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Comprehensive Plan Sanitary Sewer Sub -Element Septic to Sewer Study: Evaluation and Rankin The goal of the study was to identify and rank the areas of septic system use having disproportionately higher potential for negative lagoon, impact based on various physical and environmental factors, and to determine the feasibility of incorporating septic to sewer 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 13 201 S) and Brevard County (Save Our Lagoon Project Plan for Brevard County, Florida: TetraTech Inc and Close Waters 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 3 5 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 Community Development Department Indian River County 23 Appendix A