Law Department notice on WTC document preservation, Oct 2001

NYC 9/11 Public Portal Document

exposure, uncertainty, and technical limitations, that may justify a cleanup remedy that departs from the 1-in-1,000,000 cleanup goal.

In contrast to the above criteria, EPA’s Lower Manhattan indoor cleanup established a 1-in-10,000 risk as the goal of the cleanup for asbestos. The program does not include monitoring for the presence of the other COPCs, including dioxin and PAHs, which are known carcinogens. The COPC document established benchmarks for these two pollutants that also correspond to a 1-in- 10,000 increased risk. Although the assumption is that the cleaning methods prescribed for asbestos will clean the residence of other pollutants as well, the post-cleaning testing does not provide assurance that these other pollutants were removed. However, under Superfund guidance, the risk from exposure to multiple carcinogens is considered additive. Thus, if all three pollutants were cleaned up to levels that equate to a 1-in-10,000 risk for each pollutant, the combined risk would be considered greater than 1-in-10,000.

The TERA peer review addressed the risk level established for the COPCs. The panel suggested that the document more clearly explain how the impact of being exposed to mixtures of the COPCs was considered in developing the benchmarks. Further, panel members disagreed with the rationale for using an upper level excess lifetime cancer risk of 1-in-10,000. The workgroup’s response to the peer review panel stated the risk level was appropriate because of practical sampling limitations for asbestos, noting a sampling time of 800 hours would be required to achieve the air monitoring results needed to support a 1-in-1,000,000 increased lifetime risk level. The workgroup acknowledged that running multiple pumps concurrently could reduce total sample time, but did not judge this practical since more than 6,000 individual residences signed up for the cleaning program.

Need to Treat Impacted Buildings as a System

Tests of indoor asbestos contamination have shown that the distribution of asbestos within indoor spaces is not consistent. Selective cleaning of apartments does not ensure that uncleaned residences or uncleaned objects in apartments are free of asbestos contamination. In the case of centralized HVAC systems, selective cleaning does not ensure that cleaned apartments will not be re-contaminated by uncleaned apartments through the HVAC system. Consequently, the cleaning of contaminated buildings should proceed by treating the building as a system.

This systematic approach to cleaning would require that the exterior of the building be cleaned first before the building is re-occupied. All possible entrances for outside air should be sealed off and the building HVAC shut down during exterior cleaning. Once the exterior is cleaned, interior cleaning can begin. For buildings with centralized air and heating, the interior surfaces of supply ducts and return air plenums, fan housings, and filter housings should be cleaned. Filters should be removed, filter tracks cleaned, and new filters installed. The above

51 Report No. 2003-P-00012

NYC-WTC_000145571