Wednesday, March 4, 2009

Stormwater Antidegradation Requirements for Tier 2, 2.5, 3 Waters

The US EPA Multi-sector General Permit promulgated in 2008 (“MSGP-2008”) includes antidegradation requirements that apply to new and/or expanded discharges of stormwater from regulated industrial sites.

[What is an Antidegradation Policy?]

EPA’s approach to antidegradation requirements is based on three categories of “special” waters – Tier 2, Tier 2.5 and Tier 3.

[Read more about how Stormwater Antidegradation Tiers are defined]


Tier 2. For new or existing dischargers to Tier 2 waters, the discharger is required to notify US EPA prior to making changes at the site which “qualify the facility as a new source or that could significantly change the nature or significantly increase the quantity of pollutants discharged”. EPA may notify the facility that additional analyses, control measures, or other permit conditions are necessary to comply with the applicable antidegradation requirements, or notify the facility that an individual permit application is necessary.

Tier 2.5. Same requirements as Tier 2.

Tier 3. New or existing discharges to Tier 3 waters can not be permitted under the MSGP-2008.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

Caltha LLP Aquatic Toxicology / WQ Standards Services Website