Run-on is a term used to describe the flow of water (storm water or non-storm water) onto a site from an outside source.
Run-on entering a construction site can cause many problems. Once water enters a construction site, whether it’s storm water or not, or if it’s clean or polluted, the water becomes the responsibility of the construction site. It is then held to the same standards of any discharge or ponding water from a construction site. Unexpected run-on may be a result of compromised drains or recently made impervious surfaces that will create larger volumes of run-off from that source upstream from the site.
The best way to mitigate the effects of run-on is to divert it away from the site before it can enter.
Impervious Surfaces: are mainly artificial structures—such as pavements (roads, sidewalks, driveways and parking lots) that are covered by impenetrable materials such as asphalt (concrete, brick, stone) —and rooftops. Soils compacted by urban development are also highly impervious.
Impervious surfaces may be created upstream from the construction site and create additional run on. In some cases, these surfaces may be created during the course of construction, and drastically increased water flows may occur.
Compromised Drains: A compromised drain is a drain that in some way has a reduced capacity for water flow. This can be due to; physical blockage from waste, improper BMP setup, BMPs not cleared after a previous storm, etc.
Upstream drains that have been compromised lead to increased run-on to the construction site. Run-on results from flooding when drains are compromised. It is not always the responsibility of the site to monitor all surrounding drains; however, it will benefit you if adjacent drains are inspected and cleared when a storm is forecasted to occur. Document any potential problems and report them if necessary.
Water flow volume and intensity of rain can make a compromised drain a severe problem.