List of clean-up contractors, WTC site, Aug 2002

NYC 9/11 Public Portal Document

4. Sampling equipment shall be placed at representative locations and away from obstruction. Sampling cassette must be placed on a tripod and not taped to existing surfaces. All air sampling equipment shall be pre- and post- calibrated to insure accurate air sampling volumes.

5. The Air Sampling Technician shall perform clearance air sampling after the areas are free of dust accumulations as determined by the Project Monitor. All surfaces must be completely dry prior to the start of sampling. Clearance air sampling shall be performed at each apartment. Five samples shall be collected in each apartment and two samples shall be collected in each common space. The elevator shaft and first floor commercial spaces shall be cleared separately. Clearance air monitoring shall be performed after the completion of all clean up activities at the work site. Clearance air sampling shall be aggressive and performed in accordance with Title 15, Chapter 1 of the RCNY Section 1-43 (a)-(d).

6. Clearance air samples shall be collected in accordance with the procedures specified in the NIOSH 7400 Method. The flow rate for collection of air samples shall be at least 10 liters per minute and no more than 15 liters per minute. Air sampling cassettes must be monitored to ensure the filters do not develop dark spots that would indicate clogging. The minimum sampling volume is 3600 liters. If clogging develops, the cassette must be changed.

7. All clearance air samples and completed chain of custody forms must be transported to the laboratory immediately after sampling is completed.

Clearance Criteria

1. The following clearance levels have been established by the USEPA for clean up activities resulting from the collapse of the WTC.

Parameter Clearance Level Note Asbestos in air 0.0009 f%cc PCMe Primary clearance level Lead in settled dust <25 ft2 Primary clearance level Dioxin in settled dust <4ng/m2 Primary clearance level Fibrous glass in air <0.01 flcc Secondary clearance level Crystalline silica in air 0.5g/m3 Secondary clearance level PAHs in settled dust <0.3 mg/in2 Secondary clearance level Mercury between 1 and 2 mg/m2 mg/m2 Secondary clearance level

2. Cleaning shall not be considered compete unless the primary clearance levels are achieved. The apartment will be re-cleaned and retested if the primary clearance levels are not achieved. These clearance levels may be re-evaluated and revised if determined necessary based on field conditions and analytical limitations. Secondary clearance levels shall be considered in determining the need for additional cleanup, however failure to meet the secondary clearance levels does not automatically trigger the re-cleaning.

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NYC-WTC 000108808