Zinc in Stormwater?

Time to reevaluate the stormwater pollution prevention plan (SWPPP)

Stormwater quality management activities and tools, including the Stormwater Pollution Prevention Plan (SWPPP), are intended to reduce the potential for stormwater runoff to negatively impact surface water and groundwater resources with pollutants that could harm environmental receptors. Federal and State agencies regularly review their respective storm water management guidance and procedures to provide responsible parties with key information relevant to improving management approaches, and sometimes, stakeholder groups additionally will observe conditions that require focused attention. A recent petition from the California Stormwater Quality Association (CASQA) claims tire road wear particles (TRWP) may be a significant culprit tied to the detection of zinc (Zn) in storm water and surface water bodies, particularly in locations and facilities where zinc is not a key component of land or industrial use[1]. The report also notes aquatic organisms are negatively impacted by elevated levels of zinc in the ecosystem. The CASQA is asking the California Department of Toxic Substances Control (DTSC) to evaluate the potential to add zinc to California’s Priority Product List, an entity used to identify consumer products which contain “’Candidate Chemicals” or substances that are hazardous to people or the environment.

Proactive management of zinc in stormwater is not exclusive to California, the State of Washington Department of Ecology published a guide in 2008 which aimed to provide strategies for reducing zinc concentration in industrial stormwater discharges. The report cited several common sources of zinc in industrial operations. They are:

• Galvanized metal surfaces
• Motor oil and hydraulic fluid
• Tire dust

While stormwater regulations and permitting vary from state to state, the U.S. Environmental Protection Agency (EPA) administers the Multi-Sector General Permit (MSGP) for four states: New Mexico, Idaho, Massachusetts and New Hampshire. In the MSGP, the benchmark for zinc content is hardness dependent from 0.04 to 0.26 mg/L. In water with greater concentrations of dissolved calcium and magnesium (i.e., “harder water”), zinc is less bioavailable to aquatic organisms; a condition that can allow a higher zinc concentration storm water discharge[2]. The benchmarks or Numeric Action Levels (NALs), which is used in California, range from 0.117 mg/L (Washington) to 0.12 mg/L (Oregon) to 0.26 mg/L (California).

Zinc is a common and useful element in both industrial and consumer products. Thus, a range of Zn control techniques, including coating galvanized surfaces and proper management and disposal of zinc-containing industrial fluids are common. Tire dust, however, poses more difficult mitigation challenges considering the immense magnitude and necessity of the transportation and road network in the U.S. and elsewhere. In response to the DTSC petition, the US Tire Manufacturers Association put out a statement upholding the essential qualities of zinc oxide, for example, as a critical component in the tire vulcanization process that allows tires to stop safely and preserving the products integrity during use.[3] In the official response to the petition the UTMA concluded that, while natural zinc-containing minerals are a natural source, zinc from tires accounts for less than 10% of total zinc in the environment while numerous other industrial and consumer products, including galvanized metal, fertilizers, brake pads, and paint account for the bulk of zinc occurrence. Other consumer products including sun screen and certain medicinal products contain zinc, and zinc is an essential human element.

However, the science that has examined zinc toxicity is not new[4] and has been documented to be harmful to aquatic life. While toxicological review work continues[5], the new focused examination of zinc occurrence does result from greater reported storm water detections from facilities that have no known use of zinc products. Climatic factors also are of greater importance. For areas with regular precipitation the risk of high concentrations of zinc being transported to the environment is diminished relative to areas such as California and the desert southwest where the concept of a “first flush” might be a critical factor in the occurrence and build-up of zinc in stream bed sediments. For this condition, long periods of dryness create situations where releases of zinc in stormwater are highly concentrated. The lack of intermittent rain means accumulation of tire particles on surfaces and roadways for long stretches of time. More frequent rain periods would in theory dilute the concentrations of zinc released with each storm. This first flush concept is a main pilar in the CASQA’s argument for adding zinc to the Priority Product List because of the unique risks associated with the long California dry season.

Regardless of the cause, it is clear that monitoring for the occurrence of zinc is becoming more important. If facilities continue detecting zinc in SWPPP testing, the following are some strategies to implement to reduce transportation of zinc in storm runoff.

Potential management strategies

A simple inventory can provide an insight of the sources of zinc in your stormwater discharge and help indicate possible solutions. Walking through the facility and grounds to observe drainage patters can provide a quick, useful assessment of zinc sources and their extent. This will help you determine if a zinc source enters the runoff and where. Additionally, the State of Washington Department of Ecology guide[6] recommends implementing a regular schedule of sweeping facility grounds using appropriate sweeping equipment. High traffic areas such as parking, loading docks and other paved surfaces can be swept to remove large and small particles, motor oil, hydraulic fluid, and tire dust. The right industrial sweeping system also includes a plan for the appropriate disposal of the sweepings. The WDE also recommends sweeping your facilities grounds between once per week and once per month. Maintaining a sweeping log is a great addition to your SWPPP plan.

Although the USTMA provided statement on the potential new actions regarding zinc oxide in tires noting that prevalence of numerous common products that also contain zinc, the organization has also shown a dedication to understand and reduce environmental impact of their products. Zinc is another of those critically important elements that has both tremendous value to human health and safety but can also create potential problems depending on its occurrence. Like many natural and human-created materials, we continue to monitor and understand potential impacts so that we can continue to get the best of both worlds that improve our quality of life and protect and enhance environmental conditions.

Therefore, it is the shared responsibility among stakeholders to craft a solution that preserves both safety and environmental conditions. Like many environmental issues, the consequences of zinc releases through stormwater runoff are felt differently at the regional level. There is not a one size fits all approach for facilities and municipalities across the country. As will likely be the conclusion of the policy debate in California that is to come, proper management of both goals—safety and environmental protection—will be necessary to effectively confront this challenge and others like it. However, cooperative management of industrial behavior is not a new concept and has been successfully utilized to reduce effects of environmental degradation globally. Both goals are attainable, they just require finding the proper balance.

References

[1] https://calsafer.dtsc.ca.gov/documentitem/index/?guid=0a2ce689-1abe-4867-9d78-54c865e4118d

[2]https://www.waterboards.ca.gov/water_issues/programs/stormwater/docs/industrial/2014indgenpermit/wqo2014_0057_dwq_revmar2015.pdf

[3]https://www.ustires.org/ustma-statement-california-dtsc’s-actions-regarding-zinc-and-6ppd-automobile-tires

[4] https://www.journals.uchicago.edu/doi/pdf/10.1086/404229

[5] https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0426tr.pdf

[6] https://apps.ecology.wa.gov/publications/publications/0810025.pdf