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Comprehensive Plan <br />Septic to Sewer Study: Evaluation and Ranking <br />Sanita ry Sewer Sub -Element <br />The goal of the study Was to identify and rank the areas of septic system use having <br />disproportionately higher potential for negative lagoon impact based on various physical and <br />environmental. factors, and to determine the feasibility of incorporating septic to sewer <br />Evaluation Final Report; Ca <br />pTec Enpineerine. Inc.; February 13, 2015) and Brevard County <br />(Save Our Lagoon Project Plan for Brevard County, Florida; TetraTech; Inc and CloseWaters <br />LLC; July 28, 2016). The IRC formula was .modified from the formulas used in the Martin and <br />Brevard studies to consider and weigh physical and environmental factors that SBS and IRC staff <br />determined would better represent Indian River County conditions. In the IRC study, the <br />following factors were used in the initial ranking of the three hundred and twen -five 3251 <br />platted subdivisions currently served by septic tanks with respect to potential negative impacts <br />on the lagoon: <br />• Population Density for Loading Concentrations <br />• Proximity to Surface Waters <br />• Location of the Community in Relation to the 100 -year Flood Plain — FEMA Flood Plain <br />• Depth of the Ground Water Table <br />• Soil Conditions of the Drain Field — Soil Type <br />• Age of the Surface. Water Management System <br />• Age of the Existing Onsite Sewage Treatment and Disposal Systems (OSTDS) <br />Each factor was evaluated for every one of the 325 subdivisions and assigned an index number <br />that generallv ranged from 0 to 12. with 0 being the minimum and 12 being the maximum <br />impact. The formula used to determine the ranking was simply the sum of all factor values for <br />that subdivision. The higher the sum (the "score"). the higher the estimated Dotential negative <br />In the study, the 325 subdivisions served by septic systems were ranked in order where number <br />1 had the highest negative lagoonpact 89.19) and number 325 had the lowest negative <br />impact (26.97). Once the initial ranking was finalized, an Engineers Opinion of Probable Cost <br />(OPC.) was estimated for the top thirty five (35) ranked subdivisions having the highest <br />negative impacts. Those top 3 5 ranked subdivisions were further evaluated based on the <br />followina factors: <br />I . Aquatic Health - Environmental Impact Evaluation or the Initial Ranking <br />2. Sewer System Evaluation and Cost Data <br />3. Total Nitrogen (TN)/Total Phosphorus (TP) <br />4. Public Health - Based on the availabilitypotable water <br />Community Development Department <br />Indian River County 23 <br />Appendix A <br />