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How roofs can add pollutants to your stormwater.

Inspecting and properly maintaining your roof is an important industrial source control BMP. There is a lot of talk about roofs as an important structural BMP used to separate stormwater from potential sources of contamination. This is true, roofs and coverings are incredibly effective at pollution prevention, however, choosing the wrong roofing material or performing poor or infrequent maintenance on your roof can lead to the release of pollutants in your stormwater discharge.

Metal Roofs are a common choice in industrial areas due to their longevity and durability. These roofs, however, can be a contributor to metals such as zinc and copper. Galvanized Roofs are a prime example of this. These roofs are made by coating iron in a layer of corrosion inhibitor containing zinc. This zinc can slowly leach out into stormwater as it rains leading to elevated zinc concentrations and even benchmark exceedances. Painting or otherwise coating your galvanized roof is an effective way to prevent this zinc from leaching into your stormwater, however, this coating needs to be inspected and maintained over the life of your roof.

Shingle roofs often accumulate unsightly moss or algae in the Pacific Northwest. How this growth is dealt with can have a significant impact on your stormwater discharge. Many shingle producers offer “streak-free” or “algae-resistant” shingles. Be careful when choosing these shingles as they inhibit growth with granules of copper that can slowly be released into your stormwater resulting in elevated copper.

Several remedies available at the hardware store promise to remove and prevent moss or algae from your roof. Many of these come in powder form or a spray that you apply to your roof regularly. These work by using copper or zinc compounds that slowly release when it rains to inhibit moss growth. These copper and zinc compounds are toxic to aquatic life and can wash into your stormwater leading to elevated metals in your stormwater samples.

Other roof types can also impact your stormwater. If you have older buildings at your facility containing wooden shingles, these are often treated with arsenic and copper and can release these pollutants into your stormwater. Copper roofs and features can lead to increased copper. In 2014, Ecology ran a study looking at many different roof types and their impact on stormwater. Read the study here.

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