In accordance with the Chesapeake 2000 Agreement, the CBP implemented important modifications to (1) ambient water quality criteria for living resources and, (2) the procedures to determine attainment of those criteria. A novel statistical tool for attainment, termed the Cumulative Frequency Diagram (CFD) approach, was developed as a substantial revision of previous attainment procedures, which relied upon a simple statistical summary of observed samples. The approach was viewed as advantageous in its capacity to represent degrees of attainment in both time and space. In particular, it was recognized that the CFD could represent spatial data in a synoptic way: data that is extensively collected across diverse platforms by the CBP Water Quality Monitoring Program.
Underlying statistical properties needed to be fully established in order for the Bay Program to use the CFD approach to rigorously define regional attainments in the Chesapeake Bay. In Fall 2005, the STAC charged our working group to provide review and recommendations on the CFD attainment approach to assist the CBP in meeting these needs.