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METHODOLOGY• <br />City of Eugene Systems Development Charges <br />Appendix D <br />Stormwater System Charge Detail <br />1.0 Formula. <br />The impact analysis for the stormwater system is based on square footage of impervious surface <br />which creates an impact on the stormwater system by land use type. Impervious surface is <br />defined in Section 7.275, Eugene code, 1971 as "earth surface made impervious by development <br />to vertical downward penetration by water". Impervious surfaces typically consist of concrete, <br />asphalt and roofing materials. The impervious surface of a residential unit is usually the roof, <br />sidewalks, driveway and any patio areas. The cost of the existing stormwater system is used as <br />the basis for determining the Stormwater SDC. <br />The stormwater SDC is an improvement fee, as new development will require the construction of <br />additional system capacity. The per unit cost of additional capacity is based on existing system <br />replacement value divided by impervious surface area. The total value of the system is estimated <br />based on the replacement cost of the stormwater system components which include miles of pipe <br />and drainage channels, .stormwater cleanouts, catch basins, inlets/outlets, and manholes. For <br />current total value (Total Replacement Cost) of the stormwater system, see Table 6, section 1. <br />Assessable costs were calculated using the approach specified in the City Code. The city <br />assesses up to and including the first 24 inches of pipe diameter and in excess of 60 inches. For <br />pipe over 24 inches in diameter, the city pays a proportion of the cost. The non-assessable portion <br />of stormwater system costs (SDC eligible costs) is based on replacement costs, minus assessable <br />costs. Table 6 provides a detailed breakdown of the calculation and numerical supporting data of <br />the stormwater SDC. Figure 6 illustrates the calculation formula of the stormwater SDC. The <br />stormwater SDC rates per unit of capacity can be found in Appendix F in the cun'ent adopted SDC <br />fee schedule. <br />To determine a cost per square foot of impervious surface, the non-assessable portion (SDC <br />eligible costs) of the stormwater system cost was first divided by the total impervious acres within <br />the city limits. The total impervious surface calculated for each development is assumed to <br />contribute to the public stormwater system. The number of acres of impervious surface in each <br />type of land use was determined using runoff coefFcients currently employed by the city. The cost <br />per impervious acre is estimated based on dividing the non-assessable costs (eligible SDC Costs) <br />by the total number of acres of impervious surface in the city limits. The cost for a square foot of <br />impervious surface is calculated by dividing the cost per acre of impervious surface by the number <br />of square feet in an acre (43,560). <br />City of Eugene SDC Methodology Stormwater, Page D-1 <br />