{HEAD ~ A flow} of contaminated liquid phase water migrates toward {TAIL ~ the freeze front} and a concentration of impurities is established in front of the advancing freeze front 
migrates toward
{ HEAD ~ A flow } of contaminated liquid phase water migrates toward { TAIL ~ the freeze front } and a concentration of impurities is established in front of the advancing freeze front
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH