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42
tank " by no means answers its purpose. The volume of sewage is
so large, that it passes through this tank far too rapidly to permit
more than a comparatively trifling deposit of solid matter in it,
and, instead, the solids pass on to the land, and are there
deposited, where they interfere completely with the action of the
soil as a rapid filtering medium.
This constitutes the main difficulty, but there is no reason to
suppose that it would not be removed, if settling or precipitation
tanks were provided large enough to ensure very slow or intermittent
passage of sewage through them, whereby, especially if
assisted by chemical precipitants, the vast bulk of the solids
would be left behind, and the soil would be enabled to rapidly
purify the thus clarified sewage.
Improvements at the works are essential to prevent river
pollution and nuisance in their neighbourhood, arising from the
stagnant pools of sewage, and from the decomposition of the foul
solid matters deposited upon the surface of the soil. But it is
necessary to point out that it is of more immediate concern, that
sewage should be, at all times, effectually removed from the sewers
in the District, and it is to be hoped that the Council will adopt
no improved scheme, which will in any way permit of the
" heading back " of sewage in the sewers. Closely connected
with this " heading back " of sewage, for it is dependent upon it,
is the overflow, which exists in Mitcham, from one of the main
sewers into the river Wandle; an overflow which at the present
time permits the escape of volumes of sewage into the river,
after slight rainfall, and which occurs, moreover, at a spot near
which there is a considerable population.
These matters are, no doubt, bound up intimately with the
contemplated improvement at the works, but their existence
within the District itself, affecting, as they have been shown to
do, the health of the population, is an additional and most pressing
reason for urging, without delay, the completion of the
improvements.