The Water Supply (Water Quality) (Amendment) Regulations (Northern Ireland) 2015

Regulation 2(14)

SCHEDULE 3

“Schedule 5 Monitoring for indicative dose and analytical performance characteristics.

1.   A water undertaker may use a screening strategy for gross alpha and gross beta to monitor for the parametric indicator value for indicative dose (1). The recommended screening value for gross alpha is 0.1Bq/l and for gross beta is 1.0Bq/l.

If the gross alpha activity is less than 0.1Bq/l and the gross beta activity is less than 1.0Bq/l it may be assumed that the indicative dose is less than 0.1mSv and radiological investigation is not needed, unless it is known from the other sources of information that specific radionuclides are present in water that are liable to cause an excess of 0.1mSv. Where the screening values are exceeded then additional radiological investigation is required.

The radionuclides to be measured must be based on all relevant information about likely sources of radioactivity.

2.   Calculation of the ID

The ID must be calculated from the measured radionuclide concentrations and the dose coefficients laid down in Annex III, Table A of Directive 96/29/Euratom or more recent information recognised by the Department, on the basis of the annual intake of water (730l) for adults. Where the following formula is satisfied, it can be assumed that the ID is less than the parametric value of 0.1mSv and no further investigation is required.

where

Ci(obs) = observed concentration of radionuclide i

Ci(der) = derived concentration of radionuclide i

n = number of radionuclides detected.

Derived concentrations for radioactivity in water for human consumption(1)
Origin	Nuclide	Derived concentration
(1) This table includes values for the most common natural and artificial radionuclides; these are precise values, calculated for a dose of 0.1mSV, an annual intake of 730 litre and using the dose coefficients laid down in Annex III Table A of Directive 96/29/Euratom; derived concentration for other radionuclides can be calculated on the same basis, and values can be updated on the basis of more recent information recognised by the competent authorities.
(2) This table allows only for the radiological properties of uranium, not for its chemical toxicity.
Natural	U-238(2)	3.0 Bq/l
	U-234(2)	2.8 Bq/l
	Ra-226	0.5 Bq/l
	Ra-228	0.2 Bq/l
	Pb-210	0.2 Bq/l
	Po-210	0.1 Bq/l
Artificial	C-14	240 Bq/l
	Sr-90	4.9 Bq/l
	Pu-239/Pu-240	0.6 Bq/l
	Am-241	0.7 Bq/l
	Co-60	40 Bq/l
	Cs-134	7.2 Bq/l
	Cs-137	11 Bq/l
	I-131	6.2 Bq/l

3.   Performance characteristics and method of analysis.

For the following parameters and radionuclides, the method of analysis used must, as a minimum be capable of measuring activity concentrations with a limit of detection specified below:

Parameters and radionuclides	Limit of detection (1) (2)
(1) The limit of detection must be calculated according to the ISO standard 11929: Determination of the characteristic limits (decision threshold, detection limit, and limits of the confidence interval) for measurements of ionising radiation– Fundamentals and application, with probabilities of error of 1st and 2nd kind of 0.05 each
(2) Measurement uncertainties must be calculated and reported as complete standard uncertainties or as expanded standard uncertainties with an expansion factor of 1.96 according to the ISO Guide for the Expression of Uncertainty in Measurement.
(3) The limit of detection for tritium and for radon is 10% of its parametric value of 100 Bq/l.
(4) The limit of detection for gross alpha activity and gross beta activities are 40% of the screening values of 0.1 and 1.0 Bq/l respectively.
(5) This limit of detection applies only to initial screening for ID for a new water source, if initial checking indicates that it is not plausible that Ra-228 exceeds 20% of the derived concentration, the limit of detection may be increased to 0.08 Bq/l for routine Ra-228 nuclide specific measurements until a subsequent re-check is required.”
Tritium	10 Bq/l(3)
Radon	10 Bq/l(3)
gross alpha activity	0.04 Bq/l(4)
gross beta activity	0.4 Bq/l(4)
U-238	0.02 Bq/l
U-234	0.02 Bq/l
Ra-226	0.04 Bq/l
Ra-228	0.02 Bq/l(5)
Pb-210	0.02 Bq/l
Po-210	0.01 Bq/l
C-14	20 Bq/l
Sr-90	0.4 Bq/l
Pu-239/Pu-240	0.04 Bq/l
Am-241	0.06 Bq/l
Co-60	0.5 Bq/l
Cs-134	0.5 Bq/l
Cs-137	0.5 Bq/l
I-131	0.5 Bq/l

(1)

Where appropriate gross beta activity may be replaced by residual beta activity after subtraction of the K-40 activity concentration.