GZA has provided engineering services for the design and structural remediation of four primary settling tanks at the Bergen County Sewerage Plant. These rectangular, reinforced concrete structures, measuring 35’ x 87.5’ and 10.5’ deep, hold wastewater.


The tanks were originally constructed in the 1950s on timber piles which have since deteriorated. Tank #4 had sunk to depths nearing 12 inches in places.


GZA conducted a subsurface investigation and provided geotechnical, civil, and structural engineering assessment and design for the rehabilitation of the settling tanks. GZA determined that when a pipe gallery structure containing sludge return, air duct and electrical lines was added in 1960 adjacent to primary settling tank #4, no additional foundation support was constructed. Ensuing attempts by others to remediate the resulting differential settlement were unsuccessful. GZA’s remedial design included new micropile foundations for new slabs, walkways, and partitions. Micropiles presented less risk of adverse impact to the other structures due to pile driving vibrations and could be deployed via a compact pile installation rig designed to work in tight spaces, such as the interior of the settlement tank. The remediation will proceed in phases, beginning with primary settling tank #4. GZA prepared construction plans and technical specifications to help BCUA select a contractor for the construction. GZA also recommended implementation of a monitoring program to assess short-term and long-term settlements of the primary settling tanks. GZA was also integral to the preparation of BCUA’s I-Bank grant application, helping the client navigate the process and preparing all accompanying documentation for the multimillion-dollar request, which is pending approval.


GZA’s analysis of subsurface conditions and foundation alternatives resulted in a solution that was protective of the facility’s aging structures and cognizant of the logistical limitations of the site.