Step 6. For each 3-year time window from 1996-2006, we applied the following criteria to 
classify deep-water benthic communities as “healthy” for the purposes of generating a biological 
reference curve for the dissolved oxygen criteria assessment: at least 10 benthic 1BI scores; mean 
score > 3.0; and standard deviation of the mean < 1.0. Segment-periods (e.g. “CB6PH 1996- 
1998”) that met the above criteria were classified as “healthy.” 
Step 7. We obtained the “dissolved oxygen violation rates” for each healthy segment-period. 
These rates are an intermediate product of the dissolved oxygen criteria assessment procedure 
(see U.S. EPA 2007 and 2008). They represent the fraction of deep-water in a given segment 
that violates water quality criteria for dissolved oxygen in a given time period. Using these 
violation rates, we generated a CFD curve for each healthy segment-period. Most segment- 
periods contained 12 violation rates, but some contained only 11 rates. To account for segment- 
periods with different numbers of violation rates, all violation rates were interpolated to a 
common set of plotting positions (y values). To generate a biological reference curve that 
represented the “100 th percentile” of healthy violation rates, we then used the largest violation 
rate (across healthy segment-periods) for each “y” value of the violation CFD. The resulting set 
of violation rates represents the largest of all healthy violation rates for each plotting position. 
See chapter 3 for more details on the selection of the 100 th percentile curve. 
The following segment-periods comprised the set of “healthy” segment-periods: 
CB6PH 1996-1998 
CB7PH 1996-1998 
CB6PH 1997-1999 
CB7PH 1997-1999 
PAXMH 1997-1999 
CB7PH 1998-2000 
CB6PH 1999-2001 
CB7PH 1999-2001 
CB7PH 2000-2002 
CB7PH 2003-2005 
CB6PH 2004-2006 
CB7PH 2004-2006 
50 
