WORLD TRADE CENTER

 BACKGROUND STUDY

REPORT

INTERIM FINAL

April 2003

Prepared for:

United States Federal Emergency Management Agency 

IAG No.: EMW-2002-IA-0127

Prepared by:

United States Environmental Protection Agency, Region 2

New York City Response and Recovery Operations

290 Broadway

New York, NY 10007-1866

Approved by:

Kathleen C. Callahan

Assistant Regional Administrator

New York City Response and Recovery Operations
ii

Table of Contents

EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.0 INTRODUCTION ...........................................6

2.0 BACKGROUND AND PROJECT DESCRIPTION .................6

2.1 Background ..........................................6

2.2 Purpose/Objective .....................................6

2.3 Project Description ....................................7

2.4 Project Team/Responsibilities ............................8

2.5 Data Usage ...........................................8

3.0 SAMPLING APPROACH/RATIONALE .........................9

3.1 Selection of Sampling Area Location ......................9

3.2 Selection of Building Types and Obtaining Access ...........9

3.3 Selection Criteria for Number of Buildings, Residences and

Common Space Sampled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.4 Selection of Contaminants of Potential Concern . . . . . . . . . . . . . 10

4.0 SAMPLING METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1 Sampling Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1.1 Indoor Air Sample Collection . . . . . . . . . . . . . . . . . . . . . . . 12

4.1.2 Microvacuum Sample Collection . . . . . . . . . . . . . . . . . . . . 12

4.1.3 Wipe Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1.4 Bulk Dust Sample Collection . . . . . . . . . . . . . . . . . . . . . . . 13

4.1.5 Quality Control Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.2 Sampling Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.2.1 Air Sampling Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.2.2 Microvacuum Sampling Equipment . . . . . . . . . . . . . . . . . . 16

4.2.3 Wipe Sampling Equipment . . . 17

4.2.4 Bulk Sampling Equipment . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.3 Sample Numbering/Identification . . . . . . . . . . . . . . . . . . . . . . . . 17

4.4 Sample Shipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.5 Data Validation and Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.5.1 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.5.2 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5.0 SAMPLING PROTOCOL DEVIATIONS . . . . . . . . . . . . . . . . . . . . . . . 19

6.0 ANALYTICAL RESULTS AND DEVELOPMENT OF BACKGROUND

CONCENTRATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6.2 Results and Development of Background Concentrations . . . . . 23
iii

6.2.1 Asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6.2.2 Man-Made Vitreous Fibers . . . . . . . . . . . . . . . . . . . . . . . . . 25

6.2.3 Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6.2.4 Dioxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

6.2.5 Polycyclic Aromatic Hydrocarbons . . . . . . . . . . . . . . . . . . 28

6.3 Minerals and Total Dust Results - Development of Background

Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6.3.1 Crystalline Silica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6.3.1.1 Alpha-quartz . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6.3.1.2 Cristobalite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

6.3.1.3 Tridymite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.3.2 Calcite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6.3.3 Gypsum . . . 31

6.3.4 Portlandite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.3.5 Total Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.0 HISTORICAL STUDIES ON BACKGROUND CHARACTERIZATION

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.1 Background Literature Search Results . . . . . . . . . . . . . . . . . . . . 32

7.1.1 Residential Indoor Airborne Asbestos Measurements . . . . 33

7.1.2 Settled Asbestos Dust Measurements . . . . . . . . . . . . . . . . . 33

7.1.3 Airborne Man-Made Vitreous Fibers Measurements . . . . . 33

7.1.4 Man-Made Vitreous Fibers in Settled Dust or Soil . . . . . . 34

7.1.5 Lead Levels in the Ambient Air . . . . . . . . . . . . . . . . . . . . . 34

7.1.6 Residential Settled Lead Dust Measurements . . . . . . . . . 34

7.1.7 Dioxins in Soil and Settled Dust . . . . . . . . . . . . . . . . . . . . . 35

7.1.8 Polycyclic Aromatic Hydrocarbons in Sediment and Soil

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7.2 Comparison of WTC Background Study to Other Studies . . . . . 35

7.2.1 Comparison of Airborne Asbestos Concentrations . . . . . 35

7.2.2 Comparison of Asbestos Settled Dust Concentrations . . . . 36

7.2.3 Comparison of Airborne Man-Made Vitreous Fiber (MMVF)

Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

7.2.4 Comparison of Man-Made Vitreous Fibers in Settled Dust or

Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

7.2.5 Comparison of Lead Concentrations in the Ambient Air . . 37

7.2.6 Comparison of Settled Lead Dust Measurements . . . . . . . 37

7.2.7 Comparison of Dioxin Concentration in Settled Dust . . . . 39

7.2.8 Comparison of Polycyclic Aromatic Hydrocarbon

Concentration in Settled Dust . . . . . . . . . . . . . . . . . . . . . 39

8.0 DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
iv

FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 1 World Trade Center Background Study and WTC Dust Cleanup

Program Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 4-1 WTC Background Study Sampling and Analytical Procedures

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 4-2 WTC Background Study Field Sample Collection Summary

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 4-3 Quality Control Wipe Spike Sample Results For Lead . . . . . 48

Table 6-1 Organic and Inorganic Results Summary for Residential and

Common Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 6-2 Organic and Inorganic Results Summary for Residential Spaces

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 6-3 Organic and Inorganic Results Summary for Common Spaces

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 6-4 Mineral Compounds and Total Dust Results Summary for

Residential and Common Spaces . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 6-5 Mineral Compounds and Total Dust Results Summary for

Residential Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 6-6 Mineral Compounds and Total Dust Resu lts Summary for

Common Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 7-1 Summary of U.S. Residential Building Average Indoor

Airborne Asbestos Concentrations for Asbestos Fibers 3 5 mm

Long by Direct Transmission Electron Microscopy . . . . . . . . . . 48

Table 7-2 Summary of Settled Asbestos Surface Dust Loadings

Determined Through Microvacuum Sampling and Indirect

Analysis by Transmission Electron Microscopy . . . . . . . . . . . . . 48

Table 7-3 Household Dust Lead Measurements from Wipe Sampling in

an Old, Urban Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 7-4 Estimated Distribution of Lead Loadings (ug/ft2

) In U.S.

Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 7-5 Background Soil Concentrations of Polycyclic Aromatic

Hydrocarbons (PAHs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 8-1 Background Concentrations Derived From The Analytical

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Table 8-3 Comparison of Background Concentrations Derived From The

Analytical Results Using Values of Zero, 1⁄2 of the Detection Limit,

or the Detection Limit

ATTACHMENTS

ATTACHMENT A - World Trade Center Indoor Air Assessment:

Selecting Contaminants of Potential Concern and Setting HealthBased Benchmarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

ATTACHMENT B - Data Validation Standard Operating Procedures List

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
v

ATTACHMENT C - EMSL Analysis Standard Operating Procedures List

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

ATTACHMENT D - Sampling and Analytical Methods List . . . 49

ATTACHMENT E - Photographs of Sample Collection Activities . . . . 49

ATTACHMENT F - NIST Certificate of Analysis, Standard Reference

Material 2581 and Appendix 14.3: Procedure for the Preparation of

Field Spiked Wipe Samples of the Guidelines for the Evaluation

and Control of Lead-Based Paint Hazards in Housing. . . . . . . . . 49
vi

ACKNOWLEDGMENTS

EPA is grateful for the generous contribution of the residents of Manhattan who

provided access to EPA to sample their dwelling units, and of the building owners

who provided access to the common space areas used in this Study.

This project was designed and implemented by EPA with the support of the

Indoor Air Work Group of EPA’s Indoor Air Task Force. The work group

organizations directly involved in the development of the project included the

New York City Department of Environmental Protection; New York City

Department of Health and Mental Hygiene; New York City Mayor’s Office of

Environmental Coordination; New York City Office of Emergency Management, 

New York State Department of Health; Agency for Toxic Substances and Disease

Registry; Occupation Safety and Health Administration, EPA’s Office of Solid

Waste and Emergency Response and EPA Region 2.

EPA acknowledges the assistance of New York City’s Housing and Preservation

Department for its assistance in identifying Study locations.

Note:

This interim final report is a working document that will be subject to further

Agency and third- party review. EPA intends to excerpt, and possibly expand,

portions of this report for inclusion in manuscripts that will be submitted to

scientific journals for review and consideration for publishing.
WORLD TRADE CENTER BACKGROUND STUDY 1

EXECUTIVE SUMMARY

The United States Environmental Protection Agency (EPA) responded to the

September 11, 2001 attack upon the World Trade Center in conjunction with the

President's declaration of a national disaster. The Federal Emergency

Management Agency (FEMA), as the federal coordinating office in the disaster,

issued mission assignments to EPA in the areas of cleaning dust/debris from the

streets of lower Manhattan, sampling the ambient environment (air and dust

samples), providing washing stations for personnel working at the WTC response

and recovery site as well as equipment and dust/debris being removed from the

site, and disposal of hazardous materials found at the WTC site.

Residents of lower Manhattan began to raise their concerns about the safety and

reliability of cleaning methods to remove dust and debris from their residential

units and building facades. Traditional FEMA support programs were available.

Yet due to the unprecedented nature of the disaster and on-going concerns,

residents continued to request additional assistance. After evaluating the

concerns related to indoor impacts of dust and debris and fire related particle

deposition, EPA Administrator Christine Todd Whitman formed an Interagency

Indoor Air Task Force. This group included representatives from the following

agencies: the regional and national office of the EPA, FEMA, the New York City

Department of Health and Mental Hygiene (NYCDOHMH), the New York City

Department of Environmental Protection (NYCDEP), the New York State

Department of Environmental Conservation(NYSDEC), the New York State

Department of Health (NYSDOH) the Occupational Safety and Health Agency

(OSHA), and the Agency for Toxic Substances and Disease Registry (ATSDR). 

The group recommended various issues that could be addressed. Thus, in May

2001, EPA, FEMA and NYC announced a voluntary cleanup program for

residential units, that would run in parallel to several other efforts to address the

concerns of lower Manhattan residents regarding the potential risks from

exposure to residual WTC dust and debris. These efforts were funded by FEMA

through interagency agreements with EPA and NYC and include:

• identification of the Contaminants of Potential Concern (COPCs)

• a background study of the COPCs in upper Manhattan (Background

Study)

• inspection and cleaning of building exteriors in lower Manhattan

• Indoor Air Residential Assistance - WTC Dust Cleanup Program

• cleaning of unoccupied, uncleaned buildings, and

• a study of cleaning techniques in an unoccupied building adjacent to the

WTC site that was directly impacted by the WTC collapse (WTC
WORLD TRADE CENTER BACKGROUND STUDY 2

Residential Confirmation Cleaning Study)

These efforts have been conducted simultaneously to ensure that residents are

provided the opportunity to have any WTC residual material removed from their

units as quickly as possible. 

This report presents the results of the WTC Background Study conducted by

EPA. Results from this Study cannot account for the variability with indoor

environments in general (i.e., cross contamination from outdoors to indoors, way

of life and level of cleanliness). The measurements are limited to each specific

apartment or common area sampled at that specific time the samples were

collected. 

Project Objectives / Overview

The objective of this Background Study was to determine and/or estimate indoor

baseline levels or background concentrations for the presence of specific

contaminants related to building materials and combustion byproducts that may

be released when building materials are burned during a fire. The background

concentrations derived from this Study will be used to supplement the healthbased benchmarks established in the "World Trade Center Indoor Air

Assessment: Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks" document and were identified as a potential source of

alternate cleanup values if the health-based benchmarks were not able to be

achieved. The selected Contaminants of Potential Concern (COPC) includes

asbestos, lead, dioxins, polycyclic aromatic hydrocarbons (PAHs), fibrous glass

and minerals including crystalline silica (i.e., "-quartz, cristobalite, tridymite),

calcite, gypsum, and portlandite. 

The number of buildings, residences and common spaces samples were

determined by what could practically be achieved to avoid impeding the project.

The geographical area for the Background Study (78th Street and North) was

selected based on preliminary modeling of meteorological data on September 11,

2001 and shortly thereafter. The modeling was performed by EPA’s Office of

Research and Development. The distance of buildings sampled in the Study with

respect to the WTC site ranges from 8 to 19 kilometers (5 to 12 miles).

Sampling was conducted in fourteen residential buildings not impacted by the

airborne dust plume which emanated from the WTC site. When possible, samples

were collected from two residential units and from one common area, such as the

lobby, hallway, stairwell, or building laundry facility, in each building. In total

EPA sampled twenty-five residential units and nine common areas within the

fourteen buildings. Results of the Background Study are discussed in general

terms and are not specific to the units sampled.
WORLD TRADE CENTER BACKGROUND STUDY 3

Data Assessment

The analytical data for each sample collected were evaluated for individual

apartments and cumulatively in data sets (e.g., asbestos wipe sample data for

residential dwellings, common spaces and a combined data set for residential and

common spaces) to derive a background concentration that is representative for

Manhattan.

The evaluation for individual apartments compared the reported results for each

sample to the health-based criteria developed in the “World Trade Center Indoor

Air Assessment: Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks” report. The analytical data was presented in tabular

format for each apartment with text that explains the reported results. Any

detected concentration that exceeded the health-based benchmarks were discussed

in detail in writing and orally when requested by owner.

Cumulatively, the data were statistically evaluated in this report to provide a

mean, standard deviation, minimum and maximum. For each analyte and sample

media, a concentration representative of background for Manhattan has been

calculated (see table below). These background concentrations will be used to

supplement the health-based benchmarks established in the “World Trade Center

Indoor Air Assessment: Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks” report and may be used as an alternative cleanup

value if the health-based benchmark cannot be achieved.
WORLD TRADE CENTER BACKGROUND STUDY 4

Revised May 14, 2003

Background concentrations that were derived based on the analytical results from the

samples collected in this study. The concentrations listed in the table represent the 95%

upper confidence limit (UCL) on the arithmetic mean.

Compound Air

Settled Dust

Bulk Dust Porous

Surface

Hard Surface

Asbestos n/a (<1%) 6,192 s/cm2R

Asbestos - PCM 0.0023 s/ccR

Asbestos - TEM

AHERA

0.00024 s/ccR

Asbestos - TEM

PCMe

0.00024 s/ccR/T

MMVF 0.00006 s/ccR/T n/a (<1%) 52 s/cm2T

Lead 0.03 :g/m3T 186 mg/kgR 1.98 :g/ft2T 1.78 :g/ft2R

Dioxin 0.693 ng/m2T

PAH n/a 

(<290 :g/m2

)

Alpha-quartz

(w/o max. value)

61.9 :g/m3R

(7.8 :g/m3R)

3.66 %R 79.6 :g/ft2R

Calcite 9.3 :g/m3T 3.41 %R 132.3 :g/ft2T

Cristobalite 9.3 :g/m3T 4.69 %R 103.7 :g/ft2T

Gypsum 9.3 :g/m3T 2.33 %R 49.9 :g/ft2T

Portlandite 9.3 :g/m3T 4.69 %R 99.8 :g/ft2T

Tridymite 9.3 :g/m3T 4.69 %R 99.8 :g/ft2T

Total Dust 14.4 mg/ft2R

n/a - indicates that a upper confidence limit could not be calculated, value in parenthesis

indicates that the value is less than the detection limit 

italics - indicates a theoretical UCL due to all data being below the detection limit 

T - indicates the total data set was used 

R - indicates only the residential data set was used
WORLD TRADE CENTER BACKGROUND STUDY 5

Conclusions

In summary, the data collected from this Study, in which 1158 samples were

collected, provided calculated estimates of background concentrations for

compounds that were identified as COPCs related to the World Trade Center

collapse. The estimates were shown to be consistent with other background

studies and historical data, where comparison data were available (see table

below). These estimates also provide a upper-bound point estimate that can be

used as a background concentration for the COPC report.

Comparison of estimated background values from this study to background or historical

values reported in the scientific literature for select compounds.

Compound Estimated Background

UCL Value

Historical/Literature

Value

Asbestos - PCMe 0.00024 s/cc 0.00022 s/cc(1)

MMVF - air 0.00006 s/cc #0.0001 f/cc(2)

Lead - air 0.03 :g/m3 0.02 :g/m3(3)

Lead - wipe floors 3.91 :g/ft2 3.45 :g/ft2(4)

Dioxin - wipe 0.693 ng/m2 0.67 ng/m2(5)

(1) Consumer Product Safety Commission Study. 1987.

(2) ATSDR. 2002.

(3) Calculated value from EPA historic ambient air lead data.

(4) HUD. 2001.

(5) Christmann. 1989.

In addition, these data may provide a source to help address data gaps in scientific

literature on background concentrations of building-related materials and

combustion byproducts caused by building fires.
WORLD TRADE CENTER BACKGROUND STUDY 6

1.0 INTRODUCTION

A Background Study of the Contaminants of Potential Concern (COPCs) in upper

Manhattan was conducted in parallel to several other efforts to address the

concerns of lower Manhattan residents regarding the potential risks from

exposure to residual WTC dust and debris. These efforts were funded by FEMA

through agreements with EPA and the City of New York (NYC).

While there are background reference levels for a few indoor air pollutants,

comprehensive reference levels (i.e., normative concentrations) for typical

residences do not exist for several reasons. In contrast to the situation for many

outdoor air pollutants which have been routinely monitored for decades because

of legislative mandates, no such legislation exists for indoor air pollutants. 

Indoor monitoring has been generally limited because of its cost, the difficulty of

obtaining access to residences due to privacy issues as well as the noise and

inconvenience of sampling equipment and monitoring instrumentation. The size

of a nationally representative monitoring network for residences could also be

large and therefore require costly and complex studies because of the need to

capture variability due to regional differences in housing construction, differences

in residential types (e.g., apartments vs. single-family detached houses), seasonal

differences in operation of the residence (e.g., heating vs. air conditioning), 

differences in human activities (e.g., smoking, cleaning methods...) occupant

demographics and density, age of housing and related housing maintenance

practices (e.g., use of lead-based paint). In summary, useful reference levels for

air pollutants or contaminants indoors typically do not exist.

2.0 BACKGROUND AND PROJECT DESCRIPTION

2.1 Background

In June 2002, EPA entered into an agreement with FEMA in order to continue to

assess the impacts of possible contamination from WTC related dust in indoor

residential environments. As part of this assessment, EPA needed to identify

what levels of pollutants existed in indoor residential environments in New York

City prior to September 11, 2001. To accomplish this, EPA developed and

implemented a plan for sampling and analyzing the dust present in residential

buildings located in upper Manhattan that were not affected by the collapse of the

WTC from which to infer contamination levels in downtown residential building

prior to September 11, 2001. 

2.2 Purpose/Objective

The objective of the Background Study was to determine indoor baseline levels or

background concentrations for the presence of specific contaminants related to

materials used during the construction of buildings, materials that are typically

found within occupied buildings and any combustion byproducts caused by fires.
1

 The asbestos air samples were collected according to NIOSH 7400 (PCM). 

The sample filters were analyzed using a modified AHERA method. Although the total

TEM (AHERA) fiber count was recorded, a separate PCMe count was recorded by

modifying the AHERA method to count only fibers greater than 5:m (micrometer). It is

this modified AHERA PCMe fiber count that was the basis of the asbestos test results

and health based benchmarks. 

2

 The EPA regulates asbestos contaminated materials (ACMs) in schools via the

Asbestos Hazard Emergency Response Act (AHERA) of 1986. The AHERA schools rule 

requires all public school districts and private schools to inspect all school buildings for

ACMs; to develop plans to manage asbestos in schools; and to carry out the plans in a

timely fashion. The rule also provides an opportunity for parents, teachers, and other

school employees to become familiar with and involved in their school’s asbestos

management programs.

WORLD TRADE CENTER BACKGROUND STUDY 7

The background concentrations derived from this Study will be used to

supplement the health-based benchmarks established in the "World Trade Center

Indoor Air Assessment: Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks" document and were identified as a potential source of

alternate cleanup values if the health-based benchmarks were not able to be

achieved.

The selected COPCs include asbestos in air1

 by phase contrast microscopy

equivalent (PCMe), phase contrast microscopy (PCM) and transmission electron

microscopy (TEM) Asbestos Hazard Emergency Response Act (AHERA)2

,

asbestos in settled dust, lead in air and settled dust, dioxins in settled dust,

polycyclic aromatic hydrocarbons (PAHs) in settled dust, fibrous glass and

minerals including alpha-quartz, cristobalite and tridymite, hereinafter referred to

as crystalline silica, and other mineral dusts including calcite, gypsum, and

portlandite in both air and settled dust. These contaminants are discussed in detail

in the peer review draft report "World Trade Center Indoor Air Assessment:

Selecting Contaminants of Potential Concern and Setting Health-Based

Benchmarks" provided as Attachment A.

2.3 Project Description

Sampling was conducted in fourteen residential Manhattan buildings not 

impacted by the airborne dust plume that emanated from the WTC site. 

When possible, samples were collected from two residential units and from one

common area, such as the lobby, hallway, stairwell, or shared laundry facility in

each building. In total, EPA sampled twenty-five residential units and nine

common areas within the fourteen buildings. Results of the Study are discussed

in general terms and are not specific to the units sampled. In accordance with the

agreement for Consent for Access for Environmental Sampling for the WTC

Background Study, the addresses of the buildings and apartments, including the
WORLD TRADE CENTER BACKGROUND STUDY 8

identity of the volunteers, will remain confidential.

2.4 Project Team/Responsibilities

EPA Region 2 staff provided overall management and oversight of the project, 

identified participant buildings, obtained access to participant buildings and

implemented the field sampling portion of the project with the assistance of

EPA’s contractor, TRC Solutions Inc. (TRC). All communication regarding site

work activities, work scheduling, difficulties encountered, deviations from the

QAPP/sampling plan, and project progress was addressed by the EPA Project

Officer on a daily basis. TRC provided deliverables and services associated with

the sampling operations for this project.

2.5 Data Usage

The data generated from this Study were used to establish baseline information on

residential contaminant levels found in typical NYC dwellings. 

The analytical data collected were evaluated first for individual apartments and

common areas and second, cumulatively, which consisted of combining data sets

for residential dwellings and common areas (i.e., asbestos wipe sample data for

residential dwellings, common areas and a combined data set for residential and

common spaces) to derive background concentrations representative for

Manhattan.

The confidential evaluation prepared for individual apartments compared the

reported results for each sample to the health-based benchmarks developed in the

peer review draft of the "World Trade Center Indoor Air Assessment: Selecting

Contaminants of Potential Concern and Setting Health-Based Benchmarks"

document. The analytical data for each analyte were presented in tabular format

for each apartment with text that explains the reported results. Any sampling that

resulted in detections exceeding the health-based benchmarks was discussed in a

detailed letter and orally when requested by the resident or owner.

Cumulatively, the data were statistically evaluated to provide descriptive statistics

for each analyte and sample matrix. For each analyte, a recommended

concentration that is representative of background concentrations under a given

set of assumptions, for upper Manhattan, is discussed in Section 6.0 and presented

in Table 8-1.

Results from this Study cannot account for the variability with indoor

environments in general (e.g., cross contamination from outdoor environments to

indoor environments, way of life, and level of cleanliness). The measurements

are limited to each specific apartment or common area sampled at that specific

time the samples were collected. The selection of sample point locations within

each unit were decided in the field, on a case-by-case basis and do not represent

the entire apartment or common area sampled.
WORLD TRADE CENTER BACKGROUND STUDY 9

3.0 SAMPLING APPROACH/RATIONALE

3.1 Selection of Sampling Area Location

The geographical area (Figure 1) for the Background Study (78th Street and

North) was selected based on preliminary modeling of meteorological data on

September 11, 2001 and shortly thereafter. The modeling was performed by

EPA’s Office of Research and Development (Huber, 2003). This geographical

area is an area well north of the portion of Manhattan that may have been affected

by the deposition of particulate matter from the collapse of the WTC. The

distance of buildings sampled in the Study with respect to the WTC site ranges

from 8 to 19 kilometers (5 to 12 miles).

The modeling produced isopleth plots which present the dilution of the particulate

emissions from the WTC site. These plots indicate that the plume was dispersed

and diluted, with the concentration of particulate matter ranging from 1,000 to

10,000 times less than at the WTC site as one moves away from the WTC site in a

northeast direction. These isopleths are based on how much the plume was

dispersed and diluted by weather conditions and are not based on the amount of

emissions from the WTC site.

3.2 Selection of Building Types and Obtaining Access

EPA and other members of the Indoor Air Working Group selected the building

types designated for this Study. This Study attempted to focus on sampling sites

that are similar to the downtown residential housing stock. This stock included:

post-1920 non-doorman mid-rise apartments, high-rise condominiums, high-rise

co-operatives, and turn-of-the-century tenements. Downtown residential lofts

could not be represented in the Study, since lofts located uptown are designated

for commercial use only. 

In order to solicit volunteer participants from the targeted building types, a list of

buildings matching the housing stock described above was provided to EPA and

the NYCDOHMH by the New York City Department of Housing Preservation

and Development (NYCHPD).

Initially, the task of obtaining access to buildings that would be included in the

Study was the responsibility of NYCDOHMH. During the month of June, 2002

EPA assumed the responsibility for obtaining building access. EPA staff

exhausted the list provided by the NYCHPD. Due to the lack of willing

participants on this list, the difficulty with obtaining access, and time constraints

under the Inter-Agency Agreements (IAA), EPA initiated cold calling and

essentially door to door solicitation in order to solicit volunteers and gain access

to buildings for participation in the Study. Therefore, not all of the buildings

sampled as part of the Study were obtained from the list provided. Any building

willing to participate in the Study was considered for sampling until fourteen

buildings were obtained. This is a deviation from the initial sampling plan
WORLD TRADE CENTER BACKGROUND STUDY 10

regarding representation of the diverse housing stock mentioned above. The

buildings sampled were constructed roughly between 1892 and 1981.

EPA began the task of obtaining access to building common areas and residential

units on June 14, 2002 and continued through September 23, 2002. As access

agreements were signed and returned from volunteer participants, appointments

were scheduled for sampling of the building. Sample collection activities were

completed on September 25, 2002.

3.3 Selection Criteria for Number of Buildings, Residences and Common Space

Sampled

The number of buildings, residences and common spaces samples were

determined by what could practically be achieved to avoid impeding the project.

There were no formal criteria established for selecting the number of buildings to

be incorporated into the study or the number of residential dwellings and common

spaces to be sampled within each building due to the difficulty in obtaining access

and time constraints for conducting the Study. 

The objective of the Study was to collect samples from at least three sites within

each building: two or more residential units and one of the building common

spaces. For the most part this objective was met, however in three instances only

one common space and one apartment were sampled per building and in five

buildings access was obtained to sample two residential units per building. 

Access could not be obtained to sample the common spaces of these five

buildings. 

3.4 Selection of Contaminants of Potential Concern

Under the auspices of the EPA’s Interagency Indoor Air Task Force, a committee

was formed to identify the COPCs and associated health-based benchmarks for

the Indoor Air Residential Assistance - WTC Dust Cleanup Program. This

committee drafted the "World Trade Center Indoor Air Assessment: Selecting

Contaminants of Potential Concern and Setting Health-Based Benchmarks" report

that was peer reviewed on October 21-22, 2002. This report is currently being

revised for finalization. 

Among other purposes, this report identified the selection of contaminants for

monitoring in the WTC Background Study and provided a measure of cleaning

effectiveness by establishing health-based benchmarks and clean-up goals for

indoor air and settled dust. As such, the COPCs identified for inclusion in the

Study reflect those contaminants cited in the peer review draft of the

aforementioned report. 

The development of the COPC report began with an assessment of the indoor

environment by reviewing historical information on hazardous substances that

have been associated with building fires and collapses. Many compounds,
WORLD TRADE CENTER BACKGROUND STUDY 11

including combustion byproducts such as dioxins and PAHs were identified,

along with building materials such as asbestos and fibrous glass. In addition,

WTC ambient air, indoor air, and indoor/outdoor bulk dust monitoring data were

reviewed. Data sources included EPA's ambient air and bulk dust/debris

monitoring program www.epa.gov/wtc, OSHA's air and dust monitoring data and

the NYCDOHMH/ATSDR indoor air pilot program (NYCDOHMH 2002). A

concerted effort also was made by the COPC committee to identify and review

additional sources of WTC related data from other governmental agencies (e.g.,

U.S. Geological Survey, NYC Board of Education), academic institutions,

environmental organizations, and the private sector.

A semi-quantitative screening process was performed on the collected sampling

data, referenced above. Based on frequency-of-detection, concentration and

inherent toxicity, contaminants that exceeded health-based screening levels for

the ambient air were identified. Dioxin and PAHs were added to the COPC list

by this process. In addition, building constituents with carcinogenic (asbestos) or

irritant effects (fibrous glass, crystalline silica) that were consistently found in

bulk and indoor dust samples were identified as COPCs (NYCDOHMH 2002). 

Finally, lead was included based on a comparison of sampling data with existing

regulatory standards. Collectively, the resulting group of contaminants (asbestos,

lead, dioxin, PAHs, fibrous glass and crystalline silica) are called "contaminants

of potential concern" or COPCs in this report.

4.0 SAMPLING METHODOLOGY

Once building access was obtained and sampling scheduled, air and settled dust

samples were collected from each of the fourteen buildings and shipped to the

laboratories for analysis. All samples were collected and analyzed in accordance

with the approved Quality Assurance Project Plan (QAPP) for the WTC

Background Study, dated August 2002. The procedures used for sample

collection, analysis, data validation, data management and evaluation are

described in or provided as an attachment to the approved QAPP which will be

furnished upon request. 

4.1 Sampling Procedures

Samples were collected from twenty five residential units and 9 common spaces

(i.e., seven basement laundry rooms and two hallways). Sampling consisted of: 

indoor air samples of airborne fibers and particulate matter; microvacuum

samples of settled dust on carpeting, area rugs, upholstered fabric furniture and/or

drapery; wipe samples of settled dust from ceilings, walls, bare floors, counter

tops or table tops; and bulk dust samples from window air conditioner filters. All

samples were collected from areas routinely used and occupied by residents, such

as, living rooms or bedrooms and in common areas, such as, entrance hallways or

basement laundry rooms. 

A summary of the sample collection and analytical procedures used are provided
WORLD TRADE CENTER BACKGROUND STUDY 12

in Table 4-1 of this report. The following subsections provide brief descriptions

of the sampling procedures to place the subsequent discussion of results in

context.

4.1.1 Indoor Air Sample Collection

Airborne fibers and particulate matter were collected by drawing a known volume

of air through a filter membrane cassette following the procedures specified in

Table 4-1. The equipment used for the collection of air samples is provided in

Section 4.2 of this report. 

When available and permitted by the resident or building manager, some of the

air sampling was conducted employing the use of oscillating fans and/or operating

the window air conditioning units. How the air conditioning units were utilized

during sampling depended upon the unit’s features. For example, some units had

the option to recirculate interior air or use outside air. When this option was

available, the unit was set to recirculate interior room air. Other units did not

have this option. The intended purpose for the use of fans or window air

conditioners was to simulate typical household activity within each unit. 

The collection of air samples did not employ the use of aggressive techniques due

to the risk of dust exposure to the residents or persons in each unit during the

sampling activities. Aggressive sampling techniques employ the use of electric

leaf blowers with a maximum velocity ranging from 140 miles per hour (mph) to

225 mph, and maximum air volumes ranging from 78 cubic feet per minute (cfm)

to 425 cfm in order to agitate dust into the air. The dust then remains suspended

in air by using fans. The aggressive techniques do not simulate “normal”

household activity or living conditions. However, as the goal of the Study was to

estimate background concentrations under typical conditions, the use of nonaggressive sampling techniques is more representative of typical household

activity and living conditions. 

4.1.2 Microvacuum Sample Collection

Samples of settled dust were collected from porous surfaces using microvacuum

techniques and analyzed for asbestos and lead. Porous surfaces included carpet,

area rugs, upholstered couches, chairs, ottomans and in some cases drapery when

furniture and/or carpet were not available. 

The standard test method used for the collection of asbestos microvacuum

samples is referenced in Table 4-1. This method describes the procedures for

collecting non-airborne dust samples. It is stated in sub-section 1.2.1 of the

ASTM Standard D 5755-95 that “The collection efficiency of this technique is

unknown and will vary among substrates. Properties influencing collection

efficiency include surface texture, adhesiveness, electrostatic properties and other

factors.” Due to the limitation of the microvacuum sample collection method for

asbestos, the intended use of the method was to determine only the presence or

absence of asbestos contaminants. 
WORLD TRADE CENTER BACKGROUND STUDY 13

For the purpose of this Study, lead dust samples were collected using

microvacuum techniques for the determination of lead on a loading basis

(microgram of lead per area sampled). As stated in section 1.3 of the ASTM

Standard E 1973-99, “Due to a number of physical factors inherent in the vacuum

sampling method, analytical results for vacuum dust samples are not likely to

reflect the total dust contained within the sampling area prior to sample

collection. This practice generally will have a collection bias towards smaller,

less dense particles.” Since the bias of this method is known, microvacuum

samples collected for lead analysis were used for determining background loading

levels.

4.1.3 Wipe Sample Collection

Wipe samples of settled dust, from nonporous hard surfaces were collected from

each unit and analyzed for asbestos, lead, dioxins, PAHs, crystalline silica,

calcite, gypsum and total dust. The methods used for the collection and analysis

of wipe samples are summarized in Table 4-1. 

Wipe sampling employs the use of a cloth-like material (e.g., gauze, Ghost

WipesTM or baby wipes), wetted or pre-moistened with a solution and is

conducted by wiping an area within a template of known size.

4.1.4 Bulk Dust Sample Collection

During the development of the sampling plan and QAPP, no standard method was

found for the collection of dust and particulate matter trapped in window airconditioner filters. EPA’s contractor TRC developed a procedure to collect this

material by brushing the dust and particulate matter from the filter using a

disposable brush. The dust was collected into a foil-lined stainless steel bowl. If

sufficient material was obtained, the sample was transferred to the appropriate

sample container for shipment to the laboratory. The procedure is noted in Table

4-1 of this report. 

In several cases there was not enough material on the window air-conditioner

filter for all of the analyses to be conducted. An order prioritizing the analyses

was established in the event of insufficient material collected. The first container

was sent for the analysis of asbestos and man-made vitreous fibers (MMVF). If

sufficient sample material was collected for the remaining parameters, the second

container was sent for analysis of lead, crystalline silica, calcite and gypsum in

descending priority. 

Dust and particulate matter of sufficient amount could not be collected from any

of the apartment air-conditioning unit filters for the analysis of PAHs and dioxins. 

These parameters require a large quantity of material in order to conduct the

analyses.

4.1.5 Quality Control Samples

Quality control (QC) samples are used to assess the sampling and analytical
WORLD TRADE CENTER BACKGROUND STUDY 14

processes and to ensure that these processes are being conducted properly. QC

samples were collected during each day of sampling. These samples included

the collection of field spike wipe samples, field blanks and lot blanks. QC

samples were collected for microvacuum, wipe and air samples. QC samples

were not collected with the bulk dust samples due to insufficient material needed

to perform the analyses. Table 4-2 provides a summary of the samples collected

for this project. 

As recommended in the Guidelines for the Evaluation and Control of Lead-Based

Paint Hazards in Housing; U.S. Department of Housing and Urban Development:

Washington, DC, 1995; Appendix 13.1: Wipe Sampling for Settled LeadContaminated Dust, field spike wipe samples for lead analysis were prepared by

the laboratory. The spike samples were sent to the sampling contractor and

randomly inserted into the sample group for each building, for each day of

sampling. In total, fourteen spike samples were sent indistinguishably to the

laboratory with the actual wipe samples collected for lead analysis. These spike

samples were labeled as ceiling wipe samples on the chain of custody in order to

easily identify the sample results in the database. 

Field spike samples were collected for lead analysis in order to assess if the

laboratory digestion procedure used for the wipe material was capable of

achieving recovery within the QC limits of 80 to 120 %. A summary of the

results for the spiked samples and the calculated percent recovery is provided in

Table 4-3. The results of the spike samples indicate that the laboratory was able

to achieve the recovery required for the analysis of lead wipe samples within the

QC limits with the exception of sample numbers 2 and 3 which were barely

outside the QC limits at 79% and 78%, respectively.

Field blanks were collected for microvacuum, wipe and air samples to determine

if the sample media could become contaminated during the sampling event. For

air and microvacuum methods, these samples were collected by opening a

separate air sampling cassette during the sample collection activities to expose it

to the air and then closing the cassette. Wipe field blanks are collected by

removing the wipe from its container or package, shaking the wipe open and refolding it as would be done during the actual sampling procedure and placing the

wipe back into the sample container. The field blanks are then labeled, packaged

and shipped with the actual field samples for analysis. Results of these samples

indicate that there was no contamination above the reporting limit or health-based

benchmarks that would affect the results or quality of the data. 

Lot blanks were collected for microvacuum, wipe and air samples to determine if

the media used to collect the samples were contaminated. The lot blanks are then

labeled, packaged and shipped with the actual field samples for analysis. Results

of these samples indicate that there was no contamination above the reporting

limit or health-based benchmarks that would affect the results or quality of the

data.
WORLD TRADE CENTER BACKGROUND STUDY 15

4.2 Sampling Equipment

4.2.1 Air Sampling Equipment

ANALYTE SAMPLE

MEDIA

FLOW

RATE

SAMPLE

PERIOD

SAMPLE

PUMP

Asbestos 

(TEM and PCM)

0.8 um (25mm)

MCEF cassette

10 L/min 480 min. Thomas Medium

Volume

Diaphragm Pump

MMVF 0.8 um (25mm)

MCEF cassette

10 L/min 480 min Thomas Medium

Volume

Diaphragm Pump

Crystalline

silica, Calcite,

Gypsum,

Portlandite

5 um (37mm) PVC

cassette through an

aluminum cyclone

2.5 L/min 480 min Gillian GilAir3

personal

sampling pump

Lead 0.8 um (37mm)

MCEF cassette

10 L/min 480 min Thomas Medium

Volume

Diaphragm Pump

4.2.2 Microvacuum Sampling Equipment

ANALYTE SAMPLE

MEDIA

FLOW

RATE

SAMPLE

PERIOD

SAMPLE

PUMP

Asbestos (TEM) 0.45 um (25mm)

MCEF cassette

2.0 LPM 2 minutes Gillian GilAir3

Personal

Sampling Pump

Lead 0.8 um (37mm)

MCEF cassette

2.5 LPM Minimum of

2 minutes

Gillian GilAir3

Personal

Sampling Pump
WORLD TRADE CENTER BACKGROUND STUDY 16

4.2.3 Wipe Sampling Equipment

ANALYTE SAMPLE MEDIA WETTING

SOLUTION

SAMPLE

CONTAINER

Asbestos, MMVF 9 x 9 inch, Super

Polx 1200 Class 10

Clean room wipes,

10 to 20 milliliters of a

50 / 50 mixture of 2-

propanol and DI Water

4 oz.

polypropylene

container

Lead, Crystalline

silica, Calcite,

Gypsum, Total

Dust

15 cm x 15 cm,

Ghost WipesTM,

(SKC Inc., No. 225-

24fourteen)

DI Water 50 ml

polyethylene

centrifuge tubes

PAHs, Dioxins 3 x 3 inch, Cotton

gauze

2 milliliters of acetone 125 ml Amber

glass jars with

PTFE-lined caps

4.2.4 Bulk Sampling Equipment

Sample equipment used for the collection of bulk dust samples from the airconditioner unit filters included: disposable brushes, stainless steel bowl,

aluminum foil and 4 oz. polypropylene containers.

4.3 Sample Numbering/Identification

The sample numbering/identification scheme was specific to the addresses,

building identification numbers and apartment numbers sampled. For the purpose

of maintaining confidentiality of the building owners and residents, the sample

numbers are not provided in this report.

4.4 Sample Shipment

All samples were placed in plastic coolers with bagged ice or ice packs and

shipped to the appropriate laboratory for analysis. All sample documentation was

placed and sealed in a plastic bag and affixed to the underside of each cooler lid. 

The lid was sealed and affixed on at least two sides with custody seals so that any

sign of tampering would be visible.

TRC packaged the samples for shipment/transport to the EPA contracted

laboratory as specified in the table below and on chain of custody forms. 
WORLD TRADE CENTER BACKGROUND STUDY 17

Parameters Shipment/Transportation

Method

Laboratory

Dioxins

PAHs

Shipped Overnight Courier Paradigm Analytical

2627 Northchase Parkway SE

Wilmington, NC 28405

Asbestos

Lead

Total Dust

Crystalline silica

Calcite

Portlandite

Gypsum

MMVF (fibrous glass)

Hand Delivery: Dropped Off

Daily

EMSL would then ship all but

the asbestos samples to their

New Jersey based laboratory

EMSL 

307 West 38th Street

New York, NY

EMSL

107 Haddon Ave.

Westmont, NJ

4.5 Data Validation and Reporting

4.5.1 Validation

The validation of all organic and inorganic analytical data were performed by

EPA’s Quality Assurance Technical Support (QATS) contractor in accordance

with the Standard Operating Procedures listed in Attachment B. 

4.5.2 Verification

Any manual entry of data by the QATS contractor into the database was verified

by the following procedure. This procedure was followed from the inception of

the project for all spreadsheets sent by QATS to EPA for entry into the database.

a. The QATS data analyst entered the validated data into a spreadsheet format.

b. The analyst printed out a hard copy of the spreadsheet and placed it into the

raw data file.

c. A second QATS data review analyst then reviewed every entry that was made

into the spreadsheet.

d. The review analyst then returned file to original data entry analyst if errors

were found.

e. Any found errors were corrected and steps b through e were repeated.

f. Documentation of this review and verification is maintained for each data file

by the QATS contractor.

Once the verification of the data were complete, the electronic file was sent to the

EPA Region 2, Data Management Team and loaded into the database. All
WORLD TRADE CENTER BACKGROUND STUDY 18

analytical results were evaluated and tabulated subsequent to validation and are

presented in Tables 6-1 through 6-6. A detailed discussion of the results and

development of background concentrations is provided in Section 6.0.

5.0 SAMPLING PROTOCOL DEVIATIONS

The bulk samples collected were to be analyzed in the following order by the

contracted laboratory: asbestos, lead, crystalline silica, calcite, gypsum and

MMVF. Due to the backlog of asbestos samples at the EMSL, New York

laboratory, the samples were shipped to the EMSL, New Jersey laboratory for the

remaining analysis. In performing the analysis for the remaining parameters the

laboratory used all of the material available therefore, the asbestos analysis was

not performed on a majority of the bulk dust samples collected. This was done

without notification to the EPA Project Officer. 

Bulk dust samples were not collected from the common areas due to the absence

of window air-conditioner units. 

The following are deviations from the QAPP for each day of sampling.

August 20, 2002 - Consent to sample was only obtained for one apartment and

the basement laundry room in this building. In the apartment, there was a power

failure for two (2) minutes during sampling. Sampling time was increased by

two (2) minutes to compensate for loss of volume.

August 21, 2002 - Air samples could not be collected from the common area as

there were no power outlets in the area. Counter wipes could not be collected due

to lack of horizontal surfaces in the common area. Microvacuum samples could

not be collected from the common area due to absence of porous surfaces.

August 22, 2002 - Microvacuum samples could not be collected from the

common area due to absence of porous surfaces. In one of the apartments, the

pump used for the collection of crystalline silica, calcite and gypsum (SCG)

failed. The sample collection was terminated at that time and the sample data

reflected abbreviated sample duration. 

August 29, 2002 - There was a power failure of five (5) minutes on pump #3

being utilized for the SCG sample. The sampling time for SCG was increased by

five (5) minutes to compensate for loss of volume. Microvacuum samples could

not be collected from the common area due to absence of a porous surface. Air

samples could not be collected from the common area as there was no power

available in the area.

August 30, 2002 - Microvacuum samples could not be collected from the

common area due to absence of a porous surface. The ceiling wipe sample for

asbestos could not be collected from one apartment due to acoustical texturing.
WORLD TRADE CENTER BACKGROUND STUDY 19

September 4, 2002 - One apartment and the common area were sampled; access

was denied to the second apartment unit. Microvacuum samples could not be

collected from the common area due to absence of a porous surface. The

common area ceiling wipe sample was collected from the duct work above dryer

#3 as the ceiling had a rough stucco surface which was not suitable for wipe

sampling.

September 5, 2002 - The common area was not sampled since the access

agreement was not signed. 

September 6, 2002 - Microvacuum samples could not be collected in one

apartment and the common area from carpets/rugs or drapes as none were present. 

Ceiling samples could not be collected in the common area due to the presence of

a rough surfaced drop ceiling.

September 10, 2002 - A common area was not available for sampling.

September 12, 2002 - Couch/chair microvacuum samples could not be collected

from the apartment. Samples from the common area could not be collected due to

restricted access.

September 24, 2002 - Microvacuum samples could not be collected from the

common area due to absence of a porous surface.

September 25, 2002 - High flow air sampling pumps in the common area shut

down for twenty minutes due to power outage in part of the building. Sampling

time was extended twenty minutes to compensate for loss of volume. Air

sampling was terminated 110 minutes early in one unit at the request of the

owner. The owner was called out for the remainder of the day.

6.0 ANALYTICAL RESULTS AND DEVELOPMENT OF BACKGROUND

CONCENTRATIONS

The samples collected during this Study were analyzed to determine the

concentration of each analyte in the matrix in which it was collected. The

purpose of collecting and analyzing the samples was to establish background

concentrations for a select group of compounds that have been identified as

contaminants related to the collapse of the World Trade Center. As stated

previously, these background concentrations will be used to supplement the

health-based benchmarks established in the "World Trade Center Indoor Air

Assessment: Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks"document and may be used as an alternative cleanup

value if the health-based benchmark cannot be achieved.

6.1 Methods

Deriving a background concentration for each analyte was completed using the
3

If the distribution of the data is neither normal nor lognormal, it is recommended

to use a non-parametric (i.e., distribution-free) statistic to estimate the UCL

4

The confidence interval used to estimate the UCL was determined by the

skewness of the data. For mild to moderately skewed data sets (e.g., F in the interval of

0.5 to 1) a 95% confidence interval was used, for moderate to highly skewed data sets

(e.g., F in the interval of 1 to 2) a 97.5% confidence interval was used, and for highly to

extremely highly skewed data sets (e.g., F in the interval of 2 to 3) a 99% confidence

interval was used.

5

A UCL was calculated for any data set that had variability. In situations where

all of the samples were below the detection limit, but the detection limit varied, the UCL

that was estimated was identified as a theoretical value because the mean that was

calculated, from which the UCL was derived, was based only upon the detection limit

WORLD TRADE CENTER BACKGROUND STUDY 20

following guidance; Guidance for Characterizing Background Chemicals in Soil

at Superfund Sites (EPA 540-R-01-003, June 2001), Role of Background in the

CERCLA Cleanup Program (OSWER 9285.6-07P, April 2002), and Calculating

the Upper Confidence Limits for Exposure Point Concentrations at Hazardous

Waste Sites (OSWER 9285.6-10, December 2002). 

Evaluating environmental data that are collected to establish background

concentrations of chemicals can be done using a variety of endpoints, such as

reporting ranges, arithmetic or geometric means, or point-estimates based on a

statistical computation. The method that is used to evaluate and interpret the data

is dependent on the application of the background concentration. For this study, a

point-estimate that represented an upper-bound of the population mean was the

desired endpoint. This resulted in using a statistical approach, specifically

calculating a upper confidence limit (UCL) based on the mean, for estimating an

upper-bound point estimate for each analyte in its associated media.

Several different statistical methods can be used to estimate an UCL of a data set,

depending on the data distribution. Two key steps were completed to estimate the

UCL for these data sets:

1) Determined the distribution of the data (i.e., normal, lognormal, or

neither3) and,

2) Computed the UCL using the appropriate confidence interval4

 (e.g.,

95%, 97.5%, 99%) and statistical method for the data distribution.

These two steps were performed with the ProUCL statistical software developed

for EPA (Lockheed Martin 2001). Based on EPA guidance (Risk Assessment

Guidance for Superfund - Part A, 1989) and standard EPA Region 2 procedures,

the samples that were reported as being below the detection limit were assigned a

value equal to one-half the laboratory-reported detection limit for the statistical

calculations5

.
and it does not include actual detected concentrations. Therefore, the UCL associated

with these data sets are theoretical in nature and are reported as such.

6

 The anti-log of the log-transformed mean is equal to the geometric mean.

WORLD TRADE CENTER BACKGROUND STUDY 21

The program ProUCL tests the normality/lognormality of each data set using the

Shapiro-Wilk W Test for sample sizes of 50 or smaller, and using the Lilliefors

Test for sample sizes of 51 to 1000. The data sets for this project included

samples sizes that are less than 50 and greater than 50, therefore both tests were

used depending on the sample size for each analyte. The majority (92%) of the

data sets were neither normally (0.5%) nor lognormally (7%) distributed,

therefore a non-parametric statistic was used to estimate most of the UCLs.

Descriptive statistics, including the minimum, maximum, mean, median, standard

deviation, coefficient of variation, skewness and variance were calculated. In

addition, approximately ten different statistical methods were used to calculate

UCLs for each analyte’s data set. The output from these calculations also

reported descriptive statistics for the log-transformed data, which included mean,

standard deviation, coefficient of variation, skewness, median, 80%, 90%, 95%,

and 99% quartiles. The output also included a recommendation regarding which

calculated UCL was most representative of the data set. This UCL is reported in

Tables 6-1 through 6-6.

The UCLs were calculated with the statistical procedures based on the findings of

Singh, Singh, and Engelhardt (1997, 1999), as referenced in the ProUCL users

guide (Lockheed Martin, 2001). For normally distributed data sets, the Student’s

t-statistic, based on an arithmetic mean, was used to calculate the UCL. For

lognormally distributed data sets, one of five different computational methods

was used, based on the log-transformed mean6, depending on the skewness of the

data, which was indicated by the standard deviation of the log-transformed data,

and the samples size. For data sets that were neither normally nor lognormally

distributed, a UCL based on the non-parametric Chebyshev theorem and

arithmetic mean was used (Lockheed Martin, 2001).

As stated above, these statistical methods were completed for each analyte,

sampling matrix (i.e., bulk dust, air, microvacuum, and wipe samples), and space

tested (i.e., resident, common area, and both combined). There were also some

matrices in which multiple surfaces were sampled (e.g., counters, floors, and

walls), so additional calculations were conducted for different surfaces. The text

that follows explains the statistical evaluation of the data and the results of the

statistical analyses, as presented in tabular format (Tables 6-1 through 6-6). The

values presented in these tables provide estimates of the background

concentration for each compound and media.

An additional assessment was undertaken to provide a single recommended value

for each analyte for the air, bulk dust, porous materials, and hard surfaces. These
7

The frequency of detection, range of detection, mean and calculated UCL for the

residential and common area data sets were qualitatively compared to determine if they

were similar. If any of the parameters were identified as not being similar, the second

priority was used.

8

For this study, the term structure and fiber are used interchangeably, although

there are mineralogical nuances and counting rules that make these two terms technically

different. In general, the analyses that were completed represent fibers, however for ease

of comparison to the AHERA asbestos standard in a sister study, the term structure was

adopted for all asbestos TEM analyses.

WORLD TRADE CENTER BACKGROUND STUDY 22

values, which are summarized in Table 8-1, can be used as a representative

background concentration for Manhattan given the statistical limitations of the

data set.

The recommended values were determined using two priorities:

• as first priority, a combined data set, using both the residential and

common areas and all samples from a specific media (e.g., settled dust) to

achieve a larger sample size, was used unless the data from the separate

areas were determined not to be similar7, in which case the second priority

was used;

• the second priority used the data set for the residential areas for all

samples from a specific media, as the residential data sets had the second

largest sample size and this data set would reflect the background

concentration within a residential apartment.

6.2 Results and Development of Background Concentrations

The following sections present a summary of the analytical results, the

background values calculated, and a discussion that addresses the strengths and

weaknesses for the asbestos, MMVF, lead, dioxin and PAH data sets, as well as

the corresponding background value that was derived for each analyte, matrix,

type of space, and type of surface. The statistical results and calculated UCLs are

reported in Tables 6-1 through 6-3.

6.2.1 Asbestos8

Bulk Dust - There were three bulk dust samples collected and analyzed for

asbestos. All three samples were collected from the residential spaces. The

results for the three samples were below the detection limit of 1%. Due to the

small sample size and the results all being below the detection limit, the UCL for

asbestos in bulk dust could not be calculated. The data suggest that background

asbestos concentrations in bulk dust are less than 1%, however, the confidence in

this statement is limited due to the small sample size. 
WORLD TRADE CENTER BACKGROUND STUDY 23

Air - There were sixty-two air samples collected, forty-eight in residential spaces

and fourteen in common spaces. Each of the samples were analyzed using Phase

Contrast Microscopy (PCM), Transmission Electron Microscopy (TEM) AHERA,

and TEM Phase Contrast Microscopy equivalents (PCMe) methods.

PCM - There was a higher percentage of detections in the common space areas

(71%) than in the residential areas (42%) although the minium and maximum

detected concentrations were the same. The UCL for the common area (0.0058

f/cc) is slightly more than twice the value for the residential area (0.0023 f/cc). 

This difference may not be an unusual occurrence as common areas, such as

laundry rooms and hallways may contain more fibrous material, especially in

laundry rooms and high traffic areas. Since the common space areas and the

residential areas differ, it is recommended to use the 95% UCL for the residential

spaces of 0.0023 f/cc as the background value.

TEM AHERA - There was a higher percentage of detections in the common

space areas (14%) than in the residential areas (4%) although the minimum and

maximum detected concentrations were the same. In addition, the mean for each

data set were similar. The four samples (two common area and two residential)

that had detectable concentrations of asbestos were at the detection limit of

0.0004 s/cc. Since the frequency of detection was marginally different for the

common space areas and the residential areas, it is recommended to use the 95%

UCL for the residential spaces of 0.00024 s/cc as the background value.

TEM PCMe - There was a higher percentage of detections in the common space

areas (7%) than in the residential areas (4%) although the minimum and

maximum detected concentrations were the same. In addition, the mean for each

data set were almost equal. The three samples (two common area and one

residential) that had detectable concentrations of asbestos were at the detection

limit of 0.0004 s/cc. The UCL for the common areas (0.00029 s/cc) is marginally

higher than the UCL for the residential area (0.00024 s/cc). The combined data

set yields a UCL that is the same value (0.00024 s/cc) as the residential UCL. 

Given that the residential areas and the combined data sets provide the same

UCL, it is recommended to use the 95% UCL of 0.00024 s/cc as the background

value.

Microvacuum - There were 162 microvacuum samples collected, with 144 from

residential areas and 18 from common spaces. The microvacuum samples were

collected from porous materials, such as carpets, area rugs and couches. These

samples were analyzed for asbestos. The results from these analyses were quite

variable between different surfaces and between the different spaces. Asbestos

was detected more frequently in the common spaces (22%) and at higher

concentrations (mean = 7,145 s/cm2

) than in the residential spaces (4%) with a

mean concentration of 2,234 s/cm2

. In addition, the carpets in both spaces had

greater mean concentrations than the other porous surfaces (i.e., couches, chairs,

and drapes). As the purpose for collecting microvacuum samples for asbestos
WORLD TRADE CENTER BACKGROUND STUDY 24

was to determine the presence or absence of asbestos in porous items, a UCL was

not calculated for this data set.

Wipe - There were 146 wipe samples collected, with 104 from residential areas

and 42 from common spaces. The wipe samples were collected from hard

surfaces including floors, walls, counters, and ceilings. These samples were

analyzed for asbestos. The results from these analyses were quite variable

between different surfaces and between different spaces. Overall, asbestos was

detected about twice as frequently in the common areas (26%) than in the

residential areas (13%). The results from the common areas had several very high

concentrations reported due to detection limits being unusually high for several

samples. This might artificially increase the background concentrations and for

this reason the common space data sets were not used for determining the

background concentration.

Based on the residential data set, the mean concentration was higher in the ceiling

samples, followed by the floor samples, then the walls, and finally the counters. 

The UCLs for these surfaces were within an order of magnitude with the

exception of the UCL for the ceiling, which was one order of magnitude higher. 

However, given that the primary goal is to estimate the background concentration

for a residential space, it is recommended to use the entire residential data set,

which includes ceilings, counters, floors, and walls to establish a background

concentration for hard surfaces. The 95% UCL for this data set is 6,192 s/cm2

and would be applicable for all hard surfaces in a residential space.

6.2.2 Man-Made Vitreous Fibers

Bulk Dust - There were twenty-four bulk dust samples collected and analyzed for

MMVF. All of the samples were collected from the residential spaces. The

results for the twenty-four samples were below the detection limit of 1%. As all

of the samples were below the detection limit and the same detection limit was

used throughout the Study, the UCL for MMVF in bulk dust could not be

calculated because there was no standard deviation. The data suggest that

background MMVF concentration in bulk dust is less than 1%, however, the

confidence in this statement is limited due to the small sample size.

Air - There were sixty-two air samples collected, with forty-eight collected from

residential spaces and fourteen collected from common areas. The frequency of

detection for the common spaces (29%) was higher than the residential spaces

(2%), however the range of detections and means were very similar. The UCL

for the combined data set is the same as the UCL for the residential data set. 

Given that the UCLs are the same, it is recommended to use the 95% UCL of 0.06

s/L or 0.00006 s/cc.

Wipe - There were 141 wipe samples collected, with ninety-nine collected from

residential spaces and forty-two from common areas. The frequency of detection

was similar between the residential (9%) and the common (11%) areas, as well as
WORLD TRADE CENTER BACKGROUND STUDY 25

the range of detections and the mean for the wipe data set for each space. Each

space had wipe samples collected from hard surfaces including ceilings, counters,

floors, and walls. The samples collected from the ceiling, counters, and walls in

the common spaces were all below the detection limit and a UCL could not be

calculated for these surfaces. All of the surfaces sampled from the residential

areas had UCLs that were within a factor of three. Given that the residential data

for the different surfaces were similar, as well as the data from the common areas,

it is recommended to use the entire data set, which includes the residential and

common spaces. This data set provides a 95% UCL of 52 s/cm2 as a background

concentration for MMVF on hard surfaces.

6.2.3 Lead

Bulk Dust - There were nine bulk dust samples collected from residential spaces

and analyzed for lead. There were no bulk dust samples collected from the

common areas. Lead was detected in all of the bulk samples ranging from 44

mg/kg to 242 mg/kg with a mean concentration of 126 mg/kg. The 95% UCL for

this data set was calculated as 186 mg/kg. This UCL is recommended to be used

as a background concentration for lead in bulk dust.

Air - There were forty-six air samples collected, with thirty-two samples

collected from residential areas and fourteen collected from common areas. Only

one sample, collected from a residential area, had a concentration of lead that was

detectable and the lead concentration was equal to the detection limit. However,

as the detection limit for the common areas and residential area samples varied

slightly, a theoretical background concentration can be calculated for the common

area because the range of detection limits permits a standard deviation to be

calculated. The results indicate that the frequency of detection is similar between

the residential areas (3%) and the common areas (0%), as well as the mean

concentration. The UCL for each space is similar, 0.027 :g/m3 for common areas

and 0.032 :g/m3 for the residential area, therefore it is recommended to use the

entire data set, which includes the common area and residential area, to calculate

a background concentration. The 95% UCL for the entire data set, which should

be considered the calculated background concentration, is 0.03 :g/m3

.

Microvacuum - There were 144 microvacuum samples collected, with 114

collected in residential areas and 18 collected in common areas. The

microvacuum samples were collected from porous materials including carpets,

couches, chairs, and drapes. The frequency of detection for all of the

microvacuum samples collected in the residential areas (8%) was similar to the

samples collected in the common areas (6%), as were the ranges, mean, and

calculated UCLs for the data sets for each space and each surface. Given the

similarity between the data sets, both between spaces and between surfaces, it is

recommended to use the entire microvacuum data set for estimating the

background concentration of lead in porous surfaces. This yields a 95% UCL of

1.98 :g/ft2

 for the background concentration of lead in porous surfaces.
WORLD TRADE CENTER BACKGROUND STUDY 26

Wipe - There were 114 wipe samples collected, with 80 collected in residential

areas and 34 collected in common areas. The wipe samples were collected from

hard surfaces including counters, floors and walls. The frequency of detection

between the residential areas (49%) and the common areas (53%) for all of the

wipe samples from each areas are similar, as are the range of detections and

means, with the exception of the maximum detected concentration on the floor in

the common area, which was about five times higher than the residential area. 

Although the data sets are very similar for both the spaces and surfaces, the

inclusion of the maximum value for the floor in the common area of 49.2 :g/ft2

 in 

 Revised May 21, 2003

the entire data for areas skews the data set and results in a 95% UCL of 4.59

:g/ft2. Alternatively, if only the residential data set is used, the calculated 95%

UCL provides a value of 1.78 :g/ft2. Either value would be an acceptable

background concentration for hard surfaces, however it is recommended to use

the 95% UCL value of 1.78 :g/ft2 that was calculated using only the residential

data set because of the marginal difference in the maximum detected

concentration in the common areas and residential areas.

6.2.4 Dioxin

Wipe - There were 114 wipe samples collected, with 80 samples collected from

residential areas and 34 samples collected from common areas. The samples were

collected from hard surfaces including counters, floors, and walls. The samples

were analyzed for dioxin and furan congeners and the results were reported in

2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD) equivalents (i.e., TEQs). Any

sample which was below the detection limit for any specific congener group was

assigned a value of 1⁄2 of the detection limit before calculating the TEQ, thus for

the statistical analysis the reported TEQ was used without any further

modifications. In addition, the TEQ value that was used for estimating the

background concentration was the estimated maximum potential concentration

(EMPC). The TEQ EMPC value uses data that indicated the detected presence of

a compound above zero but did not meet all of QA/QC reporting level criteria.

The frequency of detection between the residential areas (23%) and the common

areas (20%) were similar, as were the range of detections, means, and UCLs. The

similarity between the data sets for the residential areas and the common areas

permits the use of the entire data set for estimating the background concentration. 

The 95% UCL calculated from the entire dioxin data set is 0.693 ng/m2

, which

can be used as an estimate of the background dioxin concentration on hard

surfaces. 

6.2.5 Polycyclic Aromatic Hydrocarbons
WORLD TRADE CENTER BACKGROUND STUDY 27

Wipe - There were 113 wipe samples collected, with 80 samples collected from

residential areas and 33 samples collected from common areas. The samples were

collected from hard surfaces including counters, floors, and walls. The samples

were analyzed for 23 PAH compounds, of which seven of the compounds are

used to calculate a toxicity equivalence factor (TEF). The analytical results

indicate that none of the 23 PAH compounds were detected and the TEF for each

sample would be equivalent to 290 :g/m2. The detection limit was the same for

each sample that was analyzed, therefore a UCL cannot be calculated for the

residential or common area data sets due to not having a standard deviation. The

data suggest that the background concentration of PAHs on hard surfaces is less

than the detection limit of 0.25 :g (i.e., 250 :g/m2) for individual PAHs or 290

:g/m2 for the calculated TEF.

6.3 Minerals and Total Dust Results - Development of Background

Concentrations

The following sections present a summary of the analytical results, the calculated

background values and a discussion that addresses the strengths and weaknesses

for the crystalline silica, calcite, gypsum, portlandite and total dust data sets, as

well as the corresponding background value that was derived for each analyte,

matrix, type of space and type of surface. The statistical results and calculated

UCLs are reported in Tables 6-4 through 6-6.

6.3.1 Crystalline Silica

6.3.1.1 Alpha-quartz

Bulk Dust - There were nine bulk dust samples collected from residential areas. 

These samples were analyzed for alpha-quartz. There were no bulk samples

collected from common areas. Eight of the samples detected alpha-quartz above

the detection limit with a mean value of 2.2%. The 95% UCL for alpha-quartz in

bulk dust is 3.66% and this value can be used as an estimate of the background

concentration.

Air - There were forty-six air samples collected, with thirty-two collected from

residential areas and fourteen collected from common areas. The frequency of

detection for the residential areas (25%) and the common areas (29%) are similar,

although the range of detection and mean concentrations are different. This is

primarily due to one sample value from the residential areas being elevated above

the rest of the samples in the data set. This value was determined to be a valid

result and therefore was kept in the data set. There was some variability between

the residential and common area, primarily due to one sample, however following

the priorities identified earlier it is recommended to use residential data set for

estimating the background concentration due the difference in the maximum

detected concentrations. The 95% UCL for the residential data set is 61.9 :g/m3

which can be used as an estimate of background concentration for alpha-quartz in

air.
WORLD TRADE CENTER BACKGROUND STUDY 28

Although the value estimated above has been identified as the recommended

background concentration, an additional calculation was conducted without the

elevated value to determine a UCL that is not influenced by the elevated value. 

The 95% UCL for the residential data that has the elevated value removed is 7.8

:g/m3. This value may be more representative of background, however it is

unclear how common the elevated value may be in an urban environment,

therefore the recommended UCL is 61.9 :g/m3 with the recognition that it may be

much lower (i.e., 7.8 :g/m3).

Wipe - There were 114 wipe samples collected with eighty-one collected from

residential areas and 33 collected from common areas. The wipe samples were

collected from hard surfaces including counters, floors, and walls. The frequency

of detection between the residential areas (38%) and the common areas (61%) for

combined surfaces are not similar and the mean concentration for each type of 

Revised May 14, 2003

surface sampled are not similar between the residential and common areas. Since

the primary focus of this Study was to determine background concentrations for

residential areas, it is recommended to use the data set for the residential spaces to

estimate the background concentration. The mean concentrations from each of the

surface types in the residential data set are similar, varying by less than a factor of

two, therefore it is recommended to use the entire residential data set, which

includes the results from the counters, floors, and walls. The 95% UCL for this

data set is 79.6 :g/ft2

. This value can be used as an estimate of the background

concentration for alpha-quartz on hard surfaces.

6.3.1.2 Cristobalite

Bulk Dust - There were nine bulk dust samples collected from residential areas. 

These samples were analyzed for cristobalite. There were no bulk samples

collected from common areas. None of the samples detected cristobalite above the

detection limit. However, since the detection limit for the samples varied slightly,

a theoretical background concentration can be calculated. The 95% UCL for

cristobalite in bulk dust is 4.69% and this value can be used as an estimate of the

background concentration.

Air - There were forty-six air samples collected with thirty-two collected from

residential areas and fourteen collected from common areas. The samples were

analyzed for cristobalite. Cristobalite was not detected in any sample. However,

since the detection limit for the samples varied slightly, a theoretical background

concentration can be calculated using the entire combined data set from the

residential and common areas. The 95% UCL for the combined data set is 9.3

:g/m3, which can be used as an estimate of the background concentration of

cristobalite in air. 

Wipe - There were 114 wipe samples collected with eighty samples collected in

residential areas and thirty-four in common areas. The samples were collected

from hard surfaces including counters, floors, and walls. The samples were

analyzed for cristobalite. The frequency of detection for the residential areas (0%)
WORLD TRADE CENTER BACKGROUND STUDY 29

and the common areas (3%) were similar, as were the range of detection and mean

concentrations. Based on the similarity of the data sets between spaces and

between surfaces, it is recommended to use the entire data set, combined for

surfaces, to estimate the background concentration. The 95% UCL from this data

set provides a value of 103.7 :g/ft2

 as an estimate of the background concentration

of cristobalite on hard surfaces.

6.3.1.3 Tridymite

Bulk Dust - There were nine bulk dust samples collected from residential areas. 

These samples were analyzed for tridymite. There were no bulk samples collected

from common areas. None of the samples detected tridymite above the detection

limit. However, since the detection limit for the samples varied slightly, a

theoretical background concentration can be calculated. The 95% UCL for

tridymite in bulk dust is 4.69%, and this value can be used as an estimate of the

background concentration.

Air - There were forty-six air samples collected with thirty-two collected from

residential areas and fourteen collected from common areas. The samples were

analyzed for tridymite. Tridymite was not detected in any sample. However, since

the detection limit for the samples varied slightly, a theoretical background

concentration can be calculated using the entire combined data set from the

residential and common areas. The 95% UCL for the combined data set is 9.3

:g/m3, which can be used as an estimate of the background concentration of

tridymite in air.

Wipe - There were 114 wipe samples collected with eighty collected from

residential areas and thirty-four collected from common areas. The samples were

collected from hard surfaces including counters, floors, and walls. The samples

were analyzed for tridymite. Tridymite was not detected in any sample, however

since the detection limit for the samples varied slightly, a theoretical background

concentration can be calculated using the entire combined data set for all surfaces

from the residential and common areas. The 95% UCL for the combined data set

is 99.8 :g/ft2

, which can be used as an estimate of the background concentration of

tridymite on hard surfaces.

6.3.2 Calcite

Bulk Dust - There were nine bulk dust samples collected from residential areas. 

These samples were analyzed for calcite. There were no bulk samples collected

from common areas. Only one of the samples detected calcite above the detection

limit. The 95% UCL for calcite in bulk dust is 3.41% and this value can be used as

an estimate of the background concentration. 

Air - There were forty-six air samples collected with thirty-two collected from

residential areas and fourteen collected from common areas. The samples were

analyzed for calcite. Calcite was not detected in any sample. However, since the

detection limit for the samples varied slightly, a theoretical background

concentration was calculated using the entire combined data set from the
WORLD TRADE CENTER BACKGROUND STUDY 30

residential and common areas. The 95% UCL for the combined data set is 9.3

:g/m3, which can be used as an estimate of the background concentration of calcite

in air. 

Wipe - There were 114 wipe samples collected with eighty samples collected in

residential areas and thirty-four in common areas. The samples were collected

from hard surfaces including counters, floors, and walls. The samples were

analyzed for calcite. The frequency of detection for the residential areas (3%) and

the common areas (3%) were the same, and the range of detection and mean

concentrations were similar. Based on the similarity of the data sets between

spaces and between surfaces, it is recommended to use the entire data set,

combined for surfaces, to estimate the background concentration. The 95% UCL

from this data set provides a value of 132.3 :g/ft2

 as an estimate of the background

concentration of calcite on hard surfaces.

Revised May 14, 2003

6.3.3 Gypsum

Bulk Dust - There were nine bulk dust samples collected from residential areas. 

These samples were analyzed for gypsum. There were no bulk samples collected

from common areas. Only one of the samples detected gypsum above the

detection limit. The 95% UCL for gypsum in bulk dust is 2.33%, and this value

can be used as an estimate of the background concentration. 

Air - There were forty-six air samples collected with thirty-two collected from

residential areas and fourteen collected from common areas. The samples were

analyzed for gypsum. Gypsum was not detected in any sample. However, since

the detection limit for the samples varied slightly, a theoretical background

concentration can be calculated using the entire combined data set from the

residential and common areas. The 95% UCL for the combined data set is 9.3

:g/m3, which can be used as an estimate of the background concentration of

gypsum in air.

Wipe - There were 114 wipe samples collected with eighty collected from

residential areas and thirty-four collected from common areas. The samples were

collected from hard surfaces including counters, floors, and walls. The samples

were analyzed for gypsum. Gypsum was not detected in any sample. However,

since the detection limit for the samples varied slightly, a theoretical background

concentration can be calculated using the entire combined data set for all surfaces

from the residential and common areas. The 95% UCL for the combined data set

is 49.9 :g/ft2

, which can be used as an estimate of the background concentration of

gypsum on hard surfaces.

6.3.4 Portlandite

Bulk Dust - There were nine bulk dust samples collected from residential areas. 

These samples were analyzed for portlandite. There were no bulk samples

collected from common areas. None of the samples detected portlandite above the

detection limit. However, since the detection limit for the samples varied slightly,
WORLD TRADE CENTER BACKGROUND STUDY 31

a theoretical background concentration can be calculated. The 95% UCL for

portlandite in bulk dust is 4.69% and this value can be used as an estimate of the

background concentration.

Air - There were forty-six air samples collected with thirty-two collected from

residential areas and fourteen collected from common areas. The samples were

analyzed for portlandite. Portlandite was not detected in any sample. However,

since the detection limit for the samples varied slightly, a theoretical background

concentration can be calculated using the entire combined data set from the

residential and common areas. The 95% UCL for the combined data set is 9.3

:g/m3, which can be used as an estimate of the background concentration of

portlandite in air.

Wipe - There were 114 wipe samples collected with eighty collected from

residential areas and thirty-four collected from common areas. The samples were

collected from hard surfaces including counters, floors, and walls. The samples

were analyzed for portlandite. Portlandite was not detected in any sample.

However, since the detection limit for the samples varied slightly, a theoretical

background concentration can be calculated using the entire combined data set for

all surfaces from the residential and common areas. The 95% UCL for the

combined data set is 99.8 :g/ft2

, which can be used as an estimate of the

background concentration of portlandite on hard surfaces.

6.3.5 Total Dust

Wipe - There were nine wipe samples collected from residential areas and

analyzed for total dust. Dust was detected in all nine samples with a mean

concentration of 10.9 mg/ft2

. The 95% UCL for this data set was 14.4 mg/ft2,

which can be used as an estimate of the background concentration of total dust.

7.0 HISTORICAL STUDIES ON BACKGROUND CHARACTERIZATION

7.1 Background Literature Search Results

The WTC Background Study was conducted to address the following question:

What were the baseline levels for a select group of contaminants in residential

dwellings in lower Manhattan had the Trade Center never collapsed? A complete

set of data were not available that captured the baseline levels of WTC COPCs in

the settled dust and indoor air of residential dwellings in lower Manhattan prior to

9/11/01. However, there are various sources of data that partially address the

specific aim of the WTC Background Study. This section evaluates the findings of

historical studies on background by way of a comparison to the methods and

results of the WTC Background Study.

A search of the literature was conducted for published data on residential indoor

measurements of WTC COPCs. The focus was for relevant data, collected in the

past ten to fifteen years, that may be used for comparison with the measurements

from the WTC Background Study. Worth noting are the multiple factors that limit
WORLD TRADE CENTER BACKGROUND STUDY 32

the representativeness of historical studies to the WTC Background Study. They

include: variations in sampling and analytical methods; characteristics of the

housing stock (e.g., age, type and upkeep) and seasonal variability.

7.1.1 Residential Indoor Airborne Asbestos Measurements

The literature citations on airborne asbestos measurements focused mainly on

occupational environments. Some information is available for schools and other

public buildings. Very few studies described measurements made in residential

settings. 

There are a number of analytical techniques (PCM, TEM, direct preparation, and

indirect preparation), as well as different units of measurements reported in the

literature for airborne asbestos concentration. HEI (1991) listed eleven different

measurement units that could be encountered in the literature for asbestos fibers

analyzed by TEM. Another factor to note is how the average or mean value is

determined from a set of measurements. Some studies treat all samples with no

asbestos structures/fibers counted as 0 s/cc or 0 f/cc and not as a “less than”

detection limit (Van Orden et al. 1995).

Presented in Table 7-1 is a summary of U.S. residential building average asbestos

concentrations by direct TEM as found in the literature search.

7.1.2 Settled Asbestos Dust Measurements

Ewing (2000) reported a geometric mean of 1000 s/cm2 for samples collected in

six buildings without friable asbestos-containing surfacing materials. The 28

microvacuum samples were collected and analyzed as described in the ASTM

Method D 5755-95 or the earlier draft-EPA method (Clark 1989). The sampled

surfaces would be considered non-porous and usually had visible dust on them. 

The surface types included polished stone, metal, polished wood, and plastic. 

Neither the types of buildings nor their locale were identified. The Study reported

a geometric, rather than arithmetic, mean as a measure of central tendency. Table

7-2 is extracted from that report.

7.1.3 Airborne Man-Made Vitreous Fibers Measurements

Man-made vitreous fibers (MMVFs) are also known as synthetic vitreous fibers

(SVFs). ATSDR (2001) reported that airborne concentrations of MMVFs in

outdoor and indoor air samples usually are #0.0001 f/cc. Measurements at

workplaces that manufacture MMVF have been reported to be #0.1 to 1 f/cc. 

Airborne concentrations > 1 f/cc have been observed during the installation of

insulation in a home or building, but these high levels would drop to preinstallation values within 1 or 2 days.

As summarized by ATSDR (2002), a report by Carter et al. (1999) used both PCM

and SEM to study air samples from 51 residential and commercial buildings

throughout the United States. Only 2 of the 50 samples analyzed by SEM were

found to contain respirable MMVFs. The MMVF concentrations were not
WORLD TRADE CENTER BACKGROUND STUDY 33

included in the ATSDR (2002) summary.

7.1.4 Man-Made Vitreous Fibers in Settled Dust or Soil

According to the ATSDR (2002), no data exist pertaining to the ambient levels of

MMVFs in soil or sediment. The literature search also has not located data on

MMVF loading in residences. 

7.1.5 Lead Levels in the Ambient Air

As reviewed by ATSDR (1999), lead levels in the ambient air vary widely but

usually decrease with increasing distance (both vertical and horizontal) from

emission sources. The EPA (1996) has established the National Ambient Air

Quality Standard for lead of 1.5 μg/m3, quarterly average concentration. 

Composite urban air measurements of lead for 1991 were reported at 0.08 μg/m3

(EPA 1996). In 1988, the average lead concentration for 139 urban air-monitoring

sites around the United States was 0.085 μg/m3

 and remained relatively unchanged,

at 0.04 μg/m3, when estimated between 1994 and 1995 (ATSDR, 1999). Indoor air

lead levels are generally 0.3 to 0.8 times lower than the corresponding outdoor

levels, with an average ratio of 0.5 (ATSDR 1999).

7.1.6 Residential Settled Lead Dust Measurements

Lanphear et al. (1995) reported lead loading measurements from a study of

residences of 205 children in Rochester, NY. House dust samples were collected

using two vacuum methods and a wipe method. The geometric mean values from

the microvacuum measurements were 1 μg/ft2

 and 3 μg/ft2 for noncarpeted floors

and carpeted floors, respectively. The geometric mean value from their wipe

sample measurements were 16 μg/ft2

 and 11 μg/ft2 for noncarpeted floors and

carpeted floors, respectively.

Lanphear et al. (1998) reported a geometric mean for floor dust lead loading of

13.5 μg/ft2 from their pooled analysis of 12 epidemiologic studies.

Gallicchio et al. (2002) compared household lead exposure assessment methods in

an old urban community (although the specific locale was not identified). The

median values for dust lead loading were 12 μg/ft2

 and 5 μg/ft2 for noncarpeted

floors and carpeted floors, respectively. The measurements showed a large

variation in lead load levels. Table 7-3 is extracted from the report’s statistics

summary.

The U.S. Department of Housing and Urban Development (HUD 2001) reported

the arithmetic mean for floor dust lead loading stratified by geographic location

and age of housing. Table 7-4 is extracted from the HUD summary statistics. 

7.1.7 Dioxins in Soil and Settled Dust

ATSDR (1998) concluded that concentrations of chlorinated dibenzo-p-dioxins

(CDDs) in soil are typically higher in urban areas than in rural areas. The highest
WORLD TRADE CENTER BACKGROUND STUDY 34

CDDs in soil concentrations are associated with industrial sites, with CDD levels

ranging from the hundreds to thousands parts per trillion. In general, the

concentration of CDDs in soil near the site of a municipal waste incinerator would

increase in concentration with increasing degree of chlorination. Heptachlorinated

dibenzo-p-dioxin (HpCDD) and octa-chlorinated dibenzo-p-dioxin (OCDD)

congeners are typically found at higher concentrations than the tetrachlorinated

dibenzo-p-dioxin (TCDD), pentachlorinated dibenzo-p-dioxin (PeCDD), and

hexachlorinated dibenzo-p-dioxin (HxCDD) congeners in soil and sediments.

Christmann et al. (1989) collected indoor household dust samples and analyzed the

dust samples for CDDs. The dust samples were collected with a vacuum cleaner

from rooms with furniture treated with a wood preservative. The wood

preservative contained CDD-contaminated pentachlorophenol (PCP). Average

mass concentrations of CDDs found in the dust samples were: 191 μg/kg of

OCDD, 20 μg/kg of HpCDD, 2.5 μg/kg of HxCDD, 0.9 μg/kg of PeCDD, and 0.2

μg/kg of TCDD.

7.1.8 Polycyclic Aromatic Hydrocarbons in Sediment and Soil

No citation was found during the literature search for surface loading of PAHs in

the indoor residential environment. ATSDR (1995) reported the results of several

studies, published from 1973 through 1987, for background concentrations (μg/kg)

of 15 PAHs in rural, agricultural, and urban soils from the United States and other

countries. The ATSDR summary is reproduced here as Table 7-5.

7.2 Comparison of WTC Background Study to Other Studies

Section 7.1 summarized the relevant studies that addressed background

concentrations of COPCs in the residential indoor environment. This section is

focused on the comparison of those studies to the WTC Background Study. As

previously mentioned in Section 7.1, there are numerous factors that limit the

ability to make direct comparisons between studies cited in the open literature that

characterize background levels of the COPCs and the site-specific WTC

Background Study. Thus, a qualitative discussion of study comparability needs to

viewed accordingly. Still, where studies were identified that addressed

background concentrations in a manner relevant to the WTC Background Study a

comparison was performed. Where historical studies are described as being

generally concordant with the findings in the WTC Background study, some

disparities in study design, sampling/analytical protocols and results may still

exist.

7.2.1 Comparison of Airborne Asbestos Concentrations 

The WTC Background Study obtained airborne asbestos measurements from 

residential dwellings and common spaces. Analysis was performed by TEM using

two different counting methods - total asbestos fibers greater than 0.5 μm (as per

AHERA counting rules), and asbestos fibers greater than 5 μm (PCMe) - and, by

phase contrast microscopy (PCM). The literature review focused on PCMe
WORLD TRADE CENTER BACKGROUND STUDY 35

measurements as this metric employs an analytical technique (TEM) that

distinguishes asbestos from other fibrous material and counts only long fibers (i.e.,

> 5 μm) - those most closely associated with adverse health effects (i.e., cancer).

The Consumer Product Safety Commission (CPSC 1987) Study from the literature

review was identified as providing relevant comparisons to the WTC Background

Study. This study reported on airborne asbestos concentration in houses that

contained asbestos containing material (ACM). In 15 houses in Cleveland and 15

houses in Philadelphia the mean asbestos concentration was 0.00023 f/cc and

0.00007 f/cc, respectively. A total of 30 samples were taken in Cleveland and 29

in Philadelphia (see Table 7-1). In the WTC Background Study, a total of 62

samples from residences and common spaces (see Table 6-1) were obtained. The

mean asbestos (PCMe) concentration was 0.00022 s/cc. This value is consistent

with the mean value reported from Cleveland and marginally higher than the mean

value reported in Philadelphia. 

The primary strength of the above comparison is the common metric (PCMe)

employed to measure airborne asbestos concentration. It also focuses on urban

settings similar to New York. However, there are a number of limitations. The

CPSC Study reported on houses with ACM. The known existence of ACM in the

CPSC Study homes would likely serve as a positive bias. Also the particular

housing stock differed, the CPSC Study looked at individual houses whereas the

WTC Background Study focused on apartments. The HEI (1991) summation of

the CPSC Study did not report the frequency of non-detects or what concentration

was assigned to non-detects.

7.2.2 Comparison of Asbestos Settled Dust Concentrations

The WTC Background Study collected measurements of asbestos load (fibers per

unit area) in settled dust by two methods: Microvacuum (ASTM D 5755-95) and

wipe sampling (ASTM D 6480-99). Microvacuum sampling was performed on

porous surfaces (carpets and couches) and resulted in the collection of 162

samples, while 146 wipe samples were collected on hard surfaces (ceilings,

counters, walls and floors). The arithmetic mean for asbestos loading was 2,783

s/cm2

 for the microvacuum samples and 37,174 s/cm2 for the wipe samples. The

literature search identified a study by Ewing (2000) that reported a geometric mean

of 1,000 s/cm2

 for samples collected in six buildings without friable asbestoscontaining surfacing materials. 

Little in the way of meaningful comparison can be made between the Ewing and

WTC Background Studies. Three significant shortcomings exist. First, unlike the

WTC Background Study, the Ewing Study reports a geometric, rather than

arithmetic, mean. Based on the number of samples (n=28) and maximum value

(210,000 s/cm2

), it is evident that the arithmetic mean (calculated by EPA for the

purpose of comparison) was greater (> 7,000 s/cm2

) than the geometric mean

(1,000 s/cm2

) reported in the Ewing Study. Second, the microvacuum samples in

the Ewing Study were obtained from hard surfaces, whereas the WTC Background
WORLD TRADE CENTER BACKGROUND STUDY 36

Study used microvacuum sampling only on porous surfaces. Finally, the building

type was not identified in the Ewing Study.

7.2.3 Comparison of Airborne Man-Made Vitreous Fiber (MMVF)

Concentrations

The WTC Background Study reported a mean concentration of 0.000042 s/cc

(95% UCL = 0.00006 s/cc) in a sample size of 62. ATSDR (2002) reported that

airborne concentrations of MMVFs in outdoor and indoor air samples usually are 

# 0.0001 f/cc. Accordingly, the airborne concentration of MMVFs in the WTC

Background Study appears consistent with background measurements reported in

the literature although the cited reference is very general and does not provide

sufficient information to make a detailed comparison. 

7.2.4 Comparison of Man-Made Vitreous Fibers in Settled Dust or Soil

The WTC background Study reported results of MMVF in bulk dust and wipe

samples. Of the 24 samples collected from bulk dust, all were below the detection

limit of 1%. The following results were reported for 141 wipe samples collected:

frequency of detection (14/141); range (29 - 286 s/cm2

) and mean of 38 s/cm2 (95%

UCL = 52 s/cm2

). ATSDR (2002) reports that no data exist pertaining to the

ambient levels of MMVFs in soil or sediment. The literature search also has not

located data on MMVF loading in residences. 

7.2.5 Comparison of Lead Concentrations in the Ambient Air

The WTC Background Study reported a mean concentration of 0.027 μg/m3. For

the 46 samples collected. No studies on background lead concentration in

residential dwellings were identified in the literature search. ATSDR (1999)

reported that lead levels in the ambient air vary widely but usually decrease with

increasing distance (both vertical and horizontal) from emission sources. The

composite urban air measurement of lead for 1991 was 0.08 μg/m3

 (EPA 1996). 

ATSDR (1999) estimated urban airborne levels for the years 1994-1995 to be 0.04

μg/m3

. Indoor air lead levels are generally 0.3-0.8 times lower than the

corresponding outdoor levels, with an average ratio of 0.5 (ATSDR 1999).

From the historical information reported above, a rough estimate of indoor

airborne lead concentration in urban areas can be made by multiplying the

composite ambient air concentration (0.04 μg/m3

) by 0.5 (average value of

indoor/outdoor concentrations) to give a product of 0.02 μg/m3. This value is

consistent with the mean concentration 0.027 μg/m3

 found in the WTC 

Background Study.

7.2.6 Comparison of Settled Lead Dust Measurements

The WTC Background Study recorded lead measurements in settled dust by

concentration (mass per unit mass) and load (mass per unit area). In addition, the

load measurements were obtained by wipes for hard surfaces and microvacuum for

porous surfaces. The following mean measurements were reported for residential
WORLD TRADE CENTER BACKGROUND STUDY 37

dwellings and common spaces: 

Sample Type Number of Samples Mean

bulk dust 9 119 mg/kg

microvacuum 162 1.51 μg/ft2

wipe (all samples) 114 1.75 μg/ft2

wipe (all uncarpeted floors) 34 3.91 μg/ft2

wipe (uncarpeted residential floors) 25 1.82 μg/ft2

Unlike the other contaminants included in the WTC Background Study, settled

dust lead levels in residential dwellings have been extensively studied. The study

by Lanphear et al. (1998) focused on the relationship between lead-contaminated

house dust and children’s blood lead levels. This Study evaluated pooled

epidemiologic data from many different communities, some of them with

significant sources of lead contamination from activities such as mining sand

smelting. Consequently, reported lead levels are likely to be biased high. Another

factor that compromises the comparison of results to the WTC Background Study

is that the average lead load (13.5 μg/ft2

) on floors is reported as a median rather

than mean value. Lastly, the measurements were performed by multiple sampling

procedures, including wipe sampling and both high/low flow vacuum techniques.

The study by Gallicchio et al. (2002) focused on a comparison of methods (wipe,

questionnaire, and visual inspection) to assess household lead levels. An

advantage is that its targeted community (i.e., “old and urban”) is much like New

York City. However, the Study selected low socio-economic status (SES)

households (i.e., Medicaid recipients) - which due to less available resources for

building maintenance may result in a positive bias. Also, like the Lanphear Study,

lead loadings (12 μg/ft2

 and 5 μg/ft2 for non-carpeted floors and carpeted floors,

respectively) were reported as median rather than mean values. 

The most appropriate comparison to the WTC background Study can be made with

the Housing and Urban Development (HUD 2001) survey on lead in housing. 

Table 7-4 provides the distribution of lead loading by wipe sampling methodology

in U.S. housing for uncarpeted floors. This data is broken down by census region

and building age. In the Northeast, there is a greater than five-fold increase in lead

load in pre-1939 versus post-1939 housing. Excluding the pre-1939 housing

(mean 24.0 μg/ft2

), the weighted mean lead load for 1940 - 1998 housing stock is

3.45 μg/ft2

. The results from the HUD evaluation are consistent with the results of

lead load obtained in the WTC Background Study residential units for uncarpeted

floors (i.e., mean = 1.82 μg/ft2

 and 95% UCL = 2.96 μg/ft2). This comparison

benefits from both studies reporting results in the same metric (i.e., arithmetic
WORLD TRADE CENTER BACKGROUND STUDY 38

means) for the same surfaces (uncarpeted floors) by the same methodology (wipe

sampling). A limited disadvantage of the comparison is the gross characterization

of housing by geographic location (e.g., Northeast) in the HUD survey and the

exclusion of pre-1939 housing stock. 

 

7.2.7 Comparison of Dioxin Concentration in Settled Dust

The WTC Background Study reported in a mean dioxin concentration of 0.644

ng/m2 (95% UCL = 0.693 ng/m2

) for 80 wipe samples. Results were reported for

dioxin toxicity equivalents (TEQs). The literature search identified no studies that

reported surface loading (mass per unit area) of dioxin in settled dust in residential

dwellings. The study by Christmann et al. (1989) reported concentrations (mass

per mass or μg/kg) of various dioxin congeners (see Section 7.1.7). Converting

these results into dioxin TEQs yields a value of 1.34 μg/kg (or ng/g). Multiplying

by an average dust load of 500 mg/m2

 or 0.5 g/m2 results in an estimated dioxin

TEQ load of 0.67 ng/m2

 (1.34 ng/g x 0.5 g/m2).

The dioxin TEQ load of 0.67 ng/m2 that was estimated from the Christmann Study

is consistent with the mean concentration obtained from the WTC Background

Study. However, the comparison has a number of limitations. The Christmann

Study reported dioxin results in units of concentration (mass per mass), thus

necessitating a conversion to the metric (mass per area) used in the WTC 

Revised May 14, 2003

background Study. This required employing an estimate of average dust load in a

residential dwelling, a value that can vary considerably depending on

housekeeping habits. Also, the Christmann Study collected samples from

households that contained furniture treated with a wood preservative. This may

serve to bias the results high. Finally, the Christmann Study employed a vacuum

sampling method whereas the WTC Background Study collected wipe samples. 

7.2.8 Comparison of Polycyclic Aromatic Hydrocarbon Concentration in

Settled Dust

All 80 wipe samples collected in the WTC Background Study were reported to be

below the limits of detection (290 μg/m2

, benzo[a]pyrene equivalents). No

citations were found in the literature search for surface loading of PAHs in the

indoor residential environment. Consequently, no comparison is possible with the

PAH surface loading results reported in the WTC Background Study.

8.0 DISCUSSION

The objective of this Study was to determine indoor baseline levels or background

concentrations for a specific group of compounds that are associated with the

World Trade Center collapse. These background concentrations will be used to

supplement the health-based benchmarks established in the "World Trade Center

Indoor Air Assessment: Selecting Contaminants of Potential Concern and Setting

Health-Based Benchmarks"document and may be used as an alternative cleanup
WORLD TRADE CENTER BACKGROUND STUDY 39

value if the health-based benchmark cannot be achieved.

The compounds of interest were asbestos, man-made vitreous fibers, lead, dioxin,

polycyclic aromatic hydrocarbons, and crystalline silica. In addition to these

compounds, data were also collected for calcite, gypsum, portlandite, and total

dust. A combination of air samples, microvacuum samples, wipe samples, and

bulk dust samples were collected to evaluate these compounds in residential

buildings and in common areas of residential buildings. The microvacuum

samples were collected from a variety of porous surfaces, while the wipe samples

were collected from a variety of hard surfaces. The data were evaluated separately

for each type of sample, type of space, and each compound. 

In addition, the data were evaluated for groups of similar data, such as all

residential lead wipe data. The combined of analyses provided a combination of

192 background concentrations, which represents 95% upper confidence limits on

the arithmetic means. Similar subsets of these 192 data points (e.g., by compound

or by media.) were then qualitatively compared to determine a representative

background concentration for each compound in air, bulk dust, porous materials,

and hard materials. The recommended values are presented below in Table 8-1. 

The values presented in the table are an upper-bound statistical estimation of the

true mean of the sample population. The upper-bound confidence limit is 95%,

which represents the confidence that the true mean is equal or lower to the value

that is presented in the table.
WORLD TRADE CENTER BACKGROUND STUDY 40

Revised May 14, 2003

Table 8-1. Background concentrations that were derived based on the analytical

results from the samples collected in this study. The concentrations listed in the

table represent the 95% upper confidence limit (UCL) on the arithmetic mean.

Compound Air Settled Dust

Bulk Dust Porous

Surface

Hard

Surface

Asbestos n/a

(<1%)

6,192 s/cm2R

Asbestos - PCM 0.0023 s/ccR

Asbestos - TEM

AHERA

0.00024 s/ccR

Asbestos - TEM

PCMe

0.00024 s/ccR/T

MMVF 0.00006 s/ccR/T n/a

(<1%)

52 s/cm2T

Lead 0.03 :g/m3T 186 mg/kgR 1.98 :g/ft2T 1.78 :g/ft2R

Dioxin 0.693 ng/m2T

PAH n/a

(<290 :g/m2)

Alpha-quartz

(w/o max. value)

61.9 :g/m3R

(7.8 :g/m3R)

3.66 %R 79.6 :g/ft2R

Calcite 9.3 :g/m3T 3.41 %R 132.3 :g/ft2T

Cristobalite 9.3 :g/m3T 4.69 %R 103.7 :g/ft2T

Gypsum 9.3 :g/m3T 2.33 %R 49.9 :g/ft2T

Portlandite 9.3 :g/m3T 4.69 %R 99.8 :g/ft2T

Tridymite 9.3 :g/m3T 4.69 %R 99.8 :g/ft2T

Total Dust 14.4 mg/ft2R

n/a - indicates that a upper confidence limit could not be calculated, value in parenthesis

indicates that the value is less than the detection limit

italics - indicates a theoretical UCL due to all data being below the detection limit

T - indicates the total data set was used

R - indicates only the residential data set was used
WORLD TRADE CENTER BACKGROUND STUDY 41

The estimated background concentrations that were calculated were compared to

literature values when available. Values reported in the literature regarding

asbestos and MMVF in air, and lead and dioxin in settled dust from urban

environments, that were collected and analyzed using methods similar to this

Study, are consistent to the values generated by the samples collected in this

background Study (Table 8-2). The consistent nature indicates that the

concentrations observed from this Study population are similar to other urban

environments.

The literature search conducted as part of this evaluation highlighted data gaps in

the scientific literature for several of the compounds for which data were collected. 

These compounds include MMVF, crystalline silica, calcite, gypsum, and

portlandite. The data collected and the calculated background concentrations

provide a source of data that can be used to address these data gaps.

In general, the data sets for samples that were collected in residential areas and

common areas were similar, however there were data sets in which the detected

concentrations in common area were nominally higher than the residential spaces. 

The activity pattern, amount of foot traffic, type of cleaning, and frequency of

cleaning may differ between these spaces, and some combination of these factors

may be responsible for this observation.

Table 8-2. Comparison of estimated background values from this study to

background or historical values reported in the scientific literature for select

compounds.

Compound Estimated Background

UCL Value

Historical/Literature

Value

Asbestos - PCMe 0.00024 s/cc 0.00022 s/cc(1)

MMVF - air 0.00006 s/cc #0.0001 f/cc(2)

Lead - air 0.03 :g/m3 0.02 :g/m3(3)

Lead - wipe floors 3.91 :g/ft2 3.45 :g/ft2(4)

Dioxin - wipe 0.693 ng/m2 0.67 ng/m2(5)

(1) Consumer Product Safety Commission Study. 1987.

(2) ATSDR. 2002.

(3) Calculated value from EPA historic ambient air lead data.

(4) HUD. 2001.

(5) Christmann. 1989.
WORLD TRADE CENTER BACKGROUND STUDY 42

As with any statistical evaluation, decisions made regarding the data must be

taken into consideration when discussing and applying the results. For this

evaluation, there were several decisions that were made regarding the data sets that

affect the confidence in the estimated background concentrations. 

The first is that when a sample was reported to be below the detection limit, it was

assigned a value of 1⁄2 the detection limit. A sample that is listed as being below

the detection limit may correspond to a concentration that is actually or virtually

zero, or it may correspond to a concentration that is very close to the detection

limit. By utilizing 1⁄2 of the detection limit for samples that are below the detection

limit, the true background concentration may be over- or under-estimated. 

However, this approach consistently assigns a mid-point value that should result in

an estimation that is closer to the actual mean than if either zero or the detection

limit had been assigned for each sample that was below the detection limit. This is

an important concept given that many of the data sets evaluated contained a large

percentage of samples that were below the detection limit. As illustrated in Table

8-3, the UCLs presented in Table 8-1 would decrease or increase, respectively, by

approximately the same margin if either zero or the detection limit would have

been substituted for the samples that were below the detection limit. Data sets

with a frequency of detection of less than eight percent would vary by more than

50%, although using 1⁄2 of the detection limit provides an estimated value that is

within the middle of the range and should be a better estimation of the true mean.

Another decision that was made was to calculate UCLs for all of the data sets

regardless of the sample size or frequency of detection. EPA generally estimates

UCLs for data sets that have a sample size of greater than or equal to ten. For this

assessment several UCL calculations were performed on data sets with a sample

size of less than 10. The resulting UCLs for these data sets would be viewed with

less certainty than UCLs calculated from larger data sets, but as described above,

we were unable to achieve the sample size we desired for every sample type or

compound. Additionally, there were multiple data sets for which all of the

samples were reported to be below the detection limit. Some of these data sets had

varying detection limits which made choosing a single value problematic. To

circumvent this problem, data sets that had variability due to varying detection

limits also had UCLs estimated, even if the frequency of detection was 0%. These

estimated UCLs were identified as theoretical values because the mean that was

calculated, from which the UCL was derived, was based only upon the detection

limit and it does not include actual detected concentrations. The resulting

theoretical UCL for these data sets is generally near the highest detection limit that

was used.

Conclusions

The evaluation of the data collected from this Study was able to:

• provide estimates of baseline levels or background concentrations of

compounds that were identified as COPCs related to the World Trade
WORLD TRADE CENTER BACKGROUND STUDY 43

Center collapse,

• show that the estimated background concentrations were consistent with

other background studies and historical data, when comparison data were

available

• provide a upper-bound point estimate that can be used as a background

concentration for the COPC report, and

• provide a source of data to help address data gaps in the scientific literature

on background concentrations of building-related materials.
WORLD TRADE CENTER BACKGROUND STUDY 44

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WORLD TRADE CENTER BACKGROUND STUDY 46

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concentrations in buildings following the Loma Prieta Earthquake. Regul Toxicol

Pharmacol 21:117-122.

Vogt NB, Brakstad F, Thrane K, et al. 1987. Polycyclic aromatic hydrocarbons in

soil and air: Statistical analysis and classification by the SIMCA method. Environ

Sci Technol 21:35-44.

White JB, Vanderslice RR. 1980. POM Source and Ambient Concentration Data:

Review and Analysis. Washington, DC: U.S. Environmental Protection Agency,

Office of Research and Development, EPA-600/7-80-044.

Windsor JG, Hites RA. 1979. Polycyclic aromatic hydrocarbons in Gulf of Maine

sediments and Nova Scotia sils. Geochim Cosmochim Acta 43:27-33.
See http://www.epa.gov/wtc/ for additional information

11105

10457

10474

10460

10454

00083

10456

10451

10452

10472

10453

10027

10035

10029

11106

10032

10459

10024

10025

10455

11102

11103

10031

10040

10033

10035

10473

10462

10021

10034

10026

10128

10028

10039

10030

10037

10023

10474

10468

11101

10044

10458

New Jersey

­

 FIGURE - 1 World Trade Center Background Study 

and WTC Dust Cleanup Program

1

Generalized locations include Census Block Groups near to Miles

background study buildings.

US EPA Region 2

World Trade Center Indoor Air Cleanup

Map Created 3/25/03

Background Study Locations

Cleaning Area Boundary

­

2

Miles

New Jersey

Manhattan

The Bronx

Queens

Brooklyn
Media Sampling Points Analytical Parameters Sampling Method Description Analytical Method Required Detection Limits1

Asbestos ASTM D 5755-95 

This is a micro vacuuming method. By taping three wipe-sampling 

templates together, three co-located samples were collected from 

each location.

ASTM D 5755-95 1000 structures/cc

Lead ASTM E 1973-99

This is a micro vacuuming method. By taping three wipe-sampling 

templates together, three co-located samples were collected from 

each location.

SW-846 6010B <25 ug/ft2

Asbestos ASTM D 6480-99 Wipe Samples (samples will be collected on the same wipe as MMVF) ASTM D 6480-99 (wipe) 1000 structures/cc

Lead HUD Appendix 13.1 Wipe Samples SW-846 6010B <25 ug/ft2

Dioxins ASTM D 6661-01 Wipe Samples ASTM 6661-01/SW-846 8290 <2 ng/m2

PAHs ASTM D 6661-01 Wipe Samples ASTM 6661-01/SW-846 8270C <0.3 mg/m2

Total Dust HUD Appendix 13.12 Wipe Samples No Formal Method (NIOSH 7500 Modified) No detection limit required

Silica, calcite, 

gypsum HUD Appendix 13.12 Wipe Samples. All parameters were collected on one wipe. NIOSH 7500 (XRD) Background

MMVF ASTM D 6480-99 Wipe Samples (samples will be collected on the same wipe as asbestos) EMSL MSD 0310 Background

Asbestos NIOSH 7400 Air pump operated at 10L/min for 8 hours to achieve the COPC wkgroup Practical Quantitation Limit (PQL) PCM NIOSH 7400 followed by TEM AHERA method. PCM 0.0009 f/cc TEM 0.0005 f/cc

Lead NIOSH 7300 Air pump operated at 10L/min for 8 hours to achieve the COPC wkgroup PQL SW-846 6010B 0.1 ug/m3

Silica, calcite, 

gypsum

NIOSH 7500 Air pump operated at 2.5L/min for 8 hours to achieve the COPC wkgroup PQL NIOSH 7500 (XRD) 0.5 ug/m3

MMVF3 NIOSH 7400 Air pump operated at 10L/min for 8 hours to achieve the COPC wkgroup Practical Quantitation Limit (PQL) EMSL MSD 0310 <0.01 f/cc

Asbestos: PLM NYS 198.1 followed by

TEM NYS 198.4 Background

Lead: SW-846 6010B <25 ug/ft2

Silica, calcite, gypsum: NIOSH 7500 (XRD) Background

MMVF: PLM NYS 198.1/EMSL MSD 0310 Background

Dioxins: SW-846 8290 <2 ng/m2

PAHs: SW-846 8270 <0.3 mg/m2

NOTES: 

3 No standardized sampling method exists for this parameter. On the assumpition that this fibrous material behaves in the air in the same way as asbestos, NIOSH 7400 will be utlized. 

 Analysis via EMSL MSD 0310 (see the EMSL SOP in Appendix C).

At least 10 grams of dust for PAHs and 30 grams for dioxins.

Settled Dust 

Porous Soft 

LEGEND: < = less than

surfaces

Settled Dust 

Non-porous 

Hard 

surfaces

2 Wipe samples for total dust and silica, calcite and gypsum will be collected using the HUD Appendix 13.1 method since no standardized method is available. 

Indoor Air

Bulk Dust

Horizontal surfaces of 

tables or counters and bare 

floors, ceilings and walls in 

areas of activity (living 

rooms, family rooms)

Carpets, fabric furniture or 

drapery in areas of activity 

(living rooms, family rooms)

Attachment 5 of the QAPP 

"HVAC Or Air Conditioner 

Filter Bulk Collection 

Protocol" prepared by TRC 

Solutions Inc.

AC window units (collection 

of bulk dust sample from 

the unit air filters).

Asbestos; lead; 

silica, calcite, 

gypsum; MMVF

Dioxins, PAHs

ng/m2 = nanograms per square meter

Bulk dust samples4 were collected from AC window type unit filters, 

brushed with a disposable brush into a stainless steel bowl and 

transferred into sample containers. If the volume required was not 

sufficient for all analyses, the sample analysis was prioritized as 

follows: asbestos, lead, silica, calcite, gypsum, MMVF, PAHs, and 

dioxins.

ug/ft2 = micrograms per square foot

Sampling and Analytical Procedures Summary

ug/m3 = micrograms per square meter

TABLE 4-1

WTC Background Study

1Required Detection limits are Tier III Levels from "Indoor Air Assessment: Selecting Contaminants of Potential Concern and Setting Health Based Benchmarks" prepared by

 the Contaminants of Potential Concern (COPC) Committee of the World Trade Center Indoor Air Taskforce Working Groupf/cc = fibers per square centimetermg/m2 = milligrams per square meter

4 No less than 5 grams and up to 20 grams of dust are required to analyze for asbestos, lead, silica, calcite, gypsum, and MMVF.

Areas of known activity 

(living rooms, family rooms)
Analytical Parameters Matrix

Sample Media / 

Container Preservative

Holding Time From 

Date of Sampling

Samples 

Collected Lot blanks

Field 

Blanks

Spike 

Blanks

Duplicate 

Samples

Total Field 

Samples

Asbestos Microvacuum 0.45 um MCEF 25 mm 20oC (None) Unlimited 162 14 28 0 * 204

Lead Microvacuum 0.8 um MCEF 37 mm 20oC (None) 6 months 162 14 28 0 * 204Asbestos / MMVF Wipe

9 x 9 inch Cleanroom 

Wipe 20oC (None) Unlimited 146 14 28 0 14 202

Lead Wipe 15 x 15 cm Ghost Wipes 20oC (None) 6 months 114 14 14 14** 14 170Dioxins Wipe 3 x 3 inch cotton gauze 4oC

7 days to extraction, 40 

days to analysis 114 14 14 0 14 156

PAHs Wipe 3 x 3 inch cotton gauze 4oC

7 days to extraction, 40 

days to analysis 113 14 14 0 14 155

Total Dust Wipe 15 x 15 cm Ghost Wipes 20oC (None) Unlimited 35 14 14 0 3 66

Silica, calcite, gypsum Wipe 15 x 15 cm Ghost Wipes 20oC (None) 28 days 114 14 14 0 14 156Asbestos / MMVF Air 0.45 um MCEF 25 mm 20oC (None) Unlimited 64 13 28 0 32 137Lead Air 0.8 um MCEF 37 mm 20oC (None) 6 months 46 14 29 0 14 103Silica, calcite, gypsum Air 5 um PVC filter 37 mm 20oC (None) 28 days 46 14 28 0 14 102Asbestos / MMVF Bulk Dust 4 oz. Polypropylene 20oC (None) Unlimited 24 NC NC NC NC 24Lead Bulk Dust 4 oz. Polypropylene 20oC (None) 6 months 9 NC NC NC NC 9Dioxins Bulk Dust 125 ml Amber Glass 4oC 7 days NC NC NC NC NC 0

PAHs Bulk Dust 125 ml Amber Glass 4oC

7 days to extraction, 40 

days to analysis NC NC NC NC NC 0

Silica, calcite, gypsum Bulk Dust 4 oz. Polypropylene 20oC (None) 28 days 9 NC NC NC NC 9

NOTES:NC = QC Sample was not collected due to insufficient material..

TABLE 4-2

WTC Background Study

Quality Control Samples Collected

The information provided in this table represents the number of samples and QC samples collected. It is not an indication of * Microvacuum samples were collected as co-located triplicate samples therefore duplicate samples were not collected. ** As recommended in the method, spike samples were prepared and submitted with the wipe samples into the sampling stream for lead analysis only

the 

number of sample analytical results reported since several samples were collected for multiple analytes.

Field Sample Collection Summary 
Sample Identification Number Spike Added (g) True Value (ug/wipe) +- 2% Spike Sample Results1 (ug/wipe) Percent Recovery QC Limit % Recovery

13-BG-Common Area-Wipe Ceiling 1-L 0.0919 413 361 87% 80-120%10-BG-Common Area-Wipe Ceiling 1-L 0.1018 457 397 87% 80-120%11-BG-Common Area-Wipe Ceiling 1-L 0.0997 448 405 90% 80-120%14-BG-Common Area-Wipe Ceiling 1-L 0.1063 477 414 87% 80-120%9-BG-Common Area-Wipe Ceiling 1-L 0.1031 463 404 87% 80-120%4-BG-Wipe Ceiling 1-L 0.0572 257 219 85% 80-120%2-BG-Common Area-Wipe Ceiling 1-L 0.0530 238 189 79% 80-120%

8-BG-Wipe Ceiling 1-L 0.0956 429 432 101% 80-120%3-BG-Wipe Ceiling 1-L 0.0602 270 209 78% 80-120%

5-BG-Wipe Ceiling 1-L 0.0504 226 205 91% 80-120%1-BG-Common Area-Wipe Ceiling 1-L 0.0540 242 202 83% 80-120%6-BG-Wipe Ceiling 1-L 0.0708 318 289 91% 80-120%7-BG-Common Area-Wipe Ceiling 1-L 0.0681 306 294 96% 80-120%12-BG-Common Area-Wipe Ceiling 1-L 0.0982 441 ND2 - 80-120%

1 Result of the spike sample sent indistinguishably to the lab with field samples.2 It is believed this sample was inadvertently switched at the laboratory with a counter wipe sample. The laboratory could not confirm this result, although the result of the counter wipe was 383 ug/ft2, 

where as the ceiling wipe sample was not detected.

Table 4-3

Quality Control Wipe Spike Sample Results For Lead
Table 6-1 *Minimum detected value includes values that may be 1⁄2 of the detection limit

Table 6-1. Summary of the analytical results for the organic and inorganic compounds from the background study. The table presents the samplesize, frequency of detection, minimum and maximum detected concentrations, arithmetic mean, the statistic used, and the upper confidence limit(UCL) for each compound and matrix sampled. The values in this table were calculated using the entire data set for each analyte, which includesresidential and common areas.

Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Asbestos Bulk Dust 3 0/3 <0.5% -------- -------- -------- --------

Air - PCM 64 33/64 0.0005 f/cc 0.007 f/cc 0.0017 f/cc 95% Chebyshev

(Mean, STD)

0.0027 f/cc

Air - TEM AHERA 62 4/62 0.0002 s/cc 0.0004 s/cc 0.00022 s/cc 95% Chebyshev

(Mean, STD)

0.00025 s/cc

Air - TEM PCMe 62 3/62 0.0002 s/cc 0.0004 s/cc 0.00022 s/cc 95% Chebyshev

(Mean, STD)

0.00024 s/cc

Microvacuum - All 161 21/161 317 s/cm2 72,094 s/cm2 2,783 s/cm2

Microvacuum -Carpet

69 13/69 317 s/cm2 72,094 s/cm2 3,715 s/cm2

Microvacuum -Couch

77 6/77 317 s/cm2 24,138 s/cm2 1,818 s/cm2

Wipe - All 146 25/146 592 s/cm2 3,798,910 s/cm2 37,174 s/cm2 97.5%

Chebyshev

(Mean, STD)

207,033 s/cm2
Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-1 *Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Ceiling 32 4/32 592 s/cm2 83,893 s/cm2 3,885 s/cm2 97.5%

Chebyshev

(Mean, STD)

20,109 s/cm2

Wipe - Counter 32 6/32 592 s/cm2 1,183,205 s/cm2 37,910 s/cm2 97.5%

Chebyshev

(Mean, STD)

268,632 s/cm2

Wipe - Floors 34 8/34 592 s/cm2 3,798,910 s/cm2 113,999 s/cm2 97.5%

Chebyshev

(Mean, STD)

811,379 s/cm2

Wipe - Walls 48 7/34 592 s/cm2 149,055 s/cm2 4,460 s/cm2 97.5%

Chebyshev

(Mean, STD)

23,762 s/cm2

MMVF Bulk Dust 24 0/24 <0.5 % -------- -------- -------- --------

Air 62 5/62 0.032 s/L 0.216 s/L 0.042 s/L 95% Chebyshev

(Mean, STD)

0.06 s/L

Wipe - All 141 14/141 29 s/cm2 286 s/cm2 38 s/cm2 95% Chebyshev

(Mean, STD)

52 s/cm2

Wipe - Ceiling 31 1/31 29 s/cm2 286 s/cm2 37 s/cm2 95% Chebyshev

(Mean, STD)

73 s/cm2

Wipe - Counter 31 1/31 29 s/cm2 114 s/cm2 31 s/cm2 95% Chebyshev

(Mean, STD)

43 s/cm2
Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-1 *Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Floors 33 11/33 29 s/cm2 286 s/cm2 59 s/cm2 95% Chebyshev

(Mean, STD)

103 s/cm2

Wipe - Walls 46 1/46 29 s/cm2 57 s/cm2 29 s/cm2 95% Chebyshev

(Mean, STD)

32 s/cm2

Lead Bulk Dust 9 9/9 44.5 mg/kg 242 mg/kg 126 mg/kg 95% H-UCL 186 mg/kg

Air 46 1/46 0.026 :g/m3 0.058 :g/m3 0.027 :g/m3 95% Chebyshev

(Mean, STD)

0.03 :g/m3

Microvacuum - All 162 13/162 1.16 :g/ft2 9.73 :g/ft2 1.51 :g/ft2 95% Chebyshev

(Mean, STD)

1.98 :g/ft2

Microvacuum -Carpet

69 10/69 1.16 :g/ft2 9.73 :g/ft2 1.89 :g/ft2 95% Chebyshev

(Mean, STD)

2.94 :g/ft2

Microvacuum -Couch

78 3/78 1.16 :g/ft2 3.6 :g/ft2 1.23 :g/ft2 95% Chebyshev

(Mean, STD)

1.41 :g/ft2

Wipe - All 114 57/114 0.25 :g/ft2 49.2 :g/ft2 1.75 :g/ft2 97.5%

Chebyshev

(Mean, STD)

4.59 :g/ft2

Wipe - Counter 32 15/32 0.25 :g/ft2 7 :g/ft2 1.17 :g/ft2 97.5%

Chebyshev

(Mean, STD)

3.07 :g/ft2
Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-1 *Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Floors 34 30/34 0.25 :g/ft2 49.2 :g/ft2 3.91 :g/ft2 97.5%

Chebyshev

(Mean, STD)

12.9 :g/ft2

Wipe - Walls 48 12/48 0.25 :g/ft2 4.48 :g/ft2 0.61 :g/ft2 95% Chebyshev

(Mean, STD)

1.18 :g/ft2

Dioxin (TEQEMPC(ND=1/2)

Wipe - All 114 88/114 0.475 ng/m2 1.66 ng/m2 0.644 ng/m2 95% Chebyshev

(Mean, STD)

0.693 ng/m2

Wipe - Counter 32 23/32 0.475 ng/m2 0.823 ng/m2 0.641 ng/m2 95% H-UCL 0.669 ng/m2Wipe - Floors 34 26/34 0.546 ng/m2 0.791 ng/m2 0.633 ng/m2 95% Chebyshev

(Mean, STD)

0.684 ng/m2

Wipe - Walls 48 39/48 0.518 ng/m2 1.66 ng/m2 0.653 ng/m2 95% Chebyshev

(Mean, STD)

0.756 ng/m2

PAH - TEF Wipe - All 113 0/113 290 :g/m2 -------- -------- -------- --------

Wipe - Counter 31 0/31 290 :g/m2 -------- -------- -------- --------Wipe - Floors 34 0/34 290 :g/m2 -------- -------- -------- --------Wipe - Walls 48 0/48 290 :g/m2 -------- -------- -------- --------
Table 6-2 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Table 6-2. Summary of the analytical results for the organic and inorganic compounds from the background study. The table presents the samplesize, frequency of detection, minimum and maximum detected concentrations, arithmetic mean, and the statistic used, and the upper confidence

limit (UCL) for each compound and matrix sampled. The values in this table were calculated using only the data sets from the residence areas foreach analyte.

Residential Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Asbestos Bulk Dust 3 0/3 <0.5% -------- -------- -------- --------

Air - PCM 50 21/50 0.0005 f/cc 0.007 f/cc 0.0014 f/cc 95% Chebyshev

(Mean, STD)

0.0023 f/cc

Air - TEM AHERA 48 2/48 0.0002 s/cc 0.0004 s/cc 0.00022 s/cc 95% Chebyshev

(Mean, STD)

0.00024 s/cc

Air - TEM PCMe 48 2/48 0.0002 s/cc 0.0004 s/cc 0.00022 s/cc 95% Chebyshev

(Mean, STD)

0.00024 s/cc

Microvacuum - All 143 15/143 317 s/cm2 72,094 s/cm2 2,234 s/cm2

Microvacuum - Carpet 60 10/60 317 s/cm2 72,094 s/cm2 2,861 s/cm2Microvacuum - Couch 71 4/71 317 s/cm2 24,138 s/cm2 1,732 s/cm2Microvacuum - Drapes 12 1/12 791 s/cm2 12,288 s/cm2 2,071 s/cm2 95% Chebyshev

(Mean, STD)

6,149 s/cm2

Wipe - All 104 14/104 592 s/cm2 83,893 s/cm2 2,309 s/cm2 95% Chebyshev

(Mean, STD)

6,192 s/cm2

Wipe - Ceiling 24 3/24 592 s/cm2 83,893 s/cm2 4,683 s/cm2 97.5% Chebyshev

(Mean, STD)

26,295 s/cm2
Residential Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-2 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Counter 25 3/25 592 s/cm2 2,770 s/cm2 870 s/cm2 95% Chebyshev

(Mean, STD)

1,357 s/cm2

Wipe - Floors 25 4/25 592 s/cm2 40,363 s/cm2 2,405 s/cm2 95% Chebyshev

(Mean, STD)

9,307 s/cm2

Wipe - Walls 30 4/30 592 s/cm2 12,267 s/cm2 1,530 s/cm2 95% Chebyshev

(Mean, STD)

3,473 s/cm2

MMVF Bulk Dust 24 0/24 <0.5% -------- -------- -------- --------

Air 48 1/48 0.032 s/L 0.216 s/L 0.041 s/L 95% Chebyshev

(Mean, STD)

0.06 s/L

Wipe - All 99 11/99 29 s/cm2 286 s/cm2 38 s/cm2 95% Chebyshev

(Mean, STD)

53 s/cm2

Wipe - Ceiling 23 1/23 29 s/cm2 286 s/cm2 40 s/cm2 95% Chebyshev

(Mean, STD)

87 s/cm2

Wipe - Counter 24 1/24 29 s/cm2 114 s/cm2 32 s/cm2 95% Chebyshev

(Mean, STD)

48 s/cm2

Wipe - Floors 24 8/24 29 s/cm2 172 s/cm2 52 s/cm2 95% Chebyshev

(Mean, STD)

89 s/cm2

Wipe - Walls 28 1/28 29 s/cm2 57 s/cm2 30 s/cm2 95% Chebyshev

(Mean, STD)

34 s/cm2

Lead Bulk Dust 9 9/9 44.5 mg/kg 242 mg/kg 126 mg/kg 95% H-UCL 186 mg/kg
Residential Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-2 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Air 32 1/32 0.026 :g/m3 0.058 :g/m3 0.028 :g/m3 95% Chebyshev

(Mean, STD)

0.032 :g/m3

Microvacuum - All 144 12/144 1.16 :g/ft2 9.73 :g/ft2 1.53 :g/ft2 95% Chebyshev

(Mean, STD)

2.05 :g/ft2

Microvacuum - Carpet 60 10/60 1.16 :g/ft2 9.73 :g/ft2 2.00 :g/ft2 95% Chebyshev

(Mean, STD)

3.20 :g/ft2

Microvacuum - Couch 72 2/72 1.16 :g/ft2 2.83 :g/ft2 1.20 :g/ft2 95% Chebyshev

(Mean, STD)

1.34 :g/ft2

Microvacuum - Drapes 12 0/12 1.16 :g/ft2 -------- -------- -------- --------

Wipe - All 80 39/80 0.25 :g/ft2 10.5 :g/ft2 1.04 :g/ft2 95% Chebyshev

(Mean, STD)

1.78 :g/ft2

Wipe - Counter 25 12/25 0.25 :g/ft2 5.9 :g/ft2 1.1 :g/ft2 97.5% Chebyshev

(Mean, STD)

2.98 :g/ft2

Wipe - Floors 25 21/25 0.25 :g/ft2 10.5 :g/ft2 1.82 :g/ft2 95% H-UCL 2.96 :g/ft2Wipe - Walls 30 6/30 0.25 :g/ft2 1.01 :g/ft2 0.35 :g/ft2 95% Chebyshev

(Mean, STD)

0.52 :g/ft2

Dioxin Wipe - All 80 19/80 0.475 ng/m2 0.83 ng/m2 0.629 ng/m2 95% H-UCL 0.643 ng/m2

Wipe - Counter 25 6/25 0.475 ng/m2 0.823 ng/m2 0.639 ng/m2 95% H-UCL 0.672 ng/m2Wipe - Floors 25 6/25 0.546 ng/m2 0.771 ng/m2 0.621 ng/m2 Student’s t 0.643 ng/m2
Residential Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-2 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Walls 30 7/30 0.534 ng/m2 0.83 ng/m2 0.628 ng/m2 95% H-UCL 0.650 ng/m2

PAH Wipe - All 80 0/80 290 :g/m2 -------- --------- -------- --------

Wipe - Counter 25 0/25 290 :g/m2 -------- --------- -------- --------Wipe - Floors 25 0/25 290 :g/m2 -------- --------- -------- --------Wipe - Walls 30 0/30 290 :g/m2 -------- --------- -------- --------
Table 6-3 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Table 6-3. Summary of the analytical results for the organic and inorganic compounds from the background study. The table presents the samplesize, frequency of detection, minimum and maximum detected concentrations, arithmetic mean, the statistic used, and the upper confidence limit(UCL) for each compound and matrix sampled. The values in this table were calculated using only the data sets from the common areas for eachanalyte.

Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Asbestos Bulk Dust 0 -------- -------- -------- -------- --------- --------

Air - PCM 14 10/14 0.0005 f/cc 0.007 f/cc 0.0028 f/cc 95%

Chebyshev

(Mean, STD)

0.0058 f/cc

Air - TEM AHERA 14 2/14 0.0002 s/cc 0.0004 s/cc 0.00024 s/cc 95%

Chebyshev

(Mean, STD)

0.00032 s/cc

Air - TEM PCMe 14 1/14 0.0002 s/cc 0.0004 s/cc 0.00023 s/cc 95%

Chebyshev

(Mean, STD)

0.00029 s/cc

Microvacuum - All 18 6/18 792 s/cm2 61,732 s/cm2 7,145 s/cm2

Microvacuum - Carpet 9 3/9 792 s/cm2 61,732 s/cm2 9,409 s/cm2Microvacuum - Chair 3 1/3 1,979 s/cm2 22,952 s/cm2 8,970 s/cm2Microvacuum - Couch 6 2/6 792 s/cm2 9,497 s/cm2 2,836 s/cm2
Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-3 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - All 42 11/42 592 s/cm2 3,798,910 s/cm2 123,507 s/cm2 97.5%

Chebyshev

(Mean, STD)

710,495 s/cm2

Wipe - Ceiling 8 1/8 592 s/cm2 5,916 s/cm2 1,492 s/cm2 95%

Chebyshev

(Mean, STD)

4,319 s/cm2

Wipe - Counter 7 3/7 592 s/cm2 1,183,205 s/cm2 170,193 s/cm2 99%

Chebyshev

(Mean, STD)

1,850,087

s/cm2

Wipe - Floors 9 4/9 592 s/cm2 3,798,910 s/cm2 423,979 s/cm2 99%

Chebyshev

(Mean, STD)

4,621,507

s/cm2

Wipe - Walls 18 3/18 592 s/cm2 149,055 s/cm2 9,344 s/cm2 97.5%

Chebyshev

(Mean, STD)

60,698 s/cm2

MMVF Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 4/14 0.032 s/L 0.196 s/L 0.0452 s/L 95%

Chebyshev

(Mean, STD)

0.096 s/L

Wipe - All 42 3/42 29 s/cm2 286 s/cm2 39 s/cm2 95%

Chebyshev

(Mean, STD)

69 s/cm2
Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-3 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Ceiling 8 0/8 29 s/cm2 -------- -------- -------- --------

Wipe - Counter 7 0/7 29 s/cm2 -------- -------- -------- --------Wipe - Floors 9 3/9 29 s/cm2 286 s/cm2 76 s/cm2 95%

Chebyshev

(Mean, STD)

209 s/cm2

Wipe - Walls 18 0/18 29 s/cm2 -------- -------- -------- --------

Lead Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 0/14 0.026 :g/m3 0.027 :g/m3 0.026 :g/m3 95%

Chebyshev

(Mean, STD)

0.027 :g/m3

Microvacuum - All 18 1/18 1.16 :g/ft2 3.6 :g/ft2 1.30 :g/ft2 95%

Chebyshev

(Mean, STD)

1.89 :g/ft2

Microvacuum - Carpet 9 0/9 1.16 :g/ft2 -------- -------- -------- --------

Microvacuum - Chair 3 0/3 1.16 :g/ft2 -------- -------- -------- --------Microvacuum - Couch 6 1/6 1.16 :g/ft2 3.6 :g/ft2 1.57 :g/ft2 95%

Chebyshev

(Mean, STD)

3.34 :g/ft2
Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-3 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - All 34 18/34 0.25 :g/ft2 49.2 :g/ft2 3.42 :g/ft2 97.5%

Chebyshev

(Mean, STD)

12.44 :g/ft2

Wipe - Counter 7 3/7 0.25 :g/ft2 7 :g/ft2 1.39 :g/ft2 97.5%

Chebyshev

(Mean, STD)

7.28 :g/ft2

Wipe - Floors 9 9/9 2.3 :g/ft2 49.2 :g/ft2 9.74 :g/ft2 95%

Chebyshev

(Mean, STD)

31.44 :g/ft2

Wipe - Walls 18 6/18 0.25 :g/ft2 4.48 :g/ft2 1.04 :g/ft2 97.5%

Chebyshev

(Mean, STD)

3.05 :g/ft2

Dioxin Wipe - All 34 7/34 0.518 ng/m2 1.66 ng/m2 0.677 ng/m2 95%

Chebyshev

(Mean, STD)

0.817 ng/m2

Wipe - Counter 7 3/7 0.53 ng/m2 0.709 ng/m2 0.648 ng/m2 95%

Chebyshev

(Mean, STD)

0.767 ng/m2

Wipe - Floors 9 2/9 0.57 ng/m2 0.791 ng/m2 0.665 ng/m2 95% H-UCL 0.716 ng/m2Wipe - Walls 18 2/18 0.518 ng/m2 1.66 ng/m2 0.694 ng/m2 95%

Chebyshev

(Mean, STD)

0.951 ng/m2
Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Analyte Matrix Minimum* Maximum 

Table 6-3 * Minimum detected value includes values that may be 1⁄2 of the detection limit

PAH Wipe - All 33 0/33 290 :g/m2 -------- -------- -------- --------

Wipe - Counter 6 0/6 290 :g/m2 -------- -------- -------- --------Wipe - Floors 9 0/9 290 :g/m2 -------- -------- -------- --------Wipe - Walls 18 0/18 290 :g/m2 -------- -------- -------- --------
Table 6-4 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Table 6-4. Summary of the analytical results for the mineral compounds and total dust from the background study. The table presents the samplesize, frequency of detection, minimum and maximum detected concentrations, arithmetic mean, the statistic used, and the upper confidence limit(UCL) for each compound and matrix sampled. The values in this table were calculated using the entire data set for each analyte, which includesresidential and common areas.

Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Alpha-quartz Bulk Dust 9 8/9 1.01 % 6.89 % 2.2 % 95% H-UCL 3.66 %

Air 46 12/46 2 :g/m3 259 :g/m3 9.2 :g/m3 95% Chebyshev (Mean, STD) 33.5 :g/m3

Wipe - All 114 51/114 12.5 :g/ft2 1880 :g/ft2 79.5 :g/ft2 95% Chebyshev (Mean, STD) 156.3 :g/ft2Wipe - Counter 32 13/32 12.5 :g/ft2 370 :g/ft2 67.0 :g/ft2 95% Chebyshev (Mean, STD) 134.7 :g/ft2Wipe - Floors 34 20/34 25 :g/ft2 1880 :g/ft2 125.4 :g/ft2 95% Chebyshev (Mean, STD) 367.9 :g/ft2Wipe - Walls 48 18/48 12.5 :g/ft2 270 :g/ft2 55.3 :g/ft2 95% Chebyshev (Mean, STD) 94.1 :g/ft2

Calcite Bulk Dust 9 1/9 0.425 % 4.95 % 1.56 % 95% H-UCL 3.41 %

Air 46 0/46 8 :g/m3 11 :g/m3 8.8 :g/m3 95% Chebyshev (Mean, STD) 9.3 :g/m3Wipe - All 114 3/114 50 :g/ft2 785 :g/ft2 102.6 :g/ft2 95% Chebyshev (Mean, STD) 132.3 :g/ft2Wipe - Counter 32 0/32 50 :g/ft2 100 :g/ft2 92.2 :g/ft2 95% Chebyshev (Mean, STD) 106.4 :g/ft2Wipe - Floors 33 2/33 50 :g/ft2 350 :g/ft2 104.8 :g/ft2 95% Chebyshev (Mean, STD) 147.2 :g/ft2Wipe - Walls 49 1/49 50 :g/ft2 785 :g/ft2 107.9 :g/ft2 95% Chebyshev (Mean, STD) 170.2 :g/ft2

Cristobalite Bulk Dust 9 0/9 0.04 % 4.95 % 1.45 % 97.5% Chebyshev (Mean, STD) 4.69 %
Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-4 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Air 46 0/46 8 :g/m3 11 :g/m3 8.8 :g/m3 95% Chebyshev (Mean, STD) 9.3 :g/m3Wipe - All 114 1/114 50 :g/ft2 260 :g/ft2 93.9 :g/ft2 95% Chebyshev (Mean, STD) 103.7 :g/ft2Wipe - Counter 32 0/32 50 :g/ft2 100 :g/ft2 92.2 :g/ft2 95% Chebyshev (Mean, STD) 106.4 :g/ft2Wipe - Floors 33 1/33 50 :g/ft2 260 :g/ft2 97.3 :g/ft2 95% Chebyshev (Mean, STD) 123.4 :g/ft2Wipe - Walls 49 0/49 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 103.9 :g/ft2

Gypsum Bulk Dust 9 1/9 0.02 % 2.38 % 0.76 % 97.5 Chebyshev (Mean, STD) 2.33 %

Air 46 0/46 4 :g/m3 5.5 :g/m3 4.25 :g/m3 95% Chebyshev (Mean, STD) 4.54 :g/m3Wipe - All 114 0/114 25 :g/ft2 50 :g/ft2 46.3 :g/ft2 95% Chebyshev (Mean, STD) 49.9 :g/ft2Wipe - Counter 32 0/32 25 :g/ft2 50 :g/ft2 46.7 :g/ft2 95% Chebyshev (Mean, STD) 53.2 :g/ft2Wipe - Floors 33 0/33 25 :g/ft2 50 :g/ft2 46.2 :g/ft2 95% Chebyshev (Mean, STD) 53.1 :g/ft2Wipe - Walls 49 0/49 25 :g/ft2 50 :g/ft2 46.4 :g/ft2 95% Chebyshev (Mean, STD) 51.9 :g/ft2

Portlandite Bulk Dust 9 0/9 0.04 % 4.95 % 1.45 % 97.5% Chebyshev (Mean, STD) 4.69 %

Air 46 0/46 8 :g/m3 11 :g/m3 8.8 :g/m3 95% Chebyshev (Mean, STD) 9.3 :g/m3Wipe - All 114 0/114 50 :g/ft2 100 :g/ft2 92.5 :g/ft2 95% Chebyshev (Mean, STD) 99.8 :g/ft2Wipe - Counter 32 0/32 50 :g/ft2 100 :g/ft2 92.2 :g/ft2 95% Chebyshev (Mean, STD) 106.4 :g/ft2Wipe - Floors 33 0/33 50 :g/ft2 100 :g/ft2 92.4 :g/ft2 95% Chebyshev (Mean, STD) 106.2 :g/ft2
Total Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-4 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Walls 49 0/49 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 103.9 :g/ft2

Tridymite Bulk Dust 9 0/9 0.04 % 4.95 % 1.45 % 97.5% Chebyshev (Mean, STD) 4.69 %

Air 46 0/46 8 :g/m3 11 :g/m3 8.8 :g/m3 95% Chebyshev (Mean, STD) 9.3 :g/m3Wipe - All 114 0/114 50 :g/ft2 100 :g/ft2 92.5 :g/ft2 95% Chebyshev (Mean, STD) 99.8 :g/ft2Wipe - Counter 32 0/32 50 :g/ft2 100 :g/ft2 92.2 :g/ft2 95% Chebyshev (Mean, STD) 106.4 :g/ft2Wipe - Floors 33 0/33 50 :g/ft2 100 :g/ft2 92.4 :g/ft2 95% Chebyshev (Mean, STD) 106.2 :g/ft2Wipe - Walls 49 0/49 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 103.9 :g/ft2

Total Dust Wipe 35 35/35 0.366 mg/ft2 18.1 mg/ft2 10.9 mg/ft2 95% Chebyshev (Mean, STD) 14.4 mg/ft2
Table 6-5 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Table 6-5. Summary of the analytical results for the mineral compounds and total dust from the background study. The table presents the samplesize, frequency of detection, minimum and maximum detected concentrations, arithmetic mean, the statistic used, and the upper confidence limit(UCL) for each compound and matrix sampled. The values in this table were calculated using only the data sets from the residence areas for eachanalyte.

Residential Data Set

n Freq. Of

Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Alpha-quartz Bulk Dust 9 8/9 1.01 % 6.89 % 2.2 % 95% H-UCL 3.66 %

Air 32 8/32 2 :g/m3 259 :g/m3 11.8 :g/m3 97.5% Chebyshev

(Mean, STD)

61.9 :g/m3

Wipe - All 81 31/81 12.5 :g/ft2 370 :g/ft2 50.8 :g/ft2 95% Chebyshev

(Mean, STD)

79.6 :g/ft2

Wipe - Counter 25 10/25 12.5 :g/ft2 370 :g/ft2 67.5 :g/ft2 95% Chebyshev

(Mean, STD)

148.4 :g/ft2

Wipe - Floors 26 13/26 25 :g/ft2 180 :g/ft2 54.0 :g/ft2 95% Chebyshev

(Mean, STD)

91.1 :g/ft2

Wipe - Walls 30 8/30 12.5 :g/ft2 110 :g/ft2 34.2 :g/ft2 95% Chebyshev

(Mean, STD)

51.6 :g/ft2

Calcite Bulk Dust 9 1/9 0.425 % 4.95 % 1.56 % 95% H-UCL 3.41 %

Air 32 0/32 8 :g/m3 11 :g/m3 8.78 :g/m3 95% Chebyshev

(Mean, STD)

9.4 :g/m3

Wipe - All 80 2/80 50 :g/ft2 785 :g/ft2 104.2 :g/ft2 95% Chebyshev

(Mean, STD)

145.2 :g/ft2
Residential Data Set

n Freq. Of

Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-5 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Counter 25 0/25 50 :g/ft2 100 :g/ft2 92 :g/ft2 95% Chebyshev

(Mean, STD)

108.3 :g/ft2

Wipe - Floors 24 1/24 50 :g/ft2 350 :g/ft2 102.1 :g/ft2 95% Chebyshev

(Mean, STD)

152.0 :g/ft2

Wipe - Walls 31 1/31 50 :g/ft2 785 :g/ft2 115.6 :g/ft2 95% Chebyshev

(Mean, STD)

213.8 :g/ft2

Cristobalite Bulk Dust 9 0/9 0.04 % 4.95 % 1.45 % 97.5% Chebyshev

(Mean, STD)

4.69 %

Air 32 0/32 8 :g/m3 11 :g/m3 8.78 :g/m3 95% Chebyshev

(Mean, STD)

9.4 :g/m3

Wipe - All 80 0/80 50 :g/ft2 100 :g/ft2 91.9 :g/ft2 95% Chebyshev

(Mean, STD)

100.9 :g/ft2

Wipe - Counter 25 0/25 50 :g/ft2 100 :g/ft2 92.0 :g/ft2 95% Chebyshev

(Mean, STD)

108.3 :g/ft2

Wipe - Floors 24 0/24 50 :g/ft2 100 :g/ft2 91.7 :g/ft2 95% Chebyshev

(Mean, STD)

108.6 :g/ft2

Wipe - Walls 31 0/31 50 :g/ft2 100 :g/ft2 91.9 :g/ft2 95% Chebyshev

(Mean, STD)

106.6 :g/ft2

Gypsum Bulk Dust 9 1/9 0.02 % 2.38 % 0.76 % 97.5% Chebyshev

(Mean, STD)

2.33 %
Residential Data Set

n Freq. Of

Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-5 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Air 32 0/32 4 :g/m3 5.5 :g/m3 4.23 :g/m3 95% Chebyshev

(Mean, STD)

4.59 :g/m3

Wipe - All 80 0/80 25 :g/ft2 50 :g/ft2 45.9 :g/ft2 95% Chebyshev

(Mean, STD)

50.5 :g/ft2

Wipe - Counter 25 0/25 25 :g/ft2 50 :g/ft2 46.0 :g/ft2 95% Chebyshev

(Mean, STD)

54.2 :g/ft2

Wipe - Floors 24 0/24 25 :g/ft2 50 :g/ft2 45.8 :g/ft2 95% Chebyshev

(Mean, STD)

54.3 :g/ft2

Wipe - Walls 31 0/31 25 :g/ft2 50 :g/ft2 46.0 :g/ft2 95% Chebyshev

(Mean, STD)

53.3 :g/ft2

Portlandite Bulk Dust 9 0/9 0.04 % 4.95 % 1.45 % 97.5% Chebyshev

(Mean, STD)

4.69 %

Air 32 0/32 8 :g/m3 11 :g/m3 8.78 :g/m3 95% Chebyshev

(Mean, STD)

9.4 :g/m3

Wipe - All 80 0/80 50 :g/ft2 100 :g/ft2 91.9 :g/ft2 95% Chebyshev

(Mean, STD)

100.9 :g/ft2

Wipe - Counter 25 0/25 50 :g/ft2 100 :g/ft2 92.0 :g/ft2 95% Chebyshev

(Mean, STD)

108.3 :g/ft2

Wipe - Floors 24 0/24 50 :g/ft2 100 :g/ft2 91.7 :g/ft2 95% Chebyshev

(Mean, STD)

108.6 :g/ft2
Residential Data Set

n Freq. Of

Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-5 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Walls 31 0/31 50 :g/ft2 100 :g/ft2 91.9 :g/ft2 95% Chebyshev

(Mean, STD)

106.6 :g/ft2

Tridymite Bulk Dust 9 0/9 0.04 % 4.95 % 1.45 % 97.5% Chebyshev

(Mean, STD)

4.69 %

Air 32 0/32 8 :g/m3 11 :g/m3 8.78 :g/m3 95% Chebyshev

(Mean, STD)

9.4 :g/m3

Wipe - All 80 0/80 50 :g/ft2 100 :g/ft2 91.9 :g/ft2 95% Chebyshev

(Mean, STD)

100.9 :g/ft2

Wipe - Counter 25 0/25 50 :g/ft2 100 :g/ft2 92.0 :g/ft2 95% Chebyshev

(Mean, STD)

108.3 :g/ft2

Wipe - Floors 24 0/24 50 :g/ft2 100 :g/ft2 91.7 :g/ft2 95% Chebyshev

(Mean, STD)

108.6 :g/ft2

Wipe - Walls 31 0/31 50 :g/ft2 100 :g/ft2 91.9 :g/ft2 95% Chebyshev

(Mean, STD)

106.6 :g/ft2

Total Dust Wipe 26 26/26 0.366 mg/ft2 18.1 mg/ft2 10.7 mg/ft2 95% Chebyshev

(Mean, STD)

15.0 mg/ft2
Table 6-6 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Table 6-6. Summary of the analytical results for the mineral compounds and total dust from the background study. The table presents the samplesize, frequency of detection, minimum and maximum detected concentrations, arithmetic mean, the statistic used, and the upper confidence limit(UCL) for each compound and matrix sampled. The values in this table were calculated using only the data sets from the common areas for eachanalyte.

Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Alpha-quartz Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 4/14 2 :g/m3 9 :g/m3 3.14 :g/m3 95% Chebyshev (Mean, STD) 5.64 :g/m3

Wipe - All 33 20/33 12.5 :g/ft2 1880 :g/ft2 149.9 :g/ft2 97.5% Chebyshev (Mean, STD) 508.5 :g/ft2Wipe - Counter 7 3/7 12.5 :g/ft2 220 :g/ft2 65.4 :g/ft2 95% H-UCL 288.5 :g/ft2Wipe - Floors 8 7/8 25 :g/ft2 1880 :g/ft2 357.5 :g/ft2 97.5% Chebyshev (Mean, STD) 1769.4 :g/ft2Wipe - Walls 18 10/18 25 :g/ft2 270 :g/ft2 90.6 :g/ft2 95% Chebyshev (Mean, STD) 180.1 :g/ft2

Calcite Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 0/14 8 :g/m3 10 :g/m3 8.86 :g/m3 95% Chebyshev (Mean, STD) 9.75 :g/m3Wipe - All 34 1/34 50 :g/ft2 260 :g/ft2 98.8 :g/ft2 95% Chebyshev (Mean, STD) 123.4 :g/ft2Wipe - Counter 7 0/7 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 124.0 :g/ft2Wipe - Floors 9 1/9 50 :g/ft2 260 :g/ft2 112.2 :g/ft2 95% Chebyshev (Mean, STD) 196.2 :g/ft2Wipe - Walls 18 0/18 50 :g/ft2 100 :g/ft2 94.4 :g/ft2 95% Chebyshev (Mean, STD) 111.1 :g/ft2

Cristobalite Bulk Dust 0 -------- -------- -------- -------- -------- --------
Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-6 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Air 14 0/14 8 :g/m3 10 :g/m3 8.86 :g/m3 95% Chebyshev (Mean, STD) 9.75 :g/m3Wipe - All 34 1/34 50 :g/ft2 260 :g/ft2 98.8 :g/ft2 95% Chebyshev (Mean, STD) 123.4 :g/ft2Wipe - Counter 7 0/7 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 124.0 :g/ft2Wipe - Floors 9 1/9 50 :g/ft2 260 :g/ft2 112.2 :g/ft2 95% Chebyshev (Mean, STD) 196.2 :g/ft2Wipe - Walls 18 0/18 50 :g/ft2 100 :g/ft2 94.4 :g/ft2 95% Chebyshev (Mean, STD) 111.1 :g/ft2

Gypsum Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 0/14 4 :g/m3 5 :g/m3 4.29 :g/m3 95% Chebyshev (Mean, STD) 4.83 :g/m3Wipe - All 34 0/34 25 :g/ft2 50 :g/ft2 47.1 :g/ft2 95% Chebyshev (Mean, STD) 53.2 :g/ft2Wipe - Counter 7 0/7 25 :g/ft2 50 :g/ft2 46.4 :g/ft2 95% Chebyshev (Mean, STD) 62.0 :g/ft2Wipe - Floors 9 0/9 25 :g/ft2 50 :g/ft2 47.2 :g/ft2 95% Chebyshev (Mean, STD) 59.3 :g/ft2Wipe - Walls 18 0/18 25 :g/ft2 50 :g/ft2 47.2 :g/ft2 95% Chebyshev (Mean, STD) 55.5 :g/ft2

Portlandite Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 0/14 8 :g/m3 10 :g/m3 8.86 :g/m3 95% Chebyshev (Mean, STD) 9.75 :g/m3Wipe - All 34 0/34 50 :g/ft2 100 :g/ft2 94.1 :g/ft2 95% Chebyshev (Mean, STD) 106.3 :g/ft2Wipe - Counter 7 0/7 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 124.0 :g/ft2Wipe - Floors 9 0/9 50 :g/ft2 100 :g/ft2 94.4 :g/ft2 95% Chebyshev (Mean, STD) 118.7 :g/ft2
Common Area Data Set

n Freq. Of Detection

Range

Arithmetic

Mean Statistic UCL Anaylte Matrix Minimum* Maximum 

Table 6-6 * Minimum detected value includes values that may be 1⁄2 of the detection limit

Wipe - Walls 18 0/18 50 :g/ft2 100 :g/ft2 94.4 :g/ft2 95% Chebyshev (Mean, STD) 111.1 :g/ft2

Tridymite Bulk Dust 0 -------- -------- -------- -------- -------- --------

Air 14 0/14 8 :g/m3 10 :g/m3 8.86 :g/m3 95% Chebyshev (Mean, STD) 9.75 :g/m3Wipe - All 34 0/34 50 :g/ft2 100 :g/ft2 94.1 :g/ft2 95% Chebyshev (Mean, STD) 106.3 :g/ft2Wipe - Counter 7 0/7 50 :g/ft2 100 :g/ft2 92.9 :g/ft2 95% Chebyshev (Mean, STD) 124.0 :g/ft2Wipe - Floors 9 0/9 50 :g/ft2 100 :g/ft2 94.4 :g/ft2 95% Chebyshev (Mean, STD) 118.7 :g/ft2Wipe - Walls 18 0/18 50 :g/ft2 100 :g/ft2 94.4 :g/ft2 95% Chebyshev (Mean, STD) 111.1 :g/ft2

Total Dust Wipe 9 9/9 5.3 mg/ft2 17.5 mg/ft2 10.7 mg/ft2 95% Chebyshev (Mean, STD) 17.2 mg/ft2
Table 7-1. Summary of U.S. Residential Building Average Indoor Airborne Asbestos

Concentrations for Asbestos Fibers ≥ 5 μm Long by Direct Transmission Electron Microscopy

Site Description Number

of

Samples

Asbestos Fibers ≥ 5 μm Long

(f/cc)

Reference

Range Mean

15 San Francisco

residences (houses) with

ACM

30 ND ND CPSC 1987

15 Cleveland residences

(houses) with ACM

30 ND - 0.002 0.00023 CPSC 1987

15 Philadelphia

residences (houses) with

ACM

29 ND - 0.001 0.00007 CPSC 1987

10 residential building 10 - 0.00000 Lee et al. 1992

1 San Francisco area

residential building

sampled following the

1989 Loma Prieta

earthquake

2 - 0.00213 Van Orden et al.

1995

Source: Adapted from HEI (1991), ATSDR (2001), Van Orden et al. (1995)

.

ACM = asbestos-containing material; ND = non-detect
Table 7-2. Summary of Settled Asbestos Surface Dust Loadings Determined Through

Microvacuum Sampling and Indirect Analysis by Transmission Electron Microscopy

Building

Category

Number of

Buildings

Number of

Samples 

Surface Loading of Asbestos Structures

(s/cm2

)

Range Geometric Mean

Outside buildings

in a large city

5 79 <400 to 140,000 5100

Inside buildings

with no surfacing

ACM

6 28 <240 to 210,000 1000

Areas of

buildings with

acoustical plaster

12 34 <3500 to 74 million 160,000

Source: Ewing (2000).

ACM = asbestos-containing material
Table 7-3. Household Dust Lead Measurements from Wipe Sampling in an Old, Urban

Community

Sample

Collection

Site

Number of

Samples (see

note below)

Median Range EPA

Standard

Percentage

above

standard

(μg/ft2

) (μg/ft2) (μg/ft2)

Non-carpeted

floors

124 12 3 - 369 40 23

Carpeted

floors

65 5 3 - 78 40 5

Source: Gallicchio et al. (2002)

Note: Each reported sample was a composite of wipe samples taken from three different rooms.
Table 7-4. Estimated Distribution of Lead Loadings (ug/ft2) In U.S. Housing

Uncarpeted Floors, By Census Region and Building Age Category (source: HUD 2001)

Region Age of Housing n mean std skew cv var stderr max P99 P95 P90 Q3 median Q1 P5 min detection rate % nondetects

Northeast 1978 - 1998 92 1.6 19.4 3.5 11.8 3.76e+02 0.2 11.0 11.0 5.5 3.0 1.6 1.0 0.8 0.8 0.8 21 / 92 77%Northeast 1960 - 1977 79 5.1 193.1 7.5 38.2 3.73e+04 2.0 129.6 129.6 8.0 6.0 3.0 1.0 0.8 0.8 0.8 30 / 79 62%Northeast 1946 - 1959 68 3.1 40.8 2.4 13.1 1.66e+03 0.5 17.0 17.0 15.0 9.0 3.0 1.2 0.8 0.8 0.8 30 / 68 56%Northeast 1940 - 1945 38 5.3 80.9 4.5 15.2 6.55e+03 1.3 75.0 75.0 13.0 10.0 7.0 4.1 1.0 0.8 0.8 23 / 38 39%Northeast <= 1939 155 24.0 1765.8 12.2 73.7 3.12e+06 12.9 1845.0 128.0 56.7 31.0 9.0 4.0 1.4 0.8 0.8 111 / 155 28%Midwest 1978 - 1998 87 1.5 18.8 4.6 12.5 3.52e+02 0.2 18.0 9.6 4.0 3.0 1.6 0.8 0.8 0.8 0.8 16 / 87 82%Midwest 1960 - 1977 133 2.8 74.0 5.5 26.2 5.47e+03 0.6 72.0 22.0 12.1 5.0 2.0 1.0 0.8 0.8 0.8 45 / 133 66%Midwest 1946 - 1959 85 8.4 210.9 4.3 25.1 4.45e+04 2.0 105.0 91.0 52.0 18.0 5.0 2.0 1.0 0.8 0.8 47 / 85 45%Midwest 1940 - 1945 25 15.1 269.8 2.6 17.8 7.28e+04 4.3 92.0 92.0 71.0 33.2 20.8 10.2 1.0 0.8 0.8 15 / 25 40%Midwest <= 1939 124 56.4 4087.2 10.9 72.5 1.67e+07 37.8 4830.0 386.0 107.0 47.0 15.0 5.0 0.8 0.8 0.8 92 / 124 26%South 1978 - 1998 196 2.0 200.0 9.9 99.4 4.00e+04 1.2 556.0 9.0 5.0 3.0 1.6 0.8 0.8 0.8 0.8 ?? 71%South 1960 - 1977 223 1.7 25.8 5.4 15.3 6.65e+02 0.2 28.0 12.0 6.0 3.0 1.6 1.0 0.8 0.8 0.8 ?? ??South 1946 - 1959 125 7.0 378.8 10.8 54.5 1.44e+05 3.2 315.0 315.0 14.0 6.0 3.0 1.2 0.8 0.8 0.8 ?? ??South 1940 - 1945 43 4.8 88.1 3.8 18.3 7.77e+03 1.2 56.0 56.0 17.0 9.0 5.0 2.5 1.2 0.8 0.8 ?? ??South <= 1939 80 17.2 479.3 3.9 27.8 2.30e+05 5.1 404.3 233.0 60.0 32.1 12.0 4.0 1.8 0.8 0.8 ?? ??West 1978 - 1998 115 2.7 233.6 10.7 85.5 5.46e+04 2.0 276.0 10.0 3.0 1.6 1.0 0.8 0.8 0.8 0.8 ?? ??West 1960 - 1977 195 1.6 11.5 2.7 7.2 1.32e+02 0.1 11.0 6.0 4.0 3.0 2.0 1.0 0.8 0.8 0.8 ?? ??West 1946 - 1959 77 3.9 62.3 4.0 16.0 3.88e+03 0.8 47.0 39.0 15.0 9.0 3.0 1.5 0.9 0.8 0.8 ?? ??West 1940 - 1945 21 4.0 34.1 0.9 8.5 1.16e+03 0.7 9.0 9.0 9.0 9.0 7.0 4.0 1.5 0.8 0.8 ?? ??West <= 1939 39 5.0 83.9 3.1 16.7 7.05e+03 1.2 41.0 41.0 27.0 11.0 4.0 2.1 1.1 0.8 0.8 ?? ??
Table 7-5. Background Soil Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs)

Source: ATSDR (1995)
ND=0 ND=1/2 ND=DL

UCL UCL UCL

Lead Bulk Dust 100% 186 186 186 0% 0%

Total Dust Hard Surface 100% 14.4 14.4 14.4 0% 0%

Lead Hard Surface 49% 1.69 1.78 1.88 -5% 5%

Asbestos PCM - Air 42% 0.0022 0.0023 0.0025 -6% 7%

Alpha-quartz Hard Surface 38% 68.3 79.6 91.8 -14% 15%

Asbestos Hard Surface 13% 5,462 6,192 6,965 -12% 12%

MMVF Hard Surface 10% 29 52 76 -44% 46%

MMVF Air 8% 0.034 0.060 0.088 -44% 45%

Lead Porous Surface 8% 1.00 1.98 2.95 -49% 49%

Asbestos PCMe 5% 0.00007 0.00024 0.00044 -72% 80%

Asbestos TEM AHERA - Air 4% 0.00007 0.00024 0.00043 -72% 80%

Calcite Hard Surface 3% 60.8 132.3 232.3 -54% 76%

Lead Air 2% 0.0068 0.0304 0.0549 -78% 81%

Cristobalite Hard Surface 1% 12.2 103.7 200.5 -88% 93%

Calcite Air 0% 0 9.3 18.6 -100% 100%

Cristobalite Air 0% 0 9.3 18.6 -100% 100%

Gypsum Air 0% 0 9.3 18.6 -100% 100%

Gypsum Hard Surface 0% 0 49.9 99.8 -100% 100%

Portlandite Air 0% 0 9.3 18.6 -100% 100%

Portlandite Bulk Dust 0% 0 4.69 9.37 -100% 100%

Portlandite Hard Surface 0% 0 99.8 199.7 -100% 100%

Tridymite Air 0% 0 9.3 18.6 -100% 100%

Tridymite Bulk Dust 0% 0 4.69 9.37 -100% 100%

Tridymite Hard Surface 0% 0 99.8 199.7 -100% 100%

ND=0 ND=1/2 ND=DL

UCL UCL UCL

Alpha-quartz Bulk Dust† 89% 3.88 3.66 4.97 6% 36%

Dioxin Hard Surface‡ 77% 0.087 0.693 1.330 -87% 92%

Alpha-quartz Air* 25% 45.5 61.9 48.0 -26% -22%

Calcite Bulk Dust† 11% 0.61 3.41 7.05 -82% 107%

Gypsum Bulk Dust† 11% 1.42 2.33 4.71 -39% 102%

Cristobalite Bulk Dust† 0% 0 4.69 10.70 -100% 128%

These data sets were not included in the above table because the frequency of detection or the variability in the three values that were 

calculated were altered by additional factors, thus they are reported separately:

Percent Difference 

ND=DL/ND=1/2

† These values are also influenced by a change in distribution from either non-parametric to lognormal or lognormal to non-parametric due to 

altering the values between ND=0, ND=1/2, and ND=DL. This required different statistical methods to be used which resulted in the 

comparison of the three values not being similar to comparing values that were calculated using the same statistic.

Table 8-3. An evaluation was conducted to determine how the estimated UCLs were effected by assigning 1/2 of 

the detection limit for samples that were below the detection limit (DL). In general, the variation between the 

different methods (i.e., ND=0, ND=1.2, and ND=DL) are directly related to the frequency of detection. As 

illustrated below, the lower the frequency of detection, the greater the variability, with values ranging from 100% 

less to 100% greater for data sets that contained all values below the detection limit. The use of 1/2 of the detection 

limit results in a mid-point estimate.

* These values are also influenced by a change in variability within the data set due to altering the values between ND=0, ND=1/2, and 

ND=DL. This changed the standard deviation of the data set which required a different confidence interval to be used to estimate the UCL. 

The comparison of values that use different confidence intervals resulted in the comparison not being similar to the other data sets.

Analyte Surface Freq. Of 

Detection (%)

Percent Difference 

ND=0/ND=1/2

Percent Difference 

ND=DL/ND=1/2

‡These values are also influenced by the way that the frequency of detection is calculated, as there are 17 different dioxin congeners. This 

results in the comparison with the other data being dissimilar as they are based on the frequency of detection of a single compound. For 

example, one sample may have detected one congener, while a second sample detected 15 congeners. Each sample would be considered to b

above the detection limit, however the values used to estimate the UCL would be altered for 16 congeners in one sample but only for 2 

congeners in the second sample, thus creating greater varibility from the other data sets. 

Analyte Surface Freq. Of 

Detection (%)

Percent Difference 

ND=0/ND=1/2
ATTACHMENT A

World Trade Center Indoor Air Assessment:

Selecting Contaminants of Potential Concern

and

Setting Health-Based Benchmarks
World Trade Center Indoor Air Assessment:

Selecting Contaminants of Potential Concern

and

Setting Health-Based Benchmarks

Prepared by the Contaminants of Potential Concern (COPC) Committee

of the World Trade Center Indoor Air Taskforce Working Group

Contributors:

U.S. Environmental Protection Agency New York City Department of Health

Mark Maddaloni Nancy Jeffery

Peter Grevatt Ken Carlino

Terry Smith Jeanine Prudhomme

Dore LaPosta Chris D’Andrea

Charles Nace Vince Colucci

John Schaum Caroline Bragdon

Dana Tulis James Miller

Agency for Toxic Substances and Disease Registry

Sven Rodenbeck

Danielle Devoney

New York State Department of Health

 Robert Chinery

Occupational Safety and Health Administration

David Ippolito

Dan Crane
Peer Review Draft (September, 2002)

Table of Contents

Introduction ..................................................................4

Selecting the Contaminants of Potential Concern (COPCs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Lead and Combustion By-Products (PAHs, Dioxin) .............................5

Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

PAHs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Dioxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Building Materials (Asbestos, Fibrous Glass, Crystalline Silica) ...................6

Asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Fibrous Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Crystalline Silica ..................................................7

Other Substances that Were not Selected to be COPCs . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Setting Benchmarks for the Contaminants of Potential Concern (COPCs) . . . . . . . . . . . . . . . . . 10

Developing Risk-Based Criteria for Indoor Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Developing Risk-Based Criteria for Settled Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Developing Benchmark Levels Based on Occupational Health Standards . . . . . . . . . . . 15

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

APPENDIX A

Hazardous Substances Not Included in Indoor Environment Sampling Program .......1

APPENDIX B

World Trade Center Health Effects Screening Criteria for Ambient Air . . . . . . . . . . . . . 1

APPENDIX C

 Basis for Tier III screening level of 1 E-04 ...................................1

APPENDIX D

Assessing Exposures to Indoor Air and to Residues on Indoor Surfaces .............1

APPENDIX E

IEUBK Model Results for Lead in Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Tables

Table 1. Index of NIOSH and OSHA exposure limits and estimated maximum values in Lower

Manhattan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 2. Exposure parameters for calculating clearance criteria for air samples. . . . . . . . . . . . . 12

Table 3. Exposure parameters used to calculate clearance criteria for wipe samples. . . . . . . . . 14

Table 4. Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 5. Polycyclic Aromatic Hydrocarbons (PAHs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 6. Dioxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Table 7. Asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Table 8. Fibrous Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Table 9. Crystalline silica - respirable fraction of alpha-quartz . . . . . . . . . . . . . . . . . . . . . . . . . 25
1

 Agencies include the U.S. Environmental Protection Agency (EPA), Agency for Toxics and Disease Registry

(ATSDR), New York State Department of Health (NYSDOH), New York City Department of Health (NYCDOH),

Occupational Safety and Health Administration (OSHA), New York State Department of Environmental

Conservation (NYSDEC) and New York City Department of Environmental Protection (NYCDEP).

2

EPA is conducting a pilot program in an uncleaned/unoccupied building at 110 Liberty Street to determine the

effectiveness of various cleaning methods for removing asbestos and other contaminants of potential concern from

residential dwellings.

3

Most if not all of the pollutants associated with the collapse of the World Trade Center were present in New York

City's environment prior to September 11. To establish a baseline for the presence of these contaminants in affected

residences, EPA will collect and analyze samples to look for some of these pollutants in apartments in parts of

Manhattan that were not impacted. The Agency will use the data to determine pre-existing or "background" levels of

these pollutants in interior spaces in New York City.

World Trade Center Indoor Air Assessment: 

Selecting Contaminants of Potential Concern

And Setting Health-Based Benchmarks

Introduction

Since September 11, 2001, the outdoor environment around the World Trade Center (WTC) site

and nearby areas has been extensively monitored by a group of federal, state, and local

agencies1. The agencies have taken samples of the air, dust, water, river sediments and drinking

water and analyzed them for the presence of pollutants that might pose a health risk to response

workers at the WTC site, office workers, and local residents. While some people may have

experienced acute irritant and respiratory effects from the collapse of the towers and associated

fires, extended monitoring of the ambient air at and beyond the perimeter of the WTC site over

the past year indicates that contaminant concentrations pose a low risk of long-term health

effects. During this same time period, limited investigation of the indoor environment in

residential dwellings has occurred [NYCDOH, 2002; Chatfield & Kominsky, 2001]. As the

cleanup of the WTC site is coming to an end, governmental health and environmental agencies

are directing resources to evaluate the indoor environment for the presence of pollutants that

might pose long-term health risks to local residents. Selecting Contaminants of Potential

Concern (COPCs) and setting health-based benchmarks will assist the Pilot Cleaning

Effectiveness Initiative2

 and inform the selection of contaminants in the Background Study3.

Selecting the Contaminants of Potential Concern (COPCs)

The assessment of the indoor environment began with a review of historical information on

hazardous substances that have been associated with building fires and collapses [Wallace,

1990]. Many compounds, including combustion by-products such as dioxins and polycyclic

aromatic hydrocarbons (PAHs) were identified for further investigation, along with building

materials such as asbestos and fibrous glass. In addition, ambient air, indoor air, and

indoor/outdoor bulk dust monitoring data were reviewed. Data sources included EPA’s ambient

air and bulk dust/debris monitoring program (www.epa.gov/wtc), OSHA’s air/dust monitoring
6

data and the NYCDOH/ATSDR indoor air pilot program [NYCDOH, 2002]. A concerted effort

also was made to identify and review additional sources of WTC-related data from other

governmental agencies (e.g., U.S. Geological Survey, NYC Board of Education), academic

institutions, environmental organizations, and the private sector.

A semi-quantitative screening process was performed on the collected sampling data. Based on

frequency-of-detection, concentration and inherent toxicity, contaminants that exceeded healthbased screening levels for the ambient air (see Appendix B) were identified. Dioxin and PAHs

were added to the COPC list by this process. In addition, building constituents with

carcinogenic (asbestos) or irritant effects (fibrous glass, crystalline silica) that were consistently

and significantly found in bulk debris and indoor dust samples were identified as COPCs

[NYCDOH, 2002] . Finally, lead (Pb) was included based on a comparison of sampling data with

existing regulatory standards. Collectively, the resulting group of contaminants are called

“contaminants of potential concern” or COPCs in this report.

The list of COPCs is shown in the column at the left, below. Included for each COPC is a data

summary that supports its inclusion on the list. For completeness, an additional list is included

on the right containing substances that, for various reasons, have created concern, but on closer

inspection, were either rarely detected in the ambient air and/or settled dust sampling around the

WTC, or routinely found at concentrations below the health-based screening criteria presented in

Appendix B.

 COPCs Other Substances 

Lead Benzene

PAHs PCBs

Dioxin Chromium

Asbestos Cadmium

Fibrous Glass Manganese

Crystalline Silica Mercury

Particulate Matter

Refractory Ceramic Fibers

Mold

Lead and Combustion By-Products (PAHs, Dioxin)

Lead. EPA’s ambient air monitoring data detected lead in concentrations that exceeded 1.5

ug/m3 on five occasions from September 18-27, 2001. It should be noted that the National

Ambient Air Quality Standard (NAAQS) for lead is 1.5 ug/m3

, but is based on a three-month

average. Since the ambient monitoring program began, no three-month average of the ambient

air data for lead exceeded the NAAQS of 1.5 ug/m3

. However, lead was more commonly found

at concentrations that exceeded 0.1 ug/m3, the default value employed in EPA’s Integrated

Exposure Uptake Biokinetic Model for Lead in Children [EPA, 1994]. This value represents the

upper-bound of average of ambient airborne lead concentrations in urban environments. 

Additional support for including lead as a COPC was provided by a report that characterized the
7

dust that settled over lower Manhattan after the WTC collapse [Lioy, 2002]. The lead

concentration in settled dust ranged from 101 - 625 parts per million (ppm). By itself, this range

does not represent extraordinarily high concentrations, but in combination with the mass of

material released from the collapse of the towers, it represents a potentially significant increase

in the mass of lead deposited in lower Manhattan. Therefore, lead is included as a COPC.

PAHs. Limited ambient air sampling was conducted for PAHs during the period of time

(September through December, 2001) when combustion processes were occurring at the site. 

However, concentrations in bulk dust [EPA, 2002a and Lioy, 2002] exceeded the removal

guidelines for soil in EPA’s Hazard Evaluation Handbook [EPA, 1997] of 9 ppm based on

benzo(a)pyrene equivalents. This value is risk-based, equating to an excess lifetime cancer risk

of 1x10-4 over a 30-year exposure duration for residential settings. Therefore, PAHs are included

as a COPC.

Dioxin. Ambient air samples exceeded EPA’s screening criteria (see Appendix B) at various

sampling stations during September and October, 2001. Data trend analysis for dioxin in ambient

air [EPA, 2002a] showed that concentrations significantly exceeded the risk-based screening

level of 0.001 - 0.005 ng/m3 . This range was based on an excess lifetime cancer risk of 1x10-4

over a 30 year exposure duration for residential settings, using both the existing cancer Slope

Factor [Integrated Risk Information System (IRIS), 2002] and proposed cancer Slope Factor in

EPA’s draft dioxin reassessment [EPA, 2001]. Therefore, dioxin (and related congeners) is

included as a COPC.

Building Materials (Asbestos, Fibrous Glass, Crystalline Silica)

The evaluation of building materials for inclusion as COPCs required a different approach than

that used for the combustion by-products. Those compounds (PAHs, dioxin) benefit from

consensus toxicity criteria (i.e., IRIS-established cancer Slope Factors) that allow for a

quantitative screening paradigm. With the exception of asbestos, the building materials

evaluated (including fibrous glass, crystalline silica, mica, portlandite, calcite and gypsum) do

not have IRIS inhalation toxicity criteria from which to perform quantitative risk assessments. 

Complicating this matter is the knowledge that many of these substances were deposited in a

large cloud from the collapse of the towers. Thus, the settled dust may serve as a reservoir for

re-suspension and eventual inhalation exposure. In addition, materials such as fibrous glass can

also cause contact irritation when exposed directly to the skin.

The potential for exposure to building materials in the indoor environment was assessed by

reviewing sampling data on the constituent composition of the indoor/outdoor bulk dust and

indoor/ambient air [EPA, 2002c; USGS, 2001; NYCDOH, 2002; Chatfield & Kominsky, 2001].

Toxicity criteria for building materials (with the exception of asbestos) were obtained from

occupational sources, such as the Occupational Safety and Health Administration’s permissible

exposure limits (OSHA PELs), and the American Conference of Governmental Industrial

Hygienists threshold limit values (ACGIH TLVs). The evaluation of exposure potential coupled
8

with toxicity information identified three COPCs (asbestos, fibrous glass and crystalline silica).

Asbestos. In the days immediately following the disaster, EPA analyzed the settled bulk

dust/debris for asbestos content. More than one third of the approximately 150 samples

registered an asbestos concentration greater than 1% [EPA 2002c]. Since that time, EPA has

taken the position that WTC-related dust should be considered potentially asbestos-contaminated

and handled accordingly. Additionally, indoor settled dust samples collected from residential

buildings in November and December 2001 indicated that 18% of the indoor locations sampled

contained measurable levels of asbestos [NYCDOH, 2002]. Therefore, asbestos is included as a

COPC.

Fibrous Glass. Analysis of WTC bulk dust/debris has consistently identified fibrous glass to be

a major constituent of the material [Lioy 2002, USGS 2001]. In addition, an NYCDOH/ATSDR

study [NYCDOH, 2002] found fibrous glass in the interior settled dust in 41% of the locations

sampled at concentrations up to 35%. Air samples collected in areas with fibrous glass in settled

dust indicate no fiber levels of immediate concern. Although fiber counts were found in four

areas with slightly greater than background (0.004-0.006 f/cc), subsequent re-analysis indicated

actual fibrous glass concentrations from these areas as 0.00004 to 0.00026 f/cc. Air samples

from remaining areas showed a maximum 0.003 f/cc total fiber count by PCM. These wools

may be skin, eye, and respiratory tract irritants. Although there are no standards to evaluate the

settled dust content, the presence of fibrous glass in settled dust does indicate a potential for

exposure. Therefore, fibrous glass is included as a COPC.

Crystalline Silica. Settled dust and air samples taken in indoor and outdoor areas of residential

buildings in November and December of 2001 indicate the presence of alpha-quartz. Other

forms of crystalline silica were not found. This is consistent with outdoor dust and debris

samples collected by the USGS [USGS, 2001] and subjected to mineral analysis. Quartz was

found in approximately 49% of the settled dust samples from indoor areas of residential

buildings and all of the associated outdoor areas sampled. Levels of quartz ranged as high as an

estimated 31.4% of the dust by weight in a residence. Since quartz is a common material in

sand, finding this mineral in a city where there is a great deal of concrete is not unusual. 

However, quartz in dust from a comparison area unaffected by the WTC collapse ranged from

non-detect only up to an estimated 2.2% in the residence [NYCDOH, 2002]. Seventeen

residential areas and eleven common areas had quartz levels greater than the associated

comparison area. Therefore, quartz was deemed to be elevated in some indoor areas of lower

Manhattan relative to the comparison area. Additionally, quartz was found in 13% of the

respirable fraction air samples taken in these areas, ranging from an estimated 4-19 ug/m3,

demonstrating a potential for exposure. Although below occupational standards, this estimated

concentration is above the effective NAAQS standard for the silica fraction of respirable

particulate matter. Therefore crystalline silica, measured as alpha-quartz, is included as a COPC.

In addition to crystalline silica, calcite, portlandite and gypsum were the most abundant minerals

detected in settled dust samples from residential areas in lower Manhattan following the WTC

collapse. Mica was detected with much less frequency, generally at less than 0.1% of the dust. 
9

Halite (salt) was also detected at trace levels. Calcite, portlandite, and gypsum are typical

components of concrete and gypsum based wallboard products, which were present in the WTC

buildings. While high concentrations of these minerals in airborne dust constitute a short-term

health concern in the form of eye, nose and throat irritation, persisting adverse heath effects

would not be anticipated, unless these minerals remained suspended in high concentrations. 

Indoor and street-level outdoor air sampling done in November and December of 2001 show that

the levels of these chemicals, over a time-weighted sample, were below levels associated with

irritant effects (See Table 1). Although there are methodological difficulties in quantifying these

materials by X-ray Diffraction (XRD) techniques, a semi-quantitative screening of the results

showed that the air levels were orders of magnitude below occupational standards for irritant

effects. However, since the presence of minerals in settled dust indicates there is potential for

the materials to be resuspended, these minerals should be evaluated qualitatively. Therefore,

although no screening levels are developed for these minerals as COPCs, the Pilot Cleaning

Effectiveness Initiative mentioned in the Introduction will report qualitatively on the presence of

gypsum, calcite and portlandite, while the quantitative analyses for crystalline silica (a COPC

discussed above) are being performed by XRD (following NIOSH Method 7500).

Table 1. Index of NIOSH and OSHA exposure limits and estimated maximum values in Lower

Manhattan.

Mineral NIOSH REL

(ug/m3

) OSHA PEL (ug/m3

)

*Maximum Estimated

Value (J) in Lower

Manhattan (ug/m3)

Gypsum 10,000 ug/m3

 (total)

5,000 (ug/m3 resp)

15,000 ug/m3 (total)

5,000 (resp)

14J (PM100)

15J (PM4)

Portlandite 5,000 ug/m3 15,000 ug/m3

 (total)

5,000 ug/m3

 (resp)

95J (PM100)

84J (PM4)

Calcite 10,000 ug/m3

 (total)

5,000 ug/m3

 (resp)

15,000 ug/m3

 (total)

5,000 ug/m3

 (resp)

14J (PM100)

10J (PM 4)

NIOSH = National Institute of Occupational Safety and Health, Centers for Disease 

 Control and Prevention

REL = recommended exposure level/limit

OSHA = Occupational Safety and Health Administration

PEL = permissible exposure limit.

resp = respirable

* [NYCDOH, 2002]

Other Substances that Were not Selected to be COPCs

The following summary is provided for substances that were investigated, but not included on

the COPC list. A full discussion of the reasons is provided in Appendix A.
10

Chemical Reason

Benzene Benzene is very volatile and dissipates into ambient air quickly. Grab samples

that recorded high (above the OSHA PEL of 1 ppm) concentrations on the

debris pile consistently dropped to below detection limits (20 ppb) at the site

perimeter.

PCBs In over 500 ambient air samples taken around the WTC work zone, none

exceeded EPA’s screening level of concern for ambient air (see Appendix B).

Chromium All measurements (over 300 samples) of chromium in ambient air around the

WTC work zone have been below EPA’s screening level of concern for the

ambient air (see Appendix B). Measurements in settled dust have been below

EPA Removal Action Guidelines [EPA, 1997].

Cadmium Cadmium was found in only two out of 300 air samples at levels greater than

EPA’s screening level for ambient air (Appendix B). Measurements in settled

dust have been below EPA Removal Action Guidelines [EPA, 1997].

Manganese Manganese was found in only four of over 300 air samples at levels that were

greater than EPA’s screening level for ambient air (Appendix B). 

Measurements in settled dust have been below EPA Removal Action Guidelines

[EPA, 1997].

Mercury Concern regarding mercury has been raised by a report of slightly elevated

blood mercury levels in four Port Authority Police Officers at the WTC site (69

were screened). A NYC Department of Design and Construction report

[Rottner, 2002] concluded that air and bulk data have not shown elevated Hg

levels. The report also noted that routine urine screening of NYC firefighters

assigned to the site did not indicate any sign of Hg exposure. A U.S. Geological

Survey leachability study [USGS 2001] of indoor and outdoor WTC settled dust

samples showed that it is unlikely that harmful levels of mercury could ever be

released to the air. In addition, indoor air sampling using a Lumex Analyzer at

numerous residential dwellings close to Ground Zero determined mercury vapor

concentrations to be well below EPA’s Reference Concentration (RfC) of 

.3 ug/m3 [Johnson, 2002].

Particulate

Matter

(PM)

Ambient monitoring in the WTC area has shown that, since late October, levels

of PM 10 and PM 2.5 (two commonly measured inhalable PM sizes) have been

below EPA’s level of concern for the ambient air (see Appendix B), indicating

that there is no continuing source of PM entering homes and offices. EPA’s

Environmental Data Trend Report World Trade Center, 9/11/01 - 4/24/02 [EPA,

2002a] concluded that PM 2.5 and PM 10 appear to have returned to levels of a

steady background state. 
Chemical Reason

11

Refractory

Ceramic

Fibers

(RCF)

Ceramic fiber-containing materials are not expected to be present in the WTC

buildings, as they are mainly used in industrial high temperature applications. 

Limited sampling conducted by NYCDOH, 2002 did not indicate any ceramic

fibers in four indoor air samples analyzed by scanning electron microscopy

(SEM).

Mold Mold was not directly associated with the WTC collapse. However, it may have

resulted from the combination of water damage and inoperable HVAC systems.

Guidelines for identifying and removing mold are provided through a NYCDOH

website (see Appendix A).

Setting Benchmarks for the Contaminants of Potential Concern (COPCs)

A tiered approach was used to evaluate the health risks posed by contaminants that might be

present in the indoor environment (air and settled dust). For each COPC, three levels were

established:

Tier I Level above which, after elimination of potential indoor sources (combustion

by-products, stored chemicals, etc.), aggressive clean-up action should be

taken expeditiously along with follow-up sampling to confirm attainment of

Tier III level

Tier II Range where diligent cleaning should continue, after elimination of potential

indoor sources (combustion by-products, stored chemicals, etc.), with followup sampling to confirm attainment of Tier III level

Tier III Level below which the risk is negligible or consistent with the New York City

background level found in the aforementioned Background Study ( see

Introduction).

The following hierarchal approach was employed for developing benchmark values: 1)Use of

relevant and appropriate environmental standards/regulations; 2) Calculation of risk-based

benchmarks using EPA risk assessment guidance; and, 3) Adaptation of occupational standards

with additional safety factors. Accordingly, a review of environmental standards/regulations

was conducted for each of the six COPCs. As a result of this exercise Tier I screening levels for

lead in indoor air and settled dust were set using EPA’s National Ambient Air Quality Standard

(NAAQS) and the U.S. Housing and Urban Development’s (HUD’s) standard for floors,

respectively. The clearance criteria established in the Asbestos Hazard Emergency Response Act

(AHERA, 1986) of 70 structures/mm2 was utilized to evaluate asbestos samples from the

ambient air monitoring effort. As detailed in Appendix B, the upper bound estimate for exposure

duration to contaminants in the ambient air was one year. However, given the potential for
12

extended exposure in residential dwellings, AHERA was deemed less appropriate to this setting.

In cases where appropriate standards did not exist (e.g., asbestos), risk-based criteria were

developed using established EPA risk assessment methods: for indoor air, methods described in

EPA’s “Risk Assessment Guidance for Superfund” [RAGS, 1989] were used; for settled dust,

EPA Region III’s “Wipe Sample Assessment” guidance was utilized with modifications (see

Appendix D). The risk-based criteria reflect the most current toxicity criteria (Cancer Slope

Factors and RfDs/RfCs) on EPA’s Integrated Risk Information System (IRIS), which is a

regularly updated (quarterly), online database that reports chemical toxicity reference values and

information on human health effects that may result from exposure to chemicals in the

environment.

For contaminants that lacked IRIS verified toxicity criteria, occupational standards were

employed. Additional safety factors were added to account for higher exposure and greater

sensitivity within the general population.

The clearance criteria paradigm described above is pathway and chemical specific. Accordingly,

the benchmarks for each COPC do not account for multimedia and multiple chemical exposure. 

Individual sampling results that exceed benchmark values should not be interpreted to represent

the occurrence of an adverse health effect. Because benchmark levels assume continuous

exposure for an extended duration, the average of the measured concentrations is more

appropriate for evaluating risk than individual measurements. Consequently, isolated individual

values above the benchmark level may not necessarily be indicative of a hazard.

Developing Risk-Based Criteria for Indoor Air

For carcinogenic compounds, the benchmarks were set so that a local resident’s lifetime risk of

developing cancer from exposure to WTC-related contaminants would not exceed a one-in-tenthousand probability (1x10-4) above the resident’s background risk without this exposure. The

amount of time that residents and office workers were exposed to WTC-related contaminants is

unknown. To be conservative, the Tier I screening level was chosen to be protective of a

resident who may have been exposed to WTC-related contaminants for one year. The Tier III

clearance level was chosen to be protective of a resident who is exposed to WTC-related

contaminants for 30 years, which is the upper-bound estimate for residency in one dwelling

[EPA, 1989]. Cancer risk from less-than-lifetime inhalation exposure is given as:

Risk = LAC * UR

where LAC is the air concentration averaged over a lifetime, calculated as: AC * [EF*ED/LT],

where AC is the average air concentration during the period of exposure ( g/m3), EF is the

exposure frequency (days/year), ED is the exposure duration (years), LT is lifetime (days), and

UR is the unit risk factor, expressed in units of 1/concentration.
13

The following table lists the input parameters and numerical values (along with a brief

explanation) used in this procedure. (See Appendix D for equations and a more detailed

discussion).

Table 2. Exposure parameters for calculating clearance criteria for air samples.

Input Parameter Value Explanation

Risk 1 x 10-4 See Appendix C

AT-(Averaging Time -

Carcinogens) of LT

25,550 days See Appendix D

ED (Exposure Duration) 30 years Upper-bound Estimate of Time in

Residence [EPA, 1989]

EF (Exposure Frequency) 365 days/yr Days in Residence [EPA, 1989]

IUR (Inhalation Unit Risk) 2.3 E -01 (asbestos)

2.86 E +5 (dioxin)*

7.3 E 0 (PAHs)*

IRIS, 2002

Dioxin Reassessment, EPA, 2001

IRIS, 2002

*IUR was calculated by route-to-route extrapolation of oral Slope Factor

The cancer risk level (1x10-4) employed herein reflects the upper bound of the acceptable risk

range (10-4 to 10-6) established in EPA’s Superfund regulation [Federal Register, 1990]. 

Practical Quantitation Limits (PQLs, the lowest level that can be reliably achieved within

specified limits of precision and accuracy during routine laboratory operating procedures [EPA,

1992]) and anticipated background levels [ATSDR, 1995] dictated the selection of the risk level

at 1x10-4. A more detailed discussion of this subject can be found in Appendix C.

For non-carcinogenic compounds, airborne contaminant concentration is compared to the

Reference Concentration (RfC). The RfC is an estimate of a chronic exposure concentration for

the human population, including sensitive subpopulations, that is likely to be without an

appreciable risk of deleterious effects during a lifetime [EPA, 1989]. That comparison (i.e,

chronic exposure concentration (CEC) divided by the RfC) is called the Hazard Quotient (HQ). 

HQ = CEC/RfC

where CEC is the daily averaged air concentration, calculated as: AC * [EF*ED/AT-NC], where

AC is the average air concentration during the period of exposure ( g/m3), EF is the exposure

frequency (days), ED is exposure duration (years), AT-NC is the averaging time for noncarcinogens, and RfC is the reference concentration, expressed in units of 1/concentration.

According to EPA guidelines [EPA, 1989], if the HQ is greater than one, there may be concern

for potential health effects. Therefore, for Tier III (clearance level), the benchmark screening
14

level was set at an HQ of 1. For Tier I, which equates to a sub-chronic exposure scenario, an HQ

of 10 was used, in accordance with EPA’s Hazard Evaluation Handbook [EPA, 1997]. An HQ

of 10 accounts for the fact that chronic toxicity criteria (RfDs/RfCs) are being applied to

sub-chronic exposure scenarios (i.e., exposure not expected to exceed 6 months to one year in

duration). Accordingly, an HQ of 10 was used for non-carcinogens to reflect a similar (i.e.,

upper bound of 1 year) exposure duration. Note that contaminants (both non-carcinogens and

carcinogens, alike) can exhibit acute effects from short-term, high-dose exposures. Because the

Tier I benchmark levels are based on subchronic exposure (i.e., 1 year), acute effects from

exposures that are below the benchmark levels would be unlikely. A review of EPA’s draft

Acute Exposure Guideline Levels [EPA, 2001a] and California EPA’s (CAL-EPA) Acute Risk

Levels demonstrates that the benchmark levels developed herein are categorically more stringent

than the analogous US EPA and Cal-EPA acute levels.

Developing Risk-Based Criteria for Settled Dust

There is no established national guidance, and limited scientific literature, for assessing risk from

interior surface wipe sampling (i.e., mass per unit area) data . The approach used in this report

was adapted and modified from a methodology developed by the EPA Region III Superfund

Program. It has been employed by the U.S. Army Corps of Engineers to develop risk-based

clean-up goals for interior surfaces at the Claremont Polychemical Superfund site in Region II

[Radian, 1999]. Additionally, the methodology is similar to an approach employed by the

NYSDOH for evaluating a dioxin contaminated office building [NYSDOH, 1985] and one

previously proposed by NJDEP for setting interior building surface clean-up goals [NJDEP,

1993].

A full discussion of the methodology employed for developing risk-based benchmarks based on

contact with residues on indoor surfaces is presented in Appendix D. Briefly, this methodology

provides an estimate of daily dose resulting from dermal absorption and ingestion associated

with contacting contaminated surfaces and hand-to-mouth transfers. Dose is obtained by

estimating the following: skin contact area and contact frequency with contaminated surfaces,

transfer efficiency between surface and hand, transfer efficiency between hand and mouth, oral

absorption of the contaminant and dermal absorption of residual contamination on skin.

Consistent with the approach for indoor air, toxicity criteria were obtained from IRIS. The

assessment procedure is described briefly below and in more detail in Appendix D.

For the purpose of developing risk-based clearance levels for interior surfaces, this approach is 

preferable to an approach that relies on measuring contaminant concentration on a mass per mass

(ppm) basis (as might be done for an exterior soil assessment). After cleaning has occurred, it

would be difficult to obtain the mass of dust necessary to perform a mass per mass measurement

of contaminant concentration. In addition, literature on interior lead contamination demonstrates

a strong correlation between lead load (mass per unit area) and blood lead concentration in

children (Lanphear et. al., 1998).

The following table lists the input parameters and numerical values (along with a brief
15

explanation) used in this procedure. (See Appendix D for equations and a more detailed

discussion.) 

Table 3. Exposure parameters used to calculate clearance criteria for wipe samples.

Input Parameter Value Explanation

SA (Skin Surface Area) 400 cm2 Palm Side of Hands

CF (Contact Frequency) 16/day See Appendix D

FTSS (Fraction Transferred from

Surface to Skin)

0.05 See Appendix D

EF (Exposure Frequency) 365 days/yr Days in Residence [EPA, 1989]

ED (Exposure Duration) 30 years Upper-bound Estimate of Time in

Residence [EPA, 1989]

ABSo (Oral Absorption Fraction) 1 See Appendix D

FTSM (Fraction Transferred from

Skin to Mouth)

0.1 See Appendix D

ABSd (Dermal Absorption Fraction) 0.03 (dioxin)

0.13 (PAHs)

Chemical Specific [EPA, 2001b]

BW (Body Weight) 70 kg Average Adult [EPA, 1989]

AT-NC (Averaging Time - Non

Carcinogen)

–

AT-C (Averaging Time - 

Carcinogen)

25,550 days See Appendix D

CSF (Cancer slope factor -dermal

and oral)

1.0 E+6 (dioxin)

7.3 E 0 (PAHs)

Dioxin Reassessment: EPA, 2001

IRIS, 2002

In light of the limited data for many of the input parameters used to estimate dose from exposure

to residues on surfaces, conservative exposure estimates were employed. Still, there may be a

concern for highly exposed sub-populations. Infants and young children constitute such a group

due to age-specific activities such as crawling and mouthing and increased surface-area to bodyweight ratios. In cases where non-carcinogenic effects are driving clearance levels, the

difference in dose on a mg/kg/day basis between an adult and a young child could be

considerable. However, in this document the two compounds (dioxin, PAHs) for which the

surface contact methodology has been used to develop clearance levels are carcinogens, so it is

this effect that drives the clearance levels. As such, the Tier III clearance level is strongly

influenced by overall exposure duration, which in this assessment has been set at 30 years. 
16

Consequently, weighted over 30 years, the impact of a high-exposure period (i.e., early

childhood) is diluted. It is acknowledged that Tier I (one year exposure duration) screening

levels for carcinogens may underestimate cancer risk for children, but Tier I contaminant levels

are not expected to persist, therefore the magnitude of any associated uncertainty would be

small. If a contaminant was to be added to the COPC list that had its clearance level based on a

non-carcinogenic endpoint, a separate wipe assessment analysis should be performed taking into

account childhood exposure parameters. A more complete discussion of the uncertainties

associated with the methodology for surface contact assessment is presented in Appendix D.

With the exception of asbestos, the extremely limited air sampling data for specific building

constituents in indoor air dictated that an assessment approach had to be based on historical data

relating the concentration of fibers in air (fibers per cubic centimeters or f/cc) to the load in

settled dust (fibers per square centimeters or f/cm2

) [Millette and Hays 1994]. Although the

empirical relationships (called K factors) are not rigorous enough to rely on for a firm health

decision, they are used in this report to define what might constitute elevated building material

counts that would need to be addressed on a near-term basis. This approach may overestimate

potential exposures but, as such, is protective.

Developing Benchmark Levels Based on Occupational Health Standards

For fibrous glass and silica, risk-based methods were not available for indoor air due to lack of

established environmental toxicity criteria. Therefore, benchmark levels were set based on

occupational health standards established by the American Conference of Governmental

Industrial Hygienists [ACGIH] (called “threshold limit values” or TLVs) and the Occupational

Safety and Health Administration [OSHA] (called “permissible exposure limits” or PELs). 

TLVs/PELs are established to protect employees who might have been exposed to substances

during an eight-hour day, for five days a week. For Tier I levels, TLVs/PELs were divided by

ten to be more protective of residents who might be exposed to substances twenty-four hours a

day, seven days a week. In addition, the TLVs/PELs were established to protect a healthy

worker. For Tier III levels, TLVs or PELs were divided by 100 to be protective of a more

diverse population that includes sensitive individuals such as children, older adults, and the

infirm.

The following tables show the benchmark levels developed for each contaminant of potential

concern. Each table is accompanied by risk equations, toxicity criteria and a summary of any

contaminant-specific assumptions that were made in developing the benchmark values.
17

Table 4. Lead

Tier Action Lead (settled dust) Lead (indoor air)

Level Basis Level Basis

I Aggressive

cleaning. If levels

persist, take

additional action to

reduce exposure.

>40 ug/ft2 1) HUD standard

for floors

2) Residential

Lead Hazard

Standard (TSCA

Section 403)

>1.5 ug/m3 NAAQS

(intended to

keep 99.5% of

children below

30 ug/dl)

II Maintain

recommended

cleaning methods.

Consider additional

monitoring.

40 ug/ft2

 to 25

ug/ft2

 (or

background)

25 ug/ft2

 is HUD

screening level

for floors

1.5 ug/m3

 to 

1 ug/m3

 (or

background)

1 ug/m3

 is the

calculated value

using EPA’s

IEUBK Lead

Model for

Children* 

III No further action <25 ug/ft2

 (or

background)

Level could also

be set at that

found in

background, or

unaffected, areas,

so that no

increase in risk

due to lead

would be

expected.

1 ug/m3

 (or

background)

Level could also

be set at that

found in

background, or

unaffected,

areas, so that no

increase in risk

due to lead

would be

expected.

* EPA developed the Integrated Exposure Uptake Biokinetic (IEUBK) Lead Model [EPA, 1994]

to evaluate multimedia lead exposure to children in residential settings. EPA established a goal

of attaining a 95% probability that blood lead levels in children be less than 10 ug/dl [EPA

1994a]. Setting the indoor air lead concentration at 1 ug/m3

 (and using background

concentrations for lead in water, diet, soil and dust) the IEUBK Lead Model estimates that 96%

of the blood lead probability distribution falls below 10 ug/dl. See Appendix E for model run

data files and graph of blood lead probability distribution. 
18

Table 5. Polycyclic Aromatic Hydrocarbons (PAHs)

Tier Action PAHs (settled dust) PAHs (indoor air)

Level Basis Level Basis

I Aggressive

cleaning. If levels

persist, take

additional action to

reduce exposure.

>9 mg/m2 9 mg/m2

represents a

1x10-4 risk

estimate for a 1

year exposure

>6 ug/m3 6 ug/m3

represents a

1x10-4 risk

estimate for a 1

year exposure

II Maintain

recommended

cleaning methods.

Consider additional

monitoring

9 mg/m2

 to 0.3

mg/m2

 (or

background)

0.3 mg/m2

represents a

1x10-4 risk

estimate for a 30

year exposure

6 ug/m3

 to 0.2

ug/m3

 (or

background)

0.2 ug/m3

represents a

1x10-4 risk

estimate for a

30 year

exposure

III No further action <0.3 mg/m2

 (or

background)

Level could also

be set at that

found in

background, or

unaffected,

areas, so that no

increase in risk

due to PAHs

would be

expected.

<0.2 ug/m3

 (or

background)

Level could

also be set at

that found in

background, or

unaffected,

areas, so that

no increase in

risk due to

PAHs would

be expected.

Toxicity criteria for benzo(a)pyrene:

Oral Slope Factor = 7.3 E 00 (mg/kg/day)-1 (IRIS, 2002)

(Inhalation cancer risk was calculated by route-to- route extrapolation of oral Slope Factor)

The following carcinogenic PAHs are evaluated as benzo(a)pyrene-equivalents [EPA, 1993]:

Compound Relative Potency

Benzo(a)pyrene 1

Benz(a)anthracene 0.1

Benzo(b)fluoranthene 0.1

Benzo(k)fluoranthene 0.01

Chrysene 0.001

Dibenzo(a,h)anthracene 1

Indeno(1,2,3-c,d)pyrene 0.1
19

Table 6. Dioxin

Tier Action Dioxin (settled dust) Dioxin (indoor air)

Level Basis Level Basis

I Aggressive

cleaning. If levels

persist, take

additional action to

reduce exposure.

>120 ng/m2 120 ng/m2

represents a

1x10-4 risk

estimate for a 1

year exposure

>0.03 ng/m3 0.03 ng/m3

represents a

1x10-4 risk

estimate for a 1

year exposure

II Maintain

recommended

cleaning methods.

Consider additional

monitoring

120 ng/m2

 to

4 ng/m2

 (or

background)

4 ng/m2

represents a

1x10-4 risk

estimate for a 30

year exposure

0.03 ng/m3

 to

0.001 ng/m3

 (or

background)

0.001 ng/m3

represents a

1x10-4 risk

estimate for a

30 year

exposure

III No further action <4 ng/m2

 (or

background)

Level could also

be set at that

found in

background, or

unaffected, areas,

so that no

increase in risk

due to dioxin

would be

expected.

<0.001 ng/m3

(or background)

Level could

also be set at

that found in

background, or

unaffected,

areas, so that

no increase in

risk due to

dioxin would

be expected.

Toxicity criteria for dioxin:

Oral Slope Factor = 1.0 E 06 (mg/kg/day)-1 [EPA, 2001]

(Inhalation cancer risk was calculated by route-to- route extrapolation of oral Slope Factor)

The table above reflects the proposed cancer Slope Factor for 2,3,7,8 TCDD and the toxicity

equivalence (TEQ) paradigm for carcinogenic dioxin/furan congeners present in EPA’s draft

dioxin reassessment [EPA, 2001]. An equivalent table reflecting the previous IRIS-verified

cancer Slope Factor for 2,3,7,8 TCDD would be represented by multiplying all listed values by a

factor of six. 

The methodology for estimating dose from wipe sampling data (see Appendix D) is consistent

with the approach NYSDOH used in assessing office buildings in Binghamton, with

modifications made to input parameters to reflect residential rather than occupational exposure. 

In addition, the Tier III benchmark equates to a lifetime exposure level which is approximately

one tenth of that which results from current dietary intake of dioxin (65 pg/d). It is thus
20

reasonable to assume that any lower level of exposure would result in an inconsequential

reduction in the current risk levels experienced by the general U.S. population.

Information regarding NYC background levels also would be an important consideration in

determining the appropriate longer-term value. This report proposes selecting the longer-term

value on the basis of a 1x10-4 risk level or NYC background, as determined by the WTC-directed

Background Study.
21

Table 7. Asbestos

Tier Action Asbestos (Settled Dust) Asbestos (indoor air)

Level Basis Level Basis

I Aggressive

cleaning. If levels

persist, take

additional action to

reduce exposure.

Evaluate

conditions in the

area, including

representativeness

of air samples,

asbestos settled

dust levels, and

loading.

> 30,000

f/cm2

Millette’s K factor

to estimate

airborne levels for

different activities

(see narrative

below). 

>0.028 f/cc

(PCME*)

0.028 f/cc

represents a 1x10-4

risk estimate for a

1 year exposure

II Maintain

recommended

cleaning methods. 

Consider additional

monitoring.

Evaluate

conditions in the

area including

representativeness

of air samples, 

fibrous glass

settled dust levels

and loading.

30,000

f/cm2

 to

background

--- 0.028 f/cc

0.0009 f/cc

(or

background)

0.0009 f/cc

represents a 1x10-4

risk estimate for a

30 year exposure

III No further action

required.

Background Level is set at that

found in

background, or

unaffected, areas,

so that no increase

in risk due to the

asbestos fibers

would be

expected.

0.0009 f/cc 

(PCME*) 

(or

background)

Level is set at that

found in

background, or

unaffected, areas. 

In this way, no

increase in risk due

to the asbestos

fibers would be

expected.

* PCME - fibers greater than 5 micrometers long (aspect ratio >3:1). Analysis by TEM.
22

Toxicity criteria for asbestos:

Inhalation Unit Risk = 2.3 E-01 (f/cc)-1 [IRIS, 2002]

Risk-based criteria were used to develop the Tiered benchmark levels for asbestos in air. 

Conservative assumptions of continuous exposure to a constant level of airborne fibers for either

1 year (Tier I) or 30 years (Tier III) were combined with the IRIS Slope Factor to establish

benchmarks representative of a 1x 10-4 estimate of excess lifetime cancer risk for each scenario. 

This approach makes several assumptions, chief among those is the quantification of asbestos

fibers in air based on the PCM definition of a fiber (greater than 5um in length with an aspect

ratio of 3:1 or greater) and the use of the IRIS Slope Factor which was designed to apply to

fibers so defined. Although there is some concern regarding shorter fibers, the approach used

here represents the current consensus by the US EPA for quantifying risk of airborne asbestos

fibers. It should be noted there is ongoing debate regarding the nature of health effects which

may be attributed to shorter asbestos fibers. Both EPA and ATSDR are currently pursuing

meetings to discuss and further refine these issues. However for the purposes of this response,

addressing PCM equivalent fibers is considered protective.

The Tier I level for asbestos in settled dust was based on K factors [Millette and Hays, 1994],

which are empirical relationships between concentrations of asbestos fibers in settled dust and

indoor air. Millette developed the K factors by studying matched air and settled dust samples

taken from various homes, at varying levels of activity in the home. The Tier I level was based

on the K factor for a worst case scenario of a high level of activity. Although K factors are not

rigorous enough to rely upon for a firm health decision, they are used here only to define what

might constitute elevated fiber counts, that would need to be addressed as a near-term concern. 

This approach may overestimate potential exposures, but as such, is protective.

It should be noted that the airborne Tier I level of 0.028 f/cc PCM equivalents roughly equates to

the AHERA TEM standard of 70 f/mm2

 (0.022 f/cc) in total fiber counts. Based on empirical

information from the WTC ambient air monitoring program [EPA, 2002c] that recorded less than

20% of total AHERA TEM fiber counts to be >5 um in length, the AHERA TEM standard of 70

f/mm2 (0.022 f/cc) and the alternate AHERA PCM standard of 0.01 f/cc both meet the riskbased criteria established for the Tier I screening level. 
23

Table 8. Fibrous Glass

Tier Action Fibrous Glass (settled dust) Fibrous Glass (indoor air)

Level Basis Level Basis

I Aggressive cleaning. 

If levels persist, take

additional action to

reduce exposure.

Evaluate conditions in

the area including

representativeness of

air samples, fibrous

glass settled dust

levels and loading.

> 100,000

f/cm2

Millette’s K factor

to estimate

airborne levels for

different activities

(see narrative

below).

> 0.1 f/cc ACGIH TLV of

1 f/cc (see

narrative below).

II Maintain

recommended

cleaning methods. 

Consider additional

monitoring.

Evaluate conditions in

the area including

representativeness of

air samples, fibrous

glass settled dust

levels and loading.

100,000

f/cm2

 to

background

--- 0.01 to 0.1

f/cc

---

III No further action

required

background Level is set at that

found in

background, or

unaffected, areas. 

In this way, no

increase in risk

due to the fibers

would be

expected.

< 0.01 f/cc ACGIH TLV of

1 f/cc (see

narrative below)

* Fibers with length > 5μm with an aspect ratio > 3:1, as defined in the ACGIH TLV. 

Air concentrations measured by PCM, NIOSH 7400, confirmed by SEM.

The benchmarks for airborne fibrous glass were set based on the consideration that low level

exposures to fibrous glass would not pose the potential for significant long-term health effects

given the expected low biopersistence of these materials [ATSDR, 2002]. The current

occupational exposure standards for fibrous glass (glass and mineral wools) is established to

prevent the upper respiratory tract and skin irritant effects. In order to apply this standard to a
24

general population and accounting for a longer daily exposure than seen in the occupation

setting, uncertainty factors were used to reduce the allowable airborne levels for the Tiered

bench marks. The Tier I benchmark is set at one tenth of the TLV and the Tier III level is set at

1 hundredth of the TLV. It is believed these levels will prevent conditions which may cause

irritant health effects for most individual. 

Although fibrous glass in settled dust is known to be a contact irritant, little data exist to provide

a threshold relating to what fiber loading may result in skin irritation, or airborne levels of

concern. However, as with asbestos it was deemed preferable to have a Tier I benchmark

available so that there was some upper bound to settled dust loadings that may trigger action. 

Here again Millet’s K factors were used to correlate dust loading levels to the air benchmarks.

The Tier I level for fibrous glass in settled dust was based on Millette’s K factors, which are

empirical relationships between concentrations of asbestos fibers in settled dust and indoor air. 

Millette developed the K factors by studying matched air and settled dust samples taken from

various homes, at varying levels of activity in the home. The Tier I level was based on the K

factor for a worst case scenario of a high level of activity. Although K factors are based on

activity data for asbestos, they are believed to be protective for fibrous glass, which is larger and

less airborne. In addition, although K factors are not rigorous enough to rely upon for a firm

health decision, they are used here only to define what might constitute elevated fiber counts,

that would need to be addressed as a near-term concern. This approach may overestimate

potential exposures, but as such, is protective.

The Tier I level for fibrous glass in indoor air was based on the American Conference of

Governmental Industrial Hygienists’ (ACGIH) threshold limit value (TLV) of 1 f/cc. That TLV

is based on limiting irritant effects of fibrous glass on workers. The TLV was divided by a factor

of ten to account for the different exposure durations between ACGIH’s workers and the WTC

area’s residents.

The Tier III level for fibrous glass in indoor air was based on the ACGIH TLV of 1 f/cc, divided

by a factor of 100 to account for greater exposure and the different sensitivities between

ACGIH’s healthy works and the WTC area’s more varied population.
25

Table 9. Crystalline silica - respirable fraction of alpha-quartz

Tier Action Crystalline Silica (settled dust) Crystalline Silica (indoor air)

Level Basis Level Basis

I Aggressive cleaning. If

levels persist, take

additional action to

reduce exposure.

Evaluate conditions in

the area including

representativeness of

air samples, asbestos

settled dust levels and

loading.

--- --- 10.0 μg/m3

*

OSHA PEL of

100 μg/m3

 (see

narrative

below).

II Maintain recommended

cleaning methods. 

Consider additional

monitoring.

Evaluate conditions in

the area including

representativeness of

air samples, fibrous

glass settled dust levels

and loading.

above

background

10.0 μg/m3

to 1 μg/m3

(or

background)

*

III No further action

required.

background Level is set at

that found in

background, or

unaffected, areas. 

In this way, no

increase in risk

due to the silica

in settled dust

would be

expected.

1 μg/m3

 or

background

OSHA PEL of

100 μg/m3

 (see

narrative

below).

* Silica measured in airborne respirable dust, by NIOSH 7500. 

The benchmarks for silica in indoor air were derived from the Occupational Safety and Health

Administration’s (OSHA) permissible exposure limit (PEL) for dust containing 100% respirable

silica in air of 100 μg/m3 (0.1mg/m3)as a time weighted average for an 8 hour exposure. 

Silica exposure poses risk of both cancer and non-cancer respiratory health effects. Although no

Reference Concentration (RfC) or IRIS Slope Factor exists, there are methodologies for
26

examining risks of non-occupational exposures, on which to draw upon for a risk based approach

to set benchmark levels. The approach taken here is a dual approach, where in the face of

uncertainties the quantification of the benchmarks was based on the current occupational

standards. Broader risk-based discussion of other methodologies provides support for the chosen

benchmark levels although not quantitatively employed here to derive the benchmarks.

The Tier I benchmark is set at one tenth of the OSHA PEL. A single year of exposure at this

benchmark (10ug/m3

) would provide a cumulative silica loading to the lungs less than the

1mg/m3 work-year loading which is believed to be the departure point for adverse health effects. 

Additionally this level is also the effective National Ambient Air Quality Standard for silica,

where PM10 at 50 ug/m3

 contains no more than 10% crystalline silica. A recent review by

supports the finding that this level would be protective of long-term non-cancer health effects 

[EPA, 1996]. The Tier III benchmark is set at one hundredth of the OSHA PEL. A 30 year

continuous exposure at this level would not result in a cumulative silica loading to the lungs

greater than the 1mg/m3

 year loading which is believed to be the departure point for adverse

health effects.
27

References

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U.S. Dept. of Health and Human Services, Atlanta, GA.

http://www.atsdr.cdc.gov/toxprofiles/tp61.html

Agency for Toxic Substances and Disease Registry. 2002. Technical Briefing

Paper: Health Effects from Exposure to Fibrous Glass, Rock Wool or Slag

Wool. Agency for Toxic Substances and Disease Registry, U.S. Department of

Health and Human Services, Atlanta, GA.

http://www.atsdr.cdc.gov/DT/fibrous_glass_061402.pdf

Chatfield EJ, Kominsky JR. 2001. Characterization of Particulate Found in Apartments After

Destruction of the World Trade Center. Summary Report Prepared for Ground Zero Elected

Officials Task Force, New York.

http://www.eqm.com

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http://www.epa.gov/superfund/contacts/newmisc.htm

International Agency for Research on Cancer (IARC). 1988. Monograph on Man-made Mineral

Fibers, Vol 43, p. 39. In: IARC Monographs of the Evaluation of Carcinogenic Risks to Humans.

International Agency for Research on Cancer, World Health Organization, Lyon, France.

http://www.iarc.fr/

Integrated Risk Information System (IRIS). 2002. USEPA, Office of Research and Development.

Available on line at:

http://www.epa.gov/iris

Johnson C. 2002. Mercury Vapor Levels in Dwellings in Close Proximity to the WTC Site. City

University of New York.

Electronic link not available

Lanphear B.P., Matte T.D., Rogers J., et al. 1998. The Contribution of Lead-Contaminated

House Dust and Residential Soil to Children’s Blood Lead Levels. Environ Res: (79) 51-68.

http://www.idealibrary.com/links/doi/10.1006/enrs.1998.3859

Lioy, P., et al. 2002. Characterization of the Dust/Smoke Aerosol that Settled East of the World

Trade Center (WTC) in Lower Manhattan after the Collapse of the WTC September 11, 2001. 

EHP, Vol 110 (7) P. 703 - 714.

http://157.98.13.103/members/2002/110p703-714lioy/lioy-full.html

Millette J.R., Hays S.M. 1994. Settled Asbestos Dust Sampling and Analysis. CRC Press Boca

Raton, FL.
28

Electronic link not available

New Jersey Department of Environmental Protection. 1993. Technical Basis and Background

for Cleanup Standards for Contaminated Sites. N.J.A.C. 7:26D (Draft).

New York City Department of Health and Agency for Toxic Substances and Disease Registry.

2002. Final Technical Report of the Public Health Investigation to Assess Potential Exposures to

Airborne and Settled Surface Dust in Residential Areas of Lower Manhattan. Atlanta: US

Department of Health and Human Services.

Electronic link not available

New York State Department of Health. 1985. PCB Re-Entry Guidelines. New York State

Department of Health, Bureau of Toxic Substances Assessment, Division of Environmental

Health Assessment. Albany, NY. July 17. Document 1330P.

Electronic link not available

Radian International. 1999. Development of Risk-Based Wipe Sample Cleanup Levels at the

Claremont Polychemical Superfund Site in Old Bethpage, New York. Prepared for: U.S. Army

Corps of Engineers.

Electronic link not available

Rottner, B.R. 2002. Special Technical Report: Occupational and Environmental Exposures to

Mercury at the World Trade Center Emergency Project. New York City Department of Design

and Construction.

Electronic link not available

U.S. Department of Health and Human Services. 2001. Public Health Service National

Toxicology Program, 9th Report on Carcinogens, Revised January.

http://157.98.13.104/roc/toc9.html

U.S. Environmental Protection Agency (EPA). 1989. Risk Assessment Guidance for Superfund,

Volume 1: Human Health Evaluation Manual (Part A). OSWER, EPA/540/1-89/002.

http://www.epa.gov/superfund/programs/risk/ragsa/index.htm

U.S. Environmental Protection Agency (EPA). 1992. Guidance for Data Usability in Risk

Assessment (Part A). OSWER. 9285.7-09A.

http://www.epa.gov/superfund/programs/risk/datause/parta.htm

U.S. Environmental Protection Agency (EPA). 1993. Provisional Guidance for Quantitative

Risk Assessment of Polycyclic Aromatic Hydrocarbons. Office of Research and Development.

EPA/600/R-93/089.

http://www.epa.gov/cgi-bin/claritgw?op-Display&document=clserv:epa-cinn:4308;&rank=4&te

mplate=epa
29

U.S. Environmental Protection Agency (EPA). 1994. Guidance Manual for the Integrated

Exposure Uptake Biokinetic Model for Lead in Children.

http://www.epa.gov/superfund/programs/lead/ieubk.htm

U.S. Environmental Protection Agency (EPA). 1994a. Revised Interim Soil Lead Guidance for

CERCLA Sites and RCRA Corrective Action Facilities. OSWER 9355.4-12

http://www.epa.gov/superfund/programs/lead/

U.S. Environmental Protection Agency (EPA). 1996. Ambient Levels and Noncancer Health

Effects of Inhaled Crystalline and Amorphous Silica: Health Issue Assessment. EPA/600/R95/115.

http://www.epa.gov/ncea/pdfs/0604.pdf

U.S. Environmental Protection Agency (EPA), Region III. 1997. Hazard Evaluation Handbook. 

A Guide to Removal Actions. EPA 903/B-97-006.

Electronic link not available

U.S. Environmental Protection Agency (EPA). 2001. Exposure and Human Health Reassessment of 2,3,7,8- Tetrachlorodibenzo-p-dioxin (TCDD) and Related Compounds. Office of

Research and Development. Peer Review Draft.

http://cfpub1.epa.gov/ncea/cfm/dioxreass.cfm?ActType=default

U.S. Environmental Protection Agency (EPA). 2001a. Acute Exposure Guideline Levels (Peer

Review Draft) OPPTS, Wash. D.C.

Electronic link not available

U.S. Environmental Protection Agency (EPA). 2001b. Risk Assessment Guidance for

Superfund Volume 1: Human Health Evaluation Manual (Part E, Supplemental Guidance for

Dermal Risk Assessment) Interim. EPA/540/R/99/005. Review Draft.

http://www.epa.gov/superfund/programs/risk/ragse/index.htm

U.S. Environmental Protection Agency (EPA). 2002a. Special Investigative Audit #14:

Environmental Data Trend Report, World Trade Center Disaster; Final Update - Trends for Data

Collected 9/11/01 to 4/24/02 from Lower Manhattan. Prepared by IT Corporation for Office of

Emergency and Remedial Response.

http://www.nycosh.org/WTCdraft2_102901.pdf - (Draft Version - October 2001)

U.S. Environmental Protection Agency (EPA). 2002b. Toxicological effects of fine particulate

matter derived from the destruction of the World Trade Center, April 2002 draft. National

Health and Environmental Effects Research Laboratory, Office of Research and Development.

http://www.epa.gov/ORD/scienceforum/air_abstracts/gavett.pdf

U.S. Environmental Protection Agency (EPA). 2002c. EPA Website for World Trade Center

Sampling Results. 
30

http://www.epa.gov/wtc

U.S. Geological Survey (2001) Environmental Studies of the World Trade Center after the

September 11, 2001 Attack. Open File Report OFR-010429.

http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-01-0429/

Wallace, Deborah. 1990. In the Mouth of the Dragon: Toxic Fires in the Age of Plastics. Avery

Publishing Group, Inc., New York.

Electronic link not available
APPENDIX A

Hazardous Substances Not Included in Indoor Environment Sampling Program

Benzene

Benzene is a volatile organic chemical (VOC) that was found in emissions from the open flames

and smoldering debris left after the collapse of the WTC. The benzene may have originated

from the airplanes’ residual jet fuel or from the continuous burning of plastics and other

materials contained within the collapsed towers.

Since the fires and smoldering debris persisted long after the collapse of the WTC towers, there

is a possibility that harmful levels of benzene vapor could have accumulated in nearby indoor

environments. However, because benzene is very volatile and dissipates into ambient air

quickly, the vapor plumes would have had to contain high concentrations of benzene, and the

indoor area would have had to be relatively close to the fire source in order for indoor amounts

of benzene to build up to harmful levels. In addition, unlike dioxin, benzene cannot become

adsorbed by dust particles and transported indoors to settle as a long-term potential hazard. 

Once the source of the benzene is extinguished completely from the area, then benzene will

dissipate and will not be a hazard.

Results of samples taken within the immediate WTC work zone from September 11 through midJanuary 2002, show benzene levels of up to 180,000 parts per billion (ppb). However, tests

during the same time period outside the work zone show levels of benzene that were below the

established EPA screening level of 20 ppb for the ambient air (see Appendix B), indicating how

quickly benzene dissipates in the air. A specific example, for the day of October 3, is shown

below:

From debris pile at From debris pile at From Liberty &

WTC North Tower WTC South Tower Greenwich Streets

28,000-39,000 ppb 4,300 ppb less than 20 ppb

From January 26 through April 23, 2002 (the most recent test date available) levels of benzene in

ambient air have remained below the 20 ppb screening level, except for one grab sample from

the immediate work zone on February 9 and another sample from the same location on February

12. These tests indicate that the source of harmful ambient benzene levels has been

extinguished, and therefore there is no source of benzene available to accumulate in any indoor

environment. Benzene will not be monitored in any further indoor environment testing.

Polychlorinated Biphenyls (PCBs)

PCBs were historically used as coolants and lubricants in transformers, capacitors, and other

electrical equipment. It is possible that, with the WTC collapse, PCBs could have been

dispersed into the ambient air and then transported indoors. However, in well over 500 ambient

air samples taken around the WTC site, no measurements were found above EPA’s screening

level of 730 ng/m3

 in the ambient air (see Appendix B). This indicates that PCBs in ambient air

are not considered to be at harmful levels, therefore, PCBs will not be monitored in indoor
2

environment testing.

Chromium

Chromium is a naturally occurring element commonly used in metal alloys and plumbing

coatings in high rise buildings such as the WTC. Chromium and its compounds can be found in

air as very fine dust particles that eventually settle over land, and can cause cancer and other

health problems if inhaled at high concentrations. To date, in over 300 air samples, levels of

chromium measured in ambient air around the WTC work zone have all been below EPA’s

screening level of 0.6 ug/m3 in the ambient air (see Appendix B). Measurements in settled dust

[EPA 2002c, Lioy 2002] have been below EPA Removal Action Guidelines [EPA, 1997].

Because of these low values, chromium is not being considered a hazard at the WTC site. 

Therefore, chromium will not be monitored in any indoor environment testing.

Cadmium and Manganese

Cadmium and manganese, both hazardous air pollutants, were detected in some ambient air

samples taken at the WTC site. However, in over 300 samples, cadmium was found in only two

samples at levels over EPA’s screening level of 0.2 ug/m3 in the ambient air (see Appendix B). In

over 300 samples, manganese was found in only four samples at levels above EPA’s screening

value of 0.5 ug/m3 in the ambient air (see Appendix B). Because of the low ambient

concentrations of these two metals, they will not be monitored in any indoor environment

testing.

Mercury

In late December 2001, it was reported that four New York City Port Authority police officers

were tested with elevated levels of mercury in their blood. This raised concerns over the air

quality at the WTC area. The officers were retested under medical surveillance to determine

whether the source of mercury was the air over the WTC. The retesting found that the levels of

mercury in the officers’ blood and urine were below levels of concern established by NYCDOH

and the American Conference of Governmental Industrial Hygienists. The cause of the first

elevated mercury levels is not known, but may be from something that the officers had eaten the

day before the blood tests were done, and not WTC air. In fact, Rottner [2002] has reported only

one mercury air sample above detection limits to date in the WTC area.

In addition, data from a U.S. Geological Survey leachability study [USGS, 2001] performed on

both indoor and outdoor WTC dust samples found mercury in leachate samples only at trace

levels (up to 18 parts per trillion [ppt] for outdoor dust and 130 ppt in indoor dust). Because

only trace levels of mercury appear to be present in indoor dust samples, the probability that

harmful levels could ever be released to the air is very low. Therefore, mercury will not be

monitored in any further indoor environment testing.
3

Particulate Matter

Particulate Matter (as fine dust and smoke) in the 10 micron and smaller size range is inhalable

and may cause throat and lung irritation. Because of the energy released by the WTC disaster,

dust containing particulate matter in this size range was generated. If this dust had not been able

to settle, or if there had remained a continuous source of particulates being released into the

ambient air, then there would have been a concern that hazardous dust could infiltrate nearby

homes and offices. However, ambient monitoring for fine particulate matter in the WTC area

has shown that, since late October, the levels of PM 10 (inhalable dust fraction 10 microns and

smaller) and PM 2.5 (respirable fraction 2.5 microns and smaller) have been below the levels of

concern:

PM10 150 ug/m3 NAAQS 24-hour average

PM2.5 65 ug/m3 NAAQS 24-hour average

 40 ug/m3 Air Quality Index, 24-hour average

(moderate impact)

This indicates that there is no continuing concern of hazardous fine particulate matter entering

homes and offices in the WTC area. Therefore, particulate matter will not be monitored in any

further indoor environment testing.

Refractory Ceramic Fibers (RCF)

Ceramic fibers are reasonably anticipated to be human carcinogens based on sufficient evidence

of carcinogenicity in experimental animals [IARC V.43, 1988]. When administered by

inhalation, rats of both sexes showed a significant increase in the incidence of benign and

malignant tumors of the lung. However, there are no data available to evaluate the

carcinogenicity of ceramic fibers in humans [IARC V.43, 1988].

It is not expected that ceramic fiber-containing materials were present in large quantities in the

WTC buildings, since those materials are used mainly in industrial high temperature

applications.

Some air sampling has been performed for ceramic fibers in a recently completed study by 

ATSDR and NYCDOH [NYCDOH, 2002]. During the period from November 4 through

December 11, 2001, environmental samples were collected in 30 buildings in lower Manhattan

and four locations above 59th Street. Settled dust samples were taken both indoors and out, and

analyzed for asbestos and other fibers by PLM. Although fibrous glass was reported in many

settled dust samples, RCF was not reported as a fiber present by PLM. Air samples, also taken

in these areas, were analyzed for fibers by PCM. Six of these study area air samples appeared to

contain fiber levels in air higher than the levels found above 59th Street. Four of the samples

from areas containing fibrous glass in settled dust were re-analyzed by SEM and were not found

to contain any ceramic fibers above the detection limit (0.00004 f/cc).

Even though this is a limited study, it appears to confirm limited to no use of ceramic fibers in
4

the WTC buildings. Therefore, ceramic fibers will not be monitored in any further indoor

environment testing.

Mold

Mold was not generated during the WTC collapse or associated fires. However, mold may be

present because of actions taken in response to the collapse. Substantial quantities of water were

used to extinguish the fires and to wash buildings affected by the collapse. Some of that water

entered buildings, causing indoor mold contamination. Additionally, the loss of electric power

after the collapse affected the ability of buildings’ ventilation and plumbing systems to control

indoor environments. This may have contributed to indoor mold contamination in some

buildings.

The most common symptoms of exposure to mold are runny nose, eye irritation, cough,

congestion, and aggravation of asthma. Although there is evidence documenting severe health

effects of mold in humans, most of this evidence is derived from eating mold-contaminated

foods, or occupational exposures in agricultural settings, where inhalation exposures were very

high. There are no numeric standards to define “safe” levels of mold. In addition, it is very

unlikely that the existence of mold in buildings around the WTC site can be distinguished from

mold conditions existing prior to the attack. Therefore, the guidance established below is

qualitative in nature and targeted towards detecting the presence of mold and removing it, rather

than quantifying levels that pose health risks.

When inspecting a building, investigators should:

1. Look for evidence of visible mold or water damage throughout the apartment or office. 

Pay particular attention to moldy odors.

2. Ask the building management if water damage was noted as a result of the WTC attack or

events thereafter. The investigator should be alert for situations where the loss of power

to a building may have created a situation where either the ventilation or plumbing

systems failed or leaked, creating water damage.

3. If mold contamination is encountered, it should be removed in accordance with New

York City Department of Health mold removal guidelines: 

http://www.nyc.gov/health/html/doh/html/epi/moldrpt1.html
APPENDIX B

World Trade Center Health Effects Screening Criteria for Ambient Air

Introduction

Extensive air quality monitoring data have been collected at and around the World Trade Center

(WTC) site since 9/11/01. Table 1 (Screening Criteria) is intended to provide health protective

screening values for data evaluation. Analysis has been performed on an extensive list of

potentially WTC-related contaminants. Many of the chemicals screened have demonstrated a

consistently low (i.e., below detection limits or trace amounts) trend. Consequently, the list of

contaminants in Table 1 represents those chemicals that, because of their intrinsic toxicity and 

frequency/magnitude-of -detection, pose the greatest potential hazard from exposure. This

selection process (i.e., a toxicity/concentration analysis), although qualitative, reflects the

contaminant-of-concern identification process recommended in the Risk Assessment Guidance

for Superfund. Table 1 may be expanded as additional data analysis becomes available. Two

populations have been identified for assessment: response/demolition (i.e., WTC site) workers;

and residents living in Lower Manhattan (e.g., Battery Park City, Tribeca and other residential

locations close to Ground Zero). Included in the resident category are all other workers located

in Lower Manhattan with the exception of WTC site workers.

Relevant Standards

The following paradigm has been employed to develop screening values. For each of the two

identified receptor populations (i.e., site workers and residents), existing standards are utilized 

where appropriate. Occupational standards (i.e., OSHA PELs) are used for all site workers

conducting response/demolition activities covered by OSHA. Monitoring data from demolition

areas are compared to OSHA PELs. (For example, the OSHA PEL of 1 ppm for benzene is used

to evaluate benzene air samples taken directly from within the plume on the debris pile.)

Environmental standards (e.g., NAAQS, AHERA) are utilized to evaluate monitoring data from

the site perimeter and beyond where residents or non-WTC site workers may be exposed. (For

example, lead air monitoring data from perimeter stations outside of the immediate work zone

are evaluated against the NAAQS of 1.5 ug/m3.)

Risk-Based Screening Criteria 

In cases where appropriate standards do not exist, risk-based screening criteria have been

developed for residential (including the non-WTC site workers) receptors. (In the absence of

OSHA standards, it is beyond the scope of EPA’s mission to develop “occupational” screening

values.) The risk assessment paradigm detailed in EPA’s “Hazard Evaluation Handbook: A

Guide to Removal Actions” (HEH) was employed for this initiative (except where otherwise

noted in the Table 1 footnotes). Screening levels reflect the most current toxicity criteria (Slope

Factors and RfCs) on EPA’s IRIS database.

For carcinogenic compounds excess lifetime cancer risk was set at E-04 (one-in-ten thousand). 

The residential exposure scenario in the HEH was modified for carcinogens from the default of

30 years (upper-bound estimate for residency in one dwelling) to 1 year (to reflect an upper
2

bound estimate for the length of time a resident may be potentially exposed to WTC-related

contaminants). In cases where the screening value based on a noncancer endpoint is more

stringent, screening values for both cancer and noncancer endpoints are presented. It is also

noted that the default 30 year exposure duration (and the 1 year site-specific adjustment) reflects

an apportionment between child (20% of total exposure duration) and adult (80 % of total

exposure duration) receptors. Because children have comparatively greater (as a function of

body weight) respiration rates than adults, the screening values presented in Table 1 are

marginally more stringent than values that would otherwise be derived by direct application of 

IRIS verified Unit Risk values. 

For noncarcinogenic compounds, the Hazard Quotient (chronic daily intake/RfC) was set at 10. 

A Hazard Quotient of 10 is employed in the HEH to account for the fact that chronic toxicity

criteria (RfDs/RfCs) are being applied to sub-chronic exposure scenarios that are not expected to

exceed 6 months - 1 year in duration. Accordingly, a Hazard Quotient of 10 was utilized for 

non-carcinogens in Table 1 to reflect a similar (i.e., upper bound of 1 year) exposure duration. 

It is noted that contaminants (both non-carcinogens and carcinogens, alike) can exhibit acute

effects from short-term, high-dose exposures. Because the screening values in Table 1 are based

on subchronic exposure (i.e., 1 year), acute effects from exposures that are below the screening

levels would be unlikely. Additionally, a review of California EPA’s (CAL-EPA) Acute Risk

Levels demonstrates that the screening criteria in Table 1 are categorically more stringent than

the Cal-EPA’s analogous acute levels.

NOTE: Individual sampling results that exceed screening values should not be interpreted to

represent the occurrence of an adverse health effect. Rather, such information indicates the need

for careful monitoring and the assessment of longer-term data trends for evaluation against

appropriate health criteria. That is, most of the screening levels have been developed to account

for continuous one year average exposure durations. Because these screening levels assume

continuous exposure for an extended duration, the average of the measured concentrations is

more appropriate for evaluating risk than an individual measurement. Consequently,

miscellaneous individual values above the screening level may not necessarily be indicative of

potential for concern.

Table 1

World Trade Center Screening Criteria

Contaminant Site Worker (1) Resident (2)

Inorganics

Asbestos (3) .1 f/cc (PCM) 70 S/mm2 (TEM)

Cadmium 5 ug/m3 .2 ug/m3 (9)

3 ug/m3 (5)

Chromium (4) 100 ug/m3 .6 ug/m3 (5)
Contaminant Site Worker (1) Resident (2)

3

Lead 50 ug/m3 1.5 ug/m3 (7)

Manganese 5 mg/m3 .5 ug/3 (6) 

Sulfur Dioxide 5 ppm .14 ppm (7)

Particulates

Total 15,000 ug/m3 NA

Respirable 5,000 ug/m3 NA

PM2.5 NA 40 ug/m3 (8)

65 ug/m3 (7)

PM10 NA 150 ug/3 (7,8)

Semivolatiles

Dioxin/Furans (TEQ) NA .162 ng/m3 (5)

PCBs 1,000 ug/m3 .73 ug/m3 (6)

9 ug/m3 (5)

PAHs (16) NA 6 ug/m3 (5, 17)

Volatiles

Acetone 1,000 ppm 1.5 ppm (6)

Benzaldehyde NA 860 ppm

Benzene 1 ppm .02 ppm (9)

.21 ppm (5)

Benzonitrile NA NA

1,3 Butadiene 1 ppm .01 ppm (5, 15)

Chloromethane 100 ppm .4 ppm (6)

2.6 ppm (5)

1,4 Dioxane 100 ppm .5 ppm (5)

Ethanol 1,000 ppm 45 ppm (10)

Ethylbenzene 100 ppm 2.5 ppm (6) 

Freon 22 1,000 ppm (14) 140 ppm
Contaminant Site Worker (1) Resident (2)

4

Propylene LEL (13) simple asphyxiant

Styrene 100 ppm 2.3 ppm (6)

alpha methylstyrene 100 ppm .1 ppm (6)

Tetrahydrofuran 200 ppm .9 ppm (5)

Toluene 200 ppm 1.1 ppm (6)

Xylenes 100 ppm 1 ppm (11)

Reactive Gases

Acetaldehyde 200 ppm .05 ppm (6)

1.3 ppm (5)

Formaldehyde .75 ppm .04 ppm (12)

.35 ppm (5)

Acrolein .1 ppm .0001 ppm (6)

Units

f/cc = fibers (>5 um length) per cubic centimeter of air

S/mm2 = structures (>.5 um length) per square millimeter of filter paper

ppm = parts per million in air

ug/m3 = micrograms of contaminant per cubic meter of air

ng/m3 = nanograms of contaminant per cubic meter of air

NA - Not Applicable

Footnotes:

1. “Site Workers” refers to all workers involved in the response/demolition of the World Trade

Center. Listed values are Occupational Safety and Health Administration (OSHA) Permissible

Exposure Limits (PELs), Time Weighted Averages (TWA) unless otherwise noted.

2. “Residents” refers to people living in the vicinity of the World Trade Center as well as all

other potentially exposed workers not involved in the response/demolition 

3. Resident screening value is based on Asbestos Hazard Emergency Response Act (AHERA)

methodology which uses transmission electron microscopy (TEM), and because of its basis in

“background” (vs a risk basis) includes all asbestos fibers greater than 0.5 microns in length.

Worker values are based on phase contrast microscopy (PCM, - which doesn’t distinguish

asbestos from other fibers) or, for results above the PCM screening value, TEM to derive a PCM
5

equivalence that includes all asbestos fibers greater than 5 microns in length.

4. Screening values for chromium were based on the most toxic form (hexavalent)

5. EPA - Hazard Evaluation Handbook (HEH) (carcinogen) > 1 year of continuous exposure

equating to an excess lifetime cancer risk of one-in ten thousand

6. EPA - HEH (noncarcinogen) > Hazard Quotient (HQ) = 10 

7. National Ambient Air Quality Standard (NAAQS)

- Lead is a 3 month average 

- PM2.5 is a 24 hour average

- Sulfur Dioxide is a 24 hour average primary standard 

8. Air Quality Index (AQI)

9. Non cancer effects based on CAL-EPA toxicity studies

10. American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit

Value (TLV)

11. Agency for Toxic Substances and Disease Registry (ATSDR) Inhalation minimum risk level

(MRL) x 10

12. ATSDR acute MRL

13. Lower Explosive Limit (2 - 11 %)

14. National Institute of Occupational Safety and Health (NIOSH)

15. Proposed Reference Concentration (RfC) - HEH (noncancer) > Hazard Quotient (HQ) = 10 

16. Based on Benzo(a)pyrene toxicity equivalency factor toxicity equivalency factor (TEF)

17. EPA National Center for Environmental Assessment (NCEA) provisional inhalation Slope

Factor (3.1 E 00 mg/kg/day-1)
APPENDIX C

Basis for Tier III screening level of 1 E-04

Defensible analytical methodology and sampling protocols are being chosen for future indoor

sampling and analysis activities. The methods chosen are ones that have been published by

reputable agencies and are in common practice among testing laboratories. In some cases, minor

modifications may be made to the sampling and analytical protocols, but these will be

modifications that are well established in the laboratory community. 

All protocols chosen are designed to reach the lowest level of detection that is reasonable for the

established methods. For Dioxin, Asbestos and PAHs, the sampling and analytical protocols are

designed to reach detection limits that represent risk estimate levels of 1 E-04. To reach risk

estimates of 1E-06, extraordinary modifications would have to be employed. These

modifications would either have to be incorporated into the analytical protocols to increase the

sensitivity of the required instrumentation, incorporated into the sampling protocols to achieve a

larger sample, or a combination of both. For the Chemical of Potential Concern (COPC) list, the

analytical protocols chosen are already incorporating the maximum sensitivity of the

instrumentation. Therefore, the only legitimate mechanism to lower the overall limits of

detection is to modify the sampling protocol. The two means of achieving this goal are to either

run the sampling equipment (pumps) at a higher flow rate, or for longer periods of time. For the

COPC list modifying flow rates would involve operating the equipment to achieve flow rates on

the order of 500 to 1000 liters per minute. The only equipment available to operate at such flow

rates are large units that can not be brought inside a residence. Rates this high also present

problems with creating excessive negative pressure for indoor environments, plus flow rates this

high have not been tested using the sampling protocols, and there is high likelihood of having

analyte breakthrough on the collection filters. Therefore, this is not practical. The other option

is to run the equipment for long periods of time. Again with the list of Chemicals of Potential

Concern, sampling periods of up to 800 hours (33 days of continuous operation) would be

needed to reach the E-06 risk detection levels.

For silica, the analytical and sampling protocols chosen will give detection levels in the

neighborhood of 5 ug/m3

. Instrumental sensitivity can not be set any higher to reach lower

detection levels. Also, the sampling protocols involved for this analysis have been thoroughly

validated by NIOSH. Any change in pump flow rate or sampling duration beyond what is

documented in the method will produce results that have not been validated. Therefore, the

sampling protocol should not be changed from that which is documented.

For fibrous glass the methodology is such that detection levels as low as 0.00001 f/cc can be

achieved. This is well below required levels of detection for future indoor studies.

Another consideration in setting the target risk level involved the anticipated background level of

contaminants such as asbestos, dioxin and PAHs in urban indoor environments. As previously

mentioned, EPA is currently conducting a study to characterize background conditions for WTC

COPCs in New York City residential dwellings. In advance of this study, a literature review was

conducted to provide a general estimate of background concentrations for carcinogenic COPCs

in urban indoor environments. It should be noted that the literature is limited in this regard. For
2

asbestos, ATSDR reports that “measured indoor air values range widely, depending on the

amount, type, and condition (friability) of asbestos-containing materials used in the building”

[ATSDR, 1995]. In its review ATSDR notes that the studies suffer from lack of common

measurement reporting units. Study results have been reported as ng/m3

, f/cc (TEM) and f/cc

(PCM). Using unit conversion factors recommended by the National Research Council in 1984,

ATSDR [1995] reports that the arithmetic mean concentrations of monitoring data from a

variety of indoor locations ranged from .00003 - .006 f/cc (PCM). The proposed clearance level

for WTC-impacted residential dwellings (.0009 PCM equivalents) is within this background

range.
APPENDIX D

Assessing Exposures to Indoor Air and to Residues on Indoor Surfaces

Introduction

The purpose of this Appendix is to provide further details on how procedures were selected to

estimate exposure to indoor air and to residues on indoor surfaces in residences impacted by the

WTC attack.

Indoor Air

Deriving clearance criteria for air samples was completed by using methods described in EPA’s

“Risk Assessment Guidance for Superfund” [RAGS, 1989]. These methods were developed to

assess the risk from contaminants at Superfund sites. The clearance criteria were calculated

using the formula below:

Clearance criteria = (TR x AT) / (ED x EF x IUR)

where:

TR = Target Risk EF = Exposure Frequency

AT = Averaging Time - Carcinogens IUR = Inhalation Unit Risk

ED = Exposure Duration

Target Risk

The target risk identified for these calculations was 1 x 10-4. Appendix C explains the rationale

for this value.

Averaging Time - Carcinogens

For non-carcinogens, AT is the exposure duration expressed in days. For carcinogens, exposure

is averaged over a 70-year lifetime (the factor on which the cancer slope factors are based), and

the AT is 70 years, in days (25,550).

Exposure Duration

A value of 30 years is assumed to match upper bound estimate of time in a residence (EPA,

1997b).

Exposure Frequency

A value of 365 days/year is used to represent a full time resident.

Inhalation Unit Risk

The upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an

agent at a concentration of 1 g/m3 in air. The interpretation of unit risk would be as follows: if

unit risk = 1.5 x 10-6 μg/m3, 1.5 excess tumors are expected to develop per 1,000,000 people if

exposed daily for a lifetime to 1 μg of the chemical in 1 cubic meter of air. The inhalation unit

risk values used in the calculations are 2.3 E-01 for asbestos (IRIS, 2002), 2.86 E +05 for dioxin

(Dioxin Reassessment, EPA, 2001), and 7.3 E+0 for PAHs (IRIS, 2002).
2

Residues on Indoor Surfaces

The most formal EPA guidance which addresses this issue is the “Standard Operating Procedures

(SOPs) for Residential Exposure Assessment” originally published by the Office of Pesticides in

1997 and updated in 2001 (EPA, 1997a and EPA, 2001a). This guidance was designed for

estimating exposures to pesticides. Pesticides are typically applied to indoor surfaces as liquid

or sprayed formulations which would create surface residues which are likely to be somewhat

different than the fine dust particles associated with the WTC attack. So while this guidance was

considered, a number of other sources were also reviewed including the Superfund guidance on

dermal contact (EPA,1989), the procedures used to develop re-entry guidelines for the

Binghamton State Office Building (Kim and Hawley, 1985), procedures used by NJDEP for

setting interior building surface clean-up goals (NJDEP, 1993), the building clean-up procedures

presented by Michaud et al (1994) and an approach developed by the EPA Region III Superfund

program that has been employed by the U.S. Army Corps of Engineers to develop risk-based

clean-up goals for interior surfaces at the Claremont Polychemical Superfund site in Region II

(Radian, 1999). Elements from these various methods were combined to derive the procedure

shown below. The procedures involves 3 steps: 1) estimating the amount of chemical deposited

on the skin using skin area, contact frequency and transfer efficiencies, 2) estimating the dermal

dose based on an absorption fraction and 3) estimating the ingestion dose based on the fraction

of material on hands that is transferred to the mouth.

1. Estimating Amount of Chemical Deposited on Skin

Ds = C x SA x CF x FTSS x EF x ED

Ds = Amount of chemical deposited on skin (mg)

C = Concentration of chemical on contaminated surface (mg/cm2

)

 SA = Exposed skin surface area (cm2

)

CF = Contact frequency of skin against surface (1/day)

FTSS = Fraction transferred from surface to skin

EF = Exposure frequency (days/year)

ED = Exposure duration (years)

2. Estimating Dermal Dose

Dd = (Ds x (1 - FTSM) x ABSd) / (BW x AT)

Dd = Dermal dose (mg/kg/day) BW = Body weight (kilograms)

FTSM = Fraction transferred from skin to mouth AT = Averaging time (days)

ABSd = Dermal absorption fraction

3. Estimating Oral Dose

Do = (Ds x FTSM x ABSo) / (BW x AT)
3

Do = Oral dose (mg/kg/day) BW = Body weight (kilograms)

FTSM = Fraction transferred from skin to mouth AT = Averaging time (days)

ABSo = Oral absorption fraction

The surface concentration term (C) was assumed to remain constant over the entire 30 year

exposure period. This is probably not true for surfaces in the residences impacted by the WTC

attack. Surface loadings will decline as a result of volatilization, chemical degradation, surface

cleaning and transfers to skin/clothing. While some redeposition will also occur, the net long

term effect should be a gradual decline. In this sense, the method will overestimate exposures. 

This same issue has been recognized in similar assessments involving building clean-ups and

pesticide exposures:

• Two scenarios were considered in developing the procedures used to develop re-entry

guidelines for the Binghamton State Office Building (Kim and Hawley, 1985). One

assumed a constant surface concentration and the other assumed a first order exponential

decay. 

• The OPP guidance (EPA, 1997a and EPA, 2001a) uses a “dissipation” factor to account for

degradation and other loss mechanisms after pesticide application. Similarly, Durkin et al

(1995) has proposed a time-dependent transfer coefficient method for lawn treatment

pesticides.

• Michaud et al (1994) proposed a mass balance model which accounts for losses from

surfaces associated with building clean-ups.

Thus, while methods have been proposed to deal with changes in surface residue strength over

time, it is uncertain how well these apply to the situation in residences near WTC. Thus for

purposes of this screening assessment, it was decided to assume constant levels.

4. Calculating Clearance Criteria

In order to calculate a clearance criteria for wipe samples, the formulas identified above need to

be rearranged to derive a concentration based on the target cancer risk or non-cancer hazard. 

The clearance criteria for settled dust, using a wipe sample, for each COPC can be calculated

using the formula listed below and the exposure parameters listed in Table 3 in the body of the

document.

Clearance criteria (mg/m2) = (TR x BW x AT) / [((Dd x CSFd) + (Do x CSFo)) x EF x ED]

The other terms in this procedure and associated uncertainties are discussed below:

Exposed Skin Surface Area (SA)

The skin surface area of 400 cm2 is a typical value for the palm side of adult hands (EPA, 1997b)

which is the body part that is most likely to contact surfaces. 

Contact Frequency (CF)

Michaud et al (1994) assumed 8 contacts per day, apparently based on professional judgment.
4

Low-end values of 1/day and "worst-case" rates of 24/day (3/hour) may be assumed as a matter

of professional judgment; such exposure would obviously involve a very physical job with

frequent contact with the walls and floor. The value recommended here is 16 contacts per day

and is based on professional judgement. If available, site-specific activity data should take

precedence.

Fraction Transferred from Surface to Skin (FTSS)

This will vary depending on type of surface, type of residual, hand condition, force of contact,

etc. Rodes et al. 2001 conducted experiments on particle transfer to dry skin and measured

transfers of 10% from carpets and 50% from hard surfaces. These transfer efficiencies were

found to decline with repeated contacts. The OPP guidance recommends 5% of application rate

for carpets and 10 % for hard surfaces (EPA, 1997a). USEPA has previously assumed transfer

of 0.5 for PCBs (EPA, 1987) based on an Office of Toxic Substances (OTS) assessment. 

Michaud et al (1994) assumed 0.5 for PCBs and dioxins, but stated that 0.1 might be more

realistic. In developing re-entry guidelines for the Binghamton State Office Building after a fire,

a 100% transfer was assumed (Kim and Hawley, 1985). In a study of Malathion uptake from

different surfaces, USEPA-EMSL found that FTSS of malathion from painted sheetrock to

human hands was only 0.0003. (Mean transfer from vinyl flooring to hands was 0.0018, and

from carpet to hands was 0.0152.) Malathion is a pesticide assumed to have lipophilicity more

similar to PCBs than to volatiles or metals. However, the representativeness of such a number

for PCBs and dioxins is unknown. PCBs are more lipophilic (have higher Kows) than

malathion. A value of 5% is recommended here. Although this is on the low end of the literature

values, when combined with the high contact frequency, it provides a fairly high total transfer to

skin. 

Exposure Frequency (EF)

A value of 365 days/year is used to represent a full time resident.

Exposure Duration (ED)

A value of 30 years is assumed to match upper bound estimate of time in a residence (EPA,

1997b).

Fraction Transferred from Skin to Mouth (FTSM)

Michaud et al (1994) assumed that all of the residues deposited on the fingertips would be

transferred to the mouth, twice per day. A similar approach is used in the OPP guidelines. In the

Binghamton re-entry guideline derivation, a range of factors were used: 0.05, 0.1, and 0.25

representing the fraction of residue on hand that is transferred to the mouth (Kim and Hawley,

1985). A similar value of 10% is recommended here.

Oral Absorption Fraction (ABSO)

For chemicals whose dose-response parameters are based on experiments in which the

absorption fraction is similar to the one expected in the exposure scenario, there is no need to

adjust the RfD or CSF.
5

Body Weight (BW)

A value of 70 kilograms is assumed which represents an average adult (EPA, 1997b).

Averaging Time (AT)

For non-carcinogens, AT is the exposure duration expressed in days. For carcinogens, exposure

is averaged over a 70-year lifetime (the factor on which the cancer slope factors are based), and

the AT is 70 years, in days (25,550).

Dermal Absorption Fraction (ABSd)

This parameter is chemical-specific. Dermal absorption fractions of 0.06 for PCBs and 0.03 for

dioxins from soil were first proposed in USEPA, 1992 and more recently adopted in EPA 2001b. 

Michaud et al (1994) used 0.02 for dioxins and 0.03 for PCBs uptake from a sooty surface, based

on the ranges of estimated ABSd values for soil. The Binghamton panel used a range of values

for PCBs (0.01, 0.1, and 0.5) and dioxins (0.01 and 0.1) ( Kim and Hawley, 1985).

Reported ranges for dermal uptake for PCBs in solvent vehicles are reported to range from 15 to

56%, with most of the values clustering around 20% (ATSDR, 1993). Reported ranges for

2,3,7,8-TCDD in solvent vehicles are reported to range from 1 to 40% (ATSDR, 1988). 

Therefore, it seems that even if absorption from the wall material might be enhanced by residual

solvent, the maximum possible absorption of 100% would be unrealistic even for worst-case

exposure.

The values recommended here of 3% for dioxins and 13% for PAHs are based on EPA, 2001b. 

Toxicity Values

There are two toxicity values that can be used to calculate screening values, a Reference Dose

(RfD) for non-carcinogenic compounds and a Cancer Slope Factor (CSF) for carcinogenic

compounds. The RfD is defined as an estimate (with uncertainty spanning perhaps an order of

magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that

is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be

derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied

to reflect limitations of the data used. The CSF is defined as an upper bound, approximating a

95% confidence limit, on the increased cancer risk from a lifetime exposure to an agent. This

estimate, usually expressed in units of proportion (of a population) affected per mg/kg/day, is

generally reserved for use in the low-dose region of the dose-response relationship, that is, for

exposures corresponding to risks less than 1 in 100. As the cancer endpoint was more sensitive,

CSFs were used instead of RfDs. The CSFs used to calculate the clearance criteria are: 1.0 E+6

for dioxin (Dioxin Reassessment, EPA, 2001) and 7.3 E+0 for PAHs (IRIS, 2002).
6

References

Agency for Toxic Substances and Disease Registry (ATSDR). 1988. Toxicological Profile for

2,3,7,8-Tetrachlorodibenzo-p-dioxin. United States Public Health Service, ATSDR, Atlanta,

GA.

ATSDR. 1993. Toxicological Profile Update for Polychlorinated Biphenyls. United States

Public Health Service, ATSDR, Atlanta, GA.

Durkin, P.R., L. Rubin, J. Withey, and W. Meylan. 1995. Methods of assessing dermal

absorption with emphasis on uptake from contaminated vegetation. Toxicology and Industrial

Health 11(l):63-79.

Kim N.K. and J. Hawley. 1985. Re-Entry Guidelines: Binghamton State Office Building. New

York State Dept. of Health, Bureau of Toxic Substances Assessment, Division of Health Risk

Control. Albany, NY. August. Document 0549P.

EPA. 1987. Polychlorinated Biphenyls: Spill Cleanup Policy. Final Rule. Federal Register,

Volume 52, Number 63. April 2.

EPA. 1989. Risk Assessment Guidance for Superfund. Volume I: Human Health Evaluation

Manual (Part A). Interim Final. Office of Emergency and Remedial Response, Washington,

D.C. December.

EPA. 1992. Dermal Exposure Assessment: Principles and Applications. Interim Report. Office

of Health and Environmental Assessment, Washington, D.C. January. EPA/600/891/011/B.

EPA, 1997a. Draft Standard Operating Procedures (SOPs) for Residential Exposure

Assessment. Office of Pesticides Programs. December 19, 1997.

EPA, 1997b. Exposure Factors Handbook. EPA/600/P95/002

EPA, 2001a. Science Advisory Council for Exposure. Policy Number 12 on Recommended

Revisions to the Standard Operating Procedures (SOPs) for Residential Exposure Assessments .

Revised: February 22, 2001

EPA, 2001b. Risk Assessment Guidance for Superfund Volume 1: Human Health Evaluation

Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) Interim. 

EPA/540/R/99/005. Review Draft.

Michaud, J.M., S.L. Huntley, R.A. Sherer, M.N. Gray, and D.J. Paustenbach. 1994. PCB and

dioxin re-entry criteria for building surfaces and air. Journal of Exposure Analysis and

Environmental Epidemiology 4(2):197-227.
7

New Jersey Department of Environmental Protection (NJDEP). 1993. Technical Basis and

Background for Cleanup Standards for Contaminated Sites. N.J.A.C. 7:26D (Draft).

Radian International. 1999. Development of risk-based wipe sample cleanup levels at the

Claremont Polychemical Superfund site in Old Bethpage, New York. Prepared for: U.S. Army

Corps of Engineers.

Rodes, C., R. Newsome, R Vanderpool, J Antley, R. Lewis. 2001. Experimental methodologies

and preliminary transfer factor data for estimation of dermal exposure to particles. Journal of

Exposure Analysis and Environmental Epidemiology, 11:123-139.
1

APPENDIX E

IEUBK Model Results for Lead in Air

LEAD MODEL FOR WINDOWS Version 1.0 Build 251

 

=====================================================================

 Model Version: 1.0 Build 251

 User Name: 

 Date: 

 Site Name: 

 Operable Unit: 

 Run Mode: Research

 

=====================================================================

 The time step used in this model run: 1 - Every 4 Hours (6 times a day).

 ****** Air ******

 Indoor Air Pb Concentration: 100.000 percent of outdoor.

 Other Air Parameters:

 Age Time Ventilation Lung Outdoor Air

 Outdoors Rate Absorption Pb Conc

 (hours) (m^3/day) (%) (ug Pb/m^3)

 ----------------------------------------------------------------------

 .5-1 0.000 2.000 32.000 1.000

 1-2 0.000 3.000 32.000 1.000

 2-3 0.000 5.000 32.000 1.000

 3-4 0.000 5.000 32.000 1.000

 4-5 0.000 5.000 32.000 1.000

 5-6 0.000 7.000 32.000 1.000

 6-7 0.000 7.000 32.000 1.000

 ****** Diet ******

 Age Diet Intake(ug/day)

 -----------------------------------

 .5-1 5.530

 1-2 5.780

 2-3 6.490

 3-4 6.240

 4-5 6.010

 5-6 6.340
2

 6-7 7.000

 ****** Drinking Water ******

 Water Consumption: 

 Age Water (L/day)

 -----------------------------------

 .5-1 0.200

 1-2 0.500

 2-3 0.520

 3-4 0.530

 4-5 0.550

 5-6 0.580

 6-7 0.590

 Drinking Water Concentration: 4.000 ug Pb/L

 ****** Soil & Dust ******

 Multiple Source Analysis Used

 Average multiple source concentration: 240.000 ug/g

 Mass fraction of outdoor soil to indoor dust conversion factor: 0.700

 Outdoor airborne lead to indoor household dust lead concentration: 100.000

 Use alternate indoor dust Pb sources? No

 Age Soil (ug Pb/g) House Dust (ug Pb/g)

 --------------------------------------------------------

 .5-1 200.000 240.000

 1-2 200.000 240.000

 2-3 200.000 240.000

 3-4 200.000 240.000

 4-5 200.000 240.000

 5-6 200.000 240.000

 6-7 200.000 240.000

 ****** Alternate Intake ******

 Age Alternate (ug Pb/day)

 -----------------------------------

 .5-1 0.000

 1-2 0.000

 2-3 0.000

 3-4 0.000
3

 4-5 0.000

 5-6 0.000

 6-7 0.000

 ****** Maternal Contribution: Infant Model ******

 Maternal Blood Concentration: 2.500 ug Pb/dL 

 *****************************************

 CALCULATED BLOOD LEAD AND LEAD UPTAKES: 

 *****************************************

 Year Air Diet Alternate Water

 (ug/dL) (ug/day) (ug/day) (ug/day)

 -------------------------------------------------------------------------------

 .5-1 0.640 2.521 0.000 0.365

 1-2 0.960 2.608 0.000 0.902

 2-3 1.600 2.963 0.000 0.950

 3-4 1.600 2.886 0.000 0.981

 4-5 1.600 2.842 0.000 1.040

 5-6 2.240 3.022 0.000 1.106

 6-7 2.240 3.349 0.000 1.129

 Year Soil+Dust Total Blood

 (ug/day) (ug/day) (ug/dL)

 ---------------------------------------------------------------

 .5-1 5.162 8.688 4.7

 1-2 8.113 12.583 5.2

 2-3 8.210 13.723 5.0

 3-4 8.318 13.785 4.8

 4-5 6.298 11.780 4.1

 5-6 5.714 12.081 3.7

 6-7 5.417 12.135 3.5
4
ATTACHMENT B

DATA VALIDATION 

STANDARD OPERATING PROCEDURES

The following SOPs were used by the Quality Assurance Technical Support Contractor for the 

validation of analytical data: 

SOP QATS-70-077-01 THE DATA VALIDATION OF TRANSMISSION ELECTRON 

MICROSCOPY (TEM) DATA PACKAGES GENERATED 

USING ASTM METHOD 5755-95 (Dec. 17, 2002) 

SOP QATS-70-078-01 THE DATA VALIDATION OF PHASE CONTRAST 

MICROSCOPY (PCM) DATA PACKAGES GENERATED 

USING NIOSH METHOD 7400 (Dec. 17, 2002) 

SOP QATS-70-076-01 THE DATA VALIDATION OF TRANSMISSION ELECTRON 

MICROSCOPY (TEM) DATA PACKAGES GENERATED 

USING EPA 40 CFR, PART 763, SUBPART E (Dec. 17, 2002) 

SOP QATS-70-075-01 THE DATA VALIDATION OF INORGANIC METALS DATA 

PACKAGES GENERATED USING EPA METHOD 6010B AND 

EPA METHOD 7471A (Dec. 17, 2002) 

SOP QATS-70-074-01 THE DATA VALIDATION OF HRGC/HRMS DATA 

PACKAGES GENERATED USING EPA METHOD 8290 (Dec. 

17, 2002) 

SOP QATS-70-073-02 VALIDATING SILICA DATA GENERATED BY METHOD 

MSD 0700 X-RAY DIFFRACTION (XRD) (Dec. 17, 2002) 

SOP QATS-70-071-01 THE DATA VALIDATION OF TRANSMISSION ELECTRON 

MICROSCOPY (TEM) DATA PACKAGES GENERATED 

USING ASTM METHOD D 6480-99 (Dec. 17, 2002) 

SOP QATS-70-072-01 THE DATA VALIDATION OF POLYNUCLEAR AROMATIC 

HYDROCARBON (PAH) WIPE SAMPLE DATA PACKAGES 

GENERATED USING EPA METHOD 8270C (MODIFIED) 

(Dec. 17, 2002) 

SOP QATS-70-070-01 THE DATA VALIDATION OF MAN-MADE VITREOUS 

FIBERS/MMVF) DATA PACKAGES BY POLARIZED LIGHT 

MICROSCOPY (PLM) AND SCANNING ELECTRON 

MICROSCOPY (SEM) GENERATED USING MSD 0310 
ATTACHMENT C

EMSL ANALYSIS 

STANDARD OPERATING PROCEDURES

The following SOPs were used by the contracted laboratory, EMSL for the analysis of ManMade Vitreous Fibers (MMVF) and Silica: 

EMSL MSD 0310OPERATING PROCEDURE FOR THE ANALYSIS OF MANMADE VITREOUS FIBERS FOR THE EPA RESIDENTIAL 

SAMPLING PROJECT (Feb. 2002, Modified Mar. 2002) 

EMSL MSD 0700OPERATING PROCEDURE FOR THE ANALYSIS OF SILICA (∀-quartz, 

cristobalite or tridymite) BY X-RAY DIFFRACTION FOR THE EPA RESIDENTIAL 

SAMPLING PROJECT 
ATTACHMENT D

SAMPLING AND ANALYTICAL METHODS

1. NIOSH Method 7400: Asbestos and Other Fibers by PCM; NIOSH Manual of Analytical 

Methods; U.S. Department of Health and Human Services, National Institute of 

Occupational Safety and Health: Washington, DC, 1994. 

2. AHERA Asbestos-Containing Materials in Schools. Code of Federal Regulations, Part 

763, Title 40, 2001. 

3. EMSL MSD 0300: Material Science Division Operating Procedures for Man-Made 

Vitreous Fiber ID; EMSL Analytical, Inc., NY, 2001. 

4. NIOSH Method 7300: Elements by ICP, NIOSH Manual of Analytical Methods; U.S. 

Department of Health and Human Services, National Institute of Occupational Safety and 

Health: Washington, DC, 1994. 

5. EPA SW-846 6010B: Inductively Coupled Plasma-Atomic Emission Spectrometry; Test 

Methods for Evaluating Solid Wastes Physical/Chemical Methods; U.S. Environmental 

Protection Agency, Office of Solid Waste: Washington, DC, 1996. 

6. NIOSH Method 7500: Silica, Crystalline, by XRD; NIOSH Manual of Analytical 

Methods; U.S. Department of Health and Human Services, National Institute of 

Occupational Safety and Health: Washington, DC, 1998. 

7. ASTM Standard D 5755-95: Standard Test Method for Microvacuum Sampling and 

Indirect Analysis of Dust by Transmission Electron Microscopy for Asbestos Structure 

Number Concentrations; American Society for Testing and Materials: West 

Conshohocken, PA, 2001. 

8. ASTM Standard E 1973-99: Standard Practice for Collection of Surface Dust by Air 

Sampling Pump Vacuum Technique for Subsequent Lead Determination; American 

Society for Testing and Materials: West Conshohocken, PA, 2001. 

9. ASTM Standard D 6480-99: Standard Test Method for Wipe Sampling of Surfaces, 

Indirect Preparation, and Analysis for Asbestos Structure Number Concentration by 

Transmission Electron Microscopy; American Society for Testing and Materials: West 

Conshohocken, PA, 2001. 

10. ASTM Standard D 6661-01: Standard Practice for Field Collection of Organic 

Compounds from Surfaces Using Wipe Sampling; American Society for Testing and 

Materials: West Conshohocken, PA, 2001. 
11. EPA SW-846 8290: Polychlorinated Dibenzodioxins (PCDDs) and Polychlorinated 

Dibenzofurans (PCDFs) by High-Resolution Gas Chromatography/High-Resolution 

Mass Spectrometry (HRGC/HRMS); Test Methods for Evaluating Solid Wastes 

Physical/Chemical Methods; U.S. Environmental Protection Agency, Office of Solid 

Waste: Washington, DC, 1994. 

12. EPA SW-846 8270C: Semivolatile Organic Compounds by Gas Chromatography/Mass 

Spectrometry (GC/MS); Test Methods for Evaluating Solid Wastes Physical/Chemical 

Methods; U.S. Environmental Protection Agency, Office of Solid Waste: Washington, 

DC, 1996. 

13. Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing; 

U.S. Department of Housing and Urban Development: Washington, DC, 1995; Appendix 

13.1: Wipe Sampling for Settled Lead-Contaminated Dust. 

14. NYSDOH Method 198.1: Polarized-Light Microscope Methods for Identifying and 

Quantitating Asbestos in Bulk Samples; New York State Department of Health, 

Environmental Laboratory Approval Program: Albany, NY, 1997. 

15. NYSDOH Method 198.4: Transmission Electron Microscope Methods for Identifying 

and Quantitating Asbestos in Non-Friable Organically Bound Bulk Samples; New York 

State Department of Health, Environmental Laboratory Approval Program: Albany, NY, 

1997.