Draft Appendix D – Chesapeake Bay TMDL for Nutrients and Sediment



### D

‐ 1 September 24, 2010 Appendix D. Evaluation of the Most Prot ective Bay Dissolved Oxygen Criteria

As outlined in the criteria assessment documenta tion 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 mon itoring data, only one temporal averaging period is assessed for each designa ted-use type (USEPA 2003, 2007). Because the monitoring data are not available to assess all criteria or an a ssessment 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 In sufficient 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 crit eria cannot be direc tly evaluated due to insufficient data or lack of published assessment pr otocols. 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 w ill 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, assumi ng that the temporal variability of dissolved oxygen in the Chesapeake Bay is re asonably 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 relati ve protectiveness of three disso lved 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 wa s completed in November 2008 using the Phase 5.1 version of the Chesapeake Bay Watershed M odel. 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 loadi ng scenario input decks, the findings are still relevant.

Figures D-1 and D-2 show the average disso lved oxygen criteria nona ttainment of eight mainstem Chesapeake Bay segments for three scenarios for the 1996–1998 period. The moderate reduction scenario approximates 2009 loads and th e 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 m ean criteria had the highest nonattainment in all three scen arios (Figures D-1 and D-2). The 30-day mean open-water and deep-water criteria are, ther efore, protective of the other two non-assessed dissolved oxygen criteria (open-water 7-day and instantane ous 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 ReductionAverage 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 ReductionAverage 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 InstantaneousDraft 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 cr iterion, and it is curr ently assessed using monitoring data. The deep-channel criterion is also more protec tive, based on the levels of nonattainment recorded in Figures D-1 and D-2, th an the deep-water and open-water criteria.

Looking at the results of individual designated uses strengthens these findings considerably. Using the criteria nonattainment percentages fo r the moderate reduction scenario and the 1996– 1998 assessment period, the 30-day mean, 7-day m ean, and instantaneous minimum criteria are compared across 53 of the 92 Bay segments w ith the open–water designated use. During the 1996-1998 assessment period, these 53 segment did not atta in all three open-water criteria. In all 53 segments, the 30-day mean criterion had the hi ghest 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 nonattain ment percentage in all 16 segm ents 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 qua lity 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 meanDraft 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 meanDraft 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 Qualit y Model outputs to document that the three dissolved oxygen criteria that are currently assessed—open-wa ter 30 day mean, deep-water 30 day mean and deep-channel instantaneous mini mum—are the most restri ctive criteria. These three criteria, applied during the summer period, are protective of the other four dissolved oxygen criteria across all four desi gnated 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 Ba y Program Office, Annapolis, MD.

USEPA (U.S. Environmental Protection Agency). 2007. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlor ophyll 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.