Researching alternative septic systems for our lake association, I came across a nice twp-page brochure, Septic System Landscaping, put out by the Lake George Association. We had a mound septic system installed on our own property several years ago and decided to populate it with wildflowers, rather than having to mow (ugh!) grass. It's worked out nicely.
Some good wildflower seed vendors:
The Vermont Wildflower Farm