Publication Summary

Sources of zinc in stormwater runoff from industrial facilities were inventoried at 28 industrial facilities covered by the Industrial Stormwater General Permit. Major sources considered were galvanized metal surfaces and ground areas where motor oil and hydraulic fluid could accumulate. The validity and usefulness of self-reported grab sample data were explored by comparing these data with inventory results.

Runoff at two facilities was monitored in support of the inventory process. Runoff from roof, parking, and loading dock areas were monitored at one facility. Two roofs were monitored at a second facility, one roof having galvanic metal surfaces and the other roof without.

Industrial facilities required to monitor and report pollutants under the Industrial Stormwater General Permit have reported high concentrations of zinc in stormwater discharges. In this study, sources of zinc are identified through (1) a literature search, (2) a survey of 28 facilities, and (3) monitoring at two facilities.

From the literature search, a list of potential sources of zinc in the environment was developed. These were narrowed down to those likely to be significant sources of zinc in industrial stormwater runoff.

Inventory surveys were conducted at 28 industrial facilities in the vicinity of Kent, Washington. Major sources of zinc were identified as galvanized materials, particularly on roof surfaces, as well as motor oil and hydraulic fluid accumulated on parking areas, loading docks, and paved grounds. Tire dust in areas with high volumes of trucks and forklifts may also be an important source.

As an indication of the efficacy of self-reported data, 20 of the 28 facilities inventoried appeared to have sampled and reported without error or bias. The facilities reporting lower zinc concentrations in their stormwater discharges were more likely to report data in ways appearing to introduce bias or error, and in the direction of under-reporting. Because of this, zinc concentrations in stormwater discharge from facilities studied, and perhaps facilities statewide, may be higher than self-reported data indicate.

Monitoring took place at one industrial facility to substantiate sources of zinc in stormwater runoff from roof, parking, and loading dock areas. All three of these areas were found to be major sources of zinc in stormwater runoff. Monitoring of two roofs was conducted at a second facility. Zinc concentrations of approximately 500 µg/L were found in runoff from the roof with galvanized ductwork; one-tenth of that concentration was found from the roof free of galvanized materials.

Link to EIM data for User Study ID SGOL008