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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 below 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 < 29C

Instantaneous minimum ≥ 4.3 mg/l at temperatures ≥ 29C

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 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

1700

22%

5000

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

200

13%

500

April 1 - October 31

JMSTF1

1000

13%

2500

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

200

22%

500

April 1 - October 31

JMSPH

300

22%

750

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: 19832003, 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 below 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), and 2010 (CBP/TRS 301-10, EPA 903-R-10-002) 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.


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