David E. Ross wrote:
(...)

If you really own the property, the dumping you describe is most likely
illegal.

Well, you are right, there.

You need to identify the source accurately, taking photos or
even a video. Then file a police complaint, not only for dumping but
also for trespassing. You might also consider a civil lawsuit against
the dumper.

I don't understand.

If I give money to a lawyer, how would that limit the amount of
extra soil left on my property? I know very little about the
law, but I've never seen a lawyer knowingly use a shovel
in a moral and honest manner.

You do understand that the three individuals involved all know
where I live, yes? The police in my area are busy dealing with
murder, home invasions, arson, robbery (serious stuff).
As painful as this nuisance is, I'm not interested in being
the victim of a crime that the police would find noteworthy.

--Winston