EPA review letter, 133-135 Greenwich Street

NYC 9/11 Public Portal Document

Part II - Environmental Community Monitoring Plan 133-135 Greenwich & 21-23 Thames Streets Airtek Project 05-0701— Rev 2 September 16, 2005

range of temperature and humidity. Before being weighed, both unexposed and exposed filters must be conditioned for at least 24 hours in this environment. The exposed sample filters are transported in a cooler to limit the loss of volatile material, and are then kept in a refrigerator if they are cannot be weighed within 10 days of sampling (they still must be weighed within 30 days of sampling to be valid). Unexposed filters are taken out to the site under similar controlled conditions (usually in a cooler, although this is not necessary). • Data requirements: o Backup instruments, field staff, and supplies will be maintained throughout the monitoring duration to ensure continuous operation of monitoring stations and high data recovery. o Data quality objective: 10% coefficient of variation. The coefficient of variation, CV, is the standard deviation as a fraction of the mean: cv =4. X .

• Measures of Accuracy and Bias: o Check of flow rate o Audit by collocation with a portable FRM sampler. • Measures of Precision: o Check of flow rate o Collocation (see below). • Collocation: o Monitors have a second monitor collocated at the same site, rotated between sites. o The second ("duplicate") sampler runs every 6 days. o Collocated particulate samplers must be less than 4 m apart but more than 1 m apart. The PM2.5 sampler requires enhanced quality control measures because of its unique design and operational attributes. Examples of these QC measures include: • Filter equilibration temperature control of +/-2 °C over 24 hours • A pre-sampling filter weighing within 30 days of sampling period • Retrieving the filter from the sampler within 96 hours of collection • A post-sampling filter equilibration and re-weighing within 240 hours after the sampling period

NYC-WTC 000134257