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METHODOLOGY: <br />City. of Eugene Systems Development Charges <br />Appendix E <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 defined <br />in Section 7.275, Eugene code, 1971 as "earth surface made impervious by development to vertical <br />downward penetration by water". Impervious surfaces typically consist of concrete, asphalt and <br />roofing materials. The impervious surface of a residential unit is usually the roof, .sidewalks, <br />driveway and any patio areas. The cost of the existing stormwater system is used as the basis for <br />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 assesses <br />up to and including the first 24 inches of pipe diameter and in excess of 60 inches. For pipe over <br />24 inches in diameter, the city pays a proportion of the cost. The non-assessable portion of <br />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 Storm~ivater 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 G 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 eligible <br />costs) of the stormwater system cost was first divided by the total impervious acres within the city <br />limits. The total impervious surface calculated for each development is assumed to contrib~.ate to the <br />public stom~water system. The number of acres of impervious surface in each type of land use was <br />determined using runoff coefficients currently employed by the city. The cost per impervious acre <br />is estimated based on dividing the non-assessable costs (eligible SDC Costs) by the total number <br />of acres of impervious surface in the city limits. The cost for. a square foot of impervious surface is <br />calculated by dividing the cost per acre of impervious surface by the number of square feet in an <br />acre (43,560). <br />May 1, 1997 City of Eugene SDC Methodology Page E-1 <br />