Chain of custody form for DEP environmental samples, 2001

NYC 9/11 Public Portal Document

5.6 Multiple Cleaning Events

The results indicate that meeting health-based benchmarks is achievable using the methods identified above, although they also indicate that multiple cleaning events (from one to three times) may be needed to achieve these benchmarks. The incremental increase in the number of residential units that met the health-based benchmarks is presented in Table 12.0. The data shows that dioxin and PAH met the health-based benchmarks after the first cleaning for each unit and that the majority of the units (92 percent) met the health-based benchmarks for MMVF and alpha­ quartz after the first cleaning. The number of cleaning events required to meet all of the health­ based benchmarks for each unit are presented in Table 4.0. This table illustrates that multiple cleaning events may be needed to meet the health-based benchmarks for each compound.

Compound Pre-^Cleaning First Second Third Oeuning Cleaning

2/2(100%> 4/4 (100%) ”■ iijiiiiii 3/13(23%) 9/13(69%)

Vf* 12/13/(92%) 0/2(0%)' 2/2 (1 lllljllll Mil 12/13 (92%) 1/1 (100%) lllilill III iiiliiS ;..................................................■

MMMM ’ * _________ illliiili 10/13 (77%) 13/13 (100%

An analysis was also conducted to examine if the degree of pre-cleaning contamination affected the number of cleaning events required to meet the health-based benchmarks. Table 13.0 below presents the results of this analysis. The sum of ranks for each apartment from Table 9.0 were grouped and the average number of cleaning events for each grouping was calculated. Since there were no definitive natural breaks in the sum of ranks, three separate groupings were chosen. One was based on a numeric grouping, in which the sum of ranks were assigned to four groups (10-19, 20-29, 30-39, and 40 and above).

The results suggest that there is a decreasing trend in the number of cleaning events required. The second grouping used the mid-point to create two groups (0-23 and 24-48). This grouping also indicates a decreasing trend in the average number of cleaning events required. The third grouping divided the data into an equal number of units. Although this grouping suggests a decreasing trend for most of the groupings, the decreased trend did not continue for the last set of

^"'N/A signifies that samples were not collected before cleaning. Ill

NYC-WTC_000145809