NYC-WTC_000195194

NYC 9/11 Public Portal Document

data. Overall, it appears that there may be a decreasing trend in the average number of cleaning events required to meet the clearance criteria based upon the degree of pre-cleaning contamination.

Residential Units that are More Heavily Contaminated (Lower Sum of Ranks) Required More Cleaning Events to Achieve the Clearance Criteria^ UnU Observable Cleaning Times Sum of Numeric Cleiin^ itarijki Grouping Grouping Grouping ■■III 5A significant 3A,3A,3B 3B,3B 2 liiilli 2i7: 2;7: minimal 3C significant iA,lA,3B 3 2,2 3D significant 1A,1A 2 4D significant 2A.2A 2 1.7 significant ddd/dHiA/./dY 1.6 liilill minimal 3A 1 ■ Odldd^ minimal 1B,1B 1.3 5D significant 3B 1 34 1.3 il;3 3B minimal 2 34 3A minimal 2B 35 1.7 minimal 2,2d2OA/2dH 45

It should be noted that there were two units in which the test was changed for the third cleaning event. Unit 3C was cleaned twice using Test 1 A. Test 3B was used for the third cleaning to achieve the health-based benchmarks. Unit 5C was cleaned twice using Test 3A. Test 3B was used for the third cleaning to achieve the health-based benchmarks. It is unclear if the change in the method, the additional cleaning event, or a combination of the two, was responsible for meeting the health-based benchmark.

^^Using the rankings presented in Table 10.0, a semi-quantitative evaluation was made to determine if there was a difference in the number of cleaning events needed to meet the clearance criteria based on the measured concentrations of pre-cleaning contamination. The average number of cleaning events required to meet the clearance criteria was calculated using several different groupings of the sum of ranks. The first set of calculations used numeric breakpoints of 10-19, 20-29, 30-39, and >40. This grouping indicates a decreasing trend in the average number of cleaning events required. The second set of groupings used the mid-point 23.5. 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 data. Overall, it appears that there may be a decreasing trend in the average number of cleaning events required to meet the clearance criteria based upon the degree of pre-cleaning contamination. 112

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