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The Water Framework Directive (Classification, Priority Substances and Shellfish Waters) Regulations (Northern Ireland) 2015

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The Water Framework Directive (Classification, Priority Substances and Shellfish Waters) Regulations (Northern Ireland) 2015, PART 4 is up to date with all changes known to be in force on or before 16 October 2019. There are changes that may be brought into force at a future date. Changes that have been made appear in the content and are referenced with annotations. Help about Changes to Legislation

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PART 4 F1F2F3N.I.Intermittent Discharge Standards

Table 1

Intermittent standards for dissolved oxygen in rivers

Salmonid waters
Dissolved oxygen concentration (mg/l)
Return period1 hour6 hours24 hours
1 month5.05.56.0
3 months4.55.05.5
1 year4.04.55.0
Cyprinid waters
Dissolved oxygen concentration (mg/l)
Return period1 hour6 hours24 hours
1 month4.05.05.5
3 months3.54.55.0
1 year3.04.04.5

The 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:

Where 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.

A correction factor of 3mg O2/l is added for salmonid spawning grounds.

Table 2

Intermittent standards for un-ionised ammonia in rivers

Salmonid waters
Un-ionised Ammonia concentration (mg NH3-N/l)
Return period1 hour6 hours24 hours
1 month0.0650.0250.018
3 months0.0950.0350.025
1 year0.1050.0400.030
Cyprinid waters
Un-ionised Ammonia concentration (mg NH3-N/l)
Return period1 hour6 hours24 hours
1 month0.1500.0750.030
3 months0.2250.1250.050
1 year0.2500.1500.065

The 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.

The 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.

Table 3

99th percentile standards for biochemical oxygen demand in rivers

StatusTypes of river99th percentile BOD (mg/l)
High1,2,4,6 and salmonid7.0
High3,5 and 79.0
Good1,2,4,6 and salmonid9.0
Good3,5 and 711.0
Moderate1,2,4,6 and salmonid14.0
Moderate3,5 and 714.0
Poor1,2,4,6 and salmonid16.0
Poor3,5 and 719.0

Table 4

99th percentile standards for ammonia in rivers

StatusTypes of riverTotal ammonia (mg NH4-N/l)Un-ionised ammonia (mg NH3-N/l)
99th percentile99th percentile
High1,2,4,6 and salmonid0.50.04
High3,5 and 70.70.04
Good1,2,4,6 and salmonid0.70.04
Good3,5 and 71.50.04
Moderate1,2,4,6 and salmonid1.80.04
Moderate3,5 and 72.60.04
Poor1,2,4,6 and salmonid2.60.04
Poor3,5 and 76.0-

Table 5

Types of river to which the proposed 99th percentile standards in Tables 3 and 4 apply

Alkalinity (as mg/l CaCO3)
AltitudeLess than 1010-5050-100100-200Over 200
Under 80 metresType 1Type 2Type 3Type 5Type 7
Over 80 metresType 4Type 6

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