This time of year lots of clients call us up and ask about sampling snow melt for their stormwater sample as per their stormwater permit. It's an interesting question, and one we'll discuss below.
It’s nearing the end of December, and chances are, your quarterly stormwater sample is due. Only thing is, the ground's frozen, there's ice everywhere, and your facility is covered in snow. What do you do?
Two words. Snow melt.
Most, but not all, stormwater permits will allow you to sample snow melt as a form of precipitation.
Imagine this scenario: It's a warmer day, the sun starts hitting a snow patch, and you finally see a trickle of water heading towards your stormwater outfall, so you decided to sample. If the snow melt is melting fast enough, and flowing good enough, there's a chance you could get a stormwater sample during this monitoring period.
Complications with using snow melt for stormwater samples
While it sounds easy enough, there are some restrictions and complications with using snow melt for stormwater sampling.
- Nearly all NPDES stormwater permits have some sort of time limit on when stormwater discharge samples must be taken. When it rains, you can keep an eye on your outfall to know when it starts to discharge. When snow starts melting, you might have no idea. It's important to keep an eye on your outfall if you're in a jam and need that sample. Make sure you get it in the time limit or else the sample is no good.
- You might need to record precipitation event information which might be very confusing for snow melt. For example, you might have to record and report data such as when the precipitation event began, how much precipitation there was, length of time since prior precipitation event, etc. When you are faced with a pile of snow that may represent several storm’s worth of snowfall over the past days, weeks or months, determining this kind of information can be very tricky, if not downright impossible to figure out.
- There's always the chance your NPDES stormwater permit may not allow you to sample snow melt. For the reasons discussed above, sampling snow melt discharge can be a very tricky thing, and many permits recognize this by not allowing it, or at least very strongly discouraging it. If you're permit says you cannot take a snow melt sample, don't bother taking one.
So what should you do instead? As we have said many times, stormwater sampling for stormwater permit compliance should be done according to a plan. Don't do it last minute. Think ahead, and do it as early as you can. It not only gives you breathing room, but can alert you to poor site conditions (which would cause you to get a bad sample), giving you time for resampling and reporting flexibility.
But the bottom line is this. If you are supposed to get a stormwater sample, most times you need to get it no matter what. Make it easy on yourself and do it when it’s not frozen or snow-covered, but if you must, watch for a sunny day and wait for that snow to melt!