DEVELOPMENT OF TMDL GOALS AND WET WEATHER STANDARDS FOR THE CONTROL OF HEAVY METALS IN URBAN STORMWATER RUNOFF

Studies on NPDES-permitted urban area and highway stormwater runoff have shown that the total and dissolved concentrations of several heavy metals — copper, lead, zinc, and frequently cadmium — are present in the runoff waters above US EPA worst case-based national water quality criteria. This situation can lead to violations of water quality standards at the point where the stormwater runoff enters a receiving water. Further, urban stormwater runoff-associated heavy metals can contribute to causing a waterbody to be listed as a Clean Water Act 303(d) “impaired” waterbody for which TMDLs will have to be developed to control the urban stormwater runoff discharge of heavy metals to the waterbody. The control of heavy metals in urban area and highway stormwater runoff so that their concentrations do not cause or contribute to violations of water quality standards in the receiving waters or TMDL discharge limitations will be expensive. This control will require the use of advanced wastewater treatment technology since conventional urban stormwater runoff BMPs such as detention basins are not effective in reducing the concentrations of heavy metals below worst case-based water quality standards. This paper discusses an approach to develop appropriate urban stormwater runoff heavy metal TMDL management goals and wet weather standards to protect the designated beneficial uses of waterbodies without unnecessary expenditures for heavy metal control.