Q: I have a bentonite cutoff wall containing a positive pressure inside and an overfill situation where the waste being capped will have perched water in the waste mass above the perimeter elevation. Do you have a recommendation for the perimeter connection detail for such a situation?
A: We generally use an anchor trench beyond the perimeter of the encountered bentonite cutoff walls for shedding rather than containment of infiltrated water. The anchor trench is extended at least 3.3 feet (1 m) beyond the wall (i.e., you will need real estate). Any water coming off the cap will need to be collected and removed by using a drain or swale. You do not want the water coming off the cap to impinge on the top of the cutoff wall.
Unfortunately, this detail will not work for your situation because of the perched water and positive pressure from within the cell. Therefore, your bentonite cutoff needs a cement bentonite or concrete cap to accommodate anchorage (positive fixity) with anchor bolts and batten bars. Please consult ASTM D6497, Standard Guide for Mechanical Attachment of Geomembrane to Penetrations or Structures, figure below of “Anchor Bolt Geomembrane Connection,” for specifics about such a detail. You may also want to consider a redundant barrier to back up this nontypical, very difficult detail (i.e., a geomembrane skirt with a geocomposite drain upgradient of the connection).