Industrial Stormwater Permit Guide

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Lesson 3: No Exposure Certification provisions

One of the keys to meeting a condition of No Exposure is understanding what constitutes exposure. As explained on the previous page, anything protected by a storm resistant shelter is considered not exposed.

Storm-resistant shelters

Facilities that are completely roofed and walled qualify as storm resistant shelters. In addition, structures with only a top cover but no sides can also qualify if the material under the structure is not directly exposed to precipitation or to any run-on and run-off of stormwater that would flow into and out of the shelter.

Temporary covers such as tarps are allowed for industrial activities or materials under circumstances where permanent cover is not possible. However, these can only be used between periods of permanent enclosure, such as during facility renovations.


Sometimes vehicles (including trucks, automobiles, forklifts, and trailers) can be temporarily exposed to precipitation while passing between buildings and still qualify as a "no exposure" situation. In order to qualify, the vehicles are not allowed to be industrial machinery, are not leaking contaminants such as oil, and are not a source of industrial pollutants. Vehicles waiting for maintenance that are not leaking are also not considered exposed.

Other scenarios

Particulate matter (e.g., dusts, metals, and other solids) emitted from roof stacks and vents are also a concern. If the roof stacks and vents are regulated by other environmental protection programs and do not cause stormwater contamination, they are not considered exposed. But, visible deposits of residuals and particulate matter not otherwise regulated that are evident in stormwater are considered exposed.

Another source of concern is leaking discharge pipes. If the material leaking from the pipes is exposed to stormwater, then this is a condition of exposure.

Past sources of contamination remaining on site are considered exposed. For example, residues from a spill of material that has not been cleaned up from the ground or other outside objects and structures are considered exposed.

General refuse and trash (e.g., office paper, wastes from a cafeteria, boxes, etc), is not considered exposed if the trash container (e.g., dumpster) is completely covered and no liquid can drain from holes in the bottom or be lost when loaded onto a garbage truck.

If industrial refuse and trash is left uncovered, it is considered exposed.

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