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In 2013, the United States Environmental Protection Agency released recommended water quality criteria for ammonia, superceeding USEPA 1999 Ammonia Criteria.  The new ammonia criteria vary based on pH and temperature, and under most conditions, the 2013 ammonia criteria are more stringent than the 1999 ammonia criteria when mussels are present in the receiving water. Although freshwater mussels and gill-breathing snails are widely distributed in the continental United States, they may not be present in all receiving waters. The 2013 ammonia criteria document states that, “unionid mussel species are not prevalent in some waters, such as the arid west.” and provides that, “In the case of ammonia, where a state demonstrates that mussels are not present on a site-specific basis, the recalculation procedure may be used to remove the mussel species from the national criteria dataset to better represent the species present at the site.”

In April 2014, the Central Valley Regional Water Board issued a 13267 letter to most NPDES permit holding publically owned treatment works (POTWs) in the Central Valley.  The 13267 letter requires weekly monitoring of pH and temperature of the effluent and first downstream monitoring location.  Additionally the Regional Water Board has required a response by July 15, 2014 if an agency plans to do a mussel study and if so, whether they will complete the study individually or through a group effort. 

To help facilitate understanding of the new requirements and the 13267 letter, CVCWA and Regional Water Board staff held a joint informational meeting on April 23, 2013 to discuss the new criteria.  Presentations from that meeting can be accessed below.

A second workshop is planned for Wednesday, May 28th from 9:30 to 12:30 at SRCSD's offices in Sacramento.

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