Emerging Best Management Practices In Stormwater .

Emerging Best Management Practicesin Stormwater:Addressing GalvanizedRoofingIntroductionStormwater is the leading contributor towater quality pollution in WashingtonState.1 For this reason, the WashingtonDepartment of Ecology requires businesses andmunicipalities to control stormwater pollutants,such as heavy metals and organics. Strictlimits on zinc require a number of Washingtonorganizations to use source control or treatmentmeasures to reduce zinc in runoff. Accordingto Lisa Rozmyn, the Washington StormwaterCenter’s Business Resource Manager, “Zinc isdifficult to control because it’s everywhere inindustrial sites and equipment.”With support from the Russell FamilyFoundation, the Pacific Northwest PollutionPrevention Resource Center (PPRC) is helpingbusinesses navigate a tangle of emergingzinc-reduction technologies and techniquesto achieve acceptable stormwater quality. Asan unbiased non-profit resource, PPRC seeksto promote stormwater practices that areeconomically and environmentally beneficial.This report focuses on reducing zinc runofffrom galvanized roofs. It is one in a series thatexplores emerging techniques and practices tomanage zinc in stormwater. Other report topicsinclude: Biochar as Filtration Media; MitigatingZinc in Boatyards and Street & Surface Sweepingto Reduce Stormwater Pollution.About Galvanized Roofing& StormwaterIndustrial businesses typically need costeffective roofing that covers large surfaceareas. Metal roofing, including galvanized,requires less maintenance than other optionsand has a significantly longer service life. Lowend galvanized roofing has a service life of30-50 years under normal conditions. High-endgalvanized roofing can last as long as 100 years.Galvanized roofing offers a number of benefits. Itis resistant to wind, naturally sheds snow, and isfire-retardant. Though naturally reflective, it canalso be coated with reflective paint that blocksheat transfer and helps reduce cooling costsduring warm weather. Finally, galvanized roofingis recyclable at the end of its service life, makingit a more sustainable option than many otherroofing choices. The above benefits suggest thatgalvanized roofs will remain both an option forinstallation and in service for decades to come.There are many steps in the process ofgalvanizing steel, but ultimately the steel isimmersed in a bath of 98-99 percent zinc.While galvanizing steel reduces corrosion ascompared with non-galvanized metal, all metalswill eventually suffer some corrosion. Corrosionconverts the base metal into its oxides. Inthe case of galvanized metal, contact withatmospheric carbon dioxide (CO₂) starts theoxidation process into zinc carbonates or intozinc sulfates (in the presence of sulfur dioxide,a constituent of acid rain). This unbound zincleaches off the galvanized surface and pollutesstormwater runoff.1www.pprc.org2101 Fourth Ave. Suite 1080Seattle, WA 98121(206) 352 2050

Any galvanized product exposed to outdoorelements, particularly precipitation, willleach zinc. Such products include: chain-linkfencing, roof flashing, gutters and downspouts.Marine environments, areas with acid rain, andcertain acidic industrial emissions contributeto conditions that can reduce roof lifespanand increase the rate of zinc migration fromgalvanized surfaces.Studies have shown that runoff from galvanizedroofs frequently contains very high levels ofzinc, especially if roofs are not coated or if thecoating has degraded. Some studies have foundreadings as high as 15,000 µg/L from the pointsource of one galvanized roof. For an industrialsite, the Washington State permit limit for zinc instormwater is 117 µg/L. For boatyards, the limitis 90 µg/L. Roofing with high zinc leachate canreadily contribute to overall levels of zinc thatexceed permit limits.Options to Reduce Zinc Runofffrom Galvanized Roofing Zinc runoff from galvanized roofing can bereduced or mitigated in several ways, rangingfrom low cost to high cost.Low Cost Measures Pressure wash the roof, gutter, anddownspouts to remove sediment, collectthe wash water and properly dispose of it.Removing this sediment before anticipatedrainy season(s) can help minimize thezinc-containing sediment that enters thestormwater system. Use water or neutralcleaners with a pH between 5 and 7. Acidicor caustic cleaners will cause a chemicalreaction with the zinc that can hasten theleachate process.2www.pprc.orgInstall high-metal-removal capacityplanter boxes or other filtration systemsat downspouts from zinc roofs. There areseveral options in both design and filtrationmedia. Some installations are simply filtersthat collect and filter out contaminantslike zinc. Among filtration media, sand andbiochar/compost mixtures have provenparticularly effective at removing zinc. ThePort of Vancouver has used easy-to-buildplanter boxes loaded with metal-absorbingplants. Each of these units treats about 600square feet of galvanized roof runoff toacceptable zinc levels.2Coat galvanizedgutters andthe interior ofdownspouts (includeexterior if not alreadycoated) or considerreplacing them withan alternative non-zincmaterial.Ensure alldownspouts arein good repair anddischarge is directedto the proper place draining to some formof filtration system.Higher CostMeasures Figure 2: This roof runoffis being directed into theground, and not to anappropriate treatmentsystem. It’s a good idea toensure that downspoutsare in good repair andconnecting to a stormsewer port or Low ImpactDevelopment area.Paint or coat witha zinc-free coatingsystem. Several differenttypes of coatings are effective in reducingzinc leachate to the point of compliancewith stormwater runoff limits. They canalso be reflective to reduce heat absorption.Typical coating options include urethanes,epoxies, and acrylics. Acrylic performanceis on a par with the other coatings, butis more environmentally friendly in bothmanufacture and application. Silicone, whichis self-sealing and has a longer anticipatedlifespan than other opetions, tends to costmore and may require additional or slightlydifferent prep methods.2101 Fourth Ave. Suite 1080Seattle, WA 98121(206) 352 2050

Painting existing galvanized roofing requires more preparation than a typicalpaint job. Necessary steps to minimizefuture corrosion and zinc releases include,but may not be limited to: Thoroughly cleaning to remove dirt,debris, and loose paint from any previouscoating; collecting and properly disposingof that wash water; Removing rust by mechanical means orneutralization by chemical means; Sealing and/or priming holes, gaps, andjoints and fasteners (“hot spots”); and Priming, if recommended for the type ofcoating applied.Apply an overlay-type roofing system.This typically begins with insullatingthe corrugated ribs of the galvanizedroofing. Next, a cover board, which mayprovide addtional insulation properties, ismechanically attached to the roof. Finally,a membrane is attached to provide awaterproof barrier and UV protection. Anoverlay system of this type typically requiresless maintenance and superior longevity to acoating system, but at greater initial expense.Replace aging galvanized roofing. Roofingmaterials such as modified bitumen comein peel and stick form and are more costeffective than the glue-down variety. Avoidinstalling uncoated galvanized sheet roofingon new or replacement construction. Ifconditions are such that galvanized roofing ispreferred, look for pre-coated, or install withthe intent of coating the roof.(Image courtesy Great Western Coatings.)Install centralized stormwater treatmenttechnology wherein all runoff is collected,diverted to the system, and treated beforedischarge. This is particularly useful for a sitewith multiple sources of zinc and has beenemployed successfully by Vigor Shipyardin Seattle, twoAdditional NotesDarigold plants,Ifyouchoose to paint the roofand many otheras a means of eliminatingindustrial sites.These treatment zinc runoff, select a paintingsystems must be contractor with experiencein applying coatings fordesigned withthis purpose. Ensure theirhigh enoughbid contains the necessarycapacity toremove the zinc preparation steps and theexact type of primer andto acceptablepaint or coating to be used.levels at typicalrain flow volume Review the primer and paintor coating specificationsfor the region.(e.g., Safety Data Sheet) toMost treatmentdetermine the constituentssystems willrequire quarterly of the coatings. Primers forgalvanized roofing oftenreplacement ofcontain zinc themselvesthe filtrationbecause zinc providesmedia,superior adhesion to adepending ongalvanized surface. Using acontaminantzinc-containing primer canloads, amountof precipitation, improve coating longevity.and efficacy ofMany available top coatingsthe filtrationmedia. See a list also contain zinc. Whilethe zinc in these coatings isof treatmentencapsulated, the availabilitytechnologiesof zinc-free coatings makesthat have beencertified through zinc-free the preferredWashington State product for the top coat.When soliciting contractorDepartmentbids, specify a zinc-free topof Ecology’scoat. Painting or coatingTechnologya roof is season-dependentAssessment3 in the Puget Sound area,Protocol (TAPE).and contractors’ workloadstend to increase in Augustand September. Plan well inadvance if roof coating is oneof your zinc reduction optionsto meet permit levels by acertain date. One downsideof coating is that it requiresmore frequent maintenancethan unpainted galvanizedroofing.3www.pprc.org2101 Fourth Ave. Suite 1080Seattle, WA 98121(206) 352 2050

Construct green infrastructure or lowimpact development (LID) areas thatcan capture runoff and naturally filter outpollutants including zinc. Examples includeconstructed wetlands, raingardens, andbioswales. For more in-depth information onthese strategies, check out the LID TechnicalGuidance Manual for Puget Sound, producedby the Washington State University (WSU)Puyallup Research & Extension Center andthe Puget Sound Partnership.Does Coating a GalvanizedRoof Reduce Zinc Discharge?Significant reductions of zinc in stormwaterhave been achieved using roof coatings inlaboratory tests. However, field performancedata for overlay systems and silicone coatingis not well-studied. Research suggests that when appliedproperly urethane, epoxyand acrylicpaint systemscontain zincwell.The tablebelowprovidesdata on four roofs coated using zincfree, water-based acrylic coating. In eachinstance the sample readings prior topainting the roof were much higher thanthe stormwater discharge limits for zinc(117 µg/L). All facilities achieved thedesired results, reducing zinc levels wellbelow stormwater discharge limits.(Image courtesty Aaron Clark,12,000 Raingardens.)Great Western Coatings Four Roof Coating Projects:Zinc Reduction - ResultsFacility LocationSurface TypeSurface Area (ft2)Initial Zinc (µg/L)Final Zinc 0800Galvanized Roof Painted Roof10,0002210,00039Galvanized Roof150,00073Painted Roof2,00011Disclaimer: PPRC does not endorse or guarantee any paint or coating products, or contractor services.* Data courtesy of Great Western Coatings.4If you are interested in finding out more information or details for a specific BMP, or need referrals orassistance with metal removal in stormwater, please contact PPRC : (206) 352-2050.4www.pprc.org2101 Fourth Ave. Suite 1080Seattle, WA 98121(206) 352 2050