What sources contribute to zinc in stormwater?
Are there possible contributors to zinc in our stormwater, other than atmospheric deposition from a freeway next to our facility?
Request by: metal welding facility
This question was posed from the perspective of a small metal shop that has found zinc in their stormwater above state benchmark levels. Because they do not use zinc in their operations, they assume most of the zinc is from source(s) “out of their control”, and mainly airborne deposition from the traffic on an elevated stretch of road around their facility. Zinc is released from tire use.
While the deposition from this source is not controllable by the facility, some zinc can be removed from runoff or stormwater through readily available stormwater treatment.
Sources of zinc in urban runoff have been extensively studied. A contact at the California Stormwater Quality Association (www.CASQA.org) found more than 125 references on this topic in preparing a zinc stormwater source identification study (not yet released as of June 2012). The author states that preliminary conclusions are that the major sources identified are galvanized surfaces (roofs, gutters, flashing, fencing, guard rail, and downspouts and drainage system/pipes, etc.), and wear debris from vehicle tires.
Other local sources, can be very important if they occur at or near a location, such as:
- Anticorrosion paint (often used on exterior steel) that contains zinc
- Zinc moss killers applied on walkways, decks, and roofing (and sometimes impregnated into non-metallic roofing materials)
- Air deposition from local air emissions sources (e.g., galvanizers, glow-in-the-dark product manufacturers)
- Spewing of material like tire wear debris that is re-suspended from roads (particles are large, so this only applies right next to major roads).
- Fertilizers (most likely if over-applied or an unusually high-zinc material)
- Marine antifouling coatings (usually used primarily in or near salt water)
- Wood treated with preservatives containing zinc (AZCA or zinc naphthenate)
- Zinc-content de-icing chemicals
- Cleaners/surface preparation chemicals used before painting (particularly metal surfaces)
- Sediments in gutters/drainage systems (zinc levels don’t drop until these are flushed)
- Acidic emissions from a plant where the “residue” settles on a galvanized roof and contributes to more etched or release of zinc than normal exterior weather conditions may cause.
While pollution prevention is the best option, control options are available, and zinc tends to be relatively readily removed by typical stormwater treatment devices, including filtration and some drain inserts. Note that treatment for zinc removal may be ineffective for some other metals like copper. See references below to find out more on treatment options.
Additional Research and Resources
- A Survey of Zinc Concentrations in Stormwater Runoff (2006), Washington Department of Ecology
- EPA’s NPSINFO, e-Forum Resource Center offers a venue to share practical experiences and discuss nonpoint source pollution (NPS) control issues with others
- Metals Removal Technologies for Stormwater: Filtration (no date), Penn State & University of Alabama.
- Suggested Practices to Reduce Zinc Concentrations in Industrial Stormwater Discharges (2008), Washington State Department of Ecology.
- Stormwater Filtration Media Testing for Metals Removal and Toxicity Reduction (no date), Port of Seattle, Parametrix, and Taylor Associates.
- Stormwater Source Control and Pollutant Removal/Reduction (May 2012), Washington Stormwater Center.
- Literature Review of Existing Treatment Technologies for Industrial Stormwater (July 2011), Prepared by Herrera Environmental Consultants for Science Applications International Corporation and Washington Department of Ecology.