# Presentation: 893884

## Update:WTC Dust Screening MethodU.S. EPA Office of Research and Development andU.S. EPA Region 2WTC Technical Expert Panel MeetingJuly 12, 2005

## Outline

- Recap of Hypothesis
- Overview of Study
- Sample Preparation
- Study Design
- Results
- Preliminary Comments
- Summary
- Next Steps

## Hypothesis for WTC Collapse Screening Method

- If a unit has been impacted, those materials that are found in WTC dust (markers) will be found in the dust collected from the unit. The materials under consideration are:
- 	1) slag wool (less than 2% iron)
- 	2) elements consistent with concrete
- 	3) gypsum

## Hypothesis for WTC Collapse Screening Method

- Since slag wool is a major component of WTC collapse dust, if a sample does not contain ‘significant’ levels of this marker, the unit would not be considered to contain WTC residuals.
- The other markers would be used as a secondary confirmation of the presence of WTC dust i.e. they must be present for the slag wool to be attributed to the WTC collapse.

## Overview of Study

- Obtained samples of WTC dust and dust from locations that have not been impacted by the WTC collapse i.e. ‘background’.
- Developed and standardized analytical methods for slag wool, gypsum, and elements of concrete.
- Prepared samples of ‘background dust’ spiked with known amounts of WTC dust and confirmed content of spiked samples.
- Had seven laboratories analyze 6 spiked samples and 10 background samples.  One laboratory analyzed 28 remaining background samples that had been collected.
- Data is undergoing final analysis.

## Sample Preparation

- WTC dust was spiked into known background dust at three level (1, 5, 10%) and homogenized.
- USGS performed analysis of the spiked samples prior to being sent to labs.
- The spiked samples showed varied levels of slag wool; this was expected due to the difficulty in homogenizing dust containing large fibers, and the fact that components of WTC dust will vary within a sample because of the nature of the source.
- Despite this variability, the measured levels were in the approximate range expected for the spiking percent (1, 5, 10%) and, in all but one case, each percent level was distinguishable from the other.

## USGS Spiking Material

**USGS Spiking Material**

**Spiking Level, %**

**Slag Wool Fibers/Gram Dust**

## 4 Albany Spiking Material

**4 Albany Spiking Material**

**Spiking Level, %**

**Slag Wool Fibers/Gram Dust**

## Study Design

- Five commercial labs and two government labs (EPA and USGS) conducted the validation study.
- All labs received 32 blind samples.
- 10 background samples and duplicates
- 6 WTC dust dilutions (2 WTC samples) and duplicates
- One lab received an additional 28 background samples for analysis
-  Labs used the final protocol to analyze the samples.

## Study Results

- Two labs have provided incomplete or flawed data (outside of the 95% confidence interval for all points).  These data are not considered in these results.
- All background samples considered in these results are from the Greater NY City Area; background samples from NC are not included.

## Study Results

|  | Background
(Greater NY Area) | USGS Spiked  (Collected 9/01) | 4 Albany Spiked
(Collected 9/04) |
| --- | --- | --- | --- |
| 
Slag Wool
Average
 (fibers/g dust) | AVG + SD
36,500 + 75,000
18,000 + 15,000 *

Range of Samples
ND - 370,000
ND – 44,000* | 1%   
91,000 + 276

5%  
402,000 + 174,000

10%  
755,000 + 245,000 | 1%   
17,000 + 5,200

5%  
52,000 + 8400

10%  
88,000 + 8,700 |
| 
Elements of Concrete
(% Area) | 
AVG + SD
19 + 7

Range of Samples
6 - 31
 | 1%   
19 + 1

5%  
21 + 1

10% 
19 + 1 | 1%   
23 + 3

5%  
20 + 3

10%  
21 + 4 |
| 
Gypsum
(% Area) | 
AVG + SD
10 + 4

Range of Samples
4 - 19 | 1%   
9 + 0

5%  
8 + 1

10% 
9 + 0 | 1%   
10 + 2

5%  
9 + 2

10%  
10 + 2 |

***Study Results***

- * Removing two extremely high values from NJ and LI

## Slag Wool Results

- Extremely high values from NJ and LI

## Slag Wool Results (Including Preliminary Data Collected from Impacted Locations During Method Development)

## Elements of Concrete Results

## Gypsum Results

## Q: Does slag wool (defined as containing <2% iron) appear to be a good screening tool for WTC dust?

Pure WTC dust collected by USGS during Sept of 2001 contained concentrations > 10,000,000 fibers/g in multiple samples and analyses.

Deutsche Bank samples at 130 Liberty and 4 Albany had concentrations ranging from 500,000 fibers/g to 11,000,000 fibers/g in multiple samples and analyses.

Greater NYC area background samples (many sites/samples) averaged about 36,000 fibers/g.

10% spiked Deutsche Bank samples (collected in Sept 2004)  > 80,000 fibers/g.

- Pure WTC dust collected by USGS during Sept of 2001 contained concentrations > 10,000,000 fibers/g in multiple samples and analyses.
- Deutsche Bank samples at 130 Liberty and 4 Albany had concentrations ranging from 500,000 fibers/g to 11,000,000 fibers/g in multiple samples and analyses.
- Greater NYC area background samples (many sites/samples) averaged about 36,000 fibers/g.
- 10% spiked Deutsche Bank samples (collected in Sept 2004)  > 80,000 fibers/g.

***Preliminary Comments***

## Q: Are gypsum and elements of concrete good secondary screening tools for WTC dust?

There does not appear to be a distinguishable difference between levels of concrete and gypsum in background and WTC dust

- There does not appear to be a distinguishable difference between levels of concrete and gypsum in background and WTC dust

***Preliminary Comments***

## Q: What does the data say about within and between lab variability?

There is high variability within labs as demonstrated by duplicate analysis of same sample in same laboratory (up to 55%).

There is high variability between labs as demonstrated by analysis of split samples (up to 70%).

Likely sources of variability:
Procedures to homogenize a sample did not result in ‘uniform’ distribution of fibers.  Thus, the samples received are variable in content.

As some analytical interpretation is required, analysts with more experience are likely to provide better quality data than those with less experience.

- There is high variability within labs as demonstrated by duplicate analysis of same sample in same laboratory (up to 55%).
- There is high variability between labs as demonstrated by analysis of split samples (up to 70%).
- Likely sources of variability:
- Procedures to homogenize a sample did not result in ‘uniform’ distribution of fibers.  Thus, the samples received are variable in content.
- As some analytical interpretation is required, analysts with more experience are likely to provide better quality data than those with less experience.

***Preliminary Comments***

## Preliminary Comments

- _Q:  __Given these results, specifically on slag wool and variability, can a WTC Dust Screening Method be based on slag wool alone?_
- A limit could be established for slag wool that would ensure minimal or no false negatives, while keeping a reasonable level of false positives.
- Any unit showing a slag wool level above this limit, as well as a COPC exceedance, will be offered a cleaning.
- A false positive is a slag wool measurement above the limit from a location not affected by WTC dust.

## Slag Wool, Fibers/Gram Dust

- 100

- 1,000

- 10,000

- 100,000

- 1,000,000

- 0

- 1

- 2

- 3

**Slag Wool, Fibers/Gram Dust**

- Background

- 10% 4 Albany

- 5% 4 Albany

- 1% 4 Albany

- 10% USGS

- 5% USGS

- 1% USGS

- Impacted

- Background

- Spiked Samples

- Impacted

**6.5% False Positive Rate**

**75,000**

## Slag wool appears to be an indicator for WTC dust.  A limit for this material could be established for screening purposes  Elements of concrete and gypsum have little correlation with level of WTC dust. 

Within lab and between lab variability was high.

Despite this variability, the method (using slag wool) appears to be sensitive enough to distinguish 10% WTC dust from background.

Most labs were able to complete the work in a reasonable timeframe.

Additional evaluation of the data will be performed to understand variability, and suggestions will be made to reduce variability in the future.

- Slag wool appears to be an indicator for WTC dust.  A limit for this material could be established for screening purposes  Elements of concrete and gypsum have little correlation with level of WTC dust.
- Within lab and between lab variability was high.
- Despite this variability, the method (using slag wool) appears to be sensitive enough to distinguish 10% WTC dust from background.
- Most labs were able to complete the work in a reasonable timeframe.
- Additional evaluation of the data will be performed to understand variability, and suggestions will be made to reduce variability in the future.

## Next Steps

- Study design and results are being subjected to external peer review by independent experts who have not been involved with the program.
- Expert panel will also be reviewing the study results.

## Next Steps

- Based on comments from the panel and peer reviewers, a decision will be made as to the validity of the screening method and its potential for success in determining residual WTC dust contamination.
- Once panel and reviewer comments are received, a slag wool limit will be decided based on comments, data and variability findings.