Environmental Engineering Reference
In-Depth Information
Appendix
New Federal Guideline Option 2 (30-min stagnation, four 1 l samples) compared to
new Federal Guideline Option 1 (6 h stagnation, one 1L sample
—
Tier 1, four 1 L
—
samples
Tier 2)
The objective of this Appendix is to check if the two main lead sampling protocols
are the same or whether they are different. If they were the same, then it would not
make any difference whether the 6-h stagnation protocol was used or whether to 30-
min stagnation protocol was used. To do this statistical test, we consider the entire
distribution of each and test to see if the proportion of samples greater than 10
g/L is
the same in the two distributions. To carry out this test, we use a two-tailed test.
μ
(1) The proportion of samples >10
g/L for Option 2 (1 to 4 L, 30 min stagnation)
versus proportion of samples >10
μ
g/L for Option 1 (6 h stagnation, one 1 L
sample, Tier 1, four 1 L samples, Tier 2)
μ
(a) Consider each sample as a separate sample in Table
11.3
.
Next, see Table
11.4
.
Since the null hypothesis is rejected (with a p-value of zero), we can conclude
that the proportion of lead above 10
g/L for samples (1st to 4th liter) from Ottawa
μ
6 h stagnation (Option1
—
Tier 2) is signi
cantly different from the proportion of
Table 11.3 Separate samples
Ottawa
first liter
samples 6 h
stagnation
(Option1
—
Tier 1)
Ottawa 1 to 4 L
samples 6 h stagnation
(Option1
—
Tier 2)
Ottawa 1 to 4 L
samples 30 min
stagnation
(Option 2)
Total number of
samples
30
120
316
Number of
samples >10
μ
g/L
0
22
14
Proportion of samples
where lead >10
μ
g/L
0 percent
18.3 percent
4.43 percent
Table 11.4 Testing the hypothesis that the proportion of samples above 10
μ
g/L is different (Null
hypothesis: the population proportions are equal)
Proportion of samples above 10
g/L
Two-tailed
p-value
μ
Ottawa 1 to 4 L samples 30 min stagnation (option 2) versus Ottawa 1 to 4 L
samples 6 h stagnation (option 1
—
Tier 2)
0.0000
NA
a
Ottawa 1 to 4 L samples 30 min stagnation (option 2) versus Ottawa
rst
liter samples 6 h stagnation (option 1
—
Tier 1)
a
Due to no first liter samples above 10
g/L
μ
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