By Carlos J. Moreno:

On November 15, 2010, the U.S. Environmental Protection Agency (EPA) issued a memorandum providing States with guidance on how to address ocean acidification in their Clean Water Act 303(d) impairment listings. 

Section 303(d) of the Clean Water Act requires States to list water bodies that will not meet Water Quality Standards, even after technology-based permit requirements are implemented. States must then identify every contributing source, including contributions from air emissions, and make plans to bring the impaired water body into compliance. This process results in the calculation of a Total Maximum Daily Load (TMDL). There is precedent for TMDLs addressing air emission sources, specifically in relation to atmospheric deposition of mercury. 

The EPA Memo is part of an EPA settlement with the Center for Biological Diversity (CBD), which sued EPA over 303(d) listing of coastal waters for ocean acidification. The CBD had argued that ocean acidification (the decrease in ocean pH caused by increasing CO₂ concentration in the atmosphere) required EPA to modify its Recommended Marine pH Criteria and consider ocean acidification in 303(d) list approvals. The Memo encourages States to list coastal waters for ocean acidification, based on existing Marine pH Water Quality Standards, where there is enough data to support it. For example, Puerto Rico’s 2010 303(d) list already includes five coastal water segments impaired by marine pH. At the same time, the agency recognizes that many States do not yet have enough monitoring data to make such a listing. EPA pledges to issue TMDL-specific guidance related to ocean acidification once there is more information on air deposition of carbon in coastal waters.

The EPA memo only addresses ocean acidification from a 303(d) list perspective and does not modify EPA’s Recommended Marine pH Criteria. It is unclear how these developments may affect, if at all, future EPA Ocean Discharge Criteria evaluations under Section 403 of the Clean Water Act.

For more information on the Memorandum, see:

http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/oa_memo_nov2010.cfm