154 Bui^LETiN 86 , 



inside city sewers, and the contract was held up for several weeks. 

 The pipe was from a Los Angeles factory and was mostly 8-inch 

 pipe. Many tests that were made showed that the pipe did not 

 measure up to the specifications. A committee of engineers was 

 appointed by the mayor to report on the quality of the pipe, par- 

 ticularly "as to whether the pipe is of good, first-class, and standard 

 quality, such as will provide this city with good sewers when laid." 

 The report of this committee follows: 



REPORT OF COMMITTEE 



Nov. 8th, 1916. 

 To the Mayor and Common Council of the City of Tucson. 



Gentlemen : The undersigned, your committee appointed to in- 

 vestigate and report relative to the quality of the sewer pipe now 

 being laid in your city, under contract with T. J. Shea, begs to sub- 

 mit the following report. 



In a letter from the Mayor dated Nov. 7, it is stated that you 

 desire our views "as to whether this pipe is of good, first-class and 

 standard quality, such as will provide this city with good sewers 

 when laid.'' 



The committee has personally inspected considerable of the pipe 

 stacked up alongside the streets in the north part of the city, and 

 has selected and tested nine of those pipes. We tested also three 

 pipes said to have been taken from the last carload and one addi- 

 tional pipe. 



The first test stipulated in the city specifications is that of perco- 

 lation. Our tests show that the pipes with few exceptions do not 

 withstand 15 pounds per square inch hydrostatic pressure, and some 

 of them do not stand a pressure of even 5 pounds. Tests were made 

 also with a pressure of 2^ pounds per square inch lasting 20 min- 

 utes. One specimen was sweating at the end of this time, but the 

 others were dry on the outside. 



The importance of the percolation test is mainly with reference to 

 its bearing upon the strength of the pipe, inasmuch as slow percola- 

 tion is of little moment from a sanitary or engineering point of view, 

 in all but rare cases, such as when the sewer line is laid below the 

 groundwater level and drinking supplies are obtained in the vicinity. 

 It is the common opinion of all engineers that the pores of both clay 

 and cement tiles gradually close up after they are put in service. 

 Certainly it is unnecessary to demand that new tiles should stand 

 as high as 15 or even 5 pounds internal pressure, equivalent to 35, 

 or 12 feet head of water. Our special test of 2]^ pounds pressure 

 approximates the actual conditions of the pipe in the trench, and 

 we feel safe in saying that the percolation under these conditions 

 will be negligible. 



The important test in the case of sewer pipe is that of strength, 

 particularly strength to resist external pressures, for practically all 



