I have a fire pit about 15 foot long about 7 foot wide and it used to be about 2-3 foot deep. I have been cleaning the property and have burned only wood and stumps in there. There is dirt, charcoal, ash, etc. all mixed in as it's taken about 4 months to fill it while overcoming the rain wash. What can I do with it all? I have some huge compost piles going, would it be ok to mix with some soil and fresh cut field 'grass'? I mean this is a whole lot of stuff to just dig out and pile somewhere by itself, isn't it? TIA!!