Risk and Technology Review -

Analysis of Socio-Economic Factors for Populations 

Living Near Natural Gas Transmission & Storage

Facilities

Prepared by:

EC/R Incorporated

501 Eastowne Drive, Suite 250

Chapel Hill, NC 27514

EPA Contract No. EP-D-06-119

Work Assignment No. 4-02

Prepared for:

Terri Hollingsworth, Work Assignment Manager

Sector Based Assessment Group

Office of Air Quality Planning and Standards

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina 27711

July 2011
ii

Disclaimer

Although the analysis described in this document has been funded 

wholly or in part by the United States Environmental Protection 

Agency contract EP-D-06-119 to EC/R Incorporated, it has not 

been subject to the Agency's review and therefore does not 

necessarily reflect the views of the Agency, and no official 

endorsement should be inferred.
Contents

1. Introduction 1

2. Census Data 2

3. Calculation Methods 3

3.1 Racial and Ethnic Categories and the Total Population 4

3.2 Age Categories 5

3.3 Level of Education 5

3.4 Household Income 6

3.5 Poverty Level 7

4. Results 7

5. Uncertainty Discussion 8
iv
1

1. Introduction

This document describes the approach used to evaluate the potential cancer risks 

associated with inhalation and air-related exposures to hazardous air pollutants (HAP) in 

different social, demographic, and economic groups within the populations living near natural 

gas transmission and storage facilities in the United States. This work was carried out in support 

of the U.S. Environmental Protection Agency’s Residual Risk and Technology Review (RTR) 

for natural gas transmission and storage operations emissions subject to Maximum Available 

Control Technology (MACT) requirements under 40 CFR 63 Subpart HHH. 

In the RTR analysis, the Human Exposure Model, Version 3 (HEM3)1,2 was used to 

estimate cancer and noncancer risks due to the inhalation of HAP for the populations residing 

within 50 kilometers of each natural gas transmission and storage facility in the country. HEM3 

estimates cancer and noncancer risks at the level of census blocks using the AERMOD state-ofthe-art air dispersion model developed under the direction of the American Meteorological 

Society (AMS) / EPA Regulatory Model Improvement Committee (AERMIC). Each census 

block typically includes about 50 people. Additional information on the risk analysis is available 

in the docket for the proposed National Emission Standards for Hazardous Air Pollutant 

Emissions: Natural Gas Transmission and Storage Operations rulemaking where a report is 

provided, covering the inputs and specific assumptions, and addressing uncertainties.

In the current analysis, cancer risk estimates from the natural gas transmission and 

storage HEM3 modeling effort were linked to detailed census data in order to evaluate the 

distribution of risks for different social, demographic and economic groups. (The RTR analysis 

estimated all noncancer hazard indices to be less than one for the natural gas transmission and 

storage source category; therefore a demographic analysis of potential noncancer impacts is not 

presented.) The following population categories were included in this analysis:

 Total population

 White

 Minority

 African American (or Black)

 Native Americans

 Other races and multiracial

 Hispanic or Latino

 Children 18 years of age and under

 

1. EC/R. 2006. Modeling for the Residual Risk and Technology Review Using the Human Exposure Model 

3 – AERMOD Version. Prepared by EC/R Incorporated for the U.S. Environmental Protection Agency, 

Research Triangle Park, NC. 

2. EC/R. 2008. HEM-3 User’s Guide. Prepared by EC/R Incorporated for the U.S. Environmental 

Protection Agency, Research Triangle Park, NC. http://www.epa.gov/ttn/fera/human_hem.html#guide
2

 Adults 19 to 64 years of age

 Adults 65 years of age and over

 Adults without a high school diploma

 Households earning under the national median income

 People living below the poverty line

The HEM3 results for a particular census block reflect the level of risk that would be 

experienced by an individual residing in the block for 70 years. The distributions of source 

category risks across the various demographic groups were compared to those associated with 

HAP sources at the facilities containing the source category (i.e., “facility-wide”), and to

nationwide distributions of each of the demographics groups. 

The census data used in this analysis is described in Section 2. The algorithms used to 

compute the distributions of risk and exposure are presented in Section 3. The results of this 

analysis are presented in Section 4. 

2. Census Data

Table 1 summarizes the census data used in this analysis, showing the source of each 

dataset and the level of geographic resolution. All of the data are from the 2000 Decennial 

census. Race and ethnicity data were obtained at the census block level. Age distributions, data 

on educational status, and economic data were obtained at the block group level. A census block 

contains about 50 people on average; and a block group contains about 26 blocks on average, or 

about 1,350 people. (For comparison, a census tract is larger than a block group, with each tract 

containing an average of 3 block groups, or about 4,300 people.)

Table 1. Summary of Census Data used to Analyze Risks for Different Socioeconomic Groups

Type of population category Source of data

Level of 

geographic 

resolution

Racial and ethnic categories Landview® Census block

Age groups SF3 Table P8 Block group

Level of education - adults without a high 

school diploma

SF3 Table 37 Block group

Households earning below the national 

median income

SF3 Table 52 Block group

People living below the poverty line SF3 Table P87 Block group
3

Data on race and ethnicity were obtained primarily from the Landview® database 

compiled by the Census Department.3 Landview® gives a breakdown for the population of each 

census block among different racial classifications, including: White, African American or 

Black, American Indian or Native Alaskan, Asian, Native Hawaiian or other South Pacific 

Islander, other race, and two or more races. In the current analysis, the Asian, Native Hawaiian 

or other South Pacific Islander, and other race categories were combined into a single category. 

The Landview® database also indicates the number of people in each tract that are of Hispanic 

or Latino ethnicity. Landview® covers the 50 states, the District of Columbia, and Puerto Rico, 

but does not cover the Virgin Islands. Race and ethnicity data on the Virgin Islands were 

obtained from the Virgin Islands Summary File.4

Data on age distributions, poverty status, household incomes, and education level in the 

U.S. and Puerto Rico were obtained from the 2000 Census of Population and Housing Summary

File 3 (SF3) Long Form. For the U.S. this file was accessed on a DVD version prepared by 

GeoLytics.5 SF3 data for Puerto Rico were obtained from the Census Department website,6and 

data for the Virgin Islands were retrieved from similar tables in the Virgin Islands Summary

File.4

The SF3 data set consists of over 800 separate tables, each providing information on a 

different subject. For the current analysis, data were obtained from Tables P8, P37, P52, and 

P87. Table P8 gives the estimated numbers of men and women in different age categories for 

each census block group. Table P37 analyzes the level of education attained by men and women 

over 25 years of age (e.g. some high school but no high school diploma, high school graduate, 

some college, etc.). Table P52 gives information on household income in 1999, and Table P87 

estimates the number of people living below the poverty line in each block group. 

3. Calculation Methods

The HEM3 models the cancer risk at a point near the geographic center of each census

block.7 For the current analysis, this risk estimate was assumed to apply to all individuals 

residing in the block. We used block identification codes to link the HEM3 modeling results for 

 

3. Census. 2002. LandView 5 on DVD [electronic resource] : a viewer for EPA, Census and USGS data and 

maps. U.S. Census Bureau, Washington, D.C.

4. Census. 2008. Virgin Islands Summary File. U.S. Census Bureau, Washington, D.C. 

www.factfinder.census.gov

5. Census. 2004. Census DVD 2000 Long Form SF3, Release 2.2. Geolytics, Inc., East Brunswick, NJ. 

www.geolytics.com

6. Census. 2008. SF3 Data for Puerto Rico. U.S. Census Bureau, Washington, D.C. 

www.factfinder.census.gov

7. HEM3 generally uses the coordinates given by the census for the internal point, or “centroid” of each 

block. However, when the footprint of an industrial facility includes the block centroid, the model is 

designed to identify the highest-risk point outside of the facility’s footprint.
4

each block to the appropriate census statistics. This allowed us to estimate the numbers of 

people falling into different population subcategories within each block. We then analyzed the 

distribution of estimated inhalation risks within each population subcategory, giving the numbers 

of people within the subcategory that are exposed to different risk levels. Each distribution 

involved a tabulation of all the census blocks modeled for the natural gas transmission and 

storage source category. We also computed the average risk for all individuals in each 

population subcategory. 

Distributions of risk and average risks were computed for the raw HEM3 model results 

for natural gas transmission and storage operations. For comparison, distributions of risk and 

average risks were also computed for all emission sources at the facility (including natural gas 

transmission and storage) (e.g., “facility-wide”). A nationwide demographic breakdown (i.e., 

population percentage in each demographic group for the country as a whole) is also provided in 

the results table for comparison. 

Section 3.1 describes the calculation method used for categories where block-level data 

were available -- racial and ethnic categories and the total population. Sections 3.2 through 3.5 

describe calculation methods for age categories, education status, household income, and poverty 

status, respectively. 

3.1 Racial and Ethnic Categories and the Total Population

Since race and ethnicity data were available at the census block level, the calculation of 

risk distributions for these categories involved a simple block-by-block accumulation of the 

people in each subcategory. We began by identifying a set of bins reflecting the level of risk. 

The population of each block was then assigned to the appropriate risk bin based on the modeled 

risk level in the block. The numbers of people in each risk bin were then added together for all 

of the blocks modeled for the natural gas transmission and storage source category:

H(Rab,s) = ∑i

(Ra≤Ri<Rb) [N(s,i)] (1)

where:

H(Rab,s) = the population count for risk bin Rab, which is between Ra and Rb for population 

subgroup “s”

Ri = the modeled risk level in block “í” (estimated lifetime cases of cancer per 

million population)

∑i

(Ra≤Ri<Rb) refers to the summation over all blocks i where Ri falls in bin Rab, between Ra

and Rb

N(s,i) = the number of people within population subcategory s, in block i

The same approach was used for the total population. The average risk for a given population 

subcategory or for the total population was calculated using the following equation:

A(S) = ∑i [N(s,i) × Ri] ⁄ ∑i [N(s,i)] (2)

where:

A(s) = the average risk for population subgroup “s” (estimated lifetime cases of cancer 
5

per million population)

∑i refers to the summation over all blocks “í” modeled for the emission source 

category

N(s,i) and Ri were defined above

3.2 Age Categories

Age data were retrieved from the Table P8 of the census SF3 Table, which contains data

on the numbers of males and females of different ages in each census block group. In processing 

the age data, we began by aggregating the categories in the census to the broader age groups 

studied in this analysis. For instance, the total number of children 18 years of age and under was 

calculated by adding together the number of girls under 1 year, the number of boys under 1 year, 

the number of 1-year-old girls, the number of 1-year-old boys, and so on up to and including 18-

year-old girls and boys. In this way, we calculated the number of children age 18 and under, the 

number of adults from 19 to 64, and the number of adults 65 and older in each census block 

group.

The next step was to estimate the numbers of people in each age group at the block level. 

To make this calculation, we assumed that the fraction of people in each age group was the same 

for all blocks in a given block group. Thus, the number of people in a particular age group and 

within a particular census block was estimated as follows: 

N(a,b/bg) = N(t,b/bg) × N(a,bg) ⁄ N(t,bg) (3)

where:

N(a,b/bg) = number of people within age group “a”, in block “b” of block group “bg”

N(t,b/bg) = total number of people in block “b” of block group “bg”

N(a,bg) = number of people within age group “a” in block group “bg”

N(t,bg) = total number of people in block group “bg”

Equation 1 was then applied to the block-level population estimates to generate risk distributions 

for different age groups, and Equation 2 was used to compute the average risk for each age 

group.

3.3 Level of Education

Table P37 of the SF3 dataset specifies the education status for men and women age 25 

and older for each census block group, based on the last grade completed. To obtain the total 

number of adults without a high school degree, we added together the numbers who had 

completed grades below a high school senior. Thus, the number of people without a high school 

degree equals the sum of the number of males with no schooling, the number of females with no 

schooling, the numbers of males and females who have completed nursery school through 4th

grade, up to the numbers of males and females who have completed some high school but not 

received a high school degree.
6

The number of adults without a high school degree as a fraction of the total population 

was assumed to be the same for each block in the block group. Thus, the number of adults 

without a high school degree in each block was computed as follows:

N(nhs,b/bg) = N(t,b/bg) × N(nhs,bg) ⁄ N(t,bg) (4)

where:

N(nhs,b/bg) = number of adults without a high school diploma, in block “b” of block group 

“bg”

N(t,b/bg) = total number of people in block “b” of block group “bg”

N(nhs,bg) = number of adults without a high school diploma in block group “bg”

N(t,bg) = total number of people in block group “bg”

Equation 1 was then used to generate risk distributions based on the block-level results, and 

Equation 2 was used to compute the average risk for adults without a high school diploma. 

3.4 Household Income

Table P52 of the SF3 dataset estimates the numbers of households in each block group 

with income for the year 1999 in various ranges, generally divided into $5,000 increments (e.g. 

$10,000 to $14,999, $15,000 to $19,999, etc.). The median national income for 1999 was about 

$42,000 per year. Therefore, in order to determine the number of households with incomes 

under the median income, we added the estimates for the ranges below that level. We assumed 

that the household incomes in the $40,000 to $44,999 increment were evenly distributed over 

this range. Therefore, 40% of the households in the $40,000 to $44,999 income range were 

assumed to be below the national median income of about $42,000. The following equation was 

used to estimate the fraction of households below the national median income within each census

block group:

F(sm,bg) = [C<10 + C10-15 + .... + C35-40 + (0.4×C40-45)] ⁄ CT (5)

where:

F(sm,bg) = fraction of households in block group “bg” with incomes below the median 

national income

C<10 = number of households with incomes under $10,000

C10-15 = number of households with incomes from $10,000 to $14,999

C35-40 = number of households with incomes from $35,000 to $39,999

C40-45 = number of households with incomes from $40,000 to $44,999

CT = total number of households in block group “bg”

The fraction of people living in households below the median income for each block 

within the block group was assumed to be the same as the fraction of households below the 

median income for the block group.

N(sm,b/bg) = F(sm,bg) × N(t,b/bg) (6)
7

where:

N(sm,b/bg) = number of people in block “b” of block group “bg” living in households below 

the national median income

F(sm,bg) = fraction of households in block group “bg” below the national median income

N(t,b/bg) = total number of people in block “b” of block group “bg”

Equation 1 was then used to generate risk distributions based on the block-level results, and 

Equation 2 was used to compute the average risk for adults without a high school diploma. It

must be noted that this approach neglects any potential relationship between household size and 

income level within a particular block group. However, it is expected to provide a reasonable 

indication of the risk level of people living below the national median income, relative to the 

population as a whole. 

3.5 Poverty Level

Table P87 of the SF3 dataset estimates the total number people in each block group living 

below the poverty level, as well as the numbers of people below the poverty level in different age 

groups. The current study did not include an analysis of poverty status by age group, only of the 

total population below the poverty line. The fraction of people below the poverty line was 

assumed to be the same for each block in the block group. Thus, the population below the 

poverty line in each block was computed as follows:

N(p,b/bg) = N(T,b/bg) × N(p,bg) ⁄ N(T,bg) (7)

where:

N(p,b/bg) = number of people below the poverty line in block “b” of block group “bg”

N(T,b/bg) = total number of people in block “b” of block group “bg”

N(p,bg) = number of people below the poverty line in block group “bg”

N(T,bg) = total number of people in block group “bg”

Equation 1 was then used to generate risk distributions based on the block-level results, and 

Equation 2 was used to compute the average risk for adults without a high school diploma. 

4. Results

The distribution of estimated lifetime inhalation cancer risks above 1 in a million for 

different racial and ethnic groups among the population living near natural gas transmission and 

storage facilities is shown in Table 2. For comparison purposes, Table 2 provides the 

distributions of inhalation risks for the population exposed to emissions from all source 

categories at the natural gas transmission and storage facility (i.e., facility-wide); and Table 2 

provides the nationwide percentages of the various demographic groups. Detailed demographics 

data and analyses used to create Table 2 can be found in Appendix A of this document.
8

The results of the demographic analysis presented in Table 2 indicate that there are 

approximately 2,500 people exposed to a cancer risk greater than or equal to 1-in-1-million for 

the natural gas transmission and storage source category. The demographic results for those 

impacted by the source category are below or similar to their corresponding national percentages 

for all racial, ethnic and age groups. With respect to those below the poverty level, there is a 

modest percentage increase (of 4%) compared to the corresponding national percentage (of 

13%). Additionally, the “over 25 without a high school diploma” demographic percentage is 

higher for those impacted by the source category (at 20%) than the corresponding national 

percentage (of 13%) for this demographic.

The facility-wide demographic analysis presented in Table 2 indicates that there are 

approximately 99,000 people exposed to a cancer risk greater than or equal to 1-in-1-million

resulting from all emissions from these facilities, and that about 42 percent of this population can 

be classified as minority (compared to the national minority percentage of 25%). This higher 

minority percentage is attributable to a higher African American demographic percentage (of 

40%) compared to the corresponding national percentage (of 12%). In addition, about 20 percent 

of the impacted population is below the poverty level, which is 7 percentage points higher than 

the corresponding national percentage for this demographic (of 13%). There is also a modest 

percentage increase (of 2%) for both the “ages 0 to 18” demographic and the “over 25 without a 

high school diploma” demographic compared to the corresponding national percentages for these 

demographics (of 27% and 13%, respectively).

5. Uncertainty Discussion

Our analysis of the distribution of risks across various demographic groups is subject to 

uncertainties associated with the extrapolation of census-block group data (e.g., income level and 

education level) down to the census block level. The uncertainties in the risk estimates include 

the same uncertainties in emissions data sets, in air dispersion modeling, in inhalation exposure 

and in dose response relationships that are associated with our source category risk estimates. 

We did not perform tests for statistical significance. It is likely that most of the differences 

between source category and nationwide estimates would be statistically significant because of 

the sample sizes of the nationwide data and the people at risk greater than 1 in a million from the 

source category. However, there may be select cases where the sample size of people at risk 

greater than 1 in a million is insufficient to show a statistically significant difference with the 

nationwide data.

The methodology for our demographic analyses is still evolving. While this is our best 

attempt to provide useful information now, our thinking is continuously advancing. EPA is in 

the process of developing technical guidance for environmental justice analyses. We present 

these analyses, with their associated uncertainties, to EPA decision makers and the public as 

additional analyses to inform RTR decisions.
9

Table 2. Summary of Demographic Assessment of Risk Results for the Natural Gas Transmission & Storage Category

Emissions Basis

Demographic Group

Total Minority

African 

American

Other and

Multiracial

Hispanic

or Latino

Native 

American

Ages 0 

to 18

Ages 19 

to 64

Ages 65 

and up

Below

the

Poverty 

Level

Over 25 

Without 

a HS 

Diploma

Nationwide 

Demographic 

Breakdown

n/a 285,339,128 25% 12% 12% 14% 0.9% 27% 60% 12% 13% 13%

Maximum 

Risk 

(in 1 

million)

Population With Risk Greater Than or Equal to 1 in 1 million

Source 

Category 90 2,481 8% 6% 1% 1% 0.1% 26% 61% 13% 17% 20%

Facility-wide

200 98,891 42% 40% 2% 2% 0.2% 29% 59% 12% 20% 15%

Notes:

Source Category and Facility-wide emissions are based on January 2011 NEI data.

Minority population is the total population minus the white population.

Population figures are for the population residing within 50 km of these facilities whose cancer risks are estimated to be greater than or equal to 1 in a million.

There are no hazard indices (HIs) > 1 for the natural gas transmission and storage source category.

A-1

Appendix A
A-2

Total

population White

African

American

Native 

American

Other and 

multiracial

Hispanic or 

Latino

c

0 to 1 58,363,920 40,536,534 8,078,975 459,705 9,288,706 10,727,903

1 to 5 1,937 1,749 160 1 27 28

5 to 10 435 430 1 1 3 3

10 to 20 0 0 0 0 0 0

20 to 30 101 97 0 0 4 0

30 to 40 0 0 0 0 0 0

40 to 50 0 0 0 0 0 0

50 to 100 8 8 0 0 0 0

Total number 58,366,401 40,538,818 8,079,136 459,707 9,288,740 10,727,934

0.0013 0.0014 0.001 0.0009 0.0007 0.0006

0 to 1 58,267,510 40,481,495 8,040,021 459,483 9,286,511 10,726,333

1 to 5 93,709 53,663 37,729 220 2,097 1,538

5 to 10 4,466 3,285 1,058 4 119 57

10 to 20 446 222 216 0 8 5

20 to 30 116 35 80 0 1 1

30 to 40 33 8 25 0 0 0

40 to 50 101 97 0 0 4 0

50 to 100 14 12 2 0 0 0

100 to 150 0 0 0 0 0 0

150 to 200 0 0 0 0 0 0

200 to 250 6 1 5 0 0 0

Total number 58,366,401 40,538,818 8,079,136 459,707 9,288,740 10,727,934

0.020 0.020 0.028 0.011 0.013 0.012

Notes:

c

The Hispanic or Latino population is double-counted in this analysis, since different individuals within the

category may classify themselves as White, African American, Native American, or other.

Table A-1. Distribution of Inhalation Cancer Risk for Racial and Ethnic Groups

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not adjusted for 

exposure factors.

Range of lifetime individual 

cancer risk (chance in one

million)a

Average risk (chances in 

one million)

b

Distributions by race are based on demographic information at the census block level. Risks from natural

gas transmission & storage emissions were modeled at the block level. 

Modeled risk from the natural gas 

transmission & storage category

Modeled risk from facilities containing 

natural gas transmission & storage source 

Average risk (chances in 

one million)

Numbers of people in different ranges for lifetime cancer riskb
A-3

Total 

population

Ages 0 thru 

18

Ages 19 thru 

64

Ages 65 and 

up

0 to 1 58,363,920 16,459,946 35,284,060 6,619,914

1 to 5 1,937 525 1,171 241

5 to 10 435 105 262 68

10 to 20 0 0 0 0

20 to 30 101 17 65 19

30 to 40 0 0 0 0

40 to 50 0 0 0 0

50 to 100 8 2 5 1

Total number 58,366,401 16,460,595 35,285,562 6,620,243

0.0013 0.0012 0.0013 0.0015

0 to 1 58,267,510 16,431,833 35,227,693 6,607,983

1 to 5 93,709 27,319 54,847 11,543

5 to 10 4,466 1,257 2,585 624

10 to 20 446 119 274 53

20 to 30 116 37 66 14

30 to 40 33 9 20 4

40 to 50 101 17 65 19

50 to 100 14 3 9 2

100 to 150 0 0 0 0

150 to 200 0 0 0 0

200 to 250 6 2 4 1

Total number 58,366,401 16,460,595 35,285,562 6,620,243

0.020 0.019 0.020 0.020

Notes:

Table A-2. Distribution of Risk for Different Age Groups

Modeled risk from the natural gas transmission 

& storage category

b

Distributions by age are based on modeling data at the Census block level, and age data at

the block group level. All blocks in a block group are assumed to have the same age 

Range of lifetime individual 

cancer risk (chance in one

million)a

Numbers of people in different ranges for lifetime cancer

riskb

Average risk (chances in one

million)

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and 

not adjusted for exposure factors.

Modeled risk from facilities containing natural

gas transmission & storage source category

Average risk (chances in one

million)
A-4

Total

population

Total number 

25 and older

Number 25 and older 

without a high school

diploma

0 to 1 58,363,920 36,952,859 8,189,943

1 to 5 1,937 1,254 364

5 to 10 435 305 111

10 to 20 0 0 0

20 to 30 101 75 16

30 to 40 0 0 0

40 to 50 0 0 0

50 to 100 8 6 2

Total number 58,366,401 36,954,499 8,190,436

0.0013 0.0013 0.0015

0 to 1 58,267,510 36,892,503 8,175,527

1 to 5 93,709 58,561 14,196

5 to 10 4,466 2,962 588

10 to 20 446 294 75

20 to 30 116 70 23

30 to 40 33 22 8

40 to 50 101 75 16

50 to 100 14 10 3

100 to 150 0 0 0

150 to 200 0 0 0

200 to 250 6 4 1

Total number 58,366,401 36,954,499 8,190,436

0.020 0.020 0.019

Notes:

Table A-3. Distribution of Risk for Adults with and without a High School Diploma

Modeled risk from the natural gas transmission & 

storage category

b

Distributions by education level are based on modeling data at the Census block level, and 

education data at the block group level. All blocks in a block group are assumed to have the

same education level distribution.

Range of lifetime individual cancer

risk (chance in one million)a

Numbers of people in different ranges for lifetime

cancer riskb

Average risk (chances in one

million)

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and 

not adjusted for exposure factors.

Modeled risk from facilities containing natural gas 

transmission & storage source category

Average risk (chances in one

million)
A-5

Total 

population

People living in

households below

the national median

income

c

People living 

below the 

poverty line

0 to 1 58,363,920 29,607,221 8,349,352

1 to 5 1,937 1,242 322

5 to 10 435 320 93

10 to 20 0 0 0

20 to 30 101 58 16

30 to 40 0 0 0

40 to 50 0 0 0

50 to 100 8 6 2

Total number 58,366,401 29,608,847 8,349,784

0.0013 0.0015 0.0015

0 to 1 58,267,510 29,552,048 8,330,279

1 to 5 93,709 54,013 18,748

5 to 10 4,466 2,351 648

10 to 20 446 254 58

20 to 30 116 86 25

30 to 40 33 24 6

40 to 50 101 58 16

50 to 100 14 10 3

100 to 150 0 0 0

150 to 200 0 0 0

200 to 250 6 4 1

Total number 58,366,401 29,608,847 8,349,784

0.020 0.020 0.020

Notes:

Table A-4. Distribution of Risk for People Living in Households below the

National Median Income and Below the Poverty Line

Range of lifetime individual 

cancer risk (chance in one

million)a

Numbers of people in different ranges for lifetime 

cancer riskb

Average risk (chances in one

million)

c

The median income is the national median household income in 1999, about $42,000.

Modeled risk from the natural gas transmission & 

storage category

Average risk (chances in one

million)

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration 

and not adjusted for exposure factors.

b

Distributions by income are based on modeling data at the Census block level, and 

income data at the block group level. All blocks in a block group are assumed to have the 

same income distribution.

Modeled risk from facilities containing natural 

gas transmission & storage source category