We are building an early childhood education center next to the existing elementary school. Can we exclude the play area and existing parking lot that we are only adding one space to? We aren’t actually retaining runoff from those areas since they either don’t have any impervious area requiring treatment, or the increase in impervious is too small to warrant stormwater management.  However, the two subsurface infiltration systems retain all runoff from the elementary school roof and new parking lot for up to the 25-year storm, which is generally equivalent to the 99th or 100th percentile storm.