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should stand until sufficient data are available to fully assess attainment for all appli¬ 
cable criteria components in each designated-use segment assessment unit. With 
sulficient data, states can justify moving an individual designated-use segment, or 
the segment as a whole, to another listing category. The lack of sufficient data for 
full assessment of the applicable criteria is not justification for moving a category 5 
(impaired) segment to category 3 (insufficient data). 
It a segment’s designated use was not previously listed in category 5, it can be listed 
under category 3 if insufficient data exist to assess attainment of all applicable 
criteria components. Because an individual segment may have up to five tidal-water 
designated uses (see Table V-l in Chapter 5), the states can place individual 
segments in multiple listing categories based on the criteria assessment results for 
each designated use in the segment. 
CRITERIA ATTAINMENT ASSESSMENTS 
The preceding chapters document the different Chesapeake Bay water quality 
criteria assessments. Across all Bay criteria, non-attainment is defined as any 
percentage of non-attainment (even less than 1 percent) given that the CFD-based 
criteria attainment assessment method already factors in the small percentage of 
circumstances (in time and space) in which the criteria may be exceeded and still 
fully protect the tidal-water designated use (U.S. EPA 2003a). 
DISSOLVED OXYGEN CRITERIA ATTAINMENT ASSESSMENT 
Given that multiple criteria often protect an individual designated use (e.g., separate 
30-day mean, 7-day mean, and instantaneous minimum criteria required for protec¬ 
tion of the open-water fish and shellfish designated use), full attainment of the 
dissolved oxygen criteria must involve assessment of each applicable criterion indi¬ 
vidually (U.S. EPA 2003a). In designated-use-segment assessment units for which 
data are available to assess all applicable dissolved oxygen criteria, the states can 
proceed with a full assessment of attainment of that segment’s designated use. For 
those units with insufficient data for one or more of these criteria, states should not 
make any decisions on removing that designated-use segment from part 5 during that 
listing cycle. 
Until the EPA publishes methodologies for assessing the 7-day and 1-day mean, 
along with the instantaneous minimum open-water and deep-water dissolved oxygen 
criteria components, the EPA recommends the states rely strictly on the assessment 
of the 30-day mean open-water and deep-water dissolved oxygen criteria for listing 
decisions. For those open- and deep-water designated-use segments for which the 
30-day mean criteria are in non-attainment, the jurisdictions should list the segment 
on part 5 as impaired in the absence of data or methodologies for assessing the 
remaining criteria components. For those designated-use segments in which the 30- 
day mean open- or deep-water criteria are in attainment, the jurisdictions should 
generate additional data and apply criteria assessment procedures to determine 
chapter viii 
Framework for Chesapeake Bay Tidal Waters 303(d) List Decision Making 
