PART 3Monitoring for indicative dose and analytical performance characteristics
6. A local authority may use reliable screening strategies to indicate the presence of radioactivity in water intended for human consumption.
7. The strategies referred to in paragraph 6 may include screening for—
(a)certain radionuclides or individual radionuclide; or
(b)gross alpha activity or gross beta activity (where appropriate gross beta activity may be replaced by residual beta activity after subtraction of the K-40 activity concentration).
Screening for certain radionuclides, or screening for an individual radionuclide
8. If one of the activity concentrations exceeds 20% of the corresponding derived value or the tritium concentration exceeds its parametric value listed in Part 3 of Schedule 1 an analysis of additional radionuclides is required.
9. A local authority must, in deciding which radionuclides require to be measured for each supply, take into account all relevant information about likely sources of radioactivity.
Screening strategies for gross alpha activity and gross beta activity
10. Subject to paragraph 11 the recommended screening levels are—
(a)0,1Bq/l for gross alpha activity; and
(b)1,0Bq/l for gross beta activity.
11. If the gross alpha activity exceeds 0,1Bq/l or the gross beta activity exceeds 1,0Bq/l, analysis for specific radionuclides is required.
12. The Welsh Ministers may set alternative screening levels for gross alpha activity and gross beta activity where it can be demonstrated by the local authority that the alternative levels are in compliance with an indicative dose of 0,1 mSv.
Calculation of the indicative dose
13. The indicative dose must be calculated from—
(a)the measured radionuclide concentrations and the dose coefficients laid down in Annex III, Table A of Directive 96/29/Euratom(1) ; or
(b)more recent information recognised by the Welsh Ministers, on the basis of the annual intake of water (730 1 for adults).
14. Where the following formula is satisfied, it can be assumed that the indicative dose is less than the parametric value of 0,1 mSv and no further investigation is required—
Derived concentrations for radioactivity in water intended for human consumption (1)
Origin | Nuclide | Derived concentration |
|---|---|---|
(1) This table allows only for the radiological properties of uranium, not for its chemical toxicity. | ||
| Natural | U-2383 | 3,0 Bq/l |
| U-2343 | 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 | |
| 1-131 | 6,2 Bq/l | |
Performance characteristics and methods of analysis
15. 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 (Notes 1,2) | Notes |
|---|---|---|
| Tritium | 10 Bq/l | Note 3 |
| Radon | 10 Bq/l | Note 3 |
| gross alpha | 0,04 Bq/l | Note 4 |
| gross beta | 0,4 Bq/l | Note 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 | Note 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/1 | |
| Am-241 | 0,06 Bq/l | |
| Co-60 | 0,5 Bq/1 | |
| Cs-134 | 0,5 Bq/l | |
| C2-137 | 0,5 Bq/l | |
| 1-131 | 0,5 Bq/1 |
Note 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 confidence interval) for measurements of ionising radiation — Fundamentals and application, with probabilities of errors of 1st and 2nd kind of 0,05 each.
Note 2: Measurement uncertainties must be calculated and reported as complete standard uncertainties, or as expanded uncertainties with an expansion factor of 1,96 according the ISO Guide for the Expression of Uncertainty in Measurement.
Note 3: The limit of detection for tritium and for radon is 10% of its parametric value of 100 Bq/1.
Note 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/1 respectively.
Note 5: This limit of detection applies only to initial screening for indicative dose 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/1 for routine Ra-228 nuclide specific measurements, until a subsequent re-check is required.
OJ No. L 159, 29.6.1996, p. 1, prospectively repealed and replaced by Directive 2013/59 Euratom (OJ L 13, 17.1.2014, p. 1) with effect from 6 February 2018.