BACKGROUND DOCUMENT NO. 6
HAZARDOUS WASTE MANAGEMENT SYSTEM: GENERAL;
STANDARDS APPLICABLE TO OWNERS AND OPERATORS
OF HAZARDOUS WASTE TREATMENT, STORAGE, AND DISPOSAL
FACILITIES; AND HAZARDOUS WASTE PEEWIT PROGRAM
(40 CFR 260, 264, and 122)
Permitting of Land Disposal Facilities;
Information Requirements for Permitting Discharges
This document (ms. 1941.39) provides background
information on EPA's proposed regulations for
land disposal of hazardous waste
U.S. ENVIRONMENTAL PROTECTION AGENCY
July 1981
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TABLE OF CONTENTS
INTRODUCTION Page 4
I. NEED FOR REGULATION Page 5
A. Potential for Environmental Damage
B. Actual Damage Incidents Page 7
II. ANALYSIS OF STANDARDS Page 7
1. Specific technical information
requirements for land disposal facilities - §122.25(c) Page 7
2. Informational requirements for permitting
discharges from land disposal facilities - §122.25(d) Page 13
A. Proposed Regulations and Rationale
B. Summary of Comments Page 14
C. Discussion Page 15
(1) General Page 21
(2) Predicting Leachate Volume Page 22
(a) Elements of Analysis Page 27
( b) Methods of forecasting Page 32
(c) Summary Page 36
(3) Leachate Composition Page 36
(a) Background
(b) Discussion Page 37
(i) Previous work
(ii) Alternatives
(4) Predicting Gas Emissions Page 39
(a) Identification of Gases
(b) Release of Gases and Vapors Page 41
(c) Summary Page 46
(5) Leachate Migration in the Unsaturated Zones Page 46
( a) Background
(b) Discussion Page 47
(i) Attenuation occurs Page 49
(ii) Prediction techniques are available Page 50
(iii) Technical difficulties Page 53
( iv) Precedents Page 57
(v) Consequences of not considering attenuation Page 59
(c) Summary Page 60
(6) Leachate migration in the Saturated Zone Page 60
(a) Background Page 60
(b) Trust and skepticism Page 62
(c) Acceptable levels of confidence Page 62
(d) Discussion Page 63
( i) Diffusion, Dispersion Page 64
(ii) Techniques Page 65
(e) Test case comparisons Page 67
(f) Summary Page 69
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(7) Leachate discharge from the saturated zone Page 69
(a) Background Page 69
(b) Discussion Page 70
(c) Summary Page 72
D. Regulatory Language Page 73
3. Variations in precision - §122.25(e) Page 77
A. Proposed Regulation and Rationale Page 77
B. Summary of Comments Page 78
C. Discussion Page 78
(1) Waste loadings Page 78
(2) Discharge and emission rates Page 78
(3) Migration in the unsaturated zone Page 82
(4) Attenuation in the unsaturated zone Page 82
(5) Migration in the sarurated zone Page 82
(6) Maximum locational and rate definitions Page 82
(7) Non-use withdrawal or collection Page 83
(8) Discharges into surface waters Page 83
(9) Surface discharges Page 83
(10) Ground water collection Page 84
(11) Withdrawal or collection for use Page 84
(12) Summary Page 85
D. Regulatory Language Page 86
4. Reports on hydrogeology,
climatology, and geography - §122.25(f) Page 92
5. Site investigation requirements - §122.25(g) Page 94
ISSUE; "Geologic and hydrologic factors" - §122.75(g)(1) Page 94
A. Proposed Regulation and Rationale Page 94
B. Summary of CommentsPage 94
C. DiscussionPage 94
(1) Topographic expression Page 94
(2) Characterizing unconsolidated earth materials Page 95
(3) Mapping of contact surfaces Page 98
(4) Characterizing consolidated rock Page 99
D. Regulatory Language Page 106
ISSUE; "Climatologic Factors" - §122.25(g)(2) Page 108
ISSUE; "Geographic Factors" - §122.25(g)(3 ) Page 110
ISSUE; "Special requirements based on land disposal
facility class" - §122.25(g)(4) Page 110
6. Description of monitoring and modelling - §122.25(e) Page 114
III. REFERENCES Page 115
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I. INTRODUCTION
Owners and operators of hazardous waste management facilities
who are seeking a permit for a land disposal facility are required
by the regulations to submit substantial amounts of information to
allow the permit issuing authority to perform a realistic evaluation
of the potential for the facility to cause adverse effects to human
health and the environment.
It is expected that most of this information will be submitted
in report form supplemented by appropiate drawings and basic data.
The owner or operator (or their authorized agents) will be expected
to draw analytical conclusions on the expected performance of the
facility to support the application.
The basic informational requirements are set forth in §122.25.
Paragraphs (c) , (d), (e) , ( f) , (g) and (h) describe those requirements
which are specific to land disposal facilities. Paragraphs (a)
and (b) set forth the informational requirements for all hazardous
waste management facilities and storage and treatment facilities
respectively certain of which are also applicable to land disposal
facilities. The applicable requirements of paragraphs (a) and (b)
were promulgated on 12 January 1981 at 46 PR 2889.
The information required in paragraphs (c) , (d), (e) , (f), (g),
and (h) includes specific technical design data and generic
information based on the types and amounts of waste to be disposed
of and the specific geologic, hydrologic, and climatologic setting
in which the disposal will occur. These facility specific data
must then be analyzed to predict how the waste will act within the
land disposal facility and with the environment.
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Except in the case of existing facilities where much of the
required information can be based on direct measurements, the
informational requirements must be fulfilled by techniques which
require skilled analysis of available hard data to hypothesize the
expected results within acceptable ranges of real error. This
potential for imprecision in analysis is provided for in the
regulation by requiring both a best estimate of the expected results
and a commitment on the part of the permit applicant which will
establish the error limits within which the facility must perform.
The monitoring requirements discussed in "Background Document No. 8
- Ground-water and Air Emission Monitoring" establish the means by
which such best estimates of performance and the performance limits
will be periodically reviewed during the operating life of the
facility based on monitoring data to ensure compliance and improve
definition.
I. NEED FOR REGULATION
A. Potential for Environmental Damage
EPA files contain many examples of environmental damage from
improper land disposal of hazardous waste. Although damage to
ground water is the most common occurrence, improper land disposal
has resulted in surface water and air pollution as well. The
following discussion describes reported incidents involving the
contamination of all these media as well as public health damage
that has occurred.
An EPA ground-water report, entitled "The Prevalence of
Subsurface Migration of Hazardous Chemical Substances At Selected
Industrial Waste Disposal Sites", investigated the likelihood of
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ground water contamination at hazardous waste land disposal sites.
In this study, ground waters at 50 land disposal sites which received
large quantities of industrial waste were sampled and analyzed.
The sites selected were all located East of the Mississippi River,
were representative of typical industrial land disposal facilities,
and were situated in a wide variety of geologic environments. No
previous contamination of ground water with hazardous substances
had been reported at these facilities before sampling, and waste
disposal has been in progress for a minimum of 3 years. At 43 of
the 50 sites migration of one or more hazardous constituents was
detected in the ground water. Twelve potentially hazardous inorganic
constituents were detected in ground waters above background
concentrations. The five most frequently occurring were selenium,
barium, cyanide, copper, and nickel in that order. Organic
substances that were identified in the ground water included PCBs,
chlorinated phenols, benzene and derivitives, and organic solvents.
At 26 sites, potentially hazardous inorganic constituents in
the ground-water samples from one or more of the monitoring wells
exceeded the EPA drinking water limits. Of the potentially hazardous
substances, selenium most frequently exceeded drinking water limits,
followed by arsenic, chromium, and lead.
Conclusions drawn from the study are:
0 Ground-water contamination at industrial land disposal sites
is a common occurrence.
0 Hazardous substances from industrial waste land disposal sites
are capable of migrating into and with ground water.
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0 Few hydrogeologic environments are suitable for land disposal
of hazardous waste without some risk of ground-water contamination.
0 Continued development of programs for monitoring industrial
waste land disposal sites is necessary to determine impact on
ground-water quality.
0 Many old industrial waste disposal sites, both active and
abandoned, are located in geologic environments where ground water
is particularly susceptible to contamination.
0 Many waste disposal sites are located where the underlying
aquifer system can discharge hazardous substances to a surface-water
body.
B. Actual Damage Incidents
Numerous incidents of damage which resulted from improper land
disposal are contained within EPA files. Rather than listing the
vast number of damage cases for all types of land disposal facilities
in this section, the reader is referred to summaries of damage
cases in companion background documents.
II. ANALYSIS OF STANDARDS
1. Specific technical information
requirements for land disposal facilities - §122.25(c)
A. Proposed Regulation and Rationale
N/A
B. Summary of Comments
N/A
C. Discussion
The purpose of §122.25(c) is to ensure that the permit issuing
authority is provided with the information needed to determine that
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the proposed hazardous waste land disposal facility will comply
with the applicable technical requirements of Part 264, Subparts
K, L, M, N, R, and S. Much, if not all, of this information would
routinely be recorded and analyzed by the owner or operator (or
their authorized agents) independent of the requirements for
submittal. Similar informational requirements have already been
promulgated for owners and operators of hazardous waste treatment
and storage facilties under §122.25(b).
The Agency does not believe that the requirements of §125.25(c)
place any unnecessary burden on the owners or operators of hazardous
waste disposal facilities. These requirements are organized so
that an owner or operator only needs to submit information that
pertains to his type of operation thus minimizing unnecessary
expenditures of time and money.
Paragraphs (1) and (2) of §122.25(c) address the information
requirements for surface impoundments and waste piles, respectively.
The owners or operators of these facilities must submit information
identical to that required under §122.25(b)(3) and (4) for surface
impoundments and waste piles designed to treat or store hazardous
wastes. No additional information is required in §122.25(c) for
surface impoundments and waste piles designed for disposal of
hazardous wastes, and in many cases the technical informational
requirements are reduced since leachate collection, detection, and
removal systems and secondary liners are not required.
The required technical information for land treatment,
landfills, underground injection, and seepage facilities in
§§122.25(c)(3), (4), (5), and (6) respectively are consistent with
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the types of information required for piles and surface impoundments
under §§122.25(c)(1) and (2). Since land treatment, landfills,
underground injection, and seepage facilities are not among the
types of facilities listed as land disposal facilities in §264.19
which may also be used as storage and treatment facilities, they
are not covered under §122.25(b). However, since the technical
requirements for seepage facilities are based on similar requirements
for surface impoundments, the requirements of §122.25(3) are
referenced. As in §122.25(b), the informational requirements in
§122.25(c) are limited to those needed to verify compliance with the
design and operating requirements of Part 264, Subparts M, N, R,
and S.
It should be noted that there were two codification errors in
the regulation as printed at 45 FR 11172. In §122.25( c)(1), the
proper reference is to §122.25(b)(3); and in §122.25(c)(2), the
proper reference is to §122.25(b)(4). These errors are corrected
in the following section.
D. Regulatory Language
In §122.25, paragraphs (c) through (h) are added as follows:
§122.25 Contents of Part B.
*****
(c) Specific information requirements. The following
additional information, based on the technical requirements of
Subparts K, L, N, N, R, and S (generic requirements for all land
disposal facilities are covered in paragraph (d) of this section),
is required from owners or operators of specific types of HWM
facilities that are used or to be used for land disposal:
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( 1) For all facilities that use surface impoundments for
reasons other than solely for storage or storage and treatment,
except as otherwise provided in §264.220, all of the applicable
information requirements in § 122.25(b)(3).
(2) For all facilities that use waste piles for reasons
other than solely for storage or storage and treatment, except as
otherwise provided in §264.250, all of the applicable information
requirements in § 122.25(b)(4).
(3) For all land treatment facilities, except as otherwise
provided in §264.270, the owner or operator must submit detailed
plans and specifications, and data which must collectively include
the information itemized in paragraphs (i) through (iv). For new
facilities, the plans and specifications must be in sufficient
detail to provide complete information to a contractor hired to
build the facility even if the owner or operator intends to
construct the facility without hiring a contractor. For existing
facilities, comparable detail must be provided, but the form of
presentation need not assume contractor construction except to the
extent that the facility will be modified.
(i) Detailed design drawings and specifications of the run-off
collection structures required in §264.272.
(ii) The unsaturated zone monitoring plan as required in
§264.278, including the rationale used in developing the plan and
a detailed map of the facility showing the location and depth of
the soil-pore water sampling devices.
(iii) Detailed descriptions of any inspection, testing, and
recordkeeping procedures needed to comply with §264.279.
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(iv) A description of the operating procedures including any
plans or equipment that will ensure compliance with §§264.281 and
264.282.
(4) For landfill facilities, except as otherwise provided in
§264.300, the owner or operator must submit detailed plans and
specifications accompanied by an engineering report which must
collectively include the information itemized in paragraphs (i)
through (x). For new facilities, the plans and specifications
must be in sufficient detail to provide complete information to a
contractor hired to build the facility even if the owner or operator
intends to construct the facility without hiring a contractor.
For existing facilities, comparable detail must be provided, but
the form of presentation need not assume contractor construction
except to the extent that the facility will be modified.
(i) Detailed design drawings and specifications of the of
the leachate monitoring system required in §264.301(a).
(ii) Detailed design drawings and specifications of any liner(s)
and liner base(s) present at the facility and the installation
procedures used to comply with §264.301(b).
(iii) Detailed design drawings and specifications of any
leachate collection and removal system present at the facility
demonstrating compliance with the requirements in §264.301(c).
(iv) Detailed plans and specifications and basis of design
of any structures needed to comply with the general operating
requirements in §264.302.
(v) Detailed descriptions of any inspection, testing, and
recordkeeping procedures needed to comply with §264.306.
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(vi) Detailed design drawings and specifications of the
final cover required in §264.310(a).
(vii) Detailed descriptions of all maintenance, testing and
inspection procedures to be used at the facility during the closure
and post-closure care period as needed to satisfy the requirements
of §264.310(b) and (c).
(viii) A map(s) which satisfies the requirements of §264.309(a)
and ( b). All existing facilities must submit map(s) showing the
approximate location of each hazardous waste type within each cell
for all wastes disposed of during the interim status period.
(ix) A description of the operating procedures including any
plans or equipment that will ensure compliance with §§264.312,
264.313, 264.314 and 264.315.
(x) Detailed design drawing(s) of the landfill and surrounding
geology showing the dimensions and depth of the uppermost aquifer
beneath the facility.
(5) For underground injection facilities, except as otherwise
provided in §264.430, the owner or operator must submit detailed
plans and specifications accompanied by an engineering report which
must collectively include the information itemized in paragraph
(i) through (v). For new facilities, the plans and specifications
must be in sufficient detail to provide complete information to a
contractor hired to build the facility even if the owner or operator
intends to construct the facility without hiring a contractor.
For existing facilities, comparable detail must be provided, but
the form of presentation need not assume contractor construction
except to the extent that the facility will be modified.
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(i) A statement of the maximum pressure to be applied to the
well head and basis (calculations) of establishment.
(ii) A statement of the annular pressure to be maintained
and basis (calculations) of establishment.
(iii) An analysis of the well construction material selection
including casing, cementing, tubing and packer materials.
(iv) A description of the operating procedures to comply
with §264.432.
(v) A description and justification of well plugging techniques
to be utilized at closure.
(6) For seepage facilities, except as §264.460 provides
otherwise, all applicable information requirements in §122.25(b)(3).
2. Informational requirements for permitting
discharges from land disposal facilities - §122.25(d)
A. Proposed Regulations and Rationale
In the 8 October 1980 supplemental notice of proposed
rulemaking, the Agency discussed the approach it intended to use
to regulate hazardous waste land disposal facilities. The "ground
water protection standard" was described under a heading "Presumption
against degradation" and in what was perhaps an unfortunate choice
of language it was characterized as a "nondegradation standard".
As is discussed in Background Document M>. 7 - Ground Water
Protection Standard, commenters tended to apply their own meaning
to the term "nondegradation" rather than the meaning intended by
the Agency. Many commenters ignored the most important feature of
the standard; the direct association with subsequent use.
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The information requirements, which are the subject of
discussion in this section, were described under the heading
"Permissible demonstrations that limited degradation will not
threaten public health or the environment". The applicable
informational requirements described in the notice required a
permit applicant to provide information for each of five main
subject areas as follows:
0 A description of the wastes (both qualitative and quantitative)
to be disposed of in the facility.
0 A description of discharges (including leachate and gas
migration) from the facility.
0 A description of the hydrogeologic characteristics of the
unsaturated zone and of the migration of the discharges in the
unsaturated zone.
0 A description of the hydrogeologic characteristics of the
saturated zone and of the migration of the discharges in the
saturated zone.
0 A description of all discharges to the land surface, into
surface waters, and all withdrawals of ground water that will be
mixed with discharges from the disposal facility.
B. Summary of Comments
Commenters expressed several major concerns regarding "EPA's
Intended Approach" in the 8 October 1980 notice pertaining to the
informational requirements and demonstrations required of the permit
applicant. First, the commenters contended that the required
information and demonstrations were extensive, extremely costly and
beyond the reasonable capacity of most permit applicants to provide.
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Secondly, they felt that not all of the information and
demonstrations described were needed in many cases (e.g., land
disposal facilities underlain by deep, tight clay soils and located
over deep, non-usable ground water aquifers). Thirdly, they claimed
that some of the demonstrations (e.g., prediction of the human
health risks posed by contaminants that migrate to points of water
use) were far beyond the capabilities of permit applicants if not
the state of the art. Finally, they argued that some of the
requirements (e.g., health and risk assessments) placed burdens on
the permit applicants that properly should rest with EPA or other
government agencies.
C. Discussion
EPA agrees that the information and demonstration requirements
may be quite costly and burdensome for some permit applicants and,
for others, will not be insignificant. Given the long-term hazard
potential of land disposal of hazardous wastes documented in the
damage cases, however, it believes that such requirements are
essential to making sound environmental judgments about these
disposal activities. The costs and efforts of meeting these
requirements are justified costs of doing business and of having
the privilege of depositing hazardous constituents in or on the
land where they might adversely affect people's health and welfare
for many decades.
Furthermore, EPA believes that proper siting of land disposal
facilities, proper pre-treatment of certain hazadous wastes and
tailored design of facilities for different types of wastes will
reduce the information and demonstration requirements and, thereby,
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will alleviate their costs and burdens. Fbr example, locating
facilities in areas underlain with deep ground waters or non-usable
ground waters or underlain with deep formations of low permeability
clay soils will enable the permit applicant to readily demonstrate
that contaminants will not migrate to points of water use, thus
lessening the requirements that otherwise would apply. Pre-treating
hazardous wastes so that they do not contain the more toxic or
carcinogenic hazardous constituents also will lessen these
requirements. Likewise, tailoring the disposal facility to the
types of wastes disposed so that, for example, a reduction in the
solubilization of hazardous constituents will occur could lessen
the requirements. The Agency has tried to provide, in the standards
proposed, provisions that require more or less informaton and
demonstration based on site-specific, waste-specific conditions.
For those permit applicants that insist on locating a land
disposal facility over a shallow, high quality, highly used ground
water aquifer or insist on placing highly toxic wastes in a land
disposal facility without pre-treatment or insist on otherwise
locating, designing and operating a system that is capable of
discharging contaminants that will migrate to and affect water
uses, it will be both difficult and expensive to assemble the
information and provide the demonstrations required for permitting
decisions. However, in EPA's view, these costs and burdens are
necessary to assure that the facility will not cause unacceptable
environmental degradation.
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The Agency recognizes that these assessments will require
permit applicants to gather and to submit considerable detailed
information and (in some cases) to perform difficult and complex
demonstrations. It also recognizes that the required information
and demonstrations will be difficult and time consuming to review
by EPA and State permitting officials and very likely will require
more time in processing and issuing permits than might otherwise
be required if design and operating standards or containment
standards were employed. However, EPA concludes that these
consequences must be accepted in order to provide for full
consideration of the serious implications that the facility might
have for the public's health and welfare for decades to come.
The Agency also realizes that the extensive information and
demonstration requirements of the proposed regulations will (in
some cases) be sufficiently great to deter land disposal permit
applications for many locations, for some wastes and from some
persons. As such, the proposed rule, if promulgated, will probably
reduce the number of land disposal facilities, significantly limit
the location of these facilities, limit the types of hazardous
wastes placed in these facilities, promote the use of alternative
methods of managing hazardous wastes (e.g., incineration, treatment,
recycling) and preclude potential permit applicants who lack the
resources or the technical capability to meet the information and
demonstration requirements. In the Agency's view, these are not
undesirable results. Because it frequently poses long-term hazards
to human health and the environment, EPA views land disposal as
the least desirable method of hazardous waste management and believes
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it should be used only in those situations where, because of the
location of the site, nature of the waste and adequacy of the
management technologies and operating practices used, it can be
carried out in a manner which will assure long-term protection of
human health and the environment. Clearly, the permit application
requirements will create economic and feasibility constraints that
will limit land disposal practices. The ^ency, however, does not
believe these standards and requirements will preclude land disposal
as a necessary hazardous waste management practice. It contends
that there are suitable land disposal sites, adequate land disposal
facility designs and practices and competent persons and firms to
operate land disposal facilities necessary to manage hazardous
wastes that cannot be handled by other alternatives.
Finally, the Agency recognizes that the techniques for making
the hydrogeological investigations and other studies necessary to
meet the information and demonstration requirements of the proposed
regulations are not fully developed and need to be improved and
extended. It also recognizes that the technical expertise of
undertaking these investigations and studies is limited. It
believes, however, that the techniques and expertise exist to
perform, in some degree, each of the investigatory tasks that
would be required. Certainly, advancements in the state of the
art and capabilities, which will result from the implementation of
the proposed requirements, will improve performance in the future.
EPA believes that the requirements proposed will encourage such
advancements. Evaluation of the state of the art is included in
the technical discussions which follow.
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In Section III of the the Preamble, there is a discussion
which concentrates almost exclusively on the problems associated
with those types of land disposal facilities which are designed
and operated with the primary objective of long term facility
containment of hazardous wastes. The discussion describes the
essence of the problems faced in the regulation of such forms of
land disposal of hazardous waste as the inevitable long-term
potential for the wastes or their hazardous constituents to leak
out of the facility. In the discussion it is concluded that "If it
were technically and institutionally possible to contain wastes
and their constituents in land disposal facilities forever or
until degradation mechanisms rendered them non-hazardous, then the
problem of regulating such (types of) land disposal would be
comparatively simple and straight forward. It would entail
development of reasonably specific (but flexible) design and
operating standards or, alternatively, containment performance
standards specifying total containment of hazardous wastes and
their constituents within the land disposal facility forever or
until degradation mechanisms rendered them non-hazardous, as the
case may be. Unfortunately, at the present time, it is not
technologically and institutionally possible to contain wastes and
constituents forever or for the long time periods that may be
necessary to allow adequate degradation to be achieved. Moreover,
if degradation of the hazardousness of waste does, in fact, occur,
current state-of-knowledge does not know what the degradation
periods are for most, if not all, hazardous wastes and, therefore,
does not know what containment time periods to specify.
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Consequently, the regulation of hazardous waste land disposal must
proceed from the assumption that migration of hazardous wastes and
their constituents and by-products from a land disposal facility
will inevitably occur."
Because of this inevitability of leakage from land disposal
facilities which are designed to achieve facility containment, and
especially in view of the fact that most existing land disposal
facilities have not been designed with this objective, it is
necessary that the discharges which will occur from land disposal
facilities be assessed with respect to potential effects on human
health and the environment. These assessments must be performed for
each facility on a waste specific and site specific basis. The
specific informational requirements of §122.25(d) which provides a
basic framework for the assessments are discussed in detail below.
Integrated into the discussion are certain provisions intended to
to provide maximum flexibility in implementing the informational
requirements, by allowing varying levels of precision to be employed
Section 122.25(e) outlines the framework for recognizing major
differences in the need for information, in site and waste specific
circumstances, and the inadequacies in the state of the art which
necessitate allowing some flexibility in the degree of precision
required to comply with informational requirements. Therefore,
this section is intended to limit unnecessary informational
requirements and ease the regulatory burden wherever possible
without jeopardizing the objective of the regulatory program;
assuring that an adequate assessment of potential health and
environmental effects is achieved.
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(1) General
The informational requirements for permitting discharges from
land disposal facilities include a determination and assessment of
the extent of transport of contaminants discharged or leached as a
liquid or emitted as a gas from hazardous waste land disposal
facilities. The requirement is further detailed to identify the
specific wastes and quantities placed in any operational unit,
§122.25(d)(1); the release of liquid and gaseous contaminants from
the waste deposit, §122.25(d)(2); the rates and extent of dispersion
and transport in earth materials above the zone of saturation,
§122.25(d)(3); the extent and rate of the leachate carried contamiant
transport in the zone of saturation, §122. 25(d)(4); and a description
of the rate and location of leachate carried contaminant discharge
from the zone of saturation, §122.25(d)(5 ). These informational
requirements are intended to track the potential routes of
contaminant transmission from the hazardous waste disposal facility
and to enable the assessment of the severity of the potential
effects.
The need for the requested information and description of
existing techniques to forecast performance is discussed subsequently.
The specific information of waste types and quantities is a
design/operational controlled variable which can be defined by the
applicant and may ultimately represent a limit to growth of the
operational unit or even the facility. Further discussion of this
requirement is not provided. Description of the rates at which gas
and/or leachate contaminants are emitted from the operational unit
or facility are discussed separately. The emission of leachate
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contaminants is described from two perspectives: (1) volumetric
production, and (2) the prediction of waste leachate composition
(including both the waste's constituents and decomposition products)
Contaminant transport above the zone of saturation and within the
zone of saturation are each discussed separately.
(2) Predicting Leachate Volume
The leaching process generally represents the principal mode
of transmission of contaminants from a waste deposit to the
environment for landfills and surface impoundments. Of course,
for seepage facilities where the objective of the design is to
leach liquids from the waste, it is the essential consideration.
Volatilization and release or dispersion as a gas is a secondary,
although important, factor for most land filled wastes. For surface
impoundments, land treatment facilities, and seepage facilities,
volatilization is major consideration. With respect to liquid
discharges, it is important, therefore, for any hazardous waste
disposal facility, including landfills and surface impoundments,
that an assessment be made regarding the potential for leaching of
contaminants under the specific site conditions (environmental,
designed, and operational) which the waste may be exposed to. The
principal and initial step in such an analysis is the forecasting
or estimation of volumetric discharge or leachate production.
The volumetric discharge from surface impoundments, seepage
facilities, and injection wells can be determined directly during
the active life of the facility. However, the specific needs for
quantitative, time-related information are many for landfills, land
treatment facilities, and for surface impoundments and seepage
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facilities which are closed with waste left in place. Certainly
the most important would be a determination of whether site
conditions can be expected to yield leachate. Resolution of that
question, however, requires careful assessment of a variety of
factors and site conditions. Important considerations include:
rainfall, runoff, evaporation, transpiration, waste dewatering,
and specific design controls. These factors need to be assessed
with regard to their effect on volumetric leachate production
during operational phases as well as post-closure phases of the
landfill facility. Typical results of such an assessment at
traditional landfills are that leachate is produced and the rate
of production varies substantially throughout the year in response
to climatic and hydrologic conditions.
Knowledge of leachate production rates is particularly important
in determining and forecasting leachate composition or quality.
The quality of leachate is typically a time related function;
although time itself is seldom the principal control variable.
More frequently, leachate volume or the quantity of eluant which
the waste has been exposed to is the principal control variable.
When the leachate production is low, one may therefore expect a
prolonged period of contaminant releases and transport as compared
to a relatively short period when leachate production is high. An
illustrative example is the comparative results of municipal solid
waste leaching where a moderate leaching rate yields concentrations
of contaminants significantly greater than a high leaching rate
over the same period of time (Figure 1). Similarly, the mass of
contaminants released to the environment more rapidly approaches
-------
32"/yr net infiltration
- 16"/yr net infiltration
60,000
^ 40,000
o
to
4->
o
20,000
ro
1200
1800
2400
Figure 1.
Days Since Disposal
Dependence of Contaminant Concentration on Extent of Leaching
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(25)
its unique asymptotic level for the high leaching rate as compared
to the low leaching rate (Figure 2). Thus, an understanding of
the leachate production rate is essential in describing and
forecasting leachate composition and ultimately, the length of
time over which the leachate may be determined to represent a
potential problem.
The time over which post-closure care should be maintained is
greatly influenced by volumetric leachate production. Requirements,
both technical and economic, of the post-closure care period are
therefore integrally related to the rate of leaching. An obvious
element of a typical post-closure care plan would be the costs of
operating leachate control systems such as collection and treatment
facilities.
Determination of the adequacy of leachate management options
chosen at any particular site rely in part on the volumetric leachate
production. The technical and economic feasibility of options such
as trucking collected leachate to off-site hazardous waste facilities
are particularly dependent on the volume of leachate being managed.
On-site collection and treatment facilities are likewise sensitive
to volumetric loadings.
Subsequent use of mass emission determinations are also
dependent on the volumetric production. Certainly, the assessment
of risks associated with certain constituents of hazardous waste is
dependent on their concentration during exposure, while that
concentration is in turn dependent on volumetric production.
Likewise, the extent of contaminant transport and dispersion is in
part dependent on the rate of leachate production.
-------
60.On
I/)
ID
•o
en
at
•o
O
40.0
20.0-
to
16"/yr net infiltration
32"/yr net infiltration
600
1800
1200
Days Since Disposal
Figure 2. Dependence of Mass Removal on the Extent of Leaching
2400
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(27)
The need to determine volumetric discharge or leachate
production is inherent in the technical design and evaluation of
any hazardous waste land disposal facility. The information is
necessary for assessments of related risks to human health and the
environment posed by contaminants in the discharge or leachate.
The sizing and design of any leachate management system is dependent
on the volumetric production rate. The need for leachate management
systems is irrelevant in the absence of leachate. Consequently, a
critical element in the evaluation of a hazardous waste land disposal
facility must include an assessment of the volumetric production
of discharge or leachate.
(a) Elements of Analysis
The volumetric production of leachate has been the subject of
several studies, particularly with respect to municipal solid waste
landfills. The forecast of leachate production (usually with the
water balance method) in such facilities has typically been analyzed
from the perspective of an idealized landfill in a closed or post-
closure mode of operation. This approach has been taken because
municipal solid waste has a large moisture absorptive capacity—in
the order of 1 to 2 times its own dry weight. Large quantities of
wastes are typically disposed of daily, thereby, providing a large
capacity for absorpton of incident rainfall during the uncovered
operational phase. However, not all hazardous wastes have a water
absorption capacity; in fact, many wastes such as those managed at
surface impoundments, land treatment, and seepage facilities contain
free liquids. Consequently, the forecasting of leachate production
from hazardous waste facilities must include analysis of the
operational phase as well as the post-closure phase.
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Specific sources of water or other solvents include rainfall/
run-on, irrigation of cover soils, ground water, perched water,
flood water, water derived from waste composition, alcohols and
other liquids resulting from unique decomposition processes, and
water and other liquids contained within the waste originally placed
in the facility. Proper land disposal practices and other parts of
the hazardous waste regulations (See §264.300, Subpart N-Landfills)
eliminate or greatly reduce the likelihood of water contribution
from flooding, run-on or ground water. Earth materials conducive
to perched water tables can be avoided, but may have to be dealt
with in an otherwise desirable site. Irrigation water used for
establishment and maintenance of the cover system is a manageable
source which when properly applied should not represent a significant
source of water. It should, however, be explicitly assessed.
Similarly, water derived from the decomposition of solid waste has
typically been determined to represent a very small, negligible
source; it should also be explicitly assessed for the specific
combination of wastes to be managed in the facility. The potential
for other liquids resulting from decomposition, such as alcohols
and aldehydes, should be assessed. Generally, water or other
liquids derived from the decomposition of wastes, such as described
by Charlie et al. (6) for certain papermill sludges, represents a
finite volume of liquids. Alternatively, rainfall, perched water
and irrigation water represent a continuous, although sometimes
intermittent, source of liquid, and consequently, the most important
source with respect to soluble, slowly decomposing (if at all)
hazardous wastes. Such a prioritization is generally valid, however,
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only for volumetric forecasting. Water and other liquids resulting
from the decomposition and slow dewatering of high moisture wastes
may represent the most significant source of contaminants. Wigh
and Brunner (40) have observed that the composition of initial
leachings, particularly those with a moisture absorption capacity
comparable to that of municipal solid waste, generally contain the
largest concentrations of contaminants.
Other potential sources of liquid which may contribute to
leachate production are management practices. Such techniques as
proposed by Bahland for municipal solid waste attempt to accelerate
decomposition by enhancement of leaching. Similar practices, not
necessarily intended to enhance biological decomposition, based on
the elution of hazardous materials for subsequent concentration
and management/ may significantly influence leachate production
forecasts.
There are several means or mechanisms which function as sinks
to remove water (or other liquids) from land disposed wastes.
These include: incorporation into biological cell mass or chemical
compounds, absorption to the waste, evaporation, transpiration,
collection in a leachate management system underlying the waste,
and seepage out of the facility as migrating leachate. Incorporation
of water into cell mass is at best a transitory sink for leachate.
This biological sink may in fact be a net contributor of leachate
as the cell mass decays. Incorporation into chemical compounds
represents a limited sink which may not always be effective. The
long-term utility of such a sink is minor with respect to the
long-term quantity of water introduced to the facility by
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(30)
infiltration and represents a finite capacity specifically related
to the waste and predominant to chemical reactions. The major sinks
or discharges of leachate are: collection within the facility and
discharge to surrounding soils and other geologic formations, and
eventually seepage into the ground water, or migration as a surface
discharge. losses of liquids due to evaporation and transpiration
act principally on infiltrating rainwater and irrigation water for
the final cover system. Many factors influence the rate of
evaporation and transpiration. Some of the more important factors
are: relative humidity, solar radiation, cloud cover, temperature,
wind speed, plant coverage, soil type, soil depth, and root
penetration. Evaporation may also be an effective means of reducing
quantities of moisture within the waste itself, particularly in a
biologically active waste where net gas production flushes moisture
laden gases out of the deposit.
A particularly important element of leachate forecasting is
the sensitivity of the analysis to site specific conditions, either
naturally occurring or purposely imparted through design and
operation. Rainfall and evapotranspiration are especially localized,
natural occurring phenomena. Surface runoff can be controlled to
a large extent by slope and length of run of cover materials which
can be specified in facility design. Other design alternatives
are vegetation type, soil types, and soil depths. Operating
procedures can be instituted to minimize leachate production by
careful phasing and scheduling of the filling operation to rapidly
achieve final grade and placement of the cover material.
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A summary of the sources and discharges (sinks) of land disposal
facility liquids is given in Table I. The major elements can be
generally related by a simple water balance analysis:
Liquid in = Liquid out
Rainfall + Irrigation = Evapo-Transpiration + Runoff + Collected
Leachate + Migrating Leachate
The primary element of concern to the hazardous waste land disposal
facility permitting process is the last term: Migrating Leachate.
TABLE 1
SOURCES AND SINKS OF LIQUIDS AT LAND DISPOSAL FACILITIES
Continuous Poor Practices
One time or
transient
IN: SOURCES
OUT: SINKS
Initial Waste
Moisture
Waste
Decomposition
Waste
Dewatering
Biological
Incorporation
Chemical
Incorporation
Rainfall
Irrigation
Evaporation
Transpiration
Collection
System Drainage
Leaching from
Facility
Runoff
Run-on
Flooding
Groundwater
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The forecasting of leachate production is not a simple task.
Many factors need to be included during any assessment. These
factors include: the sources and discharges of waste contaminated
or originating liquids, facility operational status, specific
facility location in the environment, and design and operational
aspects of the facility. Additionally, many of these factors are
not controllable, nor precisely predictable, being a result of
natural phenomena such as rainfall. Nevertheless, relationships
and rather limited ranges of variation do exist for these factors.
Consequently, estimates of leachate production are feasible. The
utility and accuracy of those estimates, however, must be kept in
perspective with the accuracy and predictability of the information
used to produce the estimate. A special requirement of any leachate
forecasting procedure imposed by the regulations is the flexibility
to produce reasonably expected production rates and also worst case
or maximum rates.
(b) Methods of forecasting
The prediction of leachate production is based on traditional
scientific and engineering approaches used in water resources and
agricultural management, and more recently, on computer aided
approaches. Early applications of water balance solutions to the
land disposal of solid wastes were based on the work by Thornthwaite.
Remson, et al . (37) reported on the adaption of Thornthwaite's Water
Balance tables to solid waste landfills with the aid of digital
computers. The State of California (5) suggested the use of U.S.
Bureau of Land Management (USBLM) methods of estimating infiltration
using curves which estimate peak discharge rates for small watersheds
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A series of curves are provided by the U.S. Department of Agriculture
Soil Conservation Service (USDA/SCS) which do provide a wide range of
storm distributions, slopes and rainfall. Fenn, et al . (12) adapted
the work of Thornthwaite and Remson, et al. (28) in a report entitled;
Use of the Water Balance Method for Predicting Leachate Generation
from Solid Waste Disposal Sites. Noble (25) combined Thornthwaite1s
work with the USDA/SCS curves.
More recently, Perrier and Gibson (27) adapted another USDA or
agricultural based tool: Chemicals Runoff and Erosion from
Agricultural Management Systems (CREAMS) for landfill design and
evaluation purposes. This interactive computer aided tool yields
daily estimates of infiltration, runoff and evapotranspiration.
Straub (33, 34) developed a series of models to estimate leachate
volumetric production and quality from municipal solid waste.
The U.S. Department of Agriculture (USDA) has performed field
validations of the CREAMS model for estimating the volumetric
production of leachate. The model, USDA/CREAMS (39), has been
used to provide extensive validation for crop and rangeland plots.
Although it has not yet been applied to land disposal facilities,
the background data can, nonetheless, be used for extrapolation
and validation information for land disposal sites until such time
that actual data exists.
In general, most existing forecasting techniques have estimated
evaporation-transpiration losses using tabulated observations and
the potential evaporation-transpiration concept offered by
Thornthwaite and applied by Remson and Feen. Alternatively, the
Available Water Capacity (AWC) algorithm is used by USDA/CREAMS,
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Perrier and Gibson in their Hydrologic Simulation on Solid Waste
Disposal Sites (HSSWDS), and by Straub. The former technique
approach tends to approximate events and conditions by use of
averages, while the latter, depending on the need, can more closely
approach the simulation of discrete events. A limitation of the
Thornthwaite tables is that they represent long-term averages on a
monthly frequency. The AWC algorithm can be used on a more frequent
basis. The need to consider extreme conditions during the design
and evaluation of the hazardous waste disposal facilities indicates
a preference towards the use of the AWC algorithm which is much
more sensitive to site specific managerial and locational constraints
than the Thornthwaite tables, particularly where the need for
accurate, frequent predictions is necessary.
Runoff, another major part of the water balance assessment,
can be estimated using the Rational Formula - Fenn, et al, (12) and
Remson, et al. (28) and SCS curves (27). These methods are empirical
and require consideration of the wetting history of a site in
order to select the proper coefficients or curves. The USDA/SCS
curves, provide limited consideration of this aspect by identifying
a number of storm types and intensities.
Integration of the SCS curves with the daily precipitation and
evapotranspiration analytical capacity of the USDA/CREAMS model
offers a particularly attractive capability of providing storm by
storm analysis when conditions warrant. Alternatively, this
technique can be used to provide general summaries in less critical
situations. The simplicity and relative accuracy of the Water
Balance approach using Thornthwaite's tables and either SCS curves
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or the Rational Formula should not be overlooked. Dass, et al . (19)
and Lutton (18) have indicated a good correlation between estimates
made according to Fenn and actual field data. They also indicate
that the most critical factor in the analysis is the selection of
the surface runoff coefficient.
Although, previously discussed procedures do not incorporate
analysis of the efficiency of leachate collection systems, a
procedure to estimate liner performance efficiency has been described
by Wong using traditional Darcian flow analysis of differential
permeability. Wong's (41) solutions considered the length of run
in leachate collection systems, the steepness of slope, permeabilies
of drainage and barrier soils, and incident leachate production
rates. It was clear that under conditions of: low slope, long run,
small permeability differentials, and small, but steady, leachate
flow rates, that efficiency of clay liners may be much less than
popularly assumed. Collection efficiencies of less than 50 percent
can readily be estimated for common practices.
Subsequent work by Moore (24) has led to development of an
evaluation procedure which routes water percolating from the cover
system through the waste, across barrier systems (leachate liner
and collection systems) and eventually into the native soils
underlying and surrounding the facility. This procedure recognizes
the potential for lateral (horizontal) flow in addition to vertical
flow as differential permeabilities are encountered. The procedure
also recognizes limitations of Darican flow theory when applied to
the landfill situation. Results of this evaluation procedure can
be utilized to assess the adequacy of the drainage layer in a
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leachate collection system, the adequacy of the differential
permeability of such collection systems, and the steady state
seepage rate. In addition, this procedure can provide estimates
of the total retention time and the amount of liquids in the
facility. The procedure was noticed in the Federal Register for
public review and comment, as was the Hydrologic Simulation of
Solid Waste Disposal Sites model (HSSWDS) developed by Perrier and
Gibson.
(c) Summary
There exist several methods of estimating leachate production
based on analyses of the major contributions and losses (sinks)
for liquid: rainfall, runoff, evapotranspiration and net percolation
or leachate. In addition, the efficiency of leachate collection
systems can be determined. Although, no single procedure is
currently available which also explicitly considers the generally
minor water losses and gains attributed to waste decomposition and
absorbtion, nonetheless, the available procedures can be adapted
to reflect these minor amounts. In special cases where water
losses and gains due to decomposition and absorbtion are anticipated
to be significant, these processes can be analyzed separately.
(3) Leachate Composition
(a) Background
The discussion of leachate composition addressed here is not
the composition of the liquids produced by the Extraction Procedure
developed under RCRA section 3001. That liquid analysis is intended
to simulate liquids which would be produced if the waste were
disposed of in a municipal solid waste environment. Rather, the
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leachate analysis discussed here would be typified by that liquid
originating from one or more hazardous wastes placed in a land
disposal facility, particularly that liquid after it has left the
wastes and yet before it had passed into undisturbed native soil
at the facility. The leachate would be that liquid produced by a
collection and removal system at a facility lined with a nearly
impervious material.
leachate composition includes not only information on the
types and concentrations of materials present in the initial liquid
that issues from the waste, but also information on any changes in
the types and concentration as additional infiltrating liquid (e.g.,
rain) passes through the waste.
Information on leachate composition may be needed for a variety
of purposes.
- predicting the effect of leachate releases on adjacent waters
- designing treatment systems for collected leachate
- determining the length of time after closing that the facility
will have to be monitored and maintained.
(b) Discussion
( i) Previous work
Development of the Extraction Procedure for RCRA Section 3001
was the culmination of a number of studies (2, 5, 6, 8) that examined
available leach -tests and influences of test conditions on the
leaching process. A large scale study with municipal solid waste
and industrial waste (9) is underway as a basis for evaluating the
extraction procedure. Several industries have worked on leach
tests (1, 10, 11) to examine not only the potential for leaching
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from their wastes but also to develop a realistic estimate of the
composition of the leachate which would be produced from their
wastes (disposed of in the absence of other wastes). A laboratory
study of several industrial wastes (7) developed batch procedures
for predicting the composition of leachate from large-scale land
disposal facilities. The leaching regions used in the various
techniques range from aggressive (for estimating maximum release),
to mild (for simulating mono-disposal under field conditions).
(ii) Alternatives
Applicants seeking to predict the composition of leachate may
analyze leachate from a similar existing facility over a period of
time or make use of present or past work with samples of the waste
to predict composition of its leachate. In addition to the work
described above there are several groups developing leaching tests
(3, 4) and the announcement for a future ASTM Symposium (12)
indicates that a number of private companies are actively developing
leaching tests for use in managing waste disposal practices. Though
work is somewhat limited, studies are being conducted on a variety
of wastes under different conditions and present work does outline
the: precautions to be taken, estimates of difficulties involved,
and results to be expected. The task of making a prediction of
leachate composition (assuming a sample of waste is available)
should not require unreasonable efforts on the part of the applicant,
Disposal facilities that include some control of the rate of release
of leachate (such as a leachate collection and removal system)
will generate data for adjusting the prediction soon after the
facility is in operation.
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(4) Predicting Gas Emissions
The following aspects are common to all evaluations of gaseous
emissions from land disposal facilities.
0 identify potential gases and vapors of interest and estimate
quantities anticipated
0 determine the most probable mode of transport (pressure or
diffusion gradients) and estimate the extent of movement.
The most critical aspect of this evaluation is determining what
types and quantities of gases and vapors can be anticipated.
It is obvious from the experience at love Canal that an
important mode of transport of hazardous wastes is by gaseous
movement. Occupant exposure in dwellings near the waste was
principally by volatilization of the various hazardous waste
constituents either directly from the waste deposit or more probably,
in this case, from leachate-contaminated ground water. Bnission of
explosive (methane) and toxic (hydrogen sulfides) gases from
municipal solid waste has been a concern for many years; however,
most assessments from such emissions were centered on release from
the waste mass rather than the release from migrating leachate.
The emission of gases from both the migrating leachate and the
waste deposit are considered essential in evaluating potential
risks posed by a hazardous waste facility.
(a) Identification of Gases
Gases of concern orginate from the waste itself or its
decomposition products. Review of the waste composition should
reveal information on the probability of gas emissions by direct
volatilization. Compounds with high vapor pressures should be
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carefully considered; those with low vapor pressures may still
require assessment depending on the hazard they present.
Shen and Tbfflemire (31) reported that the compounds shown in
Table 2 were detected in air near landfills. The quantities detected
seemed small , but the PCB concentration was greater than recommended
by NIOSH for a workroom environment (1.0 migrogram/cu.m) where
exposure is typically based on an 8-hour work period. Equivalent
ambient air levels would be expected to pose a greater risk. Note
also that although vapor pressure is relatively small for PCB,
there was a significant quantity found; this is indicative of the
quantity of PCB disposed at the facility. Shen and Tbfflemire
also described some of the important factors influencing the rate
of volatilization and showed how the unknown properties of a specific
waste can be estimated using properties of similar compounds.
TABLE 2
COMPOUNDS FOUND IN AIR NEAR LANDFILLS*
Vapor Pressure Reported concentration
mm of Hg @ 20 C micrograms/cu m
Benzene 270
Chlorobenzene 240
chloroform 24
Chlorotoluene 6700
PCB winter .0001-.000001 0.05-3.0
summer .001-.00001 up to 300
Tetrachloroethane 1140
Trichlorobenzene 74
Trichloroethane 73
*adapted from Shen and Tbfflemire . (31)
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(41)
The production of methane and carbon dioxide in hazardous
waste disposal facilities should not be overlooked. These gases
can be produced at rates high enough to create convective pressure
gradients. The resulting flow of gas flushes smaller quantities of
hazardous gases out of a landfill at a rate faster than those gases
would have otherwise moved. In addition, the methane itself
represents a potential hazard if it is not properly managed. There
is extensive information in the literature on the composition and
production rates and capacities of decomposing organic wastes.
(b) Release of Gases and Vapors
The release of gases from land disposal facilities can be
viewed as: (1) dispersion through the soils underlying and surrounding
the facility, (2) dispersion through the unsaturated zone in the
vicinity of leachate contaminated soils, or (3) upward release
from the waste itself. Special cases of the latter mode are
presented by impounded liquids exposed to the air as with surface
impoundments, underground seepage facilities, or intentional mixing
of hazardous wastes with soil, as with land treatment facilities.
Mixing with soil can greatly increase the surface area of the waste
and thereby increase the flux of waste or vapor to the atmosphere.
The first two modes of dispersion are similar and comparable
to that of methane moving from a municipal solid waste landfill
(Subtitle D Facility). Several investigators have proposed models
and equations to describe this flow.
Moore has described a number of models based on diffusive and
convective flow (21,22,23). The choice of model is largely one of
experience and anticipated rates of gas generation and confinement.
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Design charts were developed to provide a simple tool for rough
estimating and also as a planning tool. The design charts are
derived from the basic equations and were produced as a result of
finite element and finite difference solutions to the descriptive
equations. The design charts were adapted for use in the Subtitle D
Inventory. The various models were verified on a limited basis in
the field at a landfill in Hopkins, Minnesota where methane was
threatening nearby townhouses (23). There was a reasonably good
correlation between the predicted concentrations and locations and
the field data. Although the solutions were developed for estimating
methane movement, the chemical species is a variable in the
equations. Other compounds can, thereby, be readily incorporated
into the model. Farquhar et al . (8) has also reported on a joint
convective and diffusive flow modeling effort. Solution of the
descriptive equations is by finite element techniques. The model
has received limited validation in the field although it has been
calibrated to improve its accuracy.
Anderson and Callinan (2) concluded that gas flow in municipal
solid waste landfills was primarily the result of convection and
therefore the basic rate equation would be described by Carey' s law.
The convection theory was applied to a two-dimensional landfill
analogue (electrical conducting paper) to predict movement patterns.
Conversely, in a report to the California State Water Pollution
Control Board, molecular diffusion was identified as the most
effective transfer mechanism. Diffusivity of a porous medium was
stated to be relatively independent of soil particle size. Dry
clayey coils are not an effective gas control system.
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Most recently, Findikakis and Leckie (13) have proposed an
implicit one dimensional model for methane, carbon dioxide, and
nitrogen gas flow. The model was successfully tested at several
recently constructed field sites.
Some adaptation of the predictive techniques may be necessary
to accommodate specific hazardous wastes and compounds of special
interest. The principal gas modeled has been methane, a relatively
small molecule, insoluble in water and a gas quite common in organic
waste decomposition. While most of the predictive techniques just
described were developed for gases originating within the land
disposal facility, the same techniques can be used to describe
gaseous releases from leachate or waste contaminated soils. Some
adjustment of boundary conditions may be necessary, but the principles
of flow and mass conservation are identical.
Emission of gases through the cover soils or directly to the
atmosphere in the special cases previously described, is subject to
the same driving forces discussed for flow through porous media.
Diffusion and convection are both prevalent in gaseous releases
through the cover system. The mass rate of release of gases in
these situations are analyzed with respect to rate limiting functions
such as film transfer for release from a free liquid, partial
pressure gradients, and surface flushing or sweeping conditions
which influence partial pressure gradients.
Farmer et al. (11) found the soil density, thickness, and moisture
content to be the significant management variables which control
gas release from soil covered land disposal facilities. Density
and moisture content were important as they influenced the available
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pore volume through which mass transfer could occur, either by
diffusion or convection. Farmer's work was performed specifically
on HCB-containing wastes disposed at landfills. A flow diagram,
Figure 3, was prepared to predict the depth of soil cover required
to limit vapor flux. The study concluded placement of a cover
system that minimizes air-filled porosity is important; disturbance
of that cover system through cracking or small openings mitigates
the control. Particular attention and long-term arrangements for
maintenance of the cover system would be required in most cases.
The duration and the requirements for satisfactory performance of
the cover system can both be estimated using this technique.
Direct application of mass flux calculations for pure systems
can be very misleading. Field conditions present many moderating
or dampening situations. Even in the case of the surface impoundment,
the liquid air interface will likely not permit the maximum flux
due to impurities and non-ideal conditions. Use of cover systems
such as soils, introduce another dampening factor, an impedance to
the gas flow and consequently a reduction in the partial pressure
gradient and thence a reduction of the rate of volatilization.
Estimates of the magnitude of this dampening effect can be made for
any volatile chemical in accordance with Farmer's recommendations
or modifications such as proposed by Shen (30) or Thibodeaux (36).
Estimates of gas flow through cover systems can also be made using
many of the prediction techniques proposed for estimating the extent
of gas movement through soils surrounding the landfill facility.
Some of the techniques could accommodate simultaneous predictions.
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Estimate MAXIMUM density for soil cover and
calculate the corresponding porosity assuming
that oil porosity is air-filled ( Eqn 12)
Using the porosity corresponding
to Maximum density, use Eqn. 13
and the minimum water content
to calculate air-filled porosity.
Are soils or soil
materials (e.g
Bentonile) available
for modifying or
substituting for
on-site soils ?
<-NO
'NO—YES'
! I
:BEGINJ
Estimate MINIMUM reasonable density for
soil cover and calculate corresponding porosity
(Ear) 12) assuming all porosity is air filled.
Using the air-filled
porosity and Eon 10
is the required soil
depth technically and
economically feasible?
YES'
YES'
Using the porosity corresponding
to Minimum density, use Eqn 13
and the minimum water content
to calculate air-lilled porosity
I
NO
Using the oir- filled
porosity and Eqn 10
is the required soil
depth technically and
economically feasible ?
YES-
YES-
Repeat process for
modified cover material
Soil cover will not limit flux
to acceptable value
Seek other method of dealing
with waste
•at this stage, could cons>aer irrigation or
other treatment to maintain higher water
content (if allowed by regulatory agency)
Develop 'ondfill
design plans
Figure 3. Flow diagram for predicting depth of soil cover required to
limit vapor flux through soil cover to an acceptable value.
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(c) Summary
There are several techniques for predicting gas movement
through porous media which have been specifically developed for
land disposal situations. Similarly, the flux of gases through
soil cover systems has been described by several investigators.
While some of the techniques have been developed for specific
compounds, most of the techniques are readily adaptable for any
specific compound and will yield estimates specific for that
compound. Although there is limited field verification of the
techniques, all techniques indicate good success when predictions
are compared to field observations. With more intensive monitoring
at hazardous waste land disposal facilities, field data will be
more readily available for more extensive verification of the
prediction techniques.
(5) Leachate Migration in the Uhsaturated Zone
(a) Background
The proposed regulation assumes that all disposal facilities
will release some amount of leachate and therefore requires
applicants to predict the rate of release and the extent to which
leachate will move in soil liners and native soils during operation,
closure, and post-closure. The regulation is silent about what
assumptions are to be used in making these predictions or about
which techniques are to be used. The applicant can assume that
contaminants in the leachate will not be attenuated by interaction
with the soils. In this case mixing with water in the unsaturated
and saturated zones would be the only process limiting the spread
of leachate and the leachate contaminants would be assumed to move
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at the same rate as the wetting front moving from the facility.
The applicant also free to base the predictions on some degree of
leachate-soil intraction (attenuation). A prediction on this
basis would show that contaminants are retarded and do not move as
quickly as the liquid front from the landfill. The state of the
art for making leachate migration predictions based on no attenuation
(contaminant-soil interaction) is supported by background information;
while prediction methods that include the effect of attenuation is
limited, but progressing rapidly. Consequently there is likely to
be much more controversy surrounding permit applications where the
applicant has chosen the latter prediction methods. This basis
for allowing consideration of attenuation becomes a crucial issue
for the proposed regulation.
(b) Discussion
When predictions on leachate movement exclude contaminant-soil
interactions (e.g., adsorption, precipitation, ion exchange, etc.)
problems are reduced to one of predicting mixing (e.g., diffusion,
dispersion) of leachate with water present in the soil or aquifer
before the disposal facility was operational. Examples of the many
techniques for predicting mixing (2, 6, 13, 49, 51, 53, 54, 70, 76)
are available. Because these mixing processes are most prominent
in the saturated zone there is little discussion of them here.
Refer to Section 6 of the background document on prediction of
leachate movement in the saturated zone. There will be some mixing
of leachate in the unsaturated zone but its effect on leachate
composition and concentration will be slight when compared to the
effect of attenuation. Procedures for assessing mixing in the
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unsaturated zone have been documented (1, 35, 64, 71, 75).
Attenuation by contaminant-soil interactions such as adsorpton and
ion exchange takes place in the saturated zone as well as in the
unsaturated zone. The discussion below on techniques, problems,
etc. applies to both zones.
It is recognized that biological and chemical degradation of
organic materials occurs in soils (9, 15, 16, 62, 78). Experience
with procedures for predicting how much such degradation will affect
the concentration and composition of leachates from hazardous wastes
is limited. Most degradation data are from surface soils where
conditions are different than those expected below disposal
facilities. There is data available on migration and degradation
that will be useful (5, 13, 40, 41, 42, 45) to the permit applicant.
It may be difficult to include degradation factors in any prediction
of leachate migration without the support of field data on the
movement of leachate from a very similar waste disposed of under
similar conditions. Laboratory studies of degradation may aid in
migration predictions.
After mixing and biological degradation have been removed from
consideration there remain a number of processes (grouped under the
term attenuation) that may change the concentration and composition
of leachate as it passes through soil. Attenuation of waste
leachates, pesticides, and other materials have been studied by a
number of groups and the studies have developed techniques that
can be applied to the design of disposal facilities. Because the
techniques for predicting attenuation have had limited field testing
(compared with techniques for predicting mixing) there is likely to
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be controversy if attenuation predictions are permitted to be
included as part of facility design; nevertheless, this is no reason
to exclude such predictions. The following discussions address a
number of factors that are involved in the decision on whether or
not to include attenuation predictions in predictions of leachate
migration.
(i) Attenuation Occurs
Interactions between dissolved minerals and soils have been
studied in the context of plant growth, renovation of sewage effluent,
disposal of sewage sludge, radioactive waste, municipal waste, and
industrial waste. Laboratory studies have documented the attentuation
of metals and inorganic materials (1, 18, 20, 22, 23, 29, 33, 52,
61), pesticides, (8, 17, 27, 30, 42), and industrial and other
organic chemicals (5, 25, 26, 28, 38, 40, 44, 61) in soils. These
studies have identified differences in attenuation due to the nature
of the contaminant (9, 11, 12, 15, 17, 18, 20, 22, 25, 26, 27, 28,
40, 52, 61, 62) the soil properties (4, 5, 9, 17, 19, 22, 25, 27,
28, 29, 34, 40, 45, 52, 61, 62) and the properties of the leachate
in which the contaminant is carried (5, 19, 21, 23, 25, 28). The
effects of contaminant type, soil properties, and leachate composition
on attenuation under field conditions have been documented (1, 24,
29, 37, 52, 62). There is no doubt that the dissolved contaminants
interact with soils and that these interactions affect the rate and
total amount of leachate contaminants that will move through the
soil.
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(ii) Predictive Techniques are Available
As a result of the work listed above, a number of techniques
have been developed for predicting the movement of attenuated
contaminants through the soil. For contaminants that are not
attenuated refer to the earlier, brief discussion of the mixing of
leachate in the unsaturated and saturated zones. The predictive
techniques for attenuated contaminants have, for the most part,
been developed in studies of materials other than hazardous waste.
The predictive techniques can be applied to hazardous waste because
the contaminant-soil interactions are a function of properties of
the materials involved (soils, contaminants, etc.) rather than the
type of waste. At present, no single technique is clearly superior
to another and few have received sufficient field testing, to
establish a high level of confidence for their predictions. The
lack of field testing on hazardous wastes, however, is not a bar to
the use of the techniques. The proposed regulation recognizes that
predictions are likely to be a range of values and provides for
tri-annual refinement of the prediction using monitoring data from
the facility. Technical difficulties that must be overcome in
making this application are discussed later. The techniques available
vary in the amount of information required, the cost and technical
difficult, their applicability to complex geohydrologic settings,
applicability to different waste types, and the precision and accuracy
of the results. Some examples of the different techniques are listed
below.
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Screening procedures (16, 27, 68) use limited data and
simplifying assumptions to predict most likely routes of transport
(air, water, food chain, etc.), the relative amounts of the materials
transported, and the potential contamination to a given site. These
procedures are more useful for identifying extreme problems and
sorting site-waste combinations into broad classification than in
making precise predictions of contaminant movement which can be
verified with monitoring data.
Mixed batch techniques (18, 26, 33, 34, 62) use open or closed
vessels to contact the waste or leachate with soil and subsequently
determine the retention or release of contaminants of interest. A
sequence of batch tests where the liquid is separated from the soil
and then added to the next batch can be used to simulate passage of
leachate through a soil profile. Batch techniques are less costly
and time consuming than soil column techniques and have given
reasonably good estimates of removals observed in column studies
with disturbed soils. Batch techniques predict greater attenuation
and dilution than is observed in column studies with undisturbed
soils.
Soil thin layer chromatography (5, 17, 25, 28, 31, 32) is a
screening tool for obtaining an estimate of a contaminant's leaching
potential. It is similar to conventional thin layer chromatography
except that the soil is substituted for the usual adsorbent phases
(silica gels, oxides, etc.). This technique would be most useful
for determining the rate of movement of a contaminant relative to
the rate of movement of a material whose mobility under field
conditions is already known.
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Soil columns (9, 18, 19, 23, 29, 31) are containers filled
with either disturbed or undisturbed soils. Materials are placed
on top of the column and liquids added to leach substances downward
through the soil. In addition, leachates generated elsewhere can
also be added directly to the column. Columns may be operated
saturated, partially saturated, or unsaturated. Although they are
difficult to replicate and time consuming to operate, soil columns
have the advantage over other laboratory leaching procedures because
they include the effects of both mixing and attenuation, particularly
when undisturbed soils are used.
Simulation models (2, 6, 7, 8, 13, 14, 49, 53, 54, 55, 56, 59,
63, 64) are descriptions of how the soil-solute systems behave in
response to changes in conditions. The input information may
consist of fundamental physical and chemical properties of parts of
the system or it can consist of empirical data gathered from other
procedures, such as batch or soil column studies. Categories of
available models and a discussion of their relative merits have
been published (2, 7, 70, 72). Some models which were developed to
predict the behavior of water at the soil surface (agricultural
runoff, small watershed hydrology) include submodels for predicting
movement of water or solutes downward and laterally through soil
(10, 36, 43). This is not a complete listing of the work that is
being done on predicting movement of substances through soil. Even
if the choice were to be limited to the work cited here,
nevertheless, there are available a variety of techniques that can
be applied to the problem. These techniques vary in technical
difficulty, cost, and the precision, accuracy and complexity of
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their results. Though there is clearly a data base from which
techniques can be drawn, application of these techniques may, in
some cases, require ingenuity on the part of the applicant if such
predictive techiques are utilized.
Common to all techniques will be the need to conduct studies
with the waste and the soil from the proposed facility. Although
it may be possible to estimate soil and waste properties to screen
several sites, available information is not likely to be sufficient
to make meaningful predictions about a specific site.
(iii) Technical Difficulties
Because predictive techniques were orignially developed for
conditions other than those that will be encountered in hazardous
waste disposal, some technical difficulties will be encountered.
These must be taken into consideration by applicants attempting
predictions and by those reviewing applications.
Flow system
The path and rate of movement of liquids must be defined in
order to predict the movement of leachate contaminants. For sites
in homogeneous materials this may be much easier than predicting
attenuation; in more complex settings defining the flow properties
such as permeability or hydraulic conductivity, there exists not
only the problem of taking measurements in fine textured soils
(clays) using techniques developed for coarser textured soils (e.g.,
sands) but also the problem of variability of soil properties even
in soils that seem quite uniform (4, 48).
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Availability of leachate
Unless another facility accepting the same type of waste is
available as a source of leachate, the applicant will need to either
generate leachate in the laboratory from a sample of waste in order
to measure contaminant properties or use empirical predictive
procedures. Assuring that laboratory generated leachate is similar
to leachate from the waste under field conditions will require
careful thought and attention to detail. Procedures for doing this
are limited but, recently, work has been done in cnnection with
the development of Extraction Procedure for RCRA Section 3001 and
with attempts to develop related procedures for wastes that are not
disposed of with municipal solid waste. It should be emphasized
that the leachate used in predictive procedures should be similar
to field leachate to enhance accuracy. Refer back to Section 3 on
leachate composition for further discussion.
It will be much more difficult to generate a laboratory leachate
for facilities that accept more than one type of waste. Not only
would several wastes have to be used, but the relative proportions
would have to be similar to the field situation and the sequence of
leaching would also have to be considered unless the wastes are to
be thoroughly mixed in the field. These sort of leachate problems
will make it extremely difficult to predict leachate attenuation
for facilities that will be placing a number of wastes in contact
with each other.
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Analytical problems
The separation, cleanup, and chemical analyses of leachate
constituents from a hazardous waste is a substantial problem. Many
analytical methods have been developed to detect substances in
fairly clean matrices. Methods for analysis in sewage and industrial
wastes (25, 26, 28, 33) may require modification before being
applied to waste leachates. Once an applicant has generated a
leachate for use in a predictive method it may be necessary to adapt
existing techniques to make them applicable to leachate analysis.
Similarly, the methods for determining properties of
contaminants and soils have not been used extensively in the presence
of waste leachate and therefore may need modification. Methods
for determining many of the contaminant properties have been
documented for substances in single solutions (3, 26, 28, 29, 32,
38, 39, 41, 45, 57, 58, 60, 69). This can serve as a base for
similar work when multiple solutions of contaminants are analysed.
The contaminant-soil interaction behavior of the hydrophobic
non-ionic organic compounds has been studied with more success than
other organics. A number of studies (5, 14, 25, 26, 27, 28, 30,
40, 41) have demonstrated how to greatly reduce the number of
factors which need to be considered in accounting for attenuation
by referencing to a few properties such as soil organic content or
surface area. Several other approaches have been explored (3, 12,
47) to estimating contaminant-soil interaction properties; their
applicability is dependent on the variety of materials that have
been used in their development.
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Finally, it should be noted that most research work has been
done during adsorption of contaminants onto soil; the degree of
reversibility of this process needs further attention.
Testing predictions
Because of the uncertainties in the prediction procedures and
in the processes of gathering input data, there will be uncertainity
in the final prediction. The proposed regulation recognizes this
and provides for a tri-annual up-dating of predictions using monitoring
data from the facility. Monitoring will be conducted via wells
that draw water from the saturated zone of soils below and around
the facility. Monitoring in the unsaturated zone has not been
provided for (except for land treatment facilities) because of
reliability problems with the devices and the added difficulty of
maintenance. Where there is a thick unsaturated zone below a
facility it could be quite a long time before any contaminants
reached the monitoring points in the saturated zone and it could
also be difficult to make any check on predictions of leachate
movement within a reasonable time. Where a thick unsaturated zone
exists and the degree of uncertainty in the leachate movement
prediction is great, the applicant may consider installing
unsaturated zone monitoring (37, 46, 74) close to the bottom of
the facility which would enable him to make a predictive test
before a long time has elapsed. In such a case, the unsaturated
zone monitoring equipment would be a temporary or expendable part
of a total monitoring program.
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(iv) Precedents
Prior discussion on the attenuation of leachate contaminants
by soils have raised questions about the appropriateness of allowing
the inclusion of attenuation in the prediction of leachate movement.
Man-technical considerations for including leachate attenuation are
mentioned as background for the proposed regulation.
An Office of Solid Waste study (72) completed in 1978 examined
approaches to pollution prediction for waste disposal siting and
concluded that the simulation model approach (which includes
consideration of attenuation) would only be a suitable tool in the
long-term, after considerable development and standarization. The
regulatory approach envisioned at that time relied on standard
procedures (such as Section 3001 Detraction Procedure) that would
be specified for use in all cases. Since that time, the state of
the art in prediction procedures has become better understood and,
thus, a more flexible regulatory approach has been adopted. As a
result, through knowledge gained on predictive procedures, the
proposed regulations allow for the use of simulation models or
other predictive techniques for assessing the effect of attenuation
on leachate movement. The regulations recognize that there may be
combinations of waste types, hydrologic settings, and technical
abilities of an applicant who can make predictions of attenuation
appropriate for that case.
Several states are cited in the Office of Solid Waste study
(72) as presently requesting information from permit applicants
regarding the attenuation capacity or activity of soils and earth
materials at proposed disposal facilities. If attenuation were
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excluded from consideration in the proposed regulation it would
be reasonable to question why the Agency would not recognize and
allow consideration of an effect which could increase the
acceptability and potentially reduce the cost of land disposal
facilities.
A simplified vertical-horizontal routing model (13) was
developed for the Oregon Department of Environmental Quality.
This model includes provisions for contaminant attenuation by
soil. Although the model has not yet been extensively verified
against field data, it has been used in evaluating the impact of
various organic chemicals on ground water conditions. The Office
of Sblid Waste Report (72) notes that the results of these
evaluations were not incorporated in landfill design requirements.
However, the existence of the model and its limited use by a state
agency are a part of the background for the concepts in the proposed
regulation.
The Toxic Substances Premarket Testing Program (68) includes
some detailed consideration of the attenuation and mobility of
chemicals in soils and requires submission of that information. A
background document has been issued (69) describing methods for
collecting this information.
While none of the examples discussed above constitute a
compelling basis for including consideration of attenuation in the
proposed regulation, they do indicate that the proposed regulation
is by no means the first instance of such an inclusion and suggest
that there is a basis for doing so.
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(v) Consequences of not considering attenuation
If the proposed regulation had excluded attenuation as an
allowable consideration in predicting the mass rate of leachate
migration, the Agency could expect to be critized for ignoring the
existence of a phenomenon that is generally acknowledged to take
place. Moreover, the Agency would be guilty of failing to make
use of available, though rudimentary, technology, and also of
limiting the creativity of applicants in devising solutions to
disposal problems.
If attenuation could not be considered in predicting leachate
movement the major remaining mechanism would be limited to dilution
and dispersion. Using only these two mechanisms would yield
predictions of much greater travel distance than if attenuation
were included and would also lead to the need for much greater
buffer zones resulting in less economically viable facilities at a
time when disposal capacity is expected to be limited.
Finally, to exclude the use of attenuation in leachate movement
predictions would severely inhibit development of the ability to
make such predictions and thereby arrive at a realistic compromise
between cost and protection. Improvement in the ability to
incorporate attenuation in the prediction of leachate movement will
be costly; however a likely impetus to such a improvement would be
the need for the techniques in situations such as disposal management
where the costs (and potential savings) are great.
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(c) Summary
The proposed regulation allows consideration of attenuation
(contaminant-soil interactions) in making predictions of leachate
movement in soil. It is acknowledged that attenuation takes place
in soils and that it acts to limit the amounts and rates of movement
of pollutants. Techniques are available for predicting attenuation
and the state of the art is advancing. The proposed regulation
recognizes existing limit to the state of the art and includes
provisions to compensate for these limits.
Finally, exclusion from consideration of attenuation could
cause several adverse effects.
(6) Leachate Migration in the Saturated Zone
(a) Background
Once a substance released from a discharging facility actually
enters the saturated zone, the predictive techniques for migration
and environmental fate become much more reliable (7,19,31). The
major weakness in the development to date of contaminant transport
models in the saturated zone is due to difficulty in determining a
field coefficient of dispersion, and in quantifying chemical reaction
terms (1). As mentioned in Section 5 concerning the unsaturated
zone, mixing processes are more prominent in the saturated zone.
Contaminant-soil interactions are relatively less significant in
saturated zones; their discussion centers in Section 5.
The proposed provisions of Part 122 include a requirement
that the owner or operator must predict the migration of
contaminants from the facility in the ground water. Mathematical
simulations are one method by which these predictions could be
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made. Additionally, the owner or operator is required to implement
a ground water monitoring program capable of determining permit
compliance. Again, mathematical simulations can be utilized to
demonstrate this capability.
Mathematical simulations submitted to the Agency to demonstrate
the adequacy of the system or performance of the facility must be
documented and calibrated. Agency guidance will establish the limits
of verification and validation. Also, model capabilities may be
demonstrated using standard test cases established in Agency guidance
manuals. This background document expresses the Agency's intent
regarding the limits, utility, and procedural constraints of
mathematical simulations of the migration of contaminants which
have entered the ground water from hazardous waste management
facilities. Several dozen mathematical simulations of ground
water contamination processes useful for environmental prediction
and analysis have been cataloged by the Hoicome Institute for the
EPA (4). Saturated water models comprise the greatest and most
sophisticated portion of these, but ground water modeling is in an
early stage of development, and, as in the state of the art of
most developing disciplines, the beginning is broader than deep.
Many of the differences between competing ground water models are
less significant than the variations within each. Many which have
been designed for one application are being modified for improved
performance in another.
Anticipating the possibility that model selection, a critical
juncture in performing the required predictions, will require
review, the Agency intends to develop a review protocol. The
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objectives and procedures are addressed in this background document
after a discussion of the acceptable applications, the limitations
for regulatory purposes, and a few exemplary cases.
(b) Trust and Skepticism
The Agency's position at the time of proposal of these
regulations is to encourage skeptical, limited use of mathematical
models as a basis for predicting the fate of contaminants and for
demonstrating monitoring competence in fulfillment of the permit
application requirements. Limits of encouragement exclude very
simple hydrogeologic settings, for example, in which the rigor of
modeling is just not warranted, as well as very complex settings
in which intricate fracturing and layering elude quantification.
Skepticism is particularly encouraged with regard to selection of
the source term, the diffusion coefficients and the expressions of
soil-leachate interactions. For the vast majority of approvable
facilities, however, mathematical simulation provides an effective
method of developing and expressing the most probable direction and
rate of migration of substances which could be released by a proposed
facility.
(c) Acceptable Levels of Confidence
Model confidence factors will be developed in guidance manuals.
They will vary as dependents of data quality as determined by the
number of samples, homogenicity of site characteristics, complexity
of hydrogeologic settings, etc. Where subjective judgments are
required, the manuals will provide procedures to standardize the
values as much as possible.
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Confidence ratings will be developed by the applicant. The
level of confidence achieved will be evaluated by the permit issuing
authority in keeping with the perceived environmental and health
danger at each proposed facility.
(d) Discussion
Once leachate enters the ground water, the major determinant
of the rate and direction of movement is of course the movement of
the ground water itself (2). The problem in predicting the movement
is then a combination of ground water flow prediction with prediction
of leachate dispersion, adsorption, convection, diffusion and
other factors which may tend to differentially act on the leachate
(3, 5, 11, 13, 16, 17, 18, 30). In free flowing aquifers, the
movement due to hydraulic head differential, called advection, is
the dominant means of saturated zone contaminant flow and models
which only consider advection may be appropriate. Other models
jointly considering dispersion and advection may be more useful in
slower moving aquifers (1, 27). Complexities in the site
•
hydrogeology heighten the value of joint models because dispersion
is enhanced as contaminants migrate selectively around less permeable
strata. However, the difficulty of measuring dispersivity and the
numerical difficulties in solving the great complexity of equations
tend to detract from their value (1).
Chemical interactions may be incorporated in either advection
only or advection-dispersion models. These interactions are
difficult to separately measure or estimate; moreover, the added
complexity can be crippling to models of non-homogenous settings.
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fldvection models are useful in estimating minimum time for
arrival and probable pathways. For many applicants, these two
determinations will be sufficient, as the cost and uncertainty of
modeling to determine the probable arrival of concentrations at a
point may be stifling.
(i) Diffusion, Dispersion
Dispersivity is described as a convenient mathematical quantity
with obscure physical significance (1, 6, 48). It is not a directly
measurable field condition, but rather, it can be calculated,
differently at different scales, from several measurable values.
It is sometimes disparagingly referred to as a "fudge factor" fitted
to the model and site at the scale considered. Dispersivity is
also expressed as a characteristic mixing length of a soil or
strata; it is related to the homogeneity of the geology, which of
course varies as the modeled scale progresses from micro to macro
(29) .
This indirect or fitted nature of dispersivity is problematic
for its use in permit applications. Ideally, a reviewer would
prefer a simple, precise measure which is easy to verify. Tracers
provide the only direct pre-construction, field determination of
dispersivity. Problems incumbent with ground water tracer studies,
however, severely restrict their value for most permit application
cases. The tracer test for dispersivity involves monitoring the
rate change of the concentration of injected tracers across the
pathways from the proposed site. In order to encounter the modeled
geologic idiosyncracies at a useful scale, the minimal tracer test
will require many months to complete. Extreme care must be observed
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in selecting the length of screen for tracer sampling wells for
instance; too large a sample zone will provide a falsely mixed
sample, indicating more than actual attenuation or dispersivity.
Slug injections of tracers render vastly different results than
steady-state injections, yet the modeled facility may actually emit
a combination of steady-state and slug injections, leaving the
modeler yet another unknown. Sbrting the effects of dispersion
from other tracer decay mechanisms such as adsorption, decomposition,
soil interaction, etc., as well as behavioral differences caused by
the future leachate1s differing temperature or viscosity, for
instance, can be difficult, also. Local histories of similar
facilities may prove to be a more reliable predictor. "Environmental1
measurement of dispersivity using substances present in the aquifer
prior to testing, such as intruded sea water or tritium introduced
after atom bomb "fall out," are not generally applicable to the scale
significant for facility permit applications. Complex site geology
may suggest not only avoiding regional-scale dispersivity, but even
calculating several discrete values within the pathway of concern,
with spatial distribution segmented and longitudinal and transverse
dispersivity varying across very small increments (8, 12, 14, 16).
(ii) Techniques
There are a wide variety of modeling techniques applicable for
various phases of prediction and or monitoring system design (10,
25). Each technique has strengths and weaknesses, none are
universally suitable.
The use of models in ground-water studies has three main phases;
system conceptualization, history matching or model calibration, and
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prediction. Most applications involve each of the three phases;
however, the relative effort devoted to each phase is application
dependent.
System conceptualization involves organizing available
information on the ground-water system in an internally consistent
framework; the information is posed in terms of a qualitative model.
The qualitative model is translated into mathematical terms such as
boundary conditions, initial conditions, and hydrologic parameters.
An appropiate ground-water model, which is quantitative, can then be
applied to improve the model. The use of the model involves checking
various observations and determining the sensitivity of the system
responses to hydrologic parameters and assumptions. The results of
the system conceptualization provide a basis for designing data
collection efforts. Use of models at this stage not only forces the
hydrologist within a tested framework, but also gives guidance in
terms of data requirements (20).
History matching or model calibration will refine the estimates
of hydrologic parameters and boundary conditions by comparing model
results with observed data (28). In the early part of a study,
observed data will consist of aquifer tests. Estimates of parameters
are changed to improve the comparison. The history matching
procedure can be done by an automatic regression approach, followed
by sensitivity analysis and continuing data collection activities.
The final phase is the prediction of future system behavior,
normally the shortest part of the study. Predictions are based on
model results using the best estimate of system parameters obtained
by history matching. Assessing the uncetainty in the predicted
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results should be accomplished by reiterating the sensitivity
analysis.
(e) Test Case Comparisons
The flgency intends to develop an evaluation protocol to be
used by owners or operators in demonstrating the capabilities and
sensitivity of any mathematical model submitted in support of
monitoring systems or of predictions of migration in the saturated
zone. The protocol will consist of a set of standard test cases
representing a spectrum of facility and site characteristics and a
set of required outputs from each model for the test case. Model
performance may then be judged, at least in a comparative way, as
to relative sensitivity to certain parameters. While the Agency
does not expect this evaluation protocol to influence the confidence
ratings in paragraph cf above, it does appear to offer some measure
of assistance to the permit review process.
Model testing involves the following two determinations:
0 toes the model accurately simulate the phenomon for which it
has been designed?
0 Do the numerical approximations accurately solve the mathematical
equations that constitute the model?
Methodologies that test models include comparisons with analytical
solutions, comparisons with empirical data, and checking that
conservation properties (mass balance) hold.
Testing a numerical model consists of different levels of error
elimination; the numerical solution will be compared with known
analytical solutions to remove logic errors in solving'the equations.
Numerical solutions are compared with laboratory and field
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observations to remove logic errors in equations describing the
physics. Therefore, data required for the test cases may include
analytical solutions, laboratory results, field applications,
hypothetical problems, and/or physical analogues. There are several
analyical solutions available for subsurface flow. Classical
solutions for radial flow include those by Theis and Hantush.
Avodonin (3) presents an example analytical solution for heat and
fluid flow, whereas Ogata and Banks (22) give an example analytical
solution for solute and fluid flow (6, 9, 14, 15, 21, 23, 24, 26).
To test the represented physics and chemistry, the results may
be validated against known laboratory or field results. A feasible
approach would be to use a tracer test senario, since the geological
and hydraulic conditions might be expected to be comparitively well
defined in such a case. Laboratory studies have been performed for
many related problems. Models involving solute transport could be
compared with results from column studies such as those obtained by
Griffen and Shimp.
Another level of testing is the comparison of one code against
another. Such comparisons may be used to demonstrate the influence
of different physico-chemical parameters on the results of the
simulation of a hypothetical site. The properties of the
hypothetical site selected for the simulation should be close to
those deemed realistic for a candidate site. At this level of
comparison, the correct answers to the calculation are not known.
Considering that some of the models include effects that have a
very strong influence on the output, the results might be expected
to be scattered over a wide range.
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( £) Summary
Modeling and models are the subject of much controversy in
their regulatory application. They are seldom presented with an
air of certainty. However, it should be remembered that many
situations will occur which are well within the capabilities of
mathematical modeling. Where a prediction of plus or minus 50
percent may represent the outer limits of confidence, however, it
is still possible that the regulatory task to be assigned to model
is simply to predict the future presence or absence and not the
concentration.
The Agency intends to recognize the value of mathematical
models, to permit and encourage their limited use in demonstating
the fate of discharges to groundwater and the adequacy of monitoring
schemes for instance, and to remind users and reviewers of models of
the associated shortcomings and uncertainties (28).
(7) Leachate discharge from the saturated zone
(a) Background
One of the major uses of models intended by the Agency is as a
mechanism to test predictions of effects on flowing surface waters
and withdrawals of ground water through wells or collection devices.
Withdrawals or discharges from a migrating plume, if they exist,
represent conditions, often as boundry conditions, which must be
taken into account in the development of saturated zone models.
Therefore, the mechanics of analysis of discharges and withdrawals
from the saturated zone is an integral part of the analysis of
migration within the saturated zone. Analysis of discharges and
withdrawals is usually the objective of saturated zone modeling.
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(b) Discussion
Since the objective of the analysis of the migration of
ground water affected by discharges from hazardous waste land
disposal facilities is to predict effects on flowing surface waters
and ground water withdrawn through wells or collection devices, it
is with respect to this need that the quality of the necessary
models may be judged. In most cases, it is expected that the
analysis will be concentrated primarily on the migratory pathway of
a leachate plume in ground water as it seeks a normal discharge to
the surface environment. This is the situation which will prevail
for an owner or operator who can show that his facility will comply
with the ground-water protection standard in §264.2.
As noted in the summary to the previous section, the regulatory
task in this case will be simply to predict the future presence or
absence and not the concentration. The precision of the necessary
modeling effort will be quite variable depending on the real risk
of exposure through ground water withdrawl. If it is known, or it
can be established, that no ground water withdrawal for use exists,
or will be initiated in the future, within or proximate to the
migratory pathway of the leachate plume; simple forms of modeling
will suffice. Where the pathway to natural discharge outlets is
relatively short, limited field data will be required; and the model
may be a simple hydrologic calculation which can be accomplished by
hand. The task will be even simpler for existing facilities since
the migratory pathway may be measured, and prediction will not be
required to represent it accurately. However, it will still be
necessary to make quantitative predictions of the mass rate of waste
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constituents and byproducts which will reach surface waters, but
often the margin for acceptable error in such predictions is large
and maximum potential effects can be demonstrated on the basis of
the mass rate of deposition in a facility or a determinate mass rate
of discharge from the facility controlled to a desirable low rate
by the facility design. The necessary precision of such quantitative
predictions of potential effects on surface waters will of course
vary with the amount of flowing water in the surface water body.
Therefore, the necessary precision will be greater for facilities
located so that the ultimate discharge of affected ground water will
be to a small stream than it would be for facilities located so that
the ultimate discharge would be to a large river or the ocean.
The greatest precision in predicting (or modeling) the effects
of plume migration will exist when a variance from the ground water
protection standard is required. In such cases, the affected ground
water is being or may in the future be withdrawn or collected for
use. The objective of the Agency is to avoid such situations to the
extent that it is possible without arbitrarily denying a permit
applicant the opportunity to show that no adverse effect would result.
When active or potential use of affected ground water is a factor
that must be considered, there is no substitute for maximum possible
(i.e., state of the art) precision in predicting potential adverse
effects on the users of the ground water. It is in this circumstance
that qualitative and quantitative modeling will be a practical
requirement for a sucessful showing in the permit issuance process,
and it is quite likely that sophisticated computer modeling based on
extensive field data will be needed.
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( c) Summary
The goal associated with the use of any particular predictive
tools such as ground-water modeling in the permit issuance process
is to satisy the permit applicant, the permit issuing authority, and
the public that a permit may be issued. It should be obvious that
when the potential for interference with use is real, the data and
analysis requirements needed to assure an understanding of the
systems grow. The public whose use may be adversely affected will
demand such assurance to protect their interests, and it if is not
provided in the permit issuance process, will pursue other means to
avoid exposure to risks they fear. adequate information, as a basis
for decision, is the only viable means of overcoming that fear.
As noted, it is expected that the information required will
most often be used to show that there is no substantial or unique
risk of exposure because ground water use will not be at issue.
When ground water use is at issue, it is quite likely that permit
applicants will choose other means to meet their disposal objectives
which will avoid the need to deal with the complexity of adequate
information to show acceptable risk.
For existing facilities which do affect ground waters which are
being used, the understanding of that fact, which the informational
requirements will force, may result in the elimination of the risk
through the discontinuance of use by means independent of the permit
issuance process. If the ground waters are not presently used, the
understanding may serve as an incentive to preclude future use and
interference by restricting use. Although these examples of
potential restriction of use are not, at first glance, protective
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(or an agency objective), they may be both practical and cost
effective for the regulated community. This is especially true
since recovery of adversely affected ground water is often not
possible in a practical sense. Continued use of ground water
which is already adversely affected could potentially furthur
environmental goals by not inducing pressure to allow unaffected
ground water to be placed at risk by facility construction. In any
case, both the restriction and the discontinuance of use of affected
ground water would result in compliance with the ground-water
protection standard of §264.2 and would be means available to an
owner or operator seeking a permit under §3004 of the RCRA.
D. Regulatory Language
(d) Informational requirements for permitting discharges from
land disposal facilities. Bccept as provided in paragraph (e) of
this section, each owner or operator applying for a permit to
dispose of hazardous waste into or on the land shall file the
following information as part of his application:
(1 ) A definition of the specific hazardous wastes to be disposed
of in each disposal facility operational unit, including;
(i) the specific wastes by hazardous waste number when
applicable.
(ii) the expected rate of deposition of each specific waste
including both wastes defined as hazardous wastes in accordance
with §261.3 and any other waste to be disposed of in conjunction
with such hazardous wastes.
(iii) the maximum rate of deposition of each specific waste
described in accordance with §122.25(d)(1)(ii) for which permit
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authorization is being requested.
(2) A definition of the rate of mass transport of leachate and
gases from the land disposal facility, including;
( i) the mass rate of hazardous wastes, and the decomposition
byproducts of hazardous wastes expected to leach or otherwise
escape from the facility,
( ii) the mass rate of any other wastes and the decomposition
byproducts of such other wastes expected to leach or otherwise
escape from the facility,
(iii) the mass rate of infiltrating rainwater and other liquids
disposed of or generated within the facility expected to leach or
otherwise escape from the facility, and
( iv) the maximum mass rate of infiltrating rainwater, any other
liquids to be disposed of or generated within the facility/ hazardous
wastes and any other wastes to be disposed of within the the facility,
and the decomposition byproducts of such hazardous wastes or other
wastes including gases expected to leach or otherwise escape from
the facility.
(3) A definition of the earth materials above the zone of
saturation which will be in contact with leachate discharging
from the land disposal facility and gases released from the facility
and the leachate, including;
( i) the lateral and vertical extent of the expected migration
of leachate in any materials emplaced to control the rate of leachate
migration.
( ii) the lateral and vertical extent of the expected migration
of leachate in each natural earth material formation determined to
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exist during site investigation studies required in paragraph (g).
(iii) the lateral and vertical extent of the expected migration
of gases through any materials or wastes emplaced within the facility.
(iv) the lateral and vertical extent of migration of gases in
each natural formation determined to exist during the site
investigation studies required in paragraph (g).
(v) the maximum lateral and vertical extent of earth materials
above the zone of saturation and the area at the surface of the
ground or the waste for which authorization to be in contact
with leachate discharged from the facility or gases released
from the facility and the leachate is being requested.
(4) A definition of the earth materials in the saturated zone
which will be in contact with the leachate discharged from the
land disposal facility and the extent and rate of leaching, including;
(i) the mass rate of transport of infiltrating rainwater, any
other liquids to be disposed of or generated within the facility,
hazardous wastes or any other wastes to be disposed of within the
facility, and the decomposition byproducts of such hazardous wastes
or other wastes; expected to leach from the facility to the ground
water.
(ii) any alteration in the vertical elevation of the zone of
saturation expected to occur due to the existence of the facility
and/or the discharge from the facility to the saturated zone.
(iii) the transverse, lateral, and vertical extent of the
expected migration of leachate within each natural earth material
formation in the saturated zone determined to exist during site
investigation studies required in paragraph (g).
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(iv) the maximum transverse, lateral, and vertical extent of
earth materials in the saturated zone for which authorization to
be in contact with leachate discharged from the facility is being
requested .
(v) the maximum mass rate of transport within the saturated
zone of infiltrating rainwater, any other liquids to be disposed
of or generated within the facility, hazardous wastes or any other
wastes to be disposed of within the facility, and the decomposition
byproducts of such hazardous wastes or other wastes for which
permit authorization is being requested.
(5) A definition of the discharges and/or withdrawals of ground
water mixed with leachate, including;
(i) the mass rate of discharge from the saturated zone of
liquids to be disposed of within the facility, liquids other than
water which will be generated within the facility, hazardous wastes
or any other wastes to be disposed of within the facility, substances
solubilized from earth materials by leachate, and the decomposition
byproducts of such hazardous wastes, liquids, or other wastes or
substances; into any flowing surface waters, any standing surface
waters, or to the ground surface within the zone of containment.
( ii) the maximum mass rate of discharge from the saturated zone
of liquids to be disposed of within the facility, liquids other
than water which will be generated within the facility, hazardous
wastes or any other wastes to be disposed of within the facility,
substances solubilized from earth materials by leachate, and/or
the decomposition byproducts of such hazardous wastes, liquids, or
other wastes or substances; into any flowing surface waters, any
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standing surface waters, or to the ground surface within the zone
of containment for which permit authorization is being requested.
(iii) the mass rate of withdrawal from the saturated zone of
liquids to be disposed of within the facility/ liquids other than
water which will be generated within the facility, hazardous wastes
or any other wastes to be disposed of within the facility, substances
solubilized from earth materials by leachate, and the decomposition
byproducts of such hazardous wastes, liquids, or other wastes or
substances into any well or other ground water collection device,
except monitoring wells or collection devices installed or to be
installed to monitor or characterize the leachate and the ground
water.
(iv) the maximum mass rate of withdrawal from the saturated
zone of liquids to be disposed of within the facility, liquids
other than water which will be generated within the facility,
hazardous wastes or any other wastes to be disposed of within the
facility, substances solubilized from earth materials by leachate,
and the decomposition byproducts of such hazardous wastes, liquids,
or other wastes or substances; into any well or any other ground
water collection device, except monitoring wells or collection
devices installed or to be installed to monitor or characterize
the leachate and/or the ground water.
3. Variations in precision - §122.25(e)
A. Proposed Regulation and Rationale
This portion of the regulatory requirements for information was
not addressed in the Agency1s 8 October 1980 notice of its intended
approach to permitting hazardous waste land disposal facilities.
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B. Summary of Comments
Commenters on the 8 October 1980 notice did r.ecognize and
assert that the informational requirements discussed in the notice
were not equally applicable to all situations and suggested that
the requirements be triggered by demonstrated need.
C. Discussion
The Agency decision to include explicit statements in the
regulations concerning variation in required precision is responsive
to comment. The regulatory statements are keyed to specific
paragraphs of §122.25(d). Issues related to needed precision are
also covered in the discussion on that portion of the regulations.
(1) Waste loadings - §122.25(e)(1)
Section 122.25(d)(l) requires a definition of what wastes will
be disposed of in a facility. This information is considered a
minimum requirement for all facilities. No analysis is possible if
one is not aware what waste is to be handled in a facility.
(2) Discharge and emission rates - §122.25(e)(2) & (3)
Section 122.25(d)(2) establishes the requirement to define the
rate of releases (discharges and emissions) from a facility. Since
no discharge to ground water is allowed from facilities (surface
impoundments and waste piles) used solely for storage or storage and
treatment, paragraph (i) establishes that no definition is required
for such facilities. There is a caveat to the provision in that if
an owner or operator chooses to provide a positive collection system
in addition to a leachate detection system, information on the
expected rate of discharge is required. Such information would be
needed to evaluate the discharge and the need for treatment. Such
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a situation would exist in a storage and treatment surface
impoundment when the treatment is an in place filtering system
designed to provide solid/liquid phase separation prior to liquid
withdrawal rather than a piped outlet within the impounded waste.
Paragraph (ii) allows analysis of facilies designed to introduce
liquids into the land to be based on the liquid deposition rate.
This provision is, of course, only applicable during the active use
of a facility and in certain (areally large) seepage facilities,
rainfall loadings may be significant.
Paragraph ( iii) allows direct emissions from land disposal
facilities to the atmosphere to be considered in conjunction with
all facilitiy emissions. Direct emissions from land disposal
operational units will commonly be a minor part of the total gaseous
emissions from a major hazardous waste management facility which
may include such operational units as tanks, basins, storage areas,
handling and transfer areas, stills, evaporators, and incinerators.
Paragraph (iii) establishes the fact that the rates of discharge
from a land disposal facility cannot often be determined exactly
especially since discharge rates will often be influenced by the
variances of weather. It is implicit in the requirements that
discharge must usually be expressed by averages, ranges, and expected
extremes. As noted in the language of the paragraph, the "best
estimate" results will be subject to verification (with respect to
extremes) and improved precision based on monitoring and modelling.
Section 122.25(e)(3) more explicitly describes the type of
information expected to define the volume and character of leachate.
The need for accurate volumetric information is considered to be
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of major importance since many of the important design features of
land disposal facilities are intended to control the rate of liquid
migration. The physical characteristics of the liquid (leachate)
are also important to facility design. In most cases it will be
sufficiently accurate to consider the leachate to be physically
equivalent to water; however, it must be established that such an
assumption is valid. Liquids that will not mix with water will
usually behave differently than water, and substances which do mix
or dissolve in water can change its physical character.
Important physical parameters of liquids and leachates that
can be expected to discharge from a facility must be defined
independently. The parameters which must be defined are viscosity,
specific gravity, and surface tension as required by paragraph ( i) .
The viscosity of any liquid will vary with temperature, and the
rate at which any liquid will flow through a porous media such as
soil is inversely proportional to the kinematic viscosity. Examples
of the variability of kinematic viscosity can be expressed with
reference to familiar fluids; gasoline could have a kinematic
viscosity half that of water, whereas engine lubricating oil could
have a kinematic viscosity four hundred times that of water.
Liquids with specific gravities higher or lower than water will
tend to sink or float respectively in a water system; and the surface
tension of a liquid will influence the capillarity (based on the
adhesion of the liquid to the soil and cohesion of the liquid itself)
of the liquid in contact with the soil.
All of the above parameters are directly measurable by standard
techniques in the laboratory.
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Describing the chemical characteristics of a leachate is much
more problematic. Paragraph (ii) describes the degree of
characterization that is expected in terms of the expected or
probable fate of contaminants. The "best estimates" of contaminants
(constituents and decomposition byproducts of the waste) which will
be present in a leachate must be based on an understanding of the
probable bio-chemical reactions which the waste can be expected to
undergo. The regulation allows such "best estimates" to be based
on "reliable reference sources of data" or on "independent study".
The agency has produced a report ("Water Related Environmental
Fate of 129 Prioity Pollutants", EPA-440/4-79-029a, December 1979)
which describes the probable fate and transport of a number of toxic
chemicals in the environment with respect to a variety of chemical,
physical, and biological processes such as photolysis, hydrolysis,
volatilazation, sorption, biodegradation , biotransformation, to name
a few. This report is basically a literature survey and summary of
data available on many of the more important soluble hazardous
waste constituents. It is an example of the type of data which is
available in reference literature; a data bank which is constantly
growing and improving. The reference scientific literature on the
environmental fate of chemicals introduced into the environment
should be researched on a real time basis to ensure that recent data
is not overlooked. Much of these data are generated by sources which
are not primarily interested in waste disposal rather than the
effective and safe use of chemical products; and the best and most
reliable information is often available only from the industry or
industries which produce or market the chemical products.
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(3) Migration in the unstaurated zone - §122.25(e)(4) & (5)
The definition of the migration pathway of leachate through
the unsaturated zone required in §122.25(d)(3(ii) may be approximated
as a vertical downward extension in each homogenious earth material
formation in accordance with §122.25(e)(4). Special factors, i.e.,
boundry conditions and the effect of capillarity must however be
be taken into account. The factors influencing the migratory
pathway of gases have been described in the discussion on §122.25(d).
§122.25(e)(5) merely confirms that the predictions are recognized to
be "best estimates".
(4) Attenuation in the unsaturated zone - §122.25(e)(6)
The opportunity to ignore attenuation in the unsaturated zone is
afforded by this paragraph. The factors which should be taken into
account by a permit applicant who chooses either to account for
or ignore attenuation are discussed in detail in the discussions on
§122.25(d).
(5) Migration in the saturated zone - §122.25(e)(7)
This section requires that the factors of leachate uniformity,
viscosity, specific gravity, and surface tension be taken into
account in defining the leachate plume in the saturated zone; and
that the empirical factor of dispersivity (spreading) be accounted
for in the analysis.
(6) Maximum locational and rate definitions - §122.25(e)(8)
This section requires that the definition of the "zone of
containment", which represents the extreme limits of the migration
of leachate and gases which the applicant asserts will not be
exceeded, be based on analysis taking into account the maximum
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mass rate of liquids expected to discharge from the facility/ the
maximum mass rate of of transport in the saturated zone, and the
maximum rate of waste deposition into the facility. Uncertainty
factors may be applied in the analysis, provided they are defined.
(7) Non-use withdrawal or collection - §122.25( e)(9)
By definition, Class A & B facilities will comply with the
ground-water protection standard and no withdrawals for use will
exist within the leachate plume. However, leachate may be migrating
into wells installed in conjunction with the facility to control
the migration of leachate or to remove historical contamination.
If such wells do exist, the predicted quality of the water withdrawn
must be accounted for. In addition, passive collection devices
may be an outlet for ground water discharge. If passive collection
devices exist within the zone affected by the leachate plume, the
quality of any ground water affected by the facility which enters
them must be considered.
(8) Discharges into surface waters - §122.25(e)(10)
The discharge of ground water affected by the leachate plume
into surface waters is a major consideration for permit issuance.
Prediction of the quality of such discharges are required. The
predictions must consider the range of potential contaminants, and
it must be shown that the upper limit of the range will be less
that the maximum limit requested as a permit limit.
(9) Surface discharges - §122.25(e)(11)
If leachate discharge will occur to the ground surface or to
standing surface waters (i.e., unclassified under the Clean Water
Act) beyond the security boundry of the facility, a high degree
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of precision in predicting the quality of the discharge is required
because of the inherent potental danger which could be associated -
with direct contact with leachate. The Agency considers such an
occurance to represent a poor site location and would be inclined to
prohibit facilities which would result in ground surface discharges
if it were not for the fact that some leachates are quite innocuous.
(10) Ground water collection - §122.25( e)(12)
If leachate discharge will occur into a passive collection
device, predictions of leachate quality must be made within the
collection device and subsequent conveyance devices as well as at
the outlet of the collection or conveyance device in the same manner
as predictions are made with respect to discharges to surface waters.
Passive collection and conveyance devices offer unique routes for
human exposure, and must be carefully considered. In addition, the
physical integitry of of the devises themselves must be considered.
(11) Withdrawal or collection for use - §122.25(e)(13)
If ground water affected by leachate will be collected for use,
the quality predictions take on the greatest importance. For Class
C facilities, which only affect ground water withdrawn for purposes
other than drinking water use, quality predictions may be limited to
those contaminants which can be expected to interfere with the
particular use to which the water is put.
For Class D facilities, which will affect ground water withdrawn
for public drinking water use, all of the contaminants which might
occur in the ground water must be considered. Dilution of affected
ground water by ground water unaffected by discharge may be taken
into account.
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For Class E facilities, which will affect ground water withdrawn
for private drinking water use, all of the contaminants which might
occur in the ground water must also be considered. Since private
withdrawal of drinking water may be both itermittant and at very low
rates, dilution of the affected ground water may not be considered.
(12 ) Summary
In §122.25(e) the Agency has attempted to offer flexibility in
the degree of precision required in analysis, and in the level of
detail required to comply with the informational requirements of
§122.25(d). The required accuracy of prediction necessarily
increases when the fact or potential of interference with the use of
ground water is real and where the probability of unknowing exposure
is high. It is expected that most permit applicants who can choose
a site location will be able to avoid the more rigorous (and more
uncertain) requirements for prediction. Owners and operators of
existing facilities will not have this luxury of choice, but in most
cases they will be able to be more precise in their commitments on
maximum effects since those effects will already exist and be
directly measurable.
The required predictions are recognized as "best estimates" and
are periodically (triannually) subject to re-analysis based on
monitoring and (if necessary) modeling. This technique of prediction
and subsequent monitoring, modeling, and verification is intended to
account for the inherent uncertainties that exist with respect to
available predictive techniques and improve the understanding of the
actual system performance with time. Uncertianty must be accounted
for to assure that actual effects are within permitted maximums.
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It should be noted that the published regulation included three
codification errors. in §122.25(e)(1), the reference to
§122.75(d)(1) should have read §122.25(d)(1); in §122.25(e)(2),
the reference to §122.75 ahould have read §122.25(d)(2); and in
§122. 25(e) (2 ) ( i) , the reference to §264.19 (d) ( i) and (ii) should
have read §264.19(a)(1) and (2). These codification errors are
corrected in the following regulatory language.
D. Regulatory Language
(e) The precision of the definitions required in subsection
(d) of this section may be varied in accordance with the need for
information to establish compliance with the standards of this
regulation as follows:
(1) The informational requirements of § 122.25(d)(1) are
applicable to all types and classes of land disposal facilities
without exception.
(2) The informational requirements of § 122.25(d)(2) are
applicable to all types and classes of land disposal facilities
however;
( i) for surface impoundments and waste piles, used solely for
storage or storage and treatment which are designed to preclude
leakage, as described in §264.19(a)(1) and (2), no definition of
leachate discharge is required unless leakage is to be controlled
by a leachate collection system.
( ii) for seepage facilities and injection wells which are
designed and operated solely to introduce liquids into the land,
leachate discharge can be considered equivalent to waste deposition
unless the boundary conditions, between the liquid and the land,
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control the rate of discharge to a rate less than the rate of
deposition.
(iii) for all types of facilities, the rate of gaseous escape
which occurs directly to the atmosphere from any land disposal
facility operational unit may be considered in conjunction with
gaseous emissions from all operational units of the facility.
(iv) for all facilities from which leachate will discharge into
the land, the informational requirements of §§122.25(d)(2)(i), (ii),
and (iii) are to be considered as a best estimate of the volume
and character of the leachate which will discharge from the
facility into the land or be collected for treatment, discharge,
or disposal from within or above materials emplaced to control the
rate of leachate migration. Leachate discharge into the land
will be subject to verification and more precise definition
based on monitoring and modeling in accordance with §122.28(f).
(3) For any portion of the leachate which will discharge into
natural earth material formations, the volume of discharge must
be defined as precisely as possible ; and the character of the
leachate defined with sufficient precision to establish:
(i) The physical characteristics of the leachate to allow
definition of the locus of leachate migration through natural
earth materials including;
(A) the uniformity of the expected leachate (i.e. solubility
and miscibility in ground water and constancy with respect to
time). Immiscible portions of the leachate or substantially
differing leachates must be considered independently.
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(B) the range of viscosity of the leachate and immiscible
portions of the leachate.
(C) the range of specific gravity of the leachate and immiscible
portions of the leachate.
(D) the range of surface tension of the leachate and immiscible
portions of the leachate.
(ii) The chemical characteristics of the leachate and immiscible
portions of the leachate for the purpose of;
(A) discussing the expected or probable fate of the'contaminants
in the leachate based on independent study, or
(B) discussing the expected or probable fate of the contaminants
in the leachate based on reliable reference sources of data.
(4) The informational requirements of §122.25(d)(3)(ii) may
be approximated with respect to the extent of the zone in each
homogenious natural earth material formation as a downward vertical
extension of the overlying formation in contact with leachate
provided;
( i) expansion of the zone of vertical migration due to boundary
conditions between formations are accounted for, and
(ii) expansion of the zone due to capillary migration is
accounted for.
(5) The informational requirements of §§122.25(d)(3)(iii) and
(iv) are to be considered as a best estimate of the locus of gaseous
migration in the land and through the land to the land surface.
(6) The informational requirements of §122.25(d)(4)(i) may be
considered equivalent to the best estimates of §§122.25(d)(2)(i) ,
(ii), and (iii) unless the permit applicant elects to define and
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support the definition of;
(i) alterations of the chemical and/or physical characteristics
of the leachate which will occur within the unsaturated zone.
(ii) the exchange capacity of the earth materials for
contaminants in the leachate which will not be exhausted over
the period that the facility will discharge leachate.
(7) The informational requirements of §122.25(d)(4)(iii) shall
be defined taking into account the factors defined in paragraph
(3)(i) of this subsection, the alteration of those factors which
will occur due to mixing (for miscible leachates) with ground
water, and factors to account for the dispersivity of the leachate
in the specific natural earth material formations which will be
contacted by leachate.
(8) The maximum locational definitions required in
§§122.25(d)(3)(iv) and (4)(iv), termed the zone of containment;
and the maximum rate definitions of §§122.25(d)(2)(iv) and
(4)(v) shall be correlated with the maximum deposition rate
definition of §122.25(d)(1)(iii) . A defined factor may be applied
to each of the maximum locational and rate definitions, except
the maximum rate of deposition, to account for any recognized
imprecision or lack of confidence in the analytical determinations
of the maximurns.
(9) No information is required under §§122.25(d)(5)(iii) or (iv)
for Class A or Class B facilities unless leachate or ground water
effected by leachate will be collected or withdrawn as a function
of the facility design for treatment, discharge, or disposal; or
passive collection devices such as storm sewers, sanitary sewers,
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ditches, or agricultural drainage systems do or may in the future
exist within the zone of containment.
(10) For any portion which will discharge directly or indirectly
with ground water into surface waters; with sufficient precision
to establish :
( i) the range of concentrations of contaminants, to be defined
in accordance with §122.25(d)(5)(i), which could occur in the
surface waters, and
(ii) that the upper limit of the range of concentration of
contaminants is below that which is to be defined in accordance
with §122.25(d)(5)(ii).
(11) For any portion which will discharge to standing surface
waters or the surface of the ground, both of which should be avoided
in a land disposal facility, it will be necessary to establish:
( i) as accurate a prediction as can be achieved unless,
(ii) the location of potential exposure to effects resulting
from discharges to standing surface waters or the surface of the
ground is part of the facility to which access is controlled in
accordance with §264.14.
(12) For any portion which will be collected in a passive
collection device and discharge to surface waters or to the surface
of the ground, the precision described in paragraphs (10)(i) and
(ii) of this subsection are sufficient provided the predictions
include a definition of the range of concentration of contaminants
which could occur within the collection device and be conveyed
through or by the collection device and any subsequent conveyance
device prior to discharge.
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(13) For any portion which will be collected in a well or other
ground water collection device and withdrawn for any use, with
sufficient precision to establish:
(i) the range of concentration of contaminants, to be defined
in accordance with §122.25(d)(5)(iii), which could occur in the
ground water withdrawn; provided
(A) that for Class C facilities, the predictions may be
limited to those contaminants which could occur over the range of
withdrawal that may prevail and interfere with the specific uses
to which the ground water may be put; and
(B) that for Class D facilities the predictions include,
in addition to predictions for non-drinking uses in accordance
with paragraph (A), predictions of the full set of contaminants
which could occur over the range of rates of withdrawal that may
prevail in ground water withdrawn and supplied for drinking use;
and
(C) that for Class E facilities, the predictions include,
in addition to predictions in accordance with paragraphs (A) and
(B), predictions of the full set of contaminants which could
occur in ground water withdrawn for private drinking use assuming
no dilution of the affected ground water due to the rate of
withdrawal, and
(ii) that the upper limit of the range of concentration of
contaminants is below that which is to be defined in accordance
with §122.25(d)(5)(iv).
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4. Reports on hydrogeology, climatology, and geography - §122.25(f)
A. Proposed Regulation and Rationale
N/A
B. Summary of Comments
N/A
C. Discussion
See the preamble at 46 PR 11151-52
D. Regulatory Language
(f) A report on the hydrogeology, climatology, and geography
of the area where the facility is to be located which that be
based on the site investigation requirements in paragraph (g) and
that shall include;
(1) A description of the geology and hydrology of the area
and a listing of all pertinent published and open file text material
and mapping available from the united States Geological Survey,
the Soil Conservation Service, and State Geological Agencies.
Text material and mapping from such public sources relied upon in
preparing the description shall be referenced, and that which
was not relied upon shall be discussed with reference to the reasons
it was not used. Any other published or unpublished text material
or mapping used in preparing the description shall also be referenced
The description shall;
(i) include such mapping as is necessary to ensure an
understanding of the geology and hydrology by a lay reviewer
(e.g., a member of the public at large rather than a peer) of the
description.
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(ii) be of sufficient detail to define the various earth
material formations in the vicinity of the site and to serve as a
basis of confirming predictions of the transverse, lateral, and
vertical migration of infiltrating rainwater, any liquids to be
disposed of or generated within the facility, hazardous wastes or
any other wastes disposed of within the facility, or the
decomposition byproducts of such hazardous wastes of other wastes
that define the zone to be affected within the zone of containment.
(iii) include the logs of borings taken to establish or improve
the understanding of the geology and the hydrology of the area to
be impacted by the waste disposal activity.
(iv) include mapping to define ground surface contours,
consolidated rock contours, and ground water elevation contours.
(v) include a description of any changes in ground surface
contours, consolidated rock contours, and ground water elevation
contours that will result from the construction or operation of
the facility.
(vi) include a description of the character of each earth
material formation expected to be contacted by leachate or gases
with regard to; type of material, uniformity, permeability, porosity,
weathering (of consolidated rock), fracturing (of consolidated
rock and clay), fault zones (of consolidated rock), karst zones
(of consolidated rock), and swelling (of clay).
(vii) include a description and such mapping of the progression
of the migration of the leachate plume in the ground water flow
system during the active life of the facility, during the post-
closure care period and, unless the plume discharges to surface
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water or it can be shown that the plume will be collected or
withdrawn, subsequent to the post-closure period. The mapping
shall be adequate to ensure an understanding of the locus of the
migration of the leachate plume by a lay reviewer of the description
(2) A report on the climatologic factors based on the data
required in paragraph (g)(2).
(3) A report on the geographic factors based on the data
required in paragraph (g)(3).
5. Site investigation requirements - §122. 25(g)
ISSUE; "Geologic and hydrologic factors" - §122.75(g)(1)
A. Proposed Regulation and Rationale
N/A
B. Summary of Comments
N/A
C. Discussion
(1) Topographic expression
The topography of the site should be expressed via contour
mapping. Such maps are based on on-site vertical and horizontal
controls to represent all pertinent elevations and locations (i.e.,
to establish the spatial configuration of a HWMF site). Such
controls (e.g., stone monuments) are described in publications
available from the U.S. Geological Survey, U.S. Coast and Geodetic
Survey, and State Geologic Surveys for most areas of the U.S.
Topographic is indicative of the direction of ground-water flow in
an area, since unconfined flow may roughly simulate the topography.
Topography also defines surface drainage patterns, which is related
to unconfined ground-water flow conditions (e.g., flow direction).
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Drainage patterns can be correlated with bedrock distribution, the
attitude of stratiform rocks, the arrangement of surfaces of
weakness (e.g., joints and faults), and other structural features.
Topography can also reveal Karst terrain features.
Contour intervals on topographic maps are selected in relation
to the relief in the given area (e.g., smaller contour intervals
for flatter areas and larger contour intervals for highly sloped
areas). If the available contour maps do not provide the degree
of topographic detail necessary to adequately express the relief
in the given facility area (i.e., the contour interval is greater
than 2 meters) or a contour map is not available, then established
surveying methods can be employed to obtain the data needed to
construct topographic maps for portions of of the site area where
it is needed (e.g., La nee, 1961, Chapter 16).
(2) Characterizing unconsolidated earth materials
Knowledge of the properties of the unconsolidated earth
materials in the site area is necessary to determine the locus of
migration of a facility discharge to reach the uppermost aquifer.
Also, properties of any unconsolidated materials should be
ascertained as a sound engineering practice where such materials
will be subject to loads or used as a functioning part of a
constructed facility. The type of material (e.g., clay, mud,
sand, gravel) and its uniformity (i.e., areal extent and thickness)
in the area of the site can be established from information obtained
from existing and/or new borings. Records of existing boring data
may be obtained from governmental agencies (e.g., State Geological
Survey) or from private sources (e.g., drilling and boring
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contractors and well drillers). Material type can be identified
in the field by qualifed professionals and in the laboratory by
instrumental methods (e.g., Asphalt Institute, 1969, pp. 189-190).
Determinations of specific properties (e.g., permeability, porosity,
and fracturing) of these materials, coupled with their uniformity
and distribution, yields information which can be applied in
predicting the likelihood and preferential path of a facility
discharge to ground water. In such predictions, the attainment of
field capacity in the uppermost earth materials must be accounted
for. (Methodology for determining or describing permeability,
porosity, and fracturing are discussed further under "Characterizing
consolidated rock").
Borings can be drilled using various methods, each method
affecting the degree of disturbance (reliability) of the obtained
earth material sample (e.g., Lahee, 1961 / pp. 602-607; Johnson,
1975, pp. 163-166). Correlation of data from boring samples is
used to construct subsurface maps to define geologic structure.
This can be accomplished through comparisons of analyses of field
samples and through other surveying (logging) techniques, such as
electrical logging and micrologging, sonic logging, and radioacitve
logging (e.g., Lahee, 1961, pp. 611-628).
unconsolidated earth materials (i.e., soils) may serve as a
functioning part of a constructed facility and may be subject to
loads. For this reason, swelling, settlement (i.e., compressibility)
and plasticity of these materials should be determined.
Swelling (or shrinking) phenomena refer to volume change
deformations which occur in soils, independent of any externally
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applied load (Asphalt Institute, 1969, p. 14). Swelling and shrinking
are most pronounced in fine grained soils, especially clays. Both
swelling and shrinking processes result from a build up and release
of capillary tensile stresses within the soil's pore water and the
varying degree of affinity for water which certain clay minerals
have (e.g., Asphalt Institute, 1969, p. 14). Most high volume
change soils in the U.S. occur in belts or regions that are well
known to most soil scientists. Knowledge of the swelling (or
shrinking) properties of a given soil is used to determine the
potential effects that such natural deformations will have on the
physical integrity of a facility structure and therefore the
reliablity of its designed waste management function. Laboratory
tests are available to measure the swelling or shrinking properties
of soils (e.g., Asphalt Institute, 1969, Chapters VIII and X).
The settlement of unconsolidated earth materials arises
primarily from a change in its structure accompanied by the expulsion
of air or water, or both (Asphalt Institute, 1969, p. 13).
Compressibility and compaction are terms which denote such volume
change deformations in soil. Compressibility is influenced greatly
by soil structure and the past stress history of the deposit.
Deposits developed through sedimentation usually are more compressible
than their residual or wind-blown counterparts (Asphalt Institute,
1969, p. 13). It is important to determine the degree of settlement
a facility will cause to evaluate the potential impact to the
facility's structural integrity. Laboratory methods for determining
the relative compressibility of most soils have been devised and
are widely used (Asphalt Institute, 1969, p. 13).
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The plasticity of a material refers to its ability to be
deformed rapidly without cracking or crumbling and then maintain
that deformed shape after the deforming force has been released
(Asphalt Institute, 1969, p. 11). "This non-reversible, or plastic,
deformation is probably the sum of a large number of small slippages
at grain-to-grain contact points and minute local structural collapses
throughout the soil mass" (Asphalt Institute, 1969, p. 11).
" It has been reasoned that as the plastic deformations in a
soil become larger under the action of increasingly greater applied
loads, a reorientation of soil particles begins to take place in
certain critical zones within a soil mass. When the loads have
become sufficiently large and a sufficient number of the soil
particles in this critical zone are, perhaps, oriented parallel
to one another, the soil mass begins to fail in shear within these
critical zones. At or near this point the shearing resistance or
strength of the soil is said to have been exceeded" (Asphalt Institute,
1969, p. 11-12). Methods for determining plasticity are found in
the literature (e.g., Asphalt Institute, 1969, pp. 210-211).
Determining the plasticity of the soil, therefore, has important
implications to the structural integrity of a facility, especially
when load conditions would exceed the shearing strength. This
could lead to a rupture of "rigid" facility components resulting
in unintended discharges of waste materials.
(3) Mapping of contact surfaces
Contour mapping of the contact surface between consolidated
(i.e., bedrock) and unconsolidated earth materials is important
where leachate migration is expected to reach such a contact.
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Bedrock at this contact can act as a retarding surface upon which
ground water will accumulate forming a water table in the unconsolidated
materials above. Hence, knowledge of the contour of the contact
surface is essential to determine ground water or leachate flow
direction in the site area. Data for mapping contact zones can be
obtained through various instrumental procedures, including air
photography (e.g., Lahee, 1969, Chapters 16 and 17). Since such
contacts are hidden from view, the investigator must make use of
borings and bedrock outcrops in such studies. Contacts hidden
under surface debris may also be located by observing the
distribution of rock chips and fragments in the soil derived from
the underlying bedrock (Lahee, 1969, pp. 426-427). Contouring of
contacts employs the same principles as those for surface contouring
(e.g., establishing horizontal and vertical controls). Precision
in locating contact zones buried under a soil mantle involves
special considerations that are dependent on (1) the inclination
of the ground; (2) the thickness of the soil cover; (3) climatic
conditions; (4) the trend of the contact line; and (5) the regularity
of the contact (Lahee, 1969, p. 426). Various types of contacts
(e.g., eruptive, sedimentary) are evaluated using similar techniques,
but special considerations should be recognized in different
situations (Lahee, 1969, pp. 422-440).
(4) Characterizing consolidated rock
Where leachate migration will occur within consolidated rock,
such rock must be subject to a geologic investigation. Material
type can be determined from analysis of boring data, as for
unconsolidated materials. Porosity can be determined on boring
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(100)
samples in the laboratory by standard techniques (e.g., Freeze and
Cherry, 1979, p. 337). Such porosity determinations are applicable
to materials in both the unsaturated and saturated zones.
Permeability (i.e., hydraulic conductivity) of earth materials may
be determined by laboratory and field methods. Permeabilities of
boring samples (from the saturated or unsaturated zones) can be
determined in the lab by constant-head or falling-head permeameters,
consolidation tests, and by methods based upon grain-size
distribution (e.g., Freeze and Cherry, 1979, pp. 335-339, pp.
350-352). The accuracy of permeability values obtained are dependent
upon the nature of the material (e.g., sand and gravels) and the
degree of disturbance of the sample (e.g., cuttings versus intact
cores). For earth materials in the saturated zone, permeabilities
may be determined by field methods (e.g., piezometer tests, pumping
tests and borehole dilution tests)(Freeze and Cherry, 1979, pp.
339-350, pp. 428-430).
Where consolidated rock (bedrock) is overlain by a mantle of
unconsolidated earth materials, the relationship between these
formations must be established. Such study should consider
whether the mantle is residual (formed in situ) or -has been transported
Such knowledge can aid in determining the type of underlying bedrock
as well as in delineating the contact surface. The contact surface
may be difficult to delineate when the mantle is residual due to
the gradational effects caused by weathering processes.
Where consolidated rock lies near or is exposed at the earth's
surface, information can be obtained which is of use in predicting
leachate migration potential. Examination of the effects of weathering
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and erosion (e.g., formation of Karst features such as sinkholes)
not only helps to identify the nature of the bedrock materials
(e.g., limestone), but also reveals potential pathways for leachate
flow. It should be recognized that determining the direction(s)
of leachate flow in Karst terrain can be quite difficult due to
the randomness in the orientation of solution flow channels in the
subsurface. Conversely, Karst features may provide data on
subsurface structure, a factor which can influence leachate flow
direction (e.g., in regions where limestone strata, near the surface
of the ground, are horizontal or low-dipping, numerous sinkholes,
arranged in a row, may indicate the position and trend of faulting)
(Lahee, 1961, p. 365). Karst features can often be identifed on
topographic maps available from the sources mentioned earlier.
Knowledge of fractures (i.e., joints and faults) in consolidated
(and unconsolidated) earth materials is crucial to any site
investigation for predicting the potential migration of leachate
(or gaseous) discharges from a HWMF. A fault may be defined as a
fracture along which there has been slipping of the contiguous
masses against one another (Lahee, 1961, p. 222). Sblid rocks or
unconsolidated sands, gravels, etc. may be dislocated in this way.
A fault normally dies out at its two ends. Measured displacements
vary from microscopic to many miles, and in length faults range
from microscopic to hundreds of miles (Lahee, 1961, p. 223).
Various kinds and degrees of displacement are possible depending
upon the directions and intensities of the causative forces.
Faults are classified according to: (1) the nature of their
displacement; (2) their distribution; and (3) their relations to
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disrupted bedding or other parallel structures (Lahee, 1961, pp.
232-245). Evidences for faulting can be obtained by observing
slickensides or other marks of slipping which have been exposed
(i.e., by observing the rock structures on the two sides of the
faults) and by examination of topographic expression. Methods for
making such observations appear in the literature (e.g., Lahee,
1961, pp. 245-268).
Joints are well defined cracks in a rock, where there has
been no or only a very small amount of slippage between the blocks.
Joints are the most common kind of fractures in rocks. They are
important in promoting erosion since they serve as channels for
waters that cause disintegration and in glacial quarrying, and
inviting concentrated attacks by abrasive agents (Lahee, 1961,
p. 282). Joints display a great variety of characteristics and
are classified in regard to the type of force which created them
(e.g., compression, tension, torsion). Joints may occur in
unconsolidated and consolidated earth materials (e.g., clay and
shale) . Information on methods of identifying joints and
interpreting their characteristics in various geologic settings
are discussed in the literature (e.g., Lahee, 1961, pp. 270-282).
Other processes leading to cracks in consolidated rock are
fracture cleavage along certain parallel rock surfaces (minute
displacements in which the blocks are thin sheets); and brecciation
(resulting in rock which is intersected by closely spaced joints).
Descriptions of field identification of these features are given
in the literature (e.g., Lahee, 1961, pp. 282-286).
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The location and character (e.g., type, age, activity,
displacement magnitude and direction) of fault zones must be
investigated for potential adverse impacts to HWMF operations
(e.g., potential to impair a facility's structural integrity or
causing unfavorable or undefinable routing of a facility discharge).
Information on the locations of fault zones is available from the
USGS (e.g., N.A. Howard, et al, 1978).
In investigating consolidated rock, it is important to
understand the relationships between adjacent consolidated formations
(in both vertical and horizontal directions). Such relationships
could have a bearing on the pathway of a facility discharge migrating
in ground water (e.g., a sandstone aquifer overlying a relatively
impermeable igneous rock) and should be determined through standard
geological methods (e.g., examining boring samples and electrical
logging). Another example is the changing earth material
characteristics associated with transgression and regression of
sediment deposits in coastal areas or piedmont deposition by rivers
(Lahee, 1961, pp. 77-82). Such depositional processes result in
changing characteristics (e.g., permeability and porosity) in
both vertical and horizontal directions. Also, unconformities
(i.e., interuptions in the expected sedimentary sequence due to
erosion) must be noted, as they can affect the predicting of
discharge migration (e.g., through lateral variations in texture,
porosity and permeability). Methods for field interpretation of
data for sedimentary, igneous and metamorphic rocks (and their
inter-relationships) are presented in the literature (e.g., Lahee,
1961, Chapters 5-9).
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In order to describe the position (i.e., the attitude) of an
earth material formation, its "dip" (the maximum angle of slope of
the surface) and its "strike" (the direction of the intersection
of the surface with any horizontal plane) must be measured.
Determination of attitude can be applied to different types of
earth material formations (e.g., consolidated and unconsolidated)
and can also be used to measure contortions or structural features
within these formations (e.g., folds, fault faces, plunging folds).
Knowing the attitude of an earth material formation and the
characteristics of the material (e.g., thickness, permeability,
porosity, fracturing, etc.) is essential in predicting the fate of
a discharge from a HWMF. Field methods for determining attitude
are well established geological investigation procedures (e.g.,
Lahee, 1961, pp. 748-752, Chapters 15-16).
In order to predict the fate of a facility discharge,
information must be obtained to determine the ground-water
flow direction and rate. An early step in this process is to
determine ground-water elevations (i.e., hydraulic heads) in order
to construct a water table or po tentiometrie surface contour map.
This is accomplished through the installation of piezometers which
are narrow wells which measure the hydraulic heads at given
points in an aquifer. Methods of designing and installing
piezometers are presented in the literature (e.g., Fenn, 1977, pp.
86-90). Hydraulic head data can be measured by various techniques
(e.g., National Water Well Association, 1975, pp. 116-117). In
order to determine the directions of ground-water flow, several
piezometers must be installed. By obtaining hydraulic head data
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from several piezometers, it is possible to contour the positions
of equal hydraulic head by constructing equipotential lines.
Then, flowlines can be constructed perpendicular to the equipotential
lines (in the directions of the maximum potential gradient), forming
a flow net. Detailed instruction on flow net construction is
presented in the literature (e.g., Freeze and Cherry, 1979,
Chapter 5). Flow net analysis, performed on a periodic basis, can
reveal changes in flow directions induced by natural or human
causes (e.g., ground-water mounding beneath a HWMF, ground-water
depression due to pumpage, and changes in amounts of natural
recharge). The interpretation and usefulness of flow nets of
regional ground-water flow is discussed in the literature (e.g.,
Freeze and Cherry, 1979, Chapter 6).
New borings or new wells drilled to gather subsurface data
during a site investigation must be properly "abandoned" after
serving their purpose. Such holes, if not filled (or plugged and
sealed, if necessary), may become paths for contaminant migration
to ground water from the land surface and/or via interaquifer
exchange. Ground-water contamination through such mechanisms has
been reported in the literature (e.g., Gass, et al, 1977). Methods
to properly fill, plug and seal wells (e.g., plugging with cement,
sand and cement grout, and concrete) are explained in various
publications (e.g., National Water Well Association, 1975, pp.
133-142; Snith, 1976, Chapter 10).
Site investigations, through field surveys, must locate and
describe all existing excavations, borings, wells or other ground-water
collection devices within the "zone of containment" of facility
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discharges. This information is needed when predicting the fate
of facility discharges with respect to potential impacts upon
ground-water supplies and the effects of withdrawals on the migration
pattern of a discharge plume (e.g., effects of a pumping supply
well on plume geometry and migration rate).
D. Regulatory Language
(g) Site Investigation Requirements. Bach applicant for a
permit for a hazardous waste facility shall investigate the site
and environs of the storage, treatment, or disposal activity and
establish permanent on site vertical and horizontal controls to
allow all elevations and locations to be surveyed, expressed, and
plotted with reference to USGS and USC&GS horizontal and vertical
controls.
(1) With respect to geologic and hydrologic factors;
(i) Surface topography shall be surveyed with sufficient
accuracy to allow the plotting of surface contours at a contour
interval not greater than two meters over an area extending at
least forty meters beyond any proposed construction activity,
including excavation or filling, or any area where leachate will
migrate within ten meters of the ground surface.
(ii) unless reliable boring data is available from previous
investigations, sufficient borings shall be made in unconsolidated
earth materials in the vicinity of the site and the zone of leachate
or gaseous migration to characterize or verify the characterization
of unconsolidated earth materials with respect to type of material,
uniformity, permeability, porosity, and fracturing. In addition,
where such materials will be subject to loads or used as a
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functioning part of a constructed facility; swelling, settlement,
and plasticity shall be characterized or verified.
(iii) Where leachate migration will reach the contact surface
between unconsolidated and consolidated earth materials, the contact
surface of consolidated rock shall be surveyed with sufficient
accuracy to allow the plotting of the contact surface at a contour
interval of not greater than four meters.
(iv) Where leachate migration will occur within consolidated
rock, the effected consolidated rock shall be characterized by
geologic investigation with respect to type of material, permeability,
porosity, relationship to any overlying mantle of unconsolidated
materials, relationship to adjacent consolidated materials,
degree of weathering including the formation of karst zones, degree
of fracturing, the location and character of fault zones, and
attitude.
(v) Ground water elevations shall be determined with sufficient
accuracy to allow the plotting of water table contours at a contour
interval of not greater than two meters beneath the site where
ground water mounding may or will occur due to discharge from the
facility, and in any area where ground water affected by leachate
will migrate within ten meters of the ground surface. Beyond the
above described areas, sufficient ground water elevation data
shall be obtained to construct a ground water flow net for any
given set of conditions of discharge to the ground water, withdrawal
or discharge from the ground water, and recharge of the ground
water which may occur prior to, during, or after the active operation
of the facility.
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(vi) To the extent that new borings are made or new wells are
installed to obtain the data necessary to characterize or verify
the character of earth materials or the ground water within and
flowing through such earth materials, boring holes and wells shall
be filled and, if necessary, plugged and sealed to avoid creating
new paths for fluid migration unless the hole or well will be
maintained as a ground water sampling well in accordance with
Subpart F.
(vii) All existing excavations, borings, or wells or other
ground water collection devices within the zone of containment
shall be located by field survey, and described in detail.
ISSUE: "Climatologic Factors" - §122.25(g)(2)
A. Proposed Regulation and Rationale
N/A
B. Summary of Comments
N/A
C. Discussion
Climatologic factors must also be considered when performing
a site investigation. Knowledge of seasonal variation in ambient
temperatures (including the average monthly temperature and the
extremes during any month) are helpful in determining the likelihood
of contaminant movement to or through earth materials. Temperatures
low enough to cause freezing of the uppermost earth materials may
temporarily retard infiltration or elevated temperatures in the
location of a facility may produce a preferential route of liquid
migration. Wind conditions (including the average number of days
in any direction and at any velocity range for which data exists,
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and the direction and velocity of expected extremes) should be
determined. Such data is used to predict migration patterns of
any gaseous emissions from a HWMF. Seasonal variation in the
type, duration, intensity, and amount of precipitation (including
monthly averages and the expected extremes during any month) should
be ascertained since such data are needed to estimate leachate
formation for contaminant migration predictions. The required
climatological data is available from the U.S. Weather Bureau for
all localities within the U.S.
A water balance for the HWMF site area being investigated
manipulates precipitation data and other hydrologic factors -
run-off, infiltration and evapotranspiration - to determine the
amount of percolation (i.e., how much of the precipitation would
actually recharge the ground water) . Water balance determinations
should be performed using annual data and data for other intervals
which could represent operating extremes. Water balance methodology
is described in the literature (e.g., Fenn, et al, 1975; Thornthwaite
& Mather, 1955 and 1957).
D. Regulatory Language
(2) With respect to climatologic factors;
(i) The seasonal variation in ambient temperatures including
the average monthly temperature, and the extremes during any month.
(ii) The seasonal variation in wind conditions including the
average number of days in any direction and at any velocity range
for which data exists and the direction and velocity of expected
extremes.
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(iii) The seasonal variation in the type, duration, intensity,
and amount of precipitaion including both monthly averages and the
expected extremes during any month.
ISSUE: Geographic Factors - §122.25(g)(3)
A. Proposed Regulation and Rationale
N/A
B. Summary of Comments
N/A
C. Discussion
See the preamble at 46 FR 11152
D. Regulatory Language
(3) With respect to geographic factors;
(i) The type of land use including but not limited to:
(A) the associated densities of human population living,
working, or passing through the area.
(B) the associated density of animal population living in
or passing through the area.
(C) the associated intensity of use for the production of
food chain crops.
( ii) The controls over land use and the manner in which such
controls are implemented or are to be implemented.
(iii) Projected future land use based on trends in land use,
existing or developing plans to modify the land use.
ISSUE; Special requirements based on land disposal facility class
- §122.25(g)(4)
A. Proposed Regulation and Rationale
N/A
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(Ill)
B. Summary of Comments
N/A
C. Discussion
D. Regulatory Language
(4) With respect to the following special requirements based
on land disposal facility class:
(i) An applicant for a permit for a Class A land disposal
facility must investigate the entire aquifer to which discharge
will occur and within which leachate will migrate and establish,
based on reliable reference data or independent field investigation,
that;
(A) no part of the aquifer is now or will in the future be
used as a source of water supply for domestic, agricultural,
industrial, or commercial uses.
(B) no migration can occur from the aquifer to any other
aquifer.
(ii) An applicant for a permit for a Class B land disposal
facility must investigate the entire portion of the aquifer to
which discharge will occur and within which leachate will migrate
(which may be equivalent to or inclusive of the zone of containment)
and establish, based on reliable reference data and/or independent
field investigation, that;
(A) no part of the portion of the aquifer is now or will in
the future be used as a source of water supply for domestic,
agricultural, industrial, or commercial uses.
(B) no migration can occur from the portion of the aquifer to
any other portion of the aquifer or to any other aquifer.
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(ill) An applicant for a permit for a Class C land disposal
facility must investigate in detail each location of ground water
withdrawal or collection for use, referencing well logs or
construction records when available, with respect to the type of
well or other ground water collection device including;
(A) the age of the well or collection device, the materials
of construction, and the location of casings, screens, seals,
plugs, etc.
(B) the zone of collection or withdrawal.
(C) the rate of ground water collection or withdrawal.
(D) the possible yield of the well or other ground-water
collection device.
(E) the actual use of the collected or withdrawn ground
water.
(iv) An applicant for a permit for a Class D land disposal
facility must, in addition to the requirements of paragraph
( iii) for any ground water use other than public drinking water,
investigate each location of ground water withdrawal or collection
for use as public drinking water, referencing well logs or
construction records when available, with respect to the type of
well or other ground water collection device including;
(A) the age of the well or collection device, the materials
of construction, and the location of casings, screens, seals,
plugs, etc.
(B) the zone of collection or withdrawal.
(C) the rate of ground water collection or withdrawal.
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(D) the potential yield of the well or other ground water
collection device.
(E) the physical potential yield of the aquifer to
additional wells or other ground water collection devices in the
same zone of withdrawal.
( F) the treatment provided prior to distribution of the
ground water for use.
(v) An applicant for a permit for a Class E land disposal
facility must, in addition to the requirements of paragraph (iii)
for any ground water use other than public drinking water and the
requirement of paragraph (iv) for any ground water use as public
drinking water, investigate each location of ground water withdrawal
or collection for use as private drinking water, referencing well
logs or construction records when available, with respect to the
type of well or other ground water collection device including;
(A) the age of the well or collection device, the materials
of construction, and the location of casings, screens, seals,
plugs, etc.
(B) the zone of collection or withdrawal.
(C) the rate of ground water collection or withdrawal.
(D) the possible yield of the well or other ground-water
collection device.
(E) the physical potential yield of the aquifer to
additional wells or other ground water collection devices in the
same zone of withdrawal.
(F) the alternative sources of public or private drinking
water available to the well owner.
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6. Description of monitoring and modelling - 122.25(h)
A. Proposed Regulation and Rationale
N/A
B. Summary of Comments
N/A
C. Discussion
See the preamble at 46 FR 11153. Note that the preamble
discussion erroneously refers th §122.25(g).
D. Regulatory Language
(h) A description of the monitoring and, if planned or required,
the modeling proposed to comply with Subpart F (Ground Water and
Gaseous Bnission Monitoring) or to verify or refine the projections
of the transverse, lateral, and vertical extent of the migration
of and the mass of contaminants in the leachate, the lateral and
vertical extent of the migration of gases, and the mass of gaseous
emissions.
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III. REFERENCES
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24. Moore, C., 1980, Landfill and Surface Impoundment Performance
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3. Feather, Keith, 1980. Removal Rate of Surface Oriented Zinc
from Coal Bottom Ash in Aqueous Solutions. Thesis
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6. Ham, R., M. A. Andersonn, R. Stegman, and R. Standforth,
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Leachate Migration in the Unsaturated Zone
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Generation and Attenuation at Landfill Sites. Land
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Essex .
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Variability of Field-Measured Soil Water Properties.
Hilgardia, 42: 206-215.
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