I didn't want to hijack the first thread on this subject so, how far from house and what if a gas line is going through the gravel near the top? I say near the top, I don't know how deep the utility company buried the flexible line when they replaced the old line a few years ago.
The French drain is laid next to the foundation footing. It needs to be below the basement floor level. But you may not dig below the bottom of the footing of an existing house because that may cause the soil under the footing to slip.
You can dig leaving the gas pipe suspended in mid-air. Just be careful not to hit or bend the gas pipe either when digging or when refilling.
Do you get coverage you can count on? From the bag of fertilizer? From your lawn sprinklers?