COMBINED SEWER ELIMINATION PROJECT GRAND JUNCTION, COLORADO

There is a section of the town of Grand Junction, Colorado over five square miles in area where acombined sanitary and storm sewer system existed. The system had significant capacity constraintsduring storm events that resulted in problems with sanitary sewer conveyance, local flooding, andwastewater treatment. In 1996 the City of Grand Junction started serious planning for a project with the objective to solve the growing problems with their combined sewer system in the old part of downtown. The City was experiencing basement backups and minor overflows in the collection system, as well as increased flows at the wastewater treatment plant (WWTP) during wet weather. After considerable study, the City scoped a project to separate the sanitary and storm sewer systems.This would be done through the construction of a new storm sewer system throughout the area. The existing inlets would be utilized but disconnected from the sanitary sewer. This proposed system would then discharge into the Colorado River at five new discharge points.This Project was an exercise in careful management of many influences, resources and systems. Theengineering analysis and design of the system faced many challenges ranging from tight constraints to minimal grade to data management. From a regulatory standpoint, there were numerous obstacles and opportunities. They ranged from stormwater quality requirements as called for in NPDES Ph II to the effect of new river discharges on endangered species. There were also public relations challenges caused by ten miles of open cut construction in an extremely crowded right-of-way. Likeall projects, funding was a concern. Grant money was secured for a fixed amount for the project prior to commencement of final design. This meant that budget control through the design and construction was critical.