Using Data Merge to Create a 508 Compliant Document

I've been tasked to create a 508 compliant document from an existing InDesign document.  This is a document that uses Data Merge to fill in a form along with 2-3 photos, and a location map.  Each photo and the map need to have Alt Text descriptions.  I know how to apply Alt Text in the structure panel.  I would like to add Alt Text to these graphics in the document I am using to create the merged document.  When I do so then create the data merged document it drops all of the Alt Text.  Does anyone know a remedy for this problem?

I appreciate any input.  Thank you.

-Ben