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Visits were also made to other premises to investigate particular complaints, to check
the suitability of water supplies from other sources and to give advice. Of the total samples
402 were examined bacteriologically, 65 chemically and 374 for free chlorine content.
In spite of long periods of wet weather there was no serious contamination of well
supplies due to percolation of ground water. In only one case was it found necessary to
take the well out of service because of heavy contamination.
Air pollution
The Council continued its long.standing co.operation with the Department of Scientific
and Industrial Research in investigating the incidence of air pollution, by maintaining
regular observations of the degree of pollution of the atmosphere over the county.
Measurements at the Godalming site were discontinued but responsibility was taken for
the analysis of samples from a new site in south.east London; the number of sites remained
at 21. The following instruments were in use:
Eleven of the lead peroxide type, which measure the amount of sulphur dioxide
absorbed on a reactive surface during a month's exposure.
Seven deposit gauges, which collect falling dust, soot, rain and constituents carried
down by the rain.
Twelve instruments of the daily volumetric type, which provide an accurate measure
of the average concentrations of sulphur dioxide and ' smoke' in the air over much
shorter periods than a month. The usual sampling period is 24 hours, but this may be
shortened when required, as during fog.
Opinion is consolidating that the volumetric method provides the most useful index of
pollution. Experiments are now in hand to see if volumetric apparatus, controlled by a
process timer to run intermittently over long periods, might be used to replace the lead
peroxide instrument at sites where monthly averages only, obtained with a minimum of
labour, are deemed sufficient.
Results obtained by the volumetric method during the year show that the steady reduction
in the smoke pollution of London's air, noted since the inception of the Clean Air Act in
1957, has continued. The average concentration of smoke was about 30 per cent, below the
levels of 1955 and 1956; if the winter months alone are considered the reduction was about
35 per cent. Undoubtedly a succession of mild winters has contributed to this success, but
it remains to be seen how far the figures would revert in the event of a hard winter. The
reduction in the average sulphur dioxide concentration over the same period has been much
smaller, less than 10 per cent (nearly 15 per cent for the winter months); there was no
appreciable difference between this and the previous year. The Clean Air Act was not
expected to influence the sulphur dioxide level, which must remain largely dependent upon
the quantity and sulphur content of the fuel consumed.
At St. Paul's Cathedral, where volumetric measurements have now been in progress for
over two years, the reduction in sulphur dioxide during the winter months has been slightly
greater than the general average over the same period. This is ascribed to the closing down
of the old Bankside ' A ' power station, the flue gases from which were unwashed.
There was no occurrence during the year of the conditions known as ' smog '. On only
two occasions, during fog in January and December, did the concentration of sulphur
dioxide exceed 40 parts per hundred million in parts of central, south and west London.
There was far less smoke than has been associated with such concentrations in the past
and the fogs persisted for less than two days. Other fogs occurring during the year did not
become badly polluted.
Regular visits were made in company with the District Alkali Inspector of the Ministry
of Housing and Local Government to test the efficiency of the flue gas washing plants at
Battersea and Bankside power stations.
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