Working Toward A Common Goal To Help The Mighty Mississippi

Background:
In May 2003, South Washington Watershed District (SWWD) consolidated with the East Mississippi Watershed Management Organization and assumed taxing authority for stormwater management for the communities of Newport, St. Paul Park, and Grey Cloud Island, Minnesota. The three communities are located in shallow bedrock along the Mississippi River with bluff and floodplain topography that contributes approximately 10 square miles of runoff to the river. In this area, the Mississippi is impaired for total suspended solids (TSS) and has an approved Total Maximum Daily Load (TMDL) by the Minnesota Pollution Control Agency (MPCA). Taking a programmatic approach, SWWD began planning for the area by first assessing existing conditions. They completed WINSLAMM models to assess water quality and completed a Subwatershed Retrofit Analysis for Newport and are in the process of completing a Subwatershed Assessment in St. Paul Park to identify locations and types of best management practices (BMPs) to primarily reduce the amount of TSS entering the river. They also worked with engineering consultant HR Green to obtain data for the existing storm sewer systems and create 2D XPSWMM models for each city. During this process, SWWD and HR Green met with City staff members to explain the planning and implementation strategy to spend collected tax dollars for each community. This not only helped with stakeholder buy-in early on, but it also helped identify any drainage problem areas and potential retrofit locations. Newport and St. Paul Park are MS4 cities, so these retrofits also supplement their stormwater management efforts.
Methodology: SWWD completed subwatershed assessments for each catchment area within the East Mississippi Watershed to determine potential stormwater treatment locations to reduce TSS loading. They ranked priority projects based on the cost benefit analysis of each retrofit based on pollutant removals and practice type. As they go down the priority list, SWWD and HR Green meet on site with the communities to review feasibility of these projects and cost share responsibilities. SWWD covers the design and installation costs, and the city provides the available property and helps with regular maintenance. SWWD and HR Green use the retrofit analysis as a guide to complete an alternatives assessment for each location. They look at the location of the nearby storm sewer trunklines and amount of flow expected for the treatment source, as well as nearby utilities. With bedrock anywhere from zero to five feet below the surface, infiltration practices aren't feasible; therefore, they typically look at a compact proprietary device that meets the treatment goals for the contributing area. Cost of bedrock excavation, effectiveness of nutrient removal and maintenance feasibility using city resources typically drive the decision on which device is installed. Once a device is agreed upon, it is designed and constructed. The goal with these devices is to establish a regular maintenance schedule to ensure the consistent sediment capture prior to discharging to the river. To do that, SWWD and the communities need to understand what activities are needed and how often they are needed. In the beginning, this requires more frequent monitoring and has a steeper learning curve. These discussions are a top priority for these projects. While planning for the continuous installation of these projects, SWWD uses this opportunity to provide treatment for nearby projects that could not meet permitting requirements due to site limitations. For example, a Spanish immersion school in St. Paul Park was renovating an existing building and could not meet the total phosphorus (TP) treatment requirements of the stormwater construction permit. SWWD worked with the school to instead restore a portion of the unused greenspace onsite to a native prairie. With the already established relationships, they were then able to coordinate with the City to install storm sewer stub outs along the trunkline of the nearby street that was being reconstructed to allow for a water quality device to make up for the lost treatment. Without the relationships and planning efforts of SWWD, water quality treatment in that area would have been much more costly.
Status: To date, SWWD has installed one treatment device in Newport and one in St. Paul Park. The device in Newport was constructed in spring of 2020 and has already gone through one maintenance cycle. It is proving to be very effective at TSS removal, and has many lessons learned for the next maintenance period. The device in St. Paul Park was installed in fall of 2021 and will require a bit more maintenance. The internal filters to remove TP will require more effort than what the City can provide, but the City will vacuum out the pretreatment device on a regular basis. Another alternatives assessment is in the works for two more locations in Newport, and design on one of them will start in early 2022.
Significance: Like any common goal, all stakeholders involved need to be onboard, and a plan needs to be formulated in order to see actions with measurable outcomes. SWWD, Newport and St. Paul Park have been working together to help lessen the load on the Mississippi, and their collaboration will help ensure it continues. Teamwork makes the dream work.