PB88-185277
CORRECTIVE MEASURES FOR RELEASES TO SOIL FROM
SOLID WASTE MANAGEMENT UNITS
Alliance Technologies Corporation
Bedford, MA
Aug 85
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
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GCA-TR-85-66-G
Prepared for
PB88-185277
U.S. ENVIRONMENTAL PROTECTION AGENCY
Land Disposal Branch, Office of Solid Waste
Washington, DC 20460
Contract No. 68-01-6871
Work Assignment No. 51
EPA Work Assignment Manager
George Dixon
CORRECTIVE MEASURES
FOR RELEASES TO SOIL FROM
SOLID WASTE MANAGEMENT UNITS
Draft Final Report
August 1985
Prepared by
Steven C. Konieczny
Lisa Farrell
Michelle M. Gosae
Barbara Myatt
Brenda Kay
Ronald Bell
Theresa Murphy
Neil M. Ram, Ph.D.
GCA CORPORATION
GCA/TECHNOLOGY DIVISION
Bedford, Massachusetts 01730
REPRODUCED BY
U.S. DEPARTMENTOF COMMERCE
NATIONAL TECHNICAL
INFORMATION SERVICE
SPRINGFIELD, VA 22161
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50272-101
REPORT DOCUMENTATION
PAGE
1. REPORT NO.
EPA/530-SW-88-022
3. Recipient'! Accession No.
4. Title end Subtitle
Corrective measures for releases to soil from solid waste
management units
5, Report Date
Aug. 85
7. Aothor(s)
S.C. Konieczny
8. Performing Organization Rept. No.
9. Performing Organization Name ana Address
GCA Corp.
CCA/Technology Division
Bedford, MA 01730
10. Project/Task/Work Unit No.
WA 51
11. Contract(C) or Grant(G) No.
(068-01-6871
(G)
12. Sponsoring Organization Name and Address
U.S. Environmental Protection Agency
Office of Solid Waste
401 M Street, SW
Ti.C.. 7.0460
13. Type of Report & Period Covered
Draft Final Report
14.
15. Supplementary Notes
16. Abstract (Limit: 200 words)
Upon discovery of a release from a solid waste management unit at a RCRA facility,
a complete site investigation should be performed to determine nature and extent
of the release. Once the release and its extent has been characterized, and
determined to be a threat to human health or the environment, corrective measures
'must be implemented. The draft final report discusses the various types of
removal/containment (includes disposal) and treatment technologies which are
applicable to remediation of releases to soils.
17. Document Analysis •. Descriptors
b. Identifiers/Open-Ended Terms
c. COSATI Field/Group
18. Availability Statement
RELEASED UNLIMITED
19. Security Class (This Report)
Unclassified
20. Security Class (This Page!
Unclassified
21. No. of Pages
22. Price
(Smt ANSI—MO
See Instructions on Reverse
OPTIONAL FORM 272 (4-77)
(Formerly NTIS-35)
Department of Commerce
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DISCLAIMER
This Draft Final Report was furnished to the Environmental Protection
Agency by the GCA Corporation, GCA/Technology Division, Bedford, Massachusetts
01730, in fulfillment of Contract No. 68-01-6871, Work Assignment No. 51. The
opinions, findings, and conclusions expressed are those of the authors and noc
necessarily those of the Environmental Protection Agency or the cooperating
agencies. Mention of company or product names is not to be considered as an
endorsement by the Environmental Protection Agency.
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CONTENTS
Figures « iv
Tables v
1. Introduction 1-1
Background 1-1
Definition/Identification of Solid Waste Management
Units 1-2
Identifying Releases to Soils 1-5
2. Assessing the Need for Corrective Measures 2-1
Introduction 2-1
General Approach to Risk Characterization ........ 2-2
Summary 2-7
3. Overview of Corrective Measures 3-1
General 3-1
Proven Technologies 3-5
Imminent Technologies 3-42
4. Case Studies 4-1
Introduction 4-1
Fairchild Republic Company - Hagerstown, Maryland .... 4-4
Whitmoyer Laboratories - Myerstown, Pennsylvania 4-9
Enterprise Avenue - Philadelphia, Pennsylvania 4-12
Frontenac Site - Frontenac, Missouri 4-15
Crystal Chemical - Houston, Texas 4-19
Silresira - Lowell, Massachusetts 4-22
5. Recommendations on How to Select and Implement Corrective
Measures 5-1
Introduction 5-1
Important Considerations in Selecting Corrective Measures
for Releases to Soils 5-5
Summary 5-18
Case Study Example 5-22
References R-l
Appendices
A. Fate and Transport A-l
B. Exposure Assessment B-l
111
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FIGURES
Number Page
4-1 Worksheet for screening case studies . 4-2
4-2 Outline for case studies write-up 4-6
IV
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TABLES
Number Page
3-1 Removal (Containment)/Treatment Technologies 3-2
3-2 Summary of Proven Removal/Treatment Technologies 3-3
3-3 Unit Costs - Excavation of Uncontaminated Soil 3-7
3-4 Capping/Surface Sealing Materials 3-10
3-5 Capping/Surface Sealing Unit Costs . 3-13
3-6 Modification of Soil Parameters 3-20
3-7 Compounds or Classes of Compounds that Have Been (or could be)
Degraded by Commercially Available Microbial Augmentation
Productions 3-24
3-8 Micro-organisms Known to Metabolize Organochlorine Pesticides . 3-25
3-9 Atmospheric Reaction Rates and Residence Times of Selected
Organic Chemicals .......... 3-29
3-10 Liming Materials. 3-33
3-11 Advantages and Disadvantages Rotary Kiln Incinerator 3-40
3-12 Advantages and Disadvantages of Fluidized-Bed Incineration. . . 3-45
3-13 Relative Oxidation Power of Oxidizing Species 3-49
3-14 Oxidation Reactivity for Organic Chemical Classes 3-51
3-15 Some Chemicals That Do Not Oxidize at Soil and Clay Surfaces. . 3-52
3-16 Chemical Groups that React with Peroxides to Form More Mobile
Products 3-52
3-17 Chemical Reductive Treatment for Degradation of Paraquat in
Soil 3-54
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TABLES (continued)
Number Page
4-1 Types of Release(s) and Remedial Response(s) Implemented at
Selected Sites £-5
5-1 Pertinent Issues for Selection and Implementation of Corrective
Measures 5-2
5-2 Permit Writers' Checklist 5-19
5-3 Summary of Soil Removal/Treatment/Containment (Disposal)
Technologies 5-21
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SECTION 1
INTRODUCTION
BACKGROUND
The 1984 amendments to the Hazardous and Solid Waste Act (HSWA) provide
the Agency with additional authorities for corrective action at facilities
seeking permits, and for facilities with interim status under Section
3005(e). The amendments for corrective action address:
• continuing releases at permitted facilities (Section 206);
• corrective action beyond facility boundaries (Section 207);
• financial responsibility for corrective action (Section 208); and
• interim status corrective action orders (Section 233).
The new authorization allows EPA to require corrective action in response to a
release of hazardous waste or hazardous constituents from any solid waste
management unit (SWMU) to the environment, regardless of when the waste was
placed in such unit. This authority addresses releases to all media,
including soil.
Based on the 1984 amendments, the U.S. EPA, Office of Solid Waste (OSW),
Land Disposal Branch, must develop technical guidance for permit writers to
implement the "continuing releases" provision. Implementation of these new
requirements will typically take place in three stages: (1) determining
whether there is a release at a facility that warrants further investigation,
(2) collecting additional information to define the nature and extent of the
release, and (3) selecting and performing the corrective measures. This
report is intended to provide guidance on selecting corrective measures in
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response Co a hazardous constituent release to soil. Guidance is provided on
parameters and criteria which should be considered in selecting a particular
remedial response for specific site conditions and identified compounds.
The remainder of this section identifies and defines the various types of
solid waste management units (SWMUs). It also identifies releases to soil.
Section 2 discusses the need for corrective measures through review of the
potential for hazardous constituents released to soil to be transported to
other environmental matrices (air, surface water, ground water) and the
potential risk associated with such transport to human health and the
environment. Section 3 provides an overview of corrective measures including
surface soil treatment technologies. Section 4 discusses case studies where
releases to soil from SWMUs have occurred and identifies the corrective
measures undertaken at the site to clean up the contaminated soil. The
concluding section, Section 5, provides recommendations for the application of
corrective measures to soil releases. Finally, Appendices A and B provide
detailed information on fate and transport mechanisms, and exposure and risk
assessments, as briefly described in Section 2.
DEFINITION/IDENTIFICATION OF SOLID WASTE MANAGEMENT UNITS
Congress defined the term solid waste management unit (SWMU) to include
any unit at a facility "from which hazardous constituents might migrate,
irrespective of whether the units were intended for the management of solid
and/or hazardous wastes." SWMUs represent a broad category of waste
management units of which hazardous waste management units are a subset.
Under the new requirements, Subtitle D landfills and other units (at
facilities seeking a RCKA permit) which primarily handle nonhazardous solid
waste could be required to take corrective action if there is evidence of a
release of hazardous constituents from these units. The definition of SWMU
includes both active, or operating units, and inactive, or nonoperating
units. This definition also includes certain units that have previously been
exempted from 40 CFR Part 264 requirements, such as wastewater treatment tanks.
The new requirements also extend to spills and other releases from SWMUs
that may occur during the normal operation of these units. However, spills
that cannot be linked to SWMUs, such as those originating from production
areas or product storage tanks, are not covered under the continuing release
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provision. These spills are illegal, however, under other RCRA provisions
(Sobotka, 1985). The types of units included in the SWMU definition are (in
alphabetical order):
• container storage areas;
• incinerators;
• landfills;
• land treatment units;
• surface impoundments;
• tanks (including 90-day accumulation tanks);
• transfer stations;
• (underground) injection wells;*
• waste handling areas;
• waste piles;
• waste recycling operations; and »
• wastewater treatment tanks.
A container, as defined in 40 CFR Part 260.10, is any portable device in
which a material is stored, transported, treated, disposed of, or otherwise
handled. A container storage area is the location where the container
resides. Container storage areas typically consist of 55-gallon drums, but
may vary in size. These areas usually include a spill containment system,
typically a diked area above a low permeable barrier that underlies the
storage area, and sometimes include a cover to shed precipitation.
*Underground injection wells are not discussed in the body of this report.
By virtue of their operation, they are not as susceptible to release to soil
as other SWMUs since potential releases occur only during equipment failure
or waste spilling prior to injection into the subsurface. A detailed
discussion of the regulatory status and the potential and cause of release
from underground injection wells is provided in the Appendix of the draft
report entitled "Corrective Measures for Releases to Ground Water from Solid
Waste Management Units", prepared by GCA/Technology Division, August 1985.
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An incinerator, as defined in 40 CFR Part 260.10, is an enclosed device
using controlled flame combustion, the primary purpose of which is to
thermally break down hazardous waste. Examples of incinerators are rotary
kiln, fluidized bed, and liquid injection incinerators.
A landfill, as defined in 40 CFR Part 260.10, is a disposal tacility or
part of a facility where hazardous waste is placed in or on land and which is
not a land treatment facility, a surface impoundment, or an injection well.
This facility typically consists of wastes placed on a liner system to
collected liquids draining from waste and includes a similar liner system
(cover) on top of the waste to prevent incident precipitation from entering
the waste.
A land treatment facility, as defined in 40 CFR Part 260.10, is a
facility or part of a facility at which hazardous waste is applied onto or
incorporated into the soil surface; such facilities are disposal facilities if
the waste will remain after closure. Land treatment involves degradation of
organic compounds through physiochemical biologic degradation. Nutrient and
biological seeding frequently occurs with aeration of the soil/waste mixture
by rototilling, plowing or harrowing.
A surface impoundment or impoundment, as defined in 40 CFR Part 260.10,
means a facility or part of a facility which is a natural topographic
depression, manmade excavation, or diked area formed primarily of earthen
materials (although it may be lined with manmade materials), which is designed
to hold an accumulation of liquid wastes or wastes containing free liquids,
and which is not an injection well. Examples of surface impoundments are
holding, storage, settling, and aeration pits, ponds, and lagoons.
A tank, as defined in 40 CFR Part 260.10, is a stationary device,
designed to contain an accumulation of hazardous waste which is constructed
primarily of nonearthen materials (e.g., wood, concrete, steel, plastic) which
provide structural support.
A transfer facility, as defined in 40 CFR Part 260.10, is any
transportation related facility including loading docks, parking areas,
storage areas, and other similar areas where shipments of hazardous waste are
held during the normal course of transportation.
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Waste handling areas include container filling and emptying areas, and
transfer locations (e.g. from trucks to tanks) associated with all waste
management facilities. Waste handling areas are usually associated with waste
transfer, such as solvent reclamation staging, incineration charging, or
transfer from tank truck to tank, or drum storage area to trucks.
A (waste) pile, as defined in 40 CFR Part 260.10, is any noncontainerized
accumulation of solid, nonflowing hazardous waste that is used for treatment
or storage. This facility typically consists of wastes placed on a liner
system to collect liquids draining from the waste.
Waste recycling operations are areas where operations involving the
processing of waste materials for recovery are undertaken.
A wastewater treatment unit, as defined in 40 CFR Part 260.10, is a
device which: (1) is part of a wastewater treatment facility which is subject
to regulation under either Section 402 or Section 307(b) of the Clean Water
Act; (2) receives and treats or stores an influent wastewater which is a
hazardous waste as defined in 40 CFR Part 261.3, or generates and accumulates
a wastewater treatment sludge which is a hazardous waste as defined in 40 CFR
Part 261.3, or treats or stores a wastewater treatment sludge which is a
hazardous waste as defined in 40 CFR Part 261.3, and (3) meets the definition
of tank in 40 CFR Part 260.10 (as previously discussed).
IDENTIFYING RELEASES TO SOILS
Prior to implementation of a corrective measure at a SWMU, a release to
soil must be identified and its extent characterized. "Contaminated soils"
can be defined as affected soils found between the ground surface and the mean
high ground-water table. These soils are affected by a "release" which is
defined to include any spilling, leaking, pumping, pouring, emitting,
emptying, discharging, injecting, escaping, leaching, dumping, or disposing
into the environment, but excludes permitted discharges or releases.
Contamination in soils can be discovered in a variety of ways. If
contamination is uncovered through ground water sampling and analysis at a
RCRA facility, there is a possibility that a release from a solid waste
management unit (SWMU) has migrated through the soils and into the ground
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water, thus impacting soils. Surface water sampling and analysis could also
reveal a release from a SWMU that has contaminated soils and made its way via
surface runoff into various surface water bodies. . .
Visual observations during normal inspections, or if ordered by the EPA,
may reveal evidence of a release in the area of a SWMU. Dead or dying trees,
general vegetative stress and obvious signs, such as substrates found in
surface soils or highly discolored soils should be investigated as a sign of
release. Once suspected, soil sampling can be performed at various depths to
determine the extent of the contamination. For example, the hazardous
constituent type, migration rate, lateral and vertical extent, and impact on
ground water should be determined. Also, during inspections the lack of
physical integrity of a SWMU may indicate the need for sampling to determine
if a release has occurred. Examples of this may be the poor quality of a tank
or deterioration in a container storage area which may make these SWMUs more
susceptible to such release as leakage. Additionally, design characteristics
of various disposal units may make them more susceptible to a release. For
example, single-lined or unlined landfills may be more likely to have a
release than some other units.
Electromagnetic methods, ground penetrating radar, shallow geothermic and
remote sensing are other techniques often used to define a hazardous
constituent ground-water plume. These methods may also aid in the selection
of appropriate areas for soil sampling.
Once a release is discovered and its type and extent determined, some
type of corrective action may be necessary. There is no definition as to the
quantity of a release that represents a safe level in soils. However, if
there is a potential adverse impact to human health, welfare, or the
environment, then some corrective measure must be undertaken to ensure that
the impact is minimized or eliminated. The following section assesses the
need for and the extent of corrective measures necessary for releases to soil.
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SECTION 2
ASSESSING THE NEED FOR CORRECTIVE MEASURES
INTRODUCTION
Prior to selecting and implementing corrective measures for releases to
soils, a needs assessment should be conducted. The assessment of the need for
corrective measures under RCRA is based on protection of human health and the
environment. In the case of releases to soil, a standard for the protection
of human health and the environment is not currently available. In the
interim, the relevant and applicable standards for corrective action provided
in the CERCLA feasibility guidance should be met.
The assessment of the need for corrective measures should define facility
conditions and the extent of hazardous constituent release, identify the goal
of corrective measures, assist in the selection of corrective measures and
establish a time frame for implementation of corrective measures. The
assessment follows a stepwise process including the following six components:
source characterization; extent of contamination; fate and transport; exposure
assessment; hazard (toxicity) assessment and characterization. Each of the
components is discussed briefly below with emphasis on the assessment of
releases of hazardous constituents to soil from a SWMU. Information essential
to each component is presented in outline form for easy reference and is
comparable to a checklist.
Detailed procedures for the assessment of transport and fate are
presented in Appendix A of this report. Procedures for performing exposure
assessment are detailed in Appendix B. Appendix B also contains additional
information on hazard assessment and risk characterization; however, it should
be recognized that the subjective aspects of hazard and risk assessment should
only be performed by a trained toxicologist.
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GENERAL APPROACH TO RISK CHARACTERIZATION
Description of Facility Area
The first step in the needs assessment is to delineate the study area and
characterize the geophysical conditions that define the facility. Combined
with nearby land use patterns, this information provides a general description
of the area and population activity at or near the facility. Such information
can be helpful in identifying localized areas of potential concern, both as
sources of hazardous constituent release and hazardous constituent exposure.
The information required to adequately describe the facility or study area
should include:
1. The geographic setting:
a. local topography;
b. hydrological and geological setting;
c. ground and surface water flow; and
d. soil types.
2. The meteorological conditions with particular emphasis on:
a. seasonal variation;
b. episodic events; and
c. climatic factors that may affect the transport and fate of
chemicals.
These parameters give an indication of the potential importance of air, water
and land (.both sediment and soils) in both the transport and fate of chemical
pollutants.
13. The land use patterns including:
a. industrial - heavy/light;
b. residential;
c. agricultural;
d. recreational; and
e. wetlands and/or other protected ecosytems.
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Extent of Contamination
The next step in the needs assessment process identifies and determines,
to the extent possible, the hazardous constituents present and the
concentrations of hazardous constituents in the soil medium. To determine the
extent of contamination the following information should be obtained:
1. The identification of the hazardous constituents released at the
facility by:
a. source of contamination; and
b. location of release.
2. The concentrations of the constituents observed within the soil
medium.
3. The location (receptor sites) and chemical form of the constituents
to which exposure occurs.
4. References to the analytical methodology/models used and QA/QC
documentaion (particularly significant for enforcement activities).
Transport and Fate
The purpose of this part of the needs assessment is to describe and
quantify, when possible, the potential for migration of hazardous
constituents. This includes determining the potential for intermedia and
intramedia transport and transformation and predicting or estimating the
direction and magnitude of constituent migration. This can be accomplished by
determining:
1. The chemical and physical properties of the released hazardous
constituents including:
a. solubility;
b. Henry's Law Constant;
c. octanol/water partition coefficient;
d. vapor pressure; and
e. soil/sediment adsorption coefficients.
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2. The completed transport and fate section should characterize, the
hazardous constituents released at a facility by:
a. the chemical form of each constituent to which exposure occurs;
b. the potential chemical, physical and biological partitioning of
the constituents in various media; and
c. the reactive pathways that affect migration of the hazardous
constituents in the facility area including:
1) adsorption and desorption processes,
2) volatilization,
3) degradation/decomposition rates,
4) photolysis,
5) oxidation,
6) precipitation,
7) hydrolysis,
8) complexation,
9) half-lives.
3. The intermedia and intraraedia transport and transformation of
constituents including:
a. the potential for volatilization from soil to air;
b. the potential for leaching from soil to ground water/surface
water; and
c. the potential for adsorption to soil and subsequent movement in
air as fugitive dusts or via overland flow with surface run-off.
Exposure Evaluation
The purpose of this step of the needs assessment is to identify actual or
potential pathways and routes of exposure, characterize the populations
exposed and determine the extent of the exposure. Depending on the needs of
the facility assessment and the data available, this exposure evaluation may
be performed either as a qualitative or quantitative assessment. To
accomplish this:
1. The location and magnitude of hazardous constituent release to soil
should be identified and quantified.
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2. The constituent releases to soil at the facility should be
characterized to the extent possible by:
a. identifying all hazardous constituents;
b. quantifying the chemical loading into the receiving medium
(soil); and
c. identifying and predicting the chemical fate of hazardous
constituent releases - focusing on intermedia and intramedia
pathways.
3. The exposed populations must be characterized:
a. by age and by demographics (e.g. size and distribution);
b. by subpopulations at special health risk; and
c. by location and distance from the facility.
4. The potential exposure points must be identified for both human and
non-human populations by identifying:
a. the likely pathways of hazardous constituent release and
transport;
b. population activity and land use patterns at and near exposure
points; and
c. magnitude, source and probability of exposure to specified
hazardous constituents.
5. Identification of the contribution to the overall risk (exposure)
for each exposure route posed by releases to soil should be
determined including:
a. dermal contact with soils;
b. ingestion of soils (particularly important for ages under 6);
c. inhalation of airborne particulates (with subsequent
reingestion); and
d. ingestion of contaminated biota.
Hazard Assessment
The purpose of hazard assessment is to determine the nature and extent of
health and environmental effects associated with exposure to the hazardous
constituents identified in the assessment of the extent of contamination.
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This section can be divided into two subsections consisting of a toxicplogical
review and a dose-response assessment. Toxicological and dose-response
assessment information for hazardous constituents of concern can be found in
the Health Effects Assessment (HEA; documents available through EPAs Office of
Emergency and Remedial Respones (OERR) or in the Toxicological profiles
available through EPAs Office of Waste Programs Enforcement.
Risk Characterization
The purpose of risk characterization is to integrate the findings of all
the previously described sections in order to estimate facility specific risk
to human health and the environment. Individual lifetime risks and total
population risks can generally be calcuated for average and maximum levels of
hazardous constituents in soil and other affected media (e.g., air, biota).
1. The risk characterization should address all types of potential or
actual risks posed by the constituent release including:
a. carcinogenic risks;
b. non-carcinogenic risks; and
c. environmental risks.
2. The weight of evidence associated with each step in the risk
characterization process must be considered and include:
a. estimated uncertainties;
b. assumptions; and
c. data gaps.
3. Risk estimations can be determined for
a. carcinogens - by multiplying carcinogenic potency value by the
current and projected chronic exposure levels;
b. non-carcinogens - by comparing the projected exposure levels to
acceptable levels; and
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c. environmental risk
1) by identifying the toxic effects of exposures to the
chemicals of concern to wildlife, and
2) by discussing the effects of exposure on indigenous
species, on the food chain and on the habitat.
4. The overall risks from exposure to hazardous constituents may be
determined by:
a. estimating the exposures from individual hazardous constituents
released;
b. estimating the exposure from specific exposure routes;
c. determining the additive/synergistic/antagonistic effects that
may result from exposure to multiple constituents by various
exposure routes; and
d. reviewing the metabolic/reactive/adsorptive pathways of
hazardous constituents.
SUMMARY
The above generic approach can be used to develop a comprehensive
understanding of the risk posed by release of a hazardous constituent from a
SWMU at a RCRA facility. The underlying components of the SWMU
assessment/exposure assessment process are closely integrated and build upon
each other. An organized, logical evaluation process ensures that all issues
have been examined either qualitatively or quantitatively, and that risk
characterization efforts are developed on a sound, documented data base. This
generic approach can be used as a framework to identify the particular release
(e.g. soil) and routes of exposure at any given RCRA facility, that presents
adverse threats to public health and the environment.
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SECTION 3
OVERVIEW OF CORRECTIVE MEASURES
GENERAL
Upon discovery of a release from a solid waste management unit at a RCRA
facility, a complete site investigation should be performed to determine the
nature and extent of the release. Once the release and its extent has been
characterized, and determined to be a threat to human health or the
environment, corrective measures must be implemented. This section discusses
the various types of removal/containment (includes disposal) and treatment
technologies which are applicable to remediation of releases to soils.
Table 3-1 lists the proven and imminent removal/treatment technologies
discussed in this section, and also lists emerging technologies. Proven
technologies are those technologies that have been used successfully at
various sites to clean up hazardous wastes from soils. Imminent technologies
are those that have been proven in the laboratory and successfully used in the
field on pilot-scale studies. Emerging technologies are those technologies
that, at the present time, are in the laboratory testing stage or possibly
have been used in the field with either unknown or variable results.
Much of the information in subsequent discussions on the following proven
and imminent technologies were excerpted from a report by JRB Associates
entitled "Review of In-Place Treatment Techniques for Contaminated Surface
Soils," September 1984; these technologies include chemical oxidation,
chemical reduction, photolysis, biodegradation, sorption, attenuation,
neutralization, and extraction (soil flushing).
Table 3-2 provides an overview of the hazardous constituents which are
amenable to each proven removal/treatment technology, presented in this
report, along with some general comments about the technology. Following this
table are more detailed discussions of each proven and imminent removal/
treatment technology. In addition to these technologies, natural treatment
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TABLE 3-1. REMOVAL (CONTAINMENT)/TREATMENT TECHNOLOGIES
Proven Technologies
Imminent Technologies
Emerging Technologies
OJ
I
Excavation
Offsite Disposal
Onsite Capping
Onsite Landfill ing
Soil Solidification
In situ Biodegradation
Above-Grade Biodegradation
Photolysis
Neutralization
Adsorption
Rotary Kiln Incineration
Mobile Rotary Kiln Incineration
Vaults
Mobile Hazardous Waste Extraction
Fluidized-Bed Incineration
Mobile Advanced Electric Reactor
Attenuation
Chemical Oxidation
Chemical Reduction
Extraction (Soil Flushing)3
Multiple-Hearth Incineration
In Situ Vitrification
Chemical Degradation
(dechloronation)
Ion Exchange
Polymerization
Reduction of Volatilization
Volatilization
alncludes mobile EPA unit.
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TABLE 3-2. SUMMARY OF PROVEN REMOVAL/TREATMENT TECHNOLOGIES
Removal/Treatment Technology
Removal (ContmioMnt) Treatment
Amenable
Hazardoua Conatituenta
Excavation
Cap InatallaCion
and Surface Sealing
All conacituent Cypea
Moat conacituent Cypea*
Offaite Oiapoaal
Oaaite Landfill
All conacicuent Cypea
All Cypea of soil
contamination
SolidificaCion
Inorganics are more
amenable Chan organic!
Biodegradacion
(In iicu/Above-Grade)
Sooe organica**
Factora affecting Che feaaibilicy of thia
technology include*: depth of
contamination, and ground-water table, duat
problem, acabilicy of aoila, acceaaibility,
and volume of contaminated aoil.
Capping prevenCa direcC contacC with hazardoua
conatituenca and may minimize offaite
migration via ground-water contamination.
May not be effective in areaa with a high
ground water cable. Capping doea not comply
with RCRA regulationa for land diapoaal of
hazardoua conaciCuenCa. Regular maintenance
of Che cap ia required Co maintain the
integricy of Che unic.
Factora affecting the feaaibilicy of thia
alternative include; availability of offaice
diapoaal capacicy, hatardoua conacicuenc
toxicity, diatance to diapoaal facility,
transportation hazarda, and coata.
Faccora affeccing Che feaaibilicy of thia
technology include: depth of ground wacer
table, volume of haxardoua conacituenta to be
diapoaed, aeiamic condition!, conatituent
Coxicity, peraiacance of hazardous
conatituenta, and auitabilicy of geology for
landfill conatruction. Regular maintenance
ia required to maintain the integrity of the
unic. Can be deaigned to comply with RCRA
land diapoaal regulaciona.
Solidification altera Che phyaical and/or
chemical acate of the hazardoua conatiCuenca
within the aoil which rendera them leaa
leachable, leaa toxic, and more eaaily
handled, tranaported and diapoaed. The
primary aolidification proceaaea are
cement-baaed and pozzolanic proceaaea.
Solidified materiala generally have low
durability and rout, therefore, be protecced
from freeze/thaw and wet-dry cyclea.
Solidification greacly increaaea the volume
of hazardoua material.
Biodegradacion ia a highly effective and
generally coac-effective biological treatment
technology for hazardoua conatiCuenca which
are readily biodegradable. Shallow aoila may
be treated in aitu whereat deep concamination
may need to be excavated and treated above
grade. The rate of decompoaicion of an
organic conatituenc dependa on ita chemical
composition and choae factora which affect
the aoil environment auch aa pH, temperature,
moisture content, aeration and oxygen supply,
nutrienta, and carbon/nitrogen ratio.
(continued)
3-3
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TABLE 3-2 (continued)
Removal/Treatment Technology
Removal (Containment) Treatment
Alienable
Hazardous Constituent!
Photolysia
Neutralization
Adsorption
Organic compounds with
moderate to strong
adaorption in Che
>290 nai wavelength
range
Acidic or baaic
constituents
Heavy aetals and
organics
Rotary Kiln
Incineration
(Stationary/Mobile)
Organic constituents
Fhotodegradation results when ultraviolet
energys break the carbon-halogen bond, thus
dehalogenating the molecule. Photolysis is a
•ajor fate of many organic compounds. The
photochemical characteristics of the
hazardous constituents and climatic
conditions affect the suitability of this
process.
Neutralization can reault in metal
immobilization, decreased corrosivity,
enhanced microbial activity, etc. Factors
influencing the effectiveneas of
neutralization include: hazardoua
conatituent characterization, soil
conditions, depth of contamination, and
geological/hydrologies! conditions.
Agricultural products, sewage sludge, and
activated carbon, among other organic
materials, have been utilized to immobilize
hazardous constituents in soils. The
technology is more reliable over the short
term. In the case of organics, sorption may
immobilize constituents until they can be
biodegrade'd.
Stationary rotary kilna have proven to be
effective for incineration of - wide variety
of solid hazardous waatea. Long residence
times in the rotary kiln and high
temperatures result in complete incineration
of organic materials. High costs are
associated with thia technology. Three
commercial units available are: Rollins
Environmental Services, Deer Park, Texas;
ENSCO, El Dorado, Arkanaaa; and SCA Services,
Chicago, Illinois. Mobile rotary kilns have
also been proven to be effective for
incineration of solid wastes.
'Capping of highly soluble hazardoua constituents is not recommended.
**Only those constituents amenable to biological attack.
3-4
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mechanisms such as volatilization, photolysis and biodegradation may
effectively remove hazardous constituents from soil. Variables affecting
these mechanisms include soil and climate conditions, hazardous constituent
characteristics, toxicity, teachability and depth.
Each of the proven technologies will be discussed under the following
categories.
• General Description - discusses the technology and the various
procedures and parameters that are involved.
• Hazardous Constituents Amenable to the Technology - describes the
types of hazardous constituents that, when contained in the soil
horizon, can or cannot be adequately treated with the technology.
• Performance - presents the effectiveness of a corrective measure in
mitigating a human health or environmental risk in terms of its
overall performance.
• Reliability - discusses the demonstrated performance and operation
and maintenance requirements of corrective measures; including
various parameters that may optimize or adversely affect the
reliability of a measure.
• Implamentability - presents the various parameters that affect the
relative ease of initiating a corrective measure such as onsite and
offsite conditions along with time to characterize the
constructability of the corrective measure.
• Cost - reports the general costs for the proven technologies.
However, it must be stressed that in most cases costs are highly
variable due to various site-specific and constituent-specific
characteristics. Therefore, reported costs should only be used for
technology comparisons.
PROVEN TECHNOLOGIES
Excavation
General Description—
Excavation is an important technology for the treatment and disposal of
contaminated soils. Excavation can normally be performed in a relatively
quick, efficient, and cost-effective manner. However, if the contaminated
soils are very deep or below the water table, excavation can become expensive,
technically difficult and, therefore, may not be a viable corrective measure.
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Excavation is also performed in conjunction with other technologies.
Many corrective measures such as capping, onsite landfilling, offsite
disposal, or many treatment technologies rely on the ability to excavate the
contamination in order to be able to implement the corrective measure.
However, if hazardous constituents cannot be excavated due to economic or
technical issues, an in situ treatment method should be considered.
Excavation is widely used for removing surface and subsurface
contaminated soils. This activity is normally conducted with the following
types of equipment:
• backhoe,
• front-end loader,
• bulldozer,
• clamshell, and
• dragline.
Hazardous Constituents Amenable to the Technology—
Essentially all types of contaminated soils can be excavated with any
readily available machinery (indicated above). However, an important
consideration during excavation is the health and safety of workers. Fugitive
dust emissions which are easily generated must be minimized throughout
excavation processes by various methods of dust suppression.
Performance—
Excavation of contaminated soils is a very effective method of dealing
with a soil release from a SWMU. Once the soils are excavated there are many
options for cleanup that may be implemented. Therefore, the ability to
excavate the soils is a benefit when attempting to develop and implement a
corrective measure.
Reliability--
Excavating contaminated soils is a very reliable removal method as long
as sampling is performed to ensure that all of the contaminated soils are
removed. Removal of all contaminated soil eliminates the hazardous constituent
source and its potential impact on human health and the environment.
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Implementability—
Site conditions are the principal factors effecting the ability to
excavate contaminated soil. For example a leak or spill that has only
contaminated shallow soils may easily be removed. However, soils that are
deep (i.e., under a landfill) or below the water table may require quite
extensive excavation methods which greatly increase the time needed to
implement a corrective measure. However, once soils are removed, beneficial
results should be realized immediately and the threat to human health and the
environment should be mitigated.
Cost—
Costs for excavation must also be considered in the final overall
decision. Excavation costs can, however, vary greatly depending on the depth
of contamination and proximity to the ground-water table. Table 3-3 indicates
1985 unit costs for various types of excavation equipment. Actual costs for
excavation can be increased by 50 percent or more for health and safety
reasons (SCS Engineers, 1981).
TABLE 3-3. UNIT COSTS - EXCAVATION OF UNCONTAMINATED SOIL
Equipment
Backhoe
Dragline
Clamshell
Dozer
Front-end Loader
Gradall
Scraper
Power Shovel
1985 Unit Cost
2.44 -
1.66 -
3.23 -
.31 -
.84 -
3.11 -
2.11 -
1.25 -
(I/cubic
3.30
3.50
4.83
4.52
1.51
3.80
3.98
3.28
yard)
Source: R.S Means, 1985.
Technical difficulties can also greatly increase the cost of excavation.
If the contaminated soils are deep, below the water table or if
sheeting/shoring is needed to support the excavation, costs can greatly be
increased due to a loss of efficiency.
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Qffaite Disposal
General Description—
Offsite disposal is a removal/containment corrective measure, and can be
implemented once the extent of soil contamination is determined. It requires
additional remedial measures involving the excavation, loading and hauling of
contaminated soils to an approved facility for final disposal.
Hazardous Constituents Amenable to This Technology—
Essentially all contaminated soils can be disposed of at a properly
permitted facility. Most hazardous constituents, as a result of the 1984 HSWA
amendments, require disposal at a double-lined facility. Some contamination
such as foundry wastes, however, may be disposed of in a single-lined landfill.
Performance—
Offsite disposal is a very effective long-term disposal action for
contaminated soil. If the extent of contamination is well-defined and
sampling is performed during soil excavation then essentially all of the
contamination (i.e., soil) should be effectively removed. This measure has a
long useful life since, once removed, the contaminated soil will not cause any
additional problems at the SWMU.
Reliability—
Offsite disposal is a very reliable corrective measure since the
contaminated soils are removed from the facility and therefore, continued
operation and maintenance activities are not required. However, based on the
1984 HSWA amendments, landftiling of untreated hazardous wastes are soon to be
banned thereby, requiring that contaminated soils be treated prior to disposal.
Implementability—
The implementability of offsite disposal is subject to the limitations of
excavation which have previously been discussed. Additionally, issues such as
hauling distances, availabiity of landfill space, and quantities of soil must
also be considered since they greatly influence the implementability and costs
associated with the corrective measure. A considerable amount of time will be
3-8
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needed to complete the remedial action if the soils are difficult to excavate,
are large in quantity, or if the permitted landfill is a long distance away.
However, once the contaminated soils are removed, beneficial results should be
realized immediately.
Accidental spillage during transportation must be considered as a safety
issue. All soils must be shipped in accordance with various EPA and DOT
regulations to minimize the possibility of problems during transportation.
Cost-
Factors which effect excavation costs also influence offsite disposal
costs. Additionally, hauling distance and availability of landfill space
effect overall disposal costs. Costs have recently (March 1985) been reported
to GCA Corporation for disposal (i.e., tipping fee) by GSX Corporation of
3
Pinewood, North Carolina as being approximately $100/yd . Transportation
costs are generally high, very site-specific, and influenced by hauling
distances and equipment availability.
Cap Installation and Surface Sealing
General Description—
Cap installation and surface sealing are corrective measures which can be
performed to excavated contaminated soils or over existing in-place
contamination. Capping consists of either impermeable capping which acts to
prevent surface water infiltration and eliminates direct hazardous constituent
contact, or permeable capping which differs from impermeable in that it allows
surface water infiltration.
Impermeable capping can consist of a single synthetic or natural cover
system which includes: a topsoil layer, atop a buffer/drainage layer, atop an
impermeable layer, atop a bedding layer; or, a multimembrane system which
includes a topsoil layer, atop a synthetic membrane, atop a bedding layer,
atop a natural impermeable layer (i.e. clay).
Table 3-4 lists the types of materials used to cap contaminated soils.
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TABLE 3-4. CAPPING/SURFACE SEALING MATERIALS
Synthetic Materials Natural Materials
Asphalt
Bitumen cements or concretes Bentonite
Bituminous fabrics Clay
Butyl rubber Soil
Elasticized Polyolefin
EPDM (ethylene-propylene-unsaturated dienoterpolymer)
Hypalon
Liquid emulsified asphalts or tars
Neoprene rubber
Polyolefin (Polyethylene and chlorinated polyethylene)
Portland cements or concretes
PVC (Polyvinyl chloride)
Sulfur (thermoplastic coating)
Teflon - coated fiberglass (TFE)
Source: EPA, 1983b.
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Hazardous Constituents Amenable to the Technology—
Most types of contaminated soil can be disposed in an impermeable'capped
structure. The use of bottom liners, however, is required to comply with
various RCRA regulations.
Hazardous constituent/membrane compatability is an issue of concern when
considering impermeable capping. Hazardous constituents contacting an
impermeable membrane can lead to premature membrane degradation and failure.
Problems can arise when an impermeable cap is placed above soils contaminated
with highly soluble constituents without the added protection of a bottom
liner and leachate collection/detection system. If the cap is breeched,
constituents with high aqueous solubilities and low octanol-to-water partition
coefficients will tend to mobilize from the soils and migrate into the ground
water. Therefore, the impermeable capping of soils with soluble hazardous
constituents is not advisable unless there is a bottom liner or unless site
conditions dictate that migration is unlikely. This restriction is also
applicable to permeable capping of contaminated soil whereby permeable capping
may be acceptable if the hazardous constituents are not mobilized by surface
water infiltration.
Performance—
Impermeable capping is, in general, relatively effective as a removal/
containment measure, in that it can prevent surface water infiltration and can
preclude human contact with contaminated soil. This corrective measure is
best suited in areas where there is a safe distance between the bottom of the
contaminated soils and the mean high ground water table. This environmental
feature will act to protect ground water in the event of a breech in the cap
with subsequent hazardous constituent generation. Impermeable capping is
enhanced when site soils are of the type which minimize hazardous constituent
migration. This situation is particularly advantageous if a bottom liner is
not present. Capping suffers the disadvantage that cap failure may result in
surface water infiltration and subsequent constituent migration.
A permeable cap like the impermeable cap is a relatively effective means
of isolating contaminated soil as long as its limitations are recognized. A
permeable cap is expected to have a long useful life as long as the cover
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material is properly maintained and erosion is eliminated. However, if
erosion occurs then direct contact with the contaminated soils would be
possible.
Reliability--
Impermeable or permeable caps must be maintained to function properly.
Operation and maintenance activities such as inspections to ensure continued
cap integrity, mowing and revegetation and erosion control measures are
crucial to obtaining the maximum useful life for this type of structure.
Ground water monitoring is also required to detect leachate generation or
hazardous constituent migration. This corrective measure is often used in
conjunction with other remedial measures for site clean up. For example,
pumping or frenoh drains are used to aid in ground water cleanup. The use of
impermeable and permeable caps to isolate soils must be carefully investigated
prior to their installation at a SWMU. It must be determined that the cap
will be able to perform as intended and that the soil contamination will not
migrate or impact human health and the environment.
Implamentability—
The principal consideration in regards to implementing and installating a
cap are site conditions, and time. While permeable and impermeable caps can
usually be installed in a relatively short (i.e., several months) time period,
equipment and material constraints can increase the period of time required to
implement these measures.
Cost—
Some general costs for permeable and impermeable materials are presented
in Table 3-5. These costs do not include any costs for excavation or any
other site activities.
Onsite Landfill
An onsite landfill may be used to dispose of contaminated soil from a
release at a SWMU. However, if the SWMU is a landfill and the leak/release
can be repaired, then the newly contaminated soil can be returned to the
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TABLE 3-5. CAPPING/SURFACE SEALING UNIT COSTS
Material
Unit Cost (June 1985)*
Topsoil (sandy loam), hauling, spreading, and grading
(within 20 miles)
Clay-rich soil, hauling, spreading, and compaction
Sand, hauling, spreading, and compaction
Portland cement concrete (4 to 6 in. layer), mixed,
spread, compacted onsite
Bituminous concrete (asphalt pavement) (4 to 6 in.
layer), including base layer
Lime or Portland cement, mixed into 5 in. of cover soil
Bentonitic clay (2 in. layer) spread and compacted
Sprayed asphalt (1/4 in. layer), with cover soil,
installed
PVC membrane (20 mil), installed
Chlorinated PE membrane (20 to 30 mil), installed
Elasticized polyolefin membrane, installed
Hypalon membrane (30 mil), installed
Neoprene membrane, installed
Ethylene propylene rubber (EPDM) membrane, installed
Butyl rubber membrane, installed
Teflon-coated fiberglass (TFE) membrane (10 mil),
installed
$16.85/yd3
$11.30/yd3
$20.34/yd3
$10.17 - $16.95/yd2
$5.08 - $8.19/yd2
$2.43 - $3.39/yd2
$2.14/yd2
$2.26 - $3.84/yd2
$1.97 - $3.05/yd2
$3.67 - $4.86/yd2
$3.50 - $4.69/yd2
$8.36/yd2
$8.19/yd2
$4.07 - $5.3l/yd2
$4.07 - $5.76/yd2
$26.00/yd2
Fly ash and/or sludge spreading, grading, and rolling $1.69 - $2.82/yd2
Source: Radian Corporation, 1983.
*Costs updated to June 1985 dollars by GCA Corporation/Technology Division.
3-13
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repaired landfill. If the landfill has installation defects or quality
control was poor during installation, then conceivably a completely new
landfill may need to be constructed to adequately protect human health and the
environment.
General Description—
Landfilling of contaminated soils has been used for many years as a means
of storage and permanent disposal of all types of contaminated soils.
Landfilling generally consists of placing soils into either a lined or unlined
excavated area and then placing a cap over these soils. If the ground water
table is very shallow, landfills can also be constructed above grade in
mounds. The general types of landfills include:
• "state-of-the-art" RCRA-designed landfills,
• single-lined landfills, and
• unlined landfills.
A "state-of-the-art" RCRA-designed landfill generally consists of
impermeable liners, and leachate collection and leak-detection systems for
both its cap and bottom liner systems. Of the three types of landfills
identified above, a RCRA landfill offers the greatest amount of protection to
the environment since it essentially eliminates surface water infiltration and
hazardous constituent migration into the ground water. A 30-year post closure
ground water monitoring period is, however, required.
A single-lined landfill consists of one liner, a leachate collection
system comprised of a drainage layer and perforated pipes, and an impermeable
cap. Such landfills also require post-closure ground water monitoring for a
30-year period.
An unlined landfill consists of an unlined trench with an impermeable cap
and no leachate collection system. While this type of landfill can be
effective under certain conditions, there is always the possibility of
leachate being generated and subsequently migrating to the ground water.
Factors that must be considered when assessing the suitability of
landfill ing include:
3-14
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• The physical state and solubility of wastes within the contaminated
soils to be landfilled. The materials must be amenable to being
compacted and securely placed to eliminate differential settling and
avoid landfill failure.
• Present land use and the depth to ground water.
• Geologic conditions such as soil permeability, location of bedrock,
impermeable strata, and seismic zones.
• Location within a 100-year floodplain.
Hazardous Constituents Amenable to the Technology—
Generally most types of contaminated soil can be landfilled. However,
the compatibility of any generated hazardous constituent and the liner must be
determined prior to installation to ensure that hazardous constituents
generated will not adversely affect the integrity of the liner. Adverse
effects on the liner can lead to premature breeching and decrease in useful
life.
Performance—
RCRA landfills are expected to be very effective in containing
contaminated soils since they have many safeguards against hazardous
constituent discharge. This type of double-lined landfill encapsulates the
soils thereby minimizing hazardous constituent generation and preventing
constituent release into the environment (assuming QA/QC procedures during
construction and operation are strictly adhered to).
A single-lined landfill will be somewhat less effective in containing
contaminated soils since it only has one liner. This type of landfill is also
not expected to have as long a useful life as a double-lined RCRA landfill.
An unlined landfill is even less effective at providing protection to
human health and the environment since cap failure can occur thus allowing
hazardous constituent migration into ground water. Unlined landfills must be
carefully sited.
Reliability—
Properly designed and installed landfills are generally quite reliable.
There are, however, many operational and maintenance activities that are
necessary to ensure proper functioning of the landfill. For example,
3-15
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maintenance and repair to the cap during establishment of the vegetative cover
is a critical and extensive activity. Landfills having leachate collection
and leak detection systems also require continuous monitoring. Other
activities such as cleaning collection system drain pipes may occasionally be
necessary. All of these activities greatly effect the reliability of
landfilling contaminated soils.
Implementability--
Some of the site conditions that may affect the implementability of an
onsite landfill are:
• bedrock outcropping;
• shallow ground water table; and
• physical space for the landfill.
If the bedrock is shallow or if outcroppings are erratic then siting a
landfill may be impossible due to the lack of depth. Very shallow ground
water makes installation difficult since dewatering may be required to
excavate and place the landfill layers. In these cases an above-grade or
mounded landfill may be applicable.
Landfills can generally be constructed within a few months; however this
is greatly dependent on the amount of soil to be landfilled and the overall
site conditions. Once the soils are placed in the landfill, immediate
beneficial results should be realized, since the soils will no longer
contribute to continued contamination.
Cost—
A double-lined landfill can be constructed for approximately $60 to
$80/yd3 (GCA, 1985b)- A single-lined landfill can be constructed for
approximately 15 percent less than a double-lined facility and therefore,
ranges from $50 to $70/yd . An unlined landfill consisting of an
O
impermeable cap can be expected to cost approximately $30/yd .
3-16
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Solidification
General Description—
Soil solidification or stabilization is a process that alters the
physical and/or chemical state of the hazardous constituents within the soil
rendering them less leachable, less toxic, and more easily handled,
transported, and disposed. With current solidification technologies,
inorganic constituents are essentially the only types of constituents that are
amenable to solidification. Generally contaminated soils containing greater
than 10 to 20 percent organics cannot be solidifed (U.S. EPA, 1980). The main
types of solidification for soils consist of:
• cement-based processes; and
• pozzolanic processes.
Cement-based processes generally consist of a soil/slurry mixed with a
Portland cement. This mixture then hardens in a matter of hours or days
forming a rock-like mass incorporating the hazardous constituents into the
crystalline structure.
Most types of hazardous constituents contained in soils and slurried in
water can be solidified since suspended solids are readily incorporated into
the structure. There are also chemical reactions that occur when the
hazardous constituents and cement are combined that can alter the state of the
hazardous constituents. The final product from the process is generally
stable and inert, however, leaching can still occur. To prevent this, surface
coating for the solidified mixtures consisting of asphalt, asphalt emulsion
and vinyl have been investigated quite extensively. However, surface coatings
are currently not used with great success due to poor adhesion.
Pozzolanic solidification processes involve the reaction of lime with
fine-grained siliceous (pozzolanic) materials plus water to produce a
concrete-like mass. Pozzolanic materials generally consist of fly ash, ground
blast-furnace slag and cement-kiln dust. These products are byproducts of
commercial products with very little economic value. This activity can be
advantageous since two constituent products are combined to form a solid mass
that can be easier to dispose.
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As with the cement-based process, the pozzolanic process does not
completely eliminate leaching in all cases. Therefore, disposal" of the'se
solidified hazardous constituents necessitates the use of a specially designed
landfill that will contain and remove leachate if produced.
Hazardous Constituents Amenable to the Technology—
Inorganics are the principal types of hazardous constituents that are
amenable to solidification. During the solidification process chemical
conversions can occur as the contaminated soil and binding agent are mixed.
For example, toxic metals can be easily precipitated as insoluable hydroxides
or carbonates by the high pH of the cement. Other materials such as soluble
salts of zinc, copper, lead, manganese, and tin tend to cause variations in
setting times which greatly reduces the physical strength of the mixture.
Also, the presence of fine organic particles such as those passing through a
No. 200 mesh sieve are undesirable and tend to weaken the bond between cement
particles (EPA, 1980). Also, soils that contain high levels of sulfates
greatly increases the swelling of concrete which can cause spalling.
Performance—
Solidification is normally used on sludges and aqueous wastes. The
process of solidification is generally quite effective, however, since
leaching is not completely eliminated, disposal in a secure landfill is
necessary (EPA, 1980). Over the short term this corrective measure may
perform quite adequately, however, various processes (i.e«, freeze-thaw,
contact with water) can reduce the long-term effectiveness.
Reliability—
This process is reported to be quite reliable as long as the hazardous
constituent/solidifying agent compatibility are taken into account; types of
hazardous constituents that can be solidified have been discussed previously.
After solidification, if the material is to be landfilled, testing should be
conducted to ensure that no harmful reactions will occur if leachate is
generated.
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Imp lenient ability—
The solidification process is, in general, easily implemented. In both
the cement-based and pozzolanic processes, materials are readily available and
extensive hazardous constituent/soil dewatering is not necessary. Special
equipment is generally unnecessary since lime is a common additive and
cement-mixing is a common technology.
Cost™
The costs for solidification with Portland cement is dependent on the
physical state of the hazardous constituents and amount of soil to be
solidified. Portland cement is estimated to cost from $65 to $90/ton (Radian
Corporation, 1983).
The costs for solidification using pozzolanic processes are estimated to
be from $0.04 to $0.15/gallon for industrial sludges (EPA, 1982b).
In Situ Biodegradation
General Description—
Biodegradation is a biological treatment process which constitutes the
molecular breakdown of organic substances by living organisms. It is a
significant mechanism for degrading organic compounds in soil environments
which typically contain diverse raicrobial populations including bacteria,
actinomycetes, and fungi. Important parameters in the soil environment which
affect biodegradation include pH, soil moisture content, soil oxygen content,
nutrient concentrations, and temperature. In situ biodegradation of
contaminated soils can be enhanced by modifying soil parameters or by
supplementing existing microbial populations with other natural microbes,
adapted microbial cultures, or bioengineered microbial strains. Soil
parameters, as summarized in Table 3-6 and subsequently discussed, are
modified to enhance raicrobial growth and substrate utilization. This
includes: (1) increasing soil temperatures to between 50° and 60°C;
(2) increasing soil water potential to greater than -15 bars; (3) adjusting
soil pH to between 5 and 9; (4) adjusting the oxidation-reduction (redox)
potential of the soil; and (5) addition of nutrients. While the status of the
in situ biodegradation technology is at various stages of development,
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TABLE 3-6. MODIFICATION OF SOIL PARAMETERS
Soil Parameter
Control Method
Comment s
Temperature
Vegetation
Mulching
Irrigation
Drainage
Compaction
Tillage
Humic substance
addition
Vegetation and mulching regulate
incoming and outgoing radiation,
other methods alter the thermal
conductivity of soils themselves
Moisture content
• Irrigation
• Drainage
• Additives
Most suitable irrigation
treatment for contaminated
soils appears to be sprinkler
(overhead) irrigation due to
adjustable application rates,
uniform water distribution, and
control over erosion
Includes surface drains, i.e.,
open ditches and lateral
drains, and subsurface drains,
i.e., open ditches, buried tube
drains, and well points
Includes commercially available
water storing agents, water
repelling agents, surface
active agents and evaporation
retardants
PH
• Liming
• Sulfur or acid-
producing
substances
Calcium or calcium and
magnesium-containing compounds
used to raise the pH
Substances used to lower the pH,
little experience in field
applications
(continued)
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TABLE 3-6 (continued)
Soil Parameter
Control Method
Comments
Oxygen content • Aerobic conditions
- Tillage
- Well-point injection
- Drainage
Surface soils (<2 ft deep)
Soils >2 ft deep (saturated)
Nutrients
• Commercial fertilizers
Usually nitrogen or phosphorus
additives
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depending upon the technique used and the hazardous constituents being
treated, the control methods corresponding to each soil parameter presented in
Table 3-6 have been field tested.
Soil temperature is one of the more important factors in controlling
microbiological activity, the rate of organic matter decomposition, and the
rate of volatilization of compounds from soil. It can be modified by
regulating incoming and outgoing radiation through vegetation and mulching, or
by changing the thermal properties of the soil with irrigation/drainage,
compaction/tillage and the addition of humic substances (JRB Associates, 1982).
The degradation of hazardous organic compounds can be accelerated by
optimizing soil moisture. Limited experimentation indicates that degradation
rates are highest at a soil water potential between 0 and -.9869 atm. Typical
methods of moisture enhancement include irrigation and synthetic soil
additives. If the soil is too wet, surface erosion due to runoff will
mobilize contaminated soils and render them unavailable to biodegradation.
Therefore, soil drainage is also an important method of moisture control.
Care must be taken however not to promote hazardous constituent migration in
the process (JRB Associates, 1982).
Depending upon the nature of the hazardous constituents contaminating the
soil, it may be advantageous to optimize the soil pH for a particular segment
of the microbial population. Some fungi have a competitive advantage at
slightly acidic pH, while actinomycetes flourish at slightly alkaline pH.
Near neutral pH values are probably most conductive to microbial functioning
in general. Contaminated soil can be treated with crushed limestone or lime
products to raise the pH to the desired range, or with acid-producing
materials or sulfur to lower the pH (JRB Associates, 1982).
The oxygen content of the soil can also determine the mechanism of
biodegradation through anaerobic and aerobic processes; only aerobic processes
will be discussed in the document. Aerobic processes are more
energy-efficient and microbial decomposition processes are more rapid under
these conditions. The majority of organisms in soils decompose under aerobic
conditions. Common methods of aeration are tilling or draining the soil. If
deep soils require aeration, a backhoe (or other form of construction
equipment) or a well point system for diffusers can be used.
3-22
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Microbial degradation may also be limited by nutrient availability,
particularly if available carbon (C) is in large excess relative to the
nitrogen (N) and/or phosphorus (P) required by the microorganisms that degrade
it. If the ratio of organic C:N:P is greater than about 300:15:1 and
available (extractable) inorganic forms of N and P do not narrow the ratio to
within these limits, supplemental nitrogen and/or phosphorus should be added
(Alexander, 1977; Kowalenko, 1978).
Adding fertilizer to hasten the decomposition of crop residues is used in
agriculture (Alexander, 1977), and has been used in the treatment of hazardous
waste (oil spill) contaminated soils (Thibault and Elliott, 1980). For
detailed discussions on the soil parameters previously presented that can be
modified to promote biodegradation refer to JRB Associates (1982).
Table 3-7 lists some of the organic compounds amenable to microbial
degradation. Table 3-8 lists microbial strains which have been effective at
degrading pesticides.
Performance—
Enhanced biodegradation by soil modification has been widely and
successfully performed in the agricultural industry. The use of specially
adapted microorganisms has been demonstrated in the laboratory and has been
used successfully in several full-scale soil decontamination operations
(i.e., chemical spills).
The level of treatment for in situ biodegradation can be variable and
depends on the soil conditions and the type of contamination. High percent
removals of soil contaminants has been demonstrated after adequate pH
adjustment, nutrient addition and application of adapted microorganisms.
The optimization of soil conditions for enhanced biodegradation, however,
may result in the release and subsequent transport of hazardous constituents
via the following mechanisms: leaching, erosion, dissolution, or
precipitation.
Reliability—
The reliability of in situ biodegradation enhancement technologies for
modifying soil parameters is moderate because they require considerable
maintenance or reapplication. The use of adapted microbial populations is
3-23
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TABLE 3-7. COMPOUNDS OR CLASSES OF COMPOUNDS THAT HAVE BEEN
(OR COULD BE) DEGRADED BY COMMERCIALLY AVAILABLE
MICROBIAL AUGMENTATION PRODUCTIONS
Alcohols
n-Butyl alcohol
Dimethylaminoethanol
Alkyl Halides
Ethylene dichloride (1,2-Dichloroethane)
Methylene chloride (Dichloromethane)
Propylene dichloride (1,2-Dichloropropane)
Amines
Dimethylaniline
Trimethylaraine
Aromatic Hydrocarbons
Divinyl Benzene
Polynuclear Aromatic Hydrocarbons (PNAs)
Styrene (Vinyl Benzene)
Chlorinated Aromatic3
Polychlorinated biphenyls (PCBs)
Esters
Methacrylates
Ketones
Acetone
Nitriles
Acrylonitrile
Phenols
Phenol
Metachlorophenol
Orthochlorophenol
Pentachlorophenol
Resorcinol (1,3-Benzenediol)
t-Butylcatechol
Crude and refined oils
Emulsifiers
Detergents
Source: EPA, 1984b.
3-24
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TABLE 3-8. MICRO-ORGANISMS KNOWN TO METABOLIZE
ORGANOCHLORINE PESTICIDES
Microorganism
Pesticides
Bacteria
Arthrobacter
Bacillus
Clostridium
Escherichia
Hydrogenomonas
Klebsiella
Micrococcus
Proteus
Pseudomonas spp.
Pseudomonas spp.
Pseudomonas
Unidentified
Unidentified
Actinomycetes
Nocardia
Streptomyces
Endrin, DDT
Endrin, DDT
Lindane
DDT
DDT
DDT
Endrin, Aldrin, DDT
DDT
Endrin, Aldrin, DDT
Heptachlor
Dieldrin
Dieldrin, Aldrin, Endrin, DDT
Lindane, Aldrin
DDT, PCNB
PCNB
Aspergillus
Fusarium
Mucor
Trichoderma
Yeast
Saccharomyces
Algae
Chlamydomonas
Chlorella and Dunaliella
PCNB
DDT
Dieldrin
Dieldrin
DDT
Lindane
Aldrin
Source: DeRenzo, 1980.
3-25
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also moderately reliable due to their dependence on soil parameters.
Biodegradation generally results in less complex, though not necessarily less
toxic, compounds. For example, the degradation products of some halogenated
organica such as DOT, DDE, and ODD have been found to be more toxic and
persistant than their parent compounds.
Implementability—
The implementability of this treatment technology is variable because it
depends rather heavily on soil properties and site conditions including
moisture content, trafficability, and depth of contamination. Usually
standard agricultural equipment and techniques, and commercially available
materials are required.
Cost—
Costs for in situ biological treatment are highly variable and site
specific, and therefore are not readily approximated (Ronyak, 1985).
Above-Grade Biodegradation
General Description—
The previous discussion on biological treatment focused on ^n situ
methods for enhancing biodegradation. Above-grade biodegradation, a
biological treatment technology, differs from in situ biodegradation in that
it can be implemented in instances where in situ treatment is not possible;
for example, when the contaminated soil is at considerable depth. Other
conditions such as a high water table, potential for migration of hazardous
constituents, the need to recirculate bacterial and nutrient solutions, and
numerous other factors may require that the contaminated soils be excavated
and located above grade for subsequent biodegradation.
In above-grade biodegradation treatment, the preliminary activity is the
excavation of contaminated soils. The excavated soils are then placed in a
lined impoundment to facilitate the recycling of nutrient and bacterial
solutions, and to collect the generated leachate. Alternatively, the
excavated soil can be placed directly on natural soils for subsequent
landfarming activities.
3-26
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Performance—
The reliability of above-grade biodegradation treatment varies widely
depending upon the nature of the contaminated soils to be treated. For
example, soils contaminated with petroleum waste products may be readily
biodegradable whereas soils contaminated with PCBs may not be suitable for
treatment. The ability to effectively treat a contaminated soil can be
ascertained by laboratory and pilot field tests.
Reliability—
Provided that biodegradation of a specific hazardous constituent has been
proven to be effective, the process can be highly reliable. After treatment,
sampling can be conducted to determine the effectiveness of the process.
Higher levels of biodegradation are generally obtained when longer periods of
biotreatment are used.
Implementability—
Above-grade biodegradation is generally readily implementable.
Sufficient land must be available to spread out the contaminated soils for
treatment. Construction of aeration tanks, impoundments, and irrigation
systems are the major construction-related activities.
Cost—
As previously stated for in situ biodegradation, costs can be highly
variable and are site specific (Ronyak, 1985).
Photolysis (Photooxidation)
General Description—
Photolysis or photooxidation is the process by which ultraviolet photons
break the carbon-halogen bond (usually C-CL), resulting in a dehalogenated
molecule. Such loss of halogens is considered favorable because lower-order
halogenated organics usually have less toxic properties and are more
biodegradable. Photodegradation is enhanced by the presence of a hydrogen
donor which replaces the chlorine on the molecule. Hydrogen donors are
applied and depending on the depth of contamination, the soil is tilled to
expose hazardous constituents to the light.
3-27
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Activated carbon adsorption of organics followed by chemical addition and
photolysis has been reported by React Environmental Crisis Engineers, St.
Louis, Missouri (1983). The method involves the addition of activated carbon
to the soils, removal of the most highly contaminated materials, and mixing
the remaining soil with sodium bicarbonate to increase soil pH. The soil is
then allowed to react photochemically resulting in the photolysis of the
parent material. The level of treatment is expected to be fairly high. An
increase in soil pH is the major secondary impact of the treatment method.
Hazardous Constituents Amenable to Treatment—
Photodegradable organic constituents are amenable to this form of
treatment. Generally, this includes compounds with moderate to strong
absorption in the 290 run wavelength range. Table 3-9 lists the of compounds
which are amenable to photodegradation.
Performance—
The level of treatment achievable is potentially quite high, based on
limited experimental data. Effectiveness also depends on the amount of
tillage possible at the site and the depth of contamination. However, the
potential for the production of hazardous compounds from photodegradation
needs to be further researched. Production of hazardous compounds from the
photodegradation of pesticides has been documented, e.g., dieldrin formation
from aldrin, paraoxon formation from parathion, phosgene formation from
chloropicrin (Crosby, 1971), and the formation of PCBs from the photoreaction
of DDT (Woodrow et al., 1983). The potential for such occurrences is expected
to be high and further research is needed to identify potential toxic product
formation to ensure the safe application of this treatment methodology.
Another concern is the potential induction of volatilization of organic
constituents from the soil without subsequent photodegradation.
Reliability—
Unless the hazardous constituents in the contaminated soil and their
photodegradation products are known, this is not a reliable method, since
toxic by-products may be formed.
3-28
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TABLE 3-9. ATMOSPHERIC REACTION RATES AND RESIDENCE TIMES OF SELECTED ORGANIC CHEMICALS
Compound
Acetaldehydec
Acrolein
Acrylonitrile
Allyl chloride
Benzyl chloride
Bio(Chloromethyl) Ether
UP
N> Carbon Tetrachloride
vo
Chlorobenzene
Chloroform
Chloromethyl methyl ether
Chloroprene
o,m,p-cresole
Dich lorobenzene6
Dimethyl Nitrosamine
Dioxane
kOH x 1012 Direct
(cm-* molecule'^ Photolysis
sec~l) Probability
16 Probable
44a Probable
2
28a Possible
3a Possible
4s Possible
0.001
0.4a Possible
0.1
3a Possible
46a Probable
-«
0.3,» Possible
39a Probable
3a
Physical
Remova 1
Probability
Unlikely
Unlikely
Unlikely
Unlikely
Unlikely
Probable
Unlikely
Unlikely
Unlikely
Probable
Unlikely
Unlikely
Unlikely
-
Unlikely
Residence
Time
(Days)
0.03-0.7°
0.2
5.6
0.3
3.9
0.02-2.9d
11,000
28
120
0. 004-3. 9d
0.2
0.2
39
<0.3
3.9
Anticipated Photoproducts
H2CO, C02
OCH-CHO, H2CO, HCOOH, C02
H2CO, HC(0)CN, HCOOH, CN°
HCOOH, H2CO, CICH2CHO,
chlorinated hydroxy carbonyls,
CICH2COOH
OCHO, Cl; ring cleavage
products chloromethyl-phenols
HC1+H2CO, CIHCO,
Chloromethyl formate
C12CO, CL°
Chlorophenols, ring cleavage
products
C12CO, Cl~
Chloromethyl and methyl
formate, CIHCO
H2CO, H2C-CCICHO, OHCCHO,
CICOCHO, H2CCHCCIO,
chlorohydroxy acids, aldehydes
hydroxynitrotoluenes, ring
cleavage products
Chlorinated phenols, ring
cleavage products
aldehydes, NO
OHfOfH
2CH2OCHO, OHCOCHO
oxygenated formates
(continued)
-------
TABLE 3-9 (continued)
OJ
Compound
Dioxio
Epichlorohydrin
Ethylene Dibromide
Ethylene Dichloride
Ethylene Oxide
Formaldehyde0
Uexach lorocyc lo- pentad iene
Maleic Anhydride
Methyl Chloroform
Hethylene Chloride
Methyl Iodide
Nitrobenzene
2-Nitropropane
N-Nitrosodiethylamine
Nitrosoethylurea
Nitrosomethylurea
Nitrosomorpholine
kOH x 10 12
(cn>3 molecule"1
sec"1)
-
2a
0.25
0.22
2a
10
59a
60s
0.012
0.14
0.004a
0.06a
55«
26a
I3a
20a
28a
Direct
Photolysis
Probability
Probable
Possible
Possible
Possible
-
Probable
Probable
Possible
Possible
Possible
Possible
Possible
Possible
Probable
Possible
Possible
Possible
Physical
Reroova 1
Probability
-
Unlikely
Unlikely
Unlikely
Unlikely
Unlikely
—
Possible
Unlikely
Unlikely
Unlikely
Unlikely
Unlikely
-
-
-
-
Residence
Time
(Days)
-
5.8
45
53
5.8
0.1-1.2C
0.2
. 0.1
970
83
2,900
190
0.2
<0.4
<0.9
<0.6
<0.4
Anticipated Photoproducts
-
H2CO, OHCOCHO,
CICH20(0)OHCO
Bi, BrCH2CH2CHO, H2CO,
Br HCO
CIHCHO, H2CC1COC1, H2CO,
H2CC1CHO
OHCOCHO
CO, C02
n 1
2CO, diacyclchlorides,
ketones, Cl
C02, CO; acids, aldehydes,
and esters which should
photolyze
H2CO, C12CO, Cl-
C12CO, CO, CIHCO, Cl-
H2CO, 1°, ICHO, CO
Nitrophenols, ring cleavage
products
H2CO, CH3cHO
Aldehydes, nitroamines
Aldehydes, Nitroamines
Aldehydes, nitroamines
Aldehydes, ether.s
(continued)
-------
TABLE 3-9 (continued)
Compound
Perch loroe thy lene
Phenol
kOH x 1012
(cm^ molecule"1
sec"1)
0.17
17s
Direct
Photolysis
Probability
Possible
-
Physical
Remova 1
Probability
Unlikely
Possible
Residence
Time
(Days)
67
0.6
Anticipated Photoproducts
C12CO, C12C(OH)COC1, Cl°
Diphydroxybenzenes ,
Phosgene' ~0
Polychlorinated Biphenyls < la
POM (Benro(a)-pyrene)
Propylene Oxide 1.3
Toluene 6
Trichloroethylene 2.2
Vinylidene Chloride 4a
o-,m-,p-xylene 16
Possible
Possible Unlikely >11
Possible Probable 8
Unlikely 8.9
Unlikely 1.9
Possible Unlikely 5.2
Possible Unlikely 2.9
Unlikely ~0.7
nitrophenols, ring cleavage
products
C0
2,
, HC1
Hydroxy PCBs, ring cleavage
products
B(a)P-l,6-quinone
CH3C(0)OCHO, CH3C(0)CHO,
H2CO, HC(0)OCHO
Benzaldehyde, cresols, ring
cleavage products, nitro
compounds
C12CO, C1HCO. CO, Cl-
H2CO, C12CO, HCOOH
Substituted benzaldehydes,
hydroxy xylenes, ring clevage
products, nitro compounds
"Hate constant by method of Hendry and Kenley (1979).
''Material is not expected to exist in vapor phase at normal temperatures. Residence time calculation assumes the
chemical is substantially absorbed by aerosal particles and that the aerosol particles have a residence time ot
approximately 7 days.
cThe shorter residence time includes a photolysis rate as given in Graedel (1978).
^Decomposition in moist air is expected. The shorter residence time includes the cited decomposition rate.
eValues given are averages for the various isomers.
^Reaction with 0('D) is possible; k»3.6xlO~10 cur* molecule"! sec"*-, and [0('D)]-0.2 molecules cm~3
implies a tropospheric lifetime of 440 years. In addition, slow hydrolysis is expected.
Source: EPA, 1984b.
-------
Implementability--
Soil tilling may be easy or difficult depending on the trafficability of
the site and the depth of contamination. Runon and runoff controls may be
necessary to manage the drainage and erosion.
Cost--
Costs for this technology can be quite variable and are highly site
dependent. If contamination is at the surface, then only tilling may be
needed. If soils are somewhat deeper, then excavation followed by spreading
at the surface will be necessay, thereby increasing costs.
Neutralization
General Description—
Neutralization is the addition of chemicals to contaminated soil to
increase pH values to pH 7 or above. Control of soil pH can result in metal
immobilization, decreased corrosivity, and enhanced microbial activity. The
most common method of soil neutralization is liming, which involves the
addition of any calcium or calcium and magnesium-containing compound to soil.
The use of acidic chemicals to lower soil pH is not commonly employed at this
time. Lime correctly refers to only calcium oxide, but is commonly used to
refer to calcium hydroxide, calcium carbonate, calcium-magnesium carbonate,
and calcium silicate slags. A summary of commonly used liming materials is
presented in Table 3-10.
The choice of a liming material depends upon several factors. Calcitic
and do1oraltic limestones are the most commonly used materials. To be rapidly
effective, these materials must be ground because the velocity of reaction is
dependent on the surface in contact with the soil. The finer the materials
are ground, the more rapidly they react with the soil. However, a more finely
ground limestone product usually contains a mixture of fine and coarse
particles in order to effect a pH change rapidly and still be relatively
long-lasting as well as reasonably priced. Many states require that 75 to
100 percent of the limestone pass an 8- fo 10-mesh sieve and that 20 to
80 percent pass anywhere from an 8- to 100-mesh sieve. Calcium oxide and
calcium hydroxide are manufactured as powders and react quickly.
3-32
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TABLE 3-10. LIMING MATERIALS
Liming Material
Description
Calcium
Carbonate
Equivalent8
Comments
U)
u>
Limestone, calcitic
Limestone, dolomitic
, 100 percent purity
65 percent CaC03 + 20 percent
MgC03, 87 percent purityb
Limestone, unslaked lime, CaO, 85 percent purity
burned lime, quick lime
Hydrated lime, slaked
lime, builder's lime
Marl
Blast furnace slag
Waste lime products
Ca(OH)2, 85 percent purity
, 50 percent purity
100 Neutralization value usually
between 90-98 percent because of
impurities; pulverized to desired
fineness
89 Pure dolomite (50 percent MgC03
and 50 percent CaCC^) has
neutralizing value of 109 percent;
pulverized to desired fineness
151 Manufactured by roasting calcitic
limestone; purity depends on purity
of raw materials; white powder,
difficult to handle—caustic; quick
acting; must be mixed with soil or
will harden and cake
85 Prepared by hydrating CaO; white
powder, caustic, difficult to
handle; quick acting
50 Soft, unconsolidated deposits of
CaCOj, mixed with earth, and
usually quite moist
75-90 Byproduct in manufacture of pig
iron; usually contains magnesium
Extremely variable in composition
aCalcium carbonate equivalent (CCE): neutralizing value compared to pure calcium carbonate, which has a
neutralizing value defined as 100.
State laws specify a calcium carbonate equivalent averaging 85 percent.
Source: EPA, 19845.
-------
The amount of lime required for soil pH adjustment is dependent on
several soil factors, including soil texture, type of clay, organic matter
content, exchangeable aluminum and buffering capacity (Follett et al. , 1981).
Differences among soils in their buffering capacity reflect differences in the
soil cation exchange capacities and will directly affect the amount of lime
required to adjust soil pH. The amount of lime required is also a function of
the depth of incorporation at the site, i.e., volume of soil to be treated.
The amount of lime required to effect a pH change in a particular
site/soil/waste system is determined in laboratory short-term treatability
studies or soil-buffer tests (McLean, 1982). Lime requirements may also be
affected by acid precipitation and acid-forming fertilizers.
Hazardous Constituents Amenable to Treatment—
Soil contaminated with acidic or basic constituents.
Performance—
Liming is a common agricultural technique where the achievable level of
treatment is high, though care must be taken to ensure that hazardous
constituents are not mobilized from the change in soil pH.
Reliability—
Reliming will probably be necessary to maintain an adequate level of
treatment.
Irapleraentability—
The implementability is quite variable, depending on the trafficability
of the site and the depth of soil contamination. Because the soil
necessitates tilling, runoff controls are necessary to control drainage and
erosion. Lime is usually applied from a V-shaped truck bed with a
spinner-type propeller in the back (Follett et al., 1981). Uniform spreading
is difficult with this equipment, and wind losses can be significant. A more
accurate but slower and more costly method is a lime spreader (a covered
hopper or conveyor) pulled by a tractor. Limestone does not migrate easily in
the soil since it is only slightly soluble, and must be placed where needed.
Plowing and/or discing surface-applied lime into the soil may therefore be
required.
3-34
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The application of fluid lime is becoming more popular, especially when
mixed with fluid nitrogen fertilizer. The combination results in less trips
across the soil, and the lime is available to counteract acidity produced by
the nitrogen. Injection of a lime slurry may also be feasible to reach
contamination at relatively deep depths.
Cost—
Costs for neutralization are highly dependent on the quantities of
materials used to neutralize the waste and the type of materials used for
neutralization.
Adsorption
General Description—
Adsorption refers to the process which results in a higher concentration
of a chemical (sorbate) at a solid surface (sorbent) or within the pore
structure of the sorbent than is present in bulk solution. Actual sorption
mechanisms are often not known. Sorption is the major general retention
mechanism for many organic compounds and metals onto soils. Adsorbed
compounds are in equilibrium with the soil solution and are capable of
desorption (Bonazountas and Wagner, 1981)-
Several processes are involved in adsorption including:
• ion exchange;
• physical adsorption through weak atomic and molecular interaction
forces (van der Waal forces);
• specific adsorption exhibited by anions involving the exchange of
the ion with surface ligands to form partly covalent bonds; and
• chemisorption involving a chemical reaction between the compound and
the surface of the sorbent.
The effectiveness of utilizing sorption to immobilize a hazardous
material can generally be predicted by the compounds adsorption isotherm,
which expresses the relationship between the amount of constituent adsorbed
onto a solid and the concentration of solute in solution at equilibrium. One
frequently used relationship is the Freundlich isotherm, which is:
3-35
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X = kCN (3-1)
where: X = amount of constituent adsorbed per unit dry weight of soil,
k and N are constants, and
C = solution phase equilibrium concentration.
The percentage adsorbed under natural moisture conditions can be
estimated by:
Percent sorbed = —r-r-—- (3-2)
1 A l/N £
k X
where: 9 = fraction soil moisture content (weight basis).
When adsorption is linear, N=l, and the percent sorbed is not a function
of the amount sorbed per unit weight of soil (X). However, when adsorption is
not linear, the percent adsorbed becomes a function of X. Equation 3-2 shows
the percent of chemical adsorbed as a function of k and X.
Materials used for adsorption include various agricultural products and
by-products, sewage sludges, activated carbon, and other organics. The
organic material can be applied to the soil by harrowing or disking. The
amount of organic material which is required to immobilize the hazardous
constituent is primarily dependent on the adsorbability of the constituent and
the organic content of the soil matrix.
Desorption is also important with respect to treatment effectiveness
because of chemical release from soil into percolating water. Generally the
extent of desorption also follows the Freundlich isotherm, but with different
K and N values. Factors directly associated with desorption include the
amount of leachate (soil/water ratio) and the amount of hazardous constituent
contaminating the soil (soil/constituent ratio). The extent of desorption
will decrease with an increase of these ratios.
Hazardous Constituents Amenable to Treatment—
Heavy metals and organic constituents are amenable to adsorption.
3-36
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Performance—
Adsorption is a treatment technology which has proven to be effective for
the removal of metals or organics. It is, however, only considered as a means
of short-term soil remediation since hazardous constituents may slowly desorb
with time and, potentially, the sorbent may degrade and result in the release
of the hazardous constituents. Conversely, in the case of organic
constituents, a sorbent may immobilize the hazardous constituents until they
are naturally biodegraded. Repeated application of an adsorbent may be
required to provide a high level of performance.
Reliability-
The reliability of adsorbtion to immobilize hazardous constituents in
soils is highly dependent on the nature of the constituents and site
conditions. Degradation or mineralization of the adsorbent could result in a
release of hazardous constituents to the environment. In general, adsorbtion
is expected to be moderately reliable over the short term, and somewhat less
reliable over the long term.
Implementability—
The implementability of adsorption varies widely depending on site
conditions. Sites most suitable for treatment are those which are accessible
to heavy equipment and for which the depth of soil contamination is shallow.
The organic sorbents can then be easily applied to the surface and tilled into
the soil.
Cost—
Costs for adsorption are highly variable due to hazardous constituent
type, quantity and sorbent necessary for immobilization.
Stationary/Mobile Rotary Kiln Incineration
General Description—
Rotary kiln incineration has been in use for many years and can be used
to destroy contaminated soils from a release at a SWMU. A rotary kiln
generally consists of a cylindrical refractory-lined shell mounted at a slight
incline (i.e., less than 5 degrees). The shell rotates (5 to 25 times per
3-37
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hour) during the incineration process to control residence times and mixing
with combustion air to ensure that maximum destruction is achieved. In most
cases, a secondary chamber is used to further the destruction process.
However, the secondary unit can be used alone to burn flammable liquids.
There are two basic designs of rotary kilns, the cocurrent and
countercurrent designs. The cocurrent design is a unit that has an auxiliary
fuel burner at the front end of the incinerator where contaminated soils are
fed in. The countercurrent design has the fuel feed at the lower end of the
unit, therefore the combustion gases flow countercurrent to the flow of
contaminated soils. Each design adequately incinerates hazardous
constituents, however the countercurrent design is better suited for
constituents with a low heating value (such as saturated material) due to the
fact that temperature is controlled at both ends of the unit. This feature
tends to minimize overheating of the refractory liner (Bonner, 1981).
Residence times vary from a few seconds for highly combustible gas to a
few hours for low combustible solid wastes (i.e. contaminated soils). In
dealing with the incineration of various types of hazardous constituents and
mediums to which they are attached, the following variables must be adressed
(GCA, 1983c):
• size and physical state of the hazardous constituents within the
soil,
• chemical characteristics of the hazardous constituents within the
soil,
• rate of volatilization,
• rate of ignition,
• feed rate and volumetric heat release,
• kiln dimensions, slope, and rotational speed,
• thermal decomposition and oxidation rate,
• presence of heat sinks such as water or excessive ash,
• slag formation and composition,
• heat losses, and
• secondary chamber configuration and size.
3-38
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Incineration temperatures can be varied from 800° to 1400°C depending on the
heat requirements necessary to incinerate various hazardous constituents in
contaminated soils. For example, soils contaminated with dioxins require a
temperature of at least 1200°C to ensure adequate destruction (destruction and
removal efficiency - ORE = 99.9999%).
The rotary kiln incineration method is used at three of the largest
commercial incineration facilities (Rollins Environmental Systems in Deer
Park, Texas; Environmental Systems Company (ENSCO), El Dorado, Arkansas; and
SCA Chemical Services in Chicago, Illinois). Table 3-11 shows some of the
major advantages and disadvantages pertaining to the use of a rotary kiln.
Mobile rotary kiln incinerators are also used for the destruction of
contaminated soils. These systems consist of flat-bed mounted units that can
be trucked to a site for onsite incineration. The EPA-ORD mobile incinerator
has recently undergone a test burn for the destruction of contaminated soils,
while the ENSCO mobile rotary kiln is currently undergoing active testing.
Hazardous Constituents Amenable to the Technology—
Essentially all organic types of constituents in soils including PCBs and
dioxins can be incinerated by using a rotary kiln (Bonner, 1981). There are,
however, hazardous constituents such as heavy metals, high moisture content
wastes, inert materials, inorganic salts, and the general group of wastes that
have high inorganic content that are unlikely candidates for incineration
(Bonner, 1981).
Performance—
The previously listed commercial land-based incinerators are a very
effective means of destroying contaminated soils. Each incinerator can handle
various RCRA wastes, however, only the Rollins incinerator is permitted to
burn PCB-contaminated soils.
The mobile EPA-ORD unit has been tested on dioxin soil in Missouri and
has the capability of burning soils at a rate of 2,000 Ib/hr (Hasel, 1985).
EPA has reported a successful test burn of dioxin soils to a destruction level
of 99.9999% (Hasel, 1985). ENSCO has reported that they have two units capable
of incinerating soils and are constructing a third. These units are expected
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TABLE 3-11. ADVANTAGES AND DISADVANTAGES ROTARY KILN INCINERATOR
Advantages
1. Can incinerate a wide variety of liquid and solid hazardous wastes.
2. Can incinerate materials which are passing through a melt phase.
3. Capable of receiving liquids and solids independently or in combination.
4. Capable of receiving drums and bulk containers.
5. Adaptable to wide variety of feed mechanism designs.
6. Characterized by high turbulence and air exposure of solid wastes.
7. Continuous ash removal which does not interfere with the waste oxidation.
8. No moving parts inside the kiln (except when waste transport chains are
added).
9. Adaptable for use with a wet gas scrubbing system.
10. Retention or residence time of the nonvolatile component can be
controlled by adjusting the rotational speed.
11. Waste can be fed directly into the kiln without any preparation (such as
preheating, mixing, etc.).
12. Can be operated at temperatures in excess of 1400°C (2500°F), making them
well suited for the destruction of toxic compounds that are difficult to
thermally degrade.
13. Rotational speed control of the kiln also allows a turndown ratio
(maximum to minimum operating range) of about 50 percent.
Disadvantages
1. High capital cost for installation.
2. Operating care necessary to prevent refractory damage; thermal shock is a
particularly damaging event.
3. Airborne particles may be carried out of kiln before complete combustion.
4. Spherical or cylindrical items may roll through kiln before combustion is
completed (insufficient residence time).
5. Frequently requires additional makeup air due to air leakage via the kiln
end seals.
6. Drying or ignition grates, if used prior to the rotary kiln, can cause
problems with melt plugging of grates and grate mechanisms.
7. High particulate loadings to air pollution control equipment.
8. Relatively low thermal efficiency.
9. Maintenance of seals at either end of the kiln; a significant operating
difficulty.
10. Formation of clinker or ring residue on refractory walls, due to drying
of aqueous sludge wastes or melting of some solid wastes.
Source: Bonner, 1981.
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to have RCRA permits by the end of the year for soil incineration. One unit
is in Florida burning liquids and sludge while the other is being readied for
a test burn on dioxins in Arkansas.
Reliability—
Rotary kiln units both mobile and stationary have been used successfully
to incinerate and thus, destroy various types of contaminated soils.
Implementability—
Stationary incinerators are readily implementable for the destruction of
contaminated soils since incineration facilities are available. However,
concerns such as the ability to excavate the contaminated soils and haul
distances must be considered. Long haul distances and difficult excavation
will greatly increase the costs and time needed to destroy the soils.
Implementability is of greater concern when using a mobile incinerator in
that, in addition to excavation concerns, issues pertaining to the incinerator
location and space (land) requirements at specific sites must also be
considered. If incineration is to occur in a residential-type area, issues
concerning public health and safety must be considered.
Cost—
Stationary incinerator costs were reported by Rollins at $.65 to $.75/lb
(Murphy, 1985). SCA, Inc., which requires soils to be placed in 150 to 200 Ib
fiber or plastic bags, reported costs of £.35 to $.40/lb (Mullen, 1985).
These costs include post-incineration handling of the various residues.
However, these costs do not include excavation or hauling thereby greatly
increasing the cost of incineration.
Costs for incineration with a mobile unit were reported from ENSCO as
being $400 to $500/yd (Lanier, 1985). A consideration with onsite
incineration is that residues must be disposed of properly after
incineration. The various options depend on how the residue is classified,
i.e. hazardous vs. nonhazardous (delisted). The options consist of using the
residue as an onsite construction waste, disposal in a sanitary landfill or in
an approved RCRA landfill. There is a wide variation between these options,
thereby resulting in a wide variation in disposal costs.
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IMMINENT TECHNOLOGIES
Storage Vaults
General Description—
This type of corrective action strategy is a fairly new technology and to
date has not acquired the appropriatre RCRA permits. It may, however, prove
to be an acceptable method for long-term storage of contaminated soils.
Rollins Environmental Services has developed a vault to contain hazardous
wastes or soils with an expected useful life of approximately 50 years. The
vaults are very much like an above-grade landfill except it uses lined
concrete retaining walls to contain the soils. The basic components of the
vault consist of:
• an umbrella cap,
• storm water collection system,
• cap monitoring system,
• secondary cap,
• lined concrete containment walls,
• drain protective layers,
• leachate collection system,
• primary liner,
• leachate monitoring system,
• secondary liner, and
• a clay or concrete tertiary liner.
Like a double-lined landfill the vault appears to have sufficient layering to
adequately contain the soils in conjunction with the leachate
collection/detection systems.
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Applicability--
These vaults may be quite effective in containing contaminated soils but
at this time have limited demonstrated performance and are only recognized by
the EPA as a temporary storage unit. Rollins reports that the vaults can be
installed essentially anywhere, as long as soils are stable enough to support
the structure. Sizes can range from 10 to 30 ft high walls and cover one half
to 25 acres or more. Rollins also reports that organic sludges, soils, and
contaminated equipment can be safely disposed of in these vaults.
Mobile Hazardous Waste Extraction from Excavated Soils
General Description—
This is a new and emerging technology that is being sponsored by the
EPA. There is a unit available at this time that is capable of
decontaminating soil at a rate of 3 to 5 yd /hr. The goal of this project
is to be able to "scrub" soils clean enough so they can be redeposited in the
place from which they were excavated.
The system generally consists of a hydraulically lifted bucket, feed
hopper, and soil metering paddle that places the soil into the unit. The
soils are then washed or "scrubbed" with water and/or additives for hazardous
constituent removal. The unit contains various screens and water knives for
scrubbing purposes, along with rinsing areas and hydrocyclones for
dewatering. Once soils are completely rinsed, dewatered, and dried they may
be returned to the excavation area. Water and additives are collected and
reused to keep operating costs down.
Applicability—
It is reported that fine clays cannot be effectively "scrubbed", however,
small particles greater than 2 mm can be cleaned in this process. Also, most
inorganic compounds, most water soluble or readily oxidized organic chemicals
and some partially miscible-in-water organics can be treated with water or
water plus an additive (Milanowski and Scholz, 1983).
EPA reported that the unit has successfully removed lead from soils,
however the unit did have a number of operation problems in the field and is
presently being retrofitted (Traver, 1985). Prior to this, laboratory
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experiments on phenols, arsenic trioxide, and PCBs in two soil matrices of
sand/gravel/silt/clay and organic loam were completed and found to be quite
successful. If further testing is performed on the applicability of this
unit, it may prove to be a very effective method of treating releases to soils
from all types of SWMUs.
Fluidized-Bed Incineration
General Description—
A fluidized-bed incinerator consists of a vertical refractory-lined
cylinder that contains a bed of inert, granular material which usually
consists of sand. The diameter of the units normally ranges from a few meters
to 15 meters (GCA, 1983c). Temperatures for incineration are normally 450° to
980°C (Bonner, 1981) and are limited by the softening point of sand which is
1100°C. The sand bed particles are fluidized by blowing low velocity air
upward through the medium. This rate of air movement is a direct relation to
particle size and acts to suspend the bed in a fluid-like manner.
Hazardous waste materials including liquids, slurries, gases, sludges,
and contaminated soils can be incinerated with the fluidized bed. However,
hazardous constituents such as sludges or contaminated soils must be
pretreated involving sorting, drying, shredding, and special feed
considerations (Bonner, 1981). Generally, as with the rotary kiln, the
fluidized bed can incinerate most hazardous constituents. However, the
fluidized bed does necessitate the use of an after-burner since hazardous
constituents are volatilized from the soil in the main unit and then destroyed
in the vapor phase by the after-burner. This occurs due to the low operating
temperatures of this type of incineration. Table 3-12 lists advantages and
disadvantages of the fluidized-bed incinerator.
A recently developed circulating fluidized-bed incinerator by G.A.
Technologies of San Diego, California involves the use of the contaminated
soil as the bed material and uses an air flow of 3 to 5 times as great as that
in conventional systems. The increased air flow also increases the turbulence
which makes for a more turbulent combustion environment. This allows the use
of lower temperatures and precludes the use of an after-burner.
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TABLE 3-12. ADVANTAGES AND DISADVANTAGES OF FLUIDIZED-BED INCINERATION
Advantages
1. General applicability for the disposal of combustible hazardous solids,
liquids, and gaseous wastes.
2. Simple design concept, requiring no moving parts in the combustion zone.
3. Compact design results from high heating rate per unit volume (100,000 to
200,000 Btu/hr-ft3 (900,000 to 1,800,000 kg/cal/hr-m3)) which results
in relatively low capital costs.
4. Relatively low gas temperatures and excess air requirements which tend to
minimize nitrogen oxide formation and contribute to smaller, lower-cost
emission control systems.
5. Long incinerator life and low maintenance costs.
6. Large active surface area resulting from fluidizing action enhances the
combustion efficiency.
7. Fluctuation in the feed rate and composition are easily tolerated due to
the large quantities of heat stored in the bed.
8. Provides for rapid drying of high-moisture-content material, and
combustion can take place in the bed.
9. Proper bed material selection supresses acid gas formation; hence,
reduced emission control requirements.
Disadvantages
1. Difficult to remove residual materials from the bed.
2. Requires fluid bed preparation and maintenance.
3. Periodic feed must be selected to avoid bed degradation caused by
corrosion or reactions.
4. Hay require special operating procedures to avoid bed damage.
5. Operating costs are relatively high, particularly electric power costs.
6. Possible operating difficulties with materials high in moisture content.
7- Formation of eutectics (compounds with low melting or fusion
temperatures) is a serious problem.
8. Hazardous waste incineration practices have not been fully developed.
9. Not well suited for irregular, bulky wastes, tarry solids, or wastes with
a fusible ash content.
Source: Bonner, 1981.
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Applicability—
The circulating fluidized-bed incinerator is reported to be a
transportable unit however, it was stated that large amounts of soil would
have to be incinerated in order for a move to be made. It was also reported
that a test burn on PCB soils has been completed and preliminary results show
a very high level of destruction (G.A. Technologies, 1985). The unit that was
used in the test burn is a 16-in. inside diameter unit with the capability of
destroying 500 to 1,000 Ib/hr. G.A. Technologies also stated that if the burn
proves to be successful a commercial unit with five times the capacity could
be constructed very shortly.
Mobile Advanced Electric Reactor
General Description—
The advanced electric reactor, often referred to as a high-temperature
fluid wall reactor, uses radiant energy to destroy organic constituents by
pyrolysis (chemical decomposition) at high temperature. The radiant energy
which is produced by six electrically heated carbon electrodes is focused on
the waste through a porous ceramic core. The electrodes are heated to
approximately 400°F.
Soils that are fed into the unit must be nonflowing, nonagglomerating and
smaller than 100 mesh (Thagard Research Corporation, 1984). However, it is
expected that 10 mesh soils will be acceptable. Soils are fed through the top
of the reactor and fall through the core. Residence times for 100 mesh solids
are reported to be one-tenth of a second for a 30-ft high reactor.
Thagard Research has built a 12-in. diameter mobile unit for Vulcan
Associates. The system is truck-mounted and can incinerate 40 tons of soil
per day. However, test results are not available for this unit.
J.M. Huber has a 12-in. immobile unit and a 3 in. mobile pilot-scale
unit. The 12-in. reactor has successfully incinerated PCB-contaminated soils
and the 3-in. reactor has also destroyed dioxin-contaminated soils at Times
Beach, Missouri.
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Applicability—
This type of reactor can destroy essentially all types of hazardous
constituents including soils contaminated with PCBs and dioxins. However,
Huber may sell the license or shelf the technology until it is more applicable
(Huber, 1985).
Attenuation
General Description—
This technology generally consists of mixing contaminated soils with
clean soils to reduce concentrations of the hazardous components to acceptable
levels. It can be done only in the upper soil levels and can consist of
mixing subsoil, uncontaminated soil from another area of the site or purchased
soil with the contaminated soils.
Applicability--
Attenuation is reported to be viable only in the upper 2 ft of soil
(i.e., that within the plow layer). It is useful in the attenuation of metals
and organics although this technology has only been reported to work well with
metals (EPA, 1984b). This technology's implementation is dependent upon
site/soil trafficability considerations and depth of contamination. Other
issues that must be considered are increased erosion of tilled area, therefore
requiring runon/runoff controls and possible alteration of soil horizon
characteristics which may allow increased mobility of the hazardous
constituents. This technology is reported to have had some field applications
(EPA, 1984b).
Chemical Oxidation
General Description—
Chemicals naturally undergo reactions in soil that may transform them
into more or less toxic products, or which may increase or decrease their
mobility within the soil system. Chemical treatment of contaminated soils
entails the reaction of hazardous constituents with reagents, resulting in
products which are less toxic, or which become immobilized in the soil
column. These reactions may be classified as oxidation reactions, reduction
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reactions, and polymerization reactions. Oxidation reactions are discussed at
this point, reduction reactions will be discussed subsequently and
polymerization will not be presented because it has not yet been field tested.
Chemical oxidation is a process in which the oxidation state of an atom
is increased. This is accomplished by the transfer of electrons from the atom
to an election acceptor such as oxygen. Chemical oxidation represents a
significant treatment process in soil systems. As a result of oxidation, a
substance may be transformed, degraded, and/or immobilized in soil. Oxidation
of hazardous organic constituents in soil can be an effective method of
environmental degradation. Oxidation of heavy metals, with the exception of
arsenic however, is not usually desirable because heavy metals become more
mobile at higher oxidation states. Oxidation reactions within the soil matrix
may occur through management of the natural processes in a soil, or through
addition of an oxidizing agent.
In the natural soil environment, it is the role of the soil to provide
electron acceptors for the oxidation of organics and other compounds. Oxygen
is usually the electron acceptor. However, when oxygen is not available,
other reducible compounds such as nitrate, Mn(IV), M(III), Fe(III), and S(VI)
can function as electron acceptors. Typically, oxidation will occur in soil
systems where the redox potential (ability to accept electrons) of the soil is
greater than that of the hazardous constituent (i.e., 0.8V). It is important
to note that hazardous chemical constituents are more extensively oxidized in
less-saturated soils. Therefore, soil moisture control is desirable in
promoting natural oxidation processes.
Oxidizing agents may be utilized to degrade organic constituents in soil
systems. Oxidation reactions are usually limited in application due to their
substrate specificity and pH dependence. Common oxidizing agents considered
for in-place treatment include ozone, hydrogen peroxide, and chlorinate
(hypochloriate). The latter, however, is not desirable for in situ oxidation
of contaminated soil because it can lead to undesirable chlorinated
by-products. The relative oxidizing ability of these chemicals compared with
other well-known oxidants is indicated in Table 3-13. A serious potential
limitation to the use of oxidizing agents for soil treatment is the additional
consumption of the oxidizing agent(s) by nontarget constituents in the soil.
In some instances hydrogen peroxide and ozone have been used
simultaneously to degrade compounds which are refractory to either material
individually. When ozone is the oxidant used, the pH of the soil must be
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TABLE 3-13. RELATIVE OXIDATION POWER OF OXIDIZING SPECIES
Oxidation Relative
Species potential volts oxidation power
Fluorine 3.06 2.25
Hydroxyl radical 2.80 2.05
Atomic oxygen 2.42 1.78
Ozone 2.07 1.52
Hydrogen peroxide 1.77 1.30
Perhydroxyl radicals 1.70 1.25
Hypochlorous acid 1.49 1.10
Chlorine 1.36 1.00
Source: EPA, 1984b.
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carefully controlled since the rate of decomposition of ozone is strongly
influenced by pH. At high pH direct reactions between ozone and the hazardous
constituents in the soil are reduced. When hydrogen peroxide is used, the
metal content of the soil must be considered because metals act as catalysts
causing autodecomposition of peroxide. The result will be an increase in the
soil dissolved oxygen but no direct oxidation of hazardous constituents by the
peroxide.
One problem common to strong oxidants in general is their ability to
oxidize the natural organic matter in the soil which often acts as sorption
sites for organic constituents, resulting in decreased sorption capacity in
soils for some organics. Therefore, some hazardous constituents' mobility may
be increased. Nevertheless, successful field application of strong oxidants
has been completed. Examples of rn situ oxidation of contaminated soils using
ozone are provided in Nagel et al., 1982.
Applicability--
General characteristics of organic chemicals likely to undergo oxidation
include: (1) aromaticity, (2) fused ring structures, (3) extensive
conjugation, and (4) ring substituent fragments. Certain compounds are more
oxidizable in soils that others. The reactivity of organic chemical classes
with respect to chemical oxidation is summarized in Table 3-14.
For natural oxidation of hazardous constituents at soil surfaces, water
soluble organic substances with half-cell potential below the redox potential
of a well-oxidized soil are needed. Chemical constituents which do not
oxidize at soil surfaces are given in Table 3-15.
For in situ oxidation by addition of ozone as an oxidizing agent, the
following reactivity trends apply: (1) phenol, xylene, toluene, benzene, and
(2) dichtoro-, trichloro-tetrachlorophenol, pentachlorophenol. Constituents
not readily oxidized by ozone include:
• inorganic compounds in which cations and anions are in their highest
oxidation state;
• organics which are highly halogenated; and
• saturated aliphatic compounds which do not contain easily oxidized
functional groups, i.e., aliphatic hydrocarbons, aldehydes, and
alcohols.
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u>
i
TABLE 3-14. OXIDATION REACTIVITY FOR ORGANIC CHEMICAL CLASSES
High Moderate Low
Phenols Alcohols Halogenated hydrocarbons
Aldehydes Alkyl-substituted aromatics Saturated aliphatic compounds
Aromatic amines Nitro-substituted aromatics Benzene
Certain organic sulfur compounds Unsaturated alkyl groups Chlorinated insecticides
Aliphatic ketones
Aliphatic acids
Aliphatic esters
Aliphatic amines
JRB Associates, 1982.
Source: Compiled by EPA, 1984b.
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TABLE 3-15. SOME CHEMICALS THAT DO NOT OXIDIZE AT SOIL AND CLAY SURFACES
Chemical Name
Acetamide Q-Carotene
Acetone, anisilidene- Cyclohexylamine
-,dianisilidene- Monoethanolamine
-,dicinnaraylidene- Triethylamine
-,d ibenzyIidene-
Dragun and Helling, 1982.
Source: Compiled by EPA, 1984b.
Pesticides such as aldrin, heptachlor, DDT, parathion, and malathion are
oxidized to other hazardous compounds and are, therefore, not suited to such
treatment.
Oxidation with hydrogen peroxide has been demonstrated for cyanide,
aldehydes, dialkyl sulfides, dithionate, nitrogen compounds, phenols, and
sulfur compounds. Chemical groups incompatible with peroxide oxidation due to
their resultant increased mobility are given in Table 3-16.
TABLE 3-16. CHEMICAL GROUPS THAT REACT WITH PEROXIDES TO FORM
MORE MOBILE PRODUCTS
Acid chlorides and anhydrides Cyanides
Acids, mineral, nonoxidizing Dithio carbamates
Acids, mineral oxidizing Aldehydes
Acids, organics Metals and metal compounds
Alcohols and glycols Phenols and cresols
Alkyl halides Sulfides, inorganic
Azo, diazo compounds, hydrazine Chlorinated aromatics/alicycles
Source: EPA, 1984b.
Soil-catalyzed oxidation reactions have been tested in the field for
several chemical classes. However, factors such as aeration of the soil and
soil moisture effect the level of treatment attainable.
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The use of oxidizing agents is not that well tested in soil systems but
have been used in wastewater treatment. Care must also be taken since-
oxidizing agents can cause violent reactions when used in conjunction with
metals and also, soil hydraulic properties may be greatly affected,
particularly in a structured soil.
Chemical Reduction
General Description—
Chemical reduction is a process in which the oxidation state of an atom
is decreased. Reducing agents are electron donors, with reduction
accomplished by the addition of electrons to the atom. Reduction of chemicals
may occur naturally within the soil system. Certain compounds are more
susceptible to reduction than others because they will accept electrons.
Addition of reducing agents to soil to degrade reducible compounds can be used
as an in-place treatment technology for organics, chromium, selenium, and
sodium.
Chemical reduction using catalyzed metal powders and sodium borohydride
has been shown to degrade toxic organic constituents. Reduction with
catalyzed iron, zinc, or aluminum affect treatment through mechanisms
including hydrogenolysis, hydroxylation, saturation of aromatic structures,
condensation, ring opening, and rearrangements to transform toxic organics to
innocuous forms.
The use of catalyzed metal powders, though used successfully for aqueous
solutions passed through beds of reactant diluted with an inert solid (Sweeney,
1981), has not been demonstrated in the soil environment. However, small-scale
field experiments of chemical reduction of organic constituents in soils with
sodium borohydride and zinc have been successful. Results of reductive treat-
ment for degradation of paraquat in soil are summarized in Table 3-17. Results
indicate that sodium borohydride and powdered Zn/acetic acid combinations
achieved very effective degradation of paraquat in soil and sand media.
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TABLE 3-17. CHEMICAL REDUCTIVE TREATMENT FOR DEGRADATION OF
PARAQUAT IN SOIL
Chemical
Paraquat in soil (ppra)
Treatment
None
NaBH4-soil
NaBH4~sand
Powdered Zn acetic acid
Initial (1 day)
9,590
None detected
None detected
60
4 Months
6,300
None detected
None detected
69
Comment
Violent foaming
No foaming
Some bubbling
Staiff et al., 1981.
Source: Compiled by EPA, 1984b.
Hexavalent chromium Cr(VI) is highly toxic and mobile in soils and must
be reduced to trivalent chromium Cr(III) which is far less mobile and toxic.
The reduction can be accomplished by adding acidification agents such as
sulfur and reducing agents such as leaf litter, acid compost, or ferrous
iron. These additives are not always necessary if sufficiently acidic soil
conditions are present whereby the reaction will occur naturally. After
reduction, Cr(III) is precipitated via lime addition; Cr(III) precipitates
over a pH of 4.5 to 5.5. Caution is required, however, since trivalent
chromium can be oxidized to Cr(VI) under conditions prevalent in many soils,
i.e., under alkaline and aerobic conditions in the presence of manganese.
With the exception of lime addition, the above also holds true for hexavalent
selenium reduction to either selenite (Se(IV)) or elemental selenium Se
which are far less mobile. It is important to note, however, that selenite
(Se(lV)) is an anion which leaches at high pH and thus, selenium could not be
treated if increased pH were required as part of the treatment for other
metals.
Applicability--
Soils contaminated with chlorinated organics, unsaturated aromatics and
aliphatics, miscellaneous other reducible organics, hexavalent chromium, and
hexavalent selenium (when significant amounts of other metallic constituents
are not present) are treatable by chemical reduction.
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The achievable level of treatment is potentially high for hazardous
constituents susceptible to reduction, and for limited areas of
contamination. The soil must be without large quantities of competing
constituents susceptible to reduction, or the level of treatment may be
greatly decreased.
The use of reducing agents for organic constituents may also degrade soil
organic matter. The extent of impact on soils is not known at the present
time. The products of reduction may present problems with respect to
toxicity, mobility, and degradation however, this information is not presently
available. Iron reductants appear to be the least damaging to soil systems,
though iron has a secondary drinking water standard and is of concern with
respect to aesthetics. Addition of metals with acetic acid may possibly
increase metal mobility by decreasing soil pH. Addition of sodium borohydride
may adversely impact soil permeability, depending on the type and content of
clay and ionic constituents in the soil solution.
It is reported that this technology may not be able to treat soils to
acceptable levels during initial treatment, therefore necessitating a second
round of treatment.
Extraction (Soil Flushing)
General Description—
This technology involves the removal of hazardous constituents from the
soil horizon by flooding the site with a flushing solution and collecting the
elutriate in shallow wells to prevent migration and further contamination to
soils and ground water. Flushing solutions can include water, acidic aqueous
solutions (sulfuric, hydrochloric, nitric, phosphoric, and carbonic acid),
basic solutions (e.g., sodium hydroxide), and surfacants (e.g., aIky1benzene
sulforate). Once the soils have been properly flushed and the elutriate
collected it can then be put through a treatment system and disposed.
Sampling and analysis would then be necessary to ensure that the contamination
has been removed and also to ensure that the flushing solution has been
adequately removed.
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Another development in this technology by the EPA is a mobile _in situ
containment/treatment system. It generally consists of grout injection to
isolate the contaminated area; grout must be effective in the soil of concern
and be compatible with the hazardous constituents in the soil. The area is
then flushed with either water or appropriate additives to remove
contamination. This unit is reported to have the capability of treating an
o
area of approximately 80,000 ft . At the present time the unit is being
prepared for a field test (Fall 1985) at Air Force property in Wisconsin on a
solvent spill; this will be its first field test (Traver, 1985).
Applicability™
This technology is in initial stages of development. However, the mobile
unit or a stationary setup at a site may in the near future prove to be a
viable technology for remediation of releases to soils. Much of research at
this time is going towards the development of solvents or flushing agents that
can adequately and safely remove hazardous constituents from soils.
In general, water can be used to extract water-soluble or water-mobile
constituents; acidic solutions can be used to recover metals and basic organic
constituents; and basic solutions can be used for removal of metals and some
phenols. At present, this technology is not imp lenient able at a site.
However, after the slated field test of EPA1s mobile unit it may be a viable
corrective measure.
Multiple-Hearth Incineration
General Description—
A multiple-hearth incinerator generally consists of a refractory-lined
circular steel shell, a control shaft that rotates, a series of solid flat
hearths, a series of rabble arms with teeth in each hearth, an air blower,
wall-mounted fuel burners, an ash removal system, and a waste feeding system
(Bonner, 1981). There are also side ports for fuel injection, liquid waste
burners, and an after-burner is generally necessary for soil incineration.
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Applicability—
The multiple-hearth incinerator while designed to incinerate sewage and
hazardous type sludges may also be used to treat contaminated soils, given
sufficient pretreatraent to attain a constant size and moisture content.
Due to the low temperatures used during incineration, contaminated soils
usually require the use of an after-burner to achieve complete destruction.
Devolatilization is realized in the main chamber with the gaseous phase being
destroyed in the after—burner.
Generally the same types of hazardous constituents that can be
incinerated with a rotary kiln can also be destroyed with a multiple-hearth
incinerator. Some unlikely candidates for multiple-hearth incineration
consist of uncombustible hazardous constituents such as heavy metals, inert
material, inorganic salts, and generally substances with high organic
content. In general, the multiple-hearth incinerator is not expected to be as
effective as the rotary kiln-type incinerator.
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SECTION 4
CASE STUDIES
INTRODUCTION
GCA conducted a search for case studies which would demonstrate how to
select and implement corrective measures for releases to soils from SWMUs.
Approximately 100 sites were reviewed to develop a list of sites for potential
case study analysis. Information was obtained from several data sources
including EPA Headquarters, EPA Regional offices, and literature searches.
The site review focused on finding examples of sites where remedial
responses were either ongoing or completed. Site Selection Worksheets were
completed for sites which met this initial criteria. The worksheet (.shown in
Figure 4-1) contained information which was used to screen the sites for
potential case study evaluations.
The criteria used for final selection of case studies included:
• availability and completeness of site information and monitoring data;
• type of remedial measures implemented;
• types of wastes and hazardous constituents present at the facility;
• site characteristics;
• geographic locations; and
• waste management practices.
In reviewing potential case studies, those case studies that were designated
as being most representative ot a variety ot the above criteria and
constituents of each criterion were selected.
4-1
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SITE NAME
LOCATION
TYPE OF FACILITY
SIZE OF SITE/DISPOSAL AREA
YEARS OF OPERATION/DISCOVERY OF RELEASE (How & when release discovered)
TYPES OF RELEASES
TYPE OF WASTE DISPOSED/HAZARDOUS CONSTITUENTS PRESENT
MEDIA CONTAMINATED
CLIMATE
TOPOGRAPHY
SOILS
Figure 4-1. Worksheet for screening case studies.
4-2
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GEOLOGY
HYDROLOGY (Ground Water & Surface Water)
RESPONSE ACTIONS (Including Designed and Implemented)
MONITORING DATA AVAILABLE
SUCCESS/FAILURE OF REMEDIATION (Removal Efficiency, Containment Effectiveness)
Figure 4-1 (continued)
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A list of the selected sites and a summary of the remedial responses at
these sites is presented in Table 4-1. Case studies were prepared using the
outline shown in Figure 4-2. These case studies are presented below.
FAIRCHILD REPUBLIC COMPANY - HAGERSTOWN, MARYLAND
Facility Description
The Fairchild Republic Company used chemical solutions to clean sheet
aluminum that is used in the manufacture of airplanes. Between 1950 and 1967,
waste sludges and liquids from the cleaning processes were disposed in an open
landfill. The landfill had an irregular shape with a maximum length of about
160 ft and a refuse depth of about 5 ft.
During the mid-1960s, an improved waste treatment plant was constructed
which enhanced the removal of heavy metals through chemical addition. The
concentrated sludge was dewatered through filter presses and placed in several
permitted, clay-lined sludge lagoons. The sludge was subsequently hauled to a
licensed disposal facility. After trivalent chromium was declassified as a
hazardous substance, the trivalent chromium sludge was disposed in a local
sanitary landfill.
As a result of these disposal practices, the surrounding soil and the
underlying ground water became contaminated with chromium and organic
chemicals.
Site Characteristics
Climate—
Climate in the area of the site is continental. Average temperatures
range from 21"F I late January to early February; to 88UF (.late July). Annual
precipitation averages 37.08 in. (1953 to 1983), and is generally evenly
distributed throughout the year.
Soils—
The soils at the site consist of silty clay loam in the Hagerstown-
Diffield-Frankstown Association. These soils are generally classified as
reddish, well-drained, deep and medium textured.
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TABLE 4-1. TYPES OF RELEASE(S) AND REMEDIAL RESPONSE(S) IMPLEMENTED AT SELECTED SITES
Site Nine/Location
Type of Facility
Hazardous Constituents Preaent
Typed) of Releaaea
Remedial Response
I
Ul
1. Fairchild
Republic
Company/
Hageratoun,
Maryland
2. Uhitmoyer
Laboratories/
Myerstown,
Pennsylvania
3.
4.
5.
6.
Enterprise
Avenue/
Philadelphia,
Pennsylvania
Frontenac Site/
Frontenac,
Missouri
Crystal
Chemical/
Houston,
Texas
Silreaim/
Lowell,
Maaaachusetts
Open landfill
(3SO ft x 160 ft x SIS ft)
used for disposal of waate
•ludge from plant operations.
Uastewater generated by the
manufacturing plant treated
with lime; alurry disposed
in to unlined lagoon.
City of Philadelphia landfill
used for the disposal of
industrial wastes.
Storage tank area uaed for
waste oils and chemical
wastes.
Landfill, 5~acres used for
wastes from herbicide
manufacturing process.
Chemical reclamation facility
(5-acre).
Heavy Metals, miscellaneous
organic solvents (Cr, Cu, Zn,
Al, TCE, Xylenea, Toluene,
methyl chloride, ethyl benzene,
1,1-dichloroethylene).
Arsenic (inorganic and organic).
Volatile organics, metals,
organic halides.
2,3,7,8-TCDD (dioxin), PCBs,
1,2~trans~dichloroethylene,
tetrachloroethane.
Arsenic, phenols.
Volatile organica, PCBs,
pesticides, some metals.
Ground water, aoila
Ground water,
aurface water,
soils
Ground waterD soils
Soils, sediments
Soils (89,000
ground water,
surface water
(from runoff)
Ground water, soils,
surface runoff
• Removal of contaminated materials
(excavation)
• Backfilling
• Capping
• Grading, topsoil, and seeding
• Excavation of contaminated sludge's
and soils
• Concrete storage bins
• GW treatment and recovery
(counter pumping)
• Excavation of contaminated soils
• Offaite disposal/treatment
• Backfilling
• Capping
• Grading, topsoil, seeding
• Asphaltic concrete cap over
gravel subgrade
• Toe-trench filled with rip-rap rock
• Wire cable/steel stakes lence
around site
• Contaminated water (trom Hooding)
was removed
• Equipment and buildings removed
• Waste pits filled in
• 1-2 in. temporary clay cap and
plastic cover installed
• Proposed: permanent capping, in situ
treatment, and slurry wall
• Construction of berms and placement
ot absorbent till material in trenches
• Removal of drums and chemicals in
bulk storage
• Removal of buildings and containers
• Installation of 2 ft compacted clay
cap with gas venting system
-------
I. FACILITY DESCRIPTION
A. TYPE OF SWMU/SYSTEM DESIGN (Including any leak detection and/or
monitoring system)
B. YEARS OF OPERATION
C. TYPE OF WASTES RECEIVED/DISPOSED
D. SIZE OF SITE/DISPOSAL AREA
E. ANY PREVIOUS OPERATIONS AT THE SITE/SITE BACKGROUND
F. REGULATORY & LEGAL STATUS (NPL.CERCLA.etc.)
II. SITE CHARACTERISTICS
A. CLIMATE
B. TOPOGRAPHY
C. SOILS
D. GEOLOGY
E. HYDROLOGY (Ground Water & Surface Water)
III. RELEASES
A. TYPES/CAUSES OF RELEASES
B. MECHANISMS FOR DETECTION (Include how & when release was detected)
C. EXTENT OF CONTAMINATION & HAZARDOUS CONSTITUENTS PRESENT (Include
media contaminated, and area or volume of contamination)
IV. REMEDIAL ACTIONS
A. RESPONSE
1. IMPLEMENTED
2. UNDER CONSTRUCTION
3. DESIGNED/CONCEPTUALIZED
4. MONITORED/TESTED
B. SUCCESS/FAILURE OF REMEDIATION (Include summary of results from
available monitoring data)
Figure 4-2. Outline for case studies write-up.
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Geology—
The bedrock underlying the site is composed of limestone with numerous
fractures and cavities. The stratigraphy of the bedrock is a series of
parallel folds with the axial traces trending N 15" E, and the joint
measurements trending in two directions: strike N 80" E, dip 85" NW, and
strike W 5" E, dip 60" SE.
Hydrology—
A carbonate aquifer lies beneath the site, with the water table ranging
from 34.1 ft below the surface (during dry fall months; to 11.4 ft below the
surface (during wet winter months)-
Releases
Types/Causes of Releases—
As a result of rainfall and surface water percolating through the sludge,
the surrounding soil and ground water became contaminated with chromium and
organic chemicals. Additionally, hazardous constituents released to ground
water migrated to nearby domestic water wells.
Mechanisms for Detection—
Fairchild Republic Company had a State permit to operate two onsite sludge
lagoons, which expired in 1978. Prior to reissuing a permit for the lagoons,
the Maryland Department of Natural Resources, Water Resources Administration
(WRA) conducted ground water monitoring activities (in August 1978). WRA's
monitoring results revealed high levels of chromium contamination
approximately 40U ft away from the sludge lagoons. The source was determined
to be the nearby open landfill containing chromium sludge.
Extent of Contamination—
The major hazardous constituents found at the site included heavy metals
(such as chromium, copper, zinc, and aluminum), and organic compounds (such as
1,1,1-trichloroethane, 1,1-dichloroethylene, ethylbenzene, methylchloride,
toluene, trichloroethylene, and xylenes). Chromium was found to be the
4-7
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dominant hazardous constituent present at the site with total chromium
concentrations ranging from 20 mg/kg to 280,000 mg/kg with the natural
background level of total chromium in the range of 50 to 100 mg/kg.
The estimated volume of material in the waste disposal area is
o
5,400 yd . Approximately 50 percent of this material was determined to be
contaminated soils, with the remainder being only partially contaminated.
Contaminated materials were found to be near or directly on the bedrock in
some areas.
Remedial Actions
Response-
Contaminated soils were excavated down to the bedrock (determined by State
inspectors to be the practical limit for excavation). Composite soil samples
were then collected from the excavated area. Subsequent analyses indicated
that the total and hexavalent chromium levels were within EPA standards.
Remedial measures were continued by placing a layer of compacted clay
approximately 2 ft thick directly over the exposed bedrock to inhibit the
infiltration of precipitation. The pit was then backfilled with clean soil
and crushed rock and then compacted.
A clay cap was installed over the site area. The cap was graded to allow
runoff and to minimize surface ponding (thereby decreasing the amount of
vertical infiltration of precipitation and contaminants). A perimeter drain
was installed around the facility to further minimize the movement of runoff
water onto the site. A topsoil cap of approximately 6 to 8 in. was placed
over the clay layer and seeded with a grass-legume mixture to mitigate erosion
of the clay layer and to further inhibit water infiltration (by
evapotranspiration).
Continued monitoring of the site is being performed, using wells
previously installed, to determine the long-term effects of the response
actions.
Success/Failure of Remediation—
The remedial actions taken appear to have been effective in reducing the
chromium constituents. Ground water monitoring wells have shown a continual
decrease in chromium levels. Limited monitoring data is available for organic
4-8
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contamination and therefore, the effectiveness of the organics removal cannot
be adequately evaluated at this time. The volatile organics found on the site
are generally highly soluble and very mobile in water. However, most ot these
should volatilize, degrade chemically or biologically, or be diluted in the
ground water over time.
While the percolation of precipitation has been virtually eliminated, the
variation of ground water elevation has not been controlled. Fractured
bedrock zones remain contaminated with precipitated heavy metals. The
precipitation of heavy metals is enhanced by limestone and dolomite bedrock
because of the high pH associated with these formations. However, rising
ground water levels will lower the pH conditions, causing the metal
precipitates to become dissolved in the ground water and potentially
transporting them through the ground water regime.
Reference: U.S. EPA, 1984a.
WHITMOYER LABORATORIES - MYERSTOWN, PENNSYLVANIA
Facility Description
Beginning in 1934, and continuing to the present, Whitmoyer Laboratories
has operated a pharmaceutical manufacturing facility at the site. Until 1964,
wastewater generated by the manufacturing processes was treated with lime and
handled as a slurry. The wastewater slurry was then disposed in an unlined
lagoon.
Site Description
Climate—
The average annual precipitation in the site area is 44 in. Average
annual snowfall is 35 in. Average temperatures range from 30"F (January) to
76UF (July) with an annual average of 53"F. The average windspeed is 7.7 mph.
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Soils—
Soils overlying the site consist of a 5 to 7 ft thick layer of alluvial
sand, silt, and gravel. These soils are fairly permeable, and allow for rapid
recharge to the bedrock aquifers. . ,., ..
Geology—
Bedrock underlying the plant site consists of limestones and dolomites
which strike east-northeast and exhibit a dip of 30" to the southeast
(Ontelaunee Formation (Dolomite) = 900 ft thick; underlying Annville Formation
(.high calcium limestone) = 1,500 ft thick north of the plant).
Hydrology—
The site lies adjacent to Tulpehocken Creek (37 miles upstream from its
confluence with the Schuylkill River, which in turn flows to Delaware Bay).
f\
The drainage basin of Tulpehocken Creek covers 211 mi* and is 33.5 miles
long. The average and minimum flows at the confluence of Schuylkill River are
58 cfs and 56 cfs, respectively. The average annual flow for the creek is
approximately 200 cfs and the maximum flood flow was 9,890 cfs (on December 7,
1953). The creek flows east-northeast (following the strike of the carbonate
bedrock).
Ground water beneath the site is potable and is used by local residents
and farmers. There are some artesian wells near the site, but the static
water level in most wells lies near the ground water table. The site lies
close to a ground water divide in a system of limestone aquifers underlying
the Lebanon Valley.
Releases
Types/Causes of Releases—
Improper waste disposal in an unlined surface impoundment (lagoon) caused
releases to ground water underlying the site, soils onsite, and a nearby
stream (Tulpehocken Creek).
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Mechanisms for Detection—
In July 1964, Whitmoyer Laboratories, Inc. became a subsidiary of
Rohm & Haas Company. Extensive arsenic contamination of the soils, ground
water, and a nearby stream became apparent to Rohm & Haas Company officials
during an inspection of the facility.
Extent of Contamination—
Extensive ground water, soils, and surface water contamination exists in
the site area. Hazardous constituents primarily include organically-bound
arsenic compounds, calcium arsenate, and calcium arsenite.
Remedial Actions
Response Actions—
Onsite treatment and disposal practices were discontinued in December
1964. Sludge was removed from the lagoon. Contaminated soils underlying the
lagoon were also removed. The contaminated soil and sludge materials were
deposited in an impervious concrete storage bin, which was filled to capacity
and then covered.
Four recovery wells were used to purge ground water containing arsenic
compounds. The contaminated ground water was treated by adding two-parts
^62(80^)3 to one-part arsenic and adjusting the pH to neutral conditions
(by adding lime). Recovered water was handled in alternating batch mixing
tanks on a continuous feed treatment schedule and sent to the lagoons to
dissipate via slow percolation to the subsoil.
The plant reopened in the Spring of 1965 on a no-discharge basis. Treated
wastes were trucked to a New Jersey holding area awaiting ocean dumping. In
1966, additional wells were installed. Production wells formed cones of
depression east of the plant to stop migration of ground water. Production
rate is partially dependent on the purging rate. From 1968 to early 1971, the
purged water was discharged directly to Tulpehocken Creek.
It was decided that it would be too expensive to dredge Tulpehocken Creek,
and the constituent levels are declining through dilution. Whitmoyer
Laboratories currently supplies bottled water to area residents whose wells
remain affected.
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Success/Failure of Remediation—
The first phase of remedial action cleanup and recovery involved the
removal of sludge and contaminated soils. The manufacturing processes were
halted until a process could be developed to remove arsenic- from the
wastewater, thereby eliminating the possibility of new arsenic compounds being
added to the soils, and subsequently to the ground and surface water.
The next phase, which involved removal of the arsenic constituents from
the ground water, was also successful. The recycling and treatment of the
purged water did reduce the level of arsenic in the ground water, and
succeeded in controlling its movement.
Little has been done to remove the hazardous constituents from the
sediments and surface water of Tulpehocken Creek, because of the costs
involved in dredging miles of creek bottoms and banks. Through dilution, the
arsenic levels in the creek water have been brought within the limits set by
the U.S. Department of Health, and monitoring has shown that the levels
continue to decline.
Finally, routine monitoring of the site is being performed to ensure that
the arsenic levels do not increase, either through the release of arsenic from
bottom muds, or via spills from the plant.
Reference: EPA, 1981.
ENTERPRISE AVENUE - PHILADELPHIA, PENNSYLVANIA
Facility Description
The Enterprise Avenue landfill site occupies approximately 57 acres,
40 acres of which have been filled. The site is located in an industrial
area. The closest residential population is located approximately 2 miles
northwest of the site.
The Enterprise Avenue site was used by the city of Philadelphia for the
disposal of incineration residues, fly ash, and debris. Drums containing
various industrial and chemical wastes were illegally buried at the site by
several waste handling firms.
4-12
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Site Characteristics
Topography-"
The site is relatively flat. Vegetation is- present over most of the site
area.
Geology/Soils—
Soils overlying the site consist of a low permeability, silty clay layer
ranging in thickness from i> ft on the western boundary to 2i ft along the
eastern perimeter. Underlying the silty-clay horizon is a gravelly sand.
Hydrology—•
Two ground water aquifers underly the site. The uppermost water—bearing
zone is a perched water table and is encountered above the silty clay layer.
Portions of the shallow aquifer zone are mounded into the bottom of the fill
material. The deeper, confined aquifer is found in the sands and gravels that
lie beneath the silty clay. The ground water present in these water-bearing
zones is not used in the general area of the site. However, the deeper
aquifer may recharge sources of ground water for portions of southern New
Jersey. The observed flow in the deep aquifer is east towards the Delaware
River.
Releases
Types/Causes of Releases—
Illegal burying of drums containing industrial and chemical wastes at the
site resulted in contamination of soils and ground water onsite. Hazardous
constituents leaked from the drums to the surrounding soils and into the
underlying ground water. Infiltration of precipitation caused leaching of
hazardous constituents and further transport of constituents to soils and
ground water.
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Mechanisms for Detection—
In response to reports of unauthorized dumping of industrial wastes, the
Philadelphia Water Department (PWD) conducted exploratory excavations during
January 1979 to investigate these reports. Initially, approximately 1,700
55-gallon drums were uncovered. Most of the drums were broken and
fragmented. Subsequently, sampling and analysis activities were conducted to
determine the extent ot contamination.
Extent of Contamination—
The drums which were illegally disposed onsite contained industrial wastes
and chemical wastes such as paint sludges, solvents, oils, resins, metal
finishing wastes, and solid inorganic wastes. The total number of drums
disposed of at the site was estimated to be between 5,000 and 15,000 drums.
Approximately 532,000 yd3 of material were landtilled.
The site lies on the 100-year floodplain of the Delaware River. The
analysis of surface water samples in the site area did not indicate any
quantifiable pattern of contamination contributed by the landfill.
The shallow water-bearing zone within the site boundary was found to be
contaminated. The contamination in the shallow aquifer was localized and
primarily organic in nature. The underlying deep aquifer was essentially
unaffected by the wastes disposed at the site. The presence of the silty clay
layer under the site serves as a barrier to vertical movement of water from
the shallow to the deep aquifer.
Remedial Actions
Response—
The initial response (Phase I) at the site was funded by the Philadelphia
Water Department. Drums and drum fragments were removed and disposed
offsite. Contaminated soils were excavated and stockpiled into two piles; one
pile for offsite disposal or treatment, and the other pile for backfilling
onsite. The soils were separated on the basis of analytical results.
Indicator limits were set for TOX (25 ppra), volatile organics (.12 to 15 ppb) ,
and metals; those soils which measured above the indicator limits were placed
in the pile for offsite disposal or treatment, and those which were below the
limits were placed in the pile for backfilling onsite.
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After .12,000 yd* of soils had been excavated, the Philadelphia Water
Department ran out of funds. At this time, 17,000 yd3 of the excavated
soils were disposed offsite and the other 15,000 yd3 remained onsite.
Remedial actions continued at the site when Superfund money became
available. Stockpiled soils were resampled and analyzed by the EPA.
Excavation of the contaminated soils was continued. The contaminated soils
were disposed of offsite at an EPA-approved facility. The remainder of the
soils were backfilled onsite. The site was then graded with a layer of low
permeability clay overlain by sandy soil and topsoil. Finally, the topsoil
was reseeded and revegetated.
Success/Failure of Remediation—
Monitoring data collected has shown that the remedial action has been
effective in removing the contaminated soil material. It is expected that the
infiltration of precipitation to the ground water aquifer will be minimal.
Although measures were not taken to clean up contaminated ground water and/or
control its migration, site investigations have shown that it will probably
not present a problem to public water supply. Hazardous constituents in the
ground water are expected to volatilize, degrade chemically or biologically,
or be diluted over time.
References: Hernandez, 1985; Roy F. Weston, Inc., 1985; Versar, Inc, 1985.
FRONTENAC SITE - FRONTENAC, MISSOURI
Facility Description
During the 1970s, the Frontenac site was used as a storage area for waste
oils and chemical wastes hauled by a waste oil company. The illegal storage
and transfer of 2,3,7,8-TCDD-contarainated wastes at the site resulted in
contamination of the soils onsite and an adjacent creek (Deer Creek). Through
improper waste handling and disposal practices, oils containing chemical
contaminants were allowed to leak from storage vaults onto the surrounding
soils and drain into Deer Creek.
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Site Characteristics
Climate—
The annual average precipitation (1944 to 1983) in the site area is
36.41 in. Average daily mean temperatures (.1951 to I960; range from 32.3"F
(winter) to 76.9UF (summer) with an annual average daily mean temperature of
55.4°F- The annual average wind speed (1949 to 1983) is 4.3 m/sec.
Topography—
The Frontenac site lies at an elevation of approximately 525 ft above mean
sea level (MSL). The site is relatively flat, but slopes slightly southeast
toward Deer Creek. Onsite surface water drains toward the southeast corner of
the site into the adjacent Deer Creek by way of a drainage swale.
Soils—
The soils at the site are mostly floodplain sediments consisting of
stratified sands, silts, and clays. Gravel, cinders, and concrete fragments
are present near the site surface.
Geology—
The Frontenac site lies within the southeastern corner of the Dissected
Till Plains geologic subprovince of Missouri. Bedrock formations that
underlie the site are chiefly Mississippian-aged limestones that become shaley
toward the basal part of the Mississippian system.
Hydrology—
The Frontenac site lies adjacent to and on the 100-year floodplain of Deer
Creek, which flows approximately 7.5 miles to the southeast where it empties
into the River des Peres, a tributary of the Mississippi River.
Deer Creek is a major source of flooding within the city of Frontenac.
Flash floods which occur along this stream are generally caused by localized,
intense thunderstorm activity which is typical of the northwest. The size of
the Deer Creek watershed in the area of the site is 5.7 square miles. The
peak discharge at this location for the 10-, 50-, 100-, and 500-year floods
are 3,500, 5,700, 6,800, and 9,500 cfs (cubic feet per second), respectively.
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Ground water in the area ot the Frontenac site occurs within limestone
bedrock formations. Water may be obtained in limited quantities from wells
penetrating the limestone at depths of 150 to 200 ft. This water occurs in
fractures and dissolution channels, with highly variable yields. Most of
these wells yield a maximum of 10 to 15 gpm (gallons per minute); below this
depth the water becomes very saline and is generally unfit for use. Drinking
water in the site area is obtained from the metropolitan St. Louis area public
water supply which obtains water from the Missouri and Mississippi Rivers.
Releases
Types/Causes of Releases—
The owner/operator of the storage site illegally accepted chemical wastes
containing dioxin (2,3,7,8-TCDD) for storage at the Frontenac site and
subsequent disposal at other sites. Improper handling of these chemical
wastes caused hazardous substances (.predominantly dioxin-contarainated wastes)
to be released (through spillage, leakage, and runoff) to onsite surface soils
and an adjacent creek (Deer Creek).
Mechanisms for Detection—
A safety inspection was conducted at the site in 1976 by Industrial
Testing Laboratories and the Frontenac City Fire Chief. The ground around the
tanks was found to be so saturated with spilled material that a continuous
stream of seepage could be observed to be entering Deer Creek.
An additional site inspection, which was conducted by the U.S. EPA
Region VII Emergency Response Section in April 1977, concluded that the
Frontenac site did not have the required Spill Prevention and Countermeasure
(SPCC) Plan and thus, was in violation of 40 CFR 112.3(a),(d).
During an EPA investigation of dioxin contamination at several horse arena
sites in Missouri, it was learned that the waste oil company may have been a
responsible party. Subsequent sampling and analysis performed at the site in
1983 revealed the presence of 2,3,7,8-TCDD (dioxin).
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Extent of Contamination—
Sampling and analysis efforts conducted at the Frontenac site have
demonstrated that 2,3,7,8-TCDD exists onsite, within at least the uppermost
foot of soil. The soil contamination extends over most, if not all, of the
area where the storage tanks were formerly located. Additional 2,3,7,8-TCDD
contamination has been confirmed in sediment samples collected from a portion
of Deer Creek (200 ft of the 300 ft reach of Deer Creek adjacent to the site)
at a depth interval of 0 to 2 in. 2,3,7,8-TCDD has not been detected in
samples taken upstream and downstream of the Frontenac site.
Remedial Actions
Response—
During the period from 1977 to 1979, the sludge and waste materials were
removed from the storage tanks and the tanks were removed from the site. The
dioxin-contarainated wastes were sent to an EPA-approved incineration facility
in Louisiana. The remaining wastes were transferred into 55-gallon drums and
buried in an approved hazardous waste landfill in Missouri. Following the
removal of the storage tanks, the area where the tanks were formerly located
was covered by the owner with a layer of crushed gravel.
In April 1984, the site was listed as a CERCLA Superfund site. During
June 1984, interim remedial measures were undertaken at the Frontenac site.
The site was paved with asphaltic concrete over a newly placed gravel
subgrade. A toe-trench was dug near the creek and filled with rip-rap to
prevent erosion of the stream bank. In order to restrict access to the paved
area, a 1/2-in. wire cable was strung on 5 ft steel stakes spaced at 20 ft
intervals around the east, north, and west perimeters ot the site.
Success/Failure of Remediation—
The remedial actions taken at the Frontenac site are considered interim
measures only. Although sampling and analysis has not been performed since
the installation of the interim measures, periodic site inspections have shown
that these measures have been effective in preventing erosion and infiltration
of precipitation. Final measures are being considered at this time.
Reference: GCA, 1984c.
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CRYSTAL CHEMICAL - HOUSTON, TEXAS
Facility Description
The Crystal Chemical site is an abandoned herbicide manufacturing plant.
During 1956 through 1981, the plant produced arsenic; phenolic; and
amine-based herbicides. Wastes from the manufacturing process were placed in
four onsite evaporation ponds. Originally, there was no leak detection or
monitoring system present at the site. The site is currently on the list of
Superfund sites and is in litigation (i.e., the EPA is currently negotiating
with the responsible parties for site cleanup;.
Site Characteristics
Soils—
Soils underlying the site consist of silty clays in the upper 10 to
18 feet. Sandy silts and clays are found below this depth. Permeability of
the silty fine sands has been estimated to range from 10~-* to 10"^ cm/sec.
Geology—
The site is situated on the outcrop of the Beaumont Formation of
Pleistocene Age. The Beaumont Formation, which is found in the site area at
depths of 0 to 150 ft consists of backswamp, point bar, natural levee, and
stream channel deposits containing clay, silt, and sand. Underlying this
layer to a depth of 650 ft are the Montgomery, Bentley, and Wilis Formations
which consist of clays, silt, and sand with minor amounts ot siliceous gravel.
Hydrology—
Surface runoff from the site flows to a flood control channel (western
boundary of the site) and drains to the Brays Bayou (approximately 1-mile from
the site). Since elevated levels of arsenic were detected in the adjaent
flood control channel, it is suspected that Brays Bayou may have become
contaminated following flooding.
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Two water-bearing zones underlie the site; both are contaminated. The
depth to the first sand water-bearing zone is approximately 15 ft below the
surface. The second sand water-bearing zone is located at a depth of 3i> ft
below the surface. Although there are interconnections between the
water-bearing zones, hazardous constituents have not been detected in the
major water-bearing zone (i.e., used for Houston water supply) located
approximately 200 ft below the surface.
Releases
Types/Causes of Releases—
Raw and finished containerized materials were stored on the ground in the
open. Materials spilled occasionally and leached into the surface soils.
Additionally, arsenic trioxide was received in bulk by rail and poor
containment practices were used during unloading.
Periodic flooding occurred at the site. Dikes were used in an attempt to
convey surface water runoff from the process operation area to an area in
close proximity to the manufacturing facilities. In 1976, a significant flood
occurred which overflowed the dikes releasing hazardous constituents into an
adjacent flood control channel and possibly into Brays Bayou.
In addition to surface water and ground water relases, airborne arsenic
was released to offsite areas during mechanical aeration of the waste
evaporation ponds.
Mechanisms for Detection—
In 1971, the Texas Water Quality Board (now the Texas Department of Water
Resources) noted during an inspection that there was a potential for both
onsite and offsite contamination. During subsequent routine inspections (late
1970's), Crystal Chemical Company was cited for several license violations
including spills, poor housekeeping, worker safety violations, and discharge
of contaminated wastewater and storrawater runoff. In 1977, the company was
cited and fined by the Texas Water Quality Board for unauthorized discharge of
arsenic contaminated wastewater.
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Complaints Erom residents of nearby apartment complexes and.businesses of
discolored water resulted in further investigations by the Texas Water Quality
Control Board. Arsenic contamination was discovered in air conditioning
filters in residences immediately downwind of the waste evaporation ponds. It
was determined that the Crystal Chemical site was the source of contamination.
Extent of Contamination—
Phenol-based and arsenic-based herbicide manufacturing wastes were
disposed at the site, resulting in arsenic and phenol contamination. An
estimated 89,000 yd3 of soils onsite are contaminated with 100 mg/kg of
arsenic. Ground water under the entire site is contaminated to the 35 ft sand
layer. The contaminated ground water plume has migrated 150 ft offsite,
extending approximately 200 ft to the north in a somewhat oval-shaped
pattern. Although sampling and analysis activities have not been conducted in
Brays Bayou, it is likely that surface water contamination from surface runoff
exists in Brays Bayou.
Remedial Actions
Response—
Contaminated surface water (from the flooding incident) was removed.
Equipment and buildings were removed (i.e., site was leveled). Former waste
nits (lagoons) were backfilled and the entire site was capped with a 1 to
2 in. clay layer overlain by a plastic top to serve as a temporary cap.
Periodic sampling and analysis has been performed since 1983. Currently,
there are 13 monitoring wells in operation.
Success/Failure of Remediation—
n 1 interim measures (emergency removal actions) have been taken to
T*. RT/FS has been completed (as ot June 1984) and reviewed at EPA
date. lne R '
..„,•<, Appropriate remedial actions currently being considered by the
Headquarters. «FK
A • capping, and the construction of a slurry wall.
EPA inclua6' i- PK o
^OG- Gilrein, 1985; Versar, Inc., 1985; D'Appolonia Waste Management
References.
Services, et. al., 1984.
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SILRESIM - LOWELL, MASSACHUSETTS
Facility Description
During the period from 1971 to 1978, the site was used for the operation
of a chemical reclamation facility which was designed and licensed for the
ultimate disposal or recycling of chemical wastes. Solvents were recovered
through a distillation process (evaporation/concentration system); and wastes
were stored and/or disposed onsite. In 1978, the company's license was
revoked and the site was abandoned leaving approximately 1-million gallons of
hazardous wastes stored in drums and bulk storage tanks. The site is
currently under Superfund status.
Site Characteristics
Topography—
The vertical relief in the site area is approximately 5 ft.
Soils—
Soils in the site consist of fine- to medium-grained sands, and are
moderately well drained. The sand-silt strata is approximately 100 ft thick.
Geology—
The site is located on a glacial outwash plain. The depth to bedrock is
approximately 5 ft. The bedrock material is permeable.
Hydrology—
The ground water table is parallel to the site's surface topography. The
distance to the shallow aquifer is less than 5 ft. Maximum ground water
contamination occurs at depths of 20 ft or less. Ground water movement is to
the north at a rate of approximately 16 ft/yr.
River Meadow Brook is located approximately 300 ft west of the site. Low
levels of contamination were found in the surface water.
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Releases
Types/Causes of Releases—
Surface runoff caused hazardous constituents to be -transported to soils on
the site and to River Meadow Brook (.approximately 300 ft west of the site).
Leachate from the contaminated soils permeated the bedrock and contaminated
the shallow ground water aquifer.
Mechanisms for Detection—
In 1974, the company experienced financial problems and began to be
unselective about the types of wastes it would accept. Permit violations were
discovered during a routine MWPC inspection conducted in 1975. Additional
license violations were discovered in 1977. The company's license was revoked
in 1978, after continued violations. Operations ceased and the site was
abandoned. Site investigations and monitoring activities have been ongoing
since the original discovery of contamination.
Extent of Contamination—
Chemical reclamation wastes from over 35 different chemical processes were
disposed at the site, including acids, alkalis, solvents, pesticides, and
plating wastes. Hazardous constituents found at the site include: volatile
organic compounds, PCBs, pesticides, and some metals.
Contamination has been found in air, surface water (River Meadow Brook),
surface runoff, soils, and ground water. Maximum soil contamination occurs at
a depth of 10 ft or less below the surface. High levels of hazardous
constituents have been found in the shallow aquifer. The extent of the
hazardous constituent plume is approximately 50 ft deep, 1,000 ft north/south,
and 800 ft east/west.
Remedial Actions
Response—
In March 1978, berms were constructed and absorbent fill material was
placed in the disposal trenches (.surface impoundments) to reduce the spread of
surface contamination.
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In 1981, drums and chemicals in bulk storage tanks were removed, with the
exception of approximately 78,000 gallons of PCB-contaminated solvent waste
(in bulk storage.).
In 1982, the buildings and most of the containers were removed (with the
exception of a few underground tanks,). Approximately 6,000 gallons of
volatile organic compounds are reportedly beneath the site. It is estimated
that 8 percent by weight are in the ground water, and 92 percent by weight are
in the soil.
During 1983 and 1984, the site was capped using a 14 in. layer of
compacted clay with gas-venting system to minimize surface water and rainwater
infiltration.
Periodic sampling and analysis has been performed since 1976, using eight
monitoring wells now present on the site. A new evaluation is scheduled for
1985 because the removal of buildings, etc., is believed to have changed the
ground water table.
Success/Failure of Remediation—
Remedial response actions taken to date are considered to be interim
measures. The interim measures have slowed the migration of hazardous
constituents, but not significantly. The RI/FS is currently being prepared
(Perkins-Jordan prepared a report similar to an RI/FS in 1979). Wells
continue to be monitored to define the rate and nature of migration.
References: Ciiello, 1985; Versar, Inc., 198b.
4-24
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SECTION 5
RECOMMENDATIONS ON HOW TO SELECT AND IMPLEMENT
CORRECTIVE MEASURES
INTRODUCTION
An overview of corrective measures for soil releases has been presented in
Section 3. The proven, imminent and emerging technologies, summarized in
Table 3-1, are used to treat, destroy or dispose of contaminated soil in order
to eliminate or mitigate a threat to human health and the environment.
There are many technologies presently available that are capable of
treating or disposing of contamination within the soil horizon. These range
from such methods as excavation followed by capping or landfilling to newer
technologies such as incineration, which can typically render the hazardous
constituents non-hazardous. An important consideration in selecting
corrective measures is to examine available technologies with respect to types
of hazardous constituents prevalent at the site and site characteristics. The
most appropriate corrective action can then be selected and recommended. As
can be seen from summary Table 3-2, certain hazardous constituent types and
technologies are amenable to each other while others are not. Therefore, the
appropriateness of certain corrective measures must first be determined for
specific constituent types. Following initial screening of appropriate
technologies, the site characteristics must also be considered in selecting
the final corrective measure. For example, contamination present at great
depths may not be amenable to in situ methods of treatment. Capping and
landfilling may also be inappropriate in such circumstances if a high ground
water table is present or in conjunction with highly permeable soils. These
measures would not likely provide adequate long term protection to human
health and the environment. Table 5-1 is a summary of pertinent issues
discussed in this section.
5-1
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TABLE 5-1. PERTINENT ISSUES FOR SELECTION AND IMPLEMENTATION OF
CORRECTIVE MEASURES
Site Investigation
Characterize extent and
type of hazardous constituent
release
Soil Conditions
Site Location
Hydrogeology
Screening of Measures
Technical Considerations
Performance
• Waste types and amounts released
• Extent of migration
• Chemical and physical properties of
the waste
• Fate and transport of chemicals to
receptors
Soil type
Permeability
Porosity
Cation exchange capacity
Redox potential
Organic carbon content
Engineering parameters such as
plasticity, atterberg limits and
moisture content
Proximity of local population
Proximity of municipal and private
ground water sources
Locations of drainage areas and
surface water bodies
Local climate including precipi-
tation, temperature and wind data
Overburden characteristics
Bedrock characteristics including
extent of weathering, fracturing,
jointing and foliation
Depth to ground water
Location of uppermost and useable
aquifers
Hydraulic gradients
Hydraulic conductivity
Ground water velocity
Effectiveness of measure to perform
intended functions, including
demonstrated performance
Overall time period a measure will
adequately perform (useful life)
(continued)
5-2
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TABLE 5-1 (continued)
Reliability
Implementability
Safety
Public Health Considerations
Environmental Considerations
Institutional Considerations
Cost Considerations
Selection
• Ability to protect human health and
environment
• Operation and maintenance character-
istics of the corrective measure
• Ease of installation under given
site conditions
• Ease of installation under
conditions external to the site
• Time required to implement and
attain desired results
• Short term safety issues concerning
workers and local populations
• Long term safety issues concerning
onsite employees and local
populations
• Site contaminant, extent and nature
• Fate, transport and exposure of
contaminants
• Anticipated dose, and frequency of
exposure by receptors
• Toxicity of contaminant
• Identify impacted environments
• Ensure corrective measures address
environmental threat posed
• Assess possible future impacts from
corrective measure
• Compliance with Federal, State and
local regulations
• Identify possible non-compliance
areas where variances may be needed
• Detailed cost analysis including
direct and indirect capital costs
• Present worth analysis
• Operation and maintenance costs
• Determine most cost effective measure
• Ensure all aspects of site investi-
gation and screening are adequate
• Select measure that focuses on and
will effectively mitigate the posed
endangerment
(continued)
5-3
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TABLE 5-1 (continued)
Recommendation
Conceptual Design
Implementation
Monitoring
Permit writer must ensure that the
proposed corrective measure is
adequate and may recommend more
applicable measures if necessary
• Detailed corrective measure design
• Detailed drawings and specifications
• Work schedules
• Process descriptions
• Unit or process installation
• Field inspections
• Quality control on construction
• Monitor unsaturated zone and ground
water to determine success or
failure of corrective measure
5-4
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Section Objectives
This section of the report will develop for the permit writer an approach
for selecting and implementing a corrective measure. It will provide a
logical sequence of decision making processes and activities to guide the
permit writer in reviewing proposed corrective measures for releases to soil.
This progression involves the following important considerations:
• adequate site investigation,
• screening,
• selection,
• recommendations,
• conceptual design,
• implementation, and
• monitoring.
Case studies presented in Section 4 and corrective measures described in
Section 3 will also be used to illustrate remedial actions taken at various
SWMUs and other facilities for release to soils. These will be used to
demonstrate the success or failure of the remedial measure taken, and to
analyze why these successes and failures occurred. The interaction between
technology, hazardous constituent types, and site characteristics will be
discussed in terras of how the particular remedial action was chosen and why
expected results were or were not realized. Finally, this section will
provide the permit writer with a summary of the important issues and
considerations that are necessary in the selection process.
IMPORTANT CONSIDERATIONS IN SELECTING CORRECTIVE MEASURES FOR RELEASES TO SOILS
Once a release has been documented, or suspected to have occurred as
evidenced by a preliminary site assessment, it may be necessary to implement a
corrective measure. The correct selection of an appropriate corrective action
requires that the applicant follow a logical progression of decision making
processes presented previously, to be able to select the corrective measure
5-5
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that is the most technically sound, that will provide the most protection to
human health, the environment, and that will comply with various environmental
laws, and that is cost effective. This progression should also be performed
by the permit writer to be assured that the applicant has considered all
available corrective measures and has selected the most appropriate one.
Site Investigation
Once a preliminary site assessment indicates that a release has occurred
and that the release is a potential hazard to public health and the
environment, a thorough site investigation is necessary to determine specific
site characteristics. The permit writer must examine the available data
submitted by the applicant and decide upon the adequacy of the site
investigation with respect to selecting an appropriate corrective measure for
remediation. The permit writer should identify any data gaps that may affect
the final selected action. The following must be properly characterized:
• Hazardous constituent characteristics (migration potential),
• Extent of contamination (potential receptors),
• Soil Considerations,
• Site Location,
• Geology, and
• Hydrology.
These parameters will greatly influence the selection of an appropriate
corrective measure and its final engineering design. Many of the
characteristics needed to be identified may already be available through
previous site investigations which should be used as a base-line for any
further investigation.
Characterization of Extent and Type of Hazardous Constituent Release—
During the site investigation the extent and type of hazardous
constituents) that was released must be determined. The type of hazardous
constituent that is released will influence the selection, design and
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implementation of a corrective measure. As shown in Section 3 of this report,
certain technologies may only pertain to certain types of soil contamination.
For example, biodegradation, either in situ or above grade, is only applicable
to organic constituents.
The chemical and physical properties of a chemical type must also be known
in order to determine appropriate remedial actions. Parameters such as water
solubility, adsorbability onto soil particles, volatility and biodegradability
are important in the final selection of a corrective measure. If possible,
the amount of hazardous constituents released should be quantified to assess
the magnitude of the spill or release. Knowledge about the toxicity of the
hazardous constituent and about the fate and transport of the chemicals to
potential environmental receptors is also critical in deciding if the release
poses a potential threat to human health and the environment and if immediate
corrective actions must be taken. If highly toxic materials have been
released, and environmental receptors identified, then immediate responses may
be warranted to mitigate an impending risk to human health and the environment.
The soils at the site must be adequately defined and the hazardous
constituent levels in the soil horizon must be properly characterized. This
normally can be accomplished through the excavation of tests pits or from soil
borings if contamination is expected to be at substantial depths. Shallow
surface sampling can easily be performed to determine the extent of surficial
contamination. The sampling approach should characterize both the lateral and
vertical extent of contamination. This is needed to determine if the
contamination exists below the mean seasonal high water table, and to estimate
the amount of soils that will require excavation and/or treatment.
Soil Conditions—
The determination of soil characteristics, soil types, permeability and
porosity is needed to assess the potential of hazardous constituent migration
from the soil into ground water and resulting offsite migration to possible
receptors.
Several chemical parameters also affect hazardous constituent migration
Erom soil. Soil pH greatly effects the mobility of many metals, as well
cation exchange capacity. High cation exchange capacities, for example, tend
5-7
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to immobilize metals within the soil. The redox potential (Eh), of a s.oil also
effects the oxidation state and resulting stability of both organics and
metals in the soil.
Other parameters such as total organic carbon content, plasticity limits,
Atterberg limits, and moisture content also influence hazardous constituent
migration and should, therefore, also be examined. Such parameters will
influence the appropriateness of the selected corrective measure as well as
the engineering design and methods of implementation.
Site Location—
The site location is very important in the final selection of a corrective
measure. Factors such as proximity to local populations can effect the
corrective action selected and its implementation. For example, if there are
nearby populations and there is a release of organics to soils, biological
treatment may be considered as a viable treatment option. However, these
populations may be impacted by persistent odors generated throughout the
treatment period therefore eliminating this measure from further consideration.
The proximity of the contaminated soil to municipal or private ground
water supplies is also a major concern. Options for clean up must adequately
protect against the contamination reaching the ground water and migrating
offsite, thereby causing a possible human health concern. The proximity of
surface water bodies, such as lakes, rivers and streams, must also be
assessed. Surface water run-off from the contaminated soil must not be
allowed to impact nearby water bodies. Care must also be taken not to allow a
release, or effects from corrective action implementation, to impact local
ecological systems.
Additionally, information on the local climate is an important part of the
selection process. Temperature data including monthly, seasonal and yearly
means along with depth of frost, if applicable, are crucial parameters. Such
knowledge permits the proper scheduling and implementation of treatment
processes, which are influenced by ambient temperature. Such processes as
biological treatment are impaired by cold temperatures and, therefore, may
only be viable during warm seasons. The depth of frost is very important in
designing an impermeable cap or landfill. Adequate coverage over the
impermeable synthetic material or clay layer is necessary. Freeze-thaw cycles
5-8
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can cause cracking in clays and decrease the integrity of synthetic liners at
a rapid rate. This in turn decreases the reliability, performance and useful
life of the unit.
Monthly, seasonal, and annual precipitation values are important in
determining hazardous constituent migration rates through soils. This must
also be known to determine the water balance of the site. Corrective measure
implementation is also affected by seasonal precipitation values. This is
especially true if the measure involves extensive excavation at great depths
or if contamination is close to water table elevations. Determination of
these data are important in scheduling construction activities.
Wind direction and speed also affect corrective measures that involve
large amounts of excavation. Local populations may be subjected to fugutive
dust emissions, unless effective dust suppression methods are used. Odors may
also be carried to nearby populations through prevailing winds, thereby
creating health hazard.
Hydrogeology—
The hydrogeology of a site is one of the most important factors concerning
the selection of a corrective measure. The overburden and bedrock at the site
in the area of the release must be adequately characterized to assess the
pathways of migration. Parameters such as sand and gravel overburden^ highly
weathered bedrock, fracturing, jointing and existence of foliation can greatly
increase the hazardous constituent migration rate. All of these parameters
must be well defined through such methods as field mapping and subsurface
borings. Sites with fractured or highly jointed bedrock may not be amenable
to on-site storage because hazardous constituent migration may be quite
rapid. This type of site condition may require removal or ultimate treatment
in order to mitigate potential hazardous constituent migration.
Such hydrologic parameters as depth to water table during wet and dry
seasons and definition of the uppermost and useable aquifers must be
considered when deciding on a corrective measure, its engineering design and
implementation. Depth to ground water is important in determining if soils can
be easily excavated or if capping or landfilling are viable corrective
measures for implementation at the site in question.
5-9
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Other parameters such as hydraulic gradient, hydraulic conductivity,
porosity and ground water velocity should be considered in assessing hazardous
constituent migration from soil into ground water. Furthermore, both the
lateral and the vertical extent of contamination must be characterized -to
select an appropriate ground water interception and treatment method.
Screening
Upon adequate completion of the site investigation, the next step in
selecting a corrective measure involves the development and screening of
possible corrective measures. The initial step in the screening process is
the development of general response objectives to identify the goals and
extent of the corrective measure to be used. The site investigation should
identify the possible receptors. Corrective measures that will mitigate the
threat posed to these receptors can then be formulated. For example, if
exposure to the hazardous constituent release is determined to be by direct
contact of onsite workers or trespassers, then capping and access restriction
may be adequate. However, if the release is found to be highly toxic with the
possibility of migration into ground water, a measure that will treat the
hazardous constituents to acceptable levels, or excavation and removal may be
required.
All applicable technologies should be gathered for consideration. These
should then be screened to eliminate those that are clearly not as applicable
as others using the following criteria:
• Technical,
• Public Health,
• Environmental,
• Institutional, and
• Cost.
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Technical Considerations—
A primary concern when screening proposed measures is to identify those
that are technically feasible under given site conditions. Both proven and
imminent technologies should be investigated in some detail in terms of
engineering design and overall implementability. Some of the technical issues
that are addressed in a CERCLA feasibility study can also be considered when
assessing corrective measures for a hazardous constituent release to soil at a
RCRA facility (i.e. SWMU). The following discusses some of the technical
issues that a permit writer should consider when reviewing an application for
corrective measures implementation. The following technical considerations
will be discussed:
• Performance,
• Reliability,
• Implementability, and
• Safety.
Performance—It is important to be able to determine how well a corrective
measure will perform once implemented. In order to do this the effectiveness
of the measure or its ability to perform its intended functions must be
analyzed. Therefore, it must be demonstrated that the remedial action
selected whether it be removal, containment, destruction or treatment, will
properly perform and be effective as a corrective measure in eliminating
present and future human health and environmental impact.
Another aspect of performance is the useful life of the proposed
measures. Each measure should be examined to determine the length of time it
will be able to adequately perform. The useful life of the remedial action
must, therefore be determined to assess the overall performance of the measure.
Reliability—Each remedial measure must be assessed in terms of its
reliability in protecting human health and the environment considering both
hazardous constituents present and site conditions. Therefore, the
demonstrated performance of a corrective measure should be determined. This
assessment can consist of evaluating the performance of the technology at
similar sites or by using pilot scale studies to evaluate actual performance.
5-11
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The amount of operation and maintenance that is required by a corrective
measure also effects its reliability. A measure may be less reliable if it
involves many complicated operation and maintenance activities, whereas a
measure with simple and less frequent operating and maintenance activities can
be considered more reliable. Treatment technologies, for example, may render
contaminated soil non-hazardous, thereby enabling it to be disposed of; as per
applicable regulations.
Implementability—Each proposed measure must be evaluated in terras of its
ease of installation at the site in question. In order for a measure to be
selected for remediation it must be readily implemented in a reasonable period
of time. It must be ascertained that both site conditions and conditions
external to the site will be amenable to the proposed corrective measure.
Time to implement and the amount of time to see desired results must be
investigated. It is important that a corrective measure not take too long to
implement since contamination may migrate from the soil into the ground
water. Also, measures that quickly mitigate the threat posed by a release are
more desirable than those that take a longer period of time.
Safety—The final technical evaluation of a corrective measure is safety.
The evaluation should include the safety provided to onsite workers and
offsite local and distant populations both during and after final
implementation. Measures that expose workers and populations to potentially
hazardous conditions should not be as highly regarded as those that minimize
these conditions. Corrective measures should be designed such that they
minimize risk during the construction/implementation phase and should be
evaluated regarding the ability of the final design to provide continued
safety.
Public Health Considerations—
For a corrective measure to be implemented at a SWMU it must provide
protection to public health, including both onsite workers and offsite
residents. The key components of such an evaluation include:
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• extent and nature of sLte contamination,
• fate and transport of hazardous constituents from the site,
• exposure of local and distant populationstboth human and nonhuman) to
the hazardous constituents,
• projected dose of the contamination to environmental receptors,
• anticipated frequency of hazardous constituents exposure to
environmental receptors,
• toxicity and health hazard of the hazardous constituents, and
• risk assessment with exposure to the hazardous constituents.
The initial step in considering human health risks is to evaluate all
pertinent data from the site investigation. Factors such as constituent
types, quantities, spilled, and extent of contamination are critical issues to
be addressed. The populations) at risks should also be determined.
An important part of choosing a corrective measure is to ascertain the
potential for hazardous constituent migration and the potential exposure
routes. Mechanisms by which populations will be exposed to the contamination
greatly influences the final decision on corrective measures and their
design. If a release to soil has the potential to migrate into a useable
aquifer, then care must be taken to ensure that the measure chosen will either
treat the contaminated soil to appropriate levels or remove it so the public
will not be affected through contaminated drinking water.
Air quality standards and water quality standards must not be violated due
to the release. If standards have been exceeded due to a release, then any
corrective measures implemented should ensure that required levels be attained.
Environmental Considerations—
The next step in the screening process is to make an environmental
assessment concerning impacts to the environment. Again, data from the site
investigation is a primary source of information. It must be ensured that the
corrective measure achieve adequate protection and/or improvement to the
environment.
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Each proposed measure must be analyzed to determine the extent of
environmental benefit that will be attained through its implementation. It
must be determined what part of the environment is, or potentially will be,
impacted from the release. The following consist of environments that may be
impacted:
• Ground water,
• Surface water,
• Soils,
• Air,
• Sole source aquifers,
• Wetlands,
• Flood plains,
• Coastal zone,
• Critical habitats,
• Prime agricultural lands,
• Federal parklands,
• National forest,
• Wildlife sanctuaries/refuges, and
• Habitat productivity.
Another area of environmental concern is the affect on various human resources
such as:
• Commercial,
• Residential,
• Recreational,
• Aesthetic, and
• Cultural.
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Corrective measures must try to minimize the impact to these re-sources. For
example, loss of water supplies and unpleasant odors can reduce local property
values in a residential community.1 Migration of contamination to a stream or
lake can impact the population of the surface water body and result in a loss
of recreational area.
Another area that must be explored in the environmental assessment is the
environment which has been affected and whether or not it can be returned to
its previous condition. Additionally, potential impacts on the environment as
a result of corrective measure implementation, must also be assessed.
Institutional Considerations—
Each of the proposed corrective measures that is being screened should
consider various institutional concerns. This involves assuring that the
corrective measure used for remediation is in compliance with existing federal
(EPA), state and local laws. Some of the federal regulations that should be
considered consist of:
• Ground Water Protection Strategy.
• The Wild and Scenic Rivers Act,
• The National Historic Preservation Act,
• The Endangered Species Act,
• Archeological and historic preservation,
• The Coastal Zone Management Act,
• Fish and Wildlife Coordination Act,
• Flood Disaster Protection Act,
• Uniform Relocation Assistance and Real Property Acquisition Policies
Act, and
• Executive Order 12372, 11988 and 11990.
State regulations concerning flood plains, wetlands, surface water and
development of new aquifers should also be considered when screening
corrective measures.
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Along with federal and state regulations, local laws pertaining to. erosion
control, zoning, building permits, rights of way and sewer, water and
electrical permits should be addressed during the screening process.
A corrective measure that institutionally complies with as many
regulations as possible may be a more desirable choice since fewer permits and
variances may be necessary upon installation. This in turn may facilitate the
implementation process, which can aid in mitigating threats to human health
and the environment by expediting cleanup.
Cost Considerations—
A detailed cost analysis should be performed for each proposed corrective
measure to evaluate its overall cost effectiveness. This should include
analysis of all direct and indirect capital costs that would be incurred
during the implementation of the corrective measure. Also included should be
any operating and maintenance costs that may be necessary to ensure the
continued effectiveness of the measure. A present worth analysis should also
be performed which allows the cost of a measure to be compared to a single
present worth value. This value is equivalent to the amount of money that
must be invested in a base year and disbursed as needed to cover the cost of
the measure over its intended life. Overall cost effectiveness can be
compared by examining the present worth value of each measure.
Selection
From the site investigation and the screening process a final decision
concerning the most applicable corrective measure must be made. The permit
writer must look at all aspects of the applicant's report including the
completeness of the site investigation. As previously stated, much of the
site investigation material may be readily available fom other investigations
conducted at the site; however, the permit writer must ensure that available
information properly characterizes all parameters that may affect the release
and corrective measure implemented.
From the technology screening, the applicant should arrive at the most
appropriate measure for remediation. The permit writer should be certain that
the measure is adequately focused on the risk posed by the hazardous
5-16
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constituent release; i.e., that the endangerment or risk to human health and
the environment is mitigated by the remedial action. The permit writer should
evaluate the corrective measure in terras of each endangerment issue and should
consider the effectiveness of the remedial action in mitigating migration from
the soil horizon to other mediums such as ground water, surface water or the
air.
;
Recommendation
If the permit writer is not completely satisfied that the applicant has
properly addressed the issues in the site investigation and screening process,
then the proposed corrective action plan should not be implemented. At this
point the permit writer may convey to the applicant any deficiencies apparent
in the site investigation or thought process in obtaining the corrective
measure.
The permit writer may also suggest to the applicant other measures that he
or she feels may be more applicable to the site in question. Pilot studies to
evaluate the overall performance and effectiveness of a selected measure may
also be suggested. Such studies can be very useful in recommending and
selecting the corrective measure to be used for remediation.
Conceptual Design/Implementation
Once the corrective measure has been chosen, a detailed conceptual design
must be completed prior to implementation.
Important activities which must be carried out during the implementation
of the measure include field inspections to ensure quality control during
construction, and to ensure that design specifications for construction and
materials are being adhered to. Any alteration that occurs during
construction must be investigated by an engineer to determine if it will
affect the performance of the measure. These inspections during
implementation must include monitoring to determine that contamination is
being properly treated (i.e. to appropriate levels) or if being removed, that
all contaminated soils are adequately excavated and disposed. These
monitoring and inspection activities are important in ensuring that the
corrective measure will perform as designed.
5-17
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Monitoring
Upon completion of the corrective measure, a monitoring plan must be
initiated to ensure that the corrective measure has been properly installed
and is performing as specified. If failure or only partial success occurs,
then monitoring data can be used to determine what further type of remediation
may be necessary.
Monitoring can be done in both the upgradient and downgradient ground
water through the use of monitoring wells to reveal if contamination is
continuing to migrate into the ground water. Lysimeters can also be used to
monitor the unsaturated zone for hazardous constituent concentration and
migration. This type of monitoring can be very applicable to landfarm areas
or below landfills or capped structures. Through the use of lysimeters,
contamination can be detected prior to migration into the ground water. It
may also be applicable to monitor the area through the use of soil borings to
determine if contamination still remains in the soils and at what depths they
occur. Air quality monitoring may also be applicable in many cases.
Table 5-2 presents a checklist of important considerations that should be
addressed during the selection and implementation of a corrective measure.
The final part of this section will use a case study presented in Section 4 to
illustrate remedial actions taken for releases to soils.
SUMMARY
To assist the permit writer in reviewing applications for corrective
measures for releases to soils, a summary table was generated. Table 5-3
illustrates the type of removal, disposal, treatment and containment
corrective measures available for remediation of contaminated soils. The
applicability of measures regarding site characteristics and amenable
hazardous constituents are discussed in Section 3. Table 5-3 was developed
from detailed technology/corrective measure discussions provided in Section 3
and case studies, presented in Section 4. The usefulness of this table can be
illustrated by evaluating in detail, one of the case studies.
5-18
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TABLE 5-2. PERMIT WRITERS' CHECKLIST
SITE NAME/LOCATION
Has an adequate site investigation been conducted concerning: (yes/no)
Hazardous constituent characteristics
Extent of contamination
Soil considerations
Site locations
Site geology
Site hydrology
Have all applicable corrective measures been adequately screened
concerning technical issues? (yes/no)
• Performance
• Reliability
• Implementability
• Safety
Have public health considerations been adequately identified and
addressed? (yes/no)
Extent and nature of contamination
Fate and transport of hazardous constituent(s)
Exposure potential
Contamination dose to receptors
Frequency of exposure
Toxicity of hazardous constituent(s)
Risk assessment
Proximity of local populations
Have environmental considerations been addressed during corrective
measure screening and selection? (yes/no)
• Impact on surrounding environments
• Impact on human resources
Have institutional considerations been adequately addressed? (yes/no)
• Compliance or noncompliance with Federal regulations
• Compliance or noncompliance with State regulations
• Compliance or noncompliance with local regulations
Have accurate cost analyses been completed during the screening
process? (yes/no)
(continued)
5-19
-------
TABLE 5-2 (continued)
Selection of a corrective measure. (yes/no)
• Has an adequate site investigation been completed?
• Have screening parameters been properly addressed? _
• Has the selection considered all available technologies?
Recommendation. (yes/no)
• Does the permit reviewer have recommendations for other
corrective measures that may be more appropriate?
Has a conceptual design been adequately prepared? (yes/no)
Implementation: Are the following adequately characterized? (yes/no)
• Field inspections during construction
• Quality control check during construction
• Monitoring activities
Has an adequate monitoring plan been proposed in terms of: (yes/no)
• Soils
• Ground water
• Surface water
• Air
5-20
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TABLE 5-3. SUMMARY OF SOIL REMOVAL/TREATMENT/CONTAINMENT (DISPOSAL) TECHNOLOGIES
Removal /Containment /Treatment
Strategies
Removal /Containment
Removal /Disposal
Remova 1/Trea tment
In Situ Treatment
Removal/
Containment
(Disposal)
Technologies
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Ability to excavate the soils and hazardous
constituent types influence the applicability
of this technology. This technology does not
comply with RCRA land disposal regulations due
to the fact that there is no bottom
liner/ leachate collection system.
^ ^___ ^^^^^^^_
Implementation is dependent on the ability to
excavate the soils (refer to Section 3).
Generally quite effective technologies, however
replacement of containment unit is inevitable.
Most effective and reliable when used in
conjunction with treatment prior to disposal.
Implementation is dependent on the ability to
excavate the soils, and site specific, geologic
and hydrologic parameters. Hazardous
constituents dictate type of treatment that is
applicable. Refer to Section 3 and Table 3-2
for hazardous constituents amenable to
treatment.
Effectiveness/implementation dependent upon
site characteristics, geology, hydrology and '
hazardous constituents. Refer to the
discussion in Section 3 and Table 3-2
concerning hazardous constituents amenable to
treatment.
Ul
I
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-------
CASE STUDY EXAMPLE
The case study "Enterprise Avenue, Philadelphia, PA" will be considered in
detail. By reviewing the technology discussions in Section 3, the
applicability of the corrective measures implemented at this site can be
assessed. This facility was a landfill used for disposal of incineration
residues, flyash and debris by the city of Philadelphia. However, at some
point drums of various industial and chemical wastes were illegally buried at
the site. If applying for a RCRA permit, this type of situation would fit the
description of a SWMU requiring corrective measures, as stated in Section 1 of
this report.
The site characteristics appear to be quite well described. Site
conditions dictate that a deep aquifer below the site is protected from
contamination due to overlying silt and clay layers. This deep aquifer may
recharge municipal ground water sources for New Jersey and, therefore, if
contaminated could impact human health. A shallow and somewhat limited
aquifer was, however, impacted by the contamination.
Remediation consisted of soil excavation including sampling and analysis
to determine that contamination was adequately removed. Excavated soils that
were found to be contaminated were disposed of offsite in an approved EPA
facility. The site was then graded and capped with a low permeability clay.
This remediation was reported to be successful. No ground water recovery or
treatment was installed at this facility to clean up the contaminated shallow
ground because the source was removed and the impermeable cap minimized
further surface water infiltration through the site.
It is evident from information in this case study that soil contamination
->
did not extend to great depths. An excess of 32,000 ydj of soils was
removed which does not constitute an extremely large quantity of soil and
therefore allows excavation to be an applicable technology. Removing the
source of contamination through excavation in this case was also desirable
because the deep confined aquifer may act as a recharge to a municipal water
supply. Source removal would therefore minimize any future impacts and as
stated in the case study shallow ground water is expected to clean itself up
with time through volatilization, chemical or biological degradation and/or
dilution and therefore not impact the deeper aquifer.
5-22
-------
The corrective measures chosen for remediation at this facility appear to
have been appropriate to mitigate the threat posed to human health and the
environment. Removal followed by offsite disposal in an EPA approved facility
is a common remedial measure although expensive and dependent upon offsite
landfill capacities.
By referring to Table 5-2, it is evident that the removal/disposal
corrective measures implemented at the site for remediation of contaminated
soils are applicable. Further review of Section 3S which discusses corrective
measures and Table 3-2 which provides information concerning wastes amenable
to various treatment technologies verifies this fact.
5-23
-------
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Reference 1
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Dragun, J., and C. S. Helling. "Soil- and Clay-Catalyzed Reactions: I.
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EPA, 1984a. "Case Studies: Remedial Response at Hazardous Waste Sites."
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EPA, 1984b. "Review of In-Place Treatment Techniques for Contaminated Surface
Soils." Prepared by JRB Associates, Arthur D. Little, Inc. and Utah
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Health and Environmental Assessment. 1984.
Follett, R. H., L. S. Murphy, and R. L. Donahue. Fertilizers and Soil
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Forstner, U. and G. T. W. Wittman. Metal Pollution in the Aquatic Environ-
ment. Springer-Verlag. Berlin. 1979.
Reference 2
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GA Technologies. Telephone Conversation with R. Bell, GCA Corporation/
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Ambient Air Sampling and Monitoring at Hazardous Waste Facilities:
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Environmental Protection Agency, Office of Solid Waste, Land Disposal
Branch. EPA Contract No. 68-02-3168.
GCA Corporation/Technology Division, 1983b. "Evaluation and Selection of
Models for Estimating Air Emissions from Hazardous Waste Treatment,
Storage, and Disposal Facilities." Revised Draft Final Report. Prepared
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GCA Corporation/Technology Division, 1983c. "State of New Jersey Incinerator
Study Volume I: Technical Review and Regulatory Analysis of Industrial
and Hazardous Waste Incineration," Final Report. June 1983.
GCA Corporation/Technology Division, 1984b. "Task I: Site Investigations
Analysis Report - Frontenac Site", Detailed Review Draft. Office of
Waste Programs Enforcement, Washington, D.C. Contract No. 68-01-6789.
October 1984.
GCA Corporation/Technology Division, 1985a. "Corrective Measures for Releases
to Ground Water from Solid Waste Management Units", Draft Final Report.
Prepared for U.S. Environmental Protection Agency, Office of Solid Waste,
Land Disposal Branch. Washington, D.C. August 1985. EPA Contract
No. 68-01-6871.
GCA Corporation/Technology Division, 1985b. "Technical Guidance for Corrective
Measures — Identifying Air Releases." Prepared for the U.S.
Environmental Protection Agency, Office of Solid Waste, Land Disposal
Branch. Washington, D.C. June 1985. EPA Contract No. 68-01-6871.
Gilrein, S. U.S. Environmental Protection Agency: Region VI. Telephone
Conversations with L. Farrell, GCA Corporation/Technology Division, Re:
Crystal Chemical Site. May and July 1985.
GSX Corporation. Telephone Conversation with S. Konieczny, GCA Corporation/
Technology Division, Re: Disposal Costs. March 1985.
Hasel, Dr. R. U.S. Environmental Protection Agency, Region VII. Telephone
Conversation with M. Jasinski, GCA Corporation/Technology Division,
Re: EPA-ORD Mobile Incinerator. August 1985.
Hernandez, R. U.S. Environmental Protection Agency, Region III. Telephone
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Reference 3
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Huber, J. M. Telephone Conversation with P- Hughes, GCA Corporation/-
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Traver, R. U.S. Environmental Protection Agency. Telephone Conversation with
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*References for Appendices A and B are included in this reference list.
Reference 6
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APPENDIX A
FATE AND TRANSPORT
Hazardous constituents released to soil have the potential to migrate from
the original point of release. This movement may be within or by means of the
soil medium, or the constituents may migrate from the soil into another
medium, such as air, ground water, or surface water. In addition, the
hazardous constituents released to these media may also be subject to
degradation or removal mechanisms that decrease the amount of the contaminants
in the soil. Alternatively, the hazardous constituents may be resistant to
such degradation and may persist in the environment. An estimate of the
mobility and persistence of a contaminant within the particular soil
environment is key to evaluating the potential risk posed by the release.
Such information provides the basis for performing the exposure assessment
described in Appendix B. In addition to determining exposure potentials and
characterizing risk, one must also be able to assess potential movement within
and between environmental media to determine appropriate corrective actions to
be applied to the release.
The following sections provide a brief description of the factors
influencing contaminant transport and fate and the mechanisms by which
hazardous constituents may be transported or degraded. Guidelines are
provided to assist the permit writer in evaluating chemical and physical
parameters of hazardous constituents with respect to their potential transport
and fate from soil releases. Generalizations of environmental behavior for
selected chemical classes are also provided. Other site-specific,
environmental factors that would influence hazardous constituent transport and
fate are listed for consideration in assessing actual releases.
A-l
-------
FACTORS AFFECTING TRANSPORT AND FATE
Mechanisms Affecting Transport
A number of environmental transport and attenuation mechanisms that are
applicable to soil contaminant releases are influenced by physical and
chemical properties of the hazardous constituent. Additionally, soil
conditions and other environmental factors will influence the action of these
mechanisms on a site-specific basis. A general description of these transport
mechanisms follows:
Adsorption—
Adsorption to soil materials can immobilize contaminants or slow their
movement through soil (attenuation). Factors influencing adsorption include
soil types, charged sites and ion exchange capacity of the soil materials,
structure and charge of the hazardous constituents released, and chemical
solubility and volatility. Tendency for adsorption to soil organic matter can
be estimated for some organic chemicals by using the log of the octanol/water
partition coefficient (KQW). In addition, high solubility or volatility
could be expected to decrease adsorption tendency; therefore, these parameters
should be evaluated.
Volatilization—
Volatilization from soil may occur at soil surfaces or through pore
spacings in unsaturated soils. This mechanism may remove hazardous
constituents from the soil medium via transport into the air medium or may be
a means by which contaminants move through the unsaturated soil medium.
Factors influencing volatilization include soil pore space size, adsorption to
soil, aqueous solubility (in wet soils), and general volatility. Physical and
chemical parameters that can be used to estimate potential to volatilize
from/in soils include vapor pressure, KQW, aqueous solubility, and Henry's
Law constant. The Henry's Law constant expresses the equilibrium distribution
of a compound between air and water and indicates the relative ease with which
the compound may be removed from aqueous solution. None of the individual
A-2
-------
paramelers is adequate to predict volatilization from/in soil owing to the
complexity of the medium; rather, the factors considered together produce a
general overview of likely behavior.
Dissolution—
Dissolution or solubilization of organic and inorganic hazardous
constituents may occur in the presence of water from rainfall or other
contaminants present (solvents) that result from co-release of such
materials. For inorganics, dissolution will depend primarily on the
solubility of the compound form released, and the pH and ionic strength of the
rainfall or solvent solution introduced. Solubility data for inorganic
constituents can be found in standard reference works of Weast (1977-78) and
Dean (1979). For organic constituents, aqueous solubility values are also
often available from standard reference works. In addition, the K can be
used to assess a compound's relative preference for the neutral organic phase
(octanol) and the polar aqueous phase (water). This can be used as an
indicator of potential migration induced by infiltrating rainwater/solvents
relative to a compound's tendency to remain adsorbed onto soil organic matter.
Mechanisms Affecting Fate
Another group of mechanisms to which hazardous constituents may be
subjected are primarily involved in determining the environmental fate of
these compounds. Rather than directing the migration of the compounds within
and between media, these fate mechanisms determine persistence or rates of
degradation. In general, susceptibility of hazardous constituents to these
fate mechanisms is documented by empirical evidence (case studies and research
projects) rather than prediction based on physical/chemical parameters. If
such empirical information is not available in chemical profiles or Callahan
et al. (1979), some generalizations can be made based on compound class,
chemical structure, and using some physical and chemical properties for
support. Because of the complexity in assessing the significance of
environmental fate mechanisms, each is discussed in some detail with general
guidelines provided, where possible. In most cases, however, it is more
A-3
-------
relevant to discuss the significance of the mechanisms in a given medium to
the individual compound class or type; as appropriate, this is the approach
followed here.
Biodegradation—
Biodegradation can occur in the soil medium or in aqueous media to which
hazardous constituents may be transported. The most important factor to
consider in evaluating the role of biodegradation is that it is dependent on
local environmental conditions and a native microbial population capable of
metabolizing the hazardous constituents of concern. Therefore, it may not
occur at any given site, and its occurrence would be difficult to predict
without bench scale tests.
Surface and shallow soils are generally expected to support aerobic
degradation due to their proximity to the atmosphere and high oxygen levels.
Deeper soils (in the saturated zone) may support either aerobic or anaerobic
degradation depending on dissolved oxygen levels in the associated ground
water.
Factors which influence the rate of biodegradation in soil include:
amount of water present; temperature; soil pH; aeration or oxygen supply;
nutrient availability (N,P,K,S); soil texture and structure; and the nature of
indigenous microflora (if any). In addition, properties of the hazardous
constituents (i.e., wastes) themselves as they interact with soil are
important and include: chemical composition; physical state (liquid, slurry,
or sludge); carbon:nitrogen ratio; water content and solubility of waste;
chemical reactivity or dissolution effects of the waste on the organic matter
present in the soil; volatility; pH of the waste; biological oxygen demand
(BOD); and chemical oxygen demand (COD). This information is more readily
available in literature on land treatment, and is of greater utility for land
farming situations than for releases from other types of SWMUs. For further
information on the relevance of these waste and soil characteristics to
biodegradability refer to Parr, et al. (1983); this document is, however,
primarily directed at land farming operations.
A more general discussion and overview on biodegradation is provided in
DeRenzo (1980) as the result of experimentation on chemical mixtures.
Generalities of biodegradability (DeRenzo, 1980) are as follows:
A-4
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• Nonaromatic or cyclic compounds are preferred over aromatics.
• Materials with unsaturated bonds in their molecules (e.g., alkenes,
alkynes, tertiary amines, etc.) are preferred over materials
exhibiting saturated bonding.
• The comparative stereochemistry of certain compunds make them more or
less susceptible to attack by microbial enzymes. The n-isomers of
the lighter weight molecules are preferred over branched isomers and
complex polymeric substances.
• Soluble organic compounds are usually more readily degraded than
insoluble materials. Biological waste treatment is most efficient in
removing dissolved or colloidal materials which are more readily
attacked by enzymes and transported through cell membranes. Readily
dispersed compounds are usually degraded more rapidly because of the
increased surface area that is presented to the individual
mic roorganisms.
• The presence of key functional groups at certain locations in the
molecules can make a compound more or less amenable to
biodegradation. Alcohols, for example, are often more readily
degraded than their alkane or alkene homologues. On the other hand,
halogenation of certain hydrocarbons may make them resistant to
degradation.
Similar generalities correlating substituent groups and biodegradability
(Howard, 1975) are as follows:
• Alcohols, aldehydes, acids, esters, amides, and amino acids appear to
be more susceptible to microbial attack and breakdown than the
corresponding alkanes, olefins, ketones, dicarboxylic acids,
nitriles, amines, and chloroalkane groups.
• Meta-substituted phenols were found to be usually more resistant to
biodegradation than the ortho- or para-isomers.
Photolysis—
Photolysis is primarily a significant fate mechanism only for organic
compounds in the air medium. However, photolysis may also occur on soil
surfaces or in shallow surface waters to the depth of penetration of
sunlight. Alteration or degradation of organic constituents may occur by
direct or indirect photolysis. Direct photolysis is the reaction of the
compound as a result of its absorbing ultraviolet (UV) radiation. Indirect,
or sensitized, photolysis occurs when the UV energy is transferred via another
chemical species.
A-5
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Predicting a hazardous constituent's potential for photodegradatiqn
requires a knowledge of that constituent's tendency to absorb UV light. Some
reference works on compound degradation (Callahan, et al, 1979) contain
information on priority pollutant compounds including UV absorption maxima for
many. Having an absorption maximum in the UV range could indicate potential
for photodegradation.
Empirical information on environmental photolysis is usually limited to
photo-oxidation in the ambient atmosphere. These studies done in smog
chambers and in the presence of oxidants such as nitric oxide (NO) and ozone
are not relevant to photolysis of hazardous constituents in soil, primarily
because such oxidants would not be present at the soil surface. Photolysis
would not be expected to be a significant fate mechanism for hazardous
constituents in soil; rather, it could be important for constituents that have
volatilized from soil.
Oxidation-—
Chemical oxidation of organic compounds, for the most part, uses
mechanisms which involve free radicals or singlet oxygen compounds.
Generally, phenols, aromatic amines, olefins and dienes, and alkyl sulfides
are the most susceptible to oxidation in soil and water systems. Oxidation of
saturated compounds and their haloalkane, alcohol, ketone, and ester
derivatives occurs slowly in these media and is not significant as a fate
mechanism for these compound classes (Dilling et al, 1976).
Oxidation of inorganics is dependent on the presence of compounds in the
soil capable of oxidizing the inorganic hazardous constituents released. In
general, extremely strong oxidizers will not be present in soil because of
their rapid reaction with moisture or soil organic matter. Of primary concern
would be oxidizers co-released with other hazardous constituents. If proper
handling and disposal practices have been followed, this event would be
unlikely. Refer to 40 CFR Part 264, Appendix V, for examples of potentially
incompatible wastes, including oxidizers. It should be noted for inorganics,
particularly elemental metals, that oxidation would tend to dissolve the
hazardous constituent and permit mobilization into the aqueous phase rather
than resulting in its degradation.
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Precipitation—
Precipitate formation is-the interaction of dissolved species that exceed
their solubility product constant (K ) and form a solid that settles out of
sp
solution. Precipitates of metal ions that are most likely to occur in the
environment are sulfides, carbonates, and hydroxides that will form when these
anions are present at elevated concentrations. Precipitate formation is also
dependent on temperature and pH.
The tendency for metal precipitates to form in a given environment can be
used as an indicator of potential attenuation of metal-containing releases.
Metals that are compound forms of sulfides, carbonates and hydroxides are
likely to transport more slowly than more soluble metal salts. These latter
compound types could be leached more readily by rainwater infiltration through
soils and could thereby be transported to the ground water medium.
Hydrolysis—
Hydrolysis of organic compounds can result from a neutral reaction with
water, or it can be catalyzed in the presence of an acid or a base, with the
end result being the replacement of a functional group (-X) by a hydroxyl
group (-OH). In soils, the structure-activity rates for hydrolysis are hard
to predict. They depend on complex pH conditions at the soil surface, the
influence of metal-ion catalysis, and the presence of such functional groups
as phenols, amines, or sulfides in the soil which could lead to catalysis.
PHYSICAL AND CHEMICAL PROPERTIES AFFECTING BEHAVIOR
A number of physical and chemical properties of a hazardous constituent
can be used as indicators of the compound's probable environmental behavior.
It should be recognized that these properties are most relevant to the
transport mechanisms such as adsorption, volatilization, and dissolution.
Most are only pertinent to organic compounds and classes; an exception is
aqueous solubility which is also important (and available) for inorganic
compounds. The most useful properties and their application to assessing
potential envrionmental transport are described in some detail with examples
of their use given as appropriate. To actually find the values of the
parameters for hazardous constituents that may be released from SWMUs, refer
A-7
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to Che Health Effects Assessments (HEAs) prepared for the Offic.e of Emergency
and Remedial Response (OERR) or the Toxicity Profiles prepared for OWPE.
These profiles contain chemical/physical property data, information on
toxicity and other health hazards, and as available, information on
environmental transport and fate. Additional sources of portions of this
information are Callahan, et al. (1979), Verscheuren (1983), Dean (1979), and
Weast (1977-78). The last two references will be very important for obtaining
solubility data specific to inorganic compound forms.
Vapor Pressure
Vapor pressure is the pressure exerted by a gas in equilibrium with its
solid or liquid state at a given temperature. Generally, values are reported
for 20° to 25°C, typical ambient air temperatures, and consistent with
evaluating the transport of hazardous constituents released to soils. Vapor
pressure values are for the pure compound and represent maximum values under
equilibrium conditions; the vapor pressure of a chemical is always lowered
when it is dissolved in another substance. However, vapor pressure can be
used as an indication of the volatilities of hazardous constituents released.
High vapor pressure (>10 torr) would suggest significant potential to volatize
while low vapor pressure (<0.01 torr) suggests low volatility. By combining
vapor pressure data with aqueous solubility and adsorption tendency, one can
determine whether a constituent is more likely to be transported in the air,
water or soil medium, thereby providing focus in the evaluation of a
constituent's likely movement and environmental fate.
Vapor Density
Vapor density describes the mass per unit volume of a gas at its
equilibrium vapor pressure as described above. It is often given relative to
the density of air, defined as unity, so that one can determine the behavior
of the gas upon release from the solid or liquid phase. If the density is
significantly greater than unity, the gas will remain at the surface of the
source and will be transported along the ground. If toxic in nature, it may
thereby pose a potential health hazard. If the vapors are released below soil
A-8
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surface, they may remain there rather than rising through the pore spacings to
volatilize away from the surface soils. If the vapor density is less than or
equal to unity, the gas will rise and disperse easily.
Water Solubility
Water solubility describes the mass of a compound that dissolves in or is
miscible in water at a given temperature and pressure, usually 20° to 25°C and
one atmosphere, and usually expressed in mg/L or ppm. Water solubility is
important because it indicates a compound's affinity for the aqueous medium.
High water solubility permits greater amounts of the compound to enter the
aqueous phase and, therefore, be removed from the soil environment. High
solubility is indicative of an increased tendency to leach from soil media
while low solubility would indicate a tendency to remain adsorbed onto the
solid phase (i.e., soil). This property is particularly significant when
determining whether a release will remain relatively immobile on soil in the
unsaturated zone or whether it will migrate readily to the saturated zone via
rainwater infiltration. Solubility can be used to establish the potential of
a hazardous constituent to enter and remain in the hydrological cycle. One
might then focus on movement and reactions of the constituent in ground and
surface waters rather than pursuing volatilization and soil adsorption as
primary transport mechanisms and thus potential exposure routes.
Aqueous solubility can also be related to fate mechanisms including
biodegradation. Compounds having high aqueous solubility are generally more
biodegradable than insoluble compounds, because the former are more readily
available to microorganisms in aqueous media. Compounds with low aqueous
solubility are often less biodegradable and tend to bioaccuraulate and adsorb
to soil organic matter.
Log Octanol/Water Partition Coefficient
The log of the octanol/water partition coefficient (K ) is a measure of
the relative affinity of a compound for the neutral organic and inorganic
phases represented by n-octanol and water, respectively. It is calculated
from a ratio (P) of the equilibrium concentrations (C) of the compound in each
phase:
A-9
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c
octanol
P = -7 , and K = log P.
C. ow
water
The K has been directly correlated to a number of factors for determining
environmental fate and transport. These include adsorption on soil organic
matter, bioaccumulation, and biological uptake (Chiou, 1983, 1979 and 1977).
It also bears an inverse relationship to aqueous solubility. The K of a
hazardous constituent is very important for evaluation of adsorption on
various soil types with its resulting effect on degradation. The greater the
soil adsorption and immobilization, the slower the constituent will transport
to aquifers and surface waters. Organic constituents with an aqueous
solubility of less than 5 ppm and KQW of greater than 5 tends to accumulate
in river sediments (Lopez-Avila, 1979), and some degree of adsorption on soil
organic matter would be expected for constituents with moderate solubility
(approximately 1,000 ppm) and KQW = 2. It is essential to note that KQW
indicates potential for adsorption only on the organic matter portion of a
particular soil or sediment. It does not correlate to adsorbability by soils
that are primarily inorganic (i.e., clays and minerals).
To use a constituent's KQW to determine environmental transport and
fate, one should determine whether soils near the release are likely to have
low, medium, or high organic matter content. This is discussed in more detail
later in this section. If sufficient organic matter is present at the release
location to suggest possible adsorption, one should then examine the K of
the hazardous constituent released. If the KQW is less than 2, adsorption
will not be a significant attenuation mechanism for the hazardous
constituent. If KQW is between 2 and 4, some adsorption may occur; and if
K is greater than 4, adsorption onto soil organic matter is expected to be
significant in immobilizing the hazardous constituent.
Henry's Law Constant
The Henry's Law constant of a compound is the relative equilibrium ratio
of a compound in air and water at a constant temperature. It is more
significant to releases to water but may be considered where water is present
on the soils or accumulated nearby. The Henry's Law constant can be estimated
A-10
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using the vapor pressure, aqueous solubility, and molecular weight of the
o
compound (Thibodeaux, 1979). It is often.reported in units of atra-ra /mole.
The Henry's Law constant expresses the equilibrium distribution of the
compound between air and water and indicates the relative ease with which the
compound may be removed from aqueous solution. Increasing value of the
Henry's Law constant indicates increasing favorability of volatilization as a
transport mechanism. In addition, the constant provides more information than
a comparison of vapor pressure and aqueous solubility. It is emphasized,
however, that this constant is representative of equilibrium conditions for a
pure chemical compound and may not accurately predict behavior under actual
environmental conditions.
Other Physical Properties
Several additional physical properties influence environmental behavior
and can be used to supplement evaluations based on the properties discussed
above. Two of these properties, melting point and boiling point, are obvious
in their use. These two properties indicate the physical state of the
hazardous constituent at standard conditions. This will be the basis for
looking at how a hazardous constituent release may migrate. Use of physical
state information is discussed later in this section.
Molecular weight is another property that can be used to assess potential
transport if more specific chemical and physical property data (i.e., K
Henry's Law constant) are not available. The use of molecular weight in
assessing hazardous constituent transport and fate is somewhat less obvious
than for some properties, and warrants a brief discussion. Molecular weight
relates to the size and density of the molecules of a compound. All other
factors being equivalent (i.e., adsorptive surface, compound polarity, atomic
charge, etc.), a higher molecular weight, and thus larger compound, will
adsorb more strongly to another material than will a smaller compound.
Therefore, if one could generalize behavior by assigning a constituent to a
particular structural class, one could (based on size) extrapolate behavior of
the constituent in question relative to those members of the class for which
empirical data are available. It should be noted that molecular weight is
only a secondary factor in assessing adsorption and that it should only be
used in conjunction with other constituent properties.
A-ll
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Viscosity is another physical property that will significantly influence
hazardous constituent migration in the soil medium. Liquid compounds with
high viscosity would move more slowly through soil than would liquids with low
viscosity. However, to obtain numerical values of this property," one would
have to access reference works that may not be readily available. Therefore,
it is recommended that the reader consult the HEAs or toxicity profiles for
the hazardous constituent in question to determine whether the general
description provides an indication of viscosity. It is probable that
constituents exhibiting high viscosity will be so noted. Otherwise, a
conservative assumption is that the viscosity would be comparable to water and
that the liquid hazardous constituent would potentially move through soil at a
rate comparable to water.
ASSESSMENT OF HAZARDOUS CONSTITUENT TRANSPORT AND FATE
Hazardous constituent transport and fate is a highly complex process and
cannot be accurately predicted with information that is readily available.
However, by combining information on the chemical and physical characteristics
of the hazardous constituents released with site-specific information, such as
soil types, climate, and release area activity patterns, it is possible to
generalize potential transport and fate. This can then provide the basis for
estimating potential exposure and risk posed by the release; it can also
direct the efforts of further data gathering to focus on locations and media
of primary concern. The following is a summary of items to be considered in
assessing potential transport and fate of a hazardous constituent release. It
attempts to lay out in step-wise fashion a logical approach to collecting and
evaluating relevant information. It is not intended to provide exact answers
for all constituent releases.
Type of Hazardous Constituent Released
• Does this hazardous constituent belong to a class or type of compound
for which previous environmental behavior has been documented or
postulated?
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Very often, if a constituent can be classified or. grouped with
similar compounds, for which empirical data are available, the
behavior of an unknown constituent can be estimated based on
these structural or physiochemical similarities. Table A-l
lists organic compound classes and generalizes what is known or
postulated about their environmental behavior following release
to soils. Inorganic hazardous constituents are primarily
metals, and their environmental behavior cannot as easily be
generalized. Therefore, they have not been addressed in this
table, but guidance on clay sorption and huraic complexes of
metals are provided later in this section.
What are the physical and chemical properties of the constituents)
which may influence transport and fate?
As previously discussed, certain physical and chemical
properties can be used to estimate transport of a constituent
following release to soil. Table A-2 lists some of these
properties and broadly applies ranges of values that may result
in the specified behavior. Note that other factors such as the
presence of certain functional groups and site-specific
environmental factors may alter actual transport from that
expected when considering only physical and chemical
properties. Relevant properties for individual chemicals can be
found in HEAs available from OERR, Callahen et al. (1979),
Verscheuren (1983), Weast (1977-78), and Dean (1979).
What is the physical form of the hazardous constituents) released?
Whether the release is liquid, solid or semisolid, such as
sludge, the physical form of the release can strongly influence
transport. If the release is a solid and remains solid under
ambient conditions, then it could remain on the soil surface
unless mobilized by dissolution in rainwater or other hazardous
constituents (solvents) or by entrainment in ambient air (as
could be caused by wind or similar action). If the release is a
liquid, it is likely to move below the soil surface at rates
dependent on its viscosity and adsorptive tendencies. If the
release is a seraisolid, it may separate into two phases that
will tend to be mobilized at different rates and possibly by
different mechanisms.
Location of Release
Characterize the location of the release as fully as possible. Use
the categories below for guidance.
chemical activity - What chemicals used in the area could act to
mobilize the hazardous constituent released? Have any such
chemicals been released in the area where the hazardous
constituent(s) in question were released? What are the chances
of future releases of solvents in the same area? Chemicals of
concern would include:
A-13
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TABLE A-l. GENERAL SUSCEPTIBILITY OF SELECTED ORGANIC COMPOUND CLASSES TO MECHANISMS
AFFECTING TRANSPORT AND FATE
Compound Claaa
Aliphatic hydrocarbona
Aromatic hydrocarbona
Halogenated aliphatic*
Halogenated aromatica
Phenols
Chlorophenols
Nitro/nitroso compounds
Amines/ amides
Cyanidea/azo compounds
Bi-phenyl compounds
Polynuclear aromatics (PAHs)
Carbamate insecticides
Phenoxy acids, esters, salts
Organophoaphorus compounds
Adsorption
Low to moderate
Low to moderate
Low to moderate
Low to moderate
Low to moderate
Low to moderate
Low to moderate
Low to moderate
Low to moderate
High
Moderate to high
Moderate to high
Data not available
Moderate
Low
Volatilization
High
Moderate to high
High
Moderate to high
Low
Low
Low
Low
Low except in pre-
sence of acid or
for cyanogen halide
compounds
Low
Low
Low
Low
Low
Low
Leaching
Moderate to high
Moderate to high
Moderate to high
Moderate to high
High
High
Moderate to high
Moderate Co high
High
Low
Moderate
Low
Moderate
Moderate to high
Moderate to high
Bio trana format ion
Low to moderate
Low to moderate
Low to moderate
Low to moderate
Moderate
Low to moderate
Varies with compound;
moat low; residues
2 to 10 months in soil
Varies with complexity
of compound; simpler
are more readily
degraded
Low to moderate
Low
Low to moderate
Low; trana forma t ions
occur within the
cyclodiene class
Data not available
Low to moderate
Moderate to high
Chemical Reaction
Generally very slow in *oil
Generally very (low in soil
Generally very slow in soil
Generally very slow in soil
Low to moderate
Low to moderate
Moderate
Possible; significance unknown
Possibly moderate
Low
Low to moderate
within the cyclodiene class
Known to degrade in soil; rates
and significance unknown
Moderate to high (hydrolysis
Moderate to high
i)
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TABLE A-2. CHEMICAL PROPERTY RANGES THAT RELATE TO DEGREE OF SUSCEPTIBILITY TO MAJOR ENVIRONMENTAL
(INTERMEDIA) TRANSPORT MECHANISMS3
1
I—'
Ol
Mechanism
Adsorption
to soil
Leaching from/
through soil
Volatilization
from soil
Property
Octanol/water Parti-
tioning (Kow)
Soil typeb
Aqueous solubility
Vapor pressure
Henry's Law constant
Range and Susceptibility
Low Moderate High
<2 2 to 4 >4
Mineral Clay Organic Matter0
<10 mg/1 1,000 mg/1 > 10, 000 mg/1
£0.1 torr 1 torr >10 torr
-4 atm-m3 -3 -2 atm-m3 -1 0 attn-m3
-U mole 1U C° IU mole 10 tO 10 mole
aSummary table for general guidance only; does not consider functional groups or multiple chemical
properties.
"While not actually a chemical property of a hazardous constituent, the soil type is incuded here
because it is highly significant to transport of a substance released to the soil medium.
cThe soil organic matter content (low, medium, or high) relates to likelihood of adsorption based
on Kow predictions.
-------
chlorinated solvents;
aliphatic and aromatic hydrocarbons;
acids;
bases;
detergents;
water; and
aqueous solutions of any of the above.
Climatic Conditions - What are the typical climatic conditions
for the region and how could they influence transport and fate?
— Annual Rainfall - Rain could act as a dust supressant for
soil-adsorbed hazardous constituents; in arid climates,
generation of contaminated dust would be more likely. Rain
could act as a solvent for soluble or slightly soluble
compounds; infiltrating rain could leach hazardous
constituents out of the soil and transport them to ground
water. Surface run off from rainfall could mobilize
contaminated particles and move the contaminated soil via
overland flow.
— Temperature - Volatilization will increase with increasing
temperature. In hot weather, greater amounts of volatile
and semivolatile hazardous constituents would migrate from
soil into the vapor state.
— Prevailing Wind Direction/Magnitude - Assessment of
potential transport via fugitive dust requires knowledge of
the magnitude and direction of prevailing winds. A wind
rose, as required in the Part B permit application,
provides data by which to evaluate transport of dust and to
indicate where contaminated dusts would be most likely to
be carried.
Physical Characteristics of Release Location - Are there
conditions in the release area that will influence transport and
fate of the hazardous constituents?
— Vegetative Cover - Plants growing in the area of the
release can help reduce mobility of contaminated soils by
affording protection from wind erosion or light traffic
(foot) generation of dusts. Plant roots can hold soil so
that channeling is minimized and surface runoff does not
carry large amounts of contaminated soil from the release
area.
Surface Drainage Patterns - Surface water (or runoff) flow
patterns over the release area should be studied to
determine whether runoff is moving into or out of the
area. If significant runoff flows through the contaminated
area, there is a greater chance of movement of the
contaminated soils and also a greater chance of leaching of
A-16
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soluble or partially soluble compounds. Channeling or
manmade drainage ditches in the area of the discharge are
of special concern.
Saturated or Unsaturated Soils - The amount of moisture in
the soil will influence whether constituents can volatilize
through pore spacings or whether they will be hindered by
an inability to dissolve in the aqueous phase. For soluble
constituents, saturation can be a means of transport by
leaching the hazardous constituents from soil. In moist,
unsaturated soil, the soluble constituents may dissolve but
remain associated with soil particles through the
adsorption of water onto the particles.
Human Activity - Do people utilize the area near the release in
such a way as to enhance mobilization of the hazardous
constituents? Are heavy equipment and other vehicles operated
in the area capable of generating dust containing contaminated
soils?
Is the release to surface soil or the subsurface?
- This question is important because releases to surface and
subsurface soils present different risks of exposure and are
subject to different transport mechanisms. A release to
subsurface soils generally does not present a significant hazard
from exposure to the soil itself; rather, hazardous constituents
may move through the soil resulting in exposure via other media
such as air (vapor transport through pore spacings) or ground
water (dissolution in aqueous medium). Exposure to surface soil
releases can be by direct contact, ingestion or inhalation of
airborne particulate. This latter exposure could be caused by
wind action on contaminated soil or by activity within the
contaminated area causing dust to be generated.
What types of soil are present in the area of the release?
The type of soil to which a hazardous constituent is released
will strongly influence the transport of that constituent. For
organic constituents, a parameter used to assess soil adsorption
is the Kow; this value has been correlated to adsorption on
soil organic matter (Chiou, et al, 1979 and 1983). Therefore,
the organic carbon content of the soil is significant in
assessing transport. Because actual data are often not
available, one can look at whether the release is to a subsoil
(organic carbon content of 2 to 4 percent), topsoil (organic
carbon content of 12 to 18 percent), or to a peat type soil
(organic carbon content often greater than 50 percent).
Additional soil type information relevant to assessing transport
would be whether the soils were comprised of clay or mineral
materials. Minerals would be expected to have a rather
insignificant ability to adsorb organic or inorganic hazardous
A-17
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constituents and attenuate their movements. However, clay soils
with their high surface area and frequently large number of ion
exchange sites could be expected to adsorb both organic and
inorganic constituents. Figure A-l provides estimates (Forstner
and Wittman, 1979) of bonding strength of several heavy metals
(1) adsorbing onto and into clay lattice structures and (2)
forming insoluble complexes with natural organic materials
(humic substances).
Checklist for Assessment of Transport and Fate
A listing of the information discussed above is provided in Figure A-2 as
a checklist for investigating releases to soil from SWMUs. The two major
categories of information that are needed are physical and chemical
characterization of the hazardous constituent release and characterization of
the location of the release. Primary sources of this information are the
facility's Part B permit application including the Exposure Information Report
(EIR) and the Health Effects Assessments (HEAs) available from OERR. These
must be supplemented by site specific information obtainable from a facility
inspection and, as necessary, by chemical data from standard reference works.
Information on chemical composition of wastes handled at the SWMU at which
the release occurred should be available in the Part B permit application.
This will indicate the chemical compounds that may be expected in the release
and may possibly indicate the physical form of the release (i.e., solid,
liquid, sludge). Chemical information on the specific compounds released must
be obtained from the HEAs supplemented as necessary by standard reference
works.
Information on the location of the release must be obtained in part from
the RCRA facility's (i.e. SWMUs) Part B permit application but with extensive
input obtained during an onsite inspection and/or from interviews with
facility personnel. Human activity patterns in the area of the release and
the handling of potentially reactive wastes should be elucidated from
information required in the Part B permit application and the EIR. Other
relevant information that should be obtained from these same documents
includes rainfall data, prevailing wind direction (wind rose), and surface
runoff and drainage patterns. The EIR should also include information on site
conditions that could substantially affect transport and fate (e.g. high water
table, porous soils, etc.).
A-18
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INORGANIC/CLAY INTERACTIONS
Empirical affinity series for ion exchange adsorption
Pb > Ni > Cu > Zn
Strength of incorporation into clay lattice structure
Strong: Cu, Fe, Ag
Moderate: Pb, Mn, Zn, Co
Weak: Cd
ORGANIC (HUMIC AND FULVIC) COMPLEXES
Bonding strength
UO2,* > Hg2* > Cu2+ > Pb2+ > Zn2* > Ni2+ > Co2+
Complex stability series for soils
Pb > Cu > Ni > Co > Zn > Cd > Fe > Mn
Complex stability series for metal-humic substances
Strong: Cu, Sn, Pb
Moderate: Zn
Weak: Ca, Mg, Mn, alkali metals
Figure A-l. Metals Adsorption and Complex Formation.
A-19
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TYPE OF HAZARDOUS CONSTITUENT RELEASED
1. Compound type or class
2. Functional groups present
3. Relevant chemical/physical properties
a. Aqueous solubility
b. Octanol/water partition coefficient
c. Henry's Law Constant
d. Vapor pressure
e. Vapor density
f. Other physical properties
4. Physical form of release
LOCATION OF RELEASE
1. Characteristics of the area
a. Chemical activity (existing or potential release of other
reactive chemicals)
b. Climatic conditions
(1) annual rainfall
(2) temperature
(3) wind rose
c. Physical characteristics
(1) vegetative cover
(2) surface drainage patterns
(3) saturated or unsaturated soils
d. Human activity (potential soil disturbances)
2. Release to surface or subsurface soils
3. Soil types at release location
a. Mineral
b. Clay
c. Organic matter content
(1) low (subsoil, sandy soil)
(2) medium (top soil, loamy soil)
(3) high (peat)
Figure A-2. Checklist/Summary for Assessment of Potential
Transport and Fate.
A-20
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SUMMARY
Potential transport and fate of hazardous constituents released to the
soil can be estimated by following the procedure that has been outlined in
this appendix (Appendix A). The need for such an assessment is twofold.
First, a determination of the transport pathways and migration potential of
the hazardous constituent is necessary for one to identify potential exposures
to nearby populations and environments.
Second, migration, persistence, and potential exposure can be used to
assess the need for and effectiveness of proposed corrective actions. For
soil releases and exposures to the soil medium, the transport pathways of
concern include soil transport via surface runoff, fugitive dust, adsorption
with immobilization on surface soils, and uptake by biota. If the hazardous
constituents are expected to migrate to other media (e.g. volatilization to
ambient air, dissolution in surface water or ground water), refer to the
individual guidance documents for those media (GCA, 1985a; GCA, 1985b;
E. C. Jordan, 1985). However, if the hazardous constituents remain in the
soil medium and are expected to transport via the pathways listed above, one
should consult the remainder of this guidance document. Appendix B provides
information on conducting an exposure assessment for a hazardous constituent
release to soil. It explains what constitutes an exposure assessment and what
information is needed to conduct qualitative and quantitative exposure
assessments. General procedures for hazard and risk assessment are also
discussed in Appendix B.
A-21
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APPENDIX B
EXPOSURE ASSESSMENT
INTRODUCTION
This section has been prepared consistent with the EPA guidance set forth
in the following documents:
• Schultz, et al., Draft Supertund Exposure Assessment Manual, prepared
for the U.S. EPA, Office of Toxic Substances, August 17, 1984.
• EPA, 1984c and EPA, 1985.
• ICF, Inc., Draft Superfund Health Assessment Manual, prepared for the
U.S. EPA, Office of Emergency and Remedial Response, May 22, 1985.
Other sources ot information used in preparation of this section are
presented in the references section of this report.
Pending publication of guidance specific to RCRA enforcement, two of these
documents (e.g. Schultz, et al., 1984; ICF, Inc., 1985) developed for use in
assessment under CERCLA represent the best available information for
assessment of public exposure (and risk) resulting from soil releases.
Although these documents primarily concern human population exposure (and
risk) assessment, they also provide the basis for evaluating exposure (and
risk) to non-human populations.
The purpose of the exposure assessment is to determine all routes of
exposure to human (and non-human) populations resulting from hazardous
constituent releases to soil and other environmental media contaminated as a
result of transport from the soil medium. Determination of whether or not
exposure to humans (or other receptors) will occur at a source at-present or
in the future typically involves determination of:
B-l
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• the fate and transport of hazardous constituents to soil and" other
related environmental media through identification of likely pathways
of constituent release and transport from identified sources, and,
• human (and non-human) populations at risk o-f exposure to hazardous
constituents in soil and related environmental media through
identification of activity patterns near the source or point of
migration.
Appendix A provides guidelines for evaluating transport potential and fate
of releases of hazardous constituents to soil. Appendix B will focus on
evaluating exposure to human (and non-human) receptors from identified
releases and will provide guidance on conducting exposure assessments.
The following six subsections of Appendix B describe the components
necessary for exposure assessment, and provide guidance for the selection and
performance of an appropriate exposure assessment methodology. The first
subsection will concern exposure pathway analysis, and will provide guidance
for identifying exposure pathways and determining whether pathways are
complete. Determination of complete exposure pathways will establish the
course of subsequent exposure analysis.
Subsection 2 will discuss the types and levels of exposure analysis for
the permit writer to consider. Exposure assessments can be either qualitative
or quantitative; however, regardless of the method or level of assessment
employed, the outcome ot the exposure analysis terms as a basis for
characterizing risks to human health associated with exposure. Exposure
assessments which are qualitative in nature are usetul because they target key
pathways and routes of human exposure, and therefore can be used to derive
qualitative estimates of human risk associated with exposure. Exposure
assessments which are quantitative in nature are useful because they also
identify significant pathways and routes of human (and non-human) exposure,
and quantify actual human intake, thus establishing baseline conditions for
quantitative risk assessment.
Subsection 3 will discuss the rationale for selecting and performing
qualitative or quantitative exposure analysis. Informational requirements for
each level ot analysis will be described in detail to assist the permit writer
in selecting the most appropriate method.
B-2
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Subsections 4 and 5 will describe in detail the necessary steps f-or
performing qualitative and quantitative exposure analysis, respectively. Uses
of exposure information from these various levels of assessment (e.g.
qualitative or quantitative) will also be discussed in these sections. In
particular, guidance will be provided to assist the permit writer in utilizing
derived exposure information for two purposes:
• to determine the level and means of corrective actions necessary to
adequately reduce human exposure (and risk) associated with
identified release ot hazardous constituents to soil, and
• to provide an approach for evaluating public health impacts
associated with such releases to soils.
The sixth and final subsection will describe the risk characterization
process. Guidance will be provided to assist the permit writer in
characterizing risks to human (and non-human) populations associated with
exposure to hazardous constituents. Methodologies, informational
requirements, and limitations of risk characterization processes will also be
considered.
PATHWAY DETERMINATION
Assessment of exposure to human (and non-human) populations (e.g.
receptors) proceeds directly from identification of complete exposure
pathways. A complete exposure pathway has the following four necessary
components: (Da source of chemical release into the environment, (2) an
environmental transport medium (e.g. air, surface water) for the released
chemical, (3) a potential exposure point, and (4) a human (or non-human)
exposure route at the contact point. Identification ot exposure pathways
establishes the course of subsequent exposure analysis. Thus, the permit
writer should focus on identifying exposure pathways and determine whether the
pathway is complete. Pathways which are complete (e.g. where a release,
movement of hazardous constituents through environmental media, and likelihood
of human or non-human exposure are all evidenced), will require exposure
characterization so as to qualify or quantify the magnitude, frequency, and
B-3
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duration of human exposure to contaminated media. Pathways which are'not
complete will, in most instances, be eliminated from further analysis, or may
identify existing data gaps which must be filled in order to assess more
conclusively the potential for and impact of human exposure via those
pathways. Guidance for determining potential exposure pathways is provided in
Table B-l. For further guidance in the determination and evaluation of
potential exposure pathways, the reader is referred to ICF, Inc., 1985.
LEVELS OF EXPOSURE ASSESSMENT
Depending on the available information and the permit writer's need,
varying levels of exposure assessment can be performed. Basically, exposure
assessments can be either qualitative or quantitative. Assessments which are
qualitative are referred to as level I analyses, while those which are
quantitative are referred to as level II (or level III) analyses. In general,
a level I analysis is a qualitative evaluation which provides a preliminary
screening of on-site hazardous constituent release sources, environmental
pathways through which constituents migrate off-site, and possible human (and
non-human) population exposure points and mechanisms. A level I analysis
gives an indication of the nature and extent of public health threats
resulting from exposure to a hazardous constutuent source. Level II
(quantitative) analyses develop estimates of the quantities of the release
(e.g. mass loading) ot chemicals of concern from sources identified in level
I, and considering hazardous constituent transport and environmental fate,
estimate the degree of potential population exposure (and risk) resulting from
exposure. Level II exposure analyses also allow for estimation of intake (or
dose) incurred by human (and non-human) receptors. A further refinement of a
level II analysis is also possible given the degree of sophistication ot
existing data. This very detailed analysis is referred to as a level III
assessment. In level III assessments, those key hazardous constituent release
and exposure scenarios targeted in level II are quantitatively analysed in
detail. It is basically an indepth level II analysis, although the analytical
tools necessary for the analysis are more resource intensive than those
required for level II analysis, and the results are of significantly greater
B-4
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Name of Source:
Date:
Analyst:
QC:
TABLE B-l. POTENTIAL EXPOSURE PATHWAY DETERMINATION
Release Release Exposure Exposure
Source/Mechanism Medium Point Route
1. Contaminated air media nearby playground inhalation (pos-
surface soil sible reingestion
2.
3.
INSTRUCTIONS
1. List release source.
2. List release medium.
3. Describe the nature of the exposure point.
4. List exposure route: e.g. ingestion, inhalation, dermal contact,
including possible indirect routes, such as uptake by biota and subsequent
ingestion by humans.
ASSUMPTIONS
List all major assumptions in developing the data for this worksheet:
Source: ICF, Inc., 1985. B-5
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accuracy (e.g. computer modeling or environmental monitoring). The
characteristics of each level of analysis are briefly summarized in Table B-2
(Schultz, et al., 1984).
CRITERIA FOR SELECTING THE LEVEL OF ASSESSMENT
The determination of which level of assessment is appropriate for
evaluation of a hazardous constituent release to soils (or other environmental
media) will ultimately be a judgement decision by the permit writer; however,
the selection should be based on criteria associated with the baseline
conditions of the hazardous constituent source. These criteria concern: (1)
conditions at and around the source, (2) the level of detail needed in the
analysis, and (3) the ultimate intended use of the exposure analysis (e.g. to
establish permit conditions, determine corrective measures, etc.). Table B-3
shows how these criteria can be used to determine the level of exposure and
risk assessment appropriate for evaluation of a source of hazardous
constituent release to soils. In order to define conditions at and around the
facility, the permit writer must have available the following information:
• source background data;
• disposal history (and records, if available);
• chemical analysis data for locations at and near the source;
• source characterization data (e.g. topography, hydrogeology);
• information on local human population;
• any human body burden and health effects data (unlikely to be
available for most sources); and
• types of corrective measures considered.
The primary sources for this information are RCRA Part b Applications,
site inspections, and analytical data and reports available from past or
ongoing facility characterization. Depending on the level of need of the
permit writer, data used to evaluate baseline conditions at and around the
source can be used to determine what corrective measures, it any, should be
B-6
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TABLE B-2. CHARACTERISTICS OF EXPOSURE ASSESSMENT ANALYTICAL LEVELS
Analytical Level of Characteristic Resource
Level Nature of Analysis Detail Analytical Tools Intensiveness
Level I Qualitative: Broad
Scale Screeing
Low
Decision Networks
Low
Level II Quantitative:
Minimal targeting
Moderate Simple Estimation
Equations
Moderate
Level III Quantitative:
Highly targeted
High Computer Modeling; High
Monitoring
Source: Schultz et. al., 1984.
B-7
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TABLE B-3. CRITERIA FOR DETERMINING LEVEL OF EXPOSURE '
(AND RISK) ASSESSMENT APPROPRIATE FOR EVALUATING
A RELEASE OF HAZARDOUS CONSTITUENTS TO SOIL
Level of Assessment Necessitated
Criteria
Conditions at the
facility
(2) Conditions around
the facility
(3) Level of need
Level I
-contamination is confined
to and migrated little
from the facility, and
direct contact by human
populations is unlikely.
-topographical and geolog-
ical data indicate that
releases would travel
very slowly in environ-
mental media, and no
large or sensitive popu-
lations are located near
the facility
-the exposure assessment
need not be rigorous be-
cause the qualitative
evaluation will be used
to determine what correc-
tive actions, if any,
will be taken at the
source, or will be
utilized to establish
relative degrees of haz-
ardous contaminant release
to soils which are consi-
dered acceptable.
Reliable sources: e.g.,
analytical data, time,
money, expertise, warrant
a Level I analysis
substantial.
Level II (or Level III)
-the quantity, frequency,
and potential toxicity
of an observed release
indicates migration from
the facility into a trans-
port medium (e.g. out,
surface water).
-if exposures have already
occurred or are imminent
-topographical and geolog-
ical data indicate that
releases would travel at
moderate or rapid rates in
environmental media
-presence of a large popu-
lation near facility
(despite limited migration
potential of hazardous
constituents from the
facility)
-the exposure assessment
will be used, or is likely
to be used to determine
what corrective actions,
if any, will be taken at a
source, or to establish
acceptable levels of re-
leases to soil in the
absence of existing
standards. Available re-
sources: e.g. analytical
time, money, exper-
tise warrant a Level II
analysis necessary.
Source: IGF, Inc., 1985.
B-8
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taken at Che source, or in the case of post-remediation, to evaluate-the
efficacy of the chosen corrective measure at reducing releases of hazardous
constituents to an acceptable (target) level.
The initial decision as to which level of assessment is to be performed at
a source should be preliminarily determined (if possible) during initial
review of the baseline facility data. At this time, the extent of chemical
contamination at the source can be estimated, and based on existing conditions
at the facility and affected (e.g. exposed) population profiles, a decision on
the appropriate level of exposure (and risk) assessment can be made. Initial
selection of level I or level II, however, is not necessarily final. As the
exposure assessment proceeds it may become clear that the initial level of
analysis chosen is not appropriate when considering all available data. At
that point, the level of analysis may change. At the time of initial decision
of the level of detail required existing gaps in the quality and quantity of
available data should also be identified. If necessary, measures can be taken
to obtain information necessary for adequate exposure evaluation. For
example, should the permit writer, after review of a facility's Part B
Application, determine that a level II analysis is required but not possible
given available information requests for additional information to perform
the more detailed analysis can be specified.
QUALITATIVE ASSESSMENT OF EXPOSURE
The key element of the qualitative (level I) exposure assessment is a
comprehensive exposure pathway analysis, in which potential pathways are
indentified and characterized. The assessment involves preliminary
determination of complete exposure pathways by performing three analysis
steps. These include:
• hazardous consittuent release characterization and analysis,
• environmental fate analysis (e.g., identification of environmental
pathways through which hazardous constituents migrate from the
source), and
• exposed population analysis (e.g., identification of possible human
and non-human exposure points and mechanisms)-
B-9
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The level I exposure evaluation can have a wide range of detail, although the
extent to which hazardous constituent releases can be quantified is dependent
on previously gathered analytical data. No new analytical data, or
quantification, is generally required. Therefore, calculation of human doses
(at identified receptor points) cannot be conducted.
Once a hazardous constituent release to soils has been identified, the
permit writer can effectively perform a level I analysis by utilizing a series
of decision networks for each of the three exposure pathway analysis steps
cited above (i.e., hazardous constituent release, environmental transport and
fate, and exposure point and route analysis). The decision networks provide a
framework for performing each exposure analysis step via a series of questions
relevant to the analysis process. The answers to these questions provide
information which can serve in determination of the following:
• existing exposure pathways (e.g., release/transport/human exposure
pathways) which are complete. Those exposure pathways which are
incomplete may be eliminated from further analysis, unless subsequent
data are obtained which modifies conclusions drawn from existing
analytical data.
• the relative magnitude (e.g. low, moderate, high significance) of
exposure pathways associated with hazardous constituent release at
the facility. This can be used to target those pathways for which
more in-depth (level II) analysis is required versus those pathways
which appear of more minor significance or which can be adequately
characterized by level I analysis.
• existing gaps in the (quantity and quality of) available analytical
data. This can be used to develop strategies for acquiring
additional data in order to conduct quantitative (level II or III)
analyses if they are warranted.
• corrective measures which may be applicable for implementation at the
facility.
The three basic steps in performing a level I (qualitative) exposure
assessment include analysis of: (1) the source of hazardous
constituent release; (2) environmental transport and fate; and (3)
potentially exposed populations. The following subsections describe
these three steps of the qualitative analysis process, and provide as
guidance the decision networks with which they can be effectively
evaluated. The qualitative exposure analysis is a stepwise process;
e.g., the output of each step in the exposure analysis process serves
as input to and provides direction for the following step.
Therefore, the output of the hazardous constituent release analysis
serves as the input for the environmental fate analysis, which in
turn, serves as input for the exposed population analysis.
B-10
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Hazardous Constituent Release Analysis
Based on available information trom site inspections, analytical data and
reports available from past or ongoing source investigations, and RCRA Part B
Applications, the nature and magnitude of releases to soils from hazardous
constituent sources can be determined. Data obtainable from these sources
relevant to release characterization include:
• chemical/physical properties of the hazardous constituents;
• climatological regime of the area; and
• the location and manner of placement at the facility (e.g. buried in
landfill, present in surface lagoon).
Depending on the location of hazardous constituents and manner of waste
disposal, hazardous constituent release from a source may occur via any or all
of the following mechanisms:
• Source leaching;
• Surface runoff;
• Episodic overland flows;
• Fugitive dust generation/deposition; and
• Tracking.
The procedure for characterizing the nature and probable significance of
release (e.g., environmental loading) can be faciliated by means of a decision
network, as shown in Figure B-l. The output of this analysis, in turn, is
used as input to the second step in the evaluation process, environmental fate
analysis.
Environmental Fate Analysis
Analysis of the environmental transport and fate of hazardous constituents
released to the soil medium involves determination of two inputs: (l) the
B-ll
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ARE TOXICS PRESENT IN
SOIL? '
ARE
TOXICS
LANDFILLED?
ARE TOXICS SPILLED, LEAKED,
OR SURFACE APPLIED?
IS ONSITE TREATMENT
AN OPTION?
DOES SOIL COVER
PREVENT PERCOLATION
OF PRECIPITATION?
DOES SOIL COVER
PREVENT VAPOR
RELEASE TO AIR?
I
^
N)
IS SUR-
FACE
SOIL CON-
TAMIN-
ATED?
IS SOIL
COVER
EROD-
ING?
CONSIDER
VOLATILIZATION
RELEASE TO AIR
CONSIDER LEACHING
RELEASE TO SUBSURFACE
SOILS, GROUND HATER
CONSIDER
VOLATILIZATION
RELEASE TO AIR
CONSIDER RUNOFF
RELEASE TO SURFACE
WATER, GROUND WATER,
AIR (VIA VOLATILIZATION)
CONSIDER
FUGITIVE DUST
RELEASE TO AIR
CONSIDER RELEASE TO
SOILS OR SURFACE
WATER (RUNOFF),
GROUND WATER (LEACHING),
AIR (VOLATILIZATION)
CONSIDER
PARTICULATE
RELEASE TO AIR
(INCINERATION)
CONSIDER
GASOUS RELEASE
TO AIR
GO ON TO
ENVIRONMENTAL FATE ANALYSIS
Figure B-l. Release decision network: Hazardous constituents.
-------
extent (e.g. magnitude) of release to soil, and (2) the potential for
migration in environmental media. Both intermedia transport mechanisms (e.g.
adsorbtion and/or eTitrainment in air, and bioaccumulation) and iritramedia
transformation processes (e.g. photolysis, oxidation, hydrolysis, and
biodegradation) are qualitatively considered during this second step. The
evaluation will be based on results of the hazardous constituent release
analysis. Information required tor the environmental fate analysis is
similiar to that of the previous section, including:
• physical/chemical properties of the hazardous constituents;
• manner of placement or disposal; and
• relevant climatological, hydrogeological source condition information.
The outcome of the qualitative environmental fate analysis is a determination
of the likely extent of release to the environment from the facility (e.g.,
environmental loading). The nature of the hazardous constituents involved and
probable magnitude of their release are also considered. When the outcome of
this analysis is integrated with information concerning populations affected
by the source, subsequent evaluation of potentially exposed human populations
can be performed. Because the environmental fate analysis is such an integral
part of the exposed population analysis, decision networks used to evaluate
the former are more appropriately considered in the latter section, exposed
population analysis.
Exposed Population Analysis
The third step in performing a qualitative exposure assessment is the
exposed population analysis. Analysis of potentially exposed human (and
non-human) populations involves determination of the likely routes and extent
of population exposure to contaminants released to soils. It also considers
the duration ot expected exposure (e.g., either short-term or long-term). The
exposed population analysis is the final step in identification of those
exposure pathways which are complete, and thereby completes the level I
B-13
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qualitative assessment; it also serves as a basis for planning-and conducting
subsequent quantitative (e.g., level II and III) assessments. By determining
the magnitude of probable exposure via pathways identified, those pathways
which are considered to be of major significance may require level II (and/or
level III) analysis, while those which are considered of minor significance or
can be easily characterized may be adequately evaluated by the level II
analysis. The analysis is straightforward and involves identification of two
inputs:
(1) the land use and activity patterns of human populations near the
source; and
(2) the areas ot potential human exposure to hazardous constituents
released to soils (as identified in Step 2, the environmental fate
analysis).
The exposed population analysis can be performed via several decision
networks, one for each of the transport mediums identified in the previous
step, environmental fate analysis. Decision networks for those transport
media of concern (when considering release of hazardous constituents to soil)
are presented below. In essence, the decision networks are frameworks for the
environmental-fate-and-exposed-population analysis because they combine the
information derived from the envionroental fate analysis with the projected
likelihood of population exposure to contaminated areas (as identified by
human activity and land use patterns near the facility). They provide a
qualitative estimate of the relative magnitude of human exposure (and risk)
via identified exposure pathways and routes. The duration of expected
exposure is also determined at this step in the exposure analysis. Guidance
for determination of exposure duration is based on baseline conditions of
contamination at the facility, and can be summarized by the criteria shown in
Table B-4.
When considering releases of hazardous consituents to soil, several routes
of human (and non-human) exposure should be evaluated, including:
• direct contact with soils;
• inhalation of airborne particulates to which contamination is
adsorbed, with possible reingestion of particulates;
B-14
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TABLE B-4. DETERMINATION OF EXPOSURE DURATION: A CONSIDERATION
OF BASELINE FACILITY CONDITIONS
CRITERIA TO CONSIDER REGARDING BASELINE FACILITY CONDITIONS:
1. Access to the facility or areas contaminated as a result of migration from
the facility: Is the facility:
• accessible to,
• restricted (e.g. by a fence or physical source conditions) from, or
• otherwise unaccessed (e.g. due to great distance) by human populations?
a. If restricted, to what extent? (e.g. the presence of a fence is not
sufficient indication that access is prevented).
2. Are there natural manraade features of the source or surrounding area such
as:
• abondoned buildings,
• standing water or streams
which may attract people, in particular children?
3. Are there human use areas, such as:
• playgrounds
• schools
• parks
located near the facility which may be frequently utilized by people, in
particular children, despite efforts to restrict access to the area?
B-15
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• ingestion of soils (e.g., by a child exhibiting pica); and
• ingestion of food products into which hazardous constituents in soil
have been uptaken.
Assessment of exposure to humans (and non-humans) via ingestion of food
products and inhalation of airborne particulates (with possible reingestion)
involves consideration of intermedia transport (e.g., to air or into biota) of
hazardous constituents originally released to soils. These routes of exposure
can be evaluated via the environmental-fate-and-exposed-population networks
shown in Figures B-2 and B-3. Assessment of exposure via direct contact or
ingestion of soils (e.g., by a child exhibiting pica, an abnormal craving for
non-food items) can be performed at any hazardous constituent exposure point
because the release/transport/and human exposure media are the same (e.g.,
soil) because no intermedia transport is involved.
Once the permit writer has performed the 3 steps of the qualtitative
exposure analysis (e.g., release, transport, and exposed population analysis),
he has determined which exposure pathways are complete, and has thus set the
conditions necessary for characterizing risk (associated with exposure).
Depending on the level of need, available resources (e.g., available source
monitoring data), and projected significance of exposure (and risk), complete
exposure pathways may be used as a basis for qualitatively evaluating risk
associated exposure via those pathways and routes, or may be further evaluated
by quantitative exposure analysis (e.g., level II or III), after which
quantitative risk characterization will be performed. For instance, if the
permit writer wishes to perform the exposure assessment to determine the
relative significance (e.g., low, moderate, high) of exposure via identified
routes and does not require in-depth (e.g., quantitative) assessment of
exposure, then level I exposure analysis will be sufficient. If, on the other
hand, the permit writer does desire in-depth exposure analysis (e.g., because
the release is obviously significant or he wishes to plan corrective measures
to eliminate exposure to a defined level), then level II analysis will be
required. He will not be able to perform the level II analysis, however,
unless sufficient environmental monitoring data are available.
B-16
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HAZARDOUS CONSTITUENT
RELEASE EVALUATION
SIGNIFICANT VOLATILIZATION
OF HAZARDOUS
CONSTITUENTS FROM SITE?
SIGNIFICANT RELEASE OF FUGITIVE
DUST/HAZARDOUS CONSTITUENT
PARTICULATES FROM SITE?
CONSIDER DIRECTION AND RATE OF HAZARDOUS
CONSTITUENT MIGRATION WITHIN AIR MEDIUM.
MAJOR MECHANISMS: WIND CURRENTS, DISPERSION.
ESTIMATE AREA WITHIN REACH OF
AIRBORNE HAZARDOUS CONSTITUENTS.
CONSIDER DIRECTION AND DISTANCE OF
PARTICULATE MOVEMENT WITH WIND CURRENTS.
MAJOR MECHANISMS: WIND SPEED, PARTICLE SIZE:
GRAVITATIONAL SETTLING, PRECIPITATION.
ESTIMATE AREAS RECEIVING SIGNIFICANT
SETTLEOUT/RAINOUT OF PARTICULATE MATTER.
IS SETTLEOUT AND RAINOUT
LIKELY TO RESULT IN SUFFICIENT
SOIL CONTAMINATION TO BRING
ABOUT LEACHING TO GROUND WATER?
ARE VOLATILE OR PARTICULATE
HAZARDOUS CONSTITUENTS LIKELY
TO REACH AGRICULTURAL AREAS,
HUNTING OR FISHING AREAS?
CONSIDER HAZARDOUS CONSTITUENT
TRANSFER TO GROUND WATER.
ASSESS FATE AND
HUMAN EXPOSURE ASSOCIATED
WITH THIS MEDIUM.
CONSIDER TRANSFER OF
HAZARDOUS CONSTITUENTS TO BIOTA
USED BY HUMANS.
ASSESS FATE AND HUMAN EXPOSURE
ASSOCIATED WITH THE MEDIUM.
DO VOLATILE OR
PARTICULATE HAZARDOUS
CONSTITUENTS REACH SURFACE
WATER BODIES?
CONSIDER TRANSFER OF
HAZARDOUS CONSTITUENTS TO
SURFACE WATER. ASSESS
FATE AND HUMAN EXPOSURE
ASSOCIATED WITH THIS MEDIUM.
PERSONS RESIDING, WORKING, OR CARRYING
OUT ACTIVITIES WITHIN REACH OF AIRBORNE
HAZARDOUS CONSTITUENTS CONSTITUTE
POPULATIONS EXPOSED VIA INHALATION.
GO ON TO
RISK ASSESSMENT
Figure B-2. Environmental fate and human exposure analysis decision
network: Hazardous constituents in air.
Source: Schultz, et al., 1984.
B-17
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AMBIENT CONCENTRATION DATA
FROM AIR, WATER, GROUND WATER
FATE ANALYSES
AIR?
AGRICULTURAL AREAS,
HUNTING OR FISHING AREAS
WITHIN ZONE OF IMPACT?
SIGNIFICANT CONCENTRATIONS
OF HAZARDOUS SUBSTANCES
IN AMBIENT ENVIRONMENT?
GROUND WATER/SOIL?
IS WATER USED FOR
IRRIGATION OF CROPS,
WATERING LIVESTOCK?
SURFACE WATER?
COMMERCIAL OR SPORT
FISHERIES AFFECTED?
CONSIDER BIOTIC SPECIES WITHIN AREAS OF
ELEVATED AMBIENT HAZARDOUS SUBSTANCE
CONCENTRATIONS AS POTENTIAL VECTORS
OF HAZARDOUS SUBSTANCES
CONSIDER TRANSPORT OF HAZARDOUS MATERIAL
WITHIN BIOLOGIC MEDIA
MAJOR MECHANISMS: HUMAN COMMERCIAL ACTIVITY,
ORGANISM MIRGRATION, MOVEMENT OF HAZARDOUS
MATERIAL THROUGH FOOD CHAIN
(BIOTIC UPTAKE; BIOMAGNIFICATION)
PERSONS USING ORGANISMS OR ORGANISM
PRODUCTS CONSTITUTE EXPOSED POPULATION
CONSIDER POPULATIONS EXPOSED VIA
DIGESTION OF FOOD PRODUCTS FROM
CONTAMINATED ORGANISMS
GO ON TO
RISK ASSESSMENT
Figure B-3. Environmental fate and human exposure analysis
decision network: food chain.
Source: Schultz, et al., 1984.
B-18
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QUANTITATIVE ASSESSMENT OF EXPOSURE
The initial step of a quantitative exposure analysis is an evaluation of
available source data to determine their completeness arid adequacy, and to
identify existing data gaps which must be filled prior to performance of the
analysis. Once requisite data are acquired, quantitative evaluation of human
(and non-human) exposure (either as a level II or III analysis) can proceed
via the framework shown in Figures B-4. The first three steps of the
quantitative exposure analysis process are similiar to those for the
qualitative (e.g., level I) analysis process, and include:
• hazardous constituent release analysis;
• environmental fate analysis; and
• analysis of population exposure points and routes.
Unlike the qualitative exposure analysis process where each step in the
analysis is qualitatively evaluated, each step of the quantitative exposure
analysis process is quantitatively evaluated. Because level II (and III)
assessments are quantitative in nature, they allow for determination of
hazardous constituent intake or dose incurred by human receptors at identified
exposure points. Determination of human intake or dose is performed
subsequent to the three analyses cited above, and combines the output of each
of the analysis steps. The goal of the level II (and level III) exposure
assessment is the development of quantitative determinations of both
individual risk and risk to exposed populations, which are preferably
expressed as average versus maximum projected exposure (e.g., intake or
dose). Because the quantitative exposure (and risk) assessment is performed
by a series of analysis steps (e.g., release/transport/exposed population
analysis), all of these steps must be quantitatively defined; e.g., the output
of the release analysis must be expressed in terms of average and maximum
release values, the output of the environmental fate analysis must predict
average and maximum hazardous constituent concentrations in environmental
media, and average and maximum population exposures must be determined by the
extent to which the general population comes into contact with the average and
B-19
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MASS
LOADING TO
ENVIRONMENTAL
MEDIA
IDENTIFICATION
OF IMPORTANT
FATE AND TRANSPORT
PROCESSES
HAZARDOUS CONSTITUENT RELEASE
ANALYSIS
ENVIRONMENTAL FATE
ANALYSIS
03
NJ
o
INTEGRATED
EXPOSURE AND DOSE
ANALYSIS
CUMULATIVE,
CHEMICAL-SPECIFIC
DOSE ESTIMATES
1
RISK I
ASSESSMENT |
ENVIRONMENTAL FATE
ANALYSIS
EXPOSED POPULATIONS
ANALYSIS
CALCULATION OF
DOSE INCURRED
Figure B-4. Overview of integrated exposure assessment process,
Source: Schultz, et. al., 1984.
-------
maximum environmental concentrations. The last step of the quantitative
exposure analysis, (e.g. quantification of human intake or dose) is then
considered in conjuction with toxicological data for hazardous constituents of
concern, and serves as the baseline risk assessment. The use of exposure
information to characterize risk will be further discussed in this section.
For those sources, pathways, and routes of exposure evaluated in the level
II analysis which are determined to be of minor significance and/or are
sufficiently characterized (e.g., as determined by need), the level II
analysis alone is sufficient. However, for those sources, pathways, or
receptors which are of great magnitude or sensitivity (and available data and
level of need permit), additional level III analysis may be performed. The
primary distinctions between level II and level III quantitative analyses are
shown in Table B-2. In brief, they concern four characteristics, including:
(1) The nature of the analysis: e.g. both levels II and III are
quantitative, although level II requires minimal determination of
significance, and level III intense determination of significance of
exposure pathways and routes,
(2) Level of detail: level II are moderately and level III are highly
detailed analyses,
(3) Characteristic analytical tools required: level II involves simple
estimation equations, while level III requires either computer
modeling or environmental monitoring to quantify hazardous
constituent releases, environmental transport, and exposure point
concentrations, and
(4) Resource intensiveness: the level II is moderately and the level III
is highly resource-intensive.
The permit writer may perform either a level II or III analysis, depending
on the quality of available data and degree of detail needed. A description
of the use and methodology for performing both level II and level III analyses
will therefore be discussed in the subsequent subsections.
There are 3 basic steps in performing quantitative (level II or III)
exposure analysis. They include:
(1) hazardous constituent release analysis,
(2) environmental fate analysis, and
(3) exposed population analysis.
B-21
-------
Utilizing Che output from each of these three steps, the exposure analysis
enables the permit writer to quantify human exposure (e.g., as intake or
dose). Informational requirements and guidelines for performing the three
basic steps of the quantitative exposure-analysis and for-quantifying human
exposure (as intake or dose) are presented below. If additional information
is desired, the reader is referred to sources cited below.
Quantitative Hazardous Constituent Release Analysis
The first step of the quantitative exposure analysis is the quantitative
hazardous constituent release analysis. Quantitative analysis of releases of
hazardous constituents to soils utilizes the results of the qualitative
analysis performed at level I; e.g., the source of release identified in the
level I analysis I is re-analysed at the level II and the release rate (e.g.,
mass release per unit time) is quantified. The output of the analysis is a
measure of the mass loading of the hazardous constituents to the soil medium
as well as to other media contaminated as a result of intermedia transport.
The output of the analysis, in turn, serves as input for the second step of
the exposure analysis, quantitative environmental fate analysis. A flow chart
depicting the nesessary decision criteria for quantitative hazardous
constituent release analysis (level II and III) is shown in Figure B-5.
Both level II and III assessments yield quantitative estimates of releases
to soils based on hazardous constituent-and-site-specific factors. These
estimates represent levels of environmental hazardous constituents to which
human (and non-human) populations could potentially be exposed, either
directly at the source or at points of hazardous constituent migration (e.g.,
as determined in subsequent analysis steps 2 and 3, environmental fate
analysis and exposed population analysis). Quantification of hazardous
constituent levels at this initial step of the exposure/risk analysis process
is therefore fundamental to obtaining quantitative estimates of human exposure
(e.g., intake or dose) as the final output to the quantitative exposure
analysis process.
B-22
-------
REVIEW EXISTING
SITE DATA
CO
N)
CO
IS DATA
ADEQUATE FOR
ANALYSIS
STOP
EMISSIONS
CHARACTERIZATION
AND
QUANTIFICATION
FOR EACH
ONSITE SOURCE
MASS
LOADING TO
ENVIRONMENTAL
MEDIA
GO ON TO
ENVIRONMENTAL
FATE ANALYSIS
ADDITIONAL
DATA ACQUISITION
(MONITORING,
MODELING, ETC.)
Figure B-5. Quantitative hazardous constituent release analysis (Levels II and III).
Source: Schultz, et al., 1984.
-------
Quantitative release analyses (either at level II or level LID are
expressed as release rates (e.g. mass release per unit time). Various methods
are available for estimating release rates of hazardous constituents to
environmental media from a variety of sources. Each release medium (e.g.
soil, air) must be addressed separately; however, intermedia release of
hazardous constituents must also be considered. In the case of releases of
hazardous constituents to soils, there is one primary and two secondary
release media of concern. They include:
• soil (as a primary release medium),
• air (as a secondary release medium, via entrainment of airborne
particulates to which hazardous constituents have adsorbed), and
• biota (as a secondary and indirect release medium, via plant uptake
of hazardous constituents adsorbed to or otherwise associated with
soils).
Methods available for level II and III quantitative analysis of release to
soils are referenced in Table B-5. Quantitative methods of release analysis
to air (e.g., as a secondary environmental release medium) are also referenced
in the table. Uptake by biota, (e.g., as a secondary, indirect release
medium) can be evaluated by consideration of release to soils, since plant
uptake occurs directly from the soil medium. The limitations and assumptions
inherent in performing quantitative level II and level III contaminant release
analyses are presented below.
Assumptions/Limitations of Level II Hazardous Constituent Release Analysis—
Procedures available for calculating environmental release estimates can
be limited in that they: (1) often do not take into account the full range of
variables which affect source release (e.g., hazardous constituent-specific
and site-specific factors), and (2) often assume steady state conditions
(e.g., do not address reduction in levels of hazardous constituents present
due to release losses, and the associated reduction in release loading over
time, corresponding to the decreased reservoir of hazardous constituents).
Given these constraints, the quantitative release analysis is not expected to
B-24
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TABLE B-5. METHODS AVAILABLE FOR LEVEL II AND LEVEL 111.ANALYSIS
OF RELEASES TO SOIL AND AIR MEDIA
ANALYTICAL TOOLS
MEDIUM; Soil (e.g. from a
lagoon or pond, spill,
intentional placement
in ground)
MEDIUM: Air (e.g. via
entrainment of
dusts)
LEVEL II
Estimation equations using
analytical sampling data
(and/or monitoring data,
if available).
-surface soil: use sampling
data
• average contamination:
average sample concen-
tration
• maximum contamination:
highest sample concen-
tration
-subsurface soi/1: use
sampling data, if avail-
able, or refer to:
Schultz et. al., 1984
-refer to: IGF, Inc., 1985
and EPA, 1984c, for
hazardous constituent
release quantification
methodologies - refer to
soil conservation service
sources for site-specific
soil and climatic data for
use in above, if necessary
LEVEL III
Computer modeling;
facility monitoring data
-surface soil: use
monitoring data
• average contamination:
take average sample
concentration
• maximum contamination:
take highest sample
concentration
-subsurface soils: use
monitoring data, if
available, or use com-
puter modeling* to
derive average and maxi-
mum concentration values
of subsurface soils
-utilize air monitoring
data (both upwind and
downwind of the source)
and/or use computer
modeling to derive aver-
age and maximum contam-
ination concentrations
Models applicable to quantitative analysis of hazardous constituent release
to soil and air media are referenced in Table B-6.
B-25
-------
be wholly representative of conditions at the facility, and application of the
analysis outcome should be limited to the following situations (EPA, 1984c):
• estimation of the level of release of specific hazardous constituents
at a facility, and
• projection of approximate release reduction as a result of corrective
measures taken at the facility.
In other words, the limited applicability of the level II release analysis to
these situations should govern the permit writer's use of level II analysis in
general. If the permit writer desires an estimate of environmental release
which is highly accurate or wishes to use the analysis outcome to estimate the
efficacy of corrective measures to a specified environmental release level,
then level II analysis will not be sufficient; level III analysis will be
required to obtain a more sophisticated and accurate estimate of release.
However, if level III analyses are desired but are not able to be performed
(e.g., due to lack of resources, analytical data, etc.), then professional
judgement must be used in the level II analysis, in order to account for the
inherent reductions in release rates over time and to specify more accurate
estimates of environmental releases.
Assumptions/Limitations of Level III Hazardous Consitutent Release Analysis—
Level III hazardous constituent release analysis generally involves the
use of modelling to specify exact estimates of environmental concentrations.
Several criteria must be taken into consideration when selecting a level III
model to quantify releases of hazardous constituents to soil. They include:
• data requirements of the model versus availability and reliability of
resources; e.g., source sampling data or monitoring data, time, and
finances,
• fit of the model to site-specific and hazardous constituent-specific
parameters,
• form and content of model output: does it estimate mass loading to
soils or air (i.e., environmental loading per unit time).
B-26
-------
Models capable of quantifying release of hazardous constituents-to sur-face
soils (and the subsequent degree of contamination to subsurface soils) and air
are referenced in Table B-6. Of note, is the necessity to match available
source sampling data to the results of the model in order to validate the
model's results. The consistency of the two estimates will also provide a
measure of reliability for both sources of information.
Environmental Fate Analysis
Environmental Fate Analysis is the second step in quantitative exposure
analysis. The purpose of quantitative environmental fate analysis is to
generate estimates of the direction of migration and areal extent of
contamination as well as the ambient concentrations of hazardous constituents
within the soil media. The average release rate estimates derived from the
release analysis (Step 1) serve as input to this analysis, and by application
of environmental transport, transformation, and removal mechanisms,
environmental fate estimates are calculated. Regardless of the level of
exposure performed (e.g., level II or III), estimates of environmental
concentrations which should be determined include: (1) maximum expected
ambient concentrations (e.g., representing short-terra worst-case conditions),
and (2) average ambient concentrations (e.g., representing most-probable
conditions over a long time period).
The suggested approach for evaluation of the environmental fate of
hazardous constituents released to soils is to consider separately the major
transport and transformation processes of the constituent released to each
environmental medium of concern. In the case of releases to soil, both soil
(as a direct release medium), and air (as an indirect medium, via entrainment
of dusts) must be considered. Methods available for use in quantitative
(level II and III) analyses of environmental fate of releases to soils (and
indirectly, to air) are referenced in Table B-7. Limitations and assumptions
inherent in analyses of environmental fate at these levels (II and III) are
described briefly below.
B-27
-------
TABLE B-6. COMPUTER MODELS APPLICABLE TO QUANTITATIVE
ANALYSIS OF RELEASE AND ENVIRONMENTAL FATE
IN SOIL AND AIR MEDIA*
MEDIUM: SOIL
For available models applicable to release environmental fate analysis in
soils, the reader is referred to the following sources:
• Schultz et. al., 1984
• McNeils et. al., 1984
• EPA, 1982a.
MEDIUM; AIR
For available models applicable to release and environmental fate
analysis, the reader is referred to the following sources:
• EPA, 1982a
• GCA, 1983a
GCA, 1983b.
• Schultz et. al., 1984
• McNeils et. al. , 1984
• ICF, Inc., 1985
'descriptions and uses of available models are presented in these sources.
B-28
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TABLE B-7- EQUATIONS AND MODELS. AVAILABLE FOR LEVEL.II AND
LEVEL III ANALYSIS OF ENVIRONMENTAL (MIGRATION AND)
FATE IN SOIL AND AIR MEDIA
ANALYTICAL TOOLS
LEVEL II
Estimation equations using
analytical sampling data
(and/or monitoring data,
if available).
MEDIUM; Soil (e.g. from a -surface soil: use sampling
data
• average contamination:
take average sample
concentration
• maximum contamination:
take highest sample
concentration
-subsurface soil: use
sampling data, if avail-
able, or refer to:
Schultz et. al., 1984
lagoon or pond, spill,
intentional placement
in ground)
MEDIUM: Air (e.g. via
entrainment of
dusts)
•refer to: Schultz et. al.,
1984; ICF, Inc, 1985 for
hazardous constituent
environeratal fate
quantification method-
ologies - refer to: soil
conservation service
sources for site-specific
soil and climatic data for
use in above, if necessary
LEVEL III
Computer Modeling;
monitoring data
-surface soil: use
monitoring data
• average contamination:
take average sample
concentration
• maximum contamination:
take highest sample
concentration
-subsurface soil: use
monitoring data, if
available, or use com-
puter modeling* to
derive average and maxi-
mum concentration values
of subsurface soils
-utilize air monitoring
data (both upwind and
downwind of facility,
and/or use computer
modeling* to derive
average and maximum con-
tamination concentra-
tions
*Models applicable to quantitative analysis of environmental (migration and) fate
in soil and air media are referenced in Table B-6.
B-29
-------
Limitations/Assumptions of Level II Environmental Fate Analysis--
Level II procedures for quantifying hazardous constituent fate in soil and
air media are based on the predominant mechanisms of transport within these
media and generally disregard transfer or transformation processes. They
produce conservative estimates of final ambient concentrations and
environmental migration. The purpose of conservatism at this step in the
exposure/risk estimation process is twofold: (1) to eliminate from additional
consideration those potential exposure points which are not expected to be
affected by hazardous constituents migrating from the source, and (2) to
provide conservative estimates of hazardous constituent concentrations as
input to subsequent exposure (e.g. intake or dose) and risk assessment. By
disregarding the effects of transfer or transformation processes in the
environmental fate analysis step, environmental concentrations utilized as
input to exposure (and risk) analysis will tend to overstate actual ambient
concentrations. At best, these concentrations will represent "worst-case"
environmental constituent levels. The significance of each exposure pathway
evaluated in the exposure analysis will therefore be conservatively
estimated. This will aid in identification of those pathways which are of
minimal, moderate, and major significance under presumed "worst-case"
conditions.
Limitations/Assumptions of Level III Environmental Fate Analysis—
Level III environmental fate analyses generally involves use of computer
models to specify exact estimates of environmental concentrations. When
selecting a level III model to estimate environmental concentrations of
released hazardous constituents (e.g., to soil or air), the permit writer
should consider the following criteria (Schultz, et al., 1984):
• data requirements of the model versus availability and reliability of
available resources: (e.g., source sampling or monitoring
information, time, finances, and level of need),
• capability of the model to account for important transport,
transformation, transfer processes.
• "fit" of the model to site-specific and hazardous
constituent-specific parameters, and
• form and content of model output (e.g., does it address important
questions regarding human exposure, environmental effects?).
B-30
-------
Again, it is important to note the necessity of comparing available source
sampling and/or monitoring data to model output in order to "check" the
reliability of both sources of information. Table B-6 references the models
available for estimating environmental concentrations of hazardous
constituents which have been released to and are expected to remain in the
soil medium, and those which have been released to soils and entered the air
medium, respectively.
Exposed Population Analysis
The final step of the quantitative exposure analysis process is the
exposed population analysis. Input necessary for the exposed population
analysis is derived from previous steps, hazardous constituent release
analysis (Step 1) and environmental fate analysis (Step 2). For example,
level II analysis of air contamination will yield isopleths (lines of equal
concentrations of) hazardous constituents. Areas of soil contamination will
also be identified and the levels of contamination quantified. These
quantitative environmental levels are then considered together with
information concerning potentially exposed populations (as described below) to
identify and predict the likelihood of human (and non-human) contact with
hazardous constituents released to soil. The analysis invovles determination
of three parameters, as shown in Figure B-6. Briefly, they include:
(1) identification and enumeration of exposed populations; e.g., by
considering the areal extent of contamination (as determined in step
2, environmental fate analysis), populations which potentially or
actually come into contact with contaminated soil or air are
identified. Populations consuming contaminated food products (e.g.,
vegetables grown in contaminated soils) are similiarly identified.
(2) population characterization; e.g., determining those groups within
the exposed populations which, are expected to experience the greater
risk than the average population (e.g., a sensitive sub-population)
at a given exposure level, due to specific health effects of some
hazardous constituents. Examples of such sensitive subpopulations
include pregnant women, children, the elderly, and the chronically
ill.
B-31
-------
ENVIRONMENTAL
FATE ANALYSIS
IDENTIFICATION
AND
ENUMERATION
OF EXPOSED
POPULATION
03
CO
Si
DERMAL ABSORPTION
1
COMBINE CENSUS DATA
WITH All FATE RESULTS
'
[ WATER ] NOT GENERALLY
1
qUANl'lFlbD
COMBINE POPULATION DATA
WITH GROUND OR SURFACE
WATER FATE RESULTS
AND UTILIZATION STATISTICS
-
J
*
| FOOD | | SWIMMING |
COMBINE POPULATION DATA USE RECREATION DATA
WITH ENVIRONMENTAL TO IDENTIFY POPULATION
FATE RESULTS AND FOOD OF EXPOSED SWIMMERS, ETC.
PRODUCTION STATISTICS Al
, * *
f
| BATHING j
COMBINE PUPULATIOI. DATA
WITH GROUND OR Sl'KFACE
WATER FATE RESILTS
ID UTILIZATION STATISTICS
i
CHARACTERIZATION
OF
EXPOSED
POPULATION
DETERMINE
SITE SPECIFIC ACE/SEX
DISTRIBUTION FROM
CENSUS OF POPULATION
DETERMINE
NATIONAL ACE/SEX
DISTRIBUTION FROM
CENSUS OF POPULATION
ACTIVITY
ANALYSIS
Figure B-6. Quantitative exposed population analysis,
Source: Schultz, et. al., 1984.
-------
(3) activity analysis; e.g., determining the mix of human activities
conducted by the population through which exposure occurs. Key
activity-related exposure determinants to be quantified for each
exposure route-relevant to hazardous constituent releases to soil
(e.g., inhalation^ ingestion, and dermal contact) are shown in
Table B-8. The procedure for conducting the exposed population
analysis is the same for a level II assessment as for a level III
assessment, except for the fact that average or estimated levels of
hazardous constituents are used in level II, and more accurate,
source-specific data are used in level III. The three parameters
necessary for exposed population analysis are discussed briefly
below. The reader is referenced to other sources of information if
such information is not presented here.
Identification and Enumeration of Exposed Populations—
Identification and enumeration of exposed populations is the first
parameter necessary to perform the exposed population analysis step of the
quantitative exposure analysis. The primary population database that can be
accessed to determine the size, distribution, and demographic characteristics
of a geographically-defined population is the Census of Population. For
further information on the aquisition and use of census data, the reader is
referred to EPA, 1984c. The manual also provides guidance for the
identification and evaluation of human populations exposed to hazardous
constituents in air (via inhalation), food (via ingestion), and soil (via
inhalation/ingestion and direct contact).
Population Characterization—
Population characterization is the second parameter necessary to perform
the quantitative exposed population analysis. Again, the reader is referred
to EPA, 1984c, for guidance in defining this parameter of the exposed
population analysis.
Activity Analysis—
Activity analysis is the third and final parameter necessary to perform
quantitative exposed population analysis. The activity analysis is fairly
straightforward; however, the permit writer is required to make some
generalizations. In the analysis, the activities of the members of a given
population or subpopulation are determined in order to predict the level of
B-33
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TABLE B-8. KEY ACTIVITY-RELATED EXPOSUR DETERMINANTS TO BE
QUANTIFIED IN THE EXPOSED POPULATION PHASE FOR
EXPOSURE ROUTES RELEVANT TO RELEASES TO SOIL3
INHALATION:
• Length of time (frequency and duration) spent in each related
activity.
• Nature of the activity in terms of light, medium, heavy, or maximum
exertion (per unit time).
INGESTION:
• Amount of contaminated food or water ingested (per unit time).
DERMAL EXPOSURE:
• Length of time (frequency and duration) spent in each related
activity per unit time.
• Location of exposure (e.g. on human body) and areal extent of
exposure.
aMany of these exposure criteria are considered as "standards" in the
following sources: Schultz et. al., 1984; ICF, Inc., 1985. The reader
is referred to these information sources in his analysis of human
activity related to exposure to hazardous constituents.
Source: Schultz et. al., 1984.
B-34
-------
exposure which is actually experienced. Generalization is involved in
predicting the human activity patterns which result in exposure to
environmental contamination. For example, persons whose lifestyle or
employment involves frequent strenuous activity will ventilate larger volumes
of air per unit time than will those persons living a more leisurely
lifestyle, and will therefore experience a greater degree of exposure to
airborne constituents. Activity patterns which affect other exposure routes
are similarly analyzed. Because human behavior is difficult to predict,
hypothetical situations (i.e., scenarios) are developed to represent the
exposure associated with human activity patterns. Human activity scenarios
typically involve determination of "average" and maximum (i.e., "worst-case")
population exposures, by determining the extent (i.e., duration, frequency) to
which the population comes into contact with average and maximum environmental
concentrations. The quantitative exposed population analysis is performed by
first defining the three parameters (cited above): (1) exposed population
identification and enumeration, (2) exposed population characterization, and
(3) exposed population activity analysis. The results of the exposed
population analysis are then combined with those of the first and second steps
of the quantitative exposure analysis process (i.e., hazardous constituent
release and environmental fate analysis), and human exposure is quantified.
There are basically two measures of quantitative human exposure; they are:
(1) intake estimates, and
(2) dose estimates.
The use of a particular measure is dependent upon assumptions and
limitations inherent in the development of the measure. Both of these
measures (estimates) of human exposure are discussed briefly below; use of
these estimates in the risk characterization process and their inherent
limitations and assumptions are discussed in more detail in Section 6 risk
characterization.
B-35
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Intake Estimates—
One quantitative estimate of human exposure is intake (i.e., the amount of
substance taken into the body per unit body weight per unit time). The intake
estimate does not take into account bodily absorbtion of the hazardous
constituent, and is therefore a more conservative estimate of human exposure
than is the dose estimate. Given the limited amount of available human
absorbtion data, its use is more applicable to a variety of exposure
situations and hazardous constituents than is the dose estimate. In other
words, the permit writer is not limited (in his quantitative exposure
analysis) to the amount of available data concerning absorbtion rates for
specific chemicals through specific biological barriers. By using information
acquired from the quantitative environmental fate and exposed population
analyses (steps 2 and 3 in the overall quantitative exposure analysis)
together with standard "intake" values (e.g., average ventilation rates,
average body weights) he is able to estimate human intake resulting from
exposure. An example of intake estimation for exposure to airborne
constituents is shown below. The standard intake valves utilized in this
equation (e.g., the average ventilation rate and body weight) were derived
from ICF, Inc., 1985).
average (or maximum) average daily average body
environmental * ventilation rate — weight of
contaminant
concentration (in
airborne dusts)
of exposed
individual
exposed
individual
average (or
maximum)
daily intake
3 mg/m3
* 20m3/day _^_
adult
70 kg body = 0.857 mg/kg/day
weight (adult) intake j
Intake values are calculated separately for exposures to hazardous
constituents in each medium identified in a complete exposure pathway i.e.,
each medium identified in the release/transport/exposure pathway). For
releases to soil, relevant exposure media are soil and air (and indirectly,
biota). Standard assumptions of human intake (e.g., average ventilation rates
and average body weights) are utilized to derive the actual intake estimates
from exposure to these media. For further information and guidance on the use
of intake assumptions and equations to estimate human intake values from
B-36
-------
exposure to air contaminants, the reader is referred to Schultz, et al. ,
1984. For guidance in the assessment of less common, but potentially
significant routes of exposure (e.g., direct contact with contaminated soils,
ingestion of inhalated contaminated dusts or food products). The EPA Office
of Emergency ^nd Remedial Response (OERR) Washington, D.C., is developing
further information in this area.
Dose Estimation—
A second estimate of quantitative human exposure is the dose estimate;
i.e., the amount of substance which is actually absorbed by the body as a
result of exposure to contaminated media. It is derived by considering
existing concentrations of hazardsou constituents in environmental media
together with the frequency of exposure, route of exposure, and amount of
contaminant contacted per exposure (i.e., the "exposure coefficient"). Like
the intake estimate, the dose estimate also assumes standard population intake
rates for various routes of exposure (e.g., ventilation rates, consumption
rates). In addition, it also assumes standard rates of absorption for
chemicals into the human body. The dose estimate is, therefore, less
conservative than is the intake estimate; but, provided that the assumed
absorption rate used in the dose calculation is accurate for the hazardous
constituent and site of biological uptake of concern, it provides a more
specific and accurate measure of human exposure. Alternatively, if the
assumed absorption rate used in the dose calculation is not accurate for the
hazardous constituent and site of biological uptake of concern, then the dose
estimate will not provide an accurate measure of human exposure, but will tend
to understate it. Further information and guidance on estimating human dose
resulting from exposure to releases to soil via relevant exposure routes
(e.g., direct contact, inhalation, and ingestion), the reader is referred to
Schultz, et al., 1984. An example of dose estimation via direct contact with
hazardous constituents in soils is shown in Figure B-7, (Schultz, et al.,
1984). Assumptions inherent in the calculation of human dose estimates are
discussed under risk characterization.
B-37
-------
INHALATION
EXPOSURE COEFFICIENT
m-Vday
AMBIENT
CONCENTRATION
(0
Mg/m3
INHALATION
EXPOSURE
(Ex)
pg/day
ABSORPTION RATE
(A)
Ug absorbed
ug exposed
INHALATION DOSE
(D!>
Mg/day
Figure B-7. Inhalation dose calculation.
Source: Schultz, et al., 1984.
B-38
-------
Summary—
In summary, quantitative exposure analysis involves 3 steps, each of which
is quantitatively analyzed. These steps include:
(1) hazardous constituent release analysis,
(2) environmental fate analysis, and
(3) exposed population analysis.
The output of each of these steps serves as input to the subsequent step; the
final outcome of the analysis process is a quantitative measure of human
exposure, expressed as either intake or dose. The permit writer must decide
which estimate of human exposure will be calculated, however, consideration of
the following criteria can aide in the decision process:
(1) Toxicological Profiles: What are the hazardous constituents of
concern, and by what routes of exposure do they exert their primary
toxicological effects? Is adequate data available to define
biological absorbtion rates for the target organs of concern? For
instance, if a hazardous constituent has been widely researched,
accurate human absorbtion rates (for biological target organs of
concern) may be available, and dose estimation will be possible.
(2) Level of Need: Are estimates of human dose (resulting from
exposure) desired, given the projected level of significance of
human exposure (estimated in the level I analysis) and the intended
use of the exposure estimate in establishing permit conditions or
corrective measures?
For instance, if exposure to a hazardous constituent has been determined
in level I analysis to be only minimally or moderately significant, efforts to
define exact human dose may not be necessary; intake estimates will not only
provide more conservative estimates of human exposure for the specified
exposure pathways, but are also easier to calculate and are generally based on
fewer assumptions than are dose estimates. However, if an accurately defined
measure of human exposure is required in order to establish permit conditions
or evaluate the efficacy of corrective measures, (given the availability of
human absorbtion data), dose calculations preferred over intake estimates.
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Both human intake and dose estimates are equally useful measures of human
intake; and both can be used to form the basis of quantitative risk
characterization. Descriptions, uses, informational requirements, and
limitations of both qualitative and quantitative risk assessment strategies
will be discussed in the following section.
RISK CHARACTERIZATION
Components of the Risk Characterization Process
The process of determining the risk to human (and non-human) populations
associated with exposure to contaminant releases to soils involves input from
two components:
• Exposure Assessment to determine the magnitude, pathways, and routes
of human (and non-human) exposure to hazardous constituents; and
• Hazard Assessment, to determine the chemical toxicity and related
hazard of a contaminant to which there is exposure.
By combining the results of these two components (i.e., exposure and
hazard assessment), the actual and potential health risks resulting from
exposure to hazardous constituent releases to soils can be characterized.
Like the exposure assessment process, the risk characterization process can be
either qualitative or quantitative. Determination of the risks to human (and
non-human) populations (as a result of exposure to environmental constituents)
serves two purposes for the permit writer:
(1) It provides a way to determine the level and means of correction
measures necessary to eliminate the risks to populations associated
with release to environmental media, and in the absense of existing
standards and guidelines,
(2) It provides an approach for evaluating public health impacts
associated with hazardous constituent exposures in order to establish
permit conditions.
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The following two sections provide brief descriptions of these two
components of the risk characterization process, exposure assessment and
hazard assessment, and provide guidance for the use of these components to
qualitatively and quantitatively evaluate risk.
Hazard Assessment—
Following exposure assessment, a hazard assessment is the next component
of the risk characterization process. The hazard assessment is essentially a
two-step process involving both "hazard identification" and "dose-response"
assessment for the releases of concern. The purpose of the hazard
identification is to determine the nature and extent of health and
environmental hazards associated with exposure to hazardous constituents at
the facility.
The first step in the hazard assessment, the hazard identification, is a
qualitative evaluation of the scientific data to determine the nature and
severity of actual or potential health and environmental hazards associated
with exposure to a hazardous constituent. The hazard identification involves
a critical evaluation and interpretation of toxicity data from
epidemiological, clinical, animal and in vitro studies and results in a
toxicity profile for each hazardous constituent of concern. Toxicity profiles
present a review of the primary literature on the types of adverse effects
manifested (e.g., chronic, acute, carcinogenic, etc.), doses employed, routes
of administration (e.g., oral, dermal, inhalation, etc.), the quality and
extent of test data, the reliability of the test data and other factors.
Toxicity profiles provide the weight-of-evidence that the hazardous
constituents of concern pose potential hazards to human health or the
environment.
Once the hazard identification determines that a hazardous constituent is
likely to cause a particular adverse effect, the next step is to determine the
potency of the chemical. The second step in the hazard assessment, the
dose-response assessment, is a quantitative estimation of risk from exposure
to a toxic chemical. It defines the relationship between the dose of a
chemical and the incidence of the adverse effect. (Life Systems, Inc., 1985).
The dose-response assessment involves presentation of all pertinent
criteria, guidelines, and standards for the protection of human health and the
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environment. The dose-response assessment is performed for chemicals which
are carcinogens as well as non-carcinogens. A brief discussion of the
components of the dose-response assessment for both of these types of
chemicals is as follows.
For dose-response assessment of toxic substances (non-carcinogens) EPA has
established no observed adverse effect levels (NOAELs); no observed effect
levels (NOELS) and lowest observed adverse effect levels (LOAELs) based on
relevant toxocologic data. Using these values and incorporating a safety
factor (e.g., 10, 100, 1000, etc) the acceptable daily intake (ADI) can be
calculated. The ADI is defined as the largest amount of toxicant (in mg/day)
to which a 70-kg person can be chronically exposed which is not anticipated to
result in any adverse effects. Of importance to note is that ADIs are
calculated for individual compounds and do not reflect the possible adverse
effects resulting from exposure to other chemicals present or the synergistic
and/or antagonistic effects that a chemical mixture may produce. Use of ADI
values to assess hazard associated with chemical mixtures will be discussed in
a subsequent section.
For dose-response assessment of carcinogenic chemicals the EPA Carcinogen
Assessment group (GAG) has developed "unit risk" levels, or chemical potency
indexes. These unit risk levels are expressed as the lifetime human cancer
risk per mg/kg body weight/day. They are based on the best available human
and animal study data and are derived using mathematical models of the
chemical's dose-response relationship. They are not, however, adjusted for
facility-specific conditions.
EPA has developed toxicity hazard profiles on a number of hazardous
constituents. These profiles define the "acceptable levels" of exposure to
non-carcinogenic chemicals and the estimates of unit cancer risk for
carcinogenic chemicals. Toxicological hazard profiles of these substances can
be found in a set of Health Effects Assessments (HEAS) for hazardous chemicals
typically found at uncontrolled waste sites or which may be disposed of at
RCRA facilities. Copies of the HEAS for specific chemicals are available from
EPA's Office of Emergency and Remedial Responses (OERR) in Washington, D.C.
In addition to the HEAS, toxicological information for hazardous constituents
of concern can be found in the Toxicological Profiles available through EPA's
Office of Waste Programs Enforcement in Washington, D.C.
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The end-product of a hazard assessment is a qualitative description of the
toxic properties of the hazardous -constituents of concern'at the site and a
quantitative index of the toxicity for each constituent at the site, if the
data are sufficient for such an assessment. (Life Systems, Inc., 1985). Use
of the hazard assessment information (for both carcinogens and
non-carcinogens) together with the exposure analysis information, as generated
in the previous step, to characterize risk to human (and non-human)
populations resulting from exposure to releases to soils will be discussed in
the following section levels of risk characterization (e.g., qualitative,
quantitative) and the criteria used to select the appropriate level of risk
characterization to perform will also be presented.
LEVELS OF RJSK CHARACTERIZATION
The risk characterization process can be either qualitative or
quantitative in nature. The decision as to which level of risk analysis is to
be performed is dependent primarily on two factors: (1) the primary effect of
hazardous constituents involved (e.g., carcinogenesis or toxic effects), and
(2) the level of exposure analysis (e.g., qua-litative or quantitative)
performed prior to the risk characterization.
For chemicals which are carcinogens or suspected carcinogens quantitative
risk characterization is usually performed. For non-carcinogens, either
qualitative or quantitative risk characterizations can be performed; the
decision as to which type is to be performed is usually dependent on the level
of exposure analysis conducted prior to the risk characterization. If the
exposure analysis performed prior to the risk characterization is qualitative
in nature, qualitative risk characterization must be performed; e.g., no human
exposure estimates (such as intake or dose levels) have been calculated,
therefore quantitative risk characterization is not possible. If the previous
exposure analysis was quantitative in nature, the permit writer has a choice
as to whether to use those estimated human intake or dose levels to perform a
quantitative risk analysis or to 'simply perform a qualitative analysis. To
make this decision, the following additional criteria should be considered:
(1) the level of expertise should be needed (and available) to perform the
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risk analysis; e.g., quantitative risk characterization generally requires a
greater amount of expertise in the field of toxicology and public health than
does qualitative risk analysis due primarily to the greater number of
assumptions and generalizations needed to be made (to be discussed below); and
(2) the time available to perform the risk characterization; e.g.,
quantitative risk characterization is generally more complex and
time-consuming than is qualitative risk characterization.
The following sections describe the two levels of risk characterization
(e.g., qualitative and quantitative); guidance in the performance of these
risk characterization processes is also included. For additional information
regarding risk characterization processes, the reader is referred to sources
given below.
Qualitative Risk Characterization
A qualitative risk characterization is usually performed subsequent to a
qualitative exposure analysis and provides a relative index of human risk
associated with exposure to hazardous constituent releases to soil, and
indirectly to other contaminated media, such as air (through inhalation) or
biota (through ingestion). Qualitative risk characterizations are usually
performed for chemicals which are non-carcinogens, but can also be performed
for chemicals which are carcinogens and which have either: (1) been
qualitatively evaluated in the (previous) exposure analysis or, (2) have been
quantitatively evaluated in the previous exposure analysis and are expected to
pose little or no risk to human (or non-human) health.
The qualitative risk characterization process involves an assessment of
two components: (1) the toxicological and biomedical evidence available for
the hazardous constituents of concern (as discussed previously in the hazard
assessment), and (2) the exposure potential for constituents of concern ( as
determined previously in the exposure assessment).
The first step in the qualitative risk characterization involves an
evaluation of all pathways of human (and non-human) exposure determined to be
"complete" in the exposure analysis. The relative magnitude (significance) of
exposure (rated as high, moderate, or low) for each exposure pathway is also
considered, and provide a means of preliminarily determining which routes of
exposure potentially pose the greatest risk to human (and non-human) health.
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The next step in the qualitative risk characterization process involves an
evaluation of the toxicological and bioraedical evidence of hazardous
constituents of concern, (as determined in the previous hazard assessment
phase) to determine the nature and severity of actual or potential health (and
environmental) hazards associated with these hazardous constituents of concern.
By combining the information on the relative likelihood and significance
of exposure to human (and non-human) population via the pathways and routes
(identified in the exposure analysis) with the probability and nature of
potential hazards of the chemicals involved (identified in the hazard
assessment), the relative probability, magnitude, and type of risks to human
(and non-human) populations can be determined. Determination of risk to these
identified populations (receptors) is qualitative in nature. However, for
many conditions involving actual or potential exposure to human ( and
non-human ) populations, a qualitative characterization is adequate for
describing the risk to these receptors. Whether or not a qualitative risk
characterization is adequate is dependent primarily on: (1) the level of need
of the permit writer (e.g., the permit writer does not need to use the risk
characterization to evaluate the efficacy of corrective actions or to
establish permit conditions to a defined level), and (2) the projected
significance of the risk to specific receptors, as determined in the exposure
analysis. For instance, if the chemicals of concern are of limited toxicity,
are at low environmental levels or are not expected to be associated with
exposure to human (or non-human) receptors, a qualitative characterization may
be adequate to describe the risk to these receptors.
QUANTITATIVE RISK CHARACTERIZATION
A quantitative risk characterization is usually performed for chemicals
which are known or expected carcinogens, and is frequently performed for
chemicals which are non-carcinogens. Despite the type of hazardous
constituents involved, a quantitative risk characterization can only be
performed subsequent to a quantitative exposure analysis. In other words, if
the permit writer, upon initial consideration of a cause of action to take a
given hazardous constituent release to soils, feels that he is not in need of
an indepth evaluation of exposure (and risk) or that available analytical data
B-45
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is not complete or accurate enough to be used to perform an indepth exposure
(or risk) analysis, then he does not need to perform a quantitative risk
characterization. He should, instead, perform qualitative (risk and exposure)
analyses.
A quantitative risk characterization consists of comparing the projected
human exposure levels (e.g. the intake or dose levels, as determined in the
previous section, quantitative exposure analysis) of the hazardous
constituents present to the acceptable dose levels (e.g., standards, criteria
and guidelines) established by various goverment agencies for these
compounds. Such comparisons give an indication of the magnitude of the
adverse health and environmental effects that may result from exposure to
these substances. The type and extent of risk posed by any facility depends
upon the nature, duration, and level of exposure, as well as the type of
populations exposed. For most hazardous constituent sources, the human (and
non-human) populations and conditions of exposure potentially affected by the
facility are quite diverse and cannot be assimilated by a single condition of
exposure to give a single absolute risk for the source. For this reason, most
sources are evaluated in terms of the risk posed to populations via separate
pathways and routes of exposure. To predict the risk ot populations
associated with exposure to environmental constituents, hypothetical exposure
scenarios are developed. Exposure scenarios describes distinct exposure
conditions (e.g. estimated frequency duration exposure) to average and maximum
ambient environmental constituent levels.
Methods of quantitatively characterizing the risks to human (and
non-human) populations associated with exposure to environmental media
contaminated as a result of release to soils is presented below. Quantitative
risk characterization processes for evaluating chemicals which are
non-carcinogens as well as carcinogens is presented. In classifying a
chemical as a carcinogen (versus a non-carcinogen) it is meant that the
primary effect (endpoint) of the chemical is carcinogenesis, although the
chemical may have other non-carcinogenic (e.g. toxic) endpoints. Because it
is common for a source of hazardous constituent release to involve more than
one type of chemical, characterization of risks associated to chemical
mixtures is also presented.
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Quantitative Risk Characterization of Non-Carcinogens
A quantitative risk characterization for non-carcinogens involves
consideration of: (1) the existing standards, guidelines, and criteria
developed by various regulatory agencies which represent the best scientific
estimates of health risk at given environmental concentrations (as presented
in the hazard assessment phase) and, (2) the (human) intake estimates
calculated in the exposure analysis phase, for each exposure route of concern.
The human health guidelines established for non-carcinogens are
represented by the NOAELs, NOELs, LOAELs, and incorporating a safety factor to
account for uncertainty in the data on which these indices are based, ADI
values. The ADI is commonly defined as the largest amount of toxicant in
mg/day for a 70 kg person which is not anticipated to result in any adverse
effects after chronic exposure. To perform the risk characterization, the
first step is to consider the exposure scenarios for each route and condition
of exposure at the facility (as developed in the quantitative exposure
analysis).
For each exposure scenario (e.g., representing average, most-realistic
conditions, or maximum, worst-case conditions of exposure) the level of risk
is characterized. To characterize the risk associated with exposure
conditions represented in each scenario, the estimated (human) intake level
(for the route of exposure being evaluated in the scenario) is compared with
the ADI value for the hazardous constituent of concern. If the estimated
intake level is in excess of the ADI value, then the exposure conditions
described by the scenario represent an "unacceptable" risk to human health.
If the opposite is true, e.g. the intake value for that route of exposure and
chemical is less than the corresponding ADI value, then the conditions
represent an "acceptable" risk to human health. The intake values for each
route of exposure of concern are evaluated in a similar fashion. For releases
to soils, this the relevant routes of exposure include:
• Direct contact (with soils)-
• Inhalation (of fugitive dusts), with possible reingestion".
• Ingestion of food products and soil).
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There are limitations and assumptions inherent in any risk characterization
process especially when the characterization process involves routes of
exposure which are difficult to assess. Some of the limitations and
assumptions inherent in characterizing risks via these routes of exposure are
present in the final section.
Quantitative Risk Characterization of Carcinogens
Like the quantitative risk characterization process for non-carcinogens,
the process of characterizing risks associated with exposure to chemicals
whose primary effect is carcinogenesis involves consideration of the existing
standards, guidelines and criteria which represent the best scientific
estimates of health risk at given environmental concentrations as presented in
the hazard assessment phase. Unlike non-carcinogens, however, the second
consideration in evaluating risks associated with exposure to chemicals which
are carcinogens is the estimated dose incurred by receptors, as calculated in
the previous quantitative exposure analysis phase, for each route of exposure
of concern.
For chemicals which are carcinogens, the guidelines used to perform
quantitative risk characterizations are called "risk levels", i.e., the
incremental risk of developing cancer from exposure to the hazardous
constituent of concern. The EPA in its Ambient Water Quality Criteria
Documents uses a range of risk levels from 10 to 10 to describe the
increased risk of cancer predicted for exposure to low dose levels of
chemicals (e.g., which are typical of environmental conditions). A
one-in-one-million increase in risk (10 ) is the mean value of this range
and is often used as a baseline level. This base level does not necessarily
represent a level of "acceptable" risk, but is used as reference for which
assessments of risk to populations can be made.
The calculated environmental cancer risks are derived using the projected
exposure (e.g., dose) levels calculated in the exposure analysis phase and the
measure of chemical hazard or potency associated with that chemical (the unit
risk level presented in the hazard assessment phase. The calculated cancer
risk level is compared to the baseline value of 10 , in order to provide an
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indication of the magnitude of the risk present. These resulting risk
estimates are interpreted as probabilities of incremental cancer risks over
lifetime exposure.
To perform the quantitive risk characterization for carcinogens the first
step is to consider the exposure scenarios developed in the previous exposure
analysis phase. For each exposure scenario, (e.g., those representing
average, most-realistic conditions, as well as those representing maximum,
worst-case conditions of exposure), the risk is characterized. To
characterize the risk associated with the hypothetical exposure conditions
represented in each scenario the estimated human dose value (calculated in the
quantitative exposure analysis phase) is multiplied by the unit risk level for
the chemical of concern. The resulting estimate of risk is then compared with
the baseline risk value of 10~ to predict the incremental increase in risk
associated with the exposure route and scenario being evaluated. The flow
diagram in Figure B-8 shows how the human dose value (calculated in the
quantitative exposure analysis phase) can be used to predict risk associated
with exposure to a given medium, in this example, soils. The process depicted
in the diagram can be used to estimate the risks associated with all routes of
exposure being evaluated, provided that estimates of dose for the exposure
routes are provided.
An example of a typical risk calculation is presented below:
Risk = daily dose *(carcinogenic) unit risk factor
over 70 years
of life
Of importance to note is that this equation can only be used at low
environmental levels for hazardous constituents of concern. For sources where
chemical intakes may be large (e.g., carcinogenic risk labove 0.10), an
alternate model should be considered. In this situation, the permit writer
should consult EPA Headquarters for guidance in use of the appropriate model.
It should be recognized that, like the calculated non-carcinogenic risk
estimate, the carcinogenic risk estimate is dependent on numerous assumptions,
and many uncertainties and limitations are inherent in the process. The
following section briefly describes some of the uncertainties and assumptions
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ESTIMATED EXPOSURE CONCENTRATION
(e.g. intake dose estimate)
A: Yes
Ql: Is the primary effect of
the hazardous constituent
carcinogenesis?a
A: No
Q2:
What is the Unit
Cancer Risk (UCR)
value?
RISK CHARACTERIZATION
What is the ADI?
(or other relevant
criteria, standards
of acceptable human
exposure).
RISK CHARACTERIZATION
Q3:
What is the average
expected incremental
risk (over 70 years)?
Q3:
What is the
maximum expected
incremental risk
RISK = Carcinogenic Potency Factor
*Average (or Maximum)
expected lifetime dose
• present assumptions and
uncertainties of results
Q3: Is the estimated
exposure value
(intake) for that
route of exposure
in excess of the
ADI? (or other
relevant criteria,
standard of
acceptable human
exposure).
present assumptions and
uncertainties of results
aThis assumes that the primary effect of the hazardous constituent is carcin-
ogenesis; other noncarcinogenic endpoints can be evaluated via the method of
risk evaluation depicted here.
Figure B-8. Schematic flow diagram of alternate methods of quantitative
human risk characterization (given a determined dose incurred
by receptor populations).
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common in characterizing risks associated with exposure to releases to'soils
for exposure routes of concern (e.g., direct contact, inhalation, and
ingestion). For additional information on characterizing risks to human
populations via these routes, the reader is referred to ICF.Inc.. 1985.
ASSUMPTIONS AND UNCERTAINTIES IN THE RISK CHARACTERIZATION PROCESS
Some of the major sources of uncertainty in any risk characterization
process involve the hazard information for the chemicals of concern. Some
common sources of uncertainty include: (1) the toxicity information used to
estimate risks to human populations which is derived from animal studies, and
must be extrapolated to humans; and (2) many of the toxicity studies are
performed at high dose levels and must be applied to situations of low level
environmental contaminant levels, typical of chemical releases; extrapolation
from high to low doses increases the uncertainty in the results. Uncertainty
can also be introduced at the exposure analysis phase, such as when exposure
modeling (e.g., level II or III analysis using equations or models,
respectively) is used in the calculation of intake or dose and which is based
on many simplifying assumptions. Uncertainty is almost always introduced when
the possible routes of exposure are difficult to qualify and quantify,
although they may be extremely important to certain populations at risk. The
following subsections describe some of the assumptions and uncertainties
inherent in the characterization of risk associated with exposure via pathways
and routes relevant to hazardous constituent releases to soils; e.g., direct
contacts (with contaminated soils), inhalation of airborne particulates to
which hazardous constituents have adsorbed with possible reingestion, and
ingestion of food products (into which hazardous constituents in soil have
been uptaken).
Dermal Contact with Contaminated Soils
Dermal contact (with contaminated soils) is a route of exposure for which
there is limited information on which to base estimates of human risk.
Characterization of risk for this route of exposure therefore requires making
numerous assumptions, and a cetain degree of uncertainty is inherent in the
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evaluation. Many of these uncertainties are introduced at the exposure
analysis phase with the development human exposure scenarios and the
estimation of the frequency and duration of exposure. Other uncertainties are
introduced at the hazard assessment phase with the estimation of human
absorbtion percentages for the hazardous constituents of concern. Some of the
assumptions and uncertainties inherent in characterization of risk for this
route of exposure are as follows:
• determination of the amount of soil actually contacting the skin
(during exposure), and the relative amount of pure hazardous
constituent to which there is exposure,
• determination of the parameters associated with the part of the body
contacted (e.g., surface area, actual part of body contacted, etc.),
• the percent absorbtion of the hazardous constituent contacting the
body (e.g. based on the physical/chemical properties of constituents
involved, available human absorption data, etc.),
• age of individuals contacted,
• human activity pattern associated with exposure (e.g., frequency,
duration exposure, etc.), and
• human activity pattern after exposure (e.g. washing, bathing, eating,
etc.).
Any assumptions and uncertainties introduced into the risk characterization
process should be identified and presented. Consideration of these
limitations will help to more accurately interpret the risk estimates that are
generated.
Ingestion of Contaminated Soils (by a Child Exhibiting Pica)
Ingestion of contaminated soils is not a common route of human exposure,
and primarily involves young children who come into contact with contaminated
soils (e.g. while playing) and either accidentally ingest the soil or exhibit
pica, an abnormal craving for non-food objects. Because exposure via this
route is expected to be infrequent, and generally at low levels, the human
risks associated with the exposure are usually not considered significant. An
exception would be under circumstances involving close proximity to the
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facility of an area heavily utilized by children (e.g. a playground) i-n which
exposure via this route would be more common. The assumptions and limitations
inherent in risk characterization for this route of exposure are introduced
primarily at the exposure analysis phase (e.g. with the development of
exposure scenarios and the determination of frequency and duration of
exposure) and the hazard assessment phase (e.g. with the estimation of the
amount of absorbtion of the chemical into the body after ingestion). They are
as follows:
• determination of human use areas near the facility and the associated
human activity patterns,
• determination of the frequency, duration, and quantity of soil
exposure,
• determination of age of exposed population, and
• determination of the percent absorption of hazardous constituents
into the body upon ingestion.
Again, the assumptions and limitations introduced into the risk characteri-
zation process for this route of exposure should be presented with the
interpretation of the calculated risk estimates.
Inhalation (if Airborne Particulates to Which Hazardous Constituents Have
Adsorbed) with Possible Reingestion
The estimation of human risk assessment associated with exposure via
inhalation contaminated dusts (e.g. airborne particulates) has been widely
researched, and information relevant to the estimation and interpretation of
risk estimates calculated for this route of exposure are presented primarily
in two sources: (1) ICF, Inc., 1985 (Draft EPA Superfund Health Assessment
Manual), and (2) Schultz, et al., 1984 (Draft EPA Superfund Exposure
Assessment Manual).
Despite the availability of information for use in characterizing risks
associated with exposure via inhalation of airborne particulates, little
evidence is available for use in characterizing risks to human populations
exposed to hazardous constituents via reingestion of inhaled particulates.
Exposure via this indirect route is generally considered of limited
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significance due to Che speradic nature of the exposure and the generally low
levels of hazardous constituents to which there is exposure. In brief, some
of the assumptions and uncertainties inherent in the characterization of risk
associated with exposure via this route include:
• determination of duration, frequency, and quantity of air hazardous
constituent exposure;
• determination of the age of exposed population (e.g. as it affects
the average ventilation rate);
• determination of the percent absorbtion of the chemical of concern
within the respiratory system;
• determination of the particulate size (and its affect on absorbtion
in the respiratory tract); and
• determination of the extent to which reingestion of respired
particulates occurs, and the resulting absorbtion rate of the
chemicals in the digestive tract.
Again, any assumptions and limitations introduced into the risk characteri-
zation process should be presented.
Ingestion of Biota (Into Which Hazardous Constituents Have Been Uptaken)
Ingestion of biota is a route of human exposure for which risk characteri-
zation is generally very difficult to perform. This is due primarily to the
limited availability of data to define the potential for uptake of hazardous
constituents by plant species. Because of this common limitation, many
assumptions must be made during the risk characterization process in order to
define the extent of contaminant uptake by biota and the subsequent risk to
human populations via ingestion.
Some of these assumptions and uncertainties include:
• determination of levels of hazardous constituents in plants exposed
to contaminated soils and subsequently ingested;
• determination of the frequency, duration, and quantity of hazardous
constituent exposure;
• absorbtion rate of ingested hazardous constituents; and
• age of population exposed.
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Because there is limited information with which to perform risk "characteriza-
tions for this route of exposure, quantitative risk characterizations are
generally not possible. Quantitative risk characterization would involve
direct sampling and analysis of the food products, and oftentimes this
information is not available. Characterization of risks associated with
exposure via this route is, therefore, generally quanlitative in nature.
SUMMARY
In summary, the risk characterization process involves assessment of two
components, the exposure assessment and the hazard assessment. By combining
the information in each of these components, actual or potential risks to
human health and the environment can be characterized. Risk characterizations
can be either qualitative or quantitative. The decision as to which level is
performed is dependent primarily on the level of exposure analysis performed
prior to the risk characterization (e.g. qualitative, quantitative).
Regardless of the level of risk characterization performed, however, the
outcome of the analysis is a determination of the actual or potential risks to
human (and non-human) populations resulting from exposure to media
contaminated as a result of release to soils. Because there is no one set
method for performing risk characterizations, the risk characterization
process used to evaluate each pathway and route of exposure for a given
environmental medium involves making numerous assumptions. This is
particulary true for exposure pathways and routes which are difficult to
characterize. The making of assumptions introduces a certain amount of
uncertainty into the risk characterization process. Because of this, the
results of the risk characterization process must be cautiously interpreted.
Despite the inherent uncertainty in the results of the risk characterization
process, however, the information so derived can be used, at a minimal, to
identify potential risks to human (and non-human) population associated with
exposure to environmental contaminants (i.e., hazardous constituents).
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