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for a 1% reduction in the risk of suffering a stomach upset (EFTEC, 2002) and we
assumed a. WTP of £1.10 per 1% reduction in risk. For comparison with Scottish
bathing waters, a direct unadjusted mean value was used to determine the benefits
of increased bathing water quality resulting from the reduction in faecal loading in the
Irvine catchment. The EFTEC study is a suitable comparative site for Irvine Beach
because of similarities below listed in Table 2. The annual benefit accruing to Irvine
Beach from reducing faecal loading was calculated by accounting for the likelihood
of high discharge events. Benefits were calculated at each percentile flow (above the
72nd) for a range of reductions in loading from 25–95%.
Table 2:
Comparison of site characteristics between proposed Scottish
benefit transfer and EFTEC WTP study in England and Wales
England and Wales
Scotland
Environmental quality parameter Bathing water quality Bathing water quality
Households 24,000,000 2,200,000
Population 52,900,000 5,062,000
Average household size 2.204 2.3
Mean weekly household income £302 £296
A spreadsheet model was developed to determine the benefits accruing to society
from increased bathing water quality. Table 3 gives the equations used in the
development of this model.
Table 3:
Parameters used to model social benefits from increased bathing
water quality
Parameter Equation Components
Risk of illness (1) · C = FS concentration in
bathing water
Risk of illness
differences
(2) · r full = risk of illness at full FS
loading
Social benefits
at each
discharge
percentile
Total annual
benefits (TB)
· r %reduction = risk of illness
with reduction in loading
(3) · WTP = household WTP to
pay for risk reduction
(4)
· H = number of households
· F = percentile flow.
Lifetime
benefits (LB) (5)
· TB = future value (in year t)
· i = interest rate
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