Umbrella Criteria Workshop

Currently, analyses for determining dissolved oxygen (DO) impairments in the Open and Deep Water designated uses of the Chesapeake Bay and its tidal tributaries are conducted for only the 30-day mean DO criterion of 5.0 mg/L in Open Water, the summer 30-day mean criterion of 3.0 mg/L in Deep Water, and the summer instantaneous minimum of 1.0 mg/L in the Deep Channel designated use. The summer season (June – September) is assumed to be the limiting season in all designated uses being assessed for DO impairment. Historically, insufficient data have been available to assess higher frequency criteria (i.e. the 7-day and 1-day average concentrations).

In 2009, the Chesapeake Bay Program’s Modeling Team used output from the Water Quality Sediment Transport Model (WQSTM) to determine whether the criteria being assessed for DO are more or less protective than criteria currently left un-assessed. Analyses of WQSTM output have indicated that when the summer 30-day mean criteria are attained in Open and Deep Water designated uses, the associated higher frequency criteria are also attained. Similarly, when the instantaneous minimum criterion of 1.0 mg/L is attained in Deep Channel regions, other Deep Channel criteria are also met. In other words, the criteria currently being assessed appear to be “umbrella criteria” – the most restrictive of all available criteria. Based on these findings, the EPA Chesapeake Bay Program and its state partners are currently operating on the assumption that the criteria that are currently being assessed for listing purposes are sufficiently protective.

The recent implementation of new water quality monitoring technologies in the Bay (e.g. vertical water quality profilers, Scanfish, fixed site continuous monitors) has resulted in datasets with previously unavailable spatial high density and/or temporal high frequency measurements of Bay dynamics. By combining these datasets with data from the CBP’s long-term fixed station monitoring program, several partners in the Chesapeake Bay research and monitoring communities have conducted analyses that in some cases support, but in other cases call into question, this key “umbrella criteria” assumption. The objective of this workshop is to serve as the final step in a process that produces a consistent and question-driven set of analyses (using monthly meetings of the Tidal Monitoring and Analysis Workgroup, or “TMAW”, as the facilitating and organizing vehicle). The workshop will synthesize the results of these analyses in order to generate a report that addresses the following questions:

• Under what conditions (i.e. for which criteria, and/or in which regions, and/or during which seasons), the “umbrella criteria” assumption appears to be accurate;
• Under what conditions this assumption appears to be violated;
• For what conditions currently available data do not allow us to test this assumption
• The data that would be needed to test this assumption for all conditions