Q. If I am subject to National Pollutant Discharge Elimination System (NPDES) permitting requirements under the Clean Water Act, which of the many control technology acronyms am I subject to?
A. Short Answer: Check your permit, do what it says.
Long Answer: The type of water treatment controls you need depend on several factors, including the type of pollutants you discharge, and whether you are a new source or an existing source.
What Pollutants Are You Discharging?
The NPDES establishes effluent limitations for three different categories of pollutants. A detailed list of common pollutants under each category can be found at 40 CFR 122, Appendix D. In broad terms, the three categories are:
- Conventional Pollutants – including biochemical oxygen demand, total suspended solids, fecal coliform, pH, oil, and grease
- Non-conventional Pollutants – including nutrients and phosphorous
- Toxic Pollutants – including organics and metals
New Source or Old?
There are four levels of control technology authorized under the NPDES; from least to most stringent they are:
- BPT – Best practicable control technology currently available
- BAT – Best available control technology economically achievable
- BCT – Best conventional pollutant control technology
- BADCT – Best available demonstrated control technology
BPT is the minimum standard for existing point sources of conventional, toxic, or non-conventional pollutants. If local water quality standards require more treatment, then the permitting authority may require you to install BCT (for conventional pollutants) or BAT (for toxic or non-conventional pollutants).
New point sources are subject to BADCT for all categories of water pollution.
In addition to discharge permits and generic control technologies, the EPA has created a set of technology-based effluent guidelines and standards for over 50 industrial categories (called Categorical Standards, or Industry-Specific Standards). These Categorical Standards are codified in 40 CFR Subchapter N (specifically Parts 405 through 471).
If your site falls in one of these industrial categories, then the effluent guidelines and standards in Subchapter N automatically become part of your NPDES permit.
If your site is not included in these industrial categories, then it is up to the permit-issuer to establish a site-specific technology-based limit. While the EPA does not have a strict list of what exact controls fall under each of the four levels, the Agency does have some guidance at http://water.epa.gov/scitech/wastetech/guide/questions_index.cfm
to help regulated facilities.