(a) If not carefully made and of the best of materials, it is
subject to failure by disintegration, etc.
(b) It will not stand strong chemical action, and therefore the
smaller sizes should not be used where they are likely to be
exposed to trade wastes containing strong acids. In the larger
sizes the quantity of flow mixes so quickly with the trade
wastes that this danger is minimized, and it is very seldom
that even the smaller sizes become affected; but vitrified
pipe may be used in places where chemical action is
anticipated.
(c) If not properly made, it will be attacked by steam and hot
vapor, and by animal fats in the sewage; but, if properly
made, it is not affected by these.
(d) Unless reinforced or made very thick, it will not stand as
great a crushing load as the best vitrified stoneware pipe;
but, as sewers are not intended to be used under very heavy
pressure, this is not so very important. It is amply strong to
withstand any internal pressure or any external crushing load
to which it probably will be submitted.
(e) Under a considerable head of ground-water, it may permit water
to infiltrate through its walls for a considerable time after
it is laid, thereby temporarily increasing the flow, which, if
the sewage is to be pumped, will increase the cost of pumping.
This difficulty can be met by using a carefully selected mix
of materials in making the pipe, and by making the joints
carefully. Infiltration through concrete diminishes rapidly
after the sewer is in use; it occurs in vitrified pipe, also,
to some extent.
The house connection drain adopted in Monterrey, with the disconnecting
trap, is very much like one which the writer has seen introduced with very
bad result. These are being removed as rapidly as possible by one of his
clients, a sewerage company, in the Southern States. It has been a
fruitful cause of stoppages and bad smells; the ordinary method now in
general use is much better. In the design shown, it would seem that there
may even be some danger that the ventilation of the sewer by the
stand-pipes in the streets may force the traps.
One is rather surprised to learn that the main outfall sewer is designed
with a capacity of 90,000,000 liters per day, the present sewage being
estimated as not more than 18,000,000 liters, and the far future being
thought to require only 40,000,000 liters. Why this excessive size?
Possibly the surplus water which it is to carry is to be discharged into
the sewers from the water supply system direct, and is intended for
irrigating the land at the disposal area, when the sewage is insufficient
for this purpose. The author states that all surface water is strictly
excluded.
The method of sewage disposal gives rise to several questions. It is
proposed to use an extensive area for growing crops, which are to be
irrigated with sewage. The paper states that the underlying strata at
Monterrey contain numerous caverns, and the first question is: What will
be the effect on the water supply of other towns lower down the valley?
The writer recollects a serious outbreak of typhoid fever in Bluefield, W.
Va., caused by the pollution of the water in similar strata finding its
way through unknown underground caverns and channels to the city's water
supply.
The next question is: What crops will be grown? It is a well-known fact
that vegetables grown by the use of sewage as a fertilizer, are unsafe in
a raw state for human consumption. This is well-known to European
travelers in China and Japan, where the use of fecal matter as fertilizer
renders the various water supplies (where not filtered and disinfected)
and all green vegetables, unsafe, on account of typhoid germs. Moreover,
crops not intended for human consumption, which are grown on lands
irrigated by sewage bearing typhoid germs, etc., are unsafe for men to
handle; even to store them may cause a dissemination of disease. It is
evident, therefore, that the whole sewage flow should be in some manner
disinfected at least, if not filtered, before it is used.
The method of sewage disposal and the use of merely settled septic sewage
for irrigation seem to be open to objection. The disposal plant is not
sufficiently effective to meet the present requirements of sanitary
science; and the sludge-pit will be certain to breed a pest of flies, if
it is not also an intolerable nuisance on account of foul smells.
Monterrey would seem to be a proper place for the introduction of the
Imhoff tank, with percolating filters, and a final settling tank, the
effluent being disinfected, before entering the latter tank. The flow
might then be used safely for irrigation purposes for crops not to be
eaten uncooked by man. The writer does not see how the method provided can
possibly fulfill the object stated, to distribute on the land an effluent
which will be "innocuous and clear," or how any consequential degree of
purification can be obtained in the tanks provided.
While there are described in this paper many things to find fault with,
there are also many things to commend. The water supply system, with its
reservoirs, etc., seems to be admirable; and the methods of construction
by which the expense for forms was reduced is very interesting. The
parking and ornamentation of the grounds over the reservoir roofs cannot
fail to benefit the people and popularize the work.
RUDOLF MEYER, M. AM. SOC. C. E. (by letter).--The writer, as Engineer for
the Government (guaranteeing the concessionaires a gross return of 10% per
annum on the capital invested), and as inspector of the various works has
had exceptional opportunities to become acquainted, not only with their
construction, but also with events leading up to the granting of the final
concession under which they were built and will be extended. In order to
judge of the extent to which the different engineers, in their turn
contributed toward the design of these works, the writer has thought it
desirable to submit a complete statement of all matters relating to the
inception, investigations, surveys, tests, etc., previous to the adoption
of the present plans.
Data regarding former investigations, plans, and concessions which have
since lapsed, have been obtained from the Government archives. These refer
to periods prior to Mr. Conway's engagement, and anterior to the retaining
of Mr. Schuyler by the concessionaires, and Mr. Binckley's connection with
the scheme, and they are presented here as complementary to the
information in the paper.
Samuel M. Gray, M. Am. Soc. C. E., acting in the interest of some American
capitalists (who had been induced by Col. J. A. Robertson, of Monterrey,
to look into the merits of a concession acquired by him, for building
these works), being guided by the Government's proposition to supply the
city with water by damming the flood-waters of the Santa Catarina River in
the narrow gorge through which the stream emerges from the Sierras, some
eight miles from the city, had several soundings made and reservoir sites
surveyed in the first two box canons up the river, and prepared and
presented to the Government several alternative projects, besides the one
mentioned by Mr. Schuyler. Several different dam sites were designated by
Mr. Gray, whose investigations extended over some two years, and were
finally abandoned after he had designed the general outlay for a complete
network of water mains and sewers for the city, on account of the
unwillingness of the Government at that time, about 1897, to grant any
guaranties as to bonds or income to the concessionaire or his assigns. Mr.
Gray did not favor the general scheme of storing flood-waters as a water
supply, but strongly recommended to the attention of the Government the
greater advantages of deriving the supply from subterranean flow in the
river, by an infiltration gallery driven into the water-bearing gravels in
the Santa Catarina Canon (only a short distance above the place where Mr.
Binckley afterward established his bore-holes across the river). He
proposed to take advantage of the steep slope of the river at a turn in
the canon, and from the lower end drive a tunnel through a projecting rock
spur, which tunnel, though starting well above the ordinary reach of
floods, would terminate in water-bearing gravel, at a sufficient depth
below the surface of the river-bed to intercept part of the underflow. Mr.
Gray, through investigations made under his direction, by Nathaniel
Turner, M. Am. Soc. C. E., had ascertained that there was an abundant
subterranean flow, and work had actually been started on the proposed
tunnel.
The results of Mr. Gray's investigations were put at the disposal of
Messrs. Mackenzie, Mann & Co. by Mr. Robertson, at whose offices Mr.
Binckley prepared the first plans submitted by him for the approval of the
Government.
After Mr. Gray's investigations, Messrs. Mackin and Dillon (F. H. Dillon,
Assoc. M. Am. Soc. C. E.), under contract with the Government, prepared
the following plans: For a dam in the Santa Catarina Canon; for a pipe
line, similar to the one proposed by Mr. Gray, to a reservoir and settling
basin on the left bank of the river (a short distance above where the
provisional pumping station was established afterward by Mr. Binckley),
but on the flat above the bluff skirting the river, practically at the
same elevation as the present high-pressure reservoirs; for a complete
network of water mains and sewers in the city, indicating the approximate
direction in which the sewage would be disposed of, either by turning it
into the river or by spreading it over suitable lands, the location of
which was to be determined later; and also a complete set of
specifications.
On these data bids were invited by publication, and inquiries were
received from several parties. Finally, Messrs. Stocker and Walker, of
Scranton, Pa., entered into negotiations with the Government, and the
present concession was agreed upon and granted.
Messrs. Stocker and Walker engaged the late E. Sherman Gould, M. Am. Soc.
C. E., to prepare a plan for a storage dam in the Santa Catarina Canon,
and submitted plans for water distribution and sewers in the city,
slightly modifying the original plans of Messrs. Mackin and Dillon.
In the fall of 1905, the concession was acquired by Messrs. Mackenzie,
Mann & Co., of Toronto, Canada, together with all plans, etc.,
presented by the original concessionaires. The new concessionaires stated
that they would examine the whole situation again, for the purpose of
presenting modified plans for works.
Mr. Schuyler, in the interest of the new owners, had paid one flying visit
to Monterrey when Mr. Gray's projects were brought to his notice, and the
writer had an opportunity to show him the tunnel which had been started.
Mr. Schuyler left for Brazil and did not return until February, 1906, when
he was accompanied by the Chief Engineer appointed by the concessionaires.
Messrs. Schuyler and Binckley then prepared plans for the water
distribution and sewer systems in the city and for a provisional water
supply to be pumped at San Geronimo, some two miles up the river. The new
plans for the city work followed closely the general disposition by Mr.
Gray, the principal difference being that the main reservoirs for the
permanent water supply were located to the south instead of to the west.
This change was due to the results of an investigation, made during Mr.
Schuyler's absence in Brazil, by Mr. F. S. Hyde, late Hydraulic Engineer
of the Necaxa Water Power plant, who, accompanied by the writer, visited
the whole water-shed of the Santa Catarina River in October, 1905, in
search of suitable dam sites and prospects of power development. Mr. Hyde
extended his studies to the Santiago Canon, southeast of the city,
recommending finally that the water be brought from that canon, and that
wells be dug in different points of the Santa Catarina River between San
Geronimo and the entrance of the canon, and tested by pumping, for the
purpose of establishing levels and ascertaining the available amount of
underflow, with a view of determining the location for an infiltration
gallery high enough up the river to permit of a gravity delivery and under
good pressure in the city.
In view of Mr. Hyde's report, and as the result of a visit to the Santiago
Canon, Mr. Schuyler decided to locate the reservoirs south of the town,
intending to bring in water from the southeast, from springs in the
Santiago Canon, and also by infiltration from Santa Catarina, his and Mr.
Binckley's scheme of water supply being for the same pressure throughout
the city.
To supply water during construction, and partly meet the demands of the
city, Mr. Binckley, on his arrival, decided to establish a provisional
pumping station at the well in the river nearest to town, started by
direction of Mr. Hyde at San Geronimo. This well was situated within the
bed of inundation of high floods, on a low bank, at the foot of a
conglomerate bluff some 20 ft. high, limiting a flat which was above the
reach of any flood. It was on the same side of the river as the city, and
there was plenty of good ground on the flat above for the establishment of
a reservoir.
A slightly shorter pipe line was secured by crossing the river, building
the reservoir (a substantial concrete-lined and vaulted-over structure) on
the opposite bank, laying out the pipe line to follow that bank nearly to
the city, and finally crossing back again; but the result has been that
since the flood of August, 1909, in which the river crossings were
destroyed, the reservoir remains isolated on the other side of the river
from town, though intended to form part of the permanent works and act as
a compensating reservoir for equalizing the pressure of the high-pressure
system. Fortunately, the pumping station, the larger pumps, and the
boilers, had been moved up the bank (after a rapid rise in the river on
August 10th, 1909) to the new wells established by Mr. Conway on the line
of the proposed prolongation of the infiltration gallery. The reservoir,
however, is left to stand alone on the other side of the river, and its
usefulness will not be restored until a new line is laid across the river,
re-establishing its connection with the new pump line and the new and
permanent pipe line to be laid along the north bank from the pumping
station to the city. This will free Monterrey from the constant menace of
a water famine. At present its two main water supplies may be cut off by
unexpected floods like those of 1909 and 1910, as both supplies are
carried across the river, and though only the cast-iron pipe connecting
with the water supply from Estanzuela was carried away by the flood, the
concrete conduit of the San Geronimo low-pressure supply was seriously
threatened. Such risks are too great to be carried for any length of time;
besides, a succession of dry years would cause such a reduction in the
Estanzuela supply as to require an additional reserve in the way of
pumping stations drawing on the under-flow of the river, such as already
exists in San Geronimo.
Afterward, Messrs. Schuyler and Binckley submitted preliminary plans and
profiles for the projected concrete gravity conduit from Estanzuela to the
reservoir south of the city, and Mr. Binckley submitted excavation plans
for two reservoirs, only one of which was built, and from designs by Mr.
Conway.
Stephen E. Kieffer, M. Am. Soc. C. E., was intrusted by Mr. Binckley with
the revision of the plans of the water distribution and sewers. The
southern half was approved by the Government and executed according to his
plans; the northern part was afterward revised by Mr. Conway and has been
partly built.
The final maturing of the project of an infiltration gallery in San
Geronimo as a low-pressure gravity supply, the division of the city into
high- and low-pressure districts corresponding to the two supplies, with
one reservoir, instead of two to the south of the city, and the other to
the west at the Obispado, the entire details of both these gravity
schemes, and of the whole sewage disposal scheme, as well as the
modification introduced into the city work for the northern half, are
unquestionably due to Mr. Conway, independently of the general views which
may have been held on those points by other engineers.
In March, 1910, Mr. Conway left Monterrey, all the principal works being
finished. Since that time Vicente Saucedo, Assoc. M. Am. Soc. C. E., has
put in many additional water mains and sewers in the northern part of the
city, and is finishing the _force majeure_ work caused by the destruction
wrought in the districts along the river banks by the extraordinary
floods.
The writer, having had an opportunity to watch the earnest efforts of the
several engineers connected with these works, in the course of their
design and construction, resulting without doubt in being the first of
their kind built in Mexico, has been induced to contribute this discussion
in order to bring out clearly the share of each.
Mr. Pitkethly's apprehensions as to the adequacy of the system of
ventilation adopted have not been realized, in part perhaps because the
houses, though generally of only one story, have such high ceilings that
the tops of their vent pipes are generally higher than the ventilating
columns at the heads of the branch sewers.
GEORGE ROBERT GRAHAM CONWAY, M. AM. SOC. C. E. (by letter).--The writer
regrets that some features of the works described in this paper have
failed to call forth the many useful criticisms which he expected, and his
remarks, therefore, are limited to the few points which have been raised.
He is particularly indebted to Messrs. Schuyler, Meyer, and Saucedo for
adding supplementary information of value to the paper, but regrets that
he cannot support Mr. Binckley in his claim that "the entire general
design of the system, as well as the extensive hydrological studies and
final selection of the sources of water supply, was completed in 1906,"
etc. On May 1st, 1907, when the writer assumed responsibility as Chief
Engineer, he was unfortunately confronted with the fact that very little
data and only a few preliminary and incomplete plans were available. His
first duty was to report upon the final sources of supply, and the
recommendations made in his report (dated July 12th), received Mr. (now
Sir William) Mackenzie's approval during the same month. The final plans,
upon which the approval of the State Government was definitely obtained,
were prepared by the writer during the summer of 1907, were submitted to
the Governor of the State, Gen. Bernard Reyes, on October 19th, and
received his approval on December 12th, 1907. No works, with a long
preliminary history, such as those at Monterrey, can rightly be said to be
due to any one individual; many engineers contributed to the final result,
and the writer willingly acknowledges his indebtedness to the able men,
who, for ten years prior to the construction of the works, investigated
the particular problems which were met--problems which were not only of an
engineering and physical nature, but racial and financial. The
responsibility of constructing the works in their present form, and
leaving them practically complete, did, however, fall on the writer's
shoulders.
Messrs. Pitkethly and Hammond have criticized the basis of the
calculations upon which the sewer system was laid down. In considering
this problem, it is necessary to remember that, in designing this system,
there was practically no information upon which to base the calculations;
and the writer believed that the wisest course was to anticipate a liberal
growth, and provide a large margin of safety. In designing a sewer system
in older and well-established communities, the engineer is generally able
to compile considerable information regarding the probable sewage flow for
which it is necessary to provide. In Monterrey this quantity was
absolutely unknown. The writer's practice in other places has been to
assume that about 8% of the total daily discharge of sewage will flow off
in one hour; and, from many curves which he has plotted regarding sewage
flow in British towns, this rate appears to him to be approximately
correct. In Monterrey, however, the old Mexican traditions are rapidly
changing, and the city is now becoming one of the most Americanized in
Mexico; the old one-story houses will give way in time to buildings of
several stories--a change, already noticeable, which has occurred during
the past few years, particularly in the business portion of the city.
Taking these facts into consideration, it is believed that it would be,
not only bad engineering, but bad business, for a company whose concession
lasts 99 years, to provide sewers as small as 6 in., as Mr. Hammond would
recommend, and then be called upon, under the terms of the concession, to
relay larger sewers at a future date, thus incurring further capital
expenditure upon which no Government guaranty would apply, and no further
revenue be obtained. In matters of this kind, not only the engineering,
but the commercial, aspect of the question must be kept in view, and this
point, the writer must frankly admit, he has always seriously considered.
The writer's experience with reference to the method of ventilating sewers
by tall columns extends over many years, and he still maintains that no
other system gives such satisfactory results. In this view he finds
considerable support in a recent paper on "Salisbury Drainage," by Mr. W.
J. E. Binnie,[11] written since the system at Monterrey was installed, in
which the result of a series of experiments carried on during 1906-07 are
given. At Salisbury, England, 68 ventilators, 6 in. in internal diameter,
30 ft. high, were connected to the main sewer by 6-in. stoneware pipes.
They were placed about 540 ft. apart, and, from careful anemometer
readings, the following conclusions were reached:
[11] _Minutes of Proceedings_, Inst. C. E., Vol. CLXXXI, p. 317.
"(1) That four ventilators all lying in the lower portion of the
town acted sometimes as air-inlets and sometimes as
air-outlets, and that the other sixty-four acted as
air-outlets.
"(2) That the average velocity of the air escaping up these
columns was 3.2 feet per second, representing the circulation
of 3,600,000 cubic feet of air per diem, or sufficient to
change the air in the sewers every 10 minutes.
"(3) That the average velocity of the current of air in the
ventilating-column increases with the size of the sewer to
which it is connected, averaging 2.4 feet per second with the
7-inch sewer, 3.6 feet per second with the 9-inch sewer, 3.7
feet per second with the 12-inch sewer, and 4.1 feet per
second with the 15-inch sewer in these experiments.
"(4) That the draught in the column is very largely dependent on
the wind, being at its minimum on a still day, and could
therefore be readily increased by the use of a suitable cowl.
"(5) That the draught is very little affected by the
sewer-gradients. It was expected that, in ventilating-columns
placed in connection with the upper end of a sewer laid at a
steep gradient, a strong draught would have been obtained. No
direct connection, however, was traceable."
As the result of these experiments, Mr. Binnie rightly came to the
conclusion that this system of ventilation was efficient.
Mr. Hammond anticipates that the house connection trap system at Monterrey
will lead to bad results, but the writer has seen the system at work in
many widely different cities with excellent results. He believes that it
is in accord with the best practice of the most eminent sanitarians during
the last 20 years, and has no apology to make for introducing that system
in Monterrey.
Regarding Mr. Hammond's summary of the advantages of concrete pipes for
sewer construction, the writer is in entire agreement, and would willingly
have introduced them throughout the whole of the Monterrey system, but for
the fact that it was an exceedingly difficult matter to obtain suitable
sand for their manufacture during the early days of construction, and
considerable delays would have arisen if a complete network of such pipes
had been used. His later experience at Monterrey, when the sand difficulty
had been solved, clearly showed that concrete pipe could be laid down at
much less expense than fire clay.
Both Mr. Pitkethly and Mr. Hammond refer to the system of liquefying tanks
used at Monterrey preparatory to turning the sewage on the irrigation
lands, and both express doubts as to their efficiency. The writer is now
separated from his library and notes by many thousands of miles, and
cannot quote "chapter and verse" as accurately as he would like, in order
to support his views that the system adopted was adequate for dealing
with a system such as that at Monterrey. It must be pointed out that not
only was it intended to prevent the sewage from becoming a nuisance, but
that the sewage flow plus a large quantity of surplus water was intended
to be used profitably for irrigation purposes. With that object, the
Company--or rather its allied Company, the Monterrey Railway, Light, and
Power Company--obtained the control of 2,246 acres of the very finest
arable land, with almost perfect natural drainage conditions, so that this
land could be utilized to create a profitable revenue from the use of the
sewage. The outfall sewer was accordingly designed to carry sufficient
water and sewage to irrigate about 2,500 acres of land, which area could
be considerably extended if necessary at any future time.
Most authorities now agree that before turning sewage upon land, a
preliminary treatment is required to remove as much as possible of the
suspended matter, and then reduce the latter by subsidence in liquefying
or septic tanks, so that the quantity remaining in the effluent is so
small and finely divided that it may be readily decomposed and oxidized by
bacterial action without risk of clogging the surface or interstices of
the land upon which it may discharge.[12]
[12] See Raikes, "Sewage Disposal Works," pages 97-98.
Mr. Pitkethly quotes Messrs. Watson and O'Shaughnessy as saying, in their
evidence before the Royal Commission on Sewage Disposal, that not more
than 10% of the solids are digested in septic tanks, but it must be
remembered that in many other places evidence was given before the same
Commission showing that from 25 to 30% was actually obtained.
Mr. J. D. Watson, in his paper, "Birmingham Sewage-Disposal Works,"[13]
read in March, 1910, points out that:
[13] _Minutes of Proceedings_, Inst. C. E., Vol. CLXXXI, p. 259.
"The much-maligned sewage-farm still may be allowed (where the
conditions are favourable) to rank as one of the best methods
of sewage-disposal. Diverse opinions may be held as to what are
favourable conditions, particularly as conditions are sure to
vary widely with locality; but it may be assumed that where
there is 1 acre of suitable land per 100 persons, as in Berlin
and several other important cities, the efficiently-worked
sewage-farm, when judged solely by the standard of the effluent
produced, is still in the front rank. Effluents from such a
farm are remarkable for their paucity of micro-organisms, their
low albuminoid ammonia, and their unvarying character."
Assuming that not more than 2,000 acres of the irrigated land at Monterrey
were available for sewage purposes, this area would represent the sewage
treatment of the present population of not more than 45 persons per acre,
and on the basis of the design, that is, for a population of 200,000
persons, this represents not more than 100 persons per acre. In many
sewage farms on the continent of Europe, the number treated per acre
varies between 80 and 200 persons; for example, at Breslau it is 187, at
Berlin 105, at Brunswick 88, and at Steglitz 185.
Regarding the crops to be grown on the land, very satisfactory results
were obtained from growing Indian corn, and two excellent crops per annum
were taken from an area of 500 acres during the period in which the writer
was responsible for the works. It was also his intention to grow alfalfa,
and turn a part of the land into a pecan grove, and, although he does not
share the apprehensions of danger of either Mr. Pitkethly or Mr. Hammond
as to growing root crops, he believes the growth of alfalfa, Indian corn,
oats, barley, and pecan and fruit trees is eminently suitable for the
land, which is a deep rich loam, from 4 to 8 ft. deep, overlying the
"sillar" formation referred to in the paper. The writer has seen many
sewage farms during the last 18 years, upon which root crops of excellent
quality have been grown, and not the least suspicion has ever been raised
regarding their use.
In reference to the adoption of the monolithic form for constructing the
South Reservoir, the writer is so convinced as to its economy that had he
to build this reservoir again, he would adopt the same method. Mr.
Binckley, in drawing attention to the method of construction, has
overlooked the fact that the cost of forms for a reservoir 30 ft. deep was
a very serious item, and warranted the adoption of this new method, not
only on account of economy but because of rapidity of construction; while,
in the case of the Obispado Reservoir, which is very much shallower,
simpler forms could be and were adopted.
Mr. Saucedo's remarks regarding the repetition of the extraordinary floods
of August, 1909, in September, 1910, are particularly interesting, and
show how abnormal conditions are in so dry a section of Mexico as the
State of Nuevo Leon. These two floods, the writer believes, are among the
most instructive in North America, particularly when one remembers that
prior to 1909 the average rainfall during a period of 15 years, was less
than 22 in. per annum.