EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

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 lE-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 incoiporating 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/m^. 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 fi-om that which is documented.

For fibrous glass the methodology is such that detection levels as low as 0.00001 fZcc 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

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