Home          Transit 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.

7. A Matter of Economics