Appendix CRF - Part 3 - Northamptonshire County Council

the assumption that doses from water treatment would be similar to doses from
sewage treatment. The Environment Agency’s methodology allows for a range of
exposure groups affected by releases to a public sewer, depending on the
discharge route for treated effluent. For this assessment, only the groups
associated directly with operation of the treatment plant, farming of land
conditioned by sludge or using the estuary are considered. These groups and
the relevant exposure pathways are:
Sewage treatment workers (adults only)
External irradiation from radionuclides in raw sewage and sludge
Inadvertent inhalation and ingestion of raw sewage and sludge containing
radionuclides
Farming family living on land conditioned with sewage sludge
Consumption of food produced on land conditioned with sludge and
incorporating radionuclides
External irradiation from radionuclides in sludge conditioned soil
Inadvertent inhalation and ingestion of sludge conditioned soil
Fisherman’s family (estuary/coastal water receives treated effluent from sewage
works, typically via a river)
External irradiation from radionuclides deposited in sediments
Consumption of fish incorporating radionuclides
8.6.5 The results in Annex B are expressed as specific dose per MBq/year of activity in
the leachate treated. The groundwater assessment uses a very pessimistic
assumption regarding leachate concentrations which it is not appropriate to use
in this assessment. There is no empirical evidence on which to base leachate
activity concentrations.
8.6.6 The worst case result is for Th-232 with the “farming family” public exposure
group. If we assume a dose constraint of 0.3 mSv/yr for the public during the
operational phase, the results indicate that the maximum allowable leachate
discharge per year is 216 MBq if the leachate only comprised Th-232.
8.6.7 The proposed approach is that this scenario is not used to constrain radiological
capacity, but that it is used to derive authorisation discharge limits for the
leachate which can then be subsequently refined when empirical monitoring
results become available. Based upon the above approach the authorisation
limits for individual nuclides if the leachate comprised 100% of that nuclide, with a
0.3 mSv/y dose criterion are given in the following table. In practice authorisation
discharge limits will be set after discussion with the Environment Agency and
then optimized through operational experience such that restrictive dose criterion
are met.
Application for disposal of LLW including HV-VLLW under RSA 1993,
for the East Northants Resource Management Facility:
Supporting Information
July 2009
69
WS010001/ENRMF/CONSAPPCRF 388