ST. LOUIS WATER PURIFICATION.
Allen Hazen, C. E., not being able to agree with his associate commissioners, Benezette Williams and George V. Wisner, on the subject of the purification of the water supply at St. Louis or the proposal to use the Meramec watershed, instead of filtering the supply from the Mississippi and Missouri, recommends the immediate construction of a complete purification plant at the Chain of Rocks, with a net capacity of 150,000,000 gallons per day. The estimated cost of this he sets down in detail as follows :
Providing present sedimentation basins with baffles and new inlets, $63,600; coagulating basins and appurtenances, $353,400; vaulted masonry filter plant, complete, $t,too,000; auxiliary structures, piping, changes in railroad tracks, etc., $154,000; contingencies, including additional pipe, if any, involved in a rearrangement of structures to allow the economical extension of the plant to a capacity of 300,000,000 gallons per day, $100,000; engineering and contingencies. ten per cent., $177,000—total cost of works at Chain of Rocks, $1,948,000.
He makes further recommendations, as follows: To build at Baden, on the east side of the conduit, a covered pure water reservoir holding 50.000,000 gallons, connecting by a tnnnnel under the conduit with the pumps on the west side of the conduit. The space on the east side of the conduit is to be reserved for the construction of the very large pumping station which will be ultimately rec|tiired. The land now owned by the city at Baden is sufficient for the construction of structures of considerably larger canacity than those contemplated in the report of a majority of the commission. At Bissell’s Point the three 20,000.000-gal Ion pumps now being built would be connected with the conduit— tile old open settling basins (to cover which would cost money that would be better spent on reservoirs at Baden) and the clear well being abandoned. The present old pumping engines at Bissell’s Point use three times mote coal and more ..tuor than is needed for modern pumps. They can be dispensed with on the installation of the three new pumps, and when additional pumping is required, the new pumps should be installed at Baden, and after thirty years, when the three new pumps have served their natural life, the Bissell’s Point pumping station should be abandoned altogether in favor of that at Baden, where all the pumping machinery would be concentrated. Tbe Compton Hill reservoir should be covered. the water level raised two feet (as estimated for), and the capacity somewhat increased. The estimated cost would be as follows: Fifty milliongallon reservoir (covered), at Baden, including engineering and inspection, $440,000; covering and raising Compton Hill reservoir, $308,000—-total cost of reservoirs, $748,000. If new connections are required at Bissell’s Point, they will be comparatively inexpensive, and will be far more than covered by the sale of the property by that time, except for one portion occupied by one pumping engine, etc., no longer useful to tbe the city.
The covered reservoir should be ready as soon as the filters, but, if thev are not. that would not delay the introduction of filtered water. The estimated cost of all this would not exceed that set down by the majority of the commission—namely, $2,696,000.
Commissioner Hazen prefers his plan, first, because, on the basis of cost adopted by the other two commissioners, the purification plant is. for mativ years, at least, more economical; second, some important matters favorable to the river supply have been left out of the account; third, that the estimates are in several respects unfair to tbe river water supply and should be modified; fourth, that the difficulties and obiections alleged to the use of purified water can all be satisfactorily met. and the purified water can be made fully equal in qualitv to that obtained front tbe gravity sources; and, finally, that, even upon tbe basis of estimates used, with perpetual capitalisation, the river supply will cost less than the gravity plan.
The river plan is the more economical, and. if followed out. would enable the city to save an amount of money emtal to the entire estimated cost of tbe proposed gravity works—enough to build a supply precisely like the one now contemplated or to form a part of the cost of a larger supply, of a different supply, such as the conditions may then demand, or the city might continue to use the river water, if thought best. Owing to improved mechanical appliances and methods of construction, the reduction in the price of Portland cement, those of concrete in place of masonrv. and improved designs, the cost of the river works would be at least as low as those of the gravity, wjtfi its twq covered gravity 350,000,000-gallon reservoirs, as contrasted with the six sedimentation 174,000.000-gallon basin at Chain of Rocks.
The amount of money derived from the sale of the Bissell’s Point land should be set down at $510,000 in favor of the river supply. Even if the gravity works are in operation for four years instead of the more likely six years, filtered water could be delivered in two years, the minimum value of which is set down at $1,700,000. making, with tbe above $510,000, $2,150,000. equaling interest at three and one-half per cent, from 1906 to 1944 over $7,000,000. and over $11,000,000 in i960—making a saving, with interest, of more than $36,000,000 in 1960. So the value of two years of pure water nearly equals the cost of the works required to produce it at Chain of Rocks—would more than dp so if the installation of the gravity works took six. instead of four years. The aqueduct for the gravity system has a section equal to a circle thirteen feet in diameter and a slope of one in 10.000. The maximum carrying capacity would be reached with the aqueduct running with the water about eight inches below the top—the wetted perimeter being thirty-five feet ; area of the water section, 130 square feet ; hydraulic radius. 372 feet. The discharge from the aqueduct new and clean would be 218.000,000 gallons per twenty-four hours. The capacity of the proposed city reservoirs at the city end of the line, excluding the Compton Hill distribution reservoir, will be 350.000.000 gallons —hardly sufficient allowance to maintain the supply long enough for the aqueduct to be emptied and cleaned. If not emptied and cleaned, its discharging capacity would be reduced at least ten per cent, through its being dirty. If the supply exceeds the capacity of the aqueduct, the storage reservoirs must make up the difference. Five million gallons per day for one month represents a draft of 150,000,000 gallons from them, with 200.000,000 left in storage. To reduce this would be dangerous in case of fire, break, or accidents. Add tbe above 5.000.000 gallons to the 196.000,ooo-g.tllon capacity of the aqueduct, and the maximum consumption maintainable is 201.000.000 gallons per day per month, which, by tbe accepted schedule as proposed will be reached in 1050. when 202.300,000 gallons per day will be the maximum monthly consumption, which can thus be increased by building new reservoirs then, instead of ten years later. The permanent capacity of the source, also, is set down as 18.1.000.000 gallons per day, even during a period of drought lasting, perhaps, through a succession of years—a “higher figure than existing data will justify.” As to the Meramec supply: The approximate rough gaugings give the amount flowing from the spring and in the river from May to December, tgot. inclusive, as 17.863 million gallons—an average of 73,000,000 gallons a day. With the proposed storage reservoir full and in use on May 1. tqor. and the evaporation for the season three billion gallons, if a supply of 184 million gallons per day had been maintained from it from May to December, the water in tbe reservoir would have been reduced to eleven billions, or sixty days’ supply, as a reserve for all further shortage until s-ch time as the run-off permanently exceeded 184 million gallons per dav. Such a reserve is insufficient, and tbe capacity of the source has been rated too high.
“The structures contemplated for the river supply have a much greater capacity. Two intakes arc contemplated, namely, the present one, seven feet in diameter, and a new one, nine feet in diameter. Assuming a velocity of six feet per second, tbe two in-, takes have a capacity of 393 million gallons per day. Pumps at the Chain of Rocks with a canacitv of s6o million gallons per day are proposed. Filters, sedimentation basins, and appurtenances are proposed suitable for a net simply of 300 million gallons ner day. Two conduits from Chain of Rocks to Baden are proposed, with a combined capacity, as stated in the report, of 260 million gallons, but actually capable of carrying at least 350 million gallons, as shown by a diagram of the carrying capacity of the present conduit, which T hand you herewith. Pumps at Baden are proposed with a capacity of 390 million gallons daily. The whole plant is proposed on a 300 million-gallon basis, suitable in my judgment for meeting tbe actual conditions with a much higher average daily supply than can be safely drawn from the gravity works.”
No allowance has been made for contingencies, such, for instance, as may arise from a leakv dam— “vallevs in tbe immediate neighborhood are obviously drained by caverns in tbe limestone rock beneath.” “The presence of the Meramec spring itself is indubitable evidence of the existence of caverns as near to the darn as the location of the spring.” The charges for reversal and depreciation for parts of both the gravity and river supplies have been estimated too low, while the estimates of the cost of operation of tbe river works in the majority report have been set too high, and details—such as work done in the street department—charged to this head which should have been set under another head. Pumping expenses would also be reduced at Bissell’s Point to a sum not exceeding that at Baden. The cost of pumping at Chain of Rocks, including care and repair of buildings, care of ice, care of intake, supplies, general expenses and transportation of men, for tbe last fiscal year, as computed from records furnished, amounts to $3.13 per million gallons. The corresponding cost of pumping at Baden is $0.50 per million gallons, t he cleaning of the sedimentation basins costs about fifteen cents per million “a I Ions. The cost of operating filters, estimated on a very liberal basis, amounts to $7.43 per million gallons. If one dollar per million gallons is taken for the care of grounds, track, and conduit, which, although less than the cost reported for last year, seems a very liberal allowance, and all other items as above, the estimated cost of operating river works is as follows: Cost of pumping at Chain of Rocks as at present, $3.13; care of settling basins as at present, $0.15; operation of filter plant, estimated, $7.43; cost of pumping at Baden as at present, $6.50; care of grounds, conduits, and railroads, estimated. $1.00—total cost of operation, per million gallons. $18.21—sufficient to pump all the water to the high-level service, which is higher than the Meramec water would be available, and making no allowance of the saving which may be effected by pumping some of it against the lower head needed for the low-level service. The estimate of the majority report—namely, $20 per million gallons for operation, is more than ample, and could be considerably reduced by careful business management of the works.
The physical difficulties of purification have also been overestimated. The St. Louis water is certainly liars! to treat successfully; but the plant, as designed is “far more complete and adequate for the treatment of a water carrying an extremely large amount of sediment than any plant ever constructed.” The difficulties at St. Louis are approximately known from records of the character of the water, and the estimates are based in treating water as bad, or even somewhat worse, with every prospect of success. But, even if unforeseen difficulties should arise, there is “still a considerable margin between tbe cost of operation as estimated |by tbe minority report and that of the majority] to cover any contingencies that may arise. “The hygienic character of the filtered water will be entirely satisfactory,” for, although the river water sometimes carries very large numbers of bacteria, yet these are from the rich prairie soil, and, so far as is known, not injurious to health. The dangerous bacteria are from sewage and excrement. The typhoid death rate of the city and the comparatively small amount of sewage in proportion to the flow of the river show that the “raw water, although polluted far beyond the point where it should be used in its raw state, is very much less polluted than many or most of the river waters used by American cities.” Filtration will reduce the danger to health to an “almost inappreciable amount.” and the water will be fully equal to that of the Meramec supply, which, by the way, is “apparently largely surface water from the Dry Fork, which has come through caverns without filtration and without storage. and is subject to contamination of a surface supply without the safeguard of having to pass through large impounding reservoirs.” Tts physical appearance will be best, and for general mechanical purposes this river water will be as good, and, although for boilers it may be less desirable, yet tbe difference will not be great. Nothing objectionable can result from tbe use of coagulants, as the “alkalinity of the water is ample for the neutralisation of any amount of coagulant which it seems likely will be reouired. * * * The raw water contains practically no free carbonic acid, and is saturated with oxygen. Tt is quite normal in these respects. In total hardness, or soap-consuming power, the filtered river water * * * will not differ appreciably from the Meramec water. It will differ from it. however, in that some of the lime will be in the form of sulphate, instead of carlionate.” This is regarded as bad for boilers. Its quantity, however, is overestimated in the majority report. “Should it become desirable at some time in the future to take the supply from the Missouri river, it is apparently feasible to do so at a point four or five miles from the Chain of Rocks pumping station, through a tunnel. It would flow to the Chain of Rocks bv gravity, and would be pumped and treated nreriselv as water from the nrcsent intake would be.” This procedure, is neither necessary nor desirable at the present time, but it is possible that it may become so in the future. No close estimate of the cost of changing the intake has been made, but apparently a tunnel with a capacity of 300,000,000 gallons per day, with intake and connections, at present prices, would cost about $t,500,000.
The water from the Meramec is sometimes turbid; in the case of the river supply, “the water from the impounding reservoir will hardly have a turbidity less than that corresponding to from five to twenty parts per million of suspended matters, and this will be so fine as not to be removed in the conduits and reservoirs. The filters are designed to give an entirely clear effluent.”
The river supply will also be cheaper in the end. The gravity works must be again added to some lime in the future, which will be a more expensive operation than adding to the river supply, the cost of whose structures, discounted, is to be taken only for a period of forty years, at which time “the proposed structures for the river supply will more than equal the capacity of the proposed gravity supply,” and thereafter the operating expenses will be “capitalised on a basis of 160 million gallons per day, instead of 184 millions—160 millions bieing slightly more than the average capacity reached in 1950,” at which time the capacity of the aqueduct, moderately dirty, will be reached during the month of maximum consumption. The cost of the river project, revised, is as follows:
New works required, and depreciation charges up to and including 1945, discounted to the 1st of January, 1906, $10,670,000; approximate discounted value of operating expenses for the years 1906 to 1945, inclusive, at $20 per million gallons, January 1, 1906, $16,060,000; operating expenses after 1945, 160 million gallons per day, at $20 per million gallons, $1,169,000 per annum; capitalised at three and onemtarter per cent., $45,960,000; discounted for forty years, $ 1 0,006,000; depreciation charges after 1945, $158,577 per annum; capitalised at three and onequarter per cent., $4,879,000; discounted for forty years. $1,558,000—total cost of building and operating river works forever, with an ultimate capacity of 160 million gallons per day, discounted to January 1, 1906, $58.094,000; deduct sale value of Bissell’s Point property and value of pure water supplied two years earlier, $2,150,000—net discounted cost, river supply, $55,944.000; corresponding cost of gravity supply, as computed by a majority of the commission. $55,861,000.
On the above basis the costs, as discounted, are substantially the same. If, however, the cost of operation is taken at $18.21 per million gallons, as has been estimated, the saving in discounted operating expenses amounts to $2,450,000, and this sum will stand to the credit of the river works, with which, even neglecting the reduction in operating expenses, the advantage is with them. “For the river works the plant now required would cost $2,700,000. For the gravity plant the works would cost $31,000,000 in addition to the salvage from the old works. The estimated expenditure now required for the gravity works is ten times greater than that needed for continuing the river works.” It does not seem enough to show that “new works involving so large an expenditure can be constructed on a basis such that, at three and one-quarter per cent, interest, the cost will not he greater than continuing the present works. The city ought not to take up an enterprise of this sort unless it can he assured of a substantial profit, above the interest, commensurate with the risks involved in lending its credit to so large an undertaking.”