{"data":{"id":"us-va/9vac25-260-185","jurisdiction":"us-va","citation":"9VAC25-260-185","heading":"Criteria to protect designated uses from the impacts of nutrients and suspended sediment in the Chesapeake Bay and its tidal tributaries","body":"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.\n\nDesignated Use\n\nCriteria Concentration/Duration\n\nTemporal Application\n\nMigratory fish spawning and nursery\n\n7-day mean ≥ 6 mg/l (tidal habitats with 0-0.5 ppt salinity)\n\nFebruary 1 - May 31\n\nInstantaneous minimum ≥ 5 mg/l\n\nOpen water1\n\n30-day mean ≥ 5.5 mg/l (tidal habitats with 0-0.5 ppt salinity)\n\nyear-round2\n\n30-day mean ≥ 5 mg/l (tidal habitats with \u003e 0.5 ppt salinity)\n\n7-day mean ≥ 4 mg/l\n\nInstantaneous minimum ≥ 3.2 mg/l at temperatures \u003c 29°C\n\nInstantaneous minimum ≥ 4.3 mg/l at temperatures ≥ 29°C\n\nDeep water\n\n30-day mean ≥ 3 mg/l\n\nJune 1 - September 30\n\n1-day mean ≥ 2.3 mg/l\n\nInstantaneous minimum ≥ 1.7 mg/l\n\nDeep channel\n\nInstantaneous minimum ≥ 1 mg/l\n\nJune 1 - September 30\n\n1In 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.\n\n2Open-water dissolved oxygen criteria attainment is assessed separately over two time periods: summer (June 1- September 30) and nonsummer (October 1-May 31) months.\n\nB. 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:\n\nDesignated Use\n\nChesapeake Bay Program Segment\n\nSAV Acres1\n\nPercent Light-Through-Water2\n\nWater Clarity Acres1\n\nTemporal Application\n\nShallow water submerged aquatic vegetation use\n\nCB5MH\n\n7,633\n\n22%\n\n14,514\n\nApril 1 - October 31\n\nCB6PH\n\n1,267\n\n22%\n\n3,168\n\nMarch 1 - November 30\n\nCB7PH\n\n15,107\n\n22%\n\n34,085\n\nMarch 1 - November 30\n\nCB8PH\n\n11\n\n22%\n\n28\n\nMarch 1 - November 30\n\nPOTTF\n\n2,093\n\n13%\n\n5,233\n\nApril 1 - October 31\n\nPOTOH\n\n1,503\n\n13%\n\n3,758\n\nApril 1 - October 31\n\nPOTMH\n\n4,250\n\n22%\n\n10,625\n\nApril 1 - October 31\n\nRPPTF\n\n66\n\n13%\n\n165\n\nApril 1 - October 31\n\nRPPOH\n\n4\n\n13%\n\n10\n\nApril 1 - October 31\n\nRPPMH\n\n5,380\n\n22%\n\n13,450\n\nApril 1 - October 31\n\nCRRMH\n\n768\n\n22%\n\n1,920\n\nApril 1 - October 31\n\nPIAMH\n\n3,479\n\n22%\n\n8,014\n\nApril 1 - October 31\n\nMPNTF\n\n85\n\n13%\n\n213\n\nApril 1 - October 31\n\nMPNOH\n\n-\n\n-\n\n-\n\n-\n\nPMKTF\n\n187\n\n13%\n\n468\n\nApril 1 - October 31\n\nPMKOH\n\n-\n\n-\n\n-\n\n-\n\nYRKMH\n\n239\n\n22%\n\n598\n\nApril 1 - October 31\n\nYRKPH\n\n2,793\n\n22%\n\n6,982\n\nMarch 1 - November 30\n\nMOBPH\n\n15,901\n\n22%\n\n33,990\n\nMarch 1 - November 30\n\nJMSTF2\n\n266\n\n13%\n\n665\n\nApril 1 - October 31\n\nJMSTF1\n\n1,333\n\n13%\n\n3,332\n\nApril 1 - October 31\n\nAPPTF\n\n379\n\n13%\n\n948\n\nApril 1 - October 31\n\nJMSOH\n\n15\n\n13%\n\n38\n\nApril 1 - October 31\n\nCHKOH\n\n535\n\n13%\n\n1,338\n\nApril 1 - October 31\n\nJMSMH\n\n531\n\n22%\n\n1,328\n\nApril 1 - October 31\n\nJMSPH\n\n604\n\n22%\n\n1,510\n\nMarch 1 - November 30\n\nWBEMH\n\n-\n\n-\n\n-\n\n-\n\nSBEMH\n\n-\n\n-\n\n-\n\n-\n\nEBEMH\n\n-\n\n-\n\n-\n\n-\n\nELIPH\n\n-\n\n-\n\n-\n\n-\n\nLYNPH\n\n107\n\n22%\n\n268\n\nMarch 1 - November 30\n\nPOCOH\n\n-\n\n-\n\n-\n\n-\n\nPOCMH\n\n4,066\n\n22%\n\n9,368\n\nApril 1 - October 31\n\nTANMH\n\n13,579\n\n22%\n\n22,064\n\nApril 1 - October 31\n\n1The 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.\n\n2Percent 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.\n\nC. Chlorophyll a.\n\nDesignated Use\n\nChlorophyll a Narrative Criterion\n\nTemporal Application\n\nOpen water\n\nConcentrations 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.\n\nMarch 1 - September 30\n\nSee 9VAC25-260-310 special standard bb for numerical chlorophyll criteria for the tidal James River.\n\nD. Implementation.\n\n1. 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.\n\nChesapeake Bay Segment Description\n\nSegment Name1\n\nChesapeake Bay Segment Description\n\nSegment Name1\n\nLower Central Chesapeake Bay\n\nCB5MH\n\nMobjack Bay\n\nMOBPH\n\nWestern Lower Chesapeake Bay\n\nCB6PH\n\nUpper Tidal Fresh James River\n\nJMSTF2\n\nEastern Lower Chesapeake Bay\n\nCB7PH\n\nLower Tidal Fresh James River\n\nJMSTF1\n\nMouth of the Chesapeake Bay\n\nCB8PH\n\nAppomattox River\n\nAPPTF\n\nUpper Potomac River\n\nPOTTF\n\nMiddle James River\n\nJMSOH\n\nMiddle Potomac River\n\nPOTOH\n\nChickahominy River\n\nCHKOH\n\nLower Potomac River\n\nPOTMH\n\nLower James River\n\nJMSMH\n\nUpper Rappahannock River\n\nRPPTF\n\nMouth of the James River\n\nJMSPH\n\nMiddle Rappahannock River\n\nRPPOH\n\nWestern Branch Elizabeth River\n\nWBEMH\n\nLower Rappahannock River\n\nRPPMH\n\nSouthern Branch Elizabeth River\n\nSBEMH\n\nCorrotoman River\n\nCRRMH\n\nEastern Branch Elizabeth River\n\nEBEMH\n\nPiankatank River\n\nPIAMH\n\nLafayette River\n\nLAFMH\n\nUpper Mattaponi River\n\nMPNTF\n\nMouth of the Elizabeth River\n\nELIPH\n\nLower Mattaponi River\n\nMPNOH\n\nLynnhaven River\n\nLYNPH\n\nUpper Pamunkey River\n\nPMKTF\n\nMiddle Pocomoke River\n\nPOCOH\n\nLower Pamunkey River\n\nPMKOH\n\nLower Pocomoke River\n\nPOCMH\n\nMiddle York River\n\nYRKMH\n\nTangier Sound\n\nTANMH\n\nLower York River\n\nYRKPH\n\n1First 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.\n\n2. 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.\n\n3. 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.","path":["Title 9. Environment","Agency 25. State Water Control Board","Chapter 260. Water Quality Standards","Part II. Standards with More Specific Application"],"source_url":"https://law.lis.virginia.gov/admincode/title9/agency25/chapter260/section185/","current_through":"2026 Regular Session (effective July 1, 2026)","vintage":"","retrieved_at":"2026-09-14T04:49:14Z","sha256":"e5898edb6072ff67b8c0e9b10f66bcf00d4cc0a85a8cddc393785b33539e1f0e","source_id":"us-va-vac","stale":false,"prev":"us-va/9vac25-260-180","next":"us-va/9vac25-260-186"},"notice":"GroundRules: Original legal text. Not legal advice."}