Photo 4.1.1. June 13, 1919, looking east northeast from the Chicago and Western Indiana Railroad over a large farmed area north of 130th Street. Except for the haze, Lake Calumet would be visible on the horizon. The District purchased a 106-acre site to the north in 1920 for the Calumet Plant from the Pullman Land Association. (MWRD photo 7134.2)

Photo 4.1.2. June 13, 1919, looking east southeast from the Chicago and Western Indiana Railroad. Trees and buildings identify a farmstead north of 130th Street. The District bought this 215-acre area in 1930 from the Pullman Land Association for the second Calumet Plant. (MWRD photo 7134.3)

Photo 4.1.3. March 10, 1921, looking east on 125th Street. A track-mounted tractor is assisting the truck in navigating the unpaved roadway. The District agreed to dedicate the north half of the street for a public road and had to improve the road east to Cottage Grove Avenue for access to the plant site. (MWRD photo 8061)

Photo 4.1.4. November 18, 1920, looking northeast. This self-propelled track-mounted rotary-type scraper got bogged down in the wet farm soil. Stripping and stockpiling topsoil was the first construction activity for the Calumet Plant. (MWRD photo 7915)

Photo 4.1.5. November 18, 1920, looking northwest. This tractor-drawn ladder-type scraper appeared to be doing better. The elevators owned by the American Grain and Malting Company, an adjoining landowner, were a local landmark. (MWRD photo 7916)

Photo 4.1.6. April 11, 1921, looking east. A single nine-foot effluent conduit conveyed treated effluent from the plant to the Calumet Sewage Pumping Station. The conduit was built by the tunnel method, and passed under the dual tracks of the Chicago and Western Indiana Railroad and several tracks of the Illinois Central Railroad. (MWRD photo 8092)

Photo 4.1.7. April 11, 1921. Dual influent conduits, nearly completed, adjacent and parallel to the effluent conduit, were also built by the tunnel method. The influent conduits were 7.5 and 9 foot in size. The connection shown between the two influent tunnels existed during construction since all three tunnels shared a common construction shaft near the pumping station. (MWRD photo 8094)

Photo 4.1.8. April 29, 1921, looking south. The two influent conduits from the west turn north and will converge to pass through Venturi meters for flow measurement before entering the screen and grit chambers. The Venturi meters were located in the basement of the administration building. (MWRD photo 8127)

Photo 4.1.9. April 13, 1923, looking north. The influent raw sewage screens are followed by the grit removal tanks; these are the first steps in the treatment process. The rail-mounted structure acts as a bridge above the screens and tanks upon which workers will stand to clean the screens and remove grit from the tanks. (MWRD photo 9681)

Photo 4.1.10. March 10, 1921. Water is always a problem when excavating for buildings and tanks. The excavation for Imhoff tank batteries A and B was no different. Looking east, a timber tower is being constructed between the two batteries at their south end. The tower will be used for distribution of concrete used in tank construction. (MWRD photo 8062)

Photo 4.1.11. March 29, 1921, looking northeast. At the concrete distribution tower, bins for concrete ingredients are being built and track has been laid for materials delivery. Another landmark in the distance is a reinforced concrete elevator owned by the Michigan Central Railroad. The elevator was demolished in the 1980s. (MWRD photo 8081)

Photo 4.1.12. April 29, 1921. A closeup view of the material bins being built for construction of Imhoff batteries C and D. The bins held aggregate, Portland cement, and sand. The three ingredients and water were mixed, creating concrete. Each batch of concrete was hoisted up the tower to a desired height for distribution. (MWRD photo 8130)

Photo 4.1.13. May 19, 1921. Several towers surround the site where tanks will be constructed. The towers are guyed and connected by cable at their tops to other towers. Batches of concrete are hoisted up the tower and distributed through large-diameter hoses and sloping chutes for placement in the tanks. (MWRD photo 8189)

Photo 4.1.14. May 19, 1921, looking east northeast. The bottoms of two tanks in battery A are in the foreground and two more tanks in battery B are in the right background. Imhoff tank bottoms were shaped depressions in hard blue or hardpan clay. Steel reinforcing rods were placed before concrete was poured. Each tank had three depressions. (MWRD photo 8188)

Photo 4.1.15. May 19, 1921. Looking northwest, the triangular truss receives concrete from a hose at its apex. The concrete flows down the right leg of the triangle in a chute to the workers, who are directing the concrete placement. Concrete was placed over large distances using large hoses and chutes supported by the timber towers. (MWRD photo 8187.5)

Photo 4.1.16. June 16, 1921, looking southwest. A general view of early construction for Imhoff tank batteries A and B. Battery A is on the right; wall forms are in place for tank 1 in the right background. Batteries C and D are nearly identical to batteries A and B, and are located east of A and B. (MWRD photo 8232)

Photo 4.1.17. June 16, 1921, looking west. Forms have been erected for the north, west and south sides of tank 1 in battery A. Each tank is divided into upper and lower chambers. Reusable steel forms are used for the walls of the Imhoff tanks. (MWRD photo 8228.1)

Photo 4.1.18. June 16, 1921. A closeup of the forms and a completed wall shows that forms are also used for channels on the exterior of the wall. The walls have buttresses at intervals for structural stability and shoulders to support channels and walkways. One worker is directing a crane operator on lowering or lifting a load. (MWRD photo 8229)

Photo 4.1.19. August 24, 1921. The bottom of the Imhoff tank shows construction of transverse baffle walls between buttresses and longitudinal bases for internal separating walls. The upper chambers of the tank allow sewage solids to settle. Settled solids drop into the lower chambers where they digest, forming sludge. (MWRD photo 8382)

Photo 4.1.20. August 9, 1921. Inside the Imhoff tank, additional structures are added to support the sloping bottom and walls of the upper chambers. The triangular shapes shown here will support the sloping bottoms of the upper chambers. The apex of each triangle will support a vertical wall creating the three parallel upper chambers. (MWRD photo 8364)

Photo 4.1.21. November 7, 1921, looking east over construction of an Imhoff tank in battery D. Forms are being constructed for two upper chambers and a separating wall with vents. The upper chambers have a V-shaped bottom. The vents extend to the lower chamber to release digestion gases. (MWRD photo 8594)

Photo 4.1.22. August 24, 1921. Looking down into the first settling chamber of an Imhoff tank shows the tank wall and upper chamber wall with vents. At the bottom of the settling chamber, small openings will allow settled solids to drop into the lower chamber. Shown in the center is a separating wall with vents. To the left is another settling chamber followed by a second separating wall with vents. (MWRD photo 8381.2)

Photo 4.1.23. November 7, 1921. Forms have been stripped off one Imhoff tank upper chamber and separating wall with vents. The long narrow vents allow digestion gasses to escape from the lower chamber. In the bottom of the upper chamber, narrow slots can be observed through which settled solids will fall into the lower chamber. (MWRD photo 8597)

Photo 4.1.24. October 3, 1922. Treatment operations at the Calumet Plant are entering its third week and sewage is flowing through the Imhoff tanks in battery A. Looking east from the southwest corner of battery A, battery B lies beyond the first set of steps at right. Piping rising out of the vents convey digested sludge from the lower chamber to the drying beds. (MWRD photo 9543)

Photo 4.1.25. August 24, 1921. Looking west, preparation begins on the trickling filter tank. The tank will have a concrete floor and 10-foot-high concrete walls. All Imhoff tank upper chamber effluent will pass through the trickling filter to improve treatment quality. (MWRD photo 8377.1)

Photo 4.1.26. August 29, 1921. The trickling filter floor has been paved, and the underdrainage is being installed. Notches in the surrounding walls are for pipes to convey Imhoff tank effluent to a network of sprayers that will distribute the flow over the trickling filter. (MWRD photo 8477.2)

Photo 4.1.27. September 29, 1921, looking northwest. The concrete floor is covered with channels and a grating to provide underdrainage for the trickling filter. An 8-foot-deep layer of coarse rock will cover the grating. Imhoff tank effluent passing over the rock will form a biofilm that will further digest suspended and dissolved organic waste. (MWRD photo 8485)