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5.2.1 Calculating The Number Of ESUs Belonging To A Customer <br />ESUs are calculated differently for general storm customers than for small and medium <br />residential customers. To calculate the number of ESUs belonging to a general storm <br />customer, divide the amount of the customer's impervious surface area by 1,000, the <br />. resultant being the number of ESUs. If the result is a number with a decimal or fractional <br />element, truncate to the whole number. For example, if a restaurant has 15,670 square <br />feet of impervious surface, then the restaurant has 15,670/1,000 = 15.67 = 15 ESUs. <br />Thus, every additional 1,000 square feet of impervious surface represents an additional <br />ESU. A customer with 1,000 to 1,999 square feet of impervious surface has 1 ESU; a <br />customer with 2,000 to 2,999 square feet of impervious surface has <br />2 ESUs, etc. The minimum number of ESUs a customer can have is 1. So, customers <br />with 1 to 999 square feet of impervious surface are automatically assigned an ESU of 1. <br />See Figure 4. <br />The number of ESUs for the two residential categories is calculated differently than <br />ESUs for general .storm customers. Most residential customers fall into the small or <br />medium residential category depending on the size of their estimated building foot print. <br />If the customer's building foot print plus garage area is 1,000 square feet or less, the <br />customer falls into. the small residential category. If the customet's building foot print <br />plus garage area is between 1,000 and 3,000 square feet, the customer falls into the <br />medium residential category. See Figures 1-3. <br />While building foot print determines which category a residential customer belongs in, <br />the amount of the fee will be based on the amount of total impervious surface on a <br />typical property within a category. Driveways, sheds and cement porches are examples _ <br />of impervious surfaces that are not included in the building .foot print measurement but <br />do figure into the calculation ofthe total impervious surface for that category.. Based on <br />sample data, the ESU measurement for a small residential account is set at 1.8. Medium <br />residential accounts are set at 2.9 ESUs. <br />.The utility determines impervious area and building foot print information from <br />Assessment and Taxation records, aerial photos, building permit data, and other sources <br />as appropriate. . <br />Stormwater .Service Charge: Methodology Paper -Page 6 <br />Draft Revisions -April 10, 1995 <br />t <br />