O’Hare South Basin: APS 706b Floc Logs Clarify 75 Million Gallons

Massive earthwork for the City of Chicago O’Hare Modernization Program left long-exposed soils draining with pavement runoff into the South Basin—about 75 million gallons of sediment-contaminated water. Even with basin size and depth, colloidal suspension blocked acceptable discharge to Crystal Creek under Kane-DuPage SWCD rules. With the basin filling, fall rains coming, and winter shutdown near, OMP asked Ero-Tex (Illinois/Wisconsin APS distributor) for an economical train that could deliver discharge-quality water at 6,000 gpm through a 12-inch pump without disrupting construction or flight operations.

Site-specific laboratory chemistry selected the APS polymer blend, dosage, mix time, and floc character. Kiewit-Reyes JV set up in a day: APS 706b Floc Logs® and Erosion Eels™ (mixing “bumps”) went into the twin 66-inch × 1100+ ft infrastructure pipes just down-gradient of the inlet structure, with organic nets beyond the pipes to catch remaining suspended floc. The plan used existing discharge infrastructure for chemical introduction, mixing, and floc removal—with no fail-safe alternate during the continuous 3–4 week, 24/7 pump schedule.

The APS-based clarification system performed through the full South Basin dewatering. Success was strong enough that other site waters diverted to the South Basin so the same discharge quality could support earlier construction. Maintenance stayed typical of polymer BMPs: polymer replenishment, mixing-bump adjustments, net replacement, and floc removal as needed. For a smaller Illinois pipe train, see sixteen 706b logs in a detention-basin pipe that cut turbidity from 8,960 to 1.8 NTU, and compare pipe, ditch and flume layouts in the APS mixing system design guide, or browse all APS case studies.