Many facilities that are authorized to discharge stormwater under the State's General Industrial Stormwater Permit (NJ0088315) also have secondary containment for storing product and other associated materials. The use of secondary containment may range from facilities that have small tanks that store heating oil, chemical additives used in manufacturing, waste storage, or liquid product, to bulk storage terminals with tanks containing hundreds of thousands of gallons of product. The secondary containment systems are designed to capture the volume of material generated from leaks, spills, overfills or from catastrophic failures of a storage tank. Built into the design of secondary containment areas is the additional capacity to capture the volume of stormwater from a predetermined storm event, usually a 25 year/24 hour storm. This stormwater control feature ensures discharges of contaminated runoff from containment areas will not occur in the event of a storm, at least up to the design storm, before or during clean up activities.

More often stormwater simply accumulates from storm to storm in secondary containment areas and eventually needs to be discharged to maintain design capacity. Compliance with the General Permit requires a facility to eliminate the exposure of source material (contaminates) from coming into contact with stormwater and does not authorize discharges of contaminated stormwater from secondary containment areas. Even stormwater that is contaminated with pollutants in concentrations at the minimum detection limit are not authorized under the General Permit and can not be discharged.

Since this General Permit limit prohibits indiscriminate discharges, it is important for permittees to properly manage their facilities.

The only way to verify that stormwater from secondary containment is not contaminated is to conduct adequate testing of the water before it is discharged. For many secondary containment systems, with easily identifiable material such as petroleum, this can be done through frequent visual inspections of the containment area, tank and appurtenant piping. It takes a relatively small amount of oil to produce a visible sheen on water. It is the DEP's current policy that a visual inspection is an acceptable practice for discharging stormwater from secondary containment areas for above ground tanks which contain products that exhibit a visible sheen. But what would be considered an acceptable practice to determine no exposure of source material to stormwater for those products that don't produce a visible sheen or are miscible? Can odor or some other type of physical evaluation be used to determine if the material is present? For these types of products, the DEP determined a physical evaluation for the presence of source material is not appropriate. A case in point would be the use of odors. A chemical that is miscible in water may not produce an odor at a low concentration, but may still be toxic to aquatic organisms or humans. The only sure method to determine its presence is to analyze specifically for the material in question using an EPA approved testing methodology.

The Bureau of Nonpoint Pollution Control has prepared a separate guidance for establishing a suitable testing protocol for secondary containment stormwater discharges that can be used by facilities permitted under the General Permit. The guidance discusses EPA approved methods, QA/QC, record keeping, and the relationship of the Stormwater Pollution Prevention Plan. To receive a copy of the guidance document, please contact the bureau at (609) 633-7021. (The document will soon be available on the web.)