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1 <br /> i <br /> METHODOLOGIES: <br /> City of Eugene Systems Development Charges <br /> Appendix E <br /> Storm Sewer System Charge Detail <br /> 1.0 Formula <br /> The impact analysis for the stone sewer system is based on square footage of impervious <br /> surface which creates an impact on the storm system by land use type. This is the same <br /> approach used to calculate the current charge. ,Impervious surface is defined in Sec. 7.275, <br /> Eugene code, 1971 as "earth surface made impervious by development to vertical downward <br /> penetration by water". Impervious surfaces typically consist of concrete, asphalt and roofing <br /> materials. The impervious surface of a residential unit is usually the roof, driveway and any <br /> patio areas. The cost of the existing storm system is used as the basis for determining the <br /> SDC. <br /> The replacement cost of the storm system was determined using data from the <br /> "Infrastructure Replacement Values Report" prepared by the city's Public Works <br /> Department. The total value of the system is estimated to be $80,116,904. Assessable costs <br /> were calculated using the approach specified in the City Code. The city assesses up to and <br /> including the first 24 inches of pipe diameter and in excess of 60 inches. For pipe over 24 <br /> inches in diameter, the city pays a proportion of the cost. The non-assessable portion of <br /> <br /> .storm system costs is estimated at $36,332,006. Table 4 provides a detailed breakdown of <br /> the calculation of the stone SDC. Figure 7 illustrates the calculation of the storm system <br /> SDC. <br /> To determine a cost per square foot of impervious surface, the non-assessable portion of the <br /> system cost was first divided by the total impervious acres within the city limits. The total <br /> impervious surface calculated for each development is assumed to contnbute to the public <br /> storm 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 <br /> acre is estimated at $4,617.36. The cost for a square foot of impervious surface is calculated <br /> to be $0.106. <br /> 2.0 Single Family Dwelling and Duplex Rate <br /> The storm SDC for single family development is a flat rate based on the average lot size of <br /> 9,200 square feet in Eugene. The average lot size is multiplied by the residential run off <br /> coefficient of 0.35 to determine the average square feet of impervious surface. This amount <br /> is multiplied by $0.106 to determine the single-family residential charge of $341. The storm <br /> SDC for a duplex is calculated as two times the charge of a singlo-family home. <br /> <br /> February 24, 1993 Methodologies: City of Eugene SDCs Page E-1 <br /> <br />