Challenge

To meet growing demand, the South County Regional Wastewater Authority wastewater treatment facility needed to expand its treatment capacity. Complex subsurface conditions, including soft compressible clays, liquefiable sands, and shallow groundwater, created significant challenges related to settlement, differential movement, and construction dewatering. The project included new membrane bioreactor (MBR) facilities, clarifiers, pump stations, solids handling systems, chemical storage areas, electrical infrastructure, and pipelines. Many structures extended up to 17 feet below grade and were planned adjacent to existing facilities.

Solution

Geo-Logic Associates provided comprehensive geotechnical engineering services to support planning, design, and construction of the expansion. Our team conducted subsurface investigations using conventional borings and cone penetration testing (CPT), performed laboratory testing and engineering analyses, and developed geotechnical design recommendations. We evaluated preload strategies to reduce long-term settlements, designed ground improvement approaches to mitigate differential settlement risks between new and existing structures, and assessed dewatering feasibility for below-grade construction. GLA also provided construction observation and testing services for critical underground infrastructure, including a 32-foot-deep influent pump station.

Results

Our engineering solutions helped advance the successful design and construction of a major treatment plant expansion while reducing geotechnical risks associated with challenging soil and groundwater conditions. By integrating settlement mitigation and dewatering strategies into the project design, we supported the long-term performance of critical infrastructure and helped position the facility to meet future wastewater treatment demands for the community.