Underground Water Waste Control in New York
Two Papers Dealing with the Subject by Engineers on the Staff of the Department of Water Supply—Difficulties Aggravated by Subsurface Congestion of Pipes and Conduits.
THE following papers, both read before the New York section of the American Water Works Association at its last meeting, treat of the same subject in a practical way and complement each other in the account of the work done in the location and repair of leaks by the New York department and the methods pursued in the work. They should prove of interest to water works men in other cities.
Under the subject of water waste control, I will endeavor to tell you, in a practical way, of a few interesting leaks which I have been called upon to locate, and of the method by which their location was accomplished. With the Water Works, as in every other business in New City, time is a controlling factor, and therefore the methods adopted are those which will give the greatest return in information for the amount of time expended. With the idea in view of accomplishing the greatest amount of work in the shortest time, the method of districting the system, and measuring the flow into each shut off during the early morning hours, has been supplanted by establishing a system of control gratients, and aquaphone testing to accomplish the same end.
Leaks From Abandoned Surface Pipes Worst
The sources of leaks that offer the greatest difficulty in locating them are those from abandoned service pipes which have been bent over and hammered up, and at some later date open up and start to flow. To give you some idea of the damage caused by such waste of water, I will tell you of a leak which in the course of our regular work was located and stopped. While aquaphoning in the vicinity of 65th street and 5th avenue, a leak noise was heard on the line gate in 65th street; and on further investigation, by means of driving a bar through the street pavement, over the water main, until the bar and pipe were in contact, then listening with an aquaphone on the bar for the vibration produced by the leak until the leak noise becomes most distinct, there making an excavation, an abandoned tap was located which, when shut off, stopped the flow of water to the home of M. O. Wilson, No. 3 East 65th street. This had been running since the house was built some ten years and was suppesed to have been a spring. The flow of water into the premises was about 100,000 gallons per day. To take care of this flow of water at first, the entire cellar was water-proofed at a cost of $12,000. This failing to keep the water out, a pump was built and an electrically operated centrifugal pump was installed as well as a water siphon. After stopping the leak the monthly meter bills for water were reduced from $41.10 to $8.10, showing that the siphon consumed $33 worth of water per month or $396 per year. This, together with the electrical bill to run the turbine, Mr. Wilson’s secretary told me, amounted to $500 per annum. Something of the magnitude of this leak can be appreciated when I say that its existence for ten years cost Mr. Wilson more than $17,000 and wasted 365,000,000 gallons of water.
Another Typical Condition of Water Waste
Another very typical condition of waste, caused by an abandoned service, was exemplified in the leak I was called upon to locate, some time ago, running into the Russell Sage Foundation Building, corner of 22nd Street and Lexington avenue. The basement of the building was waterproofed to take care of the ground water, but when an old abandoned service opened up and started to flow, causing a pressure under the basement floor, the tar which had been used in water-proofing started to work up through the concrete and formed globules on the floor which grew in size until the water within them burst the globule. The abandoned service which caused this trouble was located by driving a bar through the pavement and into the ground, until the point of the bar penetrated the sub-surface water level. Then marking the bar at the street surface and withdrawing it, then measuring from the mark to the point where the water wet the bar, a point is determined on the gradient of the Sub-surface water, which if followed up will lead to the source of the flow as the gradient will rise to a maximum at the source. This leak, so I have been informed, cost the owner of the building upward of $3,000 to take care of it before we were called in to find the trouble.
No surface indications previous to the waste detection work.
Danger of Injuring Sub-Surface Pipes
So that you may not get the mistaken idea that the making of the soundings, before mentioned, is a simple matter of driving a bar into the ground, I want to state that the maze of sub-surface structures, as pipes, cables, ducts, etc., which permeate the sub-street surface in New York City, are so apt to be damaged by driving a bar through the street at random, that the method of sounding requires some one in charge, who is not only familiar with all of the underground conditions through the City, but who has had sufficient experience in this particular line of work to properly interpret the condition indicated.
As a sample of what might happen if this work was carried on carelessly, I will mention that a plumber a short while ago, while digging in the street along the line of the Lenox avenue subway in Harlem, accidentally struck a power cable with a pick and the man was not only nearly electrocuted but it cost the Interborough in the neighborhood of $75,000 to make the repairs.
Another case, which shows what a danger the waste from abandoned services is, will become evident when I tell you of a five-eighth-inch tap which was found leaking in Columbus avenue at 76th street. There was no street indication of a dangerous sub-surface condition and the leak was located by the aquaphoning and sounding method before mentioned.
When the first sounding was made and the bar had penetrated the concrete foundation of the street the next blow with a hammer drove the bar through the pavement and out of sight. An excavation was made and it was found that the water had washed out sufficient earth to leave a hole large enough to put a good sized truck in and had undermined a 30-inch gas main which together with the foundation of the street surface was the only support given to street traffic over this section.
It is very probable that if this condition had continued to exist very long, heavy trucking would have fallen into the hole as well as breaking the 30-inch gas main, which might have caused an explosion entailing considerable damage.
SECOND PAPER BY F. B. NELSON
Assistant Engineer, Department of Water Supply, Gas and Electricity, New York City
In New York City, speaking in round numbers, about one-quarter of the 390,000 services are metered; also about one-quarter of the total supply passes through meters. Thus about three-quarters of the 600 million gallons pet day delivered to the city is unguarded as to waste except for the special and limited effort which the Department of Water Supply is able to make towards even a partial control. Also the situation leaves largely to conjecture the proportion of these unguarded millions that is wilfully wasted, or that is continuously running from defective or neglected plumbing, or from underground leaks in the maze of some three thousand miles of mains and connecting service pipes.
The possibilities for the development of underground leakage depend largely on sub-surface conditions. In the Boroughs of Brooklyn, Queens and Richmond, as a rule, the existence of under-ground leakage is revealed by visible surface indications. In Manhattan and The Bronx the reverse is true, and, excluding sudden or serious breaks, the chances of a leak showing at the surface are very remote. This is due to the almost universal rock and the very uneven original surface, necessitating extensive grading as the city developed, whereby large areas now consist of loose rock fill, while others that are cut to grade include sewer pipe and conduit trenches in subways and backfill with loose brick. This condition provides numerous and ample channels to conduct leakage to the sewer or to unexpected locations, often very remote from the source of the trouble. It is therefore principally in these two boroughs that the special underground waste detection work has been carried on. The force and the methods adopted have been developed in an endeavor to most effectively meet these conditions.
Sub-Surface Congestion Renders Discovery Difficult
The difficulty of locating leaks in these boroughs is often materially increased, particularly in lower Manhattan, by the congestion of sub-surface structures, including gas mains, steam mains, high and low tension electrical conduits, as well as the frequent duplication in the same street of our own trunk and distribution mains and the high pressure fire system, all more or less rearranged by subway or other structures, which also tends to subject mains and services to unequal settlement. Since 1912 a special force under engineering supervision has been assigned principally to the work of underground waste detection in these boroughs. To date this force has located and repaired underground leakage totalling over 75 million gallons per day (an amount equal to a supply for a city of 750,000). Probably 50 millions of this, or the bulk of that located previous to 1918 represented leakage that was causing no apparent damage or complaint, and which could have continued indefinitely or until revealed by the caving in of underground paving, settling and breaking of adjacent mains, or other damage. That long continuance of such leakage without damage or public inconvenience is possible as evidenced in a number of cases. Several leaks of approximately one-half million gallons a day have been found flowing to the sewer through a clear channel directly under rock filled macadam streets, with no visible surface indications. Numerous other cases have been found in which the evidence is quite conclusive that the leak had existed for years.
Detection Work Largely on Complaint
Since 1917 it has been found profitable to utilize this special force in relieving the repair shops of cases of leaks location in which extensive street openings, traffic interference or damages could be avoided by the application of engineering methods, and the force has been increasingly utilized in this way until their waste detection work has come to be almost exclusively on complaint and emergency matters, and the systematic search for leaks has had to be abandoned. This procedure eliminated the previous policy of systematic search in sections where the greatest saving of water could be secured at the least expenditure of time, and quite frequently resulted in an expense in time and labor out of all proportion to the value of the water saved. This, together with the increase in salaries and wages has advanced the cost of the work per million gallons saved from $1.15 in 1917 to $3.19 in 1919.
Force For Leak Detection Enlarged
The emergency work is, of course, of prime importance and must not be neglected, though it is to be regretted that the systematic work effecting the greater saving of water has had to be discontinued at a time when the general increase of pressures with the introduction of the Catskill supply has so materially increased consumption and no doubt, the leakage. At the present time the list of matters for attention is far ahead of the ability of the present force to handle, and during 1919, this situation being realized, special funds were provided for increasing the waste detection force and equipment to more adequately meet the situation. This additional force and equipment could not be secured in time to be effectively utilized during that year, but it is hoped that during the present year we can get abreast of the emergency work and possibly resume some of the more aggresive systematic search for leakage.
The force for the past three or four years has consisted of an assistant engineer in charge and two field parties, each under the immediate direction of an assistant engineer, and consisting of one rodman, one caulker, three laborers, an auto engineman, and the necessary equipment including motor truck and Ford car for the engineer. The increase of force provided for is such as to provide two additional field parties to be under the direction of the same two field engineers.
Old Surface Leaks Hard to Locate
The leaks located and repaired in general average 50,000 to 75,000 gallons per day, but in case of complaint it frequently becomes necessary to spend an immense amount of time on leaks of but a few gallons a day when all ordinary methods fail and in rare cases just the primitive method of digging is the only recourse. Another class of leaks which are extremely difficult to locate are abandoned service pipes which frequently are closed by bending over and hammering the end of the pipe within the property lines to avoid the expense of street excavation necessary in properly shutting them off at the main. Here again all ordinary methods of waste detection fail, due to the fact that on account of the usual length of service pipe, little or no sound is produced which can be detected by aquaphones. In one instance in last year’s work, the practical stripping of a six-inch main became necessary and twenty-five street openings were made, the work terminating in the location of an abandoned service pipe discharging about 50,000 gallons per day. This flow was making its way underground in a northwesterly direction beneath cellars and areaways and appearing at the point of complaint in the next block 157th street. In this case the size of the leak was sufficient to have been easily located by the ordinary methods if it had occurred nearer to the street main, but on account of the length of service pipe, with, undoubtedly practically full opening at the end, no noise was traceable by ordinary soundings.
The record of the work done in 1919 may be of interest as illustrating the frequency of the different classes of leaks. The leaks stopped totalled 9,348,000 gallons per day. The average size of the leaks located was 54,000 gallons per day. The number in the different classes was as follows:
Total number of leaks 173
Openings per leak (excluding the above mentioned one requiring 25 openings), 1—2/10.
Openings per leak (including the 25 openings), 1—3/10.