The type and amount of solids in the stormwater runoff from sealed and unsealed surfaces varies from location to location and is influenced by :

• Location, type, size and use of the catchment area
• Material and type of surface
• Duration of the precipitation event preceding dry weather periods
• Duration and intensity of rainfall events
• Weather and season
• Frequency of street cleaning
• Type of street drainage systems and frequency of cleaning
• Traffic load and driver tendencies (braking and acceleration)
• Winter maintenance
• Location and distance to potential emission sources (wind drifts)