9VAC25-260-185. Criteria to protect designated uses from the impacts of nutrients and suspended sediment in the Chesapeake Bay and its tidal tributaries

A. Dissolved oxygen. The dissolved oxygen criteria in the following table apply to all Chesapeake Bay waters according to their specified designated use and supersede the dissolved oxygen criteria in 9VAC25-260-50 . Designated Use Criteria Concentration/Duration Temporal Application Designated Use Criteria Concentration/Duration Temporal Application Migratory fish spawning and nursery 7-day mean ≥ 6 mg/l (tidal habitats with 0-0.5 ppt salinity) February 1 - May 31 Migratory fish spawning and nursery 7-day mean ≥ 6 mg/l (tidal habitats with 0-0.5 ppt salinity) February 1 - May 31 Instantaneous minimum ≥ 5 mg/l Instantaneous minimum ≥ 5 mg/l Open water 1 30-day mean ≥ 5.5 mg/l (tidal habitats with 0-0.5 ppt salinity) year-round 2 Open water 1 30-day mean ≥ 5.5 mg/l (tidal habitats with 0-0.5 ppt salinity) year-round 2 30-day mean ≥ 5 mg/l (tidal habitats with > 0.5 ppt salinity) 30-day mean ≥ 5 mg/l (tidal habitats with > 0.5 ppt salinity) 7-day mean ≥ 4 mg/l 7-day mean ≥ 4 mg/l Instantaneous minimum ≥ 3.2 mg/l at temperatures < 29°C Instantaneous minimum ≥ 4.3 mg/l at temperatures ≥ 29°C Instantaneous minimum ≥ 3.2 mg/l at temperatures < 29°C Instantaneous minimum ≥ 4.3 mg/l at temperatures ≥ 29°C Deep water 30-day mean ≥ 3 mg/l June 1 - September 30 Deep water 30-day mean ≥ 3 mg/l June 1 - September 30 1-day mean ≥ 2.3 mg/l 1-day mean ≥ 2.3 mg/l Instantaneous minimum ≥ 1.7 mg/l Instantaneous minimum ≥ 1.7 mg/l Deep channel Instantaneous minimum ≥ 1 mg/l June 1 - September 30 Deep channel Instantaneous minimum ≥ 1 mg/l June 1 - September 30 1 In applying this open water instantaneous criterion to the Chesapeake Bay and its tidal tributaries where the existing water quality for dissolved oxygen exceeds an instantaneous minimum of 3.2 mg/l, that higher water quality for dissolved oxygen shall be provided antidegradation protection in accordance with 9VAC25-260-30 A 2. 2 Open-water dissolved oxygen criteria attainment is assessed separately over two time periods: summer (June 1- September 30) and nonsummer (October 1-May 31) months. 1 In applying this open water instantaneous criterion to the Chesapeake Bay and its tidal tributaries where the existing water quality for dissolved oxygen exceeds an instantaneous minimum of 3.2 mg/l, that higher water quality for dissolved oxygen shall be provided antidegradation protection in accordance with 9VAC25-260-30 A 2. 2 Open-water dissolved oxygen criteria attainment is assessed separately over two time periods: summer (June 1- September 30) and nonsummer (October 1-May 31) months. B. Submerged aquatic vegetation (SAV) and water clarity. Attainment of the shallow-water submerged aquatic vegetation designated use shall be determined using any one of the following criteria: Designated Use Chesapeake Bay Program Segment SAV Acres 1 Percent Light-Through-Water 2 Water Clarity Acres 1 Temporal Application Designated Use Chesapeake Bay Program Segment SAV Acres 1 Percent Light-Through-Water 2 Water Clarity Acres 1 Temporal Application Shallow water submerged aquatic vegetation use CB5MH 7,633 22% 14,514 April 1 - October 31 Shallow water submerged aquatic vegetation use CB5MH 7,633 22% 14,514 April 1 - October 31 CB6PH 1,267 22% 3,168 March 1 - November 30 CB6PH 1,267 22% 3,168 March 1 - November 30 CB7PH 15,107 22% 34,085 March 1 - November 30 CB7PH 15,107 22% 34,085 March 1 - November 30 CB8PH 11 22% 28 March 1 - November 30 CB8PH 11 22% 28 March 1 - November 30 POTTF 2,093 13% 5,233 April 1 - October 31 POTTF 2,093 13% 5,233 April 1 - October 31 POTOH 1,503 13% 3,758 April 1 - October 31 POTOH 1,503 13% 3,758 April 1 - October 31 POTMH 4,250 22% 10,625 April 1 - October 31 POTMH 4,250 22% 10,625 April 1 - October 31 RPPTF 66 13% 165 April 1 - October 31 RPPTF 66 13% 165 April 1 - October 31 RPPOH 4 13% 10 April 1 - October 31 RPPOH 4 13% 10 April 1 - October 31 RPPMH 5,380 22% 13,450 April 1 - October 31 RPPMH 5,380 22% 13,450 April 1 - October 31 CRRMH 768 22% 1,920 April 1 - October 31 CRRMH 768 22% 1,920 April 1 - October 31 PIAMH 3,479 22% 8,014 April 1 - October 31 PIAMH 3,479 22% 8,014 April 1 - October 31 MPNTF 85 13% 213 April 1 - October 31 MPNTF 85 13% 213 April 1 - October 31 MPNOH - - - - MPNOH - - - - PMKTF 187 13% 468 April 1 - October 31 PMKTF 187 13% 468 April 1 - October 31 PMKOH - - - - PMKOH - - - - YRKMH 239 22% 598 April 1 - October 31 YRKMH 239 22% 598 April 1 - October 31 YRKPH 2,793 22% 6,982 March 1 - November 30 YRKPH 2,793 22% 6,982 March 1 - November 30 MOBPH 15,901 22% 33,990 March 1 - November 30 MOBPH 15,901 22% 33,990 March 1 - November 30 JMSTF2 266 13% 665 April 1 - October 31 JMSTF2 266 13% 665 April 1 - October 31 JMSTF1 1,333 13% 3,332 April 1 - October 31 JMSTF1 1,333 13% 3,332 April 1 - October 31 APPTF 379 13% 948 April 1 - October 31 APPTF 379 13% 948 April 1 - October 31 JMSOH 15 13% 38 April 1 - October 31 JMSOH 15 13% 38 April 1 - October 31 CHKOH 535 13% 1,338 April 1 - October 31 CHKOH 535 13% 1,338 April 1 - October 31 JMSMH 531 22% 1,328 April 1 - October 31 JMSMH 531 22% 1,328 April 1 - October 31 JMSPH 604 22% 1,510 March 1 - November 30 JMSPH 604 22% 1,510 March 1 - November 30 WBEMH - - - - WBEMH - - - - SBEMH - - - - SBEMH - - - - EBEMH - - - - EBEMH - - - - ELIPH - - - - ELIPH - - - - LYNPH 107 22% 268 March 1 - November 30 LYNPH 107 22% 268 March 1 - November 30 POCOH - - - - POCOH - - - - POCMH 4,066 22% 9,368 April 1 - October 31 POCMH 4,066 22% 9,368 April 1 - October 31 TANMH 13,579 22% 22,064 April 1 - October 31 TANMH 13,579 22% 22,064 April 1 - October 31 1 The assessment period for SAV and water clarity acres shall be the single best year in the most recent three consecutive years. When three consecutive years of data are not available, a minimum of three years within the data assessment window shall be used. 1 The assessment period for SAV and water clarity acres shall be the single best year in the most recent three consecutive years. When three consecutive years of data are not available, a minimum of three years within the data assessment window shall be used. 2 Percent light-through-water = 100e (-KdZ) where K d is water column light attenuation coefficient and can be measured directly or converted from a measured secchi depth where K d = 1.45/secchi depth. Z = depth at location of measurement of K d . 2 Percent light-through-water = 100e (-KdZ) where K d is water column light attenuation coefficient and can be measured directly or converted from a measured secchi depth where K d = 1.45/secchi depth. Z = depth at location of measurement of K d . C. Chlorophyll a. Designated Use Chlorophyll a Narrative Criterion Temporal Application Designated Use Chlorophyll a Narrative Criterion Temporal Application Open water Concentrations of chlorophyll a in free-floating microscopic aquatic plants (algae) shall not exceed levels that result in undesirable or nuisance aquatic plant life or render tidal waters unsuitable for the propagation and growth of a balanced, indigenous population of aquatic life or otherwise result in ecologically undesirable water quality conditions such as reduced water clarity, low dissolved oxygen, food supply imbalances, proliferation of species deemed potentially harmful to aquatic life or humans, or aesthetically objectionable conditions. March 1 - September 30 Open water Concentrations of chlorophyll a in free-floating microscopic aquatic plants (algae) shall not exceed levels that result in undesirable or nuisance aquatic plant life or render tidal waters unsuitable for the propagation and growth of a balanced, indigenous population of aquatic life or otherwise result in ecologically undesirable water quality conditions such as reduced water clarity, low dissolved oxygen, food supply imbalances, proliferation of species deemed potentially harmful to aquatic life or humans, or aesthetically objectionable conditions. March 1 - September 30 See 9VAC25-260-310 special standard bb for numerical chlorophyll criteria for the tidal James River. See 9VAC25-260-310 special standard bb for numerical chlorophyll criteria for the tidal James River. D. Implementation. 1. Chesapeake Bay program segmentation scheme as described in Chesapeake Bay Program, 2004 Chesapeake Bay Program Analytical Segmentation Scheme-Revisions, Decisions and Rationales: 1983–2003, CBP/TRS 268/04, EPA 903-R-04-008, Chesapeake Bay Program, Annapolis, Maryland, and the Chesapeake Bay Program published 2005 addendum (CBP/TRS 278-06; EPA 903-R-05-004) is listed in the following table and shall be used as the spatial assessment unit to determine attainment of the criteria in this section for each designated use. Chesapeake Bay Segment Description Segment Name 1 Chesapeake Bay Segment Description Segment Name 1 Chesapeake Bay Segment Description Segment Name 1 Chesapeake Bay Segment Description Segment Name 1 Lower Central Chesapeake Bay CB5MH Mobjack Bay MOBPH Lower Central Chesapeake Bay CB5MH Mobjack Bay MOBPH Western Lower Chesapeake Bay CB6PH Upper Tidal Fresh James River JMSTF2 Western Lower Chesapeake Bay CB6PH Upper Tidal Fresh James River JMSTF2 Eastern Lower Chesapeake Bay CB7PH Lower Tidal Fresh James River JMSTF1 Eastern Lower Chesapeake Bay CB7PH Lower Tidal Fresh James River JMSTF1 Mouth of the Chesapeake Bay CB8PH Appomattox River APPTF Mouth of the Chesapeake Bay CB8PH Appomattox River APPTF Upper Potomac River POTTF Middle James River JMSOH Upper Potomac River POTTF Middle James River JMSOH Middle Potomac River POTOH Chickahominy River CHKOH Middle Potomac River POTOH Chickahominy River CHKOH Lower Potomac River POTMH Lower James River JMSMH Lower Potomac River POTMH Lower James River JMSMH Upper Rappahannock River RPPTF Mouth of the James River JMSPH Upper Rappahannock River RPPTF Mouth of the James River JMSPH Middle Rappahannock River RPPOH Western Branch Elizabeth River WBEMH Middle Rappahannock River RPPOH Western Branch Elizabeth River WBEMH Lower Rappahannock River RPPMH Southern Branch Elizabeth River SBEMH Lower Rappahannock River RPPMH Southern Branch Elizabeth River SBEMH Corrotoman River CRRMH Eastern Branch Elizabeth River EBEMH Corrotoman River CRRMH Eastern Branch Elizabeth River EBEMH Piankatank River PIAMH Lafayette River LAFMH Piankatank River PIAMH Lafayette River LAFMH Upper Mattaponi River MPNTF Mouth of the Elizabeth River ELIPH Upper Mattaponi River MPNTF Mouth of the Elizabeth River ELIPH Lower Mattaponi River MPNOH Lynnhaven River LYNPH Lower Mattaponi River MPNOH Lynnhaven River LYNPH Upper Pamunkey River PMKTF Middle Pocomoke River POCOH Upper Pamunkey River PMKTF Middle Pocomoke River POCOH Lower Pamunkey River PMKOH Lower Pocomoke River POCMH Lower Pamunkey River PMKOH Lower Pocomoke River POCMH Middle York River YRKMH Tangier Sound TANMH Middle York River YRKMH Tangier Sound TANMH Lower York River YRKPH Lower York River YRKPH 1 First three letters of segment name represent Chesapeake Bay segment description, letters four and five represent the salinity regime of that segment (TF = Tidal Fresh, OH = Oligohaline, MH = Mesohaline, and PH = Polyhaline) and a sixth space is reserved for subdivisions of that segment. 1 First three letters of segment name represent Chesapeake Bay segment description, letters four and five represent the salinity regime of that segment (TF = Tidal Fresh, OH = Oligohaline, MH = Mesohaline, and PH = Polyhaline) and a sixth space is reserved for subdivisions of that segment. 2. The assessment period shall be the most recent three consecutive years. When three consecutive years of data are not available, a minimum of three years within the data assessment window shall be used. 3. Attainment of these criteria shall be assessed through comparison of the generated cumulative frequency distribution of the monitoring data to the applicable criteria reference curve for each designated use. If the monitoring data cumulative frequency curve is completely contained inside the reference curve, then the segment is in attainment of the designated use. The reference curves and procedures to be followed are published in the USEPA, 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, April 2003 and the 2004 (EPA 903-R-03-002 October 2004), 2007 (CBP/TRS 285/07, EPA 903-R-07-003), 2007 (CBP/TRS 288/07, EPA 903-R-07-005), 2008 (CBP/TRS 290-08, EPA 903-R-08-001), 2010 (CBP/TRS 301-10, EPA 903-R-10-002), and 2017 (CBP/TRS 3 20-17 , EPA 903-R-17-002) addenda. An exception to this requirement is in measuring attainment of the SAV and water clarity acres, which are compared directly to the criteria.