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The year was similar as regards weather to 1958, but compared with that year, the
river showed a noticeable improvement. The improvement in the condition of the river
off the Northern Outfall, first noted in 1958, has continued and the suspended solids,
permanganate value and biochemical oxygen demand have all continued to decrease,
whilst the nitrate shows an increase.
(b) The incidence of sulphides in water devoid of oxygen was the lowest recorded
since regular determinations of sulphide were started in 1953. The total number of
samples, taken at high and low water off both outfalls, which were found to contain
sulphide was the lowest recorded, with the exception of 1958.
(c) The numbers of sulphate.reducing bacteria in river muds were very much smaller
than in 1959, and appreciably smaller than in 1958. This was due in part to the large
upland flow and in part to the generally improved condition of the river.
(d) For the summer quarter the average temperature of the river water off both the
Northern and Southern Outfall Works, at both high and low water, was unusually low.
The high fresh water flows and low temperature during the summer quarter, July to
September, were undoubtedly responsible in some measure for the improved condition
of the river. They were, however, insufficient to account wholly for the improvement,
which was, in some measure, quite certainly due to the improvement in the effluent discharged
from the Northern Outfall Works.
Sewers
Trade waste discharges—It has become evident from contacts and from enquiries following
the publication of last year's Annual Report of the Scientific Adviser that manufacturers
are keenly interested in the requirements of the Council with respect to trade waste discharges.
The Act which gives the Council powers to control the discharge of trade effluents to
sewers is the London County Council (General Powers) Act, 1953, Part II and under the
heading ' Certain matters not to be passed into Sewers ' section 5 gives general definitions
of such matters. With few exceptions the provisions are stated in the widest terms and
have to be interpreted by those concerned with its administration in the light of their
knowledge and experience. It is a guiding principle that, while the limits imposed shall
ensure the safety of men in the sewers and of the structure of the sewers, they shall not
be unduly restrictive to the operations at traders' premises. In this respect also, the size
and extent of the London Main Drainage system permits the reception of some matters
such as metals in solutions in much greater quantity than would otherwise be the case.
The 400 miles of L.C.C. main sewers and 2,000 miles of local sewers act in effect as balancing
tanks, so that the sewage arriving at the two treatment works remains of relatively constant
composition and is not subject to sudden surges of trade waste.
The remainder of the provisions of the Act are mainly concerned with preventing damage
to sewers and danger to men working in the sewers near to or downstream of the sewer
connections discharging trade wastes.
During the year under review 2,600 samples in connection with trade waste discharges
were examined. Of this total, 294 were from or to the river Wandle and also from the river
Ravensbourne and its tributaries. There was no recurrence during the year of discharges
to the Wandle which in 1959 caused odour nuisance. The condition of the Wandle showed
some improvement and, with improvements at sewage works on its banks and of the
diversion of a works discharge to the main drainage system, further improvement in the
condition of the water can be expected. Sampling of the river Ravensbourne was started
during the year consequent on the London County Council assuming responsibility for
the river within the county limits. Generally the river shows the presence of some well
oxidised sewage effluents: the strength is about a quarter that of the river Wandle.
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