I have a science question?

Nitrates usually come from fertilizer run-off.It's a good thing that your reading was zero.(These are most probably parts per million)Most of these are generally by-products of industrial waste.Chlorine is actually bleach,like the stuff used to whiten clothing.It makes a great disinfectant.I'd be curious if they were testing for free,combined or total chlorine.Since you just took what's known as a grab sample,it's possible that some of those chemicals could be present or not at different times of the year depending on weather and other activities.