SEGMENT 
Figure VI-3. Chlorophyll a concentration values estimated for each interpolator cell 
are compared to the appropriate criterion value on a cell-by-cell basis to determine the 
spatial extent of exceedance. 
STEP 3. IDENTIFICATION OF INTERPOLATOR CELLS 
THAT EXCEED THE CRITERION VALUE 
When the appropriate criterion value has been assigned to each interpolator cell, 
comparisons can be made on a cell-by-cell basis to determine if the estimated water 
quality values met or exceeded the criteria at the time of the monitoring event. Eval¬ 
uation of criteria exceedance is performed for each cell in a spatial unit (Figure 
VI-4a), enabling the entire spatial unit to be characterized. The percentage of cells 
that exceed the criteria represents the spatial extent of exceedance in that spatial unit 
and for that sampling event. The same process is repeated for every sampling event 
(Figure VI-4b) and the compilation of the estimates of the extent of spatial 
exceedance provides an indication of the frequency of exceedance. 
STEP 4. CALCULATION OF THE CUMULATIVE PROBABILITY 
OF EACH SPATIAL EXTENT OF EXCEEDANCE 
The spatial extent of exceedance (represented by the colored cells in Figure VI-4) is 
calculated as the percentage of area or volume exceeding the criteria. This is accom¬ 
plished by simply dividing the area or volume of all the cells exceeding the criteria 
by the total area or volume of the spatial assessment unit and multiplying by 100. 
chapter vi 
Recommended Implementation Procedures 
