Environmental Engineering Reference
In-Depth Information
Table 11.6 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 (option1
—
Tier2)
0.0000
NA
a
Ottawa 1 to 4 L samples 30 min stagnation (option 2) versus Ottawa
rst
liter samples 6 h stagnation (option1
—
Tier 1)
a
Due to no first liter samples above 10
g/L
μ
Table 11.7 Comparison of option 2 versus option 1, Tier 2
Ottawa 1 to 4 L samples
30 min stagnation (option 2)
Ottawa 1 to 4 L samples 6 h
stagnation (option 1
—
Tier 2)
Total number of samples 316 120
No. of samples >10
μ
g/L 14 22
Min 0 0.3
Max 16.9 31.0
Average lead (
μ
g/L) 3.5 6.4
Note Average lead under Option 1, Tier 2 is almost 2 times greater than that of Option 2 under the
new Federal guidelines. An increase of 8 samples above 10
g/L is observed when 6-h stagnation
μ
protocol is used instead of 30-min stagnation protocol
Table 11.8 Comparison of option 2 versus option 1, Tier 1
Ottawa 1 to 4 L samples
30-min stagnation (option 2)
Ottawa
first liter 6-h
stagnation (option 1
—
Tier 1)
Total number of samples
316
30
No. of samples >10
g/L
14
0
μ
Min
0
0.7
Max
16.9
7.7
Average lead (
μ
g/L)
3.5
3.2
Note Option 1, Tier 1 samples had no samples with lead over 10
g/L; 14 were found for Option 2.
μ
Recall that 22 samples were above 10
g/L for the
first 4 l under 6-h stagnation. Since Option 1,
Tier 1 samples had no samples with lead over 10
μ
g/L came from
samples 2 L to 4 L under the 6-h stagnation protocol (Tier 2). That is, even though we may not
nd
problem properties or houses associated with Option 1, Tier 1 there can be problem properties or
houses when Tier 2 is applied. However, Tier 2 is not applied unless more than 10 percent of sites
have lead over 15
g/L, the 22 samples over 10
μ
μ
g/L under Tier 1. Therefore, there can be many properties or houses that have
high lead concentrations in later liters but we may never
find out that this is the case since Option 1
Tier1 may never detect problems via the
first liter only. Option 1, Tier 1 underestimates the extent
of the lead corrosion problem
μ
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