PROCEEDINGS OF SECTION I. 



673 



2in. deep, and is composed from below upwards of lOin. of broken 

 stone, 24in. of coke breeze, and Gin. of bluestone shivers. The effluent 

 drains are of open-jointed brickwork. The automatic gear above- 

 mentioned is of special design, constructed by the Public Works Depart- 

 ment, and is actuated by filling and emptying of floating buckets. 

 The arrangement has proved very efficient. The final effluent passes 

 into Sugarloaf Bay, an arm of Middle Harbor. The tank effluent is 

 discharged on to each filter bed in rotation by means of a system of 

 open surface drains. The main drain conducts the effluent into a 

 number of branch box drains or open channels formed in the surface 

 of the bed. In the case of the box drains the effluent flows over the 

 sides and sinks through the material of the beds. With the open 

 channels, however, it filters directly through the bottom and sides of 

 the same. 



The number of persons served with this installation is at present 

 4,230, and the daily flow is estimated at about 100,000galls. 



On an average only one tank was in use at one time during the 

 year, and it is calculated from this that the sewage occupied about 30 

 hours in passing through the same. The general method of working 

 the tanks will be gathered from the table given below. 



Table V. — Table showing ivhich Tank ivas in Operation at the Time of 

 Taking the Monthly Sample, and also the Nvmber of Days each 

 Tank was in Operation. 



Chatswood Outfall. 



1905. 

 November 

 December 



1906. 

 January . . 

 February . 

 March . . . 

 April . . . . 



May 



June 



July 



August . . . 

 September 

 October . . 



No. of Tank in 



Operation at 



Time of 



Sampling. 



Number of Days each Tank Worked 

 during Periods between Sampling. 



Tank No. 1. 



Tank No. 2. 



Total 



2 

 3 



2&3 

 1 

 3 

 3 

 1 

 2 

 1 

 2 

 1 



7 

 15 



7 

 10 

 17 

 12 



5 



9 

 10 



9 

 16 



7 



17 days 

 14 " 



14 " 



19 " 



6 " 

 4 " 



14 " 



7 " 

 16 " 



3 " 



18 " 

 7 " 



124 days 



139 days 



Tank No. 3. 



7 days 



7 " 



12 " 



17 " 



11 " 



5 " 



9 " 



14 " 



" 



23 " 



2 " 



14 " 



121 days 



Note. — The total number of days worked by tanks is slightly in excess of the 

 actual number of days in the period covered by this report. This is due to the 

 fact that occasionally two tanks were used in combination for a few days at a time. 



The filters pass through the stages of filling, standing full, emptying, 

 and standing empty, the time for each stage depending upon the rate 

 u2 



