North 27th Street Inline Sewer System Tunnel

Project reduces overflows, experience surmounts challenges 

•    Analysis reviews alternatives, zeros in on best solution
•    Pre-work manages perceptions, prepares for variables
•    Expertise leads to successful completion

HNTB provided design and construction services for Milwaukee’s North 27th Street Inline Storage System extension, which reduces sewer overflows.

The team’s engineering analysis included hydraulic modeling of the geographic area, and identification of all potential alternatives — near-surface storage, satellite treatment facilities or tunnel storage.

The final alternative — a two-mile-long deep storage tunnel — takes hydraulics, geotechnical issues, site constraints and cost into account. Drawing on its extensive experience, HNTB created tunnel plans and specifications, easement drawings, legal descriptions, acquisition plat, geotechnical data reports and traffic control analysis.

Before boring, team members managed public perception of potential alternatives and the final design, and addressed sewer-system operational concerns. They also analyzed and prepared for variable ground conditions, high water pressure, groundwater cut-off and complex grouting.

During construction, HNTB reviewed shop drawings, contract modifications and claims, and also designed and mapped two deep shafts.