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The Urban Waste Water Treatment Regulations (Northern Ireland) 1995

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regulations 5, 6 and 11

SCHEDULE 3

PART IREQUIREMENTS FOR DISCHARGES FROM TREATMENT PLANTS

1.  Treatment plants shall be designed or modified so that representative samples of the incoming waste water and of treated effluent can be obtained before discharge to receiving waters.

2.  Discharges from urban waste water treatment plants subject to treatment in accordance with regulation 5(1) and (2) shall, subject to paragraphs 4 and 5 of Part II, meet the requirements shown in Table 1.

3.  Discharges from urban waste water treatment plants to those sensitive areas which are subject to eutrophication as identified in sub-paragraph (a) of Part 1 of Schedule 1 shall, subject to paragraphs 4 and 5 of Part II, also meet the requirements in Table 2.

4.  More stringent requirements than those shown in Table 1 and/or Table 2 shall be applied where required to ensure that the receiving waters satisfy any other relevant Community Directives.

5.  The points of discharge of urban waste water shall be chosen, as far as possible, so as to minimize the effects on receiving waters.

TABLE I

REQUIREMENTS FOR DISCHARGES FROM URBAN WASTE WATERTREATMENT PLANTS SUBJECT TO REGULATION 5(1) AND (2)

The values for concentration or for the percentage of reduction shall apply.

Reference method of measurementMinimum percentage of reduction(1)ParametersConcentration
(1)

Reduction in relation to the load of the influent.

(2)

The parameter can be replaced by another parameter: total organic carbon (TOC) or total oxygen demand (TOD) if a relationship can be established between BOD5, and the substitute parameter.

Biochemical oxygen demand (BOD5 at 20°C) without nitrification(2)25 Mg/l O270-90Homogenized, unfiltered, undecanted sample. Determination of dissolved oxygen before and after five-day incubation at 20°C ± 1°C, incomplete darkness. Addition of a nitrification inhibitor.
Chemical oxygen demand (COD)125 mg/l O275Homogenized, unfiltered, undecanted sample Potassium dichromate.

Analyses concerning discharges from lagooning shall be carried out on filtered samples; however, the concentration of total suspended solids in unfiltered water samples shall not exceed 150 mg/l.

TABLE 2

REQUIREMENTS FOR DISCHARGES FROM URBAN WASTE WATER TREATMENT PLANTS TO SENSITIVE AREAS WHICH ARE SUBJECT TO EUTROPHICATION AS IDENTIFIED IN SUB-PARAGRAPH (a) OF PART 1 OF SCHEDULE I

One or both parameters may be applied depending on the local situation. The values for concentration or for the percentage of reduction shall apply.

ParametersConcentrationMinimum percentage of reduction(1)Reference method of measurement
(1)

Reduction in relation to the load of the influent.

(2)

Total nitrogen means: the sum of total Kjeldahl-nitrogen (organic N + NH3), nitrate (NO3)-nitrogen and nitrite (NO2)-nitrogen.

Total phosphorus2 mg/l P (10,000-100,000 p.e.) 1 mg/1 P (more than 100,000 p.e.)80Molecular absorption spectrophotometry
Total nitrogen(2)15 mg/1 N (10,000-100,000 p.e.) 10 mg/1 N (more than 100,000 p.e.)70-80Molecular absorption spectrophotometry

PART IIREFERENCE METHODS FOR MONITORING AND EVALUATION OF RESULTS

1.—(a) The Department shall apply a monitoring method which corresponds at least with the level of requirements described below.

(b)Alternative methods to those mentioned in paragraphs 2, 3 and 4 may be used provided that it can be demonstrated that equivalent results are obtained.

2.—(a) Flow-proportioned or time-based 24-hour samples shall be collected at the same well-defined point in the outlet and if necessary in the inlet of the treatment plant in order to monitor compliance with the requirements for discharged waste water laid down in these Regulations.

(b)Good international laboratory practices aiming at minimising the degradation of samples between collection and analysis shall be applied.

3.  The minimum annual number of samples shall be determined according to the size of the treatment plant and be collected at regular intervals during the year:

—2,000 to 9,999 p.e.:12 samples during the first year;
4 samples in subsequent years, if it can be shown that the water during the first year complies with the provisions of these Regulations; if 1 sample of the 4 fails, 12 samples must be taken in the year that follows;
—10,000 to 49,999 p.e.:12 samples;
—50,000 p.e. or over:24 samples.

4.  The treated waste water shall be assumed to conform to the relevant parameters if, for each relevant parameter considered individually, samples of the water show that it complies with the relevant parametric value in the following way—

(a)for the parameters specified in Table 1 and sub-paragraph (b) of regulation 5(7), a maximum number of samples which are allowed to fail the requirements, expressed in concentrations and/or percentage reductions in that Table and that sub-paragraph, is specified in Table 3;

(b)for the parameters of Table 1 expressed in concentrations, the failing samples taken under normal operating conditions must not deviate from the parametric values by more than 100%;

(c)for those parameters specified in Table 2 the annual mean of the samples for each parameter shall conform to the relevant parametric values.

5.  Extreme values for the water quality in question shall not be taken into consideration when they are the result of unusual situations such as those due to heavy rain.

TABLE 3

Series of samples taken in any yearMaximum permitted number of samples which fail to conform
4-71
8-162
17-283
29-404
41-535
54-676
68-817
82-958
96-1109
111-12510
126-14011
141-15512
156-17113
172-18714
188-20315
204-21916
220-23517
236-25118
252-26819
269-28420
285-30021
301-31722
318-33423
335-35024
351-36525

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