ECONOMICAL DRAINAGE

Gisborne Times, Volume XXVII, Issue 2489, 30 April 1909, Page 6

ECONOMICAL DRAINAGE

HOW HAMILTON FARES WITH SEPTIC TANKS.

AN OFFICIAL REPORT.

Replying to an.inquiry from a meinbev of the “Gisborne Times’ ” staff Mr oydney B. Sims, the engineer who carried out the drainage system now existent in Hamilton, gives. an interesting account of how the septic tank system Works in that town. Mr Sims says : —- ' Shortly after my arrival in Hamilton in 1905 I was instructed to refJort to the. Council as to the beet method of dealing with the sewerage drainage of The low lying portion of the town, an 'area of. about 150 acres. I recommended the (adoption iof the septic tank System and submitted estimates and a 'plan showing a genera,l outline of the proposed line of sewers. ' My recommendations were approved and I was instructed to prepare detailed plans and specifications and invite tenders for the woi'k. Steps were then taken to raise the money by way of loan, and contracts totalling £SOOO were let and tlie work was commenced in August 1906. Six separate contracts were let, two being for the work pf trenching and pipe-laying, construction of tank, 'etc., and four for the supply of the various materials, the object of the separate contracts for materials -being to ■obtain more competition in • the labor 'contracts, to secure to the Council the full benefit of trade discounts, to en'sure materials of the best quality being used and to prevent skimping. The following are the details of the scheme, which was approved by the District Health Officer, Dr Frengley: The main sewers are from Gin to 12in in diameter, bedded in. lsne concrete and carefully laid at grades to ensure selfcleansing velocities at depths varying ‘from 5 loot to 20 feet, and a total length of about 3 miles. First-class stoneware pipes previously ’subjected to a hydrostatic pressure of 25 feet head were used at depths up to 12 feet, and beyond that'depth “Kielberg' 5 cement concrete pipes were used with success to withstand the external pressure. The configuration of the town rendered it necessary to divide the system Tn to, and therefore two' septic tanks were constructed, one near the bank of the Waikato River and the-second and larger one in a depression near a water course about 20 chains from the river. . t Both tanks were built on tlie same principle, being covered in with submerged inlets and outlets and divided into 4 compartments by means of dwarf walls and tlie flow directed by means of submerged baffle boards, the sewerage entering the last compartment at the bottom, which compartment with plain field tiles. Provision was also made for conveniently cleaning out the tanks when necessary. The total cost of the" works complete was £7500. No analysis has been made of the effluent, as it is recognised that purification does not take place in a septic tank. Septic tanks simply retain the solid matter in the sewage, which is subjected to bacterial action, .and the effluent is treated on filter beds where ’the purification" takes place. No purification works were considered necessary here owing to tlie enormous volume of water in the river. The fact that the effluent entered the river below the source of the town’s water supply, and because of the proximity of the tanks to dwellings, where the smell from filter beds would have been objectionable. The effluent was, therefore, conveyed direct to the river in 6 inch cast-iron pipes, and discharged 4 feet below tLclowest summer level, in tlie one ease, the effluent being diluted before reaching tlie river, by constructing a dam in the creek and leading a 2 inch pipe into tlie effluent pipe. R« Infectious. Diseases. —Hamilton has in the past had an unfavorable record in this respect. In 1905 there were 9 cases, in 1907 19. cases, and 190 S there were only 4, and I hope next year, when all the private connections are made on the drain-

age, tlie number will be nil. Everything in connection with the system is working satisfactorily, and there is no reason why it should not continue to do so.

In a subsequent note, Mr Sims says: In referring to infectious diseases in Hamilton in my letter of tlie 12th inst. I only dealt with typhoid or enteric, being tlie disease generally associated with bad drainage. I enclose a copy of the Health Department’s Inspector, his, figures are rather different from mine, which were obtained from a dif-

ferent source. However, I think yon will, agree that the report is a very satisfactory cue. —Yours faithfully, S. B. SIMS.

The Health Inspector’s Report is as follows:—I bog to submit a statement re infectious diseases in Hamilton, covering the period from October Ist, T 907, to present date, i have to congratulate the Borough Council on the very light list of notifiable diseases ’(which is less than it appears) and also on the very small number of cases of typhoid. One case of scarlet fever and two cases of diphtheria were imported, so that the list is smaller by that number. April, 1908, was the worst mouth, with three cases of typhoid and ten of

diphtheria, the latter of which were all of a very light nature. A remarkable feature in connection with the list is, that in ion’y one case wore the premises connected with the sewer, and that case was traced to its true source, viz, ty-

phoid froan drinking polluted tank water. (So that for 18 months, Hamilton has had no case of infectious disease (one exception) in premises where the drainage system lias been installed. Further comment is needless. Albert P. Bennett, A.B. San., Ins., Inspector P.H.D., and Borough.