To be safe I would ask the county air quality department for their recommendation in writing. If you go the water rout it may have to be done again in a year. If you remove them and put water over the soil it may solve your problem.

There is however another obvious serious issue here. I'm as sure as I sit here that allowing the dirt mounds to remain would constitute An Attractive Nuance. If anyone ever got injured they would be able to sue you for damages.

Here is a link that might be useful: Attractive nuisance doctrine

Oh, and by the way. If you know about the Attractive Nuance and have not informed your Insurance company about it in writing. Then you are not covered for any injuries that arise from the Attractive Nuance. Yep, you are on your own for any injuries or wrongful death lawsuit.