How is the amount of impervious surface area on my property calculated?

The amount of impervious surface area on your property is determined using a combination of data. First, the City uses geographic information system (GIS) data and aerial photos of the City that are updated approximately every five years to distinguish impervious surfaces (such as roofs and parking lots) and pervious surfaces (such as lawns and gardens). Then the square footage of impervious areas is calculated and an ERU value assigned. Information concerning the amount of impervious surface area added or removed in connection with building permits is used to update impervious surface calculations in between aerial photo updates. You can see the impervious area of your property using the City’s web map.

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1. Why is impervious surface area used to determine a property's stormwater user fee?
2. What is considered an impervious surface?
3. What is not considered an impervious surface?
4. How is the amount of impervious surface area on my property calculated?
5. What if I disagree with the amount of impervious area listed on my bill?