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 |
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 | ||
Open water1 | 30-day mean ≥ 5.5 mg/l (tidal habitats with 0-0.5 ppt salinity) | year-round2 |
30-day mean ≥ 5 mg/l (tidal habitats with > 0.5 ppt salinity) | ||
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 | ||
Deep water | 30-day mean ≥ 3 mg/l | June 1 - September 30 |
1-day mean ≥ 2.3 mg/l | ||
Instantaneous minimum ≥ 1.7 mg/l | ||
Deep channel | Instantaneous minimum ≥ 1 mg/l | June 1 - September 30 |
1In 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. 2Open-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 Acres1 | Percent Light-Through-Water2 | Water Clarity Acres1 | Temporal Application |
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 | |
CB7PH | 15,107 | 22% | 34,085 | March 1 - November 30 | |
CB8PH | 11 | 22% | 28 | March 1 - November 30 | |
POTTF | 2,093 | 13% | 5,233 | April 1 - October 31 | |
POTOH | 1,503 | 13% | 3,758 | April 1 - October 31 | |
POTMH | 4,250 | 22% | 10,625 | April 1 - October 31 | |
RPPTF | 66 | 13% | 165 | April 1 - October 31 | |
RPPOH | 4 | 13% | 10 | April 1 - October 31 | |
RPPMH | 5,380 | 22% | 13,450 | April 1 - October 31 | |
CRRMH | 768 | 22% | 1,920 | April 1 - October 31 | |
PIAMH | 3,479 | 22% | 8,014 | April 1 - October 31 | |
MPNTF | 85 | 13% | 213 | April 1 - October 31 | |
MPNOH | - | - | - | - | |
PMKTF | 187 | 13% | 468 | April 1 - October 31 | |
PMKOH | - | - | - | - | |
YRKMH | 239 | 22% | 598 | April 1 - October 31 | |
YRKPH | 2,793 | 22% | 6,982 | March 1 - November 30 | |
MOBPH | 15,901 | 22% | 33,990 | March 1 - November 30 | |
JMSTF2 | 266 | 13% | 665 | April 1 - October 31 | |
JMSTF1 | 1,333 | 13% | 3,332 | April 1 - October 31 | |
APPTF | 379 | 13% | 948 | April 1 - October 31 | |
JMSOH | 15 | 13% | 38 | April 1 - October 31 | |
CHKOH | 535 | 13% | 1,338 | April 1 - October 31 | |
JMSMH | 531 | 22% | 1,328 | April 1 - October 31 | |
JMSPH | 604 | 22% | 1,510 | March 1 - November 30 | |
WBEMH | - | - | - | - | |
SBEMH | - | - | - | - | |
EBEMH | - | - | - | - | |
ELIPH | - | - | - | - | |
LYNPH | 107 | 22% | 268 | March 1 - November 30 | |
POCOH | - | - | - | - | |
POCMH | 4,066 | 22% | 9,368 | April 1 - October 31 | |
TANMH | 13,579 | 22% | 22,064 | April 1 - October 31 | |
1The 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. | |||||
2Percent light-through-water = 100e(-KdZ) where Kd is water column light attenuation coefficient and can be measured directly or converted from a measured secchi depth where Kd = 1.45/secchi depth. Z = depth at location of measurement of Kd. | |||||
C. Chlorophyll a.
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 |
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 Name1 | Chesapeake Bay Segment Description | Segment Name1 |
Lower Central Chesapeake Bay | CB5MH | Mobjack Bay | MOBPH |
Western Lower Chesapeake Bay | CB6PH | Upper Tidal Fresh James River | JMSTF2 |
Eastern Lower Chesapeake Bay | CB7PH | Lower Tidal Fresh James River | JMSTF1 |
Mouth of the Chesapeake Bay | CB8PH | Appomattox River | APPTF |
Upper Potomac River | POTTF | Middle James River | JMSOH |
Middle Potomac River | POTOH | Chickahominy River | CHKOH |
Lower Potomac River | POTMH | Lower James River | JMSMH |
Upper Rappahannock River | RPPTF | Mouth of the James River | JMSPH |
Middle Rappahannock River | RPPOH | Western Branch Elizabeth River | WBEMH |
Lower Rappahannock River | RPPMH | Southern Branch Elizabeth River | SBEMH |
Corrotoman River | CRRMH | Eastern Branch Elizabeth River | EBEMH |
Piankatank River | PIAMH | Lafayette River | LAFMH |
Upper Mattaponi River | MPNTF | Mouth of the Elizabeth River | ELIPH |
Lower Mattaponi River | MPNOH | Lynnhaven River | LYNPH |
Upper Pamunkey River | PMKTF | Middle Pocomoke River | POCOH |
Lower Pamunkey River | PMKOH | Lower Pocomoke River | POCMH |
Middle York River | YRKMH | Tangier Sound | TANMH |
Lower York River | YRKPH | ||
1First 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 320-17, 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.
Statutory Authority
§ 62.1-44.15 of the Code of Virginia; Clean Water Act (33 USC § 1251 et seq.); 40 CFR Part 131.
Historical Notes
Derived from Virginia Register Volume 21, Issue 23, eff. June 24, 2005; amended, Volume 26, Issue 12, eff. February 1, 2010; Volume 27, Issue 6, eff. January 6, 2011; Volume 32, Issue 26, eff. June 27, 2017; Volume 35, Issue 7, eff. January 10, 2019; Volume 39, Issue 9, eff. April 18, 2023.