# The Water Framework Directive (Classification, Priority Substances and Shellfish Waters) Regulations (Northern Ireland) 2015, Part 4: Intermittent Discharge Standards

Extent: N.I.

Table 1
Intermittent standards for dissolved oxygen in rivers
Salmonid waters
Dissolved oxygen concentration (mg/l)
Return period
1 hour
6 hours
24 hours
1 month
5.0
5.5
6.0
3 months
4.5
5.0
5.5
1 year
4.0
4.5
5.0
Cyprinid waters
Dissolved oxygen concentration (mg/l)
Return period
1 hour
6 hours
24 hours
1 month
4.0
5.0
5.5
3 months
3.5
4.5
5.0
1 year
3.0
4.0
4.5
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 period
1 hour
6 hours
24 hours
1 month
0.065
0.025
0.018
3 months
0.095
0.035
0.025
1 year
0.105
0.040
0.030
Cyprinid waters
Un-ionised Ammonia concentration (mg NH3-N/l)
Return period
1 hour
6 hours
24 hours
1 month
0.150
0.075
0.030
3 months
0.225
0.125
0.050
1 year
0.250
0.150
0.065
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
Status
Types of river
99th percentile BOD (mg/l)
High
1,2,4,6 and salmonid
7.0
High
3,5 and 7
9.0
Good
1,2,4,6 and salmonid
9.0
Good
3,5 and 7
11.0
Moderate
1,2,4,6 and salmonid
14.0
Moderate
3,5 and 7
14.0
Poor
1,2,4,6 and salmonid
16.0
Poor
3,5 and 7
19.0
Table 4
99th percentile standards for ammonia in rivers
Status
Types of river
Total ammonia (mg NH4-N/l)
Un-ionised ammonia (mg NH3-N/l)
99th percentile
99th percentile
High
1,2,4,6 and salmonid
0.5
0.04
High
3,5 and 7
0.7
0.04
Good
1,2,4,6 and salmonid
0.7
0.04
Good
3,5 and 7
1.5
0.04
Moderate
1,2,4,6 and salmonid
1.8
0.04
Moderate
3,5 and 7
2.6
0.04
Poor
1,2,4,6 and salmonid
2.6
0.04
Poor
3,5 and 7
6.0
-
Table 5
Types of river to which the proposed 99th percentile standards in Tables 3 and 4 apply
Alkalinity (as mg/l CaCO3)
Altitude
Less than 10
10-50
50-100
100-200
Over 200
Under 80 metres
Type 1
Type 2
Type 3
Type 5
Type 7
Over 80 metres
Type 4
Type 6

---
Source: https://www.legislation.gov.uk/nisr/2015/351/schedule/1/part/4 (the official version)
Page: https://openlegislation.uk/water-framework-directive-classification-priority-substances-and-shellfish-waters-regulations-northern-ireland-2015/schedule-1/part-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.