Nutrients in Stormwater Runoff

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Construction

Construction sites can be significant sources of sediment in surface waters. Phosphorus loading from construction site sediments can occur due to sediment-bound phosphorus, especially if the native soils are high in phosphorus or if the soil is enriched by fertilizers or other products. In Tennessee, stormwater runoff from construction and land development is regulated under an NPDES permit for sites larger than 1 acre. The permit requires minimizing land disturbance, providing soil erosion protection, and reducing sediment loss using Best Management Practices (BMPs). TDEC provides guidance on the design, installation, and maintenance of BMPs in an Erosion and Sediment Control Handbook. Additional sediment reduction and nutrient uptake are required on construction sites near streams, wetlands, and reservoirs through the implementation of Riparian Water Quality Buffers (link to buffer info).

Municipal

Municipal runoff in 104 Tennessee municipalities is regulated under NPDES stormwater permits and state rules. Additional municipalities are being added based on the 2020 census.

Runoff from impervious surfaces in stormwater-regulated municipalities requires treatment by state rule and in their MS4 permits, with built-in incentives to reduce impervious surface areas in new development and redevelopment projects. Nutrient reduction is incorporated into the runoff treatment requirements by incentivizing green infrastructure, requiring internal water storage, and mandating extended detention and forebays. These rules must be adopted and fully implemented by small MS4s by September 2024.

Additionally, the permanent protection of riparian water quality buffers in new development and redevelopment is required by rule and by MS4 permit in stormwater-regulated municipalities.

Regulated municipalities are also required to establish and implement pollution prevention programs in their municipal operations, such as public works garages and storage yards, waste collection areas, and road maintenance facilities.

Industrial

Stormwater runoff from industries, including municipal landfills, is regulated under the Tennessee Multi-Sector NPDES permit, with monitoring requirements specific to each industrial category, including mining operations. Process areas, impervious surfaces, and operations of categorical industries require pollution prevention plans and benchmark monitoring under the NPDES TMSP. The No Exposure Certification incentive is available for facilities that eliminate the exposure of production materials or wastes to stormwater runoff.