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chamber situated immediately on the north side of the Engine
House, from whence it flows into three concrete tanks, each
108ft. by 31ft. by 4ft. 3m. deep. Two of these tanks are filled
with slates on the Dibdin principle. These are given two fillings
per day, with two hours' rest. The remaining tank is used as an
intermittent sedimentation tank, a small amount of " alumina
ferric " being used to facilitate precipitation.
The total dry weather flow of sewage treated at the works is
approximately 420,000 gallons, and of this amount about 181,000
gallons is treated through the slate beds, the remainder being
passed through the sedimentation tank, which also takes the
excess flow during storm times. Owing to the practice of
allowing roof water from the rear of houses to enter the soil
sewers, the volume of sewage received at the Works in wet or
stormy weather is very greatly increased, and each year the
difficulty of proper disposal is intensified.
The effluent from the tanks passes along an open carrier, and
is treated through six contact beds, each bed being approximately
171ft. long by 51ft. wide and 3ft. deep. Four of these beds are
constructed with concrete walls and bottoms, but the remaining
two have earth bottoms and enclosing walls.
The first four beds are capable of dealing with approximately
418,000 gallons per day, with two fillings apiece The other two
beds being of much older date have not nearly the same relative
capacity each for each as the previous beds, but the effluent
obtained from them at the present time is slightly better than the
newer beds, owing probably to their more matured condition.
Alterations involving the enlargement of the inlets were recently
made with regard to the method of filling these beds, which has
led to an improvement, and the beds can now be filled much more
quickly than previously. The capacity of three of the filters
could be increased by raising the outlet end so as to bring the
beds level longitudinally, in the same manner as Contact Bed
No. 4, the last one re-constructed. The general condition of the
contact beds is satisfactory.
The effluent, after passing through the filters, is conducted
over about 31/3 acres of land, and is finally discharged into the
Hoggsmill River, a tributary of the Thames. A portion of the