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of Venus Sewer
History in Leeds Sundials in Leeds William
Gascoigne John Feild About
VI. HIGH LEVEL TREATMENT
In 1900 the Council, anxious to extend its sewage treament
facilities, because of increasing sludge drying problems (due to lack of
space), agreed to purchase 2000 acres of Gateforth Estate, near Selby, for
£85,000 and to promote a local Act of Parliament for sewage disposal there. The
sewage was to be given preliminary treatment at Knostrop and then conveyed by
conduit 13 miles to Gateforth. The Bill however was defeated in the House of
Lords.
Taking stock of alternative approaches, the Sewerage Committee
received a report in May 1906 from the Sewerage Engineer, Mr.G.A.Hart, which made
recommendations for a sewage disposal scheme situated on the Temple Newsam
Estate, at Thorpe Stapleton, adjacent to the existing Knostrop works. His
report agreed with a previous report of experts (Messrs. Strachan, Chatteron
and Midgley Taylor in 1904) that the sewage disposal scheme should provide for
an ultimate population of 600,000 persons, with a sewage flow of 40 gallons per
head per day in dry weather - compared with the existing population of 456,000,
with a sewage flow of 36 gallons per head per day.
The proposed treatment scheme involved the following processes:
"(1) chemical precipitation of the sewage, to be followed by (2)
subsequent filtration on percolating bacteria beds, (3) the pressing of the
sludge into solid cake, to be followed by its ultimate disposal on the low
lying land available".
One serious problem with the existing treatment works at Knostrop
was the low-lying nature of the site relative to the river level. The main
outfall sewer crossed under the Aire at South Accomodation Road and its invert
level at Knostrop corresponded to the dry-weather level of the Aire at that
point (58.5 feet above Ordnance Datum). Consequently the sewage had to be
pumped up before it could receive any treatment in settling tanks. This pumping
also had to take account of the fact that the River Aire at Knostrop was
estimated to rise by about 14 feet in time of flood.
The proposed treatment works was to be constructed on higher land
which would allow an improved system of purification to take place entirely
under the force of gravity. The additional pumping costs involved in taking the
sewage from the existing main outfall sewer to the new High Level tanks would
have been considerable. A bold plan involved in the new scheme however, was the
construction of a new, 'High Level', Intercepting Sewer seven miles long which
would intercept the sewage from the more elevated, northern parts of the town
and bring it directly to the new works without pumping. This sewer, which would
progress from Morris Lane, Kirkstall to the new High Level tanks at Thorpe
Stapleton, would receive sewage from 190,000 persons out of a total population
of 456,000.
The total cost of the scheme in capital outlay was expected to be
£1,269,000, of which £163,000 would be for the new intercepting sewers. The
running costs were put at £30,250 per annum.
Legal action against the Council by the West Riding Rivers Board
in 1907 gave added reason to go ahead with Hart's scheme. The case brought by
the Rivers Board was tried before Mr.Justice Grantham on 30th July 1907 and
resulted in an Order of the Court to the effect that the dry weather flow from
the Knostrop works should not contain suspended solids in greater ratio than 11
parts per 100,000. The Corporation was allowed 12 months to carry out the
necessary remodelling of the treatment works. The terms of the Order also
required the Corporation to obtain Parliamentary Powers for a new sewage
purification scheme. As chance would have it, the owner of Templenewsam Estate
(who had resisted the extension of the sewage works) died and the Council was
able to purchase 600 acres from the new owner (the Hon.E.F.Lindley Wood).
When the necessary Parliamentary Powers to proceed were obtained,
by means of the Leeds Corporation Act in 1908, it was anticipated that High
Level Sewage Disposal Works would be fully operational by 1918. The First World
War cut across these plans. At the outbreak of hostilities in 1914, four years
after they had commenced, construction works were suspended and did not recommence
until 1919. By late 1925 the bulk of the work had been completed, but, due to
the increased cost of all materials and wages in the wake of the war, the
estimated total cost had gone up to £2,128,000.
The High Level Intercepting Sewer itself was an ambitious
engineering project. For about 7/8 of its length it was constructed in tunnel,
sometimes at great depths: in Pontefract Lane the depth to invert was 111 feet.
The size of the sewer varied from a barrel eight feet in diameter at the lower
end, to an egg shaped sewer 3 ft 9 in x 2 ft 6 in in size at the upper end.
Treacherous ground conditions were encountered along some parts of
the route, that would be taxing even with modern tunnelling equipment and
methods. As the high level sewer construction progressed under the Leeds to
Selby railway line which then belonged to the LNER Company the strata
encountered were seen to be grossly contorted. At about 18 feet below the sewer
foundation, old coal workings were discovered. These had been abandoned and filled
with an ineffective packing, locally known as "gob". Poisonous gases
emanated from this material, which was of unknown composition, and caused
illness among the miners.
Subsidence was so severe that special measures had to be taken to
provide a safe foundation for the new sewer: 31 concrete piers were sunk down
to the level of the undisturbed strata, at 12.5 feet intervals, with a concrete
semi circular arch between each pair of piers. Thus, the seven foot diameter
sewer construction took place on top of something akin to an underground
viaduct.
The Sewerage Engineer in charge of the scheme was scathing in his
comments on some of the efforts of earlier schemes. Of an 1850 vintage sewer
encountered in Regent Street, he said, "It had been constructed in a
heading, apparently by some person who either suffered from extremely defective
vision or who was constantly under the influence of liquor, since it was no
unusual thing to find it suddenly swinging out of line six inches in a distance
of six feet."
Changed construction techniques in the parts of the High Level
Sewer constructed after the First World War, compared with before, reflected
the technological advances of the time. Before 1916 the motive power was
entirely steam: steam cranes for hoisting up the shafts; steam pumps; steam
driven air compressors and fans. By 1925 however, steam cranes had been largely
replaced petrol winches; air compressors were petrol driven and many pumps and
fans used electric power.
Almost a quarter of a century after the scheme was conceived, the
last brick of the High Level Intercepting Sewer was laid, by Alderman Noon, in
February 1927. To distinguish it from the new High Level Sewer, the original
Intercepting Sewer of the 1850's, which still carried the greater part of the
City's waste water to the old Knostrop Works, became known as the Low Level
Sewer.