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20
In the case of the Tolworth Farm in its present
state, the conditions requisite for ensuring the enduring
success of this treatment are wanting. Firstly, because
the soil is not of a suitable character. There is on
the surface ordinary agricultural soil of an average
depth, so I am informed, of about 12 inches, and
beneath this is a dense layer of brick clay, consequently
though the sewage be well screened or have its solids well
precipitated and the fluid part well filtered, yet the soil is
so shallow that it speedily becomes saturated, and the
sewage in considerable quantities flows away laterally
unpurified, overflows in fact to join the effluent from land
filtration and finds its way into the neighbouring stream.
Secondly, the soil is not underdrained at a depth of at least
six feet, nor underdrained at all. Now owing to the configuration
of the natural easements for land water, i.e.
watercourses, the ground thereabouts is not nearly so well
drained as might be, but probably if these watercourses
were cleansed, deepened, and perhaps added to, the sub-soil
drainage would be generally improved, and at least the
escape of the abnormal excess of water, sewage water, on
the Farm, would be facilitated by reason of the greater
dryness of the ground. As it is, the Farm is comparatively
easily waterlogged, and I believe its efficiency is greatly
impaired for want of this relief. On the opposite side to
this sewage farm, separated only by a 20 foot road, there is
large and prosperous Brick-yard and on the other side of
the Farm, between it and the Hook Road, there called
Hook Yale, is another Brick-field.
Between these, and in a direct line is the farm. The
depth of soil varies from about 14 inches on the Hook
Road side to about 3 inches on that abutting on Tolworth
Lane. The depth of the underlying clay is about 120 to