I recently published a blog post about proposed revisions to the regulations governing the National Pollutant Discharge Elimination System (NPDES) program. In addition to clarifying the conditions under which a dilution allowance can be granted, EPA proposes to revise how states conduct reasonable potential determinations (e.g., Reasonable Potential Analysis, or RPA) by requiring that the determination be based on relevant qualitative or quantitative data, analyses or other valid and representative information. This is not a new requirement; however, EPA is proposing to clarify regulatory language regarding the types and quantities of data and information permitting authorities must consider when conducting a RPA.

The proposed revisions specifically address new dischargers where effluent data is not yet available. If site-specific data does not exist, permitting authorities would be required to consider other relevant data sources, such as existing monitoring data and other studies that have been conducted at similar facilities. In addition, if an applicant is in an industrial category for which EPA has developed effluent limitations guidelines, EPA has published development documents that provide detailed effluent characterization data that can be used to estimate the types and quantities of pollutants that might be discharged. (Note that the guidelines for a significant number of categories were last revised in the mid-1970’s).

In summary, this proposed revision would codify EPA’s long-standing policy and guidance that, while the permitting authority has the discretion to prioritize the importance of available and relevant data and information used in making a determination on a case-by-case basis, it may not disregard valid information that is useful in conducting a reasonable potential analysis.

This is an important change that will undoubtedly impact municipal and industrial dischargers in Kentucky. In the past, KPDES permits have specifically addressed situations where insufficient data exists (i.e. less than 5 data points). Permit conditions would generally require monitoring for the pollutants at a frequency of once per month for the first year, at the end of which a new reasonable potential analysis would be conducted. If necessary, the permit would be reopened to modify the conditions. Moving forward, the proposed revisions will ultimately restrict the situations where the applicant or permitting authority can claim that insufficient data exists.


William Shane is an Environmental Engineer at Smith Management Group. William can be reached at williams@smithmanage.com.