plots show problem areas and indicate their distance from criteria attainment. 
However, they are limited in evaluating the overall picture of magnitude of criteria 
exceedance for the entire Chesapeake Bay. Criteria values vary spatially and thus the 
magnitude of exceedance will depend on both actual interpolator values and the 
criteria values themselves. To address this need, a second set of interpolator plots 
illustrating the magnitude of exceedance as a percentage of the criteria values them¬ 
selves should be generated (Figure VI-13). Any estimated values below the criteria 
level will be less than one and bounded at zero, whereas estimated values above the 
criteria level will be in percentage of criteria level. 
Other information is available to evaluate the significance of the criteria attainment 
assessment results and to place them in context. This includes the size of the desig¬ 
nated use (as surface area or volume) and the percentage of the total habitat that is 
represented by the designated use. This particular data is especially useful for 
dissolved oxygen criteria attainment assessment. The information is used to under¬ 
stand the relative percentage of the total habitat that is accounted for by the 
Interpolator-Estimated 
Chlorophyll a Concentration 
(pg liter 1 ) 
Attains 
101-120 
121-120 
200-300 
300-400 
400-500 
500-600 
600-1100 
Figure VI-13. Example plot of chlorophyll a concentration (pg liter' 1 ) estimates 
generated through spatial interpolation, expressed as a percentage of a possible spring 
season criteria value, for purposes of evaluating the magnitude of criteria exceedance. 
chapter vi • Recommended Implementation Procedures 
