{
  "url": "https://openlegislation.uk/water-framework-directive-classification-priority-substances-and-shellfish-waters-regulations-northern-ireland-2015/schedule-1/part-4",
  "json_url": "https://openlegislation.uk/water-framework-directive-classification-priority-substances-and-shellfish-waters-regulations-northern-ireland-2015/schedule-1/part-4.json",
  "legislation": "nisr/2015/351",
  "legislation_title": "The Water Framework Directive (Classification, Priority Substances and Shellfish Waters) Regulations (Northern Ireland) 2015",
  "legislation_url": "https://openlegislation.uk/water-framework-directive-classification-priority-substances-and-shellfish-waters-regulations-northern-ireland-2015",
  "path": "schedule/1/part/4",
  "kind": "part",
  "number": "4",
  "heading": "Intermittent Discharge Standards",
  "text": "Table 1\nIntermittent standards for dissolved oxygen in rivers\nSalmonid waters\nDissolved oxygen concentration (mg/l)\nReturn period\n1 hour\n6 hours\n24 hours\n1 month\n5.0\n5.5\n6.0\n3 months\n4.5\n5.0\n5.5\n1 year\n4.0\n4.5\n5.0\nCyprinid waters\nDissolved oxygen concentration (mg/l)\nReturn period\n1 hour\n6 hours\n24 hours\n1 month\n4.0\n5.0\n5.5\n3 months\n3.5\n4.5\n5.0\n1 year\n3.0\n4.0\n4.5\nThe standards apply when the concurrent concentration of un-ionised ammonia concentration is below 0.02 mg/l. The following correction factors apply at higher concurrent un-ionised concentrations:\nWhere the un-ionised ammonia lies between 0.02-0.15mg NH3-N/I: the correction factor is an additioin of (0.97 x log (mg NH3-N/I) + 3.8) mg O2/l. For concentrations that exceed 0.15 mg NH3-N/I, the correction factor is +2 mg O2/litre.\nA correction factor of 3mg O2/l is added for salmonid spawning grounds.\nTable 2\nIntermittent standards for un-ionised ammonia in rivers\nSalmonid waters\nUn-ionised Ammonia concentration (mg NH3-N/l)\nReturn period\n1 hour\n6 hours\n24 hours\n1 month\n0.065\n0.025\n0.018\n3 months\n0.095\n0.035\n0.025\n1 year\n0.105\n0.040\n0.030\nCyprinid waters\nUn-ionised Ammonia concentration (mg NH3-N/l)\nReturn period\n1 hour\n6 hours\n24 hours\n1 month\n0.150\n0.075\n0.030\n3 months\n0.225\n0.125\n0.050\n1 year\n0.250\n0.150\n0.065\nThe above limits apply when the concurrent concentration of dissolved oxygen is above 5 mg/l. At lower concentrations of dissolved oxygen the following correction factor applies: For dissolved oxygen less than 5mg/l DO, multiply the standard by 0.0126 and the concentration of dissolved oxygen in mg O/litre, C, raised to the power of 2.72, that is, 0.0126 C2.72.\nThe standards also assume that the concurrent pH is greater than 7 and temperature is greater than 5 degress Centigrade. For lower pH and temperatures the following correction factors apply: Where the pH is less than 7, multiply the standard by 0.0003 and by the value of the pH, p, raised to the power of 4.17, that is: 0.0003p4.17. Where the temperature is less than 5 degrees Centigrade, multiply this correction factor by a further 0.5.\nTable 3\n99th percentile standards for biochemical oxygen demand in rivers\nStatus\nTypes of river\n99th percentile BOD (mg/l)\nHigh\n1,2,4,6 and salmonid\n7.0\nHigh\n3,5 and 7\n9.0\nGood\n1,2,4,6 and salmonid\n9.0\nGood\n3,5 and 7\n11.0\nModerate\n1,2,4,6 and salmonid\n14.0\nModerate\n3,5 and 7\n14.0\nPoor\n1,2,4,6 and salmonid\n16.0\nPoor\n3,5 and 7\n19.0\nTable 4\n99th percentile standards for ammonia in rivers\nStatus\nTypes of river\nTotal ammonia (mg NH4-N/l)\nUn-ionised ammonia (mg NH3-N/l)\n99th percentile\n99th percentile\nHigh\n1,2,4,6 and salmonid\n0.5\n0.04\nHigh\n3,5 and 7\n0.7\n0.04\nGood\n1,2,4,6 and salmonid\n0.7\n0.04\nGood\n3,5 and 7\n1.5\n0.04\nModerate\n1,2,4,6 and salmonid\n1.8\n0.04\nModerate\n3,5 and 7\n2.6\n0.04\nPoor\n1,2,4,6 and salmonid\n2.6\n0.04\nPoor\n3,5 and 7\n6.0\n-\nTable 5\nTypes of river to which the proposed 99th percentile standards in Tables 3 and 4 apply\nAlkalinity (as mg/l CaCO3)\nAltitude\nLess than 10\n10-50\n50-100\n100-200\nOver 200\nUnder 80 metres\nType 1\nType 2\nType 3\nType 5\nType 7\nOver 80 metres\nType 4\nType 6",
  "extent": "N.I.",
  "status": null,
  "version": "current",
  "annotations": [],
  "outstanding_effects": [],
  "provenance": {
    "source": "legislation.gov.uk",
    "source_url": "https://www.legislation.gov.uk/nisr/2015/351/schedule/1/part/4",
    "retrieved_at": "2026-10-29T01:00:03.181368+00:00"
  },
  "licence": "Open Government Licence v3.0",
  "licence_url": "https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/",
  "attribution": "Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives."
}