IMPACTS TO STORM SEWER INFRASTRUCTURE AND SURFACE WATER RECEPTORS FROM LONG-TERM DEWATERING DISCHARGE

While sustained pumping may be required to preserve subsurface infrastructure, disposal of the dewatering discharge via storm sewers can compromise sewer infrastructure and adversely affect water quantity and quality in surface water receptors. A recent building project in Minnesota’s Twin Cities discharged pumped water to the municipal storm sewer, because continuous dewatering was needed to prevent flooding of the lowest levels of the building that were completed below the water table and the stage of a nearby lake. The resulting impacts on surface water and sewer infrastructure were unacceptably high. Various remedies were considered, but the issue was ultimately resolved by requiring the developer to cease dewatering and flood all portions of the building beneath the water table. In the wake of the incident, city departments have revisited their permitting and review processes for developments that could require long-term groundwater discharge to storm sewers. As land use and population density increase in metropolitan areas with abundant surface water resources, development often is in close proximity to surface waters, and buildings extend to greater depths to maximize usable space. This case study should serve as a cautionary tale for future development in such settings.