An advancing freeze front is established in {TAIL ~ a porous region} adjacent to or within {HEAD ~ contaminated earth} 
An advancing freeze front is established in { TAIL ~ a porous region } adjacent to or within { HEAD ~ contaminated earth }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD