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[APD] Re: tapwater NO3 survey

>The city of Chicago report for 2002 reported 0.4ppm NO3.  It was 
>reported as high as 1.8ppm back in '99.

You are confusing NO3 with NO3-N. Actually, I think many people posting
on this topic are making the same mistake. Most water quality reports
give NO3-N, meaning the amount of nitrogen present as nitrate. The "ppm"
measure is based on weight. NO3 weighs 4.4 times as much as just a
nitrogen atom. So 4.4 ppm NO3 is only 1.0 ppm NO3-N, since in the latter
case you're not counting the weight of the oxygen atoms.

I happen to have the 2002 City of Chicago report in front of me. It
reports 0.4 ppm "Nitrate (as nitrogen)", meaning NO3-N. This means that
it's 1.8 ppm NO3.

The nitrate levels (at least out of the Jardine filtration plant) have
stayed in the 0.3-0.4 ppm NO3-N range for years. The information you saw
for 1999 probably reported levels as NO3 rather than NO3-N for some

Also, others have mentioned the MCL (and MCLG) of 10 ppm. This figure is
10 ppm NO3-N, thus 44 ppm NO3.

- Jim

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