K-35 
APPENDIX 
POWERPOINT PRESENTATION 
Benthic Index of Biotic Integrity 
(B-IBI) for 2006 303(d) List 
Alternative Assessment 
Methodology 
Roberto Llanso, Jon Volstad, Ed Weber 
Versar. Inc. 
Daniel Dauer 
Old Dominion University 
(co-PIs) 
August 23. 2005 
Summary 
The impairment assessment for each segment is based on the 
proportion of samples with ' low" B-IBI scores (i.e.. below a 
threshold) 
Two steps, estimate: 
1 Proportion of sites in a segment with scores below a threshold (P) 
2 Difference between P and the expected proportion under the null 
hypothesis (P c ), i e., if the segment were in good condition (no low 
DO, contaminant, or nutrient enrichment problems), we would still 
expect a small proportion of sites to have “low" scores (e g., because 
of natural variability) this proportion under the null hypothesis is 
defined as 5% 
appendix k - 2006 303(d) Assessment Methods for Chesapeake Bay Benthos 
