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Draft Indian River County Lagoon Management Plan Outline April 2019 4.0 PROSPECTIVE PROJECTS Projects will be selected based on the most cost-effective options in each category to maximize nutrient reductions, minimize lag time in lagoon response, Reduce risk, Revitalize natural lagoon resources, and optimize the return on investment. 4.1 UTILITIES 4.1.1 West Wabasso Septic to Sewer — Phase 2 The Utilities Department plans to convert 57 septic systems to central sewer and constru ' stub -outs for 47 vacant properties for future connection. The project area has a mixed land use of primarily resid: tial with a few commercial properties and is a financially disadvantaged community. The objective of this wor is to eliminate groundwater contamination caused by the poor treatment efficiencies of existing septic syste 's. The elimination of 57 septic systems will Reduce nutrient loading to the lagoon for an estimated 3,224 pounper year of TN and 520 pounds per year of TP. 4.1.2 Sebastian Septic to Sewer — Phase II Look at a cost share between City of Sebastian and County, also potentia for IRL NEP grant, to conduct ArcNLET modeling for these areas. This model determines the load at the recei ng waterbody, not the load from the septic system. This will be the basis for TMDL credits for septic system co ersion and assist with acquiring grant funds. 4.2 STORMWATER 4.2.1 North Relief Canal Low Energy Aquatic Plan ystem (LEAPSTM) The unique LEAPSTM will remove nutrients through a syst- m of plants that absorb nutrients from the canal water, filtering the stormwater before returning it to the canal . d IRL. This project is under final design. The project is estimated to remove up to 8,500 pounds per year of T and 1,400 pounds per year of TP. 4.2.2 North and South Relief Canal Mecha ical Water Lettuce Removal Systems This project will use a long reach excavator to ,-move water lettuce from the North and South Relief canals to prevent excess nutrient loading to the lagoo Two locations in these canals have already been identified for accumulating a large amount of water lettuce -nnually. The project is estimated to remove up to 5,900 pounds per year of TN and 1,400 pounds of per year of P. 4.2.3 Baffle Boxes Second generation/nutrient separatins baffle boxes have chambers with partitions connected to a storm drain. Stormwater flows into the first section of the box where most pollutants settle out. Water then overflows into the next section to allow further settf g before the water ultimately overflows to the stormwater pipe or receiving waterbody. Floating trays within e baffle box capture nutrients, suspended solids, organic material, trash, oils, and grease to prevent them from d. solving in the stormwater. Biosorption activated media can be added to the baffle box to create an environment with denitrification that increases nutrient removal. When regularly and properly maintained, baffle boxes s •stantially reduce TN, TP, and suspended solids. Baffle boxes could be ins ailed in areas with a lot of organic material, such as leaf litter, or trash to capture those materials before they en er the stormwater system. Baffle boxes could also be installed on County, municipality, and FDOT outfalls to major tributaries, canals, and the lagoon to reduce the amount of pollutants discharged to surface waters. OTETRA TECH 13