At $27.30 per capita treatment works would cost $157,000,000, or at the rate of $15,700 per cubic foot per second. From the standpoint of sewage treatment the water diverted may be said to be worth $15,700 per cubic foot per second to the community. ECONOMIC LOSSES AND BENEFITS In drawing conclusions upon which to base a solution of this question of diversion of water from Lake Michigan at Chicago, knowledge of the net economic loss or gain to the Nation will be of material assistance. This withdrawal of water and its introduction with large quantities of Chicago's sewage into the Illinois valley have resulted in the following detriments or damages which may be evaluated: Losses to navigation on the Great Lakes. Power losses at Niagara and on the St. Lawrence. Flood damages on the Illinois River. The following benefits have resulted: Potential waterways-Chicago to Joilet. Water supply of Chicago kept pure by use of dilution method of sewage treatment. Table 6 is a financial statement showing the condition of the national resources as affected by the operations of the sanitary district under different assumptions as to amount of diversion. The accounts show a negative balance in each case. In order that the degree of speculation in the preparation of Table 6 be known, it is best to investigate each entry. The first item in Table 6 is "Expended for dilution project," $74,000,000. This is a matter of record and involved no questions as to its accuracy. The second item, "Capital represented by power loss," involves no assumptions, other than those made in Part III, page 28. The next item in Table 6, "Capital represented by damage to navigation in the Great Lakes," is an estimate of the real damage done to navigation based on determinations made in Colonel Warren's report, referred to elsewhere. The item, "Capital represented by damage to riparian owners on Illinois River," is largely composed of existing damages for which claims have been filed. The speculative portion of this estimate is quite small. The item, "Cost of replacing dilution plant, etc.," involves no speculative estimates. The cost of treatment of sewage is quite definite, and the population to be cared for is also. TABLE 6.-Financial statement of Nation's resources as of January 1, 1924, as affected by the works of the sanitary district LIABILITIES Expended for dilution project. Capital represented by damage to navigation on Great Lakes at $326 per cubic foot per second. Capital represented by loss of 9 horsepower-years per cubic foot per second at $30. Capital represented by damages on Illinois River Old drowned out bottoms. New drowned out bottoms. Total. ASSETS Cost of replacing dilution plant by treatment plant at $15,700 per cubic foot per second of needed dilution water.. Total assets. Net economic loss. Annual loss at 5 per cent. PART IV USES OF DIVERSION AT PRESENT TIME PROTECTION OF CHICAGO'S WATER SUPPLY The entire water supply of the city of Chicago comes from Lake Michigan. It is pumped from the lake through tunnels terminating in intake cribs, the latter located at various points from 1 to 4 miles from shore. All the other lake-shore towns in the sanitary district obtain their water supply in a similar manner. None of the water is filtered; no provision is made for filtering it. The pumping plants are provided with dosing apparatus, and chlorine is used quite freely at times. About 96 per cent of the sewage of the community is discharged in a raw state into the Chicago River, the remaining 4 per cent being partially treated (at plants which are largely experimental at the present time) before being discharged into channels leading toward the Illinois Valley. It is obvious that with such facilities for obtaining a water supply and disposing of sewage it would be fatal to permit the Chicago River to discharge into the lake. To prevent such a catastrophe the Chicago River has been connected to the Des Plaines River by means of the main drainage canal, but as the flow at the lower end is restricted by controlling works and power-house gates the slope of the surface of the stream and the elevation of any portion of its surface depends upon the amount of water released through these works and gates and also upon the stage of water in Lake Michigan. If the gates at Lockport are opened wide the surface of the pool is quickly lowered. At first the slope is quite abrupt but gradually it extends up the canal and into the Chicago River until it is more or less uniformly distributed over the entire channel. If the gates are closed or partially throttled the slope flattens out and the surface of the water in the canal is everywhere at a higher elevation. Water reaching the Chicago River will flow into the lake or down the canal, depending upon which route offers a downward slope. If but little water is being passed through Lockport the slope is flat, the canal is quite full and the backwater effect is high, so that any appreciable increment to the river such as might come from a sudden storm might create a sufficient had at any point to establish flow toward the lake. Were it practicable to separate the natural drainage from the sewage flow the latter could be permanently and effectually kept out of the lake by merely establishing a grade in the opposite direction. It has been estimated that rates of storm run-off from the drainage area of the Chicago River have the following frequency: 3,000 cubic feet per second 10 to 12 times per year. In other words, if a flow of 4,167 cubic feet per second were maintained at all times through the Chicago River, Chicago's sewage would flow into the lake about seven times a year. Positive insurance against discharge of the river into the lake under present conditions would require a flow in the neighborhood of 10,000 cubic feet per second at the time of maximum flood. Were it not for the inertia of the water in the canal it would be possible to divert only 4,167 cubic feet per second regularly, and, upon due warning, increase the diversion to any necessary amount. But while a heavy storm can concentrate in 6 to 8 hours it generally takes 12 to effect any appreciable increase in flow through the Chicago River by opening the gates at Lockport so that the river might discharge into the lake for several hours before flow toward Lockport could be reestablished. However, with a little vigilance on the part of employees of the city of Chicago and of the sanitary district, coupled with the establishment of proper relations and communication with the officials of the United States Weather Bureau, the larger storms could be anticipated. The Weather Bureau could keep the officials of the sanitary district apprised of conditions favorable toward the production of heavy storms so that they would know when to expect trouble. Gauges could be installed at suitable places along the river, preferably at the bridges and under the observation of the bridge tenders, so that the behavior of the river could be watched at all times during storms. In the early stages of a heavy storm the flow could be increased at Lockport and maintained at a higher rate until the river gauges and weather reports and indications made it safe to return; 8,000 cubic feet per second is about as low a discharge as may be used safely without a flood gate. With an average flow maintained of 8,000 cubic feet per second, it is believed that if the flow were increased to 12,500 second-feet whenever a storm run-off of over 3,000 second-feet was shown to exist, there would never be occasion to fear a discharge of the river into the lake. As this run-off of 3,000 second-feet is exceeded not more than twelve times a year on the average, the yearly average discharge would not be materially increased. There are other occasions when a low rate of discharge through the drainage canal will result in a reversal of flow toward the lake. The elevation of the surface of the lake is subject to changes which at times takes place quite rapidly. If a flow of 6,000 cubic feet per second were maintained away from the lake with a stage of +1 foot low-water datum, a change in barometric pressure or action of the winds might drop the stage to -0.5 foot within a few hours and as a result the river would discharge into the lake until the surface of the water in the canal had been brought down to a low enough grade to reestablish the slope and flow away from the lake. Such changes in stage are not of infrequent occurrence and would have to be guarded against in the same way as floods. With a flow of 8,000 cubic feet per second through the canal the danger of reversal under these conditions is slight. Lower rates of discharge would increase the danger. It is therefore believed that an average flow of 8,000 cubic feet per second with authority to increase it to 12,500 as long as run-off records in excess of 3,000 second-feet are observed or during periods when the elevation of the surface of the lake has temporarily dropped materially, will protect the water supply of Chicago under present conditions. SEWAGE PURIFICATION BY DILUTION The most widely used method of disposing of sewage is that of dilution, i. e., by discharging the sewage into a stream or other body of water where the dissolved oxygen will have an opportunity to reduce the constituents to a stable and inoffensive compounds. In most cases no attempt is made to compute the amount of dilution water necessary, the sewage is turned into the body of water with the hope that offensiveness will not result. Accordingly, it is rather difficult to make a determination in the case of Chicago. However, it will be of some value to make a theoretical study to determine the extent of dilution actually obtained under present working conditions. Measurements made in 1910 at the Thirtyninth Street pumping station of the Sanitary District of Chicago showed that the daily per capita production of sewage was 289 gallons. Analyses showed that this sewage required 121 parts per million of oxygen to completely oxidize the organic constituents. As fresh water under ordinary conditions as to temperature and pressure contains 10 parts per million of oxygen, to supply enough oxygen to oxidize the organic substances 12 parts of fresh water must be added to each part of sewage. The population of the sanitary district in 1923 whose sewage is untreated is about 3,100,000. To this should be added the human equivalent of the industrial pollution, estimated at a population of 1,500,000 at the present time. Assuming a total equivalent population if 4,600,000 and a daily per capita production of 289 gallons the total amount of sewage |