Draft Appendix D – Chesapeake Bay TMDL for Nutrients and Sediment 

D‐1 September 24, 2010

Appendix D. Evaluation of the Most Protective Bay Dissolved Oxygen Criteria 

As outlined in the criteria assessment documentation in Section 3 and shown in Table D-1, seven 

different dissolved oxygen criteria are to be assessed for open-water, deep-water, and deepchannel designated uses (USEPA 2003). Using the available monitoring data, only one temporal 

averaging period is assessed for each designated-use type (USEPA 2003, 2007). Because the 

monitoring data are not available to assess all criteria or an assessment protocol has not been 

developed by the CBP partners and published by EPA, it raises the question of whether the 

assessed criteria are more or less protective of all four Chesapeake Bay designated use than the 

four criteria that are not able to be assessed. 

Table D-1. Chesapeake Bay dissolved oxygen criteria assessed with observed data for developing 

the jurisdictions’ the 303(d) lists and criteria that are not evaluated because of insufficient 

data/lack of published assessment protocols 

Designated use Instantaneous 1-day mean 7-day mean 30-day mean 

Open water Insufficient Data No Criterion Insufficient Data Assessed 

Deep water Insufficient Data Insufficient Data No Criterion Assessed 

Deep channel Assessed No Criterion No Criterion No Criterion 

It is difficult to comprehensively evaluate the protectiveness of the assessed criteria strictly based 

on monitoring data, because the unassessed criteria cannot be directly evaluated due to 

insufficient data or lack of published assessment protocols. A multi-partner effort is underway to 

develop criteria assessment protocols based on the available data, but those protocols will not be 

complete, peer reviewed and published until 2011 at the earliest. 

The full set of 7 dissolved oxygen criteria can be assessed through direct evaluation of the Bay 

Water Quality Model output. The assessments will not agree precisely with the 303(d) or Bay 

TMDL-related criteria assessment because neither of these criteria assessments uses model 

outputs directly (see Section 6.2.1). However, assuming that the temporal variability of dissolved 

oxygen in the Chesapeake Bay is reasonably well-characterized in the Bay Water Quality model, 

the relative protectiveness of different criteria evaluated directly from Bay Water Quality Model 

output would approximate the relative protectiveness of three dissolved oxygen criteria evaluated 

through monitoring data. 

All seven dissolved oxygen criteria were assessed using the direct outputs from a series of Bay 

Water Quality Model scenarios. This work was completed in November 2008 using the Phase 

5.1 version of the Chesapeake Bay Watershed Model. The Bay Water Quality Model has not 

been modified since completion of work. Given the analysis is focused evaluating temporal 

variability of dissolved oxygen in the Bay Water Quality Model outputs and uses the Bay 

Watershed Model for generation of different loading scenario input decks, the findings are still 

relevant. 

Figures D-1 and D-2 show the average dissolved oxygen criteria nonattainment of eight 

mainstem Chesapeake Bay segments for three scenarios for the 1996–1998 period. The moderate 

reduction scenario approximates 2009 loads and the large reduction scenario approximates the 

draft Bay TMDL allocation loads. 
Draft Appendix D – Chesapeake Bay TMDL for Nutrients and Sediment 

D‐2 September 24, 2010

Figure D-1. Direct model assessment of open water criteria. 

Figure D-2. Direct model assessment of deep water and deep channel criteria. 

For both open-water and deep–water designated uses, the 30-day mean criteria had the highest 

nonattainment in all three scenarios (Figures D-1 and D-2). The 30-day mean open-water and 

deep-water criteria are, therefore, protective of the other two non-assessed dissolved oxygen 

criteria (open-water 7-day and instantaneous minimum, deep-water 1-day mean and 

0.0%

0.1%

0.2%

0.3%

0.4%

0.5%

0.6%

0.7%

0.8%

0.9%

1.0%

Calibrated Model Moderate Reduction Large Reduction

Average Mainstem Non-Attainment

Direct model assessment of nonattainment—mainstem average

open water

DO Open Water Summer Instantaneous

DO Open Water Weekly

DO Open Water Summer Monthly

0%

5%

10%

15%

20%

25%

30%

Calibrated Model Moderate Reduction Large Reduction

Average Mainstem Non-Attainment

Direct model assessment of nonattainment—mainstem average

deep water and deep channel

DO Deep Water Instantaneous

DO Deep Water Daily

DO Deep Water Monthly

DO Deep Channel Instantaneous
Draft Appendix D – Chesapeake Bay TMDL for Nutrients and Sediment 

D‐3 September 24, 2010

instantaneous minimum) on average for the mainstem Bay segments. The deep–channel 

designated use has only one dissolved oxygen criterion, and it is currently assessed using 

monitoring data. The deep-channel criterion is also more protective, based on the levels of 

nonattainment recorded in Figures D-1 and D-2, than the deep-water and open-water criteria. 

Looking at the results of individual designated uses strengthens these findings considerably. 

Using the criteria nonattainment percentages for the moderate reduction scenario and the 1996–

1998 assessment period, the 30-day mean, 7-day mean, and instantaneous minimum criteria are 

compared across 53 of the 92 Bay segments with the open–water designated use. During the 

1996-1998 assessment period, these 53 segment did not attain all three open-water criteria. In all 

53 segments, the 30-day mean criterion had the highest nonattainment percentage compared to 

the 7-day mean and 1-day mean criteria (Table D-1). In the 16 Bay segments that did not attain 

all three deep water criteria during the same three year period, the 30-day mean deep-water 

criterion had the highest nonattainment percentage in all 16 segments compared with the deepwater 1-day mean and instantaneous minimum criteria (Table D-2). 

Given this is direct assessment of the Bay Water Quality Model output using inputs from the 

Phase 5.1 Bay Watershed Model and that the water quality criteria and assessment protocols that 

existed in 2008, the nonattainment values will not match with nonattainment in other parts of this 

document. 

Table D-2. Comparison of open–water dissolved oxygen 30-day mean, 7-day mean and 

instantaneous criteria for the moderate reduction scenario and the 1996–1998 assessment period 

across Bay segments for identification of the most protection criterion. 

Ches Bay 

Segment 

30-day mean 7-day mean Instantaneous 

minimum 

Most protective 

criterion 

BI2MH 3.56% 0.43% 0.00% 30-day mean 

C11TF 0.02% 0.00% 0.00% 30-day mean 

CB1TF 0.03% 0.00% 0.00% 30-day mean 

CB2OH 1.48% 0.00% 0.10% 30-day mean 

CB5MH 0.01% 0.00% 0.00% 30-day mean 

CB6PH 0.24% 0.00% 0.00% 30-day mean 

CB7PH 0.57% 0.00% 0.00% 30-day mean 

CDDOH 24.87% 20.59% 19.19% 30-day mean 

CHOMH1 7.24% 1.96% 2.53% 30-day mean 

CHOMH2 34.10% 28.45% 25.47% 30-day mean 

CHOOH 28.04% 24.18% 23.20% 30-day mean 

CHOTF 20.32% 14.31% 13.96% 30-day mean 

CHSMH 0.65% 0.00% 0.12% 30-day mean 

CHSOH 46.68% 36.62% 34.53% 30-day mean 

CHSTF 63.24% 60.63% 57.21% 30-day mean 

CMDOH 48.35% 41.64% 37.15% 30-day mean 

CNDOH 35.86% 30.44% 27.75% 30-day mean 

CRRMH 0.25% 0.00% 0.00% 30-day mean 

DCATF 2.67% 0.09% 0.29% 30-day mean 

EBEMH 1.19% 0.00% 0.00% 30-day mean 

EL1OH 9.96% 3.44% 4.14% 30-day mean 
Draft Appendix D – Chesapeake Bay TMDL for Nutrients and Sediment 

D‐4 September 24, 2010

Ches Bay 

Segment 

30-day mean 7-day mean Instantaneous 

minimum 

Most protective 

criterion 

ELIPH 27.51% 16.54% 13.56% 30-day mean 

ELKOH 9.13% 2.93% 3.77% 30-day mean 

FSBMH 8.13% 2.35% 2.83% 30-day mean 

HNGMH 1.09% 0.00% 0.13% 30-day mean 

JMSPH 1.07% 0.00% 0.00% 30-day mean 

JMSTF 0.22% 0.00% 0.13% 30-day mean 

JMSTFL 0.27% 0.00% 0.17% 30-day mean 

LCHMH 10.24% 6.17% 7.01% 30-day mean 

MA1MH 0.55% 0.00% 0.00% 30-day mean 

MAGMH 3.74% 0.00% 0.00% 30-day mean 

MANMH 0.48% 0.00% 0.00% 30-day mean 

MD5MH 0.01% 0.00% 0.00% 30-day mean 

MOBPH 1.26% 0.00% 0.02% 30-day mean 

NANMH 5.70% 3.09% 3.95% 30-day mean 

NANOH 0.04% 0.00% 0.00% 30-day mean 

PAXOH 10.68% 0.49% 0.03% 30-day mean 

PAXTF 0.95% 0.00% 0.00% 30-day mean 

PIAMH 1.93% 0.00% 0.00% 30-day mean 

PO1OH 3.83% 0.00% 0.04% 30-day mean 

POCMH 1.14% 0.03% 0.41% 30-day mean 

POTOH 3.55% 0.00% 0.03% 30-day mean 

SA1OH 10.46% 1.28% 1.36% 30-day mean 

SA2OH 8.85% 1.54% 2.19% 30-day mean 

SASOH 9.95% 1.27% 1.81% 30-day mean 

SEVMH 4.38% 0.77% 1.54% 30-day mean 

TA1MH 11.93% 6.99% 7.39% 30-day mean 

TA2MH 1.20% 0.00% 0.00% 30-day mean 

TAMMH 11.34% 6.50% 7.00% 30-day mean 

TANMH 12.85% 6.76% 6.66% 30-day mean 

TAVMH 15.43% 7.17% 5.76% 30-day mean 

VPCMH 1.62% 0.08% 0.59% 30-day mean 

YRKMH 7.42% 2.89% 3.19% 30-day mean 
Draft Appendix D – Chesapeake Bay TMDL for Nutrients and Sediment 

D‐5 September 24, 2010

Table D-3. Comparison of deep–water dissolved oxygen 30-day mean, 1-day mean and 

instantaneous criteria for the moderate reduction scenario and the 1996–1998 assessment period 

across Bay segments for identification of the most protection criterion. 

Ches Bay 

Segment 

30-day mean 1-day mean Instantaneous 

minimum 

Most protective 

criterion 

CB3MH 1.86% 0.60% 0.29% 30-day mean 

CB4MH 11.45% 10.21% 3.00% 30-day mean 

CB5MH 2.22% 1.55% 0.01% 30-day mean 

CB7PH 2.21% 0.99% 0.77% 30-day mean 

CHSMH 14.31% 12.37% 6.60% 30-day mean 

EASMH 18.11% 16.84% 9.91% 30-day mean 

MD5MH 6.08% 5.52% 0.01% 30-day mean 

PA1MH 0.11% 0.00% 0.00% 30-day mean 

PA2MH 8.11% 7.82% 3.44% 30-day mean 

PATMH 29.12% 27.75% 19.75% 30-day mean 

PAXMH 0.63% 0.00% 0.10% 30-day mean 

POMMH 0.08% 0.00% 0.00% 30-day mean 

POMMH 0.08% 0.00% 0.00% 30-day mean 

POTMH 0.08% 0.00% 0.00% 30-day mean 

RPPMH 0.01% 0.00% 0.00% 30-day mean 

SBEMH 42.50% 35.44% 22.34% 30-day mean 

EPA used direct assessment of Bay Water Quality Model outputs to document that the three 

dissolved oxygen criteria that are currently assessed—open-water 30 day mean, deep-water 30 

day mean and deep-channel instantaneous minimum—are the most restrictive criteria. These 

three criteria, applied during the summer period, are protective of the other four dissolved 

oxygen criteria across all four designated uses, across a range of nutrient reduction scenarios, and 

in all areas of the Chesapeake Bay and its tidal tributaries and embayments. 

References 

USEPA (U.S. Environmental Protection Agency). 2003. Ambient Water Quality Criteria for 

Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal 

Tributaries. EPA 903-R-03-002. Region 3 Chesapeake Bay Program Office, Annapolis, MD. 

USEPA (U.S. Environmental Protection Agency). 2007. Ambient Water Quality Criteria for 

Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal 

Tributaries–2007 Addendum. EPA 903-R-07-003. CBP/TRS 285-07. Region 3 Chesapeake Bay 

Program Office, Annapolis, MD.