Api publ 1628a 1996 scan (american petroleum institute)

A P I PUBL*1628A 9b = 0732290 0559306 bA9 = Natural Attenuation Processes API PUBLICATION 1628A FIRST EDITION, JULY 1996 Strategies for To, day4 Environmental Partnership American Petroleum Institute[.]

A P I PUBL*1628A 9b = 0 7 3 2 2 9 0 0559306 bA9 =

API PUBLICATION 1628A

FIRST EDITION, JULY 1996

Strategies for To,

-

day4 Environmental Partnership

American Petroleum Institute

Copyright American Petroleum Institute

Provided by IHS under license with API

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Environmental Partnerrhip

One of the most significant long-term trends affecting the future vitality of the petro- leum industry is the public’s concerns about the environment Recognizing this trend, API member companies have developed a positive, forward looking strategy called STEP:

Strategies for Today’s Environmental Partnership This program aims to address public concerns by improving industry’s environmental, health and safety performance; docu- menting performance improvements; and communicating them to the public The founda- tion of STEP is the API Environmental Mission and Guiding Environmental Principles

APT standards, by promoting the use of sound engineering and operational practices, are

an important means of implementing API’s STEP program

API ENVIRONMENTAL MISSION AND GUIDING

ENVIRONMENTAL PRINCIPLES

The members of the American Petroleum Institute are dedicated to continuous efforts to improve the compatibility of our operations with the environment while economically developing energy resources and supplying high quality products and services to consum- ers The members recognize the importance of efficiently meeting society’s needs and our responsibility to work with the public, the government, and others to develop and to use natural resources in an environmentally sound manner while protecting the health and safety of our employees and the public To meet these responsibilities, API members pledge to manage our businesses according to these principles:

To recognize and to respond to community concerns about our raw materials, prod- ucts and operations

To operate our plants and facilities, and to handle our raw materials and products in a manner that protects the environment, and the safety and health of our employees and the public

To make safety, health and environmental considerations a priority in our planning, and our development of new products and processes

To advise promptly appropriate officials, employees, customers and the public of information on significant industry-related safety, health and environmental hazards, and to recommend protective measures

To counsel customers, transporters and others in the safe use, transportation and dis- posal of our raw materials, products and waste materiais

To economically develop and produce natural resources and to conserve those resources by using energy efficiently

To extend knowledge by conducting or supporting research on the safety, health and environmental effects of our raw materials, products, processes and waste materials

To commit to reduce overall emissions and waste generation

To work with others to resolve problems created by handling and disposal of hazard- ous substances from our operations

To participate with government and others in creating responsible laws, regulations and standards to safeguard the community, workplace and environment

To promote these principles and practices by sharing experiences and offering assis- tance to others who produce, handle, use, transport or dispose of similar raw materi-

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Natural Attenuation Processes

Manufacturing, Distribution and Marketing Department

API PUBLICATION 1628A FIRST EDITION, JULY 1996

American Petroleum Institute

Copyright American Petroleum Institute

Provided by IHS under license with API

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Copyright O 1996 American Petroleum Institute

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FOREWORD

API publications may be used by anyone desiring to do so Every effort has been made

by the Institute to assure the accuracy and reliability of the data contained in them; how- ever, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or dam- age resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict

Suggested revisions are invited and should be submitted to the director of the Manufac- turing, Distribution and Marketing Department American Petroleum Institute, 1220 L Street, N.W., Washington, D.C 20005

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CONTENTS

SECTION 1-INTRODUCTION 1

1.1 Purpose and Scope 1

1.2 LNAPL Migration 1

1.3 Vapor and Dissolved Phase Migration 1

SECTION 2-PHYSICOCHEMICAL PROCESS 1

2.1 General 1

2.2 Adsorption and Retardation 1

2.3 Dispersion 2

2.4 Diffusion 2

SECTION 3-BIOLOGICAL PROCESS 5

3.1 General 5

3.2 Aerobic Biodegradation 6

3.3 Anaerobic Biodegradation 6

SECTION &SUGGESTED PARAMETERS TO BE MONITORED 9

4.1 General 9

4.2 Relative Plume Lengths 9

4.3 Water Quality Changes 9

4.4 Vadose Zone Air Quality Changes 9

SECTION 5 - C A S E STUDY 10

APPENDIX A-BIBLIOGRAPHY 15

Figures l-Relationship Between Aqueous Solubility and Octanol-Water Partition Coefficient for Several Groups of Organic Compounds (from Domenico and Schwartz 1990) 3

After Pfannkuch (1962) (from Domenico and Schwartz, 1990) 4

Dispersivity and Magnitude of Plume Length, After Gelhar et al., (1985) (from Domenico and Schwartz 1990) 5

Aromatic Hydrocarbons (from Cozzarelli et al., 1990) 8

(from Caldwell, et al., 1992) 12

(from Caldwell, et al., 1992) 13

Biodegradation (from Caldwell, et al., 1992) 14

2-Relationship Between Longitudinal Dispersivity and Flow Velocity, 3-Compilation of Observed Relationships Between Longitudinal &Oxidized Intermediates of Anaerobic Biodegradation of Selected 5-Summary of Results from Laboratory Microbial Evaluation 6-Results of Simulated and Predicted Distribution of BTEX Constituents 7-Results of Predicted Distribution of BTEX With and Without

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Tables 1-Field-Measured Groundwater and Soil Air Quality Parameters 10

2-Groundwater Analytical Results 11

vi

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Natural Attenuation Processes

ceases movement when the lateral and vertical spreading has disseminated it to the extent that the forces driving its movement are overcome by capillary forces in both the

vadose and saturated zones These hydrocarbons are then trapped as a residual saturation of LNAPL in these soils and are a source for continued migration in the vapor phase or in the dissolved phase

This publication describes the physical, chemical, and

biological processes that decrease the concentrations and

ultimately limit the extent of the dissolved plume migrating

from a hydrocarbon release It is primarily focused on the

more soluble hydrocarbon fraction that makes up the dissolved

plume Emphasis is given to the biological processes that can

play a major role in the attenuation of a dissolved plume

After being released into the subsurface, petroleum

hydrocarbons can be affected by the physical, chemical, and

biological processes in the immediate vicinity Initially, the

hydrocarbons migrate through the vadose zone as a separate

light non-aqueous phase liquid (LNAPL), moving down-

ward in response to gravity, and laterally in response to

changes in permeabilities encountered This migration con-

tinues until (a) the migrating volume is immobilized by cap-

illary forces and held within the pores of the soil in a

residual state, (b) the liquid reaches an impermeable layer

and perches upon it, or (c) the capillary fringe of the water

,table is encountered where the liquid begins to migrate lat-

erally downgradient When the hydrocarbons reach the cap-

illary fringe, they can migrate laterally because they are

lighter, and less dense than water The fluctuations of the

water table and capillary fringe cause this LNAPL layer to

rise and fall accordingly This coats the soils encountering

the LNAPL and, in time, creates a smear zone marking the

1.3 Vapor and Dissolved Phase Migration

Once immobilized, the hydrocarbon compounds can

migrate further as vapors or dissolved in water Those com-

pounds that can transfer by volatilization into the air in the

vadose zone can eventually migrate as a vapor phase

through the land surface and discharge into the atmosphere The compounds in contact with water transfer into the aque-

ous phase and are transported as a dissolved phase

The transfer into the vapor and dissolved phases provides the means for the hydrocarbon compounds to potentially migrate away from the hydrocarbon source area Once released from the source area, the concentrations of the hydrocarbon compounds are decreased by several physical, chemical, and biological processes Given sufficient flow distances and times, these processes can ultimately result

in the complete attenuation of the dissolved hydrocarbon compounds These processes are described in this publica- tion

2.1 General

The physicochemical processes in general decrease dis-

solved hydrocarbon concentrations by redistributing the

hydrocarbon mass In doing so, however, these processes

can render the petroleum hydrocarbon compounds more

bioavailable and hasten their attenuation by biodegrada-

tion Several major physicochemical processes are dis-

cussed in this section For further overview of these

processes, refer to the book by Domenico and Schwartz

111

2.2 Adsorption and Retardation

Because petroleum hydrocarbon molecules are to some

degree nonpolar, there is a finite limit to their solubility in a

more polar substance such as water This results in low

(<lo” mg/L) to moderate (lo3 m a ) aqueous solubility

limits for the petroleum hydrocarbon compounds, as well

their tendency to partition to other forms of organic carbon

in the subsurface This characteristic can cause their migra-

tion in the dissolved plume as micelles, that is “packs” of

organic molecules with the more hydrophilic compounds or the more hydrophilic portions of each molecule on the outer surface of the micelle It also leads to adsorption of the petroleum hydrocarbon compounds to the organic coatings

of the soil particles

The tendency to adsorb to the subsurface material is dif- ferent for each of the petroleum hydrocarbon compounds; the compounds that sorb strongly tend to migrate downgra- dient more slowly than those that sorb less strongly This

leads to a “chromatographic” effect within a migrating dis- solved plume, with the more mobile compounds arriving at

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2 API PUBLICATION 1628A

downgradient locations before the more retarded com-

pounds

This adsorption property is represented in transport equa-

tions by the reraniation factor (Rf) which is defined as:

The distribution coefficient, Kd, is derived from the rela-

tionship between aqueous concentration and degree of

adsorption as defined by a linear Freundlich isotherm Sev-

eral studies have determined a relationship in turn between the

distribution coefficient and the mass fraction of organic carbon:

Kd = Kocfoc

Where:

foc = mass fraction of organic carbon

K, = partition coefficient between soil organic carbon

These studies have also found a good statistical correla-

tion between the partition coefficient and the octanoltwater

partition coefficient, Kow and between a compound's solu-

bility and KO,,, Examples of these correlations are:

[21

and water

log(K,) = -0.21 + lOg(K0W) lOg(K,) = 0.44 0.54 lOg(Sm)

[31

log(K,) = 0.49 + 0.72 log(Kow)

[41

log(&) = 0.088 + 0.909 log(Kow) log(&) = 3.95 - 0.62 log(&')

Where:

Sm = aqueous solubility (mole fraction)

S = aqueous solubility (mg/L)

Relationships between aqueous solubility and the

ocianoltwater partition coefficient are well established

Examples of the relationship are shown in Figure 1 Conse-

quently, the parameters that typically need to be obtained in

order to assess the sorption and retardation of organic com-

pounds are the soil bulk density (%), the octanoltwater par-

tition coefficient (GW), and the mass fraction of soil organic

carbon voe)

2.3 Dispersion

The spreading and mixing of chemical compounds in

groundwater caused by diffusion and mixing due to micro-

scopic variations in velocities within and between pores is

defined as disperswn Because dissolved hydrocarbon com-

pounds typically migrate through subsurface materials that are not homogeneous, there are inherently different constit- uent migration rates in different portions of the plume This

-process can result in an apparent lateral spreading from the plume's flanks and an apparent spreading of the plume's leading edge This apparent spreading is represented by transverse and longitudinal dispersivity coefficients respec- tively Empirical field studies of dispersion have found rela- tionships with flow velocity and scale of plume Figure 2 shows the relationship between longitudinal dispersivity and flow velocity; for greater flow velocities, the apparent longitudinal dispersivity determined in the field can be sev- eral orders of magnitude greater than the dispersivity mea- sured in the laboratory

Similarly, Figure 3 shows a compilation of observed rela- tionships between longitudinal dispersivity and the magni- tude of plume length While these empirical relationships can be useful, these studies are known to be hampered by limitations in the field data (for example, large spacing between observation wells or poor definition of the initial volume occupied by injected tracer) and limited information

on field conditions (for example, definition of the perme- ability distribution or temporal fluctuations in the flow system) Recent quantitative studies that take into account the stratigraphic heterogeneity of the test site have found dispersivity values more in line with labora- tory values

2.4 Diffusion

The migration of petroleum hydrocarbon compounds because of concentration gradients is known as diffusion This is commonly described by Fick's Law:

cm2/sec in water Equations for estimating air and water diffusion coefficients for petroleum hydrocarbon com- pounds can be found in the article by Tucker and Nelken While seemingly making only a modest contribution to the redistribution in permeable settings, diffusion can be a dominant transport mechanism in low-permeability settings

in both the vadose and saturated zones [6,7] The diffusion

151

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process is also potentially important in the replenishment of

dissolved oxygen in the near-water table portion of the satu-

rated zone by influx from the vadose zone [81 For these

reasons, it can be important to determine diffusion coeffi-

cients for the petroleum hydrocarbon compounds of inter- est, and to monitor oxygen ( 0 2 ) , carbon dioxide (COz), and methane (CH4) in the soil air in the base of the vadose zone

Solubility in Water, log S, (moles per liter)

Figure 1-Relationship Between Aqueous Solubility and Octanol-water Partition Coefficient for Several Groups of

Organic Compounds (from Domenico and Schwartz, 1990)

Figure 2-Relationship Between Longitudinal Dispersiviiy and Flow Velocity, After Pfannkuch (1 962)

(from Domenico and Schwartz, 1990)

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Figure 3-Compilation of Observed Relationships Between Longitudinal Dispersivity and

Magnitude of Plume Length, After Gelhar et al, (1985)

(from Domenico and Schwartz, 1990)

3.1 General

The biological processes are chiefly responsible for the

transformation of the dissolved hydrocarbon compounds to

simpler organic and inorganic compounds These processes

are almost entirely carried out by the microbiological, or

microbial, populations inhabiting the subsurface These

microbial populations can mineralize the hydrocarbon com-

pounds, transforming them into carbon dioxide (COz),

water (H20), and salts This microbial transformation pro-

cess, known as biodegradation, is the major attenuation

mechanism for petroleum hydrocarbons in the subsurface

Note: While there has been little research on the other major removal mechanism, volatilization from the plume, this is thought to be minor in comparison to biodegradation for petroleum hydrocarbon compounds [9] A dynamic equilib- rium will be reached with the release rate of hydrocarbon compounds in the source area balanced by the biodegrada- tion rates within the dissolved phase plume, with the rate of biodegradation determining the ultimate length of the plume This equilibrium will result in a generally stabilized plume

Biodegradation of hydrocarbons is, in essence, an oxida- tion-reduction reaction mediated by the subsurface micro-