EPA to Lower the Water Quality Criteria for Ammonia – potentially cutting current values in half.  According to environmental engineer Bill Kramer, “this is probably going to affect a lot of wastewater systems.” EPA’s conservative determinations, as they apply the water quality criteria, are discussed in the proposal but basically EPA takes the position that the one hour in-stream concentration cannot exceed the acute criteria value and the 4 day average cannot exceed the chronic criteria value – and both of these events cannot occur more than once every three years.  Kramer said, “The problem with this is that the acute test is a 48-96 hour test.  The endpoint for the test is when 50% of the test organisms are killed.  They expose various organisms to a series of dilutions of the pollutant to find the concentration at which 50% of the organisms die at the 48 or 96-hour test endpoint.  With chronic it is a 28-day test.  So saying you can’t exceed acute criteria more often than once per hour over a three year period is far away from an exposure level that would cause any harm.  The criteria are based upon constant exposure for 2 to 4 days.  Likewise 4 days vs. 28 days on the chronic side.”

Read the full EPA Announcement.