Substantially Identical Outfalls - Potential Option To Reduce Sampling Costs

One option potentially available to dischargers required to conduct stormwater monitoring is the use of "Substantially Identical" outfalls. This is particularly useful to facilities with many outfalls that need to be monitored.

The availability of this option will change from State-to-State, as will the exact requirements. However, generally if the facility has two or more outfalls that discharge substantially identical effluents, the facility may be allowed to conduct visual and/or benchmark monitoring at one of the outfalls and report that the results also apply to the substantially identical outfall(s). In many cases, the facility will need to perform monitoring on a rotating basis of each substantially identical outfall. However, if stormwater contamination is identified at any substantially identical outfall, control measures may need to be installed for all identical outfalls.

In many cases, selection of substantially identical outfalls does not have to be "pre-approved". However, the risk to dischargers is that if during subsequent compliance inspections the permitting agency does not agree with the determination of substantially identical outfalls, the discharger may be subject to enforcement action. Therefore, careful consideration and documentation that the selected identical outfalls are valid is important.

[Read more about factors used to determine substantially identical outfalls]

Caltha LLP asssists dischargers nationwide in developing and implementing cost effective stormwater monitoring programs, including determination and documentation of substantially identical outfalls. To request further information, go to SWPPP and SPCC website.

For further information contact Caltha LLP at
info@calthacompany.com
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Caltha LLP Website