CHAPTER 1 
Introduction 
In April 2003, the U.S. Environmental Protection Agency (EPA) published the Ambient Water 
Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay 
and Its Tidal Tributaries which was the foundation document defining Chesapeake Bay water 
quality criteria and recommended implementation procedures for monitoring and assessment 
(U.S. EPA 2003a). In October 2003, EPA published the Technical Support Document for 
Identification of Chesapeake Bay Designated Uses and Attainability which defined the five tidal 
water designated uses to be protected through the published Bay water quality criteria (U.S. EPA 
2003b): 
• Migratory fish spawning and nursery habitat; 
• Open-water fish and shellfish habitat; 
• Deep-water seasonal fish and shellfish habitat; 
• Deep-channel seasonal refuge habitat; and 
• Shallow-water bay grass habitat. 
A total of six addendum documents have been published by EPA since April 2003. Three 
addenda were published documenting detailed refinements to the criteria attainment and 
assessment procedures (U.S. EPA 2004a, 2007a, 2008) previously published in the original April 
2003 Chesapeake Bay water quality criteria document (U.S. EPA 2003a). One addendum 
published Chesapeake Bay numerical chlorophyll a criteria (U.S. EPA 2007b). Another 
addendum addressed detailed issues involving further delineation of tidal water designated uses 
(U.S. EPA 2004b) building from the original October 2003 tidal water designated uses document 
(U.S. EPA 2003b). Finally, one addendum addressed refinements to the Chesapeake Bay 
Program analytical segmentation schemes (U.S. EPA 2005) building from the original U.S. EPA 
2004 document (U.S. EPA 2004c). 
The detailed procedures for assessing attainment of the Chesapeake Bay water quality criteria 
continued to be advanced through the collective EPA, States and District of Columbia 
partnership efforts. These partners continue to develop and apply procedures that incorporate the 
most advanced state-of-the-science, magnitude, frequency, duration, space and time 
considerations with, as available, biologically-based reference conditions and cumulative 
frequency distributions. As a rule, the best test of any new method or procedure is putting it to 
application with partner involvement and stakeholder input. Through the work of its Criteria 
Assessment Protocols Workgroup, the Chesapeake Bay Program partnership has an established 
forum for resolving issues, factoring in new scientific findings, and ensuring implementation of 
consistent bay-wide criteria assessment procedure development and implementation. The 
Workgroup draws upon the talents and input from state, federal, river basin commission and 
academic partners as well as local government and municipal stakeholders. This EPA 2010 
Chesapeake Bay Criteria addendum provides previously undocumented features of the present 
procedures as well as refinements and clarifications to the previously published Chesapeake Bay 
water quality criteria assessment procedures. 
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