Both methods result in the same error rates when duplicate records are removed and EPA's 
criteria are applied to the classification of benthic communities. However, in contrast to 
Argument 2 as described above, it is EPA’s position that this dataset does provide convincing 
biological information with regard to the degree and distribution of deep-water DO criteria 
violations that can be tolerated by the benthic community. Furthermore, by using the worst 
violation rate allowed by any healthy community at each point in time, EPA has allowed for 
greater violation rates in regions of CFD-space where CFD curves from healthy and degraded 
communities overlap. It is reasonable to postulate, based on the distribution in CFD-space of 
curves associated with healthy and degraded benthic communities, that violations occurring in 
the CFD-space circled in black in Figure B-2 lead to degradation of the benthic community. 
o> 
E 
space 
Figure B-2. Violations occurring in the CFD-space circled in black are postulated to lead to 
degradation of the benthic community. 
It is suggested from the multiple lines of evidence that the shape of the biologically-based 
reference curve is an important factor in identifying acceptable violations of the DO criteria. The 
shape of this biological reference curve also provides further support for the suitability of the 
hyperbolic 10% reference curve, in that it illustrates the sensitivity of biological communities to 
chronic violations of DO criteria. 
48 
