Do you have a plan view drawing of your septic system layout? If not, try to get one and post it. The company that did the work should have a copy and the government agency that oversees the industry should also have a copy.

Behind the garage seems like a long way to go for the basic back yard patio needs. Have you considered having a deck, basically the same level as the house floor? It would be a lot more convenient to use. You could reposition the existing steps as the way to get from the deck to the lawn.

The runs for the septic start two feet out from where the gravel ends/lawn starts at the end of table. The runs for the septic are parallel to the house running to right when looking at the picture. They run every two feet covering the rest of the back yard. We thought of a raised deck at height of patio doors but really like being lower in the yard or a combination with dining area upper level down to BBQ area. We like to BBQ in the winter and since we have lots of snow, having the BBQ area closer to the door of garage made more sense and would be easier to access keeping the snow and water fr9m tracking into the house.

Here is a rough sketch of the septic bed

Thanks Yardvaark, Here are three pictures of the whole yard. Hanks Cathy

Even though you're generally conveying the septic run, it could get to the point where precision is key. It would be better if you could post an as-built plan of the system.

I'd be leaning toward a dining area deck off of the patio doors, stepping down to a patio, which extends over toward the garage, making a parking place for the grill that is in close proximity to the garage door. You'll need space left of the garage for screening from the neighbors if you intend to get some privacy.

Here's the composite view in case anyone wants to see. (I don't have time now to do anything with it.)