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29
The depot and pigstyes at California Road have been practically
free from cricket infestation and only minor measures to
control a small infestation at the refuse tip at Norbiton Potteries
were called for. A more serious situation, however, arose at the
Norbiton Potteries due to flooding of the pit and a potential
nuisance existed for some time. Steps were taken for hard material
and clay to be dumped by contractors over the areas where the
standing water was shallow, thereby leaving one large deep pond
which would be more convenient to deal with should it become
offensive. I am sure this would have happened had not a most
beneficial circumstance accidently arisen. A quantity of yellow
coloured material was deposited at a number of points round the
lake and soon the water turned a similar colour. At this time I
was visiting daily anxiously watching for developments. The
water, however, retaining its yellow colour remained completely
inoffensive. I thought at this stage that something more should be
known of what was going on and samples of the water and the
material were sent to the Public Analyst. He found that the
water was coloured yellow by the presence of chromate (as
CrO3 ) 480 parts per million and that the yellow material on the
bank consisted essentially of compounds of chromium in various
degrees of oxidation. The effect of the presence of this chromate
in the water, which has excellent oxidising and sterilizing properties,
was to destroy much of the organic matter which normally
accumulates in stagnant water of this nature and prevented the
formation of objectionable odours.
So long as the presence of this solid matter continues to act
as a source of chromate the water will probably remain free from
any of the troubles normally associated with stagnant water accumulating
on or near the refuse tips. This was borne out by a series of
samples of the water submitted for bacteriological examination,
the water remaining consistently good. The bacteriologists remarks
regarding this were — "Coliform bacilli only become viable
when the water is diluted and it is likely, therefore, that the
chromate is exerting an inhibiting action." This was certainly
the position at the end of the year, but just how long the situation
will remain so satisfactory I cannot say. Some urgent action may
become necessary at any time during the summer months if the
strength of the chromate in the water lessens so that its inhibiting
action on bacteria breaks down. A thing that has puzzled me is
why the pit has remained flooded when in years gone by, during
summer, only a small deep pond remained.
In my last Annual Report I made reference to the fact that
during the past few years many requests have been received from
householders for assistance in destroying wasps nests. During the