If space and equipment permits, I would add soil floc or bentonite to the material that was removed from the area around the pipe, incorporate it all together, and compact as you stated as the material is replaced around the pipe.

vs. just replacing and repacking the material around the pipe after the anti-seep collars were added.

Belt and suspenders, remember? wink

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).