Stormwater suffers from the “Outta sight, outta mind” issue. Once it’s gone from my view, it’s gone, right? Of course we know that is incorrect. Its disappearance from the pavement into a conveyance system is really just the start of the earthbound portion of its cyclical life. Let’s take a look at the various ways that stormwater may be headed once it leaves your site.
Once gone from the ground surface, stormwater may have a myriad of fates. On a developed site that was constructed within the last 15 years or so, the stormwater likely goes through a manmade conveyance, be it a ditch or pipe. Once in the manmade channel, it may be routed to a stormwater quality system of various kinds. There are many proprietary systems that can be purchased and installed in a storm system, and there are also systems that are built into the ground right on the site.
Each stormwater quality systems has as its main goal the cleaning of stormwater. However, that does not mean that all stormwater quality systems are created equal. Stormwater can be subject to a wide variety of pollutants. Industrial sites can create one type, commercial sites another type, roads still another. As a result, water quality systems are different. Some remove only oils, others remove only sediments, still others only suspended pollution. Very few try to remove multiple pollutants at once. No system removes all pollutants.
The way stormwater systems endeavor to do their work is as varied as the types of pollutants they remove. Some do their work by keeping water still for some time while solids settle out, others by swirling the water around in a circle and concentrating the pollutants in the center, others by running them through a filter. There are many different types of water quality systems.
Most sites have very little in the way of water quality. Sites built before 15 or 20 years ago don’t have much at all. Some may have a down-turned elbow in the catch basins, intended to keep most of the oil floating on the top of the basin while allowing the cleaner water to flow out. Others count only on the catch basins to remove pollutants.
Once the water flows through whichever type of water quality is present (or not present), the stormwater is then discharged from the site somehow. Sometimes that means the stormwater goes directly into the ground, other times into a centralized conveyance system on its way to a local water body, and still other times directly to the water body from the site.
Now is the time when stormwater can begin to do some damage. If the water has not been treated well for its pollutant load, that pollution can find its way into the rivers, streams, lakes, and oceans in our environment. There it can kill marine life or worse.
Stormwater is a complex topic. We all know that its not just gone once it leaves our pavement. Stay tuned to continue to learn more about stormwater and the various issues it raises.