MS4 - Calculating Impervious Area
Determining the Impervious Area of a Non Residential
Property:
Aerial Imagery is used to identify the impervious area on each
non residential site. The commercial site is determined using parcel line information obtained from Montgomery County. Each parcel is then examined using the aerial photography for any impervious area and the area is outlined, calculated and stored in a database. At this point the square footage is then converted into ERU's (equivalent runoff units) and this is the number on which your bill is based. One ERU is 3,960 sq ft which is also the average residential impervious area and the rate is $1.50/ERU.
Aerial Photography,
with Parcel Lines
Calculation of
Impervious Area
Outline of Impervious
Area