Double take: A Wisconsin plant optimizes secondary treatment to maximize its wet weather capacity

It's a hot, humid July day in southeast Wisconsin. At the Henry Maier Festival Park on the shores of Lake Michigan, crowds are building at Summerfest, Milwaukee's annual 11-day music festival. Inside the park, people are strolling, basking in the summer sun, enjoying music and entertainment acts, sampling local food favorites, and forming lines at the Marcus Amphitheater in anticipation of the evening's headlining performer. A few hundred yards south of the amphitheater, just across the mouth of the Milwaukee River, all appears quiet at the Jones Island Wastewater Treatment Plant. This advanced secondary treatment plant is one of the nation's oldest activated sludge plants and deemed a historical civil engineering landmark by the American Society of Civil Engineers (Reston, Virginia). The plant treats up to 1.2 million m3/d (330 mgd) of separate and combined sewer wastewater. Beneath the calm, however, the plant's supervisory and operating personnel are on alert. They know that weather is ripe for fast-forming thunderstorms that can create high flows. In addition, plant personnel are monitoring conditions 91 m (300 ft) underground, where more than 31 km (19 mi) of deep tunnels are situated to store up to 1.5 million m3 (405 million gal) of wet weather flows for later treatment. Personnel at the Milwaukee Metropolitan Sewerage District are anticipating their own storm, as they must deal with media coverage and local environmental group outfall when such storms hit. Of particular concern are conditions where flows exceed the combined capacity of the plants and tunnels, resulting in partial treatment diversions (effluent blending), or worse yet, system overflows. Suddenly, a rumble of thunder is heard, and lightning flashes across the sky as rain falls in torrents, flooding streets and inundating combined sewers. While Summerfest crowds seek shelter, plant personnel take action to ensure flows to the treatment plants and tunnels are controlled to prevent the need for inplant diversions.