University of Iowa
Iowa Research Online
Theses and Dissertations
Fall 2011
Modeling hydrogen sulfide emissions: are current
swine animal feeding operation regulations
effective at protecting against hydrogen sulfide
exposure in Iowa?
Travis Lee Kleinschmidt
University of Iowa
Copyright 2011 Travis Lee Kleinschmidt
This thesis is available at Iowa Research Online: http://ir.uiowa.edu/etd/2728
Recommended Citation
Kleinschmidt, Travis Lee. "Modeling hydrogen sulfide emissions: are current swine animal feeding operation regulations effective at
protecting against hydrogen sulfide exposure in Iowa?." MS (Master of Science) thesis, University of Iowa, 2011.
http://ir.uiowa.edu/etd/2728.
Follow this and additional works at: http://ir.uiowa.edu/etd
Part of the Occupational Health and Industrial Hygiene Commons
MODELING HYDROGEN SULFIDE EMISSIONS: ARE CURRENT SWINE
ANIMAL FEEDING OPERATION REGULATIONS EFFECTIVE AT PROTECTING
AGAINST HYDROGEN SULFIDE EXPOSURE IN IOWA?
by
Travis Lee Kleinschmidt
A thesis submitted in partial fulfillment
of the requirements for the Master of
Science degree in Occupational and Environmental Health
in the Graduate College of
The University of Iowa
December 2011
Thesis Supervisor: Professor Patrick O'Shaughnessy
Copyright by
TRAVIS LEE KLEINSCHMIDT
2011
All Rights Reserved
Graduate College
The University of Iowa
Iowa City, Iowa
CERTIFICATE OF APPROVAL
_______________________
MASTER'S THESIS
_______________
This is to certify that the Master's thesis of
Travis Lee Kleinschmidt
has been approved by the Examining Committee
for the thesis requirement for the Master of Science
degree in Occupational and Environmental Health at the December 2011
graduation.
Thesis Committee: ___________________________________
Patrick O'Shaughnessy, Thesis Supervisor
___________________________________
Lucie Laurian
___________________________________
Marc Linderman
___________________________________
Marizen Ramirez
ACKNOWLEDGMENTS
I would like to express my gratitude to Dr. Patrick O’Shaughnessy for his
guidance, support, and encouragement as my academic advisor and thesis supervisor. My
sincere appreciation also extends to my other thesis committee members: Drs. Lucie
Laurian, Marc Linderman, and Marizen Ramirez for their valuable suggestions and
comments on this thesis and general interest in my success. With their unique
backgrounds, each provided a different and valuable perspective of my work. I am
particularly grateful to Dr. Linderman for meeting with me weekly to provide technical
GIS guidance and constructive feedback throughout the completion of this work. I would
also like to thank Ralph Altmaier for his guidance and support through weekly, and
sometimes daily conversations, on AERMOD plume dispersion modeling, the general
composition of CAFO farming practices, and how to write a Thesis.
Without the support of my family the completion of this thesis would not have
been possible. I would especially like to thank my lovely fiancée, Sarah Starks, for her
brilliant suggestions, unwavering support, encouragement, and editing skills. She did not
laugh once my incomplete sentences, poor grammer, and punctuation, errors. She has
been a great blessing in my life. I am especially appreciative of my parents, Jan and the
late Charles Kleinschmidt, for encouraging my education, giving me the opportunity to
become whatever I wanted to be, and guidance through life. To them, I will always be
“boy wonder”.
ii
TABLE OF CONTENTS
LIST OF TABLES .......................................................................................................... v
LIST OF FIGURES ........................................................................................................vi
CHAPTER I INTRODUCTION AND LITERATURE REVIEW ................................... 1
Hydrogen Sulfide Human Health Effects ....................................................... 3
Environmental Exposure from CAFOs .......................................................... 5
Hydrogen Sulfide Levels and Limits ............................................................. 8
Separation Distance Requirements .............................................................. 10
Plume Dispersion Modeling ........................................................................ 11
Plume Dispersion Modeling and Geographic Information Systems.............. 13
Study Aims ................................................................................................. 15
CHAPTER II ASSESSING THE EFFICIENCY OF SEPARATION DISTANCES
IN MITIGATING EFFECTS OF HYDROGEN SULFIDE
CONCENTRATIONS EMANATING FROM SWINE CAFOS .................. 17
Introduction ................................................................................................ 17
Study Aims ................................................................................................. 19
Material and Methods.................................................................................. 19
Optimal Setting within AERMOD Dispersion Modeling ...................... 19
ArcGIS Software .................................................................................. 22
CAFO Geodatabase Acquisition and Modification ............................... 22
Density Analyses and the Identification of Swine Weight Dense
Areas.................................................................................................... 23
Search Radius based on Hydrogen Sulfide Concentrations ................... 25
Modeling Hydrogen Sulfide Concentrations in AERMOD ................... 27
Determining if Current CAFO Setback Distance Regulations in
Iowa Protect for the HES and HEV of Hydrogen Sulfide ...................... 28
Coupling AERMOD with ArcGIS ................................................. 28
Interpolation .................................................................................. 28
Separation Distances ..................................................................... 29
Comparing Separation Distances to Estimated Hydrogen
Sulfide Concentrations .................................................................. 30
Results and Discussion ................................................................................ 30
Determination of Search Radius based on Hydrogen Sulfide
Contribution ......................................................................................... 30
Kernel Density Analysis and CAFO Point Density Analysis................. 30
Highest Swine Weight Dense Area Characteristics ............................... 31
Spatial Analysis Largest Swine CAFO ................................................. 33
First-High, Hourly, Hydrogen Sulfide Concentrations and
Separation Distance for Analysis of the HEV ................................ 34
Eighth-High, Hourly Hydrogen Sulfide Concentrations and
Separation Distance for Analysis of the HES ................................. 34
iii
Spatial Analysis of the Highest Swine Weight Dense Area ................... 35
First-High, Hourly, Hydrogen Sulfide Concentrations and
Separation Distances for Analysis of the HEV ............................... 35
Eighth-High, Hourly Hydrogen Sulfide Concentrations and
Separation Distances for Analysis of the HES ............................... 36
Conclusions ................................................................................................ 36
CHAPTER III DISCUSSION ........................................................................................ 56
REFERENCES .............................................................................................................. 59
iv
LIST OF TABLES
Table 1. Swine Weight by Swine Type .......................................................................... 54
Table 2. High Swine Weight Dense Area Characteristics ............................................... 55
v
LIST OF FIGURES
Figure 1. Largest Swine CAFO Area and Volume Sources ............................................ 39
Figure 2. Largest Swine CAFO Polar Receptor Grid ...................................................... 40
Figure 3. Uniform Cartesian Grid in Largest Swine CAFO Area .................................... 41
Figure 4. Largest Swine CAFO Average Estimated Hydrogen Sulfide
Concentrations and Distance Away from the Source ............................................. 42
Figure 5. Swine Weight Kernel Dense Areas in Iowa ..................................................... 43
Figure 6. CAFO Point Dense Areas in Iowa ................................................................... 44
Figure 7. Seven Swine Weight Dense Areas .................................................................. 45
Figure 8. Box Plot of Swine Weight Dense Areas .......................................................... 46
Figure 9. Scatter Plot of Selected Study Area CAFOs .................................................... 47
Figure 10. First-Highest, Hourly, Hydrogen Sulfide Concentrations for Largest
Swine CAFO Area ........................................................................................ 48
Figure 11. Eighth-Highest, Hourly, Hydrogen Sulfide Concentrations for Largest
Swine CAFO Area ........................................................................................ 49
Figure 12. Swine Weight Dense Area First-Highest, Hourly, Hydrogen Sulfide
Concentrations and Public Use Separated Distances ...................................... 50
Figure 13. Swine Weight Dense Area First-Highest, Hourly, Hydrogen Sulfide
Concentrations and RBCS Separated Distances ............................................. 51
Figure 14. Swine Weight Dense Area. Eighth-Highest, Hourly, Hydrogen Sulfide
Concentrations and Public Use Separated Distances ...................................... 52
Figure 15. Swine Weight Dense Area Eighth-Highest, Hourly, Hydrogen Sulfide
Concentrations and RBCS Separated Distances ............................................. 53
vi
1
CHAPTER I
INTRODUCTION AND LITERATURE REVIEW
The United States Environmental Protection Agency (EPA) estimates that
confined farm animals generate three times more excrement than is produced by humans
in the U.S. (U.S. Environmental Protection Agency, 2003a). Much of the toxic substances
emitted from Concentrated Animal Feeding Operations (CAFOs) emanate from manure
stored on-site. According to the U.S. Government Accountability Office (GAO), CAFOs
can produce approximately 2,800 tons to more than 1.6 million tons of manure from a
large CAFO facility each year depending on the animal type and number at the site (U.S.
Government Accountability Office, 2008).
Given the substantial quantity of manure, CAFOs can emit a considerable amount
of pollutants into the general environment, which include volatile organic compounds,
ammonia, hydrogen sulfide, carbon dioxide, malodorous vapors, and particles
contaminated with harmful microorganisms (Heederik et al., 2007). There is growing
concern that these pollutants may lead to adverse health effects among people living
close to the site. In particular, hydrogen sulfide is both a directly toxic substance as well
as malodorous to humans. In many states, separation distances from CAFOs to
residences, public areas, and public buildings have been established to protect human
health via the air and water. Iowa law mandates that, an individual or company seeking to
construct a CAFO over a certain size must build it at a minimum specified distance
(separation distance) from homes, schools, and other types of public areas (separated
locations) (Environmental Protection Commission, 2010).
In Iowa, few studies have been conducted to determine if current separation
distances mitigate effects of air pollution from swine units. This study will use a
validated plume dispersion modeling technique to estimate concentrations of hydrogen
sulfide emitted from the largest swine CAFO in Iowa as well as several swine CAFOs
2
located in an area of Iowa that is swine animal dense. The plumes generated will then be
compared to the separation distance requirements in Iowa to establish if these distances
protect human health based upon Iowa health effect value (HEV) and a health effects
standard (HES) of hydrogen sulfide established by a field study through the
Environmental Protection Commission (Environmental Protection Commission, 2004).
The initial estimation of hydrogen sulfide concentration will be conducted using air
plume dispersion software called AERMOD developed by Lakes Environmental (Lakes
Environmental, 2011). The spatial analysis will be performed using Geographic
Information Systems (GIS) software called ArcGIS developed by the Environmental
Systems Research Institute, Inc. (ESRI) (Environmental Services Research Institute,
2011).
The HEV for Iowa is 30 parts per billion (ppb) for a one-hour time weighted
average concentration of hydrogen sulfide. It has been established that this level of
airborne pollutant is commonly known to cause a material and verifiable adverse health
effects. However, Iowa law does not require the source of emissions to develop plans to
abate these concentration levels if they are exceeded. Instead, the state of Iowa has
determined that the Health Effects Standard (HES) for hydrogen sulfide is “exceeded at a
monitoring site when the daily maximum one-hour average concentration exceeds 30 ppb
more than seven times per year” (Environmental Protection Commission, 2010). The
Iowa Department of Natural Resources (IDNR) would develop plans and abate hydrogen
sulfide emissions from CAFOs if hydrogen sulfide levels measured at separated locations
exceeded the HES for hydrogen sulfide.
The National Agricultural Statistics Service (NASS) reports that over 31 billion
pounds of swine were produced in the U.S. in 2009. In Iowa alone, over 9.6 billion
pounds of swine were produced more than doubling the next highest producing state,
North Carolina (National Agricultural Statistics Service, 2010). Additionally, Iowa’s
population was 2,926,324 in 2000 of which 38.9% were considered to be living in rural
3
locations (U.S. Census Bureau, 2000). These hog and pig production facilities are also
located in rural areas and there may be situations where rural residents are living,
working, or playing in close proximity to these facilities. Consequently, these individuals
may be at greater risk of adverse health outcomes from swine facilities.
Furthermore, the production of hogs and pigs has undergone a trend toward
consolidation of smaller livestock operations into fewer but much larger operations. The
U.S. Government Accountability Office (GAO) estimated in 2008 that the number of
farm animals raised in large-scale industrial production facilities increased 246% from
1982 to 2002 (U.S. Government Accountability Office, 2008). This has led to intensive
production cycles, increased concentration of manure, and greater risk of exposure to
hydrogen sulfide. For a livestock operation to be defined as a CAFO, it must first be
considered an animal feeding operation (AFO). The U.S. EPA defines an AFO as a
“livestock operation that confines animals for at least 45 days in a 12-month period in an
area where grass or other vegetation is not maintained during the normal growing season”
(U.S. Environmental Protection Agency, 2003a). If a swine operation is considered an
AFO it may also be considered a CAFO if it contains a certain number of swine,
depending on the type and size of the animal, and the method in which the operation
discharges its waste (U.S. Environmental Protection Agency, 2003a). It is estimated that
there are approximately 18,800 CAFOs in the U.S. as of 2006 and this number continues
to grow (U.S. Environmental Protection Agency, 2006). These confined situations lead to
a large concentration of animals, feed, manure, urine, and inhalable pollutants including
hydrogen sulfide.
Hydrogen Sulfide Human Health Effects
Hydrogen sulfide is a colorless, flammable gas with an odor similar to rotten
eggs. It is found naturally through crude petroleum, natural gas, volcanic gases, and the
anaerobic bacterial reduction of sulfates. Additionally, it can be produced through human
4
or animal activity such as the production of coal, natural gases, paper manufacturing, and
as an agricultural by-product (World Health Organization, 2003). Concentrations of
hydrogen sulfide in ambient air as a result of natural sources have been estimated to be
between 0.00014 and 0.0004 mg per m3 (0.11 to 0.33 ppb) in the U.S. (U.S.
Environmental Protection Agency, 1993). Hydrogen sulfide life-times in air range from
approximately 1 day in the summer to 42 days in the winter (Bottenheim, 1980).
Human exposure to hydrogen sulfide exposure is primarily through inhalation.
Vulnerable populations include children, the elderly, and individuals with chronic or
acute pulmonary disorders. According to the U.S. EPA, acute exposure to hydrogen
sulfide greater than 200,000 ppb (2780 mg per m3) can result in loss of consciousness or
death within seconds to minutes suggesting that it is rapidly absorbed through the lungs
(U.S. Environmental Protection Agency, 2003b). Chronic exposure to humans and
animals has been associated with the onset of respiratory illnesses, neurobehavioral
symptoms, and psychological impairments (Hannah & Roth, 1991; Hirsch & Zavala,
1999; U.S. Environmental Protection Agency, 2003b; World Health Organization, 2003).
While there is existing data on the effects of chronic exposure to hydrogen sulfide, the
dose response relationship is not yet fully understood (U.S. Environmental Protection
Agency, 2003b). Given the sheer volume and size of CAFOs large amounts of animal
waste are produced and stored on-site in lagoons and other storage facilities. Due to
anaerobic digestion of the waste material, exposure to hydrogen sulfide is prevalent
among agricultural workers as well as the general population through inhalation (Morse
et al. 1981).
In a study by Donham et al. (2006) air sampling was collected from lawns of 35
homes neighboring three types of swine farms. They found that hydrogen sulfide
concentrations were higher near swine confinement facilities rather than hoop structure
buildings (tentlike structures) and control areas. They also found that hydrogen sulfide
concentrations exceeded Agency for Toxic Substances Disease Registry (ATSDR)
5
recommended limits of 30 ppb at two of the homes near the CAFO areas (Agency for
Toxic Substances and Disease Registry, 2006).
Environmental Exposure from CAFOs
Adverse health effects related to exposure of CAFO-related contaminants is welldocumented in CAFO workers (De Fruyt et al., 1998; Kilburn, 2003; Morse et al., 1981;
Von Essen & Donham, 1999). However, less is known about their impact on the health
of residents in nearby communities. Several studies have suggested that residents living
near CAFOs are at increased risk of adverse health effects when exposed to contaminants
emitted from these facilities. These studies are briefly described below.
Schinasi et al. (2011) examined associations of monitored air pollutants with
physical symptoms and lung function in individuals living within 1.5 miles of hog
operations. Monitors were set in 16 eastern North Carolina communities and included
101 adults who reported sitting outside their homes twice a day for 10 minutes. The
authors found that hydrogen sulfide and odor were associated with irritation and
respiratory symptoms 12 hours after exposure. Additionally, odor, endotoxin, and
Particulate Matter (PM) 2.5 were associated with wheezing, declines in forced expiratory
volume, sore throat, chest tightness, and nausea.
Wing and Wolf (2000) surveyed 155 rural residents in three communities. The
first community was in the vicinity of a 6,000 head hog operation, the second was in the
vicinity of two intensive cattle operations, and the third community did not have a
livestock operation. The authors found that respiratory and gastrointestinal problems and
mucous membrane irritation were elevated among residents in the vicinity of the hog
operation. Residents near the hog operation also reported increased occurrences of
headaches, runny nose, sore throat, excessive coughing, diarrhea, and burning eyes
compared with the community without a livestock operation. The quality of life,
6
indicated by the number of times residents could open their window or go outside, was
greatly reduced near the hog operation compared with the other two communities.
Thu et al. (1997) assessed the physical and mental health of residents living in the
vicinity of a large-scale swine confinement operation. Data was collected through 18
personal interviews of neighbors living within two miles of a 4,000 head swine
production facility and compared with a sample of rural residents who did not reside near
livestock production. Results indicated that neighbors of the large-scale swine
confinement operation experienced significantly higher rates of toxic or inflammatory
effects on the respiratory tract including inflammation of the bronchi and bronchioles,
chronic bronchitis, and hyperactive airways. These symptoms are also associated with
environmental exposures to air pollution, chronic dust exposure, and long-term cigarette
smoking. Neighbors of the large-scale swine operation also experienced increased rates
of headaches, eye irritation, nausea, weakness, and chest tightness although these
findings were not statistically significant. There was little evidence to suggest neighbors
of the large-scale swine operation suffered higher rates of anxiety or depression. A larger
sample size was needed to improve study power.
Merchant et al. (2005) studied asthma outcomes and children living in urban and
rural areas. The study group consisted of 644 children aged 17 or younger. The study
found a high prevalence of asthma health outcomes among farm children living on farms
that raised swine (44.1%, p = 0.01) and raised swine and added antibiotics to feed
(55.8%, p = 0.013) compared with children living on a farm with no swine (26.2%). The
study found that farms who added antibiotics to feed were usually much larger than other
swine production facilities indicating that larger swine facilities were associated with a
higher prevalence of asthma.
Mirabelli, Wing, Marshall, and Wilcosky (2006) also investigated asthma
symptoms of children near swine CAFOs. During the 1999-2000 school year, 169 North
Carolina adolescents aged 12 to 14 years answered questions about their respiratory
7
symptoms, allergies, medications, socioeconomic status, and household environments. In
addition, it was determined whether or not certain schools in North Carolina were
exposed to air pollution from CAFOs. The prevalence of wheezing during the past year
was slightly higher at schools that were estimated to be exposed to airborne contaminants
from CAFOs. For students who reported allergies, the prevalence of wheezing within the
past year was 5% higher at schools located within three miles of an operation relative to
those beyond three miles and 24% higher at schools in which livestock odor was
noticeable indoors twice per month.
Similarly, Sigurdarson and Kline (2006) studied asthma prevalence of children,
kindergarten through 5th grade in two Iowa schools. One school was adjacent to a CAFO
while the other was distant from any large-scale animal operation. The students were
given a questionnaire asking housing characteristics, the frequency of asthma symptoms,
medication use, possible nighttime and exercise asthma symptoms, and other asthmarelated issues. The results indicated that the school adjacent to a CAFO had significantly
increased prevalence of physician-diagnosed asthma (Odds Ratio = 5.71, p = 0.004) when
considering confounding variables. No difference was found in asthma severity between
the two groups.
Radon et al. (2007) surveyed 6,937 individuals from four German towns with a
high density of CAFOs from 2002 to 2004. The survey was designed to assess respiratory
health in neighbors of CAFOs. The authors found that the number of farm animal
production facilities near the residence was a predictor of self-reported wheezing and
decreased forced expiratory volume. However the size of the animal production facility
was not a predictor of allergic rhinitis or specific sensitization. The prevalence of selfreported asthma symptoms and nasal allergies also increased with self-reported odor
annoyance.
Schiffman et al. (1995) were able to associate adverse health effects from the
malodorous smell emanating from large-scale hog operations. Using a Profile of Mood
8
States and a total mood disturbance score on 44 subjects living near a swine operation
compared with 44 control subjects, the study found significant differences in mood
between the two groups. Person’s living near intensive swine operations who experienced
odors reported significantly greater tension, greater depression, more anger, more fatigue,
and more confusion than the control subjects.
Hydrogen Sulfide Levels and Limits
There is no consensus on the level or limit of hydrogen sulfide acute and chronic
exposure. Many organizations and agencies have developed different levels and limits to
protect human health. The dose response relationship between low levels of hydrogen
sulfide and adverse health outcomes is not well known.
While Iowa Environmental Protection Commission was determining the HEV and
HES for hydrogen sulfide, a group of researchers from Iowa State University and the
University of Iowa recommended an upper limit of 15 ppb over a one hour-time weighted
average for hydrogen sulfide at a residence or public use area and 70 ppb over a one
hour-time weighted average at the property line. No more than seven exceedences of
these levels would be allowed per calendar year without notice to residents and the IDNR
(Iowa State University and The University of Iowa Study Group, 2002). Seven
exceedences would be allowed because there may be occasions where stored manure
must be removed from their pits and hydrogen sulfide levels at or near the facilities may
be significantly higher than during normal conditions (Iowa Department of Natural
Resources, 2004b). Justification of the levels was determined by current
recommendations of several public health agencies, recommendations from surrounding
states, and the consideration of additive or synergistic effects from many different
pollutants emanating from CAFOs. Specifically, the researchers believed hydrogen
sulfide and ammonia resulted in an additive effect, thus in order to protect against
9
adverse health effects the exposure limits for each pollutant should be halved (Iowa
Department of Natural Resources, 2004b).
Through the rulemaking process by the Environmental Protection Commission, a
hydrogen sulfide HEV was agreed to be 30 ppb (0.042 mg per m3) over a one hour time
weighted average and an HES of 30 ppb over a one hour time weighted average more
than seven times per year. There were many reasons the hydrogen sulfide HEV and HES
was doubled from the recommended limits by the University study authors. First, an
IDNR field study in which monitoring equipment was set up near CAFOs determined
that high hydrogen sulfide levels and high ammonia levels did not necessarily occur at
the same time (Iowa Department of Natural Resources Ambient Air Monitoring Group,
2005). Physical mechanisms underlying the emissions and transport of hydrogen sulfide
and ammonia were determined to be different. Additionally, two research reports
supported the proposed HEV of 30 ppb with a one hour averaging period (Campagna et
al., 2004; Partti-Pellinen et al., 1996), and the rulemaking was identical to the California
ambient air quality standard (CAAS) for hydrogen sulfide (Iowa Department of Natural
Resources, 2004b).
The California recommended standard was set in 1969 (Iowa Department of
Natural Resources, 2004b). The standard was based upon the geometric mean odor
threshold measured in adults. The purpose of the standard was to decrease odor
annoyance. In 2000, California discussed whether this standard was sufficient to protect
susceptible populations from adverse health effects based upon more recent scientific
studies. There is concern that this threshold may not be the best odor threshold for both
sexes and for all age groups. Furthermore, hydrogen sulfide levels below this threshold
may cause adverse health effects in susceptible populations including children. Today,
the acute Reference Exposure Level (REL) for California is 30 ppb and the chronic REL
is 8 ppb (0.010 mg per m3) over one year based upon a scientific study demonstrating
nasal histological changes in mice (Collins et al., 2000).
10
The U.S. EPA has currently set the Acute Exposure Guideline Level-1 (AEGL-1)
of hydrogen sulfide over an 8 hour time period at 330 ppb (0.46 mg per m3). The AEGL1 level is also 510 ppb over 1 hour of exposure and 360 ppb over 4 hours of exposure.
The AEGL-1 is the threshold where the general population, including susceptible
individuals, could experience notable discomfort, irritation, or certain asymptomatic,
nonsensory effects (Committee on Acute Exposure Guideline Levels, Committee on
Toxicology, Board of Environmental Studies, Toxicology Division on Earth and Life
Studies, 2010). Currently, the U.S. EPA does not have a chronic reference dose for
hydrogen sulfide. Prior to 2003, the dose was set at 0.003 mg per kg per day orally (U.S.
Environmental Protection Agency, 2003b). The U.S. EPA also recommends that the
maximum lifetime exposure to hydrogen sulfide be 0.07 ppb for chronic residential
exposure (U.S. Environmental Protection Agency, 2011).
The Agency for Toxic Substances and Disease Registry (ATSDR) has set a
Minimum Risk Level for acute exposures to hydrogen sulfide at 70 ppb over 1-14 days.
The intermediate Minimum Risk Level is set at 20 ppb over 15-365 days (Agency for
Toxic Substances and Disease Registry, 2006). These levels were set in response to
controlled exposure studies and the protection of susceptible populations.
Separation Distance Requirements
In the United States, states differ greatly in the amount and type of regulations to
protect communities from the environmental effects of CAFOs. In many states, minimum
separation distances requirements have been established from CAFOs to residences,
public areas, and public buildings to protect human health via the air and water. States,
generally, have laws in place dealing with CAFOs and issues of air and water pollution.
In Iowa, minimum separation distances from CAFOs to other areas are required for
permitted CAFOs. Those CAFOs are usually greater than 1,000 animal units. These
separated distances in Iowa are based upon the type of structure that holds the manure in
11
the CAFO operation, the year the CAFO was built, the Animal Unit Capacity (AUC) or
Animal Weight Capacity (AWC) of the operation, if the CAFO is in an unincorporated
area, and the type of structure, building, or land the CAFO is separated from. The
separation distances can range from 457 m (1,500 ft) to 914 m (3,000 ft) for permitted
swine CAFOs in Iowa (Iowa Department of Natural Resources, 2005).
Alternatively, other states may have similar setback regulations at the state level,
no separation distance requirements but another means to protect health, or have given
local control to communities to decide the minimum separation requirements. For high
concentrations of pollution in the air, many of these setback requirements are designed to
protect individuals living nearby from odors (Patton, 1999). The neighboring state,
Missouri, has similar separation requirements as Iowa. They can range from 305 m
(1,000 ft) to 914 m (3,000 ft) from a CAFO to a nearby residence (Pfost, 2009).
Other countries require minimum separation distance requirements to protect
individuals from primarily odor emanating from these facilities as well. Canada requires
minimum separation distances from CAFOs to property lines and public use areas to
protect human health via the air. The distances can range from 152 m (500 ft) for CAFOs
less than 1,000 animal units to 1,609 m (5,280 ft) for CAFOs larger than 4,000 animal
units (Sarr, 2010). These regulations are much stiffer for larger CAFOs than those set in
Iowa. Austria, Germany, and Switzerland also require setback distances to protect against
odors. They can range from 50 m to 540 m depending on various factors (Piringer, 1999).
These levels are much less stringent than those required in Iowa.
Plume Dispersion Modeling
Modeling provides a valuable alternative to monitoring which may be expensive,
time consuming, and difficult to establish in areas of greatest concern. Plume dispersion
modeling can estimate pollutant concentrations in the air over a short period of time in
any geographical location. This provides an attractive alternative for assessing the impact
12
CAFOs have on the air quality in the surrounding area. The present study uses a Gaussian
plume air dispersion model called AERMOD view. Most models associated with gas
dispersion use a type of Gaussian plume dispersion model. AERMOD software code is
developed and written by The American Meteorological Society and Environmental
Protection Agency Regulatory Model Improvement Committee (AERMIC) (U.S.
Environmental Protection Agency, 2005). The AERMOD code was then obtained by a
private company called Lakes Environmental and put into a user-friendly platform (Lakes
Environmental, 2011). AERMIC recommends this software for local scale modeling less
than 50 kilometers (km) (U.S. Environmental Protection Agency, 2005). In addition, the
IDNR AFO Technical Workgroup determined that AERMOD was the most suitable
dispersion model for modeling CAFOs emissions (Iowa Department of Natural
Resources, 2004a).
Only two studies have been published that modeled hydrogen sulfide emissions
from CAFOs. The Minnesota Pollution Control Agency (2003) used a non-steady-state
dispersion model called CALPUFF to estimate hydrogen sulfide, ammonia, and odor
emissions from nine swine finishing facilities. This modeling was part of an
Environmental Impact Statement (EIS). The study found that four facilities needed to
implement mitigation measures or modifications to their operating practices to mitigate
air pollution emissions.
The second study by O’Shaughnessy and Altmaier (2011) determined the optimal
settings applied to AERMOD to accurately determine the spatial distribution of hydrogen
sulfide concentrations emanating from swine CAFOs. A scalable hydrogen sulfide
emission factor was determined through the comparison of modeled versus measured
data in the vicinity of CAFOs in Iowa. The emission factor can be scaled to each CAFO
based upon the swine weight within the CAFO, the area of lagoons, and volume of the
CAFO itself. These setting are constructed to calculate reliable long time-averaged
concentrations and estimating the highest concentrations regardless of when they
13
occurred during that time period. The optimal settings determined by this paper will be
used in the plume dispersion modeling portion of this study. A mean hydrogen sulfide
emission factor of 6.06 x 10-7 ug s-1 m-2 kg-1 determined in the paper is multiplied by the
swine weight capacity, area of waste lagoons, and volume of CAFO buildings for all
swine CAFOs within this study.
Other studies have primarily investigated odor emanating from CAFOs and used
different Gaussian plume models. Hoff, Bundy, and Harmon (2008) used a Community
Assessment Model for Odor Dispersion (CAM) to predict odor exposure from multiple
swine production sources. Guo et al. (2004) compared five setback distance models for
determination of livestock sites. These models were based upon odor dispersion and the
mitigation of odor annoyance. Setback distances were determined by these models to
mitigate odor disturbance. Therefore, it was determined what distance certain CAFOs
should be from public use areas and private residences.
Plume Dispersion Modeling and Geographic Information
Systems
Few peer reviewed papers have coupled a plume dispersion modeling system with
Geographic Information System (GIS) software for further analysis when determining
hydrogen sulfide emissions from CAFOs. While some GIS software can model hydrogen
sulfide plume dispersion, the capabilities of the software remain simplistic in relation to
other plume dispersion modeling software. This study requires the calculation of a firsthighest hourly average hydrogen sulfide concentration over one year and an eighthhighest hourly average hydrogen sulfide concentration over one year. GIS software
cannot accomplish these calculations without the use of intensive programming and
substantial GIS expertise. Additionally, modeling results of hydrogen sulfide from GIS
software has not been verified for low lying source emitters like CAFOs.
14
Sarr and Goita (2010) coupled AERMOD with GIS to assess the efficiency of
current buffer distance regulations in Quebec in mitigating effects of air pollution from
swine units and identified potential areas for establishing pig farm operations that are not
offensive to people. This study was conducted for ammonia emissions from CAFOs and
found that many setback distances around certain farms did not mitigate the effects of
ammonia emitted from swine CAFOs. In this investigation, we will conduct a similar
analysis for the area surrounding the largest swine CAFO in Iowa and also determine if
current buffer distance regulations in Iowa protect against hydrogen sulfide effects from
swine facilities in an area that is swine animal dense. This area may have many
overlapping hydrogen sulfide concentration plumes.
Another study conducted by Deerhake et al. (2005) coupled the plume dispersion
model ISCST3 (an earlier version of AERMOD) with ArcGIS software to predict what
influence ammonia emissions from multiple CAFOs had on watersheds and human
health. Emission factors for ammonia were derived from the literature and scaled to each
CAFO in the analysis based upon the live weight within each facility. An estimated
average annual ambient ammonium concentration was derived per county within GIS
software.
Many other studies coupled Gaussian plume dispersion models with GIS for
purposes other than analyzing CAFOs. For example, Maantay, Tu, and Maroko (2008)
integrated AERMOD with the GIS software ArcGIS to simulate air dispersion from
sources in the Bronx, New York City. Plumes were created in AERMOD and transferred
to ArcGIS to estimate human exposure to certain pollutants. The loose integration of the
two models proved to be advantageous over proximity analyses and geostatistical
methods for environmental health research. Other studies also integrated plume
dispersion models with GIS software to analyze human exposure to pollutants (Gulliver
& Briggs, 2011; Holford et al., 2010; Isakov et al., 2009).
15
Study Aims
The primary Aim of this study is to assess the adequacy of current setback
distances in mitigating adverse health effects of hydrogen sulfide emissions from swine
CAFOs. Concentrations of hydrogen sulfide will be modeled and estimated in two
specific areas of Iowa. The first area surrounds the largest swine CAFO in Iowa. The
second area analyzed will be swine animal dense as defined in a separate analysis.
The Specific Aims of the study includes:
Specific Aim 1: To identify geographical areas of Iowa with the highest swine
weight density and describe swine CAFO characteristics that lead to these areas of high
swine weight density. This includes describing the number of CAFOs influencing the
area and the swine animal weight of these particular CAFOs.
Specific Aim 2: To determine if current CAFO setback distance regulations in Iowa
protect against the HES and HEV of hydrogen sulfide near only the largest swine weight
CAFO in Iowa.
Specific Aim 3: To determine if current CAFO setback distance regulations in Iowa
protect against the HES and HEV of hydrogen sulfide for an area of Iowa which has the
greatest swine weight density.
It is hypothesized that hydrogen sulfide concentrations in the air may exceed the
HES and HEV at a distance further than minimum separation distance regulations from
CAFOs in Iowa. To analyze this hypothesis, this study investigates two unique areas of
Iowa that are estimated to have the highest concentrations of hydrogen sulfide in the air
beyond the minimum separation requirements. It is proposed that the largest swine
weight CAFO in Iowa will emanate the largest amount of hydrogen sulfide into the air in
the surrounding area because swine weight capacity of the CAFO has a direct influence
on the scalable emission factor of that CAFO. Therefore, this CAFO would be associated
with the largest emission factor of any source CAFO emitter in Iowa. Additionally, it is
estimated that the greatest swine weight dense area of Iowa will also have high
16
concentrations of hydrogen sulfide in the air because swine weight dense areas are
estimated to have a large amount of hydrogen sulfide emissions within those areas. There
is predicted to be an additive effect of hydrogen sulfide concentrations in the air from
many source emitters in the highest swine weight dense area.
17
CHAPTER II
ASSESSING THE EFFICIENCY OF SEPARATION DISTANCES IN
MITIGATING EFFECTS OF HYDROGEN SULFIDE
CONCENTRATIONS EMANATING FROM SWINE CAFOS
Introduction
The United States Environmental Protection Agency (EPA) has estimated that
confined farm animals generate three times more excrement than is produced by humans
in the U.S. (U.S. Environmental Protection Agency, 2003a). Much of the toxic substances
emitted from Concentrated Animal Feeding Operations (CAFOs) emanate from manure
stored on-site. According to the U.S. Government Accountability Office (GAO), CAFOs
can produce approximately 2,800 tons to more than 1.6 million tons of manure from a
large CAFO facility each year depending on the animal type and number at the site (U.S.
Government Accountability Office, 2008).
Given the substantial quantity of manure, CAFOs can emit a considerable amount
of pollution into the general environment, which include volatile organic compounds,
ammonia, hydrogen sulfide, carbon dioxide, malodorous vapors, and particles
contaminated with harmful microorganisms (Heederik et al., 2007). There is growing
concern that these pollutants may lead to adverse health effects among people living
close to the site. In particular, hydrogen sulfide is both a directly toxic substance as well
as malodorous to humans. In many states, separation distances from CAFOs to
residences, public areas, and public buildings have been established to protect human
health via the air and water. Iowa law mandates that an individual or company seeking to
construct a CAFO over a certain size must build it at a minimum specified distance
(separation distance) from homes, schools, and other types of public areas (separated
locations) (Environmental Protection Commission, 2010).
18
In Iowa, few studies have been conducted to determine if current separation
distances mitigate health effects of air pollution emanating from swine CAFOs. This
study will use a validated plume dispersion modeling technique to estimate
concentrations of hydrogen sulfide emitted from the largest swine CAFO in Iowa as well
as several swine CAFOs located in an area of Iowa that is swine animal dense. The
plumes generated will then be compared to the separation distance requirements in Iowa
to determine if these distances protect human health based upon the Iowa health effect
value (HEV) and a health effects standard (HES) of hydrogen sulfide established by a
field study through the Environmental Protection Commission (Environmental Protection
Commission, 2004). Two spatial software programs will be coupled together to conduct
the analysis. The initial estimation of hydrogen sulfide concentrations will be conducted
using air plume dispersion code called AERMOD which is written into user-friendly
software developed by Lakes Environmental (Lakes Environmental, 2011). The spatial
analysis comparing the separated distances to estimated hydrogen sulfide concentrations
will be performed using Geographic Information System (GIS) software called ArcMap
developed by the Environmental Systems Research Institute, Inc. (ESRI) (Environmental
Services Research Institute, 2011).
The HEV for Iowa is 30 parts per billion (ppb) for a one-hour time weighted
average concentration. It has been established that this level of airborne pollutant is
commonly known to cause a material and verifiable adverse health effects. Currently, the
state of Iowa has determined that the HES for hydrogen sulfide is “exceeded at a
monitoring site when the daily maximum one-hour average concentration exceeds 30 ppb
more than seven times per year” (Environmental Protection Commission, 2010). The
Iowa Department of Natural Resources (IDNR) would develop plans and abate hydrogen
sulfide emissions from CAFOs if hydrogen sulfide levels measured at separated locations
exceeded the HES for hydrogen sulfide.
19
Study Aims
The primary Aim of this study is to assess the adequacy of current setback
distances in mitigating adverse health effects of hydrogen sulfide emissions from swine
CAFOs. Concentrations of hydrogen sulfide will be modeled and estimated in two
specific areas of Iowa. The first area surrounds the largest swine CAFO in Iowa. The
second area analyzed will be swine animal dense as defined in a separate analysis.
There are three Specific Aims within this study. Specific Aim 1 is to identify
geographical areas of Iowa with the highest swine weight density and describe swine
CAFO characteristics that lead to these areas of high swine weight density. This includes
describing the number of CAFOs influencing the area and the swine animal weight of
these particular CAFOs. Specific Aim 2 is to determine if current CAFO setback distance
regulations in Iowa protect against the HES and HEV of hydrogen sulfide near only the
largest swine weight CAFO in Iowa. Specific Aim 3 is to determine if current CAFO
setback distance regulations in Iowa protect against the HES and HEV of hydrogen
sulfide for an area of Iowa which has the greatest swine weight density.
Material and Methods
Optimal Setting within AERMOD Dispersion Modeling
To determine if the separation distance requirements from CAFO facilities are
adequate in protecting human health from hydrogen sulfide concentrations, estimated
hydrogen sulfide concentrations emanating from CAFO facilities were modeled in
AERMOD view software (U.S. Environmental Protection Agency, 2005). AERMOD
view, version 7.1 is a user-friendly software package developed by Lakes Environmental
of Waterloo, Ontario (Lakes Environmental, 2011). The AERMOD software code within
AERMOD view was developed and written by The American Meteorological Society
and Environmental Protection Agency Regulatory Model Improvement Committee
(AERMIC) (U.S. Environmental Protection Agency, 2005). AERMIC recommends this
20
software for local scale modeling less than 50 kilometers (km) (U.S. Environmental
Protection Agency, 2005). In addition, the IDNR Animal Feeding Operation (AFO)
Technical Workgroup concluded that AERMOD was the most suitable software for
modeling CAFOs emissions (Iowa Department of Natural Resources, 2004a).
In a recent study by O’Shaughnessy et al. (2011), optimal settings were
determined within AERMOD to accurately determine the spatial distribution of hydrogen
sulfide concentrations emanating from swine CAFOs. A scalable hydrogen sulfide
emission factor was determined through the comparison of modeled versus measured
data. The emission factor can be scaled to each CAFO based upon the swine weight
attributed to each CAFO, the area attributed to each lagoon, and volume attributed to
each CAFO building. The emission factor determined in the article for lagoons and
buildings was 6.06 x 10-7 ug s-1 kg-1 (micrograms per second per kilogram), and was
scalable for each CAFO based upon the swine weight capacity in kilograms of each
CAFO and the footprint of the buildings and lagoons (O'Shaughnessy & Altmaier, 2011).
The factor was utilized in the present investigation to estimate reliable highest one-hour
hydrogen sulfide concentrations.
Optimal settings as described by the article by O’Shaughnessy et al. (2011),
included characterizing CAFO buildings as “volume” sources and waste lagoons as
“area” sources. The footprint of the volume and area sources were positioned spatially
based upon aerial photography. If the CAFO geodatabase provided by the IDNR
attributed the waste lagoon or pit as being located directly underneath the CAFO
buildings, an area source was created directly underneath a volume source. In AERMOD,
the footprint of volume sources may only be represented as squares. Based upon the
rectangular shape of many swine buildings, many square volume sources were integrated
over each swine building. Building downwash options were not set in the model and were
of little influence outside separation distances. The emission factor for volume sources in
the present investigation was scaled for each CAFO by multiplying the default emission
21
factor by the footprint of the building in square meters (m2) and swine weight capacity
(kg) of each CAFO. The emission factor of area sources was scaled by multiplying the
default emission factor by the swine weight (kg) of the CAFO attributed to the lagoon.
AERMOD also requires meteorological (met) data as inputs. All of the necessary
data in both study areas were obtained from a National Weather Service (NWS) station
which represented the climatic conditions of each study area the closest. The state of
Iowa has ten NWS stations and each county in Iowa is attributed to one station which is
considered representative of that county’s meteorological conditions (Iowa Department
of Natural Resources).
Both study areas use met data measured in Mason City, Iowa. From results
obtained during this study, the largest swine CAFO study area (LSCSA) was located
completely within the Mason City met region while the swine weight dense study area
(SWDSA) was not. Rather, the majority of the SWDSA was located within the Mason
City region while a smaller portion was located within the Waterloo region. AERMOD
allows only one met dataset per application, as such, only Mason City met data was used
in the SWDSA.
AERMOD pre-processed met data, originating from the National Weather Service
(NWS), was available through the IDNR website (Iowa Department of Natural
Resources). The most recent data available was for the year 2004. Within the Mason City
met data, each variable had a value for every hour over the year 2004. Spatial and
temporal variation in meteorological datasets can be expected in different met regions
and between different years. Met data included factors such as: wind speed, wind
direction, temperature, dew point, pressure, humidity, and solar radiation. Given this met
data, AERMOD was used to model first-highest, hourly, hydrogen sulfide concentrations
(first-highest concentrations, FHC) and eighth-highest, hourly, hydrogen sulfide
concentrations (eighth-highest concentrations, EHC) from active swine CAFOs. The
EHC was calculated because the HES could potentially be violated if areas beyond the
22
separated distances exceeded 30 ppb more than seven times per year. The FHC was
estimated to be compared with the HEV, which should not exceed 30 ppb one hour a year
beyond separation distances.
ArcGIS Software
The Geographic Information System (GIS) software, ArcMap, was used to
conduct the portion of this study that analyzed the separation distance requirements
compared to estimated hydrogen sulfide concentration plumes. ArcMap version 10.0 is
developed by the Environmental Systems Research Institute, Inc. (ESRI). This software
is widely used to address social, economic, business, and environmental concerns at a
local, regional, national, and global scale. It has the capability to address a wide variety
of spatial issues and problems through numerous analyses including the kernel density
functions, point density functions, and interpolation functions used in this study
(Environmental Services Research Institute, 2011).
CAFO Geodatabase Acquisition and Modification
An Animal Feeding Operation (AFO) geodatabase for the state of Iowa was
obtained through the Iowa DNR Natural Resources Geographic Information Systems
Library (NRGIS). This library is composed of 20,000 geographically referenced
databases which are easily imported into ArcMap software (Iowa Department of Natural
Resources, 2011). The acquired AFO geodatabase contained locations of confinement
feeding operations that are recognized by the Iowa DNR. Most of these AFO facilities
were large enough to require registration with the IDNR to become a permitted CAFO
(>1,000 animal units). The X, Y location (geocoding) of these facilities was identified by
methods including: address matching with street centerlines, public land surveys, and
interpretation of aerial photos. The accuracy of their X, Y locations varied from +/- 12 m
when interpreting aerial photos to +/- 540 m when interpreting public land surveys. The
geodatabase was last updated in January 2010 (Wolter, 2010).
23
Considerable modification of the geodatabase was required to obtain only active
swine CAFOs used within this study. There were 7,296 CAFOs in the geodatabase
including facilities that produced poultry, cattle, turkeys, as well as swine. In addition,
there were CAFOs in the geodatabase that were currently inactive and not operating. The
first step was to exclude all of the inactive CAFOs from the study by sorting the
“opStatus” variable and removing all CAFOs identified as not being an active CAFO. As
of 2010, there were 6,730 active CAFOs within the geodatabase. Next, all of the CAFOs
without swine were removed. A field was created to determine the total number of head
of swine within each CAFO. CAFOs that had no heads of swine were removed. There
were 5,990 active swine CAFOs within this geodatabase. It could not be determined
which CAFOs were active or inactive in 2004 (the year in which met data was used).
Some variation can exist in the number of swine CAFOs active in 2010 in comparison to
2004.
Additionally, a field of total swine weight (kg) per CAFO was created in the
CAFO geodatabase to be used to determine the scalable hydrogen sulfide emission factor
of each CAFO in the AERMOD analysis. Swine weight was determined by multiplying
the standard swine weight of each type of swine animal by the number of head of each
type of swine animal. The typical swine weight of each type of swine animal was
obtained through direct contact with Iowa DNR personnel and is presented in Table 1
(Hruby, 2010). As Table 1 indicates, the IDNR splits swine into six different swine types.
Each of these swine types is associated with a swine weight per one head of that swine
type.
Density Analyses and the Identification of Swine Weight
Dense Areas
It was proposed that hydrogen sulfide concentrations in the air may be greater in
areas of Iowa that are considered swine weight dense because the swine weight of
24
CAFOs contributes to the emission factor used when modeling hydrogen sulfide
emissions from CAFOs. Estimated hydrogen sulfide concentrations are greater when
greater swine weight is attributed to particular CAFOs. In these high swine weight areas,
there may be higher hydrogen sulfide levels in the air possibly exceeding the HES and
HEV beyond separated distances. The swine weight kernel density analysis was intended
to identify the spatial locations of the highest swine weight dense areas and describe the
characteristics of CAFOs within those areas. These areas are estimated to have the
highest hourly hydrogen sulfide concentrations in the air. The highest SWDSA was then
modeled in AERMOD to estimate hydrogen sulfide concentrations and determine if the
separated distance requirements of the CAFOs within that area protects against hydrogen
sulfide levels exceeding the HES and HEV limit.
A kernel density estimator (KDE) was used in this analysis. KDEs spread the
effect of each CAFOs swine weight over the surrounding area just as hydrogen sulfide
concentrations are spread about that same area. This type of analysis provides a good
indication of specific areas of Iowa that may have high hydrogen sulfide concentrations.
ArcMap has a kernel density function written into the software. Conceptually, a smoothly
curved surface is fitted over each CAFO. Swine weight is highest at the location of the
CAFO and diminishes with increasing distance from the CAFO, reaching zero at the
maximum extent of the search radius. The search radius extent was determined by
procedures in the next section. This kernel function is based on the quadratic kernel
function described in Silverman (1986). It is important to note that the quadratic kernel
function may “weight”, swine weight of CAFOs greater at middle distances from each
CAFO in question and “weight” less at the greatest spatial extent than is seen by
estimated hydrogen sulfide concentrations of each CAFO in question at these same
distances from the CAFO in question.
Parameters set in the analysis included the population (swine weight), grid
resolution, and search radius. All active swine CAFOs were used as the population of
25
points in this analysis. Each CAFO was weighted by the swine weight (kg) capacity. The
grid cell size was set to 250 m resolution, creating 2,331,222 grid cells within the state of
Iowa.
To describe swine CAFO characteristics that lead to these areas of high swine
weight density, in each swine weight dense area, a grid cell with the highest swine weight
kernel density was identified. A search radius was generated around the center of that cell
indicating the spatial extent in which active swine CAFOs have influence on the value of
that cell. This search radius was then determined to be the total study area of each swine
weight dense area.
Additionally, a CAFO point density analysis (CAFOs per km in designated search
radius) was performed within ArcMap. This analysis was performed to compare the
CAFO point density values in the highest swine weight dense areas with the CAFO point
density values attributed to the rest of Iowa. It could then be determined if many low
swine weight CAFOs, a mix of different sized CAFOs, or only a few large swine weight
CAFOs were influencing high swine weight kernel dense areas. The CAFO density
analysis in this study simply counted the number of CAFOs within the search radius of
each 250 m grid cell within Iowa and then divided the number of CAFOs by the area
(km) of the search radius. This is different than the Kernel density analysis of swine
weight because this analysis calculates the number of CAFOs within a search radius
while the swine weight density analysis “weights” each CAFO by swine weight capacity
and provides a density of swine weight within a search a search radius.
Search Radius based on Hydrogen Sulfide Concentrations
This analysis was aimed at determining the spatial extent to which hydrogen
sulfide concentrations emanating from Iowa CAFOs contribute to ambient levels of
hydrogen sulfide in the air. This analysis modeled estimated concentrations of hydrogen
sulfide in a “worst case scenario” for meteorological conditions during the year 2004.
26
The analysis was conducted by modeling first-high, hourly, hydrogen sulfide
concentrations (FHC) of the largest swine weight CAFO in Iowa using AERMOD.
By determining the average spatial extent away from the center of the largest
CAFO in which hydrogen sulfide levels reach un-measurable values, that same spatial
extent can be used as the search radius in which CAFO’s may contribute to swine weight
density in particular areas. It is assumed that if a particular CAFO does not contribute to
hydrogen sulfide concentrations in a certain area above measurable concentrations, that
same CAFO should not contribute to the kernel density function that determines swine
weight density in that same area.
For the LSCSA, an area source was included over the one attributed waste lagoon
and 120 volume sources were created over the 10 attributed swine buildings. Figure 1
provides an example of the volume and area sources placed over the CAFO buildings and
lagoon. The CAFO buildings to the north of the lagoon were poultry buildings and were
not included within the analysis.
Within AERMOD, a polar receptor grid was created over the study area to
measure FHC at each receptor location. Figure 2 illustrates the configuration of the polar
receptor grid and the spatial extent. The polar receptor grid included 2,592 points spaced
250 m apart over 71 radii. The radius measured 9 km from the center of the CAFO
facilities to the farthest spatial extent. A unique estimated hydrogen sulfide concentration
was calculated at each receptor.
It is important to note that the FHC for each receptor may have occurred during
different hours during the year 2004. The receptors were grouped based upon distance
from the center of the CAFO facilities. There were 71 receptors in each group. Each
receptor was in a unique spatial direction from the center of the largest CAFO. The
receptors in each group were then averaged. A graph was constructed indicating the
distance away from the center of the largest CAFO in which the average first high
estimated values reached 2 ppb. This value is considered the threshold in which CAFOs
27
contribute to hydrogen sulfide in the air because drift of monitoring instruments cannot
account for better precision (O'Shaughnessy & Altmaier, 2011). Thus, 2 ppb is the
threshold in which monitoring equipment cannot determine if hydrogen sulfide is
contributing to ambient levels.
Modeling Hydrogen Sulfide Concentrations in AERMOD
Concentrations of hydrogen sulfide were estimated within AERMOD software for
areas near the highest SWDSA and the LSCSA. AERMOD was used to calculate the
first-highest and eighth-highest hourly estimates of hydrogen sulfide concentrations over
the year 2004 for the SWDSA and LSCSA. Similar to the analysis of determining the
search radius based upon hydrogen sulfide concentrations within AERMOD, an area
source was included over the waste lagoons and volume sources over the swine buildings.
In the LSCSA, which is shown in Figure 1, there was one area source created over one
lagoon and 120 volume sources created over 10 swine buildings. Alternatively, in the
SWDSA, there were 114 area sources created over the lagoons and 926 volume sources
created over the swine buildings.
A uniform Cartesian receptor grid was created over the two study areas. The
highest swine weight dense grid cell and the largest CAFO were at the center of each
Cartesian receptor grid. The grid was composed of 29,241 receptors uniformly distributed
100 m apart in both study areas. The spatial extent of both studies was a 289 km2 square,
composed of 17 km on each side. Figure 3 indicates a small portion of the uniform
Cartesian grid used over the largest swine CAFO study area. At each unique receptor
point first or eighth highest hourly estimated hydrogen sulfide concentrations were
calculated for the year 2004.
28
Determining if Current CAFO Setback Distance
Regulations in Iowa Protect for the HES and HEV of
Hydrogen Sulfide
Coupling AERMOD with ArcGIS
The uniform Cartesian grid of points for each analysis was exported as a text file
from AERMOD. The exported points had unique identifiers including X and Y spatial
coordinates and an estimated hydrogen sulfide concentration value for FHC and EHC.
The map surface of the project was projected in Universal Transverse Mercator North
American Datum 1983 zone 15, the standard in Iowa. Each respective Cartesian receptor
grid was then added to ArcMap software based upon their X and Y spatial coordinates.
Interpolation
Interpolation methods were implemented to predict unknown hydrogen sulfide
concentrations between the receptor points. ArcMap affords a wide variety of
interpolation methods to estimate hydrogen sulfide concentrations between receptor
points. An interpolation method called Inverse distance weighting (IDW) was
implemented in this research because more advanced interpolation methods require an
investigation of the spatial behavior and relationship among measured receptors. As
mentioned previously, each receptor may be independent in time from all other receptor
points. Therefore, the FHC and EHC at a particular receptor may have occurred during a
completely different period of time than the receptors adjacent to that particular receptor.
Consequently, it was impossible to investigate the spatial relationship among the
measured receptors because the highest concentration values may have occurred during
different hours of the year.
For this analysis, IDW estimated cell values (hydrogen sulfide concentrations) by
averaging the hydrogen sulfide concentrations of receptors in the neighborhood of each
processing cell. The closer a receptor was to the center of the cell being estimated, the
29
more influence, or weight, it had on the averaging process. When estimating the cell
values in question, the four nearest receptor values were used in the equation. It was
assumed that geographical areas that were close together had similar hydrogen sulfide
concentration characteristics.
Separation Distances
In Iowa, the edge of each swine CAFO is required to be a minimum distance from
public use areas (cemeteries and land owned by U.S., state, or local governments which
attract the public), residences, businesses, churches, and schools when the operation is
constructed. These “separated distances” are based upon the type of structure that holds
the manure in the CAFO operation, the year the CAFO was built, the Animal Unit
Capacity (AUC) or Animal Weight Capacity (AWC) of the operation, if the CAFO is in
an unincorporated area, and the type of structure, building, or land the CAFO is separated
from. Information of the type of structure that holds the manure and the AUC and AWC
was available in the geodatabase of CAFOs through the IDNR. A table of the required
minimum separation distances for construction or expansion of CAFOs was available
through the IDNR (Iowa Department of Natural Resources, 2005).
Based upon the unique variables in the tables including required minimum
separated distances, the AUC or AWC of the CAFOs, and the type of waste structure for
each CAFO, unique separation distances were created around each CAFO facility. Each
separation distance for each CAFO was centered on the spatial point attributed by the
IDNR geodatabase. Each buffer then represented the minimum separated distance
requirements depending on the structure, building, or land the separation distances were
protecting.
30
Comparing Separation Distances to Estimated Hydrogen
Sulfide Concentrations
The spatial analysis of comparing the separation distances to the estimated
hydrogen sulfide concentrations was conducted in ArcMap 10.0. The interpolated
hydrogen sulfide plumes were overlaid with the associated separation distances of each
CAFO. If the separated distances did not protect against the HES or HEV hydrogen
sulfide concentrations, a total area in square meters was derived by ArcMap in which the
separated distances were not protective.
Results and Discussion
Determination of Search Radius based on Hydrogen
Sulfide Contribution
The results of modeling the FHC for the year 2004 at different distances from the
largest CAFO in Iowa, is shown in Figure 4. As indicated by Figure 4, the average
concentration of hydrogen sulfide decreases below 2 ppb, the level of instrument drift, at
approximately 8.5 kilometers from the center of the largest CAFO. These data suggest
that all swine CAFOs currently active and located within Iowa in 2004 will not exceed a
FHC of 2 ppb further than 8.5 km from the source. When using the kernel density
function and CAFO point density function, the search radius was set to 8.5 km.
Therefore, no CAFOs further than 8.5 km from any grid cell had influence on the kernel
density estimate or CAFO point estimate associated with that particular grid cell.
Kernel Density Analysis and CAFO Point Density Analysis
A kernel density analysis was performed to identify geographical areas of Iowa
with the highest swine weight density and to describe swine CAFO characteristics that
led to these areas of high swine weight density. Parameters set in the analysis included
the population (swine weight), grid resolution (250 m), and search radius (8.5 km).
31
Figure 5 provides a map indicating the results of the Kernel density analysis. Figure 5
illustrates how the kernel density values within the grid cells were split into nine
categories based upon the geometrical interval classification scheme. The geometrical
interval scheme produces a result that minimizes variance within classes and is well
suited for data not normally distributed. This dataset is heavily skewed to the right where
most swine weight density values are near zero. As indicated by the darkest regions of the
map, the highest swine weight dense areas of Iowa are located in the northwest, northcentral, and southeast regions of Iowa.
When investigating the geometrical interval class with the greatest values
(62,851.25 - 115,752.80), seven unique geographical areas emerged. Those areas are
circled in Figure 5. Five high swine weight dense geographical areas are spatially close
together in north-central Iowa. Another geographical area is located in northwestern Iowa
and the final geographical area is located in southwestern Iowa. These geographical areas
are associated with high swine weight density. As such, these areas are also predicted to
be associated with the highest estimated concentrations of hydrogen sulfide.
Additionally, a map (Figure 6) was created indicating the areas of Iowa with high
CAFO point density. The CAFO density values were also divided into nine categories
based upon the Geometrical interval classification scheme. Four areas emerged in the
highest category (0.2382 – 0.3789) and are circled in Figure 6. Two of the CAFO dense
areas are in north-central Iowa and the other two areas, including a very large area, are
located in northwestern Iowa.
Highest Swine Weight Dense Area Characteristics
The swine CAFO characteristics that led to areas of highest swine weight density
underwent additional analyses to describe swine CAFO characteristics that lead to these
areas of high swine weight density. In each swine weight dense area, a grid cell with the
highest swine weight kernel density was identified. An 8.5 km search radius was
32
generated around the center of the cell (with the highest swine weight density) indicating
the spatial extent in which active swine CAFOs had influence on the value of that cell.
This 8.5 km search radius was then identified as the total study area of each swine weight
dense area. Figure 7 illustrates each of the seven areas including the center grid cell, the
8.5 km study areas, active swine CAFOs, and the swine weight kernel density.
The geodatabase of active swine CAFOs within each study area was then
extracted and attributes were exported to Microsoft Excel. Table 2 and Figure 8 indicate
the differences in attributes between the identified high swine weight dense areas and the
total active swine CAFOs in the state of Iowa. The highest swine weight dense areas vary
widely in their associated attributes. The study areas range from 20 to 55 CAFOs within
the 8.5 km study areas. This results in a CAFO density range from 0.088 to 0.242 CAFOs
per sq km. The associated CAFO densities are much greater than the average CAFO
density in the state of Iowa which is 0.041 CAFOs per sq km. However, only study area
1, which had a CAFO density of 0.242 CAFOs per sq km, was within the highest
geometrical interval classification method of the CAFO point density analysis. This
suggests that the highest swine weight dense study areas are generally not located in the
most CAFO point dense areas of Iowa.
Additionally, in each study area the total swine weight of all CAFOs range from
9,699,542 kg to 17,793,204 kg. The median swine weight of each CAFO within the study
areas ranged from 162,840 kg to 567,614 kg with a median of 271,720 kg for all the high
swine weight dense study areas. In contrast, all active swine CAFOs in Iowa had a
median size of 174,179 kg. Every study area had a mean swine weight greater than the
median size of all active swine CAFOs except study area 1. In addition, as indicated in
the box plot (Figure 8), the average swine weight of each study area is heavily influenced
by large swine weight CAFO outliers. The average swine weight of the study areas
ranged from 218,961 kg to 593,274 kg with an average of 300,306 kg for all of the study
areas. Conversely, all active swine CAFOs had an average size of 215,160 kg. Each study
33
area with the exception of study area 3 had at least one CAFO outlier. As shown in Table
2 and Figure 8, each study area, with the exception of study area 3, also had greater
average size of CAFOs than median size of CAFOs.
The results suggest that high swine weight dense areas generally have a greater
median and average swine weight than all swine CAFOs in Iowa. The high swine weight
areas are also generally influenced heavily by a few very large swine CAFOs.
Additionally, these areas tend to have a high CAFO density but are not located in the
highest CAFO dense areas of Iowa as determined by the CAFO density analysis.
Study area 4 was identified as the having the highest swine weight density of all
the swine weight dense study areas. This area was then used to fulfill Specific Aim 3: to
determine if current CAFO setback distance regulations in Iowa protect for the HES and
HEV of hydrogen sulfide for an area of Iowa which has the greatest swine weight
density. The swine weight kernel density of this area reached a magnitude of 115,753 kg
per km2; the highest level in the state of Iowa. There were 51 active swine CAFOs in this
area. Figure 9 shows the distance from the center grid cell and swine weight of each
CAFO in this area. Five CAFOs exceed the swine weight of 1,000,000 kg. As such, these
are five of the 28 largest swine CAFOs in Iowa. Each of these CAFOs is identified as an
outlier in the CAFO dataset in this specific study area. The two closest CAFOs to the
highest swine weight dense grid cell are CAFOs that exceed 1,000,000 kg, and both are
indicated as outliers. The two closest CAFOs are about 900 m apart. The closest CAFO
to the highest swine weight dense grid cell is about 435 m. This study area was used to
estimate hydrogen sulfide concentrations in the air from all of the CAFOs within.
Spatial Analysis Largest Swine CAFO
The spatial analysis comparing the separation distances to the estimated hydrogen
sulfide concentrations was conducted in the area of the largest swine CAFO in Iowa. The
largest swine CAFO has a swine weight capacity of 1,741,795 kg. The interpolated
34
estimated hydrogen sulfide concentrations were overlaid with the associated 914.4 m
(3000 ft) separation distance from the largest CAFO as mandated by Iowa law
(Environmental Protection Commission, 2010). Ideally, this separation distance should
protect public use areas, residences, churches, businesses, and schools from hydrogen
sulfide concentrations emanating from this CAFO. ArcMap software may then indicate if
this separation distance protected for the HEV and HES of hydrogen sulfide
concentrations. If they did not protect, it could be determined where they don’t protect
and how much area is not protected.
First-High, Hourly, Hydrogen Sulfide Concentrations and
Separation Distance for Analysis of the HEV
The results of overlaying the FHC with the protective separation distance
attributed to the largest swine CAFO in Iowa are presented in Figure 10. As indicated,
some of the study area is attributed to having FHC in excess of 30 ppb beyond the
separation distance. This indicates that the 914.4 m (3,000 ft) separation distance does not
protect against the HEV of hydrogen sulfide for CAFOs of this size. The areas of
exceedance were found in easterly and westerly directions, as far away as 1,710 m (5609
ft), from the center of the largest CAFO facilities. FHC may reach concentrations as high
as 50 ppb beyond the separation distance in the westerly direction. Additionally, in 2004,
a total area of 423,568 m2 was estimated to exceed 30 ppb beyond the separation
distance. An area of 1,931,786 m2 (was estimated to exceed 30 ppb one time during 2004
over the total study area (226,980,069 m2).
Eighth-High, Hourly Hydrogen Sulfide Concentrations and
Separation Distance for Analysis of the HES
Figure 11 shows the results of overlaying the EHC with the protective separation
distance attributed to the largest swine CAFO in Iowa. As indicated, no areas beyond the
separation distance were estimated to have EHC in excess of 30 ppb. This suggests that
35
the 914.4 m (3,000 ft) separation distance protects against the HES of hydrogen sulfide.
EHC may reach concentrations as high as 26 ppb beyond the separation distance in the
westerly direction. An area of 666,740 m2 was estimated to exceed 30 ppb during eight
different hours in 2004 over the total study area but within the separation distance
requirements.
Spatial Analysis of the Highest Swine Weight Dense Area
First-High, Hourly, Hydrogen Sulfide Concentrations and
Separation Distances for Analysis of the HEV
The results of overlaying the FHC with the protective separation distance
attributed to all active swine CAFO in the high swine weight dense study area are
presented in Figure 12 and Figure 13. Figure 12 indicates the results when the FHC is
overlaid with minimum separation distances requirements used to separate CAFOs from
public use areas. Figure 13 indicates the results when the FHC is overlaid with minimum
distance requirements used to separate CAFOs from residences, businesses, churches,
and schools (RBCS). The RBCS separation distances can be less than public use area
separation distances for CAFOs less than 3,000 animal units depending on type of
manure structure attributed. As illustrated in the Figures, no areas beyond the separation
distances were estimated to have FHC in excess of 30 ppb. This suggests that the
separation distances protect against the HEV of hydrogen sulfide. FHC may reach
concentrations as high as 22 ppb beyond the separation distances in this study area. An
area of 55,587 m2 was estimated to exceed 30 ppb during one hour in 2004 over the total
study area but within all separation distances.
36
Eighth-High, Hourly Hydrogen Sulfide Concentrations and
Separation Distances for Analysis of the HES
The results of overlaying the EHC with the protective separation distances
attributed to all active swine CAFOs in the highest swine weight dense study area are
presented in Figure 14 and Figure 15. Figure 14 indicates the results when the EHC is
overlaid with minimum separation distances requirements used to separate CAFOs from
public use areas. Figure 15 indicates the results when the EHC is overlaid with minimum
distance requirements used to separate CAFOs from residences, businesses, churches,
and schools (RBCS). As illustrated in the figures, no areas beyond the separation distance
are estimated to have EHC in excess of 30 ppb. This indicates that the separation
distances protect against the HES of hydrogen sulfide. EHC may reach concentrations as
high as 11 ppb beyond the separation distances in this study area. No area was estimated
to exceed 30 ppb during eight different hours in 2004 over the total study area but within
the separation distances.
Conclusions
The primary goal of this research was to assess the adequacy of current separation
distances established to protect for the HES and HEV of hydrogen sulfide concentrations
emanating from swine CAFOs in Iowa. Specifically, the research examined: 1) the
characteristics of swine weight dense areas, 2) if current CAFO setback distance
regulations in Iowa protect for the HES and HEV of hydrogen sulfide nearest the largest
swine weight CAFO, and 3) if current CAFO setback distance regulations in Iowa protect
for the HES and HEV of hydrogen sulfide for an area of Iowa which has the greatest
swine weight density.
The results suggest that the highest swine weight dense areas generally have a
greater median and average swine weight per CAFO than is observed for all active swine
CAFOs in Iowa. The high swine weight areas are also generally influenced greatly by a
37
few very large swine CAFOs. Additionally, these areas tend to have a high CAFO density
but are not located in the highest CAFO dense areas of Iowa.
The HEV level of hydrogen sulfide is estimated to be exceeded in a total area of
423,568 m2 beyond the associated separated distance for the largest active swine CAFO
alone in 2004. This indicates that the 914.4 m (3,000 ft) separation distance does not
protect against the HEV of hydrogen sulfide for the largest swine CAFO. The areas of
exceedance were found in easterly and westerly directions, as far away as 1,710 m (5609
ft), from the center of the largest CAFO area. FHC may reach concentrations as high as
50 ppb beyond the separation distance in the westerly direction. It is estimated that this
area would have levels of hydrogen sulfide concentrations in the air during one hour of
2004 that may cause a material and verifiable adverse health effect if an individual was at
this location during that period of time. The designated separated distance was however
protective at the HES for hydrogen sulfide concentrations.
The estimated concentrations of hydrogen sulfide in the highest swine weight
dense area did not exceed the HES or HEV beyond the minimum separation distances in
2004. In fact, the EHC did not exceed 30 ppb at any location even though two swine
CAFOs over 1,000,000 kg were separated by 900 m within the study area. This suggests
that the swine weight of an individual CAFO may contribute to high hydrogen sulfide
levels more than the concentration of swine weight dense CAFOs in close proximity to
each other.
Overall, the separation distance requirements established in Iowa were adequate
in protecting against the HEV and HES of hydrogen sulfide for all swine CAFOs in the
two study areas except for the largest swine CAFO in Iowa. This CAFO was estimated to
exceed the HEV beyond minimum separation distance requirements but the state of Iowa
does not have any regulations or laws to abate these high concentrations even though they
may cause adverse health effects in individuals living, working, and playing nearby. This
38
is in stark contrast to the HES level where, if exceeded beyond minimum separation
distance requirements, plans would be developed to abate these emissions.
39
Figure 1. Largest Swine CAFO Area and Volume Sources
Area Source
(lagoon)
Volume Sources
(buildings)
40
Figure 2. Largest Swine CAFO Polar Receptor Grid
Figure 3. Uniform Cartesian Grid in Largest Swine CAFO Area
41
Figure 4. Largest Swine CAFO Average Estimated Hydrogen Sulfide Concentrations and Distance Away from the Source
60
1,741,795 Kg Swine CAFO
50
40
30
20
10
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
2750
3000
3250
3500
3750
4000
4250
4500
4750
5000
5250
5500
5750
6000
6250
6500
6750
7000
7250
7500
7750
8000
8250
8500
8750
9000
Concentration (ppb)
2 ppb
Distance (meters)
42
Figure 5. Swine Weight Kernel Dense Areas in Iowa
43
Figure 6. CAFO Point Dense Areas in Iowa
44
Figure 7. Seven Swine Weight Dense Areas
45
Figure 8. Box Plot of Swine Weight Dense Areas
Largest Outlier
Study Area 7
Mean
Study Area 6
Study Area 5
Study Area 4
Study Area 3
Study Area 2
Study Area 1
All Study Areas
All CAFOs
0
200,000
400,000
600,000
800,000
1,000,000 1,200,000 1,400,000 1,600,000 1,800,000 2,000,000
Swine Weight (Kg)
46
47
Figure 9. Scatter Plot of Selected Study Area CAFOs
1,200,000
Swine Weight (kg)
1,000,000
800,000
600,000
400,000
200,000
0
0
2,000
4,000
6,000
8,000
10,000
Distance From Center (meters)
Study Area 4 CAFOs
48
Figure 10. First-Highest, Hourly, Hydrogen Sulfide Concentrations for Largest Swine
CAFO Area
49
Figure 11. Eighth-Highest, Hourly, Hydrogen Sulfide Concentrations for Largest Swine
CAFO Area
50
Figure 12. Swine Weight Dense Area First-Highest, Hourly, Hydrogen Sulfide
Concentrations and Public Use Separated Distances
51
Figure 13. Swine Weight Dense Area First-Highest, Hourly, Hydrogen Sulfide
Concentrations and RBCS Separated Distances
52
Figure 14. Swine Weight Dense Area. Eighth-Highest, Hourly, Hydrogen Sulfide
Concentrations and Public Use Separated Distances
53
Figure 15. Swine Weight Dense Area Eighth-Highest, Hourly, Hydrogen Sulfide
Concentrations and RBCS Separated Distances
54
Table 1. Swine Weight by Swine Type
Swine Type
Swine Gestation (& Boars)
Swine Gilts (& Isolation)
Swine Grow to Finish
Swine Nursery
Swine Sow and Litter
Swine Wean to Finish
One Head
One Head
Swine Weight (lbs) Swine Weight (Kg)
375
170.10
160
72.57
160
72.57
30
13.61
450
204.12
140
63.50
Table 2. High Swine Weight Dense Area Characteristics
All
All CAFOs
Number of CAFOs
Outliers by Weight (kg)
Total Swine Weight (kg)
Study Area
Study Areas
1
2
3
4
5
6
7
5990
287
55
20
44
51
29
44
44
207
15
3
1
0
5
4
1
1
1,288,805,933
86,187,817
12,042,855
11,865,471
11,579,578
17,793,204
9,699,542
12,121,270
11,085,897
Median Swine Wt per CAFO (kg)
174,179
271,720
162,840
567,614
290,299
285,763
271,720
272,700
184,862
Mean Swine Wt per CAFO (kg)
215,160
300,306
218,961
593,274
263,172
348,886
334,467
275,483
251,952
Swine Weight Kernel Density*
**8,567
**79,149
70,225
63,664
72,095
115,753
63,332
94,848
74,131
CAFOs per sq km*
**0.041
**0.181
0.242
0.088
0.194
0.225
0.128
0.194
0.194
* at center grid cell
** average
55
56
CHAPTER III
DISCUSSION
Determining the adequacy of current separation distances in protecting for the
HES and HEV of hydrogen sulfide concentrations emanating from swine CAFOs in Iowa
has great significance to research in the field of Environmental Health. Laws and
regulations pertaining to the placement of new swine CAFOs in Iowa may have a large
impact on the health of individuals living, working, and playing nearby. In many cases
these laws and regulations may fail to protect individuals from the harmful effects of
pollution emanating from these CAFOs. No studies could be found that determined if the
separation distance requirements from CAFOs in Iowa protected for high concentrations
of hydrogen sulfide in the air.
The research in this study found that minimum separation distance requirements
for the largest CAFO in Iowa failed to protect for the Health Effects Value (HEV) of 30
ppb set by the Environmental Protection Commission (EPC). If another swine CAFO is
constructed as large, or larger, than the current largest swine CAFO in Iowa, the
separation distance requirements from the CAFO to public use areas, residences,
businesses, churches, and schools may not be protecting human health from high hourly
hydrogen sulfide concentrations in the air. Additionally, no laws and regulations are in
place to require the new facility to abate those high emissions as would occur if the HES
was exceeded. If the Iowa Department of Natural Resources (IDNR) and EPC intends for
the separated distance requirements to be protective of adverse health outcomes, the
minimum separation distance requirements from very large swine CAFOs needs to be
increased to distances greater than 5,609 ft or the distance in which first-high hourly
concentrations exceeded 30 ppb. Even Canada, with some of the highest separation
distance requirements in the world does not require minimum separation distances 5,609
ft from CAFOs even for their largest CAFOs.
57
There are many directions in which potential future research in this area may be
taken. It may be beneficial to determine the maximum swine weight capacity of an
individual CAFO before first-highest, hourly hydrogen sulfide concentrations (FHC)
exceed the Health Effects Value (HEV) beyond current minimum separation distance
requirements. A new minimum separation distance requirement may then be established
for those large swine CAFOs to protect human health from high-hourly hydrogen sulfide
concentrations. It may also be advantageous to model highest hourly hydrogen sulfide
concentrations from the largest swine CAFO to determine how many hours the
concentrations are estimated to exceed the HEV beyond minimum separation
requirements. In addition, scenarios may be created within AERMOD to indicate
situations where many swine CAFOs concentrated together may exceed the HEV and
HES of hydrogen sulfide concentrations. This information may then be used to prevent
those situations from occurring within Iowa.
An important strength of this research is the use of a validated plume dispersion
modeling procedure for hydrogen sulfide emissions from CAFOs. Monitoring hydrogen
sulfide concentrations may be expensive, time consuming, and difficult to establish in
areas of greatest concern. In this study, modeling provides a valuable alternative to
analyze the protective qualities of minimum separation distance requirements.
Additionally, the modeling procedure indicates greater significance when it has been
verified from monitoring data.
An additional strength of this research is the use of two software programs.
AERMOD view and ArcMap provide unique qualities and analyses that the other
program may lack. AERMOD view provides a useful medium to estimate first-highest
and eighth-highest, hourly, hydrogen sulfide concentrations which ArcMap software
cannot accomplish. ArcMap software provides a useful medium to overlay estimated
hydrogen sulfide concentrations with separation distance requirements. Additionally, it
58
provides functions which can analyze the results. Without the use of both programs this
study would not have been possible.
There are a few important limitations of this research worth noting. First, the
Animal Feeding Operation (AFO) geodatabase acquired through the IDNR had some
spatial inaccuracies. The locations of AFO could vary from +/- 12 meters when
interpreting aerial photos to +/- 540 meters when interpreting public land surveys. These
inaccuracies could result in spatial differences in the swine weight density analysis and
CAFO density analysis. Additionally, this research used swine CAFOs that were
designated as active in 2010 but hydrogen sulfide concentrations were modeled in 2004.
Some variation can exist in the number of swine CAFOs active in 2010 opposed to 2004
leading to differences in the density analyses. The AFO geodatabase was not composed
of all swine CAFOs in Iowa either. Many CAFOs, usually fewer than 1,000 animal units,
are not required to become a permitted CAFO with the IDNR, thus they would not be
included in the geodatabase. It is not however, expected that these smaller CAFOs would
contribute significantly to hydrogen sulfide concentrations within the study areas within
this research.
Another limitation of this research is that the kernel density function does not
weight, swine weight the same as estimated hydrogen sulfide concentrations as you move
further away from the center of the CAFO. Although they follow similar curves, the
kernel density function may give greater weight to swine weight of CAFOs at medium
distances from each CAFO in question and less weight at the greatest spatial extent than
is seen by estimated hydrogen sulfide concentrations each CAFO in question. Due to a
limited ability to modify the weight given in the kernel density function in ArcMap
software, this kernel density curve was the best possible option.
59
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