The adjustment factor is based on the percent of impervious cover on an individual property. It adjusts the drainage charge upwards for properties with more than 52.3% impervious cover and downwards for those with less than 52.3% impervious cover.
It is calculated for each property using this formula:
Adjustment Factor = (1.5425 x percent impervious cover) + 0.1933
The formula for the adjustment factor is based on the “weighted” average percent of impervious cover for the entire city, currently estimated at 52.3%. A weighted average is a more accurate way to calculate an average when the items being averaged are of relative importance to each other.