Tens of Millions And Counting: Consultants Present Findings of Year-Long Flooding Study

Reducing Elmhurst's flooding will require deft policy and fiscal maneuvers on the part of city officials, close work with homeowners and lots of money, aldermen learned Monday.

The city spent about $840,000 to hire Christopher Burke Engineering and RJN Group nearly a year ago to study comprehensive solutions to flooding problems as a result of the . Burke presented plans that would bring flood-prone areas up to current standards of stormwater protection, while RJN Group offered findings on how to keep stormwater out of the sewer system.

Adding it Up

Burke detailed his group's studies of 10 flood-prone areas in the city, including why flooding occurred and possible solutions.

One example Burke cited is the low spot in the Yorkfield area near Butterfield and York roads that sends water down Chatham Avenue during heavy rains.

Solutions include expanding a detention basin on Harrison Street and adding 400 feet of relief pipe from Yorkfield Avenue, at a cost starting at about $710,000 not including land acquisition. To get more protection, the city could also excavate the detention basin and add retaining walls, at a cost of $1.88 million.

Using the lowest cost estimates for each of the 10 areas results in a starting cost of about $20 million, Burke said.

As the costs rang up, 3rd Ward Alderman Michael Bram asked if the consultants had studied less expensive solutions, as it seemed to him the city was being presented with the “Cadillac of Cadillacs” in storm-proofing.

Burke told Bram that any upgrades had to be designed to meet current standards, which means pipes have to be designed to handle 10-year flooding events along with overland flow routes that bumped the system's capabilities up to handling a 100-year event. Because it is a mature community, Elmhurst lacks both high-capacity pipes and open space for drainage.

A 10-year event has a 10 percent chance of occurring in any given year. A 100-year event has a 1 percent chance of occurring in a year.

Burke also addressed the role teardowns played in the city's current storm-handling capacity. After analyzing the number and footprint of new homes, engineers found they generally cover the same surface area as older homes do because the older homes have long driveways. However, runoff from new homes often goes directly into storm drains, which quickly taxes their capacity. Also, new homes tend to have deeper basements and displace more water.

Burke's group recommends the city mandate that new homes be built at an elevation above the mark for 100-year events. Rain gardens, or areas of native, water-loving plants, and underground storage could also alleviate the impact of new homes.

Public vs. Private

On the sanitary sewer side, RJN Group's Al Hollenbeck offered some good news: The city's work to rehabilitate manhole covers in the late 1980s worked and is largely intact today. This means, however, that most of the sanitary trouble comes from private homes, specifically homes where stormwater and sanitary waste make their way into the same pipes.

Most of the sanitary sewer backups in July 2010 came from south Elmhurst, with about 42 percent from the area around Saylor Avenue and Jackson Street, Hollenbeck reported.

Hollenbeck outlined a program of public and private property rehabilitation that would target any remaining failing manhole covers and sewer-storm cross-connections, clean up outdated sump pump and driveway drain connections, install overhead sewers in select homes, increase the capacity of the sanitary pump station at Saylor and Jackson and construct a storage basin at the wastewater treatment plant, at a total cost of $17.5 million. Sixty-eight percent of that cost would be for projects on private property. The city could decide to scale this work down with the trade-off of reducing the level of protection.

When asked for a scenario that would all but guarantee that the water system could handle an event like the July 2010 flood, Hollenbeck offered the sum of $150 million for deep-tunnel storage.

Hollenbeck stressed that RJN Group was just presenting findings, and it would be up to the city's stormwater task force, and eventually aldermen, to decide what to do and how to pay for it. He also cautioned that no solution solves all problems.

“Notice that I will never use the word 'eliminating,' only 'reducing,' ” he said.

Read Christopher Burke's report here and the RJN Group's report here.