Environmental Engineering Reference
In-Depth Information
11.3 What the Regulatory Maximum Level of Lead Should
Be in Ontario
11.3.1 Overview
In the previous chapter, it was argued that the 30-min Stagnation protocol for
sampling lead is inappropriate and wrong. It has been suggested that Ontario
adopted this protocol after an Advisory Committee recommended it. But the
advisory committee relied largely on the EU Report, which was roundly criticized
in Chap. 10 . The advisory committee was told of some other constraints as to why
the consumer could not be allowed to take a 6-h stagnation sample, which would
typically have to be taken by government employees at 6 am.
If the logistic dif
culties do not make a 6-h stagnation sample possible, then
perhaps the maximum allowable contamination level of 10
g/L should be lowered.
What should that lower level be, if Ontario is constrained to continue to use the 30-
min Stagnation sample? We take a statistical simulation approach to answer this
question, using the limited available data to carry out some experiments. In other
words, we want an estimate of the new lower MCL, as if the 6-h stagnation sample
had been used. We use data from the City of Ottawa where 6-h stagnation samples
have been taken. Unfortunately, in this exercise, the samples were taken after they
had added caustic soda to raise the pH level, in order to reduce lead from leaching
into the drinking water. Hence, the
μ
first step is to consider the relationship between
lead leaching and pH. We attempt statistically to
the pH to the Ontario
Average, and then use the distribution on lead sampling to simulate what the new
reduced
reduce
or MCL should be. The result is instructive and suggests a
change in policy, after scienti
cut off,
c and chemical validation.
The estimation is carried out in three sections as follows:
(1) Section 11.3.2 : The estimation of lead from Ottawa samples that would re
ect
the average pH values for the rest of Ontario and an analysis of samples before
and after pH adjustment.
(2) Section 11.3.3 : The simulation of lead for the
1 30 min
stagnation samples to 6 h stagnation samples and an analysis of samples
before and after stagnation time adjustment.
(3) Section 11.3.4 : The estimation of the possible lower contamination level.
'
rest of Ontario
'
Then in Sect. 11.4 , we present some caveats on the limitations of our simulation
exercise.
Recall that our overall aim is to simulate and estimate lead values from samples
under the 30-min Stagnation protocol for the
'
rest of Ontario
'
in such a manner that
the outcome re
ects what it would have been if a 6 h stagnation protocol had been
1 Rest of Ontario refers to samples taken from the Ontario Tap Water Order for 36 Municipalities
in 2006 and samples which are not from Ottawa ' s Customer Lead Pilot testing done in 2006/07.
Henceforth, rest of Ontario refers to this de nition.
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