Septic System Leaching Field?

In the process of buying a home. Septic is being replaced. They installed a new leaching field. I had no idea that it would bump up the land. I don't close on the property for another week. Can I back out of the deal? Also they took all the boulders that came from the ground to dig the leaching field and tried making an ugly wall out of it probrably because they were to cheap to get rid of them. They told me "house as is" at the time there were no bouldrers or a huge bump on the land. Can I still legally get my $5000 deposit??? This happened in Machusetts.