Section 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.

	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 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: 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 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.

Historical Notes

Derived from Volume 21, Issue 23, eff. June 24, 2005; amended, Volume 26, Issue 12, eff. February 1, 2010; Volume 27, Issue 06, eff. January 6, 2011.

Statutory Authority

§ 62.1-44.15 of the Code of Virginia; 33 USC § 1251 et seq. of the federal Clean Water Act; 40 CFR Part 131.