OlAf f\fe*} United States Office of Solid Waste
^> Iflf •VI f\ .^ Environmental Protection and Emergency Response • SW-963
vwv Agency Washington DC 20460 October 1982
Solid Waste
Ground-Water Monitoring
Guidance for Owners
and Operators of Interim
Status Facilities
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GROUND-WATER MONITORING
GUIDANCE FOR OWNERS
AND OPERATORS OF INTERIM STATUS
FACILITIES
Instructions for Complying with 40 CFR Part 265, Subpart F
[OMB Clearance No. 2000-0423]
U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boufevard, 12th Floor
Crticago. /L 60604-3590
U.S. Environmental Protection Agency
Washington, D.C.
1982
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Preface
This guidance document represents the Agency's interpreta-
tion of the ground-water monitoring requirements imposed upon
hazardous waste management facilities which have achieved
interim status in accordance with Section 3005(e) of the Resource
Conservation and Recovery Act. The bases of this document
are, therefore, regulations in 40 CFR Part 265, Subpart F, as
promulgated on May 19, 1980, as amended on January 11, 1982.
This document is meant to be used by the regulated community
in implementing these requirements as they pertain to the
particular circumstances. In no way is this document to be
used as a regulation or as an amendment to existing regulations.
It is meant only to offer assistance to owners or operators of
interim status facilities as to possible means of compliance with
Subpart F.
This is a first edition guidance document. Readers are
encouraged to communicate with EPA Regional Office representa-
tives or with George Dixon (OSWER, Headquarters), any comments,
reactions and criticisms stemming from the use of the document.
This document will, of necessity, be periodically revised
to accurately reflect 40 CFR Part 265, Subpart F. In its
continuing efforts to improve all its regulations the Agency
has embarked upon several activities which upon their completion
m=»y lead to regulatory amendments. Specific to these ground-water
nonitoring requirements are two evaluation efforts which will
likely result in amendments to Subpart F and revisions to this
guidance document.
The first of these efforts is the Ground-water Monitoring
Evaluation Project. This effort involves a survey of a
statistically valid sample of interim status hazardous waste
land disposal facilities to determine the current level of
compliance with the Subpart F requirements. This survey will
establish a profile of the facilities utilizing detection
versus assessment monitoring schemes, those claiming a full or
partial waiver of ground-water monitoring requirements, and an
estimate of the number of facilities not in compliance. This
prraluation will also identify those regulatory provisions
causing compliance difficulties as a result of either
inappropriate or misunderstood requirements.
The second evaluation effort is an analysis of the
statistical comparison procedure specified in §265.93. Under
this effort the Agency will obtain background ground-water
quality data for indicator parameters from interim status
facilities across the country to establish distributions of
the concentrations of these parameters over time. With this
L',3. Envlrcr
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information on actual ground-water quality the Agency will be
able to estimate the number of facilties for which the specified
statistical comparison procedure is appropriate and further to
identify alternative data evaluation and comparison procedures
for those situations where the procedures specified in §265.93
may not be appropriate. A principle component of this evaluation
will be an estimate of the "false positive" and "false
negative" probabilities for various statistical procedures in
various circumstances of ground-water quality variability over
time.
If and when 40 CFR Part 265, Subpart F, is amended as a
result of these and other studies and evaluations, this document
will be appropriately revised.
111
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Table of Contents
Ground-Water Monitoring in Interim Status
Page
Preface. ii
List of Appendices vii
List of Figures viii
List of Tables ix
1.0 Overview 1
1.1 Purpose and Applicability of the Monitoring
Requirements 3
1.2 The Regulations and the Agency's Intent 4
1.3 Program Implementation. 13
1.3.1 Complying with the Regulation: How
Much is Enough? 15
1.3.2 Interaction with the Agency 18
2.0 Detection Program 20
2.1 Description 20
2.2 Ground-Water Monitoring Well Location 20
2.2.1 Obtaining Hydrogeological Information 21
2.2.2 How to Use Hydrogeologic Information In
Planning The Monitoring System 26
2.2.3 Location and Number of Monitoring Wells 35
2.2.4 Monitoring Well Depth 39
2.3 Design and Installation of Monitoring Wells 43
2.3.1 Design and Planning Factors 43
2.3.2 Well Construction 46
IV
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Page
2.4 Sampling and Analysis 54
2.4.1 Sampling and Analysis Plans 55
2.4.2 Sample Collection 55
2.4.3 Sample Preservation 59
2.4.4 Sample Shipment 59
2.4.5 Analytical Procedures 60
2.4.6 Coordination Between Sample Collector
and Laboratory 64
2.4.7 Field Log Book 64
2.4.8 Chain of Custody Control 66
2.4.9 Laboratory Selection 66
2. 5 Program Implementation 69
2.5.1 Sampling Schedule 69
2.5.2 Statistical Analysis 71
2.5.3 Recordkeeping and Reporting 81
2.6 Waiver Demonstration.. 83
2.6.1 Determining Potential for Contaminant
Migration from Facility to Uppermost
Aquifer 85
2.6.2 Determining Potential for Contaminant
Migration Through Uppermost Aquifer
to Water Supply Wells or Surface
Water 98
2.6.3 Documentation 106
3.0 Assessment Program 107
3.1 Description 107
3.2 Determining Rate of Contaminant Migration 109
3.2.1 Use of Darcy-Based Equation 109
3.2.2 Use of Tracers 114
3.3 Determining Extent of Contamination 116
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Page
3.3.1 Indirect Techniques 118
3.3.2 Direct Techniques , 129
3.4 Determining Concentrations of Contaminants 133
3.4.1 Simple Case Determinations , 134
3.4.2 Complex Case Determinations 136
3.5 Case Studies 137
3.6 Recordkeeping and Reporting 140
REFERENCES 142
APPENDICES 146
VI
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List of Appendices
Page
A. Interim Status Ground-Water Monitoring Regulations....
(includes January 11, 1982 amendment)
B. USGS Information Contacts 151
C. EPA Interim Primary Drinking Water Standards 161
D. Total Organic Halide, Adapted from Method
4 50.1-Interim 162
vii
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List of Figures
Page
2-1 Typical Hydrograph 31
2-2 Hydrogeologic Cross Section 32
2-3 Flow Net 34
2-4 Ground-water Flow Patterns 37
2-5 Localize Discharge from a Facility 40
2-6 Significance of Facility Orientation 41
2-7 Typical Well Casing Design 45
2-8 Well Cluster Concept 47
2-9 Typical Monitoring Well Profile 48
2-10 Well Development/Filter Packing 51
2-11 Example of Monitoring Well Installation 53
2-12 Teflon Bailer for Ground-water Sampling 58
2-13 Example of Sample Chain of Custody Form 67
2-14 Example of Sample Analysis Request Form 68
2-15 Minimum Sampling Frequency Required for
the Detection Program 70
2-16 Example of Monthly Precipitation Records 88
3-1 Electromagnetic Conductivity Responses
Recorded on a Portable Strip Chart Recorder 123
3-2 How Electrical Resistivity Surveys Can
Lower Drilling Costs 125
3-3 Isoresistivity Map of Contaminated Zone 127
3-4 Borehole/Monitoring Well Plan for
Determining Extent of Contamination 131
Vlll
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List of Tables
Page
2-1 Sources of Hydrogeologic Information 22
2-2 Methods Used to Identify the Uppermost Aquifer and
Hydraulic Gradient 24
2-3 Analytical References 61-62
2-4 The Critical t-values at the 0.01 and 0.005 Levels
of Significance 77
2-5 Data Requirements to be Considered for a Predictive
Ground-Water Flow Model 101
IX
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GROUND-WATER MONITORING GUIDANCE FOR OWNERS AND
OPERATORS OF INTERIM STATUS FACILITIES
1.0 Overview
This Manual provides guidance for owners and operators of
hazardous waste land disposal facilities in complying with the
interim status requirements for ground-water quality monitoring
in Subpart F of 40 CFR 265, (45 Fed. Reg. 33239 et seq., May
19, 1980) (see Appendix A). These regulations require owners
and operators to design and implement either a detection program
at facilities not known or assumed to be significantly affecting
ground-water quality or an assessment program for quantifying
the ground water quality effects which have occurred. Owners
or operators who assumed that ground water has been affected
by the facility were provided an opportunity waive the detection
program. In this case, they may enter directly into the
assessment program, quantifying the extent of contamination
and the rate of migration.
While these interim status monitoring programs will
provide the Agency with some useful information regarding the
national, regional, or industry-specific impacts of disposal
on ground-water quality, the primary Agency objective is to
provide specific information regarding individual facilities.
In order to lessen the initial burden, a very simple detection
program was devised for universal application, with diagnostic
investigations performed only at those facilities which are
indicated in the detection program to have significantly
affected ground water. This manual discusses the objectives
of the programs, the regulatory language and the Agency's
associated intent, and required monitoring systems, analyses
and reporting.
The guidance in this manual is applicable to EPA-
administered programs. States are encouraged to develop and
administer their own programs, and in accordance with RCRA
Section 3006, the Agency will authorize them in lieu of the
Federal program. Approved State programs may differ in style
and procedure in pursuit of their "substantially" equivalent
control. This manual is not necessarily applicable in such
States. Owners and operators are advised to consult their EPA
Regional Administrators, listed below if they are uncertain
about the status of particular State programs.
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EPA Regional Administrators
Region I
John F. Kennedy Bldg.
Boston, MA 02203
Region II
26 Federal Plaza
New York, NY 10007
Region III
6th& Walnut Streets
Philadelphia, PA 19106
Region IV
345 Courtland St., N. E.
Atlanta, GA 30365
Region V
230 South Dearborn Street
Chicago, IL 60604
Region VI
1201 Elm Street
First Intl. Building
Dallas, TX 75270
Region VII
324 E. llth
Kansas City,
Region VIII
1860 Lincoln
Denver, CO
Street
MO 64106
Street
80203
Region IX
215 Fremont Street
San Francisco, CA 94105
Region X
1200 6th Avenue
Seattle, WA 98101
The first Section of the manual discusses the purpose and
scope of ground-water monitoring requirements, presenting the
rationale and the policy issues for a better understanding on
the part of the owner or operator. The regulations are
presented, followed by commentary regarding selection of words
and the intent. The Agency's current thinking regarding the
value of interim status monitoring in eventual decisions on
facility permits is discussed. Content and format of the
required plans and schedules are discussed in this section,
followed by methods for updating and revising ongoing programs,
and the Agency's view of interaction with owners and operators
during interim status. Section 2 of this report will discuss
in detail the detection program, identifying informational
needs for ground-water monitoring well location and design,
methodology for sampling, analyses, recordkeeping, reporting,
and other specific implementation issues. Section 3 is devoted
to the assessment program.
This report is written with the assumption that the reader
has read and is thoroughly familiar with the preamble to
Subpart F of the Interim Status Standards. The pertinent
section begins at 45 FR 33191-May 19, 1980. Readers are
also referred to the Background Document accompanying the
regulation, dated May 2, 1980, which is available for viewing
in the Docket Room, Room S-269-C, Waterside Mall, 401 M Street
S.W., Washington, D.C., 20460, or at EPA Regional Libraries.
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1,1 Purpose and Applicability of the Monitoring Requirements
The purpose of any monitoring program is to provide
information. The ground-water quality monitoring program of
Part 265, Subpart F is designed to provide a preliminary
indication of the impacts of a newly regulated group of
facilities. About 4500 hazardous waste land disposal facilities,
all in existence as of November 19, 1980, the effective date
of the regulations, qualified for interim status under RCRA.
They comprise facilities of widely differing ages and degrees
of sophistication. Some have had thorough state regulatory
review, others only cursory. At present, estimates vary widely
regarding the numbers of these facilities which are currently
affecting ground-water quality. The scope of Subpart F includes
determining the drinking suitability and general quality of
aquifers underlying these facilities. It includes detection
of discharge to these aquifers where it is not known or assumed,
and quantification where it is. It also includes establishment
of the fact of "low potential for migration" from those facilities
to supply wells or surface water.
The purpose of ground-water monitoring as established in
the regulations is to discover the existence and magnitude of
ground-water impacts from hazardous waste land disposal
facilities. The purpose does not include determinations of
whether or not such facilities are environmentally acceptable.
Acceptability criteria will be developed as part of the permitting
process.
The Agency's first-level, or immediate, objective is to
determine which land disposal facilities have leaked hazardous
waste or constituents into an underlying aquifer in sufficient
quantities to cause a significant change in ground-water quality.
The second-level objective is to acquire information at
those facilities regarding the extent and nature of the ground-
water impact to provide a factual basis for decisions regarding
the need for changes in design or operation or for corrective
action.
The interim status ground-water monitoring requirements
were not specifically designed to produce evidence for enforce-
ment proceedings, nor are the programs designed to produce
statistically significant national indications of the relative
ground-water quality impact of different types of hazardous
waste management facilities. To the extent that information
generated by the program is necessary or useful as evidence or
that national trends are observable, the data will be so used.
However, the monitoring frequency, well location, and parameter
selection requirements were not designed for support of those
goals.
The monitoring requirements of Subpart F apply to owners
and operators of surface impoundments, landfills, or land
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treatment facilities which are used to manage hazardous waste
and have qualified for interim status by submission of the
notification and Part A of the RCRA permit application. The
Agency expects that detecting the occurrence of significant
impacts will be an appropriate objective at a great proportion
of the facilities; however, at those where contamination is
either unlikely to have occurred or very likely to have occurred,
owners or operators may have determined that the prescribed
detection program is not appropriate. Owners and operators of
facilities with a low potential for contaminant migration may
have chosen to waive a portion of the requirements of the
detection program; owners or operators of facilities with a
high probability that contamination has occurred may have
presumed that the detection program would indicate a significant
increase) or decrease as well for pH) in the indicators, and
proceeded with the assessment under the alternate ground-water
monitoring system provisions of §265.90(d).
1.2 The Regulations and the Agency's Intent
The ground-water monitoring requirements are presented in
five sections, numbered §265.90 through §265.94. The first
establishes the requirement to design and implement a monitoring
program and it provides waiver and alternate clauses where the
prescribed program is inappropriate. The next two sections
prescribe the sample collection system and the analyses required
for the detection program. The fourth section prescribes the
data evaluation process and the requirement and procedures for
the assessment program. The last section contains the reporting
requirements.
Portions of the text of the regulations are reproduced here,
followed by interpretive language, responsive to some of the more
commonly received inquiries. The full text is provided in
Appendix A.
The requirement for monitoring ground water is contained
in §265.90(a).
...the owner or operator of a surface impoundment, landfill
or land treatment facility which is used to manage
hazardous waste must implement a ground-water monitoring
program capable of determining the facility's impact
on the quality of ground water in the uppermost aquifer
underlying the facility...
The key word in this section is "capable". Definitive
design standards for a ground-water monitoring system
which would be applicable in all anticipated situations did
not prove feasible. Rather the Agency has described performance
requirements in general terms with certain basic minimums.
Reasonable defense of that capability is implied. The program
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must have been implemented by November 19, 1981, and capable
of producing a representative sample during the first quarter,
or by February 19, 1982.
The ground-water monitoring requirements may be,waived at
certain facilities as specified in §265.90(c):
All or part of the ground-water monitoring requirements
of this Subpart may be waived if the owner or operator
can demonstrate that there is a low potential for
migration of hazardous waste or hazardous waste
constituents from the facility via the uppermost
aquifer to water supply wells (domestic, industrial,
or agricultural) or to surface water.
The intent of this provision, as expressed in the preamble,
is narrowly confined so as to provide relief from the monitoring
requirements when, for instance, climate will not sustain
leachate production or when geology will isolate produced
leachate from any point of aquifer use. Public comment
consistently points to the existence of extremely well protected
ground water, of sites underlain by hundreds of feet of highly
attenuative clays and of arid climates in which no support for
monitoring rationale can be provided. The May 19, 1980 preamble
discussion excludes liners, unsaturated zone monitoring, and
unique waste-behavior characteristics as bases for waivers.
Although the Agency continues to expect that only a small
proportion of the facilities in interim status will qualify
for a complete waiver there is an increasing awareness of
grounds for partial waivers in which relaxation of certain
requirements may be warranted. For example, the omission of
certain indicator parameter analyses, such as total organic
halogen at facilities able to demonstrate the continued absence
of organics content in the waste, might not affect the capability
of a well designed detection program.
On January 11, 1981, the regulations were amended, by
addition of §265.90(e), to extend the waiver provisions to
apply to neutralization surface impoundments (see 47 FR 1254,
et seq). Those facilities shown to rapidly neutralize corrosive
wastes and to contain no waste exhibiting other hazardous
characteristics, are now eligible to waive the ground-water
monitoring requirements. The Agency has requested information
on other types of facilities which can be reliably demonstrated
to have low potential for migration of hazardous waste or
hazardous constituents. Waiver demonstrations, of course,
will be expected to conclusively indicate that partial waivers
will not impede monitoring program effectiveness. The Agency
expects, however, that in most parts of the United States, and
for most wastes whose purity cannot be assured, owners or
operators of land disposal facilities will install and operate
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the detection program as described in Part 265. The extent of
the investigations required to substantiate the waiver
demonstration may have discouraged some of the more questionable
cases, since complex situations require expensive geophysical
exploration which could outweigh the cost of the monitoring
system.
Striving for a reasonable approach the Agency provided
the waiver opportunity appropriate to the potential for migration,
but chose not to include time in the criterion. The expectation
was that facilities over regionally important ground-water
bodies are not eligible for a waiver whenever ground-water
migration will transport the introduced contaminants within
geologic time. Not specifying an acceptable time frame will
severely restrict the use of a complete waiver. Owners or
operators should be prepared for a critical review of waiver
demonstrations upon facility inspection.
Section 265.90(c) continues:
This demonstration must be in writing, and must be
kept at the facility. This demonstration must be
certified by a qualified geologist or geotechnical
engineer and must establish the following:
(1) the potential for migration of hazardous waste
or hazardous waste constituents from the facility
to the uppermost aquifer, by an evaluation of:
(i) a water balance of precipitation, evapo-
transpiration, runoff, and infiltration; and
(ii) unsaturated zone characteristics (i.e.,
geologic materials, physical properties,
and depth to ground water); and
(2) The potential for hazardous waste or hazardous
waste constituents which enter the uppermost
aquifer to migrate to a water supply well or
surface water, by an evaluation of:
(i) saturated zone characteristics {i.e.,
geologic materials, physical properties,
and rate of ground-water flow); and
(ii) the proximity of the facility to water
supply wells or surface water.
The waiver demonstration should be a prepared report
maintained up to date at the facility. It should describe the
rationale and present the evidence by which the owner or operator
concludes that a lesser degree of monitoring is appropriate at
the particular facility, based upon the site hydrogeology. It
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must be developed in sufficient detail to convince an EPA
inspector of the absence of unknown hydrogeologic conditions
which may serve to channel leachate. The demonstration must
have been certified by a qualified geologist or geotechnical
engineer who was present during field testing to supervise
information gathering and who has detailed first hand knowledge
of the site hydrogeology.
The detection program is also inappropriate at facilities
having a very high probability of affecting ground water quality,
The regulations have provided an opportunity for owners or
operators who know or assume that their facility is discharging
to ground water to avoid the time and expense of detection
program monitoring. Section 265.90(d) [alternate ground-water
monitoring system] states:
If an owner or operator assumes (or knows) that ground-
water monitoring of indicator parameters... would show
statistically significant increases... he may install,
operate, and maintain an alternate ground-water monitoring
system (other than the one described in §§265.91 and
265.92).
It goes on to say that if the owner or operator decides to
use an alternate ground-water monitoring system he must submit
to EPA a specific plan for an alternate ground-water monitoring
system, initiate the determinations and submit a written report,
etcetera in accordance with the assessment program requirements
in §265.93.
This Section provides the owner or operator an opportunity
for a cooperative approach to determining what if any corrective
action is needed. In doing so, the unnecessary delay during
which background and indicator parameters were statistically
compared is avoided. The owner or operator may avoid the
expense and the prolonged uncertainty of operating under the
detection system by going directly into the assessment program.
This cooperative approach, could be helpful in deciding whether
enforcement actions are necessary; it is also useful to owners
or operators who believe that their discharge to ground water
does not threaten human health or the environment. The Agency
encourages all owners and operators to implement more than the
minimum acceptable program in the belief that the additional
information is to their benefit.
The minimum acceptable ground-water sampling system is
described in §265.91 and again, the key word is "capable".
(a) . A ground-water monitoring system must be capable of
yielding ground water samples for analysis and must
consist of:
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(1) monitoring wells (at least one) upgradient...
capable of yielding [representative background
samples], and
(2) monitoring wells (at least three) downgradient...
their number, locations and depths must ensure
that they immediately detect any statistically
significant amounts of hazardous waste or
hazardous waste constituents that migrate...to
the uppermost aquifer.
The wording in paragraph (2) above, unfortunately, has
caused many questions, and needs clarification: locations and
depths which enable timely detection are considered to comply.
As set forth in Section 2.2.4, well depths are critical to
the system capability. Well clusters for monitorng at multiple
depths are encouraged so that high concentrations are not masked
by dilution with uncontaminated ground water entering a well
intake which is too long. The detection program is focused on
the uppermost aquifer, not because it is more or less worthy of
protection, but rather because contamination will be more
readily detectable. The words "significant" and "uppermost"
should guide the owner or operator to the saturated zone most
likely to exhibit the occurrence of discharge. While some
perched and discontinuous water tables may be ignored in favor
of the uppermost aquifer which underlies the whole waste
management area, samples should not be selected at sheltered
points obscure to the most direct flow paths.
Sampling and analysis for the detection program is prescribed
in §265.92. Paragraph (a) requires the owner or operator to
prepare and follow a plan for collecting and analyzing samples.
This plan is intended to standardize collection, storage and
handling techniques. For instance, the temperature and containers
used for storing samples for background determinations should
not differ for subsequent samples. Filtration of samples
warrants special consideration in plan development, because
analysis for metal and other constituents are affected by
filtration. The choice of sample filtration should be based
on the analytical techniques, on the waste (e.g., if the facility's
leachate is likely to consist of a large filterable portion,
filtered samples would not be representative) and on the
hydrogeologic setting; and it should be consistently used
throughout the detection program.
Thirty parameters are listed in §265.92(b) for which
analyses are required. The first group is the suitability
parameters listed in the National Primary Drinking Water
Regulations, §141.11-.16. The Agency objective in this
requirement is to determine the value of the resource in terms
of its drinking suitability. During the comment period, several
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commenters made the point that all ground water is not
necessarily of equal value, and that the regulatory strategy
should allow for consideration of the quality of the resource
involved. Where reliable regional data and nearby public water
supply systems' data for the radioactive parameters are available,
these may be used to assist in the required determinations.
Analysis of the suitability parameter list also provides
an initial screening of facilities in that owners and operators
must identify up and downgradient wells where samples indicate
that the ground water is unsuitable for drinking. Analyses is
only required for the first year, although owners and operators
may wish to record subsequent changes in regional suitability,
especially when trends are observed.
The second required group of parameters indicates the
general ground-water quality. These six parameters will be
used as a base of comparison if and when a ground-water quality
assessment is required. Background for these parameters must
be established by quarterly analyses the first year (i.e.,
Feb. 19, May 19, Aug. 19 and Nov. 19, 1982); thereafter, they
must be determined annually at all wells.
The contamination indicators selected for routine
comparison of background and subsequent monitoring-well data
are listed in §265,92(b)(3). Four samples must be taken in
the first year in order to determine seasonal effects. Replicates
are only required for the upgradient wells during the first
year, and the initial background arithmetic mean and variance
must be determined by pooling the values from the replicate
measurements. Only the upgradient values will constitute
background. Wells must be sampled at least twice in each
succeeding year, and for each routine comparison at least four
replicate measurements must be obtained for each parameter at
each well.
The basis for the indicator parameter selection is the
Agency's belief that significant discharges from hazardous
waste management facilities to ground water will often result
in an observable change in at least one of the four selected
indicators: pH, specific conductance, total organic halogen
(TOX) and total organic carbon (TOO. The Agency believes
there is a low probability that a major discharge could occur
without a significant change in at least one of the four
indicators in representative ground-water samples. The rationale
for employing this two level approach is that the results
will be protective of health and environment and at minimum
cost and disruption.
As expressed in the background document for the regulations,
dated May 2, 1980, the Agency rationale was to devise a
monitoring protocol that will be responsive to a large undefined
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set of chemical compounds at unspecific concentration levels
which could only be classed in general terms such as ionic,
nonionic; organic, inorganic; or dissolved or suspended in the
ground water.
Specific conductance and pH were chosen for monitoring the
inorganic constituents because they satisfy virtually every
requirement for being acceptable test procedures and there are
no alternative inorganic indicators which can provide equivalent
informational value. pH affects the solubility and mobility
of many of the toxic constituents of waste, and determines the
rate and outcome of many of the chemical reactions the pollutant
will undergo.
Specific conductance on the other hand is a numerical
expression of the summation of contributions from all ions
present in a solution. Since conductance is an additive property,
it is useful as an indicator parameter because it can effectively
determine all ions simultaneously. While pH and specific
conductance are somewhat redundant, their relative change is
informative.
TOC was chosen as an indicator parameter for organics
because of its widespread use, acceptability as an effective
test procedure, and general applicability to all types of
organic contamination. It is one of the few parameters that
provides a broad description of the organic content of water
and is replacing chemical oxygen demand in ground-water analysis.
TOC provides a more direct expression of organic content than
COD, is more sensitive, and is a less difficult procedure.
TOX was selected to measure only those organic compounds
containing halogens. Despite the somewhat more limited use of
TOX, it is included among the four indicators in view of the
relatively large amount of hazardous wastes which may contain
halogenated hydrocarbons and the higher degree of toxicity
usually associated with these compounds. The TOC test alone
will not reliably detect the minor TOC fluctuations due to
significant levels of halogenated hydrocarbon and the TOX test
alone will not provide the broad range of organic coverage
necessary.
In unusual situations where these four indicators are
inappropriate for detecting discharges due to waste composition,
the site geochemical characteristics or other circumstances,
owners or operators are encouraged to notify the Agency of the
details (see 47 FR 1254, Jan. 11, 1982). Otherwise, procedures
for the alternate system (§265.90(d)) may be followed.
Owners or operators should be prepared for the shortest
possible turnaround between the detection of significant ground-
water effects and assessment plan development. It is expected
10
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that the detection phase monitoring will provide some specificity
regarding the avenue of release and constituents of concern.
The actual assessment plan will then be able to focus on a
narrow spectrum of possible releases.
Section 265.93(d)(2,3) [specific plan for ground-water
quality assessment] states:
(2) The owner or operator must develop and submit to
the Regional Administrator a specific plan, ...
certified by a qualified geologist or geotechnical
engineer, for a ground-water quality assessment
program at the facility.
(3) The plan to be submitted under §265.90(d)(1) or
paragraph (d)(2) of this Section rajst specify:
(i) The number, location, and depth of wells;
(ii) Sampling and analytical methods for those
hazardous wastes or hazardous waste
constituents in the facility;
(iii) Evaluation procedures, including any use
of previously-gathered ground-water quality
information; and
(iv) A schedule of implementation.
The assessment plan should specify a phased program,
probably commencing with analysis of a full suite of parameters
from existing wells focusing on the characteristics of the
wastes received at the facility. In the phased assessment
program, data collection, analysis and evaluation will be
pursued iteratively. For instance, the plan may indicate that
earth resistivity surveys be conducted over a period of three
months, that the surveys be analyzed, and that the information
be evaluated so as to determine an appropriate well drilling
or other hardware emplacement scheme for subsequent months.
Well drilling, sampling and analysis should also be staged
so that a first round will be evaluated before decisions are
made regarding subsequent rounds of drilling. There is no
expectation that the plan first submitted after the notification
will be a sophisticated and rigid program of events leading
towards or producing the assessment. Rather, this detailed
plan should focus on the near term, and call for subsequent
installments of future portions of the plan.
11
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Section 265.93{d)(5 ) [assessment and report] states:
(5) The owner or operator must make his first
determination under paragraph (d)(4) of this
Section as soon as technically feasible, and
within 15 days after that determination, submit
to the Regional Administrator a written report
containing an assessment of the ground-water
quality.
The Agency recommends considering a decision-tree format
for assessment plans with notification of incremental determina-
tions rather than one-time assessments. Owners and operators,
in consultation with the certifying professional, should
determine when sufficient reportable information is accumulated
to constitute the "first determination." The first determination
should include the following information:
1. An estimate of the location and depth of the area of
highest concentrations.
2. A sample of downgradient ground water which is beyond
the limits of contamination, and an estimated location
of the "front" of contamination.
3. A list of any probably harmful constituents present
in the ground water.
Since collection and evaluation of this information may
require an extended study period, the Agency specifies a
timely submittal of the first assessment report. Subsequent
annual submission by March 1 of each year is required thereafter.
Assessments, reporting and the required determinations must
be completed in the shortest time practicable. As the required
determinations for a more complete assessment are being
submitted, each report should demonstrate that the assessment
is proceeding on schedule, and it should present as much
investigation as was practicable during each quarter.
Section 265.93(d)(7) states:
(7) If the owner or operator determines that hazardous
waste or hazardous waste constituents from the
facility have entered the ground water, then
he:
(i) Must continue to make the determinations
required under paragraph (d)(4) of this
Section on a quarterly basis until final
closure of the facility, if the ground-water
quality assessment plan was implemented
prior to final closure of the facility,...
or
12
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(ii) May cease to make the determinations
required under paragraph (d)(4) of this
Section, if the ground-water quality
assessment plan was implemented during
the post-closure care period.
Owners or operators should recognize that Part 265
provides no absolute ground-water standard for evaluation of
a facility. Determinations as to the acceptability of any
observed discharges will be judgmental. These judgments
will be made after discussions with the owner or operator,
adjacent land owners, state and local officials, and other
interests. The objective of Part 265, Subpart F, is the
determination of the facility's effect on ground water, not
to determine "guilt" or "compliance". Data shall be collected
and analyses shall be performed in accordance with the regula-
tions. Subsequent evaluations may lead to any of several
options such as imminent hazard actions under RCRA Section
7003, further analysis under RCRA Section 3013, negotiated
corrective action settlements or conclusions that continued
operation is appropriate without changes.
1.3 Program Implementation
During interim status, the Agency expects only to loosely
identify the format for onsite ground-water monitoring records.
The content and format of reports to EPA will be specified in
more detail. At several points in the regulations, program
contents are specified or implied. These are as follows:
(1) Detection system waiver demonstrations.
(2) A description of the alternate ground-water
monitoring system (when the owner or operator decides to use
an alternate system).
(3) The geologist or geotechnical engineer's description
of the detection monitoring system design which demonstrates
its capability. It should contain a description of the basis
for selection of sampling point locations (i.e., gradient and
flow path).
(4) Descriptions of well casing, screening, filter
packing, annular sealing, and well logs.
(5) The ground-water sampling and analysis plan.
(6) The records of the analysis required in the detection
monitoring program. The records should contain all determina-
tions of change in the four indicator parameters whether
confirmed by the lab error process or not.
13
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(7) Background concentrations, and determinations of the
need for change, and the history, including ground-water surface
elevation analyses of §265.93(f).
(8) The plan for the assessment program.
(9) The written assessment report.
(10) Reports of quarterly assessment until final closure.
These components need not be separately addressed in
individual documents. The format and manner of expression of
program documentation is entirely up to the owner or operator
for the implied requirements and for the portions which are to
be maintained on site. However, Agency inspectors will be
instructed to review the demonstration of each, so they should
be readily identifiable.
The assessment plan must address the techniques for
determining the presence, the rate of migration, the extent
of migration and the concentrations of the hazardous
constituents. Since rate of migration may vary for different
contaminants, and it is a dynamic factor which requires
considerable observation time, its determination may constitute
the most extensive portion of the plan. Determination of
extent of contaminant migration is largely site and facility
specific, since it will depend upon the limits of sensitivity
for the parameters of concern, their background levels, and
their seasonal fluctuations. The least involved of the
three portions of the plan may be the determination of
contaminant concentrations. Having established rate and
extent of migration, concentration isopleth mapping will
often be relatively straightforward.
The initial level of detail of the plan, depends upon
the amount of information upon which the decision to prepare
the plan has been based. If the owner or operator has rather
detailed information upon which he bases his assumption that
hazardous waste or their constituents have reached the ground
water, or if the detection program which displayed the
statistically significant change is relatively sophisticated,
the level of detail in the assessment plan would be appreciable.
When the determination or assumption is based upon scant
information, the initial level of detail of the plan may be
rather brief.
As an indication of the initial level of detail
anticipated in development of an assessment plan, a relatively
simple situation might consist of a two to five page narrative
describing site hydrogeology, two or three pages of description
of the migratory constituents, and five or ten pages describing
the paths (actual and potential) of migration and the
14
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susceptibility of those paths to each of the migrating
constituents. Beyond this background, the plan should briefly
describe the methodology appropriate for the scale anticipated
at each pathway. The initial sequence of assessment methods
may be only roughly described in the early stages of plan
development. The plan should indicate who will perform the
work and the level or range of discovery upon which subsequent
steps will be made contingent.
1.3.1 Complying with the Regulation; How much is enough?
The monitoring requirements as promulgated were designed
to be self-activating. EPA's experience in implementing the
Clean Water Act with its numerous permit actions was part of
the basis for Congress' decision to provide an interim status
period before existing hazardous waste facilities would be
issued RCRA permits. In order to achieve the smoothest
transition, the Agency has prescribed procedures in which
owners or operators of land disposal facilities would proceed
automatically, where required, from one level of monitoring
to the next without waiting for interaction with the Agency.
The Agency has prescribed a sequence of steps leading to a
ground-water quality assessment which must be automatically
followed in the case of Agency silence. However, it should
not be inferred that communication with EPA is being discouraged,
On the contrary, the Agency's willingness to participate in
ground-water quality assessments is expressed throughout
this manual. Further, the Part 265 regulations require
owners or operators to send notifications and reports to EPA.
This regulatory approach places a large measure of trust
and confidence in the owner or operator. Owners or operators
will design, install, and operate their monitoring systems,
pending eventual EPA inspection and review during the permit
process. The Agency's intended approach is to be "non-
confrontational", with extended dialogue available during
monitoring program development. The question "How much is
enough?" will be entirely site-specific, but in general,
owners or operators should ensure that convincing evidence
is established for each assumption and for demonstrating the
basic capability of the system to produce samples representative
of background and potentially impacted ground water. Examples
of such demonstrations will be presented in this manual, but
the reader should bear in mind that "enough" is a subjective
determination, both for the questions of "how much" monitoring
is necessary to detect ground water contamination and "how
much" demonstration is required to convince the Agency of
that capability.
Obviously, extensive proof and burdensome detail would
be inappropriate for use in the first-level screening or
detection system. The requirements for fulfilling the detection
program are minimal and are specifically designed not to be
15
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1
burdensome. The objective of these requirements is to produce
information for differentiating between facilities which are
significantly affecting ground-water quality and those which
are not. The detection system is cost effective and can
positively identify those facilities with gross impacts, yet
it is not particularly conservative (i.e., it minimizes
propensity to err on the side of finding false positives).
Thus for the first-level objective, a simple detection
system will suffice in a vast majority of cases. Only in
the most unusual cases, such as facilities located on a
tidally influenced aquifer, or those located along a ground-
water divide, would the detection monitoring system need to
be very sophisticated. Demonstration that the system is
adequate could consist of cursory on-site geophysical confir-
mation of the continuity of regional characteristics.
The key word in the Subpart F regulations is capable.
The owner or operator must install and implement a ground-water
monitoring system capable of determining the facility's
impact; it must be capable of yielding representative ground-
water samples for analyses. The number, locations, and
depths of the detection monitoring wells must be such that
the system is capable of the prompt detection of any
statistically significant differences in the four indicator
parameters. Separate monitoring systems for each facility
component are not required provided that the emplaced wells
are capable of detecting any discharge from the waste
management area.
At each description of the detection monitoring program
in the regulations, the Agency has chosen performance oriented
criteria to describe a sufficient system. Since it will be
a very unusual monitoring situation in which fewer downgradient
wells would insure system capability, the Agency has established
in the regulations that the minimum system will consist of
at least three wells downgradient. This is not intended,
however, to be a suggestion or a guideline concerning the
normal or typical monitoring system. Rather, it is the
minimum acceptable, and the norm may be six, ten, or even
more. It is not uncommon for monitoring system designers to
employ multiple dozens of sampling points in detection
monitoring.
The critical component in determining adequacy is
the breadth or scope. Discharges to the ground water may
originate in a variety of ways. Overtopping, spills, or
liner rupture at surface impoundments, surreptious disposal
of wastes incompatible with liners, equipment operator error
during liner emplacement, or liner puncture by bulky objects
in a landfill, are some of the obvious points of origin of
discharges to ground water. Upon discharge which could be a
16
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one-time event, a repetitive or recurrent event, or a continuous
seep, the discharge plume in the unsaturated zone could form
a narrow ribbon or quite a large conical shape with significant
lateral dimensions. Entry at the water table could be continuous,
pulsing in sync with the original discharge, or transported
by pulses of infiltration. It may behave as a point source
or as a widely dispersed areal source. The discharge could
consist of homogeneous constituents representing the full
range of waste received by the facility, or it could consist
of a unique fraction of the facility wastes. Even that
fraction might be homogeneous or it might be widely varying.
Plume bifurcation may result when oily or aromatic wastes
tend to float on the surface of the water table while higher
density fractions tend to form deeper plume configurations.
Unless the plan fully considers potential as well as actual
pathways, the occurrence of an unforeseen event could have a
negative influence on the ability to effectively implement
early corrective actions.
Assessment plans are required to be prepared professionally
(i.e., by a geologist or geotechnical engineer). These
professionals should pose an exhaustive list of possible
release mechanisms in the initial design process of the
plan. Anticipated viscosities and densities of the leachate
and temperature differentials with the ground water should
be coupled with actual and likely hydrologic flow paths at
the site (including the prospect of geophysical anomalies);
and each of the potential flow paths must be individually
assessed regarding its likelihood of occurrence.
The Agency does not expect to establish hard and fast
criteria to determine whether or not a particular flow path
must be intercepted by a sampling point. Rather, the owner
or operator must use judgment in establishing his sampling
point array. He should take advantage of the fact that some
of the flow paths may be redundant in that no leachate would
travel one without having first appeared in the other.
However, he must be capable of providing an EPA inspector
with a convincing demonstration that any discharge from a
facility would be detected by the system.
The regulations require determination of the water level,
before flushing and sampling, in each well at each sample-
taking event. These measurements should be used to compute
the water table gradient (direction and slope) in order to
demonstrate that the system continues to be located appropri-
ately. Changes in the water table gradient should be assessed
for their impact on the flow path probability; "how much
demonstration" is therefore not answered by a once-and-for-all
assessment. The system capability demonstration requires
continuous updating.
17
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At best, the information achievable from the basic detec-
tion program, without waiver or alternate, will be very
limited. Presumably, a waiver demonstration will be definitive
regarding the potential for leachate to enter ground water.
Similarly, information available if an alternate program is
selected should be far more definitive than the basic program.
However, the objective of the basic program is simply to
determine which land disposal facilities require in-depth
assessment of ground-water impacts.
1.3.2 Interaction with the Agency
The Agency intends to be cooperative and interactive with
owners or operators regarding interim status monitoring.
However, owners or operators should bear in mind that informa-
tion generated by the assessment program may, in certain
instances, be used as evidence for enforcement purposes and
that chain of custody requirements do apply. The assessment
program is not designed in and of itself to provide sufficient
evidence to support enforcement actions; rather, the program
may be used in making the threshold determination of whether
further investigation is warranted. If a disagreement persists
and the enforcement proceedings prove necessary, the collection
of additional information by the owner or operator will
usually be necessary. It is the Agency's sincere hope that
assessments will be conducted in a cooperative non-adversarial
manner and that the regulatory staff may actively participate
in review of assessment plans during drafting.
The Agency's role during interim status must be a limited
one, advising only, with no approval implied. The product
of an assessment will be the basis for negotiating alterations
to the design or operating procedures at the facility; it
will be a basis for discussions regarding the acceptability
of the discharge, the longevity of the site, or the usefulness
of a public hearing concerning the situation. To serve
these purposes best, it behooves both the Agency and the
owner or operator to assure the thoroughness of the investigation^
and the Agency may require modification of inadequate plans.
Upon completion of the assessment, owners or operators may
be required to predict the fate and effects of a continued
release of contaminants or of controlling the release by
facility modification, removal of wastes, or hydrogeologic
modification. This could be done pursuant to RCRA Section
3013 or in anticipation of an imminent hazard or enforcement
action if necessary, but preferably and most frequently,
it will be in a cooperative spirit of environmental
responsibility.
Since owners or operators of facilities which are assumed
to have affected ground-water quality have been afforded the
opportunity to commence directly with the assessment program,
18
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the detection program was designed with an assumption that
the facility has not affected ground water. The first reaction
to indications that an impact has been detected will be to
double check the data. The regulations build in one double
check against human error. The Agency suggests as a second
safeguard against false positives that the assessment plan
should prescribe analyses of waste-specific parameters from
existing wells. Special attention should be paid to constituents
known to be absent from the facility in order to determine
whether other sources are causing or contributing to the
situation. For instance, "fingerprint" analyses may form
the first phase of the assessment program. If the fingerprint
does not match, the owner or operator should return to a
monitoring program whose objective is detection. If the
fingerprint does match, the assessment plan may still emphasize
confirmation of source or the portions due to various sources.
Owners or operators are encouraged to maintain informal
communication with the Agency in addition to the required
formal reporting. The Agency will place a high priority on
responding to requests for assistance from owners or operators
during development and implementation of assessment program
plans. Owners or operators are advised that last minute or
late submissions of required notifications may be a consideration
in establishing facility inspection schedules.
As a general rule, monitoring programs must be carefully
pre-planned so that each component of the system, each datum
required, and each specified report will be meaningful and
purposeful. Changing program dimensions and improved understanding
of field conditions resulting from the experience of collecting
data may be expected to affect the usefulness of certain
items of data now being collected. Similarly, waivers and
omissions could lessen the value of the overall picture by
creating gaps in the data.
At the time of promulgation of the interim status standards,
the Agency anticipated that the permit monitoring standards
for land disposal facilities would be promulgated shortly
thereafter. Subsequent difficulties in determining appropriate
standards have caused delays resulting in unanticipated
extension of the interim status period, as well as a greater
opportunity for the Agency to interact with owners and operators
during development of monitoring programs. Therefore, ground-
water monitoring waivers and alternate programs, for instance,
have been developed with the Regional Administrator advising
(but not approving or disapproving in a formal sense)
owners or operators of system sufficiency prior to its implemen-
tation. This is more particularly true for the assessment
plan, but is applicable to the detection program as well.
19
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The Agency will attempt to maintain consistency in the
ground-water monitoring requirements throughout interim
status. However, repeatedly identified problems, if and
when they occur, will be periodically assessed with a view
towards program improvement and revisions to the regulations.
Whenever changes cannot be avoided, we will attempt to reduce
any disruption which may result with due consideration for
both owner or operator and program impacts.
2.0 Detection Program
2.1 Description
The ground-water monitoring detection program is intended
to protect human health and the environment through the
prompt detection of possible discharges of hazardous wastes
or hazardous waste constituents into the ground water from a
surface impoundment, landfill or land treatment facility.
Owners or operators of such facilities are responsible for
developing ground-water monitoring systems capable of detecting
whether a facility is affecting ground-water quality in the
uppermost aquifer underlying the facility. The purpose of
this Section is to provide guidance and technical information
to owners or operators in the development of a detection
program meeting the requirements of the RCRA 40 CFR Part
265, Subpart F. Others interested in the content of this
Section may include Agency staff, geologists involved in
designing and installing a ground-water monitoring system
and inspection personnel.
2.2 Ground-Water Monitoring Well Location
Ground-water monitoring wells must be capable of
determining whether the facility is affecting ground water
in the uppermost aquifer underlying the facility. The number
and location (including surface position and depth) of wells
must assure detection of ground-water quality changes
(i.e., facility discharges) in the uppermost aquifer. Well
location and number requirements represent only the minimum
acceptable system components. Where the minimum requirements
do not enable the owner or operator to meet the overall
performance objective, he must determine where and how many
additional wells are necessary. The regulations provide
flexibility in adapting a system to site-specific hydrogeologic
conditions. It is the responsibility of the owner or operator
to develop the monitoring system necessary to accurately
detect possible facility discharges.
Geologic factors, related chiefly to geologic formations
and their water-bearing properties, and hydrologic factors
which determine the movement of water in the formations
should be known in some detail to properly design a detection
20
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system. The geologic framework includes lithology, texture,
structure, mineralogy, and the distribution of the materials
through which ground water flows. The hydraulic properties
of the earth materials depend upon their origin and lithology,
as well as the subsequent stresses to which the materials
have been subjected.
The hydrogeology of the facility site heavily influences
the monitoring well array. Elements of the hydrogeologic
framework which should be considered include:
the spatial location and configuration of the uppermost
aquifer and its hydraulic properties (e.g., horizontal
and vertical hydraulic conductivities, depth and
location of ground-water surface, seasonal fluctuations
of ground-water surface elevation); and
hydraulic gradient.
2.2.1 Obtaining Hydrogeologic Information
Prior to initiating any field work, all existing geologic
and hydrologic data should be collected, compiled and interpreted.
Data that should be investigated include: geologic maps,
cross sections, aerial photographs, and any water-well data
including location, date drilled, depth, name of driller,
water level and date, well completion methods, use of well,
electric or radioactivity logs, or other geophysical data,
formation samples, pumping test(s) and water-quality data.
After compiling and thoroughly reviewing the collected data,
the investigator can properly begin planning the monitoring
well array needed.
The owner or operator should obtain as much regional
and site-specific information as possible. In addition, the
owner or operator is advised to consult more than one source
for a particular type of information in order to verify the
reliability of and supplement the data obtained. Table 2-1
lists possible sources of existing information.
The common field methods used for obtaining hydrogeologic
information should be employed for on-site investigations
including installation of boreholes, piezometers and/or
water table wells; remote geophysical techniques such as
electrical resistivity surveys may be used to augment direct
methods. Descriptions and applicability of boreholes, piezometers,
and water table wells are given below along with other direct
and indirect field techniques (see also Section 3.3). It
should be emphasized that some on-site investigation methods
may be appropriate in one geologic setting but not in another.
A combination of methods will likely be needed in most cases.
21
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Table 2-1
Sources of Hydrogeologic Information
U.S. Oeological Survey (USGS) [See Appendix B for specific
contacts].
State Geological Surveys
U.S. Department of Agriculture, Soil Conservation Service
State Department of Agriculture
County Surveys
State Department of Environmental Protection
State Department of Natural/Water Resources
State Solid/Hazardous Waste Division
Clean Water Act "208" and other Regional Planning Authorities
County and Regional Water Supply Agencies and Companies
(private water suppliers)
Related industry studies (mining, well drilling, quarrying,
etc. )
Professional associations (GSA, NWWA, AGU) 1
Local colleges and universities (Dept. of Geology, Earth
Sciences Civil Engineering)
Other Federal/State Agencies (ACOE, NOAA)2
1• GSA - Geological Society of America
NWWA - National Water Well Association
AGU - American Geophysical Union
2* ACOE - Army Corps of Engineers
NOAA - National Oceanic Atmospheric Administration
22
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The evaluation of hydrogeological conditions at the site
should be under the direction of a qualified geologist or
geotechnical engineer.
Boreholes
Boreholes should be drilled on-site to obtain information
(direct and indirect) on subsurface geology, including fluids
present. The following purposes for drilling boreholes
should be achieved;
- to verify results of surface geophysical surveys (e.g.,
electrical resistivity and electromagnetic conductivity;
see Section 3.3);
- to locate aquifer flow zones (i.e., probable contaminant
pathways) ;
- to determine the types, properties, and thicknesses of
earth materials penetrated by obtaining formation
samples or through use of indirect techniques (e.g.,
borehole geophysical logging; see Section 3.3);
- to enable collection of water samples through
installation of monitoring wells;
- to define the extent of a contaminant plume (areally
and at depth);
- to plot underground stratigraphy and structure by
correlating data from different boreholes; and
- to enable in situ testing (e.g., pumping tests to
determine aquifer coefficients and tracer tests to
examine contaminant transport).
A boring plan should be prepared by the geologist or
geotechnical engineer in charge of the investigation. The
plan should include proposed locations and anticipated depths
of boreholes and the type and frequency of formation sampling
required. when to terminate boreholes and/or when additional
boreholes are needed depends upon additional data needs and
site-specific hydrogeologic factors. For example, a shallow
bedrock surface of low hydraulic conductivity may indicate
the depth limit for investigation of an area. All information
obtained during boring should be recorded on standard boring
logs.
Detailed discussion of standard boring procedures may be
found in Hvorslev (1965), Acker (1974) and other standard
references (e.g., ASTM, 1978). Table 2-2 shows how boreholes
23
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and other direct and indirect methods are useful in identifying
the uppermost aquifer. For further information on the purposes
and methods of sampling subsurface solids, see Scalf, et al
(1981, pp. 72-79). See also Section 3.3 for additional
considerations concerning boreholes.
Piezometers and Water Table Wells
A piezometer is a narrow well (generally less than four
inches) used for measuring ground-water surface elevations
(i.e., heads). Care must be exercised in installing the
casing to insure that accurate water level elevation measurements
are obtained. Information for designing and installing
piezometers is given by Fenn, et al (1977, pp. 86-88).
Piezometers and/or water table wells should be used in determining
the water surface elevation in the uppermost aquifer, seasonal
fluctuations of this elevation and the hydraulic gradient.
A minimum of three piezometers should be used to determine
the hydraulic gradient. Additional piezometers will generally
be needed since three will often be inadequate to determine
the variations in ground-water flow at a specific site.
Where appropriate, piezometers can also be used as monitoring
wells, provided they meet all the specific requirements of
monitoring wells in Sections 2.2 and 2.3.
Seismic Surveys
Seismic surveys are used to determine the depth to bedrock
and the thickness of the materials overlying the bedrock.
The refraction method of seismic exploration utilizes the
principle that energy waves can be propagated through earth
materials. The velocity of propagation is governed by the
elastic properties of the earth materials through which the
waves are traveling. To determine their velocity, these
elastic waves can be timed from their initiation to arrival
at a known distance from the energy source. With known
velocities and distances, depths to the various geologic
interfaces can be calculated. The seismic reflection method
of geophysical surveying may also be used. This system, in
which the energy wave is reflected from the different geologic
horizons, can usually penetrate greater depths than the
refraction method. For more refined interpretations, well
data are correlated with the results of the seismic survey.
Where well information is not available, evaluation of seismic
data is based upon interpretation of the geologic environment
and experience in geophysics. Data interpretation of a seismic
survey requires a trained operator and an experienced geophysicist.
The complexity of the data-reduction process generally requires
the use of a computer. For further information on the use,
advantages and limitations of this methodology, see Fenn, et
al (1977, pp. 124-126).
25
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2.2.2 How to Use Hydrogeologic Information in Planning the
Monitoring System
Existing and new on-site investigation information should
be used to deduce the configuration of the site-specific
hydrogeolgic framework. This framework is the primary influence
in determining the number, locations and depths of monitoring
wells. Such information should be used to:
- prepare a site base map;
- characterize the hydrogeologic framework (including
identifying the uppermost aquifer); and
- determine the hydraulic gradient.
Preparing a Site Base Map
In order to verify that the location requirements for
upgradient and downgradient wells are being met, the Agency
recommends that a site base map be prepared. The base map
can be used extensively throughout the well location process
to summarize and display information collected. In addition
to its use for contour plots of the ground-water surface
elevation, a base map should also be used in planning and
excecuting the on-site investigation. The area to be covered
by the base map should be selected to best represent the
significant features at each facility. The base map should
extend beyond the facility area to cover other areas that
may be affected by facility discharge. USGS topographic
quadrangles and aerial photographs may help in deciding how
far to extend the base map.
Municipal tax maps available from Town Clerks at local
Town/city Halls may provide useful information for a base
map (e.g., facility boundary lines, rights-of-way, structures,
pipelines).
The base map may be prepared, in part, from information
from aerial photos (photogrammetry) yielding pertinent
information on location of surface features. Departments of
Transportation, Departments of Environmental Protection and
County Planning Departments generally catalogue state or
regional aerial photos. Agricultural, landscape design and
other related academic departments at colleges and universities
throughout the country also maintain aerial photographs.
Federal offices that serve as repositories of aerial photographs
for major regions in the country include:
26
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- National Headquarters
National Cartographic Information Center
United States Geologic Survey
507 National Center
Reston, Virginia 22092
(703) 860-6045.
- U.S. Department of Agriculture, ASCS
Aerial Photography Field Office
P.O. Box 30010
Salt Lake City, Utah 84130
(801) 524-5856; and
- Center for Cartographic and Architectural Archives
Cartographic Archives Division
National Archives and Record Service
Washington, D.C. 20408
(202) 523-3006.
An appropriate scale for a base map is one inch equal to
not more than 200 feet (1:2400), unless other factors override.
(NOTE; The USGS, in converting to metric representations,
commonly employs a scale of 1:2500, which is also a useful
scale.) Although available aerial photographs do not usually
provide this level of detail (i.e., one inch equals 2,000
feet is a commonly available scale for aerial photographs),
information obtained on land surface features and man-made
structures is very useful in base map preparation.
Important features which should be located on the base
map include:
- facility-related structures (e.g., buildings, roads,
parking lots, existing wells, pipelines, bench marks,
soil and water sampling areas, foundation test borings);
- potential contamination sources (e.g., impoundments,
landfills, storage areas, septic tank and drain field
locations);
- probable and existing background plumes from other
sources;
- surface water drainage direction and discharge points
(e.g., streams, ponds), drainage patterns and divides;
- withdrawals (e.g., wells, springs); and
- vegetation.
27
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Underground structures which must be located and avoided
when boring and installing monitoring wells should appear on
the base map, especially if they can interfere with some
types of geophysical investigations (e.g., electrical resistivity
and electromagnetic conductivity).
Vertical and horizontal controls on the site are necessary
in order to determine hydraulic gradients. Such controls
should be based upon values established by the U.S. Geological
Survey or the U.S. Coast and Geodetic Survey.
Characterizing the Hydrogeologic Framework
Data from existing sources and on-site investigations
serve as the basis for determining monitoring well locations,
numbers and depths most appropriate to a particular facility.
At a minimum the owner or operator should:
- determine hydraulic properties of formations;
- record the seasonal fluctuations in the ground-water
surface elevations to determine the hydraulic gradients,
including flow directions; and
- identify the uppermost aquifer.
Determining Hydraulic Conductivities of Formations
Hydraulic conductivity (K) of a porous medium, or the
volume of water that will move in a unit time under a unit
hydraulic gradient through a unit area measured at right
angles to the direction of flow (Lohman, et al, 1972), should
be determined. Irregularities in ground-water flow pathways
which result from variations in K of subsurface materials
should be identified. Soils and sedimentary rocks occurring
in alternating layers or zones of varying K should be identified
if they strongly influence ground-water flow patterns. Because
ground-water flow patterns and, therefore, K distributions
are a major influence on the well-location process, it is
important to establish the K values of formations underlying
the facility. Methods for determining K values of subsurface
material samples are discussed in Section 3.2.
The following hydrogeologic situations reflect how K
values can be considered in planning the monitoring system.
Low Hydraulic Conductivity Layers and Stratification
Where a shallow layer of low K is a continuous barrier
to the downward migration of water or liquids under a facility,
it will be a major influence in determining the location and
28
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depth of the monitoring wells. Therefore, if boring indicates
the presence of a shallow, low K layer, such as a clay bed,
its horizontal extent, thickness and degree of continuity in
the vicinity of the facility site should be determined.
Even within an apparently homogeneous formation zone or
aquifer, considerable differences in grain size and sorting
(i.e., stratification) can occur in horizontal layers and
should be noted. The influence of stratification on the
vertical component of ground-water flow is an important
consideration in determining the most effective depth for
monitoring. Hydraulic conductivity often tends to be
considerably higher (often at least an order of magnitude)
parallel to the stratification than across it. Stratification
and other variations in K of an aquifer should be evaluated
by comparing horizontal and vertical K values.
Sand and Gravel Aquifers
Ground-water flow in unconsolidated sand and gravel
aquifers is primarily intergranular. Because of the more
uniform nature of most sand and gravel aquifers, ground-water
flow in these formations is somewhat more predictable than
in other formation types (e.g., fractured bedrock aquifers).
Bedrock Aquifers
In contrast, most consolidated rocks have few intergranular
openings for ground-water flow and on a microscopic scale have
very low K values. Instead, ground-water flow in bedrock
aquifers takes place mainly through secondary openings such
as fractures and/or solution cavities. Owners or operators
should fully identify areas in which this factor is important.
Although regional flow patterns should be discerned, it is
often very difficult to predict ground-water flow through a
set of randomly oriented secondary openings on a site-specific
scale (e.g., in the vicinity of a monitoring well). Thus,
owners or operators of facilities located over bedrock aquifers
should employ additional investigative techniques (e.g., tracer
tests and pumping tests) to adequately determine likely ground-
water flow pathways.
Determining Seasonal Fluctuations of Ground-Water Surface
Elevation
Natural fluctuations of the ground-water surface elevation
caused by seasonal variations in the hydrologic cycle (e.g.,
precipitation amount and intensity) should be recorded.
Such fluctuations are important in determining the depth of
monitoring, especially when monitoring near the top of the
uppermost aquifer.
29
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Historical ground-water surface elevation data for any
wells in the vicinity of the facility should be obtained
(e.g., from the USGS) for the most recent 10-year period.
Hydrographs for these wells should be examined, especially for
wells with the most continuous data for the 10-year period and
best locations (i.e., nearest the facility and tapping the
same aquifer). A typical hydrograph is shown in Figure 2-1.
Each hydrograph summarizes data from one well so that seasonal
trends in the elevations are evident. The seasonal range in
ground-water surface elevation should then be identified and
its impact should be considered during the well location process.
Monitoring well locations should be demonstrated capable of
providing water samples throughout the year.
Hydrographs should be constructed for data collected from
piezometers or water table wells installed at the site. They
should reflect whether the ground-water surface underlying
the facility is being affected in any anomalous way that
deviates from seasonal trends. In cases where activities
such as localized pumping of water supply wells results in
additional fluctuations in ground-water surface elevations,
the effects of these activities must be considered in determining
monitoring locations and depths.
Preparing Subsurface Cross Sections and Identifying the
Uppermost Aquifer
Subsurface cross sections mapping vertical profiles
under the facility site should be prepared if needed to
visualize the flow system. Subsurface conditions and hydro-
geologic factors such as lithology and geologic structure
(e.g., soil or rock type and thickness), formation stratification
or layering, secondary porosity and/or hydraulic conductivity,
constitute the framework which controls the occurrence and
movement of ground water. These factors should be considered
in determining locations of monitoring wells. The construction
of subsurface cross sections, using information from boring
logs, geophysical surveys and background information, is
useful for presenting and evaluating this data, especially
for complex hydrogeological conditions. (See Figure 2-2 for
an example of a cross section.)
Subsurface cross sections used in conjunction with a site
base map add a third dimension to the facility hydrogeologic
framework that will be useful in meeting monitoring well
location requirements. At least two cross sections, preferably
perpendicular to each other with one section aligned with
the anticipated ground-water flow direction, are recommended.
30
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Figure 2-1
Typical Hydrograph
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31
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Figure 2-2
Section
BOREHOLE
.
-./^j OU.TWASH SA.N.q> ^-- •". •."•i"*
4 •'
horozontal scale 1"=260'
vertical scale I'^-IO1
52
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Using the prepared subsurface cross sections and water
surface elevation information, the depth to the ground-water
surface can be determined for purposes of selecting monitoring
depths. Subsurface cross sections should be continually
updated or improved as new data is obtained. Where complex
subsurface conditions are indicated, additional boreholes,
etc. should be drilled for verification.
Determining Hydraulic Gradient
Water from the surface percolates vertically downward
through the unsaturated zone to the saturated zone where it
then flows in a more lateral direction, from areas of higher
to lower hydraulic head. The hydraulic gradient within the
uppermost aquifer must be determined in order to effectively
locate monitoring wells (see also Section 3.2.). The hydraulic
gradient is the change in head per unit of distance in the
direction of the maximum rate of decrease in head (Lohmann, et
al; 1972). If sufficient data is available on the ground-water
elevations, a water level contour map can be constructed, and
from this hydraulic gradients should be determined through
construction of a flow net (see Figure 2-3).
The minimum information needed from the on-site investi-
gation is the ground-water surface elevations (i.e., hydraulic
heads) from three piezometers. This data should be collected
concurrently (preferably during the same day) from all three
(or more) piezometers. Because these data points are extrapolated
in constructing the ground-water surface contour map, the
more data points collected (or water level measurements
taken), the more accurate the flow net will be; (hence, a
more comprehensive determination of hydraulic gradients).
A flow net can be constructed in the following manner:
- The ground-water surface elevation at each well is
plotted on a base map of the facility area. These
water level elevations are then used to extrapolate
eguipotentials (or head contour lines) which describe
the shape and slope of the water table (see Figure 2-3).
- When assuming isotropic, homogeneous aquifer conditions,
the ground-water flow direction is defined on the
flow net by drawing ground-water flow lines that are
perpendicular to the equipotential lines.
- The hydraulic gradient is determined by using two points
on the map, located on different equipotential lines
(e.g., one upgradient and one downgradient of the
facility), and aligned on one ground-water flowline.
Divide the difference in ground-water surface elevation
33
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Figure 2-3
Flow Net"
34
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(i.e., difference in heads) between the two points by
their distance apart according to the scale of the map.
2.2.3 Location and Number of Monitoring Wells
Ground-water monitoring wells must be located so that a
contaminant discharge from the facility into the uppermost
aquifer is detected promptly. Section 265.91(a) requires a
minimum of four ground-water monitoring wells with at least
one well located hydraulically upgradient and at least three
wells located hydraulically downgradient from the waste
management area. The Agency has determined that four wells
are the least number of wells needed to detect a contaminant
discharge under the simplest of conditions. Since many
sites have complex facility design and hydrogeology, owners
or oprators of these facilities will likely need to install
more than four wells in order to meet the objective of promptly
detecting changes in ground-water quality caused by a facility.
Factors to be considered in determining both the number and
location of the wells include:
- ground-water flow patterns; and
the size, orientation, and boundaries of the facility
and the waste management area.
Section 265.91(a) requires that the upgradient ground-
water monitoring well(s) yield ground water samples that
are: representative of background ground-water quality in
the uppermost aquifer near the facility and not affected by
the facility. The distance upgradient from the waste management
area that a ground-water monitoring well should be located
is dependent upon hydrogeological factors (e.g., mounding
effects). Downgradient wells should be located in close
proximity to the waste management area boundary (without
creating a conduit for potential contaminants to enter the
ground water) to enable the prompt detection of any facility
discharge.
Ground-water Flow Patterns
The pattern and direction(s) of ground-water flow are
essential factors for determining the number of wells needed
and their placement in relation to the waste management
area. Flow patterns caused by various hydrogeologic conditions
are used to determine flow pathways that contaminants may
travel if they enter the ground-water system.
Downgradient wells should be installed in the uppermost
aquifer in the direction of flow along flow pathways most
likely to transport contaminants. These pathways should be
35
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located from data gained from existing information and on-site
investigation. Upgradient wells should be placed within
ground-water flow pathways that extend beneath the facility.
Examples of well placement for common ground-water flow
patterns are given in Figure 2-4.
Examples of Ground-Water Flow Patterns
The following examples of ground-water flow patterns that
may influence the locations and number of monitoring wells
are ideal and simplified and may only superficially reflect
actual site conditions; but the level of detail required may
often be little more than shown. (For further information
on flow patterns and monitoring methods, see Fenn, et al,
1977, Chapter 2.)
These examples are designed to accompany Figure 2-4; and
will define each flow pattern and discuss well location in
relation to such patterns.
Parallel
Such a flow pattern results when equipotential lines are
parallel; ground water is uniformly flowing in one direction.
The aquifer materials tend to be homogeneous; hydraulic
properties tend to be uniform with little restriction or
segregation of ground-water flow into discrete pathways.
Contamination spread in this flow pattern tends to be uniform
and is more predictable than many other flow situations.
Well placement with even spacing is generally suggested in
such cases.
Converging
A converging pattern results when flow lines are directed
toward a centralized point (e.g., a cone-shaped topographic
depression).
A water supply well drawing water from the uppermost
aquifer underlying the facility can also create a converging
flow pattern in the local ground-water surface. Because
water is converging towards the depression, mobile contaminants
will likely flow toward that depression. The monitoring
system in such cases should reflect these flow conditions,
but must be re-evaluated as pumping conditions change.
Diverging
Percolation into a hilltop or curved ridge may cause ground
water to flow radially outward, resulting in a diverging
ground-water flow pattern. In such cases, owners or operators
36
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~~T
1 ~©TffiT
© ©
Figure 2-4
Ground-water Flow Patterns
ection view; all other diagrams are map views.
po
-fenf iV|
c
t o»
0
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will be expected to define the effect on location of background
wells. Tn general, downgradient wells should be placed in a
pattern radiating outward from the recharge area. A large
number of wells may be necessary to adequately cover diverging
ground-water flow.
Perched
Determination of the uppermost aquifer may be difficult
because of the existence of perched water zones which may or
may not be continuous beneath the entire facility. Upgradient
and downgradient wells at such facilities should be installed
at depths which enable the detection of a facility discharge
in the appropriate flow zones. That is, to obtain suitable
samples from upgradient and downgradient wells the samples
must be extracted from wells which intercept ground-water
within the same flow system. Monitoring wells may be installed
in perched aquifers, especially when the perch is continuous
beneath the entire facility.
Random Geologic Control
Random flow patterns make monitoring well location a
difficult process. Such flow patterns may be due to:
- fractured bedrock, characterized by a complex irregular
fracture system through which water may migrate;
- solution cavities which often develop in fractures in
carbonate rock and can direct ground-water flow along
upredictable pathways; and
- discontinuous subsurface geologic conditions which may
be caused by changes of hydraulic conductivity within
the aquifer, such as is characteristic of alluvial
deposits.
Locating wells in complex flow patterns presents particular
difficulty. Flow patterns/migration pathways should be
identified using both direct and indirect techniques of
subsurface investigation (see Section 3.3). Numerous wells
may be needed to detect migration from the many possible
pathways presented by particularly complex hydrogeological
settings.
Orientation and Boundaries of Facility and Waste
Managment Area
The size of both single and multi-component facilities
must be considered in determining the number and location of
monitoring wells. A large facility may increase the potential
-------
to release contaminants through a greater number of possible
migration pathways. For example, a large facility may extend
over more than one drainage basin, with surface and ground
water flowing in several and often opposite directions. The
likely migration pathways in each basin should be monitored.
Under uniform ground-water flow conditions (e.g., sand and
gravel aquifer with uniform gradient) and with no specific (e.g.,
structurally controlled) migration pathways identified, the
spacing between monitoring wells should be close enough (e.g.,
not greater than every 250 feet of waste area frontage) so as to
detect localized discharges. Even at this spacing, a localized
facility discharge could go undetected as shown in Figure 2-5.
Also, additional monitoring wells should be installed under
unknown and/or complex subsurface conditions (e.g., when the
ground-water flow direction or likely pathways are not adequately
determined; or when geologic conditions such as bedrock fracturing
or solution cavities create random flow patterns).
At multi-component facilities, where the waste management
area is large and encompasses several waste management components,
more than three downgradient wells will likely be necessary
to detect contamination from any component.
When a waste management area is many times longer in one
dimension than in another, its orientation with respect to
the direction of ground-water flow can be a significant
factor in determining the number and location of monitoring
wells needed as shown in the example facilities in Figure 2-6.
Wells should be strategically located on the site so as
to detect potential hazardous waste migration within the
uppermost aquifer. Wells must be located and constructed in
such a manner that they will not serve as a conduit for
surface contamination to reach ground water. Special provisions
should be taken for areas of the site where ground surfaces
are contaminated (e.g., from surface spills, etc.) Protective
provisions should be initiated during drilling and casing
installation phases to help prevent interference with sample
chemistry, contamination of the aquifer and exposure of
workers to contaminants.
2.2.4 Monitoring Well Depth
No specific (i.e., numerical) well depths are specified
by the regulations. However, the chosen depths of monitoring
wells must satisfy the general performance standards stated
in §§265.91(a) and (c). For upgradient wells, depths must
be sufficient to yield ground-water samples from appropriate
aquifer flow zones that are representative of background
ground-water quality in the uppermost aquifer near the facility
39
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Figure 2-5
localized Discharge from
Facility
40
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Figure 2-6
Significance of Facility
Orientation
MW-I
(VIW-6
MW-3
MW-2.
GROUND WATER FLOW DIRECTION
MW-I
J
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and not affected by the facility. The depth of downgradient
wells must ensure that they enable the prompt detection of any
significant amounts of hazardous waste or hazardous waste
constituents that migrate from the waste management area to
the uppermost aquifer (i.e., they must enable sample collection
at depths where contaminants would likely be found).
Appropriate well depths and intake depths must be determined
on a site-specific basis. Factors which influence well
depth include:
- ground-water surface elevation (e.g., seasonal
water table fluctuations);
- any anomalous ground-water surface elevation fluctuations
(e.g., localized pumping effects); and
- contaminant behavior in the aquifer (e.g., density
effects).
Ground-water surface elevations at various locations at
the facility site will have been measured in piezometers
and/or water table wells during the on-site investigations.
This information should be considered with regard to seasonal
fluctuations in ground-water surface elevations and any
observed anomalous water table fluctuations to define the
minimum depth necessary for each well. The chosen depth
should account for any variation of the ground-water
surface caused by seasonal or man-made fluctuations.
It may be difficult to determine appropriate well depths
for an aquifer where the ground-water surface configuration
is being artifically altered (e.g., by localized water supply
well pumping or mine dewatering). The owner or operator may
need to seek additional information (e.g., from the well
owner or mine owner) in order to define the trends of the
ground-water surface elevation fluctuations. Minimum monitoring
well intake depths should be determined in regard to the
lowest expected ground-water surface elevation and provide
an additional margin of safety for any unexpected seasonal
fluctuations. In cases where anomalous effects are severe
enough to alter the local ground-water flow patterns, owners
or operators will have to periodically reassess well locations,
number, and depths.
The positioning of the well intake (e.g., screened or
perforated portion of the casing) and total depth of the
well will depend upon both the saturated thickness of the
aquifer and the anticipated contaminant behavior in the
aquifer. For example, contaminants much denser than water
would be expected to sink rather rapidly in an aquifer and
42
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Figure 2-7
Typical Well Casing Design
GROUT PIPE
(temporary)
'/4 CLEARANCE
6" ID TEMPORARY CASING
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the aquifer is extremely thick, multi-level sampling, (e.g.,
a cluster of separate wells, screened and sealed at various
depths) should be used to obtain representative water samples.
Figure 2-8 illustrates the well cluster concept.
Well Materials Selection
When selecting well materials, owners or operators should
choose construction materials that have the least potential
for affecting the sample. That is, the desired levels of
detection for required chemical analyses should be achieved
without being unduly impacted by interactions between the
well material and the sample. (For further information on
selection of well materials with regard to sampling parameters,
see Scalf, et al, 1981, pp. 19, 87-93).
An example of a typical monitoring well is shown in Figure
2-9. Only the stainless steel screen and riser pipe are in
contact with the ground water. The galvanized pipe is used
to case the upper part of the well and is not directly in
contact with the ground water. This example does not imply
that this design is the most appropriate in all monitoring
situations.
2.3.2 Well Construction
Major components of well construction include drilling
methods, filter packing, sealing and well development.
These components relate to maintaining the integrity of the
borehole, enabling sampling in the appropriate aquifer flow
zone(s) and preventing the contamination of samples.
Drilling Methods
An owner or operator should choose a drilling method that
will minimize the spread of any ground-water contamination
and minimize interference with sample chemistry. Site-specific
conditions will play an important role in choosing the method.
Factors to be considered in choosing a drilling method include:
- hydrogeologic environment (related to types of formations,
depth of drilling, desired depth of well intake, etc.)
- the required parameter lists as well as the types of
potential contaminants to be monitored if the assessment
program has begun;
- design of monitoring well desired; and
- availability of drilling equipment.
46
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Figure 2-8
Well Cluster Concept
O DEPTH
12 fli«t«rs
(40 M.)
ft DEPTH
24m«t«r«
(80ft.)
DEPTH
30meter»
(100 ft.)
DEPTH
6m«t«r*
UO ft.)
DEPTH
iamtters
(60ft.)
PLAN VIEW
S LAND
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Ul
O
o o
10 O
SECTION VIEW
-------
Figure 2-9
Typical Monitoring Well Profile
GROUND SURFACE
TOP SOIL
SAND
FLUCTUATING
WATER TABLE'
UPPERMOST
AQUIFER
\
MW-4
PROTECTIVE CAP (LOCKED)
'/Q IN. VENT
8 IN- ID. 5 FT. LONG,BLACK IRON
PI PE- PROTECTIVE CASING
INSTALLED 3 FT BELOW
=_ - •_— GROUND SURFACE
.
4 IN.ID.GALVANIZED PIPE
THREADED COUPLING WITH
TEFLON THREAD TAPE SEAL
4 IN. ID. STAINLESS STEEL
RISER PIPE
THREADED COUPLING WITH
TEFLON THREAD TAPE SEAL
NATURAL OR ARTIFICIAL
FILTER PACK
4 IN. ID., 5 FT LONG,STAINLESS
STEEL.WIRE WOUND SCREEN
STAINLESS STEEL CAP
BED ROCK
48
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A variety of dry and wet (i.e., where drilling fluids are
employed) methods are used to drill monitoring wells. Some
of the more common methods include mud rotary, air rotary,
cable tool, reverse rotary, solid-stem auger, hollow-stem
auger and jetting. The advantages and disadvantages of both
dry and wet methods are discussed in detail by Scalf, et al
(1981, pp. 19-34). In certain situations, dry methods can
facilitate the collection of more reliable formation samples
and reduce ground-water contamination that could result
from drilling fluids used in wet methods. However, some
geological conditions may necessitate wet drilling. If wet
drilling is performed, special attention must be given to
preventing drilling fluids from entering the aquifer flow
zones and to removing of any such fluids from formation
materials if they do enter by proper well development prior
to sampling. Wet drilling methods which utilize organic
additives may distort the TOX and TOC concentrations, and
thus mask possible ground-water contamination. Drilling fluid
should be clear water or bentonite mixed with water. The
owner or operator should be prepared to specify and defend
the selection of any drilling fluid used with regard to its
effects upon sampling parameter analyses. Nearby surface
water bodies such as ponds and streams may be contaminated
and, therefore, should not be used for drilling fluid purposes
unless it can be shown that required analyses will not be
adversely affected. The Agency recommends that periodic
samples of the fluid used for drilling and washing of the
drilling equiment and samples of the recirculated drilling
fluid be analyzed for the required parameters and particularly
for those listed in §265.92(b)(3).
Drilling equipment should be kept clean and out of contact
with the ground surface when not in use. Contamination
sources such as hydraulic oil, gasoline, grease and oil from
the drill rig should also be removed. Antifreeze, which is
commonly pumped into the drilling fluid hoses to keep them
from freezing during cold weather, should not be used if it
will affect the required analysis. Clean mud pans with
easily removable covers should be used in place of mud pits
dug into the ground.
Filter Packing
Section 265.91(c) requires that casings be screened or
perforated, and packed with gravel or sand where necessary.
The owner or operator should evaluate site conditions to
determine if natural packing is sufficient or if "artifical"
packing is needed. An artifically packed well has gravel or
sand placed in the borehole around the outside of the intake
area. A naturally developed well is one in which a hydraulically
graded zone around the screen is created in the formation
49
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itself by repeated surging and bailing or pumping. A well
screen located in an aquifer surrounded by hard formation
material may not need filter packing if the area remains
consolidated when pumping. Whether natural or artifical,
the purposes of filter packing are to develop a zone of
increased hydraulic conductivity around the intake (e.g.,
screen) and to prevent well clogging (see Figure 2-10).
Generally, artifical filter packing is needed in uncon-
solidated formations if the aquifer consists primarily of
homogeneous, fine grained sand or silt. Other situations
where artificial packing would likely be appropriate include:
- well-graded aquifers containing large percentages of
fine materials (to avoid settlement of material above
the screen); and
- strata containing poorly cemented sandstone.
If artificial packing is needed to properly complete a
monitoring well, appropriate materials for the filter pack
must be chosen. Selecting the filter pack grain size necessitates
sampling and grain size analysis of the aquifer materials.
Selecting the appropriate filter pack should prevent clogging
with fine materials, (e.g., clay, silt). For further information
on packing materials and procedures, see EPA, Office of
Water Supply (1977, pp. 96-100).
Sealing of Wells
Commonly, during well installation an irregular space
between the borehole and casing will result. Section 265.91(c)
requires that the annular space be sealed with a suitable
material (e.g., cement grout or bentonite slurry) to prevent
sample and ground-water contamination. Therefore, it is
imperative that an appropriate sealing procedure be initiated
to prevent cross-contamination between surface materials and
ground water.
Sealing is a process which fills the annular space
between the well casing and the borehole, preventing water
and other materials from the surface from entering and possibly
contaminating the aquifer. Cement grout and bentonite
slurry are commonly used as sealing materials. Regardless
of the method of sealing selected by the owner or operator,
the process must be effective in ensuring a continuous satisfactory
seal. For further information on well sealing materials and
procedures, see EPA, Office of Water Supply (1977 pp. 79-87).
50
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0)
Figure 2-10 ^ ^ +,
Well Development/Filter packing
-------
Well Development
Well development is necessary to:
- restore the natural hydraulic conductivity of the formation
adjacent to the borehole to permit the water to flow
into the intake easily; and
- remove the clay, silt and other fines from the formation
so that during subsequent sampling the water will not
be turbid or contain suspended matter which can easily
interfere with chemical analysis.
There are a variety of suitable methods for developing
wells, including surge block, air lift, bailer, and surging
and pumping. For further information on these methods, see
Scalf, et al; (1981, pp. 36-38). The development process is
best accomplished by causing the natural formation water
inside the well intake to move vigorously in and out in
order to agitate the clay and silt, and move these fines
into the screen. The use of water other than natural formation
water is not recommended.
To verify the adequacy of a completed well, the well
driller should test the performance of the well (e.g., by
pumping or bailing). The well should yield clear water of
sufficient volume to more than satisfy the minimum volume
required for the sampling program operation (including well
flushing). If the well cannot be developed satisfactorily
because of improper design or construction or other reasons,
it should not be used as a monitoring well. An additional
well should be drilled and constructed as a replacement.
Examples of Well Installations
Care should be given to preparation of the casing and
intake portion materials prior to installation. As a minimum,
both should be washed with a detergent and rinsed thoroughly
with clean water. Care should also be taken that these and
other sampling materials are protected from contamination by
using some type of ground cover such as plastic sheeting for
temporary storage in the work area.
Figure 2-11 presents an example of a well installation
method. A six inch (ID) temporary casing is driven through
the zone to be screened. Upon reaching the desired depth
determined by hydrogeologic investigation, the temporary
casing is withdrawn and the monitoring well screen and casing
placed inside. If an artificial filter pack (e.g., clean
sand or gravel) is to be used, it should be emplaced a few
feet at a time as the temporary casing is removed. The filter
pack materials should extend a few feet above the top of the
52
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Figure 2-11
Example Ot Monitoring Well
Installation
GROUND SURFACE,
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53
-------
screen. A seal made from material such as cement grout or
bentonite slurry should be placed in the remaining annular
space to protect against the vertical migration of fluids
through the annular space to the aquifer. This is accomplished
by pumping the material into the annular space through a 1/2
inch ID grout pipe (see Figure 2-11). The temporary casing
and grout pipe are gradually removed as the annular space
fills with the sealing material. Finally, a 5-foot long,
8-inch ID protective casing with a protective cap is installed
over the monitoring well casing to a depth of 3 feet below the
ground surface.
The major advantage of this method of well installation
is that the temporary casing minimizes contamination because
during the entire installation process a seal is maintained
between the land surface and the aquifer.
Another common method of well installation is the lowering
of casing into a borehole drilled by a solid or hollow stem
auger. Although eliminating the possibility of contamination
by drilling fluids, this method has some limitations. These
include:
the well diameter is usually restricted to a maximum
of 2 inches;
well depths usually cannot exceed 150 feet; and
the method is not well suited for drilling through
hard formations.
For further information on well installation procedures,
see EPA, Office of Water Supply, (1977, pp. 76-77) and Johnson
(1975, pp. 209-276).
Well Construction Records
The facility owner or operator should require the well
driller to keep records of all materials used, including
dimensions, amounts and types. Details of well construction
(e.g., depths of screen and casing, depths at which water
was encountered, filter pack and sealing materials placement)
should be documented. Logs of materials encountered during
drilling should be recorded. The facility owner or operator
should acquire and maintain at the facility copies of all
information relating to well design and installation.
2 . 4 Sampling and Analysis
The sampling and analysis requirements of §265.92 are
to obtain and analyze representative samples of ground water
54
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upgradient and downgradient from the waste management area
in order to determine whether the facility has affected
ground-water in the uppermost aquifer underlying the facilty.
Analyses of three groups of parameters during the first year
of monitoring provide data on background water quality.
Information from upgradient well analyses of one of these
groups (i.e., the ground water contamination indicators)
serves as initial background data for statistical comparison
to data collected after the first year of monitoring at each
individual monitoring well.
2.4.1 Sampling and Analysis Plans
§265.92(a) requires the owner or operator to develop and
follow a ground-water sampling and analysis plan. The plan
must be kept at the facility and must include procedures and
techniques for:
sample collection;
sample preservation and shipment;
analytical procedures; and
chain of custody control.
The sampling and analysis plan must be available to EPA
personnel upon facility inspection. Its format should allow
prompt review of the determinants of the program's capabilities
such as the following:
- that the sampling schedule reflects seasonal influences,
unusual ground-water flow rate situations;
- rationale for sample handling and preparation (e.g.,
filtering or not filtering); consistency;
- flushing volume appropriateness—sufficient to provide
"representative" samples yet not dilute:
- extraction methods compatible with parameters of interest;
- storage and transit methods compatible with parameters of
interest; and
- reasonable assurance of chain of custody.
2.4.2 Sample Collection
The following guidance is provided to ensure the collection
of representative samples through minimizing the introduction
of extraneous substances to the sample. (For additional
55
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guidance on withdrawing samples, see Scalf, et al, 1981, p.
44.) Also, water level measurement techniques are described.
Water Level Measurement
§265.92(e) requires that elevation of the ground-water
surface at each monitoring well be determined each time a
sample is obtained (i.e., for each sampling event). The
initial step (before well flushing and sample withdrawal) in
the sampling program is to measure the static water level in
each monitoring well. The measuring instrument should be
free of contaminants and should not be allowed to come in
contact with the ground. The water level should be measured
accurately (e.g., to the nearest 0.01 meter). Accurate
measurement of the water level in the monitoring wells is
important for several reasons, including:
determining the hydraulic gradient of the ground
water in the vicinity of the disposal facility;
- monitoring of seasonal changes in the water table;
- evaluating effects on the uppermost aquifer of water
supply well pumping near the facility, including any
modification in the direction of flow; and
determining the existence of a "ground-water mound"
(elevated water table) developing in the aquifer
beneath the facility site. This is important since
mounding could cause the flow of potentially contaminated
water in directions other than towards the "downgradient"
monitoring wells.
A variety of mechanical and electrical instruments are
available for the measurement of the water level in monitoring
wells. Mechanical methods usually involve lowering a measuring
tape or marked line into the well, withdrawing it, and measuring
the distance to the "wet spot". A variation of this method
includes attaching a mechanical sounding device to the measuring
tape, lowering the tape into the well until a sound is heard,
and noting the length of measuring tape lowered into the
well. Electronic instruments are also available for measuring
the water level in the monitoring well. Use of an electronic
instrument involves lowering a cable into the well until it
reaches water, at which point the electric circuit is closed.
Water levels are recorded by a meter at the surface. For
further information on measuring of water surface elevations
see EPA, Office of Water Supply (1977, pp. 116-117) and
Johnson (1975, pp. 88-91).
56
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Well Flushing.
Monitoring wells should be flushed prior to sample
withdrawal to avoid collection of a non-representative (i.e.,
stagnant or stratified) ground-water sample. A common procedure
is to pump or bail a consistent volume of four to 10 times
the volume of water standing in the well (for moderate to
high yield formations) and at least one times the volume
(for low yield formations) prior to sampling to ensure that
water representative of the aquifer has entered the well.
Flushing equipment selected should affect parameter analysis
to the least possible degree. For further information on
this topic, see Scalf, et al (1981, pp. 43-44).
Obtaining Samples
Sampling equipment can be selected from a variety of
possible devices for the routine withdrawal of water samples
from ground-water monitoring wells. However, once selected,
all statistically compared values should be made with the
same equipment and procedures. Bailers, portable submersible
pumps, air-lift samplers, and suction-lift pumps have been
commonly used for ground-water investigations when monitoring
in the milligrams per liter range of detection or higher.
However, when monitoring of trace constituents in the low
micrograms per liter range of detection or lower, several
possible interferences, normally insignificant at a higher
level of detection, may occur from the use of standard sampling
equipment. Owners or operators should consider the likelihood
that the assessment program will be concerned with trace
organics, for instance, and whether the detection program
sampling equipment and monitoring wells will be useful during
the assessment. Problems to be avoided when using conventional
sampling equipment include:
leaching of materials used in the construction of
sampling equipment into the sample (e.g., trace levels
of adhesives);
adsorption of organic constituents in the sample on
sampling equipment (e.g., organic constituents can
become adsorbed on PVC);
pumps may introduce trace oils or metals to the sample
(e.g., lubricants); and
excessive mixing of the sample with air may occur,
driving volatile constituents from the sample.
The teflon bailer (see Figure 2-12) is recommended when
monitoring for total organic halogen and is appropriate for
-------
Figure 2-12
Teflon Bailer for Ground-water
Sampling
NICKEL WIRE
CABLE
l-l/4"o.D.xl" 1.0. TEFLON
EXTRUDED TUBING,
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-5/16" DIAMETER
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Source.;
58
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sampling of all required parameters in §265.92(b). Other
appropriate equipment used for sampling of. ground water and
the advantages and disadvantages of each are discussed by
Scalf, et al. (1981, pp. 44-60, 87-93), including some newer
and more sophisticated sampling equipment for low level
constituent analyses. This equipment includes: nitrogen
powered, glass-teflon pump; system for grab sampling; and a
continuous sampling system for organics.
The major concern in selecting sampling equipment is that
it ideally should not alter or contaminate the sample. The
selection of sampling equipment should be geared to the
nature of the parameters of interest. Scalf, et al (1981,
pp. 87-91) present a "Summary of Procedures Based on Parameter
of Interest" which offers guidelines for sampling for various
categories of contaminants. This summary includes all detection
program parameters. Sampling equipment should be appropriately
cleaned before sampling at each well.
2.4.3 Sample Preservation
Preservation techniques serve to slow down or delay chemical
and biological action, retard hydrolysis of chemical compounds
and complexes, reduce volatility of constituents and reduce
absorption effects. General preservation methods include pH
control, chemical addition, refrigeration, and freezing.
Other practices which may aid in retaining a representative
sample for given parameter analyses include: preventing
light from penetrating the sample, filling the bottle completely
to eliminate headspace; and shipping to a laboratory to
analyze the sample as soon as possible after collection.
Specific preservatives, container types and holding times,
as described in the selected analytical procedures, should
be used to maintain sample integrity. Whatever methods an
owner or operator selects should be recorded and standardized
for all subsequent sampling at the facility.
2.4.4 Sample Shipment
The shipment of ground-water samples necessitates the
use of containers and packing materials designed to prevent
breakage, spills and contamination of the samples. Tight
packing material (e.g., 10 cm) should be provided around
each sample container. Samples requiring refrigeration
should be placed in water-proof containers and packed with
re-usable plastic freezer packs, cans of freezing gel or ice.
Containers should be securely sealed, clearly labeled, compatible
with the sample and of sufficient volume (as described in the
selected analytical procedures); and accompanied by a sample
analysis request sheet and chain of custody record. Shippers
of samples should abide by any applicable shipping regulations
(e.g., restrictions due to use of chemical preservatives).
59
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2.4.5 Analytical Procedures
The facility owner or operator should select analytical
procedures which will provide results which most truly represent
the effects of his facility on ground water. Properly installed
and developed monitoring wells should minimize the entrance
of undissolved solids into the well intake. However, any
remaining undissolved solids which may interfere with analytical
procedures or which may be incompatible with analytical
equipment should be removed prior to analysis.
For metals, except where the anaytical technique requires
otherwise, the Agency recommends that analyses be performed
by the "total recoverable" procedure, as described in Methods
for Chemical Analysis of Water and Wastes (Section 4.1.4,
pp. "Metals-6-7" of the metals discussion) (See Table 2-3
for full reference). This procedure will yield a "total"
concentration value in a sample which has not been filtered
before acidification. Likewise, for other inorganic parameters,
sample preparation should be based on measuring the total
effect of each parameter on the sample.
For organic parameters, undissolved solids should be
separated out before sample analysis when appropriate for
the chosen analytical procedure. Separatory techniques
include settling, centrifugation and filtration. When filtration
is employed, procedures should be designed to prevent the
loss of volatile organic constituents.
In any case, consistency in sample preparation and
analytical procedures must be established and recorded.
§265.92(b) requires the owner or operator to determine
the concentrations or values of three groups of parameters
in ground-water samples. A discussion of the importance of
these parameters and sampling frequency is given below:
Parameters characterizing the suitability of the ground
water as a drinking water supply;
- Arsenic - Endrin
- Barium - Lindane
- Cadmium - Methoxychlor
- Chromium - Toxaphene
- Fluoride - 2, 4-D
- Lead - 2, 4, 5-TP Silvex
- Mercury - Radium
- Nitrate (as N) - Gross Alpha
- Selenium - Gross Beta
- Silver - Coliform bacteria
60
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Table 2-3
Analytical References
Note; The references given below (some containing approved
methods from other EPA programs) provide methods which have
not undergone rigorous formal testing on ground-water monitoring
well samples. The Agency, however, is of the opinion that
these methods are appropriate for Subpart F monitoring purposes.
Therefore, the following or other appropriate references
should be used:
Methods for Chemical Analysis of Water and Wastes
(EPA-600/4-79-020); Environmental Monitoring and
and Support Laboratory (EMSL); Cincinnati, Ohio;
March 1979. f
Inductively Coupled Plasma - Atomic Emission
Spectrometric Method For Trace Element Analysis of
Water and Wastes - Method 200.7; EMSL; Cincinnati,
Ohio.1"
Methods for Organochlorine Pesticides and Chlorophenoxy
Acid Herbicides In Drinking Water and Raw Source
Water (Interim); EMSL; Cincinnati, Ohio; July 1978. +
Prescribed Procedures for Measurement of Radioactivity
in Drinking Water (EPA-600/4-80-032); EMSL; Cincinnati,
Ohio; August 1980.f
Microbiological Methods for Monitoring the Environment
(EPA 600/8-78-017); EMSL; Cincinnati, Ohio, December
1978. t
61
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(Table 2-3 continued)
- Total Organic Halide (TOX) - Adapted From Method
450.1 Interim (EPA 600/4-81-056); EMSL; Cincinnati,
Ohio; November 1980.*
- 41 FR 52780 et seq; Guidelines Establishing Test
Procedures for the Analysis of Pollutants; Amendments-
December 1, 1976;
41 FR 59566 et seq; National Interim Primary Drinking
Water Regulations - December 24, 1975.
- 41 FR 28402 et seqj Interim Primary Drinking
Water Regulations, Radionuclides - July 9, 1976.
45 FR 57332 et seq; Interim Primary Drinking Water
Regulations; Amendments - August 27, 1980.
- Standard Methods for the Examination of Water and
Wastewater. Current edition. American Public Health
Association, et al. Washington, D.C.
- Annual Book of ASTM Standards, Part 31, "Water". 1976.
- Test Methods for Evaluating Solid Waste (SW-846).
U.S. EPA, Office of Solid Waste and Emergency Response.
Washington, D.C.; Second Edition, July 1982.°
* This interim methodology for determination of "Total Organic
Halogen" appears as Appendix D.
"*" Available from:
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S.Environmental Protection Agency
26 W. St. Clair Street
Cincinnati, Ohio 45268
Available from:
U.S. Government Printing Office, Washington, D.C.
62
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These parameters are used to determine the general suit-
ability of the aquifer as a drinking water supply. The
parameters listed have been established under the Safe Drinking
Water Act as National Interim Primary Drinking Water Standards.
Frequency
Owners or operators are required to sample and analyze
for these parameters quarterly during the first year of
monitoring only. Although these parameters require sampling
for only one year, owners or operators may continue to monitor
these parameters on a longer and/or more frequent basis to
provide a more thorough characterization of the aquifer.
Analytical Methods (see Table 2-3)
Parameters used to characterize ground-water quality;
- Chloride
- Iron
- Manganese
- Phenols (Phenolics, Total Recoverable)
- Sodium
- Sulfate
These substances are ubiquitous in the environment and
are often used to characterize the suitability of a ground-water
supply for a variety of uses. Information on these parameters
will also be useful in any assessment of ground-water contami-
nation that follows a determination that the facility is
affecting ground-water quality.
Frequency
Owners or operators are required to sample and analyze
for these parameters quarterly for the first year and at
least annually for all subsequent years.
Analytical Methods (see Table 2-3)
Parameters Used as Indicators of Ground-water Contamination:
- PH
Specific Conductance
Total Organic Carbon
Total Organic Halogen (TOX)
These four indicator parameters reflect changes in the
organic and inorganic makeup of the ground water and are
used to detect if a facility may be affecting ground-water
quality.
63
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Frequency
Owners or operators are required to sample and analyze
for these parameters quarterly for the first year to establish
initial background concentrations. For all subsequent years,
sampling and analysis must be conducted at least semi-annually.
Owners or operators may monitor these parameters on a more
frequent basis to provide for more prompt detection.
Analytical Methods (see Table 2 -3)
Specific conductance and pH can be analyzed in the field
using portable test meters. Exposure to the atmosphere,
temperature change, and the addition of preservatives can
initiate changes in these parameters. Since pH is more
sensitive to such conditions than specific conductance, pH
should be determined in the field. Specific conductance may
be determined in the field or in the laboratory. Battery
operated meters are available. Newer models may be equipped
with digital display. Kits are usually complete with probes
and standardizing/calibrating solutions. Operation is simple,
usually involving calibrating prior to testing which involves
immersing a probe in the ground-water sample and reading the
output on a meter. Separate pH, specific conductance and
temperature test meters are available as well as multi-function
meters. The owner or operator should be aware of and consistently
perform any temperature corrections for pH and specific
conductance called for in the selected analytical procedures.
2.4.6 Coordination Between Sample Collector and Laboratory
In order to ensure the successful implementation of the
sampling and analysis requirements, the sample collector and
laboratory personnel should closely coordinate their functions
with regard to materials and procedures (e.g., providing
appropriate sizes, types and numbers of sample containers;
preservation materials; sample holding times, delivery
arrangements, etc.).
2.4.7 Field Log Book
The owner or operator should maintain a field log book
to record information about each sample collected during the
ground-water monitoring program. This record of field sampling
procedures, measurements, and observations will provide a
source of documentation that sampling requirements for the
ground-water monitoring program have been met. The field
log book should also serve as a reference of past procedures
for the person who is sampling. Any change in procedure
should be noted. If a change is required, the owner or
operator should decide if a re-determination of initial
background parameter levels is necessary.
64
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then migrate laterally in the lower reaches of the aquifer;
whereas, "buoyant" contaminants (e.g., lighter hydrocarbons)
would be expected to migrate near the top of an aquifer.
The well depth and position of the intake should correspond
to the most likely depth of the contaminant plume within the
aquifer.
In many cases, the precise behavior of a complex mixture
of hazardous waste contaminants in the aquifer cannot be
adequately defined. Under these circumstances, the monitoring
well network should be designed to sample the uppermost
aquifer at several depths or flow zones in a given area (see
Figure 2-8 on well clusters). Single wells with multiple
sampling points may also be employed (see Fenn, et al, 1977,
pp. 97-98).
In aquifers where ground-water flow and contaminant
migration through fractured rock or solution channels is
"random", it is difficult to pinpoint appropriate monitoring
well depths. Often, drilling by trial-and-error may be
necessary to determine at what depth ground-water flow will
be intercepted.
2.3 Design and Installation of Monitoring Wells
Regulatory objectives for monitoring wells, presented in
§265.91(c), are to maintain the integrity of the monitoring
well borehole, enable sampling at depths where appropriate
aquifer flow zones exist, and to prevent contamination of
samples and the ground water. Sound engineering design
principles and installation procedures are essential to the
performance and longevity of monitoring wells. In order to
meet the objectives of the ground-water monitoring program,
additional design features that are dictated by the uniqueness
of an individual facility setting may need to be considered.
For further information on construction of monitoring wells,
see Scalf, et al (1981, pp. 17-42).
2.3.1 Design and Planning Factors
Major elements which must be addressed in well design
are the casing (housing of the well) and the well intake.
The casing should be demonstrated to be capable of adequate
support. The intake design must provide for extraction of
representative samples, minimize formation materials from
entering the sample, and provide structural stability in
unconsolidated earth materials. Appropriate well and filter
pack materials selection must be carried out so that parameter
analyses will be minimally affected.
Other planning factors which may affect the parameter
analysis and should be considered include the drilling method,
43
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sealing, casing installation procedures, development method,
and the intended sampling method. Factors related to casings
and intakes are discussed below.
Casing Design
Casing design involves consideration of proper size (i.e.,
diameter) selection to allow for efficient sample collection
(e.g., to provide access for sampling equipment); and selection
of casing materials to ensure that sample analyses will be
minimally influenced by interactions with the casing material
(see well material selection discussion, later in this Section).
In order to assure that samples are representative of
the ground water, contamination must be avoided during the
sampling process. The casing diameter should be determined
with regard to well depth, drilling methods, earth materials
encountered, the selected method of sampling, etc. The
casing diameter should allow free movement of equipment
during well flushing and sampling. An example of a typical
well casing design is shown in Figure 2-7. For this design,
a three inch inner diameter (ID) bailer is selected for
sample extraction. The outside bailer diameter was determined
in conjunction with the minimum inside casing diameter. The
selected ID of the well shown in the Figure is 4 inches.
Site-specific factors (e.g., earth material type and
depth to ground water) will also influence well casing selection,
Well casing sizes vary accordingly with the particular require-
ments of the site (e.g., some earth material formations will
necessitate use of stronger casing materials).
Intake Portion Design
Proper design of the well intake ensures sufficient
quantities of free-flowing water to the well and minimizes
the entrance of formation materials (e.g., silt and sediment)
into the well. Where well screens are needed, screen design
should consider appropriate slot size selection to correspond
to the particular formation materials present. Location of
the well intake is critical. It should be centered in the
most probable contaminant pathway and be short enough that
the sample is not always too dilute to detect the presence of
the monitored parameters. To enable sample collection at
depths where appropriate aquifer flow zones exist, the intake
must be located within formation materials which are most
likely to yield samples showing any migrating contaminants.
On-site investigations should identify the uppermost aquifer
flow zones so that well intake location and length can be
determined (see Sections 2.2.1, 2.2.2 and 2.2.4). In cases
where the flow zone(s) cannot be adequately identified, or
44
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A standard format of log entries should be established
in order to insure that all required information is noted.
Each field effort should include, but need not be limited
to, the following information:
- facility name and address;
- name of sample collector;
- purpose of sample and type (e.g., required analyses
for initial background data);
- location(s) or source of sampling (e.g., monitoring
well number);
- time and date of sampling;
- pertinent well data (e.g., depth, water surface elevation);
- sampling method (e.g., bailer, suction-lift pump);
- preservation used (if any) - type;
- log number of each sample, volume, and container type;
- appearance of each sample (e.g., color, turbidity,
sediment, oil on surface);
- field observations/sampling conditions (e.g., weather);
- sample temperature upon sampling;
- analyses performed in the field:
0 pH
0 specific conductance (unless done only at lab);
- sample storage (e.g., where, how; conditions such as
heat and light, number of sample seal); and
- name and location of laboratory performing analyses.
At the conclusion of this decription of the field activities,
the sample collector should verify the entries and sign the
log book. The responsibility for preparing and storing the
field log books should be assigned to a person who is knowledgeable
and involved in the monitoring program.
65
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2.4.8 Chain of Custody Control
A procedure for chain of custody control, or persons
through whom samples were transferred, is a required part of
the sampling and analysis plan. This procedure should document
sample transfer from collection through storage, shipment
and analysis. An accurate written record of these events
should demonstrate sample possession throughout the entire
program and, along with the proper use of sample container
seals, should show that sample iategrity was maintained.
An example of a chain of custody record form is given
in Figure 2-13. One form should be used for as many samples
as possible, preferably for a certain "set" of. samples (e.g.,
those from one well). The chain of custody form should be
signed and dated under "Chain of Possession" each time the
samples noted on that form change hands. Prompt attention
to this procedure will aid in keeping an accurate record of
sample transfer. The facility owner or operator should
arrange for each sample handler to return a copy of the form
to the facility.
Analysis request sheets (as many as necessary) should
accompany the samples delivered to the laboratory. The
analysis requests serve as official communication to the
laboratory of the particular analysis(es) required for each
sample and further verify that the chain of custody is complete.
A copy should be returned to the owner or operator of the
facility. An example of a standard analysis request sheet is
given in Figure 2-14. A more comprehensive request form may
be used, if necessary. The laboratory may supply analysis
request sheets to the sampler.
2.4.9 Laboratory Selection
Analyses of the ground-water samples should be performed
by a competent laboratory. In selecting a laboratory (or
laboratories) the owner or operator should evaluate its
capability to perform analyses for the required monitoring
parameters (e.g., does it have the instrumentation needed to
perform the total organic halogen analysis?). In assessing
laboratory capabilities, the owner or operator may wish to
determine whether the laboratory performs analyses required
under other EPA regulatory programs (e.g., National Pollutant
Discharge Elimination System; Safe Drinking Water Act).
Laboratory selection should also include a detailed evaluation
of the laboratory's quality control program. For further
information on this topic, see Handbook for Analytical Quality
Control in Water and Wastewater Laboratories (EPA-600/4-79-019),
EMSL, March 1979 (available from EMSL; see Table 2-3 for
address).
66
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Figure 2-13
'. of Sapiplg rhaln of
Custody Fbrm
Company's Name_
Address
Collector's Sample Nos.
Telephone ( )
number street
Collector's Name
Date Sampled
Field Information
city
state
Telephone ( )
zip
Time Sampled
hours
Sample Allocation:
1.
2.
3.
name of organization
name oforgamzation
Chain of Possession
1.
signature
2.
3.
signature
signature
.name of organization
title
title
title
inclusive dates
inclusive dates
inclusive dates
67
-------
0
*J
IO
o
Ol
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o
i
o
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ai -M
t- U O
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2.5 Program Implementation
2.5.1 Sampling Schedule
Ground-water sampling for the detection program is
scheduled in two phases:
- initial background sampling for a period of one year
for:
0 measurement of the ground-water surface elevation
for each sampling event;
0 parameters characterizing the suitability of the
ground water as a drinking water supply;
0 parameters establishing ground-water quality; and
0 parameters used as indicators of ground-water
contamination (four replicates for each upgradient
well).
- sampling after the first year for:
0 measurement of the ground-water surface elevation
each time a sample is obtained;
0 parameters establishing ground-water quality;
0 parameters used as indicators of ground water
contamination (four replicates for each upgradient
and downgradient well).
Initial background sampling should be performed during
the period of November 19, 1981 through November 18, 1982
for interim status facilities. The overall schedule for the
detection program is summarized in Figure 2-15. Detection
program sampling after the first year should continue until
final closure of the facility (and for disposal facilities
until the end of the post-closure care period) or until a
ground-water quality assessment program is begun (see
Section 3).
There are certain situations in which it would be
advisable to sample more frequently than the required minimum
or to amend the sampling schedule in order to detect significant
effects upon the ground-water quality. Such situations
include:
69
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Figure 2-15
Minimum Sampling Frequency Required
for the Detection Program
First Year
Month
8 9 10 11 12
test
parameter
drinking
water
suitability X
groundwater
quality X
contamination
indicators X
groundwater
surface
elevation X
X
X
X
X
After the
X
X
X
X
First Year
X
X
X
X
Month
test
parameter
After the First Year
123456789 10 11 12
groundwater
quality X
contamination
indicators X
groundwater
surface
elevation X
70
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high ground-water flow rate situations. The ground-
water flow rate is a major factor influencing the
rate at which contaminants may migrate in the subsurface
environment. The higher the ground-water flow rate
the more frequently sampling is recommended (e.g.,
turbulent flow in fractures or solution cavities).
Flow rates in different types of aquifers can range
from a few meters per year to tens of meters per day.
(See Section 3.2 for information on measurement of
ground-water flow rate and evaluation of subsurface
factors influencing flow rates);
changes in ground-water flow direction. Changes in
flow direction can affect the ability of "upgradient"
and "downgradient" wells to adequately determine the
facility's effect on ground-water quality in the
uppermost aquifer. If such changes in flow direction
occur, then the monitoring system must be re-evaluated
and, if necessary, redesigned such that it meets the
monitoring performance standard in §265.90(a);
significant climatic changes. Characteristics of the
climate (e.g., precipitation or evapotranspiration)
will influence leachate generation, which would be
expected to accelerate during ground-water recharge
periods. Ground-water monitoring can be most effective
if it responds to these recharge periods. Due to
this consideration, the sampling schedule might be
altered with respect to frequency (e.g., instituting
monthly sampling as opposed to semi-annual) and/or
periodicity (e.g., sampling once in March, April, May
and June, then in October in addition to regular
frequency sampling). A situation in which more frequent
sampling should be considered is after an extended
period of above average precipitation during which
leachate generation would be expected to accelerate
or to become more dilute;
gradual changes in monitoring data. A noticeable
trend (as opposed to a statistically "significant
change") in monitoring results may warrant more frequent
sampling in order to keep abreast of the apparently
changing condition of the ground water;
waste type influences. Waste that is highly soluble
in water and/or mobile in soil may travel quickly in
the subsurface environment. A facility owner or
operator managing such waste should consider sampling
more frequently than the minimum; and
71
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- an "unusual" event at the facility (e.g., improper
dumping of a large amount of liquids or a visible
spill or discharge may indicate the need for more
frequent monitoring).
2.5.2 Statistical Analysis
The owner or operator of a facility must perform a
statistical analysis of the concentrations or values of the
indicator parameters, as determined from the sampling and
analysis of the required monitoring wells.
Section 265.92(c)(2) on sampling and analysis requires
that the initial background mean and variance for each indicator
parameter be determined by pooling the replicate measurements
for the respective parameter concentrations in samples obtained
from the upgradient well(s) during the first year. Replicate
analyses are not required for downgradient wells during the
first year.
After the first year of monitoring, §265.92(d)(2) on
sampling and analysis and §265.93(b) on preparation, evaluation,
and response require the owner or operator to analyze for
and calculate the mean and variance of each indicator parameter
(i.e., pH, Specific Conductance, Total Organic Carbon, and
Total Organic Halogen), based on at least four replicate
measurements on each sample, for each well in the monitoring
system. Results for each indicator parameter from each
sampling event (for each and every well in the monitoring
system) must be compared with the initial background mean
(i.e., that established for the upgradient well(s) during
the first year). The student's t-test at the 0.01 level of
significance must be used to determine statistically significant
increases (or decreases also, in the case of pH) over the
initial background values.
First Year Statistical Analysis
During the first year, the initial background mean and
variance for each indicator parameter must be determined for
samples from upgradient wells.
Arithmetic Mean
In order to perform the t-test, the raw data from the
background and monitoring wells must be reduced to specific
summary measures. These measures are the mean (an average)
and the variance (a measure of variability of the data).
For any set of data (X]_r X2, ... Xn) the mean is calculated
by
_ Xi + X2 ... + Xn
X =
n
72
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The indicator parameter values for all four quarters of the
first year are used to calculate the mean. If more than one
upgradient well is being used, the owner or operator must
calculate the overall mean value (of each indicator parameter)
for all of the upgradient wells. This can be accomplished
by summing the data from all of the upgradient wells and
dividing this sum by the total number of measurements for
each parameter. These first-year upgradient mean values are
important since they establish the initial background
concentrations to which all subsequent upgradient and
downgradient concentrations or values will be compared.
Variance
The variance is an average of the squares of the
differences between the actual value and the mean, and is a
measure of variability. The mean and variance are used in
the Student's t-test to determine whether any changes in the
concentration of the indicator parameters are statistically
significant. In this context, the variance may be defined
as: the sum of the squares of the differences of the individual
measurements and the mean, divided by one less than the number
of measurements. Symbolically, the sample variance is
calculated as follows:
where
n
S
i = 1
- X)2
s^ =
n - 1
= sample variance;
= value of each measurement;
= mean of the measurements;
= "the sum of" a set of numbers from the
first value (where i = 1) to the last value
(where i = n). In this case, the squared
differences of the measurements and the
mean are added; and
= the number of measurements.
For example, in determining the sample variance of the
background value of the pH of an upgradient well for the
first year, the owner or operator would proceed in the following
manner:
- Substract the mean pH value (e.g., 6.4) from each pH
measurement, square this value, and sum the squared
differences as follows:
73
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Measurement
Mean
Difference
Squared
Difference
1st Quarter
2nd Quarter
3rd Quarter
4th Quarter
5.7
6.3
6.8
4.8
7.5
8.2
6.9
6.1
5.7
4.3
5.5
6.2
4.7
8.6
8.9
6.0
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
6.4
-0.7
-0.1
0.4
-1.6
1.1
1.8
0.5
-0.3
-.07
-2.1
-0.9
-0.2
-1.7
2.2
2.5
-0.4
0.49
0.01
0.16
2.56
1.21
3.24
0.24
0.09
0.49
4.41
0.81
0.04
2.89
4.84
6.25
0.16
Total
27.90;
- Divide the sum of the squared differences by the number
of measurements minus one, as follows:
Sample Variance = s2 = 27.9 = 27.9 = 1.86; and
n-1 16-1
- Keep at least two decimal places for accuracy in
calculations.
The variance for specific conductance, total organic
carbon, and total organic halogen can be calculated in a
similar manner. If more than one upgradient well is being
used, the sample variance can be calculated by pooling all
the measurements (for each indicator parameter) to determine
the mean, subtracting the mean from each measurement, squaring
and summing the differences as in the first step above, and
dividing this sum by the number of measurements minus one,
as in the second step above.
Subsequent Statistical Analysis (after the first year)
After determining initial background values during the
first year, the owner or operator must, at least semi-annually,
calculate the sample mean and sample variance for four replicate
74
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measures (necessitating four aliquots from the same sample
for any destructive analyses) of pH, specific conductance,
total organic carbon, and total organic halogen, for each
upgradient and downgradient ground-water monitoring well.
These values should be determined in the manner described
previously. The mean of each of these indicator parameters
for each upgradient and downgradient well must be individually
compared to the initial background mean for each indicator
parameter by using the Student's t-test at the 0.01 level of
significance. This provides a determination of statistically
significant increases (or decreases also for pH) over the
initial background level.
Student's t-test
[Note; The methodology for application of the Student's
t-test presented in this guidance document differs from that
offered in the May 2, 1980, background document for ground-water
monitoring. Although both methods could be appropriate, the
one recommended in this guidance document is preferred.]
The Student's t-test is a statistical method used to
determine the significance of a change between initial background
and subsequent parameter values and must be calculated at
least semi-annually for each well for each indicator parameter.
Using all the available background data (nj-, readings),
calculate the background mean (Xfc,) and background variance
(s^). For the single monitoring well under investigation
b
(nm readings), calculate the monitoring mean (Xm) and
2
monitoring variance (sm).
The t-test uses these data summary measures to calculate
a t-statistic (t*) and a comparison t-statistic (tc). The
t* value is compared to the tc value and a conclusion reached
as to whether there has been a statistically significant
change in the indicator parameter value.
The t-test for the difference of two groups is given by:
xm ~ xb
t* =
75
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If the t* is negative (except for pH ) , then there is no
significant difference between the monitoring data and
background data.
The t-statistic (tc) against which t* will be compared,
necessitates finding t^ and tm from Table 2-4 where,
t]-, = Table 2-4 with (nj-,-1) degrees of freedom, 0.01 level
of significance; and
tm = Table 2-4 with (nm-l) degrees of freedom, 0.01 level
of significance.
[NR: if pH is being examined, use 0.005 as the level of
significance]. Finally, the special weightings W^ and Wm
are defined as:
2 2
sb sm '
Wb = _ and Wm = _
nb nm
and so the comparison t-statistic is
tc "
wmtm
wb + w,
'm
The t-statistic (t*) is now compared with the comparison
t-statistic (tc) using the following decision-rule:
If t* is equal to or larger that tr, then conclude that '
there most likely has been an increase in indicator
parameter. [In the case for pH, it is decrease if the
t* as originally calculated was negative, and increase
if the original t* was positive.]
If t*is less than _tc, then conclude that most likely I
there has not been a change in indicator parameter.
The procedure described above is known as Cochrans1 I
Approximation to the Behrens-Fisher solution of the comparison "-1
of two independent samples with unequal population variances.
For further information, see Snedecor and Cochran (1967) or I
Steel and Torrie (1960). " j
Example of the t-test •
These readings represent pH values collected from a "
hazardous waste disposal facility. Background well samples
76
1
-------
Table 2-4
The Critical t-values at the 0.01 and 0.005 Levels
of Significance
Degrees of
Freedom
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
40
60
120
Level of Significance
__ = 0.01 ___
31.821
6.965
4.541
3.747
3.365
3.143
2.998
2.896
2.821
2.764
Level of Significance
= 0.005
2
2
2.718
2.681
650
624
2.602
2.583
2.567
2.552
2.539
2.528
2.518
2
2
2
2
508
500
492
485
2.479
2.473
2.467
2.462
2.457
2.423
2.390
2.358
2.326
5
4
63.657
9.925
841
604
4.032
3.707
3.499
3.355
3.250
3.169
3
3
3
2
2
106
055
012
2.977
2.947
921
898
2.878
2.861
2.845
2.831
2.819
2.807
2.797
2.787
2.779
2.771
2.763
2.756
2.750
2.704
2.660
2.617
2.576
Adapted from Table III, Statistical Tables for Biological,
Agricultural and Medical Research, Fisher and Yates, 1963.
77
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were collected quarterly and four determinations made on
each quarterly sample. For the purposes of this example,
only one monitoring well will be considered.
BACKGROUND WELL MONITORING
1st Quarter 2nd Quarter 3rd Quarter 4th Quarter WELL
6
6
6
6
For
.5
.6
.5
.4
the
6
6
6
6
.3
.4
.3
.4
background
6
6
6
6
data the
6.5 + 6
.6
.4
.5
.5
mean (Xj
.3 + 6.6
6.
6.
6.
6.
>) is,
... + 6
5 .
5
4
4
.4
6
6
6
6
.6
.6
.7
.6
16 , or
6.450,
2
and the background variance (35) is,
(6.5-6.450)2 + (6.3-6.450)2 ... + (6.4-6.450)2
sb = 16-1
or
2
Sb = 0.008.
For the monitoring data, the mean (Xm) is,
_ 6.6 + 6.6 + 6.7 + 6.6
Xra = 4 , or
Xm = 6.625,
and the monitoring variance (Sjn) is
(6.6-6.625)2 + (6.6-6.62S)2 + (6.7-6.62S)2 + (6.6-6.625)2
2
sm = 4-1
2
STO = 0.0025.
_^____ f an<3 for this example,
t* =
78
-------
6.625 - 6.450
-* =
'.0025 + 0.008 , or
4 16
t* = 5.217.
Now, from Table 2-4
tb = Table 2-4 with 15 degree of freedom, significance
level = 0.005,
tb = 2.947,
tm = Table 2-4 with 3 degree of freedom,
significance level = 0.005,
tm =5.841.
The weights are:
2
En, 0.0025
Wm = = = 0.000625,
*]Tl *
and 2
Wb = Sb 0.008
= = 0.0005.
nb 16
Therefore,
wmtra
tc = , and for this example,
Wb + Wm
tc = (0.0005 x 2.947) + (0.000625 x 5.841) ,
(0.0005 + 0.000625)
giving tc = 4.555.
As t* (=5.217) is larger than tc (=4.555), the conclusion is
that there has been a statistically significant change (increase)
in pH level. In this particular example the procedure of
§265.93(c)(2) concerning obtaining, splitting and analyzing
additional samples would then be followed.
79
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Owner or Operator Response to the Statistical Analysis
Student's t-Test Results for Upgradient Wells
A student's t-test for an upgradient well that shows a
significant increase in the concentration or value of an
indicator parameter (or decrease also in pH value) may mean
that sources other than the facility may be affecting ground-
water quality. If comparisons of the concentrations of
indicator parameters for the upgradient wells show a
significant increase (or also pH decrease), the owner or
operator must submit this information in accordance with
S265.94(a)(2)(ii) (see Section 2.5.3).
Possible conditions that could cause an indication of
ground-water contamination in upgradient wells include:
- error in sampling and/or analysis of ground-water;
- actual contamination of ground water (e.g., due to a
discharge, spill or other incidents upgradient of the
facility);
- actual contamination due to a facility discharge and
a mounding effect of contaminated ground-water beneath
the facility; and
- actual contamination of ground water due to a facility
discharge and a change in hydraulic gradient, so that
the originally upgradient wells are now downgradient
relative to the facility. This condition should be
reflected by data on the ground-water surface
elevations.
Student's t-Test Results for Downgradient Wells
A student's t-test for any downgradient well that shows
a significant increase in the concentration or value of an
indicator parameter (or decrease also for pH) signals possible
ground-water contamination and is the first indication of
a possible facility discharge. Section 265.93(c)(2) requires
that if the comparisons for downgradient wells made under
§265.93(b) show a significant increase (or also a pH decrease),
the owner or operator must then immediately obtain additional
ground-water samples from those downgradient wells where a
significant difference was detected, split the samples in
two, and obtain analyses of all additional samples to determine
whether the significant difference was a result of human
error. If the previous results are refuted and no significant
change has occurred, the detection program can be resumed per
the original schedule.
80
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If the additional analyses performed under §265.93(c)(2)
confirm the significant increase (or pH decrease), the owner
or operator must provide written notice to the Regional
Administrator - within seven days of the date of such confirmation
- that the facility may be affecting ground-water quality.
The written notice should include the relevant calculation(s)
performed according to §265.93(b). The owner or operator
must then develop and submit to the EPA Regional Administrator
a ground-water quality assessment program plan within 15 days
of the written notice (see Section 3).
2.5.3 Recordkeeping and Reporting
Recordkeeping
Owners or operators are advised to keep records of all
professionally certified designs and analyses performed in
accordance with the preceding parts of this section. These
records should be maintained in an orderly fashion, possibly
part of the sampling and analysis plan if appropriate, and
be made available to Agency personnel during facility inspections.
The outline in the Table of Contents may provide a convenient
format for most facilities, but as mentioned in Section 1.3,
Program Implementation, the Agency has decided not to prescribe
a rigid format for the on-site documentation. Since lab
reports, well logs, consultant reports and other components
are not readily adjustable to a fixed format, it would be
counter-productive to suggest one.
The detection monitoring system capability should be
demonstrated first by showing the rationale for sampling
points, second by defense of the frequency (whether minimum,
additional or alternate), and third by discussion of the
adequacy of the indicator parameters to assure detection.
The system compliance with casing and sealing requirements
may take the form of a geologist's certification of inspection.
Lab reports should be clipped or inserted directly into the
records in looseleaf.
Detection program records will serve as a history of
whether the facility has affected ground-water quality of
the underlying aquifer (i.e., through statistically significant
changes in indicator parameter values). Section 265.94(a)
requires that, unless the ground water is monitored to satisfy
the requirements of §265.93(d)(4) (assessment program
monitoring), the owner or operator must keep records of the
analyses required in §265.92(c) and (d), the associated
ground-water surface elevations required in §265.92(e) and
evaluations in §265.93(b) until final closure of the facility,
and, for disposal facilities, throughout the post-closure
care period as well. Such records include:
81
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- measurements of the ground-water surface elevation at
each monitoring well for each sampling event;
- analytical results for:
0 drinking water suitability parameters;
0 ground-water quality parameters;
0 contamination indicator parameters; and
- calculated results for the contamination indicator
parameter data:
0 arithmetic mean
0 variance
0 Student's t-test.
The records of these data should be organized in such a
way as to clearly show: any relevant statistically significant
difference(s), the exact location(s) and date(s) of any such
significant difference(s), and a chronology of events of
potential contamination according to well location since the
start of ground-water monitoring at the facility. In addition,
since changes in the ground-water conditions may occur very
slowly, the values and concentrations of all the indicator
parameters should be recorded so that any gradual changes
over time and space are readily observable and can be studied.
These records will be valuable in determining the significance
of increases and decreases in indicator parameters. Since
this information may help to identify the type and extent of
any ground-water contamination, it could also aid in the
successful implementation of a ground-water quality assessment
program.
Reporting
As previously discussed, the owner or operator must
submit a report identifying parameters listed in §265.92(b)(1)
whose values exceed the maximum contaminant levels for those
parameters of 40 CFR 265 listed in Appendix III (see Appendix
C of this document). The report must be submitted within
15 days of the analysis, and separately identify the background
well and downgradient wells, the parameter exceeding, and
the concentration.
82
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monitoring requirements are not to be waived for reasons such
as:
unsuitability of the uppermost aquifer for drinking
water;
- expense of complying with ground-water monitoring
requirements; and
facility design.
The waiver mechanism allows varying degrees of deviation
from the ground-water monitoring requirements. The lower the
demonstrated potential for contaminant migration, the waiving
of more requirements may be justified. For instance, if the
unsaturated zone consists of a thick formation of very low
hydraulic conductivity and the ground water moves at a slow
rate, the potential for contaminant migration is low and may
warrant a reduced frequency of sampling of ground-water
monitoring wells. A complete waiver from the ground-water
monitoring requirements would be very difficult to demonstrate
since it must be established that there will be no potential
for migration of hazardous waste or hazardous waste constituents
through the uppermost and any interconnected aquifers to
water supply wells or surface water without regard to time.
The Regional Administrator can request, at any time, to
examine the written waiver demonstration, prepared by the
owner or operator, to evaluate the supportability of the
waiver. Also, waiver demonstrations will be routinely examined
as part of facility inspections. Appropriate data and
investigatory techniques for a waiver demonstration are
described below.
2.6.1 Determining Potential for Contaminant Migration from
Facility to the Uppermost Aquifer
In order to establish the potential for migration of
hazardous waste or hazardous waste constituents from the
facility to the uppermost aquifer, the owner or operator is
required to evaluate a site water balance and unsaturated
zone characteristics. The following discussions explain
these components.
Determining the Water Balance
The infiltration fraction of precipitation is the
principal contributor to leachate generation from a hazardous
waste management facility. Infiltration into cover material
(if present) and any subsequent percolation down to the waste
material, to the unsaturated zone, and eventually to ground
water will be determined by surface conditions of the facility
and by the hydrogeologic characteristics of the facility's
location.
85
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The water balance, as developed in the soil and water
conservation literature, is based upon the relationship among
precipitation, evapotranspiration, surface runoff and soil
moisture storage. Precipitation represents that amount of
water added. Evapotranspiration, the combined evaporation
from plant and soil surfaces and tranpiration from plants,
represents the transport of water from the earth back to the
atmosphere, the reverse of precipitation. Surface runoff
represents water which flows directly off the area of concern.
Soil moisture storage represents water which can be held in
the soil. Water balance calculations, employing the above
parameters, can be solved to determine the percolation to
ground water. Knowledge of the volume and placement of waste
material can, further, provide an estimate of the
potential amount of leachate which could be discharged from
the facility. The water balance can be expressed as:
P - R = I;
I - AET = Perc;
where P = precipitation;
R = runoff;
I = infiltration;
AET = actual evapotranspiration; and
Perc = percolation.
If I minus AET is positive, over a given time interval,
then soil moisture storage will increase. After the soil
moisture storage reaches its maximum, any excess infiltration
becomes percolation through the cover soil (if any) and waste
materials, eventually reaching ground water. Therefore,
significant percolation will occur during those time intervals
when I exceeds AET and the soil moisture storage exceeds its
maximum. For most humid areas, this will occur during the
wet season. For dry areas, significant percolation may occur
only in very short episodes if at all. For methods of
determining the water balance, see Fenn, et al (1975) and
Thornthwaite and Mather (1955, 1957).
The following discussion provides further information on
the water balance factors and also provides methods of
obtaining the needed data.
Precipitation
Precipitation data is tabulated in the form of mean
monthly values for 30-year periods for each National Weather
86
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Service station across the country. This information can be
requested from the National Climatic Center, Federal Building,
Asheville, NC 28801, 704/258-2850 (see Figure 2-16). Other
possible sources for monthly precipitation data include State
Departments of Agriculture, local universities, and associated
technical publications. On-site field measurements should be
used to validate regional data for the site; an onsite survey
will be needed if suitable data is not available.
The owner or operator should obtain mean monthly
precipitation values for the weather station closest in
location and geographic characteristics to his facility (e.g.,
a coastal station often does not accurately reflect the
precipitation characteristics of an inland location, despite
close proximity). In the case where the station does not
accurately reflect the precipitation at the facility site or
the data is incomplete (e.g., missing records) or of questionable
reliablility (e.g., discrepancies in values), the owner or
operator should obtain more accurate data from alternate
sources. Available on-site or nearby determinations are highly
desirable. Consistent relationships may be entered into a
calculated P-value. Once precipitation data has been obtained,
the mean monthly values should be tabulated for each month
and retained for later use in these calculations. Recorded
anomalies should also be tabulated when significant and
available.
Evapotranspiration
Evapotranspiration is the amount of water returned to
the atmosphere as vapor through the combined action of
evaporation and transpiration. If, as is often the case, the
overall amount of evaporation cannot reliably be measured
separately from transpiration, the two effects are considered
together as "evapotranspiration".
Several techniques are available for calculating potential
evapotranspiration. Well-known methods include: Thornthwaite
(1948), Blaney-Criddle (1962) and Penman (1948). Conversion
from potential to actual evapotranspiration is generally
performed using a soil moisture budget approach (e.g., Holmes
and Robertson, 1959).
Evapotranspiration values obtained should be tabulated
by month, as with the precipitation data. It should be noted
that no completely successful technique for estimating
evapotranspiration has been devised to date. Therefore, the
above-listed methods should be evaluated for their applicability
to site-specific conditions. Where soil temperatures, solar
loading due to slope, ground cover, etc., or wind velocity
and humidity may significantly affect AET, these should be
separately introduced into the calculation.
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Figure 2-16
Example of Monthly Precipitation
Records
PRECIPITATION NORtlRLS
CUMMOGRWW Of THE tlHHED SUUS MO. 81 |8Y STATE) ' . •'
Monthly Normals of Temperature,
Precipitation, and Heating and
Cooling Degree Days 1941-70
'
tefe:;!!
* * ^ *. - •**__.:? •." *i
CHILK«4BU«a M^| n.«MT
cnwiTan
H:t
** 1ft
*«.»f
11 -*1
88
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Runoff
Runoff is the amount of incident precipitation that becomes
overland flow before it has a chance to infiltrate. The amount
of actual surface runoff varies with the intensity and duration
of the storm, the antecedent soil moisture condition, the
permeability and infiltration capacity of the soil, the
slopes, and the amount and type of vegetation cover. Although
it is difficult to account for all these factors in estimating
runoff, most available methods account for at least some of
the above-mentioned factors.
There are several methods for estimating the runoff
fraction of incident precipitation. Although it will, in
most cases, underestimate surface runoff, the "Rational
Runoff" formula is presented here as one of the more convenient
methods. The "mean monthly surface runoff" (R) can be
calculated as follows:
R = P x CR;
where P = mean monthly precipitation; and
CR = empirical runoff coefficient (see
Chow, 1964).
The runoff coefficient CR provides the means of estimating
surface runoff quantities for given site conditions. The
coefficients take into account a variety of vegetation types,
soil types and slope steepness, and have been tabulated (e.g.,
by Chow, 1964). The owner or operator should match his site
characteristics against those listed in the tables (e.g.,
Chow, 1964) and select the coefficient for the site
characteristics which most nearly approximate his own site.
The owner or operator should tabulate the mean surface
runoff values by month.
Infiltration
Infiltration is the amount of precipitation that enters
the surface of the soil. It represents a source of moisture
that may eventually percolate through the facility and
unsaturated zone into the ground water.
Infiltration can be calculated using the values derived
in the preceding discussions as follows:
I = P - R.
This calculation should be performed for each month unless
anomalies indicate otherwise. A negative value for I indicates
that the amount of infiltration is not sufficient to exceed
soil moisture storage capacity (i.e., no percolation is likely
89
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to occur). A positive value for I indicates soil moisture
storage recharge and potential percolation.
Percolation
Percolation is calculated as follows:
Perc = I - AET.
By determining the percolation rate, the area and depth
of the waste, and waste/soil moisture storage capacity, the
owner or operator can derive a rough estimate of potential
leachate volume (see Fenn, et al, 1977, pp. 212-214 for
further details).
Facility Site-specificity
The water balance method is a useful tool for evaluating
the potential for contaminants to migrate through the unsaturated
zone. However, it must be recognized that certain site-specific
assumptions are necessary to tailor the method to a particular
site. These assumptions are incorporated into the choice of
precipitation data, and the choice of methods for determining
evapotranspiration and surface runoff. In addition, conditions
such as bare soil/lack of vegetation, irrigation (e.g., by
land treatment), frozen ground and snow-melt must be accounted
for where they affect the site (Fenn et. al., 1975).
The water balance method can be used to calculate
infiltration at land treatment facilities. In this approach,
the applied liquid waste and precipitation are volumetrically
summed as the input, and infiltration is computed as the
difference between this input and evapotranspiration. Applied
liquid waste volumes can be determined from operating records.
Precipitation volumes can usually be extrapolated from rainfall
gaging stations in nearby areas. Monthly rainfall determinations
are often suitable; however, in areas with highly variable
precipitation, such as in Southwestern States, onsite
measurements may be necessary.
Evapotranspiration from areas where land treatment is
practiced can be determined by a number of methods (Cruff
and Thompson, 1967; Blaney and Griddle, 1962; Lowry and
Johnson, 1942; Penman, 1948; and Thornthwaite, 1948). These
methods are generally based on different groupings of
climatological parameters. For example, the Blaney-Criddle
method depends primarily on temperature and percentage of
daylight hours. In general the Penman and Thornthwaite
methods ,are more applicable to humid areas, where the
BlaneyCriddle method is more applicable to semiarid areas.
Different values of evapotranspiration and consumptive use
are usually obtained for different vegetation and soil
conditions. Thus, the vegetation pattern must be known.
90
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Sufficient field tests have been conducted in many areas so
that evapotranspiration and consumptive use are well
established. In some areas, data may have to be extrapolated
from similar areas. Evapotranspiration rates will generally
be needed on at least a monthly basis, and sometimes weekly.
In the water balance for land treatment, the infiltrating
component is divided into two portions. A portion of this
component is diverted into soil moisture storage. This soil
moisture component will be gradually depleted by transpiration
during periods of zero recharge. It should be noted that
evapotranspiration calculations which continue to indicate
evapotranspiration during depleted periods give distorted,
unacceptable results. When the field capacity requirements
have been satisfied the remaining portion will percolate to
the zone of saturation.
The water balance method can also be used to calculate
discharge from surface impoundments. Waste discharge and
precipitation are volumetrically summed as the input, and
discharge is calculated as the difference between input and
evaporation. Storage changes in the impoundment must also be
taken into account. Evaporation from free-water surfaces
can be determined from measurements using land pans or floating
pans (Harbeck et al, 1958; Kohler et al, 1955; Follansbee,
1933; and Rohwer, 1933). Monthly values will often suffice;
however, in some cases weekly or daily values are necessary.
Factors such as salinity of waste liquid can affect the
evaporation rate. In general, with increasing salinity the
vapor pressure of water decreases, resulting in a lower
evaporation rate. In considering evaporation from free-water
surfaces from impoundments of different sizes, consideration
should be given to edge effects. That is, evaporation rates
depend on the characteristics of the surrounding land, for
example, whether it is cultivated or undeveloped.
When applying the water balance to landfills, precipitation
volumes must be obtained and the portion that infiltrates the
landfill determined. This portion will first go into meeting
the moisture storage requirements of the waste and cover
material. For this reason the moisture content of the waste must
be estimated. When the waste reaches field capacity percolation
will result.
The results of water balance calculations do not represent
absolute values of potential for contaminant migration.
Instead, the resulting values will be used in concert with
all other factors provided by the waiver demonstration in
evaluating the relative potential for contamination.
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Determining Unsaturated Zone Characteristics
The topsoil and materials of the unsaturated zone may
have a significant but sometimes temporary capacity to remove
a limited quantity of contaminants from downward-percolating
waters. The extent of ground-water contamination due to
waste percolation from the land surface depends strongly on
the rate and volume of recharged water. In a semiarid or
arid climate, contaminants may be retained above the water
table in a nearly permanent fashion. On the other hand, in
humid areas contaminants may be rapidly carried downward from
the land surface to the water table. Generally, in a
homogeneous porous media, percolating water will pass vertically
through the unsaturated zone. However, in a heterogeneous,
stratified material (e.g., most of the alluvial deposits of
the western U.S.), percolating water may become perched above
layers of low hydraulic conductivity. In this situation,
lateral movement for substantial distances can occur above
the water table.
The capacity for attentuation of many potential contaminants
is greatly affected by the amount and characteristics of the
geologic materials present in the unsaturated zone. This is
especially true for the sorption capacity of many organic
chemicals and trace elements. This limited capacity for
removal of some contaminants is in sharp contrast to the
almost unlimited ability of many unconsolidated materials to
remove bacteriological contaminants. The existence of many
documented case histories of ground-water contamination
indicates that the unsaturated zone may often not provide
complete protection. Problems can occur when attenuation
capacity is exceeded due to high waste loadings.
Identify Geologic Materials
The owner or operator should begin to investigate the
characteristics of the unsaturated zone by collecting available
information about the geology underlying the facility area
prior to any field testing. Background information will
provide initial identification of materials, indicate areas
where data is lacking, indicate which field tests should be
performed, and later may serve to verify field data or indicate
what further testing is needed.
Information about regional and site-specific geology
should include:
- topography, surface relief;
- geologic structure, locations and patterns
of major fractures, joints and solution
cavities;
- characteristics, thicknesses and areal
distribution of soils;
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thicknesses of formations, stratigraphy,
lithology, and formation homogeneity and
continuity? and
hydraulic conductivity.
Some sources for this information are listed in Table 2.1.
This information should be evaluated to determine existing
descriptions of geologic materials in the facility area.
Once data gaps have been identified, field techniques should
be used for verification and to supply additional information
on the identity of on-site geologic materials. For example,
boreholes are one method of direct investigation of the
subsurface, and are particularly necessary in support of
direct methods. Formation samples collected from boreholes
can provide data on the identity of geologic materials in the
unsaturated zone and on the thicknesses of formations.
Samples that have been collected from boreholes or preliminarily
identified in the field should be sent to a qualified soils
laboratory for identification confirmation and other appropriate
tests.
Indirect geophysical techniques, such as geophysical
logging, surface electrical resistivity and seismic surveys
can provide augmentation to the information about site geologic
materials. They are particularly useful in demonstrating
continuity between direct sampling points.
Discussions of procedures, applicability, advantages and
disadvantages of direct and indirect field methods of subsurface
investigation are presented in Sections 2.2.1, 2.2.2 and 3.3.
Determining Physical Properties and Depth to Ground
Water in the Unsaturated Zone
The hydraulic conductivity (K) of materials within the
unsaturated zone is an important factor in determining
contaminant pathways and the potential and/or time needed for
contaminants to reach ground water. Low K values (e.g.,
10~8 cm/sec) may be used in support of a waiver demonstration.
Such values can be found in earth materials such as unfractured
clays and shales. (Methods for determining K are presented
in Section 3.2). When gathering data concerning K values,
the owner or operator should evaluate and document, at least,
the following:
variations in K areally and with depth; and
- continuity and thicknesses of materials with given K
values.
Thick unsaturated zones (e.g., 100 meters), in conjunction
with low K values, can be supportive of a waiver demonstration.
93
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Thickness data should be established through reliable methods
(e.g., borehole logging). Such information should not be
obtained by boring through the waste management area, as this
could provide a direct conduit for hazardous wastes to reach
the ground water.
Depth to ground water should be accurately determined
within the facility area (see Sections 2.2.1 and 2.2.2
concerning historical records, piezometers and water table
wells, and water-level measurement techniques). Water level
elevation data should be used to construct flow nets which
indicate hydraulic gradients and ground-water flow directions
(see Section 2.2.2 for a discussion on flow net construction).
Water elevation and unsaturated zone thickness data are needed
to determine the distance contaminants must travel to reach
the uppermost aquifer.
Evaluating Attenuation Capabilities of the Unsaturated
Zone (adapted from Todd, et al, 1976)
Various factors and processes affect the mobility of
contaminants moving through the unsaturated zone. Close
examination and documentation of the effects of these factors
and processes may lend credence to a waiver demonstration.
Contaminant attenuation in the subsurface commonly occurs
due to the following processes: dilution, filtration,
sorption, buffering, precipitation, oxidation and reduction,
volatilization, biological degradation and assimilation.
Dilution
One of the mechanisms of attenuation frequently mentioned
in the literature is dilution. The obvious limitations for
use of dilution to substantiate a waiver preclude its use as
a primary basis at landfills and surface impoundments.
Continuous sources of contaminants in laminar flow situations
cannot be shown to be so dilute that they meet the "no or low
probability" criterion for a waiver. Dilution as discussed in
this section is of course a factor in attenuation. It may
have applicability in waiver demonstrations in unusual cases
unforeseen by the Agency, and of course, it is a necessary
consideration in design of detection programs. Therefore, it
is included here primarily for sake of completeness.
Dilution above the water table can be substantial in
humid areas and almost nonexistent in arid areas. Sources
of water for dilution include precipitation, seepage from
streams, lakes and canals, and artificial recharge. The
quality of water from each source of recharge should be
estimated if, in the judgement of the geologist or geotechnical
engineer, it might be a significant factor. A comparison of
94
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the respective quantities of water and constituent concentrations
in a waste discharge at the land surface can indicate the
extent of subsequent dilution of contaminants.
An example is presented in the following discussion.
Assume an agricultural area in the West where irrigation is
practiced in the dry summer months and rainfall occurs in the
wet winter months. Return flow over the area averages 18
inches per year and the salinity of this water is 300 parts
per million (ppm) . Rainfall is 12 inches per year and its
salinity is 10 ppm. Consideration of the water balance
analysis at the land surface indicates that 9 of the 12 inches
of rainfall percolates to the water table. The maximum
subsequent dilution, presuming thorough mixing, can be
calculated by the equation:
AVA + BVB = C;
where VA and Vg are respective percentages of water
from return flow and precipitation. A, B, and C
are the respective salinities of the return flow,
precipitation, and the mixture of the two. In this
example:
C = 300(18/27) + 10(9/27)
C = 200 + 3 = 203 ppm.
This dilution theoretically reduced the salinity by about one-
third of the original value. This simple concept can be
expanded to encompass dilution from a number of sources of
contamination. The resultant concentrations of contaminants
of concern is reduced. Technically, attenuation has occurred.
As noted, however, the contaminants are no less likely to
enter ground water, and no support is foreseen for waiver
demonstration.
Filtration
Filtration can remove many of the suspended materials
that would be of concern. However, this process is generally
not effective for dissolved and other liquid phase materials
except as precipitates form due to chemical reactions. Since
most leachate of concern is not filterable except as precipitants
too complicated to predict, no guidance is available from the
Agency on filtration as a factor.
Sorption
Sorption is probably one of the most effective but most
unpredictable processes for attenuating ground-water
contaminants. Clays, metallic oxides and hydroxides, and
organic matter can all be suitable materials for sorption of
95
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various contaminants. Many contaminants can be sorbed and
removed to some extent under favorable conditions. Under
other circumstances, however, the contaminants can move freely
through the porous media. The pH and oxidation potential
often govern the extent of sorption for specific constituents.
The sorption process depends on the type of contaminant and
the physical and chemical properties of both solution and the
containing materials.
When a contaminant in ionic form is sorbed, some other
changes must occur to compensate for loss of the ion from
solution, in ion-exchange processes, a different ion is
released by the solid to the water. However, this release is
not required if the contaminants are sorbed or electrically
neutral, such as most organics and neutral complexes of
various metals.
The sorptive capacity can be estimated based on the
density, clay content, and cation exchange capacity of the
soil and geologic materials above the water table. Values
for these parameters can be calculated from available data in
soils and ground-water reports on the area of interest. In
exceptional cases, these parameters can be determined from
detailed onsite measurements. For calculation purposes, the
thickness of the unsaturated zone is known or determined from
water level data. For simplicity, the vertical path of
contaminated water from the land surface beneath the waste
management area to the water table can be assumed to be the
distance traveled.
As an example, assume the average density of materials
in the unsaturated zone is 1.6 grams per cubic centimeter,
the clay content is 20 percent by weight, and the clay has
a cation exchange capacity of 70 millieguivalents per 100
grams. Each gram of clay will have the ability to remove 0.70
railliequivalents of the constituent of interest. For example,
for potassium (equivalent weight of 39), each gram
of clay will have the ability to remove 27.3 (0.70x39)
milligrams of potassium from the percolated waste water.
Each gram of solid material will have the ability to remove
5.5 (0.20x27.3) milligrams of potassium from the percolated
waste water. With a density of soil of 1.6 grams per cubic
centimeter, one acre-foot (1.2335xl09 cubic centimeters) of
soil would contain 1.97x10^ grams of solid material. This
soil could sorb 23,900 pounds of potassium. For an unsaturated
zone 50 feet thick, one acre of the unsaturated zone could
sorb over one million pounds of potassium, presuming uniform
applications in adsorbable doses, and no interference from
other constituents.
To determine the actual extent of adsorption, laboratory
tests can be performed utilizing soils and geologic materials
typical of the waste management site. The actual waste
-------
discharge can be used or a similar synthetic solution prepared.
Hajek (1969) summarizes laboratory procedures for such tests.
It should be noted that the percolating fluids may
subsequently remobilize species that have been sorbed. The
sorptive capacity of soils and geologic materials is finite
for most inorganic substances which cannot be biodegraded.
However, for substances which are biodegradable, such as many
bacteriological constituents and nitrogen, the sorptive
capacity may be renewed indefinitely.
Buffering
The pH is a critical factor in many reactions involving
contaminants. Buffering is the resistance to a pH change of
the soil solution. The basis of buffer capacity lies in the
adsorbed cations on the exchange complex of the soil. The
higher the exchange capacity, the greater will be the buffer
capacity. The portion of the cation exchange capacity occupied
by exchangeable bases is termed base saturation. There is
a correlation between base saturation and pH, with higher
base saturation for higher pH. The degree of buffering is
lowest at the extremes of base saturation, and highest at
intermediate base saturation values.
The extent of buffering in most cases will be relatively
unimportant if the pH of the waste discharge is between 6 and
9. These pH values correspond to those commonly found in
natural ground water. Wastes with a pH in this range will
generally be buffered to an extent that the percolating waste
water will present no unusual problem. Consideration of
buffering is thus of foremost importance in cases of disposal
of very acidic or basic wastes. Detailed considerations are
presented in Buckman and Brady (1969).
Chemical Precipitation
It is theoretically possible to precipitate almost any
dissolved species from solution. However, in soil-groundwater
systems, the necessary species often are not present in
sufficient quantities to precipitate potential contaminants.
Certain constituents are normally present and available for
reaction in most ground water, soil, and geologic materials.
Calcium, magnesium, sodium, potassium, bicarbonate, sulfate,
chloride, and silica are usually the major species in ground
water. Iron, aluminum, nitrogen, and carbonate, in addition
to the previous constituents, may be found in soil and geologic
materials.
Due to the extreme complexity, this manual is not an
appropriate vehicle for guidance on chemical precipitation.
However, references such as Hem (1970), Stumm and Morgan
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(1970), Faust and Hunter (1967), and Gould (1967), detail
thermodynamic calculations which may be used to evaluate this
phenomenon. In many field situations data are commonly
lac=ftb at qaxh ysisxhphiq ak fxportance, thus judgement is
often necessary.
Oxidation and Reduction
The oxidation of organic matter in the topsoil is one of
the most important contaminant attenuation mechanisms.
Oxidation and reduction reactions often work in conjunction
with other mechanisms for contaminant attenuation. Besides
those reactions causing precipitation, reducing conditions
can also theoretically cause the formation of native elements
which are quite insoluble. Sulfides can react with certain
metals to produce highly insoluble precipitates, such as
sulfides of arsenic, cadmium, mercury, and silver.
Volatilization
Volatilization and release as a gas can be effective for
attenuating some ground-water contamination. For example,
mercury in solution can be volatilized in anaerobic environments
or by reactions with dissolved humic acids. Several organic
compounds of arsenic are volatile, and the escape of arsenic
as a gas has been demonstrated for both aerobic and anaerobic
soils. Selenium may be subject to volatilization because of
its chemical similarity to sulfur. The microbial reduction
of nitrate to gaseous forms of nitrogen is well documented.
No quantitative procedure is proposed to evaluate the extent
of this phenomenon. It is important to be aware of the
contaminants that may be affected.
Biological Degradation and Assimilation
These processes are very important in the removal of
organic and biologic contaminants. Many organic chemicals
can be attenuated or removed by biological activity in the
unsaturated zone. Nitrate, arsenic, cyanide, mercury, and
selenium are likely candidates for biologic fixation or
volatilization.
2.6.2 Determining Potential For Contaminant Migration Through
Uppermost Aquifer to Water Supply Wells or Surface Water
It is essential in protecting human health and the
environment to establish the potential for contaminants to
migrate through the uppermost aquifer, and any interconnected
aquifers, to water supply wells or surface water. The
Agency recognizes the potential interconnections between
aquifers at different depths. The potential for contamination
of relatively deeper aquifers may be low if, for example,
the two aquifers are separated by thick strata with low K
value and no effective hydrologic interconnections exist
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(e.g., fractures; abandoned, poorly sealed wells). Characterizing
the saturated zone by determining the geologic materials,
physical properties and velocity of ground-water flow will
indicate the potential rate and extent of contaminant migration
in the saturated zone. Continuity of the hydraulic pathway
from the facility to wells and surface water is of particular
concern. The distances, the ground-water flow velocity and
the flow direction are factors influencing contaminant entry
into wells and the surface water environment.. The regulation
does not introduce time as a criterion; low probability in
terms of geologic time includes millenia.
Determining Saturated Zone Characteristics
Identify Geologic Materials
The geologic materials of the saturated zone are identified
by the same methods as previously described for the unsaturated
zone.
Determining Physical Properties and Rate of Ground-Water
Flow in the Saturated Zone
Field determination of K values within the saturated
zone is needed to identify probable contaminant pathways
(see Section 3.2 for methods of determining K). K can also
be determined in the laboratory and estimated from values
given in the literature for comparison to to field-obtained
values. Hydraulic conductivity data along with information
on porosity and hydraulic gradient can be used to compute
ground-water flow rates (see Section 3.2). Tracer techniques
can also be used to compute flow rates (see Section 3.2).
Flow rates should be determined in appropriate aquifer flow
zones in order to indicate directions of potential contaminant
migration and to calculate the time it would take contaminants
to reach any nearby water supply wells and/or surface waters.
This process should include flow net analysis as described in
the previous discussion of the unsaturated zone and Section
2.2.2.
Computer simulation and prediction models use a set of
mathematical equations that attempt to describe and quantify
the physical processes in an aquifer. These models can also
be used to estimate ground-water flow rate. In order to
determine where and when a ground-water flow model can be
applied, it is necessary to have a detailed understanding of
the aquifer's physical processes and the corresponding
mathematical model. Not all simulation models are appropriate
for all ground-water systems, and not all aquifers are amenable
to or necessarily require such modeling. For instance, those
aquifers involving a small area or a low level of hydrogeologic
complexity may have the most efficient solution to ground-
water flow rate via flow net analysis or analytical methods,
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such as application of the Darcy-based equation (see Section
3.2). A qualified person, such as the geologist or geotechnical
engineer required to certify the waiver demonstration, can
provide the expertise to judge the necessity of a modeling
study, the appropriateness of the model selected,, the need
for any modifications to the model and accurate interpretation
of the results.
Hydrogeological data which should be considered for use
of a predictive ground-water model are listed in Table 2-5.
General sources of data for ground-water flow modeling include:
geologic and hydrogeologic reports and maps;
well log data;
water level measurements; and
pumping test data.
The Holcomb Research Institute at Butler University,
Indianapolis, Indiana maintains a computerized clearinghouse
for ground-water models that can provide model users with an
annotated list of models. Additional information on groundwater
models is available from the U.S. Geological Survey, modeling
researchers, and the technical literature.
Evaluating Attenuation of Contaminants in the Saturated
Zone (adapted from Todd, et al, 1976)
Many of the attenuation processes which occur in the
unsaturated zone can also occur below the water table, but in
a modified manner. For example, the lower oxygen content
below the water table reduces the possibility of oxidation of
organic matter even when mixing does occur. Some contaminants
may be more mobile in the reduced state. Reducing conditions
are favorable, however, in some cases for contaminant removal
from water (e.g., nitrate). Another major consideration is
that organic matter, common in the topsoil, is virtually
absent in many types of geologic materials comprising the
aquifer. This would ordinarily decrease the extent of sorption
as well as reactions such as denitrification. In addition,
certain geologic materials, such as granite and limestone,
may lack many of the common substrates for sorption. The
dilution process below the water table differs greatly from
that operative in the unsaturated zone.
Processes Other Than Dilution
The attenuation processes do not generally have to be
considered in detail if the waiver demonstration is based
upon a low potential for any infiltration or leachate to
reach the saturated zone. In cases where the demonstration
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Table 2-5
Data Requirements to be Considered for a Predictive
Ground-Water Flow Model
Physical Framework
- Hydrogeologic map showing areal extent, boundaries,
and boundary conditions of all aquifers
- Topographic map showing surface-water bodies
- Water-table, bedrock-configuration, and saturated-
thickness maps
- Transmissivity map showing aquifer and boundaries
- Transmissivity and specific storage map of
confining bed
- Map showing variation in storage coefficient of
aquifer
- Relation of saturated thickness to transmissivity
- Relation of stream and aquifer (hydraulic connection)
Stresses on System
- Type and extent of recharge areas (irrigated areas,
recharge basins, recharge wells, etc.)
- Surface-water diversions
- Ground-water pumpage (distributed in time and space)
- Stream flow (distributed in time and space)
- Precipitation
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depends on saturated zone attenuation, detailed consideration
of these processes is necessary. Filtration and sorption
were treated in the unsaturated zone discussion. In saturated
flow, contaminant movement is generally horizontal and,
instead of utilizing a thickness of unsaturated zone beneath
a waste management site, a volume of the aquifer will indicate
the maximum attainable dilution. Generally, this will
correspond to the projected, aggregate pore space volume and
location of a discharged waste plume at a specific time.
This volume can be estimated by utilizing flow net analysis
to determine the vertical and horizontal direction of
groundwater movement from beneath the waste management site.
Specific distances from the waste discharge site, such as 100
feet, 500 feet, and 1000 feet, can be chosen and volumes of
materials calculated for each.
Laminar flow and other ground-water phenomena result in
incomplete mixing within the maximum potential mixing volume.
Consideration must also be given to contaminants which do not
readily mix with ground water (e.g., contaminants which
migrate along the top of the water table and those which
migrate along the bottom of the aquifer).
Buffering can be handled as discussed for the unsaturated
zone. Generally, this is not of great concern unless extremely
acidic or alkaline wastes are discharged directly to the
saturated zone. Chemical precipitation can be handled as
described for the unsaturated zone, but evapotranspiration is
not a factor in concentrating solutions. In addition, the
materials are continuously saturated below the water table
and are usually not exposed to drying. Oxidation and reduction
can be handled as for the unsaturated zone. However, in the
saturated case, oxidation is generally less important and
reduction is more important than in the unsaturated zone.
Dilution and Related Factors
Once percolating wastes reach the saturated zone, in
most dynamic ground-water systems there will be some physical
attenuation of contaminant concentrations with distance from
the intersection with the water table. The attenuation
occurring in most cases is determined by the following factors:
the volume of a waste discharge reaching the water table;
the waste loading (i.e., the mass per unit area of
contaminant reaching the water table);
areal hydraulic head distribution, as indicated by
water-level elevation contour maps;
- transmissivity of aquifer materials;
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- vertical hydraulic head gradients and vertical hydraulic
conductivities through confining beds which are present;
quantity and quality of native ground water available
for mixing;
quantity of recharge reaching the water table from
other sources at the land surface; and
- chemical characteristics of recharge reaching the
water table from other sources.
The first two factors determine the concentration of
contaminants reaching the water table. The next several
factors, along with hydraulic conductivity, determine the
direction and magnitude of ground-water flow in the area and
the quality of native ground water with which the discharged
waste will mix. The last two factors determine the effect of
recharge from other sources on contaminant concentration.
A first approximation of dilution can be obtained by
assuming that the waste discharge enters a certain part of
the aquifer; for example, the upper 10 feet, 50 feet, or 100
feet, over a certain area. Knowledge of the extent of ground-
water contamination in historical situations in the area or a
comparable area can be used to make this evalulation.
Secondly, water reaching the water table from other sources
of recharge and ground-water inflow from nearby areas usually
tends to dilute the waste discharge. The dilution can be
calculated if the volume and quality of the various sources
of water are known. Conservative constituents, such as
chloride, can be used for a first approximation of dilution.
In most cases, the contaminant of interest will be less mobile
and thus occupy a smaller plume than a mobile constituent
such as chloride. Ground-water outflow tends to carry
contaminants away from the waste management site.
Water level elevation maps and flow nets can be used to
consider whether the waste discharge is in an area of converging
or diverging ground-water flow, which affects dilution.
Vertical head gradients indicate whether wastes could move to
deeper levels of the aquifer or whether deeper aquifer water
could move up and dilute the wastes. Both cases tend to
accentuate mixing or dilution. Aquifer transmisivity can be
used to calculate ground-water flow rates into and out of an
area. The quality of sources other than the waste discharge
and native ground water will obviously affect dilution as the
lower concentration waters will exert relatively more dilution.
The foregoing factors can be integrated into a mass balance
analysis, both for the waste discharge and for the individual
contaminants.
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Wells affect dilution in several ways:
Gravel packs or perforations if improperly designed
can act to short-circuit confining beds and allow
vertical movement of contaminants near the well.
Well pumping can drastically alter flow patterns,
both horizontally and vertically.
Well pumping can remove contaminants from ground
water and expose them to subsequent loss at the land
surface or in the topsoil, by processes such as
volatilization, crop uptake, and precipitation.
Most of the above-described factors are significant for
all types of contaminants that reach the water table, whether
they are inorganic chemical, physical, organic chemical, or
bacteriological. In some cases, certain factors do not
attenuate the contaminant, but rather redirect it. An example
is the development of a large depression cone in an agricultural
area, whereby contaminants are drawn into the area from many
directions but are effectively prohibited from leaving by the
depression.
Plumes or zones of contaminated ground water may behave
as a slow moving viscous mass, but they may also be quite
erratic, especially where influenced by recharge and/or well
pumping.
Evaluation of contaminant attenuation mechanisms in the
saturated zone requires a considerable knowledge of fluid
dynamics, geochemistry, and hydrogeologic judgement. Such an
evaluation is essential in order to adequately substantiate a
waiver demonstration. Eminently qualified professionals
known for their hydrogeologic judgement combined with experience
gained from case histories are recommended for performing
this task.
Determining Proximity of Facility to Water Supply Wells
or Surface Water
The distance from the facility to water supply wells and
surface water has a bearing on how contaminants reach
receptors. As potential transmitters of contaminanted water,
wells and surface water can expose these contaminants to the
surface environment. All types of water supply wells and
surface waters must be identified within a reasonable distance
of the facility. Wells used for drinking, irrigation or any
other purposes should be located and classified, and the type
of usage should be noted. Pumping wells are of particular
concern since they will accelerate the migration of any
contaminants present in the water, and increase the likelihood
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that contaminants will reach receptors at the surface.
Surface waters, including lakes, ponds, rivers, streams,
wetlands (swamps, marshes, bogs), springs and salt-water
bodies should also be identified.
When determining the effect of the proximity of the
facility to these water supply wells and surface waters, a
reasonable area should be considered. Many site-specific
factors affect the size that a reasonable area should be,
including:
- watershed or drainage basin boundaries;
saturated zone characteristics (e.g., fractures,
solution cavities, attenuating properties);
direction of ground water flow; and
- rate of ground water flow.
A situation in which the attenuating capacity of the
saturated zone is high and the rate of ground water flow is
low, may warrant a lesser area for consideration. In some
situations, (e.g., when the aquifer underlying the facility
flows into a river located several miles from the facility),
the area considered should include the river in order to
identify this major discharge point. Another factor which
might affect the size of the area for consideration is the
number of wells and surface water bodies present in the region
of the facility.
Sources of information which can provide the location of
nearby water supply wells and surface waters include:
Existing Maps. Topographic and hydrogeologic maps have been
prepared for many areas of the united States. Each map is
drawn for a certain watershed or geologic region. Among
other things, these maps show the location of wells and
surface waters. Topographic and hydrogeologic maps may be
obtained from the United States Geological Survey, State
Geological Surveys, River Basin Commissions, and some
universities. Other Federal and State agencies identified
in Table 2-1 may also have these maps.
Prepared Mag of the Area. A map of the area around the
facility which indicates the location of water supply wells
and surface waters can be prepared from review of the existing
maps and other information sources previously described.
The map should cover at least the area of the drainage basin(s)
which could be affected by the facility. The map should
include all water supply wells and surface waters currently
located within the area being considered. The map should be
comprehensive and current.
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Other sources of information should be consulted to
verify and supplement the information about the location of
wells and surface waters, especially if existing maps are old
or not available. The other information sources include
local town engineers, state well-drilling records and published
reports/ surveys. Drilling records and reports might be
obtained from State Departments of Environmental Protection,
State Geological Surveys or Public Health Departments.
If the owner or operator cannot otherwise document
completeness, the map should be verified by performing a
field survey. Depending upon the geology and property
ownership in the area, the following tasks might be included
in the field survey:
contact other property owners to learn if any new
wells have been drilled (or old ones overlooked by
the previous research) and inquire about surface
waters present on their property;
- drive/walk through the area (where permitted) to spot
check portions of the map; and
- check state/locality files where drilling or extracting
is regulated; consult local water-well contractors.
2.6.3 Documentation
Section 265.90(c) waiver demonstrations must be in
writing, must be certified by a qualified geologist or
geotechnical engineer, and must be kept at the facility;
Section 265.90(e) waiver demonstrations must be certified by
an appropriately qualified professional (e.g., a chemist)
verifying the occurrence of the documented neutralization
reaction(s). During interim status, the written waiver
demonstration must be made available to the Regional
Administrator upon his request.
The format of the waiver demonstration under §265.90(c)
should correspond to the requirements of the regulation by
documenting the evaluations of the water balance, unsaturated
and saturated zone characteristics, and the facility's
proximity to water supply wells or surface waters, upon which
the contaminant migration potentials are estimated. The
methods used to obtain these hydrogeologic data should also
be included in the demonstration. Supplementary information
should include:
water balance calculation and how all values were
obtained;
the investigatory methods and how data were evaluated
in determining the unsaturated and saturated zone
characteristics; and
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the site-specific map and descriptions of field
surveys used to determine the proximity of the facility
to water supply wells and surface water.
In addition to the final written waiver demonstration,
under §265.90(c) or (e), reproduceable copies of all supporting
information (e.g., reports, records of field investigations
and calculations) should be kept at the facility in order
that the demonstration may be soundly documented at any time.
3.0 Assessment Program
3.1 Description
The ground-water quality assessment program must be
capable of determining presence, concentrations, rate and
extent of migration of hazardous waste or hazardous waste
constituents in the ground water coming from a discharging
facility. The owner or operator is responsible for preparing
and implementing an assessment plan under §265.93(d) when
there are significant indicator parameter changes in downgradient
wells. (See Section 1.3 for a discussion of the level of
detail for assessment plans).
If the detection program indicates that the facility is
significantly affecting ground-water quality (see statistical
analysis discussion; Section 2.5.2), a sequential response
procedure must be followed. This procedure requires the
owner or operator to respond to possible ground-water
contamination according to the following sequence:
Confirm sampling/analytical results by taking additional
(split) samples (§265.93(c)(2);
Notify the Regional Administrator within 7 days of
confirmation that the facility may be affecting ground-
water quality (§265.93 (d)(l));
Submit a specific plan for a ground-water quality
assessment program to the Regional Administrator
within 15 days of the above notification (§265.93(d)(2);
Implement the assessment plan as soon as technically
feasible (§§265.93(d)(4 ) and (5));
Submit an assessment report to the Regional Adminis-
trator within 15 days of the first determination
<§265.93(d)(5));
If the assessment indicates no ground-water contamination,
the detection program may be reinstated and the Regional
Administrator must be so notified (§265.93(d)(6));
and
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If the assessment indicates that ground water is
being contaminated, continue the ground-water quality
assessments on a quarterly basis until final closure
of the facility (§265.93(d) (7)(i)). If contamination
is first detected during post-closure, only one
assessment is required (§265.93(d)(7)(ii) ).
The plan for the assessment program must be certified by
a qualified geologist or geotechnical engineer who should
serve the lead role in implementing the plan. The plan must
specify:
- the number, location, and depth of wells;
sampling and analytical methods for those hazardous
wastes or hazardous waste constituents in the facility;
- evaluation procedures, including any use of previously
gathered ground-water quality information; and
- a schedule of implementation.
The plan must be based upon site-specific conditions to ensure
adequate assessment in the event that ground-water is being
contaminated. Guidance for determining the appropriate number,
location and depth of wells is provided in the examples given
later in this Section and in Sections 2.2.3 and 2.2.4.
Sampling and analytical methods for determining the concentration
of hazardous waste and hazardous waste constituents are discussed
in Section 3.4. The evaluation procedures include use of any
previously gathered ground-water quality information (e.g.,
data collected from the detection program). Data evaluation
procedures can also be used to indicate that ground-water
quality is being affected by a source other than the facility.
The first ground-water quality assessment must be
performed as soon as technically feasible since a discharge
to ground water may be presenting a serious risk to human
health and the environment. If the evaluation of the results
of the assessment indicates no ground-water contamination,
the owner or operator may reinstate the detection program.
The Regional Administrator must be notified of this program
change so he will be aware of which program is in progress
and which facilities are introducing hazardous waste or
hazardous waste constituents to ground water. If the assessment
shows that hazardous waste from the facility has entered the
ground water, assessments must be continued on a quarterly
basis. Any assessment which is initiated prior to facility
closure must be completed and reported to the Regional
Administrator.
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The assessment program plan and implementation are
required if the detection progam has shown that the facility
may be affecting ground-water quality. However, the owner or
operator may have chosen to use an alternate program (see
§265.90(d)), rather than the detection program, because he
assumed or knew that the detection program would show that
the facility is affecting ground-water quality. In this case
the alternate program, which is essentially equivalent to the
assessment program, must be employed and the owner or operator
was required to prepare and implement the plan by November
19, 1981 in lieu of the detection program.
3.2 Determining Rate of Contaminant Migration
Rate is primarily influenced by the hydraulic conductivity
(K) of the medium; the porosity (n) of the medium; and the
hydraulic gradient (i), a ratio of the difference in hydraulic
head and the horizontal distance between two points. This
discussion assumes that contaminants migrate at the same
rate as ground water. If the owner or operator contends
that the contaminant is migrating at a slower or faster rate
than the ground water, methods capable of quantifying such
a rate must be employed. The selected method(s) should be
best suited to the specific conditions at the facility site.
Methods for determining rate are either theoretical,
such as techniques dependent on use of a Darcy-based equation,
or they are empirical such as techniques employing tracers.
3.2.1 Use of Darcy-Based Equation
The rate at which contaminants from a facility may
migrate in the ground water can be calculated through the
solution of a modified form of the Darcy equation: "7 = -Ki;
_ n
where v is the average linear velocity of the ground water, K
is the hydraulic conductivity of the medium, i is the hydraulic
gradient, and n is the porosity of the medium.
In determining v, it is important to realize and account
for factors which contribute to variabilities in K, i, and n.
Hydraulic conductivity will often vary with the direction of
measurement (e.g., horizontal K is often greater than vertical
K in unfractured, stratified earth materials). In ground-
water monitoring, it is imperative to determine the flow
zone(s) with high K values because it is within these zones
that the rate of contaminant flow will likely be the greatest.
These flow patterns can greatly affect patterns of dilution
and other attenuation factors. Hydraulic gradient between
the source of contamination and the detection point (e.g., well)
can be affected by land use as well as hydrogeologic causes.
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Seasonal fluctuations of water levels may alter the gradient.
Caution should be given to determining gradient in situations
where there are perched water bodies, since comparison of
water levels from perched aquifers, whose retarding formations
are at different depths, will result in an invalid gradient
calculation. Also, gradient determination (as well as velocity)
can be influenced by nearby constant or periodic ground-water
supply pumping or clogged wells. Such influences should be
accounted for by the owner or operator when conducting an
assessment.
The hydraulic gradient (i) is the change in hydraulic
head (h) over a given distance (i.e., the vertical difference
in water level elevation (hj-h2) of two wells separated by
a horizontal distance (1) in the direction of maximum slope).
For example, the water level in Well A is five feet above
mean sea level and the level in Well B, 100 feet away and on
the same flowline, is four feet above mean sea level. The
maximum hydraulic gradient in this case is computed as follows:
hj - h2 5-4 1
= = = 0.01.
_
OO 100
This means that for every 100 feet horizontal distance, the
water level drops 1 foot.
An important procedure in most ground water investigations
is to identify the gradient over a specific area. The
groundwater flow net shown in Figure 2-3, can be used to
illustrate hydraulic gradient. Lines of equal "head" (equipotential
lines) are used to define slope and perpendicular flowlines
show the direction of ground-water flow between points on the
same flowline.
Water level data from at least three piezometers and/or
water table wells is necessary in establishing the maximum
hydraulic gradient (i.e., the gradient in the direction of
maximum slope). For a large facility or a facility with
complex hydrogeology, more than three piezometers will likely
be needed to establish the pattern of gradients in the area.
Porosity (total) of an earth material is its property of
containing voids or interstices and may be expressed as the
ratio of the volume of its interstices to its total volume
(Lohman, et al, 1972). A method for determining porosity is
given by Freeze and Cherry (1979, p. 237).
Effective porosity of a rock or soil refers to the amount
of interconnected pore space available for fluid transmission;
it is expressed as a percentage of the total volume occupied
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by interconnecting intersticies (Lohman, et al, 1972). When
determining n for calculating the flow rate, the Agency
recommends the use of effective porosity instead of total
porosity, since effective porosity provides a more accurate
measure of the true flow conditions. A method for determining
effective porosity is described by Fetter, 1980. Effective
porosity often varies with direction. Therefore, several
effective porosity determinations of earth material samples
in the ap£ropriate flow zone(s) should be made so that a
range of v values can be obtained.
Hydraulic conductivity of a medium is the volume of
water at the existing kinematic viscosity that will move in a
unit time under a unit hydraulic gradient through a unit area
measured at right angles to the direction of flow (Lohman, et
al; 1972). It depends primarily on the nature of the pore
space (i.e., continuity of pore inter-connections), the type
of liquid occupying it, and the strength of the gravitational
field.
Hydraulic conductivity can be determined by laboratory
and field methods. The Agency recommends that the owner or
operator employ field methods whenever possible since they
test the aquifer materials under in situ conditions. In
general, field methods can usually provide more representative
values than laboratory methods because they test a larger
volume of material, thus integrating the effects of macrostructure
and heterogeneities. Laboratory tests may be useful for
comparison purposes with field test results. For a range of
K values for different earth materials, see Freeze and Cherry
(1979, p. 29).
Laboratory Methods for Determining K
Permeameters
The saturated hydraulic conductivity of an earth material
sample can be measured in the laboratory using a constant-head
permeameter or a falling-head permeameter. (For a more
complete discussion of the apparatus and procedures, see
American Society of Testing Materials; 1967 and 1978; and
Freeze and Cherry, 1979). Klute (1965) believes that the
constant-head system is better suited to samples with
conductivities greater than 0.01 cm/min (or 1.66 x 10~4
cm/sec) while the falling-head system is more appropriate for
samples with lower conductivity. The methods described above
are applicable to common granular aquifer materials and not
clayey materials. These tests provide more accurate K values
when the sample is undisturbed. The heterogeneity common in
earth materials will be reflected in the various K values
determined for different samples. It should be recognized
that permeameter tests provide K values from only sampled
parts of an aquifer and may not be representative of the
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entire aquifer. Also, disturbance of samples during collection
and handling at the laboratory can lead to inaccurate
determinations.
Grain - Size Analysis
Grain-size analysis (as developed by Hazen, 1911) involves
sieving of granular earth material in the fine sand to gravel
range to establish the proportions of the various grain-size
diameters in the sample. A representative grain-size diameter
(e.g., average or median) is chosen and used in established
mathematical formulae to estimate saturated hydraulic conductivity
(Freeze and Cherry, 1979; pp. 350-352). Use of the median
grain-size diameter for such estimates is more powerful since
it considers the spread of the various grain-size diameters.
In concert with mathematical calculations, curves have been
developed from which K values may be read (Masch and Denny,
1966).
Grain-size analysis for estimating K is best applied to
homogeneous, unconsolidated aquifers, especially when undisturbed
earth material samples are obtained. Sample locations for
grain-size analysis should be carefully selected since only
small sample volumes are used to give an estimate of K for a
larger portion of an aquifer. The greater the heterogeneity
of grain-size distributions in an aquifer, the less precise is
this method of determining K. This technique of estimating K
is the least accurate of the techniques described in this
document.
Field Methods for Determining K (For further details, see
Freeze & Cherry, 1979, pp. 339-350).
Piezometer Tests
In situ K may be determined in tests using a single
piezometer. These tests involve the sudden introduction or
removal of a known volume of water to or from a piezometer.
Observation of the recovery of the water level in the piezometer
is then made. "Bail tests" involve removal of water, whereas
"slug tests" involve adding of water. Interpretation of
water level versus time data is dependent on the test
configuration used. Methods described by Freeze and Cherry
(1979), along with related mathematics, include one method
for a point piezometer and another for a confined aquifer.
A major limitation on slug and bail tests is their heavy
dependence on a high-quality piezometer intake. Corroded or
clogged well points or screens lead to highly inaccurate
calculated K values. Also, development of the piezometer by
surging or backwashing prior to testing may reflect the
increased K values attributed to the artificially induced
gravel pack around the intake.
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Piezometer tests are not useful for determining K if
water level recovery is too rapid to allow measurement,
especially if the volume of water added or removed is small.
Accurate piezometer tests provide in situ K values representative
only of the small volume of porous media in the immediate
vicinity of the piezometer tip. The greater the number of
piezometers used, the better the characterization of the K
distribution within the aquifer.
Pumping Tests
Pumping tests (also properly called aquifer tests)
provide in situ measurements of aquifer coefficients (e.g.,
transmissivity) which can be used to calculate K over a large
aquifer volume. K is computed as follows:
K = T/b;
where T is the transmissivity of the aquifer, and b is the
saturated thickness of the aquifer. Pumping tests to determine
K generally consist of:
- the drilling of a test well with one or more
observational piezometers;
- a pumping test to determine the value of T; and
- calculation of K.
Methodology for examining pumping test data from unconfined
and confined aquifers and references for pumping test
configurations are discussed by Freeze and Cherry (1979, pp.
343-349). A disadvantage of pumping test data can be attributed
to the nonuniqueness of its interpretation. Predicting the
effects of any proposed pumping test configuration is highly
dependent on a clear understanding of the geology involved.
Even if pumping test data matches a theoretical curve, it
does not prove that the aquifer fits the assumptions of that
curve (e.g., leakage effects if present, but not accounted
for, could lead to an erroneous K value for the aquifer of
interest). These methods generally test larger portions of
aquifers than piezometer tests. The large possibility for
non-uniqueness in interpretation, problems involved in pumping
contaminated fluids, and the expense of conducting such tests
generally preclude their use in problems of contaminant
hydrogeology.
Example of the Use of the Darcy-Based Equation
The following information was gathered for an aquifer
comprised mainly of sand:
K = 10-3 cm/s
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i = .01
n = .30.
Using the equation:
v = - Ki/n,
v is calculated to be 3.3 x 10"^ cm/s or 10.6 m/yr.
Limitations on the Use of the Darcy-Based Equation
The Darcy-based equation used in the preceding example
applies to many, but not all, ground-water flow situations.
For flow through granular materials there are at least two
situations where valid use of this equation is in question
(for more details, see Freeze and Cherry, 1979, pp. 72-75).
The first deals with flow through sediments with low K values
under very low gradients and the second deals with flow
through sediments with very high K values. This suggests
that the modified form of Darcy's equation may have both a
lower and upper limit to its range of validity. Darcian-derived
flow rates are rarely exceeded in nonindurated (i.e., not
hardened) rocks and granular materials. However, Darcian
flow rates are commonly exceeded in such important rock
formations as karstic limestones and dolomites, and cavernous
volcanics. Where the Darcy-based equation cannot be validly
used to determine flow rate, another method (e.g., use of
tracers) should be employed.
3.2.2 Use of Tracers for Determining Flow Rate
The advantage of using tracers is obvious. If the test
is large enough, and for a long enough time, the actual flow
path is measured rather than theoretical surrogates estimated.
Generally, however, the required time will not be available.
The following discussion of tracers is based mainly on
Freeze and Cherry (1979, pp. 427-430), who also provide
additional references on tracers. The use of a tracer is a
direct method for determining flow velocity. After introducing
a tracer at one point in the flow field and observing its
arrival at other points (and after making adjustments for the
effect of dispersion), velocity can be computed from the
travel time and distance data (i.e., v = d/t). Several types
of nonradioactive and radioactive tracers have been used,
including simple tracers such as salt (NaCl or CaCl2)r which
can be monitored by measurement of electrical conductance, to
radioisotopes such as 3H, 131I, 29Br, and 51Cr-EDTA (an
organic complex with S^Cr), which can be monitored using
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I
I
I
I
I
radioactive detectors. Radioisotopes are subject to government
licensing requirements for their use and can be hazardous
when used by careless workers. Fluorescent dyes (fluoroscein
and rhodamine compounds), used by many investigators, have
sometimes yielded adequate results based on visual detection.
When necessary, dye concentrations can also be measured
quantitatively to very low concentrations. Recent work
suggests that Freon (C13CF) may be a very good artificial
tracer, since it is nonreactive with geologic materials and
can be used in extremely small concentrations that are not
harmful to public waters.
Factors which should be used in selecting and using
tracers include:
ease of detection, uniqueness;
solubility in ground water (ideally moves with water
at same velocity, including direction);
stability in ground water for desired length of time;
type of emitted radiation, if any;
background levels of tracer or interfering substances
in ground water;
- chemical reactions among water, tracer and contaminant;
and
interactions of tracer with earth materials (e.g. ,
filtration, adsorption).
The advantage of properly performed tracer studies is
that they are indisputable. The major disadvantages of the
direct tracer method include:
- because ground water moves slowly, long periods of
time are normally required for tracers to move
representative, meaningful distances through the flow
system;
variegated hydrogeological settings require numerous
observation points (e.g., piezometers, wells, or
other sampling devices) to adequately monitor the
passage of the tracer through the portion of the flow
field under investigation;
if small aquifer segments are studied in order to
overcome time restraints, there is less assurance
that a representative sample of the flow field is
tested; and
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- because of the common heterogeneity of earth materials
encountered, the flow field may be significantly
distorted by the measuring devices.
Due to the above disadvantages, tracer experiments of
this type commonly require considerable effort over extended
time periods. One limited-objective technique that avoids
some of these disadvantages is known as the "borehole dilution"
or "point-dilution" method. This test can be performed in
relatively short periods of time in a single well or piezometer
and provides an estimate of the hori,atpsr slhiage flow velocity
of the ground water in the formation near the well screen. In
this test, a tracer is quickly introduced into a segment of
a well screen isolated by packers and is then subjected to
continual mixing as lateral ground-water flow gradually removes
the tracer from the well bore. The combined effect of ground-
water through-flow and mixing within the isolated well segment
produces a dilution versus time relation from which the
average horizontal velocity of ground water in the formation
beyond the sand or gravel pack, but close to the well screen,
is computed. This method is best suited for velocity
determination in steady-state lateral flow regimes.
Borehole dilution tests can be performed at various
intervals within a well screen to identify zones of highest
ground-water velocity. These zones are of prime interest
since contaminants can move through them at velocities much
higher than in other parts of the system. Identification of
such high-velocity zones, which may occur in only a thin
segment of the aquifer system, will aid in the design of a
more efficient monitoring network.
Most, borehole dilution tests described in the literature
employed radioactive tracers. However, the recent advent of
commercially available electrodes for use with portable pH
meters for rapid downhole measurement of Cl~ or F~ has made
it feasible to conduct these tests with readily available
tracers in a more convenient manner. An even simpler approach
uses salt as the tracer with down-hole measurement of electrical
conductance as the salt is flushed from the well screen.
3.3 Determining Extent of Contamination
This section describes methods to determine the extent
of contamination. The owner or operator must determine which
method(s) will be best suited to the hydrogeologic controls
at his specific site.
"Extent" refers to the spatial distribution (length,
width and depth) of hazardous wastes or hazardous waste
constituents within the ground water environment. When a
facility discharges into the subsurface, mobile constituents
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will migrate downward to the water table where they can
migrate within the ground-water system. Contaminants in
ground water often tend to travel as a "slug" or "plume", the
geometry of which depends on local heterogeneities in the
subsurface and contaminant properties. Ground-water
contamination patterns (i.e., plume configurations) are most
predictable under uniform flow conditions; however, these
conditions are rarely encountered in the field. A comprehensive
investigation is needed to delineate the characteristic shape
or configuration of the contaminant plume(s).
Due to the variety of waste types and the complex
hydrogeologic factors at many facility sites (e.g., perched
water tables, local supply well pumping effects, etc.), a
field investigation is the most effective method for determining
the extent of contaminant migration. Several direct and
indirect techniques can be utilized individually or in
combination to detect and verify the configuration (i.e.,
extent) of a contaminant plume. Data from field investigations
should be translated to site base maps and subsurface cross
sections for correlation and interpretation of the results
(see Section 2.2.2 for discussions of base maps and cross-
sections). Information from a detailed field investigation
should provide a graphic representation of the boundary or
extent of the contaminated zone (e.g., by mapping isopleths
of contaminant concentrations). Choice of investigative
techniques should be based upon the kind and amount of waste(s)
managed at the facility, the hydrogeology of the site, the
size of the facility, etc. Some of the more versatile and
reliable assessment techniques include:
Indirect Techniques (i.e., remote sensing)
aerial photography;
- electromagnetic conductivity;
electrical resistivity;
specific conductance-temperature probe; and
geophysical logging;
Direct Techniques include;
boreholes with formation sampling; and
- water sampling from monitoring wells.
Not all of the above techniques need be applied to
determine the extent of contaminant migration at any one
site. The selection of the most effective technique(s) for
a particular situation can be determined by the geologist or
geotechnical engineer supervising the investigation. Although,
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each technique can aid in detecting contaminants in the
subsurface, not every technique (especially indirect) will
work satisfactorily at every site. Often, techniques work
best in conjunction with one another. In some cases, it may
be necessary to conduct preliminary field testing to determine
the suitability of a specific technique at a given site.
Information from boreholes and monitoring wells is
necessary in a ground-water quality assessment. Data obtained
from other methods is often useful in supplementing the
information from and determining locations of boreholes and
monitoring wells. Indirect techniques can be used to reduce
costs by limiting the total number of boreholes and monitoring
wells necessary to define the plume.
3.3.1 Indirect Techniques
Aerial Photography
Aerial photography can serve as an initial detection
mechanism to aid in determining the extent of contamination.
This method provides wide surficial coverage, but is limited
by the relatively poor resolution of local details. Photographic
interpretation provides no subsurface data other than that
which is implied, but may indicate surface responses to
subsurface conditions (Benson and Glaccum, 1979). For example,
vegetative stress may indicate leachate and gas migration
where the water table is shallow or in discharge areas. The
investigator may obtain some information on the extent of
contamination by outlining the boundary of stressed vegetation.
Different types of aerial photography (e.g., black and white,
normal color or infrared) can detect vegetation stress which
may not be evident during a field inspection. Infrared
photography can be useful in determining the early effects of
less advanced stresses.
Geologic features (e.g., bedrock fractures, fault zones,
etc.) that affect ground-water flow patterns can be identified
from aerial photos. Fractures at shallow depths in consolidated
rock can serve as conduits for rapid infiltration of surface
runoff. Regions where bedrock outcrops at the surface, or is
overlain only by thin alluvium, are particularly susceptible
to contamination. Aerial photos provide a means to detect
potential avenues of contamination in areas characterized by
outcropping fractured bedrock.
Contamination of surface water bodies may be detected by
discoloration or shading in aerial photography. This
information may enable the investigator to make a quick,
rough assessment of the extent of potential contamination of
such surface water.
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Land surface elevation determinations and contour maps
(photogrammetry) can be compiled from information in aerial
photographs and ground-water flow direction in shallow systems
can be estimated using this information.
Federal and other offices serve as repositories of aerial
photographs especially for historical or pre-discharge
imagery. Photos may be purchased or information on photos
obtained from the sources identified in Section 2.2.2.
It may be necessary to retain a contractor to fly aerial
surveys of a particular area to achieve the timeliness and
level of detail desired in the area to be assessed. Enlargements
of photos can be made, but at a loss of resolution.
Conclusions drawn from the interpretation of aerial
photographs should be substantiated by surface inspection.
Aerial photography serves primarily as an aid for designing a
more detailed assessment strategy that should include other
field methods.
Advantages and Limitations of Aerial Photography
Advantages include:
it is relatively inexpensive;
it is an easily accessible technique which provides
information on a large area;
it may indicate the effects of the contamination as
well; and
- it serves as a good preliminary step in evaluating an
affected area.
Limitations include:
it provides relatively poor resolution of local
details; and
it offers no direct information on subsurface
characteristics.
Example of the Use of Aerial Photography
Low levels of some organic chemicals (trichloroethylene,
toluene and benezene) were detected in several farmers wells
in a sparsely developed, limestone valley. The suspected
source of the contaminants was a waste impoundment which was
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located approximately 1/4 mile away. There were no detailed
maps of the area; however, aerial photos taken by the U.S.
Soil Conservation Service in the winter of 1957 were available
in stereo pairs. It was apparent from the photos that the
shallow limestone bedrock had a very definite control on the
topography and other surface features. There were numerous
springs, sink holes and streams in the area that seemed to be
aligned in a general rectangular pattern.
Aerial photography was used to obtain more recent color
photos on a larger scale plus false color infra red (IR).
The IR photos were helpful in identifying springs and other
points of ground-water discharges. Areas of stressed vegetation
were identified. Two ponds and a drainage ditch in the area
also appeared to be a darker tone of color than other ponds
in the vicinity, indicating possible contaminant migration.
From the larger scale aerial photos, pertinent information
was added to a base map. The impoundment, contaminated wells
and wells yet to be sampled were located on the map. Also
included were springs, ponds, sink holes, streams, stressed
vegetation areas, stained drainage ditches and other areas of
suspected contamination. The above observations required
verification by field inspection, including groundwater sampling
and analysis. After employing these techniques, the confirmed
contaminated areas were plotted on the base map. The map
indicated that the extent of the contaminated zone reflected
the same general rectangular pattern described in the aerial
photos. The contaminants were most likely migrating through
solution cavities that were developed along joints in the
limestone bedrock.
Electromagnetic Conductivity ,
Electromagnetic conductivity (EM) is a geophysical '
technique capable of obtaining data on subsurface conditions.
EM can detect subsurface features capable of conducting an
electric current and is especially useful in defining shallow
ground-water zones characterized by high dissolved solids
(e.g.contamination plumes).
EM operates in the following manner: The transmitting
coil generates alternating magnetic fields which result in .
the flow of alternating currents that are detected by the ]
receiving coil. The intensity of alternating currents is , '
greater in areas of high conductivity and, conversely, lower
in areas of low conductivity (Griffiths and King, 1966). . I
Electromagnetic conductive properties are a function of the I
basic soil/rock matrix (e.g., grain size, porosity, and
permeability) and also of the fluids which permeate the I
matrix. Contamination often increases the free ionic content 1
of the ground water, hence increasing its conductivity. EM
I
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techniques comprise a composite measure of these properties
which, like aerial photography, supplement other data in a
contamination assessment (Benson and Glaccum, 1979, 1980).
EM equipment does not require ground connections, is
very mobile and can be operated over a variety of terrains.
The data is recorded in a series of profiles, which indicate
shape and trends of anomalous subsurface conditions.
Advantages and Limitations of EM
Advantages include:
instrumentation is fairly easy to operate;
surveys can be completed in a relatively short
period of time since ground connections are not
necessary;
- it can provide a quick preliminary assessment of
shallow contamination; and
- it is relatively inexpensive.
Limitations include:
data is limited to shallow depths;
instrumentation is sensitive to interference from
conducting bodies at or above the surface (e.g.,
transmission wires);
- it provides qualitative information which requires
substantiation by direct techniques; and
results must be compared to background information,
including local geology and ambient ground-water
chemistry.
Example of the Use of EM
Monitoring wells detected a discharge from an impoundment
containing pickeling liquors in a valley comprised of alluvial
deposits. Because a municipal well field was nearby, the
ground-water around the impoundment was carefully monitored.
Due to the presence of highly permeable, shallow, but
discontinuous channel deposits, there was concern that the
contaminants would be difficult to trace along an irregular
ground-water flow pathway.
EM was selected as an assessment method because the
contaminant was highly conductive within the shallow channel
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sand deposits. Numerous traverses of the area downgradient
from the impoundment were made in order to account for the
variability of the subsurface deposits. The responses of the
equipment were continually recorded on a portable strip chart
recorder as shown on Figure 3-1. Station points (i.e.,
flagged stakes) surveyed in for field control provided quick
references for locations, and facilitated the transfer of
data to a base map of the area. Interpretation of the results
involved primarily the recognition of significant anomalies,
the outline of which indicated the extent of the contaminated
zone. The extent of migration was verified by drilling
additional boreholes with monitoring well sampling and
analysis.
Electrical Resistivity
Owners and operators are encouraged to explore the
utility of electrical resistivity (ER) in defining the plume
of contamination. The procedure is based on transmission of
an electric current into the subsurface materials and
measurement of the materials' resistance to the flow of that
current. Low resistivity values can indicate a concentration
of free or mobile ions, such as are often found in contaminated
ground water. ER is particularly useful for facilities
receiving inorganic wastes at sites characterized by homogeneous
geological conditions.
Resistivity surveys at established plumes are in general
the cheapest and most reliable technique for defining the
edge of the plume and the rate of migration. Established
grids re-surveyed quarterly with knowledge of water table
fluctuations can provide a convincing demonstration of these
two factors.
The most commonly used approach in conducting an ER
survey utilizes the Wenner electrode configuration in which
four electrodes (copper coated steel rods) are pushed or
hammered several inches into the ground along a straight
line. The electrodes are spaced at equal intervals ("A-
spacings") determined by the depth of interest. Under uniform
conditions, the A-spacing is roughly equivalent to
the depth of interest. An electric current (I) from a battery
is applied by conduction into the ground through the outer
two electrodes. The current distributes itself throughout
the volume of earth materials in between. The resulting
voltage drop (V) is measured across the inner two electrodes.
The "apparent resistivity", Ra, is then determined for graphing
purposes. Some ER instruments can automatically compute the
apparent resistivity; otherwise it can be computed as follows:
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Figure 3-1
Electromagnetic Conductivity
Responses Recorded on a Portable
Strip Chart Recorder/
LiJ
(T
<
co
§
CO
CO
o
cr
o
cc
o
UJ
O
ID
o
o
Q
2
ID
O
c:
o
123
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Ra = 2 A V/I;
where Fa = apparent resistivity;
A = spacing between electrodes;
V = voltage; and
I = electric current.
Apparent resistivity values of subsurface materials
obtained by ER measurements made at the surface are the
composite or average values of the materials through which
the electric current travels. Irregularities (e.g., variations
in composition of earth materials) in resistivity below the
surface alter the pattern of current distribution of potential
differences.
In order to conduct an ER survey, control points,
baselines and/or grids should be established by measuring,
staking and flagging benchmarks at appropriate intervals.
The depth of interest can be determined from vertical soundings,
from which the lateral extent of the contaminated ground-
water body can then be estimated by constant-depth surveying.
ER values are plotted on a grid or base map and then contours
can be drawn between points of equal apparent resistivity.
There is no theoretical limit to the depth of an electrical
resistivity investigation. However, at depths exceeding 100-
200 feet results become more difficult to interpret (e.g.,
small anomalies are masked) because of the large volume of
earth material through which the electric current must flow.
The success of ER in contamination assessment is also dependent
on the particular contaminant's ability to affect detectable
decreases in resistivity (i.e., not all contaminants cause a
decrease in resistivity).
ER surveys can lower drilling costs (see Figure 3-2).
Wells drilled only around the perimeter of a contaminant
plume are by themselves inadequate in defining the extent of
the plume as it contracts and expands. ER can be used to
supplement the information from wells to aid in monitoring
changes in plume configuration at relatively low cost.
Advantages and Limitations of ER
Advantages include:
- it aids in defining subsurface geology and contamination;
- a survey can be re-run periodically to provide updated
monitoring data;
it is relatively inexpensive; and
- it aids considerably in defining the application of
direct techniques (e.g., boreholes and monitoring wells).
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Figure 3-2_
Haw Electrxcar"Rgsistivitv
Su rv e vs~
Drilling Costs
(A.)
i
IN THIS HYPOTHETICAL
SITUATION, ELEVEN
MONITORING WELLS
ARE INITIALLY :
INSTALLED.
CONTAMINATION
CONTAMINATION
SOt/ffCE
<2£&&!®
-------
Limitations include:
the greater the depth of interest, the less accurate
are interpretations concerning contaminant migration;
- variations in geology (e.g., clay lenses) can mask
the effects attributable to contamination;
not all contaminants result in lower ER values;
background data on natural quality of ground water and
geology is a necessary prerequisite; and
potential interferences due to conducting bodies (e.g.,
metal pipes and fences) at or below the land surface
can hinder interpretation of data.
Example of the Use of ER
Leachate from a landfill situated in a coastal plain was
determined to be contaminating several wells in the vicinity.
The contaminants consisted primarily of arsenic and various
heavy metals.
The detection of leachate by ER is a function of the
leachate's electrolytic properties. Many leachates are high
in dissolved ions and are considered good conductors (or have
low resistivity) when compared to background levels of the
natural earth materials. For this reason and because of the
relatively shallow depth of interest (i.e., depth to water
table < 100 feet), ER was selected as a technique for
determining the extent of contaminant migration.
In order to estimate the depths of investigation and
thus the electrode A-spacing, ER soundings (i.e., multi-depth
readings) were conducted at various locations downgradient
from the landfill. Once the most effective A-spacing was
determined, baselines were established and the entire area
was profiled (i.e., constant A-spacing was used) with
approximately 200 electrical resistivity measurements. The
apparent resistivity values obtained from these measurements
were plotted on a base map of the area and compared to other
sources of information. Contours of these values indicated
the areal extent of the contaminated zone (see Figure 3-3).
This information provided a basis for locating sites for
boreholes and monitoring wells for verifying the results of
the ER survey. The boreholes and wells were also needed to
determine the depth component of extent, which could not be
determined adequately by indirect techniques.
For .further information on ER concerning equipment,
procedures,data interpretation and case studies; see Roux
(1978).
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W
2
I .,
i i
3 S
> a
i !
Hi
5 5 i
Figure 3-3
Isoresistivitv^lap of
Contaminated Zone
Ill
©
o
SSo
•* e z
ecu-
127
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Specific Conductance and Temperature Probes
Since a facility discharge (i.e., leachate) may have
substantially higher temperature and specific conductance
than natural ground water, the presence of such leachate can
be detected by these two characteristics. Measurements of
these characteristics can be made by lowering a remote sensing
device into a well and recording results from surface
instrumentation. In areas with a high water table, however,
the measurements can be made without installing a well. The
method involves the use of a self-contained conductance-
temperature probe which can be pushed into soft ground or
inserted into a hand-augered hole to reach the saturated
zone. (For further information on this method see Fenn, et
al, .1977, pp 119-121. )
Geophysical Borehole Logging
Geophysical logging methods can greatly enhance the
amount of information gained from a borehole. Each method is
designed to operate in specific borehole conditions, involves
lowering a sensing device into the borehole and can be
interpreted to determine lithology, geometry, resistivity,
bulk density, porosity, permeability, moisture content and to
define the source, movement, chemical and physical
characteristics of ground water. Logs produced by geophysical
methods include: spontaneous potential, normal resistivity,
natural gamma, gamma-gamma, caliper, temperature and fluid
conductivity. Specific functions of these logs are discussed
by Scalf et al.(1981; pp. 34-36) and Keys and MacCary (1971).
Geophysical well logging is applicable only to those
subsurface investigations which include test drilling and is
therefore not an independent tool. Interpretation of well
logs is most reliable when several techniques are used and
the resulting logs are placed side by side to allow
crosschecking. Such cross-checking with the driller's/geologist's
log is also recommended. Detailed interpretation of well
logs can be used to evaluate ground-water characteristics.
Correlation is often difficult and should be done by a specialist,
Advantages and Limitations of Geophysical Borehole Logging
Advantages include:
- it can determine formation changes which aid in
determining contamination pathways; and
- it can aid in locating the vertical limits of a plume
of contamination through definition of ground-water
characteristics.
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Limitations include:
it necessitates the use of special, relatively
expensive equipment and trained operators;
- its requires drilling of boreholes; and
- results are qualitative (i.e., concentrations of
specific contaminants are not determined).
3.3.2 Direct Techniques
Direct assessment techniques involve collection,
observation and analysis of earth materials, including water
samples.
Direct methods (e.g., boreholes and monitoring wells)
which entail excavation or drilling necessitate careful and
prompt recording of all data, such as:
location of the borehole on a base map;
assignment of an identification number;
elevation of the ground surface (accurately determined
elevation of the top of casing of the well; - drilling
method;
hole diameter;
depth of samples;
method of subsurface sample collection;
description of field materials; - if borehole is
completed as a well — length, diameter and type of
casing;
length, diameter, type and setting of screen, if
used;
gravel pack (size), backfill and grouting
materials and related depths;
- date, time, weather conditions; and
name of supervising geologist.
Boreholes and Monitoring Wells
Purposes for drilling boreholes are discussed in
Section 2.2.1. Locations and depths of boreholes and monitoring
wells may be based, in part, on the findings of indirect
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methods (e.g., ER and EM) and spaced so as to provide sufficient
coverage of the areas most likely to be affected by contaminants.
Since results of indirect methods are not conclusive, the
initial boreholes should be drilled close to the probable
source of contamination. Subsequent boreholes should be
located radially outward increasing with distance until the
contaminant front is delineated.
Figure 3-4 illustrates an example of a systematic approach
for spacing which may be used in determining locations for
boreholes and monitoring wells when information on the
distribution of contaminants at a given site is limited.
(For further information on well location, number, design and
installation, see Sections 2.2 and 2.3). If well M-3 is
found to be contaminated, it may be appropriate to drill a
series of wells downgradient of the facility along a line
parallel to the direction of ground-water flow. For example,
well A-l is drilled at a location twice the distance between
M-3 and the facility. If this well is found to be contaminated,
a second well (A-2) is drilled along the same axis twice the
distance between A-l and the facility, and so on, always
doubling the spacing between wells until contaminants are not
detected in the most distant well. A-4 is then drilled
halfway between A-3 (clean) and A-2 (contaminated), A-5
between A-3 (clean) and A-4 (contaminated), etc., until the
distance the plume has traveled has been located with reasonable
accuracy.
Likewise, in delineating the width of a plume, on a line
perpendicular to the direction of ground-water flow, through
well A-2 (thought to be near the center of the plume), well B-
1 is drilled at a distance from A-2 equal to that between A-2
and the facility. If this well is free of contaminants, well
B-2 is drilled halfway between B-l and A-2, B-3 between A-2
and B-2 and so on. The same procedure is used in locating
wells between A-2 and C-l. This example approach defines the
extent of the plume with a minimum of drilling effort and
expense, since wells are clustered close to the boundaries of
the contaminated area. These wells can be used to detect
any further expansion or contraction of the plume. Plume
thickness should also be determined by using methods such as
well clustering or employing wells which enable discreet,
multiple depth sampling within a single borehole.
Boreholes and monitoring wells can be installed by a
variety of drilling techniques (see Section 2.3.2). Regardless
of the type of drilling method selected, extreme care must be
taken to insure against creating a conduit for contaminants
to flow from contaminated to uncontaminated aquifers or
aquifer zones. The geologist or geotechnical engineer
directing the assessment should work with the driller to
prevent this from occurring.
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Figure 3-4
Borehole/Monitoring Well
Plan for Determining Extent
of Contamination
I.
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Boreholes, completed as piezometers and/or monitoring
wells, can provide information on composition of earth material
formations, contaminant concentrations, water elevations,
flow directions, etc. (see Sections 2.2 and 2.3). Drilling
data should be recorded in a format which allows comparison
with published geological maps and available well-log records.
Example of the Use of Boreholes and Monitoring Wells
Contaminants from an impoundment are known to be migrating
toward a municipal well field in which wells are screened at
various depths (100 ft. to 500 ft.) within an alluvial fan
deposit. Trace levels of contaminants have been detected in a
few scattered monitoring wells, but the distribution of
contaminants within the multi-level aquifer is unknown due to
the complexity of the subsurface flow system.
To determine the extent of contamination at various
depths within this multi-level aquifer, boreholes were drilled
to obtain formation samples and to perform geophysical
logging. Monitoring wells were installed in some of the
boreholes and sampled for the indicator parameters, described
in Section 2.4.5, to screen for more specific contaminants.
Detecting low levels of contaminants requires special care
in drilling and obtaining representative solid and water
samples. The boreholes were fully cased so as to reduce caving
and contamination of samples by near-surface materials. The
drilling fluid consisted only of pure bentonite (no additives)
and clean tap water. A non-reactive tracer was added so that
the presence of drilling fluid within a sample could be
detected readily. Also the drilling fluid was periodically
tested for contamination.
Split spoon samples were obtained at least every five
feet. Geophysical logging aided in determining the depths of
the contaminated zones and for correlating strata between
boreholes.In selecting the optimum intake location, consideration
was given to the spatial distibution of the suspected
contaminant zones and the intake locations in surrounding
wells. The objective was to assure as complete a coverage as
possible of the contaminant front.
Monitoring for the indicator parameters also provided
valuable information concerning the extent of contamination
within this ground-water system. Specific conductance and
pH were measured in the field by lowering sensing devices
down wells or immersing these devices in samples of water
obtained at the site.
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Safety
Safety is an important consideration when using field
methods to define contamination. Appropriate protective
clothing, such as gloves and boots, should be worn. If the
contaminants are suspected of causing respiratory damage,
special breathing apparatus (e.g., ultra-twin respirators or
self contained breathing apparatus) will be needed. When
toxic contaminants are suspected, field testing should be
performed only by personnel trained to work with hazardous
waste and samples should be analyzed by a qualified laboratory.
3.4 Determining Concentrations of Contaminants
The term "concentration" in this discussion refers to
the mass of solute (i.e., hazardous waste or hazardous waste
constituent) present in a known volume of ground water.
Concentration is commonly expressed in milligrams per liter
(mg/1) or micrograms per liter ( g/1). Accurate determination
of the concentration of hazardous waste or hazardous waste
constituents present at each sampling location provides the
owner or operator and the Regional Administrator with
information necessary to evaluate the severity of contamination
in the ground water.
Sampling points (e.g., monitoring wells) should be
located in relation to defining the contaminant plume(s).
Information on "uncontaminated" ground-water quality upgradient
of the facility is useful in determining the severity of any
downgradient contamination and can also help to account for
any upgradient contamination sources. Contaminant concentrations
within the plume will vary (e.g., due to dilution and
attenuation effects, there may be gradation in contaminant
concentrations from high levels nearest the facility through
the middle of the plume, to lower levels near the outer limits
of the plume). Therefore, the owner or operator should obtain
ground-water samples which will reveal a range of concentrations
that exist within the plume. The concentration values obtained
from these samples should be evaluated in the context of
their location within the plume and their relationship to any
background and other sample values obtained. Concentration
isopleth maps should be prepared for parameters of concern.
Such maps should depict the lateral and vertical extent of
plume migration.
The following discussions present general procedures and
methods for obtaining accurate concentration values for
hazardous waste or hazardous waste constituents in ground
water underlying a facility. Scenarios for "simple cases"
and "complex cases" are presented.
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3.4.1 Simple Case Determinations
In a simple case, accurate information on the identity,
composition, and location of past and present wastes at the
facility is readily available through existing records. This
information is necessary for determining concentrations since
knowledge of the types of waste will aid in selecting specific
compounds and elements to be analyzed for in groundwater
samples.
Compile a List of Potential Contaminants
The first step in determining concentrations is to
compile a list of those hazardous wastes or hazardous waste
constituents to be analyzed in ground-water samples. "Hazardous
waste constituent", as defined in 40 CFR §260.10(a)(8) means
a constituent which caused the Administrator to list the
hazardous waste in 40 CFR Part 261, Subpart D, or a constituent
listed in Table 1 of 40 CFR §261.24. In addition to wastes
managed in current operations, wastes handled in the past
should be included in the sampling and analysis scheme because
of the potential persistence of ground-water contamination
over long time periods. Older wastes may have migrated
through past or recent facility discharges.
The types of information which should be used in compiling
the list of hazardous wastes and hazardous waste constituents
include:
General Waste Analysis — The facility owner or operator
is required by 40 CFR 265.13 to obtain a detailed chemical
and physical analysis of a representative sample of the
waste. This analysis must contain all the information
which must be known to treat, store or dispose of the
waste. The analysis may include data developed under 40
CFR Part 261 of the RCRA regulations for identifying
hazardous wastes, and existing published or documented
data on the hazardous waste or on waste generated from
similar processes. Applicable wastes include those
identified according to characteristics in 40 CFR Part
261, Subpart C and those listed in 40 CFR Part 261, Subpart
D. A detailed analysis will identify many different waste
properties (e.g., pH, density and viscosity), including
the composition of the waste and relative quantity of each
component. The extent to which the waste composition will
be described depends upon the complexity of the waste and
the information needed for proper waste management.
Generator Manifests — The manifest required under 40 CFR
Part 262 to accompany the shipment of hazardous waste
contains information from the waste generator describing
the wastes and the quantities of each waste by weight or
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volume. The facility owner or operator should have obtained
this manifest information from the waste transporter upon
acceptance of the waste at his facility.
Facility Operating Records -- Operating records maintained
at the facility may provide additional information on
waste composition and the identity of hazardous substances
that should be analyzed for, especially for wastes handled
in the past. When reviewing these records, the owner or
operator should pay particular attention to data on the
identity of the waste, the management processes used, the
identity of material recycled or recovered, and the identity
of generators from which waste was accepted. These types
of information will aid the owner or operator in determining
what hazardous wastes have been or are being managed at
the facility.
Additional information sources — For those periods in
which facility operating or other records are incomplete,
"historical records" may provide supplemental information.
Records such as old aerial photographs and records of
previous ownership of the facility may be used to deduce
generally what types of wastes have been managed in the
past and where they were treated, stored and/or disposed
of. In some cases, interviews with former employees may be
helpful.
Sampling Procedures
The next step in determining concentrations is to select
and implement sampling procedures appropriate for the substances
on the compiled list. In general, the sampling procedures
and methods described for the detection program in Section
2.4 should be employed. The assessment may involve specific
analyses of a variety of complex substances and mixtures in
ground water. Sampling procedures, as in detection program
monitoring, should be selected so as to have the least effect
on the quality of the monitored parameters (see Scalf, et al;
1981; pp. 43-71, 87-93).
It is strongly recommended that the owner or operator
consult with the laboratory personnel to whom he will be
submitting samples on the hazardous parameters for analysis
(refer to comprehensive list) and receive recommendations for
any specialized sample collection and/or handling procedures
necessary.
Analytical Procedures
After determining the appropriate sampling procedures,
the owner or operator must determine appropriate analytical
procedures (see Section 2.4). Acceptable procedures can be
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found in the references in Table 2-3 or from comparable analytical
references. The owner or operator should select appropriate
analytical methods in consultation with the laboratory, taking
into account the parameters to be analyzed, appropriate (i.e.,
state of the art) concentration detection limits and
instrumentation required.
After analysis, the owner or operator should receive
from the laboratory a report documenting the analyzed substances
and their respective concentrations or values found in each
sample. The owner or operator should examine the report to
ensure that all samples sent to the laboratory were analyzed
and that all requested concentration determinations have been
made. In addition, the owner or operator should note any
high or low concentration values for a particular parameter,
relative to determinatipns for all other samples. Anomalous
concentration values may indicate possible human error or
unusual site conditions that warrant closer scrutiny during
future assessments.
3.4.2 Complex Case Determinations
In a complex case, it is assumed that existing facility
records do not provide sufficient information for completing
a list of all hazardous wastes managed by the facility.
Other methods for identifying these substances must be employed
in order to compile a list.
Compiling a list
All records that do exist for waste handled during past
and present facility operations should be utilized to compile
a preliminary list of hazardous wastes. The sources described
in the preceding simple case discussion should provide any
available records on waste composition. The owner or operator
should also review the indicator parameter data for the
affected downgradient well(s) generated during the detection
program (if implemented). The data for pH, specific conductance,
total organic carbon (TOO, and total organic halogen (TOX) ,
can provide a general qualitative assessment of the ground
water, indicating the types of substances present. An increase
in specific conductance or a change in pH value would indicate
the presence of inorganic compounds. An increase in TOC and
TOX would indicate that organic substances had entered the
ground water.
Another step in identifying components of the waste is
to screen the potential contaminants in the waste management
area by collecting representative samples of the waste if
this can be done safely (e.g., at various levels of a surface
impoundment, or at different locations at a landfill). These
samples should then be analyzed by a laboratory using procedures
-------
similar to those for a general waste analysis (see simple
case discussion). Procedures for sample collection and analysis
may be those specified by the facility's written waste analysis
plan required by 40 CFR Part 265.13(b). This screening method
will provide information concerning waste composition (e.g.,
chemical classes and individual compounds). Any waste
components identified by screening of the waste management
area should be added to the list for analysis of ground-water
samples.
Data collected from on-site investigations should be
compared against the list of substances compiled from existing
records to determine if the results verify the existing list
and/or identify additional hazardous parameters that should
be analyzed. The use of both existing records and field
screening techniques aid in compiling a more comprehensive
list of contaminants. If the owner or operator does not view
the "final" list of hazardous wastes as sufficient, despite
the on-site surveys, he should request that the laboratory
scan the samples (e.g., using gas chromatography/ mass
spectrometry) to determine other specific parameters.
Sampling and Analysis Procedures
The general procedures for sampling and analysis remain
the same as for simple case determinations described earlier.
3.5 Case Studies
Two simplified case studies are presented below to
illustrate methods for conducting a ground-water quality
assessment.
Glacial Aquifer
Introduction
Wastes containing chromium have been disposed in a
surface impoundment located in a formation composed of glacial
outwash sediments. The disposal site is bounded to the south
by a small creek that may serve as a discharge area. Data
from water quality analyses (downgradient private supply
wells) indicate that chromium-containing leachate has percolated
down through the unsaturated zone, contaminating the ground-
water supply. Ground-water quality assessment efforts include
tracking the extent of the leachate plume, determining the
rate of plume migration and determining concentrations of the
parameters of interest.
Hydrogeologic Framework
Information from available literature indicates that the
impoundment is located in an aquifer composed of glacial
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outwash material with a saturated thickness of 25-43 meters.
The aquifer consists of beds and lenses of fine to coarse sand
and gravel, with thin lenses and beds of fine to medium sand
and silt interbedded with the coarser material.
Assessment Methodology
In the assessment strategy, surface geophysical techniques
can be utilized to aid in determining the extent of
contamination. Information to aid in determining the lateral
and vertical extent of the plume can be acquired by conducting
an electrical resistivity survey. Assuming there is no
interference from transmission lines or underground pipes,
etc., an unconsolidated aquifer (e.g. glacial) with a relatively
shallow water table may provide a satisfactory setting for
conducting such a survey.
The nature of the contamination indicates an apparent
resistivity 5 to 10 times lower than that of the regional
ground water. Since contaminated ground water in this
particular discharge had a high free ion content, the
resistivity values obtained were well-defined on a resistivity
contour map. Significant changes in the contours may aid in
identifying the extent of the plume. In addition, an
electromagnetic conductivity survey can corroborate the
resistivity findings and assist in planning borehole/monitoring
well locations.
On the basis of results obtained from the above surveys,
boreholes and monitoring wells were installed. The location
of boreholes/wells should provide data on background water
quality and the rate and extent of ground-water contamination.
Formation samples should be obtained at appropriate intervals
during the drilling of boreholes. The installation of
boreholes/wells should continue until the limits of contamination
can be ascertained.
Determination of hydraulic conductivity should be made
by field methods. In addition, water level elevations obtained
from the monitoring wells can be used to construct a flow net
to indicate the hydraulic gradient(s). Then, the Darcy-based
equation (v = Ki/n) can be applied to determine the average
velocity (v1) of movement.
Concentrations of the parameters of interest should be
determined for each sampling point. Contaminant concentration
isopleth maps should be drawn for parameters of interest to
depict lateral and vertical spread.
Limestone Aquifer Introduction
Significant ground-water contamination was suspected in
the vicinity of a plant site consisting of a number of surface
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impoundments which are used to settle effluent from the
industry's waste-water treatment facility. Organic solvents
(including benzene) are known to be components of the plant
waste stream.
Hydrogeologic Framework
Available historical data and field observations indicate
that the area is underlain by approximately 6 to 12 m of clay
over fractured limestone bedrock. This clay has a very low
hydraulic conductivity and may act as a confining layer for
the underlying limestone aquifer. Faults in the limestone
act as ground-water conduits, with broken and brecciated
material having a high porosity and high hydraulic conductivity.
Assessment Methodology
The water level in this area is at the limestone and
clay interface. Production wells in this area are cased in
the limestone aquifer. One downgradient production well in
the area exhibited high concentrations of benzene and other
organic solvents.
The techniques of electrical resistivity and electomagnetic
conductivity would likely be inappropriate in this setting as
the clay content of the overburden material would mask low
resistive or high conductive values commonly found in
contaminated ground water. Also, these methods would not be
appropriate to detect these contaminants. However, aerial
photography is a useful technique in this geologic setting.
The photographs may indicate surface manifestations of
fractures in the limestone formation which will be of value
in discerning the ground-water flow within the aquifer.
These fracture traces can also delineate areas where high
concentrations of contaminants are suspected. The production
well exhibiting high concentrations of benzene and other
organic solvents is 200 feet downgradient from an impoundment
excavated down to the limestone interface. Migration of
contaminants occurs along the top of the limestone formation
and through solution joints.
Considerations for determining the location of monitoring
wells should include the concentration of benzene and other
organic solvents in the production well (200 feet downgradient
from the source) and the location of fracture traces in the
limestone formation. Particular attention should be payed to
intersections of these fractures. Such monitoring wells,
cased at different intervals within the limestone formation,
can provide data concerning the movement of contaminants
through solution joints.
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Once the length, breadth and depth of the plume of
contamination have been identified, it is essential to
determine the rate of movement. This will enable rough
predictions to be made of when contaminants will reach
downgradient water supplies. The Darcy-based equation may be
applied to determine the flow rate if the suspected rate
falls within the equation's useful limits (see Freeze and
Cherry, 1979, pp. 72-73). If not within these limits, other
rate-determining methods (e.g., use of tracers) should be
used.
3.6 Recordkeeping and Reporting
Recordkeeping
The owner or operator is required by §265.94(b)(1) to
keep records of all analyses and evaluations specified in his
ground-water quality assessment plan. In this way, the most
current information on the rate and extent of contaminant
migration and the concentration of contaminants in the ground
water is readily available. These records must satisfy the
requirements of §265.93(d)(3) and must be kept until final
closure of the facility; and, for disposal facilities,
throughout the post-closure care period as well. The recorded
information must include:
- the number, location, and depth of wells; the number
and location of any other sampling locations;
sampling and analytical methods (e.g., field screening
techniques) for those hazardous wastes or hazardous
waste constituents in the facility;
evaluation procedures, including any use of
previouslygathered ground-water quality information;
and
the schedule (i.e., chronology) of implementation.
The content and organization of these records must
clearly reflect the results of the ground-water quality
assessment program according to the objectives of defining
the rate and extent of contaminant migration and the concentration
of contaminants in the ground water. Relevant site-specific
conditions should be highlighted. Records should be readily
accessible to both the owner or operator and the Regional
Administrator at all times. Data should be maintained in an
organized manner and be reproducible.
Reporting
Section 265.93(d)(5) requires reporting assessment
results to the Regional Administrator within fifteen days of
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the first determination. Subsequent assessment reports must
be submitted annually. See the "Note" in Section 2.5.3
concerning annual reports under §265.75. Assessment reports
should include:
- the calculated (or measured) rate of migration of
contaminants;
the extent of migration of contaminants (i.e., distance
traveled from source and approximate spatial
configuration of ground water affected); and
the concentration of hazardous waste or hazardous
waste constituents in the ground water.
The first assessment report will give the Agency
information about the nature of the contamination (if it has
been determined that a facility discharge entered the ground
water). This report will supplement the written notice from
the detection program (if it was implemented) that the facility
may be affecting ground-water quality. Thus, the Agency is
informed as soon as possible of the status of contaminated
aquifers.
Subsequent assessment reporting assures that the Agency
has updated information on the ground-water contamination
problem. Knowing the concentration, migration rate and extent
of hazardous waste or hazardous waste constituents in ground
water will aid the Agency in determining any potential threat
which may be posed to human health or the environment in the
vicinity of the facility and in determining any appropriate
action needed. The format of these reports should provide
a clear identification of the information given and employ
a logical order of discussion.
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Subpart F, ground-water monitoring. Washington, D.C.,
May 2, 1980. Available for viewing at EPA Headquarters
and Regional Libraries, Headquarters Docket Room S-269-C
and NTIS as PB-81-189797.
145
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Appendix A ~ Interim Status
Ground-Water Monitoring Regulations
Subpart F—Ground-Water Mbnitoring
JZ65.90 AppKcabWty.
(a) Within one year after the effective
date of these regulations, the owner or
operator of a surface impoundment,
landfill, or land treatment facility which
is used to manage hazardous waste
must implement a ground-water
monitoring program capable of
determining the facility's impact on the
quality of ground water in the
uppermost aquifer underlying the
facility, except as § 265.1 and paragraph
(c) of this Section provide otherwise.
(b) Except as paragraphs (c) and (d) of
this Section provide otherwise, the
owner or operator must install, operate,
and maintain a ground-water monitoring
system, which meets the requirements of
§ 235.91, and must comply with
§| 265.92-265.94. This ground-water
monitoring program must be carried out
during the active life of the facility, and
for disposal facilities, during the post-
closure care period as well.
(c) All or part of the ground-water
monitoring requirements of this Subpart
may be waived if the owner or operator
can demonstrate that there is a low
potential for migration of hazardous
waste or hazardous waste constituents
from the facility via the uppermost
aquifer to water supply wells (domestic,
industrial, or agricultural) or to surface
water. This demonstration must be in
writing, and must be kept at the facility.
This demonstration must be certified by
a qualified geologist or geotechnical
engineer and must establish the
following:
(!) The potential for migration of
hazardous waste or hazardous waste
constituents from the facility to the
uppermost aquifer, by an evaluation of:
(i) A water balance of precipitation,
evapo transpiration, runoff, and
infiltration; and
(ii) Unsaturated zone characteristics
(i.e., geologic materials, physical
properties, and depth to ground water);
and
(2) The potential for hazardous waste
or hazardous waste constituents which
enter the uppermost aquifer to migrate
to a water supply well or surface water,
by an evaluation of:
(i) Saturated zone characteristics (i.e.,
geologic materials, physical properties,
and rate of ground-water flow); and
(ii) The proximity of the facility to
water supply wells or surface water.
(d) If an owner or operator assumes
(or knows) that ground-water monitoring
of indicator parameters in accordance
with §§265.91 and 265.92 would show
statistically significant increases (or
decreases in the case of pH) when
evaluated under § 265.93(b), he may,
install, operate, and maintain an
alternate ground-water monitoring
system (other than the one described in
§ i 265.91 and 265.92). If the owner or
operator deddes to use an alternate
33240
Federal Register / Vol. 45, No. 98
' Monday, May ToTiSSO / Rules and Regulations
ground-water monitoring system he
must:
(1) Within one year after the effective
date of these regulations, submit to the
Regional Administrator a specific plan,
certified by a qualified geologist or
geotechnical engineer, which satisfies
the requirements of § 265.93(d)(3), for an
alternate ground-water monitoring
system;
(2) Not later than one year after the
effective date of these regulations,
initiate the determinations specified in
§ 265.93(d}(4);
(3) Prepare and submit a written
report in accordance with § 265.93(d)(5);
(4) Continue to make the
determinations specified in
§ 265.93(d)(4) on a quarterly basis until
final closure of the facility; and
(5) Comply with the recordkeeping
and reporting requirements in
§ 265.94(b).
§ 265.91 Ground-water monitoring
system.
(a) A ground-water monitoring system
must be capable of yielding ground-
water samples for analysis and must
consist of:
(1) Monitoring wells (at least one)
installed hydraulically upgradient (i.e.,
in the direction of increasing static
head) from the limit of the waste
management area. Their number,
locations, and depths must be sufficient
to yield ground-water samples that are:
(i) Representative of background
ground-water quality in the uppermost
aquifer near the facility; and
(ii) Not affected by the facility; and
(2) Monitoring wells (at least three)
installed hydraulically downgradient
(i.e., in the direction of decreasing static
head) at the limit of the waste
management area. Their number,
locations, and depths must ensure that
they immediately detect any statistically
significant amounts of hazardous waste
or hazardous waste constituents that
migrate from the waste management
area to the uppermost aquifer.
(b) Separate monitoring systems for
each waste management component of a
facility are not required provided that
provisions for sampling upgradient and
downgradient water quality will detect
any discharge from the waste
management area.
(1) In the case of a facility consisting
of only one surface impoundment,
landfill, or land treatment area, the
waste management area is described by
the waste boundary (perimeter).
(2) In the case of a facility consisting
of more than one surface impoundment,
landfill, or land treatment area, the
waste management area is described by
an imaginary boundary line which
146
circumscribes the several waste
management components.
(c) All monitoring wells must be cased
in a manner that maintains the integrity
of the monitoring well bore hole. This
casing must be screened or perforated,
and packed with gravel or sand where
necessary, to enable sample collection
at depths where appropriate aquifer
flow zones exist. The annular space (i.e.,
the space between the bore hole and
well casing) above the sampling depth
must be sealed with a suitable material
(e.g., cement grout or bentonite slurry) to
prevent contamination of samples and
the ground water.
§265.92 Sampling and analysis.
(a) The owner or operator must obtain
and analyze samples from the installed
ground-water monitoring system. The
owner ori3perator must develop and
follow a ground-water sampling and
analysis plan. He must keep this plan at
the facility. The plan must include
procedures and techniques for:
(1) Sample collection;
(2) Sample preservation and shipment;
(3) Analytical procedures; and
(4) Chain of custody control.
[Comment: See "Procedures Manual For
Ground-water Monitoring At Solid
Waste Disposal Facilities," EPA-530/
SW-611, August 1977 and "Methods for
Chemical Analysis of Water and
Wastes," EPA-300/4-79-020, March
1979 for discussions of sampling and
analysis procedures.]
(b) The owner or operator must
determine the concentration or value of
the following parameters in ground-
water samples in accordance with
paragraphs (c) and (d) of this section:
(1) Parameters characterizing the
suitability of the ground water as a
drinking water supply, as specified in
Appendix III.
(2) Parameters establishing ground-
water quality:
(i) Chloride
(ii) Iron
(iii) Manganese
(iv) Phenols
(v) Sodium
(vi) Sulfate
[Comment: These parameters are to be
used as a basis for comparison in the
event a ground-water quality
assessment is required under
§ 265.93(d).]
(3) Parameters used as indicators of
ground-water contamination:
WpH
(ii) Specific Conductance
(iii) Total Organic Carbon
(iv) Total Organic Halogen
(cjllfFor all monitoring wells, the
owner or operator must establish initial
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Federal Register / Vol. 45; No. 98 / Monday, May 19, 1980 / Rules and Regulations 33241
background concentrations or values of
all parameters specified in paragraph (b)
of this Section. He must do this
quarterly for one year.
(2) For each of the indicator
parameters specified in paragraph (b)(3)
of this Section, at least four replicate
measurements must be obtained for
each sample and the initial background
arithmetic mean and variance must be
determined by pooling the replicate
measurements for the respective
parameter concentrations or values in
samples obtained from upgradient wells
during the first year.
(d) After the first year, all monitoring
wells must be sampled and the samples
analyzed with the following frequencies;
(1) Samples collected to establish
ground-water quality must be obtained
and analyzed for the parameters
specified in paragraph (b)(2) of this
Section at least annually.
(2) Samples collected to indicate
ground-water contamination must be
obtained and analyzed for the
parameters specified in paragraph (b)(3)
of this Section at least semi-annually.
(e) Elevation of the ground-water
surface at each monitoring well must be
determined each time a sample is
obtained.
§ 265.93 Preparation, evaluation, and
response.
" (a) Within one year after the effective
date of these regulations, the owner or
operator must prepare an outline of a
ground-water quality assessment
program. The outline must describe a
more comprehensive ground-water
monitoring program (than that described
in §§ 265.91 and 265.92) capable of
determining:
(1) Whether hazardous waste or
hazardous waste constituents have
entered the ground water;
(2) .The rate and extent of migration of
hazardous waste or hazardous waste
constituents in the ground water, and
(3) The concentrations of hazardous
waste or hazardous waste constituents
in the ground water.
(b) For each indicator parameter
specified in § 265.92(b)(3), the owner or
operator must calculate the arithmetic
mean and variance, based on at least
four replicate measurements on each
sample, for each well monitored in
accordance with § 285.92(d)(2), and
compare these results with its initial
background arithmetic mean. The
comparison must consider individually
each of the wells in the monitoring
system, and must use the Student's t-test
at the 0.01 level of significance (see
Appendix IV) to determine statistically
significant increases (and decreases, in
the case of pH) over initial background.
(c)(l) If the comparisons for the
upgradient wells made under paragraph
(b) of this Section show a significant
increase (or pH decrease), the owner or
operator must submit this information in
accordance with § 265.94(a)(2)(ii).
(2) If the comparisons for
downgradient wells made under
paragraph (b) of this Section show a
significant increase (or pH decrease),
the owner or operator must then
immediately obtain additional ground-
water samples from those downgradient
wells where a significant difference was
detected, split the samples in two, and
obtain analyses of all additional
samples to determine whether the
significant difference was a result of
laboratory error,
(d)(l) If the analyses performed under
paragraph (c)(2) of this Section confirm
the significant increase (or pH
decrease), the owner or operator must
provide written notice to the Regional
Administrator—within seven days of the
date of such confirmation—that the
facility may be affecting ground-water
quality.
(2) Within 15 days after the
notification under paragraph (d)(l) of
this Section, the owner or operator must
develop and submit to the Regional
Administrator a specific plan, based on
the outline required under paragraph (a)
of this Section and certified by a
qualified geologist or geotechnical
engineer, for a ground-water quality
assessment program at the facility.
(3) The plan to be submitted under
§ 2U5.90(d)(l) or paragraph (d)(2) of this
Section must specify:
(i) The number, location, and depth of
wells;
(ii) Sampling and analytical methods
for those hazardous wastes or
hazardous waste constituents in the
facility;
(iii) Evaluation procedures, including
any use of previously-gathered ground-
water quality information; and
(iv) A schedule of implementation.
(4) The owner or operator must
implement the ground-water quality
assessment plan which satisfies the
requirements of paragraph (d)(3) of this
Section, and, at a minimum, determine:
(i) The rate and extent of migration of
the hazardous waste or hazardous
waste constituents in the ground water;
and
(ii) The concentrations of the
hazardous waste or hazardous waste
constituents in the ground water.
(5) The owner or operator must make
his first determination under paragraph
(d)(4) of this Section as soon as
technically feasible, and, within 15 days
after that determination, submit to the
Regional Administrator a written report
containing an assessment of the ground-
water quality.
(6) If the owners or operator
determines, based on the results of the
first determination under paragraph
(d)(4) of this Section, that no hazardous
waste or hazardous waste constituents
from the facility have entered the
ground water, then he may reinstate the
indicator evaluation program described
in § 265.92 and paragraph (b) of this
Section. If the owner or operator
reinstates the indicator evaluation
program, he must so notify the Regional
Administrator in the report submitted
under paragraph (d)(5) of this Section.
(7) If the owner or operator
determines, based on the first
determination under paragraph (d)(4) of
this Section, that hazardous waste or
hazardous waste constituents from the
facility have entered the ground water,
then he:
(i) Must continue to make the
determinations required under
paragraph (d)(4) of this Section on a
quarterly basis until final closure of the
facility, if the ground-water quality
assessment plan was implemented prior
to final closure of the facility; or
(ii) May cease to make the
determinations required under
paragraph (d)(4) of this Section, if the
ground-water quality assessment plan
was implemented during the post-
closure care period.
(e) Notwithstanding any other
provision of this Subpart, any ground-
water quality assessment to satisfy the
requirements of § 265.93(d)(4) which is
initiated prior to final closure of the
facility must be completed and reported
in accordance with J 265.93(d)(5).
(f) Unless the ground water is
monitored to satisfy the requirements of
§ 265.93(d)(4), at least annually the
owner or operator must evaluate the
data on ground-water surface elevations
obtained under § 265.92{e) to determine
whether the requirements under
§ 265.91 (a) for locating the monitoring
wells continues to be satisfied. If the
evaluation shows that § 265.91 (a) is no
longer satisfied, the owner or operator
must immediately modify the number,
location, or depth of the monitoring
wells to bring the ground-water
monitoring system into compliance with
this requirement.
§ 265.94 Recordkeeplng and reporting.
(a) Unless the ground water is
monitored to satisfy the requirements of
§ 265.93(d)(4), the owner or operator
must:
(1) Keep records of the analyses
required in § 265.92(c) and (cl), the
associated g(Ound-v,';itt>i' su-hs :J
iJojm required in § i05.9^je), und
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33242 Federal Register / Vol. 45, No. 98 / Monday, May 19. 1980 / Rules and Regulations
the evaluations required in § 265.93(b)
throughout the active life of the facility,
and, for disposal facilities, throughout
the post-closure care period as well; and
(2) Report the following ground-water
monitoring information to the Regional
Administrator:
(i) During the first year when initial
background concentrations are being
established for the facility:
concentrations or values of the
parameters listed in § 265.92(b)(l) for
each ground-water monitoring well
within 15 days after completing each
quarterly analysis. The owner or
operator must separately identify for
each monitoring well any parameters
whose concentration or value has been
found to exceed the maximum
contaminant levels listed in Appendix
HI.
(ii) Annually: concentrations or values
of the parameters listed in § 265.92(b)(3)
for each ground-water monitoring well,
along with the required evaluations for
these parameters under § 265.93(b). The
owner or operator must separately
identify any significant differences from
initial background found in the
upgradient wells, in accordance with
§ 265.93(c)(l). During the active life of
the facility, this information must be
submitted as part of the annual report
required under § 265.75.
(iii) As a part of the annual report
required under § 265.75: results of the
evaluation of ground-water surface
elevations under § 265.93(f), and a
description of the response to that
evaluation, where applicable.
(b) If the ground water is monitored to
satisfy the requirements of
S 265.93(d)(4), the owner or operator
must:
[1] Keep records of the analyses and
evaluations specified in the plan, which
satisfies the requirements of
§ 265.93(d}(3), throughout the active life
of the facility, and, for disposal
facilities, throughout the post-closure N
care period as well; and
(2) Annually, until final closure of the I
facility, submit to the Regional .- |
Administrator a report containing the
results of his ground-water quality
assessment program which includes, but ]
is not limited to, the calculated (or |
measured) rate of migration of
hazardous waste or hazardous waste
constituents in the ground water during I
the reporting period. This report must be |
submitted as part of the annual report
required under § 265.75,
148
I
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1254
Federal Register / Vol. 47. N
Mo,
i i, J9B/. / Ruies dad Regulations
ENVIRONMENTAL PROTECTION
AGENCY
40 CFR Part 265
[SW-FRL 1999-2]
Standards for Owners and Operators
of Hazardous Waste Disposal
Facilities; Interim Rule
AGENCY: Environmental Protection
Agency.
ACTION: Interim final amendments to
rule.
4:00 p.m., Monday through I'M
SUMMARY: EPA is today promulgating, in
interim final form, amendments to the
ground-water monitoring standards for
certain hazardous waste surface
impoundments used to neutralize
corrosive wastes. The amendments
provide for a waiver of these standards
for any surface impoundment that (1)
Contains wastes which are hazardous
only because they exhibit the corrosivity
characteristic and contains no other
hazardous wastes, and (2) is
demonstrated to rapidly neutralize the
wastes so that there is no potential for
migration of any hazardous waste out of
the impoundment.
The purpose of today's amendment is
to relieve owners and operators of
neutralization surface impoundments
from having to monitor ground water in
cases where such monitoring is not
necessary to protect human health and
the environment. Since the compliance
date for the ground-water monitoring
requirements is November 19,1981,
today's limited exception to those
requirements is being made effective
immediately.
DATE: Today's interim final amendments
are effective January 11,1982.
EPA will accept public comments on
the proposed amendments until March 9,
1982.
ADDRESSES: Comments on the interim
final amendments should be sent to
Deneen Shrader, Docket Clerk, Office of
Solid Waste (WH-562), U.S.
Environmental Protection Agency, 401 M
Street. SW., Washington, D.C. 20460.
Comments should identify the regulatory
docket as follows: "Docket No. 3004,
Amendment of § 265.90{c)". Requests for
a hearing should be addressed to John P.
Lehman, Director, Hazardous and
Industrial Waste Division, Office of
Solid Waste (WH-565), U.S.
Environmental Protection Agency,
Washington, D.C. 20460.
' The official docket for this regulation
is located in Room 2636, U.S.
Environmental Protection Agency, 401 M
Street, SW., Washington, D.C. 20460 and
is available for viewing from 9:00 a.m to
FOB FUfiTHEH iM'^SWi.i : J?:>:. •„ '.••,,'
Offiw of S-iKl Waste f',v>}
Environmental Protection Ag
Street, SVV, WV.shmgU'n D C,
a'.ii'ni^ii." • • oia.,.(t ''i-<'i'y .'-;
of Solid Wjst" ,*> v-«s' i I-: :,30ti'- ta -,^j } w!> t.h
estabusnc-.? ui iyKiiuiKftio;< wnn earlier
regulation-: I.TI •. -.iji./i,- ! aa ?• •briiciry 36,
1980 {4b J.'K j_ • • •-'•' .. r , i, the k.nndp''1
marisgHi.v .it .-,_•• .•.<• -.jul^t tiubutk- C,
of I'lt r\'.-,-: "• :• l'"^:c'>-vo.t'Cr' and
Rerfiva;,' ''ci..- :?' •• • s . iii^r.ded (4?
U.S.C ti"}^.' - -- / ;. : crt ",'n > ! the Mj
"
iid:'.ai-ic!:i.s wh'.'te '"i-ifrn'-nt -.cji'ige, and
dispci"/" f '"il'.tif": oai >•)£• t : - 'uuerim
stat'ii prTH.-' ''iij jpOj'L F ('} § -'^-; " r: :i;-»u,n3 !-',-u:b!ishtcl
grohrifi wa'"r >;•, nii-vi-:;if-; in if n:n stall's
sia.ioar.j-. -pr-!i: ii-^s T,I ii>jni ir.-ijiof a'
f a oil i tie:,
Sei'tion .'H5,9C(t.S provides t"iat d!l ur
part of the grouTun-'att-i- mo.nforirig
requii'ur. siits oi Suloari F rritiy be
waived if the owner or operator
demonstrates th.ii '.here is, a !uw
potential ".;•! mi^/at'ui'' v/ li'i^irdous
waste or i-'drdrdau'-. v/as-'e nonbtitueats
from the iHcilily viu the uppermost
aquifer to water supply w;e!!s or to
surface water. The d.-moastraHon must
be in wi'itr.ig a^il must he r.ert fied bv" a
qualified geologist or geotecniiicai
engineer and nuea
1 As exo'f.'.nec' i:, '.hi preainblo io § 265 90(c) J45
FR 33192. May 19, I960), 8 complete waiver of all
Subpari F sn jmtorii"^ requ'iamrnts ;3 available onl^-
when th; nwnti or optratu, can rierroiisirate ihat
not allow consideration of the disposed
wastes' characteristics and the facility
assign to be used as a basis for reducing
ioonitcriig requuements. At the time
that the regulation was promulgated,
EPA was concerned that the state of
knowledge about hazardous wastes and
fa< ii'fv designs was not sufficiently
•, f rtain to justify reductions in the basic
laonitoimg system during interim status.
(See 45 FR 33192, May 19,1980.)
Since tha time it promulgated
§ ?b6.90(cl, EPA has become aware of
one situation wher« it is appropriate to
a-'nv -,-i wdiver of ground-water
.ni'-rdlo^ing requirements to be based
ur-ori consideration of the facility and
the wastes disposed in the facility.
Snvbi^i indijhiries operate surface
ijup'jimdmc'nls which contain no
hazardous wastes except corrosive
wastes which themselves are hazardous
-jfuy due to theii coirosivity. In some
•rases, these wastes may be placed in
tut1 impoundment together with large
volumes of non-hazardous wastes. In
some of these cases, particularly where
active mechanical mixing is performed
:n toe impoundment, it may be reliably
demonstrated that the corrosive wastes
are neutralized shortly after being
placed in the inpoundment. In such
cases there may be no potential for any
hazardous wastes to migrate out of the
impoundment.
For the neutialization surface
impoundments described above, EPA
believes that ii makes little sense to
monitor the ground water beneath the
facilities. Therefore, EPA is amending
§ 265 90 to provide a waiver of Subpart
F requirements for these types of
facilities upon a demonstration that
there is no potential for migration of
hazardous wastes out of the facility. The
demonstration would have to show,
based on consideration of the corrosive
wastes and the impoundment, that the
corrosive wastes will be neutralized
before they migrate out of the facility.
The demonstration must be certified by
a professional qualified to make this
type of technical demonstration, rather
than necessarily by a geologist or
geotechnical engineer (as required in
§ 265.90(cJ).
If may be that there are types of
facilities other than neutralization
surface impoundments for which
reliable demonstrations can in some
instances be made, based upon
consideration of the nature of the
wastes and of the facility, to show that
there is no potential for migration of
hazardous v/aste or hazardous waste
there is no pi'ent'al for migration to water supply
wells or surface vvater.
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Federal Register / Vol. 47, No. 6 / Monday, January 11, 1982 / Rules and Regulations 1255
constituents from the facility. EPA
welcomes information (including
detailed dataj on such facilities.
II. Promulgation of Today's Amendment
in Interim Final Form
The compliance date for the existing
Subpart F ground-water monitoring
requirements is November 19,1981.
Unless today's amendment is
promulgated and takes effect
immediately, owners or operators of
neutralization surface impoundments
would be required to comply
immediately with the Subpart F
requirements even when they can
demonstrate that those requirements are
unnecessary to protect human health
and the environment. Such a result
would be contrary to the public interest.
Therefore, EPA believes that good cause
exists to promulgate today's amendment
in interim final form without prior notice
and comment.
EPA invites public comment on
today's interim final rule. Consistent
with its duty to fully consider all
comments, EPA will promulgate a final
rule as soon as gossible after the close
of the public comment period.
III. Effective date
Section 3010(b) of RCRA provides that
EPA's hazardous waste regulations take
effect six months after their
promulgation. The purpose of this
statutory requirement is to allow
persons affected by the regulations
sufficient lead time to comply with
major new regulatory requirements.
Today's amendment, however, does not
impose a new requirement but rather
relaxes an existing requirement.
•Therefore, the Agency believes it is
consistent with the intent ot Section
3010(b) to make today's amendment
immediately effective.
IV. Regulatory Analysis
Section 3(b) of Executive Order 12291,
40 FR 13193 (February 19,1981), requires
EPA to initially determine whether a
rule that it intends to propose or issue is
a major rule and to prepare regulatory
impact analyses for all major rules.
EPA has determined that the
amendment being promulgated today is
not a major rule. As discussed above,
this amendment will allow a waiver of
ground-water monitoring requirements
under a limited set of circumstances.
Accordingly, a Regulatory Impact
Analysis is not being prepared for this
amendment.
This regulation was submitted to the
Office of Management and Budget for
review as required by Executive Order
12291.
The information collection
requirements in this interim final rule
will be submitted to the Office of
Management and Budget for clearance
under the Paperwork Reduction Act of
1980. The information requirements or
recordkeeping in this interim final rule
will not take place until it has been
cleared by the Office of Management
and Budget. If OMB approves, the
information collection requirements will
take effect as set forth in this interim
final rule. If not, EPA will revise the
information requirements (and this rule
if appropriate) to comply with OMB's
determination.
Under the Regulatory Flexibility Act, 5
U.S.C. 601 et seq., EPA is required to
determine whether a regulation will
have a significant impact on a
substantial number of small entities so
as to require a regulatory analysis. The
additional waiver opportunity created
by this amendment should, if anything,
reduce the burden of compliance with
the hazardous waste disposal
regulations for small entities. Therefore,
pursuant to 5 U.S.C. 605(b), I hereby
certify that this rule will not have a
significant adverse impact on a
substantial number of small entities.
Dated: December 28,1981.
Anne M. Gotsuch,
Administrator.
PART 265—INTERIM STATUS
STANDARDS FOR OWNER AND
OPERATORS OF HAZARDOUS WASTE
TREATMENT, STORAGE, AND
DISPOSAL FACILITIES
For the reasons set out in the
preamble, Title 40 of the Code of Federal
Regulations is amended as follows:
1. The authority citation for Part 265 l
reads as follows:
Authority: Sees. 1006, 2002(a). and 3004,
Solid Waste Disposal Act as amended by the
Resource Conservation and Recovery Act of
1976, as amended (42 U.S.C. 6905, 6912(a),
and 6924).
2. Section 265.90 is amended by
adding paragraph (e) to read as follows:
§285.90 Applicability.
* « * * *
(e) The ground-water monitoring
requirements of this Subpart may be
waived with respect to any surface
impoundment that (1) Is used to
neutralize wastes which are hazardous
solely because they exhibit the
corrosivity characteristic under § 261.22
of this Chapter or are listed as
hazardous wastes in Subpart D of Part •
261 of this Chapter only for this reason, '
and (2) contains no other hazardous
wastes, if the owner or operator can
demonstrate that there is no potential
for migration of hazardous wastes from
the impoundment: The demonstration
must establish, based upon
consideration of the characteristics of
the wastes.and the impoundment, that
the corrosive wastes will be neutralized
to the extent that they no longer meet
the corrosivity characteristic before they
can migrate out of the impoundment.
The demonstration must be in writing
and must be certified by a qualified
professional.
(FR Doc. 82-823 Filed l-»-B2i 8:45 am]
BILLING CODE W60-30-M
150
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Appendix B
USGS Information Contacts
wra
Water
Resources
Division
information
guide
November 1980
U.S. Geological Survey
151
-------
H6RDQURRTGR5
U.S. GEOLOGICAL SURVEY
WATER RESOURCES DIVISION
(Mail stop no.) NATIONAL CENTER
12201 SUNRISE VALLEY DRIVE
RESTON, VIRGINIA 22092
Telephone: (703) 860 + 4-digit extension
FTS 928 + 4-digit extension
Switchboard: ext. 7000
Personnel locator: ext. 6118
Office hours: 7:45 a.m. to 4:15 p.m. Eastern Time
CHIEF HYDROLOGIST
Mail stop: 409
Room: 5A-402
Telephone: ext. 6921
ASSOCIATE CHIEF HYDROLOGIST
Mail stop: 408
Room: 5A-324
Telephone: ext. 6921
OFFICE OF INTERNATIONAL HYDROLOGY
Mail stop: 470
Room: 3B-410
Telephone: ext. 6548
OFFICE OF WATER DATA COORDINATION
Mail stop: 417
Room: 5A-116
Telephone: ext. 6931
ASSISTANT CHIEF HYDROLOGIST FOR OPERATIONS
Mail stop: 441 Room: 5A-302 Telephone: ext. 6801
ASSISTANT CHIEF HYDROLOGIST FOR SCIENTIFIC PUBLICATIONS & DATA MANAGEMENT
Mail stop: 440 Room: 5A-216 Telephone: ext. 6877
WATSTORE
(Automatic Data Section)
Mail stop: 437
Room: 5B-332
Telephone: ext. 6879
NAWDEX PROGRAM
OFFICE
Mail stop: 421
Room: 5A-130
Telephone: ext. 6031
NATIONAL WATER-USE
INFORMATION PROGRAM
Mail stop: 440
Room: 5A-213
Telephone: ext. 6877
SCIENTIFIC PUBLICATIONS
SECTION
Mail stop: 439
Room: 5A-210
Telephone: ext. 6881
ASSISTANT CHIEF HYDROLOGIST FOR RESEARCH & TECHNICAL COORDINATION
Mail stop: 414 Room: 5A-102 Telephone: ext. 6971
DEPUTY ASSISTANT CHIEF
HYDROLOGIST FOR RESEARCH
Mail stop: 413
Room: 5A-422
Telephone: ext. 6971
GROUND WATER
BRANCH
Mail stop: 411
Room: 5A-414
Telephone: ext. 6904
SURFACE WATER
BRANCH
Mail stop: 415
Room: 5A-104
Telephone: ext. 6837
QUALITY OF WATER
BRANCH
Mail stop: 412
Room: 5A-420
Telephone: ext. 6834
152
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NORTH
-------
MICHIGAN—Continued
Telephone: (517) 377-1608; FTS 374-1608
Office hours: 7:45 a.m. to 4:15 p.m. Eastern Time
MINNESOTA
Address:
District Chief, WRD
U.S. Geological Survey
Post Office Bldg., Rm. 702
St. Paul, MM 55101
Telephone: (612) 725-7841; FTS 725-7841
Office hours: 7:45 a.m. to 4:30 p.m. Central Time
NEW HAMPSHIRE See also Massachusetts
Mai/ing address:
Hydrologist-m-Charge
Subdistrict Office, WRD
U.S. Geological Survey
RFD2, Box352A
Concord, NH 03301
Office address:
Country Hills Professional Park
Bow
Telephone: (603) 224-7273; FTS 834-4739
Office hours: 7:45 a.m. to 4:15 p.m. Eastern Time
NEW JERSEY
Mailing address:
District Chief, WRD
U.S. Geological Survey
P.O. Box 1238
Trenton, NJ 08607
Office address:
Federal Bldg., Rm. 436
402 East State Street
Trenton
Telephone: (609) 989-2162; FTS 483-2162
Office hours: 8:00 a.m. to 4'30 p.m. Eastern Time
NEW YORK
Mai/ing address:
District Chief, WRD
U.S. Geological Survey
P.O. Box 1350
Albany, NY 12201
Office address:
U.S. Post Office and Courthouse, Rm. 236
Albany
Telephone: (518) 472-3107; FTS 562-3107
Office hours: 7:45 a.m. to 4:30 p.m. Eastern Time
OHIO
Address:
District Chief, WRD
U.S. Geological Survey
975 West Third Avenue
Columbus, OH 43212
OHIO—Continued
Telephone: (614) 469-5553; FTS 943-5553
Office hours: 7:45 a.m. to 4.30 p.m. Eastern Time
PENNSYLVANIA
Mailing address:
District Chief, WRD
U.S. Geological Survey
P.O. Box 1107
Harrisburg, PA 17108
Office address:
Federal Bldg., 4th Floor
228 Walnut Street
Harrisburg
Telephone: (717) 782-4514; FTS 590-4514
Office hours: 8:00 a.m. to 4.30 p.m. Eastern Time
RHODE ISLAND See also Massachusetts
Address:
Hydrologist-in-Charge
Subdistrict Office, WRD
U.S. Geological Survey
Federal Bldg. and U.S. Post Office, Rm. 224
Providence, Rl 02903
Telephone: (401) 528-4655; FTS 838-4655
Office hours: 8:00 a.m. to 4:30 p.m. Eastern Time
VERMONT See Massachusetts
VIRGINIA
Address:
District Chief, WRD
U.S. Geological Survey
200 West Grace Street, Rm. 304
Richmond, VA 23220
Telephone: (804) 771-2427; FTS 925-2427
Office hours: 8.00 a.m. to 4:45 p.m. Eastern Time
WEST VIRGINIA
Address:
District Chief, WRD
U.S. Geological Survey
Federal Bldg. and U.S. Courthouse, Rm. 3017
500 Quarrier Street, East
Charleston, WV 25301
Telephone: (304) 343-6181, ext. 310; FTS 924-1310
Office hours: 7.45 a.m. to 4'30 p.m. Eastern Time
WISCONSIN
Address:
District Chief, WRD
U.S. Geological Survey
1815 University Avenue, Rm. 200
Madison, Wl 53706
Telephone: (608) 262-2488; FTS 262-2488
Office hours: 8:00 a.m. to 4:30 p.m. Central Time
154
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SOUTHGflSTGRN R6GION
Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, Puerto Rico, South Carolina, Tennessee,
Virgin Islands
OFFICE OF THE REGIONAL HYDROLOGIST
Address:
Regional Hydrologist
U.S. Geological Survey
Richard B. Russell Federal Bldg.
75 Spring Street, SW, Rm. 772
Atlanta, GA 30303
Telephone: (404) 221-51 74; FTS 242-5174
Office hours: 7:30 a.m. to 4:15 p.m. Eastern Time
DISTRICT OFFICES
ALABAMA
Mailing address:
District Chief, WRD
U.S. Geological Survey
P.O. Box V
University, AL 35486
Office address:
Oil and Gas Board Bldg., Rm. 202
University of Alabama
Tuscaloosa
Telephone: (205) 752-8104; FTS 229-2957
Office hours: 7:30 a.m. to 4:00 p.m. Central Time
FLORIDA
Address:
District Chief, WRD
U.S. Geological Survey
325 John Knox Road, Suite F-240
Tallahassee, FL 32303
Telephone: (904) 386-1118; FTS 946-4251
Office hours: 7:45 a.m. to 4:30 p.m. Eastern Time
GEORGIA
Address:
District Chief, WRD
U.S. Geological Survey
6481 Peachtree Industrial Blvd., Suite B
Doravilie. GA 30360
Telephone: (404) 221-4858; FTS 242-4858
Office hours: 7:45 a.m. to 4:30 p.m. Eastern Time
KENTUCKY
Address:
District Chief, WRD
U.S. Geological Survey
Federal Btdg., Rm. 572
600 Federal Place
Louisville, KY 40202
155
KENTUCKY—Continued
Telephone: (502) 582-5241; FTS 352-5241
Office hours: 8:00 a.m. to 4:45 p.m. Eastern Time
MISSISSIPPI
Address:
District Chief, WRD
U.S. Geological Survey
Federal Office Bldg., Suite 710
100 West Capitol Street
Jackson, MS 39201
Telephone: (601) 969-4600; FTS 490-4600
Office hours: 7:45 a.m. to 4:30 p.m. Central Time
NORTH CAROLINA
Mailing address:
District Chief, WRD
U.S. Geological Survey
P.O. Box 2857
Raleigh, NC 27602
Office address:
Century Station, Post Office Bldg., Rm. 436
Raleigh
Telephone: (919) 755-4510; FTS 672-4510
Office hours: 8:00 a.m. to 4:45 p.m. Eastern Time
PUERTO RICO Caribbean District (Puerto Rico and U.S.
Virgin Islands)
Mailing Address:
District Chief, WRD
U.S. Geological Survey
GPO Box 4424
San Juan, PR 00934
Office address:
Building 652
Ft. Buchanan
Telephone: (809) 783-4660; FTS 967-1221,
ask operator for 753-4414
Office hours: 7:45 a.m. to 4:30 p.m. Atlantic Time
10
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SOUTH CAROLINA TENNESSEE
Address: Address:
District Chief, WRD District Chief, WRD
U.S. Geological Survey U.S. Geological Survey
-,, , „ _, . „,_, «. ~,ro Federal Bldg. and U.S. Court House,
Strom Thurmond Federal Bldg., Suite 658 Rm ^.413
1835 Assembly Street Nashville, TN 37203
Columbia, SC 29210 Telephone: (615) 251-5424; FTS 852-5424
Telephone: (803) 765-5966; FTS 677-5966 Office hours: 7:46 a-m-to 4:3° P'm- Central Time
Office hours: 7:45 a.m. to 4:30 p.m. Eastern Time VIRGIN ISLANDS See Puerto Rico
156
11
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C
-------
MONTANA—Continued
Telephone: (406) 559-5263; FTS 585-5263
Office hours: 7:45 a.m. to 4:30 p.m. Mountain Time
NEBRASKA
Address:
District Chief, WRD
U.S. Geological Survey
Federal Bldg. and U.S. Court House, Rm. 406
100 Centennial Mall N.
Lincoln, NE 68508
Telephone: (402) 471-5082; FTS 541-5082
Office hours: 7:45 a.m. to 4:30 p.m. Central Time
NEW MEXICO
Mailing address:
District Chief. WRD
U.S. Geological Survey
P.O. Box 26659
Albuquerque. NM 87125
Office address:
Western Bank Bldg., Rm. 815
505 Marquette, NW
Albuquerque
Telephone: (505) 766-2246; FTS 474-2246
Office hours: 7:45 a.m. to 4:45 p.m. Mountain Time
NORTH DAKOTA
Address:
District Chief, WRD
U.S. Geological Survey
821 East Interstate Avenue
Bismarck, ND 58501
Telephone: (701) 255-4011, ext. 601; FTS 783-4601
Office hours: 8:00 a.m. to 5:00 p.m. Central Time
OKLAHOMA
Address:
District Chief, WRD
U.S. Geological Survey
215 NW 3d Street, Rm. 621
Oklahoma City, OK 73102
Telephone: (405) 231-4256; FTS 736-4256
Office hours: 8:00 a.m. to 4:45 p.m. Central Time
SOUTH DAKOTA
Address:
District Chief, WRD
U.S. Geological Survey
Federal Bldg., Rm. 317
200 4th Street, SW
Huron, SD 57350
Telephone: (605) 352-8651, ext. 258; FTS 782-2258
Office hours: 8:00 a.m. to 5:00 p.m. Central Time
TEXAS
Address:
District Chief, WRD
U.S. Geological Survey
Federal Bldg., Rm. 649
300 East 8th Street
Austin, TX 78701
Telephone: (512) 397-5766; FTS 734-5766
Office hours: 7:45 a.m. to 4:30 p.m. Central Time
UTAH
Address:
District Chief, WRD
U.S. Geological Survey
Administration Bldg., Rm. 1016
1745 West 1700 South
Salt Lake City, UT 84104
Telephone: (801) 524-5663; FTS 588-5663
Office hours: 8:00 a.m. to 4:30 p.m. Mountain Time
WYOMING
Mailing address:
District Chief, WRD
U.S. Geological Survey
P.O. Box 1125
Cheyenne, WY 82001
Office address:
J.C. O'Mahoney Federal Center, Rm. 5017
2120 Capitol Avenue
Cheyenne
Telephone: (307) 778-2220, ext. 2153; FTS 328-2153
Office hours: 8:00 a.m. to 4:30 p.m. Mountain Time
158
13
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UU€ST(ERN REGION
Alaska, Arizona, California, Guam, Hawaii, Idaho, Nevada, Oregon, Washington
OFFICE OF THE REGIONAL HYDROLOGIST
Address:
Regional Hydrologist
U.S. Geological Survey
345 Middlefield Road, Mail Stop 66
Menlo Park, CA 94025
Telephone: (415) 323-8111, ext. 2337; FTS 467-2337
Office hours: 7:45 a.m. to 4:15 p.m. Pacific Time
DISTRICT OFFICES
ALASKA HAWAII — Continued
Address: Telephone: (808) 546-8331 ; FTS 556-0220,
733 West 4th Avenue, Suite 400 Office hours: 7:45 a.m. to 4:15 p.m. Alaska-Hawaii Time
Anchorage, AK 99501 .„,..«
Telephone: (907) 271-4138; FTS 399-0150, ' IDAHO
ask operator for 27 1 -4 1 38 Address:
Office hours: 7:45 a.m. to 4:15 p.m. Alaska-Hawaii Time District Chief, WRD
ARIZONA U.S. Geological Survey
Address: Box 036, Federal Bldg., Rm. 365
SIs^oSaKey 550 West Fort Street
Federal Bldg., 301 West Congress Street Boise. ID 83724
Tucson, AZ 85701 Telephone: (208) 334-1750; FTS 554-1750
Telephone: (602) 792-6671; FTS 762-6671 Office hours: 7:45 a.m. to 4: 15 p.m. Mountain Time
Office hours: 8:00 a.m. to 4:30 p.m. Mountain Time
CALIFORNIA NEVADA
Address: Address:
District Chief, WRD District Chief, WRD
855' Oa^cfove' Av^rTe U'S' Geol°9ical SurveV
Menlo Park CA 94025 Federal Bldg., Rm. 227, 705 North Plaza Street
Telephone: (415) 323-8111, ext. 2326; FTS 467-2326 Carson City, NV 89701
Office hours: 7:45 a.m. to 4:15 p.m. Pacific Time Telephone: (702) 882-1388; FTS 470-5911,
GUAM See also Hawaii %k °<**av>r f°r «2- 1 388
Mailing address: Office hours: 7:45 a.m. to 4:45 p.m. Pacific Time
Hydrologist-ln-Charge OREGON
Subdistrict Office, WRD ., ... ..
U.S. Geological Survey Maillng address:
P.O. Box 188 Distrlct Chief- WRD
FPO San Francisco, CA 96630 U-S- Geological Survey
Office address: P.O. Box 3202
U.S. Navy Public Works Center, Bldg. 104 Portland, OR 97208
Agana, GU 96910 Office address:
Telephone: 339-9123 (commercial operator for overseas 830 N.E. Holladay Street
call) Portland, OR 97232
Office hours: 7:45 a.m. to 4:15 p.m. Kilo Time Telephone: (503) 231-2009; FTS 429-2009
.,..., AH ,, .. ^ r^- Office hours: 7:30 a.m. to 4: 15 p.m. Pacific Time
HAWAII Hawaii— Guam District
Mailing address: WASHINGTON
District Chief, WRD Address:
U.S. Geological Survey District Chief, WRD
P.O. Box 501 66 U.S. Geological Survey
Honolulu, HI 96850 1 201 Pacific Avenue, Suite 600
Off ice address: Tacoma, WA 98402
300 Ala Moana Boulevard, Rm. 61 10 Telephone: (206) 593-6510; FTS 390-6510
Honolulu Office hours: 7:45 a.m. to 4:30 p.m. Pacific Time
159
14
-------
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U
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^ c
i1
Jj]
o-
•8
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i
(9
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EXPLANATIOI
- :•
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Gulf Coast Hydroicie
National Water-Quol
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_ o «
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-S w 73
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addition to the subd
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are locate)
1
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160
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APPENDIX C
EPA Interim Primary Drinking Water Standards
Parameter Maximum level (mg/1)
Arsenic 0.05
B.arium 1.0
Cadmium 0.01
Chromium 0.05
Fluoride 1.4-2.4
Lead 0.05
Mercury 0.002
Nitrate (as N) 10
Selenium 0.01
Silver 0.05
Endrin 0.0002
Lindane 0.004
Methoxychlor 0.1
Toxaphene 0.005
2,4-D 0.1
2,4,5-TP Silvex 0.01
Radium 5 pCi/1
Gross Alpha 15 pCi/1
Gross Beta 4 millirem/yr
Turbidity 1/TU
Coliform Bacteria 1/100 ml
i, . - ,
(Comment; Turbidity is applicable only to surface water supplies)
161
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Appendix D EPA 600/4-81-056
TOTAL ORGANIC HALIDE(TOX)
Adapted From
Method 450.1
Interim
U S. Environmental Protection Agency
Office of Research and Development
Environmental Monitoring and Support Laboratory
Physical and Chemical Methods Branch
Cincinnati, Ohio 45268
November 1980
162
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TOTAL ORGANIC HALIDE (TOX)
Method 450.1
-Scope and Application
1 .1 This method for the determination of Tbtal Organic Halides as Cl~
by carbon adsorption specifies that all samples be run at least
in duplicate. Under conditions of duplicate analysis, the reliable
limit of sensitivity is 5 pg/L. Organic halides as used in this
method are defined as all organic species containing chlorine,
bromine and iodine that are adsorbed by granular activated carbon
under the conditions of the method. Fluorine containing species
are not determined by this method.
1 .2 This is a microcoulometric-titration detection method applicable
to the determination of the compound class listed above in drinking
and ground waters.
-1.3 This method is provided as a recommended procedure. It may be
used as a reference for comparing the suitability of other methods
thought to be appropriate for measurement of TOX (i.e., by
comparison of sensitivity, accuracy and precision data).
1.4 This method should be used or supervised by analysts experienced
in the operation of a pyrolysis/microcoulometer and in the
interpretation of the results.
Summary of Method
2. L A sample of water that has been protected against the loss of
volatiles by the elimination of headspace in the sampling container,
and is free of undissolved solids, is passed through a column
containing 40 mg of activated carbon. The column is washed
163
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to remove any trapped inorganic halides, and is then pyrolyzed to
convert the adsorbed organohalides to a titratable species that can
be measured by a microcoulometric detector.
3. Interferences
. 3.1 Method interferences may be caused by contaminants, reagents,
glassware, and other sample processing hardware. All of these
materials must be routinely demonstrated to be free from
interferences under the conditions of the analysis by running
method blanks.
3.1.1 Glassware must be scrupulously cleaned. Clean all glassware
as soon as possible after use by treating with chromate
cleaning solution. This should be followed by detergent
washing in hot water. Rinse with tap water and distilled
water, drain dry, and heat in a muffle furnace at 400°C
for 15 to 30 minutes. Volumetric ware should not be heated
in a muffle furnace. Glassware should be sealed and stored
in a clean environment after drying and cooling, to prevent
any accumulation of dust or other contaminants.
3.1.2 The use of high purity reagents and gases help to minimize
interference problems.
3.2 Purity of the activated carbon must be verified before use. Only
carbon samples which register less than 1000 ng/40 mg should be
used. The stock of activated carbon should be stored in its
granular form in a glass container with a Teflon seal. Exposure to
the air must be minimized, especially during and after milling and
sieving the activated carbon. No more than a two-week supply
164
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should be prepared in advance. Protect carbon at all times from
all sources of halogenated organic vapors. Store prepared carbon
and packed columns in glass containers with Teflon seals.
3.3 This method is applicable to samples whose inorganic-halide
concentration does not exceed the organic-halide concentration by
more than 20,000 times.
x
Safety
The toxicity or carcinogenicity of each reagent in this method has not
been precisely defined; however, each chemical compound should be
treated as a potential health hazard. From this viewpoint, exposure to
these chemicals must be reduced to the lowest possible level by whatever
means available. The laboratory is responsible for maintaining a
current-awareness file of OSHA regulations regarding the safe handling
of the chemicals specified in this method. A reference file of
material-handling data sheets should also be made available to all
personnel involved in the chemical analysis.
Apparatus and Materials (All specifications are suggested. Catalog
numbers are included for illustration only).
5.1 Sampling equipment, for discrete or composite sampling
5.1.1 Grab-sample bottle - Amber glass, 250-mL, fitted with
Teflon-lined caps. Foil may be substituted for Teflon if
the sample is not corrosive. If amber bottles are not
available, protect samples from light. The container must
be washed and muffled at 400°C before use, to minimize
contamination.
165
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5.2 Adsorption System
5.2.1 Dohrmann Adsorption Module (AD-2), or equivalent,
pressurized, sample and nitrate-wash reservoirs.
5.2.2 Adsorption columns - pyrex, 5 cm long X 6-mm OD X 2-mm ID.
5.2.3 Granular Activated Carbon (GAC) - Filtrasorb-400,
Calgon-APC, or equivalent, ground or milled, and screened to
a 100/200 mesh range. Upon combustion of 40 mg of GAC, the
apparent-halide background should be 1000-mg Cl"
equivalent or less.
5.2.4 Cerafelt (available from Johns-Manville), or equivalent -
Form this material into plugs using a 2-mrn ID
stainless-steel borer with ejection rod (available from
Dohrmann) to hold 40 mg of GAC in the adsorption columns.
CAUTION: Do not touch this material with your fingers.
5.2.5 Column holders (available from Dohrtnan).
5.2.6 Volumetric flasks - 100-mL, 50-mL.
A general schematic of the adsorption system is shown in
Figure 1.
5.3 Dohrmann microcoulometric-titration system (MCTS-20 or DX-20), or
equivalent, containing the following components:
5.3.1 Boat sampler.
5.3.2 Pyrolysis furnace.
5.3.3 Microcoulometer with integrator.
5.3.4 Titration cell.
A general description of the analytical system is shown in
Figure 2.
5.4 Strip-Chart Recorder.
166
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6. Reagents
6.1 Sodium sulfite - 0.1 M, ACS reagent grade (12.6 g/L).
6.2 Nitric acid - concentrated.
6.3 Nitrate-Wash Solution (5000 mg NO^/L) - Prepare a nitrate-wash
solution by transferring approximately 8.2 gm of potassium nitrate
into a 1-litre volumetric flask and diluting to volume with reagent
water.
6.4 Carbon dioxide - gas, 99.9% purity.
6.5 Oxygen - 99.9% purity.
6.6 Nitrogen - prepurified.
6.7 70% Acetic acid in water - Dilute 7 volumes of acetic acid with 3
volumes of water.
6.8 Trichlorophenol solution, stock (1 \il - 10 ug Cl~) - Prepare a
stock solution by weighing accurately 1.856 gm of trichlorophenol
into a 100-mL volumetric flask. Dilute to volume with methanol.
6.9 Trichlorophenol solution, calibration (1 uL = 500 ng Cl") -
Dilute 5 ml of the trichlorophenol stock solution to 100 ml with
methanol.
6.10 Trichlorophenol standard, instrument-calibration - First, nitrate
wash a single column packed with 40 mg of activated carbon as
instructed for sample analysis, and then inject the column with
10 V.L of the calibration solution.
6.11 Trichlorophenol standard, adsorption-efficiency (100 ug C1~/L) -
Prepare a adsorption-efficiency standard by injecting 10 uL of
stock solution into 1 liter of reagent water.
6.12 Reagent water - Reagent water is defined as a water in which an
167
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interferent is not observed at the method detection limit of each
parameter of interest.
6.13 Blank standard - The reagent water used to prepare the calibration
standard should be used as the blank standard.
7. Calibration
7.1 Check the adsorption efficiency of each newly-prepared batch of
carbon by analyzing 100 ml of the adsorption-efficiency standard,
in duplicate, along with duplicates of the blank standard. The net
recovery should be within B% of the standard value.
7.2 Nitrate-wash blanks (Method Blanks) - Establish the repeatability
of the method background each day by first analyzing several
nitrate-wash blanks. Monitor this background by spacing nitrate-
wash blanks between each group of eight pyrolysis determinations.
7.2.1 The nitrate-wash blank values are obtained on single columns
packed with 40 mg of activated carbon. Wash with the
" * .* -
• nitrate solution as instructed for sample analysis, and then
pyrolyze the carbon.
7.3 Pyrolyze duplicate instrument-calibration standards and the blank
standard each day before beginning sample analysis. The net
response to the calibration-standard should be within 3% of the
calibration-standard value. Repeat analysis of the
instrument-calibration standard after each group of eight pyrolysis -
determinations, and before resuming sample analysis after cleaning
or reconditioning the titration cell or pyrolysis system.
8. Sample Preparation
8.1 Special care should be taken in the handling of the sample to
168
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minimize the loss of volatile organohalides. The adsorption
procedure should be performed simultaneously on ?.n replicates
8.2 Reduce residual chlorine by the addition of sulfite (1 ml of 0.1 M
per liter of sample). Addition of sulfite should be done at the
time of sampling if the analysis is meant to determine the TOX
concentration at the time of sampling. It should be recognized
that TOX may increase on storage of the sample. Samples should be
stored at 4°C without headspace.
8.3 Adjust pH of the sample to approximately 2 with concentrated HNO^
just prior to adding the sample to the reservoir.
9. Adsorption Procedure
9.1 Connect two columns in series, each containing 40 mg of
100/200-mesh activated carbon.
9.2 Fill the sample reservoir, and pass a metered amount of sample
through the activated-carbon columns at a rate of approximately
3 mL/min. NOTE: 100 ml of sample is the preferred volume for
concentrations of TOX between 5 and 500 ug/L; 50 ml for 501 to 1000
ug/L, and 25 ml for 1001 to 2000 ug/L.
9.3 Wash the columns-in-series with 2 ml of the 5000-mg/L nitrate
solution at a rate of approximately 2 mL/min to displace inorganic
chloride ions.
10. Pyrolysis Procedure
10.1 The contents of each column is pyrolyzed separately. After rinsing
with the nitrate solution, the columns should be protected from the
atmosphere and other sources of contamination until ready for
further analysis.
169
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10.2 Pyrolysis of the sample is accomplished in two stages. The
volatile components are pyrolyzed in a COp-rich atmosphere at a
low temperature to assure the conversion of brominated
trihalomethanes to a titratable species. The less volatile
components are then pyrolyzed at a high temperature in an Op-rich
atmosphere.
NOTE: The quartz sampling boat should have been previously muffled
at 800°C for at least 2 to 4 minutes as in a previous analysis,
and should be cleaned of any residue by vacuuming.
10.3 Transfer the contents of each column to the quartz boat for
individual analysis.
10.4 If the Dohrmann MC-1 is used for pyrolysis, manual instructions are
followed for gas flow regulation. If the MCT-20 is used, the
information on the diagram in Figure 3 is used for gas flow
regulation.
10.5 Position the sample for 2 minutes -in the 200°C zone of the
pyrolysis tube. For, the MCTS-20, the boat is positioned just
outside the furnace entrance.
10.6 After 2 minutes, advance the boat into the 800°C zone (center) of
the pyrolysis furnace. This second and final stage of pyrolysis
may require from 6 to 10 minutes to complete.
11. Detection
The effluent gases are directly analyzed in the microcoulometric-titra-
tion cell. Carefully follow manual instructions for optimizing cell
performance.
170
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12. Breakthrough
Because the background bias can be of such an unpredictable nature, it
can be especially difficult to recognize the extent of breakthrough of
organohalides from one column to another. All second-column
measurements for a properly operating system should not exceed
10-percent of the two-column total measurement. If the 10-percent
*
figure is exceeded, one of three events can have happened. Either the
first column was overloaded and a legitimate measure of breakthrough was
obtained - in which case taking a smaller sample may be necessary; or
channeling or some other failure occurred - in which case the sample may
need to be rerun; or a high, random, bias occurred and the result should
be rejected and the sample rerun. Because knowing which event has
occurred may not be possible, a sample analysis should be repeated often
enough to gain confidence in results. As a general rule, any analyses
that is rejected should be repeated whenever sample is available. In
the event that the second-column measurement is equal to or less than
the nitrate-wash blank value, the second-column value should be
disregarded.
13. Quality Control
13.1 Before performing any analyses, the analyst must demonstrate the
ability to generate acceptable accuracy and precision with this
procedure by the analysis of appropriate quality-control check
samples.
13.2 The laboratory must develop and maintain a statement of method
accuracy for their laboratory. The laboratory should update the
accuracy statement regularly as new recovery measurements are made.
171
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13.3 It is recommended that the laboratory adopt additional
quality-assurance practices for use with this method. The specific
practices that would be most productive will depend upon the needs
of the laboratory and the nature of the samples. Field duplicates
may be analyzed to monitor the precision of the sampling
technique. Whenever possible, the laboratory should perform
analysis of standard reference materials and participate in
relevant performance-evaluation studies.
14. Calculations
OX as Cl~ is calculated using the following formula:
(C1" ty * (C2 " C3 ^ = ug/L Total Organic Halide
\7
where:
C1 » ug Cl" on the first column in series
Cg = ug Cl" on the second column in series
C3 = predetermined, daily, average, method-blank value
(nitrate-wash blank for a 40-mg carbon column)
V » the sample volume in L
15. Accuracy and Precision
These procedures have been applied to a large number of drinking-water
samples. The results of these analysis are summarized in Tables I and
II.
16. Reference
Dressman, R.t Najar, G., Redzikowski, R., paper presented at the
Proceedings of the American Water Works Association Water Quality
Technology Conference, Philadelphia, Dec. 1979.
17;
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TABLE I
PRECISION AND ACCURACY DATA FOR MODEL COMPOUNDS
Model
Compound
CHC13
CHBrCl2
CHBr2Cl
CHBr3
Pentachlorophenol
Dose
/ig/L
98
160
155
160
120
Dose
as /ig/L Cl
88
106
79
67
80
Average
°jo Recovery
89
98
86
ill
93
Standard
Deviation
1U
9
11
8
9
No. of
Replicate's
10 ".
11
13
11
7
TABLE II
PRECISION DATA ON TAP WATER ANALYSIS
Sample
A
B
C
Avg. halide
ug Cl/L
71
9H
191
Standard
Deviation
Iu3
7.0
6.1
No. of
Replicates
8
6
k
176
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