Confronting the Problem of Lead in Drinking Water: What Can and Should Be Done - Global Drinking Water Management and Conservation - page 245

Table 11.5 Four consecutive liters under options 1 and 2
Ottawa first liter
samples 6 h
stagnation
(option 1, Tier 1)

Ottawa 1 to 4 L
samples 6 h
stagnation
(option 1, Tier 2)

Ottawa 1 to 4 L
samples 30 min
stagnation
(option 2)

Total number of samples 30 30 79

Total number of
samples >10

0 22 14

g/L

μ

Proportion of samples
where any liter contains
lead > 10

0 percent 73.3 percent 17.72 percent

g/L

μ

Number of samples where
avg lead >10

0 3 3

g/L

μ

Proportion of samples where
avg lead >10 μ g/L

0 percent 10 percent 3.80 percent

Note 17.7 percent of locations have lead over 10 g/L in at least one of the 4 l of drinking water

under the 30-min stagnation protocol while 73 percent of locations have lead over 10

μ

g/L in at
least one of the 4 l of drinking water under the 6 h stagnation protocol. 3.8 percent of locations had
average lead for first four samples above 10

μ

g/L under the 30 min stagnation protocol while
10 percent of locations had average lead for the first four liters above 10 μ g/L under the 6 h
stagnation protocol (option 1, Tier 2)

μ

lead above 10 g/L for samples from Ottawa (1st to 4th liter) 30 min stagnation

(Option 2) assuming each sample is independent of each other. Therefore, we can
say that the sampling protocol does matter.

μ

(b) Consider the four consecutive liters under Options 1 and 2 as one sample in
Table 11.5 .

Now consider the test in Table 11.6 .
Since the null hypothesis is rejected (with a p-value of zero), we can say that the
sampling protocol does matter. We can conclude that the proportion of lead above
10

g/L for samples (1st to 4th liter) from Ottawa 6 h stagnation (Option 1) is

μ

signi g/L for samples from

Ottawa (1st to 4th liter) 30-min stagnation (Option 2) assuming the

cantly different from the proportion of lead above 10

μ

rst to the

fourth samples are considered a collective sample.

(2) Comparison of the average for samples (1st to 4th liter) from Ottawa 6-h
stagnation (Option1) versus the average lead for Ottawa (1st to 4th liter) 30-
min stagnation (Option 2)

(a) Consider a comparison of Option 2 Versus Option 1, Tier 2 in
Table 11.7 .
(b) Now consider a comparison of Option 2 and Option 1, Tier 1 in
Table 11.8 .