General

Precipitation of all types falls on industrial facilities and, in so doing, transports chemicals and inert solids from wherever it physically contacts them to other parts of the environment. Any industrial site will have some contamination on all surfaces, including roofs, parking lots, storage facilities, roads, sidewalks, and grassy areas.

Since all substances are soluble to some extent in water (the universal solvent), any chemical substances in either liquid or solid form will become dissolved (to an extent equal to or less than the solubility limit for that substance) and will either percolate into the ground or be carried with the stormwater runoff. Particles that are not dissolved will be transported with the runoff, which will also contain some amount of gases that are dissolved in the runoff. Most, if not all, of the precipitation that percolates into the ground will eventually reach groundwater.

The types and amounts of materials that become incorporated into stormwater runoff depend upon the state of cleanliness of the industrial facility (i.e., the roof areas, parking lots, roadways, etc.), as well as the characteristics of the precipitation itself, in terms of intensity, duration, pH, temperature, and chemical constituents. As well, factors such as the topography of the plant site, the characteristics of the surfaces over which the runoff flows, and the stormwater management practices that have been employed will have a major influence on the quality of the stormwater as it flows off the site or percolates into the ground.

It is the quality...