Chain of custody form for DEP environmental samples, 2001

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.

lilliiii Iilil M n ♦a

................ ..............j Ml rimes Sum<^ Mid-point iliiiliiWilisi Test Cleaned Ranks Grouping Number ________ Ml I 5A 3C iiiiili mimmat 3B.3B 1A,1A,3B iliii|3liill lAlA iBiiiii s 20 2.7

lliiiBiiii liliBlii 3A iHOttmal 3B 34 1.3 1.3 minimal iiiiiiiiBiii 1 fflii’Willi I iilil minimal liiHl................. ililiiBilll 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.

^^sing 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

NYC-WTC_000145810