I imagine your facility or storm water drainage system is equipped with a flow monitor, in which case the controller settings must be proportional to the measured flow rate so as to sample rain events only.
Exactly, so how do I ensure we get a representative sample?
It will be representative compared to the volume passing through your storm pipe. Later, if you want it to be representative in terms of pollutants, you can set up hourly profiles of the flow of pollutants (if the first hour of rain produces the biggest load), your sampler should be triggered when the water in the pipe reaches a specific height, and you should install a multi-bottle unit (24) set to initiate on a timed basis; for example, take 6 samples per hour per bottle, moving on to the next bottle for the following hour.
And if you need an average sample, you can later reconstruct your sample proportionally to the flow rate per hour slot.
I hadn’t thought of reconstructing the sample. Thanks.