Developing, validating and publishing EPA-recommended methodologies for 
assessing the full array of Chesapeake Bay dissolved oxygen criteria duration 
components will also prove critical. In this chapter and its associated appendices, 
details and clarifications regarding data structure and assessment protocols are 
provided for completing Chesapeake Bay dissolved oxygen criteria attainment 
computations. 
DISSOLVED OXYGEN ASSESSMENT: 
STATIONS AND ACCEPTED DATA 
The EPA water quality criteria assessment methodologies adopted by the Chesa¬ 
peake Bay watershed jurisdictions recommend 3 consecutive years of data to 
construct the cumulative frequency distribution function to compare with the biolog¬ 
ical or other recommended reference curve (U.S. EPA 2003a). Step-by-step 
procedures of the Chesapeake Bay dissolved oxygen criteria attainment assessment 
methodology are provided for in Appendix A. A dissolved oxygen dataset was 
developed for a suite of Chesapeake Bay Program monitoring stations, and ancillary 
monitoring stations (VA), in the tidal waters of the Chesapeake Bay and its tidal trib¬ 
utaries and embayments (Appendix B) stored on-line in the Chesapeake Information 
Management System (CIMS). 
A database table was assembled for dissolved oxygen (pg/L), water temperature (°C) 
and salinity (ppt) using all tidal Chesapeake Bay Program Water Quality Monitoring 
stations from CIMS. The stations are a composite of Maryland and Virginia’s fixed 
station water quality monitoring network and the calibration and swapout data (i.e., 
swap out data is data collected when in situ water quality monitoring meters are 
switched for maintenance) from their shallow-water monitoring programs (i.e., contin¬ 
uous monitoring and DATAFLOW 1 spatially intensive monitoring). The Chesapeake 
Bay Program supported monitoring data is relatively extensive in time with a 23-year 
history, however, the temporal density of the fixed station network is biweekly to 
monthly and spatial distribution of stations is not particularly dense to meet all Chesa¬ 
peake Bay water quality criteria assessment needs. Therefore, ancillary data of 
sufficient quality is desirable and recommended for use when available to enhance the 
attainment assessments, especially where CBP data are limited or lacking. 
Ancillary data derived outside of the Chesapeake Bay Program supported water 
quality monitoring program that were considered to have sufficient quality, passing 
rigorous quality assurance/quality control standards, were added to the CIMS data. 
Examples of additional water quality monitoring data were those data provided by 
'DATAFLOW: A field sampling technology used on a boat while a watercraft is underway that collects 
spatially intensive data (hence DATA) for five environmental parameters (water temperature, salinity, 
dissolved oxygen, turbidity (ntu), and fluorescence (used to estimate chlorophyll a) collected from a 
How-through (hence FLOW) stream of water collected near the surface of the water column. The 
following website provides additional details about DATAFLOW and water quality monitoring with 
DATAFLOW: http://mddnr.chesapeakebay.net/sim/index.cfm . 
chapter iii 
Refinements to Procedures for Assessing Chesapeake Bay Dissolved Oxygen Criteria 
