING FLUIDS USED IN THE WATER WELL INDUSTRY
Water Based
1. Clean fresh water
I. Water with clay additives
3. Water with Polymeric
additives
4. Water with clay and
polymeric additives
Air Based
1. Dry air
I. Mist: Droplets of water
entrained in the airstream
3. Foam: air bubbles surrounded
oy a film of water containing
a foam-stabilizing surfactant
4. Stiff foam: Foam containing
rilm-strenghtening materials
such as polymers and bentonite
Source: Fletcher Driscoll, Groundwater and Wells, Second Edition
3-20
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fABLE 4
rYPICAL ADDITIVE CONCENTRATIONS, RESULTING VISCOSITIES, AND
REQUIRED UPHOLE VELOCITIES FOR MAJOR TYPES OF DRILLING
FLUIDS IN VARIOUS AQUIFER MATERIALS
Base
Fluid
Additive/
Concentration
Observations
Water
None
For normal drilling (sand, silt,
and clay).
Water
Clay (High-Grade
Bentonite)
Increases viscosity (lifting ca-
pacity) of water significantly.
15-25 lb/100 gal
For normal drilling conditions
(sand, si It, and clay).
^5-40 lb/100 gal
For gravel and other course-
grained, poorly consolidated
formations.
35-45 lb/100 gal
For excessive fluid losses.
Water
Polymer (Natural
Increases viscosity (lifting
capacity) of water
siginificantly.
4.0 lb/100 gal
For normal drilling conditions
(sand, silt, and clay).
6.1 lb/100 gal
For gravel and other course-
grair.ed, poorly consolidated
formations.
6.5 lb/100 gal
For excessive fluid losses.
Cuttings should be removed from
the annulus before the pump is
shut down, because polymeric
drilling fluids have very little
gel strength.
mi r
None
Fast drilling and adequate
cleaning of medium to fine cut-
tings, but may be dust problems
at the surface.
This range of annular uphole
velocities is required for the
dual-wall method of drilling.
3-21
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TABLE 4 (Continued)
Base
Fluid
Additive/
Concentration
Observations
Air
Water (Air Mist)
0.25-2 gpm
Controls dust at the surface and
is suitable for formations that
have limited entry of water.
Air
Surfactant/Water
(Air-Foam)
Extends the lifting capacity of
the compressor.
i-2 qt/100 gal
(0.25-0.5%
surfactant)
For light drilling; small water
inflow; also for sticky clay, wet
sand, fine gravel, hard rock; few
drilling problems.
2-3 qt/100 gal
(0.5-0.75%
surfactant)
For average drilling conditions;
larger diameter, deeper holes;
large cuttings; increasing volumes
of water inflow; excellent hole
cleaning.
3-4 qt/100 gal
(0.75-1%
surfactant)
For difficult drilling; deep,
iarge-diameter holes; large, heavy
cuttings; sticky and incompetent
formations; large water inflows.
injection rates of surfactant/water
mixture:
Unconsolidated
Formations 3-10 gpm
Fractured rock 3-7 gpm
Sol id rock 3-5 gpm
Air
Surfactant/Colloids/
Water (Stiff Foam)
Greatly extends lifting capacity of
the compressor.
3-4 qt/100 gal
(0.75-1% surfac-
tant
d1 us
3-6 lb polymer./lOO
gal or 30-50 lb
bentonite/100 gal
For difficult drilling; deep,
large-diameter holes; large, heavy
cuttings; sticky and incompetent
formations; large water inflows.
4-9 qt/100 gal
(1-2% surfactant)
ol us
3-6 lb polymer/100
gal or 30-50 lb
bentonite/100 gal
For extremely difficult drilling;
large, deep holes; lost circula-
tion; incompetent formations;
excessive water inflows.
(Compiled partly from information presented in Imco Services, 1975; Magcobar, 1977; and
Baroid, 1980.)
3-22
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TABLE 5
WELL CASING AND SCREEN MATERIAL
Type
Advantages
Disadvantages
PVC (Polyvinyl-
chloride)
Polypropylene
Tef1 on
Kynar
Lightweight
Excellent chemical resistance to
weak alkalies, alcohols, alipha-
tic hydrocarbons, and oils
Good chemcial resistance to strong
mineral acids, concentrated oxidi-
zing acids, and strong alkalies
Readily available
Low priced compared to stainless
steel and Teflon
resistance to
Lightweight
Excel lent chemica'
mineral acids
excellent chemical resist-
mineral acids
excellent chemical resist-
alkalies, alcohols, ketones
Good to
ance to
Good to
ance to
and esters
Good chemical resistance to oils
Fair chemical resistance to con-
centrated oxidizing acids, ali-
phatic hydrocarbons, and aromatic
hydrocarbons
Low priced compared to stainless
steel and Teflon
Lightweight
High impact strength
Outstanding resitance to chemical
attack; insoluble in all organics
except a few exotic fluorinated
solvents
Greater strength and water resist-
ance than Teflon
Resistant to most chemicals and
solvents
Lower priced than Teflon
Weaker, less rigid, and
more temperature sensi-
tive than metallic mate-
rials
May absorb some constitu-
ents from ground water
May react with and leach
some constituents from
ground water
Poor chemical resistance
to ketones, esters, and
hydrocarbons
Weaker, less rigid, and
more temperature sensi-
tive than metallic mate-
rials
May react with and leach
some constituents into
ground water
Poor machinabi1ity-it
cannot be slotted be-
cause it melts rather
than cuts
Tensile strength and wear
resistance low compared to
other engineering plastics
Expensive relative to
other plastics and stain-
less steel
Not readily available
Poor chemical resistance
to ketones, acetone
(Continued)
3-23
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TABLE 5 (Continued)
Type
Advantages
Disadvantages
Mild steel
Stainless Steel
o Strong, rigid; temperature sensi-
tivity not a problem
o Readily available
o Low priced relative to stainless
steel and Teflon
o High strength at a great range of
temperatures
o Excellent resistance to corrosion
and oxidation
o Readily available
o Moderate price for casing
Heavier than plastics
May react with and leach
some constituents into
ground water
Not as chemically resist-
ant as stainless steel
Heavier than plastics
May corrode and leach
some chromium in highly
acidic waters
May act as a catalyst in
some organic reactions
Screens are higher priced
than plastic screens
Source: Fletcher Driscoll, Groundwater and Wells, Second Edition
3-24
-------
Screens
Screens provide formation support and sand control. Common screening
materials include stainless steel, bronze, galvanized steel, and plastic.
Screens have openings of varying sizes to fit the size of the surrounding
water-bearing sands. Well screens should have the following characteristics:
o They should be constructed of a material that is inert in the
water-bearing strata
o Upen area should be maximized to facilitate rapid sample
recovery
o Slot openings should be a nonplugging design
Care should be taken in selecting a screen material because many common
screen materials can react with ground water and produce erroneous water-
auality data. When selecting a screen material, consider the following
factors:
o The contaminants to be sampled
o Chemical reactiveness
o Material strength
o tase of installation
o Material cost
Table 5 lists some common screening materials and their, advantages and
disadvantages.
Typical screen lengths are 2 to 5 feet for wells used to collect water
samples. Screens monitoring ground-water quality are generally 10 to 20 feet
iong, depending upon anticipated variations in ground-water elevation. Part
of the screen is always above the ground-water table in the vadose zone to
monitor for hydrocarbons or other volatiles that might have reached the
ground-water table.
Grouti ng
Grouting well casing involves filling the annular space between the
casing and the drilled hole to secure the casing in place and exclude water
and other materials from entering the borehole. Grouting is standard practice
in all monitoring well installations.
Most grout consists of cement or bentonite. Table 6 lists these two
grouting materials and their advantages and disadvantages.
One concern with grouting is that the seal is inadequate due to premature
hydration of the clay in a bentonite grout. Another potential grouting
problem is that if the volume of material necessary to seal the annular space
is overestimated, the grout may be forced into, the formation. This tends to
elevate the pH level of water samples.
Selection of grouting material should be made in consideration of the
formation groundwater. Refer to Table 6 for specific considerations.
3-25
-------
TABLE 6
GROUTING MATERIALS FOR MONITORING WELLS
Type
Advantages
Disadvantages
bentonite
Cement
o Readily Avai
o Inexpensive
able
o Readily available
o Inexpensive
o Can use sand and/or gravel
fi1ter
o Possible to determine how
well the cement has been
placed by temperature
'logs or acoustic bond logs
May produce chemical interfer-
ence with water-quality
analysi s
May not provide a complete seal
Decause:
-There is a limit (14 percent)
to the amount of solids that
can be pumped in a slurry.
Thus, there are few solids in
the seal; should wait for liq-
uid to bleed off so solids will
settle
-During installation, bentonite
pellets may ^hydrate before
reaching proper depth, thereby
sticking to formation or casing
and causing bridging
-Cannot determine how effec-
tively material has been olaced
-Cannot assure complete bond to
casing
May cause chemical interfer-
ences with water-quality
analysi s
Requires mixer, pump, and
tremie line; generally more
cleanup than with bentonite
Shrinks when it sets; complete
oond to formation and casing
not assured
Source: Fletcher Driscoll, Groundwater and Wells, Second Edition
3-26
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5.0 Well Development
Well development involves those steps necessary to provide the aquifer
the easiest possible path into the well. In unconsolidated formations, the
coarsest sands and gravels should be concentrated next to the well screen,
with the degree of fineness increasing as distance from the well increases
until it roughly equals that of the aquifer. As a result, water moves more
freely as it approaches the well. In consolidated formations, wells are
developed by assuring free flow from fractures or by increasing the fractures
by artificial means.
There are several methods of developing wells, either by natural means or
by gravel-packing. These include overpumping; backwashing; surging, either
with a plunger or by air; jetting; or using chemicals and explosives.
Overpumping is considered the simplest method of removing fines from
water-bearing formations. This procedure involves pumping at a higher rate
than the well will normally be pumped. Ordinarily, a test pump is used for
overpumpi ng.
Backwashing development procedures cause a reversal of flow through the
screen openings that will agitate the sediment, remove the finer fraction, and
then rearrange the remaining particles. By reversing the flow, the bridging
between large particles across screen openings is broken down. The backwash
portion of the procedure breaks down the bridging, and the inflow moves the
fine material toward the screen and into the well.
Mechanical surging is the process of operating a plunger to force water
into and out of a screen. The downstroke of the plunger forces water out of
the well and into the surrounding formation. The upstroke pulls water back
into the well, bringing with it sand, silt, and other material fine enough to
pass through the screen. By forcing water out of the well, the surge breaks
up the bridges of sand particles.
Air compressers are sometimes used to develop wells in consolidated and
unconsolidated formations. The well is alternately surged and pumped with air
oy injecting the well with air to lift the water to the surface. As it
reaches the top of the casing, the air supply is cut off to allow the aerated
column of water to fall. This helps move sediment away from the screen.
Development by high velocity jetting can be performed with either water
or air. Jetting with water almost always involves simultaneous air-lift
pumping so that the formation does not clog. Water is pumped through small
nozzles at high velocity. This allows a small area of the well to be treated,
concentrating on areas with the greatest problems, until the entire well is
developed.
Development using explosives, chemicals, and acids is useful when a
"skin" of caked clay and drilling mud is left on the borehole. Dispensing
agents added to water work well in clay formations to help break up the skin,
in hard rock, explosives are used to develop wells in fractured or faulted
areas. Acids work well when developing wells in limestone, since limestone
dissolves in acid. With fractures around the borehole opened, particles can
oe removed from openings and water can flow more freely to the well.
3-27
-------
REFERENCES
Departments of the Army and the Air Force, 1965. Well Drilling Operations.
Washington, O.C.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Prentice-Hall, Inc.
Englewood CIiffs, N.J.
Geraghty & Miller, Inc., and Booz, Allen, & Hamilton, Inc., 1982. Injection
Well Construction Practices and Technology. Prepared for U.S. EPA,
Office of Drinking Water, Washington, D.C.
Johnson Division, 1986. Groundwater and Wells. Johnson Division. St. Paul,
MN.
U.S. EPA, 1980. Procedures Manual for Ground-Water Monitoring at Solid Waste
Disposal Facilities, U.S. EPA, Office of Water and Waste Management,
Washington, D.C.
U.S. EPA, 1985. Leachate Plume Management. U.S. EPA, Office of Solid Waste.
Cincinnati, OH.
U.S. EPA, 1986. Draft RCRA Ground-Water Monitoring Technical Enforcement
Guidance Document. U.S. EPA, Office of Waste Programs Enforcement.
Wehrman, H.A., 1983. "Monitoring Well Design and Construction." Ground Water
Age. April, 1983.
3-28
-------
The following articles and tables were selected to provide additional
information on Monitoring System Design and Construction (Articles are
reprinted courtesy of the National Water Well Association.) They can be
found in Appendix A.
i. Table: Monitoring Well Design Rating System
Z. Table: Drilling Method Rating System
3. Selection of Drilling Method, Well Design and Sampling Equipment for
Wells to Monitor Organic Contamination
4. Small - vs - Large Diameter Monitoring Wells
b. An Evaluation of Nested Monitoring Wells
6. Custom Designing of Monitoring Wells for Specific Pollutants and
Hydrogeological Conditions
7. Method to Avoid Ground-Water Mixing Between Two Aquifers During Drilling
and Well Completion Procedures
8. Will My Monitoring Wells Survive Down There? Design and Installation
Techniques for Hazardous Waste Studies
9. A Technique for Renovating Clogged Monitor Wells
3-29
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CHAPTER IV
PROBLEM AREAS IN GROUNDWATER SAMPLING
4-1
-------
PROBLEM AREAS IN GROUNDWATER SAMPLING
INTRODUCTION
This paper is essentially an essay, in all senses of the
word, on groundwater sampling for waste management facilities.
It is not intended to provide exhaustive prescriptions for
sampling strategies, devices, or procedures. These subjects
are capably and voluminously addressed by many other authors
(see the attached reference list) and in any number of other
seminars and courses. Rather, the purpose of this paper is
to try opinions, to provoke thoughtful or heated discourse
about some difficult aspects of groundwater sampling.
NEGOTIATED TECHNOLOGY, NOT SCIENCE
Some preliminary axioms regarding the monitoring of waste
management facilities:
o The fundamental objective is to assure that a
facility has no (or, at least, no unacceptable)
deleterious affects.
o Therefore, samples representative of adjacent,
potentially affected environments are obtained and
analyzed chemically.
o The representativeness of samples is assured by
forestalling or removing errors associated with
sampling.
o Analyses of the samples are then used to evaluate
the deleterious effects of the facility.
Every single sample taken in this context, then, begs the
following questions:
o How is representativeness* defined?
o What are the sources of error associated with
sampling?
o What defines deleterious effects?
These three questions are clearly motivated by a concern for
the truth of the matter, by a scientific spirit. However,
they are extremely difficult to address, even in a
In response to a comment on an earlier draft:
"representativeness" is indeed a word, albeit an awkward
one. See Webster's New Collegiate Dictionary, 1974.
4-2
-------
rigorously scientific, experimental context. And they are
raised here in an engineering context: a large number of
facilities must be monitored, even-handedly, at reasonable
cost and in reasonable time. In fact, they are currently
answered, either explicitly or implicitly, in this same
context. In other words, the practical answers to these
questions are always negotiated. It is useful to think of
these negotiated, practical answers as an evolving "state of
the practice". The state of the practice is, by definition,
distinct from the "state of the art," which is avowedly
scientific and free of political concerns.
Representativeness
Every definition of representativeness incorporates, whether
explicitly or not, a definition of representative spatial
and temporal scales. Put very simply, every groundwater
sample has a finite volume and, prior to its withdrawal,
occupied a finite volume of pore space(s) in the ground.
Furthermore, the sample was withdrawn over a finite period
of time. What must the size of the sample volume be, where
and when exactly must it derive from, in order to represent
the medium being sampled? Representative scale is a funda-
mental issue of groundwater sampling, one which underlies
many arguments (negotiations) about appropriate monitoring
procedures for waste management facilities.
It is natural to think of a representative sample as one for
which an accuracy can be defined. In the purest statistical
sense, however, it is not clear how to define the accuracy
of an analysis of a groundwater sample. As Barcelona et al.
(1985, p. 11) said it, "...sampling accuracy cannot be
verified in the field since the 'true' or in situ value is
unknown and it is most unlikely that any single (or average)
value for a particular chemical constituent could be consid-
ered as the 'true' one except for very localized sites."
In part because of the complexity and difficulty of these
two issues—issues of scale and accuracy—there is a tendency
to identify representativeness with standard sampling proto-
cols, and to assume that reproducible analytical results
indicate that the protocols were implemented in an acceptable
manner. As a matter of logic only, this approach is
seriously flawed. As a practical matter, however, standardi-
zation does have value, even though standard protocols do
not and cannot address fundamental issues of representative-
ness. Standard protocols remove or control some sources of
error, and they therefore give some bounds to our ignorance.
Sources of Error
Many potential sources of error in groundwater sampling are
obvious, have been the subject of fruitful study, and can
4-3
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therefore be controlled. Obvious potential sources of error
can be seen as falling into three categories: those
involving the improper choice or use of sampling (1) mate-
rials, (2) mechanisms, and/or (3) procedures. If number of
publications is any index, the definition of the state of
the practice currently revolves around the minutia of proto-
cols intended to address these obvious sources of error.
Appendices A through C present examples of the lengths to
which the prescription of sampling protocols may be taken.
Appendix A is a portion of an example groundwater sampling
plan for use by relatively inexperienced field personnel at
a site which does not have free-phase contaminants. Appen-
dix B excerpts a portion of the RCRA Ground-Water Monitoring
Technical Enforcement Guidance Document (TEGD), and Appen-
dix C excerpts a portion of the RCRA Ground-Water Monitoring
Compliance Order Guidance. Both excerpts are exhaustive
checklists of the technical details involved in obtaining
"error-free" groundwater samples.
The Definition of Deleterious
Monitoring protocols and concentration standards are explicit
or implied in all definitions of "deleterious." Obviously,
those constituents of a sample which may be harmful (or may
indicate harm) must be identified before the sample is taken
and analyzed. Just as obviously, the results of analyses of
representative samples will be used in some way? the results
must at least be compared to concentration standards. Extant
standards range from those which are practically simple
because they have already been negotiated (e.g., maximum
contaminant levels) to those which are so complex or poorly
defined that they explicitly require further negotiation
(e.g., alternate concentration limits). The methods of com-
parison of analyses to standards also range from simple and
direct (e.g., is one concentration greater than the other?)
to complex and under development or negotiation (e.g., statis-
tical tests or risk calculations).
The definition of deleterious becomes increasingly difficult
as issues of temporal and spatial scale are drawn into the
definition. Logically, the definition of the risks posed by
a facility requires prediction of the concentrations of con-
taminants at all points of possible exposure over the entire
period during which the facility may have harmful effects.
In other words, the definition of deleterious logically
requires definition of the spatial and temporal scales which
characterize a facility and its environs. Consequently, if
the preliminary axioms of this essay (p. IV-1) hold true,
then the definitions of representativeness and deleterious
are not independent. In short, the preliminary axioms are
circular: we must take representative samples in order to
determine deleterious effects, but we cannot really define
4-4
-------
what a representative sample is until we know what those
effects might be. This explains why the establishment of an
"acceptable" groundwater sampling program must invariably be
an iterative process, one which can proceed only through
judgment and negotiation. In this process, definitions of
representativeness and deleterious are approached through
successive approximation; "final" definitions are never
attained.
EXAMPLES FROM THE PRACTICE
The issues raised above are manifested directly and
concretely in the daily discourse of hydrogeologists; they
are addressed in the evolving state of the.practice.
What is Being Sampled?
There is, of course, general agreement that a representative
sample of groundwater should consist of "undisturbed" pore
water. Whether undisturbed pore water should contain sedi-
ment (colloidal or suspended) or not is sometimes debated;
the practical solution involves filtration. There is no
debate over drilling materials: everyone agrees that they
should not be part of the sample, because they may contain
foreign substances (Figure IV-1) . However, there is evi-
dence that, even after purging and long after development by
standard procedures, the chemistry of water from some moni-
toring wells may be affected by drilling fluid additives
which remain in the formation or gravel pack (Figure IV-2).
There is also general agreement that a representative
groundwater sample should not show the effects of materials
used in the well or the sampling equipment. Consequently,
there is a general preference for relatively inert (and more
costly) materials, i.e., materials which neither release
(leach) nor adsorb contaminants (Figure IV-3). However,
because leaching and adsorption are generally not instanta-
neous, because samples are taken over a finite period of
time, and because only a fraction of any sample actually
contacts these materials, there is still debate as to the
wisdom of legislated Teflon® or stainless steel. Although
Barcelona et al. (1985) approach a resolution of the issue
(Figure IV-4), it has not yet been finally settled through
research.
Where and When is the Sample From?
For reasons of geochemistry discussed below, it is generally
agreed that, in order to be representative, the sample should
spend as little time as possible (consistent with good sam-
pling practices) in the well. Consequently, monitoring wells
are 'purged' prior to sampling, to draw in 'fresh' pore water
from the formation. Gibb et al, (1981) used equations
4-5
-------
CHEMICAL COMPOSITIONS OF DRILLING ADDITIVES
(From Brobst and Bubka, 1986)
Bentonite Approximate Percent
-MontmoriHonite 85
-Si02 7
-K,Na,Ca-Aluminosilicates 5
-lllite 2
-CaC03 0.5
-CaS04 • 2H20 0.5
-Sodium Polyacrylate 0.01
Guar Bean
-Galactomannan 80.4
-Water "I 1
-Protein 4
-Fiber 8
-Ash 1
-Fat 0.5
-Methyl Blue 0.1
-------
EFFECTS OF DRILLING FLUID
ON SAMPLE CHEMISTRY
(From Groundwater and Wells, 1986)
BOO
O
g 600
||> 400
200
0
0 10 20 30 40 50
Days after installation
(a) Undeveloped
100
80
_ 60
? 40
20
0
0 50 100 150 200
Days after installation
COD
SO.
(b) Developed
-------
RECOMMENDED MATERIALS
(From Barcelona et. al., 1984)
.1) Fluorocarbon Resins (e.g., Teflon™ )
2) Stainless Steel (316, 304)
3) Polypropylene
4) Polyethylene
5) Linear Polyethylene
6) Viton ™
7) Conventional Polyethylene
8) PVC
-------
SAMPLE CONTACT RATES (0.4 GPM)
(From Barcelona et. al., 1985)
AQUIFER
MATERIAL SOLIDS (SAND) WELL (2") TUBING (1/4")
-pa H-
I tQ
to c
5 CONTACT 66 0.72 4.0
H
<
RATE (M2/HR)
RELATIVE %
CONTACT
92
1
6
-------
developed by Papadopulos and Cooper (1967) to determine the
amount of fresh formation water in a monitoring well over a
range of purge times and transmissivities (Figure IV-5).
Their analysis suggests that very long purge times are
necessary before representative water may be obtained from
formations having low transmissivities, and that representa-
tive water may be obtained almost instantaneously from
highly transmissive formations. This analysis appears to
overlook the geometry of the well; for example, the same
equations suggest that acceptably long purge times would dry
out many wells in poorly transmissive formations (Fig-
ure IV-6). In any event, the entire problem may be circum-
vented by the simple expedient of a packer (Figure IV-7).
The question of the spatial and temporal origin of a sample
has important dimensions beyond the issue of 'stale' well
water. In the current state of the practice, control over
the spatial scale of samples is typically exerted thro;ugh
the design and location of monitoring wells (i.e., the
spacing of wells and the lengths and depths of screens);
control over temporal scale is exerted through sampling
frequency. Implicit in this practice is the assumption that
one sample represents a single point in space and time.
In fact, it is obvious that any one sample represents a
range of points and times, depending in part upon the volume
of water purged from the well prior to sampling. A very
simple analysis (Figure IV-8)—which assumes a fully pene-
trating well, a formation porosity of 30 percent, and radial
'plug' flow—indicates the radial distance from which a
sample might originate for a range of total pumpages and
three ratios of purge rate to transmissivity. For example,
after a total pumpage of 100 gallons at a purge rate/
transmissivity ratio of 0.5 feet, the water entering the
well effectively originates from points 3 feet distant from
the well screen. Depending upon the hydrodynamics- of the
natural flow system encompassed within that radius, the
entire sample could, in effect, be a composite of
'subsamples' which have had very different histories.
More complex methods may be used to analyze this problem,
and the scale of interest may be expanded. For example, it
is common practice to employ digital modeling to define
wellhead protection areas by determining the travel times of
contaminants which could enter an aquifer in the vicinity of
a well field (Figure IV-9). In effect, this approach defines
the times and locations represented by any sample taken from
the well(s) over the period of concern. In this example, it
is abundantly clear that a single sample from one of the
wells could contain subsamples having completely different
histories.
4-10
-------
PERCENT OF AQUIFER WATER
VERSUS TIME FOR DIFFERENT
TRANSMISSIVITIES
(From Gibb et. al., 1981)
100
80
£ 60
40
20
Q = 500 mL/min
DIAMETER = 5.08 cm
20
25
30
TIME, minutes
-------
CRITICAL PURGE TIMES (2")
DRAWDOWN (FT)
0.1
10
100
1,000
u>
UJ
t 100
10-1 Q
u.
M
<
CO
10
101
PURGE RATE/TRANSMISSIVITY (FT)
-------
PACKER ISOLATION OF PUMP
COMPRESSED
GAS
HOIST CABLE
COMPRESSED *>*
GAS
SAMPLE
DISCHARGE
WELL
RISER
INFLATABLE
PACKER
SAMPLING
PUMP
WELL-
SCREEN
NOT TO SCALE
Figure IV-7
4-13
-------
DISTANCE OF DRAW VS. PUMP AGE
4-
3-
0 - 5 ft
PUMP RATE
TRANSMISSIVITY
(FT)
1 -0 ft
FJ 2-
50ft
T
10
500 1000
PUMPAGE (GALLONS)
-------
COMPUTED TRAVEL TIMES (YEARS)
IN THE VICINITY OF PUMPING WELLS
Figure IV-9
4-15
-------
This point is of more than academic interest, because numbers
and kinds of wells, and frequency of sampling, are typically
major issues of negotiation (heated argument). The natural
bias of regulatory authorities (as evidenced in the defunct
1985 version of the TEGD) is toward more.wells, shorter
screens, and higher frequency—in short, toward the increas-
ing subdivision of the monitored volume. Because increasing
subdivision increases cost, the natural bias of the regulated
community is contrary. The state of the practice offers no
easy solutions; methods of defining representative scales
are poorly defined and/or too complex to be employed widely.
What Happens as the Sample is Taken?
There is general agreement that, at least in permeable
formations, some minimum number of well volumes should be
purged prior to obtaining the sample; the magic number
generally ranges from three to five. As noted above, the
purpose of purging is to obtain fresh, representative forma-
tion water. In this instance, "representative" means
representative of geochemical conditions in undisturbed parts
of the formation.
It is known that the partial pressures of certain gases
(particularly carbon dioxide, oxygen, and volatile organics)
which often are significant constituents of groundwater may
change dramatically as the water is exposed to the atmos-
phere. These changes may be significant in and of them-
selves (e.g., loss of volatile organics), or may produce
other, equally significant changes. For example, the
stability of iron species in solution is strongly dependent
on pH and Eh (Figure IV-10), which are in turn strongly
dependent upon the partial pressures of carbon dioxide and
oxygen. Some organic contaminants are readily adsorbed by
iron precipitates. Consequently, exposure of groundwaters
to the atmosphere can cause changes in pH and Eh, consequent
precipitation of iron species from solution, and consequent
loss of organics from solution through adsorption on the
precipitates.
Considerations of this kind have lead to the use of easily
measured "field parameters" (pH, Eh , conductivity, and tem-
perature) as indices of the representativeness of a sample
(Figure 4-11). These parameters are measured as a function
of well volumes purged; when they remain stable over a few
consecutive volumes, the water is considered to be repre-
sentative. Of course, there is no reason a priori to suppose
that unstable readings always indicate a; bad sample;, such
readings could simply indicate that the chemistry of the
water shows considerable natural variation.
Calibrated measurements (absolute values) of Eh are
extremely difficult to obtain in the field.
4-16
-------
STABILITY OF IRON SPECIES
(After Garrels and Christ, 1965)
Figure IV-10
4-17
-------
PURGE PARAMETERS
pH Eh
COND TEMP
10 +300
9 +200
8 +100
7 0
6 -100
5 200
4 300 |
500
400
300
200
20
15
10
100 5
WELL VOLUMES PURGED
-------
Hov are Analytical Results Evaluated?
Beyond the simple comparison of a concentration to a
standard, beyond a cookbook risk assessment, the methods for
defining the risks posed by a facility can become highly
complex.
The end result of one such highly complex evaluation is
exemplified in Figure IV-12. In brief, the figure represents
the output of a digital contaminant transport model. The
basic purpose of the model was to determine the maximum per-
missible concentrations (trigger levels) of contaminants (in
this case, 1,2-DCE) in a source zone. The model provided
the analytical linkage between the trigger levels and the
maximum permissible concentrations (in this case, 10 ppb, a
cancer risk level of 10 ) at offsite receptors.
To use the figure, one simply divides the area of the
contaminated zone (igdic^ted on the abscissa of the figure)
into the trigger (10 ft -ppm); the result is a concentration,
in ppm, which must not be exceeded in the source zone. Note
that the orientation of the source zone with respect to the
flow system affects the trigger level; the solid lines within
the figure represent widths of source zones parallel to the
gradient of the flow system.
An important feature of the procedure is that it involves
assignment of areas to a series of monitoring wells in the
source zone. Each well is taken to represent a given area,
not just the point at which it is situated; the concentration
of a contaminant in that well is assigned to the entire area.
The monitoring protocol allows for the installation of addi-
tional wells if any one source zone causes the trigger to be
exceeded.
Clearly, this method of evaluating risks, of determining the
significance and meaning of samples, involves very complex,
rigorously defined notions of representative scales. It was
produced through an equally complex and rigorous series of
investigations and negotiations.
WDR223/008
4-19
-------
COMPUTED TRIGGER LEVELS FOR 1, 2-DCE
AREA (FT2 x 103)
-------
REFERENCES
Barcelona, M. J., J. P. Gibb, J. A. Helfrich, and
E. E. Garske. Practical Guide for Ground-Water Sampling.
Illinois State Water Survey Contract Report 374. 1985.
94 pp.
Barcelona, M. J., J. A. Helfrich, and E. E. Garske.
Sampling Tubing Effects on Ground Water Samples. Analytical
Chemistry. V. 57, No. 2. 1985. Pp. 460-464.
Barcelona, M. J., J. A. Helfrich, E. E. Garske, and J. P.
Gibb. A Guide to the Selection of Materials for Monitoring
Well Construction and Ground-Water Sampling. Illinois State
Water Survey Contract Report 327. 1983. 78 pp.
Brobst, R. B. and P. M. Buszka. The Effect of Three
Drilling Fluids on Ground Water Sample Chemistry. Ground
Water Monitoring Review. Winter 1986. Pp. 62-70.
Driscoll, F. G., ed. Groundwater and Wells. 2nd ed.
Johnson Division, St. Paul. 1986. 1089 pp.
Garrels, R. M. and C. L. Christ. Solutions, Minerals, and
Equilibria. San Francisco: Freeman, Cooper, and Company.
1965. 450 pp.
Gibb, J. P., R. M. Schuller, and R. A. Griffin. Procedures
for the Collection of Representative Water Quality Data from
Monitoring Wells. Cooperative Groundwater Report 7. Illi-
nois State Water and Geological Surveys. 1981.
Gillham, R. W., M. J. L. Robin, J. F. Barker, and J. A.
Cherry. Groundwater Monitoring and Sample Bias. Environ-
mental Affairs Department, American Petroleum Institute.
1983. 206 pp.
Holden, P. W. Primer on Water Well Sampling for Volatile
Organic Compounds. Water Resources Research Center,
University of Arizona. Undated. 44 pp.
Papadopulos, I. S. and H. H. Cooper. Drawdown in a Well of
Large Diameter. Water Resources Research. V. 3, No. 1.
1967. Pp. 241-244.
Scalf, M. R., J. F. McNabb, W. J. Dunlop, R. L. Cosby, and
J. S. Fryberger. Manual of Ground-Water Quality Sampling
Procedures. National Water Well Association. 1981.
93 pp.
4-21
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Sisk, S. W. NEIC Manual for Groundwater/Subsurface
Investigations at Hazardous Waste Sites. National Enforce-
ment Investigations Center. 1981. 72 pp. and Appendices.
Wood, W. W. Guidelines for Collection and Field Analysis of
Ground-Water Samples for Selected Unstable Constituents.
Chapter D2, Techniques of Water Resources Investigators of
the United States Geological Survey. 1976. 24 pp.
WDR223/021
4-22
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SAMPLE ANALYSIS AND QUALITY ASSURANCE
by
Pat Esposito, Thomas Wagner, and William Thompson
PEI Associates, Inc.
5-1
-------
Once a ground-water monitoring system has been properly designed and
installed and the samples have been collected, it becomes necessary to perform
a number of prescribed chemical analyses. As with other aspects of ground-
water monitoring, it is necessary to ensure that all data generated in the
analytical process are valid and capable of withstanding the most rigorous of
challenges. To assure the highest quality results, these key topics must be
effectively addressed. First, good lines of communication must be established
with the analytical laboratory before any samples are delivered as well as
during and after analysis is complete. Second, proper analytical protocols
must be selected. And third, a specified quality assurance program must be
developed. Each of these three key topics is discussed below.
COMMUNICATIONS WITH LABORATORY
As early as possible in the project planning stages and prior to sample
collection, the investigation team should meet with the analytical laboratory
staff to discuss a number of specific items relative to the collection and
analysis of samples. Key subjects that should be thoroughly discussed,
explored, and mutually understood include:
1. The laboratory should clearly understand the overall project goals,
including the anticipated sampling strategy and schedule, sampling
methodologies (including QA/QC) that will be used, constituents of
concern for analysis, and anticipated levels (concentrations) to be
encountered.
2. The most reliable and appropriate analytical methods available for
the constituents of interest should be identified. Particular
attention must be given to potential interferences, the need for
special field or laboratory preparation and preservation methods,
if any, and detection limits.
3. Steps for determining the true concentration of difficult-to-measure
constituents should be explored. This includes decisions on the
fraction of samples, if any, that should be spiked with standards,
either in the lab or in the field, for purposes of determining
recovery factors.
4. The number of split samples or replicate samples that should be
prepared in the field and in the laboratory as quality control
checks on precision and accuracy should be established.
5. The volume of sample that must be collected and made available for
analytical purposes, as well as the type, size, and number of
individual sample containers must be determined. Careful attention
must be given to the methods to be used for prewashing sample
containers and sampling equipment in order to avoid interferences
during analysis.
5-2
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6. Sample shipping and arrival schedules and priorities for analytical
determinations on each sample must be addressed. Sample shelf
life, and overall laboratory workload and turn-around times must be
predetermined and used to set schedules for sample collection
intervals and analysis by the laboratory.
7. Both field and laboratory personnel should be made aware of any
potential health and safety hazards that may be associated with
specific samples and the precautions that should be taken to avoid
exposures.
8. The frequency with which blanks and controls will be integrated
into the analytical process for each constituent and each set of
samples should be established.
9. Costs per sample, on an individual sample and on a lot basis,
should be documented. Costs will vary significantly, depending on
the type of analysis, the level of QA/QC involved, "the number of
samples to be analyzed, and on priority/schedule demands.
Adequate consideration of these areas will help to minimize discovery of
"suprising" results, which cause project delays, including resampling and
analysis and increased project cost. Well defined lines of communication
will also allow development of a confident presentation of results that all
investigation parties (i.e., regulator and regulated community) can defend.
SELECTION OF ANALYTICAL METHODS
Ground-water samples collected at Superfund sites or for CERCLA programs
tend to be analyzed for different parameters and by different methods than
those collected for RCRA purposes. Current RCRA and CERCLA practices rela-
tive to ground-water sample analysis are discussed below.
RCRA
One of the fundamental building blocks of the RCRA regulatory program is
the list of hazardous constituents found in 40 CFR Part 261, known commonly
as Appendix VIII. If any constituent on the Appendix VIII list is found in a
waste, the waste can be listed as a hazardous waste, unless it can be other-
wise demonstrated that the waste poses little or no danger to man or the
environment. (See 40 CFR 261.10 for more details.) The constituents found
in Appendix VIII number more than 350. Each has been shown to possess some
type of toxic, carcinogenic, mutagenic, or teratogenic property. Table 1
presents a complete list of Appendix VIII constituents.
Ground-water protection provisions of Parts 264 and 265 currently re-
quire testing for evidence of contamination by analyzing for Appendix VIII
constituents and certain other parameters indicative of contamination including
total organic carbon (TOC), total organic halogen (TOX), pH, specific con-
ductance, iron, manganese, chloride, sodium, sulfate, phenols, fluoride,
radiation, and coliform bacteria. However, to analyze ground-water samples
5-3
-------
for aV[ Appendix VIII constituents is now considered to be unrealistic and
unnecessary.
In an effort to be responsive to both these regulatory requirements and
analytical limitations, EPA proposed in July of 1986 an alternate list of
chemicals for ground-water monitoring which is referred to as the Appendix IX
list. This list, which contains a somewhat more limited core of 250 specific
chemicals, was largely derived from Appendix VIII by adding 25 chemicals
routinely analyzed in ground water under the CERCLA program, by deleting
those chemicals that are unstable in water or not amenable to EPA's standard
analytical methods for screening (i.e., gas chromatography [GC] or gas chro-
matography /mass spectrometry [GC/MS] for organics, and atomic absorption [AA]
or inductively coupled plasma spectrometry QI CAP] for metals), and by select-
ing appropriate representatives for ionic compounds and categories. Table 2
lists the constituents of Appendix IX.
The analytical reference methods currently preferred by EPA for analyz-
ing RCRA ground-water samples are those contained in EPA's publication, "Test
Methods for Evaluating Solid Waste, Physical/Chemical Methods," which is most
commonly referred to by its publication number EPA SW-846 (Second Edition,
1982, as amended by Update I issued April 1984, and Update II issued April
1985 (see 40 CFR Part 261, Appendix III). This publication, SW-846, was
first published in 1980 and has been revised and updated to improve on the
prescribed methodologies. The document does not contain methods for analyz-
ing all of the constituents in either Appendix VIII or Appendix IX and does
not contain reference methods for measuring other required ground-water
parameters such as sulfate, phosphate, chloride, TOC, specific conductance,
etc. To augment SW-846, other analytical methods, such as those contained in
"Methods for Chemical Analysis of Water and Waste" (EPA 600/7-79-020),
"Methods for Organic Chemical Analysis of Municipal and Industrial Waste
Water" (EPA 600/4-82-057), "Standard Methods for the Examination of Water and
Wastewater," (Sixteenth Edition, American Public Health Association, Washington,
D.C., 1985), and the EPA Contract Laboratory Program (CLP) methods are all
potential alternatives that RCRA permittees may wish to propose for monitor-
ing certain constituents and parameters in their ground-water samples.
Through laboratory certification programs have not been developed for
analyses conducted by SW-846 methods, the methods are readily available and
in use by many analytical laboratories throughout the country.
CERCLA
Ground-water and soil/sediment samples from Superfund sites ere analyzed
under the EPA Contract Laboratory Program (CLP) for a specified list of
constituents known as the Hazardous Substances List (HSL). This list, which
is shown in Table 3, consists of 136 organic compounds, and 24 inorganics
including cyanide. A special set of CLP analytical procedures are used, and
only certain laboratories are approved by EPA to conduct the analyses for the
Agency. At the present time, 31 labs are authorized to analyze for HSL
organics, 11 are authorized to analyze for the HSL inorganics, and 13 are
authorized to analyze for dioxins, using the CLP methods. CLP laboratories
must utilize specific QA/QC procedures for all CLP analyses, and they are
5-4
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audited by EPA every three months. The results of the audits are used to
update, modify, or otherwise revise the analytical methods. Only CLP labora-
tories get the updates, which are frequently issued. Hence the system is
underlain by a large and ever expanding data base which is used to control
data ouality by continually improving the accuracy, precision, and detection
capabilities of each lab in the program.
The CLP methods, which are not published, are only available through CLP
contract personnel. Other parties wishing to utilize CLP analytical proce-
dures should contact the authorized EPA Contacts in their Region for details.
QUALITY ASSURANCE PROGRAMS
Quality assurance programs are developed and used by analytical labora-
tories to guarantee delivery of valid and reliable data. Quality assurance
consists of two distinct and equally important functions. One is the assess-
ment of the quality of the data by establishing their precision and accuracy
[referred to collectively as Quality Assessment (QA)]. The other function is
the control, and improvement by corrective action, of the quality of the data
by implementation of specific policies and procedures [referred to collec-
tively as Quality Control (QC)J. The two functions form a control loop--the
QA/QC plan.
QA involves analytical accuracy and precision. Accuracy is maintained
through rigorous instrument calibration and reagent standardization proce-
dures using standards specified in the analytical methods. Methods are
followed strictly and method accuracy is checked routinely with appropriate
control samples, standard reference solutions, spikes (individual compounds
and/or surrogates), internal standards, and audits (both performance and
system audits). Performance audits are external evaluations comparing
laboratory results on blind samples against standard values. System audits
are random on-site qualitative inspections and review. Analytical precision
is maintained by adherence to methods and is evaluated by comparison of
results between replicate measurements. While replicate analyses may be
precise (i.e., little deviation between results) they may not necessarily be
accurate; hence the need for utilization of accuracy evaluations.
QC involves those functions within the laboratory which control the
quality and completeness of the data collected. Functions involved include
but are not limited to:
Analytical methods - utilization of published and standardized
procedures.
° Reagent control - utilization of analytical reagents conforming to
specifications of the Committee in Analytical Reagents of the
American Chemical Society.
0 Volumetric glassware - high quality measuring devices.
5-5
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0 Calibration standards - specially prepared, known quality reagents
for system checks.
° Blanks - both batch and method blanks should be used.
° Calibration procedures and frequency - defined program to conduct
calibration tests.
° Control samples - known reference standards.
0 Duplicate analyses - replicate analyses on a defined percentage
(usually 10 percent) of samples.
0 Spiked samples - used to verify presence or absence of matrix
interference.
0 Corrective measures - defined procedures to handle accuracy and
precision problems.
° Data validation - review of results by supervisory personnel.
0 Glassware cleaning - housekeeping procedures to return equipment to
"clean" conditions.
° Equipment maintenance - routine servicing of equipment.
0 Training - utilizing technicians and staff who are qualified by
experience.
Too frequently, the staff involved with the design and operation of the
ground-water monitoring program know little about what happens to a sample
once it goes to the laboratory. Familiarity with laboratory OA/QC procedures
will help "investigators" understand and interpret the analytical results
that are ultimately produced.
5-6
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TABLE 1. APPENDIX VIII CONSTITUENTS
Acetic acid, 2,4,5-trichlorophenoxy-, salts
and esters (2,4,5-T, salts and esters)
Acetonltrile (Ethanenitrile)
Acetophenone (Ethanone. 1-phenyl)
3-( alpha-Ace tony Ibenzyl )-4-
hydroxycoumarln and salts (Warfarin)
2-Acetylaminofluorene (Acetamlde, N-(9H-
fluoren-2-yl)-)
Acetyl chloride (Ethanoyl chloride)
l-Acetyl-2-thlourea (Acetamlde, N-(amln-
othloxomethyl)-)
Acrolein (2-Propenal)
Acrylamide (2-Propenamlde)
Acrylonltrlle (2-Propenenltrlle)
Anatoxins
Aldrln (1.2,3.4.10,10-Hexachloro-
1,4,4a,5,8,8a-hexahydro-endo,exo-
1,4:5,8-dimethanonaphthalene)
Allyl alcohol (2-Propen-l-ol)
Aluminum phosphide
4-Amlnoblphenyl (Cl,l'-Blphenyll-4-amine)
8-Amlno-l,la,2,8,8a,8b-hexahydro-8-
(hydroxymethyl)-8a-methoxy-5-methyl-
carbamate azlrlnot 2,3:3,4]pyrrolo( 1,2-
allndole-4,7-dlone, (ester) (Mitomycin C)
(As)rino[2'3.3,4]pymilo(l,2-a)lndole-4.7-
dlone, 8-amino-8-[((amlno-
carbony 1 )oxy )methy 11-1 ,la,2,8,8a,8b-
hexahydro-Bamethoxy-S-methy-)
MAmlnomethyl>-3-laoxazolol (3(2H)-lsoxa-
Eolone, 5-roethyl-. 2-
(4-(l,l-dimethylethyl)phenoxyM-
methylethyl ester)
Arsenic and compounds, N.OJ3.*
Arsenic acid (Orthoarsenic acid)
Arsenic pentoxlde (Arsenic (V) oxide)
Arsenic trtoxide (Arsenic (III) oxide)
Auramlne (Benzenamine. 4.4'-
carbonimldoylblsCN.N-Dlmethyl-. mono-
hydrochloride)
Azaserine (trSerlne, dlazoacetate (ester))
Barium and compounds, N.O.S.*
Barium cyanide
Benzlclacrldlne (3,4-Benzacridlne)
Benztalanthracene (1.2-Benz»nthracene)
Benzene, 2-amino-1 -methyl (o-Toluidine)
Benzene, 4-amino-1-methyl (P-Toluidine)
Benzene (Cyclohexatriene)
Benzenearsonlc acid (Arsonlc acid, phenyl-)
Benzene, dlchloromethyl- (Benzol chloride)
Benzenethiol (Thlophenol)
Benzidine (U,l'-Blphenyl]-4,4'diamine)
BenzoCblfluoranthene (2,3-Benzofluoranth-
ene)
Benzo[J]fluoranthene (7,3-Benzofluoranth-
ene)
Benzol alpyrene (3,4-Benzopyrene)
p-Benzoqulnone i1,4-Cyclohexadlenedlone)
Benzotrlchlorlde (Benzene, trtchloromethyl-
)
, Benzyl chloride (Benzene, (chloromethyl)-)
Beryllium and compounds. N.O.S.*
Bls(2-chloroethoxy(methane (Ethane, 1.1-
[methylenebls(oxy)]bls(2-chloro-])
Bls(2-chloroethyl) ether (Ethane, 1.1-
oxyblsl2-chloro-l)
N,N-Bls< 2-chloroethyl )-2-naphthylamine
(Chlornaphazlne)
Bla(2-chlorolsopropyl) ether (Propane. 2.2"-
oxyblst2-chloro-l)
Bls(chloromethyl) ether (Methane,
oxybtetchloro-l)
Dis(2
-------
TABLE 1 (continued)
3-Chloropropene (allyl chloride)
3-Chloropropionitrlle (Propanenitrile, 3-
chloro)
Chromium and compounds. N.O.S *
Chrysene (1,2-Benzphenanthrene)
Citrus red No 2 (2-Naphthol, 1 - [< 2,5-
dimethoxyphenyDazo]-)
Coal tars
Copper cyanide
Creosote (Creosote, wood)
Cresols (Cresylic acid) (Phenol, methyl-)
Crotonaldehyde (2-Butenal)
Cyanides (soluble salts and complexes),
NO.S.*
Cyanogen (Ethanedlnltrile)
Cyanogen bromide (Bromine cyanide)
Cyanogen chloride (Chlorine cyanide)
Cycasin (beta-D-Glucopyranoslde, (methyl-
ONN-azoxy (methyl)
2Cyclohexyl-4,6dinitrophenol (Phenol, 2-
cyclohexyl-4.6-dinltro-)
Cyclophosphamide (2H-1,3,2,-Oxazaphos-
phorine. (bis(2-chloroethyl)amino)-tetra-
hydro-, 2-oxide)
Daunomycin (5,12-Naphthacenedione, (8S-
cis)-8-acetyl-l(M(3-amino-2.3,6-trideoxy>-
alpha-L-lyxo-hexopyranosyl)oxy]-7,8,9.10-
telrahydro-6,8.11-trihydroxy-l-methoxy-)
DDD (Dichlorodiphenyldichloroethane)
'Ethane. l,l-dichloro-2,2bis(p-chloro-
phenyl)- >
DDE (Ethylene, l.l-dichloro-2.2-bis(4chlor-
ophenjl)-)
DDT iDichlorodiphenyltnchloroethane)
(Eihant.'. l.l,l-trichloro-2,2 bis(p-chloro-
phenj 1)-)
Diallatc- (S-(2,3-dichloroallyl)
dnsopropylthiocarbamale)
Dibcnzla.hlacridine (1.2.5.6-Dlbenzacridine)
Dibcnzla.jlacridine (1.2,7.8-Dibenzacridine)
Dibenzla.hianthracene (1,2.5.6-Dibenzanth-
racone)
7H-Dibenzolc,g]carbazo!e (3.4.5.6-Dibenzcar-
b&zole i
Dibenzola.elpyrene (1 2,4.5-Dibenzpyrene)
Dibrnzola.hlpyrene (1,2,5.6 Dlbenzpyrene)
Dibenzota.ilpyrene (1,2.7.8-Dibenzpyrene)
1.2-Dibromo-3-chloropropane (Propane,. 1,2-
dibromo-3-chloro)
1.2-Dibromoethane (Ethylene dibromide)
DibromomeLhane (Methylene bromide)
Di-nbutjl phthalate (1,2-
Bcnzenrdicarboxvlic acid, dibutyl ester)
o-Dichlorobenzene (Benzene, 1.2-dichloro-)
m-Dichlorobenzene (Benzene. 1.3-dichloro-)
p-Dichlorobenzene (Benzene, 1,4-dichloro-)
Dirhlorobenzene. N O.S • (Benzene,
dichloro-, N O.S ")
3.3 -Dichlorobenzidine (tl.l-Biphenyl]-4,4 -
diamine. 3,3'-dichloro)
1.4-Dichloro-2bnte!ie (2-Butene. 1,4-dich-
loro-)
Dichlorodifluoromelhane (Methane, dich-
lo-odifluoro-)
l.l ijiehloroethane (Ethylidene dichloride)
1 2-Dichloroethane (Ethylene dichloride)
trans-1.2-Dichloroethene (1,2-Dichloroethy-
lene)
Dichloroethylene, N.O.S.* (Ethene, dich-
loro-, N O.S ')
1,1 Dichloroethylene (Ethene, 1,1-dichloro-)
Dichloromethane (Methylene chloride)
2,4-Dirhlorophenol (Phenol, 2,4-dichloro-)
2.6-Dichlorophenol (Phenol, 2,6-dichloro-)
2.4-Dichlorophenoxyacetic acid (2,4-D), salts
and esters (Acetic acid. 2.4-dichlorophen-
oxy , salts and esters)
Dichlorophenylarsine (Phenyl dichloroar-
sine)
Dlchloropropane, N O S.* (Propane, dich-
loro-, N.O.S •)
1,2-Dichloropropane (Propylene dichloride)
Dlchloropropanol, N.O.S.' (Propanol. dich-
loro-, NO.S*)
Dichloropropene. N.O.S.' (Propene, dich-
loro-, N.O.S.')
1,3 Dichloropropene (1-Propene, 1,3-dich-
loro-)
Dleldrin (l,2,3,4.10.10-hexaehloro-6,7-epoxy-
l,4,4a,5,6.7,8,8a-octa-hydro-endo,exo-
l,4:5,8-Dimethanonaphthalene)
l,2:3,4-Diepoxybutane (2,2-Bloxirane)
Dlethylarsine (Arslne, diethyl-)
N.N'-Diethylhydrazine (Hydrazine, 1,2-
diethy!)
O.O-Dicthyl S-methyl ester of phosphoro-
dithioic acid (Phosphorodithioic acid,
O.O-diethyl S-methyl ester
O.O-Diethylphosphoric acid, O-p-nitro-
phenyl ester (Phosphoric acid, diethyl p-
nitrophenyl ester)
Diethyl phthalate (1,2-Benzenedicarboxvlic
acid diethyl ester)
O.ODiethyl O-2-pyrazinyl phosphoroth-
loate (Phosphorothioic acid, O.O-diethyl
O p.\razinyl ester
Diethylstilbesterol (4.4-Stilbenediol,
alpha.alpha-diethyl, bis(dihydrogen phos-
phate. (E)-)
Dihydrosafrole (Benzene. 1,2-methylene-
dioxv-4propy]-)
3.4Dihydroxy-alpha-(methylamino)methyl
benzj 1 alcohol (1,2-Benzenediol, 4-[l-hy-
droxy-2(meihylamino)ethyl]-)
Dnsopropylfluorophosphate (DFP) (Phos-
phorofluoridic acid, bis(l-methylethyl)
ester)
Dimethoate (Phosphorodithioic acid, O.O-
dimethyl S [2-(methylamino)-2-oxoethyl]
ester
3.3 -Dimethoxybenzidine ([ 1.1 Biphenyl]-
4,4 diamine, 3-3-dimethoxy-)
p-Dimethylaminoazobenzene (Benzenamine,
N,N-dimethyl-4-(phenylazo)-)
7,12-Dimethylbenzla]anthracene (1,2-Ben-
zanthracene, 7,12-dimethyl-)
3.3 -Dimethylbenzidine ([l.rBipheny]]-4.4-
diamine. 3.3 -dimethyl-)
Dimethvlcarbamoyl chloride (Carbamoyl
chloride, dimethyl-)
1.1-Dimethylhydrazine (Hydrazine, 1,1-di-
methyl-)
1.2-Dimethylhydrazine (Hydrazine. 1,2-di-
methyl)
3,3Dimethyl-l-(methylthio)-2-butanone, O-
[(methylamino) carbonylloxlme (Thlo-
fanox)
alpha.alpha-Dimethylphenethylamine (Eth-
anamine, l,l-dimethyl-2-phenyl )
2,4-Dimethylphenol (Phenol, 2,4-dlmethyl-)
Dimethyl phthalate (1.2-
Benzenedicarboxyllc acid, dimethyl ester)
Dimethyl sulfate (Sulfuric acid, dimethyl
ester)
Dinitrobenzene, N.O.S.* (Benzene, dlnitro-,
N.O.S.*)
4,6-Dinitro-o-cresol and salts (Phenol, 2,4-
dinitro-6-methyl-, and salts)
2.4-Dinitrophenol (Phenol, 2,4-dlnitro-)
2,4-Dlnltrotoluene (Benzene, l-methyl-2,4-
dinitro-)
2,6-Dlnitrotoluene (Benzene, l-methyl-2,6-
dlnitro)
Di-n-octyl phthalate (1,2-
Benzenedicarboxylic acid, dioctyl ester)
1,4-Dioxane (1,4-Diethylene oxide)
Diphenylamlne (Benzenamine. N-phenyl-)
5-8
-------
TABLE 1 (continued)
1,2-Dlphenylhydrazlne (Hydrazine, 1,2-dl-
phenyl-)
Dl-n-propylnitrosamine (N-Nitroso-dl-n-pro-
pylamlne)
Disulfolon (O.O-diethyl S-12-
(ethylthio)ethyl] phosphorodithioate)
2.4-Dithiobiuret (Thlolmldodicarbonic dia-
midc)
Endosuifan (5-Norbornene, 2,3-dimethanol.
1,4,5.6,7.7-hexachloro-. cyclic sulfite)
Endrin and metabolites < 1,2.3.4.10,10-hex-
achloro-6.7-epoxy-l 4,4a,5,6,7,8,8a-
octahydro-endo.enao-1.4,5.8-
dimethanonaphthalene, and metabolites)
Ethyl cyanide (propanenjlrile)
Ethylenebisdithiocarbamlc acid, sails and
esters (1.2-Ethanediylbiscarbamodithioic
acid, salts and esters
Ethylene glycol monoethyl ether
(Exthanol. 2-eihoxy)
Ethyleneimine (Aziridine)
Ethylene oxide (Oxirane)
F.'hylenethiourea (2-Imidnzolidinethione)
Elhjl methacrylate (2-PropLnoK' acid, 2-
methyl-, ethyl ester)
Ethyi methanesulfonate (Methanesulfonlc
acid, ethyl ester)
FHioranthene (Benzotj.klfluorenel
Fluorine
2-Fluoroacetamidr (Acetamide. 2-fluoro-)
Fluoroacetic acid, sodium salt (Acetic acid,
fluoro-. sodium salt)
Formaldehyde (Methylene oxide)
Formic acid (Methanoic acid)
Glycidylaldehyde (1 -propanol-2,3-exoxy)
Halomethane, N O S"
Heptachlor (4.7-Methano-lH-indene,
1.4,5.6,7,8,8-heptachloro-3a,4,7.7a-
tetrahydro)
Heptachlor epoxide (alpha, beta, and
gamma isomers) (4.7-Methano-lH-indene,
1.4.5.6,7.8.8-heptach)oro-2,3-epoxy3a,4,7,7-
tetrahydro-, alpha, beta, and gamma iso-
mers)
Hexachlorobenzene (Benzene, hexachloro-)
Hexachlorobutadiene (1,3-Butadiene,
hexachloro-)
Hexachlorocyclohexane (all isomers) (Lin-
dane and isomers)
Hexachlorocyclopentadiene (1,3-Cyclopen-
tadiene, 1.2.3,4,5.5-hexachloro)
Hcxachlorodiben7o-/i-dioxins
Hexachlorodibenzofurans
Hexachloroethane (Ethane, hexachloro-)
1.2,3,4.10,10-Hexachloro-1.4,4a,5.8.8a-
hexahydro-l.4-5.8-endo.endo-
dimethanonaphthalene
(Hexachlorohexahydro-endo.endo-
dimethanonaphthalene)
Hexachlorophene (2,2 -Methylenebls( 3,4.8-
trlchlorophenoi))
Hexachloropropene (Propene, hexachloro-)
Hexaethyl tetraphosphate (Tetraphos-
phorlc acid, hexaethyl ester)
Hydrazine (Diamine)
Hydrocyanic acid (Hydrogen cyanide)
Hydrofluoric acid (Hydrogen fluoride)
Hydrogen sulfide (Sulfur hydride)
Hydroxydimethylarsine oxide (Cacodyllc
acid)
Indeno(1.2,3-cd)pyrene (1,10(1,2-
phenylene)pyrene)
lodomethane (Methyl iodide)
Iron dextran (Ferric dextran)
Isocyanlc acid, methyl ester (Methyl iso-
cyanate)
Isobutyl alcohol (1-Propanol, 2-methyl-)
Isosafrole (Benzene. l,2-methylenedioxy-4-
allyl-)
Kepone (Decachlorooctahydro-1,3,4-meth-
ano-2H-cyclobuta[cd]-pentalene-2-one)
Lasiocarplne (2-Butenoic acid. 2-methyl-, 7-
[(2.3-dihydroxy-2-(l-methoxyethyl)-3-
methyl-l-oxobutoxy)methyl]-2,3,5.7a-
tetrahydro-lH-pyrrolizin-l-yl ester)
Lead and compounds, N.O.S *
Lead acetate (Acetic acid, lead salt)
Lead phosphate (Phosphoric acid, lead salt)
Lead subacetate (Lead, bis(acetato-
OHetrahydroxytri-)
Maleic anhydride (2,5-Furandione)
Maleic hydrazide (1.2-Dihydro-3,6-pyridazin-
edione)
Malononitrile (Propanedinitrile)
Melphalan (Alanine, 3-[p-bis(2-
chloroethyDaminolphenyk L-)
Mercury fulminate (Fulmmic acid, mercury
salt)
Mercury and compounds. N O S.'
Methacrylonltrile < 2-Propenenitrile, 2-
methyl-)
Methanethiol (Thiomethanol)
Methapyrilene (Pyridine. 2-1(2-
dimethylamino)ethyl]-2-thenylamino)
Metholmyl (Acetimidic acid, N-
[(methylcarbamoyl)oxyHhio-, methyl
ester
Methoxychlor (Ethane, l.l.l-tnchloro-2.2-
bis(p-methoxyphenyl)-)
2-Methylaziridine (1,2-Propylenimine)
3-Methylcholanthrene
(Benztjlaceanthrylene, l,2-dihydro-3-
methyl-)
Methyl chlorocarbonate (Carbonochloridic
acid, methyl ester)
4.4'-Methylenebis(2-chloroaniline) (Benzen-
amine, 4,4'-methylenebis-(2-chloro-)
Methyl ethyl ketone (MEK) (2-Butanone)
Methyl hydrazine (Hydrazine, methyl-)
2-Methyllactonitrile (Propanenitrile, 2-hy-
droxy-2-methyI-)
Methyl methacrylate (2-Propenoic acid, 2-
methyl-, methyl ester)
Methyl methanesulfonate (Methanesulfonic
acid, methyl ester)
2-Methyl-2-(methylthlo)propionaldehyde-o-
(methylcarbonyl) oxime (Propanal, 2-
methyl-2-(met"nylthio)-, O-
C(methylamlno)carbonylloxime)
5-9
-------
TABLE 1 (continued)
N-Methyl-N'-nitro-N-nitrosoguanidine
(Cuanidine, N-nitroso-N-methylN'-nitro-)
Methyl parathion (O.O-dimethyl 0-(4- ,
nitrophenyl) phosphorothioate)
Methylthiouracil (4-lH-Pyrimidinone. 2.3-
dihydro-6-methyl-2-thioxo-)
Mustard gas (Sulfide. bis(2-chloroethyl))
Naphthalene
1.4-Naphthoqumone (1,4-Naphthalenedione)
1-Naphthylamlne (alpha-Napl]thylamine)
2-Naphthylamine (beta-Naphthylamine)
1-Naphthyl-2-thiourea (Thiourea, 1-
naphthalenyl)
Nickel and compounds, N OS."
Nickel carbonyl (Nickel tetracarbonyl)
Nickel cyanide (Nickel (II) cyanide)
Nicotine and salts (Pyridine, (S)-3-(1-methyl-
2-pyrrolidmy!)-, and salts)
Nitric oxide (Nitrogen (II) oxide)
p-Nitroanlline (Benzenamine. 4-nitro-)
Nltroberizine (Benzene, nitro-)
Nitrogen dioxide (Nitrogen (IV) oxide)
Nitrogen mustard and hydrochloride salt
(Ethanamine, 2-chloro-. N-(2-chloroethyl)-
N-methyl-, and hydrochloride salt)
Nitrogen mustard N-oxide and hydrochloride
salt (Ethanamine, 2-chloro-. N-(2-chlor-
oethyl)-N-methvl-N-oxide, and hydrochlo-
ride salt)
Nitroglycerine (1,2.3-Propanetriol, trinitrate)
4-Nitrophenol (Phenol, 4-nitro-)
2-Nitropropane (Propane, 2-nitro)
4-Nitroquinoline-l-oxide (Quinoline, 4-nitro-l-
oxide)
Nitrosamine, N.O.S.*
N-Nitrosodi-n-butylamine (1-Butanaminc. N-
butyl-N-nitroso-)
N-Nitrosodiethanolemine (Ethanol, 2.2'-
(nitrosoimino)bis-)
N-Nitrosodiethylamine (Ethanamine, N-ethyl-
N-nitroso-)
N-Nitrosodimethylamine
(Dimethylnitrosamine)
N-Nitroso-N-ethylurea. (Carbamide, N-ethyl-
N-nitroso-)
N-Nitrosomethylethvlamine (Ethanamine, N-
methyl-N-nitroso-)
N-Nitroso-N-methylurea (Carbamide, N-
methyl-N-nitroso-)
N-Nitroso-N-methylurethane (Carbumic acid,
methylnitroso-, ethyl ester)
N-Nitrosomethylvinylamine (Ethenamine, N-
methvl-N-nitroso-)
N-Nitrosomorpholine (Morpholine, N-nitro60-
)
N-Nitrosonornicotine (Nornicotine. N-
nitroso-)
N-Nitrosopiperidine (Pyridine, hexahydro-, N-
nitroso-)
Nitrosopyrrolidine (Pyrrole, tetrahydro-. N-
nitroso-J
N-Nitrososarcr sine (Sarcosine, N-nitroso-)
5-Nitro-o-toluidine (Benzenamine, 2-methyl-5-
nitro-)
Octamethylpyrophosphoramide
(Diphosphorumide, octamethyl-)
Osmium tetroxide (Osmium (Vlll) oxide)
7-Oxabicyclo[2.2,lJheptane-2.3-dicarboxylic
acid (Endothal)
Paraldehyde (1 3.5-Trioxane. 2.4.6-trimethy]-)
Parathion (Phospfioroiinu.u a "id, 0,0-diethyl
O-(p-nitrophenyl) ester
Pentachlorobenzene (Benz. rf, pentachloro-)
Pentachlorodibenzo-p-dioxins
Pentachlorodibenzofurans
Pentachloroethane (Ethane, pentachloro-)
Pentachloronitrobenzene (PCNB) (Benzene,
pentachloronitro-)
Pentachlorophenol (Phenol, pentarMoro-)
Perrnioioinethy] mercaptan (Meth.inesull-
envl chloride, trichloro-)
Phenacetin (Acetamide. N-(4-ethoxyphenyl)-)
Phenol (Benzene, hydroxy )
Phenylenediamine (Benzcnediamine)
Phenylmercury acetate (Mercury,
acetatophenjl-)
N-Phenylthiourea (Thiourea, phenyl-)
Phosgene (Carbonyl chloride)
Phosphine (Hydrogen phosphide)
Phosphorodithioic acid, 0,0-diethyl S-
l(ethylthio)methyl) ester (Phorate)
Phosphorothioic acid. O.O-dimethyl 0-[p-
((dimethylamino)sulfonyl)pheny!j ester
(Famphur)
Phthal ic acid esters, N.O.S.' (Benzene, 1,2-
dicarboxylic acid, esters, N O.S ")
Phthalic anhydride (1.2-Benzenedicarboxylic
acid anhydride)
2-Picoline (Pyridine, 2-methyl-)
Polychlonnated biphenyl, N.O.S."
Potassium cyanide
Potassium silver cyanide (Argentate(l-),
dicyano-. potassium)
Pronamide (3,5-Dichloro-N-(l,l-dimethyl-2-
propynyl)benzamide)
1,3-Propane 6ultone (1.2-Oxathiolane, 2,2-
dioxide)
Propionic acid. 2- (2.4.5-trichlorophenox>
salts ami esters (2.4,5-TP. Silvex. salts and
esters]
n-Propylamine (l-Propanamine)
Propylthiouracil (2,3-dihydro-6-propvl-2-
thioxo-4(H)-pyrimidinone)
2-Propyn l-ol (Propargyl alcohol)
Pyridine
Reserpine (Yohimban-16-carboxylic acid,
11.17-dimethoxy-18-[[3.4.5-
irimethoxybenzoyl)oxy|-, methyl ester)
Resorcinol (1,3-Benzenediol)
Saccharin and salts (1.2-Benzoisoihiazolin-3-
~nr. 1.1-dioxide. and salts)
5-10
-------
TABLE 1 (continued)
Siilrole IBenzene. 1,2-methylenedioxv-4-al-
Kl-I
Sclnmuus acid (Selenium dioxide)
Si'livmim and compounds. N O S "
Selenium sulfide (Sulfui selenidc)
Selonourea (Curbamimidoselenoic acid)
Sdvcr and compounds, N O.S.'
Silver cyanide
Sodium cymnde
Strcptozntocin (D-Glucopyranose. 2-deoxy-2-
(3-mcthyl-3-nitrosourcido)-)
Strontium sulfide
Slrj t.linine and salts (Strychnidin-10-one, and
s;dts)
l^AS-Tolriiclilorobenzene (Brnzune, 1,2,4,5-
tetra(.hloro-)
2.3,7.0-Totrachlorodibcnzo-p-dioxin (TCDD)
(Dibenzo-p-dioxin, 2.3,7,8-tetrachloro-)
Tetrachlorodibenzo-p-dioxins
Tetrachlorodibenzofurans
Tetrachloroeth;me, N.O.S.' (Ethane,
tetracbloro-. N.O.S.")
1,1,1,2-Tetrachlorethane (Ethane, 1,1,1.2-
tetrachloro-)
1,1,2,2-1 Hrachlorethane (Ethane, 1,1,2,2-
ti-'rachlo'O-)
1 etr.n.iiliiroethane (Ethene, tetrach-
loi o-)
Tclrdt-hloromethane (Carbon tetrachloride)
2.3 4,6.-Telrachlorophenol (Phenol, 2,3,4,6-
tetrachloro-)
Tetrnethyldithiopyrophosphate
(Duhiopyrophosphoric acid, tetraethyl-
ester)
TelrdPthyl lead (Plumbane. tetraethyl-)
Tetraethylpyrophosphate (Pyrophosphoric
acide. tetraethyl ester)
Tetranitrumethane (Methane, tetranitro)
Thallium and compounds. N.O.S *
Thallic oxide (Thallium (III) oxide)
Thallium (I) acetate (Acetic acid, thallium (I)
salt)
Thallium (1) carbonate (Carbonic acid.
dithallium (I) salt)
Thallium (1) chloride
Thallium (I) nitrate (Nitric acid, thallium (I)
salt)
Thallium selenite
Thallium (I) sulfate (Sulfuric acid, thallium (I)
salt)
Thioacelamide (Ethanethioamidp)
Thiosemicarbazide
(Hydrazinecarbothioamidp)
Thiourea (Carbamide th.o-)
Thiuram (Bis(dimethylthiocarbamoyl)
disulfide)
Toluene (Benzene, methyl-)
Toluenediamine (Toluene, 2,5-diamine-l
2,4-Toluenediamine
2.6-Toluenediamine
3,4-Tolucncdiamine
Toluenediamine, N O S.
o-Toluidine hydrochloride (Benzenamine. 2-
methyl-, hydrochloride)
Tolylene diisocyanate (Benzene. 2.4-and 2.6-
d iisoc\n natomethvl-1
Toxaphene (Camphene. octachloro-)
fribromomethane (Bromolorm)
1.2.4-Trichlorobenzcne (Benzene, 1.2.4-
trichloro-)
1.1.1-Trichloroethane (Methyl chloroform)
1.1.2-Trichloroethane (Ethane. 1.1.2-tnchloro-)
Trichloroethene (Trichloroethylenu)
Trichioromethanethial (Methanethiol.
trichloro-)
Trichloromonofluoromethane (Methane,
trichlorofluoro-)
2.4.5-Trichlorophenol (Phenol, 2.4,5-trichloro-)
2.4.8-Trichlorophenol (Phenol, 2,4.6-trichloro-)
Trichloropropane, N.O.S.* (Propane,
trichloro-, N.O.S.")
1.2.3-Tnchloropropane (Piopane, 1.2,3-
trichloro-)
0,0.0-Triethy! phosphorolhioate
(Phosphorothioic acid, 0,0,0-tnethyl ester)
sym-Trinitrobenzene (Benzene, 1,3,5-trinitro-)
Tris(l-azridinyl) phosphine sulfide
(Phosphine sulfide, tris(l-aziridinyl-)
Tris(2,3-dibromopropyl) phosphate (1-
T*ropanol, 2,3-dibromo-, phosphate)
Trypan blue (2,7-Naphthalenedisulfonic acid,
3,3'-|(3.3'-dimethyl(l.l'-bipheny l)-4.!'-
djyl)bis(azo)|bis(5-amino-4-hydroxy-.
tetrasodium salt)
I '"Hecamethylenediamine, N,N'-bis-
2-chlorobcnz> 1)-. dihydrochloride (N.N'-
Undecamethylenebis (2-chlorobenzyla-
mine. dihydrochloride)
Uracil mustard (Uracil 5-|bis(2-
chloroethyl)amino]-)
Vanadic acid, ammonium salt (ammonium
vanadate)
Vanadium pentoxide (Vanadium (V) oxide)
Vinyl chloride (Ethene. chloro-)
Zinc cyanide
Zinc phosphide
Source: 40 CFR Part 261, Appendix VITI. July 1, 1986, as amended by
51FR28297, August 6, 1986.
5-11
-------
TABLE 2. APPENDIX IX CONSTITUENTS
Group Constituents
Volatile organics
Semivolatile organics
Chloromethane
Bromomethane
Vinyl chloride
Chloroethane
Methylene chloride
Acetone
Carbon disulfide
1,1-Dlchloroethene
1.1-Dlchloroethane
lrans-l,2-dichloroethene
Chloroform
1.2-Dlchloroethane
2-Butanone
1,1,1-Trlchloroethane
Carbon tetrachloride
Vinyl acetate
Bromodichlorontethane
Acetonltrlle
Acrylonltrile
Acrolein
3-Chloropropene
1,2-Dlbromoethane
Dibromomethane
1.2-D1bromo-3-chloropropane
Dlchlorodlfluoromethane
1,4-Dloxane
Ethyl methacrylate
Phenol
Bis(2-chloroethy1)ether
2-Chlorophenol
1.3-D1chlorobenzene
l,4rDicMorobenzene
Benzyl alcohol
l,2-D1chlorobenzene
2-Methylphenol
Bi5(2-chloroisopropyl)ether
4-Methylphenol
N-n1troso-d1-n-propylamine
Hexachloroethane
Nitrobenzene
Isophorone
2-N1trophenol
2.4-Dlmethylphenol
Benzoic acid
B1s(2-chloretho*y)methane
2,4-Dichlorophenol
1.2.4-Trichlorobenzene
Naphthalene
4-Chloroaniline
Hexachlorobutadiene
4-Chloro-3-methylphenol
2-Methylnapthalene
Hexachlorocyclopentadiene
2,4,6-Trlchlorophenol
2.4.5-Trichlorophenol
2-Chloronaphthalene
2-Nltroaniline
Dimethyl phthalate
Acenaphthylene
3-Nltroaniline
Aramite
2-Acety1amlnof1uorene
4-Aminobiphenyl
Aniline
Benzidine
4-Benzoqulnone
2-Sec-butyl-4,6-d1nitrophenol
Chlorobenzilate
3-Chloroproplonitrlle
Oibenzo(a,e)pyrene
l;2-dichloropropane
Trans-l,3-dichloropropene
Trichloroethene
Dlbromochloromethane
1.1.2-Trlchloroethane
Benzene
C1s-l,3-d1chloropropene
2-Chloroethylvinyl ether
Bromoform
4-Methyl-2-pentanone
2-Hexanone
Tetrachlorocthene
1,1,2,2-Tetrachloroethane
Toluene
Chloro benzene
Ethylbenzene
Styrene
Total xylenes
Ethylene oxide
lodomethane
Hethacrylonitrile
Methyl methacrylate
1,1,1,2-Tetrachloroethane
Trichlorofluoromethane
1.2.3-Tr1chloropropare
Bromomethane
Acenaphthene
2,4-Dinitrophenol
4-Nitrophenol
Dibenzofuran
2,4-0initrotoluene
2.6-D1n1trotoluene
Diethyl phthalate
4-Chlorophenylphenyl ether
Fluorene
4-Nitroaniline
4,6-0initro-2-methy1 phenol
N-Ni trosodiphenyl ami ne
4-Bromophenylphenyl ether
Hexachlorobenzene
Pentachlorophenol
Phenanthrene
Anthracene
Di-n-butyl phthalate
Fluoranthene
Pyrene
Butylbenzylphthalate
3,3'-Dlchlorobenzidine
Benzo(a)anthracene
B i s-(Z-ethylhexy1(phthalate
Chrysene
D1-n-octyl phthalate
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzo(a)pyrene
Indeno(l,2,3-cd)pyrene
Dibenzo(a,h)anthracene
Benzo(g,h,1jperylene
Methapyrilene
1-Naphthylamine
2-Naphthylamle
N-NItrosodiethyl amine
N-Nitrosodimethylamine
N-NItosod1-n-butylamine
N-Nitrosomethyl.-thylamine
N-Nitrosomorphoiine
N-Nltrosopipendine
N-N1trosopyrolidine
5-Nitro-2-toluidine
(continued)
5-12
-------
TABLE 2 (continued)
Group
Constituents
Sennvolati le organics
(continued)
Pest 1 sides,
herbicides,
PCB's
Dibenzo(a,h)pyrene
D1benzo(a,1)pyrene
2,6-Dlchlorophenol
3,3'-Dlmethoxybenz1d1ne
7,12-D1methylbenz-(tt,h)-anthracene
a,a-D1methylphenethylam1ne
1.3-01 nitrobenzene
Dlphenylamine
Dlphenylhydrazlne
Hexachlorophene
Hexachloropropene
Isosafrole
3-Methylcholanthrene
4,4'-Methylenet>1s-(2-chloroan11 fne)
1.4-Naphthoqulnone
4-Dlmethyl ami noazobenzene
3,3'-D1methylbenz1dine
2-Chloro-l,3-butadiene
Allyl alcohol
T-l,4-D1chloro-2-butene
Alpha-BHC
Beta-BHC
Delta-BHC
Gatima-BHC (Lindane)
Hepttchlor
Aldrln
Heptachlor epoxide
Endosulfan I
Dieldrln
4,4'-DDE
Endrin
Endosulfan 11
4,4'-ODD
Endosulfan sulfate
4,4'-DDT
Pentachlorobenzene
Pentachloroethane
Pentachloronitrobenzene
Phenacetin
2-P1coline
Pronamide
Resorcinol
Safrole
1.2.4.5-Tetrachlorobenzene
2.3.4.6-Tetrachlorophenol
Hethyimethanesu1fonate
Pyridine
Benzenethiol
Halonltrole
Acetophenone
Ethyl cyanide
lsobutyl alcohol
2-Propyn-l-ol
Trlchloromethanethlol
Methoxychlor
Endrin ketone
Chlordane
Toxaphene
Arochlor-1016
Arochlor-1221
Arochlor-1232
Arochlor-1242
Arochlor-1248
Arochlor-1254
Arochlor-1260
Endrin aldehyde
Isodrin
Kepone
Inorganics
2.4.5-T
2,4,5-TP (Silvex)
2,4-D
0,0-d1ethyl-0-2-pyraz1nyl-
phosphrothioate
Disulfoton
Famphur
Methyl parathion
Dioxin/dibenzofuran
Fluoride
Cyanide
Sulfide
Parathion
Phorate
Tetraethyldi thiopyrophosphate
Tris(2,3-dibromopropyl)-phos-
phate
Tr1s(2,3-d1bromopropyl)-phos-
phate
Aluminum
Antimony
Barium
Beryllium
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Arsenic
Mercury
Magnesium
Manganese
Nickel
Osmium
Potassium
Silver
Sodium
Thai 1ium
Tin
Vanadium
Zinc
Selenium
Source: 51 FR 26632, July 24, 1986.
5-13
-------
TABLE 3. THE CONTRACT LABORATORY PROGRAM
HAZARDOUS SUBSTANCES LIST
Substance
CAS nuober
Volatile*
1. Chloromethjne
74-87-3
2. Bromomtthane
74-B3-9
3. Vinyl chloride
75-01-4
4. Chloroethane
75-00-3
5. Methylene chloride
75-09-2
6. Acetone
67-64-1
7. Carbon disulfide
75-15-0
B. 1,1-Dichloroethene
75-35-4
9. 1,1-Dichloroethane
75-35-3
10. Tr«ns-l,2-d1chloroethene
156-60-5
11. Chloroform
67-66-3
12. 1,2-Dlchloroethane
107-06-2
13. 2-Butanone
7B-93-3
14. 1,1,1-Tr1chloroethane
71-55-6
15. Carbon tetrachloride
56-23-5
16. Vinyl acetate
108-05-4
17. Bromodlchloromethane
75-27-4
18. 1,1,2,2-TetracHoroethane
79-3«-5
19. l,2-D1chloropropane
78-87-5
20. Trans-l,3-d1chloropropene
10061-02-6
21. Trlchloroethene
79-01-6
22. Dlbromochloromethane
124-48-1
23. 1,1,2-Tr1chloroethane
79-00-5
24. Benzene
71-43-2
25. Cls-l,3-d1chloropropene
10061-01-5
26. 2-Chloroethyl vinyl ether
110-75-8
27. Bromoforn
75-25-2
28. 2-He««none
591-7E-6
29. 4-Hethyl-2-pentanone
108-10-1
30. Tetrachloroethene
127-18-4
31. Toluene
108-88-3
32. Chlorobenzene
108-90-7
33. Ethyl benzene
100-41-4
34. Styrene
100-42-5
35. Total xylenes
Semlvolatlles
36. (*henol
10B-95-2
37. B1s(2-chloroethyl)ether
111-44-4
3e. 2-Chlorophenol
95-57-8
39. 1,3-Dlchlorobeniene
541-73-1
40. 1,4-Dichlorobenzene
106-46-7
41. Benzyl alcohol
100-51-6
42. l,2-D1chlorobenzene
95-50-1
43. 2-Hethylphenol
95-48-7
44. B1s(2-cMoro1sopropyl)ethtr
39638-32-9
45. 4-Hethylphenol
106-44-5
46. N-n1troso-d1propyl amine
621-64-7
47. Hexachloroethane
67-72-1
48. Nitrobenzene
98-95-3
49. Isophorone
78-59-1
50. 2-H1trophenol
68-75-5
51. 2,4-D1l»ethylphenol
105-67-9
52. Benzoic acid
65-85-0
53. Bis(2-chloroethoxy)methane
111-91-1
54. 2,4-D1chlorophenol
120-83-2
55. 1,2,4-Trichlorobenzene
120-82-1
56. Naphthalene
91-20-3
57. 4-Chloroan1line
106-47-8
SB. Htxachlorobutadlene
B7-68-3
59. 4-Chlore-3-nethylphenol(para-chloro-meta-cresol
59-50-7
60. 2-Hethylnaphthalene
91-57-6
61. Htxtchlorocylcopentadlene
77-47-4
62. 2,4,6-Trlehlorophenol
68-06-2
63. 2,4,5-Trlchlorophenol
95-95-4
(continued)
5-14
-------
TABLE 3 (continued)
Substince
CAS nurter
S««1volatHes (continued)
64. 2-Chloronaphthalene
91-58-7
65. 2-N1troan1l1ne
68-74-4
66. Dimethyl phthalate
131-11-3
67. Acenaphthylene
208-96-B
68. 3-N1troan1lint
99-09-2
69. Acenaphthene
83-32-9
70. 2,4-DIMtrophenol
51-26-5
71. 4-N1trophenol
100-02-7
72. Dlbeniofuran
132-64-9
73. 2,4-D1nttrotoluene
121-14-2
74. 2,6-D1n1trotoluene
606-20-2
75. Dlethylphthalate
84-66-2
76. 4-Chlorophenv) phenyl ether
7005-72-3
77. Fluorene
86-73-7
78. 4-N1troan111ne
100-01-6
79. 4,6-D1n1tro-2-*iethylphenol
534-52-1
80. N-n1trosod1phenylam1ne
86-30-6
81. 4-Bromophenyl phenyl ether
101-55-3
82. Hexachlorobenzene
118-74-1
83. Pentachlorophenol
87-86-5
84. Phenanthrene
85-01-8
85. Anthracene
120-K-7
86. 01-n-butylphthalate
84-74-2
87. Fluoranthene
206-44-0
68. Pyr*ne
120-00-0
89. Butyl benzyl phthalate
85-6B-7
90. 3,3'-D1chlorobenzldine
91-94-1
91. Ben2o(a)anthracene
56-55-3
92. B1$(2-ethylhexyl)phthal«te
117-81-7
93. Chrysene
218-01-9
94. Di-n-octyl phthalate
117-84-C
95. Benzo(b)fluoranthenp
205-99-2
96. Benzojkjfluorarthene
207-08-9
97. Benzo(a)pyrene
50-32-8
9E. lndeno(l,2,3-cd)pyrene
193-30-5
99. D1benio(a,h)anthracene
53-70-3
100. Benjolg.h.ljperylene
191-24-2
Pesticides/PCB
101. Alpha-BHC
319-84-6
102. Beta-EHC
319-85-7
103. Delta-BHC
319-86-6
104. Gamna-BHC (lindane)
58-89-9
105. Heptachlor
76-44-e
106. Aldrln
309-00-2
107. Heptachlor epoxide
1024-57-3
108. Endosulfan I
959-98-8
109. Dleldrln
60-57-1
110. 4,4'-DDE
72-55-9
111. Endrln
72-20-8
112. Endosulfan 11
33213-65-9
113. 4,4'-ODD
72-54-B
114. Endosulfan sulfate
1031-07-8
115. 4,4'-DDT
50-29-3
116. Endrln ketone
53494-70-5
117. Hetkoxychlor
72-43-5
118. Chlorodane
57-74-9
119. Toxaphene
8001-35-2
120. AROCLOR-1016
12674-11-2
121. ABOCLOR-1221
11104-28-2
122. AROCLOP-123:
11141-16-5
123. AROCLOR-1242
53469-21-9
124. AROCLOR-1248
12672-29-6
125. ABOCLOR-1254
11097-69-1
126. AR0CL0A-1260
11096-82-5
(continued)
5-15
-------
TABLE 3 (continued)
Subjtance
CAS nudxr
Metals
127. Aluminum
128. Antimony
129. Arierlc
130. Barium
131. Beryl Hun
132. Cadmium
133. Calcium
134. Chromium
135. Cobalt
136. Copper
137. Iron
138. lead
139. Kagneslum
140. Manganese
141. Hercury
142. Nickel
143. Potassim*
144. Selenium
145. Silver
146. Sodium
147. Thallium
148. Vanadium
149. Z1nc
ISO. Cyanide
5-16
-------
APPENDIX A
/V'
-------
Monitoring Well Design Rating System
Direct
Dual
Top Casing
Hollow
Cable
Mud
Reverse
Tube-Air
Drive
Air
Stem
Design Requirements
Tool
Rotary
Rotary
Rotary
Air/Mud
rotary
Auger
Piezometer
single (1"i
A. consolidated
1
5
1
2
1-4
4
4
B unconsolidated
1
5
1
2
1-4
1
4
Multiple piezometer in a single
borehole
A. consolidated
1
5
4
0
1-4
3
0
B unconsolidated
1
5
4
0
1-4
1
0
. V\ ater samples
single (2")
A. consolidated
1
5
1
2
1-4
4
3
B. unconsolidated
1
5
1
2
1-4
1
3
. Aquifer testing
single casing (6")
A consolidated
3
5
4
0
4
4
0
B unconsolidated
3
5
4
0
4
2
0
Multiple casings in a single
borehole
A consolidated
5
4
0
0
1
0
B unconsolidated
1
5
4
0
0
0
0
From: Eugene E. Luhdorff and Joseph C. Scalmanini, Consulting Engineers
A-1
-------
Drilling Method Rating System
Objectives
Cable
Tool
Direct
Mud
Reverse
Dual
Tube-Air
Top Casing
Drive
Air/Mud
Air
Hollow
Stem
1. Identification of lithology
A. consolidated formations
B. unconsolidated formations
2. Sampling of aquifer fluid
A. non-volatile
B. volatile
3. Rate of penetration
A. consolidated formations
hard
soft
B. unconsolidated formations
max size > 20mm
max size • 20mm
4. Ability to perform geophysical
logging
A. consolidated formations
B. unconsolidated formations
5. Ability to complete borehole into
monitoring well during construction
A. consolidated formations
B. unconsolidated formations
6. Ability to complete borehole
into well following time lapse for
log review
A. consolidated formations
B. unconsolidated formations
7. Ability to obtain cores or sidewall
samples
8. Ability to contain formation fluid
and drill cuttings
9. Special site conditions
A. lost circulation
B. high formation pressure
(exceeding surface elevation)
C. flammable or explosive materials
D. toxic materials
E. other site-specific problems
3-5
1-4
1-4
3-5
3-5
2-3
3-5
3-5
1-4
1-4
3-4
3-5
2-3
3-5
3-5
1-2
0-2
2-5
3-5
1-2
2-4
3-5
1-2
0-2
0-1
3-5
0-1
2-4
1-2
1-3
1-3
2-4
1-4
2-4
1-2
1-2
2-5
2-5
1-3
1-4
2-3
2-4
1-2
1-3
2-4
0-2
1-3
0-2
0-2
1-2
2-5
2-5
0^2
1-3
0-2
0-3
0-2
5
3-4
0-1
0-5
0-3
0-2
0
5
3-4
0-1
0-5
0-2
0
3-4
3-5
3-5
1-3
3-4
1-3
0-3
3-4
3-5
3-5
0-2
0-3
0-3
0-3
0-3
3-5
1-3
0-2
2-5
2-3
0-1
0-2
3-5
1-3
0-2
2-5
1-2
0-1
3-4
2-4
1-2
3-4
2-4
0-2
2-4
3-5
3-5
0-3
3-5
2-4
0-2
3-5
4
2
1
5
4
3
1
0
5
0
2
4
0
0
3
5
3
1
4
1
1
3
5
3
1
4
1
1
From: Eugene E. Luhdorff and Joseph C. Scalmanini, Consulting Engineers
A-2
-------
Selection of Drilling Method,
Well Design and Sampling
Equipment for Wells to Monitor
Organic Contamination
by Eugene E. Luhdorff, Jr. and Joseph C.
Scalmanini, Luhdorff & Scalmanini, Consulting
Engineers
In the course of ground-water investigations, includ-
ing those designed to identify and correct or control
ground-water contamination problems, some of the
most important components are the drilling of bore-
holes for exploratory purposes, the completion of those
or other boreholes into wells and the design and
ultimate operation of wells for various purposes. Yet the
attention paid to these components often seems cursory,
thus allowing an element of question to enter regarding
the accuracy of geologic or geophysical data, piezo-
metric measurements and water quality samples. Equally
as important, the cost effectiveness or. in certain
extreme cases, the pure ability to accomplish the
desired tasks become subject to serious question. This
paper investigates improvements and innovations in
drilling technology in the ground-water industry during
the past decade which make available a vast assortment
of techniques which, if properly selected, will provide
efficient means to initially investigate ground-water
quality and aquifer characteristics and to ultimately
complete and operate monitoring or other wells. The
paper further presents a methodology for rating several
drilling methods based on their ability to achieve typical
tasks in a ground-water quality investigation, and it
illustrates the application of the rating system to two
ground-water contamination problems in California.
Selection of Drilling Method
Objectives of a Drilling Program
After completion of the preliminary phases of a
ground-water investigation, which might include review
of existing data, surface geologic and geophysical
exploration and collection of water-level and water-
quality data from existing wells, subsurface exploration
and investigation follow. The selection of a drilling
method for this phase of work should be based on the
ability and cost effectiveness of a particular method to
accomplish the desired objectives of the drilling
program. The objectives should be carefully defined
prior to drilling in order to avoid costly and time-
consuming frustrations resulting from the inability of a
drilling method to penetrate the geologic conditions at
the site or to attain the necessary information from the
boreholes.
The objectives of a drilling program, or the tasks to
be accomplished by a drilling program at any given site
can include some or all of the following:
e The ability to physically penetrate all anticipated
formations and materials at the particular site, to
penetrate at a desired rate and to construct a borehole
of desired diameter
• Identification of lithology, or development of a
geologic log of all formations and materials penetrated
to the desired depth
® Collection of samples of aquifer fluid during the
drilling process and prior to well construction
»Geophysical logging of the borehole, ranging
from electrical surveys to measurements of natural
radiation, to determination of formation characteristics
using sonic or radioactive tools
• Collection of "undisturbed" formation samples
from the center line or sidewall of the borehole
o Containment of drill cuttings and fluids
o The ability to handle special conditions such as lost
circulation, high pressure, flammable or toxic sub-
stances or other site-specific problems
• Completion of the borehole into a monitoring
well during the initial construction process, i.e., con-
structing a well as the borehole is drilled or constructing
a well in the borehole immediately after the drilling
tools are removed
• Completion of a monitoring well in the borehole
after a time lapse for interpretation of geologic and
geophysical data collected from the borehole.
A-3
-------
Each groundwater investigation will have site-
specific objectives among those listed above which can
be used to select the best method of drilling at that site
I n some cases, one obiectiv e may predominate and thus
dictate a particular drilling method: in others, all the
desired ob|ectives might not be achievable and some
compromise might be required either to reduce the
objectives or increase the number of boreholes.
Drilling Methodology
The advancement of drilling techniques over the
past decade presents a wide range of choices to those
responsible for the selection of a drilling method in a
ground-water investigation. The selection of the drilling
procedure to employ on a project should be based on
an analysis of a rig's capability to develop the specific
exploration and well-completion requirements of the
project.
Seven drilling techniques have been reviewed and
relative values assigned to a series of objectives for each
type of drilling procedure.
A detailed review of each drilling procedure is
beyond the scope of this paper; however, a brief
description of each type of operation follows.
1. Cable Tool Drilling
This procedure is the oldest method of well con-
struction still widely practiced in the water well industry.
The cable tool or percussion drilling method has been
used for centuries throughout the world. It involves the
raising and lowering of a string of drilling tools sus-
pended on a drilling line in the well bore, followed by
the bailing of the drilled cuttings from the hole.
Generally, the well bore is kept open by the installation
of a casing string as the drilling operation proceeds to
the completion depth.
This practice of construction is usually much slower
than the more modern rotary drilling techniques;
however, the procedure has application in certain
monitoring well applications.
2. Direct Circulation Mud Rotary Drilling
The introduction of direct circulation rotary well
construction made possible the development of much
of the world's oil resources. Adapted to water well
construction in the early part of the 20th century, this
drilling method allowed for more rapid construction of
deeper wells for the ground-water industry. The practice
employs a drilling fluid—normally a viscous fluid,
heavier than water—which is circulated down a rotating
drill pipe, through the drilling bit. returning up the
annulus of the borehole, removing the drill cuttings in a
settling pit where the fluid is again recirculated through
the fluid system via a pump. Hole stability is ac-
complished bv the hydrostatic pressure of the drilling
fluid.
3. Reverse Circulation Rotary Drilling
The first unique drilling procedure developed bv
the water well mdustrv was the introduction ot reverse
circulation drilling The procedure ot reversing the
direction of flow—allowing the circulation of fluid from
the bit up the rotating drill pipe to the settling pir —
allowed for holes of larger diameters to be constructed.
The integrity of the borehole is achieved by hydrostatic
fluid pressures created by maintaining the hole full of
water during drilling operations. The procedure reduced
thfe need for specialized drilling mud control and
reduced the development time required for normal
mud rotary well construction completions.
4. Air Rotary Drilling
A second modification of conventional direct circu-
lation rotary drilling is the use of compressed air as a
drilling fluid instead of water or drilling mud. A high
uphole velocity of air is used to remove cuttings from
the borehole. While foaming agents and misting assist
the driller in cleaning the hole, hole maintenance relies
on the integrity of the formation to remain open during
construction without the hydrostatic pressures present
in conventional and reverse circulation drilling opera-
tions. This procedure is widely used throughout much
of the northeastern United States and elsewhere in the
country where consolidated formations exist, for domes-
tic well construction.
5. Dual-Tube Rotary Construction
In order to obtain more precise control of the drill
cuttings being returned up the hole, the air rotary
drilling method has been refined by employment of a
dual-tube drill pipe assembly. The drilling fluid (air) is
sent down the drill pipe and the cuttings returned up
the drill pipe in a second part of the "dual-tube." The
practice is further refined by the use of a smooth outer
drill pipe just slightly smaller than the hole diameter or
bit diameter thus serving as a mechanical means of
maintaining the integrity of the borehole. The drilling
procedure has had wide application in the mining
industry for material identification and for formation
fluid sampling via air lift pumping.
6. Tophead Drive, Casing Hammer, Combination
Rotary Rigs
Many rig manufacturers today provide drilling
equipment which is capable of employing either air or
drilling mud as the drilling fluid. In addition, some rigs
are further refined to include tophead drive, casing
hammer operations. Such a rig provides the ability to
alter the method of construction to meet varying hole
conditions encountered in the well. The use of a casing
hammer allows casing to be installed through difficult
drilling formations such as unconsolidated surface
deposits and then returns to either air or mud circulation
drilling for hole completion. The flexibility of the svstem
A~4
-------
does not provide tne planner an endless freedom ot
choice in the random selection of drilling medium.
Once committed to mud circulation, it is difficult to
convert the system to air circulation in the same
Sorehole. The rig flexibility allows the planner a first
loice in drilling procedures.
implies, the rig configuration is normally a continuous
rotary auger which is frequently used in soil foundation
studies. The hollow stem in the auger drill string permits
coring and water sampling during the drillingoperation.
In addition, small diameter casing can be installed
through the hollow stem prior to removal of the drill
string from the well.
7. Hollow Stem Auger Rig
While normally not considered a water well drilling
rig, the hollow stem auger rig provides a means for
construction of shallow piezometer wells commonly
associated with monitoring projects. As the name
Table 1
Drilling Method Rating System
Rating and Selection of Drilling Methods
lo address the question of selection of the best
drilling method for two recent ground-water contam-
Objectives
Cable
Tool
Direct
Mud
Reverse
Dual
Tube-Air
Top Casing
Drive
Air/Mud
Air
Hollow
Stem
3-5
1-4
1-4
3-5
3-5
2-3
3-5
3-5
1-4
1-4
3-4
3-5
2-3
3-5
3-5
1-2
0-2
2-5
3-5
1-2
2-4
3-5
1-2
0-2
0-1
3-5
0-1
2-4
1-2
1-3
1-3
2-4
1-4
2-4
1-2
1-2
2-5
2-5
1-3
1-4
2-3
2-4
1-2
1-3
2-4
0-2
1-3
0-2
0-2
1-2
2-5
2-5
0-2
1-3
0-2
0-3
0-2
5
3-4
0-1
0-5
0-3
0-2
0
5
3-4
0-1
0-5
0-2
0
3-4
3-5
3-5
1-3
3-4
1-3
0-3
3-4
3-5
3-5
0-2
,0-3
0-3
0-3
0-3
3-5
1-3
0-2
2-5
2-3
0-1
0-2
3-5
1-3
0-2
2-5
1-2
0-1
3-4
2-4
1-2
3-4
2-4
0-2
2-4
3-5
3-5
0-3
3-5
2-4
0-2
3-5
4
2
1
5
4
3
1
0
5
0
2
4
0
0
3
5
3
1
4
1
1
3
5
3
1
4
1
1
1. Identification of lithology
A. consolidated formations
B. unconsolidated formations
2. Sampling of aquifer fluid
A. non-volatile
B. volatile
3. Rate of penetration
A. consolidated formations
hard
soft
B. unconsolidated formations
max size > 20mm
max size • 20mm
4. Ability to perform geophysical
logging
A. consolidated formations
B. unconsolidated formations
5. Ability to complete borehole into
monitoring well during construction
A. consolidated formations
B. unconsolidated formations
6. Ability to complete borehole
into well following time lapse for
log review
A. consolidated formations
B. unconsolidated formations
7. Ability to obtain cores or sidewall
samples
8. Ability to contain formation fluid
and drill cuttings
9. Special site conditions
A. lost circulation
B. high formation pressure
(exceeding surface elevation)
C. flammable or explosive materials
D. toxic materials
E. other site-specific problems
A-S
-------
Well Design
Design of wells for monitoring ground-water quality
can difter from well design for ground-water develop-
ment and production As in the case of selecting the
best drilling method, monitoring well design can also be
considered in terms of a series of objectives which the
wells might be expected to achieve.
Monitoring wells generally are constructed for one
or more of three purposes:
• Measurement of water table or piezometric surface
elev&tions
® Collection of ground-water samples
• Determination of aquifer characteristics.
It can generally be concluded that all three of the
above purposes require certain similarities to produc-
tion wells: wells free of sand and turbidity, and wells
properly sealed and developed to monitor formation
fluids. Given those considerations, monitoring wells can
be sized as a function of their purpose: a minimum of
1-inch in diameter for water level measurements: a
minimum of 2 inches for water sample collection and a
minimum of 6 inches for wells to be pumped for aquifer
analysis.
If the initial drilling program, selected in a manner as
described above, is to include well construction, a
similar evaluation technique can be employed either to
add the well construction requirements to those for
drilling only (Table 1). or to consider the well construc-
tion objectives separately, which may result in more
than one drilling method being employed on a project
Table 2
Monitoring Well Design Rating System
Direct Dual Top Casing Hollow
Cable Mud Reverse Tube-Air Drive Air Stem
Design Requirements Tool Rotary Rotary Rotary Air/Mud rotary Auger
1. Piezometer
single (1")
A. consolidated
B. unconsolidated
Multiple piezometer in a single
borehole
A. consolidated
B. unconsolidated
2. Water samples
single (2")
A. consolidated
8. unconsolidated
3. Aquifer testing
single casing (6")
A. consolidated
B unconsolidated
Multiple casings in a single
borehole
A consolidated
B. unconsolidated
mation investigations and other ground-water qualitv
investigations in California, a simple and direct rating
svstem was developed to evaluate all the above drilling
methods and their abilities to accomplish the objectives
selected for each For each objective or task, values
from zero to five are assigned to each drilling method. A
value of zero indicates the inability of the drilling
method to accomplish a particular objective and, of
course, precludes either that drilling method or that
objective from further consideration. Other values are
assigned as follows to qualitatively rate the drilling
methods: 1—poor, 2—fair, 3—satisfactory, 4—good and
5— excellent After assignment of values for all the
objectives, the respective totals for the various drilling
methods provide an indication of the best method for
the particular job.
In some cases, a particular investigation may have
one or more essential objectives. In such a case, the
values assigned for those particular objectives can be
inflated to "weigh" the selection of drilling method
toward that which will best accomplish the essential
objectives.
The rating and selection system is illustrated in Table
1 with values assigned to each of the seven drilling
methods described above for the various objectives
potentially desired in any ground-water investigation
The values included in Table 1 are typical of ratings or
ranges of ratings which would be applicable to drilling
with these methods in various geologic environments.
15 12 1-4 4 4
15 12 1-4 1 4
0
0
1-4
1-4
1-4
1-4
0
0
0
0
0
0
A-B
-------
In the extreme, more than one drilling method may be
employed on a single location one method to satisfy
exploratory objectives and a second to construct
permanent monitoring wells
The rating and selection system for well design,
similar to that described above for drilling methods, is
llustrated in Table 2. In this case, the values have the
same qualitative ratings as used earlier and again, after
application to a certain set of objectives, would allow for
selection of the best equipment for monitoring well
construction.
Applications of Drilling Method Selection Criteria
The selection procedures described herein have
been effectively applied to two ground-water contam-
ination investigations in California during the last two
years. Both are briefly summarized below.
Case 1—Eastern Sacramento County
In the spring of 1981, it was determined that ground
water in eastern Sacramento County had become
contaminated. Organic and inorganic pollutants, in-
cluding chlorinated organic chemicals, phenol, per-
chlorate. arsenic and sulfates had been found in con-
centrations exceeding the State and Federal drinking
water action levels.
The State of California Water Resources Control
Board commenced a program to construct test holes
and monitoring wells in the affected area to obtain
geologic, hydrologic and water quality information in
order to determine the extent of the contamination and
to monitor its movement.
The selected drilling sites were characterized by
surface deposits of cobbles and other dredge tailings
overlying unconsolidated sand and gravel formations.
Drilling depths would range from 300 to 700 feet. All
drilling sites were restricted to existing State of California
property, normally located within freeway right-of-ways.
A summary of the evaluation of the drilling rig
selection is illustrated in Tables 3 and 4. The work was
successfully completed using a combination casing
hammer, air and mud rotary drilling program.
Case 2—San Joaquin County
A large agricultural chemical manufacturer was
required by the Environmental Protection Agency and
the State of California to implement a program of
investigation to determine if the source of ground-
water contamination found in the area was attributable
to its plant operations. The contaminants consisted of
both inorganic and organic chemicals including
pesticides.
A program of exploratory drilling was commenced
to define lithology, obtain soil and water samples from
the borehole and measure certain conservative quality
parameters in each aquifer sample as drilling continued.
The initial attempt to obtain the above samples
employed the use of a hollow stem auger rig and a
peristaltic pumping system. Drilling depths through
uniform sand and clay formations were anticipated to
be approximately 200 feet. Extreme difficulty was ex-
perienced in hole construction and sampling. As a
result, the drilling program was evaluated using the
method described above: the results are illustrated in
Table4. The drilling method was subsequently changed
to meet the desired objectives and the work was suc-
cessfully completed using a dual-tube drilling rig for soil
sample collection and fluid sampling of the aquifer.
Subsequent construction of monitoring well clusters
(three or four individual wells per site), after construction
and abandonment of all the exploratory holes, was
successfully accomplished using direct mud rotary
drilling.
Monitoring Equipment
Pumps
Much has been authored recently on the subject of
extracting samples of water from monitoring wells. The
amount of fluid that must be removed from a well
casing to truly represent the water contained in the
aquifer is still the subject of continued technical re-
search. Those who have spent a number of years in the
industry involved in pumping wells have experienced
that a minimum of several casing volumes of fluid must
be removed from a well to assure that the water being
obtained represents the water in storage in the aquifer.
The volumes to be removed from the casing should be
increased both as the age of the well increases and the
period of time between sampling increases.
To satisfy these concerns, two methods of providing
pumping equipment for monitoring wells were adopted
on specific projects in California on behalf of the Water
Quality Control Board, the agency assigned the respon-
sibility of protecting the quality of water in the state.
One method involved the permanent mounting of
small submersible pumps in a series of wells requiring
monitoring. The submersible wiring was brought to the
surface and terminated in a weatherproof junction box.
The motor controller containing the relays and capacitor
for the submersible pump was mounted on a portable
switchboard which was moved from well to well with a
portable generator. The system is designed to receive a
teflon bailer to extract an aquifer sample following well
purging by the submersible pump. The bailer is lowered
into the submersible pump discharge piping to increase
the reliability of the sample.
The use of a permanent pump in a well that will be
sampled frequently, allows the investigator the oppor-
tunity to collect samples and to define aquifer character-
istics through well testing. Water level measurements
for testing or for monitoring can be obtained using
permanently installed pneumatic transducers which are
capable of providing instantaneous readout or con-
tinuous recording of water levels.
The second method of well purging required the
development of a self-contained portable pump unit.
A-7
-------
Case 1
Table 3
Drilling Method Rating System
Objectives
Direct Dual Top Casing Hollow
Cable Mud Reverse Tube-Air Drive Air Stem
Tool Rotary Rotary Rotary Air/Mud Rotary Auger
1 Identification of lithologv
A. consolidated formations
B. unconsolidated formations
2. Sampling of aquifer fluid
A. non-volatile
B. volatile
3. Rate of penetration
A. consolidated formations
hard
soft
B. unconsolidated formations
max size > 20mm
max size < 20mm
4. Ability to perform geophysical
logging
A. consolidated formations
B. unconsolidated formations
5. Ability to complete borehole into
monitoring well during construction
A. consolidated formations
-8. unconsolidated formations
6. Ability to complete borehole into
well following time lapse for log
review
A. consolidated formations
B. unconsolidated formations
7. Ability to obtain cores of sidewall
samples
8. Ability to contain formation
fluid and drill cuttings
9 Special site conditions
A. lost circulation
B. high formation pressure
(exceeding surface elevation)
C. flammable or explosive materials
D. toxic materials
E. other site-specific problems
Totals:
NOT REQUIRED
NOT REQUIRED
NOT REQUIRED
NOT REQUIRED
NONE
16
17
Method Chosen: tophead drive, casing hammer with machi
The svstem consists of a submersible pump, hose reel,
power winch, pneumatic transducer for water-level
measurements, flowmeter and generator, all mounted
on a portable trailer. Two men can install the submersi-
ble pump to a depth of 200 feet in approximately 15 to 20
minutes. The well can then be pumped until the desired
volume is extracted from the well. Samples of the
ned air circulation
pumped fluid can be taken directly from the pumping
unit or, if desired, the sample can be obtained by the
use of a bailer. The portable equipment is also designed
to conduct pumped well tests by providing measure-
ments of the pumping rate, static and pumping water
levels and total water pumped during the pumped
period.
A-a
-------
Case 2
Table 4
Drilling Method Rating System
Objectives
Direct
Cable Mud
Tool Rotary
Dual Top Casing Hollow
Reverse Tube-Air Drive Air Stem
Rotary Rotary Air/Mud Rotary Auger
1. Identification of lithology
A. consolidated formations
B. unconsolidated formations
2. Sampling of aquifer fluid
A. non-volatile
B. volatile
3. Rate of penetration
A. consolidated formations
hard
soft
B. unconsolidated formations
max size > 20mm
max size < 20mm
4. Ability to perform geophysical
logging
A. consolidated formations
B. unconsolidated formations
5. Ability to complete borehole into
monitoring well during construction
A. consolidated formations
~ B. unconsolidated formations
6. Ability to complete borehole into
well following time lapse for log
review
A. consolidated formations
B. unconsolidated formations
7. Ability to obtain cores or sidewall
samples
8. Ability to contain formation
fluid and drill cuttings
9. Special site conditions
A. lost circulation
B. high formation pressure
(exceeding surface elevation)
C. flammable or explosive materials
D. toxic materials
E. other site-specific problems
TOTALS
3
16
5
15
NOT REQUIRED
NOT REQUIRED
NOT REQUIRED
NOT REQUIRED
18
15
Biography of Presenting Author
Eugene E Luhdortt Jr. is a partner in Luhdorff and
Scalmamni Consulting Engineers of Woodland. Cali-
fornia. an organization specializing in ground-water
hydrology. de% elopment and management. A registered
agricultural engineer in California. Luhdorff has more
than 26 years ot experience in the ground-water industry
as a water well contractor and consultant.
Luhdorff has authored several papers on water well
construction practices and has lectured frequently in
the University of California Extension system. He is a
past president of the Associated Drilling Contractors of
California, the California Irrigation Institute and the
Ground Water Institute. Additionally, he served as a
director in the National Water Well Association.
A-#
-------
SMALL-VS.
LARGE-DIAMETER
MONITORING WELLS
Well diameter is one of the most important aspects of monitoring system design.
by Marjory B. Rinaldo-Lee
Designing an effective ground-
water monitoring program and
using proper monitoring well design
is a matter of concern for both regu-
latory agencies and private industry.
Although many factors must be con-
sidered when designing a ground-
water monitoring program, such as
location of monitoring points and
the type of monitoring Installation,
well diameter is one of the Important
parts of the monitoring installation
design.
In this article, small-diameter
wells are considered 2-inch diameter
or smaller. Two-inch diameter was
chosen as the upper limit for small-
diameter wells for several reasons.
First, the drilling methods used to
install 2-inch or smaller wells are
often different from those used to
install wells with a larger diameter.
Second, until quite recently submer-
sible pumps were only available for
3-inch or larger diameter wells.
The factors which Influence
choice of well diameter for a moni-
toring program fall Into two groups:
economic and technical. Although
technical and economic factors will
be discussed separately, they should
be considered concurrently when
designing a monitoring program.
Technical factors can influence the
cost of a program and conversely
economic factors can influence the
extent of the technical program.
Technical Factors
In designing any ground-water
monitoring program, the first issue
to be addressed is the purpose of the
program. The designer must ascer-
tain what questions are to be
answered by the investigation. The
three main purposes for ground-
water monitoring are baseline data
accumulation, ground-water
resource evaluation and ground-
water contamination studies. The
approach used for each of these
types of studies is quite different.
1 Baseline data studies are usually
initiated to provide data on long-
term trends or general hvdrogeologlc
conditions in an area For some base-
line data investigations, long-term
water-level fluctuations are of inter-
est. If the monitoring points are at
remote locations, or continuous
water-level readings are needed,
automatic recorders may be desired.
Since large-diameter wells can more
easily accommodate floats for auto-
matic recorders they would be pre-
ferred for this type of investigation.
However. If the goal of the study is to
define hydrogeologic condi tions over
a broad area where many well points
are needed, small-diameter wells
may be preferred due to their com-
parative ease of installation and
lower cost Thus, depending on the
specific needs of the Investigation,
either small- or large-diameter wells
may be preferred for a baseline study.
A ground-water resource investi-
gation is quite different from a base-
line data study. These Investigations
are usually initiated in response to a
demand for a source of water supply.
A ground-water resource Investiga-
tion could be Initiated because water
is needed for drinking water. Indus-
trial processes, agricultural activity
or some other use. Alternatively, a
resource investigation could also be
initiated to determine how to
dewater an area for some activity
requiring a lowered water table, such
as construction or mining. A pump
test is often needed for determining
both the amount of water available
for use. or the amount of water
which must be withdrawn. A large-
diameter well may be needed to
accommodate a submersible pump
with a large enough capacity to
allow a pump test to be conduc.ed.
However, small-diameter wells are
adequate for observation wells to
allow monitoring of drawdown and
evaluation of pump tests. Thus, both
large- and small-diameter wells are
commonly used in ground-water
resource investigations.
Monitoring requirements for
ground-water contamination
studies are quite different from
those for the preceding studies.
Often many wells are needed in
various geologic formations to deter-
mine the extent of past contamina-
tion or the potential for contaminant
migration from a proposed site. For
ground-water contamination
studies, small-diameter wells are -
often preferred because they are less
expensive and more sampling points
can be installed for a fixed amcunt
of available funds. Another reason
for the use of small-diameter wells
in contamination studies is the com-
parative ease of sampling from such
wells.
Wells are normally purged before
sampling in contamination studies
to remove stagnant water frorr. the
borehole and to ensure that the
watec sample is representative of for-
mation water, The volume of water
which must be removed from a
small-diameter well is much less
than that from a large-diameter well
because the volume increases with
the square of the well radius As
shown in Figure 1, there are 0.16
gallons/ft of water in a 2-inch diame-
ter well and 1.47 gallons/ ft of water
In a 6-inch diameter well. Because
purging a well requires removing
72 GWMR/Winter 1983
A-tO
-------
VOLUME OF WATER IN WELL CASING
(D
Z
<
o
H
o
o
u.
\
cc
UJ
h"
<
CO
z
o
-J
<
o
2.5
2.0
1.5
1.0
0.5-
1 2 3 4 5 6 7 8
WELL DIAMETER (inches)
-r-
7
Table 1
Comparison ol Length of Well Casing
Containing One Gallon of Water with Well Diameter
I,,)Mi three to 1" volume ol water
I,,,,,, 11 it- well i.iMiiU. considerably
huh i- water must be ir moved I roil 1 J
t; inch diameter well than Irom a
2 inch diameter well. To purge 10
volnmesol water Irom a well contaln-
niii 10 leet ol waterln the casing. 16
Li.illi)i!•> of water must he removed
Irom .i 2 inch diameter well, as
opposed to 147 gallons of water
Irom a 6-inch diameter well.
Another sampling consideration
is obtaining a sufficient quantity of
water from a well for analysis. Small-
diameter wells have a much smaller
volume of water per foot of length
(Figure 1). However, for many sam-
pling situations, one gallon of water
is sufficient for a large number of
analyses. Table 1 demonstrates that
a 6 13-foot column of water in a 2-
inch diameter well produces one
gallon of sample, while a 0.68-foot
column of water produces a gallon
ol •¦•ample In a 6-Inch well.
A third factor which favors small-
diameter wells for contaminant sam-
pling is the time of recovery- Because
the time of recovery Is directly pro-
portional to the well volume, the
time for recoveiy also Increases with
the square of the well diameter. For
a given hydraulic conductivity, it
takes less time for a small-diameter
well to recover when a slug of water
is removed than for a large-diameter
well. Figure 2 illustrates the time of
recovery for various diameter wells
assuming a given hydraulic conduc-
tivity. screen length and instantane-
ous lowering of the water surface in
t he well. Assuming a hydraulic con-
ductlvity of 0.028 ft/day (1 x 10 5
cm/sec), screen length of 10 feet and
an instantaneous lowering of the
water table by 6 feet, it would take
11-1/2 minutes for a 2-lnch diame-
ter well to recover 5 feet. Twenty-
three and a half minutes would be
required for the same recovery in a
3-tnch diameter well and 42 minutes
for the same recovery In a 4-tnch
diameter well. These recovery times
are Important in contaminant sam-
pling because unlike ground-water
resource investigations, the forma-
tion being investigated for a con-
tamination study may be fairly
impermeable. Ifa large-diameter well
is purged before sampling in a fine-
grained soil, it may take many hours
to recover, while a small-diameter
well will recover more quickly.
I lydrogeologic conditions also
influence the choice of well diameter.
Hydrogeologic conditions can gener-
ally be divided Into two categories:
aquifer characteristics and the
ground-water regime. Aquifer char-
acteristics Include the formation
Figure 1 Volume ol water In well casing
Well Diameter (Inches)
Length of well casing needed to obtain
1 gallon water (feet)
parameters which Influence
ground-water movement, such as
hydraulic conductivity. Factors
Included under ground-water
regime include depth to the potentio-
metric surface, the nature of the
aquifer (whether confined or uncon-
fined) and the number of aquifers
being investigated. All of these fac-
tors influence the choice of well
diameter,
If the formation of interest has a
low hydraulic conductivity, small-
diameter wells are preferred for
monitoring Not only do small-
diameter wells recover more quickly
for water sampling, they stabilize
more quickly after Initial Installa-
2 3 4 5 6
6.13 2.72 1.53 0.98 0.68
tion. In a clay formation with a low
hydraulic conductivity (3 x 10 4-3 x
10 5 ft/day). It could take months for
a 4-inch diameter well to stabilize.
Depth to the water table from the
ground surface was once a limiting
factor In using small-diameter wells.
Bailers were the only means for wit h-
drawlng water from wells where the
potentiometrlc surface was below
the suction limit (about 25 feet)
However, with the advent of a variety
of small-diameter submersible
pumps which fit Inside 2-inch
diameter wells and various air lift
and positive displacement pumps
for 2-inch diameter or 1 -inch diame-
ter wells. It is not necessary to use a
A-11
GWMR/Winter 1983 73
-------
TIME REQUIRED FOR WELL RECOVERY WHEN SLUG OF
WATER REMOVED
WELL DIAMETER (INCHES)
ASSUMPTIONS: K = 1 *l05cm/sec,well screen = 10', 10' of water
above screen, 6' of water instantaneously
removed
Figure 2 Time required lor well recovery when slug ol water removed
bailer to remove water from small-
diameter wells.
Depth to the potentiometne sur-
face may be a limiting factor in the
use of small-diameter wells where
the water-table surface is very deep
(i.e. several hundred feet). In the
western U.S.. where aquifers may be
hundreds or thousands of feet deep,
a small-diameter well may not be
desirable due to difficulties in well
construction procedures and the
increased probability of well casing
failure at depth. Although sampling
devices have been developed for very
deep wells, It can still be difficult to
sample deep small-diameter wells.
Larger diameter wells may be pre-
ferred in this situation.
Another geologic consideration
is the number of aquifers or levels
within a single aquifer being investi-
gated by the monitoring program. If
multilevel sampling points are
needed to monitor various aquifers,
or various levels within one aquifer,
small-diameter wells are generally
preferred due to their low cost and
ease of installation.
Economic Factors
Along with technical factors,
economic factors have a significant
influence on the choice of well
diameter. Funds for a ground-water
investigation are generally limited
and it Is always desirable to obtain
the most information for the least
cost. The economic factors which
influence the cost of installing moni-
toring wells include drilling cost,
materials cost and labor cost.
Drilling costs depend on the
method of well installation and the
drilling contractor. One of the meth-
ods often used to install monitoring
wells in unconsolidated deposits is
the hollow-stem auger. Hollow-stem
augers are used because soil samples
can be taken during drilling and the
monitoring well can be installed
Inside the hollow stem without col-
lapse of the borehole. However, a nor-
mal hollow-stem auger has an inside
diameter of only 2-1/4 to 3-3/4
Inches so it cannot be used effec-
tively to install a well with a diameter
of more than 2 inches. A larger
hollow-stem auger with a 6-lnch
inside diameter can be used to
install up to 4-inch diameter wells:
but the cost of drilling using the
larger hollow-stem augers is greater.
The cost of drilling and obtaining
soil samples is about S8/ft using a
small-diameter hollow-stem auger
compared to S17.50/ft for the large
hollow-stem auger (Table 2). Gener-
ally. a water well contractor Is more
cost-effective to use for drilling a 4-
Inch or larger diameter well than a
geotechnical-soil contractor. Since
most water well contractors are not
equipped for soil sampling, if soil
sampling were required to define
subsurface conditions, it might
require hiring both types of con.
tractors.
Drilling costs for a geotechnicaJ-
soils contractor to install wells in
rock are generally higher than for
drilling through unconsolidated
deposits. The differential between
drilling in rock and drilling in
unconsolidated deposits is much
greater if rock samples are required.
Coring to obtain rock samples adds
significantly to the cost of drilling.
Rock coring by a geotechnical con-
tractor is about S26/ft for a hole
large enough for a 2-inch diameter
well and S35/ft for a hole large
enough for a 4-inch diameter well.
Generally, a water well contractor is
more cost-effective to use for Install-
ing large-diameter wells in rock for-
mations. However, water well con-
tractors are usually not equipped
for rock coring. If this is deemed
necessary to the investigation pro-
gram, two contractors may be
required to install monitoring wells
in rock formations
Labor and material costs are also
factors affecting choice of well
diameter. Well installation, well devel-
opment and well purging are all
labor costs associated with a moni-
toring program Small-diameter
wells are generally easier to install
and therefore take less time. They
also take less time to develop and
purge since a smaller volume of
water must be removed. Thus, labor
costs are lower for small-diameter
wells. Material costs are also lower
for small-diameter wells (Table 2).
The cost per foot of well casing and
, screen increases with well diameter
for both PVC and stainless steel, the
most common types of casing/
screen used in monitoring wells.
When drilling costs, labor costs
and material costs are all taken into
consideration, the total cost to
install the same type of well, using
different diameter well casings, can
be compared (Table 3). If a 50-foot
PVC well is installed with a 10-foot
PVC well screen, the total installation
cost in unconsolidated materials,
including conventional standard
split spoon sampling at intervals of
5 feet, would be S 1.200. or about
S24/ft. The cost to install a compar-
able 4-inch diameter in the same
unconsolidated material with stand-
ard sampling would be about S2.500
or about S50/ft. or more than twice
the cost for the 2-inch well. The cost
for installing a 2-inch diameter well
after conng through rock would be
about S2.600 or S52/ft. The increase
74 GWMR/Winter 1983
-------
in cost of installing a well as the
diameter of the well is increased will
influence the design of the monitor-
ing program.
Summary
Both technical and economic fac-
tors Influence monitoring well
design. Depending on the purpose
of the monitoring program, the
hydrogeologic conditions and the
economic constraints, both small-
and large-diameter wells have
advantages (Table 4). The advan-
tages of small-diameter wells are:
1) they stabilize quickly in low per-
meabllity formations: 2) they
require removing only a small
amount of water to purge them
prior to sampling: 3) they develop
more quickly: 4) they are generally
more easily installed: and 5) the
materials, labor and drilling costs
are lower than for large-diameter
wells.
There are certain monitoring
situations which may require large-
diameter wells. Pumping tests for
ground-water resource evaluation
may require large-diameter wells for
the pumping well. Ground-water
investigations in very deep aquifers
may also require large-diameter
wells. In addition, specialized mon-
itoring needs such as automatic
water-level recorders or evaluation
of remedial measures for ground-
water contamination studies may
also necessitate the installation of
large-diameter wells.
In conclusion, small-diameter
monitoring wells are economically
advantageous because they cost less
to install and less to maintain for
long-term sampling purposes. More-
over. they can be used In the majority
of monitoring situations. However,
large-diameter wells are still neces-
sary for a pumping test and may
also be needed in areas where the
water table Is very deep.
Biographical Sketch
Marjory Rinaldo-Lee received
a B.A. in geology from Mount
Holyoke college and an M.S. in
geology and water resources
management from the University
of Wisconsin. She is currently a
hydrogeologist with Empire Soils
Investigations/TTiomsen Associ-
ates in Groton, New York, where
she is responsible Jor manage-
ment of hydrogeologic projects
ranging from ground-water re-
source development to site con-
tamination investigations. Pre-
viously she worked as a hydro-
Table 2
Comparison of Approximate Cost tor Drilling and
Materials for Monitoring Wells
Well Diameter
Economic Factors
2-Inch
3-Inch
4-Inch
Drilling
Rock Coring
S26.00
S26.00
S35.00
Cost/Ft
Hollow Stem Auger
S 8.00
SI 7.50
SI 7.50
Materials
Stainless Steel
SI 1.00
SI 4.50
S20.00
Cost/Ft
PVC
S 2.50
S 5.50
S 700
Table 3
Comparison of Cost to Install Monitoring Wells
Geologic
Type of
Diameter of PVC Pipe
Material
Drilling
2-Inch
3-Inch
4-Inch
Rock Coring
82,600
S3,800
S4.300
Rock
Rock Drilling
SI.300
S2.400
S2.600
Uncon-
solidated
Drilling fir* Sampling
S 1,200
S2.200
S2.500
Deposits
Drilling
SI.050
S2.100
S2.300
Assumptions: Well depth = 50 ft., well screen = 10 ft.
Well casing and screen are PVC
Table 4
Comparison of Advantages of
Small- and Large-Diameter Wells
Advantages of large-diameter wells Advantages of small-diameter w ells
• Accommodate large submersible
pumps for pumping tests
• Accommodate automatic water
level recorders easily
• Accommodate specialized
monitoring equipment easily for
very deep wells or other specialized
monitoring requirements
• Stabilize more quickly in low
permeability formations
• Lower labor costs due to easier
Installation, quicker development
and smaller volume of water
removed during purging
• Lower materials cost
• Lower drilling costs
geologist Jor Residuals Manage-
ment Technology Inc. in Madison.
Wisconsin, where she was in-
volved with hydrogeologic inves-
tigations and feasibility studies
for waste disposal sites.
A*1$-
GWMR/Winter 1983 75
-------
AN EVALUATION OF NESTED MONITORING WELL SYSTEMS
By
Steven P. Maslansky
Geo-Environmental Consultants, Inc.
52 Avon Circle
Port Chester, New York 10573
And
Curtis A. Kraemer
Malcolm Pirnie, Inc.
2 Corporate Park Drive
White Plains, New York i0602
And
John C. Henningson
Malcolm Pirnie, Inc.
2 Corporate Park Drive
White Plains, New York 10602
ABSTRACT
The need for monitoring ground-water quality has grown dramatically
over the last decade. Concurrently, nested monitoring well systems have
evolved which produce information that better defines existing problems.
Nested monitoring systems help the ground-water hydrologist deal with
complex geologies, flow patterns, ground-water geochemistries, and pollution
sources or types.
The major types of. monitoring systems include fully screened wells,
single wells with multiple sampling points, piezometers and nested well
systems. The disadvantages and advantages of each including costs, ease of
installation, reliability, ease of sampling, volume of sample required, and
aquifer characteristics determined from each system, are discussed.
Four examples of ground-water investigations involving nested moni-
toring well systems are described. Included are geologic cross-sections and
water quality and water level data from each investigation. The conclusions
(based on the four examples) are that nested monitoring well systems provide
data unavailable from other systems, the cost of installing additional wells
is small, and the principal cost increase over the initial estimate is for
obtaining additional samples and associated analyses.
8.2.1
A-14
-------
INTRODUCTION
As the need for monitoring ground-water quality has sharply increased
over the last decade, many monitoring methods have been tried and modified,
and various methods have been developed to monitor both complex geologies
and contaminant conditions. The ground-water hydrologist usually designs a
monitoring system which can be installed during a detailed subsurface
investigation. While such systems, particularly those required by regu-
lation, are usually sufficient to provide meaningful data, they are often
abbreviated because of budget limitations. This paper evaluates nested or
clustered monitoring well networks in terms of the additional benefits they
provide and the additional costs involved. Four examples representing
varying geologies and contamination problems have been chosen to show that
nested wells do provide additional useful information.
TYPE OF MONITORING SYSTEMS
Several systems are currently available for detecting and monitoring
ground-water pollution, and recent improvements in technology have resulted
in large variations in design and operation. There are four basic types of
monitoring systems as shown in figure 1: the fully screened well, the
single well with multiple sampling points, the piezometer, and the nested
monitoring well system.
Each of these systems has advantages and disadvantages, and no one
system is any better than the rest for any given situation. Factors to be
compared are costs, ease of installation, reliability, ease of sampling,
volume of sample required, and the aquifer characateristics that can be
determined using the system.
Fully Screened Well
The system most commonly used in unconsolidated or semiconsolidated
aquifers is a monitoring well which is fully screened throughout an entire
portion of an aquifer. The well acts as an observation well for water
levels and provides ground-water samples. In some cases fully screened
wells penetrate the entire aquifer and provide composite samples.
The installation of a fully screened well in h single interval or in
the entire aquifer is relatively easy and straightforward, and almost any
drilling method can be used. Installation cost is minimal, involving no
unusual hardware: well screens, casing, sand backfill and a cement seal at
the ground surface. Only a single sample per well must be analyzed. A well
properly designed for the existing geology and protected against vandalism
should suffice.
Samples from wells in only one portion of the aquifer give no idea of
the vertical distribution of a contaminant throughout the aquifer, while
those which do fully penetrate the aquifer provide a composite sample which
8.2.2
A-^5
-------
Single Bell
Fully But ti pie lies ted
Screened Saspling Points Piezoaeters Bell Syslea
SAND ABO
GRAVEL
SAND AMD
GRAVEL
v/AU
(not to scale)
FIGURE 1
MONITORING SYSTEMS
-------
gives no information on vertical distribution, and, in addition, dilutes the
actual concentration of a contaminant. Submersible, suction or air- lift
pumps and hand bailers can all be used to evacuate water from the well and
then sample, depending upon the well diameter, depth to water, and analyses
to be performed. The well also provides a water level and can be used to
test in-situ permeability. Water levels from a series of wells covering a
site will indicate the water table or potentiometric surface contours to
provide the direction, and possibly, rate of flow. However, interpretation
may not be accurate in complex geologies where the well has penetrated
independent aquifers.
Single Well - Multiple Sample Points
Some wells are constructed so that only portions of the well are
screened and each screened area can be isolated with inflatable packers.
This monitoring well usually penetrates the entire aquifer, but allows
sampling from several discrete horizons within the aquifer. A second type
is a prefabricated multi-level sampling device, consisting of a pipe with
spaced screen sampling ports, isolated by individual recovery tubes.
This type of well is as easily installed as a fully screened well.
Installation of wells with spaced screen sampling ports takes somewhat
longer since it is usually done in the field based on existing geologic
characteristics. Almost any drilling method can be used, and the installa-
tion cost is minimal, perhaps slightly more than that of a fully screened
well. However, there are additional costs for collection and analysis of
additional samples. Although wells designed and properly installed for the
existing geology should be reasonably reliable, those with ports may have
problems if the individual sampling assemblies are not properly installed.
The multi-sample point well yields excellent information about the
vertical distribution of water quality throughout the aquifer, including the
existence and degree of any pollution stratification. However, wells with
ports are usually restricted to shallow water table depths because the
samples are taken using suction lift. In both types of multi-sampling point
wells, certain types of sample analysis may be unreliable because the
possible sampling techniques are limited. Thus the analyses to be done must
be compatible with the sampling procedure. Sampling equipment may require
some specialization, or be somewhat unique, requiring additional time and
money for its development. However, sampling procedures generally are not
difficult and the cost of sampling per sample is one of the lowest of the
various sampling systems.
Submersible, suction, or air-lift pumps can be used to sample if they
can be isolated from the other sampling levels, are acceptable for the type
of analyses being done, and do not draw in water from the other sampling
zones because of high pumping rates. Water levels can be measured in a
multiple screened well and the in-situ permeability of the different in-
tervals can be determined if other intervals can be isolated satisfactorily.
8.2.4
A-17
-------
The port well provides water levels from the different intervals if
readings can be made within the tube of each port; however, most wells are
not large enough to accept measuring devices. The ports can also be used to
test the in-situ permeability at each location, although in materials with
low to moderate permeability the relatively small cross-sectional area of
the port makes this difficult. A system of multiple-screened wells can show
water table or potentiometric surface contours to indicate direction and
possibly rate of flow.
Piezometers
A piezometer is a pressure-measuring device modified to collect water
samples. There are too many variations of piezometers to review individual-
ly, but an example of a new design is the BarCad sampling system. Each
instrument is a porous, hollow cylinder from which water is removed via a
small-diameter riser tube within a larger gas drive tube. This type of
monitoring system will sample a discrete zone within an aquifer or, if
properly designed, collect soil moisture from the zone of aeration. Most
often the piezometers are narrow enough to permit placing many within one
boring to provide samples from many different horizons within the aquifer,
thus making it a multiple-level sampling system.
The installation of a single piezometer is generally .easy, but they are
more difficult to install in groups, since great care must be taken not to
break or disrupt the confining materials between the individual piezometers.
Many drillers avoid installation of piezometers because it is difficult to
do quickly and efficiently. Many drilling methods can be used, except those
requiring a drilling fluid other than water to keep the borehole from
collapsing. The cost of installing a series of piezometers is higher than
that of either a fully screened well or a multiple sampling point well,
because of the time consumed in placing each individual piezometer within
the same borehole. Also, a series of piezometers has higher costs associ-
ated with additional collection and analyses for the additional samples.
Piezometers have been in use for many years and have become relatively
reliable.
Piezometers provide excellent information about the vertical distribu-
tion of water quality in different zones of the aquifer and help define the
degree of pollution stratification. Sampling procedures for piezometers are
somewhat limited, although recent advances in design allow them to be
sampled for most types of analysis. A possible problem is the long time
needed to sample some piezometers, particularly if an expanded analysis
program requires a large volume of sample per piezometer. Some new piezo-
meters are designed for higher yields in a shorter time, but this varies
from manufacturer to manufacturer and according to the existing conditions
of each case.
The two most frequently used sampling methods are suction pumping or
some form of air-lift pumping, although the former is limited to shallow
aquifers. Generally piezometers used for sampling do not allow water level
8.2.5
a* id
-------
measurements to be taken, a severe problem in that water levels cannot be
used to develop water table contours and help define direction, and possibly
the rate of flow. It may be possible to test the in-situ permeability
depending on the construction of the piezometer; however, most are not
designed to be used for permeability testing.
Nested Monitoring Well Systems
Nested monitoring well systems are a combination of single piezometers
and fully screened wells. They consist of two or more wells adjacent to one
another with the screens set at different levels within an aquifer. These
wells are normally constructed so that the screened portion is relatively
short and acts as a piezometer. Each well provides water samples from a
different portion of the aquifer, similar to piezometers and multiple sample
single wells.
Nested monitoring well systems are installed like fully screened wells
except that two or more wells are installed at different zones or intervals
within an aquifer(s) and adjacent to each other. A nested system can be
installed with any drilling method. In some cases all wells are installed
within one borehole, although this is somewhat time-consuming and the
borehole must be large enough to handle all the well casings. In other
cases the wells are installed in separate boreholes; the drilling of indi-
vidual boreholes is even more time-consuming, but it ensures that there is
no "leakage" between wells. As with the other multiple sampling point
systems there is an additional cost for additional sample analysis.
Nested monitoring well systems provide excellent information about the
vertical distribution of water quality in different intervals of the aquifer
and help define to what degree, if any, there is pollution stratification.
Sampling of nested well systems is not difficult and any technique can be
used. Nested well systems provide more volume than other systems except
fully screened wells. The wells may be sampled with suction, submersible,
or air-lift pumps as well as hand-bailers.
In addition to sample collection, the nested well system provides water
level data which can be used for water table or potentiometric surface
contours. The water levels within a single nested system can show differ-
ences in head, indicating whether they are in recharge or discharge areas of
the aquifer. The wells can also be used to test the in-situ permeability of
the different intervals in which the wells are screened. A wide choice of
material and well diameters can be utilized, and larger diameter wells can
be converted, if necessary, to recovery wells. The nested monitoring well
system is widely used for determining pollution stratification because of
its easy installation.
8.2.6
A-19
-------
EXAMPLE SITES
During the last several years Malcolm Pirnie, Inc. has been involved
with many ground-water contamination investigations. Four of these investi-
gations, all in the eastern United States (Massachusetts, Connecticut, New
Jersey and the Virginia coastal plain) will be used here to illustrate
nested monitoring well systems. The budgets for the projects were suffi-
cient to include some nested wells as part of each monitoring system.
Pirnie's standard operating procedure for monitoring systems is to
install wells as part of a subsurface exploration program. After all
available geologic and hydrologic data have been reviewed for a site, a
detailed subsurface exploration program is developed to provide as much
site-specific geologic and hydrologic data as possible. This is ususally
done by selecting equally spaced boring locations, although modifications
are sometimes made for complex geologic or hydrologic conditions. Continu-
ous sampling in most or all of the borings, which usually penetrate to
bedrock, provides good information about the unconsolidated soils. Most
borings to bedrock are also cored for at least 10 feet to make certain they
have not encountered a boulder and to confirm the bedrock lithology and
hydrologic properties. Monitoring wells are installed close to the bottom
of these borings, and usually constructed to act as a piezometer well. The
piezometer wells are usually constructed of either 2-inch or 4-inch P'VC with
threaded flush joints. The screens are either 5 or 10 feet long and machine
slotted to either 0.010-inch or 0.020-inch slots. A medium sized, well
rounded, quartz sand is used as backfill around the well screen and up to 2
feet above the top of the screen. A one-foot thick layer of bentonite
pellets is placed over the sand as a part of an impermeable seal. The
remainder of the annulus is tremied with a cement-bentonite grout up to the
ground surface to complete the impermeable seal. Once $ deep piezometer
well is installed, the boring rig moves two or three feet away and, without
sampling, augers a second hole to a desired depth in which a second piezome-
ter well is installed. The cost for a second shallow piezometer well placed
in a non-sampled boring is very small compared to the rest of the explora-
tion program.
The four examples selected for review are in shallow aquifer systems:
the three in the northern east coast have shallow glacial soils overlying
less permeable bedrock, and the Virginia example has shallow permeable soils
overlying impermeable soils. In all four cases the nested wells included in
the monitoring systems consist of only two wells each. The approximate
additional cost to the exploration/monitoring well installation program
ranged between 10 and 15 percent, although additional costs were incurred
for collecting and analyzing extra samples.
Site One
Site one, an industrial establishment in Connecticut, is small and has
only three monitoring locations, one of which has two nested wells. The
study area lies in a bowl-shaped basin formed by bedrock ridges occasionally
8.2.7
-------
broken with gaps, but the immediate site area has very little or no
topographic relief. The bedrock in the site area is a slightly fractured
and relatively impermeable gneiss. The glacial soils consist of about 15
feet of silt overlying the bedrock and about 55 feet of fine sand overlying
the silt. A few feet of silt overlie the fine sand. Figure 2 shows a
general geologic cross-section of the area. Ground-water samples were
analyzed for some organics, many of the heavy metals, selected inorganics
and nutrients. The chloride values from two sampling periods are shown in
figure 2'as are the recorded water level elevations.
The difference in water levels between the two wells indicates a
downward hydraulic component in the ground-water flow regime, i.e., the site
is in an area of recharge to the ground-water system. The chloride values
indicate that the well nest is within a plume and that the plume is more
concentrated towards the top of the saturated zone. The lower chloride
values in the deep well are much higher than an expected background value
and verifies the downward hydraulic component indicated by the water levels.
The water levels in the three shallow wells show very little gradient.
Without a nested well system it would be difficult to determine whether the
site is an area of recharge, and thus has potential to contaminate the
ground waters, or in an area of discharge, minimizing the impact of the
local ground-water system. The lower chloride values in the deep well show
that the plume leaving the site is not just in the upper portion of the
ground-water system as might be expected based solely on water levels in the
three shallow wells alone. It also appears that the plume is deepening as
indicated by the smaller difference in chloride values measured during the
second analysis.
Site Two
The second site, an industrial building in New Jersey, lies on a gentle
slope where some portions have been graded flat or to short steep slopes.
At the base of the slope, several hundred feet away, is an abandoned sand
and gravel pit which has been graded flat. The bedrock underlying the site,
a well fractured sandstone interbedded with shale, is a relatively good
aquifer which supplies water for local domestic wells and to the local
public water supply wells. Ground water in the bedrock comes from the
secondary porosity within the aquifer. The glacial soils overlying the
bedrock consist of 20 to 40 feet of varying amounts of silt, sand and gravel
and between 5 and 10 feet of dense glacial till. Figure 3 shows a gener-
alized geologic cross-section of the area. The nested well system at site
2 was installed to show the difference between the two aquifers. The
shallow well, B-6S, is in the glacial soils and the deep well, B-6D, is in
the bedrock. Analyses of ground-water samples included, organics, heavy
metals, selected inorganics and nutrients. Measured values for chloride,
fluoride, sodium and water level elevations for two sampling dates (June
1981 and July 1981) are presented in Table 1.
8.2.8
A-21
-------
SILT
FINE SAND
B-3S B 30
77JTT
^AVt> wtrr
777rrr
25 Feet
0
Scale
-i 50 Feet
FIGURE 2
SITE ONE
GEOLOGIC CROSS-SECTION
-------
M
a-60
B-6S
sin •
SWD. and 6*M*L
—7/asv
GUtlfcl
*JV\\\—y/A>ri
CO
»o
20 tBB*
bedrock
100 feel
SCktf
F1GURC- 3
Sl«
GEOLOGIC cross-sect
-------
TABLE 1
June 1981 July 1981
B-6S B-6D B-6S B-6D
Water level 333.9 330.8 333.6 330.3
elevation
Chloride (mg/1) 36 10 101 37
Sodium (mg/1) 21 11 32 8
Fluoride (mg/1) 0.04 0.24 0.10 0.16
The difference in water level elevations between the two wells clearly
indicates a much lower head value in the bedrock aquifer. This shows that
the site is an area of recharge to the bedrock aquifer and therefore that
any contaminant in the upper glacial soils is likely to flow down into the
bedrock. The water quality data show a measureable difference between the
two aquifers: chloride and sodium values in the glacial soils are approxi-
mately three times those' in the bedrock, whereas the fluoride value in the
bedrock is two to six times the value in the glacial soil. The threefold
change in choride values between the sampling dates in both aquifers sug-
gests that a "slug" of contaminants was passing by the wells during the
second sampling date. It is interesting to note that the chloride values
from both the shallow and deep wells increased threefold, indicating that
the plume extends down into the bedrock aquifer and that the ground-water
velocities are nearly equal.
Site Three
Site three, located within a half mile of the Atlantic Ocean on the
coastal plain of Virginia, is a sludge application field with very little
topographic relief. There are seven monitoring sites, six of which are
nested with two wells each. The soils underlying the site are Quaternary in
age and deposited in an environment where the sea level rose and fell in re-
sponse to glacial melting and reforming. The result is a deposit of al-
ternating layers of fine and coarse sediments. Figure 4 shows two geologic
cross-sections from the site area.
It had been agreed upon by the government agencies involved to monitor
the first two water-bearing zones which are the primary zones used for
drinking water. The site is adjacent to a large construction area with an
extensive dewatering operation by means of deep wells. Ground- water
samples were collected prior to any sludge applications and analyzed for
certain heavy metala, selected inorganics, and nutrients. Table 2 presents
chloride concentrations and specific conductance values, and water level
elevations.
8.2.11
A-24
-------
*-7
8-50
SILT AND CLAY
*
M
at
00
N
V-6D
V-6S
BID
SAND
i-5S W-40 1-4S «l-30 W-3S
25 Feet
N-IS
1-20 1-2S
SILT AND CLAY
600
0 Feet
Scale
FIGURE 4
SITE THREE
GEOLOGIC CROSS-SECTION
-------
TABLE 2
Water Level
Well No.
Chloride (mg/1)
Specific Conductance
Elevations (ft
Above or Below
Mean Sea Level)
IS
37
285
1.0
ID
88
695
1.1
2S
26
215
1.7
2D
18
190
1.1
3S
15
200
0.2
3D
22
250
-0.3
4S
31
415
-4.0
4D
45
710
-0.8
5S
28
520
-0.6
5D
23
570
-0.4
6S
, 322
1,900
1.2
6D
772
3,200
1.2
The differences between water levels in the shallow and deep wells are
small, indicating a very slight downward movement of the ground water. The
lower levels in wells IS, 4S, and 5S are apparently the result of the
dewatering at the adjacent construction site, and water levels in those
nested well systems should return to normal once dewatering has stopped.
The water quality data generally show a higher concentration of chloride and
a higher specific conductance value in the deeper ground-water; this is
probably due to a combination of precipitation diluting the upper ground-
water system and salt water intrusion caused by the adjacent dewatering
system.
Site Four
Site four, an industrial plant in Massachusetts, is located on a small
topographically high area surrounded by low areas with poor drainage. The
glacial soils underlying the site consist of 5 to 10 feet of outwash materi-
als, mostly sands, overlying 5 to 25 feet of dense glacial till. The
bedrock underlying the site is a relatively impermeable gneiss with many
quartz-infilled fractures. There are over twenty monitoring stations in the
area, but only three are nested systems of two *
-------
%
CO
IO
GLACIAL TILL
GIN -190
Wi\\V
BEDROCK
FIGURE 5
SITE FOUR
GEOLOGIC CROSS-SECTION
-------
6W-I9S
GO-190
-777SW
10 Feet
0
Seal e
h 100 Feet
E
GW-I7S GW-170
COURSE SAND
GLACIAL TILL
/M\\—7>AVV 7SS\<\ /7?VS\
BEDROCK
FIGURE 6
SITE FOUR
GEOLOGIC CROSS-SECTION
-------
TABLE 3
Date (1981)
Well Number April May June August
£«
GW-17S 6.4 6.1 6.6 5.6
GW-t7D 6.0 5.6 5.8 5.9
GW-19S 9.5 5.7 5.9 6.4
GW-19D 5.8 6.5 5.5 6.8
GW-22S 7.6 8.2 2.9 7.6
GW-22D 3.0 5.4 4.3 3.8
Chloride (mg/1)
GW-17S 235 204 225 210
GW-17D 375 766 510 949
GW-19S 64 72 102 40
GW-19D 1,046 536 1,633 1,999
GW-22S 480 378 434 730
GW-22D 7,200 5,360 7,450 7,990
Sulfate (mg/1)
GW-17S 930 863 1,500 875
GW-17D 3,045 2,624 6,520 3,500
GW-19S 1,675 1,774 2,530 1,350
GW-19D 1,839 1,265 6,080 3,400
GW-22S 2,620 1,880 4,330 4,050
GW-22D 27,500 33,846 59,000 26,500
Ammonia (mg/1)
GW-17S 46 48 45 56
GW-17D 315 336 358 325
GW-19S 114 126 130 108
GW-19D 609 353 974 1,204
GW-22S 675 427 490 1,081
GW-22D 4,102 2,757 2,340 2,545
8.2.16
A-29
-------
TABLE 3
(continued)
Date (1981)
Well Number April May June August
Water Level Elevations
GW-iis
78.6
78.7
78.9
">7.4
GW-17D
78.0
78.4
78.6
77.2
GW-19S
81.0
81.1
81.3
80.5
°GW-19D
81.7
82.4
81.2
80.7
GW-22S
81.5
82.0
82.1
81.4
GW-22D
80.6
80.4
81.1
8C.8
Site four has an abundance of data which provide differences in water
quality and hyrologic properties with depth and with time. The water
quality data from the deep wells generally show much higher concentrations,
even an order of magnitude larger. In the nested well system numbered
GW-17, where there is a one-foot overlap between the top of the deep well
and bottom of the shallow well, the differences in water quality are signif-
icant, although not always of equal proportion over time. This indicates
that the glaical till,, which the deep wells monitor, has a different per-
meability than the overlying soils. Thus as "waves" of contamination travel
through the system, they pass much more slowly through the glacial till.
Conversely, the soils overlying the till, with higher permeabilities, are
flushed more quickly and are somewhat diluted by precipitation. The differ-
ences in water level¦elevations between the deep and shallow wells are
significant. The nested well systems numbered GW-17 and GW-22 are areas of
recharge to the ground-water system, a condition that did not vary during
the study. Nested well system GW-19, located near a stream which crosses
the site, is in an area of discharge from the ground-water system. This is
expected since most streams receive a portion of their water from
ground-water discharge and implies that some of the contaminated water is
discharged into the stream. The water levels in the GW-19 nested system
also show that during periods of low rainfall, such as the summer, the
amount of discharge is very small.
CONCLUSIONS
o There are several different types of monitoring systems available
to the ground-water hydrologist such as fully screened wells,
single wells with multiple sampling points, piezometers, and
nested well systems.
o Each type of system has its advantages and disadvantages which
include costs, reliability, volume of sample required, ease of
sampling, ease of installation, and aquifer characteristics that
can be determined with each system.
3.2.17
A-30
-------
o Nested monitoring well systems are being used more frequently,
expecially to deal with complex geologies, ground-water geochemis-
tries, flow pattersn, and pollution sources or types.
o The four examples presented here of ground-water investigations
involving nested monitoring well systems in shallow aquifer
situations show that differences in water quality exist between
the individual wells of each nested system. The differences are
useful in defining the existance and locations of contaminant
plumes and the variation of the plumes within different zones of
the aquifer or within different aquifers.
o The nested wells also provided water levels which indicate whether
the plumes are in areas of recharge to, or discharge from, the
ground- water system. This is essential for defining the expected
path of the plume if it reaches beyond the monitoring well net-
work.
o The cost of the additional wells was approximately 10 to 15
percent more than a system of fully screened wells. The major
additional cost to the entire investigation involves obtaining the
additional samples from the extra wells, analyzing, the additional
samples, and reviewing the data provided by the additional wells.
o In all four cases, only some of the monitoring points in the
monitoring network have nested well systems. A few nested wells
in key areas can help define an extensive monitoring program with
little additional cost to the overall program. It is possible
that continued monitoring of some wells could be discontinued
based on data provided solely form the nested well systems.
o Nested well systems aid ground-water contamination investigations
significantly without substantial increases to the overall project
costs.
SELECTED REFERENCES
Nielsen, D., 1980, The importance of ground water monitoring: Water Well
Journal, V. 34, No. 11, P. 38-39.
Pickens, J.F., Cherry J.A., Coupland, R.M., Crisak, G.E., Merrit, w.F. and
Risto, B.A., 1981, A multilevel device for ground-water sampling: Ground
Water Monitoring Review, V. 1, No. 1, P. 48-51.
Procedures Manual for Ground Water Monitoring at Solid Waste Disposal
Facilities, EPA/530/SW-611, August 1977.
Water Well Journal, 1980, Monitoring device simplifies sample collection:
Water Well Journal, V. 34, No. 11, P. 48-50.
8.2.18
A-31
-------
Custom Designing of
Monitoring Wells for
Specific Pollutants and
Hydrogeologic Conditions
by Richard W. Lewis, Engineering Enterprises Inc.
It is essential that every ground-water monitoring
system be custom-designed to meet the local hydro-
geologic conditions. Without site-specific data to design
a well, the data collected in the future from that well
may be false or misleading. I n recent years, the scientific
community has made government and the public aware
of the devastating ground-water pollution brought on
by man's activities. This awareness and the need for
more water has precipitated a major interest in ground
water.
This interest was compounded by the promulgation
of first, the Safe Drinking Water Act, and later, the
Resource Conservation and Recovery Act (RCRA).
RCRA in particular has initiated the largest country-
wide program of research on aquifers in history.
These ground-water research programs have created
a demand for experienced professionals to design and
conduct investigations regarding chemicals that five
years ago could not be identified. To compound the
problems even further, little or no information was
available regarding chemical properties, mode of trans-
port or attenuation and level of toxicity of the pollutants.
When information did become available it generally
was generated through laboratory experiments, where
aquifer conditions were generally idealized. This is all
very understandable, but quite often monitoring plans
and well designs had to be made based on limited
information concerning the properties of the potential
pollutants and u nder geologic settings far from uniform.
It is not difficult to understand why monitoring
systems have in many situations been found to be
poorly designed for their particular function. Quite
often the monitoring well (or, more correctly, the well
designated as a monitoring well) was:
• Designed to serve a totally different purpose
• Designed by someone unsure of its purpose
• Designed by someone unfamiliar with aquifer
mechanics
a Installed without proper knowledge of the
geologic framework or
• Designed without adequate knowledge of the
pollutants to be monitored and their mode of migration
once they enter the aquifer.
Prior to installing or designing a well to monitor
ground water, the purpose of the well should be
evaluated. Typically, the purpose of the well will be one
or a combination of the following:
• To determine aquifer properties, both geologic
and hydraulic
o To determine the potentiometric surface of a
particular aquifer
« To allow access for the collection of water-quality
samples for detection of pollutants
• To monitor the migration of a plume of pollution.
Generally, the first three objectives are achieved
during the process of establishing an adequate monitor-
ing program. Examples of some of the tools available
and considerations to be taken into account to properly
design an aquifer water-quality monitoring program are
presented in the following case histories. These particu-
lar examples do not imply that all the steps are required
in every situation or that other techniques and methods
are not as appropriate. The drilling techniques and
materials used and discussed are widely available and
were appropriate for these instances, but may not be if a
more exotic monitoring program is required.
Example 1
This first monitoring program was conducted for an
industry that used land application for disposal/treat-
ment of biologically degradable wastes.
The initial step was a literature search for informa-
tion concerning the geologic and hydrologic properties
of the local aquifers. From this it was determined that
the prominent local aquifer was a Quaternary uncon-
A-32
187
-------
fined alluvial aquifer roughly 40 feet in total depth. The
aquifer contained wells that produced 50 to 300 gpm
and had good to poor water quality depending on the
effects of local oil-field activities.
The second step involved testing of the wastes being
disposed at the site to evaluate the potential pollutants
within the waste. To accomplish this task, composite
samples of the waste streams were obtained along with
estimates of waste application rates. These analyses
revealed that 10 to 15 percent of the wastes were
composed of long-chain petroleum residues. Several
heavy metal ions were present in the waste stream in
significant concentrations.
The third step of the monitoring program was the
on-site field investigation. Since the monitoring program
was required to meet the objectives set forth under
RCRA, a minimum of four monitoring wells needed to
be located. Three of these wells were to be downgra-
dient from the site and one upgradient. It was also
requested that the local hydrologic properties be deter-
mined so that the rate of migration within the aquifer of
any given pollutant might be determined. Existing wells
were identified near the study area, but none could be
accessed to determine pumping or static water levels.
Therefore, test holes were drilled to serve two purposes:
1. To obtain a detailed geologic profile and collect
formation samples from which monitoring wells could
be designed.
2. To determine the static ground-water elevation
and the direction of local ground-water flow.
Our test-well drilling revealed that this alluvial
aquifer was heterogeneous, having a number of inter-
bedded sand, silt and clay layers. None of the clay layers
appeared to be continuous since they were encountered
at varying depths and thicknesses from well to well.
However, to better determine exact elevations and
thicknesses of the various layers a downhole natural
gamma-ray geophysical log was run on each well. These
logs were then compared to the geologist's notes which
were collected while observing the well cuttings from
either a hollow stem auger or water rotary drilling rig.
The geophysical log revealed inaccuracies in the depths
that particular layers were thought to have been encoun-
tered during drilling. Figure 1 depicts a typical gamma-
ray log with lithologic interpretation. A surface resistivity
survey was considered to further delineate the lateral
extent of the various layers. However, underground
and above ground piping made this impossible. Split
spoon samples of the saturated zone were collected for
grain size analysis and well design. At each of the test
hole sites, 2-inch PVC slotted screens and casing were
installed. Each well was developed using a surge block
and air lift pumping equipment. The well logs indicated
that clay layers, though possibly not continuous, existed
between 11 and 18 feet. Based on the well logs and split
spoon samples, two large-diameter (5-inch) wells were
designed and constructed for evaluation of hydrologic
properties (Figure 2). These wells were drilled using a
straight rotary rig, gravel-packed and developed by
surging, jetting and air lifting. One well was completed at
ORLLER'S LOG
-I-
Tan Ano Mrtd
- 3
111 i i
Mill I
I II i |
Gray cloy
- IO
Brown mod. aand
Brown ill
¦ IS
Gray clay and alt
Fina wad. aand
Tan clay
-20
Gray mod. to
cocrta land
¦25
*
Tan tfit
-30
Tan oand and
gravel
¦35
%
*• • •
• m«
Cravat
¦40
# • »
Shata
GAMMA AAV LOG
I
20
COUNTS
Figure 1. Typical profile of study area, example 7
STEEL PROTECTIVE
COVER
*!TH HINGED LID
9CHT0NITE SEAL
PVC CASING
2 »AT£R LCv'CL
0 BORE HOLE
BENT0NI" E SEAL
GRAVEL PACK
UOP JOKNSO* PLASTIC
WELL 3CRE EN
o 030" Slot size
• ' • \-W%-\
BCDROCK
Figure 2. Typical design of a five-inch diameter well
188
A-33
-------
35 feet in the basal aquifer sands and the other at 14 feet
in the uppermost sand layers. This allowed for the
evaluation of aquifer hydraulics from pump tests in both
sand zones. Test wells constructed previously were then
used as observation wells during the pump testing of the
aquifer. The importance of conducting pumping tests in
both the upper and lower sands was twofold. First, one
of the major potential pollutants at this site was a
petroleum-base material which is immiscible with water.
Therefore, if this pollutant reached the ground water it
would flow on top of the water, but move no faster than
the hydraulic conditions of that zone. Aquifer testing of
the lower sands, where the coarsest materials existed,
provided information enabling calculation of the travel
time for the other pollutants that are soluble. These tests
also enabled us to determine if the sand layers were
hydraulically connected, Results of these tests showed
that the sand layers in the vicinity of the disposal area
were hydraulically connected. However, the clay layers
appeared to be acting as an aquitard. This was confirmed
when some preliminary ground-water quality measure-
ments were made (Table 1). Samples obtained from the
shallow portions of the aquifer were very different in
chemical nature from the lower aquifer samples.
Table 1
Water Quality of Aquifer
As reported Analysis of Analysis of
in literature shallow sands deeper sands
Chloride
200
15
299
mg/l
Sulfate mg/l
120
19
93
Iron mg/l
<1
28
<1
The water quality of the lower zones is similar to water
quality of this aquifer as reported in the literature (high
chloride and sulfate concentration). In contrast the
shallow water appears to be influenced by local recharge
and the local industrial facilities (high iron and low
chloride and sulfate concentrations).
Once this preliminary investigation was completed
and reviewed, decisions regarding the monitoring pro-
gram were made. The first consideration was the
selection of the monitoring well sites. The existing wells
were reviewed as to which were located and constructed
such that representative aquifer samples could be
collected to detect the first sign of pollution from the
disposal facility. Several operational considerations were
reviewed, including what chemical parameters were to
be determined, what method of sampling could be
used to avoid contamination or bias and what volume of
water would have to be removed to obtain a represen-
tative sample,
Typically it is recommended that five to 10well-bore
volumes be removed prior to sampling when feasible.
Therefore it benefits the sampling program if this
volume can be removed as quickly as possible. Small-
diameter wells (2-inch) are often the best since the
well-bore volume is small. However, if there is a signifi-
cant saturated thickness or if the well is deeper than 30
feet, pumping methods become limited and slow. Bail-
ing the well when there is a large saturated interval
requires a great deal of time and effort to remove the
necessary well volumes. If the water level is below 30
feet, vacuum or peristaltic pumps become unusable
due to suction lift limits. The use of recently developed
small-diameter submersible pumps is a good alternative,
but these pumps yield a very low flow rate (generallv
less than 1 gpm), hence removal of large quantities can
be quite time consuming. The advantages of bailers,
peristaltic pumps or small-diameter submersibles are:
they are easy to handle; they are rather easy to clean
between wells; they can be constructed of materials
that will not contaminate the sample; and they generally
cause minimal chemical changes through oxygenation.
Larger diameter wells (4-inch and larger) are gen-
erally most appropriate when well depths are great,
there is a significantly large saturated thickness and
formation transmissivities are high. Under these circum-
stances a pump capable of removing large volumes of
water rapidly is required. Typically, large-capacity pumps
cannot be installed in wells smaller than 4 inches in
diameter; 5- to 6-inch wells are used most because of
their greater versatility.
For the purposes of monitoring the disposal site in
this instance, the primary monitoring zone was the
shallow freshwater sand. Three of the 2-inch test wells
were appropriately located during the exploratory
drilling so that only one additional well had to be
installed. These wells were rather shallow (less than 15
feet) and contained only 5 feet of saturated material
(Figure 3). Therefore, either bailing or peristaltic pumps
could be used for sample collection with ease and little
expense.
Additional monitoring was necessary within the
deeper aquifer because the greatest ground-water flow
across the site occurs in this zone. Therefore, the
monitoring program was expanded to include one
upgradient and one downgradient well in this aquifer.
These wells were completed below 30 feet with screens
and gravel pack designed from earlier sampling and
testing data. Large-diameter (5-inch) wells were deemed
most appropriate for these deep wells since a large
volume of water would have to be removed prior to
each sampling. These wells then could accommodate
submersible pumps for easier sampling.
Several specific modifications were made during this
monitoring system design specifically related to the
anticipated pollutants and the local aquifer characteris-
tics. First, as shown in Figure 3, the shallow 2-inch-
diameter wells were screened so that open screen
existed above and below the water table. This was tc
allow for petroleum pollutants to enter the well if any
seeped down to the water table. This design also was to
allow for fluctuation in water levels due to natura
seasonal effects. Secondly, the materials used in wel"
construction and sampling equipment were evaluatec
to avoid sample contamination. Care to avoid use ot
PVC glue and metal parts in anything that contacted the
samples was necessary to avoid biasing the laboratory
A-34
189
-------
determinations.
An additional item of concern during well design
was the drilling fluid used. Air-rotary techniques could
not be used since the formation would not remain open
for well construction. Therefore, a hollow stem auger
was used for construction of the 2-inch wells. For the
larger wells, water rotary was attempted, but proved
unsuccessful. Thus, an organic mud (RevertTB) was used.
This choice was made since heavy metal concentrations
were to be monitored and use of inorganic bentonite-
base muds could bias the laboratory determinations by
adsorption or absorption of the heavy metal ions.
Thorough development of every well was also done to
ensure efficient well performance and removal of all
materials introduced during drilling.
Example 2
The second monitoring program again centered
around RCRA monitoring requirements. However, this
program was for a hazardous waste storage lagoon.
The initial hydrogeologic literature survey indicated
that the site was situated on Permian age shale. The
shallowest significant ground-water aquifer lay beneath
the shale and was composed of interbedded sandstone
and shale layers. The static water level in this aquifer was
determined from wells within a mile of the site to be at
least 200 feet below land surface. However, the sand-
stone/shale aquifer outcrops less than a mile to the east
and recharge from precipitation was well documented.
The waste materials in the lagoon contained both
organic compounds related to the manufacture of
plastics and several heavy metal ions.
An initial site evaluation was made to determine in
more detail the local hydrogeologic conditions. To
accomplish this, an air rotary rig was used to drill six test
holes from 20 to 100 feet in depth. By using air rotary in
this instance, we are able to readily determine water-
bearing zones if encountered. It was apparent from the
well cuttings that state Geological Survey maps were in
error. The locally predominant Permian shale layers
shown on the maps had been eroded away at this site,
thereby exposing the lower Permian sandstone/shale
aquifer. Figure 4 is a typical profile and log of the
materials encountered. The report detailing the depth
to ground water was also in error. Water-bearing
sandstone layers were encountered at 20 feet, 35 feet
and 40 feet below ground level. Since the sandstone
layers were very fine grained (effective grain size
,15mm) and rather thin, downhole natural gamma-ray
geophysical logs were taken.
Once the test holes were drilled and logged, the
holes were left open and the water levels allowed to
come to equilibrium. Water level elevations were then
determined. Based on this data, the direction of ground-
water flow appeared to be to the northwest. Review of
the drilling and gamma-ray logs raised some concern as
to which sandstone layer or layers should be monitored.
The degree to which these sandstone layers were
hydraulically connected was also unknown. Therefore,
Test Hole *3 was completed with two piezometers. The
ST£tl. oftQTECTiVt
WITH HiNGEO UO
8ENT0NITE SEAL
ALLUVIAL SCOlWCNTS
&" 90B C hOlC
WATER r*BLC
UOP JOMfjfSO* PL'ASriC
WCLL SCftetN
0 020' 5L0T SIZE
figure 3. Typicai c/esign of a two-inch diameter weft
DRILLERS LOG
GAMMA RAY lOG
-:
Dork 8r SaMr
C'oy
1 -t 1
10 20V 30
R«d Cloy
COUNTS
3
XT
Rid Sn« Sontf
u.
20
c
£
«
a
~2
GfOy Silt
s
%
Q
23
90
~z~
Rttf Shai#
t
35
40
¦%»
*v
Rt0 fm# qrom
Sondttont
\
Figure 4. Typical profile of study area, example 2
-------
shallow screen was set from 18 to 23 feet and thesecond
from 35 to 40 feet. The interval between the well screens
was sealed with bentonite pellets. Once installed, both
piezometers were developed by bailing. Water-level
measurements made on the following day showed that
these two sandstone layers were not hydraulically
connected since a head differential of 4 feet existed
between them.
This new data raised several questions:
1. What was the real direction of ground-water flow
in both zones?
2. What was the lateral extent of these water-bearing
zones?
3. What was the anticipated rate of transport of any
pollutant once it reached either zone?
To determine the position of the potentiometric
surface and the lateral extent of each sandstone layer, a
second set of wells was drilled. In each new well two
piezometers were installed. By extending the area of
drilling it was determined that the ground water encoun-
tered at 20 feet was not areally extensive. The ground
water in this zone was probably due to local recharge
creating a perched water zone. The lower aquifer was
apparently continuous and the direction of ground-
water flow in it was from the southwest to the northeast.
Development of these wells indicated that both
aquifers were low yielding. Therefore, rather than
pumping the wells to determine aquifer properties, slug
tests were performed. These tests yielded an average
horizontal aquifer permeability of 5 feet/day (33.2
gpd/ft2).
Once these factors had been established, the final
monitoring system could be determined. Special consid-
erations in this site evaluation were:
• Should the perched zone or just the lower aquifer
be monitored or both?,
• What materials could be used for the well con-
struction without sample contamination?
• What would be the means of sampling the aquifer?
A review of the RCRA requirements revealed that
the monitoring network should evaluate the uppermost
ground-water aquifer. However, in this instance monitor-
ing the perched zone could provide an early warning of
pollutant seepage, although the perched zone is not as
significant as the lower aquifer. Therefore wells were
constructed to monitor both zones. The wells penetrat-
ing the lower water-bearing zone were designated as
the site's primary monitoring system. These wells were
monitored for all required water-quality parameters.
The shallow wells were treated as a secondary system
and monitored for only the pollution indicator
parameters.
To avoid introducing any drilling fluid contaminants,
wells were constructed using an air rotary drilling rig.
Because plastics and their derivatives and additives were
potential pollutants, stainless steel screens and casing
were selected. Figure 5 shows a typical example of the
four monitoring installations with both gravel pack and
bentonite seals. After construction each well was then
thoroughly developed by bailing and air lift pumping
techniques.
A small-diameter (1-3/4-inch) bladder pump was
selected for sample collection. The pump was driven by
compressed air which never came in contact with the
sample. The internal pump components that did contact
the sample were constructed from viton or teflon which
are relatively inert. In this way sampling was done easily
without contaminating or significantly affecting the
chemical stability of the sample.
3'8UM»m StMl CMhg
Ion#-7 7
Figure 5. Detail of two well installation
Conclusions
These examples were selected to emphasize the
importance of thoroughly understanding the details of
the hydrogeological environment and the chemical
parameters anticipated in designing and constructing a
monitoring system. It is essential that final design and
construction techniques be made in the field as the
local hydrogeologic conditions become clear. Designing
monitoring wells in the office based only on published
literature seldom will accomplish the desired results.
Some may feel that the examples described are overly
elaborate and extensive. However, experience has
shown us at many hazardous waste facilities the terrible
consequences of pollution that have occurred when
undetected by a poorly designed monitoring program.
For this reason, proper design of a monitoring system
cannot be overemphasized.
Biography of Presenting Author
Richard W. Lewis is currently a senior hydrogeologist
for Engineering Enterprises Inc., Norman, Oklahoma,
A-ae
-------
where he is in charge of aquifer evaluations, RCRA
monitoring programs and aquifer restoration from
petroleum spills and other oilfield-related activities. He
received his B.S. in both geology and biology from the
State University of New York at Brockport, New York, in
1975. and his M.S. in geology from the State University
of New York at Fredonia, New York, in 1977. Lewis
attended post graduate courses in hazardous waste
management and toxicology at Oklahoma University.
In 1978 and part of 1979 he served as staff geologist for
the Industrial Waste Division of Oklahoma's State
Department of Health, where he was in charge of
hazardous waste site permit reviews and pollution
investigations.
Questions and Answers
Q. How do you complete a well with a screen
extending above and below the water table? What
method of development is used? Do you develop until
you get a clean clear flow or do you anticipate field-
filtering all samples you collect?
A. To complete a well with screen above and below
the static water level, one must have information on the
depth to ground water and the degree of seasonal water
level changes. Once you know these two factors, you
should choose screens of adequate length to accommo-
date seasonal level changes. Once the well has been
constructed, it is very beneficial to develop-out any fine
grained material in the screened zone. A developed
well is a much more efficient water-producing well and
samples gathered are less turbid. There are a number of
development methods available that work very well. A
few of the most common are: bailing, jetting or surging
with a surge block followed by air lift pumping or just air
lift pumping by itself. The length of time to complete
development will often vary greatly from well to well.
This is primarily controlled by the screen slot size and
grain size distribution of the formation. Generally,
development is considered complete when the dis-
charge water clears. However, when dealing with 2-inch
wells in a very fine grained aquifer, development may
only reduce turbidity, not eliminate it. When the water
is turbid, filtering the samples is beneficial. Of course, all
samples that require acid treatment for preservation
should be filtered regardless of the visual clarity of the
sample.
Q. What length of time was there between air rotary
drilling and sampling of ground water from the com-
pleted wells? What effect have you observed or would
you expect on volatile organic contaminants in ground
water from aeration during air rotary drilling? What
precautions do you observe to minimize such effects?
A. The length of time between drilling each of the
wells and sampling was at least two days. To minimize
the effects of contaminants introduced during well
construction, a considerable amount of water was
withdrawn from each well during development. An
additional five to 10 well bore volumes of water were
also removed from each well prior to sample collection.
This was done to ensure that samples representative of
the formation fluids were obtained. Through this pro-
cess, we hoped to remove any ground water that had
been altered by the well construction.
Q. 1) In your decision,to use an organic drilling
mud for wells intended to monitor concentrations of
trace metals, did you consider the possibility of com-
plexation of the metals by the organic compounds in
the mud, or is this not considered to bea problem? 2) Is
stainless steel casing considered acceptable for wells
intended for monitoring trace metal concentrations?
A. In monitoring well construction, one is often
faced with compromises. Project budgets, drilling equip-
ment availability and formation characteristics all place
their own restraints on the way in which the well can be
completed and what materials are used. In this particular
instance, the local formations were not competent
enough to keep the hole open during well construction
without use of drilling muds. Organic muds were
selected since they would biodegrade if they were not
removed during well development. These muds were,
therefore, thought to be less likely to bias heavy metal
determinations than inorganic, bentonite clay base
muds.
Stainless steel screen and casing were used for two
reasons. First, a number of the parameters to be
monitored were constituents in plastics such as PVC.
Secondly, stainless steel is relatively inert, compared to
other well construction materials. Therefore, stainless
steel was selected since it would bias the water quality
analyses less than other readily available well con-
struction materials.
Q. The wells described in both your examples did
not comply with RCRA requirements, i.e. screen 10 ft.
into first aquifer. Did you negotiate with EPA for
deviation from requirements?
A. To my knowledge, there is no requirement in the
United States Environmental Protection Agency's Re-
source Conservation and Recovery Act regulations
requiring monitoring wells to be screened 10 feet into
the first aquifer.
Q. Could you please describe equipment and tech-
niques employed in developing 2-inch wells? How was
sand or silt drawn into the wells by development
removed?
A. Methods of well development are described in
the first answer and are discussed further by Herman
Bouwer, 1978, in Groundwater Hydrology and in Ground
Water and Wells, which is published by Johnson
Division, Universal Oil Products Co. (1974).
Q. During installation of multiple screen wells in
your second site example, how did you ensure that your
drilling did not allow contamination access to either
aquifer?
A. Contamination of the hydraulically isolated
aquifers, in this instance, was felt to be minimal since the
rotary drilling through clay layers between the aquifers
tended to create a mud cake along the upper aquifer.
This mud cake formed a partial seal for that aquifer.
However, this was not what we depended upon for
elimination of any cross contamination. Once the wells
A-37
-------
were constructed and the bentonite seals were in place,
each well was developed and considerable quantities of
water were removed. In this way, if any communication
between the aquifers had occurred, these fluids would
have been removed. However, if these aquifers were
very permeable and the water quality was significantly
different between them, then more extensive steps
would have been taken to avoid communication.
Q. In your first example, what levels of metallic ions
did you encounter in the refinery waste? What are the
chances of saturating the vadose zone with heavy
metals?
A. The waste analysis of the materials being applied
at the land treatment facility is as follows:
Arsenic
.005 mg/l
Barium
.07 mg/l
Cadmium
0.1 mg/l
Chromium
1.2 mg/l
Lead
1.6 mg/l
Mercury
.0022 mg/l
Selenium
.08 mg/l
Silver
.04 mg/l
In this instance, at the anticipated loading rates and
the local soil cation exchange capacity, the expected
time required to saturate just the first foot of the vadose
zone with heavy metal ions is more than 60 years.
A-38
-------
METHOD TO JWOK)
GROUND-WATER MIXING
BETWEEN TWO AQUIFERS
DURING DRILLING AND
WELL COMPLETION
PROCEDURES
The authors describe a new cost-effective approach utilizing temporarily placed casing.
by Patrick W. Burklund and Ellen Raber
Introduction
Many hazardous waste landfill sites are underlain
by multiple aquifers Isolated from one another by layers
of fairly impermeable bedrock (possible confi ning beds).
In cases where aquifer contamination is believed to
have occurred, It Is important to know the actual
distribution of contamination in both a vertical and
lateral sense. To do this, one must be able to effectively
Isolate and sample the ground water from within the
individual aquifers. This involves avoiding any mixing
between the suspected contaminated aquifer and other.
It is hoped, uncontaminated aquifer(s) during drilling
and well completion procedures. This is Important for
two main reasons: (1) to avoid creating a pathway for
the spread of contaminants, and (2) to be able to
determine whether contamination has actually spread
to deeper aquifers. Also, it is very time consuming,
costly and sometimes impossible to remove all contam-
ination Incurred as a result of temporary aquifer
interconnection.
An alternative procedure which could be employed
to avoid ground-water mixing Involves the use of a
multi-cased well designed to seal off the upper con-
taminated zone before deeper drilling is performed
(Edwards et al. 1983). This Is achieved by drilling a
relatively large-diameter borehole, inserting a perma-
nent steel casing sealed at the bottom with grout and
then drilling through the grout to the lower level. This
type of approach, although effective, requires an indivld-
. ual monitoring well for each specific zone to be sampled.
Additionally, costs are increased due to the expense of
the permanent steel casing required for each well.
Another approach would be to drill a larger diameter
borehole for packer emplacements to isolate the indi
vidua! aquifers. Problems associated with this method
are packer blowouts and formation water leakage past
the packer bladders. Expense may be prohibitive due to
the costs of packers and associated equipment for
installation.
Where the water table is relatively deep, the most
cost-effective approach to ground-water monitoring is
to install multi-level sampling wells. This article reports
a method that has been developed which avoids mixing
of ground water between two different aquifers (water-
table and underlying confi ned iwithinasingleborehole
during theentire drilling and well completion operation.
This eliminates problems associated with potential
cross-contamination of ground water between aquifers,
and allows valid multi-level ground-water sampling.
The method assumes that some knowledge of the local
hydrogeologic conditions already exists. However, it
does allow for the identification of previously undetected
perched aquifer conditions.
The basic approach utilizes a combination of air-
rotary and continuous wire-line core drilling, although
other drilling methods may be employed. Both aquifers
are isolated by the use of temporarily placed casing
while instrumentation is installed. Water sampling
devices and pressure transducers are then permanently
emplaced at the appropriate depths; first in the lower
aquifer and then in the upper aquifer. Each set of
instrumentation is isolated from the other using a
combination of bentonite seals and cement grout. If
desired, a standpipe piezometer may be placed in the
uppermost aquifer. Although not discussed here, more
than two aquifers could be isolated by this method This
would involve several temporarily placed casings (one
Inside the other) which would be installed in the same
manner and removed sequentially (from the bottom
up). However, this would require drilling a much larger
diameter initial borehole.
An illustrated step-by-step explanation of this
approach is presented. Additionally, a cost comparison
is made between this approach and the alternative two
borehole method. The total depth of boreholes drilled
ranged from 200 to 400 feet. This method of completion
was used in three boreholes and was successful i n two.
Fall 1983
Ar-39
-------
It has proven effective and relatively simple except for
some problems encountered due to very unstable bore-
hole conditions In a lower aquifer.
Description of the Method
Drilling Procedure
Boreholes were drilled uslngan lngersoll-RandTH-60
Cyclone Drill, although other drilling equipment should
be just as effective. This is a very versatile piece of
equipment that permits drilling with high pressure air
(750 CFM at 250 psi) as well as with water and/or mud
and is capable of both rotary drilling and continuous
coring. Prior toanv drilling activities, the drill rigandall
drilling equipment were thoroughly cleaned by steam
cleaning and washing. The equipment included hollow-
stem augers, drill steel, casing, core rods, core barrels,
tri-cone drill bits and any other associated equipment
that would go downhole. This cleaning process was
repeated after each borehole was drilled and before
movi ng to the next location. Although time consuming,
this effort was necessary to minimize the potential for
introducing contamination into the subsurface. Addi-
tionally. special precautions were employed to minimize
the use of drilling lubricants, since these are sometimes
used in large quantities and they may contain many of
the priority pollutants to be monitored.
Depending on the chemical constituents to be
monitored, an assessment regarding the best drilling
approach should be made.- Additives or proprietary
drilling muds and/or foams have been found to cause
contamination problems in previous investigations as
they remain in the borehole despite vigorous attempts
to flush the well clean (Absaion and Starr 1980).
Therefore, for our studies, the methods employed were
auger!ng. rotary and wire-line core drilling using air or
water only. There are, however, some problems wtiicn
may be encountered when drilling with high-pressure
air. First, the possibility of entrained oil and/or lubricant
from the drill rig air compressor exists, so this must be
monitored. The equipment used in this investigation
was relatively new and we did not experience any such
problems. Second, one must expect that substantial
aeration will occur downhole, especially in the upper-
most water-bearing formation. Depending on the yield
of the aquifer, it may take several months for certain
parameters to reach steady-state equilibrium values.
This will also be true when drilling with water if
injection Is into a more reducing environment. However,
the amount of area affected by water-injection will
usually be less than with air injection.
For this investigation, boreholes were started in
unconsolidated material by using an 8.0-inch contin-
uous flight, hollow-stem auger to advance holes and
obtain soil samples. Once augering through the uncon-
solidated materials was completed, drilling was con-
tinued by using a combination of air rotary drill! ng and
HQ wire-line core drilling. Rotary drilling with air and
coring using air was successfully accomplished to
depths of between 60 and 100 feet below ground
surface in both unconsolidated and indurated mate-
rials. In this manner, the borehole was advanced down
through the first aquifer into the confining bed.
After the top of the confining bed beneath the water-
table aquifer was reached and identified, the wire-line
core tools were removed and the borehole was then
reamed to a 6.75-inch diameter down to the confining
bed using a standard tri-cone roller bit (Figure 1).
Geophysical logs were run in the borehole at this time.
In our investigations, these included natural gamma,
gamma-gamma density, self-potential, resistivity and
Steel casing
Ground surface
Open borehole -
Overburden
Water table
1—
Water table aquifer
(sandstone)
Claystone
Confining bed
(cleystone/siltstone)
Confined aquifer
(sandstone)
Figure 1 Borehole drilled to confining bed
A-40
Right-hand
square thread
Left-hand
square thread
Left-hand
square thread-
Stainless steel
coupling (collar)
-Stainless steel
casing section
Figure 2. Hght-handAefMiand square thread casing
Fall 1983 *9
-------
caliper logs. Temporary casing was then set to within 6
Inches of the bottom of the borehole in the manner
described below.
The lowermost casing section consisted of flush-
joint stainless steel with a left-hand, square thread. It
was connected to a right-hand square thread, flush-
joint carbon steel casing by a stainless steel coupling
threaded right-hand at the upper end and left-hand at
the lower end. An Illustration of this casing design is
shown In Figure 2. The stainless steel casing section is
the same inside and outside diameter as the carbon
steel casing and 8 feet in length Including the right-
hand thread to left-hand thread coupling. Thin wall
casing was selected in order to maximize working room
inside the casing and to minimize borehole diameter.
Flush joint casing was used to facilitate casing removal
from the borehole. It Is possible that casing couplings
could cause problems during casing removal, if borehole
swelling or borehole collapse occurred during the drill-
ing or completion of the lower aquifer. Steel casing Is
recommended for this method rather than PVC since
PVC casing could be broken by the drill rods while
drilling inside of it (I.e., by rod whip or chatter).
The lower stainless steel casing section (threaded
left-hand) was hand-tightened to the left-hand threaded
end of the coupling. The coupling and stainless steel
casing section were then attached to the carbon steel
casing and the coupling was wrench-tightened to the
temporary steel casing. All. of the remaining casing
sections were then wrench-tightened as the casing was
lowered down the borehole (Figure 3). After the casing
was In place, a quick-setting expansive grout plug (Cal-
seal, a trademark of Halliburton Corp.) was poured via a
tremle pipe Into the borehole and allowed to circulate
both Inside and outside the stainless steel casing
section. The amount of grout was calculated to encase
only 6 feet of the 8-foot casing section (Figure 4). The
grout was allowed to set two to four hours.
Before drilling was resumed, all standing water in
the casing was removed. The well was then allowed to
stand for at least one hour to determine whether there
were any leaks in the casing or the grout seal through
which formation water could enter the borehole. Once it
was determined that there were no leaks in either the
casing or the grout seal, drilling resumed. Wire-line core
drilling was resumed by drilling through the grout plug
and out the bottom of the casing through the confining
layer Into the lower aquifer to total depth (Figure 5).
When total depth was reached, drilling tools were
removed from the borehole and geophysical logs were
run in the bottom section of the hole. By using the
stratigraphic Information obtained from the geophysi-
cal logs and geological cores, instrument locations were
determined.
Wall Completion Procedure
Most available instruments maybe used in conjunc-
tion with this method, including bundle-type piezo-
meters and various multi-level sampling devices. Bore-
hole sizes may vary depending on the instrument
selected. The ground-water sampling devices used in
this Investigation, which was primarily concerned with
toxic inorganic constituents, were gas-drive type
(Barcad. a trademark of Barcad Systems Inc.) samplers.
In addition, vibrating-wire type strain gauge trans-
ducers were placed at each sampling point to determine
plezometric pressure. Each transducer was attached to
the tubing just above the sampler. The entire assembly
. Flush joint
. steel casing -
Open borehole -
Threaded left hand -
Stainless steel
casing
Ground surface
Overburden
Water table
z.
Water table aquifer
(sandstone)
Claystone
- Threaded right hand
Confining bed
(claystone/siltstone)
Flush joint.
. steel casings
Open borehole -
Coupling level
Stainless steel
casing
Ground surface
Overburden
Water table ¦
Water table aquifer
(sandstone)
Claystone
;Top of grout.
Cal-seat grout
Confining bed
(claystone/siltitone)
Confined aquifer
(sandstone)
Confined aquifer
(sandstone)
Figure 3. Temporary casing set in open borehole drilled
to confining layer
Figure 4. Grouted lower stainless steel casing joint
SO
Fall 1983
A-41
-------
was then placed in a polypropylene filter "sock" and
backfilled with No. 3 sand (Figure 6). All instrumenta-
tion was tested on the surface for proper operation
before being Installed in the borehole.
Well completion of the lower confined aquifer was
now ready to begin. A No. 3 sand footing was placed on
the bottom of the borehole through the tremie pipe.
The first sampler-transducer assembly was then low-
ered down the borehole and landed on the sand footing.
Once the sampler-transducer assembly was in place,
No. 3 sand was placed in the borehole through the
tremie pipe to completely cover the unit. It should be
noted that all instrument and backfill material loca-
tions were measured with a weighted tag line and that
all stemming materials were placed with the use of
tremie pipe. The sand quantities varied based on the
vertical length of the borehole to be sampled. After the
sampler-transducer assembly was completely covered
with the No. 3 sand, a fine sand "cap" was placed on top
of the No. 3 sand. No. 0 sand was used in this case: 2 feet
was found to be sufficient. The purpose of the fine sand
is to prevent bentonite and grout intrusion Into the No.
3 sandpack. With the No. 0 fine sand "cap" in place, the
area above the sampler was then sealed with a 5-foot
bentonite plug. This was accomplished by washing
Vinch diameter bentonite pellets down the tremie
pipe. The borehole was then grouted to 2 feet below the
next sampler-transducer location and the above pro-
cedure was repeated.
After the appropriate number of sampler-transducer
units were installed, the borehole was grouted back Into
the stainless steel casing section, sealing off the under-
lying aquifer(s) (Figure 7). After the grout had cured,
any standing water in the casing was removed and the
borehole was monitored for at least one hour to deter-
mine If there was any leakage into the temporary casing
from the lower formation. When it had been determined
that there were no leaks, the temporary casing was
removed from the borehole. Removing the casing was
accomplished by turning the entire casing string to the
right (clockwise) and unscrewing from the left-hand
threaded, stainless steel casing joint. The carbon steel
casing sections were then removed from the borehole
(Figure 8).
The upper part of the borehole was then open to the
formation and could be Instrumented. The well comple-
tion in the upper aquifer was similar to the lower
aquifer except that a standpipe piezometer was installed
as the uppermost (water-table) aquifer sampling point
The standpipe piezometer was constructed of 3 '/Hnch
diameter PVC with square threads and flush joints. No
glues or solvents were used during piezometer assembly
to avoid problems associated with degradation and
leaching of contaminants from organic coupling
cements (Baker 1980). The slotted sections of casing
were typically 5-foot lengths with 0.020 slot width: 15
feet of slotted section was commonly used. The slotted
section was packed with the No. 3 sand over its entire
length. A 2-foot No. 0 sand "cap" was placed on top of the
No. 3 sand to prevent bentonite or grout Intrusion into
the No. 3 sand pack. The borehole was then grouted to
the surface. The subsurface portion of the monitoring
well was now complete (Figure 9).
The surface completions for all multiple-completion
Ground surface
. Flush joint
. iteel casing—^
Open borehole -
Cal-teal grout plug
Open borehole -
Stainless stew
casing
Overburden .
Water table
'JL
Water table aquifer
(sandstone)
Claystone
Confining bed
(clayitone/siltstone)
Confined aquifer
(sandstone)
Transducer
cable
T ransducer
I
i:r
/
/
ji
I
t
1
Barcad (.
sampler^
Sample tube
• • • e4.r_uVl.fvij
m
1 Alumina filter
No. 3 sand
Polypropylene sock
Figure 5 Borehole drilled to underlying confined aquifer
Figure 6, Instrumentation package
A-42T
Fall 1983
51
-------
wells consisted of labeled, weather-tight enclosures
mounted on steel support legs. The support legs were
anchored into the ground with concrete a few feet from
the well-head. The sampler tubes and pressure trans-
ducer cables were passed through a flexible conduit
which serves as protection. The conduit is grouted to
the top of the well and attached to the enclosure with
weather-proof seals. The sampler tubes are plumbed to
a prefabricated manifold mounted in the enclosure.
These tubes are labeled with aluminum tags and kept
Inside the enclosure until used, protecting them from
weather and vandalism. The surface completion is
Illustrated in Figures 10 and 11.
Field Problems Encountered
The procedure to isolate ground-water flow between
two aquifers was relatively trouble free. However, there
were a few problems encountered. As previously stated,
this procedure was used in three boreholes with two
successful completions.
Rotary drilling with air and coring using air was
usually successfully accomplished. However, once the
water table was encountered, wash boring was usually
necessary to prevent mud collar buildup on the drill
rods. This was due to the high clay content of the
formations encountered at the project site. The main
problem was associated with unstable borehole condi-
tions below the temporary casing. Once the borehole
was drilled to total depth and the wire-line core rods
were removed to install instrumentation, the uncased
lower portion of the borehole would often collapse.
Sampler tubes
Ground surface
Open borehole -
Stainless iteel casing
(left hand thread)-
Grout seal
Sand pack
Sampler
Overburden ¦
Water table
z.
Water table aquifer
(sandstone)
Claystone
Confining bed
(claystone/siltstone)
Open borehole
Confined aquifer
(sandstone)
Benton ite seal
or grout
Figure 8. Steel casing sections removed from borehole
~ Sampler tubes
. Flush joint.
steel casing-
Open borehole -
Sand pack -
Sampler-
Ground surface
Overburden .:
Water table
2.
Water table aquifer
(sandstone)
Claystone
Stainless steel
casing
Grout seal
Confining bed
(claystone/siltstone)
Open borehole
Confined aquifer
(sandstone)
Bentonite seal
or grout
Grout seal
Ground surface
Standpipe piezometer
(PVC casing)-
Sand pack
.. Open borehole -
Slotted PVC casing -
' Bentonite seal.
or grout-
Sand pack
Stainless steel
casing
Grout seal
Sand pack
Sampler
Overburden
Water table
X
Wpter table aquifer
(sandstone)
Claystone
Sampler
Confining bed
(claystone/siltstone)
Open borehole
Confined aquifer
(sandstone)
Bentonite seal
or grout
Figure 7. Instrumentation placed in lower aquifer Figure 9. Completed monitoring well
52 foil 1983 A-43
-------
When collapse occurred, the borehole was re-entered
with the wire line core drilling rods (no core bit) by
using water injection (low flow rate) to "wash" the rods
down to the bottom of the borehole. After reaching total
depth with the wire-line drill rods, the transducer-
sampler unit and sandpack wereemplaced through the
drill rods. The rods were then carefully pulled back,
using a light water injection to avoid binding. By
completing the borehole in this manner, usinga tagllne
to measure borehole depth, the bottom part of the
borehole was instrumented and stemming materials
emplaced. Tag-line measurements are imperative to
verify satisfactory placement of backfill materials and to
detect collapse following wire-line rod withdrawal. If it is
suspected that unstable borehole conditions exi9t. It
may be desirable to initially plan to complete through
the rods. Wire-line coring In unconsolidated materials
Is an effective way to advance an unstable borehole.
Although core recovery was minimal at times, the
borehole is protected from collapse while drilling, since
the rods always remain in the hole.
A more critical problem arises when the borehole
collapses just below the confining layer, shortly after the
grout has been poured. This displaces the grout plug up
Into the temporary carbon steel casing. This was the
case with the one unsuccessful completion. After the
grout had cured (two to four hours) and the temporary
casing was removed, the sampler-transducer tubes,
which were grouted into the temporary casing were
pulled apart. Therefore., there was no way to salvage the
lower instrumented portion of the borehole.
Figure 11. Qoseup ol wellhead enclosure
Figure 10. Typical wellhead completion
A-44
Foil 1983
53
-------
improvements
It is suggested that the stainless steel casing section
be longer in well completions of this type. Based upon
this study, we recommend that It be at least 12 feet in
length so that a good seal Is ensured and grout
quantities do not have to be as precise. With a 12-foot
casing section and a 6- to 8-foot grout stage, this would
allow more room In the stainless steel casing for the
grout. This Is Important In the event that the bottom
portion of the borehole collapses and grout is displaced
upwards or grout quantities are slightly miscalculated.
Cost Comparison
A comparison was made between this method and
an alternative approach to isolate two separate aquifers.
This comparison is based on a 400-foot deep borehole.
To accomplish the same sampling strategy discussed in
this article, without the use of the retrievable casing
method, two individual boreholes would need to be
drilled. One well would be similar to the multi-cased well
design described by Edwards et al. (1983). Figure 12
Illustrates the two-borehole approach which can be
compared directly to the single-borehole method illus-
trated In Figure 9. The two boreholes necessary would
be as follows: One borehole is drilled to 180 feet total
depth to sample the water-table aquifer. The second
borehole Is then drilled to 400 feet total depth to sample
the confined aquifer only, isolating it from the water-
table aquifer. This is accomplished by drilling through
the water-table aquifer into the confining bed above the
confined aquifer. A permanent casing must then be set
into the confining bed at the base of the water-table
aquifer and grouted In place. Then drilling would
— Sand pack
- Grout seal -
-Slotted
PVC
eating
Permanent
"steel
casing :
Benton ite seal
Sampler
t
Ground surface
Overburden^
Water table-
Water table
aquifer
(sandstone)
Claystone
Confining bed
(claystone/
siltstone)
Confined aquifer
(sandstone)
continue through the bottom of the permanent casing
into the lower confined aquifer, which could then be
instrumented.
The dollar values in Table 1 are based on the actual
costs of materials and services, except where otherwise
stated. The labor chaises are estimated at S35. per
person per hour and may need to be adjusted depending
on actual labor costs. As Table 1 illustrates, the single
borehole method is definitely more cost-effective, repre-
senting a savings of approximately 30 percent.
Single borehole
Two borehole
method*
method* *
Total drilling cost
11,040
16,560
($27 60/foot includes drillers labor)
Sampler/transducer
3,662
3,662
Completion materials
2,401
4,134
Surface completion
581
1.163
Labor costs
5.250
7.875
($35.00 per person per hour)
Total cost
$22,935
$33,394
Figure 12 Two borehole completion method
* Baifd on 400 ft dMP bonhol#
•• 3it*d on ona borahola it 180 It and tha tacorxl borahola at 400 ft
Table 1. Cost Comparisons
Conclusions
This borehole drilling and completion method has
proven to be very useful In Instrumenting relatively
deep water-table aquifers with underlying confined
aquifers. The method avoids mixing of ground water
between two different aquifers within a single borehole,
eliminating potential cross-contamination of aquifers
and biasing of sampling points. It is a cost-effective
approach which does not require the drilling and
completing of two separate monitoring wells. Also, since
this method can be accomplished in a relatively small
borehole, overall drilling costs are minimized. With
good field planning, this can be an extremely useful
monitoring well completion method for hazardous
waste landfill Investigations.
Acknowledgment
The authors would like to thank both D.W. Carpenter,
D.G. Wilder, and D.O. Emerson of Lawrence Livermore
National Laboratory for their contributions in the
initial planning of this method and for their technical
review of this document.
References
Absalon. J.R and R.S. Starr. 1980. Practical aspects of
ground-water monitoring at existing disposal sites.
U.S. EPA Conference on Management of Uncon-
trolled Hazardous Waste Sites. October 15-17.
Washington. D C.
Baker, J. 1980. Field methods in contaminant hydro-
geology. University ofWaterloo. Canada Short course
notes.
Edwards. RE.. NA Speed and D.E. Verwoert February
21.1983. Cleanup of chemically contaminated sites.
Chemical Engineering, pp. 73-81.
Biographical Sketches
Patrick W. Burklund joined the Lawrence Liver-
more National Laboratory in 1977 and is a senior
technologist assigned to the Nuclear Test Engineer-
ing Division. As lead technician for many geotech-
54
Fall 1983
A-45
-------
Will My Monitoring Wells
Survive Down There?: Design
and Installation Techniques for
Hazardous Waste Studies
by Henry R. Richrer and Michael C. Collentine
Introduction
Field experiences at hazardous waste management
facilities, hydrocarbon spills and sanitary landfills have
shown the necessity for on-site flexibility in the design
and installation of successful monitoring wells. It is the
authors' opinion that although the initial design criteria
for a monitoring well network are typically reviewed
"in-office," the final design criteria must be confirmed
on the basis of site-specific field observations.
It is the objective of this paper to describe various
design and installation methods used by the authors to
complete monitoring wells and to critically evaluate
those methods based on site-specific applications. Mon-
itoring well sites presented herein include a diversity of
geographic settings in Wyoming. Hydrogeologicsettings
include unconfined and semi-confined ground-water
conditions in 1) Quaternary alluvial terraces, alluvium,
aeolian sand and scoria and 2) Cretaceous shale, clay-
stone and sandstone.
This paper describes the following:
• Design of monitoring wells
—Drilling methods
—Completion and development practices
• Decontamination
• Field examples.
Principal Factors Controlling Monitoring Well
Design
Principal factors controlling monitoring well design
include:
• Drilling methods
—Geologic applicability—the types of geologic
materials to be drilled and sampled will influ-
ence the selection of well casing and the size of
the well screen
—Borehole diameter—the borehole should be of
sufficient diameter to allow the emplacement
of a gravel or sand pack and necessary formation
sealing materials such as bentonite or cement
—Site accessibility—may limit type of drilling
equipment
—Availability of equipment
—Budget
• Completion and development practices
—Chemical constituents—the types of chemical
constituents to be monitored will strongly influ-
ence the decision to use galvanized steel, PVC
or yelomine (fiberglass) casing. Obviously, the
asing material must not deteriorate or con-
tribute chemical constituents by deterioration
to the sampled formation water
—Well diameter—the well diameter should be
adequate for well development, water sampling
and pump testing
—Contaminant cleanup—the well should be of
adequate design for use as an active contami-
nant cleanup well
—Hydrogeologic environment—under confined
conditions, the confining layers must be sealed
off from the contaminated aquifer or aquifers.
Multiple completion wells may be required
where several minor aquifers exist
—Availability of equipment
—Budget.
Drilling Methods
Drilling methods used by the authors at monitoring
well project sites include 1) hollow stem auger, 2) air
rotary, 3) mud (or foam) rotary, 4) casing hammer and
air rotary, 5) drive point and 6) backhoe. Other drilling
methods commonly used include cable tool and solid
stem auger A comparative summary of drilling methods
is 'isted in Table 1.
A-49
-------
Comparative Summary of Commonly Used Drilling Methods
Comparative criteria Hollow stem auger Air rotary
Mud rotary
and/or foam
Casing hammer
and air rotary
Geologic applicability
(dnllable formations)
Depth restrictions
Diameter of hole
Rig mobility
Quality of formation
samples
Cross-contamination
potential
Drilling rate
Rig availability
Cost
Comments
Unconsolidated materials
and soft bedrock Poor in
saturated "flowing" mater-
ials. Poor below water table
Best application to soils.
± 100
9 to 12 inches
No restrictions
No restrictions
None
None
None
None
Excellent; truck, skid and Good to poor, difficulty Good to poor, difficulty
tractor mount. increases with size of rig. increases with size of rig.
Excellent undisturbed sam- Poor, nearly impossible to Poor at best Not recom-
ples when accompanied obtain undisturbed sam- mended for sampling,
with split spoon above water pies. Difficult to identify
table Poor sampling below intervals of less than 6
water table. inches. Easy to miss minor
contaminated zones.
Low, causes little formation Large, may cause air iniec-
damage and generally does tion, circulation of fluids,
not promote circulating Difficult to thoroughly
fluids. Potential increases if decontaminate bit.
cotter-pins on auger flights
are not cleaned. Augers are
easy to clean Few parts
contact formation material.
Large, induces circulation
of fluids.
Unconsolidated materials
and soft bedrock. Generally
not good where boulders
are present. Not good i0r
hard rock.
Type of geologic material
and pull capacity of rig
Limited by hammer, gener-
ally less than 12 inches
Good to poor, difficulty
increases with size of rig
Good to fair Can obtain
some moderately disturbed
samples. Better control than
conventional rotary. Can
determine minor contami-
nated lenses. Good sam-
pling below water table
Low, limited chance for
cross-contamination Seals
off contaminated intervals
Slow
Poor
$8 to 18/ft.
When accompanied with
split spoon sampler, this is
the best method for precise
sampling. Limited by drill-
ing depth, geologic mate-
rials and availability. Poor
method where large cob-
bles and boulders are pres-
ent. Limited by inside
diameter of hollow stem.
Poor method if samples
below water table are
required, Drilling problems
below water table. Difficult
to place gravel pack around
well casing due to restricted
annulus. Can determine
saturated zones quickly.
Can determine minor con-
taminated laminae easily in
samples Can run packer
tests easily. Can sample
fluids within hollow stem.
Preferred method of
authors at most locations.
Poor availability of rigs with
larger than 4-inch hollow
stems in Rocky Mountain
area. Many rigs are under-
powered and have limited
drilling depths.
Fast; variable
Excellent
$6 to 24/ft.
Good when just making
hole. Poor when formation
sampling is critical Increas-
es potential for cross-con-
tamination Increases per-
sonnel exposure to con-
taminants by blowing out
samples and fluids. Diffi-
cult to quickly identify
saturated zones Rigs are
generally larger than neces-
sary for shallow monitor-
ing wells. Costs are gener-
ally higher.
Fast; variable
Excellent
$10 to 32/ft
Not recommended unless
making hole is only objec-
tive Mud seals off low perm-
eability zones. Easy to miss
contaminated lenses. May
seal off water-bearing
zones. Promotes cross-con-
tamination by inducing
fluid circulation. Time con-
suming when decontami-
nating. Logistical problems
when drilling in sub-zero
weather. Frequent fluid
freezing problems Good
method if formationsslough
and/or swell.
Slow
Poor, usually must special
order hammer, drive casing
and drive shoe.
$15 to 35/ft.
Good method in soft
sloughing materials Can
obtain good samples Limited
by driving hammer capac-
ity, Can cause problems
when pulling casing; casing
may get stuck May dam-
age production casingwhen
pulling surface casing. Good
method when precisescreen-
ing placement ot produc-
tion casing is required Easv
to complete wells inside sur-
face casing Very slow drill-
ing. Most rigs are not set up
to run casing hammer
Expensive
A*4?1
-------
Fable 1
Comparative Summary of Commonly Used Drilling Methods
(continued)
Comparative criteria Drive point
Backhoe
Cable tool
Solid stem auger
Geologic applicability
(drillable formations)
Depth restrictions
Diameter of hole
Rig mobility
Quality of formation
samples
Cross-contamination
potential
Drilling rate
Rig availability
Cost
Comments
Unconsolidated material Unconsolidated material
Most materials, best in Unconsolidated materials
rubble and boulder debris, and soft bedrock. ,
Type of geologic material. Length of arm,
Generally less than 50 ft. less than 14 ft
Less than 8 inches
Unlimited
None. Generally driven by Good
hand hammer or trailer-
mount hammer.
No samples of formation Good
are obtained.
generally Up to 400 ft.
Unlimited
Good to poor
± 200 ft.
18 to 20 inches
Excellent truck, skid and
tractor mount.
Good. Undtsturbedsamples Moderately disturbed sam-
can be readily obtained pies above water table. Poor
Limited recommendation to inaccurate sampling
when samples are critical below water table
None
Extreme
Limited by speed of hammer. Fast
Good Good
$10 to 20/ft. 425 to 50/hr.
Quick, inexpensive way to Not recommended for
install water-level and sampling. Easy way toexca-
chemical quality monitoring vate shallow pits and to
points. Good where depth install very large-diameter
to water is shallow. casing.
Low
Moderate
Poor to Good
$8 to 14/ft.
Easy and accurate sampling.
Easy to determine saturated
zones Can test saturated
zones. Easy completion
when surface casing is in-
stalled. Excellent where
boulders cause drilling
problems. Can damage pro-
duction casing when pulling
surface casing. Only ma|or
disadvantages are drilling
times in consolidated rock
and rig availability in the
Rocky Mountain area.
Low
Slow
Poor
J5 to 10/ft
Good for making hole. Poor
if materials slough. Larger-
diameter holes are possible
with solid stem than hollow
stem.
Completion and Development Practices
Monitoring well completion and development
practices are frequently determined more by the pre-
judices of the individual in charge of the monitoring
program than by the objectives of the monitoring
program. Careful decisions should be made concerning
the diameter of the monitoring well, casing material and
type of well development technique., It is the authors'
opinion that flexibility in completion and development
practices must be maintained, with the controlling
factor being the objective of the monitoring well.
One of the first considerations in monitoring well
design is casing diameter. The focus of current discus-
sions seems to be: which is best 2-, 4-, or 6-inch
diameter casing? Each size casing has distinct advan-
tages; however, the principal issue is which one will best
satisfy the monitoring objective.
When determining casing diameter, the following
factors should be considered:
• Cost—unit costs for 4- and 6-inch casing can be
two to 10 times the unit cost for 2-inch casing
• Well development—large-diameter wells can be
developed faster; however, costs of development equip-
ment and rig time are generally greater. Large-diameter
wells produce water with less silt, thus reducing filtration
time during sampling. Larger sediment storage capacity
is also available in large-diameter wells
• Aquifer testing—2-inch diameter wells are gen-
erally not suitable for pump testing
• Sampling—although new sampling devices are
being manufactured for 2-inch wells, it is generally
agreed that larger-diameter wells are easier to sample
and there is a greater number of sampling devices
suitable for large wells. Large volumes of water must be
evacuated from large-diameter wells prior to sampling
• Contaminant cleanup—2-inch wells are generally
not useful for activities other than sampling and monitor-
ing water levels, whereas larger-diameter wells can be
used for the above-mentioned activities, as well as
active contaminant cleanup
• Hydrogeologic environment—multiple comple-
tion wells are generally more suitable to 2-inch diameter
casing because of cost.
Another factor in completion design is casing mater-
ial. Frequently used materials include galvanized steel,
PVC and yelomine (fiberglass). Although casing costs
vary greatly depending on the type of material, the
principatcomideratian should be to utilize material that
-------
will not react with the chemical constituents to be
monitored. Other considerations include well depth,
well use duration, strength and material availability.
Decontamination
Decontamination of drilling and sampling equip-
ment consists of physically removing contaminants
and/or altering the contaminant chemical character-
istics to innocuous substances. The extent of decon-
tamination depends on a number of factors, of which
the most critical factor is the type of contaminants
involved.
There is no method to immediately determine the
effectiveness of field decontamination of drilling equip-
ment. Discoloration, corrosion and materials adhering
to equipment may indicate contaminants have not been
removed; however, observable effects identify surface
contamination and not permeation. Also, many con--
taminants are not easily observed while field cleaning
equipment.
At best, field personnel must rely on their own best
judgment while cleaning. Care and attention to detail
must be exercised during the decontamination process
and, realistically, one can only hope that the cleaning
was complete.
The authors' experience with decontamination of
field and drilling equipment in remote parts of Wyoming
has been frustrating. Subzero temperatures of -40 F
have at times rendered conventional decontamination
(with soap and water) impossible. Similarly, these tem-
peratures have rendered steam cleaning impossible
because intake lines from the water trucks freeze before
the water can be heated.
A principal controlling factor in decontamination
has been local climatic conditions. Experience in
decontamination of field and drilling equipment at
remote project sites under extreme temperature condi-
tions requires drillers to have "extra" supplies on-site so
that pre-cleaned equipment is used at each new hole.
When supplies are exhausted, the equipment is loaded
and transported to a constructed wash pad so that
cleaning solutions and wash water can be recycled or
collected for later disposal. Steam cleaning or high-
pressure spraying utilizing water with a general purpose
low-sudsing soap and detergent is recommended.
Physical scrubbing by disposable or easily decontami-
nated brushes may be necessary to loosen packed-on
materials. Hot water is more effective than cold water,
and flushing or rinsing should be done under high
pressure to assure to removal of all soap. A thorough
inspection of equipment, supplemented by a swipe test,
is recommended and should be the controlling factor
for length and method of decontamination. It is essential
that all parts of the drilling equipment including drill
pipe, collars, kelly derrick, under carriage, chassis and
cab, be thoroughly cleaned.
A brief summary of decontamination solutions fre-
quently used and various remarks are listed in Table 2.
Upon completion of decontamination, the decon-
tamination process employed and the results of the
visual inspection and swipe tests should be documented
in an appropriate log book. As a rule, drillerj initial the
log book, indicating that all equipment was cleaned and
inspected.
Table 2
Decontamination Solutions
Name of solution
Remarks
Sodium bicarbonate
Sodium carbonate
Trisodium phosphate
Calcium hypochlorite
Effective for acids and bases,
amphoteric, 5-15 percent
aqueous solution
Effective frr inorganic acids,
good water softener, 10-20
percent aqueous solution
Good rinsing solution or
detergent, 10 percent aqueous
solution.
Excellent disinfectant,
bleaching and oxidizing agent.
10 percent aqueous solution.
Field Examples
Monitoring well projects supervised by the authors
include the following:
• An industrial facility utilizing land farm, landfill,
high strength, waste water evapoiation pond and excess
service water containment facilities
• A petroleum pipeline spill onto agricultural land
c An industrial facility assessing the potential for a
spilled hydrocarbon recovery program
« A municipal landfill containing unrecorded quant-
ities of hazardous, toxic and sanitary substances.
The purpose of this section is to briefly present
selected project examples where monitoring well
design was significantly changed from initial design
based on key field observations and water-quality
analyses.
Example 1
Example 1 involves an industrial facility utilizing a
landfill, a chemical evaporation pond and excess service
water containment facilities. A ground-water monitor-
ing network was designed to comply with regulations
specified under the Resource Conservation and Re-
covery Act (RCRA). The project site was located in
Wyoming, and hydrogeologic environments included
recent aeolian sand, quaternary alluvium and alluvial
terrace deposits, and cretaceous shale and sandstone
deposits. Ground-water conditions were unconfined to
semi-confined and static water levels ranged from a few
feet to about 25 feet below the ground surface.
Initially, monitoring wells were drilled using air,
mud or foam rotary techniques. Wells were constructed
with nominal 4-inch schedule 40 galvanized steel pipe,
joined by threaded, galvanized steel collars. Well screens
were 3 feet in length and constructed of galvanized
steel. All wells were backfilled with washed silica frac-
sand and drill cuttings. Galvanized steel pipe was
believed necessary because of possible contact with
organic solvents and corrosive water.
Logistical problems were encountered almost im-
-------
mediately with the rotary drilling. Hole collapse and
collection of poorly correlated samples were the princi-
pal obstacles. Hole collapse was remedied by use of
heavy weigh; mud: however, the mud masked drill
cuttings, thus making observations of contaminated
cuttings nearly impossible. The heavy mud also plugged
off low-permeability sand lenses that had a high con-
tamination potential.
To correct the hole collapse and sampling,problems,
a casing hammer and air rotary drilling program was
initiated. This method proved to be satisfactory for well
installation: however, drilling and completion time was
nearly tripled. The increased time significantly elevated
costs and a halt to drilling was called so that other
drilling techniques could be evaluated.
During the drilling shutdown .water-quality samples
were collected and analyzed. It was found that although
previously reported, there were no organic solvents or
corrosive water encountered in the sampled aquifer.
This allowed us to eliminate the use of galvanized steel
casing. Also during this time, one of only two hollow
stem auger operators in the state was contacted.
It was then decided that as long as galvanized steel
casing was not required, PVC casing and screens would
be used. It was also agreed that the hollow stem auger
would be used: however, the diameter of the hollow
stem was only 3 inches and so all wells were reduced to
2-inch diameter.
The result of these final design changes allowed
more monitoring wells to be installed in less time and at
a lesser cost than had originally been estimated. The
increased number of monitoring wells facilitated a
better delineation of the contamination plume and
ultimately expedited abatement procedures.
Example 2
Example 2 involves a petroleum pipeline spill onto
agricultural lands. The spill occurred several years prior
to the site investigation. The authors were contacted
and requested to conduct a three-hour reconnaissance
survey of the potentially contaminated area. The authors
were informed that a drilling rig was available for use.
The hydrogeologic setting included a scoria aquifer
overlain by clay. Depths to water ranged from 6 to 10
feet. The objective of the reconnaissance survey was to
visually determine if hydrocarbons were present in the
aquifer. Water-quality sampling was not an objective.
Because of the limited time allowed for the survey,
the authors tried to determine the quickest way to
penetrate the clay and reach the water table and also
cover the greatest possible area. A steel tape and an Oil
Recovery Systems I nc. Probe'" were available for hydro-
carbon detection.
The authors believed that a rotary drilling rig would
be too slow. Because the water table was relatively
shallow in the area, it was decided that a backhoe could
be effectively used for excavation of test pits. The
backhoe proved to be adequate and six test pits were
excavated and tested. Four of the six test pits contained
variable quantities of hydrocarbon product.
Although the areal extent of the hydrocarbon
plume could not be delineated during the 'Hree-hour
survey, sufficient evidence was obtained to document
the need for further studies. Although the authors co
not recommend this practice for investigating hydro-
carbon spills, nonetheless, it accomplished the objective.
Example 3
The final example involves an industrial facili =y
experiencing possible contamination of an alluvial
aquifer by a leaking chemical evaporation pond. The
owners of the facility requested that monitoring wells
be drilled at appropriate locations so that any con-
tamination from the pond could be detected. The
facility owners were interested only in obtaining water-
quality analyses.
The alluvial aquifer was 8 to 10 feet thick. Depth to
water ranged from 3 to 5 feet. The lithologic character of
the alluvial deposits was well-known to the authors
because the authors had installed numerous monitoring
wells in the alluvium adjacent to this particular site.
Although the facility owners had requested that a
drilling program be initiated, it was thought that drilling
numerous shallow monitoring wells would be unjustifi-
ably expensive and time consuming. It was the authors'
opinion that hand-driving sand-point or drive-pont
wells would accomplish the monitoring objectives and
do so at the lowest possible cost. For example, by ccst
comparison, the drive-point wells could be installed ai a
cost ranging between $25 and $45 per hour, whereas
drilling costs for rotary and hollow-stem auger rigs we'e
$150 and $105 per hour respectively.
Summary
Numerous design criteria must be considered when
drilling and completing monitoring wells at hazardous
waste management facilities. It has been the intent of
this paper to present what the authors believe are the
principal controlling factors. However, the ultima:e
criterion in monitoring well design is making sure that
the well(s) meet the objectives of the monitoring
project.
The authors have found that designing monitorirg
wells in the office based only on published data does
not always meet the objective of the monitoring pro-
gram. Although the authors believe that in-office design
is necessary and a good place to start, it is, however,
critical that on-site flexibility in design be employed. As
field information becomesavailable. it is not uncommon
to make changes in drilling methods, casing, completion
and development. Often these changes decrease costs
and improve the efficiency of the well.
References
Minning, R.C. 1982. Monitoring well design and
installation. Proceedings of the Second NationalSym-
posium on Aquifer Restoration and Ground Water
Monitoring. National Water Well Association, Worth-
ington, Ohio, pp. 194-197.
Schalla, R. and P.L. Oberlander. 1983. Variation in the
diameter of monitoring wells. Water Well Journal,
v. 37, no. 5, pp. 56-57.
Schmidt, K.D. 1962. The case for large-diameter mon-
-------
itormg wells. Water Well Journal, v. 36, no. 12, pp.
28-29.
Biographical Sketches
Henry R. Richter is currently a hydrogeologist-
project coordinator with Western Water Consultants
I nc.. a Wyoming-based water resources consulting firm.
He has supervisory experience in photogeologic and
field geologic mapping, hydrogeologic data acquisition
and interpretation, ground-water exploration and
resource evaluation, identification and quantification of
hazardous wastes in ground-water systems and design
and implementation of monitoring well systems. He
received his B.S degree in geology from Juniata College
and his M.S. degree in hydrogeology from the University
of Wyoming. Richter is a member of the National Water
Well Association, Wyoming Water Well Association,
Colorado Ground Water Association and Wyoming
Geological Association.
Michael G. Collentine is currently a hydrogeologist
with Western Water Consultants Inc., a Wyoming-
based water resources consulting firm. He received his
B S. degree in geology and his M.S degree in water
resources management, both from the University of
Wisconsin—Madison. His experience includes ground-
water resource exploration and evaluation, design and
installation of ground-water monitoring systems, analysis
of ground-water/hydrocarbon interaction and geologic
field mapping. He is a member of the National Water
Well Association, theWyomingWater Well Association
and the Colorado Ground Water Association.
Questions and Answers
Q. What decontamination procedures would you
recommend when drilling and sampling at sites contam-
inated with PCB?
Kim Kesler
A. According to a representative at the General
Electric Oil Testing Lab in Denver, Colorado, there are
several solvents available that can be used to decontam-
inate PCB contaminated metal or glass drilling and
sampling equipment. The solvents include acetone,
hexane, trichlorobenzene, trichloroethane and a host
of other "electrical grade solvents." All clothes, rags,
rubber compounds or plastics used and/or possibly
contaminated with PCB during drilling, sampling or
cleaning, should be burned in an EPA-approved incin-
erator or disposed of at an approved disposal site. Such
materials absorb PCB and cannot be decontaminated.
Special care should be taken during cleaning to
avoid personal contact with contaminated rinse water,
solvents or cleaning materials and to ensure that PCB
contaminated water, solvents or cleaning materials do
not come in contact with soils in the cleaning area. A
self-contained pad should be required where PCB
contaminated equipment is cleaned.
Q. How significant is adsorption of organics from
incompletely developed 2-inch monitoring wells; and
don't you run the risk of obtaining non-representative
samples by filtering the water samoled from a poorly
developed well?
/. Tomko
A. In most cases, the concentration of organics in
the sampled water after filtration in the field or lab is
equal to the concentration in water from an adequately
developed well, assuming that the silts and clays that
remain in the formation have adsorbed as much of the
organics as they are capable of. The analytical results will
still be representative of the sampled water, and the
filtered sediments will be representative of the extent of
adsorption of organics that has taken place on the clays
and silts in the formation.
Q. When working at hazardous waste sites, have
you used acetone and hexane to clean your drilling
tools and sampling equipment?
Bill Clarke
A. We have used acetone to clean tools and equip-
ment. Our usual practice is to completely submerge the
tool or sampler in acetone and then rinse it with hot
water under pressure. This has proven to be a satis-
factory method for decontaminating materials made of
metal and glass.
Q. Do you use rubber seals between sections of
hollow stem augers? If not, how do you avoid inflow at
joints and subsequent cross-contamination?
Rich Anderson
A. Yes, we use rubber seals called 'O-nngs" be-
tween the auger sections.
Q. In redeveloping silted-in wells, it is impractical to
use air to accomplish the process in all cases (i.e. clays
from voids, caves, etc.). What is your view toward
utilizing water to blow out accumulated sediments?
C.F Bieie
A. When dealing with clays packed into the bottom
of a well, it is our opinion that jetting with either air or
water is equally effective, since air jetting essentially
moves water into the sediments at a high velocity
Experience has shown that the packed clays can only be
removed by physical means such as brushing or ream-
ing to loosen the sediments, followed by either air or
water jetting.
Other methods, such as the addition of dispersing
agents which react with clay and silt particles by placing
a small, but similar electrical charge on each particle
causing the particles to repel one another, are available.
Again, methods which disperse the sediments should
be followed by jetting.
Q. In utilizing the rotary air technique, problems
with "jamming" (i.e. friction) often hinder drilling.
What is your view on utilizing a common dishwashing
fluid to facilitate lubrication? This assumes such fluid is
analyzed for possible cross-contamination.
C. F Sieze
A-51
-------
A. I can'tsee any reason why common dishwashing
tluid would present any problems. The drilling fluid
must be of sufficient viscosity to carry drill cuttings out
of the borehole. I would suggest clearing any such fluid
with your driller before assuming that the fluid will
provide both lubrication for the drill bit and sufficient
viscosity to move cuttings away from the bit. Drilling
foam is a soaplike substance commonly used to provide
lubrication and cutting removal.
Q. What is your opinion of installing small-diameter
wells in bedrock in borings drilled with double tube
diamond coring equipment?
B. Camlin
A. The coring method is best utilized in areas where
the monitoring system objective is to install shallow
wells in bedrock units which crop out at the surface.
Samples obtained from the borehole may be accurately
correlated to depth and/or tested for vertical perme-
ability This method may be extremely slow where the
well depth requires repeated withdrawal of the core
barrel.
Q. Shouldn't well screen design take into account
potential for direct ground-water flow measurement?
For instance, maximizing directional accuracy and lower-
ing resistance to flow?
William B. Kerfoot
A. As stated in our paper, the most important
consideration in the well design should be the objective
of the monitoring system. The primary reason to design
the well screen as described in the question is to
accommodate measurements with a ground-water flow-
meter.
Where this instrument will be utilized, wells should
certainly be designed to give the least distortion possi-
ble to the flow of ground water.
It is our opinion, however, that the present state of
the art of ground-water flowmeters does not warrant
their use as a reliable tool to estimate ground-water flow
direction. It has been our experience in the field that
currently available flowmeters give misleading results.
When it comes to estimating the flow direction of
hazardous wastes in ground water, we have found that
the potentiometric surface determined from water
levels in properly installed monitoring wells is the most
reliable method.
A-02
-------
A Technique for Renovating
Clogged Monitor Wells
by William H. McTigue and Robert G. Kunzel
This paper describes a technique for renovating 2-
inch PVC monitor wells that have been clogged by
intrusion of silt from the surrounding soil and that have,
in this case, been cross-contaminated by bailer sampling.
For about two years, a series of 2-inch diameter PVC
monitor wells had been sampled by using the same
bailer. As a result, there was extensive cross-contamina-
tion, especially by volatile organic compounds. Further-
more, the large slot size of the well screen and the
uniform gradation of the surrounding pea gravel "filter
pack" had allowed silt to be drawn into the well, com-
pletely filling the well screen in some cases.
The wells were cleaned by simple jetting with clean
water to remove the silt and the contaminated water.
Then, a 1-1/2-inch diameter gas-displacement sampling
device was lowered into the screen section and sur-
rounded by a suitably graded filter sand. Samples taken
from the gas-displacement samplers over more than a
year have shown no cross-contamination and no tur-
bidity or intrusion of silt.
Turbid ground-water samples and clogged monitor
wells are becoming common experience. Most fre-
quently, these situations occur where monitor wells are
installed in low-yield saturated materials, such as silt,
clay or glacial till. Our experience indicates that this
often is a result of inappropriate design of either the
well screen, the filter pack material, or both.
Design of monitor wells has naturaHy evolved from
water well design. These design concepts have neces-
sarily been extended from application to saturated
media of high permeability to those of very low
permeability. However, it is not uncommon in fine-
grained materials (silt, very fine sand, till), that monitor
wells that have been designed and installed by profes-
sionals will produce turbid samples and th® wells them-
selves become clogged with intruded silt and clay
particles.
A fundamental criterion of well design is to allow
pore water to flow through the surrounding porous
media and into the well screen, while fine particles in
the media are excluded. In a more productive (k=10'-'
cm/sec) water-bearing medium, such as might provide
a yield of 50 gallons per minute to a 2-inch gravel pack
well, sizing of the well screen slot and gravel pack are
matters of general experience. However, in fine-grained
materials, say k=10"5 cm/sec, the yield of the same 2-inch
well would be reduced to about 0.07 gpm. Not surpris-
ingly, wells are seldom installed in such low-yield
material, except for construction dewatering and
ground-water monitoring applications. Hence, when
the demand for monitor wells to obtain ground water
from such fine-grained materials expanded dramatically,
the frequent results were customary "gravel pack" wells
of smaller diameter, which failed to exclude fine soil
particles when water was extracted from the well. In
fact, little attention is given to this aspect of design in
reference and practice manuals, e.g., EPA 1980 and EPA
1982.
An example of this type of monitor well failure
occurred at a hazardous waste disposal site in Illinois,
where 35 monitor wells were designed and carefully
installed to monitor ground water in loess and glacial till
deposits. Following two years of sampling with a bailer,
most of these wells had substantial amounts of silt
intruded into the well, in many cases completely filling
the screened section, Ground-water samples were
turbid and, because a single bailer was used in sampling
all the wells, considerable cross-contamination had
occurred.
The design of the monitor wells is shown schemati-
cally in Figure 1. A 2-inch plastic well casing and screen
was surrounded by a gravel pack described as "pea
A-63
-------
BENTONITE
SEAL
SAMPLER
RISER (3/4")
FILTER
SAND
GAS-DRIVE
SAMPLER
Figure 7 Typical monitor well installation
PARTICLE SIZE DISTRIBUTION
6*4JK V/t >* *u I mtrt/H
JO' 0003
COA*U "*t COUSt mtOHj* rml
SUT 0» CLdT
Figure 2. Partical size distribution relationships
gravel." Figure 2 shows particle size distribution curves
for the natural formation materials, characterized by the
right-hand curve; and the gravel pack majerial, charac-
terized by the left-hand curve. Considering only these
two materials, it is readily evident that fine particles from
the formation would easily move through the very
coarse, uniformly graded gravel pack.
The shaded areas of Figure 2 depict two criteria
commonly used for designing filter materials to exclude
fine formation particles from a pumping w*H. The John-
son criteria (Johnson Div., UOP1975) are recommended
for water-supply well design, with the assumption that
the well will be aggressively developed, i.e., as much as
30 to 50 percent of the formation fines will be drawn
into the well during the development operation. This
criterion also assumes significant gradation of the par-
ticle sizes in the natural media; it will be less effective in
uniform-grained media, such as pure silt. The trape-
zoidal shaded area represents criteria employed in
construction dewatering well design (Powers 1981); the
particle size distribution curve of an acceptable filter
must pass through the shaded area, in the manner of the
line shown.
The two shaded areas of Figure 2 have been fixed by
applying these criteria to the natural formation curve
shown on the right. It is evident that the dewatering
design criteria produce filter materials of finer average
particle size and somewhat wider allowable gradation.
As a result, these criteria have been found to produce
good filtering effectiveness, allowing very slight move-
ment of fine particles, even in uniform fine sands and
silts.
As a general approach to the design of filter packs
for monitor wells, an appropriate filter material might
be specified to lie within the boundaries defined by the
two criteria shown in Figure 2. Additionally, the finer
boundary might be preferred in the case of uniform,
very fine-grained natural formations.
In this case, it was evident that the gravel pack was
allowing intrusion of large amounts of the natural fine-
grained materials each time the well was bailed. The
objective of the renovation program was to clean out
the monitor wells and to reconstruct them in such a way
as to produce clear ground-water samples and permit
accurate measurement of the piezometric surface. This
was to be done, if possible, without redrilling and
complete reconstruction of the monitor wells.
The technique selected consisted of the installation
of a properly filtered gas-displacement sampler inside
the 2-inch PVC casing and screen of the existing moni-
tor wells. The first step in the procedure was thorough
cleaning of each monitor well. This was accomplished
by a water jetting system, using clean water from the
municipal water system, which was not recirculated
after being introduced into the well. A truck-mounted
tank, small centrifugal pump and simple piping were
used in a manual jetting procedure. Progress of the
manual procedure was rapid, even at the maximum well
depth of 40 feet. Jetting tools were cleaned after each
well was jetted.
After the intruded silt had been washed out of the
casing and screen of each well, and after the jetting
water returned consistently clear, the jetting tools were
withdrawn from the well casing, making sure that the
water level in the casing was not allowed to drop during
the withdrawal. This procedure maintained a positive
head inside the well and prevented the tendency for
intrusion of fine materials from the silt-clogged filter
pack during the withdrawal of jetting tools.
A gas-displacement sampler with a porous polyethy-
lene tip section and rigid PVC riser pipe was inserted
A~54>
-------
,hP clean monitor well and screen. The outside
Titers of sampler and riser pipe were 1-1/2 and 1
h respectively. The sampler unit itself was approxi-
'nC 'iv 16 inches in length. All piping connections were
Traded and no solvents or glue were used. The
' eneral arrangement is diagrammed in Figure 3^
After the sampler unit was carefully centered in the
II filter sand was poured slowly into the well casing.
This filter sand filled the space between the sampler and
he well screen so as to produce a new, properly graded
Lier throughout the full length of the monitor well
' en section. The purpose of this filter sand was to
^low the movement of ground water into the monitor
^ ell and into the gas drive sampler while excluding the
fine particles now lodged in the original gravel pack.
Selection of the filter sand was based on the application
of dewatenng criteria which, conveniently, were satis-
fied by a locally available, sterilized "play sand" that was
readily available at local hardware stores. Uniformity of
the sand grain size distribution was particularly impor-
tant, so that the sand would not segregate while being
poured into the water-filled well.
The filter sand was placed in the monitor well until
us measured depth indicated that the screen section
had been completely filled. The filter sand was tamped
frequently with a tamping rod to eliminate voids and to
measure the amount of sand in place. A seal of bento-
mte pellets was placed in the well casing at the top of the
filter sand column. The remainder of the well casing was
then filled with readily available material to complete
the inst. Ilation as shown in Figure 3.
After installation, the gas-displacement sampler was
operated as a pump to extract residual wash water in the
filter sand and to ensure that the entire system was
purged and refilled with natural ground water. Because
of the low permeability of the surrounding formation,
comparatively long times were required for the sam-
pling device to refill after purging. In the shallower
wells, periods of four to eight hours were required to
accumulate one liter of sample. Clear ground-water sam-
ples were obtained from all renovated monitor wells and
evidence of cross-contamination had disappeared by
the end of the second sampling and testing cycle.
The device installed in the well was a dual-function
sampler/piezometer. The fluid level in the 3/4-inch
riser pipe (Figure 3) moves freely in response to changes
in water pressure in the media surrounding the porous
tip. Therefore, water levels can be measured at any time,
using an ordinary electric well probe inside the 3/4-inch
riser pipe.
The renovated monitor well installation, in addition
to achieving the initial objectives of clear samples, no
risk of cross-contamination, and maintenance-free
operation, has several further advantages, resulting
from the gas-displacement sampling technique. Because
the sampler device and the 3/4-inch riser pipe involve
the storage of smaller sampler volumes, the time
required to recharge the sampler after purging is much
less than that required for the predecessor monitor well
casing. Because the ground-water sample is displaced
by gas under pressure, the pressure in the sample fluid is
\
BENTONITE /
SEAL
WELL
SCREEN
l°.\
MONITOR WELL
/ CASING (2")
i L.
i
GRAVEL
PACK
Figure 3. Renovated monitoring well showing gas-
displacement sampler
not reduced during sampling, which tends to prevent
the vaporization of volatile constituents of the sample.
Smaller volumes of purged water are involved, which
simplifies procedures if this water must be separately
managed, and the sampling becomes a one-man, rather
than two-man, operation. Finally, the sampling proce-
dure is simple and easily controlled, particularly in
winter or other adverse weather conditions or when
contact with sampled fluid is to be avoided.
Renovation of these 35 monitor wells, which aver-
aged 25 to 30 feet in depth, was accomplished during
adverse weather and site conditions in March 1982 at an
average cost of $350 per well. Recent experience with
similar renovation projects indicates that this is a rela-
tively high unit cost.
References
Johnson Division, UOP Inc. 1975. Ground water and
wells.
Powers. |.P 1981. Construction dewatering: a guide to
theory and practice. John Wiley and Sons. New York.
A-55
-------
vation of water and wastewater. EPA-600/4-82-029.
EPA. 1980. Procedures manual for ground-water moni-
toring at solid waste disposal facilities. SW-611.
Biographical Sketches
William H. McTigue is president of GeoEngineering
Inc. He has more than 25 years experience in heavy
construction, geotechnical engineering, water resource
development, ground-water control systems, business
administration and management. McTigue received his
B.S. from Massachusetts Instituteof Technology and his
M.S. from New Jersey Institute of Technology. He is also
a past president of the Association of Soil and Founda-
tion Engineers and of the Consulting Engineers Council
of New England. McTigue is a licensed professional
engineer in the states of New York and New Jersey.
Robert C. Kunzel is an associate and currently the
senior technician of GeoEngineering Inc. Kunzel has
nearly six years experience in a broad range of field
activities, including geotechnical drilling, sampling and
instrument installation, geophysical surveys, topo-
graphic and location surveys and aquifer pumping tests.
He is responsible for the production, marketing and
installation of the Ceomon™ Ground-Water Sampler/
Piezometer System. During this time he has been
involved in design, installation and operation of ground-
water monitoring systems throughout the U nited States
and in Europe.
A-58
-------
APPENDIX B
AN EXAMPLE PRESCRIPTIVE GROUNDWATER
SAMPLING PROTOCOL
(NO IMMISCIBLES)
WDR223/009/1
-------
SAMPLING PROCEDURES
Groundwater sample collection procedures are discussed in
several steps:
o Measurement of static water level
o Purging
o Measurement of field parameters
o Sample withdrawa]
o Decontamination
Measurement of Static Water Elevation
Measurements of static water elevations are used to
determine groundwater hydraulic gradients, which in turn are
used to predict groundwater flow directions and velocities.
Steps in the measurement process are described below.
Figure A.l is a diagram showing typical well construction
and specific well measurement points.
o All sampling team members wear new and clean
disposable gloves or thoroughly decontaminated
rubber gloves to protect team members from
exposure to potentially contaminated groundwater,
and to minimize the potential for contaminating
the sample (sampling team members are a potential
source of contamination).
o Remove the lock from the locking cap covering the
well. The measurement reference point should be
marked on the top of the protector casing below
the locking cap. The elevation of that reference
point should be established in relation to mean
sea level within an accuracy of ±0.01 foot.
o DO NOT remove the bailer from the well prior to
measuring the static water elevation.
o Place a clean, flat object across the top of the
protector casing, centered on the measurement
reference point.
o Lower a thoroughly decontaminated measurement
instrument to the water surface. A narrow steel
tape or an electric probe may be used. If a tape
is used, the bottom few feet of the tape are
chalked and lowered into the well to the
anticipated water depth so that the chalked
portion of the tape is in the water. Subtract the
measurement from the wetted portion of the chalk
from the tape reading at the flat object which is
B-1
-------
Measurement
Reference Point,
Elevation Surveyed
to! 0.01 Feet
Locking Cap
Protector Casing
Cement Grout
ry
—Bentonite
Water Table
Sandpack
Well Screen
Bottom of Well
Height of Water Column (ft) = (A to C) - (A to B)
Well Volume (gal) = Height of Water Column (ft) X Inside Area of Well (ft2) X 7.48 gallons/ft3
Figure A.1
Diagram for Static Water Elevation Measurements
B-2
-------
at the measurement reference point to determine
the distance to the water surface. Align an even
foot mark on the tape with the measurement
reference point to simplify calculations. Lower
the tape continuously to that even foot mark. If
the tape is lowered below the foot mark an
erroneous reading will result. If an electric
probe is used, it should give an audible or visual
signal (a light or a milliammeter) upon contact
with the water surface.
Record the distance from the reference point to
the water surface to the nearest 0.01 foot.
Table A.l provides conversions from inches to
decimals of a foot.
If the well has a dedicated bailer, remove the
dedicated bailer and place the rope and bailer on
a clean surface ("Dedicated" meaning that the
bailer is used for one well only, and is removed
only to collect samples.) If the bailer gets
soiled or otherwise contaminated, it should be
cleaned before it is placed back in the well. If
the rope gets dirty or contaminated, it should be
replaced with new rope constructed of inert
material (e.g., polypropylene).
Lower the measurement probe to the bottom of the
well. Record the depth to the bottom of the well
to the nearest 0.01 foot.
Remove the measurement probe, decontaminating the
probe as it is brought to the surface. The
decontamination procedure is as follows:
Saturate clean paper towel with 20 percent
methanol solution. All decontamination
solution solvents should be reagent quality
or higher. Water used to make up the
solution should be from a clean, potable
supply.
Wipe along the length of the probe,
discarding and replacing the towel as it
becomes soiled.
Rinse the rewound spool of the probe with
clean water, using a hand sprayer (household
plant spray bottles work well).
Place the measurement probe in a clean
container. The probe is ready for use at the
next well.
B-3
-------
Table A-l
INCHES CONVERTED TO DECIMALS OF A FOOT
Foot
.0O»\
.0U62
.0078
.OJCM
.0130 ,
.0156 ,
.0182 ,
.02081
.0234
.(toS60!
.0286!
.03131
.0339],
.0365
.0391
.0417
.0443 .
0169
.0406;
.05211.
,0547|
.0073
.0099 ,
.06251.
.0051
.0677.
.0703
.0729 ,
.0755
.078],
.0807
0833 .1667
0659.169*
(W85.1719
0911 .1745
0W8.1771
0964' 1797
owol.itta
1016! .1849
|042|.lfi75
0W|.1901
Oftl! .19-^7
1^.1953
1461.1979
17^ .48005
198 .2031
2M .2057
250 . 2083
276 .2109
302 . 2135
3vS6' .2161
354!.2188,
3*0 .2214!
406 .£*40
432 2266
45fl' .2292
4H4 .2iirt,
510,. 2*4-4!
536 .&170|
563 2396
589;. 2422'
615, .2448;
641 .2474
1
.2500 .3333
.2526: .3359
.2552' 3385
.257B 3411
.2604 .34^8
.2630. .3464
.2666 .3490'
.2682 .3516'
,2708
2734
.3542!
3568;
2700 .3594;
2786
2813
2839
2805
2891
2917
2943
,2969
2995
3021
3017
3073
8099
.3620]
.3646
. 3672
.3698,
.8724!
.3750
.3770
.38021
.3828
.srm;
.3880
.3906
.3932
.4167 . 5000
.4193,. 5026
.4219'.5052
.42451.5078
.4271 .5101
.4297 . 5130
.4323; .5156
.43491.5182
.4375 .5208
.4401 .5234
.4427;. 5260
.44531.5286
.4479 . 5313
4505
.4531
.4557
5339
.5365
.5391
3125 .3958
31511.39*4
31771.4010
3201'. 40%
3229!.40tU;
.32551 4089
,32H1 .4115
3307 4141
8
4
.4583 . 5417
.4609 . 5443
.4635 . 5469
.4661!.5495
,468fc!'.5521
.47141.5547
.4740!.5573
.4760! .5599
.47921.5625
4M18..5C51
.4844,.5677
,4M70;.5703
.48% .5729
.4922;. 5755
4948 . 5781
.4974 5807
6
.5833
.5859
.5885
.5911!
.5938
.59M
.5990
.60l6j
.6012
.6068.
.60941
.6120
.6146;
.6172:
.6198;
.6224;
.6250!
.6276
.6302
.6328;
.63M
.63801
.6406!
.&432I
.6458'
.64*1:
.6510
.6546
.6563
.6589
.0615
.6641
—r
,6667!.
,669:1..
,6719 .
,6745
,6771
,6797
,6823
.6849
.3875
.69011
.69271
.6953
,6979!
.7005
,7031
.7057
,7083 . 7917
.7109..7W3
,7135 . 7969
.7161!.7990
,7188 . 8021
.7214 .8047
7240 .8073
.7266 . 8099
.7292! .8125
.7118 .8151
~*44 8177
7370;. 8203
73H6 .8229
7422'.8255
7448 .8281
7474 .8307
7500
7526
7552
7578',
7604
7630,
7656.
,7682
7708'
7734
7760
7780
7813
7839
7H65
7891
8
9
10
.8333
.8359,
.8385
.8411
.8438,
.8464!
.8490
.8516
.8M2;
.8568;
.85941
.8020'
.8646!
.8672
.8098
.8724
.8750
.8776
.8802
.8828
.8851
.8880
.R90G
.8932
.8958
.8984
.9010
.9036
.9003
.9069
.9115
.9141
10
U
la.
,9167
9193
.9219
.9245
.9271
.9297
.9323
.9349
,9375
.9401
.9427
.9453
,s«79
.9505
.9531
.9557
0
1-32
1-16
8-32
1-8
5-32
8-16
7-32
1-4
9-32
6-16
11-32
3-8
13-32
7-16
15-32
9583 1-2
,9009|17-32
.9635
.9661
.968S
.9714
9-10
19-32
6-6
21-3-2
9740! 1J -1C
.9700 23-32
.9792
.9818
9tM4
S-4
5-32
3-16
.9870 27-32
.9896 7-8
.9922129-32
.9948'l5-16
.9974 ai-SJ
11
B-4
-------
Purging
Standing water should be purged from the well, allowing
formation water representative of in situ conditions to flow
into the well for sampling. Purging procedures vary
depending on the yield of the well. High yielding wells
recharge rapidly enough to be purged continuously until they
are sampled. Low yielding wells are purged intermittently
prior to sampling.
Higher yielding wells may be purged either with a pump or a
bailer. Separate purging procedures are described below:
Purging With a Pump
o Sampling team members wear either new and clean
disposable gloves, or decontaminated rubber
gloves.
o Lower the thoroughly decontaminated pump down the
well. For wells with a low volume of water in the
well, it is recommended that the same pump be used
for both purging and sampling. For large diameter
(4-inch ID or greater) and/or deep wells, a
separate, higher yield pump may benefit the
monitoring program. If a second pump is used, it
will also require decontamination between each
use.
o Calculate the volume of water in the well,
multiplying the height of the water column (depth
of the well minus the depth to the water surface)
by the inside area of the well. Figure A-l
demonstrates how to make this calculation.
Table A. 2 presents casing dimensions and volumes
for various well pipe sizes.
o Collect discharge in a graduated container for
volume measurements.
o Measure the following field parameters after each
well volume of purge water: pH, Eh, conductivity,
and temperature. These parameters are physically
or cheically unstable when groundwater is exposed
to the atmosphere, and should be measured in an
air-tight chamber connected to the discharge
tubing. A diagram of this setup is shown in
Figure A-2.
o Record field measurements on a table. A suggested
format is shown in Table A.3. Continue purging
until the following stability criteria are met.
B-5
-------
Table A-2
WELL CASING DIMENSIONS AND VOLUMES
8CM. 5
8CH 10
SCH. 80
Nominal Pipe
O.D.
1.0.
VOL.
O.D.
1.0.
VOL.
O.D.
I.D.
Vol.
Sin, Inchn
Inch
Inch
Sit/ft
Inch
huh
|al/ft
Inch
Inch
gaim
1
1.32
1.19
0.06
1.32
1.05
0.04
1.32
0.96
0.04
1.90
1.77
0.13
1.90
1.61
0.11
1.90
1.50
0.09
2
2.38
2.25
0.21
2.38
2.07
0.17
2.38
1.94
0.15
3
3.50
3.33
0.45
3.50
3.07
0.38
3.50
2.90
0.34
4
4.50
4.33
0.77
4.50
4.03
0.66
4.50
3.83
0.60
5
5.56
5.35
1.17
5.56
5.05
1.04
5.56
4.41
0.79
6
6.63
6.41
1.67
6.63
6.07
1.50
6.63
5.76
1.35
8
8.63
8.41
2.88
8.63
7.98
2.60
8.63
7.63
2.37
Conversion Formulas
3785 ml - 3.785 liters - 1 gallon 1 gallon water at 62 deg.F - 8.34 pounds
7.46 gallons ¦ 1 cubic foot 1 psi - 2.307 feet water head » 2.04 inches of mercury
B-e
-------
Conductivity Meter Thermometer
pH Meter
Eh Meter
Probes
Graduated
Container
Protector
Casing
Air-Tight
Chamber
Ground Surface
- -Well
Discharge Tubing
Pump
Figure A.2
Diagram of Field Parameter
Measurement Apparatus
B-7
-------
Table A.3
FORMAT FOR DATA TABLE FOR RECORDING GROUNDWATER FIELD PARAMETERS
Pump Pump* Pumping
Start Stop Time Volume pH Eh Conductivity Temperature
(x) (x) Time (minutes) (gallons) (units) (mv) (umhos/cm) (°C)
SB
I
Well No.: Date:
Site No.: Purge Interval: From To
Pump Depth: Sampling Team:
~Rationale for stopping the pump before the purging process
is completed should be explained on the data sheet.
WDR166/036
-------
Conductivity, temperature, and pH values vary
less than +10 percent for three consecutive
well volumes.
Eh values vary less than 50 millivolts or
+10 percent for three consecutive well
volumes, whichever is larger.
o Purged water should be disposed on the ground
surface such that the water can infiltrate. Water
should not be disposed into surface waters or the
well.
o When stability criteria are met, the pump may be
shut off temporarily in order to prepare for
sample collection.
Purging with a Bailer
o Sampling team members wear either new and clean
disposable gloves, or decontaminated rubber
gloves.
o If a dedicated bailer is already in the well, no
bailer decontamination step is required.
o If a new bailer or portable bailer ("portable"
meaning that the bailer is used for more than one
well) is used, the bailer must be decontaminated
by rinsing with a steam cleaner and/or washing the
bailer with three bailer volumes of trisodium
phosphate (TSP) solution followed by three bailer
volumes of a 20 percent methanol solution. The
outside of the bailer and cord should be
decontaminated by wiping with a clean paper towel
saturated with a 20 percent methanol solution,
then rinsed with clean water using a hand sprayer.
For the purposes of this monitoring plan, "clean
water" is defined as water transferred directly
from a drinking water supply tap to a detergent-
washed and tap-water rinsed container.
o Lower the bailer into the well. The bailer should
be lowered slowly to minimize splashing.
o Bring the bailer to the surface, emptying purge
water into a graduated bucket to measure purge
volumes. Prevent contact of the bailer and rope
with the ground surface.
o When a well volume of water is purged, empty the
bailer into a separate container and measure and
record field parameters. These measurements may
B-9
-------
be affected by exposure to the atmosphere, but
still provide the best means of determining when
representative formation water has reached the
well. Use the stability criteria described
previously (in "purging with a pump") for
determining when the purging process is complete.
Purging Low Yield Wells
Low yield monitoring wells are defined for the purpose of
this report as those that do not recharge rapidly enough to
be purged continuously. For these wells, the purging
process is as follows:
o Remove water from the well with a dedicated or a
decontaminated portable bailer until all water in
the well has been removed.
o Empty purge water into a graduated container.
o Measure and record field parameters.
o Allow the well to recharge, closing and locking
the well cap if the sampling team moves to another
location.
o If feasible, purge a second well volume from the
well, measuring and recording field parameters.
o Once the well has recharged (based on
remeasurement of the water level), remove a
sufficient volume to measure and record field
parameters. The remaining volume will be
withdrawn for samples.
Sample Withdrawal
Samples should be withdrawn either with a positive
displacement bladder pump or with a bailer. All sampling
and purging equipment should be decontaminated before they
are lowered into a monitoring well.
Sampling With a Pump
After the purging process is complete pump the water sample
directly into sample bottles bypassing the field parameter
measurements chamber. Special procedures are required for
volatile organic analysis samples and filtered samples, as
described below.
Volatile Organic Analysis Samples. The pump.discharge must
be adjusted to achieve a flow rate low enough to fill a
volatile organic analysis (VOA) vial or a total organic
B-10
-------
halide (TOX) bottle without aerating the sample. If the
flow cannot be adequately controlled, VOA and TOX samples
should be collected with a bailer, as described below.
Invert filled VOA vials and TOX bottles and check for air
bubbles. Discard the sample and refill if any air bubbles
are present.
Filtering Samples. When sampling for dissolved metal
constituents, samples should be filtered prior to
preservation. To filter samples, attach the pump discharge
tubing to the inlet side of a filtering apparatus.
Discharge from the filter should flow directly into the
appropriate sample container.
Sampling With a Bailer
o Lower the bailer slowly through the water column;
avoid aeration or agitation.
o Withdraw the bailer slowly; keep the bailer rope
clean.
o Pour the sample slowly into sample jars, filling
to the proper volume. Check VOA vials for air
bubbles and refill if any air bubbles are present.
Filtering Bailed Samples. When a bailer is used to collect
a samplej pour the sample into a clean container and use a
small pump to transfer the sample from the container through
the filter and into the sample jar. A hand-powered or small
electric pump is recommended. The transfer pump should be
decontaminated between each use.
Decontamination
This discussion on decontamination applies to portable
sampling equipiment that is used at more than one well or
sampling location. This equipment must be thoroughly
cleaned prior to taking each sample to minimize the
potential for the sampling equipment to be a source of
contamination.
Decontamination requirements are reduced for dedicated or
single-use disposable sampling equipment. Dedicated or
disposable equipment should be handled in such a way that it
does not come into contact with dirty and potentially
contaminated surfaces (including the sampling team members'
hands). If dedicated equipment does come into contact with
potentially contaminated surfaces, it should be cleaned
using the decontamination procedures outlined for portable
equipment. If the dedicated apparatus is difficult to
decontaminate (such as a bailer rope), it should be
replaced.
B-11
-------
Decontamination of Pumps
o Sampling team members wear new and clean
disposable gloves or decontaminated rubber gloves.
o While withdrawing the tubing and pump from the
well, decontaminate the exterior of tubing by
spraying with a trisodium phosphate (TSP) solution
and wiping with clean paper towel saturated with a
20 percent methanol solution. Once all of the
tubing has been removed from the well, cleaned,
and wound onto a spool, rinse the tubing with
clean water from a sprayer.
o Decontaminate the exterior of the pump by spraying
with the 20 percent methanol solution.
o Place the pump (with the exterior now cleaned)
into a decontamination tube consisting of a
section of PVC pipe with a water-tight cap on the
bottom. The decontamination tube should be
approximately 2 feet longer than the pump.
o Fill the decontamination tube with a TSP solution
and turn on the pump. While pumping, add a total
of 2 gallons of TSP solution followed by 2 gallons
of methanol solution into the tube. Discharge
water should be allowed to infiltrate into the
soil away from the well. When the pump is no
longer discharging any solution, turn the pump
off. Store the pump in the decontamination tube
until it is ready to be placed in the next well.
The tube should be occasionally rinsed to keep it
clean.
Note: Storing the pump in the decontamination
tube for extended periods of time (e.g., between
seasonal sampling events) may deteriorate the pump
unless the tube is thoroughly dried.
Decontamination of Bailers
Dedicated bailers do not need to be decontaminated if
sampling team members wear clean gloves and the equipment is
only in contact with,clean surfaces. New and clean plastic
bags or plastic sheeting are suitable for placing dedicated
sampling equipment in or on once that equipment has been
removed from the well. This plastic should not be reused at
another well unless it is decontaminated.
For portable bailers, the bailer should be filled and
drained twice with TSP solution; then filled and drained
twice with a 20 percent methanol solution. The exterior and
B-12
-------
interior of the bailer should be cleaned with the methanol
solution, wiped with a clean towel, then rinsed with clean
water.
Decontamination of Filtration Apparatus
o Sampling team members wear new and clean
disposable gloves or decontaminated rubber gloves.
o Disassemble filtration apparatus, discarding any
disposable filters, prefilters, etc.
o Spray all interior surfaces of the filtration
apparatus with a TSP solution followed by a
methanol solution, placing all parts on a clean
surface.
o Reassemble filtration apparatus with filters in
place.
o Store the filtration apparatus in a clean
container, ready for use at the next site.
Note: Single-use disposable filter apparatus with self-
contained filters are available through sampling
equipment manufacturers. These are connected directly
to the pump discharge tube and disposed after each
sample.
SAMPLING EQUIPMENT
A combination of proper sampling procedures and sampling
equipment is necessary to collect groundwater samples that
are representative of actual conditions in the field. A
positive-displacement bladder pump is recommended for
collecting groundwater samples. Other groundwater sampling
mechanisms have a greater potential for altering the in-situ
chemistry of the groundwater. Positive-displacement bladder
pumps typically pump at a rate between 0.25 and 1.5 gallons
per minute (gpm). Table A.4 contains general recommendations
for groundwater sampling mechanisms.
The pump, as well as other tools and instruments lowered
into the well, should be constructed from inert materials
which will minimize chemical alteration, microbial
colonization, sorption effects, or leaching effects.
Recommendations for rigid and flexible materials in sampling
applications are provided in Tables A.5 and A.6 respectively.
WDR223/010
B-1 3
-------
Table A.4
PERFORMANCE EVALUATION OF GROUNDWATER SAMPLING MECHANISMS
Mechanism Category
Overall
Performance Ranking
Remarks.
Positive displacement
(bladder)
Above average Expected to provide both efficient well
purging and representative samples
over a range of conditions with minimal
difficulty in field operations.
Grab samplers
(conventional bailer)
(dual-check valve bailer)
(syringe pump)
Average
Average
Average—below average
Unsuitable for well purging; requires
very careful operation and sample
handling precautions under field
conditions; field performance open to
question.
Positive displacement
(mechanical)
Average—below average
Suitable for well purging; sampling
performance very dependent on specific
design and operational details.
Gas displacement
(gas drive; not gas lift)
Average—below average
May be suitable for well purging if used
in conventional installations; malfunc-
tions are difficult to assess or repair;
significantly lower recoveries of purge-
able organic compounds and gases may
occur depending on field conditions and
operator experience.
Suction (peristaltic)
Below average Suitable for well purging at depths to
approximately 20 feet; significantly
lower recoveries of purgeable organic
compounds and gases will result from '
sampling with this mechanism.
Reference: Practical Guide for Ground-Water Sampling, Illinois State Water Survey,
ISWS Contract Report 374. 1985.
WDR223/011
B-14
-------
Table A.5
RECOMMENDATIONS FOR RIGID MATERIALS IN SAMPLING APPLICATIONS
(In decreasing order of preference)
Material Recommendations
Teflon Recommended for most monitoring situations
(flush threaded) with detailed organic analytical needs,
particularly for aggressive, organic leach-
ate impacted hydrogeologic conditions.
Virtually an ideal material for corrosive
situations where inorganic contaminants
are of interest.
Recommended for most monitoring situations
with detailed organic analytical needs,
particularly for aggressive, organic
leachate impacted hydrogeologic conditions.
May be prone to slow pitting corrosion in
contact with acidic high total dissolved
solids aqueous solutions. Corrosion
products limited mainly to Fe and possibly
Cr and Ni.
Recommended for limited monitoring situa-
tions where inorganic contaminants are of
interest and it is known that aggressive
organic leachate mixtures will not be
contacted. Cemented installations have
caused documented interferences. The
potential for interaction and interfer-
ences from PVC well casing in contact
with aggressive aqueous organic mixtures
is difficult to predict. PVC is not
recommended for detailed organic
analytical schemes.
Recommended for monitoring inorganic
contaminants in corrosive, acidic in-
organic situations. May release Sn or Sb
compounds from the original heat stabil-
izers in the formulation after long
exposures.
May be superior to PVC for exposures to
aggressive aqueous organic mixtures.
These materials must be very carefully
cleaned to remove oily manufacturing
residues. Corrosion is likely in high
dissolved solids acidic environments,
particularly when sulfides are present.
Products of corrosion are mainly Fe and
Mn, except for galvanized steel which
may release Zn and Cd. Weathered steel
surfaces present very active adsorption
sites for trace organic and inorganic
chemical species.
~National Sanitation Foundation approved materials carry the NSF logo
indicative of the product's certification based on meeting industry
standards for performance and formulation purity.
Reference: Practical Guide for Ground-Water Sampling. Illinois State
Water Survey, ISWS Contract Report 374. 1985.
WDR223/012/1
B-15
Stainless Steel 316
(flush threaded)
Stainless Steel 304
(flush threaded)
PVC
(flush threaded)
other noncemented connections,
only NSF* approved materials
for well casing or potable
water applications
Low-Carbon Steel
Galvanized Steel
Carbon Steel
-------
Table A. 6
RECOMMENDATIONS FOR FLEXIBLE MATERIALS IN SAMPLING APPLICATIONS
(In decreasing order of preference)
Material Recommendations
Teflon Recommended for most monitoring work, par-
ticularly for detailed organic analytical
schemes. The material least likely to
introduce significant sampling bias or im-
precision. The easiest material to clean
in order to prevent cross-contamination.
Strongly recommended for corrosive high
dissolved solids solutions. Less likely to
introduce significant bias into analytical
results than polymer formulations (PVC) or
other flexible materials with the exception
of Teflon.
PVC (flexible) Not recommended for detailed organic ana-
lytical schemes. Plasticizers and stabil-
izers make up a sizable percentage of the
material by weight as long as it remains
flexible. Documented interferences are
likely with several priority pollutant
classes.
Flexible elastomeric materials for gaskets,
O-rings, bladder and tubing applications.
Performance expected to be a function of
exposure type and the order of chemical
resistance as shown. Recommended only when
a more suitable material is not available for
the specific use. Actual controlled expo-
sure trials may be useful in assessing the
potential for analytical bias.
Reference: Practical Guide for Ground-Water Sampling. Illinois State
Water Survey, ISWS Contract Report 374. 1985.
Polypropylene
Polyethylene (linear)
Viton
Silicone
(medical grade only)
WDR223/012/2
B-16
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Table A.7
PROCEDURE CHECKLIST FOR GROUNDWATER SAMPLING
Procedure
Pre-Sampling Preparations
1. Prepare sample bottles with proper preservatives
and coordinate schedule with the laboratory.
2. Prepare Site Safety Plan.
3. Collect equipment needed for all tasks (see
equipment checklist).
Sampling Procedures
4. Unlock well.
5. Perform air monitoring as required by Site Safety
Plan.
6. Measure and record water level in well.
7. Measure and record depth of well.
8. Decontaminate water level measuring equipment.
9. Set up to purge well with either pump or bailer.
10. Purge well until parameters are stabilized.
11. Decontaminate purging equipment if necessary.
12. Set up to collect water samples including any
blanks and duplicates.
13. Collect samples and filter if necessary.
14. Decontaminate water sampling equipment.
15. Close and lock well.
16. Move to next sampling location.
17. Prepare samples for shipping to laboratory at the
end of the day.
WDR223/013/1
B-17
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Table A.8
EQUIPMENT CHECKLIST FOR GROUNDWATER SAMPLING
Equipment
1.
Key to well locks
2.
Disposable or rubber gloves
3.
Health and safety equipment required by Site
Safety Plan
4.
Water level measurement device
5.
Logbook and permanent marker
6.
Tape measure or wooden rule
7.
Hand sprayer with clean water
8.
Hand sprayer with 20 percent methanol solution
9.
Paper towels
10.
Plastic garbage bags
11.
Groundwater purge and sampling pump with tubing
and power source
12.
Graduated bucket
13.
pH meter with probe and calibration buffer
solutions
14.
Eh meter with probe
15.
Conductivity meter with probe
16.
Thermometer
17.
Air-tight chamber for field parameter measurement
18.
Sample jars (with preservatives already in them,
as appropriate)
19.
Filter apparatus
20.
PVC decontamination tube for pump with stand
21.
Bailer, and rope
22.
TSP
23.
Twenty percent (20%) methanol solution
24.
Chain-of-custody forms
25.
Coolers with ice to store collected samples
WDR223/013/2
B-18
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APPENDIX C
EXCERPT OF THE RCRA GROUND-WATER MONITORING
TECHNICAL ENFORCEMENT GUIDANCE DOCUMENT (1986)
WDR223/009/2 /"
( n . , 7
-------
SAMPLING AND ANALYSIS WORKSHEET
The following worksheets have been designed to assist the enforcement
officer in evaluating the techniques an owner/operator uses to collect and
analyze ground-water samples. This series of worksheets has been compiled
based on the information provided in Chapter 4 of the TEGD.
I. Review of Sample Collection Procedures
A. Measurement of well depths elevation:
1. Are measurements of both depth to standing water
and depth to the bottom of the well made? (Y/N)_
2. Are measurements taken to the nearest centimeter
or 0.01 foot? (Y/N)_
3. What device is used?
4. Is there a reference point(s) established by a
licensed surveyor? (Y/N)_
B. Detection of immiscible layers:
1. Are procedures used which will detect light phase
immiscible layers? (Y/N)_
2. Are procedures used which will detect dense phase
immiscible layers? (Y/N)_
C. Sampling of immiscible layers:
1. Are the immiscible layers sampled separately prior to
well evacuation? (Y/N)_
2. Do the procedures used minimize mixing
with water soluble phase? (Y/N}_
D. Well evacuation:
1. Are low yielding wells evacuated to dryness? (Y/N)_
2. Are high yielding wells evacuated so that at least
three casing volumes are removed? (Y/N)
3. What device is used to evacuate the wells?
4. If any problems are encountered (e.g., equipment
malfunction) are they noted in a field logbook? (Y/N)
E. Sample withdrawal:
1. For low-yielding wells, are first samples tested for
pH, temperature, and specific conductance after the
well recovers? (Y/N)
C-1
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OSWER-9950.1
2. Are samples collected and containerized in order of
the parameters volatilization sensitivity? (Y/N)_
3. For higher-yielding wells, are samples retested for
pH, temperature, and specific conductance to determine
purging efficiency? (Y/N)_
4. Are samples withdrawn with either fluorocarbon resins
or stainless steel (304, 316, 2205) sampling devices? (Y/N)_
5. Are sampling devices either bottom valve bailers
or positive gas displacement bladder pumps? (Y/N)_
6. If bailers are used, is fluorocarbon resin-coated wire,
single strand stainless steel wire, or monofilament
used to raise and lower the bailer? (Y/N)_
7. If bladder pumps are used, are they operated in a
continuous manner to prevent aeration of the sample? (Y/N)_
8. If bailers are used, are they lowered slowly to
prevent degassing of the water? (Y/N)_
9. If bailers are used, are the contents transferred
to the sample container in a way that will minimize
agitation and aeration? (Y/N}_
Is care taken to avoid placing clean sampling equipment
on the ground or other contaminated surfaces prior to
insertion into the well? (Y/N)_
If dedicated sampling equipment is not used, is
equipment disassembled and thoroughly cleaned between
samples? (Y/N)_
If samples are for inorganic analysis, does the clean-
ing procedure include the following sequential steps:
a. Nonphosphate detergent wash? (Y/N)_
b. Dilute acid rinse (HNO3 or HC1)? (Y/N)_
c. Tap water rinse? (Y/N)_
d. Type II reagent grade water? (Y/N)_
13. If samples are for organic analysis, does the cleaning
procedure include the following sequential steps:
a. Nonphosphate detergent wash? (Y/N)_
b. Tap water rinse? (Y/N)_
c. Distilled/deionized water rinse? (Y/N)_
d. Acetone rinse? (Y/N)_
e. Pesticide-grade hexane rinse? (Y/N)_
Is sampling equipment thoroughly dry before use? (Y/N)_
Are equipment blanks taken to ensure that sample
cross-contamination has not occurred? (Y/N)
If volatile samples are taken with a positive gas
displacement bladder pump, are pumping rates below
100 ml/min? (Y/N)
10.
11.
12.
14.
15.
16.
C-2
-------
F. In-situ or field analyses:
1. Are the following labile (chemically unstable) parameters
determined in the field:
a.
pH?
(Y/N)
b.
Temperature?
(Y/N)
c.
Specific conductivity?
(Y/N)
d.
Redox potential?
(Y/N)
e.
Chlorine?
(Y/N)
f.
Dissolved oxygen?
(Y/N)
9-
Turbidity?
(Y/N)
h.
Other (specify)
For
in-situ determinations, are they made after well
evacuation and sample removal? (Y/N)_
3. If sample is withdrawn from the well, is parameter
measured from a split portion? (Y/N)
4. Is monitoring equipment calibrated according to
manufacturers' specifications and consistent with
SW-846? (Y/N)
5. Is the date, procedure, and maintenance for equipment
calibration documented in the field logbook? (Y/N)
II. Review of Sample Preservation and Handling Procedures
A. Sample containers:
1. Are samples transferred from the sampling device
directly to their compatible containers? (Y/N)_
2. Are sample containers for metals (inorganics) analyses
polyethylene with polypropylene caps? (Y/N)_
3. Are sample containers for organics analysis glass
bottles with fluorocarbon resin-lined caps? (Y/N)_
4. If glass bottles are used for metals samples are
the caps fluorocarbon resin-lined? (Y/N)_
5. Are the sample containers for metal analyses cleaned
using these sequential steps?
a. Nonphosphate detergent wash? (Y/N)_
b. 1:1 nitric acid rinse? (Y/N)_
c. Tap water rinse? (Y/N)_
d. 1:1 hydrochloric acid rinse? (Y/N)_
e. Tap water rinse? (Y/N)_
f. Type II reagent grade water rinse? (Y/N)_
6. Are the sample containers for organic analyses cleaned
using these sequential steps?
a. Nonphosphate detergent/hot water wash? (Y/N)
b. Tap water rinse? (Y/N)
c. Distilled/deionized water rinse? (Y/N)
d. Acetone rinse? (Y/N)
e. Pesticide-grade hexane rinse? (Y/N)
C-3
-------
OSWER-9950.1
7. Are trip blanks used for each sample container type
to verify cleanliness? (Y/N)_
B. Sample preservation procedures:
1. Are samples for the following analyses cooled to 4°C:
a. TOC? (Y/N)_
b. TOX? (Y/N)_
c. Chloride? (Y/N)_
d. Phenols? (Y/N)_
e. Sulfate? (Y/N)
f. Nitrate? (Y/N).
g. Pesticides/Herbicides? (Y/N)
h. Coliform bacteria? (Y/N)
i. Cyanide? (Y/N)
j. Oil and grease? (Y/N)
k.. Volatile, semi-volatile, and nonvolatile organics? (Y/N)
2. Are samples for the following analyses field acidified to
pH <2 with HN03:
a. Iron? (Y/N)
b. Manganese? (Y/N)
c. Sodium? (Y/N)
d. Total metals? (Y/N)
e. Dissolved metals? (Y/N)
f. Radium? (Y/N)
g. Gross alpha? (Y/N)
h. Gross beta? (Y/N)
3. Are samples for the following analyses field acidified
to pH <2 with H2SO4:
a. Phenols? (Y/N)
b. Oil and grease? (Y/N)
4. Is the sample for TOC analyses field acidified to
pH <2 with H2S04 or HC1? (Y/N)
5. Is the sample for TOX analysis preserved with
1 ml of 1.1 M sodium sulfite? (Y/N)
6. Is the sample for cyanide analysis preserved with
NaOH to pH >12? (Y/N)
7. Are pesticides pH adjusted to between 6 and 8 with
NaOH or H2S04? (Y/N)
C. Special handling considerations:
1. Are organic samples handled without filtering? (Y/N)
2. Are samples for volatile organics transferred to
the appropriate vials to eliminate headspace over
the sample? (Y/N)
3. Are samples for metal analysis split into two
portions? (Y/N)
4. Is the sample for dissolved metals filtered
through a 0.45 micron filter? (Y/N)
C-4
-------
5. Is the second portion not filtered and analyzed
for total metals? (Y/N)
6. Is one equipment blank prepared each day of
ground-water sampling? (Y/N)
III. Review of Analytical Procedures
A. Laboratory analysis procedures:
1. Are all samples analyzed using an EPA-approved
method (SW-846)? (Y/N)_
2. Are appropriate QA/QC measures used in laboratory
analysis (e.g., blanks, spikes, standards)? (Y/N)_
3. Are detection limits and percent recovery (if
applicable) provided for each parameter? (Y/N)_
4. If a new analytical method or laboratory is used,
are split samples run for comparison purposes? (Y/N)_
5. Are samples analyzed within specified holding
times? (Y/N)
B. Laboratory logbook:
1. Is a laboratory logbook maintained? (Y/N)_
2. Are experimental conditions (e.g., temperature,
humidity, etc.) noted? (Y/N)_
3. If a sample for volatile analysis is received
with headspace, is this noted? (Y/N)
4. Are the results for all QC samples identified? (Y/N)
5. Is the time, date, and name of person noted
for each processing step? (Y/N)
IV. Review of Chain-of-Custody Procedures
A. Sample labels:
1. Are sample labels used? (Y/N)_
2. Do they provide the following information:
a. Sample identification number? (Y/N)_
b. Name of collector? (Y/N)_
c. Date and time of collection? (Y/N)_
d. Place of collection? (Y/N)_
e. Parameter(s) requested: (Y/N)_
3. Do they remain legible even if wet? (Y/N)_
B. Sample seals:
1. Are sample seals placed on those containers to
ensure the samples are not altered? (Y/N)
C-6
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APPENDIX D
EXCERPT OF THE RCRA GROUND-WATER MONITORING
COMPLIANCE ORDER GUIDANCE (1985)
WDF2 2 3/009/3
-------
Examples of Basic
Elements Required
by Performance
Standards
Examples of Technical
Inadequacies that may
Constitute Violations
Regulatory
Citations
7. Samples from
background and down-
gradient wells must be
properly collected and
analyzed
failure to evacuate stagnant water
from the well before sampling
failure to sample wells within a
reasonable amount of time after
wall evacuation
improper decisions regarding
filtering or non-filtering of samples
prior to analysis (e.g., use of filtra-
tion on samples to be analyzed
for volatile organics)
use of an inappropriate sampling
device
use of improper sample preserva-
tion techniques
samples collected with a device
that is constructed of materials
that interfere with sample integrity
samples collected with a non-
dedicated sampling device that is
not cleaned between sampling
events
improper use of a sampling
device such that sample quality is
affected (e.g., degassing of sam-
ple caused by agitation of bailer)
§265.90(a)
§265.92(a)
§265.93(d)(4)
§270.14(c)(4)
§265.90(a)
§265.92(a)
§265.93(dX4)
§270.14(c)(4)
§265.90(a)
§265.92(a)
§265.93(dK4)
§270.14(C)(4)
§265.90(a)
§265.92(a)
§265.93(d)(4)
§270.14(c)(4)
§265.90(a)
§265.92(a)
§265.93(d)(4)
§270.14(c)(4)
§265.90(a)
§265.92(a)
§265.93(dK4)
§270.14(c)(4)
§265.90(a)
§265.92(a)
§265.93(dX4)
§270.14(c)(4)
§265.90(a)
§265.92(a)
§265.93(d)(4)
§270.14(c)(4)
D-1
-------
Examples of Basic
Elements Required
by Performance
Standards
Examples of Technical
Inadequacies that may
Constitute Violations
Regulatory
Citations
Samples from background
and downgradient wells
must be properly collected
and analyzed (continued)
• improper handling of samples
(e.g.. failure to eliminate
headspace from containers of
samples to be analyzed for
volatiles)
§265.90(a)
§265.92(a)
§265.93
-------
Examples of Basic
Elements Required
by Performance
Standards
Examples of Technical
Inadequacies that may
Constitute Violations
Regulatory
Citations
8. In Part 265 assessment
monitoring the 0/0 must
sample for the correct
substances
o failure of the 0/0's list of sam-
pling parameters to include cer-
tain wastes that are listed in
§261.24 or §261.33, unless ade-
quate justification is provided
§265.93(dX4)
• failure of the 0/0's list of sam-
pling parameters to include
Appendix VII constituents of all
wastes listed under §§261.31 and
261.32, unless adequate justifica-
tion is provided
§265.93(0X4)
9. In defining the Appendix
• failure of the 0/0's list of sam-
§270.14(cX4)
VIII makeup of a plume the
0/0 must sample for the
correct substances
10. In Part 265 assessment
monitoring and in defining
the Appendix VIII makeup of
a plume the 0/0 must use
appropriate sampling
methodologies
11. Part B applicants who
have either detected con-
tamination or failed to imple-
ment an adequate part 265
GWM program must deter-
mine with confidence
whether a plume exists and
must characterize any
plume
piing< parameters to include all
Appendix VIII constituents, unless
adequate justification is provided
« failure of sampling effort to iden- §265.93(dX4)
tify areas outside the plume §270.l4(cX4)
• number of wells was insufficient §265.93(dX4)
to determine vertical and horizon- §270.i4{cX4)
tal gradients in contaminant
concentrations
• total reliance on indirect methods §265.93(d)(4)
to characterize plume (e.g., elec- §270.14(c)(4)
tncal resistivity, borehole
geophysics)
® failure of 0/0 to implement a §270.14(cX4)
monitoring program that is
capable of detecting the existence
of any plume that might emanate
from the facility
• failure of 0/0 to sample both §270.14(c)(4)
upgradient and downgradient
wells for all Appendix VIII
constituents
See also items #1, 82
D-3
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