Why do we hate combined sewers?

By Kevin L. Shafer, PE

People have talked about the evils of combined sewers ever since I joined the Milwaukee Metropolitan Sewerage District in 1998.

They tell me, "It's the old combined sewers in Milwaukee causing all those overflows. Milwaukee needs to separate these single sewers into two sewers; one for sanitary flows and one for storm-water flows." In fact, as I have grown in this job, I have learned that this discussion has been going on for at least 20 years.

Combined sewers are owned by the city of Milwaukee and village of Shorewood. They are found in about 23 square miles, or 5 percent, of our 420-square-mile service area. These sewers capture huge amounts of storm-water runoff in our most urban areas and send this flow to our sanitary treatment system. Occasionally, this large volume of water can overwhelm the sanitary system and requires overflows to protect basements from backing up.

On the upside, combined sewers provide a huge improvement to the quality of water in our area's rivers and in Lake Michigan. Ninety-nine percent of the time, combined sewers collect and treat the sanitary flows and the storm-water runoff from the most traveled, impervious areas in our region.

Scientific analysis of runoff from developed areas shows that some of this storm water is as polluted or more polluted than a combined-sewage overflow. Unfortunately, polluted storm water in the separate-sewer area gets spilled directly into our rivers every time it rains. Providing collection and treatment for this polluted nonpoint runoff is very important to clean water and public health.

The combined-sewer challenge for the region and the MMSD is to work to reduce combined-sewer overflows while maximizing the water-quality benefits combined sewers deliver.

Prior to the deep tunnel project, the region averaged 8 billion to 9 billion gallons of sanitary and storm-water overflows entering Lake Michigan each year. Since the deep tunnel went on line in 1993, that volume has dropped to 1.8 billion gallons annually. The deep tunnel is making our rivers cleaner, so much so that the Wisconsin Department of Natural Resources is reintroducing lake sturgeon to the Milwaukee River. Today, we see thousands of condominiums and restaurants that have been added along Milwaukee's downtown River Walk. What a change from just 12 years ago.

To decide on how best to build on this progress, the MMSD started the Water Quality Initiative more than two years ago. To make the best use of our limited tax dollars to improve water quality, we need to base our planning on science and common sense.

The Water Quality Initiative will do just that by looking at all of the sources of the pollution entering the waterways and identifying the most cost-effective approaches to reducing it. All options are on the table for this watershed-based effort.

Many people aren't aware that Milwaukee is paying to separate some sewers, like along Canal Street in the Menomonee Valley, with environmentally sensitive strategies to reduce the volume of storm water entering the system. But we need to be careful to avoid sewer separations that fail to treat or minimize the highly polluted storm-water runoff before it spills directly into our rivers.

As part of the Water Quality Initiative, the MMSD continues to meet with engineers from local governments and several contractors to evaluate additional locations where it might make sense to separate the sewer system. These meetings were labeled as historic in a local newspaper.

That may be true, but I think they're an outgrowth of the better communication, cooperation and trust we're building as a region in our efforts to protect the environment. After these locations for potential sewer separations are identified and modeled, we'll determine if it makes sense, both economically and environmentally, to pursue them further.

Love them or hate them, combined sewers are a piece of our existing infrastructure that help protect our rivers and Lake Michigan. Our region needs to maximize their value to the environment and work together to plan the next steps needed to make our beaches and waterways even cleaner.