001 D85100
5251
ALTERNATE CONCENTRATION LIMIT GUIDANCE
BASED ON §264.94(b) CRITERIA
PART I
INFORMATION REQUIRED IN ACL DEMONSTRATIONS
DRAFT
Office of Solid Waste
Waste Management and Economics Division
U.S. Environmental Protection Agency
401 M Street, S.W.
US. Environment,! Fraction Agency Washington, D.C. 20460
230 South Doarbom £ treat
Chicago, Illinois 60604 June 1985
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CONTENTS
Page
Executive Summary ES-1
I. Introduction 1
II. Physical and Chemical Characteristics of the Waste
Constituents 11
III. Hydrogeological Characteristics 16
IV. Ground-Water Flow Direction and Quantity 22
V. Engineered Characteristics of the Site 29
VI. Patterns of Rainfall 36
VII. Proximity of Surface Water and Ground-Water Users 40
VIII. Current and Future Uses of Ground Water and Surface
Water in the Area 46
IX. Existing Quality of Ground Water and Surface Water
and Other Sources of Contamination 51
X. Potential Health Risks 57
XI. Potential Damage to Wildlife, Vegetation, Agriculture,
and Physical Structures 66
XII. Persistence and Permanence of Potential Adverse
Effects 80
XIII. Institutional Ground-Water Use Restrictions 84
XIV. Summary and Conclusions --. 87
References 91
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EXECUTIVE SUMMARY
The hazardous waste regulations under the Resource Conservation
and Recovery Act (RCRA) require owners and operators of hazardous
waste facilities to utilize design features and control measures
that prevent the leaking of hazardous waste into ground water.
Further, all regulated units (i.e., all surface impoundments,
waste piles, land treatment units, and landfills that received
hazardous waste after July 26, 1982), are also subject to the
ground-water monitoring and corrective action standards of 40
CFR Part 264, Subpart F. The ground-water protection standard
(GWPS) under Subpart F (40 CFR 264.92) requires the Regional
Administrator to establish in the facility permit, for each
hazardous constituent entering the ground water from a regulated
unit, a concentration limit beyond which degradation of ground-
water quality will not be allowed. The concentration limits
determine when corrective action is required.
There are three possible concentration levels that can be
used to establish the GWPS:
1. Background levels of the hazardous constituents,
2. Maximum concentration limits listed in Table 1 of
Section 264.94(a) of the regulations, or
3. Alternate concentration limits (ACL).
The first two levels are established in the facility permit unless
the facility owner or operator applies for an ACL.
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To obtain an ACL, a permit applicant must demonstrate
that the hazardous constituents detected in the ground water will
not pose a substantial present or potential hazard to human health
or the environment at the ACL levels. ACLs are granted through
the permit process under Parts 264 and 270 and are established
in the context of the facility GWPS. This document provides
guidance to RCRA facility permit applicants and writers concerning
the establishment of alternate concentration limits (ACLs).
The factors that are used to evaluate ACL requests, or demon-
strations, are listed in Section 264.94(b) of the regulation.
These factors are:
1. Potential adverse effects on ground-water quality
considering:
0 The physical and chemical characteristics of the
waste in the regulated unit, including its potential
for migration,
0 The hydrogeological characteristics of the facility
and surrounding land,
0 The quantity of ground water and the direction of
ground-water flow,
0 The proximity and withdrawal rates of ground-water
users,
0 The current and future uses of ground water in the
area,
0 The existing quality of ground water, including
other sources of contamination and their cumulative
impact on the ground-water quality,
0 The potential for health risks caused by human
exposure to waste constituents,
0 The potential for damage to wildlife, crops, vegetation,
and physical structures caused by exposure to waste
constituents,
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0 The persistence and permanence of the potential
adverse effects, and
2. Potential adverse effects on hydraulically-connected
surface water quality, considering:
0 The volume and physical and chemical characteristics
of the waste in the regulated unit,
0 The hydrogeological characteristics of the facility
and surrounding land,
0 The quantity and quality of ground water and the
direction of ground-water flow,
0 The patterns of rainfall in the region,
0 The proximity of the regulated unit to surface waters,
0 The current and future uses of surface waters in the
area and any water quality standards established for
those surface waters,
0 The existing quality of surface water, including
other sources of contamination and the cumulative impact
on surface-water quality,
0 The potential for health risks caused by human
exposure to waste constituents,
0 The potential for damage to wildlife, crops,
vegetation, and physical structures caused by exposure
to waste constituents, and
0 ' The persistence and permanence of the potential
adverse effects.
Information on each of these criteria is not required in every
ACL demonstration because each demonstration requires different
types and amounts of information, depending on the site-specific
characteristics. A separate chapter of this document is devoted
to each of these criteria. The criteria are briefly discussed,
along with the type, quantity, and quality of information that
should be provided depending on the site-specific characteristics.
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Chapter I is an introduction to the ACL guidance. This chapter
discusses the purpose, intent, and organization of the document.
It also defines an ACL and describes how ACLs fit into the RCRA
permitting process. A major portion of the information required
for an ACL demonstration is also required for a RCRA Part B permit
application. This chapter points out the overlap between these
two informational requirements.
Chapter II discusses the data that the permit applicant
must submit on the physical and chemical characteristics of the
waste constituents. The permit applicant should already know about
the hazardous constituents present in the ground water at the
facility by the time an ACL demonstration is submitted. Additional
ground-water sample collection is probably not necessary for ACL
purposes. The permit applicant should submit the hazardous
constituent information in terms of three-dimensional represen-
tations of constituent concentrations. The permit applicant
needs to submit data on any factors relating to the stability
and mobility of the waste constituents in the ground water.
These factors may include density, solubility, vapor pressure,
viscosity, and octanol-water partitioning coefficient of each
constituent for which an ACL is requested.
Chapter III discusses the data needed to describe the
hydrogeologic properties of the site. The geologic and hydrologic
properties of each of the individual strata beneath a site that
are likely to affect ground-water contaminant migration should
be submitted in the ACL demonstration. Much of the data should
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already be available to the permit applicant if other RCRA per-
mitting requirements have been fulfilled. The important geologic
attributes of a site include:
1. Soil and rock characteristics,
2. Geologic structure, and
3. Geomorphology and topography.
In ACL demonstrations where soil and other matrix attenua-
tion mechanisms are used to 'justify that exposure to ground-water
contaminants will be minimal or prevented, data on attenuative
properties must be discussed. The near-surface stratigraphic units
located in the zone of saturation must be characterized for the
hydrologic parameters of hydraulic conductivity (vertical and
horizontal), specific yield (unconfined aquifer) or specific stor-
age (confined aquifer), and effective porosity.
Chapter IV discusses ground-water quantity and flow direction
which are used to assess contaminant transport. The general RCRA
permit requirements specify the submittal of ground-water flow
information. This data should be adequate for ACL demonstration
purposes and the permit applicant probably will not have to
collect additional field data. Ground-water quantity can be
estimated from hydrologic parameters such as specific yield
for unconfined aquifers and specific storage for confined aquifers.
The use of Darcy's law for determining ground-water flow quantity
is acceptable.
The hydrogeologic portion of the ACL demonstration must
include an adequate description of both horizontal and vertical
ground-water flow components. The horizontal ground-water flow
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description should include a flow net based on ground-water eleva-
tion measurements taken from monitoring wells or peizometers,
screened at the same elevation in the same saturated zone.
Facilities should have several nested piezometers for vertical
gradient determinations. Facilities that are located in environ-
mental settings that exhibit temporal variation in ground-water
flow direction should define the extent to which the flow change
occurs.
Chapter V discusses man-made hydraulic barrier systems
that may be used to augment natural attenuation. Although
man-made barriers are not listed in the Section 264.94(b)
criteria, they are discussed in this guidance document because
they can be an important factor in assessing exposure to hazardous
constituents. Ground-water control structures that can be
used to justify ACLs are plume management mechanisms that
either steer contaminated ground water away from exposure
points or reduce the ground-water transport velocity so that a
natural attenuation mechanism can reduce contaminant concentrations
to acceptable levels. The engineered ground-water control
measures that will be considered include low permeability
barriers such as slurry walls. These measures can be used
either separately or together to prevent or limit exposure to
the contaminated ground water. Design and construction considerations
must be evaluated in order to assess the adequacy of all subsurface
barrier systems. In cases where ground-water control structures
are proposed for preventing or limiting exposure, the applicant
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must submit a plan detailing a methodology that will demonstrate
the effectiveness of the engineered system.
Chapter VI discusses the types of precipitation data that
should be submitted in an ACL demonstration. The permit applicant
should focus the discussions of precipitation around the site's
hydrologic regime. If the applicant's ACL demonstration clearly
shows that ground-water discharge to surface waters is unlikely,
then the discussion of precipitation events can be limited to
effects on infiltration and ground-water recharge. However, if
ground-water discharge to surface water is an important element
of the ACL demonstration, then precipitation events should be
related to ground-water recharge and discharge.
Chapter VII discusses the proximity of surface water and
ground-water users and the information that should be submitted
on these users. The level of information necessary to satisfy
the proximity of users requirement depends on the basis of the
ACL. If a downgradient surface water body is the primary focus
of a demonstration, then data related to the specific characteristics
of the surface water body are necessary. If the permit applicant
argues that downgradient surface water bodies are unaffected by
the ACL constituents, then general information on the distance
of the surface water bodies from the facility is necessary. In
order to assess the likelihood of exposure of current ground-water
users, every ACL demonstration must discuss the proximity of
ground-water users to the facility.
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Chapter VIII discusses the factors needed to determine
current and future uses of ground water and surface water in the
vicinity of the facility. The permit applicant should examine
pertinent aspects of both ground-water and surface water uses.
Permit applicants must submit information on the types of ground-
water uses in the vicinity of the facility, unless they can
successfully argue that no exposure to the contaminated ground
water will occur. The permit applicant should discuss the ground
water in the vicinity of the facility in terms of the three
classes discussed in the U.S. EPA Ground-Water Protection Strategy,
Surface water uses should be discussed by the permit appli-
cant if contaminated ground water can migrate to surface waters.
Surface water use information is especially critical for ACLs
based on surface water dilution.
Chapter IX is concerned with the existing quality of ground
water and surface water and other sources of contamination. In
order for "benchmark" levels of contamination to be set, the
background levels of hazardous constituents in the ground water
and surface water must be established. For ACL purposes,
background water quality is the quality that would be expected
to be found if the facility's regulated unit(s) was not leaking
contaminants. Background monitoring wells must yield ground-water
samples from the uppermost aquifer representative of the quality
of ground water that has not been affected by leakage from a
facility's regulated unit. Background surface water quality
need only be assessed in cases where surface waters are likely
to receive contaminated ground-water discharges.
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The permit applicant should also examine the possibility of
other sources of contamination if the upgradient waters in the
vicinity of the facility are contaminated. This will give the
permit applicant information for assessing cumulative impacts
associated with any contamination emanating from the facility.
Chapter X discusses the health risk assessment. A health
risk assessment should be submitted if human exposure to the
ground-water contaminants is not prevented. The purpose of the
health risk assessment is to determine acceptable concentrations
at a point of exposure for the constituents for which ACLs are
requested. There are two major components to a determination of
health risks. First, the applicant must perform an exposure
assessment characterizing the populations that may be exposed
to the contaminants, and the potential pathways to human exposure.
Second, the health effects associated with exposure to each
contaminant and mixture of contaminants must be examined.
The potential point of exposure to the ground-water
contaminants is assumed to be at the facility waste management
boundary unless use restrictions have been implemented. If
there are ground-water use controls beyond the facility waste
management boundary that will prevent use of the affected resource,
the potential ground-water exposure point will be at any point
downgradient of the waste management boundary. In order to
designate the property boundary as the point of exposure, a
facility must ensure that there are permanent prohibitions on
the use of on-site ground water as a source of drinking water or
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for any other use that would not be protective of human health
or the environment. These restrictions must apply to the owner
of the facility, as well as to any successive owners. In order
to designate a potential point of exposure beyond the facility
property boundary, ground-water use restrictions must be in
place off-site to prevent any use of the contaminated ground
water. The point of exposure for surface water bodies is assumed
to be the water body closest to the facility in the pathway of
contaminant migration.
If human exposure can occur, the permit applicant is responsible
for providing information on the health effects of the hazardous
constituents present in the ground water for which ACLs are
requested. The health risk assessment should be based on conservative
health assumptions. The applicant should distinguish between
ground-water contaminants having threshold (toxic) and non-threshold
(carcinogenic) effects. The Agency is currently compiling toxicity
information on many of the hazardous constituents and this
information should be useful in preparing ACL demonstrations.
Chapter XI discusses data that should be submitted on the
potential impacts to the environment. The initial step in
assessing possible environmental impacts is to determine the
probable exposure pathways for hazardous constituents to reach
environmental receptors. For ACL purposes, the receptors of
concern include wildlife and vegetation in aquatic and terrestrial
environments; agricultural crops, products, and lands; and physical
structures. The permit applicant must examine the potential
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impacts to all of the receptors discussed above if exposure to
hazardous constituents is likely to occur. Otherwise, the permit
applicant should discuss specific data that support no probable
exposure and explain why the potential environmental impact
assessment is not needed. if there is a likely pathway for
wildlife and vegetation to become exposed to contaminants, then
environmental toxicity factors should be examined.
The permit applicant is responsible for surveying the area
near the facility and determining the presence of any endangered
or threatened species in terrestrial or surface water environments.
If any endangered or threatened species are in the area, then
the potential impacts of the contaminated ground water on the
species, including critical habitat impacts, should be discussed.
Physical structures can also be adversely affected by hazardous
constituents in the ground water. The determination of potential
impacts to and contamination of physical structures in the area
around the facility requires the examination of exposure pathways,
waste characteristics, and construction materials and techniques.
Physical structures of concern include buildings, buried cables
and pipes, railroad beds, roads, parking areas, and machinery.
Chapter XII discusses data needed to determine the persistence
of the contaminants in the environment and the permanence of the
adverse effects. The applicant should discuss the process by which
each ACL constituent will degrade, either from a ground-water
perspective, surface water perspective, or a combination of both
depending on the site-specific situation. Information on the
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permanence of the adverse effects resulting from exposure to the
ACL constituents will be required only if the ACL demonstration
is based on an acceptable level of exposure -to receptors. Information
on permanence is needed to determine the long-term effects associated
with exposure to the ACL constituents.
Chapter XIII discusses institutional controls that can be
used to prevent or minimize exposure by controlling access to the
contaminated ground water. Institutional ground-water use controls
are not specifically listed in the Section 264.94(b) criteria
but they can be important factors in assessing exposure to hazardous
constituents. However, they are discussed in this document
because use controls are frequently implemented in situations
concerning ground-water contamination. The permit applicant
must submit evidence supporting all use controls that are being
proposed as a means of preventing exposure. The use controls
must prevent contact with the contaminated ground water as well
as encompass the existing and projected areal extent of the
ground-water contamination plume. The institutional controls
used to prevent exposure to the ACL constituents must contain
some type of enforcement provision to guarantee the existence of
the use control for as long as the ground-water protection standard
is exceeded.
Chapter XIV presents the summary and conclusions of the ACL
guidance document. This chapter emphasizes the independent nature
of each ACL demonstration and presents the time frame of the ACL
process. Information on each of the criteria discussed in this
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guidance document is not required in every ACL demonstration.
Each ACL demonstration must reflect site specific environmental
properties and waste characteristics. As part of the ground-water
protection standard, an ACL is in effect during the compliance
period. If, at the end of the compliance period, the owner or
operator is engaged in a corrective action program, the compliance
period is extended until the owner or operator can demonstrate
that the GWPS, which may contain ACLs, has not been exceeded for
a period of three consecutive years.
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Chapter I
Introduction
Hazardous waste facilities permitted under the Resource
Conservation and Recovery Act (RCRA) regulations (40 CFR Parts 264
and 270) are required to be designed and operated in a manner
that will prevent ground-water contamination. Therefore, the
concentration limits for hazardous constituents detected in
ground water at RCRA facilities (the "ground-water protection
standards") will generally be set at background levels or RCRA
adopted maximum concentration limits. These maximum concentration
limits are established for 14 hazardous constituents, as set by
the National Interim Primary Drinking Water Standards, and are
listed in Table 1 of Section 264.94(a) of the regulations.
Variances are available from these standards if the permit applicant
can demonstrate that the constituents will not pose a substantial
present or potential hazard to human health or the environment.
In such cases, the applicant may ask for an "alternate concentration
limit" (ACL) under Section 264.94 of the regulations. This
section of the regulations lists 10 criteria to be applied in ACL
demonstrations.
This guidance document serves to elaborate on these 10 criteria
and thus provide guidance to permit applicants seeking ACLs and
permit writers evaluating ACL demonstrations. The document is
divided into 14 chapters which include an introduction, an
explanation of each of the 10 criteria in the regulation, a
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discussion of the use of man-made barriers, a review of the use
of institutional ground-water use controls, and a conclusion.
This document is intended to be used by RCRA permit applicants
and permit writers. It may also be useful for Record of Decision
preparations pursuant to the EPA Superfund program (CERCLA) or
for State permit writers. In applying this guidance for Superfund
or for State permits, the users must be cognizant of any differences
between the requirements of their programs and the RCRA regulations
and permitting programs.
Alternate concentration limits are discussed in the RCRA
Standards for Owners and Operators of Hazardous Waste Treatment,
Storage, and Disposal Facilities under Subpart F: Ground-water
Protection (U.S. EPA 1982a). ACLs are granted through the permit
process under Parts 264 and 270. The permit applicant and reviewer
should become familiar with the ground-water protection regulations
and supporting preamble before proceeding with this guidance.
The Subpart F Ground-Water Protection regulations and applicable
parts of the preamble to the July 26, 1982, Federal Register are
reprinted in Appendix 1 (U.S. EPA 1982b). These documents will
give the permit applicant and reviewer a proper perspective on
both the requirements and the intent of the ground-water protection
regulations.
Alternate concentration limits are established in the context
of the facility ground-water protection standards. The standard
establishes a limit on the amount of ground-water contamination
that can be allowed without endangering public health or the
environment. The ground-water protection standard is an essential
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element in the Agency's strategy to ensure that public health and
the environment are not endangered by any contamination of ground-
water resulting from the treatment, storage, or disposal of
hazardous wastes. As such, the standard will indicate when
corrective action will be necessary to control contamination that
has emerged from a regulated unit.
The principal elements of the ground-water protection standard
are discussed in Section 264.92. For each hazardous constituent
entering the ground water from a regulated unit, a concentration
limit must be established that will serve as a limit beyond which
degradation of ground-water quality will not be allowed. There
are three possible concentration levels that can be used to
establish the ground-water protection standard:
1. Background levels of the constituents,
2. Maximum concentration limits listed in Table 1 of Section
264.94(a), or
3. Alternate concentration limits as described in this guidance.
Section 264.94 establishes the criteria that must be used to
specify concentration limits. The approach used by the regulation
is to adopt widely accepted environmental performance standards,
when available, as concentration limits. However, because of the
lack of currently available standards, specific concentration
limits for only a few specific constituents have been included in
the regulations. These limits are those standards that were
established by the National Interim Primary Drinking Water Regulations,
If a constituent is not one of these compounds, then no degradation
beyond background water quality becomes the standard. In such
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cases, the concentration limit should be set at background.
However, a specified amount of degradation beyond background levels
can be allowed by establishing alternate concentration limits.
Alternate concentration limits can be established only after the
applicant successfully shows that these concentrations of
hazardous constituents will not adversely affect public health or
the environment.
The criteria that the applicant must use when preparing
requests for ACLs are specified in Section 264.94(b). Essentially,
the applicant must be able to demonstrate that as long as the
concentration of the hazardous constituent does not exceed the
requested alternate concentration limit at the point of compliance,
no substantial current or potential hazards to human health or the
environment will result.
An ACL demonstration is essentially a risk assessment and risk
management process in which a determination of acceptable ground-
water contamination is made. Site specific information, such as
local hydrogeological characteristics, the facility's waste
constituents, and local environmental factors, is needed to assess
the potential impact of each hazardous constituent present in the
ground water on human health or the environment. There are two
approaches that an applicant can take in an ACL demonstration:
1. There will be no exposure to the ground-water
contaminants, or
2. The exposure to the ground-water contaminants will
be at concentration levels that do not pose a substan-
tial current or potential hazard to human health and the
environment.
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In the second approach, the ACL demonstration depends upon
determining concentration levels of the ground-water contaminants
that do not pose a substantial current or potential hazard to human
health and the environment at a potential point of exposure.
The ACLs for the ground-water contaminants are derived from
these acceptable concentrations and are set at the facility's
point of compliance.
All Agency published acceptable exposure levels for the
protection of human health and the environment can be used as ACLs
without going through elaborate exposure pathway analyses or fate
and transport modeling. For example, a health based acceptable
ground-water exposure concentration for a constituent detected in
the ground water can be used as an ACL at the point of compliance.
However, the acceptable level used as an ACL may need to be modified
to include an assessment of any cumulative effects associated with
exposure to the ACL constituent. It is anticipated that the Agency
will periodically publish and update a list of acceptable dose
levels that can be used by permit applicants in preparing ACL
demonstrations.
The type and amount of information needed for an ACL
demonstration depends on site-specific characteristics and which
approach (either no exposure or acceptable risk) is chosen. Both
approaches require information on the physical and chemical charac-
teristics of the waste, flow direction and quantity of the ground
water, and hydrogeological characteristics of the site. An ACL
demonstration based on the second approach requires additional
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information. Depending on the basis for the demonstration, one
or more of the following must be addressed in greater detail:
1. Current and future uses of ground water and surface
water (if applicable),
2. The proximity of the user of the water resources to the
facility,
3. The existing ground-water quality,
4. The potential human health risks and environmental
damage from exposure to the contaminants, and
5. The permanence of the potential adverse effects resulting
from exposure to the contaminants.
For any of the above factors that are not part of the ACL basis,
justification is required to explain why they do not need to be
addressed. Depending on the site characteristics, either approach
may require information on the engineered characteristics of the
facility, the rainfall patterns in the area, the existing quality
of ground-water and surface water (if applicable), and any current
or future institutional ground-water use restrictions.
The ACL demonstration for each constituent must be independent,
It may cross reference many sections of the Part B Permit
Application and it will cross reference each individual ACL
constituent demonstration. Information required from the following
sections of the Part B Permit Application portion of the
regulations should be included in all ACL demonstrations:
270.14(b) General information requirements for all hazardous
waste management facilities.
(1) General description of the facility.
(2) Chemical and physical analyses of the hazardous
waste, in accordance with Part 264.
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(8) Description of the procedures, structures, or
equipment used at the facility to prevent
contamination of water supplies.
(11) Facility location information:
(i) Identification of the political
jurisdiction (e.g., county or township)
in which the facility is located,
(ii) If the facility is located in an area
listed in Appendix VI of Part 264, information
must be submitted to demonstrate compliance
with the seismic standard under §264.18(a),
(iii) Identification of whether a facility is
located within a 100-year floodplain,
(iv) Information required if a facility is
located in a 100-year floodplain.
(19) A topographic map clearly showing:
(i) Map scale (at least one inch: 200 feet)
and date,
(ii) 100-year floodplain area,
(iii) Surface waters including intermittent streams,
(iv) Surrounding land uses,
(vi) Orientation of the map,
(vii) Legal boundaries of the facility,
(ix) Injection and withdrawal wells both on-site
and off-site,
(x) Buildings; treatment, storage, or disposal
operations, or other structures,
(xi) Barriers for drainage or flood controls, and
(xii) Location of operational units within the
facility site, where hazardous waste is
or will be.
270.14(c) Additional information required for the protection of
ground water for hazardous waste surface impoundments,
piles, land treatment units, and landfills.
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(1) A summary of the interim status ground-water
monitoring data.
(2) Identification of the uppermost aquifer and
aquifers hydraulically interconnected beneath the
facility property, including ground-water flow
direction and rate, and the basis for .such
identification.
(3) Additional information to be included on the
topographic map:
(a) Delineation of the waste management area, the
property boundary, and the proposed "point
of compliance";
(b) The location of ground-water monitoring wells;
(c) The hydrogeologic information required under
§270.14(c)(2).
(4) A description of any plume of contamination that
has entered the ground water that:
(i) Delineates the extent of the plume on the
topographic map, and
(ii) Identifies the concentration of each
Part 261 Appendix VIII constituent throughout
the plume, or identifies the maximum concen-
trations of each Appendix VIII constituent
in the plume.
(7) Information needed to establish a compliance
monitoring program under §264.99:
(i) A description of the wastes previously
handled at the facility;
(ii) A characterization of the contaminated
ground water, including concentrations of
hazardous constituents;
(iii) A list of hazardous constituents for which
compliance monitoring will be undertaken
in accordance with $5264.97 and 264.99;
(iv) Proposed concentration limits for each
hazardous constituent, based on the criteria
set forth in S264.94(a), including a
justification for establishing any ACLs;
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(v) Detailed plans and an engineering report
describing the proposed ground-water
monitoring program to be implemented to
meet the requirements of §264.97; and
(vi) A description of the proposed sampling,
analysis, and statistical comparison
procedures to be utilized in evaluating
ground-water monitoring data.
The following sections of the Part B permit application could
be used in an ACL demonstration, if they apply to the site-specific
characteristics:
270.14(b)(5) General inspection requirements under §264.15(b),
if applicable to the ACL demonstration.
(13) A copy of the closure plan and the post-closure
plan, if applicable to the ACL demonstration.
(20) Additional information necessary to satisfy other
Federal law requirements under §270.3. These laws
may include:
(a) The Wild and Scenic Rivers Act (16 USC 1273),
(b) The National Historic Preservation Act of 1966
(16 USC 470),
(c) The Endangered Species Act (16 UC 1531),
(d) The Coastal Zone Management Act (16 USC 1451), or
(e) The Fish and Wildlife Coordination Act
(16 USC 661).
270.14(c)(8) Information needed to establish either a corrective
action program which meets the requirements of
§264.100, if applicable to the ACL demonstration,
or a compliance monitoring program which meets the
requirements of §264.99 and §270.14(c)(6).
The information presented in the demonstration on proposed
concentration limits is only one source that should be reviewed by
the permit writer. Independent research by the permit writer is
essential in reviewing the applicant's ACL demonstration. The
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permit writer should examine references that are listed both in
this document and in the applicant's demonstration. The reviewer
should also consult U.S. EPA headquarters for-the latest policy
guidance concerning ACLs.
The permit applicant will not receive an ACL by showing that
adverse effects on human health and the environment will be delayed.
The permit applicant should provide evidence that adverse impacts
will be prevented. A consideration that must be remembered is
that if data on which the demonstration is based is subject to
considerable uncertainty, the U.S. EPA may not establish the requested
concentration limits.
Organization of the Guidance
This document provides guidance on the specific factors
involved in the preparation of an ACL demonstration. Since ACLs
are based upon combinations of one or more criteria listed in
Section 264.94(b), a separate chapter is devoted to each of the
Section 264.94(b) criteria. Basically, the criteria are designed
around four major topics:
1. The potential for ground-water contaminant migration,
2. The quality of the contaminant plume as it migrates,
3. The current and future uses of ground water and surface water
in the area, and
4. The health and environmental effects associated with
exposure to the ground-water contaminants.
The criteria are briefly discussed, along with the type, quantity,
and quality of information that should be provided by the permit
applicant. Each chapter of this document discusses how each
criterion fits into one or more of the four main topics.
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Chapter II
Physical and Chemical Characteristics of the Waste Constituents
(§264.94(b)(l)(i) and (2)(i))
The first step in an ACL demonstration is to identify the
chemicals of concern. These "hazardous constituents" are chemicals
listed in Appendix VIII of Part 261 of the regulations that have
been detected in the ground water and may reasonably be expected
to be related to the hazardous waste facility. Once the hazardous
constituents are identified, their physical and chemical
characteristics must be determined in order to effectively model
their transport through the environment and their ultimate fate.
This chapter discusses the information that is needed to adequately
characterize the physical and chemical properties of the hazardous
constituents.
The permit applicant should already know which hazardous
constituents are present in the ground water at the facility by the
time an ACL demonstration is submitted. The Section 270.14(c)
permitting requirements specify that the permit applicant must
determine the extent of ground-water contamination when a signif-
icant increase in a ground-water contaminant occurs at the compli-
ance point. Additional ground-water sample collection and analysis
is usually not necessary for ACL purposes.
The hazardous constituents of concern during the permitting
process can be any of the 375 contaminants listed in 40 CFR Part
261, Appendix VIII. The Agency does not require sampling for
Appendix VIII substances that are unstable in ground water or for
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which no EPA-approved analytical method exists (U.S. EPA, 1984a).
An Appendix VIII determination is required whenever any leakage
from a facility's unit is detected by Section 264.98 monitoring
because it is difficult to assure the absence of particular
hazardous constituents emanating from a regulated unit simply by
recordkeeping. Wastes other than those that are currently received
might have been placed in the unit in pre-recordkeeping times.
In addition, there is the potential for unpredicted reactions
and the formation of breakdown products.
The fulfillment of the Section 270.14(c) permitting require-
ments should result in the spatial characterization of each
hazardous constituent found at the site. The permit applicant
should submit, as part of the ACL demonstration, the data gathered
to satisfy these requirements and present the information in terms
of three-dimensional representations of constituent concentrations.
The three-dimensional representation of ground-water contamination
may not necessitate three-dimensional modeling of the contaminant
plume. A two-dimensional model in the vertical and longitudinal
planes may be sufficient in many cases if the site hydrogeology
is fairly homogeneous, and if sufficient monitoring data exists
to describe the plume.
The permit applicant should also submit, as part of the ACL
demonstration, information on the chemical and physical character-
istics of the wastes in the regulated unit which was gathered
pursuant to Section 264.13. This general waste analysis provision
should result in an assessment of the ability of the waste constit-
uents to migrate based on the quantity and special characteristics
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of the waste. This data will enable the ACL reviewer to have a
better understanding of what may be expected to show up in the
ground water. Generally, additional waste constituent analyses
need not be conducted for the ACL demonstration if the applicant
has fulfilled the requirements of Section 264.13.
Several physical and chemical characteristics of hazardous
constituents are critical to the modeling of contaminant transport
in ground water. Permit applicants need to submit data on the
following characteristics of the constituents for which ACLs
are requested: density, solubility, vapor pressure, viscosity,
and octanol-water partitioning coefficient. For example, consider
a facility that is leaking a hazardous constituent at a concentra-
tion level near to or above the constituent's solubility level.
In this situation, there is a good possibility that a two-phase
plume could result. One phase would be the dissolved constituent
plume in the ground water, and the other would consist of rela-
tively pure hazardous constituent. This later phase could either
be floating on top of the water table or sinking to an aquitard,
depending on its density. The two phases would probably move at
different rates due to viscosity differences.
Even when there is only one phase present, transport modeling
results for plumes with mixtures of contaminants are dependent on
the physical and chemical characteristics of the constituents.
This is because attenuation parameters for transport models depend
on specific characteristics of the hazardous constituents. The
permit applicant should submit density, solubility, vapor pressure,
viscosity, and octanol-water partitioning coefficient values of
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the hazardous constituents in tabular form. Appendix 2 contains
an example of a summary sheet that can be used to list the important
properties of the ground-water ACL constituents.
An ACL demonstration that is based on attenuation must be
supported by data on fate-related characteristics of the ACL
constituents. The objective of any ACL demonstration is to show
either no exposure or acceptable exposure to hazardous constituents.
If a permit applicant argues that the presence of an ACL constituent
at the point of compliance presents no possibility for exposure
because it is not persistent in the ground water, then special
fate and stability related characteristics of the constituent
must be discussed in the ACL demonstration.
The stability of waste constituents in the subsurface
environment can be affected by chemical, biological, and physical
processes. Important subsurface chemically mediated processes
may involve oxidation, reduction, and hydrolysis. Important
biologically mediated processes include biodegradation and
biotransformation reactions. The subsurface physically mediated
processes can involve ion exchange, precipitation, and complexation
reactions. If the ACL demonstration is based on any of these
processes, then the results of site-specific tests should be
submitted. Most of the degradation processes depend on the
properties of contaminants as well as environmental factors such
as microbial populations, solid surfaces, and dissolved constituents
present in the ground water. Because the relevant environmental
factors are unevenly distributed in nature, degradation and
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reaction rates are not constant in ground-water environments and
must be assessed on a site-specific basis. Therefore, the use
of general information gathered from the literature will be of
limited value when assessing the stability of waste constituents.
It may be possible to group hazardous constituents that are
detected in the ground water at a facility according to stability
characteristics. If site specific tests support the grouping of
constituents, then the fate and mobility of each constituent
within a group can be based on the stability characteristics of
the most mobile and most persistent compounds in the group. This
would result in the fate and mobility coefficients for each
constituent being set at the coefficient values for the most
mobile and most stable compounds in the group. Although it is
difficult to decide on which groupings of constituents are
appropriate, the grouping of constituents can reduce the amount
of predictive modeling necessary for quantifying environmental
concentrations and exposure pathways.
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Chapter III
Hydrogeologic Characteristics
(§264.94(b)(1)(ii) and (2)(ii))
The assessment of ground-water movement near a facility is
essential to every ACL demonstration. The main route of exposure
to ground-water contaminants usually involves the movement of
the hazardous constituents through the soil to the ground water and
on to an existing or potential point of use. This chapter describes
the information needed to adequately determine the hydrogeologic
properties required for characterizing ground-water movement at
a site.
During the general RCRA permitting process, the permit
applicant is required under Section 270.14(c) to identify the
uppermost aquifer. The uppermost aquifer is defined in the
regulations as the geologic formation nearest the natural ground
surface that is an aquifer as well as lower aquifers that are
hydraulically interconnected with this aquifer within the facility's
property boundary. Saturated zones above the uppermost aquifer
are also of interest as contaminant migration pathways. Therefore,
the geologic and hydrologic properties of each of the individual
strata beneath a facility that are likely to influence ground-water
contaminant migration should be submitted in the ACL demonstration.
This information is needed to adequately characterize ground-water
transport mechanisms. Much of the data should already be available
to the permit applicant if the Section 270.14(c) requirements
have been fulfilled.
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The important geologic attributes of a facility include:
1. Soil and rock characteristics,
2. Geologic structure, and
3. Geomorphology and topography.
When describing the soil characteristics of a facility, the permit
applicant should use the Unified Soil Classification. Each soil
type beneath the site and within the areal extent of the ground-
water contaminant plume should be investigated along with soils
that are in the expected path of contaminant migration. The permit
applicant should submit data describing the thickness, areal extent,
and hydraulic properties of each soil type. The soil information
should be submitted in both tabular and graphic form. The areal
extent of soil types should be presented on a map with a scale
no greater than one inch:200 feet. Vertical profiles and cross-
sections of soil types should be provided by the applicant to
present three-dimensional perspectives of the soils.
If the applicant uses soil or other matrix attenuation
mechanisms to justify a claim of no exposure or minimal exposure
to the ground-water contaminants, the applicant must submit
additional data and calculations used to define the attenuative
properties. Otherwise, the applicant needs only to present the
soil data previously discussed.
Attenuation mechanisms that may be relevant to an ACL demon-
stration are:
1. Dispersion, including hydrodynamic dispersion,
2. Retardation, including all sorptive properties, and
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3. Degradation, including mechanisms of biodegradation,
oxidation, reduction, and hydrolysis.
The permit applicant should submit data describing the organic
and mineral content, the cation and anion exchange capacity, and
the grain size of each soil type in the expected path of contaminant
migration. Aquifer matrix characteristics that affect the stability
of the ACL constituents (see Chapter II) should also be described
if they are used to support attenuation claims. The results of
tests to substantiate any attenuation claims should be submitted
by the applicant. Likewise, sampling and laboratory procedures
used to determine the attenuation properties should be presented
and results tabulated. Brady (1974), Black (1965), and Freeze
and Cherry (1979) provide in-depth discussions of these specific
soil characteristics. The permit applicant and reviewer should
consult these references for assistance.
The permit applicant should submit a set of maps that adequately
depicts the subsurface stratigraphy. The near-surface stratigraphic
units in the zone of saturation that affect or are likely to affect
ground-water contaminant migration should be described. The areal
and vertical extent of the hydrogeologic units can be presented
in several ways. For complex settings, the most desirable presen-
tation is a series of structural contour maps for the top or bottom
of each unit. Vertical sections and isopach maps can also be used
since they are generally more graphic and are useful as supplements
to the structural contour maps. Because the construction of any
of these diagrams involves interpolation and extrapolation of
limited data, the diagrams should show the location of control
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points and the corresponding value at each control point. The
site maps should include the depth, thickness, and areal extent
of each stratigraphic unit. The maps should also adequately
depict all stratigraphic zones and lenses within the near-surface
zone of saturation. The site-specific stratigraphic maps should
be detailed and have a scale no greater than one inch:200 feet.
The applicant should also submit regional stratigraphy maps in
order to show unique regional characteristics and their relation-
ships to the site, and to justify claims concerning the ultimate
fate of a contaminant plume. A table that summarizes the subsurface
geologic information should be submitted.
Each of the stratigraphic units located in the zone of
saturation must be characterized for the hydrologic parameters
of hydraulic conductivity (vertical and horizontal), specific
yield (unconfined aquifer) or specific storage (confined aquifer),
and effective porosity. Hydraulic conductivity and porosity of
aquifer material can be determined by using laboratory or field
methods. It is recommended that all tests that are conducted to
define the hydraulic properties of each stratigraphic unit be
performed in the field. Laboratory tests may be used to substan-
tiate field test results, but should not be the sole basis for
determining aquifer characteristics. Only in special cases will
the submittal of laboratory analyses be considered adequate for
describing aquifer characteristics. Literature value estimates
for these parameters will rarely be acceptable.
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Each of the hydrologic parameters can vary from point to
point, even within the same aquifer. Therefore, the areal
variations of the parameters within the strati-graphic units
should be determined. The amount of data necessary to characterize
a stratigraphic unit will increase with the increasing heterogeneity
of the unit. As an example, an aquifer of extensive homogeneous
beach sand will require less investigation than a glacial unit
consisting of lenticular deposits of outwash sand and gravel
interbedded with clayey till.
There are many field methods for measuring hydraulic
conductivity and porosity. Hydraulic conductivity is most
effectively determined from the analysis of pump test data. For
units having low hydrologic conductivity, single well tests are
generally used (i.e., a slug test). For hydraulic units having
high hydraulic conductivity, multi-well pumping tests are necessary.
The pump test methods are normally designed to evaluate the
transmissivity and storativity (storage coefficient) of the
aquifer. Hydraulic conductivity is determined by di- .ding
transmissivity by the aquifer thickness. More information on
determining aquifer characteristics can be found in Freeze and
Cherry (1979), Kruseman and De Ridder (1979), U.S. EPA (1983a),
Walton (1970), and Appendices 3 and 4 of this document.
Different laboratory methods can be used to substantiate
field data. Hydraulic conductivity may be determined on a core
sample of the aquifer by using either a constant-head or a
falling head permeameter. A description of the method can be
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found in Todd (1980) and Bouwer (1978) (see Appendices 3 and 4).
In the laboratory, effective porosity can be determined as the
ratio of the volume of water yielded by gravity flow to the
volume of soil or rock material.
If an aquitard separates two distinct ground-water zones,
then the physical and hydraulic characteristics of that aquitard
must be provided in sufficient detail to illustrate the degree of
interconnection between the two aquifers. This requirement can
be fulfilled by providing the results of an aquifer pump test
designed to show the effect of the pumping of the deeper aquifer
has on the shallow aquifer (see Appendix 4). The shallow aquifer
will exhibit significant drawdown during the pump test if the
two aquifers are interconnected.
A summary of the hydraulic properties of each stratigraphic
zone within the zone of saturation should be submitted by the
permit applicant. This data should be provided in a table that
includes the aquifer name, stratigraphic zone, vertical conductivity,
horizontal conductivity, specific yield, transmissivity, and
storage coefficient.
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Chapter IV
Ground-Water Flow Direction
and Quantity (§264,94(b)(1)(iii) .and (2)(iii))
The amount or quantity of ground water at a site and the
direction in which it flows are two essential components of an
analysis of the fate and transport of hazardous constituents in
the ground water. The ultimate fate of contaminated ground-water
is a principal topic of every ACL demonstration. A contaminate
plume can discharge into and mix with other ground water or a sur-
face water body. This chapter describes methods that can be used
to determine ground-water flow direction and quantity at a site.
The primary processes that control the migration of contam-
inants in subsurface environments include:
1. Advection (movement of the ground water),
2. Hydrodynamic dispersion (mixing of ground water having
different levels of contamination), and
3. Chemical reactions.
For ACL purposes, advection is defined as the migration of hazardous
constituents by actual motion or flow and is generally assumed
to be caused by natural ground-water flow. Consideration of
advection alone presents the worst-case calculations in terms of
peak arrival times and concentration strengths. Furthermore,
qualitative and quantitative evaluation of advection in terms of
flow pathways is possible.
The Section 270.14(c) permit requirements specify the
submittal of ground-water flow information. This data should be
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adequate for ACL demonstration purposes and the permit applicant
probably will not have to collect additional field data. The permit
applicant should evaluate ground-water flow in terms of the flow
regime that is present at the facility. Flow from the facility
to the water table will generally occur in the unsaturated zone,
although it may go via surface water. Where subsurface
heterogeneities are not significant, it is reasonable to assume
that flow through the unsaturated zone will be predominantly
downward. This assumption is justified because gravity is the
primary force acting on a fluid in the unsaturated zone.
Once in the saturated zone, dissolved constituents will move
with the ground water. Evaluation of advective transport in the
saturated zone for miscible constituents can generally be based
on the observed ground-water flow field and hydraulic properties
(hydraulic conductivity and effective porosity). The observed
flow field can be determined by a combination of areal water
level maps and vertical sections showing water levels.
Calculations of ground-water quantity will require the use
of the subsurface hydrogeologic parameters described in Chapter
III. Ground-water quantity can be estimated from the hydrologic
parameters, which are specific yield for unconfined aquifers and
specific storage for confined aquifers. The use of Darcy's law
for determining ground-water flow quantity is acceptable, and
can be found in any standard ground-water textbook (e.g., Freeze
and Cherry (1979)). Darcy's law can be used to calculate specific
discharge or volume rate of flow through a cross sectional area
perpendicular to the flow direction.
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The determination of ground-water flow rates and directions,
in concept, is simple. If the distribution of hydraulic head and
the hydrologic properties at the site are known, then a flow net
or water level contour map in conjunction with the use of Darcy's
law can be used to determine flow rates and directions.
The permit applicant should be aware of a number of factors
that can make accurate determination of ground-water flow difficult.
These include:
1. Low horizontal gradients,
2. High vertical gradients,
3. Temporal variations in water levels,
4. Heterogeneous properties, and,
5. Anisotropic properties.
In areas of low horizontal gradients, small errors in water
level measurements or small transient changes in water levels can
make determination of flow direction and rates unreliable. High
vertical gradients often exist in surficial units. In recharge
areas, head decreases with depth; whereas in discharge areas, it
increases with depth. Often, a shallow water table aquifer
may overlie an aquifer of higher permeability, resulting in
vertical head gradients. A very common mistake is made when
water level contour maps are constructed using wells or piezometers
at different depths, since calculated horizontal flow directions
may be inaccurate.
Water levels can vary temporally because of short-term stresses,
tidal effects, seasonal effects, and long-term trends. In determining
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flow direction, the annually averaged water levels are of primary
interest. Consideration of short-term effects is more important
at sites with low hydraulic gradients. In evaluating any water
level data, the uncertainty introduced by neglecting short-term
effects must be estimated. Seasonal variations in recharge can
result in significant water level variations in unconfined aquifers,
Artificial recharge and certain types of ground-water pumpage
often lead to seasonal changes in water levels. These changes
may occur under both confined and unconfined conditions.
The degree of heterogeneity in aquifers may range from fairly
moderate to extreme. The potentiometric surfaces or water levels
in heterogeneous aquifers are not smooth regular surfaces. At
the contact between two geologic materials, the hydraulic gradient
will be discontinuous. For some aquifers, such as fractured rock
and karst aquifers, the heterogeneity is much more complex.
Another property of an aquifer is its anisotropy. Hydraulic
conductivity is a property that is dependent on direction and
has three principal components. If the principal components are
equal, then the aquifer is isotropic. If not, the aquifer is
anisotropic. For anisotropic aquifers, flow lines are not
perpendicular to equipotential lines or water levels. Many
aquifers display a horizontal-vertical anisotropy. However, if
the two horizontal components of hydraulic conductivity are
equal, then, from an areal perspective, flow lines will be
perpendicular to lines of equal potential. Aquifers that may
demonstrate horizontal anisotropy include aquifers in fractured
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rocks or steeply inclined strata. Ground-water flow direction
is difficult to determine from water level data in these types
of anisotrophic aquifers.
The factors that make the determination of flow rates and
directions unreliable can often be overcome by an expanded effort
in water level monitoring. For seasonal variations in water
levels, a higher frequency monitoring schedule is necessary.
For low horizontal gradients, the effects of short-term changes
in water levels can be analyzed by installation of continuous
recorders in selected wells. In aquifers having significant
vertical gradients, piezometers completed at various depths may
be required in order to provide a three-dimensional description
of the flow field. For heterogeneous and anisotropic aquifers,
more water level monitoring wells and more field tests for
hydraulic properties are required.
The hydrogeologic portion of the ACL demonstration must
include an adequate description of both horizontal and vertical
ground-water flow components. This requirement has very obvious
implications from the standpoint of determining where the hazardous
constituents may migrate. The horizontal ground-water flow
description should include a flow net based on ground-water elevation
measurements taken from monitoring wells or peizometers, screened
at the same elevation in the same saturated zone. It must be
designed to provide reliable results of the ground-water flow
direction in the zone of saturation. There may be sites that
will require the applicant to monitor for hazardous constituents
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at more than one ground-water elevation. When this situation
occurs, the permit applicant must be especially careful to ensure
that the monitoring plan is designed correctly.
Information obtained from analyses of the hydrogeological
properties and flow direction will allow the calculation of the
interstitial flow velocity. The use of flow nets is described
in Appendix 4. Well identifier codes, well depths, screened
intervals, ground water elevations, and sampling data should
be presented in tabular form. The flow net data should be
graphically portrayed on a site map that includes ground-water
elevations, isopleths, and flow vectors. As discussed before,
the interstitial ground-water velocity can be determined by a
simple modification of Darcy's eguation (see Appendix 4). All
calculations and assumptions should be included in the discussion
of flow rates.
Vertical ground-water gradients and flow should also be
described. Facilities should have several nested piezometers
for vertical gradient determinations. Vertical flow gradient
will aid in determining discharge and recharge zones, aquitard
characteristics, and whether the monitoring wells are located
and screened at the appropriate depths. The permit applicant
should refer to Appendices 3 and 4 for further discussion of
nested piezometers. The data that should be submitted in tabular
form for each well nest includes well identification code/
well depth, screened interval, ground-water elevation, and sampling
date. All calculations and assumptions should be described in
detail.
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Facilities that are located in environmental settings that
exhibit temporal variation in ground-water flow direction should
define the extent to which the flow change occurs. The main
causes of ground-water flow variation are:
1. Seasonality of recharge or discharge,
2. Ground-water withdrawals,
3. Underground injection, and
4. Surface water elevation changes.
In cases of seasonal ground-water flow variation, the permit
applicant should provide information that describes those temporal
changes in ground-water flow direction using records compiled over
a period of no less than one year.
The rate of withdrawal of ground water is an important
factor that influences ground water and contaminant movement,
and exposure to contaminated water. The rate of ground-water
withdrawal in the vicinity of the facility should be summarized
in tabular form and include well location, depth, type of user,
and withdrawal rates. The zone of impact created by any major
well or well field withdrawal should be identified on a USGS
topographic map. The map should include drawdown isolines out
to the 10 centimeter drawdown level. Modeling of drawdown curves
should use low recharge assumptions such as drought conditions.
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Chapter V
Engineered Characteristics of the Site
While the two previous chapters dealt with natural
hydrogeologic characteristics of a facility's site, this chapter
discusses man-made hydraulic barrier systems that may be used to
alter the natural hydrogeology. Man-made hydraulic barriers are
not specifically mentioned in the criteria listed in Section
264.94(b) of the regulation but they can be an important factor
in assessing exposure to hazardous constituents (see Section
264.94(b)(viii and ix)). However, they are discussed in this
document because man-made barriers to ground-water movement,
such as slurry walls, frequently come into consideration as
control devices in cases of ground-water contamination. Man-made
ground-water control structures must meet one of the following
criteria before they will be accepted as the basis for ACLs:
1. Exposure to the ACL constituent will be prevented
by the control structure, or
2. Exposure levels to the ACL constituents will be reduced
to levels that are protective of human health and the
environment by the use of hydraulic barriers.
It must be stressed that a demonstration that claims perpetual
containment of contaminated ground water is not acceptable
for purposes of justifying ACLs. This is because engineered
systems eventually leak and therefore by themselves do not preclude
the ACL constituent from "posing a substantial present or potential
hazard" as specified by Section 264.94(a) of the regulation.
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This is not to say that containment measures (e.g., slurry
walls) cannot be used as part of a corrective action-measure for
a facility. For example, a containment structure could be used
in conjunction with withdrawal wells to remove contaminants from
the ground water. Such corrective action measures must be initiated
and completed within a "reasonable period of time" under Section
264.100. The permit writer may specify the duration of such
corrective action measures after considering the need for prompt
action at the site and the technical capacity of the owner or
operator.
Any owner or operator that uses man-made hydraulic barriers
to restrict exposure or augment attenuation must demonstrate
that there will be a permanent monitoring system present to
ensure that the proposed control technology functions according
to the specified performance standards. Appendix 5 contains
information on the types of monitoring systems needed to ensure
the effectiveness of slurry walls. Similar monitoring systems
are required for other types of engineered structures.
The permit applicant has the opportunity to demonstrate that
a ground-water control structure will augment natural attenuation
of the ACL constituents in the ground water, thereby limiting
exposure. Ground-water control structures that can be used to
justify ACLs are plume management mechanisms that either steer
contaminated ground water away from exposure points or reduce the
ground-water transport velocity so that natural attenuation mechanisms
can reduce contaminant concentrations to acceptable levels.
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Demonstration Objectives
Attenuation of ground-water contaminants occurs naturally
through several mechanisms:
1. Dilution of contaminants by mixing with
"uncontaminated" ground water,
2. Adsorption of contaminants by the aquifer matrix, or
3. Degradation of contaminants by processes occurring
in the ground water.
These processes depend on both spatial and temporal factors.
A ground-water control system can act to delay ground-water
transport so that natural attenuation is enhanced, aiding adsorp-
tion or degradation by increasing the time for processes to
occur or by increasing the contact time with the aquifer matrix.
Control systems can also act to increase the distance of travel
to exposure points or to prevent short-circuits via fractures,
sand lenses, or other hydrologic channels. An increase in transport
distance can be effective in attenuating contaminants because of
greater dilution or increased adsorption. Greater dilution
could result from an increase in the volume of ground water and
increased adsorption would result from more aquifer matrix coming
in contact with the hazardous constituents.
The objective of an ACL demonstration based on man-made
control mechanisms is to show that the control system is
effective in reducing contaminant concentrations to acceptable
levels. Control structures could result in acceptable exposures
if they steer ground-water contaminants to major surface water
dilution sources where the effects of the contaminants are minimal.
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Engineered Ground-Water Controls
The various methods of engineered ground-water control that
will be considered include barriers of low permeability such as
slurry walls, cutoff walls, and grout curtains. The low permeability
barriers can be used to limit exposure to the contaminated ground
water. Low permeability barrier systems will be considered in
ACL demonstrations only when they are used to steer or manage
ground-water plumes.
Slurry walls and cutoff walls are subsurface barriers that
can reduce, retard, or redirect the flow of ground water. In
general, they consist of an excavated trench that is refilled
with either a soil-bentonite mixture, a bentonite-cement mixture,
or an asphalt mixture. In most instances, they will be keyed into
an impermeable layer or bedrock. There are several design and
construction considerations that must be evaluated in order to
assess the adequacy of such a system. The permit applicant must
submit the results of a thorough hydrogeologic and geotechnical
investigation (see Chapters III and IV). The applicant must also
submit detailed information regarding:
1. Hazardous constituent compatability;
2. Barrier wall constituent mixture ratios, and method of
mixing;
3. Method of excavation;
4. Method of keying the slurry wall into the aquitard or
bedrock;
5. Method of determining the effectiveness of the barrier
wall;
6. Location;
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7. Length, width, and depth;
8. Hydraulic conductivity and sorption capacity; and,
9. Changes in the hydrologic regime.
All information submitted to the agency describing the design
considerations should be accompanied by the signature of a
professional engineer or qualified geologist or geotechnical
engineer attesting to the appropriateness of the barrier wall
system to the site geohydrology.
Grout curtains are another method of ground-water control.
In general, grouting is accomplished by drilling holes to the
desired depth and injecting the grout under pressure into
the holes. The grout mixture itself may be one of two types,
either suspension grout or chemical grout. For a more detailed
description of grout types, see Appendix 5.
As with designing a slurry wall system, hydrogeologic
and geotechnical testing must be performed prior to installing
a grout curtain. All the information needed for an evaluation
of a slurry wall system must be submitted by the permit applicant,
In addition, the following information is needed:
1. Detailed drilling information,
2. Grid design,
3. Type of grout used,
4. Grout losses and injection pressure, and
5. Curing time (if applicable).
Ground-water pumping systems that are considered corrective
action measures may be used to augment plume management. Again,
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the permit applicant must submit the detailed hydrogeologic
and geotechnical information as described in Chapters III and IV.
In addition, the applicant must submit an analysis describing
the predicted effect that the ground-water pumping system will
have on the natural flow regime. The applicant must consider
the effects that the pumping system has on:
1. Production wells in the site vicinity,
2. Injection wells in the site vicinity, and
3. Facility withdrawal and/or injection wells.
A computer modeling analysis should be performed to predict
the above effects.
All hydrogeological parameters used for the computer
modeling analysis should be field-determined values. Parameter
values that are taken from the literature or represent "reasonable"
assumptions should not be accepted in lieu of actual facility-
specific parameter values except in those rare instances
when the literature data is unquestionably applicable to the
site.
In cases where ground-water control structures are proposed
for limiting exposure, the applicant must submit a plan detailing
a methodology that will demonstrate both the effectiveness of
the engineered system and the steps that will be taken if the
system fails. This plan must include a ground-water monitoring
program, a control structure testing plan, a modeling plan assessing
effectiveness, and an exposure assessment describing the consequences
of system failure. Failure of the system to meet specifications
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for its effectiveness is a violation of the permit equally as
serious as exceeding the ACL at the point of compliance. Such
failure will require reevaluation of the ground-water protection
standards and possibly corrective action.
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Chapter VI
Patterns of Rainfall
(§264.94(b)(2)(iv))
Precipitation is a driving factor for ground-water recharge
and ground-water discharge. These processes are basic components
of the hydrogeology at a facility. To verify a claim of no expo-
sure or exposure to acceptable levels of contaminants, precipi-
tation data in support of ground-water flow and contaminant trans-
port information must be submitted. This chapter describes the
type of precipitation data that should be submitted in support of
an ACL demonstration.
The permit applicant should focus the discussion of precipi-
tation around the site's hydrologic regime. If the applicant's
ACL demonstration clearly shows that ground-water discharge to
surface waters is unlikely, then the discussion of precipitation
events can be limited to effects on infiltration and ground-water
recharge. However, if ground-water discharge to surface water is
an important element of the ACL demonstration, then precipitation
events should be related to recharge and discharge of ground water.
Precipitation events are variable and occur with different
intensities, volumes, and durations. The geographical distribution
of rainfall also varies from one area to another within a region.
However, over a long period of time (years), the precipitation
data for an area can be represented by events with definite volumes
that occur at various frequencies. These frequencies are classified
in terms of duration and yearly return periods. For example, a one
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day/10-year storm event is defined as the amount of rainfall that
is expected to occur during a 24-hour period, once every 10 years.
The precipitation volume of a storm of specific retunn period and
duration is used to produce an estimate for the volume of precipi-
tation for a given geographical area.
All permit applicants must submit general information on the
precipitation characteristics of a site. This includes data on
rainfall and snowfall, expressed as its equivalent in rainfall.
Monthly precipitation data gathered over a period of at least 12
months should be submitted. Historical data can be used if it is
from an area within 15 km of the facility. The regional rainfall
data from areas greater than 15 km of the facility should be corre-
lated with available on-site data. The National Oceanographic
and Atmospheric Administration or climate data in Ruffner (1980
and 1981) may be a source of this precipitation information if
on-site data is unavailable. The monthly mean and range of this
data, the specific time period the data comes from, and the loca-
tion of the rain gauge(s) in relation to the facility should be
provided. The permit applicant should discuss the precipitation
data in terms of temporal effects on infiltration and seasonal
ground-water recharge. These processes should be related to any
effects on contaminant transport.
If the facility is located near surface water bodies (see
Chapter VII), or if surface water dilution is used as an argument
in an ACL demonstration, then more detailed information on precipi-
tation events should be submitted. Otherwise, the permit applicant
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can proceed to the next chapter. The permit applicant should sub-
mit data on specific storm frequency patterns and discuss how
these storms relate to flood and infiltration/discharge character-
istics of the facility.
The predicted volume of precipitation produced over a 24-hour
period by storms of return frequencies of 1, 10, 25, and 100-years
should be submitted. The 1-year and 10-year storm frequency
information gives insight into ground-water infiltration and dis-
charge patterns. The 25-year and 100-year storm frequency data
are useful in assessing discharge during flood conditions.
The 100-year floodplain should be described on a USGS topogra-
phic map. The floodplain information should be readily available
to the applicant since it is required by Section 270.l4(b) permit-
ting requirements. Federal Insurance Administration flood maps
can be a useful source for this information. If the facility
has any special flood prevention devices, they should also be
shown on the map. These devices could include any dikes, berms,
and special flood retention walls. The effect of these devices
on ground-water infiltration and discharge should be discussed.
Furthermore, any special site conditions that affect infiltration
and discharge should be discussed. These include site topography,
solar orientation of the regulated unit, and wind patterns.
The ground-water discharge patterns at the facility should
also be delineated on a topographic map. All streams, ditches,
culverts, and sewers that receive ground water should be clearly
identified. Normal ground-water discharge patterns (1-year storm)
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;;:: rr;::
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Chapter VII
Proximity of Surface Water and Ground-Water Users
(S264.94(b)(l)(iv) and (2)(v))
This chapter and the next chapter discuss important factors
necessary for assessing probable exposure pathways for the ACL
constituents through surface and ground water. This chapter dis-
cusses the location of surface water and ground-water users in the
vicinity of the facility. The uses of surface and ground water
in the vicinity of the facility are discussed in Chapter VIII.
A key factor involved in assessing exposure is the proximity
of surface water and ground-water users to the facility. This
factor is considered in the evaluation of existing or potential
off-site migration of hazardous constituents and in the assessment
of the uses of the specific water resources. For ACL demonstrations,
"proximity" is liberally defined to include both spatial and temporal
concepts. Linear distance may be more appropriate for judging poten-
tial surface water exposures, while time of travel is important for
ground-water exposures. Proximity should be expressed in terms of
both linear distance and time required for ground-water flow
and contaminant transport.
The level of information necessary to satisfy the proximity
of users requirement depends on the basis of the ACL. If a down-
gradient surface water body is the primary focus of a demonstration,
then data related to the specific characteristics of the water body
are necessary. The permit applicant may use surface water dilution
as an argument for acceptable exposure limits for an ACL constituent.
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An ACL demonstration based on dilution should be supported
by data on specific physical attributes of the surface water body.
This includes information necessary to estimate the dilution
potential and mixing mechanisms of the water body. If the permit
applicant argues that no exposure will take place in downgradient
water bodies, then general information on the distance of
the water bodies from the facility is necessary, along with
time of travel estimates for contaminant migration to the
water bodies. Likewise, the same arguments apply to the
level of information necessary to assess exposure of ground-water
users. This will be discussed further in the following sections.
Surface Water
All ACL demonstrations should include a discussion of the
potential effects of the facility on surface waters. The
initial evaluation includes assessing the facility's proximity
to surface waters and involves:
1. Identifying each surface water body in the vicinity of
the facility,
2. Determining the distance from the waste management area
boundary to each surface water body,
3. Identifying ground-water discharge pathways to surface
waters, and
4. Estimating time of travel of waste constituents -to water
bodies.
Each water body within five kilometers downgradient (or
downstream) of the facility boundary should be identified. The
owner or operator of the facility -must supply a USGS topographic
map identifying each water body. All streams, rivers, ponds,
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lakes, estuaries, and marine waters should be clearly marked.
All ditches, streams, sewers, and runoff pathways that serve as
ground-water discharge or infiltration areas should be delineated
on the topographic map. A table specifying the name of each
water body and the distance from the waste management area to the
closest part of each water body should be provided by the owner
or operator of the facility.
The travel time of the ACL constituents from the facility to
the discharge areas should be discussed by the permit applicant.
Ground water and hazardous constituents may move at different
rates due to different physical and chemical properties. Therefore,
discharge calculations should include estimates of both hydraulic
transport and waste transport. The ground-water transport models
and methods discussed previously in Chapter IV should be used to
estimate the hydraulic and hazardous constituent loading rates.
Actual seepage measurements may be necessary to verify model
estimates if ground-water discharges are estimated to be a
significant portion of the annual hydraulic load to a water body.
A greater level of detail on characteristics of surface water
bodies is needed in ACL demonstrations that include dilution in
surface waters as an argument or in cases where surface waters
are likely to be exposed to ACL contaminants due to their proxiiuity
to 'the facility. In these cases, the physical characteristics
of each identified downgradient (or downstream) water body should
be included in a table. Important lake and pond characteristics
are:
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1. Surface area,
2. Mean depth,
3. Volume,
4. Temperature stratification, and
5. Hydraulic residence time.
Information on estuarine and marine areas should include:
1. Surface area,
2. Mean depth, and
3. Tidal periodicity and amplitude.
Pertinent stream and river characteristics are:
1. Mean width;
2. Mean depth;
3. Flow rate, including average flow and lowest flow that
would be expected to occur during a continuous 7-day
period, once every 10 years (07-10); and
4. Lowest recorded flow rate.
This information is necessary to estimate the dilution potential
and mixing mechanisms of each type of surface water in the vicinity
of the facility. The temporal and spatial variability of flow
rates, tidal factors, and hydraulic residence times are also
essential factors for establishing dilution potential.
The permit applicant should synthesize this information to
support arguments of acceptable surface water exposures or no
significant exposures due to dilution in surface waters. The
expected amount of dilution and the mixing zones of probable
«
discharge areas should be factored into this discussion. The
permit applicant should be aware that certain States have approved
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surface water dilution models that are used in the NPDES
permitting program. If approved models are available, they should
be used by the applicant to determine mixing zones and dilution
in surface waters.
Ground Water
As a matter of general policy for ACL demonstrations, the
potential ground-water exposure point is the waste management
boundary of the facility. If there are ground-water use controls
beyond the facility waste management boundary, the potential
groundwater exposure point will be at any point downgradient of
the waste management boundary. In order to designate the property
boundary as the point of exposure, a facility must ensure that
there are permanent prohibitions on the use of on-site ground
water. These restrictions must apply to the owner of the facility,
as well as to any successive owners. In order to designate a
potential point of exposure beyond the property boundary, ground-
water use restrictions must be in place off-site to prevent any
use of the contaminated ground water. Ground-water use restrictions
are discussed in Chapter XIII.
In order to assess the likelihood of exposure of current
ground-water users, every ACL demonstration must discuss the
proximity of ground-water users to the facility. This requires
determining:
1. The distance of each ground-water user from the facility,
and
2. The hydrologic transport time for the contaminants
to reach the closest users.
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The users of ground water within a five kilometer radius of
the facility boundary must be identified. The applicant should
delineate each ground-water withdrawal or injection well on a
USGS topographic map. The distance of each well from the waste
management area should be given in a table. The following uses
of each well should be clearly marked:
1. Potable (municipal and residential),
2. Domestic, non-potable,
3. Industrial,
4. Agricultural, and
5. Recharge.
The permit applicant has the opportunity to discuss the like-
lihood of exposure at the facility's property boundary. Although
it is not required in every ACL demonstration, it may be to the permit
applicant's advantage to submit information on the projected future
users of the ground water. Several factors should be examined:
1. Demography of the surrounding ar-ea,
2. Zoning patterns and projected changes in zonings,
3. Projected population growth,
4. Projected ground-water use, and
5. Restrictions on ground-water use.
Each of these factors should be concisely described in a
narrative format. The projections in zoning changes, population
growth, and ground-water use should include median and maximum
estimates. Discussions of ground-water use restrictions should
explicitly state the legal nature of any restrictions and the
duration of such - restrictions.
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Chapter VIII
Current and Future Uses of Ground Water and Surface
Water in the Area
(§264.94(b)(l)(v) and (2)(vi))
Once the location of the surface water and ground-water users
has been determined, the nature of the use must be considered.
A major objective of an ACL demonstration can be to show that
ground-water contamination at a facility will not adversely affect
any water use. The supporting arguments for the ACL can center
around the fact that the ground-water contamination at the facil-
ity is not degrading the designated beneficial uses of the water
resources. This requires the permit applicant to review federal,
state, and local standards or guidelines that govern the uses of
both ground and surface water to ensure that the presence of a
contaminant plume is not inconsistent with any published regula-
tions, ordinances, or guidelines. This chapter points out the types-
of water uses that should be investigated, and the information that
should be submitted on those water uses- to support an ACL demonstration.
An ACL demonstration based on a claim of no degradation of a
water resource should discuss the current uses of all water resources
near the facility. Information gathered to satisfy data requirements
on the proximity of water resource users (see Chapter VII) will be
adequate to identify major water resources near the facility. In
order to aid the permit reviewer, the water resource use information
should be structured around the following general categories: '
1. Agricultural - irrigation and animal watering; .
2. Industrial - process, cooling, and boiler water;
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3. Domestic and municipal - potable and lawn/garden watering;
4. Environmental - ground-water recharge or discharge,
fish and wildlife propagation, unique areas; and
5. Recreational - fishing, swimming, boating, and
other contact uses.
The permit applicant should examine pertinent aspects of both
ground water and surface water uses. Both the current uses and the
likely future uses of the water resources should be examined.
Permit applicants must submit information on the ground-water uses
in the vicinity of the facility, unless they can successfully
argue that no exposure to the contaminated ground water will occur.
The specific type of ground-water use information is described in
the following section.
Ground-Water Uses
The U.S. EPA has developed a Ground-Water Protection Strategy
(U.S. EPA, 1984b). An important part of this strategy is to
adopt guidelines for consistency in the Agency's ground-water
protection efforts. The strategy states that ground water should
be protected to its highest beneficial use. Guidelines for
classifying ground water should be available in the fall of 1985.
Three general classes of ground water are recognized:
Class I: Special ground waters are those that are highly vulnerable
to contamination because of the hydrological characteristics
of the areas under which they occur, and that are also
characterized by either of the following two factors:
a) Irreplaceable—no reasonable alternative source of
drinking water is available to substantial populations,
or
b) Ecologically vital—the aquifer provides the base
flow for a particularly sensitive ecological system
that, if polluted, would destroy a unique habitat.
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Class II: Current and potential sources of drinking water and
waters with other beneficial uses include all other
ground waters that are currently used or potentially
available for drinking water or other beneficial uses.
Class III: Ground waters not considered potential sources
of drinking water and of limited beneficial use are
those that are heavily saline, with total dissolved
solids (TDS) levels over 10,000 mg/1, or are otherwise
contaminated beyond levels that allow cleanup using
methods that are reasonably employed in public water
system treatment. These ground waters also must not
migrate to Class I or II ground waters or have a
discharge to surface water that could cause degradation.
The permit applicant should discuss the ground water
classification in the vicinity of the facility in terms of these
three classes or other appropriate State approved classification
schemes. This classification information may be found in State
ground-water plans (208 plans) or State ground-water classification
documents. The data should be presented in tabular form in
order to expedite its review. Certification by the state and/or
local government as to the beneficial use of the ground water
should be included if the State has classified the ground water.
Otherwise, the permit applicant should have its ground-water
classification data reviewed by the State. The State's review
should be included in the ACL demonstration.
It should be obvious that the ground-water use can be
critical in the setting of ACLs at a facility. Facilities that
are contaminating, or have the potential to contaminate, Class
I or Class II ground waters must incorporate human health factors
into their ACL demonstration (see Chapter X). The Agency's
Ground-Water Protection Strategy states that the Agency's polic'y
is to-not grant ACLs at hazardous waste facilities situated
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above Class I ground waters. Before this policy can be fully
implemented in the ACL process, it will be necessary to define
Class I ground waters in regulations and to appropriately amend
the ACL regulations. In the interim, this guidance document
emphasizes the careful consideration of contaminant impacts on
Class I ground waters during the ACL process.
If the ground water is Class III, then health-based concerns
may be secondary to environmental-based concerns in the setting
of ACLs. More information on ACLs in Class III ground water is
presented in Appendix 6. Two situations are envisioned in which
ACLs could be proposed based on poor ground-water quality:
1. The existing risk from potential consumption or use of
the ground water may be already so great that the increase
of the concentration of a specific constituent would
pose no additional risk, or
2. The ground water has been declared unfit for use by the
State government, and controls are in place to prevent
its use (see Chapter XIII).
Surface Water Uses
Surface water uses should be discussed by the permit
applicant if contaminated ground water can migrate to surface
waters. Surface water use information is especially critical
for ACLs "based on surface water dilution. The previous chapter
on proximity of surface .waters should aid in deciding which
water bodies are of interest. If no surface water impacts .are
likely, then the data discussed in this section are not required
to be submitted.
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The statutory established guidelines, criteria, and/or
standards for each water body identified in Chapter VII must
be examined. The permit applicant should list in a table the
designated use of each water body, a citation of the local,
state, or federal regulations governing the use, and the agency
responsible for implementing the regulation. The following
general use categories should be used by the permit applicant in
preparing the table:
1. Drinking water source,
2. Fish and wildlife propagation area,
3. Industrial or agricultural water source,
4. Area of special ecological concern, and
5. Recreational area.
It should be noted that many States have generic restrictions
on the discharges of "toxic pollutants in toxic amounts" and of
"potential carcinogens" to surface waters.
The surface water use information will aid in determining
appropriate ACLs by identifying surface water exposures that can
occur. The data gathered to fulfill the requirements of this
section will be used to prioritize the likely exposure pathways and
to determine whether human health and environment factors should be
assessed in further detail (see Chapters X and XI).
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Chapter IX
Existing Quality of Ground Water and Surface Water,
and Other Sources of Contamination
-------
wells must yield ground-water samples from the uppermost aquifer
that represent the quality of ground water that has not been
affected by leakage from a facility's regulated unit. For most
sites, this is an upgradient area that can be determined readily
from the water level data. The permit applicant is directed to
the Draft RCRA Permit Writers' Manual for Ground-Water Protection
(U.S. EPA, 1983a) for further guidance on ground-water monitoring
and station locations. Background surface water quality must
be assessed only in cases where surface waters are likely to
receive contaminated ground-water discharges (see Chapter VIII).
Background surface water quality should be determined upstream
of the facility to ensure that any leakage from the facility is
not affecting the monitoring results.
The permit applicant should submit a site map that identifies
the location of background sampling stations and monitoring wells-
and the direction of both ground-water movement and stream flow.
Any flood discharge pathways and directions should also be shown
on the site map.
The permit applicant may find historical ground-water
monitoring studies and ambient surface water monitoring programs
to be useful when assessing background water quality. The USGS,
U.S.EPA, State, and local environmental program offices can be
good sources of historical data. The background concentrations '
in both ground water and surface water of Appendix VIII consti-
«
tuents for which ACLs are being proposed should be included- in
a summary table. Each distinct aquifer and surface water body
52
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that is likely to be exposed to contaminants should be listed
separately. If additional monitoring studies are necessary for
determining background water quality, the EPA Regional Office
may assist by reviewing the monitoring work plans. Regardless
of the source of the background water quality data, the permit
applicant should submit available quality assurance and quality
control information on sample collection, sample analysis, well
construction, and environmental conditions. Documents from
which any data were taken should be available for review if
they are requested by the permit writer.
Ground-Water Contamination Sources
The permit applicant should investigate other sources of
ground-water contamination if background monitoring wells exhibit
contamination. If no contamination is found, the permit applicant
can omit the following discussion and proceed to the surface
water discussion. The types of upgradient pollution sources
and the impacts of the contamination on ground-water use are
important and should be considered. Identifying potential
pollution sources is necessary in order to assess the cumulative
impact of pollution sources on human health and the environment.
The following potential pollution sources should be identified
within a five kilometer radius of the site:
1. Other RCRA facilities,
2. Superfund sites,
3. Landfills,
4. Industrial areas,
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5. Surface impoundments,
6. Chemical storage areas,
7. Deep well injection sites,
8. Agricultural areas,
9. Septic tanks, and
10. Underground storage tanks.
Each potential contamination source should be delineated on a
USGS topographic map. The distance of each source from both
the facility and the upgradient monitoring wells should be
discussed. All pertinent ground-water data on any of the
identified sources should also be discussed.
Some areas may have hazardous constituents present in the
ground water because of natural processes occurring in the
ground water. For example, some metals may be found at fairly
high levels in certain ground waters. However, natural sources
of synthetic organic compounds (e.g., chlorinated solvents)
are not expected. If synthetic organic compounds are found in
background samples, then the permit applicant should attempt to
to identify the the source of contamination.
The water-use impacts from the contamination should be
discussed by the permit applicant if upgradient ground water
is impaired by any source of contamination. In Chapter VIII
of this guidance, the current and future uses of ground water
are discussed 'in more detail.
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Surface Water Contamination Sources
The permit applicant should examine other sources of surface
water contamination if the applicant's facility affects surface
water resources. Consideration should be given to both point
and non-point sources of contamination. Any point sources of
pollutant loading to surface waters should be identified on a
USGS topographic map. The point sources should include:
1. Discharges from industrial facilities,
2. Discharges from Publicly Owned Treatment Works (POTW),
and
3. Past waste discharges.
The permit applicant should submit a table that includes
the name of each point source and the water body into which
the point source discharges. The discharge rate and NPDES permit
number of each point source should also be included in this
table. Any waste load allocations, permit discharge conditions,
and mixing zones should be discussed. The applicant should
focus these discussions around the impact of the facility's
discharge on these factors. For example, a lake may have an
established waste load of 5 grams of lead/day, of which 4 grams
are allocated to a NPDES permitted facility. The discharge of
lead from the applicant's facility to the lake is estimated to
be 3 grams/day. In this situation, an appropriate ACL for
lead may be one that results in a loading rate of one gram/day
to the lake, thus requiring some type of corrective action to
reduce the lead concentration to the ACL. Copies of available
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NPDES permit compliance and permit application monitoring data
should be submitted if they contain information on the specific
ACL constituents.
Any non-point sources of pollution to surface waters that
may affect the ACL decision should also be discussed. The permit
applicant should submit information on:
1. Urban storm run-off,
2. Agricultural run-off,
3. Ground-water infiltration, and
4. Other RCRA facilities.
Actual monitoring data may be submitted along with loading
model calculations, if they are applicable.
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Chapter X
Potential Health Risks
(§264.94(b)(1)(vii) and (2)(viii))
A health risk assessment should be included in an ACL demon-
stration if human exposure to the ground-water contaminants is
not prevented. There are two major components to a determination
of health risks. First, an exposure assessment must be performed
that characterizes the current and future populations that may
be exposed to the contaminants, and the current and potential
human exposure pathways. Second, the health effects associated
with exposure to each contaminant and mixture of contaminants
must be examined. The purpose of the health risk assessment is
to determine acceptable concentrations at a point of exposure
for the constituents for which ACLs are requested. These acceptable
concentrations can be used as a basis to calculate the ACLs at
the point of compliance. This chapter describes the information
necessary to sufficiently support proposed acceptable concentrations
for constituents in an ACL demonstration.
The type of information needed to satisfy the health risk
requirement depends on the exposure pathway. If the contaminated
ground water is discharging into a downgradient surface water
body that is a source of drinking water and a sustained fishery,
the health risk information must be based on exposure from the
consumption of contaminated water and aquatic organisms. In
this case, an ACL demonstration could be based on surface water
dilution of the contaminated ground water to an acceptable level.
57
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If the primary exposure pathway is from a ground-water source of
drinking water, the health risk information must be based on the
consumption of contaminated drinking water. Ijn this case/ attenuation
mechanisms in the saturated zone may be the basis for the ACL
demonstration.
The health risk assessment may be based on the following
types of likely exposure pathways:
1. Drinking water exposure from either a ground water or a
surface water source,
2. Ingestion of contaminated food (e.g., aquatic organisms
or agricultural products),
3. Dermal contact (e.g., recreational use of surface waters,
or bathing),
4. Inhalation of volatile organics, or
5. Any combination of the above pathways.
The inhalation exposure pathway usually does not have to be
addressed in great detail in an ACL demonstration. It should
only be considered in cases where significant quantities of vola-
tile organic compounds are either likely to degas from the contami-
nated ground water during use or can be expected to penetrate sub-
surface structures such as basements. The permit applicant should
comment on the probability of the occurrence of these two.types of
exposures. The applicant will have to address inhalation in the
health assessment in these situations where the use of ground
water or the presence of subsurface structures allows for probable
exposures.
When determining potential health risks, certain assumptions
are usually made when complete data on specific human effects
58
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are lacking. Both the information that is needed to make a
reasonable determination of potential health risks and the areas
where assumptions may be necessary are discussed in the following
sections.
Exposure Assessment
The location of the potential sources of exposure from surface
and ground water is discussed in Chapter VII. The potential point
of exposure to the ground-water contaminants is assumed to be at
the facility waste management boundary unless use restrictions discussed
in Chapter XIII have been implemented. The point of exposure for
surface water bodies is assumed to be the water body closest to the
facility in the pathway of contaminant migration. Once the location
of the potential sources of exposure are identified, the applicant
should determine whether a characterization of the populations
that may be exposed at each point is necessary. In cases where
the probability of exposure is not high because of no current off-
site contamination or no large population centers, the exposure
assessment can be based on standard assumptions (e.g., a 70 kg
adult consuming 2 liters of water per day). The permit applicant
does not need to assess population characteristics of the site but
should follow the Agency's proposed guidelines for exposure assess-
ments (U.S. EPA, 1984c). -
However, the permit applicant should specifically characterize
the exposed population in three specific situations:
1. Exposure to hazardous constituents is occurring due to '
the u"s*e of contaminated off-site water resources,
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2. Exposure to hazardous constituents is highly probable
due to off-site migration of contaminants, and
3. Probability of exposure is high due to a larg'e population
near the facility.
These situations of likely exposure are defined for ACL purposes to
be cases either where hazardous contaminants have moved off-site
via either ground-water or surface water pathways, or where the
facility is located within a standard metropolitan statistical area
(SMSA) as defined by the U. S. Department of Commerce. The following
population characteristics should be determined in these cases:
1. Sex and age distributions,
2. Growth rates, and
3. Sensitive subgroups.
Most of this information can be obtained through the Bureau of
the Census, U.S. Department of Commerce.
The presence of sensitive groups such as pregnant women,
children, or chronically ill individuals within an exposed population
directly affects the assumptions used to determine an acceptable
concentration for an ACL constituent (U.S. EPA, 1980). The
applicant should identify the most sensitive group within the
exposed population. This subgroup should form the basis for the
exposure assumptions used in deriving the acceptable concentrations
for the ground-water contaminants. , The U.S. Department of
Health and Human Services, National Center for Health Statistics
may be a good source of information on sensitive individuals in
the region. All of this information should be presented in
tabular form to facilitate easy reference.
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Health Risk Assessment
Certain assumptions are usually made when determining health
risks. Assumptions must be made concerning either intake rates
of food, water, and air, or body surface area and weight.
Absorption and excretion rates may be assumed to estimate
equivalent oral doses based on data from inhalation or dermal
exposure studies. The permit applicant should use generally-
accepted standard factors in the exposure assessment. Some of
the common factors used are listed in Appendix 7.
The permit applicant should identify the compounds that can
be grouped together based on similar physical and chemical properties,
since health effects data are sometimes listed for broad groupings
such as polynuclear aromatic hydrocarbons (PAHs), halomethanes,
or polychlorinated biphenyls (PCBs).
The permit applicant may find it advantageous to use groupings
of hazardous constituents in order to simplify the development of
ACLs. The acceptable exposure level of each hazardous constituent
within a group can be based on the toxicity of the most toxic
compound within the group. This would.result in the acceptable toxic
effect level for each constituent being set at the acceptable
level for the most toxic compound within the group. This con-
servative approach to risk assessment could reduce the amount of
data needed to quantify potential human health effects. However,
it must be emphasized that the grouping of compounds into specific
categories can be difficult, and approved methods are not available.
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The applicant should perform a comprehensive literature search
for health effects data on the contaminants or groups of contaminants
found in the ground water for which ACLs are requested. Health
effects data are available for compounds with established concentration
levels such as Ambient Water Quality Criteria. Site-specific
water quality criteria may be available at the State level.
Guidance on modifying national criteria is available in the
Water Quality Standards Handbook (U.S. EPA, 1983b). Appendix 8
contains a list of health and environmental effects profiles
and assessments, available through the U.S. EPA, Environmental
Criteria and Assessment Office. The Agency is currently compiling
toxicity information on many of the hazardous constituents and this
information should be useful in preparing ACL demonstrations.
In order to account for cumulative impacts of the hazardous
constituents for which ACLs are requested, an assessment of the
existing concentrations of the ACL constituents in the potentially
impacted ground water or surface water should be performed.
This information is necessary for determining the total concentration
of the ACL constituents in the affected water resource, the
health effects associated with the concentrations, and the relative
contribution of the ACL constituents emanating from the site to
the total concentration.
- The applicant should distinguish between ground-water con-
taminants having threshold (toxic) and non-threshold (carcinogenic)
effects. • Toxicity data should be submitted for the toxic (threshold)
contaminants. Draft guidance on the use of ADIs has been proposed
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by the Agency (U.S. EPA, 1984d). If Agency compiled data on
threshold contaminants are not available, then the submitted data
should contain dose/response information reflecting the acute,
subchronic, chronic, and "no effect" levels for the threshold
contaminants. Acceptable concentrations can be derived by applying
appropriate exposure assumptions to established acceptable daily
intake values or alternate dose levels derived from the literature.
The National Academy of Sciences (NAS, 1977) defines and outlines
the use of uncertainty factors in determining acceptable dose levels
Non-threshold compounds, or carcinogens, should be subjected
to the same review as the other toxic compounds. Cancer risk
models, such as the linear non-threshold model, produce carcinogen
potency factors or unit cancer risk (UCR) values. A UCR value
represents the largest possible linear slope at low extrapolated
doses that is consistent with the dose-response data (U.S. EPA,
1980). The uncertainties and extrapolation techniques that are
used to es.timate UCRs from cancer risk models should be clearly
stated. Unit cancer risk values are used to estimate hazardous
constituent concentrations that correspond to statistical lifetime
cancer risk values. For example, a contaminant concentration
corresponding to a lifetime cancer risk of 10~6., assuming that a
70 kg adult consumes 2 liters of water per day, is estimated by
the following formula:
Exposure level (mg/1) = 70 x 10~6
2 x UCR
Unit cancer risk values have been derived for many compounds by
the Carcinogen Assessment Group (CAG, 1984) and are also available
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from Ambient Water Quality Criteria. Reference citations should
accompany each exposure level based on a UCR.
The acceptable concentration of non-threshold compounds,
or carcinogens, is determined through the risk management process.
In general, the Agency has made decisions to allow concentrations
of carcinogens where the individual risk values have been within
the range of 10"^ to 10~8. in setting ACLs the following factors
should be considered in determining an acceptable risk level to
any exposed individual within the 10~^ to 10"^ range:
1. Other environmental health factors borne by the affected
population,
2. Level of uncertainty in the data base and models used in
the risk analysis,
3. Level of uncertainty involved in predicting exposures
including the expected effectiveness and reliability of
man-made systems affecting exposure,
4. Current and expected future use of the affected resource,
and
5. Impacts upon the environment.
It may be useful to also determine the total population that
is currently exposed or likely to be exposed in the future, when
weighing the importance of the five factors. As a general matter,
a level of 10"^, the middle of the range, should be used as the
point of departure when proposing a risk level within the 10~4
to 10~8 range for a particular facility.
The permit applicant should discuss any other effects associated
with the contaminants, including odor and taste effects, mutagenic
effects, teratogenic effects, arrd synergistic or antagonistic
effects. At a minimum, an additive approach based on contaminants .
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that produce the same effects by similar mechanisms should be
used to estimate health effects from exposure to mixtures of
contaminants. The applicant should investigate criteria development
for entire classes of compounds. Ambient Water Quality Criteria
have been developed for classes of compounds such as polynuclear
aromatic hydrocarbons (PAHs) and halomethanes. A reference
citation and a summary should be submitted for each study that
was used to determine the type of effect for each contaminant.
The permit applicant is responsible for providing information
on health effects of the hazardous constituents present in the
ground water for which ACLs are requested. Appendix 9 of this
document contains a survey sheet on health effect factors that
can be used to summarize the toxics information. The applicant
should submit available health effects numbers _for each ACL
constituent. The health risk assessment should be based on
conservative health based numbers. If the applicant uses less
conservative numbers as a basis for the health risk assessment,
the applicant must submit information to justify the use of
these numbers. As discussed previously, the acceptable.exposure
levels for a group of constituents can be based on the toxicity
'of the most potent constituent within that group, if such a
grouping is sufficiently justified. If sufficient toxicity.
information on any of the compounds has not been submitted, the
ground-water protection standard will be set at background levels
or at the maximum concentration levels listed in Table 1 of
Section 264.94(a) of the regulations.
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Chapter XI
Potential Damage to Wildlife., Vegetation,
Agriculture, and Physical Structures
(§264.94(b) (l).(viii) and (2)(ix))
In addition to risks to human health, environmental risks
must be addressed in an ACL demonstration. Unless an ACL demon-
stration is based on no exposure to hazardous constituents,
risks to animals, plants, and structures resulting from exposure
to the hazardous constituents must be considered. This environ-
mental risk assessment involves an exposure assessment and an
effects assessment similar to the human health risk assessment.
This chapter delineates the information needed to perform the
assessments of risks other than those to human health.
The initial step in assessing possible environmental impacts
is to determine the probable exposure pathways for hazardous
constituents to reach environmental receptors. For ACL purposes,
the receptors of concern include wildlife and vegetation in aquatic
and terrestrial environments; agricultural crops, products, and
lands; and physical structures. The exposure assessment involves
examining the extent of the hazardous contaminant plume, the
potential migration of hazardous constituents, and the location
of receptors and environments of concern. The exposure assessment
will result in delineation of likely exppsure pathways. Information
submitted to fulfill requirements discussed in previous chapters
should be adequate to determine probable surface water and terrestrial
exposure pathways. The permit applicant should ,examine the data
requirements of Chapters VII and VIII, before proceeding with
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this chapter. The data necessary for assessing the effects of
exposure of physical structures and agricultural crops, lands,
and products to the hazardous constituents are discussed in
subsequent sections of this chapter.
The permit applicant must examine the potential impacts to
all the receptors discussed above if exposure to hazardous constit-
uents is likely to occur. Otherwise, the permit applicant should
discuss specific data that supports no probable exposure as well
as justify why the potential impacts assessment is unnecessary.
Generally, data on chronic toxicity levels of the hazardous
constituents are sufficient to characterize potential environmental
impacts. However, chronic environmental toxicity data may not be
available for many waste constituents likely to be the subjects
of ACL requests. In the absence of environmental toxicity data,
ACL applicants may be able to argue that a contaminant will have
no adverse environmental effects. This argument could be based
upon considerations of exposure levels and the toxicities of. similar
chemical compounds. If environmental receptors are actually being
exposed to ACL constituents above chronic toxicity levels, or
above background levels if no chronic toxicity levels are established,
then field assessments of the impacts can be performed to support
the proposed ACLs. The types of field studies that should be
carried out are discussed in more detail in the following sections. .
Terrestrial Impact Assessment
The quantification of adverse terrestrial environmental
effects is difficult. However, examination of several environmental
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factors will provide an estimate of potential impacts to the
environment due to exposure to contaminated ground water.
Potential impacts to terrestrial wildlife and vegetation can
be assessed by examining exposure and environmental toxicity factors.
The exposure assessment involves determining whether the contaminated
ground water at a facility has the potential to impact any terrestrial
environment. The specific data necessary to assess exposure are
discussed in Chapters II, III, and IV. If there is a likely pathway
for wildlife and vegetation to become exposed to contaminants,
then environmental toxicity factors should be examined. It is
expected that ACL applicants will not need to address terrestrial
environmental impacts in detail, where there are no direct exposure
routes between terrestrial systems and ground water. In these cases,
the permit applicant can omit this section and move on to the
endangered species section of this chapter.
The toxicity and bioaccumulation of hazardous constituents
by terrestrial flora and fauna should be examined by the permit
applicant. Terrestrial species can be exposed to toxicants
either directly through assimila.tion of or contact with contaminated
ground water, or indirectly through food web interactions.
Toxicants can accumulate in exposed biota and increase to levels
that are lethal or have chronic effects. The permit applicant
should perform a comprehensive literature search for toxicity
and'bioaccumulation values for the ACL constituents found in the
ground water. The information should be summarized in a table
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that includes information on the toxicants, the test species, the
specific effects, the effect levels, the bioaccumulation potential,
and the reference. The permit applicant can base the potential
terrestrial toxicity assessment on the most toxic constituent within
a group of constituents, if appropriate groupings of constituents
exist for a facility. If literature information is sparse or non-
existent, then a more thorough analysis of potential environmental
impacts may be necessary. This could be based on consideration of
exposure levels and the toxicities of similar chemical compounds.
Bioassays could also be used to support the proposed ACLs; however,
techniques for performing bioassays on terrestrial ecosystems
are not an exact science, and they involve considerable time and
expense to carry out. If the permit applicant plans to perform
bioassays, then he should consult either U.S. EPA (1983c) or U.S.
EPA (1984e) for more discussions on the use of bioassays to
characterize chemical waste sites.
If terrestrial environments are presently being exposed to
contaminants above chronic toxicity levels, or above background
levels for constituents without established chronic toxicity
levels, then field studies can be used to support the proposed
ACLs. The permit applicant should examine the dominant terres-
trial habitats in the vicinity of the facility. Evidence of
any stressed vegetation should be documented and can be supported
with aerial IR photography, or ground photography and vegetation
surveys. Both a topographic map and low level aerial photographs
delineating any stressed terrestrial environments should be submitted,
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Vegetation survey data on species and abundance information on
macrofloral types, usually trees and shrubs, should be collected.
However, if the dominant habitat is an alpine or prairie environment,
grasses and other plants should be examined. The community
floral diversity can be calculated from the species information.
Discussions of diversity should include species richness and
community structure. This diversity information should be summarized
in tabular form. Any differences between the background and
affected habitats should be explained. The selection of the
background habitat should be carefully planned so as to ensure
that it is outside the influence of the facility. Sampling
protocols for diversity and productivity studies should be submitted
by the applicant, along with the data collected and a complete
discussion of results.
Endangered Species Impact Assessment
Endangered and threatened species near the facility should
be identified. The facility owner or operator should contact the
U.S. Department of the Interior, Fish and Wildlife Service, for a
current list of endangered or threatened species in the vicinity
of the facility. The permit applicant is responsible for -surveying
the area and determining the presence of these species in any
terrestrial or surface water environment. If any endangered or
threatened species are in the area, then the potential impacts of
the contaminated ground water on the species, including critical
»
habitat impacts, should be discussed. -A table should be submitted
that lists the endangered and threatened species.
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Aquatic Impact Assessment
The permit applicant should assess potential aquatic environ-
mental effects by examining exposure and aquatic toxicity factors.
The exposure assessment for surface waters was discussed in
Chapters VII and VIII. Ground-water contaminants, flow direction,
discharge areas, and proximity of surface waters are important
considerations. The permit applicant should examine potential
pathways of contaminant migration to surface waters. If exposure
to contaminants is likely, then aquatic toxicity factors should
be examined. If no hazardous constituents can reach surface waters,
then the permit applicant should provide supporting evidence of
this fact. The aquatic impact assessment can be omitted if suffi-
cient evidence is available to support a claim of no surface water
exposure.
The aquatic toxicity and bioaccumulation of hazardous con-
stituents found in the ground water should be examined by the
permit applicant if migration of the constituents to .surface
waters is likely. The U.S. EPA has published Water Quality Criteria
for 64 toxic contaminants or contaminant groups (U.S. EPA, 1980).
These water quality criteria specify concentrations of contaminants
which, if they are not exceeded, are expected to normally result
in aquatic ecosystems suitable for fish and wildlife propagation
and water recreation. A summary of the water quality criteria
is provided in Appendix 10. The permit applicant should calculate .
surface water contaminant concentrations from predicted ground-
water discharge volumes and hazardous constituent concentrations.
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Conservative assumptions should be used, such as low flow (Q7-10)
conditions and small mixing zones (see Chapter VIIX. The
predicted contaminant concentrations should be compared to acute
toxicity values within the mixing zone and chronic toxicity values
outside of the mixing zone. If compounds for which ACLs are
requested do not have U.S. EPA or State approved water quality
criteria, the permit applicant should complete a comprehensive
literature search for aquatic toxicity data. This data may be
available from commercial computer data bases. The aquatic toxicity
data should be taken from studies that used test species comparable
to the aquatic species present in the water body. The toxic data
should be summarized in a table that includes information on the
toxicant, test species, specific effects, effect levels and the
references. The permit applicant can base the potential aquatic
toxicity assessment on the most toxic constituent within a group
of constituents, if appropriate groupings of constituents exist
for a facility.
Bioaccumulation values'should also be summarized from the
literature. If aquatic toxicity information for an ACL constit-
uent is missing, a more thorough analysis of potential aquatic
impacts is necessary. This could include consideration of exposure
levels and toxicities of similar chemical compounds. The analysis
could also include field studies and possibly bioassays to justify
an ACL. If the permit applicant intends to use bioassay data to
support ACLs, the aquatic bioassay protocols and guidelines found
in U.S. EPA (1980) and U.S. EPA (1983c) should be followed. All
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aquatic toxicity and bioaccumulation data collected by the permit
applicant should be submitted. Appendix 11 contains a survey form
that can be used to summarize environmental effects data.
The permit applicant could also submit available information
on aquatic community exposure to support an ACL demonstration.
Initially, the applicant could perform a literature search for
aquatic community effects information on the ACL constituents.
Aquatic effects can include fishery impacts, habitat impacts, and
productivity changes. Submitted information could contain data
on contaminant concentrations, environmental habitats, aquatic
effects, and literature citations.
If aquatic environments are being exposed to contaminants
above chronic toxicity levels, or above background levels if no
chronic toxicity levels are established, field assessments of
impacts may be necessary to support the proposed ACLs. Studies
can be performed to verify either environmental impact or no impact
to the exposed environment. A habitat assessment can be used to
identify affected habitats in exposed surface waters. The exposed
surface waters must be identified, along with their specific physical
characteristics (see Chapter VII). The habitat assessment of such
surface waters involves examining habitat alterations that are
the result of ground-water contaminants. A control site in an
unaffected area should be used for comparative purposes.
A comprehensive examination involving water and sediment
sampling of each nearby water body that is downgradient (down-
stream) of the facility and likely to receive contaminated
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ground-water discharges is also required. Each contaminant for
which an ACL is requested should be analyzed in each of these
media. The resulting data should be presented in a table that
identifies the water body, the media, the specific contaminants
and corresponding concentrations, the sampling locations and the
date of sampling. The data should be discussed in detail.
Affected aquatic environments should be delineated on a USGS
topographic map. The site-specific sampling protocol and data
should also be submitted.
The U.S. EPA publication, Water Quality Standards Handbook
(1983b), contains information on evaluating the habitats and
water quality of surface water environments. The types of
environmental studies that are needed to evaluate the attainability
of water quality standards are discussed. This handbook can be
used as guidance by the permit applicant during the assessment
of surface-water impacts. Appendix 12 contains two chapters of
this handbook that may be useful.
The permit applicant should examine community structure
parameters for aquatic environments near the facility. Evidence
of floral and faunal impacts can include:
1. "Stressed vegetation in surface waters or along shorelines,
2. Sparsely populated communitites,
3. Changes in community diversity, and,
4. Altered community structure.
These determinations may require an ecological survey of
habitats in each surface water body that is downgradient from the
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facility and likely to receive contaminants above chronic toxicity
levels, or above background levels for constituents without established
chronic toxicity levels. Floral surveys of dominant macrophyte
vegetation will require information on the number of species and
their abundance. Macrobenthic surveys should be used to obtain
abundance information on benthic fauna. Sport and commercial fishery
impacts should be assessed. The permit applicant should submit all
sampling protocols and data used to examine community structure and
diversity. The diversity and species abundance information should
be summarized in a table. Any difference in diversity between control
and impacted areas should be discussed. Data discussions should
include both experimental design and sampling protocols.
Agricultural Impact Assessment
The potential impacts of ground-water contamination on agriculture
must be examined by the permit applicant. Exposure pathways, crop
impacts, and livestock impacts should be included in the assessment.
The exposure assessment is used to determine if there are likely
pathways for ground-water contaminants to reach any agricultural
lands or products. As part of the exposure assessment, data on the
agricultural land uses near the facility should be submitted by the
permit applicant. Specific uses such as row crops, rangeland, grazing
tree farming and timber should be depicted on a USGS topographic
map. A table that lists acreages of the specific uses should
also be submitted.
The potential exposure pathways that the permit applicant should
examine include shallow ground water, ground-water irrigation, and
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surface water irrigation. The shallow ground-water flow direction,
aquifer attenuation mechanisms, and ground-water elevation are
important characteristics that are used to determine exposure
due to direct crop uptake of ground water. These topics were
discussed in Chapters III and IV, and must be evaluated by the
permit applicant during this exposure assessment. The irrigation
wells near the facility should be identified and delineated on a
USGS topographic map. Chapter VIII lists specific use information
that is necessary for this assessment of the irrigation wells.
Surface waters that are used for irrigation and have the potential
to be impacted by ground-water contamination must be evaluated
(see Chapter VII). The current and projected irrigation withdrawal
rates should be determined from each irrigation source.
Agricultural crop impacts should be assessed by the permit
applicant if exposure to ACL constituents is likely to occur.
The agricultural damage assessment can be omitted if a condition
of no exposure is demonstrated. The following potential agricul-
tural impacts should be assessed:
1. Direct crop impacts and reduced productivity, and
2. Bioaccumulation of contaminants.
The permit applicant may be able to estimate the expected crop
and productivity impacts resulting from exposure to hazardous
contaminants in the ground water by examining the literature.
Literature values that exist on crop impacts from exposure to the
contaminants should be summarized in a table that includes the
contaminant, the crop tested, the effect level, the bioaccumulation
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potential, and the specific reference. The U.S. Department of
Agriculture (USDA) can be a source of crop effects information
and testing methods. If literature information does not exist,
and crops are likely to be exposed to ACL constituents, the ACL
demonstration may be denied and the ground-water standards may
be set at background levels. However, the permit applicant has
the opportunity to carry out experiments to estimate potential
crop impacts. The applicant should be aware that standard experimental
protocols do not exist and that all data to support the ACL
demonstration must be submitted in a timely fashion. If tests
are performed by the permit applicant, all protocols and data
should be submitted..
The permit applicant should describe potential livestock
impacts that may occur from direct and indirect exposure to
contaminants found in the ground water. Direct exposure would
include livestock contact through watering. Indirect exposure
could include contact during animal grazing and foraging. The
applicant should submit any available information on potential
livestock impacts of the ACL contaminants. If literature values
exist, the information should be summarized in tabular form and
include the factors discussed above in the crop impacts section.
The USDA may have- information on this topic. Permit applicants .
are not normally expected to carry out experiments on exposed
livestock because of the high costs and long-term nature of such
experiments. If exposure modeling, shows that livestock exposure
occurs and sufficient literature information does not exist to
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support an ACL, then the ground-water protection standard may be
set at background levels.
Physical Structure Impact Assessment
Physical structures can be adversely affected by hazardous
constituents in the ground water. The situation at Love Canal,
N.Y., where toxicants entered basements of homes, is just one
example. The determination of potential damage to and contamination
of physical structures in the area around the facility requires
the examination of exposure pathways, waste characteristics,
environmental factors, and construction materials and techniques.
Potential exposure of the physical structures to waste con-
taminants requires identifying physical structures in the area
and exposure pathways. All manmade structures including buildings,
buried cables and pipes, railroad beds, roads, -parking areas, and
machinery near the facility should be identified and delineated
on a vicinity map. The possible exposure pathways of the ground-
water contaminants to the physical structures should be identified.
The permit applicant should refer to Chapter IV to determine what
information should be submitted in order to determine contaminant
migration pathways. If the exposure assessment determines that
physical structures are likely to come in contact with ACL contaminants,
then the potential effects of the contaminants on the physical
structures should be examined. Otherwise, the permit applicant
needs only to explain why the assessment is not needed.
The hazardous constituent characteristics of primary concern
for the physical structure impact assessment are reactivity,
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ignitability, and migration potential. Two important categories
of reactive chemicals are corrosives and solvents. The ground-
water contaminants that fall into either of these two categories
should be listed in a table by the permit applicant. The potential
effects of these compounds on building materials such as concrete,
iron, steel, plastic, wood, asphalt, and limerock should be
identified and summarized in a table. The ability of the
contaminants to permeate these materials should also be discussed.
The permit applicant should submit data on the flammability and
ignitability of the ACL constituents which have the potential
to permeate subsurface structures. Volatile organic compounds
should be given special attention since they have been implicated
in sewer-line explosions.
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Chapter XII
Persistence and Permanence of Potential Adverse Effects
(S264.94(b)(l)(ix) and (2)(x))
Many of the chapters in this guidance document discuss
informational needs for ACL demonstrations that are related to
the persistence and permanence of the ACL constituents. The
general ACL policy will be to assume a worst case approach of no
degradation of the ACL constituents unless information on the
persistence of the ACL constituents in the environment is submitted,
Similarly, if there is a potential for exposure to the ACL
constituents resulting in adverse effects, the adverse effects
will be considered permanent unless it is generally accepted not
to be permanent or information is submitted by the permit applicant
to justify it is not permanent. This chapter describes the
information that is needed to characterize the persistence of
the ACL constituents in the environment and the permanence of
their adverse effects, if exposure occurs.
Persistence
Information on the persistence of the contaminants in the
environment should be discussed in varying detail, depending
on the basis of the ACL demonstration. The applicant should
discuss the process by which each ACL constituent will degrade,
either.from a ground-water perspective, surface water perspective,
or a .combination of both depending .on the site-specific situation.
'Contaminant degradation in ground water occurs predominantly
through chemically mediated processes. If the applicant is
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claiming attenuation as a means of reducing the contaminant
concentrations, the applicant must discuss the types of processes
that may occur. These processes can include biodegradation,
hydrolysis, oxidation, reduction, or precipitation, all of
which were discussed in Chapter II.
If surface water exposure is involved, bioconcentration and
biotransformation processes are important. Bioconcentration
factors are important for evaluating human intake levels of contam-
inants from consumption of aquatic organisms and for assessing
the permanence of ecological effects. Bioconcentration factors
can be derived by experimentation or calculation. The applicant
should provide justification for the use of any bioconcentration
factors. Biotransformation is primarily carried out by micro-
organisms in the surrounding media. A lag time or acclimation
period usually occurs before the biodegradation process begins.
If biotransformation is used in the ACL demonstration, the
applicant should determine whether the microbes are acclimated
to the contaminant. A discussion of biotransformation and the
use of bioconcentration factors can be found in U.S. EPA (1980)
• and U.S. EPA (1979) .
If degradation processes are used in the ACL demonstration,
the process rates should be calculated. Whether the mechanism
of degradation is biological or chemical, all rates describing
the processes should be included in the ACL demonstration. The
parameters, coefficients, and assumptions used by the permit
applicant to calculate the degradation rates for each contaminant
should be submitted in tabular form. . .
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Permanence
Information on the permanence of the adverse effects resulting
from exposure to the ACL constituents will be required only if
the ACL demonstration is risk based. This information should be
included in the demonstration's health risk assessment (Chapter X)
and the environmental risk assessment (Chapter XI). Permanence
information is necessary in order to give the permit reviewer
some idea of the long-term effects associated with exposure to
each ACL constituent, as well as a better understanding of
which ground-water contaminants are of most concern.
Many environmental systems exhibit a high degree of resiliency,
If the damage is limited to individuals within the population
and the gene pool is not irreparably depleted, the environmental
damage may be reversible. However, if irretrievable habitat
change has occurred, then environmental damage may be permanent.
The permit applicant should examine the literature on the con-
taminant's environmental effects to determine the permanenc.e of
likely ecological impacts. Many biological evaluations can be
performed to examine the resiliency and stability of an environ-
mental system. Some examples include tissue analyses to determine
bioaccumulation, diversity and recovery studies to estimate
elasticity, and intolerant species analyses to-determine the degree
of degradation. A detailed explanation of these studies is
presented in the Technical Support Manual; Waterbody Surveys
and Assessments for Conducting Use Attainability Analyses
(U.S. EPA, 1983d) . The permanence of the adverse effects is
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related to the contaminant's concentration level at the point of
exposure. The acute and chronic effects levels for-each contaminant
should be determined if the ACL demonstration is based on risk
considerations. The effects should be classified as either
reversible or irreversible.
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Chapter XIII
Institutional Ground-Water Use Restrictions
Exposure to a contaminant is a function of the pollutant path-
way, the type of water resource use, and the proximity of receptors
to the water resources. This chapter discusses institutional
controls that can be used to prevent or minimize exposure by
controlling access to the contaminated ground water. Institutional
ground-water controls are not specifically mentioned in the
criteria listed in Section 264.94(b) of the regulations but they
can be important factors in assessing exposure to hazardous
constituents (see 264.94(b)(vii and ix)).
The permit applicant must submit evidence supporting all
use controls that are being proposed as a means of preventing
exposure. The use controls must prevent contact with the contam-
inated ground water and encompass the existing and projected
areal extent of the ground-water contamination plume. The
institutional controls used to prevent exposure to the ACL
constituents must contain some type of enforcement provision to
guarantee the existence of the use control for as .long as the
ground-water protection standard is exceeded. In addition, the
use and projected uses of the affected ground-water resource
must be considered.
States' ground-water allocation rules are generally categorized
into three types:
1. Absolute ownership, where the landowner essentially owns
the ground-water underlying the landowner's property;
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2. Reasonable use, where the courts can place reasonable
limits on the use and withdrawal of ground water; and
3. Prior appropriation, where states, through common law
and statutory schemes, have the authority to allocate
ground-water rights and regulate ground-water use
(Henderson, et al., 1984).
States that utilize the reasonable use rule or prior
appropriation rule may contain ground-water use restrictions that
include state enforced:
1. Ground-water extraction controls,
2. New well prohibitions, and
3. Existing well closures.
If the permit applicant uses arguments that depend on state
use controls such as these, then the applicant must submit
evidence that the State has authority to prevent exposure to the
contaminated ground water.
Another institutional option for preventing exposure to
contaminated ground water is a deed restriction. If the permit
applicant owns the property over a contaminated ground-water
plume, then the applicant may use deed restrictions that prevent
the use of the water. These must be enforceable covenants running
with the land that prevent exposure to the ground water, and
must apply to both current and future property owners. However,
if in the future the contamination no- longer presents a threat
to human health and the environment, a termination provision may
be allowed in the deed restriction. In order to remove the deed
restriction, the petitioner must submit evidence to the U.S.
EPA that the use restrictions are no longer necessary. This
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evidence must include long-term ground-water monitoring data
that supports the removal of the restriction. The permit applicant
could also use zoning restrictions to prevent the use of the
contaminated ground water.
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Chapter XIV
Summary and Conclusions
The factors involved in preparing and supporting an ACL
demonstration were discussed in the previous chapters. Information
on each of the criteria discussed in this guidance document is
not required in every ACL demonstration. Every RCRA facility is
unique, with different environmental properties and waste
characteristics. This necessitates that each ACL demonstration
reflect site-specific conditions and that flexibility be integrated
in applying the criteria. Much of the information required for
an ACL demonstration may be taken from the facility's Part B permit
application. This guidance document points out when additional
information that satisfies the criteria should be submitted and
also when it may not be necessary. However, the burden is always
on the permit applicant to justify all arguments used for not
submitting information on specific criteria. Appendix 13 contains
a list of tables and figures that can be submitted as part of an
ACL demonstration. The use of these tables and figures will
greatly facilitate the review of the ACL demonstration by the
permit writers. Appendix 14 contains a summary' outline of the
information that can be required to support an ACL demonstration.
The permit applicant should be sure to submit all data necessary
to fulfill the information requirements outlined in this Appendix.
Permit applicants who anticipate the need for an ACL demon-
stration should do some advance planning to enable themselves
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to make the demonstration quickly if ground-water contamination
is detected. However, in recognition of the fact that a permit
application requesting an ACL will contain more information and
analysis than an application based on the other types of
concentration limits, the ground-water regulations allow for
additional time to submit the data necessary to justify an ACL.
Within 90 days after detecting a significant increase in the,
concentration of hazardous constituents at the compliance point,
the permit applicant must indicate whether he intends to' seek an
ACL variance for any Appendix VIII constituents detected in the
ground water. The permit applicant indicates his choice by
proposing established concentration limits, or offering background
concentration limits, or giving notice that he intends to seek
ACLs. The permit applicant has an additional 90 days to submit
the actual information to support the proposed ACLs.
Once the data have been submitted by the permit applicant,
the permit writer must assess the quality of the submitted infor-
mation and determine the appropriateness of the potential point
of use, the acceptable concentrations of contaminants at the
point exposure, and of the ACLs at the point of compliance. In
many cases, the permit writer will have to use professional
judgement in determining the adequacy of the submitted information,
The Agency will indicate its decision on the merits of the.
ACL demonstration when .it issues the compliance monitoring permit.
The permit will contain a ground-water protection standard (GWPS)
for each ground-water contaminant. The GWPS will contain either
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background values or the National Interim Primary Drinking Water
Regulation limits listed in Table 1 of Section 264.94(a) (if EPA
rejects the ACL demonstration), or it will contain ACLs. The
need for corrective action will be averted if the ACL for each
hazardous constituent is established at a level higher than its
concentration at the facility's compliance point. If any consti-
tuent exceeds its ACL, corrective action will be necessary. The
ACL then becomes the benchmark for the intensity and duration of
the corrective action.
As part of the ground-water protection standard, an ACL is
in effect during the compliance period. The compliance period
is the number of years equal to the active life of the waste
management area, including the closure period. If, at the end
of the compliance period, the owner or operator is engaged in a
corrective action program, the compliance period is extended
until the owner or operator can demonstrate that the GWPS, which
may contain ACLs, has not been exceeded for a period of three
consecutive years.
Once the ground-water protection standard'has been set in
the permit* the permittee can only seek ACLs through permit
modifications under the procedures outlined in 40 CFR Part 124.
Such modifications are always major and the burden of proof to
justify the variance is on the applicant. If a facility owner
or operator violates the ground-water protection standards, he
cannot .postpone corrective action in order to argue for ACL
changes.
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The cost of ground-water corrective actions can be consider-
able. Therefore, there is a strong incentive for permit applicants
to forestall imposition of corrective action requirements by
submitting an ACL demonstration. In balancing the risks of
setting ACLs as opposed to requiring corrective action, permit
writers must consider that unwarranted and unnecessary corrective
actions not only constitute inefficient use of resources but
also could cause considerable adverse environmental impacts.
Actions necessary to remove hazardous constituents could result
in ground-water depletion, subsidence, and ecosystem dewatering.
It is essential that the preparation of an ACL demonstration be
fully supported, and that decisions on the demonstration be made
expeditiously.
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References
Black, C.A., 1965. Methods of Soil Analysis. American Society of
Agronomy, Madison, WI.
Bouwer, H., 1978. Ground-water Hydrology. McGraw Hill, New York, NY.
Brady, N.C., 1974. The Nature and Property of Soils. The MacMillan
Company, New York, NY.
CAG (Carcinogen Assessment Group), 1984. Relative Carcinogenic
Potencies Among 54 Chemicals Evaluated by the Carcinogen Assessment
Group as Suspect Human Carcinogens, Health Assessment Document for
Polychlorinated-Dibenzo-p-Dioxins. EPA-600/8-84-041A, May, 1984.
Freeze, A.R. and J.A. Cherry, 1979. Groundwater. Prentice-Hall Inc.,
Englewood Cliffs, NJ.
Henderson, T.R., J. Trauberman and T. Gallagher, 1984. Groundwater;
Strategies for State Action. Environmental Law Institute, Washington,
D.C.
Kruseman, G.P. and N.A. De Ridder, 1979. Analysis and Evaluation of
Pumping Test Data. International Institute for Land Reclamation
and Improvement Bulletin 11, Wageningen, The Netherlands.
NAS (National Academy of Sciences), 1977. Drinking Water and Health.
NAS, Washington, D.C.
Ruffner, J.A., 1980. Climates of the States. Gale Research Company,
Detroit, MI.
Ruffner, J.A. and F.E. Blair, 1981. The Weather Almanac. Gale
Research Company, Detriot, MI.
Todd, O.K., 1980. Ground-water Hydrology. 2nd Ed., John Wiley and
Sons, Inc., New .York, NY.
U.S. Environmental Protection Agency, 1979. Water-Related Environ-
mental Fate of 129 Priority Pollutants Volumes I and II. EPA-440/
4-79-029a and b, Washington, D.C.
U.S. Environmental Protection Agency, 1980. Water Quality Criteria
Documents; Availability. Federal Register 45:79318-79357, November
28, 1980.
.U.S. Environmental Protection Agency, 1982a. Subpart F-Ground-water
Protection. Federal Register 47:32350-32356, July 26, 1982
U.S. Environmental Protection Agency, 1982b. Preamble-Section D:
Ground-water Protection (Part 264 Subpart F). Federal Register
47:32291-32312, July 26, 1982.
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U.S. Environmental Protection Agency, 1933a. Draft RCRA Permit
Writers' Manual for Ground-water Protection. Contract No. 68-01-6464,
October 4, 1983.
U.S. Environmental Protection Agency, 1983b. Water Quality
Standards Handbook, Office of Water Regulations and Standards.
Washington, D.C., December, 1983.
U.S. Environmental Protection Agency, 1983c. Draft Guidelines for
Deriving Numerical National Water Quality Criteria for the
Protection of Aquatic Life and Its Uses. Washington, D.C.,
July 5, 1983.
U.S. Environmental Protection Agency, 1983d. Technical Support
Manual: Waterbody Surveys and. Assessments for Conducting Use
Attainability Analyses. Office of Water Regulations and Standards,
Washington, D.C., November, 1983.
U.S. Environmental Protection Agency, 1984a. Hazardous Waste
Management System; Ground Water Testing and Monitoring Activities;
Proposed Rule. Federal Register 49: 38786-38809, October 1, 1984.
U.S. Environmental Protection Agency, 1984b. Ground-Water Protection
Strategy. Office of Ground-Water Protection, Washington, D.C.
*
U.S. Environmental-Protection Agency, 1984c. Proposed Guidelines
for Exposure Assessment; Request for Comments. Federal Register
49:46304-46312, November 23, 1984.
U.S. Environmental Protection Agency, 1984d. Guidance and Methods
for the use of Acceptable Daily Intakes (ADIs) in Health Risk
Assessment. Environmental Criteria and Assessment Office/
Cincinnati, OH.
U.S. Environmental Protection Agency, 1984e. Characterization of
Chemical Waste Site Contamination and Its Extent Using Bioassays
(Draft Report). Contract No. DE-AC06-76RLO 1830, December, 1984.
Walton, W.C., 1970. Ground-water Resource Evaluation. McGraw-Hill
Publishing Company, New York, NY.
Other resource documents
U.S. Environmental Protection Agency, 1978. Investigation of
Landfill Leachate Pollutant Attenuation by Soils. EPA 600/2-
78-158. . -
U.S. Environmental Protection Agency, 1980. Adsorption, Movement,
and Biological Degradation of Large Concentrations of Selected
Pesticides in Soils. EPA 600/ 2-80-124.
U.S. Environment! Protection Agency
Rog;on V. Library
230 South C^rV^n Street
,Chirar;r>, Illinois 60604 '
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U.S. Environmental Protection Agency, 1982. Handbook for Performing
Exposure Assessments (Draft). Washington, D.C., November, 1982.
U.S. Environmental Protection Agency, 1982. Handbook for Remedial
Action at Waste Disposal Sites. EPA-625/6-82-006, Washington,
D.C., June, 1982.
U.S. Environmental Protection Agency, 1983. Protocol for
Bioassessment of Hazardous Waste Sites. EPA-600/2-83-054,
July, 1983.
U.S. Environmental Protection Agency/ 1984. Soil Properties,
Classification; and Hydraulic Conductivity Testing (Draft Report).
SW-925.
U.S. Environmental Protection Agency,.1984. Slurry Trench
Construction for Pollution Migration Control. EPA-540/2-84-001,
Washington, D.C., February, 1984.
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