Zinc Sources in Industrial Stormwater
Zinc can be a particularly problematic compound for industrial sites to deal with, because the source of zinc in stormwater is often hard to determine. Industrial stormwater often contains a mix of metals, sediment, oil & grease, and other potential pollutants with many potential sources from your industrial site or your neighbors (or nearby non-industrial operations).
Potential Zinc Sources
Zinc can come from your own processes (e.g. plating), but many times the source is not readily apparent. If you operate a facility with exposed soil or maybe in an area with mining operations, zinc could be coming from naturally occuring sources in the ground. Aerial deposition from building material processing or even track out from neighbors (and then track on to your site via trucks or employee vehicles) could be the source of your troubles. Likewise, galvanized fences, roofing, and sidewalls could be leaching zinc into your stormwater system. Finally, forklift tires can contain zinc from the rubber vulcanization process…forklifts that turn and pivot a lot grind small particulates of rubber (with zinc) off and leave it on the ground surface. As if that was not enough potential sources, motor, lube, and hydraulic oil can be another potential source of zinc (along with other metals) and additives are a topic of much debate in the motor industry.
What is a stormwater superhero to do?
For galvanized metal surfaces, painting can reduce the surface contact with stormwater. Likewise, looking at stormwater piping and sample points to ensure there are not galvanized parts right before sampling might help. Aerially deposited dust with zinc compounds can be washed off of the roof on a regular basis. Why? Zinc issues often go hand in hand with sediment issues. Remove the sediment and you remove (most of) the zinc. In addition, zinc filters, which usually contain zeolites, can be installed on roof downspouts to remove zinc prior to discharge on the ground surface. A planter with a nice looking tree/shrub can go a long way towards removing roof sediment from runoff and the zinc that might be in it. The best BMP around, housekeeping, can do a lot towards keeping sediment and zinc particulates out of the stormwater system. Regular sweeping and not just a quick whisk, but a deep sweep weekly or monthly, does wonders. Just make sure to get into the corners, crannies, and along the curb to grab every last bit of sediment that lurks. Lastly, it may be worthwhile to re-route employee traffic or designate no drive zones in industrial areas if track-on is an issue.
How do you prevent the zinc from getting into stormwater from motor oil (zinc from this source usually shows up as dissolved zinc in stormwater samples)? You can swaddle your truck or equipment just like you do a newborn. No really, truck diapers can work. Also, a robust preventative maintenance program, aggressive clean up methods, and a kick-ass training program (e.g. pre-trip truck inspections and immediate repair of drips) all help.
Tried all the above and cannot get the zinc out of your samples?
Look to your neighbor next. Is run-on coming from their site, which may or may not have a permit and probably does not take stormwater as seriously as you? What about the historical sediments in your stormwater system? When was the last time you gave your stormwater system a deep clean? Jet and vac anyone?
Finally, still stumped?
Try x-ray flourescence (XRF) to trace back potential zinc problems to the source.