2.4 Apportioning results by designated use 
2.5 Water quality criteria assessment, attainment and violations 
Step 2.4 above, carried forward the Step 4-Pointwise Compliance considerations of a statistical 
decision-making framework originally published in U.S. EPA 2007a Chapter II: Refinements to 
Chesapeake Bay Water Quality Criteria Assessment Methodology (pp. 17-18) and revisited in 
U.S. EPA 2008 (Appendix A). This section on pointwise compliance states: 
“While interpolation allows for standardization of many types of data, pointwise 
attainment allows for standardization of many criteria. Because attainment is 
determined at moments in time and points in space, it is possible to vary the 
criterion in time and space. If different levels of a water quality criterion are 
acceptable in different seasons, then the criterion can vary seasonally. It is 
possible to implement different criteria over space for a segment that bridges, for 
example, oligohaline and mesohaline, salinity zones. It might even be possible to 
let the criterion be a continuous function of some ancillary variable such as 
temperature or salinity, although this situation requires that such data exist for 
every interpolator cell. The only requirement is that the final attainment 
determination be “yes” or “no” for each interpolator cell.” 
The implicit assumption of the Chesapeake Bay partners was that if no pycnoclines were found 
for a particular sampling event then the open-water designated use and its respective dissolved 
oxygen criteria were being applied, i.e. that water column dynamics including “episodic 
pycnoclines” were accounted for as part of the criteria assessment computations. The U.S. EPA 
Chesapeake Bay Program Office's criteria assessment computer code, however, applied the 
long-term average pycnocline depth(s) to those water quality monitoring cruise sampling events 
when no pycnocline was found for those 13 segments, identified in U.S. EPA 2004 where deep¬ 
water and/or deep channel designated uses applied during the June-September time period. 
Therefore, under special cases, on the basis of pre-determined characterization, there were errors 
in designated use classification. 
REVISING A PROCEDURAL ANOMALY IN THE DESIGNATED USE DELINEATION 
Identification of a Procedural Anomaly 
During 2009, a procedural anomaly was discovered between EPA published dissolved oxygen 
criteria assessment protocols through 2008 for pycnocline delineation that defined the boundaries 
for the open-water, deep-water and/or deep-channel designated uses and the assessment 
procedures as defined in the criteria assessment computer code developed by the EPA 
Chesapeake Bay Program Office and used by the states and the District. The published 
procedures set forth that attainment is determined at moments in time and space given that the 
designated uses, their boundaries and the applicable dissolved oxygen criteria will also vary in 
time and space (U.S. EPA 2003). U.S. EPA (2008) published details of the computations for 
identifying pycnoclines where they exist on a water quality monitoring cruise-by-cruise basis. 
EPA also identified 13 Chesapeake Bay segments where deep-water and (or) deep-channel 
designated uses applied during the June-September time period (U.S. EPA 2004, page 5, Figure 
9 
