| While water
quality reports from Arizona Water Company indicate that dichloromethane
was detected in the Oracle water supply at a concentration of 0.6 parts
per billion (ppb), the actual amount present could have been twice that
amount or 1.2 ppb.
The Maximum Contaminant Level (MCL)
set by the EPA for dichloromethane is 5 ppb.
A contamination level of 1.2 ppb
would represent 24% the Maximum Contaminant Level for dichloromethane.
Samples of water to be analyzed
for contaminants are taken where the water is deposited into the distribution
system. The point where water enters the distribution system is called
a Point of Entry (or POE).
According Arizona Water Company
officials, the water supply for Oracle has two POE's. In 1997 samples
of water were taken from each of the POE's for Oracle then combined prior
to being analyzed for contaminants. |
Combining
samples reduces the number of tests that have to be conducted, and lowers
testing costs.
However, combining two water samples
into a single composite sample could result in diluting the composite sample
making it appear that the amount of dichloromethane detected was only half
as much as was actually present.
For example, if the water sample
taken at POE #1 had a contamination level of 1.2 ppb and the sample taken
at POE #2 had a contamination level of 0 ppb, the composite sample would
show a contamination level 0.6 ppb, half of the amount actually present.
The water found to have 0.6 ppb to 1.2
ppb of dichloromethane comes from the same aquifer that supplies SaddleBrooke
and several other communities. |
