Pinnacle Engineering was hired to conduct a geotechnical investigation for the Winona Commercial Dock facility in order to identify coal fill removal requirements prior to initiating a site paving project. The property had historically been used as a coal handling facility, and the owner intended to lease it for use as a truck staging facility.
The goal of this project was to minimize the impact of sediment runoff into the nearby Mississippi River and incorporate a stormwater management system meeting Minnesota Pollution Control Agency (MPCA) requirements for special waters into the design of a paved lot. The stormwater runoff from the site could not be released directly into the nearby slough of the Mississippi River, so a storm sewer system design was required to retain and collect sediment before releasing runoff into the river.
Based on the results of the geotechnical investigation, Pinnacle recommended options for site grading and stormwater management in conjunction with a pavement area suitable for heavy truck traffic and parking. All coal handling equipment and storage facilities, as well as all abandoned subsurface structures and layers of coal, were removed prior to site grading and paving. Excavated coal was transferred to a designated landfill, and clean fill material was imported to the site. The site was graded to ensure that stormwater would drain away from the river and flow to a stormwater pond that was designed to collect runoff from the asphalt pavement; because the site was flat, a piping and catch basin system was constructed to convey a portion of the site runoff into the pond. The pond was designed to release stormwater through an overflow when it reached full capacity, maximizing the stormwater retention volume and allowing for all captured sediment to settle out in the pond and remain on site. Additional erosion and sediment control measures were implemented during the construction phase; erosion control mats and seeding were used on exposed soils around the pond, and concrete barriers were placed along the top of the river bank to channel stormwater runoff.