components, continuous monitors mounted to buoys or piers will be required. At 
least one continuous monitor should be located at each assessment location. The 
continuous record will then be combined with fixed-station data, used to calibrate 
the spectral-analysis model (described below), and all criteria components could be 
quantified using that model. Individual criteria component estimates would be 
assessed at all fixed locations and interpolated for incorporation in a cumulative 
frequency distribution. 
'Adequate' Level of Monitoring 
Assuming that funding will not be available for the ‘recommended’ monitoring 
approach, an alternative would be to place a limited number of continuous monitors 
at representative locations in the Chesapeake Bay and tidal tributaries. The number 
of continuous monitors would be relatively small, but the number would be estab¬ 
lished to characterize different types of settings in the Chesapeake Bay. Those 
representative temporal records would then be combined with fixed-station data in 
similar settings, and spectral models would be developed for each fixed-station loca¬ 
tion. Dissolved oxygen criteria components would be assessed based on the spectral 
models, interpolated and used to develop the cumulative frequency distributions. 
This approach would entail much greater uncertainty in the assessments. The 
absolute variation would be characterized well by regular monthly measurements at 
the fixed-stations. However, the higher frequency assessments would be based on 
data collected at only a few locations, which would then be extrapolated over large 
distances. 
'Marginal' Level of Monitoring 
Assuming that funding will not be available for even the ‘adequate’ level of moni¬ 
toring, assessments would need to rely on the fixed-station data only. As stated 
above, this type of monitoring was designed for long-term assessments and would 
only be truly appropriate for the 30-day mean criteria component. If the ‘marginal’ 
level of monitoring was selected, it is likely that higher frequency criteria compo¬ 
nents would not be assessed in most designated use areas. 
Assessing Dissolved Oxygen Criteria Attainment 
Addressing Duration Issues. The dissolved oxygen criteria have several 
different durations: 30-day mean, 7-day mean, 1-day mean (deep-water only) and 
instantaneous minimum. A state’s ability to assess these criteria and to have certainty 
in the results depends on the time scale of available data and on the capacity of 
models to estimate conditions at those time scales. At present, long-term, fixed- 
station, midchannel water quality monitoring in the Chesapeake Bay and its tidal 
tributaries provides dissolved oxygen measurements twice monthly at most or 
approximately every 15 days between April and August. Proposed enhancements to 
the tidal water quality monitoring program include shallow-water monitoring, as 
chapter vi 
Recommended Implementation Procedures 
