Trustees on the River Forest village board still need to decide if and how they might tackle a flooding problem in the north section of the village that may not be completely solved by a new sewer line.
The board heard more information on sewer system options from the engineering firm of Christopher Burke and Associates on Monday night, but questions remain about how the village would pay for the installation of a new sewer line, which option would be best and whether it’s even worth the cost at all because there’s still a possibility certain streets could flood in the event of a major storm.
Burke presented the board with options for sewer systems last month, including a review of a report by the water services firm FluidClarity, which gave trustees the first opinion earlier this year. Burke showed simulations of the options during hypothetical 25- and 50-year storms and from an actual storm in July 2011, which he said was extreme but could happen again.
Currently, the Elmwood Park outfall sewer runs under North Avenue and holds waste from Chicago, Elmwood Park and the area north of Division Street in River Forest. The simulations showed the 2011 storm caused flooding up to 2.7 feet at Greenfield and Berkshire streets. FluidClarity recommended upgrading the sewer so that it holds more water and reversing lateral pipes so they drain into the Greenfield Street sewer. Burke said that option would not cause surface flooding during 25-year and 50-year storms, but basements could still flood up to 1.4 feet in an extreme storm because the sewer would be backed up.
Separate mainline sewers under North Avenue or Greenfield Street would decrease the likelihood of basement flooding and eliminate dependence on the Deep Tunnel reservoir and the Terminal Reservoir, a water-holding system that will be completed in 2029. During an extreme storm, street flooding could be about 0.6 feet and 0.3 feet, respectively, with those options. Burke said the North Avenue option requires a large-diameter sewer in the street and the other option requires a new sanitary system south of Greenfield Street.
A Greenfield Street alternative combined sewer using existing laterals would have a smaller diameter and lower level of protection, but a lower cost because the lateral sewers are already built. In the event of a storm like July 2011, Berkshire and Division streets could flood about two feet.
Burke said the entire process of obtaining necessary permits for the project, surveying for utilities, designing, bidding and construction could take between two and three years. He said the downside to the project is the sewer system could still be overwhelmed if a severe storm occurs. The options range from $15 million to $20 million in expected cost.
Village staff will conduct a cost analysis of each sewer system option, which the board will discuss at their Jan. 22 meeting.