- 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