The City allows certain small developments or infill lots to provide rain gardens on private property to manage stormwater when no stormwater main exists within the right-of-way fronting that particular property.
The square footage of the rain garden should be equivalent to 10% of the total new plus replaced impervious area of the site. There may be additional requirements for sites within a geologic hazard overlay area, Natural Resource Overlay District, with high groundwater or contaminated soils.
Peruse an outline of Requirements for a Typical Rain Garden (PDF).