360 Theodore Sedgwick Johnson 
COMrARISONS AND CONCLUSIONS 
The comparison of the two tanks will be made on the basis of 
their cost, clarification efficiency and general qualifications. 
COST 
In discussing the estimated cost of the tanks, two methods will 
suggest themselves. One way would be to assume the same 
unit costs for all items under both tanks and this would resolve 
itself in a question of comparative quantities, plus whatever extra 
appurtenances were to be found in either tank. 
Several objections can be maintained against this method. 
First, there will undoubtedly be a difference in the cost of forms, 
in the circular tank requiring more lumber waste, more carpen- 
ter work and more difficult construction. Secondly, the bend- 
ing and placing of reinforcement takes more time and labor and 
is more expensive to hold in place. Again, the placing of con- 
crete may be found to be more difficult in the circular forms. 
The method of estimating costs that will be followed herein 
is as follows: 
A detailed list of every operation necessary to the construction 
of each tank will be made, the quantities of each and unit costs 
for same. The products of quantities and costs, together with 
whatever operations are scheduled as lump sums, will be equal 
to the total cost of the tanks. 
It may be stated here that cost data that will effectually dis- 
tinguish between circular and rectangular construction is ex- 
tremely unreliable and variable. Differences in prices of ma- 
terials and labor, faulty or insufficient accounting systems, 
location with respect to supplies and management prevent any 
adequate or convincing figures. 
In the present estimates, only those items which would be liable 
of any variance will be affected by different prices. 
The following items to be found in the construction of both 
tanks may be said to have probable differences: 
Sheeting. This, if necessary for good work in concreting, might 
seem to be different, but if ordinary sheet piling be used or sheet- 
ing supported and braced by waling pieces, the difference in cost 
would be negligible, for the possible added cost of erection in 
the circular tank would be offset by the smaller quantity required. 
