2 
dissolved oxygen, water clarity, and chlorophyll a; the EPA-recommended tidal 
water designated uses; and the EPA-established criteria assessment procedures into 
their respective state water quality standards regulations. All four jurisdictions 1 
promulgated narrative chlorophyll a criteria in their standards regulations. Virginia 
promulgated numerical segment- and season-specific chlorophyll a criteria for the 
tidal James River. The District of Columbia promulgated numerical chlorophyll a 
criteria for its reach of the tidal Potomac River and its remaining tidal waters, having 
previously adopted numerical chlorophyll a criteria for protection of the tidal 
Anacostia River. 
The April 2003 Regional Criteria Guidance and the October 2004 addendum docu¬ 
ments published the criteria attainment assessment methods (U.S. EPA 2003, 2004). 
These methods characterize the spatial and temporal variability of the appropriate 
water quality parameters and provide a clear basis for deciding whether a criterion 
or set of criteria protecting a designated use in a specific segment of the mainstem 
Chesapeake Bay or one of the tidal tributaries or embayments were in attainment. 
The methods were quite detailed; however, specific technical and procedural issues 
remained in applying the methods as specified in the original publication by EPA 
from April 2003. These issues required resolution to allow Delaware, Maryland, 
Virginia, and the District of Columbia to assess attainment of their new Chesapeake 
Bay water quality standards regulations fully. 
This second addendum documents the revised, refined, and new criteria assessment 
methods for the published Chesapeake Bay dissolved oxygen, water clarity, and 
chlorophyll a criteria. 
• Chapter 2 documents refinements to and recommendations for further devel¬ 
opment of the spatial interpolation and statistical aspects of the overall 
Chesapeake Bay water quality criteria attainment assessment methodology. 
• Chapter 3 documents the resolution of and recommended procedures for 
addressing a series of overarching Chesapeake Bay water quality criteria 
assessment issues. 
• Chapter 4 documents refinements and additions to the procedures for 
assessing the previously published Chesapeake Bay dissolved oxygen criteria. 
• Chapter 5 documents refinements and additions to the procedures for 
assessing the previously published Chesapeake Bay water clarity criteria and 
determining attainment of the shallow-water bay grass designated use. 
• Chapter 6 documents refinements and additions to the procedures for 
assessing attainment of state-adopted numerical concentration-based chloro¬ 
phyll a criteria. 
'References throughout the text to “states” or “jurisdictions” means a collective reference to the states 
of Delaware and Maryland, the Commonwealth of Virginia, and the District of Columbia. All four have 
Chesapeake Bay tidal waters within their jurisdictional boundaries. 
chapter i 
Introduction 
