Stormwater-Associated Contaminants
Issues Concerning Reliable Assessment & Regulation

Nature of Stormwater Runoff & Runoff Events
Render Conventional Criteria/Standards & Evaluation/Management Approaches Unreliable

Some Key Issues in Evaluating & Regulating
Stormwater-Associated Contaminants:
See Our Publications on These Issues:
  • Stormwater Runoff from urban and rural/agricultural areas contains chemicals in concentrations that exceed US EPA water quality criteria & state water quality standards
    - Such stormwater discharges can cause violations of water quality standards in receiving water at points of discharge
    - Exceedance of water quality standard caused by stormwater runoff does not necessarily result in impairment of designated beneficial uses of receiving waters - e.g., protection of aquatic life
  • US EPA water quality criteria & state standards based on them are based on worst-case assumptions. Meant to be protective in receiving waters under worst-case conditions:
    - Long-term (chronic) exposure
    - Critical lifestage exposure
    - Exceedence no more frequent than once in three years
    - Contaminants present in biologically available forms
  • Stormwater runoff-associated violations of water quality standards at/near point of discharge:
    - Short-term, episodic events
    - Chemical forms tend to be unavailable/non-toxic
  • Application of US EPA criteria/state water quality standards to stormwater runoff generally inappropriate & technically unjustifiably stringent
  • Application of US EPA criteria/state water quality standards in receiving water at runoff points of discharge tends to over-regulate urban and rural stormwater runoff-associated chemicals
    - Exceedance in receiving water in area of stormwater discharge indicates need for detailed study of actual impacts of chemicals in stormwater runoff to establish degree of regulation needed for those chemicals that are causing impact
    - Cannot presume that chemicals that appear in elevated total concentrations in runoff are cause of observed impacts
    - Total concentrations in stormwater unreliable indicator of potential impacts
    - Must examine watershed & conduct TIEs to determine actual cause of water quality impacts



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