Monitoring and auditing: after the decision - Introduction to Environmental Impact Assessment - page 213

Total: all predictions 69 100

( Source: Chadwick & Glasson 1999.)

Table 7.5 Accuracy of auditable Sizewell B
predictions

% error in prediction No. of predictions % of total

None: prediction correct or within predicted range 15 26

Less than 10% 9 16

10-20% 11 19

20-30% 5 9

30-40% 5 9

40-50% 2 3

Over 50% 8 14

Prediction incorrect, but % error cannot be calculated 3 5

Prediction cannot be audited 11 -

Total: all predictions 69 100

Notes: For quantified predictions, the predicted value was used as the denominator in the
calculation of the % errors in the table. For non-quantified predictions, the % error could not be
calculated and predictions were classified as either “correct” or “incorrect”, based on assessment by
the research team. ( Source: Chadwick & Glasson 1999.)

and mitigation measures revealed (Table 7.5) that many of the predictions used in the
Sizewell B public inquiry were reasonably accurate—although there was an
underestimate of the build-up of construction employment and an overestimate of the
secondary effects on the local economy. Predictions of traffic impacts, and on the local
proportion of the construction workforce, were very close to the actual outcomes.
Mitigation measures also appeared to have some effect. Overall, approximately 60 per
cent of the predictions had errors of less than 20 per cent. Explanations of variations from
the predictions included the inevitable project modification (particularly associated with
new-technology projects, with few or no comparators at the time of prediction), and the
very lengthy project authorization process (with a gap of almost 10 years between the
predictions and peak construction). Other local issues have been revealed by monitoring,
allowing some modifications to manage the project better in the community.
Unfortunately, such systematic monitoring is still discretionary in the UK and very much
dependent on the goodwill of developers.
Information gained from monitoring can also provide vital intelligence for the
planning and assessment of future projects. This is particularly so when the subsequent
project is of the same type, and in the same location, as that which has been monitored.
Nuclear Electric applied for consent to build and operate a replica of Sizewell B, to be
known as Sizewell C. A full EIS was produced for the project (Nuclear Electric 1993). Its