OFALLON, MO Gonzalez Cos. designed a 6,000-ft long sanitary interceptor for the City of O’Fallon, Missouri. The 30-inch gravity sewer receives pumped sewage from Public Water Supply District No. 2 of St. Charles County (PWSD2) and discharges to an existing City sewer at Peruque Creek.
The need for a new sewer was determined through Gonzalez’ planning studies and hydraulic analysis of an existing lift station and interceptor sewer. The studies considered dry and wet weather capacity, sewerage demand from anticipated land development, and projected flows from PWSD2. After evaluating alternative sewer alignments, Gonzalez prepared complete bid documents, including alternate bid items for conventional and trenchless construction methods. Working with subconsultants, Gonzalez furnished surveys, soils investigations, Section 404 and Missouri DNR permitting, and easement documents. Submittal reviews and consultation were provided during construction.
Excavation depths ranged up to 22 feet, with a varying rock profile and areas of poor surface drainage. A key issue was the maintenance of tractor-trailer access and the restoration of heavy concrete pavement in an industrial area. The alignment crosses sensitive residential yards, forested bottomland, and a rocky hillside. A vortex structure and several drop bowl inserts were provided for odor control and turbulence reduction. Other design features include streambank restoration, wetland plantings, vibration monitoring, and a 67-ft jack and bore. Construction was completed in late 2020 at an approximate cost of $2.5 million.
