160 NEW WATER SUPPLY SYSTEM AT TAMPA, FLORIDA.

 The preparation of plans and specifications for the plant was in chge
of my associate, Mr. Horace H. Chase, in collaboration with my partner,
Mr. Stuart K. Knox, and my associate, Mr. A. T. Ricketts. Mr. George I.
Buck of my staff was.resident engineer and was assisted in the field by
Mr. E. L. Hyde and Mr. A. J. Barclay. Mr. Chase has also had general
supervision of construction. The,preliminary chemical and biological work
was in charge of my laboratory.


 DIscussIoN.
 FRANK A. MABsToN.* I would like to express my appreciation* of
Mr. Hill's courtesy in giving us this excellent paper. '
 It was my privilege in January, 1926, to visit the Tampa plant, and
 I was much interested in-the provisions made to give flexibility in operation.
 It has been well provided for, and I think Mr. Hill is to be commended for
 the excellent plant that he has laid out. It is, also, very attractive; in fact,
 as it stands today it is one of the most attractive filter plants in the State /
 of Florida. Various features of the plant which he has called attention to
 are of special interest to those who have such plants to design. .
 There are one or two things in particular which attracted my attention,'
 one being the mixing tanks. The scheme provides motor-driven propellers
to agitate the water. It has been found in certain cases that after once
agitating water with altun, it should not be agitated violently again,i but
I notice that the mixing tanks are, as it were, in pairs, one propeller agit4ting
the water and chemical, and then after passing under a baffle, the water is
agitated in a similar manner the second time. I assume that the time
interval is so short that the second agitation will not have any objectionable
effects; but I would like to raise a question as to whether Mr. Hil has
experimented to see the effect on alum floc by that method of agitati n.
 Another question occurs to me. What is the ratio of the area of the
 waterways in the under-drainage system of the filters to the net area of
 the sand? We are in the habit of thinking the ratio should be about 063,oi
 0.5 of 1 per cent. for a perforated pipe system. It would be interestingito
 know what the proportion is in the Tampa under-drainage system.
 MR. HILL. In answer to the first question, the results we hav ob--
 tained at the experimental plant seem to indicate that the secondary
 agitation with the water we had to treat produced better results, and we
 could use a smaller ,amount of chemical by so doing, but we also have
 designed with a view. to making it unnecessary to have secondary agittion
 if we find it advisable not to do so.
 With regard to the other .question, I cannot answer you offhand, but
 I wilLsay this: that the proportion is very much larger than in the ordihry
 grid. I could not give you a definite figure without consulting my notes.
 Of Metcalf & Eddy, Consulting Engineers, Boston, Mass.
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