If I had a dollar for every time I heard this, I'd be rich. We get asked "what do my stormwater monitoring results mean?" all the time.
Great question, because the answer is very, very important. Simply put, your stormwater monitoring results will mean the difference between being in compliance, or being out of compliance and possible enforcement. A bad sample can lead to laborious stormwater treatment or additional stormwater BMPs.
Since you don’t want to waste time or money by being out of compliance it’s important you understand one of the most basic environmental benchmarks out there today – stormwater monitoring results.
Most NPDES stormwater permits require some form of stormwater sampling and testing. It might be once or twice per year, quarterly, or very rarely, monthly. There’s usually some restrictions on when your sample can be taken, and certainly on where it can be taken. Normally, stormwater samples should be taken at designated outfall locations during a valid storm event, all depending on the specifications in your state's stormwater permit. And, you likely have to have your samples analyzed by a lab for common pollutants. After the lab analyzes your stormwater samples, you'll get your stormwater results.
But what do you do with stormwater results when you’ve received them back from the lab?
Many NPDES stormwater permits utilize a concept called benchmarking when it comes to stormwater results. Benchmarks are very different from limits, which are enforceable. Benchmarks are target levels of pollutants that a facility should expect to be able to stay under provided they have properly implemented a program of effective stormwater BMPs. Exceed them, and you need to fine-tune your stormwater BMPs, depending on site specific conditions. Due to the variable nature of stormwater runoff, that’s why benchmarks are usually used.
For the more controlled (and more polluted) discharges of wastewater or process wastewater, results are almost always judged against limits. Part of the reasoning for this is that it is expected that the technological fixes used to treat process wastewater should be capable of delivering high quality runoff, and you’ll be penalized if you don’t.
In other words, exceed a limit, and you’ll get in trouble. Exceed a benchmark, and you'll get in less trouble.
Your first step is to take a look at your NPDES stormwater permit, and determine your benchmarks or limits, and figure out what they are. Highlight them in the permit, post them on the wall, do whatever you need to do to get familiar with those numbers! Whenever you get a stormwater sample, you should compare your results to the target values of your permit. If you exceeded those numbers, figure out why and what you can do to improve via your stormwater BMPs. If you are below the benchmarks you can rest easy. Keep doing what you're doing!
We usually advise those with stormwater permits to make a chart, and enter all data by date along with the applicable benchmark values. That way, you can continually keep tabs on how you’re doing all year long. In some states, NPDES stormwater permits require reporting of benchmark exceedances along with a plan of attack on how you expect to stay below the level in the future via enhanced BMPs. Bottom line is learn your regulations and do what's necessary to stay in compliance.
The only way you’re going to know where you stand and where you need to go relative to your NPDES stormwater permits is by digging into those stormwater results every time you get them, comparing them to your benchmark, and see what your next step is. Getting those results and just burying them in a file or your stormwater plan won’t help you at all, and will leave you at the mercy of your environmental agency.
If you're unsure about where you stand with stormwater monitoring results, or need help on understanding you stormwater permits, click here to contact us, or call us at 609-693-8301 to discuss your stormwater permit needs.