All backfilling activity in reserve pits on the North Slope is done in the winter when the pit contents are frozen and the material used as fill is frozen. After careful study, it was discovered that the caps collapse because the material used as backfill is ice-rich. During the short cool arctic summers, the entrained ice melts very slowly over a period of several years. The total amount of shrinkage is generally 25%. If the seasonal thaw penetrates to the depth of the covered drilling waste, the weight of the fill material presses the pore fluids from the drilling waste into the gravel cap. This leachate is the source of contaminants that end up in the water pools on top of the gravel cap.

Once it was determined how and why the ponds form in reserve pit caps and the source for the contaminants in the water, a new cap design was made that allows for the collapse of the cap. The end result is a cap that collapses exactly onto itself but remains above grade so surface water ponds do not form. Although simple to design and construct, this new innovative engineered design is a significant advance in the backfilling, reclamation and long term stability of North Slope drilling waste reserve pits.