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Hazardous Waste Management, Volume I

Sukalyan Sengupta

Environmental engineers are primarily responsible for restor-ing hazardous waste sites to a condition where they will not cause adverse effect to human health and the environment and for creating a waste-handling architecture that prevents future industrial wastes from causing any damage. This book presents a roadmap for hazardous waste management.

Beginning with the legal framework that defi nes what a hazardous waste is and when a waste becomes hazardous, a practicing engineer needs to have a general idea of en-vironmental audits, toxicology, site characterization, treat-ment processes, and site-monitoring protocol. In addition, the toxic compounds of concern may partition into the soil, groundwater, and air. Thus, any attempt to deal with such a situation requires integration of law, science, technology, and social policy. This book guides the reader with the help of numerous solved examples with a clear goal of showing how these topics are integrated in practice.

Sukalyan Sengupta is professor of environmental engineer-ing in the civil and environmental engineering department at the University of Massachusetts Dartmouth. A registered professional engineer in Massachusetts, he has more than 22 years of academic and research experience in environ-mental engineering treatment processes. He is the editor of Remediation of Polluted Waters, Volume 3 of the Elsevier Series on Comprehensive Water Quality and Purifi cation, 1st edition, released in October 2013. He is currently the sec-tion editor (Water Pollution) of Current Pollution Reports, a wide-ranging review journal published by Springer that cov-ers signifi cant developments in the fi eld of environmental pollution. Sukalyan Sengupta

ENVIRONMENTAL ENGINEERINGCOLLECTIONFrancis J. Hopcroft, Collection Editor

S k l S t

Hazardous Waste Management, Volume I

HAZARDOUS WASTE

MANAGEMENT, VOLUME I

HAZARDOUS WASTE

MANAGEMENT, VOLUME I

SUKALYAN SENGUPTA

Hazardous Waste Management, Volume I Copyright © Momentum Press®, LLC, 2018.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means—electronic, mechanical, photocopy, recording, or any other except for brief quotations, not to exceed 250 words, without the prior permission of the publisher.

First published in 2018 by Momentum Press, LLC 222 East 46th Street, New York, NY 10017 www.momentumpress.net

ISBN-13: 978-1-94561-288-6 (print) ISBN-13: 978-1-94561-289-3 (e-book)

Momentum Press Environmental Engineering Collection

Cover and interior design by S4Carlisle Publishing Service Private Ltd. Chennai, India First edition: 2018

10 9 8 7 6 5 4 3 2 1

Printed in the United States of America

ABSTRACT

Environmental engineers are primarily responsible for restoring hazardous waste sites to a condition where they will not cause adverse effect to human health and the environment and for creating a waste-handling architecture that prevents future industrial wastes from causing any damage. This book presents a roadmap for hazardous waste management. Beginning with the legal framework that defines what a hazardous waste is and when a waste becomes hazardous, a practicing engineer needs to have a general idea of environmental audits, toxicology, site characterization, treatment processes, and site-monitoring protocol. In addition, the toxic compounds of concern may partition into the soil, groundwater, and air. Thus, any attempt to deal with such a situation requires integration of law, science, technology, and social policy. This book guides the reader with the help of numerous solved examples with a clear goal of showing how these topics are integrated in practice.

KEYWORDS

Carcinogen potency factor, CERCLA, Henry’s constant, no observed adverse effect level, octanol–water partition coefficient, RCRA, reference dose, slope factor, solubility product, vapor pressure.

CONTENTS

LIST OF FIGURES xi

LIST OF TABLES xiii

ACKNOWLEDGMENTS xv

1 HAZARDOUS WASTE LANDSCAPE 1

1.1 Landmark Episodes 1

1.1.1 Rachel Carson’s Silent Spring 1

1.1.2 Minamata Bay Disaster 2

1.1.3 Love Canal 2

1.1.4 Times Beach, Missouri 3

1.2 Regulatory Framework 3

1.2.1 Resource Conservation and Recovery Act (RCRA) 3

1.2.1.1 Definition of Solid Waste 4

1.2.1.2 General Definition of Hazardous Waste 4

1.2.1.3 RCRA Provisions 5

1.2.1.4 The Mixture Rule 7

1.2.1.5 Derived Waste 7

1.2.1.6 Hazardous Waste Generators—40 CFR Part 262 8

1.2.1.6.1 Categories of Hazardous Waste Generator 8

1.2.1.7 Transporters—Sec 3003 40 CFR Part 263 9

1.2.1.8 Treat, Store, Dispose Sec. 3004 40 CFR Part 264, 265, 266, 268 10

viii • CONTENTS

1.2.1.9 1984 Land Disposal Regulations 11

1.2.2 Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) 12

1.2.2.1 Difference between Hazardous Substance versus Pollutant or Contaminant 13

1.2.2.2 Petroleum Exclusion 13

1.2.2.3 CERCLA Release 13

1.2.2.4 CERCLA Action 14

1.2.2.5 National Contingency Plan 15

1.2.2.6 Site Cleanup Standards 16

1.2.2.7 Definition of an ARAR 17

1.2.2.8 Liability 18

1.2.2.9 Effect of CERCLA on Real Estate and Business Transactions 19

1.2.2.10 Settlements with Potentially Responsible Parties (PRPs) 19

1.2.2.11 Contributory Parties (CP) 20

1.2.2.12 Statute of Limitations 20

References 20

2 ENVIRONMENTAL CHEMISTRY 21

2.1 Vapor Pressure 21

2.1.1 Vapor Pressure of a Mixture 21

2.1.2 Relationship of Vapor Pressure with Temperature 23

2.2 Solubility 25

2.2.1 Aqueous Solubility of a Liquid Organic Compound 26

2.2.2 Aqueous Solubility of a Volatile Organic Compound 28

2.3 Partitioning 29

2.3.1 Octanol–Water Partition Coefficient 29

2.3.2 Bioconcentration Factor 31

2.4 Sorption 32

References 32

CONTENTS • ix

3 FATE AND TRANSPORT OF CONTAMINANTS 33

3.1 Groundwater Contaminant Transport 33

3.1.1 Darcy’s Law 33

3.1.2 Diffusion 35

3.1.3 Dispersion 37

3.1.4 Advective–Dispersive Equation 39

3.2 Atmospheric Contaminant Transport 48

References 51

4 TOXICOLOGY 53

4.1 Dose–Response Relationship 53

4.2 Pharmacokinetics 54

4.3 Noncarcinogenic Effects 57

4.4 Carcinogenic Effects 64

References 66

5 RISK ASSESSMENT 69

5.1 Concept of Risk 69

5.2 Hazard Identification 70

5.3 Exposure Assessment 70

5.4 Toxicity Assessment 74

5.5 Risk Characterization 74

References 75

APPENDIX A 77

APPENDIX B 107

APPENDIX C 109

APPENDIX D 111

ABOUT THE AUTHOR 115

INDEX 117

LIST OF FIGURES

Figure 3.1 Sketch of solute spread over time due to diffusion 36

Figure 3.2 Factors governing longitudinal dispersion at the scale of individual pores 37

Figure 3.3 Flow paths in a porous medium causing lateral hydrodynamic dispersion 38

Figure 3.4 Sketch of transport and spread of a solute slug with time due to advection and dispersion 40

Figure 3.5 Sketch of the atmospheric dispersion model 48

Figure 4.1 A typical dose---response curve for a toxic substance (Image credit: coep.pharmacy.arizona .edu/curriculum/tox_basics/teach_tox_slides.ppt) 54

Figure 4.2 Location of NOAEL and LOAEL on a typical dose–response curve for a toxic agent (Image credit: NIH) 58

Figure 4.3 Dose–response curve for a complete carcinogen (Image credit: http://slideplayer.com/slide/ 4021950/) 64

LIST OF TABLES

Table 1.1 RCRA Provisions 4

Table 3.1 Pasquill chart for classifying atmospheric stability (based on Turner, 1974) 50

ACKNOWLEDGMENTS

The author expresses his gratitude to Professor Francis Hopcroft, editor, whose constant support, editorial insights, and frequent reminders helped complete this book.

The author also owes his students over the past twenty-three years a debt of gratitude for their comments and questions which helped clarify so many topics/concepts. From his students, the author learned a lot; this book would not have been possible without their input.

CHAPTER 1

HAZARDOUS WASTE LANDSCAPE

The harmful effects of some of the chemicals used by society were known from the beginning of early civilizations, but there was no systematic procedure to deal with this challenge. The problem grew much worse with the advent of the Industrial Revolution. The quantum leap in industrial production needed robust methods of resource extraction, and these two combined to produce huge amounts of toxic wastes. The environmental and health effects of these activities were not understood or recognized initially, much less quantified. This was because it took a long time (decades, even generations) for the effects to be manifested in human populations in significant numbers and science had not progressed enough to provide irrefutable explanations for these situations. The 20th century witnessed some landmark episodes which propelled public sentiment toward a proactive approach to deal with this situation. Some of these episodes are presented here in brief. The reader is advised to get additional information about these instances, which is available from a multitude of print and online sources.

1.1 LANDMARK EPISODES

1.1.1 RACHEL CARSON’S SILENT SPRING

The Industrial Revolution resulted in mass urbanization, as factories needed labor force that was located nearby for daily shifts. This resulted in a massive reduction of farm labor. To maintain the agricultural production that was needed for an ever-growing population, but with a shrinking farm

2 • HAZARDOUS WASTE MANAGEMENT, VOLUME I

labor force, mechanization of agriculture became a necessity, as did the increasing use of chemicals and fertilizers in agriculture. In the 1950s, Rachel Carson focused her attention on the widespread and indiscriminate use of a particular pesticide, DDT. In her landmark book, Silent Spring published in 1962, Rachel Carson comprehensively documented how DDT exposure was associated with many public health and environmental effects. The book served as a “wake-up call” to enforce measures to deal with toxic wastes.

1.1.2 MINAMATA BAY DISASTER

In the mid-1950s, doctors in the Minamata Bay area of Japan started seeing many patients with symptoms of a disease of the central nervous system. Detailed investigations revealed that a common feature of all the victims was that they resided in fishing hamlets along the shore of the Minamata Bay. The primary suspect then was consumption of fish and shellfish from the bay. Further investigations showed that extremely high levels of mercury discharged from a local chemical factory had contaminated the bay and its bioaccumulation (see chapter 2) by fish and shellfish had resulted in massive amounts of mercury ingestion by the local population. This epidemic served as another warning to the global population that aggressive measures were needed to deal with the discharge of toxic industrial wastes.

1.1.3 LOVE CANAL

Love Canal, situated in the city of Niagara Falls in New York State, was originally built as a shipping lane in the 1890s, but the plan was abandoned soon. The defunct canal then became a hazardous waste disposal site, but was sold to the Niagara School District in 1952. An elementary school built on this site was soon surrounded by many homes. In the 1970s, homeowners complained of a strong odor and puddles of oil or colored liquid in yards and basements. Investigations revealed the presence of numerous toxic contaminants in the air, groundwater, and soil. Pioneering reporting by Michael Brown of the Niagara Gazette, who also documented birth defects and many physical abnormalities among the residents of this neighborhood, focused national attention on this site. Public pressure by the community culminated in President Carter declaring Love Canal to be a federal disaster site in 1978.

HAZARDOUS WASTE LANDSCAPE • 3

1.1.4 TIMES BEACH, MISSOURI

Times beach was a small community near St. Louis. A local entrepreneur, Russell Martin Bliss, discovered that spraying of waste oil on his horse arena and farm controlled dust very well. Impressed with its efficacy, other farm owners contracted Bliss to spray waste oils on their farms and barns. Soon, birds began to drop dead and horses started to develop sores, lose hair, and die. Investigations revealed that the waste oil contained excessively high levels of dioxins. The Environmental Protection Agency (EPA) bought all the properties in 1983 and evacuated the residents in 1983.

1.2 REGULATORY FRAMEWORK

As the people became aware of these episodes and numerous others, they started demanding government action to manage hazardous wastes so that public health and the environment are protected. The U.S. Congress took a two-pronged approach in meeting this goal:

1. Managing currently generated hazardous waste 2. Remediation of contaminated sites

The Resource Conservation and Recovery Act (RCRA) of 1976, along with the Hazardous and Solid Waste Amendments (HSWA) of 1984, was passed to achieve “Cradle to Grave” control of hazardous waste through regulations on

1. Generators 2. Transporters 3. Owners/Operators of Treatment, Storage or Disposal (TSD)

Facilities.

1.2.1 RESOURCE CONSERVATION AND RECOVERY ACT (RCRA)

RCRA descended from Solid Waste Disposal Act (1965) and Resource Recovery Act (1970). These two were primarily concerned with safe handling, management, and disposal of solid waste, along with encouragement of waste minimization, waste recycle, and material and energy conservation.


1.2.1.1 Definition of Solid Waste

The term “solid waste” means any garbage, refuse, sludge from a waste treatment plant, water supply treatment plant, or air pollution control facility and other discarded material, including solid, liquid, semisolid, or contained gaseous materials resulting from industrial, commercial, mining and agricultural operations, and from community activities, but does not include solid or dissolved materials in irrigation return flows or industrial discharges which are point sources subject to permits under section 402 of the Federal Water Pollution Control Act, as amended (86 Stat. 880), or source, special nuclear, or byproduct material as defined by the Atomic Energy Act of 1954, as amended (68 Stat. 923).

1.2.1.2 General Definition of Hazardous Waste

A solid waste, or combination of solid wastes, which because of its quantity, concentration, or physical, chemical, or infectious characteristics, may

a. cause, or significantly contribute to, an increase in mortality or an increase in serious, irreversible, or incapacitating reversible, illness; or

b. pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed.

Table 1.1 lists the provisions of RCRA. This volume focuses only on Subtitles A and C.

Table 1.1 RCRA Provisions

Subtitle Provisions

A General Provisions

B Office of Solid Waste; Authorities of the Administrator and Interagency Coordinating Committee

C Hazardous Waste D Nonhazardous Waste

E Duties of the Secretary of Commerce in Resource and Recovery

F Federal Responsibilities


Subtitle Provisions

G Miscellaneous Provisions

H Research, Development, Demonstration, and Information

I Regulation of Underground Storage Tanks

J Standards for the Tracking And Management of Medical Waste

1.2.1.3 RCRA Provisions

Subtitle A

Goals and objectives of Subtitle A include the following:

1. Generation of hazardous waste to be reduced or eliminated 2. Land disposal should be the least favored method for disposal of

hazardous waste 3. All waste must be handled to minimize present and future threats

to human health and the environment

Subtitle B

The goals and objectives listed in Subtitle A are achieved by the following:

a. Proper management of hazardous waste b. Minimization of the generation of hazardous waste c. Minimization of land disposal of hazardous waste d. Prohibition of open dumping e. Encouragement of state assumption of RCRA f. Encouragement of Research & Development (R&D) g. Promotion of recovery, recycle, and treatment.

Subtitle C

The procedure for defining a hazardous waste includes the following:

1. A waste listed by EPA in 40 CFR Part 261 Subpart D. This in turn is comprised of those: a. From nonspecific sources, i.e., solvents. These are designated

as “F” wastes. b. From specific sources, i.e., still bottoms. These are designated

as “K” wastes.


c. Discarded commercial products, off-spec materials, spills of them, and containers from them. If toxic, they are designated as Code P; if acutely hazardous, they are designated as Code U.

Please see Appendix A for a partial list of “listed wastes.” RCRA is triggered whenever any chemical on the list is discarded either on purpose or by accident. A hazardous waste generator can exercise small volume generator exemption. A generator can also request delisting of F, K, P, or U waste if it can prove that the waste is not hazardous, i.e., submit analysis showing it does not contain waste constituents which are hazardous or treat the waste to prevent leaching and so on.

2. A waste that exhibits any of four hazardous waste characteristics in 40 CFR Part 261 Subpart C. The characteristics are as follows: (1) ignitability; (2) corrosivity; (3) reactivity; and (4) toxicity. a. Ignitability—capable of causing or making a fire worse during

routine handling. Code D001 is a.1 nonaqueous liquid,


This is based on a standard leaching test at low pH. If the leachate contains any contaminant at 100X the maximum contaminant level (MCL) in drinking water, the matrix from which it was leached is considered as a hazardous waste. Two tests that are performed for this purpose are as follows:

• Extraction procedure (EP) toxicity test • Toxicity characteristic leaching procedure (TCLP)—zero

headspace extraction

1.2.1.4 The Mixture Rule

Any mixture of a hazardous waste and a nonhazardous waste is considered as a hazardous waste unless:

1. The mixture does not have hazardous characteristic, i.e., ignitability, corrosivity, reactivity, and toxicity.

2. Mixture is wastewater + dilute hazardous waste subject to regulations under the Clean Water Act (CWA).

3. Mixture is de minimis.

It is noted that the mixtures above are exempt only if mixture occurs during normal production or waste management. The mixture cannot be intentional dilution.

1.2.1.5 Derived Waste

Any waste that is derived from the treatment, storage, and disposal (TSD) of a hazardous waste is considered as a hazardous waste. Exceptions include the following: The waste can be delisted,

1. if derived from TSD of listed waste, 2. if the derived waste does not exhibit any “characteristic” property,

and 3. if the derived waste is reclaimed from solid waste for beneficial

use, except as fuel or in a manner constituting disposal.


1.2.1.6 Hazardous Waste Generators—40 CFR Part 262

Generator—person or company which causes or produces a hazardous waste as defined by 40 CFR Part 261. Explicit for site—i.e., if company has >1 generation sites, it must meet all applicable regulations, individually, at each site.

Responsibilities of the Generator: The generator must

1. determine whether any waste is a hazardous waste. Keep test data for 3 years after the waste is handed to a TSD facility.

2. obtain EPA ID No. The generator cannot handle any hazardous waste, legally, until and unless a valid ID# is obtained.

3. prepare waste manifest, a. name and ID of generator, transporter, and TSD facility, b. describe waste regarding DOT regulations, c. certify packaging and labeling, d. certification statement regarding efforts to reduce volume and

toxicity of waste and selection of TSD, e. exception report if generator does not receive copy of

manifest from transporter/TSD facility (TSDF) in 45 days, f. package and label waste according to DOT regulation 49 USC

1802. If container is


b. Small quantity generators (SQGs): Generate more than 100 kilograms, but less than 1,000 kilograms of hazardous waste per month.

c. Large quantity generators (LQGs): Generate 1,000 kilograms per month or more of hazardous waste or more than one kilogram per month of acutely hazardous waste. • LQGs may only accumulate waste on site for 90 days. • LQGs do not have a limit on the amount of hazardous waste

accumulated on site. • Hazardous waste generated by LQGs must be managed

in tanks, containers, drip pads, or containment buildings subject to the requirements found at 40 CFR §§ 262.17(a)(1)-(4).

• LQGs must comply with the hazardous waste manifest requirements at 40 CFR Part 262 Subpart B and the pretransport requirements at 40 CFR §§262.30 through 262.33.

• LQGs must comply with the preparedness, prevention, and emergency procedure requirements at 40 CFR Part 262 Subpart M and the land disposal restriction requirements at 40 CFR Part 268.

• LQGs must submit a biennial hazardous waste report.

1.2.1.7 Transporters—Sec 3003 40 CFR Part 263

A transporter is defined as any person or agency which transports hazardous waste off the generation site.

The regulations for the transportation of hazardous waste and hazardous materials are set by the Department of Transportation under the Hazardous Materials Transport Act. The transporter must obtain an ID Number. The transporter signs and takes charge of manifest. DOT regulations cover labeling, marking, placarding, using proper containers, and reporting spills. When transferring waste, the transporter signs and dates the manifest, keeps a copy, and gives a copy to the receiver. There is a three-year time for record storage. The transporter is a generator if it mixes different wastes in the same container, or imports hazardous waste from a foreign country.

If a spill occurs during transport, the transporter must

a. take immediate action to protect human health and the environment b. treat or contain the spill c. notify the local police and fire department


d. notify the national response center e. file a written report

1.2.1.8 Treat, Store, Dispose Sec. 3004 40 CFR Part 264, 265, 266, 268

All TSD facilities must obtain an EPA Registration Number. Regulations cover the location, design, operation, closure, and general and type-specific standards.

Treatment is defined as any method to change the physical, chemical, biological character, or composition of hazardous waste to neutralize, recover energy, recover material resources, render the waste less hazardous, render the waste safer to transport, store or dispose of the waste, or reduce the volume of the waste.

Storage is defined as holding of the hazardous waste for a temporary period.

A disposal site is defined as a location where waste is intentionally placed and remains after closure.

Disposal is defined as placing of hazardous waste or hazardous materials in or at a disposal site.

General Standards for Operating a TSDF include:

1. Obtain a RCRA permit number. TSDFs must receive a permit before they begin construction to demonstrate they can manage hazardous waste safely and responsibly. The permitting agency (i.e., the state or EPA) reviews the permit application and decides whether to grant or deny the facility a RCRA permit. Permits are typically granted for a period up to 10 years.

2. Obtain a detailed chemical and physical analysis of the waste from the generator.

3. Security system—24-hr. surveillance or barrier. 4. Location standards if in seismic or flood plain. 5. TSD personnel receive training in regulations, safety, and

technology. 6. Special care must be taken in handling ignitable, reactive, or

incompatible wastes (§264/265.17). Ignitable and reactive wastes must be protected from ignition sources. “No Smoking” signs must be placed where ignitable and reactive wastes are stored and separate smoking areas must be designated (§264/265.17(a)).


Owners and operators must also take precautions to prevent waste reactions (§264/265.17(b)). Owners and operators for whom §264.17(a) and (b) are applicable must document their compliance with those sections (§264.17(c)).

7. Safety equipment on site. 8. Contingency plan in case of accident. 9. Record keeping: accept manifest, sign, date, copy to transporter

and generator. 10. Complete record of all shipments and disposition of waste on site

for life of facility. 11. Closure requirements—period from end of waste acceptance to

completion of treatment. 12. Postclosure plan—30 years after. Including groundwater monitoring

and monitoring of waste containment systems. 13. Financial responsibility requirements to insure funds available for

11 and 12.

1.2.1.9 1984 Land Disposal Regulations

The purpose of these regulations is to minimize reliance on land disposal and encourage advanced treatment and recycling of hazardous wastes. Its special features include the following:

a. Ban the disposal of noncontainerized liquid in landfills. b. Minimize the disposal of containerized liquid in landfills. c. Prohibit the landfill disposal of liquids absorbed in materials that

biodegrade or release liquid when compressed during landfill operation.

d. Ban the landfill disposal of any hazardous waste unless the best demonstrated available technology (BDAT) is used to pretreat the waste. d.1. Became applicable to dioxin and solvent containing waste by

11/86. BDAT was defined as incineration for dioxin and as chemical/physical treatment for solvents.

d.2. Ban the land disposal of California list wastes. d.3. The EPA ranked wastes in terms of hazard and volume, with

the ban going into effect for 1/3 of list at a time. The last date for the ban to become applicable to any waste was 5/90.


The ban does not apply to any waste for which the EPA can demonstrate that the waste poses no threat to human health or the environment.

The publication of each ban had to include the technology needed to diminish toxicity and hazard to the point where it is allowable to put the treated material on land.

These regulations also included “Hammer Provisions” which stated that if EPA does not meet the schedule, an immediate ban on all land disposal would go into effect.

1.2.2 COMPREHENSIVE ENVIRONMENTAL RESPONSE, COMPENSATION, AND LIABILITY ACT (CERCLA)

CERCLA was originally enacted in 1980. It underwent a major revision in 1986 and was called the Superfund Amendments and Reauthorization Act (SARA). The purpose of CERCLA and SARA is to provide funding and enforcement authority for the federal cleanup of hazardous waste sites and for responding to spills of hazardous substances.

CERCLA applies to all media, i.e., air, surface water, groundwater, and soil and to any type of facility (industrial, commercial, or even noncommercial). CERCLA is designed to cope with the release or “threat of release” into the environment of the following:

a. A hazardous substance as defined under CERCLA Section 101(14) Any substance EPA has designated for special consideration

under the Clean Air Act, the Clean Water Act, the Toxic Substances Control Act, any substance defined as a hazardous waste under RCRA, or any substance EPA designates as presenting a substantial danger to human health or the environment.

All substances that meet any of these definitions are compiled in a list of hazardous substances in 40 CFR Part 302 (Appendix D of this book).

Two basic substances excluded are petroleum and gasoline used for fuel.

b. A pollutant or contaminant under CERCLA 101 (33) is defined as follows:

Any substance not on the list of hazardous substances which will, or may reasonably be anticipated to, cause any types of adverse effects in organisms and their offspring.

The same exclusion applies for petroleum and gas (fuel).


1.2.2.1 Difference between Hazardous Substance versus Pollutant or Contaminant

EPA can respond to a release or threat of release of a hazardous substance, a pollutant, or a contaminant. However, Private Parties are liable for cleanup costs only for hazardous substances, and Private Parties must report releases only of hazardous substances. It is noted that, while all RCRA wastes are regulated under CERCLA, all CERCLA substances are not RCRA wastes.

CERCLA is much more encompassing because if a substance (not necessarily a waste) contains any amount of a listed hazardous substance, it is regulated under CERCLA, whereas to be regulated under RCRA, it must be defined as a hazardous waste.

1.2.2.2 Petroleum Exclusion:

While the normal constituents of petroleum are on the CERCLA hazardous substances list, EPA clarified in a 1987 ruling that:

1. The presence of hazardous substances which are normally indigenous to petroleum does not abrogate or nullify the petroleum exclusion.

2. Petroleum contaminated with hazardous substances not normally present or indigenous to petroleum does abrogate the petroleum exclusion.

1.2.2.3 CERCLA Release

Any entrance into the environment is defined as a release under CERCLA, except the following:

a. workplace exposure covered by OSHA b. vehicular engine exhaust c. radioactive contamination covered by other statutes d. normal application of fertilizer e. releases under federal permits from other statutes—Private Parties

are exempt from liability or the need to report releases under CERCLA, but not under the Federal Statute under which the permit was issued.


1.2.2.4 CERCLA Action

Sec. 104—In the event of a release, or the substantial threat of a release, of a hazardous substance, a pollutant, or a contaminant which may present an imminent and substantial danger, EPA is authorized to undertake removal/remediation actions to minimize or remove the threat.

Removal—short-term response (fix dike, build wall, and so on) Remediation: long-term response (eliminate hazard from site) Removal limit—12 months, $2 million, unless performed by

potentially responsible party (PRP) Prerequisites to EPA action

1. If the PRP will not, or cannot, carry out remediation, the state must agree to share costs with EPA.

The state share is required to be at least 50 percent if the release is on a state operated site.

The state share is required to be at least 10 percent if the release is on a private site.

2. The site must be on National Priority List. Section 105 requires EPA to develop criteria for establishing

priorities among sites needing remediation.

The National Priorities List (NPL) is the list of hazardous waste sites in the United States that are eligible for long-term remedial action (cleanup) financed under the federal Superfund program. EPA regulations define a formal process for assessing hazardous waste sites and determining whether a particular site should be placed on the NPL or not.

The process of placing a site under NPL is triggered when EPA receives a report of a potentially hazardous waste site from an individual, state government, or responsible federal agency. EPA first enters the potentially contaminated facility into a database known as the Compre- hensive Environmental Response, Compensation, and Liability Information System (CERCLIS). Following this, EPA or the state environmental regulatory agency in which the potentially contaminated facility is located, conducts a preliminary assessment. The objective of this preliminary assessment is to decide whether the facility poses a threat to human health and/or the environment. If the preliminary assessment shows the possibility of contamination, EPA or the state environmental regulatory agency conducts a more detailed site inspection. EPA then uses the Hazard Ranking System (HRS) to review any available data on the site to determine whether its environmental or health risks are enough to qualify


the facility for a Superfund cleanup. Generally, a facility with an overall score of 28.50 or greater on the HRS is eligible to be placed on the NPL.

An additional pathway for a site to be placed on the NPL is if a state or territory designates one top-priority site within its jurisdiction, regardless of the site’s HRS score.

Finally, a site can also be included in the NPL if it meets the following three requirements:

1. The Agency for Toxic Substances and Disease Registry (ATSDR) has issued a health advisory that recommends removing people from the facility.

2. EPA determines that the site poses a significant threat to public health.

3. EPA believes that it will be more cost-effective to use its remedial authority (which is only available at NPL facilities) than to use its emergency removal authority in responding to the facility.

As of May 16, 2017, the latest date for which information is available, there are 1336 NPL sites (1179 Non-Federal and 157 Federal) with 53 “Proposed NPL sites” (50 Non-Federal and 3 Federal).

1.2.2.5 National Contingency Plan

The National Contingency Plan (NCP) sets forth procedures and standards for cleanup of hazardous waste sites. The NCP establishes the framework for preliminary assessments, site investigations, the HRS, the NPL, and the requirements for remediation and removal.

Steps in Remedial Process

1. Remedial Investigation/Feasibility Report (RI/FS) 2. Selection of Remedy in Record of Decision (ROD)

Can do for site as a whole, or breakup the site into several operable units (OU). Each OU will have a separate RI/FS and ROD

The RI outcome must:

a. identify the source of the contamination b. identify the extent of the contamination c. identify the pathways for release of the contaminant to the

environment d. identify the extent of human and environmental exposure


Data from the RI provide the basis for the evaluation of various remedial alternatives during the FS phase.

The FS identifies and develops specific engineering and construction alternatives for cleaning up the site, including costs, feasibility, and environmental impacts expected to be associated with the remedial activities.

An RI/FS generally requires more than 1 year and can cost several million dollars.

A work plan is required to precede the RI/FS. The work plan provides details on:

The type and number of samples to be collected of various media, the location, depth, and number of monitoring wells to be installed, the timing for accomplishing certain tasks, and generally the degree to which the site will be studied and how alternatives will be developed.

The resulting ROD is a decision document in which EPA explains its selection of remedial activity to be undertaken at a site. A preliminary ROD must have public comment and public participation. To insure participation, EPA can give grants of up to $50,000 to facilitate public participation (CERCLA Section 117).

A ROD must also have significant state involvement throughout its development (CERCLA Sec. 121).

1.2.2.6 Site Cleanup Standards

This set of standards answers the question, “How clean is clean?” General guidelines by SARA (1986) include the following:

1. protect human health and the environment 2. attain “Applicable” or “Relevant and Appropriate” Requirements

(ARARs) 3. be cost-effective 4. utilize permanent solutions, treatment technology, or resource

recovery to the maximum extent practicable

In considering alternatives in the ROD, EPA must consider the following:

• the goals and requirements of RCRA, • the uncertainties and the availability of land disposal under RCRA, • the persistence, toxicity, mobility, and tendency of the subject

contaminants to bioaccumulate,


• the short-term and long-term threats to human health, • the long-term maintenance costs of the proposed solutions, • the potential for future cleanup costs if the remedy was to fail, and • the potential threat to human health and the environment associated

with excavation, transportation, redisposal, or containment of the subject contaminants.

1.2.2.7 Definition of an ARAR

An ARAR is defined under CERCLA as follows:

1. Any standard from any other federal environmental law or regulation

2. For contamination which remains, or is expected to remain, on site, state standards which are stricter than the applicable CERCLA standards

3. Federal water quality criteria (FWQC) and maximum contaminant level goals (MCLG) which are stricter than the applicable CERCLA standards

ARAR can be based on health or risk-based standards for water, air, or soil. It can also be location specific, e.g., ARAR for a site on a floodplain can be different from that of a site which is not (in a floodplain). ARAR can also specify a technology to be used at a particular site to achieve cleanup standards.

The result of any acceptable ARAR is to require cleanup far in excess of the most cost-effective technology. For example, if 1 million gives protection level 10 and 10 million gives protection to level 10.5, but ARAR requires 10.5, there is no option but to adopt the more expensive solution.

Cleanup regulations are developed from Sec. 121 of CERCLA. Some pertinent rules are as follows:

1. Treatment is strongly preferred over off-site disposal or leaving the contaminants in place. Off-site transport and disposal is allowed if a. the disposal site is not releasing any hazardous waste to soil,

groundwater, or surface water, and b. all activities at the cleanup site are under an approved RCRA

corrective action program 2. EPA must

a. review each remediated site every 5 years


b. take action at these sites in the future when warranted (if regulations change) and

c. report to Congress on all sites, reviews, and actions.

Exceptions to the ARAR Rules:

a. the selected action is only part of a total remedial action that will comply with the ARAR requirements when completed

b. compliance with the ARAR requirements would present greater health/environmental risks than alternative options

c. compliance with the ARAR requirements is “technically impracticable from an engineering perspective”

d. the selected remedy will attain a “standard of performance” which is “equivalent” to an ARAR required standard through use of another “method or approach”

e. with respect to a state requirement, the state has not demonstrated consistent application of the requirement in similar circumstances

f. where the remedy is to be CERCLA fund financed (as opposed to private-party financed), meeting the ARAR standard would not provide “balance” between the need for cleanup at the site in question considering the amount of fund resources that must be utilized at other sites in need of cleanup

1.2.2.8 Liability

Parties that are potentially liable for cleanup costs include the following:

1. present and past site owners 2. parties who transported waste to the site, even in de minimis

amounts and even if the site was legally licensed to accept the wastes at the time of disposal at the site

3. generators who arranged for wastes to be disposed or treated, either directly with an owner/operator, or indirectly with a transporter

Nature of liability:

1. Retroactive: to actions prior to CERCLA 2. Strict: liability need not be proven 3. Joint and several: one party out of many may be held liable for

more than his share under any fair allocation, and may, in fact, be held liable for the entire site cleanup


4. Liability is for cleanup costs and natural resource damage from substances which have escaped. Natural resource damages are determined by regulations of the Department of Interior 40 CFR 300.72-300.74.

1986 Amendments

1. Exempts state or local government from liability if property is taken by involuntary actions, i.e., tax delinquencies, abandonments, and so on.

2. Owners of facilities acquired after all disposal has taken place and all reasonable efforts were made by present owners to determine whether hazardous wastes and so on were on site.

1.2.2.9 Effect of CERCLA on Real Estate and Business Transactions

In property transfers, all businesses should have site assessments done to determine whether the site is clean prior to sale. Many states now require the same. If the site is not clean, the purchasing company will acquire liability unless the contract with the seller states otherwise. In addition, if Company A buys Company B, it acquires the generator liability at any site Company B sent wastes to unless the purchase contract states otherwise.

1.2.2.10 Settlements with Potentially Responsible Parties (PRPs)

EPA can

1. conduct the cleanup using Superfund money and then sue the PRP under Sec. 107

2. compel the PRP to conduct the cleanup under Sec. 106 3. arrive at a settlement for the PRP to pay for a portion of the cleanup

A modification in 1985 relaxed the settlement policy to:

1. Negotiate for a substantial portion of the total costs 2. Allow use of Superfund money for “orphan shares (OS),” which

are defined as the portion of the wastes for which no PRP can be found, or all PRPs are insolvent, unknown, dead, or judgment proof


3. Willingness to accept “De Minimis” Contributors’ Cash-Out settlements by minor parties by making an early cash payment to EPA

4. “Release” from Liability or “covenant not to sue” with respect to potential future liabilities

5. The “Release from liability” or “Covenant not to sue” is not final. Settlement for cleanup at a Superfund site is subject to a “Reopener” by EPA, if a. previously unknown conditions are discovered b. additional scientific information becomes available about the

conditions known at the time of the agreement

1.2.2.11 Contributory Parties (CP)

If EPA only sues some of the PRPs, the others (CP) can be brought into the suit by the original defendants.

If a party has settled with the EPA for its contribution to a site, it cannot be brought into a subsequent suit by other defendants.

1.2.2.12 Statute of Limitations

With respect to EPA cost recovery actions,

a. EPA must bring a suit within three years after “completion of the removal” for removal actions,

b. initial cost recovery action must be commenced by EPA within 6 years after initiation of physical on-site construction for remedial action, and

c. subsequent actions must be initiated within 3 years after the date of completion of all responsible action.

REFERENCES

1. LaGrega, M. D., Buckingham, P. L., and Evans, J. C. (2010). Hazardous Waste Management. Long Grove, IL: Waveland Press.

2. https://www.epa.gov/rcra/resource-conservation-and-recovery-act-rcra-regulations. Accessed June 30, 2017.

3. https://www.epa.gov/superfund/superfund-cercla-overview. Accessed June 30, 2017.

4. https://www.epa.gov/superfund/superfund-amendments-and-reauthorization-act-sara. Accessed June 30, 2017.

CHAPTER 2

ENVIRONMENTAL CHEMISTRY

2.1 VAPOR PRESSURE

When a chemical compound is present in the liquid phase, it has a tendency to leave the liquid as a vapor. The compound will distribute itself between the two phases and at equilibrium, the rate (moles/area/time) of molecules leaving the liquid phase will equal the rate of molecules entering the liquid phase. This property, termed vapor pressure, is defined as the pressure exerted by the vapor of the compound on the liquid at equilibrium. By definition, the vapor pressure of a pure gas is taken to be 1 atm on the surface of the earth.

2.1.1 VAPOR PRESSURE OF A MIXTURE

In most hazardous waste contamination scenarios, one does not encounter a single volatile chemical at the site. Rather, the situation contains a mixture of many volatile liquids that are present in the contaminated site. The vapor pressure of any component in this mixture can be determined by Raoult’s law which states that the partial vapor pressure of each component in any ideal mixture of liquids is equal to the product of the vapor pressure of the pure component and its mole fraction in the mixture. It can be represented as follows:

* i i ip p x= (2.1)

where pi is the partial vapor pressure of the component i in the gas phase above the solution mixture,


*ip is the vapor pressure of the pure component i (typically available from

standard references), and xi is the mole fraction of the component i in the solution mixture. Raoult’s law is usually used in conjunction with Dalton’s law of partial pressures which states that in a mixture of nonreacting gases, the total pressure of the mixture is equal to the sum of partial pressures of the individual gases. It is mathematically represented as follows:

=

= 1

n

total ii

p p (2.2)

Example problem 1.1 illustrates how these two concepts are combined in hazardous waste characterization situations.

Example Problem 2.1

An accidental release of 750 lb. of a mixture of 40 percent styrene, 35 percent tetrachloroethylene (also known as perchloroethylene or simply perc), and 25 percent toluene, by weight, at a temperature of 20ºC (68ºF) has resulted in a pool of light, nonaqueous (not dissolved in water), phase liquid (LNAPL) that has migrated through the unsaturated zone of the soil at a hazardous waste site. Estimate the partial pressure of each component in the mixture and the total pressure exerted by the mixture in the soil gas immediately above the LNAPL pool.

Solution

Compound Molecular Formula

Molecular Weight (g/mol)

Vapor Pressure (mm Hg)

Temperature (ºC)

Styrene C8H8 104.16 5.12 20

Perc C2Cl4 165.82 14.0 20

Toluene C7H8 92.15 22.0 20

Mass of styrene = 40% of 750 lb. = 750 lb. * 0.4 = 300 lb.

Mass of perc = 35% of 750 lb. = 750 lb. * 0.35 = 262.5 lb.

Mass of toluene = 25% of 750 lb. = 750 lb. * 0.25 = 187.5 lb.

ENVIRONMENTAL CHEMISTRY • 23

Moles of styrene = 300 lb

1309.17 molesg lb

104.16 * 0.0022 mol g

=

Moles of perc = 262.5 lb

719.56 molesg lb

165.82 * 0.0022mol g

=

Moles of toluene = 187.5 lb

924.88 molesg lb

92.15 * 0.0022 mol g

=

Mole fraction of styrene = ( )styrene1309.17

0.4431309.17 719.56 924.88

x = =+ +

Mole fraction of perc = ( )perc719.56

0.2441309.17 719.56 924.88

x = =+ +

Mole fraction of toluene = ( )toluene924.88

0.3131309.17 719.56 924.88

x = =+ +

Using equation 2.1,

= = =*styrene styrene styrene 5.12 mm Hg 0.443 2.268 mm Hg* *p p x

= = =*perc perc perc 14.0 mm Hg 0.244 3.416 mm Hg* * p p x

= = =*toluene toluene toluene 22.0 mm Hg 0.313 6.886 mm Hg* *p p x

Using equation 2.2, total pressure exerted by the mixture in the soil gas immediately above the LNAPL pool = 2.268 + 3.416 + 6.886 = 12.57 mm Hg

2.1.2 RELATIONSHIP OF VAPOR PRESSURE WITH TEMPERATURE

Vapor pressure varies strongly with temperature and can be represented as follows (Schwarzenbach et al., 1993):


00

1 22

P HdP

dT RT

Δ= (2.3)

Where

P0 = vapor pressure of the compound (atm or mm Hg)

T = absolute temperature (K)

ΔH1 2 = heat of vaporization, i.e., the energy required to convert one mole of liquid into a vapor without any increase in temperature

R = universal gas constant

Equation 2.3 can be modified as follows:

0

1 22

ln Hd P

dT RT

Δ= (2.4)

Integration of equation 2.4 yields the following:

0ln B

P AT

= − + (2.5)

where B = ΔHvap/R. As may be noted from equation 2.5, if the vapor pressure of a compound is known (or experimentally determined) at certain temperatures, the plot of ln P0 versus 1/T enables computation of the constants B and A. And this in turn allows the determination of the vapor pressure at any desired temperature. Example problem 2.2 illustrates this with an important hazardous chemical trichloroethylene.

Example Problem 2.2

What is the vapor pressure of trichloroethylene (C2HCl3) at 25ºC if the values at 11.9, 31.4, 67, and 86.7ºC are 40, 100, 400, and 760 mm Hg, respectively.

Solution

The information provided is used to create the following table.

T (°C) P0 (mm Hg) T (K) 1/T (K–1) ln P0 (mm Hg)

11.9 40 285.06 0.003508 3.688879454

31.4 100 304.56 0.003283 4.605170186

67 400 340.16 0.00294 5.991464547

86.7 760 359.86 0.002779 6.633318433


Plot of ln P0 (mm Hg) vs. 1/T (K–1) yields the following:

Thus, B = 4038.2 and A = 17.859 Therefore, if the temperature is 25ºC, which is equal to 298.16 K,

0 04038.2ln 17.859 4.315; 25 74.8 mm Hg298.16

P P at= − + = ∴ =℃

2.2 SOLUBILITY

The degree to which a compound, the solute, “likes” or “dislikes” being surrounded by another substance, the solvent, is referred to as solubility. The most common solvent is water and therefore, unless mentioned otherwise, whenever the term solubility is used, it should be taken as aqueous solubility. The formal definition of aqueous solubility of a chemical compound is (Schwarzenbach et al., 1993), “the abundance of the chemical per unit volume in the aqueous phase when the solution is in equilibrium with the pure compound in its actual aggregation state (gas, liquid, solid) at a specified temperature and pressure (e.g., 25ºC, 1 atm).” This is also referred to as a saturated solution of the chemical and is denoted as Cwsat.

y = –4038.2x + 17.859

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

0.002 0.0025 0.003 0.0035 0.004

ln P

0 (m

m H

g)

1/T (K–1)


2.2.1 AQUEOUS SOLUBILITY OF A LIQUID ORGANIC COMPOUND

If an organic compound is present as a liquid at standard temperature and pressure, its mole fraction in water at solubility is given as follows (Schwarzenbach et al., 1993):

( )sat sat

sat sat 1w ww wsat

ww

1; mol L

0.018

x xx C

Vγ−= ≅ ≅ (2.6)

Where

γ satw = activity coefficient of the organic liquid in water at saturation Vw = molar volume of water = 0.018 mol L–1

satwx = mole fraction solubility of the organic liquid in water at

saturation

In most cases, the data for satwC at 25°C are available from standard

references. Appendix B provides the same for some common organic liquids. However, often the value of solubility of an organic liquid is needed at a temperature other than 25°C, or at a temperature corresponding to one at which the solubility data are not available. In such instances, the temperature dependence of the mole fraction solubility of a liquid is based on the following equation ((Schwarzenbach et al., 1993):

satw

2

ln

esd x H

dT RT

Δ= (2.7)

where Δ esH = enthalpy of solubility of a liquid (in kJ. Mol–1) and all other

symbols are the same as for equation 2.3

Integration of equation 2.7 yields the following:

satwln constant

esHC

R T

Δ= − + (2.8)

Note that a linear plot of satwlnC vs. 1/T has a slope of .

esH

R

Δ−

Example problem 2.3 demonstrates this principle.


Example Problem 2.3

Arnold et al. (1958) report that the saturation solubility of benzene in water at 0, 15, 30, and 61 (all in ºC) is 1.53, 1.79, 1.84, and 2.26, respectively (all in g/L). What is its solubility at 50ºC?

Solution

The molar weight of benzene is 78 g/mol. The information provided is used to create the following table.

T(°C) Cwsat (g/L) Cwsat (mol/L) T (K) 1/T (K–1) Ln Cwsat (mol/L)

0 1.53 0.0196 273.16 0.0037 –3.9329

15 1.79 0.0229 288.16 0.0035 –3.7759

30 1.84 0.0236 303.16 0.0033 –3.7484

61 2.26 0.0289 334.16 0.0030 –3.5428

Plot of satwmol

Ln L

C

vs. 1/T (K–1) yields the following:

If the temperature is 50ºC, which is equal to 323.16 K,

satw

mol 555.64ln 1.8855 3.605

L 323.16C

= − − = −

sat satw w2.719

mol E – 02. 2.12 g / L

LC C

∴ =

=

y = –555.64x –1.8855

–4

–3.95

–3.9

–3.85

–3.8

–3.75

–3.7

–3.65

–3.6

–3.55

–3.5

0.0028 0.003 0.0032 0.0034 0.0036 0.0038 0.004

Ln C

wsa

t (m

ol/L

)

1/T (K–1)


2.2.2 AQUEOUS SOLUBILITY OF A VOLATILE ORGANIC COMPOUND

Many hazardous compounds are volatile; i.e., they have a strong tendency to move out of the water phase and into the air immediately above the water surface. In such cases, partitioning of the hazardous chemical between the air and the water phases becomes a critical parameter and equilibrium distribution of the compound (between the two phases) needs to be quantified. Henry’s law relates the solubility of a gas in a liquid to the partial pressure of the gas above the liquid. It can be expressed as follows:

Hw

iPKC

= (2.9)

where

KH = Henry’s constant

Pi = partial pressure of the gas

Cw = concentration of the hazardous chemical in water

If Pi and Cw are reported in atm and mol/m3, respectively, the units of KH are atm-m3/mol. Henry’s constant values for common hazardous compounds are available from standard references, but it should be noted that this constant varies strongly with temperature. Often, the following regression relationship is used to get this constant at a temperature that is representative of the hazardous waste site:

( )/HA B TK e −= (2.10)

where A and B are regression constants for the chemical and T is the temperature in kelvin. KH has units of atm. m3/mol. See a standard reference (e.g., Haynes, 2016) for the values of A and B for commonly encountered hazardous chemicals. If, however, the values of A and B are not available, Henry’s constant may be approximated by the following:

vapHp

KS

= (2.11)

where pvap is the vapor pressure of the chemical (in atm) and S is its aqueous solubility (in mol/m3). KH has units of atm–m3/mol.


Example Problem 2.4

Estimate the Henry’s constant for chloroform at 30ºC. Use equation 2.11 to estimate the same for a temperature of 25ºC. Comment on the result.

Solution

The values of A and B for chloroform are 9.84 and 4.61 × 103, respectively. For a temperature of 30ºC, T = 303.16 K.

Thus,

34.61 x 109.84

303.16 3H 4.67E 03 atm m / molK e

−

= = − −

pvap and S at 25ºC are 0.257 atm and 64.565 mol/m3, respectively.

Thus, 3

3

0.257 atm using equation 2.11

64.565 mol / m

3.98E 03 atm m / mol

HK =

= − −

It may be noted that the two values estimated, using two different formulae at two different temperature values, are reasonably close.

2.3 PARTITIONING

In hazardous waste decontamination projects, it is often necessary to understand how a hazardous compound will distribute itself between two phases. The two most encountered cases are (1) partitioning between two immiscible liquids, and (2) partitioning between a solid phase (such as soil, sediment, microbial surface) and water.

2.3.1 OCTANOL–WATER PARTITION COEFFICIENT

The octanol–water partition coefficient is a dimensionless constant defined as the distribution of a chemical compound in n-octanol—a surrogate, water immiscible, organic, solvent—and water. It is represented as Kow and is defined as follows:


μ

μow

mg gconcentration in water saturated octanol or

L L

mg gconcentration in octanol saturated water or

L L

n

K

n

− − = − −

(2.12)

It is a measure of the hydrophobicity of the chemical and, thus, its capacity to move from the aqueous phase and become concentrated in soil, biota, sediments, etc. It may be noted that the aqueous solubility of a chemical is a measure of its hydrophilicity, but this alone cannot be inversely correlated to hydrophobicity, or Kow, because some of the water is soluble in n-octanol (2.3 mol/L) and some of the n-octanol is soluble in water (5.5 × 10–3 mol/L).

Values of Kow vary from 1 × 10–3 to 1 × 108 and, therefore, it is more convenient to report the value as log Kow. Appendix B provides log Kow for some widely encountered hazardous chemicals in the environment. If those data are not available for a particular compound from Appendix B or a standard reference, an estimate can be obtained by the following equation:

satow wlog log K a C b= − + (2.13)

where “a” and “b” are constants available for classes of compounds, as shown in the following example.

Example Problem 2.5

Estimate the Kow for anthracene from its aqueous solubility data.

Solution

Anthracene is a polycyclic aromatic hydrocarbon (PAH). Schwarzenbach et al. (1993) report that, for PAHs, “a” and “b” are 0.87 and 0.68, respectively. The same reference also reports that the − satwlogC for

anthracene is 4.48 (mol/L).

Thus, ( )ow4.58

ow

log for anthracene 0.87 4.48 0.68

4.58; 10 3.8E 04

K

K

= × + = ∴ = = +


2.3.2 BIOCONCENTRATION FACTOR

The Bioconcentration Factor (BCF) is an indicator of the ability of a chemical to partition between an aquatic organism and water. It is expressed as follows:

orgC

BCFC

= (2.14)

where

Corg = equilibrium concentration in the aquatic organism (mg/kg or ppm)

C = equilibrium concentration in water (ppm)

Since most chemicals tend to accumulate in the lipids of the aquatic organism, the lipid content is an important metric in the estimation of the BCF. The BCF varies from species to species, but for general classes of aquatic organisms, its value serves as an essential factor in environmental risk assessment. Example problem 2.6 demonstrates this principle.

Example Problem 2.6

Toxaphene was a globally used insecticide in agriculture. Its BCF in fathead minnow (Eisler & Jacknow, 1985) is 52,000 (L/kg). If the concentration of toxaphene in a lake is 100 μg/L, what is its estimated concentration in the tissues of a fathead minnow residing in that lake (in mg/kg)?

Solution

From equation 2.14, toxaphene concentration in fathead minnow = 52,000 L/kg × 100 μg/L = 5.2 × 106 μg/kg = 5,200 mg/kg.

Since BCF is related to the partitioning of a chemical from water to the lipid (of the aquatic animal) which is a hydrophobic substance, it is natural that BCF is positively correlated to Kow. Neely et al. (1974) have established the following relationship for BCF in rainbow trout for chlorinated aliphatics and aromatics:

owlog 0.542log 0.124 BCF K= + (2.15)

Example Problem 2.7

Estimate the BCF of chloroform (CHCl3, a chlorinated aliphatic also known as trichloromethane) in rainbow trout.


Solution

The log Kow of chloroform is 1.93. From equation 2.15, log BCF = [(0.542 × 1.93) + 0.124] = 1.17. Thus, BCF = 101.17 = 14.79 mg/kg

2.4 SORPTION

Sorption involves the preferential movement of a chemical from one phase to another. In hazardous waste remediation, the two phases are liquid (water) and solid. The chemical that accumulates at the interface is called the sorbate, and the solid phase on which this accumulation (adsorption) occurs is called the sorbent. The interaction of the sorbent and the sorbate with the solvent (water) is a complex process; it is divided into the following driving forces for simplification:

• Electrical attraction • Van der Waals forces • Covalent bonds • Hydrogen bonds • Hydrophobic interaction

Volume 2 (chapter 1) discusses sorption in more detail and that discussion is omitted here.

REFERENCES

1. Arnold, D., Plank, C., Erickson, E., and Pike, F. (1958). Solubility of Benzene in Water. Industrial & Engineering Chemistry Chemical and Engineering Data Series, 3(2), 253–256.

2. Haynes, W. H. Ed. (2016). Handbook of Chemistry and Physics, 96th ed. Boca Raton, FL: CRC.

3. Eisler, R. and Jacknow, J. (1985). Toxaphene hazards to fish, wildlife, and invertebrates: a synoptic review. U.S. Fish and Wildlife Service Biological Report, 85(1.4).

4. Neely, W. B., Branson, D. R., and Blau, G. E. (1974). Partition coefficient to measure bioconcentration potential of organic chemicals in fish. Environmental Science & Technology, 8(13), 1113–1115.

5. Schwarzenbach, R. P., Gschwend, P. M., and Lmboden, D. M. (1993). Environmental Organic Chemistry. Hoboken, NJ: Wiley-Interscience.

CHAPTER 3

FATE AND TRANSPORT OF CONTAMINANTS

When a hazardous waste release is suspected at a site, the primary responsibility of the regulatory agency is to mitigate its effect on human health and the environment. To achieve this objective, it becomes indispensable to (i) identify the contaminants, (ii) determine the concentration of the contaminants, and (iii) determine how the contaminants are transformed and transported in the environment. Since the hazardous compound can partition into solid (primarily soil or sediment), liquid (water), and gas (atmosphere) phases, steps (ii) and (iii) are needed for each phase. This chapter covers step (iii) as the contaminant moves through groundwater and air.

3.1 GROUNDWATER CONTAMINANT TRANSPORT

3.1.1 DARCY’S LAW

The movement of water through a porous medium was first experimentally studied by Henry Darcy in 1856 and it was demonstrated that the unidirectional flow of the water along the length of a pipe packed with sand is proportional to the cross-sectional area and head loss along the pipe and inversely proportional to the flow length. Darcy’s law can be written as:

dh

Q KAdl

= − (3.1)


where Q = volumetric flow rate (L3/T) K = proportionality constant, here referred to as hydraulic conductivity (L/T) A = cross-sectional area (L2) dh

dl = hydraulic head gradient (dimensionless)

This equation is also written in terms of specific discharge, or Darcy’s flux, q, which is the volumetric flow rate (Q) divided by the area of cross-section (A).

dh

q Kdl

= − (3.2)

Example Problem 3.1

In an unconfined aquifer with a hydraulic conductivity of 1 m day and a

porosity of 0.3, the contents of a 55-gallon drum containing a K037 waste (wastewater treatment sludge from the production of disulfoton, see Appendix A) are spilled. At the point of the spill, the sum of the pressure and elevation heads is 5m. There is a drinking water well situated 200m downstream of the spill point. If the sum of the pressure and elevation heads at the drinking water well is 1m, how long does it take (in days) for the K037 waste to reach there?

FATE AND TRANSPORT OF CONTAMINANTS • 35

Solution

2

(5 1)1 .

2006.67 10

0.3w

m mhk

mday mLV

n d−

−Δ × Δ = = = ×

Time taken for the spill pressure to reach the drinking water well

2

200 3,000

6.67 10 s

w

L mt days

mVday

−= = =

×

3.1.2 DIFFUSION

Transport phenomenon caused by concentration gradients A solute in an aqueous medium will travel from a zone of higher

concentration to the zone of lower concentration. This phenomenon is called molecular diffusion, or diffusion. The diffusion process will continue as long as a concentration gradient exists, even when the fluid is still. The mass of solute diffusing is proportional to the concentration gradient and is expressed as Fick’s first law. For one-dimensional diffusion, Fick’s first law is:

ddc

F Ddx

= −

(3.3)

where

F = mass flux of solute per unit area per unit time 2

ML

T

Dd = diffusion coefficient ( )2L T c = solute concentration ( )3M L dc

dx = concentration gradient

3M

LL

The negative sign indicates that the movement is from a zone of higher concentration to that of lower concentration. When the concentration varies with time, Fick’s second law is applied. For a 1-D system:


2

2d

c cD

t x

∂ ∂=∂ ∂

(3.4)

where c

t

∂∂

= change in concentration with time 3

ML

T

For a porous media, the rate of diffusion is slower as compared to that in water, since ions have to cover longer pathways, travelling around mineral grains. This is accounted by using an effective diffusion, D*

D* = w Dd (3.5)

The coefficient, w, relates to the tortuosity of the medium (Bear, 1972). Tortuosity is a function of the shape of the flow path followed by

water molecules in a porous media. If L is the straight-line distance between the two ends of a tortuous flow path of length Le, the tortuosity,

T, is defined as T = .eL L In porous media, T is always greater than 1.

Diffusion causes a solute to spread away from its point of introduction into a porous medium, even for a no groundwater flow condition. Figure 3.1 shows the profile of a solute at concentration c0, at time t0, for an interval (x – a) to (x + a). At subsequent time t1, and t2, the solute has spread out, leading to lower concentration within the interval (x – a) to (x + a) but increasing concentration outside of this interval.

Figure 3.1. Sketch of solute spread over time due to diffusion


3.1.3 DISPERSION

Groundwater moves at rates both greater and lesser than the average linear velocity. On a microscopic scale, i.e., over a range with sufficient volume that the effects of single, isolated pores are averaged out, three causal agents exist for this phenomenon:

1. the moving fluid will move faster in the center of the pores than at the edges,

2. some of the fluid particles could travel along longer path in the porous media than other particles to cover the same linear distance, and

3. some pores are bigger than the others, allowing the fluids through them to move faster. These factors are shown in Figure 3.2.

Figure 3.2. Factors governing longitudinal dispersion at the scale of individual pores

If all the groundwater molecules containing a solute move at exactly the same flow rate, it would displace water that does not have the solute and form an abrupt interface between the two waters. Since the incoming solute bearing water does not travel at the same velocity, mixing takes place along the path. This mixing is known as mechanical dispersion, and it causes dilution of the solute near the advancing of flow. The mixing that takes place along the direction of the flow path is called longitudinal dispersion.


An advancing solute front will also tend to spread along the direction normal to the flow due to the divergence of the flow paths at the pore scale, as shown in Figure 3.3. This mixing in directions normal to the flow trajectory is called transverse dispersion.

Figure 3.3. Flow paths in a porous medium causing lateral hydrodynamic dispersion

Assuming that the mechanical dispersion is described by Fick’s law for diffusion (eqs. 2.1 and 2.2) and the amount of mechanical dispersion depends on the average linear velocity, a coefficient of mechanical dispersion can be introduced. This coefficient is equal to a medium property known as dynamic dispersivity, or simply dispersivity, ∝, times the average linear velocity. If i is the principal direction of flow, the following definitions apply:

Coefficient of longitudinal mechanical dispersion = i iϑ∝ (3.6)


where

iϑ = the average linear velocity in the i direction ( )L T i∝ = the dynamic dispersivity in the i direction (L)

And,

Coefficient of transverse mechanical dispersion = j iϑ∝ (3.7)

where

iϑ = the average linear velocity in the i direction ( )L T i∝ = the dynamic dispersivity in the j direction (L)

3.1.4 ADVECTIVE–DISPERSIVE EQUATION

The phenomenon of molecular diffusion cannot be divorced from mechanical dispersion in the flowing groundwater. The two are combined to define a parameter called the hydrodynamic dispersion coefficient, D. It is defined by the following formulae.

*L L iD Dϑ= ∝ + (3.8a)

where

LD = hydrodynamic dispersion coefficient parallel to principal

direction of flow (longitudinal)

L∝ = longitudinal dynamic dispersivity

*T T iD Dϑ= ∝ + (3.8b)

where

TD = hydrodynamic dispersion coefficient perpendicular to

principle direction of flow (transversal)

L∝ = transversal dynamic dispersivity

Figure 3.4 shows the process of hydrodynamic dispersion. A mass of solute is instantaneously injected into the aquifer at time t0 over the interval x = 0 + a. The initial concentration is c0. The advecting groundwater carries

the solute mass with it. This spreads the solute slug, decreasing the maximum concentration with time, as shown for times t1 and t2.


Figure 3.4. Sketch of transport and spread of a solute slug with time due to advection and dispersion

Based on the diffusion model of hydrodynamic dispersion, it can be predicted that the concentration curve will have a Gaussian distribution described by the mean and the variance.

The flowing groundwater carries along with it some dissolved solids. This process is defined as advective transport, or advection. The amount of transport of the solute depends upon its concentration in the groundwater and the flow rate of the groundwater. For one-dimensional flow perpendicular to a unit cross-sectional area of the porous media, the flow rate of water is equal to the average linear velocity times the effective porosity. The rate at which the water flux moves across the unit cross-sectional area of the pore space is defined as the average linear velocity, Vx. It is not the average rate of the movement of the water molecules along individual flow paths, which, due to tortuosity, is greater than the average linear velocity. The porosity through which the flow occurs is the medium’s effective porosity, ne. The effective porosity does not include non-interconnected and dead-end pores.

xe

K dh

n dlϑ = (3.9)


where

( ) ( ) L Lverage linear velocity Khydraulic conductivity T Tx aϑ = e effective porosityn =

( )Lhydraulic gradient Ldhdl =

The one-dimensional mass flux, Fx, due to advection, is equal to the flow rate times the concentration of dissolved solid and is expressed by equation 3.10

x x eF n cϑ= (3.10)

The one-dimensional advection transport equation is

xc c

t xϑ∂ ∂= −

∂ ∂ (3.11)

Solution of the advective transport equation gives a sharp concentration front. On the advancing edge of the front, the concentration is equal to that of the approaching groundwater, whereas on the other side of the front, the concentration is the same as the background value. This is termed as plug flow, with the invading solute front replacing all the pore fluid. Since the geologic materials are heterogeneous, advective transport in different strata leads to differential spreading of the solute fronts in each stratum. For example, a sample of water obtained from a borehole penetrating several strata would be a sample of the composite of water from each stratum, and thus the solute in the sample would be coming from one stratum and uncontaminated groundwater coming from a different stratum, where the average linear velocity is lower. Therefore, the concentration of the contaminant in the composite sample would be less than in the source. In this text, the advection-dispersion equation has been derived based on the works of Freeze and Cherry (1979), Jacob (1972), and Ogata (1970). The following assumptions are made:

1. The porous medium is homogeneous, isotropic, and saturated with fluid.

2. Darcy’s law is valid.

The derivation follows from the conservation of mass of solute flux into and out of a small control volume of the porous media. The flow is


considered at a macroscopic scale, implying it accounts for flow variations across the pores.

The velocity along the groundwater flow direction is taken as Vx. The

solute concentration is C (mass per unit volume of solution). Mass of solute per unit volume of aquifer is porosity, ne, times C. Since the aquifer is assumed to be homogeneous, porosity is taken as a constant.

The solute transport will take place by advection and hydrodynamic dispersion. In i direction, the solute transports can be written as

Advection transport i eV n CdA= (3.12)

Dispersive transport e iC

n D dAi

∂=∂

(3.13)

where dA = cross-sectional area of the element and i direction is normal to that cross-sectional face.

The total mass of solute per unit cross-section area transported in the i direction per unit time, Fi, is the total of the advective and the dispersive components and is expressed as

i i e e iC

F V n C n Di

∂= −∂

(3.14)

The negative sign indicates that the dispersive flux is from a zone of higher concentration to lower.

The total mass of solute entering the control volume is

x y zF dzdy F dxdz F dxdy+ + (3.15)

The total mass of solute leaving the control volume is

yx zx y zFF F

F dx dzdy F dy dxdz F dz dxdyx y z

∂ ∂ ∂ + + + + + ∂ ∂ ∂ (3.16)

The difference between the mass entering and leaving is

yx zFF F

dxdydzx y z

∂ ∂ ∂− + + ∂ ∂ ∂

(3.17)

The rate of mass change in the control volume is


ec

n dxdydzt

∂∂

(3.18)

By the law of mass conversation, the rate of mass change in the control volume is equal to the difference in the mass of the solute entering and the mass leaving.

yx z eFF F C

nx y z t

∂∂ ∂ ∂+ + = −∂ ∂ ∂ ∂

(3.19)

From equation 3.14, it is possible to estimate Fx, Fy, and Fz. Substituting

them in equation 3.19 yields the following, after cancelling ne

( )

x y z

x

C C CD D D

x x y y z z

CV C

x t

∂ ∂ ∂ ∂ ∂ ∂ + + ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ − = ∂ ∂

(3.20)

Equation 3.20 is the three-dimensional mass transport equation for a conservative solute. That is, the solute does not interact with the porous media or undergo biological or radioactive decay.

In a homogeneous medium, , , x y zD D and D show no spatial variation.

Since the coefficient of hydrodynamic dispersion depends on the flow direction, therefore, even for homogeneous isotropic medium, Dx ≠ Dy ≠ Dz , where the average linear velocity Vx is uniform in space, equation 3.20 for 1-D flow in a homogeneous, isotropic, and porous media is

2

2x x

C C CD V

x tx

∂ ∂ ∂− =∂ ∂∂

(3.21)

If the initial and boundary conditions are described as:

C (l, 0) = 0 for l ≥ 0

C (0, t) = C0 for t ≥ 0

C (∞, 0) = 0 for t ≥ 0

an analytical solution to the differential equation 3.21 is available (Ogata, 1970):


0

.1erfc exp erfc

2 2 2x x x

xx x

l V t V l l V tc

c DD t D t

− + = +

(3.22)

The term “erfc” refers to the complementary error function. By definition,

erfc(x) = 1– erf(x) (3.23)

where erf = error function of the argument (x) and is defined as:

( ) 2 20

1 2erf

x xt t

x

x e dt e dtπ π

+ +− −

−

= = (3.24)

Values of the error function and the complementary error function are provided in Appendix D.

Example problem 3.2 demonstrates the use of this equation.

Example Problem 3.2

Using a cylindrical laboratory column (10 cm diameter, 30 cm long) of homogeneous sand, an experiment with a step function input of a nonreactive tracer is conducted. The porosity of the sand is 35 percent;

flow = 0.1 L ;hr hydraulic gradient = 0.05. The

0

0.5c

c= point on the

breakthrough curve arrived 2.0 hr after the tracer initially entered the

column. The 0

0.25c

c= point arrived at 1.4 hr. Estimate the dispersivity of

the sand.

Solution

0

.1erfc exp erfc

2 2 2x x x

xx x

l V t V l l V tc

c DD t D t

− + = +

For conditions when the dispersivity is large, the second term of the equation is negligible.

The dispersivity is measured by ignoring the second term and then checking whether the assumption is correct.


.xQ

VA n

=

2 2L0.1 ; (10 cm) 78.54 cmhr 4

Q Aπ= = × =

3

3

2

L cm hr0.1 1000

cmhr L 3600s1.01 10

. 78.54 cm 0.35xQ

VA n s

−

× = = = ×

×

10.25 erfc ;

2 2

0.5 erfc and 0.4772 2

x

x

x x

x x

l V t

D t

l V t l V t

D t D t

− =

− − ∴ = =

( ) ( )3 cm s30 cm 1.01 10 1.4hr 3600 s hr2 0.477

24.91 cm

xx

l V tD t −

−= = − × × ×

×

=

2 22 2 1620.49 cm cm(24.91) 620.49 cm ; 1.23 10

s s1.4 hr 3600 hrx xD t D

−= = = = ××

For a homogeneous medium with a uniform velocity field, equation 3.20 for two-dimensional flow in the direction of flow parallel to the x-axis is given as

2 2

2 2L T x

C C C CD D V

x tx y

∂ ∂ ∂ ∂+ − =∂ ∂∂ ∂

(3.25)

where DL = the longitudinal hydrodynamic dispersion (L2/T) DT = the transverse hydrodynamic dispersion (L2/T)

The generalized advective-dispersive differential equation in 3-D (Cartesian coordinates) is provided in equation 3.20. With the same approach as that followed for equation 3.21, i.e., with the application of initial and boundary conditions, the following analytical solution can be obtained:


2 2 2

3 3

2 2

( )exp

4 4 48

x

x y zx y z

x V tM y zC

D t D t D tn t D D Dπ

−= × − + +

(3.26)

Example problem 3.3 demonstrates the use of this approach to tackle a groundwater contaminant transport problem.

Example Problem 3.3

As a result of the rupture of a storage tank, 10 m3 liquid containing 100 kg of dissolved arsenic rapidly infiltrated into an aquifer. The average groundwater velocity is 0.7 m/day, the dispersity is 0.15 m, and the coefficient of molecular diffusion of arsenic = 2 × 10–10 m2/s. Arsenic does not absorb or precipitate. Estimate the maximum concentration after the cloud has travelled 600 m. What are the approximate dimensions of the cloud? Assume leakage is a point source and that the aquifer is a homogeneous mixture with uniform flow. The porosity is 0.4.

Solution

2 2 2

3 3

2 2

( )exp

4 4 48

x

x y zx y z

x V tM y zC

D t D t D tn t D D Dπ

−= × − + +

*x L xD V Dα= +

m0.7 dayxV =

0.15 mLα =

2* 10 m2 10 sD−= ×

210daym m0.15 m 0.7 2 10 day 86400 s sxD−= × × + ×

26 m1.215 10 s−= ×

2* 10 m2 10 syD D−= = ×


2* 10 m2 10 szD D−= = ×

600 mm0.7 day

x

x

Lt

V= =

28.57 10 days= ×

77.406 10 seconds= ×

3 3

2 28 x y z

Mc

n t D D Dπ=

( )

6

33 7 6 10 102

100 10

8 0.4 7.406 10 1.215 10 2 10 2 10

mgkg

kg

π − − −

×=

× × × × × × × × × ×

7

3

mg mg4 10 4000

Lmc = × =

Dimensions of the cloud:

26 7m3 2 2 1.215 10 7.406 10 13.45 m

sx xD t sσ −= = × × × × =

26 7m3 2 2 1.215 10 7.406 10 0.17 m

sy yD t sσ −= = × × × × =


3.2 ATMOSPHERIC CONTAMINANT TRANSPORT

The release of a contaminant to the outdoor air can trigger a series of processes resulting in its transport over long distances and time. This transport phenomenon is affected by the wind velocity, dispersion, atmospheric conditions, the surrounding terrain, the nature of the contaminant (its form, reactivity, etc.), and the source of the release. As discussed in chapter 4, inhalation of a hazardous contaminant can trigger many adverse health effects. Therefore, it becomes important to develop a model that can estimate the concentration of a particular contaminant as a function of the distance from the source (in three dimensions) and time. The basic dispersion model is based on Gifford (1961), Pasquill (1961), Pasquill and Smith (1983), and Panofsky and Dutton (1985). The main assumptions of this model are as follows (Turner, 1974):

i. The plume spread has a Gaussian distribution in both the horizontal and vertical planes, with standard deviations of plume concentration distribution in the horizontal and vertical of σy and σz, respectively,

ii. The mean wind speed affecting the plume is u, iii. The emission rate of pollutants is uniform and is denoted by Q, and iv. Total reflection of the plume takes place at the earth’s surface, i.e.,

there is no deposition or reaction at the surface. Figure 3.5 provides a sketch of this model and the coordinate system used.

Figure 3.5. Sketch of the atmospheric dispersion model


The 3-D concentration distribution is calculated by the following equation:

( )πσ σ σ

σ σ

= −

− + − + −

2

2 2

1, , exp

2 2

1 1exp exp

2 2

y z y

z z

Q yC x y z

u

z H z H

(3.27)

where C = concentration of the pollutant at the given coordinates x, y, z (μg/m3) Q = emission rate of the pollutant (μg/s) σy = horizontal dispersion coefficient (m) σz = vertical dispersion coefficient (m) u = mean wind velocity (m/s) x = downward distance along the centerline of the plume (m) y = horizontal distance from the centerline of the plume (m) z = vertical distance from ground level (m) H = plume height (m)

Example problem 3.4 illustrates the use of this equation.

Example Problem 3.4

A factory emits SO2 at a rate of 1500 g/s on a sunny afternoon. The wind velocity is 4 m/s. The atmospheric temperature is 25°C, while that of the stack gas is 320°C. The height of the stack is 130 m; plume height is 150 m, and diameter is 1.5 m. The exit velocity is 12 m/s.

a. What is the centerline concentration 3 km downstream of the release at the plume height?

b. What is the concentration at a point 3 km downstream with a horizontal offset of +500 m and at a height of 60 m from the ground level?

Solution

The following table is used to classify atmospheric stability for the prevalent conditions:

hazardous waste management, volume i · 2018. 5. 3. · 1.2 regulatory framework 3 1.2.1 resource...

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