I have a wooden deck that allows water to flow through and onto the surface below the deck. Is that considered Impervious?

It depends on how the surface of the deck was identified by the land cover data used for the assessment.  Wood decks that are located above an impervious area (IA) such as concrete or compacted stone are definitely included as impervious.  Since the aerial imagery is unable to show the surface beneath wood decks, it would be necessary for customers to contact LCWSA about wood decks above pervious areas such as loose stone, sand, soil or grass to determine the impact on the IA calculations.