How can new nutrient (nitrogen and phosphorus) criteria be implemented in existing NPDES permits?
This question is not entirely specific to nutrients, and therefore, is answered the same as for any other water quality criteria. The permitting authority may be able to modify an existing permit (a new nutrient standard may be an allowable cause for modification) during the existing permit term, wait until the end of the permit term, or use an overlay permit that captures multiple facilities and provides additional flexibility. Permitting authorities are encouraged to consider a watershed-based permitting approach, which allows for the coordinated reissuance of permits with applicable limits throughout a watershed and may expedite implementation of new criteria while lowering administrative burden. The Virginia Chesapeake Bay and the Connecticut Long Island Sound Permits are examples where states have utilized the overlay permit to implement new nutrient criteria. Refer to 40 CFR 122.62 and Chapter 11 of the NPDES Permit Writers’ Manual [PDF – 84 KB – 19 pp] for regulatory requirement
