We've been diving into pH in stormwater lately because we've been getting a lot of questions on it. It can be somewhat confusing, so hopefully we're helping to ease the problems with testing the pH in your stormwater sample with these posts.
In most NPDES stormwater permits, you're required to monitor your stormwater discharges for pH. The USEPA has established specific protocols and standard methods for how to monitor the pH of a stormwater sample. One criteria of these methods is the time limit set for which you can perform the analysis, which is 15 minutes. As soon as you obtain your stormwater sample to be analyzed, the clock starts and you have 15 minutes to run the test. As a State Certified Environmental Laboratory, we know just how fast those 15 minutes disappear.
Here are the reasons why 15 minutes matter, and how to make them count!
So why 15 minutes? USEPA Standard Methods.
The specific testing method protocol for testing pH of a stormwater sample is SM 4500-H-B-11. This method describes how to measure pH and since most NPDES permits require you to monitor for it, you’re going to have to comply with these methods. It tells you how to calibrate your meter, how to obtain your sample, and that you only have 15 minutes to perform the analysis.
But do 15 minutes really matter?
The answer is yes! The USEPA set 15 minutes as the window to perform a pH analysis of a liquid because the pH of a liquid can actually change over time. The longer a sample sits reacting with the air around it, the greater the chance the pH value of that liquid will change.
It’s a simple chemical equation. The air surrounding us contains carbon dioxide (CO2), and when given the chance to be absorbed by a liquid (H2O), a weak acid will be produced, carbonic acid (H2CO3).
Carbonic acid changes the pH value of any liquid. More interaction time means more change, which is why the USEPA set 15 minutes for the time limit to perform the pH test.
What you can do to make the most of 15 minutes!
Have your equipment set and ready to go. Since you only have 15 minutes it is very important to be prepared to perform the analysis. We strongly recommend that you have your pH meter calibrated before obtaining your sample. We also recommend you use an accurate and reliable pH meter. The calibration of a pH meter can take upwards of 15 minutes alone, so trying to squeeze that in after you get your sample while the clock is ticking is not a good idea. Have your meter calibrated and have any paper work or forms ready to be filled out as you perform the analysis.
And practice. Practice practice practice. Everyone has heard that before, but practice performing the analysis, either by sampling random liquids, or learning how to use the meter through the calibration process, will give you the ability and knowledge to perform the test fast and smooth each time. Since 15 minutes is all you get, learn to make each minute count!
Sampling the pH of stormwater can be tricky the first few times around. If you're struggling to get the pH of your stormwater samples, click here to contact us or give us a call at 609-693-8301 to discuss your needs.