“De minimis” degradation

Today most states allow some amount of new pollution, called “de minimis” degradation, before an antidegradation review is triggered. De minimis impacts currently allowed by some states include:

• temporary degradation
• new discharges that require “only” a given percentage of available dilution (e.g. 10-25% erosion of existing quality)
• existing discharges that increase “only” by a certain percentage (e.g., 10% more)

Some states define an overall cap for de minimis to address cumulative pollutant loading.

De minimis degradation has been taken to an extreme in many states – creating a giant loophole that allows virtually any new activity to be allowed with little or no antidegradation review. Neither the CWA, nor the regulations, nor the guidance in the WQS Handbook suggest a de minimis exemption from antidegradation review and protections.

< Back to Previous Page