﻿GEOLOGY OF THE NEW YORK CITY AQUEDUCT 1 43 



tain drill holes which showed sustained flow of water. (2) Pres- 

 sure tests in which water was pumped into holes which had been 

 sealed off and pressure and leakage noted. (3,) Pumping tests in 

 which water was pumped from 4 inch drill holes by means of deep 

 well pump of the type used in oil wells, and fall of ground water 

 during pumping and subsequent rise after cessation of pumping 

 noted. A description of the first two and the results obtained from 

 them follows : 



A substantial flow of water was observed from the following 

 holes : 



11/17: 50 gallons per minute through 2 x / 2 inch pipe, static head 

 10 feet 



10/17: 30 gallons per minute through V/2. inch pipe, static head 

 18 feet 



20/17: 10 gallons per minute through }i inch pipe, static head 

 7.5 feet 



The static head was observed by adding on lengths of pipe until 

 the water ceased to flow over. It will be noticed in the case 

 of hole no. 10 that the flow from the 1^2 inch pipe is not that due 

 to static head of 18 feet, but that due to a head of only y 2 foot. In 

 other words the friction head is about 17.5 feet, and the velocity 

 head only ^ foot. This same condition holds true of the other 

 holes from which a flow was obtained. This would seem to indicate 

 that the amount of water is not very great but that it is under con- 

 siderable pressure. It is believed that this pressure is caused by 

 gas. 



A slight flow was observed from the following holes: 12/17, 

 H/17, 23/17, 31/44, 39/22, and 5./NE. 



The flow from most of these holes has ceased since the pipe used 

 in boring was withdrawn. There is still some flow from the follow- 

 ing holes: n/17, 20/17, 25/17 and 5/NE. 



The flow from hole n/17 is constant at about 10 gallons per 

 minute. The others are too small to be measured. It will be noted 

 that the only substantial flows encountered were from the High 

 Falls shale, Binnewater sandstone and Shawangunk grit, and that 

 it was possible to force water into these rocks in greater quantities 

 and at a less pressure than in the other shales and limestones. 



Porosity tests. The method of making these tests was as 

 follows : 



Wash pipe equipped with a device for sealing the hole was 

 lowered to the desired elevation. The seal consisted of alternate 

 layers of rubber and wood around the pipe preventing the water 

 from escaping between the walls of the hole and the pipe. Water 

 was then pumped in and pressure and leakage noted. 



The result of the pressure tests was to show in a general way: 

 d) That the pressure increased with the depth of seal. (2) That 

 the leakage decreased with the depth of seal. (3) The maximum 

 pressure in the grit was 140 pounds to the square inch and minimum 



