• A practical description of how monitoring information may be used to assess 
attainment, including statistical estimation methods for addressing assessment 
of the short-interval criteria, such as the 7-day mean, 1-day mean and instanta¬ 
neous minimum dissolved oxygen criteria; and 
• A description of how mathematical model-simulated information may be used 
to assess the effect on future criteria attainment under various nutrient/sediment 
reduction scenarios, which support decisions on load reductions and caps on 
loadings to maximize the beneficial effect on attainment. 
DEFINING CRITERIA ATTAINMENT 
DISSOLVED OXYGEN CRITERIA 
The Chesapeake Bay dissolved oxygen criteria were derived to protect species and 
communities in the five tidal-water designated uses during specific seasons (Table 
VI-1). See Chapter III for detailed information on the designated use-specific criteria 
and appropriate periods for applying them. Refer to Appendix A and the Technical 
Support Document for the Identification of Chesapeake Bay Designated Uses and 
Attainability (U.S. EPA 2003) for details on the five designated uses and their bound¬ 
aries. The Chesapeake Bay dissolved oxygen criteria should not be applied to a 
designated use or during a period of the year for which they were not specifically 
derived (see Chapter III). 
The EPA expects the states to adopt the full set of dissolved oxygen criteria that will 
protect the refined tidal-water designated uses, presented in Table VI-1. Given recog¬ 
nized limitations in direct monitoring at the temporal scales required for assessing 
attainment of the instantaneous minimum, 1-day mean and 7-day mean criteria (see 
section titled “Monitoring to Support the Assessment of Criteria Attainment” for 
more details), states can waive attainment assessments for these criteria until moni¬ 
toring at the required temporal scales is implemented or apply statistical methods to 
estimate probable attainment. Where sufficient data at these temporal scales exist for 
specific regions or local habitats, states should assess attainment of the full set of 
applicable dissolved oxygen criteria. 
WATER CLARITY CRITERIA 
The Chesapeake Bay water clarity criteria were derived based on the minimum 
percent light-through-water (PLW) requirements of underwater bay grasses (Table 
VI-2). These criteria apply only to shallow-water designated use habitats. The water 
clarity criteria are not intended to apply in areas where underwater bay grasses are 
precluded from growing by non-water clarity-related factors such as excessive wave 
action or at depths where natural and other physical habitat factors will prevent 
sufficient light penetration required by the plants. See Chapter IV for a discussion of 
the salinity regime-specific criteria and time periods for application. Refer to 
chapter vi 
Recommended Implementation Procedures 
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