FLOOD AND POLLUTION CONTROL IN METROPOLITAN CHICAGO Prepared by the City of Chicago Department of Public Works, Index I. General Aspects of Urban Runoff and Water Pollution by Combined Sewer Overflow. II. Flood and Pollution Problems in Metropolitan Chicago. III. Proposed Projects for Controlling Flooding and Pollution. IV Chicago Underflow Plan. V. Summary and Conclusions. VI. Bibliography. I GENERAL ASPECTS OF URBAN RUNOFF AND WATER POLLUTION BY COMBINED SEWER OVERFLOW The fall of rain and snow through the atmosphere cleans the air by dissolving out contaminants and physically washing out particulate matters. The flow of waters over the land in the form of runoff to watercourses adds further soluble and insoluble natural contaminants to the water cycle. Even the percolation of waters into the soil and their eventual flow into watercourses and lakes adds soluble and insoluble substances which may or may not be of a pollutional nature. Thus even without the effect of man's urban existence, nature creates pollutional conditions. The urban environment magnifies these pollution producing conditions. The air washing of the urban atmosphere contributes more and more diverse pollutional substances to precipitation. The drainage of the urban area adds contaminants that far exceed those nature-induced pollutants added to runoff by solution and erosion in open non-urban areas. The conversion of pervious open land to impervious urban surfaces, such as roads, walks, streets, roofed structures, parking areas, shopping centers, and airports, produces greater faster runoff along with scour pollution. The use of water for public and industrial services produces waste waters containing the waste products of human life and living as well as industrial processing. The discharge of these waters into receiving waters constitutes the major water pollution problem. The ever-increasing amounts of such pollutants and the growing complexity of these water-borne wastes have created a deepened concern for the safety and usefulness of the nation's water resources. There is a direct relationship between the cleanliness of the urban environment and the cleanliness of storm-water runoff-or, conversely, between poor urban housekeeping and the pollutional effect of runoff waters which come in contact with urban-created street and land debris and aerial pollutants. Regardless of the sources of urban pollution of this nature, the connecting link is the street inlet structure to the separate storm sewer or the combined sewer. The relationship between urban cleanliness and water pollution appears obvious; what is not so obvious is the extent of this relationship and what can be done to eliminate or reduce it. So little has been done in the past to correlate the influence of street debris and air pollutants with the delivery of these contaminants to separate storm or combined sewers, precipitation, and runoff, that the problem must be approached as a relatively unexplored area of urban operations. Separate storm sewers, as well as combined sewers, are potential recipients of the type of urban pollution. In addition these separate storm conduits are utilized as discharge points for other wastes not classified as "out-of-doors" pollutants that are the result of urban environment conditions. These other waste waters include: so-called clean waters discharged from cooling and refrigeration systems, contaminated waters from stack-washing operation in commercial and industrial establishments, and surreptitious or illegal discharges of actual waste waters from commercial and industrial operations into separate storm sewers. Indeed, it is not unknown for municipalities to provide relief for surcharged sanitary sewers by diverting their excess flow into storm sewer systems. In some cases, illegal discharges of individual septic tank systems have been made into convenient separate storm sewer lines. In combined sewers, waste discharges can be considered, more or less, as indigenous components of the combined sanitary storm-water flows. In the case of separate storm sewers, these pollutants are not treated and they add a burden to receiving waters. Thus, combined sewer overflows constitute a significant part of the nation's total water pollution problem. It is important to recognize, however, that the overflow problem must be evaluated in terms of the total effects on water and land resources from all overflows, discharges and spills of waste waters, not as an isolated and unrelated source of water pollution. Despite current concern over the problems of combined sewers and their overflows, U.S. communities continue to build combined sewers to replace and extend sewer systems. Active programs to eliminate or minimize the volume and strength of overflow wastes are impeded by the high cost of such projects and the inconvenience to urban life and activities. In the case of multiple community regional operations, some of the communities which utilize joint facilities are sewered as separate systems but they discharge separate sanitary flows into combined collection sewers of older central cities. This separate sanitary sewage thus becomes combined wastes and contributes to the overflow problem "by association." This general problem also occurs frequently in communities which have both separate and combined sewers. The flow from the separate sanitary sewers enters the combined sewers, thus contributing to overflows. Executive infiltration into combined sewers usurps valuable sewer capacities and increases the frequency and duration of overflows. Infiltration frequently exceeds design and code limits. Correction of excessive infiltration could reduce the overflow problem by providing increased in-system capacity for the storage of more combined sewage flows. While sewer separation has been advocated as a positive method for eliminating combined sewer overflows, and separation projects are reported to be the most commonly used corrective measure, most separation work has been carried out on only portions of sewer systems, seldom involving the entire system. Sewer separation is not the panacea of all combined sewer problems. Other overflow corrective measures have merit, not only in terms of comparative cost to separation, but also in terms of cost and convenience to property owners and the general public. Other than sewer separation, surface control, storage and off-system treatment are considered to be promising methods of reducing or eliminating the pollutional effects of overflows. II-FLOOD AND POLLUTION PROBLEMS IN METROPOLITAN CHICAGO A. The flood control problem Since the end of the Second World War, Metropolitan Chicago has undergone a period of extensive urban development. This development has caused a tremendous increase in the impervious area and larger surface runoff during storm periods. To alleviate local flooding of basements and underpasses throughout Chicagoland, hundreds of millions of dollars have been expended in the construction of new sewerage. While greatly reducing the undesirable storage of water in basements and underpasses, a new and increasing problem of flood control in the rivers and canals is becoming apparent. During the heavy storm period of October 9-11, 1954, the Union Station and other downtown buildings were flooded. To reduce the flood stage in the river, the locks at the mouth of the Chicago River were opened allowing polluted water to enter Lake Michigan. This was the first time since the locks were constructed in 1938 that they were opened to permit river water to flow into the lake. Since that time the locks have been opened during storms of July 12-13, 1957, September, 1961 and August, 1968. The frequency of requiring lock openings to the Lake for river flood control is greatly increasing, and will continue to increase as new outlet sewer capacity is added. The normal and desirable outlet for all storm water is to the southwest along the Sanitary and Ship Canal to Lockport, the DesPlaines River through Joliet to the confluence of the Kankakee River and through the Illinois River Waterway System to the Mississippi River. The Sanitary and Ship Canal designed for a capacity of 10,000 cubic feet per second was completed in 1900. Because of drawdown of the water surface at Lockport during heavy storms, the Canal has been able to handle a peak discharge, for short periods of time, of up to 24,000 cfs. Figure 1, shows the accumulated growth of outlet capacity of sewers in the City of Chicago. The total projected outlet capacity of 65,000 cfs will be reached in 1975. This, of course, is not the required capacity of the waterway system because of channel storage and offsetting of the sewer discharge peaks; however, it is a good indicator of the future flood control problems that lie ahead. The DesPlaines River North of Hofmann Dam in Riverside has inadequate capacity to drain its fastly urbanizing tributary area. Large storage reservoirs and/or increased conveyance capacity must be provided to handle the increasing runoff. In the Calumet Area, large acreage is only a few feet above normal water level of the Calumet River and waterway systems. In many places this provides only small graduates for the tributary streams and sewer. During large storms, the O'Brien Locks must be opened permitting river water to flow through the Calumet River to Lake Michigan. But even this will not keep the stage sufficiently low in the largest storm periods. B. The waterway pollution problem The pollution of the waterway system is another vital problem confronting the Chicago Metropolitan Area. This same problem exists for nearly every other large metropolitan area in the Country. Most of these urban concentrations are drained by systems of combined sewers which spill to the open water courses when the sanitary intercepting sewers or treatment plants are overloaded. Combined sewers have been estimated to carry approximately 3 percent of the annual sewage volume to the waterways during storm overflow periods, thus 97 percent of the annual sewage volume is delivered to the treatment plants. The actual annual pollution load which is discharged from combined sewers to the waterways is somewhat greater. This is due to the cleansing of the sewer inverts during periods of high storm runoff. In addition to the pollution of the river caused by the combined sewer systems, other major contributors are the sewage treatment plants. Three major treatment plants handle the household and industrial wastes for the City of Chicago and much of the suburban area within the Metropolitan Sanitary District. These plants are the North Side Treatment Works, the West-Southwest Treatment Works and the Calumet Treatment Works. The U.S. Public Health Service study, "Great Lakes, Illinois River Basin Project" (1) (GLIRBP) in two separate periods of study in 1961 found the combined effluent of the three plants was 1238 and 1682 MGD; at a population equivalent (PE) of 969,000 and 793,000; which is equal to 78.2 and 66.2 tons of 5 day B.O.D. per day, respectively. The average overall efficiency for these two periods was 88.3 percent. The reduction in the effluent PE during the second period was attributed to the heavy rainfalls occurring during that period, resulting in the direct overflow of pollutants to the watercourses by combined sewers and therefore not measured at the plants. Extensive sludge deposits are formed in the waterways downstream of the treatment plants and the many large outfall sewers. These sludge deposits have a significant oxygen demand and thereby use up a large part of the natural oxygen content in the waterways. At many places where these large sluge deposits occur, gaseous bubbles are released to dot the water surface and result in extensive odors along the river channel. Other sources of pollution of the rivers are the discharges from industries, and leakage from boats and barges. Industries also use river water for cooling purposes increasing the temperature by several degrees; this reduces the amount of dissolved oxygen the water can hold. The dissolved oxygen (DO) is one of the most important constitutents of the waterway system. All of the above sources of pollution tend to deplete the dissolved oxygen. The low dissolved oxygen throughout much of the length of the waterway system indicates the poor condition, especially in the summer season. Insufficient DO is available to support desirable fish and aquatic life in the stream. The GLIRBP study has shown that the Waterway System through Chicago and downstream to the Kankakee River is in an extremely polluted condition and can be considered as a hazard to human health. III PROPOSED PROJECTS FOR CONTROLLING FLOODING AND POLLUTION A number of alternatives have been studied for solving the problems of waterway pollution caused by the spillages from combined sewers. Also for solving the problems of flood control of the waterways during severe storm periods. Among those advanced are the following: Separation of sewers A complete study of the separation of sewers has been made for the 300 square mile area of Chicago and vicinity, and would require nearly ten thousand miles of sanitary sewers, many lift stations and interceptors. It has been estimated that the cost of this separation would be in the range of 32 to 4 billion dollars. Even if separation were to be accomplished at this tremendous cost and with its concomitant disruption of traffic in almost every street, the inconvenience to all of the people, the reworking of house and building plumbing, and the adjustment and relocation of public and private utilities, it is questionable as to whether it would solve the problems associated with delivering all wastes to the treatment plants. Accidental or illegal connections to the wrong sewer and the possible leakage between sanitary and storm sewers, would make policing of the six to eight mile long sewer systems impractical. In addition, it has been shown that storm water itself carries considerable pollution to the waterways. The separation of sewers would not provide any flood benefit to the waterway system. Storage in existing sewers Consideration was given to storing the runoff of the smaller storms in the existing sewer systems by the use of inflatable dams. Such storage, if entirely used, would amount to approximately 3,200 acre-feet or 0.2 inches over the 192,000 acres of the combined sewered area. The entrapment of combined flow for storms having a runoff of this magnitude would result in a reduction of spillage of approximately 65 percent. This storage would reduce the frequency of combined sewer spillages from an average of 60 per year to about 15 per year. However, because of the flat slope of the sewers in the Chicago Metropolitan area, this method of reducing the spillages was not further considered. The velocity generated in the sewers in the post storm period would not be sufficient to scour the sediment deposited during the storage period, and would result in extensive maintenance problems. Also, this method would not contribute anything toward the solution of the flood control problem. Underflow-storage plan This plan proposes the construction of a pattern of large tunnels in the dense Niagaran limestone rock formation, 200 to 300 feet below the surface waterway system. These tunnels would be sized to provide a linear distribution of storage volume and conveyance capacity in a pattern which would intercept all of the approximately 400 outfalls of the existing combined sewers. The tunnels would be sloped down to low points, and pumping facilities, opposite the existing sewage treatment plants. Overflow from the combined sewers, during storm periods, would drop through shafts to the large storage tunnels. In the post storm period, the tunnels would be dewatered by pumping directly to the existing treatment works. The Underflow-Storage Plan takes advantage of the lower water level to be established in the Illinois Waterway at Lockport, Illinois, for improvement of navigation and flood control of the waterway system. The new water level, 70 feet or more below the level of Lake Michigan, will allow the construction of tunnels with large underflow conveyance capacity to Lockport and provide flood protection for the largest storm of record. Storage of 18,000 acre-feet or 1.12 inches of runoff in the tunnel system will provide 98.5% reduction of pollutants entering the waterway from combined sewer spillages. Subsequent paragraphs will provide the details of this plan. Deep tunnel plan (Harza and Bauer, consulting engineers) This plan is a multi-purpose plan, including hydro-electric power development, with a "pumped-storage" scheme, now widely used throughout the world as adjuncts to hydropower developments on surface streams or to thermal power plants. In the Deep Tunnel Plan, storage for hydropower would be provided in rock caverns, 600 feet or more below the surface and in surface reservoirs above ground in the vicinity of the underground caverns. Reversible pump-generator units would be used intermittently to move water upward and to develop power during downflow. Power would be generated and sold to the Commonwealth Edison Company daily during the hours of peak demand for electricity. Power would be purchased for pumping, daily, during the periods of low demand for other uses in the Metropolitan area. Based on an estimated net revenue, in excess of cost of operation, revenue bonds would be sold by the Metropolitan Sanitary District to provide capital for a portion of the multi-purpose project. The underground caverns and the surface reservoir would be oversized beyond the needs for power development to provide for entrapment and storage of excess spillage from the combined sewer outlets. Primary sedimentation would be pro |