The Town will use impervious area as their rate structure, with an Equivalent Residential Unit (ERU) as the basis for the stormwater enterprise fee. An impervious area rate structure in which the unit of charge is based on the median amount of impervious area on a single-family residential parcel is a common, court-tested, defensible, and fair stormwater enterprise fee rate structure.
In Lexington, 1 ERU is 3,290 square feet of impervious area.
According to an April 2009 fact sheet titled “Funding Stormwater Programs” by the U.S. Environmental Protection Agency (EPA), impervious area is used as the basis for the fee in more than 80 percent of stormwater utilities. The amount of impervious area on a property directly impacts volume and speed by which stormwater flow enters the stormwater conveyance system and reduces the amount of pervious area where stormwater flows could infiltrate the ground. Likewise, increased imperviousness is associated with increased stormwater pollution that enters local waterways. The Town has developed a dataset with the measured impervious area for each parcel within the service area.