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

PART 4 N.I. Intermittent Discharge Standards

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