As part of an 80-acre industrial site property transfer, Pinnacle Engineering was retained to restore a large stormwater infiltration pond present on the property. Over an approximately 40 year period, the pond had filled in with up to six feet of silt, which restricted infiltration. Debris from previous site operations needed to be removed from pond side slopes and in a few locations within the pond footprint. The pond was adjacent to a closed landfill that contained structural concrete debris. The presence of the landfill was of concern to the buyer due to the potential for leaching of contaminants to the pond from the landfill.
Pinnacle’s civil engineering staff designed a pond restoration plan that included reducing pond slopes, installing a new manhole and discharge pipe, placing a clay layer on the pond side slope to isolate the landfill, and implementing erosion control measures around the pond. A dewatering program was included in the plan to allow for removal of sediments, which required implementation of a pre-treatment system of Weir tanks and 50 micron bag filters to filter and remove suspended solids prior to discharge to the sanitary sewer system. Pinnacle worked with the Metropolitan Council and the City to secure permits needed to complete the project.