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Comprehensive Plan Sanitary Sewer Sub -Element conversion mitigation projects into a 10 -year Capital Improvements Plan. As part of the study, a specific formula for the utility service area of Indian River County (IRC) was developed and modeled after similar studies performed for Martin County (Martin County Septic System Evaluation Final Report; CapTec Engineering, Inc.; February 13, 2015) and Brevard County (Save Our Lagoon Project Plan for Brevard County, Florida; TetraTech, Inc and CloseWaters LLC; July 28, 2016). The IRC formula was modified from the formulas used in the Martin and Brevard studies to consider and weigh physical and environmental factors that SBS and IRC staff determined would better represent Indian River County conditions. In the IRC study, the following factors were used in the initial ranking of the three hundred and twenty-five (325) platted subdivisions currently served by septic tanks with respect to potential negative impacts on the lagoon: • Population Density for Loading Concentrations • Proximity to Surface Waters • Location of the Community in Relation to the 100 -year Flood Plain — FEMA Flood Plain • Depth of the Ground Water Table • Soil Conditions of the Drain Field — Soil Type • Age of the Surface Water Management System • Age of the Existing Onsite Sewage Treatment and Disposal Systems (OSTDS) Each factor was evaluated for every one of the 325 subdivisions and assigned an index number that generally ranged from 0 to 12, with 0 being the minimum and 12 being the maximum impact. The formula used to determine the ranking was simply the sum of all factor values for that subdivision. The higher the sum (the "score"), the higher the estimated potential negative impact to the Indian River Lagoon (IRL). SBS and IRC staff agreed to weight the "Population Density" and "Proximity to Surface Waters" factors in the IRC study, because those two factors are believed to cause a higher negative impact than the other factors. In the study, the 325 subdivisions served by septic systems were ranked in order where number 1 had the highest negative lagoon impact (89.19) and number 325 had the lowest negative impact (26.97). Once the initial ranking was finalized, an Engineers Opinion of Probable Cost (OPC) was estimated for the top thirty five (35) ranked subdivisions having the highest negative impacts. Those top 35 ranked subdivisions were further evaluated based on the following factors: 1. Aquatic Health - Environmental Impact Evaluation or the Initial Ranking 2. Sewer System Evaluation and Cost Data 3. Total Nitrogen (TN)/Total Phosphorus (TP) 4. Public Health - Based on the availability of potable water The study evaluated the total nitrogen (TN) and total phosphorus (TP) that could be removed from the environment by septic to sewer conversion and calculated a cost per pound for TN removal for each of the top 35 ranked subdivisions. TP calculations were removed from the analysis since most technical references and studies show that phosphorus is adequately removed by a properly functioning septic Community Development Department Indian River County 22 AttadnAent 4